Influence of cholestyramine on synthesis of cholesterol and bile acids in germfree rats

Probiotic interventions promote metabolic health in high fat-fed hamsters in association with gut microbiota and endocannabinoidome alterations

Probiotics represent a promising tool to improve metabolic health, including lipid profiles and cholesterol levels. Modulation of the gut microbiome and the endocannabinoidome - two interrelated systems involved in several metabolic processes influenced by probiotics - has been proposed as a potential mechanism of action. This study establishes the impact of probiotics on metabolic health, gut microbiota composition and endocannabinoidome mediators in an animal model of hypercholesterolaemia. Syrian hamsters were fed either a low-fat low-cholesterol or high-fat high-cholesterol (HFHC) diet to induce hypercholesterolaemia and gavaged for 6 weeks with either Lactobacillus acidophilus CL1285, Lactiplantibacillus plantarum CHOL-200 or a combination of the two. Globally, probiotic interventions ameliorated, at least partially, lipid metabolism in HFHC-fed hamsters. The interventions, especially those including L. acidophilus, modified the gut microbiota composition of the small intestine and caecum in ways suggesting reversal of HFHC-induced dysbiosis. Several associations were observed between changes in gut microbiota composition and endocannabinoidome mediators following probiotic interventions and both systems were also associated with improved metabolic health parameters. For instance, potential connexions between the Eubacteriaceae and Deferribacteraceae families, levels of 2‑palmitoylglycerol, 2‑oleoylglycerol, 2‑linoleoylglycerol or 2‑eicosapentaenoylglycerol and improved lipid profiles were found. Altogether, our results suggest a potential crosstalk between gut microbiota and the endocannabinoidome in driving metabolic benefits associated with probiotics, especially those including L. acidophilus, in an animal model of hypercholesterolaemia.

Interrupting bile-acid handling and lipid and glucose control: Effects of colesevelam on glucose levels

The digestive tract plays a key role in lipid metabolism and in cardiovascular risk through the physiology of bile acids on lipid absorption, enterohepatic recycling of bile acids, and cholesterol oxidation in synthesis of bile acids. Recent evidence associates the activation of farnesoid X receptor by bile acids with alterations in high-density lipoprotein cholesterol, triglyceride metabolism, and glucose metabolism. Bile-acid sequestrants augment cholesterol excretion via enhanced conversion to bile acids to lower low-density lipoprotein cholesterol. Several recent studies have demonstrated a role for the bile-acid sequestrant colesevelam hydrochloride in improving glycemic control as well as lipid profiles in subjects with type 2 diabetes. This work reviews the mechanisms of action of colesevelam hydrochloride in interrupting bile acid reabsorption and in lipid transport and glucose control.

Statins as potential treatment for cholesterol gallstones: an attempt to understand the underlying mechanism of actions

INTRODUCTION

Statin therapy is widely used across the globe for the treatment and prevention of cardiovascular disease (CVD). It is well established that statin therapy is associated with significant decreases in low-density lipoprotein cholesterol (LDL-C) and plasma cholesterol levels. Cholesterol gallstones are a common problem, resulting in hospital admission and surgery, throughout western healthcare systems.

AREAS COVERED

This review describes the mechanisms, and addresses the potential, for statins to be used as a treatment for gallstones. Medline was searched for the risk factors and treatment of cholesterol gallstones.

EXPERT OPINION

Obesity, metabolic syndrome, non-alcoholic fatty liver disease (NAFLD), insulin resistance and high-fat diets (unsaturated fats) rich in cholesterol are all associated risk factors for cholesterol gallstones. In view of the high prevalence of cholesterol gallstones, there is an urgent need to understand whether pharmacological therapies can be harnessed for the treatment of cholesterol gallstones. Gallstones are shown to be associated with an increased risk, not only of mortality, but also of CVD. Statins, widely used in prevention of CVD and hypercholesteremia, have been shown to dissolve cholesterol gallstones in animal models and human studies, highlighting the potential for a pharmacological therapy for gallstones. More studies are required to understand the role of statins in the treatment of gallstones and for comparison with current treatment strategies.

Effect of cholesterol, cholic acid and cholestyramine administration on the intestinal mRNA expressions related to cholesterol and bile acid metabolism in the rat

BACKGROUND AND AIM

To evaluate the importance of cholesterol and bile acid concentrations in the intestinal lumen to cholesterol homeostasis, we investigated the effect of cholesterol-, bile salt- or cholestyramine-administration on the regulation of intestinal mRNA related to cholesterol and bile acid metabolism.

METHODS

Male Wistar rats fed on standard laboratory chow (AIN-93) were allocated into four experimental groups: (i) control group; (ii) cholesterol group (CH), which was fed cholesterol in diet (2% [w/w]) for 14 days; (iii) cholic acid (CA) group, which was fed CA in diet (1% [w/w]) for 14 days; (iv) cholestyramine (CT) group, which was fed CT in diet (5% [w/w]) for 14 days. Blood, liver and small intestine were obtained after 14 days. Serum lipids and bile acids were measured by colorimetric assays, and hepatic and intestinal mRNA relating to lipid and bile acid metabolism was studied by reverse transcription-polymerase chain reaction.

RESULTS

Intestinal ABCG8, liver X receptor alpha, small heterodimer partner (SHP) and sterol regulatory element binding protein 1c (SREBP-1c) mRNA expressions were markedly increased in the CH group. Intestinal multidrug resistance associated protein (MRP) 2 and MRP3 mRNA expressions were markedly increased in the CA group. In the CT group intestinal MRP2, ABCG5, ABCG8, SHP and SREBP-1c mRNA expressions were markedly decreased.

CONCLUSION

The bile acid availability in the intestinal lumen alters the expression of various intestinal mRNA relating to not only bile acid metabolism, but also lipid metabolism. Though the mechanism of the intestinal SHP elevation is unclear, cholesterol feeding may affect the intestinal bile acid metabolism via intestinal SHP expression.

Rationale and design of a prospective clinical trial program to evaluate the glucose-lowering effects of colesevelam HCl in patients with type 2 diabetes mellitus

BACKGROUND

Dyslipidemia and type 2 diabetes mellitus (T2DM) increase atherosclerotic coronary heart disease (CHD) risk. In patients with T2DM, improving lipid parameters reduces CHD risk, while optimizing glucose levels reduces microvascular complications and, possibly, macrovascular disease such as CHD. Unfortunately, many patients with T2DM do not achieve either lipid or glucose treatment targets.

OBJECTIVE

Colesevelam HCl is a specifically engineered bile-acid sequestrant (BAS) indicated to reduce elevated low-density lipoprotein cholesterol concentrations. Earlier studies have demonstrated that BAS not only reduce cholesterol levels, but also lower glucose levels in patients with T2DM. These findings have prompted a robust, prospective phase 3 clinical trial program to further evaluate the safety and tolerability of colesevelam HCl when added to T2DM patients previously treated with metformin, insulin or a sulfonylurea. A limitation of these clinical trials is that none of them assessed colesevelam HCl monotherapy, nor directly compared the glucose-lowering effects of colesevelam HCl to established oral antidiabetes drugs. Nonetheless, this clinical trial program will better determine whether a single agent added to existing diabetes therapy can improve both lipid and glucose parameters in T2DM, which may allow more patients to achieve lipid and glucose treatment targets.

CONCLUSIONS

This phase 3 clinical trial program will evaluate colesevelam's glucose-lowering effects in patients with T2DM. In addition, based upon a review of the relevant medical literature through an online electronic PubMed search (without restriction to date other than otherwise occurs through PubMed), potential mechanisms as to how BAS may lower glucose levels are discussed.

Bile acids reduce SR-BI expression in hepatocytes by a pathway involving FXR/RXR, SHP, and LRH-1

Hepatic SR-BI mediates uptake of circulating cholesterol into liver hepatocytes where a part of the cholesterol is metabolised to bile acids. In the hepatocytes, bile acids reduce their own synthesis by a negative feedback loop to prevent toxic high levels of bile acids. Bile acid-activated FXR/RXR represses expression of CYP7A1, the rate-limiting enzyme during bile acid synthesis, by inducing the expression of SHP, which inhibits LXR/RXR and LRH-1-transactivation of CYP7A1. The present paper presents data indicating that CDCA suppresses SR-BI expression by the same pathway. As previously reported, LRH-1 induces SR-BI promoter activity. Here we show that CDCA or over-expression of SHP inhibit this transactivation. No FXR-response element was identified in the bile acid-responsive region of the SR-BI promoter (-1200bp/-937bp). However, a binding site for LRH-1 was characterised and shown to specifically bind LRH-1. The present study shows that also the SR-BI-mediated supply of cholesterol, the substrate for bile acid synthesis, is feedback regulated by bile acids.

Neuroprotective role of curcumin from curcuma longa on ethanol-induced brain damage

In the present study, curcumin from Curcuma longa was screened for neuroprotective activity using ethanol as a model of brain injury. Oral administration of curcumin to rats caused a significant reversal in lipid peroxidation, brain lipids and produced enhancement of glutathione, a non-enzymic antioxidant in ethanol intoxicated rats, revealing that the antioxidative and hypolipidaemic action of curcumin is-responsible for its protective role against ethanol induced brain injury.

Bile acid synthesis in young and old rats

Bile acid synthesis from orally administered (14)C-cholesterol or from (14)C-mevalonic acid administered intravenously were examined in male and female 2-, 12- and 24-month-old rats. About 5-9% of the '4C-cholesterol administered was recovered as bile acids from the small intestine 3 days after administration. The value in the case of (14)C-mevalonic acid was about 1/10 that of (14)C-cholesterol. Major bile acids were cholic acid and beta-muricholic acid, and the formation ratio of cholic acid increased in aged rats, although no further difference was found between 12- and 24-month-old animals of either sex. Male rats formed more beta-muricholic acid than females at all ages examined. In addition, no significant difference was found in the bile acid composition between both precursors, (14)C-cholesterol and (14)C-mevalonic acid.

Feedback regulation of bile acid synthesis in the rat by dietary vs. intravenous cholate or taurocholate

The regulation of bile acid synthesis was studied (i) in intact or colectomized rats receiving cholate or taurocholate as a dietary supplement and (ii) in experiments using chow-fed animals with a graded intravenous or intraduodenal taurocholate infusion. After the 2-week diet period a bile fistula was established and rates of taurocholate, tauromuricholate and taurochenodeoxycholate secretion were quantitated by high-performance liquid chromatography. During the infusion experiments taurocholate production was calculated from the difference in specific activity of [14C]taurocholate between infusate and bile, whereas tauromuricholate and taurochenodeoxycholate synthesis was derived directly from their secretion rates after pool depletion. Both the 0.5% cholate and taurocholate diet suppressed tauromuricholate and taurochenodeoxycholate secretion nearly totally, but only cholate led to a prolonged inhibition taurocholate synthesis. The diets stimulated total bile acid secretion and expanded the total bile acid pool size 2- to 3-fold, but they also prompted a dramatic increase in the biliary secretion of taurodeoxycholate. In contrast, colectomized animals did not secrete taurodeoxycholate following the cholate diet and, despite a comparable increase in bile acid pool size, tauromuricholate and taurochenodeoxycholate secretion was inhibited to a lesser extent. In addition, the rate of bile acid secretion and synthesis was significantly enhanced when compared to that of intact rats. To determine whether taurocholate affected bile acid synthesis directly, the bile acid was infused intravenously or intraduodenally at varying rates up to 300 mumoles per kg per hr for 54 hr, i.e. a rate exceeding normal total bile acid secretion in these acute bile fistula animals nearly 3-fold.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of Triton WR 1339 and orotic acid on lipid metabolism in rats

In order to investigate the effect of hepatic cholesterol flux on biliary bile acids, Triton WR 1339 and orotic acid were administered to rats, and the biliary cholesterol, phospholipids and bile acids were analyzed together with serum lipoproteins and hepatic lipids. Triton, which raised serum very low density lipoprotein and lipid levels and decreased serum high density lipoprotein liver lipid levels, increase the biliary cholic acid group/chenodeoxycholic acid group ratio (CA/CDCA) in the bile without affecting the total amount of bile acids and the other biliary lipids. Orotic acid, which decreased serum lipid and lipoprotein concentrations and increased liver lipid levels, increased the biliary excretion of cholesterol and phospholipids, but produced no significant change in the total amount of bile acids and in the CA/CDCA ratio in bile.

Effect of cholestyramine on bile acid metabolism in conventional rats

Effects of cholestyramine on biliary secretion of cholesterol, phospholipids and bile acids and fecal excretion of sterols and bile acids were examined in Wistar male rats. Six rats were fed a basal diet, and the other six were fed a basal diet supplemented with 5% cholestyramine for eight days. Bile flow and biliary secretion of bile acids and phospholipids (per hour per rat) decreased with cholestyramine treatment, while biliary cholesterol secretion (per hour per rat) remained unchanged. In the biliary bile acid composition, a marked increase of chenodeoxycholic acid with a concomitant decrease of beta-muricholic acid was observed in cholestyramine-treated rats. Fecal excretion of total sterols and bile acids increased about three- and four-fold, respectively, after cholestyramine treatment. The increase of fecal bile acids derived from cholic acid was more predominant than that derived from chenodeoxycholic acid, resulting in an increase of the cholic acid group/chenodeoxycholic acid group ratio.

Effects of feeding chenodeoxycholic acid on metabolism of cholesterol and bile acids in germ-free rats

The aim of this investigation was to study the influence of chenodeoxycholic acid administration on cholesterol and bile acid synthesis in germ-free rats. Seven rats were fed a basal diet and 2 groups of 4 rats received the same diet supplemented with 0.4 and 1% chenodeoxycholic acid, respectively. After 6 weeks, feces were collected in one 3- and one 4-day pool for analysis of cholesterol and bile acids. When the sampling period was finished, the rats were killed and the liver microsomal fractions isolated. The activities of HMG CoA reductase and cholesterol 7 alpha-hydroxylase were determined, the 7 alpha-hydroxylase by a mass fragmentographic method. The 2 dominating bile acids in the untreated rats were cholic acid and beta-muricholic acid. During treatment with chenodeoxycholic acid, 60--70% of this bile acid was converted into alpha- and beta-muricholic acid, indicating a high activity of the 6 beta-hydroxylase. The excretion of cholic acid was almost completely inhibited and the 7 alpha-hydroxylase activity was decreased ca 75% in the rats fed 1% chenodeoxycholic acid. The activity of the hepatic HMG CoA reductase as unchanged. The fecal excretion of cholesterol increased 2--3 times. An accumulation of cholesterol was seen in the rats treated with 1% chenodeoxycholic acid, which was probably a result of the decreased catabolism of cholesterol to bile acids.

The effect of cholestyramine on bile acid kinetics in healthy controls

Serum lipids and the kinetics of the two primary bile acids, cholic acid (C) and chenodeoxycholic acid (CD), were studied in six normolipidaemic subjects before and during treatment with cholestyramine (12 g/day). After therapy, total serum and low-density lipoprotein cholesterol decreased by about 15%. These changes were accompanied by significant increases in the pool size, synthesis, and fractional turnover rate (FTR) of C and in the synthesis and FTR of CD. In spite of the enhanced formation of CD, the CD pool size decreased in all subjects, on average by more than 50%. The combined pool size of C and CD remained constant, but the mean total bile acid formation increased by a factor of 2.9. It is suggested that the different responses of C and CD, with an augmented contribution of C to the total amounts of bile acid produced, reflect an enhanced hepatic cholesterogenesis and, possibly, that C and CD to some extent originate from different cholesterol precursor pools.