Gut Microbiota and Atherosclerotic Plaque Instability: Cellular and Molecular Mechanisms

Atherosclerosis is a chronic multifactorial inflammatory vascular disease and the major risk factor for cardiovascular diseases (CVDs), characterized by arterial wall thickening, loss of arterial elasticity and the progressive accumulation of lipids and immune cells, ultimately leading to plaque formation and the development of unstable, rupture-prone plaques. Several studies suggest that gut microbiota might contribute to atherosclerosis, mainly by converting dietary and endogenous molecules into bioactive metabolites, such as trimethylamine N-oxide (TMAO), short-chain fatty acids (SCFAs), and the Gram-negative cell-wall component lipopolysaccharide (LPS). Such metabolites can promote key mechanisms involved in the development and progression of atherosclerotic plaque, and, importantly, plaque vulnerability. Specifically, they can worsen endothelial dysfunction, induce macrophage-driven inflammatory responses, and cause oxidative stress and extracellular matrix degradation. These processes are crucial for thinning of the fibrous cap and destabilization of atherosclerotic plaques. As a result, the risk of plaque rupture and related cardiovascular events increases. In this review, we summarize potential mechanisms by which the gut microbiota and their compounds induce the formation of vulnerable atherosclerotic plaques and discuss findings from experimental models and clinical studies that reveal the crucial role of microbiota-host dynamics in atherosclerosis. In contrast to previous reviews that primarily focused on atherosclerosis development, we specifically highlight the cellular and molecular mechanisms linking gut microbiota to plaque vulnerability and destabilization. We also address future research priorities to define microbiota-driven pathways better and develop targeted therapeutic interventions to reduce plaque vulnerability and cardiovascular risk.