Pinoline May be Used as a Probe for CYP2D6 Activity

Abstract

ABSTRACT:Pinoline, 6-methoxy-1,2,3,4-tetrahydro-␤-carboline, is a serotonin analog that selectively inhibits the activity of monoamine oxidase-A and shows antidepressant activity. Our previous study using a panel of recombinant cytochrome P450 (P450) enzymes suggests that pinoline O-demethylation may be selectively catalyzed by polymorphic CYP2D6. The current study, therefore, aimed to delineate the impact of CYP2D6 status on pinoline metabolism. Enzyme kinetic studies using recombinant CYP2D6 allelic isozymes revealed that CYP2D6.2 exhibited 5-fold lower enzyme efficiency (V max /K m ) toward pinoline compared with CYP2D6.1, and CYP2D6.10 did not show any catalytic activity. Inhibition study showed that quinidine (1 M) completely blocked pinoline O-demethylase activity in human liver microsomes, whereas other P450 isoform-selective inhibitors had no or minimal effects. Pinoline O-demethylase activities in 10 human liver microsomes showed significantly strong correlation with bufuralol 1-hydroxylase activities (R 2 ‫؍‬ 0.93; p < 0.0001) and CYP2D6 contents (R 2 ‫؍‬ 0.82; p ‫؍‬ 0.005), whereas no appreciable correlations with enzymatic activities of other P450 enzymes were found. Furthermore, we compared pinoline urinary metabolic ratio (pinoline/6-hydroxy-1,2,3,4-tetrahydro-␤-carboline) between CYP2D6-humanized and wild-type control mice after intraperitoneal injection of pinoline (30 mg/kg). Results indicated that the two genotyped mice were clearly distinguished by pinoline metabolic ratio (mean ؎ S.D.), which was much higher in wild-type mice (0.29 ؎ 0.19, n ‫؍‬ 4) than in CYP2D6-humanized transgenic mice (0.0070 ؎ 0.0048, n ‫؍‬ 4). Our findings suggest that pinoline O-demethylation is governed by CYP2D6 status, and pinoline, at a proper concentration or dose, may be a good probe to evaluate CYP2D6 activity.

Detection of an Endogenous Urinary Biomarker Associated With Cyp2D6 Activity Using Global Metabolomics

“…Several endogenous substrates have been proposed as CYP2D6 substrates. They include 5-methoxy- N,N -dimethyltryptamine [26], pinoline [27], progesterone [28], anandamide [29,30] and a number of compounds up- or downregulated in CYP2D6-transgenic mice [31]. However, the identification and validation of endogenous biomarkers for CYP2D6 phenotyping, particularly in humans, is immature.…”

Effects of monoamine oxidase inhibitor and cytochrome P450 2D6 status on 5-methoxy-N,N-dimethyltryptamine metabolism and pharmacokinetics

“…CYP2D6 phenotype or genotype of each hepatocyte sample was provided by the manufacturers, which was then classified as CYP2D6 extensive metabolizer (EM) or poor metabolizer (PM) hepatocytes as described [18]. CYP2D6 allelic isoforms were expressed using baculovirus-mediated system and purified as reported [19–21]. All other reagents or organic solvents used were either analytical or high-performance liquid chromatography (HPLC) grade.…”

Pharmacokinetic Interactions between Monoamine Oxidase A Inhibitor Harmaline and 5-Methoxy-N,N-Dimethyltryptamine, and the Impact of CYP2D6 Status

“…Enzyme incubations were carried out as reported using purified CYP2D6.1 enzyme (Yu et al, 2002;Jiang et al, 2009;Zhang et al, 2009). In particular, each reaction was incubated in 100 mM potassium phosphate buffer (pH 7.4) in a final volume of 200 ml at 37°C for 20 minutes, which consisted of 0.02 mM CYP2D6.1, 0.2 mM cytochrome P450 reductase, 10 mg L-a-dilauroylphosphatidylcholine, and 2 or 10 mM 5-MeO-DMT in the absence or presence of harmaline (2 or 20 mM).…”