Diabetic encephalopathy, characterized by impaired cognitive functions and neurochemical and structural abnormalities, may involve direct neuronal damage caused by intracellular glucose. The study assesses the direct effect of chronic hyperglycemia on the function of brain mitochondria, the major site of reactive species production, in diabetic streptozotocin (STZ) rats. Oxidative stress plays a central role in diabetic tissue damage. Alongside enhanced reactive oxygen species (ROS) levels, both nitric oxide (NO) levels and mitochondrial nitric oxide synthase expression were found to be increased in mitochondria, whereas glutathione (GSH) peroxidase activity and manganese superoxide dismutase protein content were reduced. GSH was reduced and GSH disulfide (GSSG) was increased in STZ rats. Oxidative and nitrosative stress, by reducing the activity of complexes III, IV and V of the respiratory chain and decreasing ATP levels, might contribute to mitochondrial dysfunction. In summary, this study offers fresh evidence that, besides the vasculardependent mechanisms of brain dysfunction, oxidative and nitrosative stress, by damaging brain mitochondria, may cause direct injury of neuronal cells.

Alongside increased proteolysis, the inability to repair damaged skeletal muscle is a characteristic feature of uncontrolled diabetes. This study evaluates the role of oxidative stress in muscle-specific gene regulatory regions and myosin chain synthesis in streptozotocin (STZ)-induced diabetic and ZDF rats. In the gastrocnemius muscle of diabetic rats, prooxidant compounds were seen to increase while antioxidant levels fell. Myogenic regulatory factors-Myo, myogenin, and Jun D-were also reduced, and muscle enhancer factor (MEF)-1 DNA binding activity was impaired. Moreover, synthesis of muscle creatine kinase and both heavy and light chains of myosin were impaired, suggesting that oxidative stress triggers the cascade of events that leads to impaired muscle repair. Dehydroepiandrosterone has been reported to possess antioxidant properties. When it was administered to diabetic rats, in addition to an improved oxidative imbalance there was a recovery of myogenic factors, MEF-1 DNA binding activity, synthesis of muscle creatine kinase, and myosin light and heavy chains. Vitamin E administration to STZ-induced diabetic rats reverses oxidative imbalance and improves muscle gene transcription, reinforcing the suggestion that oxidative stress may play a role in diabetes-related impaired muscle repair. Diabetes

No abstract

Free radical overproduction contributes to tissue damage induced by acute hyperglycemia. Dehydroepiandrosterone, which has recently been found to have antioxidant properties, was administered i.p. to rats at different doses (10, 50 or 100 mg/kg body weight) 3 h before treatment with dextrose (5 g/kg). Lipid peroxidation was evaluated on liver, brain and kidney homogenates, measuring both steady-state concentrations of thiobarbituric acid reactive substances, and fluorescent chromolipids, evaluated as hydroxynonenal adducts. Formation of thiobarbituric acid reactive substances was significantly higher in hyperglycemic than in normoglycemic animals. Three hours (but not 1 h) dehydroepiandrosterone-pretreatment protected tissues against lipid peroxidation induced by dextrose; both thiobarbituric acid reactive substances and hydroxynonenal adducts in liver, kidney and brain homogenates were significantly lower in dehydroepiandrosterone-pretreated animals. Dehydroepiandrosterone did not modify the cytosolic level of antioxidants, such as alpha-tocopherol or glutathione, nor the activities of glutathione peroxidase, reductase or transferase. The results of this study indicate that the 'in vivo' administration of dehydroepiandrosterone increases tissue resistance to lipid peroxidation triggered by acute hyperglycemia.

Both chronic hyperglycemia and ischemia/reperfusion (IR) cause an imbalance in the oxidative state of tissues. Normoglycemic and streptozotocin (STZ)-diabetic rats were subjected to bilateral carotid artery occlusion for 30 min followed by reperfusion for 60 min. Rats had either been treated with dehydroepiandrosterone (DHEA) for 7, 14, or 21 days (2 or 4 mg/day per rat) or left untreated. Oxidative state, antioxidant balance, and membrane integrity were evaluated in isolated synaptosomes. IR increased the levels of reactive species and worsened the synaptic function, affecting membrane Na/K-ATPase activity and lactate dehydrogenase release in all rats. The oxidative imbalance was much severer when transient IR was induced in STZ-diabetic rats. DHEA treatment restored H 2 O 2 , hydroxyl radical, and reactive oxygen species to close to control levels in normoglycemic rats and significantly reduced the level of all reactive species in STZ-diabetic rats. Moreover, DHEA treatment counteracted the detrimental effect of IR on membrane integrity and function: the increase of lactate dehydrogenase release and the drop in Na/K-ATPase activity were significantly prevented in both normoglycemic and STZ-diabetic rats. The results confirm that DHEA, an adrenal steroid that is synthesized de novo by brain neurons and astrocytes, possesses a multitargeted antioxidant effect. They also show that DHEA treatment is effective in preventing both derangement of the oxidative state and neuronal damage induced by IR in experimental diabetes. Diabetes