Deficit of coenzyme Q in heart and liver mitochondria of rats with streptozotocin-induced diabetes

Mitochondrial dysfunction and oxidative stress participate in the developme nt of diabetic complications, however, the mechanisms of their origin are n ot entirely clear. Coenzyme Q has an important function in mitochondrial bi oenergetics and is also a powerful antioxidant. Coenzyme Q (CoQ) regenerate s alpha-tocopherol to its active form and prevents atherogenesis by protect ing low-density lipoproteins against oxidation. The aim of this study was t o ascertain whether the experimentally induced diabetes mellitus is associa ted with changes in the content of endogenous antioxidants (alpha-tocophero l, coenzymes Q(9) and Q(10)) and in the intensity of lipoperoxidation. Thes e biochemical parameters were investigated in the blood and in the isolated heart and liver mitochondria. Diabetes was induced in male Wistar rats by a single intravenous injection of streptozotocin (45 mg.kg(-1)), insulin wa s administered once a day for 8 weeks (6 U.kg(-1)). The concentrations of g lucose, cholesterol, alpha-tocopherol and CoQ homologues in the blood of th e diabetic rats were increased. The CoQ(9)/cholesterol ratio was reduced. I n heart and liver mitochondria of the diabetic rats we found an increased c oncentration of alpha-tocopherol, however, the concentrations of CoQ(9) and CoQ(10) were decreased. The formation of malondialdehyde was enhanced in t he plasma and heart mitochondria. The results have demonstrated that experi mental diabetes is associated with increased lipoperoxidation, in spite of the increased blood concentrations of antioxidants alpha-tocopherol and CoQ . These changes may be associated with disturbances of lipid metabolism in diabetic rats. An important finding is that heart and liver mitochondria fr om the diabetic rats contain less CoQ(9) and CoQ(10) in comparison with the controls. We suppose that the deficit of coenzyme Q can participate in dis turbances of mitochondrial energy metabolism of diabetic animals.