Flavin-containing monooxygenase mediated metabolism of psychoactive drugs by human brain microsomes

doi:10.1016/0006-8993(94)01135-5

Brain Research

Volume 672, Issues 1–2, 20 February 1995, Pages 276-280

https://doi.org/10.1016/0006-8993(94)01135-5 Get rights and content

Abstract

Flavin-containing monooxygenases (FMO) catalyze the oxidation of certain xenobiotics and drugs which contain a nucleophilic heteroatom. Here we report the first assessment of human brain flavin-containing monooxygenase from tissues obtained at autopsy from seven traffic accident victims. Human brain microsomes catalyzed the S-oxidation or N-oxidation of model substrates methimazole and N,N-dimethylaniline, respectively. The psychoactive drugs chlorpromazine, imipramine and fluoxetine, were also metabolized by human brain FMO. ‘Western’ immunoblot analyses revealed immunological cross-reactivity of the human brain FMO with rabbit pulmonary FMO. Immunocytochemistry further revealed the localization of the FMO predominantly in the neuronal cell bodies in the magnocellular reticular nuclei, colliculi and substantia nigra. Human brain clearly contains an active FMO system, and it is conceivable that such enzyme(s) are significantly involved in the local metabolism and modulation of pharmacological effects of psychoactive drugs.

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Cited by (43)

Unraveling the metabolic pathway of choline-TMA-TMAO: Effects of gypenosides and implications for the therapy of TMAO related diseases
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Citation Excerpt :
Laboratory-extracted microsomal enzymes mainly include P450 enzymes and FMO3. It has been reported that the P450 enzyme is inactive under high pH, while the FMO3 enzyme is significantly increased in enzyme activity [27]. When we used different enzyme culture conditions, it was found that FMO3 enzymes were greatly inhibited under the conditions of FMO3 enzyme inhibitor methimazole, organic solvents, and high temperature, while the oxidation activity of FMO3 could be greatly increased at pH 9 (Fig. 1E-F).
Trimethylamine-N-oxide (TMAO) has emerged as a promising new therapeutic target for the treatment of central nervous system diseases, atherosclerosis and other diseases. However, its origin in the brain is unclear. Gynostemma pentaphyllum (Thunb.) Makino can reduce the increase of TMAO level caused by a high fat diet. But its effective chemical composition and specific mechanism have not been reported. The study confirmed that TMA was more easily to penetrate blood brain barrier than TMAO, the MAO enzyme was partly involved in the transformation of the TMA in brain, which further supplemented the choline-TMA-TMAO pathway. Based on the above metabolic pathway, using multi-omics approaches, such as microbiodiversity, metagenomics and lipidomics, it was demonstrated that the reduction of plasma TMAO levels by gypenosides did not act on FMO3 and MAO in the pathway, but remodeled the microbiota and affected the trimethylamine lyase needed in the conversion of choline to TMA in intestinal flora. At the same time, gypenosides interfered with enzymes associated with TCA and lipid metabolism, thus affecting TMAO and lipid metabolism. Considering the bidirectional transformation of phosphatidycholine and choline, lipid metabolism and TMAO metabolism could affected each other to some extent. In conclusion, our study revealed the intrinsic correlation between long-term application of gypenosides to lipid reduction and nervous system protection, and explained why gypenosides were used to treat brain diseases, even though they had a poor ability to enter the brain. Besides, it provided a theoretical basis for clinical application of gypenosides and the development of new drugs.
A sensitive capillary LC-UV method for the simultaneous analysis of olanzapine, chlorpromazine and their FMO-mediated N-oxidation products in brain microdialysates
2017, Talanta
Citation Excerpt :
Expression of FMO in the human brain indicates a potential relevance for FMO in the central nervous system. It has been suggested that FMO can significantly be involved in the local metabolism and modulation of the pharmacological activity of psychoactive drugs [15]. Relatively little is known concerning substrate preferences for the different FMOs, although FMO-3 tends to prefer oxidation of smaller nucleophilic heteroatoms compared to FMO-1, which prefers drugs with bulkier side-chains [16].
A specific and sensitive capillary liquid chromatography-ultraviolet detection (cap-LC-UV) method in combination with a micro-extraction by packed sorbent (MEPS) sample clean-up procedure has been developed and validated for the simultaneous analysis of chlorpromazine, olanzapine and their flavin-containing monooxygenase (FMO) mediated N-oxides in rat brain microdialysates. Chromatographic separation was obtained on an Acclaim Pepmap RP C18 column with an ID of 300 µm. An injection volume of 20 µL was used to inject the largely aqueous samples and was shown to have no influence on the obtained peak shape of the compounds of interest. Optimal conditions for MEPS extraction were obtained on a mixed-mode M1 (80% C8, 20% SCX) cartridge after diluting microdialysate samples with phosphate buffer pH 2.5 (1:3 v/v). The method was validated and lower limits of quantification (LLOQ) were determined at 0.5 nM for all compounds. Linearity was demonstrated between the LLOQ and 1 µM for all compounds (R²>0.995). MEPS recoveries were between 92% and 98%, with intra- and interday variabilities below 15%. The applicability of the developed method was successfully demonstrated by analysing rat brain microdialysates. The capillary LC-UV method in combination with MEPS sample treatment provides a simple, sensitive method to quantify all compounds of interest in 45 min and can be applied for routine therapeutic monitoring and pharmacokinetic studies of olanzapine, chlorpromazine and their respective N-oxides.
Phase I biotransformation reactions-flavin monooxygenase
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Mammalian flavin-containing monooxygenases: Structure/function, genetic polymorphisms and role in drug metabolism
2005, Pharmacology and Therapeutics
Flavin-containing monooxygenase (FMO) oxygenates drugs and xenobiotics containing a “soft-nucleophile”, usually nitrogen or sulfur. FMO, like cytochrome P450 (CYP), is a monooxygenase, utilizing the reducing equivalents of NADPH to reduce 1 atom of molecular oxygen to water, while the other atom is used to oxidize the substrate. FMO and CYP also exhibit similar tissue and cellular location, molecular weight, substrate specificity, and exist as multiple enzymes under developmental control. The human FMO functional gene family is much smaller (5 families each with a single member) than CYP. FMO does not require a reductase to transfer electrons from NADPH and the catalytic cycle of the 2 monooxygenases is strikingly different. Another distinction is the lack of induction of FMOs by xenobiotics.
In general, CYP is the major contributor to oxidative xenobiotic metabolism. However, FMO activity may be of significance in a number of cases and should not be overlooked. FMO and CYP have overlapping substrate specificities, but often yield distinct metabolites with potentially significant toxicological/pharmacological consequences.
The physiological function(s) of FMO are poorly understood. Three of the 5 expressed human FMO genes, FMO1, FMO2 and FMO3, exhibit genetic polymorphisms. The most studied of these is FMO3 (adult human liver) in which mutant alleles contribute to the disease known as trimethylaminuria. The consequences of these FMO genetic polymorphisms in drug metabolism and human health are areas of research requiring further exploration.
Cell-, tissue-, sex- and developmental stage-specific expression of mouse flavin-containing monooxygenases (Fmos)
2004, Biochemical Pharmacology
Citation Excerpt :
The abundance of FMO mRNAs in the kidney, in female, is FMO1>FMO5≥FMO4>FMO3>FMO2 and in male FMO1≈FMO5>FMO4>FMO2>FMO3. FMO activity has been detected in human [47,48] and rat [49,50] brain and FMO4 mRNA in rabbit brain [51]. It is also known that, in mouse and rat, the neurotoxin N-methyl-1,2,3,6-tetrahydropyridine (MPTP) undergoes N-oxidation by FMOs [52,53].
The cell-, tissue-, sex- and developmental stage-specific expression profiles of five members of the flavin-containing monooxygenase (FMO) family, FMO1, 2, 3, 4 and 5, were investigated in 129/SV mice, using isoform-specific antisense RNA probes. In situ hybridization localized FMO1 and 5 mRNAs to the perivenous, and FMO 2, 3 and 4 mRNAs to the periportal, regions of the liver. In kidney, each FMO mRNA is localized to the distal and proximal tubules and collecting ducts; FMO1 mRNA is present also in the glomerulus. In lung, FMO1 and 3 mRNAs are expressed in the terminal bronchiole, and FMO1 mRNA also in the alveoli. FMO1 mRNA is present in neurons of the cerebrum and in the choroid plexus. RNase protection assays showed that the most abundant isoform in newborn liver, lung, kidney and brain, and in adult lung and kidney is FMO1, but in adult liver FMO5 is present in greatest amounts. In liver, lung and kidney, expression of Fmo1, 3 and 5 peaks at 3 or 5 weeks of age, but in the brain, Fmo1 expression is greatest in newborns. In the kidney, FMO5 mRNA abundance is fourfold greater in males than in females, at all stages of development. Our results demonstrate that Fmo1, 2, 3, 4 and 5 exhibit distinct cell-, tissue-, sex- and developmental stage-specific patterns of expression.
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2020, Yakugaku Zasshi

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Short communicationFlavin-containing monooxygenase mediated metabolism of psychoactive drugs by human brain microsomes

Abstract

Life Sci.

Anal. Biochem.

J. Biol. Chem.

Arch. Biochem. Biophys.

J. Biol. Chem.

Biochem. Pharmacol.

Brain Res.

Deficient nicotine N-oxidation in two sisters with trimethylaminuria

Br. J. Clin. Pharmacol.

Short communication
Flavin-containing monooxygenase mediated metabolism of psychoactive drugs by human brain microsomes