Alteration of urinary sorbitol excretion in WBN-kob diabetic rats - treatment with an aldose reductase inhibitor.

An accelerated polyol pathway in diabetes contributes to the development of diabetic complications. To elucidate diabetic nephropathy involving also renal tubular damage, we measured urinary sorbitol concentration concomitantly with urinary N-acetyl-D-glucosaminidase (NAG) excretion in WBN-kob diabetic rats.Twenty-four-hour urinary sorbitol concentrations increased in the diabetic rats in parallel with whole blood sorbitol concentrations. An increase in 24-h urinary NAG excretion coincided with the elevated urinary sorbitol levels in the diabetic rats. The administration of epalrestat, an aldose reductase inhibitor, reduced the increased whole blood and urinary sorbitol concentrations and urinary NAG excretion concomitantly with renal aldose reductase inhibition in the diabetic rats. These results indicate that diabetic nephropathy involves distorted cell function of renal tubules, and that treatment with epalrestat may prevent at least the progress of the nephropathy.

Urinary sorbitol measurement and the effect of an aldose reductase inhibitor on its concentration in the diabetic state.

The amounts of sorbitol (SOR) excreted in 24-h urine were determined on two groups, i.e., diabetic and nondiabetic patients, using an improved method in which ion exchange resin column processing was applied, and these levels were compared with SOR levels in whole blood. Urinary SOR concentration was also determined in diabetic and normal rats in the same manner and its relationship to aldose reductase (AR) activity in whole blood was investigated. Changes in SOR levels in urine and whole blood were compared in diabetic rats after administration of an AR inhibitor (ARI). Whole blood SOR levels and urinary SOR excretion were significantly higher in diabetic patients than in nondiabetic patients. The same results were obtained in the animal models. In diabetic rats, the urinary SOR excretion was about five times higher than that in control rats, and the AR activity in whole blood was also significantly higher. The increase in urinary SOR excretion and whole blood SOR levels, as well as AR activity, in blood in the diabetic state was inhibited by ARI administration. The influence of the diabetic state and the efficacy of the ARI were more marked in urinary SOR excretion than in whole blood SOR levels. These data indicate that determinations of urinary SOR excretion and AR activity are easily measurable and of benefit to assessing the diabetic condition.

Evaluation of antilipid peroxidative action of propolis ethanol extract.

The antilipid peroxidative action of the ethanol extract of Brazilian propolis at a concentration of 47% (w/v) was evaluated by examining the inhibitory effect of the extract on the formation of hydroperoxide- and endoperoxide-type lipid peroxides during heating of authentic polyunsaturated fatty acids and on Fe(3+)-ADP/ascorbic acid- and Fe(3+)-ADP/NADPH-dependent lipid peroxidation reactions in rat liver microsomes. Hydroperoxide-type lipid peroxides were measured by the haemoglobin-methylene blue method and endoperoxide-type lipid peroxides by the thiobarbituric acid (TBA), Fe(3+)-TBA and LPO-586 methods. Propolis ethanol extract inhibited dose-dependently the formation of hydroperoxide- and endoperoxide-type lipid peroxides during heating of linoleic acid, linolenic acid or arachidonic acid and the amount of the extract causing a half inhibition of these lipid peroxide formations ranged between 20 and 75 microg. Propolis ethanol extract inhibited dose-dependently both Fe(3+)-ADP/ascorbic acid- and Fe(3+)-ADP/NADPH-dependent lipid peroxidation reactions in rat liver microsomes when lipid peroxides produced in both reactions were measured by the TBA method. The amount of propolis extract causing a half inhibition of the Fe(3+)-ADP/ascorbic acid-dependent lipid peroxidation was about 5 microg, while that of the extract causing a half inhibition of the Fe(3+)-ADP/NADPH-dependent lipid peroxidation was about 0.15 microg. These results indicate that the propolis ethanol extract exerts an antilipid peroxidative action at very low doses.