| For medical practitioners and the general public - Cholesterol Journal Article Catalog. |
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| Effect of cholesterol, fatty acyl chain composition, and bilayer curvature on the interaction of cytochrome b5 with liposomes of phosphatidylcholines Taylor, K. M. and M. A. Roseman (1995), Biochemistry 34(11): 3841-50. Abstract: To determine the effect of cholesterol and lipid packing on the solubility of membrane proteins in bilayers, cytochrome b5 incorporation into phosphatidylcholine (PC) liposomes was determined as a function of bilayer curvature (SUVs versus LUVs), fatty acyl chain composition, and cholesterol content. The equilibrium affinity constant for the formation of a 1:1 b5/PC complex, Kp, and the number of PC's per "site" at saturation, n, were determined from binding isotherms, which were obtained by measuring the increase in intrinsic tryptophan fluorescence. With LUVs, n was also determined directly by gel filtration. The following results were obtained: (1) Both Kp and the saturating level of b5 binding, s (n-1), are significantly greater for SUVs than for LUVs. In LUVs, a binding site must consist of several surrounding lipid layers. (2) Cholesterol reduces Kp and s by factors that range from 1 to > 100. Binding inhibition is highly sensitive to the liposome size and to the fatty acyl composition of the PC; the latter correlates with the condensing effects on PC: C1satC2mono > C1satC2di approximately natural mixtures > C1unsat-C2unsat. (3) With POPC LUVs, the binding inhibition was 3.6-, 1.4- and 17-fold within the ranges of 0-20, 20-33, and 33-50 mole percent cholesterol, respectively. (4) The equilibrium binding constant to SUVs is greater for liposomes that are prepared from natural PC mixtures than for vesicles of a single synthetic phospholipid. The reductions in b5 binding correlate with reductions in bilayer free volume, which were calculated from monolayer studies of the lipid mixtures. The sensitivity of liposome saturability to bilayer curvature, fatty acyl chain composition, and cholesterol content may account for the disparate results among previous studies of cholesterol-protein interactions. A more significant implication is that in biological membranes with high levels of cholesterol, subtle variations in the fatty acyl chain composition could substantially affect the solubility and physical states of integral membrane proteins. |
| Effect of cholesterol/phospholipid ratio on stimulatory GTP-binding protein function Bai, L. and H. Youguo (1998), Biochem Mol Biol Int 45(6): 1155-62. Abstract: The effect of different cholesterol/phospholipid (C/P) ratios on the coupling function between stimulatory GTP-binding protein(Gs) and adenylyl cyclase (AC) in proteoliposomes, and its relationship to the conformational change of Gs were investigated. The results showed that Gs activities of both binding GTP gamma S and stimulating adenylyl cyclase were the highest in proteoliposomes with a proper content of cholesterol similar to physiological situation while the lowest with higher cholesterol content similar to pathological situation. In addition, the conformational change of Gs in proteoliposomes was also detected by steady-state and nanosecond time-resolved fluorescence using acrylodan as a probe. It is suggested that a proper C/P ratio similar to physiological situation regulates the function of Gs by inducing a change in the physical state of lipid bilayer, which would favor the formation of a suitable conformation of Gs with higher activities of both binding GTP and stimulating adenylyl cyclase. But if C/P ratio is higher, such as in pathological situation, this is unfavorable for motion of Gs in membrane, which results in inhibition of Gs function significantly. |
| Effect of cholesterol-5 alpha,6 alpha-epoxide supplementation to cultured cardiomyocytes Hrelia, S., A. Bordoni, et al. (1994), Biochem Mol Biol Int 32(3): 565-73. Abstract: In order to evaluate the effect of one of the main oxysterols derived from cholesterol oxidation, cholesterol-5 alpha,6 alpha-epoxide (epox), on cardiac cells, we have supplemented the culture medium of neonatal rat cardiomyocytes with scalar concentrations of epox (0.1-100 microM). While 0.1 microM epox supplementation was ineffective, epox supplementation in the range 1-100 microM determined a reduction in cellular protein level, without affecting cell viability, and a dose-dependent epox incorporation into cardiomyocyte lipids. Furthermore, in the same concentration range of epox supplementation, a gas chromatographic peak unambiguously identified by gas chromatography-mass spectrometry as cholestane-3 beta,5 alpha,6 beta-triol, an hydrolytic metabolite of epox, was detected. The mechanism of cytotoxicity of epox to cardiomyocytes could be due to the insertion of epox itself into cellular lipids, and to its metabolization to the more toxic triol. |
| Effect of cholesterol-enriched diet on liver and heart enzymes in male rabbits Konecka, A. M. and T. Jezierski (1997), Comp Biochem Physiol B Biochem Mol Biol 118(3): 505-8. Abstract: White New Zealand male rabbits were fed a high-cholesterol (1%) diet for 7 weeks. The activity of alkaline phosphatase (AP), alanine (AlaAT), aspartate (AspAT) aminotransferases and level of glucose in the blood plasma of rabbits was determined and compared with those of a control group of animals. The cholesterol-enriched diet resulted in increases in plasma AlaAT and AP activity and a decrease in plasma glucose. In the liver, cholesterol treatment decreased the activity of AspAT, AlaAT, AP, phosphoglucomutase, phosphofructokinase, pyruvate kinase and lactate dehydrogenase. Activities of glucosephosphate isomerase, aldolase and the level of glycogen were not affected. No statistically significant changes in the activity of examined enzymes in heart of rabbits fed with cholesterol-enriched diet were observed. Chronic intake of cholesterol in the diet had a negative effect on liver metabolism but not on heart metabolism in rabbits. |
| Effect of cholesterol-loaded cyclodextrin on the cryosurvival of bull sperm Purdy, P. H. and J. K. Graham (2004), Cryobiology 48(1): 36-45. Abstract: Bull sperm were treated with several levels of cholesterol-loaded cyclodextrin (CLC) and frozen in egg yolk diluents containing either Tris or sodium citrate, to determine the CLC concentration that best benefits bull sperm cryosurvival. After thawing, higher percentages of motile (60%) and viable (55%) sperm were obtained when 1.5mg/ml CLC was added to sperm prior to freezing, than for sperm frozen in egg yolk Tris alone (42 and 46%, respectively; P < 0.05). Increasing concentration of CLCs, maintained higher percentages of viable sperm up to addition of 6.0mg/ml CLC when the percentages of viable sperm began to decline (50%; P < 0.05). Addition of 1.5mg/ml CLC to sperm frozen in sodium citrate diluent resulted in 53% motile sperm compared to 37% for control, although these were not different (P > 0.05). The beneficial effects of CLC addition were observed regardless of whether sperm incubated with CLC at 22 or 37 degrees C (P > 0.05) and maximum effects were observed when sperm incubated with CLC for 15min. Longer incubation times, up to 60min, resulted in similar results (P > 0.05). The amount of cholesterol that incorporated into sperm, increased with increasing CLC concentration, in a linear fashion, and each sperm incorporates a similar amount of cholesterol (coefficient of variation=12.9+/-0.7%). In addition, the cholesterol incorporates into all sperm membranes. Increasing membrane cholesterol levels, by adding CLCs to cells, prior to freezing, is a simple technology that increases the cryosurvival of bull sperm, and may benefit the cryosurvival of many cell types. |
| Effect of cholesterol-lowering therapy on coronary endothelial vasomotor function in patients with coronary artery disease Vita, J. A., A. C. Yeung, et al. (2000), Circulation 102(8): 846-51. Abstract: BACKGROUND: Improved endothelial function may contribute to the beneficial effects of cholesterol-lowering therapy. METHODS AND RESULTS: In this randomized, double-blind study, we compared the effect of 6 months of simvastatin (40 mg/d) treatment with that of placebo on coronary endothelial vasomotor function in 60 patients with coronary artery disease. Simvastatin lowered LDL-cholesterol by 40+/-12% from 130+/-28 mg/dL (P<0.001). Peak intracoronary acetylcholine infusion produced epicardial coronary constriction at baseline in both the simvastatin (-17+/-13%) and placebo (-24+/-16%) groups. After treatment, acetylcholine produced less constriction in both groups (-12+/-19% and -15+/-14%, respectively, P=0.97). The increase in coronary blood flow during infusion of the peak dose of substance P was blunted at baseline in both the simvastatin (42+/-50%) and placebo (55+/-71%) groups, reflecting impaired endothelium-dependent dilation of coronary microvessels. After treatment, the flow increase was 82+/-81% in the simvastatin group and 63+/-53% in the placebo group (P=0.16). CONCLUSIONS: Six months of cholesterol-lowering therapy has no significant effect on coronary endothelial vasomotor function in the study population of patients with coronary artery disease and mildly elevated cholesterol levels. These findings suggest that the effects of cholesterol lowering on endothelial function are more complex than previously thought. |
| Effect of cholesterol-lowering therapy on endothelial function Houghton, J. L. (2001), Circulation 104(2): E6. |
| Effect of cholesterol-lowering treatment on coronary heart disease morbidity and mortality: the evidence from trials, and beyond Katan, M. B. (1990), Cardiology 77 Suppl 4: 8-13. Abstract: Evidence from controlled clinical trials shows convincingly that reducing serum cholesterol levels by diet or drug treatment reduces the incidence of coronary heart disease. On a population basis, the most important effect of cholesterol lowering might be postponement of the first symptoms of disease rather than postponement of death, because most cardiac deaths occur at an advanced age. No enhanced cancer mortality is seen either in populations with low serum cholesterol levels or in patients who, through a genetic defect, have a low-density-lipoprotein cholesterol of zero. This makes it unlikely that cholesterol-lowering treatment as such promotes cancer. Still, specific side effects and toxicity of drugs need careful scrutiny, and diet remains the treatment of choice for mild hypercholesterolemia. |
| Effect of cholesterol-rich diets with and without added vitamins E and C on the severity of atherosclerosis in rabbits Mahfouz, M. M., H. Kawano, et al. (1997), Am J Clin Nutr 66(5): 1240-9. Abstract: Oxysterols as oxidation products of cholesterol are considered an atherogenic factor in the development of atherosclerosis in the arteries of cholesterol-fed rabbits. We compared the atherogenic effects of diets enriched either with 0.5% oxidized cholesterol (OC; characterized by high amounts of oxysterols) or with pure cholesterol (PC). The effects of antioxidant vitamins E and C added to the PC diet were also evaluated in view of their antioxidative properties for lipoproteins and cholesterol and how this could affect the severity of atherosclerosis. Four groups of rabbits were fed the following for 11 wk: 1) a nonpurified stock diet, 2) this stock diet plus 0.5% OC, 3) the stock diet plus 0.5% PC, and 4) the stock diet plus 0.5% PC and 1000 mg vitamin E and 500 mg vitamin C/kg diet (PC + antioxidants). The OC and PC diets were equally hyperlipidemic and hypercholesterolemic. The severity of atherosclerotic lesions was highest with the OC diet and lowest with the PC + antioxidants diet. The plasma oxysterol concentration was proportional to the severity of atherosclerosis in all three groups of cholesterol-fed rabbits. beta-Very-low-density-lipoprotein modification was minimized by vitamins E and C as indicated by its polyacrylamide gel electrophoretic pattern and its increased binding to the rabbit liver membrane in vitro. This study indicated that OC and PC were equally atherogenic but that the addition of antioxidants to the PC diet significantly reduced its severity, even when hypercholesterolemia persisted. This indicated that atherogenesis can result from an excessive accumulation of oxidation products of cholesterol in the plasma. |
| Effect of cholesterol-supplemented diet in heritable hyperlipidemic Yoshida rats: functional and morphological characterization of thoracic aorta Chinellato, A., E. Ragazzi, et al. (1994), Atherosclerosis 106(1): 51-63. Abstract: In this study we have considered the possibility of inducing vascular damage in Yoshida Pittsburg (YOS) rat, an inbred strain which has endogenous hyperlipidemia without vascular atherosclerotic damage. Cholesterol-enriched diet (4% cholesterol plus 1% cholic acid and 0.5% thiouracil) was administered to YOS rats, in order to induce atherogenesis. The results indicate that, despite significant increase in serum (about 2-fold) and aortic tissue cholesterol (about 6-fold), no morphological damage occurred. A reduction in acetylcholine-mediated relaxation (of about 37%) was observed. No inhibition of ATP- or sodium nitrite-induced relaxation, or of contraction induced by norepinephrine was seen. Serum triglyceride concentration did not vary after administration of a cholesterol-enriched diet. Our results suggest that in heritable hyperlipidemic Yoshida rat, after 2 months of cholesterol-enriched diet, despite increased serum cholesterol levels, no atheromatous plaque developed on the aortic wall. Impaired vascular function and reductions in the response to acetylcholine were related to changed endothelial cell function. Administration of a high cholesterol diet to YOS rat may represent a new model of mixed endogenous and exogenous hyperlipidemia that can resemble many human dislipidemic diseases and therefore may become a useful tool for the study of isolated endothelial dysfunction. |
| Effect of cholesteryl ester on the distribution of fluorescent cholesterol analogues in triacylglycerol-rich emulsions Li, Q. T. and W. H. Sawyer (1993), Biochim Biophys Acta 1166(2-3): 145-53. Abstract: Lipid emulsions consisting of a surface monolayer of phospholipid enclosing a core of neutral lipid (cholesteryl ester and/or triacylglycerol) are useful models of the lipid phase of lipoproteins. The physical state of the emulsion surface may determine the extent and nature of interaction of enzymes and lipid transfer proteins (e.g., lipoprotein lipase, cholesteryl ester transfer protein) with the particle. Unesterified cholesterol, which is a major determinant of the physical state of the surface phase, is able to partition between surface and core compartments. This report describes a fluorescence quenching method which determines the equilibrium distribution of a fluorescent cholesterol analogue (dehydroergosterol) between the surface and core compartments of triacylglycerol-rich emulsions. Quenching by iodide is used to distinguish a pool of unesterified cholesterol readily accessible to the aqueous phase. Quenching by 5-nitroxystearate identifies a pool of unesterified cholesterol in the phospholipid monolayer and the pool of unesterified cholesterol in the core compartment is found by difference. It is shown that the substitution of cholesteryl oleate for triolein in the core of the emulsion substantially increases the partition of unesterified cholesterol into the core compartment with a consequent depletion of unesterified cholesterol in the surface monolayer. The distribution of unesterified cholesterol between surface and core compartments is largely enthalpically driven. |
| Effect of cholestyramine in early weaning on later response to serum and fecal steroid levels and cholesterol 7 alpha-hydroxylase activity to high-cholesterol diet in ExHC rats Lu, Y. F., K. Imaizumi, et al. (1990), J Nutr Sci Vitaminol (Tokyo) 36(2): 131-40. Abstract: Male ExHC (exogenous hypercholesterolemic) rats were either prematurely weaned at 17 days of age or allowed to nurse until 35 days of age. The prematurely weaned rats were either fed a diet containing cholestyramine or cholestyramine-free diet until 35 days of age. Cholestyramine supplementation markedly increased fecal bile acid excretion and modified the composition. After giving a stock diet for 7 weeks, all rats received a cholesterol-enriched diet for 9 weeks. The serum cholesterol level in later time was not affected by early dietary manipulation. The activity of hepatic cholesterol 7 alpha-hydroxylase and fecal bile acid excretion at the end of the cholesterol challenge decreased in the cholestyramine-pretreated group, when compared to the normally weaned group. Fecal excretion and the ratio of the secondary (deoxycholic and lithocholic acids) to the primary (cholic and chenodeoxycholic acids) bile acids significantly decreased in the early cholestyramine-treated group. These results suggest that a modification of bile acid metabolism in early life may strongly influence the hepatic and possibly colonic bile acid metabolism in later life, when challenged with a high-cholesterol diet. |
| Effect of cholestyramine on angiopathies in cholesterol-fed mice and diabetic mice Sugiura, M., H. Suenaga, et al. (1995), J Smooth Muscle Res 31(6): 400-2. |
| Effect of cholylsarcosine on hepatic cholesterol and bile acid synthesis and bile secretion in rats Heuman, D. M., Z. R. Vlahcevic, et al. (1992), Gastroenterology 103(5): 1641-8. Abstract: The regulatory and secretory properties of cholylsarcosine (C-sar), a synthetic conjugated bile acid analogue that resists deconjugation and dehydroxylation, were compared with those of the natural conjugates of cholic acid. After continuous intraduodenal infusion of cholylsarcosine (C-sar), cholyltaurine (C-tau), or cholylglycine (C-gly) at 36 mumol/100 g.h, the infused bile acid in each case became the predominant biliary bile acid. After 48 hours, infusion of C-sar, C-tau, and C-gly suppressed the activity of cholesterol 7 alpha-hydroxylase (C7 alpha H; rate-limiting for bile acid synthesis) by 65%, 78%, and 92%, respectively, compared with biliary fistula controls. After C-sar infusion, levels of C7 alpha H protein, messenger RNA, and transcriptional activity were depressed to the same extent as specific activity, indicating that C-sar, like C-tau, down-regulates C7 alpha H principally at the level of gene transcription. All three bile acids also suppressed activity of 3-hydroxy-3-methylglutaryl-coenzyme A reductase (rate-limiting for cholesterol synthesis). Both short- and long-term, the three cholyl conjugates caused similar increases in bile flow and in biliary secretion of cholesterol and phospholipid. It is concluded that in the rat, cholyl conjugates per se can suppress cholesterol and bile acid biosynthesis without prior conversion to deoxycholate. The effects of C-sar on hepatic cholesterol and bile acid synthesis as well as on induced bile flow and biliary lipid secretion are essentially identical to those of the naturally occurring cholyl conjugates. |
| Effect of chronic cholesterol loading in the development of acute ischemic renal failure in rats Iaina, A., G. Benyamin, et al. (1994), Ren Fail 16(1): 117-23. Abstract: The effect of chronic cholesterol loading and lovastatin administration in renal artery clamping acute renal failure in rats is not known. Acute renal failure was induced by 60-min left renal artery clamping immediately after right nephrectomy. The changes in renal function after renal artery clamping in the hyperlipidemic rats were unexpected. The acute renal failure in the cholesterol-loaded groups was less severe than in the nonhyperlipidemic rats. The lovastatin administration had some favorable effect on renal function after ischemia; however, this effect was not additive to the high dietary cholesterol administration. Our results seems to favor the concept that in this special form of experimental renal ischemic acute renal failure, serum cholesterol levels, elevated through diet, may have protective effects with respect to renal tubular lesions during or following the acute ischemic insult. |
| Effect of chronic glucagon administration on lipoprotein composition in normally fed, fasted and cholesterol-fed rats Guettet, C., N. Rostaqui, et al. (1991), Lipids 26(6): 451-8. Abstract: Male adult Wistar rats received daily (at 9 a.m. and 5 p.m.) 10 micrograms of zinc-protamine glucagon by subcutaneous injection for 8 days. Plasma cholesterol levels were decreased by 36% in fed rats, 33% in cholesterol-fed rats and by 55% in fasted rats. Lipoproteins were separated into 22 fractions by ultracentrifugation using a density gradient. Glucagon administration decreased the cholesterol content in all lipoproteins except low density lipoprotein (LDL1) (1.006-1.040) and very low density lipoprotein (VLDL) from cholesterol-fed rats. The main decrease (-57 to -81%) was observed in 1.050-1.100 g/mL lipoproteins (LDL2 and HDL2), which contained a large amount of apo E, while HDL3 cholesterol was not affected. Triacylglycerol levels were decreased only in chylomicrons and VLDL (-70%) of fed and cholesterol-fed rats, while plasma and lipoprotein triacylglycerol levels were not changed in fasted rats treated with glucagon. In normally fed rats glucagon administration increased by 42% the fractional catabolic rate of 125IHDL2 while the absolute catabolic rate appeared to be unchanged. Glucagon seems to be a potent hypolipidemic agent affecting mainly the apo E-rich lipoproteins. Its chronic administration limits lipoprotein accumulation which occurs upon cholesterol feeding. |
| Effect of chylomicron remnants on cholesterol metabolism in cultured rabbit hepatocytes: production of very low density lipoproteins and bile acids Novikov, D. K., V. A. Kosykh, et al. (1990), Biokhimiia 55(10): 1902-10. Abstract: Primary cultures of rabbit hepatocytes were used to investigate the effect of purified (B-100 free) chylomicron remnants (CR) on lipid and bile acid metabolism. ApoB-100-containing lipoproteins were removed from the CR-enriched plasma fraction by affinity column chromatography on Sepharose 4B conjugated with anti-apoB-100 monoclonal antibodies. CR were shown to stimulate the accumulation of neutral lipids in hepatocytes in a dose-response manner. After 24-hour preincubation of rabbit hepatocytes with 50 micrograms protein/ml CR the cellular neutral lipid content increased: 1.9-4-fold for triglycerides, 1.5-3.7-fold for free cholesterol and 1.5-2.5-fold for esterified cholesterol. This accumulation was accompanied by a decreasing incorporation of 14C acetate into cholesterol (80-90%) and triglycerides (70-80%). At the same time the incorporation of 14oleate into triglycerides increased by 50-65%. The inhibited biosynthesis of fatty acids might account for this effect. No effect of CR on cholesterol esterification by 14Coleate was observed. CR increased the amount of triglycerides and free cholesterol secreted in very low density lipoproteins (VLDL). The secretion of taurocholic acid was decreased. These data confirm our hypothesis that dietary cholesterol is preferentially secreted by hepatocytes within VLDL but is not accumulated as cholesterol esters or oxidized to bile acids. |
| Effect of chylomicron remnants on cholesterol metabolism in cultured rabbit hepatocytes: very low density lipoprotein and bile acid production Kosykh, V. A., D. K. Novikov, et al. (1991), Lipids 26(10): 799-805. Abstract: The interrelationship between very low density lipoprotein (VLDL) secretion and bile acid production was studied in primary culture of rabbit hepatocytes. Chylomicron remnants (CR) were added to the cultures to study their effect on VLDL secretion and bile acid production. After 24 hr preincubation of cells with CR (10-50 micrograms protein/mL), intercellular neutral lipid content was increased 1.5-4-fold in a dose-dependent manner. Neutral lipid accumulation was accompanied by a 70-90% reduction of 14Cacetate incorporation into cholesterol, while no stimulation of 14Coleate incorporation into cholesteryl esters was observed. Incubation of cells with CR increased secretion of free cholesterol, triacylglycerol and apoproteins B and E in VLDL. Stimulation of VLDL cholesterol secretion was accompanied by a reduction of taurocholic acid synthesis. These data demonstrate the existence of an inverse relationship between secretion of VLDL cholesterol and bile acid production under conditions of effective uptake of triacylglycerol-rich CR by hepatocytes. |
| Effect of clentiazem on lipid profile, lipoprotein composition and aortic fatty streaks in cholesterol-fed rabbits Levy, E., J. Tardif, et al. (1991), Atherosclerosis 90(2-3): 141-8. Abstract: Numerous experimental studies have reported that common antihypertensive drugs such as diuretics, beta-blockers, and methyldopa have adverse effects on plasma lipids and lipoproteins. The present study was designed to define the effect of clentiazem (10 mg/kg/day) an antihypertensive drug, on hyperlipidemia in rabbits on a cholesterol-rich diet (1%) for 12 weeks. Compared with controls, clentiazem treated rabbits had lower plasma concentrations of triglycerides (55%), total cholesterol (24%), free cholesterol (27%), esterified cholesterol (23%) and phospholipids (24%). The decrease in cholesterol was accounted for by a reduction of VLDL-cholesterol (13%), IDL-cholesterol (24%) and primarily LDL-cholesterol (45%). Neither HDL-cholesterol nor chemical composition of VLDL, IDL, LDL and HDL was altered. When the aortic atherosclerotic involvement was evaluated by computerized planimetry, a 24% reduction of lesions was noted in clentiazem treated animals (P less than 0.05). Similarly, cholesterol content extracted from aortic wall was decreased. Our data therefore demonstrated that clentiazem is a potential antiatherosclerotic agent capable of decreasing plasma lipids and atherogenic lipoproteins as well as aortic fatty streaks. |
| Effect of coffee lipids (cafestol and kahweol) on regulation of cholesterol metabolism in HepG2 cells Rustan, A. C., B. Halvorsen, et al. (1997), Arterioscler Thromb Vasc Biol 17(10): 2140-9. Abstract: We studied the effect of the coffee diterpene alcohols, cafestol and kahweol, on cholesterol metabolism in HepG2 cells. Uptake of 125I-tyramine cellobiose-labeled LDL was decreased by 15% to 20% (P <.05) after 18 hours of preincubation with cafestol (20 micrograms/mL), whereas 25-hydroxycholesterol reduced uptake by 55% to 65% (P <.05). Degradation of LDL in the presence of cafestol was decreased by 20% to 30% (P <.05) under the same conditions. The effect of cafestol (20 micrograms/mL) on uptake and degradation of LDL was greatest (35% to 40%, P <.05) after 6 and 10 hours of preincubation, respectively. Furthermore, the effect of cafestol was also dependent on its concentration, and a significant decrease in the LDL uptake (19%) was observed at 10 micrograms/mL (P <.05). Specific binding of LDL was reduced by 17% (P <.05) and 60% (P <.05) after preincubation with cafestol (20 micrograms/mL) and 25-hydroxycholesterol (5 micrograms/mL) for 6 hours, respectively, compared with control cells. Analysis of LDL binding showed that cafestol reduced the number of binding sites for LDL on the cell surface (capacity) by 35% (P <.05). In contrast, no significant effect on the level of mRNA for the LDL receptor was observed after incubation with cafestol, whereas 25-hydroxycholesterol reduced the mRNA level for the LDL receptor by 40% to 50% (P <.05). A fusion gene construct consisting of a synthetic sterol regulatory element-1 (SRE-1) promoter for the human LDL receptor coupled to the reporter gene for chloramphenicol acetyltransferase (CAT) was transfected into HepG2 cells. No change was observed in CAT activity in SRE-1-transfected cells after incubation with cafestol, whereas 25-hydroxycholesterol reduced CAT activity by 30% to 40% (P <.05). Incorporation of 14Cacetate into unesterified cholesterol and 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activity were unaffected in cells incubated with cafestol as well as the cafestol-kahweol mixture compared with control cells. Moreover, cafestol and the cafestol-kahweol mixture did not promote increased incorporation of radiolabeled 14Coleic acid into cholesteryl esters after short-term incubation compared with control cells. On the other hand, 25-hydroxycholesterol caused a 70% to 90% reduction of cholesterol synthesis (P <.05) and HMG-CoA reductase activity (P <.05), decreased HMG-CoA reductase mRNA level by 70% to 80% (P <.05), and promoted a twofold increase in cholesterol esterification (P <.05). Finally, no effect of the coffee diterpenes on bile acid formation was observed. These results suggest that cafestol (and kahweol) may reduce the activity of hepatic LDL receptors and thereby cause extracellular accumulation of LDL. |