Abstract
Atherosclerosis (AS) is closely associated with abnormally chronic low-grade inflammation and gut dysbiosis. Flaxseed oil (FO) rich in omega-3 polyunsaturated fatty acids (PUFAs), which are mainly composed of alpha-linolenic acid (ALA, 18:3 omega-3), has been demonstrated to exhibit pleiotropic benefits in chronic metabolic diseases. However, the impact of dietary ALA-rich FO on AS and its associated underlying mechanisms remain poorly understood. Thus, the present study was designed as two phases to investigate the effects in atherosclerotic Apolipoprotein E (ApoE)-/- mice. In the initial portion, the ApoE -/- mice were randomly allocated to three groups: control group (CON), model group (MOD), and FO-fed model group (MOD/FO) and were treated for 12 weeks. The second phase used antibiotic (AB)-treated ApoE -/- mice were divided into two groups: AB-treated model group (AB/MOD) and FO-fed AB-treated model group (AB/FO). In the results, the dietary ALA-rich FO administration ameliorated atherosclerotic lesion, as well as the parameters of AS (body weights (BWs) and the total bile acids (TBA). Chronic systemic/vascular inflammatory cytokines and in situ macrophages (Mψs) were reduced with FO intervention. In addition, the FO improved the gut integrity and permeability by decreasing the plasma lipopolysaccharide (LPS). Moreover, gut dysbiosis and metabolites [short-chain fatty acids (SCFAs) and bile acids (BAs)] in AS were modulated after FO treatment. Intriguingly, during an AB-treated condition, a significantly weakened amelioration of FO-treated on AS proposed that the intestinal microbiota contributed to the FO effects. A correlation analysis showed close relationships among gut bacteria, metabolites, and inflammation. Collectively, these results suggested that the dietary ALA-rich FO ameliorated the AS in ApoE -/- mice via the gut microbiota-inflammation-artery axis.
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Key Points
Chronic inflammation has been involved in the occurrence and the development of AS. During the pathological injury of AS, a variety of pro-inflammatory cytokines, including the tumor necrosis factor (TNF)-α, the interleukin (IL)-1β, and IL-6 were increased. A Toll-like receptor (Tlr4)−/− and/or myeloid differentiation factor (Myd)88−/− have declined the production of inflammatory cytokines in Apolipoprotein E (ApoE)−/− mice, thereby reducing the formation of aortic plaque. Furthermore, inflammation was attenuated by inhibiting the Jun N-terminal kinase (JNK) and the nuclear factor kappa-B (NF-κB) pathways in atherosclerotic LDL−/− mice. Clinical studies have shown a significantly increased inflammation in the AS lesion. This study was aimed to investigate the effectiveness of the dietary ALA-rich FO on the occurrence and the development of AS in ApoE−/− mice, with or without gut microbiota, which may potentially contribute to the further understanding of complicated mechanisms among AS, gut microbiota, and inflammation.
In this study, the phyla Bacteriodetes and Firmicutes were kept predominantly in diverse groups, which are paralleled with previous studies. An increase in Firmicutes/Bacteriodetes ratio is closely related to chronic metabolic diseases. In this study, the increased ratio of Firmicutes/Bacteriodetes in AS was rectified by the dietary FO administration, suggesting that FO could markedly modulate the gut microbiota by decreasing the predominant Firmicutes/Bacteriodetes in phylum level. At the genus level, the reduced intestinal bacteria after the FO administration, including Anaerotruncus, Enterorhabdus, Lachnoclostridium, Negativibacillus, and Bilophila, were Gram-negative bacteria and anaerobic bacteria, which were closely related to the production of LPS. The improvement of FO intervention on AS may be due to the rectification of gut dysbiosis. In order to determine the crucial role of gut microbiota in the effectiveness of FO on the development of AS, the AB cocktails were used to eliminate the effect of gut microbiota in ApoE−/− mice. After 3 weeks of AB cocktails, gut microflora was found with difficulty by 16S rRNA sequencing, demonstrating that mimic germ-free mice were successfully established. During the subsequent 12 weeks of treatments in diverse groups, a significantly weakened amelioration of dietary FO treatment on AS suggested that intestinal microbiota contributed to the FO effectiveness. This study highlighted that the dietary ALA-rich FO mainly ameliorated the HFD-induced AS via gut microbiota-inflammation-artery axis in ApoE−/− mice, which potentially served as the inexpensive interventions for the prevention and treatment of the disease.