Serum noncholesterol sterols related to cholesterol metabolism in familial hypercholesterolemia

Serum cholesterol precursor levels and plant sterol were related to parameters of cholesterol metabolism in 22 patients with heterozygous familial hypercholesterolemia. The serum levels of cholesterol precursor sterols were inversely related to fractional absorption of dietary cholesterol and subsequently positively to overall cholesterol synthesis. The serum plant sterol levels, on the contrary, were significantly associated with fractional cholesterol absorption and negatively with overall cholesterol synthesis. These results were confirmed also with multivariate analyses. Fecal lanosterol, a cholesterol precursor, was related positively to cholesterol synthesis measured by sterol balance and serum precursors and negatively to serum plant sterols. The serum precursor and plant sterol levels were inversely significantly related to each other, indicating that the higher cholesterol absorption efficiency the higher are the serum plant sterol levels and the lower the precursor sterol contents and the overall cholesterol synthesis.     

Immunomodulation by statins: inhibition of cholesterol vs. isoprenoid biosynthesis.

Due to their ability to inhibit the synthesis of cholesterol, statins are widely used in medical practice and are the principal therapy for hypercholesterolemia. In addition, various findings suggest that statins also exert anti-inflammatory properties and may so play a role in modulating the immune system. Because of these properties, statins could provide a potential treatment for various chronic inflammatory diseases, including neuroinflammatory disorders such as multiple sclerosis. Here, we will review the effect of statins on the expression and function of a variety of immune relevant molecules and the underlying mechanisms that contribute to the immunomodulatory properties of statins. In this discussion we will also evaluate the effects of statins on central nervous system cells to emphasize the potential of these agents in the treatment of neuroinflammatory disorders.     

Disruption of cholesterol homeostasis by plant sterols

The ABC transporters ABCG5 and ABCG8 limit absorption and promote excretion of dietary plant sterols. It is not known why plant sterols are so assiduously excluded from the body. Here we show that accumulation of plant sterols in mice lacking ABCG5 and ABCG8 (G5G8-/- mice) profoundly perturbs cholesterol homeostasis in the adrenal gland. The adrenal glands of the G5G8-/- mice were grossly abnormal in appearance (brown, not white) due to a 91% reduction in cholesterol content. Despite the very low cholesterol levels, there was no compensatory increase in cholesterol synthesis or in lipoprotein receptor expression. Moreover, levels of ABCA1, which mediates sterol efflux, were increased 10-fold in the G5G8-/- adrenals. Adrenal cholesterol levels returned to near-normal levels in mice treated with ezetimibe, which blocks phytosterol absorption. To determine which plant sterol(s) caused the metabolic changes, we examined the effects of individual plant sterols on cholesterol metabolism in cultured adrenal cells. Addition of stigmasterol, but not sitosterol, inhibited SREBP-2 processing and reduced cholesterol synthesis. Stigmasterol also activated the liver X receptor in a cell-based reporter assay. These data indicate that selected dietary plant sterols disrupt cholesterol homeostasis by affecting two critical regulatory pathways of lipid metabolism.     

Reduction of excess cholesterol in the rabbit aorta by inhibition of endogenous cholesterol synthesis

Hepatic cholesterol synthesis in rabbits, as measured by the incorporation of C¹⁴-labelled acetate, was inhibited by addition of non-toxic amounts of vanadyl sulfate (0.05 per cent VOSO₄·2H₂O) to the diet. This diet reduced excess aortic cholesterol in cholesterol prefed rabbits when fed during the 6 weeks immediately following a 4 week period of cholesterol feeding.     

Serum plant sterols and lathosterol related to cholesterol absorption in coeliac disease

The concentrations of the plant sterols, campesterol and beta-sitosterol in serum, normally correlate with the efficiency of cholesterol absorption, whereas the concentration of lathosterol, a cholesterol precursor sterol, closely parallels changes in cholesterol synthesis. In this study we explored whether the plant sterol concentrations in serum in coeliac disease are determined by cholesterol absorption and whether they alone or with the serum lathosterol concentration, could be used for screening the activity of coeliac disease. In six patients the plant sterol concentrations in serum were significantly lower than in 17 control subjects, the reduction being more marked for campesterol than for beta-sitosterol: the serum lathosterol concentration was significantly higher than in the control subjects. The opposite changes in serum plant sterols and lathosterol were recorded in patients on a gluten-free diet. The plant sterol concentrations in serum (nmol/mg of cholesterol) were positively correlated with each other, and with the percentage absorption of cholesterol and with xylose absorption; they were negatively correlated with faecal fat, but not with faecal plant sterols. Thus, the low plant sterol concentrations in serum in coeliac disease were attributable to their impaired absorption, which in turn was closely associated with the absorption of cholesterol. The serum campesterol concentration clearly distinguished the untreated patients from the controls, whereas the use of serum beta-sitosterol, and the serum ratios of lathosterol/plant sterol resulted in some overlapping with the controls. It is suggested that the plant sterols in serum might be worth of determining when screening patients for coeliac disease and especially when testing their adherence to the gluten-free diet.     

Assay of plant sterols by use of cholesterol oxidase.

The cholesterol esterase/cholesterol oxidase enzyme kit can be used for analysis of plant sterols. The results are comparable to those obtained by conventional colorimetric analysis.     

Removal of intravenous Intralipid in patients with familial hypercholesterolemia during inhibition of cholesterol absorption and synthesis

BACKGROUND: While plant stanols are known to upregulate low density lipoprotein (LDL) receptors, we studied the effects of plant stanol (STA) and sterol (STE) ester spreads on triglyceride-rich lipoprotein (TRL) removal in statin-treated patients with familial hypercholesterolemia (FH) using intravenous Intralipid-squalene fat tolerance test. METHODS: Five patients consumed STA and STE in a randomized, crossover study for 4 weeks. TRL removal was studied at baseline and at the end of both periods. Serum, chylomicron (CM), and very low density lipoprotein lipids, squalene, and plant sterols were measured. RESULTS: LDL cholesterol was decreased by both spreads (15-16%, p<0.05). Plant sterol concentrations were doubled in serum and CM by STE vs. STA. After the injection of Intralipid, CM squalene and sitosterol, but not triglycerides (TG), reached higher peak levels (and area under the incremental curve (AUIC) of squalene) by both spreads than at baseline. Despite different plant sterol concentrations by STE vs. STA, the incremental curves for plant sterols were similar by the spreads. CONCLUSIONS: Despite the retarded removal of TRL lipids by STA and STE in the statin-treated subjects with FH, improvement of the fasting lipid profile was suggested important in consideration of combination of cholesterol absorption inhibitor with statins even in FH.     

Serum cholesterol determination by gas-liquid chromatography

A gas-liquid chromatographic (GLC) method adapted from Schmit and Mater is described for the measurement of total and free cholesterol in serum. The method has been found to be simple, sensitive and precise. The results have been compared with the colorimetric method of Carr and Drekter for total cholesterol and the method of Sperry and Webb for free cholesterol. For total cholesterol lower values were obtained by the GLC method both in sera from patients without signs of liver disease and in sera with high total bilirubin. There was a tendency for somewhat higher values for free cholesterol by the GLC method than by the colorimetric method. This difference was not significant. The present study has demonstrated that the GLC method for total and free cholesterol determination is more specific than colorimetric methods. Gas-liquid chromatography should be given consideration as a reference method for the estimation of free cholesterol and total cholesterol.     

Serum cholesterol determination by mass fragmentography

A highly sensitive and accurate reference method for estimation of total cholesterol in serum is described. A fixed amount of [2,2,3,4-²H₄] cholesterol is added to a fixed amount of serum (usually corresponding to 10 μl). After saponification and extraction with hexane, the amount of unlabelled cholesterol is determined from the ratio between the recordings at m/e 386 and m/e 389 obtained after analysis with a mass spectrometer equipped with an MID (multiple ion detector) unit. The relative standard deviation of the method is about 1.3%. The method was compared with the Liebermann—Burchard method using sera with a range of cholesterol levels. The method can be used for determination of cholesterol down to a level of 10 pmoles (4 ng).     

Plasma cholesterol and endogenous cholesterol synthesis during refeeding in anorexia nervosa

Normal or high levels of cholesterol have been measured in patients with anorexia nervosa (AN). Given that cholesterol intake in AN is usually very low, the reasons for this anomaly are not clearly understood. We studied lipid and lipoprotein profiles and endogenous cholesterol synthesis, estimated by serum lathosterol, in a population of 14 girls with AN, before and during a period of 30 days refeeding. The initial body mass index (BMI) of the patients was 13.41+/-1.62 kg/m(2). No changes were observed during refeeding in endocrine parameters (ACTH, cortisol and estradiol). At Day 0 the lipids data measured here showed normal levels of triglycerides, and total cholesterol at the upper limits of the normal range (5.44+/-1 mmol/l). At this time, total and LDL cholesterol were negatively correlated with transthyretin and BMI. Serum lathosterol (a precursor in cholesterol synthesis pathway) increased significantly (5.99+/-1.75 (Day 0) vs. 8.39+/-2.96 (Day 30); P=0.02) while there was a significant decrease in apo B (0.79+/-0.33 (Day 0) vs. 0. 60+/-0.17 g/l (Day 30), P=0.02) with refeeding. Thus, patients with initial high cholesterol levels have the worst nutritional status and high cholesterol levels are not related to a de novo synthesis. This profile returns to normal with refeeding. An increase of cellular cholesterol uptake may be responsible for this apparently paradoxical evolution with increase of cholesterol synthesis and decrease of apo B during renutrition.     

Stroke risk, cholesterol and statins.

The natural statins should be used as first line agents in the prevention of stroke. The effects of the synthetic statins on the prevention of coronary events and stroke have not been reported at this time. The National Stroke Association's Stroke Prevention Advisory Board has prepared a consensus statement on risk reducing intervention. The Board identified hypertension, MI, atrial fibrillation, hyperlipidemia and asymptomatic carotid artery stenosis (60% to 99% occlusion) as proven stroke risk factors. The Board's recommendations for the prevention of a first stroke are: 1. Hypertension should be treated with lifestyle, pharmacologic and multidisciplinary management strategies. 2. Aspirin post MI and warfarin (international normalized ratio, 2 to 3) for patients with atrial fibrillation, left ventricular thrombus or significant left ventricular dysfunction. Statin agents should be used post MI. 3. Atrial fibrillation patients age 75 or older should be treated with warfarin. Younger patients 65 to 75 with atrial fibrillation and risk factors should be treated with warfarin [corrected]. Younger patients 65 to 75 with atrial fibrillation without risk factors should be treated with warfarin or aspirin [corrected]. 4. Patients with hyperlipidemia and coronary artery disease should be on statin agents. 5. Carotid endarterectomy is recommended for asymptomatic carotid stenosis (60% to 99%) when surgical morbidity and mortality are less than 3%. 6. Adherence to a low-fat diet, smoking avoidance, mild alcohol use, and physical activity should follow published guidelines.     

Contributions of other sterols to the estimation of cholesterol.

The responses of 5alpha-cholestan-3beta-ol, 5alpha-cholest-7-ene-3beta-ol and cholesta-5,7-dien-3beta-ol, normally found in human serum, were examined by: (1) the Liebermann-Burchard reaction, (2) the Zak (ferric chloride) reaction, (3) an enzymatic cholesterol method monitored by estimating the amount of hydrogen peroxide produced, (4) an enzymatic cholesterol method monitored by observing the change in absorbance at 240 nm, and (5) gas chromatography. The results show that none of these methods is specific for cholesterol; contributions from the sterols examined range from zero to more than 150% relative to cholesterol. For the first four methods contributions depend on the conditions under which each test is performed.     

The role of cholesterol and statins in Alzheimer's disease

OBJECTIVE: To briefly discuss the impact of elevated total and low-density-lipoprotein cholesterol levels, as well as the potential relationship of hydroxymethylglutaryl coenzyme A reductase inhibitor (statin) use, on the development of Alzheimer's disease (AD). DATA SOURCES: Biomedical literature was accessed through MEDLINE and International Pharmaceutical Abstracts (1966-June 2003). The authors independently reviewed literature for possible inclusion in this article. STUDY SELECTION AND DATA EXTRACTION: Clinical studies were selected and reviewed from the data sources, with special emphasis on those dealing with statin use and AD. DATA SYNTHESIS: The impact of AD is significant, as it is rapidly becoming one of our country's most debilitating and costly diseases. Data from epidemiologic trials indicate that statins may have some protective effect against the development of AD. These trials also allude to theories regarding possible mechanisms of action for this use, data implicating possible superiority of one statin over another, and their lack in certain populations, specifically the very old elderly population. CONCLUSIONS: Preliminary evidence suggests that statins may offer a protective effect against the development of AD. However, review of the literature does not lend credence to the use of statins in the general nondemented population without hyperlipidemia. Potential confounding variables have not been considered in the majority of trials. Placebo-controlled clinical trials are ongoing and should yield more definitive results.     

Effects of weight reduction on squalene, methyl sterols and cholesterol and on their synthesis in human adipose tissue

Abstract. Quantitation of cholesterol and its precursors from human adipose tissue biopsies revealed very high squalene and moderately high methyl sterol concentrations. The squalene and cholesterol values were correlated with each other. Weight reduction in obese subjects following a jejuno-ileal bypass resulted in a significant but transient increase in adipose tissue cholesterol. The squalene concentration was also increased post-operatively, the maximum being reached about 6 months later than that of cholesterol as if the mobilization of squalene from shrunken adipocytes had been slow. Weight reduction with a 2–14 day total fast significantly reduced the adipocyte size but had no consistent effect on adipose tissue squalene, methyl sterol and cholesterol concentrations or on their adipocyte contents. Incubation of adipose tissue with labelled acetate and mevalonate revealed that the bulk of the labels in non-saponifiable lipids stayed in the large intermediate pools of methyl sterols and squalene in particular, fairly little being found in the cholesterol fraction itself. The total fast inhibited the incorporation of both ¹⁴C-acetate and ³H-mevalonate to squalene, methyl sterols and cholesterol, suggesting that cholesterol synthesis was inhibited before and after the mevalonate step.     

Beneficial effects of statins in coronary artery disease--beyond lowering cholesterol

OBJECTIVE: To review the benefits of statins in coronary artery disease management beyond their cholesterol-lowering effects. DATA SOURCES: A MEDLINE search (1966-May 2000) was conducted using the following terms: lovastatin, pravastatin, simvastatin, atorvastatin, fluvastatin, cerivastatin, endothelium, plaque stabilization, antithrombotic effects. STUDY SELECTION: English-language human studies and case reports. DATA EXTRACTION: Studies published demonstrating other mechanisms of statins' clinical beneficial effects were evaluated and reviewed. DATA SYNTHESIS: The understanding of the pharmacologic effects of statins has led to the realization that the benefits of these agents extend beyond simply lowering cholesterol. These properties include beneficial effects on vessel endothelial tissue; decreased low-density lipoprotein oxidation and inflammation; ability to stabilize atherosclerotic plaques and perhaps promote regression; proliferative effects on smooth-muscle growths, possibly strengthening atherosclerotic plaques; antithrombotic effects by inhibiting platelet aggregation and stimulation of fibrinolytic factors; and improvement of blood viscosity and flow. With these actions, statins may benefit the situation of long-term atherosclerotic plaque formation and the setting of acute coronary syndrome. CONCLUSIONS: Further large-scale studies are needed to determine the clinical importance and validity of these postulated beneficial effects of statins.     

Surfactant inhibition of cholesterol oxidase

Little is known of the effect of surfactants upon the activity of cholesterol oxidase. This study demonstrates the interrelationship of surfactant, enzyme and substrate, and illustrates a possible source of inaccuracy within an enzymatic cholesterol assay.Using the rate at which cholesterol is converted to Δ⁴-cholestenone, the reaction was followed directly by monitoring the increase in absorbance at 240 nm. Inhibition of cholesterol oxidase was demonstrated with three surfactants, hydroxypolyethoxydodecane, Tween 20 and Triton-X-405. A fourth, Triton-X-100, produced high enzyme activity, although low concentrations resulted in incomplete substrate dispersal and high concentrations caused high blank values. Hydroxypolyethoxydodecane was studied more closely and the mechanism of inhibition is suggested as poor substrate dispersal at low surfactant concentration and a competitive inhibition at higher concentrations.     

Lipoprotein metabolism by rat hepatomas. Studies on the etiology of defective dietary feedback inhibition of cholesterol synthesis.

In contrast to normal liver, it is known that in vivo hepatomas fail to decrease their rate of cholesterol biosynthesis in response to increased dietary cholesterol. From a consideration of the available data it has been hypothesized that the defect might lie in the delivery of cholesterol to the hepatoma cell. To study this further, lipoprotein interactions with rat hepatoma cells in tissue culture (HTC 7288C) and with the same cell line in vivo were investigated. HTC cells grown in a medium containing 10% calf serum exhibited saturable, specific, calcium-dependent binding of rat 125I-chylomicron remnants at 4 degrees C with half maximal saturation at 4.8 micrograms protein/ml and maximum binding of 96 ng protein/10(6) cells. At 4 degrees C, HTC cells also bound human 125I-low density lipoprotein (LDL) specifically, but bound it with a much lower affinity. These cells also exhibited specific binding for rat LDL and rat hypercholesterolemic very low density lipoprotein (VLDL). All these lipoproteins were degraded by HTC cells. Thus, it was concluded that hepatoma cells possess lipoprotein receptors that recognize and process LDL, VLDL, and chylomicron remnants. Overnight incubation of HTC cells in lipid-depleted medium containing 0.5 microM compactin increased binding of rat chylomicron remnants and of hypercholesterolemic VLDL approximately 1.7-fold without a significant change in binding affinity. LDL binding also increased, by approximately 3.5-fold. These changes were also observed when binding and internalization were measured at 37 degrees C. After HTC cells were incubated in lipid-depleted medium, the rate at which [14C]acetate was incorporated into [14C]cholesterol increased 2.5-fold. Inclusion of rat chylomicron remnants at 5-10 micrograms protein/ml prevented this increase in acetate incorporation or, if added after culture in lipid-depleted medium, reduced the increased levels back to control values. However, the rate of acetate incorporation into cholesterol by cells grown in complete medium was not decreased to levels below base line by rat chylomicron remnants. Inclusion of human LDL only partially prevented the rise or only partially reduced the increased levels back to control and did not reduce control levels below base line. Hypercholesterolemic VLDL, which contain more cholesterol per particle than chylomicron remnants, did reduce [14C]acetate incorporation to below control levels. Therefore, the intracellular mechanism for down regulation of cholesterol synthesis by lipoproteins is intact in these cells. Based on these results we hypothesized that a relative lack of lipoprotein receptors expressed by hepatomas in vivo in comparison with those expressed by normal liver would explain the apparent absence of feedback inhibition of cholesterol synthesis. Consistent with this hypothesis, the binding of chylomicron remnants to liver cell membranes was 3-5 times greater than to membranes from tumors grown in vivo subcutaneously or intramuscularly. Membranes from tumor cells grown in vitro bound remnants least well. It is proposed that the relative lack of receptors places the hepatoma at a disadvantage in competing with the liver for lipoproteins of dietary origin and may account for the lack of feedback regulation of cholesterol synthesis in hepatomas.