| For medical practitioners and the general public - Cholesterol Journal Article Catalog. |
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| Time dependent changes of arterial distensibility induced by cholesterol and balloon injury in rabbits: an in vivo intravascular ultrasound study Ribbing, M., A. Dorszewski, et al. (2002), Int J Cardiovasc Imaging 18(6): 405-13. Abstract: The aim of this study was to validate in vivo measurement of intravascular ultrasound (IVUS) for the analysis of structural and functional vessel wall alterations in a chronic animal model. Furthermore, the relation between functional and structural alteration of the vessel wall should be investigated. Fifteen cholesterol-fed rabbits (1%) and 15 control rabbits underwent balloon injury of the abdominal aorta. Immediately before and after balloon traumatization as well as 2 and 6 weeks later IVUS depiction of 10 aortal vessel segments was performed (n = 1,100 measurements). In vivo IVUS measurements and morphometric analysis of the neointimal area of same aortal segments showed a high correlation (n = 148, r = 0.844, p < 0.001). Plaque area determined by morphometry revealed larger areas than the evaluation by IVUS (0.162 +/- 0.138 vs. 0.130 +/- 0.126 mm2, p < 0.001). Before balloon traumatization, pulsatility of the aortal vessel segments was less in cholesterol-fed rabbits (0.067 vs. 0.090, p < 0.01) and neointimal index higher (0.003 vs. 0). Investigation using IVUS 2 and 6 weeks after balloon traumatization demonstrated a continuous loss of arterial distensibility and an increase of neointimal index, being more pronounced in the cholesterol-fed group. As demonstrated by IVUS the loss of distensibility preceded the atherosclerotic alterations. Our investigation suggests using IVUS in this animal model is a reliable setting for long-term investigation of characteristics of the vessel wall. We could demonstrate that altered function of the vessel wall precedes the structural atherosclerotic vessel wall alterations. |
| Time response of cholesterol synthesis inhibition by compactin-related compounds. In vitro quantitation of the "escape phenomenon" Sviridov, D. D., A. Endo, et al. (1993), Lipids 28(6): 569-71. Abstract: The time course of the inhibition of cholesterol synthesis by low and high doses of mevinolin and monacolin X were studied in normal human skin fibroblasts, fibroblasts without low density lipoprotein receptor and HepG2 hepatoma cells. Low doses of the inhibitors (0.2 ng/mL) caused a sharp decrease in the rate of cholesterol synthesis during the first 2-3 h, which gradually increased to about 40% during the next 6 h. Further incubation led to a decrease or stabilization of the cholesterol synthesis rate. High doses of the drugs (100 mg/mL) strongly inhibited cholesterol synthesis during the first 2-3 h, followed by a moderate increase during the next 20 h. No drug or tissue selectivity was observed. |
| Time trends in serum cholesterol before cancer death Sharp, S. J. and S. J. Pocock (1997), Epidemiology 8(2): 132-6. Abstract: Following evidence of an association between low serum cholesterol and cancer from several prospective studies, this paper concentrates on individual time trends in serial measurements of serum cholesterol before a cancer-related death. The Framingham Heart Study contains repeated measurements of cholesterol at approximately 2-year intervals in 5,209 subjects, of whom 539 died from cancer during 30 years of follow-up. We quantify (1) the change in serum total cholesterol level before cancer death, and (2) the association between fall in serum total cholesterol and odds of cancer death. The mean fall in serum total cholesterol in the 4- to 6-year period before cancer death is 8.06 (95% confidence interval = 4.58-11.54) mg per dl, with some evidence of lowered cholesterol before that period. This pattern is corroborated by evidence of a substantially increased odds of cancer death if a large fall in cholesterol occurs over any 4- to 6-year period. We suggest that these time trends can plausibly be attributed to the effects of prevalent cancer on lowering serum cholesterol; our findings add weight to the argument that the low cholesterol-cancer mortality relation does not arise because of any causal contribution of low serum total cholesterol to the risk of cancer. |
| Time trends in the use of cholesterol-lowering agents in older adults: the Cardiovascular Health Study Lemaitre, R. N., C. D. Furberg, et al. (1998), Arch Intern Med 158(16): 1761-8. Abstract: OBJECTIVES: To describe recent temporal patterns of cholesterol-lowering medication use and the characteristics that may have influenced the initiation of cholesterol-lowering therapy among those aged 65 years or older. SUBJECTS AND METHODS: A cohort of 5201 adults 65 years or older were examined annually between June 1989 and May 1996. We added 687 African American adults to the cohort in 1992-1993. We measured blood lipid levels at baseline and for the original cohort in the third year of follow-up. We assessed the use of cholesterol-lowering drugs at each visit. RESULTS: The prevalence of cholesterol-lowering drug use in 1989-1990 was 4.5% among the men and 5.9% among the women; these figures increased over the next 6 years to 8.1% and 10.0%, respectively, in 1995-1996. There was a 4-fold increase in the use of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors during the 6 years of follow-up, from 1.9% of all participants in 1989-1990 to 7.5% in 1995-1996. The use of bile acid sequestrants, nicotinic acid, and probucol declined from initial levels of less than 1% each. Among the participants who were untreated in 1989-1990, but eligible for cholesterol-lowering therapy after a trial of dietary therapy according to the 1993 guidelines of the National Cholesterol Education Panel, less than 20% initiated drug therapy in the 6 years of follow-up, even among subjects with a history of coronary heart disease. Among participants untreated at baseline but eligible for either cholesterol-lowering therapy or dietary therapy, initiation of cholesterol-lowering drug therapy was directly associated with total cholesterol levels, hypertension, and a history of coronary heart disease, and was inversely related to age, high-density lipoprotein cholesterol levels, and difficulties with activities of daily living. Other characteristics that form the basis of the 1993 National Cholesterol Education Panel guidelines-diabetes, smoking, family history of premature coronary heart disease, and total number of risk factors-were not associated with the initiation of cholesterol-lowering drug therapy. CONCLUSIONS: Given the clinical trial evidence for benefit, those aged 65 to 75 years and with prior coronary heart disease appeared undertreated with cholesterol-lowering drug therapy. |
| Time-course of medial and intimal thickening in pig venous arterial grafts: relationship to endothelial injury and cholesterol accumulation Angelini, G. D., A. J. Bryan, et al. (1992), J Thorac Cardiovasc Surg 103(6): 1093-103. Abstract: With use of an established model of pig saphenous vein grafts in the carotid artery, the time-course of the following changes was related: (1) medial and intimal size by morphometry of transverse sections, (2) cell number by deoxyribonucleic acid concentration, (3) cell density by deoxyribonucleic acid concentration per milligram wet weight and by counting nuclei in transverse sections, (4) endothelial morphology by scanning electron microscopy, and (5) cholesterol concentration. In the first week after grafting, medial and intimal thickening occurred associated with an increase in cell number. Between 1 and 4 weeks after grafting, further rapid medial and intimal thickening occurred with no further increase in cell number but with a reduction in cell density, which suggested that cell migration, hypertrophy, and the laying down of extracellular matrix were responsible. Between 4 and 39 weeks after grafting, a slower increase in medial and intimal size occurred, associated with a parallel increase in cell number and no further change in cell density. The endothelium of grafts showed only localized abnormalities, including loss of cells and leukocyte adhesion, either 1 or 4 weeks after grafting. Cholesterol concentration was slightly elevated 1 week after grafting but returned to values similar to those in vein by 4 weeks after grafting. Distention to 600 mm Hg during surgical preparation of vein for grafting resulted in lower graft patency after either 1 or 4 weeks and caused significant medial and endothelial injury. Distention did not, however, affect changes in medial or intimal size, deoxyribonucleic acid, or cholesterol concentration caused by grafting. We conclude that three processes contribute to medial and intimal thickening, namely: (1) an initial phase of rapid smooth muscle cell proliferation, (2) smooth muscle cell migration, hypertrophy, and synthesis of extracellular matrix, and (3) a late phase of slower smooth muscle cell proliferation. The incomplete late suppression of smooth muscle cell proliferation occurs despite regeneration of a morphologically intact endothelium and in the absence of progressive cholesterol accumulation. |
| Time-dependent change in the effect of probucol in subjects with elevated cholesterol Fujimura, A., K. Ohashi, et al. (1992), Eur J Clin Pharmacol 43(3): 299-301. Abstract: A time-dependent change in the cholesterol-lowering effect of probucol has been evaluated in 20 subjects with elevated cholesterol. Probucol 500 mg was given once daily at 07.00 h (day trial) or 19.00 h (night trial) for 3 months according to a crossover design. Fasting blood samples were obtained during the control period and at the end of each treatment period. Serum concentrations of total and HDL-cholesterol were significantly decreased by both the treatments with probucol total cholesterol (mmol.l-1): control 6.58; day trial 5.41; night trial 5.10; HDL-cholesterol (mmol.l-1): control 1.35; day trial 1.06; night trial 0.96. These parameters were significantly lower in the night trial than in the day trial. The data indicate that the cholesterol-lowering effect of probucol varies with its time of administration in subjects with elevated cholesterol. |
| Time-dependent changes in biochemical bone markers and serum cholesterol in ovariectomized rats: effects of raloxifene HCl, tamoxifen, estrogen, and alendronate Frolik, C. A., H. U. Bryant, et al. (1996), Bone 18(6): 621-7. Abstract: Bone loss associated with postmenopausal osteoporosis can be reduced by treatment with antiresorptive agents such as estrogen or bisphosphonates. Whereas bisphosphonates primarily affect bone loss, estrogens have an advantage of also lowering serum cholesterol levels, although they have a detrimental effect in the uterus. Recently, raloxifene HCl, a selective estrogen receptor modulator (SERM), has been shown to decrease both bone loss and cholesterol levels without the negative uterine effects. These antiresorptive agents reduce bone turnover, which can be evaluated by measuring bone turnover markers. To compare the effects of estrogen, two SERMs (raloxifene HCl and tamoxifen), and alendronate, a bisphosphonate that inhibits bone loss by an estrogen-independent pathway, on metabolic bone markers and cholesterol levels, rats were ovariectomized 2 weeks prior to 3 weeks of daily oral treatment with raloxifene HCl (3 mg/kg), ethynyl estradiol (0.1 mg/kg), tamoxifen (3 mg/kg), or alendronate (3 mg/kg). Raloxifene HCl, tamoxifen, and ethynyl estradiol reduced serum cholesterol to levels below control values within 4 days after initiation of treatment, whereas alendronate had no effect. After 3 weeks of treatment, serum cholesterol values in ethynyl estradiol treated animals, although still below the control value, had risen 6.4-fold; raloxifene HCl and tamoxifen values rose by only 1.4-1.5-fold. Therefore, compared with estrogen, SERMs may have a longer-term suppressive effect on serum cholesterol. At 4 days of treatment, ovariectomized rats had a 1.4-fold increase in serum osteocalcin level compared with controls. Ethynyl estradiol lowered this level within 1 week of treatment by 18%, with a more pronounced reduction of 34% at 3 weeks. In contrast, raloxifene HCl, tamoxifen, or alendronate had very little effect after the first week (6% to 13% reduction), although there was an 18% to 25% reduction by 3 weeks. Urinary pyridinoline levels, elevated 1.4-fold in the ovariectomized rat compared with controls 2 weeks after surgery, were reduced to control values after 2 weeks of treatment with raloxifene HCl, ethynyl estradiol, tamoxifen, or alendronate. These data support the concept that estrogen, raloxifene HCl, tamoxifen, and alendronate inhibit bone loss in the ovariectomized animal by reducing bone resorption. The results also indicate that for treatment of postmenopausal osteoporosis, raloxifene HCl may have an advantage over the other antiresorptives studied in having both non-uterotrophic and hypocholesterolemic effects in addition to its ability to inhibit bone resorption. |
| Time-resolved fluorescence and fourier transform infrared spectroscopic investigations of lateral packing defects and superlattice domains in compositionally uniform cholesterol/phosphatidylcholine bilayers Cannon, B., G. Heath, et al. (2003), Biophys J 84(6): 3777-91. Abstract: Time-resolved fluorescence and Fourier transform infrared spectroscopies were used to investigate the lateral organization of lipids in compositionally uniform and fully equilibrated 1-palmitoyl-2-oleoyl-phosphatidylcholine/cholesterol (POPC/CHOL) liposomes prepared by a recently devised low-temperature trapping method. Independent fluorescence decay lifetime and rotational dynamics parameters of diphenylhexatriene (DPH) chain-labeled phosphatidylcholine (DPH-PC) in these liposomes were recovered from the time-resolved fluorescence measurements as a function of cholesterol molar fraction (X(CHOL)) at 23 degrees C. The results indicate significantly greater lifetime heterogeneity, shorter average lifetime, rotational correlation time, and lower order parameter of the DPH moiety at X(CHOL) approximately 0.40 and 0.50 as compared to the adjacent cholesterol concentrations. Less prominent changes were also detected at, for example, X(CHOL) approximately 0.20 and 0.33. These X(CHOL)'s coincide with the "critical" X(CHOL)'s predicted by the previously proposed superlattice (SL) model, thus indicating that POPC and cholesterol molecules tend to form SL domains where the components tend to be regularly distributed. The data also support another prediction of the SL model, namely that lateral packing defects coexist with the ordered SL domains. It appears that unfavorable interaction of the DPH-moiety of DPH-PC with cholesterol results in a preferential partition of DPH-PC to the defect regions. Fourier transform infrared analysis of the native lipid O=P=O, C=O, and C-H vibrational bands of POPC/CHOL liposomes in the absence of DPH-PC revealed an increase in the conformational order of the acyl chains and a decrease in the conformational order (or increased hydration) of the interfacial and headgroup regions at or close to the predicted critical X(CHOL)'s. This provides additional but probe-independent evidence for SL domain formations in the POPC/CHOL bilayers. We propose that the defect regions surrounding the putative SL domains could play an important role in modulating the activity of various membrane-associated enzymes, e.g., those regulating the lipid compositions of cell membranes. |
| Tissue distribution of alpha-tocopherol following dietary supplementation in the rat: effects of concomitant cholesterol feeding Konneh, M. K., C. Rutherford, et al. (1995), Proc Soc Exp Biol Med 210(2): 156-61. Abstract: Vitamin E is a potent, naturally occurring, lipid-soluble antioxidant, which is reported to be protective against several disease processes, including coronary atherosclerosis. We have measured the alpha-tocopherol content of the aorta, liver, skeletal muscle, and kidney of rats fed one of the following diets for 10 weeks: a normal control chow diet (i); or the same diet containing 1% cholesterol (ii); 0.5% vitamin E (iii); or 1% cholesterol plus 0.5% vitamin E (iv). The alpha-tocopherol content of serum and tissue extracts was measured by HPLC using gamma-tocopherol as an internal standard. Tissue and serum cholesterol content was measured using a cholesterol oxidase enzyme reagent kit. In all animals receiving the 1% cholesterol diet, serum cholesterol levels increased significantly (P < 0.005). By the 10th week, mean serum alpha-tocopherol levels rose significantly in both groups of animals receiving dietary vitamin E supplements (P < 0.0001) compared with their respective control group. This was accompanied by a significant increase in the absolute alpha-tocopherol content of liver (8- to 9-fold) and aorta (3- to 4-fold). The alpha-tocopherol content of renal and skeletal muscle tissue was raised 1- to 2-fold in both groups of rats on vitamin E supplements, however the increased attained significance only for the renal tissue. The aortic tissue alpha-tocopherol/cholesterol ratio was 4-fold higher in the rats receiving concomitant 1% cholesterol plus 0.5% vitamin E compared with animals receiving 1% cholesterol alone (P < 0.02), and was 5-fold higher in the rats receiving 0.5% vitamin E compared with those receiving control chow (P < 0.01). These data suggest that dietary vitamin E supplementation results in a differential uptake of alpha-tocopherol, which may be dependent, in part, on selective lipoprotein particle accumulation. |
| Tissue expression studies on the mouse acyl-CoA: cholesterol acyltransferase gene (Acact): findings supporting the existence of multiple cholesterol esterification enzymes in mice Meiner, V., C. Tam, et al. (1997), J Lipid Res 38(9): 1928-33. Abstract: Cholesterol esterification is involved in the regulation of cellular cholesterol content and has been hypothesized to play a role in important physiologic processes including intestinal cholesterol absorption, hepatic lipoprotein production, and macrophage foam cell formation in atherosclerotic lesions. Although initial studies of the mouse acyl CoA:cholesterol acyltransferase gene (Acact) suggested that its gene product was responsible for cholesterol esterification in most tissues, we observed recently that Acact-/- mice have only tissue-specific reductions in cholesterol esterification. To better understand the role of Acact in cholesterol esterification, we used in situ hybridization and immunoblotting to perform tissue expression studies in wild-type mice. We found high levels of Acact expression in steroidogenic tissues, sebaceous glands, and atherosclerotic lesions, but not in the liver or the small intestine. These data support the hypothesis that multiple cholesterol esterification enzymes exist in mammals and that another enzyme is likely to be responsible for cholesterol esterification activity in mouse liver and intestine. |
| Tissue factor pathway inhibitor is expressed by human monocyte-derived macrophages: relationship to tissue factor induction by cholesterol and oxidized LDL Petit, L., P. Lesnik, et al. (1999), Arterioscler Thromb Vasc Biol 19(2): 309-15. Abstract: Lipid-laden macrophages express tissue factor (TF), which may activate the extrinsic coagulation pathway on rupture of the atherosclerotic plaque. Tissue factor pathway inhibitor (TFPI) is a major regulator of TF-induced coagulation. We evaluated the possibility that monocyte-derived macrophages express this protein, thereby contributing to regulation of TF activity (TFact). Equally, we investigated the effect of cholesterol and of oxidized LDL (Ox-LDL) on the expression of TFPI and TF by human monocyte-derived macrophages (HMDMs). Northern blot analysis of TFPI mRNA from cultured HMDMs revealed a single band at 4.2 kb with weak intensity; this finding was confirmed by reverse transcription-polymerase chain reaction. Gel filtration of HMDM supernatants showed the presence of an active 100-kDa form of TFPI, which was confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under nonreducing conditions; under reducing conditions, however, the immunoblot revealed a 40-kDa form of TFPI. The TFPI in HMDM supernatants possessed heparin-binding affinity, suggesting potential interaction of TFPI with heparan sulfate proteoglycans. Stimulation of foam cell formation by incubation of macrophages for 48 hours with exogenous free cholesterol indicated that neither the biological activity nor the de novo synthesis of TFPI protein was affected. In contrast, cholesterol loading with exogenous free cholesterol induced significant upregulation of total TFact (2.6-fold: 25.0 versus 9.4 mU/mg cell protein, cholesterol-treated versus control cells; P<0. 05); such induction was not correlated with an elevation in TF antigen (8.5 versus 7.8 ng/mg cell protein, cholesterol-treated versus control cells). Similarly, cholesterol-rich Ox-LDL induced an increase in TFact (1.9-fold: 18.9 versus 10.0 mU/mg cell protein, Ox-LDL-treated versus control cells; P<0.05); by contrast, the amount of TF antigen remained unchanged (7.1 versus 7.9 ng/mg cell protein, Ox-LDL-treated versus control cells). Our data indicate that enhancement of the procoagulant activity of TF in macrophage-derived foam cells is not counterbalanced by upregulation of TFPI activity, suggesting that lesion foam cells are in a procoagulant state; they may therefore contribute to thrombus generation on plaque rupture. |
| Tissue-selective inhibition of cholesterol synthesis in vivo by pravastatin sodium, a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor Koga, T., Y. Shimada, et al. (1990), Biochim Biophys Acta 1045(2): 115-20. Abstract: Tissue selectivity of pravastatin sodium (pravastatin) in inhibition of cholesterol synthesis was investigated and its effect was compared with other 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, such as lovastatin, simvastatin and ML-236B. Inhibition of cholesterol synthesis in vivo was measured by incorporation of radioactivity into the sterol fraction 1 h after intraperitoneal injection of 14Cacetate to mice. The drugs were orally administered to mice 2 h before the acetate injection. When pravastatin at a dose of 20 mg/kg was administered to mice, about 90% inhibition of cholesterol synthesis was observed in liver and ileum, but the inhibition was less than 14% in kidney, spleen, adrenal, testis, prostate and brain. This tissue selectivity of pravastatin was also demonstrated even in varying doses (5-100 mg/kg) and time (75-180 min) after drug administration. Other 3-hydroxyl-3-methylglutaryl coenzyme A reductase inhibitors did not show such a tissue-selective inhibition of sterol synthesis under the same conditions. These results obtained with the in vivo study were confirmed in vitro by the inhibition of sterol synthesis in various cultured cells and rats lenses, as well as by cellular uptake of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors. |
| Tissue-specific coordinate regulation of enzymes of cholesterol biosynthesis: sciatic nerve versus liver Toews, A. D., H. Jurevics, et al. (1996), J Lipid Res 37(12): 2502-9. Abstract: Exposure of weanling rats to a diet containing the element tellurium results in specific inhibition of squalene epoxidase, an obligate enzyme in cholesterol biosynthesis. Liver responds to the resulting intracellular sterol deficit by up-regulating, in parallel and to the same extent, expression of mRNA for squalene epoxidase and for HMG-CoA reductase, the major rate-limiting enzyme in the pathway. This increased mRNA expression, coupled with additional translational and posttranslational activation of the pathway allows normal levels of cholesterol synthesis in liver despite tellurium-induced inhibition of squalene epoxidase. The response to tellurium challenge in sciatic nerve is very different. In this tissue, cholesterol synthesis is prominent because of the large amount of cholesterol required for synthesis and maintenance of myelin. Although nerve shows an initial (at 1 day) up-regulation of mRNA expression for both enzymes in response to tellurium exposure, this is followed quickly by parallel down-regulation of both enzymes, in concert with down-regulation of mRNA expression for myelin proteins. We suggest that the tellurium-induced deficit in sterols leads to a coordinate down-regulation of synthesis of myelin components. The initial early up-regulation of cholesterol biosynthesis in sciatic nerve due to the cholesterol deficit is countered by down-regulation which is coordinated with overall control of the program of myelin assembly. This tissue-specific control of cholesterol synthesis in sciatic nerve is a point of vulnerability to toxicants, and may be related to the need for coordinate synthesis of all components of myelin. |
| Tissue-specific expression and cholesterol regulation of acylcoenzyme A:cholesterol acyltransferase (ACAT) in mice. Molecular cloning of mouse ACAT cDNA, chromosomal localization, and regulation of ACAT in vivo and in vitro Uelmen, P. J., K. Oka, et al. (1995), J Biol Chem 270(44): 26192-201. Abstract: Acyl-coenzyme A:cholesterol acyltransferase (ACAT) catalyzes the esterification of cholesterol with long chain fatty acids and is believed to play an important part in the development of atherosclerotic lesions. To facilitate the study of ACAT's role in this process, we have used the human ACAT K1 clone previously described (Chang, C. C. Y., Huh, H. Y., Cadigan, K. M. and Chang, T. Y. (1993) J. Biol. Chem. 268, 20747-20755) to isolate mouse ACAT cDNA from a liver cDNA library. The 3.7-kilobase cDNA clone isolated contains a 1620-base pair open reading frame which encodes a protein of 540 amino acids. The predicted mouse ACAT protein is 87% identical to the protein product of human ACAT K1 and shares many of the same secondary structural features, including two transmembrane domains, a leucine heptad motif consistent with dimer or multimer formation, and five regions homologous to the "signature sequences" found in other enzymes that catalyze acyl adenylation followed by acyl thioester formation and acyl transfer. Using the cDNA as a hybridization probe, we mapped the gene encoding mouse ACAT to chromosome 1 in a region syntenic to human chromosome 1 where the ACAT gene is located. Northern blot analysis and RNase protection assays of mouse tissues revealed that ACAT mRNA is expressed most highly in the adrenal gland, ovary, and preputial gland and is least abundant in skeletal muscle, adipose tissue, heart, and brain. To study the dietary regulation of ACAT mRNA expression in mouse tissues, we fed C57BL/6J mice a high-fat, high-cholesterol (HF/HC) atherogenic diet for 3 weeks and measured ACAT mRNA levels in various tissues by RNase protection. The HF/HC diet had little effect on ACAT mRNA levels in the small intestine, aorta, adrenal, or peritoneal macrophages, whereas hepatic ACAT mRNA levels were doubled in mice fed the atherogenic diet. ACAT activity in liver microsomes was similarly increased in cholesterol-fed mice, suggesting that mouse ACAT is regulated at least in part at the level of mRNA abundance. Additionally, a significant positive correlation was observed between ACAT activity and microsomal free cholesterol levels in chow- and cholesterol-fed mice, supporting the concept of cholesterol availability as a regulator of ACAT. To further investigate the regulation of ACAT activity under controlled conditions, ACAT-deficient Chinese hamster ovary cells were stably transfected with the mouse ACAT cDNA clone driven by a cytomegalovirus promoter. Two transfected Chinese hamster ovary cell lines that expressed the mouse ACAT transgene regained the ability to esterify cholesterol.(ABSTRACT TRUNCATED AT 250 WORDS) |
| Tissue-specific expression of the human gene for lecithin: cholesterol acyltransferase in transgenic mice alters blood lipids, lipoproteins and lipases towards a less atherogenic profile Mehlum, A., B. Staels, et al. (1995), Eur J Biochem 230(2): 567-75. Abstract: Lecithin:cholesterol acyltransferase (LCAT) is a key enzyme in the reverse cholesterol pathway but its role in lipid metabolism is still unclear. We have generated mice transgenic for a 7-kb genomic DNA fragment comprising the 6 exons and 5 introns of the LCAT gene with 1932 bp of 5' flanking and 908 bp of 3' flanking sequences. One line had integrated about 30 copies and expressed about 40-fold increased LCAT activity in a human test system. The expression showed correct tissue specificity of the human LCAT gene. Increased LCAT activity resulted in a decrease of plasma triacylglycerols below 50% of fasting controls. This reduction was seen in all lipoprotein fractions. Lipoprotein lipase activity did not change significantly, whereas hepatic triacylglycerol lipase increased markedly. Plasma total cholesterol was similar in fasting transgenic and control mice, but low-density lipoprotein and very low-density lipoprotein cholesterol were reduced to about 50%. High-density lipoprotein cholesterol increased about 20%, accompanied by a correspondingly increased size and a higher cholesterol efflux-stimulating activity of transgenic LCAT high-density lipoprotein. Both apolipoprotein A-I and A-II plasma concentrations increased in transgenic mice. Plasma triacylglycerol and cholesteryl ester fatty acid distribution showed an increased proportion of palmitic acid, whereas oleic, linoleic and arachidonic acid decreased, thus resembling more closely the human situation. Overexpression of the human LCAT gene provokes major changes in plasma lipoprotein and apolipoprotein concentrations, resulting in a less atherogenic plasma lipoprotein profile through a reduction in atherogenic and an increase in anti-atherogenic lipoproteins. |
| Tissue-specific transcriptional regulation of the cholesterol biosynthetic pathway leads to accumulation of testis meiosis-activating sterol (T-MAS) Tacer, K. F., T. B. Haugen, et al. (2002), J Lipid Res 43(1): 82-9. Abstract: Lanosterol 14alpha-demethylase (CYP51) produces follicular fluid meiosis-activating sterol (FF-MAS), which is converted further to testis meiosis-activating sterol (T-MAS). MAS are intermediates in the cholesterol biosynthetic pathway, with the ability to trigger resumption of oocyte meiosis in vitro. In contrast to the liver, where pre- and post-MAS genes are upregulated coordinately at the level of transcription by a cholesterol feedback mechanism through sterol regulatory element-binding proteins (SREBP), regulation differs in the testis. Genes encoding pre-MAS enzymes HMG-CoA synthase (SYN), HMG-CoA reductase (RED), farnesyl diphosphate synthase (FPP), squalene synthase (SS), and CYP51 are upregulated during sexual development of the testis, although not all genes are turned on at the same time. Furthermore, two post-MAS genes, C-4 sterol methyl oxidase and sterol Delta(7)-reductase, are expressed at low levels and are not upregulated either in rat or human. This transcriptional discrepancy seems to be SREBP independent. Besides cAMP/cAMP-responsive element modulator, other unknown transcription factors control expression of individual cholesterogenic genes during spermatogenesis. HPLC analysis shows an 8-fold increase in T-MAS during development of rat testis whereas MAS is barely detectable in livers of the same animals.We propose that the lack of a coordinate transcriptional control over the cholesterol biosynthetic pathway contributes importantly to overproduction of the signaling sterol T-MAS in testis. |
| TMP-153, a novel ACAT inhibitor, inhibits cholesterol absorption and lowers plasma cholesterol in rats and hamsters Sugiyama, Y., E. Ishikawa, et al. (1995), Atherosclerosis 113(1): 71-8. Abstract: Effects of TMP-153, N-4-(2-chlorophenyl)-6,7-dimethyl-3-quinolyl-N'-(2,4-difluorophe nyl)urea, on intestinal and hepatic acyl-CoA:cholesterol acyltransferase (ACAT) activities, cholesterol absorption and plasma cholesterol level in rats and hamsters were studied. TMP-153 has IC50 values of around 5-10 nM for the hepatic and intestinal ACAT from various animals. The most potent inhibition was observed in the intestinal ACAT from Golden hamsters (IC50 = 2.3 nM). The inhibition mode of TMP-153 was non-competitive for rat intestinal ACAT. TMP-153 inhibited cholesterol esterification both in human colonic adenocarcinoma cells, LS180, and in human hepatoma cells, HepG2 (IC50 = 150 nM and 330 nM, respectively). 14Ccholesterol and cold cholesterol absorption from the small intestine was markedly inhibited by oral administration of TMP-153 (1 mg/kg) without affecting lymph flow and triglyceride absorption. When the compound was given as a dietary admixture, plasma cholesterol was reduced in rats fed a cholesterol diet (ED50 = 0.25 mg/kg/day), but not in those fed a stock diet. On the other hand, TMP-153 showed more prominent hypocholesterolemic effect in Golden hamsters fed the stock diet (ED50 = 0.81 mg/kg/day) than in those fed the cholesterol diet (ED50 = 8.01 mg/kg/day). In hamsters fed the stock diet, TMP-153 markedly decreased the hepatic unesterified cholesterol in addition to esterified cholesterol content, but did not affect bile flow and the biliary secretion of bile acid and lipids. Different mechanisms for plasma cholesterol lowering by TMP-153 between rats and hamsters was discussed. |
| TMP-153, a novel ACAT inhibitor, lowers plasma cholesterol through its hepatic action in golden hamsters Sugiyama, Y., H. Odaka, et al. (1995), Atherosclerosis 118(1): 145-53. Abstract: The mechanism of the hypocholesterolemic action of N-4-(2-chlorophenyl)-6,7-dimethyl-3-quinolyl-N'-(2, 4-difluorophenyl) urea (TMP-153), a potent acyl-CoA:cholesterol acyltransferase (ACAT) inhibitor, was studies in Golden hamsters. TMP-153 (0.5-1.5 mg/kg) dose-dependently reduced plasma total- and low density lipoprotein (LDL)-cholesterol without affecting high density lipoprotein (HDL)-cholesterol. TMP-153 markedly reduced the cholesterol influx into the plasma upon intravenous injection of Triton WR-1339. The compound also decreased cholesterol absorption calculated from dietary intake, biliary secretion and the absorption co-efficient. Hepatic cholesterol secretion was calculated by substracting the cholesterol absorption from the cholesterol influx. In hamsters, the liver accounted for 92% of the cholesterol influx with the remaining 8% coming from the intestine, and both were markedly decreased by TMP-153. Thus, it is likely that TMP-153 lowers plasma cholesterol through its hepatic action. In the liver, the compound significantly reduced the unesterified cholesterol content in addition to markedly reducing the content of esterified cholesterol. In accordance with this reduction, the half-life time of 125I-LDL was significantly shortened by the compound, suggesting an increase in LDL receptors. However, the hepatic cholesterogenesis from 14Cacetate was decreased by TMP-153 treatment. This effect seems to be secondary, since the compound did not inhibit cholesterogenesis from 14Cacetate in HepG2 cells. From the data described above, the contribution of hepatic secretion and intestinal absorption of cholesterol to the plasma cholesterol level in Golden hamsters are discussed. |
| TNFRSF1B in genetic predisposition to clinical neuropathy and effect on HDL cholesterol and glycosylated hemoglobin in type 2 diabetes Benjafield, A. V., C. L. Glenn, et al. (2001), Diabetes Care 24(4): 753-7. Abstract: OBJECTIVE: Genetic variation in the tumor necrosis factor (TNF) receptor 2 gene (TNFRSF1B) has shown association with insulin resistance in type 2 diabetes, hypercholesterolemia, coronary artery disease, and essential hypertension. Here we tested the TNFRSF1B marker used in the latter studies in type 2 diabetes patients. RESEARCH DESIGN AND METHODS: A case-control study of a microsatellite marker with five alleles (CA13- CA17) in intron 4 of TNFRSF1B was performed in 357 well-characterized white patients and 183 healthy control subjects. RESULTS: The CA16 allele was associated with clinical neuropathy (frequency = 27% in 69 patients with the condition versus 16% in 230 subjects without the condition; chi2 = 9.0, P = 0.011; odds ratio = 2.1 95% CI 1.2-3.8). No association was seen with other complications or diabetes itself. The CA16 allele tracked with elevation plasma HDL cholesterol (1.3 +/- 0.2, 1.2 +/- 0.4, and 1.1 +/- 0.2 for CA16/CA16, CA16/-, and -/-, respectively; n = 9, 110, and 218, respectively; P = 0.009) and reduction in plasma glycosylated hemoglobin (6.6 +/- 0.3, 8.3 +/- 0.2, and 8.1 +/- 0.1 for CA16/CA16, CA16/-, and -/-, respectively; n = 9, 102, 205, respectively; P = 0.007) Significance remained after Bonferroni correction for multiple testing. CONCLUSIONS: Genetic variation in or near TNFRSF1B may predispose clinical neuropathy, reduced glycosylated hemoglobin, and increased HDL cholesterol in type 2 diabetes patients. The latter could be part of a protective response. |
| To compare the total cholesterol and HDL-cholesterol before and after ultra-centrifugation in lipemic samples Jabbar, J., I. Siddiqui, et al. (2005), J Pak Med Assoc 55(6): 239-42. Abstract: OBJECTIVE: It is an everyday routine in laboratories to encounter interference in the analysis of lipids. These likely interferences (hemolysis, icterus and lipemia) are countered by asking physicians and patients to send fresh and properly collected samples. At the Aga Khan University (AKU) Laboratory, we receive 2-3 lipemic/turbid samples per day. Previously it was our departmental policy to advise these patients to go for lipoprotein electrophoresis, which though accurate was time consuming and not cost effective. We therefore studied ultra centrifugation/airfuge as an alternate method to clear lipid interference and provide accurate, reliable and cost effective results. METHODS: Daily 2-3 grossly turbid samples are identified on the lipid bench, 48 samples were received in 4 months (February to May 2004). These samples were analyzed for total cholesterol (TC) and High Density Lipoprotein-Cholesterol (HDL-C) before and after ultra centrifugation/airfuge. RESULTS: There was a positive correlation between the lipemia and the false high TC and HDL-C. The mean TC and HDL-C before ultra centrifugation were 263.06 mg/dl and 39.42 mg/dl respectively and after centrifugation these became 191.77 mg/dl and 33.06 mg/dl. P value showed a significant difference in both results. CONCLUSION: This study suggests that the removal of turbidity by ultra centrifugation/airfuge is cost effective, less time consuming and provides accurate reliable results of TC and HDL-C in patients with lipemia interference. |