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Investigation for natural extract inhibitors of bovine lens aldose reductase responsible for the formation of diabetis dependent cataract

Onay, Melih
In the polyol pathway, Aldose reductase (AR) is an important enzyme in reduction of aldehydes and aldosugars to their suitable alcohols. AR, using NADPH as a coenzyme, has a molecular weight of 37 000 dalton. AR in its activated form, known to increase the sorbitol accumulation in lens, is responsible for the cataract formation in diabetis diseases. Therefore, the inhibition of aldose reductase is important to prevent the incedence of cataract formation in diabetus mellitus. In the treatment of diabetis dependent cataract, chemically synthetized drugs were sometimes less than beneficial due to the severe side effects they cause. Recently a huge amount of study has been intensified on developing new drugs from natural compounds and even by utilizing plant extracts for their easily metabolizing polyphenolic compounds. In this study, BLAR, source of enzyme, was obtained as crude via differential centrifugation and ammonium sulfate precipitation. The enzyme assay conditions were optimized for the protein, substrate, coenzyme, and salt concentrations, also for the effects of pH and temperature. Ocimum basilicum, Lavandula stoechas, Melissa officinalis, Glycyrrhiza glabra L. and Tilia tomentosa were selected as commonly used alternative medicine plants. Plant extracts were prepared in ethanol and ethyl acetate and their inhibitory effects were tested on crude bovin lens aldose reductase enzyme. Fifty percent inhibitory concentrations (IC50) were found between values of 25.53 g/mL and 54.15 g/mL for ethanol extracts and between 41.55 g/mL and 82.96 g/mL for the ethyl acetate extracts of selected plants. In addition, the plant extracts were also characterized for their antioxidant activities by of 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging method and test of total phenolic content (TPC) .