Defective cholesterol biosynthesis associated with the Smith-Lemli-Opitz syndrome

BACKGROUND

The Smith-Lemli-Opitz syndrome (frequency, 1:20,000 to 1:40,000) is defined by a constellation of severe birth defects affecting most organ systems. Abnormalities frequently include profound mental retardation, severe failure to thrive, and a high infant-mortality rate. The syndrome has heretofore been diagnosed only from its clinical presentation.

METHODS

Using capillary-column gas chromatography-mass spectrometry, we measured the sterol composition of plasma, erythrocytes, lens, cultured fibroblasts, and feces from five children with the syndrome (three girls and two boys).

RESULTS

Plasma cholesterol levels were abnormally low (8 to 101 mg per deciliter [0.20 to 2.60 mmol per liter]) in every patient, being well below the 5th percentile for age- and sex-matched controls. Concentrations of the cholesterol precursor 7-dehydrocholesterol (cholesta-5,7-dien-3 beta-ol), which was not detectable in most of our controls, were elevated (11 to 31 mg per deciliter) more than 2000-fold above normal and were similar to the levels of cholesterol in all tissues from all patients. An isomeric dehydrocholesterol with a structure similar to that of 7-dehydrocholesterol was also detected.

CONCLUSIONS

The combination of abnormally low plasma cholesterol levels and a high concentration of the cholesterol precursor 7-dehydrocholesterol points to a major block in cholesterol biosynthesis at the step in which the C-7(8) double bond of 7-dehydrocholesterol is reduced, forming cholesterol. The block may be sufficient to deprive an embryo or fetus of cholesterol and prevent normal development, whereas the incorporation of 7-dehydrocholesterol into all membranes may interfere with proper membrane function.

Inhibition of intestinal cholesterol absorption by ezetimibe in humans

BACKGROUND

Ezetimibe has been shown to inhibit cholesterol absorption in animal models, but studies on cholesterol absorption in humans have not been performed thus far.

METHODS AND RESULTS

The effect of ezetimibe (10 mg/d) on cholesterol absorption and synthesis, sterol excretion, and plasma concentrations of cholesterol and noncholesterol sterols was investigated in a randomized, double-blind, placebo-controlled, crossover study in 18 patients with mild to moderate hypercholesterolemia. Treatment periods lasted 2 weeks with an intervening 2-week washout period. Fractional cholesterol absorption rates averaged 49.8+/-13.8% on placebo and 22.7+/-25.8% on ezetimibe, indicating a reduction of 54% (geometric mean ratio; P< 0.001). Cholesterol synthesis increased by 89% from 931+/-1027 mg/d on placebo to 1763+/-1098 mg/d on ezetimibe (P<0.001), while the ratio of lathosterol-to-cholesterol, an indirect marker of cholesterol synthesis, was increased by 72% (P<0.001). Bile acid synthesis was insignificantly increased (placebo: 264+/-209 mg/d, ezetimibe: 308+/-184 mg/d; P=0.068). Mean percent changes from baseline for LDL and total cholesterol after ezetimibe treatment were -20.4% and -15.1%, respectively (P<0.001 for both), whereas campesterol and sitosterol were decreased by -48% and - 41%, respectively.

CONCLUSION

In humans, ezetimibe inhibits cholesterol absorption and promotes a compensatory increase of cholesterol synthesis, followed by clinically relevant reductions in LDL and total cholesterol concentrations. Ezetimibe also reduces plasma concentrations of the noncholesterol sterols sitosterol and campesterol, suggesting an effect on the absorption of these compounds as well.

Determination of cholesterol oxidation products in human plasma by isotope dilution-mass spectrometry

A method based on isotope dilution-mass spectrometry was developed for the determination of nine cholesterol oxidation products in human plasma. The cholesterol oxidation products determined were cholest-5-ene-3 beta,7 alpha-diol, cholest-5-ene-3 beta,7 beta-diol (7 alpha- and 7 beta-hydroxycholesterol, respectively), 3 beta-hydroxycholest-5-en-7-one(7-oxocholesterol),5,6 alpha-epoxy-5 alpha- cholestan-3 beta-ol (cholesterol-5 alpha,6 alpha-epoxide),5,6 beta-epoxy-5 beta-cholestan-3 beta-ol (cholesterol-5 beta,6 beta-epoxide), (cholesterol-5 beta,6 beta-epoxide), cholestane-3 beta,5 alpha,6 beta-triol, cholest-5-ene-3 beta,24-diol (24-hydroxycholesterol), cholest-5-ene-3 beta,25-diol (25-hydroxycholesterol), and cholest-5-ene-3 beta,27-diol (27-hydroxycholesterol). A corresponding deuterium-labeled internal standard, containing 3 to 6 deuterium atoms, was synthesized for each cholesterol oxidation product except 5 beta,6 beta-epoxycholesterol which was determined using the internal standard for 5 alpha,6 alpha-epoxycholesterol. Plasma from 31 healthy volunteers was analyzed by the new method and 27-, 24-, and 7 alpha-hydroxycholesterol were the most abundant cholesterol oxidation products (mean values 154, 64, and 43 ng/ml, respectively). The other oxysterols determined were present in concentrations lower than 30 ng/ml. Males had higher 27-hydroxycholesterol concentrations in plasma than females. The 5,6-oxygenated products were present mainly unesterified while the other oxidation products were mostly in esterified form.

Metabolism of beta-sitosterol in man

The metabolism of beta-sitosterol was compared to that of cholesterol in 12 patients. Sterol balance methods were supplemented by radiosterol studies, with the following results. (a) Plasma concentrations of beta-sitosterol ranged from 0.30 to 1.02 mg/100 ml plasma in patients on intakes of beta-sitosterol typical of the American diet. Plasma levels were raised little when intakes were increased greatly, and on fixed intakes they were constant from week to week. On diets devoid of plant sterols, the plasma and feces rapidly became free of beta-sitosterol. (b) The percentage of esterified beta-sitosterol in the plasma was the same as for cholesterol. However, the rate of esterification of beta-sitosterol was slower than that for cholesterol. (c) Specific activity-time curves after simultaneous pulse labeling with beta-sitosterol-(3)H and cholesterol-(14)C conformed to two-pool models. The two exponential half-lives of beta-sitosterol were much shorter than for cholesterol, and pool sizes were much smaller. Values of turnover for beta-sitosterol obtained by the sterol balance method agreed closely with those derived by use of the two-pool model. There was no endogenous synthesis of beta-sitosterol in the patients studied; hence, daily turnover of beta-sitosterol equaled its daily absorption. Absorption of beta-sitosterol was 5% (or less) of daily intake, while cholesterol absorption ranged from 45 to 54% of intake. (d) About 20% of the absorbed beta-sitosterol was converted to cholic and chenodeoxycholic acids. The remainder was excreted in bile as free sterol; this excretion was more rapid than that of cholesterol. (e) The employment of beta-sitosterol as an internal standard to correct for losses of cholesterol in sterol balance studies is further validated by the results presented here.

Genetic dissection of complex traits with chromosome substitution strains of mice

Chromosome substitution strains (CSSs) have been proposed as a simple and powerful way to identify quantitative trait loci (QTLs) affecting developmental, physiological, and behavioral processes. Here, we report the construction of a complete CSS panel for a vertebrate species. The CSS panel consists of 22 mouse strains, each of which carries a single chromosome substituted from a donor strain (A/J) onto a common host background (C57BL/6J). A survey of 53 traits revealed evidence for 150 QTLs affecting serum levels of sterols and amino acids, diet-induced obesity, and anxiety. These results demonstrate that CSSs greatly facilitate the detection and identification of genes that control the wide diversity of naturally occurring phenotypic variation in the A/J and C57BL/6J inbred strains.

Identification of a new inborn error in bile acid synthesis: mutation of the oxysterol 7alpha-hydroxylase gene causes severe neonatal liver disease

We describe a metabolic defect in bile acid synthesis involving a deficiency in 7alpha-hydroxylation due to a mutation in the gene for the microsomal oxysterol 7alpha-hydroxylase enzyme, active in the acidic pathway for bile acid synthesis. The defect, identified in a 10-wk-old boy presenting with severe cholestasis, cirrhosis, and liver synthetic failure, was established by fast atom bombardment ionization-mass spectrometry, which revealed elevated urinary bile acid excretion, a mass spectrum with intense ions at m/z 453 and m/z 510 corresponding to sulfate and glycosulfate conjugates of unsaturated monohydroxy-cholenoic acids, and an absence of primary bile acids. Gas chromatography-mass spectrometric analysis confirmed the major products of hepatic synthesis to be 3beta-hydroxy-5-cholenoic and 3beta-hydroxy-5-cholestenoic acids, which accounted for 96% of the total serum bile acids. Levels of 27-hydroxycholesterol were > 4,500 times normal. The biochemical findings were consistent with a deficiency in 7alpha-hydroxylation, leading to the accumulation of hepatotoxic unsaturated monohydroxy bile acids. Hepatic microsomal oxysterol 7alpha-hydroxylase activity was undetectable in the patient. Gene analysis revealed a cytosine to thymidine transition mutation in exon 5 that converts an arginine codon at position 388 to a stop codon. The truncated protein was inactive when expressed in 293 cells. These findings indicate the quantitative importance of the acidic pathway in early life in humans and define a further inborn error in bile acid synthesis as a metabolic cause of severe cholestatic liver disease.

Evidence for ozone formation in human atherosclerotic arteries

Here, we report evidence for the production of ozone in human disease. Signature products unique to cholesterol ozonolysis are present within atherosclerotic tissue at the time of carotid endarterectomy, suggesting that ozone production occurred during lesion development. Furthermore, advanced atherosclerotic plaques generate ozone when the leukocytes within the diseased arteries are activated in vitro. The steroids produced by cholesterol ozonolysis cause effects that are thought to be critical to the pathogenesis of atherosclerosis, including cytotoxicity, lipid-loading in macrophages, and deformation of the apolipoprotein B-100 secondary structure. We propose the trivial designation "atheronals" for this previously unrecognized class of steroids.

Effects of cholesteryl ester transfer protein inhibition on high-density lipoprotein subspecies, apolipoprotein A-I metabolism, and fecal sterol excretion

OBJECTIVE

Pharmacological inhibition of the cholesteryl ester transfer protein (CETP) in humans increases high-density lipoprotein (HDL) cholesterol (HDL-C) levels; however, its effects on apolipoprotein A-I (apoA-I) containing HDL subspecies, apoA-I turnover, and markers of reverse cholesterol transport are unknown. The present study was designed to address these issues.

METHODS AND RESULTS

Nineteen subjects, 9 of whom were taking 20 mg of atorvastatin for hypercholesterolemia, received placebo for 4 weeks, followed by the CETP inhibitor torcetrapib (120 mg QD) for 4 weeks. In 6 subjects from the nonatorvastatin cohort, the everyday regimen was followed by a 4-week period of torcetrapib (120 mg BID). At the end of each phase, subjects underwent a primed-constant infusion of (5,5,5-2H3)-L-leucine to determine the kinetics of HDL apoA-I. The lipid data in this study have been reported previously. Relative to placebo, 120 mg daily torcetrapib increased the amount of apoA-I in alpha1-migrating HDL in the atorvastatin (136%; P<0.001) and nonatorvastatin (153%; P<0.01) cohorts, whereas an increase of 382% (P<0.01) was observed in the 120 mg twice daily group. HDL apoA-I pool size increased by 8+/-15% in the atorvastatin cohort (P=0.16) and by 16+/-7% (P<0.0001) and 34+/-8% (P<0.0001) in the nonatorvastatin 120 mg QD and BID cohorts, respectively. These changes were attributable to reductions in HDL apoA-I fractional catabolic rate (FCR), with torcetrapib reducing HDL apoA-I FCR by 7% (P=0.10) in the atorvastatin cohort, by 8% (P<0.001) in the nonatorvastatin 120 mg QD cohort, and by 21% (P<0.01) in the nonatorvastatin 120 mg BID cohort. Torcetrapib did not affect HDL apoA-I production rate. In addition, torcetrapib did not significantly change serum markers of cholesterol or bile acid synthesis or fecal sterol excretion.

CONCLUSIONS

These data indicate that partial inhibition of CETP via torcetrapib in patients with low HDL-C: (1) normalizes apoA-I levels within alpha1-migrating HDL, (2) increases plasma concentrations of HDL apoA-I by delaying apoA-I catabolism, and (3) does not significantly influence fecal sterol excretion.

Serum cholestanol and plant sterol levels in relation to cholesterol metabolism in middle-aged men

Serum cholestanol was studied in relation to fecal cholestanol excretion and cholesterol metabolism in a random middle-aged population of 61 men. The serum concentrations of cholestanol ranged from 1.6 to 10.8 mumol/L and were positively correlated with those of serum total LDL and HDL cholesterol. In terms of millimole per mole of cholesterol, these correlations disappeared; inverse associations were found with VLDL cholesterol and triglyceride levels, the P/S ratio of dietary fat, and the amount of fecal plant sterols, but not with fecal cholestanol. The serum contents of cholestanol (1) were also closely positively associated with those of serum plant sterols (campesterol and sitosterol) and fractional cholesterol absorption, (2) were inversely related to the fecal excretion of neutral sterols and cholesterol synthesis which were measured either by the sterol balance technique or serum cholesterol precursor sterols (desmosterol and lathosterol), and (3) were unrelated to bile acid synthesis. Fecal cholestanol (mean = 12.5 mg/d) was (1) clearly higher than the dietary cholestanol intake (less than 2 mg/d), (2) unrelated to serum cholestanol, and (3) positively correlated with the intestinal cholesterol (dietary plus endogenous) flux as well as fecal plant sterols, neutral sterols, and bacterial products of cholesterol. The study emphasizes that, in normal men, high serum cholestanol levels reflect high efficiency of intestinal sterol absorption and low cholesterol synthesis. Thus, the changes in the serum contents of cholestanol are parallel with those of plant sterols and opposite to those of cholesterol precursor sterols.

Noncholesterol sterols and cholesterol lowering by long-term simvastatin treatment in coronary patients: relation to basal serum cholestanol

Coronary patients with low baseline ratios of serum cholestanol and plant sterols to cholesterol (indicating low cholesterol absorption) but not those with high ratios (high absorption) experienced reduced recurrences of coronary events during simvastatin treatment in the Scandinavian Simvastatin Survival Study. Thus, in the present study, serum cholesterol, its precursor sterols (reflecting cholesterol synthesis), plant sterols (campesterol and sitosterol), and cholestanol were measured before and during a 5-year period of placebo treatment (n=433) and simvastatin treatment (n=434) in patients from a subgroup of the Scandinavian Simvastatin Survival Study to determine whether changes in cholesterol synthesis and serum levels were related to cholesterol absorption. Serum cholesterol level was unchanged, the ratios of cholesterol precursor sterols to cholesterol were decreased, and the ratios of plant sterols to cholesterol were increased in relation to increasing baseline ratios of cholestanol quartiles. The latter predicted 5-year ratios and simvastatin-induced reductions of the precursor sterols, with the lowering of the ratios (cholesterol synthesis reduction) being almost twice higher in the lowest versus the highest quartile. The ratios of plant sterols, especially campesterol, to cholesterol were markedly increased during simvastatin treatment, mostly in subjects with the highest baseline cholestanol quartiles. Simvastatin reduced serum cholesterol more (P=0.003) in the lowest versus the highest cholestanol quartile during the 5-year treatment period. The results show for the first time that baseline cholesterol metabolism, measured by serum noncholesterol sterols, predicts the effectiveness of simvastatin in reducing cholesterol synthesis and serum levels of cholesterol. The drug suppresses the synthesis of cholesterol markedly more effectively in subjects with high than with low baseline synthesis but reduces respective serum cholesterol levels less markedly than synthesis. Subjects with high cholesterol absorption and low synthesis may need a combination therapy to lower more effectively their serum cholesterol levels and prevent an increase in the levels of plant sterols.

Reduction of serum cholesterol in postmenopausal women with previous myocardial infarction and cholesterol malabsorption induced by dietary sitostanol ester margarine: women and dietary sitostanol

BACKGROUND

Reduction of serum cholesterol decreases mortality in primary and especially in secondary prevention. We investigated how effectively postmenopausal women with a previous myocardial infarction reduced their serum cholesterol with dietary means by using sitostanol ester rapeseed oil margarine, alone and in combination with statins, and to what extent cholesterol metabolism was affected.

METHODS AND RESULTS

The first study group consisted of 22 randomly chosen women with angiographically documented coronary artery disease. Baseline studies on home diet were followed by double-blind, randomized, cross-over studies on margarine without and with sitostanol (3 g/d) ester for 7 weeks in random order. A second group of 10 women on simvastatin consumed sitostanol ester margarine for 12 weeks. Sitostanol ester margarine lowered serum total cholesterol by 13% (P<.05) and LDL cholesterol by 20% (P<.01). Sitostanol ester margarine reduced total cholesterol in all patients, LDL cholesterol <2.6 mmol/L (<100 mg/dL) in 32%, and <3.4 mmol/L (<133 mg/dL) in 73% versus none and 27% during the home diet (P<.01 for both). Combined with simvastatin, sitostanol still reduced total and LDL cholesterol by 11+/-3% and 16+/-5% (P<.01 for both). Sitostanol reduced absorption (-45%), increased fecal elimination (+45% as neutral sterols), and stimulated synthesis (+39%) of cholesterol. High cholestanol and plant sterol (high cholesterol absorption) and low baseline precursor sterol proportions (low cholesterol synthesis) predicted high decreases in serum cholesterol.

CONCLUSIONS

Dietary use of sitostanol ester margarine normalizes LDL cholesterol in about one third of women with previous myocardial infarction, especially in those with high baseline absorption and low synthesis of cholesterol, and in combination with statins reduces the needed drug dose.

On the rate of translocation in vitro and kinetics in vivo of the major oxysterols in human circulation: critical importance of the position of the oxygen function

Oxysterols possess powerful biological activities. Some of their effects on the regulation of key enzymes are similar to those of cholesterol, but are much more potent. One of the critical properties of oxysterols is their ability to pass lipophilic membranes at a high rate. Transfer of unesterified 25-hydroxycholesterol from red blood cells to plasma has been reported to occur more than 1,000 times faster than cholesterol. Here we have measured the relative rate of such translocation of the three major oxysterols in human circulation: 27-hydroxycholesterol, 24S-hydroxycholesterol, and 4beta-hydroxycholesterol. The distance from the 3beta-hydroxyl group to the additional hydroxyl group is the greatest possible in 27-hydroxycholesterol and the least possible in 4beta-hydroxycholesterol. The rate of exchange between erythrocytes and plasma was found to be high for 27-hydroxycholesterol and 24S-hydroxycholesterol, and hardly possible to measure for 4beta-hydroxycholesterol and cholesterol. When injected intravenously into humans, deuterium labeled 24- and 27-hydroxycholesterol caused an immediate high enrichment of the corresponding plasma sterols followed by a decay. After injection of labeled 4beta-hydroxycholesterol, the maximum deuterium enrichment occurred after 2-3 h, when secretion of the oxysterol from the liver is likely to be the limiting factor. When radiolabeled cholesterol was injected under the same conditions, maximum appearance of label occurred after about 2 days. The results illustrate the importance of the position of the additional oxygen in oxysterols and are discussed in relation to the rate of metabolism and biological effects of these oxysterols.

No Association Between Plasma Levels of Plant Sterols and Atherosclerosis in Mice and Men

OBJECTIVE

Sitosterolemia is characterized by elevated plasma levels of plant sterols, hypercholesterolemia and premature coronary heart disease (CHD). CHD develops in some subjects with sitosterolemia, despite having normal plasma cholesterol levels, suggesting that high circulating levels of plant sterols may be atherogenic. We tested whether elevated plasma levels of plant sterols (sitosterol and campesterol) were associated with atherosclerosis in genetically modified mice and in middle-aged men and women.

METHODS AND RESULTS

Wild-type and hypercholesterolemic female mice with >20-fold higher plasma levels of plant sterols because of inactivation of the ATP-binding cassette (ABC) half transporters G5 and G8 (G5G8-/-mice) were fed chow or Western diets for 7 months. No significant differences in aortic lesion area were found when the sitosterolemic mice were compared with littermate controls. To determine whether plasma levels of plant sterols were associated with coronary atherosclerosis in humans, the relationship between plasma plant sterols and coronary calcium (detected by electron beam computer tomography) was examined in 2542 subjects aged 30 to 67 years. Plasma levels of cholesterol, but not sitosterol or campesterol, were significantly higher in subjects with coronary calcium.

CONCLUSIONS

The results of this study do not support an association between elevated plasma levels of plant sterols and atherosclerosis.

Side chain oxidized oxysterols in cerebrospinal fluid and the integrity of blood-brain and blood-cerebrospinal fluid barriers

The side chain oxidized oxysterol 24S-hydroxycholesterol (24-OH-chol) is formed almost exclusively in the brain, and there is a continuous passage of this oxysterol through the circulation to the liver. 27-Hydroxycholesterol (27-OH-chol) is produced in most organs and is also taken up by the liver. The 27-OH-chol-24-OH-chol ratio is about 0.1 in the brain and about 2 in the circulation. This ratio was found to be about 0.4 in cerebrospinal fluid (CSF) of asymptomatic patients, consistent with a major contribution from the circulation in the case of 27-OH-chol. In accordance with this, we demonstrated a significant flux of deuterium labeled 27-OH-chol from plasma to the CSF in a healthy volunteer. Patients with a defective blood-brain barrier were found to have markedly increased absolute levels (up to 10-fold) of both 27-OH-chol and 24-OH-chol in CSF, with a ratio between the two sterols reaching up to 2. There was a significant positive correlation between the levels of both oxysterols in CSF and the albuminCSF-albuminplasma ratio. The 27-OH-cholCSF-24-OH-cholCSF ratio was found to be about normal in patients with active multiple sclerosis and significantly increased in patients with meningitis, polyneuropathy, or hemorrhages. Results are discussed in relation to the possible use of 24-OH-cholCSF as a surrogate marker of central nervous system demyelination and/or neuronal death.

Trans fatty acids may impair biosynthesis of long-chain polyunsaturates and growth in man

Human diet contains large amounts of trans fatty acids originating primarily from hydrogenated fats. Consumption of trans fatty acids is considered safe for man, but side effects, including impaired biosynthesis of long-chain polyunsaturated fatty acids with 20 and 22 carbon atoms and reduced growth have been observed in animals. We studied whether or not there are indications of untoward effects of trans fatty acids in 29 premature infants (birth weight 1700 +/- 127 g, gestational age 33.6 +/- 1.4 weeks, mean +/- SD). Plasma samples obtained on day 4 of life were analysed for fatty acid composition. Trans octadecenoic acid and total trans fatty acids in plasma lipid fractions (% wt/wt) were not related to the precursor essential fatty acids linoleic and alpha-linolenic acids but correlated inversely to n - 3 and n - 6 long-chain polyunsaturated fatty acids and to the product/substrate ratios of long-chain polyunsaturate biosynthesis. Trans fatty acids were also inversely correlated to birth weight but not to gestational age. These data indicate a potential impairment of essential fatty acid metabolism and early growth by trans isomers in man, and question the safety of high dietary trans isomer intakes during pregnancy and the perinatal period.

Correlation of severity and outcome with plasma sterol levels in variants of the Smith-Lemli-Opitz syndrome

OBJECTIVES

To determine whether type I and the more severe type II variant of Smith-Lemli-Opitz syndrome have the same metabolic defect and to learn which plasma sterol measurements best predict survival.

METHODS

Plasma sterols were measured in 33 individuals (24 type I, 9 type II) with a clinical diagnosis of the syndrome.

RESULTS

Cholesterol levels were abnormally low (61 +/- 34 mg/dl) in type I subjects, whereas concentrations of the cholesterol precursor 7-dehydrocholesterol and its isomer 8-dehydrocholesterol were elevated 40- to 10,000-fold. Plasma cholesterol levels were significantly lower and total dehydrocholesterol levels higher in type II than in type I. Six children with the type II variant died by 13 weeks with mean plasma cholesterol levels 6.2 +/- 3.1 mg/dl, versus 17 +/- 11 mg/dl in the three surviving children with type II (p < 0.05). No child with a cholesterol level 7 mg/dl or less lived longer than 13 weeks.

CONCLUSIONS

Patients with type I and type II variants of Smith-Lemli-Opitz syndrome have markedly reduced activity of the enzyme that converts 7-dehydrocholesterol to cholesterol, but the extent of the block is far more complete in type II. Survival correlates strongly with higher plasma cholesterol concentrations.

Cholesterol absorption efficiency and sterol metabolism in obesity

Role of enterohepatic cholesterol metabolism in obesity-induced increase of cholesterol synthesis was studied in healthy lean (BMI <24) and overweight (BMI >31) subjects by measuring serum lipids (including plant sterols, cholestanol and cholesterol precursors), cholesterol absorption % (double-label method), sterol balance and biliary lipids. New aspects of sterol metabolism in obesity were as follows: low efficiency of cholesterol absorption, reduced ratios to cholesterol of serum and biliary plant sterols and cholestanol (5alpha-derivative of cholesterol), and a marked increase of serum and biliary cholesterol precursor sterols. Percent of cholesterol absorption was positively related to serum cholestanol and plant sterols, and negatively to cholesterol synthesis, measured by the sterol balance technique or cholesterol precursor sterols in serum or bile. Total and endogenous cholesterol fluxes into the intestine were increased, but owing to low absorption percent, mass of cholesterol absorption was within control limits in the obese subjects. Thus, per gram of their large liver tissue the entry of intestinal cholesterol may even be subnormal. Percent of cholesterol absorption was insignificantly negatively (r=-0.256) related to intestinal cholesterol pool, but significantly to biliary concentrations of cholesterol (r=-0.581), bile acids (r=-0.513) and phospholipids (r=-0.469). Thus, dilution of labeled dietary cholesterol by expanded intestinal cholesterol pool could have contributed to subnormal efficiency of cholesterol absorption, or transfer of labeled dietary cholesterol from intestinal oil phase to micellar phase may be competitively inhibited by expanded biliary secretion, resulting in reduced absorption of dietary cholesterol. These mechanisms could have contributed to changes in metabolism of non-cholesterol sterols, especially of cholestanol and plant sterols.

Cholesterol reduction by different plant stanol mixtures and with variable fat intake

Our aim was to investigate (1) whether different campestanol/sitostanol mixtures in margarine differ in reducing serum cholesterol, and (2) whether sitostanol ester in butter decreases serum cholesterol and alters cholesterol absorption and metabolism. Twenty-three postmenopausal women replaced 25 g dietary fat with (1) sitostanol ester-rich (campestanol to sitostanol ratio 1:11) and (2) campestanol ester-rich (campestanol to sitostanol ratio 1:2) rapeseed oil margarine, (3) butter, and (4) sitostanol ester-rich (campestanol to sitostanol ratio 1:13) butter. The respective scheduled stanol intake was 3.18, 3.16, and 2.43 g/d. The 6-week margarine periods and, after an 8-week washout, 5-week butter periods were double-blind and in random order. Serum cholesterol precursor sterols (indicators of cholesterol synthesis) and plant sterols (indicators of cholesterol absorption) were quantified with gas-liquid chromatography (GLC). Low-density lipoprotein (LDL) cholesterol was reduced by 8% and 10% with the sitostanol and campestanol ester-rich margarines versus baseline (P < .05 for both) and high-density lipoprotein (HDL) cholesterol was increased by 6% and 5% (P < .05), so the LDL/HDL cholesterol ratio was reduced by 15% (P < .05 for both). Sitostanol ester-rich butter decreased LDL cholesterol 12% and the LDL/HDL cholesterol ratio 11% (P < .05 for both) versus the butter period. The serum proportions of plant sterols and cholestanol were similarly reduced and those of cholesterol precursor sterols were similarly increased during all periods (P < .05 for all). Serum proportions of sitostanol and campestanol were slightly increased, indicating that their absorption related to their dietary intake. During all stanol interventions, serum vitamin D and retinol concentrations and alpha-tocopherol to cholesterol ratios were unchanged, whereas those of alpha- and beta-carotenes were significantly reduced. We conclude that varying the campestanol to sitostanol ratio from 1:13 to 1:2 in margarine and in butter similarly decreased cholesterol absorption, LDL cholesterol, and the LDL/HDL cholesterol ratio such that the serum lipids became less atherogenic.

Apolipoprotein E participates in the regulation of very low density lipoprotein-triglyceride secretion by the liver

ApoE-deficient mice on low fat diet show hepatic triglyceride accumulation and a reduced very low density lipoprotein (VLDL) triglyceride production rate. To establish the role of apoE in the regulation of hepatic VLDL production, the human APOE3 gene was introduced into apoE-deficient mice by cross-breeding with APOE3 transgenics (APOE3/apoe-/- mice) or by adenoviral transduction. APOE3 was expressed in the liver and, to a lesser extent, in brain, spleen, and lung of transgenic APOE3/apoe-/- mice similar to endogenous apoe. Plasma cholesterol levels in APOE/apoe-/- mice (3.4 +/- 0.5 mM) were reduced when compared with apoe-/- mice (12.6 +/- 1.4 mM) but still elevated when compared with wild type control values (1.9 +/- 0.1 mM). Hepatic triglyceride accumulation in apoE-deficient mice was completely reversed by introduction of the APOE3 transgene. The in vivo hepatic VLDL-triglyceride production rate was reduced to 36% of control values in apoE-deficient mice but normalized in APOE3/apoe-/- mice. Hepatic secretion of apoB was not affected in either of the strains. Secretion of (3)H-labeled triglycerides synthesized from [(3)H]glycerol by cultured hepatocytes from apoE-deficient mice was four times lower than by APOE3/apoe-/- or control hepatocytes. The average size of secreted VLDL particles produced by cultured apoE-deficient hepatocytes was significantly reduced when compared with those of APOE3/apoe-/- and wild type mice. Hepatic expression of human APOE3 cDNA via adenovirus-mediated gene transfer in apoE-deficient mice resulted in a reduction of plasma cholesterol depending on plasma apoE3 levels. The in vivo VLDL-triglyceride production rate in these mice was increased up to 500% compared with LacZ-injected controls and correlated with the amount of apoE3 per particle. These findings indicate a regulatory role of apoE in hepatic VLDL-triglyceride secretion, independent from its role in lipoprotein clearance.

Measurement of oxysterols and alpha-tocopherol in plasma and tissue samples as indices of oxidant stress status

Oxidant stress seems to play a role in several setting of human pathology, such as atherosclerosis, cancer, and aging. The study of oxidant stress in human disease should be based on the evaluation of either sensitive and specific markers of enhanced oxidant stress, such as oxysterols, or antioxidant defense, by measuring alpha-tocopherol. We have developed a rapid method to measure the oxysterols 7beta-hydroxycholesterol and 7-ketocholesterol in plasma (50 healthy subjects) and tissue as an index of oxidant stress in vivo, and from the same sample alpha-tocopherol content. The mean plasma concentration of 7beta-hydroxycholesterol and 7-ketocholesterol was 4.6+/-1.1 and 13.4+/-7.6 ng/mL, respectively. Plasma alpha-tocopherol concentration was 5.8+/-1.0 micromol/mol cholesterol. Samples from atherosclerotic plaques contained 20 times more cholesterol, about 45 times higher oxysterols levels, and 600 times more alpha-tocopherol compared to normal arteries. No significant difference in cholesterol and oxysterol content was observed between cirrhotic and normal liver. However, cirrhotic liver contained significantly smaller concentration of alpha-tocopherol compared to normal liver. In conclusion, we have developed a rapid and reliable method for the assay of cholesterol oxidation products and alpha-tocopherol in plasma and tissue useful for estimation of oxidant stress/antioxidant balance.

High doses of simvastatin, pravastatin, and cholesterol reduce brain cholesterol synthesis in guinea pigs

Recent epidemiological studies suggest that inhibitors of 3-hydroxy-3-methyl-glutaryl CoA reductase, so-called statins, are effective in lowering the prevalence of Alzheimer's disease. Whether the effect of statins is due to a local inhibition of cholesterol synthesis in the brain or whether it is mediated by the reduced levels of cholesterol in the circulation is not known. In the present work, we tested the possibility that high doses of lipophilic and hydrophilic statins, simvastatin and pravastatin, respectively, or a diet high in cholesterol could affect cholesterol homeostasis in the brain of guinea pigs. The total brain cholesterol levels were not affected by high-dose simvastatin or pravastatin treatment. Significantly lower levels of the cholesterol precursor lathosterol and its ratio to cholesterol were found in the brains of simvastatin and pravastatin-treated animals. 24S-Hydroxycholesterol, the transportable form of cholesterol across the blood-brain barrier, was significantly lower in the brain of pravastatin-treated animals. Excessive cholesterol feeding resulted in higher serum cholesterol levels but did not affect total brain cholesterol level. However, de novo cholesterol synthesis in the brain seemed to be down-regulated, as indicated by lower absolute levels and cholesterol-related ratios of lathosterol compared with controls. The passage of deuterium-labeled cholesterol across the blood-brain barrier in one animal was found to be approximately 1%. Our results suggest that brain cholesterol synthesis in guinea pigs can be slightly, but significantly, influenced by high doses of lipophilic and hydrophilic statins as well as by high dietary cholesterol intake, while total brain cholesterol content and thus, cholesterol homeostasis is maintained.