Hepatic clearance of ONO-5046, a novel neutrophil elastase inhibitor, in rats and in the rat perfused liver.

Abstract

The hepatic clearance of ONO-5046 (N-[2-[4-(2,2-dimethylpropionyloxy)phenylsulphonylamino]benz oyl]aminoacetic acid), a low-molecular-weight neutrophil elastase inhibitor, has been investigated in rats and in the rat perfused liver. This ester was easily hydrolysed to its inactive metabolite EI-601 (N-[2-[(4-hydroxyphenyl)sulphonylamino]benzoyl]aminoacetic acid) in liver homogenate and in erythrocytes suspension in-vitro. On the other hand, it was stable in biological media such as plasma and whole blood, which contain plasma proteins. Scatchard plot analysis of ONO-5046 binding to bovine serum albumin (BSA) in-vitro indicated that the association constant (K) and number of binding sites (n) were 6.91 x 10(4) (M(-1)) and 4.33, respectively. Thus, ONO-5046 (100 microM) would bind to plasma proteins to an extent >99% at physiological plasma-protein concentrations. The total plasma clearance of ONO-5046 in rats was constant (approximately 9 mL min(-1) kg(-1)) under different steady-state plasma concentrations (5-50 microM) a value equivalent to the hepatic clearance. In the rat perfused liver, the hepatic extraction ratio of ONO-5046 was significantly reduced by adding BSA to the dosing solution. Thus, the relatively low hepatic clearance of ONO-5046, which has an ester linkage in its structure and is naturally susceptible to enzymatic hydrolysis, was found to be because of the extremely high protein-binding of the compound.