Inhibition of Aldose Reductase and Sorbitol Accumulation by Hydroalcoholic Extract of Propolis

Increased polyol pathway activity and subsequent occurrences, and particular sorbitol accumulation are noticed in the development of various secondary complications of diabetes. Aldose reductase (ALR2) or aldo-ketoreductase (AKR1B1) as the first and rate limiting enzyme of this pathway is a good target for new drugs for diabetes complications. A good inhibitor should inhibit aldehyde reductase (ALR1), the other member of this family lesser than ALR2. Bee propolis is a known substance in ancient medicine, but its effect on polyol pathway is unknown. The current study aimed to investigate the effect of hydroalcoholic extract of propolis (HAEP) on partial purified bovine lens ALR2, also the effect of HAEP on sorbitol accumulation in human erythrocytes in high-glucose condition (ex vivo). Total protein was determined by lowery method. Bovine lens ALR2 was partially purified by gel filtration chromatography on sephadexTM G25. Bovine cortex kidney ALR1 was partially purified by diethylaminoethyl (DEAE) precipitation. The hydroalcoholic extract was obtained from frozen propolis. The enzyme activity and sorbitol accumulation in erythrocytes were determined spectroflourimetrically. It was found that ethyl acetate (EthAc) fraction (the more potent fraction) of HAEP inhibited ALR2 by IC50 value of 1.12 mg/mL up to 50% and this fraction can inhibit ALR2 8.25-fold greater than ALR1. In addition, it was found that this fraction could decrease sorbitol accumulation in human erythrocytes under high-glucose condition. The obtained results indicated that propolis may be a good candidate for more studies to find new drugs for the treatment of secondary complications of diabetes.