Body Cholesterol Synthesis Research Articles

Plasma lathosterol measures rates of cholesterol synthesis and efficiency of dietary phytosterols in reducing the plasma cholesterol concentration

Because the plasma campesterol/cholesterol ratio does not differ between groups that absorb different amounts of cholesterol, the authors investigated whether the plasma Phytosterols (PS) relate to the body's cholesterol synthesis rate measured as non-cholesterol sterol precursors (lathosterol). The authors studied38non-obese volunteers (58±12years; Low-Density Lipoprotein Cholesterol ‒ LDL-C≥ 130mg/dL) randomly assigned to consume 400mL/day of soy milk (Control phase) or soy milk+PS (1.6 g/day) forfourweeks in a double-blind, cross-over study. PS and lathosterol were measured in plasma by gas chromatography coupled to mass spectrophotometry. PS treatment reduced plasma total cholesterol concentration (-5.5%, p<0.001), LDL-C (-7.6%, p<0.001), triglycerides (-13.6%, p<0.0085), and apolipoprotein B (apoB) (-6.3%, p<0.008), without changing high density lipoprotein cholesterol (HDL-C concentration), but plasma lathosterol, campesterol and sitosterol expressed per plasma cholesterol increased. The lathosterol-to-cholesterol plasma ratio predicted the plasma cholesterol response to PS feeding. The highest plasma lathosterol concentration during the control phase was associated with a lack of response of plasma cholesterol during the PS treatment period. Consequently, cholesterol synthesis in non-responders to dietary PS being elevated in the control phase indicates these cases resist to further synthesis rise, whereas responders to dietary PS, having in the control phase synthesis values lower than non-responders, expand synthesis on alimentary PS. Responders absorb more PS than non-responders, likely resulting from responders delivering into the intestinal lumen less endogenous cholesterol than non-responders do, thus facilitating greater intestinal absorption of PS shown as increased plasma PS concentration.

Cholesterol metabolism in mice models of genetic hypercholesterolemia.

Monogenic familial hypercholesterolemia is characterized by impaired cellular uptake of apolipoprotein B containing lipoproteins. However, its consequences on whole-body cholesterol metabolism are unclear. We investigated cholesterol metabolism in wild-type mice (control) and in knockout (KO) mice for the low-density lipoprotein receptor (LDLR-KO) and for apolipoprotein E (apoE-KO) containing the genetic basis of the C57BL/6J mice, under a cholesterol-free diet. Cholesterol and "non-cholesterol" sterols (cholestanol, desmosterol, and lathosterol) were measured in plasma, tissues, as well as in feces as cholesterol and its bacterial modified products (neutral sterols) using gas chromatography/mass spectrometry, and bile acids were measured by an enzymatic method. Compared to controls, LDLR-KO mice have elevated plasma and whole-body cholesterol concentrations, but total fecal sterols are not modified, characterizing unaltered body cholesterol synthesis together with impaired body cholesterol excretion. ApoE-KO mice presented the highest concentrations of plasma cholesterol, whole-body cholesterol, cholestanol, total fecal sterols, and cholestanol, compatible with high cholesterol synthesis rate; the latter seems attributed to elevated body desmosterol (Bloch cholesterol synthesis pathway). Nonetheless, whole-body lathosterol (Kandutsch-Russel cholesterol synthesis pathway) decreased in both KO models, likely explaining the diminished fecal bile acids. We have demonstrated for the first time quantitative changes of cholesterol metabolism in experimental mouse models that explain differences between LDLR-KO and apoE-KO mice. These findings contribute to elucidate the metabolism of cholesterol in human hypercholesterolemia of genetic origin.

Impact of proprotein convertase subtilisin/kexin type 9 inhibition with evolocumab on the postprandial responses of triglyceride-rich lipoproteins in type II diabetic subjects

Monoclonal antibodies to proprotein convertase subtilisin/kexin type 9 (PCSK9) significantly lower the levels of low-density lipoprotein and very-low-density lipoproteins (VLDL), but their effect on postprandial lipoprotein metabolism in dyslipidemic subjects is unclear. This study aimed to investigate the effects of evolocumab on postprandial lipid responses, ectopic fat depots, whole-body cholesterol synthesis, hepatic lipogenesis, and fat oxidation in patients with type II diabetes. The trial was a single-phase, nonrandomized study of 12-week treatment with evolocumab 140mgsubcutaneously every 2weeks in 15 patients with type II diabetes on background statin therapy. Cardiometabolic responses to a high-fat mixed meal were assessed before and at the end of the intervention period. Evolocumab treatment reduced significantly postprandial rises in plasma total triglyceride (by 21%; P<.0001) and VLDL1 triglyceride (by 15%; P=.018), but the increase in chylomicron triglyceride after the meal was not significantly perturbed (P=.053). There were reduced postprandial responses in plasma total apolipoprotein C-III (by 14%; P<.0001) and apolipoprotein B-48 concentration (by 17%; P=.0046) and in "remnant-like particles" cholesterol (by 29%; P<.0001) on the PCSK9 inhibitor. Treatment reduced the steady-state (ie, fasting and postprandial) concentrations of VLDL2 cholesterol by 50% (P<.0001) and VLDL2 triglyceride by 29% (P<.0001), in addition to the 78% reduction of low-density lipoprotein cholesterol (P<.001). The changes in apolipoprotein C-III associated significantly with reduction in postprandial responses of remnant-like particles cholesterol and triglyceride-rich lipoprotein cholesterol. Evolocumab therapy did not influence liver fat accumulation, hepatic de novo lipogenesis, or fasting β-hydroxybutyrate but did increase total body cholesterol synthesis (P<.01). Evolocumab treatment improved postprandial responses of triglyceride-rich lipoproteins and measures of cholesterol-enriched remnant particles in type II diabetic subjects. These results indicate that postprandial phenomena need to be taken into account in assessing the full range of actions of PCSK9 inhibitors in dyslipidemic individuals.

Statins redux: A re-assessment of how statins lower plasma cholesterol.

Obesity associated dyslipidemia and its negative effects on the heart and blood vessels have emerged as a major healthcare challenge around the globe. The use of statins, potent inhibitors of hydroxyl-methyl glutaryl (HMG) Co-A reductase, a rate-limiting enzyme in cholesterol biosynthesis, has significantly reduced the rates of cardiovascular and general mortality in patients with coronary artery disease. How statins lower plasma cholesterol levels presents a mechanistic conundrum since persistent exposure to these drugs in vitro or in vivo is known to induce overexpression of the HMG Co-A reductase gene and protein. In an attempt to solve this mechanistic puzzle, Schonewille et al, studied detailed metabolic parameters of cholesterol synthesis, inter-organ flux and excretion in mice treated with 3 common statins, rosuvastatin, atorvastatin or lovastatin, each with its unique pharmacokinetics. From the measurements of the rates of heavy water (D2O) and [13C]-acetate incorporation into lipids, the authors calculated the rates of whole body and organ-specific cholesterol synthesis in control and statin-treated mice. These analyses revealed dramatic enhancement in the rates of hepatic cholesterol biosynthesis in statin-treated mice that concomitantly elicited lower levels of cholesterol in their plasma. The authors have provided strong evidence to indicate that statin treatment in mice led to induction of compensatory metabolic pathways that apparently mitigated an excessive accumulation of cholesterol in the body. It was noted however that changes in cholesterol metabolism induced by 3 statins were not identical. While sustained delivery of all 3 statins led to enhanced rates of biliary excretion of cholesterol and its fecal elimination, only atorvastatin treated mice elicited enhanced trans-intestinal cholesterol excretion. Thus, blockade of HMGCR by statins in mice was associated with profound metabolic adaptations that reset their cholesterol homeostasis. The findings of Schonewille et al, deserve to be corroborated and extended in patients in order to more effectively utilize these important cholesterol-lowering drugs in the clinic.

Statins increase hepatic cholesterol synthesis and stimulate fecal cholesterol elimination in mice

Statins are competitive inhibitors of HMG-CoA reductase, the rate-limiting enzyme of cholesterol synthesis. Statins reduce plasma cholesterol levels, but whether this is actually caused by inhibition of de novo cholesterol synthesis has not been clearly established. Using three different statins, we investigated the effects on cholesterol metabolism in mice in detail. Surprisingly, direct measurement of whole body cholesterol synthesis revealed that cholesterol synthesis was robustly increased in statin-treated mice. Measurement of organ-specific cholesterol synthesis demonstrated that the liver is predominantly responsible for the increase in cholesterol synthesis. Excess synthesized cholesterol did not accumulate in the plasma, as plasma cholesterol decreased. However, statin treatment led to an increase in cholesterol removal via the feces. Interestingly, enhanced cholesterol excretion in response to rosuvastatin and lovastatin treatment was mainly mediated via biliary cholesterol secretion, whereas atorvastatin mainly stimulated cholesterol removal via the transintestinal cholesterol excretion pathway. Moreover, we show that plasma cholesterol precursor levels do not reflect cholesterol synthesis rates during statin treatment in mice. In conclusion, cholesterol synthesis is paradoxically increased upon statin treatment in mice. However, statins potently stimulate the excretion of cholesterol from the body, which sheds new light on possible mechanisms underlying the cholesterol-lowering effects of statins.

Sustained and selective suppression of intestinal cholesterol synthesis by Ro 48-8071, an inhibitor of 2,3-oxidosqualene:lanosterol cyclase, in the BALB/c mouse

The small intestine plays a fundamentally important role in regulating whole body cholesterol balance and plasma lipoprotein composition. This is articulated through the interplay of a constellation of genes that ultimately determines the net amount of chylomicron cholesterol delivered to the liver. Major advances in our insights into regulation of the cholesterol absorption pathway have been made using genetically manipulated mouse models and agents such as ezetimibe. One unresolved question is how a sustained pharmacological inhibition of intestinal cholesterol synthesis in vivo may affect cholesterol handling by the absorptive cells. Here we show that the lanosterol cyclase inhibitor, Ro 48-8071, when fed to BALB/c mice in a chow diet (20mg/day/kg body weight), leads to a rapid and sustained inhibition (>50%) of cholesterol synthesis in the whole small intestine. Sterol synthesis was also reduced in the large intestine and stomach. In contrast, hepatic cholesterol synthesis, while markedly suppressed initially, rebounded to higher than baseline rates within 7 days. Whole body cholesterol synthesis, fractional cholesterol absorption, and fecal neutral and acidic sterol excretion were not consistently changed with Ro 48-8071 treatment. There were no discernible effects of this agent on intestinal histology as determined by H&E staining and the level of Ki67, an index of proliferation. The mRNA expression for multiple genes involved in intestinal cholesterol regulation including NPC1L1 was mostly unchanged although there was a marked rise in the mRNA level for the PXR target genes CYP3A11 and CES2A.

Efficacy and Plasma Drug Concentrations With Nondaily Dosing of Rosuvastatin

BackgroundNondaily statin dosing is an alternative for patients unable to tolerate daily dosing. The higher potency and longer half-life of rosuvastatin lends itself to this regimen. The basis of this improved tolerability is not understood, but might be related to lower plasma drug concentrations. We examined the efficacy of nondaily rosuvastatin in previously statin-intolerant patients and determined plasma drug concentrations at various dose regimens. MethodsA retrospective analysis at a specialty lipid clinic identified 58 patients eligible for evaluation after therapy with nondaily rosuvastatin. Plasma rosuvastatin levels were measured by liquid chromatography-mass spectrometry in 12 patients taking 10 mg nondaily rosuvastatin and in 11 and 12 age- and sex-matched patients taking 10 mg and 5 mg rosuvastatin daily, respectively. Whole body cholesterol synthesis was estimated from serum lathosterol measured by liquid chromatography-mass spectrometry. ResultsIn patients with a previous history of statin intolerance, nondaily rosuvastatin (average of 29.4 mg per week) lowered low-density lipoprotein cholesterol by 34.4 ± 21.3% (P < 0.001). Serum lathosterol levels were significantly higher in patients on nondaily regimens, as expected. However, mean plasma rosuvastatin levels of patients taking 10 mg nondaily did not significantly differ from those taking 10 mg daily. ConclusionsIn statin intolerant patients, nondaily rosuvastatin resulted in clinically relevant reductions in low-density lipoprotein cholesterol levels, with improved compliance. Whole body cholesterol synthesis was higher in patients taking nondaily rosuvastatin, but no differences in plasma drug concentrations were observed, suggesting that the improved tolerability was independent of plasma rosuvastatin levels.

Whole body cholesterol metabolism is impaired in Huntington's disease

We previously reported impaired cholesterol biosynthesis in rodent Huntington Disease (HD) models and HD patients’ fibroblasts and post mortem brains. We also found that plasma levels of 24S-hydroxycholesterol (24OHC), the brain specific elimination product of cholesterol considered a marker of brain cholesterol turnover, were significantly reduced in HD patients at any disease stage. In the present study we analysed by mass spectrometry the fasting plasma levels of cholesterol, its biosynthetic precursors lanosterol and lathosterol, of the whole-body elimination products 27-hydroxycholesterol and of brain 24OHC in a cohort of premanifest and HD patients at different disease stages. We found that the cholesterol precursors lanosterol and lathosterol (both index of whole body cholesterol synthesis), the levels of the bile acid precursor 27-hydroxycholesterol, and of the brain specific 24OHC, were all significantly reduced in manifest HD patients, suggesting that whole-body and brain cholesterol homeostasis are both impaired in HD.

HDL-C concentration is related to markers of absorption and of cholesterol synthesis: Study in subjects with low vs. high HDL-C

Background The antiatherogenic functions of high density lipoprotein (HDL-C) include its role in reverse cholesterol transport, but to what extent the concentration of HDL-C interferes with the whole-body cholesterol metabolism is unknown. Therefore, we measured markers of body cholesterol synthesis (desmosterol and lathosterol) and of intestinal cholesterol absorption (campesterol and β-sitosterol) in healthy subjects that differ according to their plasma HDL-C concentrations. Methods Healthy participants presented either low HDL-C (< 40 mg/dl, n = 33, 17 male and 16 female) or high HDL-C (> 60 mg/dl, n = 33, 17 male and 16 female), BMI < 30 kg/m 2, were paired according to age and gender, without secondary factors that might interfere with their plasma lipid concentrations. Plasma concentrations of non-cholesterol sterols were measured by the combined GC–MS analysis. Results Plasma desmosterol did not differ between the two groups; however, as compared with the high HDL-C participants, the low HDL-C participants presented higher concentration of lathosterol and lower concentration of the intestinal cholesterol absorption markers campesterol and β-sitosterol. Conclusion Plasma concentrations of HDL, and not the activities of LCAT and CETP that regulate the reverse cholesterol transport system, correlate with plasma sterol markers of intestinal cholesterol absorption directly, and of cholesterol synthesis reciprocally.

H03 Cerebral and extracerebral cholesterol biosynthesis is impaired in Huntington's disease patients

BackgroundCholesterol in the CNS is fundamental for membrane trafficking, signal transduction and synaptogenesis and almost all the brain cholesterol is synthetised locally. Homeostasis is maintained through a neuronal specific cholesterol...

Effect of Endurance Exercise Training on Markers of Cholesterol Absorption and Synthesis

PURPOSE: Abnormal cholesterol metabolism, including low intestinal cholesterol absorption and elevated cholesterol synthesis, is prevalent in individuals with diabetes, hyperlipidemia, obesity, and the metabolic syndrome. Diet-induced weight loss improves cholesterol absorption in these populations; the purpose of this study is to investigate if endurance exercise training also improves cholesterol homeostasis. METHODS: We measured circulating levels of campesterol, sitosterol, lathosterol, and cholesterol by GC/mass spectrometry from 65 sedentary subjects (34 women, 31 men, average age = 59) with at least 1 metabolic syndrome risk factor before and after 6 months of endurance exercise training. Campesterol and sitosterol are plant sterols that correlate with intestinal cholesterol absorption, while lathosterol, a precursor in the cholesterol synthetic pathway, is a marker of whole body cholesterol synthesis. We also measured plasma glucose, insulin, VO2max, and body composition by DEXA and CT scanning before and after the intervention. RESULTS: Following the intervention, plasma levels of total plant sterols (campesterol + sitosterol) were increased by 10% (p < 0.05), but there was no change in plasma lathosterol. In addition, total and LDL-cholesterol were both reduced by ~6 mg/dL (p < 0.05 for each), while HDL-C levels increased by 3.3mg/dL (p < 0.05). Furthermore, the change in total plant sterols (campesterol + sitosterol) was positively correlated with the change in VO2max (r = 0.310, p = 0.004), independent of other metabolic syndrome risk factors. CONCLUSIONS: These data indicate that exercise training reduces plasma cholesterol despite increasing cholesterol absorption in middle-to older-aged subjects with risk factors for metabolic syndrome.

The lipid-lowering effect of ezetimibe in pure vegetarians

Results of previous studies have shown that ezetimibe (10 mg/day) reduces LDL cholesterol in patients with mild hypercholesterolemia on a normal-cholesterol diet (dietary intake of 200-500 mg/day) by 16-22%. However, the LDL cholesterol-lowering effect of ezetimibe in subjects with an extremely low dietary cholesterol intake (vegetarians) has not been studied. We conducted a randomized, double-blind, placebo-controlled, two-phase crossover study in 18 healthy pure vegetarians to assess the effect of ezetimibe (10 mg/day) on plasma lipids, cholesterol absorption, and its synthesis. Treatment periods lasted 2 weeks each, with an intervening 2 week washout period. Fractional cholesterol absorption was determined using the continuous dual stable isotope feeding method. Mean dietary cholesterol intake in the pure vegetarians was extremely low and averaged 29.4 +/- 16.8 and 31.4 +/- 14.4 mg/day during the placebo and ezetimibe administration phases, respectively. Fractional cholesterol absorption during the placebo phase was 48.2 +/- 8.2% and was decreased by 58% during ezetimibe treatment to 20.2 +/- 6.2% (P < 0.001). This change in intestinal cholesterol absorption was followed by a significant reduction in LDL cholesterol of 17.3%. In individuals with extremely low dietary cholesterol intake, treatment with ezetimibe (10 mg/day) leads to a significant reduction of cholesterol absorption and a clinically relevant decrease of plasma LDL cholesterol, comparable to that of subjects with a normal dietary cholesterol intake. Thus, the lipid-lowering effect of ezetimibe is mediated mainly through a reduction of the absorption of endogenous (biliary) cholesterol.

The response of lipoproteins to dietary fat and cholesterol in lean and obese persons

Individuals differ in the response of their blood lipoproteins to cholesterol-lowering diets. One characteristic clearly associated with susceptibility to diet is leanness; many studies show that total cholesterol, low-density lipoprotein cholesterol, and high-density lipoprotein cholesterol concentrations respond more strongly to dietary fat and cholesterol in lean subjects than in obese subjects. This is unlikely to be due to differences in dietary compliance. A metabolic explanation is that obese people have a higher rate of total body cholesterol synthesis. The low-density lipoprotein receptors in their liver cells are partly suppressed by this large stream of endogenous cholesterol coming in from their enterohepatic circulation, and the amount added by dietary cholesterol relative to the endogenous pool would be less than in lean people. Whatever the mechanism, diets low in saturated fat and cholesterol are less effective in the obese. The most effective way for obese people to normalize their blood lipids is to lose weight, which is, unfortunately, hard to do in our society.

Effects of diet and metamorphosis upon the sterol composition of the butterfly Morpho peleides

Whole body sterol metabolism in insects has seldom been studied. We were able to design an appropriate study at a butterfly farm in Belize. We collected six larvas of butterfly (Morpho peleides), their food (leaves of Pterocarpus bayessii), and their excretions. In addition, six adult butterflies were collected. The sterols of the diet, the larva, and adult butterfly were analyzed by gas-liquid chromatography. The structures of these sterols were identified by digitonin precipitation, GC-MS, and NMR. Four sterols (cholesterol, campesterol, stigmasterol, and sitosterol) and a sterol mixture were found in the food, the body, and the excreta of the larva. The tissue sterol content of the larva was 326 microg. They consumed 276 microg of sterols per day. Their excretion was 185 microg per day as sterols. The total tissue sterol contents of the larva and butterfly were similar, but they had different sterol compositions, which indicated interconversion of sterols during development. There was a progressive increase in the cholesterol content from larva to butterfly and a decrease in the content of sitosterol and other plant sterols, which were likely converted to cholesterol. Our data indicated an active sterol metabolism in butterfly larva. Diet played an important role in determining its sterol composition. During metamorphosis, there was an interconversion of sterols. This is the first paper documenting the fecal sterol excretion in insects as related to dietary intakes.

Effect of Endurance Exercise Training on Markers of Cholesterol Absorption and Synthesis

Recent studies have shown that circulating levels of plant sterols (campesterol and sitosterol) are markers of cholesterol absorption, while lathosterol, a precursor in the cholesterol synthetic pathway, is a marker for whole body cholesterol synthesis. Endurance exercise training is known to have favorable effects on plasma cholesterol levels, but it is not known if this is mediated in part by changes in rates of cholesterol absorption or synthesis. To examine this, we measured circulating levels of campesterol, sitosterol, and lathosterol by GC/mass spectroscopy from plasma samples of 30 sedentary subjects (20 women, 10 men, average age = 59) before and after 6 months of endurance exercise training. There was no change in sitosterol or lathosterol levels in response to the exercise training intervention. However, there was a trend for an increase in plasma campesterol levels of 20% following the intervention (p = 0.07). Other changes in lipids included the following: there was no change in total or LDL-C levels in response to the exercise intervention; however, HDL-C and the HDL2-C subfraction increased 4.0mg/dL and 2.2mg/dL, respectively (p < .01), and total triglyceride levels decreased by 20mg/dL (p < 0.001). The increase in plasma campesterol indicates that endurance exercise training may have a significant impact on rates of cholesterol absorption. Reduced levels of cholesterol absorption have been linked to the development of the “metabolic syndrome.” As a result, this exercise induced increase in campesterol levels may suggest a previously unrecognized benefit of exercise training on cholesterol metabolism.

The response of lipoproteins to dietary fat and cholesterol in lean and obese persons

Individuals differ in the response of their blood lipoproteins to cholesterol-lowering diets. One characteristic clearly associated with susceptibility to diet is leanness; many studies show that total cholesterol, low-density lipoprotein cholesterol, and high-density lipoprotein cholesterol concentrations respond more strongly to dietary fat and cholesterol in lean subjects than in obese subjects. This is unlikely to be due to differences in dietary compliance. A metabolic explanation is that obese people have a higher rate of total body cholesterol synthesis. The low-density lipoprotein receptors in their liver cells are partly suppressed by this large stream of endogenous cholesterol coming in from their enterohepatic circulation, and the amount added by dietary cholesterol relative to the endogenous pool would be less than in lean people. Whatever the mechanism, diets low in saturated fat and cholesterol are less effective in the obese. The most effective way for obese people to normalize their blood lipids is to lose weight, which is, unfortunately, hard to do in our society.

Bile acid synthesis is increased in chilean hispanics with gallstones and in gallstone high-risk Mapuche Indians

Background & Aims : Gallstone disease is an important, costly health-care problem in Western societies. It is still unclear whether hepatic lipid regulatory enzymes play primary or secondary roles in gallstone formation. In this study, the aim was to investigate whether the synthesis of bile acids and cholesterol is increased in gallstone disease and to test whether such a metabolic change, if present, might occur before gallstone formation. Methods : A total of 125 Chilean Hispanic women (80 without gallstones and 45 with gallstones) matched for age and body mass index were investigated, along with 40 Chilean Mapuche Indian women (20 without gallstones and 20 with gallstones), a population group in which the prevalence for gallstone disease is very high. Fasting blood plasma samples were assayed for 7α-hydroxy-4-cholesten-3-one and lathosterol, 2 strong indicators for hepatic bile acid and body cholesterol synthesis, respectively. Results : Plasma 7α-hydroxy-4-cholesten-3-one levels, corrected for plasma cholesterol, were significantly increased by 50% in Hispanic women with gallstones as compared with gallstone-free Hispanics ( P < 0.006). As compared with Hispanic women without gallstones, plasma 7α-hydroxy-4-cholesten-3-one levels were increased by ≥100% ( P < 0.002) in Mapuche Indian women, independently of whether gallstones were present. Plasma lathosterol, corrected for plasma cholesterol, was significantly increased by 22% in Hispanic women with gallstones and in Mapuche Indian women compared with Hispanic women. Conclusions : The results indicate that the synthesis of bile acids and cholesterol is induced in gallstone disease and precedes gallstone development. These inductions presumably occur as a response to an increased intestinal loss of bile acids.

Statin rebound effect?

J Lab Clin Med 2003;141:235-6.

Efficiency of intestinal cholesterol absorption in humans is not related to apoE phenotype

The present study investigated the role of apolipoprotein E (apoE) phenotype on intestinal cholesterol absorption and cholesterol synthesis. Studies were carried out in eight subjects homozygous for the apoE4 and 12 subjects homozygous for the E2 allele (six normocholesterolemic volunteers and six patients with type III hyperlipoproteinemia). Cholesterol absorption did not differ between the three groups of subjects and averaged 38 +/- 2% (mean +/- SEM) in normolipemic E2/2, 37 +/- 4% in type III hyperlipemic E2/2, and 41 +/- 3% in E4/4 subjects, respectively. Dietary intake of fat and cholesterol had no influence on cholesterol absorption efficiency. A positive correlation between efficiency of cholesterol absorption and the ratio of campesterol to cholesterol in plasma, an indirect marker for cholesterol absorption, was observed after combining the results of the three groups (r = 0.504; P < 0.02). Bile acid and total cholesterol synthesis were also not affected by the different apoE alleles, but the well-known relationship between body weight and cholesterol synthesis was noticed (r = 0.574; P < 0.01). Thus, the present study provides evidence that the efficiency of intestinal absorption and synthesis of cholesterol in humans are not related to the apoE phenotype.

ATP-binding cassette transporter A1 (ABCA1) affects total body sterol metabolism

Members of the family of ABC transporters are involved in different processes of sterol metabolism, and ABCA1 was recently identified as a key regulator of high-density lipoprotein (HDL) metabolism. Our aim was to further analyze the role of ABCA1 in cholesterol metabolism. ABCA1-deficient mice (ABCA1-/-) and wild-type mice were compared for different aspects of sterol metabolism. Intestinal cholesterol absorption was determined by a dual stable isotope technique, and analysis of fecal, plasma, and tissue sterols was performed by gas chromatography/mass spectrometry. Key regulators of sterol metabolism were investigated by Northern and Western blot analyses or enzyme activity assays. ABCA1-disrupted sv129/C57BL/6 hybrid mice showed a significant reduction in intestinal cholesterol absorption. The decrease in cholesterol absorption was followed by an enhanced fecal loss of neutral sterols, whereas fecal bile acid excretion was not affected. Total body cholesterol synthesis was significantly increased, with enhanced 3-hydroxy-3-methyglutaryl-coenzyme A (HMG-CoA) reductase observed in adrenals and spleen. In addition, ABCA1-/- mice showed markedly increased concentrations of cholesterol precursors in the plasma, lung, intestine, and feces. Reduced HMG-CoA reductase messenger RNA and enzyme activity in the liver suggest that enhanced cholesterol synthesis in ABCA1-/- mice occurs in peripheral tissues rather than the liver. The metabolism of cholesterol and cholesterol precursors is markedly affected by a lack of ABCA1 function.