Effects of overexpression of antioxidants on the release of cytochrome c and apoptosis-inducing factor in the model of ischemia

Glutathione Peroxidase 1 Protects Against Peroxynitrite-Induced Spiral Ganglion Neuron Damage Through Attenuating NF-κB Pathway Activation

Glutathione peroxidase 1 (GPX1) is a crucial antioxidant enzyme that prevented the harmful accumulation of intra-cellular hydrogen peroxide. GPX1 might contribute in limiting cochlear damages associated with aging or acoustic overexposure, but the function of GPX1 in the inner ear remains unclear. The present study was designed to investigate the effect of GPX1 on cochlear spiral ganglion neurons (SGNs) against oxidative stress induced by peroxynitrite, a versatile oxidant generated by the reaction of superoxide anion and nitric oxide. Here, we first found that the expression of GPX1 in cultured SGNs was downregulated after peroxynitrite exposure. Then, the GPX1 mimic ebselen and the gpx1 knockout (gpx1^–/–) mice were used to investigate the role of GPX1 in SGNs treated with peroxynitrite. The pretreatment with ebselen significantly increased the survived SGN numbers, inhibited the apoptosis, and enhanced the expression of 4-HNE in the cultured SGNs of peroxynitrite + ebselen group compared with the peroxynitrite-only group. On the contrary, remarkably less survived SGNs, more apoptotic SGNs, and the higher expression level of 4-HNE were detected in the peroxynitrite + gpx1^–/– group compared with the peroxynitrite-only group. Furthermore, rescue experiments with antioxidant N-acetylcysteine (NAC) showed that the expression of 4-HNE and the apoptosis in SGNs were significantly decreased, while the number of surviving SGNs was increased in peroxynitrite + NAC group compared the peroxynitrite-only group and in peroxynitrite + gpx1^–/– + NAC group vs. peroxynitrite + gpx1^–/– group. Finally, mechanistic studies showed that the activation of nuclear factor-kappa B (NF-κB) was involved in the SGNs damage caused by peroxynitrite and that GPX1 protected SGNs against peroxynitrite-induced damage, at least in part, via blocking the NF-κB pathway activation. Collectively, our findings suggest that GPX1 might serve as a new target for the prevention of nitrogen radical-induced SGNs damage and hearing loss.

Antioxidants as Renoprotective Agents for Ischemia during Partial Nephrectomy

Small renal masses have been diagnosed increasingly in recent decades, allowing surgical treatment by partial nephrectomy. This treatment option is associated with better renal function preservation, in comparison with radical nephrectomy. However, for obtaining a bloodless field during surgery, occlusion of renal artery and veins is often required, which results in transitory ischemia. The renal ischemia-reperfusion injury is associated with increased reactive oxygen species production leading to renal tissue damage. Thus, the use of antioxidants has been advocated in the partial nephrectomy perioperative period. Several antioxidants were investigated in regard to renal ischemia-reperfusion injury. The present manuscript aims to present the literature on the most commonly studied antioxidants used during partial nephrectomy. The results of experimental and clinical studies using antioxidants during partial nephrectomy are reported. Further, alimentary sources of some antioxidants are presented, stimulating future studies focusing on perioperative antioxidant-rich diets.

ADNP Plays a Key Role in Autophagy: From Autism to Schizophrenia and Alzheimer's Disease

Activity-dependent neuroprotective protein (ADNP), discovered in our laboratory in 1999, has been characterized as a master gene vital for mammalian brain formation. ADNP de novo mutations in humans result in a syndromic form of autism-like spectrum disorder (ASD), including cognitive and motor deficits, the ADNP syndrome (Helsmoortel-Van Der Aa). One of the most important cellular processes associated with ADNP is the autophagy pathway, recently discovered by us as a key player in the pathophysiology of schizophrenia. In this regard, given the link between the microtubule and autophagy systems, the ADNP microtubule end binding protein motif, namely, the neuroprotective NAP (NAPVSIPQ), was found to enhance autophagy while protecting microtubules and augmenting ADNP's association with both systems. Thus, linking autophagy and ADNP is proposed as a major target for intervention in brain diseases from autism to Alzheimer's disease (AD) and our findings introduce autophagy as a possible novel target for treating schizophrenia.

Hyperbaric oxygen preserves neurotrophic activity of carbon monoxide-exposed astrocytes

In astrocytes, carbon monoxide (CO) poisoning causes oxidative stress and mitochondrial dysfunction accompanied by caspase and calpain activation. Impairment in astrocyte function can be time-dependently reduced by hyperbaric (3bar) oxygen (HBO). Due to the central role of astrocytes in maintaining neuronal function by offering neurotrophic support we investigated the hypothesis that HBO therapy may exert beneficial effect on acute CO poisoning-induced impairment in intrinsic neurotrophic activity. Exposure to 3000ppm CO in air followed by 24-72h of normoxia caused a progressive decline of gene expression, synthesis and secretion of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) to different extent. 1h treatment with 100% oxygen disclosed a pressure- and time-dependent efficacy in preserving astrocytic neurotrophic support. The beneficial effect was most evident when the astrocytes were exposed to HBO 1-5h after exposure to CO. The results further support an active role of hyperbaric, not normobaric, oxygenation in reducing dysfunction of astrocytes after acute CO poisoning. By preserving endogenous neurotrophic activity HBO therapy might promote neuronal protection and thus prevent the occurrence of late neuropsychological sequelae.

The effectiveness of oxygen therapy in carbon monoxide poisoning is pressure- and time-dependent: a study on cultured astrocytes

Carbon monoxide (CO) poisoning causes neuronal and glial apoptosis that can result in delayed neurological symptoms. The damage of brain cells can be prevented by oxygen therapy. Based on the central role of astrocytes in maintaining neuronal function and viability we investigated the toxic effects of 3000ppm CO in air followed by 24h of normoxia and evaluated the possible protective influence of 100% normobaric oxygen or 100% oxygen at a pressure of 3bar (hyperbaric) against CO poisoning in these cells. CO/normoxia caused a progressive decline of viability, increase in reactive oxygen species and decline of mitochondrial membrane potential and intracellular ATP levels in cultured rat astrocytes. Increased caspase-9, caspase-8 and calpain activity converged in activation of caspase-3/7. 1h treatment with oxygen disclosed pressure- and time-dependent efficacy in restoring astrocytic mitochondrial function and the prevention of apoptosis. The protective effect was most evident when the astrocytes were exposed to hyperbaric oxygen, but not normobaric oxygen, 1-5h after exposure to CO.

Ginsenoside Rb1 attenuates oxygen-glucose deprivation-induced apoptosis in SH-SY5Y cells via protection of mitochondria and inhibition of AIF and cytochrome c release

To investigate the role of mitochondria in the protective effects of ginsenoside Rb1 on cellular apoptosis caused by oxygen-glucose deprivation, in this study, MTT assay, TUNEL staining, flow cytometry, immunocytochemistry and western blotting were used to examine the cellular viability, apoptosis, ROS level, mitochondrial membrane potential, and the distribution of apoptosis inducing factor, cytochrome c, Bax and Bcl-2 in nucleus, mitochondria and cytoplasm. We found that pretreatment with GRb1 improved the cellular viability damaged by OGD. Moreover, GRb1 inhibited apoptosis in SH-SY5Y cells induced by OGD. Further studies showed that the elevation of cellular reactive oxygen species levels and the reduction of mitochondrial membrane potential caused by OGD were both counteracted by GRb1. Additionally, GRb1 not only suppressed the translocation of apoptosis inducing factor into nucleus and cytochrome c into cytoplasm, but also inhibited the increase of Bax within mitochondria and alleviated the decrease of mitochondrial Bcl-2. Our study indicates that the protection of GRb1 on OGD-induced apoptosis in SH-SY5Y cells is associated with its protection on mitochondrial function and inhibition of release of AIF and cytochrome c.

Differential gene expression in the brain of the African lungfish, Protopterus annectens, after six days or six months of aestivation in air

The African lungfish, Protopterus annectens, can undergo aestivation during drought. Aestivation has three phases: induction, maintenance and arousal. The objective of this study was to examine the differential gene expression in the brain of P. annectens during the induction (6 days) and maintenance (6 months) phases of aestivation as compared with the freshwater control using suppression subtractive hybridization. During the induction phase of aestivation, the mRNA expression of prolactin (prl) and growth hormone were up-regulated in the brain of P. annectens, which indicate for the first time the possible induction role of these two hormones in aestivation. Also, the up-regulation of mRNA expression of tyrosine 3-monooxygenase/tryptophan 5-monooxygenase activation protein γ polypeptide and the down-regulation of phosphatidylethanolamine binding protein, suggest that there could be a reduction in biological and neuronal activities in the brain. The mRNA expression of cold inducible RNA-binding protein and glucose regulated protein 58 were also up-regulated in the brain, probably to enhance their cytoprotective effects. Furthermore, the down-regulation of prothymosin α expression suggests that there could be a suppression of transcription and cell proliferation in preparation for the maintenance phase. In general, the induction phase appeared to be characterized by reduction in glycolytic capacity and metabolic activity, suppression of protein synthesis and degradation, and an increase in defense against ammonia toxicity. In contrast, there was a down-regulation in the mRNA expression of prl in the brain of P. annectens during the maintenance phase of aestivation. In addition, there could be an increase in oxidative defense capacity, and up-regulation of transcription, translation, and glycolytic capacities in preparation for arousal. Overall, our results signify the importance of reconstruction of protein structures and regulation of energy expenditure during the induction phase, and the needs to suppress protein degradation and conserve metabolic fuel stores during the maintenance phase of aestivation.

NF-κB-dependent and -independent pathways in the protective effects of activated protein C in hippocampal and cortical neurons at excitotoxicity

The transcription factor NF-κB regulates the expression of multiple genes involved in inflammation, apoptotic cell death and cell survival. We previously demonstrated that activated protein C (APC), a serine protease of hemostasis with anticoagulant activity, protected cultured rat cortical and hippocampal neurons against glutamate-induced excitotoxicity, a model of ischemic stroke. We reported that APC suppressed the translocation of NF-κBp65/RelA into the nucleus of neurons. However, it is not known whether APC-induced protection of neurons against cell death occurs via regulation of NF-κB activation or NF-κB-independent p53 expression. It is also unclear whether cleaved caspase-3 and caspase-independent AIF and Bax/Bcl-2 expression are involved at excitotoxicity. To elucidate the NF-κB dependent and -independent mechanisms in the APC-mediated cell survival, we analyzed in cortical and hippocampal neurons the effects of helenalin, a specific inhibitor of NF-κB activity, and APC on neuronal cell death and on the level of nuclear AIF, p53, caspase-3 and the apoptotic index (Bax/Bcl-2 ratio). We could demonstrate that helenalin (5 μM), like APC (1 nM), protects cultured neurons from glutamate-induced excitotoxicity. Both APC and helenalin inhibit AIF release from mitochondria and its translocation into the nucleus. They decrease the apoptotic index in neurons at excitotoxicity. However, APC, but not helenalin, reduced the glutamate-induced activation of caspase-3. Incubation of neurons with APC blocked the glutamate-induced increase in the nuclear level of p53 via NF-κB-independent pathway. Our findings demonstrate that, in the protective effect of APC in neurons at excitotoxicity, the NF-κB pathway is an important, but not the only pathway, and is significantly connected with neuronal survival at excitotoxicity.

Therapeutic potential of targeting hydrogen peroxide metabolism in the treatment of brain ischaemia

For many years after its discovery, hydrogen peroxide (H₂O₂) was viewed as a toxic molecule to human tissues; however, in light of recent findings, it is being recognized as an ubiquitous endogenous molecule of life as its biological role has been better elucidated. Indeed, increasing evidence suggests that H₂O₂ may act as a second messenger with a pro-survival role in several physiological processes. In addition, our group has recently demonstrated neuroprotective effects of H₂O₂ on in vitro and in vivo ischaemic models through a catalase (CAT) enzyme-mediated mechanism. Therefore, the present review summarizes experimental data supporting a neuroprotective potential of H₂O₂ in ischaemic stroke that has been principally achieved by means of pharmacological and genetic strategies that modify either the activity or the expression of the superoxide dismutase (SOD), glutathione peroxidase (GPx) and CAT enzymes, which are key regulators of H₂O₂ metabolism. It also critically discusses a translational impact concerning the role played by H₂O₂ in ischaemic stroke. Based on these data, we hope that further research will be done in order to better understand the mechanisms underlying H₂O₂ functions and to promote successful H₂O₂ signalling based therapy in ischaemic stroke.

Role of catalase on the hypoxia/reoxygenation stress in the hypoxia-tolerant Nile tilapia

The specific contribution of each antioxidant enzyme to protection against the reoxygenation-associated oxidative stress after periods of hypoxia is not well understood. We assessed the physiological role of catalase during posthypoxic reoxygenation by the combination of two approaches. First, catalase activity of Nile tilapias ( Oreochromis niloticus ) was 90% suppressed by intraperitoneal injection of 3-amino-1,2,4-triazole (ATZ, 1g/kg). In ATZ-injected fish, liver GSH levels, oxidative stress markers, and activities of other antioxidant enzymes remained unchanged. Second, animals with depleted catalase activity (or those saline-injected) were subjected to a cycle of severe hypoxia (dissolved O2= 0.28 mg/l for 3 h) followed by reoxygenation (0.5 to 24 h). Hypoxia did not induce changes in the above-mentioned parameters, either in saline- or in ATZ-injected animals. Reoxygenation increased superoxide dismutase activity in saline-injected fish, whose levels were similar to ATZ-injected animals. The activities of glutathione S-transferase, selenium-dependent glutathione peroxidase, and total-GPX and the levels of GSH-eq, GSSG, and thiobarbituric acid reactive substances remained unchanged during reoxygenation in both saline- and ATZ-injected fish. The GSSG/GSH-eq ratio in ATZ-injected fish increased at 30 min of reoxygenation compared with saline-injected ones. Reoxygenation also increased carbonyl protein levels in saline-injected fish, whose levels were similar to the ATZ-injected group. Our work shows that inhibition of liver tilapia catalase causes a redox imbalance during reoxygenation, which is insufficient to induce further oxidative stress. This indicates the relevance of hepatic catalase for hypoxia/reoxygenation stress in tilapia fish.

Methyl deficient diet aggravates experimental colitis in rats

Inflammatory bowel diseases (IBD) result from complex interactions between environmental and genetic factors. Low blood levels of vitamin B12 and folate and genetic variants of related target enzymes are associated with IBD risk, in population studies. To investigate the underlying mechanisms, we evaluated the effects of a methyl-deficient diet (MDD, folate, vitamin B12 and choline) in an experimental model of colitis induced by dextran sodium sulphate (DSS), in rat pups from dams subjected to the MDD during gestation and lactation. Four groups were considered (n= 12–16 per group): C DSS⁻ (control/DSS⁻), D DSS⁻ (deficient/DSS⁻), C DSS⁺ (control/DSS⁺) and D DSS⁺ (deficient/DSS⁺). Changes in apoptosis, oxidant stress and pro-inflammatory pathways were studied within colonic mucosa. In rat pups, the MDD produced a decreased plasma concentration of vitamin B12 and folate and an increased homocysteine (7.8 ± 0.9 versus 22.6 ± 1.2 μmol/l, P < 0.001). The DSS-induced colitis was dramatically more severe in the D DSS⁺ group compared with each other group, with no change in superoxide dismutase and glutathione peroxidase activity, but decreased expression of caspase-3 and Bax, and increased Bcl-2 levels. The mRNA levels of tumour necrosis factor (TNF)-α and protein levels of p38, cytosolic phospolipase A2 and cyclooxygenase 2 were significantly increased in the D DSS⁺ pups and were accompanied by a decrease in the protein level of tissue inhibitor of metalloproteinases (TIMP)3, a negative regulator of TNF-α. MDD may cause an overexpression of pro-inflammatory pathways, indicating an aggravating effect of folate and/or vitamin B12 deficiency in experimental IBD. These findings suggest paying attention to vitamin B12 and folate deficits, frequently reported in IBD patients.

Minocycline protects oligodendroglial precursor cells against injury caused by oxygen-glucose deprivation

Ischemic brain injury is widely modeled in vitro with paradigms of oxygen-glucose deprivation (OGD), which leads to cell death. The prevention and attenuation of brain injury by the tetracycline antibiotic minocycline has been attributed largely to suppression of microglial activation, but its benefits in oligodendrocyte cells have not been well characterized. Using primary cultures of rat oligodendroglial precursor cells (OPC) exposed to OGD, we investigated the direct effects of minocycline on the survival, proliferation, and maturation of oligodendroglial lineage cells. OGD for 2 hr caused a decrease in the total number of OPC and the amount of proliferating progenitors by 50%, which was attenuated by inclusion of minocycline. The reduced numbers of immature oligodendroglial cells at 72 hr and of mature oligodendrocytes at 120 hr after OGD were partially restored by minocycline. In OPC, OGD caused an increase of reactive oxygen species (ROS) and production of TUNEL-positive cell numbers, which was abolished by minocycline. Minocycline preferentially increased the expression of superoxide dismutase under OGD but not in control OPC. Minocycline also prevented the OGD-induced downregulation of the transcription factors Sox10 and Olig2 and of myelin-specific genes 2'3' cyclic nucleotide phosphodiesterase (CNP) and myelin basic protein (MBP) in response to OGD. These studies demonstrate direct protective actions of minocycline on oligodendroglial-lineage cells, suggesting potential benefit in white matter injury involving OGD.

Glutathione peroxidase-1 in health and disease: from molecular mechanisms to therapeutic opportunities

Reactive oxygen species, such as superoxide and hydrogen peroxide, are generated in all cells by mitochondrial and enzymatic sources. Left unchecked, these reactive species can cause oxidative damage to DNA, proteins, and membrane lipids. Glutathione peroxidase-1 (GPx-1) is an intracellular antioxidant enzyme that enzymatically reduces hydrogen peroxide to water to limit its harmful effects. Certain reactive oxygen species, such as hydrogen peroxide, are also essential for growth factor-mediated signal transduction, mitochondrial function, and maintenance of normal thiol redox-balance. Thus, by limiting hydrogen peroxide accumulation, GPx-1 also modulates these processes. This review explores the molecular mechanisms involved in regulating the expression and function of GPx-1, with an emphasis on the role of GPx-1 in modulating cellular oxidant stress and redox-mediated responses. As a selenocysteine-containing enzyme, GPx-1 expression is subject to unique forms of regulation involving the trace mineral selenium and selenocysteine incorporation during translation. In addition, GPx-1 has been implicated in the development and prevention of many common and complex diseases, including cancer and cardiovascular disease. This review discusses the role of GPx-1 in these diseases and speculates on potential future therapies to harness the beneficial effects of this ubiquitous antioxidant enzyme.

Apoptosis-inducing factor: structure, function, and redox regulation

Apoptosis-inducing factor (AIF) is a flavin adenine dinucleotide-containing, NADH-dependent oxidoreductase residing in the mitochondrial intermembrane space whose specific enzymatic activity remains unknown. Upon an apoptotic insult, AIF undergoes proteolysis and translocates to the nucleus, where it triggers chromatin condensation and large-scale DNA degradation in a caspase-independent manner. Besides playing a key role in execution of caspase-independent cell death, AIF has emerged as a protein critical for cell survival. Analysis of in vivo phenotypes associated with AIF deficiency and defects, and identification of its mitochondrial, cytoplasmic, and nuclear partners revealed the complexity and multilevel regulation of AIF-mediated signal transduction and suggested an important role of AIF in the maintenance of mitochondrial morphology and energy metabolism. The redox activity of AIF is essential for optimal oxidative phosphorylation. Additionally, the protein is proposed to regulate the respiratory chain indirectly, through assembly and/or stabilization of complexes I and III. This review discusses accumulated data with respect to the AIF structure and outlines evidence that supports the prevalent mechanistic view on the apoptogenic actions of the flavoprotein, as well as the emerging concept of AIF as a redox sensor capable of linking NAD(H)-dependent metabolic pathways to apoptosis.