Protective effect of ursodeoxycholic acid on liver mitochondrial function in rats with alloxan-induced diabetes: link with oxidative stress

We investigated the effects of ursodeoxycholic acid (UDCA) on mitochondrial functions and oxidative stress and evaluated their relationships in the livers of rats with alloxan-induced diabetes. Diabetes was induced in male Wistar rats by a single alloxan injection (150 mg kg^− 1 b.w., i.p.). UDCA (40 mg kg^− 1 b.w., i.g., 30 days) was administered from the 5th day after the alloxan treatment. Mitochondrial functions were evaluated by oxygen consumption with Clark oxygen electrode using succinate, pyruvate + malate or palmitoyl carnitine as substrates and by determination of succinate dehydrogenase and NADH dehydrogenase activities. Liver mitochondria were used to measure chemiluminiscence enhanced by luminol and lucigenin, reduced liver glutathione and the end-products of lipid peroxidation. The activities of both NADH dehydrogenase and succinate dehydrogenase as well as the respiratory control (RC) value with all the substrates and the ADP/O ratio with pyruvate + malate and succinate as substrates were significantly decreased in diabetic rats. UDCA developed the beneficial effect on the mitochondrial respiration and oxidative phosphorylation parameters in alloxan-treated rats, whereas the activities of mitochondrial enzymes were increased insignificantly after the administration of UDCA. The contents of polar carbonyls and MDA as well as the chemiluminescence with luminol were elevated in liver mitochondria of diabetic rats. The treatment with UDCA normalized all the above parameters measured except the MDA content. UDCA administration prevents mitochondrial dysfunction in rats treated with alloxan and this process is closely connected with inhibition of oxidative stress by this compound.     

金雀异黄素对大鼠氧化应激损伤的保护作用研究

目的观察金雀异黄素(又称染料木黄酮,genistein,Gen)对β淀粉样蛋白(Aβ)致大鼠氧化应激损伤的保护作用。方法 30只健康雄性SD大鼠随机分为假手术组、模型组和Gen干预组,每组10只。Gen组灌胃剂量为30 mg/(kg.d),假手术组和模型组灌胃等量的0.5%羧甲基纤维素钠。连续灌胃14 d后,模型组和Gen组大鼠双侧海马CA1区注射Aβ25-35,假手术组注射等量生理盐水,于术后7 d,生物化学方法检测脑组织中SOD、GSH-Px、MDA的活性或含量,HE染色观察大鼠海马的形态学改变。结果 (1)与假手术组比较,模型组脑组织SOD及GSH-Px活力明显降低,MDA含量明显升高(P0.01),而Gen组脑组织SOD及GSH-Px活力较模型组升高,MDA含量较模型组降低(P0.05)。(2)假手术组HE染色可见大鼠海马锥体细胞排列整齐、均匀,细胞结构完整,形态正常;模型组可见海马锥体细胞脱失、排列紊乱,结构不清,部分胞核固缩、深染;Gen组海马锥体细胞排列较整齐、均匀,结构尚清晰,形态基本正常。结论 Gen能保护海马神经细胞免受Aβ的损伤,这种作用可能与改善机体氧化还原状态,提高抗氧化水平有关。     

Protective effects of ascorbic acid on hepatotoxicity and oxidative stress caused by carbon tetrachloride in the liver of Wistar rats

This study was planned to investigate the protective effect of l (+)‐ascorbic acid (Vit C) on CCl₄‐induced hepatotoxicity and oxidative stress in the liver of Wistar rats (Rattus Norvegicus, strain Wistar). Twenty‐four adult male Wistar rats were fed with standard rat chow diet for 10 days and randomly were divided into four groups of six each as follows: (1) control, (2) CCl₄, (3) “CCl₄ + Vit C”, (4) Vit C groups. CCl₄ was applied to rats belonging to CCl₄ and “CCl₄ + Vit C” groups subcutaneously at 1 mg kg^?1 dose CCl₄ for 3 days. Vit C applied to “CCl₄ + Vit C” and “Vit C” group rats intraperitoneally at 300 mg kg^?1 dose for 3 days. All rats were sacrificed and livers were quickly removed on the fourth day of the experiment. MDA, total glutathione (T.GSH) levels and superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH‐PX) activities were measured in the liver of all groups of rats and also serum alanine amino transferase (ALT) and aspartate amino transferase (AST) activities were detected to determine liver functions in all groups of rats. Histopathological changes were evaluated by light and transmission electron microscopes. In “CCl₄ + Vit C” group, MDA level was significantly decreased (p < 0.05) and SOD, CAT, GSH‐PX activities were significantly increased (p < 0.005, 0.01, 0.05) respectively, T.GSH level was significantly increased (p < 0.005) and serum ALT and AST activities were significantly decreased (p < 0.01, 0.05), respectively, when compared with CCl₄ group. These results show that Vit C has a highly protective effect on hepatotoxicity and oxidative stress caused by CCl₄. Copyright © 2009 John Wiley & Sons, Ltd.     

Oxidative stress in mouse liver caused by dietary amino acid deprivation: protective effect of methionine

The aim of this work was to evaluate the effects of a diet depleted of amino acids (protein-free diet, or PFD), as well as the supplementation with methionine (PFD+Met), on the antioxidant status of the female mouse liver. With this purpose, cytosolic protein spots from two-dimensional non-equilibrium pH gel electrophoresis were identified by several procedures, such as mass spectrometry, Western blot, gel matching and enzymatic activity. PFD decreased the contents of catalase (CAT), peroxiredoxin I (Prx-I), and glutathione peroxidase (GPx) by 67%, 37% and 45%, respectively. Gene expression analyses showed that PFD caused a decrease in CAT (−20%) and GPx (−30%) mRNA levels but did not change that of Prx-I. It was also found that, when compared to a normal diet, PFD increased the liver contents of both reactive oxygen species (+50%) and oxidized protein (+88%) and decreased that of glutathione (−45%). Supplementation of PFD with Met prevented these latter effects to varying degrees, whereas CAT, Prx-I and GPx mRNA levels resulted unmodified. Present results suggest that dietary amino acid deprivation deranges the liver antioxidant defences, and this can be, in part, overcome by supplementation with Met.     

Time-dependent oxidative stress caused by benznidazole

Abstract

Benznidazole (BZN) is a nitroimidazole derivative which has a notable trypanocide activity, and it is the only drug used in Brazil and Argentina for the treatment of Chagas' disease. The drug in current use is thought to act, at least in part, by inducing oxidative stress within the parasite. Imidazolic compounds are involved in the production of reactive oxygen species (ROS). In order to evaluate the effect of BZN on ROS production and on the antioxidant status of the host, male rats were treated for different periods of time (2, 4, 6, 10 and 30 days) with 40 mg BZN/kg body weight. After treatment, biomarkers of oxidative stress such as the activities of catalase (CAT), superoxide dismutase (SOD), glutathione-S-transferase (GST) and glutathione reductase (GR), and also thiobarbituric acid reactive species (TBARS), reduced glutathione (GSH), total glutathione (TG) and oxidized glutathione (GSSG) concentrations, were measured in crude hepatic homogenates. Our results revealed that BZN is able to cause tissue damage as shown by increased TBARS content, inhibition of some antioxidants and induction of other antioxidants in a concentration- and time-dependent manner. The tissue damage measured as TBARS increased up to the 10th day of treatment. GST activity was inhibited during the BZN treatment. On the other hand, CAT and GR showed similar increased activities at the beginning, followed by decreased activities at the end of the treatment. After 30 days of treatment, GR activity remained low while CAT activity was high, compared to controls. The SOD activities remained unchanged throughout the experimental period. GSH showed lower values at the beginning of BZN treatment but the hepatic concentrations were enhanced at the end of the experimental period. Total glutathione showed a similar profile, and oxidized glutathione showed higher values in rats treated with BZN. In conclusion, these results indicate that, at therapeutic doses, BZN treatment elicits an oxidative stress in rat hepatocytes.     

Time-dependent oxidative stress caused by benznidazole

Benznidazole (BZN) is a nitroimidazole derivative which has a notable trypanocide activity, and it is the only drug used in Brazil and Argentina for the treatment of Chagas' disease. The drug in current use is thought to act, at least in part, by inducing oxidative stress within the parasite. Imidazolic compounds are involved in the production of reactive oxygen species (ROS). In order to evaluate the effect of BZN on ROS production and on the antioxidant status of the host, male rats were treated for different periods of time (2, 4, 6, 10 and 30 days) with 40 mg BZN/kg body weight. After treatment, biomarkers of oxidative stress such as the activities of catalase (CAT), superoxide dismutase (SOD), glutathione-S-transferase (GST) and glutathione reductase (GR), and also thiobarbituric acid reactive species (TBARS), reduced glutathione (GSH), total glutathione (TG) and oxidized glutathione (GSSG) concentrations, were measured in crude hepatic homogenates. Our results revealed that BZN is able to cause tissue damage as shown by increased TBARS content, inhibition of some antioxidants and induction of other antioxidants in a concentration- and time-dependent manner. The tissue damage measured as TBARS increased up to the 10th day of treatment. GST activity was inhibited during the BZN treatment. On the other hand, CAT and GR showed similar increased activities at the beginning, followed by decreased activities at the end of the treatment. After 30 days of treatment, GR activity remained low while CAT activity was high, compared to controls. The SOD activities remained unchanged throughout the experimental period. GSH showed lower values at the beginning of BZN treatment but the hepatic concentrations were enhanced at the end of the experimental period. Total glutathione showed a similar profile, and oxidized glutathione showed higher values in rats treated with BZN. In conclusion, these results indicate that, at therapeutic doses, BZN treatment elicits an oxidative stress in rat hepatocytes.     

Development of oxidative stress and cell damage in the liver of rats with water-immersion restraint stress

We examined how oxidative stress and cell damage develop in the liver of rats subjected to water-immersion stress (WIRS). In rats subjected to WIRS for 1.5, 3 or 6 h, serum alanine aminotransferase and aspartate aminotransferase activities increased time-dependently. In the liver tissue, vacuolization and apoptosis occurred at 1.5 h of WIRS and vacuolization further developed without further appearance of apoptosis at 3 h or 6 h. Serum lipid peroxide (LPO) and NOx (nitrite/nitrate) concentrations increased at 3 h of WIRS and these increases were enhanced at 6 h. In liver tissue, increases in LPO and NOx concentrations and myeloperoxidase activity and decreases in ascorbic acid and reduced glutathione concentrations and superoxide dismutase activity occurred at 3 h of WIRS and these changes were enhanced at 6 h, although vitamin E concentration and xanthine oxidase activity were unchanged. These results indicate that oxidative stress in the liver of rats with WIRS develops after the appearance of cell damage in the tissue, and suggests that oxidative stress is caused through disruption of the antioxidant defense system and increases in NO generation and neutrophil infiltration in the liver, which may contribute to the progression of cell damage in the tissue.     

Causal role of oxidative stress in liver preconditioning by thyroid hormone in rats

Hepatic ischemia-reperfusion (IR) injury, a major clinical drawback during surgery, is abolished by L-3,3',5-triiodothyronine (T(3)) administration. Considering that the triggering mechanisms are unknown, the aim of this study is to assess the role of oxidative stress in T(3) preconditioning using N-acetylcysteine (NAC) before T(3) administration. Male Sprague-Dawley rats given a single dose of 0.1 mg of T(3)/kg were subjected to 1 h ischemia followed by 20 h reperfusion, in groups of animals pretreated with 0.5 g of NAC/kg 0.5 h before T(3) or with the respective control vehicles. At the end of the reperfusion period, blood and liver samples were taken for analysis of serum aspartate aminotransferase (AST) and hepatic histology, glutathione (GSH) and protein carbonyl contents, and nuclear factor-kappaB (NF-kappaB) and activating protein 1 (AP-1) DNA binding. The IR protocol used led to a 4.5-fold increase in serum AST levels and drastic changes in liver histology, with significant GSH depletion and enhancement of protein carbonyl levels and of the protein carbonyl/GSH content ratio, whereas NF-kappaB and AP-1 DNA binding was decreased and enhanced, respectively. In a time window of 48 h, T(3) exerted protection against hepatic IR injury, with 88% reduction in the protein carbonyl/GSH ratio and normalization of NF-kappaB and AP-1 DNA binding, changes that were suppressed by NAC administration before T(3). Data presented suggest that a transient increase in the oxidative stress status of the liver is an important trigger for T(3) preconditioning, evidenced in a warm IR injury model through antioxidant intervention.     

Proteinase-proteinase inhibitor complex in rats under oxidative stress caused by administration of cobalt chloride

Mechanisms of proteinase-inhibitor proteinase system response was estimated following of cobalt chloride injection. The increase proteinase activity, which led to significant decrease of alpha-2-macroglobulin (alpha-2-MG) level was established that indicated to the removal of the proteinase in complex with alpha-2-MG from the organism. Increase of alpha-1-proteinase inhibitor (alpha-1-PI) trypsin-inhibitory activity in the kidneys testify about removal of oxidative alpha-1-PI.     

Protective effect of ascorbic acid against oxidative stress induced by inorganic arsenic in liver and kidney of rat

Ascorbic acid treatment in arsenic trioxide treated rats increased arsenic excretion, inhibited lipid peroxidation, improved GSH status, regulated GSSG turnover and also restored glutathione-S-transferases activity in liver and kidney. Suitable mechanisms leading to ascorbic acid protection have been discussed. Upregulation of GSH dependent enzymes was found to be necessary for a protective effect. Protection is finally attributed to higher GSH levels observed in the liver and kidney of ascorbic acid and inorganic arsenic treated rats. It is also concluded that ascorbic acid protection is influenced by gender dependent factors. Arsenic poisoning is a global problem now. Gender differences need to be considered while applying therapeutic measures.     

Creatine and pyruvate prevent behavioral and oxidative stress alterations caused by hypertryptophanemia in rats

It is known that the accumulation of tryptophan and its metabolites is related to brain damage associated with both hypertryptophanemia and neurodegenerative diseases. In this study, we investigated the effect of tryptophan administration on various parameters of behavior in the open-field task and oxidative stress, and the effects of creatine and pyruvate, on the effect of tryptophan. Forty, 60-day-old male Wistar rats, were randomly divided into four groups: saline, tryptophan, pyruvate + creatine, tryptophan + pyruvate + creatine. Animals received three subcutaneous injections of tryptophan (2 μmol/g body weight each one at 3 h of intervals) and/or pyruvate (200 μg/g body weight 1 h before tryptophan), and/or creatine (400 μg/g body weight twice a day for 5 days before tryptophan twice a day for 5 days before training); controls received saline solution (NaCl 0.85%) at the same volumes (30 μl/g body weight) than the other substances. Results showed that tryptophan increased the activity of the animals, suggesting a reduction in the ability of habituation to the environment. Tryptophan induced increase of TBA-RS and total sulfhydryls. The effects of tryptophan in the open field, and in oxidative stress were fully prevented by the combination of creatine plus pyruvate. In case these findings also occur in humans affected by hypertryptophanemia or other neurodegenerative disease in which tryptophan accumulates, it is feasible that oxidative stress may be involved in the mechanisms leading to the brain injury, suggesting that creatine and pyruvate supplementation could benefit patients affected by these disorders.     

Glycine nano-selenium prevents brain oxidative stress and neurobehavioral abnormalities caused by MPTP in rats

BackgroundParkinson's disease (PD) is a common degenerative disease of the central nervous system in the elderly. In recent years, the results of clinical and experimental studies have shown that oxidative stress is one of the important pathogenesis of PD. Selenium is one of the minor elements reported to possess antioxidant properties. Thus, the purpose of this study was to investigate the recovery effect of glycine nano-selenium on neurobehavioral abnormalities and oxidative stress caused by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in rat.Materials and methodsSD male rats weighing 280−310 g were purchased from the Chengdu Dossy Experimental Animals Company, China. All rats were housed in a temperature-controlled room, with a 12 h light–dark cycles and had free access to food and water ad libitum. Rats were randomly divided into 4 groups with 8 animals in each group: the control group (normal saline), 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine group (MPTP), MPTP + 0.05 mg/kg glycine nano-selenium (MPTP + 0.05 Se), MPTP + 0.1 mg/kg glycine nano-selenium (MPTP + 0.1 Se). Behavioral assessment, clinical symptoms, Immunohistochemistry analysis of tyrosine hydroxylase (TH) and antioxidant activity were accessed to determine the protective effects glycine nano-selenium have on PD rats.ResultsFrom the results, Rats showed a decrease in spontaneous motor behavior and an increase in pole test score. Also, the number of TH⁺ neurons were also significantly decreased (P < 0.05) after treated with MPTP for 7 days indicating that MPTP could successfully induce neurobehavioral abnormalities in rats. Furthermore, the lipid peroxide (MDA) levels of the PD model group were significantly increased and the antioxidant activities (SOD and GSH-PX) were significantly inhibited (P < 0.05) compared to the control group indicating the important role oxidative stress played in dopaminergic neuron death and neurobehavioral abnormalities in PD rats. Compared with the PD model group, glycine nano-selenium administration could significantly improve behavior and increase the number of TH⁺ neurons (P < 0.05) to protect against the loss of dopaminergic neurons. At the same time, glycine nano-selenium could decrease the MDA levels and increase the activities of SOD and GSH-PX significantly (P < 0.05).ConclusionIn conclusion, PD rat model was successfully developed by intraperitoneal injection of MPTP and the intragastric administration of glycine nano-selenium reduced neurobehavioral abnormalities by decreasing oxidative stress in rat brain.     

Evaluation of oxidative stress during apoptosis and necrosis caused by carbon tetrachloride in rat liver

After 12, 18, and 24 h of oral administration of carbon tetrachloride (as a 1:1 mixture with mineral oil: 4 ml/kg body weight) to rats, the activity of caspase-3-like protease in the liver increased significantly compared to that in the control group that was given mineral oil (4 ml/kg). In plasma, the activity of caspase-3 was barely detectable in the control rat, but increased significantly 24 h after drug administration along with a dramatic increase in glutamate oxaloacetate transaminase. These results indicate that carbon tetrachloride causes apoptosis in the liver by activating caspase-3, which is released to plasma by secondary necrosis. After 18 and 24 h of carbon tetrachloride administration, the liver concentration of hydrophilic vitamin C was decreased significantly, while that of hydrophobic vitamin E was not affected. The plasma concentration of vitamins C and E was not influenced significantly. These results suggest that carbon tetrachloride induces oxidative stress mainly in the aqueous phase of the liver cell.     

楮实子对药物性肝损伤大鼠氧化应激因子的影响

为了探讨楮实子对对乙酰氨基酚(APAP)诱导的药物性肝损伤大鼠的保护作用以及对过氧化物酶体增殖物激活受体γ(PPAR-γ)、过氧化物酶体增殖物激活受体α(PPAR-α)、C-Ros癌基因1(ROS1)的调控作用。实验将50只SD大鼠随机分为正常组、模型组、水飞蓟宾组(44mg/kg)和楮实子高、低剂量组(4.2、1.05g生药/kg),每组10只。灌胃给予对乙酰氨基酚(1.2kg/kg)制备肝损伤模型,给药组造模的同时给予相应药物治疗,连续30天。实验结束,收集血清、肝组织标本进行指标检测。结果显示,楮实子各剂量均能降低药物性肝损伤大鼠血清中谷丙转氨酶(ALT)和谷草转氨酶(AST)活性,降低总胆红素(TBIL)和直接胆红素(TBIL)的含量,升高血清中谷胱甘肽(GSH)含量、超氧化物歧化酶(SOD)和谷胱甘肽过氧化物酶(GSH-Px)活性,降低丙二醛(MDA)含量以及ROS1的表达,上调PPAR-αmRNA的表达,下调PPAR-γmRNA的表达。以上研究结果表明,楮实子能防治对乙酰氨基酚所致肝损伤,其作用机制可能是通过降低ROS1的表达、调节转录因子PPAR-α和PPAR-γ的基因表达,从而缓解氧化应激损伤来实现的。     

Melatonin reduces rat hepatic macromolecular damage due to oxidative stress caused by delta-aminolevulinic acid

Delta-aminolevulinic acid, precursor of heme, accumulates in a number of organs, especially in the liver, of patients with acute intermittent porphyria. The potential protective effect of melatonin against oxidative damage to nuclear DNA and microsomal and mitochondrial membranes in rat liver, caused by delta-aminolevulinic acid, was examined. Changes in 8-hydroxy-2'-deoxyguanosine (8-OHdG) levels, an index of DNA damage, and alterations in membrane fluidity (the inverse of membrane rigidity) and lipid peroxidation in microsomal and mitochondrial membranes, as indices of damage to lipid and protein molecules in membranes, were estimated. Measurements were made in rat liver after a 2 week treatment with delta-aminolevulinic acid (40 mg/kg b.w., every other day). To test the potential protective effects of melatonin, the indole was injected (i.p. 10 mg/kg b.w.) 3 times daily for 2 weeks. 8-OHdG levels and lipid peroxidation in microsomal membranes increased significantly whereas microsomal and mitochondrial membrane fluidity decreased as a consequence of delta-aminolevulinic acid treatment. Melatonin completely counteracted the effects of delta-aminolevulinic acid. Melatonin was highly effective in protecting against oxidative damage to DNA as well as to microsomal and mitochondrial membranes in rat liver and it may be useful as a cotreatment in patients with acute intermittent porphyria.     

Gamma-hydroxybutyric acid induces oxidative stress in cerebral cortex of young rats

GHB is a naturally occurring compound in the central nervous system (CNS) whose tissue concentration are highly increased during drug abuse and in the inherited deficiency of succinic semialdehyde dehydrogenase (SSADH) activity. SSADH deficiency is a neurometabolic-inherited disorder of the degradation pathway of gamma-aminobutyric acid (GABA). It is biochemically characterized by increased concentrations of gamma-hydroxybutyric acid (GHB) in tissues, cerebrospinal fluid (CSF), blood and urine of affected patients. Clinical manifestations are variable, ranging from mild retardation of mental, motor, and language development to more severe neurological symptoms, such as hypotonia, ataxia and seizures, whose underlying mechanisms are practically unknown. In the present study, the in vitro and in vivo effects of GHB was investigated on some parameters of oxidative stress, such as chemiluminescence, thiobarbituric acid-reactive substances (TBA-RS), total radical-trapping antioxidant potential (TRAP), total antioxidant reactivity (TAR), as well as the activities of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPX) in homogenates from cerebral cortex of 15-day-old Wistar rats. In vitro, GHB significantly increased chemiluminescence and TBA-RS levels, while TRAP and TAR measurements were markedly diminished. In contrast, the activities of the antioxidant enzymes SOD, CAT and GPX were not altered by GHB in vitro. Acute administration of GHB provoked a significant enhance of TBA-RS levels and a decrease of TRAP and TAR measurements. These results indicate that GHB induces oxidative stress by stimulating lipid peroxidation and decreasing the non-enzymatic antioxidant defenses in cerebral cortex of young rats. If these effects also occur in humans, it is possible that they might contribute to the brain damage found in SSADH-deficient patients and possibly in individuals who consume GHB or its prodrug gamma-butyrolactone.     

Early oxidative stress in the diabetic kidney: effect of DL-alpha-lipoic acid

Oxidative stress is implicated in the pathogenesis of diabetic nephropathy. The attempts to identify early markers of diabetes-induced renal oxidative injury resulted in contradictory findings. We characterized early oxidative stress in renal cortex of diabetic rats, and evaluated whether it can be prevented by the potent antioxidant, DL-alpha-lipoic acid. The experiments were performed on control rats and streptozotocin-diabetic rats treated with/without DL-alpha-lipoic acid (100 mg/kg i.p., for 3 weeks from induction of diabetes). Malondialdehyde plus 4-hydroxyalkenal concentration was increased in diabetic rats vs. controls (p <.01) and this increase was partially prevented by DL-alpha-lipoic acid. F(2) isoprostane concentrations (measured by GCMS) expressed per either mg protein or arachidonic acid content were not different in control and diabetic rats but were decreased several-fold with DL-alpha-lipoic acid treatment. Both GSH and ascorbate (AA) levels were decreased and GSSG/GSH and dehydroascorbate/AA ratios increased in diabetic rats vs. controls (p <.01 for all comparisons), and these changes were completely or partially (AA) prevented by DL-alpha-lipoic acid. Superoxide dismutase, glutathione peroxidase, glutathione reductase, glutathione transferase, and NADH oxidase, but not catalase, were upregulated in diabetic rats vs. controls, and these activities, except glutathione peroxidase, were decreased by DL-alpha-lipoic acid. In conclusion, enhanced oxidative stress is present in rat renal cortex in early diabetes, and is prevented by DL-alpha-lipoic acid.