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Trimethylamine-N-oxide (TMAO) is associated with chronic disease risk. However, little is known about the metabolic fate of dietary TMAO. This study sought to quantitatively elucidate the metabolic fate of orally consumed TMAO in humans. As part of a crossover feeding study, healthy young men (n=40) consumed 50-mg deuterium-labeled methyl d9-TMAO (d9-TMAO), and enrichments of TMAO and its derivatives were measured in blood for 6 h, urine and stool, as well as skeletal muscle in a subset of men (n=6). Plasma d9-TMAO was detected as early as 15 min, increased until 1 h and remained elevated through the 6-h period. TMAO exhibited an estimated turnover time of 5.3 h, and ~96% of the dose was eliminated in urine by 24 h, mainly as d9-TMAO. No d9-TMAO was detected in feces. Notably, d9-TMAO and d9-trimethylamine were detected in skeletal muscle (n=6) at 6 h, and the enrichment ratio of d9-TMAO to d9-trimethylamine was influenced by a genetic variant in flavin-containing monooxygenase isoform 3 (FMO3 G472A). These results suggest that the absorption of orally consumed TMAO is near complete and does not require processing by gut microbes. TMAO exhibits fast turnover in the circulation with the majority being eliminated in urine within 24 h. A small portion of the dose, however, is taken up by extrahepatic tissue in a manner that appears to be under the influence of FMO3 G472A polymorphism. This trial was registered at clinicaltrials.gov as NCT02558673. [ABSTRACT FROM AUTHOR]

Flavin‐containing monooxygenase 1 (FMO1) largely remains to be characterized in cynomolgus macaque kidney. Immunoblotting showed expression of cynomolgus FMO1 in kidneys where activities of FMO1 (benzydamine N‐oxygenation) were detected. No sex differences were observed in their contents or activities. These results suggest the functional role of cynomolgus FMO1 in kidney. [ABSTRACT FROM AUTHOR]

S-Alk(en)yl- l-cysteine sulfoxides are cysteine-derived secondary metabolites highly accumulated in the genus Allium. Despite pharmaceutical importance, the enzymes that contribute to the biosynthesis of S-alk-(en)yl- l-cysteine sulfoxides in Allium plants remain largely unknown. Here, we report the identification of a flavin-containing monooxygenase, As FMO1, in garlic ( Allium sativum), which is responsible for the S-oxygenation reaction in the biosynthesis of S-allyl- l-cysteine sulfoxide (alliin). Recombinant As FMO1 protein catalyzed the stereoselective S-oxygenation of S-allyl- l-cysteine to nearly exclusively yield ( RC SS)- S-allylcysteine sulfoxide, which has identical stereochemistry to the major natural form of alliin in garlic. The S-oxygenation reaction catalyzed by As FMO1 was dependent on the presence of nicotinamide adenine dinucleotide phosphate (NADPH) and flavin adenine dinucleotide (FAD), consistent with other known flavin-containing monooxygenases. As FMO1 preferred S-allyl- l-cysteine to γ-glutamyl- S-allyl- l-cysteine as the S-oxygenation substrate, suggesting that in garlic, the S-oxygenation of alliin biosynthetic intermediates primarily occurs after deglutamylation. The transient expression of green fluorescent protein ( GFP) fusion proteins indicated that As FMO1 is localized in the cytosol. As FMO1 mRNA was accumulated in storage leaves of pre-emergent nearly sprouting bulbs, and in various tissues of sprouted bulbs with green foliage leaves. Taken together, our results suggest that As FMO1 functions as an S-allyl- l-cysteine S-oxygenase, and contributes to the production of alliin both through the conversion of stored γ-glutamyl- S-allyl- l-cysteine to alliin in storage leaves during sprouting and through the de novo biosynthesis of alliin in green foliage leaves. [ABSTRACT FROM AUTHOR]

Abstract: Mammalian flavin-containing monooxygenase (FMO) is active towards many drugs with a heteroatom having the properties of a soft nucleophile. Thiocarbamides and thiones are S-oxygenated to the sulfenic acid which can either react with glutathione and initiate a redox-cycle or be oxygenated a second time to the unstable sulfinic acid. In this study, we utilized LC–MS/MS to demonstrate that the oxygenation by hFMO of the thioureas under test terminated at the sulfenic acid. With thiones, hFMO catalyzed the second reaction and the sulfinic acid rapidly lost sulfite to form the corresponding imidazole. Thioureas are often pulmonary toxicants in mammals and, as previously reported by our laboratory, are excellent substrates for hFMO2. This isoform is expressed at high levels in the lung of most mammals, including non-human primates. Genotyping to date indicates that individuals of African (up to 49%) or Hispanic (2–7%) ancestry have at least one allele for functional hFMO2 in lung, but not Caucasians nor Asians. In this study the major metabolite formed by hFMO2 with thioureas from Allergan, Inc. was the sulfenic acid that reacted with glutathione. The majority of thiones were poor substrates for hFMO3, the major form in adult human liver. However, hFMO1, the major isoform expressed in infant and neonatal liver and adult kidney and intestine, readily S-oxygenated thiones under test, with K m s ranging from 7 to 160μM and turnover numbers of 30–40min−1. The product formed was identified by LC–MS/MS as the imidazole. The activities of the mouse and human FMO1 and FMO3 orthologs were in good agreement with the exception of some thiones for which activity was much greater with hFMO1 than mFMO1. [Copyright &y& Elsevier]

Abstract: Flavin-containing monooxygenase (FMO) oxygenates drugs/xenobiotics containing a soft nucleophile through a C4a hydroperoxy-FAD intermediate. Human FMOs 1, 2 and 3, expressed in Sf9 insect microsomes, released 30–50% of O2 consumed as H2O2 upon addition of NADPH. Addition of substrate had little effect on H2O2 production. Two common FMO2 (the major isoform in the lung) genetic polymorphisms, S195L and N413K, were examined for generation of H2O2. FMO2 S195L exhibited higher “leakage”, producing much greater amounts of H2O2, than ancestral FMO2 (FMO2.1) or the N413K variant. S195L was distinct in that H2O2 generation was much higher in the absence of substrate. Addition of superoxide dismutase did not impact H2O2 release. Catalase did not reduce levels of H2O2 with either FMO2.1 or FMO3 but inhibited H2O2 generated by FMO2 allelic variants N413K and S195L. These data are consistent with FMO molecular models. S195L resides in the GxGx S G/A NADP+ binding motif, in which serine is highly conserved (76/89 known FMOs). We hypothesize that FMO, especially allelic variants such as FMO2 S195L, may enhance the toxicity of xenobiotics such as thioureas/thiocarbamides both by generation of sulfenic and sulfinic acid metabolites and enhanced release of reactive oxygen species (ROS) in the form of H2O2. [Copyright &y& Elsevier]

Highlights: [•] We generated rotenone model in primary midbrain dopaminergic neurons. [•] We examined the relationship between FMO, parkin and neuron apoptosis. [•] FMO and parkin was decreased in rotenone model, accompanied by caspase 3 activation. [•] FMO dysfunction was a reason for the apoptosis of DA neurons in rotenone model. [•] Parkin function was compromised in neuro-pathological states. [ABSTRACT FROM AUTHOR]

Abstract: In our previous study, a batch fermentation of recombinant Escherichia coli DH5α cells harboring the fmo gene from Methylophaga aminisulfidivorans MPT produced indirubin (5.0mg/L) and indigo (920mg/L) in a 5L fermenter containing tryptophan medium (2g/L tryptophan, 5g/L yeast extract, 10g/L NaCl). In this study, it was found that indirubin production greatly increased when 0.36g/L cysteine was added to the tryptophan medium, although cysteine inhibited the growth of the recombinant E. coli harboring the fmo gene. However, the addition of cysteine did not inhibit the expression level and activity of FMO in the cell. Indigo was synthesized by the dimerization of two 3-hydroxyindole molecules under the non-enzymatic reaction. Cysteine influenced the regioselectivity of FMO and enhanced the synthesis of 2-hydroxyindole instead of 3-hydroxyindole, which might function to increase indirubin production. The optimal culture conditions for indirubin production in tryptophan medium were determined from the response surface methodology analysis: 2g/L tryptophan, 5g/L yeast extract, 10g/L NaCl, 0.36g/L (3mM) cysteine, pH 8.0 at 35°C. Under these conditions, the recombinant E. coli cells were capable of producing 223.6mg/L of indirubin from 2g/L of tryptophan. The intracellular accumulation of the indirubin crystals might stress the cell, which may be a main reason for the poor growth of the recombinant E. coli pBlue 1.7. [Copyright &y& Elsevier]

Statistical studies have demonstrated that various agents may reduce the risk of cancer's development. One of them is activity of flavin-dependent enzymes such as flavin-containing monooxygenase (FMO)GS-OX1, FAD-dependent 5,10-methylenetetrahydrofolate reductase and flavin-dependent monoamine oxidase. In the last decade, many papers concerning their structure, reaction mechanism and role in the cancer prevention were published. In our work, we provide a more in-depth analysis of flavin-dependent enzymes and their contribution to the cancer prevention. We present the actual knowledge about the glucosinolate synthesized by flavin-containing monooxygenase (FMO)GS-OX1 and its role in cancer prevention, discuss the influence of mutations in FAD-dependent 5,10-methylenetetrahydrofolate reductase on the cancer risk, and describe FAD as an important cofactor for the demethylation of histons. We also present our views on the role of riboflavin supplements in the prevention against cancer. [ABSTRACT FROM AUTHOR]

Abstract: Loss-of-function mutations of flavin-containing monooxygenase 3 (FMO3), the enzyme responsible for trimethylamine N-oxygenation, cause the inherited disorder trimethylaminuria, or fish odor syndrome. The aim of this study was to further investigate the inter-individual variations of FMO3 activity in a Japanese cohort that we had studied previously. The subjects were 640 Japanese volunteers with self-reported trimethylaminuria; genomic DNA was sequenced in those that had 10–70% FMO3 metabolic capacity in urine tests. A heterozygote for the novel single nucleotide substitution p.Ile441Thr (proband 1) and a heterozygote for the novel single nucleotide substitution p.Ser195Leu (proband 2) were identified. The biological parents of probands 1 and 2 were heterozygous and had >90% trimethylamine N-oxygenation metabolic capacity. In addition, single nucleotide substitutions p.Val58Ile, p.Pro70Leu, and p.Gly421Val in FMO3 were found in probands 3–7. In the course of DNA sequencing, another FMO3 variant, p.Thr488Ala, was found in two unrelated heterozygous subjects. Variant FMO3 proteins recombinantly expressed in Escherichia coli membranes exhibited decreased activity toward typical FMO3 substrates. Although the allele frequencies of these six novel variants were low (<1%), the present results suggest that individuals homozygous or heterozygous for any of the six novel missense FMO3 variants or known nonsense mutations such as p.Cys197stop or p.Arg500stop may possess abnormal trimethylamine N-oxygenation. [Copyright &y& Elsevier]

Abstract: Human flavin-containing monooxygenase 3 (hFMO3) is a microsomal drug-metabolizing monooxygenase that catalyzes the NADPH-dependent oxygenation of a wide range of drugs and xenobiotics which contain a soft-nucleophiles, usually sulfur or nitrogen. As the release from the microsomal membranes can facilitate the in vitro experimental determination of drug metabolism by hFMO3, in this work we identified and eliminated the membrane anchoring sequence without affecting the activity of the enzyme and producing a soluble active enzyme. The truncated hFMO3 carrying a C-terminal deletion of 17 amino acids (tr-hFMO3) was expressed and purified from the cytosolic fraction. The tr-hFMO3 proves to be detached from the membrane, properly folded and fully active towards well-known marker substrates such as benzydamine and sulindac sulfide with measured apparent K m values of 45±8μM and 25±4μM, respectively. Its activity was further tested with newly discovered Aurora kinase inhibitors, Tozasertib and Danusertib, and compared to those of the wild type enzyme. The use of this soluble form of the hFMO3 enzyme as opposed to the usual microsomal preparations is advantageous for in vitro drug metabolism studies that are a requirement in the early phases of drug development by pharmaceutical industry. [Copyright &y& Elsevier]

Abstract: A bacterial flavin-containing monooxygenase (bFMO) catalyses the oxygenation of indole to produce indigoid compounds. In the reductive half of the indole oxygenation reaction, NADPH acts as a reducing agent, and NADP+ remains at the active site, protecting bFMO from reoxidation. Here, the crystal structures of bFMO and bFMO in complex with NADP+, and a mutant bFMOY207S, which lacks indole oxygenation activity, with and without indole are reported. The crystal structures revealed overlapping binding sites for NADP+ and indole, suggestive of a double-displacement reaction mechanism for bFMO. In biochemical assays, indole inhibited NADPH oxidase activity, and NADPH in turn inhibited the binding of indole and decreased indoxyl production. Comparison of the structures of bFMO with and without bound NADP+ revealed that NADPH induces conformational changes in two active site motifs. One of the motifs contained Arg-229, which participates in interactions with the phosphate group of NADPH and appears be a determinant of the preferential binding of bFMO to NADPH rather than NADH. The second motif contained Tyr-207. The mutant bFMOY207S exhibited very little indoxyl producing activity; however, the NADPH oxidase activity of the mutant was higher than the wild-type enzyme. It suggests a role for Y207, in the protection of hydroperoxyFAD. We describe an indole oxygenation reaction mechanism for bFMO that involves a ping-pong-like interaction of NADPH and indole. [Copyright &y& Elsevier]

Flavin-containing monooxygenase (FMO), like cytochrome P450 (CYP), is a monooxygenase that uses the reducing equivalents of NADPH to reduce one atom of molecular oxygen to water, while the other atom is used to oxidize the substrate. Recently, it was shown that some CYP isoforms have been subject to positive selection. However, it is unknown whether the highly conserved phase I detoxification enzyme, FMO, has undergone similar positive Darwinian selection. We used maximum-likelihood models of codon substitution, evolutionary fingerprinting, and cross species comparison to investigate the occurrence of adaptive evolution in FMO sequences. We used recent genomic data from a range of species, including vertebrates and invertebrates. We present the evidence for the occurrence of adaptive evolution in mammalian FMO 3, 4, 5, and fugu FMOs but not in mammalian FMO 1, FMO 2, frog FMOs, other fish FMOs and invertebrate FMOs. The sites under adaptive evolution were significantly associated with the insertion domain in mammalian FMO 5. We identified specific amino acid sites in FMOs 3-5 that are likely targets for selection based on the patterns of parallel amino acid change. The most likely role of adaptive evolution is the repair of mutations that permitted optimal NADP+ binding and improved catalytic efficiency. The occurrence of positive selection during the evolution of phase I detoxification enzymes such as FMOs 3-5 and fugu FMO suggests the occurrence of both high selection pressure acting on species within their unique habitats and significant changes in intensity and direction (forms of xenobiotics and drugs) resulting from changes in microhabitat and food. [ABSTRACT FROM AUTHOR]

Abstract: Bio-indigo was produced in 3000-L batch and 5-L continuous fermentation of a recombinant Escherichia coli DH5α harboring a novel gene encoding flavin-containing monooxygenase (FMO). Batch fermentation in a 3000-L fermenter produced 911±22mgL−1 of indigo from 2gL−1 tryptophan as a substrate (yield 46.9%) under the following culture conditions as follows: culture temperature 30°C, pH 7.0, agitation speed 200rpm, and aeration 3vvm. Sufficient oxygen (aeration rate and agitation speed) was critical for bio-indigo production. For continuous fermentation in a 5-L fermenter, the volumetric productivity was found to be 11.3mgL−1 h−1 up to 110h (final accumulated bio-indigo was 23g) with a constant dilution rate (D) of 0.084h−1 (constant feeding rate of 0.167Lh−1 with medium containing 3gL−1 tryptophan). Recombinant E. coli cells have the ability to withstand the toxicity of high concentration of accumulated indigo in batch fermentation. In continuous fermentation, the recombinant cells exhibited high plasmid stability up to 110h, after which they lost the plasmid. [Copyright &y& Elsevier]

Human flavin-containing monooxygenases are the second most important class of drug-metabolizing enzymes after cytochromes P450. Here we report a simple but functional and stable enzyme-electrode system based on a glassy carbon (GC) electrode with human flavin-containing monooxygenase isoform 3 (hFMO3) entrapped in a gel cross-linked with bovine serum albumin (BSA) by glutaraldehyde. The enzymatic electrochemical responsiveness is characterised by using well-known substrates: trimethylamine (TMA), ammonia (NH), triethylamine (TEA), and benzydamine (BZD). The apparent Michaelis–Menten constant ( K′) and apparent maximum current ( I′) are calculated by fitting the current signal to the Michaelis–Menten equation for each substrate. The enzyme-electrode has good characteristics: the calculated sensitivity was 40.9 ± 0.5 mA mol L cm for TMA, 43.3 ± 0.1 mA mol L cm for NH, 45.2 ± 2.2 mA mol L cm for TEA, and 39.3 ± 0.6 mA mol L cm for BZD. The stability was constant for 3 days and the inter-electrode reproducibility was 12.5%. This is a novel electrochemical tool that can be used to investigate new potential drugs against the catalytic activity of hFMO3. [ABSTRACT FROM AUTHOR]

Abstract: Flavin-containing monooxygenases often are thought not to be inducible but we recently demonstrated aryl hydrocarbon receptor (AHR)-dependent induction of FMO mRNAs in mouse liver by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (Celius et al., Drug Metab Dispos 36:2499, 2008). We now evaluated FMO induction by other AHR ligands and xenobiotic chemicals in vivo and in mouse Hepa1c1c7 hepatoma cells (Hepa-1). In mouse liver, 3-methylcholanthrene (3MC) induced FMO3 mRNA 8-fold. In Hepa-1 cells, 3MC and benzo[a]pyrene (BaP) induced FMO3 mRNA >30-fold. Induction by 3MC and BaP was AHR dependent but, surprisingly, the potent AHR agonist, TCDD, did not induce FMO3 mRNA in Hepa-1 cells nor did chromatin immunoprecipitation assays detect recruitment of AHR or ARNT to Fmo3 regulatory elements after exposure to 3MC in liver or in Hepa-1 cells. However, in Hepa-1, 3MC and BaP (but not TCDD) caused recruitment of p53 protein to a p53 response element in the 5′-flanking region of the Fmo3 gene. We tested the possibility that FMO3 induction in Hepa-1 cells might be mediated by Nrf2/anti-oxidant response pathways, but agents known to activate Nrf2 or to induce oxidative stress did not affect FMO3 mRNA levels. The protein synthesis inhibitor, cycloheximide (which causes “superinduction” of CYP1A1 mRNA in TCDD-treated cells), by itself caused dramatic upregulation (>300-fold) of FMO3 mRNA in Hepa-1 suggesting that cycloheximide prevents synthesis of a labile protein that suppresses FMO3 expression. Although FMO3 mRNA is highly induced by 3MC or TCDD in mouse liver and in Hepa-1 cells, FMO protein levels and FMO catalytic function showed only modest elevation. [Copyright &y& Elsevier]

Abstract: Flavin-containing monooxygenase (FMO) expression in male mouse liver is altered after 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure or castration. Because TCDD is slowly eliminated from the body, we examined hepatic Fmo mRNA alterations for up to 32 days following 10 or 64μg/kg TCDD exposure by oral gavage in male C57BL/6J mice. Fmo2 mRNA was significantly induced at 1, 4, and 8 days whereas Fmo3 mRNA was also induced at 32 days relative to controls. Fmo3 mRNA levels exhibited a dose-dependent increase at 4, 8, and 32 days after exposure; Fmo1, Fmo4, and Fmo5 mRNA did not exhibit clear trends. Because castration alone also increased Fmo2, Fmo3, and Fmo4 mRNA we examined the combined effects of castration and TCDD treatment on FMO expression. A greater than additive effect was observed with Fmo2 and Fmo3 mRNA expression. Fmo2 mRNA exhibited a 3–5-fold increase after castration or 10μg/kg TCDD exposure by oral gavage, whereas an approximately 20-fold increase was observed between the sham-castrated control and castrated TCDD-treated mice. Similarly, treatment with 10μg/kg TCDD alone increased Fmo3 mRNA 130- and 180-fold in the sham-castrated and castrated mice compared to their controls respectively, whereas, Fmo3 mRNA increased approximately 1900-fold between the sham control and castrated TCDD-treated mice. An increase in hepatic Fmo3 protein in TCDD-treated mice was observed by immunoblotting and assaying methionine S-oxidase activity. Collectively, these results provide evidence for isoform distinct time-, dose-, and castration-dependent effects of TCDD on FMO expression and suggest cross-talk between TCDD and testosterone signal transduction pathways. [Copyright &y& Elsevier]

Abstract: Loss-of-function mutations in the flavin-containing monooxygenase 3 gene (FMO3) cause the inherited disorder trimethylaminuria (TMAuria), or fish-odour syndrome. Here we describe the identification in a family from northern Norway of a novel causative mutation of TMAuria. A female child within the family presented with a TMAuria-like phenotype. The child and her mother were found to be heterozygous for a novel mutation (R238Q) in exon 6 of FMO3. The child’s father lacked this mutation, but was heterozygous for a double polymorphic variant, E158K/E308G, which was not present in the child. During a consultation with her doctor the mother mentioned an uncle whom she remembered as having a strong body odour. This discussion led to genetic counselling of the uncle and analysis of his DNA showed him to be homozygous for the R238Q mutation. Analysis of the mutant FMO3 expressed in bacteria revealed that the R238Q mutation abolished catalytic activity of the enzyme and is thus a causative mutation for TMAuria. The specificity constant (kcat/KM ) of the K158/G308 variant was 43% of that of ancestral FMO3. Because the child is heterozygous for the R238Q mutation and no other mutation known to cause TMAuria was detected in her DNA she is predicted to suffer from transient childhood TMAuria, whereas her great-uncle has primary TMAuria. [Copyright &y& Elsevier]

Abstract: The disorder trimethylaminuria (TMAu) often manifests itself in a body odor for individuals affected. TMAu is due to decreased metabolism of dietary-derived trimethylamine (TMA). In a healthy individual, 95% or more of TMA is converted by the flavin-containing monooxygenase 3 (FMO3, EC 1.14.13.8) to non-odorous trimethylamine N-oxide (TMA N-oxide). Several single nucleotide polymorphisms (SNPs) of the FMO3 gene have been described and result in an enzyme with decreased or abolished functional activity for TMA N-oxygenation thus leading to TMAu. Herein, we report two novel mutations observed from phenotyping and genotyping two self-reporting individuals. Sequence analysis of the exon regions of the FMO3 gene of a young woman with severe TMAu revealed heterozygous mutations at positions 187 (V187A), 158 (E158K), 308 (E308G), and 305 (E305X). Familial genetic analysis showed that the E158K/V187A/E308G derived from the same allele from the mother, and the E305X was derived from the father. FMO3 variants V187A and V187A/E158K were characterized for oxygenation of several common FMO3 substrates (i.e., 5- and 8-DPT, mercaptoimidazole (MMI), TMA, and sulindac sulfide) and for its thermal stability. Our findings show that with the combination of V187A/E158K mutations in FMO3, the enzyme activity is severely affected and possibly contributes to the TMAu observed. In another study, genotyping analysis of a 17year old female revealed a mutation that caused a frame shift after K415 and resulted in a protein variant with only 486 amino acid residues that was associated with severe TMAu. [Copyright &y& Elsevier]

A novel flavin-containing monooxygenase (FMO)-like gene, designated as TsFMO, was cloned from Thellungiella halophila by reverse-transcriptase polymerase chain reaction (RT-PCR) coupled with rapid amplification of cDNA ends approach. The cDNA sequence of TsFMO had a complete open reading frame encoding a putative protein of 461 amino acids, which contained the conserved domains of FMOs. Sequence analysis showed that it had highest similarity with Arabidopsis FMOGS-OX1. RT-PCR analysis revealed that TsFMO was constitutively expressed in all examined tissues including the roots and rosette leaves of the seedlings and mature plants, bolts, and open flowers. Real-time PCR suggested that the gene was quickly and significantly upregulated in the leaves exposed to NaCl stress, which showed that TsFMO might be regulated with the redox state of plant cell. TsFMO was found to complement and rescue the retardant growth to dithiothreitol of yeast fmo mutant strain. In addition, TsFMO was expressed in Escherichia coli and the recombinant protein was purified to produce polyclonal antibody. Western blot with T. halophila extracts showed that the polyclonal antibody was effective and specific. [ABSTRACT FROM AUTHOR]

Abstract: Flavin-containing monooxygenase 3 (FMO3) is important for oxidative xenobiotic metabolism, but regulation of the FMO3 gene remains poorly understood. FMO3 is not expressed in HepG2 cells, a commonly employed model for hepatic gene regulation studies. Transcription factor transient expression and treatment with histone deacetylase or DNA methylase inhibitors identified decreased hepatic nuclear factor (HNF) 4α levels and DNA hypermethylation as mechanisms suppressing HepG2 FMO3 expression. The absence of major deficiencies in transcriptional machinery suggested that within limits, the HepG2 model is suitable for the study of FMO3 regulation. DNA–protein binding studies with HepG2 cell and hepatic tissue nuclear protein extracts and reporter construct transient expression experiments were performed to characterize FMO3 sequences from position −494 to −439 (domain I), previously demonstrated to significantly impact promoter function. Although both HNF3β and CCAAT enhancer-binding protein (C/EBP) were observed to specifically interact with this element using HepG2 cell nuclear proteins, only C/EBP DNA–protein interactions were observed using adult liver nuclear proteins. No specific DNA/protein interactions were observed using fetal liver nuclear proteins. Mutation of a putative HNF3β element had no effect on FMO3 promoter activity, while mutagenesis of a distinct, but overlapping C/EBP element resulted in a 55% reduction in activity. Furthermore, promoter activity was regulated as a function of defined C/EBPβ liver activating protein:liver inhibitory protein ratios through this same element. Chromatin immunoprecipitation demonstrated C/EBPβ binding to the FMO3 domain I element in intact cells and adult liver tissue. These results are consistent with C/EBPβ being important for regulating hepatic FMO3 expression. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]

Generally, the flavin-containing monooxygenase of mammalian systems has been considered a detoxication enzyme converting nucleophilic heteroatom-containing chemicals into polar, more readily excreted metabolites. The beneficial effects of this process are thought to be participation in the detoxication of foodstuffs and other xenobiotics that might otherwise be bioactivated by other enzyme systems. The physiological role of mammalian FMO is unknown although it has been observed that many heteroatom-containing chemicals in plants are efficiently oxygenated by FMO. Recently, a plant FMO-like enzyme has been characterized and it appears to possess many of the same functional properties of mammalian FMO. The advantage of studying the FMO-like genes and enzymes in Arabidopsis as a model system allows for the investigation of the role of FMO-like enzymes in plant growth and development. The Arabidopsis FMO-like gene product, while resembling the mammalian counterpart in many respects, is quite distinct. However, study of the Arabidopsis FMO-like enzyme may provide considerable insight into the possible role of mammalian FMOs in biogenic amine metabolism. [ABSTRACT FROM AUTHOR]