Lipoprotein composition changes induced by fenofibrate in dysbetalipoproteinemia type III

Hypertriglyceridemia

Hypertriglyceridemia (HTG) is commonly encountered in lipid and cardiology clinics. Severe HTG warrants treatment because of the associated increased risk of acute pancreatitis. However, the need to treat, and the correct treatment approach for patients with mild to moderate HTG are issues for ongoing evaluation. In the past, it was felt that triglyceride does not directly contribute to development of atherosclerotic plaques. However, this view is evolving, especially for triglyceride-related fractions and variables measured in the non-fasting state. Our understanding of the etiology, genetics and classification of HTG states is also evolving. Previously, HTG was considered to be a dominant disorder associated with variation within a single gene. The old nomenclature includes the term "familial" in the names of several hyperlipoproteinemia (HLP) phenotypes that included HTG as part of their profile, including combined hyperlipidemia (HLP type 2B), dysbetalipoproteinemia (HLP type 3), simple HTG (HLP type 4) and mixed hyperlipidemia (HLP type 5). This old thinking has given way to the idea that genetic susceptibility to HTG results from cumulative effects of multiple genetic variants acting in concert. HTG most is often a "polygenic" or "multigenic" trait. However, a few rare autosomal recessive forms of severe HTG have been defined. Treatment depends on the overall clinical context, including severity of HTG, concomitant presence of other lipid disturbances, and the patient's global risk of cardiovascular disease. Therapeutic strategies include dietary counselling, lifestyle management, control of secondary factors, use of omega-3 preparations and selective use of pharmaceutical agents.

Disappearance of angina pectoris by lipid-lowering in type III hyperlipoproteinemia

Type III hyperlipoproteinemia is a rare familial disease characterized by marked elevations of serum cholesterol and triglyceride levels caused by an accumulation of remnant lipoproteins in apolipoprotein E2/E2 homozygotes. It is associated with an increased risk for premature atherosclerotic vascular disease. A 55-year-old woman was diagnosed as having type III hyperlipoproteinemia on the basis of skin lesions, serum lipid levels, lipid electrophoresis, and apolipoprotein E genotyping and stable angina pectoris on the basis of typical symptoms and treadmill exercise electrocardiographic results. After 1 year of combination therapy with atorvastatin and fenofibrate, skin xanthomata disappeared, leaving minimal remnants. In addition, there was no exertional chest pain, and treadmill exercise electrocardiographic results were negative. This finding was confirmed by coronary computed tomographic angiography. This case suggests that proper medical therapy can induce the regression of uncomplicated coronary lesions in type III hyperlipoproteinemia.

Peroxisome proliferator-activated receptor alpha target genes

The peroxisome proliferator-activated receptor alpha (PPARα) is a ligand-activated transcription factor involved in the regulation of a variety of processes, ranging from inflammation and immunity to nutrient metabolism and energy homeostasis. PPARα serves as a molecular target for hypolipidemic fibrates drugs which bind the receptor with high affinity. Furthermore, PPARα binds and is activated by numerous fatty acids and fatty acid-derived compounds. PPARα governs biological processes by altering the expression of a large number of target genes. Accordingly, the specific role of PPARα is directly related to the biological function of its target genes. Here, we present an overview of the involvement of PPARα in lipid metabolism and other pathways through a detailed analysis of the different known or putative PPARα target genes. The emphasis is on gene regulation by PPARα in liver although many of the results likely apply to other organs and tissues as well.

Polymorphisms in the peroxisome proliferator activated receptor alpha gene are associated with levels of apolipoprotein CIII and triglyceride in African-Americans but not Caucasians

BACKGROUND

We tested whether single nucleotide polymorphisms (SNPs) in the PPARalpha gene (PPARA) are associated with variations in levels of plasma apolipoprotein CIII (apoCIII) levels, as well as other lipids and lipoproteins, in African-Americans and Caucasians.

METHODS AND RESULTS

We initially identified an intronic SNP (rs4253728) in PPARA that was associated with plasma apoCIII level (p<0.05) in a subset of 435 individuals from the total study population (n=944; 335 African-Americans and 609 Caucasians). This SNP was then genotyped in a second subset of 476 individuals (total 911 subjects with available data), and a previously described PPARA coding SNP (L162V) which was shown to be in moderate linkage disequilibrium with the intronic SNP (r(2)=0.18) was genotyped in 928 subjects from the same study population. The minor allele frequencies for both SNPs were significantly lower in African-Americans compared with Caucasians (7.2% vs. 27.3% for rs4253728, 1.5% vs. 6.1% for L162V, both p<0.0001). African-Americans had significantly lower levels of TG and apoCIII compared with Caucasians after adjusting for age, sex, body mass index (BMI), waist circumference and other baseline characteristics. However, racial differences in TG levels were attenuated after adjusting for apoCIII levels. The minor alleles for both PPARA SNPs were associated with higher TG and apoCIII levels. Race modified the associations of L162V with TG (p for interaction=0.0056) and apoCIII (p for interaction=0.0011). Levels of both TG and apoCIII were lower in African-American but not Caucasian homozygotes for the major allele compared with carriers of the minor allele. Similar results were obtained for the intronic SNP, but the findings were no longer significant in a model that also contained L162V.

CONCLUSIONS

Two PPARA SNPs, L162V and rs4253728 (intronic), are less prevalent in African-Americans than in Caucasians and in African-Americans only are associated with higher apoCIII and TG levels.

Long-term effects of fenofibrate on VLDL and HDL subspecies in participants with type 2 diabetes mellitus

AIMS/HYPOTHESIS

Low HDL-cholesterol (HDL-C) is frequently accompanied by high triacylglycerol levels in diabetic dyslipidaemia, increasing the risk of CHD. In the Fenofibrate Intervention and Event Lowering in Diabetes (FIELD) study, fenofibrate treatment lowered triacylglycerol levels, but the initial 5% increase in HDL-C attenuated over 5 years. We explored the changes in VLDL and HDL subspecies during fenofibrate treatment in a statin-free FIELD cohort.

METHODS

We randomised 171 participants with type 2 diabetes mellitus, who had been recruited to the FIELD study in Helsinki, to micronised fenofibrate (200 mg/day) or placebo in double-blind study design. VLDL and HDL subspecies were separated by ultracentrifugation at baseline and at the second and fifth year. Apolipoprotein (apo)A-I and apoA-II were measured by immunoturbidometric methods and lipoprotein (Lp)A-I and LpAI-AII particles by differential immunoassay.

RESULTS

Fenofibrate reduced plasma triacylglycerol levels by 26%, resulting from a marked reduction in VLDL1 triacylglycerol (0.62 vs 0.29 mmol/l, p < 0.001). Fenofibrate caused an increase in LDL size (Delta 0.80 nm, p < 0.001). HDL-C was similar between the groups. HDL2-C was decreased by fenofibrate (-27.5% at 5th year, p < 0.001) and HDL3-C increased (13.0% at 5th year, p < 0.001). Fenofibrate had no effect on apoA-I, whereas apoA-II increased. Thus, LpA-I decreased while LpAI-AII increased. Activities of cholesteryl ester transfer protein, phospholipids transfer protein and lecithin:cholesterylacyl transferase were unchanged by fenofibrate. High homocysteine levels were associated with a slight decrease in HDL-C and apoA-I.

CONCLUSIONS/INTERPRETATION

Fenofibrate markedly reduced large VLDL particles and produced a clear shift in HDL subspecies towards smaller particles. The HDL3-C increase in conjunction with unchanged apoA-I [corrected] levels is a dilemma with regard to cardiovascular disease.

Effects of fenofibrate on apolipoprotein kinetics in patients with coexisting dysbetalipoproteinemia and heterozygous familial hypercholesterolemia

Dysbetalipoproteinemia (dysb) and familial hypercholesterolemia (FH) are two genetic disorders giving rise to severe disturbances of lipid homeostasis and premature atherosclerosis. The co-occurrence of both metabolic abnormalities is very rare and is estimated to affect 1 individual per 2,500,000 in the general population. However, the relative contribution of these two dyslipidemias to the combined lipoprotein phenotype is unknown. The two objectives of this study were (1) to compare the in vivo kinetics of triglyceride-rich lipoprotein (TRL) apolipoprotein (apo) B48, VLDL, IDL and LDL apo B100 as well as plasma apo A-l labelled with a stable isotope (l-(5,5,5-D3) leucine) in two subjects presenting both heterozygous FH and dysbetalipoproteinemia (FH+/dysb+), in six FH heterozygotes and in five normolipidemic controls, and (2) to examine the impact of a 6-week treatment with micronized fenofibrate 200 mg/d on apolipoprotein kinetics in FH+/dysb+. As compared with FH heterozygotes and controls, the two FH+/dysb+ subjects showed elevated TRL apo B48 and VLDL, IDL apo B100 pool sizes (PS) mainly due to lower fractional catabolic rates (FCR). Moreover, as compared with FH heterozygotes, FH+/dysb+ subjects presented lower LDL apo B100 PS due to a higher FCR. Pool size, FCR and production rate (PR) of apo A-l were higher in FH+/dysb+ subjects than in FH heterozygotes. In FH+/dysb+ subjects, fenofibrate treatment was associated with a decreased TRL apo B48 PS (-52 and -61%), VLDL apo B100 (-61 and -63%) and IDL apo B100 (-37 and -16%) and an increased FCR of TRL apo B48 (10 and 67%), VLDL apo B100 (123 and 57%) and IDL apo B100 (29 and 10%). Fenofibrate also increased LDL apo B100 PS (3 and 57%) due to an increase in PR (80 and 26%) but had divergent effects on LDL apo B100 FCR. These results indicate that the coexistence of dysbetalipoproteinemia and heterozygous FH results in a mixed lipoprotein phenotype that is intermediate between the two pure phenotypes and that fenofibrate treatment partially reverses lipoprotein abnormalities, mostly through changes in PR and FCR of apo B48- and B100-containing lipoproteins.

Profiling of hepatic gene expression in rats treated with fibric acid analogs

Peroxisome proliferator-activated receptors (PPARs) are a group of nuclear receptors whose ligands include fatty acids, eicosanoids and the fibrate class of drugs. In humans, fibrates are used to treat dyslipidemias. In rodents, fibrates cause peroxisome proliferation, a change that might explain the observed hepatomegaly. In this study, rats were treated with multiple dose levels of six fibric acid analogs (including fenofibrate) for up to two weeks. Pathological analysis identified hepatocellular hypertrophy as the only sign of hepatotoxicity, and only one compound at the highest dose caused any significant increase in serum ALT or AST activity. RNA profiling revealed that the expression of 1288 genes was related to dose or length of treatment and correlated with hepatocellular hypertrophy. This gene list included expression changes that were consistent with increased mitochondrial and peroxisomal beta-oxidation, increased fatty acid transport, increased hepatic uptake of LDL-cholesterol, decreased hepatic uptake of glucose, decreased gluconeogenesis and decreased glycolysis. These changes are likely linked to many of the clinical benefits of fibrate drugs, including decreased serum triglycerides, decreased serum LDL-cholesterol and increased serum HDL-cholesterol. In light of the fact that all six compounds stimulated similar or identical changes in the expression of this set of 1288 genes, these results indicate that hepatomegaly is due to PPARalpha activation, although signaling through other receptors (e.g. PPARgamma, RXR) or through non-receptor pathways cannot be excluded.

Long term efficacy and safety of atorvastatin in the treatment of severe type III and combined dyslipidaemia

BACKGROUND

Fibric acid derivatives and HMG-CoA reductase inhibitors are effective in combination for treating patients with familial dysbetalipoproteinaemia and severe combined dyslipidaemia, but combination therapy affects compliance and increases the risk of side effects.

AIM

To evaluate the efficacy and safety of monotherapy with atorvastatin, an HMG-CoA reductase inhibitor with superior efficacy in lowering low density lipoprotein cholesterol and triglyceride concentrations, in patients with dysbetalipoproteinaemia and severe combined dyslipidaemia.

METHODS

Atorvastatin was tested as single drug treatment in 36 patients with familial dysbetalipoproteinaemia and 23 patients with severe combined dyslipidaemia.

RESULTS

After 40 weeks of 40 mg atorvastatin treatment decreases in total cholesterol, triglycerides, and apolipoprotein B of 40%, 43%, and 41%, respectively, were observed in the combined dyslipidaemia group, and of 46%, 40%, and 43% in the dysbetalipoproteinaemic patients. Target concentrations of total cholesterol (< 5 mmol/l) were reached by 63% of the patients, and target concentrations of triglycerides (< 3.0 mmol/l) by 66%. Treatment with atorvastatin was well tolerated and no serious side effects were reported.

CONCLUSIONS

Atorvastatin is very effective as monotherapy in the treatment of familial dysbetalipoproteinaemia and severe combined dyslipidaemia.

Peroxisome proliferator-activated receptors (PPARs): novel therapeutic targets in renal disease

Peroxisome proliferator-activated receptors (PPARs): Novel therapeutic targets in renal disease. Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptor superfamily of ligand-dependent transcription factors. PPARs play an important role in the general transcriptional control of numerous cellular processes, including lipid metabolism, glucose homeostasis, cell cycle progression, cell differentiation, inflammation and extracellular matrix remodeling. Three PPAR isoforms, designated PPARalpha, PPARbeta and PPARgamma, have been cloned and are differentially expressed in several tissues including the kidney. PPARalpha primary regulates lipid metabolism and modulates inflammation. PPARalpha is the molecular target of the hypolipidemic fibrates including bezafibrate and clofibrate. PPARbeta participates in embryonic development, implantation and bone formation. PPARgamma is a key factor in adipogenesis and also plays an important role in insulin sensitivity, cell cycle regulation and cell differentiation. Antidiabetic thiazolidinediones (TZDs) such as troglitazone and rosiglitazone are specific ligands of PPARgamma, and this interaction is responsible for the insulin-sensitizing and hypoglycemic effect of these drugs. The kidney has been shown to differentially express all PPAR isoforms. PPARalpha is predominantly expressed in proximal tubules and medullary thick ascending limbs, while PPARgamma is expressed in medullary collecting ducts, pelvic urothelium and glomerular mesangial cells. PPARbeta is ubiquitously expressed at low levels in all segments of nephron. Accumulating data has begun to emerge suggesting physiological and pathophysiological roles of PPARs in several tissues including the kidney. The availability of PPAR-selective agonists and antagonists may provide a new approach to modulate the renal response to diseases including glomerulonephritis, glomerulosclerosis and diabetic nephropathy.

Polymorphisms in the insulin response element of APOC-III gene promoter influence the correlation between insulin and triglycerides or triglyceride-rich lipoproteins in humans

OBJECTIVE

To assess whether the -455 and -482 mutations in APOC-III gene insulin response element affect the relationships between plasma insulin and triglyceride-rich lipoprotein levels.

DESIGN

Population-based studies.

SUBJECTS

The population sample was composed of 983 subjects (485 men and 498 women), aged between 35 and 65 y, randomly sampled from the electoral rolls in Northern France and stratified on gender and 10 y age groups.

MEASUREMENTS

Plasma triglyceride, apolipoprotein C-III, apoB, LpC-III:B and LpE:B lipoprotein particles and insulin levels were measured. Two polymorphisms in APOC-III gene insulin response element (T-->C at -455 and/or C-->T at -482) were determined.

RESULTS

Plasma insulin was positively correlated to triglyceride levels (P<0.0001), apo C-III (P<0.003), LpC-III:B (P<0.0001), apoB (P<0.0001) and LpE:B (P<0.0001). This association differed significantly according to APOC-III insulin response element polymorphisms. The relationship between insulin and LpC-III:B (P<0.02) or apoB (P<0.02) was greater in women bearing the C allele of -455 than the T allele. Similarly, the relationship between insulin and LpC-III:B (P<0.02) or LpE:B (P<0.05) was greater in women bearing the T allele of -482 than the C allele. There was no evidence for any effect in men.

CONCLUSION

These results suggest that the relationship between plasma insulin and triglyceride-rich lipoprotein levels is partly influenced by polymorphisms in APOC-III insulin response element.

The role of fibric acid derivatives in the secondary prevention of coronary heart disease

Fibric acid derivatives effectively lower triglycerides and raise high-density lipoprotein (HDL) cholesterol, but their effect on low-density lipoprotein (LDL) cholesterol is weakly beneficial (small decreases) to adverse (small increases) and varies according to the triglyceride level. Early primary prevention studies of atherosclerosis using the fibric acid derivative clofibrate showed only modest effects on atherosclerosis and an alarming increase in mortality in the intervention group. Although the Helsinki Heart Study later demonstrated that gemfibrozil decreased cardiac endpoints in primary prevention without increasing total mortality, the efficacy of fibric acid derivatives in both primary and secondary prevention of atherosclerosis has remained widely in doubt. Nevertheless, many patients with atherosclerosis have normal or even low LDL cholesterol, but elevated triglyceride, and low HDL cholesterol; furthermore, even aggressive LDL cholesterol lowering with HMG Co-A (3-hydroxy 3-methylglutaryl coenzyme A) reductase inhibitors (statins) fails to prevent the majority of atherosclerotic events. These findings have kindled increased interest in the use of fibric acid derivatives in atherosclerosis prevention, especially through treatment of non-LDL dyslipidemias. Recent studies with angiographic and clinical end-points have now provided evidence for a beneficial effect of at least some drugs in this class in the secondary prevention of atherosclerosis.

Coexisting dysbetalipoproteinemia and familial hypercholesterolemia. Clinical and laboratory observations

Type III dysbetalipoproteinemia and familial hypercholesterolemia (FH) are two metabolic disorders giving rise to severe disturbances of lipid homeostasis and premature atherosclerosis. Both metabolic abnormalities have a genetic basis and co-occurrence in the same patient has seldom been described. Because of the unique structure of the French Canadian population, there was an opportunity to observe patients with both dysbetalipoproteinemia (E2/2 homozygotes) and FH (N=14) and to compare their clinical data with that of patients with type III (N=75), patients with FH (N0.7 and the presence of beta-VLDL on electrophoresis. Presence of a low density lipoprotein receptor, LDL-R, mutation should be suspected in a type III patient with a LDL-C level above 3.0 mmol/l and a family history of premature CAD. In the group of patients studied, the coexistence of dysbetalipoproteinemia and heterozygous FH does not appear to increase the prevalence of cardiovascular complications above that observed among control type III or control E3/3-FH patients. Thus, the presence of two epsilon2 alleles in these patients affects the expression of the abnormal LDL-R allele and the resulting phenotype substantiates the non additive effects of alleles at these two loci (epistasis).

Micronized fenofibrate: a new fibric acid hypolipidemic agent

OBJECTIVE

To review the efficacy and safety of fenofibrate in the management of hyperlipidemias.

DATA SOURCES

A MEDLINE search (1974-October 1998), Current Contents search, additional references from article bibliographies, and the package insert from the manufacturer were used to identify data for evaluation. Studies evaluating fenofibrate (peer-reviewed publications, package insert data) were considered for inclusion. Abstracts and data on file with the manufacturer were not considered for inclusion.

STUDY SELECTION

English-language literature was reviewed to evaluate the pharmacology, pharmacokinetics, clinical use, and tolerability of fenofibrate. Data from animals and in vitro systems were included only when necessary to explain the drug's pharmacology.

DATA SYNTHESIS

Micronized fenofibrate is a fibric acid derivative approved by the Food and Drug Administration (FDA) in February 1998 for the treatment of types IV and V hyperlipidemia. Data from the peer-reviewed literature also support the use of fenofibrate in types IIa, IIb, and III hyperlipidemias. Micronized fenofibrate 67-201 mg/d is useful as monotherapy or as an adjunct to other hypolipidemics and dietary therapy. In placebo-controlled clinical trials, regular formulation fenofibrate 300-400 mg/d lowered serum triglyceride (TG) concentrations by 24-55%, total cholesterol by 9-25%, low-density lipoprotein cholesterol (LDL-C) concentrations by 6-35%, and raised high-density lipoprotein cholesterol (HDL-C) concentrations by 8-38%. Few comparative data exist regarding fenofibrate versus clofibrate and gemfibrozil. In noncomparative and comparative clinical trials, fenofibrate appeared to be well tolerated. The most common causally related adverse events were digestive, musculoskeletal, and dermatologic in nature. Concurrent use of fenofibrate and a hydroxymethylglutaryl-coenzyme A inhibitor may increase the risk of myopathy and/or rhabdomyolysis, although recent data suggest that concurrent use of fenofibrate with low-dose simvastatin or pravastatin is safe. Fenofibrate may enhance the effect of oral anticoagulants.

CONCLUSIONS

Fenofibrate reduces serum TG, total cholesterol, and LDL-C, and raises HDL-C to clinically relevant degrees. Its spectrum of activity appears to exceed that recommended for types IV and V hyperlipidemia to encompass types IIa, IIb, and III hyperlipidemias as well. To this extent, it may be considered a broader-spectrum fibrate than is indicated by its FDA approval. Adverse effects of fenofibrate appear to be similar to those of other fibrates and require routine monitoring (clinical, liver function). Long-term safety data are readily available from drug registries in many countries where the product has been available for nearly two decades. Cost-effectiveness studies comparing fenofibrate with other hypolipidemics demonstrate benefits of fenofibrate over simvastatin in types IIa and IIb hyperlipidemia. The need for dosage titration of the micronized preparation from 67 mg/d upward to a final dose of 200 mg/d is also not supported by peer-reviewed literature (except in the case of renal impairment). Although preliminary data on plaque regression are encouraging, published clinical studies evaluating the impact of fenofibrate on cardiovascular morbidity and mortality are awaited. Micronized fenofibrate is worthy of formulary inclusion.

High-density lipoprotein subclasses and apolipoprotein A-I

Epidemiological and clinical studies showing an association between decreased concentrations of high-density lipoprotein (HDL) cholesterol and increased risk of premature coronary artery disease have generated interest in the mechanism through which HDL prevents atherosclerosis. Recognition of the importance of apolipoproteins (apo(s)) has led to the separation of HDL into subpopulations according to their apolipoprotein composition. It is now recognised that HDL comprises at least two types of apo A-I-containing lipoproteins: LpA-I:A-II containing both apo A-I and apo A-II and LpA-I containing apo A-I but not apo A-II. A majority of studies support the fact that LpA-I is more effective than LpA-I:A-II in promoting cellular cholesterol efflux, the first step in reverse cholesterol transport. Studies in transgenic animals have revealed that the gene transfer of human apo A-I in mice and rabbits increases plasma apo A-I and HDL cholesterol levels and particularly apo A-I-rich HDL particle concentrations, leading to inhibition of the development of dietary or genetically induced atherosclerosis. On the other hand, gene transfer of apo A-II in mice gives conflicting results. The conclusions of some experiments indicate either an atherogenic, or a poorly anti-atherogenic, or even a strongly anti-atherogenic role for apo A-II and for apo A-II-rich HDL lipoproteins. Although these experimental results have been obtained in animals, they confirm previous studies obtained in human clinical studies, indicating that apo A-I-rich HDL (tested as LpA-I in clinical studies) are generally strong plasma markers of atherosclerosis protection while the clinical significance of apo A-I + apo A-II HDL (tested as LpA-I:A-II in clinical studies) is more controversial. The introduction of immunological methods to measure LpA-I and LpA-I:A-II levels in blood make large-scale studies feasible to confirm the clinical significance of these HDL particles.

Sialic acid-containing components of lipoproteins influence lipoprotein-proteoglycan interactions

Sialic acid is a negatively charged sugar associated with the protein and lipid portions of lipoproteins. Sialic acid has been hypothesised to play an anti-atherogenic role in lipoprotein metabolism through the electrostatic inhibition of lipoprotein interactions with chondroitin-6-sulphate-rich arterial proteoglycans (APG). We conducted a series of studies using native and modified lipoproteins (VLDL1 Sf 60-400, VLDL2 Sf 20-60, IDL1 Sf 16-20, IDL2 Sf 12-16, LDL(A) Sf 8-12, and LDL(B) Sf0-8) that vary in their sialic acid content to examine the relationship between lipoprotein sialic acid content and its interaction with APG. Lipoprotein sialic acid was greatest in VLDL1 and decreased progressively with particle density until the IDL2 fraction (VLDL1 > VLDL2 > IDL1 > IDL2 = LDL(A) = LDL(B)). The pattern of reactivity of each fraction with APG was different from the pattern observed for lipoprotein sialic acid content (IDL2 > LDL(A) > LDL(B) > IDL1 > VLDL2 > VLDL1). Levels of sialic acid were lower in subjects with CHD as compared to control subjects but the presence of CHD had no effect on lipoprotein-APG complex formation when sex and plasma triglyceride levels were taken into account. There was also no significant relationship between the lipoprotein sialic acid content and the reactivity with APG within each lipoprotein fraction. Treatment of hypertriglyceridaemic subjects with ciprofibrate decreased lipoprotein-APG complex formation in all lipoprotein fractions. This was associated with a decrease in the total sialic acid content of apo B100-containing lipoproteins suggesting that the total sialic acid content of apo B100-containing lipoproteins has no influence on lipoprotein-APG complex formation. We next conducted in vitro experiments to manipulate LDL sialic acid content. Enzymatic removal of sialic acid from LDL with neuraminidase resulted in an increase in LDL-APG complex formation. This was accompanied by an increase in the exposure of free amino groups on LDL possibly due to disruption of interactions between free amino groups and sialic acid-containing components on LDL. Increasing LDL sialic acid content through incubation with ganglioside resulted in a decrease in lipoprotein-APG complex formation without any changes in the exposure of free amino groups on LDL. We conclude that total sialic acid content of lipoproteins is not a major determinant of their binding to APG. However, specific sialic acid-containing components on lipoproteins can affect their interaction with APG.

Developmental and pharmacological regulation of apolipoprotein C-II gene expression. Comparison with apo C-I and apo C-III gene regulation

Increased plasma triglyceride concentrations are often observed in metabolic disorders predisposing to coronary heart disease. Among the major determinants of plasma triglyceride metabolism are the apolipoproteins (apos) of the C class, C-I, C-II, and C-III. Whereas physiological concentrations of apo C-II are required for lipolysis of triglycerides by lipoprotein lipase (LPL), overexpression of all 3 C apolipoproteins leads to hypertriglyceridemia. In the present study, we investigated apo C-II gene regulation under conditions associated with profound changes in plasma triglyceride metabolism, ie, during postnatal development and after treatment with the triglyceride-lowering fibrate drugs, and compared its expression to that of apo C-I and apo C-III. Whereas the expression of both apo C-I and apo C-III is low in fetal liver, increases gradually after birth, and attains maximal levels after weaning, apo C-II gene expression is already detectable in the fetal liver, increases rapidly immediately after birth, and remains elevated throughout suckling. Thus, the increased ingestion of lipids during suckling is met by an earlier induction of apo C-II, the obligatory activator for LPL, compared with apo C-III and apo C-I, which antagonize triglyceride catabolism. Treatment of rats with fibrates decreased apo C-II gene expression in the liver, but not in the intestine, whereas apo C-I gene expression did not change. The decrease of liver apo C-II mRNA levels after fenofibrate occurred in a time- and dose-dependent manner and was reversible but appeared less pronounced than the decrease of apo C-III mRNA. Apo C-II mRNA levels were not affected after treatment with BRL49653, a peroxisome proliferator-activated receptor (PPAR)gamma-specific ligand, suggesting that fibrates act on apo C-II expression via PPARalpha. Addition of fenofibric acid to primary rat and human hepatocytes resulted in a decrease of apo C-II expression. In conclusion, fibrates decrease gene expression of apo C-II and apo C-III, but not apo C-I, in rat and human hepatocytes. This decrease of apo C-II and apo C-III gene expression, together with a lowered apo C-III to apo C-II ratio, should result in an improved clearance of triglyceride-rich remnant lipoproteins from plasma, without hampering triglyceride lipolysis by LPL.

Mechanism of action of fibrates on lipid and lipoprotein metabolism

Treatment with fibrates, a widely used class of lipid-modifying agents, results in a substantial decrease in plasma triglycerides and is usually associated with a moderate decrease in LDL cholesterol and an increase in HDL cholesterol concentrations. Recent investigations indicate that the effects of fibrates are mediated, at least in part, through alterations in transcription of genes encoding for proteins that control lipoprotein metabolism. Fibrates activate specific transcription factors belonging to the nuclear hormone receptor superfamily, termed peroxisome proliferator-activated receptors (PPARs). The PPAR-alpha form mediates fibrate action on HDL cholesterol levels via transcriptional induction of synthesis of the major HDL apolipoproteins, apoA-I and apoA-II. Fibrates lower hepatic apoC-III production and increase lipoprotein lipase--mediated lipolysis via PPAR. Fibrates stimulate cellular fatty acid uptake, conversion to acyl-CoA derivatives, and catabolism by the beta-oxidation pathways, which, combined with a reduction in fatty acid and triglyceride synthesis, results in a decrease in VLDL production. In summary, both enhanced catabolism of triglyceride-rich particles and reduced secretion of VLDL underlie the hypotriglyceridemic effect of fibrates, whereas their effect on HDL metabolism is associated with changes in HDL apolipoprotein expression.

The nuclear receptors peroxisome proliferator-activated receptor alpha and Rev-erbalpha mediate the species-specific regulation of apolipoprotein A-I expression by fibrates

Fibrates are widely used hypolipidemic drugs which activate the nuclear peroxisome proliferator-activated receptor (PPAR) alpha and thereby alter the transcription of genes controlling lipoprotein metabolism. Fibrates influence plasma high density lipoprotein and its major protein, apolipoprotein (apo) A-I, in an opposite manner in man (increase) versus rodents (decrease). In the present study we studied the molecular mechanisms of this species-specific regulation of apoA-I expression by fibrates. In primary rat and human hepatocytes fenofibric acid, respectively, decreased and increased apoA-I mRNA levels. The absence of induction of rat apoA-I gene expression by fibrates is due to 3 nucleotide differences between the rat and the human apoA-I promoter A site, rendering a positive PPAR-response element in the human apoA-I promoter nonfunctional in rats. In contrast, rat, but not human, apoA-I transcription is repressed by the nuclear receptor Rev-erbalpha, which binds to a negative response element adjacent to the TATA box of the rat apoA-I promoter. In rats fibrates increase liver Rev-erbalpha mRNA levels >10-fold. In conclusion, the opposite regulation of rat and human apoA-I gene expression by fibrates is linked to differences in cis-elements in their respective promoters leading to repression by Rev-erbalpha of rat apoA-I and activation by PPARalpha of human apoA-I. Finally, Rev-erbalpha is identified as a novel fibrate target gene, suggesting a role for this nuclear receptor in lipid and lipoprotein metabolism.

Regulation of apo A-I gene expression by fibrates

Fibrate hypolipidemic drugs regulate the concentrations of plasma high density lipoproteins (HDL), which are inversely correlated to the development of atherosclerosis. In rodents fibrates lower HDL levels due to a decreased transcription of its major apolipoprotein, apo A-I, in liver, whereas in man fibrates increase plasma levels of HDL via an induction of human apo A-I gene expression. The fibrate effect on human apo A-I is mediated by the transcription factor PPAR-alpha (peroxisome proliferator-activated receptor) which interacts with a positive PPAR-response element (PPRE) in its promoter. The lack of induction of apo A-I expression by fibrates in rodents is due to three nucleotide differences in the rodent apo A-I promoter eliminating binding of PPAR and activation by fibrates. These in vitro observations were extended in vivo in transgenic mice and rabbits overexpressing the human apo A-I gene under control of its homologous promoter containing the human apo A-I PPRE. Whereas the endogenous mouse apo A-I gene is repressed, treatment with fibrates results in the transcriptional induction of human apo A-I gene expression. This induction is accompanied by increased plasma concentrations of human apo A-I and HDL. To determine whether fibrates increase HDL and apo A-I concentrations without inducing hepatomegaly and peroxisome proliferation, their effects were tested in rabbits, an animal model more resistant to peroxisome proliferation. In contrast to normal rabbits, in which plasma lipoprotein levels remain unchanged, fibrate treatment of transgenic apo A-I rabbits results in increased plasma HDL and human apo A-I concentrations due to the induction of human apo A-I gene expression in liver, without affecting liver weight or peroxisomal acyl-CoA oxidase activity. In conclusion; (1) fibrates regulate plasma HDL concentrations, at least partly, due to their effects on apo A-I gene transcription; (2) the opposite effects of fibrates on apo A-I gene expression in rodents and humans are due to sequence differences in regulatory elements in their respective genes; (3) solely the presence of the human apo A-I gene is sufficient to confer fibrate-responsiveness on HDL; and (4) the beneficial effects of fibrates on lipoprotein metabolism are independent of any undesirable proliferation of peroxisomes.

Effects of n-3 fatty acids and fenofibrate on lipid and hemorrheological parameters in familial dysbetalipoproteinemia and familial hypertriglyceridemia

There is increasing evidence that hemorrheological abnormalities are associated with an enhanced risk of atherosclerosis. The n-3 fatty acids (n-3-FA) have been shown to have beneficial effects on atherosclerosis in patients with dyslipoproteinemias. We studied 23 patients with elevated plasma triglycerides to evaluate the influence of fish oil and fenofibrate therapy on hemorrheological parameters (15 patients with familial hypertriglyceridemia [FHTG] and eight with familial dysbetalipoproteinemia [FDL]). The patients (one woman and 22 men aged 45.7 +/- 2.0 years) were treated with increasing doses of n-3-FA (1.8 to 3.6 g/d: 0.9 to 1.8 g eicosapentaenoic acid and 0.6 to 1.2 g docosahexaenoic acid) for 8 weeks. Lipid parameters, whole-blood viscosity at different shear rates, plasma viscosity, fibrinogen concentration, and red blood cell aggregation (RCA) were measured at baseline and at weeks 2, 4, 8 (end of n-3-FA therapy), and 12. Compliance was ensured by measuring plasma concentrations of eicosapentaenoic acid and docosahexaenoic acid. After 12 weeks, patients began treatment with fenofibrate (250 mg daily); investigations were performed again at week 20. Total triglycerides (from 6.90 +/- 1.70 to 3.61 +/- 0.78 mmol/L in FDL and 7.44 +/- 1.50 to 4.15 +/- 0.55 in FHTG), very-low-density lipoprotein (VLDL) triglycerides, and VLDL cholesterol were significantly decreased with n-3-FA therapy in both groups (P < .05). In FHTG, low-density lipoprotein (LDL) cholesterol increased significantly (from 2.75 +/- 0.28 to 3.97 +/- 0.35 mmol/L, P < .01); in FDL, total cholesterol decreased (from 9.76 +/- 1.32 to 7.34 +/- 1.07 mmol/L, P < .05). No significant changes were observed in hemorrheological parameters, except for reduced RCA with 3.6 g n-3-FA in FHTG. However, with fenofibrate therapy, in addition to comparable lipoprotein changes seen with fish oil, fibrinogen levels and plasma and blood viscosity decreased in patients with FDL. We conclude that n-3-FA and fenofibrate have comparable effects on lipid parameters in patients with FDL and FHTG. Because of additional beneficial effects on hemorrheological parameters, fenofibrate may be preferred for the treatment of FDL.

The peroxisome proliferator activated receptors (PPARS) and their effects on lipid metabolism and adipocyte differentiation

The three types of peroxisome proliferator activated receptor (PPAR), alpha, beta (or delta), and gamma, each with a specific tissue distribution, compose a subfamily of the nuclear hormone receptor gene family. Although peroxisome proliferators, including fibrates and fatty acids, activate the transcriptional activity of these receptors, only prostaglandin J2 derivatives have been identified as natural ligands of the PPAR gamma subtype, which also binds thiazolidinedione antidiabetic agents with high affinity. Activated PPARs heterodimerize with RXR and alter the transcription of target genes after binding to specific response elements or PPREs, consisting of a direct repeat of the nuclear receptor hexameric DNA core recognition motif spaced by one nucleotide. The different PPARs can be considered key messengers responsible for the translation of nutritional, pharmacological and metabolic stimuli into changes in the expression of genes, more specifically those genes involved in lipid metabolism. PPAR alpha is involved in stimulating beta-oxidation of fatty acids. In rodents, a PPAR alpha-mediated change in the expression of genes involved in fatty acid metabolism lies at the basis of the phenomenon of peroxisome proliferation, a pleiotropic cellular response, mainly limited to liver and kidney and which can lead to hepatocarcinogenesis. In addition to their role in peroxisome proliferation in rodents, PPAR is also involved in the control of HDL cholesterol levels by fibrates and fatty acids in rodents and humans. This effect is, at least partially, based on a PPAR-mediated transcriptional regulation of the major HDL apolipoproteins, apo A-I and apo A-II. The hypotriglyceridemic action of fibrates and fatty acids also involves PPARs and can be summarized as follows: (1) an increased lipolysis and clearance of remnant particles, due to changes in LPL and apo C-III levels, (2) a stimulation of cellular fatty acid uptake and their conversion to acyl-CoA derivatives by the induction of FAT, FATP and ACS activity, (3) an induction of fatty acid beta-oxidation pathways, (4) a reduction in fatty acid and triglyceride synthesis, and finally (5) a decrease in VLDL production. Hence, both enhanced catabolism of triglyceride-rich particles as well as reduced secretion of VLDL particles are mechanisms that contribute to the hypolipidemic effect of fibrates and FFAs. Whereas for PPAR beta no function so far has been identified, PPAR gamma triggers adipocyte differentiation by inducing the expression of several genes critical for adipogenesis.

Fibrates increase human apolipoprotein A-II expression through activation of the peroxisome proliferator-activated receptor

In view of the evidence linking plasma high density lipoprotein (HDL)-cholesterol levels to a protective effect against coronary artery disease and the widespread use of fibrates in the treatment of hyperlipidemia, the goal of this study was to analyze the influence of fibrates on the expression of apolipoprotein (apo) A-II, a major protein constituent of HDL. Administration of fenofibrate (300 mg/d) to 16 patients with coronary artery disease resulted in a marked increase in plasma apo A-II concentrations (0.34 +/- 0.11 to 0.45 +/- 0.17 grams/liter; P < 0.01). This increase in plasma apo A-II was due to a direct effect on hepatic apo A-II production, since fenofibric acid induced apo A-II mRNA levels to 450 and 250% of control levels in primary cultures of human hepatocytes and in human hepatoblastoma HepG2 cells respectively. The induction in apo A-II mRNA levels was followed by an increase in apo A-II secretion in both cell culture systems. Transient transfection experiments of a reporter construct driven by the human apo A-II gene promoter indicated that fenofibrate induced apo A-II gene expression at the transcriptional level. Furthermore, several other peroxisome proliferators, such as the fibrate, Wy-14643, and the fatty acid, eicosatetraynoic acid (ETYA), also induced apo A-II gene transcription. Unilateral deletions and site-directed mutagenesis identified a sequence element located in the J-site of the apo A-II promoter mediating the responsiveness to fibrates and fatty acids. This element contains two imperfect half sites spaced by 1 oligonucleotide similar to a peroxisome proliferator responsive element (PPRE). Cotransfection assays showed that the peroxisome proliferator activated receptor (PPAR) transactivates the apo A-II promoter through this AII-PPRE. Gel retardation assays demonstrated that PPAR binds to the AII-PPRE with an affinity comparable to its binding affinity to the acyl coA oxidase (ACO)-PPRE. In conclusion, in humans fibrates increase plasma apo A-II concentrations by inducing hepatic apo A-II production. Apo A-II expression is regulated at the transcriptional level by fibrates and fatty acids via the interaction of PPAR with the AII-PPRE, thereby demonstrating the pivotal role of PPAR in controlling human lipoprotein metabolism.

The effects of fibrates on lipoprotein and hemostatic coronary risk factors

The effects of fibrates on lipoprotein profiles and lipoprotein physiology, as well as on selected coagulation and fibrinolytic factors are reviewed. It is concluded that the action of fibrates on these systems is such as to render the fibrates beneficial in atherosclerosis prevention.

Impact of apolipoprotein E polymorphism on lipoproteins and risk of myocardial infarction. The ECTIM Study

Human apolipoprotein (apo) E, a polymorphic protein with three common alleles, epsilon 2, epsilon 3, and epsilon 4, plays an important role in lipoprotein metabolism. This article describes the association of this polymorphism with lipids, apolipoproteins, and lipoproteins with a particular regard to lipoprotein particles, as defined by their apolipoprotein content, as well as the risk of myocardial infarction in a multicenter population-based case-control study (ECTIM study). In the ECTIM study, 574 male patients aged 25 to 64 were examined 3 to 9 months after myocardial infarction in four regions participating in the World Health Organization MONICA project: Belfast (Northern Ireland) and Lille, Strasbourg, and Toulouse (France). Control subjects (n = 722) were randomly selected from the regional populations. The distribution of apoE phenotypes was significantly different across the four control samples (P = .04), with a higher frequency of the epsilon 4 allele in Belfast (14.3%) than in Toulouse (8.2%). The association of apoE polymorphism with biological measurements was studied in the control groups (n = 640) after men with coronary heart disease or those taking hypolipidemic drugs were omitted, with the apoE3/3 phenotype as a reference after adjustment for concomitant factors. Individuals carrying the epsilon 2 allele had lower levels of plasma cholesterol, low-density lipoprotein cholesterol (LDL-C), and apoB and higher levels of triglycerides, very-low-density lipoprotein cholesterol (VLDL-C), apoC-III, apoE, lipoprotein (Lp) C-III:B, and Lp E:B. However, the effect of the epsilon 2 allele on triglyceride, VLDL-C, apoE, and Lp E:B parameters was heterogeneous across the populations.(ABSTRACT TRUNCATED AT 250 WORDS)

Protein composition determines the anti-atherogenic properties of HDL in transgenic mice

High-density lipoprotein (HDL) contains two major proteins, apolipoprotein A-I (apoA-I) and apolipoprotein A-II (apoA-II), comprising about 70% and 20% of the total HDL protein mass, respectively. HDL exists in human plasma in two main forms, one containing apoA-I with apoA-II (AI/AII-HDL) and another containing apoA-I without apoA-II (AI-HDL). A strong inverse relationship exists between total plasma HDL concentration and atherosclerosis, but the results of studies examining the relationship between AI-HDL and AI/AII-HDL and atherosclerosis have been conflicting. To determine whether these two HDL populations have different effects on atherogenesis, human apoA-I (AI) and human apoA-I and apoA-II (AI/AII) transgenic mice were produced in an atherosclerosis-susceptible strain. Following an atherogenic diet, despite similar total cholesterol and HDL cholesterol concentrations, the area of atherogenic lesions in the AI/AII mice was 15-fold greater than in the AI animals. These studies show that the protein composition of HDL significantly affects its role in atherogenesis and that AI-HDL is more antiatherogenic than AI/AII-HDL.

Treatment of E2E2 homozygous familial dysbetalipoproteinemic subjects with gemfibrozil does not enhance the binding of their d < 1.019 lipoprotein fraction to the low-density lipoprotein receptor

Six E2E2 homozygous familial dysbetalipoproteinemic (FD) patients were treated with gemfibrozil (2 x 600 mg/d) for a period of 4 weeks. For all subjects, normalization of serum cholesterol concentrations with treatment did not result in a significant change in the cholesterol/triglyceride ratio of the d < 1.019 lipoprotein fraction. In addition, the binding efficiency of this lipoprotein fraction to the low-density lipoprotein (LDL) receptor on HepG2 cells did not change consistently with treatment. We conclude that normalization of serum cholesterol concentrations in FD patients by treatment with gemfibrozil is the result of an effect of gemfibrozil on the synthesis of d < 1.019 lipoproteins rather than an effect on the receptor-mediated clearance of these particles.

Effect of simvastatin on the apparent size of LDL particles in patients with type IIB hyperlipoproteinemia

After 15 weeks of simvastatin therapy (20 mg/day), low density lipoprotein particle size in sera of 16 patients with type IIb hyperlipoproteinemia increased significantly from 233 +/- 5.0 A to 237 +/- 7.0 A (P less than 0.05), analyzed by 2-16% polyacrylamide gradient gel electrophoresis. Under simvastatin therapy the concentrations of total cholesterol, total triglyceride, very low density lipoprotein cholesterol and triglyceride, low density lipoprotein cholesterol and apolipoprotein B in serum fell significantly by 30%, 30%, 43%, 28%, 36% and 26%, respectively, and the concentration of high density lipoprotein cholesterol rose significantly by 14%. The changes of low density lipoprotein particle size induced by simvastatin therapy were correlated best with the changes of very low density lipoprotein triglyceride concentration (r2 = 0.438, P less than 0.01). Our results suggest that simvastatin therapy, additionally to a reduction of the serum cholesterol concentration, increases low density lipoprotein particle size which may contribute to reduction of the risk of coronary heart disease in patients with type IIb hyperlipoproteinemia.

A phenocopy of type III dysbetalipoproteinemia occurring in a candidate family for a putative apo E receptor defect

On theoretical grounds, an apo E receptor defect should be manifested by the accumulation of lipoprotein remnants that are normally cleared by this receptor and cannot be processed by the normal apo B, E receptor (LDL-receptor). Furthermore, the defect should not be selective for a specific apo E phenotype since none of the isoforms would be cleared preferentially. Our search for such an occurrence led us to the discovery, in five members of a family of ten, of a unique dyslipoproteinemia mimicking type III. As in type III, plasma levels of cholesterol, triglycerides, VLDL-cholesterol, VLDL-triglycerides and apo E, as well as the VLDL-C/TG ratio, were high. LDL-cholesterol and HDL-cholesterol tended to be low. The clearance of plasma triglycerides after a fat load was impaired. Tubero-eruptive xanthomas, arcus corneae and manifestations of atherosclerosis were present in some individuals. In contrast to type III, the dyslipoproteinemia occurred in subjects bearing three different apo E phenotypes: E4/2, E4/3 and E3/2. VLDL-apo B levels were markedly increased, the VLDL-C/VLDL-B ratio was low and a double pre-beta band was present on lipoprotein electrophoresis. In spite of high apo E and borderline high apo CIII plasma levels, levels of the lipoprotein particles LpCIII:B and LpE:B, which characterize type III, were not raised. Rapid weight loss or treatment with a fibrate was observed to normalize the lipoprotein profile. It is surmised that the apo E-rich lipoprotein particles accumulating in this type III phenocopy with "hyperapoprebetalipoproteinemia" could be those that are normally cleared by an apo E receptor.

Lipoprotein particles in homozygous familial hypercholesterolemic patients treated with portacaval shunt and LDL apheresis

Lipoprotein particles containing apolipoproteins (Apo) were studied by enzyme-linked-immunosorbent assay in two homozygous familial hypercholesterolemic patients (1 male and 1 female) with portacaval shunts, and in controls. Total Apo B, total cholesterol and LDL cholesterol were increased in both patients while complex Apo B containing particles, Lp CIII: B, were not increased in these FH patients. The dextran-sulfate cellulose columns (Liposorber LA-40) had an excellent adsorption selectivity and adsorption capacity for lipoprotein particles containing Apo B and a minimum adsorption capacity in Apo AI and Apo AII-containing particles. This apheresis technique selectively depleted plasma of atherogenic Apo B-containing particles with a minimal loss of antiatherogenic Apo AI-containing particles.