| For medical practitioners and the general public - Cholesterol Journal Article Catalog. |
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| LXR/RXR activation enhances basolateral efflux of cholesterol in CaCo-2 cells Murthy, S., E. Born, et al. (2002), J Lipid Res 43(7): 1054-64. Abstract: Regulation of gene expression of ATP-binding cassette transporter (ABC)A1 and ABCG1 by liver X receptor/retinoid X receptor (LXR/RXR) ligands was investigated in the human intestinal cell line CaCo-2. Neither the RXR ligand, 9-cis retinoic acid, nor the natural LXR ligand 22-hydroxycholesterol alone altered ABCA1 mRNA levels. When added together, ABCA1 and ABCG1 mRNA levels were increased 3- and 7-fold, respectively. T0901317, a synthetic non-sterol LXR agonist, increased ABCA1 and ABCG1 gene expression 11- and 6-fold, respectively. ABCA1 mass was increased by LXR/RXR activation. T0901317 or 9-cis retinoic acid and 22-hydroxycholesterol increased cholesterol efflux from basolateral but not apical membranes. Cholesterol efflux was increased by the LXR/RXR ligands to apolipoprotein (apo)A-I or HDL but not to taurocholate/phosphatidylcholine micelles. Actinomycin D prevented the increase in ABCA1 and ABCG1 mRNA levels and the increase in cholesterol efflux induced by the ligands. Glyburide, an inhibitor of ABCA1 activity, attenuated the increase in basolateral cholesterol efflux induced by T0901317. LXR/RXR activation decreased the esterification and secretion of cholesterol esters derived from plasma membranes. Thus, in CaCo-2 cells, LXR/RXR activation increases gene expression of ABCA1 and ABCG1 and the basolateral efflux of cholesterol, suggesting that ABCA1 plays an important role in intestinal HDL production and cholesterol absorption. |
| Lymph chylomicron composition and size are modified by level of intestinally infused cholesterol and triglyceride source in rats Kalogeris, T. J. and J. A. Story (1992), J Nutr 122(5): 1045-55. Abstract: Mesenteric lymph chylomicrons were characterized following acute continuous intestinal infusion of triglyceride emulsions in rats. Emulsions were prepared using corn, olive or butter oils with graded doses of cholesterol (0, 3, 10, 20, 30, 60, 100 mg/g triglyceride) added to each. Chylomicron cholesterol content varied directly with dose of cholesterol infused, ranging from approximately 1.5% (by weight) with no added cholesterol to 5-10% at 100 mg cholesterol/g triglyceride. Minimum effective dose for increasing chylomicron cholesterol content (about twofold) was 20 mg/g triglyceride regardless of the triglyceride source. Esterified cholesterol accounted for most of the increase in chylomicron total cholesterol with corn oil infusion, whereas increases in the unesterified fraction accounted for 10-30% of the increase in total cholesterol during infusion of olive or butter oils. The effect of infused cholesterol on chylomicron lipid composition was dependent on triglyceride source: no effect on phospholipid:triglyceride ratio with corn and butter oils, but increased phospholipid:triglyceride ratio with olive oil at cholesterol doses greater than 20 mg/g triglyceride. Infusion of butter emulsions produced smaller chylomicrons than those produced during infusion of corn or olive oil emulsions. |
| Lymphatic absorption of fatty acids and cholesterol in the neonatal rat Ee, L. C., S. Zheng, et al. (2000), Am J Physiol Gastrointest Liver Physiol 279(2): G325-31. Abstract: High-fat diets are essential in suckling animals to ensure adequate calories for postnatal growth, but their lymphatic transport of dietary lipids has not been characterized. We established a lymph fistula model in suckling rats to quantify intestinal uptake and lymphatic transport of dietary lipids and analyzed lipoprotein fractions. Suckling 19-day-old Sprague-Dawley rats had their mesenteric lymph ducts cannulated and gastroduodenal tubes inserted. After overnight recovery, (3)Htriolein and (14)Ccholesterol were infused for 6 h. Of the total dose, only 38% of triolein and 24% of cholesterol were transported in the lymph of suckling rats. Analyses of residual luminal contents and intestinal mucosal homogenate showed neither reduced absorption nor delayed mucosal processing of ingested lipids to be the cause. Thin-layer chromatographic analysis of radioactive mucosal lipids, however, showed a predominance of free fatty acids (60%) and free cholesterol (67%), implying impaired esterification capacity in these animals. We speculate that this reduced esterification allows for portal transport or direct enterocyte metabolism of dietary lipids. |
| Lymphatic absorption of oxidized cholesterol in rats Osada, K., E. Sasaki, et al. (1994), Lipids 29(8): 555-9. Abstract: The absorption of cholesterol and of cholesterol oxidation products (oxidized cholesterols) was compared in lymph-cannulated rats. We found that the lymphatic absorption of an intragastrically administered, emulsified lipid meal containing 25 mg of cholesterol or 25 mg of oxidized cholesterols, within 24 h, was approximately 67 and 30%, respectively. The absorption rate of individual oxidized cholesterols differed considerably and was approximately 30% for 7 alpha-hydroxycholesterol, 42% for 7 beta-hydroxycholesterol, 32% for 5 beta-epoxycholesterol, 28% for 5 alpha-epoxycholesterol, 15% for cholestanetriol and 12% for 7-ketocholesterol. Moreover, cholesterol oxidation products delayed the absorption of oleic acid as triolein. Approximately 35 and 48% of cholesterol was recovered in chylomicrons (CM) and very low density lipoprotein (VLDL), respectively. In contrast, 54 and 40% of the oxidized cholesterols was recovered in CM and VLDL, respectively, although there was a significant difference in the distribution of individual oxidized cholesterols. The results of the present study indicate that oxidized cholesterols are absorbed to a lesser extent than is cholesterol, that they disturb fat absorption and that they distribute differently between lymphatic lipoproteins. |
| Lymphatic absorption of structured glycerolipids containing medium-chain fatty acids and linoleic acid, and their effect on cholesterol absorption in rats Ikeda, I., Y. Tomari, et al. (1991), Lipids 26(5): 369-73. Abstract: The effects of various structured triglycerides containing medium-chain (caprylic or capric acids) and long-chain (linoleic acid) fatty acids on fatty acid and cholesterol absorption were studied in lymph-cannulated rats. A considerable portion of capric and caprylic acid was absorbed through the lymph duct, although to a lesser extent than was linoleic acid. Capric and linoleic acid located at the 2-position of 2-decanoyl-1,3-dilinoleoyl-glycerol (18:2/10:0/18:2) and 2-linoleoyl-1,3-didecanoyl-glycerol (10:0/18:2/10:0), respectively, tended to be absorbed more efficiently than those located at the 1- and 3-position or those from tricaprin (10:0/10:0/10:0) or trilinolein (18:2/18:2/18:2). A similar trend was observed when the medium-chain fatty acid was caprylic acid instead of capric acid. Caprylic acid absorption from 2-octanoyl-1,3-dilinoleoyl-glycerol (18:2/8:0/18:2) was significantly greater (p less than 0.05) than from 2-linoleoyl-1,3-dioctanoyl-glycerol (8:0/18:2/8:0) or tricaprylin (8:0/8:0/8:0). Preferential absorption of caprylic and linoleic acid was not observed when the 1 to 2 and the 2 to 1 mixtures of 8:0/8:0/8:0 and 18:2/18:2/18:2, respectively, were administered. The structured lipids did not affect the lymphatic absorption of cholesterol. The results suggest that structured triglycerides composed of medium-chain fatty acids and linoleic acid may be more useful for the treatment of lipid malabsorption than are mixtures of medium-chain triglyceride (MCT) and long-chain triglyceride (LCT). |
| Lymphatic transport of cholesterol in normocholesterolemic rats treated with pravastatin, an inhibitor of HMG-CoA reductase Sakono, M., T. Ibi, et al. (1996), Atherosclerosis 124(1): 95-102. Abstract: Lymphatic absorption and transport of cholesterol and triacylglycerols were examined in rats treated with pravastatin, an inhibitor of 3-hydroxy-3-methyglutaryl-CoA (HMG-CoA) reductase. Pravastatin-treatment for 1, 7 and 28 days did not affect the recovery of cholesterol and triacylglycerols during 24 h after the lipid administration: the recovery was 52-59% and 82-93% for cholesterol and triacylglycerols, respectively. Rats treated with pravastatin for 28 days had a higher lymphatic recovery of the lipids during 3-6 h after the lipid administration than did control rats. Pravastatin treatment did not affect the ratio of phospholipid to cholesterol in the gut mucosa, the fatty acid composition of the lymph and mucosal lipids. We concluded that an inhibitor of HMG-CoA reductase would exert no adverse effect on absorption of fat-soluble nutrients by gut. |
| Lymphatic transport of dietary cholesterol oxidation products, cholesterol and triacylglycerols in rats Tomoyori, H., O. Carvajal, et al. (2002), Biosci Biotechnol Biochem 66(4): 828-34. Abstract: Rats were fed on a diet containing 0.5% cholesterol oxidation products (oxysterols) or 0.5% cholesterol for 30 min, and their lymph was collected for 7 h. The amount of each of the individual oxysterols absorbed in the lymph depended on the ingested amounts, but the recovery was the highest for 5alpha,6alpha-epoxycholesterol (10.5%), this being followed by 7-ketocholesterol (5.8%), cholestanetriol (5.2%), 7beta-hydroxycholesterol (4.8%), 7alpha-hydroxycholesterol (3.4%), 5beta,6beta-epoxycholesterol (2.2%), and 25-hydroxycholesterol (1.8%). A diet enriched with oxysterol, but not cholesterol, resulted in increased transport of triacylglycerols in the lymph. These results suggest that the absorption rate of oxysterols depends on the type, and indicate that the effect of dietary oxysterols on the lymphatic transport of triacylglycerols differs from that of dietary cholesterol. It therefore remains to be determined which oxysterol was responsible for the triacyglycerol transport. |
| Lymphatic transport of eicosapentaenoic and docosahexaenoic acids as triglyceride, ethyl ester and free acid, and their effect on cholesterol transport in rats Ikeda, I., Y. Imasato, et al. (1993), Life Sci 52(16): 1371-9. Abstract: Lymphatic transport of docosahexaenoic (DHA) and eicosapentaenoic (EPA) acids given in the forms of triglyceride, ethyl ester of free acid and their effect on cholesterol transport was compared in lymph-cannulated rats. Lymphatic recovery of DHA and EPA given by stomach tube in the form of triglyceride in which they were mainly located at the 2-position was significantly higher than that of the ethyl ester or free acid during the first 6 hr after the administration and the tendency continued until 9 hr. In contrast, the 9 to 24 hr recovery of DHA and EPA in the forms of ethyl ester and free acid was considerably higher than that of triglyceride. Consequently, cumulative 24 hr recovery of EPA was comparable among the three forms. However, the 24 hr recovery of DHA was highest in free acid, lowest in ethyl ester and intermediate in triglyceride. Recovery of the free acid between 9 and 24 hr after administration was significantly higher than that given in the forms of triglyceride or ethyl ester. Cholesterol recovery in lymph of rats given with ethyl ester or free acid was lower than that given with triglyceride at an early stage after the administration in both EPA and DHA. Cumulative 24 hr recovery of cholesterol in rats given these fatty acids as ethyl ester was significantly lower than in those given as the other two forms. |
| Lymphatic transport of stearic acid and its effect on cholesterol transport in rats Ikeda, I., Y. Imasato, et al. (1994), J Nutr Sci Vitaminol (Tokyo) 40(3): 275-82. Abstract: Lymphatic transport of stearic acid, given as completely hydrogenated rapeseed oil (R10), 9 to 1 (R9) and 5 to 5 (R5) mixtures of R10, and soybean oil and completely hydrogenated tallow (T) was examined in the rat cannulated thoracic duct. R10, R9, R5, and T contained 91.4, 81.5, 46.5, and 63.6% stearic acid, respectively. A large portion of the remaining fatty acids in T was palmitic acid (31%). These fats were emulsified with bile salt and albumin, and administered via a stomach tube. Lymphatic recovery of stearic acid at 24 h was lowest in R10 and highest in R5, and intermediate in R9 and T. Recovery of oleic and linoleic acids in rats given R5 was almost complete and significantly higher than that of stearic acid. When T was given, the 24 h recovery of stearic acid was significantly lower than that of palmitic acid. A highly inverse correlation between the recovery and the content of stearic acid in administered fats was observed in R10, R9, and R5. Lymphatic recovery of cholesterol was almost parallel with that of stearic acid. Although the content of stearic acid in T was lower than that in R9, the recovery of stearic acid and cholesterol was almost similar. The results indicate that the rate of lymphatic recovery of stearic acid is affected by the quantity and quality of coexisting fatty acids. |
| Lymphocyte T subset counts in children with elevated low-density lipoprotein cholesterol levels Sarria, A., L. A. Moreno, et al. (1995), Atherosclerosis 117(1): 119-23. Abstract: The aim of this study was to determine blood lymphocyte T subset counts in children with elevated levels of low-density lipoprotein cholesterol. We studied 107 children, ages 2.0 to 15.9 years, from 79 families who were referred to our Lipid Research Clinic because total cholesterol serum levels higher than 200 mg/dl had been detected in at least one child. At the time of diagnosis we analyzed serum lipoprotein profile and blood lymphocyte T subsets (CD3, CD4 and CD8). Children were classified according to LDL-C levels into three groups: (1) normal, if levels were between the 5th and 75th percentiles (50 and 125 mg/dl, respectively); (2) at moderate risk, if levels were between the 75th and 95th percentiles (125 and 150 mg/dl, respectively); and (3) at high risk, if levels were above the 95th percentile (150 mg/dl). In children aged 2.0 to 6.9 years, all lymphocyte T subset counts were higher in the high risk group than in the normal group (P < 0.05 and P < 0.01). In children aged 11.0 to 15.9 years, the CD4 subset count was also significantly higher in the high risk group in the other two groups (P < 0.05 and P < 0.01). These results are in agreement with pathologic findings in the atheromatous plaque. |
| Lyophilized carrot ingestion lowers lipemia and beneficially affects cholesterol metabolism in cholesterol-fed C57BL/6J mice Nicolle, C., E. Gueux, et al. (2004), Eur J Nutr 43(4): 237-45. Abstract: BACKGROUND: Several lines of evidence indicate that diet rich in fruit and vegetable can protect against cardiovascular diseases by acting on cholesterol metabolism and on oxidative stress. AIM OF THE STUDY: The aim of this study was to assess whether daily carrot consumption (provided as lyophilized powder) could differentially influence the consequences of cholesterol supplementation on lipid metabolism and oxidative stress in C57BL/6J mice. METHODS: Fourteen mice were randomized in four groups. Mice were fed either control diets (without or with 0.25% cholesterol added) or lyophilized carrot enriched diets (20% wt/wt without or with 0.25 % cholesterol added) for 4 weeks. Cholesterol and triglycerides in plasma and in liver were measured at the end of the experimental period. Fecal excretion of sterols was evaluated. Vitamin E and carotenoid concentrations were also determined. Several biomarkers relative to oxidative stress such as FRAP (Ferric Reducing Ability of Plasma) and isoprostanes were investigated. RESULTS: Feeding the carrot diet resulted in a decrease of cholesterol (-41%) and triglycerides (-49 %) in plasma and in the liver (-41% and -39%, respectively) in animals fed cholesterol-supplemented diets. Carrot diet induced an increase of total neutral sterols fecal excretion, which inhibits digestive cholesterol absorption. Carrot diet increased antioxidant status in cholesterol-fed mice as related by the 16% higher FRAP values. Although vitamin E was not affected by carrot diet, vitamin E/TG ratio was significantly higher in animals fed carrot diets. The carrot diet induced an increase of vitamin E in the heart in both cholesterol-free and cholesterol-supplemented mice suggesting a higher protection of this tissue. CONCLUSION: This study shows that carrot ingestion decreases lipemia and improves antioxidant status in mice. Such results suggest that carrot intake may exert a protective impact against CVD linked to atherosclerosis. It is likely that these effects could be due to the synergistic effect of fiber and associated antioxidants. |
| Lysine: arginine ratio of a protein influences cholesterol metabolism. Part 1--Studies on sesame protein having low lysine: arginine ratio Rajamohan, T. and P. A. Kurup (1997), Indian J Exp Biol 35(11): 1218-23. Abstract: The effect of globulin fraction with a lysine: arginine (lys:arg) ratio 0.67, isolated from sesame (Sesamum Indicum) seeds on cholesterol metabolism was studied in rats fed cholesterol free and cholesterol containing diet and compared with casein (lys:arg ratio-2.0). Rats fed sesame seed globulin showed significantly lower concentrations of cholesterol in the serum and aorta. The decrease in serum was manifested in both HDL and LDL + VLDL fractions. There was increased cholesterogenesis in the liver as was evident from increased incorporation of labeled acetate into cholesterol and increased activity of 3-Hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase. Increased hepatic diversion of cholesterol to bile acid synthesis and increased fecal excretion of bile acids and sterols were also observed in rats fed sesame seed globulins. Rats fed sesame globulins also showed significantly higher activity of lipoprotein lipase in the heart and adipose tissue and that of plasma Lecithin: cholesterol acyltransferase (LCAT). These studies suggest that low lysine: arginine ratios of a protein exert hypocholesterolemic effects. |
| Lysinuric protein intolerance with chronic interstitial lung disease and pulmonary cholesterol granulomas at onset Kerem, E., O. N. Elpelg, et al. (1993), J Pediatr 123(2): 275-8. Abstract: Hyperammonemia and encephalopathy developed in an 11-year-old girl with chronic interstitial lung disease and cholesterol casts in her lung biopsy specimen. She had decreased plasma levels of ornithine, lysine, and arginine and excessive urinary excretion of lysine and arginine, consistent with the diagnosis of lysinuric protein intolerance. Analysis of plasma and urinary amino acids should be considered in the diagnostic evaluation of patients with interstitial lung disease of uncertain origin. |
| Lyso-PAF analogues and lysophosphatidylcholines from the marine sponge Spirastrella abata as inhibitors of cholesterol biosynthesis Shin, B. A., Y. R. Kim, et al. (1999), J Nat Prod 62(11): 1554-7. Abstract: A series of phospholipids, including previously undescribed compounds 4-7, were isolated by a bioactivity-guided fractionation from the marine sponge Spirastrella abata as inhibitors of cholesterol biosynthesis in human liver cells. These compounds were identified as lyso-PAF analogues (1-5) and lysophosphatidylcholines (6, 7) based on NMR and MS analyses. Compounds 1-7 specifically blocked the conversion of lanosterol into cholesterol in the Chang liver cell. |
| Lysophosphatidylcholine promotes cholesterol efflux from mouse macrophage foam cells Hara, S., T. Shike, et al. (1997), Arterioscler Thromb Vasc Biol 17(7): 1258-66. Abstract: We examined the effects of lysophosphatidylcholine (lyso-PC) on promoting cholesterol efflux from macrophage foam cells. Mouse peritoneal macrophages were converted to foam cells by incubation with 3Hcholesteryl linoleate-labeled or unlabeled acetyl-LDL. When these cells were incubated with lyso-PC, 3Hcholesterol release was promoted in relation to both dose and time, and cellular cholesterol mass was decreased, while medium cholesterol mass was increased. These cholesterol efflux-promotive effects of lyso-PC were confirmed by the fact that the lyso-PC-treated cells showed less oil red O staining than the control cells. ApoE secretion, estimated by Western blotting of the medium, was also augmented by lyso-PC. Both the cholesterol and apoE released by lyso-PC treatment were floated by ultracentrifugation of the medium after its density had been adjusted to 1.210 g/mL. By electron microscopic analysis, vesicular lipoproteins were observed in ultracentrifugally concentrated conditioned medium of lyso-PC. Monensin, a protein secretion inhibitor, effectively inhibited 3Hcholesterol release induced by lyso-PC but not by apoA-I. These results suggest that lyso-PC may inhibit the development of atherosclerosis or enhance its regression by stimulating cholesterol efflux from macrophage foam cells. |
| Lysosomal accumulation of unesterified cholesterol in model macrophage foam cells Tangirala, R. K., F. H. Mahlberg, et al. (1993), J Biol Chem 268(13): 9653-60. Abstract: Lysosomal accumulation of unesterified (free) cholesterol, following the phagocytic incorporation of cholesteryl oleate lipid droplets, was quantitatively characterized in a murine J774 macrophage foam cell model. The induction of phagocytic incorporation by the macrophages, using an inverted culture technique, allowed the rapid delivery of large amounts of cholesteryl ester droplets to the lysosomes, leading to the subsequent generation of free cholesterol. The lysosomally generated free cholesterol was differentiated from the membrane cholesterol by a double radiolabeling procedure. Free cholesterol accumulation was quantitated in a population of low density lipid-filled lysosomes prepared by ultracentrifugal isolation of a floating lipid fraction from a homogenate of the cholesteryl ester-loaded cells. About 10% of the total N-acetyl-beta-glucosaminidase activity, a lysosomal marker, was recovered in the lipid fraction. Negligible amounts of alkaline phosphodiesterase-1, a plasma membrane marker, or membrane cholesterol were present in this fraction. Electron microscopic and cytochemical analysis of the isolated lipid fraction revealed the presence of lysosomes in the fraction with a diameter ranging from 1.5 to 4 microns. Continued hydrolysis of incorporated cholesteryl ester over a 24-h incubation resulted in approximately 30% of the generated free cholesterol in lipid-filled lysosomes. The accumulation of free cholesterol occurred whether or not the cholesterol esterifying enzyme, acyl-CoA: cholesterol acyltransferase, was inhibited. In addition, substantial amounts of free cholesterol accumulated even in the presence of efficient cholesterol acceptor particles, apolipoprotein high density lipoprotein-phosphatidylcholine complexes which stimulate cholesterol efflux. Also, increased accumulation of free cholesterol in the lipid fraction was observed when cholesteryl ester-loaded cells were treated with the compound U-18666A which blocks the movement of lysosomal cholesterol. The data demonstrate that the phagocytic incorporation and hydrolysis of cholesteryl ester lipid droplets by macrophage foam cells lead to a substantial accumulation of free cholesterol in the lipid-filled lysosomes. This process could result in a build-up of lysosomal free cholesterol in macrophage foam cells during the progression of atherosclerotic plaque. |
| Lysosomal cholesterol derived from mildly oxidized low density lipoprotein is resistant to efflux Yancey, P. G. and W. G. Jerome (2001), J Lipid Res 42(3): 317-27. Abstract: In atherosclerotic lesions, macrophages store lipid in cytoplasmic inclusions and lysosomes. Regression studies show that lysosomal lipid is not as easily cleared as cytoplasmic inclusion lipid. Macrophages enriched with mildly oxidized low density lipoprotein (oxLDL) accumulate cholesteryl ester (CE) and free cholesterol (FC) in lysosomes. We examined whether lysosomal stores of cholesterol from oxLDL are cleared from THP-1 and mouse macrophages. As in previous studies, oxLDL-enriched THP-1 macrophages accumulated substantial lysosomal cholesterol. Surprisingly, less than 12% of oxLDL-derived lysosomal CE was cleared to efficient FC acceptors (e.g., cyclodextrins, apolipoprotein/phosphatidylcholine vesicles, and fetal bovine serum). Filipin staining showed that lysosomes of oxLDL-treated THP-1 cells contained FC, and despite removal of most of the cell FC (70--80%) by incubation with cyclodextrins, filipin staining of FC in lysosomes did not diminish. Also, when THP-1 macrophages were incubated with (3)HCE oxLDL, 73--76% of the (3)HCE was retained in a lysosomal hydrolysis resistant pool. In contrast, greater than 90% of acetylated low density lipoprotein (acLDL) (3)HCE was hydrolyzed. Furthermore, (3)HFC liberated from oxLDL (3)HCE was released at a slower rate to cyclodextrins than was (3)HFC from acLDL (3)HCE. In contrast, only 27% of oxLDL (3)HCE was resistant to hydrolysis in mouse macrophages, and the (3)HFC generated from oxLDL and acLDL (3)HCE was released to cyclodextrins at similar rates. We conclude that lack of hydrolysis and efflux of oxLDL cholesterol is not exclusively inherent in oxLDL, but also requires specific cell factors present in one cell type but not the other.--Yancey, P. G., and W. G. Jerome. Lysosomal cholesterol derived from mildly oxidized low density lipoprotein is resistant to efflux. J. Lipid Res. 2001. 42: 317--327. |
| Lysosomal destabilization during macrophage damage induced by cholesterol oxidation products Yuan, X. M., W. Li, et al. (2000), Free Radic Biol Med 28(2): 208-18. Abstract: We have previously shown that oxidized low-density lipoprotein (LDL) induces damage to the macrophage lysosomal membranes, with ensuing leakage of lysosomal contents and macrophage cell death. Cholesterol oxidation products (ChOx) have been reported to be the major cytotoxic components of oxidized LDL/LDL- and also to stimulate cholesterol accumulation in vascular cells. In the present study, we characterized the initial events during macrophage damage induced by cholesterol oxidation products (ChOx). Within 24 h of exposure, ChOx caused lysosomal destabilization, release to the cytosol of the lysosomal marker-enzyme cathepsin D, apoptosis, and postapoptotic necrosis. Enhanced autophagocytosis and chromatin margination was found 12 h after the exposure to ChOx, whereas apoptosis and postapoptotic necrosis was pronounced 24 and 48 h after the exposure. Some lysosomal vacuoles were then filled with degraded cellular organelles, indicating phagocytosis of apoptotic bodies by surviving cells. Because caspase-3 activation was detected in the ChOx-exposed cells, lysosomal destabilization may associate with the leakage of lysosomal enzymes, and activation of the caspase cascade. MnSOD mRNA levels were markedly increased after 24 h of exposure to ChOx, suggesting associated induction of mitochondrial protection repair or turnover. We conclude that ChOx-induced damage to lysosomes and mitochondria are sequelae to the cascade of oxysterol cytotoxic events. The early disruption of lysosomes induced by ChOx, with resultant autophagocytosis may be a critical event in apoptosis and/or necrosis of macrophages/foam cells during the development of atherosclerotic lesions. |
| Lysosomal membrane cholesterol dynamics Schoer, J. K., A. M. Gallegos, et al. (2000), Biochemistry 39(26): 7662-77. Abstract: Although the majority of exogenous cholesterol and cholesterol ester enters the cell by LDL-receptor-mediated endocytosis and the lysosomal pathway, the assumption that cholesterol transfers out of the lysosome by rapid (minutes), spontaneous diffusion has heretofore not been tested. As shown herein, lysosomal membranes were unique among known organellar membranes in terms of cholesterol content, cholesterol dynamics, and response to cholesterol-mobilizing proteins. First, the lysosomal membrane cholesterol:phospholipid molar ratio, 0.38, was intermediate between those of the plasma membrane and other organellar membranes. Second, a fluorescence sterol exchange assay showed that the initial rate of spontaneous sterol transfer out of lysosomes and purified lysosomal membranes was extremely slow, t(1/2) >4 days. This was >100-fold longer than that reported in intact cells (2 min) and 40-60-fold longer than from any other known intracellular membrane. Third, when probed with several cholesterol-binding proteins, the initial rate of sterol transfer was maximally increased nearly 80-fold and the organization of cholesterol in the lysosomal membrane was rapidly altered. Nearly half of the essentially nonexchangeable sterol in the lysosomal membrane was converted to rapidly (t(1/2) = 6 min; fraction = 0.06) and slowly (t(1/2) = 154 min; fraction = 0.36) exchangeable sterol domains/pools. In summary, the data revealed that spontaneous cholesterol transfer out of the lysosome and lysosomal membrane was extremely slow, inconsistent with rapid spontaneous diffusion across the lysosomal membrane. In contrast, the very slow spontaneous transfer of sterol out of the lysosome and lysosomal membrane was consistent with cholesterol leaving the lysosome earlier in the endocytic process and/or with cholesterol transfer out of the lysosome being mediated by additional process(es) extrinsic to the lysosome and lysosomal membrane. |
| Lysosomal sequestration of free and esterified cholesterol from oxidized low density lipoprotein in macrophages of different species Yancey, P. G. and W. G. Jerome (1998), J Lipid Res 39(7): 1349-61. Abstract: Macrophage foam cells of atherosclerotic lesions store lipid in lysosomes and cytoplasmic inclusions. Oxidized low density lipoprotein (oxLDL) has been proposed to be the atherogenic particle responsible for the free and esterified cholesterol stores in macrophages. Currently, however, there is a paucity of data showing that oxLDL can induce much cholesterol accumulation in cells. The present studies compare the ability of mildly oxLDL (TBARS = 5 to 10 nmols/mg LDL protein) with acetylated LDL to induce free cholesterol (FC) and esterified cholesterol (EC) accumulation in pigeon, THP-1, and mouse macrophages. Mildly oxLDL stimulated high levels of loading comparable to acLDL where the cellular cholesterol concentrations ranged from 160 to 420 microg/mg cell protein with EC accounting for 52-80% of the cholesterol. Pigeon and THP-1 macrophages stored most (60-90%) of oxLDL cholesterol (both FC and EC) in lysosomes, and the bulk (64-88%) of acLDL cholesterol in cytoplasmic inclusions. Consistent with lysosomal accumulation, cholesterol esterification was 75% less in THP-1 macrophages enriched with oxLDL cholesterol compared with acLDL. Furthermore, addition of an acyl-CoA:cholesterol acyltransferase inhibitor did not significantly affect either cholesterol loading or the percent distribution of FC and EC in THP-1 and pigeon cells incubated with oxLDL. Surprisingly, mouse macrophages stored most of oxLDL (71%) and acLDL (83%) cholesterol within cytoplasmic inclusions. Also, in mouse macrophages, esterification paralleled cholesterol loading, and was 3-fold more in oxLDL treated cells compared with acLDL treated cells. Inhibition of ACAT led to a 62% and 90% reduction in the %EC in oxLDL and acLDL treated mouse macrophages, respectively. The results demonstrate that mildly oxidized low density lipoprotein (oxLDL) stimulates macrophage foam cell formation and lipid engorgement of lysosomes. However, the fate of oxLDL cholesterol markedly differs in macrophages of different species. |