Melatonin in preservation solutions prevents ischemic injury in rat kidneys.

Transplantation is lifesaving and the most effective treatment for end-stage organ failure. The transplantation success depends on the functional preservation of organs prior to transplantation. Currently, the University of Wisconsin (UW) and histidine-tryptophan-ketoglutarate (HTK) are the most commonly used preservation solutions. Despite intensive efforts, the functional preservation of solid organs prior to transplantation is limited to hours. In this study, we modified the UW solution containing components from both the UW and HTK solutions and analyzed their tissue-protective effect against ischemic injury. The composition of the UW solution was changed by reducing hydroxyethyl starch concentration and adding Histidine/Histidine-HCl which is the main component of HTK solution. Additionally, the preservation solutions were supplemented with melatonin and glucosamine. The protective effects of the preservation solutions were assessed by biochemical and microscopical analysis at 2, 10, 24, and 72 h after preserving the rat kidneys with static cold storage. Lactate dehydrogenase (LDH) activity in preservation solutions was measured at 2, 10, 24, and 72. It was not detectable at 2 h of preservation in all groups and 10 h of preservation in modified UW+melatonin (mUW-m) and modified UW+glucosamine (mUW-g) groups. At the 72nd hour, the lowest LDH activity (0.91 IU/g (0.63-1.17)) was measured in the mUW-m group. In comparison to the UW group, histopathological damage score was low in modified UW (mUW), mUW-m, and mUW-g groups at 10, 24, and 72 hours. The mUW-m solution at low temperature was an effective and suitable solution to protect renal tissue for up to 72 h.

Evaluation of Oxidative Stress and Inflammatory Biomarkers Pre and Post-Treatment in New Diagnosed Atherosclerotic Patients.

Atherosclerosis is a chronic vascular inflammatory disease associated to oxidative stress and endothelial dysfunction. It is characterized by lipid accumulation in the arterial wall, increased hyperlipidemia, oxidative stress, lipid peroxidation, and protein oxidation. Our study included 45 patients ages of 40-60 and 45 healthy volunteers with similar demographic characteristics without any chronic disease as well. Fasting plasma glucose, BUN, creatinine, LDL-cholesterol, HDL-cholesterol, triglyceride, total cholesterol, HbA1c, and C-reactive protein (CRP) levels were measured using commercial kits by autoanalyzer. The oxidative stress biomarkers total oxidant status (TOS), total antioxidant status (TAS), total thiol (TT), native thiol (NT), catalase (CAT), paraoxonase (PON1), and arylesterase (ARES) enzyme activities were measured using photometric methods. The inflammatory biomarkers interleukin 1 beta (IL-1ß), tumor necrosis factor-α (TNF-α), presepsin (PSPN), and raftlin (RFTN1) levels were measured with ELISA Kits. Oxidative stress index (OSI) and disulfide (DIS) were calculated. The clinical, biochemical biomarkers such as BUN, creatinine, HDL, LDL, total cholesterol, triglyceride, and CRP levels were found to be higher than the control group and lower post-treatment compared to the pre-treatment group (p <0.001). The oxidative stress parameters, TOS, OSI, and DIS levels were found to be higher than the control group, and the levels before the treatment were statistically significantly higher than after the treatment (p < 0.001). Antioxidant biomarkers TAS, TT, and NT levels were low in the patient group. Inflammatory biomarkers were highest before treatment and decreased with treatment. Oxidative stress and inflammation, which increased in atherosclerosis patients may guide disease prognosis and treatment strategies.

Early-adulthood caloric restriction is beneficial to improve renal redox status as future anti-aging strategy in rats.

AIMS: Caloric restriction (CR) is an experimental approach proposed to alleviate age-related oxidative damage. In the present study, we investigated the consequences of CR on renal redox homeostasis in rats at a specific time frame in early-adulthood.. METHODS: Three groups of male Sprague-Dawley rats; young control at 6-month-old, 2-year-old subjected to 40% CR between 18th-24th months of age, and their non-CR controls were sacrificed, and numerous redox status biomarkers including protein oxidation, glycation, lipid peroxidation, glycation end products, thiol groups, and superoxide dismutase were assayed. It was also ensured that CR rats and their non-CR corresponding rats had similar body weights at the end of the study to decrease the confounding effects of different body weights on redox homeostasis and caloric restriction. RESULTS: After CR, the detrimental effects of the protein oxidation, glycation, and lipid peroxidation were significantly improved in the renal tissue CR rats when compared to their non-CR control group. However, there were no significant difference in thiol fractions between younger controls and both of the elderly groups. CONCLUSION: Detrimental consequences of renal senescence on redox homeostasis are significantly improved via CR especially applied in early-adulthood.

Caloric restriction and redox homeostasis in various regions of aging male rat brain: Is caloric restriction still worth trying even after early-adulthood?: Redox homeostasis and caloric restriction in brain.

Despite recent studies have shown that caloric restriction (CR) could improve some functional loss associated with brain aging, the biochemical effects of CR on brain aging are still not well understood on a quantifiable biochemical basis, including whether CR could be protective when started around middle adulthood, when age-related neurodegenerative diseases are thought to set in. Therefore, in the light of more than ever aging societies and increasing neurodegenerative diseases, we aimed to test the biochemical effects of CR on redox homeostasis in different parts of male Sprague-Dawley rat brain by using the biomarkers we consistently validated in our previous work (TOS, PCO, AOPP, AGEs, sRAGE, P-SH, LHPs, 4-HNE, TAS, Cu, Zn-SOD). Our results indicate that oxidative stress biomarkers are lower in CR group, implying a more favorable redox status that has been previously shown to be correlated with better neural function. PRACTICAL APPLICATIONS: We report that the beneficial effects of caloric restriction (CR) on various brain tissues result in significant improvements in biochemical markers, even though CR is not started in early adulthood. Hence, our select age group provides a sound redox status-related neurochemical understanding for many recent CR studies, where a functional loss was detected at this age.

Galactose-induced Aging Model in Rat Testicular Tissue.

OBJECTIVE: To examine whether the D-galactose induced aging model is an appropriate model for further aging research. STUDY DESIGN: Experimental study. PLACE AND DURATION OF STUDY: Aziz Sancar Institute of Experimental Medicine, Istanbul University, Turkey, June 2015- June 2017. METHODOLOGY: The study comprises 3 groups of rats. Group I is young control (YC) 5-month-old rats. Group II is 5-month- old rats, which were mimetically aged (MA) for 6 weeks via intraperitoneal D-galactose (60 mg/kg body weight/day, 0.5 mL) administration. Group III is naturally aged (NA) 24-month-old rats. Group I and III received intraperitoneal saline (0.9% 0.5 mL) for 6 weeks as vehicle. Group I and Group II received injections at 21 weeks age and Group III rats 6 weeks before 24 months age. Tissues were harvested when rats became 6.5-month-old (Group I and Group II) and 24-month-old (Group III). Quantitative biochemical analyses of proteins, lipids, DNA biomarkers and Cu, Zn-SOD were conducted. Statistical analysis of the data was conducted using ANOVA, followed by post-hoc Bonferroni test. RESULTS: Higher magnitude of oxidative damage and diminished antioxidant defence capacity were found in both mimetically aged and naturally aged testicular tissues. It is observed that D-galactose aging model group shares significant similarities in terms of impaired redox homeostasis with the naturally aged rats. CONCLUSION: D-galactose induced testicular aging model successfully mimics aging process. Therefore, D-galactose induced aging model may be used as an accelerated aging model to study the age related alterations and interventions.

The effects of lipoic acid on redox status in brain regions and systemic circulation in streptozotocin-induced sporadic Alzheimer's disease model.

While the deterioration of insulin-glucose metabolism (IGM), impaired redox homeostasis (IRH), ß-amyloid accumulation was reported in Sporadic Alzheimer's Disease (SAD) model, aforementioned factors related to lipoic acid administration and anthropometric indexes (AIs) are not yet studied with integrative approach. ß-amyloid accumulation, redox homeostasis biomarkers and AIs are investigated in SAD model. Streptozotocin-induced inhibition of insulin-signaling cascade but not GLUT-2 and GLUT-3 transporters takes a role in ß-amyloid accumulation. Inhibition types are related to IRH in cortex, hippocampus and systemic circulation. Lipoic acid (LA) shows both antioxidant and prooxidant effect according to the anatomical location. LA administration also leads to improved AIs during GLUT-2 inhibition and cortical redox status in GLUT-3 inhibited group. Optimal LA action could be possible if its redox behavior is balanced to antioxidant effect. Diagnostic usage of systemic IRH parameters as biomarkers and their possible correlations with deteriorated IGM should be investigated. Graphical abstract ᅟ.

Gender and chronological age affect erythrocyte membrane oxidative indices in citrate phosphate dextrose adenine-formula 1 (CPDA-1) blood bank storage condition.

It is well known that in vitro storage lesions lead to membrane dysfunction and decreased number of functional erythrocytes. As erythrocytes get older, in storage media as well as in peripheral circulation, they undergo a variety of biochemical changes. In our study, the erythrocytes with different age groups in citrate phosphate dextrose adenine-formula 1 (CPDA-1) storage solution were used in order to investigate the possible effect of gender factor on oxidative damage. Oxidative damage biomarkers in erythrocyte membranes such as ferric reducing antioxidant power, pro-oxidant-antioxidant balance, protein-bound advance glycation end products, and sialic acid were analyzed. Current study reveals that change in membrane redox status during blood-bank storage condition also depends on both gender depended homeostatic factors and the presence of CPDA-1. During the storage period in CPDA-1, erythrocytes from the male donors are mostly affected by free radical-mediated oxidative stress but erythrocytes obtained from females are severely affected by glyoxidative stress.

Ameliorative Effects of Testosterone Administration on Renal Redox Homeostasis in Naturally Aged Rats.

BACKGROUND: Testosterone biosynthesis gradually decreases with age. Impaired redox homeostasis-related oxidative damage in cellular macromolecules has a high risk for the development of renal insufficiency. Our aim was to study the effects of testosterone replacement therapy on redox homeostasis. METHODS: We investigated various oxidative damage biomarkers in kidney. Experimental animals were separated into three groups-naturally aged rats, testosterone-administered naturally aged rats (single dose of 25 mg/kg testosterone enanthate), and their respective young controls. RESULTS: Our results showed that the testosterone-administered naturally aged group shared significant similarities with the young rats with respect to their redox status. In testosterone-administered naturally aged rats, kynurenine, protein carbonyl, advanced oxidation protein products, lipid peroxidation markers, and xanthine oxidase activities were significantly lower and Cu-Zn superoxide dismutase activities and testosterone levels were higher than naturally aged rats. In testosterone-administered naturally aged rats, catalase activities, ferric reducing anti-oxidant power, and testosterone levels were significantly lower and dityrosine, N-formyl kynurenine, protein carbonyl, and protein hydroperoxides were significantly higher than in young rats. On the other hand, in naturally aged rats, Cu-Zn superoxide dismutase, catalase activities, ferric reducing anti-oxidant power, and testosterone levels were lower and dityrosine, kynurenine, protein carbonyl, protein hydroperoxide, advanced oxidation protein products, lipid peroxidation markers, advanced glycation end products, and xanthine oxidase activities were higher than controls. CONCLUSIONS: Our results showed that a single dose of testosterone administration has a positive effect on the redox status of the aged kidney. Future studies are needed to clarify the exact molecular mechanism(s) involved in the action of testosterone in maintaining kidney redox homeostasis.

Oxidative stress in breast cancer.

The present study was undertaken to evaluate the place of oxidative stress on breast cancer. Lipid peroxidation as evidenced by malondialdehyde (MDA) and the status of the antioxidants superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) were estimated in tissues of 10 fibroadenoma and 40 breast cancer patients. Lipid peroxidation in breast cancer tissues was enhanced compared to nonmalignant tissues (p < 0.001). Similarly, antioxidants SOD (p < 0.001) and GPx (p = 0.007) in tumor tissues significantly were increased. On the contrary, CAT activity was found significantly decreased (p < 0.001). We found that oxidant/antioxidant status was independent from any prognostic factors concerning breast cancer. The results of our study have shown higher oxygen-free-radical production and decreased CAT activity support the oxidative stress hypothesis in breast carcinogenesis.

Effects of flurbiprofen and tiaprofenic Acid on oxidative stress markers in osteoarthritis: A prospective, randomized, open-label, active- and placebo-controlled trial.

BACKGROUND: The relationship between oxidative stress and osteoarthritis (OA) has been widely investigated. Serum malondialdehyde (MDA), nitric oxide (NO), and Cu/Zn superoxide dismutase (SOD) levels are useful markers of oxidative stress. Because of the importance of oxidative stress markers in the pathogenesis of OA, treatment might involve modification of these markers to control oxidative stress. OBJECTIVE: The aim of this study was to compare the effects of 2 conventionalNSAIDs on markers of oxidative stress in patients with OA of the knee. METHODS: This 3-week, prospective, randomized, open-label, active- and placebo-controlled study was conducted at the Cerrahpasa Faculty of Medicine, Istanbul University, Istanbul, Turkey. Adult patients with clinically and radiographically diagnosed moderate OA of the knee who were previously untreated were enrolled. Patients were randomly assigned to 1 of 3 treatment groups: flurbiprofen 100 mg PO (tablets) BID, tiaprofenic acid 300 mg PO (tablets) BID, or placebo tablets BID. Patients were evaluated using clinical assessment and laboratory testing before treatment (week 0; baseline) and at the end of week 3. The primary end points were the differences in serum MDA, NO, and SOD levels versus placebo. Clinical parameters-pain at rest and on motion-were evaluated using a 10-cm visual analog scale (0 = no pain to 10 = worst pain imaginable). The duration (in minutes) of morning stiffness was recorded by patients, using patient diaries. The differences between treatment groups were assessed using multivariate analysis. RESULTS: Thirty-nine patients (20 women, 19 men; mean [SD] age, 59.0 [11.3]years) were included in the study. Mean serum MDA and NO levels were significantly decreased at 3 weeks compared with baseline in the 2 active-treatment groups (all, P < 0.001); these values remained statistically similar to baseline in the placebo group. Serum SOD levels were increased significantly from baseline in the 2 active-treatment groups (both, P < 0.001), but not in the placebo group. No significant differences in serum MDA and NO levels were found between the group receiving flurbiprofen and that receiving tiaprofenic acid. Serum SOD levels were significantly higher in the flurbiprofen group compared with the tiaprofenic acid and placebo groups (both, P < 0.01). The mean (SD) score for pain at rest was significantly lower at 3 weeks compared with baseline with flurbiprofen and tiaprofenic acid (both, P < 0.001), but not with placebo. The mean score for pain on motion was significantly reduced from baseline values only with tiaprofenic acid (P < 0.001). The duration of morning stiffness was significantly shorter at 3 weeks compared with baseline in all 3 study groups (all, P < 0.001). The mean scores for pain on motion and duration of morning stiffness were significantly reduced with tiaprofenic acid compared with placebo (both, P < 0.05). The study had some limitations (ie, small sample size, no blinding, the short duration of the study, and the weak correlation between serum and synovial fluid levels of NO). CONCLUSIONS: In this comparison of the effects of 3 weeks of treatment withflurbiprofen 100 mg BID and tiaprofenic acid 300 mg BID in patients with knee OA, both treatments effectively reduced serum MDA and NO levels compared with placebo. Only tiaprofenic acid significantly improved pain at rest and on motion and duration of morning stiffness compared with placebo.

Green tea polyphenol (-)-epigallocatechin gallate prevents oxidative damage on periventricular white matter of infantile rats with hydrocephalus.

Hydrocephalus causes damage to periventricular white matter at least in part through chronic ischemia. Emphasizing the periventricular ischemia/hypoxia in hydrocephalus, various authors indicated the secondary biochemical impairment and oxidative damage in experimentally induced and congenital hydrocephalic rat brain. (-)-Epigallocatechin gallate (EGCG), the main constituent of green tea polyphenols, has been shown to be of some protective value in various models of neurological injury as a free oxygen radical scavenger. In the present study the effects of EGCG were examined on the periventricular oxidative damage in experimental childhood-onset hydrocephalus. Hydrocephalus was induced in 3 weeks-old rat pups by kaolin injection into the cisterna magna. A single daily dose of 50 mg/kg of EGCG injected into the peritoneum of the rats for 15 days significantly reduced periventricular white matter malondialdehyde levels when compared to non-treated hydrocephalic animals. Our results indicate that EGCG may have a protective effect against periventricular white matter oxidative damage in hydrocephalus induced infantile rats.

Effect of regular training on plasma thiols, malondialdehyde and carnitine concentrations in young soccer players.

Physical activity is known to induce oxidative stress in individuals subjected to intense exercise. Contrarily, there are enzymatic and nonenzymatic defence systems against oxygen radicals in aerobic organisms. Sulphydryl groups such as thiol and glutathione (GSH) can be given as an example to non-enzymatic low molecular weight antioxidants. Carnitine may be related to the performance enhancement in high intensity intermittent exercises and might probably improve the aerobic capacity by stimulating lipid oxidation in muscle cells during long term exercise. But, the effects caused by this supplement during physical activity have not been fully described in the literature. The aim of the study was to compare plasma thiols (PSH), malondialdehyde (MDA) and carnitine levels and maximal oxygen uptake (VO2(max)) of the soccers under regular training with the values of the healthy controls. Our results demonstrates that soccers seem to be under less oxidative stress, as their MDA levels were significantly lower (P < 0.001) when compared with the control group while their PSH levels were significantly elevated (P < 0.001), during resting condition. In addition, the plasma carnitine concentrations of the soccer group yields lower values while the VO2(max) yields a higher value when compared with the control group. The differences between the soccer and the control groups are significant (for both, P < 0.001). The present research reveals the fact that regular soccer training shows beneficial effect on decreasing of lipid peroxidation levels. Furthermore; the sportsmen who are under intense training programs have low plasma carnitine values which do not cause negative effect on their sportive performance.

Neuroprotective effects of GYKI 52466 on experimental spinal cord injury in rats.

OBJECT: The toxic effects of glutamate in the central nervous system are well known. This neurotoxicity occurs through metabotropic and ionotropic receptors, the latter group composed of N-methyl-D-aspartate, alpha-amino-3-hydroxy-5-methylisoxazole-4-proprionic acid (AMPA), and kainate receptors. The authors investigated the neuroprotective effects of GYKI 52466, a 2,3-benzodiazepine that is a selective and potent AMPA receptor antagonist, in a rat spinal cord trauma model. METHODS: Sixty Wistar albino rats were studied in three groups of 20 animals each: sham-operated controls (Group 1); spinal cord-injured rats (Group 2); and spinal cord-injured plus GYKI 52466-treated rats (Group 3). In Groups 2 and 3, spinal cord injury (SCI) was induced at the thoracic level by applying an aneurysm clip to the cord for 1 minute. One minute after the clip was removed, the rats in Group 3 received an intraperitoneal injection of 15 mg/kg GYKI 52466. Responses to injury and treatment were evaluated based on biochemical parameters (lipid peroxidation and adenosine 5'-triphosphate [ATP] levels in tissue), and on light and transmission electron microscopy findings in cord tissue collected at different times post-SCI. Five rats from each group underwent assessment of functional recovery at 1, 3, and 5 days after SCI; evaluation was performed using the inclined-plane technique and Tarlov motor grading scale. The mean lipid peroxidation levels in Groups 1 and 2 were 21.73 +/- 4.35 and 35.53 +/- 2.99 nmol/g of wet tissue, respectively. The level in Group 3 was 27.98 +/- 3.93 nmol/g of wet tissue, which was significantly lower than that in Group 2 (p < 0.01). The mean ATP levels in Groups 1 and 2 were 166.21 +/- 25.57 and 41.72 +/- 12.28 nmol/g of wet tissue, respectively. The ATP level in Group 3 was 85.82 +/- 13.92 nmol/g of wet tissue, which was significantly higher than that in Group 2 (p < 0.01). Light microscopic examination of Group 2 tissues showed hemorrhage, necrosis, polymorphonuclear leukocyte infiltration, and vascular thrombi. In contrast, the examination of Group 3 tissues showed limited hemorrhage and no necrosis or vascular thrombi. The most prominent findings in Group 2 were hemorrhage and necrosis, whereas the most prominent findings in Group 3 were focal hemorrhage and leukocyte infiltration. Electron microscopy demonstrated that GYKI 52466 protected the neurons, myelin, axons, and intracellular organelles. The mean inclined-plane angles in Groups 1, 2, and 3 were 65 degrees, 40 to 45 degrees, and 55 degrees, respectively. Motor scale results in all groups showed a similar trend. CONCLUSIONS: The findings in this rat model suggest that GYKI 52466 may provide significant therapeutic protection from secondary damage after acute SCI. This agent may be a viable alternative treatment for SCI.

The effect of vitamin E treatment on oxidative stress generated in trained rats.

The aim of this study was to investigate the effect of vitamin E treatment on increased oxidative stress in rats exposed to a swimming exercise protocol. In order to examine the effects of physical swimming training on the antioxidant defences of tissues and on their susceptibility to damage induced by exercise, the levels of glutathione (GSH) and thiobarbituric acid reacting substances (TBARS) levels, on indicator of lipid peroxidation in various tissues, have been determined. In this study, four groups of female rats were used while the rats were trained to swim for 30 minutes a day and five days a week which lasted eight weeks and vitamin E (vit. E) supplementation (30 mg/kg/day) has been carried out for five days a week. TBARS levels are significantly found lower in both trained and sedentary vit. E supplemented groups, since vit. E is the most important antioxidant in an earlier line of defence in lipid peroxidation. Also, in vit. E supplemented trained rats, the glutathione response is observed to be significantly higher, supporting with the TBARS levels and in accordance with the literature. But in the sedentary group without vit. E supplementation, the GSH levels of the liver and the heart tissues were significantly lower than both vit. E supplemented sedentary and trained groups. These results evaluate that vit. E confers protection to GSH levels in these tissues where the GSH levels were found significantly lower in the groups not supplemented with vit. E.

Curcumin's effects on sialic acid level and sialidase activity in Ehrlich ascites tumor bearing mice.

In this study, we determined curcumin's anticancer and chemopreventive effects in mice bearing Ehrlich ascites tumor by evaluation of cancer biomarkers, sialic acid level and sialidase activity. Both plasma sialic acid level and sialidase activity increased significantly in the mice group with Ehrlich ascites tumor. When the tumor groups fed with curcumin and fed with sesame oil were compared, sialic acid level and sialidase activity in ascites fluid significantly reduced in the group fed with curcumin in addition to the increases of plasma sialic acid level and sialidase activity. The tumor group fed with curcumin lived twice longer than the one fed with sesame oil. Curcumin as a phenolic compound decreased all these parameters in Ehrlich ascites tumors and lengthened survival by 88% in the mice with tumor. We concluded that curcumin has anticancer activity.

Tissue and serum sialic acid levels in an animal head injury model.

BACKGROUND: Significant elevations of serum sialic acid level have been documented in various diseases including in a variety of central nervous system disorders. But, in head injury, there is no any study on the serum and brain tissue sialic acid levels. So, we planned an experimental study to evaluate serum and brain tissue sialic acid levels in head injury. METHODS: Marmarou's impact-acceleration model was used in rats to produce diffuse brain injury. Rats were divided into equal three groups. In Group I, 450 g weight was fell from 1 m height to heads of subjects, and from 2 m in Group II. Group III was control group. Sialic acid levels were measured in both sera and brain tissue supernatants after trauma. RESULTS: It was observed that serum sialic acid level was decreased according to the severity and period of trauma increased; and there was no change in brain tissue sialic acid levels. CONCLUSION: Serum sialic acid level might be used as a marker to show the degree of diffuse brain injury.

N-acetylcysteine reduced the effect of ethanol on antioxidant system in rat plasma and brain tissue.

Chronic ethanol administration is able to induce an oxidative stress in the central nervous system. N-Acetylcysteine (NAC) has antioxidant properties; as a sulphydryl donor, it contributes to the regeneration of glutathione and it acts through a direct reaction with hydroxyl radicals. In this study we investigated a possible beneficial effect of NAC on some of the free radical related parameters. Twenty four male Wistar rats were divided in to three groups and were given ethanol (Group 1), ethanol and NAC (Group 2) and isocaloric dextrose (Group 3). Ethanol and NAC were given intragastrically at doses of 6 g/kg/day and 1 g/kg/day, respectively. Our results show that chronic ethanol intake elicits statistically significant increase in MDA and NO levels and decrease in SOD and GSH levels in both plasma and brain (p < 0.001). GPx levels decreased in erythrocytes (p < 0.001). CAT activity showed significant decrease only in brain samples (p < 0.001). NAC administration effectively restores the above results to nearly normal levels. Therefore we suggest that reactive free radicals are, at least partly, involved in the ethanol-induced injury of brain cells and NAC mitigate the toxic effects of ethanol on the oxidant-antioxidant system of rat plasma and brain.