Involvement of increased stability of mitochondrial membrane potential and overexpression of Bcl-2 in enhanced anoxic tolerance induced by hypoxic preconditioning in cultured hypothalamic neurons

Hydrogen sulfide attenuates homocysteine-induced neurotoxicity by preventing mitochondrial dysfunctions and oxidative damage: In vitro and in vivo studies

Elevated homocysteine (Hcy) levels have been implicated in neurodevelopmental and neurodegenerative disorders. Induction of oxidative stress and apoptosis has been reported as major mechanism in Hcy-induced neurotoxicity. Hydrogen sulfide (H₂S), as an antioxidant molecule has been reported to exhibit novel protective effect against Hcy-induced cell damage. However, the mechanisms involved in protective effect of H₂S against Hcy-induced toxicity in neurons have not been fully elucidated. Herein, effect of sodium hydrogen sulfide (NaHS, a source of H₂S) on Hcy-induced neurotoxicity was studied on Neuro-2a (N2a) cells in vitro and in animals subjected to hyperhomocysteinemia. DCFH-DA staining revealed that NaHS effectively attenuated Hcy-induced oxidative damage by reducing intracellular reactive oxygen species (ROS) generation. JC-1 staining and western blot results showed that NaHS pre-treatment prevented Hcy-induced mitochondrial dysfunctions and mitochondria-mediated apoptosis. MTT assay, cell cycle analysis, ethidium bromide/acridine orange (EB/AO) and Hoechst staining results demonstrated that NaHS significantly alleviated Hcy-induced cytotoxicity in N2a cells by preventing oxidative damage. Importantly, the results from agarose gel electrophoresis, comet and TUNEL assay indicated that NaHS also prevented neurodegeneration by reducing DNA damage and apoptotic cell death in animals with hyperhomocysteinemia. Taken together, the results demonstrate that the protective potential of H₂S against Hcy-induced neurotoxicity is mediated by preventing oxidative DNA damage and mitochondrial dysfunctions. The findings validate that H₂S is a promising therapeutic molecule in neurodegenerative conditions associated with hyperhomocysteinemia.

Comparative Study on the Protective Effects of Salidroside and Hypoxic Preconditioning for Attenuating Anoxia-Induced Apoptosis in Pheochromocytoma (PC12) Cells

BACKGROUND Hypoxia is an important sign that can result from body injuries or a special condition such as being at a high altitude or deep water diving. In the current studies, hypoxic preconditioning (HPC) plays a key role in reducing hypoxia-induced apoptosis. We aimed to study the pharmacologic preconditioning effects of salidroside versus those of HPC in hypoxia-/anoxia-induced apoptosis in PC12 cells (pheochromocytoma). MATERIAL AND METHODS PC12 cells were treated by different experimental conditions: control condition, hypoxia condition, HPC condition, low-/middle-/high-dose condition of salidroside, cyclosporine A (CsA), and oratractyloside (ATR). The cell viability, lactate dehydrogenase (LDH) activity, apoptosis, mitochondrial membrane potential (MMP), intracellular Ca2+, caspase-3 activity, and expression of Bcl-2 were detected in PC12 cells after the hypoxia treatment. Salidroside, extracted from the traditional Chinese herb Rhodiola rosea L, plays an essential role in reducing hypoxia-induced apoptosis in PC12 cells by the mitochondrial pathway. RESULTS Salidroside decreased the apoptosis and increased the viability of hypoxia-induced PC12 cells more effectively than HPC Moreover, salidroside markedly stabilized MMP and intracellular Ca2+, reduced or inhibited LDH and caspase-3 activity, and up-regulated Bcl-2; CsA and ATR showed corresponding function. CONCLUSIONS Salidroside administration restrains apoptosis induced by hypoxia in PC12 cells. The protective effects are mediated by preservation of mitochondrial integrity and MMP to inhibit the excessive Ca2+ influx and caspase-3 activity and to promote the Bcl-2 expression, providing a potential clinical and effective therapeutic mechanism to reduce deaths from ischemic or hypoxic injury.

Asymmetrical dimethylarginine antagonizes glutamate-induced apoptosis in PC12 cells

Overproduction of nitric oxide (NO) plays an important role in glutamate-induced excitotoxicity. Asymmetric dimethylarginine (ADMA) is an endogenous nitric oxide synthase (NOS) inhibitor. The aim of this study is to explore whether ADMA antagonizes the excitotoxicity of glutamate to neuronal cells and the underlying molecular mechanisms. In this work, we investigated the effects of ADMA on glutamate-induced toxicity in neuronal cells by studying PC12 cells, a clonal rat pheochromocytoma cell line. We show that ADMA obviously protects PC12 cells against glutamate-induced cytotoxicity and apoptosis. We also found that ADMA treatment results in prevention of glutamate-induced mitochondrial membrane potential loss and caspase-3 activation. Moreover, ADMA prevents glutamate-caused down-regulation of bcl-2 protein expression. These results indicate that ADMA protects against glutamate-induced apoptosis and excitotoxicity and the underlying mechanism may be involved in preservation of mitochondrial function by up-regulating the expression of bcl-2. Our study suggests a promising future of ADMA-based therapies for neuropathologies associated with an excess of NO.

Hydrogen sulfide prevents formaldehyde-induced neurotoxicity to PC12 cells by attenuation of mitochondrial dysfunction and pro-apoptotic potential

Hydrogen sulfide (H(2)S) has been shown to act as a neuroprotectant and antioxidant. Numerous studies have demonstrated that exposure to formaldehyde (FA) causes neuronal damage and that oxidative stress is one of the most critical effects of FA exposure. Accumulation of FA is involved in the pathogenesis of Alzheimer's disease (AD). The aim of present study is to explore the inhibitory effects of H(2)S on FA-induced cytotoxicity and apoptosis and the molecular mechanisms underlying in PC12 cells. We show that sodium hydrosulfide (NaHS), a H(2)S donor, protects PC12 cells against FA-mediated cytotoxicity and apoptosis and that NaHS preserves the function of mitochondria by preventing FA-induced loss of mitochondrial membrane potential and release of cytochrome c in PC12 cells. Furthermore, NaHS blocks FA-exerted accumulation of intracellular reactive oxygen species (ROS), down-regulation of Bcl-2 expression, and up-regulation of Bax expression. These results indicate that H(2)S protects neuronal cells against neurotoxicity of FA by preserving mitochondrial function through attenuation of ROS accumulation, up-regulation of Bcl-2 level, and down-regulation of Bax expression. Our study suggests a promising future of H(2)S-based preventions and therapies for neuronal damage after FA exposure.

ACS6, a Hydrogen sulfide-donating derivative of sildenafil, inhibits homocysteine-induced apoptosis by preservation of mitochondrial function

BACKGROUND

The hydrogen sulfide-releasing sildenafil, ACS6, has been demonstrated to inhibit superoxide formation through donating hydrogen sulfide (H2S). We have found that H2S antagonizes homocysteine-induced oxidative stress and neurotoxicity. The aim of the present study is to explore the protection of ACS6 against homocysteine-triggered cytotoxicity and apoptosis and the molecular mechanisms underlying in PC12 cells.

METHODS

Cell viability was determined by Cell Counting Kit-8 assay. Cell apoptosis was observed using the chromatin dye Hoechst 33258 and analyzed by Flow Cytometry after propidium iodide staining. Mitochondrial membrane potential was monitored using the fluorescent dye Rh123. Intracellular reactive oxygen species were determined by oxidative conversion of cell permeable 2',7'-dichlorfluorescein-diacetate to fluorescent 2',7'-dichlorfluorescein. The expression of cleaved caspase-3 and bcl-2 and the accumulation of cytosolic cytochrome c were analyzed by Western blot.

RESULTS

We show that ACS6 protects PC12 cells against cytotoxicity and apoptosis induced by homocysteine and blocks homocysteine-triggered cytochrome c release and caspase-3 activation. ACS6 treatment results in not only prevention of homocysteine-caused mitochondrial membrane potential (Δψ) loss and reactive oxygen species (ROS) overproduction but also reversal of Bcl-2 down-expression.

CONCLUSIONS

These results indicate that ACS6 protects PC12 cells against homocysteine-induced cytotoxicity and apoptosis by preservation of mitochondrial function though inhibiting both loss of Δψ and accumulation of ROS as well as modulating the expression of Bcl-2. Our study provides evidence both for a neuroprotective effect of ACS6 and for further evaluation of ACS6 as novel neuroprotectants for Alzheimer's disease associated with homocysteine.

Neuroprotection induced in vitro by ischemic preconditioning and postconditioning: modulation of apoptosis and PI3K-Akt pathways

Preconditioning and postconditioning are mild ischemic exposures before or after severe injurious ischemia, respectively, that elicit endogenous neuroprotective responses. Molecular mechanisms of neuroprotection through preconditioning and postconditioning are not completely understood. Here we optimized the in vitro oxygen and glucose deprivation (OGD) models of preconditioning and postconditioning in primary cortical neuron cultures that allow the studies of the corresponding molecular mechanisms of neuroprotection. We found that the cortical cells preconditioned with a single 45-min OGD treatment administered 24 h prior to injurious 2 h OGD were robustly protected after both 3 h and 16 h of reperfusion. For the postconditioning treatment, we found that three cycles of 15 min OGD followed by 15 min reperfusion, applied immediately after injurious 2 h OGD and prior to complete reperfusion, resulted in effective neuroprotection at both 3 h and 16 h of reperfusion. Using real-time RT-PCR arrays focused on genes of the apoptosis and PI3K-Akt pathways, we found that injurious OGD mainly induced apoptosis-related and repressed PI3K-Akt pathway-related genes after either 3 h or 16 h of reperfusion. Preconditioning treatment resulted in the activation of both pro-survival and anti-apoptotic pathways after 3 h of reperfusion and mainly anti-apoptotic pathway after 16 h of reperfusion. In contrast, the activation of PI3K-Akt pathway mainly contributed to the neuroprotective effect by the postconditioning treatment after 3 h of reperfusion, but differential gene expression likely contributed minimally, if at all, to the neuroprotection observed after 16 h of reperfusion. Among the novel markers of neuroprotection, Nol3 gene upregulation was observed after 3 h of reperfusion following either preconditioning or postconditioning treatments and after 16 h of reperfusion following preconditioning treatment.

The anti-necrosis role of hypoxic preconditioning after acute anoxia is mediated by aldose reductase and sorbitol pathway in PC12 cells

It has been demonstrated that hypoxic preconditioning (HP) enhances the survival ability of the organism against the subsequent acute anoxia (AA). However, it is not yet clear whether necrosis induced by AA can be prevented by HP, and what are the underlying mechanisms. In this study, we examined the effect of HP (10% O(2), 48 h) on necrosis induced by AA (0% O(2), 24 h) in PC12 cells. We found that HP delayed the regulatory volume decrease and reduced cell swelling after 24 h of exposure to AA. Since aldose reductase (AR) is involved in cell volume regulation, we detected AR mRNA expression with reverse transcription-polymerase chain reaction (RT-PCR) techniques. The AR mRNA level was dramatically elevated by HP. Furthermore, an HP-induced decrease in cell injury was reversed by berberine chloride (BB), the inhibitor of AR. In addition, sorbitol synthesized from glucose catalyzed by AR is directly related to cell volume regulation. Subsequently, we tested sorbitol content in the cytoplasm. HP clearly elevated sorbitol content, while BB inhibited the elevation induced by HP. Further study showed that a strong inhibitor of sorbitol permease, quinidine, completely reversed the protection induced by HP after AA. These data provide evidence that HP prevents necrosis induced by AA and is mediated by AR and sorbitol pathway.

Toll-like receptor signaling in endogenous neuroprotection and stroke

Stroke and other cerebral vascular diseases are a leading cause of morbidity and mortality in the United States. Despite intensive research to identify interventions that lessen cerebrovascular injury, no major therapies exist. Development of stroke prophylaxis involves an understanding of the mechanisms of damage following cerebral ischemia, and elucidation of the endogenous mechanisms that combat further brain injury. Toll-like receptors (TLRs) are critical components of the innate immune system that have been shown recently to mediate ischemic injury. Paradoxically, TLR ligands administered systemically induce a state of tolerance to subsequent ischemic injury. Herein we suggest that stimulation of TLRs prior to ischemia reprograms TLR signaling that occurs following ischemic injury. Such reprogramming leads to suppressed expression of pro-inflammatory molecules and enhanced expression of numerous anti-inflammatory mediators that collectively confer robust neuroprotection. Our findings indicate that numerous preconditioning stimuli lead to TLR activation, an event that occurs prior to ischemia and ultimately leads to TLR reprogramming. Thus genomic reprogramming of TLR signaling may be a unifying principle of tolerance to cerebral ischemia.

Molecular physiology of preconditioning-induced brain tolerance to ischemia

Ischemic tolerance describes the adaptive biological response of cells and organs that is initiated by preconditioning (i.e., exposure to stressor of mild severity) and the associated period during which their resistance to ischemia is markedly increased. This topic is attracting much attention because preconditioning-induced ischemic tolerance is an effective experimental probe to understand how the brain protects itself. This review is focused on the molecular and related functional changes that are associated with, and may contribute to, brain ischemic tolerance. When the tolerant brain is subjected to ischemia, the resulting insult severity (i.e., residual blood flow, disruption of cellular transmembrane gradients) appears to be the same as in the naive brain, but the ensuing lesion is substantially reduced. This suggests that the adaptive changes in the tolerant brain may be primarily directed against postischemic and delayed processes that contribute to ischemic damage, but adaptive changes that are beneficial during the subsequent test insult cannot be ruled out. It has become clear that multiple effectors contribute to ischemic tolerance, including: 1) activation of fundamental cellular defense mechanisms such as antioxidant systems, heat shock proteins, and cell death/survival determinants; 2) responses at tissue level, especially reduced inflammatory responsiveness; and 3) a shift of the neuronal excitatory/inhibitory balance toward inhibition. Accordingly, an improved knowledge of preconditioning/ischemic tolerance should help us to identify neuroprotective strategies that are similar in nature to combination therapy, hence potentially capable of suppressing the multiple, parallel pathophysiological events that cause ischemic brain damage.

Alternol inhibits proliferation and induces apoptosis in mouse lymphocyte leukemia (L1210) cells

Alternol is a novel compound purified from the fermenting products by microorganisms named as Alternaria alternata var. monosporus from the bark of Yew. In this study, we tested its effect on mouse lymphocyte leukemia L1210 cells. Alternol was found to inhibit the proliferation and induce apoptosis in L1210 cells. When the cells were treated with Alternol, chromatin condensation and phosphatidylserine externalization were observed with the down-regulation of the pro-survival gene Bcl-2 and the activation of caspase-3, caspase-9, but not caspase-8. Moreover, exposure of cells to Alternol resulted in a significant increase in reactive oxygen species (ROS) and mitochondrial transmembrane potential (DeltaPsim) depolarization. Taken together, these results demonstrate that Alternol is a potent agent in inducing L1210 cells to apoptosis, which involve caspase activation and ROS generation.

Curcumin protects PC12 cells against 1-methyl-4-phenylpyridinium ion-induced apoptosis by bcl-2-mitochondria-ROS-iNOS pathway

The aim of present study is to explore the cytoprotection of curcumin against 1-methyl-4-phenylpridinium ions (MPP(+))-induced apoptosis and the molecular mechanisms underlying in PC12 cells. Our findings indicated that MPP(+) significantly reduced the cell viability and induced apoptosis of PC12 cells. Curcumin protected PC12 cells against MPP(+)-induced cytotoxicity and apoptosis not only by inducing overexpression of Bcl-2, but also reducing the loss of mitochondrial membrane potential (MMP), an increase in intracellular reactive oxygen species (ROS) and overexpression of inducible nitric oxide synthase (iNOS). The selective iNOS inhibitor AG partly blocked MPP(+)-induced apoptosis of PC12 cells. The results of present study suggested that the cytoprotective effects of curcumin might be mediated, at least in part, by the Bcl-2-mitochondria-ROS-iNOS pathway. Because of its non-toxic property, curcumin could be further developed to treat the neurodegenerative diseases which are associated with oxidative stress, such as Parkinson's disease (PD).

The regulation, control, and consequences of mitochondrial oxygen utilization and disposition in the heart and skeletal muscle during hypoxia

The major oxygen-dependent function of mitochondria partitions molecular oxygen between oxidative phosphorylation and reactive oxygen species generation. When oxygen becomes limiting, the modulation of mitochondrial function plays an important role in overall biologic adaptation. This review focuses on mitochondrial biology in the heart and skeletal muscle during hypoxia. The disparate mitochondrial responses discussed appear to be dependent on the degree of hypoxia, on the age at exposure to hypoxia, and on the duration of exposure. These hypoxia-induced changes include modulation in mitochondrial respiratory capacity; activation of the mitochondrial biogenesis regulatory program; induction of mitochondrial antioxidant defense systems; regulation of antiapoptotic mitochondrial proteins, and modulation of mitochondrial sensitivity to permeability transition. The mitochondria-derived reactive oxygen species signal-transduction events in response to hypoxia also are reviewed. The cardiac and skeletal muscle phenotypic signatures that result from mitochondrial adaptations include an amelioration of resistance to cardiac ischemia and modulations in exercise capacity and oxidative fuel preference. Overall, the data demonstrate the plasticity in mitochondrial regulation and function that facilitates adaptations to a limited oxygen supply. Moreover, data supporting the role of mitochondria as oxygen-sensing organelles, integrated into global cellular signal transduction are discussed.

Protection of oxidative preconditioning against apoptosis induced by H2O2 in PC12 cells: mechanisms via MMP, ROS, and Bcl-2

The present study is designed to investigate the effects of preconditioning with different doses of hydrogen peroxide (H2O2) on oxidative stress-induced apoptosis and the changes in mitochondrial membrane potential (MMP), intracellular reactive oxygen species (ROS) level, and expression of Bcl-2 during H2O2 preconditioning in rat pheochromocytoma (PC12) cells. It was shown that (1) H2O2 induced apoptosis in PC12 cells in a dose-dependent manner; (2) the preconditioning with 10 micromol L(-1) or 20 micromol L(-1) H2O2 can significantly protect PC12 cells against apoptosis induced by 50 or 100 micromol L(-1) H2O2, low (5 micromol L(-1)) and higher (30 micromol L(-1)) concentrations of H2O2 had no cytoprotections; (3) high concentration (100 micromol L(-1)) of H2O2 reduced MMP and expression of Bcl-2, and increased ROS level, but these effects were blocked by preconditioning with 10 micromol L(-1) H2O2; (4) the preconditioning with 10 micromol L(-1) H2O2 induced overexpression of Bcl-2. These results suggested that the preconditioning with low dose of H2O2 could protect the oxidative stress-induced PC12 cells apoptosis not only by preventing the reduction of MMP and expression of Bcl-2 as well as increase in ROS level, but also through overexpression of Bcl-2. It was indicated that overexpression of Bcl-2 may play a key role in the cytoprotection induced by preconditioning with low dose of H2O2 in PC12 cells.

Low dose (-)deprenyl is cytoprotective: it maintains mitochondrial membrane potential and eliminates oxygen radicals

Hypoxia leads to a collapse in mitochondrial transmembrane potential (Deltapsi(M)), a fall in the ATP/ADP ratio, and finally cell death. Since (-)deprenyl directly modulates Deltapsi(M) and production of reactive oxygen species (ROS) by altering the respiratory function of mitochondria, we were interested in the dose-response relations of these effects. The changes in JC-1 red/green signal ratios {mitochondrial transmembrane potential}, and the changes in the cerium staining (intracellular ROS) in hypoxic and normoxic PC12 cell cultures were measured following 1 h of Argon hypoxia and 24 h of re-oxygenation in the absence and in the presence of various concentrations of (-)deprenyl. Deltapsi(M) shifted to lower values following hypoxia/re-oxygenation and all cells had decreased and uniform Deltapsi(M) levels. The amount of ROS increased. Following 24 h of treatment with various concentrations of (-)deprenyl during the re-oxygenation period, survival increased, the Deltapsi(M) shift caused by oxygen deprivation was reversed and the peroxy radical levels decreased except for at 10(-3) M.