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John Y. L. Chiang - One of the best experts on this subject based on the ideXlab platform.
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Up to date on Cholesterol 7 Alpha-Hydroxylase (CYP7A1) in bile acid synthesis
Liver Research, 2020Co-Authors: John Y. L. Chiang, Jessica M. FerrellAbstract:Abstract Cholesterol 7 Alpha-Hydroxylase (CYP7A1, EC1.14) is the first and rate-limiting enzyme in the classic bile acid synthesis pathway. Much progress has been made in understanding the transcriptional regulation of CYP7A1 gene expression and the underlying molecular mechanisms of bile acid feedback regulation of CYP7A1 and bile acid synthesis in the last three decades. Discovery of bile acid-activated receptors and their roles in the regulation of lipid, glucose and energy metabolism have been translated to the development of bile acid-based drug therapies for the treatment of liver-related metabolic diseases such as alcoholic and non-alcoholic fatty liver diseases, liver cirrhosis, diabetes, obesity and hepatocellular carcinoma. This review will provide an update on the advances in our understanding of the molecular biology and mechanistic insights of the regulation of CYP7A1 in bile acid synthesis in the last 40 years.
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Bile synthesis in rat models of inflammatory bowel diseases.
European Journal of Clinical Investigation, 2007Co-Authors: Nektarios Dikopoulos, John Y. L. Chiang, Gail K. Adler, Roland M. Schmid, Max G. Bachem, Klaus Buttenschoen, H. WeidenbachAbstract:BACKGROUND A broad spectrum of hepatobiliary disorders are found in patients with inflammatory bowel diseases. The aim of the present work was to study interactions between gut and liver in experimental rat models of colitis and small bowel inflammation. MATERIALS AND METHODS Colitis was induced either by trinitrobenzene sulphonic acid or dextran sodium sulphate. Small-bowel inflammation was induced by indomethacin. Bile acid secretion, bile acid pool, and Cholesterol 7-alpha hydroxylase were studied. Cholesterol 7-alpha hydroxylase protein expression was analysed in the microsomal liver fraction. As portal mediators released form the inflamed gut we measured lipopolysaccharide, tumour necrosis factor-alpha and interleukin-1beta in portal serum. The hepatic inflammatory response was evaluated by binding activity of nuclear factor-kappaB, activator protein-1 and alpha-2-macroglobulin. RESULTS Increased bile acid secretion, total bile acid content in gut and liver (bile acid pool size), and hepatic Cholesterol 7-alpha hydroxylase protein and mRNA levels were found in the two colitis models associated with only a minor hepatic acute phase and cytokine response. In contrast, during indomethacin-induced small-bowel inflammation bile acid secretion, pool size, and Cholesterol 7-alpha hydroxylase decreased in parallel to a strong hepatic cytokine and acute phase response. CONCLUSIONS Colitis without portal cytokine release and acute phase reaction shows an induction of bile acid secretion, pool size, and Cholesterol 7-alpha hydroxylase. In contrast, intestinal inflammation after indomethacin treatment is associated with an acute phase response and a repression of bile acid synthesis.
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Identification of a bile acid response element in the Cholesterol 7 Alpha-Hydroxylase gene CYP7A.
American Journal of Physiology-Gastrointestinal and Liver Physiology, 1997Co-Authors: D. Stroup, M. Crestani, John Y. L. ChiangAbstract:The transcriptional activity of the Cholesterol 7 Alpha-Hydroxylase gene CYP7A is repressed by bile acids. Taurine conjugates of chenodeoxycholate and deoxycholate, but not cholate and ursodeoxycholate, inhibited the CYP7A promoter/luciferase reporter activity in transient transfection assays in Hep G2 cells. A region from nucleotide (nt) -74 to -55 was found to mediate bile acid response. However, deletion of this bile acid response element (BARE-I) enhanced reporter activity but did not eliminate the bile acid response. This is due to the presence of another BARE-II located in a conserved region between nt -149 and -128. Deletion or mutations of these sequences reduced promoter activity and abolished bile acid repression. This BARE-II shares an identical AGTTCAAG core sequence with BARE-I. Electrophoretic mobility shift assays of BARE-I and BARE-II probes using Hep G2 nuclear extract and the partially purified binding activity of nt -65/-54 DNA-affinity column revealed that the same or a similar nuclear protein might bind to both BAREs. BARE-II is the major BARE involved in the transcriptional repression of the CYP7A gene by hydrophobic bile acids.
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Transcriptional regulation of the human Cholesterol 7 Alpha-Hydroxylase gene (CYP7A) in HepG2 cells.
Journal of lipid research, 1996Co-Authors: D P Wang, Diane Stroup, Maria Marrapodi, Maurizio Crestani, G. Galli, John Y. L. ChiangAbstract:A stable HepG2 cell line harboring a human Cholesterol 7 Alpha-Hydroxylase (CYP7A) minigene/luciferase reporter gene construct was selected for studying transcriptional regulation of CYP7A gene promoter. Insulin and phorbol 12-myristate-13-acetate (PMA) strongly repressed the promoter activity as measured with luciferase activity expressed in the cells. The promoter activity of the 5' progressive deletion/luciferase reporter gene constructs was studied in a transient transfection assay in HepG2 cells. PMA represses the promoter activity and the response elements were localized in the -184/-151 and -134/-81 regions. Insulin also represses the promoter activity and response element was mapped in the -298/-81 region. Surprisingly, glucocorticoid receptor (GR) strongly inhibited promoter activity in the presence of dexamethasone, and response elements were localized in the -298/-151 and the -150/+24 regions. Thyroid hormone receptor also repressed promoter activity and response elements were localized in the -150/+24 and upstream regions. Cotransfection of CYP7A chimeric constructs with an expression vector carrying liver-enriched transcription factor HNF3 alpha stimulated the reporter gene activity, but cotransfection with GR plasmid interfered with the HNF3 alpha-stimulated activity possibly through competition for binding to overlapping GR/HNF3 binding sites. Thus, human Cholesterol 7 Alpha-Hydroxylase gene promoter is strongly repressed by insulin, PMA, and steroid/thyroid hormones and results in the low level of Cholesterol 7 Alpha-Hydroxylase expression in the human liver.
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Hormonal regulation of the Cholesterol 7 Alpha-Hydroxylase gene (CYP7).
Journal of lipid research, 1995Co-Authors: Maurizio Crestani, Diane Stroup, John Y. L. ChiangAbstract:The transcriptional regulation of the rat Cholesterol 7 Alpha-Hydroxylase gene (CYP7) by hormones and signal transduction pathways was studied by transient transfection assay of the promoter activity. HepG2 cells were transfected with deletion mutants of the CYP7 upstream region linked to the luciferase reporter gene. The transcription of CYP7/luciferase chimeric genes was higher in confluent than in subconfluent cultures of HepG2 cells. Glucocorticoid receptors, in the presence of dexamethasone, up-regulated the CYP7 gene through two regions located between -3262 and -2803, and between -344 and -222, respectively. Thyroid hormones did not have any effect on the promoter activity. Insulin inhibited the promoter activity through sequences located between -344 and -222, and abolished the stimulation by dexamethasone. Hence, the insulin effect was dominant over that of glucocorticoids. Treatment of transfected HepG2 cells with phorbol 12-myristate 13-acetate (PMA), a known activator of protein kinase C (PKC), resulted in a time-dependent inhibition of the CYP7 promoter activity. The negative phorbol ester-response sequences were mapped between -344 and -222, and between -200 and -161, respectively. The CYP7 promoter activity was induced nearly 5-fold by all-trans-retinoic acid through sequences in the region from -200 to -129. Finally, cyclic AMP and protein kinase A (PKA) stimulated the expression of the CYP7/luciferase gene through multiple sequences in the distal and proximal regions, and both positive and negative response regions were mapped. Our results revealed that the -416 fragment of the rat CYP7 gene confers the activation by glucocorticoids and retinoic acid, and inhibition by insulin, phorbol esters and cAMP. It appears that this proximal promoter may contain a pleiotropic domain that regulates the effects of multiple signals.
Sarah Shefer - One of the best experts on this subject based on the ideXlab platform.
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hepatic Cholesterol and bile acid synthesis low density lipoprotein receptor function and plasma and fecal sterol levels in mice effects of apolipoprotein e deficiency and probucol or phytosterol treatment
Metabolism-clinical and Experimental, 2001Co-Authors: Mohammed H Moghadasian, Gerald Salen, Sarah Shefer, Ashok K. Batta, Lien B. Nguyen, Jiri FrohlichAbstract:Abstract We compared hepatic Cholesterol metabolism in apolipoprotein (apo) E-knockout (KO) mice with their wild-type counterparts. We also investigated the effects of treatment with phytosterols or probucol on the activity of hepatic 3-hydroxy-3-methyl-glutaryl coenzyme A (HMG-CoA) reductase (Cholesterol synthesis), Cholesterol 7[alpha ]-hydroxylase and sterol 27-hydroxylase (bile acid synthesis), and low-density lipoprotein (LDL) receptor function in this animal model of atherogenesis. These findings were then related to treatment-induced changes in plasma, hepatic, and fecal sterol concentrations. Mouse liver membranes have binding sites similar to LDL receptors; the receptor-mediated binding represents 80% of total binding and is LDL concentration-dependent. These binding sites have higher affinity for apo E-containing particles than apo B only-containing particles. Deletion of apo E gene was associated with several-fold increases in plasma Cholesterol levels, 1.5-fold increase in hepatic Cholesterol concentrations, 50% decrease in HMG-CoA reductase activity, 30% increase in Cholesterol 7[alpha ]-hydroxylase and 25% decrease in LDL receptor function. Treatment of apo E-KO mice with either probucol or phytosterols significantly reduced plasma Cholesterol levels. Phytosterols significantly increased the activity of hepatic HMG-CoA reductase, and probucol significantly increased Cholesterol 7[alpha ]-hydroxylase activity. Neither treatment significantly altered hepatic LDL receptor function. Phytosterols, but not probucol, significantly increased fecal sterol excretion and decreased hepatic Cholesterol concentrations. Plasma Cholesterol lowering effects of phytosterols and probucol are due to different mechanisms: stimulation of Cholesterol catabolism via increased bile acid synthesis by probucol and decreased Cholesterol absorption by phytosterols. In the absence of apo E, hepatic LDL receptors could not be upregulated and did not contribute to the Cholesterol lowering effects of either agent.
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Increased bile acid pool inhibits Cholesterol 7 Alpha-Hydroxylase in Cholesterol-fed rabbits
Gastroenterology, 1997Co-Authors: Gerald Salen, G. Stephen Tint, Betsy T Kren, Sarah Shefer, T. Chen, Lien B. Nguyen, Clifford J. Steer, L Salen, David J. GreenblattAbstract:Abstract BACKGROUND & AIMS: Cholesterol feeding unexpectedly inhibits Cholesterol 7 Alpha-Hydroxylase in rabbits. The aim of this study was to explore the mechanism. METHODS: Twenty male New Zealand white rabbits were fed regular chow with and without 2% Cholesterol for 10 days followed by 7 days of bile drainage. The activities of hepatic Cholesterol 7 Alpha-Hydroxylase and sterol 27-hydroxylase that control bile acid synthesis in classic and alternative pathways were related to the size and composition of bile acid pool. RESULTS: After feeding Cholesterol, plasma and hepatic Cholesterol concentrations increased, the bile acid pool doubled (from 254 +/- 44 to 533 +/- 51 mg; P CONCLUSIONS: Feeding Cholesterol increased hepatic Cholesterol and stimulated sterol 27- hydroxylase and alternative bile acid synthesis, which expanded the bile acid pool and inhibited Cholesterol 7 Alpha-Hydroxylase in rabbits. In distinction, hepatic sterol 27-hydroxylase was insensitive to changes in the bile acid pool. (Gastroenterology 1997 Dec;113(6):1958-65)
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Regulation of bile acid synthesis by deoxycholic acid in the rat: different effects on Cholesterol 7 Alpha-Hydroxylase and sterol 27-hydroxylase.
Hepatology (Baltimore Md.), 1995Co-Authors: Sarah Shefer, C J Steer, L B Nguyen, Gerald Salen, G. Stephen Tint, Betsy T Kren, T. Chen, Ashok K. BattaAbstract:We examined the effects of feeding deoxycholic acid (1% and 0.4% of diet), alone and in combination with ursodeoxycholic acid, on serum and biliary bile acid concentrations, hepatic morphology, and the activities and steady-state messenger RNA (mRNA) levels of HMG-CoA reductase and Cholesterol 7 Alpha-Hydroxylase in the rat. Feeding 1% deoxycholic acid increased serum bile acid concentrations (cholestasis), produced portal triad inflammation, bile duct proliferation, and severe hepatocyte necrosis with nuclear pleomorphism. Hepatic damage was prevented when ursodeoxycholic acid (1%) was combined with the deoxycholic acid (1%), or when deoxycholic acid intake was reduced to 0.4%. HMG-CoA reductase and Cholesterol 7 Alpha-Hydroxylase activities were markedly inhibited (-56% and -55%, respectively) with either 1% or 0.4% deoxycholic acid. Ursodeoxycholic acid alone produced an insignificant decline in HMG-CoA reductase and Cholesterol 7 Alpha-Hydroxylase activities, and when combined with 1% deoxycholic acid did not lessen the inhibitory effect of the latter. Steady-state mRNA levels increased 20-fold for HMG-CoA reductase and 53-fold for Cholesterol 7 Alpha-Hydroxylase in rats fed 1% deoxycholic acid. In contrast, 0.4% deoxycholic acid decreased HMG-CoA reductase mRNA levels 76%, and Cholesterol 7 Alpha-Hydroxylase mRNA levels 82%. Ursodeoxycholic acid alone did not affect HMG-CoA reductase or Cholesterol 7 Alpha-Hydroxylase steady-state mRNA levels. Steady-state mRNA levels and activities of sterol 27-hydroxylase, a key enzyme in the alternative acidic pathway of bile acid synthesis, did not change with either high or low doses of deoxycholic acid.(ABSTRACT TRUNCATED AT 250 WORDS)
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Unexpected inhibition of Cholesterol 7 Alpha-Hydroxylase by Cholesterol in New Zealand white and Watanabe heritable hyperlipidemic rabbits.
Journal of Clinical Investigation, 1995Co-Authors: Gerald Salen, Sarah Shefer, Lien B. Nguyen, Gene C. Ness, Thomas S. Parker, Thomas S. Chen, Zhihong Zhao, Thomas M. Donnelly, G. Stephen TintAbstract:We investigated the effect of Cholesterol feeding on plasma Cholesterol concentrations, hepatic activities and mRNA levels of HMG-CoA reductase and Cholesterol 7 Alpha-Hydroxylase and hepatic LDL receptor function and mRNA levels in 23 New Zealand White (NZW) and 17 Watanabe heritable hyperlipidemic (WHHL) rabbits. Plasma Cholesterol concentrations were 9.9 times greater in WHHL than NZW rabbits and rose significantly in both groups when Cholesterol was fed. Baseline liver Cholesterol levels were 50% higher but rose only 26% in WHHL as compared with 3.6-fold increase with the Cholesterol diet in NZW rabbits. In both rabbit groups, hepatic total HMG-CoA reductase activity was similar and declined > 60% without changing enzyme mRNA levels after Cholesterol was fed. In NZW rabbits, Cholesterol feeding inhibited LDL receptor function but not mRNA levels. As expected, receptor-mediated LDL binding was reduced in WHHL rabbits. Hepatic Cholesterol 7 Alpha-Hydroxylase activity and mRNA levels were 2.8 and 10.4 times greater in NZW than WHHL rabbits. Unexpectedly, Cholesterol 7 Alpha-Hydroxylase activity was reduced 53% and mRNA levels were reduced 79% in NZW rabbits with 2% Cholesterol feeding. These results demonstrate that WHHL as compared with NZW rabbits have markedly elevated plasma and higher liver Cholesterol concentrations, less hepatic LDL receptor function, and very low hepatic Cholesterol 7 Alpha-Hydroxylase activity and mRNA levels. Feeding Cholesterol to NZW rabbits increased plasma and hepatic concentrations greatly, inhibited LDL receptor-mediated binding, and unexpectedly suppressed Cholesterol 7 Alpha-Hydroxylase activity and mRNA to minimum levels similar to WHHL rabbits. Dietary Cholesterol accumulates in the plasma of NZW rabbits, and WHHL rabbits are hyperCholesterolemic because reduced LDL receptor function is combined with decreased catabolism of Cholesterol to bile acids.
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The effect of increased hepatic sitosterol on the regulation of 3-hydroxy-3-methylglutaryl-coenzyme A reductase and Cholesterol 7 Alpha-Hydroxylase in the rat and sitosterolemic homozygotes.
Hepatology (Baltimore Md.), 1994Co-Authors: Sarah Shefer, L B Nguyen, Gerald Salen, S Lerner, J Bullock, G C Ness, Z Vhao, P F Belamarich, I Chowdhary, Ashok K. BattaAbstract:We investigated hepatic Cholesterol homeostasis in four homozygous sitosterolemic subjects from two unrelated families who showed enhanced absorption, diminished removal and increased tissue and plasma concentrations of sitosterol (24-ethyl Cholesterol). Measurements of hepatic 3-hydroxy-3-methylglutaryl coenzyme A reductase activities were correlated with steady state messenger RNA levels and related to Cholesterol 7 Alpha-Hydroxylase activities in the sitosterolemic homozygotes and nine controls. Similar determinations were made in rats infused intravenously with sitosterol so that hepatic and plasma sitosterol concentrations increased to about 10% of total sterols to resemble the human disease sitosterolemia. In the four sitosterolemic homozygotes, hepatic 3-hydroxy-3-methylglutaryl coenzyme A reductase activities were markedly reduced (12% of normal), and steady state 3-hydroxy-3-methylglutaryl coenzyme A reductase messenger RNA levels barely detected. In contrast, hepatic 3-hydroxy-3-methylglutaryl coenzyme A reductase activities and messenger RNA levels were not decreased in rats with similarly elevated hepatic sitosterol concentrations. However, hepatic Cholesterol 7 Alpha-Hydroxylase activity was inhibited 30% in both the sitosterolemic homozygotes and rats with high liver sitosterol concentrations. Plasma Cholesterol concentrations increased 120% in the sitosterol-infused rats and 29% in the untreated human homozygotes. These results demonstrate that high-tissue sitosterol concentrations do not inhibit hepatic 3-hydroxy-3-methylglutaryl coenzyme A reductase activityor steady state messenger RNA levels and that they competitively block Cholesterol 7 Alpha-Hydroxylase activity and raise plasma Cholesterol levels. Thus the deficiency of 3-hydroxy-3-methylglutaryl coenzyme A reductase in the liver of sitosterolemic homozygotes is inherited and not due to the hepatic accumulation of sitosterol.(ABSTRACT TRUNCATED AT 250 WORDS)
Gene C. Ness - One of the best experts on this subject based on the ideXlab platform.
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Unexpected inhibition of Cholesterol 7 Alpha-Hydroxylase by Cholesterol in New Zealand white and Watanabe heritable hyperlipidemic rabbits.
Journal of Clinical Investigation, 1995Co-Authors: Gerald Salen, Sarah Shefer, Lien B. Nguyen, Gene C. Ness, Thomas S. Parker, Thomas S. Chen, Zhihong Zhao, Thomas M. Donnelly, G. Stephen TintAbstract:We investigated the effect of Cholesterol feeding on plasma Cholesterol concentrations, hepatic activities and mRNA levels of HMG-CoA reductase and Cholesterol 7 Alpha-Hydroxylase and hepatic LDL receptor function and mRNA levels in 23 New Zealand White (NZW) and 17 Watanabe heritable hyperlipidemic (WHHL) rabbits. Plasma Cholesterol concentrations were 9.9 times greater in WHHL than NZW rabbits and rose significantly in both groups when Cholesterol was fed. Baseline liver Cholesterol levels were 50% higher but rose only 26% in WHHL as compared with 3.6-fold increase with the Cholesterol diet in NZW rabbits. In both rabbit groups, hepatic total HMG-CoA reductase activity was similar and declined > 60% without changing enzyme mRNA levels after Cholesterol was fed. In NZW rabbits, Cholesterol feeding inhibited LDL receptor function but not mRNA levels. As expected, receptor-mediated LDL binding was reduced in WHHL rabbits. Hepatic Cholesterol 7 Alpha-Hydroxylase activity and mRNA levels were 2.8 and 10.4 times greater in NZW than WHHL rabbits. Unexpectedly, Cholesterol 7 Alpha-Hydroxylase activity was reduced 53% and mRNA levels were reduced 79% in NZW rabbits with 2% Cholesterol feeding. These results demonstrate that WHHL as compared with NZW rabbits have markedly elevated plasma and higher liver Cholesterol concentrations, less hepatic LDL receptor function, and very low hepatic Cholesterol 7 Alpha-Hydroxylase activity and mRNA levels. Feeding Cholesterol to NZW rabbits increased plasma and hepatic concentrations greatly, inhibited LDL receptor-mediated binding, and unexpectedly suppressed Cholesterol 7 Alpha-Hydroxylase activity and mRNA to minimum levels similar to WHHL rabbits. Dietary Cholesterol accumulates in the plasma of NZW rabbits, and WHHL rabbits are hyperCholesterolemic because reduced LDL receptor function is combined with decreased catabolism of Cholesterol to bile acids.
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Developmental regulation of the expression of genes encoding proteins involved in Cholesterol homeostasis
American Journal of Medical Genetics, 1994Co-Authors: Gene C. NessAbstract:The developmental patterns of expression of HMG-CoA reductase, farnesyl pyrophosphate synthase, Cholesterol 7 Alpha-Hydroxylase, and LDL receptor were investigated using Northern blotting analysis to quantitate mRNA levels. It was found that HMG-CoA reductase and farnesyl pyrophosphate synthase mRNA levels in brain reached peaks at age 4 days which correlates with the time of peak enzyme activity and the onset of rapid brain growth and myelination. In liver, HMG-CoA reductase and Cholesterol 7 Alpha-Hydroxylase mRNA both rose dramatically at weaning. This is consistent with the concept that de novo synthesized Cholesterol is the preferred substrate for Cholesterol 7 Alpha-Hydroxylase and may also be involved in the induction of the enzyme. In testes, HMG-CoA reductase activity was highest at age 21 days and then declined, while LDL receptor mRNA levels rose from age 31 to 120 days. These studies suggest a major role for de novo Cholesterol synthesis in developing brain, liver, and testes.
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Differing effects of Cholesterol and taurocholate on steady state hepatic HMG-CoA reductase and Cholesterol 7 Alpha-Hydroxylase activities and mRNA levels in the rat.
Journal of lipid research, 1992Co-Authors: Sarah Shefer, Gerald Salen, Ashok K. Batta, Lien B. Nguyen, Gene C. Ness, Indu R. Chowdhary, S Lerner, G. Stephen TintAbstract:We investigated the effects of Cholesterol, cholestyramine, and taurocholate feeding on steady state specific activities and mRNA levels of hepatic 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase and Cholesterol 7 Alpha-Hydroxylase in the rat. Interruption of the enterohepatic circulation of bile acids (cholestyramine feeding) increased total HMG-CoA reductase activity 5-fold. Cholesterol and taurocholate administration suppressed total microsomal HMG-CoA reductase activities 87% and 65%, respectively. HMG-CoA reductase mRNA levels increased 3-fold with cholestyramine, did not decrease significantly with Cholesterol feeding, but were markedly decreased after taurocholate treatment. Cholesterol 7 Alpha-Hydroxylase activity increased 4-fold with cholestyramine and 29% during Cholesterol feeding, but decreased 64% with taurocholate. Cholesterol 7 Alpha-Hydroxylase mRNA levels rose 150% and 50% with cholestyramine and Cholesterol feeding, respectively, but decreased 73% with taurocholate. The administration of Cholesterol together with taurocholate prevented the decline in Cholesterol 7 Alpha-Hydroxylase mRNA levels, but inhibition of enzyme activity persisted (-76%). Hepatic microsomal Cholesterol concentrations increased 2-fold with Cholesterol feeding but did not change with taurocholate or cholestyramine treatment. These results demonstrate that mRNA levels of HMG-CoA reductase are controlled by the hepatic taurocholate flux, whereas mRNA levels of Cholesterol 7 Alpha-Hydroxylase are controlled by the Cholesterol substrate supply. These end products, Cholesterol and bile acids, exert post-transcriptional regulation on HMG-CoA reductase and Cholesterol 7 Alpha-Hydroxylase, respectively.
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Regulation of Cholesterol 7 Alpha-Hydroxylase by hepatic 7 alpha-hydroxylated bile acid flux and newly synthesized Cholesterol supply.
The Journal of biological chemistry, 1991Co-Authors: Sarah Shefer, Gerald Salen, G. Stephen Tint, Ashok K. Batta, Lien B. Nguyen, Gene C. Ness, Stephen L. Hauser, I RaniAbstract:We measured hepatic Cholesterol 7 Alpha-Hydroxylase activity, mass, and catalytic efficiency (activity/unit mass) in bile fistula rats infused intraduodenally with taurocholate and its 7 beta-hydroxy epimer, tauroursocholate, with or without mevalonolactone to supply newly synthesized Cholesterol. Enzyme activity was measured by an isotope incorporation assay and enzyme mass by densitometric scanning of immunoblots using rabbit anti-rat liver Cholesterol 7 Alpha-Hydroxylase antisera. Cholesterol 7 Alpha-Hydroxylase activity increased 6-fold, enzyme mass 34%, and catalytic efficiency 5-fold after interruption of the enterohepatic circulation for 48 h. When taurocholate was infused to the bile acid-depleted animals at a rate equivalent to the hepatic bile acid flux (27 mumol/100-g rat/h), Cholesterol 7 Alpha-Hydroxylase activity and enzyme mass declined 60 and 61%, respectively. Tauroursocholate did not significantly decrease Cholesterol 7 Alpha-Hydroxylase activity, mass and catalytic efficiency. The administration of mevalonolactone, which is converted to Cholesterol, modestly increased Cholesterol 7 Alpha-Hydroxylase activity and enzyme mass in the bile acid-depleted rats. However, when taurocholate was infused together with mevalonolactone, Cholesterol 7 Alpha-Hydroxylase activity and catalytic efficiency were markedly depressed while enzyme mass did not change as compared with bile acid-depleted rats. These results show that (a) hepatic bile acid depletion increases bile acid synthesis mainly by activating Cholesterol 7 Alpha-Hydroxylase with only a small rise in enzyme mass, (b) replacement with taurocholate for 24 h decreases both Cholesterol 7 Alpha-Hydroxylase activity and mass proportionally, (c) when Cholesterol is available (mevalonolactone supplementation), the infusion of taurocholate results in the formation of a catalytically less active Cholesterol 7 Alpha-Hydroxylase, and (d) tauroursocholate, the 7 beta-hydroxy epimer of taurocholate, does not inhibit Cholesterol 7 Alpha-Hydroxylase. Thus, bile acid synthesis is modulated by the catalytic efficiency and mass of Cholesterol 7 Alpha-Hydroxylase. The enterohepatic flux of 7 alpha-hydroxylated bile acids and the formation of hepatic Cholesterol apparently control Cholesterol 7 Alpha-Hydroxylase by different mechanisms.
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Thyroid hormone. Basis for its hypoCholesterolemic effect.
The Journal of the Florida Medical Association, 1991Co-Authors: Gene C. NessAbstract:The liver is the key organ involved in Cholesterol homeostasis. Thyroid hormone binds to nuclear receptors in the liver and thereby acts to alter the expression of several genes coding for proteins involved in Cholesterol homeostasis. The expression of apo B-100, the major protein of LDL, is markedly decreased by thyroid hormone while expression of apo A-I, the major protein of HDL, is profoundly increased by thyroid hormone. The thyroid hormone acts to increase hepatic LDL receptor and Cholesterol 7 alpha hydroxylase gene expression. The increase in Cholesterol 7 alpha hydroxylase, the enzyme which catalyzes the rate-limiting reaction in the degradation of Cholesterol to form bile acids, occurs the most rapidly (within one hour) and requires low physiological doses of hormone. Inspection of the 5' flanking region of the Cholesterol 7 alpha hydroxylase gene revealed two possible thyroid responsive elements, suggesting that thyroid hormone may exert a primary effect on this gene. The alterations in gene expression produced by thyroid hormone would be expected to result in decreased LDL levels because of decreased apo B-100 synthesis, increased HDL to assist in reverse Cholesterol transport from peripheral tissue to the liver, increased removal of LDL from blood by increased hepatic LDL receptors, and increased elimination of Cholesterol as neutral sterols and bile acids due to increased Cholesterol 7 alpha hydroxylase. These actions would lead to lower serum Cholesterol levels.
Ashok K. Batta - One of the best experts on this subject based on the ideXlab platform.
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hepatic Cholesterol and bile acid synthesis low density lipoprotein receptor function and plasma and fecal sterol levels in mice effects of apolipoprotein e deficiency and probucol or phytosterol treatment
Metabolism-clinical and Experimental, 2001Co-Authors: Mohammed H Moghadasian, Gerald Salen, Sarah Shefer, Ashok K. Batta, Lien B. Nguyen, Jiri FrohlichAbstract:Abstract We compared hepatic Cholesterol metabolism in apolipoprotein (apo) E-knockout (KO) mice with their wild-type counterparts. We also investigated the effects of treatment with phytosterols or probucol on the activity of hepatic 3-hydroxy-3-methyl-glutaryl coenzyme A (HMG-CoA) reductase (Cholesterol synthesis), Cholesterol 7[alpha ]-hydroxylase and sterol 27-hydroxylase (bile acid synthesis), and low-density lipoprotein (LDL) receptor function in this animal model of atherogenesis. These findings were then related to treatment-induced changes in plasma, hepatic, and fecal sterol concentrations. Mouse liver membranes have binding sites similar to LDL receptors; the receptor-mediated binding represents 80% of total binding and is LDL concentration-dependent. These binding sites have higher affinity for apo E-containing particles than apo B only-containing particles. Deletion of apo E gene was associated with several-fold increases in plasma Cholesterol levels, 1.5-fold increase in hepatic Cholesterol concentrations, 50% decrease in HMG-CoA reductase activity, 30% increase in Cholesterol 7[alpha ]-hydroxylase and 25% decrease in LDL receptor function. Treatment of apo E-KO mice with either probucol or phytosterols significantly reduced plasma Cholesterol levels. Phytosterols significantly increased the activity of hepatic HMG-CoA reductase, and probucol significantly increased Cholesterol 7[alpha ]-hydroxylase activity. Neither treatment significantly altered hepatic LDL receptor function. Phytosterols, but not probucol, significantly increased fecal sterol excretion and decreased hepatic Cholesterol concentrations. Plasma Cholesterol lowering effects of phytosterols and probucol are due to different mechanisms: stimulation of Cholesterol catabolism via increased bile acid synthesis by probucol and decreased Cholesterol absorption by phytosterols. In the absence of apo E, hepatic LDL receptors could not be upregulated and did not contribute to the Cholesterol lowering effects of either agent.
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Regulation of bile acid synthesis by deoxycholic acid in the rat: different effects on Cholesterol 7 Alpha-Hydroxylase and sterol 27-hydroxylase.
Hepatology (Baltimore Md.), 1995Co-Authors: Sarah Shefer, C J Steer, L B Nguyen, Gerald Salen, G. Stephen Tint, Betsy T Kren, T. Chen, Ashok K. BattaAbstract:We examined the effects of feeding deoxycholic acid (1% and 0.4% of diet), alone and in combination with ursodeoxycholic acid, on serum and biliary bile acid concentrations, hepatic morphology, and the activities and steady-state messenger RNA (mRNA) levels of HMG-CoA reductase and Cholesterol 7 Alpha-Hydroxylase in the rat. Feeding 1% deoxycholic acid increased serum bile acid concentrations (cholestasis), produced portal triad inflammation, bile duct proliferation, and severe hepatocyte necrosis with nuclear pleomorphism. Hepatic damage was prevented when ursodeoxycholic acid (1%) was combined with the deoxycholic acid (1%), or when deoxycholic acid intake was reduced to 0.4%. HMG-CoA reductase and Cholesterol 7 Alpha-Hydroxylase activities were markedly inhibited (-56% and -55%, respectively) with either 1% or 0.4% deoxycholic acid. Ursodeoxycholic acid alone produced an insignificant decline in HMG-CoA reductase and Cholesterol 7 Alpha-Hydroxylase activities, and when combined with 1% deoxycholic acid did not lessen the inhibitory effect of the latter. Steady-state mRNA levels increased 20-fold for HMG-CoA reductase and 53-fold for Cholesterol 7 Alpha-Hydroxylase in rats fed 1% deoxycholic acid. In contrast, 0.4% deoxycholic acid decreased HMG-CoA reductase mRNA levels 76%, and Cholesterol 7 Alpha-Hydroxylase mRNA levels 82%. Ursodeoxycholic acid alone did not affect HMG-CoA reductase or Cholesterol 7 Alpha-Hydroxylase steady-state mRNA levels. Steady-state mRNA levels and activities of sterol 27-hydroxylase, a key enzyme in the alternative acidic pathway of bile acid synthesis, did not change with either high or low doses of deoxycholic acid.(ABSTRACT TRUNCATED AT 250 WORDS)
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The effect of increased hepatic sitosterol on the regulation of 3-hydroxy-3-methylglutaryl-coenzyme A reductase and Cholesterol 7 Alpha-Hydroxylase in the rat and sitosterolemic homozygotes.
Hepatology (Baltimore Md.), 1994Co-Authors: Sarah Shefer, L B Nguyen, Gerald Salen, S Lerner, J Bullock, G C Ness, Z Vhao, P F Belamarich, I Chowdhary, Ashok K. BattaAbstract:We investigated hepatic Cholesterol homeostasis in four homozygous sitosterolemic subjects from two unrelated families who showed enhanced absorption, diminished removal and increased tissue and plasma concentrations of sitosterol (24-ethyl Cholesterol). Measurements of hepatic 3-hydroxy-3-methylglutaryl coenzyme A reductase activities were correlated with steady state messenger RNA levels and related to Cholesterol 7 Alpha-Hydroxylase activities in the sitosterolemic homozygotes and nine controls. Similar determinations were made in rats infused intravenously with sitosterol so that hepatic and plasma sitosterol concentrations increased to about 10% of total sterols to resemble the human disease sitosterolemia. In the four sitosterolemic homozygotes, hepatic 3-hydroxy-3-methylglutaryl coenzyme A reductase activities were markedly reduced (12% of normal), and steady state 3-hydroxy-3-methylglutaryl coenzyme A reductase messenger RNA levels barely detected. In contrast, hepatic 3-hydroxy-3-methylglutaryl coenzyme A reductase activities and messenger RNA levels were not decreased in rats with similarly elevated hepatic sitosterol concentrations. However, hepatic Cholesterol 7 Alpha-Hydroxylase activity was inhibited 30% in both the sitosterolemic homozygotes and rats with high liver sitosterol concentrations. Plasma Cholesterol concentrations increased 120% in the sitosterol-infused rats and 29% in the untreated human homozygotes. These results demonstrate that high-tissue sitosterol concentrations do not inhibit hepatic 3-hydroxy-3-methylglutaryl coenzyme A reductase activityor steady state messenger RNA levels and that they competitively block Cholesterol 7 Alpha-Hydroxylase activity and raise plasma Cholesterol levels. Thus the deficiency of 3-hydroxy-3-methylglutaryl coenzyme A reductase in the liver of sitosterolemic homozygotes is inherited and not due to the hepatic accumulation of sitosterol.(ABSTRACT TRUNCATED AT 250 WORDS)
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Differing effects of Cholesterol and taurocholate on steady state hepatic HMG-CoA reductase and Cholesterol 7 Alpha-Hydroxylase activities and mRNA levels in the rat.
Journal of lipid research, 1992Co-Authors: Sarah Shefer, Gerald Salen, Ashok K. Batta, Lien B. Nguyen, Gene C. Ness, Indu R. Chowdhary, S Lerner, G. Stephen TintAbstract:We investigated the effects of Cholesterol, cholestyramine, and taurocholate feeding on steady state specific activities and mRNA levels of hepatic 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase and Cholesterol 7 Alpha-Hydroxylase in the rat. Interruption of the enterohepatic circulation of bile acids (cholestyramine feeding) increased total HMG-CoA reductase activity 5-fold. Cholesterol and taurocholate administration suppressed total microsomal HMG-CoA reductase activities 87% and 65%, respectively. HMG-CoA reductase mRNA levels increased 3-fold with cholestyramine, did not decrease significantly with Cholesterol feeding, but were markedly decreased after taurocholate treatment. Cholesterol 7 Alpha-Hydroxylase activity increased 4-fold with cholestyramine and 29% during Cholesterol feeding, but decreased 64% with taurocholate. Cholesterol 7 Alpha-Hydroxylase mRNA levels rose 150% and 50% with cholestyramine and Cholesterol feeding, respectively, but decreased 73% with taurocholate. The administration of Cholesterol together with taurocholate prevented the decline in Cholesterol 7 Alpha-Hydroxylase mRNA levels, but inhibition of enzyme activity persisted (-76%). Hepatic microsomal Cholesterol concentrations increased 2-fold with Cholesterol feeding but did not change with taurocholate or cholestyramine treatment. These results demonstrate that mRNA levels of HMG-CoA reductase are controlled by the hepatic taurocholate flux, whereas mRNA levels of Cholesterol 7 Alpha-Hydroxylase are controlled by the Cholesterol substrate supply. These end products, Cholesterol and bile acids, exert post-transcriptional regulation on HMG-CoA reductase and Cholesterol 7 Alpha-Hydroxylase, respectively.
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Regulation of Cholesterol 7 Alpha-Hydroxylase by hepatic 7 alpha-hydroxylated bile acid flux and newly synthesized Cholesterol supply.
The Journal of biological chemistry, 1991Co-Authors: Sarah Shefer, Gerald Salen, G. Stephen Tint, Ashok K. Batta, Lien B. Nguyen, Gene C. Ness, Stephen L. Hauser, I RaniAbstract:We measured hepatic Cholesterol 7 Alpha-Hydroxylase activity, mass, and catalytic efficiency (activity/unit mass) in bile fistula rats infused intraduodenally with taurocholate and its 7 beta-hydroxy epimer, tauroursocholate, with or without mevalonolactone to supply newly synthesized Cholesterol. Enzyme activity was measured by an isotope incorporation assay and enzyme mass by densitometric scanning of immunoblots using rabbit anti-rat liver Cholesterol 7 Alpha-Hydroxylase antisera. Cholesterol 7 Alpha-Hydroxylase activity increased 6-fold, enzyme mass 34%, and catalytic efficiency 5-fold after interruption of the enterohepatic circulation for 48 h. When taurocholate was infused to the bile acid-depleted animals at a rate equivalent to the hepatic bile acid flux (27 mumol/100-g rat/h), Cholesterol 7 Alpha-Hydroxylase activity and enzyme mass declined 60 and 61%, respectively. Tauroursocholate did not significantly decrease Cholesterol 7 Alpha-Hydroxylase activity, mass and catalytic efficiency. The administration of mevalonolactone, which is converted to Cholesterol, modestly increased Cholesterol 7 Alpha-Hydroxylase activity and enzyme mass in the bile acid-depleted rats. However, when taurocholate was infused together with mevalonolactone, Cholesterol 7 Alpha-Hydroxylase activity and catalytic efficiency were markedly depressed while enzyme mass did not change as compared with bile acid-depleted rats. These results show that (a) hepatic bile acid depletion increases bile acid synthesis mainly by activating Cholesterol 7 Alpha-Hydroxylase with only a small rise in enzyme mass, (b) replacement with taurocholate for 24 h decreases both Cholesterol 7 Alpha-Hydroxylase activity and mass proportionally, (c) when Cholesterol is available (mevalonolactone supplementation), the infusion of taurocholate results in the formation of a catalytically less active Cholesterol 7 Alpha-Hydroxylase, and (d) tauroursocholate, the 7 beta-hydroxy epimer of taurocholate, does not inhibit Cholesterol 7 Alpha-Hydroxylase. Thus, bile acid synthesis is modulated by the catalytic efficiency and mass of Cholesterol 7 Alpha-Hydroxylase. The enterohepatic flux of 7 alpha-hydroxylated bile acids and the formation of hepatic Cholesterol apparently control Cholesterol 7 Alpha-Hydroxylase by different mechanisms.
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cyclosporine a impairs the macrophage reverse Cholesterol transport in mice by reducing sterol fecal excretion
PLOS ONE, 2013Co-Authors: Ilaria Zanotti, Lorenzo Arnaboldi, G Lusardi, Francesca Zimetti, Francesco Poti, Alberto Corsini, D Greco, Franco BerniniAbstract:Despite the efficacy in reducing acute rejection events in organ transplanted subjects, long term therapy with cyclosporine A is associated with increased atherosclerotic cardiovascular morbidity. We studied whether this drug affects the antiatherogenic process of the reverse Cholesterol transport from macrophages in vivo. Cyclosporine A 50 mg/kg/d was administered to C57BL/6 mice by subcutaneous injection for 14 days. Macrophage reverse Cholesterol transport was assessed by following [3H]-Cholesterol mobilization from pre-labeled intraperitoneally injected macrophages, expressing or not apolipoprotein E, to plasma, liver and feces. The pharmacological treatment significantly reduced the amount of radioactive sterols in the feces, independently on the expression of apolipoprotein E in the macrophages injected into recipient mice and in absence of changes of plasma levels of high density lipoprotein-Cholesterol. Gene expression analysis revealed that cyclosporine A inhibited the hepatic levels of Cholesterol 7-Alpha-Hydroxylase, concomitantly with the increase in hepatic and intestinal expression of ATP Binding Cassette G5. However, the in vivo relevance of the last observation was challenged by the demonstration that mice treated or not with cyclosporine A showed the same levels of circulating beta-sitosterol. These results indicate that treatment of mice with cyclosporine A impaired the macrophage reverse Cholesterol transport by reducing fecal sterol excretion, possibly through the inhibition of Cholesterol 7-Alpha-Hydroxylase expression. The current observation may provide a potential mechanism for the high incidence of atherosclerotic coronary artery disease following the immunosuppressant therapy in organ transplanted recipients.