The inhibition of cytoplasmic acetoacetyl-CoA thiolase by a triyne carbonate (L-660, 631)

The compound L-660, 631 (2-oxo-5-(1-hydroxy-2,4,6-heptatriynyl)-1,3-dioxolane-4 heptanoic acid), a natural product isolated from an Actinomycete culture, was found to inhibit rat liver cytosolic acetoacetyl-CoA thiolase, the first step in the cholesterol biosynthesis pathway, with an IC50 of 1.0 x 10(-8) M. The inhibitor had no effect on other sulfhydryl containing enzymes of lipid synthesis such as HMG-CoA synthase, HMG-CoA reductase, and fatty acid synthase. When tested in cultured human liver Hep G2 cells the compound inhibited the incorporation of 14C-acetate and 14C-octanoate into sterols 56% and 48% respectively at 3 x 10(-6) M with no effect on fatty acid synthesis. No noticeable effect was seen on fatty acid biosynthesis. This strongly suggests that the locus of inhibition of acetate incorporation into sterols found with this compound is the acetoacetyl-CoA thiolase step in the cholesterol biosynthesis pathway.     

Regulation of low-density lipoprotein receptors in the human hepatoma cell line Hep G2

The human hepatoma cell line Hep G2 can be maintained in continuous culture and secretes numerous plasma proteins and lipoproteins into the medium. To better characterize cholesterol homeostasis in these cells we have examined the binding, internalization and degradation of [125I]LDL by cultured Hep G2 cells. Hep G2 cells express high-affinity low-density lipoprotein (LDL) receptors which facilitate the binding, internalization and degradation of [125I]LDL; these receptors can be induced by growth in LDL-depleted medium and repressed by further incubation in medium supplemented with LDL. The degradation of [125I]LDL by derepressed Hep G2 cells was inhibited by greater than 90% by monensin. Incubation of Hep G2 cells in the presence of increasing concentrations of LDL also inhibited cholesterol biosynthesis. Our results indicate that Hep G2 cells possess high affinity LDL receptors which are subject to metabolic regulation and suggest that this cell line affords a valuable model to further examine cholesterol and lipoprotein metabolism in human liver cells.     

Transformation of 3beta-(2-hydroxyethoxy)-5alpha-cholest-8(14)-en-15-one in a polar metabolite in HepG2 hepatoma cells

Incubation of 3 beta-(2-hydroxy-2[3H]-ethoxy)-5 alpha-cholest-8(14)-en-15-one with Hep G2 cells led to the accumulation of a radioactive polar product in the culture medium, which was identified as 3 beta-(2-hydroxyethoxy)-15-keto-5 alpha-cholest-8(14)-ene-24-oic acid. Its structure was confirmed by a chemical counter synthesis. The labeled ketosterol was rapidly (tau 1/2 = 6 min) and reversibly bound by Hep G2 cells. The intracellular concentration of 15-ketosterol decreased during incubation mainly due to the formation of a polar metabolite, secreted to the medium. The level of cholesterol biosynthesis was 22 +/- 5% of the control value in Hep G2 cells at a 15-ketocholesterol concentration in the medium of 30 microM. However, further incubation for 3 h in the medium without the ketosterol led to restoration of the level of biosynthesis to 85 +/- 11% of the control value. These results suggest that inhibition of the cholesterol biosynthesis by 15-ketocholesterol in Hep G2 cells depends on the intracellular concentration of the inhibitor, which, in turn, is determined by the rate of its conversion into the polar metabolite. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2003, vol. 29, no. 6; see also http://www.maik.ru.     

The effect of 15-ketosterol analogues with a 5,6-dimethylhept-3-en-2-yl chain at C17 on cholesterol metabolism in Hep G2 hepatoma cells

The effect on cholesterol metabolism in Hep G2 hepatoma cells was studied for new analogues of 15-ketosterol [3beta-hydroxy-5alpha-cholest-8(14)-en-15-one] (I): (24S)-3beta-hydroxy-24-methyl-5alpha-cholesta-8(14),22-diene-15-one (II), (24S)-3alpha-hydroxy-24-methyl-5-alpha-cholesta-8(14),22-diene-15-one (III), and (24S)-24-methyl-5alpha-cholesta-8(14),22-diene-3,15-dione (IV). Analogues (I) and (II) were found to be equally effective inhibitors of cholesterol biosynthesis after a 3-h incubation with Hep G2 cells; however, (II) produced a stronger inhibitory effect after a 24-h incubation or after an incubation of cells preliminarily treated with the inhibitor in a medium containing no ketosterol. The ability of ketosterols to inhibit cholesterol biosynthesis decreased in the order (II) > (IV) > (III). Ketosterol (II) inhibited, whereas ketosterol (III) stimulated the biosynthesis of cholesteryl esters. (IV) stimulated the biosynthesis of cholesteryl esters at a concentration of 1-10 microM and exerted no marked effect at a concentration of 30 microM. These results indicate that delta8(14)-15-ketosterols containing a modified side chain are of interest as regulators of cholesterol metabolism in liver cells. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2004, vol. 30, no. 5; see also http: // www.maik.ru.     

The effects of (22S,23S)-and (22R,23R)-3β-hydroxy-22,23-oxido-5α-ergost-8(14)-en-15-ones on lipid biosynthesis and metabolism of exogenous cholesterol in Hep G2 cells

Novel synthetic oxysterols (22S,23S)-3β-hydroxy-22,23-oxido-5α-ergost-8(14)-en-15-one (I) and (22R,23R)-3β-hydroxy-22,23-oxido-5α-ergost-8(14)-en-15-one (II) efficiently inhibited cholesterol biosynthesis in human hepatoma Hep G2 cells during short-term incubation in a serum free medium (IC₅₀ values of 1.9 ± 0.2 and 0.6 ± 0.2 μ M, respectively). Cultivation of Hep G2 cells in the presence of 5 μM concentration of either (I) or (II) resulted in significant reduction of cholesterol biosynthesis (52% and 57% from control), and also changes in biosynthesis of fatty acids, triglycerides, and cholesteryl esters. Compounds (I) and (II) stimulated transformation of exogenous cholesterol to polar products secreted into the culture medium (156 % and 175% of control) as it that was shown in experiments in Hep G2 cells prelabeled with [³H]cholesterol.     

Hypolipidemic action of ascofuranone in hepatoblastoma G2 cell culture]

Ascofuranone, an isoprenoid antibiotic, suppressed 14C acetate incorporation into cholesterol, cholesterol ethers, triglycerides, phospholipids and free fatty acids in Hep G2 cell culture. Such a complex action of the antibiotic on lipid synthesis and metabolism was not connected with the inhibition of protein synthesis and the antibiotic toxicity.     

The hypolipidemic action of antibiotic 86/88 (enniatin B) in a hepatoblastoma G2 cell culture]

A cyclodepsipeptide antibiotic 86/88 (enniatin B) with strong hypolipidemic action was isolated from the culture liquid of the fungus INA F-86/88 identified as Fusarium lateritium Nees var. stilboides (Wr.) Bilai. In the Hep G2 cell culture the antibiotic suppressed 14C-acetate incorporation into cholesterol (IC50 1.75 microM), cholesterol ethers (IC50 1 microM), triglycerides (IC50 1.3 microM) and free fatty acids (IC50 2.2 microM). The most pronounced effect of the drugs, i.e. the suppression of the cholesterol ethers synthesis is likely due not only to the ACAT inhibition but also to the inhibition of the triglyceride synthesis and the diminishing of the free fatty acids pool in the cells.     

Effect of geraniol on fatty-acid and mevalonate metabolism in the human hepatoma cell line Hep G2.

Monoterpenes have multiple pharmacological effects on the metabolism of mevalonate. Geraniol, a dietary monoterpene, has in vitro and in vivo anti-tumor activity against several cell lines. We have studied the effects of geraniol on growth, fatty-acid metabolism, and mevalonate metabolism in the human hepatocarcinoma cell line Hep G2. Up to 100 micromol geraniol/L inhibited the growth rate and 3-hydroxymethylglutaryl coenzyme A reductase (HMG-CoA) reductase activity of these cells. At the same concentrations, it increased the incorporation of cholesterol from the medium in a dose-dependent manner. Geraniol-treated cells incorporated less 14C-acetate into nonsaponifiable lipids, inhibiting its incorporation into cholesterol but not into squalene and lanosterol. This is indicative of an inhibition in cholesterol synthesis at a step between lanosterol and cholesterol, a fact confirmed when cells were incubated with 3H-mevalonate. The incorporation of 3H-mevalonate into protein was also inhibited, whereas its incorporation into fatty acid increased. An inhibition of delta5 desaturase activity was demonstrated by the inhibition of the conversion of 14C-dihomo-gamma-linolenic acid into arachidonic acid. Geraniol has multiple effects on mevalonate and lipid metabolism in Hep G2 cells, affecting cell proliferation. Although mevalonate depletion is not responsible for cellular growth, it affects cholesterogenesis, protein prenylation, and fatty-acid metabolism.     

Geraniol and simvastatin show a synergistic effect on a human hepatocarcinoma cell line

Simvastatin is a competitive inhibitor of 3‐hydroxymethylglutaryl coenzyme A reductase activity, whereas geraniol is a monoterpene with multiple pharmacologic effects on mevalonate metabolism. Both of them inhibit growth and proliferation of many cell lines. The present study was designed to determine the action of geraniol, in combination with simvastatin, by assessing their effects in vitro on human hepatocarcinoma cell line (Hep G2). The treatment of Hep G2 cells with concentrations of simvastatin or geraniol that did not inhibit cell proliferation (5 µmol·l^‐1 of simvastatin and 50 µmol·l^‐1 of geraniol) resulted in a significant inhibition of cell proliferation. We also examined the effect of simvastatin, geraniol and the combination of both on the biosynthesis of lipids from [¹⁴C]‐acetate. Our results demonstrate that the combination of simvastatin and geraniol synergistically inhibited cholesterol biosynthesis and proliferation of Hep G2 cell line, contributing to a better understanding of the action of a component of essential oils targeting a complex metabolic pathway, which would improve the use of drugs or their combination in the fight against cancer and/or cardiovascular diseases. Copyright © 2011 John Wiley & Sons, Ltd.     

Effect of ethanol on cell growth and cholesterol metabolism in cultured Hep G2 cells.

The Hep G2 human hepatoma cell line has been recognized as an excellent in vitro human model system. For this reason, this line was used to study the effect of ethanol on HMG-CoA reductase activity concerning cell growth and cholesterol metabolism. Cells were incubated in ethanol-containing medium (0-400 mmol/L) for up to 102 h. Ethanol caused an inhibition in the growth rate and in HMG-CoA reductase activity that could be reverted by the removal of ethanol from the culture medium, indicating no cellular damage. These changes cannot be ascribed to the regulatory effect of cholesterol levels, since its content was not modified either in the cells or in the medium. The addition of mevalonate to the culture medium could not revert the growth rate inhibition evoked by ethanol. Moreover, ethanol produced an increment in the cholesterol efflux in [3H]cholesterol-prelabeled cells. We conclude that the decrease in HMG-CoA reductase activity evoked by ethanol treatment on Hep G2 cells would not be the cause but the consequence of the impairment in cellular growth, since this impairment could not be reverted by the addition of mevalonate to the culture medium.     

Screening of natural immunosuppressors by their ability to modify steroid synthesis in hepatocytes]

In the programme for screening sterol synthesis inhibitors with the use of actinomycetes and fungi 702 strains were tested. The effect of alcohol extracts of the mycelium of fungi and actinomycetes at a dilution of 1/10(3) on sterol synthesis by the Hep G2 hepatome cells was determined by incorporation of 3H acetate into sterols and proteins. Lovastatin (200 pg/ml) was used as the control: the sterol synthesis was decreased by 49 +/- 4% without inhibiting the protein synthesis. A number of the cultures produced compounds inhibiting under the experimental conditions the synthesis of sterols by 70 to 80% with simultaneous inhibition of the protein synthesis at least by 60 to 70%. Three compounds from that group produced by streptomycetes were subjected to a more detailed investigation. The compounds were demonstrated to be active antifungal antibiotics (MIC 0.1-1 mcg/ml). In a dose of 0.1-1 mcg/ml they showed high immunosuppressive activity in models of lymphocyte transformation in mice, whereas cyclosporin was active in a dose of 1 mcg/ml. Therefore, the model for screening hypolipidemic compounds could be considered useful for screening promising natural immunosuppressors.     

NA22598, a Novel Antitumor Compound, Reduces Cyclin D1 Levels, Arrests Cell Cycle at G1 Phase, and Inhibits Anchorage-Independent Growth of Human Tumor Cells

NA22598, a novel antitumor compound isolated from a microbial cultured broth, inhibited the growth of human colon cancer DLD-1 cells in suspension cultures (anchorage-independent growth) severalfold more strongly than in substratum-attached monolayer cultures. It arrested the cell cycle progression at early G1 phase under both these culture conditions. Rb phosphorylation, cyclin D1 expression, and cdk2 activation in G1 progression were all inhibited by NA22598, but the amounts of cdk2 and p27 were not affected. Among these effects the inhibition of cyclin D1 expression was most prominent, and NA22598 was found to inhibit the synthesis of cyclin D1 without affecting mRNA expression or protein degradation. p27 binding to cdk2 was more markedly increased in suspension cultures than in attached cultures by NA22598, but the compound had no effect on total p27. Apparently, the decrease of cyclin D1 induced redistribution of p27 from the cyclin D1/cdk4 to the cyclin E/cdk2 complexes during G1 phase in the suspension cultures. Because p27 is upregulated during suspension culture, a greater amount of it was associated with cyclin E/cdk2, thus producing greater growth inhibition. An agent, like NA22598, which induces the downregulation of cyclin D1 might offer a new anticancer strategy.     

Effect of 25-hydroxycholesterol and bile acids on the regulation of cholesterol metabolism in Hep G2 cells.

The effect of 25-hydroxycholesterol (25-OH-cholesterol) and chenodeoxycholic (CDC) acid on apoprotein secretion, low-density lipoprotein receptor activity, and [3H]triacylglycerol secretion in Hep G2 cells was studied. Both 25-OH-cholesterol and CDC acid increased the secretion of apolipoprotein (apo) E by Hep G2 cells. The secretion of apo A-I was slightly lowered (less than 10% disease). The maximal increase in apo E secretion was observed in culture medium containing 2 micrograms of 25-OH-cholesterol/ml or 10 micrograms of CDC acid/ml plus 10% fetal calf serum. Cholesterol, 7-OH-cholesterol and other bile acids were ineffective in inducing increases in apo E secretion. Another cholesterol synthesis inhibitor, mevinolin, was also ineffective in generating an increase in apoprotein secretion. The data indicated a specific interaction between 25-OH-cholesterol or CDC acid and apo E secretion in Hep G2 cells. Cholesterol synthesis, as measured by the incorporation of [14C]acetic acid into sterols, was repressed in Hep G2 cells in the presence of 25-OH-cholesterol (17% of control value). CDC acid, on the other hand, increased [14C]acetic acid incorporation (156% of control value). The number of LDL receptors in Hep G2 cells was decreased after incubation with 25-OH-cholesterol (62% of control value), but increased significantly after incubation with CDC acid (149% of control value). The secretion of [3H]triacylglycerol by Hep G2 cells incubated with 25-OH-cholesterol was greatly increased (248% of control value). On the contrary, CDC acid did not cause any increase in [3H]triacylglycerol secretion. The above results suggest that 25-OH-cholesterol and CDC acid have different effects on lipid metabolism in Hep G2 cells. The mRNA levels of apo E increased in cells preincubated with 25-OH-cholesterol and CDC acid, which suggested that the increase in apo E secretion is at least partly due to an increase in synthesis.     

Stimulation of the LDL receptor activity in the human hepatoma cell line Hep G2 by high-density serum fractions

The regulation of the LDL receptor activity in the human hepatoma cell line Hep G2 was studied. In Hep G2 cells, in contrast with fibroblasts, the LDL receptor activity was increased 2.5-fold upon increasing the concentration of normal whole serum in the culture medium from 20 to 100% by volume. Incubation of the Hep G2 cells with physiological concentrations of LDL (up to 700 micrograms/ml) instead of incubation under serum-free conditions resulted in a maximum 2-fold decrease in LDL receptor activity (10-fold decrease in fibroblasts). Incubation with physiological concentrations of HDL with a density of between 1.16 and 1.20 g/ml (heavy HDL) resulted in an approximately 7-fold increase in LDL receptor activity (1.5-fold increase in fibroblasts). This increased LDL receptor activity is due to an increase in the number of LDL receptors. Furthermore, simultaneous incubation of Hep G2 cells with LDL and heavy HDL (both 200 micrograms/ml) resulted in a 3-fold stimulation of the LDL receptor activity as compared with incubation in serum-free medium. 3-Hydroxy-3-methylglutaryl-CoA reductase activity was also stimulated after incubation of Hep G2 with heavy HDL (up to 3-fold). The increased LDL receptor activity in Hep G2 cells after incubation with heavy HDL was independent of the action of lecithin:cholesterol acyltransferase during that incubation. However, previous modification of heavy HDL by lecithin:cholesterol acyltransferase resulted in an enhanced ability of heavy HDL to stimulate the LDL receptor activity. Our results indicate that in Hep G2 cells the heavy HDL-mediated stimulation of the LDL receptor activity overrules the LDL-mediated down-regulation and raises the suggestion that in man the presence of heavy HDL and the action of lecithin:cholesterol acyltransferase in plasma may be of importance in receptor-mediated catabolism of LDL by the liver.     

Transformation of 3β-(2-Hydroxyethoxy)-5α-cholest-8(14)-en-15-one to a Polar Metabolite in Hepatoma Hep G2 Cells

Incubation of 3-(2-hydroxy-2[³H]-ethoxy)-5-cholest-8(14)-en-15-one with Hep G2 cells led to the accumulation of a radioactive polar product in the culture medium, which was identified as 3-(2-hydroxyethoxy)-15-keto-5-cholest-8(14)-ene-24-oic acid. Its structure was confirmed by a chemical counter synthesis. The labeled ketosterol was rapidly (t _1/2 = 6 min) and reversibly bound by Hep G2 cells. The intracellular concentration of 15-ketosterol decreased during incubation mainly due to the formation of a polar metabolite, secreted to the medium. The level of cholesterol biosynthesis was 22 ± 5% of the control value in Hep G2 cells at a 15-ketocholesterol concentration in the medium of 30 M. However, further incubation for 3 h in the medium without the ketosterol led to restoration of the level of biosynthesis to 85 ± 11% of the control value. These results suggest that inhibition of the cholesterol biosynthesis by 15-ketocholesterol in Hep G2 cells depends on the intracellular concentration of the inhibitor, which, in turn, is determined by the rate of its conversion into the polar metabolite.     

Lipid and lipoprotein metabolism in Hep G2 cells

Lipid composition, lipid synthesis and lipoprotein secretion by the Hep G2 cell line have been studied with substrate and insulin supplied under different conditions. The lipid composition of Hep G2 cells was close to that of normal human liver, except for a higher content in sphingomyelin (P less than 0.005) and a lower phosphatidylcholine/sphingomyelin ratio. Most of the [14C]triacylglycerols secreted into the medium were recovered by ultracentrifugation at densities of 1.006 to 1.020 g/ml. The main apolipoproteins secreted were apo B-100 and apo A-I. Hep G2 mRNA synthesized in vitro the pro-apolipoproteins A-I and E. Triacylglycerol secretion was 7.38 +/- 1.04 micrograms/mg cell protein per 20 h with 5.5 mM glucose in the medium and increased linearly with glucose concentration. Oleic acid (1 mM) increased the incorporation of [3H]glycerol into the medium and cell triacylglycerols by 251 and 899%, with a concomitant increment in cell triacylglycerols and cholesterol ester. Insulin (1 mU or 7 pmol/ml) inhibited triacylglycerol secretion and [35S]methionine incorporation into secreted protein by 47 and 28%, respectively, with a corresponding increase in the cells. Preincubation of cells with 2.5-10 mM mevalonolactone decreased the incorporation of [14C]acetate into cholesterol 6.2-fold, indicating an inhibitory effect on HMG-CoA reductase. It is concluded that in spite of some differences between Hep G2 and normal human hepatocytes, this line offers an alternative and reliable model for studies on liver lipid metabolism.     

Rapid identification of elaiophylin and geldanamycin inStreptomyces fermentation broths using CPC coupled with a photodiode array detector and LC-MS methodologies

During the course of screening microbial broth extracts in various high through-put bioassays (eg receptor binding or enzyme inhibition), several actinomycete cultures were discovered to produce active metabolites. The natural products elaiophylin and/or geldanamycin are produced by severalStreptomyces violaceusniger strains, and the bioactivity of the extracts from these cultures was frequently associated with the fractions containing these metabolites. CPC coupled to a photodiode array detector and LC-MS techniques were applied to these broth extracts to ascertain rapidly when these natural products were present. These methodologies allowed us to identify the metabolites quickly in the crude extract, and the application demonstrated further the utility of CPC-photodiode array detection and LC-MS as powerful, initial analytical tools in analyses of the complex metabolite profiles produced by microorganisms.     

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.     

Bile acid synthesis in cell culture

Confluent cultures of Hep G2 cells were found to synthesize chenodeoxycholic and cholic acids continually. Chenodeoxycholic acid was synthesized at the rate of 58 +/- 8.6 micrograms/96 h, a rate more than 7-fold greater than that for cholic acid. Addition of 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha-triol but not the -3 alpha, 7 alpha-diol was followed by an increase in cholic acid synthesis, thus indicating a relatively low 12 alpha-hydroxylase activity. Endogenous synthesis of monohydroxy bile acid ester sulfates was found, with maximum rates of 135 and 74 micrograms/96 h for lithocholic and 3 alpha-hydroxy-5-cholenoic acids, respectively. Incubation of Hep G2 cells in medium containing 25% D2O permitted a comparison of the precursor/product relationship of cholesterol with 3 beta-hydroxy-5-cholenoic acid. The pattern of incorporation of deuterium was in accordance with that expected, thus allowing the conclusion that this monohydroxy bile acid is derived from cholesterol and should be considered together with chenodeoxycholic and cholic acids as a primary bile acid.     

Enhancing effect of taurine on CYP7A1 mRNA expression in Hep G2 cells

Summary. Taurine has been reported to enhance cholesterol 7α-hydroxylase (CYP7A1) mRNA expression in animal models. However, no in vitro studies of this effect have been reported. The Hep G2 human hepatoma cell line has been recognized as a good model for studying the regulation of human CYP7A1. This work characterizes the effects of taurine on CYP7A1 mRNA levels of Hep G2 cells in a dose- and time-dependent manner. In the dose-dependent experiment, Hep G2 cells were treated with 0, 2, 10 or 20 mM taurine in the presence or absence of cholesterol 0.2 mM for 48 h. In the time-dependent experiment, Hep G2 cells were treated with 0 or 20 mM taurine for 4, 24 and 48 h with and without cholesterol 0.2 mM. Our data revealed that taurine showed time- and dose-response effects on CYP7A1 mRNA levels in Hep G2 cells. However, glycine – a structural analogue of taurine – did not have an effect on CYP7A1 gene expression. These results show that, in agreement to previous studies on animal models, taurine induces the mRNA levels of CYP7A1 in Hep G2 cells, which could enhance cholesterol conversion into bile acids. Also, Hep G2 cell line may be an appropriate model to study the effects of taurine on human cholesterol metabolism.