| For medical practitioners and the general public - Cholesterol Journal Article Catalog. |
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| Evidence for secretory coupling of phosphatidylcholine molecular species to cholesterol in rat bile Berr, F., H. C. Jaeger, et al. (1997), J Hepatol 26(5): 1069-78. Abstract: BACKGROUND/AIMS: Hepatocytes secrete cholesterol into bile within lipid vesicles of selected phosphatidylcholines, mainly palmitoyl-linoleoyl-phosphatidylcholines, palmitoleoyl-oleoyl-phosphatidylcholines and palmitoleoyl-arachidonyl-phosphatidylcholines, which could in part determine the secreted amount of cholesterol. AIMS: To study whether increased secretion of cholesterol, as caused by manipulation of cholesterol synthesis rate, changes the composition of phosphatidylcholines secreted in bile. METHODS: Livers from control rats (Control), rats fed pravastatin for 7 days (Pravastatin) and livers isolated 5-7 or 8-11 hours after pravastatin had been withdrawn (Rebound5-7h; Rebound8-11h) were isolated perfused during infusion of taurocholic acid (400 nmol/min/100 g rat), to study biliary secretion of bile salts, cholesterol and phosphatidylcholine molecular species. RESULTS: Bile salt secretion rate was similar in all four groups, secretion of cholesterol and phosphatidylcholines was similar in Control and Pravastatin. With duration of pravastatin withdrawal the secretion rates of phosphatidylcholine and cholesterol progressively increased by +38% and +122% in Rebound5-7h and by +70% and +300% in Rebound8-11h (vs Control), respectively. In parallel, the secretion rates of palmitoleoyl-oleoyl- and palmitoleoyl-arachidonyl-phosphatidylcholines rose up to sixfold and twofold, respectively, while the secretion rate of palmitoyl-linoleoylphospatidylcholines remained constant. The secretion rate of cholesterol was correlated (p < 0.01) with the secretion rates of palmitoleoyl-oleoyl-phosphatidylcholines (r = 0.83) and palmitoleoyl-arachidonyl-phosphatidylcholines (r = 0.81). Bilirubin ditaurate or taurodehydrocholate reduced (p < 0.05) biliary secretion of phosphatidylcholines (-33%; -72%) without changes in cholesterol/phosphatidylcholine secretory ratio or phosphatidylcholine species. CONCLUSIONS: The secretion of the major molecular species of phosphatidylcholine in bile could be coregulated with the amount of cholesterol destined for biliary secretion. |
| Evidence for segregation of sphingomyelin and cholesterol during formation of COPI-coated vesicles Brugger, B., R. Sandhoff, et al. (2000), J Cell Biol 151(3): 507-18. Abstract: In higher eukaryotes, phospholipid and cholesterol synthesis occurs mainly in the endoplasmic reticulum, whereas sphingomyelin and higher glycosphingolipids are synthesized in the Golgi apparatus. Lipids like cholesterol and sphingomyelin are gradually enriched along the secretory pathway, with their highest concentration at the plasma membrane. How a cell succeeds in maintaining organelle-specific lipid compositions, despite a steady flow of incoming and outgoing transport carriers along the secretory pathway, is not yet clear. Transport and sorting along the secretory pathway of both proteins and most lipids are thought to be mediated by vesicular transport, with coat protein I (COPI) vesicles operating in the early secretory pathway. Although the protein constituents of these transport intermediates are characterized in great detail, much less is known about their lipid content. Using nano-electrospray ionization tandem mass spectrometry for quantitative lipid analysis of COPI-coated vesicles and their parental Golgi membranes, we find only low amounts of sphingomyelin and cholesterol in COPI-coated vesicles compared with their donor Golgi membranes, providing evidence for a significant segregation from COPI vesicles of these lipids. In addition, our data indicate a sorting of individual sphingomyelin molecular species. The possible molecular mechanisms underlying this segregation, as well as implications on COPI function, are discussed. |
| Evidence for superoxide anion generation in aortas of cholesterol-fed rabbits treated with L-arginine Simonet, S., A. Rupin, et al. (2004), Eur J Pharmacol 492(2-3): 211-6. Abstract: The inducible form of nitric oxide synthase (iNOS) is present in advanced atherosclerotic lesions. The aim of the present paper was to compare the functionality of iNOS in rabbits fed a 0.3% cholesterol-diet for 24 weeks (Baseline), and 36 weeks, with l-arginine (l-Arg) or vehicle supplementation (Saline) for the last 12 weeks. N-iminoethyl-l-lysine (l-NIL; 10 microM), a selective inhibitor of iNOS, potentiated the contractions to phenylephrine in aortas from Baseline, Saline and l-Arg rabbits confirming the presence of a functional iNOS. In l-Arg rabbits, the contractions induced by l-NIL were less pronounced than those noted in Baseline and Saline rabbits; superoxide dismutase (150 U/ml) significantly increased the phenylephrine-induced contractions only in the l-Arg rabbits. In the presence of NADPH, aortas from l-Arg rabbits produced more superoxide anions than aortas from saline rabbits as evidenced by the lucigenin-enhanced chemiluminescence technique. In conclusion, our results show functional and biochemical evidence for an increased superoxide anion production in atherosclerotic aortas from hypercholesterolemic rabbits treated with l-Arg for 12 weeks. These data may thus help to explain the lack of beneficial effects of l-Arg on atherosclerosis progression in long-term experimental hypercholesterolemia as well as in severely atherosclerotic humans. |
| Evidence for the biosynthesis of DHEA from cholesterol by first-trimester human placental tissue: source of androgens Loganath, A., K. L. Peh, et al. (2002), Horm Metab Res 34(3): 116-20. Abstract: With a view to establishing whether first-trimester human placentas possess the ability to synthesize DHEA from cholesterol, homogenates of this tissue obtained from two groups of women undergoing elective termination of normally progressing pregnancy between 10 - 12 weeks gestation (n = 5, age 23 - 29 years and n = 5, age 21 - 27 years) were incubated separately with 26-(14)Ccholesterol for the generation of 14Cisocaproic acid + pregnenolone and 7n-3Hpregnenolone for the biosynthesis of 3HDHEA. Controls consisted of homogenates heated in a boiling water bath for 10 min. Using the reverse-isotope dilution analysis, desmolase efficiency expressed as mean specific activity of 14Cisocaproic acid varied from 282 to 725 dpm/mmol, while that of 17 alpha-hydroxylase and steroid C-17,20-lyase, catalyzed conversion of 7n-3Hpregnenolone to 3HDHEA varied from 3498 to 26 258 dpm/mmol. The corresponding efficiencies of enzymicconversion varied between 5.8 x 10(-2) and 1.5 x 10(-1) % for 14Cisocaproic acid, but between 5.5 x 10(-2) and 4.1 x 10(-1) % for 3HDHEA. No such metabolite was evident in the controls of heat-denatured homogenates. These are the first study results to demonstrate that early placentas are capable of converting cholesterol to pregnenolone to DHEA, contrary to the widely held concept of DHEA production by fetal and maternal adrenal glands. This finding has important physiological implications and could provide a new dimension to the concept of fetoplacental steroidogenesis. |
| Evidence for the role of the secretory pattern of growth hormone in the regulation of serum concentrations of cholesterol and apolipoprotein E in rats Oscarsson, J., L. M. Carlsson, et al. (1991), J Endocrinol 128(3): 433-8. Abstract: Adult male Sprague-Dawley rats were hypophysectomized and connected to an automatic i.v. infusion system. The same daily dose of human GH (hGH) was given either as eight daily pulses (3-h intervals) to mimic the male specific secretory pattern of GH or as a continuous infusion of GH, to mimic the female secretory pattern. Hypophysectomized rats received i.v. replacement therapy with L-thyroxine and cortisol. The rats were treated for 5 days. The serum cholesterol concentration was higher when hGH was given continuously than when hGH was given as eight daily pulses. The concentration of high-density lipoprotein (HDL)-cholesterol was not influenced by intermittent GH treatment, but increased when hGH was given as a continuous infusion. The serum concentration of apolipoprotein (Apo) E increased following treatment with a continuous infusion of hGH, whereas eight daily pulses of hGH had no effect. The serum concentration of ApoA-I was unaffected by hGH treatment. The serum concentration of ApoB decreased to the same degree whether hGH was given as a continuous infusion or as eight daily pulses. The serum concentration of triglycerides was not affected by hGH treatment. These results indicate that the higher serum HDL-cholesterol and serum ApoE concentrations of female rats may be due to their more continuous secretion of GH. In contrast, the effects of GH on the serum concentration of ApoB, which is not sexually differentiated, may be independent of the mode of GH secretion. |
| Evidence for transbilayer, tail-to-tail cholesterol dimers in dipalmitoylglycerophosphocholine liposomes Harris, J. S., D. E. Epps, et al. (1995), Biochemistry 34(11): 3851-7. Abstract: The behavior of multilamellar liposomes of 2,3-dipalmitoyl-sn-glycero-1-phosphocholine (DPPC) was studied by differential scanning calorimetry (DSC) in the presence of < or = 5 mol % of the amphiphilic solutes methyl oleate, cholesterol, pregnenolone, and dehydroandrosterone. The DSC thermograms indicate that the solutes are miscible only with the liquid-disordered (Id) phase, and not with the solid-ordered (so) phase. The slopes of the Tm vs solute concentration curves confirm this conclusion: It appears that the so-1d phase transition of DPPC, which corresponds to the melting of the phospholipid chains, can be treated as a simple melting process and, thus, could be used as a cryoscopic system. In that case, its melting point depression constant, Kf, can be calculated a priori from the experimentally measured heat of fusion per gram of DPPC, lf, and the temperature of the phase transition of pure DPPC, T(o), by the equation Kf = RTo2/(1000lf) = 12.3 +/- 0.9 K g M-1 cm3. With methyl oleate as the solute, the Tm vs methyl oleate concentration plot is linear, and from the slope we calculate Kf = 12.9 +/- 0.8 K g M-1 cm3. Thus, methyl oleate appears to form an ideal cryoscopic system with dipalmitoyllecithin liposomes: It is fully miscible with the 1d phase but is apparently insoluble in the s(o) phase. Pregnenolone and dehydroandrosterone also form ideal cryoscopic systems with dipalmitoyllecithin liposomes: The Tm vs solute concentration plots are linear and yield the correct MWs for these solutes.(ABSTRACT TRUNCATED AT 250 WORDS) |
| Evidence for two pools of cholesterol in the Acholeplasma laidlawii strain B membrane: a deuterium NMR and DSC study Monck, M. A., M. Bloom, et al. (1993), Biochemistry 32(12): 3081-8. Abstract: Recent investigations have indicated that there exists a well-defined range of membrane hydrocarbon order compatible with good growth of the microorganism Acholeplasma laidlawii B Monck, M., Bloom, M., Lafleur, M., Lewis, R. N. A. H., McElhaney, R. N., & Cullis, P. R. (1992) Biochemistry 31, 10037-10043. Since cholesterol increases hydrocarbon order in membranes, it was of interest to examine the effect of cholesterol on the hydrocarbon order and growth characteristics of A. laidlawii B. Cholesterol is normally absent from A. laidlawii membranes since it is neither biosynthesized nor required for the growth or survival of the microorganism. However, cholesterol will be incorporated into the membrane if exogenously supplied to the A. laidlawii culture. For membranes prepared from cells grown in the presence of cholesterol, chemical determinations indicated cholesterol represented as much as 40 mol% of the total membrane lipid. However, 2H NMR order parameter measurements and DSC studies of the same membrane preparation suggested that cholesterol was present at significantly lower levels (approximately 10-15 mol%) in the membrane lipid bilayer. Further incorporation of cholesterol into the A. laidlawii lipid bilayer was found to occur with an increase in temperature or by lyophilization and rehydration at high temperatures, suggesting that sterol present in a separate pool in the membrane preparation could then gain access to the bilayer. 2H NMR spectra of A. laidlawii membrane preparations containing deuterium-labeled cholesterol indicate that the bulk of the cholesterol present in this separate pool is in a solid form. |
| Evidence of association between plasma high-density lipoprotein cholesterol and risk factors for breast cancer Boyd, N. F. and V. McGuire (1990), J Natl Cancer Inst 82(6): 460-8. Abstract: Females in western societies have higher plasma levels of high-density lipoprotein cholesterol (HDL-C) than males. The difference in plasma lipids between the sexes is believed to contribute to differences in risk of heart disease. The evidence reviewed here demonstrates that plasma levels of HDL-C are also associated with factors influencing risk of breast cancer, a leading cause of death in women in western societies. Both breast cancer risk and HDL-C levels are higher in women who live in northern European countries than in those who live in Asia, in women who have never been pregnant compared with those who have, and in women of higher socioeconomic status. HDL-C levels are also affected by several other known or suspected factors in breast cancer risk; these include dietary fat intake, alcohol consumption, endogenous hormones, and premenopausal leanness. Increases in any of these factors are known to increase the level of HDL-C. Preliminary work has also shown HDL-C levels to be higher in subjects with mammographic dysplasia and a family history of breast cancer. Further, in serum-free culture systems, HDL-C appears to possess biologic properties that may be relevant to carcinogenesis. In other areas, evidence of a relationship between increased HDL-C levels and increased breast cancer risk is either incomplete or contradictory. These areas include obesity (in the risk of postmenopausal breast cancer), use of exogenous hormones (oral contraceptives or postmenopausal estrogens), and physical exercise. In addition, both elevated and depressed levels of HDL-C have been reported in women with breast cancer. Our findings suggest an association between high HDL-C levels and the epidemiology of breast cancer risk. We recommend additional studies of plasma lipid level as a possible risk factor for this disease. |
| Evidence of foam cell and cholesterol crystal formation in macrophages incubated with oxidized LDL by fluorescence and electron microscopy Klinkner, A. M., C. R. Waites, et al. (1995), J Histochem Cytochem 43(10): 1071-8. Abstract: Macrophage-derived foam cells are a prominent component of developing atherosclerotic lesions. We describe an in vitro model of foam cell formation which mimics some aspects of the evolution of foam cells in mature atherosclerotic lesions. Thioglycollate-elicited mouse peritoneal macrophages were incubated with copper-oxidized LDL (ox-LDL) for periods up to 168 hr. Identifiable foam cells were present after incubation with ox-LDL at 24, 72, and 168 hr. Control cells incubated without ox-LDL did not form foam cells. Fluorescence microscopy after staining with Nile red exhibited progressive accumulation of lipids, and transmission electron microscopy (TEM) showed distinct ultrastructural changes over time. Macrophages at 24 hr had a few non-membrane-bound lipid droplets but were otherwise identical to control cells. These lipid droplets fluoresced yellow-gold after Nile red staining. After 72 hr of incubation with ox-LDL, in addition to increased numbers of non-membrane-bound lipid inclusions, macrophages contained membrane-bound multilamellar lipoid structures. These multilamellar structures corresponded to areas of reddish-orange fluorescence after Nile red staining. In macrophages incubated with ox-LDL for 168 hr, the amount of cellular lipid was further increased and cholesterol crystal profiles were apparent within some multilamellar lipoid structures. Biochemical analysis showed that the total cholesterol content steadily increased over 168 hr. The increase in total cholesterol was accompanied by a dramatic increase in free cholesterol between 72 and 168 hr. These results demonstrate that long-term incubation of macrophages with ox-LDL increased lipid deposition in cultured cells and that, under the conditions studied, cholesterol crystals formed in macrophage foam cells. Moreover, this system allows investigation of the evolution of foam cells showing some characteristics of those found in atherosclerotic lesions. |
| Evidence of QTLs on chromosomes 1q42 and 8q24 for LDL-cholesterol and apoB levels in the HERITAGE family study Feitosa, M. F., I. B. Borecki, et al. (2005), J Lipid Res 46(2): 281-6. Abstract: Genome-wide multipoint linkage analyses were performed to identify chromosomal regions harboring genes influencing LDL-cholesterol, total apolipoprotein B (apoB), and LDL-apoB levels using 654 markers. They were assessed in a sedentary state (baseline) and after a 20 week endurance training program. Strong evidence for two quantitative trait loci (QTLs) for baseline levels was found. There is linkage evidence in black families on chromosomes 1q41-q44 at marker D1S2860, 238 centimorgan (cM), with a maximum log of the odds (LOD) score of 3.7 for LDL-apoB and in white families on chromosome 8q24 (at marker D8S1774, 142 cM, with LOD scores of 3.6, 3.3, and 2.5 for baseline LDL-cholesterol, LDL-apoB, and apoB, respectively). There were no strong signals for the lipoprotein training responses (as computed as the difference in posttraining minus baseline levels). In conclusion, QTLs for baseline apoB and LDL-cholesterol levels on chromosomes 1q41-q44 (in blacks) and 8q24 (in whites) were found. As there are no known strong candidate genes in these regions for lipids, follow-up studies to determine the source of those signals are needed. |
| Evidence supporting cholesterol-lowering therapy for postmenopausal women with heart disease Goldstein, M. R. (1997), Jama 278(8): 633-4. |
| Evidence that 24- and 27-hydroxylation are not involved in the cholesterol-induced down-regulation of hydroxymethylglutaryl-CoA reductase in mouse liver Lund, E., O. Breuer, et al. (1992), J Biol Chem 267(35): 25092-7. Abstract: Several authors have suggested that 27-hydroxycholesterol may be an important physiological regulator of cholesterol homeostasis. In the present study we investigated the possibility that 24- or 27-hydroxylation of cholesterol is of importance for the down-regulation of hydroxymethylglutaryl (HMG)-CoA reductase in mouse liver induced by dietary cholesterol. Using an accurate method based on isotope dilution-mass spectrometry with deuterated internal standards, we were able to detect significant levels of both 24- and 27-hydroxycholesterol in liver homogenates from normal mice. Feeding cholesterol, 2% for 4 days, increased the levels by 80 and 30%, respectively. No significant hepatic levels of 25-hydroxycholesterol could be demonstrated in untreated mice, and the level of this steroid in cholesterol-treated mice was just above the detection limit. Mouse liver mitochondria were able to catalyze 24- as well as 27-hydroxylation, but not 25-hydroxylation of cholesterol. There was no such conversion in liver microsomes. When using 24-2H2- or 23,23,24,24,25-2H5-labeled cholesterol as substrate a kinetic isotope effect of about 4.5 was observed for the mitochondrial 24-hydroxylation. When using 26,26,26,27,27,27-2H6-labeled cholesterol as substrate a kinetic isotope effect of about 2.5 was observed for the 27-hydroxylation. Use of those deuterium-labeled cholesterol species thus allowed a specific suppression of the rate of 24- and 27-hydroxylation. Feeding mice with 0.05% unlabeled pure cholesterol in the diet for 24 h inhibited the hepatic HMG-CoA reductase activity by about 50%. The same degree of suppression was obtained after feeding with 23,23,24,24,25-2H5- and 26,26,26,27,27,27-2H6-labeled cholesterol. Were mitochondrial 24- and 27-hydroxylation of importance, one would expect reduced suppression of HMG-CoA reductase when feeding deuterated cholesterol, due to the isotope effects. As this was not the case, it is concluded that neither 24-hydroxylation nor 27-hydroxylation are critical for the cholesterol-induced down-regulation of HMG-CoA reductase in mouse liver. |
| Evidence that accumulation of ceramides and cholesterol esters mediates oxidative stress-induced death of motor neurons in amyotrophic lateral sclerosis Cutler, R. G., W. A. Pedersen, et al. (2002), Ann Neurol 52(4): 448-57. Abstract: Amyotrophic lateral sclerosis (ALS) is characterized by degeneration of motor neurons in the spinal cord resulting in progressive paralysis and death. The pathogenic mechanism of ALS is unknown but may involve increased oxidative stress, overactivation of glutamate receptors, and apoptosis. We report abnormalities in sphingolipid and cholesterol metabolism in the spinal cords of ALS patients and in a transgenic mouse model (Cu/ZnSOD mutant mice), which manifest increased levels of sphingomyelin, ceramides, and cholesterol esters; in the Cu/ZnSOD mutant mice, these abnormalities precede the clinical phenotype. In ALS patients and Cu/Zn-SOD mutant mice, increased oxidative stress occurs in association with the lipid alterations, and exposure of cultured motor neurons to oxidative stress increases the accumulation of sphingomyelin, ceramides, and cholesterol esters. Pharmacological inhibition of sphingolipid synthesis prevents accumulation of ceramides, sphingomyelin, and cholesterol esters and protects motor neurons against death induced by oxidative and excitotoxic insults. These findings suggest a pivotal role for altered sphingolipid metabolism in the pathogenesis of ALS. |
| Evidence that acute insulin administration enhances LDL cholesterol susceptibility to oxidation in healthy humans Quinones-Galvan, A., A. M. Sironi, et al. (1999), Arterioscler Thromb Vasc Biol 19(12): 2928-32. Abstract: Increased free radical production and hyperinsulinemia are thought to play a role in experimental and human atherosclerosis, but the relation between the 2 abnormalities has not been studied. In 23 healthy volunteers, we measured the susceptibility of circulating low-density lipoprotein (LDL) cholesterol particles to in vitro copper sulfate oxidation (measured as the lag phase) and cell-mediated oxidative modification (measured as malondialdehyde generation in LDL during incubation with human umbilical vein endothelial cells), as well as the vitamin E content of LDL cholesterol at baseline and after 2 hours of physiological hyperinsulinemia (euglycemic insulin clamp). The lag time of LDL oxidation decreased from control values of 108+/-3 and 107+/-3 minutes (at baseline and after 2 hours of saline infusion) to 101+/-3 minutes after 2 hours of clamping (P<0.0001). At corresponding times, cell-mediated malondialdehyde generation in LDL rose from 4.96+/-0.11 and 4.98+/-0.10 to 5.28+/-0.10 nmol/L (P=0. 0006), whereas the LDL vitamin E content decreased from 6.78+/-0.06 and 6.77+/-0.06 to 6.64+/-0.06 microg/mg (P<0.04). The insulin-induced shortening of the lag phase was directly related to the decrement of vitamin E in LDL; furthermore, in subjects with higher baseline serum triglyceride levels, insulin induced a greater shortening of the lag phase than in subjects with low baseline triglycerides. We conclude that in healthy humans acute physiological hyperinsulinemia enhances the oxidative susceptibility of LDL cholesterol particles. This effect may have pathogenic significance for atherogenesis in insulin resistant states. |
| Evidence that apolipoprotein A-IMilano has reduced capacity, compared with wild-type apolipoprotein A-I, to recruit membrane cholesterol Bielicki, J. K., M. R. McCall, et al. (1997), Arterioscler Thromb Vasc Biol 17(9): 1637-43. Abstract: Human carriers of apolipoprotein (apo) A-IMilano are heterozygous for an Arg173-->Cys substitution in the apoA-I primary sequence; despite severe reductions in HDL cholesterol concentrations, affected individuals do not develop coronary heart disease, suggesting that apoA-IMilano may possess antiatherogenic properties. As the beneficial effects of wild-type apoA-I are linked to its role in HDL cholesterol transport, we examined the capacity of apoA-IMilano to recruit cell cholesterol and activate lecithin:cholesterol acyltransferase (LCAT) (two key events in the antiatherogenic reverse cholesterol transport pathway). ApoA-IMilano and wild-type apoA-I were expressed in Chinese hamster ovary cells, and their ability to recruit membrane phospholipid and cholesterol for the assembly of nascent HDL was compared. Both clonal cell lines exhibited similar levels of apolipoprotein accumulation in serum-free medium (approximately 2 micrograms/mg cell protein per 24 hours), and 15% of each apolipoprotein was associated with membrane lipids to form nascent HDL (d = 1.063 to 1.21 g/mL). SDS-PAGE showed that a majority (66 +/- 12%) of the lipidated apoA-IMilano was in the homodimer form. Compositional analyses revealed that apoA-IMilano nascent HDL had a significantly lower (P <.001) unesterified cholesterol/phospholipid mole ratio (0.47 +/- 0.10) than wild-type apoA-I complexes (1.29 +/- 0.14), indicating that apoA-IMilano had a reduced capacity to recruit cell cholesterol. In addition to the reduced unesterified cholesterol/phospholipid ratio, apoA-IMilano nascent HDL consisted mostly of small 7.4-nm particles compared with wild-type apoA-I, in which 11- and 9-nm particles predominated. Despite these changes in nascent HDL particle size and composition, apoA-IMilano activated LCAT normally. We conclude that, even though apoA-IMilano is a normal activator of LCAT, it is less efficient that wild-type apoA-I in recruiting cell cholesterol, suggesting that the putative antiatherogenic properties attributed to apoA-IMilano may be unrelated to the initial stages of reverse cholesterol transport. |
| Evidence that high-density lipoprotein cholesterol is an independent predictor of acute platelet-dependent thrombus formation Naqvi, T. Z., P. K. Shah, et al. (1999), Am J Cardiol 84(9): 1011-7. Abstract: Plasma total and low-density lipoprotein (LDL) cholesterol are established risk factors for atherosclerotic vascular disease and may also contribute to a prothrombotic risk via enhanced platelet reactivity. This study examines whether high-density lipoprotein (HDL) cholesterol, which is inversely correlated with coronary artery disease, is associated with a reduced thrombogenic potential. Platelet thrombus formation was evaluated by exposing porcine aortic media placed in Badimon perfusion chambers to flowing nonanticoagulated venous blood for 5 minutes at a shear rate of 1,000 s(-1). Forty-five subjects, 23 normal (LDL 104 +/- 31, HDL 50 +/- 15 mg/dl) and 22 hypercholesterolemic (LDL 181 +/- 45, HDL 41 +/- 10 mg/dl) patients without coronary artery disease were studied. Platelet aggregation and CD62 antigen expression, and assay for circulating prothrombotic factors were also performed. In univariate analysis platelet thrombus formation correlated with weight (r = 0.33, p = 0.03), diastolic blood pressure (r = 0.39, p = 0.01), HDL cholesterol (r = -0.45, p = 0.003), total/HDL cholesterol (r = 0.43, p = 0.004) and LDL/HDL (r = 0.38, p = 0.01) ratios, and platelet CD62 expression (r = 0.41, p = 0.02). In multiple regression analysis only HDL cholesterol showed significant correlation with platelet thrombus formation (p = 0.03). Platelet aggregation and circulating prothrombotic factors did not correlate with platelet thrombus formation. A comparison between normal and hypercholesterolemic subjects revealed enhanced thrombus area (0.026 +/- 0.20 vs 0.045 +/- 0.039 mm2/mm; p = 0.04), resting CD62 expression (6 +/- 7% vs 15 +/- 10% positive platelets, p = 0.02), and platelet aggregation (16.7 +/- 5.2 vs 21.7 +/- 6.7 ohms, p = 0.04) in hypercholesterolemic subjects. Our results demonstrate that HDL cholesterol is a significant independent predictor of ex vivo platelet thrombus formation. |
| Evidence that hydrogen peroxide blocks hormone-sensitive cholesterol transport into mitochondria of rat luteal cells Behrman, H. R. and R. F. Aten (1991), Endocrinology 128(6): 2958-66. Abstract: In luteal and granulosa cells, hydrogen peroxide abruptly inhibits activation of adenylate cyclase by receptor-bound gonadotropin and blocks steroidogenesis. In the present studies a post-cAMP site of peroxide action on inhibition of steroidogenesis was investigated. Steroidogenesis, stimulated by dibutyryl or 8-bromo-cAMP, was inhibited by hydrogen peroxide. Yet, cAMP-dependent protein kinase activation in cytosol or intact cells was unaffected by peroxide treatment. Hydrogen peroxide also did not inhibit the activity of cholesterol esterase and acyl coenzyme-A:acyltransferase. Progesterone synthesis was maximally increased 5- to 50-fold with 25- and 22-hydroxycholesterol, respectively. Unlike that seen with cAMP analogs and LH, however, progestin synthesis stimulated by these cell- and mitochondria-permeant cholesterol analogs was not inhibited by hydrogen peroxide. Treatment of animals with amino-glutethimide produces a marked accumulation of steroidogenic cholesterol substrate and a large increase in hormone-independent steroidogenesis in subsequently isolated and washed luteal tissue. In this paradigm, hydrogen peroxide did not inhibit elevated basal progesterone synthesis in luteal cells produced by in vivo aminoglutethimide treatment, yet LH-stimulated steroidogenesis was blocked. However, treatment of luteal cells with hydrogen peroxide inhibited pregnenolone synthesis in isolated mitochondria, an effect partially reversed by the addition of luteal cell cytosol. In summary, while peroxide inhibited cAMP-dependent steroidogenesis, it did not appear to inhibit protein kinase activation or mobilization of cholesterol from intracellular esterified stores. Although peroxide inhibited pregnenolone synthesis, it had no effect on steroidogenesis when substrate was made available by either addition of cholesterol analogs or prior treatment with aminoglutethimide in vivo. We conclude, therefore, that hydrogen peroxide inhibits steroidogenesis by blocking intracellular transport of cholesterol to mitochondria or translocation of cholesterol across the outer mitochondrial membrane. |
| Evidence that leptin contributes to intestinal cholesterol absorption in obese (ob/ob) mice and wild-type mice Igel, M., B. Lindenthal, et al. (2002), Lipids 37(2): 153-7. Abstract: In the present study, the effect of leptin on intestinal cholesterol absorption was investigated in C57 BL/6 OlaHsd Lep(ob)/Lep(ob) obese (ob/ob) mice and lean C57 BL/6 (wild-type) mice. Animals were treated either with or without recombinant leptin for 2 wk. Cholesterol absorption was measured by the constant isotope feeding method and indirectly by the ratio of campesterol to cholesterol in serum. In ob/ob mice, cholesterol absorption was significantly higher compared to wild-type mice 83.4 +/- 2.3% (SD) vs. 77.6 +/- 1.5%, P < 0.01. Treatment with leptin significantly reduced cholesterol absorption in both ob/ob and wild-type mice by 8.5 (P < 0.001) and 5.2% (P < 0.05), respectively. Serum concentrations of campesterol and the ratio of campesterol to cholesterol in ob/ob mice were significantly higher compared to wild-type mice (2.2 +/- 0.3 mg/dL vs. 1.2 +/- 0.3 mg/dL, P< 0.001; and 36.8 +/- 2.8 microg/mg vs. 28.0 +/- 3.3 microg/mg, P < 0.001). After treatment of ob/ob mice with leptin, concentrations of campesterol and its ratio to cholesterol were significantly lower (2.2 +/- 0.3 mg/dL vs. 1.0 +/- 0.2 microg/mg, P < 0.001; and 36.8 +/- 2.8 microg/mg vs. 13.2 +/- 2.2 microg/mg, P < 0.001, respectively). In wild-type mice, the ratio of campesterol to cholesterol in serum was also significantly lower after treatment with leptin (28.0 +/- 3.3 microg/mg vs. 22.6 +/- 5.0 microg/mg, P < 0.05). A significant positive correlation (r = 0.701, P < 0.01) between cholesterol absorption and the ratio of campesterol to cholesterol in serum was found. It is concluded that leptin contributes to intestinal cholesterol absorption in ob/ob mice and lean wild-type mice. |
| Evidence that macrophages transfer arachidonic acid and cholesterol to tissues in vivo Peres, C. M., P. I. Homem de Bittencourt, Jr., et al. (2003), Cell Biochem Funct 21(4): 317-23. Abstract: Our previous studies have shown that (14)C-labelled cholesterol (CHOL) and arachidonic acid (AA) are transferred from macrophages (Mphi) to lymphocytes (LY) when these cells are co-cultured. In this study, we investigated whether these lipids can be transferred from control and thioglycollate-elicited Mphi (THIO-elicited Mphi) to various tissues and organs in vivo. For this purpose, control and THIO-elicited Mphi were pre-treated with (14)C-AA and (3)H-CHOL and then injected into the jugular vein of adult rats. More than 75% of the radioactivity injected was found in the liver of rats treated with (14)C-AA labelled-Mphi either control and THIO-stimulated. The radioactivity of (3)H-CHOL labelled Mphi was transferred mainly to the liver (51% in the control Mphi and 23% in the thioglycollate Mphi7) but it was also found in the kidney, lung and spleen. These results support the proposition that the transfer of lipids between cells also occurs in vivo. The full significance of this phenomenon however remains to be elucidated. |
| Evidence that newly synthesized esterified cholesterol is deposited in existing cytoplasmic lipid inclusions Kellner-Weibel, G., B. McHendry-Rinde, et al. (2001), J Lipid Res 42(5): 768-77. Abstract: Esterified cholesterol (EC) and triglyceride (TG) can be stored in cells as cytoplasmic inclusions. The physical state of the EC in these lipid droplets varies from liquid to liquid crystalline, depending on a number of factors, including the amount of TG co-deposited in the inclusion. The lipid in these droplets undergoes turnover via hydrolysis and resynthesis. We determined whether newly synthesized lipid is incorporated into existing cytoplasmic droplets, forms a discrete cytoplasmic droplet, or forms a small inclusion that fuses with an existing droplet. This was accomplished by monitoring the physical state of the lipid within the cytoplasmic inclusions following sequential deposition of TG and EC. Fu5AH cells were initially grown in media containing oleic acid to produce TG-rich, isotropic inclusions. The cells were then incubated with medium containing free cholesterol-phospholipid dispersions to promote synthesis and deposition of EC. To inhibit cytoplasmic TG hydrolysis, the lipase inhibitor, diethylumbelliferyl phosphate (UBP), was added at the time of cholesterol enrichment. The phase behavior of lipid droplets isolated from the lipid-rich cells was determined using polarizing light flow cytometry and microscopy. An anisotropic droplet population (EC-rich inclusions) was not detected, although there was an increase in cellular EC mass and no change in cellular TG mass. Therefore, under conditions where there is no turnover of cytoplasmic TG, newly synthesized EC is incorporated into existing TG inclusions. |