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Journal of Lipid Research Mar 2003The recent identification of the aberrant transport proteins ABCG5 and ABCG8 resulting in sitosterolemia suggests that intestinal uptake of cholesterol is an unselective... (Comparative Study)
Comparative Study
The recent identification of the aberrant transport proteins ABCG5 and ABCG8 resulting in sitosterolemia suggests that intestinal uptake of cholesterol is an unselective process, and that discrimination between cholesterol and plant sterols takes place at the level of sterol efflux from the enterocyte. Although plant sterols are structurally very similar to cholesterol, differing only in their side chain length, they are absorbed from the intestine to a markedly lower extent. In order to further evaluate the process of discrimination, three different sterols (cholesterol, campesterol, sitosterol) and their corresponding 5 alpha-stanols (cholestanol, campestanol, sitostanol) were compared concerning their concentration in the proximal small intestine, in serum, and in bile after a single oral dose of deuterated compounds. The data obtained support the hypothesis that i) the uptake of sterols and stanols is an extremely rapid process, ii) discrimination probably takes place on the level of reverse transport back into the gut lumen, iii) plant stanols are taken up, but not absorbed to a measurable extent, and iv) the process of discrimination probably also exists at the level of biliary excretion. The range of structural alterations that decrease intestinal absorption and increase biliary excretion is: 1) campesterol, 2) cholestanol-sitosterol, and 3) campestanol-sitostanol.
Topics: Animals; Bile; Cholestanols; Cholesterol; Cholesterol, Dietary; Intestinal Absorption; Intestine, Small; Male; Mice; Phytosterols; Plant Extracts; Sitosterols
PubMed: 12562824
DOI: 10.1194/jlr.M200393-JLR200 -
Proceedings of the National Academy of... Dec 2002Cholesterol and other sterols exit the body primarily by secretion into bile. In patients with sitosterolemia, mutations in either of two ATP-binding cassette (ABC)...
Cholesterol and other sterols exit the body primarily by secretion into bile. In patients with sitosterolemia, mutations in either of two ATP-binding cassette (ABC) half-transporters, ABCG5 or ABCG8, lead to reduced secretion of sterols into bile, implicating these transporters in this process. To elucidate the roles of ABCG5 and ABCG8 in the trafficking of sterols, we disrupted Abcg5 and Abcg8 in mice (G5G8(-/-)). The G5G8(-/-) mice had a 2- to 3-fold increase in the fractional absorption of dietary plant sterols, which was associated with an approximately 30-fold increase in plasma sitosterol. Biliary cholesterol concentrations were extremely low in the G5G8(-/-) mice when compared with wild-type animals (mean = 0.4 vs. 5.5 micromol ml) and increased only modestly with cholesterol feeding. Plasma and liver cholesterol levels were reduced by 50% in the chow-fed G5G8(-/-) mice and increased 2.4- and 18-fold, respectively, after cholesterol feeding. These data indicate that ABCG5 and ABCG8 are required for efficient secretion of cholesterol into bile and that disruption of these genes increases dramatically the responsiveness of plasma and hepatic cholesterol levels to changes in dietary cholesterol content.
Topics: ATP Binding Cassette Transporter, Subfamily G, Member 5; ATP Binding Cassette Transporter, Subfamily G, Member 8; ATP-Binding Cassette Transporters; Animal Feed; Animals; Bile; Biological Transport; Chimera; Cholestanol; Cholesterol; Cholesterol, Dietary; Crosses, Genetic; Dietary Fats; Female; Gene Targeting; Intestinal Absorption; Intestinal Mucosa; Lipoproteins; Liver; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Phytosterols; Sitosterols
PubMed: 12444248
DOI: 10.1073/pnas.252582399 -
Journal of Clinical Pathology Nov 2002To assess the specificity and sensitivity of the commonly used enzymatic colorimetric test for plasma cholesterol determination.
AIM
To assess the specificity and sensitivity of the commonly used enzymatic colorimetric test for plasma cholesterol determination.
METHODS
Interference with an enzymatic method for cholesterol measurement by several non-cholesterol sterols (beta sitosterol, campesterol, stigmasterol, stigmastanol, desmosterol, and lathosterol) was assessed. Some of these compounds are present in plasma at higher than normal concentrations either in rare genetic disorders, such as phytosterolaemia, or after the consumption of phytosterol enriched foods.
RESULTS
The non-cholesterol sterols were detected by the assay in a linear manner. There was no competitive interference in the presence of cholesterol.
CONCLUSIONS
This crossreactivity may affect the diagnosis and treatment of non-cholesterol dyslipidaemias, including phytosterolaemia and cerebrotendinous xanthomatosis. Similarly, changes in plasma lipid compositions after the consumption of phytosterol enriched foods cannot be specifically determined by this enzymatic assay. Until a more specific enzymatic assay is developed, alternative methods such as gas chromatography should be used to differentiate between cholesterol and non-cholesterol sterols.
Topics: Cholesterol; Colorimetry; Cross Reactions; Humans; Hyperlipidemias; Phytosterols; Sensitivity and Specificity; Sterols
PubMed: 12401826
DOI: 10.1136/jcp.55.11.859 -
Journal of Lipid Research Nov 2000We measured the percent absorption, turnover, and distribution of campestanol (24-methyl-5alpha-cholestan-3beta-ol) in a sitosterolemic homozygote, her obligate...
We measured the percent absorption, turnover, and distribution of campestanol (24-methyl-5alpha-cholestan-3beta-ol) in a sitosterolemic homozygote, her obligate heterozygous mother, and three healthy human control subjects. For reasons relating to sterol hyperabsorption, the homozygote consumed a diet low in plant sterols that contained campestanol at about 2 mg/day. The heterozygote and three control subjects were fed a diet supplemented with a spread that contained campestanol at 540 mg/day and sitostanol (24-ethyl-5alpha-cholestan-3beta-ol) at 1.9 g/day as fatty acid esters. Plasma campestanol concentrations determined by capillary gas-liquid chromatography were 0.72 +/- 0.03 mg/dl in the homozygote, 0.09 +/- 0.04 mg/dl in the heterozygote, and 0.05 +/- 0.03 mg/dl for the control mean. After simultaneous pulse labeling with [3alpha-(3)H]campestanol intravenously and [23-(14)C]campestanol orally, the maximum percent absorption measured by the plasma dual-isotope ratio method as a single time point was 80% in the homozygote, 14.3% in the heterozygote, and 5.5 +/- 4.3% as the mean for three control subjects. Turnover (pool size) values estimated by mathematical analysis of the specific activity versus time [3alpha-(3)H]campestanol decay curves were as follows: 261 mg in the homozygote, 27.3 mg in the heterozygote, and 12.8 +/- 7.6 mg in the three control subjects (homogygote vs. controls, P < 0.001). The calculated production rate (mg/24 h) equivalent to actual absorption in the presence of dietary sterols and stanols was 0.67 mg/day or 31% of intake in the homozygote, 2.1 mg/day or 0.3% of intake in the heterozygote, and 0.7 +/- 0.3 mg/day or 0.1% of intake in the three control subjects. However, the excretion constant from pool A (K(A)) was prolonged markedly in the homozygote, but was 100 times more rapid in the heterozygote and three control subjects.Thus, campestanol, like other noncholesterol sterols, is hyperabsorbed and retained in sitosterolemic homozygotes. However, campestanol absorption was only slightly increased in the sitosterolemic heterozygote and removal was as rapid as in control subjects.
Topics: Adolescent; Adult; Carbon Radioisotopes; Cholesterol; Diet; Female; Half-Life; Heterozygote; Homozygote; Humans; Intestinal Absorption; Kinetics; Lipid Metabolism, Inborn Errors; Male; Middle Aged; Phytosterols; Sitosterols; Tritium
PubMed: 11060358
DOI: No ID Found -
Journal of Lipid Research Apr 1999We investigated the changes of cholesterol and non-cholesterol sterol metabolism during plant stanol ester margarine feeding in 153 hypercholesterolemic subjects.... (Clinical Trial)
Clinical Trial Randomized Controlled Trial
We investigated the changes of cholesterol and non-cholesterol sterol metabolism during plant stanol ester margarine feeding in 153 hypercholesterolemic subjects. Rapeseed oil (canola oil) margarine without (n = 51) and with (n = 102) stanol (2 or 3 g/day) ester was used for 1 year. Serum sterols were analyzed with gas-liquid chromatography. The latter showed a small increase in sitostanol peak during stanol ester margarine eating. Cholestanol, campesterol, and sitosterol proportions to cholesterol were significantly reduced by 5-39% (P < 0.05 or less for all) by stanol esters; the higher their baseline proportions the higher were their reductions. The precursor sterol proportions were significantly increased by 10- 46%, and their high baseline levels predicted low reduction of serum cholesterol. The decrease of the scheduled stanol dose from 3 to 2 g/day after 6-month feeding increased serum cholesterol by 5% (P < 0. 001) and serum plant sterol proportions by 8-13% (P < 0.001), but had no consistent effect on precursor sterols. In twelve subjects, the 12-month level of LDL cholesterol exceeded that of baseline; the non-cholesterol sterol proportions suggested that stimulated synthesis with relatively weak absorption inhibition contributed to the non-responsiveness of these subjects. In conclusion, plant stanol ester feeding lowers serum cholesterol in about 88% of subjects, decreases the non-cholesterol sterols that reflect cholesterol absorption, increases the sterols that reflect cholesterol synthesis, but also slightly increases serum plant stanols. Low synthesis and high absorption efficiency of cholesterol results in the greatest benefit from stanol ester consumption.
Topics: Anticholesteremic Agents; Body Mass Index; Cholestanol; Cholesterol; Dietary Fats, Unsaturated; Esters; Fatty Acids, Monounsaturated; Humans; Hypercholesterolemia; Kinetics; Margarine; Phytosterols; Rapeseed Oil; Sitosterols; Sterols
PubMed: 10191283
DOI: No ID Found -
The Journal of Clinical Investigation Feb 1997Unesterified cholesterol (UC) that is taken up by the liver from lipoproteins is rapidly mixed by exchange with liver UC. Thus, it is not possible to quantitate the...
Unesterified cholesterol (UC) that is taken up by the liver from lipoproteins is rapidly mixed by exchange with liver UC. Thus, it is not possible to quantitate the transport of UC from different lipoproteins into bile using radiolabeled UC. However, plant sterols do not exchange with UC and are secreted in bile with the same kinetics as UC. To compare the contribution to bile of sterols from different lipoproteins, we perfused isolated rat livers with VLDL, LDL, and HDL that were obtained from patients with hereditary phytosterolemia and were rich in plant sterols. After 30-min recirculating perfusions, hepatic concentrations of plant sterols were not different after different lipoproteins were perfused. However, biliary plant sterol secretion was markedly different: with the perfusion of either VLDL or LDL there was no increase in plant sterols in bile, but with perfusion of HDL, the secretion of plant sterols was increased two- to threefold (P = 0.0005). The increase in biliary plant sterols was detected 5-10 min after HDL was added to perfusates and was similarly large for each of three individual plant sterols that was tracked. Results show that when sterol transport from lipoproteins into bile can be determined, only HDL provides a vehicle for UC elimination in bile that is consistent with its putative function in reverse cholesterol transport.
Topics: Animals; Bile; Biological Transport; Cholesterol; Chromatography, High Pressure Liquid; Humans; Hypolipoproteinemias; Lipoproteins, HDL; Lipoproteins, LDL; Lipoproteins, VLDL; Liver; Male; Perfusion; Phytosterols; Rats; Rats, Sprague-Dawley; Sitosterols
PubMed: 9022069
DOI: 10.1172/JCI119170 -
Journal of Lipid Research Aug 1996Effectiveness of a simultaneous inhibition of cholesterol absorption and synthesis, caused by sitostanol ester margarine and pravastatin, was studied to control mild... (Clinical Trial)
Clinical Trial Comparative Study Randomized Controlled Trial
Effectiveness of a simultaneous inhibition of cholesterol absorption and synthesis, caused by sitostanol ester margarine and pravastatin, was studied to control mild hypercholesterolemia in men with non-insulin-dependent diabetes mellitus (NIDDM) (n = 8). Margarine, 24 g daily, was a basal dietary treatment. Four 7-week intervention periods included margarine, sitostanol (3 g/day) ester margarine, pravastatin (40 mg/day), and sitostanol ester margarine plus pravastatin in a random order. Pravastatin lowered serum total (-32%) and LDL cholesterol (-38%) and apolipoprotein B (-39%) because of enhanced removal (+20%) and decreased production (-26%) of LDL apolipoprotein B, and reduced synthesis (-9%) and turnover (-8%) of cholesterol, which resulted in reduced biliary cholesterol seretion (-18%). Even though serum triglycerides were lowered by 28%, VLDL, IDL, and light and dense LDL became triglyceride-enriched. Despite increasing cholesterol synthesis, sitostanol lowered LDL cholesterol (-14%) by inhibiting cholesterol absorption (-68%) and LDL apolipoprotein B production rate (-20%). Combination of pravastatin and sitostanol ester lowered serum total, VLDL, IDL, and LDL cholesterol and LDL apolipoprotein B by the highest rate, 35%, 50%, 35%, 44%, and 45% from the control margarine period, respectively, because of reduced apolipoprotein B transport rate (but unchanged removal), in both the total and dense LDL subfractions. HDL cholesterol and apolipoprotein A-I kinetics were unchanged. In spite of decreased absorption, cholesterol synthesis was not compensatorily increased. In conclusion, simultaneous inhibition of cholesterol absorption and synthesis lowers LDL cholesterol and apolipoprotein B by 44-45% solely through inhibition of LDL apolipoprotein B production rate in hypercholesterolemic NIDDM patients. A combination of statin to sitostanol ester margarine-resistant patients offers a safe and effective measure to normalize abnormally high cholesterol values, probably with a lowered statin dose.
Topics: Absorption; Anticholesteremic Agents; Blood Specimen Collection; Cholesterol; Diabetes Mellitus, Type 2; Double-Blind Method; Humans; Hypercholesterolemia; Lipoproteins; Male; Middle Aged; Patient Selection; Pravastatin; Sitosterols; Triglycerides
PubMed: 8864962
DOI: No ID Found -
Journal of Lipid Research Jan 1996The hepatic uptake, transport, and secretion into bile of unesterified cholesterol cannot be directly quantitated because of extensive exchange and equilibration between...
The hepatic uptake, transport, and secretion into bile of unesterified cholesterol cannot be directly quantitated because of extensive exchange and equilibration between different pools of unesterified cholesterol. Plant sterols are structurally similar to cholesterol but because of poor intestinal absorption are ordinarily not present in the liver. To quantitate hepatic sterol uptake and transport in the absence of exchange with endogenous sterols, isolated rat livers were perfused with the plant sterol, sitostanol, incorporated in phosphatidylcholine liposomes. Appreciable amounts of sitostanol were taken up by the liver and uptake was independent of the presence of bile salt. In contrast, like unesterified cholesterol, the secretion of sitostanol in bile required bile salt. Sitostanol was detected in bile within 5 min after a perfusion was begun and reached a plateau by about 20 min. The rate of appearance of sitostanol in bile was precisely the same as unesterified cholesterol when both sterols were perfused together. Furthermore, the output of sitostanol in bile was directly proportional to the output of cholesterol. At the peak of biliary sitostanol secretion, the amount of sitostanol relative to unesterified cholesterol was much greater in bile (40-50% of sterols) than in the whole liver (11% of sterols). Selective biliary secretion of sitostanol was associated with much greater concentrations of sitostanol in canalicular membranes than in the interior membranes of the hepatocyte and in newly secreted high density lipoproteins compared to newly secreted very low density lipoproteins. These results indicate that sitostanol parallels the secretion from and distribution of unesterified cholesterol in the liver and suggest that sitostanol can be used as a physiologic analog of unesterified cholesterol to trace the transport of sterols through the liver.
Topics: Animals; Bile; Bile Acids and Salts; Cholesterol; In Vitro Techniques; Liver; Male; Perfusion; Radioactive Tracers; Rats; Rats, Sprague-Dawley; Sitosterols
PubMed: 8820098
DOI: No ID Found -
Clinical and Experimental Immunology Jan 1996An antibody reactive with cholesterol sulphate (CS) was characterized in human sera by ELISA, erythrocyte and liposome absorption. This antibody was found evenly...
An antibody reactive with cholesterol sulphate (CS) was characterized in human sera by ELISA, erythrocyte and liposome absorption. This antibody was found evenly distributed between the IgA and IgM classes, and whilst this was present at low titres in the serum of 16% of healthy individuals studied, it was significantly elevated in 78% of Trypanosoma cruzi-infected subjects. No association was found between antibody levels and the degree of myocardial damage. No significant difference in immunoreactivity was found between healthy and chagasic subjects using dehydro-epiandrosterone sulphate and pregnenolone sulphate and cholesterol, ergosterol, lanosterol, stigmastanol, beta-stigmasterol, pregnenolone, prednisolone and dehydroepiandrosterone as antigens, suggesting that in chagasic sera the whole sterol molecule is important for optimal antibody binding. CS-reactive antibodies were easily purified by absorption either with CS-bearing liposomes or with dextran sulphate gel and further elution with 1.5 M NaCl. The optimal pH of CS-antibody interaction was 4.0 with 85% binding at pH 7.0. Polylysine strongly decreased the binding of these antibodies to the corresponding antigen. Furthermore, these antibodies were strongly absorbed by rabbit and guinea pig erythrocyte but not by rat or human erythrocyte. In contrast with anti-sulphatide antibodies, no significant increase in CS-reactive antibodies was found in dilated cardiomyopathies. Whilst CS itself was not detected in T. cruzi lipid extracts, there is an unidentified sulphated sterol, which migrates close to standard CS and which strongly binds chagasic but not control sera. This latter sterol might be acting in chagasic patients as a powerful antigen, triggering specific autoantibody production.
Topics: Animals; Antibodies, Protozoan; Antibody Specificity; Autoantibodies; Binding Sites, Antibody; Carbohydrates; Chagas Disease; Cholesterol Esters; Chromatography, Gel; Chronic Disease; Enzyme-Linked Immunosorbent Assay; Erythrocytes; Humans; Hydrogen-Ion Concentration; Immunoglobulins; Lipids; Liposomes; Osmolar Concentration; Peptides; Polyglutamic Acid; Polylysine; Trypanosoma cruzi
PubMed: 8565284
DOI: 10.1046/j.1365-2249.1996.877569.x -
Proceedings of the National Academy of... Dec 1995This study examines the question of whether apolipoprotein E (apoE) alters steady-state concentrations of plasma cholesterol carried in low density lipoproteins (LDL-C)...
Apolipoprotein E competitively inhibits receptor-dependent low density lipoprotein uptake by the liver but has no effect on cholesterol absorption or synthesis in the mouse.
This study examines the question of whether apolipoprotein E (apoE) alters steady-state concentrations of plasma cholesterol carried in low density lipoproteins (LDL-C) by acting as a competitive inhibitor of hepatic LDL uptake or by altering the rate of net cholesterol delivery from the intestinal lumen to the liver. To differentiate between these two possibilities, rates of cholesterol absorption and synthesis and the kinetics of hepatic LDL-C transport were measured in vivo in mice with either normal (apoE+/+) or zero (apoE-/-) levels of circulating apoE. Rates of cholesterol absorption were essentially identical in both genotypes and equaled approximately 44% of the daily dietary load of cholesterol. This finding was consistent with the further observation that the rates of cholesterol synthesis in the liver (approximately 2,000 nmol/h) and extrahepatic tissues (approximately 3,000 nmol/h) were also essentially identical in the two groups of mice. However, the apparent Michaelis constant for receptor-dependent hepatic LDL-C uptake was markedly lower in the apoE-/- mice (44 +/- 4 mg/dl) than in the apoE+/+ animals (329 +/- 77 mg/dl) even though the maximal transport velocity for this uptake process was essentially the same (approximately 400 micrograms/h per g) in the two groups of mice. These studies, therefore, demonstrate that apoE-containing lipoproteins can act as potent competitive inhibitors of hepatic LDL-C transport and so can significantly increase steady-state plasma LDL-C levels. This apolipoprotein plays no role, however, in the regulation of cholesterol absorption, sterol biosynthesis, or hepatic LDL receptor number, at least in the mouse.
Topics: Animals; Apolipoproteins E; Binding, Competitive; Carbon Radioisotopes; Cholesterol; Cholesterol, Dietary; Cholesterol, HDL; Cholesterol, LDL; Cholesterol, VLDL; Crosses, Genetic; Female; Humans; Intestinal Absorption; Intestine, Small; Lipoproteins, LDL; Liver; Male; Mice; Mice, Inbred C57BL; Mice, Inbred Strains; Mice, Mutant Strains; Receptors, LDL; Sitosterols
PubMed: 8618929
DOI: 10.1073/pnas.92.26.12500