RT Journal Article SR Electronic T1 HYDROLYSIS OF ANGIOTENSIN II RECEPTOR BLOCKER PRODRUG OLMESARTAN MEDOXOMIL BY HUMAN SERUM ALBUMIN AND IDENTIFICATION OF ITS CATALYTIC ACTIVE SITES JF Drug Metabolism and Disposition JO Drug Metab Dispos FD American Society for Pharmacology and Experimental Therapeutics SP 1911 OP 1919 DO 10.1124/dmd.105.006163 VO 33 IS 12 A1 Shen-Feng Ma A1 Makoto Anraku A1 Yasunori Iwao A1 Keishi Yamasaki A1 Ulrich Kragh-Hansen A1 Noriyuki Yamaotsu A1 Shuichi Hirono A1 Toshihiko Ikeda A1 Masaki Otagiri YR 2005 UL http://dmd.aspetjournals.org/content/33/12/1911.abstract AB In the present study, we investigated the esterase-like activity of human serum albumin (HSA) and the mechanism by which it hydrolyzes, and thereby activates, olmesartan medoxomil (CS-866), a novel angiotensin II receptor antagonist. CS-866 has previously been shown to be rapidly hydrolyzed in serum in which HSA appeared to play the most important role in catalyzing the hydrolysis. We found that the hydrolysis of CS-866 by HSA followed Michaelis-Menten kinetics. Compared with the release of p-nitrophenol from p-nitrophenyl acetate (PNPA), CS-866 showed lower affinity to HSA and a lower catalytic rate of hydrolysis. Thermodynamic data indicated that PNPA has a smaller value of activation entropy (ΔS) than CS-866; consequently, PNPA is more reactive than CS-866. Ibuprofen and warfarin acted as competitive inhibitors of hydrolysis of CS-866, whereas dansyl-l-asparagine, n-butyl p-aminobenzoate, and diazepam did not. These findings suggest that the hydrolytic activity is associated to parts of site I and site II for ligand binding. All chemically modified HSA derivatives (Tyr-, Lys-, His-, and Trp-modifications) had significantly lower reactivity than native HSA; Lys-HSA and Trp-HSA had especially low reactivity. All the mutant HSAs tested (K199A, W214A, and Y411A) exhibited a significant decrease in reactivity, suggesting that Lys-199, Trp-214, and Tyr-411 play important roles in the hydrolysis. Results obtained using a computer docking model are in agreement with the experimental results, and strongly support the hypotheses that we derived from the experiments. The American Society for Pharmacology and Experimental Therapeutics