Loss of Hepatic Leucine-Rich Repeat-Containing G-Protein Coupled Receptors 4 and 5 Promotes Nonalcoholic Fatty Liver Disease.

The roof plate-specific spondin-leucine-rich repeat-containing G-protein coupled receptor 4/5 (LGR4/5)-zinc and ring finger 3 (ZNRF3)/ring finger protein 43 (RNF43) module is a master regulator of hepatic Wnt/ß-catenin signaling and metabolic zonation. However, its impact on nonalcoholic fatty liver disease (NAFLD) remains unclear. The current study investigated whether hepatic epithelial cell-specific loss of the Wnt/ß-catenin modulator Lgr4/5 promoted NAFLD. The 3- and 6-month-old mice with hepatic epithelial cell-specific deletion of both receptors Lgr4/5 (Lgr4/5dLKO) were compared with control mice fed with normal diet (ND) or high-fat diet (HFD). Six-month-old HFD-fed Lgr4/5dLKO mice developed hepatic steatosis and fibrosis but the control mice did not. Serum cholesterol-high-density lipoprotein and total cholesterol levels in 3- and 6-month-old HFD-fed Lgr4/5dLKO mice were decreased compared with those in control mice. An ex vivo primary hepatocyte culture assay and a comprehensive bile acid (BA) characterization in liver, plasma, bile, and feces demonstrated that ND-fed Lgr4/5dLKO mice had impaired BA secretion, predisposing them to develop cholestatic characteristics. Lipidome and RNA-sequencing analyses demonstrated severe alterations in several lipid species and pathways controlling lipid metabolism in the livers of Lgr4/5dLKO mice. In conclusion, loss of hepatic Wnt/ß-catenin activity by Lgr4/5 deletion led to loss of BA secretion, cholestatic features, altered lipid homeostasis, and deregulation of lipoprotein pathways. Both BA and intrinsic lipid alterations contributed to the onset of NAFLD.

Synthetic phospholipids as specific substrates for plasma endothelial lipase.

We designed and prepared synthetic phospholipids that generate lyso-phosphatidylcholine products with a unique mass for convenient detection by LC-MS in complex biological matrices. We demonstrated that compound 4, formulated either as a Triton X-100 emulsion or incorporated in synthetic HDL particles can serve as a substrate for plasma EL with useful specificity.

Harnessing RNA Interference for Cholesterol Lowering: The Bench-to-Bedside Story of Inclisiran.

Lowering low-density lipoprotein cholesterol (LDL-C) is a cornerstone of reducing risk for atherosclerotic cardiovascular disease. Despite the approval of nonstatin therapies for LDL-C lowering over the past 2 decades, these medications are underused, and most patients are still not at guideline-recommended LDL-C goals. Barriers include poor adherence, clinical inertia, concern for side effects, cost, and complex prior authorization processes. With atherosclerotic cardiovascular disease-related mortality increasing globally, there remains a need for additional therapeutic options for lowering LDL-C as part of an atherosclerotic cardiovascular disease prevention strategy. Following the identification of PCSK9 (proprotein convertase subtilisin/kexin type 9) as a promising therapeutic target, inclisiran was developed using the natural process of RNA interference for robust, sustained prevention of hepatic PCSK9 synthesis. Twice-yearly maintenance subcutaneous inclisiran (following initial loading doses at Day 1 and Day 90) reduces circulating LDL-C levels by ≈50% versus placebo when added to maximally tolerated statins. Long-term safety and tolerability of inclisiran have been assessed, with studies underway to evaluate the effects of inclisiran on cardiovascular outcomes and to provide additional safety and effectiveness data. In 2021, <20 years after the discovery of PCSK9, inclisiran became the first RNA interference therapeutic approved in the United States for LDL-C lowering in patients with established atherosclerotic cardiovascular disease or familial hypercholesterolemia and has since been approved for use in patients with primary hyperlipidemia. This article reviews the journey of inclisiran from bench to bedside, including early development, the clinical trial program, key characteristics of inclisiran, and practical points for its use in the clinic.

Effects of CETP inhibition on triglyceride-rich lipoprotein composition and apoB-48 metabolism.

Cholesteryl ester transfer protein (CETP) facilitates the transfer of HDL cholesteryl ester to triglyceride-rich lipoproteins (TRL). This study aimed to determine the effects of CETP inhibition with torcetrapib on TRL composition and apoB-48 metabolism. Study subjects with low HDL cholesterol (<40 mg/dl), either untreated (n = 9) or receiving atorvastatin 20 mg daily (n = 9), received placebo for 4 weeks, followed by torcetrapib 120 mg once daily for the next 4 weeks. A subset of the subjects not treated with atorvastatin participated in a third phase (n = 6), in which they received torcetrapib 120 mg twice daily for an additional 4 weeks. At the end of each phase, all subjects received a primed-constant infusion of [5,5,5-(2)H(3)]L-leucine, while in the constantly fed state, to determine the kinetics of TRL apoB-48 and TRL composition. Relative to placebo, torcetrapib markedly reduced TRL CE levels in all groups (≥-69%; P < 0.005). ApoB-48 pool size (PS) and production rate (PR) decreased in the nonatorvastatin once daily (PS: -49%, P = 0.007; PR: -49%, P = 0.005) and twice daily (PS: -30%, P = 0.01; PR: -27%, P = 0.13) cohorts. In the atorvastatin cohort, apoB-48 PS and PR, which were already lowered by atorvastatin, did not change with torcetrapib. Our findings indicate that CETP inhibition reduced plasma apoB-48 concentrations by reducing apoB-48 production but did not have this effect in subjects already treated with atorvastatin.

Identification of a PCSK9-LDLR disruptor peptide with in vivo function.

Proprotein convertase subtilisin/kexin type 9 (PCSK9) regulates plasma low-density lipoprotein cholesterol (LDL-C) levels by promoting hepatic LDL receptor (LDLR) degradation. Therapeutic antibodies that disrupt PCSK9-LDLR binding reduce LDL-C concentrations and cardiovascular disease risk. The epidermal growth factor precursor homology domain A (EGF-A) of the LDLR serves as a primary contact with PCSK9 via a flat interface, presenting a challenge for identifying small molecule PCSK9-LDLR disruptors. We employ an affinity-based screen of 1013in vitro-translated macrocyclic peptides to identify high-affinity PCSK9 ligands that utilize a unique, induced-fit pocket and partially disrupt the PCSK9-LDLR interaction. Structure-based design led to molecules with enhanced function and pharmacokinetic properties (e.g., 13PCSK9i). In mice, 13PCSK9i reduces plasma cholesterol levels and increases hepatic LDLR density in a dose-dependent manner. 13PCSK9i functions by a unique, allosteric mechanism and is the smallest molecule identified to date with in vivo PCSK9-LDLR disruptor function.

Common genetic variation in multiple metabolic pathways influences susceptibility to low HDL-cholesterol and coronary heart disease.

A low level of HDL-C is the most common plasma lipid abnormality observed in men with established coronary heart disease (CHD). To identify allelic variants associated with susceptibility to low HDL-C and CHD, we examined 60 candidate genes with key roles in HDL metabolism, insulin resistance, and inflammation using samples from the Veterans Affairs HDL Intervention Trial (VA-HIT; cases, n = 699) and the Framingham Offspring Study (FOS; controls, n = 705). VA-HIT was designed to examine the benefits of HDL-raising with gemfibrozil in men with low HDL-C (≤40 mg/dl) and established CHD. After adjustment for multiple testing within each gene, single-nucleotide polymorphisms (SNP) significantly associated with case status were identified in the genes encoding LIPC (rs4775065, P < 0.0001); CETP (rs5882, P = 0.0002); RXRA (rs11185660, P = 0.0021); ABCA1 (rs2249891, P = 0.0126); ABCC6 (rs150468, P = 0.0206; rs212077, P = 0.0443); CUBN (rs7893395, P = 0.0246); APOA2 (rs3813627, P = 0.0324); SELP (rs732314, P = 0.0376); and APOC4 (rs10413089, P = 0.0425). Included among the novel findings of this study are the identification of susceptibility alleles for low HDL-C/CHD risk in the genes encoding CUBN and RXRA, and the observation that genetic variation in SELP may influence CHD risk through its effects on HDL.

Effects of cholesteryl ester transfer protein inhibition on apolipoprotein A-II-containing HDL subspecies and apolipoprotein A-II metabolism.

This study was designed to establish the mechanism responsible for the increased apolipoprotein (apo) A-II levels caused by the cholesteryl ester transfer protein inhibitor torcetrapib. Nineteen subjects with low HDL cholesterol (<40 mg/dl), nine of whom were also treated with 20 mg of atorvastatin daily, received placebo for 4 weeks, followed by 120 mg of torcetrapib daily for the next 4 weeks. Six subjects in the nonatorvastatin cohort participated in a third phase, in which they received 120 mg of torcetrapib twice daily for 4 weeks. At the end of each phase, subjects underwent a primed-constant infusion of [5,5,5-(2)H(3)]L-leucine to determine the kinetics of HDL apoA-II. Relative to placebo, torcetrapib significantly increased apoA-II concentrations by reducing HDL apoA-II catabolism in the atorvastatin (-9.4%, P < 0.003) and nonatorvastatin once- (-9.9%, P = 0.02) and twice- (-13.2%, P = 0.02) daily cohorts. Torcetrapib significantly increased the amount of apoA-II in the alpha-2-migrating subpopulation of HDL when given as monotherapy (27%, P < 0.02; 57%, P < 0.003) or on a background of atorvastatin (28%, P < 0.01). In contrast, torcetrapib reduced concentrations of apoA-II in alpha-3-migrating HDL, with mean reductions of -14% (P = 0.23), -18% (P < 0.02), and -18% (P < 0.01) noted during the atorvastatin and nonatorvastatin 120 mg once- and twice-daily phases, respectively. Our findings indicate that CETP inhibition increases plasma concentrations of apoA-II by delaying HDL apoA-II catabolism and significantly alters the remodeling of apoA-II-containing HDL subpopulations.

Effects of an inhibitor of cholesteryl ester transfer protein on HDL cholesterol.

BACKGROUND: Decreased high-density lipoprotein (HDL) cholesterol levels constitute a major risk factor for coronary heart disease; however, there are no therapies that substantially raise HDL cholesterol levels. Inhibition of cholesteryl ester transfer protein (CETP) has been proposed as a strategy to raise HDL cholesterol levels. METHODS: We conducted a single-blind, placebo-controlled study to examine the effects of torcetrapib, a potent inhibitor of CETP, on plasma lipoprotein levels in 19 subjects with low levels of HDL cholesterol (<40 mg per deciliter [1.0 mmol per liter]), 9 of whom were also treated with 20 mg of atorvastatin daily. All the subjects received placebo for four weeks and then received 120 mg of torcetrapib daily for the following four weeks. Six of the subjects who did not receive atorvastatin also participated in a third phase, in which they received 120 mg of torcetrapib twice daily for four weeks. RESULTS: Treatment with 120 mg of torcetrapib daily increased plasma concentrations of HDL cholesterol by 61 percent (P<0.001) and 46 percent (P=0.001) in the atorvastatin and non-atorvastatin cohorts, respectively, and treatment with 120 mg twice daily increased HDL cholesterol by 106 percent (P<0.001). Torcetrapib also reduced low-density lipoprotein (LDL) cholesterol levels by 17 percent in the atorvastatin cohort (P=0.02). Finally, torcetrapib significantly altered the distribution of cholesterol among HDL and LDL subclasses, resulting in increases in the mean particle size of HDL and LDL in each cohort. CONCLUSIONS: In subjects with low HDL cholesterol levels, CETP inhibition with torcetrapib markedly increased HDL cholesterol levels and also decreased LDL cholesterol levels, both when administered as monotherapy and when administered in combination with a statin.

Effects of the cholesteryl ester transfer protein inhibitor torcetrapib on apolipoprotein B100 metabolism in humans.

OBJECTIVE: Cholesteryl ester transfer protein (CETP) inhibition with torcetrapib not only increases high-density lipoprotein cholesterol levels but also significantly reduces plasma triglyceride, low-density lipoprotein (LDL) cholesterol, and apolipoprotein B (apoB) levels. The goal of the present study was to define the kinetic mechanism(s) by which CETP inhibition reduces levels of apoB-containing lipoproteins. METHODS AND RESULTS: Nineteen subjects, 9 of whom were pretreated with 20 mg atorvastatin, received placebo for 4 weeks, followed by 120 mg torcetrapib once daily for 4 weeks. Six subjects in the nonatorvastatin group received 120 mg torcetrapib twice daily for an additional 4 weeks. After each phase, subjects underwent a primed-constant infusion of deuterated leucine to endogenously label newly synthesized apoB to determine very low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL) and LDL apoB100 production, and fractional catabolic rates (FCRs). Once-daily 120 mg torcetrapib significantly reduced VLDL, IDL, and LDL apoB100 pool sizes by enhancing the FCR of apoB100 within each fraction. On a background of atorvastatin, 120 mg torcetrapib significantly reduced VLDL, IDL, and LDL apoB100 pool sizes. The reduction in VLDL apoB100 was associated with an enhanced apoB100 FCR, whereas the decreases in IDL and LDL apoB100 were associated with reduced apoB100 production. CONCLUSIONS: These data indicate that when used alone, torcetrapib reduces VLDL, IDL, and LDL apoB100 levels primarily by increasing the rate of apoB100 clearance. In contrast, when added to atorvastatin treatment, torcetrapib reduces apoB100 levels mainly by enhancing VLDL apoB100 clearance and reducing production of IDL and LDL apoB100.

Discovery of a Novel Piperidine-Based Inhibitor of Cholesteryl Ester Transfer Protein (CETP) That Retains Activity in Hypertriglyceridemic Plasma.

Herein we describe the discovery and characterization of a novel, piperidine-based inhibitor of cholesteryl ester transfer protein (CETP) with a core structure distinct from other reported CETP inhibitors. A versatile synthesis starting from 4-methoxypyridine enabled an efficient exploration of the SAR, giving a lead molecule with potent CETP inhibition in human plasma. The subsequent optimization focused on improvement of pharmacokinetics and mitigation of off-target liabilities, such as CYP inhibition, whose improvement correlated with increased lipophilic efficiency. The effort led to the identification of an achiral, carboxylic acid-bearing compound 16 (TAP311) with excellent pharmacokinetics in rats and robust efficacy in hamsters. Compared to anacetrapib, the compound showed substantially reduced lipophilicity, had only modest distribution into adipose tissue, and retained potency in hypertriglyceridemic plasma in vitro and in vivo. Furthermore, in contrast to torcetrapib, the compound did not increase aldosterone secretion in human adrenocortical carcinoma cells nor in chronically cannulated rats. On the basis of its preclinical efficacy and safety profile, the compound was advanced into clinical trials.

The L162V polymorphism at the peroxisome proliferator activated receptor alpha locus modulates the risk of cardiovascular events associated with insulin resistance and diabetes mellitus: the Veterans Affairs HDL Intervention Trial (VA-HIT).

BACKGROUND: The Veterans Affairs HDL Intervention Trial (VA-HIT) showed that gemfibrozil, which activates peroxisome proliferator-activator receptor alpha (PPARalpha), significantly reduced the risk of cardiovascular (CV) events in men with low HDL cholesterol (< 40 mg/dl) and established coronary heart disease. Treatment was particularly beneficial in those with insulin resistance (IR) or diabetes mellitus (DM). We hypothesized that the association between a functional polymorphism at the PPARA locus (L162V) and the risk of a CV event, as well as response to fibrate therapy, might be greatest in those with either IR or DM (DM/IR) in VA-HIT. METHODS AND RESULTS: A total of 827 men (placebo, n = 413; gemfibrozil, n = 414) from the VA-HIT were genotyped. This population included a high proportion of subjects with DM/IR. In VA-HIT, the PPARA V162 allele was associated with reduced levels of HDL cholesterol and the presence of DM/IR at baseline. It was also associated with reduced risk of CV events in those with DM/IR but not in those with neither (DM/IR *PPARA genotype, P = 0.005). Among subjects with DM/IR, treatment with gemfibrozil reduced CV events in non-carriers from 29.9 to 17.8% and carriers of the V162 allele from 14.7 to 4.8%. In contrast, carriers of the V162 allele with no DM/IR who were treated with gemfibrozil experienced significantly more CV events than did those who received placebo (20.6% versus 13.6%; P = 0.01). CONCLUSIONS: The effect of the L162V polymorphism at the PPARA locus on CV risk depends on the presence of DM/IR. Among subjects treated with gemfibrozil, the V162 allele was associated not only with reduced CV risk in subjects with DM/IR, but also with significantly increased CV risk in the absence of these traits, identifying this genetic variant as a potential marker for predicting which subjects may have a favorable response to fibrate therapy.

Effects of cholesteryl ester transfer protein inhibition on high-density lipoprotein subspecies, apolipoprotein A-I metabolism, and fecal sterol excretion.

OBJECTIVE: Pharmacological inhibition of the cholesteryl ester transfer protein (CETP) in humans increases high-density lipoprotein (HDL) cholesterol (HDL-C) levels; however, its effects on apolipoprotein A-I (apoA-I) containing HDL subspecies, apoA-I turnover, and markers of reverse cholesterol transport are unknown. The present study was designed to address these issues. METHODS AND RESULTS: Nineteen subjects, 9 of whom were taking 20 mg of atorvastatin for hypercholesterolemia, received placebo for 4 weeks, followed by the CETP inhibitor torcetrapib (120 mg QD) for 4 weeks. In 6 subjects from the nonatorvastatin cohort, the everyday regimen was followed by a 4-week period of torcetrapib (120 mg BID). At the end of each phase, subjects underwent a primed-constant infusion of (5,5,5-2H3)-L-leucine to determine the kinetics of HDL apoA-I. The lipid data in this study have been reported previously. Relative to placebo, 120 mg daily torcetrapib increased the amount of apoA-I in alpha1-migrating HDL in the atorvastatin (136%; P<0.001) and nonatorvastatin (153%; P<0.01) cohorts, whereas an increase of 382% (P<0.01) was observed in the 120 mg twice daily group. HDL apoA-I pool size increased by 8+/-15% in the atorvastatin cohort (P=0.16) and by 16+/-7% (P<0.0001) and 34+/-8% (P<0.0001) in the nonatorvastatin 120 mg QD and BID cohorts, respectively. These changes were attributable to reductions in HDL apoA-I fractional catabolic rate (FCR), with torcetrapib reducing HDL apoA-I FCR by 7% (P=0.10) in the atorvastatin cohort, by 8% (P<0.001) in the nonatorvastatin 120 mg QD cohort, and by 21% (P<0.01) in the nonatorvastatin 120 mg BID cohort. Torcetrapib did not affect HDL apoA-I production rate. In addition, torcetrapib did not significantly change serum markers of cholesterol or bile acid synthesis or fecal sterol excretion. CONCLUSIONS: These data indicate that partial inhibition of CETP via torcetrapib in patients with low HDL-C: (1) normalizes apoA-I levels within alpha1-migrating HDL, (2) increases plasma concentrations of HDL apoA-I by delaying apoA-I catabolism, and (3) does not significantly influence fecal sterol excretion.

Emerging role of high-density lipoprotein in the prevention of cardiovascular disease.

In major statin trials, the relative risk reduction is typically in the range 25-35%, thus indicating that the majority of cardiac events continues to occur despite statin therapy. Hence, there is a considerable interest in identifying novel therapies capable of further reducing cardiovascular disease risk. One such potential therapeutic target is a low level of high-density lipoprotein (HDL) cholesterol. Emerging targets involved in HDL metabolism are: (i) liver X receptor and peroxisome proliferator-activated receptor agonists; (ii) cholesteryl ester transfer protein inhibitors; (iii) HDL mimetics (ETC-216); (iv) apolipoprotein A-I synthetic peptides; and (v) HDL delipidation and reinfusion. Although they are at various stages of development, each of these therapies has promise for the treatment of cardiovascular disease in humans.

A promoter polymorphism in cholesterol 7alpha-hydroxylase interacts with apolipoprotein E genotype in the LDL-lowering response to atorvastatin.

Bile-acid biosynthesis is a key determinant of intracellular cholesterol and, in turn, cholesterol synthesis rate in hepatocytes. This suggests that variation in the cholesterol 7alpha-hydroxylase gene (CYP7A1), a key enzyme in bile-acid biosynthesis, may influence the statin response. To test this hypothesis, a promoter polymorphism (A-204C) in CYP7A1 was examined in 324 hypercholesterolemic patients treated with atorvastatin 10mg. The variant C allele was significantly and independently associated with poor LDL cholesterol reductions; -39% in wild type allele homozygotes, -37% in variant allele heterozygotes, and -34% in variant allele homozygotes (p<0.0001 for trend). Differences were more striking in men, and were enhanced by the coexistence of common variants of apolipoprotein E gene (APOE), epsilon2 or epsilon4. In subjects having wild type alleles at both loci, the mean reduction in LDL cholesterol was -40%, while the value in subjects having two CYP7A1 variant alleles and at least one variant APOE allele was -31% (p<0.0001). Combination analysis of these two loci more accurately predicted the achievement of goal LDL cholesterol, than did both single locus analysis. We concluded that the CYP7A1 A-204C promoter variant was associated with poor response to atorvastatin, which were additively enhanced by common variants in another locus, APOE.

Gender-specific effects of estrogen receptor alpha gene haplotype on high-density lipoprotein cholesterol response to atorvastatin: interaction with apolipoprotein AI gene polymorphism.

Statins can modestly raise the levels of HDL cholesterol and apolipoprotein A-I (APOA1). Recently, associations between polymorphisms in the estrogen receptor alpha (ESR1) and the HDL cholesterol response to hormone replacement therapy were reported. To test the hypothesis that common polymorphisms in ESR1 and APOA1 genes are associated with the response to statin therapy, two ESR1 (PvuII and XbaI) and two APOA1 (G-75A and +83) polymorphisms were examined in 338 hypercholesterolemic patients treated with atorvastatin 10mg. The ESR1 PvuII-XbaI+ haplotype was significantly, and independently, associated with a greater response of HDL raising in women (+13% versus +7%, p=0.010) but not in men (+9% versus +7%, p=0.248). Effects of the APOA1+83 variant allele on HDL cholesterol response also differed significantly by gender (p=0.012). The APOA1+83 variant allele was associated with higher basal LDL cholesterol levels in men as well, but not in women. Finally, significant interactions were observed between the ESR1 PvuII-XbaI+ haplotype and the APOA1+83 variant allele regarding both HDL (p=0.042) and LDL (p=0.031) cholesterol responses. In conclusion, the ESR1 haplotype was associated with a greater HDL-raising to atorvastatin in a gender-specific manner, and the interactions between ESR1 and APOA1 genotypes regarding HDL and LDL cholesterol response were also gender specific.

Cholesteryl ester transfer protein TaqI B2B2 genotype is associated with higher HDL cholesterol levels and lower risk of coronary heart disease end points in men with HDL deficiency: Veterans Affairs HDL Cholesterol Intervention Trial.

OBJECTIVE: We have previously reported that genetic variation at the cholesteryl ester transfer protein (CETP) TaqIB locus is correlated with plasma lipid levels and coronary heart disease (CHD) risk in the Framingham Offspring Study (FOS). In FOS, the B2 allele was associated with increased levels of high density lipoprotein (HDL) cholesterol (HDL-C), decreased CETP activity, and reduced CHD risk for men having the B2B2 genotype. The present study was undertaken to further define the relationship between this polymorphism and CHD risk at the population level. METHODS AND RESULTS: We tested for associations between the CETP TaqIB genotype and plasma lipoprotein levels, response to gemfibrozil therapy, and CHD end points in 852 men participating in the Veterans Affairs HDL-C Intervention Trial (VA-HIT), a study designed to explore the potential benefits of raising HDL levels in men having established CHD with low HDL-C (< or =40 mg/dL) as their primary lipid abnormality. In VA-HIT, 13.9% of the men had the B2B2 genotype relative to 19.1% of the men in FOS (-27%, P<0.03), whereas more men in VA-HIT had the B1B1 genotype (15%, P<0.05). Similar to our finding in FOS, B2B2 men in VA-HIT had the highest mean level of HDL-C (32.6+/-4.8 mg/dL), followed by B1B2 men (32.0+/-5.3 mg/dL), and, last, by B1B1 men (30.9+/-4.9 mg/dL). Interestingly, B1B1 men, who had the least favorable plasma lipid profile at baseline, had the greatest triglyceride-lowering response to gemfibrozil (-34%, P=0.006). CETP TaqIB genotype was also associated with the risk of CHD end points in VA-HIT, with an adjusted risk ratio of 0.52 for B2B2 men (P=0.08). CONCLUSIONS: Our data demonstrate that in men with CHD and HDL deficiency, the CETP TaqI B2B2 genotype is (1) significantly reduced and (2) associated with higher levels of plasma HDL-C and lower CHD risk. Together with our earlier report, these results support the concept that increased HDL-C levels, resulting from reduced CETP activity, are associated with decreased CHD risk.

Pharmacogenetics of HMG-CoA reductase inhibitors: exploring the potential for genotype-based individualization of coronary heart disease management.

Despite the benefit of statin therapy in the prevention of coronary heart disease, a considerable inter-individual variation exists in its response. It is well recognized that genetic variation can contribute to differences in drug disposition and, consequently, clinical efficacy at the population level. Pharmacogenetics, exploring genetic polymorphisms that influence response to drug therapy, may one day allow the clinician to customize treatment strategies for patients in order to improve the success rate of drug therapies. To date, 41 studies have investigated the relationships between common genetic variants and response to statin therapy in terms of lipid effects and clinical outcomes; 16 candidate genes involved in lipoprotein metabolism and 3 in pharmacokinetics. APOE is the most extensively studied locus, and absolute difference in LDL cholesterol reduction across genotypes remained 3-6%. Moreover, none of the associations was striking enough to justify genetic analysis in clinical practice. Reported data have suggested that larger studies (>1000 participants) or combination analyses with >2 different polymorphisms would enable us to find clinically or biologically meaningful difference, which could be assumed as >10% absolute difference, and that genes influencing cholesterol biosynthesis in the liver, such as ABCG5/G8, CYP7A1, HMGCR, would be good candidates for future studies.

Interactions between common genetic polymorphisms in ABCG5/G8 and CYP7A1 on LDL cholesterol-lowering response to atorvastatin.

Cholesterol excretion by ATP binding cassette transporters G5 and G8 (ABCG5/G8) and bile acid biosynthesis by cholesterol 7alpha-hydroxylase (CYP7A1) are major pathways for the removal of cholesterol into bile. To investigate the interactions between common polymorphisms in ABCG5/G8 and CYP7A1 and statin response, we examined the relationships between five non-synonymous polymorphisms in ABCG5/G8 (Q604E, D19H, Y54C, T400K, and A632V) and a promoter variant in CYP7A1 (A-204C) in 337 hypercholesterolemic patients treated with atorvastatin 10mg. The ABCG8 H19 allele was significantly associated with a greater LDL cholesterol reduction relative to the wild type D19 allele (39.6% versus 36.6%, P = 0.043). This difference was enhanced in non-carriers of the CYP7A1 promoter polymorphism (42.7% versus 38.2%, P = 0.048), and was diminished in accordance with the number of CYP7A1 variant alleles (1.8% in heterozygotes and 0.2% in homozygotes). Combination analysis of these polymorphisms explained a greater percentage of LDL cholesterol response variation (8.5% difference across subgroups) than did single polymorphism analysis (4.2% in CYP7A1 and 3.0% in ABCG8 D19H). The other ABCG5/G8 polymorphisms did not show any significant interactions with the CYP7A1 polymorphism. We conclude that the ABCG8 H19 and CYP7A1 C-204 alleles appear to interact in a dose-dependent manner on atorvastatin response.

ATP-binding cassette transporter A1 locus is not a major determinant of HDL-C levels in a population at high risk for coronary heart disease.

ATP-binding cassette transporter A1 (ABCA1) transports cellular cholesterol to lipid-poor apolipoproteins. Mutations in the ABCA1 gene are linked to rare phenotypes, familial hypoalphalipoproteinemia (FHA) and Tangier disease (TD), characterized by markedly decreased plasma high-density lipoprotein cholesterol (HDL-C) levels. The aim was to test if the ABCA1 locus is a major locus regulating HDL-C levels in the homogenous Finnish population with a high prevalence of coronary heart disease (CHD). Firstly, the ABCA1 locus was tested for linkage to HDL-C levels in 35 families with premature CHD and low HDL-C levels. Secondly, 62 men with low HDL-C levels and CHD were screened for the five mutations known to cause FHA. Thirdly, polymorphisms of the ABCA1 gene were tested for an association with HDL-C levels in a population sample of 515 subjects. The ABCA1 locus was not linked to HDL-C levels in the CHD families, and no carriers of the FHA mutations were found. The AA596 genotype was associated with higher HDL-C levels compared with the GG and GA genotypes in the women, but not in the men. The G596A genotypes explained 4% and the A2589G genotypes 3% of the variation in plasma HDL-C levels in women. The data suggest that the ABCA1 locus is of minor importance in the regulation of HDL-C in Finns.

In vivo metabolism of apolipoprotein E within the HDL subpopulations LpE, LpE:A-I, LpE:A-II and LpE:A-I:A-II.

High-density lipoproteins can be separated into distinct particles based on their apolipoprotein content. In the present study, the in vivo metabolism of apoE within the apoE-containing HDL particles LpE, LpE:A-I, LpE:A-II and LpE:A-I:A-II was assessed in control subjects and in patients with abetalipoproteinemia (ABL), in whom HDL are the sole plasma lipoproteins. The metabolism of apoE within these HDL subspecies was investigated in three separate studies which differed by donor or recipient status: (1) particles purified from normolipidemic plasma and reassociated with 125I or 131I-labeled apoE injected into normolipidemic subjects (study 1); (2) particles purified from ABL plasma injected into normolipidemic subjects (study 2); and (3) particles purified from ABL plasma injected into ABL subjects (study 3). The plasma residence times (RT, hours) in study 1 were 14.3+/-2.9, 11.3+/-3.4, and 9.1+/-1.2 for apoE within LpE:A-I:A-II, LpE:A-II and LpE:A-I, respectively, while those in study 2 were 10.1+/-2.2, 9.7+/-2.4, 7.9+/-1.0 and 7.3+/-0.8 for apoE within LpE:A-I:A-II, LpE:A-II, LpE:A-I and LpE, respectively. In study 3, RTs for apoE within LpE:A-I:A-II and LpE were 8.7+/-0.9 and 6.8+/-0.9, respectively. In comparison, RT for apoA-I on LpA-I:A-II has been reported to be 124.1+/-5.5 h and that for apoA-I on LpA-I 105.8+/-6.2 h. Thus, apoE within the different apoE-containing HDL particles was metabolized rapidly and at a similar rate in control and ABL subjects. The plasma RT of apoE was longest when injected on LpE:A-I:A-II particles and shortest when injected on LpE. In summary, our data show that: (1) the plasma RT of apoE within HDL is approximately ten times shorter than that of apoA-I within HDL, and (2) apoE within HDL is metabolized at a slower rate when apoproteins A-I and A-II are present (LpE:A-I:A-II RT>LpE:A-II>LpE:A-I>LpE). These differences were related to the lipid and apolipoprotein composition of the HDL subspecies, and, in control subjects, to the transfer of apoE from HDL subspecies to apoB-containing lipoproteins as well.