Timothy P. Carr

A glucomannan and chitosan fiber supplement decreases plasma cholesterol and increases cholesterol excretion in overweight normocholesterolemic humans

Objective: Both chitosan and glucomannan have demonstrated hypocholesterolemic effects. A recent study in rats indicates that the combination of the two is also a potent hypocholesterolemic agent that increases fecal fat excretion. The objective of the present study was to determine the hypocholesterolemic effect of a supplement containing equal amounts of chitosan and glucomannan on blood lipid concentrations and fecal excretion of fat, neutral sterols and bile acids. Methods: Twenty-one overweight normocholesterolemic subjects (11 males and 10 females) were fed 2.4 g/day of a supplement containing equal amounts of chitosan and glucomannan. Prior to taking the supplement (initial period) and after 28 days (final period), blood was drawn for measurement of serum lipids and a three-day fecal sample collected for determination of fat, neutral sterol and bile acid excretion. Subjects maintained their normal dietary and activity patterns during the study. Results: Caloric intake and intake of fat and dietary fiber (excluding the supplement) did not differ between the initial and final periods. Serum total, HDL and LDL cholesterol concentrations were significantly lower (p < 0.05) in the final period compared to the initial period. Serum triacylglycerol concentration did not change between periods. There was a trend towards greater fecal excretion of neutral sterols and bile acids (p = 0.13 and 0.16, respectively) in the final period. However, fecal fat excretion did not differ between periods. Conclusions: Serum cholesterol reduction by a chitosan/glucomannan supplement is likely mediated by increased fecal steroid excretion and is not linked to fat excretion.

Repression of Proinflammatory Gene Expression by Lipid Extract of Nostoc commune var sphaeroides Kützing, a Blue-green Alga, via Inhibition of Nuclear Factor-κB in RAW 264.7 Macrophages

We investigated whether lipid extract from a blue-green alga, N commune, modulates proinflammatory gene expression in RAW 264.7 macrophages. The cells were incubated with N commune lipid extract (0-100 microg/mL) and subsequently activated by LPS (100 ng/mL). Quantitative real-time PCR analysis showed that mRNA abundance of proinflammatory mediators, including TNF-alpha, COX-2, IL-1beta, IL-6, and iNOS, was significantly reduced by N commune lipid extract in a dose-dependent manner. Secretion of TNF-alpha and IL-1beta into cell culture medium was also significantly decreased by N commune lipid extract. Thin-layer chromatography-densitometry analysis showed that N commune lipid extract contained approximately 15% of fatty acids. To determine whether the inhibition of proinflammatory mediator production by N commune lipid extract is primarily conferred by fatty acids in the lipid extract, macrophages were incubated with 100 microg/mL of N commune lipid extract or 15 microg/mL of a fatty acid mixture, which was formulated to reflect the fatty acid composition of N commune lipid extract. The fatty acid mixture significantly reduced RNA abundance of TNF-alpha and COX-2, but to a lesser extent than did the N commune lipid extract, suggesting the presence of additional bioactive compounds with an antiinflammatory property in the lipid extract. As NF-kappaB is a major regulator for the proinflammatory gene expression, we measured its DNA-binding activity. DNA-binding activity of NF-kappaB was significantly reduced by N commune lipid extract. In conclusion, our study suggests that N commune lipid extract represses the expression of proinflammatory genes in RAW 264.7 macrophages, at least in part, by inhibiting the activation of NF-kappaB pathway.

Diet-Induced Alterations of Host Cholesterol Metabolism Are Likely To Affect the Gut Microbiota Composition in Hamsters

ABSTRACT The gastrointestinal microbiota affects the metabolism of the mammalian host and has consequences for health. However, the complexity of gut microbial communities and host metabolic pathways make functional connections difficult to unravel, especially in terms of causation. In this study, we have characterized the fecal microbiota of hamsters whose cholesterol metabolism was extensively modulated by the dietary addition of plant sterol esters (PSE). PSE intake induced dramatic shifts in the fecal microbiota, reducing several bacterial taxa within the families Coriobacteriaceae and Erysipelotrichaceae. The abundance of these taxa displayed remarkably high correlations with host cholesterol metabolites. Most importantly, the associations between several bacterial taxa with fecal and biliary cholesterol excretion showed an almost perfect fit to a sigmoidal nonlinear model of bacterial inhibition, suggesting that host cholesterol excretion can shape microbiota structure through the antibacterial action of cholesterol. In vitro experiments suggested a modest antibacterial effect of cholesterol, and especially of cholesteryl-linoleate, but not plant sterols when included in model bile micelles. The findings obtained in this study are relevant to our understanding of gut microbiota-host lipid metabolism interactions, as they provide the first evidence for a role of cholesterol excreted with the bile as a relevant host factor that modulates the gut microbiota. The findings further suggest that the connections between Coriobacteriaceae and Erysipelotrichaceae and host lipid metabolism, which have been observed in several studies, could be caused by a metabolic phenotype of the host (cholesterol excretion) affecting the gut microbiota.

Sitosterol reduces messenger RNA and protein expression levels of Niemann-Pick C1-like 1 in FHs 74 Int cells

Intake of plant sterols has long been shown to reduce cholesterol absorption and subsequently plasma cholesterol concentrations. Despite competition between plant sterols and cholesterol for incorporation into mixed micelles as a suggested major mechanism for the inhibition of cholesterol absorption by plant sterols, studies exist to support an alternative mechanism. For example, another mechanism may be the action of plant sterols to reduce cholesterol absorption at the cellular level. This study was undertaken to test the hypothesis that plant sterols can modulate the expression of transporters such as Niemann-Pick C1-like 1 (NPC1L1) and scavenger receptor class B, type I (SR-BI) to lower intestinal cholesterol absorption. FHs 74 Int cells, a human small intestine epithelial cell line, were used as a model of enterocytes. The cells were treated with 25alpha-hydroxycholesterol (25 micromol/L) or 250 micromol/L of sitosterol, stigmasterol, and cholesterol for 24 hours to measure genes involved in cholesterol absorption and metabolism by quantitative real-time polymerase chain reaction. 25Alpha-hydroxycholesterol, cholesterol, and sitosterol significantly reduced the messenger RNA (mRNA) expression of NPC1L1 and hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, whereas SR-BI mRNA was not altered by the sterols. Western blot analysis confirmed the reduction in NPC1L1 by sterols. Depletion of cellular cholesterol by mevinolin, a cholesterol synthesis inhibitor, increased NPC1L1 and HMG-CoA reductase mRNA; and repletion of cholesterol abolished the increase. Sitosterol, but not stigmasterol, reduced the mRNA levels of NPC1L1 and HMG-CoA reductase to a similar extent of cholesterol. In conclusion, sitosterol can inhibit the expression of NPC1L1 in the enterocytes, which could be an alternate mechanism for plant sterols to reduce intestinal cholesterol uptake.

Stearate-Enriched Plant Sterol Esters Lower Serum LDL Cholesterol Concentration in Normo- and Hypercholesterolemic Adults

Studies in our laboratory have previously demonstrated in hamsters a superior cholesterol-lowering ability of plant sterol (PS) esters enriched in stearate compared with linoleate. We therefore conducted a randomized, double-blind, 2-group parallel, placebo-controlled study to test the cholesterol-lowering properties of stearate-enriched PS esters in normo- and hypercholesterolemic adults. Thirty-two adults, 16 per group with equal number of males and females in each group, participated in the 4-wk study. Participants consumed 3 g/d (1 g three times per day with meals) of either PS esters or placebo delivered in capsules. Serum LDL cholesterol concentration significantly decreased 0.42 mmol/L (11%) and the LDL:HDL cholesterol ratio decreased 10% with PS ester supplementation, whereas LDL particle size and lipoprotein subclass particle concentrations (as measured by NMR) were not affected. The percent change in LDL cholesterol was positively correlated with baseline lathosterol concentration (r = 0.729; P = 0.0014), indicating an association between the magnitude of LDL change and the rate of whole-body cholesterol synthesis. Serum campesterol (but not sitosterol) concentration significantly increased in the PS ester group. Serum tocopherol, retinol, and beta-carotene concentrations were not affected by PS ester supplementation. Thus, our findings demonstrate the usefulness of a novel stearate-enriched PS ester compound in decreasing LDL cholesterol in both normo- and hypercholesterolemic adults. The extent to which PS ester fatty acid composition affects intestinal micelle formation and cholesterol absorption in humans requires further study.

Plant sterol and stanol substrate specificity of pancreatic cholesterol esterase.

Consumption of plant sterols or stanols (collectively referred to as phytosterols) and their esters results in decreased low-density lipoprotein cholesterol, which is associated with decreased atherosclerotic risk. The mechanisms by which phytosterols impart their effects, however, are incompletely characterized. The objective of the present study is to determine if pancreatic cholesterol esterase (PCE; EC 3.1.1.13), the enzyme primarily responsible for cholesterol ester hydrolysis in the digestive tract, is capable of hydrolyzing various phytosterol esters and to compare the rates of sterol ester hydrolysis in vitro. We found that PCE hydrolyzes palmitate, oleate and stearate esters of cholesterol, stigmasterol, stigmastanol and sitosterol. Furthermore, we found that the rate of hydrolysis was dependent on both the sterol and the fatty acid moieties in the following order of rates of hydrolysis: cholesterol>(sitosterol=stigmastanol)>stigmasterol; oleate>(palmitate=stearate). The addition of free phytosterols to the system did not change hydrolytic activity of PCE, while addition of palmitate, oleate or stearate increased activity. Thus, PCE may play an important but discriminatory role in vivo in the liberation of free phytosterols to compete with cholesterol for micellar solubilization and absorption.

Plant sterols alter bile acid metabolism and reduce cholesterol absorption in hamsters fed a beef-based diet

This study examined the cholesterol-lowering properties of dietary plants sterols (PS) when consumed in a beef-based diet. Male Syrian hamsters were fed freeze-dried ground beef supplemented with maltodextrin, vegetable oil, vitamins, minerals, and soybean sterol esters at 0.0, 0.3, 1.0, or 3.0% sterol by weight of the diet. After 4 weeks, plasma and liver total cholesterol concentrations were significantly and incrementally reduced at all levels of dietary PS tested compared to no dietary PS. Cholesterol absorption was also significantly reduced by dietary PS, resulting in greater fecal excretion of neutral steroids. Total bile acid excretion was also significantly increased with PS feeding. A novel finding in the present study was that PS feeding caused an alteration in the gallbladder bile acid profile, resulting in a significantly lower hydrophobicity index. The present study demonstrates that the consumption of ground beef containing PS can significantly lower plasma cholesterol concentration at relatively low doses, indicating that ground beef can be used as a functional food to lower cholesterol while providing superior nutritional benefits over the high fat PS-containing margarines and salad dressings currently available.

Food Components that Reduce Cholesterol Absorption

Publisher Summary This chapter focuses on the compounds that are known to lower plasma cholesterol by inhibiting cholesterol absorption in the small intestine, including plant sterols and stanols, soluble fibers, saponins, soy protein, phospholipids (SM and PC), and stearic acid. All of these compounds—except, perhaps, stearic acid—appear to exert their effects mainly by interfering with micellar solubilization of cholesterol within the intestinal lumen. This can be the result of displacing cholesterol from the micelle, binding or precipitating cholesterol, impeding the movement of cholesterol by forming a viscous matrix, inhibiting digestive enzymes, binding bile acids and decreasing their participation in micelle formation, or down regulating cholesterol transporters within the enterocyte. Stearic acid appears to work systemically by incorporating into hepatic and biliary phospholipids, which destabilizes micelles and reduces cholesterol solubility. These compounds are attractive to food and nutraceutical companies because, in most cases, they are regulated as foods and not drugs.

Raising intestinal contents viscosity leads to greater excretion of neutral steroids but not bile acids in hamsters and rats

To examine the effect of intestinal contents viscosity on fecal steroid excretion independent of colonic fermentation, hamsters and rats were fed cholesterol-containing diets containing either cellulose or different viscosity grades of hydroxypropyl methylcellulose (HPMC), a non-fermentable fiber, as the dietary fiber source. HPMC feeding relative to cellulose significantly lowered plasma cholesterol in hamsters and liver cholesterol in rats. Fecal neutral steroid excretion was significantly greater in both species consuming HPMC compared to cellulose. Fecal bile acid excretion was not altered in hamsters, but was reduced in rats fed HPMC compared to cellulose. Thus, greater intestinal contents supernatant viscosity results in reduced plasma (hamster) or liver (rat) cholesterol and greater neutral steroid excretion, whereas bile acid excretion is unaffected or reduced. This suggests that viscosity is the principal characteristic of dietary fiber responsible for cholesterol lowering, and that this effect is due to increased excretion of cholesterol from the body.

Cholesterol-lowering phytosterols: factors affecting their use and efficacy

Phytosterols are essential components of plant cells and therefore naturally present in the human diet. When used therapeutically, phytosterols can significantly lower serum cholesterol con- centrations. Meta-analyses of clinical trials indicate about 10% reduction of low-density lipoprotein cholesterol when phytosterols are consumed at the recommended dose of 2 g/d. Thus, phytosterols can be an important part of an overall dietary strategy to manage cholesterol levels, particularly for patients who cannot tolerate cholesterol-lowering drugs. Although other health benefits have been attributed to phytosterols, including anti-inflammatory, anticancer, and immune regulatory effects, this review will focus on the therapeutic use of phytosterols related to serum cholesterol, their mechanisms of action, and the various types of phytosterols available to consumers.