Effect of probucol treatment on lipoprotein cholesterol and drug levels in blood and lipoproteins in familial hypercholesterolemia

Prevention of ferroptosis in acute scenarios: an in vitro study with classic and novel anti-ferroptotic compounds

Ferroptosis, an iron-dependent form of cell death, has critical roles in diverse pathologies. Data on the temporal events mediating the prevention of ferroptosis are lacking. Focused on temporal aspects of cytotoxicity/protection, we investigated the effects of classic (Fer-1) and novel [2,6-di-tert-butyl-4-(2-thienylthio)phenol (C1) and 2,6-di-tert-butyl-4-(2-thienylselano)phenol (C2)] anti-ferroptotic agents against RSL3-, BSO- or glutamate-induced ferroptosis in cultured HT22 neuronal cell line, comparing their effects with those of the antioxidants trolox, ebselen and probucol. Glutamate (5 mM), BSO (25 μM) and RSL3 (50 nM) decreased approximately 40% of cell viability at 24 h. At these concentrations, none of these agents changed cell viability at 6 h after treatments; RSL3 increased lipoperoxidation from 6 h, although BSO and glutamate only did so at 12 h after treatments. At similar conditions, BSO and glutamate (but not RSL3) decreased GSH levels at 6 h after treatments. Fer-1, C1 and C2 exhibited similar protective effects against glutamate-, BSO- and RSL3-cytotoxicity, but this protection was limited when the protective agents were delivered to cells at time-points characterized by increased lipoperoxidation (but not glutathione depletion). Compared to Fer-1, C1 and C2, the anti-ferroptotic effects of trolox, ebselen and probucol were minor. Cytoprotective effects were not associated with direct antioxidant efficacies. These results indicate that the temporal window is central in affecting the efficacies of anti-ferroptotic drugs in acute scenarios; ferroptosis prevention is improbable when significant rates of lipoperoxidation were already achieved. C1 and C2 displayed remarkable cytoprotective effects, representing a promising new class of compounds to treat ferroptosis-related pathologies.

Probucol aggravates long QT syndrome associated with a novel missense mutation M124T in the N-terminus of HERG

Patients with LQTS (long QT syndrome) with a mutation in a cardiac ion channel gene, leading to mild-to-moderate channel dysfunction, may manifest marked QT prolongation or torsade de pointes only upon an additional stressor. A 59-year-old woman had marked QT prolongation and repeated torsade de pointes 3 months after initiation of probucol, a cholesterol-lowering drug. We identified a single base substitution in the HERG gene by genetic analysis. This novel missense mutation is predicted to cause an amino acid substitution of Met(124)-->Thr (M124T) in the N-terminus. Three other relatives with this mutation also had QT prolongation and one of them had a prolonged QT interval and torsade de pointes accompanied by syncope after taking probucol. We expressed wild-type HERG and HERG with M124T in Xenopus oocytes and characterized the electrophysiological properties of these HERG channels and the action of probucol on the channels. Injection of the M124T mutant cRNA into Xenopus oocytes resulted in expression of functional channels with markedly smaller amplitude. In both HERG channels, probucol decreased the amplitude of the HERG tail current, decelerated the rate of channel activation, accelerated the rate of channel deactivation and shifted the reversal potential to a more positive value. The electrophysiological study indicated that QT lengthening and cardiac arrhythmia in the two present patients were due to inhibition of I(Kr) (rapidly activating delayed rectifier K(+) current) by probucol, in addition to the significant suppression of HERG current in HERG channels with the M124T mutation.

Effects of probucol on phase transition and fluidity of phosphatidylcholine membranes: a spin label study

Spin labeling methods were applied to study the structure and dynamics of phosphatidylcholine membranes as a function of temperature and the mole fraction of probucol. Multilamellar liposomes made of dimyristoylphosphatidyclcholine, dipalmitoylphosphatidylcholine both saturated, and egg yolk phosphatidylcholine, an unsaturated membrane, were used. In fluid phase membranes probucol was found to increase the order and decrease the motional freedom of alkyl chains of lipids as shown with stearic acid spin labels. The effect of probucol on order and motional freedom is more pronounced in the membrane center (16-doxylstearic acid spin label position) than in the near polar headgroup region (5-doxylstearic acid spin label position). The presence of unsaturation in alkyl chains significantly decreased the ordering effect of probucol. The main phase transition temperature of saturated bilayers was lowered by 2 degrees C in the presence of 3 mol% of probucol and significantly broadened at higher concentrations as measured with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) partitioning. Also, pretransition was no longer observed in the presence of probucol. In gel phase membranes, the effect of probucol was complex. Close to the main phase transition the motion of alkyl chains was increased, showing a regulatory effect of probucol on membrane fluidity. It is proposed that probucol is located in the membrane center as opposed to vitamin E, which locates its phenolic -OH group at the membrane surface; therefore, it inhibits lipid peroxidation in this region which is less accessible to vitamin E.

Positive correlation between probucol in low density lipoprotein and LDL-lowering

The relationship between the content of probucol in plasma and lipid lowering was studied after administration of probucol. The study group consisted of 44 patients with Type II hyperlipidaemia (mean age 56 y). Total cholesterol level was decreased from 293 to 232 mg.dl-1 by the administration of probucol. The plasma probucol concentration was 2.03 mg.dl-1 after 4 weeks of administration of 500 mg b.d. Although there was no relationship between the change in total cholesterol and the plasma probucol, a linear relation was observed between the decrease in LDL-cholesterol concentration and the probucol concentration in LDL. Neither the VLDL nor the HDL-probucol content were related to the magnitude of the decrease in lipoprotein cholesterol. The present study has demonstrated that an increase in the probucol content in LDL was associated with a decrease in plasma LDL-cholesterol.

Probucol as an antioxidant and antiatherogenic drug

Recently, interest has increased in the hypothesis that low-density lipoprotein (LDL) modified by oxidation may lead to the initiation and to the development of atherosclerosis. In vitro studies of cellular interactions with LDL have revealed that various cells, including endothelial cells and smooth muscle cells, can oxidize LDL. The biochemical changes in LDL may further enhance its atherogenic potential. In addition to these in vitro studies, there is in vivo evidence for oxidized LDL in atherosclerotic lesions and for circulating antibodies against oxidized LDL. Probucol, 4,4'-(isopropylidenedithio)bis(2,6-di-tert-butylphenol), is a widely used cholesterol-lowering drug. Recently, there has been accumulating evidence for other mechanisms of probucol's antiatherogenic effects apart from cholesterol-lowering action. Attention has especially focused on probucol's antioxidant action in the mechanism of antiatherogenesis. In the present article, we will summarize the antiatherogenic and antioxidant actions of probucol.

Probucol reduces plasma lipid peroxides in man

Although primarily used as a lipid lowering drug, probucol also possesses anti-oxidant activity and has been shown in animal models to inhibit or delay the progression of atherosclerosis. It has been suggested that this anti-atherosclerotic effect may occur through inhibition of free radical oxidation of low density lipoprotein. The aim of this study was to investigate the effects of probucol on free radical activity in hyperlipidaemic patients. Plasma lipid peroxides were measured before probucol treatment, at 4 and 12 weeks treatment and then 4 weeks after stopping probucol. Lipid peroxide concentrations were significantly reduced during and 4 weeks after stopping treatment with probucol, when compared with baseline values. There were no changes in plasma vitamin E concentrations. The results of this study indicate that probucol reduces lipid peroxidation in patients, an effect which may occur through a free radical scavenging action.

Probucol pretreatment enhances the chemotaxis of mouse peritoneal macrophages

To investigate the effects of probucol on macrophage chemotaxis, we preincubated mouse peritoneal macrophages with probucol for 20 hours in vitro and using a modified Boyden chamber system compared their chemotactic responses with those of control macrophages that were preincubated with vehicle. Probucol pretreatment enhanced the macrophage chemotactic responses to zymosan-activated serum, acetylated low density lipoprotein (LDL), and native LDL. Probucol pretreatment also enhanced the basal migration observed when there was no stimulant in the lower chamber of a modified Boyden chamber. The chemoattracting potency of native LDL was weaker than that of zymosan-activated serum in control macrophages; however, both substances became equally potent when the macrophages were preincubated with probucol. The degree of the enhancement to native LDL after probucol preincubation reached fourfold to eightfold. The fashion of the enhanced migration of macrophages to native LDL after preincubation with probucol was predominantly chemotactic rather than chemokinetic. Time-course experiments revealed that it took more than 12 hours of probucol preincubation to show clearly enhanced macrophage chemotaxis to native LDL. Macrophages preincubated with probucol together with cycloheximide showed markedly reduced chemotaxis compared with macrophages preincubated only with probucol. Probucol pretreatment also enhanced macrophage chemotactic responses to high density lipoprotein, oxidized LDL, and lipoprotein-deficient serum.(ABSTRACT TRUNCATED AT 250 WORDS)

Probucol increases cholesteryl ester transfer protein activity in hypercholesterolaemic patients

Probucol, a widely used lipid lowering drug, reduces both low- and high-density (LDL and HDL) lipoprotein levels and can induce a regression of tissue lipid deposits in both animals and man. The suggested mechanism(s) involve the prevention of LDL oxidative modifications and, possibly, an improvement in the reverse cholesteryl ester transport system. Probucol administration to 10 hypercholesterolaemic patients increased the activity of the cholesteryl ester transfer protein (CETP) by 50%. The rise of CETP activity was significantly related with the plasma steady-state drug levels (r = 0.51, P less than 0.005), thus suggesting that probucol may directly stimulate CEPT synthesis and/or release. Furthermore, CETP activity was inversely related with HDL-cholesterol levels, both in the whole series of 10 patients (r = -0.56, P less than 0.001) and, more so, in the single individuals (r between -0.77 and -0.97), thus suggesting that the reduction of plasma HDL-cholesterol levels is a direct consequence of CETP stimulation. These findings support the hypothesis that an improvement in the reverse cholesteryl ester transport is a major mechanism of probucol and that this may explain the drug induced plasma lipoprotein changes.

Probucol, a superoxide free radical scavenger in vitro

Free radical (FR) mediated oxidation of low density lipoproteins (LDL) has been implicated in atherogenesis. Probucol is a lipid lowering agent with antioxidant properties which may protect the LDL from FR mediated damage. The specific mechanism by which probucol acts as an antioxidant has not previously been reported. We therefore studied the FR scavenging properties of probucol in vitro and results show that this drug is a powerful superoxide scavenger. This property may be relevant in its use as a lipid lowering drug in the retardation of the atherosclerotic process.

Preservation of the endogenous antioxidants in low density lipoprotein by ascorbate but not probucol during oxidative modification

Several lines of evidence indicate that the oxidative modification of low density lipoproteins (LDL) may provide an important link between plasma LDL and the genesis of the atherosclerotic lesion. Ascorbate is an important water-soluble, chain-breaking antioxidant in humans. Probucol, a lipid-soluble antioxidant drug has been shown to retard the progression of atherosclerosis. The aim of the present study was to compare the effects of probucol and physiologic levels of ascorbate on the oxidative modification of LDL in both a cell-free (2.5 microM Cu++ in phosphate-buffered saline) and cellular system (human monocyte macrophages in Ham's F-10 medium). Both ascorbate and probucol inhibited the oxidative modification of LDL in both systems to a similar degree as evidenced by the thiobarbituric acid-reacting substance activity, electrophoretic mobility, and degradation by macrophages. However, whereas co-incubation with physiologic levels of ascorbate resulted in a substantial preservation of the alpha-tocopherol, gamma-tocopherol, and beta-carotene of the LDL, probucol in concentrations ranging from 10 to 80 microM failed to protect these antioxidants. Thus, in addition to being as potent as probucol in inhibiting the oxidation of LDL, ascorbate in contrast preserves the endogenous antioxidants in the LDL.

Antioxidant activity of probucol and its effects on phase transitions in phosphatidylcholine liposomes

The effect of probucol on the phase behavior of dimyristoylphosphatidylcholine (DMPC) was examined by fluorescence polarization and differential scanning calorimetry (DSC). Probucol broadens and shifts the temperature of the main phase transition of DMPC liposomes as measured by fluorescence polarization with diphenylhexatriene and trimethyl-ammonium-diphenylhexatrine at concentrations as low as 5 mole%. As measured by DSC, probucol reduces the transition temperature of the gel----liquid-crystalline phase transition of DMPC by approx. 2 C degrees at all concentrations above about 5 mole% probucol and eliminates the pretransition at less than 1 mole%. In addition, the phase transition of DMPC is broadened and the enthalpy of the transition reduced by approx. 50%. Even at high concentrations of probucol, the gel----liquid-crystalline phase transition of DMPC is not eliminated. Similar effects are observed with dipalmitoylphosphatidylcholine liposomes. Based on these DSC measurements, measurements of the melting of probucol in dry mixtures with DMPC and observations of probucol mixtures with DMPC under polarizing optics, the maximum solubility of probucol in DMPC is approx. 10 mole%. This concentration exceeds that required (approx. 0.5 mole%) to prevent peroxidation of 10 mole% arachidonic acid in DMPC liposomes for 30 min in the presence of 0.05 mM Fe(NH4)(SO4)2 at 4 degrees C. Thus, probucol has a limited solubility in saturated phosphatidylcholine bilayers, but is an effective antioxidant at concentrations lower than its maximum solubility.

Probucol. A reappraisal of its pharmacological properties and therapeutic use in hypercholesterolaemia

Probucol is a lipid-regulating agent structurally dissimilar to other known agents, with a unique pharmacodynamic and clinical profile. It is effective in the treatment of primary Type IIa and IIb hyperlipoproteinaemias, including polygenic (non-familial) hypercholesterolaemia and both heterozygous and homozygous forms of familial hypercholesterolaemia, with reductions in plasma total cholesterol and low density lipoprotein (LDL)-cholesterol levels of about 10 to 20% being attained. Marked effects on cutaneous and tendinous xanthomas have been observed, with significant regression often apparent after 2 or 3 months' therapy. Preliminary trials also indicate efficacy in hyperlipoproteinaemia secondary to nephrotic syndrome and diabetes mellitus. The mechanism of the reduction in LDL-cholesterol levels is yet to be fully elucidated, but it is thought that the decrease results from enhanced catabolism, and there is preliminary evidence of an independent antioxidant effect. In contrast with all other known lipid-lowering agents, probucol also effects a consistent reduction in serum high density lipoprotein (HDL)-cholesterol levels, of around 20 to 30%; the clinical significance of this observation is unclear, although some preliminary investigations suggest a beneficial effect in enhancing reverse cholesterol transport. The influence of probucol treatment on cardiovascular morbidity and mortality remains to be fully investigated; a large trial quantifying the potential effect of probucol against the development of atherosclerotic lesions is currently in progress. Adverse effects of probucol are generally mild, seldom requiring treatment withdrawal, with gastrointestinal effects such as diarrhoea predominating. However, indications of an increased frequency of ventricular arrhythmias and sudden death in association with QT interval prolongation in some animals have prompted some concern. Although there is evidence of a degree of QT prolongation in a number of trials in humans, the nature and clinical significance of this effect requires clarification, as no increased incidence of cardiac arrhythmias is apparent. Thus, probucol appears to be of benefit in primary and secondary hyperlipoproteinaemia of Types IIa and IIb, and particularly in homozygous familial hypercholesterolaemia, with marked effects on xanthomas, and a generally favourable adverse effect profile. There is no evidence to date causally relating occasional QT interval prolongation in patients to any incidence of arrhythmias or sudden death. Pharmacodynamic investigations are likely to clarify further the place of probucol in therapy, particularly with respect to its distinctive lowering of plasma HDL-cholesterol levels.

Comparison of lovastatin and probucol in treatment of familial and non-familial hypercholesterolemia: different effects on lipoprotein profiles

In order to compare the effects of lovastatin and probucol on lipoprotein profiles, we treated 32 familial hypercholesterolemia (FH) heterozygotes and 26 patients with non-familial hypercholesterolemia for 14 weeks with either probucol (1 g/d) or lovastatin (40-80 mg/d) in a randomized double-blind study. Lovastatin at 80 mg/d reduced low density lipoprotein (LDL)-cholesterol and apo B by more than 40% in both familial and non-familial hypercholesterolemia (non-FH). Probucol reduced LDL-cholesterol by 10-17% while LDL-apo B levels were not influenced at all (FH) or fell by 13% (non-FH). Analysis of LDL composition demonstrated that the LDL-cholesterol lowering effect of probucol in FH was entirely due to reduction in the proportion of cholesterol in LDL with no reduction in LDL mass. Serum high density lipoprotein2 (HDL2)-cholesterol levels fell by 27-33% during probucol, whereas HDL2-cholesterol increased by 10-18% with lovastatin 80 mg/d. These changes in HDL2 were not mediated by lipoprotein lipase or hepatic lipase, both of which are known to participate in regulation of this lipoprotein.

Changes in high-density lipoprotein subfraction distribution and increased cholesteryl ester transfer after probucol

The effects of probucol (500 mg twice daily) on high-density lipoprotein (HDL) subfractions and cholesteryl ester transfer from HDL to lower density lipoproteins were tested in a series of patients with Type II hypercholesterolemia. In this placebo-controlled crossover trial, patients received probucol or placebo for 8 weeks, then switched to the other agent for another 8 weeks. Probucol significantly lowered total, low-density lipoprotein and HDL cholesterol levels. HDL subfractions, separated by rate zonal ultracentrifugation, showed a dramatic reduction in HDL2, whereas changes in HDL3 were not significant. Both subfractions eluted at a characteristically lower volume, indicating a reduced flotation rate. These findings were confirmed by gradient gel electrophoretic separation, which showed a typical reduction or disappearance of HDL2b particles and the prevalence of particles in the HDL3a-HDL3b electrophoretic range in almost all patients. After treatment, cholesteryl ester transfer from HDL to lower density lipoproteins was significantly increased in all patients. These data suggest that probucol may accelerate HDL particle conversion, leading to improvement in reverse cholesterol transport from the periphery to the liver, through HDL and very low density lipoprotein.

Influence of probucol administration on lipoprotein cholesterol and apolipoproteins in normolipemic males

In order to interpret the known lipoprotein changes in probucol-treated patients, serum concentrations of apolipoproteins (A-I, A-II, B, C-II, C-III, E) were measured before, during and after probucol administration (2 X 500 mg p.d.), in 16 healthy males (30.3 +/- 5.6 years old). Cholesterol concentrations were determined in LDL and VLDL fractions as well as in HDL subfractions which were isolated by preparative ultracentrifugation. In addition, apolipoprotein A-I and A-II concentrations were measured in the HDL subfractions. Compared with the baseline values, significant apolipoprotein changes were found in the serum apolipoprotein A-I (151 +/- 18 to 115 +/- 31 mg/dl; P less than 0.001) and C-II levels during administration. The HDL subfraction analysis showed that the decrease of HDL-cholesterol and apolipoprotein A-I (59.9 +/- 23.5 to 34.4 +/- 16.4 mg/dl, P less than 0.001, and 65.7 +/- 49.0 to 37.5 +/- 23.5 mg/dl, P less than 0.05, respectively) was predominantly related to the HDL2b subfraction (d = 1.063-1.100 g/ml).

Probucol reduces the rate of association of apolipoprotein C-III with dimyristoylphosphatidylcholine

The effect of low concentrations of probucol and cholesterol on the association of dimyristoylphosphatidylcholine with human plasma apolipoprotein C-III was studied. Liposomes of dimyristoylphosphatidylcholine with or without probucol or cholesterol were prepared by swelling the lipids in buffer at 37 degrees C. The association of apolipoprotein C-III with the liposomes was determined at 24 degrees C by measuring the rate of clearing of turbidity at 400 nm following addition of protein. At a weight ratio of probucol/dimyristoylphosphatidylcholine of 1:25 (5 mol% probucol), the rate of clearing of liposomes was decreased by 60%; 5 mol% cholesterol had no effect on the clearing rate. Liposomes were then added to the preformed apolipoprotein C-III/lipid micelles. In the absence of probucol, the added liposomes cleared rapidly regardless of the presence or absence of cholesterol. With 5 mol% probucol, almost no decrease in absorbance was noted on addition of liposomes to the micelles. These data show that probucol reduces the rate of association of an apolipoprotein with lipid and suggests that the interaction of probucol with lipid may modify the assembly and/or metabolism of lipoproteins.

Probucol in long-term treatment of hypercholesterolemia

Over 15 yr of clinical experience with probucol seems to indicate that the drug is a safe and moderately effective hypocholesterolemic drug even in long-term treatment. Adverse effects are infrequent and usually tolerable. Probucol prolongs QT-interval but this does not seem to be connected with harmful effects in man. Its hypocholesterolemic action is not sufficient in all patients but this can be substantially improved by combining other hypolipidemic drugs with different mode of action. Interference with lipoprotein structure may contribute to the hypocholesterolemic action of probucol, and despite the lowering of HDL cholesterol probucol has been shown to regress peripheral cholesterol deposits. There is also tentative evidence that the drug may protect from CHD in primary prevention. The newly-discovered antioxidant property of probucol preventing harmful LDL modification in vitro might partly explain the favorable effects of probucol independently of its effects on LDL- or HDL-cholesterol levels.

Hypercholesterolemia and atherosclerosis: present and future therapy including LDL-apheresis

Atherosclerosis-induced coronary heart disease remains the major cause of death and disability in industrialized countries. Hypercholesterolemia is recognized as a causative factor in the development of atherosclerosis. While the lowering of cholesterol levels as a treatment goal has met with general agreement and acceptance, the preferred methods for doing so are still open to conjecture. This literature review discusses various factors in the hypercholesterolemia-atherosclerosis link and surveys a variety of treatment protocols including diet modification, drug therapy, surgical intervention, and plasmapheresis. Evidence is accumulating to prove that the ideal hypercholesterolemia therapy is one that reduces LDL levels while maintaining or increasing HDL levels. Because LDL-apheresis has this potential, this paper also reviews the various LDL-apheresis methods, including immunoadsorption, chemical affinity, and double-membrane filtration.

Probucol prevents the progression of atherosclerosis in Watanabe heritable hyperlipidemic rabbit, an animal model for familial hypercholesterolemia

In this study, we questioned whether in vivo probucol could prevent the progression of atherosclerosis in homozygous Watanabe heritable hyperlipidemic (WHHL) rabbits, an animal model for familial hypercholesterolemia. At 2 months of age, eight WHHL rabbits were divided into two groups. Group A (n = 4) was fed standard rabbit chow for 6 months. Group B (n = 4) was fed standard rabbit chow containing 1% probucol for 6 months. At the end of the experiments, average plasma concentrations of cholesterol were 704 +/- 121 mg/dl in group A and 584 +/- 61 mg/dl in group B, respectively. The percentage of surface area of total thoracic aorta with visible plaques in group A versus group B was 54.2% +/- 18.8% versus 7.0% +/- 6.3%, respectively. What was noteworthy was that the percentage of plaque in the descending thoracic aorta was almost negligible (0.2% +/- 0.2%) in group B rabbits compared to that in group A rabbits (41.1% +/- 20.2%). Low density lipoproteins (LDL) isolated from WHHL rabbits under treatment with probucol (group B) were shown to be highly resistant to oxidative modification by cupric ion and to be minimally recognized by macrophages. On the contrary, LDL from group A rabbits incubated with cupric ion showed a 7.4-fold increase in peroxides (thiobarbituric acid-reactive substances) and a 4.3-fold increase in the synthesis of cholesteryl ester in macrophages compared to those of LDL from group B rabbits. Thus, probucol could definitely prevent the progression of atherosclerosis in homozygous WHHL rabbits in vivo by limiting oxidative LDL modification and foam cell transformation of macrophages.

Adverse effects of hypolipidaemic drugs

Cholestyramine, colestipol, clofibrate, gemfibrozil, nicotinic acid (niacin), probucol, neomycin, and dextrothyroxine are the most commonly used drugs in the treatment of hyperlipoproteinaemic disorders. While adverse reaction data are available for all of them, definitive data regarding the frequency and severity of potential adverse effects from well-controlled trials using large numbers of patients (greater than 1000) are available only for cholestyramine, clofibrate, nicotinic acid and dextrothyroxine. In adult patients treated with cholestyramine, gastrointestinal complaints, especially constipation, abdominal pain and unpalatability are most frequently observed. Continued administration along with dietary manipulation (e.g. addition of dietary fibre) and/or stool softeners results in diminished complaints during long term therapy. Large doses of cholestyramine (greater than 32 g/day) may be associated with malabsorption of fat-soluble vitamins. Most significantly, osteomalacia and, on rare occasions, haemorrhagic diathesis are reported with cholestyramine impairment of vitamin D and vitamin K absorption, respectively. Paediatric patients have been reported to experience hyperchloraemic metabolic acidosis or gastrointestinal obstruction. Concurrent administration of acidic drugs may result in their reduced bioavailability. Serious adverse reactions to clofibrate will probably limit its role in the future. Of particular concern are ventricular arrhythmias, induction of cholelithiasis and cholecystitis, and the potential for promoting gastrointestinal malignancy which far outweigh the reported benefits in preventing new or recurrent myocardial infarction, cardiovascular death and overall death. Patients with renal disease are particularly prone to myositis, secondary to alterations in protein binding and impaired renal excretion of clofibrate. Drug interactions with coumarin anticoagulants and sulphonylurea compounds may produce bleeding episodes and hypoglycaemia, respectively. Nicotinic acid produces frequent adverse effects, but they are usually not serious, tend to decrease with time, and can be managed easily. Dermal and gastrointestinal reactions are most common. Truncal and facial flushing are reported in 90 to 100% of treated patients in large clinical trials. Significant elevations of liver enzymes, serum glucose, and serum uric acid are occasionally seen with nicotinic acid therapy. Liver enzyme elevations are more common in patients given large dosage increases over short periods of time, and in patients treated with sustained release formulations.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of probucol on the composition and in vitro catabolism of LDL in type IIa hypercholesterolemia

A possible mechanism of action of probucol on low density lipoprotein uptake was examined in 7 type IIa hypercholesterolemic subjects. Probucol administration effectively lowered plasma cholesterol. Both apo B-associated cholesterol and HDL cholesterol were decreased but a great inter-patient variability was noted. Plasma triglycerides were unchanged and phospholipids decreased. The composition of the isolated LDL was unaffected. The LDL displaceable activity of reference [125I]LDL measured by competition assays in control fibroblasts, was increased in 3 subjects, decreased in 1 subject and unchanged in the other 3. No correlation was found between the change in apo B-associated cholesterol and the change in the in vitro catabolism of LDL of treated patients. The results did not allow a simple mechanism of action to be ascribed to the drug, but questioned the origin of the hypercholesterolemia.