| For medical practitioners and the general public - Cholesterol Journal Article Catalog. |
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| Evaluation of the precision of the Friedewald's formula for the calculation of low density lipoprotein cholesterol concentration in serum Chotkowska, E., P. Kurjata, et al. (2001), Pol Merkuriusz Lek 11(64): 348-51. Abstract: The low density lipoproteins (LDL) is one of the important risk factor of coronary heart disease. Evaluation of LDL by direct method of ultracentrifugation (U-LDL), which is the most proper one, is not available in standard laboratories. Instead the Friedewald's formula is commonly used (F-LDL), which calculates level of LDL applying the values of fasting total cholesterol (CH), cholesterol of high density lipoproteins (HDL) and triglicerydes (TG). This formula can be used only in these samples, in which the level TG is below 4.5 mmol/l (400 mg/dl). The aim of the study was the examination of the accuracy of Friedewald's formula while compared with the concentration of LDL cholesterol determined by ultracentrifugation method and evaluate the possibility of extending the range of triglyceride concentration above 4.5 mmol/l (400 mg/dl) in this formula. The data of the study included 2213 samples of the fasting blood serum of consecutive patients in whom the direct measurement of lipoprotein fraction and calculation by Friedewald's formula were performed in years 1992-1999. All serum samples were analysed by the same standardized procedures according to National Heart, Lung and Blood Institute (NHLBI) guidelines. The data of 29 samples with extremely high value of triglyceride level (TG > 5.6 mmol/l, it is 500 mg/dl) were excluded from analysis. The main results showed that agreement between two methods of LDL evaluation was satisfactory also in extended range of TG 4.5-5.6 mmol/l (400-500 mg/dl). The mean values of U-LDL were significant higher than F-LDL (by mean 0.07 mmol/l it is 2.6 mg/dl) in group with TG < or = 4.5 mmol/l, but non significantly lower (by mean 0.13 mmol/l it is 4.9 mg/dl) in group with TG 4.5-5.6 mmol/l. Linear Pearson's and interclass correlations between U-LDL and F-LDL were high and significant in all analyses. |
| Evaluation of the role of His447 in the reaction catalyzed by cholesterol oxidase Kass, I. J. and N. S. Sampson (1998), Biochemistry 37(51): 17990-8000. Abstract: Cholesterol oxidase catalyzes the oxidation and isomerization of cholesterol to cholest-4-en-3-one via cholest-5-en-3-one. It has been proposed that His447 acts as the general base catalyst for oxidation, and that the resulting imidazolium ion formed acts as an electrophile for isomerization. In this work, we undertook an assessment of the proposed dual roles of His447 in the oxidation and isomerization reactions. To test its role, we constructed five mutants, H447Q, H447N, H447E, H447D, and H447K, that introduce hydrogen bond donors and acceptors and carboxylate bases at this position, and a sixth mutant, E361Q, to test the interplay between His447 and Glu361. These mutants were characterized using steady-state kinetics and deuterium substrate and solvent isotope effects. For those mutants that catalyze either oxidation of cholesterol or isomerization of cholest-5-en-3-one, the Km's vary no more than 3-fold relative to wild type. H447K is inactive in both oxidation (> 100,000-fold reduced) and isomerization assays (> 10,000-fold reduced). H447E and H447D do not catalyze oxidation (> 100,000-fold reduced), but do catalyze isomerization, 10(4) times slower than wild type. The k(cat) for H447Q is 120-fold lower than wild type for oxidation, and the same as wild type for isomerization. The k(cat) for H447N is 4400-fold lower than wild type for oxidation, and is 30-fold lower than wild type for isomerization. E361Q does not catalyze isomerization (> 10,000-fold reduced), and the k(cat) for oxidation is 30-fold lower than wild type. The substrate deuterium kinetic isotope effects for the wild-type and mutant-catalyzed oxidation reactions suggest that mutation of His447 to an amide results in a change of the rate-determining step from hydride transfer to hydroxyl deprotonation. The deuterium solvent and substrate kinetic isotope effects for isomerization indicate that an amide at position 447 is an effective electrophile to catalyze formation of a dienolic intermediate. Moreover, consideration of kinetic and structural results together suggests that a hydrogen bonding network involving His447, Glu361 and Asn485, Wat541, and substrate serves to position the substrate and coordinate general base and electrophilic catalysis. That is, in addition to its previously demonstrated role as base for deprotonation of carbon-4 during isomerization, Glu361 has a structural role and may act as a general base during oxidation. The His447, Asn485, Glu361, and Wat541 residues are conserved in other GMC oxidoreductases. Observation of this catalytic tetrad in flavoproteins of unknown function may be diagnostic for an ability to oxidize unactivated alcohols. |
| Evaluation of the use of beta-sitostanol as a nonabsorbable marker for quantifying cholesterol absorption Terry, J. G., B. L. McGill, et al. (1995), J Lipid Res 36(10): 2267-71. Abstract: For over a decade investigators have quantified cholesterol absorption by comparison of dietary intake and fecal excretion of isotopic cholesterol with that of beta-sitosterol as a "nonabsorbable" marker. However, beta-sitosterol might not be ideal due to its potential for absorption. We therefore carried out two studies to evaluate a new marker with less potential for absorption, 3Hbeta-sitostanol. In the first study (Study I, n = 22), we compared absorption of 3Hbeta-sitostanol and 14Cbeta-sitosterol in a simultaneous dual-label continuous feeding ("phytosterol absorption") experiment. We observed a consistently higher ratio of 3Hbeta-sitostanol/14Cbeta-sitosterol in the stool relative to diet on the first day of fecal collection (6.1% +/- 3.2% loss of 3Hbeta-sitosterol, range 3-12%), but thereafter, the ratio in stool was similar to that in diet. In Study II (n = 23), we compared cholesterol absorption directly using 3Hbeta-sitosterol and 14Ccholesterol, and, separately, 3Hbeta-sitostanol and 14Ccholesterol. We found that mean absorption between the two methods was similar (45% +/- 11% versus 44% +/- 10%, respectively, P difference = 0.40), and the two methods correlated well with one another (r = 0.83) when samples from all available days were used. Variability between the two methods was greater in individuals who absorbed more than 40% of cholesterol. Cholesterol loss on day 2 estimated from use of beta-sitostanol as a nonabsorbable marker was predictive of absorption using ratios from days 4-6 (r = 0.80). These results suggest that, for the majority of subjects, beta-sitosterol is a valid nonabsorbable marker for cholesterol absorption. |
| Evaluation of the use of serum lathosterol concentration to assess whole-body cholesterol synthesis in rabbits Meijer, G. W., J. G. Van der Palen, et al. (1992), J Lipid Res 33(2): 281-6. Abstract: Serum lathosterol concentration in rabbits was assessed as a possible indicator of whole-body cholesterol synthesis. In random-bred New Zealand White (NZW) rabbits fed a control diet or a diet containing either cholesterol, simvastatin, or cholestyramine, neither serum lathosterol concentration nor the serum lathosterol:total cholesterol ratio systematically corresponded with the anticipated rate of cholesterol synthesis. In control rabbits and those fed simvastatin or cholestyramine, whole-body cholesterol synthesis, which was calculated from the sterol balance, was correlated with serum lathosterol concentration when expressed relative to cholesterol in very low, intermediate, and low density lipoproteins (VLDL + IDL + LDL) (r = 0.61; n = 23; P = 0.002). The low correlation coefficient indicates that the predictive value of the lathosterol: (VLDL + IDL + LDL) cholesterol ratio is limited when applied to individual rabbits. Cholesterol and simvastatin feeding reduced the group mean serum lathosterol:(VLDL + IDL + LDL) cholesterol ratio, whereas cholestyramine in the diet raised the group mean ratio in the NZW rabbits. We conclude that the serum lathosterol:(VLDL + IDL + LDL) cholesterol ratio may be an indicator of group mean rates of whole-body cholesterol synthesis in rabbits but may not yield reliable information on individual rabbits. The lathosterol:(VLDL + IDL + LDL) cholesterol ratio predicted that in hyperresponsive inbred rabbits, showing an excessive hypercholesterolemia after cholesterol feeding, baseline whole-body cholesterol synthesis is lower than in hyporesponsive rabbits. Addition of cholesterol to the diet caused a reduction of predicted cholesterol synthesis in hypo- but not in hyper-responsive rabbits. |
| Evaluation of two different homogeneous assays for LDL-cholesterol in lipoprotein-X-positive serum Fei, H., S. Maeda, et al. (2000), Clin Chem 46(9): 1351-6. Abstract: BACKGROUND: The purpose of this study was to evaluate the performance of two homogeneous assays for LDL-cholesterol (LDL-C), a polyethylene/cyclodextrin (PC) assay and a detergent (D) assay, which are based on different principles, in cholestatic serum. METHODS: We compared serum LDL-C concentrations determined by the two assays for healthy normolipidemic subjects (n = 42) and cholestatic patients (n = 51). LDL-C concentrations obtained with the homogeneous assays were also compared with those obtained by HPLC for patients' sera. In the interference study, conjugated bile acids were added to normal serum, and their effects on the two assays were examined. The effects of lipoprotein-X (LP-X), intermediate-density lipoprotein (IDL), and apolipoprotein (apo) E-rich HDL on the LDL-C assays were also investigated by adding these lipoproteins to normal serum. RESULTS: The LDL-C concentrations obtained with the D assay were higher than those obtained with the PC assay in the serum with high LP-X. The bias for LDL-C vs LP-X in cholestatic serum correlated with LP-X concentration (r = 0.582; P: <0.0001; n = 51). In the interference study, no effect of bile acids on the LDL-C assays was observed. However, the D assay measured 51.0% of the cholesterol in LP-X, whereas no reactivity was observed for LP-X in the PC assay. In addition, the D assay and the PC assay measured IDL-cholesterol at 31.2% and 52.4%, respectively, and measured apo E-rich HDL-C at 7.6% and 17.8%, respectively. CONCLUSIONS: Although both homogeneous LDL-C assays are suitable for most cases, the present study showed that each homogeneous assay has a different limitation for cholestatic serum with gross alterations in lipoproteins. |
| Evaluation of two extraction methods for the determination of egg yolk cholesterol Van Elswyk, M. E., L. S. Schake, et al. (1991), Poult Sci 70(5): 1258-60. Abstract: Controversy concerning egg cholesterol values exists in recent literature due to varying procedures used for cholesterol determination. The purpose of the present study was to investigate the efficacy of direct sample saponification (Method A) versus saponification of a lipid extract (Method B) for analysis of yolk cholesterol. Method A resulted in a value of 19.1 +/-.4 (SE) mg cholesterol/g of yolk for the National Institute of Standards and Technology (NIST) reference (cholesterol in whole egg powder) as compared with the NIST certified value of 19.0 +/-.2 mg/g. Method B resulted in a significantly lower value of 14.6 +/-.5 mg/g. Egg yolk cholesterol values were determined to be 196 +/- 4.2 mg per egg by Method A and 132 +/- 11 mg per egg by Method B. Various amounts (1.5.25 g) of yolk cholesterol assayed by either method proportionately decreased cholesterol values as yolk amount decreased; however, Method B consistently resulted in lower yolk cholesterol. These data suggest that both Methods A and B are valid for determining relative differences between treatments; however, the NIST standard data indicate that for quantification of absolute cholesterol values, direct saponification is more accurate. The NIST standard of cholesterol in whole egg powder should be used as a control for comparing cholesterol data regardless of extraction method used. |
| Evaluation of two homogeneous methods for measuring high-density lipoprotein cholesterol Huang, Y. C., J. T. Kao, et al. (1997), Clin Chem 43(6 Pt 1): 1048-55. Abstract: We evaluated the performance of two homogeneous assays for quantifying HDL cholesterol (HDL-C) and compared them with the phosphotungstic acid (PTA)/ MgCl2 assay. Both homogeneous HDL-C assays were precise, having a within-run CV of < 1.20% and a between-run CV of < 4.07%. The HDL-C values (y) measured by the two homogeneous methods correlated well with those by the PTA/MgCl2 method (x): y = 1.00x + 64.98 mg/L, r = 0.987, Sy/x = 27.99 mg/L (n = 152) for the polyethylene glycol-modified enzymes/alpha-cyclodextrin sulfate (PEGME) assay (Kyowa), and y = 0.84x + 106.51 mg/L, r = 0.984, Sy/x = 26.10 mg/L (n = 152) for the polyanion-polymer/detergent (PPD) assay (Daiichi). The specificity of the PEGME method seemed better than that of the PPD method, as the PPD method was markedly interfered with by supplemental LDL-C. Addition of 20 g/L triglycerides produced a negative error of approximately 18% in both homogeneous assays. Bilirubin and hemoglobin had little influence on the PEGME method; hemoglobin had little effect on the PPD method. Bilirubin, however, markedly decreased the readings by the PPD method. We found the PEGME assay superior to the PPD assay for routine HDL-C testing, because the PPD assay is relatively inaccurate and not specific. |
| Evaluation of within-day precision of serum cholesterol measured by a portable analyzer Kaminsky, L. A. and M. H. Whaley (1992), Med Sci Sports Exerc 24(1): 134-8. Abstract: The use of dry-chemistry analyzers for the measurement of cholesterol in mass screening settings has received considerable attention. Less is known about the efficacy of these types of analyzers in the clinical office or laboratory setting. Thus, we investigated the within-day precision of cholesterol measurements performed by the Reflotron method with specific comparisons made between two trained technicians and two instruments. Forty serum specimens were analyzed eight times (twice by each technician on both instruments) with the identity of the specimen blinded from the technician. Each specimen was also analyzed by two different methods commonly accepted in the clinical laboratory to estimate the accuracy of the Reflotron cholesterol measures. Small, significant (P less than 0.05) main effect differences were observed in cholesterol concentrations between technicians (1.8%) and instruments (0.8%). The overall coefficient of variation (CV) of the serum cholesterol measures was 2.5%, which meets the Laboratory Standardization Panel's "ideal" goal. However, three individual cases (one specimen's eight analyses) had CV greater than 5%, and three other cases had CV greater than 3%. Most of these cases could be traced to one outlier value. Review of all 320 Reflotron analyses revealed that only 10 (3.1%) were outliers (greater than 5% from specimen mean value). When operated in a laboratory with regular quality control procedures, the Reflotron method can meet national standards for precision. In this setting, differences between technicians and instruments are not of clinical importance. |
| Evangelists and snails redux: the case of cholesterol screening Davidoff, F. (1996), Ann Intern Med 124(5): 513-4. |
| Everolimus/cyclosporine interactions on bile flow and biliary excretion of bile salts and cholesterol in rats Deters, M., G. Kirchner, et al. (2004), Dig Dis Sci 49(1): 30-7. Abstract: As a possible explanation for everolimus/cyclosporine-induced hypercholesterolemia seen in transplant recipients, we investigated the interactions of the immunosuppressants everolimus and cyclosporine on bile flow and biliary excretion of bile salts and cholesterol in a subchronic bile fistula model in rats because biliary excretion is a main elimination route of cholesterol. After 2 weeks of daily treatment, everolimus (1 mg/kg i.p.) and cyclosporine (5 mg/kg i.p) decreased bile flow (-45 and -36%) and biliary excretion of bile salts (-34 and -54%) and cholesterol (-25 and -39%) and increased serum concentrations of cholesterol (+40 and +17%) and triglycerides (+220 and +110%). Bile salt serum concentration was elevated only by cyclosporine (+100%), and not by everolimus. Everolimus/cyclosporine slightly enforced the cyclosporine-induced hyperlipidemia but not reduction of bile parameters, while the cyclosporine-induced increase in bile salts in serum was totally prevented. From these results we conclude that bile salt synthesis could be impaired by everolimus, which could be one reason for everolimus-induced hypercholesterolemia. |
| Evidence against a role for phosphorylation/dephosphorylation in the regulation of acyl-CoA:cholesterol acyl transferase Corton, J. M. and D. G. Hardie (1992), Eur J Biochem 204(1): 203-8. Abstract: 1. As detailed below, we have been able to reproduce observations of time-dependent changes in the activity of acyl-CoA:cholesterol acyl transferase (ACAT) in rat liver microsomes, that were suggested to represent evidence of a role for reversible phosphorylation in the regulation of cholesterol ester formation. 2. ACAT in washed rat liver microsomes was inactivated in a time-dependent manner in the presence of Mg2+. However, this effect of Mg2+ appears to be caused by aggregation of microsomal vesicles rather than dephosphorylation, since it could be abolished by rehomogenization, and was mimicked by Ca2+, another agent which causes aggregation. Fluoride did not prevent this effect of Mg2+, but masked it by causing a rapid activation that appeared to be a non-specific effect of increased ionic strength. 3. Under conditions where other proteins were rapidly dephosphorylated, microsomal ACAT activity from rat liver was not affected by incubation with the purified catalytic subunits of protein phosphatases 1, 2A or 2C. Similar results were obtained using protein phosphatases 1 or 2A on microsomes from a macrophage cell line (J774.2 cells). Incubation of cultured J774.2 cells with a cell-permeable inhibitor of these two protein phosphatases, okadaic acid, also had no effect on cholesterol ester formation. 4. A high-speed-centrifugation supernatant fraction (S303) from rat liver activated ACAT in the presence of MgATP. This effect was not abolished by prior heat-treatment of the fraction, and the supernatant fraction could not be replaced by purified AMP-activated protein kinase or a variety of other protein kinases. 5. The results above were obtained using assays involving endogenous cholesterol as the substrate. The MgATP-dependent activation by S303 was reduced or abolished when the assays were carried out in the presence of the detergent Triton WR-1339 plus cholesterol, or detergent alone. 6. These results do not support the idea that ACAT is regulated by reversible phosphorylation. The most likely explanation for the effect of S303 is that it is an artefact caused by changes in the availability of endogenous cholesterol to the enzyme. |
| Evidence for a cholesterol transport pathway from lysosomes to endoplasmic reticulum that is independent of the plasma membrane Underwood, K. W., N. L. Jacobs, et al. (1998), J Biol Chem 273(7): 4266-74. Abstract: We have studied the movement of low density lipoprotein (LDL)-derived cholesterol in cultured Chinese hamster ovary cells. Our hypothesis is that when LDL cholesterol is effluxed from lysosomes, the bulk of LDL cholesterol is mobilized to the plasma membrane, while another pathway delivers LDL cholesterol from lysosomes to acyl-CoA/cholesterol acyltransferase (ACAT) in the endoplasmic reticulum. Three lines of evidence support this model. First, LDL cholesterol transport to ACAT can be blocked without inhibiting the movement of cholesterol from lysosomes to plasma membrane or from plasma membrane to endoplasmic reticulum. Second, LDL cholesterol transport to ACAT is normal in a Chinese hamster ovary mutant with defective plasma membrane-to-ACAT movement. Third, LDL cholesterol is not diluted by the plasma membrane cholesterol pool before reaching ACAT. Our evidence supports a vesicular model of cholesterol transport from lysosomes to the endoplasmic reticulum that is independent of the plasma membrane. |
| Evidence for a cholesterol-lowering gene in a French-Canadian kindred with familial hypercholesterolemia Sass, C., L. M. Giroux, et al. (1995), Hum Genet 96(1): 21-6. Abstract: We describe a four-generation kindred with familial hypercholesterolemia (FH) in which two of the eight heterozygotes for a 5-kb deletion (exons 2 and 3) in the low density lipoprotein (LDL) receptor gene were found to have normal LDL-cholesterol levels. In our search for a gene responsible for the cholesterol-lowering effect in this family, we have studied variation in the genes encoding the LDL receptor, apolipoprotein (apo) B, 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, apoAI-CIII-AIV, and lipoprotein lipase. The analysis showed that it was unlikely that variation in any of these genes was responsible for the cholesterol-lowering effect. Expression of the LDL receptor, as assessed in vitro with measurements of activity and mRNA levels, was similar in normo and hyperlipidemic subjects carrying the deletion. Analysis of the apo E isoforms revealed that most of the e2 allele carriers in this family, including the two normolipidemic 5-kb deletion carriers, were found to have LDL-cholesterol levels substantially lower than subjects with the other apo E isoforms. Thus, this kindred provides evidence for the existence of a gene or genes, including the apo e2 allele, with profound effects on LDL-cholesterol levels. |
| Evidence for a common biliary cholesterol and VLDL cholesterol precursor pool in rat liver Stone, B. G. and C. D. Evans (1992), J Lipid Res 33(11): 1665-75. Abstract: Hepatic free cholesterol levels are influenced by cholesterol synthesis and ester formation, which, in turn, might regulate cholesterol secretion into bile and plasma. We manipulated the rates of hepatic cholesterol synthesis and esterification and measured biliary and very low density lipoprotein (VLDL) cholesterol secretion, and bile acid synthesis. Mevalonate decreased HMG CoA reductase by 80%, increased acyl coenzyme A: cholesterol acyltransferase (ACAT) by 60% and increased 3Holeate incorporation into microsomal and VLDL cholesteryl esters by 174% and 122%, respectively. Microsomal and biliary free cholesterol remained constant at the expense of increased microsomal and VLDL cholesteryl ester content. Mevalonate did not change bile acid synthesis. 25-OH cholesterol decreased HMG-CoA reductase by 39%, increased ACAT by 24%, but did not effect 7 alpha-hydroxylase. 25-OH cholesterol increased 3Holeate in microsomal and VLDL cholesterol esters by 71% and 120%. Biliary cholesterol decreased by 40% and VLDL cholesteryl esters increased by 83%. A small and unsustained decrease in bile acid synthesis (14CO2 release) occurred after 25-OH cholesterol. After orotic acid feeding, HMG-CoA reductase increased 352%, and 3Holeate in microsomal and VLDL cholesteryl esters decreased by 43% and 89%. Orotic acid decreased all VLDL components including free cholesterol (68%) and cholesteryl esters (55%), and increased biliary cholesterol by 160%. No change in bile acid synthesis occurred. Hepatic cholesterol synthesis and esterification appear to regulate a cholesterol pool available for both biliary and VLDL secretion. Changing cholesterol synthesis and esterification did not alter bile acid synthesis, suggesting that either this common bile/VLDL secretory pool is functionally distinct from the cholesterol pool used for bile salt synthesis, or that free cholesterol availability in this precursor pool is not a major determinant of bile acid synthesis. |
| Evidence for a correlation between ambient cholesterol levels and soluble plasma sialyltransferase enzyme activity Maguire, T. M., M. F. Ryan, et al. (1996), Glycoconj J 13(4): 525-8. Abstract: While soluble forms of the sialyltransferase (sialyl-T) enzyme have been detected in significant quantities in serum, the exact source(s) of the enzyme, or the factors controlling its secretion are poorly understood. In this study, we have examined the relationship between ambient plasma cholesterol concentrations and sialyl-T-activities and also levels of constituent plasma sialoglycoproteins (SGP). There was an inverse relationship between levels of the alpha 2, 6 sialyl-T enzyme and both total plasma cholesterol and HDL, although no such relationship was observed for the alpha 2,3 enzyme. While there was no correlation between total cholesterol and the levels of plasma SGPs, there was an inverse relationship between the HDL component and alpha 2,3 SGPs. |
| Evidence for a gene influencing fasting LDL cholesterol and triglyceride levels on chromosome 21q North, K. E., M. B. Miller, et al. (2005), Atherosclerosis 179(1): 119-25. Abstract: High levels of low-density lipoprotein (LDL) cholesterol, low levels of high-density lipoprotein (HDL) cholesterol, and high levels of triglycerides (TG) are strong predictors of cardiovascular disease risk. Motivated by previous evidence for pleiotropy between cholesterol and TG levels, we conducted bivariate linkage analysis of LDL cholesterol and TG concentration among participants of the Hypertension Genetic Epidemiolgy Network (HyperGEN), one of four networks in the NHLBI sponsored Family Blood Pressure Program Project. All available hypertensive siblings and their first-degree relatives were recruited. Both phenotypes were similarly adjusted for ethnicity, study center, sex, age, age-by-sex interactions, smoking, alcohol consumption, hormone use, diabetes medication use, and waist circumference. Variance component linkage analysis was performed as implemented in SOLAR, using ethnicity-specific marker allele frequencies derived from founders and multipoint IBDs calculated in MERLIN. A maximum genome-wide empirical LOD score of 3.9 was detected on chromosome 21 at 54cM, between markers D21S2055 and D21S1446. This signal overlaps with suggestive and/or significant linkages for total cholesterol, LDL cholesterol, and apolipoprotein B in three other studies and is suggestive of one or more genes on chromosome 21q jointly regulating LDL cholesterol and TG concentration. |
| Evidence for a major gene accounting for mild elevation in LDL cholesterol: the NHLBI Family Heart Study Coon, H., M. F. Leppert, et al. (1999), Ann Hum Genet 63 (Pt 5): 401-12. Abstract: Studies of rare Mendelian disorders of low density lipoprotein cholesterol (LDL-C) metabolism have identified specific genetic mutations in the LDL receptor and apolipoprotein B. Although these rare mutations account for a small proportion of LDL-C variation, twin and adoption studies indicate that at least 50% of the overall LDL-C observed variation is genetically determined. In a heterogeneous sample of 3227 subjects from the NHLBI Family Heart Study collected from four US centres, we find evidence for a common major gene accounting for mild elevations (1.25 standard deviations) in LDL-C. The analysis favored a recessive model with a frequency of 0.52 for the gene influencing elevated LDL-C, phenotypic means of 113 mg/dl for the normal genotypes and 146 mg/dl for the abnormal genotype, and a significant polygenic heritability. This statistically-inferred major gene accounted for 24% of the variation in LDL-C, with polygenes accounting for another 28% of the variation. Using parameters for major gene transmission estimated in the segregation analysis, LDL-C showed no linkage to the LDL receptor gene (LDLR), nor to the apolipoprotein E gene (APOE), nor to the cholesterol 7alpha-hydroxylase gene (CYP7A1), indicating the major gene effect influencing mild elevation in LDL-C is not explained by any of these candidate loci. |
| Evidence for a potential role for HDL as an important source of cholesterol in human adrenocortical tumors via the CLA-1 pathway Imachi, H., K. Murao, et al. (1999), Endocr J 46(1): 27-34. Abstract: CLA-1, a human homologue of rodent scavenger receptor class B1 (SR-B1), has been identified as a receptor for high density lipoprotein (HDL) and is highly expressed in the adrenal gland. Several studies have indicated that HDL might be a source of cholesterol for steroidogenesis in the adrenal gland. In this study, we show that ACTH and its second messenger cAMP stimulated CLA-1 protein expression in a human adrenocortical cell line. We also determined whether CLA-1 plays an important role in steroidogenesis by investigating CLA-1 expression levels in various adrenal tumors including the adenomas of Cushing's and Conn's syndrome. Western blot analysis showed that CLA-1 expression was much higher in the tumors of Cushing's syndrome than in non-tumor lesions of Conn's syndrome and pheochromocytoma. We were able to detect a strong CLA-1 signal in tumors of Conn's syndrome, too. On the other hand, much less CLA-1 expression was detected in Cushing's adenoma adjacent adrenal glands. The immunohistochemical analysis showed that CLA-1 was expressed in the outer region of the adrenal cortex mainly in plasma membranes of the cortical cells but not in the medulla. These findings demonstrated for the first time that ACTH increased CLA-1 protein in cultured human adrenocortical cells, and that cortisol- and aldosterone-secreting adenomas had high CLA-1 proteins in their cell surfaces. |
| Evidence for a QTL on chromosome 19 influencing LDL cholesterol levels in the general population Beekman, M., B. T. Heijmans, et al. (2003), Eur J Hum Genet 11(11): 845-50. Abstract: The genetic basis of cardiovascular disease (CVD) with its complex etiology is still largely elusive. Plasma levels of lipids and apolipoproteins are among the major quantitative risk factors for CVD and are well-established intermediate traits that may be more accessible to genetic dissection than clinical CVD end points. Chromosome 19 harbors multiple genes that have been suggested to play a role in lipid metabolism and previous studies indicated the presence of a quantitative trait locus (QTL) for cholesterol levels in genetic isolates. To establish the relevance of genetic variation at chromosome 19 for plasma levels of lipids and apolipoproteins in the general, out-bred Caucasian population, we performed a linkage study in four independent samples, including adolescent Dutch twins and adult Dutch, Swedish and Australian twins totaling 493 dizygotic twin pairs. The average spacing of short-tandem-repeat markers was 6-8 cM. In the three adult twin samples, we found consistent evidence for linkage of chromosome 19 with LDL cholesterol levels (maximum LOD scores of 4.5, 1.7 and 2.1 in the Dutch, Swedish and Australian sample, respectively); no indication for linkage was observed in the adolescent Dutch twin sample. The QTL effects in the three adult samples were not significantly different and a simultaneous analysis of the samples increased the maximum LOD score to 5.7 at 60 cM pter. Bivariate analyses indicated that the putative LDL-C QTL also contributed to the variance in ApoB levels, consistent with the high genetic correlation between these phenotypes. Our study provides strong evidence for the presence of a QTL on chromosome 19 with a major effect on LDL-C plasma levels in outbred Caucasian populations. |
| Evidence for a regular distribution of cholesterol in phospholipid bilayers from diphenylhexatriene fluorescence Tang, D., B. Wieb van der Meer, et al. (1995), Biophys J 68(5): 1944-51. Abstract: Cholesterol/dimyristoylphosphatidylcholine (DMPC) multilamellar vesicles were studied by steady-state fluorescence using diphenylhexatriene (DPH) as a probe. A series of dips were found in the plot of DPH fluorescence intensity versus cholesterol concentration at certain specific cholesterol concentrations. This observation indicates that there are dominant domains in which cholesterol molecules are regularly distributed on a hexagonal superlattice in the acyl chain matrix of DMPC at critical cholesterol concentrations. These concentrations can be predicted by an equation or a mathematical series, except the one at 33 mol %. These dips of DPH fluorescence intensity are temperature dependent. The excellent agreement between experimental data and calculated values as well as similar previous findings of dips and/or kinks in the excimer-over-monomer fluorescence in pyrenephosphatidylcholine/phospholipid mixtures confirm our conclusion about lateral organizations of cholesterol and acyl lipid chains in cholesterol/phospholipid multilamellar vesicles. The regular distribution model at critical concentration is consistent with the phase diagram of cholesterol/DMPC. Using the model of regular distribution, the physical origin of the liquid-disordered (Ld) phase, liquid-ordered phase (Lo), and coexistence of liquid-disordered phase and Lo phase (Lo + Ld) is discussed on the molecular level. |