Sensitive assay of trimethylamine N-oxide in liver microsomes by headspace gas chromatography with flame thermionic detection

Simultaneous determination of choline, L-carnitine, betaine, trimethylamine, trimethylamine N-oxide, and creatinine in plasma, liver, and feces of hyperlipidemic rats by UHPLC-MS/MS

BACKGROUND

Due to the close correlation between choline, L-carnitine, betaine and their intestinal microbial metabolites, including trimethylamine (TMA) and trimethylamine N-oxide (TMAO), and creatinine, there has been an increasing interest in the study of these compounds in vivo.

METHODS

In this study, a rapid stable isotope dilution (SID)-UHPLC-MS/MS method was developed for the simultaneous determination of choline, L-carnitine, betaine, TMA, TMAO and creatinine in plasma, liver and feces of rats. The method was validated using quality control (QC) samples spiked at low, medium and high levels. Second, we applied the method to quantify the effects of Rosa Roxburghii Tratt juice (RRTJ) on plasma, liver, and fecal levels of choline, L-carnitine, betaine, TMA, TMAO, and creatinine in high-fat diet-induced hyperlipidemic rats, demonstrating the utility of the method.

RESULTS

The limits of detection (LOD) were 0.04-0.027 µM and the limits of quantification (LOQ) were 0.009-0.094 µM. The linear ranges for each metabolite in plasma were choline1.50-96 µM; L-carnitine: 2-128 µM; betaine: 3-192 µM; TMA: 0.01-40.96 µM; TMAO: 0.06-61.44 µM and creatinine: 1-64 µM (R2 ≥ 0.9954). The linear ranges for each metabolite in liver were Choline: 12-768 µM; L-carnitine: 1.5-96 µM; betaine: 10-640 µM; TMA: 0.5-32 µM; TMAO: 0.02-81.92 µM and creatinine: 0.2-204.8 µM (R2 ≥ 0.9938). The linear ranges for each metabolite in feces were choline: 1.5-96 µM; L-carnitine: 0.01-40.96 µM; Betaine: 1.5-96 µM; TMA: 1-64 µM; TMAO: 0.02-81.92 µM and Creatinine: 0.02-81.92 µM (R2 ≥ 0.998). The intra-day and inter-day coefficients of variation were < 8 % for all analytes. The samples were stabilized after multiple freeze-thaw cycles (3 freeze-thaw cycles), 24 h at room temperature, 24 h at 4 °C and 20 days at -80 °C. The samples were stable. The average recovery was 89 %-99 %. This method was used to quantify TMAO and its related metabolites and creatinine levels in hyperlipidemic rats. The results showed that high-fat diet led to the disorder of TMAO and its related metabolites and creatinine in rats, which was effectively improved after the intervention of Rosa Roxburghii Tratt juice（RRTJ）.

CONCLUSIONS

A method for the determination of choline, L-carnitine, betaine, TMA, TMAO and creatinine in plasma, liver and feces samples was established, which is simple, time-saving, high precision, accuracy and recovery.

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.

Genetic Variant in Flavin-Containing Monooxygenase 3 Alters Lipid Metabolism in Laying Hens in a Diet-Specific Manner

Genetic variant T329S in flavin-containing monooxygenase 3 (FMO3) impairs trimethylamine (TMA) metabolism in birds. The TMA metabolism that under complex genetic and dietary regulation, closely linked to cardiovascular disease risk. We determined whether the genetic defects in TMA metabolism may change other metabolic traits in birds, determined whether the genetic effects depend on diets, and to identify genes or gene pathways that underlie the metabolic alteration induced by genetic and diet factors. We used hens genotyped as FMO3 c.984 A>T as well as those with the homozygous normal genotype. For each genotype, hens were provided with either a corn-soybean meal basal diets (SM), which contains lower levels of TMA precursor, or the basal diets supplemented with 21% of rapeseed meal (RM), which contains higher levels of TMA precursor. An integrative analysis of metabolomic and transcriptomic was used to explore the metabolic patterns of FMO3 genetic variant in hens that were fed the two defined diets. In birds that consumed SM diets, the T329S mutation increased levels of plasma TMA and lipids, FMO3 mRNA levels, and the expression of genes involved in long chain polyunsaturated fatty acid biosynthesis. In birds that consumed RM diets, the T329S mutation induced fishy odor syndrome, a repression in LXR pathway and a reciprocal change in lipid metabolism. Variations in TMA and lipid metabolism were linked to the genetic variant in FMO3 in a diet-specific manner, which suggest FMO3 functions in TMA metabolism and lipid homeostasis. LXR pathway and polyunsaturated fatty acid metabolism are two possible mechanisms of FMO3 action in response to dietary TMA precursor.

Electrochemical sensing of trimethylamine based on polypyrrole-flavin-containing monooxygenase (FMO3) and ferrocene as redox probe for evaluation of fish freshness

Amperometric and impedimetric biosensor for detecting trimethylamine (TMA) which represents good parameters for estimating fish freshness has been developed. The biosensor is based on a conducting polypyrrole substituted with ferrocenyl, where flavin-containing monooxygenase 3 (FMO3) enzyme was immobilised by covalent bonding. FMO3 catalyzes the monooxygenation TMA to trimethylamine N-oxide (TMO). For catalysis FMO require flavin adenine (FAD) as a prosthetic group, NADPH as a cofactor and molecular oxygen as cosubstrate. Ferrocenyl group substituted on the polypyrrole matrix will serve as redox probe for monitoring the response of the biosensor to TMA. The construction of the biosensor was characterized by FT-IR, cyclic voltammetry and impedance measurements. Detection is done through the analysis of the current of oxidation signal of the ferrocenyl groups and compared to the measurement of impedance related to the electrical properties of the layers. Amperometric and impedimetric response were measured as a function of TMA concentration in range of 0.4 μgm L(-1)-80 μgm L(-1) (6.5 μmol L(-1)-1.5 mmol L(-1)). Amperometric measurements show a decrease in current response which is in correlation with the increase of the charge transfer resistance demonstrated by impedance. Calibration curve obtained by impedance spectroscopy shows a high sensitivity with a dynamic range from (0.4 μgm L(-1) to 80 μgm L(-1)). We demonstrated, using ferrocene as redox probe for catalytic reaction of FMO3, that high sensitivity and dynamic range was obtained. The biosensor was stable during 16 days. The biosensor shows high selectivity and its sensitivity to TMA in real samples was evaluated using fish extract after deterioration during storage.