Cholera toxin-induced PGE(2) activity is reduced by chemical reaction withL-histidine

Mediators of cholera toxin (CT)-induced fluid secretion include 3',5'-adeno sine monophosphate (cAMP), prostaglandin E-2 (PGE(2)), and 5-hydroxytryptam ine (5-HT). Administration Of L-histidine significantly reduced the net sec retory response of the small intestine of mice challenged with CT and reduc ed the capacity of PGE(2) to stimulate Na+ transport in Ussing chambers. We demonstrated that L-histidine chemically modified the structure of PGE(2) but had no direct effect on cAMP or 5-HT. L-Histidine and imidazole reacted with PGE(2) in vitro in cell-free mixtures incubated at 37 degreesC and pH 7.0 under an atmosphere of N-2 with the formation of PGE(2)-imidazole and PGE(2)-histidine covalent adducts. Nuclear magnetic resonance (NMR) spectro scopy and mass spectrometry (MS) analysis of the purified adduct showed tha t imidazole catalyzed the dehydration of PGE(2). A Michael adduct then was formed between C11 of 11-deoxy-Delta (10) PGE(2) (PGA(2)) and the tau nitro gen in the imidazole ring of L-histidine. Importantly, the isolated PGE(2)- imidazole and PGE(2)-histidine adducts inhibited CT-induced fluid loss and cAMP accumulation in mouse intestinal loops. The protection provided by PGE (2)-imidazole. PGE(2)-histidine, and L-histidine against intestinal fluid l oss could provide a basis for future therapy against cholera, (C) 2001 Else vier Science B.V. All rights reserved.