163 Molecular and Cellular Biochemistry 246: 163–170, 2003. © 2003 Kluwer Academic Publishers. Printed in the Netherlands. Diabetes and mitochondrial oxidative stress: A study using heart mitochondria from the diabetic Goto-Kakizaki rat Dario Loureiro Santos, 1 Carlos Marques Palmeira, 2,3 Raquel Seiça, 2,4 José Dias, 5 José Mesquita, 5 António Joaquim Moreno 2,3 and Maria Sancha Santos 2,3 1 University of Trás-os-Montes e Alto Douro, Vila Real; 2 Center for Neurosciences and Cell Biology of Coimbra, 3 Department of Zoology, 4 Faculty of Medicine, 5 Department of Botany, University of Coimbra, Coimbra, Portugal Abstract Increasing evidence shows that the overproduction of reactive oxygen species, induced by diabetic hyperglycemia, contrib- utes to the development of several cardiopathologies. The susceptibility of diabetic hearts to oxidative stress, induced in vitro by ADP-Fe 2+ in mitochondria, was studied in 12-month-old Goto-Kakizaki rats, a model of non-insulin dependent diabetes mellitus, and normal (non-diabetic) Wistar rats. In terms of lipid peroxidation the oxidative damage was evaluated on heart mitochondria by measuring both the O 2 consumption and the concentrations of thiobarbituric acid reactive substances. Dia- betic rats display a more intense formation of thiobarbituric acid reactive substances and a higher O 2 consumption than non- diabetic rats. The oxidative damage, assessed by electron microscopy, was followed by an extensive effect on the volume of diabetic heart mitochondria, as compared with control heart mitochondria. An increase in the susceptibility of diabetic heart mitochondria to oxidative stress can be explained by reduced levels of endogenous antioxidants, so we proceeded in determin- ing α-tocopherol, GSH and coenzyme Q content. Although no difference of α-tocopherol levels was found in diabetic rats as compared with control rat mitochondria, a significant reduction in GSH (21.5% reduction in diabetic rats) and coenzyme Q levels of diabetic rats was observed. The data suggest that a significant decrease of coenzyme Q 9 , a potent antioxidant involved in the elimination of mitochondria-generated reactive oxygen species, may be responsible for an increased susceptibility of diabetic heart mitochondria to oxidative damage. (Mol Cell Biochem 246: 163–170, 2003) Key words: heart mitochondria, diabetes, reactive oxygen species, coenzyme Q, α-tocopherol, Goto-Kakizaki rat Introduction Diabetes mellitus Type 2 or non-insulin-dependent diabetes mellitus (NIDDM) is a metabolic disorder characterised by hyperglycemia due to a decrease in the response of periph- eral tissues (e.g. liver, skeletal muscle, adipose tissue, pan- creatic β-cells) to insulin [1]. It has been well established that patients with diabetes mellitus, exhibit a high incidence of cardiac dysfunction and mortality [2]. Clinical studies sug- gested that diabetic patients have a significantly greater in- cidence and severity of several cardiopathies (e.g. angina, acute myocardial failure, atherosclerosis) [3, 4], and approxi- mately 80% of all patients with diabetes die of cardiovascu- lar disease [3]. Mitochondria play an important role in the development of NIDDM, which agrees with an age-related decline in the capacity for oxidative phosphorylation, and consequently contributes to its pathophysiology [5, 6]. In several animal models, a relationship has been established between diabe- tes and some dysfunctions in mitochondrial oxidative events [7, 8], suggesting the occurrence of bioenergetic alterations at the mitochondrial level [7, 9]. Mitochondria which play Address for offprints: M.S. Santos, Center for Neurosciences and Cell Biology of Coimbra, Department of Zoology, University of Coimbra, 3004-517 Coimbra, Portugal (E-mail: mssantos@ci.uc.pt)