Serum CETP concentration is not associated with measures of body fat: The NEO study

Obesity and Dyslipidemia: A Review of Current Evidence

PURPOSE OF REVIEW

Obesity is accompanied by atherogenic dyslipidemia, a specific lipid disorder characterized by both quantitative and qualitative changes of plasma lipoproteins. The main alterations in the lipid profile include hypertriglyceridemia, reduced high-density lipoprotein (HDL) cholesterol level, and elevated small dense low-density lipoprotein (LDL) particles. Epidemiological data show that obesity is more common in women and is a frequent risk factor for reproductive disorders, metabolic complications in pregnancy, and cardiometabolic disease later in life. The aim of this narrative review is to discuss recent advances in the research of dyslipidemia in obesity, with an emphasis on female-specific disorders and cardiometabolic risk.

RECENT FINDINGS

The focus of current research on dyslipidemia in obesity is moving toward structurally and functionally modified plasma lipoproteins. Special attention is paid to the pro-atherogenic role of triglyceride-rich lipoproteins and their remnants. Introduction of advanced analytical techniques enabled identification of novel lipid biomarkers with potential clinical applications. In particular, proteomic and lipidomic studies have provided significant progress in the comprehensive research of HDL's alterations in obesity. Obesity-related dyslipidemia is a widespread metabolic disturbance in polycystic ovary syndrome patients and high-risk pregnancies, but is seldom evaluated with respect to its impact on future cardiometabolic health. Obesity and associated cardiometabolic diseases require a more depth insight into the quality of lipoprotein particles. Further application of omics-based techniques would enable a more comprehensive evaluation of dyslipidemia in order to reduce an excessive cardiovascular risk attributable to increased body weight. However, more studies on obesity-related female reproductive disorders are needed for this approach to be adopted in daily clinical practice.

Study of effect modifiers of genetically predicted CETP reduction

Genetic variants in drug targets can be used to predict the long-term, on-target effect of drugs. Here, we extend this principle to assess how sex and body mass index may modify the effect of genetically predicted lower CETP levels on biomarkers and cardiovascular outcomes. We found sex and body mass index (BMI) to be modifiers of the association between genetically predicted lower CETP and lipid biomarkers in UK Biobank participants. Female sex and lower BMI were associated with higher high-density lipoprotein cholesterol and lower low-density lipoprotein cholesterol for the same genetically predicted reduction in CETP concentration. We found that sex also modulated the effect of genetically lower CETP on cholesterol efflux capacity in samples from the Montreal Heart Institute Biobank. However, these modifying effects did not extend to sex differences in cardiovascular outcomes in our data. Our results provide insight into the clinical effects of CETP inhibitors in the presence of effect modification based on genetic data. The approach can support precision medicine applications and help assess the external validity of clinical trials.

Sphingolipidomic profile and HDL subfractions in obese dyslipidemic type 2 diabetic patients

PURPOSE

The aim of the study was to investigate changes in serum sphingolipid levels and high density lipoprotein (HDL) subtypes with relation to low-density lipoprotein cholesterol (LDL-C), non-HDL-C and triglyceride (TG) levels in type 2 diabetes mellitus (T2DM) patients.

METHODS

Blood was obtained from 60 patients with T2DM. Levels of sphingosine-1-phosphate (S1P), C16-C24 sphingomyelins (SMs), C16-C24 ceramides (CERs), and C16 CER-1 P were determined by LC-MS/MS. Serum concentrations of cholesterol ester transfer protein (CETP), lecithin-cholesterol acyltransferase (LCAT) and apolipoprotein A-1 (apoA-I) were analyzed by enzyme-linked immunosorbent assay (ELISA). HDL subfraction analysis was performed by Disc polyacrylamide gel electrophoresis.

RESULTS

C16 SM, C24 SM, C24-C16 CER and C16 CER-1 P levels were significantly increased in T2DM patients with LDL-C above 160 mg/dL, compared to those with LDL-C below 100 mg/dL. A significant correlation was observed between C24:C16 SM, C24:C16 CER ratios and LDL-C, non HDL-C levels. Higher serum levels of C24 SM, C24-C18 CER and C24:C16 SM ratio was seen in obese T2DM patients (BMI>30) compared to those with BMI 27-30. Patients with fasting TG levels below 150 mg/dL had significantly increased HDL-large and significantly decreased HDL-small fractions compared to those with fasting TG levels above 150 mg/dL.

CONCLUSION

Obese dyslipidemic T2DM patients had increased levels of serum sphingomyelins, ceramides and HDL-small fractions. The ratio of serum C24:C16 SM, C24:C16 CER and long chain CER levels may be used as diagnostic and prognostic indicators of dyslipidemia in T2DM.

CETP (Cholesteryl Ester Transfer Protein) Concentration: A Genome-Wide Association Study Followed by Mendelian Randomization on Coronary Artery Disease

BACKGROUND

We aimed to identify independent genetic determinants of circulating CETP (cholesteryl ester transfer protein) to assess causal effects of variation in CETP concentration on circulating lipid concentrations and cardiovascular disease risk.

METHODS

A genome-wide association discovery and replication study on serum CETP concentration were embedded in the NEO study (Netherlands Epidemiology of Obesity). Based on the independent identified variants, Mendelian randomization was conducted on serum lipids (NEO study) and coronary artery disease (CAD; CARDIoGRAMplusC4D consortium).

RESULTS

In the discovery analysis (n=4248), we identified 3 independent variants (P<5×10^-8) that determine CETP concentration. These single-nucleotide polymorphisms were mapped to CETP and replicated in a separate subpopulation (n=1458). Per-allele increase (SE) in serum CETP was 0.32 (0.02) µg/mL for rs247616-C, 0.35 (0.02) µg/mL for rs12720922-A, and 0.12 (0.02) µg/mL for rs1968905-G. Combined, these 3 variants explained 16.4% of the total variation in CETP concentration. One microgram per milliliter increase in genetically determined CETP concentration strongly decreased high-density lipoprotein cholesterol (-0.23 mmol/L; 95% confidence interval, -0.26 to -0.20), moderately increased low-density lipoprotein cholesterol (0.08 mmol/L; 95% confidence interval, 0.00-0.16), and was associated with an odds ratio of 1.08 (95% confidence interval, 0.94-1.23) for CAD risk.

CONCLUSIONS

This is the first genome-wide association study identifying independent variants that largely determine CETP concentration. Although high-density lipoprotein cholesterol is not a causal risk factor for CAD, it has been unequivocally demonstrated that low-density lipoprotein cholesterol lowering is proportionally associated with a lower CAD risk. Therefore, the results of our study are fully consistent with the notion that CETP concentration is causally associated with CAD through low-density lipoprotein cholesterol.

Hepatic triglyceride content does not affect circulating CETP: lessons from a liraglutide intervention trial and a population-based cohort

Cholesteryl ester transfer protein (CETP) is mainly expressed by Kupffer cells in the liver. A reduction of hepatic triglyceride content (HTGC) by pioglitazone or caloric restriction is accompanied by a decrease in circulating CETP. Since GLP-1 analogues also reduce HTGC, we assessed whether liraglutide decreases CETP. Furthermore, we investigated the association between HTGC and CETP in a population-based cohort. In a placebo-controlled trial, 50 patients with type 2 diabetes were randomly assigned to treatment with liraglutide or placebo added to standard care. In this trial and in 1,611 participants of the Netherlands Epidemiology of Obesity (NEO) study, we measured HTGC and circulating CETP by proton magnetic resonance spectroscopy and ELISA, respectively. The HTGC was decreased in the liraglutide group (-6.3%; 95%CI of difference [-9.5, -3.0]) but also in the placebo group (-4.0%; 95%CI[-6.0, -2.0]), without between-group differences. CETP was not decreased by liraglutide (-0.05 µg/mL; 95%CI[-0.13, 0.04]) or placebo (-0.04 µg/mL; 95%CI[-0.12, 0.04]). No association was present between HTGC and CETP at baseline (β: 0.002 µg/mL per %TG, 95%CI[-0.005, 0.009]) and between the changes after treatment with liraglutide (β: 0.003 µg/mL per %TG, 95%CI[-0.010, 0.017]) or placebo (β: 0.006 µg/mL per %TG, 95%CI[-0.012,0.024]). Also, in the cohort n o association between HTGC and CETP was present (β: -0.001 µg/mL per SD TG, 95%CI[-0.005, 0.003]). A reduction of HTGC after treatment with liraglutide or placebo does not decrease circulating CETP. Also, no association between HTGC and CETP was present in a large cohort. These findings indicate that circulating CETP is not determined by HTGC.Clinical Trial Registration: Clinicaltrials.gov (NCT01761318).

Metabolic liver inflammation in obesity does not robustly decrease hepatic and circulating CETP

BACKGROUND AND AIMS

We recently showed that plasma cholesteryl ester transfer protein (CETP) is mainly derived from VSIG4-positive Kupffer cells. Activation of these cells by the bacterial endotoxin lipopolysaccharide (LPS) strongly decreases CETP expression. As Kupffer cell activation plays a detrimental role in the progression of non-alcoholic fatty liver disease (NAFLD), we aimed to study if metabolic liver inflammation is also associated with a decrease in hepatic and circulating CETP.

METHODS

We collected plasma and liver biopsy samples at various stages of NAFLD from 93 obese individuals who underwent bariatric surgery. Liver lobular inflammation was histologically determined, and liver CETP expression, CETP positive cells, circulating CETP concentrations, and liver VSIG4 expression were quantified.

RESULTS

Mean (SD) plasma CETP concentration was 2.68 (0.89) μg/mL. In the presence of liver inflammation, compared to the absence of pathology, the difference in hepatic CETP expression was -0.03 arbitrary units (95% CI -0.26, 0.20), the difference in number of hepatic CETP positive cells (range 11-140 per mm²) was -20.0 per mm² (95% CI -41.6, 1.9), and the difference in plasma CETP was -0.35 μg/mL (95% CI -0.80, 0.10). Hepatic VSIG4 expression was not associated with liver inflammation (0.00; 95% CI -0.15, 0.15).

CONCLUSIONS

We found no strong evidence for a strong negative association between metabolic liver inflammation and CETP-related outcomes in obese individuals, although we observed consistent trends. These data indicate that metabolic liver inflammation does not mimic the strong effects of LPS on the hepatic expression and production of CETP by Kupffer cells.

HDL cholesterol efflux capacity and cholesteryl ester transfer are associated with body mass, but are not changed by diet-induced weight loss: A randomized trial in abdominally obese men

BACKGROUND AND AIMS

Obesity is associated with a lower HDL-mediated cholesterol efflux from macrophages and a higher CETP (cholesteryl ester transfer protein) activity, but effects of weight loss are not clear. In addition, associations with visceral and subcutaneous adipose tissue are not known. We therefore investigated effects of diet-induced weight loss on HDL-mediated cholesterol efflux and cholesterol ester (CE) transfer in abdominally obese men. Differences between normal-weight and abdominally obese men were also examined.

METHODS

Twenty-five apparently healthy, normal-weight men (waist circumference: <94 cm) and 52 abdominally obese men (waist circumference: 102-110 cm) were included. Abdominally obese subjects were randomly allocated to a dietary weight-loss intervention group or a no-weight loss control group. Individuals from the intervention group followed a very-low-calorie diet for 6 weeks to obtain a waist circumference below 102 cm, followed by a 2-week weight-stable period. Cholesterol efflux was measured in BODIPY-labeled murine J774 macrophages. CE transfer was measured by quantifying the transfer of CE from radiolabeled exogenous HDL to apoB-containing lipoproteins.

RESULTS

Cholesterol efflux capacity was 9 percentage point (pp) lower in abdominally obese than in normal-weight men (p≤0.001), while CE transfer was 5 pp higher (p≤0.01). Diet-induced weight-loss of 10.3 kg did not change cholesterol efflux and CE transfer. In addition, stepwise regression analysis did not suggest that the different fat depots are differently related to efflux capacity and CE transfer.

CONCLUSIONS

After a 2-week weight-stable period, dietary weight loss of 10 kg did not improve ABCA1-mediated cholesterol efflux and CE transfer in abdominally obese men.