The intestinal absorption mechanism of temocapril, an ester-type prodrug of temocaprilat, was evaluated using Caco-2 cell monolayers with or without active carboxylesterase (CES)-mediated hydrolysis. The inhibition of CES-mediated hydrolysis was achieved by pretreatment of the monolayers with bis-p-nitrophenyl phosphate (BNPP), which inhibited 94% of the total hydrolysis of temocapril in the Caco-2 cells. The remaining 6% hydrolysis was due to the presence of serine esterases, other than CES, on the cell membranes. Transport experiments under CES-inhibited conditions showed temocapril not to be a substrate for peptide transporter 1 (PEPT1) or organic anion transporting polypeptides (OATPs), but to be an inhibitor of PEPT1; P-glycoprotein (P-gp) and breast-cancer-resistant protein (BCRP) were responsible for the efflux of temocapril, which was mainly absorbed by passive diffusion at low apical pH. In Caco-2 cell monolayers with CES-mediated hydrolysis intact, temocaprilat derived from temocapril, was 2.5-fold more rapidly transported into the apical compartment than into the basolateral compartment due to the presence of microvilli on the apical membrane. In contrast, temocaprilat at low intracellular concentrations, was preferentially transported across the basolateral membrane under CES-inhibited conditions.
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