Reversal of clofibrate-induced cholesterol oversaturation of bile with chenodeoxycholic acid.

Giving clofibrate 2 g daily to seven patients significantly increased the biliary cholesterol concentration while the proportion of bile acids fell. Five patients on established clofibrate treatment were given 750 mg of chenodeoxycholic acid (CDCA) daily for one month. Biliary lipid analysis after the CDCA treatment showed a significant fall in the proportion of cholesterol and a rise in that of bile acids. The serum lipid concentrations, which had already been reduced by diet and clofibrate, showed a further significant reduction after the introduction of CDCA. This study suggests that CDCA may be usefully combined with clofibrate to reverse the tendency towards cholesterol saturation of bile and enhance the effect of lowering serum lipid concentrations.     

Effect of short-term clofibrate on glucose metabolism and insulin secretion in patients with mild maturity-onset diabetes mellitus

The effect of 1 week clofibrate administration on glucose and insulin responses to oral glucose and to intravenous tolbutamide was evaluated in 21 patients with mild maturity-onset diabetes (fasting plasma glucose 108-152 mg/100 ml). After treatment, oral glucose tolerance and hypoglycaemic effect of tolbutamide were significantly improved; plasma insulin response was reduced after glucose and unmodified after tolbutamide; fasting plasma glucose was also significantly reduced. These findings did not correlate with the observed fall in serum lipids. Short-term clofibrate improves glucose metabolism in mild diabetes irrespective of its effects on lipid metabolism. It is suggested that the drug's action may be mediated by reduced insulin resistance.     

Ischaemic Heart Disease: A Secondary Prevention Trial Using Clofibrate

A trial is reported of the effects of giving clofibrate to prevent progression of pre-existing ischaemic heart disease. There were two groups randomly distributed between clofibrate (350 patients) and placebo (367 patients) regimens. The trial lasted about six years and was conducted in 19 hospitals in Scotland. The criteria of acceptance into the trial were precise and were monitored by one observer. The standards of diagnosis of events were defined and all protocols and electrocardiograms were read blind by one observer.Three categories of patients were admissible to the trial: (1) patients with one myocardial infarction (W.H.O. E.C.G. criteria) between 8 and 16 weeks before the start of the trial; (2) patients with angina of a duration of 3 to 24 months, provided their E.C.G. showed signs of myocardial ischaemia at rest or after exercise; and (3) patients with one recent myocardial infarction and pre-existing angina as defined above.There were fewer deaths in patients with angina (categories 2 and 3 above) treated with clofibrate than in those on placebo. The mortality in the former group was reduced by 62%, and this is a statistically significant difference. Clofibrate did not have any statistically significant effect in reducing the rate of non-fatal infarction in patients with angina or in those with myocardial infarction and pre-existing angina, though a beneficial trend was evident when both subgroups were combined (a 44% reduction compared with the placebo group). There was a significant reduction in all events (fatal and non-fatal) in patients with angina (“all anginas”) in the clofibrate-treated group; the rate was reduced by 53%.Clofibrate did not alter the overall mortality or morbidity rates in patients admitted to the trial with recent myocardial infarction without preceding angina of more than three months'' duration. In one subgroup there was a statistically significant adverse effect in the clofibrate-treated group. The lack of any overall effect in patients with myocardial infarction might be related to the unexpectedly low mortality rate (2·97%) in the placebo group; it is usually in the region of 4-9% per annum after first myocardial infarction.In patients categorized as “all anginas” there was significant reduction in events whether the initial serum cholesterol level was high (greater than 260 mg/100 ml) or normal. Clofibrate seemed to have a small but not significant beneficial effect in patients with myocardial infarction with initially high serum cholesterol levels, but was of no value in those with initially normal serum cholesterol levels. There was no significant relationship between the response or lack of response of serum cholesterol to clofibrate and the incidence of events either in patients with angina or in those with infarction.The main conclusion of this trial is that clofibrate had a beneficial effect in reducing mortality and, to a lesser extent, morbidity in patients who presented with angina (“all anginas”). This effect was independent of initial serum cholesterol levels or the extent to which serum cholesterol was lowered. The drug had no significant overall effect on prognosis in patients with myocardial infarction alone.     

Hypolipidemic drug clofibrate induces hepatic dedifferentiation

The effect of clofibrate on rat liver enzymes and metabolites was compared with that produced by partial hepatectomy and an extrahepatic tumor. Clofibrate administration produced decrease in gamma-glutamyltranspeptidase (GGT) activity with concomitant increase in glutathione concentration. The drug was able to exert its GGT-lowering effect even when fed to tumor-bearing animals. Presence of an extrahepatic neoplasm as well as administration of clofibrate resulted in marked decrease in activities of hepatic arginase and ornithine transaminase. Administration of clofibrate to the tumor-bearing rat produced a further decrease in activities of these two enzymes. These results suggest that clofibrate causes hepatic dedifferentiation and simulates an extrahepatic tumor. However, clofibrate did not induce any significant increase in polyamine profile unlike the other two experimental conditions.     

Effects of clofibrate on plasma tryptophan, growth hormone, and prolactin and on brain tryptophan and serotonin in prepubertal rats

The effects of clofibrate administration (200 mg/kg, po) on somatic growth, plasma levels of lipids, tryptophan, growth hormone (GH), and prolactin (PRL), as well as on brain concentrations of tryptophan and 5-hydroxytryptamine (5-HT) were studied in prepubertal male rats. The drug did not significantly alter ponderal growth, but an appreciable reduction of tail length was observed in rats treated for 30 days. Triglyceride concentrations in plasma showed a 43% diminution after 30 days of treatment, whereas free fatty acid (FFA) levels were not modified. Clofibrate administration for 7, 15, or 30 days caused a fall in total tryptophan and a significant increase of the free fraction in plasma with no change in brain tryptophan levels. Brain 5-HT was generally unaffected but a marked elevation of this parameter was noted in rats treated for 15 days. Plasma GH and PRL concentrations remained unaltered. It may be concluded from these findings that the slight reduction of somatic growth, the diminution of triglycerides, and the increase of free tryptophan in plasma, induced by chronic clofibrate treatment, are not associated with variations in brain tryptophan and 5-HT levels or with modifications of plasma GH and PRL titers.     

Effect of clofibrate on peroxisomal and mitochondrial beta-oxidation in chicken liver

The effect of a 0.25% clofibrate diet for 2 weeks on peroxisomal and mitochondrial beta-oxidation in chicken liver was studied. The activities of antimycin antimycin A-insensitive palmitoyl-CoA oxidation (peroxisomal beta-oxidation) and carnitine acetyltransferase increased about two-fold. The activities of palmitoyl-CoA-dependent O2 consumption (mitochondrial beta-oxidation) and carnitine palmitoyltransferase were also slightly activated by the administration of clofibrate, but not significant. Thus, clofibrate may be a typical drug which activates the peroxisomal beta-oxidation more than the mitochondrial one in various species. The effect of clofibrate on peroxisomal carnitine acetyltransferase was the same as that on the mitochondrial one in chicken liver. Serum lipids were not lowered, but hepatomegaly was observed in the present experiment with chicken.     

Uncoupling of lipolysis from cyclic AMP by procaine: a tool for studying the mechanism of action of antilipolytic agents.

The initial rate of net glycerol release in norepinephrine-stimulated adipose tissue fragments was inhibited (40-78%) by procaine-HCl (1-5mM), whereas basal (unstimulated) lipolysis was unaffected. A dose-related inhibition of norepinephrine-induced lipolysis by procaine-HCl (0.1-1 mM) also occurred in adipocytes. Procaine-induced antilipolysis was associated with an augmented rather than a reduced hormone-stimulated increment in intracellular cyclic AMP. The dissociation of lipolysis from cyclic AMP accumulation has been termed the uncoupling effect of procaine. This effect of procaine was employed to define the precise mechanism of action of the antilipolytic drug clofibrate (Atromid-S) which inhibits lipolysis by reducing cyclic AMP. A reduction in cyclic AMP by clofibrate was demonstrated in norepinephrine-stimulated cells exposed to procaine (uncoupled system). Thus, the inhibitory effect of clofibrate on cyclic AMP could not be attributed to accumulation of products of lipolysis. Because neither procaine-HCl nor clofibrate had any effect on the low Km 3':5'-cyclic-AMP phosphodiesterase (EC 3.1.4.17) activity in hormone stimulated cells, the clofibrate-induced reduction in cyclic AMP was attributed to its direct action on adipocyte adenylate cyclase.     

Evidence for permanent enhancement of residual ADH induced by antidiuretic agents (chlorpropamide, carbamazepine, clofibrate) in patients with pituitary diabetes insipidus.

Excretion of free water was studied in 7 patients with pituitary diabetes insipidus before treatment and after withdrawal of antidiuretic drugs (chlorpropamide, carbamazepine, clofibrate) used on a long-term basis. A statistically significant decrease in free water clearance was found after 2-4 weeks of withdrawal of antidiuretic agents. This was considered as a clinical evidence for the permanently enhanced release of residual ADH induced by chlorpropamide, carbamazepine and clofibrate in patients with partial defect in ADH secretion.     

Risk factors evaluation in some cardiovascular diseases

Cardiovascular risk factors are associated with limitations of blood fluidity. Rheological behaviour of blood in transient flow may result from the internal organization, which in turn depends upon many parameters, which may be considered as possible elements of a profiling algorithm for diagnostic and prognostic values in various pathophysiological states. This study was designed to investigate haemorheological parameters in patients being treated for hypertension, coronary heart disease and myocardial infarct. On the basis of plasma viscosity, whole blood viscosity, haematocrit, red cell aggregation and red cell deformation, the risk was evaluated. In cases of hypertension there was a significant rise in plasma viscosity, whole blood viscosity, red cell aggregation and a fall in red cell deformability. In cases of coronary disease, plasma viscosity and red cell aggregation was increased, while in patients with myocardial infarcts, where the degree of severity is greater it was found that there was a significant rise in both plasma and whole blood viscosity. Haematocrit values were unaffected in all three groups.     

The effect of halofenate and clofibrate on aggregation and release of serotonin by human platelets.

The hypolipidemic drugs halofenate and clofibrate inhibit the aggregation of human platelets induced by ADP, collagen and epinephrine. The effect of the drugs is primarily on the “second wave” of aggregation which is associated with the platelet release reaction. The drugs also inhibit the release of serotonin from platelets suggesting that the effect on aggregation is attributable to an inhibition of the release reaction. Halofenate is much more potent than clofibrate in inhibiting both the release of serotonin and the second wave of aggregation.     

Mechanism of clofibrate hepatotoxicity: mitochondrial damage and oxidative stress in hepatocytes

Peroxisome proliferators have been found to induce hepatocarcinogenesis in rodents, and may cause mitochondrial damage. Consistent with this, clofibrate increased hepatic mitochondrial oxidative DNA and protein damage in mice. The present investigation aimed to study the mechanism by which this might occur by examining the effect of clofibrate on freshly isolated mouse liver mitochondria and a cultured hepatocyte cell line, AML-12. Mitochondrial membrane potential (Delta Psi(m)) was determined by using the fluorescent dye 5,5',6,6'-tetrachloro-1,1', 3,3'-tetraethyl-benzimidazolylcarbocyanine iodide (JC-1) and tetramethylrhodamine methyl ester (TMRM). Application of clofibrate at concentrations greater than 0.3 mM rapidly collapsed the Delta Psi(m) both in liver cells and in isolated mitochondria. The loss of Delta Psi(m) occurred prior to cell death and appeared to involve the mitochondrial permeability transition (MPT), as revealed by calcein fluorescence studies and the protective effect of cyclosporin A (CsA) on the decrease in Delta Psi(m). Levels of reactive oxygen species (ROS) were measured with the fluorescent probes 5-(and-6)-carboxy-2',7'-dichlorofluorescein diacetate (DCFDA) and dihydrorhodamine 123 (DHR123). Treatment of the hepatocytes with clofibrate caused a significant increase in intracellular and mitochondrial ROS. Antioxidants such as vitamin C, deferoxamine, and catalase were able to protect the cells against the clofibrate-induced loss of viability, as was CsA, but to a lesser extent. These results suggest that one action of clofibrate might be to impair mitochondrial function, so stimulating formation of ROS, which eventually contribute to cell death.     

Inhibition of rat and human adipocyte adenylate cyclase in the antilipolytic action of insulin, clofibrate, and nicotinic acid.

Clofibrate (Atromid-S), nicotinic acid, and insulin are known to be potent hypolipidemic and antilipolytic agents. The present study was undertaken to define the mechanism of action of this latter effect on isolated rat and human fat cells. Sodium clofibrate (0.42 mM), nicotinic acid (0.42 mM), and insulin (100 microU/mL) were shown to inhibit norepinephrine-stimulated lipolysis in rat and human adipose cells and this inhibition was associated with a reduction in intracellular 3',5'-cyclic AMP levels. A similar cyclic AMP lowering effect was demonstrated with insulin in the presence of procaine-HCL, which uncouples the adenylate cyclase system from lipolysis. This insulin effect was attributed to inhibition of adenylate cyclase. A direct and significant inhibition of adenylate cyclase in membrane fractions obtained from isolated human adipocytes was demonstrated for all three antilipolytic agents. The common membrane site of action of these agents whereby adenylate cyclase activity is depressed, thus decreasing cyclic AMP production and free fatty acid (FFA) mobilization from adipose stores, implies a central role for the adenylate cyclase system. These findings are consistent with the view that the hypotriglyceridemic effects of clofibrate, nicotinic acid, and insulin may be partly explained by deprivation of FFA substrate for hepatic very low density lipoprotein synthesis.     

Clofibrate,Serum Enzymes,and Muscle Pain

Serum creatine kinas (C.K.), aspartate amino-transferase (G.O.T.), and alkaline phosphatase (A.P.) activities were measured in 211 men with serum cholesterol concentrations in the upper one-third of the normal distribution. Of these, 110 were receiving clofibrate and 101 were given identical capsules containing olive oil. These investigations were also carried out on 85 healthy men with low serum cholesterol levels not receiving clofibrate.No differences were observed in C.K. and G.O.T. activities between any of these groups; A.P. was significantly lower in the clofibrate-treated group. No significant alterations in C.K. occurred during serial observations made in 15 patients with ischaemic heart disease over a period of five months. No instance of myalgia or muscle stiffness was recorded in 452 men who had received clofibrate for one year.It is concluded that raised C.K. and G.O.T. concentrations and the occurrence of myalgia are uncommon accompaniments of clofibrate treatment.     

Differential effect of clofibrate on acetyl-CoA carboxylase mRNA level in rat white and brown adipose tissue

Regulation of some lipogenic enzyme gene expression by clofibrate was studied in rat white and brown adipose tissue. In white adipose tissue the drug administration for 14 days to rats resulted in the increase in acetyl-CoA carboxylase, ATP-citrate lyase, and glucose 6-phosphate dehydrogenase mRNA levels. Opposing effect of clofibrate on the acetyl-CoA carboxylase, ATP-citrate lyase, and glucose 6-phosphate dehydrogenase mRNA levels was found in brown adipose tissue. These data indicate a tissue specificity of clofibrate action on lipogenic enzyme gene expression. The results presented in this paper provide further evidence that hypolipidaemia caused by the treatment with clofibrate cannot be related to the inhibition of fatty acid synthesis in white adipose tissue in rat.     

Effect of clofibrate on the hepatic concentrations of citric acid cycle intermediates and malonyl-CoA in the rat

The effect of clofibrate [ethyl 2-(4-chlorophenoxy)-2-methylpropionate] administered subcutaneously to rats (600 mg/kg per day for 7 days) on the hepatic concentrations of the citric acid cycle intermediates and malonyl-CoA was studied. The concentration of isocitrate increased by 40%, whereas that of oxaloacetate, succinyl-CoA and malate tended to decrease. No significant changes were found in the concentrations of 2-oxoglutarate, fumarate, succinate and citrate. A significant decrease in hepatic malonyl-CoA content was found. This reduction of malonyl-CoA may be the reason for the reported increase in hepatic fatty acid oxidation during clofibrate treatment.     

Halofenate versus clofibrate in the management of true diabetes insipidus

The antidiuretic effect of two chemically related drugs, clofibrate and halofenate, was tested in a patient with pitressin-sensitive diabetes insipidus. The conventional daily dosage of 2 g clofibrate failed to control the symptoms of this patient; in order to obtain an adequate response the dosage had to be increased to 4 g daily.Halofenate at a dosage of 2 g daily, an amount equivalent in hypolipidemic activity to 4 g per day of clofibrate, significantly reduced water intake and output, while urinary osmolarity was markedly increased.It is concluded that (1) the antidiuretic effect of clofibrate may be dose-related, and that (2) halofenate also possesses some antidiuretic activity.     

Regulation of the biosynthesis of two distinct fatty acid-binding proteins in rat liver and intestine. Influences of sex difference and of clofibrate

Two distinct fatty acid-binding proteins (FABPs) have been identified in rat intestine, gFABP (15,063 Da) which is confined to intestinal epithelium and hFABP (14,184 Da) which is found in both liver and intestine. We have examined the influence of sex difference and the effect of clofibrate, both of which affect cellular fatty acid metabolism and hFABP levels, on the concentration, and mRNA levels of both hepatic and intestinal FABPs. In the liver, hFABP concentration was approximately 2-fold greater in females and in clofibrate-treated males than in untreated male rats. These differences were not accompanied by changes in the fractional turnover of the polypeptide but rather by parallel increases in hFABP mRNA. In the intestine, the two FABPs exhibited different regulatory responses. Intestinal hFABP turnover was 33% greater in females than in males, whereas mRNA concentration was 50% greater. Thus, unlike hFABP in liver, there was no sex-related difference in the steady-state level of hFABP in intestine. However, clofibrate treatment, similar to its effects in the liver, doubled intestinal hFABP protein and mRNA concentration. In contrast to hFABP, neither gFABP protein nor mRNA concentration were sex dependent, whereas clofibrate produced only a modest increase in gFABP concentration without significantly changing gFABP mRNA levels. The results indicate that the influence of sex difference and the effect of clofibrate on hepatic fatty acid metabolism are both associated with changes in hFABP synthesis mediated pretranslationally. The differential response of hFABP and gFABP in intestine suggests that these proteins play distinct roles in the cellular metabolism of fatty acids.     

Specific repression of transthyretin gene expression in rat liver by a peroxisome proliferator clofibrate.

The effect of clofibrate, a hypolipidemic drug and a potent peroxisome proliferator, on expression of a nonperoxisomal transthyretin (prealbumin) gene was studied using rats fed clofibrate for various periods. Upon feeding a diet containing clofibrate, the level of transthyretin mRNA was down-regulated, reaching 20% of the control level, in an almost reciprocal time course to that of increases in the levels of peroxisomal mRNAs. Studies on expression of other steroid hormone regulated genes suggest that clofibrate may down-regulate several but not all types of steroid hormone regulated mRNA expression.     

Propylthiouracil-induced hypothyroid hyperlipidemic chick: A model for clofibrate-induced toxicity

1. An animal model for clinically observed clofibrate (p-chlorophenoxy isobutyrate, CPIB)-induced toxicity has been tested.2. It is demonstrated that propylthiouracil-induced hypothyroid-hyperlipidemic chick develops severe toxic manifestations following clofibrate administration.3. Toxic symptoms are characterized by listlessness, drowziness, and extreme muscular weakness.4. This is associated with elevation of blood urea nitrogen, creatine phosphokinase, uric acid and glutamic oxaloacetic transaminase.5. Histological examination of muscle specimen from chicks exhibiting toxic syndrome showed degeneration and vacuolization of muscle fibers.6. The biochemical and histological changes observed are quite similar to those reported in clinical practice in some patients given clofibrate.7. It is suggested that this chick model could be used to investigate the biochemical basis of clofibrate toxicity.