Elovanoid-N34 modulates TXNRD1 key in protection against oxidative stress-related diseases

The thioredoxin (TXN) system is an NADPH + H+/FAD redox-triggered effector that sustains homeostasis, bioenergetics, detoxifying drug networks, and cell survival in oxidative stress-related diseases. Elovanoid (ELV)-N34 is an endogenously formed lipid mediator in neural cells from omega-3 fatty acid precursors that modulate neuroinflammation and senescence gene programming when reduction-oxidation (redox) homeostasis is disrupted, enhancing cell survival. Limited proteolysis (LiP) screening of human retinal pigment epithelial (RPE) cells identified TXNRD1 isoforms 2, 3, or 5, the reductase of the TXN system, as an intracellular target of ELV-N34. TXNRD1 silencing confirmed that the ELV-N34 target was isoform 2 or 3. This lipid mediator induces TXNRD1 structure changes that modify the FAD interface domain, leading to its activity modulation. The addition of ELV-N34 decreased membrane and cytosolic TXNRD1 activity, suggesting localizations for the targeted reductase. These results show for the first time that the lipid mediator ELV-N34 directly modulates TXNRD1 activity, underling its protection in several pathologies when uncompensated oxidative stress (UOS) evolves.

The molecular evaluation of thioredoxin (TXN1 & TXN2), thioredoxin reductase 1 (TXNRd1), and oxidative stress markers in a binary rat model of hypo- and hyperthyroidism after treatment with gallic acid

Oxidative stress plays an important role in the pathology of thyroid disorders. This study examined the effect of gallic acid (GA) on the oxidative status and expression of liver antioxidant genes including thioredoxin (TXN1 & TXN2) and thioredoxin reductase1 (TXNRd1) in hypo- and hyperthyroid rat models. Forty-nine male Wistar rats were randomly assigned into seven groups as follows: control group, hypothyroid and hyperthyroid groups respectively induced by propylthiouracil and levothyroxine, hypo- and hyper thyroid-treated groups (where the groups were separately treated with 50 and 100 mg/kg of GA daily, orally). The levels of thyroid hormones and serum oxidative stress markers were evaluated after 5 weeks. The relative expression of TXN1,2 and TXNRd1 genes was measured via real-time qRT-PCR. The mean level of total antioxidant capacity (TAC), malondialdehyde, and uric acid index diminished in the hypothyroid group. Increased TAC reached almost the level of control in hypothyroid groups treated with GA. Elevation of thiol index in the hypothyroid group was observed (p < 0.01), which diminished to the control level after GA treatment. The relative expression of TXN1, TXNRd1, and TXN2 genes in the hypothyroid and hyperthyroid groups significantly increased compared to the control group (p ≥ 0.05), but in the groups treated with GA, the expression of these genes declined significantly (p ≥ 0.05). Our results indicated GA can affect the expression of TXN system genes in the rat liver. Also, the results suggest GA has a more positive effect on modulating serum oxidative parameters in hypothyroid rat models than in hyperthyroid.

Thioredoxin reductase 1 regulates hepatic inflammation and macrophage activation during acute cholestatic liver injury

BACKGROUND AND AIMS

Cholestatic liver diseases, including primary sclerosing cholangitis, are characterized by periportal inflammation with progression to hepatic fibrosis and ultimately cirrhosis. We recently reported that the thioredoxin antioxidant response is dysregulated during primary sclerosing cholangitis. The objective of this study was to examine the impact of genetic and pharmacological targeting of thioredoxin reductase 1 (TrxR1) on hepatic inflammation and liver injury during acute cholestatic injury.

APPROACH AND RESULTS

Primary mouse hepatocytes and intrahepatic macrophages were isolated from 3-day bile duct ligated (BDL) mice and controls. Using wildtype and mice with a liver-specific deletion of TrxR1 (TrxR1LKO), we analyzed the effect of inhibition or ablation of TrxR1 signaling on liver injury and inflammation. Immunohistochemical analysis of livers from BDL mice and human cholestatic patients revealed increased TrxR1 staining in periportal macrophages and hepatocytes surrounding fibrosis. qPCR analysis of primary hepatocytes and intrahepatic macrophages revealed increased TrxR1 mRNA expression following BDL. Compared with sham controls, BDL mice exhibited increased inflammation, necrosis, and increased mRNA expression of pro-inflammatory cytokines, fibrogenesis, the NLRP3 inflammatory complex, and increased activation of NFkB, all of which were ameliorated in TrxR1LKO mice. Importantly, following BDL, TrxR1LKO induced periportal hepatocyte expression of Nrf2-dependent antioxidant proteins and increased mRNA expression of basolateral bile acid transporters with reduced expression of bile acid synthesis genes. In the acute BDL model, the TrxR1 inhibitor auranofin (10 mg/kg/1 d preincubation, 3 d BDL) ameliorated BDL-dependent increases in Nlrp3, GsdmD, Il1β, and TNFα mRNA expression despite increasing serum alanine aminotransferase, aspartate aminotransferase, bile acids, and bilirubin.

CONCLUSIONS

These data implicate TrxR1-signaling as an important regulator of inflammation and bile acid homeostasis in cholestatic liver injury.

Targeted inhibition of TXNRD1 prevents cartilage extracellular matrix degeneration by activating Nrf2 pathway in osteoarthritis

Osteoarthritis, a prevalent orthopedic disease, can affect the elderly and causes impairment. The degradation and aberrant homeostasis of cartilage extracellular matrix figure pivotally in the progression of osteoarthritis. Thioredoxin systems plays a role in a wide range of biological processes, including cell proliferation, apoptosis, and oxidative stress. The present study aimed to investigate the unique function and underlying pathophysiological mechanism of TXNRD1 in chondrocytes. An upregulated expression of TXNRD1 was observed in the articular cartilage of osteoarthritis patients compared with normal articular cartilage. Furthermore, in vitro experiments showed that the expression of TXNRD1 was also abnormally increased in IL-1β-induced primary mouse chondrocytes. Silencing TXNRD1 using siRNA in chondrocytes could effectively inhibit the expression of ADAMTS5 and MMP13, and enhance the expression of COL2A1 and SOX9. The same was true for auranofin, an inhibitor of TXNRD1. This phenomenon indicated that inhibition of TXNRD1 attenuated il-1β-induced metabolic imbalance of extracellular matrix (ECM) and the progression of chondrocyte osteoarthritis. Further mechanism analysis revealed that the activation of Nrf2 signaling pathway and the expression of heme oxygenase-1 (HO-1) were increased upon TXNRD1 inhibition. Furthermore, auranofin was found to attenuate DMM-induced osteoarthritis progression in vivo. Therefore, the pharmacological downregulation of TXNRD1 may provide an effective novel therapy for OA.

Menadione Potentiates Auranofin-Induced Glioblastoma Cell Death

Glioblastoma (GBM) is the most aggressive primary brain tumor. Recently, agents increasing the level of oxidative stress have been proposed as anticancer drugs. However, their efficacy may be lowered by the cytoprotective activity of antioxidant enzymes, often upregulated in neoplastic cells. Here, we assessed the mRNA and protein expression of thioredoxin reductase 1 (TrxR1), a master regulator of cellular redox homeostasis, in GBM and non-tumor brain tissues. Next, we examined the influence of an inhibitor of TrxR1, auranofin (AF), alone or in combination with a prooxidant menadione (MEN), on growth of GBM cell lines, patient-derived GBM cells and normal human astrocytes. We detected considerable amount of TrxR1 in the majority of GBM tissues. Treatment with AF decreased viability of GBM cells and their potential to form colonies and neurospheres. Moreover, it increased the intracellular level of reactive oxygen species (ROS). Pre-treatment with ROS scavenger prevented the AF-induced cell death, pointing to the important role of ROS in the reduction of cell viability. The cytotoxic effect of AF was potentiated by treatment with MEN. In conclusion, our results identify TrxR1 as an attractive drug target and highlights AF as an off-patent drug candidate in GBM therapy.

Selenide Chitosan Sulfate Improved the Hepatocyte Activity, Growth Performance, and Anti-oxidation Capacity by Activating the Thioredoxin Reductase of Chickens In Vitro and In Vivo

Chicken hepatocytes were cultured in vitro and 240 specific pathogen-free (SPF) white leghorns chickens (7 days old) were obtained. The hepatocytes and chickens were randomly allocated to one of six treatment groups: control group; chitosan (COS) group; sodium selenite (Na₂SeO₃) group; selenide chitosan (COS-Se) group; chitosan sulfate (LS-COS) group; and selenide chitosan sulfate (LS-COS-Se) group. Our results showed that LS-COS-Se increased (P < 0.05) the activities of thioredoxin reductase (TXNRD), anti-superoxide anion radical (antiO₂^-), and superoxide dismutase (SOD), the mRNA levels of thioredoxin reductase 1 (TXNRD1) and thioredoxin reductase 3 (TXNRD3), and the chicken body weight, but reduced (P < 0.05) the malondialdehyde (MDA) content and the lactate dehydrogenase (LDH) activity. Compared with COS and LS-COS, the LS-COS-Se treatment increased (P < 0.05) the activities of TXNRD, SOD, catalase (CAT), and the mRNA levels of TXNRD1 and TXNRD3, but reduced (P < 0.05) the MDA content in vitro, whereas, in vivo, it increased (P < 0.05) body weight on day 28; the activities of TXNRD, antiO₂^-, and SOD; and the mRNA levels of TXNRD1 and TXNRD3. Compared with Na₂SeO₃ and COS-Se, the LS-COS-Se treatment increased (P < 0.05) the TXNRD and SOD activities, the mRNA levels of TXNRD1 and TXNRD3 in vitro, increased (P < 0.05) the chicken body weight on day 28, and the TXNRD, antiO₂^-, and SOD activities, but reduced (P < 0.05) the MDA content. These results indicated that LS-COS-Se was a useful antioxidant that improved hepatocyte activity, growth performance, and anti-oxidation capacity in hepatocytes (in vitro) and SPF chicken (in vivo) by activating the TXNRD system.

Thioredoxin Reductase 1 Modulates Pigmentation and Photobiology of Murine Melanocytes in vivo

Pigment-producing melanocytes overcome frequent oxidative stress in their physiological role of protecting the skin against the deleterious effects of solar UV irradiation. This is accomplished by the activity of several endogenous antioxidant systems, including the thioredoxin antioxidant system, in which thioredoxin reductase 1 (TR1) plays an important part. To determine whether TR1 contributes to the redox regulation of melanocyte homeostasis, we have generated a selective melanocytic Txnrd1-knockout mouse model (Txnrd1mel‒/‒), which exhibits a depigmentation phenotype consisting of variable amelanotic ventral spotting and reduced pigmentation on the extremities (tail tip, ears, and paws). The antioxidant role of TR1 was further probed in the presence of acute neonatal UVB irradiation, which stimulates melanocyte activation and introduces a spike in oxidative stress in the skin microenvironment. Interestingly, we observed a significant reduction in overall melanocyte count and proliferation in the absence of TR1. Furthermore, melanocytes exhibited an elevated level of UV-induced DNA damage in the form of 8-oxo-2'-deoxyguanosine after acute UVB treatment. We also saw an engagement of compensatory antioxidant mechanisms through increased nuclear localization of transcription factor NRF2. Altogether, these data indicate that melanocytic TR1 positively regulates melanocyte homeostasis and pigmentation during development and protects against UVB-induced DNA damage and oxidative stress.

Association between genetic variants in oxidative stress-related genes and osteoporotic bone fracture. The Hortega follow-up study

The most widely accepted etiopathogenesis hypothesis of the origin of osteoporosis and its complications is that they are a consequence of bone aging and other environmental factors, together with a genetic predisposition. Evidence suggests that oxidative stress is crucial in bone pathologies associated with aging. The aim of this study was to determine whether genetic variants in oxidative stress-related genes modified the risk of osteoporotic fracture. We analysed 221 patients and 354 controls from the HORTEGA sample after 12-14 years of follow up. We studied the genotypic and allelic distribution of 53 SNPs in 24 genes involved in oxidative stress. The results showed that being a carrier of the variant allele of the SNP rs4077561 within TXNRD1 was the principal genetic risk factor associated with osteoporotic fracture and that variant allele of the rs1805754 M6PR, rs4964779 TXNRD1, rs406113 GPX6, rs2281082 TXN2 and rs974334 GPX6 polymorphisms are important genetic risk factors for fracture. This study provides information on the genetic factors associated with oxidative stress which are involved in the risk of osteoporotic fracture and reinforces the hypothesis that genetic factors are crucial in the etiopathogenesis of osteoporosis and its complications.

Correlation between TXNRD1/HO-1 expression and response to neoadjuvant chemoradiation therapy in patients with esophageal squamous cell carcinoma

BACKGROUND

Thioredoxin reductase 1 (TXNRD1) and heme oxygenase-1 (HO-1) are both involved in the nuclear factor erythroid 2-related factor 2 (Nrf2) pathway and play key roles in antioxidant responses. In patients with esophageal squamous cell carcinoma (ESCC), the correlation between the expression of these two proteins and the therapeutic response to neoadjuvant chemoradiation therapy (NACRT), as well as the difference in their expression after chemoradiotherapy, remains unknown.

METHODS

Proteins involved in the Nrf2 pathway were immunolocalized in carcinoma cells in ESCC patients on NACRT with 5-fluorouracil and cisplatin, followed by esophagectomy. The 8-hydroxydeoxyguanosine (8-OHdG) levels were used to quantify reactive oxygen species. The changes in immunoreactivity before and after NACRT (Δ) were assessed.

RESULTS

Tumor reduction following NACRT was significantly attenuated in pre-therapeutic biopsy specimens associated with high HO-1 status. TXNRD1Δ, HO-1Δ, and 8-OHdGΔ were significantly different in the ineffective and effective groups. The overall survival was significantly lower in high Nrf2 and TXNRD1 groups. In addition, high TXNRD1 expression was an independent prognostic factor in the multivariate analysis of overall survival.

CONCLUSIONS

The study findings indicate that HO-1 status in pre-therapeutic biopsy specimens could predict response to NACRT, and TXNRD1 status could predict overall survival of ESCC patients.

Thioredoxin reductase-1 levels are associated with NRF2 pathway activation and tumor recurrence in non-small cell lung cancer

Activating mutations in the KEAP1/NRF2 pathway characterize a subset of non-small cell lung cancer (NSCLC) associated with chemoresistance and poor prognosis. We herein evaluated the relationship between 64 oxidative stress-related genes and overall survival data from 35 lung cancer datasets. Thioredoxin reductase-1 (TXNRD1) stood out as the most significant predictor of poor outcome. In a cohort of NSCLC patients, high TXNRD1 protein levels correlated with shorter disease-free survival and distal metastasis-free survival post-surgery, including a subset of individuals treated with platinum-based adjuvant chemotherapy. Bioinformatics analysis revealed that NSCLC tumors harboring genetic alterations in the NRF2 pathway (KEAP1, NFE2L2 and CUL3 mutations, and NFE2L2 amplification) overexpress TXNRD1, while no association with EGFR, KRAS, TP53 and PIK3CA mutations was found. In addition, nuclear accumulation of NRF2 overlapped with upregulated TXNRD1 protein in NSCLC tumors. Functional cell assays and gene dependency analysis revealed that NRF2, but not TXNRD1, has a pivotal role in KEAP1 mutant cells' survival. KEAP1 mutants overexpress TXNRD1 and are less susceptible to the cytotoxic effects of the TXNRD1 inhibitor auranofin when compared to wild-type cell lines. Inhibition of NRF2 with siRNA or ML-385, and glutathione depletion with buthionine-sulfoximine, sensitized KEAP1 mutant A549 cells to auranofin. NRF2 knockdown and GSH depletion also augmented cisplatin cytotoxicity in A549 cells, whereas auranofin had no effect. In summary, these findings suggest that TXNRD1 is not a key determinant of malignant phenotypes in KEAP1 mutant cells, although this protein can be a surrogate marker of NRF2 pathway activation, predicting tumor recurrence and possibly other aggressive phenotypes associated with NRF2 hyperactivation in NSCLC.

Menadione inhibits thioredoxin reductase 1 via arylation at the Sec498 residue and enhances both NADPH oxidation and superoxide production in Sec498 to Cys498 substitution

The selenoprotein thioredoxin reductase 1 (TrxR1; TXNRD1) participates in multiple cellular processes and is regarded as a cellular target in anti-tumor drug discovery and development. TrxR1 has been reported to reduce menadione to menadiol and to produce superoxide anion radicals. However, the details of TrxR1-mediated menadione reduction have rarely been studied. In this study, we found that wild-type TrxR1 could reduce menadione in a less efficient way, but the U498C mutant variant supported high-efficiency menadione reduction in a Sec-independent manner. Meanwhile, the site-directed mutagenesis results showed that Cys⁶⁴ mutant increased the K_m values and decreased the catalytic efficiency, which was associated with a charge-transfer complex between FAD-Cys⁶⁴. Mass spectrometry (MS) revealed that in NADPH pre-reduced TrxR1 but not oxidized TrxR1, the highly active Sec⁴⁹⁸ of wild-type TrxR1 was arylated by menadione and strongly impaired the DTNB reducing activity in a dose-dependent manner. TrxR1 reduced menadione more efficiently than glutathione reductase (GR), and interestingly menadione did not inhibit the GSSG reducing activity of GR. In summary, our results demonstrate that TrxR1 catalyzes the reduction of menadione in a Sec-independent manner, which highly depend on Cys⁴⁹⁸ instead of N-terminal redox motif, and the Sec⁴⁹⁸ of TrxR1 is the primary target of menadione. The interaction between menadione and TrxR1 revealed in this study may provide a valuable reference for the development of anticancer drugs targeting selenoprotein TrxR1.

Egg yolk oils exert anti-inflammatory effect via regulating Nrf2/NF-κB pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Egg yolk oils (EYO) is a traditional Chinese medicine obtained from Gallus gallus domesticus Brisson, which has been used to treat inflammatory related diseases such as cheilitis, ulceration and acute anal fissure. However, the detailed anti-inflammatory mechanism of EYO is still unknown.

AIM OF THE STUDY

The anti-inflammatory activity and mechanism of EYO were investigated in tumor necrosis factor (TNF)-α induced Caco-2 cells.

MATERIALS AND METHODS

EYO was obtained by direct-heat extraction (HE), ethanol extraction (EE) and petroleum ether extraction (PE), respectively. Fatty acid compositions of three EYO were measured by gas chromatography (GC). Cell viability, enzyme-linked immunosorbent assay (ELISA), transcriptome, RT-PCR and Western blotting were also performed.

RESULTS

Fatty acid compositions of three EYO were different with varied extraction methods. EYO significantly reduced interleukin (IL)-8 secretion. EYO exerted anti-inflammatory effect via coordinating regulation of Nrf2/NF-κB pathways based on the results of transcriptome, Q-PCR and Western blotting. In detail, PE and HE inhibited the NF-κB pathway, whereas EE exerted anti-inflammatory activity via the Nrf2/NF-κB pathways.

CONCLUSIONS

The aforementioned results showed the anti-inflammatory mechanism of EYO. These findings might be beneficial to clinical applications of EYO.

miR‑875‑5p regulates IR and inflammation via targeting TXNRD1 in gestational diabetes rats

Gestational diabetes mellitus (GDM) is a serious life‑threatening disease that affects the mother and fetus. However, the pathogenesis of GDM is still unclear. microRNAs (miRs) play vital roles in the regulation of various cell functions. The present study aimed to investigate the effects of miR‑875‑5p and thioredoxin reductase 1 cytoplasmic (TXNRD1) in GDM rats and analyze the associated underlying mechanism. A GDM rat model was induced using an intraperitoneal injection of streptozotocin. miR‑875‑5p knockdown plasmids or TXNRD1 knockdown plasmids were injected into the rats via the caudal vein. miR‑875‑5p and TXNRD1 expression in the serum were detected using reverse transcription‑quantitative PCR (RT‑qPCR) or western blot (WB) analyses. The fasting blood‑glucose (FBG), fasting serum insulin, triglyceride and high density lipoprotein levels were detected by specific commercial kits. The inflammatory response and the induction of oxidative stress were analyzed by assessing the expression of associated markers via WB, RT‑qPCR or commercial kits. The pancreatic and placental injuries were detected by hematoxylin and eosin staining. The results indicated that miR‑875‑5p expression levels were downregulated, whereas TXNRD1 levels were upregulated in GDM rats compared with normal pregnancy rats. miR‑875‑5p significantly regulated TXNRD1 expression in GDM rats. miR‑875‑5p silencing notably reduced FBG and insulin resistance, which was accompanied by reduced expression levels of blood lipid and pro‑inflammatory markers as well as reduced oxidative stress. However, the effects of miR‑875‑5p could be reversed by TXNRD1 silencing. Therefore, the present study indicated that miR‑875‑5p regulated IR and inflammation by targeting TXNRD1 in GDM rats. miR‑875‑5p and TXNRD1 may be considered as potential targets for treating GDM.

System-wide identification and prioritization of enzyme substrates by thermal analysis

Despite the immense importance of enzyme-substrate reactions, there is a lack of general and unbiased tools for identifying and prioritizing substrate proteins that are modified by the enzyme on the structural level. Here we describe a high-throughput unbiased proteomics method called System-wide Identification and prioritization of Enzyme Substrates by Thermal Analysis (SIESTA). The approach assumes that the enzymatic post-translational modification of substrate proteins is likely to change their thermal stability. In our proof-of-concept studies, SIESTA successfully identifies several known and novel substrate candidates for selenoprotein thioredoxin reductase 1, protein kinase B (AKT1) and poly-(ADP-ribose) polymerase-10 systems. Wider application of SIESTA can enhance our understanding of the role of enzymes in homeostasis and disease, opening opportunities to investigate the effect of post-translational modifications on signal transduction and facilitate drug discovery.

SECISBP2 is a novel prognostic predictor that regulates selenoproteins in diffuse large B-cell lymphoma

The overexpression of glutathione peroxidase 4 (GPX4; an enzyme that suppresses peroxidation of membrane phospholipids) is considered a poor prognostic predictor of diffuse large B-cell lymphoma (DLBCL). However, the mechanisms employed in GPX4 overexpression remain unknown. GPX4 is translated as a complete protein upon the binding of SECISBP2 to the selenocysteine insertion sequence (SECIS) on the 3'UTR of GPX4 mRNA. In this study, we investigated the expression of SECISBP2 and its subsequent regulation of GPX4 and TXNRD1 in DLBCL patients. Moreover, we determined the significance of the expression of these selenoproteins in vitro using MD901 and Raji cells. SECISBP2 was positive in 45.5% (75/165 cases) of DLBCL samples. The SECISBP2-positive group was associated with low overall survival (OS) as compared to the SECISBP2-negative group (P = 0.006). Similarly, the SECISBP2 and GPX4 or TXNRD1 double-positive groups (P < 0.001), as well as the SECISBP2, GPX4, and TXNRD1 triple-positive group correlated with poor OS (P = 0.001), suggesting that SECISBP2 may serve as an independent prognostic predictor for DLBCL (hazard ratio (HR): 2.693, P = 0.008). In addition, western blotting showed a decrease in GPX4 and TXNRD1 levels in SECISBP2-knockout (KO) MD901 and Raji cells. Oxidative stress increased the accumulation of reactive oxygen species in SECISBP2-KO cells (MD901; P < 0.001, Raji; P = 0.020), and reduced cell proliferation (MD901; P = 0.001, Raji; P = 0.030), suggesting that SECISBP2-KO suppressed resistance to oxidative stress. Doxorubicin treatment increased the rate of cell death in SECISBP2-KO cells (MD901; P < 0.001, Raji; P = 0.048). Removal of oxidative stress inhibited the altered cell death rate. Taken together, our results suggest that SECISBP2 may be a novel therapeutic target in DLBCL.

Overexpression of thioredoxin reductase 1 can reduce DNA damage, mitochondrial autophagy and endoplasmic reticulum stress in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disease characterized by the loss of dopaminergic neurons in the substantia nigra (SN). Several factors, including neuroinflammation, neuronal excitotoxicity, genetic mutations and incorrect protein folding are involved in PD pathophysiology. However, the precise mechanism that contributes to the decreased number of dopaminergic neurons is unknown. A growing body of research suggests that oxidative stress is a major factor in PD. Therefore, antioxidant therapy is an important approach for treating PD. The thioredoxin system is an important antioxidant system, and thioredoxin reductase 1 (TR1) is a major member of the thioredoxin system. The present study demonstrates that oxidative stress is increased and that the expression of TR1 is decreased in the SNc of A53T mice; TR1 has emerged as an important antioxidant agent in dopaminergic neurons. Therefore, we over-expressed TR1 in the MPP⁺-induced cellular model and in the A53T transgenic mouse model of PD. We confirmed that the overexpression of TR1 in neuronal cells decreased DNA damage and malondialdehyde (MDA) and ROS generation, increased T-SOD and GSH production, and decreased the ER stress, and autophagy in the PD model. In summary, our findings demonstrate that the overexpression of TR1 could be effective as a novel neuroprotective strategy for PD. This research suggests a novel direction in the treatment of PD.

Accessing the transcriptional status of selenoproteins in skin cancer-derived cell lines

BACKGROUND

Selenoproteins are selenocysteine (Sec)-containing proteins that exhibit numerous physiological functions, mainly antioxidative activities. Studies have suggested that several human selenoproteins play an important role in tumor initiation and progression, including melanoma.

METHODS

Using RNA-seq data set from Sequence Reads Archive (SRA) experiments published at the National Center for Biotechnology Information (NCBI), we determined and compared the transcriptional levels of the 25 selenoproteins-coding sequences found in 16 human-derived melanoma cell lines and compared to four melanocyte controls.

RESULTS

15 selenoprotein-coding genes were found to be expressed in melanoma and normal melanocyte cells, and their mRNA levels varied among the cell lines. All melanoma cells analyzed with BRAF or NRAS mutations presented upregulated levels of SELENOI, TXNRD1, and SELENOT transcripts and downregulated levels of SELENOW and SELENON transcripts in comparison with melanocytes controls. Moreover, SELENOW, SELENON, SELENOI, TXNRD1, and SELENOT-coding transcripts were affected when BRAF-mutated A375 cells were treated with CPI203, A771726 or Vorinostat drugs.

CONCLUSION

Our results indicate that melanoma cells can modify, in a different manner, the selenoprotein transcript levels, as a possible mechanism to control tumor progression. We suggest that the usage of diet and supplements containing selenium should be carefully used for patients with melanoma.

Control of protein function through oxidation and reduction of persulfidated states

Irreversible oxidation of Cys residues to sulfinic/sulfonic forms typically impairs protein function. We found that persulfidation (CysSSH) protects Cys from irreversible oxidative loss of function by the formation of CysSSO_1-3H derivatives that can subsequently be reduced back to native thiols. Reductive reactivation of oxidized persulfides by the thioredoxin system was demonstrated in albumin, Prx2, and PTP1B. In cells, this mechanism protects and regulates key proteins of signaling pathways, including Prx2, PTEN, PTP1B, HSP90, and KEAP1. Using quantitative mass spectrometry, we show that (i) CysSSH and CysSSO₃H species are abundant in mouse liver and enzymatically regulated by the glutathione and thioredoxin systems and (ii) deletion of the thioredoxin-related protein TRP14 in mice altered CysSSH levels on a subset of proteins, predicting a role for TRP14 in persulfide signaling. Furthermore, selenium supplementation, polysulfide treatment, or knockdown of TRP14 mediated cellular responses to EGF, suggesting a role for TrxR1/TRP14-regulated oxidative persulfidation in growth factor responsiveness.

A sub-individual multilevel approach for an integrative assessment of CuO nanoparticle effects on Corbicula fluminea

Because they are widely used, copper oxide nanoparticles (CuO NPs) are likely to enter the aquatic environment and then reach the sediment. We have examined the effect of CuO NPs in the freshwater endobenthic bivalve Corbicula fluminea. Some previous studies have investigated effects at biochemical and physiological levels, but molecular endpoints are still poorly studied despite they are sensitive in early detection of NPs effect. In the present study, we have investigated short-term effects (96 h) of CuO NP (12, 30 nm; 0, 20 and 100 μg/L) using molecular endpoints as well as more conventional biochemical and physiological markers. The expression of antioxidant (CuZnSOD, MnSOD, Cat, Se-GPx, Trxr) and antitoxic (GST-Pi, HSP70, MT, Pgp, MRP1) related genes was measured at the mRNA level while antioxidant (SOD, TAC) and antitoxic (GST, ACP) defenses, energetic reserves and metabolism (ETS, Tri, LDH), and cellular damages (LPO) were assessed using a biochemical approach. The filtration rate measured at 96 h provided information at the physiological scale. Gene expression and filtration rate were responsive to CuO NPs but the effects differed according to the NP size. The results suggest that defense mechanisms may have been set up following 30 nm-NP exposure. The response to 12 nm-NP was lower but still showed that exposure to 12 nm-NP led to activation of cellular elimination mechanisms. The lowering of the filtration rate may have protected the organisms from the contamination. However, this raised the question of further repercussions on organism biology. Together, the results (i) indicate that CuO NP may exert effects at different levels even after a short-term exposure and (ii) point out the precocity of molecular response.

Glutathione S-Transferase Regulates Mitochondrial Populations in Axons through Increased Glutathione Oxidation

Mitochondria are essential in long axons to provide metabolic support and sustain neuron integrity. A healthy mitochondrial pool is maintained by biogenesis, transport, mitophagy, fission, and fusion, but how these events are regulated in axons is not well defined. Here, we show that the Drosophila glutathione S-transferase (GST) Gfzf prevents mitochondrial hyperfusion in axons. Gfzf loss altered redox balance between glutathione (GSH) and oxidized glutathione (GSSG) and initiated mitochondrial fusion through the coordinated action of Mfn and Opa1. Gfzf functioned epistatically with the thioredoxin peroxidase Jafrac1 and the thioredoxin reductase 1 TrxR-1 to regulate mitochondrial dynamics. Altering GSH:GSSG ratios in mouse primary neurons in vitro also induced hyperfusion. Mitochondrial changes caused deficits in trafficking, the metabolome, and neuronal physiology. Changes in GSH and oxidative state are associated with neurodegenerative diseases like Alzheimer's. Our demonstration that GSTs are key in vivo regulators of axonal mitochondrial length and number provides a potential mechanistic link.

Reversing ROS-mediated neurotoxicity by chlorogenic acid involves its direct antioxidant activity and activation of Nrf2-ARE signaling pathway

Chlorogenic acid (CA), the ester of caffeic acid and quinic acid, is one of the most abundant polyphenols in coffee, and has multiple pharmacological functions. The present study is designed to explore the protection provided by CA against hydrogen peroxide (H₂ O₂ )-induced oxidative damages in the rat pheochromocytoma cells, and the underlying mechanisms engaged in this process. CA displays robust free radical-scavenging activity in vitro. More importantly, CA strikingly rescues the cells from the H₂ O₂ -mediated oxidative insults. Mechanistic studies revealed that CA upregulates a panel of phase II cytoprotective species, such as heme oxygenase-1, NAD(P)H: quinone oxidoreductase 1, glutathione, thioredoxin reductase 1, and thioredoxin 1. This neuroprotection is dependent on the activation of the transcription factor Nuclear factor erythroid 2-related factor 2 (Nrf2), as knockdown of Nrf2 abolishes such effect. Our results demonstrate that CA provides dual neuroprotection via directly neutralizing free radicals and indirectly inducing expression of Nrf2-driven cytoprotective enzymes, and suggest a potential therapeutic usage of CA as a neuroprotective agent. Coffee is one of the most popular drinks in the world, and our discovery may also contribute to understanding the beneficial effects of regular coffee consumption. © 2019 BioFactors, 45 (4):616-626, 2019.

Treatment of Caenorhabditis elegans with Small Selenium Species Enhances Antioxidant Defense Systems

SCOPE

Small selenium (Se) species play a key role in Se metabolism and act as dietary sources of the essential trace element. However, they are redox-active and trigger pro- and antioxidant responses. As health outcomes are strongly species-dependent, species-specific characteristics of Se compounds are tested in vivo.

METHODS AND RESULTS

In the model organism Caenorhabditis elegans (C. elegans), immediate and sustained effects of selenite, selenomethionine (SeMet), and Se-methylselenocysteine (MeSeCys) are studied regarding their bioavailability, incorporation into proteins, as well as modulation of the cellular redox status. While all tested Se compounds are bioavailable, only SeMet persistently accumulates and is non-specifically incorporated into proteins. However, the protection toward chemically-induced formation of reactive species is independent of the applied Se compound. Increased thioredoxin reductase (TXNRD) activity and changes in mRNA expression levels of antioxidant proteins indicate the activation of cellular defense mechanisms. However, in txnrd-1 deletion mutants, no protective effects of the Se species are observed anymore, which is also reflected by differential gene expression data.

CONCLUSION

Se species protect against chemically-induced reactive species formation. The identified immediate and sustained systemic effects of Se species give rise to speculations on possible benefits facing subsequent periods of inadequate Se intake.

Differential induction of nuclear factor-like 2 signature genes with toll-like receptor stimulation

Inflammation is associated with production of reactive oxygen species (ROS) and results in the induction of thioredoxin (TXN) and peroxiredoxins (PRDXs) and activation of nuclear factor-like 2 (Nrf2). In this study we have used the mouse RAW 264.7 macrophage and the human THP-1 monocyte cell line to investigate the pattern of expression of three Nrf2 target genes, PRDX1, TXN reductase (TXNRD1) and heme oxygenase (HMOX1), by activation of different Toll-like receptors (TLRs). We found that, while the TLR4 agonist lipopolysaccharide (LPS) induces all three genes, the pattern of induction with agonists for TLR1/2, TLR3, TLR2/6 and TLR7/8 differs depending on the gene and the cell line. In all cases, the extent of induction was HMOX1>TXNRD1>PRDX1. Since LPS was a good inducer of all genes in both cell lines, we studied the mechanisms mediating LPS induction of the three genes using mouse RAW 264.7 cells. To assess the role of ROS we used the antioxidant N-acetylcysteine (NAC). Only LPS induction of HMOX1 was inhibited by NAC while that of TXNRD1 and PRDX1 was unaffected. These three genes were also induced by phorbol myristate acetate (PMA), a ROS-inducer acting by activation of protein kinase C (PKC). The protein kinase inhibitor staurosporine inhibited the induction of all three genes by PMA but only that of HMOX1 by LPS. This indicates that activation of these genes by inflammatory agents is regulated by different mechanisms involving either ROS or protein kinases, or both.

The antimetastatic effect and underlying mechanisms of thioredoxin reductase inhibitor ethaselen

Treating cancer metastasis is of vital importance to prolong patients' survival. Thioredoxin reductase (TrxR) is overexpressed in many cancer types and has been recognized as an anti-cancer target. The organoselenium compound ethaselen (BBSKE) has been proved to be a TrxR inhibitor and inhibit various types of tumor growth. However, whether BBSKE could inhibit tumor metastasis remains unclear. In this study, we aim to explore the antimetastatic effect of BBSKE and underlying mechanisms. BBSKE was found to dose-dependently suppress migration and invasion of MCF-7 and LoVo cells in vitro. The underlying mechanisms may include inhibition of TrxR activity, elevation of reactive oxygen species (ROS), decrease of EGFR activation and HER2 expression. Besides, the epithelial to mesenchymal transition process and expression of CD44, MMP-9, VEGFR2 and PD-L1 were also abrogated. Decreased migration and invasion, lower expression levels of EGFR, HER2, N-cadherin, CD44, MMP-9, VEGFR2 and PD-L1 were also observed in TrxR1-knockdown MCF-7 and LoVo cells. In the mouse breast cancer 4T1 model, BBSKE not only inhibited progression of primary tumor, but also suppressed formation of metastatic lung nodules and liver micro-metastases, indicating that BBSKE could effectively abolish tumor metastasis. In conclusion, our findings show that BBSKE is able to inhibit migration and invasion of cancer cells in vitro and in vivo, and may be used to prevent and treat metastasis.

LPS protects macrophages from AIF-independent parthanatos by downregulation of PARP1 expression, induction of SOD2 expression, and a metabolic shift to aerobic glycolysis

In inflamed tissues or during ischemia-reperfusion episodes, activated macrophages produce large amounts of reactive species and are, thus, exposed to the damaging effects of reactive species. Here, our goal was to investigate the mechanism whereby activated macrophages protect themselves from oxidant stress-induced cell death. Hydrogen peroxide-treated mouse bone marrow-derived macrophages (BMDM) and THP-1 human monocyte-derived cells were chosen as models. We found a gradual development of resistance: first in monocyte-to-macrophage differentiation, and subsequently after lipopolysaccharide (LPS) exposure. Investigating the mechanism of the latter, we found that exposure to intense hydrogen peroxide stress causes poly(ADP-ribose) polymerase-1 (PARP-1) dependent programmed necrotic cell death, also known as parthanatos, as indicated by the protected status of PARP-1 knockout BMDMs and the protective effect of the PARP inhibitor PJ-34. In hydrogen peroxide-treated macrophages, however, apoptosis inducing factor (AIF) proved dispensable for parthanatos; nuclear translocation of AIF was not observed. A key event in LPS-mediated protection against the hydrogen peroxide-induced AIF independent parthanatos was downregulation of PARP1 mRNA and protein. The importance of this event was confirmed by overexpression of PARP1 in THP1 cells using a viral promoter, which lead to stable PARP1 levels even after LPS treatment and unresponsiveness to LPS-induced cytoprotection. In BMDMs, LPS-induced PARP1 suppression lead to prevention of NAD⁺ depletion. Moreover, LPS also induced expression of antioxidant proteins (superoxide dismutase-2, thioredoxin reductase 1 and peroxiredoxin) and triggered a metabolic shift to aerobic glycolysis, also known as the Warburg effect. In summary, we provide evidence that in macrophages intense hydrogen peroxide stress causes AIF-independent parthanatos from which LPS provides protection. The mechanism of LPS-mediated cytoprotection involves downregulation of PARP1, spared NAD⁺ and ATP pools, upregulation of antioxidant proteins, and a metabolic shift from mitochondrial respiration to aerobic glycolysis.

Up-regulation of antioxidative proteins TRX1, TXNL1 and TXNRD1 in the cortex of PTZ kindling seizure model mice

Oxidative stress has been considered as one of pathogenesis of brain damage led by epilepsy. Reducing oxidative stress can ameliorate brain damage during seizures. However, expression levels of important antioxidative enzymes such as thioredoxin-1 (TRX1), thioredoxin-like 1 protein (TXNL1) and thioredoxin reductase 1 (TXNRD1) during seizures have not been investigated. In this study, we examined protein and mRNA expression levels of TRX1, TXNL1 and TXNRD1 in different brain regions in PTZ induced seizure model mice. We found that protein expression levels of TRX1, TXNL1 and TXNRD1 are simultaneously up-regulated by 2- or 3-fold in the cortex of both acute and chronic seizure model mice. But there is no unified expression pattern change of these enzymes in the hippocampus, cerebellum and diencephalon in the seizure model mice. Less extent up-regulation of mRNA expression of these enzymes were also observed in the cortex of seizure mice. These data suggest that antioxidative enzymes may provide a protective effect against oxidative stress in the cortex during seizures.

New Platinum(II) agent induces bimodal death of apoptosis and autophagy against A549 cancer cell

Agents with multiple modes of tumor cell death can be effective chemotherapeutic drugs. One example of a bimodal chemotherapeutic approach is an agent that can induce both apoptosis and autophagic death. Thus far, no clinical anticancer drug has been shown to simultaneously induce both these pathways. Mono-functional platinum complexes are potent anticancer drug candidates which act through mechanisms distinct from cisplatin. Here, we describe the synthesis and characterize of two mono-functional platinum complexes containing 8-substituted quinoline derivatives as ligands. In comparison to cisplatin, n-Mon-Pt-1 exhibited a greater in vitro cytotoxicity, was more effective in resistant cells and elicited a better anticancer effect. Mechanistic experiments indicate that n-Mon-Pt-1 mainly accumulates in mitochondria, and stimulates significant TrxR inhibition, ROS release and an ER stress response, ultimately resulting in a simultaneous induction of apoptosis and autophagy. Importantly, compared to cisplatin, n-Mon-Pt-1 exhibits lower acute toxicity and better anticancer activity in a murine tumor model.

Expression of Selenoprotein Genes and Association with Selenium Status in Colorectal Adenoma and Colorectal Cancer

Dietary selenium (Se) intake is essential for synthesizing selenoproteins that are important in countering oxidative and inflammatory processes linked to colorectal carcinogenesis. However, there is limited knowledge on the selenoprotein expression in colorectal adenoma (CRA) and colorectal cancer (CRC) patients, or the interaction with Se status levels. We studied the expression of seventeen Se pathway genes (including fifteen of the twenty-five human selenoproteins) in RNA extracted from disease-normal colorectal tissue pairs, in the discovery phase of sixty-two CRA/CRC patients from Ireland and a validation cohort of a hundred and five CRC patients from the Czech Republic. Differences in transcript levels between the disease and paired control mucosa were assessed by the Mann-Whitney U-test. GPX2 and TXNRD3 showed a higher expression and GPX3, SELENOP, SELENOS, and SEPHS2 exhibited a lower expression in the disease tissue from adenomas and both cancer groups (p-values from 0.023 to <0.001). In the Czech cohort, up-regulation of GPX1, SELENOH, and SOD2 and down-regulation of SELENBP1, SELENON, and SELENOK (p-values 0.036 to <0.001) was also observed. We further examined the correlation of gene expression with serum Se status (assessed by Se and selenoprotein P, SELENOP) in the Irish patients. While there were no significant correlations with both Se status markers, SELENOF, SELENOK, and TXNRD1 tumor tissue expression positively correlated with Se, while TXNRD2 and TXNRD3 negatively correlated with SELENOP. In an analysis restricted to the larger Czech CRC patient cohort, Cox regression showed no major association of transcript levels with patient survival, except for an association of higher SELENOF gene expression with both a lower disease-free and overall survival. Several selenoproteins were differentially expressed in the disease tissue compared to the normal tissue of both CRA and CRC patients. Altered selenoprotein expression may serve as a marker of functional Se status and colorectal adenoma to cancer progression.

Effect of Arsenic Exposure on NRF2-KEAP1 Pathway and Epigenetic Modification

Arsenic (As) is a known toxic element and carcinogen. Transcription factor nuclear factor-erythroid 2-related factor 2 (NRF2) controls cellular adaptation to oxidants and electrophiles by inducing antioxidant genes in response to redox stress. To explore associations between As level and NRF2-regulated cytoprotective genes expression, an observational study was conducted in a population of 61 occupationally exposed men with median (Me) age 50 years (interquartile range (IQR) 42-54) and in a control group of 52 men aged 40 (IQR 31-51.5) without occupational exposure. NRF2, KEAP1, GSTP1, HMOX1, NQO1, PRDX1, and TXNRD1 transcript levels were determined by means of quantitative real-time PCR along with the gene expression, methylation of NRF2 and KEAP1, as well as global DNA methylation were assessed. The median urine As tot. level in the exposed and control group was found to be 21.8 μg/g creat. (IQR 15.5-39.8 μg/g creat.) and 3.8 μg/g creat. (IQR 2.5-9.3) (p < 0.001). Global DNA methylation was significantly higher in occupationally exposed workers than in controls (Me 14.1 (IQR 9.5-18.1) vs Me 8.5 (IQR 5.9-12.6) p < 0.0001). NRF2 mRNA level was positively correlated with expression of all investigated NRF2-target genes in both groups (0.37 > R < 0.76, all p values < 0.0001). The multivariate linear regression adjusting for global methylation showed that As(III) level was significantly associated with expression of TXNRD1, GSTP1, HMOX1, and PRDX1. The results of this study indicate that arsenic occupational exposure is positively associated with global DNA methylation. The findings provide evidence for rather inactivation of NRF2-KEAP1 pathway in response to chronic arsenic exposure.

A panel of three oxidative stress-related genes predicts overall survival in ovarian cancer patients received platinum-based chemotherapy

Ovarian cancer yields the highest mortality rate of all lethal gynecologic cancers, and the prognosis is unsatisfactory with the major obstacle in resistance to chemotherapy. The generation of reactive oxygen species (ROS) in tumor tissues was associated with chemotherapeutic effectiveness by mediating cellular longevity. In this study, we screened the prognostic values of oxidative stress-related genes in ovarian cancer patients received platinum-based chemotherapy, and conducted a prognostic gene signature composing of three genes, TXNRD1, GLA and GSTZ1. This three-gene signature was significantly associated with overall survival (OS), but not progression-free survival (PFS), in both training (n=276) and validation cohorts (n=230). Interestingly, we found that the prognostic value of three-gene signature was reinforced in platinum-sensitive patients. Subgroup analysis further suggested that patients with elder age, higher pathological grades and advanced tumor stages in low-risk score group could benefit from platinum-based chemotherapy. Functional analysis showed that the inactivation of several signaling pathways, including cell cycle, insulin-like growth factor 1 (IGF1) /mTOR and Fas pathways, was affected by three genes. Collectively, our results provided evidence that a panel of three oxidative stress-related gene signature had prognostic values for ovarian cancer patients received platinum-based chemotherapy.

Selenium Supplementation Alters Hepatic Energy and Fatty Acid Metabolism in Mice

Background

Human and animal studies have raised concerns that supplemental selenium can increase the risk of metabolic disorders, but underlying mechanisms are unclear.

Objective

We used an integrated transcriptome and metabolome analysis of liver to test for functional pathway and network responses to supplemental selenium in mice.

Methods

Male mice (8-wk-old, C57BL/6J) fed a standard diet (0.41 ppm Se) were given selenium (Na2SeO4, 20 μmol/L) or vehicle (drinking water) for 16 wk. Livers were analyzed for selenium concentration, activity of selenoproteins, reduced glutathione (GSH) redox state, gene expression, and high-resolution metabolomics. Transcriptomic and nontargeted metabolomic data were analyzed with biostatistics, bioinformatics, pathway enrichment analysis, and combined transcriptome-metabolome-wide association study (TMWAS).

Results

Mice supplemented with selenium had greater body mass gain from baseline to 16 wk (55% ± 5%) compared with controls (40% ± 3%) (P < 0.05); however, no difference was observed in liver selenium content, selenoenzyme transcripts, or enzyme activity. Selenium was higher in the heart, kidney, and urine of mice supplemented with selenium. Gene enrichment analysis showed that supplemental selenium altered pathways of lipid and energy metabolism. Integrated transcriptome and metabolome network analysis showed 2 major gene-metabolite clusters, 1 centered on the transcript for the bidirectional glucose transporter 2 (Glut2) and the other centered on the transcripts for carnitine-palmitoyl transferase 2 (Cpt2) and acetyl-CoA acyltransferase (Acaa1). Pathway analysis showed that highly associated metabolites (P < 0.05) were enriched in fatty acid metabolism and bile acid biosynthesis, including acylcarnitines, triglycerides and glycerophospholipids, long-chain acyl-coenzyme As, phosphatidylcholines, and sterols. TMWAS of body weight gain confirmed changes in the same pathways.

Conclusions

Supplemental selenium in mice alters hepatic fatty acid and energy metabolism and causes increases in body mass. A lack of effect on hepatic selenium content suggests that signaling involves an extrahepatic mechanism.

Fish oil omega-3 polyunsaturated fatty acids attenuate oxidative stress-induced DNA damage in vascular endothelial cells

Objective

Omega-3 fatty acids, particularly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), likely prevent cardiovascular disease, however their mechanisms remain unclear. Recently, the role of DNA damage in atherogenesis has been receiving considerable attention. Here, we investigated the effects of EPA and DHA on DNA damage in vascular endothelial cells to clarify their antiatherogenic mechanisms.

Methods and results

We determined the effect of EPA and DHA on H₂O₂-induced DNA damage response in human aortic endothelial cells. Immunofluorescence staining showed that γ-H2AX foci formation, a prominent marker of DNA damage, was significantly reduced in the cells treated with EPA and DHA (by 47% and 48%, respectively). H₂O₂-induced activation of ATM, a major kinase orchestrating DNA damage response, was significantly reduced with EPA and DHA treatment (by 31% and 33%, respectively). These results indicated EPA and DHA attenuated DNA damage independently of the DNA damage response. Thus the effects of EPA and DHA on a source of DNA damage were examined. EPA and DHA significantly reduced intracellular reactive oxygen species under both basal condition and H₂O₂ stimulation. In addition, the mRNA levels of antioxidant molecules, such as heme oxygenase-1, thioredoxin reductase 1, ferritin light chain, ferritin heavy chain and manganese superoxide dismutase, were significantly increased with EPA and DHA. Silencing nuclear factor erythroid 2-related factor 2 (NRF2) remarkably abrogated the increases in mRNA levels of antioxidant molecules and the decrease in intracellular reactive oxygen species. Furthermore, EPA and DHA significantly reduced H₂O₂-induced senescence-associated β-galactosidase activity in the cells (by 31% and 22%, respectively), which was revoked by NRF2 silencing.

Conclusions

Our results suggested that EPA and DHA attenuate oxidative stress-induced DNA damage in vascular endothelial cells through upregulation of NRF2-mediated antioxidant response. Therefore omega-3 fatty acids likely help prevent cardiovascular disease, at least in part, by their genome protective properties.

Redox regulation of the tumor suppressor PTEN by the thioredoxin system and cumene hydroperoxide

Intracellular redox status influences the oxidation and enzyme activity of the tumor suppressor phosphatase and tensin homolog on chromosome 10 (PTEN). Cumene hydroperoxide (CuHP), an organic hydroperoxide, is a known tumor promoter. However, molecular targets and action mechanism of CuHP in tumor promotion have not been well characterized. In this study, we investigated the effect of CuHP on the redox state of PTEN in HeLa cells. In addition, the intracellular reducing system of oxidized PTEN was analyzed using a biochemical approach and the effect of CuHP on this reducing system was also analyzed. While PTEN oxidized by hydrogen peroxide is progressively converted to its reduced form, PTEN was irreversibly oxidized by exposure to CuHP in HeLa cells. A combination of protein fractionation and mass analysis showed that the reducing system of PTEN was comprised of NADPH, thioredoxin reductase (TrxR), and thioredoxin (Trx). Although CuHP-mediated PTEN oxidation was not reversible in cells, CuHP-oxidized PTEN was reactivated by the exogenous Trx system, indicating that the cellular Trx redox system for PTEN is inactivated by CuHP. We present evidence that PTEN oxidation and the concomitant inhibition of thioredoxin by CuHP results in irreversible oxidation of PTEN in HeLa cells. In addition, ablation of peroxiredoxin (Prdx) enhanced CuHP-induced PTEN oxidation in cells. These results provide a new line of evidence that PTEN might be a crucial determinant of cell fate in response to cellular oxidative stress induced by organic hydroperoxides.

Modulation of signaling mechanisms in the heart by thioredoxin 1

Myocardial ischemia/reperfusion and heart failure are the major cardiac conditions in which an imbalance between oxidative stress and anti-oxidant mechanisms is observed. The myocardium has endogenous reducing mechanisms, including the thioredoxin (Trx) and glutathione systems, that act to scavenge reactive oxygen species (ROS) and reduce oxidized proteins. The Trx system consists of Trx, Trx reductase (TrxR), and an electron donor, NADPH, where Trx is maintained in a reduced state in the presence of TrxR and NADPH. Trx1, a major isoform of Trx, is abundantly expressed in the heart and exerts its oxidoreductase activity through conserved Cys32 and Cys35, reducing oxidized proteins through thiol disulfide exchange reactions. In this review, we will focus on molecular targets of Trx1 in the heart, including transcription factors, microRNAs, histone deactylases, and protein kinases. We will then discuss how Trx1 regulates the functions of its targets, thereby affecting the extent of myocardial injury caused by myocardial ischemia/reperfusion and the progression of heart failure.

Homozygous mutation in TXNRD1 is associated with genetic generalized epilepsy

Increased oxidative stress has been widely implicated in the pathogenesis in various forms of human epilepsy. Here, we report a homozygous mutation in TXNRD1 (thioredoxin reductase 1) in a family with genetic generalized epilepsy. TXNRD1 is an essential selenium-containing enzyme involved in detoxification of reactive oxygen species (ROS) and redox signaling. The TXNRD1 mutation p.Pro190Leu affecting a highly conserved amino acid residue was identified by whole-exome sequencing of blood DNA from the index patient. The detected mutation and its segregation within the family - all siblings of the index patient were homozygous and the parents heterozygous - were confirmed by Sanger sequencing. TXNRD1 activity was determined in subcellular fractions from a skeletal muscle biopsy and skin fibroblasts of the index patient and the expression levels of the mutated protein were assessed by ⁷⁵Se labeling and Western blot analysis. As result of the mutation, the activity of TXNRD1 was reduced in the patient's fibroblasts and skeletal muscle (to 34±3% and 16±8% of controls, respectively). In fibroblasts, we detected reduced ⁷⁵Se-labeling of the enzyme (41±3% of controls). An in-depth in vitro kinetic analysis of the recombinant mutated TXNRD1 indicated 30-40% lowered k_cat/Se values. Therefore, a reduced activity of the enzyme in the patient's tissue samples is explained by (i) lower enzyme turnover and (ii) reduced abundance of the mutated enzyme as confirmed by Western blotting and ⁷⁵Se labeling. The mutant fibroblasts were also found to be less resistant to a hydrogen peroxide challenge. Our data agree with a potential role of insufficient ROS detoxification for disease manifestation in genetic generalized epilepsy.

Perturbation of redox balance after thioredoxin reductase deficiency interrupts autophagy-lysosomal degradation pathway and enhances cell death in nutritionally stressed SH-SY5Y cells

Oxidative damage and aggregation of cellular proteins is a hallmark of neuronal cell death after neurotrauma and chronic neurodegenerative conditions. Autophagy and ubiquitin protease system are involved in degradation of protein aggregates, and interruption of their function is linked to apoptotic cell death in these diseases. Oxidative modification of cysteine groups in key molecular proteins has been linked to modification of cellular systems and cell death in these conditions. Glutathione and thioredoxin systems provide reducing protons that can effectively reverse protein modifications and promote cell survival. The central role of Thioredoxin in inhibition of apoptosis is well identified. Additionally, its involvement in initiation of autophagy has been suggested recently. We therefore aimed to investigate the involvement of Thioredoxin system in autophagy-apoptosis processes. A model of serum deprivation in SH-SY5Y was used that is associated with autophagy and apoptosis. Using pharmacological and RNA-editing technology we show that Thioredoxin reductase deficiency in this model enhances oxidative stress and interrupts the early protective autophagy and promotes apoptosis. This was associated with decreased protein-degradation in lysosomes due to altered lysosomal acidification and accumulation of autophagosomes as well as impairment in proteasome pathway. We further confirmed that the extent of oxidative stress is a determining factor in autophagy- apoptosis interplay, as upregulation of cellular reducing capacity by N-acetylcysteine prevented impairment in autophagy and proteasome systems thus promoted cell viability. Our study provides evidence that excessive oxidative stress inhibits protein degradation systems and affects the final stages of autophagy by inhibiting autolysosome maturation: a novel mechanistic link between protein aggregation and conversion of autophagy to apoptosis that can be applicable to neurodegenerative diseases.

Details in the catalytic mechanism of mammalian thioredoxin reductase 1 revealed using point mutations and juglone-coupled enzyme activities

The mammalian selenoprotein thioredoxin reductase 1 (TrxR1) is a key enzyme in redox regulation, antioxidant defense, and cellular growth. TrxR1 can catalyze efficient reduction of juglone (5-hydroxy-1,4-naphthoquinone; walnut toxin) in a reaction which, in contrast to reduction of most other substrates of TrxR1, is not dependent upon an intact selenocysteine (Sec, U) residue of the enzyme. Using a number of TrxR1 mutant variants, we here found that a sole Cys residue at the C-terminal tail of TrxR1 is required for high-efficiency juglone-coupled NADPH oxidase activity of Sec-deficient enzyme, occurring with mixed one- and two-electron reactions producing superoxide. The activity also utilizes the FAD and the N-terminal redox active disulfide/dithiol motif of TrxR1. If a sole Cys residue at the C-terminal tail of TrxR1, in the absence of Sec, was moved further towards the C-terminal end of the protein compared to its natural position at residue 497, juglone reduction was, surprisingly, further increased. Ala substitutions of Trp407, Asn418 and Asn419 in a previously described "guiding bar", thought to mediate interactions of the C-terminal tail of TrxR1 with the FAD/dithiol site at the N-terminal domain of the other subunit in the dimeric enzyme, lowered turnover with juglone about 4.5-fold. Four residues of Sec-deficient TrxR1 were found to be easily arylated by juglone, including the Cys residue at position 497. Based upon our observations we suggest a model for involvement of the juglone-arylated C-terminal motif of TrxR1 to explain its high activity with juglone. This study thus provides novel insights into the catalytic mechanisms of TrxR1. One-electron juglone reduction by TrxR1 producing superoxide should furthermore contribute to the well-known prooxidant cytotoxicity of juglone.

Association of genetic variations of selenoprotein genes, plasma selenium levels, and prostate cancer aggressiveness at diagnosis

BACKGROUND

Genetic variations in some of the selenoprotein genes, alone or together with an individual's selenium status, may influence risk or progression of prostate cancer. We investigated the impact of genetic variants of selenoproteins on plasma selenium levels and cancer aggressiveness at diagnosis in men with localized prostate cancer (PCa).

METHODS

The study cohort comprised 722 patients seen at Dana-Farber Cancer Institute who had localized/locally advanced PCa (i.e., stage T3 or less, N0, and M0) from 1994 to 2001. Fifty-five tagging single nucleotide polymorphisms (SNPs) from six selenoprotein genes (TXNRD1, TXNRD2, SEP15, GPX3, SELENBP1, and SEPP1) were analyzed. Logistic regression is used to examine associations of genotypes and plasma selenium levels with risk of aggressive disease, defined as D'Amico intermediate/high risk categories. Step down permutation was applied to adjust for multiple comparisons.

RESULTS

Three hundred and forty-eight patients (48%) had aggressive disease at diagnosis. Two SNPs were associated with cancer aggressiveness at diagnosis (unadjusted P = 0.017 and 0.018, respectively). The odds ratio for aggressive disease in patients carrying TXNRD2 rs1005873-AG/GG genotypes or SELENBP1 rs10788804-AG/AA genotypes was 1.54 (95% CI = 1.08, 2.20) and 1.45 (95% CI = 1.07, 1.98), respectively, compared to TXNRD2 rs1005873-AA or SELENBP1 rs10788804-GG carriers. Four SNPs in TXNRD2 (rs1005873, rs13054371, rs3788310, and rs9606174) and the rs230820 in SEPP1 were associated with plasma selenium levels (unadjusted P < 0.05). Permutation adjusted P-values were not statistically significant for all these comparisons at the cut-off point of 0.05.

CONCLUSION

We identified polymorphisms in selenoproteins that may influence the plasma selenium levels and may be associated with the risk of presenting with aggressive PCa in men with localized or locally advanced PCa. These results should be validated in other independent datasets.

Interplay between the chalcone cardamonin and selenium in the biosynthesis of Nrf2-regulated antioxidant enzymes in intestinal Caco-2 cells

Selenoenzymes and nuclear factor erythroid 2-related factor 2 (Nrf2)-regulated phase II enzymes comprise key components of the cellular redox and antioxidant systems, which show multiple interrelations. Deficiency of the micronutrient selenium (Se) and impaired biosynthesis of selenoproteins have been reported to result in induction of Nrf2 target genes. Conversely, transcription of the selenoenzymes glutathione peroxidase 2 (GPx2) and thioredoxin reductase 1 (TrxR1) is up-regulated upon Nrf2 activation. Here, we have studied the interplay between Se and the secondary plant metabolite cardamonin, an Nrf2-activating chalcone, in the regulation of Nrf2-controlled antioxidant enzymes. Se-deficient and Se-repleted (sodium selenite-supplemented) human intestinal Caco-2 cells were exposed to cardamonin. Uptake of cardamonin by the Caco-2 cells was independent of their Se status. Cardamonin strongly induced gene expression of GPx2 and TrxR1. However, cardamonin treatment did not result in elevated GPx or TrxR activity and protein levels, possibly relating to a concomitant down-regulation of O-phosphoseryl-tRNA(Sec) kinase (PSTK), an enzyme involved in translation of selenoprotein mRNAs. On the other hand, induction of the Nrf2-regulated enzyme heme oxygenase 1 (HO-1) by cardamonin was diminished in Se-replete compared to Se-deficient cells. Our findings suggest that cardamonin interferes with the biosynthesis of Nrf2-regulated selenoenzymes, in contrast to the Nrf2-activating isothiocyanate compound sulforaphane, which has been shown earlier to synergize with Se-mediated cytoprotection. Conversely, the cellular Se status apparently affects the cardamonin-mediated induction of non-selenoprotein antioxidant enzymes such as HO-1.

Oxidation of structural cysteine residues in thioredoxin 1 by aromatic arsenicals enhances cancer cell cytotoxicity caused by the inhibition of thioredoxin reductase 1

Thioredoxin systems, composed of thioredoxin reductase (TrxR), thioredoxin (Trx) and NADPH, play important roles in maintaining cellular redox homeostasis and redox signaling. Recently the cytosolic Trx1 system has been shown to be a cellular target of arsenic containing compounds. To elucidate the relationship of the structure of arsenic compounds with their ability of inhibiting TrxR1 and Trx1, and cytotoxicity, we have investigated the reaction of Trx1 system with seven arsenic trithiolates: As(Cys)3, As(GS)3, As(Penicillamine)3, As(Mercaptoethanesulfonate)3, As(Mercaptopurine)3, As(2-mercaptopyridine)3 and As(2-mercaptopyridine N-oxide)3. The cytotoxicity of these arsenicals was consistent with their ability to inhibit TrxR1 in vitro and in cells. Unlike other arsenicals, As(Mercaptopurine)3 which did not show inhibitory effects on TrxR1 had very weak cytotoxicity, indicating that TrxR1 is a reliable drug target for arsenicals. Moreover, the two aromatic compounds As(2-mercaptopyridine)3 and As(2-mercaptopyridine N-oxide)3 showed stronger cytotoxicity than the others. As(2-mercaptopyridine)3 which selectively oxidized two structural cysteines (Cys62 and Cys69) in Trx1 showed mild improvement in cytotoxicity. As(2-mercaptopyridine N-oxide)3 oxidized all the Cys residues in Trx1, exhibiting the strongest cytotoxicity. Oxidation of Trx1 by As(2-mercaptopyridine)3 and As(2-mercaptopyridine N-oxide)3 affected electron transfer from NADPH and TrxR1 to peroxiredoxin 1 (Prx1), which could result in the reactive oxygen species elevation and trigger cell death process. These results suggest that oxidation of structural cysteine residues in Trx1 by aromatic group in TrxR1-targeting drugs may sensitize tumor cells to cell death, providing a novel approach to regulate cellular redox signaling and also a basis for rational design of new anticancer agents.

Methylglyoxal, the foe and friend of glyoxalase and Trx/TrxR systems in HT22 nerve cells

Methylglyoxal (MGO) is a major glycating agent that reacts with basic residues of proteins and promotes the formation of advanced glycation end products (AGEs) which are believed to play key roles in a number of pathologies, such as diabetes, Alzheimer's disease, and inflammation. Here, we examined the effects of MGO on immortalized mouse hippocampal HT22 nerve cells. The endpoints analyzed were MGO and thiol status, the glyoxalase system, comprising glyoxalase 1 and 2 (GLO1/2), and the cytosolic and mitochondrial Trx/TrxR systems, as well as nuclear Nrf2 and its target genes. We found that nuclear Nrf2 is induced by MGO treatment in HT22 cells, as corroborated by induction of the Nrf2-controlled target genes and proteins glutamate cysteine ligase and heme oxygenase 1. Nrf2 knockdown prevented MGO-dependent induction of glutamate cysteine ligase and heme oxygenase 1. The cystine/glutamate antiporter, system xc(-), which is also controlled by Nrf2, was also induced. The increased cystine import (system xc(-)) activity and GCL expression promoted GSH synthesis, leading to increased levels of GSH. The data indicate that MGO can act as both a foe and a friend of the glyoxalase and the Trx/TrxR systems. At low concentrations of MGO (0.3mM), GLO2 is strongly induced, but at high MGO (0.75 mM) concentrations, GLO1 is inhibited and GLO2 is downregulated. The cytosolic Trx/TrxR system is impaired by MGO, where Trx is downregulated yet TrxR is induced, but strong MGO-dependent glycation may explain the loss in TrxR activity. We propose that Nrf2 can be the unifying element to explain the observed upregulation of GSH, GCL, HO1, TrxR1, Trx2, TrxR2, and system xc(-) system activity.

The 15kDa selenoprotein and thioredoxin reductase 1 promote colon cancer by different pathways

Selenoproteins mediate much of the cancer-preventive properties of the essential nutrient selenium, but some of these proteins have been shown to also have cancer-promoting effects. We examined the contributions of the 15kDa selenoprotein (Sep15) and thioredoxin reductase 1 (TR1) to cancer development. Targeted down-regulation of either gene inhibited anchorage-dependent and anchorage-independent growth and formation of experimental metastases of mouse colon carcinoma CT26 cells. Surprisingly, combined deficiency of Sep15 and TR1 reversed the anti-cancer effects observed with down-regulation of each single gene. We found that inflammation-related genes regulated by Stat-1, especially interferon-γ-regulated guanylate-binding proteins, were highly elevated in Sep15-deficient, but not in TR1-deficient cells. Interestingly, components of the Wnt/β-catenin signaling pathway were up-regulated in cells lacking both TR1 and Sep15. These results suggest that Sep15 and TR1 participate in interfering regulatory pathways in colon cancer cells. Considering the variable expression levels of Sep15 and TR1 found within the human population, our results provide insights into new roles of selenoproteins in cancer.

Green tea polyphenol (-)-epigallocatechin-3-gallate triggered hepatotoxicity in mice: responses of major antioxidant enzymes and the Nrf2 rescue pathway

(-)-Epigallocatechin-3-gallate (EGCG), a constituent of green tea, has been suggested to have numerous health-promoting effects. On the other hand, high-dose EGCG is able to evoke hepatotoxicity. In the present study, we elucidated the responses of hepatic major antioxidant enzymes and nuclear factor erythroid 2-related factor 2 (Nrf2) rescue pathway to high-dose levels of EGCG in Kunming mice. At a non-lethal toxic dose (75mg/kg, i.p.), repeated EGCG treatments markedly decreased the levels of superoxide dismutase, catalase, and glutathione peroxidase. As a rescue response, the nuclear distribution of Nrf2 was significantly increased; a battery of Nrf2-target genes, including heme oxygenase 1 (HO1), NAD(P)H:quinone oxidoreductase 1 (NQO1), glutathione S-transferase (GST), and those involved in glutathione and thioredoxin systems, were all up-regulated. At the maximum tolerated dose (45mg/kg, i.p.), repeated EGCG treatments did not disturb the major antioxidant defense. Among the above-mentioned genes, only HO1, NQO1, and GST genes were significantly but modestly up-regulated, suggesting a comprehensive and extensive activation of Nrf2-target genes principally occurs at toxic levels of EGCG. At a lethal dose (200mg/kg, i.p.), a single EGCG treatment dramatically decreased not only the major antioxidant defense but also the Nrf2-target genes, demonstrating that toxic levels of EGCG are able to cause a biphasic response of Nrf2. Overall, the mechanism of EGCG-triggered hepatotoxicity involves suppression of major antioxidant enzymes, and the Nrf2 rescue pathway plays a vital role for counteracting EGCG toxicity.

Loss of the thioredoxin reductase Trr1 suppresses the genomic instability of peroxiredoxin tsa1 mutants

The absence of Tsa1, a key peroxiredoxin that scavenges H2O2 in Saccharomyces cerevisiae, causes the accumulation of a broad spectrum of mutations. Deletion of TSA1 also causes synthetic lethality in combination with mutations in RAD51 or several key genes involved in DNA double-strand break repair. In the present study, we propose that the accumulation of reactive oxygen species (ROS) is the primary cause of genome instability of tsa1Δ cells. In searching for spontaneous suppressors of synthetic lethality of tsa1Δ rad51Δ double mutants, we identified that the loss of thioredoxin reductase Trr1 rescues their viability. The trr1Δ mutant displayed a Can(R) mutation rate 5-fold lower than wild-type cells. Additional deletion of TRR1 in tsa1Δ mutant reduced substantially the Can(R) mutation rate of tsa1Δ strain (33-fold), and to a lesser extent, of rad51Δ strain (4-fold). Loss of Trr1 induced Yap1 nuclear accumulation and over-expression of a set of Yap1-regulated oxido-reductases with antioxidant properties that ultimately re-equilibrate intracellular redox environment, reducing substantially ROS-associated DNA damages. This trr1Δ -induced effect was largely thioredoxin-dependent, probably mediated by oxidized forms of thioredoxins, the primary substrates of Trr1. Thioredoxin Trx1 and Trx2 were constitutively and strongly oxidized in the absence of Trr1. In trx1Δ trx2Δ cells, Yap1 was only moderately activated; consistently, the trx1Δ trx2Δ double deletion failed to efficiently rescue the viability of tsa1Δ rad51Δ. Finally, we showed that modulation of the dNTP pool size also influences the formation of spontaneous mutation in trr1Δ and trx1Δ trx2Δ strains. We present a tentative model that helps to estimate the respective impact of ROS level and dNTP concentration in the generation of spontaneous mutations.

Protective effects of the thioredoxin and glutaredoxin systems in dopamine-induced cell death

Although the etiology of sporadic Parkinson disease (PD) is unknown, it is well established that oxidative stress plays an important role in the pathogenic mechanism. The thioredoxin (Trx) and glutaredoxin (Grx) systems are two central systems upholding the sulfhydryl homeostasis by reducing disulfides and mixed disulfides within the cell and thereby protecting against oxidative stress. By examining the expression of redox proteins in human postmortem PD brains, we found the levels of Trx1 and thioredoxin reductase 1 (TrxR1) to be significantly decreased. The human neuroblastoma cell line SH-SY5Y and the nematode Caenorhabditis elegans were used as model systems to explore the potential protective effects of the redox proteins against 6-hydroxydopamine (6-OHDA)-induced cytotoxicity. 6-OHDA is highly prone to oxidation, resulting in the formation of the quinone of 6-OHDA, a highly reactive species and powerful neurotoxin. Treatment of human cells with 6-OHDA resulted in an increased expression of Trx1, TrxR1, Grx1, and Grx2, and small interfering RNA for these genes significantly increased the cytotoxic effects exerted by the 6-OHDA neurotoxin. Evaluation of the dopaminergic neurons in C. elegans revealed that nematodes lacking trxr-1 were significantly more sensitive to 6-OHDA, with significantly increased neuronal degradation. Importantly, both the Trx and the Grx systems were also found to directly mediate reduction of the 6-OHDA-quinone in vitro and thus render its cytotoxic effects. In conclusion, our results suggest that the two redox systems are important for neuronal survival in dopamine-induced cell death.

Mitochondrial thioredoxin reductase inhibition, selenium status, and Nrf-2 activation are determinant factors modulating the toxicity of mercury compounds

The thioredoxin system has essential functions in the maintenance of cellular redox homeostasis in the cytosol, nucleus, and mitochondria. Thioredoxin (Trx) and thioredoxin reductase (TrxR) are targets for mercury compounds in vitro and in vivo. This study aimed at understanding mechanistically how the mitochondrial and cytosolic thioredoxin systems were affected by mercurials, including the regulation of TrxR transcription. The effects of coexposure to selenite and mercurials on the thioredoxin system were also addressed. Results in HepG2 cells showed that TrxR1 expression was enhanced by Hg(2+), whereas exposure to MeHg decreased expression. Selenite exposure also increased the expression of TrxR1 and resulted in higher specific activity. Coexposure to 2 µM selenite and up to 5 µM Hg(2+) increased even further TrxR1 expression. This synergistic effect was not verified for MeHg, because TrxR1 expression and activity were reduced. Analysis of Nrf-2 translocation to the nucleus and TrxR mRNA suggests that induction of TrxR1 transcription was slower upon exposure to MeHg in comparison to Hg(2+). Subcellular fractions showed that MeHg affected the activity of the thioredoxin system equally in the mitochondria and cytosol, whereas Hg(2+) inhibited primarily the activity of TrxR2. The expression of TrxR2 was not upregulated by any treatment. These results show important differences between the mechanisms of toxicity of Hg(2+) and MeHg and stress the narrow range of selenite concentrations capable of antagonizing mercury toxicity. The results also highlight the relevance of the mitochondrial thioredoxin system (TrxR2 and Trx2) in the development of mercury toxicity.

Thioredoxin-related protein of 14 kDa is an efficient L-cystine reductase and S-denitrosylase

Thioredoxin-related protein of 14 kDa (TRP14, also called TXNDC17 for thioredoxin domain containing 17, or TXNL5 for thioredoxin-like 5) is an evolutionarily well-conserved member of the thioredoxin (Trx)-fold protein family that lacks activity with classical Trx1 substrates. However, we discovered here that human TRP14 has a high enzymatic activity in reduction of l-cystine, where the catalytic efficiency (2,217 min(-1)⋅µM(-1)) coupled to Trx reductase 1 (TrxR1) using NADPH was fivefold higher compared with Trx1 (418 min(-1)⋅µM(-1)). Moreover, the l-cystine reduction with TRP14 was in contrast to that of Trx1 fully maintained in the presence of a protein disulfide substrate of Trx1 such as insulin, suggesting that TRP14 is a more dedicated l-cystine reductase compared with Trx1. We also found that TRP14 is an efficient S-denitrosylase with similar efficiency as Trx1 in catalyzing TrxR1-dependent denitrosylation of S-nitrosylated glutathione or of HEK293 cell-derived S-nitrosoproteins. Consequently, nitrosylated and thereby inactivated caspase 3 or cathepsin B could be reactivated through either Trx1- or TRP14-catalyzed denitrosylation reactions. TRP14 was also, in contrast to Trx1, completely resistant to inactivation by high concentrations of hydrogen peroxide. The oxidoreductase activities of TRP14 thereby complement those of Trx1 and must therefore be considered for the full understanding of enzymatic control of cellular thiols and nitrosothiols.

Postprandial oxidative stress is modulated by dietary fat in adipose tissue from elderly people

We have investigated whether dietary fat modifies the postprandial oxidative stress in adipose tissue of elderly people. Twenty participants received three diets for 4 weeks each: SFA-rich diet, Mediterranean (Med) diet enriched in MUFA with virgin olive oil, and a low-fat, high-carbohydrate diet enriched in n-3 PUFA (α-linolenic acid from plant origin) (CHO-PUFA diet). After 12 h of fasting, volunteers received a breakfast reflecting the fatty acid composition of the diet ingested in the preceding dietary period. Med diet induced higher postprandial SOD2 and TrxR mRNA levels, and CHO-PUFA diet induced higher GPx1 and TrxR mRNA levels compared with SFA-rich diet. Med and CHO-PUFA breakfasts induced a postprandial increase in plasma reduced glutathione (GSH), and a greater postprandial GSH/oxidized glutathione ratio compared to the SFA-rich diet. Our study suggests that the consumption of Med and CHO-PUFA diets may reduce postprandial oxidative stress compared to an SFA-rich diet, which may be due to higher antioxidant enzymes gene expression in adipose tissue.

Gene expression changes for antioxidants pathways in the mouse cochlea: relations to age-related hearing deficits

Age-related hearing loss - presbycusis - is the number one neurodegenerative disorder and top communication deficit of our aged population. Like many aging disorders of the nervous system, damage from free radicals linked to production of reactive oxygen and/or nitrogen species (ROS and RNS, respectively) may play key roles in disease progression. The efficacy of the antioxidant systems, e.g., glutathione and thioredoxin, is an important factor in pathophysiology of the aging nervous system. In this investigation, relations between the expression of antioxidant-related genes in the auditory portion of the inner ear - cochlea, and age-related hearing loss was explored for CBA/CaJ mice. Forty mice were classified into four groups according to age and degree of hearing loss. Cochlear mRNA samples were collected and cDNA generated. Using Affymetrix® GeneChip, the expressions of 56 antioxidant-related gene probes were analyzed to estimate the differences in gene expression between the four subject groups. The expression of Glutathione peroxidase 6, Gpx6; Thioredoxin reductase 1, Txnrd1; Isocitrate dehydrogenase 1, Idh1; and Heat shock protein 1, Hspb1; were significantly different, or showed large fold-change differences between subject groups. The Gpx6, Txnrd1 and Hspb1 gene expression changes were validated using qPCR. The Gpx6 gene was upregulated while the Txnrd1 gene was downregulated with age/hearing loss. The Hspb1 gene was found to be downregulated in middle-aged animals as well as those with mild presbycusis, whereas it was upregulated in those with severe presbycusis. These results facilitate development of future interventions to predict, prevent or slow down the progression of presbycusis.

Resolution of oxidative stress by thioredoxin reductase: Cysteine versus selenocysteine

Thioredoxin reductase (TR) catalyzes the reduction of thioredoxin (TRX), which in turn reduces mammalian typical 2-Cys peroxiredoxins (PRXs 1-4), thiol peroxidases implicated in redox homeostasis and cell signaling. Typical 2-Cys PRXs are inactivated by hyperoxidation of the peroxidatic cysteine to cysteine-sulfinic acid, and regenerated in a two-step process involving retro-reduction by sulfiredoxin (SRX) and reduction by TRX. Here transient exposure to menadione and glucose oxidase was used to examine the dynamics of oxidative inactivation and reactivation of PRXs in mouse C10 cells expressing various isoforms of TR, including wild type cytoplasmic TR1 (Sec-TR1) and mitochondrial TR2 (Sec-TR2) that encode selenocysteine, as well as mutants of TR1 and TR2 in which the selenocysteine codon was changed to encode cysteine (Cys-TR1 or Cys-TR2). In C10 cells endogenous TR activity was insensitive to levels of hydrogen peroxide that hyperoxidize PRXs. Expression of Sec-TR1 increased TR activity, reduced the basal cytoplasmic redox state, and increased the rate of reduction of a redox-responsive cytoplasmic GFP probe (roGFP), but did not influence either the rate of inactivation or the rate of retro-reduction of PRXs. In comparison to roGFP, which was reduced within minutes once oxidants were removed reduction of 2-Cys PRXs occurred over many hours. Expression of wild type Sec-TR1 or Sec-TR2, but not Cys-TR1 or TR2, increased the rate of reduction of PRXs and improved cell survival after menadione exposure. These results indicate that expression levels of TR do not reduce the severity of initial oxidative insults, but rather govern the rate of reduction of cellular factors required for cell viability. Because Sec-TR is completely insensitive to cytotoxic levels of hydrogen peroxide, we suggest TR functions at the top of a redox pyramid that governs the oxidation state of peroxiredoxins and other protein factors, thereby dictating a hierarchy of phenotypic responses to oxidative insults.