Genetic Polymorphisms of Human Flavin Monooxygenase 3 in Sulindac-Mediated Primary Chemoprevention of Familial Adenomatous Polyposis

N- and S-oxygenation activity of truncated human flavin-containing monooxygenase 3 and its common polymorphic variants

Human flavin-containing monooxygenase 3 (FMO3) is a membrane-bound, phase I drug metabolizing enzyme. It is highly polymorphic with some of its variants demonstrating differences in rates of turnover of its substrates: xenobiotics including drugs as well as dietary compounds. In order to measure its in vitro activity and compare any differences between the wild type enzyme and its polymorphic variants, we undertook a systematic study using different engineered proteins, heterologously expressed in bacteria, purified and catalytically characterized with 3 different substrates. These included the full-length as well as the more soluble C-terminal truncated versions of the common polymorphic variants (E158K, V257M and E308G) of FMO3 in addition to the full-length and truncated wild-type proteins. In vitro activity assays were performed with benzydamine, tamoxifen and sulindac sulfide, whose products were measured by HPLC. Differences in catalytic properties between the wild-type FMO3 and its common polymorphic variants were similar to those observed with the truncated, more soluble versions of the enzymes. Interestingly, the truncated enzymes were better catalysts than the full-length proteins. The data obtained point to the feasibility of using the more soluble forms of this enzyme for in vitro drug assays as well as future biotechnological applications possibly in high throughput systems such as bioelectrochemical platforms and biosensors.

Predictive Value of FMO3 Variants on Plasma Disposition and Adverse Reactions of Oral Voriconazole in Febrile Neutropenia

BACKGROUND AND OBJECTIVES

With the increasing number of patients with febrile neutropenia (FN), voriconazole (VRC) has been widely used in hospitals for first-line treatment of FN. The study was designed for evaluating the influence of FMO3 mutation on the plasma disposition and adverse reactions of VRC in FN.

MATERIALS AND METHODS

A single-center observational study was conducted in the inpatient ward for 4 years. The genotypes of FMO3 and cytochrome P450 (CYP) 2C19 were detected by PCR-restriction fragment length polymorphism. Patients with neutropenia were screened according to the CYP2C19 metabolic phenotype and other inclusion criteria. Five days after empirical administration of VRC, blood concentrations of VRC and nitrogen oxides in patients' blood were determined by liquid chromatography-electrospray tandem mass spectrometry (LC-ESI MS/MS). Serum parameters and clinical adverse reaction symptoms in the medical records were collected and statistically analyzed.

RESULTS

A total of 165 patients with neutropenia with the intermediate metabolic phenotype of CYP2C19 were screened. At the initial stage of oral VRC treatment, patients with the FMO3 E308G genotype had a poorer plasma disposal ability to VRC than those with the wide type of FMO3 (WT) genotype (p = 0.0005). Moreover, patients with the FMO3 E308G genotype were more likely to have adverse drug reactions and abnormal serum parameters after receiving VRC treatment. For example, the serum potassium level in the FMO3 E308G genotype group was significantly lower than that in the WT group (p = 0.028), the abnormal level of total bilirubin in the FMO3 E308G genotype group was significantly higher than that in the WT group (p = 0.049), and the aspartate aminotransferase level in the E308G group was significantly higher than that in the WT group (p = 0.05). The incidence of atopic dermatitis and visual impairment in the FMO3 E308G genotype group was 67 and 75%, respectively, and the incidences of peripheral neuroedema, headache, and diarrhea were 57, 50, and 60%, respectively, which were significantly different from those in the WT group.

CONCLUSION

FMO3 E308G reduces the activity of the FMO3 enzyme by decreasing the metabolic ability of VRC, which increases the plasma concentration of VRC and may also lead to adverse reactions in patients with FN.

Population Pharmacokinetics of Sulindac and Genetic Polymorphisms of FMO3 and AOX1 in Women with Preterm Labor

PURPOSE

This prospective study aimed to evaluate the effects of genetic polymorphisms in sulindac-related metabolizing enzyme genes including FMO3 and AOX1 on the population pharmacokinetics of sulindac in 58 pregnant women with preterm labor.

METHODS

Plasma samples were collected at 1.5, 4, and 10 h after first oral administration of sulindac. Plasma concentrations of sulindac and its active metabolite (sulindac sulfide) were determined, and pharmacokinetic analysis was performed with NONMEM 7.3.

RESULTS

The mean maternal and gestational ages at the time of dosing were 32.5 ± 4.4 (range, 20-41) years and 27.4 ± 4.4 (range, 16.4-33.4) weeks, respectively. In the population pharmacokinetic analysis, one depot compartment model of sulindac with absorption lag time best described the data. The metabolism of sulindac and sulindac sulfide was described using Michaelis-Menten kinetics. In stepwise modeling, gestational age impacted volume of distribution (Vc), and FMO3 rs2266782 was shown by the Michaelis constant to affect conversion of sulindac sulfide to sulindac (K_M32); these were retained in the final model.

CONCLUSIONS

Genetic polymorphisms of FMO3 and AOX1 could affect the pharmacokinetics of sulindac in women who undergo preterm labor. The results of this study could help clinicians develop individualized treatment plans for administering sulindac.

Genetic and Nongenetic Factors Associated with Protein Abundance of Flavin-Containing Monooxygenase 3 in Human Liver

Hepatic flavin-containing mono-oxygenase 3 (FMO3) metabolizes a broad array of nucleophilic heteroatom (e.g., N or S)-containing xenobiotics (e.g., amphetamine, sulindac, benzydamine, ranitidine, tamoxifen, nicotine, and ethionamide), as well as endogenous compounds (e.g., catecholamine and trimethylamine). To predict the effect of genetic and nongenetic factors on the hepatic metabolism of FMO3 substrates, we quantified FMO3 protein abundance in human liver microsomes (HLMs; n = 445) by liquid chromatography-tandem mass chromatography proteomics. Genotyping/gene resequencing, mRNA expression, and functional activity (with benzydamine as probe substrate) of FMO3 were also evaluated. FMO3 abundance increased 2.2-fold (13.0 ± 11.4 pmol/mg protein vs. 28.0 ± 11.8 pmol/mg protein) from neonates to adults. After 6 years of age, no significant difference in FMO3 abundance was found between children and adults. Female donors exhibited modestly higher mRNA fragments per kilobase per million reads values (139.9 ± 76.9 vs. 105.1 ± 73.1; P < 0.001) and protein FMO3 abundance (26.7 ± 12.0 pmol/mg protein vs. 24.1 ± 12.1 pmol/mg protein; P < 0.05) compared with males. Six single nucleotide polymorphisms (SNPs), including rs2064074, rs28363536, rs2266782 (E158K), rs909530 (N285N), rs2266780 (E308G), and rs909531, were associated with significantly decreased protein abundance. FMO3 abundance in individuals homozygous and heterozygous for haplotype 3 (H3), representing variant alleles for all these SNPs (except rs2066534), were 50.8% (P < 0.001) and 79.5% (P < 0.01), respectively, of those with the reference homozygous haplotype (H1, representing wild-type). In summary, FMO3 protein abundance is significantly associated with age, gender, and genotype. These data are important in predicting FMO3-mediated heteroatom-oxidation of xenobiotics and endogenous biomolecules in the human liver.

Flavin Containing Monooxygenases and Metabolism of Xenobiotics

This review summarizes recent information concerning the pharmacological and toxicological significance of the flavin-containing monooxygenases (FMOs). FMOs are a family of microsomal enzymes involving in the oxygenation of certain xenobiotics and drugs containing nucleophilic heteroatoms. The activities of FMOs in drug metabolism and their relationships with diseases are the areas of research requiring further exploration. Future studies on FMOs may provide considerable information about the pathophysiology of diseases and the information related to this enzyme family may be important for drug designs in future.

Effects of FMO3 Polymorphisms on Pharmacokinetics of Sulindac in Chinese Healthy Male Volunteers

Sulindac is a nonsteroidal anti-inflammatory drug, which is clinically used for the ailments of various inflammations. This study investigated the allele frequencies of FMO3 E158K and E308G and evaluated the influences of these two genetic polymorphisms on the pharmacokinetics of sulindac and its metabolites in Chinese healthy male volunteers. Eight FMO3 wild-type (FMO3 HHDD) subjects and seven FMO3 homozygotes E158K and E308G mutant (FMO3 hhdd) subjects were recruited from 247 healthy male volunteers genotyped by PCR-RFLP method. The plasma concentrations of sulindac, sulindac sulfide, and sulindac sulfone were determined by UPLC, while the pharmacokinetic parameters of the two different FMO3 genotypes were compared with each other. The frequencies of FMO3 E158K and E308G were 20.3% and 20.1%, respectively, which were in line with Hardy-Weinberg equilibrium (D′ = 0.977, r² = 0.944). The mean values of C_max, AUC_0–24, and AUC_0–∞ of sulindac were significantly higher in FMO3 hhdd group than those of FMO3 HHDD group (P < 0.05), while the pharmacokinetic parameters except T_max of sulindac sulfide and sulindac sulfone showed no statistical difference between the two groups. The two FMO3 mutants were in close linkage disequilibrium and might play an important role in the pharmacokinetics of sulindac in Chinese healthy male volunteers.

Donors FMO3 polymorphisms affect tacrolimus elimination in Chinese liver transplant patients

AIM

Flavin-containing monooxygenase (FMO) variants were potentially involved in tacrolimus metabolism in kidney transplantion. The influences of FMO3 genotypes on tacrolimus elimination in Chinese liver transplant patients remained unclear.

PATIENTS & METHODS

FMO3 SNPs and CYP3A5 rs776746 were analyzed in 110 Chinese patients.

RESULTS

Donor FMO3 rs1800822 allele T and rs909530 allele T were associated with fast tacrolimus elimination. Combination of polymorphisms of donor FMO3 rs1800822 and rs909530 genotype impacted on tacrolimus elimination (p = 0.0221). The number of donor rs1800822 allele T and rs909530 allele T was confirmed to be an independent predictor of the tacrolimus concentration-to-dose ratios for weeks 2, 3 and 4 in the multivariate analysis.

CONCLUSION

Donor's FMO3 polymorphisms might affect tacrolimus elimination.

Fish oil affects the metabolic process of trimethylamine N-oxide precursor through trimethylamine production and flavin-containing monooxygenase activity in male C57BL/6 mice

Fish oil supplements could affect TMAO metabolic process through gut microbiota and FMOs.

Drug metabolism by flavin-containing monooxygenases of human and mouse

INTRODUCTION

Flavin-containing monooxygenases (FMOs) play an important role in drug metabolism. Areas covered: We focus on the role of FMOs in the metabolism of drugs in human and mouse. We describe FMO genes and proteins of human and mouse; the catalytic mechanism of FMOs and their significance for drug metabolism; differences between FMOs and CYPs; factors contributing to potential underestimation of the contribution of FMOs to drug metabolism; the developmental and tissue-specific expression of FMO genes and differences between human and mouse; and factors that induce or inhibit FMOs. We discuss the contribution of FMOs of human and mouse to the metabolism of drugs and how genetic variation of FMOs affects drug metabolism. Finally, we discuss the utility of animal models for FMO-mediated drug metabolism in humans. Expert opinion: The contribution of FMOs to drug metabolism may be underestimated. As FMOs are not readily induced or inhibited and their reactions are generally detoxifications, the design of drugs that are metabolized predominantly by FMOs offers clinical advantages. Fmo1^(-/-),Fmo2^(-/-),Fmo4^(-/-) mice provide a good animal model for FMO-mediated drug metabolism in humans. Identification of roles for FMO1 and FMO5 in endogenous metabolism has implications for drug therapy and initiates an exciting area of research.

Relationships between flavin-containing mono-oxygenase 3 (FMO3) genotype and trimethylaminuria phenotype in a Japanese population

AIM

The aim of this study was to investigate relationships between flavin-containing mono-oxygenase 3 (FMO3) genotype and phenotype (conversion of odorous trimethylamine into non-odorous trimethylamine N-oxide) in a large Japanese cohort suffering from trimethylaminuria.

METHODS

Urinary excretion of trimethylamine and trimethylamine N-oxide was determined for 102 volunteers with self-reporting symptoms of trimethylaminuria. For each we determined the sequence of the entire coding region, plus 1.3 kb of flanking intronic and 2.5 kb of the upstream region of the FMO3 gene. The affect of upstream variants on transcription was determined with a reporter gene assay.

RESULTS

Seventy-eight subjects were diagnosed as suffering from trimethylaminuria, based on urinary excretion of <90% of total TMA as TMA N-oxide. Of these, 13 were classified as severe, 56 as moderate and nine as mild cases, excreting <43%, 48-70% and 73-83% of trimethylamine as trimethylamine N-oxide, respectively. Twenty-seven mutations were identified in FMO3, 15 in the coding region, of which eight abolish or severely impair FMO3 activity (Pro70Leu, Cys197fsX, Thr201Lys, Arg205Cys, Met260Val, Trp388Ter, Gln470Ter and Arg500Ter), and 12 in the upstream region. The mutations segregate into 19 haplotypes, including four different combinations of upstream mutations, each of which reduces transcriptional activity in comparison with the ancestral upstream sequence of FMO3.

CONCLUSIONS

Comparisons of genotype and phenotype reveal that severe trimethylaminuria is caused by loss of function mutations in FMO3. For moderate and mild cases the situation is more complex, with most resulting from factors other than FMO3 genotype. Our results have implications for the diagnosis and management of the disorder.

Sulindac compounds facilitate the cytotoxicity of β-lapachone by up-regulation of NAD(P)H quinone oxidoreductase in human lung cancer cells

β-lapachone, a major component in an ethanol extract of Tabebuia avellanedae bark, is a promising potential therapeutic drug for various tumors, including lung cancer, the leading cause of cancer-related deaths worldwide. In the first part of this study, we found that apoptotic cell death induced in lung cancer cells by high concentrations of β-lapachone was mediated by increased activation of the pro-apoptotic factor JNK and decreased activation of the cell survival/proliferation factors PI3K, AKT, and ERK. In addition, β-lapachone toxicity was positively correlated with the expression and activity of NAD(P)H quinone oxidoreductase 1 (NQO1) in the tumor cells. In the second part, we found that the FDA-approved non-steroidal anti-inflammatory drug sulindac and its metabolites, sulindac sulfide and sulindac sulfone, increased NQO1 expression and activity in the lung adenocarcinoma cell lines CL1-1 and CL1-5, which have lower NQO1 levels and lower sensitivity to β-lapachone treatment than the A549 cell lines, and that inhibition of NQO1 by either dicoumarol treatment or NQO1 siRNA knockdown inhibited this sulindac-induced increase in β-lapachone cytotoxicity. In conclusion, sulindac and its metabolites synergistically increase the anticancer effects of β-lapachone primarily by increasing NQO1 activity and expression, and these two drugs may provide a novel combination therapy for lung cancers.

Effects of single-nucleotide polymorphisms of FMO3 and FMO6 genes on pharmacokinetic characteristics of sulindac sulfide in premature labor

This study aimed to investigate the effects of polymorphisms of the flavin-containing mono-oxygenase 3 (FMO3) and flavin-containing mono-oxygenase 6 (FMO6) genes on the pharmacokinetics of sulindac sulfide, the active metabolite of sulindac, in patients with preterm labor. Ten single-nucleotide polymorphisms (SNPs) were genotyped, and plasma sulindac sulfide concentrations were measured at 0, 1.5, 4, and 10 hours after drug administration. The area under the curve from time 0 to the last sampling time point (AUC(last)) for sulindac sulfide was obtained. The AUC(last) of sulindac sulfide was significantly higher in patients with variant-type homozygotes of FMO3 (rs909530) than those with ancestral alleles or heterozygotes. FMO3 (rs2266780) was in complete linkage disequilibrium with FMO6 (rs7885012), and there was marginal significance between the genotypes (P = 0.049). From multiple linear regression models, FMO3 (rs909530) was found to have significant influence on the AUClast of sulindac sulfide after adjusting for gestational age, weight, and all studied SNPs. The predictive contribution of rs909530 to the variability of sulindac sulfide AUC(last) was 27.0%. In conclusion, the results of this study could help clinicians predict the efficacies and side effects of sulindac in the development of individualized treatment of patients with preterm labor.

Trimethylaminuria (fish odor syndrome): genotype characterization among Portuguese patients

Trimethylaminuria (TMAu) or "fish odor syndrome" is a metabolic disorder characterized by the inability to convert malodorous dietarily-derived trimethylamine (TMA) to odorless TMA N-oxide by the flavin-containing monooxygenase 3 (FMO3). Affected individuals unable to complete this reaction exude a "fishy" body odor due to the secretion of TMA in their corporal fluids leading to a variety of psychosocial problems. Interindividual variability in the expression of FMO3 gene may affect drug and foreign chemical metabolism in the liver and other tissues. Therefore, it is important to screen for common TMAu mutations but also extend the search to other genetic variants in order to correlate genotype and disease-associated phenotypes. In this study, 25 Portuguese patients with phenotype suggestive of TMAu were evaluated for molecular screening of the FMO3 gene. Herein, we found 16 variants in the FMO3 coding region, some of which had not been previously documented (Gly38Trp, Asp232Val, Thr307Pro, Ser310Leu). Whenever common variants (Glu158Lys, Glu308Gly) were considered in combination a distinct pattern between the control population and patients was observed, mainly in what concerns the presence of Lys158 and Gly308 in homozygous state. Further studies are necessary to clarify the pathogenicity of novel variants identified in this study, as well as the effect of the common single nucleotide polymorphisms, which may play an important role in disease presentation and/or protective mechanism to xenobiotics drugs or environment.

Flavin-containing monooxygenase 3 gene polymorphisms in Turkish population

Flavin-containing monooxygenases (FMOs) represent the second most important human monooxygenase system, after cytochrome P450s (CYPs) and catalyze the oxygenation of many chemicals containing nitrogen-, sulphur-, phosphorous-, selenium- and other nucleophilic heteroatoms. FMO3 is the prominent FMO form in adult human liver. For FMO3, both interindividual variability within a single ethnic group and variability between ethnic groups have been reported. In our study, three prevalent functional FMO3 variants (E158K, V257M, and E308G) were genotyped in healthy Turkish people by polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) methods. The frequencies of alleles and haplotypes were compared with those obtained from different populations. It was found that FMO3 158K, 257M and 308G alleles, demonstrate impaired metabolism toward many FMO3 substrates, were observed frequently in Turkish population similar to the other populations. Also, the frequencies of haplotypes were determined based on individual allelic frequencies and it was observed that the most common haplotypes were haplotip EVE and KVE (E158K/V257M/E308G), which together accounted for 80% of all haplotypes. The obtained data from the present study could be useful for further studies assessing sensitivity to therapeutic drugs, environmental toxicants and common disease.

Flavin-containing monooxygenase-3: induction by 3-methylcholanthrene and complex regulation by xenobiotic chemicals in hepatoma cells and mouse liver

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.

Flavin-containing monooxygenase 3 polymorphisms in 13 ethnic populations from Europe, East Asia and sub-Saharan Africa: frequency and linkage analysis

Aims: To investigate intra- and inter-ethnic differences in three widespread (E158K, V257M and E308G) and two African-specific (D132H and L360P) flavin-containing monooxygenase 3 (FMO3) polymorphisms. Materials & methods: Allele frequencies were determined by TaqMan® allelic discrimination assay in 2152 healthy volunteers from Europe (Swedes, Italians and Turks), East Asia (Japanese) and sub-Saharan Africa (nine ethnic groups covering eastern, southern and western regions), followed by haplotype and linkage analysis. Results: Significant subpopulation differences (p < 0.001) in allele frequencies were found for E158K, V257M and E308G in Europeans and regional differences (p < 0.01) for D132H among Africans. No carrier of P360 was identified. Cis-linkage between G308 and K158 was confirmed with the compound variant (K158/G308) being found in a high proportion (12.0–38.3%) of non-African subjects, but rarely (1.3%) among Africans. Conclusions: Distribution of functionally relevant FMO3 polymorphisms varies not only between ethnicities but also within. The K158/G308 variant may have potential clinical importance primarily in non-African populations due to its low prevalence in Africa.

The Role of Flavin-Containing Monooxygenase (FMO) in the Metabolism of Tamoxifen and Other Tertiary Amines

Tamoxifen is utilized in breast cancer therapy and in chemoprevention. Tamoxifen may enhance risk for other neoplasias, especially endometrial cancer. The risk:benefit depends on the rate of metabolic activation versus detoxication. Cytochrome P450-dependent alpha-hydroxylation, followed by sulfonation, represents a metabolic activation pathway, producing products capable of covalent DNA adduction. In contrast, tamoxifen N-oxygenation represents a detoxication pathway, with the caveat that N-oxides can be reduced back to the parent amines. The N-oxygenation pathway will be the focus for this review. Dr. David Kupfer pioneered studies on cytochrome P450 and flavin-containing monooxygenase (FMO) tamoxifen metabolism. We collaborated with Dr. Kupfer's laboratory and recently determined that the low level of tamoxifen N-oxide production in human liver microsomes may be explained by the kinetics of FMO1 versus FMO3.

PhRMA white paper on ADME pharmacogenomics

Pharmacogenomic (PGx) research on the absorption, distribution, metabolism, and excretion (ADME) properties of drugs has begun to have impact for both drug development and utilization. To provide a cross-industry perspective on the utility of ADME PGx, the Pharmaceutical Research and Manufacturers of America (PhRMA) conducted a survey of major pharmaceutical companies on their PGx practices and applications during 2003-2005. This white paper summarizes and interprets the results of the survey, highlights the contributions and applications of PGx by industrial scientists as reflected by original research publications, and discusses changes in drug labels that improve drug utilization by inclusion of PGx information. In addition, the paper includes a brief review on the clinically relevant genetic variants of drug-metabolizing enzymes and transporters most relevant to the pharmaceutical industry.

Defining drug disposition determinants: a pharmacogenetic-pharmacokinetic strategy

In preclinical and early clinical drug development, information about the factors influencing drug disposition is used to predict drug interaction potential, estimate and understand population pharmacokinetic variability, and select doses for clinical trials. However, both in vitro drug metabolism studies and pharmacogenetic association studies on human pharmacokinetic parameters have focused on a limited subset of the proteins involved in drug disposition. Furthermore, there has been a one-way information flow, solely using results of in vitro studies to select candidate genes for pharmacogenetic studies. Here, we propose a two-way pharmacogenetic-pharmacokinetic strategy that exploits the dramatic recent expansion in knowledge of functional genetic variation in proteins that influence drug disposition, and discuss how it could improve drug development.

Flavin-containing monooxygenase 3 and human disease

This review summarizes information concerning the association of the human flavin-containing monooxygenase 3 (FMO3) and human diseases. Human FMO3 oxygenates a wide variety of nucleophilic heteroatom-containing xenobiotics, including endogenous substrates and various clinically important drugs. In this article, the authors discuss the association of FMO3 with human disease, including: i) direct association of FMO3 genetic mutations to human genetic disease; ii) association of FMO3 genetic polymorphism to altered drug metabolism and, therefore, indirect association of FMO3 with drug therapeutic efficacy of human disease; and iii) the potential impact and/or effect of FMO3 transcriptional regulation during disease states. Even though many studies discussed for the latter two points are at a preliminary stage and require much more research to bring to a definite conclusion, the authors include these studies to stimulate general interest and invite further discussion.

Sulindac and its metabolites induce carcinogen metabolizing enzymes in human colon cancer cells

Sulindac is a nonsteroidal antiinflammatory drug that has been demonstrated to be a potent chemopreventive agent against colorectal cancer in both human and animal models. In vivo, sulindac may be reversibly reduced to the active antiinflammatory compound, sulindac sulfide, or irreversibly oxidized to sulindac sulfone. Sulindac has also been shown to inhibit polycyclic aromatic hydrocarbon (PAH)-induced cancer, but the molecular mechanisms of its antitumor effect remain unclear. In this study, we investigated the effects of sulindac and its metabolites on the expression of enzymes that metabolize and detoxify PAHs in 2 human colon cancer cell lines, LS180 and Caco-2. Sulindac and sulindac sulfide induced a sustained, concentration-dependent increase in CYP enzyme activity as well as an increase in the mRNA levels of CYP1A1, CYP1A2 and CYP1B1. Sulindac and sulindac sulfide induced the transcription of the CYP1A1 gene, as measured by the level of heterogeneous nuclear CYP1A1 RNA and verified by the use of actinomycin D as a transcription inhibitor. Chromatin immunoprecipitation assays demonstrated that sulindac and sulindac sulfide also increased the nuclear level of activated aryl hydrocarbon receptor, the transcription factor which mediates CYP expression. Additionally, sulindac and both metabolites increased the activity and mRNA expression of the carcinogen detoxification enzyme NAD(P)H:quinone oxidoreductase, as well as the expression of UDP-glucuronosyltransferase mRNA. These results show an overall upregulation of carcinogen metabolizing enzymes in colon cancer cells treated with sulindac, sulindac sulfide and sulindac sulfone that may contribute to the established chemoprotective effects of these compounds.

Molecular evolution and balancing selection in the flavin-containing monooxygenase 3 gene (FMO3)

OBJECTIVES

Flavin-containing monooxygenase 3 (FMO3) is involved in the metabolism of foreign chemicals, including therapeutic drugs, and thus mediates interactions between humans and their chemical environment. Loss-of-function mutations in the gene cause the inherited disorder trimethylaminuria, or fish-odour syndrome. The objective was to gain insights into the evolutionary history of FMO3.

METHODS

Genetic diversity within FMO3 was characterized by sequencing 6.3 kb of genomic DNA, encompassing the entire coding sequence, some intronic and 3'-untranslated region, and 3.4 kb of 5'-flanking sequence, in 23 potential trimethylaminuric Japanese, and the same 3.4 kb 5'-flanking region in 45 unaffected Japanese. Mutational relationships among haplotypes were inferred from a reduced-median network. The time depth of the variation and ages of individual mutations were estimated by maximum-likelihood coalescent analysis. Test statistics were used to investigate whether the variation is compatible with neutral evolution.

RESULTS

Sixteen single-nucleotide polymorphisms (SNPs) were identified, which segregated as seven distinct haplotypes. Estimated ages of the mutations indicate that almost all predated migration out of Africa. Analysis of the heterozygosity of FMO3 SNPs indicates that genetic differentiation among continental populations is low (FST=0.050). Test statistics, based on allele-frequency spectrum, number and diversity of haplotypes, linkage disequilibrium and interspecific sequence comparisons, showed a significant departure from neutral expectations, because of an excess of intermediate-frequency SNPs and haplotypes, a ragged pairwise mismatch distribution and an excess of replacement polymorphisms.

CONCLUSION

The results provide evidence that FMO3 has been the subject of balancing selection. Finally, we identify mutations that are potential targets for selection.

Genetic polymorphisms of human flavin-containing monooxygenase 3: implications for drug metabolism and clinical perspectives

Flavin-containing monooxygenase 3 (FMO3) is a hepatic microsomal enzyme that oxidizes a host of drugs, xenobiotics and other chemicals. Numerous variants in the gene encoding FMO3 have been identified, some of which result in altered enzymatic activity and, consequently, altered substrate metabolism. Studies also implicate individual and ethnic differences in the frequency of FMO3 polymorphisms. In addition, new variants continue to be identified with potentially important clinical implications. For example, the role of FMO3 variants in the pathophysiology of gastrointestinal diseases is an evolving area of research. Two commonly occurring polymorphisms of FMO3, E158K and E308G, have been associated with a reduction in polyp burden in patients with familial adenomatous polyposis who were treated with sulindac sulfide, an FMO3 substrate. These findings suggest a potential role for prospective genotyping of common FMO3 polymorphisms in the treatment of disease states that involve the use of drugs metabolized by FMO3. This review summarizes the current state of research on the genetic polymorphisms of FMO3, with a focus on their clinical implications in gastrointestinal diseases.

Pharmacogenetics and diseases of the colon

PURPOSE OF REVIEW

The deciphering of the human genome sequence has enabled the identification of genetic polymorphisms that are responsible for inter-individual variation in the response to drug therapy. This field is referred to as pharmacogenetics. We review the impact of pharmacogenetics on therapy in diseases of the colon using three common variant enzyme systems as examples.

RECENT FINDINGS

Many enzyme systems impact the treatment of diseases of the colon. Examples include thiopurine S-methyltransferase, dihydropyrimidine dehydrogenase and flavin monooxygenase 3. They affect the management of inflammatory bowel disease, colorectal cancer and the chemoprevention of colorectal adenoma by influencing the metabolism of their respective substrates, azathioprine/6-mercaptopurine, 5-fluorouracil and sulindac. Recent studies have implicated the significance of genetic polymorphisms in each of the three drug-metabolizing enzymes, which impacts on the therapeutic outcome of the stated diseases. These studies highlight the potential role of pharmacogenetics in the design of a therapeutic plan which would increase efficacy and limit toxicity.

SUMMARY

Pharmacogenetics of drug-metabolizing systems continues to gain significance in the drug therapy of a variety of disease states including those of the gastrointestinal tract.

Allele and genotype frequencies of polymorphicFMO3 gene in two genetically distinct populations

The aims of this study were to analyze flavin-containing monooxygenase 3 (FMO3) polymorphisms and allele and genotype frequencies in 256 Han Chinese and 50 African-American individuals, to compare the allele and genotype frequencies of these populations with those of other world populations. For Han Chinese, genotyping of three common single nucleotide polymorphisms, E158K, V257M and E308G was performed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). For African-Americans, genotyping of all coding exons was performed by modified PCR-single strand conformational polymorphism (SSCP). Evolutionary rates of FMO3 were estimated computationally. We found that there were significant differences in allele and genotype frequencies among Han Chinese, African-Americans and other world populations. In Han Chinese, the minor allele frequencies (MAFs) were 0.229 (E158K), 0.203 (V257M) and 0.148 (E308G), respectively. In African-Americans, MAFs were 0.48 (E158K), 0.05 (V257M) and 0 (E308G), respectively. There was rapid evolution during the divergence of primate FMO3. This is the first report comparing FMO alleles and genotypes between Han Chinese and African-Americans. A Han Chinese population database has been established for three gene polymorphisms. The data presented here justify further pharmacogenetic studies for potentially optimizing recommended drug dosages and evaluating relationships with disease processes.

Haplotype Frequency Distribution and Linkage Disequilibrium Analysis of Single Nucleotide Polymorphisms at the Human FMO3 Gene Locus

We analyzed flavin-containing monooxygenase 3 (FMO3) polymorphisms, haplotype structure, and linkage disequilibrium (LD) in 256 Han Chinese and 50 African-American individuals to compare their haplotype frequencies and LD with other world populations. For the Han Chinese, genotyping of three haplotype tag single nucleotide polymorphisms (E158K, V257M, and E308G) was performed by polymerase chain reaction (PCR)-restriction fragment length polymorphism. For the African-Americans, genotyping of all coding exons was performed by modified PCR-single strand conformational polymorphism. Haplotype frequencies, LD, and evolutionary rates were inferred and estimated computationally. There were significant differences in haplotype frequency distribution and LD pattern among Han Chinese, African-Americans, and other world populations. Four major haplotypes of Han Chinese were EVE, KVE, EME, and EVG. Two major haplotypes of African-Americans were EVE and KVE. We found that sites 158 and 257 are in significant LD in both populations. This is the first report comparing FMO haplotypes and LD of Han Chinese with African-Americans. The data presented here justify further pharmacogenetic studies for potentially optimizing recommended drug dosages and evaluating relationships with disease processes.

Mitochondrial Uncoupling by the Sulindac Metabolite, Sulindac Sulfide

Sulindac is a non-steroidal antiinflammatory drug (NSAID) known to inhibit cyclooxygenases (COX) 1 and 2, and at present of interest for cancer prevention. However, its therapeutic use has been limited by its toxicity to the gastrointestinal tract and liver. We address the effects of sulindac, of the pharmacologically inactive metabolite, sulindac sulfone, and of the pharmacologically active metabolite, sudindac sulfide, on isolated rat liver mitochondria and HepG2 cells. Sulindac sulfide, but not sulindac sulfone or sulindac itself, caused mitochondrial uncoupling, released preaccumulated Ca2+ from the organelle, and decreased Hep-G2 cell viability in apparent association with cell ATP depletion resulting from mitochondrial uncoupling-associated membrane potential dissipation.

Investigation of structure and function of a catalytically efficient variant of the human flavin-containing monooxygenase form 3

To characterize the contribution of amino acid 360 to the functional activity of the human flavin-containing monooxygenase form 3 (FMO3) and form 1 (FMO1) in the oxygenation of drugs and chemicals, we expressed four FMO3 variants (i.e., Ala360-FMO3, His360-FMO3, Gln360-FMO3, and Pro360-FMO3) and one FMO1 variant (i.e., Pro360-FMO1) and compared them to wild-type enzymes (Leu360-FMO3 and His360-FMO1, respectively). The amino acid substitutions were introduced into wild-type FMO3 or FMO1 cDNA by site-directed mutagenesis. The thermal stability of variants of Leu360 FMO3 was also studied, and the thermal stability was significantly different from that of wild-type FMO3. The influence of different substrates to modulate the catalytic activity of FMO3 variants was also examined. Selective functional substrate activity was determined with mercaptoimidazole, chlorpromazine, and 10-[(N,N-dimethylaminopentyl)-2-(trifluoromethyl)]phenothiazine. Compared with wild-type FMO3, the Ala360-FMO3 and His360-FMO3 variants were less catalytically efficient for mercaptoimidazole S-oxygenation. N-Oxygenation of chlorpromazine was significantly less catalytically efficient for His360-FMO3 compared with wild-type FMO3. Human Pro360-FMO1 was significantly more catalytically efficient at S-oxygenating mercaptoimidazole and chlorpromazine compared with wild-type FMO1. The data support the mechanism that the Pro360 loci affect thermal stability of FMO3. Because different amino acids at position 360 affect substrate oxygenation in a unique fashion compared with that of FMO3 stimulation, we conclude that the mechanism of stimulation of FMO3 is distinct from that of enzyme catalysis. A molecular model of human FMO3 was also constructed to help explain the results. The increase in catalytic efficiency observed for Pro360 in human FMO3 was also observed when the His of FMO1 was replaced by Pro at loci 360.

Human flavin-containing monooxygenases

This review summarizes recent information concerning the pharmacological and toxicological significance of the human flavin-containing monooxygenase (FMO, EC 1.14.13.8). The human FMO oxygenates nucleophilic heteroatom-containing chemicals and drugs and generally converts them into harmless, polar, readily excreted metabolites. Sometimes, however, FMO bioactivates chemicals into reactive materials that can cause toxicity. Most of the interindividual differences of FMO are due to genetic variability and allelic variation, and splicing variants may contribute to interindividual and interethnic variability observed for FMO-mediated metabolism. In contrast to cytochrome P450 (CYP), FMO is not easily induced nor readily inhibited, and potential adverse drug-drug interactions are minimized for drugs prominently metabolized by FMO. These properties may provide advantages in drug design and discovery, and by incorporating FMO detoxication pathways into drug candidates, more drug-like materials may be forthcoming. Although exhaustive examples are not available, physiological factors can influence FMO function, and this may have implications for the clinical significance of FMO and a role in human disease.

Mutation, polymorphism and perspectives for the future of human flavin-containing monooxygenase 3

Flavin-containing monooxygenases (FMOs) catalyze NADPH-dependent monooxygenation of soft-nucleophilic nitrogen, sulfur, and phosphorous atoms contained within various drugs, pesticides, and xenobiotics. Flavin-containing monooxygenase 3 (FMO3) is responsible for the majority of FMO-mediated xenobiotic metabolism in the adult human liver. Mutations in the FMO3 gene can result in defective trimethylamine (TMA) N-oxygenation, which gives rise to the disorder known as trimethylaminuria (TMAU) or "fish-odour syndrome". To date 18 mutations of FMO3 gene have been reported that cause TMAU, and polymorphic variants of the gene have also been identified. Interindividual variability in the expression of FMO3 may affect drug and foreign chemical metabolism in the liver and other tissues. It is important therefore to study how base sequence variation of the FMO3 gene might affect the ability of individuals and different ethnic population groups to deal with the variety of environmental chemicals and pharmaceutical products that are substrates for FMO3.

Genetic polymorphisms of flavin monooxygenase 3 in sulindac-induced regression of colorectal adenomas in familial adenomatous polyposis

Sulindac is a nonsteroidal antiinflammatory drug with a chemopreventive effect in patients with familial adenomatous polyposis (FAP). In vivo, the active form of sulindac is sulindac sulfide, which is inactivated by the hepatic microsomal enzyme, flavin monooxygenase 3 (FMO3). In humans, numerous polymorphisms exist in FMO3, which alter enzymatic activity and subsequent substrate metabolism. We recently showed that certain polymorphic forms of FMO3 with reduced activity were associated with a more favorable response to sulindac in preventing the formation of adenomas in patients with FAP without polyps at baseline. Here, we determined whether these FMO3 polymorphisms correlated with the ability of sulindac to regress polyposis in patients with FAP who had polyps prior to treatment. Nineteen patients were treated with 150 mg sulindac twice a day for 6 months. The size and number of polyps in each patient was assessed at baseline (prior to the administration of sulindac), and at 3 and 6 months. Genotyping was done on seven established FMO3 polymorphisms with functional significance-M66I, E158K, P153L, V257M, E305X, E308G, and R492W. Statistical analyses were done with Wilcoxon rank sum test. Of the loci examined, only E158K and E308G showed polymorphic changes. Six patients exhibited polymorphisms in both E158K and E308G loci and were designated as genotype combination 1. The remaining patients were designated as genotype combination 2. Over the course of treatment, patients with genotype combination 1 had a greater reduction in both the size and number of polyps than those with genotype combination 2. These results suggest that combined polymorphic changes in the E158K and E308G alleles may protect against polyposis in patients with FAP treated with sulindac.

Flavin-containing monooxygenase genetic polymorphism: impact on chemical metabolism and drug development

The flavin-containing monooxygenases (FMOs) metabolize a broad range of therapeutics. Consisting of five gene products in humans (FMO1–5), the different FMO family members exhibit pronounced tissue- and temporal-specific expression patterns. Substantial interindividual differences are also observed, and the inability to modulate with exogenous agents is consistent with an important role for genetic variation. Several rare FMO3 alleles causative for trimethylaminuria have been well characterized. However, the identification and characterization of functional FMO1–5 polymorphisms has been more recent. Although none of these polymorphisms has been associated with an adverse drug reaction, the continued broadening of our therapeutic armamentarium makes such an event likely in the future. Furthermore, at least one example has been reported for a direct association between FMO3 polymorphism and therapeutic efficacy. Thus, it is anticipated that knowledge regarding functionally-relevant FMO genetic variability will become increasingly important for making drug development and patient therapeutic choices.