The effect of (-)-hydroxycitrate on the activity of the low-density-lipoprotein receptor and 3-hydroxy-3-methylglutaryl-CoA reductase levels in the human hepatoma cell line Hep G2.
(-)-Hydroxycitrate, a potent inhibitor of ATP citrate-lyase, was tested in Hep G2 cells for effects on cholesterol homoeostasis. After 2.5 h and 18 h incubations with (-)-hydroxycitrate at concentrations of 0.5 mM or higher, incorporation of [1,5-14C]citrate into fatty acids and cholesterol was strongly inhibited. This most likely reflects an effective inhibition of ATP citrate-lyase. Cholesterol biosynthesis was decreased to 27% of the control value as measured by incorporations from 3H2O, indicating a decreased flux of carbon units through the cholesterol-synthetic pathway. After 18 h preincubation with 2 mM-(-)-hydroxycitrate, the cellular low-density-lipoprotein (LDL) receptor activity was increased by 50%, as determined by the receptor-mediated association and degradation. Measurements of receptor-mediated binding versus LDL concentration suggests that this increase was due to an increase in the numbers of LDL receptors. Simultaneously, enzyme levels of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase as determined by activity measurements increased 30-fold. Our results suggest that the increases in HMG-CoA reductase and the LDL receptor are initiated by the decreased flux of carbon units in the cholesterol-synthetic pathway, owing to inhibition of ATP citratelyase. A similar induction of HMG-CoA reductase and LDL receptor was also found after preincubations of cells with 0.3 microM-mevinolin, suggesting that the underlying mechanism for this induction is identical for both drugs.
Berkhout
T A
TA
Smith Kline and French Research Laboratories, Welwyn, Herts, U.K.
Havekes
L M
LM
Pearce
N J
NJ
Groot
P H
PH
D000255:Adenosine Triphosphate / Q000378:metabolism; D006528:Carcinoma, Hepatocellular; D002460:Cell Line; D002784:Cholesterol / Q000096:biosynthesis; D002951:Citrates / Q000378:metabolism* / Q000494:pharmacology*; D006801:Humans; D006903:Hydroxymethylglutaryl CoA Reductases / Q000378:metabolism*; D007536:Isomerism; D007700:Kinetics; D008055:Lipids / Q000096:biosynthesis; D008077:Lipoproteins, LDL / Q000378:metabolism; D008113:Liver Neoplasms; D011973:Receptors, LDL / Q000187:drug effects / Q000378:metabolism*
D002951:Citrates; D008055:Lipids; D008077:Lipoproteins, LDL; D011973:Receptors, LDL; D000255:Adenosine Triphosphate; C007999:hydroxycitric acid; D002784:Cholesterol; D006903:Hydroxymethylglutaryl CoA Reductases