Trimethylamine, a gut bacteria metabolite and air pollutant, increases blood pressure and markers of kidney damage including proteinuria and KIM-1 in rats

BACKGROUND: Trimethylamine oxide (TMAO) is a biomarker in cardiovascular and renal diseases. TMAO originates from the oxidation of trimethylamine (TMA), a product of gut microbiota and manufacturing industries-derived pollutant, by flavin monooxygenases (FMOs). The effect of chronic exposure to TMA on cardiovascular and renal systems is undetermined. METHODS: Metabolic, hemodynamic, echocardiographic, biochemical and histopathological evaluations were performed in 12-week-old male SPRD rats receiving water (controls) or TMA (200 or 500 µM/day) in water for 18 weeks. TMA and TMAO levels, the expression of FMOs and renin-angiotensin system (RAS) genes were evaluated in various tissues. RESULTS: In comparison to controls, rats receiving high dose of TMA had significantly increased arterial systolic blood pressure (126.3 ± 11.4 vs 151.2 ± 19.9 mmHg; P = 0.01), urine protein to creatinine ratio (1.6 (1.5; 2.8) vs 3.4 (3.3; 4.2); P = 0.01), urine KIM-1 levels (2338.3 ± 732.0 vs. 3519.0 ± 953.0 pg/mL; P = 0.01), and hypertrophy of the tunica media of arteries and arterioles (36.61 ± 0.15 vs 45.05 ± 2.90 µm, P = 0.001 and 18.44 ± 0.62 vs 23.79 ± 2.60 µm, P = 0.006; respectively). Mild degeneration of renal bodies with glomerulosclerosis was also observed. There was no significant difference between the three groups in body weight, water-electrolyte balance, echocardiographic parameters and RAS expression. TMA groups had marginally increased 24 h TMA urine excretion, whereas serum levels and 24 h TMAO urine excretion were increased up to 24-fold, and significantly increased TMAO levels in the liver, kidneys and heart. TMA groups had lower FMOs expression in the kidneys. CONCLUSIONS: Chronic exposure to TMA increases blood pressure and increases markers of kidney damage, including proteinuria and KIM-1. TMA is rapidly oxidized to TMAO in rats, which may limit the toxic effects of TMA on other organs. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12967-022-03687-y

Species-specific comparison of TMAO, TMA and other metabolites concentrations in plasma and urine.

Species-specific comparison of TMAO, TMA and other metabolites concentrations in plasma and urine.</p

FMO3 and FMO5 in the liver.

Western blot analysis of FMO3 (A) and FMO5 (C) protein levels from total protein extract prepared from the liver in rats, mice and guinea pigs. (B) A representative immunoblot. Immunolabeled FMO3 and beta actin loading control bands were quantified using a Molecular Imager. Relative levels of the test proteins are plotted in arbitrary units. Abbreviations: FMO, Flavin-containing monooxygenase. All data are expressed as the median, mean, Q1, Q3, MIN, MAX (n = 4–6); ANOVA followed by post-hoc Tuckey test. **P < 0.01; ***P < 0.001.</p

Western blotting–original images.

IntroductionIncreased plasma trimethylamine oxide (TMAO) is observed in cardiovascular and metabolic diseases, originating from the gut microbiota product, trimethylamine (TMA), via flavin-containing monooxygenases (FMOs)-dependent oxidation. Numerous studies have investigated the association between plasma TMAO and various pathologies, yet limited knowledge exists regarding tissue concentrations of TMAO, TMAO precursors, and interspecies variability.MethodsChromatography coupled with mass spectrometry was employed to evaluate tissue concentrations of TMAO and its precursors in adult male mice, rats, and guinea pigs. FMO mRNA and protein levels were assessed through PCR and Western blot, respectively.ResultsPlasma TMAO levels were similar among the studied species. However, significant differences in tissue concentrations of TMAO were observed between mice, rats, and guinea pigs. The rat renal medulla exhibited the highest TMAO concentration, while the lowest was found in the mouse liver. Mice demonstrated significantly higher plasma TMA concentrations compared to rats and guinea pigs, with the highest TMA concentration found in the mouse renal medulla and the lowest in the rat lungs. FMO5 exhibited the highest expression in mouse liver, while FMO3 was highly expressed in rats. Guinea pigs displayed low expression of FMOs in this tissue.ConclusionDespite similar plasma TMAO levels, mice, rats, and guinea pigs exhibited significant differences in tissue concentrations of TMA, TMAO, and FMO expression. These interspecies variations should be considered in the design and interpretation of experimental studies. Furthermore, these findings may suggest a diverse importance of the TMAO pathway in the physiology of the evaluated species.</div

Species-specific comparison of choline and carnitine concentrations in various tissues.

Species-specific comparison of choline and carnitine concentrations in various tissues.</p

Three species comparison–Tissues, continuation.

Comparison of the concentrations of TMA, TMAO and the TMAO/TMA ratios in the renal cortex and renal medulla. Abbreviations: TMA, Trimethylamine; TMAO, Trimethylamine oxide. All data are expressed as the individual values and median; Kruskal-Wallis test followed by post-hoc Dunn’s test; *P<0.05; **P<0.01; ***P<0.001.</p