title: Hydrolysis of angiotensin II receptor blocker prodrug olmesartan medoxomil by human serum albumin and identification of its catalytic active sites.
abstract: 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 (deltaS) 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.
authors.affiliation: Graduate School of Pharmaceutical Sciences, Kumamoto University, 5-1 Oe-honmachi, Kumamoto 862-0973, Japan.
authors.forename: Shen-Feng
authors.initials: SF
authors.lastname: Ma
authors.forename: Makoto
authors.initials: M
authors.lastname: Anraku
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Iwao
authors.forename: Keishi
authors.initials: K
authors.lastname: Yamasaki
authors.forename: Ulrich
authors.initials: U
authors.lastname: Kragh-Hansen
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Yamaotsu
authors.forename: Shuichi
authors.initials: S
authors.lastname: Hirono
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Ikeda
authors.forename: Masaki
authors.initials: M
authors.lastname: Otagiri
mesh_terms: D047228:Angiotensin II Type 1 Receptor Blockers / Q000737:chemistry*; D001665:Binding Sites; D002384:Catalysis; D006801:Humans; D006868:Hydrolysis; D007093:Imidazoles / Q000737:chemistry*; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D000068557:Olmesartan Medoxomil; D012709:Serum Albumin / Q000502:physiology*; D013777:Tetrazoles / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D047228:Angiotensin II Type 1 Receptor Blockers; D007093:Imidazoles; D012709:Serum Albumin; D013777:Tetrazoles; D000068557:Olmesartan Medoxomil