Propyl gallate induces cell death in human pulmonary fibroblast through increasing reactive oxygen species levels and depleting glutathione

Propyl gallate (PG) exhibits an anti-growth effect on various cell types. The present study investigated the impact of PG on the levels of reactive oxygen species (ROS) and glutathione (GSH) in primary human pulmonary fibroblast (HPF) cells. Moreover, the effects of N-acetyl cysteine (NAC, an antioxidant), L-buthionine sulfoximine (BSO, a GSH synthesis inhibitor), and small interfering RNA (siRNAs) against various antioxidant genes on ROS and GSH levels and cell death were examined in PG-treated HPF cells. PG (100-800 μM) increased the levels of total ROS and O2·- at early time points of 30-180 min and 24 h, whereas PG (800-1600 μM) increased GSH-depleted cell number at 24 h and reduced GSH levels at 30-180 min. PG downregulated the activity of superoxide dismutase (SOD) and upregulated the activity of catalase in HPF cells. Treatment with 800 μM PG increased the number of apoptotic cells and cells that lost mitochondrial membrane potential (MMP; ΔΨm). NAC treatment attenuated HPF cell death and MMP (ΔΨm) loss induced by PG, accompanied by a decrease in GSH depletion, whereas BSO exacerbated the cell death and MMP (ΔΨm) loss without altering ROS and GSH depletion levels. Furthermore, siRNA against SOD1, SOD2, or catalase attenuated cell death in PG-treated HPF cells, whereas siRNA against GSH peroxidase enhanced cell death. In conclusion, PG induced cell death in HPF cells by increasing ROS levels and depleting GSH. NAC was found to decrease HPF cell death induced by PG, while BSO enhanced cell death. The findings shed light on how manipulating the antioxidant system influence the cytotoxic effects of PG in HPF cells.

The cadmium tolerance enhancement through regulating glutathione conferred by vacuolar compartmentalization in Aspergillus sydowii

Aspergillus was found to be a vital hyperaccumulation species for heavy metal removal with admirable tolerance capacity. But the potential tolerance mechanism has not been completely studied. This study quantified the amounts of total cadmium (Cd), Cd2+, glutathione (GSH), and reactive oxygen species (ROS) in the protoplasts and vacuoles of mycelium. We modulated GSH synthesis using buthionine sulfoximine (BSO) and 2-oxothiazolidine-4-carboxylic acid (OTC) to investigate the subcellular regulatory mechanisms of GSH in the accumulation of Cd. The results confirmed that GSH plays a crucial role in vacuolar compartmentalization under Cd stress. GSH and GSSG as a redox buffer to keep the cellular redox state in balance and GSH as a metal chelating agent to reduce toxicity. When regulating the decreased GSH content with BSO, and increased GSH content with OTC, the system of Cd-GSH-ROS can change accordingly, this also supported that vacuolar compartmentalization is a detoxification strategy that can modulate the transport and storage of substances inside and outside the vacuole reasonably. Interestingly, GSH tended to be distributed in the cytoplasm, the battleground of redox takes place in the cytoplasm but not in the vacuole. These finding potentially has implications for the understanding of tolerance behavior and detoxification mechanisms of cells. In the future bioremediation of Cd in soil, the efficiency of soil remediation can be improved by developing organisms with high GSH production capacity.

Inhibition of the glutamate-cysteine ligase catalytic subunit with buthionine sulfoximine enhances the cytotoxic effect of doxorubicin and cyclophosphamide in Burkitt lymphoma cells

Burkitt lymphoma (BL) is a highly aggressive lymphoma that mainly affects children and young adults. Chemotherapy is effective in young BL patients but the outcome in adults is less satisfactory. Therefore, there is a need to enhance the cytotoxic effect of drugs used in BL treatment. Glutathione (GSH) is an important antioxidant involved in processes such as regulation of oxidative stress and drug detoxification. Elevated GSH levels have been observed in many cancers and were associated with chemoresistance. We previously identified GCLC, encoding an enzyme involved in GSH biosynthesis, as an essential gene in BL. We now confirm that knockout of GCLC decreases viability of BL cells and that the GCLC protein is overexpressed in BL tissues. Moreover, we demonstrate that buthionine sulfoximine (BSO), a known inhibitor of GCLC, decreases growth of BL cells but does not affect control B cells. Furthermore, we show for the first time that BSO enhances the cytotoxicity of compounds commonly used in BL treatment, doxorubicin, and cyclophosphamide. Given the fact that BSO itself was not toxic to control cells and well-tolerated in clinical trials, combination of chemotherapy with BSO may allow reduction of the doses of cytotoxic drugs required to obtain effective responses in BL patients.

Development of a mouse model expressing a bifunctional glutathione-synthesizing enzyme to study glutathione limitation in vivo

Glutathione (GSH) is a highly abundant tripeptide thiol that performs diverse protective and biosynthetic functions in cells. While changes in GSH availability are associated with inborn errors of metabolism, cancer, and neurodegenerative disorders, studying the limiting role of GSH in physiology and disease has been challenging due to its tight regulation. To address this, we generated cell and mouse models that express a bifunctional glutathione-synthesizing enzyme from Streptococcus thermophilus (GshF), which possesses both glutamate-cysteine ligase and glutathione synthase activities. GshF expression allows efficient production of GSH in the cytosol and mitochondria and prevents cell death in response to GSH depletion, but not ferroptosis induction, indicating that GSH is not a limiting factor under lipid peroxidation. CRISPR screens using engineered enzymes further revealed genes required for cell proliferation under cellular and mitochondrial GSH depletion. Among these, we identified the glutamate-cysteine ligase modifier subunit, GCLM, as a requirement for cellular sensitivity to buthionine sulfoximine, a glutathione synthesis inhibitor. Finally, GshF expression in mice is embryonically lethal but sustains postnatal viability when restricted to adulthood. Overall, our work identifies a conditional mouse model to investigate the limiting role of GSH in physiology and disease.

Acquired Radiation Resistance Induces Thiol-dependent Cisplatin Cross-resistance

Resistance to radiation remains a significant clinical challenge in non-small cell lung carcinoma (NSCLC). It is therefore important to identify the underlying molecular and cellular features that drive acquired resistance. We generated genetically matched NSCLC cell lines to investigate characteristics of acquired resistance. Murine Lewis lung carcinoma (LLC) and human A549 cells acquired an approximate 1.5-2.5-fold increase in radiation resistance as compared to their parental match, which each had unique intrinsic radio-sensitivities. The radiation resistance (RR) was reflected in higher levels of DNA damage and repair marker γH2AX and reduced apoptosis induction after radiation. Morphologically, we found that radiation resistance A549 (A549-RR) cells exhibited a greater nucleus-to-cytosol (N/C) ratio as compared to its parental counterpart. Since the N/C ratio is linked to the differentiation state, we next investigated the epithelial-to-mesenchymal transition (EMT) phenotype and cellular plasticity. We found that A549 cells had a greater radiation-induced plasticity, as measured by E-cadherin, vimentin and double-positive (DP) modulation, as compared to LLC. Additionally, migration was suppressed in A549-RR cells, as compared to A549 cells. Subsequently, we confirmed in vivo that the LLC-RR and A549-RR cells are also more resistance to radiation than their isogenic-matched counterpart. Moreover, we found that the acquired radiation resistance also induced resistance to cisplatin, but not carboplatin or oxaliplatin. This cross-resistance was attributed to induced elevation of thiol levels. Gamma-glutamylcysteine synthetase inhibitor buthionine sulfoximine (BSO) sensitized the resistant cells to cisplatin by decreasing the amount of thiols to levels prior to obtaining acquired radiation resistance. By generating radiation-resistance genetically matched NSCLC we were able to identify and overcome cisplatin cross-resistance. This is an important finding arguing for combinatorial treatment regimens including glutathione pathway disruptors in patients with the potential of improving clinical outcomes in the future.

The nonessential amino acid cysteine is required to prevent ferroptosis in acute myeloid leukemia

ABSTRACT

Cysteine is a nonessential amino acid required for protein synthesis, the generation of the antioxidant glutathione, and for synthesizing the nonproteinogenic amino acid taurine. Here, we highlight the broad sensitivity of leukemic stem and progenitor cells to cysteine depletion. By CRISPR/CRISPR-associated protein 9-mediated knockout of cystathionine-γ-lyase, the cystathionine-to-cysteine converting enzyme, and by metabolite supplementation studies upstream of cysteine, we functionally prove that cysteine is not synthesized from methionine in acute myeloid leukemia (AML) cells. Therefore, although perhaps nutritionally nonessential, cysteine must be imported for survival of these specific cell types. Depletion of cyst(e)ine increased reactive oxygen species (ROS) levels, and cell death was induced predominantly as a consequence of glutathione deprivation. nicotinamide adenine dinucleotide phosphate hydrogen oxidase inhibition strongly rescued viability after cysteine depletion, highlighting this as an important source of ROS in AML. ROS-induced cell death was mediated via ferroptosis, and inhibition of glutathione peroxidase 4 (GPX4), which functions in reducing lipid peroxides, was also highly toxic. We therefore propose that GPX4 is likely key in mediating the antioxidant activity of glutathione. In line, inhibition of the ROS scavenger thioredoxin reductase with auranofin also impaired cell viability, whereby we find that oxidative phosphorylation-driven AML subtypes, in particular, are highly dependent on thioredoxin-mediated protection against ferroptosis. Although inhibition of the cystine-glutamine antiporter by sulfasalazine was ineffective as a monotherapy, its combination with L-buthionine-sulfoximine (BSO) further improved AML ferroptosis induction. We propose the combination of either sulfasalazine or antioxidant machinery inhibitors along with ROS inducers such as BSO or chemotherapy for further preclinical testing.

The role of thioredoxin and glutathione systems in arsenic-induced liver injury in rats under glutathione depletion

Antioxidant systems like thioredoxin (Trx) and glutaredoxin (Grx) maintain oxidative stress balance. These systems have cross-talk supported by some in vitro studies. We investigated the underlying mechanisms of arsenic-induced liver injury in glutathione-deficient rats and whether there was any cross-talk between the Trx and Grx systems. The rats in arsenic-treated groups were administered with sodium arsenite (10, 20 mg/kg b w/d) for four weeks. In buthionine sulfoximine (BSO, an inhibitor of GSH) and 20 mg/kg arsenic combined groups, rats were injected with 2 mmol/kg BSO intraperitoneally twice per week. BSO exacerbated arsenic-induced liver injury by increasing arsenic accumulation in urine, serum, and liver while decreasing glutathione activity and resulting in upregulated mRNA expression of the Trx system and downregulation of Grx mRNA expression. The impact of Trx lasted longer than that of the Grx. The Trx system remained highly expressed, while GSH, Grx1, and Grx2 levels were decreased. The inhibitory effect of only BSO treatment on Grx1 and Grx2 was not pronounced. However, the combined impact of arsenic and BSO upregulated Trx expression, primarily related to further reduction of GSH. As a result, the suppressed Grxs were protected by the upregulated Trxs, which serve as a backup antioxidant defense system in the liver.

The Role of Glutathione and Sulfhydryl Groups in Cadmium Uptake by Cultures of the Rainbow Trout RTG-2 Cell Line

The aim of this study is to investigate the role of cellular sulfhydryl and glutathione (GSH) status in cellular cadmium (Cd) accumulation using cultures of the rainbow trout cell line RTG-2. In a first set of experiments, the time course of Cd accumulation in RTG-2 cells exposed to a non-cytotoxic CdCl2 concentration (25 μM) was determined, as were the associated changes in the cellular sulfhydryl status. The cellular levels of total GSH, oxidized glutathione (GSSG), and cysteine were determined with fluorometric high-performance liquid chromatography (HPLC), and the intracellular Cd concentrations were determined with inductively coupled plasma mass spectrometry (ICP-MS). The Cd uptake during the first 24 h of exposure was linear before it approached a plateau at 48 h. The metal accumulation did not cause an alteration in cellular GSH, GSSG, or cysteine levels. In a second set of experiments, we examined whether the cellular sulfhydryl status modulates Cd accumulation. To this end, the following approaches were used: (a) untreated RTG-2 cells as controls, and (b) RTG-2 cells that were either depleted of GSH through pre-exposure to 1 mM L-buthionine-SR-sulfoximine (BSO), an inhibitor of glutathione synthesis, or the cellular sulfhydryl groups were blocked through treatment with 2.5 μM N-ethylmaleimide (NEM). Compared to the control cells, the cells depleted of intracellular GSH showed a 25% reduction in Cd accumulation. Likewise, the Cd accumulation was reduced by 25% in the RTG-2 cells with blocked sulfhydryl groups. However, the 25% decrease in cellular Cd accumulation in the sulfhydryl-manipulated cells was statistically not significantly different from the Cd accumulation in the control cells. The findings of this study suggest that the intracellular sulfhydryl and GSH status, in contrast to their importance for Cd toxicodynamics, is of limited importance for the toxicokinetics of Cd in fish cells.

Buthionine sulfoximine and chemoresistance in cancer treatments: a systematic review with meta-analysis of preclinical studies

Buthionine sulfoximine (BSO) is a synthetic amino acid that blocks the biosynthesis of reduced glutathione (GSH), an endogenous antioxidant cellular component present in tumor cells. GSH levels have been associated with tumor cell resistance to chemotherapeutic drugs and platinum compounds. Consequently, by depleting GSH, BSO enhances the cytotoxicity of chemotherapeutic agents in drug-resistant tumors. Therefore, the aim of this study was to conduct a systematic review with meta-analysis of preclinical studies utilizing BSO in cancer treatments. The systematic search was carried out using the following databases: PubMed, Web of Science, Scopus, and EMBASE up until March 20, 2023, in order to collect preclinical studies that evaluated BSO, alone or in association, as a strategy for antineoplastic therapy. One hundred nine investigations were found to assess the cytotoxic potential of BSO alone or in combination with other compounds. Twenty-one of these met the criteria for performing the meta-analysis. The evidence gathered indicated that BSO alone exhibits cytotoxic activity. However, this compound is generally used in combination with other antineoplastic strategies, mainly chemotherapy ones, to improve cytotoxicity to carcinogenic cells and treatment efficacy. Finally, this review provides important considerations regarding BSO use in cancer treatment conditions, which might optimize future studies as a potential adjuvant antineoplastic therapeutic tool.

Increasing glutathione levels by a novel posttranslational mechanism inhibits neuronal hyperexcitability

Glutathione (GSH) depletion, and impaired redox homeostasis have been observed in experimental animal models and patients with epilepsy. Pleiotropic strategies that elevate GSH levels via transcriptional regulation have been shown to significantly decrease oxidative stress and seizure frequency, increase seizure threshold, and rescue certain cognitive deficits. Whether elevation of GSH per se alters neuronal hyperexcitability remains unanswered. We previously showed that thiols such as dimercaprol (DMP) elevate GSH via post-translational activation of glutamate cysteine ligase (GCL), the rate limiting GSH biosynthetic enzyme. Here, we asked if elevation of cellular GSH by DMP altered neuronal hyperexcitability in-vitro and in-vivo. Treatment of primary neuronal-glial cerebrocortical cultures with DMP elevated GSH and inhibited a voltage-gated potassium channel blocker (4-aminopyridine, 4AP) induced neuronal hyperexcitability. DMP increased GSH in wildtype (WT) zebrafish larvae and significantly attenuated convulsant pentylenetetrazol (PTZ)-induced acute 'seizure-like' swim behavior. DMP treatment increased GSH and inhibited convulsive, spontaneous 'seizure-like' swim behavior in the Dravet Syndrome (DS) zebrafish larvae (scn1Lab). Furthermore, DMP treatment significantly decreased spontaneous electrographic seizures and associated seizure parameters in scn1Lab zebrafish larvae. We investigated the role of the redox-sensitive mammalian target of rapamycin (mTOR) pathway due to the presence of several cysteine-rich proteins and their involvement in regulating neuronal excitability. Treatment of primary neuronal-glial cerebrocortical cultures with 4AP or l-buthionine-(S,R)-sulfoximine (BSO), an irreversible inhibitor of GSH biosynthesis, significantly increased mTOR complex I (mTORC1) activity which was rescued by pre-treatment with DMP. Furthermore, BSO-mediated GSH depletion oxidatively modified the tuberous sclerosis protein complex (TSC) consisting of hamartin (TSC1), tuberin (TSC2), and TBC1 domain family member 7 (TBC1D7) which are critical negative regulators of mTORC1. In summary, our results suggest that DMP-mediated GSH elevation by a novel post-translational mechanism can inhibit neuronal hyperexcitability both in-vitro and in-vivo and a plausible link is the redox sensitive mTORC1 pathway.

Inhibition of glutathione generation in hepatic steatotic rats augments oxidative stress

Fatty liver disease has been strongly associated with a low glutathione (GSH) level in hepatocytes with increased oxidative stress, which is critically involved in the initiation and progression of the disease. The study investigated whether the GSH deficiency induced by buthionine sulfoximine (BSO), an inhibitor of γ-glutamyl cysteine synthetase, can be restored by the administration of GSH ester. We showed that mice fed a diet with cholesterol plus sodium cholate developed steatosis followed by hepatic GSH reduction. Moreover, the GSH level in the cytosol and mitochondria of steatosis plus BSO decreased than that of steatosis alone. Subsequent studies with the liver tissues and plasma of BSO plus steatosis revealed the accumulation of cholesterol in the hepatocytes, downregulating the concentration of GSH, antioxidant enzymes, and GSH metabolizing enzymes with a significant rise in reactive oxygen species (ROS), blood glucose level and plasma lipid profile. The administration of GSH ester in BSO-administered mice, prevented the depletion of GSH by upregulating the GSH concentration, antioxidant enzymes, and GSH metabolizing enzymes, followed by a reduction in ROS and plasma lipid concentration. The histopathological analysis showed a marked increase in inflammation followed by hepatocytes ballooning in BSO-induced group and steatosis control group, which was ameliorated by GSH ester administration. In conclusion, our data suggest that the restoration of GSH in the cytosol and mitochondria through the injection with GSH ester plays a principal role in maintaining the GSH level in the liver, thereby delaying the progression of fatty liver disease.

Iron-based metal-organic framework co-loaded with buthionine sulfoximine and oxaliplatin for enhanced cancer chemo-ferrotherapy via sustainable glutathione elimination

BACKGROUND

Emerging ferroptosis-driven therapies based on nanotechnology function either by increasing intracellular iron level or suppressing glutathione peroxidase 4 (GPX4) activity. Nevertheless, the therapeutic strategy of simultaneous iron delivery and GPX4 inhibition remains challenging and has significant scope for improvement. Moreover, current nanomedicine studies mainly use disulfide-thiol exchange to deplete glutathione (GSH) for GPX4 inactivation, which is unsatisfactory because of the compensatory effect of continuous GSH synthesis.

METHODS

In this study, we design a two-in-one ferroptosis-inducing nanoplatform using iron-based metal-organic framework (MOF) that combines iron supply and GPX4 deactivation by loading the small molecule buthionine sulfoxide amine (BSO) to block de novo GSH biosynthesis, which can achieve sustainable GSH elimination and dual ferroptosis amplification. A coated lipid bilayer (L) can increase the stability of the nanoparticles and a modified tumor-homing peptide comprising arginine-glycine-aspartic acid (RGD/R) can achieve tumor-specific therapies. Moreover, as a decrease in GSH can alleviate resistance of cancer cells to chemotherapy drugs, oxaliplatin (OXA) was also loaded to obtain BSO&OXA@MOF-LR for enhanced cancer chemo-ferrotherapy in vivo.

RESULTS

BSO&OXA@MOF-LR shows a robust tumor suppression effect and significantly improved the survival rate in 4T1 tumor xenograft mice, indicating a combined effect of dual amplified ferroptosis and GSH elimination sensitized apoptosis.

CONCLUSION

BSO&OXA@MOF-LR is proven to be an efficient ferroptosis/apoptosis hybrid anti-cancer agent. This study is of great significance for the clinical development of novel drugs based on ferroptosis and apoptosis for enhanced cancer chemo-ferrotherapy.

Glutathione depression alters cellular mechanisms of skeletal muscle fatigue in early stage of recovery and prolongs force depression in late stage of recovery

The effects of reduced glutathione (GSH) on skeletal muscle fatigue were investigated. GSH was depressed by buthionine sulfoximine (BSO) (100 mg/kg body wt/day) treatment for 5 days, which decreased GSH content to ∼10%. Male Wistar rats were assigned to the control (N = 18) and BSO groups (N = 17). Twelve hours after BSO treatment, the plantar flexor muscles were subjected to fatiguing stimulation (FS). Eight control and seven BSO rats were rested for 0.5 h (early stage of recovery), and the remaining were rested for 6 h (late stage of recovery). Forces were measured before FS and after rest, and physiological functions were estimated using mechanically skinned fibers. The force at 40 Hz decreased to a similar extent in both groups in the early stage of recovery and was restored in the control but not in the BSO group in the late stage of recovery. In the early stage of recovery, sarcoplasmic reticulum (SR) Ca2+ release was decreased in the control greater than in the BSO group, whereas myofibrillar Ca2+ sensitivity was increased in the control but not in the BSO group. In the late stage of recovery, SR Ca2+ release decreased and SR Ca2+ leakage increased in the BSO group but not in the control group. These results indicate that GSH depression alters the cellular mechanism of muscle fatigue in the early stage and delays force recovery in the late stage of recovery, due at least in part, to the prolonged Ca2+ leakage from the SR.

Human Wharton's Jelly-derived mesenchymal stem cells prevent acetaminophen-induced liver injury in a mouse model unlike human dermal fibroblasts

The persistence of hepatotoxicity induced by N-acetyl-para-aminophenol (Acetaminophen or Paracetamol, abbreviated as APAP) as the most common cause of acute liver failure in the United States, despite the availability of N-acetylcysteine, illustrates the clinical relevance of additional therapeutic approaches. While human mesenchymal stem cells (MSCs) have shown protection in mouse models of liver injury, the MSCs used are generally not cleared for human use and it is unclear whether these effects are due to xenotransplantation. Here we evaluated GMP manufactured clinical grade human Wharton's Jelly mesenchymal stem cells (WJMSCs), which are currently being investigated in human clinical trials, in a mouse model of APAP hepatotoxicity in comparison to human dermal fibroblasts (HDFs) to address these issues. C57BL6J mice were treated with a moderate APAP overdose (300 mg/kg) and WJMSCs were administered 90 min later. Liver injury was evaluated at 6 and 24 h after APAP. WJMSCs treatment reduced APAP-induced liver injury at both time points unlike HDFs, which showed no protection. APAP-induced JNK activation as well as AIF and Smac release from mitochondria were prevented by WJMSCs treatment without influencing APAP bioactivation. Mechanistically, WJMSCs treatment upregulated expression of Gclc and Gclm to enhance recovery of liver GSH levels to attenuate mitochondrial dysfunction and accelerated recovery of pericentral hepatocytes to re-establish liver zonation and promote liver homeostasis. Notably, preventing GSH resynthesis with buthionine sulfoximine prevented the protective effects of WJMSCs. These data indicate that these GMP-manufactured WJMCs could be a clinically relevant therapeutic approach in the management of APAP hepatotoxicity in humans.

Anti-Cancer Effects of Auranofin in Human Lung Cancer Cells by Increasing Intracellular ROS Levels and Depleting GSH Levels

Auranofin, as a thioredoxin reductase (TrxR) inhibitor, has promising anti-cancer activity in several cancer types. However, little is known about the inhibitory effect of auranofin on lung cancer cell growth. We, therefore, investigated the antigrowth effects of auranofin in various lung cancer cells with respect to cell death, reactive oxygen species (ROS), and glutathione (GSH) levels. Treatment with 0~5 µM auranofin decreased cell proliferation and induced cell death in Calu-6, A549, SK-LU-1, NCI-H460, and NCI-H1299 lung cancer cells at 24 h. In addition, 0~5 µM auranofin increased ROS levels, including O2•−, and depleted GSH levels in these cells. N-acetyl cysteine (NAC) prevented growth inhibition and mitochondrial membrane potential (MMP, ∆Ψm) loss in 3 and 5 µM auranofin-treated Calu-6 and A549 cells at 24 h, respectively, and decreased ROS levels and GSH depletion in these cells. In contrast, L-buthionine sulfoximine (BSO) enhanced cell death, MMP (∆Ψm) loss, ROS levels, and GSH depletion in auranofin-treated Calu-6 and A549 cells. Treatment with 3 and 5 µM auranofin induced caspase-3 activation and poly (ADP ribose) polymerase (PARP) cleavage in Calu-6 and A549 cells, respectively. Both were prevented by NAC, but enhanced by BSO. Moreover, TrxR activity was reduced in auranofin-treated Calu-6 and A549 cells. That activity was decreased by BSO, but increased by NAC. In conclusion, these findings demonstrate that auranofin-induced cell death is closely related to oxidative stress resulted from increased ROS levels and GSH depletion in lung cancer cells.

A Potent Strategy of Combinational Blow Toward Enhanced Cancer Chemo-Photodynamic Therapy via Sustainable GSH Elimination

Excessive glutathione (GSH), which is produced owing to abnormal metabolism of tumor cells, scavenges photo-induced reactive oxygen species (ROS) and consumes chemotherapeutic drugs, thereby attenuating the efficacy of photodynamic therapy and chemotherapy, respectively. Predominant strategies for GSH inhibition involve its chemical depletion, which only leads to a temporary therapeutic effect because GSH is replenished via various compensatory routes in tumor cells. Here, a versatile GSH-inhibiting nanosystem (termed PCNPs) for persistent synergistic therapy of cancer is reported. The porous skeleton of PCNPs allows easy encapsulation of buthionine sulfoximine (BSO) to sustainably suppress the biosynthesis of GSH. Thus, PCNPs not only demonstrate a prolonged release of BSO and improve drug utilization for efficient chemotherapy, but also act as an efficient photo-induced singlet oxygen radical generator that prevents the loss of ROS, thereby enhancing photodynamic therapy. In addition, the liposomal coating prevents cargo release in the blood, improves the accumulation of PCNPs at the tumor site, and promotes the cellular uptake of oxaliplatin and BSO. This strategy is applicable to ROS-based therapy and chemotherapy, which are suppressed by GSH, and may further enhance the synergistic effect of GSH-restrained therapy.

Effects of antioxidant capacity on micronucleus induction by cigarette smoke in mammalian cells

We have compared micronucleus (MN) induction by cigarette smoke in the L5178Y, TK6, and CHL/IU cell lines. The test sample was total particulate matter of 3R4F reference cigarette smoke, suspended in DMSO. After 3-h treatment, with or without a rat liver S9 metabolic activation system, followed by 24-h recovery, dose-dependent MN increases were seen in all cell lines. However, CHL/IU and TK6 cells were more resistant than L5178Y cells (comparison by Benchmark Doses with PROAST software). 3R4F smoke generates reactive oxygen species (ROS). Therefore, we explored the relationship between the sensitivities to 3R4F smoke and the antioxidant capacities of the cell lines. While the total antioxidant capacities were not significantly different among the cell lines, cellular glutathione (GSH) was higher in CHL/IU cells than in L5178Y cells. Pretreatment of CHL/IU cells with a GSH precursor, N-acetylcysteine (NAC), reduced the genotoxicity/cytotoxicity of 3R4F, whereas an inhibitor of GSH biosynthesis, buthionine sulfoximine (BSO), enhanced it. The effects of NAC and BSO were also seen after treatment with allyl isothiocyanate, a ROS-generating chemical, but not with mitomycin C, a ROS-independent genotoxicant. Pretreatment with NAC increased cellular thiol levels. From the present results, the genotoxicity and cytotoxicity of cigarette smoke differs among these cell lines in a manner that may be related to their antioxidant thiol levels.

Glutathione Metabolism Is a Regulator of the Acute Inflammatory Response of Monocytes to (1→3)-β-D-Glucan

(1→3)-β-D-Glucan (BDG) represents a potent pathogen-associated molecular pattern (PAMP) in triggering the host response to fungal and some bacterial infections. Monocytes play a key role in recognizing BDG and governing the acute host response to infections. However, the mechanisms regulating monocyte's acute response to BDG are poorly understood. We sought to investigate the response of monocytes to BDG at the epigenetic, transcriptomic, and molecular levels. Response of human monocytes to 1, 4, and 24 hours of BDG exposure was investigated using RNA-seq, ATAC-seq, H3K27ac and H3K4me1 ChIP-seq. We show that pathways including glutathione metabolism, pentose phosphate pathway, and citric acid cycle were upregulated at the epigenetic and transcriptomic levels in response to BDG exposure. Strikingly, unlike bacterial lipopolysaccharides, BDG induced intracellular glutathione synthesis. BDG exposure also induced NADP synthesis, increased NADPH/NADP ratio, and increased expression of genes involved in the pentose phosphate pathway in a GSH-dependent manner. By inhibiting GSH synthesis with L-buthionine sulfoximine (BSO) before BDG exposure we show that the GSH pathway promotes cell survival and regulates monocyte's effector functions including NO production, phagocytosis, and cytokine production. In summary, our work demonstrates that BDG induces glutathione synthesis and metabolism in monocytes, which is a major promoter of the acute functional response of monocytes to infections.

RNAi-mediated gene knockdown of progesterone 5β-reductases in Digitalis lanata reduces 5β-cardenolide content

Studying RNAi-mediated DlP5βR1 and DlP5βR2 knockdown shoot culture lines of Digitalis lanata, we here provide direct evidence for the participation of PRISEs (progesterone 5β-reductase/iridoid synthase-like enzymes) in 5β-cardenolide formation. Progesterone 5β-reductases (P5βR) are assumed to catalyze the reduction of progesterone to 5β-pregnane-3,20-dione, which is a crucial step in the biosynthesis of the 5β-cardenolides. P5βRs are encoded by VEP1-like genes occurring ubiquitously in embryophytes. P5βRs are substrate-promiscuous enone-1,4-reductases recently termed PRISEs (progesterone 5β-reductase/iridoid synthase-like enzymes). Two PRISE genes, termed DlP5βR1 (AY585867.1) and DlP5βR2 (HM210089.1) were isolated from Digitalis lanata. To give experimental evidence for the participation of PRISEs in 5β-cardenolide formation, we here established several RNAi-mediated DlP5βR1 and DlP5βR2 knockdown shoot culture lines of D. lanata. Cardenolide contents were lower in D. lanata P5βR-RNAi lines than in wild-type shoots. We considered that the gene knockdowns may have had pleiotropic effects such as an increase in glutathione (GSH) which is known to inhibit cardenolide formation. GSH levels and expression of glutathione reductase (GR) were measured. Both were higher in the Dl P5βR-RNAi lines than in the wild-type shoots. Cardenolide biosynthesis was restored by buthionine sulfoximine (BSO) treatment in Dl P5βR2-RNAi lines but not in Dl P5βR1-RNAi lines. Since progesterone is a precursor of cardenolides but can also act as a reactive electrophile species (RES), we here discriminated between these by comparing the effects of progesterone and methyl vinyl ketone, a small RES but not a precursor of cardenolides. To the best of our knowledge, we here demonstrated for the first time that P5βR1 is involved in cardenolide formation. We also provide further evidence that PRISEs are also important for plants dealing with stress by detoxifying reactive electrophile species (RES).

Design and synthesis of isothiocyanate-containing hybrid androgen receptor (AR) antagonist to downregulate AR and induce ferroptosis in GSH-Deficient prostate cancer cells

Sustained androgen receptor (AR) signaling and apoptosis evasion are among the main hurdles of castration-resistant prostate cancer (CRPC) treatment. We designed and synthesized isothiocyanate (ITC)-containing hybrid AR antagonist (ITC-ARi) and rationally combined ITC-ARi with GSH synthesis inhibitor buthionine sulfoximine (BSO) to efficiently downregulate AR/AR splice variant and induce ferroptosis in CRPC cells. The representative ITC-ARi 13 is an AR ligand that contains an N-acetyl cysteine-masked ITC moiety and gradually releases parental unconjugated ITC 12b in aqueous solution. The in vitro anti-PCa activities of 13, such as growth inhibition and AR downregulation, are significantly enhanced when combined with BSO. The drug combination caused notable lipid peroxidation and the cell viability was effectively rescued by iron chelator, antioxidants or the inhibitor of heme oxygenase-1, supporting the induction of ferroptosis. 13 and BSO cooperatively downregulate AR and induce ferroptosis likely through increasing the accessibility of 13/12b to cellular targets, escalating free intracellular ferrous iron and attenuating GSH-centered cellular defense and adaptation. Further studies on the combination of ITC-ARi and GSH synthesis inhibitor could result in a new modality against CRPC.

Cell-based high-throughput screening for the evaluation of reactive metabolite formation potential

Here, we established a high-throughput in vitro assay system to predict reactive metabolite (RM) formation. First, we performed the glutathione (GSH) consumption assay to monitor GSH levels as an index of RM formation potential using HepaRG cells pretreated with 500 μM D,L-buthionine-(S,R)-sulfoximine (BSO) and then treated with ticlopidine and diclofenac. Both drugs, under GSH-reduced conditions, significantly decreased relative cellular GSH content by 70% and 34%, respectively, compared with that in cells not pretreated with BSO. Next, we examined the correlation between GSH consumption and covalent binding assays; the results showed good correlation (correlation coefficient = 0.818). We then optimized the test compound concentration for evaluating RM formation potential using 76 validation compound sets, and the highest sensitivity (53%) was observed at 100 μM. Finally, using HepG2 cells, PXB-cells, and human primary hepatocytes, we examined the cell types suitable for evaluating RM formation potential. The expression of CYP3A4 was highest in HepaRG cells, suggesting the highest sensitivity (56.4%) of the GSH consumption assay. Moreover, a co-culture model of PXB-cells and HepaRG cells showed high sensitivity (72.7%) with sufficient specificity (85.7%). Thus, the GSH consumption assay can be used to effectively evaluate RM formation potential in the early stages of drug discovery.

Anti-Cancer Effects and Tumor Marker Role of Glutathione S-Transferase Mu 5 in Human Bladder Cancer

Our previous study demonstrated that the glutathione S-transferase Mu 5 (GSTM5) gene is highly CpG-methylated in bladder cancer cells and that demethylation by 5-aza-dC activates GSTM5 gene expression. The aim of the present study was to investigate the role of GSTM5 in bladder cancer. The levels of GSTM5 gene expression and DNA methylation were analyzed in patients with bladder cancer, and functional studies of GSTM5 were conducted using GSTM5 overexpression in cultured bladder cancer cells. Clinical analysis revealed that the GSTM5 mRNA expression was lower in bladder cancer tissues than in normal tissues and that the level of GSTM5 DNA methylation was higher in bladder cancer tissues than in normal urine pellets. Overexpression of GSTM5 decreased cell proliferation, migration and colony formation capacity. Glutathione (GSH) assay results indicated that cellular GSH concentration was decreased by GSTM5 expression and that GSH supplementation reversed the decrease in proliferation and migration of cells overexpressing GSTM5. By contrast, a GSH synthesis inhibitor significantly decreased 5637 cell GSH levels, survival and migration. Furthermore, GSTM5 overexpression inhibited the adhesion of cells to the extracellular matrix protein fibronectin. To elucidate the effect of GSTM5 on anticancer drugs used to treat bladder cancer, cellular viability was compared between cells with or without GSTM5 overexpression. GSTM5-overexpressed cells showed no significant change in the cytotoxicity of cisplatin or mitomycin C in 5637, RT4 and BFTC 905 cells. Though a degree of resistance to doxorubicin was noted in 5637 cells overexpressing GSTM5, no such resistance was observed in RT4 and BFTC 905 cells. In summary, GSTM5 plays a tumor suppressor role in bladder cancer cells without significantly affecting chemoresistance to cisplatin and mitomycin C, and the cellular GSH levels highlight a key mechanism underlying the cancer inhibition effect of GSTM5. These findings suggest that low gene expression and high DNA methylation levels of GSTM5 may act as tumor markers for bladder cancer.

Enhanced glutathione content improves lateral root development and grain yield in rice plants

Enhanced glutathione content improves lateral root development by positively regulating the transcripts of root development genes responsive to glutathione treatment, thereby increasing the overall productivity of rice plants. Glutathione is primarily known as a cellular antioxidant molecule, but its role in lateral root development in rice plants has not been elucidated. Here, we have investigated its role in lateral root development of rice Oryza sativa L. Exogenous glutathione (GSH) promoted both the number and length of lateral roots in rice, and the GSH biosynthesis inhibitor buthionine sulfoximine (BSO) significantly reduced these parameters, compared to untreated plants. The inhibition by BSO was reversed with exogenous GSH. Transcript profiling by RNA-seq revealed that expression of the transcription factor genes DREB and ERF and the hormone-related genes AOS, LOX, JAZ, and SAUR were significantly downregulated in the BSO-treated plants and, in contrast, upregulated in plants treated with GSH and with GSH and BSO together. We generated OsGS-overexpressing transgenic plants in which the transgene is controlled by the abiotic-stress-inducible OsRab21 promoter to study the effect of endogenously increased GSH levels. In cold stress, transgenic rice plants enhanced stress tolerance and lateral root development by maintaining redox homeostasis and improving upregulating the expression of transcription factors and hormone-related genes involved in lateral root development. We observed improved root growth of OsGS-overexpressing plants in paddy fields compared to the wild-type controls. These traits may have alleviated transplanting stress during early growth in the field and accounted for the increased productivity. These results provide information and perspectives on the role of GSH in gene expression, lateral root development, and grain yield in rice.

Zinc L-Carnosine Protects CCD-18co Cells from L-Buthionine Sulfoximine-Induced Oxidative Stress via the Induction of Metallothionein and Superoxide Dismutase 1 Expression

Zinc L-carnosine (ZnC) is the chelate form of zinc and L-carnosine and is one of the zinc supplements available in the market. This study aims to determine the protective effects of ZnC against L-buthionine sulfoximine (BSO)-induced oxidative stress in CCD-18co human normal colon fibroblast cell line. CCD-18co cells were pretreated with ZnC (0-100 μM) for 24 h before the induction of oxidative stress by BSO (1 mM) for another 24 h. Results from this present study demonstrated that ZnC up to the concentration of 100 μM was not cytotoxic to CCD-18co cells. Induction with BSO significantly increased the intracellular reactive oxygen species (ROS) levels and reduced the intracellular glutathione (GSH) levels in CCD-18co cells. Pretreatment with ZnC was able to attenuate the increment in intracellular ROS level in CCD-18co cells significantly in a concentration-dependent manner. However, ZnC did not have any effects on intracellular GSH levels and Nrf2 activation. Mechanistically, pretreatment with ZnC was able to upregulate the expression of metallothionein (MT) and superoxide dismutase 1 (SOD1) in CCD-18co cells. Results from dual-luciferase reporter gene assay reported that ZnC was able to increase the MRE-mediated relative luciferase activities in a concentration-dependent manner, suggesting that the induction of MT expression by ZnC was due to the activation of MTF-1 signaling pathway. Taken together, our current findings suggest that ZnC can protect CCD-18co cells from BSO-induced oxidative stress via the induction of MT and SOD1 expression.

S-nitrosocysteine and glutathione depletion synergize to induce cell death in human tumor cells: Insights into the redox and cytotoxic mechanisms

Nitric oxide (NO)-dependent signaling and cytotoxic effects are mediated in part via protein S-nitrosylation. The magnitude and duration of S-nitrosylation are governed by the two main thiol reducing systems, the glutathione (GSH) and thioredoxin (Trx) antioxidant systems. In recent years, approaches have been developed to harness the cytotoxic potential of NO/nitrosylation to inhibit tumor cell growth. However, progress in this area has been hindered by insufficient understanding of the balance and interplay between cellular nitrosylation, other oxidative processes and the GSH/Trx systems. In addition, the mechanistic relationship between thiol redox imbalance and cancer cell death is not fully understood. Herein, we explored the redox and cellular effects induced by the S-nitrosylating agent, S-nitrosocysteine (CysNO), in GSH-sufficient and -deficient human tumor cells. We used l-buthionine-sulfoximine (BSO) to induce GSH deficiency, and employed redox, biochemical and cellular assays to interrogate molecular mechanisms. We found that, under GSH-sufficient conditions, a CysNO challenge (100-500 μM) results in a marked yet reversible increase in protein S-nitrosylation in the absence of appreciable S-oxidation. In contrast, under GSH-deficient conditions, CysNO induces elevated and sustained levels of both S-nitrosylation and S-oxidation. Experiments in various cancer cell lines showed that administration of CysNO or BSO alone commonly induce minimal cytotoxicity whereas BSO/CysNO combination therapy leads to extensive cell death. Studies in HeLa cancer cells revealed that treatment with BSO/CysNO results in dual inhibition of the GSH and Trx systems, thereby amplifying redox stress and causing cellular dysfunction. In particular, BSO/CysNO induced rapid oxidation and collapse of the actin cytoskeletal network, followed by loss of mitochondrial function, leading to profound and irreversible decrease in ATP levels. Further observations indicated that BSO/CysNO-induced cell death occurs via a caspase-independent mechanism that involves multiple stress-induced pathways. The present findings provide new insights into the relationship between cellular nitrosylation/oxidation, thiol antioxidant defenses and cell death. These results may aid future efforts to develop NO/redox-based anticancer approaches.

Oxidative Stress Experienced during Early Development Influences the Offspring Phenotype

AbstractOxidative stress (OS) experienced early in life can affect an individual's phenotype. However, its consequences for the next generation remain largely unexplored. We manipulated the OS level endured by zebra finches (Taeniopygia guttata) during their development by transitorily inhibiting the synthesis of the key antioxidant glutathione ("early-high-OS"). The offspring of these birds and control parents were cross fostered at hatching to enlarge or reduce its brood size. Independent of parents' early-life OS levels, the chicks raised in enlarged broods showed lower erythrocyte glutathione levels, revealing glutathione sensitivity to environmental conditions. Control biological mothers produced females, not males, that attained a higher body mass when raised in a benign environment (i.e., the reduced brood). In contrast, biological mothers exposed to early-life OS produced heavier males, not females, when allocated in reduced broods. Early-life OS also affected the parental rearing capacity because 12-day-old nestlings raised by a foster pair with both early-high-OS members grew shorter legs (tarsus) than chicks from other groups. The results indicate that environmental conditions during development can affect early glutathione levels, which may in turn influence the next generation through both pre- and postnatal parental effects. The results also demonstrate that early-life OS can constrain the offspring phenotype.

Cell line-dependent difference in glutathione levels affects the cigarette sidestream smoke-induced inhibition of nucleotide excision repair

We recently reported that cigarette sidestream smoke (CSS) induced inhibition of nucleotide excision repair (NER) and the cause was NER molecule degradation by aldehydes contained in CSS [Carcinogenesis39, 56-65, 2018; Mutat. Res.834, 42-50, 2018]. In this study, we examined the relationship between intracellular glutathione (GSH) levels and CSS-induced NER inhibition. CSS treatment decreased the intracellular GSH level in human keratinocytes HaCaT, in which the repair of pyrimidine (6-4) pyrimidone photoproducts (6-4PPs) after UVB irradiation was suppressed. We used l-buthionine-(S,R)-sulfoximine (BSO) to artificially deplete intracellular GSH level. BSO treatment remarkably accelerated the CSS-induced NER inhibition. The NER inhibition by CSS was attributed to the delay of accumulation of NER molecules (TFIIH and XPG) to DNA damaged sites, which was further enhanced by BSO treatment. CSS degraded TFIIH, and BSO promoted it as expected. Formaldehyde (FA), a major constituent of CSS, showed similar intracellular GSH reduction and NER inhibition, and BSO promoted its inhibitory effect. Five cultured cell lines showed considerable variability in intrinsic GSH levels, and CSS-induced NER inhibitory effect was significantly correlated with the GSH levels. Chemicals like aldehydes are known to react not only with proteins but also with DNA, causing DNA lesions targeted by NER. Our results suggest that the tissues and cells with low intrinsic GSH levels are susceptible to treatment with CSS and electrophilic compounds like aldehydes through NER inhibition, thus leading to higher genotoxicity and carcinogenicity.

S-1-propenylmercaptocysteine protects murine hepatocytes against oxidative stress via persulfidation of Keap1 and activation of Nrf2

The onion-derived metabolite, S-1-propenylmercaptocysteine (CySSPe), protects against oxidative stress and exhibits anti-inflammatory effects by modulating cellular redox homeostasis. We sought to establish whether CySSPe activates nuclear factor erythroid 2-related factor 2 (Nrf2) and whether activation of Nrf2 by CySSPe involves modification of the Kelch-like ECH-associated protein-1 (Keap1) to manifest these effects. We found that CySSPe stabilized Nrf2 protein and facilitated nuclear translocation to induce expression of antioxidant enzymes, including NQO1, HO-1, and GCL. Moreover, CySSPe attenuated tert-butyl hydroperoxide-induced cytotoxicity and dose-dependently inhibited reactive oxygen species production. Silencing experiments using Nrf2-siRNA confirmed that CySSPe conferred protection against oxidative stress by activating Nrf2. CySSPe enhanced cellular pool of reduced glutathione (GSH) and improved GSH:GSSG ratio. Pretreatment of cells with l-buthionine-S,R-sulfoximine (BSO) confirmed that CySSPe increases de novo synthesis of GSH by upregulating expression of the GSH-synthesizing enzyme GCL. Treatment of cells with CySSPe elevated hydrogen sulfide (H₂S) production. Inhibition of H₂S-synthesizing enzymes, cystathionine-gamma-lyase (CSE) and cystathionine-beta-synthase (CBS), by pretreating cells with propargylglycine (PAG) and oxyaminoacetic acid (AOAA) revealed that H₂S production was partially dependent on a CSE/CBS-catalyzed β-elimination reaction with CySSPe that likely produced 1-propenyl persulfide (RSSH). Depleting cells of their GSH pool by exposure to BSO and diethylmaleate attenuated H₂S production, suggesting a GSH-dependent formation of H₂S, likely via the reduction of RSSH by GSH. Finally, treatment of cells with CySSPe persulfidated Keap1, which may be the mechanism involved for the stabilization of Nrf2 by CySSPe. Taken together, our results showed that attenuation of oxidative stress by CySSPe is associated with its ability to produce H₂S or RSSH, which persulfidates Keap1 and activates Nrf2 signaling. This study provides insights on the potential of CySSPe as an onion-derived dietary agent that modulates redox homeostasis and combats oxidative stress.

ReactELISA method for quantifying methylglyoxal levels in plasma and cell cultures

Methylglyoxal (MG) is a toxic glycolytic by-product associated with increased levels of inflammation and oxidative stress and has been linked to ageing-related diseases, such as diabetes and Alzheimer's disease. As MG is a highly reactive dicarbonyl compound, forming both reversible and irreversible adducts with a range of endogenous nucleophiles, measuring endogenous levels of MG are quite troublesome. Furthermore, as MG is a small metabolite it is not very immunogenic, excluding conventional ELISA for detection purposes, thus only more instrumentally demanding LC-MS/MS-based methods have demonstrated convincing quantitative data. In the present work we develop a novel bifunctional MG capture probe as well as a high specificity monoclonal antibody to finally setup a robust reaction-based ELISA (ReactELISA) method for detecting the highly reactive and low-level (nM) metabolite MG in human biological specimens. The assay is tested and validated against the current golden standard LC-MS/MS method in human blood plasma and cell-culture media. Furthermore, we demonstrate the assays ability to measure small perturbations of MG levels in growth media caused by a small molecule drug buthionine sulfoximine (BSO) of current clinical relevance. Finally, the assay is converted into a homogenous (no-wash) AlphaLISA version (ReactAlphaLISA), which offers the potential for operationally simple screening of further small molecules capable of perturbing cellular MG. Such compounds could be of relevance as probes to gain insight into MG metabolism as well as drug-leads to alleviate ageing-related diseases.

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MG is challenging to quantify, here we present a simple and specific ReactELISA based approach and validate against LC-MS/MS.

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Sensitivity at low (nM) endogenous concentration in both human blood plasma and cell culture media.

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Impact of BSO treatment of HEK293 cells can be profiled in culture media.

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Potential use in cell-based phenotypic screen for small molecules modulating MG metabolism.

Arabidopsis γ-glutamylcyclotransferase affects glutathione content and root system architecture during sulfur starvation

γ-Glutamylcyclotransferase initiates glutathione degradation to component amino acids l-glutamate, l-cysteine and l-glycine. The enzyme is encoded by three genes in Arabidopsis thaliana, one of which (GGCT2;1) is transcriptionally upregulated by starvation for the essential macronutrient sulfur (S). Regulation by S-starvation suggests that GGCT2;1 mobilizes l-cysteine from glutathione when there is insufficient sulfate for de novo l-cysteine synthesis. The response of wild-type seedlings to S-starvation was compared to ggct2;1 null mutants. S-starvation causes glutathione depletion in S-starved wild-type seedlings, but higher glutathione is maintained in the primary root tip than in other seedling tissues. Although GGCT2;1 is induced throughout seedlings, its expression is concentrated in the primary root tip where it activates the γ-glutamyl cycle. S-starved wild-type plants also produce longer primary roots, and lateral root growth is suppressed. While glutathione is also rapidly depleted in ggct2;1 null seedlings, much higher glutathione is maintained in the primary root tip compared to the wild-type. S-starved ggct2;1 primary roots grow longer than the wild-type, and lateral root growth is not suppressed. These results point to a role for GGCT2;1 in S-starvation-response changes to root system architecture through activity of the γ-glutamyl cycle in the primary root tip. l-Cysteine mobilization from glutathione is not solely a function of GGCT2;1.

S-Alk(en)ylmercaptocysteine suppresses LPS-induced pro-inflammatory responses in murine macrophages through inhibition of NF-κB pathway and modulation of thiol redox status

The Allium vegetable-derived metabolite, S-alk(en)ylmercaptocysteine (CySSR), has been reported to modulate oxidative stress and inflammatory responses. However, the underlying mechanisms of action and structure-activity relationships are not completely understood. We investigated the mechanistic basis of the protective effects of CySSR on pro-inflammatory responses involving redox/oxidative stress induced by E. coli lipopolysaccharide (LPS) using RAW 264.7 cells. CySSR (R = allyl, "A" or 1-propenyl, "Pe") pre-treatments conferred concentration-dependent reductions in cytokines (TNF-α, IL-1β and IL-6), NO production and iNOS (inducible nitric synthase) overexpression, and attenuated oxidant production in LPS-stimulated RAW 264.7 cells where viability remained > 90%. These protective effects were manifested through inhibited activation of the nuclear factor-kappa B (NF-κB) signaling pathway via suppression of the IκB kinases (IKK) phosphorylation possibly by transforming growth factor β-activated kinase 1 or a kinase further upstream the canonical NF-κB signaling pathway. The attenuation of LPS-induced inflammation by CySSRs was associated with enhanced levels of cellular cysteine (CySH) and glutathione (GSH) mediated by cellular import/reduction of CySSR and the induction of glutamate cysteine ligase (GCL), one of > 200 nuclear factor erythroid 2-related factor 2 (Nrf2) regulated proteins. The reduction of anti-inflammatory effect of CySSR following pretreatment of cells with L-buthionine-S,R-sulfoximine (BSO) implicates GSH having a major role in reducing inflammation, likely in the context of other Nrf2-regulated antioxidant enzymes that scavenge H₂O₂ and peroxides using GSH as co-substrate. The anti-inflammatory effect of CySSPe was significantly greater than CySSA for almost all indicators measured, and cell metabolites of CySSRs may have a role in attenuating NF-κB signaling.

Capsicodendrin from Cinnamosma fragrans Exhibits Antiproliferative and Cytotoxic Activity in Human Leukemia Cells: Modulation by Glutathione

Capsicodendrin (CPCD, 1), an epimeric mixture of a dimeric drimane-type sesquiterpene, is one of the major compounds present in the three endemic species of Madagascan traditional chemopreventive plants: Cinnamosma species ( C. fragrans, C. macrocarpa, and C. madagascariensis). Despite the popular use of Cinnamosma in Madagascan traditional medicine and the reported antiproliferative properties of CPCD, elucidation of its mechanism(s) of action is still to be accomplished. In the present study, CPCD at low micromolar concentrations was cytotoxic and induced apoptosis in human myeloid leukemia cells in a time- and concentration-dependent manner. The activity of CPCD in HL-60 and K562 cells was modulated by glutathione (GSH), since depletion of this intracellular thiol-based antioxidant with buthionine sulfoximine resulted in significantly ( p < 0.05) greater potency in antiproliferation assays. GSH depletion also significantly potentiated the cytotoxic activity in CPCD-treated human HL-60 cells. Single-cell gel electrophoresis (Comet) assays revealed that GSH depletion in HL-60 cells enhanced the formation of DNA strand breaks in the presence of CPCD. Although CPCD does not contain an obvious Michael acceptor in its structure, ¹H NMR analyses indicated that cinnamodial (2), a monomer of CPCD, was formed within a few hours when dissolved in DMSO- d₆ and interacts with GSH to form a covalent bond via Michael addition at the C-7 carbon. Together the results strongly suggest that 2 is responsible for the DNA-damaging, pro-apoptotic, and cytotoxic effects of CPCD and that depletion of GSH enhances overall activity by diminishing covalent interaction between GSH and this 2-alkenal decomposition product of CPCD.

Phenyl sulfate, indoxyl sulfate and p-cresyl sulfate decrease glutathione level to render cells vulnerable to oxidative stress in renal tubular cells

In chronic kidney disease patients, oxidative stress is generally associated with disease progression and pathogenesis of its comorbidities. Phenyl sulfate is a protein-bound uremic solute, which accumulates in chronic kidney disease patients, but little is known about its nature. Although many reports revealed that protein-bound uremic solutes induce reactive oxygen species production, the effects of these solutes on anti-oxidant level have not been well studied. Therefore, we examined the effects of protein-bound uremic solutes on glutathione levels. As a result, indoxyl sulfate, phenyl sulfate, and p-cresyl sulfate decreased glutathione levels in porcine renal tubular cells. Next we examined whether phenyl sulfate-treated cells becomes vulnerable to oxidative stress. In phenyl sulfate-treated cells, hydrogen peroxide induced higher rates of cell death than in control cells. Buthionine sulfoximine, which is known to decrease glutathione level, well mimicked the effect of phenyl sulfate. Finally, we evaluated a mixture of indoxyl sulfate, phenyl sulfate, and p-cresyl sulfate at concentrations comparable to the serum concentrations of hemodialysis patients, and we confirmed its decreasing effect on glutathione level. In conclusion, indoxyl sulfate, phenyl sulfate, and p-cresyl sulfate decrease glutathione levels, rendering the cells vulnerable to oxidative stress.

Thymoquinone protects against cobalt chloride-induced neurotoxicity via Nrf2/GCL-regulated glutathione homeostasis

The prevalence of neurodegenerative diseases worldwide has increased dramatically in the last decades. Hypoxia and oxidative stress play a central role in the pathogenesis of neurodegenerative diseases. Thymoquinone (TQ) is a monoterpenoid hydrocarbon compound that possesses potent antioxidant activity. In the current study, we investigated the neuroprotective effects of TQ against CoCl2, a widely used hypoxia-inducing agent. We found that TQ inhibited CoCl2-indcued cytotoxicity in vitro, as reflected by an increase of cell viability and decrease of apoptosis in CoCl2-treated PC12 cells. TQ exhibited a potent protective effect against CoCl2-induced neurotoxicity in vivo, as evidenced by decreased time spent to find the platform site in the Probe trials, reduced escape latencies, decreased traveling distance and reduction of apoptotic cell death in brains in CoCl2-treated rats. CoCl2-resulted decrease of glutathione (GSH) and increase of malondialdehyde (MDA) levels were significantly inhibited by TQ. Inhibition of GSH synthesis by buthionine sulphoximine (BSO) significantly attenuated TQ-induced neuroprotective effects against CoCl2 in rats and in PC12 cells. TQ could upregulate nuclear factor (erythroid-derived 2)-like 2 (Nrf2)/glutamate-cysteine ligase catalytic subunit (GCLc) and Nrf2/glutamate-cysteine ligase modifier subunit (GCLm) pathway which contributed to antioxidant and neuroprotective effects of TQ. In summary, we found that TQ exhibited protective effects against neurotoxicity via upregulation of Nrf2/GCL signaling. Upregulation of Nrf2/GCL signaling promoted the synthesis of GSH and contributed to attenuation of oxidative stress, neuronal cell apoptosis and neurotoxicity. These data have appointed a new path toward the understanding of the neuroprotective activities of TQ.

Suberoylanilide hydroxamic acid induces thioredoxin1-mediated apoptosis in lung cancer cells via up-regulation of miR-129-5p

Histone deacetylase (HDAC) inhibitors, especially suberoylanilide hydroxamic acid (SAHA) induce apoptosis in various cancer cells. Here, we investigated the effect of SAHA on apoptosis in lung cancer cells and addressed the role of reactive oxygen species (ROS), glutathione (GSH), and thioredoxin1 (Trx1) levels in this process. We also identified the miRNAs that down-regulate Trx1 expression at RNA level and thereby influence apoptotic cell death of SAHA increased intracellular ROS levels and promoted apoptotic cell death in cancerous cells but not in non-cancerous normal lung cells. Likewise, SAHA induced GSH depletion specifically in cancerous cells. While N-acetyl cysteine (NAC) reduced ROS level and reversed the effect of SAHA on cell death, L-buthionine sulfoximine (BSO) further enhanced GSH depletion, and promoted cell death. SAHA decreased the mRNA and protein levels of Trx1 in lung cancer cells. Knockdown/suppression of Trx1 intensified apoptosis in SAHA-treated lung cancer cells whereas overexpression of Trx1 prevented the cell death in these cells. SAHA up-regulated the level of miR-129-5p, which binds to 3' untranslated region (3'UTR) of Trx1 and down-regulates Trx1 expression. Down-regulation of Trx1 led to activation of apoptosis-signal regulating kinase (ASK), which induced apoptotic cell death by triggering ASK-JNK or ASK-p38 kinase pathway. In conclusion, changes in ROS and GSH levels in SAHA-treated lung cancer cells partially co-related with cell death. SAHA induced apoptosis via the down-regulation of Trx1, which was regulated by miR-129-5p.

Real-time quantification of subcellular H2O2 and glutathione redox potential in living cardiovascular tissues

Detecting and measuring the dynamic redox events that occur in vivo is a prerequisite for understanding the impact of oxidants and redox events in normal and pathological conditions. These aspects are particularly relevant in cardiovascular tissues wherein alterations of the redox balance are associated with stroke, aging, and pharmacological intervention. An ambiguous aspect of redox biology is how redox events occur in subcellular organelles including mitochondria, and nuclei. Genetically-encoded Rogfp2 fluorescent probes have become powerful tools for real-time detection of redox events. These probes detect hydrogen peroxide (H₂O₂) levels and glutathione redox potential (E_GSH), both with high spatiotemporal resolution. By generating novel transgenic (Tg) zebrafish lines that express compartment-specific Rogfp2-Orp1 and Grx1-Rogfp2 sensors we analyzed cytosolic, mitochondrial, and the nuclear redox state of endothelial cells and cardiomyocytes of living zebrafish embryos. We provide evidence for the usefulness of these Tg lines for pharmacological compounds screening by addressing the blocking of pentose phosphate pathways (PPP) and glutathione synthesis, thus altering subcellular redox state in vivo. Rogfp2-based transgenic zebrafish lines represent valuable tools to characterize the impact of redox changes in living tissues and offer new opportunities for studying metabolic driven antioxidant response in biomedical research.

The diverse roles of glutathione-associated cell resistance against hypericin photodynamic therapy

The diverse responses of different cancers to treatments such as photodynamic therapy of cancer (PDT) have fueled a growing need for reliable predictive markers for treatment outcome. In the present work we have studied the differential response of two phenotypically and genotypically different breast adenocarcinoma cell lines, MCF7 and MDA-MB-231, to hypericin PDT (HYP-PDT). MDA-MB-231 cells were 70% more sensitive to HYP PDT than MCF7 cells at LD50. MCF7 were found to express a substantially higher level of glutathione peroxidase (GPX4) than MDA-MB-231, while MDA-MB-231 differentially expressed glutathione-S-transferase (GSTP1), mainly used for xenobiotic detoxification. Eighty % reduction of intracellular glutathione (GSH) by buthionine sulfoximine (BSO), largely enhanced the sensitivity of the GSTP1 expressing MDA-MB-231 cells to HYP-PDT, but not in MCF7 cells. Further inhibition of the GSH reduction however by carmustine (BCNU) resulted in an enhanced sensitivity of MCF7 to HYP-PDT. HYP loading studies suggested that HYP can be a substrate of GSTP for GSH conjugation as BSO enhanced the cellular HYP accumulation by 20% in MDA-MB-231 cells, but not in MCF7 cells. Studies in solutions showed that L-cysteine can bind the GSTP substrate CDNB in the absence of GSTP. This means that the GSTP-lacking MCF7 may use L-cysteine for xenobiotic detoxification, especially during GSH synthesis inhibition, which leads to L-cysteine build-up. This was confirmed by the lowered accumulation of HYP in both cell lines in the presence of BSO and the L-cysteine source NAC. NAC reduced the sensitivity of MCF7, but not MDA-MB-231, cells to HYP PDT which is in accordance with the antioxidant effects of L-cysteine and its potential as a GSTP substrate. As a conclusion we have herein shown that the different GSH based cell defense mechanisms can be utilized as predictive markers for the outcome of PDT and as a guide for selecting optimal combination strategies.

D-penicillamine combined with inhibitors of hydroperoxide metabolism enhances lung and breast cancer cell responses to radiation and carboplatin via H2O2-mediated oxidative stress

D-penicillamine (DPEN), a copper chelator, has been used in the treatment of Wilson's disease, cystinuria, and rheumatoid arthritis. Recent evidence suggests that DPEN in combination with biologically relevant copper (Cu) concentrations generates H₂O₂ in cancer cell cultures, but the effects of this on cancer cell responses to ionizing radiation and chemotherapy are unknown. Increased steady-state levels of H₂O₂ were detected in MB231 breast and H1299 lung cancer cells following treatment with DPEN (100µM) and copper sulfate (15µM). Clonogenic survival demonstrated that DPEN-induced cancer cell toxicity was dependent on Cu and was significantly enhanced by depletion of glutathione [using buthionine sulfoximine (BSO)] as well as inhibition of thioredoxin reductase [using Auranofin (Au)] prior to exposure. Treatment with catalase inhibited DPEN toxicity confirming H₂O₂ as the toxic species. Furthermore, pretreating cancer cells with iron sucrose enhanced DPEN toxicity while treating with deferoxamine, an Fe chelator that inhibits redox cycling, inhibited DPEN toxicity. Importantly, DPEN also demonstrated selective toxicity in human breast and lung cancer cells, relative to normal untransformed human lung or mammary epithelial cells and enhanced cancer cell killing when combined with ionizing radiation or carboplatin. Consistent with the selective cancer cell toxicity, normal untransformed human lung epithelial cells had significantly lower labile iron pools than lung cancer cells. These results support the hypothesis that DPEN mediates selective cancer cell killing as well as radio-chemo-sensitization by a mechanism involving metal ion catalyzed H₂O₂-mediated oxidative stress and suggest that DPEN could be repurposed as an adjuvant in conventional cancer therapy.

The determination of hepatic glutathione at tissue and subcellular level

INTRODUCTION

Glutathione (GSH) through its important function in the antioxidant protection of cells and in the conjugation of drugs and xenobiotics has crucial importance in pharmacology and toxicology. Since GSH is most often measured in liver tissue and different cell organelles it is important to choose the method that best suits for the determination of GSH.

METHODS

The GSH content of cell organelles isolated from control and BSO-treated liver tissues was determined by the GSH-NEM-HPLC-UV, monochlorobimane-GSH-HPLC-fluorescence method and DTNB-GSH recycling assay to find the most suitable method for GSH determination from cell organelles.

RESULTS

The GSH level of organelles could easily be measured by the monochlorobimane-HPLC-fluorescent method. The addition of monochlorobimane to the homogenisation buffer prevented the oxidation of GSH during isolation. The formation of monochlorobimane-GSH adduct was accelerated by the intrinsic GST activity of samples, however the omission of GST from the GSH standards could cause the overestimation of GSH content of biological samples. NEM is an excellent thiol protective agent and the GSH-NEM conjugate can be directly analysed by HPLC-UV, but the relatively high limit of detection made the method unsuitable for the determination of GSH from cell organelles. Although the DTNB-GSH recycling assay is quite simple and rapid the stabilization of GSH and the efficiency of detection lag behind the monochlorobimane-HPLC-fluorescent method.

DISCUSSION

The monochlorobimane-HPLC-fluorescent method can be advised for the determination of GSH from pharmacologically and toxicological relevant cell organelles and liver tissue whilst addition of monochlorobimane to the homogenisation buffer prevented the autoxidation of GSH.

Phytochelatins play key roles for the difference in root arsenic accumulation of different Triticum aestivum cultivars in comparison with arsenate uptake kinetics and reduction

In the previous studies, we have found that arsenic (As) accumulation in roots of bread wheat (Triticum aestivum L.) seedlings were significantly different among different wheat cultivars, and As(V) tolerant wheat cultivars have much higher capacities of root As accumulation. However, the reason for the difference remains unclear. Four wheat cultivars with high (MM45 and FM8) or low (QF1 and HM29) levels of arsenic (As) accumulation were selected to investigate the relationship between root As(V) uptake kinetics and root As accumulation. MM45 and HM29 were also used to examine As(V) reduction ability and non-protein thiol (cysteine [Cys], glutathione [GSH], and phytochelatins [PCs]) concentrations in wheat seedlings. MM45 had the lowest Michaelis-Menten constant (K_m) and maximum influx rate (V_max). No difference in the K_m values was found among the three other cultivars. No difference in As(V) reduction capacity was observed between MM45 and HM29. GSH and PC₂ were significantly induced by 10 μM As(V) in roots of wheat seedlings, particularly in MM45. Synthesis of GSH and PCs was completely suppressed in the presence of l-buthionine sulfoximine (BSO), a specific inhibitor of γ-glutamylcysteine synthetase. BSO markedly decreased the As tolerance of wheat seedlings and decreased the accumulation of As in roots, but increased As accumulation in shoots. No significant difference in As concentrations was found between MM45 and HM29 under the BSO treatment. GSH and PCs are the reason why As accumulation and As(V) tolerance differ in roots of different wheat cultivars.

Phytochelatin synthesis in Dunaliella salina induced by arsenite and arsenate under various phosphate regimes

This study investigated the dynamic variations in thiol compounds, including cysteine (Cys), glutathione (GSH), and phytochelatins (PCs), in Dunaliella salina samples exposed to arsenite [As(III)] and arsenate [As(V)] under various phosphate (PO₄^3-) regimes. Our results showed that GSH was the major non-protein sulfhydryl compound in D. salina cells. As(III) and As(V) induced PC syntheses in D. salina. PC₂, PC₃, and PC₄ were all found in algal cells; the PC concentrations decreased gradually while exposed to As for 3 d. The synthesis of PC_2-3 was significantly affected by As(III) and As(V) concentrations in the cultures. More PCs were detected in the As(V)-treated algal cells compared with the As(III) treatment. PC levels increased with As(III)/As(V) amount in the medium, but remained stable after 112μgL^-1 As(V) exposure. In contrast, significant (p<0.001) positive correlations were observed between PC synthesis and intracellular As(III) content or As accumulation in As(III)-treated algal cells during the 72-h exposure. PO₄^3- had a significant influence on the PC synthesis in algal cells, irrespective of the As-treated species. Reductions in As uptake and subsequent PC synthesis by D. salina were observed as the PO₄^3- concentration in the growth medium increased. L-Buthionine sulfoximine (BSO) differentially influenced PC synthesis in As-treated D. salina under different extracellular PO₄^3- regimes. Overall, our data demonstrated that the production of GSH and PCs was affected by PO₄^3- and that these thiols played an important role in As detoxification by D. salina.

Characterization of cadmium chloride-induced BiP accumulation in Xenopus laevis A6 kidney epithelial cells

Endoplasmic reticulum (ER) stress can result in the accumulation of unfolded/misfolded protein in the ER lumen, which can trigger the unfolded protein response (UPR) resulting in the activation of various genes including immunoglobulin-binding protein (BiP; also known as glucose-regulated protein 78 or HSPA5). BiP, an ER heat shock protein 70 (HSP70) family member, binds to unfolded protein, inhibits their aggregation and re-folds them in an ATP-dependent manner. While cadmium, an environmental contaminant, was shown to induce the accumulation of HSP70 in vertebrate cells, less information is available regarding the effect of this metal on BiP accumulation or function. In this study, cadmium chloride treatment of Xenopus laevis A6 kidney epithelial cells induced a dose- and time-dependent increase in BiP, HSP70 and heme oxygenase-1 (HO-1) accumulation. Exposure of cells to a relatively low cadmium concentration at a mild heat shock temperature of 30°C greatly enhanced BiP and HSP70 accumulation compared to cadmium at 22°C. Treatment of cells with the glutathione synthesis inhibitor, buthionine sulfoximine, enhanced cadmium-induced BiP and HSP70 accumulation. Immunocytochemistry revealed that cadmium-induced BiP accumulation occurred in a punctate pattern in the perinuclear region. In some cells treated with cadmium chloride or the proteasomal inhibitor, MG132, large BiP complexes were observed that co-localized with aggregated protein or aggresome-like structures. These BiP/aggresome-like structures were also observed in cells treated simultaneously with cadmium at 30°C or in the presence of buthionine sulfoximine. In amphibians, the association of BiP with unfolded protein and its possible role in aggresome function may be vital in the maintenance of cellular proteostasis.

Redox-Sensitive Cerium Oxide Nanoparticles Protect Human Keratinocytes from Oxidative Stress Induced by Glutathione Depletion

Cerium oxide nanoparticles (CeNPs) have gathered much attention in the biomedical field due to its unique antioxidant property. It can protect cells and tissues from oxidative stress induced damage due to its autoregenerative redox cycle. Our study explores the antioxidant and antigenotoxic behavior of PEGylated CeNPs toward oxidative insult produced by buthionine sulfoximine (BSO) in human keratinocytes (HaCaT cells). BSO inhibits the γ-glutamylcysteinesynthetase (γ-GCS) enzyme and thus acts as a glutathione (GSH) depleting agent to modulate the cellular redox potential. GSH is a natural ROS scavenger present in the mammalian cells, and its depletion causes generation of reactive oxygen species (ROS). In this study, we challenged HaCaT cells (keratinocytes) with BSO to alter the redox potential within the cell and monitored toxicity, ROS generation, and nuclear fragmentation. We also followed changes in expressions of related proteins and genes. We found that PEGylated CeNPs can protect HaCaT cells from BSO-induced oxidative damage. BSO-exposed cells, preincubated with PEGylated CeNPs, showed better cell survival and significant decrease in the intracellular levels of ROS. We also observed decrease in lactate dehydrogenase (LDH) release and nuclear fragmentation in CeNP-treated cells that were challenged with BSO as compared to treatment with BSO alone. Exposure of HaCaT cells with BSO leads to altered expression of antioxidant genes and proteins, i.e., thioredoxin reductase (TrxR) and peroxiredoxin 6 (Prx6) whereas, in our study, pretreatment of PEGylated CeNPs reduces the need for induction of genes that produce enzymes involved in the defense against oxidative stress. Since, growing evidence argued the involvement of ROS in mediating death of mammalian cells in several ailments, our finding reinforces the use of PEGylated CeNPs as a potent pharmacological agent under the lower cellular GSH/GSSG ratios for the treatment of diseases mediated by free radicals.

Involvement of glutathione in β-cyclodextrin-hemin complex-induced lateral root formation in tomato seedlings

β-cyclodextrin-hemin complex (β-CDH) was shown to induce lateral root (LR) formation in tomato. However, the molecular mechanism is still elusive. In this report, the role of reduced glutathione (GSH) in the induction of lateral root triggered by β-CDH was investigated. Similar to the responses of β-CDH, exogenously applied with 0.1 mΜ GSH not only increased endogenous GSH content determined by spectrophotography and the monochlorobimane (MCB)-dependent fluorescent analysis, but also induced, thereafter, LR formation. Meanwhile, both β-CDH- and GSH-induced lateral root primordia (LRP) exhibited a similar accelerated anatomic structure. Above inducible responses were blocked significantly when the _L-buthionine-(S,R)-sulfoximine (BSO), a potent and specific inhibitor of the enzyme catalyzing the first step of GSH biosynthesis, was separately applied. Upon β-CDH treatment, the changes of endogenous GSH content determined by spectrophotography and fluorescent analysis were consistent with the transcripts of two GSH synthetic genes, GSH1 and GSH2 encoding γ-glutamyl cysteine synthetase and glutathione synthetase, respectively. Exogenously applied with β-CDH could rescue N-1-naphthylphthalamic acid (NPA; IAA depletion)-triggered inhibition of LR formation. Further molecular evidence revealed that both β-CDH and GSH modulated gene expression of cell cycle regulatory genes (CYCA2;1, CYCA3;1, CYCD3;1, and CDKA1) and auxin signaling genes (ARF7 and RSI-1), six marker genes responsible for LR formation. By contrast, above changes were sensitive to the co-treatment with BSO. All together, these results suggest a role for GSH in the regulation of tomato LR development triggered by β-CDH.

Loss of C/EBPδ enhances IR-induced cell death by promoting oxidative stress and mitochondrial dysfunction

Exposure of cells to ionizing radiation (IR) generates reactive oxygen species (ROS). This results in increased oxidative stress and DNA double strand breaks (DSBs) which are the two underlying mechanisms by which IR causes cell/tissue injury. Cells that are deficient or impaired in the cellular antioxidant response are susceptible to IR-induced apoptosis. The transcription factor CCAAT enhancer binding protein delta (Cebpd, C/EBPδ) has been implicated in the regulation of oxidative stress, DNA damage response, genomic stability and inflammation. We previously reported that Cebpd-deficient mice are sensitive to IR and display intestinal and hematopoietic injury, however the underlying mechanism is not known. In this study, we investigated whether an impaired ability to detoxify IR-induced ROS was the underlying cause of the increased radiosensitivity of Cebpd-deficient cells. We found that Cebpd-knockout (KO) mouse embryonic fibroblasts (MEFs) expressed elevated levels of ROS, both at basal levels and after exposure to gamma radiation which correlated with increased apoptosis, and decreased clonogenic survival. Pre-treatment of wild type (WT) and KO MEFs with polyethylene glycol-conjugated Cu-Zn superoxide dismutase (PEG-SOD) and catalase (PEG-CAT) combination prior to irradiation showed a partial rescue of clonogenic survival, thus demonstrating a role for increased intracellular oxidants in promoting IR-induced cell death. Analysis of mitochondrial bioenergetics revealed that irradiated KO MEFs showed significant reductions in basal, adenosine triphosphate (ATP)-linked, maximal respiration and reserved respiratory capacity and decrease in intracellular ATP levels compared to WT MEFs indicating they display mitochondrial dysfunction. KO MEFs expressed significantly lower levels of the cellular antioxidant glutathione (GSH) and its precursor- cysteine as well as methionine. In addition to its antioxidant function, GSH plays an important role in detoxification of lipid peroxidation products such as 4-hydroxynonenal (4-HNE). The reduced GSH levels observed in KO MEFs correlated with elevated levels of 4-HNE protein adducts in irradiated KO MEFs compared to respective WT MEFs. We further showed that pre-treatment with the GSH precursor, N-acetyl L-cysteine (NAC) prior to irradiation showed a significant reduction of IR-induced cell death and increases in GSH levels, which contributed to the overall increase in clonogenic survival of KO MEFs. In contrast, pre-treatment with the GSH synthesis inhibitor- buthionine sulfoximine (BSO) further reduced the clonogenic survival of irradiated KO MEFs. This study demonstrates a novel role for C/EBPδ in protection from basal as well as IR-induced oxidative stress and mitochondrial dysfunction thus promoting post-radiation survival.

Cytokinin Determines Thiol-Mediated Arsenic Tolerance and Accumulation

The presence of arsenic in soil and water is a constant threat to plant growth in many regions of the world. Phytohormones act in the integration of growth control and stress response, but their role in plant responses to arsenic remains to be elucidated. Here, we show that arsenate [As(V)], the most prevalent arsenic chemical species in nature, causes severe depletion of endogenous cytokinins (CKs) in the model plant Arabidopsis (Arabidopsis thaliana). We found that CK signaling mutants and transgenic plants with reduced endogenous CK levels showed an As(V)-tolerant phenotype. Our data indicate that in CK-depleted plants exposed to As(V), transcript levels of As(V)/phosphate-transporters were similar or even higher than in wild-type plants. In contrast, CK depletion provoked the coordinated activation of As(V) tolerance mechanisms, leading to the accumulation of thiol compounds such as phytochelatins and glutathione, which are essential for arsenic sequestration. Transgenic CK-deficient Arabidopsis and tobacco lines show a marked increase in arsenic accumulation. Our findings indicate that CK is an important regulatory factor in plant adaptation to arsenic stress.

Diverse effects of taurine on vascular response and inflammation in GSH depletion model in rabbits

OBJECTIVE

A reduction in GSH and an increase in free radicals are observed in inflammatory diseases, indicating oxidative stress. Taurine protects cells from the cytotoxic effects of inflammation. There have been limited studies to date evaluating the effect of taurine in oxidative stress-induced vascular dysfunction and its role in vascular inflammatory diseases. Therefore, we aimed to investigate the effect of taurine on the regulation of vascular tonus and vascular inflammatory markers in rabbit aortae and carotid arteries in oxidative stress-induced by GSH depletion.

MATERIALS AND METHODS

Rabbits were treated subcutaneously with buthionine sulfoximine (BSO), GSH-depleting compound and/or taurine. Cumulative concentration-response curves for acetylcholine (ACh), phenylephrine and 5-hydroxytriptamine (5-HT) were constructed with or without Nω-nitro-L-arginine (LNA) in the carotid artery and aorta rings. Immunohistochemical staining was performed for TNF-α and IL-1β.

RESULTS

BSO increased ACh-induced NO-dependent relaxations, phenylephrine-induced contractions in the carotid artery and 5-HT induced-contractions in both the carotid artery and the aorta. BSO decreased EDHF dependent relaxations only in the aorta. ACh-induced NO-dependent relaxations and augmented contractions were normalized by taurine. BSO increased TNF-α expressions in both carotid arteries and aortas, which were reversed by taurine. The BSO-induced increase in IL-1β was reversed by taurine only in aortae.

CONCLUSIONS

Treatment with BSO resulted in vascular reactivity changes and increased immunostaining of TNF-α in mainly carotid arteries in this model of oxidative stress. The effect of taurine on BSO-induced vascular reactivity changes varied depending on the vessel. The inhibition of the increase in TNF-α expression by taurine in both carotid arteries and aortae supports the proposal that taurine has a beneficial effect in the treatment of inflammatory diseases such as atherosclerosis.

A Low Glutathione Redox State Couples with a Decreased Ascorbate Redox Ratio to Accelerate Flowering in Oncidium Orchid

Glutathione (GSH) plays multiple roles in plants, including stress defense and regulation of growth/development. Previous studies have demonstrated that the ascorbate (AsA) redox state is involved in flowering initiation in Oncidium orchid. In this study, we discovered that a significantly decreased GSH content and GSH redox ratio are correlated with a decline in the AsA redox state during flowering initiation and high ambient temperature-induced flowering. At the same time, the expression level and enzymatic activity of GSH redox-regulated genes, glutathione reductase (GR1), and the GSH biosynthesis genes γ-glutamylcysteine synthetase (GSH1) and glutathione synthase (GSH2), are down-regulated. Elevating dehydroascorbate (DHA) content in Oncidium by artificial addition of DHA resulted in a decreased AsA and GSH redox ratio, and enhanced dehydroascorbate reductase (DHAR) activity. This demonstrated that the lower GSH redox state could be influenced by the lower AsA redox ratio. Moreover, exogenous application of buthionine sulfoximine (BSO), to inhibit GSH biosynthesis, and glutathione disulfide (GSSG), to decrease the GSH redox ratio, also caused early flowering. However, spraying plants with GSH increased the GSH redox ratio and delayed flowering. Furthermore, transgenic Arabidopsis overexpressing Oncidium GSH1, GSH2 and GR1 displayed a high GSH redox ratio as well as delayed flowering under high ambient temperature treatment, while pad2, cad2 and gr1 mutants exhibited early flowering and a low GSH redox ratio. In conclusion, our results provide evidence that the decreased GSH redox state is linked to the decline in the AsA redox ratio and mediated by down-regulated expression of GSH metabolism-related genes to affect flowering time in Oncidium orchid.

The role of glutathione detoxification pathway in MCLR-induced hepatotoxicity in SD rats

In the present study, we investigated the role of glutathione (GSH) and its related enzymes in Sprague Dawley (SD) rats subjected to microcystin-leucine-arginine (MCLR)-induced hepatotoxicity. SD rats were intraperitoneally (i.p.) injected with MCLR after pretreating with or without buthionine-(S,R)-sulfoximine (BSO), an inhibitor of GSH synthesis. The depletion of GSH with BSO enhanced MCLR-induced oxidative stress, resulting in more severe liver damage and higher MCLR accumulation. Similarly, the contents of malondialdehyde (MDA), total GSH (T-GSH), oxidized GSH (GSSG) and GSH were significantly enhanced in BSO pretreated rats following MCLR treatment. The study showed that the transcription of GSH-related enzymes such as glutathione-S-transferase (GST), γ-glutamylcysteine synthetase (γ-GCS), glutathione reductase (GR) varied in different ways (expect for glutathione peroxidase (GPx), whose gene expression was induced in all treated groups) with or without BSO pretreatment before MCLR exposure, suggesting an adaptative response of GSH-related enzymes at transcription level to combat enhancement of oxidative stress induced by MCLR when pretreated with BSO. These data suggested the tissues with low GSH concentration are highly vulnerable to MCLR toxicity and GSH was critical for the detoxification in MCLR-induced hepatotoxicity in vivo.

Glutathione plays an essential role in nitric oxide-mediated iron-deficiency signaling and iron-deficiency tolerance in Arabidopsis

Iron (Fe) deficiency is a common agricultural problem that affects both the productivity and nutritional quality of plants. Thus, identifying the key factors involved in the tolerance of Fe deficiency is important. In the present study, the zir1 mutant, which is glutathione deficient, was found to be more sensitive to Fe deficiency than the wild type, and grew poorly in alkaline soil. Other glutathione-deficient mutants also showed various degrees of sensitivity to Fe-limited conditions. Interestingly, we found that the glutathione level was increased under Fe deficiency in the wild type. By contrast, blocking glutathione biosynthesis led to increased physiological sensitivity to Fe deficiency. On the other hand, overexpressing glutathione enhanced the tolerance to Fe deficiency. Under Fe-limited conditions, glutathione-deficient mutants, zir1, pad2 and cad2 accumulated lower levels of Fe than the wild type. The key genes involved in Fe uptake, including IRT1, FRO2 and FIT, are expressed at low levels in zir1; however, a split-root experiment suggested that the systemic signals that govern the expression of Fe uptake-related genes are still active in zir1. Furthermore, we found that zir1 had a lower accumulation of nitric oxide (NO) and NO reservoir S-nitrosoglutathione (GSNO). Although NO is a signaling molecule involved in the induction of Fe uptake-related genes during Fe deficiency, the NO-mediated induction of Fe-uptake genes is dependent on glutathione supply in the zir1 mutant. These results provide direct evidence that glutathione plays an essential role in Fe-deficiency tolerance and NO-mediated Fe-deficiency signaling in Arabidopsis.