Serum Trimethylamine-N-Oxide Is Strongly Related to Renal Function and Predicts Outcome in Chronic Kidney Disease

Abstract

Background: The microbial metabolite Trimethylamine-N-oxide (TMAO) has been linked to adverse cardiovascular outcome and mortality in the general population.

Objective: To assess the contribution of TMAO to inflammation and mortality in chronic kidney disease (CKD) patients ranging from mild-moderate to end-stage disease and 1) associations with glomerular filtration rate (GFR) 2) effect of dialysis and renal transplantation (Rtx) 3) association with inflammatory biomarkers and 4) its predictive value for all-cause mortality.

Methods: Levels of metabolites were quantified by a novel liquid chromatography/tandem mass spectrometry-based method in fasting plasma samples from 80 controls and 179 CKD 3-5 patients. Comorbidities, nutritional status, biomarkers of inflammation and GFR were assessed.

Results: GFR was the dominant variable affecting TMAO (β = -0.41; p<0.001), choline (β = -0.38; p<0.001), and betaine (β = 0.45; p<0.001) levels. A longitudinal study of 74 CKD 5 patients starting renal replacement therapy demonstrated that whereas dialysis treatment did not affect TMAO, Rtx reduced levels of TMAO to that of controls (p<0.001). Following Rtx choline and betaine levels continued to increase. In CKD 3-5, TMAO levels were associated with IL-6 (Rho = 0.42; p<0.0001), fibrinogen (Rho = 0.43; p<0.0001) and hsCRP (Rho = 0.17; p = 0.022). Higher TMAO levels were associated with an increased risk for all-cause mortality that remained significant after multivariate adjustment (HR 4.32, 95% CI 1.32-14.2; p = 0.016).

Conclusion: Elevated TMAO levels are strongly associated with degree of renal function in CKD and normalize after renal transplantation. TMAO levels correlates with increased systemic inflammation and is an independent predictor of mortality in CKD 3-5 patients.

Fig 1. Increasing plasma levels of TMAO in CKD patients stage 3 (n = 30), stage 4 (n = 28) and stage 5 (n = 116) compared to healthy controls (n = 80).

Values are expressed as median (10^th -90^th percentile). P-values analyzed by Kruskal–Wallis’ one-way ANOVA, followed by Dunn’s multiple comparison test.

Fig 2. Comparison of plasma levels of metabolites in a cohort of CKD 5 patients (n = 74) followed from baseline and reassessed 12 months after start of dialysis and/or 12 months and 24 months after renal transplantation (Rtx).

Choline and betaine levels increased with dialysis and Rtx whereas TMAO levels remained unchanged during dialysis and normalized after Rtx. Due to missing samples box-plots represents 34/74 patients at 12 months of dialysis, 47/74 patients at 12 months and 29/74 patients at 24 months follow-up after Rtx. Values are expressed as median (10^th -90^th percentile) P-values analyzed by Kruskal–Wallis’ one-way ANOVA, followed by Dunn’s multiple comparison test.

Fig 3. Comparative analysis of metabolites in inflamed (hsCRP ≥10 mg/L) and non-inflamed (hsCRP < 10 mg/L) CKD 3–5 patients (n = 179).

Higher hsCRP levels associated with higher TMAO levels and decreased betaine levels. Values are expressed as median (10^th -90^th percentile). P-values analyzed by Kruskal–Wallis’ one-way ANOVA, followed by Dunn’s multiple comparison test.

Fig 4. Kaplan-Meier analysis of TMAO levels and all-cause mortality in CKD 3–5 patient (n = 179).

Data presented as tertiles. CKD patients with the highest TMAO levels (Combined middle (32.2–75.2 μM/L) + high tertile (>72.2 μM/L)) had a significantly lower survival compared with patients in the lowest TMAO tertile.