| For medical practitioners and the general public - Cholesterol Journal Article Catalog. |
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| Cholesterol awareness after case-finding: do patients really know their cholesterol numbers? Murdoch, M. and T. J. Wilt (1997), Am J Prev Med 13(4): 284-9. Abstract: BACKGROUND: Patients who are informed of their cholesterol status have been shown to take steps subsequently to reduce their risks for coronary heart disease. Accordingly, as part of a population-based strategy to reduce disease burden due to high cholesterol, the National Cholesterol Education Program (NCEP) recommends that physicians tell all patients their cholesterol test results in a clear, understandable manner and encourage all patients, regardless of their risk factor status, to reduce their fat intake. OBJECTIVES: Our objective was to assess compliance with these NCEP recommendations at a 432-bed, Midwestern, university-affiliated VA Medical Center. METHODS: We surveyed, within a year of their cholesterol measurement, 250 randomly selected men and women who had had their cholesterol checked by physician order between January 1993 and 1994. Survey results were validated against laboratory data. RESULTS: Approximately one third of the men and women said their cholesterol had not been checked, and about one half said they had not been told their test results. Only 59% knew their cholesterol status, and only 19% accurately recalled their cholesterol number. More than half did not remember receiving dietary advice. Female gender and more years of education were correlated with cholesterol awareness on both bivariable and multivariable analyses (adjusted odds ratio OR = 2.00, 95% confidence intervals CI = 1.10, 3.67 and OR = 2.62, 95% CI = 1.43, 4.78, respectively). Respondents were more likely to accurately recall their cholesterol number if they remembered being told their test results or remembered receiving dietary advice (OR = 7.70, 95% CI = 2.04, 29.0 and OR = 2.65, 95% CI = 1.15, 6.07, respectively). CONCLUSIONS: We conclude that compliance with the NCEP population-based guidelines is poor. Physicians should endeavor to improve patients' awareness of their cholesterol status and be more diligent in prescribing dietary therapy. |
| Cholesterol awareness and treatment in patients with coronary artery disease participating in cardiac rehabilitation Bairey Merz, C. N., M. N. Felando, et al. (1996), J Cardiopulm Rehabil 16(2): 117-22. Abstract: OBJECTIVES: To survey cholesterol management practices among patients with coronary artery disease enrolled and not enrolled in cardiac rehabilitation. BACKGROUND: The National Cholesterol Education Program (NCEP) initially established guidelines regarding cholesterol awareness and treatment in 1987. Serum cholesterol reduction is most effective for reducing cardiac events in patients with established coronary artery disease, yet surveys of cholesterol awareness and treatment have not included these patients. METHODS: Three hundred seventy-nine men and women with coronary artery disease were surveyed according to cholesterol awareness, serum cholesterol level, frequency of lipid-lowering medication use, and frequency of achievement of a serum total cholesterol < 5.2 mmol/L (200 mg/dL) corresponding the 1987 NCEP guidelines for coronary artery disease patients, which were in place at the time of the study survey. RESULTS: Overall, 72% of the patients were aware of their cholesterol level, with an average serum total cholesterol of 5 5 +/- 1.0 mmol/L (213 +/- 39 mg/dL). Use of lipid-lowering medication was 26%. Forty-three percent had a total cholesterol < 5.2 mmol/L (200 mg/dL). Patients enrolled in a long-term cardiac rehabilitation program demonstrated enhanced cholesterol awareness (78%), lower total cholesterol values (5.2 +/- 0.9 mmol/L 203 +/- 36 mg/dL), higher use of lipid-lowering the therapy (34%), and more frequent achievement of total serum cholesterol of < 5.2 mmol/L (200 mg/dL) (48%) compared to the other patient groups (all P <.05). CONCLUSIONS: Patients with coronary artery disease demonstrate relatively low rates of cholesterol awareness, lipid-lowering medication use, and achievement of total serum cholesterol < 5.2 mmol/L (200 mg/dL) corresponding to the 1987 NCEP guidelines. Participation in long-term cardiac rehabilitation is associated with enhancement of these rates. Further efforts to educate physicians and develop programs to optimize cholesterol management in patients with coronary artery disease are needed. |
| Cholesterol awareness--key to preventing coronary artery disease Witztum, J. L. (1993), West J Med 158(4): 423-4. |
| Cholesterol balance and metabolism in mice with loss of function of Niemann-Pick C protein Xie, C., S. D. Turley, et al. (1999), Am J Physiol 276(2 Pt 1): E336-44. Abstract: Type C Niemann-Pick disease is due to a mutation in Niemann-Pick C (NPC) protein, a putative determinant of intracellular cholesterol transport. This study quantifies cholesterol balance in vivo across all tissues in mice with this defect. Cholesterol balance in the heterozygous animal is normal, but in the homozygous mouse the whole animal cholesterol pool expands continuously from birth, reaching 5, 442 mg/kg at 7 wk. The size of this pool in each organ is proportional to the rate at which each tissue clears low-density lipoprotein-cholesterol. Despite this expansion, however, cholesterol synthesis is increased so that whole animal synthesis equals 180 mg. day-1. kg-1. Forcing additional cholesterol into the liver through the clathrin-coated pit pathway increases the hepatic cholesterol pool in control mice, all of which is esterified, while there is a much greater increase in this pool in mutant mice, all of which is unesterified. These findings are consistent with the view that there is a block in sterol movement from the lysosome to the sites of regulation in NPC disease and have important implications for understanding the function of the NPC protein in intracellular cholesterol metabolism, in general, and in the brain, in particular. |
| Cholesterol based antineoplastic strategies Lenz, M., W. P. Miehe, et al. (1997), Anticancer Res 17(2A): 1143-6. Abstract: Manipulation of cholesterol metabolism open several possibilities of interfering with the growth of malignant cells. Deprivation of cholesterol decreases the velocity of growth and alters the composition of the cell membrane. The high requirement for LDL of malignant cells can be utilized for drug targeting. Proliferation assays were performed with neuroblastoma cells and cell lines of acute myeloid leukemia deprived of cholesterol by inhibition of HMG-CoA-reductase or culture in LDL-deficient medium. The cholesterol content of the cell membrane when reduced to 50% had no effect on the toxicity of LAK-cells but the toxicity of the fluorescent dye merocyanine MC 540 was enhanced two-fold. LDL-mediated drug targeting to AML cells was performed with oxidized LDL and showed toxic reactions. These results proved that cholesterol deprivation could be used to support some therapeutic approaches. |
| Cholesterol bile duct stones with no stones in the gallbladder Garg, P. K., U. Venkatachalam, et al. (1995), J Clin Gastroenterol 20(4): 296-9. Abstract: Common bile duct stones are usually associated with stones in the gallbladder. During the period 1989-1991, however, we encountered 17 patients with common bile duct (CBD) stones without gallbladder stones who had presented with obstructive jaundice and cholangitis. Their ages ranged between 30 and 72 years; 10 were female and seven male. Five of them had a deceptive presentation and were initially misdiagnosed as having a malignant lesion. It was endoscopic retrograde cholangiopancreatography that correctly diagnosed the presence of CBD stones in all 17 patients. Therapeutic sphincterotomy led to subsidence of cholangitis in 16 patients and retrieval of stones in 13 of them. Three patients required nasobiliary decompression because stones could not be retrieved. One patient required emergency surgery due to flare-up of cholangitis. Cholesterol concentration of the retrieved stones was 70-92% of the dry weight. Thus, these 17 patients formed a distinct subgroup who had cholesterol CBD stones with stoneless gallbladder, and five of these 17 patients had presentations mimicking malignant lesions. |
| Cholesterol biliary lithiasis (risk factors) Mendez-Sanchez, N., J. Jessurun, et al. (1991), Rev Gastroenterol Mex 56(3): 125-30. Abstract: The prevalence of gallstone disease in the world is heterogenous, it exist a wide range between different geographic areas, sex and age groups. Its distribution seems to be influenced by various factors such as age, sex, socieconomic class, genetic and ethnic influences and diseases like diabetes mellitus and obesity. Therefore, in this study, we will analyse the importance of each of those factors in the development of cholesterol gallstone disease. |
| Cholesterol binding at the cholesterol recognition/ interaction amino acid consensus (CRAC) of the peripheral-type benzodiazepine receptor and inhibition of steroidogenesis by an HIV TAT-CRAC peptide Li, H., Z. Yao, et al. (2001), Proc Natl Acad Sci U S A 98(3): 1267-72. Abstract: We previously defined a cholesterol recognition/interaction amino acid consensus (CRAC; ATVLNYYVWRDNS) in the carboxyl terminus of the peripheral-type benzodiazepine receptor (PBR), an outer mitochondrial membrane protein involved in the regulation of cholesterol transport into the mitochondria, the rate-determining step in steroid biosynthesis. We examined (i) the PBR-cholesterol interaction by UV crosslinking of the C17 side-chain containing progestin, promegestone, and (ii) the role of the CRAC domain of PBR in Leydig cell steroidogenesis by using a transducible peptide composed of the TAT domain of HIV and the CRAC domain of PBR. (3)HPromegestone photoincorporated into recombinant PBR, and this labeling was displaced by cholesterol. (3)HPromegestone also photoincorporated into the TAT-CRAC peptide. (3)HPromegestone crosslinking to TAT-CRAC could be displaced by cholesterol and promegestone, with IC50 values of 1 and 200 microM, respectively. TAT-CRAC efficiently transduced into MA-10 Leydig cells and inhibited the hCG- and cAMP-stimulated steroid production in a dose-dependent manner. TAT-CRAC did not affect the hCG-induced cAMP synthesis and the 22R-hydroxycholesterol-supported steroidogenesis. Mutated TAT-CRAC lost its ability to bind (3)Hpromegestone and to inhibit the hCG-stimulated steroidogenesis. These results show that TAT-CRAC binds cholesterol and competes for cholesterol interaction with endogenous PBR, suggesting that the cytosolic carboxyl-terminal domain of PBR is responsible for taking up and bringing steroidogenic cholesterol into the mitochondria. |
| Cholesterol binding by the bacterial type III translocon is essential for virulence effector delivery into mammalian cells Hayward, R. D., R. J. Cain, et al. (2005), Mol Microbiol 56(3): 590-603. Abstract: A ubiquitous early step in infection of man and animals by enteric bacterial pathogens like Salmonella, Shigella and enteropathogenic Escherichia coli (EPEC) is the translocation of virulence effector proteins into mammalian cells via specialized type III secretion systems (TTSSs). Translocated effectors subvert the host cytoskeleton and stimulate signalling to promote bacterial internalization or survival. Target cell plasma membrane cholesterol is central to pathogen-host cross-talk, but the precise nature of its critical contribution remains unknown. Using in vitro cholesterol-binding assays, we demonstrate that Salmonella (SipB) and Shigella (IpaB) TTSS translocon components bind cholesterol with high affinity. Direct visualization of cell-associated fluorescently labelled SipB and parallel immunogold transmission electron microscopy revealed that cholesterol levels limit both the amount and distribution of plasma membrane-integrated translocon. Correspondingly, cholesterol depletion blocked effector translocation into cultured mammalian cells by not only the related Salmonella and Shigella TTSSs, but also the more divergent EPEC system. The data reveal that cholesterol-dependent association of the bacterial TTSS translocon with the target cell plasma membrane is essential for translocon activation and effector delivery into mammalian cells. |
| Cholesterol binding of Helicobacter pylori Ansorg, R., K. D. Muller, et al. (1992), Zentralbl Bakteriol 276(3): 323-9. Abstract: H. pylori cells grown on cholesterol-free medium adsorb cholesterol from serum, egg yolk, and VDRL reagent. The binding of cholesterol does not influence the hydrophobicity of the cells. The haemagglutinating activity is slightly diminished. The cell-bound haemolytic activity is completely inhibited. The affinity of H. pylori for cholesterol probably acts as factor of chemotaxis and adherence. |
| Cholesterol binding to cytochrome P450 7A1, a key enzyme in bile acid biosynthesis Mast, N., S. E. Graham, et al. (2005), Biochemistry 44(9): 3259-71. Abstract: The conversion of cholesterol to 7alpha-hydroxycholesterol catalyzed by cytochrome P450 7A1 (CYP7A1) initiates the major pathway for cholesterol elimination in mammals. In the present work we focused on identification of determinants of the CYP7A1 substrate specificity inside the active site using a homology model with a novel P450-fold, site-directed mutagenesis, and substrate-binding and kinetic studies. Forty-one mutants, encompassing twenty-six amino acid residues, were generated and characterized, and of these, seven residues appear to determine cholesterol binding in the active site. In addition, four cholesterol derivatives were used as active site probes in the wild type and the seven mutant enzymes, and the spectral binding constants and products were analyzed. It was concluded that Asn288 in the I helix plays a key role in the P450-cholesterol contacts by hydrogen bonding to the steroid 3beta-hydroxyl, while Val280 and Ala284 are beside and the Trp283 is above the steroid nucleus orienting the cholesterol molecule. Leu360 and Ala358 between the K helix and the beta1-4 strand and Leu485 in the beta4 sheet-turn appear to define the size of the active site over the heme pyrrole ring A, thus limiting the orientation and size of the substrate at the steroid A ring. Additionally, the A358V mutant was found to form two new products, one being 7beta-hydroxycholesterol. Our data indicate that a tight fit of cholesterol in the enzyme active site is in part responsible for the high efficiency of cholesterol turnover by CYP7A1. |
| Cholesterol binding, efflux, and a PDZ-interacting domain of scavenger receptor-BI mediate HDL-initiated signaling Assanasen, C., C. Mineo, et al. (2005), J Clin Invest 115(4): 969-77. Abstract: The binding of HDL to scavenger receptor-BI (SR-BI) mediates cholesterol movement. HDL also induces multiple cellular signals, which in endothelium occur through SR-BI and converge to activate eNOS. To determine the molecular basis of a signaling event induced by HDL, we examined the proximal mechanisms in HDL activation of eNOS. In endothelial cells, HDL and methyl-beta-cyclodextrin caused comparable eNOS activation, whereas cholesterol-loaded methyl-beta-cyclodextrin had no effect. Phosphatidylcholine-loaded HDL caused greater stimulation than native HDL, and blocking antibody against SR-BI, which prevents cholesterol efflux, prevented eNOS activation. In a reconstitution model in COS-M6 cells, wild-type SR-BI mediated eNOS activation by both HDL and small unilamellar vesicles (SUVs), whereas the SR-BI mutant AVI, which is incapable of efflux to SUV, transmitted signal by only HDL. In addition, eNOS activation by methyl-beta-cyclodextrin was SR-BI dependent. Studies of mutant and chimeric class B scavenger receptors revealed that the C-terminal cytoplasmic PDZ-interacting domain and the C-terminal transmembrane domains of SR-BI are both necessary for HDL signaling. Furthermore, we demonstrated direct binding of cholesterol to the C-terminal transmembrane domain using a photoactivated derivative of cholesterol. Thus, HDL signaling requires cholesterol binding and efflux and C-terminal domains of SR-BI, and SR-BI serves as a cholesterol sensor on the plasma membrane. |
| Cholesterol binds to synaptophysin and is required for biogenesis of synaptic vesicles Thiele, C., M. J. Hannah, et al. (2000), Nat Cell Biol 2(1): 42-9. Abstract: Here, to study lipid-protein interactions that contribute to the biogenesis of regulated secretory vesicles, we have developed new approaches by which to label proteins in vivo, using photoactivatable cholesterol and glycerophospholipids. We identify synaptophysin as a major specifically cholesterol-binding protein in PC12 cells and brain synaptic vesicles. Limited cholesterol depletion, which has little effect on total endocytic activity, blocks the biogenesis of synaptic-like microvesicles (SLMVs) from the plasma membrane. We propose that specific interactions between cholesterol and SLMV membrane proteins, such as synaptophysin, contribute to both the segregation of SLMV membrane constituents from plasma-membrane constituents, and the induction of synaptic-vesicle curvature. |
| Cholesterol biosensors prepared by layer-by-layer technique Ram, M. K., P. Bertoncello, et al. (2001), Biosens Bioelectron 16(9-12): 849-56. Abstract: The analysis of formation, deposition and characterization of cholesterol oxidase (COX) layer-by-layer films were performed. Initially, a layer of polyanion, poly(styrene sulfonate) (PSS) was adsorbed followed by a layer of polycation, poly(ethylene imine) (PEI) on each solid substrate from aqueous solutions. The alternating layers were formed by consecutive adsorption of polycations (PEI) and negatively charged proteins (COX) and cholesterol esterase (CE). A strong interaction between protein and polyelectrolyte improves the stability of the alternating multilayer; however, it can change a native protein conformation and impair the protein activity. The PSS/PEI/COX, PSS/PEI/COX/PEI/CE, PSS/PEI/COX-CE/PEI etc. layered structures were prepared on the surface of a platinum electrode, ITO coated glass plate, quartz crystal microbalance, quartz plates, mica and silicon substrates. Optical and gravimetric measurements based on an ultraviolet-visible absorption spectroscopy and a quartz crystal microbalance revealed that the enzyme multilayers thus prepared consist of molecular layered of the proteins. The surface morphology of such bilayer films was investigated by using atomic force microscopy. The electrochemical redox processes of the enzyme-layered films deposited either on platinum or ITO coated glass plate were investigated. The response current of cholesterol oxidase electrode with concentration of cholesterol was investigated at length. |
| Cholesterol biosynthesis and metabolism Russell, D. W. (1992), Cardiovasc Drugs Ther 6(2): 103-10. Abstract: Cholesterol plays an essential role in cell membrane synthesis and in cell growth and differentiation. In mammalian cells, cholesterol can be synthesized from acetate precursors or taken up from dietary or exogenous sources. The major catabolic route for disposal of cholesterol involves conversion into excretable bile acids. The maintenance of cholesterol homeostasis is influenced and carefully controlled by multiple feedback mechanisms. The key regulatory targets of these feedback mechanisms are 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase in cholesterol biosynthesis, the low-density lipoprotein (LDL) receptor in cholesterol uptake, and cholesterol 7 alpha-hydroxylase in cholesterol catabolism. The elucidation of regulatory mechanisms in cholesterol metabolism has been greatly facilitated by the discovery of a new class of lipid-lowering drugs, the HMG-CoA reductase inhibitors. In addition to proving therapeutically useful in the treatment of hypercholesterolemia, these drugs have revealed novel regulatory steps in cholesterol metabolism and several new targets for future drug development. This manuscript reviews recent developments in the cholesterol biosynthetic pathway and the regulatory mechanisms that maintain cholesterol homeostasis. |
| Cholesterol biosynthesis and regulation: role of peroxisomes Kovacs, W. J. and S. Krisans (2003), Adv Exp Med Biol 544: 315-27. |
| Cholesterol biosynthesis from lanosterol. A concerted role for Sp1 and NF-Y-binding sites for sterol-mediated regulation of rat 7-dehydrocholesterol reductase gene expression Kim, J. H., J. N. Lee, et al. (2001), J Biol Chem 276(21): 18153-60. Abstract: The 7-dehydrocholesterol reductase (Dhcr7) is the terminal enzyme in the pathway of cholesterol biosynthesis. We have previously reported that sterol depletion in vivo caused a significant induction of both liver mRNA and enzyme activity of Dhcr7 (Bae, S.-H., Lee, J. N., Fitzky, B. U., Seong, J., and Paik, Y.-K. (1999) J. Biol. Chem. 274, 14624-14631). In this paper, we also observed liver cell-specific sterol-mediated Dhcr7 gene induction in vitro by sterol depletion in rat hepatoma cells, suggesting the presence of sterol-mediated regulatory elements in the Dhcr7 gene. To understand the mechanisms responsible for regulating Dhcr7 expression, we have isolated the 5'-flanking region of the gene encoding rat Dhcr7 and have characterized the potential regulatory elements of the gene that are responsible for sterol-mediated regulation. The Dhcr7 promoter contains binding sites for Sp1 (at -177, -172, -125, and -20), NF-Y (at -88 and -51), and SREBP-1 or ADD1 (at -33). Deletion analysis of the Dhcr7 gene promoter (-1053/+31), employing a nested series of Dhcr7-luciferase constructs, demonstrated that the -179 upstream region of the gene is necessary and sufficient for optimal efficient sterol-regulated transcription. DNase I footprinting and electrophoretic mobility shift assay showed that the SRE1/E box (-33/-22) involved in sterol response of many sterol-related enzyme genes was protected specifically by the overexpressed recombinant ADD1. Mutational analysis for the functional relationship between the identified cis-elements in this region indicate that one of the binding sites for Sp1 (GC box at -125) and NF-Y (CCAAT box at -88) plays a cooperative role in the sterol-mediated activation, in which the latter site also acts as a co-regulator for SREBP-activated Dhcr7 promoter activity. We believe that Dhcr7 is the first enzyme characterized with a sterol-regulatory function in the post-lanosterol pathway. This may be important for understanding the coordinated control of cholesterol biosynthesis as well as the molecular mechanism of Smith-Lemli-Opitz syndrome-related protein in mammals. |
| Cholesterol biosynthesis from lanosterol. Molecular cloning, tissue distribution, expression, chromosomal localization, and regulation of rat 7-dehydrocholesterol reductase, a Smith-Lemli-Opitz syndrome-related protein Bae, S. H., J. N. Lee, et al. (1999), J Biol Chem 274(21): 14624-31. Abstract: The cDNA encoding the 471-amino acid rat 7-dehydrocholesterol reductase (DHCR), an enzyme that has been implicated in both cholesterol biosynthesis and developmental abnormalities (e.g. Smith-Lemli-Opitz syndrome) in mammals, has been cloned and sequenced, and the primary structure of the enzyme has been deduced. The DHCR gene was mapped to chromosome 8q2.1 by fluorescence in situ hybridization. Rat DHCR, calculated molecular mass of 54.15-kDa polypeptide, shares a close amino acid identity with mouse and human DHCRs (96 and 87%, respectively) as compared with its other related proteins (e.g. fungal sterol Delta14-reductase) and exhibits high hydrophobicity (>68%) with 9 transmembrane domains. Five putative sterol-sensing domains were predicted to be localized in transmembrane domains 4-8, which are highly homologous to those found in 3-hydroxymethylglutaryl-CoA reductase, sterol regulatory element-binding protein cleavage-activating protein, and patched protein. The polypeptide encoded by DHCR cDNA was expressed in yeast as a 55.45-kDa myc-tagged fusion protein, which was recognized with anti-myc monoclonal antibody 9E10 and shown to possess full DHCR activity with respect to dependence on NADPH and sensitivity to DHCR inhibitors. Northern blot analysis indicates that the highest expression of DHCR mRNA was detected in liver, followed by kidney and brain. In rat brains, the highest level of mRNA encoding DHCR was detected in the midbrain, followed by the spinal cord and medulla. Feeding rats 5% cholestyramine plus 0.1% lovastatin in chow resulted in both approximately a 3-fold induction of DHCR mRNA and a 5-fold increase of the enzymic activity in the liver. When rats were fed 0.1% (w/w) AY-9944 (in chow) for 14-days, a complete inhibition of DHCR activity and a significant reduction in serum total cholesterol level were observed. However, the level of hepatic DHCR mRNA fell only slightly, suggesting that AY-9944 may act more rapidly at the protein level than at the level of transcription of the DHCR gene under these conditions. |
| Cholesterol biosynthesis from lanosterol: development of a novel assay method and characterization of rat liver microsomal lanosterol delta 24-reductase Bae, S. H. and Y. K. Paik (1997), Biochem J 326 (Pt 2): 609-16. Abstract: The membrane-bound sterol delta 24-reductase (24-reductase) catalyses anaerobic reduction of the 24(25)-enes of lanosterol and other obligatory intermediates of cholesterol biosynthesis from lanosterol. A novel assay method and properties of the 24-reductase are described. More than a 120-fold induction of the 24-reductase activity was achieved by feeding rats a diet containing 5% cholestyramine plus 0.1% lovastatin in chow and by modulating diurnal variation. With this enzyme induction condition, lanosterol was converted efficiently into dihydrolanosterol in both intact hepatic microsomes and freshly isolated hepatocytes only when either miconazole or CO was added to inhibit 14 alpha-demethylation of lanosterol. AR45 cells, which are deficient in 14 alpha-methyl demethylase (14 alpha-DM), exhibit lanosterol 24-reductase activity without addition of either CO or miconazole. Conversely, inhibition of the 24-reductase was not required for the expression of 14 alpha-DM activity. Studies on the substrate specificities for the 24-reductase using different 24(25)-enes showed that the most reactive substrate was 5 alpha-cholesta-7,24-dien-3 beta-ol, which exhibited a maximal 18-fold higher kcat than that of lanosterol without the aid of the 14 alpha-DM inhibitor. In addition, both the kinetic behaviour of lanosterol substrate in relation to the 24-reductase and a non-competitive inhibition mode of U18666A (Ki 0. 157 microM) as well as Triparanol (Ki 0.523 microM), two well-known 24-reductase inhibitors, were determined. On the basis of our new findings on the preferred substrate and on the negative effect of 14 alpha-DM on the 24-reductase, we suggest that C-24 reduction of sterols takes place straight after sterol delta 8-->7 isomerization of zymosterol, which occurs several steps after C-32 demethylation of lanosterol in the 19-step pathway of cholesterol biosynthesis from lanosterol. |
| Cholesterol biosynthesis from lanosterol: differential inhibition of sterol delta 8-isomerase and other lanosterol-converting enzymes by tamoxifen Cho, S. Y., J. H. Kim, et al. (1998), Mol Cells 8(2): 233-9. Abstract: The fact that administration of tamoxifen (Tam) to humans and laboratory animals (e.g., rats and monkeys) results in both a drastic reduction in cholesterol and a marked accumulation of certain sterol intermediates in their serum led us to undertake more direct biochemical studies on the mechanism of Tam's inhibitory action on the cholesterogenic enzymes. Of the five rat hepatic lanosterol-converting enzymes examined, the enzyme most sensitive to inhibition by Tam was sterol delta 8-isomerase (delta 8-SI) (a 208-fold inhibition relative to lanosterol 14 alpha-methyl demethylase), followed by sterol delta 24-reductase (13-fold) and sterol delta 14-reductase (5.2-fold). The inhibition patterns of all four affected enzymes were found to be noncompetitive, despite widely different inhibition constants (Ki) of 0.21 to 23.5 microM. The inhibitory activity of Tam on delta 8-SI was not affected by detergent-mediated solubilization of the microsomes. In Chinese hamster ovary cells, inhibition of delta 8-SI activity (IC50 = 0.15 microM) was paralleled by a decreased rate of 14C-mevalonate incorporation into cholesterol (IC50 = 0.70 microM). Our results should provide more insight into an underlying mechanism of Tam's cardioprotective role by interfering the operation of the pathway of cholesterol biosynthesis from lanosterol in mammals. |