Resistance training responses across race and ethnicity: a narrative review

OBJECTIVES

Although the physiological mechanisms are not fully understood, race/ethnicity differences vary across cardiometabolic disease risk factors. Resistance training (RT) is an effective therapy for improving these risk factors in addition to body composition and physical performance. Thus, the purpose of this study was to determine the effects of RT over time on different racial and ethnic populations across cardiometabolic, body composition, and physical performance outcomes.

DESIGN

Electronic databases Scopus and PubMed were searched for studies that compared different racial/ethnic responses to RT across cardiometabolic, body composition, and physical performance parameters. Inclusion criteria for the studies were as follows: (1) published in the English language; (2) compared races or ethnicities across cardiometabolic risk factors, body composition, or physical performance variables following a RT intervention; (3) included adults 18 years or older, and (4) included an isolated RT intervention group.

RESULTS

Nine studies were found that met the inclusion criteria. The identified studies involved cohorts of White American (WA), South Asian, European Chilean, Mapuche Chilean, White Scottish, and African American (AA) males and females. Race/ethnicity differences following a RT intervention were found for fat-free mass preservation and changes in blood pressure, endothelial function, brachial artery stiffness, cardiac autonomic function, inflammatory and oxidative stress markers, insulin sensitivity, body mass index, waist circumference, % body fat, and muscular strength. With the exception of changes in systolic blood pressure and brachial artery stiffness, AAs consistently showed more beneficial adaptations compared to WAs to RT across studies.

CONCLUSION

Race and ethnicity play a role in how adults adapt to chronic RT. These data may aid in better understanding the social, biological, and environmental factors that likely influenced these racial/ethnic differences in response to RT, assist in creating tailored exercise prescriptions for various racial/ethnic populations, and inform policies for determining resource allocations to address health inequities.

Identification of a Gain-of-Function LIPC Variant as a Novel Cause of Familial Combined Hypocholesterolemia

BACKGROUND

Atherosclerotic cardiovascular disease is the main cause of mortality worldwide and is strongly influenced by circulating low-density lipoprotein (LDL) cholesterol levels. Only a few genes causally related to plasma LDL cholesterol levels have been identified so far, and only 1 gene, ANGPTL3, has been causally related to combined hypocholesterolemia. Here, our aim was to elucidate the genetic origin of an unexplained combined hypocholesterolemia inherited in 4 generations of a French family.

METHODS

Using next-generation sequencing, we identified a novel dominant rare variant in the LIPC gene, encoding for hepatic lipase, which cosegregates with the phenotype. We characterized the impact of this LIPC-E97G variant on circulating lipid and lipoprotein levels in family members using nuclear magnetic resonance-based lipoprotein profiling and lipidomics. To uncover the mechanisms underlying the combined hypocholesterolemia, we used protein homology modeling, measured triglyceride lipase and phospholipase activities in cell culture, and studied the phenotype of APOE*3.Leiden.CETP mice after LIPC-E97G overexpression.

RESULTS

Family members carrying the LIPC-E97G variant had very low circulating levels of LDL cholesterol and high-density lipoprotein cholesterol, LDL particle numbers, and phospholipids. The lysophospholipids/phospholipids ratio was increased in plasma of LIPC-E97G carriers, suggestive of an increased lipolytic activity on phospholipids. In vitro and in vivo studies confirmed that the LIPC-E97G variant specifically increases the phospholipase activity of hepatic lipase through modification of an evolutionarily conserved motif that determines substrate access to the hepatic lipase catalytic site. Mice overexpressing human LIPC-E97G recapitulated the combined hypocholesterolemic phenotype of the family and demonstrated that the increased phospholipase activity promotes catabolism of triglyceride-rich lipoproteins by different extrahepatic tissues but not the liver.

CONCLUSIONS

We identified and characterized a novel rare variant in the LIPC gene in a family who presents with dominant familial combined hypocholesterolemia. This gain-of-function variant makes LIPC the second identified gene, after ANGPTL3, causally involved in familial combined hypocholesterolemia. Our mechanistic data highlight the critical role of hepatic lipase phospholipase activity in LDL cholesterol homeostasis and suggest a new LDL clearance mechanism.

Remnant Cholesterol and Common Carotid Artery Intima-Media Thickness in Patients With Ischemic Stroke

BACKGROUND

Remnant cholesterol makes great contribution to residual risk of cardiovascular disease, but population-based evidence on the relationship between remnant cholesterol and atherosclerosis is rare. Common carotid artery intima-media thickness (cIMT) is an imaging marker of subclinical atherosclerosis. We aimed to explore the association between remnant cholesterol levels and cIMT in patients with ischemic stroke.

METHODS

One thousand four hundred ninety-six ischemic stroke patients with baseline serum lipids and carotid artery imaging data were included in this analysis. Fasting remnant cholesterol was calculated as total cholesterol minus HDL (high-density lipoprotein) cholesterol minus LDL (low-density lipoprotein) cholesterol. Abnormal cIMT was defined as mean cIMT and maximum cIMT value ≥1 mm. Logistic regression and restricted cubic spline models were used to assess the relationships between remnant cholesterol levels and abnormal cIMT.

RESULTS

The multivariable-adjusted odds ratios (95% CIs) for the highest versus lowest quartile of remnant cholesterol were 2.06 (1.46-2.91) for abnormal mean cIMT and 1.70 (1.23-2.35) for abnormal maximum cIMT. There were linear associations between remnant cholesterol levels and both abnormal mean cIMT (P for linearity, <0.001) and abnormal maximum cIMT (P for linearity, 0.003). Moreover, the remnant cholesterol-cIMT association remained significant in the subsample of patients with optimal LDL cholesterol levels (n=179).

CONCLUSIONS

Elevated fasting remnant cholesterol levels were positively associated with mean cIMT and maximum cIMT in patients with ischemic stroke, even in patients with optimal LDL cholesterol levels. Future prospective studies are needed to verify our findings and to assess the effect of remnant cholesterol-lowering interventions in patients with ischemic stroke.

HDL (High-Density Lipoprotein) and ApoA-1 (Apolipoprotein A-1) Potentially Modulate Pancreatic α-Cell Glucagon Secretion

OBJECTIVE

Subjects with low levels of HDL (high-density lipoprotein) and ApoA-1 (apolipoprotein A-1) have increased risk to develop type 2 diabetes. HDL levels are an independent predictor of β-cell function and positively modulate it. Type 2 diabetes is characterized by defects in both β and α-cell function, but the effect of HDL and ApoA1 on α-cell function is unknown. Approach and Results: We observed a significant negative correlation (r=-0.422, P<0.0001) between HDL levels and fasting glucagon in a cohort of 132 Italian subjects. In a multivariable regression analysis including potential confounders such as age, sex, BMI, triglycerides, total cholesterol, fasting and 2-hour postload glucose, and fasting insulin, the association between HDL and fasting glucagon remained statistically significant (β=-0.318, P=0.006). CD1 mice treated with HDL or ApoA-1 for 3 consecutive days showed a 32% (P<0.001) and 23% (P<0.05) reduction, respectively, in glucagon levels following insulin-induced hypoglycemia, compared with controls. Treatment of pancreatic αTC1 clone 6 cells with HDL or ApoA-1 for 24 hours resulted in a significant reduction of glucagon expression (P<0.04) and secretion (P<0.01) after an hypoglycemic stimulus and increased Akt (RAC-alpha serine/threonine-protein kinase) and FoxO1 (forkhead/winged helix box gene, group O-1) phosphorylation. Pretreatment with Akt inhibitor VIII, PI3K (phosphatidylinositol 3-kinase) inhibitor LY294002, and HDL receptor SCARB-1 (scavenger receptor class B type 1) inhibitor BLT-1 (block lipid transport-1) restored αTC1 cell response to low glucose levels.

CONCLUSIONS

These results support the notion that HDL and ApoA-1 modulate glucagon expression and secretion by binding their cognate receptor SCARB-1, and activating the PI3K/Akt/FoxO1 signaling cascade in an in vitro α-cell model. Overall, these results raise the hypothesis that HDL and ApoA-1 may have a role in modulating glucagon secretion.

HDL (High-Density Lipoprotein) Remodeling and Magnetic Resonance Imaging-Assessed Atherosclerotic Plaque Burden: Study in a Preclinical Experimental Model

OBJECTIVE

HDL (high-density lipoprotein) role in atherosclerosis is controversial. Clinical trials with CETP (cholesterylester transfer protein)-inhibitors have not provided benefit. We have shown that HDL remodeling in hypercholesterolemia reduces HDL cardioprotective potential. We aimed to assess whether hypercholesterolemia affects HDL-induced atherosclerotic plaque regression. Approach and Results: Atherosclerosis was induced in New Zealand White rabbits for 3-months by combining a high-fat-diet and double-balloon aortic denudation. Then, animals underwent magnetic resonance imaging (basal plaque) and randomized to receive 4 IV infusions (1 infusion/wk) of HDL isolated from normocholesterolemic (NC-HDL; 75 mg/kg; n=10), hypercholesterolemic (HC-HDL; 75 mg/Kg; n=10), or vehicle (n=10) rabbits. Then, animals underwent a second magnetic resonance imaging (end plaque). Blood, aorta, and liver samples were obtained for analyses. Follow-up magnetic resonance imaging revealed that NC-HDL administration regressed atherosclerotic lesions by 4.3%, whereas, conversely, the administration of HC-HDLs induced a further 6.5% progression (P<0.05 versus basal). Plaque characterization showed that HC-HDL administered animals had a 2-fold higher lipid and cholesterol content versus those infused NC-HDL and vehicle (P<0.05). No differences were observed among groups in CD31 levels, nor in infiltrated macrophages or smooth muscle cells. Plaques from HC-HDL administered animals exhibited higher Casp3 (caspase 3) content (P<0.05 versus vehicle and NC-HDL) whereas plaques from NC-HDL infused animals showed lower expression of Casp3, Cox1 (cyclooxygenase 1), inducible nitric oxide synthase, and MMP (metalloproteinase) activity (P<0.05 versus HC-HDL and vehicle). HDLs isolated from animals administered HC-HDL displayed lower antioxidant potential and cholesterol efflux capacity as compared with HDLs isolated from NC-HDL-infused animal and vehicle or donor HDL (P<0.05). There were no differences in HDL-ApoA1 content, ABCA1 (ATP-binding cassette transporter A1) vascular expression, and SRB1 (scavenger receptor B1) and ABCA1 liver expression.

CONCLUSIONS

HDL particles isolated from a hypercholesterolemic milieu lose their ability to regress and stabilize atherosclerotic lesions. Our data suggest that HDL remodeling in patients with co-morbidities may lead to the loss of HDL atheroprotective functions.

Cholesterol Efflux Pathways Suppress Inflammasome Activation, NETosis, and Atherogenesis

BACKGROUND

The CANTOS trial (Canakinumab Antiinflammatory Thrombosis Outcome Study) showed that antagonism of interleukin (IL)-1β reduces coronary heart disease in patients with a previous myocardial infarction and evidence of systemic inflammation, indicating that pathways required for IL-1β secretion increase cardiovascular risk. IL-1β and IL-18 are produced via the NLRP3 inflammasome in myeloid cells in response to cholesterol accumulation, but mechanisms linking NLRP3 inflammasome activation to atherogenesis are unclear. The cholesterol transporters ATP binding cassette A1 and G1 (ABCA1/G1) mediate cholesterol efflux to high-density lipoprotein, and Abca1/g1 deficiency in myeloid cells leads to cholesterol accumulation.

METHODS

To interrogate mechanisms connecting inflammasome activation with atherogenesis, we used mice with myeloid Abca1/g1 deficiency and concomitant deficiency of the inflammasome components Nlrp3 or Caspase-1/11. Bone marrow from these mice was transplanted into Ldlr^-/- recipients, which were fed a Western-type diet.

RESULTS

Myeloid Abca1/g1 deficiency increased plasma IL-18 levels in Ldlr^-/- mice and induced IL-1β and IL-18 secretion in splenocytes, which was reversed by Nlrp3 or Caspase-1/11 deficiency, indicating activation of the NLRP3 inflammasome. Nlrp3 or Caspase-1/11 deficiency decreased atherosclerotic lesion size in myeloid Abca1/g1-deficient Ldlr^-/- mice. Myeloid Abca1/g1 deficiency enhanced caspase-1 cleavage not only in splenic monocytes and macrophages, but also in neutrophils, and dramatically enhanced neutrophil accumulation and neutrophil extracellular trap formation in atherosclerotic plaques, with reversal by Nlrp3 or Caspase-1/11 deficiency, suggesting that inflammasome activation promotes neutrophil recruitment and neutrophil extracellular trap formation in atherosclerotic plaques. These effects appeared to be indirectly mediated by systemic inflammation leading to activation and accumulation of neutrophils in plaques. Myeloid Abca1/g1 deficiency also activated the noncanonical inflammasome, causing increased susceptibility to lipopolysaccharide-induced mortality. Patients with Tangier disease, who carry loss-of-function mutations in ABCA1 and have increased myeloid cholesterol content, showed a marked increase in plasma IL-1β and IL-18 levels.

CONCLUSIONS

Cholesterol accumulation in myeloid cells activates the NLRP3 inflammasome, which enhances neutrophil accumulation and neutrophil extracellular trap formation in atherosclerotic plaques. Patients with Tangier disease, who have increased myeloid cholesterol content, showed markers of inflammasome activation, suggesting human relevance.

V-ATPase (Vacuolar ATPase) Activity Required for ABCA1 (ATP-Binding Cassette Protein A1)-Mediated Cholesterol Efflux

Objective- We have shown that ABCA1 (ATP-binding cassette protein A1) mediates unfolding of the apoA1 (apolipoprotein A1) N-terminal helical hairpin during apoA1 lipidation. Others have shown that an acidic pH exposes the hydrophobic surface of apoA1. We postulated that the V-ATPase (vacuolar ATPase) proton pump facilitates apoA1 unfolding and promotes ABCA1-mediated cholesterol efflux. Approach and Results- We found that V-ATPase inhibitors dose-dependently decreased ABCA1-mediated cholesterol efflux to apoA1 in baby hamster kidney cells and RAW264.7 cells; and similarly, siRNA knockdown of ATP6V₀C inhibited ABCA1-mediated cholesterol efflux to apoA1 in RAW264.7 cells. Although ABCA1 expression did not alter total cellular levels of V-ATPase, ABCA1 increased the cell surface levels of the V₀A1 and V₁E1 subunits of V-ATPase. We generated a fluorescein isothiocyanate/Alexa647 double-labeled fluorescent ratiometric apoA1 pH indicator whose fluorescein isothiocyanate/Alexa647 emission ratio decreased as the pH drops. We found that ABCA1 induction in baby hamster kidney cells led to acidification of the cell-associated apoA1 pH indicator, compared with control cells without ABCA1 expression. The V-ATPase inhibitor bafilomycin A1 dose-dependently inhibited the apoA1 pH shift in ABCA1-expressing cells, without affecting the levels of cell-associated apoA1. However, we were not able to detect ABCA1-mediated extracellular proton release. We showed that acidic pH facilitated apoA1 unfolding, apoA1 solubilization of phosphatidycholine:phosphatidyserine liposomes, and increased lipid fluidity of these liposomes. Conclusions- Our results support a model that ABCA1 recruits V-ATPase to the plasma membrane where V-ATPase mediates apoA1 acidification and membrane remodeling that promote apoA1 unfolding and ABCA1-mediated HDL (high-density lipoprotein) biogenesis and lipid efflux.

SREBF1/MicroRNA-33b Axis Exhibits Potent Effect on Unstable Atherosclerotic Plaque Formation In Vivo

Objective- Atherosclerosis is a common disease caused by a variety of metabolic and inflammatory disturbances. MicroRNA (miR)-33a within SREBF2 (sterol regulatory element-binding factor 2) is a potent target for treatment of atherosclerosis through regulating both aspects; however, the involvement of miR-33b within SREBF1 remains largely unknown. Although their host genes difference could lead to functional divergence of miR-33a/b, we cannot dissect the roles of miR-33a/b in vivo because of lack of miR-33b sequences in mice, unlike human. Approach and Results- Here, we analyzed the development of atherosclerosis using miR-33b knock-in humanized mice under apolipoprotein E-deficient background. MiR-33b is prominent both in human and mice on atheroprone condition. MiR-33b reduced serum high-density lipoprotein cholesterol levels and systemic reverse cholesterol transport. MiR-33b knock-in macrophages showed less cholesterol efflux capacity and higher inflammatory state via regulating lipid rafts. Thus, miR-33b promotes vulnerable atherosclerotic plaque formation. Furthermore, bone marrow transplantation experiments strengthen proatherogenic roles of macrophage miR-33b. Conclusions- Our data demonstrated critical roles of SREBF1-miR-33b axis on both lipid profiles and macrophage phenotype remodeling and indicate that miR-33b is a promising target for treating atherosclerosis.

Comparison of Conventional Lipoprotein Tests and Apolipoproteins in the Prediction of Cardiovascular Disease

BACKGROUND

Total cholesterol and high-density lipoprotein cholesterol (HDL-C) measurements are central to cardiovascular disease (CVD) risk assessment, but there is continuing debate around the utility of other lipids for risk prediction.

METHODS

Participants from UK Biobank without baseline CVD and not taking statins, with relevant lipid measurements (n=346 686), were included in the primary analysis. An incident fatal or nonfatal CVD event occurred in 6216 participants (1656 fatal) over a median of 8.9 years. Associations of nonfasting lipid measurements (total cholesterol, HDL-C, non-HDL-C, direct and calculated low-density lipoprotein cholesterol [LDL-C], and apolipoproteins [Apo] A1 and B) with CVD were compared using Cox models adjusting for classical risk factors, and predictive utility was determined by the C-index and net reclassification index. Prediction was also tested in 68 649 participants taking a statin with or without baseline CVD (3515 CVD events).

RESULTS

ApoB, LDL-C, and non-HDL-C were highly correlated (r>0.90), while HDL-C was strongly correlated with ApoA1 (r=0.92). After adjustment for classical risk factors, 1 SD increase in ApoB, direct LDL-C, and non-HDL-C had similar associations with composite fatal/nonfatal CVD events (hazard ratio, 1.23, 1.20, 1.21, respectively). Associations for 1 SD increase in HDL-C and ApoA1 were also similar (hazard ratios, 0.81 [both]). Adding either total cholesterol and HDL-C, or ApoB and ApoA, to a CVD risk prediction model (C-index, 0.7378) yielded similar improvement in discrimination (C-index change, 0.0084; 95% CI, 0.0065, 0.0104, and 0.0089; 95% CI, 0.0069, 0.0109, respectively). Once total and HDL-C were in the model, no further substantive improvement was achieved with the addition of ApoB (C-index change, 0.0004; 95% CI, 0.0000, 0.0008) or any measure of LDL-C. Results for predictive utility were similar for a fatal CVD outcome, and in a discordance analysis. In participants taking a statin, classical risk factors (C-index, 0.7118) were improved by non-HDL-C (C-index change, 0.0030; 95% CI, 0.0012, 0.0048) or ApoB (C-index change, 0.0030; 95% CI, 0.0011, 0.0048). However, adding ApoB or LDL-C to a model already containing non-HDL-C did not further improve discrimination.

CONCLUSIONS

Measurement of total cholesterol and HDL-C in the nonfasted state is sufficient to capture the lipid-associated risk in CVD prediction, with no meaningful improvement from addition of apolipoproteins, direct or calculated LDL-C.

Impact of training primary care physicians in behavioral counseling to reduce cardiovascular disease risk factors in Ecuador

OBJECTIVE

To assess the feasibility of implementing a physician-based, patient-centered counseling intervention model in Ecuador to improve the ability of primary care physicians (PCPs) to reduce cardiovascular disease (CVD) risk factors among patients.

METHODS

This was a randomized clinical trial conducted in primary care clinics in Quito in 2014 - 2016. Participants included 15 PCPs and their adult patients at high risk of developing type-2 diabetes. A physician-based and patient-centered counseling program was delivered to eight PCPs. Seven PCPs who did not receive the training comprised the control group. The patient experience was assessed by a patient exit interview (PEI). Assessment of the patient's anthropometrics, blood pressure, and blood biochemistry parameters were conducted. Changes within and between groups were estimated utilizing chi-square, ANOVA, paired t-tests, and coefficient with intervention.

RESULTS

A total of 197 patients participated, 113 in the intervention care group (ICG) and 84 in the usual care group (UCG); 99 patients (87.6%) in the ICG and 63 (75%) in the UCG completed the study. Counseling steps, measured by the PEI, were significantly higher in the ICG (8.9±1.6 versus 6.6±2.3; P = 0.001). Comparison of the estimated difference between the ICG and the UCG showed greater decreases in HbA1c and total cholesterol in the ICG. Within the ICG, there were significant improvements in weight, BMI, HbA1C, total cholesterol, and LDL-cholesterol.

CONCLUSIONS

Training PCPs in a patient-centered behavioral intervention for CVD risk factor reduction is feasible and efficacious for reducing CVD risk factors in Ecuador. Developed and developing countries alike could benefit from such an intervention.

Role of Blood Lipids in the Development of Ischemic Stroke and its Subtypes: A Mendelian Randomization Study

BACKGROUND AND PURPOSE

Statin therapy is associated with a lower risk of ischemic stroke supporting a causal role of low-density lipoprotein (LDL) cholesterol. However, more evidence is needed to answer the question whether LDL cholesterol plays a causal role in ischemic stroke subtypes. In addition, it is unknown whether high-density lipoprotein cholesterol and triglycerides have a causal relationship to ischemic stroke and its subtypes. Our aim was to investigate the causal role of LDL cholesterol, high-density lipoprotein cholesterol, and triglycerides in ischemic stroke and its subtypes through Mendelian randomization (MR).

METHODS

Summary data on 185 genome-wide lipids-associated single nucleotide polymorphisms were obtained from the Global Lipids Genetics Consortium and the Stroke Genetics Network for their association with ischemic stroke (n=16 851 cases and 32 473 controls) and its subtypes, including large artery atherosclerosis (n=2410), small artery occlusion (n=3186), and cardioembolic (n=3427) stroke. Inverse-variance-weighted MR was used to obtain the causal estimates. Inverse-variance-weighted multivariable MR, MR-Egger, and sensitivity exclusion of pleiotropic single nucleotide polymorphisms after Steiger filtering and MR-Pleiotropy Residual Sum and Outlier test were used to adjust for pleiotropic bias.

RESULTS

A 1-SD genetically elevated LDL cholesterol was associated with an increased risk of ischemic stroke (odds ratio: 1.12; 95% confidence interval: 1.04-1.20) and large artery atherosclerosis stroke (odds ratio: 1.28; 95% confidence interval: 1.10-1.49) but not with small artery occlusion or cardioembolic stroke in multivariable MR. A 1-SD genetically elevated high-density lipoprotein cholesterol was associated with a decreased risk of small artery occlusion stroke (odds ratio: 0.79; 95% confidence interval: 0.67-0.90) in multivariable MR. MR-Egger indicated no pleiotropic bias, and results did not markedly change after sensitivity exclusion of pleiotropic single nucleotide polymorphisms. Genetically elevated triglycerides did not associate with ischemic stroke or its subtypes.

CONCLUSIONS

LDL cholesterol lowering is likely to prevent large artery atherosclerosis but may not prevent small artery occlusion nor cardioembolic strokes. High-density lipoprotein cholesterol elevation may lead to benefits in small artery disease prevention. Finally, triglyceride lowering may not yield benefits in ischemic stroke and its subtypes.

From High-Density Lipoprotein Cholesterol to Measurements of Function: Prospects for the Development of Tests for High-Density Lipoprotein Functionality in Cardiovascular Disease

The evidence is strong that biological functions contained in high-density lipoproteins (HDL) are antiatherogenic. These functions may track with HDL cholesterol or apolipoprotein A1 concentration to explain the strongly inverse risk curve for cardiovascular disease. Moreover, there are harmful as well as protective HDL subspecies in regard to cardiovascular disease, which could be responsible for paradoxical responses to HDL-directed treatments. Recent metabolic studies show that apolipoprotein A1-containing HDL is secreted into the circulation as mostly spherical cholesterol ester-rich lipoproteins that span the HDL size range. Most of the flux of apolipoprotein A1 HDL into and out of the circulation occurs in these spherical cholesterol-replete particles. Discoidal cholesterol-poor HDL comprises a minority of HDL secretion. We propose that much cholesterol in reverse cholesterol transport enters and exits medium and large size HDL without changing a size category, and its flux may be estimated provisionally from holoparticle clearance of cholesterol ester-rich HDL. An accurate framework for metabolism of HDL is essential to finding steady-state biomarkers that reflect HDL function in vivo. Whereas cholesterol efflux from cells to mainly discoidal HDL, mediated by ABCA1 (ATP-binding cassette transporter ABCA1), predicts cardiovascular disease, cholesterol transfers to spherical HDL also can be measured and may be relevant to protection against atherosclerosis. We propose several investigative paths on which human HDL biology may be investigated leading to convenient biomarkers of HDL quality and function having potential not only to improve risk prediction but also to more accurately target drug treatments.

Blood Calcification Propensity, Cardiovascular Events, and Survival in Patients Receiving Hemodialysis in the EVOLVE Trial

BACKGROUND AND OBJECTIVES

Patients receiving hemodialysis are at risk of cardiovascular events. A novel blood test (T50 test) determines the individual calcification propensity of blood.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

T50 was determined in 2785 baseline serum samples of patients receiving hemodialysis enrolled in the Evaluation of Cinacalcet Therapy to Lower Cardiovascular Events (EVOLVE) trial and the T50 results were related to patient outcomes.

RESULTS

Serum albumin, bicarbonate, HDL cholesterol, and creatinine were the main factors positively/directly and phosphate was the main factor negatively/inversely associated with T50. The primary composite end point (all-cause mortality, myocardial infarction [MI], hospitalization for unstable angina, heart failure, or peripheral vascular event [PVE]) was reached in 1350 patients after a median follow-up time of 619 days. After adjustments for confounding, a lower T50 was independently associated with a higher risk of the primary composite end point as a continuous measure (hazard ratio [HR] per 1 SD lower T50, 1.15; 95% confidence interval [95% CI], 1.08 to 1.22; P<0.001). Furthermore, lower T50 was associated with a higher risk in all-cause mortality (HR per 1 SD lower T50, 1.10; 95% CI, 1.02 to 1.17; P=0.001), MI (HR per 1 SD lower T50, 1.38; 95% CI, 1.19 to 1.60; P<0.001), and PVE (HR per 1 SD lower T50, 1.22; 95% CI, 1.05 to 1.42; P=0.01). T50 improved risk prediction (integrated discrimination improvement and net reclassification improvement, P<0.001 and P=0.001) of the primary composite end point.

CONCLUSIONS

Blood calcification propensity was independently associated with the primary composite end point, all-cause mortality, MI, and PVE in the EVOLVE study and improved risk prediction. Prospective trials should clarify whether T50-guided therapies improve outcomes.

Identification of Genetic Variants Linking Protein C and Lipoprotein Metabolism: The ARIC Study (Atherosclerosis Risk in Communities)

OBJECTIVE

Previous studies have identified common genetic variants in 4 chromosomal regions that together account for 14% to 15% of the variance in circulating levels of protein C. To further characterize the genetic architecture of protein C, we obtained denser coverage at some loci, extended investigation of protein C to low-frequency and rare variants, and searched for new associations in genes known to influence protein C.

APPROACH AND RESULTS

Genetic associations with protein C antigen level were evaluated in ≤10 778 European and 3190 black participants aged 45 to 64 years. Analyses included >26 million autosomal variants available after imputation to the 1000 Genomes reference panel along with additional low-frequency and rare variants directly genotyped using the Illumina ITMAT-Broad-CARe chip and Illumina HumanExome BeadChip. Genome-wide significant associations (P<5×10^-8) were found for common variants in the GCKR, PROC, BAZ1B, and PROCR-EDEM2 regions in whites and PROC and PROCR-EDEM2 regions in blacks, confirming earlier findings. In a novel finding, the low-density lipoprotein cholesterol-lowering allele of rs12740374, located in the CELSR2-PSRC1-SORT1 region, was associated with lower protein C level in both whites and blacks, reaching genome-wide significance in a meta-analysis combining results from both groups (P=1.4×10^-9). To further investigate a possible link between lipid metabolism and protein C level, we conducted Mendelian randomization analyses using 185 lipid-related genetic variants as instrumental variables. The results indicated that triglycerides, and possibly low-density lipoprotein cholesterol, influence protein C levels.

CONCLUSIONS

Discovery of variants influencing circulating protein C levels in the CELSR2-PSRC1-SORT1 region may indicate a novel genetic link between lipoprotein metabolism and hemostasis.

Subfractions of High-Density Lipoprotein-Cholesterol and Carotid Intima-Media Thickness: The Northern Manhattan Study

BACKGROUND AND PURPOSE

Recent drug trials have challenged the high-density lipoprotein-cholesterol (HDL-C) antiatherosclerotic hypothesis, suggesting that total level of HDL-C may not be the best target for intervention. HDL-C subfractions may be better markers of vascular risk than total levels of HDL-C. The objective of this cross-sectional study was to investigate the relationship between HDL2-C and HDL3-C fractions and carotid intima-media thickness (cIMT) in the population-based Northern Manhattan Study.

METHODS

We evaluated 988 stroke-free participants (mean age, 66±8 years; 60% women; 66% Hispanic, and 34% non-Hispanic) with available data on HDL-C subfractions using precipitation method and cIMT assessed by a high-resolution carotid ultrasound. The associations between HDL-C subfractions and cIMT were analyzed by multiple linear regression models.

RESULTS

The mean HDL2-C was 14±8 mg/dL, HDL3-C 32±8 mg/dL, and the mean total HDL-C was 46±14 mg/dL. The mean cIMT was 0.90±0.08 mm. After controlling for demographics and vascular risk factors, HDL2-C and total HDL-C were inversely associated with cIMT (per 2 SDs, β=-0.017, P=0.001 and β=-0.012, P=0.03, respectively). The same inverse association was more pronounced among those with diabetes mellitus (per 2SDs, HDL2-C: β=-0.043, P=0.003 and HDL-C: β=-0.029, P=0.02). HDL3-C was not associated with cIMT.

CONCLUSIONS

HDL2-C had greater effect on cIMT than HDL3-C in this large urban population. The effect of HDL2-C was especially pronounced among individuals with diabetes mellitus. More research is needed to determine antiatherosclerotic effects of HDL-C subfractions and their clinical relevance.

Type 1 Deiodinase Regulates ApoA-I Gene Expression and ApoA-I Synthesis Independent of Thyroid Hormone Signaling

OBJECTIVE

Plasma levels of high-density lipoprotein cholesterol (HDL-C) and apolipoprotein A-I (ApoA-I) are reduced in individuals with defective insulin signaling. Initial studies using liver-specific insulin receptor (InsR) knockout mice identified reduced expression of type 1 deiodinase (Dio1) as a potentially novel link between defective hepatic insulin signaling and reduced expression of the ApoA-I gene. Our objective was to examine the regulation of ApoA-I expression by Dio1.

APPROACH AND RESULTS

Acute inactivation of InsR by adenoviral delivery of Cre recombinase to InsR floxed mice reduced HDL-C and expression of both ApoA-I and Dio1. Overexpression of Dio1 in InsR knockout mice restored HDL-C and ApoA-I levels and increased the expression of ApoA-I. Dio1 knockout mice had low expression of ApoA-I and reduced serum levels of HDL-C and ApoA-I. Treatment of C57BL/6J mice with antisense to Dio1 reduced ApoA-I mRNA, HDL-C, and serum ApoA-I. Hepatic 3,5,3'-triiodothyronine content was normal or elevated in InsR knockout mice or Dio1 knockout mice. Knockdown of either InsR or Dio1 by siRNA in HepG2 cells decreased the expression of ApoA-I and ApoA-I synthesis and secretion. siRNA knockdown of InsR or Dio1 decreased activity of a region of the ApoA-I promoter lacking thyroid hormone response elements (region B). Electrophoretic mobility shift assay demonstrated that reduced Dio1 expression decreased the binding of nuclear proteins to region B.

CONCLUSIONS

Reductions in Dio1 expression reduce the expression of ApoA-I in a 3,5,3'-triiodothyronine-/thyroid hormone response element-independent manner.

Micro-RNAs and High-Density Lipoprotein Metabolism

Improved prevention and treatment of cardiovascular diseases is one of the challenges in Western societies, where ischemic heart disease and stroke are the leading cause of death. Early epidemiological studies have shown an inverse correlation between circulating high-density lipoprotein-cholesterol (HDL-C) and cardiovascular diseases. The cardioprotective effect of HDL is because of its ability to remove cholesterol from plaques in the artery wall to the liver for excretion by a process known as reverse cholesterol transport. Numerous studies have reported the role that micro-RNAs (miRNA) play in the regulation of the different steps in reverse cholesterol transport, including HDL biogenesis, cholesterol efflux, and cholesterol uptake in the liver and bile acid synthesis and secretion. Because of their ability to control different aspects of HDL metabolism and function, miRNAs have emerged as potential therapeutic targets to combat cardiovascular diseases. In this review, we summarize the recent advances in the miRNA-mediated control of HDL metabolism. We also discuss how HDL particles serve as carriers of miRNAs and the potential use of HDL-containing miRNAs as cardiovascular diseases biomarkers.

High-Density Lipoprotein Proteomic Composition, and not Efflux Capacity, Reflects Differential Modulation of Reverse Cholesterol Transport by Saturated and Monounsaturated Fat Diets

BACKGROUND

Acute inflammation impairs reverse cholesterol transport (RCT) and reduces high-density lipoprotein (HDL) function in vivo. This study hypothesized that obesity-induced inflammation impedes RCT and alters HDL composition, and investigated if dietary replacement of saturated (SFA) for monounsaturated (MUFA) fatty acids modulates RCT.

METHODS AND RESULTS

Macrophage-to-feces RCT, HDL efflux capacity, and HDL proteomic profiling was determined in C57BL/6j mice following 24 weeks on SFA- or MUFA-enriched high-fat diets (HFDs) or low-fat diet. The impact of dietary SFA consumption and insulin resistance on HDL efflux function was also assessed in humans. Both HFDs increased plasma (3)H-cholesterol counts during RCT in vivo and ATP-binding cassette, subfamily A, member 1-independent efflux to plasma ex vivo, effects that were attributable to elevated HDL cholesterol. By contrast, ATP-binding cassette, subfamily A, member 1-dependent efflux was reduced after both HFDs, an effect that was also observed with insulin resistance and high SFA consumption in humans. SFA-HFD impaired liver-to-feces RCT, increased hepatic inflammation, and reduced ABC subfamily G member 5/8 and ABC subfamily B member 11 transporter expression in comparison with low-fat diet, whereas liver-to-feces RCT was preserved after MUFA-HFD. HDL particles were enriched with acute-phase proteins (serum amyloid A, haptoglobin, and hemopexin) and depleted of paraoxonase-1 after SFA-HFD in comparison with MUFA-HFD.

CONCLUSIONS

Ex vivo efflux assays validated increased macrophage-to-plasma RCT in vivo after both HFDs but failed to capture differential modulation of hepatic cholesterol trafficking. By contrast, proteomics revealed the association of hepatic-derived inflammatory proteins on HDL after SFA-HFD in comparison with MUFA-HFD, which reflected differential hepatic cholesterol trafficking between groups. Acute-phase protein levels on HDL may serve as novel biomarkers of impaired liver-to-feces RCT in vivo.

Cholesteryl Ester Transfer Protein Inhibition With Anacetrapib Decreases Fractional Clearance Rates of High-Density Lipoprotein Apolipoprotein A-I and Plasma Cholesteryl Ester Transfer Protein

OBJECTIVE

Anacetrapib (ANA), an inhibitor of cholesteryl ester transfer protein (CETP) activity, increases plasma concentrations of high-density lipoprotein cholesterol (HDL-C), apolipoprotein A-I (apoA)-I, apoA-II, and CETP. The mechanisms responsible for these treatment-related increases in apolipoproteins and plasma CETP are unknown. We performed a randomized, placebo (PBO)-controlled, double-blind, fixed-sequence study to examine the effects of ANA on the metabolism of HDL apoA-I and apoA-II and plasma CETP.

APPROACH AND RESULTS

Twenty-nine participants received atorvastatin (ATV) 20 mg/d plus PBO for 4 weeks, followed by ATV plus ANA 100 mg/d for 8 weeks (ATV-ANA). Ten participants received double PBO for 4 weeks followed by PBO plus ANA for 8 weeks (PBO-ANA). At the end of each treatment, we examined the kinetics of HDL apoA-I, HDL apoA-II, and plasma CETP after D3-leucine administration as well as 2D gel analysis of HDL subspecies. In the combined ATV-ANA and PBO-ANA groups, ANA treatment increased plasma HDL-C (63.0%; P<0.001) and apoA-I levels (29.5%; P<0.001). These increases were associated with reductions in HDL apoA-I fractional clearance rate (18.2%; P=0.002) without changes in production rate. Although the apoA-II levels increased by 12.6% (P<0.001), we could not discern significant changes in either apoA-II fractional clearance rate or production rate. CETP levels increased 102% (P<0.001) on ANA because of a significant reduction in the fractional clearance rate of CETP (57.6%, P<0.001) with no change in CETP production rate.

CONCLUSIONS

ANA treatment increases HDL apoA-I and CETP levels by decreasing the fractional clearance rate of each protein.

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.

HDL particle size is a critical determinant of ABCA1-mediated macrophage cellular cholesterol export

RATIONALE

High-density lipoprotein (HDL) is a heterogeneous population of particles. Differences in the capacities of HDL subfractions to remove cellular cholesterol may explain variable correlations between HDL-cholesterol and cardiovascular risk and inform future targets for HDL-related therapies. The ATP binding cassette transporter A1 (ABCA1) facilitates cholesterol efflux to lipid-free apolipoprotein A-I, but the majority of apolipoprotein A-I in the circulation is transported in a lipidated state and ABCA1-dependent efflux to individual HDL subfractions has not been systematically studied.

OBJECTIVE

Our aims were to determine which HDL particle subfractions are most efficient in mediating cellular cholesterol efflux from foam cell macrophages and to identify the cellular cholesterol transporters involved in this process.

METHODS AND RESULTS

We used reconstituted HDL particles of defined size and composition, isolated subfractions of human plasma HDL, cell lines stably expressing ABCA1 or ABCG1, and both mouse and human macrophages in which ABCA1 or ABCG1 expression was deleted. We show that ABCA1 is the major mediator of macrophage cholesterol efflux to HDL, demonstrating most marked efficiency with small, dense HDL subfractions (HDL3b and HDL3c). ABCG1 has a lesser role in cholesterol efflux and a negligible role in efflux to HDL3b and HDL3c subfractions.

CONCLUSIONS

Small, dense HDL subfractions are the most efficient mediators of cholesterol efflux, and ABCA1 mediates cholesterol efflux to small dense HDL and to lipid-free apolipoprotein A-I. HDL-directed therapies should target increasing the concentrations or the cholesterol efflux capacity of small, dense HDL species in vivo.

Circulating cholesteryl ester transfer protein and coronary heart disease: mendelian randomization meta-analysis

BACKGROUND

The cholesteryl ester transfer protein (CETP) plays a central role in reverse cholesterol transport. Currently, it remains unresolved whether circulating CETP is causally associated with coronary heart disease (CHD). We aimed to investigate this causal association using CETP gene rs708272 polymorphism as an instrument in a Mendelian randomization meta-analysis.

METHODS AND RESULTS

We searched PubMed and EMBASE before May 2014. Data and study quality were assessed in duplicate. Thirty-four articles (17 813 CHD patients and 22 203 controls) were qualified. Overall analyses revealed a significant association of rs708272-B1 allele with a reduced CHD risk compared with B2 allele under allelic (odds ratio and 95% confidence interval: 0.87 and 0.82-0.92; P<0.001), homozygous genotypic (0.74 and 0.66-0.83; P<0.001), and dominant (0.87 and 0.80-0.94; P<0.001) models. Carriers of rs708272-B1B1 genotype (weighted mean difference and 95% confidence interval: -0.21 and -0.41 to 0.00 μg/dL; P=0.052) or B1 allele (-0.15 and -0.30 to 0.00 μg/dL; P=0.056) had a marginally lower circulating CETP level compared with B2B2 genotype carriers. In Mendelian randomization analysis, there was a 25% (odds ratio and 95% confidence interval: 0.75 and 0.19-0.91) and a 17% (0.83 and 0.41-0.96) significantly reduced risk of CHD by a reduction of 0.2 μg/mL in circulating CETP for the comparison of B1B1 genotype and B1 allele with B2B2 genotype, respectively. There were low probabilities of publication bias.

CONCLUSIONS

Our findings demonstrate that the long-term genetically reduced circulating CETP might be causally associated with the low risk of CHD.

Differential association of plasma angiopoietin-like proteins 3 and 4 with lipid and metabolic traits

OBJECTIVE

Angiopoietin-like protein 3 (ANGPTL3) and 4 (ANGPTL4) are secreted proteins that inhibit lipoprotein lipase in vitro. Genetic variants at the ANGPTL3 and ANGPTL4 gene loci are significantly associated with plasma lipid traits. The aim of this study was to evaluate the association of plasma ANGPTL3 and ANGPTL4 concentrations with lipid and metabolic traits in a large community-based sample.

APPROACH AND RESULTS

Plasma ANGPTL3 and ANGPTL4 levels were measured in 1770 subjects using a validated ELISA assay. A Pearson unadjusted correlation analysis and a linear regression analysis adjusting for age, sex, and race were performed. ANGPTL3 levels were significantly positively associated with low-density lipoprotein cholesterol and high-density lipoprotein cholesterol levels (both P<2×10(-5)) but not triglycerides. In contrast, ANGPTL4 levels were significantly negatively associated with low-density lipoprotein cholesterol and high-density lipoprotein cholesterol (both P<2×10(-5)) and positively associated with triglycerides (P=0.003). In addition, ANGPTL4, but not ANGPTL3, levels were significantly positively associated with fasting blood glucose and metabolic syndrome.

CONCLUSIONS

Despite having similar biochemical effects in vitro, plasma ANGPTL3 and ANGPTL4 concentrations have nearly opposite relationships with plasma lipids. ANGPTL4 is strongly negatively associated with low-density lipoprotein cholesterol and high-density lipoprotein cholesterol and positively with multiple features of the metabolic syndrome including triglycerides, whereas ANGPTL3 is positively associated with low-density lipoprotein cholesterol and high-density lipoprotein cholesterol and not with metabolic syndrome traits including triglycerides. Although ANGPTL3 and ANGPTL4 both inhibit lipoprotein lipase in vitro and influence lipoprotein metabolism in vivo, the physiology of these related proteins and their effects on lipoproteins is clearly divergent and complex.

High-density lipoprotein and atherosclerosis regression: evidence from preclinical and clinical studies

High-density lipoprotein (HDL) particles transport (among other molecules) cholesterol (HDL-C). In epidemiological studies, plasma HDL-C levels have an inverse relationship to the risk of atherosclerotic cardiovascular disease. It has been assumed that this reflects the protective functions of HDL, which include their ability to promote cholesterol efflux. Yet, several recent pharmacological and genetic studies have failed to demonstrate that increased plasma levels of HDL-C resulted in decreased cardiovascular disease risk, giving rise to a controversy regarding whether plasma levels of HDL-C reflect HDL function, or that HDL is even as protective as assumed. The evidence from preclinical and (limited) clinical studies shows that HDL can promote the regression of atherosclerosis when the levels of functional particles are increased from endogenous or exogenous sources. The data show that regression results from a combination of reduced plaque lipid and macrophage contents, as well as from a reduction in its inflammatory state. Although more research will be needed regarding basic mechanisms and to establish that these changes translate clinically to reduced cardiovascular disease events, that HDL can regress plaques suggests that the recent trial failures do not eliminate HDL from consideration as an atheroprotective agent but rather emphasizes the important distinction between HDL function and plasma levels of HDL-C.

MicroRNA control of high-density lipoprotein metabolism and function

Recent discoveries of microRNAs (miRNAs) that control high-density lipoprotein abundance and function have expanded our knowledge of the mechanisms regulating this important lipoprotein subclass. miRNAs have been shown to regulate gene networks that control high-density lipoprotein biogenesis and uptake, as well as discrete steps in the reverse cholesterol transport pathway. Furthermore, high-density lipoprotein itself has been shown to transport miRNAs selectively in health and disease, offering new possibilities of how this lipoprotein may alter gene expression in distal target cells and tissues. Collectively, these discoveries offer new insights into the mechanisms governing high-density lipoprotein metabolism and function and open new avenues for the development of therapeutics for the treatment of cardiovascular disease.

Inhibition of arthritis in the Lewis rat by apolipoprotein A-I and reconstituted high-density lipoproteins

OBJECTIVE

This study questions whether high-density lipoproteins (HDLs) and apolipoprotein A-I inhibit joint inflammation in streptococcal cell wall peptidoglycan-polysaccharide (PG-PS)-induced arthritis in female Lewis rats.

APPROACH AND RESULTS

Administration of PG-PS to female Lewis rats caused acute joint inflammation after 4 days, followed by remission by day 8. The animals subsequently developed chronic joint inflammation that persisted until euthanasia at day 21. Treatment with apolipoprotein A-I 24 hours before and 24 hours after PG-PS administration reduced the acute and chronic joint inflammation. Treatment with apolipoprotein A-I at days 7, 9, and 11 after PG-PS administration reduced the chronic joint inflammation. Treatment with apolipoprotein A-I or reconstituted HDLs consisting of apolipoprotein A-I complexed with phosphatidylcholine 24 hours before and at days 1, 7, 9, and 11 after PG-PS administration reduced acute and chronic joint inflammation. Treatment with apolipoprotein A-I also reduced the inflammatory white blood cell count, synovial fluid proinflammatory cytokine levels, synovial tissue macrophage accumulation, as well as toll-like receptor 2, and inflammatory cytokine expression. At the molecular level, preincubation of human monocyte-derived macrophages with apolipoprotein A-I or reconstituted HDLs before PG-PS stimulation inhibited the PG-PS-induced increase in toll-like receptor 2 and myeloid differentiation primary response gene (88) mRNA levels, nuclear factor-κB activation, and proinflammatory cytokine production. The effects of apolipoprotein A-I and reconstituted HDLs were abolished by transfecting the human monocyte-derived macrophages with ATP-binding cassette transporter A1 or G1 siRNA.

CONCLUSIONS

Apolipoprotein A-I and reconstituted HDLs attenuate PG-PS-induced arthritis in the rat. Studies in human monocyte-derived macrophages indicate that this benefit may be because of the inhibition of toll-like receptor 2 expression and decreased nuclear factor-κB activation in macrophages.

Apolipoprotein A-I protection against atherosclerosis is dependent on genetic background

OBJECTIVE

Inbred mouse strains have different susceptibilities to experimental atherosclerosis. The C57BL/6 strain is among the most sensitive and has, therefore, been the most widely used in atherosclerosis studies, whereas many strains are resistant. The FVB/N strain is highly resistant to atherosclerosis on the apolipoprotein E (apoE)- and low-density lipoprotein (LDL) receptor-deficient backgrounds. High-density lipoprotein and its major apoprotein, apoA-I, have been shown to be protective against atherogenesis on the C57BL/6 background. We here examine the influence of genetic background on the atheroprotective nature of apoA-I.

APPROACH AND RESULTS

ApoE-deficient/apoA-I-deficient mice were generated in the C57BL/6 and FVB/N strains from apoE-deficient mice. After 6 to 10 weeks on a Western-type diet, plasma lipids and atherosclerotic lesion size were assessed. Macrophage recruitment, cholesterol regulation, and blood monocyte levels were examined as potential mechanisms driving lesion size differences. FVB/N knockout mice had higher plasma very-LDL/LDL cholesterol than their C57BL/6 counterparts. ApoA-I deficiency decreased very-LDL/LDL cholesterol in C57BL/6 mice but not in FVB/N mice. FVB/N single and double knockout mice had less lesion than C57BL/6 6 to 10 weeks on diet. ApoA-I deficiency augmented lesion development only in C57BL/6 mice. Macrophage recruitment to thioglycollate-treated peritoneum and diet-induced blood monocyte levels reflected the pattern of lesion development among the 4 genotypes. ApoA-I deficiency increased macrophage cholesterol content only in C57BL/6. FVB/N plasma was a better acceptor for macrophage cholesterol efflux than C57BL/6.

CONCLUSIONS

ApoA-I is atheroprotective only in certain genetic contexts. In the C57BL/6 context, but not FVB/N, apoA-I decreases inflammatory macrophage recruitment and monocytosis, contributors to lesion formation.

High-density lipoprotein maintains skeletal muscle function by modulating cellular respiration in mice

BACKGROUND

Abnormal glucose metabolism is a central feature of disorders with increased rates of cardiovascular disease. Low levels of high-density lipoprotein (HDL) are a key predictor for cardiovascular disease. We used genetic mouse models with increased HDL levels (apolipoprotein A-I transgenic [apoA-I tg]) and reduced HDL levels (apoA-I-deficient [apoA-I ko]) to investigate whether HDL modulates mitochondrial bioenergetics in skeletal muscle.

METHODS AND RESULTS

ApoA-I ko mice exhibited fasting hyperglycemia and impaired glucose tolerance test compared with wild-type mice. Mitochondria isolated from gastrocnemius muscle of apoA-I ko mice displayed markedly blunted ATP synthesis. Endurance capacity during exercise exhaustion test was impaired in apoA-I ko mice. HDL directly enhanced glucose oxidation by increasing glycolysis and mitochondrial respiration rate in C2C12 muscle cells. ApoA-I tg mice exhibited lower fasting glucose levels, improved glucose tolerance test, increased lactate levels, reduced fat mass, associated with protection against age-induced decline of endurance capacity compared with wild-type mice. Circulating levels of fibroblast growth factor 21, a novel biomarker for mitochondrial respiratory chain deficiencies and inhibitor of white adipose lipolysis, were significantly reduced in apoA-I tg mice. Consistent with an increase in glucose utilization of skeletal muscle, genetically increased HDL and apoA-I levels in mice prevented high-fat diet-induced impairment of glucose homeostasis.

CONCLUSIONS

In view of impaired mitochondrial function and decreased HDL levels in type 2 diabetes mellitus, our findings indicate that HDL-raising therapies may preserve muscle mitochondrial function and address key aspects of type 2 diabetes mellitus beyond cardiovascular disease.

Endothelin-1 overexpression exacerbates atherosclerosis and induces aortic aneurysms in apolipoprotein E knockout mice

OBJECTIVE

Endothelin (ET)-1 plays a role in vascular reactive oxygen species production and inflammation. ET-1 has been implicated in human atherosclerosis and abdominal aortic aneurysm (AAA) development. ET-1 overexpression exacerbates high-fat diet-induced atherosclerosis in apolipoprotein E(-/-) (Apoe(-/-)) mice. ET-1-induced reactive oxygen species and inflammation may contribute to atherosclerosis progression and AAA development.

APPROACH AND RESULTS

Eight-week-old male wild-type mice, transgenic mice overexpressing ET-1 selectively in endothelium (eET-1), Apoe(-/-) mice, and eET-1/Apoe(-/-) mice were fed high-fat diet for 8 weeks. eET-1/Apoe(-/-) had a 45% reduction in plasma high-density lipoprotein (P<0.05) and presented ≥ 2-fold more aortic atherosclerotic lesions compared with Apoe(-/-) (P<0.01). AAAs were detected only in eET-1/Apoe(-/-) (8/21; P<0.05). Reactive oxygen species production was increased ≥ 2-fold in perivascular fat, media, or atherosclerotic lesions in the ascending aorta and AAAs of eET-1/Apoe(-/-) compared with Apoe(-/-) (P<0.05). Monocyte/macrophage infiltration was enhanced ≥ 2.5-fold in perivascular fat of ascending aorta and AAAs in eET-1/Apoe(-/-) compared with Apoe(-/-) (P<0.05). CD4(+) T cells were detected almost exclusively in perivascular fat (3/6) and atherosclerotic lesions (5/6) in ascending aorta of eET-1/Apoe(-/-) (P<0.05). The percentage of spleen proinflammatory Ly-6C(hi) monocytes was enhanced 26% by ET-1 overexpression in Apoe(-/-) (P<0.05), and matrix metalloproteinase-2 was increased 2-fold in plaques of eET-1/Apoe(-/-) (P<0.05) compared with Apoe(-/-).

CONCLUSIONS

ET-1 plays a role in progression of atherosclerosis and AAA formation by decreasing high-density lipoprotein, and increasing oxidative stress, inflammatory cell infiltration, and matrix metalloproteinase-2 in perivascular fat, vascular wall, and atherosclerotic lesions.

Therapeutic silencing of microRNA-33 inhibits the progression of atherosclerosis in Ldlr-/- mice--brief report

OBJECTIVE

To study the efficacy of anti-miRNA-33 therapy on the progression of atherosclerosis.

APPROACH AND RESULTS

Ldlr(-/-) mice were injected subcutaneously with PBS, control, or anti-miR-33 oligonucleotides weekly and fed a Western diet for 12 weeks. At the end of treatment, the expression of miR-33 target genes was increased in the liver and aorta, demonstrating effective inhibition of miR-33 function. Interestingly, plasma high-density lipoprotein (HDL)-cholesterol was significantly increased in anti-miR-33-treated mice but only when they were fed a chow diet. However, HDL isolated from anti-miR-33-treated mice showed an increase cholesterol efflux capacity compared with HDL isolated from nontargeting oligonucleotide-treated mice. Analysis of atherosclerosis revealed a significant reduction of plaque size and macrophage content in mice receiving anti-miR-33. In contrast, no differences in collagen content and necrotic areas were observed among the 3 groups.

CONCLUSIONS

Long-term anti-miR-33 therapy significantly reduces the progression of atherosclerosis and improves HDL functionality. The antiatherogenic effect is independent of plasma HDL-cholesterol levels.