Investigating intestinal permeability and gut microbiota roles in acute coronary syndrome patients

Abstract

Background: Acute Coronary Syndrome (ACS) is a leading cause of morbidity and mortality. Perturbed gut- microbiota (dysbiosis) and increased intestinal permeability (leaky-gut) with translocation of bacterial antigens, play critical role in obesity and metabolic syndrome, which are also major ACS risk factors. Additionally, Trimethylamine-N-Oxide (TMAO), a metabolite produced by phylum Proteobacteria in gut is implicated in developing ACS. As Proteobacteria is a major source of translocated antigen lipopolysaccharides (LPS), we hypothesized that ACS patients have leaky-gut condition characterized by dysbiosis with increased Proteobacteria, leading to elevated blood levels of TMAO and LPS.

Methods: In a pilot case-control study, we enrolled 19 ACS patients (within 72-h of cardiac events) and 19 healthy-controls. Gut barrier function was determined using lactulose-to-mannitol urinary excretion ratio (L/M ratio). Stool microbiome composition was examined using16S sequencing and predictive functional analysis for LPS biosynthesis pathway by PICRUSt tool. Serum TMAO and LPS levels were measured.

Results: ACS patients had increased Gammaproteobacteria compared to controls:1.8 ±3.0 vs. 0.2 ±0.4% (P =0.04). Though Proteobacteria level was increased but not statistically significant: 4.1 ±3.8 vs. 2.1 ±1.7% (P =0.056). L/M-ratio was three times higher in ACS patients; 0.06 ±0.07 vs 0.023 ±0.02, (P =0.014). Surprisingly, there was no difference in the mean serum LPS or TMAO levels. However, PICRUSt analysis indicated increased Proteobacteria population increasingly contributed to LPS biosynthesis in ACS patients only.

Conclusions: ACS patients likely to have leaky-gut and perturbed gut microbiota. Further studies are required to precisely define the role of dysbiosis in ACS.

Keywords: Acute coronary syndrome; Dysbiosis; Endotoxins; Intestinal permeability; Proteobacteria; TMAO.

Fig. 1.

Lactulose to mannitol (L/M) ratio, trimethyamineoxide (TMAO) and lipopolysaccharide (LPS) levels. (A–B) L/M ratio in ACS patients and healthy controls, and mean L/M ratio in both groups. (C) TMAO serum levels in ACS patients and healthy controls. (D) LPS serum levels in ACS patients compared to healthy controls. *Healthy controls. **Acute coronary syndrome. ***Lactulose to mannitol ratio.

Fig. 2.

Diversity of the intestinal microbiome in ACS patients and healthy controls. (A–C) Rarefaction plots showing number of OTUs, phylogenetic diversity and Chao1 index for individual subjects. (D) Chao1 index per group. (E) Weighted unique fraction group distances. (F) Principal component analysis of weighted unique fraction distance. *Operational taxonomic unit. ** Principal component analysis.

Fig. 3.

Relative abundance of major bacterial phyla in ACS patients and healthy controls. (A) Relative abundance of bacterial phyla per group. (B) Relative abundance of bacterial phyla per subject. (C–F) Levels of fecal Proteobacteria, Bacteroidetes, Firmicutes, and Actinobacteria in ACS patients compared to healthy controls. *Acute coronary syndrome. **Healthy controls.

Fig. 4.

Relative abundance of Gammaproteobacteria, Enterobacteriaceae and other bacterial genera in study subjects. (A–B) Levels of fecal Gammaproteobacteria and Enterobacteriaceae in ACS patients compared to healthy controls. (C) Summary of Proteobacteria, Gammaproteobacteria and Enterobacteriaceae levels per group. (D, E) Relative abundance of bacteria per group and per subject at the genus level, for legend refer to Supplementary Fig. 1 (S1 Figure). (F) Bacterial genera with more than 2-fold difference between the two groups. Red color indicates higher abundance. (G) Bacterial phyla contribution to LPS synthesis in ACS patients and healthy controls. *Acute coronary syndrome. **Healthy controls.