Weight status constitutes a significant role in the progression of atherosclerotic disease
[39]. Obesity is characterized by excessive expansion of visceral white adipose tissue mass, also known as adiposopathy. Adiposopathy is comprised of adipocyte hypertrophy, decreased adipose tissue blood flow, altered oxygen levels within the tissue, a state of chronic low-grade inflammation and blunted lipid metabolism
[40][41][42]. The latter includes impaired capacity for storing the surplus of dietary lipids, resulting in deposition of ectopic fat accumulating in body locations where it is not physiologically stored, such as the liver and muscle, and a shift to visceral adipose tissue (fat storage in the intraperitoneal and retroperitoneal spaces), contributing to increased circulating free fatty acids, oxidative stress, systemic inflammation, adipokine dysregulation and insulin resistance
[40][41][42][43][44][45]. However, epicardial adipose tissue has several unique properties that distinguish it from other depots of visceral fat due to the common microcirculation of epicardial tissue and the underlying myocardium
[46]. The accumulation of epicardial fat is closely associated with an impaired myocardial microcirculation, cardiac diastolic filling abnormalities, increased vascular stiffness, and left atrial dilatation in obese people
[47][48]. More specifically, high levels of TNF-α induce the secretion of adhesion and chemoattractant molecules such as vascular cell adhesion molecule-1, intercellular adhesion molecule-1, and monocyte chemoattractant protein-1 while reducing nitric oxide availability. Resistin hormone stimulates the proliferation of smooth muscle cells and the over-secretion of endotelin-1, leading to endothelial dysfunction
[49]. Obesity-related reductions in myocardial blood flow due to CMVD, combined with increased cardiac metabolic demand due to increases in ventricular mass, volume expansion, higher filling pressures, and greater cardiac output, may create a perfect background for the occurrence of myocardial oxygen supply–demand mismatch
[36]. Finally, an unfavorable correlation was observed between CFR and increased LDL cholesterol where treatment with pioglitazone and lipid-lowering therapy seemed to improve CFR
[50].
2.5. Gut Microbiota
This term describes the various commensal microbial species in the gastrointestinal tract
[51]. During the last decade, several studies reported the potential association between gut microbiota and atherosclerosis
[51][52]. Choline, betaine and L-carnitine are metabolized to trimethylamine (TMA) which is generated to trimethylamine N-oxide (TMAO), a gut microbe-dependent metabolite
[51][52]. Studies showed that increased TMAO level induced the activation of NF-kappa B (NF-κB) pathway and increased the expression of pro-inflammatory genes including inflammatory cytokines, adhesion molecules and chemokines
[53]. Oxidative stress and NOD-like receptor protein 3 (NLRP3) inflammasome activation could also be triggered by TMAO and inflammatory cytokines such as IL-18 and IL-1β released. As such, diet has an important role in affecting the concentration of TMAO levels and the progression of atherosclerosis
[54][55]. Latest studies showed that the use of broad-spectrum antibiotics for 3 to 4 weeks suppressed TMAO levels, ameliorating age-related oxidative stress and arterial dysfunction in mice
[56]. The ability of CAD patients’ microbiota to generate ‘secondary’ bile acids enhanced the variety of the bile acid pool in both feces and serum. Under a high fat diet, this mechanism impeded hepatic bile acid synthesis and resulted in higher blood cholesterol levels. The CAD microbiota enhanced circulatory lipopolysaccharides levels as well as pro-inflammatory cytokine expression, while activating intestinal and systemic T help responses and decreasing Treg cell dispersion
[57]. Finally, the use of probiotics, synbiotics, and probiotic functional products in a study of 90 obese patients with CAD proved beneficial, controlling plasma TMAO and HDL-C levels
[58]. Further studies are needed to evaluate the efficacy of inhibiting various steps of TMAO production for the management atherosclerotic
disease.
disease.