Background and Aims

Elevated low-density lipoprotein (LDL) cholesterol is a causal factor for atherosclerotic cardiovascular disease. Growing evidence suggests a crucial role for the gut microbiome in cholesterol metabolism and cardiovascular health. Here, we examined the influence of the gut microbiota-dependent metabolite proprionic acid (PA) on cholesterol metabolism and its interaction with the intestinal immune system.

Methods and Results

Apolipoprotein E^-/- (ApoE^-/-) mice were fed either a standard chow diet (SCD, n=12) or a high fat diet (HFD, n=23) for 6 weeks. After two weeks mice were treated with either PA (150mM) or control vehicle via daily oral gavage. Assessment of lipoprotein fractions in plasma using fast-performance liquid chromatography revealed reduced total cholesterol (TC) (TC: HFD vs. HFD+PA: 451 ± 119mg/dl vs. 309 ± 70mg/dl, n=10-13, p<0.001) and LDL (LDL: HFD vs. HFD+PA: 184 ± 53.5mg/dl vs. 113 ± 37.2mg/dl, n=10-13, p<0.001) upon PA-treatment. Using qRT-PCR altered gene expression of cholesterol regulating genes (Srebp-2, Npc1l1) in PA-treated mice was observed. Histological staining of the aortic root displayed reduced atherosclerotic lesions upon PA-treatment (HFD vs. HFD+PA: 12.2 ± 2.5% of aortic root area vs. 6.6 ± 2.1% of aortic root area, n=8-11, p<0.001). Furthermore, flow cytometry and cytometric bead assay indicated increased regulatory T-cell numbers and IL-10 levels within the intestinal microenvironment by PA-treatment. Subsequent in vivo blockade of IL-10 receptor signaling by intraperitoneal injection of anti-IL-10 receptor monoclonal antibody in ApoE^-/- mice (n=8) reversed PA-mediated reduction of TC (HFD+PA vs. HFD+PA +anti-IL-10R: 309 ± 70mg/dl vs. 410 ± 50.1mg/dl, n= 8-13, p=0.002) and LDL (HFD+PA vs. HFD+PA + anti-IL-10R: 113 ± 37.2mg/dl vs. 182 ± 23.3mg/dl, n=8-13, p<0.001) in plasma and increased atherosclerotic lesion size in HFD fed mice (HFD+PA vs. HFD+PA +anti-IL-10R: 6.6 ± 2.1% of aortic root area vs. 16.4 ± 5.5% of aortic root area, n=7-11, p<0.001). Additionally, incubation of intestinal epithelial organoids of murine origin with recombinant mouse IL-10 illustrated a dose-dependent downregulation of Npc1l1, a major intestinal cholesterol transporter.

Conclusion

Oral administration of PA reduces LDL levels and atherosclerotic lesion size in hypercholesterolemic (ApoE^-/-) mice. Our findings reveal a regulatory role of PA on intestinal cholesterol absorption via modulation of the intestinal immune system representing a novel concept to treat dyslipidemia and prevent atherosclerotic cardiovascular disease.