胡黄连苷Ⅱ对H2O2损伤L-02细胞的保护作用

目的:探讨胡黄连苷Ⅱ(picroside Ⅱ)对氧化应激损伤L-02细胞的保护作用.方法:H2O2损伤的L-02细胞作为氧化应激损伤模型,MTT法检测细胞增殖状况,膜联蛋白(Annexin-Ⅴ)和碘化丙啶(PI)染色流式细胞术(flow cytometry,FCM)检测细胞凋亡,罗丹明123染色FCM检测细胞线粒体膜电位(mitochondrial potential membrane,△Ψm),双氢罗丹明123染色FCM检测细胞内活性氧(reactive oxygen species,ROS)的含量.结果:0.6 mmol/L H2O2可诱导L-02细胞凋亡.细胞内ROS浓度增加,细胞线粒体跨膜电位明显下降.预先经过0.05,0.5,5 mmol/L浓度的胡黄连苷Ⅱ处理后,H2O2诱导的L-02细胞凋亡明显减少(30.8%±9.09%,10.2%±9.82%,8.2%±7.10%vs 42.8%±8.28%,均P＜0.01),同时明显减弱H2O2对细胞内ROS浓度和线粒体跨膜电位的影响.结论:胡黄连苷Ⅱ对氧化应激损伤L-02细胞具有保护作用,其机制可能与降低细胞内ROS含量,进而抑制△Ψm的降低有关.     

异丙酚对过氧化氢导致PC12细胞损伤的影响及机制

目的探讨异丙酚对过氧化氢(H2O2)导致的PC12细胞损伤的影响及机制。方法以H2O2损伤PC12细胞作为氧化应激细胞损伤模型,加入10μmol/L的异丙酚,采用MTT法分析细胞存活率,Hoechst33258染色检测细胞核形态变化,罗丹明123染色检测细胞线粒体膜电位变化,双氯荧光黄乙酸乙酯(DCF-DA)染色检测细胞内活性氧(ROS)的含量,免疫印迹法检测pAkt蛋白表达;在此基础上,探讨异丙酚保护作用机制时再加入LY294002,分别检测细胞上述指标及pAkt的表达。结果 H2O2可致PC12细胞存活率下降,凋亡增加,异丙酚(10μmol/L)可使PC12细胞的存活率增加,凋亡率降低;异丙酚可抑制H2O2导致ROS和膜电位变化;增加Akt磷酸化水平;PI3K抑制剂LY294002可拮抗异丙酚的保护作用,使细胞存活率降低、ROS生成增加、膜电位下降。结论异丙酚可减轻H2O2导致的PC12细胞损伤,这一作用是通过激活PI3K/Akt通路实现的。     

当归补血汤超滤物对大鼠心肌细胞线粒体凋亡通路的影响

目的探讨当归补血汤超滤膜提取物对大鼠心肌细胞线粒体凋亡通路的影响。方法原代培养Wistar大鼠乳鼠心肌细胞,阿霉素诱导心肌细胞凋亡。实验分正常组、阿霉素组(2.5 mg/L)、当归补血汤超滤膜提取物低、中、高剂量干预组(阿霉素造模前,预先给予含30,60,120 mg/L当归补血汤超滤膜提取物完全培养基培养2 h)。MTT法检测各组细胞存活率,荧光显微镜下各组细胞凋亡形态学观察,激光共聚焦技术测定各组心肌细胞线粒体膜电位水平,蛋白印迹法测定各组Bax,Bcl-2,Caspase-3蛋白表达水平。结果与正常组相比,阿霉素组心肌细胞存活数明显降低,可见细胞凋亡及线粒体膜电位降低;Bcl-2蛋白表达水平下降,Bax、Caspase-3表达水平升高(P0.05);与阿霉素组比较,当归补血汤超滤膜提取物干预组的心肌细胞存活数明显升高,凋亡细胞数目减少,线粒体膜电位升高,Bax、Caspase-3表达水平下调,Bcl-2蛋白表达水平上调(P0.05)。结论线粒体凋亡通路的激活是阿霉素诱导心肌细胞凋亡的机制之一,当归补血汤超滤膜提取物可调控该通路发挥心肌细胞保护作用。     

异丙酚对过氧化氢导致PCI2细胞损伤的影响及机制

目的探讨异丙酚对过氧化氢（H2O2）导致的PCI2细胞损伤的影响及机制。方法以H2O2损伤PCI2细胞作为氧化应激细胞损伤模型,加入10μmol／L的异丙酚,采用MTF法分析细胞存活率,Hoechst33258染色检测细胞核形态变化,罗丹明123染色检测细胞线粒体膜电位变化,双氯荧光黄乙酸乙酯（DCF—DA）染色检测细胞内活性氧（ROS）的含量,免疫印迹法检测pAkt蛋白表达;在此基础上,探讨异丙酚保护作用机制时再加入LY294002,分别检测细胞上述指标及pAkt的表达。结果H2O2可致PCI2细胞存活率下降,凋亡增加,异丙酚（10μmol／L）可使PCI2细胞的存活率增加,凋亡率降低;异丙酚可抑制H2O2导致ROS和膜电位变化;增加Akt磷酸化水平;P13K抑制剂LY294002可拮抗异丙酚的保护作用,使细胞存活率降低、ROS生成增加、膜电位下降。结论异丙酚可减轻H2O2导致的PCI2细胞损伤,这一作用是通过激活P13K／Akt通路实现的。     

血管紧张素(1-7)抑制异丙肾上腺素诱导的H9c2心肌细胞凋亡

目的观察血管紧张素(1-7)[Ang(1-7)]对心肌细胞凋亡的影响,探讨其可能的作用机制。方法应用异丙肾上腺素(ISO)处理H9c2心肌细胞12 h建立心肌细胞凋亡模型,Ang(1-7)或PI3K抑制剂LY294002与H9c2心肌细胞共处理12 h观察对ISO诱导的心肌细胞凋亡的影响。显微镜下观察H9c2心肌细胞生长情况,采用MTS法检测各组细胞的相对细胞活性,TUNEL法检测各组细胞凋亡率。JC-1荧光探针检测线粒体膜电位,Western blot检测cleaved Caspase-3、p-Akt及Akt蛋白的表达量。结果 ISO呈浓度依赖性抑制H9c2心肌细胞的相对细胞活性,Ang(1-7)呈浓度依赖性逆转ISO诱导的H9c2心肌细胞相对活性的降低;与对照组比较,ISO组细胞凋亡率及cleaved Caspase-3蛋白表达量显著增加,线粒体膜电位和p-Akt蛋白表达量显著降低;Ang(1-7)可抑制ISO诱导的H9c2心肌细胞凋亡率的增加,减少cleaved Caspase-3蛋白的表达,增加线粒体膜电位和p-Akt蛋白表达量。LY294002预处理后Ang(1-7)对ISO诱导的H9c2心肌细胞的保护作用明显减弱,表现为心肌细胞凋亡率及cleaved Caspase-3蛋白的表达量明显增加,p-Akt蛋白表达量减少。结论 ISO能诱导H9c2心肌细胞线粒体途径的细胞凋亡,而Ang(1-7)能抑制ISO诱导的线粒体途径的细胞凋亡。PI3K/Akt信号通路可能在Ang(1-7)抑制ISO诱导的H9c2心肌细胞凋亡中起到关键作用。     

sRAGE对缺氧/复氧大鼠心肌细胞线粒体膜电位的影响

目的观察可溶性糖基化终产物受体(sRAGE)对缺氧/复氧(H/R)大鼠心肌细胞线粒体凋亡途径的影响。方法取大鼠心肌细胞培养72 h,以缺氧3 h、复氧2 h复制H/R模型,实验分为4组:对照组、对照+sRAGE组、H/R组、H/R+sRAGE组。以荧光探针JC-1方法检测线粒体膜电位,酯化钙黄绿素和氯化钴共孵育测定线粒体通透性转换孔(mPTP)开放,Western blot方法检测心肌细胞凋亡。结果与对照组比较,H/R组mPTP开放增多,线粒体膜电位去极化程度增加,凋亡率升高(P均<0.05);与H/R组比较,H/R+sRAGE组mPTP开放减少,线粒体膜电位去极化程度减轻,凋亡率下降(P均<0.05)。结论 sRAGE可通过抑制线粒体凋亡途径,拮抗心肌H/R损伤。     

氧化应激对培养心肌细胞线粒体酶活性的影响

目的 :观察氧化应激对心肌细胞线粒体酶活性的影响和褪黑素的保护作用。方法 :胰酶消化法分离培养原代心肌细胞 ,随机分为 :H2 O2 处理组 （10 0μmol/ L ）和褪黑素 （MT）预处理组 （10 0μm ol/ L MT+10 0μm ol/ L H2 O2 ）。用 H2 O2 模拟心肌细胞的氧化应激 ,用四唑盐比色试验 （MTT法 ）检测 H2 O2 处理后不同时间点的线粒体酶活性 ;用台盼蓝排斥试验检测处理前和处理后 40 min细胞的存活率。结果 :H2 O2 处理组光密度 （OD490 ）逐渐降低 ,组内不同时间点差异显著 （P<0 .0 1） ;而 MT预处理组组内无差异 （P>0 .0 5 ） ;40 m in内两组细胞存活率均无变化。结论 :低浓度的 H2 O2 随着时间的延长可以使线粒体酶活性逐渐降低 ,而褪黑素能保护氧化应激中的心肌细胞。     

瘦素-p38MAPK通路介导高糖对H9c2心肌细胞的损伤

目的 探讨瘦素-p38丝裂原激活蛋白激酶（MAPK）通路在高糖损伤H9c2心肌细胞中的作用。方法 应用35 mmol/L葡萄糖处理H9c2心肌细胞以建立高糖损伤细胞模型。应用细胞计数试剂盒检测细胞存活率;双氯荧光素染色荧光显微镜照相测定胞内活性氧水平;Hoechst 33258核染色检测凋亡细胞形态与数量的改变;罗丹明123染色荧光显微镜照相测定线粒体膜电位;Western blot检测瘦素和p38MAPK蛋白的表达水平。结果 35 mmol/L葡萄糖处理H9c2心肌细胞明显促进瘦素的表达。在高糖处理H9c2心肌细胞前,应用50 μg/L瘦素拮抗剂预处理24 h明显抑制高糖对磷酸化p38MAPK表达的上调作用。瘦素拮抗剂预处理24 h或p38MAPK抑制剂（SB203580）预处理60 min均能抑制高糖对H9c2心肌细胞的损伤作用,使细胞存活率升高,凋亡细胞数量减少,活性氧生成及线粒体膜电位丢失减小。结论 瘦素-p38MAPK通路参与高糖对心肌细胞的损伤。     

虎杖苷通过激活Nrf2/HO-1信号抑制氧化应激诱导的心肌细胞损伤

目的研究过氧化氢(H2O2)诱导的H9c2细胞损伤模型中,虎杖苷对心肌细胞的保护作用及机制。方法建立H2O2诱导的H9c2细胞损伤模型,MTT检测细胞生存能力;Western印迹检测细胞蛋白表达;试剂盒检测细胞培养上清液中超氧化物歧化酶(SOD)及丙二醛(MDA)水平。结果MTT实验筛选药物剂量为100μmol/L;H2O2有效刺激剂量为100μmol/L;虎杖苷预处理抑制了H2O2诱导的细胞活性下降,抑制了H2O2诱导的细胞凋亡。虎杖苷促进了核因子E2相关因子(Nrf)2和血红素加氧酶(HO)-1蛋白的表达,降低了SOD的水平,同时使MDA水平升高。Nrf2抑制剂ML385与虎杖苷同时预处理后细胞凋亡得到抑制,同时Nrf2和HO-1蛋白的表达水平下降,SOD的水平升高而MDA水平下降。结论虎杖苷抑制H2O2诱导的H9c2细胞凋亡,其机制与激活Nrf2/HO-1信号通路有关。     

上调Yes相关蛋白对缺氧复氧心肌细胞损伤保护作用的实验研究

目的研究Yes相关蛋白(YAP)在缺氧复氧(H/R)心肌细胞损伤中的作用。方法用过表达YAP重组慢病毒感染心肌细胞,给予H/R处理,用real-time PCR和Western blot检测细胞中YAP表达情况。CCK8法测定增殖变化,二硝基苯肼显色法检测乳酸脱氢酶(LDH)漏出率,流式细胞术检测凋亡变化,Western blot检测活化型Caspase-3和Caspase-9蛋白水平,DCFH-DA法检测活性氧(ROS)水平,黄嘌呤氧化法检测超氧化物歧化酶(SOD)活性,JC-1法检测线粒体膜电位,Western blot法检测胞浆和线粒体中细胞色素C(Cytochrome C)蛋白水平。结果过表达YAP重组慢病毒感染可以提高H/R条件下心肌细胞中YAP表达水平。H/R处理后的心肌细胞增殖活性降低,LDH漏出率升高,细胞凋亡率升高,细胞中活化型Caspase-3和Caspase-9蛋白水平升高,ROS水平也升高,SOD活性降低,线粒体膜电位下降,胞浆中Cytochrome C蛋白水平升高,线粒体中Cytochrome C蛋白水平降低。上调YAP可以提高H/R条件下心肌细胞增殖活性,降低LDH漏出率,减少细胞凋亡,降低细胞中活化型Caspase-3和Caspase-9蛋白水平表达,提高SOD活性,减少细胞中ROS水平,提高线粒体膜电位,降低胞浆中Cytochrome C蛋白水平,提高线粒体中Cytochrome C蛋白水平。结论上调YAP减轻缺氧复氧心肌细胞损伤,减少细胞凋亡,作用机制可能与提高抗氧化酶活性,减少细胞内ROS水平,抑制线粒体凋亡途径有关。     

Cyclosporin A causes oxidative stress and mitochondrial dysfunction in renal tubular cells

Reactive oxygen species (ROS) have been implicated in cyclosporin A (CsA) nephrotoxicity. As mitochondria are one of the main sources of ROS in cells, we evaluated the role of CsA in mitochondrial structure and function in LLC-PK1 cells. We incubated cells with CsA 1 microM for 24 hours and studies were performed with flow citometry and confocal microscopy. We studied mitochondrial NAD(P)H content, superoxide anion (O2.-) production (MitoSOX Red), oxidation of cardiolipin of inner mitochondrial membrane (NAO) and mitochondrial membrane potential (DIOC2(3)). Also we analyzed the intracellular ROS synthesis (H2DCF-DA) and reduced glutation (GSH) of cells. Our results showed that CsA decreased NAD(P)H and membrane potential, and increased O2.- in mitochondria. CsA also provoked oxidation of cardiolipin. Furthermore, CsA increased intracellular ROS production and decreased GSH content. These results suggest that CsA has crucial effects in mitochondria. CsA modified mitochondrial physiology through the decrease of antioxidant mitochondrial compounds as NAD(P)H and the dissipation of mitochondrial membrane potential and increase of oxidants as O2.-. Also, CsA alters lipidic structure of inner mitochondrial membrane through the oxidation of cardiolipin. These effects trigger a chain of events that favour intracellular synthesis of ROS and depletion of GSH that can compromise cellular viability. Nephrotoxic cellular effects of CsA can be explained, at least in part, through its influence on mitochondrial functionalism.     

Role of mitochondrial dysfunction in hydrogen peroxide-induced apoptosis of intestinal epithelial cells

AIM: To study the role of mitochondrial dysfunction in hydrogen peroxide-induced apoptosis of intestinal epithelial cells.METHODS: Hydrogen peroxide-induced apoptosis of human intestinal epithelial cell line SW-480 was established. Cell apoptosis was determined by Annexin-V and PI doublestained flow cytometry and DNA gel electrophoresis.Morphological changes were examined with light and electron microscopy. For other observations, mitochondrial function,cytochrome c release, mitochondrial translocation and membrane potential were determined simultaneously.RESULTS: Percentage of apoptotic cells induced with 400μmol/L hydrogen peroxide increased significantly at 1 h or 3 h after stimulation and recovered rapidly. Meanwhile percentage of apoptotic cells induced with 4 mmol/L hydrogen peroxide increased with time. In accordance with these changes, we observed decreased mitochondrial function in 400μmol/L H2O2-stimualted cells at 1 h or 3 h and in 4 mmol/L H2O2-stimualted cells at times examined.Correspondingly, swelling cristae and vacuole-like mitochondria were noted. Release of cytochrome c,decreased mitochondrial membrane potential and mitochondrial translocation were also found to be the early signs of apoptosis.CONCLUSION: Dysfunctional mitochondria play a role in the apoptosis of SW-480 cell line inline induced by hydrogen peroxide.     

Diversity in mitochondrial function explains differences in vascular oxygen sensing

Renal arteries (RAs) dilate in response to hypoxia, whereas the pulmonary arteries (PAs) constrict. In the PA, O2 tension is detected by an unidentified redox sensor, which controls K+ channel function and thus smooth muscle cell (SMC) membrane potential and cytosolic calcium. Mitochondria are important regulators of cellular redox status and are candidate vascular O2 sensors. Mitochondria-derived activated oxygen species (AOS), like H2O2, can diffuse to the cytoplasm and cause vasodilatation by activating sarcolemmal K+ channels. We hypothesize that mitochondrial diversity between vascular beds explains the opposing responses to hypoxia in PAs versus RAs. The effects of hypoxia and proximal electron transport chain (pETC) inhibitors (rotenone and antimycin A) were compared in rat isolated arteries, vascular SMCs, and perfused organs. Hypoxia and pETC inhibitors decrease production of AOS and outward K+ current and constrict PAs while increasing AOS production and outward K+ current and dilating RAs. At baseline, lung mitochondria have lower respiratory rates and higher rates of AOS and H2O2 production. Similarly, production of AOS and H2O2 is greater in PA versus RA rings. SMC mitochondrial membrane potential is more depolarized in PAs versus RAs. These differences relate in part to the lower expression of proximal ETC components and greater expression of mitochondrial manganese superoxide dismutase in PAs versus RAs. Differential regulation of a tonically produced, mitochondria-derived, vasodilating factor, possibly H2O2, can explain the opposing effects of hypoxia on the PAs versus RAs. We conclude that the PA and RA have different mitochondria.     

Molecular mechanisms of angiotensin II-mediated mitochondrial dysfunction: linking mitochondrial oxidative damage and vascular endothelial dysfunction

Mitochondrial dysfunction is a prominent feature of most cardiovascular diseases. Angiotensin (Ang) II is an important stimulus for atherogenesis and hypertension; however, its effects on mitochondrial function remain unknown. We hypothesized that Ang II could induce mitochondrial oxidative damage that in turn might decrease endothelial nitric oxide (NO.) bioavailability and promote vascular oxidative stress. The effect of Ang II on mitochondrial ROS, mitochondrial respiration, membrane potential, glutathione, and endothelial NO. was studied in isolated mitochondria and intact bovine aortic endothelial cells using electron spin resonance, dihydroethidium high-performance liquid chromatography -based assay, Amplex Red and cationic dye fluorescence. Ang II significantly increased mitochondrial H2O2 production. This increase was blocked by preincubation of intact cells with apocynin (NADPH oxidase inhibitor), uric acid (scavenger of peroxynitrite), chelerythrine (protein kinase C inhibitor), N(G)-nitro-L-arginine methyl ester (nitric oxide synthase inhibitor), 5-hydroxydecanoate (mitochondrial ATP-sensitive potassium channels inhibitor), or glibenclamide. Depletion of p22(phox) subunit of NADPH oxidase with small interfering RNA also inhibited Ang II-mediated mitochondrial ROS production. Ang II depleted mitochondrial glutathione, increased state 4 and decreased state 3 respirations, and diminished mitochondrial respiratory control ratio. These responses were attenuated by apocynin, 5-hydroxydecanoate, and glibenclamide. In addition, 5-hydroxydecanoate prevented the Ang II-induced decrease in endothelial NO. and mitochondrial membrane potential. Therefore, Ang II induces mitochondrial dysfunction via a protein kinase C-dependent pathway by activating the endothelial cell NADPH oxidase and formation of peroxynitrite. Furthermore, mitochondrial dysfunction in response to Ang II modulates endothelial NO. and generation, which in turn has ramifications for development of endothelial dysfunction.     

Regulation of bcl-2 family proteins during development and in response to oxidative stress in cardiac myocytes: association with changes in mitochondrial membrane potential

Cardiac myocyte apoptosis is potentially important in many cardiac disorders. In other cells, Bcl-2 family proteins and mitochondrial dysfunction are probably key regulators of the apoptotic response. In the present study, we characterized the regulation of antiapoptotic (Bcl-2, Bcl-xL) and proapoptotic (Bad, Bax) Bcl-2 family proteins in the rat heart during development and in oxidative stress-induced apoptosis. Bcl-2 and Bcl-xL were expressed at high levels in the neonate, and their expression was sustained during development. In contrast, although Bad and Bax were present at high levels in neonatal hearts, they were barely detectable in adult hearts. We confirmed that H(2)O(2) induced cardiac myocyte cell death, stimulating poly(ADP-ribose) polymerase proteolysis (from 2 hours), caspase-3 proteolysis (from 2 hours), and DNA fragmentation (from 8 hours). In unstimulated neonatal cardiac myocytes, Bcl-2 and Bcl-xL were associated with the mitochondria, but Bad and Bax were predominantly present in a crude cytosolic fraction. Exposure of myocytes to H(2)O(2) stimulated rapid translocation of Bad (<5 minutes) to the mitochondria. This was followed by the subsequent degradation of Bad and Bcl-2 (from approximately 30 minutes). The levels of the mitochondrial membrane marker cytochrome oxidase remained unchanged. H(2)O(2) also induced translocation of cytochrome c from the mitochondria to the cytosol within 15 to 30 minutes, which was indicative of mitochondrial dysfunction. Myocytes exposed to H(2)O(2) showed an early loss of mitochondrial membrane potential (assessed by fluorescence-activated cell sorter analysis) from 15 to 30 minutes, which was partially restored by approximately 1 hour. However, a subsequent irreversible loss of mitochondrial membrane potential occurred that correlated with cell death. These data suggest that the regulation of Bcl-2 and mitochondrial function are important factors in oxidative stress-induced cardiac myocyte apoptosis.     

O2 sensing in the human ductus arteriosus: regulation of voltage-gated K+ channels in smooth muscle cells by a mitochondrial redox sensor

Functional closure of the human ductus arteriosus (DA) is initiated within minutes of birth by O2 constriction. It occurs by an incompletely understood mechanism that is intrinsic to the DA smooth muscle cell (DASMC). We hypothesized that O2 alters the function of an O2 sensor (the mitochondrial electron transport chain, ETC) thereby increasing production of a diffusible redox-mediator (H2O2), thus triggering an effector mechanism (inhibition of DASMC voltage-gated K+ channels, Kv). O2 constriction was evaluated in 26 human DAs (12 female, aged 9+/-2 days) studied in their normal hypoxic state or after normoxic tissue culture. In fresh, hypoxic DAs, 4-aminopyridine (4-AP), a Kv inhibitor, and O2 cause similar constriction and K+ current inhibition (I(K)). Tissue culture for 72 hours, particularly in normoxia, causes ionic remodeling, characterized by decreased O2 and 4-AP constriction in DA rings and reduced O2- and 4-AP-sensitive I(K) in DASMCs. Remodeled DAMSCs are depolarized and express less O2-sensitive channels (including Kv2.1, Kv1.5, Kv9.3, Kv4.3, and BK(Ca)). Kv2.1 adenoviral gene-transfer significantly reverses ionic remodeling, partially restoring both the electrophysiological and tone responses to 4-AP and O2. In fresh DASMCs, ETC inhibitors (rotenone and antimycin) mimic hypoxia, increasing I(K) and reversing constriction to O2, but not phenylephrine. O2 increases, whereas hypoxia and ETC inhibitors decrease H2O2 production by altering mitochondrial membrane potential (DeltaPsim). H2O2, like O2, inhibits I(K) and depolarizes DASMCs. We conclude that O2 controls human DA tone by modulating the function of the mitochondrial ETC thereby varying DeltaPsim and the production of H2O2, which regulates DASMC Kv channel activity and DA tone.     

Mitochondria are selective targets for the protective effects of heat shock against oxidative injury.

Heat shock (HS) proteins (HSPs) induce protection against a number of stresses distinct from HS, including reactive oxygen species. In the human premonocytic line U937, we investigated in whole cells the effects of preexposure to HS and exposure to hydrogen peroxide (H2O2) on mitochondrial membrane potential, mass, and ultrastructure. HS prevented H2O2-induced alterations in mitochondrial membrane potential and cristae formation while increasing expression of HSPs and the protein product of bcl-2. Protection correlated best with the expression of the 70-kDa HSP, hsp70. We propose that mitochondria represent a selective target for HS-mediated protection against oxidative injury.     

Hydrogen peroxide, potassium currents, and membrane potential in human endothelial cells

BACKGROUND: Hydrogen peroxide (H2O2) and reactive oxygen species are implicated in inflammation, ischemia-reperfusion injury, and atherosclerosis. The role of ion channels has not been previously explored. METHODS AND RESULTS: K+ currents and membrane potential were recorded in endothelial cells by voltage- and current-clamp techniques. H2O2 elicited both hyperpolarization and depolarization of the membrane potential in a concentration-dependent manner. Low H2O2 concentrations (0.01 to 0.25 micromol/L) inhibited the inward-rectifying K+ current (KIR). Whole-cell K+ current analysis revealed that H2O2 (1 mmol/L) applied to the bath solution increased the Ca2+-dependent K+ current (KCa) amplitude. H2O2 increased KCa current in outside-out patches in a Ca2+-free solution. When catalase (5000 micro/mL) was added to the bath solution, the outward-rectifying K+ current amplitude was restored. In contrast, superoxide dismutase (1000 u/mL) had only a small effect on the H2O2-induced K+ current changes. Next, we measured whole-cell K+ currents and redox potentials simultaneously with a novel redox potential-sensitive electrode. The H2O2-mediated KCa current increase was accompanied by a whole-cell redox potential decrease. CONCLUSIONS: H2O2 elicited both hyperpolarization and depolarization of the membrane potential through 2 different mechanisms. Low H2O2 concentrations inhibited inward-rectifying K+ currents, whereas higher H2O2 concentrations increased the amplitude of the outward K+ current. We suggest that reactive oxygen species generated locally increases the KCa current amplitude, whereas low H2O2 concentrations inhibit KIR via intracellular messengers.     

Visualization of the antioxidative effects of melatonin at the mitochondrial level during oxidative stress-induced apoptosis of rat brain astrocytes

Oxidative stress-induced mitochondrial dysfunction has been shown to play a crucial role in the pathogenesis of a wide range of diseases. Protecting mitochondrial function, therefore, is vital for cells to survive during these disease processes. In this study, we demonstrate that melatonin, a chief secretory product of the pineal gland, readily rescued mitochondria from oxidative stress-induced dysfunction and effectively prevented subsequent apoptotic events and death in rat brain astrocytes (RBA-1). The early protection provided by melatonin in mitochondria of intact living cells was investigated by the application of time-lapse conventional, confocal, and multiphoton fluorescent imaging microscopy coupled with noninvasive mitochondria-targeted fluorescent probes. In particular, we observed that melatonin effectively prevented exogenously applied H2O2-induced mitochondrial swelling in rat brain astrocytes at an early time point (within 10 min) and subsequently reduced apoptotic cell death (150 min later). Other early apoptotic events such as plasma membrane exposure of phosphatidyl serine and the positive YOPRO-1 staining of the early apoptotic nucleus were also prevented by melatonin. A mechanistic study at the mitochondrial level related to the early protection provided by melatonin revealed that the indole molecule significantly reduced mitochondrial reactive oxygen species (ROS) formation induced by H2O2 stress. Melatonin also prevented mitochondrial ROS generation caused by other organic hydroperoxides including tert-butyl hydroperoxide and cumene hydroperoxide. This antioxidative effect of melatonin is more potent than that of vitamin E. Via its ability to reduce mitochondrial ROS generation, melatonin prevented H2O2-induced mitochondrial calcium overload, mitochondrial membrane potential depolarization, and the opening of the mitochondrial permeability transition (MPT) pore. As a result, melatonin blocked MPT-dependent cytochrome c release, the downstream activation of caspase 3, the condensation and karyorrhexis of the nucleus and apoptotic fragmentation of nuclear DNA. Thus, the powerful mitochondrial protection provided by melatonin reinforces its therapeutic potential to combat a variety of oxidative stress-induced mitochondrial dysfunctions as well as mitochondria-mediated apoptosis in various diseases.     

Uncoupling protein-2 overexpression inhibits mitochondrial death pathway in cardiomyocytes

Uncoupling proteins (UCPs) are located in the mitochondrial inner membrane and partially dissipate the transmembrane proton electrochemical gradient. UCP2 is expressed in various human and rodent tissues, including the heart, where its functional role is unknown. In the present study, we tested the hypothesis that UCP2 overexpression could protect cardiomyocytes from oxidative stress-induced cell death by reducing reactive oxygen species (ROS) production in mitochondria. Using an adenoviral vector containing human UCP2, we investigated the effects of UCP2 overexpression on the mitochondrial death pathway induced by oxidative stress (100 micromol/L H2O2) in cultured neonatal cardiomyocytes. UCP2 overexpression significantly suppressed markers of cell death, including TUNEL positivity, phosphatidylserine exposure, propidium iodide uptake, and caspase-3 cleavage. Furthermore, UCP2 remarkably prevented the catastrophic loss of mitochondrial inner membrane potential induced by H2O2, which is a critical early event in cell death. Ca2+ overload and the production of ROS in mitochondria, both of which contribute to mitochondrial inner membrane potential loss, were dramatically attenuated by UCP2 overexpression. Thus, overexpression of UCP2 attenuates ROS generation and prevents mitochondrial Ca2+ overload, revealing a novel mechanism of cardioprotection.