Flavin-containing Monooxygenase 3 Gene Research Articles

Flavin-Dependent Monooxgenase Confers Resistance to Chlorantraniliprole and Spinetoram in the Rice Stem Borer Chilo suppressalis Walker (Lepidoptera: Crambidae).

Understanding the role of flavin-containing monooxygenases (FMOs) in the genetic mechanisms of insecticide resistance is essential for developing effective management strategies against the rice stem borer, Chilo suppressalis. In this study, we identified five FMO genes in C. suppressalis, examined their expression patterns, and revealed overexpression of FMO3B and FMO3C in field populations resistant to multiple insecticides, including chlorantraniliprole and spinetoram. Functional characterization using transgenic Drosophila indicated that FMO3B and FMO3C do not confer resistance to abamectin or methoxyfenozide but do mediate resistance to chlorantraniliprole and spinetoram. Knockdown of FMO3B and FMO3C increased sensitivity to these insecticides in C. suppressalis. Molecular docking studies indicated direct binding of chlorantraniliprole and spinetoram to these FMOs, underscoring their role in metabolic resistance. These findings indicate that FMOs are key enzymes in the metabolic resistance of C. suppressalis to chlorantraniliprole and spinetoram, enhancing our understanding of insecticide resistance and aiding the development of management strategies.

De novo assembling a high-quality genome sequence of Amur grape (Vitis amurensis Rupr.) gives insight into Vitis divergence and sex determination.

To date, there has been no high-quality sequence for genomes of the East Asian grape species, hindering biological and breeding efforts to improve grape cultivars. This study presents ~522Mb of the Vitis amurensis (Va) genome sequence containing 27 635 coding genes. Phylogenetic analysis indicated that Vitis riparia (Vr) may have first split from the other two species, Va and Vitis vinifera (Vv). Divergent numbers of duplicated genes reserved among grapes suggests that the core eudicot-common hexaploidy (ECH) and the subsequent genome instability still play a non-negligible role in species divergence and biological innovation. Prominent accumulation of sequence variants might have improved cold resistance in Va, resulting in a more robust network of regulatory cold resistance genes, explaining why it is extremely cold-tolerant compared with Vv and Vr. In contrast, Va has preserved many fewer nucleotide binding site (NBS) disease resistance genes than the other grapes. Notably, multi-omics analysis identified one trans-cinnamate 4-monooxygenase gene positively correlated to the resveratrol accumulated during Va berry development. A selective sweep analysis revealed a hypothetical Va sex-determination region (SDR). Besides, a PPR-containing protein-coding gene in the hypothetical SDR may be related to sex determination in Va. The content and arrangement order of genes in the putative SDR of female Va were similar to those of female Vv. However, the putative SDR of female Va has lost one flavin-containing monooxygenase (FMO) gene and contains one extra protein-coding gene uncharacterized so far. These findings will improve the understanding of Vitis biology and contribute to the improvement of grape breeding.

Evaluation of the Feasibility of In Vitro Metabolic Interruption of Trimethylamine with Resveratrol Butyrate Esters and Its Purified Monomers.

Resveratrol (RSV), obtained from dietary sources, has been shown to reduce trimethylamine oxide (TMAO) levels in humans, and much research indicates that TMAO is recognized as a risk factor for cardiovascular disease. Therefore, this study investigated the effects of RSV and RSV-butyrate esters (RBE) on the proliferation of co-cultured bacteria and HepG2 cell lines, respectively, and also investigated the changes in trimethylamine (TMA) and TMOA content in the medium and flavin-containing monooxygenase-3 (FMO3) gene expression. This study revealed that 50 µg/mL of RBE could increase the population percentage of Bifidobacterium longum at a rate of 53%, while the rate was 48% for Clostridium asparagiforme. In contrast, co-cultivation of the two bacterial strains effectively reduced TMA levels from 561 ppm to 449 ppm. In addition, regarding TMA-induced HepG2 cell lines, treatment with 50 μM each of RBE, 3,4'-di-O-butanoylresveratrol (ED2), and 3-O-butanoylresveratrol (ED4) significantly reduced FMO3 gene expression from 2.13 to 0.40-1.40, which would also contribute to the reduction of TMAO content. This study demonstrated the potential of RBE, ED2, and ED4 for regulating TMA metabolism in microbial co-cultures and cell line cultures, which also suggests that the resveratrol derivative might be a daily dietary supplement that will be beneficial for health promotion in the future.

Molecular and functional characterization of flavin-containing monooxygenases (FMO1–6) in tree shrews

Flavin-containing monooxygenases (FMOs) are a family of important drug oxygenation enzymes that, in humans, consist of five functional enzymes (FMO1–5) and a pseudogene (FMO6P). The tree shrew is a non-rodent primate-like species that is used in various biomedical studies, but its usefulness in drug metabolism research has not yet been investigated. In this study, tree shrew FMO1–6 cDNAs were isolated and characterized by sequence analysis, tissue expression, and metabolic function. Compared with human FMOs, tree shrew FMOs showed sequence identities of 85–90 % and 81–89 %, respectively, for cDNA and amino acids. Phylogenetic analysis showed that each tree shrew and human FMO were closely clustered. The genomic and genetic structures of the FMO genes were conserved in tree shrews and humans. Among the five tissue types analyzed (lung, heart, kidney, small intestine, and liver), FMO3 and FMO1 mRNAs were most abundant in liver and kidney, respectively. Recombinant tree shrew FMO1–6 proteins expressed in bacterial membranes all mediated benzydamine and trimethylamine N-oxygenations and methyl p-tolyl sulfide S-oxygenation. The selective human FMO3 substrate trimethylamine was predominantly metabolized by tree shrew FMO3. Additionally, tree shrew FMO6 was active toward trimethylamine, as is cynomolgus macaque FMO6, in contrast with the absence of activity of the human FMO6P pseudogene product. Tree shrew FMO1–6, which are orthologous to human FMOs (FMO1–5 and FMO6P) were identified, and tree shrew FMO3 has functional and molecular features generally comparable to those of human FMO3 as the predominant FMO in liver.

Flavin-Containing Monooxygenases (FMO) Genes in Garlic Allium sativum L.: Genome-Wide Identification, Characterization, and Expression Analysis in Response to Fusarium proliferatum

Flavin-Containing Monooxygenases (FMO) Genes in Garlic Allium sativum L.: Genome-Wide Identification, Characterization, and Expression Analysis in Response to Fusarium proliferatum

Flavin-Containing Monooxygenases (<i>FMO</i>) Genes in Garlic <i>Allium sativum</i> L.: Genome-Wide Identification, Characterization, and Expression Analysis in Response to <i>Fusarium proliferatum</i>

In this study, 39 flavin-containing monooxygenase genes were identified in the garlic (Allium sativum L.) genome. The distribution of AsFMOs into three phylogenetic clades associated with N-oxygenation (22 proteins), auxin biosynthesis (13 proteins), and S-oxygenation (4 proteins) has been shown. FAD and NADPH binding, FMO-identifying, and FATGY motifs were found in the AsFMO sequences. AsFMOs transcripts were present in all garlic organs with a maximum in roots, leaves, peduncle, and aerial bulbs. In response to infection with the pathogenic fungus Fusarium proliferatum, differential expression of clade I genes (AsFMO4, AsFMO11, AsFMO12, and AsFMO35) was detected in the roots of cv. Sarmat and Strelets, contrasting in Fusarium rot resistance. At the same time, the expression response of the clade III AsFMO18 gene involved in the alliin biosynthesis was similar for both cultivars, regardless of their resistance/susceptibility to Fusarium. This suggests the clades I and III genes redundancy in plant responses to infection. The AsFMO35 coding and regulatory sequences were analyzed in the Sarmat and Strelets cultivars. It was shown that the AsFMO35 promoter differs in the presence of the ABA-associated cis-regulatory element ABRE in cv. Strelets susceptible to Fusarium rot.

Strategy for efficiently utilizing Escherichia coli cells producing isobutanol by combining isobutanol and indigo production systems.

Isobutanol is a potential biofuel, and its microbial production systems have demonstrated promising results. In a microbial system, the isobutanol produced is secreted into the media; however, the cells remaining after fermentation cannot be used efficiently during the isobutanol recovery process and are discarded as waste. To address this, we aimed to investigate the strategy of utilizing these remaining cells by combining the isobutanol production system with the indigo production system, wherein the product accumulates intracellularly. Accordingly, we constructed E. coli systems with genes, such as acetolactate synthase gene (alsS), ketol-acid reductoisomerase gene (ilvC), dihydroxyl-acid dehydratase (ilvD), and alpha-ketoisovalerate decarboxylase gene (kivD), for isobutanol production and genes, such as tryptophanase gene (tnaA) and flavin-containing monooxygenase gene (FMO), for indigo production. This system produced isobutanol and indigo simultaneously while accumulating indigo within cells. The production of isobutanol and indigo exhibited a strong linear correlation up to 72h of production time; however, the pattern of isobutanol and indigo production varied. To our knowledge, this study is the first to simultaneously produce isobutanol and indigo and can potentially enhance the economy of biochemical production.

T329S Mutation in the FMO3 Gene Alleviates Lipid Metabolic Diseases in Chickens in the Late Laying Period.

Simple SummaryThe lipid deposition and health status of egg-laying hens is crucial to the development of the poultry industry. This study aimed to evaluate the effects of genetic variations in the flavin-containing monooxygenase 3 (FMO3) on the lipid metabolic diseases of laying hens during the late laying period. The results showed that the T329S mutation in FMO3 moderated the lipid parameters and decreased the atherosclerotic lesions and hepatic steatosis in laying hens with homozygous T329S mutation. In conclusion, the T329S mutation in FMO3 is closely associated with the improvement of lipid metabolic diseases in laying hens during the late laying period. The results of this study may contribute to overcoming the challenge of lipid metabolic diseases in laying hens during the late laying period.The T329S mutation in flavin-containing monooxygenase 3 (FMO3) impairs the trimethylamine (TMA) metabolism in laying hens. The TMA metabolic pathway is closely linked to lipid metabolic diseases, such as atherosclerosis and fatty liver disease. We aimed to evaluate the effects of the T329S mutation in FMO3 on lipid metabolism in chickens during the late laying period. We selected 18 FMO3 genotyped individuals (consisting of six AA, six AT, and six TT hens) with similar body weight and production performance. The lipid metabolism and deposition characteristics of the laying hens with different genotypes were compared. The T329S mutation moderated the serum-lipid parameters in TT hens compared to those in AA and AT hens from 49 to 62 weeks. Furthermore, it reduced the serum trimethylamine N-oxide concentrations and increased the serum total bile acid (p < 0.05) and related lipid transporter levels in TT hens. Moreover, it significantly (p < 0.01) decreased atherosclerotic lesions and hepatic steatosis in TT hens compared to those in the AA and AT hens. Our findings may help improve the health status in laying hens during the late laying period.

Transcriptional Responses of Flavin-Containing Monooxygenase Genes in Scallops Exposed to PST-Producing Dinoflagellates Implying Their Involvements in Detoxification

Flavin-containing monooxygenase (FMO) is one of the most prominent xenobiotic metabolic enzymes. It can catalyze the conversion of heteroatom-containing chemicals to polar, readily excretable metabolites and is considered an efficient detoxification system for xenobiotics. Bivalves can accumulate paralytic shellfish toxins (PSTs) produced by dinoflagellates, especially during outbreaks of harmful algal blooms. Exploring FMO genes in bivalves may contribute to a better understanding of the adaptation of these species and the mechanisms of PSTs bioavailability. Therefore, through genome screening, we examined the expansion of FMO genes in two scallops (Patinopecten yessoensis and Chlamys farreri) and found a new subfamily (FMO_like). Our expression analyses revealed that, in both scallops, members of the FMO_N-oxide and FMO_like subfamilies were mainly expressed from the D-stage larvae to juveniles, whereas the FMO_GS-OX subfamily genes were mainly expressed at and prior to the trochophore stage. In adult organs, higher expressions of FMOs were observed in the kidney and hepatopancreas than in other organs. After exposure to PST-producing algae, expression changes in FMOs occurred in hepatopancreas and kidney of both scallops, with more members being up-regulated in hepatopancreas than in kidney for Alexandrium catenella exposure, while more up-regulated FMOs were found in kidney than in hepatopancreas of C. farreri exposed to A. minutum. Our findings suggest the adaptive functional diversity of scallop FMO genes in coping with the toxicity of PST-producing algae.

NHR-49/PPAR-α and HLH-30/TFEB cooperate for C. elegans host defense via a flavin-containing monooxygenase

The model organism Caenorhabditis elegans mounts transcriptional defense responses against intestinal bacterial infections that elicit overlapping starvation and infection responses, the regulation of which is not well understood. Direct comparison of C. elegans that were starved or infected with Staphylococcus aureus revealed a large infection-specific transcriptional signature, which was almost completely abrogated by deletion of transcription factor hlh-30/TFEB, except for six genes including a flavin-containing monooxygenase (FMO) gene, fmo-2/FMO5. Deletion of fmo-2/FMO5 severely compromised infection survival, thus identifying the first FMO with innate immunity functions in animals. Moreover, fmo-2/FMO5 induction required the nuclear hormone receptor, NHR-49/PPAR-α, which controlled host defense cell non-autonomously. These findings reveal an infection-specific host response to S. aureus, identify HLH-30/TFEB as its main regulator, reveal FMOs as important innate immunity effectors in animals, and identify the mechanism of FMO regulation through NHR-49/PPAR-α during S. aureus infection, with implications for host defense and inflammation in higher organisms.

Trimethylaminuria and Vascular Complications

Background: Trimethylaminuria (Fish-Odour Syndrome) is a rare metabolic disorder characterized by an unpleasant odour in body secretions similar to rotting fish. The disorder is most commonly caused from mutations affecting the Flavin containing monooxygenase 3 (FMO3) gene, the vital enzyme for the metabolism of trimethylamine. Although uncommon, it is important to be conscious of this condition, which can be devastating psychosocially even with reliable diagnostic tests. We present here an individual with this syndrome who, in addition to the psychosocial difficulties, presented physical complications that we relate to the disease’s physiopathology. Case: R.M.F., 56 years old, lawyer, self-diagnosed at 25 after identifying himself with a disease description in a local newspaper. He describes fish odour symptoms from infancy and his mother used to demand excessive hygiene habits. He has always suffered from social disturbances. At 44, a physician’s investigation detected FMO3 mutation. The patient is not obese, has never smoked and denies any comorbidity, except erectile dysfunction for 10 years. He presented 4 years ago extensive acute venous thrombosis in the right lower limb femoral veins, lateral and medial gastrocnemius, solar and fibular popliteal veins. Laboratory investigation excluded other causes and negative antibodies. Besides, ENMG confirmed last year peripheral motor sensitive polyneuropathy, axonal pattern, distal both lower extremities. The patient failed treatment with modifications in diet and hygiene, but achieved symptomatic improvement after metronidazole. Genetic analysis showed a new homozygotic variant in the FMO3 gene, with substitution of adenine for cytosine and exchange of Threonine for proline at position 307 of the FMO3 protein with protein dysfunction computably predicted. Comments: Considering the deep venous thrombosis and symmetrical peripheral neuropathy developed by the patient, we searched for a possible association with TMAU but we did not find previous reports. However, Weifei Zhu et al. (Circulation, 135(17), 1671–73,2017) have shown TMAO generated by gut microbes contributing to platelet hyper reactivity and causing a prothrombotic phenotype in vivo. Plasma TMAO levels could predict incident thrombosis risk. Also, direct TMAO exposure enhanced platelet activation from multiple agonists stimulus. Although the “chemical sensor” for TMAO within platelets remains unknown, these findings could increase our understanding of the relationship between TMAO and CVD risk. Although the disorder might not appear to be a significant health problem, its social and psychological burden can be devastating, since the few treatments available provide modest benefits. In addition, it may be associated with other complications, including CVD, to which we would like to draw attention with this report

Transcription factors NHR-49/PPARα and HLH-30/TFEB promote host defense in C. elegans via a flavin-containing monooxygenase

Abstract During bacterial infection, the host is confronted with multiple overlapping signals that are integrated at the organismal level to produce defensive host responses. How multiple infection signals are sensed by the host and how they elicit the transcription of host defense genes is much less understood at the whole-animal level than at the cellular level. The model organism Caenorhabditis elegans is known to mount transcriptional defense responses against intestinal bacterial infections that elicit overlapping starvation and infection responses, but the regulation of such responses is not well understood. Direct comparison of C. elegans that were starved or infected with Staphylococcus aureus revealed a large infection-specific transcriptional signature. This signature was almost completely abrogated by the deletion of transcription factor hlh-30/TFEB, except for six genes including a flavin-containing monooxygenase (FMO) gene, fmo-2/FMO5. Deletion of fmo-2/FMO5 severely compromised infection survival, thus identifying the first FMO with innate immunity functions in animals. Further, fmo-2/FMO5 was specifically induced by Gram-positive pathogens and Gram-positive natural microbiota of C. elegans. Moreover, the mechanism of fmo-2/FMO5 induction required the nuclear receptor, NHR-49/PPARα, which induced fmo-2/FMO5 and host defense cell non-autonomously. These findings for the first time reveal an infection-specific host response to S. aureus, identify HLH-30/TFEB as its main regulator, reveal that FMOs are important innate immunity effectors in animals, and identify the mechanism of FMO regulation through NHR-49/PPARα in C. elegans, with important implications for innate host defense in higher organisms.

Expression profiles of glucosinolate biosynthetic genes in turnip (Brassica rapa var. rapa) at different developmental stages and effect of transformed flavin-containing monooxygenase genes on hairy root glucosinolate content.

Glucosinolates (GSLs) are secondary metabolites, mainly existing in Brassica vegetables. Their breakdown products have health benefits and contribute to the distinctive taste of these vegetables. Because of their high value, there is a lot of interest in developing breeding strategies to increase the content of beneficial GSLs in Brassica species. GSLs are synthesized from certain amino acids and their biological roles depend largely on the structure of their side chains. Flavin-containing monooxygenase (FMOGS-OX ) genes are involved in the synthesis of these side chains. To better understand GSL biosynthesis, we sequenced the transcriptomes of turnip (Brassica rapa var. rapa) tubers at four developmental stages (S1-S4) and determined their GSL content. The total GSL content was high at the early stage (S1) of tuber development and increased up to S3, then decreased at S4. We detected 61 differentially expressed genes, including five FMOGS-OX genes, that were related for GSL biosynthesis among the four developmental stages. Most of these genes were highly expressed at stages S1 to S3, but their expression was much lower at S4. We estimated the effect of the five FMOGS-OX genes on GSL content by overexpressing them in turnip hairy roots and found that the amount of aliphatic GSLs increased significantly in the transgenic plants. The transcriptome data and characterization of genes involved in GSL biosynthesis, particularly the FMOGS-OX genes, will be valuable for improving the yield of beneficial GSLs in turnip and other Brassica crops. © 2019 Society of Chemical Industry.

Novel Association between Flavin-Containing Monooxygenase 3 Gene Polymorphism and Antithyroid Drug-Induced Agranulocytosis in the Han Population

Some effective antithyroid drugs (ATDs) have been widely used for patients with Graves’ disease (GD) but are associated with ATD-induced agranulocytosis. We selected 29 ATD-induced agranulocytosis patients, 44 ATD-induced neutropenia patients, and 140 GD controls among the Chinese Han population who were recruited at the First Affiliated Hospital of Xi’an Jiao Tong University. We assessed their response to ATDs treatment by performing genotyping for a candidate gene association study of samples from patients receiving treatment. Human flavin-containing monooxygenase 3 (FMO3), which is the major hepatic enzyme involved in the production of N-oxide of trimethylamine, catalyzes the oxygenation of a variety of drug compounds. Six single SNP, genotype, haplotype (HAP), and association analyses of the FMO3 gene with ATD-induced agranulocytosis/neutropenia under different models (i.e., additive, dominant, and recessive models) were performed. Rs1736557, which caused an amino acid variation V257M, showed a strong association between ATD-induced agranulocytosis and GD controls after Bonferroni correction (p = 0.011, OR 2.301, 95% CI 1.201–4.409). The presence of HAP 3 (HAP3) in the FMO3 gene HAP was statistically associated with ATD-induced agranulocytosis (p = 0.038, permutation p value). Our findings indicate that genetic variations in the FMO3 gene are associated with the response to ATDs maintenance treatment in ATD-induced agranulocytosis patients of ­Chinese Han population.

Goose FMO3 gene cloning, tissue expression profiling, polymorphism detection and association analysis with trimethylamine level in the egg yolk

Flavin-containing monooxygenase 3 (FMO3) plays a critical role in catalyzing the conversion of trimethylamine (TMA) to trimethylamine-N-oxide (TMAO) in vivo. Despite the well-documented association between FMO3 mutations and a ‘fishy’ off-flavor eggs in chicken and quail, little information is available regarding the molecular characteristic of goose (Anser cygnoides) FMO3 and its relationship with the yolk TMA content. To fill these gaps, we cloned the full-length cDNA sequence of goose FMO3, which comprised 1851bp encoding 531 amino acids. FMO3 mRNA was dramatically expressed in liver than in other tissues in the geese. Eight single nucleotide polymorphisms (SNPs) were detected in the entire coding region. The CC genotype at the T669C site, GG at the A723G site, and AA at the G734A site of FMO3 were highly significantly associated with elevated TMA content in goose egg yolk (P<0.001). Carriers of the A allele of G734A or C allele of T885C had yolk TMA content that had a high probability of being elevated after feeding with additional choline chloride (P=0.0429, OR=4.1300, 95%CI=1.0390–16.4270, and P=0.0251, OR=4.6060, 95%CI=1.1620–18.2620, respectively). This work lays a foundation for studying the function of FMO3 and yolk TMA content in goose. However, studies using larger sample sizes and more goose breeds are required to determine whether the fishy off-flavor trait exists in goose.

Targeted sequencing identifies genetic polymorphisms of flavin-containing monooxygenase genes contributing to susceptibility of nicotine dependence in European American and African American.

BackgroundSmoking is a leading cause of preventable death. Early studies based on samples of twins have linked the lifetime smoking practices to genetic predisposition. The flavin‐containing monooxygenase (FMO) protein family consists of a group of enzymes that metabolize drugs and xenobiotics. Both FMO1 and FMO3 were potentially susceptible genes for nicotine metabolism process.MethodsIn this study, we investigated the potential of FMO genes to confer risk of nicotine dependence via deep targeted sequencing in 2,820 study subjects comprising 1,583 nicotine dependents and 1,237 controls from European American and African American. Specifically, we focused on the two genomic segments including FMO1,FMO3, and pseudo gene FMO6P, and aimed to investigate the potential association between FMO genes and nicotine dependence. Both common and low‐frequency/rare variants were analyzed using different algorithms. The potential functional significance of SNPs with association signal was investigated with relevant bioinformatics tools.ResultsWe identified different clusters of significant common variants in European (with most significant SNP rs6674596, p = .0004, OR = 0.67, MAF_EA = 0.14, FMO1) and African Americans (with the most significant SNP rs6608453, p = .001, OR = 0.64, MAF_AA = 0.1, FMO6P). No significant signals were identified through haplotype‐based analyses. Gene network investigation indicated that both FMO1 and FMO3 have a strong relation with a variety of genes belonging to CYP gene families (with combined score greater than 0.9). Most of the significant variants identified were SNPs located within intron regions or with unknown functional significance, indicating a need for future work to understand the underlying functional significance of these signals.ConclusionsOur findings indicated significant association between FMO genes and nicotine dependence. Replications of our findings in other ethnic groups were needed in the future. Most of the significant variants identified were SNPs located within intronic regions or with unknown functional significance, indicating a need for future work to understand the underlying functional significance of these signals.

Nicotine dependence is associated with functional variation in FMO3, an enzyme that metabolizes nicotine in the brain.

A common haplotype of the flavin-containing monooxygenase gene FMO3 is associated with aberrant mRNA splicing, a two-fold reduction in in vivo nicotine N-oxidation and reduced nicotine dependence. Tobacco remains the largest cause of preventable mortality worldwide. CYP2A6, the primary hepatic nicotine metabolism gene, is robustly associated with cigarette consumption but other enzymes contribute to nicotine metabolism. We determined the effects of common variants in FMO3 on plasma levels of nicotine-N-oxide in 170 European Americans administered deuterated nicotine. The polymorphism rs2266780 (E308G) was associated with N-oxidation of both orally administered and ad libitum smoked nicotine (p ≤ 3.3x10−5 controlling for CYP2A6 genotype). In vitro, the FMO3 G308 variant was not associated with reduced activity, but rs2266780 was strongly associated with aberrant FMO3 mRNA splicing in both liver and brain (p ≤ 6.5x10−9). Surprisingly, in treatment-seeking European American smokers (n=1558) this allele was associated with reduced nicotine dependence, specifically with a longer time to first cigarette (p=9.0x10−4), but not with reduced cigarette consumption. Since N-oxidation accounts for only a small percentage of hepatic nicotine metabolism we hypothesized that FMO3 genotype affects nicotine metabolism in the brain (unlike CYP2A6, FMO3 is expressed in human brain) or that nicotine-N-oxide itself has pharmacological activity. We demonstrate for the first time nicotine N-oxidation in human brain, mediated by FMO3 and FMO1, and show that nicotine-N-oxide modulates human α4β2 nicotinic receptor activity in vitro. These results indicate possible mechanisms for associations between FMO3 genotype and smoking behaviors, and suggest nicotine N-oxidation as a novel target to enhance smoking cessation.

A compound heterozygous mutation in the FMO3 gene: the first pediatric case causes fish odor syndrome in Korea.

Trimethylaminuria (TMAuria), known as “fish odor syndrome,” is a congenital metabolic disorder characterized by an odor resembling that of rotting fish. This odor is caused by the secretion of trimethylamine (TMA) in the breath, sweat, and body secretions and the excretion of TMA along with urine. TMAuria is an autosomal recessive disorder caused by mutations in flavin-containing monooxygenase 3 (FMO3). Most TMAuria cases are caused by missense mutations, but nonsense mutations have also been reported in these cases. Here, we describe the identification of a novel FMO3 gene mutation in a patient with TMAuria and her family. A 3-year-old girl presented with a strong corporal odor after ingesting fish. Genomic DNA sequence analysis revealed that she had compound heterozygous FMO3 mutations; One mutation was the missense mutation p.Val158Ile in exon 3, and the other was a novel nonsense mutation, p.Ser364X, in exon 7 of the FMO3 gene. Familial genetic analyses showed that the p.Val158Ile mutation was derived from the same allele in the father, and the p.Ser364X mutation was derived from the mother. This is the first description of the p.Ser364X mutation, and the first report of a Korean patient with TMAuria caused by novel compound heterozygous mutations.

Oxidative stress-responsive transcription factor NRF2 is not indispensable for the human hepatic Flavin-containing monooxygenase-3 (FMO3) gene expression in HepG2 cells

The flavin-containing monooxygenases (FMOs) are important for the oxidation of a variety of endogenous compounds and xenobiotics. The hepatic expression of FMO3 is highly variable and until recently, it was thought to be uninducible. In this study, human FMO3 gene regulation by the oxidative stress transcription factor, nuclear factor (erythroid-derived 2)-like 2 (NRF2) was examined. Constitutive FMO3 gene expression is repressed in HepG2 cells, thus this cell can be a good model for FMO3 gene regulation studies. Over-expression of NRF2 in HepG2 cells increased NRF2 target gene expression, heme oxygenase-1 (HMOX1) and NAD(P)H:quinone oxidoreductase-1 (NQO1), but did not alter FMO3 gene expression. Co-transfection studies with NRF2 or its cytosolic regulatory protein, Kelch-like ECH-associated protein 1 (KEAP1), expression vectors, along with FMO3 promoter luciferase reporter constructs of various lengths (5kb or 6kb), did not change FMO3 reporter gene activity significantly. Furthermore, treatment with tert-butyl hydroperoxide (tBHP) and tert-butyl hydroquinone (tBHQ) did not alter FMO3 reporter construct activity. In summary, in vitro results suggest that the transcriptional regulation of FMO3 might not involve the NRF2-KEAP1 regulatory pathway.

Genetic polymorphism of FMO3 and its role in drug metabolism and toxicity

The flavin-containing monooxygenase 3 (FMO3) is an important hepatic microsomal enzyme. Numerous mutations of FMO3 gene have been reported, and polymorphic varients of the gene have been identified. Several studies indicated that variability in the expression of FMO3 involved in some nitrogen, or sulfur-containing durg metabolism. This review summarizes the genetic polymorphism of FMO3 and its role in drug metabolism and toxicity.