Formation of aliphatic amine precursors of N-nitrosodimethylamine after oral administration of choline and choline analogues in the rat

Effects of different duck rearing systems on egg flavor and quality and microbial diversity

The fishy odor of duck eggs has restricted their consumption and industrial development, a problem that producers need to address. We estimated the effects of cage, floor, and pond rearing systems on duck egg flavor, egg quality, and microbial diversity by evaluating yolk trimethylamine (TMA) content, egg quality, and the differences between duck cecum (cage cecum, CC; floor cecum, FC; pond cecum, PC) and the environment (cage environment, CE; floor environment, FE; pond environment, PE). The results show that the yolk TMA content of the floor-rearing and pond-rearing systems was significantly higher than that of the cage-rearing system (P < 0.001), with no difference between the floor and pond-rearing systems. No significant differences were detected in egg quality among the rearing systems. Firmicutes, Actinobacteria, and Bacteroidetes were the dominant phyla in the cecum, and in the rearing environment, Firmicutes, Actinobacteria, Bacteroidetes, and Proteobacteria were the dominant phyla. The results of α and β diversity analyses show that changes in the rearing system affected the composition and diversity of duck cecal microbes. In addition, we screened several genera that may be related to the production of TMA in duck cecum under different rearing systems using LEfSe analysis; for example, Subdoligranulum in the CC group; Romboutsia in the FC group; and Lactobacillus, Clostridium, and Streptococcus in the PC group. In conclusion, the rearing system affects the cecal microbes of ducks, which in turn affect the deposition of TMA in duck eggs but have no adverse effect on egg quality. This study provides a basis for the development of rearing strategies to reduce the fishy odor of egg yolk in the duck industry.

Choline diet improves serum lipid parameters and alters egg composition in breeder ducks

Background

Choline is an important nutrient, playing key roles in numerous metabolic pathways relevant to animal health.

Objectives

The objective of this study was to evaluate the effect of dietary choline on the lipid parameters, cardiovascular health (CVH), and levels of egg trimethylamine (TMA) and cholesterol in breeder ducks during the late laying period.

Methods

A total of 60 Jingjiang ducks were randomly separated into six replicates of 10 ducks each. After peak production until 65 weeks of age, the birds were fed a control basal diet. The same ducks served as the control group until 65 weeks of age, when the same ducks served as the choline‐supplemented group, after 15 days of dietary choline supplementation at 2955 mg/kg choline above and over the basal diet initially provided. The 15 days of choline supplementation included an initial 5‐day acclimatisation period.

Results

Dietary choline supplementation increased serum TMA (p < 0.01), high‐density lipoprotein cholesterol, very low‐density lipoprotein, and triglyceride levels in older breeder ducks. However, it did not change the levels of trimethylamine N‐oxide but decreased the atherosclerosis index compared with those of the control group (p < 0.01). Moreover, it increased (p < 0.01) the egg yolk TMA levels but did not change the concentrations of cholesterol in egg yolk.

Conclusions

Dietary choline supplementation had a beneficial effect on lipid parameters and CVH in older breeder ducks, although it increased the serum and egg yolk TMA levels.

Effects of acute heat stress on salivary metabolites in growing pigs: an analysis using nuclear magnetic resonance-based metabolomics profiling

Heat stress (HS) causes adverse impacts on pig production and health. A potential biomarker of HS is required to predict its occurrence and thereby better manage pigs under HS. Information about the saliva metabolome in heat-stressed pigs is limited. Therefore, this study was aimed to investigate the effects of acute HS on the saliva metabolome and identify metabolites that could be used as potential biomarkers. Growing pigs (n = 6, 3 boars, and 3 gilts) were raised in a thermal neutral (TN; 25°C) environment for a 5-d adaptation period (CON). After adaptation, the pigs were first exposed to HS (30°C; HS30) and then exposed to higher HS (33°C; HS33) for 24 h. Saliva was collected after adaptation, first HS, and second HS, respectively, for metabolomic analysis using ¹H-nuclear magnetic resonance spectroscopy. Four metabolites had significantly variable importance in the projection (VIP > 1; p < 0.05) different levels in TN compared to HS groups from all genders (boars and gilts). However, sex-specific characteristics affected metabolites (glutamate and leucine) by showing the opposite results, indicating that HS was less severe in females than in males. A decrease in creatine levels in males and an increase in creatine phosphate levels in females would have contributed to a protective effect from protein degradation by muscle damage. The results showed that HS led to an alteration in metabolites related to energy and protein. Protection from muscle damage may be attributed to the alteration in protein-related metabolites. However, energy-related metabolites showed opposing results according to sex-specific characteristics, such as sex hormone levels and subcutaneous fat layer. This study had shown that saliva samples could be used as a noninvasive method to evaluate heat-stressed pigs. And the results in this study could be contributed to the development of a diagnostic tool as a noninvasive biomarker for managing heat-stressed pigs.

Fishy Odor and TMA Content Levels in Duck Egg Yolks

The differences between the trimethylamine (TMA) content levels in duck and chicken egg yolks under normal dietary conditions were compared. Moreover, the association between the polymorphisms of the duck FMO3 gene and TMA content levels in duck egg yolks was analyzed. Then, to detect the mutations associated with the fish-flavor trait, duck populations were selected for a high-choline diet experiment, which was followed by full-length sequencing of the FMO3 exons. The results showed that the TMA content levels in duck eggs (3.60 μg/g) were significantly higher than those in chicken eggs (2.35 μg/g) under normal dietary conditions (P < 0.01). With regard to the high-choline diet, the average TMA content levels in duck egg yolks (9.21 μg/g; P < 0.01) increased significantly. Furthermore, 5 SNPs reported in Ensembl database were detected in duck FMO3 exons. However, no mutation loci were found to be significantly associated with the TMA content levels in duck egg yolks. Besides, duck liver FMO3 mRNA expression levels were not associated with the TMA content levels. The results indicated that excessive TMA deposition in duck eggs is one of main factors causing the fishy odor in duck eggs, and the addition of choline in the ducks' diets was responsible for inducing an increase in the TMA content levels in duck eggs.

PRACTICAL APPLICATION

Our study can help to diminish the fishy taste in duck eggs by reducing the amount of supplemented choline. Furthermore, this study laid a solid foundation for revealing the genetic factors involved in the fishy odor in duck eggs.

Plasma trimethylamine-N-oxide following supplementation with vitamin D or D plus B vitamins

SCOPE

We compared the effect of supplementation with vitamin D + B or vitamin D on plasma trimethylamine N-oxide (TMAO) and choline metabolites.

METHODS AND RESULTS

This is a randomized single-blinded nonplacebo-controlled study. Twenty-seven participants received 1200 IU vitamin D3 and 800 mg calcium, and 25 participants received additionally 0.5 mg folic acid, 50 mg B6, and 0.5 mg B12 for 1 year. Plasma homocysteine (Hcy), TMAO, and choline metabolites were measured at baseline and 12 months later. TMAO declined in the vitamin D arm by 0.5 versus 2.8 μmol/L in the D + B arm (p = 0.005). Hcy decreased and betaine increased in the D + B compared to the D arm. Within-subject levels of plasma choline and dimethylglycine and urine betaine increased in both arms and changes did not differ between the arms. TMAO reduction was predicted by higher baseline TMAO and lowering Hcy in stepwise regression analysis. The test-retest variations of TMAO were greater in the D + B arm compared to vitamin D arm.

CONCLUSION

B vitamins plus vitamin D lowered plasma fasting TMAO compared to vitamin D. Vitamin D caused alterations in choline metabolism, which may reflect the metabolic flexibility of C1-metabolism. The molecular mechanisms and health implications of these changes are currently unknown.

A multiplexed targeted assay for high-throughput quantitative analysis of serum methylamines by ultra performance liquid chromatography coupled to high resolution mass spectrometry

Methylamines are biologically-active metabolites present in serum and urine samples, which play complex roles in metabolic diseases. Methylamines can be detected by proton nuclear magnetic resonance (NMR), but specific methods remain to be developed for their routine assay in human serum in clinical settings. Here we developed and validated a novel reliable "methylamine panel" method for simultaneous quantitative analysis of trimethylamine (TMA), its major detoxification metabolite trimethylamine-N-oxide (TMAO), and precursors choline, betaine and l-carnitine in human serum using Ultra Performance Liquid Chromatography (UPLC) coupled to High Resolution Mass Spectrometry (HRMS). Metabolite separation was carried out on a HILIC stationary phase. For all metabolites, the assay was linear in the range of 0.25-12.5 μmol/L and enabled to reach limit of detection of about 0.10 μmol/L. Relative standard deviations were below 16% for the three levels of concentrations. We demonstrated the strong reliability and robustness of the method, which was applied to serum samples from healthy individuals to establish the range of concentrations of the metabolites and their correlation relationships and detect gender differences. Our data provide original information for implementing in a clinical environment a MS-based diagnostic method with potential for targeted metabolic screening of patients at risk of cardiometabolic diseases.

Metabonomic deconvolution of embedded toxicity: application to thioacetamide hepato- and nephrotoxicity

We present here the potential of an integrated metabonomic strategy to deconvolute the biofluid metabolic signatures in experimental animals following multiple organ toxicities, using the well-known hepato- and nephrotoxin, thioacetamide. Male Han-Wistar rats were dosed with thioacetamide (150 mg/kg, n = 25), and urine, plasma, liver, and kidney samples were collected postdose for conventional NMR and magic angle spinning (MAS) NMR spectroscopy. These data were correlated with histopathology and plasma clinical chemistry collected at all time points. 1H MAS NMR data from liver and kidney were related to sequential 1H NMR measurements in urine and plasma using pattern recognition methods. One-dimensional 1H NMR spectra were data-reduced and analyzed using principal components analysis (PCA) to show the time-dependent biochemical variations induced by thioacetamide toxicity. From the eigenvector loadings of the PCA, those regions of the 1H NMR spectra, and hence the combinations of endogenous metabolites marking the main phase of the toxic episode, were identified. The thioacetamide-induced biochemical manifestations included a renal and hepatic lipidosis accompanied by hypolipidaemia; increased urinary excretion of taurine and creatine concomitant with elevated creatine in liver, kidney, and plasma; a shift in energy metabolism characterized by depleted liver glucose and glycogen; reduced urinary excretion of tricarboxylic acid cycle intermediates and raised plasma ketone bodies; increased levels of tissue and plasma amino acids leading to amino aciduria verifying necrosis-enhanced protein degradation and renal dysfunction; and elevated hepatic and urinary bile acids indicating secondary damage to the biliary system. This integrated metabonomic approach has been able to identify the tissue of origin for biomarkers present in the metabolic profiles of biofluids, following the onset and progression of a multiorgan pathology, and as such highlights its potential in the evaluation of embedded toxicity in novel drug candidates.

NMR and pattern recognition studies on the time-related metabolic effects of alpha-naphthylisothiocyanate on liver, urine, and plasma in the rat: an integrative metabonomic approach

We present here a novel integrative metabonomic approach to probe toxic effects of drugs in experimental animals using alpha-naphthylisothiocyanate (ANIT) as a model hepatotoxicant. Male Han-Wistar rats were dosed with ANIT (150 mg/kg, n = 25), and plasma and liver samples were collected for NMR and magic-angle spinning (MAS) NMR spectroscopy at 3, 7, 24, 31, and 168 h postdosing. Urine was collected continuously for 3 days prior to dosing and up to 168 h postdose. Histopathology and plasma clinical chemistry was also performed at all time points. Liver samples were analyzed either intact by 600 MHz 1H MAS NMR techniques or using high resolution (liquid state) 1H NMR of water-acetonitrile extracts. These data were related to sequential 1H NMR measurements in urine and plasma using pattern recognition methods. 1D 1H NMR spectra were data-reduced and analyzed using principal components analysis (PCA) to show the time-dependent biochemical variations induced by ANIT toxicity. From the eigenvector loadings of the PCA, those regions of the 1H NMR spectra and hence the combinations of endogenous metabolites marking the main phase of the toxic episode were identified. The ANIT-induced biochemical manifestations included a hepatic lipidosis associated with hyperlipidaemia; hyperglycaemia and glycosuria; increased urinary excretion of taurine and creatine; a shift in energy metabolism characterized by increased plasma ketone bodies with reduced urinary excretion of tricarboxylic acid cycle intermediates and raised hepatic bile acids leading to bile aciduria. The integration of metabolic data derived from several sources gives a holistic approach to the study of time-related toxic effects in the intact system and enables the characterization of key metabolic effects during the development and recovery from a toxic lesion.

Dietary precursors of trimethylamine in man: a pilot study

An increased urinary excretion of trimethylamine and its N-oxide were observed in man following the oral intake (15 mmol) of choline (63% dose as trimethylamine and its N-oxide), D,L-carnitine (31% dose) and trimethylamine N-oxide (78% dose). Similar ingestion of betaine, creatinine or lecithin failed to elicit any significant increases. Of 46 different foods investigated, only fish and other sea-products gave rise to significant increases in urinary trimethylamine and N-oxide. Ingestion of fruits, vegetables, cereal and dairy produce, and meats had no measurable effects. Reasons for the apparent lack of trimethylamine provision by foods previously thought to be precursors are given and the role of gut microflora highlighted.

Dimethylamine formation in the rat from various related amine precursors

Dimethylamine is the immediate precursor of dimethylnitrosamine, a known potent carcinogen in a wide variety of animal species. Although small amounts of dimethylamine are ingested directly, the major dietary source is believed to be via choline and related materials. Owing to quantitative recoveries following oral administration, urinary dimethylamine levels provide good overall measures of body exposure. The oral administration of equimolar amounts (1 mmol/kg body weight) of potential amine precursors to male Wistar rats produced only small increases in urinary dimethylamine after choline (+ 11%; 0.60 +/- 0.36% dose), dimethylaminopropanol (+ 32%; 1.49 +/- 0.30% dose), dimethylaminoethyl chloride (+ 110% 5.38 +/- 1.72% dose) and trimethylamine (+ 51%; 1.6 +/- 0.80% dose) input, whereas significantly larger increases were found following trimethylamine N-oxide ingestion (+ 355%; 12.93 +/- 1.13% dose; t-test, P < 0.001). These data suggest that trimethylamine N-oxide is a major dietary source of dimethylamine, by direct conversion and not by sequential reduction (to trimethylamine) and demethylation, and that in this respect it is of greater importance, on a molar basis, than choline.

Fate of dimethylamine in man

1. The fate of [14C]-dimethylamine was investigated following oral administration to four male volunteers. 2. The major route of excretion was urine, with 94% of the administered radioactivity being voided over 3 days (87% during the first 24 h). Small amounts (1-3%) of radioactivity were found in the faeces and expired air. 3. Metabolism was limited with only 5% being demethylated to methylamine. The remainder of the dose was excreted unchanged. 4. Pharmacokinetic studies indicated rapid (t1/2ab = 8 min) and extensive absorption (bioavailability = 82%) from the gastrointestinal tract followed by widespread distribution and a fairly prompt excretion (t1/2el = 6-7 h) with a plasma clearance of 190 ml/min.

The FAD-containing monooxygenase-catalyzed N-oxidation and demethylation of trimethylamine in rat liver microsomes

Trimethylaminuria (TMAuria), the excessive urinary excretion of the odorous trimethylamine (TMA), accompanies elimination of TMA in sweat and corresponding "fish-odor" syndrome. TMA was oxidized in vitro in rat liver microsomes from male Sprague-Dawley rats to TMA N-oxide and N-demethylated to dimethylamine (DMA). Both reactions were inhibited to 1-3% of normal activity by preincubation of microsomes without NADPH-generating system at 37 degrees C for 10 minutes indicating the FAD-containing monooxygenase-catalyzed reactions. On the other hand, the reactions were not inhibited by gas phase containing up to 80% carbon monoxide/20% oxygen mixture. The results are compatible with the hypothesis that in rat liver microsomes the N-oxygenation and N-demethylation of TMA are catalyzed only or predominantly by FAD-containing monooxygenases, and the cytochrome P-450 monooxygenases play a negligible, if any, role.

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.