Citrulline and long-term mortality in patients with cardiovascular disease.

BACKGROUND: Cardiovascular disease (CVD) is associated with intestinal barrier dysfunction and increased intestinal permeability. Increased intestinal permeability to gut microbial metabolites may accelerate the progression of CVD. Plasma citrulline levels are a marker of functional enterocyte mass, and reduced citrulline levels indicate intestinal epithelial damage. Citrulline was reported as a useful prognostic marker in critically ill patients. However, data are lacking on the association of citrulline with long-term mortality in patients with CVD and with the levels of trimethylamine N-oxide (TMAO), a microbiota-derived metabolite which has been implicated in the pathogenesis of CVD. OBJECTIVES: To assess the effect of citrulline levels, a marker of intestinal barrier disruption, on long-term mortality in patients with CVD. Moreover, the relationship between the concentrations of 2 biomarkers - citrulline and TMAO - was assessed. MATERIAL AND METHODS: Serum citrulline levels were retrospectively assessed in 1036 consecutive patients with CVD (median age: 62 years; 61% men) hospitalized between 2013 and 2015. Associations of citrulline levels with 5-year mortality rates as well as anthropometric and biochemical parameters were evaluated for the entire study group and in subgroups of patients with acute coronary syndrome (ACS), chronic coronary syndrome, chronic heart failure (chronic HF), and atrial fibrillation (AF). Correlations between serum citrulline and TMAO levels were assessed. RESULTS: The median citrulline level in the study population was 22.5 µM (interquartile range (IQR): 17.8-27.9). Citrulline levels were not associated with 5-year mortality in patients with CVD (hazard ratio (HR) = 0.99; 95% confidence interval (95% CI): 0.97-1.00; p = 0.49). Median citrulline levels differed significantly between deceased patients and survivors at 5 years in patients with ACS (p = 0.025). There were no significant correlations between citrulline and TMAO levels (Kendall's tau = 0.027). CONCLUSIONS: Decreasing citrulline levels do not predict long-term mortality of hospitalized patients with CVD. Moreover, they are not associated with the serum levels of TMAO in these patients.

Trimethylamine N-oxide in cardiovascular disease.

Although traditional cardiovascular risk factors are well established and understood, mortality and morbidity in patients with cardiovascular disease (CVD) remains high. Exploring new pathophysiological pathways enables a better understanding of CVD at both the molecular and clinical levels. Gut microbiota as a potential modulator of CVD are the subject of extensive research. In recent years, trimethylamine N-oxide (TMAO), a biologically active molecule generated by the gut microbiota, has been widely tested in studies on various populations of patients. The ultimate TMAO levels depend on individual features and gut microbiota composition. Most of the research on TMAO has focused on atherosclerotic CVD and heart failure (HF). Studies conducted so far support the use of TMAO as a prognostic marker in CVD. Several studies describe diverse interventions aimed at reducing the concentration of TMAO and its harmful effects. This article summarizes the findings from research, discusses the major insights into TMAO metabolism and related pathophysiological processes, as well as indicates the directions for future research.