Pentose phosphate pathway, glutathione-dependent enzymes and antioxidant defense during oxidative stress in diabetic rodent brain and peripheral organs: effects of stobadine and vitamin E.

The aim of the present study was to investigate the effects of treatment with antioxidant stobadine (ST) on the activities of enzymes related with pentose phosphate pathway and glutathione-dependent metabolism and the other markers of oxidative stress in brain and peripheral organs of diabetic rats, and to compare the effects of ST treatment alone with the effects of treatments with another antioxidant vitamin E and ST plus vitamin E. Rats were made diabetic by the injection of streptozotocin (STZ; 55 mg/kg IP), and, 2 days later, some control and diabetic rats were left untreated or treated with ST (24.7 mg/kg/day, orally), vitamin E (400-500 U/kg/day, orally), or both substances together. In the brain, although 6-phosphogluconate dehydrogenase activity (6-PGD) did not change, glucose-6-phosphate dehydrogenase activity (G-6PD) was markedly increased in diabetic rats compared with controls; only combined treatment with ST and vitamin E produced a partial prevention on this alteration. The aorta G-6PD and 6-PGD of diabetic rats were 52% and 36% of control values, respectively. Neither single treatments with each antioxidant nor their combination altered the G-6PD and 6-PGD in aorta of diabetic rats. Glutathione peroxidase (GSHPx) activity was increased by STZ-diabetes in brain, heart, and kidney. In diabetic brain, vitamin E alone or combination with ST kept GSHPx at normal levels. Diabetes-induced stimulation in GSHPx did not decrease in response to the treatment with vitamin E in heart and kidney, but was greatly prevented by ST alone. The activity of glutathione reductase (GR) was decreased in brain and heart of diabetic rats. The treatment with each antioxidant or with a combination of both agents completely prevented this deficiency and resulted in further activation of GR in diabetic tissues. Glutathione S-transferase (GST) activity did not significantly change in diabetic brain and aorta. GST was stimulated by all treatment protocols in the brain of diabetic rats and was depressed in aorta of control rats. Catalase (CAT) was activated in diabetic heart but depressed in diabetic kidney. Diabetes-induced abnormalities in CAT activity did not respond to vitamin E alone in heart, was moderately ameliorated by the treatment with this vitamin in kidney, and was completely prevented by ST alone in both tissues. Superoxide dismutase (SOD) activity of brain and heart was unchanged by the diabetes but inhibited in diabetic kidney after the treatment ST alone or ST plus vitamin E. The lipid peroxidation (MDA) was increased in diabetic brain and heart. ST or vitamin E alone partly prevented diabetes-induced increase in MDA in brain and heart; however, antioxidant combination achieved a completely amelioration in MDA of these tissues of diabetic rats. Kidney MDA levels were similar in control and untreated diabetic animals. ST and vitamin E treatments, when applied separately or together, significantly reduced kidney MDA in both control and diabetic rats; and the combined effect of antioxidants was greater than that of each alone. These results are consistent with the degenerative role of hyperglycemia on cellular reducing equivalent homeostasis and antioxidant defense, and provide further evidence that pharmacological intervention of different antioxidants may have significant implications in the prevention of the prooxidant feature of diabetes and protects redox status of the cells.

In vivo treatment with stobadine prevents lipid peroxidation, protein glycation and calcium overload but does not ameliorate Ca2+ -ATPase activity in heart and liver of streptozotocin-diabetic rats: comparison with vitamin E.

Hyperglycemia leads to excess production of reactive oxygen species (ROS), lipid peroxidation and protein glycation that may impair cellular calcium homeostasis and results in calcium sequestration and dysfunction in diabetic tissues. Stobadine (ST) is a pyridoindole antioxidant has been postulated as a new cardio- and neuroprotectant. This study was undertaken to test the hypothesis that the treatment with ST inhibits calcium accumulation, reduces lipid peroxidation and protein glycation and can change Ca2+,Mg2+-ATPase activity in diabetic animals. The effects of vitamin E treatment were also evaluated and compared with the effects of combined treatment with ST. Diabetes was induced by streptozotocin (STZ, 55 mg/kg i.p.). Some of diabetic rats and their age-matched controls were treated orally with a low dose of ST (24.7 mg/kg/day), vitamin E (400-500 IU/kg/day) or ST plus vitamin E for 10 weeks. ST and vitamin E separately produced, in a similar degree, reduction in diabetes-induced hyperglycemia. Each antioxidant alone significantly lowered the levels of plasma lipid peroxidation, cardiac and hepatic protein glycation in diabetic rats but vitamin E treatment was found to be more effective than ST treatment alone. Diabetes-induced increase in plasma triacylglycerol levels was not significantly altered by vitamin E treatment but markedly reduced by ST alone. The treatment with each antioxidant completely prevented calcium accumulation in diabetic heart and liver. Microsomal Ca2+,Mg2+-ATPase activity significantly decreased in both tissues of untreated diabetic rats. ST alone significantly increased microsomal Ca2+,Mg2+-ATPase activity in the heart of normal rats. However, neither treatment with ST nor vitamin E alone, nor their combination did change cardiac Ca2+,Mg2+-ATPase activity in diabetic heart. In normal rats, neither antioxidant had a significant effect on hepatic Ca2+,Mg2+-ATPase activity. Hepatic Ca2+,Mg2+-ATPase activity of diabetic rats was not changed by single treatment with ST, while vitamin E alone completely prevented diabetes-induced inhibition in microsomal Ca2+,Mg2+-ATPase activity in liver. Combined treatment with ST and vitamin E provided more benefits in the reduction of hyperglycemia and lipid peroxidation in diabetic animals. This study describes potential mechanisms on cellular effects of ST in the presence of diabetes-induced hyperglycemia that may delay or inhibit the development of diabetic complications. The use of ST together with vitamin E can better control hyperglycemia-induced oxidative stress.