Elevated Circulating Levels of Gut Microbe-Derived Trimethylamine N-Oxide Are Associated with Systemic Sclerosis

Abstract

Background/Objectives: Alterations in fecal microbial communities in patients with systemic sclerosis (SSc) are common, but the clinical significance of this observation is poorly understood. Gut microbial production of trimethylamine (TMA), and its conversion by the host to trimethylamine N-oxide (TMAO), has clinical and mechanistic links to cardiovascular and renal diseases. Direct provision of TMAO has been shown to promote fibrosis and vascular injury, hallmarks of SSc. We sought to determine levels of TMAO and related metabolites in SSc patients and investigate associations between the metabolite levels with disease features. Methods: This is an observational case:control study. Adults with SSc (n = 200) and non-SSc controls (n = 400) were matched for age, sex, indices of renal function, diabetes mellitus, and cardiovascular disease. Serum TMAO, choline, betaine, carnitine, γ-butyrobetaine, and crotonobetaine were measured using stable isotope dilution liquid chromatography tandem mass spectrometry. Results: Median TMAO concentration was higher (p = 0.020) in SSc patients (3.31 [interquartile range 2.18, 5.23] µM) relative to controls (2.85 [IQR 1.88, 4.54] µM). TMAO was highest among obese and male SSc participants compared to all other groups. Following adjustment for sex, BMI, age, race, and eGFR in a quantile regression model, elevated TMAO levels remained associated with SSc at each quantile of TMAO. Conclusions: Patients with SSc have increased circulating levels of TMAO independent of comorbidities including age, sex, renal function, diabetes mellitus, and cardiovascular disease. As a potentially modifiable factor, further studies examining the link between TMAO and SSc disease severity and course are warranted.

Keywords: case-control studies; choline; cluster analysis; gamma-butyrobetaine; gastrointestinal microbiome; scleroderma; sclerosis; systemic; trimethylamine N-oxide.

Figure 1

Comparative analysis of serum TMAO concentration. Each comparison is shown with and without outlier observations. For the comparison of control and SSc groups, box plots of TMAO in the control and SSc groups is shown with (A) and without (D) the outlier observations in both groups. For the comparison based on SSc group and obesity, box plots of TMAO in each group are shown with (B) and without (E) the outlier observations in the non-obese groups (2 in control group and 1 in SSc group). For the comparison based on SSc group and sex, box plots of TMAO in each group are shown with (C) and without (F) the outlier observations in the female groups (two in control group and one in SSc group). Data shown are median with interquartile range. (G) Quantile regression analysis of the differences in TMAO at each quantile between the SSc and control groups. After adjusting for sex, BMI, age, race, and eGFR, SSc participants had an elevated TMAO level in comparison to control participants at all quantile of TMAO. Quantile regression estimated coefficients at each TMAO quantile are shown in Table 1.

Figure 2

Heat map of serum metabolite concentrations in the SSc cohort. Metabolites are represented in the columns and individual participants are represented in the rows. As described in the text, 7 hierarchical clusters were initially identified and then regrouped into 2 clusters based on sample sizes. The final 2 groups are indicated on the left side of the figure by dark brown (n = 92) or tan (n = 108).