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The involvement of oxidative stress in the pathogenesis of diabetes mellitus has been confirmed by numerous studies. In this study, the expression of two antioxidant enzymes, superoxide dismutase (SOD), and catalase which are involved in the detoxification of reactive oxygen species was studied in the streptozotocin-induced diabetic rat liver tissues. The enzyme assays showed a significant decrease in both enzymes activities compared to control animals. The RT-PCR and Western-blot analysis results demonstrated that this decrease in activity is regulated at the level of gene expression, as both catalase and Cu-Zn SOD mRNA and protein expressions were also suppressed. Supplementing the animals with vitamin C, a powerful antioxidant increased both SOD and catalase activities with no change in both mRNA and protein expressions suggesting a role of post-translational modification. However, even though mRNA expressions of both catalase and Cu-Zn SOD were not changed, the protein levels increased in parallel to activities in the case of another antioxidant, alpha-lipoic acid. An increase in the rate of translation, without changing the rate of transcription indicates a translational effect of lipoic acid in changing the activities of antioxidant enzymes to prevent the oxidative damage in diabetes.

Increased oxidative stress and impaired antioxidant defense mechanisms are believed to be the important factors contributing to the pathogenesis and progression of diabetes mellitus. In this study, we have reported the effects of the streptozotocin-induced diabetes on the gene expression and the activities of two antioxidant enzymes, manganese superoxide dismutase (MnSOD) and glutathione peroxidase (GPx). We also studied the effects of two antioxidants, vitamin C and DL-alpha-lipoic acid (LA), on the system. Our results showed no significant change in both enzymes activities in diabetic animals compared to controls. Similarly, mRNA and protein profiles of MnSOD showed no change. Though the mRNA expression of GPx did not show any change, Western-blot analysis results demonstrated that protein expression is increased. LA, which is a water- and lipid-soluble antioxidant, decreased the protein expression of MnSOD, though mRNA levels and activities remained unchanged. LA treatment increased the GPx activities in diabetic tissues, significantly, and RT-PCR and Western-blot analysis results demonstrated that this increase in activity is not regulated at the gene level, as both mRNA and protein levels did not change. Supplementing the animals with vitamin C, a powerful water-soluble antioxidant, increased the mRNA expression of MnSOD, though the protein expression and the activity did not change statistically. On the other hand GPx activity increased significantly through post-translational modifications, as both mRNA and protein expressions did not change. These results together with our previous findings about the gene expressions of catalase and Cu-Zn SOD indicate the presence of very intricate control mechanisms regulating the activities of antioxidant enzymes in order to prevent the damaging effects of oxidative stress.

One hundred healthy Turkish volunteers (70 male, 30 female) aged from 19 to 56 years were given 5 mg coumarin p.o. after an overnight fast. Urine samples were collected before and 2, 4 and 8 h after drug administration. The extent and rate of formation of 7-OH-coumarin (7OHC) was determined by the urinary excretion of the metabolite as measured with the fluorometric method. On average, 80% of 7OHC formed was excreted in 2 h. The total amount of 7OHC formed was 59.8% (21.5%) (mean and SD, n = 100, range 17-100%) of the given dose. The percentage of 7OHC excreted during the first 2 h compared with the 7OHC excretion at 8 h was a constant and stable individual characteristic for the rate of the formation of 7OHC ('2 h coumarin test'). Although four individuals had relatively slow coumarin test values (34-40%), no clear-cut polymorphism in the rate of 7OHC formation was found. However, 7OHC formation was lower in males and in cigarette smokers.

Background In diabetes mellitus, increased formation of reactive oxygen species due to high level of glucose in both blood plasma and tissues creates oxidative stress and damages the tissues. Antioxidants together with the antioxidant enzymes are very important in order to protect the cells against oxidative damage. Methods Differential expressions of both mRNA and proteins of major antioxidant enzymes in streptozotocin‐induced diabetic rat kidneys were measured with the help of real‐time polymerase chain reaction and western blot analysis, respectively. Furthermore, effects of two strong antioxidants α‐lipoic acid, vitamin C and their combination on the regulation of both expressions and the activities of antioxidant enzymes were also studied. Results In diabetic rat kidney tissue, both catalase and glutathione peroxidase activities were reduced (although mRNA expression for both was greatly increased) when compared with controls. No significant change was observed in superoxide dismutase (SOD) activity. Alpha‐lipoic acid increased catalase activity towards the control values. Combined administration of alpha‐lipoic acid and vitamin C increased the activities of both catalase and SOD, demonstrating a posttranslational effect. Glutathione concentrations were decreased in diabetic kidney; alpha‐lipoic acid treatment partially restored the glutathione levels. Conclusions All data showed the importance of post‐transcriptional and translational regulation of the antioxidant enzyme activities against oxidative stress that is associated with diabetes. Copyright © 2011 John Wiley & Sons, Ltd.