Berberine and plant stanols synergistically inhibit cholesterol absorption in hamsters
Introduction
Berberine (BBR) has been used for thousands of years as a traditional herbal medicine to treat bacterial infection, gastro-intestinal disorders, and many other illnesses, with no toxic effects reported to date in a body of preclinical and clinical studies [1], [2], [3], [4]. Recently, interest in understanding the cardiovascular protective effects of BBR appears to be mounting [3], [5]. The cholesterol-lowering properties of BBR have been observed in human and animal studies [3], [6], with an efficacy that is comparable or greater than most of the current natural products [7], [8], [9] but moderate compared to statin drugs [10]. The cholesterol-lowering mechanism of BBR is not yet fully elucidated. It is reported that BBR increases LDL-receptor (LDLR) expression in the liver [3], [5]. A few studies have demonstrated that BBR increases bile formation and secretion [11], [12], [13]. In dogs with a ligatured bile duct, BBR at doses of 0.001–1 g kg−1 considerably increased bile formation [13]. Intravenous injection of 10 mg kg−1 BBR in dogs increased bile flow and the output of bile acids [12]. It has also been shown that BBR is able to interact with micelles through hydrophilic and hydrophobic binding sites to form alkaloid–bile salt agglomerates [14], [15], which is thought to decrease the capacity of micelles to solubilize cholesterol and thus affects cholesterol absorption. However, the effect of BBR on cholesterol absorption has not been studied. It is important to investigate the effect of BBR on multiple cholesterol metabolic pathways, leading to a better understanding of mechanisms by which BBR lowers blood cholesterol. In addition, it is of great interest to determine whether BBR can be used in combination with other natural compounds, which lower cholesterol through different mechanisms, thereby acting additively or synergistically to improve cholesterol-lowering efficacy.
Regarding this notion, phytosterols are promising agents, which lower plasma cholesterol levels via decreasing cholesterol solubilisation in micelles by competing with cholesterol and thus inhibiting cholesterol absorption in the small intestine [7], [16]. Phytosterols are widely used in the management of patients with hyperlipidemia and many studies have consistently shown a moderate effect on plasma cholesterol [16], [17]. In a recent study [18], we investigated the effect of BBR and plant stanols (PS) alone and in combination on plasma cholesterol levels in rats of diet-induced hypercholesterolemia. BBR slightly, but not significantly, reduced plasma cholesterol, while PS showed a significant cholesterol-lowering effect. However, when administrated in combination, BBR and PS markedly and synergistically lowered plasma cholesterol. The objective of the present study was to determine the effect of BBR and its combination with PS on plasma cholesterol in a different animal model—diet-induced hypercholesterolemic hamsters, which are regarded as a good correlate for human cholesterol metabolism [19]. In addition, we have investigated the underlying mechanisms by focusing on multi-metabolic pathways of cholesterol homeostasis including absorption, synthesis, LDLR-mediated liver clearance of LDL-cholesterol (LDL-C), and the expression of genes related to bile acid synthesis in the liver and to sterol transport in the small intestine.
Section snippets
Animals and diets
Sixty male Golden Syrian hamsters (Charles River Laboratories, Montreal, QC, Canada), weighing 100–120 g, were housed one per cage with a 12 h light:dark cycle. Hamsters were fed a regular rodent chow containing 23% protein, 4.5% fat and 6.8% fibre (Agribrands Purina Canada, Woodstock, Canada), with free access to food and water. After 2 wk of adaptation, hamsters were weighed and randomly divided into 4 groups (n = 15/group). Control hamsters (CT) were given a semi-purified
Effect of BBR and PS on body weight and food intake
During the 4-wk study period, no animals died or were excluded. There were no treatment effects on food intake during the first 3 wk of the study. In week 4, animals supplemented with BBR had lower food intake (5.58 ± 0.14 g d−1) as compared with controls (6.25 ± 0.17 g d−1, p < 0.05) and those supplemented with PS (6.30 ± 0.16 g d−1, p < 0.01), yet did not differ from those treated with BBRPS (5.70 ± 0.13 g d−1). There were no differences between the BBRPS and control groups. The weekly body weights were not
Discussion
Cholesterol homeostasis is affected by several factors in different metabolic pathways that involve absorption, synthesis, clearance and excretion. The small intestine plays a critical role in regulating circulating cholesterol levels through affecting cholesterol absorption. An inhibition of intestinal absorption results in lower levels of circulating cholesterol [7], [33]. In line with previous studies [7], [24], PS showed a significant cholesterol-lowering effect through inhibiting
Acknowledgements
This research was supported by the National Research Council Canada—Institute for Nutrisciences and Health (NRC-INH), Charlottetown, PE, Canada. The authors appreciate Mr. Stephen Locke for his technical assistance in the use of stable isotope ratio mass spectrometer (IRMS). The authors thank Dr. Gen Wang and Mr. Aleks Spurmanis, at the NRC-INH for their assistance in animal sacrifice and tissue collection. Our thanks are also extended to Mr. Len Ward at the Canadian Food Inspection Agency,
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