Toxicity of cigarette smoke on isolated lung,heart, and brain mitochondria: induction of oxidative stress and cytochrome c release

Cigarette smoking is one of the main risk factors for premature human death which is associated with a variety of respiratory and vascular diseases, and cancer due to exposure to hundreds of toxicants. Rat mitochondria were obtained by differential ultracentrifugation and incubated with different concentrations (1%, 10%, or 100%) of standardized cigarette smoke extract (CSE). Our results showed that CSE induced a rise in mitochondrial reactive oxygen species (ROS) formation, lipid peroxidation, and mitochondrial membrane potential (MMP) collapse before mitochondrial swelling ensued in isolated pulmonary mitochondria. Disturbance in oxidative phosphorylation was also confirmed by decrease in ATP concentration in the CSE-treated mitochondria. In addition, collapse of MMP and mitochondrial swelling produced release of cytochrome c via outer membrane rupture or mitochondrial permeability transition (MPT) pore opening. Our results suggested that CSE-induced toxicity in lung tissue is the result of disruptive effect on mitochondrial respiratory chain that leads to ROS formation, lipid peroxidation, MMP decline, and cytochrome c expulsion which results in apoptosis signaling and cell loss.     

Toxicity of depleted uranium on isolated liver mitochondria: a revised mechanistic vision for justification of clinical complication of depleted uranium (DU) on liver

Depleted uranium (DU) is widely used in military anti-armor weapons. Recent evidence suggested that oxidative stress and mitochondrial dysfunction may contribute to DU-induced toxicity. However, the underlying mechanisms of DU toxicity in mitochondria are not well understood. In this study, liver mitochondria were obtained from Wistar rats treated with DU in the form of uranyl acetate (UA) (0.5, 1 or 2 mg/kg i.p.) using differential centrifugation. For in vitro experiments, control rat liver mitochondria were incubated with different concentrations of UA (50, 100 or 200 μM) for 1 hr. Mitochondrial reactive oxygen species (ROS) production, collapse of mitochondrial membrane potential, and mitochondrial swelling were examined by flow cytometry. Mitochondrial sources of ROS formation were determined using specific substrates and inhibitors. Extent of lipid peroxidation (LPO) and glutathione (GSH) oxidation, and also complex II and IV activities were detected via spectroscopy. Further, the concentration of ATP and ATP/ADP ratio was measured using luciferase enzyme and release of cytochrome c from mitochondria which was detected by ELISA kit. UA induced succinate-supported mitochondrial ROS production, elevated LPO levels, GSH oxidation, and mitochondrial complex II inhibition. UA also induced mitochondrial permeability transition and increase in cytochrome c release which subsequently disturbed oxidative phosphorylation and reduced the mitochondrial ATP concentration. Data suggest that mitochondrial oxidative stress and uncoupling of oxidative phosphorylation may play key roles in DU-induced hepatic toxicity.     

Vitamins E and C reduce oxidative stress and mitochondrial permeability transition caused by camptothecin – an in vitro study

Camptothecin (CPT), a broad spectrum antineoplastic agent, is known to induce oxidative stress and mitochondria are among the main sources of intracellular reactive oxygen species (ROS). We investigated the merit of vitamins E and C supplementation on CPT-induced mitochondrial alterations in vitro. Following treatment of isolated liver mitochondria with CPT, we assessed the mitochondrial membrane permeability transition (MPT), concentration of malondialdehyde, antioxidants and activities of the enzymes of the respiratory chain and Krebs cycle. Our results provide evidence that CPT caused mitochondrial swelling, increased lipid peroxidation and transition of mitochondrial permeability. The CPT lowered the levels of reduced mitochondrial thiols suggesting that thiol oxidation is the mechanism underlying CPT-induced MPT. Identical experiments were also performed after preincubating the mitochondria with vitamins E and C. It was found that vitamins E and C pretreatment inhibited the deleterious effects of CPT and loss of enzyme activity was restored by antioxidant supplementation. Our results suggest that the toxicity of CPT was mediated by an increase in ROS production by mitochondria. However, the addition of vitamins E or C ameliorated the oxidative stress. We propose that an attempt to counteract the deleterious consequences of chemotherapy with nutritional therapies may be a rational approach in superior patient care especially in a disease like cancer.     

Thallium(I) and thallium(III) induce apoptosis in isolated rat hepatocytes by alterations in mitochondrial function and generation of ROS

Environmental metal toxins, generated through diverse anthropogenic activities, constitute one of the major contaminants that have led to global dispersion of these toxic metals in the ecosystem. Thallium is one of these widely dispersed metals that produce severe adverse effects on human and biological systems. The influence of thallium(I) and thallium(III) on the early events that trigger apoptosis signaling were examined in freshly isolated rat hepatocytes. In addition, the role of oxidative stress, and mitochondria in the induction of apoptosis were also investigated. Incubation of thallium(I) and thallium(III) with isolated rat hepatocytes generated reactive oxygen species (ROS), collapse of mitochondrial membrane potential, activation of caspases cascade, and appearance of apoptosis phenotype. Mitochondrial permeability transition (MPT) pore sealing agents (cyclosporine A and carnitine) and ATP generators (L-glutamine, fructose, and xylitol) inhibited the activation of caspase-3 and apoptosis, indicating that both the cations activated apoptosis signaling via mitochondrial pathway. Pretreatment of hepatocytes with antioxidants (α-tocopherol or deferoxamine) also blocked caspase-3 activation induced by these cations, suggesting that oxidative stress may be directly involved in a mitochondrial MPT pore opening and activation of caspases cascade. These findings contribute to a better understanding of the mechanisms that mediate thallium-induced apoptosis in isolated rat hepatocytes.     

微囊藻毒素对束丝藻细胞生长和抗氧化系统的影响

为从活性氧(ROS)角度探讨微囊藻毒素(MC)导致藻类细胞死亡的机理及揭示藻细胞对MC诱发的氧化胁迫的响应机制,采用50和500μg·L-1的微囊藻毒素LR(MC-LR)处理束丝藻(Aphanizomenon sp. DC01)细胞,测定了细胞生长、细胞内活性氧(ROS)含量及抗氧化系统的变化.结果表明,50μg·L-1的MC-LR处理对藻细胞的生长无显著影响,而500μg·L-1的MC-LR处理可诱导藻细胞死亡.50μg·L-1的MC-LR处理的藻细胞ROS含量在处理第2d显著高于对照;但藻细胞能通过还原型谷胱甘肽(GSH)含量,超氧化物歧化酶(SOD)、谷胱甘肽过氧化物酶(GPX)活性改变修复氧化损伤,使ROS水平在处理第3d恢复到对照水平.500μg·L-1的MC-LR处理可显著降低藻细胞GSH含量和SOD与GPX活性,刺激藻细胞生成过量的ROS;ROS在毒素处理4d后突然暴发,过量的ROS引起膜质过氧化,并最终导致藻细胞死亡。     

Involvement of mitochondrial-mediated caspase-3 activation and lysosomal labilization in acrylamide-induced liver toxicity

Acrylamide (ACR) is a chemical frequently used in both industrial and synthetic processes and may be produced during food processing. ACR at very high concentrations is postulated to exert its toxicity through the stimulation of an oxidative stress. ACR in excessive doses induces the central nervous system, reproduction, and genetic toxicity. However, ACR effects on the liver, a major organ of drug metabolism, have not been adequately explored. In addition, the role of mitochondria in an ACR-mediated hepatotoxicity is still unclear. The aim of this study was to investigate the cytotoxic mechanisms attributed to ACR using isolated rat hepatocytes. Hepatocytes were isolated by the collagenase perfusion method and incubated with an EC50_2hr concentration of ACR for 3 hr. The EC50_{2 hr} of ACR on isolated rat hepatocytes was determined to be 1 mM. Based on our results, hepatocytes cytotoxicity of ACR (1 mM) was mediated by a reactive oxygen species formation and lipid peroxidation. Incubation of hepatocytes with ACR produced rapid hepatocyte glutathione depletion which is another marker of the cellular oxidative stress. ACR cytotoxicity was also associated with mitochondrial injury as evidenced by the decline of mitochondrial membrane potential and lysosomal membrane leakiness. Our results also showed that ACR induced caspase-3 activation, the final mediator of apoptosis signaling. These findings contribute to a better understanding underlying mechanisms involved in ACR hepatotoxicity originating from the oxidative stress and ending in mitochondrial/lysosomal damage and cell death signaling.     

Ameliorated effects of garlic (Allium sativum) on biomarkers of subchronic acrylamide hepatotoxicity and brain toxicity in rats

Acrylamide (ACR) exerts its toxicity through stimulation of the oxidative stress; yet, its effect on neurotransmitter catabolic enzymes has not been elucidated. We investigated the effects of ACR exposure on brain and hepatic tissues antioxidant enzymes activities and different markers such as, acetylcholinesterase (AChE), nitric oxide (NO), monoamine oxidase (MAO), and lipid profile, and to evaluate the protective effects of garlic against ACR toxicity. Male Sprague-Dawley rats were exposed to ACR (1 mg kg^?1 body weight) with or without diet containing 1.5% of garlic powder for 40 days. ACR administration showed a decrease in AChE activity associated with an increase in MAO activity in both brain and hepatic tissues. In addition, ACR administration increased the lipid peroxidation and NO levels of both tissues while decreased the activities of glutathione (GSH), superoxide dismutase, and glutathione-S-transferase (GST). On the other hand, the activities of glutathione peroxidase (GPx) and catalase activities increased as a consequence of GSH depletion after ACR exposure. Finally, ACR exposure increased the brain and liver lipid profile of cholesterol, triglycerides and total lipid, while phospholipids level was decreased. Coadministration of garlic powder with ACR significantly attenuated oxidative stress, MAO activity, and inflammation in brain and hepatic tissues but did not ameliorate AChE activity. In conclusion, our results emphasized the role of garlic as a potential adjuvant therapy to prevent ACR neurotoxicity and hepatotoxicity.     

Pre-administration of beta-carotene protects tissue glutathione and lipid peroxidation status following exposure to gamma radiation

The present study has been aimed to investigate the protective effect of beta-carotene against radiation-induced oxidative stress in mice tissues using lipid peroxidation and glutathione (GSH) as end points. Fourteen days oral priming administration of beta-carotene (35 mg/kg body weight) followed by an acute dose of gamma radiation (5 Gy) inhibited the augmented level of thiobarbituric acid reactive substance (TBARS) and a statistically significant protection against GSH depletion. Results evaluated from this study clearly indicate the antioxidative property of beta-carotene against gamma radiation, which is suggestive of free radical scavenging and singlet oxygen quenching.     

Studies on mercuric sulfide,a component of cinnabar,a Chinese herbal medicine,on celluar functions in mouse lung and fibroblasts

Although the cytotoxic effects of mercuric chloride (HgCl₂) and methylmercury chloride (MeHg) have been extensively studied, the insoluble mercuric sulfide (HgS) has been the subject of fewer studies. Since the traditional Chinese mineral drug, cinnabar (containing >95% HgS) continues to be used as an ingredient for infant sedation, the pharmacological and toxicological effects of HgS need to be clarified. In previous experiments, HgS and cinnabar were shown to be absorbed from the gastrointestinal tract (GIT) and distributed in various tissues including the lungs. Thus, a preliminarily examination of whether HgS might exert any oxidative stress on a mouse lung was undertaken. HgS reduced GSH content and increased lipid peroxidation in the lung. Further studies on the cytotoxic effects and the possible mechanisms of action of HgS were compared with HgCl₂ and MeHg in cultured lung fibroblast V₇₉ cells. The results showed that HgS produced cytotoxicity at a concentration (400–1200 µM)in a dependent manner with IC₅₀ of 795.6 µM, as compared to HgCl₂ and MeHg, 8.1 µM and 5.9 µM, respectively. In addition, the HgS induced the phenomena of DNA fragmentation, increasing reactive oxygen species (ROS) and decreasing mitochondrial membrane potential, accompanied by decreased levels of intracellular ATP and GSH and higher lipid peroxidation levels, similar to HgCl₂ and MeHg, but with different toxicokinetic properties. These findings provide evidence for understanding the mechanisms underlying the toxic effects of HgS.     

Comparison of cellular and molecular cytotoxic mechanisms of Cochlodinium polykrikoides in isolated trout and rat hepatocytes

Harmful algal blooms produced by the marine ichthyotoxic dinoflagellate Cochlodinium polykrikoides are responsible for mass mortalities of wild and farmed fish globally. This study compared the cytotoxic mechanisms of C. polykrikoides total extract on both trout and rat liver hepatocytes. Trout hepatocytes were more sensitive than rat hepatocytes against C. polykrikoides extract. The effective concentration 50 after 3 hour incubation (EC50_3hr) concentrations found for C. polykrikoides extract in trout and rat hepatocytes (i.e., 50% membrane lysis in 3 hr) were Eq. 1 cell/ml and Eq. 240 cell/ml, respectively. C. polykrikoides extract exposure in both isolated trout and rat hepatocytes resulted in membrane lysis, reactive oxygen species formation, glutathione depletion, collapse of mitochondrial membrane potential, ATP depletion, increase in adenosine diphosphate (ADP)/adenosine triphosphate (ATP) ratio, cytochrome c release into the hepatocyte cytosol, and activation of caspases cascade. Trout hepatocyte toxicity was also associated with lysosomal membrane injury. Mitochondrial permeability transition in both trout and rat hepatocytes produced cytochrome c release from the mitochondrial intramembrane space into the cytosol. Thus, the cytochrome c release triggered activation of caspase-3 and apoptosis. Finally, data demonstrated that C. polykrikoides extract may induce more apoptotic phenotype in rat than trout hepatocytes, which in the latter favored predominantly necrotic mode of cell death.     

Fluoride induces DNA damage and cytotoxicity in human hepatocellular carcinoma cells

Humans are primarily exposed to fluoride (Fl), a widespread environmental pollutant, via contaminated drinking water and foodstuffs. The aim of this study was to examine whether sodium fluoride (NaF) exerted cytotoxic effects in human hepatocarcinoma (HepG2) cells. HepG2 cells were incubated with different concentrations of NaF and reactive oxygen species (ROS) levels, cell cycle, apoptosis, and DNA damage determined. Concentration-dependent studies showed that exposure to HepG2 cells with different concentrations of NaF for 24 hr significantly decreased cell viability and intracellular antioxidant capacity. Furthermore, NaF exposure increased lipid peroxidation levels and accumulation of intracellular ROS; and lowered antioxidant glutathione concentrations. In addition to oxidative impairments, NaF treatment enhanced HepG2 cell death via apoptotic pathway as evidenced by DNA fragmentation and cell cycle arrest. Sodium fluoride treatment unregulated p53 level, and Bax and Bcl2 expression. Diminished cell viability and changes in cell cycle accompanied a rise in p53 expression.     

蒽对二种海洋微藻抗氧化系统的影响

研究了多环芳烃（PAHs)－蒽对2种海洋微藻抗氧化系统的影响。结果表明,随着蒽浓度的增加,小新月菱形藻和亚心形扁藻的非酶性系统中的类胡萝卜素（CAR）和还原型谷胱甘肽（GSH）含量下降,酶性系统中的超氧化物歧化酶（SOD）和过氧化氢酶（CAT）活性下降,当加入抗氧化剂GSH时,蒽对两种海洋微藻的伤害作得以缓解,说明,蒽使海洋微藻的抗氧化系统破坏,损及体内活性氧化作用,对微藻的膜系统产生伤害。图6参12     

Toxicity of 4-methylimidazole on isolated brain mitochondria: using both in vivo and in vitro methods

4-methylimidazole (4MI) is a compound widely used in various industrial and consumer applications. The most important sources of exposure include chemical caramel coloring, ammoniated molasses, dyes and pigments, rube, cleaning and agricultural chemicals. Toxicity attributed to 4MI in foods has recently become a focus of research. Recent studies showed that 4MI induced adverse changes in various target tissues. Brain is known to be a target organ for 4MI-induced toxicity but its cytotoxic mechanisms have not yet been elucidated. In this study, experiments were divided into two parts: (1) using in vivo methodology, doses of 4MI at 100, 200, or 300 mg/kg were administered orally to mice daily for 14 to obtain brain mitochondria; and (2) utilizing in vitro methodology, brain mitochondria were incubated with 4MI at 400, 800, or 1600 μM concentrations. Subsequently, the neurotoxicity of 4MI was assessed using mitochondrial dysfunction tests, including reactive oxygen species (ROS) formation, mitochondrial membrane potential (MMP) collapse, mitochondrial swelling, and cytochrome c release. Our results from both in vivo and in vitro experiments on isolated brain mitochondria showed a significant decrease in complex II activity and also marked elevation in the ROS formation, MMP collapse, mitochondrial swelling, and enhanced release of cytochrome c. Data indicated that 4MI induced neurotoxicity through the impairment of electron transfer chain especially at complex II and elevated ROS formation leading to subsequent oxidative stress events including mitochondrial membrane depolarization, mitochondrial swelling, and release of cytochrome c, which is the starting point of mitochondrial-mediated apoptosis signaling and neurodegeneration.     

Induction of apoptosis and cytokine markers in colon cancer cells by magnesium oxide (MgO) nanoparticles

Magnesium oxide nanoparticles (MgONP) are predominantly utilized in industrial products. This study was undertaken to elucidate the mechanisms underlying toxic effect of MgONP in human colon cancer (HT 29) cells over 48 hr period. Cytotoxicity was evaluated by using MTT and neutral red uptake assays. Data demonstrated that MgONP reduced cell viability in concentration- and time-dependent manner. MgONP induced oxidative stress by decreasing glutathione (GSH) concentrations and elevation of reactive oxygen species (ROS) and lipid peroxidation levels. Increased caspase-3 enzyme activity and greater condensed, damaged chromosome was observed following MgONP exposure in HT 29 cells. The level of interleukin-4 (IL-4), tumor necrosis factor (TNF-α), and DNA fragmentation were significantly higher in MgONP incubated cells. The results showed that MgONP-induced toxicity in HT 29 cells may be mediated through oxidative stress.     

Direct toxicity of amyloid beta peptide on rat brain mitochondria: preventive role of Mangifera indica and Juglans regia

Role of mitochondrial dysfunction and oxidative stress has been well documented in various cognitive-related disorders such as Alzheimer's disease (AD). Evidence indicates that Aß formation impairs mitochondrial function and that mitochondrial dysfunction is an early event in the pathogenesis of AD. The present study was, therefore, designed to investigate the direct toxicity of Aß peptide on isolated mitochondria obtained from rat brain. Various mitochondrial toxicity/integrity parameters such as succinate dehydrogenase activity, reactive oxygen species (ROS) formation, mitochondrial membrane potential collapse (MMP), mitochondrial swelling, and cytochrome c release were measured following the addition of Aß peptide on isolated mitochondria and then, mitoprotective effect of aqueous extracts of Mangifera indica and Juglans regia against mitochondrial toxicity endpoints parameters induced by Aß peptide were assessed. Our results showed that exposure to Aß peptide (30 nM) in isolated brain mitochondria induced mitochondrial ROS formation, MMP collapse, mitochondrial swelling, and cytochrome c release which is the starting point of apoptosis signaling. All these mitochondrial toxic endpoints induced by Aß peptide inhibited by aqueous extracts of Mangifera indica (100–400 µg/ml) and Juglans regia (200–400 µg/ml). To our knowledge, this is one of the first apparent studies to claim directly targeting of brain mitochondria and induction of apoptosis by Aß peptide as a new hypothesis for etiology of AD and other related neurodegenerative diseases as well as mitopreventive role of common antioxidant nutritional products including walnut and mango.     

活性氧介导砷诱导的蚕豆保卫细胞死亡

采用蚕豆(Vicia fabaL.)表皮条生物法,研究砷的细胞毒性作用机制。结果发现,一定浓度的NaAsO2可使气孔保卫细胞活性降低,部分细胞死亡,细胞死亡率呈浓度依赖性增高;砷处理组保卫细胞内活性氧(reactive oxygen species,ROS)水平升高。抗氧化剂抗坏血酸和过氧化氢酶及Ca2+特异性螯合剂EGTA、Ca2+通道抑制剂LaC13与NaAsO2共同作用时,砷诱发的细胞死亡被显著抑制;MAPK激酶抑制剂PD98059亦能有效阻止NaAsO2诱发的细胞死亡。研究结果表明,砷胁迫引起的胞内ROS合成增加可能通过Ca2+信号途径介导了保卫细胞的死亡过程,MAPK途径参与了砷诱导的细胞死亡。     

In vitro effects of metal ions on lipid peroxidation induced by alcohol in mice liver homogenate

The study is aimed to estimate the effect of different heavy metals such as Hg2+, Cd2+, Mn2+, Cr3+, Ni2+, Se2O3(2-), As2O3 water solution and combined effects of Hg2+, Mn2+, Cr3+ on lipid peroxidation in mice liver homogenate in vitro. Lipid peroxidation was determined as thiobarbituric acid-reacting materials (TBA). We select five different concentrations of selected ions for experiments. Correlations used to identify the concentration of ions associated with lipid peroxidation. The rate of lipid peroxide formation in mice liver homogenate increased with the gradual addition of alcohol. When alcohol dose was up to 0.5 ml, the rate of lipid peroxide formation was greatest. At tested concentrations, the effects of metal ions on lipid peroxidation induced by alcohol were classified into three groups, and are as follows: (1) simulative, Hg2+. (2) inhibitory, Mn2+, Cr3+, Ni2+, Se2O3(2-). (3) ambiguous, Cd2+, As2O3 water solution. When Hg2+, Mn2+ and Cr3+ were added to the mice liver homogenate with alcohol at the same time, Hg2+, Mn2+ were the main agents for the rate of alcohol induced lipid peroxidation. The simulative effect of Hg2+ on lipid peroxidation induced by alcohol indicate that alcohol-drinkers will have further health risk when they are exposed in polluted regions than others, and Mn2+, Cr3+, Ni2+, Se2O3(2-) may act as free radical scavengers and preventive remedy for alcoholism in part. Furthermore, analysis of combined effect of Hg2+Mn2+ and Cr3+ provide us a new way to estimate the combined effect of multi-materials.     

活性氧和钙信号参与铅对酵母细胞的毒性作用

以模式生物酵母菌为材料,研究铅对细胞的毒性效应,探讨胞内活性氧(ROS)和Ca~(2+)在铅诱导细胞死亡中的作用。结果显示,浓度为5~100 mg·L~(-1)的硝酸铅可降低酵母细胞活性,诱导酵母细胞死亡,随着铅浓度的提高和作用时间的延长,细胞死亡率增高。在铅处理组酵母细胞中,ROS和Ca~(2+)水平显著升高,线粒体膜电位明显下降;用1 mmol·L~(-1)的外源抗坏血酸(AsA)能降低铅引发的酵母细胞死亡,0.5 mmol·L~(-1)的钙离子螯合剂乙二醇双四乙酸(EGTA)或0.1 mmol·L~(-1)的质膜Ca~(2+)通道特异性抑制剂氯化镧(LaCl_3)亦可明显抑制铅引起的酵母细胞死亡。研究结果表明,铅诱发的酵母细胞死亡与处理组胞内ROS和Ca~(2+)升高有关,高浓度的Ca~(2+)可能通过诱导线粒体膜通透性转变孔道开放,或者高水平ROS可能损伤线粒体膜,致线粒体膜电位下降,继而激活相关下游信号导致细胞死亡。     

ROS介导的氧化应激在INH诱导的细胞毒性中的作用及槲皮素的干预

为探讨ROS介导的氧化应激在异烟肼(INH)诱导L-02细胞毒性中的作用及槲皮素的干预作用,建立体外培养INH诱导L-02细胞氧化损伤模型,实验分为对照组(A)、INH组(B)、槲皮素低剂量组(C)及槲皮素高剂量组(D)。采用生化分析法检测L-02细胞培养液中天冬氨酸氨基转移酶(AST)和丙氨酸氨基转移酶(ALT)的活性;利用荧光探针检测L-02细胞线粒体内活性氧(ROS)水平;应用比色法检测L-02细胞内丙二醛(MDA)、谷胱甘肽(GSH)的含量以及主要抗氧化物酶的活性。结果表明,与对照组相比,INH能显著增加L-02细胞培养液中AST和ALT的活性、细胞线粒体内ROS水平及细胞内MDA的含量(P0.01),并显著减少L-02细胞内GSH的含量及超氧化物歧化酶(SOD)、谷胱甘肽过氧化物酶(GSH-Px)的活性(P0.01)。与INH组比较,槲皮素低剂量组L-02细胞培养液中AST的活性、线粒体内ROS水平及细胞内MDA的含量明显降低(P0.05),而细胞内SOD的活性明显增加(P0.05);高剂量槲皮素能显著降低L-02细胞培养液中AST和ALT的活性、细胞线粒体内ROS水平及细胞内MDA的含量(P0.01),并能显著增高L-02细胞内GSH的含量和主要抗氧化物酶的活性(P0.01)。与槲皮素低剂量组相比,槲皮素高剂量组的保护效应更明显(P0.05)。可见,ROS介导的氧化应激在INH诱导的L-02细胞毒性中发挥了重要作用,且槲皮素对INH诱导的L-02细胞氧化损伤具有保护作用。     

Mechanism of toxicity of ionic copper and copper complexes to algae

The mechanism of toxicity of ionic copper and copper complexes to growth, photosynthesis, respiration, ATP levels and mitochondrial electron-transport chain-activity in two marine diatoms, Nitzschia closterium (Ehrenberg) W. Smith (Hasle, 1964) and Asterionella glacialis Castracane, and one freshwater green alga, Chlorella pyrenoidosa Chick was investigated. Copper ions depressed both cell division and photosynthesis in A. glacialis and C. pyrenoidosa, whereas ionic copper concentrations which were inhibitory to cell division in N. closterium had no effect on photosynthesis, respiration, ATP production, electron transport or membrane ultrastructure. This suggests that in N. closterium, copper does not act on the chloroplast, the mitochondrion, or the cell membrane, since if it did, the above parameters should be affected. Copper-ethylxanthogenate was exceptional amongst the copper complexes in that it stimulated respiration, mitochondrial electrontransport and ATP formation in N. closterium under conditions of strongly inhibited cell division and slightly stimulated photosynthesis. Ionic copper toxicity may result from an intracellular reaction between copper and reduced glutathione (GSH), leading to a lowering of the GSH:GSSG ratio and suppression of mitosis. In addition, copper inhibits the enzyme catalase and reduces cell defence mechanisms against H₂O₂ and oxygen-free radicals. Lipid-soluble copper complexes are more toxic than ionic copper because both the metal and the ligand are introduced into the cell. Toxicity of ionic copper is ameliorated by trivalent metal ions in the growth medium, including those of Mn, Co, Al, Fe and Cr which form a layer of metal (III) hydroxide around the algal cell, adsorb copper and reduce its penetration into the cell. The degree of insolubility of the metal (III) hydroxide is related to its ability to protect against copper toxicity. In addition, manganese and cobalt catalytically scavenge damaging H₂O₂ and superoxide radicals, respectively, produced by the cell.