January 1999, Volume 126, Issue 1, Pages 61 - 68

Original Article

Enantioselective inhibition of the biotransformation and pharmacological actions of isoidide dinitrate by diphenyleneiodonium sulphate Jodan D. Ratz, John J. McGuire & Brian M. Bennett1 Department of Pharmacology and Toxicology, Faculty of Health Sciences, Queen's University, Kingston, Ontario, Canada K7L 3N6     1Author for correspondence: E-mail: bennett@post.queensu.ca.

Keywords

Biotransformation;   diphenyleneiodonium sulphate;   glutathione S-transferase;   glyceryl trinitrate;   haemodynamics;   isoidide dinitrate;   NADPH-cytochrome P450 reductase;   pharmacokinetics

Abstract

1   We have shown previously that the D- and L- enantiomers of isoidide dinitrate (D-IIDN and L-IIDN) exhibit a potency difference for relaxation and cyclic GMP accumulation in isolated rat aorta and that this is related to preferential biotransformation of the more potent enantiomer (D-IIDN). The objective of the current study was to examine the effect of the flavoprotein inhibitor, diphenyleneiodonium sulphate (DPI), on the enantioselectivity of IIDN action. 2   In isolated rat aortic strip preparations, exposure to 0.3 µM DPI resulted in a 3.6 fold increase in the EC50 value for D-IIDN-induced relaxation, but had no effect on L-IIDN-induced relaxation. 3   Incubation of aortic strips with 2 µM D- or L-IIDN for 5 min resulted in significantly more D-isoidide mononitrate formed (5.0±1.5 pmol mg protein-1) than L-isoidide mononitrate (2.1±0.7 pmol mg protein-1) and this difference was abolished by pretreatment of tissues with 0.3 µM DPI. DPI had no effect on glutathione S-transferase (GST) activity or GSH-dependent biotransformation of D- or L-IIDN in the 105,000×g supernatant fraction of rat aorta. 4   Consistent with both the relaxation and biotransformation data, treatment of tissues with 0.3 µM DPI significantly inhibited D-IIDN-induced cyclic GMP accumulation, but had no effect on L-IIDN-induced cyclic GMP accumulation. 5   In the intact animal, 2 mg kg-1 DPI significantly inhibited the pharmacokinetic and haemodynamic properties of D-IIDN, but had no effect L-IIDN. 6   These data suggest that the basis for the potency difference for relaxation by the two enantiomers is preferential biotransformation of D-IIDN to NO, by an enzyme that is inhibited by DPI. Given that DPI binds to and inhibits NADPH-cytochrome P450 reductase, the data are consistent with a role for the cytochromes P450-NADPH-cytochrome P450 reductase system in this enantioselective biotransformation process.

Received 27 April 1998; Revised 1 October 1998; Accepted 5 October 1998

^© Macmillan Publishers Ltd 1999