Elevated levels of trimethylamine oxide in deep-sea fish: evidence for synthesis and intertissue physiological importance

Tissue levels of trimethylamine oxide (TMAO) were compared for seven teleost and two elasmobranch species captured from three depth ranges: shallow (<150 m), moderate (500-700 m), and deep (1,000-1,500 m). Within the teleosts, the deep-caught species had significantly greater TMAO content than shallow- or moderate-caught species. In all teleosts, muscle had substantially more TMAO than all other tissues. Kidney or, in some cases, liver had elevated trimethylamine (TMA) content, 2.20-9.65 mmol/kg, along with appreciable trimethylamine oxidase (TMAoxi) activity, suggesting active TMAO synthesis. No correlation was found between TMAoxi activity and TMAO content. The elasmobranchs in this study, Squalus acanthias and Centroscyllium fabricii from shallow and deep water, respectively, were both squaliform sharks. The deep-caught species had significantly more TMAO in all tissues than the shallow species. Furthermore, urea was significantly less in the deep species in all tissues except liver, while the urea:TMAO ratio was significantly less in all tissues. As with teleosts, the TMAO content of muscle was substantially higher for both elasmobranchs than in all other tissues. TMAoxi was below levels of detection in both elasmobranch species, suggesting that TMAO is obtained solely from the diet. This study expands the trend of increased muscle TMAO in deep-sea fish to a variety of other tissues. The accumulation of TMAO in various tissues in deep-sea teleosts and the accumulation of TMAO and concurrent urea decrease in a deep-sea elasmobranch in comparison to a shallow water species strongly support the contention that TMAO is of physiological importance in deep-sea fish.     

The little skate Raja erinacea exhibits an extrahepatic ornithine urea cycle in the muscle and modulates nitrogen metabolism during low-salinity challenge

Urea synthesis via the hepatic ornithine urea cycle (OUC) has been well described in elasmobranchs, but it is unknown whether OUC enzymes are also present in extrahepatic tissues. Muscle and liver urea, trimethylamine oxide (TMAO), and other organic osmolytes, as well as selected OUC enzymes (carbamoyl phosphate synthetase III, ornithine transcarbamoylase, arginase, and the accessory enzyme glutamine synthetase), were measured in adult little skates (Raja erinacea) exposed to 100% or 75% seawater for 5 d. Activities of all four OUC enzymes were detected in the muscle. There were no changes in muscle OUC activities in skates exposed to 75% seawater; however, arginase activity was significantly lower in the liver, compared to controls. Urea, TMAO, and several other osmolytes were significantly lower in the muscle of little skates exposed to 75% seawater, whereas only glycerophosphorylcholine was significantly lower in the liver. Urea excretion rates were twofold higher in skates exposed to 75% seawater. Taken together, these data suggest that a functional OUC may be present in the skeletal muscle tissues of R. erinacea. As well, enhanced urea excretion rates and the downregulation of the anchor OUC enzyme, arginase, in the liver may be critical in regulating tissue urea content under dilute-seawater stress.     

Decreasing urea∶trimethylamine N-oxide ratios with depth in chondrichthyes: a physiological depth limit?

In marine osmoconformers, cells use organic osmolytes to maintain osmotic balance with seawater. High levels of urea are utilized in chondrichthyans (sharks, rays, skates, and chimaeras) for this purpose. Because of urea's perturbing nature, cells also accumulate counteracting methylamines, such as trimethylamine N-oxide (TMAO), at about a 2∶1 urea∶methylamine ratio, the most thermodynamically favorable mixture for protein stabilization, in shallow species. However, previous work on deep-sea teleosts (15 species) and chondrichthyans (three species) found an increase in muscle TMAO content and a decrease in urea content in chondrichthyans with depth. We hypothesized that TMAO counteracts protein destabilization resulting from hydrostatic pressure, as is demonstrated in vitro. Chondrichthyans are almost absent below 3,000 m, and we hypothesized that a limitation in urea excretion and/or TMAO retention might play a role. To test this, we measured the content of major organic osmolytes in white muscle of 13 chondrichthyan species caught with along-contour trawls at depths of 50-3,000 m; the deepest species caught was from 2,165 m. Urea and TMAO contents changed significantly with depth, with urea∶TMAO declining from 2.96 in the shallowest (50-90 m) groups to 0.67 in the deepest (1,911-2,165 m) groups. Urea content was 291-371 mmol/kg in the shallowest group and 170-189 mmol/kg in the deepest group, declining linearly with depth and showing no plateau. TMAO content was 85-168 mmol/kg in the shallowest group and 250-289 mmol/kg in the deepest groups. With data from a previous study for a skate at 2,850 m included, a second-order polynomial fit suggested a plateau at the greatest depths. When data for skates (Rajidae) were analyzed separately, a sigmoidal fit was suggested. Thus, the deepest chondrichthyans may be unable to accumulate sufficient TMAO to counteract pressure; however, deeper-living specimens are needed to fully test this hypothesis.     

Metabolism of trimethylamines in kelp bass (Paralabrax clathratus) and marine and freshwater pink salmon (Oncorhynchus gorbuscha)

Summary ³H or¹⁴C labeled tracers were used to investigate the metabolism of trimethylamine (TMA), trimethylamine oxide (TMAO), choline, and betaine in free swimming kelp bass (Paralabrax clathratus). An indwelling cannula in the ventral aorta was used to administer tracer and withdraw blood samples. The concentrations of TMA and TMAO were determined in liver, muscle, and plasma. The TMA liver content is higher than that of muscle (0.85 vs 0.01 moles/g wet tissue) while the amount of TMAO in muscle greatly exceeds its liver concentration (60 vs 0.04 moles/g wet tissue). Prolonged fasting (21 and 75 days) or feeding the fish a squid diet containing high levels of TMAO did not alter the tissue concentrations of TMA or TMAO, suggesting that these compounds are endogenous in origin and that their tissue concentrations are subject to regulation. Comparison of the radiospecific activities of TMA and TMAO, and the administered TMA tracer suggest that TMA is channled directly to TMAO in the liver without equilibration in the hepatic TMA pool. The conversion kinetics of TMA to TMAO and the distribution of these amines in liver and muscle with time suggest that labeled TMA is rapidly taken up into a sequestered pool from which it is slowly released, oxidized to TMAO in the liver, and then transported via the circulation to the muscle mass. The location of this proposed sequestered TMA pool was not determined. Experiments with labeled choline and betaine suggest that these compounds are interconverted in the liver and that enzymes are present for conversion of choline betaine TMA TMAO. Labeled dimethylamine (DMA) was not metabolized and is, therefore, probably not a precursor of TMA and TMAO. [¹⁴C]Trimethylamine (TMA) was also used to investigate the possible role of trimethylamine oxide (TMAO) as an osmoregulatory compound in migrating prespawning cannulated Pacific pink salmon (Oncorhynchus gorbuscha) taken from marine or fresh water environments. Marine and fresh water salmon oxidized administered [¹⁴C]TMA to TMAO; labeled metabolites other than TMA and TMAO were not detected. Four hours after [¹⁴C]TMA injection about 10% of the administered dose was present in muscle as labeled TMAO and about 33% as TMA. Unlike our finding in kelp bass, [¹⁴C]TMAO was not recovered in liver, although low amounts of labeled TMA were found (0.4% of administered dose). Labeled TMA and TMAO, however, were detected in liver after [¹⁴C]betaine adminstration to a marine salmon, indicating that TMA-mono-oxygenase is present in salmon liver. The presence of labeled choline indicates that choline and betaine are interconverted as in kelp bass. The amount of [¹⁴C]TMA oxidized to [¹⁴C]TMAO and then accumulated in the muscle mass is the same in marine and fresh water salmon, as is the amount of chemical TMAO present (4.6 moles/g muscle).     

Serum pharmacokinetics of choline,trimethylamine, and trimethylamine-N-oxide after oral gavage of phosphatidylcholines with different fatty acid compositions in mice

Little is known about the pharmacokinetics of phosphatidylcholine (PC)-derived choline, trimethylamine (TMA), and trimethylamine-N-oxide (TMAO). We therefore aim to investigate serum choline, TMA, and TMAO pharmacokinetics following different PCs gavage and compare the difference between PC emulsions and liposomes (SOL). Serum choline, TMA, and TMAO levels were measured after orally gavaged egg yolk PC emulsion (EGE), squid PC emulsion (SQE), soybean PC emulsion (SOE), and SOL in fasted mice. Time to reach peak concentration (Tmax) and productions for TMA and TMAO were more slow and less in SQE group compared with EGE and SOE groups. Tmax for choline, TMA, and TMAO prolonged, and the productions of them were significantly declined in SOL group compared to SOE group. These findings indicated that marine source squid PC could counter-regulate the potential risks of TMAO generation, and the use of liposome as the form of PC supplementary may eliminate TMAO production.     

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.     

Mechanism of biosynthesis of trimethylamine oxide from choline in the teleost tilapia, Oreochromis niloticus, under freshwater conditions

The mechanism of biosynthesis of trimethylamine oxide (TMAO) from dietary precursors in the teleost tilapia (Oreochromis niloticus) was investigated. Diets supplemented with quaternary ammonium choline, glycine betaine, carnitine or phosphatidylcholine were administered and significant increases in TMAO levels in the muscle were only observed with choline. [Methyl-14C] and [1,2-14C] cholines were given through dietary and intraperitoneal injection routes, but 14C-TMAO was detected only in fish with dietary administration of [methyl-14C] choline. Dietary treatment with [15N] choline resulted in the formation of [15N] TMAO in the muscle. The incorporation of radioactivity into TMAO was also observed both following dietary administration and intraperitoneal injection of [14C] trimethylamine (TMA). When choline was introduced into the isolated intestine, marked increases in TMA levels occurred. These increases were significantly suppressed in the presence of penicillin. [14C]-TMA derived from [methyl-14C] choline was detected in the cavity of the isolated intestine. The introduction of [15N] choline into the intestinal cavity resulted in the formation of [15N] TMA. TMA mono-oxygenase activities were detected in the liver and kidney. We conclude that tilapia possess the ability to produce TMAO from choline, which is related to intestinal microorganisms and tissue mono-oxygenase under freshwater conditions.     

Changes in some nitrogenous compounds in the blood and tissues of freshwater pikeperch (Sander lucioperca) during salinity acclimation

The effect of ambient salinity changes (0.9, 6 and 12 psu) on the levels of dissolved ammonia (DA), ninhydrin positive substances (NPS), trimethylamine (TMA) and trimethylamine oxide (TMAO) in the blood and tissue of medium-acclimated Sander lucioperca L. (also Stizostedion lucioperca) were investigated. In freshwater, blood and tissue total free amino acid levels (measured as NPS) were 3.62 mM and 60.61 mM, respectively. The NPS content increased significantly (P<0.05) in the tissue and blood on acclimation to 6 and 12 psu salinities. The mass-specific tissue TMAO concentration of pikeperch acclimated to normal freshwater was 0.413+/-0.084 micromol TMAO g(-1). Results reveal that TMAO levels are positively influenced by the external salinity medium where significant differences in mean levels occurred between the groups (P<0.05). The calculated p[NH(3)] and [NH(4)(+)] gradients reveal that the [NH(3)] gradient was consistently low (cf. the [NH(4)(+)] gradient). The gradient of p[NH(3)] decreased with the medium increased salinities. The results suggest that freshwater pikeperch may be able to resist salinity changes by manipulation of nitrogen metabolism. Free amino acids and TMAO are involved in mediating response to salinity exposure in freshwater pikeperch.     

Structural mechanism for bacterial oxidation of oceanic trimethylamine into trimethylamine N‐oxide

Trimethylamine (TMA) and trimethylamine N‐oxide (TMAO) are widespread in the ocean and are important nitrogen source for bacteria. TMA monooxygenase (Tmm), a bacterial flavin‐containing monooxygenase (FMO), is found widespread in marine bacteria and is responsible for converting TMA to TMAO. However, the molecular mechanism of TMA oxygenation by Tmm has not been explained. Here, we determined the crystal structures of two reaction intermediates of a marine bacterial Tmm (RnTmm) and elucidated the catalytic mechanism of TMA oxidation by RnTmm. The catalytic process of Tmm consists of a reductive half‐reaction and an oxidative half‐reaction. In the reductive half‐reaction, FAD is reduced and a C4a‐hydroperoxyflavin intermediate forms. In the oxidative half‐reaction, this intermediate attracts TMA through electronic interactions. After TMA binding, NADP⁺ bends and interacts with D317, shutting off the entrance to create a protected micro‐environment for catalysis and exposing C4a‐hydroperoxyflavin to TMA for oxidation. Sequence analysis suggests that the proposed catalytic mechanism is common for bacterial Tmms. These findings reveal the catalytic process of TMA oxidation by marine bacterial Tmm and first show that NADP⁺ undergoes a conformational change in the oxidative half‐reaction of FMOs.     

Transmission of Atherosclerosis Susceptibility with Gut Microbial Transplantation

Recent studies indicate both clinical and mechanistic links between atherosclerotic heart disease and intestinal microbial metabolism of certain dietary nutrients producing trimethylamine N-oxide (TMAO). Here we test the hypothesis that gut microbial transplantation can transmit choline diet-induced TMAO production and atherosclerosis susceptibility. First, a strong association was noted between atherosclerotic plaque and plasma TMAO levels in a mouse diversity panel (n = 22 strains, r = 0.38; p = 0.0001). An atherosclerosis-prone and high TMAO-producing strain, C57BL/6J, and an atherosclerosis-resistant and low TMAO-producing strain, NZW/LacJ, were selected as donors for cecal microbial transplantation into apolipoprotein e null mice in which resident intestinal microbes were first suppressed with antibiotics. Trimethylamine (TMA) and TMAO levels were initially higher in recipients on choline diet that received cecal microbes from C57BL/6J inbred mice; however, durability of choline diet-dependent differences in TMA/TMAO levels was not maintained to the end of the study. Mice receiving C57BL/6J cecal microbes demonstrated choline diet-dependent enhancement in atherosclerotic plaque burden as compared with recipients of NZW/LacJ microbes. Microbial DNA analyses in feces and cecum revealed transplantation of donor microbial community features into recipients with differences in taxa proportions between donor strains that were transmissible to recipients and that tended to show coincident proportions with TMAO levels. Proportions of specific taxa were also identified that correlated with plasma TMAO levels in donors and recipients and with atherosclerotic lesion area in recipients. Atherosclerosis susceptibility may be transmitted via transplantation of gut microbiota. Gut microbes may thus represent a novel therapeutic target for modulating atherosclerosis susceptibility.     

Suppression of intestinal microbiota-dependent production of pro-atherogenic trimethylamine N-oxide by shifting L-carnitine microbial degradation

Aims

Trimethylamine-N-oxide (TMAO) is produced in host liver from trimethylamine (TMA). TMAO and TMA share common dietary quaternary amine precursors, carnitine and choline, which are metabolized by the intestinal microbiota. TMAO recently has been linked to the pathogenesis of atherosclerosis and severity of cardiovascular diseases. We examined the effects of anti-atherosclerotic compound meldonium, an aza-analogue of carnitine bioprecursor gamma-butyrobetaine (GBB), on the availability of TMA and TMAO.

Main methods

Wistar rats received L-carnitine, GBB or choline alone or in combination with meldonium. Plasma, urine and rat small intestine perfusate samples were assayed for L-carnitine, GBB, choline and TMAO using UPLC-MS/MS. Meldonium effects on TMA production by intestinal bacteria from L-carnitine and choline were tested.

Key findings

Treatment with meldonium significantly decreased intestinal microbiota-dependent production of TMA/TMAO from L-carnitine, but not from choline. 24 hours after the administration of meldonium, the urinary excretion of TMAO was 3.6 times lower in the combination group than in the L-carnitine-alone group. In addition, the administration of meldonium together with L-carnitine significantly increased GBB concentration in blood plasma and in isolated rat small intestine perfusate. Meldonium did not influence bacterial growth and bacterial uptake of L-carnitine, but TMA production by the intestinal microbiota bacteria K. pneumoniae was significantly decreased.

Significance

We have shown for the first time that TMA/TMAO production from quaternary amines could be decreased by targeting bacterial TMA-production. In addition, the production of pro-atherogenic TMAO can be suppressed by shifting the microbial degradation pattern of supplemental/dietary quaternary amines.     

A microbial biosensor for trimethylamine using Pseudomonas aminovorans cells

A biosensor system based on the difference in the oxygen uptake response of two microbial electrodes was developed to monitor trimethylamine (TMA). The first electrode, constructed using Pseudomonas aminovorans grown on TMA, was sensitive to TMA, trimethylamine N-oxide (TMAO), dimethylamine (DMA) and monomethylamine (MMA). The second electrode responding to TMAO, DMA and MMA was prepared using Ps. aminovorans grown on TMAO. The difference in oxygen uptake was linearly related to the TMA concentration in the range of 5-26 microM. The minimum detectable level was 2.6 microM and the relative standard deviation was determined to be 14% for 16 repeated analyses. When operated and stored at 30 degrees C, the response of the system was stable for only 2 days. However, when the biosensor system was operated at 30 degrees C but stored overnight at 4 degrees C, the system was stable up to 20 days. The biosensor system was applicable for the determination of TMA in fish tissue extracts and the results compared well with those determined by HPLC.     

Stable isotopes and elasmobranchs: tissue types, methods, applications and assumptions

Stable-isotope analysis (SIA) can act as a powerful ecological tracer with which to examine diet, trophic position and movement, as well as more complex questions pertaining to community dynamics and feeding strategies or behaviour among aquatic organisms. With major advances in the understanding of the methodological approaches and assumptions of SIA through dedicated experimental work in the broader literature coupled with the inherent difficulty of studying typically large, highly mobile marine predators, SIA is increasingly being used to investigate the ecology of elasmobranchs (sharks, skates and rays). Here, the current state of SIA in elasmobranchs is reviewed, focusing on available tissues for analysis, methodological issues relating to the effects of lipid extraction and urea, the experimental dynamics of isotopic incorporation, diet-tissue discrimination factors, estimating trophic position, diet and mixing models and individual specialization and niche-width analyses. These areas are discussed in terms of assumptions made when applying SIA to the study of elasmobranch ecology and the requirement that investigators standardize analytical approaches. Recommendations are made for future SIA experimental work that would improve understanding of stable-isotope dynamics and advance their application in the study of sharks, skates and rays.     

An improved method for separation of leucocytes from peripheral blood of the little skate (Leucoraja erinacea)

Cartilaginous fish, especially sharks, rays and skates (elasmobranchs), hold interest as comparative models in immunology because they are thought to be among the organisms most closely related to the ancestor animal that first developed acquired immunity. The aim of this study was to improve methods used for the purification of viable leucocytes from peripheral blood of elasmobranchs. Here we describe modifications of density gradient centrifugation and medium formulation that improve isolation and analysis of highly purified leucocytes from peripheral blood of a model elasmobranch, Leucoraja erinacea, the little skate. These techniques contribute to the preparation of elasmobranch immune cells that can be reliably analyzed by a variety of means, including the study of immune function.     

Higher elasmobranch phylogeny and biostratigraphy

Living sharks, skates and rays share several derived skeletal characters that are absent in most extinct elasmobranchs, suggesting a monophyletic group of 'higher' elasmobranchs. Within this group opinions vary as to phylogenetic relationships, although three broad groups are generally recognized. Arguments for and against monophyly of these group (batoids; squalomorphs; galeomorphs) are examined. Many of their contained taxa are also of questionable validity. Cladistic analysis of living galeomorphs reveals a sequence of characters supporting monophyly of the group as whole, but not of its more generalized contained taxa. The temporal distribution of fossil galeomorphs corroborates the hypothesis of relationship suggested by neontological data; i.e. there is considerable stratigraphic harmony with Recent phylogenetic data.     

Osmolyte-induced folding enhances tryptic enzyme activity

Osmolytes form a class of naturally occurring small compounds known to protect proteins in their native folded and functional states. Among the osmolytes, trimethylamine-N-oxide (TMAO) has received special interest lately because it has shown an extraordinary capability to support folding of denatured to native-like species, which show significant functional activity. Most enzymes and/or proteins are commonly stored in glycerol to maintain their activity/function. In the present study, we tested whether TMAO can be a better solute than glycerol for two commonly used proteases, trypsin and chymotrypsin. Our enzyme kinetic data suggest that the enzyme activity of trypsin is significantly enhanced in TMAO compared to glycerol, whereas chymotrypsin activity is not significantly changed in either case. These results are in accordance with the osmolyte effects on the folding of these enzymes, as judged by data from fluorescence emission spectroscopy. These results suggest that TMAO may be a better solute than glycerol to maintain optimal tryptic enzyme activity.     

The measurement of dimethylamine, trimethylamine, and trimethylamine N-oxide using capillary gas chromatography-mass spectrometry

We have developed a method for measuring dimethylamine (DMA), trimethylamine (TMA), and trimethylamine N-oxide (TMAO) in biological samples using gas chromatography with mass spectrometric detection. DMA, TMA, and TMAO were extracted from biological samples into acid after internal standards (labeled with stable isotopes) were added. p-Toluenesulfonyl chloride was used to form the tosylamide derivative of DMA. 2,2,2-Trichloroethyl chloroformate was used to form the carbamate derivative of TMA. TMAO was reduced with titanium(III) chloride to form TMA, which was then analyzed. The derivatives were chromatographed using capillary gas chromatography and were detected and quantitated using electron ionization mass spectrometry (GC/MS). Derivative yield, reproducibility, linearity, and sensitivity of the assay are described. The amounts of DMA, TMA, and TMAO in blood, urine, liver, and kidney from rats and humans, as well as in muscle from fishes, were determined. We also report the use of this method in a pilot study characterizing dimethylamine appearance and disappearance from blood in five human subjects after ingesting [13C]dimethylamine (0.5 mumol/kg body wt). The method we describe was much more reproducible than existing gas chromatographic methods and it had equivalent sensitivity (detected 1 pmol). The derivatized amines were much more stable and less likely to be lost as gases when samples were stored. Because we used GC/MS, it was possible to use stable isotopic labels in studies of methylamine metabolism in humans.     

Influence of respiratory substrate on the cytochrome content of Shewanella putrefaciens

Shewanella putrefaciens can use trimethylamine oxide (TMAO) as electron acceptor under anoxic conditions. The associated cytochromes induced during growth under various respiratory conditions have been separated by liquid chromatography (DEAE Sepharose CL6b) and SDS-PAGE and characterized spectrophotometrically and by redox potentiometry. Two major low potential cytochromes and at least three minor low potential cytochromes, likely to be involved in TMAO reduction, were found. No cytochrome specific for TMAO reductase was found.     

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.     

Temperature effects on trimethylamine oxide accumulation and the relationship between plasma concentration and tissue levels in smelt (Osmerus mordax)

Rainbow smelt (Osmerus mordax) were maintained in a long term acclimation study to elucidate temperature effects on the accumulation of trimethylamine oxide (TMAO) and to determine if the activity of trimethylamine oxidase (TMAoxi) plays a role in modulating the seasonally variable levels of TMAO. In the same experiment, the TMAO content was determined for several tissues at varying plasma TMAO concentrations. TMAO accumulation begins at 5-7 degrees C, well above that which might be normally associated with an antifreeze response. The plasma concentration reached a plateau of 20 mM as temperatures reached 0 degrees C. Plasma TMAO concentration drops to pre-accumulation levels, less than 5 mM, when fish are held at elevated temperature (8-11 degrees C) and increases when fish are chilled below ambient seawater temperatures. However, despite temperatures near or below 0 degrees C, plasma TMAO decreases after the winter season. Changes in TMAoxi activity do not correlate with TMAO levels, suggesting that the activity of this enzyme does not play a key role in regulating TMAO concentrations in smelt. For the first time in any teleost fish, tissue TMAO contents in liver, kidney, brain, and intestine were found to strongly correlate with plasma TMAO concentrations. For these tissues, the intracellular and extracellular concentration of TMAO appears to be approximately equal. Conversely, the heart and white muscle accumulate TMAO, and in the case of white muscle, intracellular concentration is maintained at a constant level of approximately 35 mmol/kg, despite fluctuating plasma concentrations over a range from 0 to over 25 mM.