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Sarah Shefer - One of the best experts on this subject based on the ideXlab platform.
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regulation of early cholesterol biosynthesis in rat liver effects of sterols bile acids lovastatin and bm 15 766 on 3 hydroxy 3 methylglutaryl coenzyme a synthase and acetoacetyl coenzyme a thiolase activities
Hepatology, 1998Co-Authors: Akira Honda, Gerald Salen, Ashok K. Batta, Lien B. Nguyen, Guorong Xu, Stephen G Tint, Sarah SheferAbstract:Cytosolic 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) synthase catalyzes the formation of HMG-CoA, the substrate for the rate-controlling enzyme in the cholesterol biosynthetic pathway. To explore the regulation in liver, we developed a new, accurate, and reliable reversed-phase ion-pair chromatographic assay that uses nonradioactive substrates and n-propionyl coenzyme A as an internal recovery standard. The hepatic activities were measured in rats treated with cholesterol, sitosterol, cholic acid, deoxycholic acid, ursodeoxycholic acid, cholestyramine, bile fistula, lovastatin, and BM 15.766, an inhibitor of 7-dehydrocholesterol Δ7-reductase, and were compared with microsomal HMG-CoA reductase and cytosolic acetoacetyl coenzyme A (AcAc-CoA) thiolase activities. HMG-CoA synthase activity was effectively suppressed in synchrony with HMG-CoA reductase activity by treatments with cholesterol (−41%, P< .05), cholic acid (−72%, P< .005), and deoxycholic acid (−62%, P< .05). However, ursodeoxycholic acid increased activity 84% (P< .05) and intravenous sitosterol did not change activity. AcAc-CoA thiolase activities also paralleled HMG-CoA reductase and HMG-CoA synthase activities, but differences were not statistically significant. In contrast to inhibition, up-regulation of hepatic HMG-CoA synthase activities by cholestyramine, bile fistula, and lovastatin was much less than HMG-CoA reductase activities. In addition, BM 15.766 did not stimulate synthase activity, whereas lovastatin increased activity 2.4-fold. Thus, hepatic HMG-CoA synthase activity was regulated coordinately with HMG-CoA reductase, and responded more forcefully to regulatory stimuli than acetoacetyl-CoA thiolase activity but usually less than HMG-CoA reductase.
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down regulation of cholesterol biosynthesis in sitosterolemia diminished activities of acetoacetyl coa thiolase 3 hydroxy 3 methylglutaryl coa synthase reductase squalene synthase and 7 dehydrocholesterol delta7 reductase in liver and mononuclear leu
Journal of Lipid Research, 1998Co-Authors: Akira Honda, Gerald Salen, G. Stephen Tint, Ashok K. Batta, Lien B. Nguyen, Sarah SheferAbstract:Sitosterolemia is a recessively inherited disorder characterized by abnormally increased plasma and tissue plant sterol concentrations. Patients have markedly reduced whole body cholesterol biosynthesis associated with sup- pressed hepatic, ileal, and mononuclear leukocyte 3-hydroxy- 3-methylglutaryl coenzyme A (HMG-CoA) reductase, the rate- controlling enzyme in cholesterol biosynthetic pathway, coupled with significantly increased low density lipoprotein (LDL) receptor expression. To investigate the mechanism of down- regulated cholesterol biosynthesis, we assayed several other key enzymes in the cholesterol biosynthetic pathway includ- ing acetoacetyl-CoA thiolase, HMG-CoA synthase, squalene synthase, and 7-dehydrocholesterol D 7 -reductase activities in liver and freshly isolated mononuclear leukocytes from four sitosterolemic patients and 19 controls. Hepatic acetoacetyl- CoA thiolase, HMG-CoA synthase, reductase, and squalene synthase activities were significantly decreased ( P , 0.05) 2 39%, 2 54%, 2 76%, and 2 57%, respectively, and 7-dehydro- cholesterol D 7 -reductase activity tended to be lower ( 2 35%) in the sitosterolemic compared with control subjects. The re- duced HMG-CoA synthase, reductase, and squalene synthase activities were also found in mononuclear leukocytes from a sitosterolemic patient. Thus, reduced cholesterol synthesis is caused not only by decreased HMG-CoA reductase but also by the coordinate down-regulation of entire pathway of choles- terol biosynthesis. These results suggest that inadequate cholesterol production in sitosterolemia is due to abnormal down-regulation of early, intermediate, and late enzymes in the cholesterol biosynthetic pathway rather than a single in- herited defect in the HMG-CoA reductase gene.— Honda, A., G. Salen, L. B. Nguyen, G. S. Tint, A. K. Batta, and S. Shefer. Down-regulation of cholesterol biosynthesis in sitosterolemia: diminished activities of acetoacetyl-CoA thiolase, 3-hydroxy-3- methylglutaryl-CoA synthase, reductase, squalene synthase, and 7-dehydrocholesterol D 7 -reductase in liver and mononu- clear leukocytes. J. Lipid Res. 1998. 39: 44-50.
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Regulation of bile acid synthesis by deoxycholic acid in the rat: Different effects on cholesterol 7α-hydroxylase and sterol 27-hydroxylase
Hepatology, 1995Co-Authors: Sarah Shefer, C J Steer, L B Nguyen, Thomas T. Chen, Gerald Salen, G. Stephen Tint, Betsy T Kren, Ashok K. BattaAbstract:Abstract 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 7α-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 7α-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 7α-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 7α-hydroxylase in rats fed 1% deoxycholic acid. In contrast, 0.4% deoxycholic acid decreased HMG-CoA reductase mRNA levels 76%, and cholesterol 7α-hydroxylase mRNA levels 82%. Ursodeoxycholic acid alone did not affect HMG-CoA reductase or cholesterol 7α-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. In conclusion, 1% deoxycholic acid induced hepatocyte destruction and regeneration associated with increased mRNA levels for HMG-CoA reductase and cholesterol 7α-hydroxylase, but significantly suppressed both enzyme activities. Thus, high-dose deoxycholic acid uncouples HMG-CoA reductase and cholesterol 7α-hydroxylase mRNA levels from enzyme function. In contrast, lower-dose deoxycholic acid (0.4%) inhibited both activities and mRNA levels of HMG-CoAreductase and cholesterol 7α-hydroxylase. Adding 1% ursodeoxycholic acid to 1% deoxycholic acid prevented the rise in mRNA levels but did not lessen the inhibitory effect of the latter. This inhibition occurred without change in hepatic histology, which suggests a regulatory role for deoxycholic acid that is independent of liver damage. Conversely, sterol 27-hydroxylase activity and mRNA levels are not affected by deoxycholic acid treatments.
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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.
Ashok K. Batta - One of the best experts on this subject based on the ideXlab platform.
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regulation of early cholesterol biosynthesis in rat liver effects of sterols bile acids lovastatin and bm 15 766 on 3 hydroxy 3 methylglutaryl coenzyme a synthase and acetoacetyl coenzyme a thiolase activities
Hepatology, 1998Co-Authors: Akira Honda, Gerald Salen, Ashok K. Batta, Lien B. Nguyen, Guorong Xu, Stephen G Tint, Sarah SheferAbstract:Cytosolic 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) synthase catalyzes the formation of HMG-CoA, the substrate for the rate-controlling enzyme in the cholesterol biosynthetic pathway. To explore the regulation in liver, we developed a new, accurate, and reliable reversed-phase ion-pair chromatographic assay that uses nonradioactive substrates and n-propionyl coenzyme A as an internal recovery standard. The hepatic activities were measured in rats treated with cholesterol, sitosterol, cholic acid, deoxycholic acid, ursodeoxycholic acid, cholestyramine, bile fistula, lovastatin, and BM 15.766, an inhibitor of 7-dehydrocholesterol Δ7-reductase, and were compared with microsomal HMG-CoA reductase and cytosolic acetoacetyl coenzyme A (AcAc-CoA) thiolase activities. HMG-CoA synthase activity was effectively suppressed in synchrony with HMG-CoA reductase activity by treatments with cholesterol (−41%, P< .05), cholic acid (−72%, P< .005), and deoxycholic acid (−62%, P< .05). However, ursodeoxycholic acid increased activity 84% (P< .05) and intravenous sitosterol did not change activity. AcAc-CoA thiolase activities also paralleled HMG-CoA reductase and HMG-CoA synthase activities, but differences were not statistically significant. In contrast to inhibition, up-regulation of hepatic HMG-CoA synthase activities by cholestyramine, bile fistula, and lovastatin was much less than HMG-CoA reductase activities. In addition, BM 15.766 did not stimulate synthase activity, whereas lovastatin increased activity 2.4-fold. Thus, hepatic HMG-CoA synthase activity was regulated coordinately with HMG-CoA reductase, and responded more forcefully to regulatory stimuli than acetoacetyl-CoA thiolase activity but usually less than HMG-CoA reductase.
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down regulation of cholesterol biosynthesis in sitosterolemia diminished activities of acetoacetyl coa thiolase 3 hydroxy 3 methylglutaryl coa synthase reductase squalene synthase and 7 dehydrocholesterol delta7 reductase in liver and mononuclear leu
Journal of Lipid Research, 1998Co-Authors: Akira Honda, Gerald Salen, G. Stephen Tint, Ashok K. Batta, Lien B. Nguyen, Sarah SheferAbstract:Sitosterolemia is a recessively inherited disorder characterized by abnormally increased plasma and tissue plant sterol concentrations. Patients have markedly reduced whole body cholesterol biosynthesis associated with sup- pressed hepatic, ileal, and mononuclear leukocyte 3-hydroxy- 3-methylglutaryl coenzyme A (HMG-CoA) reductase, the rate- controlling enzyme in cholesterol biosynthetic pathway, coupled with significantly increased low density lipoprotein (LDL) receptor expression. To investigate the mechanism of down- regulated cholesterol biosynthesis, we assayed several other key enzymes in the cholesterol biosynthetic pathway includ- ing acetoacetyl-CoA thiolase, HMG-CoA synthase, squalene synthase, and 7-dehydrocholesterol D 7 -reductase activities in liver and freshly isolated mononuclear leukocytes from four sitosterolemic patients and 19 controls. Hepatic acetoacetyl- CoA thiolase, HMG-CoA synthase, reductase, and squalene synthase activities were significantly decreased ( P , 0.05) 2 39%, 2 54%, 2 76%, and 2 57%, respectively, and 7-dehydro- cholesterol D 7 -reductase activity tended to be lower ( 2 35%) in the sitosterolemic compared with control subjects. The re- duced HMG-CoA synthase, reductase, and squalene synthase activities were also found in mononuclear leukocytes from a sitosterolemic patient. Thus, reduced cholesterol synthesis is caused not only by decreased HMG-CoA reductase but also by the coordinate down-regulation of entire pathway of choles- terol biosynthesis. These results suggest that inadequate cholesterol production in sitosterolemia is due to abnormal down-regulation of early, intermediate, and late enzymes in the cholesterol biosynthetic pathway rather than a single in- herited defect in the HMG-CoA reductase gene.— Honda, A., G. Salen, L. B. Nguyen, G. S. Tint, A. K. Batta, and S. Shefer. Down-regulation of cholesterol biosynthesis in sitosterolemia: diminished activities of acetoacetyl-CoA thiolase, 3-hydroxy-3- methylglutaryl-CoA synthase, reductase, squalene synthase, and 7-dehydrocholesterol D 7 -reductase in liver and mononu- clear leukocytes. J. Lipid Res. 1998. 39: 44-50.
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Regulation of bile acid synthesis by deoxycholic acid in the rat: Different effects on cholesterol 7α-hydroxylase and sterol 27-hydroxylase
Hepatology, 1995Co-Authors: Sarah Shefer, C J Steer, L B Nguyen, Thomas T. Chen, Gerald Salen, G. Stephen Tint, Betsy T Kren, Ashok K. BattaAbstract:Abstract 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 7α-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 7α-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 7α-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 7α-hydroxylase in rats fed 1% deoxycholic acid. In contrast, 0.4% deoxycholic acid decreased HMG-CoA reductase mRNA levels 76%, and cholesterol 7α-hydroxylase mRNA levels 82%. Ursodeoxycholic acid alone did not affect HMG-CoA reductase or cholesterol 7α-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. In conclusion, 1% deoxycholic acid induced hepatocyte destruction and regeneration associated with increased mRNA levels for HMG-CoA reductase and cholesterol 7α-hydroxylase, but significantly suppressed both enzyme activities. Thus, high-dose deoxycholic acid uncouples HMG-CoA reductase and cholesterol 7α-hydroxylase mRNA levels from enzyme function. In contrast, lower-dose deoxycholic acid (0.4%) inhibited both activities and mRNA levels of HMG-CoAreductase and cholesterol 7α-hydroxylase. Adding 1% ursodeoxycholic acid to 1% deoxycholic acid prevented the rise in mRNA levels but did not lessen the inhibitory effect of the latter. This inhibition occurred without change in hepatic histology, which suggests a regulatory role for deoxycholic acid that is independent of liver damage. Conversely, sterol 27-hydroxylase activity and mRNA levels are not affected by deoxycholic acid treatments.
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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.
G. Stephen Tint - One of the best experts on this subject based on the ideXlab platform.
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down regulation of cholesterol biosynthesis in sitosterolemia diminished activities of acetoacetyl coa thiolase 3 hydroxy 3 methylglutaryl coa synthase reductase squalene synthase and 7 dehydrocholesterol delta7 reductase in liver and mononuclear leu
Journal of Lipid Research, 1998Co-Authors: Akira Honda, Gerald Salen, G. Stephen Tint, Ashok K. Batta, Lien B. Nguyen, Sarah SheferAbstract:Sitosterolemia is a recessively inherited disorder characterized by abnormally increased plasma and tissue plant sterol concentrations. Patients have markedly reduced whole body cholesterol biosynthesis associated with sup- pressed hepatic, ileal, and mononuclear leukocyte 3-hydroxy- 3-methylglutaryl coenzyme A (HMG-CoA) reductase, the rate- controlling enzyme in cholesterol biosynthetic pathway, coupled with significantly increased low density lipoprotein (LDL) receptor expression. To investigate the mechanism of down- regulated cholesterol biosynthesis, we assayed several other key enzymes in the cholesterol biosynthetic pathway includ- ing acetoacetyl-CoA thiolase, HMG-CoA synthase, squalene synthase, and 7-dehydrocholesterol D 7 -reductase activities in liver and freshly isolated mononuclear leukocytes from four sitosterolemic patients and 19 controls. Hepatic acetoacetyl- CoA thiolase, HMG-CoA synthase, reductase, and squalene synthase activities were significantly decreased ( P , 0.05) 2 39%, 2 54%, 2 76%, and 2 57%, respectively, and 7-dehydro- cholesterol D 7 -reductase activity tended to be lower ( 2 35%) in the sitosterolemic compared with control subjects. The re- duced HMG-CoA synthase, reductase, and squalene synthase activities were also found in mononuclear leukocytes from a sitosterolemic patient. Thus, reduced cholesterol synthesis is caused not only by decreased HMG-CoA reductase but also by the coordinate down-regulation of entire pathway of choles- terol biosynthesis. These results suggest that inadequate cholesterol production in sitosterolemia is due to abnormal down-regulation of early, intermediate, and late enzymes in the cholesterol biosynthetic pathway rather than a single in- herited defect in the HMG-CoA reductase gene.— Honda, A., G. Salen, L. B. Nguyen, G. S. Tint, A. K. Batta, and S. Shefer. Down-regulation of cholesterol biosynthesis in sitosterolemia: diminished activities of acetoacetyl-CoA thiolase, 3-hydroxy-3- methylglutaryl-CoA synthase, reductase, squalene synthase, and 7-dehydrocholesterol D 7 -reductase in liver and mononu- clear leukocytes. J. Lipid Res. 1998. 39: 44-50.
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Regulation of bile acid synthesis by deoxycholic acid in the rat: Different effects on cholesterol 7α-hydroxylase and sterol 27-hydroxylase
Hepatology, 1995Co-Authors: Sarah Shefer, C J Steer, L B Nguyen, Thomas T. Chen, Gerald Salen, G. Stephen Tint, Betsy T Kren, Ashok K. BattaAbstract:Abstract 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 7α-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 7α-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 7α-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 7α-hydroxylase in rats fed 1% deoxycholic acid. In contrast, 0.4% deoxycholic acid decreased HMG-CoA reductase mRNA levels 76%, and cholesterol 7α-hydroxylase mRNA levels 82%. Ursodeoxycholic acid alone did not affect HMG-CoA reductase or cholesterol 7α-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. In conclusion, 1% deoxycholic acid induced hepatocyte destruction and regeneration associated with increased mRNA levels for HMG-CoA reductase and cholesterol 7α-hydroxylase, but significantly suppressed both enzyme activities. Thus, high-dose deoxycholic acid uncouples HMG-CoA reductase and cholesterol 7α-hydroxylase mRNA levels from enzyme function. In contrast, lower-dose deoxycholic acid (0.4%) inhibited both activities and mRNA levels of HMG-CoAreductase and cholesterol 7α-hydroxylase. Adding 1% ursodeoxycholic acid to 1% deoxycholic acid prevented the rise in mRNA levels but did not lessen the inhibitory effect of the latter. This inhibition occurred without change in hepatic histology, which suggests a regulatory role for deoxycholic acid that is independent of liver damage. Conversely, sterol 27-hydroxylase activity and mRNA levels are not affected by deoxycholic acid treatments.
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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.
Gerald Salen - One of the best experts on this subject based on the ideXlab platform.
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regulation of early cholesterol biosynthesis in rat liver effects of sterols bile acids lovastatin and bm 15 766 on 3 hydroxy 3 methylglutaryl coenzyme a synthase and acetoacetyl coenzyme a thiolase activities
Hepatology, 1998Co-Authors: Akira Honda, Gerald Salen, Ashok K. Batta, Lien B. Nguyen, Guorong Xu, Stephen G Tint, Sarah SheferAbstract:Cytosolic 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) synthase catalyzes the formation of HMG-CoA, the substrate for the rate-controlling enzyme in the cholesterol biosynthetic pathway. To explore the regulation in liver, we developed a new, accurate, and reliable reversed-phase ion-pair chromatographic assay that uses nonradioactive substrates and n-propionyl coenzyme A as an internal recovery standard. The hepatic activities were measured in rats treated with cholesterol, sitosterol, cholic acid, deoxycholic acid, ursodeoxycholic acid, cholestyramine, bile fistula, lovastatin, and BM 15.766, an inhibitor of 7-dehydrocholesterol Δ7-reductase, and were compared with microsomal HMG-CoA reductase and cytosolic acetoacetyl coenzyme A (AcAc-CoA) thiolase activities. HMG-CoA synthase activity was effectively suppressed in synchrony with HMG-CoA reductase activity by treatments with cholesterol (−41%, P< .05), cholic acid (−72%, P< .005), and deoxycholic acid (−62%, P< .05). However, ursodeoxycholic acid increased activity 84% (P< .05) and intravenous sitosterol did not change activity. AcAc-CoA thiolase activities also paralleled HMG-CoA reductase and HMG-CoA synthase activities, but differences were not statistically significant. In contrast to inhibition, up-regulation of hepatic HMG-CoA synthase activities by cholestyramine, bile fistula, and lovastatin was much less than HMG-CoA reductase activities. In addition, BM 15.766 did not stimulate synthase activity, whereas lovastatin increased activity 2.4-fold. Thus, hepatic HMG-CoA synthase activity was regulated coordinately with HMG-CoA reductase, and responded more forcefully to regulatory stimuli than acetoacetyl-CoA thiolase activity but usually less than HMG-CoA reductase.
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down regulation of cholesterol biosynthesis in sitosterolemia diminished activities of acetoacetyl coa thiolase 3 hydroxy 3 methylglutaryl coa synthase reductase squalene synthase and 7 dehydrocholesterol delta7 reductase in liver and mononuclear leu
Journal of Lipid Research, 1998Co-Authors: Akira Honda, Gerald Salen, G. Stephen Tint, Ashok K. Batta, Lien B. Nguyen, Sarah SheferAbstract:Sitosterolemia is a recessively inherited disorder characterized by abnormally increased plasma and tissue plant sterol concentrations. Patients have markedly reduced whole body cholesterol biosynthesis associated with sup- pressed hepatic, ileal, and mononuclear leukocyte 3-hydroxy- 3-methylglutaryl coenzyme A (HMG-CoA) reductase, the rate- controlling enzyme in cholesterol biosynthetic pathway, coupled with significantly increased low density lipoprotein (LDL) receptor expression. To investigate the mechanism of down- regulated cholesterol biosynthesis, we assayed several other key enzymes in the cholesterol biosynthetic pathway includ- ing acetoacetyl-CoA thiolase, HMG-CoA synthase, squalene synthase, and 7-dehydrocholesterol D 7 -reductase activities in liver and freshly isolated mononuclear leukocytes from four sitosterolemic patients and 19 controls. Hepatic acetoacetyl- CoA thiolase, HMG-CoA synthase, reductase, and squalene synthase activities were significantly decreased ( P , 0.05) 2 39%, 2 54%, 2 76%, and 2 57%, respectively, and 7-dehydro- cholesterol D 7 -reductase activity tended to be lower ( 2 35%) in the sitosterolemic compared with control subjects. The re- duced HMG-CoA synthase, reductase, and squalene synthase activities were also found in mononuclear leukocytes from a sitosterolemic patient. Thus, reduced cholesterol synthesis is caused not only by decreased HMG-CoA reductase but also by the coordinate down-regulation of entire pathway of choles- terol biosynthesis. These results suggest that inadequate cholesterol production in sitosterolemia is due to abnormal down-regulation of early, intermediate, and late enzymes in the cholesterol biosynthetic pathway rather than a single in- herited defect in the HMG-CoA reductase gene.— Honda, A., G. Salen, L. B. Nguyen, G. S. Tint, A. K. Batta, and S. Shefer. Down-regulation of cholesterol biosynthesis in sitosterolemia: diminished activities of acetoacetyl-CoA thiolase, 3-hydroxy-3- methylglutaryl-CoA synthase, reductase, squalene synthase, and 7-dehydrocholesterol D 7 -reductase in liver and mononu- clear leukocytes. J. Lipid Res. 1998. 39: 44-50.
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Regulation of bile acid synthesis by deoxycholic acid in the rat: Different effects on cholesterol 7α-hydroxylase and sterol 27-hydroxylase
Hepatology, 1995Co-Authors: Sarah Shefer, C J Steer, L B Nguyen, Thomas T. Chen, Gerald Salen, G. Stephen Tint, Betsy T Kren, Ashok K. BattaAbstract:Abstract 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 7α-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 7α-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 7α-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 7α-hydroxylase in rats fed 1% deoxycholic acid. In contrast, 0.4% deoxycholic acid decreased HMG-CoA reductase mRNA levels 76%, and cholesterol 7α-hydroxylase mRNA levels 82%. Ursodeoxycholic acid alone did not affect HMG-CoA reductase or cholesterol 7α-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. In conclusion, 1% deoxycholic acid induced hepatocyte destruction and regeneration associated with increased mRNA levels for HMG-CoA reductase and cholesterol 7α-hydroxylase, but significantly suppressed both enzyme activities. Thus, high-dose deoxycholic acid uncouples HMG-CoA reductase and cholesterol 7α-hydroxylase mRNA levels from enzyme function. In contrast, lower-dose deoxycholic acid (0.4%) inhibited both activities and mRNA levels of HMG-CoAreductase and cholesterol 7α-hydroxylase. Adding 1% ursodeoxycholic acid to 1% deoxycholic acid prevented the rise in mRNA levels but did not lessen the inhibitory effect of the latter. This inhibition occurred without change in hepatic histology, which suggests a regulatory role for deoxycholic acid that is independent of liver damage. Conversely, sterol 27-hydroxylase activity and mRNA levels are not affected by deoxycholic acid treatments.
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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.
Lien B. Nguyen - One of the best experts on this subject based on the ideXlab platform.
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down regulation of cholesterol biosynthesis in sitosterolemia diminished activities of acetoacetyl coa thiolase 3 hydroxy 3 methylglutaryl coa synthase reductase squalene synthase and 7 dehydrocholesterol delta7 reductase in liver and mononuclear leu
Journal of Lipid Research, 1998Co-Authors: Akira Honda, Gerald Salen, G. Stephen Tint, Ashok K. Batta, Lien B. Nguyen, Sarah SheferAbstract:Sitosterolemia is a recessively inherited disorder characterized by abnormally increased plasma and tissue plant sterol concentrations. Patients have markedly reduced whole body cholesterol biosynthesis associated with sup- pressed hepatic, ileal, and mononuclear leukocyte 3-hydroxy- 3-methylglutaryl coenzyme A (HMG-CoA) reductase, the rate- controlling enzyme in cholesterol biosynthetic pathway, coupled with significantly increased low density lipoprotein (LDL) receptor expression. To investigate the mechanism of down- regulated cholesterol biosynthesis, we assayed several other key enzymes in the cholesterol biosynthetic pathway includ- ing acetoacetyl-CoA thiolase, HMG-CoA synthase, squalene synthase, and 7-dehydrocholesterol D 7 -reductase activities in liver and freshly isolated mononuclear leukocytes from four sitosterolemic patients and 19 controls. Hepatic acetoacetyl- CoA thiolase, HMG-CoA synthase, reductase, and squalene synthase activities were significantly decreased ( P , 0.05) 2 39%, 2 54%, 2 76%, and 2 57%, respectively, and 7-dehydro- cholesterol D 7 -reductase activity tended to be lower ( 2 35%) in the sitosterolemic compared with control subjects. The re- duced HMG-CoA synthase, reductase, and squalene synthase activities were also found in mononuclear leukocytes from a sitosterolemic patient. Thus, reduced cholesterol synthesis is caused not only by decreased HMG-CoA reductase but also by the coordinate down-regulation of entire pathway of choles- terol biosynthesis. These results suggest that inadequate cholesterol production in sitosterolemia is due to abnormal down-regulation of early, intermediate, and late enzymes in the cholesterol biosynthetic pathway rather than a single in- herited defect in the HMG-CoA reductase gene.— Honda, A., G. Salen, L. B. Nguyen, G. S. Tint, A. K. Batta, and S. Shefer. Down-regulation of cholesterol biosynthesis in sitosterolemia: diminished activities of acetoacetyl-CoA thiolase, 3-hydroxy-3- methylglutaryl-CoA synthase, reductase, squalene synthase, and 7-dehydrocholesterol D 7 -reductase in liver and mononu- clear leukocytes. J. Lipid Res. 1998. 39: 44-50.
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regulation of early cholesterol biosynthesis in rat liver effects of sterols bile acids lovastatin and bm 15 766 on 3 hydroxy 3 methylglutaryl coenzyme a synthase and acetoacetyl coenzyme a thiolase activities
Hepatology, 1998Co-Authors: Akira Honda, Gerald Salen, Ashok K. Batta, Lien B. Nguyen, Guorong Xu, Stephen G Tint, Sarah SheferAbstract:Cytosolic 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) synthase catalyzes the formation of HMG-CoA, the substrate for the rate-controlling enzyme in the cholesterol biosynthetic pathway. To explore the regulation in liver, we developed a new, accurate, and reliable reversed-phase ion-pair chromatographic assay that uses nonradioactive substrates and n-propionyl coenzyme A as an internal recovery standard. The hepatic activities were measured in rats treated with cholesterol, sitosterol, cholic acid, deoxycholic acid, ursodeoxycholic acid, cholestyramine, bile fistula, lovastatin, and BM 15.766, an inhibitor of 7-dehydrocholesterol Δ7-reductase, and were compared with microsomal HMG-CoA reductase and cytosolic acetoacetyl coenzyme A (AcAc-CoA) thiolase activities. HMG-CoA synthase activity was effectively suppressed in synchrony with HMG-CoA reductase activity by treatments with cholesterol (−41%, P< .05), cholic acid (−72%, P< .005), and deoxycholic acid (−62%, P< .05). However, ursodeoxycholic acid increased activity 84% (P< .05) and intravenous sitosterol did not change activity. AcAc-CoA thiolase activities also paralleled HMG-CoA reductase and HMG-CoA synthase activities, but differences were not statistically significant. In contrast to inhibition, up-regulation of hepatic HMG-CoA synthase activities by cholestyramine, bile fistula, and lovastatin was much less than HMG-CoA reductase activities. In addition, BM 15.766 did not stimulate synthase activity, whereas lovastatin increased activity 2.4-fold. Thus, hepatic HMG-CoA synthase activity was regulated coordinately with HMG-CoA reductase, and responded more forcefully to regulatory stimuli than acetoacetyl-CoA thiolase activity but usually less than HMG-CoA reductase.
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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.
