Biol. Pharm. Bull. 29(3) 588—591 (2006)

dietary consumption of fruit and vegetables results in lower risks of certain cancers and cardiovascular disease. There is accumulating evidence that these effects of fruit and vegetables attribute to antioxidants nutrients such as carotenoids, vitamins, and phenolic phytochemicals. Recent studies have shown that antioxidant vitamins and carotenoids may have a protective effect against diabetes mellitus. Satsuma mandarin (Citrus unshiu MARC.) is the most frequently consumed domestic fruit in Japan. Numerous antioxidants such as b-cryptoxanthin, vitamins, and flavonoids exist in pulp of this fruit. Previously, we found inverse association of the prevalence of diabetes mellitus with frequency of Satsuma mandarin intake based on data from 6049 participants on a self-administered questionnaire in crosssectionally. Furthermore, very recently, Kamata et al. reported that the chronic administration of Satsuma mandarin fruit extract improved endothelial dysfunction in the aorta in streptozotocin (STZ)-induced diabetic rats without lowering plasma cholesterol. Hyperglycemia increases the generation of free radicals by glucose auto-oxidation. Oxidative stress resulting from the increased production of reactive oxygen species plays a key role in the development of diabetic mellitus or its complications. Therefore, Satsuma mandarin would be expected to protect against the development of diabetes mellitus or the pathogenesis of diabetic complications. On the other hand, the liver plays an important role in glucose metabolism, and it is a major site of insulin clearance. Oxidative stress induced by hyperglycemia may lead to liver cell damage. Wohaieb et al. found that the antioxidant enzyme activities and glutathione level in STZ-induced diabetic rat liver significantly decreased compared with those in control rats and that the impairment of the antioxidant defense system in STZ-induced diabetic rat liver was reversed by insulin treatment. These results indicate that oxidative stress induced by hyperglycemia may lead to liver dysfunction. In this study, we expected that Satsuma mandarin would inhibit liver injury induced by hyperglycemia and investigated the effects of the chronic administration of Satsuma mandarin on the antioxidant defense system: i.e., the superoxide dismutase (SOD), catalase, glutathione peroxidase (GPx), glutathione reductase (GR), and glutathione levels in an STZ-induced type-1 diabetic model rat liver.