ATP depletion inhibits glucocorticoid-induced thymocyte apoptosis

Influence of Ce3+ Substitution on Antimicrobial and Antibiofilm Properties of ZnCexFe2-xO4 Nanoparticles (X = 0.0, 0.02, 0.04, 0.06, and 0.08) Conjugated with Ebselen and Its Role Subsidised with γ-Radiation in Mitigating Human TNBC and Colorectal Adenocarcinoma Proliferation In Vitro

Cancers are a major challenge to health worldwide. Spinel ferrites have attracted attention due to their broad theranostic applications. This study aimed at investigating the antimicrobial, antibiofilm, and anticancer activities of ebselen (Eb) and cerium-nanoparticles (Ce-NPs) in the form of ZnCexFe2-XO4 on human breast and colon cancer cell lines. Bioassays of the cytotoxic concentrations of Eb and ZnCexFe2-XO4, oxidative stress and inflammatory milieu, autophagy, apoptosis, related signalling effectors, the distribution of cells through the cell-cycle phases, and the percentage of cells with apoptosis were evaluated in cancer cell lines. Additionally, the antimicrobial and antibiofilm potential have been investigated against different pathogenic microbes. The ZOI, and MIC results indicated that ZnCexFe2-XO4; X = 0.06 specimen reduced the activity of a wide range of bacteria and unicellular fungi at low concentration including P. aeruginosa (9.5 mm; 6.250 µg/mL), S. aureus (13.2 mm; 0.390 µg/mL), and Candida albicans (13.5 mm; 0.195 µg/mL). Reaction mechanism determination indicated that after ZnCexFe2-xO4; X = 0.06 treatment, morphological differences in S.aureus were apparent with complete lysis of bacterial cells, a concomitant decrease in the viable number, and the growth of biofilm was inhibited. The combination of Eb with ZFO or ZnCexFe2-XO4 with γ-radiation exposure showed marked anti-proliferative efficacy in both cell lines, through modulating the oxidant/antioxidant machinery imbalance, restoring the fine-tuning of redox status, and promoting an anti-inflammatory milieu to prevent cancer progression, which may be a valuable therapeutic approach to cancer therapy and as a promising antimicrobial agent to reduce the pathogenic potential of the invading microbes.

Metabolic reprogramming of acute lymphoblastic leukemia cells in response to glucocorticoid treatment

Glucocorticoids (GCs) are metabolic hormones with immunosuppressive effects that have proven effective drugs against childhood acute lymphoblastic leukemia (ALL). Yet, the role of metabolic reprogramming in GC-induced ALL cell death is poorly understood. GCs efficiently block glucose uptake and metabolism in ALL cells, but this does not fully explain the observed induction of autophagy and cell death. Here, we have performed parallel time-course proteomics, metabolomics, and isotope-tracing studies to examine in detail the metabolic effects of GCs on ALL cells. We observed metabolic events associated with growth arrest, autophagy, and catabolism prior to onset of apoptosis: nucleotide de novo synthesis was reduced, while certain nucleobases accumulated; polyamine synthesis was inhibited; and phosphatidylcholine synthesis was induced. GCs suppressed not only glycolysis but also entry of both glucose and glutamine into the TCA cycle. In contrast, expression of glutamine-ammonia ligase (GLUL) and cellular glutamine content was robustly increased by GC treatment, suggesting induction of glutamine synthesis, similar to nutrient-starved muscle. Modulating medium glutamine and dimethyl-α-ketoglutarate (dm-αkg) to favor glutamine synthesis reduced autophagosome content of ALL cells, and dm-αkg also rescued cell viability. These data suggest that glutamine synthesis affects autophagy and possibly onset of cell death in response to GCs, which should be further explored to understand mechanism of action and possible sources of resistance.

Involvement of p-CREB and phase II detoxifying enzyme system in neuroprotection mediated by the flavonoid calycopterin isolated from Dracocephalum kotschyi

PURPOSE

There is an increasing amount of experimental evidence that oxidative stress has a central role in the neuropathology of neurodegenerative diseases. It has been suggested that the loss of cell function results from the increased oxidative damage to proteins and DNA. Herein, we investigated the effect of a natural neuroprotective flavonoid, calycopterin, on H₂O₂-induced disruption of phase II detoxifying enzyme system and cAMP response element binding protein (CREB) phosphorylation.

METHODS

PC12 cells were treated with 25, 50 and 100 μM of calycopterin for 3h, followed by adding H₂O₂ (150 μM) for 24 h. The extent of apoptosis was assessed by comet assay. The level of phosphorylated CREB, nuclear factor erythroid 2-related factor 2 (Nrf2), glutamylcysteine synthetase (γ-GCS) and heme oxygenase 1 (HO-1) were measured by western blot method. The concentration of glutathione (GSH) was determined in whole cell lysate using dithionitrobenzoic acid method. Superoxide dismutase (SOD) activity was measured by colorimetric assay.

RESULT

Morphological analysis of protection induced by calycopterin, determined by comet assay, showed that calycopterin reduced DNA in tail. We found that H₂O₂ decreased mitochondrial membrane potential (MMP), while, calycopterin prevented this decrease in MMP in presence of H₂O₂. In H₂O₂-treated cells, calycopterin also suppressed cytochrome C release to cytosol that is necessary for maintaining mitochondrial homeostasis in survived cells. Moreover, calycopterin, in presence of H₂O₂ inhibited the decrease caused by oxidative stress in stress-sensing transcription factors, CREB and Nrf2, which play an important role in antioxidant capacity of the cell. There was also an increase in γ-GCS and HO-1 levels in calycopterin pretreated cells. In the presence of H₂O₂, calycopterin inhibited decrease in GSH level and SOD activity.

CONCLUSION

We provided documentation of neuroprotective effect of a natural flavone, calycopterin, against H₂O₂-induced oxidative stress in differentiated PC12 cells by modulating the level of CREB phosphorylation and Nrf2 pathway.

Synthetic polyamines activating autophagy: effects on cancer cell death

The ability of symmetrically substituted long chain polymethylene tetramines, methoctramine (1) and its analogs 2-4 to kill cancer cells was studied. We found that an elevated cytotoxicity was correlated with a 12 methylene chain length separating the inner amine functions (6-12-6 carbon backbone), together with the introduction of diphenylethyl moieties on the terminal nitrogen atoms (compound 4) of a tetramine backbone. Compound 4 triggered dissipation of mitochondrial transmembrane potential and increased intracellular peroxide levels, leading to a caspase-independent HeLa cell death associated with a rapid activation of autophagy. The antioxidant N-acetylcysteine inhibited cell death and activation of autophagy, indicating a link between oxidative stress and autophagy. Autophagy was rapidly triggered even by tetramines 2 and 3, indicating that is related to their polyamine structure. Autophagy did not protect HeLa cells against cytotoxicity elicited by compound 4. The present study shows that, by modifications of the methoctramine structure, it is possible to design polyamine derivatives highly cytotoxic against tumor cells and that the appropriate design of molecules bearing polyamine-like structures leads to powerful inducers of autophagy.

Investigation of 1-(4-morpholinophenyl)-3-(4-fluorophenyl)-propenone and 1-(4-morpholinophenyl)-3-(3-fluorophenyl)-propenone as new apoptosis inducers on Spodoptera frugiperda (Sf9) cells

The objective of this study was to examine the toxicity of 1-(4-morpholinophenyl)-3-(4-fluorophenyl)-propenone (A) and 1-(4-morpholinophenyl)-3-(3-fluorophenyl)-propenone (B) on Spodoptera frugiperda (Sf9) cells and the mechanism of the toxicity. By cell-based thiazolyl blue tetrazolium bromide (MTT) assay, we found that the IC(50) were 35.45 μM for A and 31.97 μM for B respectively. Formation of apoptotic bodies was observed at 24 h in the treated cells. There was a significant increase of DNA ladders in the treated Sf9 cells compared to controls. In the presence of 50 μM compound A and B for 24 h, ATP content of Sf9 cells reduced by approximately 50%. Compared to the controls, the significant over-expression of caspase-3 in treated cells was measured by caspase-3 activity kit, and the loss of mitochondrial membrane potential (ΔΨm) was detected in apoptosis cells. The results suggested that the two compounds could be identified as new potent cell apoptosis inducers.

Role of nicotinamide in DNA damage, mutagenesis, and DNA repair

Nicotinamide is a water-soluble amide form of niacin (nicotinic acid or vitamin B3). Both niacin and nicotinamide are widely available in plant and animal foods, and niacin can also be endogenously synthesized in the liver from dietary tryptophan. Nicotinamide is also commercially available in vitamin supplements and in a range of cosmetic, hair, and skin preparations. Nicotinamide is the primary precursor of nicotinamide adenine dinucleotide (NAD⁺), an essential coenzyme in ATP production and the sole substrate of the nuclear enzyme poly-ADP-ribose polymerase-1 (PARP-1). Numerous in vitro and in vivo studies have clearly shown that PARP-1 and NAD⁺ status influence cellular responses to genotoxicity which can lead to mutagenesis and cancer formation. This paper will examine the role of nicotinamide in the protection from carcinogenesis, DNA repair, and maintenance of genomic stability.

Absence of mitochondrial uncoupling protein 1 affects apoptosis in thymocytes, thymocyte/T-cell profile and peripheral T-cell number

Our laboratory has previously demonstrated the presence of constitutively expressed mitochondrial uncoupling protein 1 in mouse thymocytes. In our endeavours to understand the role of mitochondrial uncoupling protein 1 in thymocyte function, we compared cell profiles in thymus and spleen of wild-type with those of UCP 1 knock-out mice, which in turn led to comparative investigations of apoptotic potential in thymocytes from these mice. We demonstrate that spleen cell numbers were reduced approximately 3-fold in UCP 1 knock-out mice compared to wild-type mice. We record a halving of CD8 single positive cell numbers in thymus with a significant incremental increase in CD4/CD8 double positives cell numbers in the thymus of UCP 1 knock-out mice compared to wild-type mice. These data are mirrored by an approximate halving of CD8 single positive cell numbers and a doubling of CD4/CD8 double positive cell numbers in the spleen of UCP 1 knock-out mice compared to wild-type mice. These differences are most probably explained by our observations of decreased apoptotic potential and higher ATP levels in thymocytes of UCP 1 knock-out mice when compared to wild-type controls. We conclude that constitutively expressed UCP 1 is a factor in determining T-cell population selection in mice.

Caffeic acid, tyrosol and p-coumaric acid are potent inhibitors of 5-S-cysteinyl-dopamine induced neurotoxicity

Parkinson's disease is characterized by a progressive and selective loss of dopaminergic neurons in the substantia nigra. Recent investigations have shown that conjugates such as the 5-S-cysteinyl-dopamine, possess strong neurotoxicity and may contribute to the underlying progression of the disease pathology. Although the neuroprotective actions of flavonoids are well reported, that of hydroxycinnamates and other phenolic acids is less established. We show that the hydroxycinnamates caffeic acid and p-coumaric acid, the hydroxyphenethyl alcohol, tyrosol, and a Champagne wine extract rich in these components protect neurons against injury induced by 5-S-cysteinyl-dopamine in vitro. The protection induced by these polyphenols was equal to or greater than that observed for the flavonoids, (+)-catechin, (-)-epicatechin and quercetin. For example, p-coumaric acid evoked significantly more protection at 1muM (64.0+/-3.1%) than both (-)-epicatechin (46.0+/-4.1%, p<0.05) and (+)-catechin (13.1+/-3.0%, p<0.001) at the same concentration. These data indicate that hydroxycinnamates, phenolic acids and phenolic alcohol are also capable of inducing neuroprotective effects to a similar extent to that seen with flavonoids.

Rottlerin stimulates apoptosis in pancreatic cancer cells through interactions with proteins of the Bcl-2 family

Rottlerin is a polyphenolic compound derived from Mallotus philipinensis. In the present study, we show that rottlerin decreased tumor size and stimulated apoptosis in an orthotopic model of pancreatic cancer with no effect on normal tissues in vivo. Rottlerin also induced apoptosis in pancreatic cancer (PaCa) cell lines by interacting with mitochondria and stimulating cytochrome c release. Immunoprecipitation results indicated that rottlerin disrupts complexes of prosurvival Bcl-xL with Bim and Puma. Furthermore, siRNA knockdown showed that Bim and Puma are necessary for rottlerin to stimulate apoptosis. We also showed that rottlerin and Bcl-2 and Bcl-xL inhibitor BH3I-2' stimulate apoptosis through a common mechanism. They both directly interact with mitochondria, causing increased cytochrome c release and mitochondrial depolarization, and both decrease sequestration of BH3-only proteins by Bcl-xL. However, the effects of rottlerin and BH3I-2' on the complex formation between Bcl-xL and BH3-only proteins are different. BH3I-2' disrupts complexes of Bcl-xL with Bad but not with Bim or Puma, whereas rottlerin had no effect on the Bcl-xL interaction with Bad. Also BH3I-2', but not rottlerin, required Bad to stimulate apoptosis. In conclusion, our results demonstrate that rottlerin has a potent proapoptotic and antitumor activity in pancreatic cancer, which is mediated by disrupting the interaction between prosurvival Bcl-2 proteins and proapoptotic BH3-only proteins. Thus rottlerin represents a promising novel agent for pancreatic cancer treatment.

An induction in hepatic HDL secretion associated with reduced ATPase expression

Linoleic acid-phospholipids stimulate high-density lipoprotein (HDL) net secretion from liver cells by blocking the endocytic recycling of apoA-I. Experiments were undertaken to determine whether apoA-I accumulation in the cell media is associated with membrane ATPase expression. Treatment of HepG2 cells with dilinoeoylphosphatidylcholine (DLPC) increased apoA-I secretion fourfold. DLPC also significantly reduced cell surface F1-ATPase expression and reduced cellular ATP binding cassette (ABC)A1 and ABCG1 protein levels by approximately 50%. In addition, treatment of HepG2 cells with the ABC transporter inhibitor, glyburide, stimulated the apoA-I secretory effects of both DLPC and clofibrate. Pretreatment of HepG2 cells with compounds that increased ABC transport protein levels (TO901317, N-Acetyl-L-leucyl-L-leucyl-L-norleucinal, and resveratrol) blocked the DLPC-induced stimulation in apoA-I net secretion. Furthermore, whereas HepG2 cells normally secrete nascent prebeta-HDL, DLPC treatment promoted secretion of alpha-migrating HDL particles. These data show that an linoleic acid-phospholipid induced stimulation in hepatic HDL secretion is related to the expression and function of membrane ATP metabolizing proteins.

NAD and axon degeneration: from the Wlds gene to neurochemistry

Neurodegenerative diseases have become a global issue due to the aging population. These disorders affect a vast patient population and represent a huge area of unmet therapeutic need. Axon degeneration is a common pathological character of those neurodegenerative diseases. It results in the loss of communication between neurons. Two decades ago, the Wallerian degeneration slow (Wlds) mouse strain was identified, in which the degeneration of transected axons is delayed. The phenotype is attributed to the overexpression of a chimeric protein Wlds which contains a short fragment of the ubiquitin assembly protein UFD2 and the full-length nicotinamide adenine dinucleotide (NAD) synthetic enzyme Nicotinamide mononucleotide adenylyl-transferase-1 (Nmnat-1). However, the underlying molecular mechanism remains largely unknown. Recently, it's reported by independent researchers that the full length coding sequence of mouse Nmnat-1 could mimic the axonal protective effect of the Wlds gene when overexpressed in primary neural cultures. Together with a significant number of subsequential reports, this finding highlighted the substantial role of nicotinamide adenine dinucleotide (NAD) in the process of axon degeneration. Here we reviewed the history of axon degeneration research from a neurochemical standpoint and discuss the potential involvement of NAD synthesis, NAD consumption and NAD-dependent proteins and small molecules in axon degeneration.

Differential gene expression during apoptosis induced by a serum factor: role of mitochondrial F0-F1 ATP synthase complex

The number of genes that are up regulated or down regulated during apoptosis is large and still increasing. In an attempt to characterize differential gene expression during serum factor induced apoptosis in AK-5 cells (a rat histiocytoma), we found subunit 6 and subunit 8 of the transmembrane proton channel and subunit alpha of the catalytic core of the mitochondrial F(0)-F(1) ATP synthase complex to be up regulated during apoptosis. The increase in the expression levels of these subunits was concomitant with a transient increase in the intracellular ATP levels, suggesting that the increase in cellular ATP content is a result of the increase in the expression of ATP synthase subunits' gene and de novo protein synthesis. Depleting the cellular ATP levels with oligomycin inhibited apoptosis significantly, pointing to the requirement of ATP during apoptosis. Caspase 1 and caspase 3 activity and the loss of mitochondrial membrane potential were also inhibited by oligomycin during apoptosis in these cells, suggesting that the oligomycin induced inhibition of apoptosis could be due to inhibition of caspase activity and inhibition of mitochondrial depolarization. However, cytochrome C release during apoptosis was found to be completely independent of intracellular ATP content. Besides the ATP synthase complex genes, other mitochondrial genes like cytochrome C oxidase subunit II and III also showed elevated levels of expression during apoptosis. This kind of a mitochondrial gene expression profile suggests that in AK-5 cells, these genes are upregulated in a time-linked manner to ensure sufficient intracellular ATP levels and an efficient functioning of the mitochondrial respiratory chain for successful completion of the apoptotic pathway.

Alteration of mitochondrial function and cell sensitization to death

Stimulation of cell death is a powerful instrument in the organism's struggle with cancer. Apoptosis represents one mode of cell death. However, in a variety of tumor cells proapoptotic mechanisms are downregulated, or not properly activated, whereas antiapoptotic mechanisms are upregulated. Mitochondria are known as key players in the regulation of apoptotic pathways. Specifically, permeabilization of the mitochondrial outer membrane and subsequent release of proapoptotic proteins from the intermembrane space are viewed as decisive events in the initiation and/or execution of apoptosis. Disruption of mitochondrial functions by anticancer drugs, which induce oxidative stress, inhibit mitochondrial respiration, or uncouple oxidative phosphorylation, can sensitize mitochondria in these cells and facilitate outer membrane permeabilization.

Inhibitors of metabolism rescue cell death in Huntington's disease models

Huntington's disease (HD) is a fatal inherited neurodegenerative disorder. HD is caused by polyglutamine expansions in the huntingtin (htt) protein that result in neuronal loss and contribute to HD pathology. The mechanisms of neuronal loss in HD are elusive, and there is no therapy to alleviate HD. To find small molecules that slow neuronal loss in HD, we screened 1,040 biologically active molecules to identify suppressors of cell death in a neuronal cell culture model of HD. We found that inhibitors of mitochondrial function or glycolysis rescued cell death in this cell culture and in in vivo HD models. These inhibitors prevented cell death by activating prosurvival ERK and AKT signaling but without altering cellular ATP levels. ERK and AKT inhibition through the use of specific chemical inhibitors abrogated the rescue, whereas their activation through the use of growth factors rescued cell death, suggesting that this activation could explain the protective effect of metabolic inhibitors. Both ERK and AKT signaling are disrupted in HD, and activating these pathways is protective in several HD models. Our results reveal a mechanism for activating prosurvival signaling that could be exploited for treating HD and possibly other neurodegenerative disorders.

Chaperones are the target in aloe-emodin-induced human lung nonsmall carcinoma H460 cell apoptosis

Our previous study has demonstrated that aloe-emodin induced a significant change in the expression of apoptosis-related proteins in H460 cells. However, the molecular mechanisms underlying the biological effects of aloe-emodin still remain unknown. The present study applied 2D electrophoresis (pH range 4-7) to the proteins involved in aloe-emodin (40 muM)-induced H460 cell apoptosis. Eleven proteins were found to markedly change. These altered proteins were identified as ATP synthase, vimentin, HSP60, HSP70 and protein disulfide isomerase. Aloe-emodin caused a time-dependent decrease in intracellular ATP levels, which might be related to direct inhibition of ATP synthase. We also observed that the activity of mitochondria was injured by aloe-emodin. These data clearly demonstrated that mitochondria may play a critical role in aloe-emodin-induced H460 cell death. Many reports emphasize that chaperones have a complex role in apoptosis. The present study suggested that the increasing protein expression of HSP60, HSP70, 150 kDa oxygen-regulated protein and protein disulfide isomerase is involved in aloe-emodin-induced H460 cell apoptosis. HSP70, 150 kDa oxygen-regulated protein and protein disulfide isomerase are endoplasmic reticulum chaperone. Therefore, we hypothesized that the increasing endoplasmic reticulum stress serves to promote H460 cell apoptosis after treatment with aloe-emodin. We also demonstrated aloe-emodin-induced H460 cell death through caspase-3 apoptotic pathway, but not apoptosis-inducing factor apoptotic pathway.

Increasing glycolytic flux in Torulopsis glabrata by redirecting ATP production from oxidative phosphorylation to substrate-level phosphorylation

AIMS

This study aimed at further increasing the pyruvate productivity of a multi-vitamin auxotrophic yeast Torulopsis glabrata by redirecting ATP production from oxidative phosphorylation to substrate-level phosphorylation.

METHODS AND RESULTS

We examined two strategies to decrease the activity of F0F1-ATPase. The strategies were to inhibit F0F1-ATPase activity by addition of oligomycin, or to disrupt F0F1-ATPase by screening neomycin-resistant mutant. The addition of 0.05 mmol l(-1) oligomycin to the culture broth of T. glabrata CCTCC M202019 resulted in a significantly decreased intracellular ATP level (35.7%) and a significantly increased glucose consumption rate (49.7%). A neomycin-resistant mutant N07 was screened and selected after nitrosoguanidine mutagenesis of the parent strain T. glabrata CCTCC M202019. Compared with the parent strain, the F0F1-ATPase activity of the mutant N07 decreased about 65%. As a consequence, intracellular ATP level of the mutant N07 decreased by 24%, which resulted in a decreased growth rate and growth yield. As expected, glucose consumption rate and pyruvate productivity of the mutant N07 increased by 34% and 42.9%, respectively. Consistently, the activities of key glycolytic enzymes of the mutant N07, including phosphofructokinase, pyruvate kinase and glyceraldehyde-3-phosphate dehydrogenase, increased by 63.7%, 28.8% and 14.4%, respectively. In addition, activities of the key enzymes involved in electron transfer chain of the mutant N07 also increased.

CONCLUSIONS

Impaired oxidative phosphorylation in T. glabrata leads to a decreased intracellular ATP production, thereby increasing the glycolytic flux.

SIGNIFICANCE AND IMPACT OF THE STUDY

The strategy of redirecting ATP production from oxidative phosphorylation to substrate-level phosphorylation provides an alternative approach to enhance the glycolytic flux in eukaryotic micro-organisms.

Mitochondrial perturbation attenuates bile acid-induced cytotoxicity

Hydrophobic bile acids such as deoxycholate (DOC) are known to damage liver cells during cholestasis and promote colon cancer. Cellular stresses induced by bile acids, which include mitochondrial and endoplasmic reticulum (ER) stresses, can result in apoptosis. We found that inhibition of mitochondrial complexes I-V with rotenone, thenoyltrifluoroacetone (TTFA), antimycin A, myxothiazol or oligomycin strongly protected against DOC-induced apoptosis of HCT-116 cells. To understand the mechanism of this protection, we explored the ability of these specific inhibitors to reduce DOC-induced mitochondrial and ER stresses. Different inhibitors markedly reduced DOC-induction of mitochondrial condensation, the DOC-induced decrease in mitochondrial membrane potential and the DOC-induced dilatation of the ER (evidence of ER stress). A dramatic induction of nucleolar segregation by antimycin A and myxothiazol, two distinct complex III inhibitors, was also observed. These findings strongly implicate mitochondrial crosstalk with apoptotic signaling pathways and mitochondrial-nucleolar crosstalk in the development of apoptosis resistance in the colon.

Normal immune development and glucocorticoid-induced thymocyte apoptosis in mice deficient for the T-cell death-associated gene 8 receptor

T-cell death-associated gene 8 (TDAG8) is a G-protein-coupled receptor transcriptionally upregulated by glucocorticoids (GCs) and implicated by overexpression studies in psychosine-mediated inhibition of cytokinesis and in GC-induced apoptosis. To examine the physiological function of TDAG8, we generated knockout (KO) mice by homologous recombination. An enhanced green fluorescent protein reporter was knocked into the disrupted tdag8 locus to allow the analysis of TDAG8 expression in living cells. Interestingly, we found that during thymocyte development, TDAG8 expression resembled the dynamic regulation described for known modulators of GC-induced apoptosis, including Bcl-2, Notch1, and GC receptor. TDAG8 was expressed in double-negative cells, was downregulated at the double-positive transition, and was upregulated in single-positive thymocytes. However, despite this striking expression pattern, maturation and selection of thymocytes, as well as major immune functions, were not affected in TDAG8 KO mice. In contrast to previous overexpression results, TDAG8 was dispensable for psychosine-induced formation of multinucleated cells. Furthermore, TDAG8 KO thymocytes showed normal apoptosis following in vivo and in vitro GC treatment. These results, while establishing a useful reporter strain to study T-lymphocyte maturation, argue against a critical role for TDAG8 in immune development, psychosine-mediated inhibition of cytokinesis, and GC-induced cell death.

Acrolein-induced cell death in PC12 cells: role of mitochondria-mediated oxidative stress

Oxidative stress has been implicated in acrolein cytotoxicity in various cell types, including mammalian spinal cord tissue. In this study we report that acrolein also decreases PC12 cell viability in a reactive oxygen species (ROS)-dependent manner. Specifically, acrolein-induced cell death, mainly necrosis, is accompanied by the accumulation of cellular ROS. Elevating ROS scavengers can alleviate acrolein-induced cell death. Furthermore, we show that exposure to acrolein leads to mitochondrial dysfunction, denoted by the loss of mitochondrial transmembrane potential, reduction of cellular oxygen consumption, and decrease of ATP level. This raises the possibility that the cellular accumulation of ROS could result from the increased production of ROS in the mitochondria of PC12 cells as a result of exposure to acrolein. The acrolein-induced significant decrease of ATP production in mitochondria may also explain why necrosis, not apoptosis, is the dominant type of cell death. In conclusion, our data suggest that one possible mechanism of acrolein-induced cell death could be through mitochondria as its initial target. The subsequent increase of ROS then inflicts cell death and further worsens mitochondria function. Such mechanism may play an important role in CNS trauma and neurodegenerative diseases.

Rotenone-induced caspase 9/3-independent and -dependent cell death in undifferentiated and differentiated human neural stem cells

We used human neural stem cells (hNSCs) and their differentiated cultures as a model system to evaluate the mechanism(s) involved in rotenone (RO)- and camptothecin (CA)-induced cytotoxicity. Results from ultrastructural damage and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining indicated that RO-induced cytotoxicity resembled CA-induced apoptosis more than H(2)O(2)-induced necrosis. However, unlike CA-induced, caspase 9/3-dependent apoptosis, there was no increased activity in caspase 9, caspase 3 or poly (ADP-ribose) polymerase (PARP) cleavage in RO-induced cytotoxicity, in spite of time-dependent release of cytochrome c and apoptosis-inducing factor (AIF) following mitochondrial membrane depolarization and a significant increase in reactive oxygen species generation. Equal doses of RO and CA used in hNSCs induced caspase 9/3-dependent apoptosis in differentiated cultures. Time-dependent ATP depletion occurred earlier and to a greater extent in RO-treated hNSCs than in CA-treated hNSCs, or differentiated cultures treated with RO or CA. In conclusion, these results represent a unique ultrastructural and molecular characterization of RO- and CA-induced cytotoxicity in hNSCs and their differentiated cultures. Intracellular ATP levels may play an important role in determining whether neural progenitors or their differentiated cells follow a caspase 9/3-dependent or -independent pathway in response to acute insults from neuronal toxicants.

S-nitrosylated GAPDH initiates apoptotic cell death by nuclear translocation following Siah1 binding

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) influences cytotoxicity, translocating to the nucleus during apoptosis. Here we report a signalling pathway in which nitric oxide (NO) generation that follows apoptotic stimulation elicits S-nitrosylation of GAPDH, which triggers binding to Siah1 (an E3 ubiquitin ligase), nuclear translocation and apoptosis. S-nitrosylation of GAPDH augments its binding to Siah1, whose nuclear localization signal mediates translocation of GAPDH. GAPDH stabilizes Siah1, facilitating its degradation of nuclear proteins. Activation of macrophages by endotoxin and of neurons by glutamate elicits GAPDH-Siah1 binding, nuclear translocation and apoptosis, which are prevented by NO deletion. The NO-S-nitrosylation-GAPDH-Siah1 cascade may represent an important molecular mechanism of cytotoxicity.

Camptothecin-induced imbalance in intracellular cation homeostasis regulates programmed cell death in unicellular hemoflagellate Leishmania donovani

Leishmania, a unicellular trypanosomatid protozoan parasite, causes a wide range of human diseases ranging from the localized self-healing cutaneous lesions to fatal visceral leishmaniasis. However, it undergoes a process of programmed cell death during treatment with the topoisomerase I poison camptothecin (CPT). The present study shows that CPT-induced formation of reactive oxygen species increases the level of cytosolic calcium through the release of calcium ions from intracellular stores as well as by influx of extracellular calcium. Elevation of cytosolic calcium is responsible for depolarization of mitochondrial membrane potential (DeltaPsim), which is followed by a significant decrease in intracellular pH levels. CPT-induced oxidative stress also causes impairment of the Na+ - K+ -ATPase pump and subsequently decreases the intracellular K+ level in leishmanial cells. A decrease in both intracellular pH and K+ levels propagates the apoptotic process through activation of caspase 3-like proteases by rapid formation of cytochrome c-mediated apoptotic complex. In addition to caspase-like protease activation, a lower level of intracellular K+ also enhances the activation of apoptotic nucleases at the late stage of apoptosis. This suggests that the physiological level of pH and K+ are inhibitory for apoptotic DNA fragmentation and caspase-like protease activation in leishmanial cells. Moreover, unlike mammalian cells, the intracellular ATP level gradually decreases with an increase in the number of apoptotic cells after the loss of DeltaPsim. Taken together, the elucidation of biochemical events, which tightly regulate the process of growth arrest and death of Leishmania donovani promastigotes, allows us to define a more comprehensive view of cell death during treatment with CPT.

Oligomycin and antimycin A prevent nitric oxide-induced apoptosis by blocking cytochrome C leakage

Nitric oxide (NO) is a potent inducer of apoptosis, and its cytotoxicity is closely related to mitochondrial dysfunction. In this study we investigated the effects of a F0F1-ATPase inhibitor, oligomycin, and a mitochondrial respiratory chain complex III inhibitor, antimycin A, on NO-induced apoptosis. We used a normal rat gastric-epithelium cell line, RGM-1, treated with a pure NO donor, NOC-1 -1-hydroxy-2-oxo-3,3-bis(2-aminoethyl)-1-triazene - in the presence or absence of oligomycin or antimycin A. Changes in the expressions of Bax or Bcl-2 proteins, release of cytochrome C from mitochondria into the cytosol, activation of caspase-3, and changes in the mitochondrial membrane potential (DeltaPsi) were measured with the use of Western blotting, c43 lorimetric assays, and a mitochondrial potential sensor, JC-1 dye. Treatment with NOC-18 induced dose-dependent apoptotic cell death in RGM-1 cells. Cell death was accompanied by mitochondrial depolarization, increases in Bax protein expression and cytochrome C leakage, and, subsequently, caspase-3 activation. Oligomycin and antimycin A prevented NO-induced apoptosis in a dose-dependent fashion by preventing cytochrome C release independent of Bcl-2 expression. However, neither compound affected the up-regulation of Bax protein. On the one hand, oligomycin treatment was not accompanied by a decline in DeltaPsi. On the other hand, antimycin A treatment decreased DeltaPsi regardless of NOC-18 treatment. The findings of this study suggest that various functional molecules that constitute the mitochondrial respiratory chain may contribute to cytochrome C release that occurs during NO-induced apoptosis.

5-Aminoimidazole-4-carboxamide riboside induces apoptosis in Jurkat cells, but the AMP-activated protein kinase is not involved

5-Aminoimidazole-4-carboxamide (AICA) riboside, a precursor of purine nucleotide biosynthesis, induces apoptosis in Jurkat cells. Incorporation of AICAriboside into the cells is necessary for this effect since addition of nitrobenzylthioinosine, a nucleoside-transport inhibitor, completely protects Jurkat cells from apoptosis. Adenosine, but not other nucleosides, also protects Jurkat cells from AICAriboside-induced apoptosis. The apoptotic effect is caspase-dependent since caspases 9 and 3 are activated and the caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (Z-VAD.fmk) blocks apoptosis. Furthermore, AICAriboside induces mitochondrial cytochrome c release. AICAriboside, when phosphorylated to AICAribotide (ZMP), is a specific activator of the AMP-activated protein kinase (AMPK) in certain cell types. However, AICAriboside does not activate AMPK in Jurkat cells. Moreover, 5-iodotubercidin, an inhibitor of AICAriboside phosphorylation, does not inhibit apoptosis in Jurkat cells. These results indicate that AICAriboside induces apoptosis independently of ZMP synthesis and AMPK activation in Jurkat cells.

Mitochondrial complex I inhibitor rotenone induces apoptosis through enhancing mitochondrial reactive oxygen species production

Inhibition of mitochondrial respiratory chain complex I by rotenone had been found to induce cell death in a variety of cells. However, the mechanism is still elusive. Because reactive oxygen species (ROS) play an important role in apoptosis and inhibition of mitochondrial respiratory chain complex I by rotenone was thought to be able to elevate mitochondrial ROS production, we investigated the relationship between rotenone-induced apoptosis and mitochondrial reactive oxygen species. Rotenone was able to induce mitochondrial complex I substrate-supported mitochondrial ROS production both in isolated mitochondria from HL-60 cells as well as in cultured cells. Rotenone-induced apoptosis was confirmed by DNA fragmentation, cytochrome c release, and caspase 3 activity. A quantitative correlation between rotenone-induced apoptosis and rotenone-induced mitochondrial ROS production was identified. Rotenone-induced apoptosis was inhibited by treatment with antioxidants (glutathione, N-acetylcysteine, and vitamin C). The role of rotenone-induced mitochondrial ROS in apoptosis was also confirmed by the finding that HT1080 cells overexpressing magnesium superoxide dismutase were more resistant to rotenone-induced apoptosis than control cells. These results suggest that rotenone is able to induce apoptosis via enhancing the amount of mitochondrial reactive oxygen species production.

Molecular pathways in cerebral ischemia: cues to novel therapeutic strategies

Stroke is one of the leading causes of death and severe disability in most industrialized countries. Despite the extensive research efforts of both academic and industrial laboratories during the last few decades, no changes have been brought about by the design of neuroprotective therapies. The progressive decrease of stroke-induced death and disability is entirely attributable to improvements in the identification and reduction of risk factors. Over the past few years, experimental research has led to the emergence of a wealth of information regarding the complex and interrelated processes of neuronal degeneration and death triggered by ischemia. This unprecedented insight has led to new theories on the mechanisms of ischemic damage, and has suggested new targets and strategies for therapeutic intervention designed to reduce the clinical consequences of stroke. Among current developments, three strategies seem particularly appealing namely, the limitation of initial or secondary neuronal death by inhibition of apoptotic mechanisms, the enhancement of the endogenous capacity of nervous structures to restore lost function, and the replacement of lost cells by transplantation therapy.

Delta 9-tetrahydrocannabinol disrupts mitochondrial function and cell energetics

We have observed rapid and extensive depletion of cellular energy stores by Delta(9)-tetrahydrocannabinol (THC) in the pulmonary transformed cell line A549. ATP levels declined dose dependently with an IC(50) of 7.5 microg/ml of THC after 24-h exposure. Cell death was observed only at concentrations >10 microg/ml. Studies using JC-1, a fluorescent probe for mitochondrial membrane potential, revealed diminished mitochondrial function at THC concentrations as low as 0.5 microg/ml. At concentrations of 2.5 or 10 microg/ml of THC, a decrease in mitochondrial membrane potential was observed as early as 1 h after THC exposure. Mitochondrial function remained diminished for at least 30 h after THC exposure. Flow cytometry studies on cells exposed to particulate smoke extracts indicate that JC-1 red fluorescence was fivefold lower in cells exposed to marijuana smoke extract relative to cells exposed to tobacco smoke extract. Comparison with a variety of mitochondrial inhibitors demonstrates that THC produced effects similar to that of carbonyl cyanide p-trifluoromethoxyphenylhydrazone, suggesting uncoupling of electron transport. Loss of red JC-1 fluorescence by THC was suppressed by cyclosporin A, suggesting mediation by the mitochondrial permeability transition pore. This disruption of mitochondrial function was sustained for at least 24 h after removal of THC by extensive washing. These results suggest that exposure of the bronchopulmonary epithelium to THC may have important health and physiological consequences.

Dehydroepiandrosterone and alpha-estradiol limit the functional alterations of rat brain mitochondria submitted to different experimental stresses

The effects of dehydroepiandrosterone (DHEA), dehydroepiandrosterone-sulfate (DHEA-S), alpha-estradiol and beta-estradiol on the main functions of purified rat brain mitochondria were investigated in basal conditions and after being submitted to various stresses including anoxia-reoxygenation, uncoupling and apoptosis. In basal conditions, DHEA (1 microM) and alpha-estradiol (1 microM) inhibited the respiratory control ratio (RCR) from 3.1 to 2.3 (25%). After anoxia-reoxygenation, DHEA (1 microM) and alpha-estradiol (1 microM) reversed significantly (P<0.01) the RCR decrease from 1.4 to 2.0 (21.5%) by restoring the state 4. This effect was observed when DHEA was added either before anoxia or before reoxygenation and when alpha-estradiol was added before anoxia. The mitochondrial membranes damaged after the anoxia-reoxygenation were 70 and 50%, respectively, protected by DHEA and alpha-estradiol at 1 microM. They also limited by about 50%, the cytochrome c release induced by the anoxia-reoxygenation. The oxygen consumption of mitochondria in presence of NADH (130 microM) and cytochrome c (5 microM) was significantly inhibited by DHEA and alpha-estradiol with high EC(50) of 30 and 22 pM, respectively. At 1 microM, they also inhibited the 10 microM carbonyl cyanide m-chlorophenylhydrazone-induced uncoupling to about 35% whereas beta-estradiol only decreased it to 9%. Our results indicated that DHEA and alpha-estradiol partly preserved the mitochondrial functions altered by an anoxia-reoxygenation with a concentration-dependent effect. The mechanism involved was independent of the classical genomic effect of steroids, the antioxidant properties but implicated a direct action on the mitochondrial membranes.

Resveratrol-induced limitation of dysfunction of mitochondria isolated from rat brain in an anoxia-reoxygenation model

Resveratrol protection on the main functions of purified rat brain mitochondria submitted to anoxia-reoxygenation was investigated. Resveratrol (<0.1 microM) reversed partly (23.3%) the respiratory control ratio (RCR) decrease by protecting both states 3 and 4. This effect was both observed when resveratrol was added before anoxia or reoxygenation. Resveratrol fully inhibited the release of cytochrome c in a concentration-dependent manner and significantly decreased the superoxide anion (O2(0-)) production at a concentration of 1 nM. The mitochondrial membranes damaged after the anoxia-reoxygenation were partly protected (about 70%) by resveratrol at 0.1 microM. The oxygen consumption of mitochondria in presence of NADH and cytochrome c was significantly inhibited by resveratrol with a low EC50 of 18.34 pM. Resveratrol inhibited the CCCP-induced uncoupling from about 20%. The effects of resveratrol on oxidative phosphorylation parameters were also investigated in rats after pretreatment (0.4, 2 and 10 mg/kg/day) for one week. After the isolation of brain mitochondria, the RCR was significantly less decreased in the resveratrol group compared to the control group. These results showed that resveratrol could preserve the mitochondrial functions with at least three mechanisms: antioxidant properties, action on complex III and a membrane stabilizing effect.

Human mitochondrial thioredoxin. Involvement in mitochondrial membrane potential and cell death

Thioredoxins (Trx) are a class of small multifunctional redox-active proteins found in all organisms. Recently, we reported the cloning of a mitochondrial thioredoxin, Trx2, from rat heart. To investigate the biological role of Trx2 we have isolated the human homologue, hTrx2, and generated HEK-293 cells overexpressing Trx2 (HEK-Trx2). Here, we show that HEK-Trx2 cells are more resistant toward etoposide. In addition, HEK-Trx2 are more sensitive toward rotenone, an inhibitor of complex I of the respiratory chain. Finally, overexpression of Trx2 confers an increase in mitochondrial membrane potential, DeltaPsi(m). Treatment with oligomycin could both reverse the effect of rotenone and decrease the membrane potential suggesting that Trx2 interferes with the activity of ATP synthase. Taken together, these results suggest that Trx2 interacts with specific components of the mitochondrial respiratory chain and plays an important role in the regulation of the mitochondrial membrane potential.

C5a receptor and thymocyte apoptosis in sepsis

In sepsis, apoptosis occurs in many different organs. The mediators responsible for induction of apoptosis are not clearly known, although there are some suggestions that C5a and the C5a receptor (C5aR) might be directly linked to apoptosis. In the cecal ligation/puncture (CLP) model of sepsis in rats, apoptosis occurs early in a variety of organs, especially in the thymus. We demonstrate that thymocytes from normal rats show specific, saturable, and high affinity binding of 125I-labeled recombinant rat C5a. C5a binding to thymocytes was significantly increased 3 h after CLP and also when thymocytes from normal rats were first incubated in vitro with lipopolysaccharide (LPS) or IL-6. The expression of C5aR mRNA in thymocytes was markedly increased 3, 6, and 12 h after CLP and increased similarly when normal thymocytes were first exposed to LPS or IL-6 in vitro. Thymocytes obtained 2 or 3 h after CLP and exposed in vitro to C5a, but not normal thymocytes, underwent increased apoptosis, as demonstrated by annexin-V binding, coinciding with increased activation of caspases 3, 6, and 8. These data provide the first direct evidence that in the early onset of sepsis, increased expression of C5aR occurs in thymocytes, which increases their susceptibility to C5a-induced apoptosis.

An early oxygen-dependent step is required for dexamethasone-induced apoptosis of immature mouse thymocytes

The roles of oxygen and reactive oxygen intermediates in apoptosis are unclear at present. Although oxygen and reactive oxygen intermediates are not required for the execution of apoptosis, oxygen may be involved in at least some forms of apoptosis. In this study we show that dexamethasone (Dex)-induced apoptosis of immature mouse thymocytes is completely inhibited by hypoxic culture. In contrast, anti-CD95 thymocyte apoptosis is unaffected by hypoxia, indicating the existence of two forms of thymocyte apoptosis: an oxygen-dependent pathway (Dex induced) and an oxygen-independent pathway (anti-CD95 induced). Furthermore, hypoxia inhibited mitochondrial permeability transition (PT) in Dex-treated, but not in anti-CD95-treated, thymocytes, suggesting that the oxygen-sensitive step is upstream of mitochondria. Both Dex- and anti-CD95-induced PT and apoptosis were dependent on activation of IL-converting enzyme-like protease, as PT and apoptosis were inhibited by preincubation with Cbz-Val-Ala-Asp-fluoromethyl ketone, an irreversible inhibitor of IL-converting enzyme-like proteases. In addition, hypoxia inhibited the activation by Dex of caspase-3 (CPP32)-like proteases. Our data show that the private signaling pathways of Dex (oxygen dependent) and anti-CD95 (oxygen independent) both converge upstream of mitochondrial changes. The oxygen-dependent step in Dex-induced apoptosis lies upstream of caspase-3-like protease activation. Our observations support a model of apoptosis signaling in which independent pathways (oxygen dependent and oxygen independent) particular to each stimuli converge at a central point in the apoptotic cascade.

Caspase-3-like activity determines the type of cell death following ionizing radiation in MOLT-4 human leukaemia cells

Caspases, a family of cysteine proteases, play a central role in the pathways leading to apoptosis. Recently, it has been reported that a broad spectrum inhibitor of caspases, the tripeptide Z-VAD-fmk, induced a switch from apoptosis to necrosis in dexamethasone-treated B lymphocytes and thymocytes. As such a cell death conversion could increase the efficiency of radiation therapy and in order to identify the caspases involved in this cell death transition, we investigated the effects of caspase-3-related proteases inhibition in irradiated MOLT-4 cells. Cells were pretreated with Ac-DEVD-CHO, an inhibitor of caspase-3-like activity, and submitted to X-rays at doses ranging from 1 to 4 Gy. Our results show that the inhibition of caspase-3-like activity prevents completely the appearance of the classical hallmarks of apoptosis such as internucleosomal DNA fragmentation or hypodiploid particles formation and partially the externalization of phosphatidylserine. However, this was not accompanied by any persistent increase in cell survival. Instead, irradiated cells treated by this inhibitor exhibited characteristics of a necrotic cell death. Therefore, functional caspase-3-subfamily not only appears as key proteases in the execution of the apoptotic process, but their activity may also influence the type of cell death following an exposure to ionizing radiation.

Inhibition of glucocorticoid-induced apoptosis by the expression of antisense gene of mitochondrial ATPase subunit 6(1)

To isolate the apoptosis-linked genes involved in the cell death of thymocytes induced by glucocorticoids, we developed a functional cloning assay. Murine CD4(+)CD8(+) thymic cell line 2-257-20 cells were transfected with cDNA expression libraries obtained from a dexamethasone-resistant cell line. The transfected cells were selected in the presence of dexamethasone, and the plasmids which episomally expanded were then extracted from the surviving cells. One of the rescued cDNAs was found to be an antisense cDNA fragment identical to the mouse mitochondrial ATPase 6 gene. In the stable transfectants with the ATPase 6 antisense gene, the induction of apoptosis by dexamethasone was significantly delayed. Furthermore, the ATP synthesis in these transfectants was also reduced to some extent. ATPase 6 is a subunit of F(o)F(1) ATPase and our results support that ATP synthesis from the mitochondria is necessary for the induction of apoptosis induced by glucocorticoids.

Glucocorticoids in T cell development and function*

Glucocorticoids are small lipophilic compounds that mediate their many biological effects by binding an intracellular receptor (GR) that, in turn, translocates to the nucleus and directly or indirectly regulates gene transcription. Perhaps the most recognized biologic effect of glucocorticoids on peripheral T cells is immunosuppression, which is due to inhibition of expression of a wide variety of activationinduced gene products. Glucocorticoids have also been implicated in Th lineage development (favoring the generation of Th2 cells) and, by virtue of their downregulation of fasL expression, the inhibition of activation-induced T cell apoptosis. Glucocorticoids are also potent inducers of apoptosis, and even glucocorticoid concentrations achieved during a stress response can cause the death of CD4(+)CD8(+ )thymocytes. Perhaps surprisingly, thymic epithelial cells produce glucocorticoids, and based upon in vitro and in vivo studies of T cell development it has been proposed that these locally produced glucocorticoids participate in antigen-specific thymocyte development by inhibiting activation-induced gene transcription and thus increasing the TCR signaling thresholds required to promote positive and negative selection. It is anticipated that studies in animals with tissue-specific GR-deficiency will further elucide how glucocorticoids affect T cell development and function.

Oxidative stress and adenine nucleotide control of mitochondrial permeability transition

Mitochondria can initiate apoptosis by releasing cytochrome c after undergoing a calcium-dependent permeability transition (MPT). Although the MPT is enhanced by oxidative stress and prevented by adenine nucleotides such as adenosine 5'-diphosphate (ADP), the hypothesis has not been tested that oxidants regulate the effects of exogenous adenine nucleotides on the MPT and cytochrome c release. We found that cytochrome c release from intact rat liver mitochondria depended strictly on pore opening and not on membrane potential, and that MPT-enhancing oxidative stress also augmented cytochrome c release. At low oxidative stress, micromolar (ADP) and low adenosine 5'-triphosphate (ATP)/ADP ratio inhibited the MPT and cytochrome c release, whereas ATP or high ATP/ADP had only a slight effect. In freshly isolated mitochondria, the time to half-maximal MPT was related to the log of the ATP/ADP ratio. This function was shifted to shorter times by oxidative stress which decreased ADP protection and caused ATP to accelerate the calcium-dependent MPT. By comparison, mitochondria treated with reducing agents and those isolated from septic rats were protected from the MPT by both nucleotides. These results indicate that oxidation-sensitive site(s) in the membrane regulate the effects of adenine nucleotides on the MPT. The oxidant-based differences in the effects of ADP and ATP on the pore support the novel hypothesis that failure of the cell to consume ATP and provide adequate ADP at the adenine nucleotide transporter during oxidative stress predisposes to cytochrome c release and initiation of apoptosis.

Mitochondrial phospholipid hydroperoxide glutathione peroxidase suppresses apoptosis mediated by a mitochondrial death pathway

Phospholipid hydroperoxide glutathione peroxidase (PHGPx) is a key enzyme in the protection of biomembranes exposed to oxidative stress. We investigated the role of mitochondrial PHGPx in apoptosis using RBL2H3 cells that overexpressed mitochondrial PHGPx (M15 cells), cells that overexpressed non-mitochondrial PHGPx (L9 cells), and control cells (S1 cells). The morphological changes and fragmentation of DNA associated with apoptosis occurred within 15 h in S1 and L9 cells upon exposure of cells to 2-deoxyglucose (2DG). The release of cytochrome c from mitochondria was observed in S1 cells after 4 h and was followed by the activation of caspase-3 within 6 h. Overexpression of mitochondrial PHGPx prevented the release of cytochrome c, the activation of caspase-3, and apoptosis, but non-mitochondrial PHGPx lacked the ability to prevent the induction of apoptosis by 2DG. An ability to protect cells from 2DG-induced apoptosis was abolished when the PHGPx activity of M15 cells was inhibited by diethylmalate, indicating that the resistance of M15 cells to apoptosis was indeed due to the overexpression of PHGPx in the mitochondria. The expression of members of the Bcl-2 family of proteins, such as Bcl-2, Bcl-xL, Bax, and Bad, was unchanged by the overexpression of PHGPx in cells. The levels of hydroperoxides, including hydrogen and lipid peroxide, in mitochondria isolated from S1 and L9 cells were significantly increased after the exposure to 2DG for 2 h, while the level of hydroperoxide in mitochondria isolated from M15 cells was lower than that in S1 and L9 cells. M15 cells were also resistant to apoptosis induced by etoposide, staurosporine, UV irradiation, cycloheximide, and actinomycin D, but not to apoptosis induced by Fas-specific antibodies, which induces apoptosis via a pathway distinct from the pathway initiated by 2DG. Our results suggest that hydroperoxide, produced in mitochondria, is a major factor in apoptosis and that mitochondrial PHGPx might play a critical role as an anti-apoptotic agent in mitochondrial death pathways.

Inhibition of PARP prevents oxidant-induced necrosis but not apoptosis in LLC-PK1 cells

Oxidant-induced cell injury has been implicated in the pathogenesis of several forms of acute renal failure. The present studies examined whether activation of poly(ADP-ribose)polymerase (PARP) by oxidant-induced DNA damage contributes to oxidant injury of renal epithelial cells. H2O2 exposure resulted in an increase in PARP activity and decreases in cell ATP and NAD content. These changes were significantly inhibited by 10 mM 3-aminobenzamide (3-ABA), a PARP inhibitor. In contrast, H2O2-induced DNA damage was not prevented by 3-ABA. Exposure of LLC-PK(1) cells to 1 mM H2O2 for 2 h induced necrotic cell death as measured by increased lactate dehydrogenase (LDH) release. 3-ABA completely prevented the H2O2-induced LDH release. Live/dead fluorescent staining confirmed the protection by 3-ABA. These results are consistent with the view that oxidant-induced DNA damage activates PARP and that the subsequent ATP and NAD depletion contribute to necrotic cell death. Of note, although protected from necrosis, cells treated with H2O2 and 3-ABA underwent apoptosis as evidenced by DNA fragmentation and bis-benzimide staining. In conclusion, activation of PARP contributes to oxidant-induced ATP depletion and necrosis in LLC-PK1 cells. However, PARP inhibition may target cells toward an apoptotic form of cell death.

Uncouplers of oxidative phosphorylation can enhance a Fas death signal

Recent work suggests a participation of mitochondria in apoptotic cell death. This role includes the release of apoptogenic molecules into the cytosol preceding or after a loss of mitochondrial membrane potential DeltaPsim. The two uncouplers of oxidative phosphorylation carbonyl cyanide m-chlorophenylhydrazone (CCCP) and 2, 4-dinitrophenol (DNP) reduce DeltaPsim by direct attack of the proton gradient across the inner mitochondrial membrane. Here we show that both compounds enhance the apoptosis-inducing capacity of Fas/APO-1/CD95 signaling in Jurkat and CEM cells without causing apoptotic changes on their own account. This amplification occurred upstream or at the level of caspases and was not inhibited by Bcl-2. The effect could be blocked by the cowpox protein CrmA and is thus likely to require caspase 8 activity. Apoptosis induction by staurosporine in Jurkat cells as well as by Fas in SKW6 cells was unaffected by CCCP and DNP. The role of cytochrome c during Fas-DNP signaling was investigated. No early cytochrome c release from mitochondria was detected by Western blotting. Functional assays with cytoplasmic preparations from Fas-DNP-treated cells also indicated that there was no major contribution by cytochrome c or caspase 9 to the activation of effector caspases. Furthermore, an increase of rhodamine-123 uptake into intact cells, which has been explained by mitochondrial swelling, occurred considerably later than the caspase activation and was blocked by Z-VAD-fmk. These data show that uncouplers of oxidative phosphorylation can presensitize some but not all cells for a Fas death signal and provide information about the existence of separate pathways in the induction of apoptosis.

Glucose protection from MPP+-induced apoptosis depends on mitochondrial membrane potential and ATP synthase

MPP+ inhibits mitochondrial complex I and alpha-ketoglutarate dehydrogenase causing necrosis or apoptosis of catecholaminergic neurons. Low glucose levels or glycolytic blockade has been shown to potentiate MPP+ toxicity. We found that MPP+ caused concentration-dependent apoptosis of neuronally differentiated PC12 cells and that glucose, but not pyruvate, supplementation reduced apoptosis. Oligomycin concentrations sufficient to inhibit ATP synthase blocked the decreased apoptosis afforded by glucose supplementation. Laser-scanning confocal microscope imaging of chloromethyl-tetramethylrosamine methyl ester fluorescence to estimate DeltaPsiM showed that MPP+ and atractyloside reduced DeltaPsiM, while cyclosporin A (CSA) and glucose supplementation reversed decreases in DeltaPsiM caused by MPP+. Oligomycin blocked the effect of glucose supplementation on DeltaPsiM. These findings show that (i) MPP+-induced and atractyloside-induced apoptosis are associated with reduced DeltaPsiM; (ii) CSA maintains DeltaPsiM and reduces MPP+-induced apoptosis; and (iii) glucose supplementation maintains DeltaPsiM, likely by glycolytic ATP-dependent proton pumping at ATP synthase and reduces MPP+-induced apoptosis.

Immunosuppressant deoxyspergualin induces apoptotic cell death in dividing cells

Deoxyspergualin (DSG) has been found to have an antitumour and immunosuppressive activity. However, the precise mechanism of action of DSG has not been clarified. We have used its analogue, methyldeoxyspergualin (MeDSG) for in vitro culture studies of DSG since it shows good stability in aqueous solution and retains strong immunosuppressive activity. In the present study, we found that MeDSG inhibited proliferation of rapidly dividing murine T-cell hybridomas, resulting in cell death. The cell death was accompanied by chromatin condensation and DNA cleavage at the linker regions between nucleosomes. Furthermore, MeDSG induced a reduction in mitochondrial transmembrane potential. When murine thymocytes were treated with MeDSG for 48 hr, a slight increase of DNA fragmentation was constantly observed, and selective depletion of CD4- CD8- cells was noticed. In contrast, CD4+ CD8+ cells were hardly affected. Moreover, splenic T-cells are resistant to MeDSG-induced apoptosis, as evaluated by measuring DNA cleavage. Our findings may account for the immunosuppressive and antitumour properties of DSG which were described in a number of previous studies.

ATP converts necrosis to apoptosis in oxidant-injured endothelial cells

Cell death due to necrosis results in acute inflammation, while death by apoptosis generally does not. The effect of adenosine triphosphate (ATP) on the pattern of cell death induced by oxidants was examined in bovine endothelial cells. ATP levels were altered by hydrogen peroxide (H2O2), glutamine (Gln), and metabolic inhibition (MI), to determine if necrosis can be shifted to apoptosis during oxidant injury. The form of cell death was determined by fluorescence microscopic techniques and the pattern of DNA degradation on agarose gels. ATP levels were measured using the luciferase-luciferin assay. Apoptosis occurred with 100 microM H2O2 without an alteration in ATP levels. ATP was significantly lowered with 5 mM H2O2, and necrosis occurred. MI, in combination with 100 microM H2O2, decreased ATP and resulted in necrosis. MI alone, however, did not cause cell death. Gln partially restored ATP levels in cells injured with 5 mM H2O2 and resulted in a significant increase in apoptosis. DNA laddering on agarose gels confirmed the apoptotic changes seen by fluorescence microscopy. In summary, a threshold level of ATP 25% of basal levels is required for apoptosis to proceed after oxidant stress, otherwise necrosis occurs. Agents like glutamine that enhance ATP levels in oxidant-stressed cells may be potent means of shifting cell death during inflammation to the noninflammatory form of death--apoptosis.

Mitochondrial control of apoptosis: the role of cytochrome c

Mitochondrial cytochrome c (cyt c) has been found to have dual functions in controlling both cellular energetic metabolism and apoptosis. Through interaction with apoptotic protease activating factors (Apaf), cyt c can initiate the activation cascade of caspases once it is released into the cytosol. The loss of a component of the mitochondrial electron transport chain also triggers the generation of superoxide. Although cyt c can be released independent of the mitochondrial permeability transition (MPT), the accompanying cellular redox change can trigger the MPT. Since another apoptotic protease, AIF, is released by MPT, the two separate pathways provide redundancy that ensures effective execution of the cell death program. Anti-apoptotic Bcl-2 family proteins function as gatekeepers to prevent the release of both cyt c and AIF. In spite of their stabilization effect on the mitochondrial outer membrane, Bcl-2 proteins may also be involved in the direct binding of Apaf molecules as regulatory elements further downstream from the mitochondrial apoptotic signals.

Energy metabolism of rat colonocytes changes during the tumorigenic process and is dependent on diet and carcinogen

Alterations in ATP production, intracellular energy levels and mitochondrial function have been shown to trigger cytokinetic events in vitro, including inhibition of cell division, abnormal or blocked differentiation and inhibition of apoptosis. Changes in colonic cytokinetics are directly related to colon tumorigenesis but alterations in energy metabolism during the tumorigenic process have never been reported. We conducted a 2 x 2 x 3 factorial design study in 120 male Sprague-Dawley rats with two diets (pectin or cellulose-supplemented), two injected subgroups (with or without the carcinogen azoxymethane, AOM) and three termination time points (6, 16 and 36 wk post-second injection). Colonocytes were isolated and incubated with their primary energy substrates (radiolabeled butyrate, glucose, glutamine and beta-hydroxybutyrate) for 60 min. Production of lactate, ketone bodies and CO2 were determined. At 6 wk, there were no significant differences in metabolism among treatments. In contrast, at 16 wk, AOM-injected rats had dramatically lower rates of CO2 production (P < 0.001) from both glucose and butyrate and lower rates of lactate and ketone body production than their saline counterparts. At 36 wk, when tumors developed, the depressed production of lactate and ketone bodies seen in AOM-injected rats at 16 wk returned to control values. However, in AOM-injected rats, CO2 production from glucose and butyrate remained depressed. Cellulose feeding resulted in decreased oxidation of glucose, butyrate and glutamine and an increased production of ketone bodies from butyrate by colonocytes compared with pectin feeding at 36 wk. We conclude that colonocyte energy metabolism differs in AOM-injected rats vs. saline controls and changes during tumorigenesis, and suggest a relationship between intracellular energy status and changes in cell kinetics. This is the first report that such a relationship may exist in vivo.

Inhibition of etoposide-induced apoptosis with peptide aldehyde inhibitors of proteasome

Recent investigations have indicated the involvement of proteasome in programmed cell death. The present studies show that although peptide aldehyde inhibitors of proteasome are by themselves weak inducers of apoptosis, they inhibit the apoptotic effect of the anticancer drug etoposide in rat thymocytes. Acetyl-Leu-Leu-norvalinal (LLnV-al) and other related peptide aldehydes inhibited the increase in caspase activity and DNA fragmentation that followed treatment with etoposide and their effect was related to their potency as proteasome inhibitors. To inhibit etoposide-induced apoptosis, LLnV-al must be present within 3 h of treatment with etoposide, in the same way as the inhibitor of protein synthesis cycloheximide must be. Etoposide caused a rapid accumulation of p53 protein that was not inhibited by LLnV-al, which was also a strong inducer of p53. Peptide aldehydes were also weak activators of caspase activity, suggesting that the same mechanism, i.e. the blocking of proteasome function, both triggers apoptosis and inhibits the effect of etoposide. These results are consistent with a model in which proteasome is selectively involved in the pathway used by etoposide to induce cell suicide.

Inhibition of glucocorticoid-induced apoptosis with 5-aminoimidazole-4-carboxamide ribonucleoside, a cell-permeable activator of AMP-activated protein kinase

The AMP-activated protein kinase (AMPK) is related to a growing family of protein kinases that are believed to protect cells against environmental and nutritional stress. In the present study the hypothesis of a protective role for AMPK against thymocyte apoptosis has been tested. It is shown that AMPK is expressed in rat thymocytes that contain the transcript for the a1 isoform of the AMPK catalytic subunit and can be activated by treatment with 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR), a well-established activator of AMPK. AICAR is not toxic and prevents glucocorticoid-induced apoptosis in the same concentration range used to activate AMPK. At concentrations higher than 1 mM, AICAR fully restores cell viability and inhibits DNA laddering in dexamethasone-treated thymocytes. Furthermore, AICAR blocks the dexamethasone-induced activation of caspase 3-like enzymes, which are believed to play a pivotal role in apoptotic cell death. Activation of AMPK by oligomycin, which depletes thymocytes of ATP, is also correlated to inhibition of caspase 3-like activity in dexamethasone-treated cells. However, AICAR and oligomycin do not exert any protective action when apoptosis is induced by staurosporine. These results indicate that AICAR is a powerful inhibitor of glucocorticoid-induced apoptosis and suggest that AMPK activation may interfere with a step in the apoptotic cascade triggered by dexamethasone.

Mitochondrial photodamage and PDT-induced apoptosis

Four photosensitizers with specific targets (mitochondria, lysosomes and plasma membrane) were used to delineate the mechanism of PDT-induced apoptosis in murine leukemia cells. Additional studies were carried out with two sensitizers which caused photodamage to both mitochondria and lysosomes, but varied with regard to membrane photodamage. PDT induced an apoptotic response after mitochondrial photodamage, but not after selective damage to lysosomes or to the cell membrane. Moreover, the latter could delay or inhibit the appearance of apoptosis after mitochondrial photodamage. We had previously reported that exposure of cells to high porphycene concentrations caused an apoptotic response in the dark; this was also associated with mitochondrial damage. These results are consistent with recent proposals that release of mitochondrial components can trigger an apoptotic response. ATP depletion after mitochondrial photodamage does not appear to play a role in initiation of the apoptotic program.