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PubMedDate not supplied

Evaluation of the carcinogenic potential of clofibrate in the FVB/Tg.AC mouse after dermal application--part II.

This study was conducted as part of the International Life Sciences Institute (ILSI) Alternatives to Carcinogenicity Testing program and evaluated the carcinogenic potential of clofibrate, a nongenotoxic, peroxisome proliferator-activated receptor (PPAR) alpha agonist following dermal application to transgenic Tg.AC and nontransgenic FVB mice for a minimum of 26 weeks. Clofibrate doses of 12, 28, or 36 mg/200 microl/day were used. Positive controls for papilloma formation were benzene (174.8 mg/200 microl), and 12-o-tetradecanoylphorbol-13-acetate (TPA [0.00250 mg/200 microl]). Clofibrate was tolerated at doses up to 36 mg/200 microl. In Tg.AC mice, clofibrate produced a dose-related increase in the incidence of mice with cutaneous papillomas; and dose-related decreases in mean time to first tumor, mean multiplicity of tumors per mouse, and mean weeks to maximal yield, as well as numerous nonneoplastic microscopic lesions in the liver, kidney, spleen, and skin. Benzene and TPA induced both neoplastic and/or non-neoplastic proliferative lesions in Tg.AC mice. Clofibrate did not increase the incidence or multiplicity of papillomas, or any other tumors in FVB mice. These data show that the Tg.AC dermal model has increased sensitivity in detecting skin papillomas caused by the nongenotoxic rodent carcinogen, clofibrate, compared to wild type FVB mice, at systemic exposures that are 3x higher than the systemic exposure observed in humans taking clofibrate (AUC = 1100 microg.h/ml) at the recommended maximum therapeutic dose of 500 mg. In addition, this study supports the proposed concept that Tg.AC model may detect compounds with nongenotoxic carcinogenic potential in a shorter timeframe than conventional mouse carcinogenicity bioassays.

Administration, Cutaneous↗
PubMed1992

Interaction of carnitine and propionate with pyruvate oxidation by hepatocytes from clofibrate-treated rats: importance of coenzyme A availability.

Propionate interferes with normal hepatic metabolic regulation secondary to accumulation of propionyl- and methylmalonyl-CoA. Clofibrate-treatment increases hepatic CoA content and carnitine acetyltransferase activity, both of which may modulate propionate toxicity. Therefore, inhibition of pyruvate oxidation by propionate was studied in hepatocytes isolated from rats maintained on a control or 0.5% clofibrate diet for 7-9 d. Propionate (10 mmol/L) inhibited 14CO2 formation from [1-14C]pyruvate (10 mmol/L) by 60 +/- 2% in hepatocytes from control rats, but by only 46 +/- 3% in cells from clofibrate-treated rats (P less than 0.05). The smaller inhibitory effect of propionate in hepatocytes from clofibrate-treated rats occurred despite increased cellular propionyl-CoA content as compared with controls, but was associated with increased CoASH and total CoA contents. Despite greater carnitine acetyltransferase activity (20-fold) and propionylcarnitine production (2.5-fold) in hepatocytes from clofibrate-treated rats, reversal of propionate's inhibition of pyruvate oxidation by 10 mmol/L carnitine was small (8.7 +/- 3.9%) and not different from that observed in cells from control animals (6.7 +/- 2.4%). Carnitine (10 mmol/L) decreased hepatocyte total acid-soluble CoA content by 20-30% in cells from both control and clofibrate-treated rats. This carnitine-induced decrease in CoA content may limit the efficacy of carnitine under conditions of acyl-CoA accumulation. Clofibrate-induced increased CoA content provides partial protection against propionate toxicity. Metabolic toxicity of propionate is the result of both the increased cellular propionyl-CoA content and the depletion of cellular unesterified CoA.

Animals↗
PubMed1991

Both induction and activation of the branched-chain 2-oxo acid dehydrogenase complex in primary-cultured rat hepatocytes by clofibrate.

Clofibrate administration to rats caused both the activation and induction of the branched-chain 2-oxo acid dehydrogenase complex in the liver; the former phenomenon occurred within the first 6 h after clofibrate administration whereas the latter occurred after 12 h. Essentially the same results were obtained with primary cultures of rat hepatocytes in the presence of 0.5 mM clofibrate, though about three-fourths of the enzyme complex in control cells (without clofibrate addition) was inactivated during a culture for 44 h, with little reduction of the enzyme amount. This was also confirmed by immunotitration analysis with antibodies raised against the purified decarboxylase and transacylase components of the enzyme complex. On the other hand, the activity of dihydrolipoamide dehydrogenase (a constituent of the complex) was little affected by clofibrate administration. The half lives of the decarboxylase and transacylase components in the primary cultures were estimated to be in the range of 22-26 h, and were unchanged in the presence of clofibrate, when determined with the use of cycloheximide and by a pulse-chase experiment. On the contrary, the rates of synthesis of these two enzyme components had increased to about 1.9-fold after 32 h cultivation in the presence of clofibrate. Thus, the increase in the synthesis of both the components resulted in induction of the complex.

3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)↗
PubMed1975

Lack of effect of cholestyramine on the pharmacokinetics of clofibrate in man.

The study was undertaken to determine whether cholestyramine (16 g daily) interfered with clofibrate absorption when the two drugs were given together. Fifteen patients taking 1 g of clofibrate twice daily (for 2 to 416 weeks) participated in the study. Clofibrate (as the acid, p-chlorophenoxyisobutyric acid, CPIB) was quantified by thin-layer and gas-liquid chromatography. In patients taking clofibrate only, mean plasma CPIB concentration before the morning dose of clofibrate was 123 mug/ml. Peak levels were reached 3.5 hours after drug intake, the mean peak plasma CPIB concentration being 193 mug/ml. Absorption of CPIB exceeded 99%. Ninety-eight percent of the daily CPIB-intake was excreted in the urine, 61% being conjugated. In vivo degradation of CPIB did not occur. Free and conjugated CPIB was present in bile (mean fasting level being 55 mug/ml. The decay of radioactive CPIB in plasma was not log-linear: the mean t 1/2 of the first exponential was 0.45 hours, and of the second 15.1 hours. The pool size in 3 patients 3 hours after the morning dose of clofibrate was 1054 mg. CPIB was not detectable in adipose tissue, and kinetic data gave no hint of drug accumulation in patients on long-term therapy. In 6 patients given cholestyramine together with clofibrate, there was no significant alteration in fasting plasma CPIB levels, 24-hour urinary and faecal excretion of CPIB or in the half-life and pool size of the drug. A short delay in reaching peak plasma CPIB levels was the only consistent finding.

Adolescent↗
PubMed1998

Comparison of the effects of gemfibrozil and clofibric acid on peroxisomal enzymes and cholesterol synthesis of rat hepatocytes.

We studied whether the peroxisomal proliferation, induction of 3-hydroxy-3-methylglutaryl-CoA reductase (HMG-CoA reductase) and activation of cholesterol synthesis by gemfibrozil shown in whole body (Hashimoto F., Ishikawa T., Hamada S. and Hayashi H., Biochemical. Pharm., 49, 1213-1221 (1995)) is also detected at a culture cell level, and we made a comparative analysis of the effects of clofibric acid. Gemfibrozil at 0.25 mM increased the activity of some peroxisomal enzymes (catalase and the cyanide-insensitive fatty acyl-CoA oxidizing system) after incubation for 72 h. However, contrary to whole body experiments, gemfibrozil decreased the activity of HMG-CoA reductase and cholesterol synthesis from [14C]acetate. At 1 mM, gemfibrozil decreased not only the activity of HMG-CoA reductase and cholesterol synthesis, but also the protein content of the cells and peroxisomal enzyme activity, indicating nonspecific inhibition at this concentration. Clofibric acid (0.25 and 1 mM) increased the activity of peroxisomal enzymes, but decreased the activity of HMG-CoA reductase and cholesterol synthesis. With respect to the direct effect on HMG-CoA reductase in the cell homogenate, gemfibrozil at 0.25 mm did not affect the activity, but it clearly inhibited the activity at 2 mM and above. Clofibric acid at 2 mM hardly affected the activity, but it clearly decreased the activity at 5 mM and over. That is, gemfibrozil directly inhibited the activity more strongly than clofibric acid. The direct inhibition of the enzyme itself required higher concentrations of both agents than did inhibition at the culture cell level. These results suggest that the cytotoxicity of gemfibrozil is greater than that of clofibric acid, and that gemfibrozil, as well as clofibric acid, can induce peroxisomal enzymes in the culture cell level. In contrast to whole body results, gemfibrozil may suppress cholesterol synthesis from [14C]acetate through the inhibition of HMG-CoA reductase at the culture cell level. The decreases in the reductase activity caused by gemfibrozil and clofibric acid at the culture cell level may not be caused by the direct inhibition of the enzyme.

Animals↗
PubMed1988

Improvement of glucose tolerance in NIDDM by clofibrate. Randomized double-blind study.

A randomized double-blind study was performed to examine the effect of clofibrate on glucose tolerance in subjects with non-insulin-dependent diabetes mellitus (NIDDM). Clofibrate (1.5 g/day) or placebo was administered to 70 patients and an oral glucose tolerance test (OGTT) was performed before and 12 wk after treatment. Blood glucose levels were significantly improved in clofibrate-treated groups at all time points during OGTT, whereas there was no change in insulin levels. Improvement of fasting glucose levels required 8 wk of clofibrate treatment. Insulin binding to erythrocytes demonstrated no significant change in the clofibrate-treated subjects. These results suggest that clofibrate improves glucose tolerance in NIDDM subjects without a change in insulin receptors and that clofibrate increases insulin sensitivity through an unknown postreceptor mechanism.

Blood Glucose↗
PubMed1975

Colestipol, clofibrate, cholestyramine and combination therapy in the treatment of familial hyperbetalipoproteinaemia.

Fifty-seven patients, mean age 26 years, suffering from familial hyperbetalipoproteinaemia (Fredrickson type lla and llb), were treated on a low cholesterol, modified polyunsaturated fat diet for a period of 6-12 weeks prior to the introduction of drug therapy. No significant reduction in the serum levels of total cholesterol, low density lipoprotein (LDL) cholesterol or triglyceride was found. Fifty patients were then treated with colestipol for 6 weeks; total and LDL cholesterol decreased by 23%, but triglyceride levels were unaffected. During the following 6 weeks, placebo was administered, and total and LDL cholesterol returned to pretreatment levels. The patients were then randomly allocated into two groups of 16. The first group continued with clofibrate therapy, while the second group received cholestyramine. In the clofibrate group a reduction in total and LDL cholesterol of the order of 17% was noted, similar to cholestethat achieved in this group on colestipol. Triglyceride levels were 15% lower on clofibrate therapy than on colestipol. In the cholestyramine group, there was a 25% decrease in total and LDL cholesterol, compared with pretreatment levels. This reduction was similar to that found when colestipol was administered. Triglyceride values were significantly raised during cholestyramine therapy. Thirteen patients were then subjected to a 6-week period of combination therapy, either clofibrate or colestipol, or clofibrate and cholestyramine. Total and LDL cholesterol were reduced by 32% on combination therapy compared with 18% on colestipol and 23% on either clofibrate or cholestyramine alone. Furthermore, on combined therapy, triglyceride concentrations fell by 20% when compared with the levels found when colestipol, clofibrate or cholestyramine were administered on their own.

Adolescent↗
PubMed1978

[Combination or monotherapy of hyperlipoproteinemia typus IIb, IV, V with clofibrate and m-inositolnicotinate or clofibrinic acid (author's transl)].

Clofibrate and m-Inositolnicotinate in a daily dosage of 1,5 g Clofibrate and 1,2 g m-Inositolnicotinate during long term treatment effected a good triglyceride fall in all three lipoprotein fractions, especially in VLDL. The changing of the hyperlipoproteinemia phenotypus IV to the phenotypus IIb or IIa under monotherapy with Clofibrate or clofibrinic acid could not be avoided by the combination of Clofibrate with m-Inositolnicotinate. Approximately every fourth hyperlipoproteinemia phenotypus IV or V, treated with a combination therapy, had an increase of beta-Cholesterol in the pathological range of more than 210 mg/dl. The combination of Clofibrate with nicotinic acid is not of greater value than the monotherapy with Clofibrate (Atromid S). A combination of Clofibrate and nicotinic acid is useful when pure nicotinic acid (3 to 4g/daily) or its esters, for example m-Inositol-nicotinate (4 to 6g/daily) or beta-Pyridylcarbinol (800 to 1200 mg/daily) are administered in therapeutic doses. With the increased dosage of nicotinic acid, one must expect a large "drop out" of these appropriate hyperlipoproteinemia patients because of the side-effects resulting from this particular treatment with nicotinic acid.

Cholestanol↗
PubMed1991

Effect of clofibrate treatment on hepatic prostaglandin catabolism and action.

Prostaglandins (PG) modulate hepatocyte glucose and lipid metabolism. Hepatocytes rapidly metabolize PG via beta-oxidation, terminating PG action. Clofibrate induces hepatic peroxisomal beta-oxidative activity, for which PG are substrates. To determine the effect of clofibrate-treatment on liver PG metabolism and action, hepatocytes were isolated from rats maintained on a control or clofibrate-supplemented (0.5%) diet for 7 to 9 days. Rates of PG catabolism were determined by high performance liquid chromatography resolution of [3H]PG from [3H]metabolites. Clofibrate treatment enhanced the rates of PGE2, PGF2, and PGD2 degradation by 85%, 278% and 137%, respectively. Rates of PG degradation were correlated with hepatocyte carnitine acetyltransferase activity, a marker of peroxisomal proliferation. Further evidence of enhanced hepatocyte peroxisomal beta-oxidation of PG after clofibrate-treatment was obtained by confirming loss of the 1-position carbon from [1-14C]PGE2 during PGE2 metabolism and failure of the carnitine acyltransferase inhibitor acetyl-DL-aminocarnitine to inhibit PGE2 metabolism. Associated with the faster degradation of PGE2 by hepatocytes from clofibrate-treated rats was loss of inhibition of hepatocyte glucagon-stimulated glycogenolysis by exogenous PGE2. Thus, clofibrate's induction of peroxisomal beta-oxidation is associated with accelerated catabolism of PG and decreased PG action. Alterations in PG breakdown provide a mechanism for modulating hepatic PG effects.

Animals↗
PubMed1980

Effects of clofibrate on water permeability and short-cicuit current of toad urinary bladder.

The effects of the oral antidiuretic drug clofibrate on water permeability of the urinary bladder of the toad, Bufo marinus, were studied. Clofibrate did not alter control water flow along an osmotic gradient. Water flow increases due to vasopressin were reversibly inhibited by 1 to 10 mM clofibrate from the serosal side. Clofibrate in the serosal bathing medium inhibited water flow increases due to cyclic AMP but not due to theophylline. Serosal clofibrate concentrations less than 1 mM or clofibrate in the mucosal solution (1 mM) was ineffective in inhibiting the osmotic water permeability response to vasopressin. Clofibrate in the serosal bathing medium (1 mM) inhibited base-line short-circuit current but had no effect on vasopressin-stimulated short-circuit current.

Animals↗
PubMed1983

Comparison of clofibrate and ethyl-5-(p-chlorophenoxy)-3-hydroxy-3-methylpentanoate induced changes in serum lipoprotein cholesterol and hepatic peroxisome proliferation in the normal rat.

Clofibrate and ethyl-5(p-chlorophenoxy)-3-hydroxy-3-methylpentanoate (HMP), at 0.1 and 0.25% in the diet, were evaluated in normal rats. Effects on serum lipoprotein cholesterol, liver cholesterol and peroxisome proliferation changes were compared. Both doses of HMP significantly lowered high density lipoprotein cholesterol (HDL-C) and total cholesterol (mean 22% and 18%). The distribution of cholesterol in the lipoproteins was altered (p less than 0.05) and liver weights were increased 18% by the 0.25 dose of HMP. Clofibrate treatment increased (p less than 0.01) the combination of very low and low density lipoprotein cholesterol (VLDL + LDL-C) by 42% at the 0.1% dose and lowered HDL-C by 28% at the 0.25% dose; total-C was not changed from control values. Both levels of clofibrate shifted the distribution of lipoprotein cholesterol, increased liver weights (mean 69%) and reduced liver cholesterol (mean 33%). Image analysis of peroxisome changes showed that both doses of HMP and clofibrate increased peroxisome numbers (mean 71% vs 218%), with activity of HMP significantly lower than clofibrate. Measurement of carnitine acetyltransferase (CAT) activity (nmCoASH released/mg protein/minute) showed no significant increases in liver samples from HMP-treated rats, while clofibrate induced large increases in CAT activity, which were significant compared to control and HMP values. While having chemical structural similarity to clofibrate, HMP appears to cause comparable hypocholesterolemic activity without comparable levels of hepatomegaly and peroxisome proliferation.

Animals↗
PubMed1981

Effect of clofibrate on fatty acid desaturation of rats treated with ethanol.

The effect of clofibrate and ethanol in the rat was studied on the following aspects of lipid composition and metabolism: liver delta 5, delta 6 and delta 9 fatty acid desaturases, fatty acid synthetase and fatty acid desaturase microsomal electron transport chain activity and serum cholesterol, triacylglycerols and high (HDL), low (LDL) and very low density lipoprotein (VLDL) levels. Clofibrate administered for 9 days (0.3% W/W) did not modify the relative composition of liver phospholipids and cholesterol, but did diminish triacylglycerol levels increased by ethanol. This effect could be explained by the possible beta-adrenergic blocking properties of clofibrate or by an increased activity of peroxisomal beta-oxidation. Clofibrate also promoted a decrease in serum cholesterol and triacylglycerol levels, delta 6 desaturase activity and a suppression of the electron transport chain as measured by NADH cytochrome b5 reductase and NADH cytochrome c reductase. The drug increased delta 9 desaturase activity and fatty acid synthetase, while no effect could be found in delta 5 desaturase activity. The hypocholesterolenic effect of clofibrate can not be explained through the delta 6 desaturase inhibition, or the fatty acid synthetase enhancement. Ethanol increased the HDL and VLDL and lowered LDL serum concentrations, while clofibrate reversed these results. Considering that clofibrate could have antiatherosclerotic effect in the rat, it is difficult to explain it through these changes in lipoprotein levels, since according to Miller and Miller low HDL levels are predictive of coronary heart disease.

Animals↗
PubMed1980

[Metabolism and pharmacokinetics of etofylline clofibrate, new antilipemic].

Upon investigations on metabolism and pharmacokinetics of 1-(theophyllin-7-yl)-ethyl-2-[2-(chlorophenoxy)-2-methylpropionate] (etofylline clofibrate, ML 1024, Duolip) is reported. As can be seen from in vivo tests in rats and dogs ML 1024 is cleaved to the metabolites clofibric acid and etofylline. This could be further demonstrated in vitro by incubation with lipases and human serum. The pharmacokinetic parameters of the metabolites after oral application of 2 capsules Duolip, corresponding to 500 mg etofylline clofibrate, were evaluated in 7 healthy volunteers. The serum fluctuations of the main metabolites could be adapted to an open two-compartment model (etofylline). The following mean values were found: the invasion half-life is 1 h 4 min for clofibric acid and 1 h 52 min for etofylline. The maximum concentration after approximately 4 h is 22.75 micrograms/ml for clofibric acid and 6.57 micrograms/ml for etofylline. The elimination half-life is 12.12 h for clofibric and 4.33 h for etofylline. Via urine 20 mg clofibric acid and 15.7 mg etofylline were excreted within 8 h. The elimination process after 8 h is not yet terminated.

Animals↗
PubMed1993

Alterations by clofibric acid of glycerolipid metabolism in rat-kidney.

Alterations induced by p-chlorophenoxyisobutyric acid (clofibric acid) in glycerolipid metabolism in rat-kidney were studied. (1) The treatment of rats with clofibric acid markedly decreased renal level of triacylglycerol, which seemed to be due to a reduced formation of triacylglycerol, since the in vivo incorporation of [14C]oleic acid (18:1), [14C]linoleic acid (18:2) and [3H]glycerol into triacylglycerol was decreased in clofibric acid-fed rats. (2) The administration of clofibric acid to rats increased proportions of 18:1 and 18:2 and decreased a proportion of arachidonic acid (20:4) in phosphatidylcholine; the contents of two major molecular species of renal diacylglycerophosphocholine (diacyl-GPC), palmitoyl-arachidonoyl (16:0-20:4) and stearoylarachidonoyl (18:0-20:4), were both decreased markedly. The treatment did not alter renal content of phosphatidylcholine. (3) By contrast, clofibric acid changed, to a lesser extent, the composition of molecular species of diacylphosphatidylethanolamine. (4) The decrease in the level of diacyl-GPC that contains 20:4 seemed to be due to the clofibric acid-caused reduction in the concentration of free 20:4 in kidney. The reduction in renal concentration of free 20:4 seemed to be caused by a decrease in serum concentration of lipids that contain 20:4, but not by a decrease in the activities of desaturation and chain elongation that participate in biosynthesis of 20:4. (5) The reduction by clofibric acid in the renal content of diacyl-GPC containing 20:4 resulted in the decrease in the formation of prostaglandin E2 in kidney.

Animals↗
PubMed1997

Rapid and extensive lethal action of clofibrate on hepatoma cells in vitro.

Clofibrate, for a long time in use as a hypolipidemic drug, is a well known peroxisomal proliferator (PP) and hepatocarcinogen in rodents. We show here that in vitro 1 mM clofibrate induces a rapid and massive death of rat AH-130 hepatoma cells. Cell death was prominent already after 4 h of treatment, with a characteristic ;apoptotic' pattern by conventional microscopy. This was further supported by the pronounced chromatin condensation detectable on 4',6-diamine-2'-phenylindole dihydrochloride (DAPI) staining, the clearcut internucleosomal DNA fragmentation on agarose-gel electrophoresis (ladder pattern), and the accumulation of markedly hypochromic cells observed in flow cytometric DNA histograms. Consistently with the apoptotic features of the process, some parameters commonly used to detect cell death, such as plasma membrane permeabilization to trypan blue or propidium iodide, lack of mitochondrial retention of rhodamine 123, or extracellular release of lactate dehydrogenase, were all virtually negative. However, these same parameters became markedly positive after 24 h of treatment, which was suggestive for the occurrence of ;secondary' necrosis among AH-130 cells. By a combination of flow cytometric parameters, after 4 h on 1 mM clofibrate only 41% of the AH-130 cells could still be categorized as viable (i.e., non-apoptotic and non-necrotic), while 46% of cells appeared apoptotic and 13% necrotic. At 24 h, 67% of cells were necrotic, 20% apoptotic and only 13% non-apoptotic and non-necrotic. Apoptosis was also extensive in AH-130 cells treated with another PP such as nafenopin at 1 mM concentration and in human hepatoma HepG2 cells treated with clofibrate. By contrast, clofibrate did not cause apoptosis on primary rat hepatocyte cultures. These observations indicate that: (i) apart from their well-known cell growth-promoting action, PPs such as clofibrate or nafenopin may exert a substantial cytotoxic action on targets such as the AH-130 or HepG2 hepatoma cells; (ii) this cell death evolves from an initial 'apoptotic' to an eventual ;necrotic' pattern; (iii) detection of cell death requires the adoption of a full panel of tests, adequate to cover the whole evolving death pattern, while such tests may even be substantially misleading whenever applied individually; (iv) the cytotoxicity of clofibrate and similar agents on normal and, particularly, tumoural cells may deserve careful reevaluation.

Journal Article↗
PubMed1985

Effects of long-term administration of clofibric acid on peroxisomal beta-oxidation, fatty acid-binding protein and cytosolic long-chain acyl-CoA hydrolases in rat liver.

Long-term effects of rho-chlorophenoxyisobutyric acid (clofibric acid) on inductions of peroxisomal beta-oxidation, fatty acid-binding protein and cytosolic acyl-CoA hydrolases in rat liver were studied. Male rats were fed clofibric acid at a dietary concentration of 0.25% for 22 weeks. The induction of peroxisomal beta-oxidation activity lasted throughout the long-term treatment of rats, the activity being a half that of rats treated with clofibric acid for 2 weeks. cytosolic long-chain acyl-CoA hydrolase I and II were both induced by the long-term and the short-term treatment of age-matched rats with clofibric acid, although the ability to induce hydrolase I decreased greatly by aging of rats. There was little difference in the inducing effect on fatty acid-binding protein between the long-term treatment and the short-term treatment. These results suggest that the inductions of peroxisomal beta-oxidation, fatty acid-binding protein and two cytosolic long-chain acyl-CoA hydrolases are essential responses of rats to clofibric acid (but not the brief events which occur in only the first stage of the continuous treatment with clofibric acid).

Animals↗
PubMed1998

Activation of human liver 3alpha-hydroxysteroid dehydrogenase by clofibrate derivatives.

The NADP+-dependent dehydrogenase activity of a predominant isoenzyme of human liver 3alpha-hydroxysteroid dehydrogenase was activated by antihyperlipidemic drugs, such as bezafibrate and clinofibrate, and by clofibric acid and fenofibric acid (active metabolites of clofibrate and fenofibrate, respectively). The optimal pH of the activation by the drugs was about 7.5, and the concentrations giving maximum stimulation (1.8- to 2.4-fold) were 100, 50, 400 and 50 microM for bezafibrate, clinofibrate, clofibric acid and fenofibric acid, respectively. Clofibrate and fenofibrate acted as weak inhibitors, and the clofibric acid derivatives that lack the chloro group, methyl group on the alpha-carbon or carboxyl group greatly decreased the stimulatory effects. The activation by the drugs increased both Km and kcat (turnover number) values for the coenzyme and substrates. Kinetic analysis with respect to NADP+ showed that bezafibrate, clinofibrate, clofibric acid and fenofibric acid were nonessential activators showing dissociation constants of 32, 6, 103 and 11 microM, respectively. The combined activators experiments with one of the above drugs and sulfobromophthalein, a known activator specific for this enzyme, and comparison of their effects on the activities of mutant enzymes (with Met replacing Lys-270 or Arg-276) indicated that sulfobromophthalein and the drugs bind to an identical site on the enzyme. These results suggest that the long-term therapy with the antihyperlipidemic drugs influences the metabolism of steroid hormones, bile acids and several ketone-containing drugs mediated by the enzyme.

Alcohol Oxidoreductases↗
PubMed2000

Clofibrate pretreatment in mice confers resistance against hepatic lipid peroxidation.

Pretreatment with peroxisome proliferators protects mice against various hepatotoxicants. Since our previous work suggested that the hepatoprotection may involve an increased ability to cope with oxidative stress, the present work directly addressed this possibility. Several observations indicated a heightened defense against oxidative stress accompanies the hepatoprotection produced by clofibrate. Firstly, the carbonyl content of hepatic proteins from clofibrate-pretreated mice was 40% lower than those from vehicle-treated controls. Secondly, liver homogenates from clofibrate-pretreated mice produced less thiobarbituric acid reactive substances upon incubation under aerobic conditions or exposure to ferrous sulfate. This effect was not due to lower levels of peroxidation-prone polyunsaturated fatty acids in clofibrate-treated livers. Thirdly, in vitro experiments indicated that the antioxidant factor in liver homogenates from clofibrate-pretreated mice was not glutathione. Rather, since it was inactivated by proteases and heat treatment, we concluded that a protein is involved. Collectively, our results suggest that a resistance to lipid peroxidation develops in mouse liver during exposure to clofibrate. The identity of the putative antioxidant protein and its contribution to the protection against liver toxicity observed in this and other laboratories awaits future investigation.

2,4,5-Trichlorophenoxyacetic Acid↗