Contribution of Individual Cytochrome P450 Isozymes to theO-Demethylation of the Psychotropic β-Carboline Alkaloids Harmaline and Harmine

Abstract

The psychotropic ␤-carboline alkaloids, showing high affinity for 5-hydroxytryptamine, dopamine, benzodiazepine, and imidazoline receptors and the stimulation of locus coeruleus neurons, are formed endogenously from tryptophan-derived indolealkylamines through the Pictet-Spengler condensation with aldehydes in both plants and mammals. Cytochromes P450 1A1 (18.5), 1A2 (20), and 2D6 (100) catalyzed the O-demethylation of harmaline, and CYP1A1 (98.5), CYP1A2 (35), CYP2C9 (16), CYP2C19 (30), and CYP2D6 (115) catalyzed that of harmine (relative activities). The dehydrogenation/aromatization of harmaline to harmine was not carried out by aromatase (CYP19), CYP1A2, CYP2C9, CYP2D6, CYP3A4, pooled recombinant cytochromes P450, or human liver microsomes (HLMs). Kinetic parameters were calculated for the O-demethylations mediated by each isozyme and by pooled HLMs. K cat (min Ϫ1 ) and K m (M) values for harmaline were: CYP1A1, 10. 8 and 11.8; CYP1A2, 12.3 and 13.3; CYP2C9, 5.3 and 175; CYP2C19, 10.3 and 160; and CYP2D6, 39.9 and 1.4. Values for harmine were: CYP1A1, 45.2 and 52.2; CYP1A2, 9.2 and 14.7; CYP2C9, 11.9 and 117; CYP2C19, 21.4 and 121; and CYP2D6, 29.7 and 7.4. Inhibition studies using monoclonal antibodies confirmed that CYP1A2 and CYP2D6 were the major isozymes contributing to both harmaline (20% and 50%, respectively) and harmine (20% and 30%) O-demethylations in pooled HLMs. The turnover numbers for CYP2D6 are among the highest ever reported for a CYP2D6 substrate. Finally, CYP2D6-transgenic mice were found to have increased harmaline and harmine O-demethylase activities as compared with wild-type mice. These findings suggest a role for polymorphic CYP2D6 in the pharmacology and toxicology of harmine and harmaline.The ␤-carboline alkaloids are present in plants and have been of interest due to their psychotropic properties (Picada et al., 1997). They may be formed endogenously from tryptophan-derived indolealkylamines through the Pictet-Spengler condensation with simple aldehydes or with pyruvic acid in mammals, including humans (Airaksinen and Kari, 1981;Melchior and Collins, 1982). Moreover, certain ␤-carbolines, such as pinoline, tryptoline, 6-hydroxy-tetrahydro-␤-carboline, harman, and norharman (Table 1), have been reported as normal constituents of human tissues and body fluids. Their levels in humans are usually elevated after drinking alcohol. The association of ␤-carbolines with alcohol dependence and brain damage has been suggested (Melchior and Collins, 1982;Collins, 2002).Endogenous and exogenous ␤-carboline alkaloids were reported to exert a wide spectrum of psychopharmacological and behavioral effects in the brain (Airaksinen and Kari, 1981). Most ␤-carbolines are strong reversible inhibitors of monoamine oxidase (MAO). Among them, harmaline and harmine (Table 1) exhibit the most potent inhibition toward purified MAO-A activity (Kim et al., 1997), and these are the principal active agents in Peganum harmala, a plant that has been used in traditional medicine for two millennia (Lamchou...

Identification and characterization of novel sequence variations in the cytochrome P4502D6 (CYP2D6) gene in African Americans

“…1 This is not surprising in light of recent reports describing CYP2D6 activity towards endogenous substrates found in the human brain. 2,3 The CYP2D6 gene locus is highly polymorphic and currently there are 51 allelic variants (CYP2D6*1 to *51 including the ones described within this report) and over 30 additional subvariants defined. 4 As a consequence, CYP2D6 activity ranges widely within a population comprising ultrarapid (UM), extensive (EM), intermediate (IM) and poor (PM) metabolizer phenotypes.…”

Liposomes coated with N-trimethyl chitosan to improve the absorption of harmine in vivo and in vitro

“…A previous study reported that the O-demethylation of HM was catalyzed by CYP1A1 (98.5), CYP1A2 (35), CYP2C9 (16), CYP2C19 (30), and CYP2D6 (115), which may exist in the GIT. 24 Degradation in the GIT could be attributed to the first-pass effect and the low oral bioavailability of HM at 25.25%±6.05%. As shown in Figures 9-11, the uptake of HM into Caco-2 cells through passive diffusion mechanism was not dependent on concentration and not affected by energy inhibitors and endocytosis inhibitors.…”

Pharmacokinetic study of harmane and its 10 metabolites in rat after intravenous and oral administration by UPLC-ESI-MS/MS

“…Harmane and harmine also exist in various human diets and foodstuff in particularly high ng/g concentrations, such as in espresso coffee brews, alcoholic beverages and cigarette smoke (Anderson et al 2006;Alves et al 2007). Moreover, harmane and harmine endogenously occur in mammalian tissues and body fluids, including the central nervous system (CNS), heart, kidney, liver, brain, adrenal tissue, platelets, plasma and urine (Yu et al 2003). Harmane is highly lipophilic and more easily distributed into brain tissues than peripheral tissues.…”