Identification of the active metabolite of ticlopidine from rat in vitro metabolites

Abstract

1 Ticlopidine is a well-known anti-platelet agent, but is not active by itself in vitro. We identified a metabolite with anti-platelet activity, which was generated after incubation of 2-oxo-ticlopidine with phenobarbital-induced rat liver homogenate in vitro. 2 An active moiety (UR-4501) was isolated by high-performance liquid chromatography after largescale preparation of metabolites. 3 The chemical structure of UR-4501 was determined by a combination of liquid chromatography mass/mass spectrometry (LC/MS/MS) and nuclear magnetic resonance (NMR) analysis. 4 UR-4501 produced a concentration-dependent inhibition (3-100 mM) of ADP (10 mM)-induced human platelet aggregation, whereas 2-oxo-ticlopidine (3-100 mM) did not elicit inhibitory responses. 5 UR-4501 (10-100 mM) strongly inhibited ADP-and collagen-induced aggregation and slightly inhibited thrombin-induced aggregation. 6 The inhibition of rat washed platelet aggregation by UR-4501 (100 mM) persisted, even after the platelets had been washed twice. 7 These results suggest that UR-4501 is the molecule responsible for the in vivo activities of ticlopidine.

Metabolism of Ticlopidine in Rats: Identification of the Main Biliary Metabolite as a Glutathione Conjugate of TiclopidineS-Oxide

“…The pharmacologically active metabolite was generated by incubation of 2-oxo-ticlopidine with rat liver microsomes (Fig. 12) as reported previously (Yoneda et al, 2004). ROT, a novel thiophene ring-opened metabolite with a thioketone group and a carboxylic function, was also found during in vitro oxidation from 2-oxo-ticlopidine (Fig.…”

“…In the 1980s, metabolic studies suggested that N-dealkylation, N-oxidation, and oxidation of the thiophene ring followed by ring opening appeared to be the main routes, but numerous highly polar urinary and biliary metabolites in both humans and animals remained unidentified (Tuong et al, 1981;Panak et al, 1983). More recently, novel ticlopidine metabolites such as the S-oxide form (Ha-Duong et al, 2001) and the pharmacologically active metabolite (Yoneda et al, 2004) have been detected. However, the whole metabolism of ticlopidine has remained unclarified.…”

Mechanism-Based Inhibition of Human Cytochrome P450 2B6 by Ticlopidine, Clopidogrel, and the Thiolactone Metabolite of Prasugrel

“…The thiolactone metabolites of ticlopidine and clopidogrel are produced by P450-mediated oxidation (Yoneda et al, 2004;Kurihara et al, 2005), whereas R-95913 is produced by esterase-mediated hydrolysis of prasugrel (Williams et al, 2008). The hydrolysis of prasugrel is very rapid both in vitro and in vivo, such that it is not detected in human plasma even at early time points after oral administration .…”

“…The hydrolysis of prasugrel is very rapid both in vitro and in vivo, such that it is not detected in human plasma even at early time points after oral administration . The thiolactones of each of these agents are converted to the pharmacologically active metabolites, each of which possesses a thiol group, by P450-mediated oxidation (Yoneda et al, 2004;Kurihara et al, 2005;Rehmel et al, 2006). Because of the P450 dependency of the metabolic pathways, ticlopidine, clopidogrel, and the thiolactone metabolites of ticlopidine, clopidogrel, and prasugrel could have the potential to cause a drug-drug interaction through the inhibition of P450s.…”

“…Prasugrel, also a prodrug, is first hydrolyzed to a thiolactone metabolite (R-95913), which is then converted to the pharmacologically active metabolite (R-138727) through a single, P450-mediated oxidation step (Fig. 1) (Rehmel et al, 2006;Williams et al, 2008).The thiolactone metabolites of ticlopidine and clopidogrel are produced by P450-mediated oxidation (Yoneda et al, 2004;Kurihara et al, 2005), whereas R-95913 is produced by esterase-mediated hydrolysis of prasugrel (Williams et al, 2008). The hydrolysis of prasugrel is very rapid both in vitro and in vivo, such that it is not detected in human plasma even at early time points after oral administration .…”