| For medical practitioners and the general public - Cholesterol Journal Article Catalog. |
| First Page | Previous Page | Next Page | Last Page |
| Metal ions, pH, and cholesterol regulate the interactions of Alzheimer's disease amyloid-beta peptide with membrane lipid Curtain, C. C., F. E. Ali, et al. (2003), J Biol Chem 278(5): 2977-82. Abstract: The interaction of A beta peptides with the lipid matrix of neuronal cell membranes plays an important role in the pathogenesis of Alzheimer's disease. By using EPR and CD spectroscopy, we found that in the presence of Cu(2+) or Zn(2+), pH, cholesterol, and the length of the peptide chain influenced the interaction of these peptides with lipid bilayers. In the presence of Zn(2+), A beta 40 and A beta 42 both inserted into the bilayer over the pH range 5.5-7.5, as did A beta 42 in the presence of Cu(2+). However, A beta 40 only penetrated the lipid bilayer in the presence of Cu(2+) at pH 5.5-6.5; at higher pH there was a change in the Cu(2+) coordination sphere that inhibited membrane insertion. In the absence of the metals, insertion of both peptides only occurred at pH < 5.5. Raising cholesterol to 0.2 mol fraction of the total lipid inhibited insertion of both peptides under all conditions investigated. Membrane insertion was accompanied by the formation of alpha-helical structures. The nature of these structures was the same irrespective of the conditions used, indicating a single low energy structure for A beta in membranes. Peptides that did not insert into the membrane formed beta-sheet structures on the surface of the lipid. |
| Metalloenzyme-like activity of Alzheimer's disease beta-amyloid. Cu-dependent catalytic conversion of dopamine, cholesterol, and biological reducing agents to neurotoxic H(2)O(2) Opazo, C., X. Huang, et al. (2002), J Biol Chem 277(43): 40302-8. Abstract: Beta-amyloid (Abeta) 1-42, implicated in the pathogenesis of Alzheimer's disease, forms an oligomeric complex that binds copper at a CuZn superoxide dismutase-like binding site. Abeta.Cu complexes generate neurotoxic H(2)O(2) from O(2) through Cu(2+) reduction, but the reaction mechanism has been unclear. We now report that Abeta1-42, when binding up to 2 eq of Cu(2+), generates the H(2)O(2) catalytically by recruiting biological reducing agents as substrates under conditions where the Cu(2+) or reducing agents will not form H(2)O(2) themselves. Cholesterol is an important substrate for this activity, as are vitamin C, L-DOPA, and dopamine (V(max) for dopamine = 34.5 nm/min, K(m) = 8.9 microm). The activity was inhibited by anti-Abeta antibodies, Cu(2+) chelators, and Zn(2+). Toxicity of Abeta in neuronal culture was consistent with catalytic H(2)O(2) production. Abeta was not toxic in cell cultures in the absence of Cu(2+), and dopamine (5 microm) markedly exaggerated the neurotoxicity of 200 nm Abeta1-42.Cu. Therefore, microregional catalytic H(2)O(2) production, combined with the exhaustion of reducing agents, may mediate the neurotoxicity of Abeta in Alzheimer's disease, and inhibitors of this novel activity may be of therapeutic value. |
| Metformin modulates insulin receptor signaling in normal and cholesterol-treated human hepatoma cells (HepG2) Meuillet, E. J., N. Wiernsperger, et al. (1999), Eur J Pharmacol 377(2-3): 241-52. Abstract: The effects of the biguanide anti-hyperglycemic agent, metformin (N,N'-dimethyl-biguanide), on insulin signaling was studied in a human hepatoma cell line (HepG2). Cells were cultured in the absence (control cells) or in the presence of 100 microM of a cholesterol derivative, hemisuccinate of cholesterol. Cholesterol hemisuccinate-treatment alters cholesterol and lipid content of HepG2 and modulates membrane fluidity. Cholesterol hemisuccinate-treatment induces a decrease in insulin responsiveness and creates an 'insulin-resistant' state in these cells. Exposure to 100 microM of metformin resulted in a significant enhancement of insulin-stimulated lipogenesis in control and cholesterol hemisuccinate-treated cells. In control cells, metformin altered glycogenesis in a biphasic manner. In cholesterol hemisuccinate-treated cells, metformin inhibited basal glycogenesis but restored insulin-stimulated glycogenesis. Hence, to understand the mechanism of metformin action, we analyzed early steps in the insulin signaling pathway, including insulin receptor autophosphorylation, mitogen-activated-protein kinase and phosphatidylinositol 3-kinase activities, in both control and cholesterol hemisuccinate-treated cells. Overall, the results suggest that metformin may interact with the insulin receptor and/or a component involved in the early steps of insulin signal transduction. |
| Metformin reduces weight, centripetal obesity, insulin, leptin, and low-density lipoprotein cholesterol in nondiabetic, morbidly obese subjects with body mass index greater than 30 Glueck, C. J., R. N. Fontaine, et al. (2001), Metabolism 50(7): 856-61. Abstract: We studied 31 nondiabetic, habitually (> or =5 years) morbidly obese subjects (mean +/- SD body mass index BMI 43 +/- 8.7, median 43). Our specific aim was to determine whether metformin (2.55 g/d for 28 weeks) would ameliorate morbid obesity and reduce centripetal obesity; lipid and lipoprotein cholesterol, insulin, and leptin levels; and plasminogen activator inhibitor activity (PAI-Fx), risk factors for coronary heart disease (CHD). The patients were instructed to continue their prestudy dietary and exercise regimens without change. After 2 baseline visits 1 week apart, the 27 women and 4 men began receiving metformin, 2.55 g/d, which was continued for 28 weeks with follow-up visits at study weeks 5, 13, 21, and 29. Daily food intake was recorded by patients for 7 days before visits then reviewed with a dietitian. Kilocalories per day and per week were calculated. At each visit, fasting blood was obtained for measurement of lipid profile, insulin, leptin, and PAI-Fx. The mean +/- SD kilocalories consumed per day, 1,951 +/- 661 at entry, fell by week 29 to 1,719 +/- 493 (P =.014) but did not differ at weeks 5, 13, and 21 from that at week 29 (P >.2). Weight fell from 258 +/- 62 pounds at entry to 245 +/- 54 pounds at week 29 (P =.0001). Girth was reduced from 51.8 +/- 6.2 to 49.2 +/- 4.5 inches (P =.0001). Waist circumference fell from 44.0 +/- 6.4 inches to 41.3 +/- 5.9 (P =.0001). The waist/hip ratio fell from 0.85 +/- 0.09 to 0.84 +/- 0.09 (P =.04). Fasting serum insulin, 28 +/- 15 microU/mL at entry, fell to 21 +/- 11 microU/mL at week 29 (P =.0001), and leptin fell from 79 +/- 33 ng/mL to 55 +/- 27 ng/mL (P =.0001). On metformin, there were linear trends in decrements in weight, girth, waist circumference, waist/hip ratio, insulin, and leptin throughout the study period (P <.007). Low-density lipoprotein (LDL) cholesterol, 126 +/- 34 mg/dL at study entry, fell to 112 +/- 43 mg/dL at week 29 (P =.001), with a linear trend toward decreasing levels throughout (P =.036). By stepwise linear regression, the higher the entry weight, the larger the reduction in weight on metformin therapy (partial R(2) = 31%, P =.001). The greater the reduction in kilocalories consumed per day, the greater the decrease in weight on metformin therapy (partial R(2) = 15%, P =.011). The higher the waist/hip ratio at entry, the greater its reduction on metformin therapy (partial R(2) = 11%, P =.004). The higher the entry serum leptin, the greater its reduction on metformin therapy (partial R(2) = 29%, P =.002). The greater the reduction in insulin on metformin, the greater the reduction in leptin (partial R(2) = 8%, P =.03). The higher the entry PAI-Fx, the greater the reduction in PAI-Fx on metformin (partial R(2) = 43%, P =.0001). Metformin safely and effectively reduces CHD risk factors (weight, fasting insulin, leptin, LDL cholesterol, centripetal obesity) in morbidly obese, nondiabetic subjects with BMI > 30, probably by virtue of its insulin-sensitizing action. |
| Methionine content of dietary proteins affects the molecular species composition of plasma phosphatidylcholine in rats fed a cholesterol-free diet Sugiyama, K., A. Yamakawa, et al. (1997), J Nutr 127(4): 600-7. Abstract: The effects of dietary protein types and methionine supplementation on phospholipid metabolism were investigated to clarify the mechanism of the hypocholesterolemic action of soybean protein in rats fed a cholesterol-free diet. The effect of switching from a casein diet to a soybean protein diet was also investigated. Rats were fed casein, soybean protein or soybean protein + methionine diet for 14 d. Compared with casein diet, feeding of soybean protein diet led to significantly higher proportions of linoleic acid and linoleic acid-containing molecular species, especially 16:0-18:2, in plasma and liver microsomal phosphatidylcholine (PC). In addition, significantly lower plasma cholesterol concentration, hepatic S-adenosylmethionine concentration and liver microsomal PC:phosphatidylethanolamine ratio resulted. These alterations caused by the soybean protein diet were significantly suppressed by supplementing methionine to the level of the casein diet (3.4 g/kg diet). The proportion of the sum of certain plasma PC molecular species, which contain 18:1 or 18:2 in the sn-2 position, increased in response to the switch from the casein diet to the soybean protein diet at a rate similar to the decrease in plasma cholesterol concentration; there was a significant correlation between the two variables (r = -0.992, P < 0.001). These results indicate that about 40% of the hypocholesterolemic action of soybean protein is due to the low methionine content of the protein and might be associated with alterations of the plasma phospholipid molecular species profile. |
| Methionine supplementation did not augment oxidative stress, atherosclerotic changes and hepatotoxicity induced by high cholesterol diet in C57BL/6J mice Balkan, J., S. Dogru-Abbasoglu, et al. (2004), J Nutr Sci Vitaminol (Tokyo) 50(4): 258-64. Abstract: The purpose of this study was to investigate the effect of a high-methionine plus cholesterol diet (HM+HC) on plasma, erythrocyte, liver and aorta lipid, lipid peroxide levels, and the liver antioxidant system, as well as hepatic and aortic histopathology in CS 7BL/6J mice, and to compare these results to those observed following administration of a high-methionine (HM) or high-cholesterol diet (HC) alone. Mice were fed diets containing 1.5% methionine, 1.5%, cholesterol and 0.5% cholic acid, or a combination of the two diets, for 4 mo. The HM diet did not alter cholesterol or diene conjugate (DC) levels in the plasma or aorta, but this diet caused increases in cholesterol, triglyceride, malondialdehyde (MDA) and DC levels and a decrease in a-tocopherol levels without any change in the levels of glutathione and ascorbic acid or the activities of superoxide dismutase, glutathione peroxidase and glutathione transferase in the liver of mice. However, the HC diet alone was found to further increase cholesterol, triglyceride. MDA and DC levels in the plasma and liver together with changes in hepatic antioxidant system elements, but aortic cholesterol and DC levels remained unchanged as compared to the control group. There were no changes in blood hemoglobin and erythrocyte MDA levels or erythrocyte hemolysis values in both the HM and HC groups. However, the parameters related to lipid and lipid peroxide and antioxidant systems did not change in the plasma or tissues of the HM+HC and HC groups. Only plasma cholesterol was observed to increase in the HM+HC group as compared to the HC group. In addition, histopathological findings in the liver and aorta were similar in the HC and HM+HC groups. In conclusion, our results indicate that the addition of methionine to the HC diet did not augment oxidative stress, hepatotoxicity or atherosclerotic changes induced by the HC diet in mice. |
| Method for quantitative assessment of transformation of non-micellar cholesterol carriers in model bile systems Yamashita, Y., S. Tazuma, et al. (1996), J Gastroenterol Hepatol 11(9): 864-9. Abstract: Aggregation and fusion of non-micellar particulate species, such as unilamellar vesicle and phospholipid lamellae, are believed to precede the nucleation of cholesterol crystals in bile. However, little is known about the time sequence relationship between transformation of non-micellar particles and the initial appearance of cholesterol crystals, as no adequate technique is available for assessing such transformations quantitatively. We have developed a novel method for quantitatively estimating vesicle transformation in supersaturated model bile systems, using a spectrophotometric technique to determine the time sequence relationship between such transformations and cholesterol crystal nucleation. We also investigated the potency of a given effector substance on this transformation. This method permits simultaneous quantitative determination of vesicle aggregation and of cholesterol crystal growth. Maximal vesicular aggregation as determined from turbidity, coincided with initiation of cholesterol crystal nucleation. The addition of divalent cations, Ca2+ and Mg2+, to the model bile solutions promoted vesicle aggregation and cholesterol crystal nucleation and growth. In contrast, apolipoproteins A-1 and A-2 retarded such processes. These data were highly reproducible and reliable. The method described is easy to perform, provides reproducible results and permits the determination of the potency of effector substances on vesicle transformation and on the nucleation of cholesterol crystals. |
| Method for remnant lipoproteins--quantitative analysis of serum remnant-like particle cholesterol (RLP-C) Nambu, S. (1999), Nippon Rinsho 57(12): 2740-4. Abstract: The important role of remnant lipoprotein, which is linked up to serum insulin, in the development of atherosclerosis is well known. So, measurement of remnant has a benefit as the indicator of cardiovascular disease-risk. Recently, Nakajima et al have developed a simple, rapid assay method, using a immunoaffinity gel mixture of anti-apo B-100 and anti-apo A1 monoclonal antibodies coupled with Sepharose 4B. The apoprotein composition of RLP which is unbound with mixed gel is as similar to apo-E rich VLDL. Clinical significance of RLP-C has been already indicated by many reports. |
| Method for simultaneous measurements of traces of heptadeuterated cholesterol and cholesterol by gas chromatography-mass spectrometry: application in humans Beaumier-Gallon, G., J. Lanfranchi, et al. (1998), J Chromatogr B Biomed Sci Appl 718(1): 23-32. Abstract: An assay was developed to quantify deuterated cholesterol (used as a tracer) and cholesterol using gas chromatography-mass spectrometry. Ergosterol and epicoprostanol were used as internal standards. Deuterated cholesterol was quantified by comparing its peak area to that of epicoprostanol and cholesterol to ergosterol. The mean absolute recovery in spiked serum was 99.96%; the precision was in the range 0.16-10.9% and accuracy 90.4-100%; the limit of detection in plasma was 3x10(-5) mmol l(-1). Using two internal standards, the method described herein seems particularly suitable for application in humans i.e., measuring traces of deuterated cholesterol (range: 0-6.26 x 10(-4) mmol l(-1)) along with natural cholesterol (range: 0.065-4.42 mmol l(-1)) in human plasma and lipid fractions postprandially. |
| Method of administration influences the serum cholesterol-lowering effect of psyllium Wolever, T. M., D. J. Jenkins, et al. (1994), Am J Clin Nutr 59(5): 1055-9. Abstract: To determine whether psyllium must be mixed with food to lower serum cholesterol, 18 modestly hypercholesterolemic subjects were studied for three 2-wk periods, in random order, separated by a 2-wk return to a National Cholesterol Education Program Step 2 diet. Compared with values for subjects consuming control wheat-bran cereal (63 g/d), after 2 wk of 54 g psyllium-enriched cereal/d containing 7.3 g psyllium, serum total, LDL, and HDL cholesterol, respectively, were reduced by 8% (6.15 +/- 0.15 vs 6.71 +/- 0.19 mmol/L, P < 0.01), 11% (4.24 +/- 0.15 vs 4.78 +/- 0.19 mmol/L, P < 0.02), and 7% (0.99 +/- 0.05 vs 1.07 +/- 0.05 mmol/L, P < 0.01). When 7.6 g of the same type of psyllium as in the test cereal was taken between meals, serum total (6.50 +/- 0.19 mmol/L), LDL (4.50 +/- 0.21 mmol/L), and HDL (1.06 +/- 0.06 mmol/L) cholesterol were no different from control values, and total cholesterol was greater than after psyllium cereal (P < 0.05). We conclude that psyllium must be mixed with foods to have the maximum effect on serum cholesterol. |
| Method-dependent changes in "HDL-cholesterol" with recombinant apolipoprotein A-I(Milano) infusion in healthy volunteers Cole, T. G., W. L. Nowatzke, et al. (2002), Clin Chem 48(4): 680-1. |
| Methods for measurement of fatty acid and cholesterol metabolism Hellerstein, M. K. (1995), Curr Opin Lipidol 6(3): 172-81. Abstract: The measurement of dynamic fluxes of lipids (biosynthesis, oxidation, and intermediary metabolism) poses difficult challenges. Two fundamental advances have been made recently for measuring the biosynthesis of lipids, namely mass isotopomer distribution analysis and labeled water incorporation. These techniques have resolved the central methodologic problem in biosynthesis by establishing the true precursor isotope enrichment. Mass isotopomer distribution analysis also permits uncontaminated pulse-chase decay curves and intracellular precursor fluxes to be measured. In contrast, the isotopic measurement of lipid oxidation rates remains unreliable because of the wide variability in the recovery of labeled carbon dioxide. |
| Methods for measurement of LDL-cholesterol: a critical assessment of direct measurement by homogeneous assays versus calculation Nauck, M., G. R. Warnick, et al. (2002), Clin Chem 48(2): 236-54. Abstract: BACKGROUND: Because LDL-cholesterol (LDL-C) is a modifiable risk for coronary heart disease, its routine measurement is recommended in the evaluation and management of hypercholesterolemia. We critically examine here the new homogeneous assays for direct determination of LDL-C. APPROACH: This review relies on published studies and data of the authors using research and routine methods for LDL-C determination. We review experience with methods from their earlier use in lipid research laboratories through the transition to routine clinical testing and the recent development of homogeneous assays. We focus on comparative evaluations and characterizations and the performance of the assays. CONTENT: Homogeneous assays seem to be able to meet current National Cholesterol Education Program (NCEP) requirements for LDL-C testing for precision (CV <4%) and accuracy (bias <4%), when samples collected from nonfasting individuals are used. In addition, all five currently available assays have been certified by the Cholesterol Reference Methods Laboratory Network. The homogeneous methods also appear to better classify individuals into NCEP cutpoints than the Friedewald calculation. However, the limited evaluations to date raise questions about their reliability and specificity, especially in samples with atypical lipoproteins. CONCLUSIONS: Available evidence supports recommending the homogeneous assays for LDL-C to supplement the Friedewald calculation in those cases where the calculation is known to be unreliable, e.g., triglycerides >4000 mg/L. Before the homogeneous assays can be confidently recommended to replace the calculation in routine practice, more evaluation is needed. |
| Methods of cholesterol determination: conventional procedure or "dry chemistry"? Riesen, W. and H. Keller (1990), Ther Umsch 47(6): 456-66. Abstract: The search for the cardiovascular risk factor cholesterol should essentially be done in the physicians' laboratory. The majority of such analyses is performed by 'dry' chemistry tests. This review compares this technique with conventional methods for the determination of cholesterol. The reagents and the reaction mechanisms are principally the same for both techniques, i.e. fully enzymatic methods are used. In 'dry' chemistry the reagents are fixed on a solid carrier. The reactive state is provided by the liquid of the specimen. Two principles are employed: the technique of strips which is already utilised in urinary analysis and the system of multiple film layers as it is common in color-film technique. Three already introduced systems are discussed: the Seralyzer (Ames), the Ektachem (Kodak), and the Reflotron (Boehringer, Mannheim), and one system which is still in evaluation (the Clinistat, Ames). All the systems give a good agreement provided that they are operated by well-trained operators. Problems arise with quality control, since matrix effects are particularly important. The exactitude of the results depends on the calibration. Both, the Reflotron and the Clinistat are calibrated by the manufactories himself, the employer has no influence and is entirely dependent on the reliability of the producer. Although clinical chemistry analyses are facilitated by 'dry' chemistry it is by no means devoid of risks because the errors are more difficult to recognize. |
| Methods of total cholesterol measurement in the baseline survey of the WHO MONICA Project Doring, A., A. Pajak, et al. (1990), Rev Epidemiol Sante Publique 38(5-6): 455-61. Abstract: In the WHO MONICA Project (Monitoring of Trends and Determinants of Cardiovascular Disease) total cholesterol was measured in representative samples from 51 study populations in 26 countries. The biochemical measurements were done locally by the collaborating centres' laboratories. Differences in measurement procedures among the populations were found in the following factors: fasting status, posture of the subject, tourniquet use, use of serum or plasma, storage conditions, and the analytical method itself. This paper gives an overview of the methods used, and discusses the possible effects of the differences on the comparability of the results. The use of a posture other than that recommended and the use of EDTA (ethylene diaminetetraacetate) plasma are considered to be the most important factors, and were found in 9 out of the 51 populations. |
| Methyl-beta-Cyclodextrin treatment and filipin staining reveal the role of cholesterol in surface membrane antigen sequestration of Schistosoma mansoni and S. haematobium lung-stage larvae Tallima, H. and R. El Ridi (2005), J Parasitol 91(3): 720-5. Abstract: Ex vivo lung-stage larvae of Schistosoma mansoni and S. haematobium do not bind specific antibodies in the indirect membrane immunofluorescence test (IF), probably as a result of confinement of the surface membrane antigens in immobile, lipid-rich sites. Treatment with the membrane-impermeable, cholesterol-extracting drug methyl-beta-cyclodextrin (MBCD) and staining with filipin III (filipin), a fluorescent polyene antibiotic widely used for the detection and quantitation of cholesterol in biomembranes, allowed us to examine the role of cholesterol in surface membrane antigen sequestration of S. mansoni and S. haematobium ex vivo lung-stage larvae. Treatment of S. mansoni larvae with MBCD elicited appreciable cholesterol depletion as judged by filipin-cholesterol fluorescence diminution, which was accompanied by a considerable increase in specific antibody binding in IF, thus suggesting that cholesterol plays a predominant role in sequestration of the surface membrane antigens of S. mansoni lung-stage schistosomula. Despite that, MBCD induced an almost complete depletion of cholesterol from the outer membrane of S. haematobium larvae; no increase in specific antibody binding in IF was evident, implying that cholesterol is not responsible for masking surface membrane antigens of S. haematobium lung-stage larvae. |
| Methyl-beta-cyclodextrins and liposomes as water-soluble carriers for cholesterol incorporation into membranes and its evaluation by a microenzymatic fluorescence assay and membrane fluidity-sensitive dyes Hartel, S., H. A. Diehl, et al. (1998), Anal Biochem 258(2): 277-84. Abstract: A variety of methods to incorporate cholesterol into lipid membrane systems have been applied with varying success. We tested an incorporation method based on cholesterol-loaded methyl-beta-cyclodextrins and compared it to a method that uses cholesterol-loaded liposomes. With methyl-beta-cyclodextrin, we increased the cholesterol content in microsomal membranes to almost the fourfold of the original content. With cholesterol-loaded liposomes instead, we achieved an elevation of 140%. Short incubation times and well-defined carrier properties favor the beta-cyclodextrin method. For direct detection of membrane cholesterol, we slightly modified a microenzymatic fluorescence assay originally developed for precise cholesterol detection in serum. Without the need to perform lipid extraction, this assay was reliable for cholesterol detection in liposomes and in microsomes. Additionally, we compared the sensitivity of the fluidity-sensitive fluorescent dyes pyrene, pyrene-methanol, bis-pyrene, 1-6-phenyl-1,3,5,-hexatrien, and 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5,-hexatrien in order to detect cholesterol indirectly by the dynamically relevant changes exerted on lipid matrices. These dyes differ not only in their membrane location but also in their dynamical behavior. We calibrated the dyes in liposomes of defined cholesterol content and used the most suited ones to follow and quantify the cholesterol incorporation into liposomal and microsomal membranes. |
| Methylflavonolamine protects aorta from atherosclerosis in cholesterol-fed rabbits Zhang, M. S., E. F. Zhou, et al. (1993), Zhongguo Yao Li Xue Bao 14(2): 133-6. Abstract: The effect of methylflavonolamine 4'-methyl-7-(2-hydroxy-3-isopropylamino-propoxy)-flavone hydrochloride, MFA, synthesized recently by the Shanghai Institute of Pharmaceutical Industry, on the development of atherosclerosis was studied in male New Zealand white rabbits fed cholesterol for 10 wk. MFA, 7 mg.kg-1 daily ip, did not significantly alter the serum total cholesterol, HDL, and triglyceride levels, but significantly lowered the aortic cholesterol and calcium contents. Atheromatous lesions covered 53.3 +/- 11.8% of the intimal surface of the aorta in the saline group and 11.3 +/- 2.3% in the MFA group (P < 0.01). We conclude that MFA suppresses cholesterol-induced atherosclerosis. |
| Mevinolin, a competitive inhibitor of hydroxymethylglutaryl coenzyme A reductase, suppresses enterocyte esterification of exogenous but not endogenous cholesterol Fellermann, K., F. M. Reimann, et al. (1992), Biochim Biophys Acta 1165(1): 78-83. Abstract: Mevinolin (lovastatin), a competitive inhibitor of hydroxymethylglutaryl-coenzyme A reductase, directly inhibited acyl-CoA cholesteryl acyltransferase in rabbit intestinal microsomes at a dose of 20 micrograms/ml or more. Lineweaver-Burk analysis showed a competitive type of inhibition with respect to oleoyl-CoA. In cultured intestinal Caco-2 cells, mevinolin reduced 14Coleate incorporation into cholesteryl-esters by 86% of controls at doses as low as 0.1 micrograms/ml. However, in cells whose activity of acyl-CoA cholesteryl acyltransferase was stimulated 7-fold by 10 mM mevalonolactone, a significant inhibitory effect on cholesteryl-ester formation could not be detected, even at 40 micrograms/ml of mevinolin. In contrast, cells supplied with liposomal cholesterol or cholesterol derived from low-density lipoproteins showed a marked reduction of cholesteryl-ester formation in the presence of 10 or 0.1 micrograms/ml of mevinolin, respectively. It is concluded that the observed suppressive effects of mevinolin on cholesterol esterification in cultured Caco-2 cells are indirect and possibly caused by changes in the acyl-CoA cholesteryl acyltransferase substrate pool or intracellular cholesterol transport. |
| Mice expressing the human CYP7A1 gene in the mouse CYP7A1 knock-out background lack induction of CYP7A1 expression by cholesterol feeding and have increased hypercholesterolemia when fed a high fat diet Chen, J. Y., B. Levy-Wilson, et al. (2002), J Biol Chem 277(45): 42588-95. Abstract: Cholesterol 7alpha-hydroxylase (CYP7A1) catalyzes the rate-limiting step in the pathway responsible for the formation of the majority of bile acids. Transcription of the gene is regulated by the size of the bile acid pool and dietary and hormonal factors. The farnesoid X receptor and the liver X receptor (LXR) are responsible for regulation by bile acids and cholesterol, respectively. To study the effects of dietary cholesterol and fat upon expression of the human CYP7A1 gene, mice were generated by crossing transgenic mice carrying the human CYP7A1 gene with mice that were homozygous knock-outs (CYP7A1(-/-)). The mice (mCYP7A1(-/-)/hCYP7A1) expressed the human gene at much higher levels than did the transgenics bred in the wild-type background. A diet containing 1% cholic acid reduced the expression of the human gene in mCYP7A1(-/-)/hCYP7A1 mice to undetectable levels. Cholestyramine (5%) increased the level of expression of the human gene and the mouse gene. Thus, farnesoid X receptor-mediated regulation was preserved. A diet containing 2% cholesterol increased expression of the mouse gene in wild-type mice, but it did not affect expression of the human gene in mCYP7A1(-/-)/hCYP7A1 mice. None of the diets altered the serum cholesterol or triglyceride levels in these mice; 1% cholic acid caused a redistribution of cholesterol from the high density lipoprotein to the low density lipoprotein density in the humanized mice but not in wild-type mice. A diet containing 30% saturated fat and 2% cholesterol caused a decrease in CYP7A1 levels in mCYP7A1(-/-)/hCYP7A1 mice. The serum cholesterol levels rose in all mice fed this diet. The increase was greater in the mCYP7A1(-/-)/hCYP7A1 mice. Together, these data suggest that the lack of an LXR element in the region from -56 to -49 of the human CYP7A1 promoter may account for some of the differences in response to diets between humans and rodents. |