Butyrylcholinesterase and Erythrocyte Sulfhydryl-dependent Enzyme Hydrolyze Gabexate in Human Blood

Gabexate (GB), a serine protease inhibitor that is widely used for the treatment of acute pancreatitis and disseminated intravascular coagulation, has been reported to be partly hydrolyzed by human serum albumin. However, other enzymes responsible for GB hydrolysis in human blood remain unclear. In this study, we examined in vitro metabolism of GB with human blood samples. The hydrolytic activities of the plasma and erythrocytes at 100µM of GB were 167 ± 26 and 151 ± 9n mol/min/ml blood fraction (mean ± S.D., n = 8), respectively. Kinetic analysis indicated that Vmax and Km values were 1.75µmol/min/ml blood fraction and 529µ Mf or the plasma and 10.6µmol/min/ml blood fraction and 7360µ Mf or the erythrocytes, respectively. The activity of human plasma wa si nhibited by ethopropazine, a butyrylcholinesterase inhibitor (27% inhibition at 100µM). Furthermore, the plasma activity was inhibited by 5,5 � -dithiobis(2-nitrobenzoic acid) (DTNB) (40% inhibition at 5000µM), suggesting the involvement of albumin in the plasma GB hydrolysis. The erythrocyte activity was also decreased by DTNB (56% inhibition at 5000µM), implying that this activity was dependent on the presence of sulfhydryl group(s), while little or no inhibition of the activity was seen with phenylmethylsulfonyl fluoride, diisopropyl fluorophosphate, and BW284C51. Butyrylcholinesterase from human serum showed GB hydrolytic activity with Vmax of 363 nmol/min/m gp rotein and Km of 263µM. These results suggest that, in addition to albumin, butyrylcholinesterase and erythrocyte sulfhydryl-dependent enzyme are responsible for GB hydrolysis in human blood.