DS-4574

We evaluated the protective effect of DS-4574 (6-(2-cyclohexylethyl)-[1,3,4]thiadiazolo[3,2-a]-1,2,3- triazolo[4,5-d]pyrimidin-9(3H)-one), a peptidoleukotriene receptor antagonist, against intestinal mucosal injury evoked by endotoxin in rats by exploring changes in hematocrit and plasma leakage along with morphological features. Treatment with Escherichia coli endotoxin (5 mg/kg i.v.) alone elicited hemoconcentration, vasocongestion and a marked mucosal necrosis. DS-4574 (10-50 mg/kg) effectively prevented these changes on either oral or intraduodenal administration. These results demonstrate that peptidoleukotrienes may be key mediators in the intestinal injury induced by endotoxin in rats.

A sensitive radioimmunoassay (RIA) method for DS-4574, an antiallergic drug, in plasma has been developed. As the three major metabolites have a hydroxyl group on the cyclohexyl ring, the triazole ring in the terminal part of molecule was attached to ovalbumin with a spacer of beta-chloropropionic acid succinimido ester to prepare an immunogen. Anti-DS-4574 antisera was obtained in rabbits immunized with the immunogen emulsified in Freund's complete adjuvant. The detection limit of the present RIA method was 1 mg/mL of plasma, which was 100-fold more sensitive than the HPLC method developed previously. Cross-reactivities with three major metabolites were less than 3%. The precision of the assay based on triplicate samples showed intra- and inter-assay coefficients of variations of less than 5% and 4%, respectively. This RIA method was applied to plasma samples of six volunteers who had received a single oral 10 mg dose of DS-4574. Plasma concentrations increased rapidly and reached 60 ng/mL at 0.5 h after administration. The concentration decreased to near the detection limit at 4 h postdose. The present RIA method was shown to possess adequate sensitivity to evaluate pharmacokinetic properties of the drug for clinical study, which was not possible by the HPLC method.