In vitro Characterization of the Oxidation of a Pyridinium Metabolite of Haloperidol by Human Placenta: The Effect of Smoking
AbstractPurpose. The antipsychotic drug haloperidol can be metabolised to pyridinium metabolites haloperidol pyridinium (HP+) and reduced haloperidol pyridinium (RHP+). These pyridinium metabolites were proposed to contribute to the extrapyramidal side effects of haloperidol, because they are structural analogues of N-methyl-4-phenylpyridinium (MPP+), a well-known neurotoxin. RHP+ can be oxidized to HP+ by CYP1A1. In the current study, the oxidation of RHP+ to HP+ was investigated using human placenta microsomal preparations which contain relatively high levels of CYP1A1. Methods. Cytochrome P450 isoenzymes responsible for the metabolism of RHP+ were characterized in vitro using human placenta microsomal preparations from smokers and non-smokers. Results. A comparison of the metabolic activities between smokers and non-smokers suggests that smokers had higher activities for the oxidation of RHP+. A selective antibody against CYP1A1 was a partial inhibitor of RHP+ oxidase in placenta from smokers but had no effect in placenta from non-smokers. Furafylline and ketokonazole were shown to be stronger inhibitors of the oxidation of RHP+ to HP+ in liver than in placenta. This seems to indicate important contributions of CYP1A1 and CYP3A7 as compared to CYP1A2 and CYP3A4, respectively, because furafylline and ketokonazole are stronger inhibitors of CYP1A2 and CYP3A4 than CYP1A1 and CYP3A7, respectively. Interestingly, α-naphathoflavone enhanced the metabolic activity in liver microsomes due to its activator effect on CYP3A4. On the other hand, α-naphathoflavone partially inhibited the activity in placenta microsomes, indicating a role played by CYP1A1 or CYP1A2 in the oxidation of RHP+ in placenta. Conclusions. These data indicate that CYP1A1 plays an important role in the oxidation of RHP+ to HP+ in placenta from smokers. CYP3A7 and CYP3A4 could also play important roles in the metabolism of RHP+ in placenta microsomes. This article is open to POST-PUBLICATION REVIEW. Registered readers (see “For Readers”) may comment by clicking on ABSTRACT on the issue’s contents page.
How to Cite
This is an open access journal with with free of charge submission and non-commercial download. At the time of submission, authors will be asked to transfer the copyright to the accepted article to the Journal of Pharmacy and Pharmaceutical Sciences. The author may purchase the copyright for $500 upon which he/she will have the exclusive copyright to the article. Nevertheless, acceptance of a manuscript for publication in the Journal is with the authors' approval of the terms and conditions of the Creative Commons copyright license Creative Common license (Attribution-ShareAlike) License for non-commercial uses.
CLOCKSS system has permission to collect, preserve, and serve this Archival Unit.