Monogenic causes of elevated HDL cholesterol and implications for development of new therapeutics

Effect of Bariatric Surgery on High-Density Lipoprotein (HDL) Cholesterol in Non-diabetic Patients with Severe Obesity

BACKGROUND

This study evaluated changes in serum high-density lipoprotein cholesterol (HDL-C) induced by laparoscopic bariatric surgery (BS) in non-diabetic obese subjects with low (L-HDL-C) or normal (N-HDL-C) levels of HDL-C. We assessed whether increased HDL-C is associated with weight loss, serum non-HDL cholesterol (non-HDL-C), serum triglycerides (TG), and physical activity (PA) before and 6 and 15 months after BS.

METHODS

In this prospective cohort study, 71 subjects undergoing BS (42 by Roux-en-Y gastric bypass and 29 by sleeve gastrectomy) were evaluated for the % Excess Weight Loss (%EWL), waist circumference (WC), serum levels of glucose, glycosylated hemoglobin, TG, HDL-C, non-HDL-C, and LDL-C, and the degree, time, and energy expenditure related to PA. The short version of the International Physical Activity Questionnaire was used to assess PA.

RESULTS

Levels of HDL-C significantly increased 15 months after BS (p < 0.001) in subjects with low (p < 0.001) or normal (p = 0.017) values at baseline. A similar %EWL, decrease in WC, glucose, non-HDL-C, and LDL-C levels and increase in energy expenditure related to PA, was observed in both groups (L-HDL-C and N-HDL-C) at 15 months after BS. However, the L-HDL-C group presented greater decrease in TG levels compared with N-HDL-C group (p = 0.004). In subjects with increased HDL-C 15 months after BS, there was an association between this increase and the %EWL (p = 0.030), but there was no association with the change in PA.

CONCLUSIONS

Irrespective of PA after BS, subjects with low and normal HDL-C levels at baseline showed an increase in HDL-C after BS, and this increase was associated with %EWL induced by BS.

Multiplexed Targeted Resequencing Identifies Coding and Regulatory Variation Underlying Phenotypic Extremes of High-Density Lipoprotein Cholesterol in Humans

BACKGROUND

Genome-wide association studies have uncovered common variants at many loci influencing human complex traits, such as high-density lipoprotein cholesterol (HDL-C). However, the contribution of the identified genes is difficult to ascertain from current efforts interrogating common variants with small effects. Thus, there is a pressing need for scalable, cost-effective strategies for uncovering causal variants, many of which may be rare and noncoding.

METHODS

Here, we used a molecular inversion probe target capture approach to resequence both coding and regulatory regions at 7 HDL-C-associated loci in 797 individuals with extremely high HDL-C versus 735 low-to-normal HDL-C controls. Our targets included protein-coding regions of GALNT2, APOA5, APOC3, SCARB1, CCDC92, ZNF664, CETP, and LIPG (>9 kb) and proximate noncoding regulatory features (>42 kb).

RESULTS

Exome-wide genotyping in 1114 of the 1532 participants yielded a >90% genotyping concordance rate with molecular inversion probe-identified variants in ≈90% of participants. This approach rediscovered nearly all established genome-wide association studies associations in GALNT2, CETP, and LIPG loci with significant and concordant associations with HDL-C from our phenotypic extremes design at 0.1% of the sample size of lipid genome-wide association studies. In addition, we identified a novel, rare, CETP noncoding variant enriched in the extreme high HDL-C group (P<0.01, score test).

CONCLUSIONS

Our targeted resequencing of individuals at the HDL-C phenotypic extremes offers a novel, efficient, and cost-effective approach for identifying rare coding and noncoding variation differences in extreme phenotypes and supports the rationale for applying this methodology to uncover rare variation-particularly noncoding variation-underlying myriad complex traits.

Unravelling HDL-Looking beyond the Cholesterol Surface to the Quality Within

High-density lipoprotein (HDL) particles have experienced a turbulent decade of falling from grace with widespread demotion from the most-sought-after therapeutic target to reverse cardiovascular disease (CVD), to mere biomarker status. HDL is slowly emerging from these dark times due to the HDL flux hypothesis wherein measures of HDL cholesterol efflux capacity (CEC) are better predictors of reduced CVD risk than static HDL-cholesterol (HDL-C) levels. HDL particles are emulsions of metabolites, lipids, protein, and microRNA (miR) built on the backbone of Apolipoprotein A1 (ApoA1) that are growing in their complexity due to the higher sensitivity of the respective “omic” technologies. Our understanding of particle composition has increased dramatically within this era and has exposed how our understanding of these particles to date has been oversimplified. Elucidation of the HDL proteome coupled with the identification of specific miRs on HDL have highlighted the “hormonal” characteristics of HDL in that it carries and delivers messages systemically. HDL can dock to most peripheral cells via its receptors, including SR-B1, ABCA1, and ABCG1, which may be a critical step for facilitating HDL-to-cell communication. The composition of HDL particles is, in turn, altered in numerous disease states including diabetes, auto-immune disease, and CVD. The consequence of changes in composition, however, on subsequent biological activities of HDL is currently poorly understood and this is an important avenue for the field to explore in the future. Improving HDL particle quality as opposed to HDL quantity may, in turn, prove a more beneficial investment to reduce CVD risk.

Novel polymorphisms associated with hyperalphalipoproteinemia and apparent cardioprotection

BACKGROUND

Hyperalphalipoproteinemia (HALP) is inversely correlated with coronary heart disease (CHD) although genetic variants associated with high serum levels of high-density lipoprotein cholesterol (HDL-C) have not been shown to be cardioprotective.

OBJECTIVE

The objective of the study was to uncover novel genetic variants associated with HALP and possibly with reduced risk of CHD.

METHODS

Exome sequencing data, HDL-C, and triglyceride levels were analyzed in 1645 subjects. They included the University of Maryland outpatients with high HDL-C (n = 12), Cardiovascular Health Study (n = 210), Jackson Heart Study (n = 402), Multi-Ethnic Study of Atherosclerosis (n = 404), Framingham Heart Study (n = 463), and Old Order Amish (n = 154).

RESULTS

Novel nonsynonymous single-nucleotide polymorphisms (nsSNPs) were identified in men and women with primary HALP (mean HDL-C, 145 ± 30 mg/dL). Using PolyPhen-2 and Combined Annotation Dependent Depletion to estimate the predictive effect of each nsSNP on the gene product, rare, deleterious polymorphisms in UGT1A3, PLLP, PLEKHH1, ANK2, DIS3L, ACACB, and LRP4 were identified in 16 subjects with HALP but not in any tested subject with low HDL-C (<40 mg/dL). In addition, a single novel polymorphism, rs376849274, was found in OSBPL1A. The majority of these candidate genes have been implicated in fat and lipid metabolism, and none of these subjects has a history of CHD despite 75% of subjects having risk factors for CHD. Overall, the probability of finding these nsSNPs in a non-high HDL-C population ranges from 1 × 10-17 to 1 × 10-25.

CONCLUSION

Novel functional polymorphisms in 8 candidate genes are associated with HALP in the absence of CHD. Future study is required to examine the extent to which these genes may affect HDL function and serve as potential therapeutic targets for CHD risk reduction.

HDL Cholesterol Metabolism and the Risk of CHD: New Insights from Human Genetics

PURPOSE OF REVIEW

Elevated high-density lipoprotein cholesterol levels in the blood (HDL-C) represent one of the strongest epidemiological surrogates for protection against coronary heart disease (CHD), but recent human genetic and pharmacological intervention studies have raised controversy about the causality of this relationship. Here, we review recent discoveries from human genome studies using new analytic tools as well as relevant animal studies that have both addressed, and in some cases, fueled this controversy.

RECENT FINDINGS

Methodologic developments in genotyping and sequencing, such as genome-wide association studies (GWAS), exome sequencing, and exome array genotyping, have been applied to the study of HDL-C and risk of CHD in large, multi-ethnic populations. Some of these efforts focused on population-wide variation in common variants have uncovered new polymorphisms at novel loci associated with HDL-C and, in some cases, CHD risk. Other efforts have discovered loss-of-function variants for the first time in genes previously implicated in HDL metabolism through common variant studies or animal models. These studies have allowed the genetic relationship between these pathways, HDL-C and CHD to be explored in humans for the first time through analysis tools such as Mendelian randomization. We explore these discoveries for selected key HDL-C genes CETP, LCAT, LIPG, SCARB1, and novel loci implicated from GWAS including GALNT2, KLF14, and TTC39B. Recent human genetics findings have identified new nodes regulating HDL metabolism while reshaping our current understanding of known candidate genes to HDL and CHD risk through the study of critical variants across model systems. Despite their effect on HDL-C, variants in many of the reviewed genes were found to lack any association with CHD. These data collectively indicate that HDL-C concentration, which represents a static picture of a very dynamic and heterogeneous metabolic milieu, is unlikely to be itself causally protective against CHD. In this context, human genetics represent an extremely valuable tool to further explore the biological mechanisms regulating HDL metabolism and investigate what role, if any, HDL plays in the pathogenesis of CHD.

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.

Antilipidemic Drug Therapy Today and in the Future

The armamentarium for the treatment of dyslipidemia today comprises six different modes of action with overall around 24 different drugs. The treatment of lipid disorders was revolutionized with the introduction of statins which have become the most important therapeutic option available today to reduce and prevent atherosclerosis and its detrimental consequences like cardiovascular diseases and stroke. With and optimized reduction of elevated LDL levels with statins, the risk for cardiovascular diseases (CVD) can be reduced by 30%, indicating a residual remaining risk of 70% for the development and progression of CVD notifying still a high medical need for more effective antilipidemic drugs. Consequently, the search for novel lipid-modifying drugs is still one of the most active areas in research and development in the pharmaceutical industry. Major focus lies on approaches to LDL-lowering drugs superior to statins with regard to efficacy, safety, and patient compliance and on approaches modifying plasma levels and functionality of HDL particles based on the clinically validated inverse relationship between high-plasma HDL levels and the risk for CVD. The available drugs today for the treatment of dyslipidemia are small organic molecules or nonabsorbable polymers for binding of bile acids to be applied orally. Besides small molecules for novel targets, biological drugs such as monoclonal antibodies, antisense or gene-silencing oligonucleotides, peptidomimetics, reconstituted synthetic HDL particles and therapeutic proteins are novel approaches in clinical development are which have to be applied by injection or infusion. The promising clinical results of several novel drug candidates, particularly for LDL cholesterol lowering with monoclonal antibodies raised against PCSK9, may indicate more than a decade after the statins, the entrance of new breakthrough therapies to treat lipid disorders.