| For medical practitioners and the general public - Cholesterol Journal Article Catalog. |
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| Probucol reduces hepatic cholesterol secretion in hyperlipidemic Yoshida rats Bravo, E., G. Ortu, et al. (1996), Atherosclerosis 119(2): 223-33. Abstract: In this study, perfused livers from Yoshida rats, either on a normal diet or on a diet with 0.3% probucol, were examined. The analysis of liver lipid content and of bile and lipoprotein secretion changes showed that probucol had a relevant effect on liver lipid biosynthesis. In particular, it reduced the production of triacylglycerols and, to a much greater extent that of cholesterol. In addition, probucol reduced plasma cholesterol concentration by decreasing esterified cholesterol in HDL1 and HDL2 fractions. Furthermore, HDL1 composition of both hepatic neosynthetized and circulating particles was strongly modified by probucol. Finally, probucol did not appear to induce significant differences in lipid bile secretion while phospholipid secretion from perfused livers was increased. These facts suggest that the hypolipidemic action of probucol is not mediated by an increase in bile steroid secretion, but rather by a direct reduction in hepatic lipoprotein cholesterol secretion. This secretion induces a modified plasma profile of HDL particles such that these variations are advantageous in terms of reverse cholesterol transport. |
| Probucol reduces plasma and aortic wall oxysterol levels in cholesterol fed rabbits independently of its plasma cholesterol lowering effect Hodis, H. N., A. Chauhan, et al. (1992), Atherosclerosis 96(2-3): 125-34. Abstract: To understand further the antiatherogenic mechanism of probucol, the antioxidant effect of this agent was studied on specific cholesterol oxidation products in plasma and aortic wall in equally hypercholesterolemic New Zealand white rabbits. In order to maintain equal plasma total cholesterol levels, five control rabbits (C group) received a 1% followed by a 0.5% cholesterol enriched diet, while the probucol treated rabbits (C+P group) received a graded increase in the cholesterol supplemented diet from 1% to 3%; probucol supplementation was constant at 1%. After 9 weeks of feeding, the plasma oxysterols, cholest-5-ene-3 beta,7 alpha-diol, cholest-5-ene-3 beta,7 beta-diol, 5,6 beta-epoxy-5 alpha-cholestan-3 beta-ol, 5,6 alpha-epoxy-5 alpha-cholestan-3 alpha-ol and 5 alpha-cholestane-3 beta,5,6 beta-triol significantly increased over baseline levels in both experimental groups. However, the increase in all these products in plasma was 20-60% less in the C+P group than the C group (P < 0.05). Furthermore, the C+P aortic wall cholesterol oxide concentrations were 50-90% less than the C group (P < 0.05). The oxysterol pattern of the aortic wall was similar to plasma. Additionally, the aortic wall cholesterol content in the C+P group was 50% less than the C group (P < 0.05). The plasma cholesterol levels were not significantly different at any time point during the study and the cholesterol oxide content in the diets was the same. These results are consistent with the contention that the antioxidant properties of probucol serve as the basis for its antiatherogenic effects in vivo. |
| Probucol reduces the cellularity of aortic intimal thickening at anastomotic regions adjacent to prosthetic grafts in cholesterol-fed rabbits Baumann, D. S., M. Doblas, et al. (1994), Arterioscler Thromb 14(1): 162-7. Abstract: Intimal hyperplasia is a persistent problem after implantation of prosthetic grafts. Although the mechanisms underlying this hyperplastic response are unknown, it has been proposed that such responses may be due to chronic vascular injury similar to that of atherogenesis. Thus, the role of oxidation was explored using the potent antioxidant drug probucol. Adult New Zealand White rabbits fed a modestly (0.25%) cholesterol-enriched diet had a polytetrafluoroethylene prosthetic graft placed into the lower aorta. After the grafting procedure, a group of 11 rabbits was placed on the cholesterol-enriched diet supplemented with 1% wt/wt probucol while a control group of 10 rabbits was placed on the cholesterol-enriched diet alone. The rabbits were maintained for a further 10 weeks before histological examination of the area surrounding the graft. Although administration of probucol did not significantly alter the dimensions of lesions at the anastomotic sites, the drug promoted striking histological changes in the surrounding tissue. Both groups of rabbits had a similar intimal hyperplastic response of the aortic tissue surrounding the graft. The vascular lesions present in the perigraft region of the control group consisted of a normal-appearing media but a thickened intima. The thickened intima contained numerous smooth muscle cells in a network of extracellular matrix. Regions in the neointima that were rich in smooth muscle cells exhibited modest staining for proliferating cell nuclear antigen. A few macrophages were present in the control group as determined by immunostaining with the monoclonal antibody RAM-11. In contrast, administration of probucol led to a marked reduction in the presence of RAM-11-staining macrophages.(ABSTRACT TRUNCATED AT 250 WORDS) |
| Probucol selectively increases oxidation of atherogenic lipoproteins in cholesterol-fed mice and in Watanabe heritable hyperlipidemic rabbits Lauridsen, S. T. and A. Mortensen (1999), Atherosclerosis 142(1): 169-78. Abstract: The anti-atherogenic and cholesterol-lowering drug probucol (0.5-1%) or quercetin (1%), a natural antioxidant, was given to cholesterol-fed (1.5%) mice for a period of 6 weeks and to Watanabe heritable hyperlipidemic (WHHL) rabbits for a period of 8 weeks to investigate the oxidative changes in plasma and lipoproteins. Oxidation was measured as the total amount of malondialdehyde (nmol MDA/g protein) by a very specific MDA-HPLC method. A large and significant increase in MDA was seen in LDL from probucol treated WHHL rabbits (1778.7+/-585.5 nmol/g vs. 394.4+/-144.5 nmol/g, P < 0.001) and cholesterol-fed mice (579.7 + 47.3 nmol/g vs. 408.1+/-85.8 nmol/g, P < 0.05) as compared to controls while LDL cholesterol was lowered (WHHL rabbits: P < 0.05; mice: P < 0.01). In WHHL rabbits VLDL oxidation was determined additionally, and also revealed a large increase in the probucol group (2102.7+/-1156.1 nmol/g vs. 455.0+/-207.8 nmol/g, P< 0.01). In contrast, the oxidation of plasma and HDL from probucol treated animals was not statistically significantly increased, implying that probucol mediates a selective oxidation of atherogenic cholesterol-transporting lipoproteins. Quercetin treated animals did not show increased oxidation of LDL (and VLDL in rabbits) and cholesterol levels were not decreased. Furthermore, no protective antioxidant effect of quercetin was seen. In conclusion, the results suggest that a prooxidant mechanism rather than antioxidative effects influences lipoprotein metabolism in these animals. It is hypothesized that the oxidation of lipoproteins might be a physiological mechanism performed by macrophages or other cells for uptake and degradation (by macrophages and liver) of excessive amounts of LDL or VLDL and that probucol oxidizes atherogenic lipoproteins and thereby leads to a decrease in cholesterol levels. |
| Procedure for the determination of eight cholesterol oxides in poultry meat using on-column and solvent venting capillary gas chromatography Garcia Regueiro, J. A. and C. Maraschiello (1997), J Chromatogr A 764(2): 279-93. Abstract: A procedure for the determination of eight relevant cholesterol oxides in poultry meat has been developed. The method consists of the enrichment of cholesterol oxides by means of the combined use of solid-phase fractionation and thin-layer chromatography. Florisil and silica columns of 10 g permitted the handling of the total cholesterol oxides content included in the lipid bulk obtained after the Folch's extraction of 20 g of muscle meat. The determination of cholesterol oxides under their trimethylsilyl derivatives was performed by using capillary gas chromatography. The use of a fused-silica open tubular capillary column 30 m x 0.25 mm I.D. coated with 5% phenylmethylsilicone and with a film width of 0.25 micron permitted the separation of all the species. Two modes of injection (on-column and solvent venting) were evaluated and compared for the analysis of cholesterol oxides. On-column capillary gas chromatography (cGC) gave better absolute areas relative standard deviation (R.S.D.) values: 3% to 6% vs. 5% to 7% for solvent venting cGC. Regression analysis for each cholesterol oxide was performed for the two modes of injection. The possibility of large volume injection (10 microliters) by using the solvent venting mode was also evaluated in order to increase the sensitivity of the detection of cholesterol oxides. R.S.D. values for absolute areas ranging from 6% to 14% were obtained. The validation of the method was carried out within the range of 0.1-1 ppm. Absolute and relative recovery values ranging from 80% to 100% were obtained. Statistical analysis revealed that the method was reproducible. cGC-mass spectrometry was also used to confirm the peaks detected by cGC: the total ion chromatogram mode was used for the analysis of samples containing concentrations down to 0.1 ppm of cholesterol oxides. The analysis of fresh and cooked chicken meat revealed the presence of cholesterol oxides proceeding from the autoxidation of the cholesterol B-ring. Finally, saponification was found to be not as accurate as the described procedure for cholesterol oxides analysis. |
| Prodromal and early epileptic seizures in acute stroke: does higher serum cholesterol protect? Devuyst, G., T. Karapanayiotides, et al. (2003), Neurology 61(2): 249-52. Abstract: In a case-control study, patients (n = 43/3,628) presenting seizures <1 week before (n = 6), < or =3 hours after (n = 26), and 3 to 24 hours after (n = 11) a first-ever stroke were studied. On multivariate analysis, they were characterized by lower levels of serum cholesterol (5.86 +/- 0.51 vs 6.34 +/- 0.58; p < 0.0001). Mortality and functional outcome at discharge were not influenced. Early poststroke seizures occur mainly during the critical 3-hour window for thrombolysis. Hypercholesterolemia appears to protect against seizures and cerebral ischemia. |
| Product of side-chain cleavage of cholesterol, isocaproaldehyde, is an endogenous specific substrate of mouse vas deferens protein, an aldose reductase-like protein in adrenocortical cells Lefrancois-Martinez, A. M., C. Tournaire, et al. (1999), J Biol Chem 274(46): 32875-80. Abstract: Mouse vas deferens protein (MVDP) is an aldose reductase-like protein that is highly expressed in the vas deferens and adrenal glands and whose physiological functions were unknown. We hereby describe the enzymatic characteristics of MVDP and its role in murine adrenocortical Y1 cells. The murine aldose reductase (AR) and MVDP cDNAs were expressed in bacteria to obtain recombinant proteins and to compare their enzymatic activities. Recombinant MVDP was functional and displayed kinetic properties distinct from those of murine AR toward various substrates, a preference for NADH, and insensitivity to AR inhibitors. For MVDP, isocaproaldehyde, a product of side-chain cleavage of cholesterol generated during steroidogenesis, is the best natural substrate identified so far. In Y1 cells, we found that NADH-linked isocaproaldehyde reductase (ICR) activity was much higher than NADPH-linked ICR activity and was not abolished by AR inhibitors. We demonstrate that in Y1 cells, forskolin-induced MVDP expression enhanced NADH-linked ICR activity by 5-6-fold, whereas no variation in ICR-linked NADPH activity was observed in the same experiment. In cells stably transfected with MVDP antisense cDNA, NADH-linked ICR activity was abolished even in the presence of forskolin, and the isocaproaldehyde toxicity was increased compared with that of intact Y1 cells, as measured by isocaproaldehyde LD(50). In Y1 cells transfected with MVDP antisense cDNA, forskolin-induced toxicity was abolished by aminoglutethimide. These results indicate that in adrenocortical cells, MVDP is responsible for detoxifying isocaproaldehyde generated by steroidogenesis. |
| Production of androsta-1,4-diene-3,17-dione from cholesterol using immobilized growing cells of Mycobacterium sp. NRRL B-3683 adsorbed on solid carriers Lee, C. Y. and W. H. Liu (1992), Appl Microbiol Biotechnol 36(5): 598-603. Abstract: Living cells of Mycobacterium sp. NRRL B-3683 were immobilized by adsorption on different types of solid carriers in order to produce androsta-1,4-diene-3,17-dione (ADD) from cholesterol. Activated alumina proved to be the most preferred carrier for long-term operation when glucose and peptone were added to the reaction medium. In a repeated-batch process, the maximum productivity of ADD was about 0.19 g/l per day with a molar conversion rate of 77% when 1.0 g/l of cholesterol was added to the reaction medium. The half-life of the immobilized cells was more than 45 days and the system could be reactivated by incubating the immobilized cells in a cell growth medium. |
| Production of apolipoprotein E-rich LDL by the liver. The effect of dietary cholesterol and some lipid lowering agents Teramoto, T., T. Matsushima, et al. (1990), Ann N Y Acad Sci 598: 301-7. Abstract: We reported previously that cholesterol feeding induced an increase in hepatic secretion of VLDL and a decrease in that of LDL, especially LDL-apo B100, using monkey liver perfusion. In the present study we conducted rat liver perfusion using the HMG Co A reductase inhibitor (CS-514) and Kampo medicine (Daisaikoto) to elucidate the mechanism of the effect of dietary cholesterol on hepatic lipoprotein and apolipoprotein synthesis. Although the secretion of VLDL was increased by cholesterol feeding, that of LDL and especially of apo B100 of LDL were markedly decreased, and apo E of the LDL was increased as observed in the monkey liver perfusion experiments. The effect of CS-514 was clearly different from the effect of dietary cholesterol in spite of the suppression of hepatic cholesterogenesis which was comparable to that induced by cholesterol feeding, suggesting that the decrease in secretion of LDL-apo B100 induced by the dietary cholesterol is not due to suppressed cholesterogenesis. Daisaikoto, which was added to the diet together with cholesterol, diminished the effects of dietary cholesterol on the plasma and hepatic cholesterol levels. When the liver treated with Daisaikoto was perfused, the effect of dietary cholesterol on the production of lipoprotein and apolipoprotein was markedly diminished. This evidence indicates that the decrease in LDL-apo B100 and the increase in apo E were mediated by the hepatic cholesterol level. |
| Production of cholesterol-enriched nascent high density lipoproteins by human monocyte-derived macrophages is a mechanism that contributes to macrophage cholesterol efflux Kruth, H. S., S. I. Skarlatos, et al. (1994), J Biol Chem 269(39): 24511-8. Abstract: Atherosclerotic lesions have a lipid core containing crystals and liposomes enriched in unesterified cholesterol as well as numerous monocyte-macrophages enriched in cholesteryl ester. Sufficient amounts of plasma-derived high density lipoproteins (HDL) may not reach and efficiently remove the cholesterol deposited in lesion macrophages or in the lipid core of lesions. We examined the potential of human monocyte-macrophages to produce nascent HDL and to solubilize cholesterol derived from interaction of monocyte-macrophages with lipoprotein and non-lipoprotein sources of cholesterol. Monocyte-macrophages produced discoidal (25 +/- 6 nm long and 6 +/- 1 nm wide (mean +/- S.D.)) and vesicular (89 +/- 41 nm in diameter) lipoprotein particles following and during enrichment of macrophages with cholesterol from acetylated low density lipoprotein (AcLDL) or cholesterol crystals. During cholesterol enrichment, discoidal particles progressively accumulated in the medium for up to 6 days. In contrast, vesicles did not increase past 2 days of incubation. Both the discoidal and vesicular lipoprotein particles had a peak density of about 1.09-1.10 g/ml. The discoidal particles contained apolipoprotein E (apoE), whereas the vesicles contained a major protein constituent with a molecular mass of 22,000 daltons. The vesicles did not contain detectable apoE and the 22,000-dalton protein was not the 22,000-dalton thrombolytic fragment of apoE. Following cholesterol enrichment of macrophages with AcLDL or cholesterol crystals, macrophages excreted much of their accumulated cholesterol, even in the absence of exogenously added cholesterol acceptors. Most of this excreted cholesterol was recovered from the culture medium and was carried in the apoE discoidal particles that showed cholesterol enrichment up to a 2:1 unesterified cholesterol to phospholipid molar ratio. The findings suggest that sufficient production of these nascent HDL by macrophages within atherosclerotic lesions should facilitate removal of cellular and extracellular cholesterol, even in the absence of plasma-derived HDL. |
| Production of phosphatidylinositol 3,4,5-trisphosphate and phosphatidic acid in platelet rafts: evidence for a critical role of cholesterol-enriched domains in human platelet activation Bodin, S., S. Giuriato, et al. (2001), Biochemistry 40(50): 15290-9. Abstract: Glycosphingolipid- and cholesterol-enriched membrane microdomains, called rafts, can be isolated from several mammalian cells, including platelets. These microdomains appear to play a critical role in signal transduction in several hematopoietic cells, but their function in blood platelets remains unknown. Herein, we first characterized the lipid composition, including the fatty acid composition of phospholipids, of human platelet rafts. Then their role in platelet activation process was investigated. Interestingly, thrombin stimulation led to morphological changes of rafts correlating with the production of lipid second messengers in these microdomains. Indeed, we could demonstrate for the first time that a large part of the stimulation-dependent production of phosphatidic acid and phosphoinositide 3-kinase products was concentrated in rafts. Moreover, cholesterol depletion with methyl-beta-cyclodextrin disrupted platelet rafts, dramatically decreased the agonist-dependent production of these lipid signaling molecules, and impaired platelet secretion and aggregation. Cholesterol repletion restored the physiological platelet responses. Altogether our data indicate that rafts are highly dynamic platelet membrane structures involved in critical signaling mechanisms linked to the production of lipid second messengers. The demonstration of phosphatidylinositol 3,4,5-trisphosphate production in rafts may have general implications for the understanding of the role of this key second messenger found ubiquitously in higher eucaryotic cells. |
| Production of progesterone from de novo-synthesized cholesterol in cumulus cells and its physiological role during meiotic resumption of porcine oocytes Yamashita, Y., M. Shimada, et al. (2003), Biol Reprod 68(4): 1193-8. Abstract: To investigate the role of factors secreted by cumulus cells during meiotic resumption of porcine oocytes, 1, 5, 10, or 20 cumulus-oocyte complexes (COCs) were cultured in each well of a culture dish containing 300 microl of maturation medium for 20 h. There was a significant positive correlation between the rate of germinal vesicle breakdown (GVBD) and the number of COCs cultured in each well for 20 h. The level of progesterone in the medium in which COCs had been cultured for 20 h also rose significantly with an increase in the number of COCs cultured in each well. A significantly small proportion of GVBD in oocytes when one COC was cultured in each well for 20 h was improved by the addition of progesterone. This proportion of GVBD was fully comparable to that of COCs cultured in the absence of additional progesterone with 20 COCs. Thus, progesterone secreted by COCs plays a positive role in GVBD induction in porcine oocytes. Furthermore, we also examined the role of sterol biosynthesis on progesterone production by cumulus cells and in oocyte GVBD. The results showed that the addition of ketoconazole, which suppressed the sterol biosynthetic pathway produced by demethylation of lanosterol, decreased the rate of GVBD, as well as progesterone production in COCs cultured for 20 h. However, the suppression of GVBD by ketoconazole was overtaken by the addition of progesterone. These results demonstrate that a high level of progesterone produced by cumulus cells was responsible for an acceleration of GVBD in porcine oocytes. |
| Production of testosterone from cholesterol using a single-step microbial transformation of Mycobacterium sp Liu, W. H. and C. K. Lo (1997), J Ind Microbiol Biotechnol 19(4): 269-72. Abstract: A novel single-step microbial transformation process for the production of testosterone (TS) from cholesterol by Mycobacterium sp was investigated. It was found that the supply of reducing power, NADH, from the metabolism of glucose was necessary for the reduction of androst-4-en-3,17-dione (AD) to TS. The cultivation time for the maximum accumulation of TS and the residual glucose increased in parallel with the amount of glucose supplemented in fermentation cultures. After the glucose in the fermentation culture was completely consumed, most of the TS was oxidized to AD. Adding a larger amount of glucose could prevent oxidation of TS to AD. Under optimal fermentation conditions, the maximum molar conversion rate of TS from cholesterol was 51% in a 5-L surface-aerated fermentor after 120 h cultivation. |
| Production performance, serum/yolk cholesterol and immune competence of white leghorn layers as influenced by dietary supplementation with probiotic Panda, A. K., M. R. Reddy, et al. (2003), Trop Anim Health Prod 35(1): 85-94. Abstract: An experiment was conducted to measure the influence of a dietary probiotic on the production performance, the concentrations of cholesterol in the serum and yolk and immune competence in White Leghorn layers from 25 to 72 weeks of age. One hundred and twenty commercial White Leghorn layers, aged 24 weeks, with an average of 62% hen-day egg production, were equally and randomly distributed into three groups, with eight replicates of 5 birds in each. The birds were reared in individual laying cages. They were placed on one of three dietary treatments: basal, or basal with probiotic supplementation at a rate of 100 or 200 mg/kg feed. The addition of probiotic significantly increased the egg production, shell weight, shell thickness and serum calcium, and reduced the concentrations of cholesterol in the serum and yolk. However, no differences in these traits was observed between the groups receiving 100 or 200 mg probiotic. Feed conversion, egg weight, serum phosphorus and serum alkaline phosphatase activity were not influenced by supplementation with probiotic. Antibody production in response to the inoculation of sheep red blood cells and the cutaneous basophilic hypersensitivity (CBH) responses to inoculation with phytohaemagglutinin did not differ significantly among the dietary groups at either 24 or 40 weeks of age. The antibody titre was significantly higher in the groups supplemented with probiotic at 64 weeks of age. The addition of 100 mg/kg of probiotic in the diet significantly increased the CBH response at 64 weeks of age. |
| Products of the reaction of cholesterol with hypochlorite anion Momynaliev, K. T., S. V. Osipova, et al. (1997), Biochemistry (Mosc) 62(2): 158-64. Abstract: Products of the reaction of cholesterol with hypochlorite (OCI) in various systems (egg phosphatidylcholine liposomes, low-density lipoproteins, and aqueous colloidal dispersion of cholesterol) were separated and analyzed by TLC, HPLC, and gas chromatography-mass spectrometry. The reactions of hypochlorite with cholesterol result in the same reaction products in all treated systems. Eighteen fractions were isolated from the reaction mixture by normal-phase HPLC in hexane-isopropanol (95:5 v/v); these were then examined by gas chromatography-mass spectrometry. Six products less polar than cholesterol were isolated from the reaction mixture; two of them were identified as 4,6-cholesten-3-one and 4-cholesten-3,6-dione. Among the oxidation products more polar than cholesterol, nine compounds were identified; they are 5,7-cholestadien-3 beta-ol,3,5-cholestadien-7-one, 4-cholesten-3 beta, 6 beta-diol, 5-cholesten-3 beta, 7 beta-diol, cholestan-3 beta, 5 alpha, 6 beta-triol, 5 alpha-cholestan-3 beta-ol-6-one, 5-cholesten-3 beta-ol-7-one, 5 alpha, 6 alpha-epoxycholestan-3 beta-ol, and 5 alpha-cholesten-3,6-dione. |
| Profile of cholesterol-related sterols in aged amyloid precursor protein transgenic mouse brain Lutjohann, D., A. Brzezinka, et al. (2002), J Lipid Res 43(7): 1078-85. Abstract: Cholesterol is implicated to play a role in Alzheimer disease pathology. Therefore, the concentrations of cholesterol, its precursors, and its degradation products in brain homogenates of aging wild-type and beta-amyloid precursor protein transgenic mice carrying the Swedish mutation (APP23) were analyzed. Among the sterols measured, lanosterol is the first common intermediate of two different pathways, which use either desmosterol or lathosterol as the predominant precursors for de novo synthesis of brain cholesterol. In young mice, cholesterol is mainly synthesized via the desmosterol pathway, while in aged mice, lathosterol is the major precursor. 24S-hydroxycholesterol (cerebrosterol), which plays a key role in the removal of cholesterol from the brain, modestly increased during aging. No differences in the levels of cholesterol, its precursors, or its metabolites were found between wild-type and APP23 transgenic mice. Moreover, the levels of the exogenous plant sterols campesterol and sitosterol were significantly elevated in the brains of APP23 animals at age 12 and 18 months. This time point coincides with abundant plaque formation. |
| Profound induction of hepatic cholesteryl ester transfer protein transgene expression in apolipoprotein E and low density lipoprotein receptor gene knockout mice. A novel mechanism signals changes in plasma cholesterol levels Masucci-Magoulas, L., A. Plump, et al. (1996), J Clin Invest 97(1): 154-61. Abstract: The plasma cholesteryl ester transfer protein (CETP) mediates the transfer of cholesteryl esters from HDL to other lipoproteins and is a key regulated component of reverse cholesterol transport. Dietary hypercholesterolemia results in increased hepatic CETP gene transcription and higher plasma CETP levels. To investigate the mechanisms by which the liver senses hypercholesterolemia, mice containing a natural flanking region CETP transgene (NFR-CETP transgene) were bred with apo E or LDL receptor gene knockout mice (E0 or LDLr0 mice). Compared to NFR-CETP transgenic (Tg) mice with intact apo E genes, in NFR-CETP Tg/E0 mice there was an eightfold induction of plasma CETP levels and a parallel increase in hepatic CETP mRNA levels. Other sterol-responsive genes (LDL receptor and hydroxymethyl glutaryl CoA reductase) also showed evidence of altered regulation with decreased abundance of their mRNAs in the E0 background. A similar induction of plasma CETP and hepatic CETP mRNA levels resulted from breeding the NFR-CETP transgene into the LDL receptor gene knockout background. When placed on a high cholesterol diet, there was a further increase in CETP levels in both E0 and LDLr0 backgrounds. In CETP Tg, CETP Tg/E0, and CETP Tg/LDLr0 mice on different diets, plasma CETP and CETP mRNA levels were highly correlated with plasma cholesterol levels. The results indicate that hepatic CETP gene expression is driven by a mechanism which senses changes in plasma cholesterol levels independent of apo E and LDL receptors. Hepatic sterol-sensitive genes have mechanisms to sense hypercholesterolemia that do not require classical receptor-mediated lipoprotein uptake. |
| Progesterone blocks cholesterol translocation from lysosomes Butler, J. D., J. Blanchette-Mackie, et al. (1992), J Biol Chem 267(33): 23797-805. Abstract: Fluorescent microscopic examination of fibroblasts cultured with low density lipoprotein (LDL) and progesterone (10 micrograms/ml) for 24 h revealed extensive filipin-cholesterol staining of perinuclear lysosomes. Levels of unesterified cholesterol were 2-fold greater than in fibroblasts cultured with LDL alone. Progesterone strongly blocked cholesteryl ester synthesis. When cellular uptake of LDL was monitored in the presence of 58035, a specific inhibitor of acyl-CoA:cholesterol acyltransferase, excess unesterified cholesterol was not stored in lysosomes. Discontinuation of LDL uptake in conjunction with progesterone washout markedly reversed the filipin-cholesterol staining of lysosomes. Reversal of the lysosomal cholesterol lipidosis was associated with a rapid burst of cholesteryl ester synthesis and a normalization of the cellular levels of free and esterified cholesterol. In contrast to normal cells, progesterone removal from Niemann-Pick C fibroblasts did not reverse the lysosomal cholesterol accumulation of these mutant cultures. The metabolic precursor of progesterone, pregnenolone, also induced extensive accumulation of cholesterol in lysosomes. Other steroids induced less vacuolar cholesterol accumulation in the following decreasing order: corticosterone and testosterone, promegestone, RU 486. The relative inhibition of cellular cholesterol esterification by the steroids paralleled their respective abilities to sequester cholesterol in lysosomes rather than their inhibition of acyl-CoA:cholesterol acyltransferase activity in cell-free extracts. The progesterone-related inhibition and restoration of lysosomal cholesterol trafficking is a useful experimental means of studying intracellular cholesterol transport. A particularly important feature of its utility is the facile reversibility of the steroid-induced block. The lysosomal cholesterol lipidosis established with a hydrophobic amine, U18666A, was not as readily reversed. |
| Progesterone blocks intracellular translocation of free cholesterol derived from cholesteryl ester in macrophages Mazzone, T., M. Krishna, et al. (1995), J Lipid Res 36(3): 544-51. Abstract: Macrophage foam cells must accommodate continuing fluxes of free cholesterol in spite of a greatly expanded store of cholesteryl ester. Though endogenous free cholesterol synthesis is suppressed, free cholesterol continues to enter the cell via endocytosis of oxidized/modified lipoproteins. It has been shown previously that this free cholesterol is released into the lysosomal compartment and rapidly transported to the plasma membrane prior to its esterification. A substantial amount of free cholesterol is also presented via the continuous hydrolysis of cholesteryl ester during the cholesteryl ester cycle. We addressed the question of whether the intracellular free cholesterol derived from the hydrolysis of cholesteryl ester formed a protected pool for rapid re-esterification. Incubation of macrophage foam cells with cyclic AMP to enhance cholesteryl ester hydrolysis, and with S58035 to inhibit acyl-CoA:cholesterol acyltransferase (ACAT) activity, led to conversion of cellular cholesteryl ester to free cholesterol and transport of this free cholesterol to the plasma membrane. Addition of progesterone, previously demonstrated to be an inhibitor of free cholesterol transport in other cell types, also led to conversion of cholesteryl ester to free cholesterol even though progesterone was only a weak inhibitor of ACAT activity. Free cholesterol in the plasma membrane was an important source of ACAT substrate to balance the constitutive hydrolysis of cholesteryl ester in cholesterol-loaded macrophages. Treatment of cells with progesterone, however, prevented free cholesterol derived from cholesteryl ester hydrolysis from moving to the plasma membrane. The sequestration of free cholesterol by progesterone could be reversed by incubation with human HDL3.(ABSTRACT TRUNCATED AT 250 WORDS) |
| Progesterone inhibits cholesterol biosynthesis in cultured cells. Accumulation of cholesterol precursors Metherall, J. E., K. Waugh, et al. (1996), J Biol Chem 271(5): 2627-33. Abstract: Cells acquire cholesterol through endogenous synthesis and through receptor-mediated uptake of cholesterol-rich low density lipoprotein (LDL). Esterification of LDL-derived cholesterol is catalyzed by acyl-CoA:cholesterol acyltransferase (ACAT) in the endoplasmic reticulum (ER). Progesterone inhibits esterification, and, although the mechanism of inhibition is not completely understood, this inhibition results from progesterone's ability to inhibit the activity of multiple drug resistance (MDR) P-glycoproteins (P. DeBry and J. E. Metherall, submitted for publication). In the current manuscript, we demonstrate that progesterone inhibits cholesterol biosynthesis resulting in the accumulation of a number of sterol precursors. In Chinese hamster ovary (CHO) cells, high concentrations (100 microM) of progesterone completely blocked cholesterol production, resulting in the accumulation of lanosterol and a lanosterol precursor. Lower concentrations (40 microM) of progesterone cause plasma membrane accumulation of several sterol products. The majority of these sterols are precursors of cholesterol since they were efficiently converted to cholesterol upon removal of progesterone from the culture medium. Although very high concentrations (> 200 microM) of progesterone killed CHO cells, their growth was restored by the addition of cholesterol to the growth medium, indicating that progesterone toxicity resulted from cholesterol auxotrophy. The effect of progesterone was not unique to CHO cells; progesterone also inhibited cholesterol biosynthesis in all human cell lines tested. These observations suggest that a common progesterone-sensitive pathway is involved in both cholesterol biosynthesis and the processing of LDL-derived cholesterol. |