Search

Brain-derived neurotrophic factor (BDNF), a member of the neurotrophins, has been reported to ameliorate hyperglycemia in obese diabetic animal models. To elucidate the mechanism of BDNF on glucose metabolism, we determined the glucose turnover under basal and euglycemic hyperinsulinemic (insulin infusion rate, 54 pmol · kg−1 · min−1) clamp conditions in obese insulin-resistant rats, male Zucker fatty rats, which had been acutely administered a subcutaneous injection of BDNF (20 mg/kg) (n = 9, BDNF) or vehicle (n = 8, vehicle). Under the basal condition, acute administration of BDNF did not affect the blood glucose level, plasma insulin level, rate of glucose disappearance (Rd), and endogenous glucose production (EGP). Under the clamp condition, the glucose infusion rate (GIR) was significantly higher in BDNF than in vehicle (mean ± SD, 61.4 ± 19.1 v 41.4 ± 4.9 μmol · kg−1 · min−1, P

An antibody has been raised against fructated lysine in proteins by immunizing fructated lysine-conjugated ovalbumin in rabbits. The affinity-purified antibody specifically recognized proteins incubated with fructose but not with other reducing sugars such as glucose, galactose or ribose, as judged by immunoblotting and ELISA techniques. Competitive binding to this antibody was observed specifically by fructated lysine but not by glucated lysine, glucose, fructose or lysine. The antibody binds specifically to fructated lysine residues in the protein but not to borohydride-reduced material or advanced glycation end products, indicating that the antibody recognizes only the reducing, carbonyl-containing forms produced in the early stage of the fructation reaction. When BSA was incubated with various concentrations of fructose, the reactivity of the antibody increased in a dose- and time-dependent manner. When soluble proteins prepared from either normal or streptozotocin-induced diabetic rat eyes were analysed by ELISA with this antibody, an increase in the reactive components was observed as a function of aging as well as under diabetic conditions. Western blotting analysis showed that lens crystallin reacted highly with this antibody. Because fructose is biosynthesized largely through the polyol pathway, which is enhanced under diabetic conditions, and lens is known to have a high activity of enzymes in this pathway, this antibody is capable of recognizing fructated proteins in vivo. Thus it is a potentially useful tool for investigating two major issues that seem to be involved in diabetic complications, namely the glycation reaction and the polyol pathway.

Sorbitol dehydrogenase (SDH) is involved in the polyol pathway, which plays an important role in the pathogenesis of diabetic complications. We have measured the tissue distributions of SDH mRNA, both the immunoreactive enzyme levels and the enzyme activity. SDH mRNA was especially abundant in liver, kidney and testis. Both the activity and enzyme content are high in liver and kidney but not in testis. The discrepancy between mRNA and immunoreactive enzyme levels and the activity of SDH observed in testis was also seen in livers of streptozotocin-induced diabetic rats. SDH was found to exist in both glycated and non-glycated forms, with larger amounts of the glycated protein in the diabetic liver. Moreover, after incubation of purified enzyme with glucose or fructose, its activity was markedly decreased. These results indicate that glycation causes a decrease in SDH activity in liver under diabetic conditions. The same post-transcriptional event might occur to decrease the activity of SDH in testis in normal animals.

The glycation reaction by fructose, as well as that by glucose, in control and diabetic rat lens was analyzed by using antibodies which specifically recognize adducts of lysine with fructose and with glucose. Levels of fructose adducts in diabetic rat lens were 2.5 times that of the control, and correlated with sorbitol levels. This was mainly due to enhanced glycation of β- and γ-crystallins by fructose under diabetic conditions. These data suggest that glycation by fructose may also play a role in cataract formation under conditions of diabetes and aging.

We examined age-related changes in the protein and the mRNA expression of aldose reductase in livers of Long-Evans with a cinnamon-like color (LEC) rats, which develop hereditary hepatitis and hepatoma with aging, using Long-Evans with an agouti color rats as controls. The levels of the protein and mRNA of aldose reductase increased after 20 weeks, at the stage of acute hepatitis, and were maintained at 60 weeks of age, while those of aldehyde reductase seemed to be constant at all ages. The expression of aldose reductase was marked in cancerous lesions in hepatoma-bearing LEC rat liver compared to uninvolved surrounding tissues. These results indicated that elevation of aldose reductase accompanied hepatocarcinogenesis and may be related to the acquisition of immortality of the cancer cells through detoxifying cytotoxic aldehyde compounds.