Inactivation of NADP(+)-dependent isocitrate dehydrogenase by reactive oxygen species

Thiram exposure in environment: A critical review on cytotoxicity

Thiram is used in large quantities in agriculture and may contaminate the environment by improper handling or storage in chemical plants and warehouses. A review of the literature has shown that thiram can affect different organs in animals and its toxic mechanisms can be elucidated in more detail at molecular level. We have summarized several impacts of thiram on animals: the effects of the perspectives of oxidative stress, mitochondrial damage, autophagy, apoptosis, and the IHH/PTHrP pathway on regulating abnormal skeletal development in particular tibial dyschondroplasia and kyphosis; angiogenesis inhibition was investigated from the perspective of angiogenesis factor inhibition, PI3K/AKT signaling pathway and CD147; the inhibition effect of thiram on fibroblasts and erythrocytes via the perspective of oxidative stress, mitochondrial damage and inhibition of growth factors in animal skin fibroblasts and erythrocytes; studied fertilized egg size, reduced fertility, neurodegeneration, and immune damage from the perspectives of CYP51 inhibition and dopamine-b-hydroxylase inhibition in the reproductive system, vitamin D deficiency in the nervous system, and inflammatory damage in the immune system; embryonic dysplasia in terms of thyroid hormone repression in animal embryonic development and repression of the SOX9a transcription factor. The elucidation of the mechanisms of toxicity of thiram on various organs of animals at molecular level will enable a more detailed understanding of the mechanisms of toxicity of thiram in animals and will facilitate the exploration of the treatment of thiram poisoning at molecular level.

Oral administration of thiram inhibits brush border membrane enzymes, oxidizes proteins and thiols, impairs redox system and causes histological changes in rat intestine: A dose dependent study

Pesticides are extensively employed worldwide, especially in agriculture to control weeds, insect infestation and diseases. Besides their targets, pesticides can also affect the health of non-target organisms, including humans The present study was conducted to study the effect of oral exposure of thiram, a dithiocarbamate fungicide, on the intestine of rats. Male rats were administered thiram at doses of 100, 250, 500 and 750 mg/kg body weight for 4 days. This treatment reduced cellular glutathione, total sulfhydryl groups but enhanced protein carbonyl content and hydrogen peroxide levels. In addition, the activities of all major antioxidant enzymes (catalase, thioredoxin reductase, glutathione peroxidase and glutathione-S-transferase) except superoxide dismutase were decreased. The antioxidant power of the intestine was impaired lowering the metal-reducing and free radical quenching ability. Administration of thiram also led to inhibition of intestinal brush border membrane enzymes, alkaline phosphatase, γ-glutamyl transferase, leucine aminopeptidase and sucrase. Activities of enzymes of pentose phosphate pathway, citric acid cycle, glycolysis and gluconeogenesis were also inhibited. Histopathology showed extensive damage in the intestine of thiram-treated rats at higher doses. All the observed effects were in a thiram dose-dependent manner. The results of this study show that thiram causes significant oxidative damage in the rat intestine which is associated with the marked impairment in the antioxidant defense system.

Safety and Efficacy Assessments to Take Antioxidants in Glioblastoma Therapy: From In Vitro Experiences to Animal and Clinical Studies

Glioblastoma (GBM) is considered one of the most common malignant brain tumors, occurring as over 15% of all primary central nervous system and brain neoplasms. The unique and standard treatment option towards GBM involves the combination of surgical resection followed by radiotherapy (RT) and chemotherapy (CT). However, due to the aggressive nature and heterogeneity of GBMs, they remained difficult to treat. Recent findings from preclinical studies have revealed that disruption of the redox balance via using either oxidative or anti-oxidative agents in GBM presented an effective and promising therapeutic approach. A limited number of clinical trials substantially encouraged their concomitant use with RT or CT. Thus, treatment of GBMs may benefit from natural or synthetic antioxidative compounds as novel therapeutics. Despite the presence of variegated in vitro and in vivo studies focusing on safety and efficacy issues of these promising therapeutics, nowadays their translation to clinics is far from applicability due to several challenges. In this review, we briefly introduce the enzymatic and non-enzymatic antioxidant defense systems as well as potential signaling pathways related to the pathogenesis of GBM with a special interest in antioxidant mechanisms. In addition, we describe the advantages and limitations of antioxidant supplementation in GBM cases or disease models as well as growing challenges for GBM therapies with antioxidants in the future.

Impact of ROS-Induced Damage of TCA Cycle Enzymes on Metabolism and Virulence of Salmonella enterica serovar Typhimurium

Salmonella enterica serovar Typhimurium (STM) is exposed to reactive oxygen species (ROS) originating from aerobic respiration, antibiotic treatment, and the oxidative burst occurring inside the Salmonella-containing vacuole (SCV) within host cells. ROS damage cellular compounds, thereby impairing bacterial viability and inducing cell death. Proteins containing iron–sulfur (Fe–S) clusters are particularly sensitive and become non-functional upon oxidation. Comprising five enzymes with Fe–S clusters, the TCA cycle is a pathway most sensitive toward ROS. To test the impact of ROS-mediated metabolic perturbations on bacterial physiology, we analyzed the proteomic and metabolic profile of STM deficient in both cytosolic superoxide dismutases (ΔsodAB). Incapable of detoxifying superoxide anions (SOA), endogenously generated SOA accumulate during growth. ΔsodAB showed reduced abundance of aconitases, leading to a metabolic profile similar to that of an aconitase-deficient strain (ΔacnAB). Furthermore, we determined a decreased expression of acnA in STM ΔsodAB. While intracellular proliferation in RAW264.7 macrophages and survival of methyl viologen treatment were not reduced for STM ΔacnAB, proteomic profiling revealed enhanced stress response. We conclude that ROS-mediated reduced expression and damage of aconitase does not impair bacterial viability or virulence, but might increase ROS amounts in STM, which reinforces the bactericidal effects of antibiotic treatment and immune responses of the host.

Cancer cells change their glucose metabolism to overcome increased ROS: One step from cancer cell to cancer stem cell?

Cancer cells can adapt to low energy sources in the face of ATP depletion as well as to their high levels of ROS by altering their metabolism and energy production networks which might also have a role in determining cell fate and developing drug resistance. Cancer cells are generally characterized by increased glycolysis. This is while; cancer stem cells (CSCs) exhibit an enhanced pentose phosphate pathway (PPP) metabolism. Based on the current literature, we suggest that cancer cells when encountering ROS, first increase the glycolysis rate and then following the continuation of oxidative stress, the metabolic balance is skewed from glycolysis to PPP. Therefore, we hypothesize in this review that in cancer cells this metabolic deviation during persistent oxidative stress might be a sign of cancer cells' shift towards CSCs, an issue that might be pivotal in more effective targeting of cancer cells and CSCs.

A metabolomics strategy to assess the combined toxicity of polycyclic aromatic hydrocarbons (PAHs) and short-chain chlorinated paraffins (SCCPs)

The combined toxicity of mixed chemicals is usually evaluated according to several specific endpoints, and other potentially toxic effects are disregarded. In this study, we provided a metabolomics strategy to achieve a comprehensive understanding of toxicological interactions between mixed chemicals on metabolism. The metabolic changes were quantified by a pseudotargeted analysis, and the types of combined effects were quantitatively discriminated according to the calculation of metabolic effect level index (MELI). The metabolomics strategy was used to assess the combined effects of polycyclic aromatic hydrocarbons (PAHs) and short-chain chlorinated paraffins (SCCPs) on the metabolism of human hepatoma HepG2 cells. Our data suggested that exposure to a combination of PAHs and SCCPs at human internal exposure levels could result in an additive effect on the overall metabolism, whereas diverse joint effects were observed on various metabolic pathways. The combined exposure could induce a synergistic up-regulation of phospholipid metabolism, an additive up-regulation of fatty acid metabolism, an additive down-regulation of tricarboxylic acid cycle and glycolysis, and an antagonistic effect on purine metabolism. SCCPs in the mixture acted as the primary driver for the acceleration of phospholipid and fatty acid metabolism. Lipid metabolism disorder caused by exposure to a combination of PAHs and SCCPs should be an important concern for human health.

Hydrogen Peroxide Is Involved in β-Cyclodextrin-hemin Complex-Induced Lateral Root Formation in Tomato Seedlings

Although previous results showed that β-cyclodextrin-hemin complex (β-CDH) could induce tomato lateral root (LR) formation, the corresponding downstream messengers are still not fully understood. In this report, similar to the inducing effects of exogenously applied hydrogen peroxide (H₂O₂), we discovered that β-CDH elicited RBOH1 transcript upregulation, endogenous H₂O₂ accumulation, and thereafter tomato LR development. Above responses were sensitive to dimethylthiourea (DMTU) and ascorbic acid (AsA), two membrane-permeable scavengers of H₂O₂, showing that accumulation of H₂O₂ and LR formation were significantly blocked. The test with diphenyleneiodonium (DPI; the inhibitor of NADPH oxidase) revealed that H₂O₂ mainly produced by NADPH oxidase, might be involved in LR formation triggered by β-CDH. qPCR combined with pharmacological and anatomical analyses showed that β-CDH-modulated several marker genes responsible for LR formation, such as CYCA3;1, CYCA2;1, CYCD3;1, and CDKA1 (four cell cycle regulatory genes), ARF7 and RSI-1 (two auxin signaling genes), LAX3 (an auxin influx carrier), IAA14 (encoding a member of the Aux/IAA protein family), PIN3 and PIN7 (two auxin efflux carriers), isocitrate dehydrogenase [NADP], NADH-cytochrome b₅ reductase 1, and L-ascorbate oxidase homolog genes (two reactive oxygen species-associated genes and one LR formation-related gene), were causally related to above H₂O₂ signaling. Particularly, representative proteins related to H₂O₂ metabolism and lateral rooting, were specifically induced in β-CDH-treated tomato seedlings. Overall, the results clearly suggested a vital role of H₂O₂ in the β-CDH-induced tomato LR formation, and β-CDH-elicited H₂O₂-related target proteins responsible for LR formation might be, at least partially, regulated at transcriptional and translational levels.

IDH2 knockdown sensitizes tumor cells to emodin cytotoxicity in vitro and in vivo

Although reactive oxygen species (ROS) work as second messengers at sublethal concentrations, higher levels of ROS can kill cancer cells. Since cellular ROS levels are determined by a balance between ROS generation and removal, the combination of ROS generators, and the depletion of reducing substances greatly enhance ROS levels. Emodin (1,3,8-trihydroxy-6-methyl anthraquinone), a natural anthraquinone derivative from the root and rhizome of numerous plants, is a ROS generator that induces apoptosis in cancer cells. The major enzyme to generate mitochondrial NADPH is the mitochondrial isoenzyme of NADP⁺-dependent isocitrate dehydrogenase (IDH2). In this report, we demonstrate that IDH2 knockdown effectively enhances emodin-induced apoptosis of mouse melanoma B16F10 cells through the regulation of ROS generation. Our findings suggest that suppression of IDH2 activity results in perturbation of the cellular redox balance and, ultimately, exacerbate emodin-induced apoptotic cell death in B16F10 cells. Our results strongly support a therapeutic strategy in the management of cancer that alters the intracellular redox status by the combination of a ROS generator and the suppression of antioxidant enzyme activity.

Redox-implications associated with the formation of complexes between copper ions and reduced or oxidized glutathione

Binding of copper by reduced glutathione (GSH) is generally seen as a mechanism to lower, if not abolish, the otherwise high electrophilicity and redox activity of its free ions. In recent years, however, this concept has been contradicted by new evidence revealing that, rather than stabilizing free copper ions, its binding to GSH leads to the formation of a Cu(I)-[GSH]2 complex capable of reducing molecular oxygen into superoxide. It is now understood that, under conditions leading to the removal of such radicals, the Cu(I)-[GSH]2 complex is readily oxidized into Cu(II)-GSSG. Interestingly, in the presence of a GSH excess, the latter complex is able to regenerate the superoxide-generating capacity of the complex it originated from, opening the possibility that a GSH-dependent interplay exists between the reduced and the oxidized glutathione forms of these copper-complexes. Furthermore, recent evidence obtained from experiments conducted in non-cellular systems and intact mitochondria indicates that the Cu(II)-GSSG complex is also able to function in a catalytic manner as an efficient superoxide dismutating- and catalase-like molecule. Here we review and discuss the most relevant chemical and biological evidence on the formation of the Cu(I)-[GSH]2 and Cu(II)-GSSG complexes and on the potential redox implications associated with their intracellular occurrence.

Drug-repositioning screening identified piperlongumine as a direct STAT3 inhibitor with potent activity against breast cancer

Signal transducer and activator of transcription (STAT) 3 regulates many cardinal features of cancer including cancer cell growth, apoptosis resistance, DNA damage response, metastasis, immune escape, tumor angiogenesis, the Warburg effect and oncogene addiction and has been validated as a drug target for cancer therapy. Several strategies have been used to identify agents that target Stat3 in breast cancer but none has yet entered into clinical use. We used a high-throughput fluorescence microscopy search strategy to identify compounds in a drug-repositioning library (Prestwick library) that block ligand-induced nuclear translocation of Stat3 and identified piperlongumine (PL), a natural product isolated from the fruit of the pepper Piper longum. PL inhibited Stat3 nuclear translocation, inhibited ligand-induced and constitutive Stat3 phosphorylation, and modulated expression of multiple Stat3-regulated genes. Surface plasmon resonance assay revealed that PL directly inhibited binding of Stat3 to its phosphotyrosyl peptide ligand. Phosphoprotein antibody array analysis revealed that PL does not modulate kinases known to activate Stat3 such as Janus kinases, Src kinase family members or receptor tyrosine kinases. PL inhibited anchorage-independent and anchorage-dependent growth of multiple breast cancer cell lines having increased pStat3 or total Stat3, and induced apoptosis. PL also inhibited mammosphere formation by tumor cells from patient-derived xenografts. PL's antitumorigenic function was causally linked to its Stat3-inhibitory effect. PL was non-toxic in mice up to a dose of 30 mg/kg/day for 14 days and caused regression of breast cancer cell line xenografts in nude mice. Thus, PL represents a promising new agent for rapid entry into the clinic for use in treating breast cancer, as well as other cancers in which Stat3 has a role.

Caspase-2 maintains bone homeostasis by inducing apoptosis of oxidatively-damaged osteoclasts

Osteoporosis is a silent disease, characterized by a porous bone micro-structure that enhances risk for fractures and associated disabilities. Senile, or age-related osteoporosis (SO), affects both men and women, resulting in increased morbidity and mortality. However, cellular and molecular mechanisms underlying senile osteoporosis are not fully known. Recent studies implicate the accumulation of reactive oxygen species (ROS) and increased oxidative stress as key factors in SO. Herein, we show that loss of caspase-2, a cysteine aspartate protease involved in oxidative stress-induced apoptosis, results in total body and femoral bone loss in aged mice (20% decrease in bone mineral density), and an increase in bone fragility (30% decrease in fracture strength). Importantly, we demonstrate that genetic ablation or selective inhibition of caspase-2 using zVDVAD-fmk results in increased numbers of bone-resorbing osteoclasts and enhanced tartrate-resistant acid phosphatase (TRAP) activity. Conversely, transfection of osteoclast precursors with wild type caspase-2 but not an enzymatic mutant, results in a decrease in TRAP activity. We demonstrate that caspase-2 expression is induced in osteoclasts treated with oxidants such as hydrogen peroxide and that loss of caspase-2 enhances resistance to oxidants, as measured by TRAP activity, and decreases oxidative stress-induced apoptosis of osteoclasts. Moreover, oxidative stress, quantified by assessment of the lipid peroxidation marker, 4-HNE, is increased in Casp2^-/- bone, perhaps due to a decrease in antioxidant enzymes such as SOD2. Taken together, our data point to a critical and novel role for caspase-2 in maintaining bone homeostasis by modulating ROS levels and osteoclast apoptosis during conditions of enhanced oxidative stress that occur during aging.

α -Ketoglutarate accumulation is not dependent on isocitrate dehydrogenase activity during tellurite detoxification in Escherichia coli

Tellurite is toxic to most microorganisms because of its ability to generate oxidative stress. However, the way in which tellurite interferes with cellular processes is not fully understood to date. In this line, it was previously shown that tellurite-exposed cells displayed reduced activity of the α-ketoglutarate dehydrogenase complex (α-KGDH), which resulted in α-ketoglutarate (α-KG) accumulation. In this work, we assessed if α-KG accumulation in tellurite-exposed E. coli could also result from increased isocitrate dehydrogenase (ICDH) and glutamate dehydrogenase (GDH) activities, both enzymes involved in α-KG synthesis. Unexpectedly both activities were found to decrease in the presence of the toxicant, an observation that seems to result from the decreased transcription of icdA and gdhA genes (encoding ICDH and GDH, resp.). Accordingly, isocitrate levels were found to increase in tellurite-exposed E. coli. In the presence of the toxicant, cells lacking icdA or gdhA exhibited decreased reactive oxygen species (ROS) levels and higher tellurite sensitivity as compared to the wild type strain. Finally, a novel branch activity of ICDH as tellurite reductase is presented.

Tissue-specific changes in fatty acid oxidation in hypoxic heart and skeletal muscle

Exposure to hypobaric hypoxia is sufficient to decrease cardiac PCr/ATP and alters skeletal muscle energetics in humans. Cellular mechanisms underlying the different metabolic responses of these tissues and the time-dependent nature of these changes are currently unknown, but altered substrate utilization and mitochondrial function may be a contributory factor. We therefore sought to investigate the effects of acute (1 day) and more sustained (7 days) hypoxia (13% O₂) on the transcription factor peroxisome proliferator-activated receptor α (PPARα) and its targets in mouse cardiac and skeletal muscle. In the heart, PPARα expression was 40% higher than in normoxia after 1 and 7 days of hypoxia. Activities of carnitine palmitoyltransferase (CPT) I and β-hydroxyacyl-CoA dehydrogenase (HOAD) were 75% and 35% lower, respectively, after 1 day of hypoxia, returning to normoxic levels after 7 days. Oxidative phosphorylation respiration rates using palmitoyl-carnitine followed a similar pattern, while respiration using pyruvate decreased. In skeletal muscle, PPARα expression and CPT I activity were 20% and 65% lower, respectively, after 1 day of hypoxia, remaining at this level after 7 days with no change in HOAD activity. Oxidative phosphorylation respiration rates using palmitoyl-carnitine were lower in skeletal muscle throughout hypoxia, while respiration using pyruvate remained unchanged. The rate of CO₂ production from palmitate oxidation was significantly lower in both tissues throughout hypoxia. Thus cardiac muscle may remain reliant on fatty acids during sustained hypoxia, while skeletal muscle decreases fatty acid oxidation and maintains pyruvate oxidation.

What do we know about IDH1/2 mutations so far, and how do we use it?

Whole genome analyses have facilitated the discovery of clinically relevant genetic alterations in a variety of diseases, most notably cancer. A prominent example of this was the discovery of mutations in isocitrate dehydrogenases 1 and 2 (IDH1/2) in a sizeable proportion of gliomas and some other neoplasms. Herein the normal functions of these enzymes, how the mutations alter their catalytic properties, the effects of their D-2-hydroxyglutarate metabolite, technical considerations in diagnostic neuropathology, implications about prognosis and therapeutic considerations, and practical applications and controversies regarding IDH1/2 mutation testing are discussed.

Impaired TCA cycle flux in mitochondria in skeletal muscle from type 2 diabetic subjects: marker or maker of the diabetic phenotype?

The diabetic phenotype is complex, requiring elucidation of key initiating defects. Recent research has shown that diabetic myotubes express a primary reduced tricarboxylic acid (TCA) cycle flux. A reduced TCA cycle flux has also been shown both in insulin resistant offspring of T2D patients and exercising T2D patients in vivo. This review will discuss the latest advances in the understanding of the molecular mechanisms regulating the TCA cycle with focus on possible underlying mechanism which could explain the impaired TCA flux in insulin resistant human skeletal muscle in type 2 diabetes. A reduced TCA is both a marker and a maker of the diabetic phenotype.

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.

Cultured senescent myoblasts derived from human vastus lateralis exhibit normal mitochondrial ATP synthesis capacities with correlating concomitant ROS production while whole cell ATP production is decreased

The free radical theory of aging says that increased oxidative stress and mitochondrial dysfunction are associated with old age. In the present study we have investigated the effects of cellular senescence on muscle energetic by comparing mitochondrial content and function in cultured muscle satellite cells at early and late passage numbers. We show that cultured muscle satellite cells undergoing senescence express a reduced mitochondrial mass, decreased whole cell ATP level, normal to increased mitochondrial ATP production under ATP utilization, increased mitochondrial membrane potential and increased superoxide/mitochondrial mass and hydrogen peroxide/mitochondrial mass ratios. Moreover, the increased ROS production correlates with the corresponding mitochondrial ATP production. Thus, myotubes differentiated from human myoblasts undergoing senescence have a reduced mitochondrial content, but the existent mitochondria express normal to increased functional capabilities. The present data suggest that the origin of aging lies outside the mitochondria and that a malfunction in the cell might be preceding and initiating the increase of mitochondrial ATP synthesis and concomitant ROS production in the single mitochondrion in response to decreased mitochondrial mass and reduced extra-mitochondrial energy supply. This then can lead to the increased damage of DNA, lipids and proteins of the mitochondria as postulated by the free radical theory of aging.

Knockdown of cytosolic NADP(+) -dependent isocitrate dehydrogenase enhances MPP(+) -induced oxidative injury in PC12 cells

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and its toxic metabolite 1-methyl-4-phenylpyridium ion (MPP(+)) have been shown to induce Parkinson's disease-like symptoms as well as neurotoxicity in humans and animal species. Recently, we reported that maintenance of redox balance and cellular defense against oxidative damage are primary functions of the novel antioxidant enzyme cytosolic NADP(+) -dependent isocitrate dehydrogenase (IDPc). In this study, we examined the role of IDPc in cellular defense against MPP(+) -induced oxidative injury using PC12 cells transfected with IDPc small interfering RNA (siRNA). Our results demonstrate that MPP(+) -mediated disruption of cellular redox status, oxidative damage to cells, and apoptotic cell death were significantly enhanced by knockdown of IDPc.

Photo-oxidation of proteins

Photo-induced damage to proteins occurs via multiple pathways. Direct damage induced by UVB (λ 280-320 nm) and UVA radiation (λ 320-400 nm) is limited to a small number of amino acid residues, principally tryptophan (Trp), tyrosine (Tyr), histidine (His) and disulfide (cystine) residues, with this occurring via both excited state species and radicals. Indirect protein damage can occur via singlet oxygen ((1)O(2)(1)Δ(g)), with this resulting in damage to Trp, Tyr, His, cystine, cysteine (Cys) and methionine (Met) residues. Although initial damage is limited to these residues multiple secondary processes, that occur both during and after radiation exposure, can result in damage to other intra- and inter-molecular sites. Secondary damage can arise via radicals (e.g. Trp, Tyr and Cys radicals), from reactive intermediates generated by (1)O(2) (e.g. Trp, Tyr and His peroxides) and via molecular reactions of photo-products (e.g. reactive carbonyls). These processes can result in protein fragmentation, aggregation, altered physical and chemical properties (e.g. hydrophobicity and charge) and modulated biological turnover. Accumulating evidence implicates these events in cellular and tissue dysfunction (e.g. apoptosis, necrosis and altered cell signaling), and multiple human pathologies.

Enzymatic characterization of isocitrate dehydrogenase from an emerging zoonotic pathogen Streptococcus suis

Streptococcus suis, a Gram-positive coccus, is an emerging zoonotic pathogen for both humans and pigs, but little is known about the properties of its metabolic enzymes. Isocitrate dehydrogenase (IDH) is a key regulatory enzyme in the citric acid cycle that catalyzes the oxidative decarboxylation of isocitrate yielding α-ketoglutarate and NAD(P)H. Here, we report the overexpression and enzymatic characterization of IDH from S. suis Serotype 2 Chinese highly virulent strain 05ZYH33 (SsIDH). The molecular weight of SsIDH was estimated to be 74 kDa by gel filtration chromatography, suggesting a homodimeric structure. Additionally, SsIDH was divalent cation-dependent and Mg(2+) was found to be the most effective cation. The optimal pH of SsIDH was 7.0 (Mn(2+)) and 8.5 (Mg(2+)), and the maximum activity was around 30 °C (Mn(2+)) and 50 °C (Mg(2+)), respectively. Heat inactivation studies showed that SsIDH retained 50% activity after 20 min of incubation at 49 °C. Sequence comparison revealed that SsIDH had a significantly homologous identity to bacterial homodimeric IDHs. The recombinant SsIDH displayed a 117-fold (k(cat)/K(m)) preference for NAD(+) over NADP(+) with Mg(2+), and a 80-fold greater specificity for NAD(+) than NADP(+) with Mn(2+). Therefore, SsIDH has remarkably high coenzyme preference toward NAD(+). This current work is expected to shed light on the functions of metabolic enzymes in S. suis and provide useful information for SsIDH to be considered as a possible candidate for serological diagnostics and detection of S. suis infection.

The role of feeding regimens in regulating metabolism of sexually mature broiler breeders

A trial was conducted to determine the effects of different rearing feed regimens on plasma hormone and metabolite levels and hepatic lipid metabolism and gene expression on sexually mature broiler breeders. Cobb 500 birds were divided into 2 groups at 4 wk and fed either an everyday (ED) or skip-a-day (SKP) regimen. At 24 wk of age, all birds were switched over to an ED regimen. At 26.4 wk, breeder hens were randomly selected and killed at intervals after feeding. Livers were sampled from 4 hens at 4-h intervals for 24 h for a total of 28 samples per treatment. Blood was sampled from 4 hens per sampling time; sampling times were 0, 30, and 60 min and 2 and 4 h after feeding and then every 4 h up to 24 h for a total of 36 samples per treatment. Main feeding regimen, time, and interaction effects were analyzed. Significant interaction effects were found between time and feeding regimen for acetyl-coenzyme A carboxylase and malic enzyme mRNA expression. The peak for acetyl-coenzyme A carboxylase expression was higher in ED-reared birds, whereas the peak for malic enzyme expression was higher in SKP-reared birds. Overall, plasma levels of insulin-like growth factor-II were higher in SKP-reared birds. Overall, plasma corticosterone levels were also higher in SKP-reared birds and significant interaction effects between time and feeding regimen were seen. The expression of apolipoprotein A1 was significantly higher in ED-reared birds: significant interaction effects were also noted. Other researchers also found some of the differences observed in the present study in 16-wk-old pullets. In summary, different feeding regimens alter metabolic responses, some of which carry over into sexual maturity.

Enhanced expression of mitochondrial superoxide dismutase leads to prolonged in vivo cell cycle progression and up-regulation of mitochondrial thioredoxin

Mn superoxide dismutase (MnSOD) is an important mitochondrial antioxidant enzyme, and elevated MnSOD levels have been shown to reduce tumor growth in part by suppressing cell proliferation. Studies with fibroblasts have shown that increased MnSOD expression prolongs cell cycle transition time in G1/S and favors entrance into the quiescent state. To determine if the same effect occurs during tissue regeneration in vivo, we used a transgenic mouse system with liver-specific MnSOD expression and a partial hepatectomy paradigm to induce synchronized in vivo cell proliferation during liver regeneration. We show in this experimental system that a 2.6-fold increase in MnSOD activity leads to delayed entry into S phase, as measured by reduction in bromodeoxyuridine (BrdU) incorporation and decreased expression of proliferative cell nuclear antigen (PCNA). Thus, compared to control mice with baseline MnSOD levels, transgenic mice with increased MnSOD expression in the liver have 23% fewer BrdU-positive cells and a marked attenuation of PCNA expression. The increase in MnSOD activity also leads to an increase in the mitochondrial form of thioredoxin (thioredoxin 2), but not in several other peroxidases examined, suggesting the importance of thioredoxin 2 in maintaining redox balance in mitochondria with elevated levels of MnSOD.

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.

Cytosolic NADP(+)-dependent isocitrate dehydrogenase regulates cadmium-induced apoptosis

Cadmium ions have a high affinity for thiol groups. Therefore, they may disturb many cellular functions. We recently reported that cytosolic NADP(+)-dependent isocitrate dehydrogenase (IDPc) functions as an antioxidant enzyme to supply NADPH, a major source of reducing equivalents to the cytosol. Cadmium decreased the activity of IDPc both as a purified enzyme and in cultured cells. In the present study, we demonstrate that the knockdown of IDPc expression in HEK293 cells greatly enhances apoptosis induced by cadmium. Transfection of HEK293 cells with an IDPc small interfering RNA significantly decreased the activity of IDPc and enhanced cellular susceptibility to cadmium-induced apoptosis as indicated by the morphological evidence of apoptosis, DNA fragmentation and condensation, cellular redox status, mitochondria redox status and function, and the modulation of apoptotic marker proteins. Taken together, our results suggest that suppressing the expression of IDPc enhances cadmium-induced apoptosis of HEK293 cells by increasing disruption of the cellular redox status.

Glutathionylation regulates cytosolic NADP+-dependent isocitrate dehydrogenase activity

Cytosolic NADP+-dependent isocitrate dehydrogenase (IDPc) is susceptible to inactivation by numerous thiol-modifying reagents. This study now reports that Cys269 of IDPc is a target for S-glutathionylation and that this modification is reversed by dithiothreitol as well as enzymatically by cytosolic glutaredoxin in the presence of GSH. Glutathionylated IDPc was significantly less susceptible than native protein to peptide fragmentation by reactive oxygen species and proteolytic digestion. Glutathionylation may play a protective role in the degradation of protein through the structural alterations of IDPc. HEK293 cells treated with diamide displayed decreased IDPc activity and accumulated glutathionylated enzyme. Using immunoprecipitation with an anti-IDPc IgG and immunoblotting with an anti-GSH IgG, we purified and positively identified glutathionylated IDPc from the kidneys of mice subjected to ischemia/reperfusion injury and from the livers of ethanol-administered rats. These results suggest that IDPc activity is modulated through enzymatic glutathionylation and deglutathionylation during oxidative stress.

An SOD mimic protects NADP+-dependent isocitrate dehydrogenase against oxidative inactivation

The isocitrate dehydrogenases (ICDs) catalyse the oxidative decarboxylation of isocitrate to alpha-ketoglutarate and can use either NAD(+) or NADP(+) as a cofactor. Recent studies demonstrate that the NADP(+)-dependent isocitrate dehydrogenase, as a source of electrons for cellular antioxidants, is important for protection against oxidative damage. ICD, however, is susceptible to oxidative inactivation, which in turn compromises cellular antioxidant defense. This study investigates the effect of a superoxide dismutase (SOD) mimic, MnTM-2-PyP(5+), on the inactivation of NADP(+)-dependent ICD in SOD-deficient Escherichia coli and in diabetic rats. The findings show that E. coli ICD is inactivated by superoxide, but the inactivated enzyme is replaced by de novo protein synthesis. Statistically significant decrease of ICD activity was found in the hearts of diabetic rats. MnTM-2-PyP(5+) protected ICD in both models.

Regulation of heat shock-induced apoptosis by sensitive to apoptosis gene protein

Heat shock may increase oxidative stress due to increased production of reactive oxygen species and/or the promotion of cellular oxidation events. Sensitive to apoptosis gene (SAG) protein, a novel zinc RING finger protein that protects mammalian cells from apoptosis by redox reagents, is a metal chelator and a potential reactive oxygen species scavenger, but its antioxidant properties have not been completely defined. In this report, we demonstrate that modulation of SAG expression in U937 cells regulates heat shock-induced apoptosis. When we examined the protective role of SAG against heat shock-induced apoptosis with U937 cells transfected with the cDNA for SAG, a clear inverse relationship was observed between the amount of SAG expressed in target cells and their susceptibility to apoptosis. We also observed a significant decrease in the endogenous production of reactive oxygen species and oxidative DNA damage in SAG-overexpressed cells compared to control cells on exposure to heat shock. In addition, transfection of PC3 cells with SAG small interfering RNA markedly decreased the expression of SAG, enhancing the susceptibility of heat shock-induced apoptosis. Taken together, these results indicate that SAG may play an important role in regulating the apoptosis induced by heat shock presumably through maintaining the cellular redox status.

An Examination of the Role of Feeding Regimens in Regulating Metabolism During the Broiler Breeder Grower Period. 1. Hepatic Lipid Metabolism

A trial was conducted to determine the effects of feeding regimens on hepatic lipid metabolism in 16-wk-old broiler breeder pullets. A flock of 350 Cobb 500 breeder pullets was divided into 2 at 4 wk of age and fed either every day (ED) or skip-a-day (SKIP) from 4 to 16 wk of age. Total feed intake did not differ between the 2 groups. At 112 d, 52 randomly selected ED-fed pullets, and 76 SKIP-fed pullets were individually caged and fed a 74-g (ED) or 148-g (SKIP) meal. Four pullets from each group were killed at intervals after feeding and livers were collected, weighed, and snap-frozen for determination of lipogenic gene expression. Total RNA was isolated from livers using Trizol reagent and then quantitatively measured by noting the optical density 260:280 ratio and qualitatively measured by gel electrophoresis. The expression of certain regulatory genes in metabolism [acetyl coenzyme A carboxylase; fatty acid synthase; malic enzyme (MAE); isocitrate dehydrogenase (ICDH); and aspartate aminotransferase (AAT)] were determined by real-time reverse-transcription PCR. Remaining liver portions were analyzed for enzyme activity of MAE, ICDH, and AAT as well as glycogen and lipid contents. Liver weight was higher in SKIP than in ED birds. Feeding caused dramatic increases in liver weight, glycogen, and lipids of SKIP birds. Expression of acetyl coenzyme A carboxylase, FAS, and MAE genes were increased in SKIP birds 12 and 24 h after feeding, with the increases in MAE expression from 0 to 24 h after feeding being of the greatest magnitude. In contrast, SKIP decreased ICDH and AAT gene expression, which parallels findings noted in fasting-refeeding experiments conducted with much younger birds. Skip-a-day feeding resulted in far greater changes in gene expression compared with ED, which was indicative of the inconsistent supply of nutrients in such regimens. Enzyme activity of MAE, ICDH, and AAT was reflective of noted changes in gene expression. In summary, the feeding regimen greatly affected hepatic gene expression in breeder pullets.

Protein oxidation and cellular homeostasis: Emphasis on metabolism

Reactive oxygen species (ROS) are generated as the result of a number of physiological and pathological processes. Once formed ROS can promote multiple forms of oxidative damage, including protein oxidation, and thereby influence the function of a diverse array of cellular processes. This review summarizes the mechanisms by which ROS are generated in a variety of cell types, outlines the mechanisms which control the levels of ROS, and describes specific proteins which are common targets of ROS. Additionally, this review outlines cellular processes which can degrade or repair oxidized proteins, and ultimately describes the potential outcomes of protein oxidation on cellular homeostasis. In particular, this review focuses on the relationship between elevations in protein oxidation and multiple aspects of cellular metabolism. Together, this review describes a potential role for elevated levels of protein oxidation contributing to cellular dysfunction and oxidative stress via impacts on cellular metabolism.

Oxidative inactivation of reduced NADP-generating enzymes in E. coli: iron-dependent inactivation with affinity cleavage of NADP-isocitrate dehydrogenase

Treatment of E. coli extract with iron/ascorbate preferentially inactivated NADP-isocitrate dehydrogenase without affecting glucose-6-phosphate dehydrogenase. NADP-Isocitrate dehydrogenase required divalent metals such as Mg(2+), Mn(2+ )or Fe(2+) ion. Iron/ascorbate-dependent inactivation of the enzyme was accompanied with the protein fragmentation as judged by SDS-PAGE. Catalase protecting the enzyme from the inactivation suggests that hydroxyl radical is responsible for the inactivation with fragmentation. TOF-MS analysis showed that molecular masses of the enzyme fragments were 36 and 12, and 33 and 14 kDa as minor components. Based on the amino acid sequence analyses of the fragments, cleavage sites of the enzyme were identified as Asp307-Tyr308 and Ala282-Asp283, which are presumed to be the metal-binding sites. Ferrous ion bound to the metal-binding sites of the E. coli NADP-isocitrate dehydrogenase may generate superoxide radical that forms hydrogen peroxide and further hydroxyl radical, causing inactivation with peptide cleavage of the enzyme. Oxidative inactivation of NADP-isocitrate dehydrogenase without affecting glucose 6-phosphate dehydrogenase shows only a little influence on the antioxidant activity supplying NADPH for glutathione regeneration, but may facilitate flux through the glyoxylate bypass as the biosynthetic pathway with the inhibition of the citric acid cycle under aerobic growth conditions of E. coli.

Lupeol and its ester exhibit protective role against cyclophosphamide-induced cardiac mitochondrial toxicity

Cyclophosphamide (CP), an anti-cancer and immunosuppressant drug, causes fatal cardiotoxicity during high dose chemotherapy. Lupeol, a pentacyclic triterpene, isolated from Crataeva nurvala stem bark and its ester, lupeol linoleate, possess wide range of medicinal properties. The objective of this study was to establish the pharmacological efficacy of lupeol and its ester against CP-induced mitochondrial-cardiomyopathy. Male albino rats of Wistar strain were injected with a single dose of CP (200 mg/kg body weight, i.p.). A decrease in the activities of TCA cycle enzymes such as succinate dehydrogenase, malate dehydrogenase, and isocitrate dehydrogenase were noted in CP-treated rats. Simultaneously there was a decrease in the activities of mitochondrial complexes of electron transport chain. Electron microscopical observations were also in agreement with the above changes. Mitochondria were swollen with numerous electron dense granules and showed damaged cristae, revealing the cytotoxic effect of CP. Lupeol (50 mg/kg body weight for 10 days orally) and its ester, lupeol linoleate (50 mg/kg body weight for 10 days orally) showed reversal of the above alterations induced by CP. These data suggest that the protective effects of lupeol and its ester against CP-induced cardiac damage were achieved by restoration of mitochondrial structure and function.

Regulation of mitochondrial NADP-isocitrate dehydrogenase in rat heart during ischemia

The changes in the regulation of at mitochondrial NADP-isocitrate dehydrogenase (NADP-ICDH) in a rat heart during have been analysed. Increase of enzyme activity in the cytosol and mitochondria of the heart ischemia was detected. Catalytic properties of the mitochondrial NADP-ICDH at norm and pathology have been compared on homogeneous enzyme preparations. Enzyme from the normoxic and ischemic heart showed the same electrophoretical mobility and molecular mass. Enzyme isolated from the ischemic heart mitochondria demonstrated higher activation energy and lower thermal stability. NADP-isocitrate dehydrogenase at the normoxic and ischemic conditions exhibited different Km for substrates and regulatory behaviour in relation to ATP, ADP, 2-oxoglutarate, citrate, malate, reduced and oxidised glutathione. The inhibitory effect of the Fe2+ and H2O2 mixture associated with the generation of hydroxyl radicals was lower in the ischemic enzyme. We hypothesise that the specific features of regulation behaviour of NADP-ICDH from the ischemic tissues permits the enzyme to supply NADPH to the glutathione reductase/glutathione peroxidase system.

Effects of excess corticosterone on NADPH generating enzymes and glucose oxidation in Leydig cells of adult rats

Clinical and experimental studies have shown the adverse effects of excess glucocorticoid on testicular testosterone production. The NADPH co-enzyme has been recognized as an important factor that regulates several steps in steroidogenesis, while glucose oxidation acts as a limiting factor on testicular testosterone production. Nevertheless, the impact of excess corticosterone, the stress hormone on testicular NADPH availability and glucose oxidation is unknown. Therefore, the present study was designed to assess the specific effects of excess corticosterone on Leydig cell NADPH generating enzymes and glucose oxidation. Adult Wistar rats (200-250 g, b.w.) were treated with corticosterone-21-acetate (2 mg/ 100 g, b.w., i.m., twice daily) for 10 days and corticosterone-21-acetate plus luteinizing hormone (LH) (100 microg/kg b.w., i.m., daily) for 10 days. After the treatment period, experimental animals and controls were killed, blood was collected and the sera separated for testosterone assay. Testes were removed and Leydig cells were isolated, purified and used for estimating the specific activity of NADPH generating enzymes and 14C-glucose oxidation. Serum testosterone, Leydig cellular 14C-glucose oxidation and the specific activities of 6-phosphogluconate dehydrogenase (6-PGDH), NADP-isocitrate dehydrogenase (ICDH) and malic enzyme were significantly decreased in corticosterone-treated rats. Co-administration of LH with corticosterone maintained the specific activities of 6-PGDH and ICDH and 14C-glucose oxidation at control level. Nevertheless, serum testosterone and Leydig cellular malic enzyme activity showed a significant decrease in these rats. In conclusion, the inhibitory effects of excess corticosterone on Leydig cell steroidogenesis are mediated through impaired glucose oxidation and defective NADPH generation. Co-administration of LH with corticosterone failed to prevent the decrease in serum testosterone and Leydig cell malic enzyme activity, suggesting the dominant inhibitory effects of excess corticosterone.

Regulation of mitochondrial NADP+-dependent isocitrate dehydrogenase activity by glutathionylation

Recently, we demonstrated that the control of mitochondrial redox balance and oxidative damage is one of the primary functions of mitochondrial NADP(+)-dependent isocitrate dehydrogenase (IDPm). Because cysteine residue(s) in IDPm are susceptible to inactivation by a number of thiol-modifying reagents, we hypothesized that IDPm is likely a target for regulation by an oxidative mechanism, specifically glutathionylation. Oxidized glutathione led to enzyme inactivation with simultaneous formation of a mixed disulfide between glutathione and the cysteine residue(s) in IDPm, which was detected by immunoblotting with anti-GSH IgG. The inactivated IDPm was reactivated enzymatically by glutaredoxin2 in the presence of GSH, indicating that the inactivated form of IDPm is a glutathionyl mixed disulfide. Mass spectrometry and site-directed mutagenesis further confirmed that glutathionylation occurs to a Cys(269) of IDPm. The glutathionylated IDPm appeared to be significantly less susceptible than native protein to peptide fragmentation by reactive oxygen species and proteolytic digestion, suggesting that glutathionylation plays a protective role presumably through the structural alterations. HEK293 cells and intact respiring mitochondria treated with oxidants inducing GSH oxidation such as H(2)O(2) or diamide showed a decrease in IDPm activity and the accumulation of glutathionylated enzyme. Using immunoprecipitation with anti-IDPm IgG and immunoblotting with anti-GSH IgG, we were also able to purify and positively identify glutathionylated IDPm from 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated mice, a model for Parkinson's disease. The results of the current study indicate that IDPm activity appears to be modulated through enzymatic glutathionylation and deglutathionylation during oxidative stress.

Gene expression reveals vulnerability to oxidative stress and interstitial fibrosis of renal outer medulla to nonhypertensive elevations of ANG II

The present study was designed to determine whether nonhypertensive elevations of plasma ANG II would modify the expression of genes involved in renal injury that could influence oxidative stress and extracellular matrix formation in the renal medulla using microarray, Northern, and Western blot techniques. Sprague-Dawley rats were infused intravenously with either ANG II (5 ng. kg(-1). min(-1)) or vehicle for 7 days (n = 6/group). Mean arterial pressure averaged 110 +/- 0.6 mmHg during the control period and 113 +/- 0.4 mmHg after ANG II. The mRNA of 1,751 genes ( approximately 80% of all currently known rat genes) that was differentially expressed (ANG II vs. saline) in renal outer and inner medulla was determined. The results of 12 hybridizations indicated that in response to ANG II, 11 genes were upregulated and 25 were downregulated in the outer medulla, while 11 were upregulated and 13 were downregulated in the inner medulla. These differentially expressed genes, most of which were not known previously to be affected by ANG II in the renal medulla, were found to group into eight physiological pathways known to influence renal injury and kidney function. Particularly, expression of several genes would be expected to increase oxidative stress and interstitial fibrosis in the outer medulla. Western blot analyses confirmed increased expression of transforming growth factor-beta1 and collagen type IV proteins in the outer medulla. Results demonstrate that nonhypertensive elevations of plasma ANG II can significantly alter the expression of a variety of genes in the renal outer medulla and suggested the vulnerability of the renal outer medulla to the injurious effect of ANG II.

Feed restriction significantly alters lipogenic gene expression in broiler breeder chickens

Broiler breeder pullets were divided into two groups at 21 wk of age. One group was given free access to feed (ad libitum) and the other fed a limited amount of feed (restricted). At 22 wk, all birds were photostimulated and maintained throughout an egg-laying cycle ending at 36 wk. Samples of liver and abdominal fat pad were collected just before photostimulation (prelight), after photostimulation at first egg and at peak egg production (plateau). Hepatic expression of sterol regulatory element binding protein-1, ATP-citrate lyase, fatty acid synthase, malic enzyme, acetyl-CoA carboxylase and stearoyl-CoA (Delta9) desaturase 1 genes in ad libitum birds declined from their highest levels just before photostimulation as the birds came into and maintained egg production. In contrast, the restricted birds had significant (P < 0.05) increases in the expression of these genes after photostimulation at first egg with a subsequent decline as they reached peak egg production. Hepatic expression of fatty acid binding protein, VLDL apolipoprotein (apoVLDL-II) and apoB genes increased significantly (P < 0.05) in both ad libitum and restricted breeders after photostimulation, whereas apoA1 gene expression declined during this time. Abdominal fat pad weights were significantly (P < 0.05) higher in the ad libitum compared with restricted birds after photostimulation. Lipoprotein lipase in this tissue showed a pattern of expression similar to that observed for the hepatic lipogenic enzyme genes. In conclusion, feed restriction during the pullet-to-breeder transition period significantly (P < 0.05) altered hepatic lipogenic gene expression in broiler breeders.