Abstract
BackgroundBile acids play a pivotal role in cholesterol metabolism via the enterohepatic circulation. This study investigated the effects of medium-chain triglycerides (MCTs)/medium-chain fatty acids (MCFAs) on the reduction of bile acid absorption in the small intestine and the mechanisms of action in vivo and partially verified in vitro.MethodsThirty-six C57BL/6 J mice with hypercholesterolaemia were randomly divided into 3 groups: fed a cholesterol-rich diet (CR group), fed a cholesterol-rich and medium-chain triglyceride diet (CR-MCT group) and fed a cholesterol-rich and long-chain triglyceride diet (CR-LCT group). Body weights and blood lipid profiles were measured in all groups after 16 weeks of treatment. The concentrations of bile acids in bile and faeces were analysed using HPLC-MS (high-performance liquid chromatography-mass spectrometry). Gene transcription and the expression levels associated with bile acid absorption in the small intestines were determined using real-time PCR and Western blot. Ileal bile acid binding protein (I-BABP) was analysed using immunofluorescence. The effects of MCFAs on the permeability of bile acid (cholic acid, CA) in Caco-2 cell monolayers and I-BABP expression levels in Caco-2 cells treated with caprylic acid (C8:0), capric acid (C10:0), stearic acid (C18:0) and oleic acid (C18:1) were determined.ResultsMice in the CR-MCT group exhibited lower body weights and serum total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) levels and a higher HDL-C/LDL-C ratio than the CR-LCT group (P < 0.05). The concentrations of primary bile acids (primarily CA) and secondary bile acids in faeces and secondary bile acids in bile in the CR-MCT group were significantly higher than in the CR-LCT group (P < 0.05). C8:0 and C10:0 decreased the permeability of CA in Caco-2 cell monolayers. MCT/MCFAs (C8:0 and C10:0) inhibited I-BABP gene expression in the small intestines and Caco-2 cells (P < 0.05).ConclusionsMCT slowed the body weight increase and promoted the excretion of bile acids. MCT lowered serum cholesterol levels at least partially via reduction of bile acid absorption in the small intestine by inhibition of I-BABP expression. Our results provide the basis for clinical trials of MCT as a dietary supplement for lowering plasma cholesterol and reducing risk of CHD.
Highlights
Bile acids play a pivotal role in cholesterol metabolism via the enterohepatic circulation
Effects of medium-chain triglycerides (MCTs) on body weight and blood lipid profiles No significant differences in body weight were observed between the cholesterolrich and medium-chain triglyceride (CR-MCT), cholesterol-rich and long-chain triglyceride (CR-Long-chain triglycerides (LCTs)) and CR groups prior to
Some previous investigations reported that MCTs/medium-chain fatty acids (MCFAs) were beneficial in lipid metabolism and some diseases (e.g., cardiovascular diseases (CVDs) and Alzheimer’s disease) [14,15,16,17,18,19]
Summary
High blood cholesterol is a crucial risk factor for CVDs [1]. Bile acids play a pivotal role in cholesterol metabolism via the enterohepatic circulation. Bile acids are converted from cholesterol in liver cells, and 90%–95% of bile acids are reabsorbed into the intestinal epithelial cells at the end of the ileum and transported to the blood circulation to re-enter liver cells. Approximately 5% of bile acids in the intestine are excreted in the stool. The physiological significance of enterohepatic circulation of bile acids is to make the limited bile acid reusable for maintaining cholesterol homeostasis, and to facilitate the elimination of excess cholesterol from the body [3]
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