| For medical practitioners and the general public - Cholesterol Journal Article Catalog. |
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| Homogeneous assay for direct determination of high-density lipoprotein cholesterol evaluated Nauck, M., W. Marz, et al. (1996), Clin Chem 42(3): 424-9. Abstract: We evaluated a new homogeneous assay for quantifying high-density lipoprotein cholesterol (HDL-C). The assay included four reagents: polyethylene glycol for "wrapping" chylomicrons, very-low-density lipoproteins (VLDL), and low-density lipoproteins (LDL); antibodies specific for apolipoprotein (apo) B and apo C-III to produce aggregates of chylomicrons, VLDL, and LDL; enzymes for the enzymatic cholesterol determination of the noncomplexed lipoproteins with 4-aminoantipyrine as the color reagent; and guanidine salt to stop the enzymatic reaction and to solubilize the complexes of apo B-containing lipoproteins, which would otherwise interfere with the reading of absorbance. The total CVs of the new method ranged between 2.4% and 8.4%. The HDL-C values (y) were in good agreement with those by a comparison phosphotungstic acid/MgCl2 method (x): y= 0.987x + 17.2 mg/L (68th percentile of the residuals on the regression line= 21.49, r= 0.970). At triglyceride concentrations of 20 g/L (Intralipid) the homogeneous HDL-C concentrations increased by 2%. Hemoglobin markedly increased the results, whereas bilirubin reduced them. The homogeneous HDL-C assay was easy to handle and allows full automation. This test should considerably facilitate the screening of individuals at an increased risk of cardiovascular disease. |
| Homogeneous assay for measuring low-density lipoprotein cholesterol in serum with triblock copolymer and alpha-cyclodextrin sulfate Sugiuchi, H., T. Irie, et al. (1998), Clin Chem 44(3): 522-31. Abstract: We have developed a fully automated method for measuring LDL-cholesterol (LDL-C) in human serum without the need for prior separation, using a nonionic surfactant, polyoxyethylene-polyoxypropylene block copolyether (POE-POP), and a sodium salt of sulfated cyclic maltohexaose, alpha-cyclodextrin sulfate. Of the surfactants tested, POE-POP with a higher molecular mass of the POP block and a greater hydrophobicity reduced the reactivity of cholesterol in lipoprotein fractions; the reactivity in descending order was LDL >> VLDL > chylomicron approximately HDL. Gel filtration chromatographic studies revealed that POE-POP removed lipids selectively from the LDL fraction and allowed them to participate in the cholesterol esterase-cholesterol oxidase coupling reaction system. By contrast, alpha-cyclodextrin sulfate reduced the reactivity of cholesterol, especially in chylomicrons and VLDL. A combination of POE-POP with alpha-cyclodextrin sulfate provided the required selectivity for the determination of LDL-C in serum in the presence of magnesium ions and a small amount of dextran sulfate without precipitating lipoprotein aggregates. There was a good correlation between the results of LDL-C assayed by the proposed method and the beta-quantification reference method involving 161 sera with triglyceride concentrations ranging from 0.3 to 22.6 mmol/L. |
| Homogeneous HDL-cholesterol assay versus ultracentrifugation/dextran sulfate-Mg2+ precipitation and dextran sulfate-Mg2+ precipitation in healthy population and in hemodialysis patients Bairaktari, E., M. Elisaf, et al. (1999), Clin Biochem 32(5): 339-46. Abstract: OBJECTIVES: To evaluate the analytical performance of a new homogeneous HDL-cholesterol assay (Olympus Diagnostica). To investigate possibly discrepant results in chronic hemodialysis patients who commonly exhibit quantitative and qualitative lipoprotein abnormalities, responsible for atherogenic complications in these patients. DESIGN AND METHODS: Serum samples were collected from 50 healthy subjects and 65 chronic hemodialysis patients. HDL-C levels measured by the homogeneous assay were compared with the routine dextran sulfate-Mg2+ precipitation method and the ultracentrifugation/dextran sulfate-Mg2+ precipitation as reference method. RESULTS: The homogeneous assay was linear up to at least 220 mg/dL. The analytical precision was estimated with three different sets of commercial controls and one set of human pooled serum control. The within-day CV ranged between 1.7% and 3.8% and the between-day CV ranged between 1.0% and 2.3%. HDL-C values in both populations correlated highly with the dextran sulfate-Mg2+ precipitation method and the ultracentrifugation/dextran sulfate-Mg2+ precipitation method (r > or = 0.96, bias between -0.9 and 2.3 mg/dL). Lipemia up to triglyceride concentration of 600 mg/dL did not alter the HDL-C value. CONCLUSIONS: The homogeneous assay for HDL-C (Olympus) uses much less sample, is accurate and convenient to handle, and allows full automation. The test should considerably facilitate the screening of individuals at an increased risk of cardiovascular disease, including hemodialysis patients. |
| Hormonal changes with cholesterol reduction: a double-blind pilot study Ormiston, T., O. M. Wolkowitz, et al. (2004), J Clin Pharm Ther 29(1): 71-3. Abstract: BACKGROUND: The lowering of high serum cholesterol levels may be associated with increased non-cardiac mortality due to behavioral changes, although such endpoints are likely rare. OBJECTIVE: This current study sought to determine if hormonal changes accompany pharmacologically induced decreases in serum cholesterol levels. METHOD: Cholesterol, dopamine, homovanillic acid (HVA), serotonin, 5-HIAA, testosterone, cortisol and pregnenolone were measured at baseline and after 4 weeks of treatment. RESULTS: Subjects' cholesterol levels significantly declined within 4 weeks. Concomitant significant increase in dopamine and HVA were noted. CONCLUSION: Although this study is limited in size, it raises the possibility that cholesterol-lowering drug treatment is associated with hormonal perturbations. |
| Hormonal control of cholesterol cholelithiasis in the female hamster Ayyad, N., B. I. Cohen, et al. (1995), J Lipid Res 36(7): 1483-8. Abstract: Male golden Syrian hamsters from Sasco form cholesterol gallstones when fed a lithogenic diet; in contrast, female hamsters are resistant to stones when fed the identical diet. Upon addition of the synthetic androgen, methyl-testosterone, to the diet, the incidence of cholesterol gallstones in female hamsters increased from 0% to 40% after 3 weeks and from 0% to 86% after 6 weeks. Cholesterol cholelithiasis remained high in the males. Biliary cholesterol and phospholipid levels were elevated in the females fed the hormone and approached those of the males. The cholesterol saturation of bile in the females increased from 36% to 75% after 3 weeks and from 54% to 109% after 6 weeks. In addition, an appreciable proportion of the cholesterol in the bile of female hamsters was now present in the form of vesicles. The bile acid composition was significantly altered by methyltestosterone even though the total bile acid concentration did not change; the bile acid composition of the female hamsters approached that of the males. The glycine to taurine ratio of the bile acids was drastically reduced by methyltestosterone in the females and to a lesser extent in males. In summary, in female hamsters the addition of methyltestosterone to the lithogenic diet induced cholesterol gallstones, elevated total biliary phospholipid and cholesterol, altered the bile acid composition, and changed the distribution of cholesterol from micelles to vesicles. The data obtained so far do not enable us to define the precise mechanism of action of methyltestosterone. |
| Hormonal regulation of cholesterol 7 alpha-hydroxylase mRNA levels and transcriptional activity in primary rat hepatocyte cultures Hylemon, P. B., E. C. Gurley, et al. (1992), J Biol Chem 267(24): 16866-71. Abstract: In primary cultures of adult rat hepatocytes the level of cholesterol 7 alpha-hydroxylase steady-state mRNA markedly decreased by 72 h. However, the addition of L-thyroxine (T4) and dexamethasone synergistically returned cholesterol 7 alpha-hydroxylase steady-state mRNA levels near to that of cholestyramine-fed animals. The maximal responses to T4 and dexamethasone in serum-free medium were at 1.0 and 0.1 microM, respectively. The addition of T4 in combination with dexamethasone resulted in an 11-fold increase in transcriptional activity of the cholesterol 7 alpha-hydroxylase gene as compared to no addition controls. The specific activities of cholesterol 7 alpha-hydroxylase in microsomes prepared from cultures treated with dexamethasone and T4 were 1.56 +/- 1.17 nmol/h/mg protein which is similar to that of intact liver (1.70 +/- 0.062 nmol/h/mg protein), but lower than cholestyramine-fed animals. Cholesterol 7 alpha-hydroxylase activity was not detectable (less than 0.020 nmol/h/mg protein) at 72 h in cultures without the addition of both dexamethasone and T4. In the presence of optimal concentrations of dexamethasone and T4, glucagon (0.2 microM), or dibutyryl cAMP (50 microM) decreased (90%) cholesterol 7 alpha-hydroxylase mRNA within 6 h. Transcriptional activity decreased (62%) in 6 h following the addition of glucagon (0.2 microM) to the culture medium. The results reported in this paper suggest an important role for multiple hormones in the regulation of cholesterol 7 alpha-hydroxylase in the liver. |
| Hormonal regulation of cholesterol 7alpha-hydroxylase specific activity, mRNA levels, and transcriptional activity in vivo in the rat Pandak, W. M., D. M. Heuman, et al. (1997), J Lipid Res 38(12): 2483-91. Abstract: In primary cultures of rat hepatocytes, transcription of the cholesterol 7alpha-hydroxylase gene is induced synergistically by glucocorticoid and thyroid hormones. The objective of the present study was to evaluate the role of endogenous glucocorticoid and thyroid hormones in the maintenance of cholesterol 7alpha-hydroxylase gene expression in vivo. Male Sprague-Dawley rats underwent adrenalectomy (A), thyroidectomy (T), adrenalectomy + thyroidectomy (A + T), hypophysectomy (H), or sham surgery (paired controls). Ten days post surgery, livers were harvested and choles terol 7alpha-hydroxylase specific activity, steady-state mRNA levels, and transcriptional activity were determined. Serum corticosterone levels were <2% of paired controls in A, A + T, and H rats. Free thyroxine index was <32% of paired controls in rats with T and H. When compared to sham-operated controls, A + T and H led to decreases in cholesterol 7alpha-hydroxylase specific activities of 44 +/- 8% and 57 +/- 3%, respectively (P < 0.03 and < 0.05). Similar changes were observed in cholesterol 7alpha-hydroxylase steady-state mRNA levels, which decreased by 43 +/- 10% (P < 0.001) and 56 +/- 19% (P < 0.05), respectively. Cholesterol 7alpha-hydroxylase transcriptional activity in A + T and H rats decreased by 34 +/- 11% (P < 0.01) and 61 +/- 4% (P < 0.001), respectively. The observed decreases were greater after H than after A + T, suggesting the possibility that another pituitary hormone plays a role in regulation of cholesterol 7alpha-hydroxylase. Thyroidectomy alone led to a decrease in cholesterol 7alpha-hydroxylase specific activity of 37 +/- 7% (P < 0.05) and a trend toward decreased steady-state mRNA levels (21 +/- 12%; P = ns). Adrenalectomy did not significantly decrease cholesterol 7alpha-hydroxylase specific activity or mRNA levels. Neither thyroidectomy nor adrenalectomy alone affected transcriptional activity. We conclude that under physiologic circumstances, full expression of the cholesterol 7alpha-hydroxylase gene requires synergistic action of glucocorticoids and thyroid hormone. |
| Hormone replacement therapy prevents coronary artery disease in ovariectomized cholesterol-fed rabbits Haarbo, J., B. F. Hansen, et al. (1991), Apmis 99(8): 721-7. Abstract: The prevention of coronary artery disease in women is of considerable importance. We have therefore investigated the influence of oestrogen monotherapy and oestrogen-progestogen replacement therapy on coronary artery disease using a simple morphometric method. We studied sixty-three cholesterol-fed rabbits for nineteen weeks. They were randomized to either ovariectomy (51 rabbits) or a sham operation (12 rabbits). The ovariectomized rabbits were randomized to receive either 17 beta-estradiol, 17 beta-estradiol plus norethisterone acetate, 17 beta-estradiol plus levonorgestrel, or placebo. The rabbits with the sham operation received placebo. The hormone therapies reduced the development of coronary artery disease compared to placebo (p less than 0.0001). Furthermore, the coronary artery disease was attended by atherosclerosis in the more distal parts of the coronary arteries (p less than 0.0001), the thoracic aorta (p less than 0.0001) and the abdominal aorta (p less than 0.0001), and by a reduced relative heart weight (p less than 0.05). We conclude that coronary atherosclerosis can be determined quantitatively by morphometry in rabbit arteries. Estradiol monotherapy reduces coronary atherosclerosis in cholesterol-fed rabbits and the addition of norethisterone acetate or levonorgestrel does not attenuate this beneficial effect. |
| Hormone replacement therapy, hormone levels, and lipoprotein cholesterol concentrations in elderly women Paganini-Hill, A., R. Dworsky, et al. (1996), Am J Obstet Gynecol 174(3): 897-902. Abstract: OBJECTIVE: Our purpose was to assess the relationships of lipid and lipoprotein cholesterol levels to hormone replacement therapy and hormone levels in elderly women. STUDY DESIGN: A sample of 292 postmenopausal women 55 to 99 years old (mean 76 years) was drawn from Leisure World Laguna Hills, California, an upper-middle-class, white independent-living population. We compared 84 women receiving unopposed estrogen replacement therapy and 38 women taking combination hormone replacement therapy with 170 women who had never used hormone replacement therapy. Nonparametric tests for differences in lipid and lipoprotein cholesterol levels among groups and multiple stepwise regression models were used. RESULTS: Estrogen users (with and without progestin) had lower total and low-density lipoprotein cholesterol and higher high-density lipoprotein and high-density lipoprotein subfraction types 2, 2a, and 2b cholesterol levels. High density lipoprotein type 3 subfractions were lower in combination hormone replacement therapy users but higher in unopposed estrogen users relative to nonusers. The conjugated equine estrogen dose was negatively correlated with total (p = 0.0009) and low-density lipoprotein cholesterol (p <0.0001) levels and positively correlated to high-density lipoprotein cholesterol (p = 0.002) and its subfractions. The medroxyprogesterone acetate dose showed no consistent effect on cholesterol levels. CONCLUSION: The associations found here reaffirm the significant role of estrogen replacement therapy on lipid and lipoprotein cholesterol levels and provide no evidence of a reduction in the beneficial effect of estrogen with the addition of a progestational agent to the replacement regimen. |
| Hormone-induced changes in cardiolipin from Leydig cells: possible involvement in intramitochondrial cholesterol translocation Gasnier, F., C. Rey, et al. (1998), Biochem Mol Biol Int 45(1): 93-100. Abstract: The rate-limiting and hormonally regulated step in steroid hormone biosynthesis is the delivery of cholesterol from the outer to the inner mitochondrial membrane where cytochrome P450scc resides. Although the exact mechanism of intramitochondrial cholesterol translocation remains unknown, the formation of contact sites between outer and inner mitochondrial membranes appears as a necessary component for cholesterol transfer. Several pieces of evidence suggest that local formation of intermembrane contact is a consequence of a non-bilayer arrangement of polymorphic lipids which are enriched in the junctions. As a step toward clarifying mitochondrial contact sites formation and thus cholesterol translocation in steroidogenic cells, we have undertaken studies to identify the factors which might result in non-bilayer structure to be adopted by mitochondrial phospholipids on stimulation of MA-10 Leydig cells. Our results demonstrate that an increase in the unsaturation of the cardiolipin acyl groups on hormonal stimulation might favor the formation of non-bilayer adhesion points. |
| Hormone-sensitive cholesterol ester hydrolase in adrenal tumor cells: activation by corticotropin and tetradecanoyl phorbol acetate Balkow, C., W. H. Trzeciak, et al. (1990), Endocr Res 16(2): 205-19. Abstract: The effects of corticotropin (ACTH) and tetradecanoyl phorbol acetate (TPA) on cholesterol ester hydrolase, intracellular cholesteryl ester concentration and steroid hormone formation were studied in mouse adrenal tumor cells (Y-1) in monolayer culture. Cholesterol ester hydrolase activity increased about 2-fold during 7 min incubation with ACTH, dibutyryl 3',5'-cyclic AMP (dbcAMP) and TPA at maximally effective concentrations; whereas, incubation with phorbol monoacetate had no effect. Long-term exposure to ACTH and dbcAMP markedly lowered intracellular cholesteryl 3H-oleate concentration and highly increased steroid hormone output, while TPA treatment resulted in lowering cholesteryl 3H-oleate content without affecting steroid hormone formation. Calcium activated phospholipid-dependent protein kinase C was detected in Y-1 cell cytosol. It is concluded that the mouse adrenal tumor cells in monolayer culture respond to ACTH in a fashion similar to normal adrenocortical cells; whereas, the response to the phorbol ester TPA (possibly mediated through protein kinase C) involves activation of cholesterol ester hydrolase and cholesteryl ester depletion, however, without affecting steroid hormone secretion. |
| Host but not parasite cholesterol controls Toxoplasma cell entry by modulating organelle discharge Coppens, I. and K. A. Joiner (2003), Mol Biol Cell 14(9): 3804-20. Abstract: Host cell cholesterol is implicated in the entry and replication of an increasing number of intracellular microbial pathogens. Although uptake of viral particles via cholesterol-enriched caveolae is increasingly well described, the requirement of cholesterol for internalization of eukaryotic pathogens is poorly understood and is likely to be partly organism specific. We examined the role of cholesterol in active host cell invasion by the protozoan parasite Toxoplasma gondii. The parasitophorous vacuole membrane (PVM) surrounding T. gondii contains cholesterol at the time of invasion. Although cholesterol-enriched parasite apical organelles termed rhoptries discharge at the time of cell entry and contribute to PVM formation, surprisingly, rhoptry cholesterol is not necessary for this process. In contrast, host plasma membrane cholesterol is incorporated into the forming PVM during invasion, through a caveolae-independent mechanism. Unexpectedly, depleting host cell plasma membrane cholesterol blocks parasite internalization by reducing the release of rhoptry proteins that are necessary for invasion. Cholesterol back-addition into host plasma membrane reverses this inhibitory effect of depletion on parasite secretion. These data define a new mechanism by which host cholesterol specifically controls entry of an intracellular pathogen. |
| How accurate is the Reflotron cholesterol analyzer? 1. Accuracy of reflotron misrepresented in study van Beurden, E. and R. James (1993), Am J Public Health 83(3): 428-9. |
| How accurate is the Reflotron cholesterol analyzer? 2. Reflotron screenings considered a success Feil, J. M. (1993), Am J Public Health 83(3): 428-9. |
| How can high-density lipoprotein cholesterol levels be elevated? Cunnigham, E. (2003), J Am Diet Assoc 103(7): 860. |
| How cells handle cholesterol Simons, K. and E. Ikonen (2000), Science 290(5497): 1721-6. Abstract: Cholesterol plays an indispensable role in regulating the properties of cell membranes in mammalian cells. Recent advances suggest that cholesterol exerts many of its actions mainly by maintaining sphingolipid rafts in a functional state. How rafts contribute to cholesterol metabolism and transport in the cell is still an open issue. It has long been known that cellular cholesterol levels are precisely controlled by biosynthesis, efflux from cells, and influx of lipoprotein cholesterol into cells. The regulation of cholesterol homeostasis is now receiving a new focus, and this changed perspective may throw light on diseases caused by cholesterol excess, the prime example being atherosclerosis. |
| How cholesterol drug raises many questions Roberts, H. J. (1990), J Fla Med Assoc 77(1): 13-4. |
| How cholesterol homeostasis is regulated by plasma membrane cholesterol in excess of phospholipids Lange, Y., J. Ye, et al. (2004), Proc Natl Acad Sci U S A 101(32): 11664-7. Abstract: How do cells sense and control their cholesterol levels? Whereas most of the cell cholesterol is located in the plasma membrane, the effectors of its abundance are regulated by a small pool of cholesterol in the endoplasmic reticulum (ER). The size of the ER compartment responds rapidly and dramatically to small changes in plasma membrane cholesterol around the normal level. Consequently, increasing plasma membrane cholesterol in vivo from just below to just above the basal level evoked an acute (<2 h) and profound (approximately 20-fold) decrease in ER 3-hydroxy-3-methylglutaryl-CoA reductase activity in vitro. We tested the hypothesis that the sharply inflected ER response to cholesterol is governed by the thermodynamic activity (fugacity) of plasma membrane cholesterol. The following two independent measures of plasma membrane cholesterol activity in human red cells and fibroblasts were used: susceptibility to cholesterol oxidase and cholesterol transfer to cyclodextrin. Both indicators revealed a threshold at the physiologic set point of plasma membrane cholesterol. Incrementing the phospholipid compartment in the plasma membrane with lysophosphatidylcholine, previously shown to decrease cholesterol oxidase susceptibility, reduced the transfer of plasma membrane cholesterol to cyclodextrin and to the ER. Conversely, the membrane intercalator, n-octanol, increased cholesterol oxidation, transfer, and ER pool size, perhaps by displacing cholesterol from plasma membrane phospholipids. We conclude that the activity of the fraction of cholesterol in excess of other plasma membrane lipids sets the cholesterol level in the ER. Cholesterol-sensitive elements therein respond by nulling the active plasma membrane pool, thereby keeping the cholesterol matched to the other plasma membrane lipids. |
| How cholesterol modulates the signal Ingham, P. W. (2000), Curr Biol 10(5): R180-3. Abstract: By coupling to cholesterol, Hedgehog can be anchored to the cells where it is made, yet to act as a morphogen, it must be able to move away from its source. Novel genes have now been identified that control the release and dispersal of Hedgehog, shedding new light on the part played by cholesterol in these processes. |
| How cholesterol-dependent cytolysins bite holes into membranes Walz, T. (2005), Mol Cell 18(4): 393-4. Abstract: In a show piece for electron microscopy (EM), Tilley at al. used single-particle cryo-EM to visualize the structural rearrangements in the bacterial toxin pneumolysin that occur when it assembles into a membrane-associated prepore and when the prepore subsequently transitions into a fully membrane-inserted pore. |