Selective reduction of cholesterol in HDL2 fraction by probucol in familial hypercholesterolemia and hyperHDL2 cholesterolemia with abnormal cholesteryl ester transfer

Probucol Trial for Secondary Prevention of Atherosclerotic Events in Patients with Coronary Heart Disease (PROSPECTIVE)

AIMS

Although intensive statin therapy reduced cardiovascular risks, cardiovascular events have not been completely prevented. Probucol is a potent antioxidant and reduces tendon xanthomas in familial hypercholesterolemia patients despite reduction of high-density lipoprotein (HDL)-cholesterol (HDL-C). We investigated whether probucol can reduce cardiovascular events on top of conventional lipid-lowering therapy in patients with coronary heart disease (CHD).

METHODS

PROSPECTIVE is a multicenter, randomized, prospective study that recruited 876 Japanese patients with CHD and dyslipidemia with a low-density lipoprotein (LDL)-cholesterol (LDL-C) level of ≥ 140 mg/dL without medication or those treated with lipid-lowering drugs. Lipid-lowering agents were administered during the study period in the control group (n=438), and probucol 500 mg/day was added to lipid-lowering therapy in the probucol group (n=438). Patients were randomly assigned to two treatment groups by adjusting the LDL-C level and presence of diabetes and hypertension and followed up for more than 3 years. The primary end point was a composite of cerebrovascular and cardiovascular events (cardiovascular disease death including sudden death, nonfatal myocardial infarction, nonfatal stroke, hospitalization for unstable angina, hospitalization for heart failure, or coronary revascularization). The secondary end point was carotid intima-media thickness in a subset of patients.

RESULTS

The incidence of the primary end point showed a trend to be lower in the probucol group compared with that in the control group despite reduced HDL-C without serious adverse events. Anti-atherogenic effects of probucol may be attributed to its potent antioxidative function and enhancement of reverse cholesterol transport.

CONCLUSION

Since there was no statistical significance between the probucol and control groups despite a marked reduction of HDL-C, further studies on the clinical outcomes of probucol on top of conventional therapy may be necessary in the future (UMIN000003307).

Recent advances in synthetic pharmacotherapies for dyslipidaemias

Despite the demonstrated benefits of statins and injectable biologics, there is a need for new and safe oral agents for addressing classical lipid targets, low-density lipoprotein cholesterol (LDL-C), triglycerides and high-density lipoprotein cholesterol (HDL-C). LDL-C is unquestionably causal in the development of atherogenesis and atherosclerotic cardiovascular disease, but new options are required to address triglyceride-rich lipoproteins and lipoprotein(a). For hypercholesterolaemia, pitavastatin provides a very low dose and potent statin that does not adversely affect glucose metabolism; bempedoic acid acts at a biochemical step preceding hydroxymethylglutaryl-CoA reductase and is not associated with muscular side effects. For hypertriglyceridaemia, pemafibrate displays a unique and selective agonist activity on peroxisomal proliferator activated receptor-α that does not elevate homocysteine or creatinine. Although omega-3 fatty acids supplementation is not effective in secondary prevention, high dose eicosapentaenoic ethyl ester can lead to a remarkable fall in first and recurrent events in high risk patients with hypertriglyceridaemia/low HDL-C. Gemcabene, a dicarboxylic acid regulating apolipoprotein B-100, is effective in reducing both cholesterol and triglycerides. Among cholesteryl ester transfer protein antagonists that elevate HDL-C, only anacetrapib reduces cardiovascular events. Probucol stimulates reverse cholesteryl ester transport, lowers LDL-C stabilizing plaques and may lower incidence of cardiovascular events. These agents, which act through novel mechanisms, afford good and potentially safe treatment choices that may increase adherence and the attainment of therapeutic targets.

Shotgun proteomic analysis reveals proteome alterations in HDL of patients with cholesteryl ester transfer protein deficiency

BACKGROUND

We previously reported that the patients with cholesteryl ester transfer protein (CETP) deficiency (CETP-D) show marked changes in the size and lipid compositions of high-density lipoprotein (HDL) and that they are not protected from atherosclerotic cardiovascular diseases, despite increased serum HDL-cholesterol (HDL-C) levels. HDL particles carry a variety of proteins, some of which are known to have antiatherogenic functions.

OBJECTIVE

This study aimed to investigate the protein composition of HDL particles in patients with CETP-D.

METHODS

Eight patients with complete deficiency of CETP and 8 normolipidemic healthy subjects were enrolled. We performed shotgun proteomic analysis to investigate the proteome of ultracentrifugally isolated HDL.

RESULTS

We identified 79 HDL-associated proteins involved in lipid metabolism, protease inhibition, complement regulation, and acute-phase response, including 5 potential newly identified HDL-associated proteins such as angiopoietin-like3 (ANGPTL3). Spectral counts of apolipoprotein (apo) E were increased in patients with CETP-D compared with controls (60.3 ± 6.9 vs 43.7 ± 2.5, P < .001), which is concordant with our previous report. Complement regulatory proteins such as C3, C4a, C4b, and C9 were also significantly enriched in HDL from patients with CETP-D. Furthermore, apoC-III and ANGPTL3, both of which are now known to associate with increased atherosclerotic cardiovascular diseases, were enriched in patients with CETP-D compared with normolipidemic subjects (35.9 ± 5.3 vs 27.1 ± 3.7, 2.3 ± 1.1 vs 0.4 ± 1.1, respectively; P < .01).

CONCLUSION

We have characterized HDL-associated proteins in patients with CETP-D. We identified a significant increase in the amount of apoE, apoC-III, ANGPTL3, and complement regulatory proteins. These proteomic changes might be partly responsible for the enhanced atherogenicity of patients with CETP-D.

Particle number analysis of lipoprotein subclasses by gel permeation HPLC in patients with cholesteryl ester transfer protein deficiency

Objective

We previously reported that patients with cholesteryl ester transfer protein (CETP) deficiency (CETP-D) have a higher prevalence of atherosclerotic cardiovascular disease, in spite of increased HDL-C levels. However, characterization of HDL in CETP-D has not been well described. Therefore, we examined HDL particle number (PN) rather than HDL-C level.

Approach and results

Nine patients with CETP-D and 9 normolipidemic subjects were enrolled. We performed gel permeation high-performance liquid chromatography (GP-HPLC) analysis, determined the cholesterol and triglyceride composition of all lipoprotein subclasses, and calculated the PN of each subclass, which consisted of 3 VLDL (large, medium, and small), 4 LDL (large, medium, small, and very small), and 5 HDL (very large, large, medium, small, and very small) subclasses. The PNs of large and medium LDL were significantly lower in CETP-D than that in healthy subjects (0.66- and 0.63-fold decrease, respectively; p<0.001), whereas the PN of very small LDL, which is known to be atherogenic, was significantly higher (1.36-fold increase, p = 0.016). The PNs of very large and large HDL in CETP-D were markedly higher than that in healthy subjects (19.9- and 4.5-fold increase, respectively; p<0.001), whereas the PNs of small and very small HDL, which have more potent anti-atherogenic functions, were significantly lower (0.76- and 0.61-fold decrease, respectively; p<0.001).

Conclusion

We have assessed the PNs of detailed subclasses of patients with CETP-D for the first time. The PN of larger HDL was markedly increased, that of smaller HDL was decreased, and that of very small LDL was increased, suggesting that CETP-D has pro-atherogenic lipoprotein properties.

Re-evaluation of cholesteryl ester transfer protein function in atherosclerosis based upon genetics and pharmacological manipulation

PURPOSE OF REVIEW

To re-evaluate the functions of plasma cholesteryl ester transfer protein (CETP) in atherosclerosis based upon recent findings from human genetics and pharmacological CETP manipulation.

RECENT FINDINGS

CETP is involved in the transfer of cholesteryl ester from HDL to apolipoprotein B-containing lipoproteins, a key step of reverse cholesterol transport (RCT). CETP inhibitors have been developed to raise serum HDL-cholesterol (HDL-C) levels and reduce cardiovascular events. However, outcome studies of three CETP inhibitors (torcetrapib, dalcetrapib and evacetrapib) were prematurely terminated because of increased mortality or futility despite marked increases in HDL-cholesterol and decreases in LDL-cholesterol except for dalcetrapib. Patients with CETP deficiency show remarkable changes in HDL and LDL and are sometimes accompanied by atherosclerotic cardiovascular diseases. Recent prospective epidemiological studies demonstrated atheroprotective roles of CETP. CETP inhibition induces formation of small dense LDL and possibly dysfunctional HDL and downregulates hepatic scavenger receptor class B type I (SR-BI). Therefore, CETP inhibitors may interrupt LDL receptor and SR-BI-mediated cholesterol delivery back to the liver.

SUMMARY

For future drug development, the opposite strategy, namely enhancers of RCT via CETP and SR-BI activation as well as the inducers of apolipoprotein A-I or HDL production might be a better approach rather than delaying HDL metabolism by inhibiting a main stream of RCT in vivo.

Rationale and Design of the PROSPECTIVE Trial: Probucol Trial for Secondary Prevention of Atherosclerotic Events in Patients with Prior Coronary Heart Disease

BACKGROUND

Reduction of serum LDL-cholesterol by statins was shown to improve clinical outcomes in patients with coronary heart disease (CHD). Although intensive statin therapy significantly reduced cardiovascular risks, atherosclerotic cardiovascular events have not been completely prevented. Therefore, effective pharmacologic therapy is necessary to improve "residual risks" in combination with statins. Probucol has a potent antioxidative effect, inhibits the oxidation of LDL, and reduces xanthomas. Probucol Trial for Secondary Prevention of Atherosclerotic Events in Patients with Prior Coronary Heart Disease (PROSPECTIVE) is a multicenter, randomized, prospective study designed to test the hypothesis that the addition of probucol to other lipid-lowering drugs will prevent cerebro- and cardiovascular events in patients with prior coronary events and high LDL cholesterol levels.

STUDY DESIGN

The study will recruit approximately 860 patients with a prior CHD and dyslipidemia with LDL-C level ≥140 mg/dl without any medication and those treated with any lipid-lowering drugs with LDL-C level ≥100 mg/dl. Lipid-lowering agents are continuously administered during the study period in control group, and probucol (500 mg/day, 250 mg twice daily) is added to lipid-lowering therapy in the test group. The efficacy and safety of probucol with regard to the prevention of cerebro- and cardiovascular events and the intima-media thickness of carotid arteries as a surrogate marker will be evaluated.

SUMMARY

PROSPECTIVE will determine whether the addition of probucol to other lipid-lowering drugs improves cerebro- and cardiovascular outcomes in patients with prior coronary heart disease. Furthermore, the safety of a long-term treatment with probucol will be clarified.

Did we abandon probucol too soon?

PURPOSE OF REVIEW

Probucol is a potent antioxidative drug that has been used for prevention and treatment of atherosclerotic cardiovascular diseases and xanthoma. Probucol has been used as a lipid-lowering drug for a long time especially in Japan, although Western countries quitted its use because of the reduction in serum HDL-cholesterol (HDL-C). This review highlights both basic and clinical studies that provide new insights into the pleiotropic effects of probucol.

RECENT FINDINGS

Recently, the mechanisms for the pharmacologic actions of probucol have been elucidated at the molecular level with a special focus on HDL metabolism and its functions. Probucol enhances plasma cholesteryl ester transfer protein activity and hepatic scavenger receptor class B type I, causing a decrease in HDL-C. It also accelerates the antioxidative function of HDL via increase in paraoxonase 1 activity. Recent retrospective analyses of probucol-treated patients with heterozygous familial hypercholesterolemia and those after coronary revascularization demonstrated a strong beneficial effect of probucol on secondary prevention of cardiovascular events and mortality.

SUMMARY

Probucol has pleiotropic and beneficial therapeutic effects on cardiovascular system. Although statins are effective for lowering LDL-cholesterol (LDL-C) and reducing coronary heart disease risk, probucol should be considered as an option in case statins are not effective.

A randomized, open-label, multicentre study to evaluate plasma atherosclerotic biomarkers in patients with type 2 diabetes mellitus and arteriosclerosis obliterans when treated with Probucol and Cilostazol

Objectives

To evaluate the plasma atherosclerotic biomarkers in patients with type 2 diabetes mellitus (T2DM) and arteriosclerosis obliteran (ASO) when treated with Probucol plus Cilostazol in combination and individually.

Methods

In this open-label study, patients aged 40–75 years were randomized to receive conventional therapy alone, or with Cilostazol 100 mg bid, or with Probucol 250 mg bid, or with both in combination. Endpoints included changes in plasma biomarker and safety at 12 weeks.

Results

Of the 200 randomized patients, 165 for per-protocol and 160 for the safety (QTc intervals) were set, respectively. Probucol significantly reduced total cholesterol (P < 0.001), low-density lipoprotein cholesterol (LDL-C), (P = 0.01), and high-density lipoprotein cholesterol (HDL-C) (P < 0.001) compared with conventional therapy. Cilostazol was effective in increasing HDL-C (P = 0.002) and reducing triglycerides levels (P < 0.01) compared with conventional therapy. A trend towards significance was observed for the difference between conventional therapy alone and Probucol plus Cilostazol group for the change in oxidized low-density lipoprotein (Ox-LDL, P = 0.065). No significant effects on the majority of the remaining biomarkers were found across the treatment groups.

Conclusions

We have confirmed that Ox-LDL could be a possible plasma atherosclerotic biomarker among the evaluated biomarkers, which reflected the synergetic effect of Cilostazol plus Probucol in patients with T2DM and ASO shown previously in preclinical studies.

Pharmacologic suppression of hepatic ATP-binding cassette transporter 1 activity in mice reduces high-density lipoprotein cholesterol levels but promotes reverse cholesterol transport

BACKGROUND

The role of hepatic ATP-binding cassette transporter 1 (ABCA1) in maintaining plasma high density lipoprotein cholesterol (HDL-C) levels is well established, but its role in reverse cholesterol transport (RCT) is unclear. Probucol is a compound that reduces HDL-C levels but also reduces atherosclerosis in animal models and xanthomas in humans. The aim of the present study was to test the hypothesis that probucol inhibits hepatic ABCA1 activity, thereby reducing HDL-C levels but promoting RCT from macrophages.

METHODS AND RESULTS

Wild-type (WT) C57BL/6 mice and scavenger receptor class B type I (SR-BI) knockout mice were fed a chow diet containing 0.5% probucol or normal chow for 2 weeks. In WT mice, probucol, despite decreasing HDL-C by >80%, effectively maintained macrophage RCT. In SR-BI knockout mice, probucol also substantially reduced HDL-C but significantly increased macrophage RCT. Furthermore, probucol significantly enhanced the excretion of HDL-derived cholesterol into feces in both WT and SR-BI knockout mice. Probucol inhibited ABCA1-dependent cholesterol efflux from mouse primary hepatocytes, and this effect was shown to be responsible for the effect of probucol on increasing the fecal excretion of HDL-derived cholesterol in vivo.

CONCLUSIONS

We demonstrate that pharmacological inhibition of hepatic ABCA1 activity with probucol reduced HDL-C levels but promoted RCT through diversion of HDL-derived cholesterol from efflux back into plasma instead to excretion in the bile. These results explain the beneficial effects of probucol on atherosclerosis and xanthomas despite its HDL-lowering effects and suggest that inactivation of hepatic ABCA1 leads to increased RCT despite reducing plasma HDL-C levels.

Long-term probucol treatment prevents secondary cardiovascular events: a cohort study of patients with heterozygous familial hypercholesterolemia in Japan

AIM

The POSITIVE study assessed whether long-term treatment with probucol. a potent anti-oxidant and cholesteryl ester transfer protein (CETP) activator is associated with a lowered risk of cardiovascular events in a very high-risk population: familial hypercholesterolemia (FH).

METHODS

The study cohort included 410 patients with heterozygous FH, diagnosed between 1984 and 1999 by cardiovascular and metabolic experts at fifteen centers. Traceable patients were screened using predefined eligibility criteria. The primary outcome measure for comparison between probucol exposure and non-exposure was the time to the first cardiovascular event involving hospitalization.

RESULTS

Analysis revealed significant differences in baseline characteristics and follow-up treatment between exposure and non-exposure. An observed indication bias was the use of probucol in more severe FH at diagnosis, both for primary and secondary prevention. When the multivariate Cox regression procedure was used after adjustment for possible confounding factors, probucol lowered the risk (hazard ratio [HR], 0.13; 95% confidence interval [CI], 0.050.34) in secondary prevention (n=74) and was statistically significant (p<0.001), although not significant (HR, 1.5; 95% CI, 0.484.67; p=0.49) in primary prevention (n=233). Safety assessment found no specific difference between exposure and non-exposure.

CONCLUSION

Long-term probucol treatment may prevent secondary attack in a higher cardiovascular risk population of heterozygous FH.

Distribution of dolichol in the serum and relationships between serum dolichol levels and various laboratory test values

We examined the correlations between serum dolichol levels and laboratory test parameters in patients affected by disease, as well as the distribution of dolichol in sera from patients with hyperbetalipoproteinemia and hyperalphalipoproteinemia. Serum dolichol was evaluated by a reverse-phase HPLC method. After centrifugation, the serum dolichol found in healthy controls was mainly associated with medium-sized particles of the high-density lipoprotein (HDL) fraction. For patients with hyperbetalipoproteinemia, serum dolichol was also associated with the medium HDL fractions. However, for hyperalphalipoproteinemia patients the levels of large HDL and serum dolichol were increased, and serum dolichol was mainly associated with the large HDL fraction. On laboratory tests of components, the dolichol level was not correlated with the values for markers of the liver and biliary system, with the values of renal function markers, with creatine kinase activity, amylase activity or uric acid concentration, but was correlated with total cholesterol, HDL-cholesterol and apoA-I concentrations, and with lactate dehydrogenase (LDH) activity. These results suggest that serum dolichol exclusively localized in HDL, and in subpopulation, that in normocholesterolemia or hyperbeta-cholesterolemia is associated with HDL(3), which is small sized and high density HDL, however, that in hyperalphacholesterolemia is associated with HDL(2), which is large sized and lower density HDL.

Cholesteryl ester transfer protein (CETP) expression protects against diet induced atherosclerosis in SR-BI deficient mice

OBJECTIVE

To determine whether expression of the human CETP transgene protects against diet-induced atherosclerosis in SR-BI deficient mice.

METHODS AND RESULTS

SR-BI deficient (-/-) mice were crossed with CETP transgenic (CETPtg) mice to produce a colony of SR-BI(-/-) x CETPtg mice in a C57Bl/6 background. Age and sex matched groups of genetically modified and wild-type C57Bl/6 mice were fed a high fat, high cholesterol diet for 22 weeks. In both wild-type and SR-BI(-/-) mice, expression of the CETP transgene reduced the cholesterol content and increased the density of lipoprotein particles in the HDL density range. In SR-BI(-/-) x CETPtg mice, CETP activity inversely correlated with total plasma cholesterol levels and shifted the buoyant HDL typical of SR-BI deficiency toward a more normal density HDL particle. Atherosclerosis at the level of the aortic arch was evident in both male and female SR-BI deficient mice but occurred to a greater extent in the females. Expression of CETP markedly attenuated the development of atherosclerosis in SR-BI deficient mice fed an atherogenic diet (P<0.003).

CONCLUSIONS

Expression of the human CETP transgene protects SR-BI deficient mice from atherosclerosis, consistent with a role for CETP in remodeling HDL and providing an alternative pathway for the selective uptake of HDL-CE by the liver.

Probucol enhances the expression of human hepatic scavenger receptor class B type I, possibly through a species-specific mechanism

OBJECTIVE

Scavenger receptor class B type I (SR-BI) is a major receptor for high-density lipoproteins (HDL) in the liver, which is the terminus of reverse cholesterol transport. Overexpression of SR-BI attenuated experimental atherosclerosis in murine models, concomitant with a reduction in plasma HDL-cholesterol levels. Probucol is known to be a potent hypolipidemic drug to regress xanthoma formation and carotid atherosclerosis in conjunction with a marked reduction in HDL-cholesterol levels. The aim of the present study was to know the effect of probucol on the expression of SR-BI and the underlying mechanism.

METHODS AND RESULTS

We found that probucol increased the expression of SR-BI proteins in in vitro human liver cells and an in vivo rabbit model, but not in wild-type C57Bl6 mice. The decay curve of SR-BI protein was markedly retarded in probucol-treated HepG2 cells in the presence of cycloheximide, indicating that probucol may stabilize human SR-BI protein. To determine the underlying mechanism for the observed species-specific effect, we conducted the following host-swap experiments, in which SR-BI was transfected or expressed in heterologous cells or hosts. Probucol did not increase human SR-BI protein in the liver of transgenic mice carrying the entire human SR-BI genome. Although probucol could stabilize even murine SR-BI, when transfected into a human cell line, HepG2, human SR-BI was not stabilized in a mouse hepatoma cell line, Hepa 1-6, treated with probucol.

CONCLUSIONS

Probucol enhances hepatic SR-BI protein expression, possibly through species-specific stabilization of the protein.

Effort Angina in a Middle-Aged Woman With Abnormally High Levels of Serum High-Density Lipoprotein Cholesterol A Case of Cholesteryl-Ester Transfer Protein Deficiency

A 54-year-old female was admitted to hospital complaining of oppressive anterior chest pain during exercise. Treadmill exercise ECG testing showed significant ischemic ECG changes, and electron-beam computed tomography demonstrated patchy calcifications in the coronary artery. Coronary angiography revealed a significant stenotic lesion of the right coronary artery. On routine investigations, no classical coronary risk factors were found, although a very high concentration (209 mg/dl) of high-density lipoprotein cholesterol (HDL-C) was detected. The serum concentration of cholesteryl-ester transfer protein (CETP), which plays a central role in the reverse cholesterol transport system, was measured and found to be less than the measurable minimum. The patient showed one of the typical genetic CETP mutations (intone 14 splicing defect), and her lipid profile was improved by administration of probucol for 3 months. A very high concentration of HDL-C with a defect of CETP activity may be a specific biochemical indicator pointing to an increased risk of premature coronary artery disease, and the lipid profile can be improved by use of lipid-lowering drugs.

Pharmacological modulation of cholesteryl ester transfer protein, a new therapeutic target in atherogenic dyslipidemia

In mediating the transfer of cholesteryl esters (CE) from antiatherogenic high density lipoprotein (HDL) to proatherogenic apolipoprotein (apo)-B-containing lipoprotein particles (including very low density lipoprotein [VLDL], VLDL remnants, intermediate density lipoprotein [IDL], and low density lipoprotein [LDL]), the CE transfer protein (CETP) plays a critical role not only in the reverse cholesterol transport (RCT) pathway but also in the intravascular remodeling and recycling of HDL particles. Dyslipidemic states associated with premature atherosclerotic disease and high cardiovascular risk are characterized by a disequilibrium due to an excess of circulating concentrations of atherogenic lipoproteins relative to those of atheroprotective HDL, thereby favoring arterial cholesterol deposition and enhanced atherogenesis. In such states, CETP activity is elevated and contributes significantly to the cholesterol burden in atherogenic apoB-containing lipoproteins. In reducing the numbers of acceptor particles for HDL-derived CE, both statins (VLDL, VLDL remnants, IDL, and LDL) and fibrates (primarily VLDL and VLDL remnants) act to attenuate potentially proatherogenic CETP activity in dyslipidemic states; simultaneously, CE are preferentially retained in HDL and thereby contribute to elevation in HDL-cholesterol content. Mutations in the CETP gene associated with CETP deficiency are characterized by high HDL-cholesterol levels (>60 mg/dL) and reduced cardiovascular risk. Such findings are consistent with studies of pharmacologically mediated inhibition of CETP in the rabbit, which argue strongly in favor of CETP inhibition as a valid therapeutic approach to delay atherogenesis. Consequently, new organic inhibitors of CETP are under development and present a potent tool for elevation of HDL in dyslipidemias involving low HDL levels and premature coronary artery disease, such as the dyslipidemia of type II diabetes and the metabolic syndrome. The results of clinical trials to evaluate the impact of CETP inhibition on premature atherosclerosis are eagerly awaited.

CGP 43371 paradoxically inhibits development of rabbit atherosclerotic lesions while inducing extra-arterial foam cell formation

Ansamycins are hypolipidemic compounds which, when administered to various animal species, dramatically lower high density lipoprotein (HDL) cholesterol levels, in addition to reducing the levels of other lipoprotein classes. The current study tested one of these ansamycins (CGP 43371) for its hypolipidemic and anti-atherosclerotic activity in cholesterol-fed rabbits. Rabbits were fed a 0.25% cholesterol-enriched diet with or without admixed CGP 43371, equivalent to 30 mg/kg per day for 16 weeks. Compared with control rabbits, CGP 43371 treatment lowered total cholesterol levels (46%, P<0.05) and lipoprotein cholesterol levels (HDL, 58%; VLDL, 49% [both P<0.05]; LDL, 28% [not significant]). Despite the dramatic lowering of HDL cholesterol levels, aortic atherosclerosis, assessed by grossly visible sudanophilia, was significantly inhibited versus controls (total aorta=38%; aortic arch=32%; thoracic aorta=60%). Of particular note in CGP 43371-treated rabbits was a striking splenomegaly, which correlated with the presence of massive accumulations of macrophage foam cells in the splenic red pulp. We speculate that CGP 43371 inhibits the development of atheroselerotic lesions in rabbits by both a hypolipidemic mechanism, and by a mechanism(s) in which macrophage foam cells accumulate in the spleen.

Molecular biology and pathophysiological aspects of plasma cholesteryl ester transfer protein

Plasma cholesteryl ester transfer protein (CETP) facilitates the transfer of cholesteryl ester (CE) from high density lipoprotein (HDL) to apolipoprotein B-containing lipoproteins. Since CETP regulates the plasma levels of HDL cholesterol and the size of HDL particles, CETP is considered to be a key protein in reverse cholesterol transport, a protective system against atherosclerosis. CETP, as well as plasma phospholipid transfer protein, belongs to members of the lipid transfer/lipopolysaccharide-binding protein (LBP) gene family, which also includes the lipopolysaccharide-binding protein (LBP) and bactericidal/permeability-increasing protein. Although these four proteins possess different physiological functions, they share marked biochemical and structural similarities. The importance of plasma CETP in lipoprotein metabolism was demonstrated by the discovery of CETP-deficient subjects with a marked hyperalphalipoproteinemia (HALP). Two common mutations in the CETP gene, intron 14 splicing defect and exon 15 missense mutation (D442G), have been identified in Japanese HALP patients with CETP deficiency. The deficiency of CETP causes various abnormalities in the concentration, composition, and functions of both HDL and low density lipoprotein. Although the pathophysiological significance of CETP in terms of atherosclerosis has been controversial, the in vitro experiments showed that large CE-rich HDL particles in CETP deficiency are defective in cholesterol efflux. Epidemiological studies in Japanese-Americans and in the Omagari area where HALP subjects with the intron 14 splicing defect of CETP gene are markedly frequent, have shown an increased incidence of coronary atherosclerosis in CETP-deficient patients. The current review will focus on the recent findings on the molecular biology and pathophysiological aspects of plasma CETP, a key protein in reverse cholesterol transport.

Probucol promotes reverse cholesterol transport in heterozygous familial hypercholesterolemia. Effects on apolipoprotein AI-containing lipoprotein particles

In order to investigate the effect of Probucol therapy on reverse cholesterol transport, apo AI-containing lipoprotein particles were isolated and characterized, and their cholesterol effluxing capacity and LCAT activity were assayed in four familial hypercholesterolemia patients before and after 12 weeks of Probucol therapy. Four major subpopulations of apo A-containing lipoprotein particles are separated before and after drug treatment; LpAI, LpAI:AII, LpAIV, LpAI:AIV:AII. Probucol reduces both total plasma and LDL-cholesterol (-17 and -14%, respectively). Apo B decreases slightly (-7.6%). Plasma HDL-cholesterol and apo AI decrease by 36.6 and 34.7%. LpA-I showed a marked decrease (-46%). Moreover, plasma LCAT and CETP activities were markedly increased under Probucol treatment. Analysis of lipoprotein particles showed that Probucol induces a decrease of protein content and an increase of cholesterol and triglycerides contents. Interestingly, Probucol induces an enhancement of LCAT activity in LpAI (4.5-fold). This drug induces a trend toward greater cholesterol efflux from cholesterol-preloaded adipose cells promoted by Lp AI and Lp AIV but not by Lp AI:AII. This study confirms the hypothesis, in addition to the lowering LDL-cholesterol levels and antioxidant effects of Probucol, that HDL reduction was not an atherogenic change in HDL system but may cause an antiatherogenic action by accelerating cholesterol transport through HDL system, promoting reverse cholesterol transport from peripheral tissues.

Molecular mechanisms, lipoprotein abnormalities and atherogenicity of hyperalphalipoproteinemia

Hyperalphalipoproteinemia (HALP) is caused by a variety of genetic and environmental factors. Among these, plasma cholesteryl ester transfer protein (CETP) deficiency is the most important and frequent cause of HALP in the Asian populations. CETP facilitates the transfer of cholesteryl ester (CE) from high density lipoprotein (HDL) to apolipoprotein (apo) B-containing lipoproteins, and is a key protein in the reverse cholesterol transport system. The deficiency of CETP causes various abnormalities in the concentration, composition, and function of both HDL and low density lipoprotein (LDL). The significance of CETP in terms of atherosclerosis had been controversial. However, the in vitro evidence showed large CE-rich HDL particles in CETP deficiency are defective in cholesterol efflux. Similarly, scavenger receptor BI (SR-BI) knockout mice show a marked increase in HDL-cholesterol but accelerated atherosclerosis in atherosclerosis-susceptible mice. Recent epidemiological studies in Japanese-Americans and in Omagari area where HALP subjects with the intron 14 splicing defect of CETP gene are markedly frequent, have demonstrated an increased incidence of coronary atherosclerosis in CETP-deficient patients. Thus, CETP deficiency is a state of impaired reverse cholesterol transport which may possibly lead to the development of atherosclerosis. The current review will focus on the molecular mechanisms and atherogenicity of HALP, especially CETP deficiency.

Opposite effects on serum cholesteryl ester transfer protein levels between long-term treatments with pravastatin and probucol in patients with primary hypercholesterolemia and xanthoma

Long-term effects of pravastatin and probucol on serum cholesteryl ester transfer protein (CETP) and xanthoma/xanthelasma size were compared. Twenty-three patients with primary hypercholesterolemia and xanthoma/xanthelasma, including 11 patients with heterozygous familial hypercholesterolemia, were treated with pravastatin (20 mg/day) or probucol (1000 mg/day) for 24 months. Serum CETP levels were measured by sandwich ELISA. In 11 patients (six men and five women, 55 +/- 2 [SE] yr) treated with pravastatin, serum cholesterol levels decreased from 262 +/- 13 to 229 +/- 13 mg/dl during the 24-month treatment period (P = 0.05). Serum HDL cholesterol levels were not changed. Serum CETP levels decreased from 2.5 +/- 0.2 to 2.0 +/- 0.2 microg/ml (-21%, P = 0.002). By contrast, in 12 patients (four men and eight women, 57 +/- 4 year) treated with probucol, serum cholesterol levels did not significantly decrease from 236 +/- 11 to 207 +/- 13 mg/dl. Serum HDL cholesterol levels decreased from 44 +/- 2 to 30 +/- 2 mg/dl (P = 0.009). Serum CETP levels increased from 2.3 +/- 0.1 to 2.8 +/- 0.2 microg/ml (+23%, P = 0.02). Xanthelasma regression was found in two of four patients (50%) each treated with pravastatin and probucol, respectively. In contrast, Achilles' tendon xanthoma regressed in four of five patients (80%) treated with pravastatin, but only in two of five patients (40%) treated with probucol. Patients with xanthoma/xanthelasma regression after 2 years treatment had higher baseline levels of serum CETP than those without regression (2.7 +/- 0.2 microg/ml [n = 9] versus 2.1 +/- 0.2 microg/ml [n = 7], P = 0.05). Serial changes in serum CETP levels during treatment with pravastatin and probucol were discordant, but not related to the degree of xanthoma regression. However, higher level of serum HDL3 cholesterol was an independent factor in the smaller size of Achilles' tendon xanthoma at baseline. In addition, higher levels of serum HDL3 triglyceride on lipid-lowering therapy (6 months) appear to be a common predictor of regression of Achilles' tendon xanthoma in the treatment with either pravastatin or probucol.

Effect of probucol on hypercholesterolemia in renal transplant patients

BACKGROUND

Hypercholesterolemia is a well-known complication in kidney transplant recipients, although its pathogenesis may be multifactorial. The therapeutic effect of probucol on post-transplant hypercholesterolemia was prospectively evaluated.

METHODS

Twelve hypercholesterolemic kidney transplant patients with serum total cholesterol > or = 250 mg/dl without diabetes mellitus or hypoproteinemia were prospectively treated with probucol (250 mg, bid, for three months). Before initiating and at the end of treatment, blood was drawn after at least a 12-hour fast to measure lipids in serum and lipoprotein fractions, apoproteins (apo), lipoprotein fractions, lethicin cholesterol acyl transferase (LCAT), free fatty acids (FFAs), and cholesterol ester. The lipid profiles of 17 healthy subjects were also examined.

RESULTS

After treatment with probucol, serum total cholesterol, low-density lipoprotein (LDL) cholesterol, high-density lipoprotein (HDL) cholesterol, and apo AI were significantly decreased, whereas cholesterol ester increased significantly.

CONCLUSIONS

Post-transplant hypercholesterolemia is featured with abnormalities in very low-density lipoprotein (VLDL) metabolism. Although HDL cholesterol decreased, probucol might have acted as an antiatherogenic by modulating HDL metabolism and stimulating reverse transfer of cholesterol from peripheral tissue.

Genetic cholesteryl ester transfer protein deficiency is extremely frequent in the Omagari area of Japan. Marked hyperalphalipoproteinemia caused by CETP gene mutation is not associated with longevity

Low levels of HDL cholesterol have been clearly demonstrated to be associated with an increased incidence of coronary heart disease, strongly suggesting that HDL particles have an antiatherogenic function. However, little information has been available concerning the atherogenicity of a marked hyperalphalipoproteinemia (HALP). There is no agreement about whether plasma cholesteryl ester transfer protein (CETP) deficiency is associated with an antiatherogenic state or not, although this disorder was reported to be one of the major causes of marked HALP. In the current study, we have found a unique area (Omagari City, Akita Prefecture, Japan) where CETP deficiency caused by a G-to-A mutation at the 5' splice donor site of intron 14 in the CETP gene is extremely frequent. In Omagari City, the mutation was detected more than 20 times more frequently and the prevalence of a marked HALP with plasma HDL cholesterol > or = 2.58 mmol/L (100 mg/dL) was 5 to 10 times higher than in other areas of Japan. This discovery has made it possible to perform a large population-based study concerning the atherogenicity of a marked elevation of HDL cholesterol in a genetically more homogeneous population. There was a statistically significant U-shaped relationship between HDL cholesterol levels and the incidence of ischemic changes in electrocardiograms. In cases of HDL cholesterol < 1.81 mmol/L (70 mg/dL), the incidence increased in proportion to the levels of HDL cholesterol. The frequency of the CETP gene mutation was higher in patients with coronary heart disease than in healthy control subjects. In subjects aged > 80 years, the prevalence of both marked HALP and the intron 14 splicing defect was significantly lower than in the younger generation. The current study indicated for the first time that a marked HALP caused by CETP gene mutation may not represent a longevity syndrome, suggesting the importance of reevaluation of the clinical significance and pathophysiology of a marked HALP.

A comparative study of the therapeutic effect of probucol and pravastatin on xanthelasma

We examined and compared the effects of probucol and pravastatin on the regression of xanthelasma. Thirty-six cases treated by probucol and 18 cases by pravastatin were evaluated for 12 months. Thirteen of the 36 cases treated with probucol showed regression of xanthelasma. However, one of the 18 cases treated with pravastatin showed regression. These data were statistically significantly. The average total cholesterol value in both groups decreased during drug therapy. However, the average of HDL-cholesterol values in the probucol treatment group showed significant decreases, but those in the pravastatin treatment group did not. We discussed the mechanisms of the two drugs on the regression of xanthelasma and the mechanisms of development of xanthelasma.

Preventive effects of probucol on restenosis after percutaneous transluminal coronary angioplasty

This protocol was performed to elucidate the preventive effects of probucol on restenosis after percutaneous transluminal coronary angioplasty (PTCA). A total of 118 patients with 134 vessels undergoing successful PTCA was randomly and prospectively assigned to the probucol group (group P) or the control group (group C). The subjects consisted of 91 men and 27 women, with a mean age of 63.4 +/- 2.3 years. Sixty-six vessels of 59 patients in group P and 68 vessels of 59 patients in group C were evaluated by coronary angiography at 3 months after PTCA. Probucol (0.5 mg/day) was administered between >7 days before PTCA and 3 months after PTCA. The serum total cholesterol (TC) level and the formula low-density lipoprotein cholesterol (formula LDL-C) in group P decreased from 203.8 +/- 43.1 to 169.6 +/- 39.4 mg/dl and from 131.4 +/- 0.7 to 108.7 +/- 2.5 mg/dl, whereas in group C, the levels decreased only from 202.3 +/- 32.1 to 194.2 +/- 29.8 mg/dl and from 129.2 +/- 38.1 to 124.3 +/- 31.7 mg/dl, respectively. The restenosis rate was significantly lower in group P (19.7%; 13 of 66 vessels) than in group C (39.7%; 27 of 68 vessels; p < 0.05). In group P, the probucol blood concentration was significantly higher in the subjects without restenosis (31 +/- 9 microg/ml) than in those with restenosis (18 +/- 8 microg/ml; p < 0.01), but the serum TC and formula LDL-C levels were not significantly different between these two groups. In summary, long-term administration of probucol significantly reduces the incidence of restenosis after PTCA. it was suggested that the mechanism of this preventive effect was not reducing the serum TC or formula LDL-C levels, but rather an inhibitory action on smooth muscle cell proliferation.

Atherosclerotic disease in marked hyperalphalipoproteinemia. Combined reduction of cholesteryl ester transfer protein and hepatic triglyceride lipase

Hyperalphalipoproteinemia (HALP) has been regarded as a beneficial state accompanied by a longevity syndrome. However, we reported the cases of markedly hyperalphalipoproteinemic subjects with juvenile corneal opacification. The patients had reduced postheparin hepatic triglyceride lipase (HTGL) activities, and one of them has recently been identified to be homozygous for a missense mutation in exon 15 (D442: G) in the cholesteryl ester transfer protein (CETP) gene. In the current study, to elucidate the clinical significance of and atherogenicity in marked HALP, we determined the incidence of atherosclerotic cardiovascular disease (ACD) in patients with marked HALP and characterized the lipoprotein abnormalities in those who had ACD, focusing especially on CETP and HTGL. The subjects were 201 patients (111 males and 90 females) with marked HALP ( > or = 2.58 mmol/L [100 mg/dL]), 67% of whom were demonstrated to have the CETP gene mutations in the intron 14 splice donor site or in exon 15. Their mean age was 54 +/- 15 years. Plasma levels of total cholesterol, HDL cholesterol, and triglyceride in all subjects were 6.28 +/- 1.78, 3.15 +/- 0.90, and 1.08 +/- 0.53 mmol/L, respectively. Ten of the male patients (9.0%) and two of the female patients (2.2%) had apparent ACD such as myocardial infarction, angina pectoris, and peripheral vascular diseases. Ten patients with HALP who had ACD were identified to be heterozygotes for CETP deficiency. To further clarify the characteristics of marked HALP in patients with ACD, we compared the plasma lipids, lipoproteins, CETP, and HTGL activities between heterozygotes for CETP deficiency who were with and without ACD.

Natural antioxidants for the prevention of atherosclerosis

Hypercholesterolemia, cigarette smoking, hypertension, and obesity are known contributing risk factors for the development of atherosclerotic coronary artery disease (CAD). However, they account for only half of all cases of CAD, and the complete pathologic process underlying atherosclerosis remains unknown. Growing evidence suggests that oxidative modification of low-density lipoprotein (LDL) may be of particular importance in the pathogenesis. Oxidized LDL exhibits proatherogenic effects. Therefore, current research has focused on inhibiting the oxidation of LDL as a means of inhibiting the atherosclerotic process. One such approach is to enhance the endogenous antioxidant defense systems within the LDL particle with lipophilic antioxidants such as alpha-tocopherol and beta-carotene, or by supplementing the aqueous-phase antioxidant capacity with ascorbic acid. Observational data suggest a protective effect of antioxidant supplementation on the incidence of CAD; however, specific doses cannot be recommended since the data are inconclusive.

Frequency of exon 15 missense mutation (442D:G) in cholesteryl ester transfer protein gene in hyperalphalipoproteinemic Japanese subjects

Cholesteryl ester transfer protein (CETP) transfers cholesteryl ester from high density lipoprotein (HDL) to apo B-containing lipoproteins. The hyperalphalipoproteinemia caused by CETP deficiency is fairly common in Japan and one of the most common mutations in the CETP gene is the splicing defect of the intron 14, the allelic frequency of which has been shown to be 0.0049 in the Japanese general population. Recently, we have reported a missense mutation in exon 15 of the CETP gene (442D:G), showing a dominant effect on the CETP activity and HDL-cholesterol level. In the current study, we determined the frequency of this new mutation in Japanese hyperalphalipoproteinemic (HDL-cholesterol > or = 100 mg/dl) subjects. A rapid and easy screening method for this new mutation was developed using a polymerase chain reaction (PCR)-mediated site-directed mutagenesis. Among 117 Japanese hyperalphalipoproteinemic subjects (HDL-cholesterol; 116.7 +/- 16.5 mg/dl, mean +/- S.D.) without the intron 14 splice defect, three homozygotes (2.5%) and 34 heterozygotes (29.1%) were found to have the 442D:G mutation. The relative allelic frequency of this mutation was calculated to be 0.17. One of the homozygotes for the 442D:G mutation was the patient previously described by us as having hyperalphalipoproteinemia with corneal opacity and coronary heart disease. This was the first reported subject homozygous for the CETP deficiency who also demonstrated atherosclerotic symptoms. In homozygous subjects, CETP activity ranged from 37% to 62% of the normal value, which was consistent with the results obtained from the transient expression experiment previously reported; however, the specific activity of CETP was not as low as expected.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased plasma cholesteryl ester transfer protein in obese subjects. A possible mechanism for the reduction of serum HDL cholesterol levels in obesity

It is well known that obesity is frequently associated with low levels of serum high-density lipoprotein (HDL) cholesterol. However, the mechanism for this reduction has not been fully clarified. Cholesteryl ester transfer protein (CETP) transfers cholesteryl ester from HDL to apolipoprotein B-containing lipoproteins and plays an important role in regulating the concentration and composition of HDL. To elucidate the mechanism for the reduction of serum HDL cholesterol in obesity, we analyzed serum lipoproteins, CETP, and postheparin lipoprotein lipase (LPL) and hepatic triglyceride lipase (HTGL) activities in 30 obese subjects (17 women and 13 men, age 44 +/- 14 years, mean +/- SD). We also investigated the relationship between these variables, total adiposity, and indices of body fat distribution. The average body mass index of the obese subjects was 33.1 +/- 4.8 kg/m2 (range, 26.4 to 43.8 kg/m2). The obese subjects showed significantly lower serum HDL cholesterol levels than control subjects (1.04 +/- 0.28 versus 1.50 +/- 0.34 mmol/L, P < .01). In the obese subjects, both activities and protein mass of CETP and postheparin HTGL activities were significantly increased, whereas postheparin LPL activities were significantly decreased. CETP activities, independent of postheparin HTGL and LPL activities, were correlated negatively with HDL cholesterol (r = -.39, P < .05) and the cholesteryl ester to triglyceride ratio of HDL2 and HDL3 (r = -.36, P < .05; r = -.46, P < .05, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Drug control of reverse cholesterol transport

Reverse cholesterol transport identifies a series of metabolic events resulting in the transport of excess cholesterol from peripheral tissues to the liver. High-density lipoproteins (HDL) are the vehicle of cholesterol in this reverse transport, a function believed to explain the inverse correlation between plasma HDL levels and atherosclerosis. An attempt to stimulate, by the use of drugs, this transport process may hold promise in the prevention and treatment of arterial disease. Among the agents affecting lipoprotein metabolism, only probucol exerts significant effects on reverse cholesterol transport, by stimulating the activity of the cholesteryl ester transfer protein and, consequently, altering HDL subfraction composition/distribution. Another approach to the stimulation of reverse cholesterol transport consists of raising plasma HDL levels; studies in animals, either by exogenous supplementation or by endogenous overexpression, have shown a consistent benefit in terms of atherosclerosis regression and/or non-progression. Thus, it is time to consider different future treatments of atherosclerosis, combining the classical lipid-lowering treatments with innovative methods to promote cholesterol removal from the arterial wall.

Effects of probucol and pravastatin on plasma lipids, activities of postheparin lipoprotein lipase, and lecithin cholesterol acyltransferase and apo A-I containing lipoproteins with and without apo A-II in patients with moderate hypercholesterolemia

In this study, plasma HDL fractions were separated by ultracentrifugation and apo A-I containing lipoproteins (A-I Lp) were then isolated using anti-apo A-I immunoaffinity chromatography. The A-I Lp were further separated into two fractions with the use of anti-apo A-II immunoaffinity chromatography. One fraction, Lp A-I, contained apo A-I without apo A-II, while the other, Lp A-I/A-II, contained both apo A-I and apo A-II. These techniques were applied to investigate the changes in HDL apoprotein composition in hypercholesterolemic subjects treated with either probucol or pravastatin. Treatment with probucol (500 mg/day) or pravastatin (10 mg/day) reduced mean plasma total cholesterol concentrations by 24% (p < 0.01) and 16% (p < 0.05), respectively. Both drugs caused some reduction in lipoprotein lipase activity, but neither had any influence on the activity of hepatic triglyceride lipase or lecithin cholesterol acyltransferase. Their effects on HDL-cholesterol levels and apoprotein composition differed markedly. Probucol significantly decreased the HDL-cholesterol concentration, the plasma apo A-I/apo A-II ratio, and the number of large particles of diameter greater than 10.4 nm. When the ratios of Lp A-I and Lp A-I/A-II for the probucol-treated subjects were compared with those in the normolipidemic controls, and with the ratios before and after administration of probucol, a remarkable decrease in the level of Lp A-I was apparent. It is presumed that the decrease in HLD-cholesterol by prolonged probucol administration reflects the decrease of Lp A-I more than the decrease of Lp A-I/A-II.(ABSTRACT TRUNCATED AT 250 WORDS)

Frequency of intron 14 splicing defect of cholesteryl ester transfer protein gene in the Japanese general population--relation between the mutation and hyperalphalipoproteinemia

Cholesteryl ester transfer protein (CETP) deficiency, which has been found only in Japan, is characterized by marked hyperalphalipoproteinemia (HALP) and abnormalities of both low density and high density lipoproteins. We have reported that this deficiency is commonly associated with a G-->A mutation at the intron 14 splice donor site of the CETP gene (Yamashita et al., Biochem. Biophys. Res. Commun., 170 (1990) 1346-1351). In the current study, we determined the frequency of this mutation in Japanese subjects by using polymerase chain reaction. A single primer-template mismatch of one base pair from the CETP gene mutation permitted the introduction of a cleavage site for Nde I in mutant alleles but not in normal ones. Out of 171 patients with marked HALP whose serum HDL-cholesterol was more than 100 mg/dl, 6 (3.5%) subjects were homozygous and 48 (28.1%) were heterozygous for this mutation. Furthermore, in unrelated 512 healthy Japanese subjects, 5 (0.98%) were identified as heterozygotes. Relative allelic frequency of A at the intron 14 splice donor site was 0.0049 and the frequency of homozygous CETP deficiency was estimated to be approximately 1/42,000. These results demonstrate that this common mutation may be frequent in the Japanese population. Although HALP is very heterogenous, this mutation could be one of the major causes of marked HALP.

The effects of probucol on the levels, structure, composition and metabolism of plasma lipoprotein in rats

The effects of probucol administration on the levels, structure, composition and metabolism of plasma lipoproteins were determined in male rats. Probucol caused a 25% decrease of plasma cholesterol and a 20% decrease of plasma triacylglycerols. The effect was more pronounced on lipoproteins of density less than 1.063 g/ml (-35%) than on density greater than 1.063 g/ml (-21%). The density of LDL, HDL-1 and HDL-2 separated by ultracentrifugation on a zonal rotor was shifted towards a higher density. The content of cholesteryl esters increased in VLDL and LDL and decreased in HDL-1 and HDL-2. LDL, HDL-1 and HDL-2 were relatively enriched with proteins. The intravascular metabolism of 125I-labeled apo A-I was identical in control and probucol-treated rats with a circulating half-lifetime of 9.5 h. The circulating half-lifetime of LDL labeled biosynthetically with [3H]cholesteryl esters was also identical, 6.5 h. The circulating half-lifetime of [3H]cholesteryl esters in HDL-2, in contrast, was 9.5 h in control rats and 7.5 h in probucol-treated animals. Plasma cholesterol ester transfer activity was almost undetectable in either control or probucol treated animals. The investigation demonstrates a pronounced effect of probucol on plasma lipid and lipoprotein levels in rats, on cholesterol ester distribution between lipoproteins and on lipoprotein transport rates in the plasma. These effects may contribute to the anti-atherogenetic action of probucol.

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.

Polydisperse low-density lipoproteins in hyperalphalipoproteinemic chronic alcohol drinkers in association with marked reduction of cholesteryl ester transfer protein activity

Long-term heavy alcohol intake is well known to increase serum high-density lipoprotein (HDL) cholesterol concentrations. Epidemiologic studies have shown that the protective effect of alcohol intake against coronary heart disease (CHD) is observed in moderate alcohol drinkers, but not in heavy ones. To clarify whether heavy alcohol intake may cause abnormalities in lipoprotein metabolism, we analyzed the plasma lipoproteins in eight male chronic heavy alcohol drinkers with marked hyperalphalipoproteinemia. Although their serum HDL cholesterol levels were remarkably high, ranging from 2.67 to 3.58 mmol/L, three patients had CHD and corneal arcus was present in seven patients. Cholesteryl ester transfer protein (CETP) activity was reduced in all subjects (7.3% +/- 4.2%/10 microL/18 h in alcohol drinkers v 20.5% +/- 2.4%/10 microL/18 h in control; mean +/- SD, P < .001). The CETP mass levels were also markedly reduced in these subjects. The analysis of low-density lipoprotein (LDL) on nondenaturing polyacrylamide gradient gel electrophoresis revealed that four subjects with severely low CETP activity (< 25% of control) had polydisperse LDLs, similar to those observed in genetic CETP deficiency. The other four subjects with approximately half the normal CETP activity had homogeneous but smaller-sized LDLs, as compared with control subjects. Particle size of HDL was larger than that of normal control HDL in all subjects. After cessation of alcohol intake, plasma HDL cholesterol levels were decreased and LDLs became more homogeneous and normal in size, in parallel with elevation of CETP activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Low-density lipoproteins in hyperalphalipoproteinemic heavy alcohol drinkers have reduced affinity for the low-density lipoprotein receptor

Heavy alcohol intake causes a marked inhibition of cholesteryl ester transfer protein (CETP) activity resulting in cholesterol ester enrichment of HDL. In this study we have characterized LDL of 35 chronic heavy alcohol drinkers with hyperalphalipoproteinemia to clarify the effect of alcohol on the metabolism of LDL. Serum concentrations of LDL-cholesterol and apolipoprotein B were normal, while the chemical composition of LDL was characterized by depletion of cholesteryl ester and enrichment of triglyceride. The LDL particles of the drinkers were significantly smaller in size than those of controls and had reduced affinity for LDL receptors of normal human fibroblasts. After cessation of alcohol, these abnormal characteristics returned toward normal along with elevation of CETP activity. These results suggest that heavy alcohol intake alters the compositions and particle size of LDL, consequently reducing their affinity for LDL receptors. This may be attributed, at least in part, to the reduction of CETP activity.

Non-macrophage-related accumulation of cholesterol during probucol treatment in familial hypercholesterolemia: report of two cases

Two patients receiving long-term (3-4 years) treatment with probucol for familial hypercholesterolemia (FH) developed diffuse yellow lesions over the upper eyelids suggesting lipid storage in those tissues (diffuse lipid-storage lesions). Interestingly, each patient had shown a substantial reduction in their cholesterol levels together with a marked regression of their tendon xanthomas or typical xanthelasmas during treatment. To evaluate the role of probucol in this unusual finding we conducted histological and immunochemical evaluations of the lesions (removed surgically) and compared them with those of a non-probucol-treated subject with FH and typical audinal xanthelasma. In both probucol-treated patients the lesions were filled with foam cells and contained large amounts of cholesteryl ester. However, immunochemical analysis of the lesions of one patient using anti-monocyte monoclonal antibody (HAM56) demonstrated that they were not composed of macrophage-derived foam cells in contrast to those of the non-probucol-treated subject which stained clearly with anti-monocyte monoclonal antibody. In each case the foam cells did not react with muscle-actin-specific monoclonal antibody (HHF35). It appears that non-macrophage-related diffuse lipid-storage lesions may occur even during treatment with probucol despite the reduction in cholesterol levels and the regression of xanthomas, suggesting that probucol may alter the distribution of cholesterol from the macrophage to other cells.