Epicardial adipose tissue microbial colonization and inflammasome activation in acute coronary syndrome

Epicardial adipose tissue (EAT) has a close functional and anatomic relationship with epicardial coronary arteries. Accumulating evidence suggests that host microbiome alterations may play a role in several inflammatory/immune disorders, triggering a robust proinflammatory response also involving interleukin-1β (IL-1β) and the NALP3 inflammasome. In the current study, we explore the hypothesis that in patients with non-ST elevation acute coronary syndrome (ACS), EAT contains potentially pro-atherosclerotic bacteria that might elicit inflammasome activation.

EAT samples were obtained during coronary artery bypass grafting from ACS (n=18) and effort stable angina (SA; n=16) patients, and as controls, from patients with angiographically normal coronary arteries undergoing surgery for mitral insufficiency (MVD; n=13). In all patients, NALP3 and proIL-1β mRNA expressions were evaluated with qRT-PCR. In 3 patients from each group, EAT microbiota composition was determined using next-generation sequencing technologies.

In EAT, mRNA expression of both NALP3 and pro-IL1β was significantly higher in ACS than in SA and MVD (P=0.028 and P=0.005, respectively). A broad range of bacterial species (n=76) was identified in both ACS and SA, with different predominant species. In contrast, microbial DNA was barely observed in MVD.

Our study demonstrated the presence of bacterial DNA directly into EAT, surrounding diseased coronary arteries, of patients with ACS. Furthermore, ACS is associated with NALP3/inflammasome pathway activation in EAT. Our data suggest that the EAT environment is susceptible to microbial colonization that might stimulate a proinflammatory response. These findings add new elements to the pathogenesis of ACS and suggest novel therapeutic targets.