Small polydisperse low density lipoproteins in familial hyperalphalipoproteinemia with complete deficiency of cholesteryl ester transfer activity

Cholesteryl Ester Transfer Protein (CETP) Variations in Relation to Lipid Profiles and Cardiovascular Diseases: An Update

Lipid metabolism plays an essential role in the pathogenesis of cardiovascular and metabolic diseases. Cholesteryl ester transfer protein (CETP) is a crucial glycoprotein involved in lipid metabolism by transferring cholesteryl esters (CE) and triglycerides (TG) between plasma lipoproteins. CETP activity results in reduced HDL-C and increased VLDL- and LDL-C concentrations, thus increasing the risk of cardiovascular and metabolic diseases. In this review, we discuss the structure of CETP and its mechanism of action. Furthermore, we focus on recent experiments on animal CETP-expressing models, deciphering the regulation and functions of CETP in various genetic backgrounds and interaction with different external factors. Finally, we discuss recent publications revealing the association of CETP single nucleotide polymorphisms (SNPs) with the risk of cardiovascular and metabolic diseases, lifestyle factors, diet and therapeutic interventions. While CETP SNPs can be used as effective diagnostic markers, diet, lifestyle, gender and ethnic specificity should also be considered for effective treatment.

Don't Turn Off the Tap! The Importance of Discovery Science to the Australian Cardiovascular Sector and Improving Clinical Outcomes Into the Future

Despite significant advances in interventional and therapeutic approaches, cardiovascular disease (CVD) remains the leading cause of death and mortality. To lower this health burden, cardiovascular discovery scientists need to play an integral part in the solution. Successful clinical translation is achieved when built upon a strong foundational understanding of the disease mechanisms involved. Changes in the Australian funding landscape, to place greater emphasis on translation, however, have increased job insecurity for discovery science researchers and especially early-mid career researchers. To highlight the importance of discovery science in cardiovascular research, this review compiles six science stories in which fundamental discoveries, often involving Australian researchers, has led to or is advancing to clinical translation. These stories demonstrate the importance of the role of discovery scientists and the need for their work to be prioritised now and in the future. Australia needs to keep discovery scientists supported and fully engaged within the broader cardiovascular research ecosystem so they can help realise the next game-changing therapy or diagnostic approach that diminishes the burden of CVD on society.

HDL Receptor in Schistosoma japonicum Mediating Egg Embryonation: Potential Molecular Basis for High Prevalence of Cholesteryl Ester Transfer Protein Deficiency in East Asia

Schistosomiasis is a life-threatening parasitic disease caused by blood flukes, Schistosomes. In its intestinal type, the parasites reside in visceral/portal veins of the human hosts and lay eggs to excrete in feces via intestinal tracts, and some of the aberrant eggs plug into the liver via the portal blood flow. Ectopic growth of these eggs causes fatal granulomatosis and cirrhosis of the liver. The parasites ingest nutrients from the host blood plasma by using nonspecific and specific transport via their body surface and alimentary tracts. It is especially important for the female adults to obtain lipid molecules because they synthesize neither fatty acids nor sterols and yet produce egg yolk. Low-density lipoprotein receptors have been identified in the body of the Schistosomes but their functions in the parasite life cycle have not clearly been characterized. On the other hand, CD36-related protein was identified in the body and the eggs of Asian blood fluke, Schistosoma japonicum, and characterized as a molecule that mediates selective uptake of cholesteryl ester from the host plasma high-density lipoproteins (HDLs). This reaction was shown crucial for their eggs to grow to miracidia. Interestingly, abnormal large HDL generated in lack of cholesteryl ester transfer protein (CETP) is a poor substrate for this reaction, and, therefore, CETP deficiency resists pathogenic ectopic growth of the aberrant parasite eggs in the liver. This genetic mutation is exclusively found in East Asia, overlapping with the current and historic regions of Schistosoma japonicum epidemic, so that this infection could be related to high prevalence of CETP deficiency in East Asia.

Hyperalphalipoproteinemia and Beyond: The Role of HDL in Cardiovascular Diseases

Hyperalphalipoproteinemia (HALP) is a lipid disorder characterized by elevated plasma high-density lipoprotein cholesterol (HDL-C) levels above the 90th percentile of the distribution of HDL-C values in the general population. Secondary non-genetic factors such as drugs, pregnancy, alcohol intake, and liver diseases might induce HDL increases. Primary forms of HALP are caused by mutations in the genes coding for cholesteryl ester transfer protein (CETP), hepatic lipase (HL), apolipoprotein C-III (apo C-III), scavenger receptor class B type I (SR-BI) and endothelial lipase (EL). However, in the last decades, genome-wide association studies (GWAS) have also suggested a polygenic inheritance of hyperalphalipoproteinemia. Epidemiological studies have suggested that HDL-C is inversely correlated with cardiovascular (CV) risk, but recent Mendelian randomization data have shown a lack of atheroprotective causal effects of HDL-C. This review will focus on primary forms of HALP, the role of polygenic inheritance on HDL-C, associated risk for cardiovascular diseases and possible treatment options.

Distinct Differences in Lipoprotein Particle Number Evaluation between GP-HPLC and NMR: Analysis in Dyslipidemic Patients Administered a Selective PPARα Modulator, Pemafibrate

Aim: We established a method to evaluate the lipid concentrations, size and particle numbers (PNs) of lipoprotein subclasses by gel permeation chromatography (GP-HPLC). Nuclear magnetic resonance (NMR) is widely used to analyze these parameters of lipoprotein subclasses, but differences of the two methods are unknown. Current study compared the PNs of each lipoprotein subclass measured by GP-HPLC and NMR, and assessed the effect of a selective PPARα modulator, pemafibrate.

Methods: Lipoprotein profiles of 212 patients with dyslipidemia who participated in the phase 2 clinical trial of a selective PPARα modulator, pemafibrate, were analyzed by two methods, GP-HPLC and NMR, which were performed with LipoSEARCH (Skylight Biotech) and LipoProfile 3 (LabCorp), respectively. GP-HPLC evaluated the PNs of 18 subclasses, consisting of CM, VLDL1-5, LDL1-6, and HDL1-6. NMR evaluated the PNs of 9 subclasses, consisting of large VLDL & CM, medium VLDL, small VLDL, IDL, large LDL, small LDL, large HDL, medium HDL and small HDL.

Results: Three major classes, total CM&VLDL, total LDL and total HDL were obtained by grouping of corresponding subclasses in both methods and PNs of these classes analyzed by GP-HPLC were correlated positively with those by NMR. The correlation coefficients in total CM&VLDL, total LDL and total HDL between GP-HPLC and NMR was 0.658, 0.863 and 0.798 (all p ＜0.0001), respectively. The PNs of total CM&VLDL, total LDL and total HDL analyzed by GP-HPLC was 249.5±51.7nM, 1,679±359 nM and 13,273±1,564 nM, respectively, while those by NMR was 124.6±41.8 nM, 1,514±386 nM and 31,161±4,839 nM, respectively. A marked difference in the PNs between the two methods was demonstrated especially in total HDL.

The number of apolipoprotein (Apo) B molecule per one ApoB-containing lipoprotein particle, total CM&VLDL plus total LDL, was 1.10±0.05 by GP-HPLC, while 1.32±0.18 by NMR. The number of ApoA-I per one HDL particle was 3.40±0.17 by GP-HPLC, but only 1.46±0.15 by NMR, much less than reported previously.

From the phase 2 clinical trial, randomizing 212 patients to pemafibrate 0.025-0.2 mg BID, fenofibrate 100 mg QD, or placebo groups, pemafibrate reduced the PNs of CM, large VLDL1-VLDL3 and medium VLDL4, but not small VLDL5 by GP-HPLC. It significantly decreased the PNs of smaller LDL and larger HDL particles, but increased those of larger LDL and smaller HDL particles. In contrast, NMR showed marked variations in the effect of pemafibrate on lipoprotein PNs, and no significant size-dependent changes.

Conclusions: GP-HPLC evaluates the lipoprotein PNs more accurately than NMR and can be used for assessing the effects of lipid-lowering drugs on lipoprotein subclasses.

Evacetrapib reduces preβ-1 HDL in patients with atherosclerotic cardiovascular disease or diabetes

BACKGROUND AND AIMS

Cholesteryl ester transfer protein (CETP) inhibitor-mediated induction of HDL-cholesterol has no effect on the protection from cardiovascular disease (CVD). However, the mechanism is still unknown. Data on the effects of this class of drugs on subclasses of HDL are either limited or insufficient. In this study, we investigated the effect of evacetrapib, a CETP inhibitor, on subclasses of HDL in patients with atherosclerotic cardiovascular disease or diabetes.

METHODS

Baseline and 3-month post-treatment samples from atorvastatin 40 mg plus evacetrapib 130 mg (n = 70) and atorvastatin 40 mg plus placebo (n = 30) arms were used for this purpose. Four subclasses of HDL (large HDL, medium HDL, small HDL, and preβ-1 HDL) were separated according to their size and quantified by densitometry using a recently developed native polyacrylamide gel electrophoresis (PAGE) system.

RESULTS

Relative to placebo, while evacetrapib treatment dramatically increased large HDL and medium HDL subclasses, it significantly reduced small HDL (27%) as well as preβ-1 HDL (36%) particles. Evacetrapib treatment reduced total LDL, but also resulted in polydisperse LDL with LDL particles larger and smaller than the LDL subclasses of the placebo group.

CONCLUSION

Evacetrapib reduced preβ-1 HDL and small HDL in patients with ASCVD or diabetes on statin. Preβ-1 HDL and medium HDL are negatively interrelated. The results could give a clue to understand the effect of CETP inhibitors on cardiovascular outcomes.

Primary genetic disorders affecting high density lipoprotein (HDL)

There is extensive evidence demonstrating that there is a clear inverse correlation between plasma high density lipoprotein cholesterol (HDL-C) concentration and cardiovascular disease (CVD). On the other hand, there is also extensive evidence that HDL functionality plays a very important role in atheroprotection. Thus, genetic disorders altering certain enzymes, lipid transfer proteins, or specific receptors crucial for the metabolism and adequate function of HDL, may positively or negatively affect the HDL-C levels and/or HDL functionality and subsequently either provide protection or predispose to atherosclerotic disease. This review aims to describe certain genetic disorders associated with either low or high plasma HDL-C and discuss their clinical features, associated risk for cardiovascular events, and treatment options.

Cholesteryl ester transfer protein and its inhibitors

Most of the cholesterol in plasma is in an esterified form that is generated in potentially cardioprotective HDLs. Cholesteryl ester transfer protein (CETP) mediates bidirectional transfers of cholesteryl esters (CEs) and triglycerides (TGs) between plasma lipoproteins. Because CE originates in HDLs and TG enters the plasma as a component of VLDLs, activity of CETP results in a net mass transfer of CE from HDLs to VLDLs and LDLs, and of TG from VLDLs to LDLs and HDLs. As inhibition of CETP activity increases the concentration of HDL-cholesterol and decreases the concentration of VLDL- and LDL-cholesterol, it has the potential to reduce atherosclerotic CVD. This has led to the development of anti-CETP neutralizing monoclonal antibodies, vaccines, and antisense oligonucleotides. Small molecule inhibitors of CETP have also been developed and four of them have been studied in large scale cardiovascular clinical outcome trials. This review describes the structure of CETP and its mechanism of action. Details of its regulation and nonlipid transporting functions are discussed, and the results of the large scale clinical outcome trials of small molecule CETP inhibitors are summarized.

Efficacy and Safety of the Cholesteryl Ester Transfer Protein Inhibitor Evacetrapib in Combination With Atorvastatin in Japanese Patients With Primary Hypercholesterolemia

BACKGROUND

Inhibition of cholesteryl ester transfer protein by evacetrapib when added to atorvastatin may provide an additional treatment option for patients who do not reach their low-density lipoprotein cholesterol (LDL-C) goal.Methods and Results:This multicenter, randomized, 12-week, double-blind, parallel-group, placebo-controlled, outpatient, phase 3 study evaluated the efficacy of evacetrapib with atorvastatin in reducing LDL-C in 149 Japanese patients (evacetrapib/atorvastatin, n=53; ezetimibe/atorvastatin, n=50; placebo/atorvastatin, n=46) with primary hypercholesterolemia. The primary efficacy measure was percent change from baseline to week 12 in LDL-C (β quantification). Treatment with evacetrapib 130 mg daily for 12 weeks resulted in a statistically significant treatment difference of -25.70% compared with placebo in percentage decrease in LDL-C (95% CI: -34.73 to -16.68; P<0.001). Treatment with evacetrapib 130 mg also resulted in a statistically significant difference of 126.39% in the change in high-density lipoprotein cholesterol (HDL-C) compared with placebo (95% CI: 113.54-139.24; P<0.001). No deaths or serious adverse events were reported. Four patients (3 in the evacetrapib group and 1 in the ezetimibe group) discontinued due to adverse events.

CONCLUSIONS

Evacetrapib daily in combination with atorvastatin was superior to placebo in lowering LDL-C after 12 weeks, and resulted in a statistically significant increase of HDL-C compared with placebo. Also, no new safety risks were identified.

Evacetrapib and Cardiovascular Outcomes in High-Risk Vascular Disease

BACKGROUND

The cholesteryl ester transfer protein inhibitor evacetrapib substantially raises the high-density lipoprotein (HDL) cholesterol level, reduces the low-density lipoprotein (LDL) cholesterol level, and enhances cellular cholesterol efflux capacity. We sought to determine the effect of evacetrapib on major adverse cardiovascular outcomes in patients with high-risk vascular disease.

METHODS

In a multicenter, randomized, double-blind, placebo-controlled phase 3 trial, we enrolled 12,092 patients who had at least one of the following conditions: an acute coronary syndrome within the previous 30 to 365 days, cerebrovascular atherosclerotic disease, peripheral vascular arterial disease, or diabetes mellitus with coronary artery disease. Patients were randomly assigned to receive either evacetrapib at a dose of 130 mg or matching placebo, administered daily, in addition to standard medical therapy. The primary efficacy end point was the first occurrence of any component of the composite of death from cardiovascular causes, myocardial infarction, stroke, coronary revascularization, or hospitalization for unstable angina.

RESULTS

At 3 months, a 31.1% decrease in the mean LDL cholesterol level was observed with evacetrapib versus a 6.0% increase with placebo, and a 133.2% increase in the mean HDL cholesterol level was seen with evacetrapib versus a 1.6% increase with placebo. After 1363 of the planned 1670 primary end-point events had occurred, the data and safety monitoring board recommended that the trial be terminated early because of a lack of efficacy. After a median of 26 months of evacetrapib or placebo, a primary end-point event occurred in 12.9% of the patients in the evacetrapib group and in 12.8% of those in the placebo group (hazard ratio, 1.01; 95% confidence interval, 0.91 to 1.11; P=0.91).

CONCLUSIONS

Although the cholesteryl ester transfer protein inhibitor evacetrapib had favorable effects on established lipid biomarkers, treatment with evacetrapib did not result in a lower rate of cardiovascular events than placebo among patients with high-risk vascular disease. (Funded by Eli Lilly; ACCELERATE ClinicalTrials.gov number, NCT01687998 .).

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.

Disease-associated marked hyperalphalipoproteinemia

Marked hyperalphalipoproteinemia (HAL) is a heterogeneous syndrome. To clarify the pathophysiological significance of HAL, we compared clinical profiles between marked HAL subjects with and without cholesteryl ester transfer protein (CETP) deficiency. CETP deficiency was associated with cardiovascular diseases and strokes in the HAL population, particularly in female. HAL women without CETP deficiency tended to have higher prevalence with cancer history. HAL may not always be a longevity marker, but be sometimes accompanied with pathological conditions.

Different effects of compounds decreasing cholesteryl ester transfer protein activity on lipoprotein metabolism

PURPOSE OF REVIEW

Review literature on the effect of decreasing cholesteryl ester transfer protein (CETP) activity through pharmacological inhibition or modulation in preclinical and clinical settings compared to human CETP deficiency on lipoprotein characteristics, HDL remodelling and function.

RECENT FINDINGS

Torcetrapib, anacetrapib and dalcetrapib inhibited the heterotypic transfer of cholesteryl ester from HDL to LDL and/or VLDL with similar potency, although the potency of dalcetrapib was time dependent. Homotypic transfer of cholesteryl ester from HDL3 to HDL2 via recombinant human CETP was inhibited by torcetrapib and anacetrapib (CETP inhibitors, CETPi) but not by dalcetrapib (CETP modulator, CETPm). In a hamster model of reverse cholesterol transport, only dalcetrapib increased efflux of fecal sterols from macrophages to feces. In clinical studies, dose-responses of CETPi and CETPm demonstrate qualitative and quantitative changes in HDL and LDL particle composition and distribution.

SUMMARY

Recent studies of the CETPi torcetrapib and anacetrapib and the CETPm dalcetrapib have shown differences in the resulting increase in HDL-cholesterol and in the level of HDL remodelling and potential for effective reverse cholesterol transport. Results from ongoing clinical outcomes studies with anacetrapib and dalcetrapib will clarify the relevance of CETP inhibition versus modulation towards HDL remodelling in the treatment of cardiovascular diseases.

Activation of lipoprotein lipase increases serum high density lipoprotein 2 cholesterol and enlarges high density lipoprotein 2 particles in rats

It is known that postheparin plasma lipoprotein lipase (LPL) activity correlates with serum high density lipoprotein cholesterol (HDL-C) levels in humans and animals. Furthermore, LPL has been reported to cause enlargement of HDL particle size in vitro. However, these effects have not yet been experimentally proven. The aim of this study was to determine whether LPL has a role in increase in HDL-C and enlargement of HDL particle by activating the LPL function with NO-1886, the LPL promoting agent. NO-1886 administration increased postheparin plasma LPL activity without influencing hepatic triglyceride lipase activity. NO-1886 increased serum HDL(2)-cholesterol (HDL(2)-C) concentration and enlarged HDL(2) particle size, but did not increase serum HDL(3)-cholesterol concentration or enlarge HDL(3) particle size. Also, serum HDL(2)-C concentrations were positively correlated with HDL(2) particle size (r=0.910). Our study demonstrates that the LPL activation induced with NO-1886 may cause production of HDL(2)-C by catabolism of triglyceride-rich lipoproteins and enlarges HDL(2) particle size in rats.

Anacetrapib: hope for CETP inhibitors?

Inhibition of cholesteryl ester transfer protein (CETP), a key protein involved in reverse cholesterol transport, can lead to increases in high-density lipoprotein cholesterol (HDL-C) levels and thus, is under evaluation as an antiatherogenic strategy. Several CETP inhibitors have been under development including anacetrapib, dalcetrapib, and torcetrapib. To date, anacetrapib demonstrates the greatest HDL-C raising and low-density lipoprotein cholesterol (LDL-C) lowering potential. Phase I and phase II trials with anacetrapib have revealed that anacetrapib is well-tolerated and does not seem to possess the pressor effects associated with torcetrapib. This article will briefly review the HDL-C raising through CETP inhibition as an antiatherogenic strategy with a specific focus on anacetrapib.

High density lipoprotein cholesterol: an evolving target of therapy in the management of cardiovascular disease

Since the pioneering work of John Gofman in the 1950s, our understanding of high density lipoprotein cholesterol (HDL-C) and its relationship to coronary heart disease (CHD) has grown substantially. Numerous clinical trials since the Framingham Study in 1977 have demonstrated an inverse relationship between HDL-C and one’s risk of developing CHD. Over the past two decades, preclinical research has gained further insight into the nature of HDL-C metabolism, specifically regarding the ability of HDL-C to promote reverse cholesterol transport (RCT). Recent attempts to harness HDL’s ability to enhance RCT have revealed the complexity of HDL-C metabolism. This review provides a detailed update on HDL-C as an evolving therapeutic target in the management of cardiovascular disease.

CETP genotypes and HDL-cholesterol phenotypes in the HERITAGE Family Study

Associations between cholesteryl ester transfer protein (CETP) polymorphisms and high-density lipoprotein cholesterol (HDL-c) levels before and after 20 wk of endurance training were investigated in the HERITAGE Family Study. Plasma HDL-c, HDL2-c, HDL3-c, and apolipoprotein (apo)A1 levels were measured, and 13 CETP single nucleotide polymorphisms (SNPs) were genotyped in 265 blacks and 486 whites. Three haplotypes defined by SNPs at the −1337, −971, and −629 sites were strongly associated with baseline HDL-c levels in whites. Both C−1337T and C−629A were associated with baseline HDL-c ( P < 0.001) and apoA1 ( P < 0.01) when tested separately. However, only C−629A remained significant in a combined model. G−971A was not associated with HDL phenotypes, but showed significant interactions with C−629A ( P = 0.002) on baseline traits. Genotype-by-sex interactions were observed at the −629 locus for HDL3-c ( P = 0.004) and apoA1 ( P = 0.02) training responses in whites. In women, the −629 A/A homozygotes showed greater increases in HDL3-c ( P = 0.02) and apoA1 ( P = 0.02) levels than the other genotypes. Finally, apolipoprotein E (APOE) genotype and the CETP C−629A locus contributed independently and in additive fashion to the HDL traits, explaining 6.0–8.8% of the variance. The CETP −1337T and −629A alleles are associated with higher baseline HDL-c and apoA1 levels. The beneficial effects of endurance training on plasma HDL3-c and apoA1 levels are evident in white women homozygous for the −629A allele. The CETP and APOE genotypes account for up to 9% of the variance in HDL-c phenotypes in the HERITAGE Family Study.

Relationship Between Lipid Abnormalities and Insulin Resistance in Japanese School Children

Objective— Dyslipidemia and insulin resistance (IR) are risk factors for coronary heart disease (CHD) in adults. To help prevent the development of CHD, it may be useful to understand the relationship between lipid abnormalities and IR during childhood.

Methods and Results— IR was assessed by the homeostasis model approximation index. We studied 1175 Japanese school children (642 boys and 533 girls), aged between 7 and 12 years. Obesity was defined by the body mass index standard deviation score (BMISD) (obese: BMISD ≥2.0). BMISD was most significantly associated with IR in nonobese children ( P =0.000). Associations of IR with lipid-related parameters were affected by BMISD. After being corrected by BMISD, in nonobese children, log triglycerides (TG), apoB and low-density lipoprotein (LDL) size in boys and log TG, LDL size, and high-density lipoprotein (HDL) cholesterol in girls were still significantly associated with IR ( P =0.000 to 0.017). In obese children, all parameters except for LDL cholesterol in boys and LDL size in girls were significantly associated with IR ( P =0.000 to 0.030). Multiple regression analysis showed that log TG and LDL size in nonobese children, log TG in obese boys and LDL size in obese girls were independently associated with IR. Children with IIb and IV hyperlipidemia had significantly higher IR than those with normolipidemia and IIa, even after correcting for BMISD and age.

Conclusion— Our results suggest that in addition to controlling body weight, it may be important for school children to characterize lipid phenotypes to prevent progression to CHD and/or type 2 diabetes and to identify subjects who are at high risk for these disorders.

Adipose tissue-specific CETP expression in mice: impact on plasma lipoprotein metabolism

Adipose tissue appears to be a highly conserved site of cholesteryl ester transfer protein (CETP) expression across species. To investigate the impact of adipose CETP expression on lipid metabolism, we created adipose tissue-specific CETP transgenic (CETPTg) mice. CETP mRNA is predominantly expressed in adipose tissue. Plasma CETP mass and activity are readily detectable in CETPTg mice but not in controls. Plasma lipoprotein analysis shows marked reductions in HDL cholesterol and phospholipids, increases non-HDL lipids, decreases apolipoprotein A-I (apoA-I), and increases apoB. Unexpectedly, CETPTg adipocytes are significantly smaller than those in control mice (44%), triglyceride and cholesterol in adipose tissue were significantly decreased compared with controls (50% and 37%, respectively), and phospholipids showed no significant changes. To study the mechanism, we measured peroxisome proliferator-activated receptor gamma, sterol-regulatory element binding protein-1c, LPL, and hormone-sensitive lipase (HSL) in aP2-CETPTg adipose tissue and controls and found that, except for HSL, all mRNA levels are significantly decreased in the transgenic mice compared with controls (26, 33, and 22%). In conclusion, adipose tissue CETP makes a major contribution to CETP in the circulation, reduces HDL, and increases non-HDL cholesterol levels. Moreover, adipose tissue CETP expression changes triglyceride and cholesterol content and the size of adipocytes.

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.

Molecular mechanisms of cholesteryl ester transfer protein deficiency in Japanese

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 (RCT), a protective system against atherosclerosis. The importance of plasma CETP in lipoprotein metabolism was demonstrated by the discovery of CETP-deficient subjects with marked hyperalphalipoproteinemia (HALP). Genetic CETP deficiency is the most important and common cause of HALP in the Japanese. Ten mutations of the CETP gene have been demonstrated as causes of HALP, including two common mutations: an intron 14 splicing defect (Int14 + 1 G --> A) and an exon 15 missense mutation (D442G). The subjects with CETP deficiency show a variety of abnormalities in the concentration, composition, and function of both HDL and low density lipoprotein (LDL). CETP deficiency is considered a physiological state of impaired RCT, which may possibly lead to the development of atherosclerosis despite high HDL cholesterol levels. However, the pathophysiological significance of CETP in terms of atherosclerosis has been controversial. Epidemiological studies in Japanese-Americans living in Hawaii and Japanese in the Omagari area, where HALP subjects with an intron 14 splicing defect of the CETP gene are markedly frequent, have shown a relatively increased incidence of coronary atherosclerosis in CETP deficiency. On the other hand, the TaqIB polymorphism-B2 allele with low CETP mass and increased HDL cholesterol has been related to a decreased risk for coronary heart disease (CHD) in many studies, including the Framingham Offspring Study. The current review focused on the characterization of the Japanese subjects with CETP deficiency, including our recent findings.

A review of CETP and its relation to atherosclerosis

Although the atheroprotective role of HDL cholesterol (HDL-c) is well documented, effective therapeutics to selectively increase plasma HDL-c levels are not yet available. Recent progress in unraveling human HDL metabolism has fuelled the development of strategies to decrease the incidence and progression of coronary artery disease (CAD) by raising HDL-c. In this quest for novel drugs, cholesteryl ester transfer protein (CETP) represents a pivotal target. The role of this plasma protein in HDL metabolism is highlighted by the discovery that genetic CETP deficiency is the main cause of high HDL-c levels in Asian populations. The use of CETP inhibitors to effectively increase HDL-c concentration in humans was recently published and data with regard to the effect on human atherosclerosis are expected shortly. This review discusses the potential of CETP inhibitors to protect against atherosclerosis in the context of the current knowledge of CETP function in both rodents and humans.

Regulation of plasma high-density lipoprotein levels by the ABCA1 transporter and the emerging role of high-density lipoprotein in the treatment of cardiovascular disease

High-density lipoproteins (HDL) protect against cardiovascular disease. HDL removes and transports excess cholesterol from peripheral cells to the liver for removal from the body. HDL also protects low-density lipoproteins (LDL) from oxidation and inhibits expression of adhesion molecules in endothelial cells, preventing monocyte movement into the vessel wall. The ABCA1 transporter regulates intracellular cholesterol levels in the liver and in peripheral cells by effluxing excess cholesterol to lipid-poor apoA-I to form nascent HDL, which is converted to mature alpha-HDL by esterification of cholesterol to cholesteryl esters (CE) by lecithin cholesterol acyltransferase. The hepatic ABCA1 transporter and apoA-I are major determinants of levels of plasma alpha-HDL cholesterol as well as poorly lipidated apoA-I, which interact with ABCA1 transporters on peripheral cells in the process of reverse cholesterol transport. Cholesterol in HDL is transported directly back to the liver by HDL or after transfer of CE by the cholesteryl ester transfer protein (CETP) by the apoB lipoproteins. Current approaches to increasing HDL to determine the efficacy of HDL in reducing atherosclerosis involve acute HDL therapy with infusions of apoA-I or apoA-I mimetic peptides and chronic long-term therapy with selective agents to increase HDL, including CETP inhibitors.

CETP gene variation: relation to lipid parameters and cardiovascular risk

PURPOSE OF REVIEW

Over the past decade lowering of low-density lipoprotein-cholesterol levels has been established as the foundation for preventing coronary artery disease, but substantial additional risk reduction remains to be gained by modifying risk factors other than low-density lipoprotein-cholesterol. Raising high-density lipoprotein-cholesterol levels by inhibiting activity of the cholesteryl ester transfer protein (CETP) is a prime target. Research on naturally occurring variants in the CETP gene has yielded numerous insights that have been relevant for understanding lipoprotein metabolism, and crucial to the development of pharmacological CETP inhibition.

RECENT FINDINGS

This review discusses a number of recently published studies, including a haplotype analysis of the CETP promoter region confirming that the -629 C-->A variant, not the TaqIB variant, is instrumental in determining CETP activity, as previously suggested. In addition, we discuss a recent meta-analysis which confirms that the I405V and TaqIB variants are indeed associated with lower CETP activity and higher high-density lipoprotein-cholesterol levels. Also, we review two subanalyses of large randomized controlled pravastatin trials which found no evidence for a proposed pharmacogenetic interaction between the CETP TaqIB variant and pravastatin treatment.

SUMMARY

The currently available evidence suggests that several genetic variants in the CETP gene are associated with altered CETP plasma levels and activity, high-density lipoprotein-cholesterol plasma levels, low-density lipoprotein and high-density lipoprotein particle size, and perhaps the risk of coronary artery disease. No evidence exists for a pharmacogenetic interaction between the CETP TaqIB variant and pravastatin efficacy.

Hypertriglyceridemia in pregnancy does not contribute to the enhanced formation of remnant lipoprotein particles

BACKGROUND

During pregnancy, serum cholesterol (TC) and triglyceride (TG) concentrations are known to increase significantly, but whether remnant lipoprotein particles (RLP) increase has not been shown.

METHODS

We compared lipid profiles in 22 healthy pregnant women to 31 healthy nonpregnant women and 24 patients with diabetes mellitus (DM), by measuring cholesterol and TG concentrations in major lipoprotein classes after HPLC separation and immunoseparation of RLP.

RESULTS

Serum TG and TC concentrations were significantly higher in the pregnant group than in the healthy control or DM groups. Cholesterol and TG concentrations of all major lipoprotein classes were also significantly higher in the pregnant group than the control and DM groups, except for VLDL-TG in the DM group. RLP-C and RLP-TG concentrations were significantly higher in the pregnant group (8.7 mg/dl and 25.4 mg/dl on average) than the control group (2.4 mg/dl and 5.7 mg/dl), but not different from the DM group (8.8 mg/dl and 24.1 mg/dl). RLP-TG to RLP-C ratios were similar among the three groups and correlated with the VLDL-TG to VLDL-C ratio. The percentages of RLP-C in VLDL-C and RLP-TG in VLDL-TG in the pregnant group (15.9% and 15.7%) were significantly lower than those of the control (48.5% and 35.6%) and the DM (32.7% and 20.8%) groups.

CONCLUSIONS

RLP increased moderately during gestation with the increase in VLDL and TG, but the percentage of RLP in VLDL was significantly lower in the pregnant women compared with the control and DM patients, suggesting that hypertriglyceridemia in pregnancy is not primarily due to an increase in the atherogenic RLP.

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.

Association of cholesteryl ester transfer protein activity and TaqIB polymorphism with lipoprotein variations in Japanese subjects

Cholesteryl ester transfer protein (CETP) facilitates the transfer of cholesteryl ester from high-density lipoprotein (HDL) to apolipoprotein (apo)B-containing lipoproteins, whereby it potentially regulates steady-state concentrations of HDL-cholesterol (HDL-C), as well as low-density lipoprotein-cholesterol (LDL-C). We performed a multicenter trial to assess the association of CETP activity with plasma lipoprotein levels in 591 Japanese subjects. Women had significantly higher CETP activity (15%) and mass (24%) compared to men. For both genders CETP activity was negatively correlated with HDL-C and HDL(2)-C, but positively correlated with LDL-C. B2 allele frequency in TaqIB polymorphism was 40%, with no gender difference. TaqIB genotypes were significantly associated with CETP activity and HDL-C level (both P <.001). B1B1 had the highest CETP activity and the lowest HDL-C concentrations, whereas B2B2 had the lowest CETP activity and the highest HDL-C concentrations. However, no statistically significant differences in triglycerides (TG) or LDL-C were observed across TaqIB genotypes. Multivariate analysis revealed that determinants of HDL-C were age, gender, body mass index (BMI), smoking, alcohol intake, exercise, CETP activity, and TG, and for LDL-C were BMI, age, and CETP. These data demonstrate that CETP activity is a significant determinant of HDL-C and LDL-C levels and that TaqIB CETP gene polymorphism affects CETP activity and HDL-C level in Japanese population examined.

Cholesteryl ester transfer protein: a novel target for raising HDL and inhibiting atherosclerosis

Cholesteryl ester transfer protein (CETP) promotes the transfer of cholesteryl esters from antiatherogenic HDLs to proatherogenic apolipoprotein B (apoB)-containing lipoproteins, including VLDLs, VLDL remnants, IDLs, and LDLs. A deficiency of CETP is associated with increased HDL levels and decreased LDL levels, a profile that is typically antiatherogenic. Studies in rabbits, a species with naturally high levels of CETP, support the therapeutic potential of CETP inhibition as an approach to retarding atherogenesis. Studies in mice, a species that lacks CETP activity, have provided mixed results. Human subjects with heterozygous CETP deficiency and an HDL cholesterol level >60 mg/dL have a reduced risk of coronary heart disease. Evidence that atherosclerosis may be increased in CETP-deficient subjects whose HDL levels are not increased is difficult to interpret and may reflect confounding or bias. Small-molecule inhibitors of CETP have now been tested in human subjects and shown to increase the concentration of HDL cholesterol while decreasing that of LDL cholesterol and apoB. Thus, it seems important and timely to test the hypothesis in randomized trials of humans that pharmacological inhibition of CETP retards the development of atherosclerosis.

Prevalence and phenotypic spectrum of cholesteryl ester transfer protein gene mutations in Japanese hyperalphalipoproteinemia

A patient with cholesteryl ester transfer protein (CETP) deficiency presents with marked hyperalphalipoproteinemia (HALP). To investigate the contribution of CETP deficiency to the cause of HALP (HDL-C> or =1.94 mmol/l, 75 mg/dl), we investigated the CETP activities and the prevalence of genetic CETP mutations among 624 Japanese HALP subjects. The subjects were screened for four known genetic CETP mutations (intron 14 splicing defect (In14), exon 15 missense mutation (Ex15), intron 10 splicing defect (In10) and exon 6 nonsense mutation (Ex6)). We found the frequency of the patients with reduced CETP activity (<75% of normal controls) to be 55.5 and 64.1% in a high HDL group (1.94< or =HDL-C<2.59 mmol/l) and a marked HALP group (HDL-C> or =2.59 mmol/l, 100 mg/dl), respectively. At least one of the four mutations was identified in 65.7% of subjects with reduced CETP activities and 57.5% of subjects with marked HALP. The In14 and Ex15 mutations were very common in HALP subjects and the frequency of In10 mutation and Ex6 mutation was quite low. To investigate the impact of genetic CETP mutation on the phenotypes, we compared the plasma lipid levels and CETP activities between the subjects with two common mutations. All In14 homozygotes showed marked HALP, while marked HALP is less frequent (64.3%) in Ex15 homozygotes. HDL-C levels in Ex15 heterozygotes were significantly higher than those of In14 heterozygotes, suggesting the mutation has dominant negative effects on CETP activity in vivo. Some cases with In14 (5.7%) or Ex15 (7.2%) mutation showed low HDL-C levels. We conclude that CETP deficiency is a major cause of HALP; nevertheless CETP deficiency is not necessarily HALP.

CETP gene mutation (D442G) increases low-density lipoprotein particle size in patients with coronary heart disease

BACKGROUND

Small, dense low-density lipoprotein (LDL) in subjects with the atherogenic pattern B has been established as a risk factor of atherosclerosis. Cholesteryl ester transfer protein (CETP) plays an important role in the transfer and exchange of cholesteryl esters and triglycerides between the lipoprotein classes of human plasma. It has been shown that CETP can also change the particle size of high-density lipoprotein (HDL) and LDL subfractions in vitro. Previous clinical studies about CETP gene mutations mainly focused on abnormalities in HDL, few involved those in LDL.

OBJECTIVES

To investigate the effect of the D442G mutation in the CETP gene on major peak size of LDL particles in patients with coronary heart diseases (CHD).

METHODS

D442G mutation in the CETP gene was detected using the PCR-RFLP. LDL particles sizes were analyzed by 2-16% nondenaturing polyacrylamide gradient gels in CHD patients with D442G mutation in the CETP gene.

RESULTS

Six heterozygotes and one homozygote were found to have the D442G mutation among 200 CHD patients. The frequency of this mutation was 3.5%. The major peak size of LDL in patients with gene mutation (n=7) was significantly larger than that in patients without the mutation (n=40) (26.92 +/- 0.79 nm vs. 25.71 +/- 0.66 nm, respectively; P<0.01). All the patients with the gene mutation expressed pattern A, whereas only about half of the patients without the mutation expressed this pattern. The patients with gene mutation had decreased plasma CETP concentration, while increased concentration of HDL-C and apolipoprotein A-I compared with controls.

CONCLUSIONS

CETP gene mutation (D442G) increases LDL particle size. This suggests that CETP play an antiatherogenic role.

Two novel missense mutations in the CETP gene in Japanese hyperalphalipoproteinemic subjects: high-throughput assay by Invader assay

Cholesteryl ester transfer protein (CETP) deficiency is one of the most important and common causes of hyperalphalipoproteinemia (HALP) in the Japanese. CETP deficiency is thought to be a state of impaired reverse cholesterol transport, which may possibly lead to the development of atherosclerotic cardiovascular disease despite high HDL-cholesterol (HDL-C) levels. Thus, it is important to investigate whether HALP is caused by CETP deficiency. In the present study, we identified two novel missense mutations in the CETP gene among 196 subjects with a marked HALP (HDL-C > or = 2.59 mmol/l = 100 mg/dl). The two missense mutations, L151P (CTC-->CCC in exon 5) and R282C (CGC-->TGC in exon 9), were found in compound heterozygous subjects with D442G mutation, whose plasma CETP levels were significantly lower when compared with those in D442G heterozygous subjects. In COS-7 cells expressing the wild type and mutant CETP, these two mutant CETP showed a marked reduction in the secretion of CETP protein into media (0% and 39% of wild type for L151P and R282C, respectively). These results suggested that two novel missense mutations cause the decreased secretion of CETP protein into circulation leading to HALP. By using the Invader assay for seven mutations, including two novel mutations of the CETP gene, we investigated their frequency among 466 unrelated subjects with HALP (HDL-C > or = 2.07 mmol/l = 80 mg/dl). Two novel mutations were rare, but L151P mutation was found in unrelated subjects with a marked HALP. Furthermore, we demonstrated that CETP deficiency contributes to 61.7% and 31.4% of marked HALP and moderate HALP in the Japanese, respectively.

Expression of cholesteryl ester transfer protein in human atherosclerotic lesions and its implication in reverse cholesterol transport

Reverse cholesterol transport (RCT) is the major protective system against atherosclerosis. In this system, cholesteryl ester transfer protein (CETP) is known to facilitate the transfer of neutral lipids between lipoproteins in plasma. We reported the pathophysiological significance of CETP by clinical studies with genetic CETP deficiency, showing that this protein plays a crucial role in the RCT system. However, information about the expression of this protein in the initial step of RCT, macrophages (Mphi) in the blood vessels, is still very limited. In the present study, we have performed immunohistochemical analyses on the expression of CETP in human atherosclerotic lesions. The immunoreactive mass of CETP was abundantly detected in foam cells in human aortic and coronary atherosclerotic lesions, but not in the normal arterial wall. A double immunostaining showed that the majority of CETP-positive foam cells were derived from Mphi and a minor population appeared to derive from smooth muscle cells. Transient transfection of CETP cDNA into COS-7 cells showed that high density lipoprotein (HDL)-mediated efflux of free cholesterol from the cells expressing CETP was much higher than that from mock-transfected cells, while uptake of HDL-lipids was not affected in cells transfected with CETP cDNA. Efflux of free cholesterol from the Mphi obtained from CETP deficiency was significantly decreased compared with that from normal subjects. These data indicate that CETP is expressed in Mphi in the atherosclerotic lesions and may possess an anti-atherogenic function to remove cholesterol from the cells, suggesting another role of CETP at the initial step of RCT.

Point mutation (-69 G-->A) in the promoter region of cholesteryl ester transfer protein gene in Japanese hyperalphalipoproteinemic subjects

Cholesteryl ester transfer protein (CETP) transfers cholesteryl ester (CE) from HDL to apolipoprotein (apo) B-containing lipoproteins and plays a crucial role in reverse cholesterol transport, which is a major protective system against atherosclerosis. Genetic CETP deficiency is the most common cause of a marked hyperalphalipoproteinemia (HALP) in the Japanese, and various mutations have been identified in the coding region as well as in the exon/intron boundaries in the CETP gene. In the present study, we identified a novel mutation in the promoter region of the CETP gene. This mutation was a G-to-A substitution at the -69 nucleotide of the promoter region (-69 G-->A), corresponding to the second nucleotide of the PEA3/ETS binding site (CGGAA) located upstream of the putative TATA box. Four (2.0%) of 196 unrelated subjects with a marked HALP (HDL cholesterol >/=2.59 mmol/L=100 mg/dL) were revealed to be heterozygous for the -69 G-->A mutation, and the allelic frequency of the mutant was 0.0102 in the subjects with a marked HALP. The subjects with the -69 G-->A mutation had low plasma CETP levels. Reporter gene assay showed that this mutation markedly reduced the transcriptional activities in HepG2 cells (8% of wild type). These results suggested that this mutation would be dominant negative. In conclusion, a novel -69 G-->A mutation in the CETP gene causes the decreased transcriptional activity leading to HALP.

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.

Particle size analysis of high density lipoproteins in patients with genetic cholesteryl ester transfer protein deficiency

We investigated the detailed distribution of high-density lipoproteins (HDL) particle size in patients with cholesteryl ester transfer protein (CETP) deficiency. Serum samples pre-stained with Sudan black B were electrophoresed using 4-30% polyacrylamide gradient gels, and the Stokes diameter of HDL particles was determined in 23 patients with genetic CETP deficiency, nine patients with hyperalphalipoproteinemia and seven subjects with normal HDL cholesterol concentrations. The mean Stokes diameter of HDL particles in CETP deficient patients (11.2+/-0.6 nm) was significantly greater than hyperalphalipoproteinemia (10.7+/-0.3 nm, P<0.05) and normal subjects (9.5+/-0.4 nm, P<0.01). A significant relationship was found between mean HDL size and serum CETP mass concentrations (P<0.05). When the particle size of all detected HDL bands was investigated, extra-large HDL particles larger than 12 nm were found in 14 of the 23 patients with CETP deficiency, which were not found in any of the hyperalphalipoproteinemia patients or normal subjects. Serum low-density lipoproteins (LDL) cholesterol and total cholesterol concentrations were lower in CETP deficiencies with extra-large HDL particles than those in non-carriers (P<0.01). These results indicate that extra-large HDL may be an index to clarify the relationship between genetic CETP deficiency and atherosclerosis.

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.

Expression of human scavenger receptor class B type I in cultured human monocyte-derived macrophages and atherosclerotic lesions

The scavenger receptor class B type I (SR-BI) and its human homologue CLA-1 (CD36 and LIMPII Analogous-1) have recently been identified to bind HDL and mediate the selective uptake of HDL lipids. Tissue distribution of both murine and human receptors is quite similar, in that they are expressed abundantly in liver and steroidogenic tissues. However, expression and function of the human SR-BI (hSR-BI), in the periphery of reverse cholesterol transport such as macrophages, are still unclear. In the present study, we have raised two different kinds of anti-hSR-BI polypeptide antibodies (Abs): one against the extracellular domain and the other against the intracellular domain. We have investigated the expression of hSR-BI mRNA and immunoreactive mass in freshly isolated cultured human monocyte-derived macrophages (hMphi) and in atherosclerotic lesions. Contrary to the earlier report, hSR-BI mRNA was expressed in cultured hMphi and markedly upregulated with differentiation, determined by Northern blot and reverse transcriptase-based polymerase chain reaction analyses. The mRNA expression pattern during differentiation of hMphi was very similar to those of SR class A and another member of SR class B, CD36. Protein expression was confirmed by Western blot analyses with the above Abs to show a major 83-kDa band. Modified lipoproteins such as oxidized LDL and acetylated LDL induced a 5-fold increase in mRNA and protein expression of hSR-BI. Confocal immunofluorescence microscopy demonstrated that hSR-BI immunoreactive mass was detectable as a heterogeneous, punctate staining pattern. Furthermore, immunohistochemical analysis showed that immunoreactive mass of hSR-BI was detected in foam cells in human aortic atherosclerotic lesions and that there was no significant difference of staining patterns between the two Abs. This study clearly demonstrates that hSR-BI is expressed in the lipid-laden macrophages in human atherosclerotic lesions, suggesting that it is very important to know its function and regulation in hMphi to understand the biological utility of this molecule.

Upregulated synthesis of both apolipoprotein A-I and apolipoprotein B in familial hyperalphalipoproteinemia and hyperbetalipoproteinemia

A family was identified with vertical transmission through three generations with simultaneous increases of apolipoprotein A-I (apoA-I), apolipoprotein B (apoB), low-density lipoprotein (LDL)-cholesterol, and high-density lipoprotein (HDL)-cholesterol, which we have designated familial hyperalphalipoproteinemia and hyperbetalipoproteinemia (HA/HBL). Affected patients develop xanthomas and coronary artery disease (CAD). HA/HBL apoA-I and LDL-apoB were isolated and characterized. The in vivo kinetics of radiolabeled apoA-I and LDL-apoB were evaluated in two HA/HBL probands and three controls. Structural and metabolic characterization showed normal apoA-I and LDL-apoB. The kinetics of metabolism of HA/HBL apoA-I in the HA/HBL subjects showed that elevated apoA-I levels were solely due to an increased synthesis rate (15.2 to 17.6 mg/kg/d v 11.1 to 11.4 mg/kg/d) with a normal apoA-I residence time in plasma (4.2 to 5.4 days v 5.1 to 5.3 days). The elevation of LDL-apoB levels resulted from both an increased synthetic rate (16.6 to 22.9 mg/kg/d v 12.3 to 13.8 mg/kg/d) and a prolonged residence time (3.3 to 3.8 days v 1.4 to 1.9 days). In addition, we evaluated another HA/HBL proband of an unrelated family with HA/HBL to confirm the kinetic data. LDL-receptor binding studies of HA/HBL fibroblasts showed normal binding, uptake, and degradation of LDL isolated from a normolipemic control. The serum concentration of the cholesterol ester transfer protein (CETP) was normal in the studied probands. An apoB 3500 and apoB 3531 mutant, respectively, was ruled out by polymerase chain reaction (PCR). In conclusion, the site of the molecular defect in HA/HBL subjects may be involved in the coordinate regulation of metabolism for both LDL and HDL.

Antiatherogenic effects of a novel lipoprotein lipase-enhancing agent in cholesterol-fed New Zealand white rabbits

Following our report that administration of 4-diethoxyphosphorylmethyl-N-(4-bromo-2-cyanophenyl) benzamide (NO-1886) to rats elevated postheparin lipoprotein lipase (LPL) activity through an increase in the enzyme mass, we now investigate antiatherogenic effects of NO-1886 in cholesterol-fed New Zealand White rabbits. For 20 weeks, four groups of male rabbits received regular rabbit chow (the normal control), 0.25% cholesterol-containing chow (the control), and cholesterol chow supplemented with 0.5% and 1.0% NO-1886, respectively. Postheparin LPL activity at week 10 was raised by 30% in 0.5% of the NO-1886 group and 40% in 1.0% of the NO-1886 group compared with those in the control. The area under the curve of plasma cholesterol level was not different in three cholesterol-fed groups whereas the area under the curve of HDL cholesterol was approximately twofold greater in the two NO-1886 groups than in the control, and the area under the curve of plasma triglyceride was reduced to the level of the normal control. LPL activity was correlated with HDL cholesterol (r = .764, n = 18) and triglyceride (r = -.627, n = 18). Relative atheromatous area, aortic cholesterol, and triglyceride contents were reduced to approximately 25%, 60%, and 55%, respectively, of the control values by NO-1886 ingestion. Multiple regression analysis of LPL, HDL cholesterol, and triglyceride indicated that HDL cholesterol was the most powerful protector against aortic cholesterol accumulation, and triglyceride was the one to protect against the atheromatous area. We concluded that NO-1886 prevented the development of atherosclerosis through increasing LPL activity with a consequent increase in HDL cholesterol and a decrease in triglyceride without a significant influence of plasma cholesterol level.

Beneficial effects of alcohol withdrawal on LDL particle size distribution and oxidative susceptibility in subjects with alcohol-induced hypertriglyceridemia

LDL subclass pattern B, reported to have a higher prevalence in hypertriglyceridemics (HTGs), is considered to be associated with an increased risk for coronary artery disease, and the small dense LDL characteristic of this pattern is susceptible to oxidative modification. Alcohol is considered one of the most frequent causes of increases in plasma triglyceride (TG) levels. We investigated the effects of alcohol withdrawal on LDL subclass distribution and oxidizability in drinkers with different plasma TG levels. Thirty-seven male subjects with relatively heavy alcohol-consumption habits were divided into four groups; normotriglyceridemic (NTG)/withdrawal (n = 11), NTG/control (n = 8), hypertriglyceridemic (HTG)/withdrawal (n = 10), and HTG/control (n = 8). Both withdrawal groups abstained form alcohol for 4 weeks, while the control subjects maintained their usual intake of alcohol. Peak LDL particle diameter (PPD) was smaller in the combined HTG groups than in the combined NTG groups before abstinence, although PPD increased significantly (P < .01) from 25.5 to 26.1 nm in the HTG/withdrawal group. Before abstinence, lag times preceding LDL oxidation in the combined HTG groups were shorter than in the combined NTG groups; after withdrawal, lag time was prolonged significantly (P < .01) from 49.9 to 57.3 minutes in the HTG-withdrawal group. No significant changes in PPD and lag time were observed in the other three groups. Significant correlations (P < .05) were observed between the change (delta) in the lag time and delta TG and between delta lag time and delta PPD. We conclude that in alcohol-induced HTG subjects, alcohol withdrawal has beneficial effects on the LDL profile by shifting the particle size from smaller to larger and decreasing its susceptibility to oxidation.

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.

The novel compound NO-1886 elevates plasma high-density lipoprotein cholesterol levels in hamsters and rabbits by increasing lipoprotein lipase without any effect on cholesteryl ester transfer protein activity

Lipoprotein lipase (LPL) and cholesteryl ester transfer protein (CETP) are determinants of high-density lipoprotein (HDL) cholesterol concentrations in plasma. We have previously reported that NO-1886, by increasing LPL activity, causes elevation of HDL cholesterol levels in rats. In the present study, we studied the effect of NO-1886 on CETP activity in experimental animals. Since previous reports suggest that rats may lack CETP, we examined hamsters and rabbits, as well as rats. We found that NO-1886 increased LPL activity, resulting in elevation of plasma HDL cholesterol in all three animals. We confirmed that rats lack CETP and that both hamsters and rabbits have high CETP activity. NO-1886 had no effect on CETP activity in hamsters and rabbits. These results demonstrate that the compound NO-1886 elevates HDL cholesterol in experimental animals by selectively increasing LPL activity without any effect on CETP. Animals with low CETP and high LPL activities appear to be more sensitive to NO-1886 than those with high CETP and low LPL activities.

LDL particle size in subjects with previously unsuspected coronary heart disease: relationship with other cardiovascular risk markers

Low density lipoprotein (LDL) particle diameters were determined by non-denaturing gradient gel electrophoresis in 53 subjects with previously unrecognised coronary heart disease (CHD) and 167 control subjects matched by age, sex and total plasma cholesterol. The mean diameter of the major LDL peak was found not to be significantly different between the two groups, but the CHD subjects were found to have a broader distribution of the predominant LDL species ((25.0 (24.7-25.3)nm versus 24.8 (24.7-24.9)nm)) (median (25-75%)), a greater proportion of larger particles (chi 2 = 19.8, P < 0.001) and to be more likely to have multiple numbers of LDL species than the control subjects (chi 2 = 22.7, P < 0.001). A negative correlation was found between the diameter of the predominant LDL species and fasting plasma triglyceride (r = -0.21, P = 0.0015), waist to hip ratio (WHR) (r = -0.15, P = 0.026) and body mass index (BMI) (r = -0.20, P = 0.002), and in a subgroup of subjects (n = 106), postprandial analysis revealed a negative correlation with the incremental postprandial response of plasma insulin (r = -0.19, P = 0.025). Male subjects had a significantly smaller diameter of the major LDL peak (24.8 +/- 0.0 nm) than female subjects (25.0 +/- 0.0 nm, P < 0.001). The present study failed to confirm an association between small LDL particles and the presence of coronary heart disease but did demonstrate more LDL heterogeneity in those with CHD. In addition, significant relationships were evident between the diameter of the major LDL peak and a number of other risk factors for coronary disease.