Kinetics and molecular docking studies of kaempferol and its prenylated derivatives as aldose reductase inhibitors.

Aldose reductase inhibitors (ARIs) suppressing the hyperglycemia-induced polyol pathway have been provided as potential therapeutic candidates in the treatment and prevention of diabetic complications. Based upon structure-activity relationships of desmethylanhydroicaritin (1) and sophoflavescenol (2) as promising ARIs, 3,4'-dihydroxy flavonols with a prenyl or lavandulyl group at the C-8 position and a hydroxyl or methoxy group at the C-5 position are important for aldose reductase (AR) inhibition. In order to prove the above results, a combination of computational prediction and enzyme kinetics has begun to emerge as an effective screening technique for the potential. In the present study, we predicted the 3D structure of AR in rat and human using a docking algorithm to simulate binding between AR and prenylated flavonoids (1 and 2) and kaempferol (3) and scrutinized the reversible inhibition of AR by these ARIs. Docking simulation results of 1-3 demonstrated negative binding energies (Autodock 4.0=-9.11 to -7.64 kcal/mol; Fred 2.0=-79.54 to -51.84 kcal/mol) and an additional hydrogen bond through Phe122 and Trp219, in addition to the previously proposed interaction of AR and phenolics through Trp20, Tyr48, His110, and Trp111 residues, indicating that the presence of 8-prenyl and 5-methyl groups might potentiate tighter binding to the active site of the enzyme and more effective AR inhibitors. Moreover, types of AR inhibition were different depending on the presence or absence of the 8-prenyl group, in that 1 and 2 are mixed inhibitors with respective Ki values of 0.69 μM and 0.94 μM, while 3 showed noncompetitive inhibition with a Ki value of 4.65 μM. The present study suggests that an effective strategy for screening potential ARIs could be established by predicting 3D structural conformation of prenylated flavonoids and the orientation within the enzyme as well as by simultaneously determining the mode of enzyme inhibition.