Thematic review series: patient-oriented research. What have we learned about HDL metabolism from kinetics studies in humans?

Increased Apolipoprotein B/Apolipoprotein A-I Ratio Is Associated With Decline in Lung Function in Healthy Individuals: The Kangbuk Samsung Health Study

BACKGROUND

Lung dysfunction and high apolipoprotein B/apolipoprotein A-I (apoB/apoA-I) ratio are both recognized risk factors for cardiovascular disease. However, few studies have examined the association between the apoB/ApoA-I ratio and lung function. Therefore, we investigated whether this ratio is associated with decreased lung function in a large healthy cohort.

METHODS

We performed a cohort study on 68,418 healthy Koreans (34,797 males, mean age: 38.1 years) who underwent a health examination in 2019. ApoB/apoA-I ratio was categorized into quartiles. Spirometric values at the fifth percentile in our population were considered the lower limit of normal (LLN), which was used to define lung function impairment. Adjusted odds ratios (aORs) and 95% confidence intervals (CIs), using the lowest quartile as the reference, were estimated to determine lung function impairment.

RESULTS

Mean apoB/apoA-I ratio was 0.67 ± 0.21. Subjects with the highest quartile of this ratio had the lowest predicted forced expiratory volume in one second (FEV1%) and forced vital capacity (FVC%) after controlling for covariates (P < 0.001). However, FEV1/FVC ratio was not significantly different among the four quartiles (P = 0.059). Compared with the lowest quartile (Q1, reference), the aORs (95% CI) for FEV1% < LLN across increasing quartiles (from Q2 to Q4) were 1.216 (1.094-1.351), 1.293 (1.156-1.448), and 1.481 (1.311-1.672) (P for trend < 0.001), respectively. Similarly, the aORs for FVC% < LLN compared with the reference were 1.212 (1.090-1.348), 1.283 (1.147-1.436), and 1.502 (1.331-1.695) with increasing quartiles (P for trend < 0.001). However, the aORs for FEV1/FVC < LLN were not significantly different among groups (P for trend = 0.273).

CONCLUSION

High apoB/apoA-I ratio was associated with decreased lung function. However, longitudinal follow-up studies are required to validate our findings.

Beer, wine, and spirits differentially influence body composition in older White adults ‐ a UK Biobank study

BACKGROUND

Aging is characterized by body composition alterations, including increased visceral adiposity accumulation and bone loss. Alcohol consumption may partially drive these alterations, but findings are mixed. This study primarily aimed to investigate whether different alcohol types (beer/cider, red wine, white wine/Champagne, spirits) differentially associated with body composition.

METHODS

The longitudinal UK Biobank study leveraged 1869 White participants (40–80 years; 59% male). Participants self‐reported demographic, alcohol/dietary consumption, and lifestyle factors using a touchscreen questionnaire. Anthropometrics and serum for proteomics were collected. Body composition was obtained via dual‐energy X‐ray absorptiometry. Structural equation modeling was used to probe direct/indirect associations between alcohol types, cardiometabolic biomarkers, and body composition.

RESULTS

Greater beer/spirit consumptions were associated with greater visceral adiposity (β = 0.069, p < 0.001 and β = 0.014, p < 0.001, respectively), which was driven by dyslipidemia and insulin resistance. In contrast, drinking more red wine was associated with less visceral adipose mass (β = −0.023, p < 0.001), which was driven by reduced inflammation and elevated high‐density lipoproteins. White wine consumption predicted greater bone density (β = 0.051, p < 0.005).

DISCUSSION

Beer/spirits may partially contribute to the “empty calorie” hypothesis related to adipogenesis, while red wine may help protect against adipogenesis due to anti‐inflammatory/eulipidemic effects. Furthermore, white wine may benefit bone health in older White adults.1

Safety and Tolerability of ACP-501, a Recombinant Human Lecithin:Cholesterol Acyltransferase, in a Phase 1 Single-Dose Escalation Study

RATIONALE

Low high-density lipoprotein-cholesterol (HDL-C) in patients with coronary heart disease (CHD) may be caused by rate-limiting amounts of lecithin:cholesterol acyltransferase (LCAT). Raising LCAT may be beneficial for CHD, as well as for familial LCAT deficiency, a rare disorder of low HDL-C.

OBJECTIVE

To determine safety and tolerability of recombinant human LCAT infusion in subjects with stable CHD and low HDL-C and its effect on plasma lipoproteins.

METHODS AND RESULTS

A phase 1b, open-label, single-dose escalation study was conducted to evaluate safety, tolerability, pharmacokinetics, and pharmacodynamics of recombinant human LCAT (ACP-501). Four cohorts with stable CHD and low HDL-C were dosed (0.9, 3.0, 9.0, and 13.5 mg/kg, single 1-hour infusions) and followed up for 28 days. ACP-501 was well tolerated, and there were no serious adverse events. Plasma LCAT concentrations were dose-proportional, increased rapidly, and declined with an apparent terminal half-life of 42 hours. The 0.9-mg/kg dose did not significantly change HDL-C; however, 6 hours after doses of 3.0, 9.0, and 13.5 mg/kg, HDL-C was elevated by 6%, 36%, and 42%, respectively, and remained above baseline ≤4 days. Plasma cholesteryl esters followed a similar time course as HDL-C. ACP-501 infusion rapidly decreased small- and intermediate-sized HDL, whereas large HDL increased. Pre-β-HDL also rapidly decreased and was undetectable ≤12 hours post ACP-501 infusion.

CONCLUSIONS

ACP-501 has an acceptable safety profile after a single intravenous infusion. Lipid and lipoprotein changes indicate that recombinant human LCAT favorably alters HDL metabolism and support recombinant human LCAT use in future clinical trials in CHD and familial LCAT deficiency patients.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT01554800.

Therapeutic effect of high-dose green tea extract on weight reduction: A randomized, double-blind, placebo-controlled clinical trial

BACKGROUND AND AIMS

To examine the effect and safety of high-dose green tea extract (Epigallocatechin gallate, EGCG) at a daily dosage of 856.8 mg on weight reduction and changes of lipid profile and obesity-related hormone peptides in women with central obesity.

METHODS

We conducted a randomized, double-blind trial registered under ClinicalTrials.gov Identifier no. NCT02147041. A total of 115 women with central obesity were screened at our clinic. 102 of them with a body mass index (BMI) ≥ 27 kg/m(2) and a waist circumference (WC) ≥ 80 cm were eligible for the study. These women were randomly assigned to either a high-dose green tea group or placebo group. The total treatment time was 12 weeks. The main outcome measures were anthropometric measurements, lipid profiles, and obesity related hormone peptides including leptin, adiponectin, ghrelin, and insulin.

RESULTS

Significant weight loss, from 76.8 ± 11.3 kg to 75.7 ± 11.5 kg (p = 0.025), as well as decreases in BMI (p = 0.018) and waist circumference (p = 0.023) were observed in the treatment group after 12 weeks of high-dose EGCG treatment. This study also demonstrated a consistent trend of decreased total cholesterol, reaching 5.33%, and decreased LDL plasma levels. There was good tolerance of the treatment among subjects without any side effects or adverse events. Significantly lower ghrelin levels and elevated adiponectin levels were detected in the study group than in the placebo group.

CONCLUSION

12 weeks of treatment with high-dose green tea extract resulted in significant weight loss, reduced waist circumference, and a consistent decrease in total cholesterol and LDL plasma levels without any side effects or adverse effects in women with central obesity. The antiobestic mechanism of high-dose green tea extract might be associated in part with ghrelin secretion inhibition, leading to increased adiponectin levels.

Reduction of paraoxonase-1 activity may contribute the qualitative impairment of HDL particles in patients with type 2 diabetes

AIMS

Cholesterol efflux with high-density lipoprotein (HDL) particles has an important role in the first step of reverse cholesterol transport (RCT). However, HDL function in type 2 diabetes has not been well investigated thoroughly. We measured cholesterol efflux in 36 patients with type 2 diabetes compared with 9 controls without diabetes.

METHODS

The HDL fraction was separated with polyacrylamide gel and recovered using the protein recovery system. Concentration adjusted HDL fraction was used to determine HDL-mediated cholesterol efflux (Efflux-hdl) from THP-1 derived macrophages. We measured paraoxonase-1 (PON 1) activity to determine antioxidation capacity, serum amyloid A protein (SAA) to determine inflammatory response, and carboxymethyl-lysin (CML) to determine antiglucoxidative capacity.

RESULTS

Efflux-hdl demonstrated no correlation with plasma apoprotein A-1 (ApoA-I) or HDL-cholesterol in patients with diabetes. PON1 activity in the patients' HDL fraction was positively correlated with Efflux-hdl (r=0.39, p=0.02), and showed a negative tendency with HbA1c levels (r=-0.28, p=0.10). SAA and CML levels did not demonstrate correlation with Efflux-hdl in patients with diabetes.

CONCLUSION

We confirmed the functional changes in HDL particles in the patients. Efflux-hdl from macrophages was reduced depending upon the decrease in PON1 activity, which was inversely related to HbA1c levels.

The value of apolipoprotein B/A1 ratio in the diagnosis of metabolic syndrome in a Korean population

OBJECTIVE

The ratio of apolipoprotein B (apoB) to apolipoprotein A1 (apoA1) has been reported to be associated with the metabolic syndrome (MetS). However, the optimal cut-off value of apoB/A1 ratio for detecting subjects with MetS has remained undetermined. In the present study, we aimed to investigate whether apoB/A1 ratio can be an indicator of MetS and to determine the optimal cut-off value of apoB/A1 ratio in detecting subjects with MetS in a Korean population.

DESIGN

This cross-sectional study was conducted at the Asan Medical Center, Seoul, Republic of Korea.

SUBJECTS AND MEASUREMENTS

We collected the data of 10,940 subjects who participated in a routine health screening examination regarding conventional risk factors and serum levels of apoB and apoA1.

RESULTS

The odds for MetS were significantly higher in the highest compared with the lowest apoB/A1 ratio quartiles, after adjustment for confounding variables, in both men [odds ratio (OR) = 4·07, 95% CI = 3·42-4·84] and women (OR = 8·41, 95% CI = 5·85-12·08). The optimal apoB/A1 ratio cut-off value for the detection of MetS was 0·65, which had a sensitivity of 63·5% and a specificity of 61·3% (area under the curve = 0·67, 95% CI = 0·66-0·68, P < 0·001) in men and 0·62, which had a sensitivity of 67·9% and a specificity of 61·9% (area under the curve = 0·70, 95% CI = 0·69-0·71, P < 0·001) in women.

CONCLUSIONS

These results suggest that apoB/A1 ratio is independently associated with MetS and that an apoB/A1 ratio >0·65 in men and 0·62 in women is a marker of MetS independent from conventional risk factors.

LCAT cholesterol esterification is associated with the increase of ApoE/ApoA-I ratio during atherosclerosis progression in rabbit

Apolipoprotein A-I and Apolipoprotein E promote different steps of reverse cholesterol transport, including lecithin-cholesterol acyltransferase stimulation. Our aim was to study the changes in the levels of Apolipoprotein A-I, Apolipoprotein E, and lecithin-cholesterol acyltransferase activity during atherosclerosis progression in rabbits. Quantitative echocardiographic parameters were analyzed in order to evaluate, for the first time, whether atherosclerosis progression in rabbit is associated to apolipoproteins changes and alteration of indices of cardiac function, such as systolic strain and strain rate of the left ventricle. Atherosclerosis was induced by feeding rabbits for 8 weeks with 2 % cholesterol diet. The HDL levels of cholesterol and cholesteryl esters were measured by HPLC. The lecithin-cholesterol acyltransferase activity was evaluated both ex vivo, as cholesteryl esters/cholesterol molar ratio, and in vitro. Apolipoproteins levels were analyzed by ELISA. The HDL levels of cholesterol and cholesteryl esters increased, during treatment, up to 3.7- and 2.5-fold, respectively, compared to control animals. The lecithin-cholesterol acyltransferase activity in vitro was halved after 4 weeks. During cholesterol treatment, Apolipoprotein A-I level significantly decreased, whereas Apolipoprotein E concentration markedly increased. The molar ratio Apolipoprotein E/Apolipoprotein A-I was negatively correlated with the enzyme activity, and positively correlated with both increases in the intima-media thickness of common carotid wall and cardiac dysfunction signs, such as systolic strain and strain rate of the left ventricle.

New insights into the mechanism of low high-density lipoprotein cholesterol in obesity

Obesity, a significant risk factor for various chronic diseases, is universally related to dyslipidemia mainly represented by decreasing high-density lipoprotein cholesterol (HDL-C), which plays an indispensible role in development of cardiovascular disease (CVD). However, the mechanisms underlying obesity and low HDL-C have not been fully elucidated. Previous studies have focused on the alteration of HDL catabolism in circulation following elevated triglyceride (TG). But recent findings suggested that liver and fat tissue played pivotal role in obesity related low HDL-C. Some new molecular pathways like microRNA have also been proposed in the regulation of HDL metabolism in obesity. This article will review recent advances in understanding of the potential mechanism of low HDL-C in obesity.

Reverse cholesterol transport in type 2 diabetes mellitus

High-density lipoprotein (HDL) plays an important protective role against atherosclerosis, and the anti-atherogenic properties of HDL include the promotion of cellular cholesterol efflux and reverse cholesterol transport (RCT), as well as antioxidant, anti-inflammatory and anticoagulant effects. RCT is a complex pathway, which transports cholesterol from peripheral cells and tissues to the liver for its metabolism and biliary excretion. The major steps in the RCT pathway include the efflux of free cholesterol mediated by cholesterol transporters from cells to the main extracellular acceptor HDL, the conversion of free cholesterol to cholesteryl esters and the subsequent removal of cholesteryl ester in HDL by the liver. The efficiency of RCT is influenced by the mobilization of cellular lipids for efflux and the intravascular remodelling and kinetics of HDL metabolism. Despite the increased cardiovascular risk in people with type 2 diabetes, current knowledge on RCT in diabetes is limited. In this article, abnormalities in RCT in type 2 diabetes mellitus and therapeutic strategies targeting HDL and RCT will be reviewed.

Adenoviral expression of human lecithin-cholesterol acyltransferase in nonhuman primates leads to an antiatherogenic lipoprotein phenotype by increasing high-density lipoprotein and lowering low-density lipoprotein

Lecithin-cholesterol acyltransferase (LCAT), a key enzyme in high-density lipoprotein (HDL) metabolism, has been proposed to have atheroprotective properties by promoting reverse cholesterol transport. Overexpression of LCAT in various animal models, however, has led to conflicting results on its overall effect on lipoproteins and atherosclerosis. In this study, the effect of overexpression of LCAT in nonhuman primates on lipoprotein metabolism is examined. Human LCAT was expressed with adenovirus in squirrel monkeys (n = 8), resulting on day 4 in a 22-fold increase of LCAT activity (257 +/- 23 vs 5618 +/- 799 nmol mL(-1) h(-1), P < .0001). At its peak, LCAT was found to nearly double the level of HDL cholesterol from baseline (113 +/- 7 vs 260 +/- 24 mg/dL, P < .01). High-density lipoprotein formed after treatment with the adenovirus was larger in size, as assessed by fast protein liquid chromatography (FPLC) analysis. By kinetic studies, it was determined that there was a decrease in apolipoprotein (Apo) A-I resident time (0.373 +/- 0.027 vs 0.685 +/- 0.045 d(-1), P < .0001) and almost a doubling in the ApoA-I synthetic rate (22 +/- 2 vs 41 +/- 3 mg kg(-1) d(-1), P < .0001), but no overall change in ApoA-I levels. In addition, increased expression of LCAT was associated with a 37% reduction of ApoB levels (12 +/- 1 vs 19 +/- 1 mg/dL, P < .05) due to increased low-density lipoprotein catabolism (fractional catabolic rate = 1.7 +/- 0.1 d(-1) in controls vs 4.2 +/- 0.3 d(-1) in LCAT-treated group, P < .05). In summary, overexpression of LCAT in nonhuman primates leads to an antiatherogenic lipoprotein profile by increasing HDL cholesterol and lowering ApoB, thus making LCAT a potential drug target for reducing atherosclerosis.

Very low density lipoprotein metabolism and plasma adiponectin as predictors of high-density lipoprotein apolipoprotein A-I kinetics in obese and nonobese men

CONTEXT

Hypercatabolism of high-density lipoprotein (HDL) apolipoprotein (apo) A-I results in low plasma apoA-I concentration. The mechanisms regulating apoA-I catabolism may relate to alterations in very low density lipoprotein (VLDL) metabolism and plasma adiponectin and serum amyloid A protein (SAA) concentrations.

OBJECTIVE

We examined the associations between the fractional catabolic rate (FCR) of HDL-apoA-I and VLDL kinetics, plasma adiponectin, and SAA concentrations.

STUDY DESIGN

The kinetics of HDL-apoA-I and VLDL-apoB were measured in 50 obese and 37 nonobese men using stable isotopic techniques.

RESULTS

In the obese group, HDL-apoA-I FCR was positively correlated with insulin, homeostasis model of assessment for insulin resistance (HOMA-IR) score, triglycerides, VLDL-apoB, and VLDL-apoB production rate (PR). In the nonobese group, HDL-apoA-I FCR was positively correlated with triglycerides, apoC-III, VLDL-apoB, and VLDL-apoB PR and negatively correlated with plasma adiponectin. Plasma SAA was not associated with HDL-apoA-I FCR in either group. In multiple regression analyses, VLDL-apoB PR and HOMA-IR score, and VLDL-apoB PR and adiponectin were independently predictive of HDL-apoA-I FCR in the obese and nonobese groups, respectively. HDL-apoA-I FCR was positively and strongly associated with HDL-apoA-I PR in both groups.

CONCLUSIONS

Variation in VLDL-apoB production, and hence plasma triglyceride concentrations, exerts a major effect on the catabolism of HDL-apoA-I. Insulin resistance and adiponectin may also contribute to the variation in HDL-apoA-I catabolism in obese and nonobese subjects, respectively. We also hypothesize that apoA-I PR determines a steady-state, lowered plasma of apoA-I, which may reflect a compensatory response to a primary defect in the catabolism of HDL-apoA-I due to altered VLDL metabolism.

HDL metabolism in context: looking on the bright side

PURPOSE OF REVIEW

To review new data concerning HDL metabolism and cardiovascular disease, the concept of HDL 'functionality', and HDL kinetics in the metabolic syndrome.

RECENT FINDINGS

HDL-apoA-I and apoA-II may be better predictors of cardiovascular disease than HDL-cholesterol. Cholesteryl ester transfer protein inhibition with torcetrapib does not benefit cardiovascular disease; whether this is related to 'congestion' of HDL transport or a specific off-target vasopressor effect remains unclear. Accelerated catabolism of HDL particles in metabolic syndrome could be due to increased hepatic secretion of apoB and apoC-III, hepatic steatosis, and low plasma adiponectin. The role of serum amyloid A and homocysteine is uncertain. In metabolic syndrome, therapies that could favourably alter HDL transport include weight loss, fish oils, higher dose statins, and fibrates; 'balancing feedback' may offset reduced catabolism of HDL, fenofibrate being the only agent hitherto shown to increase apoA-I production.

SUMMARY

Elevating HDL-apoA-I and apoA-II may be a more important therapeutic objective than increased HDL-cholesterol. Recent studies underscore the potential value of studying HDL functionality, particularly in the metabolic syndrome. Reverse cholesterol transport can only be reliably probed at present by studying the kinetics of HDL particles or apolipoproteins; new methods are needed for investigating cellular and whole body cholesterol turnover. In metabolic syndrome, HDL-raising therapies have differential impact on HDL kinetics, the optimal endpoint being to increase transport and concentration with unchanged or accelerated catabolism.

Sex-specific interaction between APOE genotype and carbohydrate intake affects plasma HDL-C levels: the Strong Heart Family Study

Low plasma levels of high-density lipoprotein cholesterol (HDL-C) are identified as a risk factor for cardiovascular disease (CVD). Sexual dimorphism, however, is widely reported in both HDL-C and CVD, with the underlying explanations of these sexual differences not fully understood. HDL-C is a complex trait influenced by both genes and dietary factors. Here we examine evidence for a sex-specific effect of APOE and the macronutrient carbohydrate on HDL-C, triglycerides (TG) and apoprotein A-1 (ApoA-1) in a sample of 326 male and 423 female participants of the Strong Heart Family Study (SHFS). Using general estimating equations in SAS to account for kinship correlations, stratifying by sex, and adjusting for age, body mass index (BMI) and SHS center, we examine the relationship between APOE genotype and carbohydrate intake on circulating levels of HDL-C, TG, and ApoA-1 through a series of carbohydrate-by-sex interactions and stratified analyses. APOE-by-carbohydrate intake shows significant sex-specific effects. All males had similar decreases in HDL-C levels associated with increased carbohydrate intake. However, only those females with APOE-4 alleles showed significantly lower HDL-C levels as their percent of carbohydrate intake increased, while no association was noted between carbohydrate intake and HDL-C in those females without an APOE-4 allele. These findings demonstrate the importance of understanding sex differences in gene-by-nutrient interaction when examining the complex architecture of HDL-C variation.

Enhanced cellular uptake of remnant high-density lipoprotein particles: a mechanism for high-density lipoprotein lowering in insulin resistance and hypertriglyceridemia

A low level of high-density lipoprotein (HDL) cholesterol is characteristic of insulin resistance and hypertriglyceridemia and likely contributes to the increased risk of cardiovascular disease associated with these conditions. One pathway involves enhanced clearance of lipolytically modified HDL particles, but the underlying mechanisms remain poorly understood. Here, we examine the effect of triglyceride enrichment and hepatic lipase hydrolysis on HDL binding, internalization, and degradation in cultured liver and kidney cells. Maximal binding of remnant HDL (HDL enriched with triglycerides followed by hepatic lipase hydrolysis), but not binding affinity, was markedly higher than native and triglyceride-rich HDL in both HepG2 cells and HEK293 cells. Compared with native and triglyceride-rich HDL, remnant HDL was internalized to a greater extent in both cell types and was more readily degraded in HEK293 cells. The increased binding of remnant HDL was not mediated by the low-density lipoprotein receptor or scavenger receptor class B type I (SR-BI), because enhanced remnant HDL binding was observed in low-density lipoprotein receptor-deficient cells with or without SR-BI overexpression. Disruption of cell surface heparan sulfate proteoglycans or blockage of apolipoprotein E-mediated lipoprotein binding also did not abolish the enhanced remnant HDL binding. Our observations indicate that remodeling of triglyceride-enriched HDL by hepatic lipase may result in enhanced binding, internalization, and degradation in tissues involved in HDL catabolism, contributing to rapid clearance and overall lowering of plasma HDL cholesterol in insulin resistance and hypertriglyceridemia.

Computational lipidology: predicting lipoprotein density profiles in human blood plasma

Monitoring cholesterol levels is strongly recommended to identify patients at risk for myocardial infarction. However, clinical markers beyond "bad" and "good" cholesterol are needed to precisely predict individual lipid disorders. Our work contributes to this aim by bringing together experiment and theory. We developed a novel computer-based model of the human plasma lipoprotein metabolism in order to simulate the blood lipid levels in high resolution. Instead of focusing on a few conventionally used predefined lipoprotein density classes (LDL, HDL), we consider the entire protein and lipid composition spectrum of individual lipoprotein complexes. Subsequently, their distribution over density (which equals the lipoprotein profile) is calculated. As our main results, we (i) successfully reproduced clinically measured lipoprotein profiles of healthy subjects; (ii) assigned lipoproteins to narrow density classes, named high-resolution density sub-fractions (hrDS), revealing heterogeneous lipoprotein distributions within the major lipoprotein classes; and (iii) present model-based predictions of changes in the lipoprotein distribution elicited by disorders in underlying molecular processes. In its present state, the model offers a platform for many future applications aimed at understanding the reasons for inter-individual variability, identifying new sub-fractions of potential clinical relevance and a patient-oriented diagnosis of the potential molecular causes for individual dyslipidemia.

HDL-cholesterol modulation and its impact on the management of cardiovascular risk

There is strong epidemiological evidence that HDL-cholesterol (HDL-C) is an independent cardiovascular risk factor. A low HDL-C is a common finding in the general population, and is a feature of metabolic syndrome, the prevalence of which is increasing globally. The importance of HDL-C as a coronary risk factor is generally accepted, and has been incorporated into most of the commonly applied risk engines. There are several causes of a low HDL-C, including rare genetic abnormalities, and more common conditions associated with lifestyle and drug therapy. Not all of these are associated with an increased risk of coronary disease. A better understanding of HDL metabolism and the mechanisms by which it may exert its protective effects has revealed why this may be the case. New therapeutic targets have also been identified that may allow HDL-C to be raised in patients with low levels. However, good clinical endpoint studies are still required to enable the setting of absolute target values for HDL-C in patients at high cardiovascular risk.

Genetic factors affecting HDL levels, structure, metabolism and function

PURPOSE OF REVIEW

HDL is a recognized negative risk factor for the cardiovascular diseases. Establishing the genetic determinants of HDL concentration and functions would add to the prediction of cardiovascular risk and point to the biochemical mechanisms underlying this risk. The present review focuses on various approaches to establish genetic determinants of the HDL concentration, structure and function.

RECENT FINDINGS

While many genes contribute to the HDL concentration and collectively account for half of the variability, polymorphism of individual candidate genes contributes little. There are strong interactions between environmental and genetic influences. Recent findings have confirmed that APOA1 and ABCA1 exert the strongest influence on HDL concentrations and risk of atherosclerosis. CETP and lipases also affect the HDL concentration and functionality, but their connection to the atherosclerosis risk is conditional on the interaction between environmental and genetic factors.

SUMMARY

Analysis of genetic determinants of HDL-cholesterol in patients with specific disease states or in response to the environmental condition may be a more accurate way to assess variations in HDL concentration. This may result in defining the rules of interaction between genetic and environmental factors and lead to understanding the mechanisms responsible for the variations in HDL concentration and functionality.

Thematic review series: Patient-Oriented Research. Design and analysis of lipoprotein tracer kinetics studies in humans

Lipoprotein tracer kinetics studies have for many years provided new and important knowledge of the metabolism of lipoproteins. Our understanding of kinetics defects in lipoprotein metabolism has resulted from the use of tracer kinetics studies and mathematical modeling. This review discusses all aspects of the performance of kinetics studies, including the development of hypotheses, experimental design, statistical considerations, tracer administration and sampling schedule, and the development of compartmental models for the interpretation of tracer data. In addition to providing insight into new metabolic pathways, such models provide quantitative information on the effect of interventions on lipoprotein metabolism. Compartment models are useful tools to describe experimental data but can also be used to aid in experimental design and hypothesis generation. The SAAM II program provides an easy-to-use interface with which to develop and test compartmental models against experimental models. The development of a model requires that certain checks be performed to ensure that the model describes the experimental data and that the model parameters can be estimated with precision. In addition to methodologic aspects, several compartment models of apoprotein and lipid metabolism are reviewed.