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

Abstract

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.

Keywords: Chronic kidney disease; Hypertension; Kidney damage; Proteinuria; Trimethylamine; Trimethylamine oxide.

Fig. 1

TMA/TMAO balance. a the amount of TMA consumed per day; b the amount of TMA excreted per day; c the amount of TMAO excreted per day in rats maintained either on tap water (control group) or low and high dose of TMA. TMA, trimethylamine; TMAO, trimethylamine oxide. All data are expressed as the median (n = 9); Kruskal–Wallis test followed by post-hoc Dunn’s test; ***P < 0.001 vs tap water group; ^###P < 0.001 vs low dose group

Fig. 2

Urine biochemical analysis. a protein concentration in urine; b protein to creatinine ratio in urine; c Kim-1 concentration in urine; d glucose concentration in urine in rats maintained either on tap water (control group) or low and high dose of TMA. TMA trimethylamine, UPCR urine protein creatinine ratio. All data are expressed as the median (n = 9); Kruskal–Wallis test followed by post-hoc Dunn’s test for urine protein, UPCR and urine glucose; ANOVA followed by post-hoc Tuckey test for urine Kim-1; *P < 0.05 vs tap water group

Fig. 3

FMOs genes expression. FMOs in the kidney, liver and lungs. RT-qPCR analysis of FMO1, FMO3 and FMO5 transcript levels in the a renal cortex, b renal medulla, c liver and d lungs in rats maintained either on tap water (control group) or low and high dose of TMA. TMA trimethylamine; FMO Flavin-containing monooxygenase. All data are expressed as the median, Q1, Q3, MIN, MAX (n = 6; use arbitrary units); Kruskal–Wallis test followed by post-hoc Dunn’s test. *P < 0.05 vs tap water group; **P < 0.01 vs tap water group

Fig. 4

Histopathology of the kidney. a Renal convoluted tubules (original magnification 10X, H&E stain), b renal medium size artery (original magnification 10×, H&E stain), c renal medium size artery (original magnification 40×, H&E stain) in rats maintained either on tap water (control group) or low and high dose of TMA. TMA trimethylamine, L lumen of convoluted renal tubules, Black arrow – vacuoles of various sizes within the cell cytoplasm, White arrow – endothelium

Fig. 5

Histopathology of the heart. a Myocardium of left ventricle (original magnification 10×, H&E stain), b myocardium of left ventricle (original magnification 40X, H&E stain) in rats maintained either on tap water (control group) or low and high dose of TMA. TMA trimethylamine