2007 Volume 53 Issue 1 Pages 60-66
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 100 μM of GB were 167 ± 26 and 151 ± 9 nmol/min/ml blood fraction (mean ± S.D., n = 8), respectively. Kinetic analysis indicated that Vmax and Km values were 1.75 μmol/min/ml blood fraction and 529 μM for the plasma and 10.6 μmol/min/ml blood fraction and 7360 μM for the erythrocytes, respectively. The activity of human plasma was inhibited by ethopropazine, a butyrylcholinesterase inhibitor (27% inhibition at 100 μM). Furthermore, the plasma activity was inhibited by 5,5′-dithiobis(2-nitrobenzoic acid) (DTNB) (40% inhibition at 5000 μM), suggesting the involvement of albumin in the plasma GB hydrolysis. The erythrocyte activity was also decreased by DTNB (56% inhibition at 5000 μM), 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/mg protein and Km of 263 μM. These results suggest that, in addition to albumin, butyrylcholinesterase and erythrocyte sulfhydryl-dependent enzyme are responsible for GB hydrolysis in human blood.
