Evidence for a nonabsorptive antihypercholesterolemic action of phytosterols in the chicken

7β-Hydroxysitosterol crosses the blood-brain barrier more favored than its substrate sitosterol in ApoE-/- mice

In this study, we compare the distribution of intraperitoneally injected sitosterol, 7β-hydroxysitosterol or vehicle only (control) for 28days in male ApoE-/- mice. Furthermore we examine its impact on surrogate markers of cholesterol biosynthesis and sterol absorption rate in plasma, brain and liver tissues from these animals. Injection of sitosterol revealed a 32.1% (P=0.013) lower plasma total cholesterol compared with control. Cholesterol corrected plasma and absolute brain and liver levels of sitosterol are 4.1-, 1.7-, and 7.2-fold (P<0.001 for all) higher, respectively. This is in accordance with a reduced plasma campesterol to cholesterol ratio (-16.2%; P=0.018) together with a 24.1% (P=0.047) lower concentration of hepatic lathosterol. After injection of 7β-hydroxysitosterol the concentrations of 7β-hydroxysitosterol in plasma, brain and liver are 21.0-, 65.8- and 42.7-fold (P<0.001 for all) higher, respectively, compared with control. Injection of 7β-hydroxysitosterol revealed significantly lower plasma cholesterol corrected cholestanol and campesterol (-44.2%; P=0.001 and -24.5; P=0.004) as well as lower absolute liver cholestanol levels (-31.9%; P<0.001) compared with control. Intraperitoneally injected sitosterol and 7β-hydroxysitosterol differently influence cholesterol metabolism in plasma and liver. We conclude that the polar 7β-hydroxysitosterol compound can pass the blood brain barrier with higher efficacy than its substrate, sitosterol. Though present in higher amounts in the brain, both, sitosterol and 7β-hydroxysitosterol do not influence cholesterol metabolism in the brain as proven by our surrogate markers.

Triglyceride-Lowering Response to Plant Sterol and Stanol Consumption

Phytosterols (PS) have long been recognized for their cholesterol-lowering action, however, recent work has highlighted triglyceride (TG)-lowering responses to PS that may have been overlooked in previous human interventions and mechanistic animal model studies. This review assesses the current state of knowledge regarding the effect of dietary PS supplementation on blood TG concentrations by examining the average therapeutic response, potential mechanisms, and metabolic and genetic factors that may contribute to inter-individual variability. Data from human intervention trials demonstrates that, compared to baseline concentrations, PS supplementation results in a variable TG-lowering response ranging from 0.8 to 28%. It is evident that hypertriglyceridemic individuals (>1.7 mmol/L) have a greater TG-lowering response to PS (11-28%) than subjects with normal plasma TG concentrations (0.8-7%). Although a genetic basis for the variable TG-lowering effects of PS is probable, there are only limited studies to draw on. The available data suggest that polymorphisms in the apolipoprotein E (apoE) gene may affect responsiveness, with PS-induced reductions in TG more readily evident in apoE2 than apoE3 or E4 subjects. Although only a minimal number of animal model studies have been conducted to specifically examine the mechanisms whereby PS may reduce blood TG concentrations, it appears that there may be multiple mechanisms involved including interruption of intestinal fatty acid absorption and modulation of hepatic lipogenesis and very low density lipoprotein packaging and secretion. In summary, the available data suggest that PS may be an effective therapy to lower blood TG, particularly in hypertriglyceridemic individuals. However, before PS can be widely recommended as a TG-lowering therapy, studies that are specifically powered and designed to fully access therapeutic responses and the mechanisms involved are required.

Hepatic nuclear sterol regulatory binding element protein 2 abundance is decreased and that of ABCG5 increased in male hamsters fed plant sterols

The effect of dietary plant sterols on cholesterol homeostasis has been well characterized in the intestine, but how plant sterols affect lipid metabolism in other lipid-rich tissues is not known. Changes in hepatic cholesterol homeostasis in response to high dietary intakes of plant sterols were determined in male golden Syrian hamsters fed hypercholesterolemia-inducing diets with and without 2% plant sterols (wt:wt; Reducol, Forbes Meditech) for 28 d. Plasma and hepatic cholesterol concentrations, cholesterol biosynthesis and absorption, and changes in the expression of sterol response element binding protein 2 (SREBP2) and liver X receptor-beta (LXRbeta) and their target genes were measured. Plant sterol feeding reduced plasma total cholesterol, non-HDL cholesterol, and HDL cholesterol concentrations 43% (P < 0.0001), 60% (P < 0.0001), and 21% (P = 0.001), respectively, compared with controls. Furthermore, there was a 93% reduction (P < 0.0001) in hepatic total cholesterol and >6-fold (P = 0.029) and >2-fold (P < 0.0001) increases in hepatic beta-sitosterol and campesterol concentrations, respectively, in plant sterol-fed hamsters compared with controls. Plant sterol feeding also increased fractional cholesterol synthesis >2-fold (P < 0.03) and decreased cholesterol absorption 83% (P < 0.0001) compared with controls. Plant sterol feeding increased hepatic protein expression of cytosolic (inactive) SREBP2, decreased nuclear (active) SREBP2, and tended to increase LXRbeta (P = 0.06) and ATP binding cassette transporter G5, indicating a differential modulation of the expression of proteins central to cholesterol metabolism. In conclusion, high-dose plant sterol feeding of hamsters changes hepatic protein abundance in favor of cholesterol excretion despite lower hepatic cholesterol concentrations and higher cholesterol fractional synthesis.

From Tryptophan to Hydroxytryptophan: Reflections on a Busy Life

Given the very difficult odyssey of my early years, who could have imagined the incredible and successful journey that constituted my life path after age 13? I was born into a Jewish family in Breslau, Germany, right before the rise of Nazism and Hitler's election. After Kristallnacht, when my father was taken to Buchenwald Concentration Camp, we had to leave Germany as soon as possible. The first opportunity came in May of 1939, when we boarded the SS St. Louis bound for Havana, Cuba. Almost all passengers were denied entrance into Cuba, and the ship had to go back to Europe, where I ended up in France. In December of 1939, during World War II, I was fortunate to be able to leave France. This time I made it to Cuba, where my father was already in residence. A year later, my entire family was allowed into the United States. I took advantage of all the educational resources in this land of opportunity. I graduated valedictorian of my high school class and earned a four-year scholarship to Rutgers University, where I obtained a Bachelor of Science degree. I went on to earn a Master's degree from the University of Connecticut and finally a PhD from the University of Illinois. Within two months after graduating from Illinois, I was hired as an assistant professor of nutritional biochemistry at Rutgers, where I enjoyed a most productive research and teaching career. My PhD research involved tryptophan and niacin metabolism in the chick, and upon arrival at Rutgers I continued amino acid studies with the goal of assessing the essential amino acid requirements for egg production. This research was crowned with success and was followed with amino acid requirement studies for maintenance and for growth in rabbits, and ultimately with a reevaluation of requirements in adult humans. An outgrowth of the maintenance requirements led to a series of investigations into the metabolism of histidine, histamine, and carnosine (a histidine-containing dipeptide). Histamine, we found, plays an important role in wound healing and stress management. Pyridoxal phosphate is the cofactor for the enzyme histidine decarboxylase required for histamine synthesis and similarly serves as a cofactor for hydroxytryptophan decarboxylase, the enzyme that is part of the pathway to serotonin synthesis. Investigations into these pathways led to interesting findings: brain concentrations of serotonin could be increased by supplementing the diet of rats with tryptophan and pyridoxine; the elevated brain serotonin levels had behavioral consequences. Alcohol craving, addiction, and withdrawal symptoms are affected by serotonin concentrations in the brain, and alleviation of these conditions can be achieved with simultaneous administration of serotonin and dopamine agonists. In the midst of our early amino acid studies, we serendipitously also became involved with lipid metabolism in relation to atherosclerosis and blood cholesterol in a chicken model. This work led to the recognition that soluble fibers, like pectin, had strong cholesterol-lowering properties that were beneficial in lowering the incidence of coronary plaque formation. The research success that I have enjoyed has been coupled with the gift of three accomplished children who are making important contributions as professionals in their fields of endeavor. My wife and I are also blessed with 10 wonderful grandchildren, our pride and joy!

New insights into the molecular actions of plant sterols and stanols in cholesterol metabolism

Plant sterols and stanols (phytosterols/phytostanols) are known to reduce serum low-density lipoprotein (LDL)-cholesterol level, and food products containing these plant compounds are widely used as a therapeutic dietary option to reduce plasma cholesterol and atherosclerotic risk. The cholesterol-lowering action of phytosterols/phytostanols is thought to occur, at least in part, through competition with dietary and biliary cholesterol for intestinal absorption in mixed micelles. However, recent evidence suggests that phytosterols/phytostanols may regulate proteins implicated in cholesterol metabolism both in enterocytes and hepatocytes. Important advances in the understanding of intestinal sterol absorption have provided potential molecular targets of phytosterols. An increased activity of ATP-binding cassette transporter A1 (ABCA1) and ABCG5/G8 heterodimer has been proposed as a mechanism underlying the hypocholesterolaemic effect of phytosterols. Conclusive studies using ABCA1 and ABCG5/G8-deficient mice have demonstrated that the phytosterol-mediated inhibition of intestinal cholesterol absorption is independent of these ATP-binding cassette (ABC) transporters. Other reports have proposed a phytosterol/phytostanol action on cholesterol esterification and lipoprotein assembly, cholesterol synthesis and apolipoprotein (apo) B100-containing lipoprotein removal. The accumulation of phytosterols in ABCG5/G8-deficient mice, which develop features of human sitosterolaemia, disrupts cholesterol homeostasis by affecting sterol regulatory element-binding protein (SREBP)-2 processing and liver X receptor (LXR) regulatory pathways. This article reviews the progress to date in studying these effects of phytosterols/phytostanols and the molecular mechanisms involved.

Efficacy and safety of sitosterol in the management of blood cholesterol levels

Elevated levels of plasma LDL cholesterol (LDL-C) represent a major risk factor for cardiovascular disease. Treatments aimed at reducing levels of circulating LDL are regarded, therefore, as cardioprotective. The cholesterol lowering properties of plant sterols have been known for some time and many clinical studies have confirmed the efficacy of sitosterol in lowering plasma LDL-C concentrations. Animal studies have also shown reductions in LDL by sitosterol. The use of animal models has been useful in facilitating the elucidation of specific mechanisms by which this sterol exerts its hypocholesterolemic action. It is well known that plant sterols compete with cholesterol for space within bile salt micelles in the intestinal lumen thereby reducing cholesterol absorption. The understanding of the function of plant sterols in impeding cholesterol absorption has been clarified with the discovery of the adenosine binding cassette transporters, ABCG5/8, involved in the regulation of sterol absorption and secretion into the enterocyte and hepatocyte. Compared to cholesterol and other sterols, sitosterol is preferentially pumped out to the intestinal lumen by the ABCG5/8 transporters. This selective binding of sitosterol to the transporters ultimately results in significant lowering of plasma cholesterol. However, some findings support the hypothesis that plant sterols might be an additional risk factor for coronary heart disease. From the review of these studies, it is apparent that sitosterol is a useful dietary supplement for the lowering of plasma cholesterol. Nevertheless, this plant sterol should be used with caution in certain individuals who have a higher absorption rate of sitosterol.

Phytosterols in the prevention of human pathologies

Coronary heart disease is a major health problem in developed countries. Many studies have shown that elevated serum concentrations of total or low-density-lipoprotein cholesterol (LDL cholesterol) are high risk factors, whereas high concentrations of high-density-lipoprotein cholesterol (HDL cholesterol) or a low LDL to HDL cholesterol ratio may protect against coronary heart disease. Plant sterols and stanols derived from vegetable oils or wood pulp have been shown to lower total and LDL cholesterol levels in humans by inhibiting cholesterol absorption from the intestine. These findings may lead to new therapeutic options to treat hypercholesterolemia. In addition, phytosterols may influence cell growth and apoptosis of tumor cells. However, they can interfere with the absorption of fat soluble vitamins and carotenoids.

Development of novel water-soluble phytostanol analogs: disodium ascorbyl phytostanyl phosphates (FM-VP4): preclinical pharmacology, pharmacokinetics and toxicology

FM-VP4 is a novel inhibitor of cholesterol absorption that has lipid lowering and body weight reducing properties. In vitro and in vivo studies were performed to investigate the lipid-lowering effects, mechanism of action, pharmacokinetics, and toxicity of FM-VP4. FM-VP4 decreased cholesterol accumulation in Caco-2 cells by approximately 50%; its activity appeared to be independent of pancreatic lipase, p-glycoprotein, or cholesterol incorporation in micelles. In animal studies, FM-VP4 was added to the diet or drinking water and the following results were obtained. In gerbils 2% FM-VP4 produced mean 56 and 53% reduction in total cholesterol (TC) after 4 and 8 weeks, respectively. This reduction was entirely due to the loss of the low-density lipoprotein (LDL) pool, which was reduced to undetectable levels at either time point. At 8 weeks, high-density lipoprotein (HDL) concentration had risen by a mean of 34% whereas total triglyceride (TG) concentrations had decreased by a mean of 60%. FM-VP4 also had a profound effect on body weight in these animals. At 8 weeks, the mean body weight was in the 4% FM-VP4 treatment group 25% lower than in the control group. No hepatic or renal toxicity was associated with these changes. In Apo E-deficient mice, after 4- and 8-week treatments FM-VP4 caused a significant decrease in both TC and TG concentrations compared to controls. After 12 weeks, the areas of atherosclerotic lesion involvement in the aortic roots were decreased by a mean of 80% in the 0.5, 1, and 2% FM-VP4 treatment groups compared to controls. Taken together, these results suggest that FM-VP4 is a potential new drug with lipid-lowering and weight loss potential, without apparent toxicity.

Injected phytosterols/stanols suppress plasma cholesterol levels in hamsters

Although plant sterols are known to suppress intestinal cholesterol absorption, whether plasma and hepatic lipid levels are influenced through non-gut related internal mechanisms has not been established. To examine this question 50 male hamsters were divided into 5 groups and fed semi-purified diets containing 20% energy as fat and 0.25% (w/w) cholesterol ad libitum for 60 days. The control group (i) received diet alone, while four additional groups consumed the diet plus one of four equivalent phytosterol mixtures (5 mg/kg/day) given either as (ii) tall oil phytosterols/stanols mixed with diet (oralSA), (iii) tall oil phytosterols/stanols subcutaneously injected (subSA), (iv) soybean oil phytosterols alone mixed with diet (oralSE), or (v) soybean oil subcutaneous injected phytosterols alone (subSE). The control group and both orally supplemented groups also received placebo subcutaneous sham injections. Neither food consumption, body weight, nor liver weight differed across treatment groups. Subcutaneous administration of SA and SE decreased plasma total cholesterol levels by 21% and 23% (p < 0.0001) and non-apolipoprotein-A cholesterol concentrations by 22% and 15% (p < 0.0002), respectively, compared to control. HDL cholesterol and TG concentrations remained unchanged across all groups, except for a decline of 25% (p < 0.0001) in HDL concentration in the subSE group versus control. Plasma campesterol levels were lower (p < 0.05) in the subSA group relative to all other groups. Plasma campesterol:cholesterol and campesterol:sitosterol ratios were, however, higher (p < 0.0001) for both the oral and subSE groups. Hepatic cholesterol levels were higher (p < 0.0001) in the oral and subSE phytosterol groups by 30% and 31%, respectively, relative to control. We conclude that low doses of subcutaneously administered plant sterols reduce circulating cholesterol levels through mechanisms other than inhibiting intestinal cholesterol absorption.

Effects of dietary phytosterols on cholesterol metabolism and atherosclerosis: clinical and experimental evidence

Although plant sterols (phytosterols) and cholesterol have similar chemical structures, they differ markedly in their synthesis, intestinal absorption, and metabolic fate. Phytosterols inhibit intestinal cholesterol absorption, thereby lowering plasma total and low-density lipoprotein (LDL) cholesterol levels. In 16 recently published human studies that used phytosterols to reduce plasma cholesterol levels in a total of 590 subjects, phytosterol therapy was accompanied by an average 10% reduction in total cholesterol and 13% reduction in LDL cholesterol levels. Phytosterols may also affect other aspects of cholesterol metabolism that contribute to their antiatherogenic properties, and may interfere with steroid hormone synthesis. The clinical and biochemical features of hereditary sitosterolemia, as well as its treatment, are reviewed, and the effects of cholestyramine treatment in 12 sitosterolemic subjects are summarized. Finally, new ideas for future research into the role of phytosterols in health and disease are discussed.

Cholesterol-lowering efficacy of a sitostanol-containing phytosterol mixture with a prudent diet in hyperlipidemic men

BACKGROUND

Dietary plant sterols (phytosterols) have been shown to lower plasma lipid concentrations in animals and humans. However, the effect of phytosterol intake from tall oil on cholesterol and phytosterol metabolism has not been assessed in subjects fed precisely controlled diets.

OBJECTIVE

Our objective was to examine the effects of sitostanol-containing phytosterols on plasma lipid and phytosterol concentrations and de novo cholesterol synthesis rate in the context of a controlled diet.

DESIGN

Thirty-two hypercholesterolemic men were fed either a diet of prepared foods alone or a diet containing 1.7 g phytosterols/d for 30 d in a parallel study design.

RESULTS

No overall effects of diet on total cholesterol concentrations were observed, although concentrations were lower with the phytosterol-enriched than with the control diet on day 30 (P < 0.05). LDL-cholesterol concentrations on day 30 had decreased by 8.9% (P < 0.01) and 24.4% (P < 0.001) with the control and phytosterol-enriched diets, respectively. HDL-cholesterol and triacylglycerol concentrations did not change significantly. Moreover, changes in circulating campesterol and beta-sitosterol concentrations were not significantly different between phytosterol-fed and control subjects. In addition, there were no significant differences in fractional (0.091 +/- 0.028 and 0.091 +/- 0.026 pool/d, respectively) or absolute (0.61 +/- 0.24 and 0.65 +/- 0.23 g/d, respectively) synthesis rates of cholesterol observed between control and phytosterol-fed subjects.

CONCLUSION

Addition of blended phytosterols to a prudent North American diet improved plasma LDL-cholesterol concentrations by mechanisms that did not result in significant changes in endogenous cholesterol synthesis in hypercholesterolemic men.

Dietary sitostanol reciprocally influences cholesterol absorption and biosynthesis in hamsters and rabbits

The aim of this study was to examine the efficacy of variable dietary sitostanol (SI) concentrations on cholesterol absorption, synthesis and excretion rates in two animal models. Hamsters and rabbits were fed semi-purified diets supplemented with cholesterol and 1% (w/w) phytosterols containing either 0.007, 0.17, 0.8 or 1% (w/w) SI. The control (0% (w/w) SI) groups consumed the same diets but no phytosterols were added. The dual-isotope plasma ratio of [13C]- and [18O]cholesterol and deuterium incorporation methods were applied to measure simultaneously cholesterol absorption and fractional synthesis, respectively. Plasma total cholesterol levels were lower in rabbits and hamsters fed 0.8 and 1% (w/w) SI, respectively, as compared to their controls. Percent cholesterol absorption was lower (P = 0.03) in hamsters fed 1% (w/w) SI (42.5 +/- 13.3%) than control (65.1 +/- 13.4%). Moreover, cholesterol excretion in the feces was 77 and 57% higher (P = 0.017) in the 1% (w/w) SI- relative to control- and 0.17% (w/w) SI-fed groups, respectively. In rabbits, cholesterol excretion was 64% higher (P = 0.018) in 0.8% (w/w) SI- compared with control-fed groups. Fractional synthesis rate was higher (P = 0.033) in hamsters fed 1% (w/w) SI (0.116 +/- 0.054 pool day(-1)) as compared to control (0.053 +/- 0.034 pool day(-1)). However, cholesterol synthesis rates did not vary among groups fed variable concentrations of SI. In rabbits, percent cholesterol absorption and its fractional synthesis rate varied but did not reach significance. Fractional synthesis rate in hamsters was correlated (r = -0.32, P = 0.03) with percent cholesterol absorption. In conclusion, dietary SI exhibited a dose-dependent action in inhibiting cholesterol absorption while increasing cholesterol excretion and upregulating cholesterogenesis in hamsters resulting in lower circulating lipid levels.

Dietary sitostanol reduces plaque formation but not lecithin cholesterol acyl transferase activity in rabbits

The effects of graded amounts of dietary sitostanol (0.01, 0.2 and 0.8% (w/w)) were examined on plasma lipid-profile, coronary artery plaque development and lecithin:cholesterol acyl transferase activity in male New Zealand White rabbits given semi-purified diets for 10 weeks. All diets provided < 10% energy in the form of fat and contained 0.5% (w/w) cholesterol (C). Rabbits fed the semi-purified diet with 0.8% (w/w) (0.64 g/day) sitostanol had lower plasma total cholesterol (TC) (p = 0.006) (15.2 +/- 4.80 mmol/l) and very low-density lipoprotein-cholesterol (VLDL-C) (p = 0.007) (6.31 +/- 3.11 mmol/l) levels compared to the atherogenic control group (n = 6) (29.6 +/- 5.52 and 17.16 +/- 7.43 mmol/l, respectively). Dietary sitostanol at 0.8% (w/w) depressed plaque accretion in coronary arteries (p = 0.0014) and ascending aorta (p = 0.0004) compared with the atherogenic control, 0.01 and 0.2% (w/w) sitostanol-fed groups. No differences (p = 0.24) in the activity of lecithin:cholesterol acyl transferase (LCAT) were observed across groups, although plasma cholesterol fractional esterification rate was higher (p = 0.004) in the 0.8% (w/w) sitostanol fed animals compared with the atherogenic control. Significant negative correlations were demonstrated between sitostanol intake and plasma TC, LDL-C and VLDL-C levels. Hepatic campesterol levels were correlated (r = 0.3, p = 0.03) with plasma but not hepatic TC concentrations. These results demonstrate that dietary sitostanol at a concentration of 0.8% (w/w) or 0.64 g/day lowered plasma cholesterol levels and depressed atherosclerosis development in rabbits, but did not alter LCAT activity.

Enhanced efficacy of sitostanol-containing versus sitostanol-free phytosterol mixtures in altering lipoprotein cholesterol levels and synthesis in rats

To investigate the action and mechanism of a dietary phytosterol mixture naturally containing sitostanol, derived from tall-oil, on circulating cholesterol and lipoprotein levels, five groups of rats were fed a control elemental diet (group 1), a control elemental diet with 1% cholesterol alone (group 2) or with sitostanol mixtures or a sitostanol-free mixture supplemented at 0.2% (group 3), 0.5% (group 4) or 1% (group 5) of dietary levels. One per cent supplementation of sitostanol (21%) compared with sitostanol-free mixtures decreased (P < 0.02) total serum cholesterol. Dietary sitostanol (16% or 21%) mixture at 1% dietary levels decreased (P < 0.05) low density lipoprotein (LDL) cholesterol and increased (P < 0.05) high density lipoprotein (HDL) cholesterol levels. The decrease of LDL and increase of HDL cholesterol were correlated (P < 0.01) with the level of sitostanol mixture in the diet. Consumption of the sitostanol-containing mixture (1% dietary levels) caused a compensatory increase in cholesterol synthesis as indicated by elevated (P < 0.05) lathosterol/ cholesterol ratios in plasma and hepatic cholesterol fractional synthesis rate (FSR) (P < 0.02). Both sitostanol and sitostanol-free mixtures at 0.5% or 1% dietary intake levels increased plasma campesterol and beta-sitosterol levels, while plasma sitostanol levels were negligible. The absence of sitostanol in plasma and the increase in cholesterol synthesis induced by dietary sitostanol mixtures in addition to elevation of plasma campesterol and beta-sitosterol by sitostanol or sitostanol-free mixtures suggest that sitostanol mixtures effectively modify circulating lipoprotein cholesterol concentrations at the level of the intestine, rather than internally at the level of cholesterogenesis.

Dietary phytosterols: a review of metabolism, benefits and side effects

Most animal and human studies show that phytosterols reduce serum/or plasma total cholesterol and low density lipoprotein (LDL) cholesterol levels. Phytosterols are structurally very similar to cholesterol except that they always contain some substitutions at the C24 position on the sterol side chain. Plasma phytosterol levels in mammalian tissue are normally very low due primarily to poor absorption from the intestine and faster excretion from liver compared to cholesterol. Phytosterols are able to be metabolized in the liver into C21 bile acids via liver other than normal C24 bile acids in mammals. It is generally assumed that cholesterol reduction results directly from inhibition of cholesterol absorption through displacement of cholesterol from micelles. Structure-specific effects of individual phytosterol constituents have recently been shown where saturated phytosterols are more efficient compared to unsaturated compounds in reducing cholesterol levels. In addition, phytosterols produce a wide spectrum of therapeutic effects in animals including anti-tumour properties. Phytosterols have been shown experimentally to inhibit colon cancer development. With regard to toxicity, no obvious side effects of phytosterol have been observed in studies to date, except in individual with phytosterolemia, an inherited lipid disorder. Further characterization of the influence of various phytosterol subcomponents on lipoprotein profiles in humans is required to maximize the usefulness of this non-pharmacological approach to reduction of atherosclerosis in the population.

Effect of sitosterol on the rate-limiting enzymes in cholesterol synthesis and degradation

Attempts were made to develop an animal model for phytosterolemia. Infusion of Intralipid containing 0.2% sitosterol in rats gave circulating levels of sitosterol of about 2.5 mmol/l, which is similar to or higher than those present in patients with untreated phytosterolemia. In addition, the infusions gave serum levels of cholesterol nearly twice those obtained in rats infused with Intralipid alone or Intralipid containing 0.2% cholesterol. The hepatic HMG-CoA reductase activity was unaffected or slightly increased by the sitosterol infusions (not statistically significant). The cholesterol 7 alpha-hydroxylase activity was slightly depressed (ca. 30%). In the case of 7 alpha-hydroxylation of endogenous cholesterol, the depression reached statistical significance (p less than 0.05). The microsomal content of sitosterol in the sitosterol-infused rats was about 30% of that of microsomal cholesterol. The effect of sitosterol on 7 alpha-hydroxylation of cholesterol was investigated by incubations of acetone powder of rat liver microsomes with mixtures of cholesterol and sitosterol. Sitosterol mixed with cholesterol to a composition similar to that found in the above microsomal fraction had a depressing effect on 7 alpha-hydroxylation of cholesterol. This degree of depression was of the same magnitude as that found in the sitosterol infusion experiments. The possibility is discussed that the hypercholesterolemia obtained in the beta-sitosterol-infused rats is due to the inhibitory effect of sitosterol on the cholesterol 7 alpha-hydroxylase.

Effects of soy protein and saponins on serum, tissue and feces steroids in rat

Four groups of rats were fed, for 45 days, one of the following semipurified diets containing sucrose 55% (w/w) and (a) casein 25%, (b) casein 24%, saponins (from Saponaria officinalis) 1%, (c) isolated soy protein 25%, (d) soy protein 24%, saponins 1%. The soy protein diet, compared to the casein one, produced an increase in the fecal excretion of neutral sterols on the 29th and 42nd days, without any modification in the liver, aorta and serum cholesterol concentrations. The effect of soy protein cannot be attributed to its saponin content but other substances associated to soy protein may interfere. With the casein diet, added saponins increased the fecal excretion of neutral sterols and bile acids and decreased liver and aorta cholesterol levels. Serum cholesterol was found unchanged. The effects of saponins were suppressed or greatly reduced with the soy protein diet. These results could be explained by binding of the sterols in insoluble forms.

The distribution of dietary plant sterols in serum lipoproteins and liver subcellular fractions of rats

Rats were fed plant sterols containing campesterol and beta-sitosterol in the differerent proportions, and their distribution in serum lipoproteins and in liver subcellular fractions was determined. In serum lipoproteins, the percentage as well as the concentration of plant sterols increased with the increase in the density of lipoproteins. Thus, high density lipoprotein (HDL) contained the highest and very low density lipoprotein (VLDL), the lowest. Also, there were distinct differences in the ratio of campesterol to sitosterol among lipoproteins, it was the highest in VLDL and lowest in HDL. Quantitatively, more than 75% of campesterol and 80% of sitosterol were carried in HDL; the values were significantly different from those of cholesterol (ca. 70%) in relation to total cholesterol. The distribution of plant sterols in liver subcellular fractions was virtually the same with that of cholesterol. Both nuclei and microsomes contained approximately 40% of total plant sterols.

Effect of dietary factors on serum and egg yolk cholesterol levels of laying hens

Effects of dietary lipid factors (saturated and unsaturated oil, cholesterol and plant sterols) on the serum and egg yolk cholesterol levels of the laying hen were investigated. Single Comb White Leghorn laying hens, at thirty weeks of age, were used in two trials by feeding two basal diets containing 8.0% hydrogenated coconut oil or safflower oil, with or without supplemental cholesterol (1.0%), soysterols (2.0%) or combinations of both. Safflower oil, per se, had a superior property to hydrogenated coconut oil in suppressing cholesterol levels, in both serum and egg yolk. Cholesterol supplementation to the safflower oil basal diet resulted in a significant (P less than 0.01) elevation of serum and egg yolk cholesterol levels, whereas cholesterol in combination with hydrogenated coconut oil did not change the serum level. Cholesterol lowering effect of soysterols was clearly demonstrated in both serum and egg yolk by feeding soysterols alone as well as by feeding soysterols in combination with cholesterol.

The influence of turmeric and curcumin on cholesterol concentration of eggs and tissues

An experiment was conducted in order to study the hypocholesteremic effect of tumeric and its coloring principle namely curcumin both in the presence and absence of dietary cholesterol. Laying hens were used as the experimental animals and they were fed the experimental diets for a duration of 8 weeks. The results of the experiment showed that tumeric or various levels of curcumin had no adverse effect on egg production, egg weight and feed to egg ratio. Moreover tumeric or various levels of curcumin both in the presence and absence of dietary cholesterol did not reduce the fat or cholesterol levels of plasma, liver or the egg yolk. An interesting finding from this experiment was that the egg yolk cholesterol levels of cholesterol fed groups sharply increased at the beginning of the experiment, and thereafter they gradually decreased and tended to approach the normal levels at the termination of the experiment. The possible reasons for variation in egg yolk cholesterol levels of cholesterol-fed groups with time is discussed.

Effect of soy sterols on cholesterol synthesis in the rat

Soy sterols increased the incorporation of acetate into cholesterol by rat liver slices and prevented the depression of cholesterogenesis caused by dietary cholesterol. Acetate incorporation into cholesterol by intestinal slices was not affected by soy sterols but was decreased by cholesterol. The results with liver slices agree with the view that soy sterols, by interfering with the intestinal absorption of cholesterol, prevent the feedback inhibition of hepatic cholesterogenesis.