The fish odour syndrome: biochemical, familial, and clinical aspects

Metabolomic and genomic insights into TMA degradation by a novel halotolerant strain - Paracoccus sp. PS1

Trimethylamine N-oxide (TMAO) is a gut metabolite that acts as a biomarker for chronic diseases, and is generated by the oxidation of trimethylamine (TMA) produced by gut microflora. Since, microbial degradation of TMA is predicted to be used to restrict the production of TMAO, we aimed to isolate bacterial strains that could effectively degrade TMA before being oxidized to TMAO. As marine fish is considered to have a rich content of TMAO, we have isolated TMA degrading isolates from fish skin. Out of the fourteen isolates, depending on their rapid TMA utilization capability in mineral salt medium supplemented with TMA as a sole carbon and nitrogen source, isolate PS1 was selected as our desired isolate. Its TMA degrading capacity was further confirmed through spectrophotometric, Electrospray Ionization Time-of-Flight Mass Spectrometry (ESI TOF-MS) and High performance liquid chromatography (HPLC) analysis and in silico analysis of whole genome (WG) gave further insights of protein into its TMA degradation pathways. PS1 was taxonomically identified as Paracoccus sp. based on its 16S rRNA and whole genome sequence analysis. As PS1 possesses the enzymes required for degradation of TMA, clinical use of this isolate has the potential to reduce TMAO generation in the human gut.

The evolving role of methanogenic archaea in mammalian microbiomes

Methanogenic archaea (methanogens) represent a diverse group of microorganisms that inhabit various environmental and host-associated microbiomes. These organisms play an essential role in global carbon cycling given their ability to produce methane, a potent greenhouse gas, as a by-product of their energy production. Recent advances in culture-independent and -dependent studies have highlighted an increased prevalence of methanogens in the host-associated microbiome of diverse animal species. Moreover, there is increasing evidence that methanogens, and/or the methane they produce, may play a substantial role in human health and disease. This review addresses the expanding host-range and the emerging view of host-specific adaptations in methanogen biology and ecology, and the implications for host health and disease.

Gut microbiota: A new target for traditional Chinese medicine in the treatment of depression

ETHNIC PHARMACOLOGICAL RELEVANCE

The causes of depression are complex. Many factors are involved in its pathogenesis, including the individual's biological and social environment. Although numerous studies have reported that the gut microbiota plays a significant role in depression, drugs that regulate the gut microbiota to treat depression have not yet been comprehensively reviewed. At the same time, more and more attention has been paid to the characteristics of traditional Chinese medicine (TCM) in improving depression by regulating gut microbiota. In ancient times, fecal microbiota transplantation was recorded in TCM for the treatment of severe diseases. There are also records in Chinese ancient books about the use of TCM to adjust gut microbiota to treat diseases, which has opened up a unique research field in TCM. Therefore, this article focuses on the pharmacological effects, targets, and mechanisms of TCM in improving depression by mediating the influence of gut microbiota.

AIM OF THIS REVIEW

To summarize the role the gut microbiota plays in depression, highlight potential regulatory targets, and elucidate the anti-depression mechanisms of TCMs through regulation of the gut microbiota.

METHODS

A systematic review of 256 clinical trials and pharmaceutical studies published until June 2022 was conducted in eight electronic databases (Web of Science, PubMed, SciFinder, Research Gate, ScienceDirect, Google Scholar, Scopus, and China Knowledge Infrastructure), according to the implemented PRISMA criteria, using the search terms "traditional Chinese medicine," "depression," and "gut microbiota."

RESULTS

Numerous studies reported the effects of different gut bacteria on depression and that antidepressants work through the gut microbiota. TCM preparations based on compound Chinese medicine, the Chinese Materia Medica, and major bioactive components exerted antidepressant-like effects by improving levels of neurotransmitters, short-chain fatty acids, brain-derived neurotrophic factor, kynurenine, and cytokines via regulation of the gut microbiota.

CONCLUSION

This review summarized the anti-depression effects of TCM on the gut microbiota, providing evidence that TCMs are safe and effective in the treatment of depression and may provide a new therapeutic approach.

FMO3 deficiency of duck leads to decreased lipid deposition and increased antibacterial activity

Background

Most duck eggs possess a fishy odor, indicating that ducks generally exhibit impaired trimethylamine (TMA) metabolism. TMA accumulation is responsible for this unpleasant odor, and TMA metabolism plays an essential role in trimethylaminuria (TMAU), also known as fish odor syndrome. In this study, we focused on the unusual TMA metabolism mechanism in ducks, and further explored the unclear reasons leading to the debilitating TMA metabolism.

Methods

To achieve this, transcriptome, proteome, and metagenome analyses were first integrated based on the constructed duck populations with high and low TMA metabolism abilities. Additionally, further experiments were conducted to validate the hypothesis regarding the limited flavin-containing monooxygenase 3 (FMO3) metabolism ability of ducks.

Results

The study demonstrated that liver FMO3 and cecal microbes, including Akkermansia and Mucispirillum, participated in TMA metabolism in ducks. The limited oxidation ability of FMO3 explains the weakening of TMA metabolism in ducks. Nevertheless, it decreases lipid deposition and increases antibacterial activity, contributing to its survival and reproduction during the evolutionary adaptation process.

Conclusions

This study demonstrated the function of FMO3 and intestinal microbes in regulating TMA metabolism and illustrated the biological significance of FMO3 impairment in ducks.

Balancing the Equation: A Natural History of Trimethylamine and Trimethylamine-N-oxide

Trimethylamine (TMA) and its N-oxide (TMAO) are ubiquitous in prokaryote and eukaryote organisms as well as in the environment, reflecting their fundamental importance in evolutionary biology, and their diverse biochemical functions. Both metabolites have multiple biological roles including cell-signaling. Much attention has focused on the significance of serum and urinary TMAO in cardiovascular disease risk, yet this is only one of the many facets of a deeper TMA-TMAO partnership that reflects the significance of these metabolites in multiple biological processes spanning animals, plants, bacteria, and fungi. We report on analytical methods for measuring TMA and TMAO and attempt to critically synthesize and map the global functions of TMA and TMAO in a systems biology framework.

A series of simple detection systems for genetic variants of flavin-containing monooxygenase 3 (FMO3) with impaired function in Japanese subjects

Increasing numbers of single-nucleotide substitutions of the human flavin-containing monooxygenase 3 (FMO3) gene are being recorded in mega-databases. Phenotype-gene analyses revealed impaired FMO3 variants associated with the metabolic disorder trimethylaminuria. Here, a series of reliable FMO3 genotyping confirmation methods was assembled and developed for 45 impaired FMO3 variants, mainly found in Japanese populations, using singleplex or duplex polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) methods and singleplex, duplex, or tetraplex allele-specific PCR methods. Nine PCR-RFLP procedures with single restriction enzymes and fourteen duplex PCR-RFLP procedures (for p.Trp41Ter and p.Thr329Ala, p.Met66Val and p.Leu163Pro, p.Pro70Leu and p.Glu308Gly, p.Asn114Ser and p.Ser195Leu, p.Glu158Lys and p.Ile441Thr, p.Cys197Ter and p.Trp388Ter, p.Arg205Cys and p.Val257Met, p.Arg205His and p.Cys397Ser, p.Met211ArgfsTer10 and p.Arg492Trp, p.Arg223Gln and p.Leu473Pro, p.Met260Val and p.Thr488Ala, p.Tyr269His and p.Ala311Pro, p.Ser310Leu and p.Gly376Glu, and p.Gln470Ter and p.Arg500Ter) were newly established along with eight singleplex (for p.Pro153GlnfsTer14, p.Gly191Cys, p.Pro248Thr, p.Ile486Met, and p.Pro496Ser, among others), one duplex (p.Ile199Ser and p.Asp286Tyr), and one tetraplex (p.Ile7Thr, p.Val58Ile, p.Thr201Lys, and p.Gly421Val) allele-specific PCR systems. This series of systems should facilitate the easy detection in a clinical setting of FMO3 variants in Japanese subjects susceptible to low drug clearances or drug reactions possibly caused by impaired FMO3 function.

Impact of trimethylaminuria on daily psychosocial functioning

BACKGROUND

Trimethylaminuria (TMAU) (OMIM #602079) is a rare inherited metabolic condition. TMAU is associated with decreased hepatic trimethylamine N-oxidation, which leads to an excess of the volatile trimethylamine (TMA) instead of substrate conversion to trimethylamine N-oxide (TMAO). TMA is a tertiary amine derived from the enterobacterial metabolism of precursors such as choline and phosphatidylcholine present in the diet, and is also a bacterial metabolite of TMAO, a normal constituent of saltwater fish. When the involved enzyme flavin mono-oxygenase 3 is deficient, TMA builds up and is released in the person's sweat, urine, and breath, giving off a strong body odor. We have recently reported the biochemical and genetic characteristics of 13 Irish adult patients with TMAU attending the main Irish Reference Center. Research on the behavioral and psychosocial aspects of this condition is limited. This study explores the patients' perspectives of living with TMAU in Ireland.

METHODS

A qualitative descriptive phenomenological approach was used. Six adults participated in this study. Data were gathered through semi-structured interviews, which were transcribed and analyzed.

RESULTS

The results suggest that the participants experienced a negative journey to diagnosis. Fear, anxiety, paranoia, and dysfunctional thinking are a constant struggle. Participants reported using avoidant coping mechanisms and strategic planning to navigate daily life.

CONCLUSION

It is considered that the results from this study will inform future interventions with this unique patient cohort.

How Can Drug Metabolism and Transporter Genetics Inform Psychotropic Prescribing?

Many genetic variants in drug metabolizing enzymes and transporters have been shown to be relevant for treating psychiatric disorders. Associations are strong enough to feature on drug labels and for prescribing guidelines based on such data. A range of commercial tests are available; however, there is variability in included genetic variants, methodology, and interpretation. We herein provide relevant background for understanding clinical associations with specific variants, other factors that are relevant to consider when interpreting such data (such as age, gender, drug-drug interactions), and summarize the data relevant to clinical utility of pharmacogenetic testing in psychiatry and the available prescribing guidelines. We also highlight areas for future research focus in this field.

Impact of biological wastewater treatment on the reactivity of N-Nitrosodimethylamine precursors

N-Nitrosodimethylamine (NDMA) is a probable human carcinogen which forms during chloramination of wastewater-impacted drinking waters. Municipal wastewater effluents are considered as major sources of NDMA precursors affecting downstream water quality. To evaluate the deactivation mechanisms and efficiencies of NDMA precursors during secondary treatment with the activated sludge (AS) process, NDMA formation potentials (FPs) of selected model precursor compounds and sewage components (i.e., blackwaters and greywaters) were monitored in batch AS treatment tests. After 24-h incubation with four different types of AS (i.e., domestic rural, domestic urban, textile and lab-grown AS), NDMA FP of trimethylamine (TMA) and minocycline (MNCL) decreased by 77-100%, while there was only 29-46% reduction in NDMA FP of sumatriptan (SMTR). The reduction in NDMA FP associated with ranitidine (RNTD) varied between 34% and 87%. The decrease in NDMA FP of RNTD depended on the AS type, hydraulic retention time (HRT) and solids retention time (SRT). The domestic AS (rural and urban) achieved higher decreases in NDMA FPs of the tested model precursors than the textile AS or lab-grown AS. Increasing the HRT or SRT enhanced NDMA FP decrease for RNTD. Among different processes tested (i.e., biodegradation, biosorption and volatilization), biosorption was the major mechanism responsible for the NDMA FP decrease of RNTD, MNCL and SMTR, while biodegradation was the major NDMA FP reduction mechanism for TMA. The reduction in NDMA FP of RNTD via biodegradation depended on the AS activity which may vary with sampling seasons and SRT. NDMA FPs in all tested sewage components (i.e., blackwaters and greywaters) decreased after 24-h AS treatment. Urine in blackwater was the predominant (i.e., >90%) contributor to NDMA FP in domestic sewage and AS-treated effluents.

Plasma Trimethylamine N-Oxide and Its Precursors: Population Epidemiology, Parent-Child Concordance, and Associations with Reported Dietary Intake in 11- to 12-Year-Old Children and Their Parents

BACKGROUND

Trimethylamine N-oxide (TMAO) is a microbiome- and diet-derived metabolite implicated in adverse cardiovascular outcomes. To date, studies of plasma TMAO concentrations have largely focused on individuals with metabolic disease. As such, data on TMAO concentrations in population settings and parent-child dyads are lacking.

OBJECTIVES

This study aimed to investigate parent-child concordance, age, and sex effects on plasma concentrations of TMAO and its precursors [l-carnitine, choline, betaine, and dimethylglycine (DMG)]. Associations between concentrations of TMAO and its precursors and self-reported dietary intakes of animal protein (i.e., red meat, meat products, chicken, fish, milk products, and cheese) and fast-food meals were also investigated.

METHODS

A total of 1166 children (mean ± SD age: 11 ± 0.5 y, 51% female) and 1324 parents (mean ± SD age: 44 ± 5.1 y, 87% female) had a biomedical assessment as part of Growing Up in Australia's Child Health Checkpoint. Plasma TMAO and precursor concentrations were quantified using ultra-high-pressure LC coupled with tandem MS.

RESULTS

Familial dyads significantly contributed to plasma TMAO and precursor concentrations (P < 0.0001), explaining 37% of variance for TMAO concentrations. Least-square mean ± SE plasma TMAO was lower in children (0.79 ± 0.02 µM on the log-scale) than in adults (1.22 ± 0.02 µM). By contrast, children's betaine (40.30 ± 0.34 µM) and DMG concentrations (1.02 ± 0.01 µM on the log-scale) were higher than adults' betaine (37.50 ± 0.32 µM) and DMG concentrations (0.80 ± 0.01 µM) (P < 0.0001). Mean values of all metabolites, except adult TMAO, were higher in males than in females (P < 0.001). Greater reported intake of red meat and fish was associated with higher TMAO concentrations in both children [estimates (95% CIs) for red meat: 0.06 (0.01, 0.10); fish: 0.11 (0.06, 0.17)] and adults [red meat: 0.13 (0.08, 0.17); meat products: 0.07 (0.03, 0.12); and fish: 0.09 (0.04, 0.14)].

CONCLUSIONS

Age, sex, and shared family factors, including diet, contribute to variation in plasma concentrations of TMAO and its precursors.

Endogenous Roles of Mammalian Flavin-Containing Monooxygenases

Flavin-containing monooxygenases (FMOs) catalyze the oxygenation of numerous foreign chemicals. This review considers the roles of FMOs in the metabolism of endogenous substrates and in physiological processes, and focuses on FMOs of human and mouse. Tyramine, phenethylamine, trimethylamine, cysteamine, methionine, lipoic acid and lipoamide have been identified as endogenous or dietary-derived substrates of FMOs in vitro. However, with the exception of trimethylamine, the role of FMOs in the metabolism of these compounds in vivo is unclear. The use, as experimental models, of knockout-mouse lines deficient in various Fmo genes has revealed previously unsuspected roles for FMOs in endogenous metabolic processes. FMO1 has been identified as a novel regulator of energy balance that acts to promote metabolic efficiency, and also as being involved in the biosynthesis of taurine, by catalyzing the S-oxygenation of hypotaurine. FMO5 has been identified as a regulator of metabolic ageing and glucose homeostasis that apparently acts by sensing or responding to gut bacteria. Thus, FMOs do not function only as xenobiotic-metabolizing enzymes and there is a risk that exposure to drugs and environmental chemicals that are substrates or inducers of FMOs would perturb the endogenous functions of these enzymes.

Effects of Grape Pomace Polyphenolic Extract (Taurisolo®) in Reducing TMAO Serum Levels in Humans: Preliminary Results from a Randomized, Placebo-Controlled, Cross-Over Study

Trimethylamine N-oxide (TMAO) is considered a novel risk factor for cardiovascular diseases. Several studies demonstrated that polyphenols are able to inhibit the growth of TMA-producing bacterial strains, and resveratrol (RSV) reduced TMAO levels in mice. In the present study, we evaluated the TMAO-reducing effect of a novel nutraceutical formulation containing grape pomace extract in humans (Taurisolo®). The Taurisolo® polyphenol content was evaluated by a High Performance Liquid Chromatography-diode-array detector (HPLC-DAD) method, and RSV was monitored as an indicative marker. After in vitro GI digestion, intestinal bioaccessibility of RSV was 92.3%. A randomized, placebo-controlled, cross-over trial was carried out to evaluate the TMAO-reducing effect of Taurisolo®. In acute, the maximum levels of RSV were detected both in serum and whole blood 60 min after the administration of Taurisolo®; in chronic, a significant increase of RSV was detected in serum after the 4-week treatment. After 4 weeks, the levels of TMAO were significantly decreased in the treatment group compared to placebo (63.6% vs. 0.54%, respectively, P < 0.0001). In conclusion, our data show that Taurisolo® may represent a novel and useful natural remedy to reduce prognostic markers for incident cardiovascular events. Undoubtedly, further in vitro and in vivo studies need to be performed in order to elucidate possible mechanisms of action and corroborate our preliminary results.

Gut Colonization with Methanogenic Archaea Lowers Plasma Trimethylamine N-oxide Concentrations in Apolipoprotein e-/- Mice

A mechanistic link between trimethylamine N-oxide (TMAO) and atherogenesis has been reported. TMAO is generated enzymatically in the liver by the oxidation of trimethylamine (TMA), which is produced from dietary choline, carnitine and betaine by gut bacteria. It is known that certain members of methanogenic archaea (MA) could use methylated amines such as trimethylamine as growth substrates in culture. Therefore, we investigated the efficacy of gut colonization with MA on lowering plasma TMAO concentrations. Initially, we screened for the colonization potential and TMAO lowering efficacy of five MA species in C57BL/6 mice fed with high choline/TMA supplemented diet, and found out that all five species could colonize and lover plasma TMAO levels, although with different efficacies. The top performing MA, Methanobrevibacter smithii, Methanosarcina mazei, and Methanomicrococcus blatticola, were transplanted into Apoe^−/− mice fed with high choline/TMA supplemented diet. Similar to C57BL/6 mice, following initial provision of the MA, there was progressive attrition of MA within fecal microbial communities post-transplantation during the initial 3 weeks of the study. In general, plasma TMAO concentrations decreased significantly in proportion to the level of MA colonization. In a subsequent experiment, use of antibiotics and repeated transplantation of Apoe^−/− mice with M. smithii, led to high engraftment levels during the 9 weeks of the study, resulting in a sustained and significantly lower average plasma TMAO concentrations (18.2 ± 19.6 μM) compared to that in mock-transplanted control mice (120.8 ± 13.0 μM, p < 0.001). Compared to control Apoe^−/− mice, M. smithii-colonized mice also had a 44% decrease in aortic plaque area (8,570 μm [95% CI 19587–151821] vs. 15,369 μm [95% CI [70058–237321], p = 0.34), and 52% reduction in the fat content in the atherosclerotic plaques (14,283 μm [95% CI 4,957–23,608] vs. 29,870 μm [95% CI 18,074–41,666], p = 0.10), although these differences did not reach significance. Gut colonization with M. smithii leads to a significant reduction in plasma TMAO levels, with a tendency for attenuation of atherosclerosis burden in Apoe^−/− mice. The anti-atherogenic potential of MA should be further tested in adequately powered experiments.

Trimethylamine N-oxide: breathe new life

Association between elevated levels of systemic trimethylamine N-oxide (TMAO) and increased risk for adverse cardiovascular events have been proposed in recent years. Increasing experimental and clinical evidence in the last decade has implicated TMAO as an important contributor to the pathogenesis of cardiovascular diseases. TMAO, the oxygenated product of trimethylamine (TMA), belongs to the class of amine oxides. Most of the TMA derived from the metabolism of choline and L-carnitine by gut bacteria is absorbed into the bloodstream and gets rapidly oxidized to TMAO by the hepatic enzyme, flavin-containing monooxgenase-3. Here, we discussed the biosynthesis of TMAO and clinical studies that have assessed TMAO as a biomarker for various cardiovascular and other diseases such as kidney failure, thrombosis, atherosclerosis, obesity, diabetes and cancer. We also summarized the interaction of TMAO with synthetic and traditional molecules that together affect circulating TMAO levels.

LINKED ARTICLES

This article is part of a themed section on Spotlight on Small Molecules in Cardiovascular Diseases. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.8/issuetoc.

Effect of Flavin-Containing Monooxygenase Genotype, Mouse Strain, and Gender on Trimethylamine N-oxide Production, Plasma Cholesterol Concentration, and an Index of Atherosclerosis

The objectives of the study were to determine the contribution, in mice, of members of the flavin-containing monooxygenase (FMO) family to the production of trimethylamine (TMA) N-oxide (TMAO), a potential proatherogenic molecule, and whether under normal dietary conditions differences in TMAO production were associated with changes in plasma cholesterol concentration or with an index of atherosclerosis (Als). Concentrations of urinary TMA and TMAO and plasma cholesterol were measured in 10-week-old male and female C57BL/6J and CD-1 mice and in mouse lines deficient in various Fmo genes (Fmo1^−/−, 2^−/−, 4^−/−, and Fmo5^−/−). In female mice most TMA N-oxygenation was catalyzed by FMO3, but in both genders 11%–12% of TMA was converted to TMAO by FMO1. Gender-, Fmo genotype-, and strain-related differences in TMAO production were accompanied by opposite effects on plasma cholesterol concentration. Plasma cholesterol was negatively, but weakly, correlated with TMAO production and urinary TMAO concentration. Fmo genotype had no effect on Als. There was no correlation between Als and either TMAO production or urinary TMAO concentration. Our results indicate that under normal dietary conditions TMAO does not increase plasma cholesterol or act as a proatherogenic molecule.

A highly sensitive liquid chromatography electrospray ionization mass spectrometry method for quantification of TMA, TMAO and creatinine in mouse urine

Our method describes the quantification in mouse urine of trimethylamine (TMA), trimethylamine N-oxide (TMAO) and creatinine. The method combines derivatization of TMA, with ethyl bromoacetate, and LC chromatographic separation on an ACE C₁₈ column. The effluent was continuously electrosprayed into the linear ion trap mass spectrometer (LTQ), which operated in selective ion monitoring (SIM) modes set for targeted analytes and their internal standards (IS). All validation parameters were within acceptable ranges of analytical method validation guidelines. Intra- and inter-day assay precision and accuracy coefficients of variation were <3.1%, and recoveries for TMA and TMAO were 97–104%. The method developed uses a two-step procedure. Firstly, TMA and TMAO are analyzed without a purification step using a 5-min gradient cap-LC- SIMs analysis, then creatinine is analyzed using the same experimental conditions. The method is robust, highly sensitive, reproducible and has the high-throughput capability of detecting TMA, TMAO and creatinine at on-column concentrations as low as 28 pg/mL, 115 pg/mL and 1 ng/mL, respectively. The method is suitable for analysis of TMA, TMAO and creatinine in both male and female mouse urine.

The key benefits of the method are:

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The small sample volume of urine required, which overcomes the difficulties of collecting sufficient volumes of urine at defined times.

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No sample pre-treatment is necessary.

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The quantification of TMA, TMAO and creatinine using the same cap-LC-MS method.

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.

Trimethylamine and Trimethylamine N-Oxide, a Flavin-Containing Monooxygenase 3 (FMO3)-Mediated Host-Microbiome Metabolic Axis Implicated in Health and Disease

Flavin-containing monooxygenase 3 (FMO3) is known primarily as an enzyme involved in the metabolism of therapeutic drugs. On a daily basis, however, we are exposed to one of the most abundant substrates of the enzyme trimethylamine (TMA), which is released from various dietary components by the action of gut bacteria. FMO3 converts the odorous TMA to nonodorous TMA N-oxide (TMAO), which is excreted in urine. Impaired FMO3 activity gives rise to the inherited disorder primary trimethylaminuria (TMAU). Affected individuals cannot produce TMAO and, consequently, excrete large amounts of TMA. A dysbiosis in gut bacteria can give rise to secondary TMAU. Recently, there has been much interest in FMO3 and its catalytic product, TMAO, because TMAO has been implicated in various conditions affecting health, including cardiovascular disease, reverse cholesterol transport, and glucose and lipid homeostasis. In this review, we consider the dietary components that can give rise to TMA, the gut bacteria involved in the production of TMA from dietary precursors, the metabolic reactions by which bacteria produce and use TMA, and the enzymes that catalyze the reactions. Also included is information on bacteria that produce TMA in the oral cavity and vagina, two key microbiome niches that can influence health. Finally, we discuss the importance of the TMA/TMAO microbiome-host axis in health and disease, considering factors that affect bacterial production and host metabolism of TMA, the involvement of TMAO and FMO3 in disease, and the implications of the host-microbiome axis for management of TMAU.

Unraveling the environmental and genetic interactions in atherosclerosis: Central role of the gut microbiota

Recent studies have convincingly linked gut microbiota to traits relevant to atherosclerosis, such as insulin resistance, dyslipidemia and inflammation, and have revealed novel disease pathways involving microbe-derived metabolites. These results have important implications for understanding how environmental and genetic factors act together to influence cardiovascular disease (CVD) risk. Thus, dietary constituents are not only absorbed and metabolized by the host but they also perturb the gut microbiota, which in turn influence host metabolism and inflammation. It also appears that host genetics helps to shape the gut microbiota community. Here, we discuss challenges in understanding these interactions and the role they play in CVD.

The contributory role of gut microbiota in cardiovascular disease

Our group recently discovered that certain dietary nutrients possessing a trimethylamine (TMA) moiety, namely choline/phosphatidylcholine and L-carnitine, participate in the development of atherosclerotic heart disease. A meta-organismal pathway was elucidated involving gut microbiota-dependent formation of TMA and host hepatic flavin monooxygenase 3-dependent (FMO3-dependent) formation of TMA-N-oxide (TMAO), a metabolite shown to be both mechanistically linked to atherosclerosis and whose levels are strongly linked to cardiovascular disease (CVD) risks. Collectively, these studies reveal that nutrient precursors, gut microbiota, and host participants along the meta-organismal pathway elucidated may serve as new targets for the prevention and treatment of CVD.

Archaebiotics: proposed therapeutic use of archaea to prevent trimethylaminuria and cardiovascular disease

Trimethylamine (TMA) is produced by gut bacteria from dietary ingredients. In individuals with a hereditary defect in flavin-containing monooxygenase 3, bacterial TMA production is believed to contribute to the symptoms of trimethylaminuria (TMAU; fish-odor syndrome). Intestinal microbiota TMA metabolism may also modulate atherosclerosis risk by affecting trimethylamine oxide (TMAO) production levels. We propose that reducing TMA formation in the gut by converting it to an inert molecule could be used to prevent or limit these human diseases, while avoiding the major drawbacks of other clinical interventions. Reducing TMA levels by microbiological interventions could also be helpful in some vaginoses. Particular members of a recently discovered group of methanogens, that are variably present in the human gut, are unusual in being apparently restricted to utilizing only methyl compounds including TMA as substrates. We confirmed experimentally that one of these strains tested, Methanomassiliicoccus luminyensis B10, is able to deplete TMA, by reducing it with H 2 for methanogenesis. We therefore suggest that members of this archaeal lineage could be used as treatments for metabolic disorders.

Quail FMO3 gene cloning, tissue expression profiling, polymorphism detection and association analysis with fishy taint in eggs

Quail eggs comprise a significant and favourable part of table eggs in certain countries. Some quail eggs, however, present fishy off-flavor which directly influences their quality. It is reported that flavin-containing monooxygenase 3 (FMO3) is associated with fish-odour trait in human and animal products. FMO3 is responsible for the degradation of trimethylamine (TMA) in vivo. Loss-of-function mutations in FMO3 gene can result in defective TMA N-oxygenation, giving rise to disorder known as “fish-odour syndrome” in human, as well as the fishy off-flavor in cow milk and chicken eggs. In order to reveal the genetic factor of fishy taint in quail eggs, we cloned the cDNA sequence of quail FMO3 gene, investigated FMO3 mRNA expression level in various tissues, detected SNPs in the coding region of the gene and conducted association analysis between a mutation and the TMA content in quail egg yolks. The 1888 bp cDNA sequence of quail FMO3 gene encoding 532 amino acids was obtained and characterized. The phylogenetic analysis revealed quail FMO3 had a closer relationship with chicken FMO3. The FMO3 mRNA was highly expressed in liver and kidney of quail. Nine SNPs were detected in the coding sequence of quail FMO3 gene, including a nonsense mutation (Q319X) which was significantly associated with the elevated TMA content in quail egg yolks. Genotype TT at Q319X mutation loci was sensitive to choline. With addition of choline in the feed, the quails with homozygote TT at the Q319X mutation loci laid fish-odour eggs, indicating an interaction between genotype and diet. The results indicated that Q319X mutation was associated with the fishy off-flavor in quail eggs. Identification of the unfavorable allele T of quail FMO3 gene can be applied in future quail breeding to eliminate fishy off-flavor trait in quail eggs.

A review of trimethylaminuria: (fish odor syndrome)

Trimethylaminuria, better known as fish odor syndrome, is a psychologically disabling condition in which a patient emits a foul odor, which resembles that of rotting fish. The disorder is most commonly caused by an inherited deficiency in flavin monooxygenase 3, the vital enzyme for the metabolism of trimethylamine, which is the compound responsible for the unpleasant odor. The condition is uncommon, but there has been recent research to suggest that the diagnosis may often be overlooked. Moreover, it is important to be cognizant of this condition because there are reliable diagnostic tests and the disorder can be devastating from a psychosocial perspective. While there is no cure, many simple treatment options exist that may drastically improve the quality of life of these patients. This article will review the literature with an emphasis on the psychosocial impact and treatment options.

Disposition and Metabolite Kinetics of Oral L-carnitine in Humans

The pharmacokinetics of L-carnitine and its metabolites were investigated in 7 healthy subjects following the oral administration of 0, 0.5, 1, and 2 g 3 times a day for 7 days. Mean plasma concentrations of L-carnitine across an 8-hour dose interval increased significantly (P < .05) from a baseline of 54.2 +/- 9.3 microM to 80.5 +/- 12.5 microM following the 0.5-g dose; there was no further increase at higher doses. There was a significant increase (P < .001) in the renal clearance of L-carnitine indicating saturation of tubular reabsorption. Trimethylamine plasma levels increased proportionately with L-carnitine dose, but there was no change in renal clearance. A significant increase in the plasma concentrations of trimethylamine-N-oxide from baseline was evident only for the 2-g dose of L-carnitine (from 34.5 +/- 2.0 to 149 +/- 145 microM), and its renal clearance decreased with increasing dose (P < .05). There was no evidence for nonlinearity in the metabolism of trimethylamine to trimethylamine-N-oxide. In conclusion, the pharmacokinetics of oral L-carnitine display nonlinearity above a dose of 0.5 g 3 times a day.

Trimethylaminuria: an under-recognised and socially debilitating metabolic disorder

Primary flavin mono-oxygenase 3 deficiency, an inborn error of choline metabolism, leads to an accumulation of trimethylamine, which because of its associated pungent odour of rotting fish, is a socially crippling disorder. Although it often has its onset in early childhood, it may take years or even decades before the diagnosis is established. In this review the clinical biochemical and genetic features of the disorder are reported. The principles of therapy will also be covered, including dietary, pharmacological approaches, as well as techniques used to manipulate the gastrointestinal environment as a strategy to reduce the gastrointestinal load of trimethylamine.

Trimethylaminuria (fish malodour syndrome) in chronic renal failure

Trimethylaminuria (fish malodour syndrome) is a rare genetic metabolic disorder presented with a body odour which smells like a decaying fish. This odour is highly objectionable, that can be destructive for the social, and work life of the patient. Trimethylamine is derived from the intestinal bacterial degradation of foods that are rich of choline and carnitine. Trimethylamine is normally oxidised by the liver to odourless trimethylamine N-oxide which is excreted in the urine, so, uremia may worsen the condition. Uremia itself may cause more or less unpleasant odour. Poor uremic control may worsen the odour. We reported this case because Trimethylaminuria is not usually considered in the differential diagnosis of malodour in chronic renal failure and it is the first case that shown the association with Trimethylaminuria and chronic renal failure in the literature.

Stability and robustness of human metabolic phenotypes in response to sequential food challenges

High-resolution spectroscopic profiles of biofluids can define metabolic phenotypes, providing a window onto the impact of diet on health to reflect gene-environment interactions. (1)H NMR spectroscopic profiling was used to characterize the effect of nutritional intervention on the stability of the metabolic phenotype of 7 individuals following a controlled 7 day dietary protocol. Inter-individual metabolic differences influenced proportionally more of the spectrum than dietary modulation, with certain individuals displaying a greater stability of metabolic phenotypes than others. Correlation structures between urinary metabolites were identified and used to map inter-individual pathway differences. Choline degradation was the pathway most affected by the individual, suggesting that the gut microbiota influence host metabolic phenotypes. This influence was further emphasized by the highly correlated excretion of the microbial-mammalian co-metabolites phenylacetylglutamine, 4-cresylsulfate (r = 0.87), and indoxylsulfate (r = 0.67) across all individuals. Above the background of inter-individual differences, clear biochemical effects of single type dietary interventions, animal protein, fruit and wine intake, were observed; for example, the spectral variance introduced by fruit ingestion was attributed to the metabolites tartrate, proline betaine, hippurate, and 4-hydroxyhippurate. This differential metabolic baseline and response to selected dietary challenges highlights the importance of understanding individual differences in metabolism and provides a rationale for evaluating dietary interventions and stratification of individuals with respect to guiding nutrition and health programmes.

Genital malodor in women: a modern reappraisal

Genital malodor is a common distressing complaint that brings a woman to her physician's office. Vaginal infections, primarily bacterial vaginosis and trichomoniasis, still remain the commonest causes and are relatively easy to diagnose and treat. However, in approximately one third of women who present with malodor, no cause is identified. Although data on the management of vaginal discharge are extensive, the management of genital odor beyond common vaginal infections remains poorly studied. This presents a frustrating situation for both the patient and her physician. Often, patients resort to home remedies and over-the-counter preparations, which, while providing short-term relief for some women, almost never address the cause and, in some cases, can exacerbate symptoms. In this review, we have attempted to consolidate the known and documented causes of genital malodor including the nonvaginal causes and provide case studies that will help clinicians understand the possible settings for the various causes. We also provide an algorithm for the management of this symptom beyond vaginal infections.

Epilepsy and trimethylaminuria: A new case report and literature review

Trimethylaminuria is a metabolic disorder characterized by the excessive excretion of trimethylamine in bodily secretions, which confers a very unpleasant odour resembling that of dead fish. Literature reports only two cases affected by trimethylaminuria and epilepsy. We describe a third patient who, from the age of seven, was affected by temporal focal seizures with nocturnal episodes of nausea, vomiting, anxiety and autonomic activation followed by headache. EEG showed focal paroxysmal abnormalities prevailing on the right temporo-parieto-occipital regions. We began administering levetiracetam and seizures stopped. Our patient also showed learning disabilities despite a normal intelligence quotient (IQ), while another described patient had an IQ varying from borderline to mild mental retardation. We discuss the association between trimethylaminuria and epilepsy, and formulate some hypotheses on the relationship between trimethylamine convulsive effect and the anticonvulsive role of levetiracetam.

Trimethylaminuria: causes and diagnosis of a socially distressing condition

Trimethylaminuria is a disorder in which the volatile, fish-smelling compound, trimethylamine (TMA) accumulates and is excreted in the urine, but is also found in the sweat and breath of these patients. Because many patients have associated body odours or halitosis, trimethylaminuria sufferers can meet serious difficulties in a social context, leading to other problems such as isolation and depression. TMA is formed by bacteria in the mammalian gut from reduction of compounds such as trimethylamine-N-oxide (TMAO) and choline. Primary trimethylaminuria sufferers have an inherited enzyme deficiency where TMA is not efficiently converted to the non-odorous TMAO in the liver. Secondary causes of trimethylaminuria have been described, sometimes accompanied by genetic variations. Diagnosis of trimethylaminuria requires the measurement of TMA and TMAO in urine, which should be collected after a high substrate meal in milder or intermittent cases, most simply, a marine-fish meal. The symptoms of trimethylaminuria can be improved by changes in the diet to avoid precursors, in particular TMAO which is found in high concentrations in marine fish. Treatment with antibiotics to control bacteria in the gut, or activated charcoal to sequester TMA, may also be beneficial.

[Primary trimethylaminuria: the fish odor syndrome]

Primary trimethylaminuria, or fish odor syndrome, is a congenital metabolic disorder characterized by a failure in the hepatic trimethylamine (TMA) oxidation route to trimethylamine N-oxide (TMANO). TMA is mostly derived from dietary precursors such as choline, carnitine and TMANO. The presence of abnormal amounts of TMA in the urine, sweat, exhaled air and other body secretions confers a very unpleasant body odor resembling that of decaying fish. As a consequence, patients can suffer from serious psychosocial sequelae. We present a case of primary trimethylaminuria with the aim of raising awareness about this condition.

Trimethylaminuria (fish-odour syndrome) and oral malodour

A small but important percentage of oral malodour cases have an extra-oral aetiology and certain of these fall into the category of 'blood-borne halitosis'. Odoriferous substances generated within the body and transported to the lungs via the circulatory system may, if sufficiently volatile, leave with the exhaled air and impart a foetid odour to the breath. The aliphatic tertiary amine, trimethylamine, is such a volatile compound that is generated to excess in patients with a metabolic disorder known as trimethylaminuria (fish-odour syndrome). This article highlights this condition and draws attention to its potential role in the causation of recalcitrant oral malodour.

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.

Involvement of enzymes other than CYPs in the oxidative metabolism of xenobiotics

Although the majority of oxidative metabolic reactions are mediated by the CYP superfamily of enzymes, non-CYP-mediated oxidative reactions can play an important role in the metabolism of xenobiotics. The (major) oxidative enzymes, other than CYPs, involved in the metabolism of drugs and other xenobiotics are: the flavin-containing monooxygenases, the molybdenum hydroxylases (aldehyde oxidase and xanthine oxidase), the prostaglandin H synthase, the lipoxygenases, the amine oxidases (monoamine, polyamine, diamine and semicarbazide-sensitive amine oxidases) and the alcohol and aldehyde dehydrogenases. In a similar manner to CYPs, these oxidative enzymes can also produce therapeutically active metabolites and reactive/toxic metabolites, modulate the efficacy of therapeutically active drugs or contribute to detoxification. Many of them have been shown to be important in endobiotic metabolism, and, consequently, interactions between drugs and endogenous compounds might occur when they are involved in drug metabolism. In general, most non-CYP oxidative enzymes appear to be noninducible or much less inducible than the CYP system, although some of them may be as inducible as some CYPs. Some of these oxidative enzymes exhibit polymorphic expression, as do some CYPs. It is possible that the contribution of non-CYP oxidative enzymes to the overall metabolism of xenobiotics is underestimated, as most investigations of drug metabolism in discovery and lead optimisation are performed using in vitro test systems optimised for CYP activity.

Identification and Functional Analysis of Common Human Flavin-Containing Monooxygenase 3 Genetic Variants

Flavin-containing monooxygenases (FMOs) are important for the disposition of many therapeutics, environmental toxicants, and nutrients. FMO3, the major adult hepatic FMO enzyme, exhibits significant interindividual variation. Eighteen FMO3 single-nucleotide polymorphism (SNP) frequencies were determined in 202 Hispanics (Mexican descent), 201 African Americans, and 200 non-Latino whites. Using expressed recombinant enzyme with methimazole, trimethylamine, sulindac, and ethylenethiourea, the novel structural variants FMO3 E24D and K416N were shown to cause modest changes in catalytic efficiency, whereas a third novel variant, FMO3 N61K, was essentially devoid of activity. The latter variant was present at an allelic frequency of 5.2% in non-Latino whites and 3.5% in African Americans, but it was absent in Hispanics. Inferring haplotypes using PHASE, version 2.1, the greatest haplotype diversity was observed in African Americans followed by non-Latino whites and Hispanics. Haplotype 2A and 2B, consisting of a hypermorphic promoter SNP cluster (-2650C>G, -2543T>A, and -2177G>C) in linkage with synonymous structural variants was inferred at a frequency of 27% in the Hispanic population, but only 5% in non-Latino whites and African Americans. This same promoter SNP cluster in linkage with one or more hypomorphic structural variant also was inferred in multiple haplotypes at a total frequency of 5.6% in the African-American study group but less than 1% in the other two groups. The sum frequencies of the hypomorphic haplotypes H3 [15,167G>A (E158K)], H5B [-2650C>G, 15,167G>A (E158K), 21,375C>T (N285N), 21,443A>G (E308G)], and H6 [15,167G>A (E158K), 21,375C>T (N285N)] was 28% in Hispanics, 23% in non-Latino whites, and 24% in African Americans.

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.

Diagnosis and management of trimethylaminuria (FMO3 deficiency) in children

Persistent trimethylaminuria in children is caused by autosomal recessively inherited impairment of hepatic trimethylamine (TMA) oxidation due to deficiency of flavin monooxygenase 3 (FMO3) secondary to mutations in the FMO3 gene. Trimethylaminuria or 'fish odour syndrome' is due to excessive excretion into body fluids and breath of TMA derived from the enterobacterial metabolism of dietary precursors. The disorder is present from birth but becomes apparent as foods containing high amounts of choline or of trimethylamine N-oxide (TMAO) from marine (sea or saltwater) fish are introduced into the diet. In our experience, trimethylaminuria (FMO3 deficiency) in children is rare. We have compared the dynamics and diagnostic efficacy of choline loading with marine fish meals in six children with trimethylaminuria. Loading with a marine fish meal provides a simple and acceptable method for confirmation of diagnosis of suspected trimethylaminuria in children, with the effects being cleared more quickly than with a choline load test. However, oral loading with choline bitartrate allows estimation of residual oxidative capacity in vivo and is a useful adjunct to molecular studies. Patients homozygous for the 'common' P153L mutation in the FMO3 gene showed virtual complete lack of residual TMA N-oxidative capacity, consistent with a nonfunctional or absent FMO3 enzyme, whereas a patient with the M82T mutation showed some residual oxidative capacity. A patient compound heterozygous for two novel mutations, G193E and R483T, showed considerable residual N-oxidative capacity. A further patient, heterozygous for two novel sequence variations in the FMO3 gene, consistently showed malodour and elevated urinary TMA/TMAO ratios under basal conditions but a negative response to both choline and marine fish meal loading. Comparison of the effects of administration of antibiotics (metronidazole, amoxicillin, neomycin) on gut bacterial production of trimethylamine from choline showed they all reduced TMA production to a limited extent, with neomycin being most effective. 'Best-practice' diagnostic and treatment guidelines are summarized.

Effects of the dietary supplements, activated charcoal and copper chlorophyllin, on urinary excretion of trimethylamine in Japanese trimethylaminuria patients

Trimethylaminuria (TMAU) is a metabolic disorder characterized by the inability to oxidize and convert dietary-derived trimethylamine (TMA) to trimethylamine N-oxide (TMAO). This disorder has been relatively well-documented in European and North American populations, but no reports have appeared regarding patients in Japan. We identified seven Japanese individuals that showed a low metabolic capacity to convert TMA to its odorless metabolite, TMAO. The metabolic capacity, as defined by the concentration of TMAO excreted in the urine divided by TMA concentration plus TMAO concentration, in these seven individuals ranged from 70 to 90%. In contrast, there were no healthy controls examined with less than 95% of the metabolic capacity to convert TMA to TMAO. The intake of dietary charcoal (total 1.5 g charcoal per day for 10 days) reduced the urinary free TMA concentration and increased the concentration of TMAO to normal values during charcoal administration. Copper chlorophyllin (total 180 mg per day for 3 weeks) was also effective at reducing free urinary TMA concentration and increasing TMAO to those of concentrations present in normal individuals. In the TMAU subjects examined, the effects of copper chlorophyllin appeared to last longer (i.e., several weeks) than those observed for activated charcoal. The results suggest that the daily intake of charcoal and/or copper chlorophyllin may be of significant use in improving the quality of life of individuals suffering from TMAU.

Pharmacokinetics of L-carnitine

L-Carnitine is a naturally occurring compound that facilitates the transport of fatty acids into mitochondria for beta-oxidation. Exogenous L-carnitine is used clinically for the treatment of carnitine deficiency disorders and a range of other conditions. In humans, the endogenous carnitine pool, which comprises free L-carnitine and a range of short-, medium- and long-chain esters, is maintained by absorption of L-carnitine from dietary sources, biosynthesis within the body and extensive renal tubular reabsorption from glomerular filtrate. In addition, carrier-mediated transport ensures high tissue-to-plasma concentration ratios in tissues that depend critically on fatty acid oxidation. The absorption of L-carnitine after oral administration occurs partly via carrier-mediated transport and partly by passive diffusion. After oral doses of 1-6g, the absolute bioavailability is 5-18%. In contrast, the bioavailability of dietary L-carnitine may be as high as 75%. Therefore, pharmacological or supplemental doses of L-carnitine are absorbed less efficiently than the relatively smaller amounts present within a normal diet.L-Carnitine and its short-chain esters do not bind to plasma proteins and, although blood cells contain L-carnitine, the rate of distribution between erythrocytes and plasma is extremely slow in whole blood. After intravenous administration, the initial distribution volume of L-carnitine is typically about 0.2-0.3 L/kg, which corresponds to extracellular fluid volume. There are at least three distinct pharmacokinetic compartments for L-carnitine, with the slowest equilibrating pool comprising skeletal and cardiac muscle.L-Carnitine is eliminated from the body mainly via urinary excretion. Under baseline conditions, the renal clearance of L-carnitine (1-3 mL/min) is substantially less than glomerular filtration rate (GFR), indicating extensive (98-99%) tubular reabsorption. The threshold concentration for tubular reabsorption (above which the fractional reabsorption begins to decline) is about 40-60 micromol/L, which is similar to the endogenous plasma L-carnitine level. Therefore, the renal clearance of L-carnitine increases after exogenous administration, approaching GFR after high intravenous doses. Patients with primary carnitine deficiency display alterations in the renal handling of L-carnitine and/or the transport of the compound into muscle tissue. Similarly, many forms of secondary carnitine deficiency, including some drug-induced disorders, arise from impaired renal tubular reabsorption. Patients with end-stage renal disease undergoing dialysis can develop a secondary carnitine deficiency due to the unrestricted loss of L-carnitine through the dialyser, and L-carnitine has been used for treatment of some patients during long-term haemodialysis. Recent studies have started to shed light on the pharmacokinetics of L-carnitine when used in haemodialysis patients.

Deleterious mutations in the flavin-containing monooxygenase 3 (FMO3) gene causing trimethylaminuria

The primary genetic form of trimethylaminuria (TMAU) is caused by inherited defects in the flavin-containing monooxygenase 3 (FMO3) gene. Defective FMO3 has a decreased ability to catalyze the N-oxygenation of the dietary-derived malodourous amine, trimethylamine. We report two novel deleterious mutations identified in two unrelated individuals affected by the disorder. Sequence analysis of the FMO3 coding exons amplified from genomic DNA revealed that the mutation from individual 1 was heterozygous for a G>A missense mutation in exon 2 of the FMO3 gene. The mutation changed a GAG encoding Glu at codon 32 to AAG encoding Lys. Wild-type and mutant E32K FMO3 were expressed in Escherichia coli as maltose binding-fusion proteins and assayed for their ability to catalyze oxygenation of various FMO3 substrates. The results showed that the E32K mutation abrogated the catalytic activity of the enzyme. Individual 2 was identified as heterozygous for the P153L mutation. In addition, individual 2 was also heterozygous for a novel single nucleotide deletion of A191 in exon 3 at codon 64. The deletion resulted in a frame shift and caused premature termination of the FMO3 gene immediately after codon 65. Family pedigree analysis revealed that the P153L and the deletion mutation were carried on different alleles for this individual. Therefore, both alleles of the FMO3 gene for individual 2 were affected by mutations abolishing the catalytic activity of the enzyme, explaining the severe TMAU condition. The two deleterious mutations reported herein were rare mutations with estimated allelic frequencies of less than 1%.

Two new polymorphisms of the FMO3 gene in Caucasian and African-American populations: comparative genetic and functional studies

To characterize the contribution of the human flavin-containing monooxygenase form 3 (FMO3) in the metabolism and disposition of drugs and xenobiotics, we determined the single nucleotide polymorphisms in the coding region and adjacent splice junctions of FMO3 in 134 African Americans and 120 Caucasians from the United States. In the regions examined, DNA resequencing or high throughput MassEXTEND studies coupled with mass spectrometric genotyping showed that 12 sites of variation were present. Three variants encoding synonymous mutations and four polymorphisms were observed in the noncoding region. Another three variants, Lys158-FMO3, Met257-FMO3 and Gly308-FMO3, previously reported in similar populations, were prominent polymorphisms. Two new polymorphisms, His132-FMO3 and Pro360-FMO3, were identified in this study. Both variants were found only in African Americans. To evaluate the effect of the amino acid substitutions on the function of FMO3, each amino acid substitution was introduced by site-directed mutagenesis into a wild-type FMO3 cDNA. Selective functional activity was studied with methimazole, trimethylamine, and 10-(N,N-dimethylaminopentyl)-2-(trifluoromethyl) phenothiazine. Both His132-FMO3 and Pro360-FMO3 variants were able to metabolize the substrates examined. Compared with wild-type FMO3, the His132-FMO3 was less catalytically efficient. The His132-FMO3 variant moderately altered the catalytic efficiency of FMO3 (decrease of 30%, 60% and 6% with methimazole, trimethylamine and 10-(N,N-dimethylaminopentyl)-2-(trifluoromethyl)phenothiazine, respectively). The Pro360-FMO3 variant was more catalytically efficient than wild-type FMO3. Pro360-FMO3 oxygenated methimazole, trimethylamine and 10-(N,N-dimethylaminopentyl)-2-(trifluoromethyl)phenothiazine, respectively, 3-, 5- and 2-fold more efficiently than wild-type FMO3. Based on the functional activity of the variant FMO3 enzymes, it is likely that population differences exist for compounds primarily metabolized by FMO3.

Fish odour syndrome with features of both primary and secondary trimethylaminuria

We report a patient with the fish odour syndrome who has both primary and secondary trimethylaminuria. The diagnosis was made using biochemical and genetic analysis in the apparent absence of any characteristic smell. Differentiation of primary and secondary trimethylaminuria is usually made on urinary analysis of trimethylamine and its metabolite trimethylamine N-oxide, with different, characteristic patterns of both compounds in primary and secondary trimethylaminuria. Our patient had biochemical analysis consistent with a diagnosis of secondary trimethylaminuria, while analysis of the flavin-containing mono-oxygenase 3 gene, the causative gene in primary trimethylaminuria, demonstrated three sequence polymorphisms, two of which are known to reduce enzyme activity. The patient showed temporary clinical and biochemical response to treatment with metronidazole and neomycin. It is important to be aware of this diagnosis in patients without obvious clinical signs, and of the subjective benefits of treatment.

[Primary trimethylaminuria or fish odor syndrome. A novel mutation in the first documented case in Spain]

BACKGROUND AND OBJECTIVE

Trimethylaminuria or fish odor syndrome is a metabolic disorder characterized by a failure in the oxidation route from trimethylamine (TMA) to trimethylamineN-oxide (TMA-O). Primary trimethylaminuria is an inherited autosomic recessive disease due to mutations in the human FMO3 gene. High levels of free TMA in urine and other body fluids confer an unpleasant body odor resembling that of fish. Here we report a case of primary trimethylaminuria in a 4-year-old girl.

PATIENT AND METHOD

A 4-year-old girl who presented with a strong corporal scent resembling that of fish from the age of 9 months agreeing with the introduction of fish in the diet. The patient did not have other relevant personal history and had a correct psychomotor and growing development. Liver function, urea and creatinine levels were normal. The biochemical diagnosis was done by spectrometry, measuring the amount of TMA and TMA-O prior to and after fish intake.

RESULTS

Genetic analysis evinced that the patient was homozygous for a novel mutation in exon 3, R51G (c. 151A > G). Both parents were heterozygous.

CONCLUSIONS

R51G (c. 151 A > G) mutation had not been found in other patients with trimethylaminuria.