In vivo effect of 5‐ and 8‐methoxypsoralens and cimetidine on R,S‐warfarin metabolism in rat

Abstract

Several forms of cytochrome P-450 (CYP) metabolize R,S-warfarin in a regio- and enantioselective manner, therefore R,S-warfarin can be recognized as a metabolic probe for a number of CYP isoforms. We have applied a warfarin model in vivo in order to estimate the inhibitory properties of 5- and 8-methoxypsoralens on the activity of rat CYP isoforms. The area under the serum concentration versus time curve (AUC) values from time zero to 5 h for R- and S-warfarin and their metabolites were calculated. R,S-Warfarin kinetics measurements were made three times on each rat: a week before the 7-days inhibitor treatment, 3 h after the last dose of inhibitor and 3-7 days after the inhibitor was withdrawn. The inhibitory effect of cimetidine on CYP 2C11 and CYP 2C6 activities was confirmed in this approach and can be recognized as a positive control in validation of the in vivo experiment. Both 5- and 8-methoxypsoralen inhibited CYP 2C6 activity as the respective AUC for metabolite/warfarin enantiomer ratio decreased significantly. The activity of CYP 2C6 in 5- and 8-methoxypsoralen-treated rats increased over control values after the inhibitor was withdrawn. It was also observed that cimetidine additionally inhibits the absorption of R,S-warfarin and a decrease in the sum of AUC for R- and S-enantiomers became evident in spite of inhibition of the activity of both CYPs. 5-Methoxypsoralen modified the serum R-warfarin/S-warfarin ratio and a selective increase in AUC(S-warfarin) was observed, the most pronounced being after the inhibitor was withdrawn. This effect is not likely to be mediated by P-glycoprotein (P-gp) because quinidine--, a P-gp inhibitor at a dose of 15 mg kg(-1) body wt.--did not influence the AUC for either enantiomer.

Impact of gastric acid suppressants on cytochrome P450 3A4 and P-glycoprotein: Consequences for FK506 assimilation

“…Subsequent exploration of the observations made in patients with studies in healthy volunteers showed that treatment with cimetidine caused a decrease of overall CYP activity, according to in vitro findings [9,10]. However, no specific effect on CYP3A4 activity in vivo was noted.…”

“…However, numerous studies have demonstrated a modulating effect of both cimetidine and omeprazole-and to a lesser extent ranitidineon several CYP isozymes, implicating a potential effect on bioavailability and clearance of CYP3A4 dependent immunosuppressants. Most of these studies have been done in vitro or ex vivo, which does not allow an easy extrapolation to clinical practice [9][10][11][12].…”

CC12, a high-affinity ligand for [3H]cimetidine binding, is an improgan antagonist

“…However, a closely related substance, 4(5)-(benzylthiomethyl)-1H-imidazole (which has the structure of CC12 without the iodosubstituent), was reported to be a weak inhibitor of histamine synthesis (Swett and Yellin, 1970), and an inhibitor of microsomal drug oxidation (Wilkinson et al, 1974;Wilkinson et al, 1972). Interactions between imidazole-containing histamine antagonists and some cytochrome P-450 proteins are well known (Szutowski et al, 2002,Alves-Rodrigues et al, 1996. The modulation of a cytochrome P-450 protein by CC12 could be the basis for this drug's antianalgesic action, since a P-450 pathway has been implicated in supraspinal opioid analgesic signaling (Vaughan et al, 1997).…”

Quantification of Warfarin in Dried Rat Plasma Spots by High-Performance Liquid Chromatography with Tandem Mass Spectrometry

“…Initially, the analytical method of high-performance liquid chromatography (HPLC) with ultraviolet (UV) spectrum detection was used for the quantification of warfarin [6–8]. In these works, warfarin was isolated from plasma or serum by solid-phase extraction on a semipermeable surface guard column [6] or by liquid/liquid extraction with ice-cold acetonitrile [7] or with diethyl ether [8]. Although a 100  μ L [6, 7] or 1 mL aliquot of plasma [8] was used, such an analytical method was questionable due to low specificity and sensitivity of UV detection.…”

“…In these works, warfarin was isolated from plasma or serum by solid-phase extraction on a semipermeable surface guard column [6] or by liquid/liquid extraction with ice-cold acetonitrile [7] or with diethyl ether [8]. Although a 100  μ L [6, 7] or 1 mL aliquot of plasma [8] was used, such an analytical method was questionable due to low specificity and sensitivity of UV detection. Therefore, several methods of HPLC with mass spectrometry (MS) and HPLC with tandem mass spectrometry (MS/MS) have been developed for warfarin quantification in single-reaction monitoring mode [5, 9, 10] or multiple-reaction monitoring mode [4, 11–13].…”