| For medical practitioners and the general public - Cholesterol Journal Article Catalog. |
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| Cholesterol absorption efficiency and sterol metabolism in obesity Miettinen, T. A. and H. Gylling (2000), Atherosclerosis 153(1): 241-8. Abstract: Role of enterohepatic cholesterol metabolism in obesity-induced increase of cholesterol synthesis was studied in healthy lean (BMI <24) and overweight (BMI >31) subjects by measuring serum lipids (including plant sterols, cholestanol and cholesterol precursors), cholesterol absorption % (double-label method), sterol balance and biliary lipids. New aspects of sterol metabolism in obesity were as follows: low efficiency of cholesterol absorption, reduced ratios to cholesterol of serum and biliary plant sterols and cholestanol (5alpha-derivative of cholesterol), and a marked increase of serum and biliary cholesterol precursor sterols. Percent of cholesterol absorption was positively related to serum cholestanol and plant sterols, and negatively to cholesterol synthesis, measured by the sterol balance technique or cholesterol precursor sterols in serum or bile. Total and endogenous cholesterol fluxes into the intestine were increased, but owing to low absorption percent, mass of cholesterol absorption was within control limits in the obese subjects. Thus, per gram of their large liver tissue the entry of intestinal cholesterol may even be subnormal. Percent of cholesterol absorption was insignificantly negatively (r=-0.256) related to intestinal cholesterol pool, but significantly to biliary concentrations of cholesterol (r=-0.581), bile acids (r=-0.513) and phospholipids (r=-0.469). Thus, dilution of labeled dietary cholesterol by expanded intestinal cholesterol pool could have contributed to subnormal efficiency of cholesterol absorption, or transfer of labeled dietary cholesterol from intestinal oil phase to micellar phase may be competitively inhibited by expanded biliary secretion, resulting in reduced absorption of dietary cholesterol. These mechanisms could have contributed to changes in metabolism of non-cholesterol sterols, especially of cholestanol and plant sterols. |
| Cholesterol absorption efficiency declines at moderate dietary doses in normal human subjects Ostlund, R. E., Jr., M. S. Bosner, et al. (1999), J Lipid Res 40(8): 1453-8. Abstract: While unphysiologically large cholesterol doses are known to reduce percent cholesterol absorption, smaller amounts are reported to have no effect in human subjects. To determine the dose;-response relation between dietary cholesterol consumed and the efficiency of intestinal cholesterol absorption, we fed 18 normal subjects two test meals containing different amounts of natural cholesterol. In each test pentadeuterated cholesterol tracer was given orally, hexadeuterated cholesterol tracer was given intravenously, and the tracer ratio was measured in plasma 4 days later by gas chromatography/negative ion mass spectrometry. Baseline cholesterol absorption in the presence of 26 mg cholesterol tracer was 40.7 +/- 2.3%. This decreased by 4.9 percentage points (P = 0.05) when a total of 188 mg cholesterol was included in the meal and by 15.6 percentage points (P = 0.006) when 421 mg cholesterol was given, showing that the efficiency of cholesterol absorption declines appreciably even with modest increases in cholesterol dose. Considerable variation was noted in the response of different subjects and, on the higher cholesterol dose, dietary cholesterol absorption varied 5-fold from 40 mg to 212 mg. Fasting plasma insulin was correlated with the ability to absorb higher cholesterol doses without loss of efficiency (r(s) = 0.700, P = 0.036). Percent cholesterol absorption in a single meal is significantly influenced by the amount of cholesterol in that meal, suggesting that acute dietary factors influencing cholesterol absorption need further study. |
| Cholesterol absorption inhibition: a strategy for cholesterol-lowering therapy Miettinen, T. A. (2001), Int J Clin Pract 55(10): 710-6. Abstract: A clear relationship has been documented between plasma levels of low-density lipoprotein cholesterol (LDL-C) and the risk of coronary heart disease. LDL-C is believed to be key in the pathogenesis of coronary atherosclerosis, although increasing evidence suggests that low levels of high-density lipoprotein cholesterol and elevated triglyceride levels are contributory factors. Chylomicron remnants formed via the exogenous (dietary and biliary) pathway of cholesterol metabolism may also have atherogenic potential. Dietary modification, especially with plant stanol (sterol) ester margarine, which inhibits cholesterol absorption and improves the fatty acid pattern, lowers LDL-C sufficiently in many hypercholesterolaemic patients, and is also a useful adjunct to pharmacological therapy. Cholesterol absorption inhibitors typically lower LDL-C by 10-20%. Ezetimibe, the first selective cholesterol absorption inhibitor, has been shown to lower LDL-C by approximately 18% following a once-daily 10 mg dose, either as monotherapy or as combination therapy. Combination therapy with selective cholesterol absorption inhibitors such as ezetimibe along with statins or fibrates may allow more patients with hypercholesterolaemia to achieve target LDL-C levels compared with treatment with monotherapy. Ezetimibe may be useful in the management of patients who respond poorly to or are unable to tolerate statins, or in patients with hereditary or drug-induced phytosterolaemia. |
| Cholesterol absorption inhibitor Ezetimibe blocks uptake of oxidized LDL in human macrophages Seedorf, U., T. Engel, et al. (2004), Biochem Biophys Res Commun 320(4): 1337-41. Abstract: Ezetimibe belongs to a group of selective and very effective 2-azetidione cholesterol absorption inhibitors which act on the level of cholesterol entry into enterocytes. Recent data indicated that the drug prevents the formation of a heterocomplex consisting of annexin-2 and caveolin-l and leads to specific inhibition of an NPCILI-dependent cholesterol uptake pathway required for uptake of micellar cholesterol into enterocytes. Earlier studies have shown that caveolin-l and annexin-2 are also expressed in human macro-phages and we show in this study that human macrophages express NPC1L1. Moreover in human macrophages, Ezetimibe(SCH58235) and its analogue, SCH354909, are bound to specific cell surface receptors followed by endocytosis via the classical endocytic pathway. SCH58235 had no effect on uptake and/or processing of acetylated LDL (Ac-LDL). In contrast, the compound inhibited uptake of oxidized LDL (Ox-LDL) by -50% in a dose-dependent manner. SCH58235 blocked the lipid-induced induction of LXR/RXR target genes ABCAI, ABCGI, and apolipoprotein E distinctively more effectively in macrophages loaded with Ox-LDL than in those loaded with Ac-LDL. Based on these findings, we presume that the caveolin-l-, annexin-2-, and NPClLI-dependent cholesterol uptake system that is operating in enterocytes may also contribute to class B scavenger receptor-dependent uptake of Ox-LDL in human monocyte-derived macrophages. |
| Cholesterol absorption inhibitors for the treatment of hypercholesterolaemia Sudhop, T. and K. von Bergmann (2002), Drugs 62(16): 2333-47. Abstract: The benefits of lipid lowering therapy on coronary heart disease have been clearly established in many clinical trials on primary and secondary prevention. Despite the availability of potent lipid lowering drugs, many patients do not reach the current treatment goals. This paper reviews new therapeutic approaches in lipid lowering drugs focusing on compounds which lower cholesterol absorption. The role of plant sterols and stanols, new acyl-CoA:cholesterol O-acyl transferase (ACAT) inhibitors, microsomal triglyceride transfer protein (MTP) inhibitors, and ezetimibe are summarised. Although the lipid lowering effect of plant sterols and plant stanols is only moderate, their use as functional foods is beneficial for patients with mild hypercholesterolaemia and is able to enhance the lipid lowering effect of HMG-CoA reductase inhibitors (statins). The role of ACAT inhibitors that might also inhibit cholesterol absorption remains unclear. Avasimibe, the first oral bioavailable ACAT inhibitor, has entered phase III trials. However, the presently available data in humans do not indicate a clear clinical benefit. The role of MTP inhibitors, which exhibit remarkable effects on all plasma lipids, also remains unclear, as safety concerns must first be addressed. Ezetimibe, the first available 2-azetidinone, succeeded in phase III trials showing remarkable effects in inhibition of cholesterol absorption as well as cholesterol lowering. The synergistic effect of co-administration of ezetimibe with statins seemingly offers a new approach in reaching the therapeutic goals. |
| Cholesterol absorption inhibitors in development as potential therapeutics Kajinami, K. and N. Takekoshi (2002), Expert Opin Investig Drugs 11(6): 831-5. Abstract: Drugs that lower low-density lipoprotein cholesterol through their actions in the gastrointestinal tract have been used for > 30 years. Bile acid sequestrants have very excellent safety profiles but their poor tolerability means they have limited clinical use. Recently developed new compounds are better tolerated in clinical trials and show greater benefit in reducing low-density lipoprotein cholesterol level, as compared to "older" sequestrants. Cholesterol absorption inhibitors and bile acid transporter inhibitors have recently been reported to show clinical efficacy and safety as novel gut-acting drugs for lowering cholesterol. Further advances in our understanding of the cholesterol absorption mechanism will provide novel therapeutic targets, such as the ATP-binding cassette transporter. This approach in the treatment of lowering cholesterol appears to play a more significant role in the clinical field of atherosclerotic vascular disease. |
| Cholesterol absorption inhibitors: defining new options in lipid management Brown, W. V. (2003), Clin Cardiol 26(6): 259-64. Abstract: Although many studies have documented that reduction of plasma cholesterol levels decreases the risk of coronary artery disease, it remains the most common cause of death in the Western world. Current therapeutic options are effective in lowering cholesterol, especially in clinical trials, but clinical application is not optimized for many reasons. Dietary restriction for long-term management of hypercholesterolemia is helpful but usually insufficient to reduce low-density lipoprotein cholesterol (LDL-C) to goal levels. Powerful drugs are available, but these are often insufficient to meet the clinical demands for cholesterol-lowering therapy. Phytosterols and phytostanols have been partially effective by providing some inhibition of absorption of cholesterol. Compounds that specifically and more effectively block intestinal absorption of dietary and biliary cholesterol should provide a significant new agent for altering lipoprotein concentrations favorably. Ezetimibe is the first of this class of compounds that act at the gut epithelium to reduce cholesterol absorption in the milligram dose range markedly. Clinical studies indicate that ezetimibe effectively decreases LDL-C by 15 to 20% as monotherapy, with a favorable safety profile. Moreover, results from preliminary clinical trials indicate that ezetimibe given concomitantly with a statin provides additive efficacy. The combination represents a new approach to lipid management, achieving greater LDL-C and triglyceride reductions and greater improvements in HDL-C than statin monotherapy. This could offer another important option in clinical practice for management of hypercholesterolemic patients. |
| Cholesterol absorption is mainly regulated by the jejunal and ileal ATP-binding cassette sterol efflux transporters Abcg5 and Abcg8 in mice Duan, L. P., H. H. Wang, et al. (2004), J Lipid Res 45(7): 1312-23. Abstract: In the present study, we investigated whether intestinal sterol efflux transporters Abcg5 and Abcg8 play a major role in determining variations in cholesterol (Ch) absorption efficiency, and we compared the physiological functions of the duodenal, jejunal, and ileal Abcg5 and Abcg8 on the absorption of Ch and sitostanol in inbred mice challenged with various amounts of Ch, sitostanol, hydrophilic, or hydrophobic bile acids. We found that Abcg5 and Abcg8 in the jejunum and ileum, but not in the duodenum, were main factors in determining, in part, variations in Ch absorption efficiency. The jejunal and ileal Abcg5 and Abcg8 played a major regulatory role in response to high dietary cholesterol and were more sensitive in the regulation of Ch absorption when compared with sitostanol absorption. These results, combined with different sterol uptake rates, suggest that the absorption efficiency of Ch and sitostanol is determined by the net results between influx and efflux of intraluminal Ch and sitostanol molecules crossing the apical membrane of the enterocyte. Hydrophilic and hydrophobic bile acids influenced Ch absorption through mediating Ch solubilization and its physical-chemical state within the small intestinal lumen. We conclude that Ch absorption is mainly regulated by the jejunal and ileal Abcg5 and Abcg8 in mice. |
| Cholesterol absorption, elimination, and synthesis related to LDL kinetics during varying fat intake in men with different apoprotein E phenotypes Miettinen, T. A., H. Gylling, et al. (1992), Arterioscler Thromb 12(9): 1044-52. Abstract: Cholesterol absorption, fecal elimination, and synthesis and low density lipoprotein (LDL) metabolism were measured in 29 middle-aged men while on their normal diet and a diet low in fat and cholesterol, and the obtained values were related to apoprotein (apo) E phenotypes. Basal cholesterol absorption efficiency was positively related to production rate (PR) for LDL apo B and negatively to cholesterol synthesis (measured by fecal steroids and dietary cholesterol), which in turn was negatively associated with the LDL level and positively with the fractional removal (FCR) of LDL apo B. The apo E subscript (e.g., E2/2 = 1, E2/3 = 2, etc.) was positively associated with cholesterol absorption and the LDL apo B and cholesterol levels and negatively with cholesterol synthesis and FCR for LDL apo B. Effective bile acid and cholesterol synthesis, fecal elimination of cholesterol, removal of LDL apo B, and low cholesterol absorption characterized men with the epsilon 2 allele. Reduction of dietary fat and cholesterol intakes lowered LDL cholesterol levels and cholesterol absorption but increased cholesterol synthesis proportionally to the apo E subscript; the FCR and PR for LDL apo B were significantly increased and decreased, respectively. The decrease in absorption was related to enhanced removal of LDL apo B and synthesis of cholesterol. During the modified diet, cholesterol metabolism was poorly related to LDL, apo E phenotypes, and LDL apo B kinetics. A positive correlation of cholesterol absorption with dietary fat intake in combined studies suggests that a dietary fat reduction-associated decrease in LDL cholesterol is at least partly caused by reduced cholesterol absorption.(ABSTRACT TRUNCATED AT 250 WORDS) |
| Cholesterol absorption, synthesis, and fecal output in postmenopausal women with and without coronary artery disease Rajaratnam, R. A., H. Gylling, et al. (2001), Arterioscler Thromb Vasc Biol 21(10): 1650-5. Abstract: Hypercholesterolemia is a prominent risk factor for coronary artery disease (CAD), yet cholesterol metabolism has not been evaluated in women with CAD. The objective of this study was to determine the interrelations of CAD, serum squalene and sterols, and cholesterol metabolism with each other in postmenopausal women. For this purpose, we measured serum squalene and sterols and fecal steroids (cholesterol and bile acids) and squalene by gas-liquid chromatography and evaluated cholesterol absorption and synthesis in postmenopausal women with CAD (n=29) and age-matched controls (n=20). On similar dietary lipid intake, the cholesterol absorption efficiency and mean serum cholesterol level were comparable, but the squalene-to-cholesterol ratio was higher in cases than in controls. The presence of CAD was inversely associated with fecal total steroids (logistic regression coefficient beta/SE=-2.11, P=0.04) and cholesterol synthesis (beta/SE=-2.14, P=0.04) and turnover (beta/SE=-2.19, P=0.03) after adjustment for dietary cholesterol, family history of CAD, smoking, low and high density lipoprotein cholesterol, and serum triglyceride levels. A high serum squalene ratio was not related to cholesterol synthesis but was inversely related to fecal squalene excretion, which was lower in cases than in controls. In conclusion, the presence of CAD in postmenopausal women is independently associated with altered cholesterol metabolism, as reflected by low synthesis and inefficient elimination of cholesterol. |
| Cholesterol absorption, synthesis, and LDL metabolism in NIDDM Gylling, H. and T. A. Miettinen (1997), Diabetes Care 20(1): 90-5. Abstract: OBJECTIVE: Cholesterol and lipoprotein metabolism was studied in mildly hypercholesterolemic nonobese men with NIDDM to find out which metabolic parameters regulate serum cholesterol level in these NIDDM subjects. RESEARCH DESIGN AND METHODS: Nonobese NIDDM subjects (n = 13) and control subjects (n = 18) with serum cholesterol > or = 6.0 and triglycerides < or = 2.5 mmol/l were studied on a similar monoene-enriched diet. Cholesterol absorption was studied with peroral double isotopes and by measuring serum plant sterols with gas-liquid chromatography; cholesterol synthesis was studied by measuring sterol balance and by measuring serum cholesterol precursor sterols; and LDL kinetics was measured with 131I-labeled autologous apoprotein (apo) B. RESULTS: Cholesterol absorption was significantly lower in NIDDM subjects than in the control subjects, as detected by low serum plant sterol levels and absorption percentage (23 vs. 29%, P < 0.05). Cholesterol synthesis was significantly higher in NIDDM subjects than in the control subjects, as detected by precursor sterols or balance data (18 vs. 12 mg.kg-1.day-1, P < 0.01), cholesterol turnover (19 vs. 13 mg.kg-1.day-1, P < 0.01), and LDL apo B removal (0.343 vs. 0.267 pools/day, P < 0.01). Serum total and LDL cholesterol levels were inversely correlated with cholesterol synthesis, which was positively related to the catabolism of LDL apo B and negatively related to cholesterol absorption efficiency. CONCLUSIONS: In this small selected group of mildly hypercholesterolemic nonobese NIDDM subjects, the regulation of serum cholesterol levels was achieved by the homeostasis between cholesterol absorption, synthesis, and LDL fractional catabolism. Cholesterol turnover and removal of LDL apo B were high in NIDDM subjects, compared with the control subjects, whereas cholesterol absorption efficiency was abnormally low Because of the relatively small number of selected subjects, the present results are not directly applicable to the overall NIDDM population. |
| Cholesterol accumulates in cell bodies, but is decreased in distal axons, of Niemann-Pick C1-deficient neurons Karten, B., D. E. Vance, et al. (2002), J Neurochem 83(5): 1154-63. Abstract: Niemann-Pick type-C (NPC) disease is characterized by a progressive loss of neurons and an accumulation of unesterified cholesterol within the endocytic pathway. Unlike other tissues, however, NPC1-deficient brains do not accumulate cholesterol but whether or not NPC1-deficient neurons accumulate cholesterol is not clear. Therefore, as most studies on cholesterol homeostasis in NPC1-deficient cells have been performed in fibroblasts we have investigated cholesterol homeostasis in cultured murine sympathetic neurons lacking functional NPC1. These neurons did not display obvious abnormalities in growth or morphology and appeared to respond normally to nerve growth factor. Filipin staining revealed numerous cholesterol-filled endosomes/lysosomes in NPC1-deficient neurons and the mass of cholesterol in cell bodies was greater than in wild-type neurons. Surprisingly, however, the cholesterol content of NPC1-deficient and wild-type neurons as a whole was the same. This apparent paradox was resolved when the cholesterol content of NPC1-deficient distal axons was found to be less than of wild-type axons. Cholesterol sequestration in cell bodies did not depend on exogenously supplied cholesterol since the cholesterol accumulated before birth and did not disperse when neurons were cultured without exogenous cholesterol. The altered cholesterol distribution between cell bodies and axons suggests that transport of cholesterol, particularly that synthesized endogenously, from cell bodies to distal axons is impaired in NPC1-deficient neurons. |
| Cholesterol accumulates in senile plaques of Alzheimer disease patients and in transgenic APP(SW) mice Mori, T., D. Paris, et al. (2001), J Neuropathol Exp Neurol 60(8): 778-85. Abstract: Mounting evidence suggests that cholesterol may contribute to the pathogenesis of Alzheimer disease (AD). We examined whether cholesterol might be present in senile plaques, a hallmark neuropathological feature of AD. We employed 2 different fluorometric-staining techniques (filipin staining and an enzymatic technique) for the determination of cholesterol in brains of postmortem confirmed AD patients and in nondemented, age-matched histopathologically normal controls. AD patient brains showed abnormal accumulation of cholesterol in congophilic/birefringent dense cores of senile plaques that was essentially absent in histopathologically normal controls. To determine whether increased senile plaque-associated cholesterol occurred generally in all plaques or was restricted to a specific subset, quantitative analysis was performed. Data indicate abnormal accumulation of cholesterol in cores of mature plaques but not in diffuse or immature plaques. Additionally, transgenic mice that overexpress the "Swedish" amyloid precursor protein (Tg APP(SW), line 2576) exhibited a similar pattern of abnormal cholesterol accumulation in mature, congophilic amyloid plaques at 24 months of age that was absent in their control littermates or in 8-month-old Tg APP(SW) mice (an age prior to amyloid deposition). Taken together, our results imply a link between cholesterol and AD pathogenesis and suggest that cholesterol plays an important role in the formation and/or progression of senile plaques. |
| Cholesterol accumulation in human cornea: evidence that extracellular cholesteryl ester-rich lipid particles deposit independently of foam cells Gaynor, P. M., W. Y. Zhang, et al. (1996), J Lipid Res 37(9): 1849-61. Abstract: The cornea is a connective tissue site where lipid accumulates as a peripheral arcus lipoides. We found that cholesterol, in predominantly esterified form, progressively accumulated with age in the peripheral corneas of 20- to 90-yr-old individuals. Ultrastructural studies showed extracellular solid spherical lipid particles (< 200 nm in diameter) enmeshed between collagen fibers. Immunostaining showed significant apoE and apoA-I, but very little apoB in the peripheral cornea. Lipid particles were extracted from minced corneas into a buffer and subjected to isopycnic density gradient centrifugation. The lipid particles had a density < 1.02 g/ml, contained > 75% of their cholesterol in esterified form, and were distributed in two populations with average diameters of 22 +/- 5 nm (SD) and 79 +/- 26 nm. Gel-filtration chromatographic analysis of the corneal lipid particles showed that most cholesterol eluted with the larger particles and these larger particles lacked apoB. ApoA-I was associated with lipid particles the size of HDL. Most apoE was associated with lipid particles larger than the apoA-I-containing lipid particles and smaller than the large lipid particles that carried most of the corneal cholesterol. Thus, the cholesteryl ester-rich lipid particles that accumulate in the cornea are 1) similar to lipid particles previously localized within and isolated from human atherosclerotic lesions, 2) accumulate without foam cells, and 3) may be derived from low density lipoproteins that have lost their apoB and fused. |
| Cholesterol accumulation in J774 macrophages induced by triglyceride-rich lipoproteins. Comparison of very low density lipoprotein from subjects with type III, IV, and V hyperlipoproteinemias Huff, M. W., A. J. Evans, et al. (1991), Arterioscler Thromb 11(2): 221-33. Abstract: The capacity of human triglyceride-rich lipoproteins to induce cholesterol accumulation in the murine J774 macrophage cell line was investigated with large very low density lipoprotein (VLDL, Sf 60-400) obtained from subjects with type III, IV, and V hyperlipoproteinemias. After incubation for 24 hours, VLDLs from type IV and type V subjects were similar in their ability to raise cellular cholesterol deposition threefold to fourfold and cellular triglyceride 16-fold. The increase in cholesterol was entirely due to the dramatic increase in cholesterol ester, from less than 1 to greater than 50 micrograms/mg cell protein. Total cholesterol accumulation was fourfold to fivefold greater than the cholesterol accumulation observed for VLDL or low density lipoprotein (LDL) from normal subjects. Cholesterol esterification (acyl coenzyme A: cholesterol acyltransferase ACAT activity) paralleled the rate of cholesterol accumulation in these cells. Treating the macrophages with the ACAT inhibitor 58035, which is known to downregulate the LDL receptor in these cells, diminished cholesterol accumulation by 40% for type IV VLDL and by 23% for normal LDL. Since hypertriglyceridemic VLDL carries excess apoprotein (apo) E molecules, we investigated the role of normal and abnormal apo E. An anti-apo E monoclonal antibody, known to block the binding of apo E to the LDL receptor, blocked type IV VLDL-induced cholesterol ester accumulation by approximately 70%. In contrast to type IV subjects, VLDL from type III subjects (homozygous for apo E2) when incubated with J774 macrophages (which do not secrete apo E) caused only a modest 1.5-2-fold increase in cellular cholesterol. Pre-beta- and beta-migrating VLDL subfractions from type III subjects were equally ineffective in causing cholesterol accumulation. By contrast, beta-VLDL from cholesterol-fed rabbits caused a sevenfold to eightfold increase in cellular cholesterol content. These results indicate that triglyceride-rich lipoproteins from type IV and type V subjects can cause substantial cholesterol ester accumulation and enhanced cholesterol esterification in J774 cells. The lower cholesterol accumulation with type IV VLDL in the presence of apo E antibodies and VLDL from type III subjects demonstrates the importance of functional apo E in this process. |
| Cholesterol accumulation in NPC1-deficient neurons is ganglioside dependent Gondre-Lewis, M. C., R. McGlynn, et al. (2003), Curr Biol 13(15): 1324-9. Abstract: Niemann-Pick type C (NPC) disease is a lysosomal disorder commonly caused by a recessive mutation in NPC1, which encodes an integral membrane protein with regions of homology to the morphogen receptor, Patched, and to 3-hydroxy-3-methylglutaryl coenzyme A reductase. Neurons in NPC disease exhibit extensive storage of free cholesterol and glycosphingolipids (GSLs), including GM2 and GM3 gangliosides. Most studies have viewed cholesterol storage as primary, with NPC1 functioning as a retroendocytic transporter for regulation of cholesterol homeostasis. Here, we analyze the effects of genetically depriving NPC neurons of complex gangliosides by creating mice doubly deficient in both NPC1 and the GSL synthetic enzyme, GM2/GD2 synthase (GalNAcT). Ganglioside and cholesterol expression in neurons of NPC1(-/-)/GalNAcT(+/+), NPC1(-/-)/GalNAcT(-/-), NPC1(+/+)/GalNAcT(-/-), and WT mice was examined in situ by immunocytochemical and histochemical methods. Neurons in double-deficient mice lacked intraneuronal GM2 accumulation as expected, but remarkably also exhibited absence or dramatic reduction in free cholesterol. Neurons storing cholesterol consistently showed GM3 accumulation but some GM3-positive neurons lacked cholesterol storage. These findings provide a compelling argument that cholesterol sequestration in NPC1-deficient neurons is ganglioside dependent and suggest that the function of NPC1 in these cells may be more closely linked to homeostatic control of GSLs than cholesterol. |
| Cholesterol accumulation in plasma membrane and changes of membrane enzyme activity of Acholeplasma laidlawii cells during culture ageing Kapitanov, A. B., V. F. Ivanova, et al. (1990), Mech Ageing Dev 55(2): 161-9. Abstract: The data presented in this report show that the microviscosity of the plasma membrane and the cholesterol/phospholipid molar ratio of its lipid bilayer increases during ageing of Acholeplasma laidawii cultures. At the same time the age changes of other lipid components content do not correlate with the change of membrane viscosity. It is also shown that membrane enzyme activities of mycoplasma cell decrease with age. These results confirm the membrane hypothesis of ageing according to which increased microviscosity is the essential factor of cell ageing. |
| Cholesterol accumulation in tissues of the Niemann-pick type C mouse is determined by the rate of lipoprotein-cholesterol uptake through the coated-pit pathway in each organ Xie, C., S. D. Turley, et al. (1999), Proc Natl Acad Sci U S A 96(21): 11992-7. Abstract: Niemann-Pick type C (NPC) disease is associated with the accumulation of unesterified cholesterol in nearly all tissues and with progressive neurodegeneration. A murine model of this disease, the NPC mouse, was used to determine whether this sequestered cholesterol represented sterol carried in low density lipoprotein (LDL) and chylomicrons (CMs) taken up into the tissues through the coated-pit pathway. By 7 weeks of age, the sterol pool in the NPC mice had increased from 2,165 to 5,669 mg/kg body weight because of the daily sequestration of 67 mg of cholesterol per kg in the various organs. This was 7-fold greater than the rate of accumulation in control mice. The rate of LDL clearance in the NPC mouse was normal (523 ml/day per kg) and accounted for the uptake of 78 mg/day per kg of cholesterol in LDL whereas 8 mg/day per kg was taken up from CMs. Deletion of the LDL receptor in NPC mice altered the concentration of unesterified cholesterol in every organ in a manner consistent with the changes also observed in the rate of LDL cholesterol uptake in those tissues. Similarly, altering the flow of cholesterol to the liver through the CM pathway changed the concentration of unesterified cholesterol in that organ. Together, these observations strongly support the conclusion that, in NPC disease, it is cholesterol carried in LDL and CMs that is sequestered in the tissues and not sterol that is newly synthesized and carried in high density lipoprotein. |
| Cholesterol addition to ER membranes alters conformation of SCAP, the SREBP escort protein that regulates cholesterol metabolism Brown, A. J., L. Sun, et al. (2002), Mol Cell 10(2): 237-45. Abstract: Sterol accumulation in membranes blocks the exit of SCAP from the ER, preventing SREBP cleavage and reducing cholesterol synthesis. Sterols act through SCAP's sterol-sensing domain by an obscure mechanism. Here, we show that addition of cholesterol to ER membranes in vitro causes a conformational change in SCAP, detected by the unmasking of closely spaced trypsin cleavage sites. Two mutant forms of SCAP (Y298C and D443N) that are refractory to sterol regulation in vivo are also refractory to sterol-induced conformational change in vitro. 25-hydroxycholesterol, a potent regulator of SCAP in vivo, fails to change SCAP's conformation in vitro, suggesting that oxysterols act in intact cells by translocating cholesterol from plasma membrane to ER. These studies demonstrate an in vitro effect of cholesterol on the sterol regulatory machinery. |
| Cholesterol affects African swine fever virus infection Bernardes, C., A. Antonio, et al. (1998), Biochim Biophys Acta 1393(1): 19-25. Abstract: African swine fever virus (ASFV) enters cells by receptor mediated endocytosis and requires a fusion event between the viral envelope and the limiting membrane of the endosome at low pH. In order to investigate the role of cholesterol in the early stages of ASFV infection, we have studied the effect of the removal of cell and viral membrane cholesterol by cholesterol oxidase treatment of cells and virions, as well as the effect of some inhibitors of cholesterol synthesis on the infectious pathway. In addition, we have investigated viral infection in cholesterol-depleted Vero cells. Both cholesterol-depleted and cholesterol oxidase-treated Vero cells were unaltered in their ability to bind or internalize the virus, but were blocked in ASFV fusion and subsequent virus replication. Our results indicate that ASFV infection is affected by cholesterol in the target membrane. |