| For medical practitioners and the general public - Cholesterol Journal Article Catalog. |
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| Hepatic sinusoidal fibrosis induced by cholesterol and stilbestrol in the rabbit: 1. Morphology and inhibition of fibrogenesis by dipyridamole Wanless, I. R., J. Belgiorno, et al. (1996), Hepatology 24(4): 855-64. Abstract: This study documents the hepatic morphology and the ultrastructure of a model of hepatic fibrosis in rabbits. Rabbits were given a cholesterol-supplemented diet (1%), a stilbestrol diet (10 mg subcutaneously twice a week), or both treatments simultaneously for 7 weeks. Rabbits given the combined treatment developed sinusoidal and portal fibrosis with only a mild disturbance of acinar vascular relationships. Ultrastructurally, there was marked widening of the spaces of Disse by collagen fibers, basement membrane material adjacent to endothelial cells and hepatocytes, blunted hepatocellular microvilli, activated stellate cells, lipid droplets in endothelial cells and hepatocytes, and degranulated platelets in sinusoids. The hepatic hydroxyproline content was markedly increased (12.0 +/- 5.2 vs. 4.8 +/- 1.5 mmol/g of liver dry weight; P <.001). Plasma bile acids were markedly increased (222 +/- 180 vs. 12 +/- 5 in controls; P <.001). Dipyridamole (25 mg every 12 hours) that was given in addition to cholesterol and stilbestrol decreased the hepatic collagen content (-49% and -48%, in two experiments; P <.05 in both) and splenomegaly. This model provides a reliable method for the production of extensive sinusoidal fibrosis with capillarization of sinusoids. Hepatocellular degeneration is only mild to moderate, and fibrosis occurs slowly without the sudden pathological changes that occur with other models of hepatic fibrosis, such as with the administration of CCl4 or galactosamine. The mechanism of injury may involve the accumulation of bile salts or the generation of free radicals from cholesterol oxidation products. The possibility that the sinusoidal release of platelet-derived factors may have a role in the activation of stellate cells (lipocytes) is supported by the suppression of fibrogenesis by dipyridamole. |
| Hepatic sinusoidal fibrosis induced by cholesterol and stilbestrol in the rabbit: 2. Hemodynamic and drug disposition studies Mastai, R., S. Laganiere, et al. (1996), Hepatology 24(4): 865-70. Abstract: We assessed hepatic functions and systemic and splanchnic hemodynamics in a new model of hepatic sinusoidal fibrosis. Fibrosis was induced by the simultaneous administration for 8 weeks of diethyl-stilbestrol (DES) (10 mg twice weekly, subcutaneously) and cholesterol-supplemented diet (1%) in rabbits. A marked and progressive impairment of hepatic function was observed during the 8 weeks of treatment with a significant decrease in indocyanine green (ICG) systemic clearance (-89%; P <.001) and aminopyrine elimination (-69%; P <.001). In fibrotic animals, hyperdynamic circulation was found with an increased cardiac output (+73%, P < 0.01) and a decreased peripheral vascular resistance (-50%; P <.005), as evaluated by the microsphere technique in animals that were awake. The total portal venous inflow was not significantly modified in fibrotic rabbits. However, since there was a marked increase in the liver weight, the portal venous inflow was significantly decreased when expressed per gram of liver weight (-30%; P <.05). In contrast, the hepatic artery blood flow was markedly increased, even when expressed per gram of liver weight (+95%; P <.01). Portal pressure was significantly increased in treated rabbits (from 7.4 +/-.4 to 14.4 +/-.6 mm Hg, P <.01). This new experimental model could prove useful to evaluate the influence of extensive perisinusoidal fibrosis on exchanges between plasma and hepatocytes, particularly of protein-bound substances. |
| Hepatic transport and secretion of unesterified cholesterol in the rat is traced by the plant sterol, sitostanol Robins, S. J., J. M. Fasulo, et al. (1996), J Lipid Res 37(1): 15-21. Abstract: The hepatic uptake, transport, and secretion into bile of unesterified cholesterol cannot be directly quantitated because of extensive exchange and equilibration between different pools of unesterified cholesterol. Plant sterols are structurally similar to cholesterol but because of poor intestinal absorption are ordinarily not present in the liver. To quantitate hepatic sterol uptake and transport in the absence of exchange with endogenous sterols, isolated rat livers were perfused with the plant sterol, sitostanol, incorporated in phosphatidylcholine liposomes. Appreciable amounts of sitostanol were taken up by the liver and uptake was independent of the presence of bile salt. In contrast, like unesterified cholesterol, the secretion of sitostanol in bile required bile salt. Sitostanol was detected in bile within 5 min after a perfusion was begun and reached a plateau by about 20 min. The rate of appearance of sitostanol in bile was precisely the same as unesterified cholesterol when both sterols were perfused together. Furthermore, the output of sitostanol in bile was directly proportional to the output of cholesterol. At the peak of biliary sitostanol secretion, the amount of sitostanol relative to unesterified cholesterol was much greater in bile (40-50% of sterols) than in the whole liver (11% of sterols). Selective biliary secretion of sitostanol was associated with much greater concentrations of sitostanol in canalicular membranes than in the interior membranes of the hepatocyte and in newly secreted high density lipoproteins compared to newly secreted very low density lipoproteins. These results indicate that sitostanol parallels the secretion from and distribution of unesterified cholesterol in the liver and suggest that sitostanol can be used as a physiologic analog of unesterified cholesterol to trace the transport of sterols through the liver. |
| Hepatic uptake and processing of cholesterol and cholesteryl ester from chylomicron remnants: an in vivo study in the rat Bravo, E., T. Guldur, et al. (1992), Biochim Biophys Acta 1123(1): 85-91. Abstract: The metabolic fate of cholesterol in chylomicron remnants was studied after intravenous infusion into biliary drained rats. The remnants were radiolabelled with 3Hcholesterol in vivo, so that radioactivity was incorporated into both the unesterified (27% of label) and esterified (73% of label) cholesterol fractions, or with 14C-labelled unesterified cholesterol after exchange in vitro. Blood and bile samples were collected at intervals for 180 min, after which the animals were killed for analysis. The total amount of radioactivity found in the liver (46%) and bile (4.5%) after infusion of 3H remnants was higher than that found when the label was 14C (33 and 2.7%, respectively). Radioactivity from 14C-labelled unesterified cholesterol was cleared more rapidly from the blood, but the distribution of the label between the lipoprotein fractions VLDL + LDL, HDL2 and HDL3 at the end of the experiment was similar to that found when total 3Hcholesterol was used. In experiments with both types of label, approximately 94% of the total radioactivity secreted into bile was associated with the bile acid, with only about 6% in biliary unesterified cholesterol, and these proportions did not change during 180 min. When the chylomicron remnants were labelled with total 3Hcholesterol the specific radioactivity of the bile acid, taurochenodeoxycholic acid, in the bile was approximately twice that observed when the label was unesterified 14Ccholesterol. The specific radioactivity of unesterified biliary cholesterol was very low in the latter case, but higher and more comparable to that of taurochenodeoxycholic acid in the former. Thus, the metabolic fate of chylomicron remnant cholesterol differs, depending on whether it is in the esterified or unesterified form, suggesting that hepatic cholesterol originating from the two fractions may mix to a different extent with the various intracellular pools. In addition, the experiments with 14C indicate that the behaviour of chylomicron remnant unesterified cholesterol resembles that exhibited by cholesterol in HDL more than that carried in VLDL or LDL. |
| Hepatic uptake and processing of free cholesterol from different lipoproteins with and without sodium taurocholate administration. An in vivo study in the rat Bravo, E. and A. Cantafora (1990), Biochim Biophys Acta 1045(1): 74-80. Abstract: The metabolic fate of 14Ccholesterol carried in the VLDL, LDL, HDL2 and HDL3 lipoprotein fractions has been investigated in bile-fistula rats with jugular vein cannulation. After the depletion of bile salt pool, the labelled lipoprotein fraction was administered either with or without the continuous infusion of sodium taurocholate. The proportion of labelled steroids secreted in the bile within 3 h after the lipoprotein administration was generally higher when the exogenous bile salt was infused. Specifically, the HDL2 fraction induced the secretion of relatively high proportions of labelled steroids, mainly bile salts, either with or without the taurocholate infusion. The other lipoprotein fractions increased the proportion of free cholesterol in steroid bile secretion under taurocholate administration. The label associated to the LDL fraction showed a higher biliary secretion and a more steady clearance from plasma if the exogenous bile salt was not administered. In this same condition, the administration of HDL3 fraction gave the highest values of radioactivity recovered in the liver (mainly as free cholesterol) and a significant increase of cholesterol in the biliary secretion. The present results suggest that each lipoprotein fraction tested may contribute in a peculiar manner to bile salt and cholesterol biliary secretion. Both the expression of apo-E and apo B,E receptors and the levels of circulating bile salts appear to have a role in this process. |
| Hepatic uptake of beta-VLDL in cholesterol-fed rabbits Gudmundsen, O., T. Berg, et al. (1993), J Lipid Res 34(4): 589-600. Abstract: The hepatic uptake of intravenously injected beta-very low density lipoprotein (beta-VLDL) in rabbits fed 2% (w/w) cholesterol for 3 weeks was investigated. In vitro studies were also conducted to examine the specificity and the capacity of the uptake in isolated liver parenchymal cells. The hepatic uptake of beta-VLDL was 15.8 +/- 6.7% (n = 6) in the cholesterol-fed rabbits as compared to 26.6 +/- 7.5% (n = 6) of the injected dose in control rabbits (P < 0.05). Although this is a fractional reduction, it represents a more than 10-fold increase in absolute hepatic uptake of lipoproteins in the cholesterol-fed rabbits. In these animals the liver parenchymal, endothelial, and Kupffer cells took up 10.2 +/- 2.7%, 3.0 +/- 0.9%, and 1.8 +/- 0.4% of the injected dose, respectively, compared to 25.9 +/- 6.1%, 3.6 +/- 1.6%, and 1.5 +/- 0.8% of the injected dose in chow-fed controls. However, taking into account the high plasma lipoprotein levels in the cholesterol-fed rabbits, the absolute cellular uptake was 10-fold increased in the parenchymal liver cells and more than 20-fold increased in the nonparenchymal cells. In vitro results indicated a 40% down-regulation of the specific receptor for beta-VLDL in the parenchymal cells, and this, together with an increased competition for binding sites in the hypercholesterolemic rabbits, probably explains the reduced uptake of beta-VLDL in terms of % of injected dose observed in vivo. In vitro data suggested that the receptor involved in both hypercholesterolemic and normolipemic rabbits was the apolipoprotein (apo) B,E receptor. On a per cell basis, parenchymal cells from chow-fed control animals took up 2.4 +/- 0.8% of the injected dose per 10(9) cells; this uptake was reduced to 1.1 +/- 0.5% in hypercholesterolemic animals. No differences in uptake of beta-VLDL in nonparenchymal liver cells were observed on a per cell basis between the two feeding groups, indicating that binding sites involved in this uptake are not down-regulated by cholesterol feeding. On the contrary, the absolute uptake in the nonparenchymal liver cells is greatly increased in hypercholesterolemic rabbits as compared to controls. In cholesterol-fed rabbits the three different liver cell types took up approximately the same amount of beta-VLDL per cell. The liver nonparenchymal cells, therefore, assume a prominent role in uptake of beta-VLDL in hypercholesterolemic rabbits, accounting for more than 30% of the total hepatic uptake as compared to 16% in control animals.(ABSTRACT TRUNCATED AT 400 WORDS) |
| Hepatobiliary cholesterol transport is not impaired in Abca1-null mice lacking HDL Groen, A. K., V. W. Bloks, et al. (2001), J Clin Invest 108(6): 843-50. Abstract: The ABC transporter ABCA1 regulates HDL levels and is considered to control the first step of reverse cholesterol transport from the periphery to the liver. To test this concept, we studied the effect of ABCA1 deficiency on hepatic metabolism and hepatobiliary flux of cholesterol in mice. Hepatic lipid contents and biliary secretion rates were determined in Abca1(-/-), Abca1(+/-), and Abca1(+/+) mice with a DBA background that were fed either standard chow or a high-fat, high-cholesterol diet. Hepatic cholesterol and phospholipid contents in Abca1(-/-) mice were indistinguishable from those in Abca1(+/-) and Abca1(+/+) mice on both diets. In spite of the absence of HDL, biliary secretion rates of cholesterol, bile salts, and phospholipid were unimpaired in Abca1(-/-) mice. Neither the hepatic expression levels of genes controlling key steps in cholesterol metabolism nor the contribution of de novo synthesis to biliary cholesterol and bile salts were affected by Abca genotype. Finally, fecal excretion of neutral and acidic sterols was similar in all groups. We conclude that plasma HDL levels and ABCA1 activity do not control net cholesterol transport from the periphery via the liver into the bile, indicating that the importance of HDL in reverse cholesterol transport requires re-evaluation. |
| Hepatocyte nuclear factor-1alpha is an essential regulator of bile acid and plasma cholesterol metabolism Shih, D. Q., M. Bussen, et al. (2001), Nat Genet 27(4): 375-82. Abstract: Maturity-onset diabetes of the young type 3 (MODY3) is caused by haploinsufficiency of hepatocyte nuclear factor-1alpha (encoded by TCF1). Tcf1-/- mice have type 2 diabetes, dwarfism, renal Fanconi syndrome, hepatic dysfunction and hypercholestrolemia. Here we explore the molecular basis for the hypercholesterolemia using oligonucleotide microchip expression analysis. We demonstrate that Tcf1-/- mice have a defect in bile acid transport, increased bile acid and liver cholesterol synthesis, and impaired HDL metabolism. Tcf1-/- liver has decreased expression of the basolateral membrane bile acid transporters Slc10a1, Slc21a3 and Slc21a5, leading to impaired portal bile acid uptake and elevated plasma bile acid concentrations. In intestine and kidneys, Tcf1-/- mice lack expression of the ileal bile acid transporter (Slc10a2), resulting in increased fecal and urinary bile acid excretion. The Tcf1 protein (also known as HNF-1alpha) also regulates transcription of the gene (Nr1h4) encoding the farnesoid X receptor-1 (Fxr-1), thereby leading to reduced expression of small heterodimer partner-1 (Shp-1) and repression of Cyp7a1, the rate-limiting enzyme in the classic bile acid biosynthesis pathway. In addition, hepatocyte bile acid storage protein is absent from Tcf1-/- mice. Increased plasma cholesterol of Tcf1-/- mice resides predominantly in large, buoyant, high-density lipoprotein (HDL) particles. This is most likely due to reduced activity of the HDL-catabolic enzyme hepatic lipase (Lipc) and increased expression of HDL-cholesterol esterifying enzyme lecithin:cholesterol acyl transferase (Lcat). Our studies demonstrate that Tcf1, in addition to being an important regulator of insulin secretion, is an essential transcriptional regulator of bile acid and HDL-cholesterol metabolism. |
| Hepatolithiasis and cholesterol and bile acid metabolism Cetta, F., F. Lombardo, et al. (1996), Gastroenterology 110(3): 963-5. |
| HepG2 cell LDL receptor activity and the accumulation of apolipoprotein B and E in response to docosahexaenoic acid and cholesterol Sorci-Thomas, M., C. L. Hendricks, et al. (1992), J Lipid Res 33(8): 1147-56. Abstract: In the present study, the accumulation of apolipoproteins (apo) A-I, B, and E in culture medium was measured after 0, 3, 6, 12, and 24 h of incubation with 150 microM docosahexaenoic acid complexed to 75 microM bovine serum albumin (BSA-22:6), either in the presence or absence of 50 micrograms/ml cholesterol and 4 micrograms/ml 25-hydroxycholesterol (C/25-OH). HepG2 cells incubated with BSA + C/25-OH for 24 h accumulated approximately 2.0-fold greater apoE and B as compared to BSA-treated cells. Moreover, HepG2 cell apoB accumulation after 24 h of BSA-22:6 treatment was approximately 2.0-fold greater than apoB accumulation from cells treated with BSA alone. When BSA-22:6 and C/25-OH were both included in the incubation, apoB accumulation was approximately 5.0-fold greater than BSA-treated cells. Comparative studies using BSA-18:1 were carried out for 24 h and showed similar levels of apoA-I, B, and E accumulation in culture medium as compared to BSA-22:6-treated cells. In addition, apoA-I, B, and E mRNA abundance were found to be unaffected by type of fatty acid treatment or length of incubation, averaging 48.2 +/- 7.5, 222 +/- 33.6, and 17.1 +/- 0.7 pg mRNA/micrograms RNA (mean +/- SEM), respectively. As the accumulation of apoB and apoE in culture medium may be modified by HepG2 cell LDL receptor expression, LDL receptor mRNA abundance and LDL receptor activity were quantified at various times over the course of the study. By 6 h of BSA + C/25-OH treatment, LDL receptor mRNA was reduced approximately 2.3-fold, while receptor activity was reduced approximately 1.5-fold, as compared to BSA controls. In an experiment designed to determine uptake of HepG2 cell lipoproteins, 3H-labeled apoB-containing lipoproteins derived from HepG2 cells were prepared. The 3H-labeled lipoproteins were 1.25-fold more likely to be removed from the media of HepG2 cells treated with BSA than from cells treated with BSA + C/25-OH. From these results, we postulate that HepG2 cell LDL receptor activity mediates the removal of apoB, E-containing lipoproteins from culture medium and contributes to the lower accumulation of apoB and E observed in culture medium from cells treated with BSA as compared to cells treated with C/25-OH. |
| Heptanol-induced decrease in cardiac gap junctional conductance is mediated by a decrease in the fluidity of membranous cholesterol-rich domains Bastiaanse, E. M., H. J. Jongsma, et al. (1993), J Membr Biol 136(2): 135-45. Abstract: To assess whether alterations in membrane fluidity of neonatal rat heart cells modulate gap junctional conductance (gj), we compared the effects of 2 mM 1-heptanol and 20 microM 2-(methoxy-ethoxy)ethyl 8-(cis-2-n-octylcyclopropyl)-octanoate (A2C) in a combined fluorescence anisotropy and electrophysiological study. Both substances decreased fluorescence steady-state anisotropy (rss), as assessed with the fluorescent probe 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH) by 9.6 +/- 1.1% (mean +/- SEM, n = 5) and 9.8 +/- 0.6% (n = 5), respectively, i.e., both substances increased bulk membrane fluidity. Double whole-cell voltage-clamp experiments showed that 2 mM heptanol uncoupled cell pairs completely (n = 6), whereas 20 microM A2C, which increased bulk membrane fluidity to the same extent, did not affect coupling at all (n = 5). Since gap junction channels are embedded in relatively cholesterol-rich domains of the membrane, we specifically assessed the fluidity of the cholesterol-rich domains with dehydroergosterol (DHE). Using DHE, heptanol increased rss by 14.9 +/- 3.0% (n = 5), i.e., decreased cholesterol domain fluidity, whereas A2C had no effect on rss (-0.4 +/- 6.7%, n = 5). Following an increase of cellular "cholesterol" content (by loading the cells with DHE), 2 mM heptanol did not uncouple cell pairs completely: gj decreased by 80 +/- 20% (range 41-95%, n = 5). The decrease in gj was most probably due to a decrease in the open probability of the gap junction channels, because the unitary conductances of the channels were not changed nor was the number of channels comprising the gap junction. The sensitivity of nonjunctional membrane channels to heptanol was unaltered in cholesterol-enriched myocytes. These results indicate that the fluidity of cholesterol-rich domains is of importance to gap junctional coupling, and that heptanol decreases gj by decreasing the fluidity of cholesterol-rich domains, rather than by increasing the bulk membrane fluidity. |
| Herbs for serum cholesterol reduction: a systematic view Thompson Coon, J. S. and E. Ernst (2003), J Fam Pract 52(6): 468-78. Abstract: OBJECTIVES: To systematically review the clinical evidence for herbal medicinal products in the treatment of hypercholesterolemia. STUDY DESIGN: A systematic review of randomized clinical trials of herbal medicinal products used to lower serum cholesterol. Systematic literature searches were conducted in 6 electronic data-bases. The reference lists of all papers and our files were searched for more relevant publications. Experts in the field and manufacturers of identified herbal medicinal products were contacted for published and unpublished data. No language restrictions were imposed. OUTCOMES MEASURED: All randomized clinical trials of serum cholesterol reduction, in which mono-preparations of herbal medicinal products were administered as supplements to human subjects, were included. RESULTS: Twenty-five randomized clinical trials involving 11 herbal medicinal products were identified. Guggul (Commiphora mukul), fenugreek (Trigonella foenum-graecum), red yeast rice, and artichoke (Cynara scolymus) have been most extensively studied and have demonstrated reductions in total serum cholesterol levels of between10% and 33%. The methodological quality as assessed by the Jadad score was less than 3 (maximum, 5) for 13 of the 25 trials. CONCLUSIONS: Many herbal medicinal products have potential hypocholesterolemic activity and encouraging safety profiles. However, only a limited amount of clinical research exists to support their efficacy. Further research is warranted to establish the value of these extracts in the treatment of hypercholesterolemia. |
| Heritability analysis of lipids and three gene loci in twins link the macrophage scavenger receptor to HDL cholesterol concentrations Knoblauch, H., A. Busjahn, et al. (1997), Arterioscler Thromb Vasc Biol 17(10): 2054-60. Abstract: We studied 100 healthy monozygotic and 72 dizygotic twin pairs (mean age, 34 +/- 14 years) to test for genetic influences on blood lipids and to examine relevant gene loci. Total cholesterol (TC), LDL cholesterol (LDL-C), HDL cholesterol (HDL-C), and triglyceride (TG) levels were determined after a 12-hour fast. Zygosity was determined with the use of microsatellite markers. Heritability estimates were conducted by using the lisrel 8 program; a sib-pair analysis was conducted by using the sibpal program. Linear regression analyses were carried out between identical-by-descent status and squared within-pair differences of TC, LDL-C, HDL-C, and TG values. Heritability estimates of the lipid serum concentrations ranged from.58 to.66. A significant linkage relationship was found for HDL-C (P =.008) and TGs (P =.05) with D8S261 on chromosome 8p. However, no linkage was found between any of the lipid variables and the lipoprotein lipase gene locus (LPL GZ14/15 and D8S282). Because D8S261 is located approximately halfway between the LPL and macrophage scavenger receptor genes, we examined the nearby markers D8S549 and D8S1731. Linkage was found for HDL-C and D8S549 (P =.001) and for HDL-C and D8S1731 (P =.04). On the other hand, we found no linkage between the LDL receptor gene locus and LDL-C serum concentrations nor between the LPL gene locus and the various other lipid fractions. Our data suggest a significant influence of the macrophage scavenger receptor gene locus on HDL-C and weak influence on TG levels. We suggest that inherited variability in the macrophage scavenger receptor gene has an influence on serum lipid concentrations. |
| Heteroacid phosphatidylcholines with different amounts of unsaturation respond differently to cholesterol Hernandez-Borrell, J. and K. M. Keough (1993), Biochim Biophys Acta 1153(2): 277-82. Abstract: The effectiveness of cholesterol in removing the gel to liquid crystal phase transition of dispersions of pure molecular species of phosphatidylcholines (PC) that is detectable by differential scanning calorimetry (DSC) has been explored. The effect of cholesterol on 16:0-18:0 PC, 16:0-18:1 PC, 16:0-18:2 PC, 16:0-20:4 PC and 16:0-22:6 PC has been determined. Cholesterol caused a concentration-dependent removal of the detectable phase transitions in all cases. It required very little cholesterol to remove the phase transition 16:0-18:2 PC (< 17 mol% of cholesterol in PC). It required > or = 35 mol% cholesterol to remove delta H for 16:0-18:0 PC and 16:0-22:6 PC. About 20-25 mol% cholesterol caused disappearance of the transitional endotherm of 16:0-18:1 PC and 16:0-20:4 PC. The findings indicate that the magnitude of the influence of cholesterol on phospholipid is dependent on the degree of unsaturation in the lipid. |
| Heterocyclic amides: inhibitors of acyl-CoA:cholesterol O-acyl transferase with hypocholesterolemic activity in several species and antiatherosclerotic activity in the rabbit White, A. D., C. F. Purchase, 2nd, et al. (1996), J Med Chem 39(20): 3908-19. Abstract: A series of heterocyclic amides were synthesized and evaluated as inhibitors of acyl-CoA: cholesterol O-acyltransferase (ACAT) in vitro and for cholesterol lowering in cholesterol-fed rats. Compounds were evaluated for cell-based macrophage ACAT inhibition, bioactivity, and adrenal toxicity. Candidates were selected for evaluation in cholesterol-fed dogs and, ultimately, the injured cholesterol-fed rabbit model of atherosclerosis. The heterocyclic amides potently inhibited rabbit liver ACAT (IC50's = 0.014-0.11 microM), and the majority of compounds significantly lowered plasma cholesterol (42-68%) in an acute cholesterol-fed rat model at 3 mg/kg. The most efficacious compounds in the rat were evaluated for bioactivity in vivo and arterial ACAT inhibition in a cell-based macrophage ACAT assay. Two highly bioactive analogs, (+/-)-2-(3-dodecylisoxazol-5-yl)-2-phenyl-N-(2,4,6-trimethoxypheny l) acetamide (13a) and (+/-)-2-(5-dodecylisoxazol-3-yl)-2-phenyl-N-(2,4,6-trimethoxypheny l) acetamide (16a), were selected for further study and were found to be nontoxic in a guinea pig model of adrenal toxicity. Compounds 13a and 16a lowered total cholesterol in the cholesterol-fed rat, rabbit, and dog models of pre-established hypercholesterolemia. Compound 13a in the injured cholesterol-fed rabbit model of atherosclerosis was effective in slowing the development of cholesteryl ester-rich thoracic aortic lesions, reducing lesion coverage by 53% at a dose of 1 mg/kg. |
| Heterocyclic ureas: inhibitors of acyl-CoA:cholesterol O-acyltransferase as hypocholesterolemic agents White, A. D., M. W. Creswell, et al. (1996), J Med Chem 39(22): 4382-95. Abstract: A series of diaryl-substituted heterocyclic ureas was prepared, and their ability to inhibit acyl-CoA: cholesterol O-acyltransferase (ACAT) in vitro and to lower plasma total cholesterol in cholesterol-fed animal models in vivo was examined. N-(2,6-Diisopropylphenyl)-N'-tetrazole or isoxazole-substituted heterocyclic ureas proved optimal. A carbon chain of 11-14 carbons substituted 1,3 with respect to the amine provided the optimal side chain. Substitution of the alkyl chain generally lowered activity. Tetrazole urea 2i dosed at 3 mg/kg lowered plasma total cholesterol (TC) 67% in an acute, cholesterol-fed (C-fed) rat model of hypercholesterolemia and 47% in C-fed dogs. Tetrazole 2i, dosed at 10 mg/kg, also lowered TC 52% and raised HDL cholesterol 113% in rats with pre-established hypercholesterolemia. |
| Heterogeneity at the CETP gene locus. Influence on plasma CETP concentrations and HDL cholesterol levels Kuivenhoven, J. A., P. de Knijff, et al. (1997), Arterioscler Thromb Vasc Biol 17(3): 560-8. Abstract: This study was designed to investigate the association(s) between heterogeneity at the cholesteryl ester transfer protein (CETP) gene locus, CETP plasma concentrations, and HDL cholesterol levels. Healthy men with the lowest, median, and highest deciles of HDL cholesterol were selected from a large population database. We accounted for factors that are known to influence HDL cholesterol levels, such as smoking, exercise, body mass index, alcohol consumption, and blood pressure. Plasma CETP concentrations were measured, and we determined the allele frequency distribution of six CETP DNA polymorphisms. The group with low HDL cholesterol exhibited a significant increase in CETP concentration compared with both the median and high HDL cholesterol groups, whereas CETP concentrations did not differ among the groups with median and high HDL cholesterol. The allele frequency distributions of the TaqIB (intron 1), Msp I (intron 8), and Rsa I (exon 14) polymorphisms differed significantly between the groups with low and high HDL cholesterol. Further analysis revealed that the Msp I polymorphism had a 1.5-fold larger impact on CETP concentration than the TaqIB polymorphism and a fivefold larger impact than the Rsa I polymorphism. In conclusion, we demonstrated that heterogeneity at the CETP gene locus is correlated with CETP plasma concentrations and HDL cholesterol levels. More specifically, our data indicate the presence of a strong association between common variants of the CETP gene, high plasma CETP concentrations, and consequently hypoalphalipoproteinemia in healthy white men. |
| Heterogeneity in hand veins responses to acetylcholine is not associated with polymorphisms in the G-protein beta3-subunit (C825T) and endothelial nitric oxide synthase (G894T) genes but with serum low density lipoprotein cholesterol Grossmann, M., D. Dobrev, et al. (2001), Pharmacogenetics 11(4): 307-16. Abstract: Vascular responses to acetylcholine (ACh) are notoriously variable, the reason for this phenomenon is unknown. We tested the hypothesis that the variability in venous response to acetylcholine may be associated with two recently identified genetic polymorphisms for proteins involved in the signal transduction pathway, i.e. the G-protein beta3-subunit (GNB3) and endothelial nitric oxide synthase (eNOS). The dorsal hand vein technique was used in 37 healthy subjects. Hand veins were preconstricted with the alpha1-adrenoceptor agonist phenylephrine and the venodilator response to local ACh infusion was measured with and without comedication of acetylsalicylic acid or co-infusion of N(G)-monomethyl-L-arginine (L-NMMA). In addition, all subjects received routine laboratory tests and 26 of them were genotyped for the C825T polymorphism of the GNB3 gene and for the G894T polymorphism of the eNOS gene. A striking variability in venous response to ACh was found with dilation observed in the low ACh concentration range and reduced dilation or even constriction at high concentrations. ACh-induced venodilation was mediated by muscarinic receptors and abolished in the presence of both acetylsalicylic acid and L-NMMA suggesting dependence on endothelium. We did not find any association of the variability in ACh response with GNB3 or eNOS allele status. On the other hand, a significant positive correlation between ACh responsiveness and low density lipoprotein-cholesterol status was detected. Two recently discovered gene polymorphisms are not responsible for the profound heterogeneity in venodilator response to ACh. Surprisingly, this variability appears to relate to the lipid status of the subjects. The exact nature of this new finding requires further study. |
| Heterogeneity of rat liver parenchyma in cholesterol 7 alpha-hydroxylase and bile acid synthesis Ugele, B., H. J. Kempen, et al. (1991), Biochem J 276 (Pt 1): 73-7. Abstract: Periportal and perivenous hepatocytes were isolated from rat liver by digitonin/collagenase perfusion for investigating the acinar distribution of bile acid synthesis. The specific activity of cholesterol 7 alpha-hydroxylase (EC 1.14.13.17) was 7.9-fold higher in perivenous cells than in periportal hepatocytes. Mass production of bile acids differed 4.4-fold between cultured perivenous and periportal hepatocytes. In contrast, the levels of free cholesterol in homogenates and microsomes derived from both subfractions were similar. Feeding of rats with the bile-acid-sequestering anion-exchange resin colestid resulted in a pronounced stimulation of cholesterol 7 alpha-hydroxylase activity and bile acid mass production, but decreased the perivenous/periportal ratio of both parameters. These results demonstrate that bile acid mass production, but decreased the perivenous hepatocytes, possibly owing to feedback suppression by bile acids from the enterohepatic circulation. Furthermore, the opposite acinar localization of cholesterol and bile acid biosynthesis provides an interesting alternative to current views of the regulation of their metabolic pathways. |
| Heterogeneous distribution of acetylcholine receptors in chick myocytes induced by cholesterol enrichment Lasalde, J. A., A. Colom, et al. (1995), Biochim Biophys Acta 1235(2): 361-8. Abstract: The cholesterol concentration at the cell surface of cultured chick myocytes was increased in order to determine the effects of high levels of cholesterol on the ion channel properties of the nicotinic acetylcholine receptor. Single channel recordings and fluorescence polarization studies using 1,6-diphenyl-1,3,5-hexatriene (DPH) were performed under equivalent conditions for normal and cholesterol enriched myocytes. In cell attached patches from myocytes with a cholesterol to phospholipid molar ratio (c/p) of 0.24 and a microviscosity of 1.35 poise a single conductance of 51 pS was detected. The cholesterol enriched myocytes with a c/p of 0.52 and a microviscosity of 2.05 poise showed two conductances, a 54 pS and a 39 pS channel: both were blocked by alpha-bungarotoxin. The 39 pS channel was detected with the simultaneous appearance of a slow component of tau m (modulation time) for DPH fluorescence measured by phase demodulation. The 80% reduction in the open time constant (tau 2) of the 39 pS channel suggest an inhibition of the normal conformational state. The combined results suggest that cholesterol enrichment may induced a more heterogeneous lipid environment and that the two types of channel properties could result from the distribution of the receptors in different domains. |