Regulation of high glucose-induced apoptosis by mitochondrial NADP+-dependent isocitrate dehydrogenase

IDH2 gene deficiency accelerates unilateral ureteral obstruction-induced kidney inflammation through oxidative stress and activation of macrophages

Mitochondrial NADP⁺-dependent isocitrate dehydrogenase 2 (IDH2) produces NADPH, which is known to inhibit mitochondrial oxidative stress. Ureteral obstruction induces kidney inflammation and fibrosis via oxidative stress. Here, we investigated the role and underlying mechanism of IDH2 in unilateral ureteral obstruction (UUO)-induced kidney inflammation using IDH2 gene deleted mice (IDH2^-/-). Eight- to 10-week-old female IDH2^-/- mice and wild type (IDH2^+/+) littermates were subjected to UUO and kidneys were harvested 5 days after UUO. IDH2 was not detected in the kidneys of IDH2^-/- mice, while UUO decreased IDH2 in IDH2^+/+ mice. UUO increased the expressions of markers of oxidative stress in both IDH2^+/+ and IDH2^-/- mice, and these changes were greater in IDH2^-/- mice compared to IDH2^+/+ mice. Bone marrow-derived macrophages of IDH2^-/- mice showed a more migrating phenotype with greater ruffle formation and Rac1 distribution than that of IDH2^+/+ mice. Correspondently, UUO-induced infiltration of monocytes/macrophages was greater in IDH2^-/- mice compared to IDH2^+/+ mice. Taken together, these data demonstrate that IDH2 plays a protective role against UUO-induced inflammation through inhibition of oxidative stress and macrophage infiltration.

Mitochondrial Glutathione: Recent Insights and Role in Disease

Mitochondria are the main source of reactive oxygen species (ROS), most of them deriving from the mitochondrial respiratory chain. Among the numerous enzymatic and non-enzymatic antioxidant systems present in mitochondria, mitochondrial glutathione (mGSH) emerges as the main line of defense for maintaining the appropriate mitochondrial redox environment. mGSH’s ability to act directly or as a co-factor in reactions catalyzed by other mitochondrial enzymes makes its presence essential to avoid or to repair oxidative modifications that can lead to mitochondrial dysfunction and subsequently to cell death. Since mitochondrial redox disorders play a central part in many diseases, harboring optimal levels of mGSH is vitally important. In this review, we will highlight the participation of mGSH as a contributor to disease progression in pathologies as diverse as Alzheimer’s disease, alcoholic and non-alcoholic steatohepatitis, or diabetic nephropathy. Furthermore, the involvement of mitochondrial ROS in the signaling of new prescribed drugs and in other pathologies (or in other unmet medical needs, such as gender differences or coronavirus disease of 2019 (COVID-19) treatment) is still being revealed; guaranteeing that research on mGSH will be an interesting topic for years to come.

Mitochondrial NADP+-dependent isocitrate dehydrogenase deficiency increases cisplatin-induced oxidative damage in the kidney tubule cells

Mitochondrial NADP⁺-dependent isocitrate dehydrogenase (IDH2) plays an important role in the formation of NADPH, which is critical for the maintenance of mitochondrial redox balance. Cis-diamminedichloroplatinum II (cisplatin), an effective anticancer drug, induces oxidative stress-related nephrotoxicity, limiting its use. Therefore, we investigated whether IDH2, which is a critical enzyme in the NADPH-associated mitochondrial antioxidant system, is involved in cisplatin nephrotoxicity. Idh2 gene-deleted (Idh2^−/−) mice and wild-type (Idh2^+/+) littermates were treated with cisplatin, with or without 2-(2,2,6,6-tetramethylpiperidin-1-oxyl-4-ylamino)-2-oxoethyl) triphenylphosphonium chloride (Mito-T), a mitochondria-specific antioxidant. Cisplatin-induced renal functional and morphological impairments were greater in Idh2^−/− mice than in Idh2^+/+ mice. Mito-T mitigated those impairments in both Idh2^−/− and Idh2^+/+ mice and this mitigation was greater in Idh2^−/− than in Idh2^+/+ mice. Cisplatin impaired IDH2 function in the mitochondria, decreasing mitochondrial NADPH and GSH levels and increasing H₂O₂ generation; protein, lipid, and DNA oxidation; mitochondrial damage; and apoptosis. These cisplatin-induced changes were much more severe in Idh2^−/− mice than in Idh2^+/+ mice. Mito-T treatment attenuated cisplatin-induced alterations in both Idh2^−/− and Idh2^+/+ mice and this mitigation was greater in Idh2^−/− than in Idh2^+/+ mice. Altogether, these data demonstrate that cisplatin induces the impairment of the mitochondrial IDH2-NADPH-GSH antioxidant system and IDH2 deficiency aggravates cisplatin-induced mitochondrial oxidative damage, inducing more severe nephrotoxicity. This suggests that the mitochondrial IDH2-NADPH-GSH antioxidant system is a target for the prevention of cisplatin-induced kidney cell death.

IDH2 deficiency increases the liver susceptibility to ischemia-reperfusion injury via increased mitochondrial oxidative injury

Mitochondrial NADP⁺-dependent isocitrate dehydrogenase 2 (IDH2) is a major producer of mitochondrial NADPH, required for glutathione (GSH)-associated mitochondrial antioxidant systems including glutathione peroxidase (GPx) and glutathione reductase (GR). Here, we investigated the role of IDH2 in hepatic ischemia-reperfusion (HIR)-associated mitochondrial injury using Idh2-knockout (Idh2^-/-) mice and wild-type (Idh2^+/+) littermates. Mice were subjected to either 60min of partial liver ischemia or sham-operation. Some mice were administered with 2-(2,2,6,6-tetramethylpiperidin-1-oxyl-4-ylamino)-2-oxoethyl) triphenylphosphonium chloride (mito-TEMPO, a mitochondria-targeting antioxidant). HIR induced severe histological and functional damages of liver in both Idh2^+/+ mice and Idh2^-/- mice and those damages were more severe in Idh2^-/- mice than in wild-type littermates. HIR induces dysfunction of IDH2, leading to the decreases of NADPH level and mitochondrial GR and GPx functions, consequently resulting in mitochondrial and cellular oxidative injury as reflected by mitochondrial cristae loss, mitochondrial fragmentation, shift in mitochondrial fission, cytochrome c release, and cell death. These HIR-induced changes were greater in Idh2^-/- mice than wild-type mice. The mito-TEMPO supplement significantly attenuated the aforementioned changes, and these attenuations were much greater in Idh2^-/- mice when compared with wild-type littermates. Taken together, results have demonstrated that HIR impairs in the IDH2-NADPH-GSH mitochondrial antioxidant system, resulting in increased mitochondrial oxidative damage and dysfunction, suggesting that IDH2 plays a critical role in mitochondrial redox balance and HIR-induced impairment of IDH2 function is associated with the pathogenesis of ischemia-reperfusion-induced liver failure.

Effect of Soluble Nickel on Cellular Energy Metabolism in A549 Cells

Iron is an essential nutrient to most organisms, and is actively involved in oxygen delivery, electron transport, DNA synthesis, and many other biochemical reactions important for cell survival. We previously reported that nickel (Ni) ion exposure decreases cellular iron level and converts cytosolic aconitase (c-aconitase) to iron-regulatory proteln-1 in A549 cells (Chen H, Davidson T, Singleton S, Garrick MD, Costa M. Toxicol Appl Pharmacol 206:275–287, 2005). Here, we further investigated the effect of Ni ion exposure on the activity of mitochondrial iron-sulfur (Fe-S) enzymes and cellular energy metabolism. We found that acute Ni Ion treatment up to 1 mM exhibits minimal toxicity in A549 cells. Ni ion treatment decreases the activity of several Fe-S enzymes related to cellular energy metabolism, including mitochondrial aconitase (m-aconitase), succinate dehydrogenase (SDH), and NADH:ublquinone oxldoreductase (complex I). Low doses of Ni ion for 4 weeks resulted in an increased cellular glycolysis and NADH to NAD+ (NADH/NAD+) ratio, although glycolysis was inhibited at higher levels. Collectively, our results show that Ni Ions decrease the activity of cellular iron (Fe)-containing enzymes, Inhibit oxidative phosphorylation (OxPhos), and increase cellular glycolytic activity. Since increased glycolysis is one of the fundamental alterations of energy metabolism in cancer cells (the Warburg effect), the inhibition of Fe-S enzymes and subsequent changes in cellular energy metabolism caused by Ni Ions may play an Important role in Ni carcinogenesis.

Mitochondrial NADP+-Dependent Isocitrate Dehydrogenase Deficiency Exacerbates Mitochondrial and Cell Damage after Kidney Ischemia-Reperfusion Injury

Mitochondrial NADP⁺-dependent isocitrate dehydrogenase (IDH2) catalyzes the oxidative decarboxylation of isocitrate to α-ketoglutarate, synthesizing NADPH, which is essential for mitochondrial redox balance. Ischemia-reperfusion (I/R) is one of most common causes of AKI. I/R disrupts the mitochondrial redox balance, resulting in oxidative damage to mitochondria and cells. Here, we investigated the role of IDH2 in I/R-induced AKI. I/R injury in mice led to the inactivation of IDH2 in kidney tubule cells. Idh2 gene deletion exacerbated the I/R-induced increase in plasma creatinine and BUN levels and the histologic evidence of tubule injury, and augmented the reduction of NADPH levels and the increase in oxidative stress observed in the kidney after I/R. Furthermore, Idh2 gene deletion exacerbated I/R-induced mitochondrial dysfunction and morphologic fragmentation, resulting in severe apoptosis in kidney tubule cells. In cultured mouse kidney proximal tubule cells, Idh2 gene downregulation enhanced the mitochondrial damage and apoptosis induced by treatment with hydrogen peroxide. This study demonstrates that Idh2 gene deletion exacerbates mitochondrial damage and tubular cell death via increased oxidative stress, suggesting that IDH2 is an important mitochondrial antioxidant enzyme that protects cells from I/R insult.

The Role of Mitochondrial NADPH-Dependent Isocitrate Dehydrogenase in Cancer Cells

Isocitrate dehydrogenase 2 (IDH2) is located in the mitochondrial matrix. IDH2 acts in the forward Krebs cycle as an NADP⁺-consuming enzyme, providing NADPH for maintenance of the reduced glutathione and peroxiredoxin systems and for self-maintenance by reactivation of cystine-inactivated IDH2 by glutaredoxin 2. In highly respiring cells, the resulting NAD⁺ accumulation then induces sirtuin-3-mediated activating IDH2 deacetylation, thus increasing its protective function. Reductive carboxylation of 2-oxoglutarate by IDH2 (in the reverse Krebs cycle direction), which consumes NADPH, may follow glutaminolysis of glutamine to 2-oxoglutarate in cancer cells. When the reverse aconitase reaction and citrate efflux are added, this overall “anoxic” glutaminolysis mode may help highly malignant tumors survive aglycemia during hypoxia. Intermittent glycolysis would hypothetically be required to provide ATP. When oxidative phosphorylation is dormant, this mode causes substantial oxidative stress. Arg172 mutants of human IDH2—frequently found with similar mutants of cytosolic IDH1 in grade 2 and 3 gliomas, secondary glioblastomas, and acute myeloid leukemia—catalyze reductive carboxylation of 2-oxoglutarate and reduction to D-2-hydroxyglutarate, which strengthens the neoplastic phenotype by competitive inhibition of histone demethylation and 5-methylcytosine hydroxylation, leading to genome-wide histone and DNA methylation alternations. D-2-hydroxyglutarate also interferes with proline hydroxylation and thus may stabilize hypoxia-induced factor α.

Proteomic profile of primary isolated rat mesangial cells in high-glucose culture condition and decreased expression of PSMA6 in renal cortex of diabetic rats

Diabetic nephropathy (DN) is one of the most important complications of diabetic patients and is characterized histologically by an accumulation of extracellular matrix (ECM) protein in the glomerular mesangium. Therefore, mesangial cells likely play an important role in the development of diabetic nephropathy. Here, we employed proteomic techniques to investigate the protein profile of rat mesangial cells under high-glucose culture conditions. Primary isolated rat glomerular mesangial cells were cultured under different concentrations of glucose (5.4 mmol.L-1 for normal control and 30 mmol.L-1 for high glucose) for 0, 8, 16, and 72 h, as well as for 25 days. Cellular total proteins were isolated from these cells and employed for two-dimensional gel electrophoresis (2-DE). Differentially expressed proteins were identified by matrix-assisted laser desorption - ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and some of these proteins were documented in rat models of diabetes by Western blot. Rat mesangial cells were successfully isolated in the laboratory and their proliferation rates were significantly inhibited by high glucose. Two-dimensional gel electrophoresis analyses revealed 28 differentially expressed protein spots between the normal and high-glucose groups. After MALDI-TOF-MS analysis, all 28 protein spots were successfully identified with the peptide mass fingerprint (PMF) method. Representatively, SOD1, PCBP1 and PSMA6 were validated by Western blot analysis following protein extractions from the normal and high-glucose groups. Abundance of these proteins was consistent with that found in 2-DE. Moreover, expression of SOD1, PCBP1, and PSMA6 in renal cortex was further examined in two rat models of diabetes (streptozotocin-induced and spontaneous OLETF diabetic models). Abundance of SOD1 and PCBP1 proteins did not show any significant difference between normal control and diabetic rats. However, abundance of the PSMA6 protein was significantly reduced in the renal cortex of both STZ-induced and spontaneous OLETF diabetic rats. Proteomic analysis identified 28 differentially expressed proteins in primary isolated rat mesangial cells between normal and high glucose treatments. Expression of one identified protein was found to be consistent with expression in the renal cortex of two rat diabetic models. Therefore, identification of protein expression patterns in mesangial cells can be employed to develop a therapeutic target for treatment of diabetic nephropathy.

Suppression of mitochondrial NADP(+)-dependent isocitrate dehydrogenase activity enhances curcumin-induced apoptosis in HCT116 cells

Curcumin is a polyphenol derived from the plant Curcuma longa that induces apoptotic cell death in malignant cancer cell lines. It has been shown previously that mitochondrial NADP(+)-dependent isocitrate dehydrogenase (IDPm) plays an essential role in defense against oxidative stress by supplying NADPH for antioxidant systems. This study demonstrates that curcumin decreased the activity of IDPm, both as a purified enzyme and in cultured cells. It also shows that curcumin-induced apoptosis in the colon cancer cell line HCT116 is significantly enhanced by suppression of IDPm activity. Transfection of HCT116 cells with an IDPm small interfering RNA (siRNA) markedly decreased activity of IDPm, enhancing cellular susceptibility to curcumin-induced apoptosis, as reflected by DNA fragmentation, cellular redox status, mitochondria dysfunction and modulation of apoptotic marker proteins. Together, these results suggest that application of curcumin together with IDPm siRNA may be an effective combination modality in the treatment of cancer.

Isocitrate dehydrogenase 1 and 2 mutations in cancer: alterations at a crossroads of cellular metabolism

Dysregulation of metabolism is a common phenomenon in cancer cells. The NADP(+)-dependent isocitrate dehydrogenases 1 and 2 (IDH1 and IDH2) function at a crossroads of cellular metabolism in lipid synthesis, cellular defense against oxidative stress, oxidative respiration, and oxygen-sensing signal transduction. We review the normal functions of the encoded enzymes, frequent mutations of IDH1 and IDH2 recently found in human cancers, and possible roles for the mutated enzymes in human disease. IDH1 and IDH2 mutations occur frequently in some types of World Health Organization grades 2-4 gliomas and in acute myeloid leukemias with normal karyotype. IDH1 and IDH2 mutations are remarkably specific to codons that encode conserved functionally important arginines in the active site of each enzyme. To date, all IDH1 mutations have been identified at the Arg132 codon. Mutations in IDH2 have been identified at the Arg140 codon, as well as at Arg172, which is aligned with IDH1 Arg132. IDH1 and IDH2 mutations are usually heterozygous in cancer, and they appear to confer a neomorphic enzyme activity for the enzymes to catalyze the production of D-2-hydroxyglutarate. Study of alterations in these metabolic enzymes may provide insights into the metabolism of cancer cells and uncover novel avenues for development of anticancer therapeutics.

The role of reactive oxygen species in apoptosis of the diabetic kidney

Increased levels of reactive oxygen species (ROS) by hyperglycemia can induce apoptosis of renal cells and diabetic nephropathy. The redox balance in the renal cell seems, therefore, of the utmost importance. ROS-mediated apoptosis may be further aggravated by an inadequate cytoprotective response against ROS. When there are insufficient cytoprotective and ROS scavenging molecules, ROS lead to considerable cellular damage and to a point of no return in apoptosis. Induction of cytoprotective proteins may prevent or attenuate apoptosis, renal cell injury, and finally diabetic nephropathy. Here, we discuss some mechanisms of apoptosis and several strategies that have been probed to ameliorate, or to prevent apoptosis in the diabetic kidney.

NAD+/NADH and NADP+/NADPH in cellular functions and cell death: regulation and biological consequences

Accumulating evidence has suggested that NAD (including NAD+ and NADH) and NADP (including NADP+ and NADPH) could belong to the fundamental common mediators of various biological processes, including energy metabolism, mitochondrial functions, calcium homeostasis, antioxidation/generation of oxidative stress, gene expression, immunological functions, aging, and cell death: First, it is established that NAD mediates energy metabolism and mitochondrial functions; second, NADPH is a key component in cellular antioxidation systems; and NADH-dependent reactive oxygen species (ROS) generation from mitochondria and NADPH oxidase-dependent ROS generation are two critical mechanisms of ROS generation; third, cyclic ADP-ribose and several other molecules that are generated from NAD and NADP could mediate calcium homeostasis; fourth, NAD and NADP modulate multiple key factors in cell death, such as mitochondrial permeability transition, energy state, poly(ADP-ribose) polymerase-1, and apoptosis-inducing factor; and fifth, NAD and NADP profoundly affect aging-influencing factors such as oxidative stress and mitochondrial activities, and NAD-dependent sirtuins also mediate the aging process. Moreover, many recent studies have suggested novel paradigms of NAD and NADP metabolism. Future investigation into the metabolism and biological functions of NAD and NADP may expose fundamental properties of life, and suggest new strategies for treating diseases and slowing the aging process.

Reactive oxygen species in mitochondria-mediated cell death

In addition to the well-established role of the mitochondria in energy metabolism, regulation of cell death has recently emerged as a second major function of these organelles. This, in turn, seems to be intimately linked to their role as the major intracellular source of reactive oxygen species (ROS) which are mainly, generated at Complex I and III of the respiratory chain. Excessive ROS production can lead to oxidation of macromolecules and has been implicated in mtDNA mutations, ageing, and cell death. Although mitochondrial dysfunction can cause ATP depletion and necrosis, these organelles are also involved in the regulation of apoptotic cell death by mechanisms, which have been conserved through evolution. Thus, many lethal agents target the mitochondria and cause release of cytochrome c and other pro-apoptotic proteins, which can trigger caspase activation and apoptosis. Taken together, these findings have placed the mitochondria in the focus of current cell death research.

Mitochondrial oxidative stress: implications for cell death

In addition to the established role of the mitochondria in energy metabolism, regulation of cell death has emerged as a second major function of these organelles. This seems to be intimately linked to their generation of reactive oxygen species (ROS), which have been implicated in mtDNA mutations, aging, and cell death. Mitochondrial regulation of apoptosis occurs by mechanisms, which have been conserved through evolution. Thus, many lethal agents target the mitochondria and cause release of cytochrome c and other pro-apoptotic proteins into the cytoplasm. Cytochrome c release is initiated by the dissociation of the hemoprotein from its binding to the inner mitochondrial membrane. Oxidation of cardiolipin reduces cytochrome c binding and increases the level of soluble cytochrome c in the intermembrane space. Subsequent release of the hemoprotein occurs by pore formation mediated by pro-apoptotic Bcl-2 family proteins, or by Ca(2+) and ROS-triggered mitochondrial permeability transition, although the latter pathway might be more closely associated with necrosis. Taken together, these findings have placed the mitochondria in the focus of current cell death research.

Mitochondrial isocitrate dehydrogenase protects human neuroblastoma SH-SY5Y cells against oxidative stress

The neuroprotective effect of mitochondrial isocitrate dehydrogenase (IDPm), an enzyme involved in the reduction of NADP(+) to NADPH and the supply of glutathione (GSH) in mitochondria, was examined using SH-SY5Y cells overexpressing IDPm (S1). S1 cells showed higher NADPH and GSH levels than vector transfectant (V) cells and were more resistant to staurosporine-induced cell death than controls. Staurosporine-induced cytochrome c release, caspase-3 activation, and production of reactive oxygen species (ROS) were significantly attenuated in S1 cells as compared to V cells and reduced by antioxidants, trolox and GSH-ethyl ester (GSH-EE). Staurosporine-induced the release of Mcl-1 from mitochondria that formed a complex with Bim. Mcl-1 was then cleaved to a shortened form in a caspase-3 dependent manner; its release was attenuated far more in S1 than in V cells after staurosporine treatment. Finally, the staurosporine-induced decrease in mitochondrial membrane potential (Deltapsi(m)) was correlated with the time of mitochondrial Mcl-1 release; the loss of Deltapsi(m) was attenuated significantly in S1 cells as compared to that in V cells. These results suggest that the neuroprotective effect of IDPm may result from increases in NADPH and GSH levels in the mitochondria. This, in turn, inhibits mitochondrial ROS production after cytochrome c release, which seems to be mediated through Mcl-1 release.

Cytosolic NADP-isocitrate dehydrogenase of pea plants: genomic clone characterization and functional analysis under abiotic stress conditions

NADPH is an essential electron donor in numerous biosynthetic and detoxification reactions. In animal, yeast and bacteria, the NADP-dependent isocitrate dehydrogenase (NADP-ICDH), which catalyzes the production of NADPH, is being recognized as an essential component of the antioxidative defence mechanisms. In plant cells, there is little information on the antioxidant properties of NADP-ICDH. Using a pea cDNA lambdagt11 library, the full-length cDNA of a NADP-ICDH was obtained. In pea leaves, the analyses of activity, protein and transcript expression of NADP-ICDH under six different abiotic stress conditions (CL, continuous light, HLI, high light intensity, D, continuous dark, LT, low-temperature HT, high-temperature and W, mechanical wounding) revealed a differential regulation at transcriptional and post-translational level depending on the abiotic stress. The activity and protein expression of NADP-ICDH and catalase increased only under HLI but the NADP-ICDH transcripts were up-regulated by cold stress (70%) and W (40%). Under the same conditions, the transcript analysis of glutathione reductase (GR), monodehydroascorbate reductase (MDAR) and ascorbate peroxidase (APX), key components of the antioxidative ascorbate-glutathione cycle, showed similar inductions. These data indicate that in pea plants the cytosolic NADP-ICDH shows a differential response, at mRNA and activity level, depending on the type of abiotic stress and suggests that this dehydrogenase could have a protective antioxidant role against certain environmental stresses in plants.

Implication du glutamate, de l'isocitrate et de la malate déshydrogénases dans l'assimilation de l'azote chez la tomate stressée par le cadmium

Tomato seedlings grown on nitric medium and treated with various cadmium concentrations (0 to 50 microM) were used. Results obtained show that cadmium remains predominantly located in the roots, which then seem to play the role of trap-organs. Increasing cadmium concentration in the medium leads particularly to a decrease in NO3- accumulation, together with a decrease in the activity of glutamine synthetase and in the quantity of plastidic isoform ARNm (GS2), and, on the contrary, to an increase of the cytosolic isoform ARNm (GS1). On the other hand, stimulations were observed for NADH-dependent glutamate synthase, NADH-dependent glutamate dehydrogenase, ARNm quantity of this enzyme, ammonium accumulation, and protease activity. In parallel, stimulations were observed for NAD+ and NADP+-dependent malate dehydrogenase and NADP+-dependent isocitrate dehydrogenase. These results were discussed in relation to the hypothesis attributing to the dehydrogenase enzymes (GDH, MDH, ICDH) an important role in the plant defence processes against cadmium-induced stresses.

The effect of alpha-phenyl-N-t-butylnitrone on ionizing radiation-induced apoptosis in U937 cells

Ionizing radiation induces the production of reactive oxygen species (ROS), which play an important causative role in apoptotic cell death. alpha-Phenyl-N-t-butylnitrone (PBN) is one of the most widely used spin-trapping compounds for investigating the existence of free radicals in biological systems. We investigated the effects of PBN on ionizing radiation-induced apoptosis in U937 cells. Upon exposure to 2 Gy of gamma-irradiation, there was a distinct difference between the control cells and the cells pre-treated with 2 mM PBN for 2 h in regard to apoptotic parameters, cellular redox status, mitochondria function and oxidative damage to cells. PBN effectively suppressed morphological evidence of apoptosis and DNA fragmentation in U937 cells exposed to ionizing radiation. The [GSSG]/[GSH+GSSG] ratio and the generation of intracellular ROS were higher and the [NADPH]/[NADP+ +NADPH] ratio was lower in control cells compared to PBN-treated cells. The ionizing radiation-induced mitochondrial damage reflected by the altered mitochondrial permeability transition, the increase in the accumulation of ROS, and the reduction of ATP production were significantly higher in control cells compared to PBN-treated cells. PBN pre-treated cells showed significant inhibition of apoptotic features such as activation of caspase-3, up-regulation of Bax and p53, and down-regulation of Bcl-2 compared to control cells upon exposure to ionizing radiation. This study indicates that PBN may play an important role in regulating the apoptosis induced by ionizing radiation presumably through scavenging of ROS.

Detection and purification of glucose 6-phosphate dehydrogenase, malic enzyme, and NADP-dependent isocitrate dehydrogenase by blue native polyacrylamide gel electrophoresis

We describe a blue native polyacrylamide gel electrophoretic technique that allows the facile detection, quantitation and purification of three NADPH-producing enzymes. Glucose 6-phosphate dehydrogenase, malic enzyme and NADP-dependent isocitrate dehydrogenase were detected simultaneously. Activity staining based on the formation of NADPH from the respective substrates and the subsequent precipitation of formazan enabled the relative quantitation of enzymatic activities, while Coomassie staining on one-dimensional or two-dimensional gels helped monitor the amount of protein associated with these enzymatic activities. This technique provides a simple and effective route to obtain homogeneous protein for further analyses and also enables the screening of these NADPH-producing enzymes in various cellular systems.