Slowly progressive cell death induced by GPx4-deficiency occurs via MEK1/ERK2 activation as a downstream signal after iron-independent lipid peroxidation.

Glutathione peroxidase 4 (GPx4) is an antioxidant enzyme that reduces phospholipid hydroperoxide. Studies have reported that the loss of GPx4 activity through anticancer drugs leads to ferroptosis, an iron-dependent lipid peroxidation-induced cell death. In this study, we established Tamoxifen-inducible GPx4-deficient Mouse embryonic fibroblast (MEF) cells (ETK1 cells) and found that Tamoxifen-inducible gene disruption of GPx4 induces slow cell death at ~72 h. In contrast, RSL3- or erastin-induced ferroptosis occurred quickly within 24 h. Therefore, we investigated the differences in these mechanisms between GPx4 gene disruption-induced cell death and RSL3- or erastin-induced ferroptosis. We found that GPx4-deficiency induced lipid peroxidation at 24 h in Tamoxifen-treated ETK1 cells, which was not suppressed by iron chelators, although lipid peroxidation in RSL3- or erastin-treated cells induced ferroptosis that was inhibited by iron chelators. We revealed that GPx4-deficient cell death was MEK1-dependent but RSL3- or erastin-induced ferroptosis was not, although MEK1/2 inhibitors suppressed both GPx4-deficient cell death and RSL3- or erastin-induced ferroptosis. In GPx4-deficient cell death, the phosphorylation of MEK1/2 and ERK2 was observed 39 h after lipid peroxidation, but ERK1 was not phosphorylated. Selective inhibitors of ERK2 inhibited GPx4-deficient cell death but not in RSL3- or erastin-induced cell death. These findings suggest that iron-independent lipid peroxidation due to GPx4 disruption induced cell death via the activation of MEK1/ERK2 as a downstream signal of lipid peroxidation in Tamoxifen-treated ETK1 cells. This indicates that GPx4 gene disruption induces slow cell death and involves a different pathway from RSL3- and erastin-induced ferroptosis in ETK1 cells.

Deferasirox Targeting Ferroptosis Synergistically Ameliorates Myocardial Ischemia Reperfusion Injury in Conjunction With Cyclosporine A.

BACKGROUND: Ferroptosis, an iron-dependent form of regulated cell death, is a major cell death mode in myocardial ischemia reperfusion (I/R) injury, along with mitochondrial permeability transition-driven necrosis, which is inhibited by cyclosporine A (CsA). However, therapeutics targeting ferroptosis during myocardial I/R injury have not yet been developed. Hence, we aimed to investigate the therapeutic efficacy of deferasirox, an iron chelator, against hypoxia/reoxygenation-induced ferroptosis in cultured cardiomyocytes and myocardial I/R injury. METHODS AND RESULTS: The effects of deferasirox on hypoxia/reoxygenation-induced iron overload in the endoplasmic reticulum, lipid peroxidation, and ferroptosis were examined in cultured cardiomyocytes. In a mouse model of I/R injury, the infarct size and adverse cardiac remodeling were examined after treatment with deferasirox, CsA, or both in combination. Deferasirox suppressed hypoxia- or hypoxia/reoxygenation-induced iron overload in the endoplasmic reticulum, lipid peroxidation, and ferroptosis in cultured cardiomyocytes. Deferasirox treatment reduced iron levels in the endoplasmic reticulum and prevented increases in lipid peroxidation and ferroptosis in the I/R-injured myocardium 24 hours after I/R. Deferasirox and CsA independently reduced the infarct size after I/R injury to a similar degree, and combination therapy with deferasirox and CsA synergistically reduced the infarct size (infarct area/area at risk; control treatment: 64±2%; deferasirox treatment: 48±3%; CsA treatment: 48±4%; deferasirox+CsA treatment: 37±3%), thereby ameliorating adverse cardiac remodeling on day 14 after I/R. CONCLUSIONS: Combination therapy with deferasirox and CsA may be a clinically feasible and effective therapeutic approach for limiting I/R injury and ameliorating adverse cardiac remodeling after myocardial infarction.

Doxorubicin causes ferroptosis and cardiotoxicity by intercalating into mitochondrial DNA and disrupting Alas1-dependent heme synthesis.

Clinical use of doxorubicin (DOX) is limited because of its cardiotoxicity, referred to as DOX-induced cardiomyopathy (DIC). Mitochondria-dependent ferroptosis, which is triggered by iron overload and excessive lipid peroxidation, plays a pivotal role in the progression of DIC. Here, we showed that DOX accumulated in mitochondria by intercalating into mitochondrial DNA (mtDNA), inducing ferroptosis in an mtDNA content-dependent manner. In addition, DOX disrupted heme synthesis by decreasing the abundance of 5'-aminolevulinate synthase 1 (Alas1), the rate-limiting enzyme in this process, thereby impairing iron utilization, resulting in iron overload and ferroptosis in mitochondria in cultured cardiomyocytes. Alas1 overexpression prevented this outcome. Administration of 5-aminolevulinic acid (5-ALA), the product of Alas1, to cultured cardiomyocytes and mice suppressed iron overload and lipid peroxidation, thereby preventing DOX-induced ferroptosis and DIC. Our findings reveal that the accumulation of DOX and iron in mitochondria cooperatively induces ferroptosis in cardiomyocytes and suggest that 5-ALA can be used as a potential therapeutic agent for DIC.

Iron Overload via Heme Degradation in the Endoplasmic Reticulum Triggers Ferroptosis in Myocardial Ischemia-Reperfusion Injury.

Ischemia-reperfusion (I/R) injury is a promising therapeutic target to improve clinical outcomes after acute myocardial infarction. Ferroptosis, triggered by iron overload and excessive lipid peroxides, is reportedly involved in I/R injury. However, its significance and mechanistic basis remain unclear. Here, we show that glutathione peroxidase 4 (GPx4), a key endogenous suppressor of ferroptosis, determines the susceptibility to myocardial I/R injury. Importantly, ferroptosis is a major mode of cell death in I/R injury, distinct from mitochondrial permeability transition (MPT)-driven necrosis. This suggests that the use of therapeutics targeting both modes is an effective strategy to further reduce the infarct size and thereby ameliorate cardiac remodeling after I/R injury. Furthermore, we demonstrate that heme oxygenase 1 up-regulation in response to hypoxia and hypoxia/reoxygenation degrades heme and thereby induces iron overload and ferroptosis in the endoplasmic reticulum (ER) of cardiomyocytes. Collectively, ferroptosis triggered by GPx4 reduction and iron overload in the ER is distinct from MPT-driven necrosis in both in vivo phenotype and in vitro mechanism for I/R injury. The use of therapeutics targeting ferroptosis in conjunction with cyclosporine A can be a promising strategy for I/R injury.

Ethoxyquin is a Competent Radical-Trapping Antioxidant for Preventing Ferroptosis in Doxorubicin Cardiotoxicity.

ABSTRACT: Doxorubicin (DOX) is an effective anti-cancer agent for various malignancies. Nevertheless, it has a side effect of cardiotoxicity, referred to as doxorubicin-induced cardiomyopathy (DIC), that is associated with a poorer prognosis. This cardiotoxicity limits the clinical use of DOX as a therapeutic agent for malignancies. Recently, ferroptosis, a form of regulated cell death induced by the accumulation of lipid peroxides, has been recognized as a major pathophysiology of DIC. Ethoxyquin is a lipophilic antioxidant widely used for food preservation and thus may be a potential therapeutic drug for preventing DIC. However, the efficacy of ethoxyquin against ferroptosis and DIC remains to be fully elucidated. Here, we investigated the inhibitory action of ethoxyquin against GPx4-deficient ferroptosis and its therapeutic efficacy against DOX-induced cell death in cultured cardiomyocytes and cardiotoxicity in a murine model of DIC. In cultured cardiomyocytes, ethoxyquin treatment effectively prevented GPx4-deficient ferroptosis. Ethoxyquin also prevented DOX-induced cell death, accompanied by the suppression of malondialdehyde (MDA) and mitochondrial lipid peroxides, which were induced by DOX. Furthermore, ethoxyquin significantly prevented DOX-induced cell death without any suppression of caspase cleavages representing apoptosis. In DIC mice, ethoxyquin treatment ameliorated cardiac impairments, such as contractile dysfunction and myocardial atrophy, and lung congestion. Ethoxyquin also suppressed serum lactate dehydrogenase and creatine kinase activities, decreased the levels of lipid peroxides such as MDA and acrolein, inhibited cardiac fibrosis, and reduced TUNEL-positive cells in the hearts of DIC mice. Collectively, ethoxyquin is a competent antioxidant for preventing ferroptosis in DIC and can be its prospective therapeutic drug.

Mitochondrial glutathione peroxidase 4 is indispensable for photoreceptor development and survival in mice.

Glutathione peroxidase 4 (GPx4) is known for its unique function in the direct detoxification of lipid peroxides in the cell membrane and as a key regulator of ferroptosis, a form of lipid peroxidation-induced nonapoptotic cell death. However, the cytosolic isoform of GPx4 is considered to play a major role in inhibiting ferroptosis in somatic cells, whereas the roles of the mitochondrial isoform of GPx4 (mGPx4) in cell survival are not yet clear. In the present study, we found that mGPx4 KO mice exhibit a cone-rod dystrophy-like phenotype in which loss of cone photoreceptors precedes loss of rod photoreceptors. Specifically, in mGPx4 KO mice, cone photoreceptors disappeared prior to their maturation, whereas rod photoreceptors persisted through maturation but gradually degenerated afterward. Mechanistically, we demonstrated that vitamin E supplementation significantly ameliorated photoreceptor loss in these mice. Furthermore, LC-MS showed a significant increase in peroxidized phosphatidylethanolamine esterified with docosahexaenoic acid in the retina of mGPx4 KO mice. We also observed shrunken and uniformly condensed nuclei as well as caspase-3 activation in mGPx4 KO photoreceptors, suggesting that apoptosis was prevalent. Taken together, our findings indicate that mGPx4 is essential for the maturation of cone photoreceptors but not for the maturation of rod photoreceptors, although it is still critical for the survival of rod photoreceptors after maturation. In conclusion, we reveal novel functions of mGPx4 in supporting development and survival of photoreceptors in vivo.

Mitochondria-dependent ferroptosis plays a pivotal role in doxorubicin cardiotoxicity.

Doxorubicin (DOX), a chemotherapeutic agent, induces a cardiotoxicity referred to as doxorubicin-induced cardiomyopathy (DIC). This cardiotoxicity often limits chemotherapy for malignancies and is associated with poor prognosis. However, the molecular mechanism underlying this cardiotoxicity is yet to be fully elucidated. Here, we show that DOX downregulated glutathione peroxidase 4 (GPx4) and induced excessive lipid peroxidation through DOX-Fe2+ complex in mitochondria, leading to mitochondria-dependent ferroptosis; we also show that mitochondria-dependent ferroptosis is a major cause of DOX cardiotoxicity. In DIC mice, the left ventricular ejection fraction was significantly impaired, and fibrosis and TUNEL+ cells were induced at day 14. Additionally, GPx4, an endogenous regulator of ferroptosis, was downregulated, accompanied by the accumulation of lipid peroxides, especially in mitochondria. These cardiac impairments were ameliorated in GPx4 Tg mice and exacerbated in GPx4 heterodeletion mice. In cultured cardiomyocytes, GPx4 overexpression or iron chelation targeting Fe2+ in mitochondria prevented DOX-induced ferroptosis, demonstrating that DOX triggered ferroptosis in mitochondria. Furthermore, concomitant inhibition of ferroptosis and apoptosis with ferrostatin-1 and zVAD-FMK fully prevented DOX-induced cardiomyocyte death. Our findings suggest that mitochondria-dependent ferroptosis plays a key role in progression of DIC and that ferroptosis is the major form of regulated cell death in DOX cardiotoxicity.

Involvement of GPx4-Regulated Lipid Peroxidation in Idiopathic Pulmonary Fibrosis Pathogenesis.

The imbalanced redox status in lung has been widely implicated in idiopathic pulmonary fibrosis (IPF) pathogenesis. To regulate redox status, hydrogen peroxide must be adequately reduced to water by glutathione peroxidases (GPx). Among GPx isoforms, GPx4 is a unique antioxidant enzyme that can directly reduce phospholipid hydroperoxide. Increased lipid peroxidation products have been demonstrated in IPF lungs, suggesting the participation of imbalanced lipid peroxidation in IPF pathogenesis, which can be modulated by GPx4. In this study, we sought to examine the involvement of GPx4-modulated lipid peroxidation in regulating TGF-ß-induced myofibroblast differentiation. Bleomycin-induced lung fibrosis development in mouse models with genetic manipulation of GPx4 were examined. Immunohistochemical evaluations for GPx4 and lipid peroxidation were performed in IPF lung tissues. Immunohistochemical evaluations showed reduced GPx4 expression levels accompanied by increased 4-hydroxy-2-nonenal in fibroblastic focus in IPF lungs. TGF-ß-induced myofibroblast differentiation was enhanced by GPx4 knockdown with concomitantly enhanced lipid peroxidation and SMAD2/SMAD3 signaling. Heterozygous GPx4-deficient mice showed enhancement of bleomycin-induced lung fibrosis, which was attenuated in GPx4-transgenic mice in association with lipid peroxidation and SMAD signaling. Regulating lipid peroxidation by Trolox showed efficient attenuation of bleomycin-induced lung fibrosis development. These findings suggest that increased lipid peroxidation resulting from reduced GPx4 expression levels may be causally associated with lung fibrosis development through enhanced TGF-ß signaling linked to myofibroblast accumulation of fibroblastic focus formation during IPF pathogenesis. It is likely that regulating lipid peroxidation caused by reduced GPx4 can be a promising target for an antifibrotic modality of treatment for IPF.

Hepatic ferroptosis plays an important role as the trigger for initiating inflammation in nonalcoholic steatohepatitis.

Nonalcoholic steatohepatitis (NASH) is a metabolic liver disease that progresses from simple steatosis to the disease state of inflammation and fibrosis. Previous studies suggest that apoptosis and necroptosis may contribute to the pathogenesis of NASH, based on several murine models. However, the mechanisms underlying the transition of simple steatosis to steatohepatitis remain unclear, because it is difficult to identify when and where such cell deaths begin to occur in the pathophysiological process of NASH. In the present study, our aim is to investigate which type of cell death plays a role as the trigger for initiating inflammation in fatty liver. By establishing a simple method of discriminating between apoptosis and necrosis in the liver, we found that necrosis occurred prior to apoptosis at the onset of steatohepatitis in the choline-deficient, ethionine-supplemented (CDE) diet model. To further investigate what type of necrosis is involved in the initial necrotic cell death, we examined the effect of necroptosis and ferroptosis inhibition by administering inhibitors to wild-type mice in the CDE diet model. In addition, necroptosis was evaluated using mixed lineage kinase domain-like protein (MLKL) knockout mice, which is lacking in a terminal executor of necroptosis. Consequently, necroptosis inhibition failed to block the onset of necrotic cell death, while ferroptosis inhibition protected hepatocytes from necrotic death almost completely, and suppressed the subsequent infiltration of immune cells and inflammatory reaction. Furthermore, the amount of oxidized phosphatidylethanolamine, which is involved in ferroptosis pathway, was increased in the liver sample of the CDE diet-fed mice. These findings suggest that hepatic ferroptosis plays an important role as the trigger for initiating inflammation in steatohepatitis and may be a therapeutic target for preventing the onset of steatohepatitis.

Lipid Peroxidation-Dependent Cell Death Regulated by GPx4 and Ferroptosis.

Glutathione peroxidase 4 (Phospholipid hydroperoxide glutathione peroxidase, PHGPx) can directly reduce phospholipid hydroperoxide. Depletion of GPx4 induces lipid peroxidation-dependent cell death in embryo, testis, brain, liver, heart, and photoreceptor cells of mice. Administration of vitamin E in tissue specific GPx4 KO mice restored tissue damage in testis, liver, and heart. These results indicate that suppression of phospholipid peroxidation is essential for cell survival in normal tissues in mice. Ferroptosis is an iron-dependent non-apoptotic cell death that can elicited by pharmacological inhibiting the cystine/glutamate antiporter, system Xc- (type I) or directly binding and loss of activity of GPx4 (Type II) in cancer cells with high level RAS-RAF-MEK pathway activity or p53 expression, but not in normal cells. Ferroptosis by Erastin (Type I) and RSL3 (RAS-selective lethal 3, Type II) treatment was suppressed by an iron chelator, vitamin E and Ferrostatin-1, antioxidant compound. GPx4 can regulate ferroptosis by suppression of phospholipid peroxidation in erastin and RSL3-induced ferroptosis. Recent works have identified several regulatory factors of erastin and RSL3-induced ferroptosis. In our established GPx4-deficient MEF cells, depletion of GPx4 induce iron and 15LOX-independent lipid peroxidation at 26 h and caspase-independent cell death at 72 h, whereas erastin and RSL3 treatment resulted in iron-dependent ferroptosis by 12 h. These results indicated the possibility that the mechanism of GPx4-depleted cell death might be different from that of ferroptosis induced by erastin and RSL3.

Roles of mitochondria-generated reactive oxygen species on X-ray-induced apoptosis in a human hepatocellular carcinoma cell line, HLE.

HLE, a human hepatocellular carcinoma cell line was transiently transfected with normal human MnSOD and MnSOD without a mitochondrial targeting signal (MTS). Mitochondrial reactive oxygen species (ROS), lipid peroxidation and apoptosis were examined as a function of time following 18.8 Gy X-ray irradiation. Our results showed that the level of mitochondrial ROS increased and reached a maximum level 2 hours after X-ray irradiation. Authentic MnSOD, but not MnSOD lacking MTS, protected against mitochondrial ROS, lipid peroxidation and apoptosis. In addition, the levels of mitochondrial ROS were consistently found to always correlate with the levels of authentic MnSOD in mitochondria. These results suggest that only when MnSOD is located in mitochondria is it efficient in protecting against cellular injuries by X-ray irradiation and that mitochondria are the critical sites of X-ray-induced cellular oxidative injuries.

Muscle choline kinase beta defect causes mitochondrial dysfunction and increased mitophagy.

Choline kinase is the first step enzyme for phosphatidylcholine (PC) de novo biosynthesis. Loss of choline kinase activity in muscle causes rostrocaudal muscular dystrophy (rmd) in mouse and congenital muscular dystrophy in human, characterized by distinct mitochondrial morphological abnormalities. We performed biochemical and pathological analyses on skeletal muscle mitochondria from rmd mice. No mitochondria were found in the center of muscle fibers, while those located at the periphery of the fibers were significantly enlarged. Muscle mitochondria in rmd mice exhibited significantly decreased PC levels, impaired respiratory chain enzyme activities, decreased mitochondrial ATP synthesis, decreased coenzyme Q and increased superoxide production. Electron microscopy showed the selective autophagic elimination of mitochondria in rmd muscle. Molecular markers of mitophagy, including Parkin, PINK1, LC3, polyubiquitin and p62, were localized to mitochondria of rmd muscle. Quantitative analysis shows that the number of mitochondria in muscle fibers and mitochondrial DNA copy number were decreased. We demonstrated that the genetic defect in choline kinase in muscle results in mitochondrial dysfunction and subsequent mitochondrial loss through enhanced activation of mitophagy. These findings provide a first evidence for a pathomechanistic link between de novo PC biosynthesis and mitochondrial abnormality.

A congenital muscular dystrophy with mitochondrial structural abnormalities caused by defective de novo phosphatidylcholine biosynthesis.

Congenital muscular dystrophy is a heterogeneous group of inherited muscle diseases characterized clinically by muscle weakness and hypotonia in early infancy. A number of genes harboring causative mutations have been identified, but several cases of congenital muscular dystrophy remain molecularly unresolved. We examined 15 individuals with a congenital muscular dystrophy characterized by early-onset muscle wasting, mental retardation, and peculiar enlarged mitochondria that are prevalent toward the periphery of the fibers but are sparse in the center on muscle biopsy, and we have identified homozygous or compound heterozygous mutations in the gene encoding choline kinase beta (CHKB). This is the first enzymatic step in a biosynthetic pathway for phosphatidylcholine, the most abundant phospholipid in eukaryotes. In muscle of three affected individuals with nonsense mutations, choline kinase activities were undetectable, and phosphatidylcholine levels were decreased. We identified the human disease caused by disruption of a phospholipid de novo biosynthetic pathway, demonstrating the pivotal role of phosphatidylcholine in muscle and brain.

Role of calcium-induced mitochondrial hydroperoxide in induction of apoptosis of RBL2H3 cells with eicosapentaenoic acid treatment.

Eicosapentaenoic acid (EPA) was previously shown to induce caspase-independent apoptosis in rat basophilic leukemia cells (RBL2H3 cells) by translocation of apoptosis-inducing factor (AIF) [Free Radic Res (2005) 39, 225-235]. Here, we attempted to investigate the mechanism of EPA-induced apoptosis. A rapid and sustained increase in calcium was observed in mitochondria at 2 h after the addition of EPA prior to apoptosis. Coincidently, hydroperoxide was generated in the mitochondria after exposure to EPA. Production of mitochondrial hydroperoxide was significantly reduced by ruthenium red, an inhibitor of mitochondrial calcium uniporter, and BAPTA-AM, a cytoplasmic calcium chelator, indicating that generation of hydroperoxide is triggered by an accumulation of calcium in the mitochondria. The production of mitochondrial hydroperoxide was markedly attenuated by overexpression of phospholipid hydroperoxide glutathione peroxidase (PHGPx) in the mitochondria. Apoptosis was therefore, significantly prevented through inhibition of mitochondrial hydroperoxide generation with mitochondrial PHGPx, ruthenium red or BAPTA-AM. However, accumulation of calcium in the mitochondria was not prevented by mitochondrial PHGPx although apoptosis was blocked, indicating that elevated calcium does not directly induce apoptosis. Taken together, our results show that calcium-dependent hydroperoxide accumulation in the mitochondria is critical in EPA-induced apoptosis.

Involvement of hydroperoxide in mitochondria in the induction of apoptosis by the eicosapentaenoic acid.

Eicosapentaenoic acid (EPA) induced apoptosis of rat basophilic leukemia cells (RBL2H3 cells), whereas 100 microM linoleic acid (LA) had no significant effect. Cytochrome c was released at 4 h. Apoptosis was detected at 6 h after exposure to EPA and docosahexaenoic acid (DHA), and preceded the activation of caspase-3. Liberation of apoptosis-inducing factor (AIF) from mitochondria and its translocation into the nucleus were observed at 4 h. A broad-specificity caspase inhibitor, z-VAD-fmk, failed to suppress the apoptosis, suggesting that EPA induced caspase-independent apoptosis. On other hand, a poly (ADP-ribose) polymerase-1 (PARP-1) inhibitor that blocks AIF translocation to the nucleus suppressed EPA-induced apoptosis. The level of hydroperoxide in the cells and mitochondria increased at the early phase of apoptosis within 2 h. On the contrary, elevation of hydroperoxide in mitochondria was not observed after treatment with LA. The EPA-induced apoptosis was abolished by prevention of the hydroperoxide elevation in mitochondria via overexpression of mitochondrial phospholipid hydroperoxide glutathione peroxidase (PHGPx). Neither cytochrome c nor AIF were released from mitochondria in the mitochondrial PHGPx-overexpressing cells. EPA also induced apoptosis in HeLa cells, but not in L929 or RAW264.7 cells. Enhancement of the hydroperoxide level in mitochondria was found in the EPA-sensitive HeLa cells after treatment with EPA, whereas no such enhancement was observed in the apoptosis-resistant L929 and RAW264.7 cells. These results suggest that the generation of hydroperoxide in mitochondria induced by EPA is associated with AIF release from mitochondria and the induction of apoptosis.

Protection from inactivation of the adenine nucleotide translocator during hypoglycaemia-induced apoptosis by mitochondrial phospholipid hydroperoxide glutathione peroxidase.

We demonstrated that mitochondrial phospholipid hydroperoxide glutathione peroxidase (PHGPx) first suppressed the dissociation of cytochrome c (cyt c) from cardiolipin (CL) in mitochondrial inner membranes and then apoptosis caused by the hypoglycaemia by the prevention of peroxidation of CL [Nomura, Imai, Koumura, Arai and Nakagawa (1999) J. Biol. Chem. 274, 29294-29302; Nomura, Imai, Koumura, Kobayashi and Nakagawa (2000) Biochem. J. 351, 183-193]. The present study shows the involvement of peroxidation of CL in the inactivation of adenine nucleotide translocator (ANT) and the opening of permeability transition pores by using the system of ANT-reconstituted liposome and isolated mitochondria. ANT activity appeared in dioleoyl phosphatidylcholine proteoliposome containing 10% (mol/mol) CL or phosphatidylglycerol (PG), but not other classes of phospholipids. ANT activity was competitively inhibited by the addition of cardiolipin hydroperoxide (CLOOH) in reconstituted liposomes containing CL. However, phosphatidylcholine hydroperoxide failed to inactivate the activity of ANT. The activity of ANT in reconstituted liposomes, including CLOOH, recovered when CLOOH in reconstituted liposome was reduced to hydroxycardiolipin by incubation with PHGPx. The activity of ANT was determined in rat basophil leukaemia RBL2H3 cells after their exposure to 2-deoxyglucose. ANT activity decreased to 50% of the control level by 4 h in response to apoptosis. In parallel, cyt c and apoptosis-inducing factor (AIF) were released from mitochondria. Suppression of the accumulation of CLOOH by overexpression of PHGPx in mitochondria effectively prevented the inactivation of ANT, the opening of permeability transition pores and the release of cyt c and AIF from mitochondria in hypoglycaemia-induced apoptotic cells. These findings suggest that mitochondrial PHGPx might be involved in the modulation of the activity of ANT and the opening of pores for the release of cyt c via the modulation of levels of CLOOH in the mitochondria.