HDL Measures, Particle Heterogeneity, Proposed Nomenclature, and Relation to Atherosclerotic Cardiovascular Events

High-density Lipoprotein Over Midlife and Future Cognition in Women: The SWAN HDL Ancillary Study

CONTEXT

Limited data provides evidence-based insights on the association between the comprehensive metrics of high-density lipoproteins (HDL) and cognitive performance, especially in midlife women for whom the benefit might be the greatest.

OBJECTIVE

To assess the associations of serum HDL metrics including HDL lipid content [HDL cholesterol, phospholipid (HDL-PL), triglyceride], proteins/subclasses [apolipoprotein A-1 (apoA-1); small, medium, large, total HDL particle (HDL-P); and HDL size], and cholesterol efflux capacity with cognitive performance in midlife women.

METHODS

This prospective cohort study was conducted among 503 midlife women (1234 observations) from the Study of Women's Health Across the Nation HDL ancillary study. Joint models were applied to examine associations of HDL metrics assessed at midlife (50.2 ± 2.9 years, baseline of the current study) and their changes over midlife (6.1 ± 3.9 years of duration) with subsequent cognitive performance [working memory (Digit Span Backward Test), processing speed (Symbol Digit Modalities Test), and episodic memory immediate and delayed recall (East Boston Memory Test)] assessed repeatedly (maximum 5 times) 1.5 ± 1 years later over 7.72 ± 4.10 years of follow-up.

RESULTS

Higher total HDL-P and smaller HDL size at midlife were associated with a better subsequent immediate recall, delayed recall, and/or processing speed. Greater increase in HDL-PL, apoA-1, medium HDL-P, and total HDL-P and less increase in HDL size over midlife were associated with a better subsequent immediate and/or delayed recall.

CONCLUSION

Enhancing specific serum HDL metrics during midlife could be promising in cognitive restoration, particularly memory, the initial and predominant symptom of Alzheimer's disease.

Causal relationships between metabolic syndrome, plasma metabolites, and female reproductive diseases: insights from a two-step mendelian randomization approach

BACKGROUND

Female reproductive diseases-including endometriosis (EMs), uterine fibroids (UFs), polycystic ovary syndrome (PCOS), gestational diabetes mellitus (GDM), eclampsia, ectopic pregnancy (EP), infertility, miscarriage, and ovarian aging-pose significant global health challenges. Metabolic syndrome (MetS) is characterized by a series of metabolic irregularities and has been linked to distinct plasma metabolomic profiles. Investigating the etiological connections among MetS, plasma metabolites, and female reproductive diseases is essential for devising effective prevention and treatment strategies.

OBJECTIVE

This study sought to evaluate the causal relationships among MetS, plasma metabolites, and female reproductive diseases using a two-step Mendelian randomization (MR) methodology.

METHODS

Initially, MR investigations were conducted to determine the causative impact of MetS on nine female reproductive diseases utilizing genome-wide association study (GWAS) data procured from European-descent populations. Statistically significant associations were identified for five diseases: UF, PCOS, GDM, eclampsia, and miscarriage. One hypothesis is that plasma metabolites may contribute to these associations. Subsequently, comprehensive MR analyses were performed using GWAS data on 233 plasma metabolites to examine causal relationships between these MetS-associated reproductive conditions and eight distinct classes of plasma metabolites. Sensitivity analyses, replication studies, and colocalization assessments were performed to validate the reliability of the outcomes.

RESULTS

MetS was identified as a causal factor for increased risks of UF, PCOS, GDM, eclampsia, and miscarriage. Further MR analyses revealed that specific plasma metabolites might causally affect the risk of female reproductive diseases: Eclampsia: Protective associations were observed with lipid molecules in large and very large high-density lipoprotein (HDL) particles, including cholesterol esters and total cholesterol. Conversely, triglycerides in large HDL particles and indicators related to small HDL particles were linked to increased risk. PCOS: Risk factors included elevated levels of triglycerides in HDL particles, various very low-density lipoprotein metabolites, acetone, 3-hydroxybutyrate, and conjugated linoleic acid. GDM: Increased glucose levels were associated with increased GDM risk.

CONCLUSIONS

This investigation established that MetS causally elevates the risk of certain female reproductive diseases and identified plasma metabolites that influence these conditions. These findings enhance the understanding of the etiological pathways involved in MetS and reproductive disorders, highlighting plasma metabolites as potential biomarkers or therapeutic targets.

Distinct roles of size-defined HDL subpopulations in cardiovascular disease

PURPOSE OF REVIEW

Doubts about whether high-density lipoprotein-cholesterol (HDL-C) levels are causally related to atherosclerotic cardiovascular disease (CVD) risk have stimulated research on identifying HDL-related metrics that might better reflect its cardioprotective functions. HDL is made up of different types of particles that vary in size, protein and lipid composition, and function. This review focuses on recent findings on the specific roles of HDL subpopulations defined by size in CVD.

RECENT FINDINGS

Small HDL particles are more effective than larger particles at promoting cellular cholesterol efflux because apolipoprotein A-I on their surface better engages ABCA1 (ATP binding cassette subfamily A member 1). In contrast, large HDL particles bind more effectively to scavenger receptor class B type 1 on endothelial cells, which helps prevent LDL from moving into the artery wall. The specific role of medium-sized HDL particles, the most abundant subpopulation, is still unclear.

SUMMARY

HDL is made up of subpopulations of different sizes of particles, with selective functional roles for small and large HDLs. The function of HDL may depend more on the size and composition of its subpopulations than on HDL-C levels. Further research is required to understand how these different HDL subpopulations influence the development of CVD.

Sepsis and high-density lipoproteins: Pathophysiology and potential new therapeutic targets

In 2020, sepsis has been defined a worldwide health major issue (World Health Organization). Lung, urinary tract and abdominal cavity are the preferred sites of sepsis-linked infection. Research has highlighted that the advancement of sepsis is not only related to the presence of inflammation or microbial or host pattern recognition. Clinicians and researchers now recognized that a severe immunosuppression is also a common feature found in patients with sepsis, increasing the susceptibility to secondary infections. Lipopolysaccharides (LPS) are expressed on the cell surface of Gram-negative, whereas Gram-positive bacteria express peptidoglycan (PGN) and lipoteichoic acid (LTA). The main mechanism by which LPS trigger host innate immune responses is binding to TLR4-MD2 (toll-like receptor4-myeloid differentiation factor 2), whereas, PGN and LTA are exogenous ligands of TLR2. Nucleotide-binding oligomerization domain (NOD)-like receptors are the most well-characterized cytosolic pattern recognition receptors, which bind microbial molecules, endogenous by-products and environmental triggers. It has been demonstrated that high-density lipoproteins (HDL), besides their major role in promoting cholesterol efflux, possess diverse pleiotropic properties, ranging from a modulation of the immune system to anti-inflammatory, anti-apoptotic, and anti-oxidant functions. In addition, HDL are able at i) binding LPS, preventing the activating of TLR4, and ii) inducing the expression of ATF3 (Activating transcription factor 3), a negative regulator of the TLR signalling pathways, contributing at justifying their capacity to hamper infection-based illnesses. Therefore, reconstituted HDL (rHDL), constituted by apolipoprotein A-I/apolipoprotein A-IMilano complexed with phospholipids, may be considered as a new therapeutic tool for the management of sepsis.

Regulation of Platelet Function by HDL

Over the past decade, increasing the capacity of HDL (high-density lipoprotein) cholesterol to mediate macrophage reverse cholesterol transport has been a target of interest in the treatment of cardiovascular diseases (CVDs). However, clinical studies reporting the limited efficacy of HDL or its main apolipoprotein, APOA1, in reducing cardiovascular events have emerged. Although HDL cholesterol is unlikely to play a direct causal role in CVD, its inverse, albeit modest, association with CVD risk, consistently observed in large population studies, suggests it may influence alternative pathways beyond cholesterol metabolism. Given the diverse functions of HDL and its components, it is conceivable that its impact on CVD occurs through less direct mechanisms. A potential hypothesis is that HDL modulates platelet function, a crucial player in the initiation and progression of atherothrombosis, which may contribute to its observed relationship with CVD risk. In this review, we focus on how HDL and its components, with an emphasis on APOA1, interact with platelets (and their precursors or activation products) to modulate atherothrombotic responses.

Analysis of TEM micrographs with deep learning reveals APOE genotype-specific associations between HDL particle diameter and Alzheimer's dementia

High-density lipoprotein (HDL) particle diameter distribution is informative in the diagnosis of many conditions, including Alzheimer's disease (AD). However, obtaining an accurate HDL size measurement is challenging. We demonstrated the utility of measuring the diameter of more than 1,800,000 HDL particles with the deep learning model YOLOv7 (you only look once) from micrographs of 183 HDL samples, including patients with dementia or normal cognition (controls). This method was shown to be more efficient and accurate than conventional image analysis software. Using this method, we found a higher abundance of small HDLs in participants with dementia compared to controls in patients with the apolipoprotein E (APOE) ε3ε4 genotype, whereas patients with the APOE ε3ε3 genotype had higher variability in the abundance of different HDL subclasses. Our results show an example of accurate individual HDL particle diameter measurement for large-scale clinical samples, which can be expanded to characterize the relationship between disease risk and other nanoparticles in the sub-20-nm diameter size range.

Dynamics of HDL-Cholesterol Following a Post-Myocardial Infarction Cardiac Rehabilitation Program

Background

Exercise-based cardiac rehabilitation programs (CRP) are recommended for patients following acute coronary syndrome to potentially improve high-density lipoprotein cholesterol (HDL-C) levels and prognosis. However, not all patients reach target HDL-C levels. Here we analyze the dynamics and predictors of HDL-C increase during CRP in patients following ST-segment elevation myocardial infarction or occlusion myocardial infarction.

Methods

We conducted a prospective study of myocardial infarction patients who completed exercise-based Phase 2 CRP. Data was collected on clinical variables, cardiovascular risk factors, treatment goals, pharmacological therapy, and health outcomes through questionnaires at the beginning and at the end of Phase 2 CRP. Lipid profile analysis was performed before discharge, 4 to 6 weeks after discharge, and at the end of Phase 2 CRP. Changes in lipid profiles were evaluated, and predictors of failure to increase HDL-C levels were identified by binary logistic regression analysis.

Results

Our cohort comprised 121 patients (mean age 61.67 ± 10.97 years, 86.8% male, and 47.9% smokers before admission). A significant decrease in total cholesterol, triglycerides, and low-density lipoprotein cholesterol (LDL-C) were noted, along with an increase in HDL-C (43.87 ± 9.18 vs. 39.8 ± 10.03 mg/dL, p < 0.001). Patients achieving normal HDL-C levels (>40 mg/dL in men and >50 mg/dL in women) significantly increased from 34.7% at admission to 52.9% the end of Phase 2. Multivariable analysis revealed smoking history (hazard ratio [HR] = 0.35, 95% confidence interval [CI], 0.11-0.96, p = 0.04), increased reduction in total cholesterol (HR = 0.94, 95% CI, 0.89-0.98, p = 0.004), and increased reduction in LDL-C (HR = 0.94, 95% CI, 0.89-0.99, p = 0.01) were inversely associated with failure to increase HDL-C levels. Conversely, higher HDL-C before CRP (HR = 1.15, 95% CI, 1.07-1.23, p < 0.001) and increased lipoprotein (a) (HR = 1.01, 95% CI, 1-1.02, p = 0.04) predicted failure to increase HDL-C levels. No significant correlations were found with Mediterranean diet adherence, weekly physical activity, training modalities, or physical fitness parameters.

Conclusions

Participation in an exercise-based Phase 2 CRP led to mild but significant increases in HDL-C. Smoking history and patients experiencing substantial reductions in total cholesterol and LDL-C were more likely to experience HDL-C increases, unlike those with higher HDL-C and lipoprotein (a) levels before CRP.

Effect of phospholipid transfer protein on plasma sphingosine-1-phosphate

Plasma phospholipid transfer protein (PLTP) is a risk factor for cardiovascular diseases. Sphingosine-1-phosphate (S1P), carried by high-density lipoprotein (HDL), is a potent lipid mediator and is also associated with cardiovascular diseases. We found that germline Pltp gene knockout (KO) mice have decreased circulating S1P without influencing apoM, a major S1P carrier on HDL. We then hypothesized that, like apoM, PLTP is another S1P carrier. We established inducible Pltp-KO, Apom-KO, and Pltp/Apom double KO mice and measured plasma lipoprotein and S1P levels under different diets. We found that PLTP deficiency, and the double deficiency have a similar effect on HDL reduction. Importantly, we found that all mice have about 50% reduction in plasma S1P levels, compared to WT mice, and PLTP deficiency significantly reduces apoM levels (about 40%), while apoM deficiency has no effect on PLTP activity, indicating that PLTP depletion reduces S1P through HDL reduction. To further evaluate this HDL reduction-mediated effect, we overexpressed PLTP which also caused a reduction of HDL. We found that the overexpression reduces S1P and apoM as well as apoA-I, a major apolipoprotein on HDL. Furthermore, we found that albumin (another reported S1P carrier) deficiency in mice has no effect on plasma S1P. We also found that the influence of PLTP on HDL may not require its direct binding to the particle. In conclusion, PLTP is not a direct S1P carrier. PLTP depletion or overexpression in adulthood dramatically reduces plasma S1P through HDL reduction. ApoM, but not albumin, deficiency reduces plasma S1P levels.

Quantification of high-density lipoprotein particle number by proton nuclear magnetic resonance: don't believe the numbers

PURPOSE OF REVIEW

Proton nuclear magnetic resonance (NMR) can rapidly assess lipoprotein concentrations and sizes in biological samples. It may be especially useful for quantifying high-density lipoprotein (HDL), which exhibits diverse particle sizes and concentrations. We provide a critical review of the strengths and limitations of NMR for quantifying HDL subclasses.

RECENT FINDINGS

Recent studies using NMR have shed light on HDL's role in various disorders, ranging from residual cardiovascular risk to host susceptibility to infection. However, accurately quantifying HDL particle number, size, and concentration (HDL-P) remains a challenge. Discrepancies exist between NMR and other methods such as gel electrophoresis, ion mobility analysis and size-exclusion chromatography in estimating the abundance of HDL species and the ratio of apolipoprotein A-I (APOA1) to HDL particles.

SUMMARY

NMR is a low-cost method for quantifying HDL-P that is readily applicable to clinical and translational studies. However, inconsistencies between the results of NMR quantification of HDL-P and other independent methods hinder the interpretation of NMR results. Because proton NMR apparently fails to accurately quantify the sizes and concentrations of HDL, the relevance of such studies to HDL biology poses challenges. This limits our understanding of pathophysiological implications of HDL-P as determined by NMR, particularly in determining cardiovascular disease (CVD) risk.

Association between the proportion of HDL-cholesterol subclasses and the severity of coronary artery stenosis in patients with acute myocardial infarction

BACKGROUND

Past research has shown an inverse correlation between high-density lipoprotein (HDL) and coronary heart disease (CHD), while recent studies have shown that extremely high or low HDL levels increase the risk of cardiovascular death.

OBJECTIVE

To explore the relationships between HDL subtypes and the degree of coronary artery stenosis in patients with acute myocardial infarction (AMI).

METHODS

This was a single-center cross-sectional study. Ultimately, we included 1,200 adult participants with AMI hospitalized from 2017 to 2023. Patients were classified into mild and moderate-severe groups according to their Gensini score. Restricted cubic spline and multivariate logistic regression models were used to explore the associations between HDL subclasses and the severity of coronary stenosis.

RESULTS

The adjusted odds ratios (ORs), 95% confidence intervals (CIs), and p values for HDL subclasses in the multivariate logistic model (adjusted for age, gender, hypertension status, diabetes status, stroke status, and kidney disease status) were as follows: HDL-2b: 0.97 (0.95-1.00, p= 0.018) and HDL-3: 0.98 (0.97-0.99, p= 0.008). Subgroup analysis revealed that HDL-3 exhibited a statistically significant impact on the severity of coronary stenosis among individuals <75 years of age and among men, and the influence of HDL-2b on the severity of coronary stenosis was statistically significant only in individuals aged ≥75 years.

CONCLUSION

The relationship between reduced levels of HDL-2b and HDL-3 and the risk of coronary stenosis exhibited a linear pattern and was significantly modified by age. Subgroup analysis identified specific populations that warrant attention regarding HDL-2b and HDL-3.

Contributions of Lipid-Related Metabolites and Complement Proteins to Early and Intermediate Age-Related Macular Degeneration

Objective

Our objective was to determine the effects of lipids and complement proteins on early and intermediate age-related macular degeneration (AMD) stages using machine learning models by integrating metabolomics and proteomic data.

Design

Nested case-control study.

Subjects and Controls

The analyses were performed in a subset of the Singapore Indian Chinese Cohort (SICC) Eye Study. Among the 6753 participants, we randomly selected 155 Indian and 155 Chinese cases of AMD and matched them with 310 controls on age, sex, and ethnicity.

Methods

We measured 35 complement proteins and 56 lipids using mass spectrometry and nuclear magnetic resonance, respectively. We first selected the most contributing lipids and complement proteins to early and intermediate AMD using random forest models. Then, we estimated their effects using a multinomial model adjusted for potential confounders.

Main Outcome Measures

Age-related macular degeneration was classified using the Beckman classification system.

Results

Among the 310 individuals with AMD, 166 (53.5%) had early AMD, and 144 (46.5%) had intermediate AMD. First, high-density lipoprotein (HDL) particle diameter was positively associated with both early and intermediate AMD (odds ratio [OR]early = 1.69; 95% confidence interval [CI],1.11-2.55 and ORintermediate = 1.72; 95% CI, 1.11-2.66 per 1-standard deviation increase in HDL diameter). Second, complement protein 2 (C2), complement C1 inhibitor (IC1), complement protein 6 (C6), complement protein 1QC (C1QC) and complement factor H-related protein 1 (FHR1), were associated with AMD. C2 was positively associated with both early and intermediate AMD (ORearly = 1.58; 95% CI, 1.08-2.30 and ORintermediate = 1.56; 95% CI, 1.04-2.34). C6 was positively (ORearly = 1.41; 95% CI, 1.03-1.93) associated with early AMD. However, IC1 was negatively associated with early AMD (ORearly = 0.62; 95% CI, 0.38-0.99), whereas C1QC (ORintermediate = 0.63; 95% CI, 0.42-0.93) and FHR1 (ORintermediate = 0.73; 95% CI, 0.54-0.98) were both negatively associated with intermediate AMD.

Conclusions

Although both HDL diameter and C2 levels show associations with both early and intermediate AMD, dysregulations of IC1, C6, C1QC, and FHR1 are only observed at specific stages of AMD. These findings underscore the complexity of complement system dysregulation in AMD, which appears to vary depending on the disease severity.

Financial Disclosures

The authors have no proprietary or commercial interest in any materials discussed in this article.

Investigation of Electrocardiographic Changes in Individuals with Three or More Cardiovascular Risk Factors on Santiago Island-The Cross-Sectional PrevCardio.CV Study

Cerebrocardiovascular diseases represent one of the greatest public health concerns globally. In Cabo Verde, non-communicable diseases, such as cerebrocardiovascular diseases, have become leading causes of morbidity and mortality. This study aimed to correlate risk factors with cardiac electrical changes in adult individuals residing on Santiago Island-Cabo Verde. A cross-sectional population-based study using simple random sampling was conducted in 2021 with individuals aged 18 and over, of both sexes, having authorization 35/2021 from the Cabo Verde Ethics Commission. The sample size was calculated based on Santiago Island's projected population for 2021, considering an estimated prevalence of 50%, a 95% confidence interval, and a standard error of 4%, resulting in a sample of 599 individuals. The data were collected through a questionnaire on risk factors and cerebrocardiovascular diseases, blood pressure measurement, capillary blood glucose evaluation, and a 12-lead electrocardiogram. The study sample was predominantly female (54.8%), with the largest age group being 18-27 years (21%). Among the sample, 9.3% had no risk factors, 27.5% had one risk factor, 36.2% had two risk factors, and 26.9% had three or more risk factors. Of those who underwent electrocardiography, 60.24% showed electrocardiographic changes, with the most prevalent being ventricular repolarization changes, nonspecific repolarization changes, and early repolarization. A relationship was observed between cerebrocardiovascular disease risk factors and the electrocardiographic changes found in the study participants.

Thermal Remodeling of Human HDL Particles Reveals Diverse Subspecies

High-density lipoproteins (HDL) are micelle-like particles consisting of a core of triglycerides and cholesteryl esters surrounded by a shell of phospholipid, cholesterol, and apolipoproteins. HDL is considered "good" cholesterol, and its concentration in plasma is used clinically in assessing cardiovascular health. However, these particles vary in structure, composition, and therefore function, and thus can be resolved into subpopulations, some of which have specific cardioprotective properties. Mass measurements of HDL by charge detection mass spectrometry (CD-MS) previously revealed seven distinct subpopulations which could be delineated by mass and charge [Lutomski, C. A. et al. Anal. Chem. 2018]. Here, we investigate the thermal stabilities of these subpopulations; upon heating, the particles within each subpopulation undergo structural rearrangements with distinct transition temperatures. In addition, we find evidence for many new families of structures within each subpopulation; at least 15 subspecies of HDL are resolved. These subspecies vary in size, charge, and thermal stability. While this suggests that these new subspecies have unique molecular compositions, we cannot rule out the possibility that we have found evidence for new structural forms within the known subpopulations. The ability to resolve new subspecies of HDL particles may be important in understanding and delineating the role of unique particles in cardiovascular health and disease.

High-Density Lipoprotein Subclasses and Their Role in the Prevention and Treatment of Cardiovascular Disease: A Narrative Review

The association between high-density lipoprotein cholesterol (HDL-C) and cardiovascular disease (CVD) is controversial. HDL-C is one content type of high-density lipoprotein (HDL). HDL consists of diverse proteins and lipids and can be classified into different subclasses based on size, shape, charge, and density, and can change dynamically in disease states. Therefore, HDL-C levels alone cannot represent HDLs' cardioprotective role. In this review, we summarized the methods for separating HDL subclasses, the studies on the association between HDL subclasses and cardiovascular risk (CVR), and the impact of lipid-modifying medications and nonpharmacological approaches (exercise training, dietary omega fatty acids, and low-density lipoprotein apheresis) on HDL subclasses. As HDL is a natural nanoplatform, recombinant HDLs (rHDLs) have been used as a delivery system in vivo by loading small interfering RNA, drugs, contrast agents, etc. Therefore, we further reviewed the HDL subclasses used in rHDLs and their advantages and disadvantages. This review would provide recommendations and guidance for future studies on HDL subclasses' cardioprotective roles.

High-Density Lipoprotein Particle Concentration and Size Predict Incident Coronary Artery Disease Events in a Cohort With Type 1 Diabetes

BACKGROUND

The cholesterol efflux capacity of high density lipoprotein (HDL) is negatively associated with cardiovascular risk. Small HDL particles account almost quantitatively for cholesterol efflux capacity, perhaps mediated through efflux of cholesterol and outer leaflet plasma membrane phospholipids by ABCA1 (ATP binding cassette subfamily A member 1). People with type 1 diabetes are at increased coronary artery disease (CAD) risk despite normal HDL-cholesterol concentrations. We therefore tested the hypothesis that small HDL particles (HDL-P)-rather than HDL-cholesterol-predict incident CAD in type 1 diabetes.

METHODS AND RESULTS

Incident CAD (CAD death, myocardial infarction, or coronary revascularization) was determined in 550 individuals with childhood-onset type 1 diabetes. HDL-P was quantified by calibrated ion mobility analysis and cholesterol efflux capacity was quantified with validated assays. During a median follow-up of 26 years, 36.5% of the participants developed incident CAD, for an incidence density of 181.3 per 10 000 person-years. In multivariable Cox models, neither HDL-cholesterol nor apolipoprotein A1 concentration was significantly associated with CAD risk. In contrast, higher extra-small HDL-P concentrations were significantly associated with decreased CAD risk (hazard ratio [HR], 0.26 [95% CI, 0.14-0.50]). Weaker associations were observed for total HDL-P (HR, 0.88 [95% CI, 0.83-0.93]), small HDL (HR, 0.83 [95% CI, 0.68-1.02]), medium HDL (HR, 0.79 [95% CI, 0.71-0.89]), and large HDL (HR, 0.72 [95% CI, 0.59-0.89]). Although cholesterol efflux capacity was negatively associated with incident CAD, this association was no longer significant after adjustment for total HDL-P.

CONCLUSIONS

Lower concentrations of total HDL-P and HDL subpopulations were positively associated with incident CAD independently of HDL-cholesterol, apolipoprotein A1, and other common CVD risk factors. Extra-small HDL was a much stronger predictor of risk than the other HDLs. Our data are consistent with the proposal that extra-small HDL plays a critical role in cardioprotection in type 1 diabetes, mediated by macrophage cholesterol efflux by the ABCA1 pathway.

Imbalance of APOB Lipoproteins and Large HDL in Type 1 Diabetes Drives Atherosclerosis

BACKGROUND

Individuals with type 1 diabetes (T1D) generally have normal or even higher HDL (high-density lipoprotein)-cholesterol levels than people without diabetes yet are at increased risk for atherosclerotic cardiovascular disease (CVD). Human HDL is a complex mixture of particles that can vary in cholesterol content by >2-fold. To investigate if specific HDL subspecies contribute to the increased atherosclerosis associated with T1D, we created mouse models of T1D that exhibit human-like HDL subspecies. We also measured HDL subspecies and their association with incident CVD in a cohort of people with T1D.

METHODS

We generated LDL receptor-deficient (Ldlr-/-) mouse models of T1D expressing human APOA1 (apolipoprotein A1). Ldlr-/-APOA1Tg mice exhibited the main human HDL subspecies. We also generated Ldlr-/-APOA1Tg T1D mice expressing CETP (cholesteryl ester transfer protein), which had lower concentrations of large HDL subspecies versus mice not expressing CETP. HDL particle concentrations and sizes and proteins involved in lipoprotein metabolism were measured by calibrated differential ion mobility analysis and targeted mass spectrometry in the mouse models of T1D and in a cohort of individuals with T1D. Endothelial transcytosis was analyzed by total internal reflection fluorescence microscopy.

RESULTS

Diabetic Ldlr-/-APOA1Tg mice were severely hyperglycemic and hyperlipidemic and had markedly elevated plasma APOB levels versus nondiabetic littermates but were protected from the proatherogenic effects of diabetes. Diabetic Ldlr-/-APOA1Tg mice expressing CETP lost the atheroprotective effect and had increased lesion necrotic core areas and APOB accumulation, despite having lower plasma APOB levels. The detrimental effects of low concentrations of larger HDL particles in diabetic mice expressing CETP were not explained by reduced cholesterol efflux. Instead, large HDL was more effective than small HDL in preventing endothelial transcytosis of LDL mediated by scavenger receptor class B type 1. Finally, in humans with T1D, increased concentrations of larger HDL particles relative to APOB100 negatively predicted incident CVD independently of HDL-cholesterol levels.

CONCLUSIONS

Our results suggest that the balance between APOB lipoproteins and the larger HDL subspecies contributes to atherosclerosis progression and incident CVD in the setting of T1D and that larger HDLs exert atheroprotective effects on endothelial cells rather than by promoting macrophage cholesterol efflux.

HDL abnormalities in type 2 diabetes: Clinical implications

Atherosclerotic cardiovascular disease (ASCVD) represents the primary cause of mortality among patients with Type 2 Diabetes Mellitus (T2DM). In this population, High-Density Lipoprotein (HDL) particles exhibit abnormalities in number, composition, and function, culminating in diminished anti-atherosclerotic capabilities despite normal HDL cholesterol (HDL-C) concentrations. Hyperglycemic conditions contribute to these alterations in HDL kinetics, composition, and function, causing T2DM patients' HDL particles to exhibit decreased concentrations of diverse lipid species and proteins. Treatment of hyperglycemia has the potential to correct abnormal HDL particle attributes in T2DM; however, pharmacological interventions, including metformin and thiazolidinediones, yield inconsistent outcomes with respect to HDL-C concentrations and functionality. Despite numerous attempts with diverse drugs, pharmacologically augmenting HDL-C levels has not resulted in clinical benefits in mitigating ASCVD risk. In contrast, reducing Low Density Lipoprotein cholesterol (LDL-C) via statins and ezetimibe has demonstrated significant efficacy in curtailing CVD risk among T2DM individuals. Promising results have been observed in animal models and early-phase trials utilizing recombinant HDL and Lecitin Cholesterol Acyl Transferase (LCAT) -enhancing agents, but the evaluation of their efficacy and safety in large-scale clinical trials is ongoing. While aberrant HDL metabolism constitutes a prevalent aspect of dyslipidemia in T2DM, HDL cholesterol concentrations and composition no longer offer valuable insights for informing therapeutic decisions. Nevertheless, HDL metabolism remains a critical research area in T2DM, necessitating further investigation to elucidate the role of HDL particles in the development of diabetes-associated complications.

Lipoprotein Insulin Resistance Score and Mortality Risk Stratification in Heart Failure

BACKGROUND

Higher total serum cholesterol is associated with lower mortality in heart failure. Evaluating associations between lipoprotein subfractions and mortality among people with heart failure may provide insights into this observation.

METHODS

We prospectively enrolled a community cohort of people with heart failure from 2003 to 2012 and assessed vital status through 2021. Plasma collected at enrollment was used to measure lipoprotein subfractions via nuclear magnetic resonance spectroscopy. A composite score of 6 lipoprotein subfractions was generated using the lipoprotein insulin resistance index (LP-IR) algorithm. Using covariate-adjusted proportional hazards regression models, we evaluated associations between LP-IR score and all-cause mortality.

RESULTS

Among 1382 patients with heart failure (median follow-up 13.9 years), a one-standard-deviation (SD) increment in LP-IR score was associated with lower mortality (hazard ratio [HR] 0.93; 95% confidence interval [CI], 0.97-0.99). Among LP-IR parameters, mean high-density lipoprotein (HDL) particle size was significantly associated with lower mortality (HR per 1-SD decrement in mean HDL particle size = 0.83; 95% CI, 0.78-0.89), suggesting that the inverse association between LP-IR score and mortality may be driven by smaller mean HDL particle size.

CONCLUSIONS

LP-IR score was inversely associated with mortality among patients with heart failure and may be driven by smaller HDL particle size.

High-density lipoprotein in diabetes: Structural and functional relevance

Low levels of high-density lipoprotein-cholesterol (HDL-C) is considered a major cardiovascular risk factor. However, recent studies have suggested a more U-shaped association between HDL-C and cardiovascular disease. It has been shown that the cardioprotective effect of HDL is related to the functions of HDL particles rather than their cholesterol content. HDL particles are highly heterogeneous and have multiple functions relevant to cardiometabolic conditions including cholesterol efflux capacity, anti-oxidative, anti-inflammatory, and vasoactive properties. There are quantitative and qualitative changes in HDL as well as functional abnormalities in both type 1 and type 2 diabetes. Non-enzymatic glycation, carbamylation, oxidative stress, and systemic inflammation can modify the HDL composition and therefore the functions, especially in situations of poor glycemic control. Studies of HDL proteomics and lipidomics have provided further insights into the structure-function relationship of HDL in diabetes. Interestingly, HDL also has a pleiotropic anti-diabetic effect, improving glycemic control through improvement in insulin sensitivity and β-cell function. Given the important role of HDL in cardiometabolic health, HDL-based therapeutics are being developed to enhance HDL functions rather than to increase HDL-C levels. Among these, recombinant HDL and small synthetic apolipoprotein A-I mimetic peptides may hold promise for preventing and treating diabetes and cardiovascular disease.

High-Density Lipoprotein Modifications: Causes and Functional Consequences in Type 2 Diabetes Mellitus

High-density lipoprotein (HDL) is a group of small, dense, and protein-rich lipoproteins that play a role in cholesterol metabolism and various cellular processes. Decreased levels of HDL and HDL dysfunction are commonly observed in individuals with type 2 diabetes mellitus (T2DM), which is also associated with an increased risk for cardiovascular disease (CVD). Due to hyperglycemia, oxidative stress, and inflammation that develop in T2DM, HDL undergoes several post-translational modifications such as glycation, oxidation, and carbamylation, as well as other alterations in its lipid and protein composition. It is increasingly recognized that the generation of HDL modifications in T2DM seems to be the main cause of HDL dysfunction and may in turn influence the development and progression of T2DM and its related cardiovascular complications. This review provides a general introduction to HDL structure and function and summarizes the main modifications of HDL that occur in T2DM. Furthermore, the potential impact of HDL modifications on the pathogenesis of T2DM and CVD, based on the altered interactions between modified HDL and various cell types that are involved in glucose homeostasis and atherosclerotic plaque generation, will be discussed. In addition, some perspectives for future research regarding the T2DM-related HDL modifications are addressed.

Pleiotropic functions and clinical importance of circulating HDL-PON1 complex

High density lipoprotein (HDL) functions are mostly mediated through a complex proteome, particularly its enzymes. HDL can provide a scaffold for the assembly of several proteins that affect each other's function. HDL particles, particularly small, dense HDL3, are rich in paraoxonase 1 (PON1), which is an important enzyme in the functionality of HDL, so the antioxidant and antiatherogenic properties of HDL are largely attributed to this enzyme. There is an increasing need to represent a valid, reproducible, and reliable method to assay HDL function in routine clinical laboratories. In this context, HDL-associated proteins may be key players; notably PON1 activity (its arylesterase activity) may be a proper candidate because its decreased activity can be considered an important risk factor for HDL dysfunctionality. Of note, automated methods have been developed for the measurement of serum PON1 activity that facilitates its assay in large sample numbers. Arylesterase activity is proposed as a preferred activity among the different activities of PON1 for its assay in epidemiological studies. The binding of PON1 to HDL is critical for the maintenance of its activity and it appears apolipoprotein A-I plays an important role in HDL-PON1 interaction as well as in the biochemical and enzymatic properties of PON1. The interrelationships between HDL, PON1, and HDL's other components are complex and incompletely understood. The purpose of this review is to discuss biochemical and clinical evidence considering the interactions of PON1 with HDL and the role of this enzyme as an appropriate biomarker for HDL function as well as a potential therapeutic target.

Serum Levels of Adiponectin Are Strongly Associated with Lipoprotein Subclasses in Healthy Volunteers but Not in Patients with Metabolic Syndrome

Metabolic syndrome (MS) is a widespread disease in developed countries, accompanied, among others, by decreased adiponectin serum levels and perturbed lipoprotein metabolism. The associations between the serum levels of adiponectin and lipoproteins have been extensively studied in the past under healthy conditions, yet it remains unexplored whether the observed associations also exist in patients with MS. Therefore, in the present study, we analyzed the serum levels of lipoprotein subclasses using nuclear magnetic resonance spectroscopy and examined their associations with the serum levels of adiponectin in patients with MS in comparison with healthy volunteers (HVs). In the HVs, the serum levels of adiponectin were significantly negatively correlated with the serum levels of large buoyant-, very-low-density lipoprotein, and intermediate-density lipoprotein, as well as small dense low-density lipoprotein (LDL) and significantly positively correlated with large buoyant high-density lipoprotein (HDL). In patients with MS, however, adiponectin was only significantly correlated with the serum levels of phospholipids in total HDL and large buoyant LDL. As revealed through logistic regression and orthogonal partial least-squares discriminant analyses, high adiponectin serum levels were associated with low levels of small dense LDL and high levels of large buoyant HDL in the HVs as well as high levels of large buoyant LDL and total HDL in patients with MS. We conclude that the presence of MS weakens or abolishes the strong associations between adiponectin and the lipoprotein parameters observed in HVs and disturbs the complex interplay between adiponectin and lipoprotein metabolism.

Effect of Empagliflozin with or without the Addition of Evolocumab on HDL Subspecies in Individuals with Type 2 Diabetes Mellitus: A Post Hoc Analysis of the EXCEED-BHS3 Trial

Evolocumab and empagliflozin yield a modest rise in plasma high-density lipoprotein cholesterol (HDL-C) through unknown mechanisms. This study aims to assess the effect of evolocumab plus empagliflozin vs. empagliflozin alone on HDL subspecies isolated from individuals with type 2 diabetes mellitus (T2D). This post hoc prespecified analysis of the EXCEED-BHS3 trial compared the effects of a 16-week therapy with empagliflozin (E) alone or in combination with evolocumab (EE) on the lipid profile and cholesterol content in HDL subspecies in individuals with T2D divided equally into two groups of 55 patients. Both treatments modestly increased HDL-C. The cholesterol content in HDL subspecies 2a (7.3%), 3a (7.2%) and 3c (15%) increased from baseline in the E group, while the EE group presented an increase from baseline in 3a (9.3%), 3b (16%) and 3c (25%). The increase in HDL 3b and 3c was higher in the EE group when compared to the E group (p < 0.05). No significant interactive association was observed between changes in hematocrit and HDL-C levels after treatment. Over a 16-week period, empagliflozin with or without the addition of evolocumab led to a modest but significant increase in HDL-C. The rise in smaller-sized HDL particles was heterogeneous amongst the treatment combinations.

Elevated high-density lipoprotein cholesterol and adverse outcomes in women with symptoms of ischemic heart disease

Background

Emerging data in the general population and those with coronary artery disease demonstrate higher risk of adverse outcomes with high (>70 mg/dL) HDL-C levels. There are limited data on the risk of adverse outcomes in women with suspected ischemic heart disease.

Objective

To investigate relationships between high (>70 mg/dL), average (50-70 mg/dL), and low (<50 mg/dL) HDL-C levels with major adverse cardiac events (MACE) (death, myocardial infarction, stroke, and heart failure hospitalization), and all-cause mortality in women referred for coronary angiography for suspected myocardial ischemia.

Methods

A total of 607 women enrolled in the Women's Ischemia Syndrome Evaluation (WISE) original cohort (NCT00000554) with available HDL-C values were included in this analysis. Associations between HDL-C level and outcomes were evaluated using both multivariate Cox proportional hazard regression and spline regression analysis.

Results

The mean age was 59 ± 12 years, 62 % had 3 or more cardiac risk factors, and 66 (10.9 %) had a high HDL-C. High and low HDL-C were both associated with higher MACE risk compared to average HDL-C after adjusting for demographic and clinical characteristics (HR 1.80, CI 1.03-3.14, p = 0.038; HR 1.63, CI 1.09-2.42, p = 0.016, respectively). Similarly, high, and low HDL-C were associated with higher risk of all-cause mortality (HR 3.64, CI 1.84-7.20, p < 0.001; HR 2.81, CI 1.67-4.71, p < 0.001, respectively).

Conclusions

High and low HDL-C levels are both independently associated with higher MACE and all-cause mortality in women with suspected ischemia undergoing coronary angiography.

High-throughput measurement of the content and properties of nano-sized bioparticles with single-particle profiler

We introduce a method, single-particle profiler, that provides single-particle information on the content and biophysical properties of thousands of particles in the size range 5-200 nm. We use our single-particle profiler to measure the messenger RNA encapsulation efficiency of lipid nanoparticles, the viral binding efficiencies of different nanobodies, and the biophysical heterogeneity of liposomes, lipoproteins, exosomes and viruses.

Lipid Profile and Cardiovascular Risk Modification after Hepatitis C Virus Eradication

The eradication of the hepatitis C virus (HCV) has revolutionized the hepatology paradigm, halting the progression of advanced liver disease in patients with chronic infection and reducing the risk of hepatocarcinoma. In addition, treatment with direct-acting antivirals can reverse the lipid and carbohydrate abnormalities described in HCV patients. Although HCV eradication may reduce the overall risk of vascular events, it is uncertain whether altered lipid profiles increase the risk of cerebrovascular disease in certain patients. We have conducted a review on HCV and lipid and carbohydrate metabolism, as well as new scientific advances, following the advent of direct-acting antivirals.

Advanced Oxidation Protein Products Are Strongly Associated with the Serum Levels and Lipid Contents of Lipoprotein Subclasses in Healthy Volunteers and Patients with Metabolic Syndrome

The association between advanced oxidation protein products (AOPPs) and lipoprotein subclasses remains unexplored. Therefore, we performed comprehensive lipoprotein profiling of serum using NMR spectroscopy and examined the associations of lipoprotein subclasses with the serum levels of AOPPs in healthy volunteers (HVs) and patients with metabolic syndrome (MS). The serum levels of AOPPs were significantly positively correlated with the serum levels of very-low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), and low-density lipoprotein (LDL); however, they were significantly negatively correlated with high-density lipoprotein (HDL). These lipoproteins (and their subclasses) differed markedly regarding the direction of correlations between their lipid contents and AOPPs. The strength of the correlations and the relative contributions of the subclasses to the correlations were different in the HVs and patients with MS. As revealed by orthogonal partial least squares discriminant analyses, the serum levels of IDL were strong determinants of AOPPs in the HVs, whereas the serum levels of VLDL and the lipid content of LDL were strong determinants in both groups. We conclude that IDL, VLDL, and LDL facilitate, whereas HDL diminishes the bioavailability of serum AOPPs. The presence of MS and the lipid contents of the subclasses affect the relationship between lipoproteins and AOPPs.

Flipped C-Terminal Ends of APOA1 Promote ABCA1-Dependent Cholesterol Efflux by Small HDLs

BACKGROUND

Cholesterol efflux capacity (CEC) predicts cardiovascular disease independently of high-density lipoprotein (HDL) cholesterol levels. Isolated small HDL particles are potent promoters of macrophage CEC by the ABCA1 (ATP-binding cassette transporter A1) pathway, but the underlying mechanisms are unclear.

METHODS

We used model system studies of reconstituted HDL and plasma from control and lecithin-cholesterol acyltransferase (LCAT)-deficient subjects to investigate the relationships among the sizes of HDL particles, the structure of APOA1 (apolipoprotein A1) in the different particles, and the CECs of plasma and isolated HDLs.

RESULTS

We quantified macrophage and ABCA1 CEC of 4 distinct sizes of reconstituted HDL. CEC increased as particle size decreased. Tandem mass spectrometric analysis of chemically cross-linked peptides and molecular dynamics simulations of APOA1, the major protein of HDL, indicated that the mobility of C-terminus of that protein was markedly higher and flipped off the surface in the smallest particles. To explore the physiological relevance of the model system studies, we isolated HDL from LCAT-deficient subjects, whose small HDLs (like reconstituted HDLs) are discoidal and composed of APOA1, cholesterol, and phospholipid. Despite their very low plasma levels of HDL particles, these subjects had normal CEC. In both the LCAT-deficient subjects and control subjects, the CEC of isolated extra-small HDL (a mixture of extra-small and small HDL by calibrated ion mobility analysis) was 3- to 5-fold greater than that of the larger sizes of isolated HDL. Incubating LCAT-deficient plasma and control plasma with human LCAT converted extra-small and small HDL particles into larger particles, and it markedly inhibited CEC.

CONCLUSIONS

We present a mechanism for the enhanced CEC of small HDLs. In smaller particles, the C-termini of the 2 antiparallel molecules of APOA1 are "flipped" off the lipid surface of HDL. This extended conformation allows them to engage with ABCA1. In contrast, the C-termini of larger HDLs are unable to interact productively with ABCA1 because they form a helical bundle that strongly adheres to the lipid on the particle. Enhanced CEC, as seen with the smaller particles, predicts decreased cardiovascular disease risk. Thus, extra-small and small HDLs may be key mediators and indicators of the cardioprotective effects of HDL.

The menopausal transition period and cardiovascular risk

The menopausal transition period spans, on average, 2-8 years before the final menstrual period and is associated with an increase in clinical and subclinical cardiovascular risk. In this Review, we discuss the metabolic and cardiovascular changes that occur during the menopausal transition period and the role of ovarian ageing, chronological ageing and other ageing-related risk factors in mediating these changes. Disentangling the relative contributions of chronological and reproductive ageing to cardiovascular risk is challenging, but data from longitudinal studies in women transitioning from premenopause to post-menopause have provided valuable insights. We also discuss evidence on how cardiovascular risk is altered by premature or early menopause, surgical menopause, and vasomotor and other menopausal symptoms. Whether targeted interventions can slow the progression of atherosclerosis and subclinical disease during the menopausal transition, thus delaying or preventing the onset of cardiovascular events, remains to be determined. Furthermore, we consider the recommended strategies for cardiovascular risk reduction in women undergoing menopausal transition using the framework of the American Heart Association's Life's Essential 8 key measures for improving and maintaining cardiovascular health, and discuss the cardiovascular risks and benefits of menopausal hormone therapy. Finally, we also discuss novel therapies that might benefit this population in reducing cardiovascular risk.

Sex differences in the associations of HDL particle concentration and cholesterol efflux capacity with incident coronary artery disease in type 1 diabetes: The RETRO HDLc cohort study

BACKGROUND

In type 1 diabetes, women lose their relative protection (compared to men) against coronary artery disease (CAD), while high-density lipoprotein cholesterol (HDL-C) is less strongly associated with lower CAD risk in women.

OBJECTIVE

We aimed to assess whether sex differences in the HDL particle concentration (HDL-P) and cholesterol efflux capacity (CEC) association with CAD may explain these findings.

METHODS

HDL-P (calibrated differential ion mobility analysis) and total and ATP binding cassette transporter A1 (ABCA1)-specific CEC were quantified among 279 men and 271 women with type 1 diabetes (baseline mean age 27·8 years; diabetes duration, 19·6 years). Clinical CAD was defined as CAD death, myocardial infarction and/or coronary revascularization.

RESULTS

Women had higher large HDL-P levels and marginally lower concentrations of small HDL-P and ABCA1-specific CEC than men. No sex differences were observed in extra-small HDL-P, medium HDL-P and total CEC. During a median follow-up of 26 years, 37·6 % of men and 35·8 % of women developed CAD (p = 0·72). In multivariable Cox models stratified by sex (pTotal HDL-P x sex interaction=0·01), HDL-P was negatively associated with CAD incidence in both sexes. However, associations were stronger in men, particularly for extra-small HDL-P (hazard ratio (HR)men=0·11, 95 % confidence interval (CI): 0·04-0·30; HRwomen=0·68, 95 % CI: 0·28-1·66; pinteraction=0·001). CEC did not independently predict CAD in either sex.

CONCLUSION

Despite few absolute differences in HDL-P concentrations by sex, the HDL-P - CAD association was weaker in women, particularly for extra-small HDL-P, suggesting that HDL-P may be less efficient in providing atheroprotection in women and perhaps explaining the lack of a sex difference in CAD in type 1 diabetes.

The Association of HDL2b with Metabolic Syndrome Among Normal HDL-C Populations in Southern China

Background

The annual prevalence of metabolic syndrome (MetS) is increasing. Therefore, early screening and recognition of MetS are critical. This study aimed to evaluate the association between high-density lipoprotein (HDL) subclasses and MetS and to examine whether they could serve as early indicators in a Chinese community-based population with normal high-density lipoprotein cholesterol (HDL-C) levels.

Methods

We used microfluidic chip technology to measure HDL subclasses in 463 people with normal HDL levels in 2018. We assessed how HDL subclasses correlated with and predicted insulin resistance (IR) and metabolic syndrome (MetS), evaluated by homeostatic model insulin resistance index (HOMA-IR) and the 2009 International Diabetes Federation (IDF), the American Heart Association (AHA), and the National Heart, Lung, and Blood Institute (NHLBI) criteria, respectively. We used correlation tests and ROC curves for the analysis.

Results

The results indicate that there was a negative association between HDL2b% and the risk of IR and MetS in both sexes. Subjects in the highest quartile of HDL2b% had a significantly lower prevalence of IR and MetS than those in the lowest quartile (P<0.01). Correlation analysis between HDL2b% and metabolic risk factors showed that HDL2b% had a stronger association with these factors than HDL-C did in both sexes. ROC curve analysis also showed that HDL2b% had significant diagnostic value for IR and MetS compared to other lipid indicators.

Conclusion

This study showed that MetS alters the distribution of HDL subclasses even when HDL-C levels are within the normal range. HDL-2b% has better diagnostic value for IR and MetS than HDL-C alone and may be a useful marker for early screening.

HDL subfractions determined by microfluidic chip electrophoresis predict the vulnerability of intracranial plaque: A HRMRI study

AIM

High-density lipoprotein (HDL) can be divided into several subfractions based on density, size and composition. Accumulative evidence strongly suggests that the subfractions of HDL have very different roles in the pathogenesis of atherosclerosis. The purpose of this study was to further delineate the relationship between HDL subfractions extracted by microfluidic chip electrophoresis and the vulnerability of plaques in patients with intracranial atherosclerosis with a high-resolution magnetic resonance imaging (HRMRI) study.

METHODS

We prospectively enrolled patients with single atherosclerotic plaque in the middle cerebral artery (MCA) or basilar artery (BA) between July 2020 and Dec 2022 and performed 3-tesla HRMRI on the relevant artery. The HDL cholesterol concentration and HDL subfractions (HDL-2a, HDL-2b and HDL-3) percentage were analyzed in serum samples from the same patients by electrophoresis on a microfluidics system.

RESULTS

A total of 81 MCA or BA plaques [38 (46.9%) symptomatic and 43 (53.1%) asymptomatic] in 81 patients were identified on HRMRI. Patients with symptomatic plaques had a significantly lower HDL-2b level than asymptomatic plaques [symptomatic vs. asymptomatic: 0.16 (0.10-0.18) vs. 0.27(0.21-0.34), p = 0.001]. After adjusting for demographics and vascular risk factors, logistic regression showed that HDL-2b was inversely associated with asymptomatic plaques (B = -0.04, P = 0.017). According to receiver operating characteristic (ROC) curve model analysis, the cutoff point of HDL-2b in predicting asymptomatic plaques was 0.21 mmol/L (Area under curve: 0.719, specificity: 73.7%, sensitivity: 72.1%). Furthermore, plaque enhancement on HRMRI (P < 0.001), positive remodeling (P < 0.001), plaque load (P < 0.001) and luminal stenosis (P < 0.001) were superior among patients with HDL-2b < 0.21 mmol/L.

CONCLUSIONS

Our data showed that serum HDL-2b levels may serve as a biomarker for predicting vulnerability in intracranial atherosclerotic plaques.

Association Between HDL2-C and HDL3-C with Cardiovascular Disease: A Nested Case-Control Study in an Iranian Population

Background

The contribution of high-density lipoprotein cholesterol (HDL-C) subclasses to incident cardiovascular disease (CVD) and coronary heart disease (CHD) remains a subject of debate.

Objectives

The objective of this study was to investigate these associations in a population with a high prevalence of dyslipidemia and CVD.

Methods

In a nested case-control study, HDL-C and its subclasses (HDL2-C and HDL3-C) in 370 age and gender-matched case and control subjects were determined. This study employed multivariable-adjusted conditional logistic regression to calculate the odds ratios (ORs) for the associations between HDL-C, HDL2-C, HDL3-C, and HDL2-C/HDL3-C (both as continuous and categorical variables) with incident CVD and CHD. The present study models were adjusted for a comprehensive set of confounders, including body mass index, current smoking, hypertension, type 2 diabetes mellitus, use of lipid-lowering drugs, family history of premature CVD, non-HDL-C, and triglycerides.

Results

In multivariate analysis, when considering lipoprotein parameters as continuous variables, a 1-unit increase in HDL-C and HDL3-C was associated with a reduced risk of incident CVD and CHD. For CVD, the ORs (95% confidence intervals [CI]) were 0.95 (0.92 - 0.98) and 0.95 (0.93 - 0.98) for HDL-C and HDL3-C, respectively. The corresponding values for CHD were 0.94 (0.91 - 0.97) and 0.94 (0.91 - 0.97). In the categorical approach to lipoprotein parameters, higher quartiles of HDL-C and HDL3-C, compared to the first quartile, were significantly associated with a lower risk of incident CVD and CHD. The ORs (95% CI) for the fourth quartiles were 0.43 (0.25 - 0.74, P for trend = 0.003) and 0.46 (0.27 - 0.78, P for trend = 0.005) for HDL-C and HDL3-C regarding CVD and 0.32 (0.17 - 0.59) and 0.32 (0.18 - 0.59) (all P for trend = 0.001) regarding CHD, respectively. Paradoxically, across quartiles of HDL2-C/HDL3-C, this lipid ratio was associated with a higher risk of CHD (92% higher risk in the fourth quartile).

Conclusions

The results showed that HDL3-C, but not HDL2-C, was primarily responsible for the protective effect of HDL-C against CVD, particularly CHD, in Iranian adults.

Understanding HDL Metabolism and Biology Through In Vivo Tracer Kinetics

HDL (high-density lipoprotein), owing to its high protein content and small size, is the densest circulating lipoprotein. In contrast to lipid-laden VLDL (very-low-density lipoprotein) and LDL (low-density lipoprotein) that promote atherosclerosis, HDL is hypothesized to mitigate atherosclerosis via reverse cholesterol transport, a process that entails the uptake and clearance of excess cholesterol from peripheral tissues. This process is mediated by APOA1 (apolipoprotein A-I), the primary structural protein of HDL, as well as by the activities of additional HDL proteins. Tracer-dependent kinetic studies are an invaluable tool to study HDL-mediated reverse cholesterol transport and overall HDL metabolism in humans when a cardiovascular disease therapy is investigated. Unfortunately, HDL cholesterol-raising therapies have not been successful at reducing cardiovascular events suggesting an incomplete picture of HDL biology. However, as HDL tracer studies have evolved from radioactive isotope- to stable isotope-based strategies that in turn are reliant on mass spectrometry technologies, the complexity of the HDL proteome and its metabolism can be more readily addressed. In this review, we outline the motivations, timelines, advantages, and disadvantages of the various tracer kinetics strategies. We also feature the metabolic properties of select HDL proteins known to regulate reverse cholesterol transport, which in turn underscore that HDL lipoproteins comprise a heterogeneous particle population whose distinct protein constituents and kinetics likely determine its function and potential contribution to cholesterol clearance.

Dyslipidemia in adults with congenital heart disease: A systematic review and meta-analysis

AIMS

Several particular characteristics of patients with congenital heart disease could affect lipid levels. The objectives of this study were: a) to analyze the prevalence of dyslipidemia in congenital heart disease patients; 2) to compare lipid levels between congenital heart disease patients and a control group.

DATA SYNTHESIS

This systematic review and meta-analysis was performed according to PRISMA guidelines (PROSPERO CRD42023432041). A literature search was performed to detect studies that have reported lipid levels or the prevalence of dyslipidemia in congenital heart disease patients. We performed a qualitative analysis (studies that reported dyslipidemia prevalence) and quantitative analysis (studies that compared lipid values between congenital heart disease patients and controls). In total, 29 observational studies involving 22,914 patients with congenital heart disease and 641,086 controls were eligible for this review. The reported presence of "hyperlipidemia" or "dyslipidemia" ranged from 14.3% to 69.9%. When studies analyzed lipid variables dichotomously between congenital heart disease patients and controls, the results were conflicting. The quantitative analysis showed that patients with congenital heart disease have lower levels of total cholesterol (MD: -18.9 [95% CI: -22.2 to -15.7]; I2 = 93%), LDL-C (MD: -10.7 [95% CI: -13.1 to -8.3]; I2 = 90%) and HDL-C (MD: -6.3 [95% CI: -7.7 to -4.9]; I2 = 95%) compared to controls.

CONCLUSIONS

The qualitative analysis showed some concerns, but the quantitative analysis indicates that congenital heart disease patients showed lower levels of total cholesterol, LDL-C, and HDL-C compared to controls. New research should be developed to clarify this relevant topic.

HDL Particle Concentration and Size Predict Incident Coronary Artery Disease Events in People with Type 1 Diabetes

Background

Cholesterol efflux capacity (CEC) negatively correlates with cardiovascular disease risk. Small HDL particles account almost quantitively for CEC, perhaps mediated through efflux of outer leaflet plasma membrane phospholipids by ABCA1. People with type 1 diabetes (T1D) are at increased risk of coronary artery disease (CAD) despite normal levels of HDL-cholesterol (HDL-C). We therefore tested the hypotheses that small HDL particles (HDL-P)-rather than HDL-C levels-predict incident CAD in T1D.

Methods

Incident CAD (CAD death, myocardial infarction, and/or coronary revascularization) was determined in a cohort of 550 participants with childhood-onset T1D. HDL-P was quantified by calibrated ion mobility analysis. CEC and phospholipid efflux were quantified with validated assays.

Results

During a median follow-up of 26 years, 36.5% of the participants developed incident CAD. In multivariable Cox models, levels of HDL-C and apolipoprotein A-I (APOA1) did not predict CAD risk. In contrast, extra-small HDL particle levels strongly and negatively predicted risk (hazard ratio [HR]=0.25, 95% confidence interval [CI]=0.13-0.49). An increased concentration of total HDL particles (T-HDL-P) (HR=0.87, CI=0.82-0.92) and three other HDL sizes were weaker predictors of risk: small HDL (HR=0.80, 0.65-0.98), medium HDL (HR=0.78, CI=0.70-0.87) and large HDL (HR=0.72, CI=0.59-0.89). Although CEC negatively associated with incident CAD, that association disappeared after the model was adjusted for T-HDL-P. Isolated small HDLs strongly promoted ABCA1-dependent efflux of membrane outer leaflet phospholipids.

Conclusions

Low concentrations of T-HDL-P and all four sizes of HDL subpopulations predicted incident CAD independently of HDL-C, APOA1, and other common CVD risk factors. Extra-small HDL was a much stronger predictor of risk than the other HDLs. Our data are consistent with the proposal that small HDLs play a critical role in cardioprotection in T1D, which might be mediated by macrophage plasma membrane outer leaflet phospholipid export and cholesterol efflux by the ABCA1 pathway.

Flipped C-Terminal Ends of APOA1 Promote ABCA1-dependent Cholesterol Efflux by Small HDLs

Background

Cholesterol efflux capacity (CEC) predicts cardiovascular disease (CVD) independently of HDL cholesterol (HDL-C) levels. Isolated small HDL particles are potent promoters of macrophage CEC by the ABCA1 pathway, but the underlying mechanisms are unclear.

Methods

We used model system studies of reconstituted HDL and plasma from control and lecithin-cholesterol acyltransferase (LCAT)-deficient subjects to investigate the relationships among the sizes of HDL particles, the structure of APOA1 in the different particles, and the CECs of plasma and isolated HDLs.

Results

We quantified macrophage and ABCA1 CEC of four distinct sizes of reconstituted HDL (r-HDL). CEC increased as particle size decreased. MS/MS analysis of chemically crosslinked peptides and molecular dynamics simulations of APOA1 (HDL's major protein) indicated that the mobility of that protein's C-terminus was markedly higher and flipped off the surface in the smallest particles. To explore the physiological relevance of the model system studies, we isolated HDL from LCAT-deficient subjects, whose small HDLs-like r-HDLs-are discoidal and composed of APOA1, cholesterol, and phospholipid. Despite their very low plasma levels of HDL particles, these subjects had normal CEC. In both the LCAT-deficient subjects and control subjects, the CEC of isolated extra-small HDL (a mixture of extra-small and small HDL by calibrated ion mobility analysis) was 3-5-fold greater than that of the larger sizes of isolated HDL. Incubating LCAT-deficient plasma and control plasma with human LCAT converted extra-small and small HDL particles into larger particles, and it markedly inhibited CEC.

Conclusions

We present a mechanism for the enhanced CEC of small HDLs. In smaller particles, the C-termini of the two antiparallel molecules of APOA1 are flipped off the lipid surface of HDL. This extended conformation allows them to engage with ABCA1. In contrast, the C-termini of larger HDLs are unable to interact productively with ABCA1 because they form a helical bundle that strongly adheres to the lipid on the particle. Enhanced CEC, as seen with the smaller particles, predicts decreased CVD risk. Thus, extra-small and small HDLs may be key mediators and indicators of HDL's cardioprotective effects.

Atherosclerotic Cardiovascular Disease in Women: Providing Protection With Lipid-altering Agents

PURPOSE

Atherosclerotic cardiovascular disease (ASCVD) is the leading cause of death in women, yet it remains underdiagnosed, undertreated, and understudied in women compared with men. Although estrogen has provided observational evidence of cardioprotection, randomized controlled trials using hormone replacement therapy have generally produced unfavorable results.

METHODS

For this narrative review, a literature search was performed using the key words cardiovascular disease, women, and dyslipidemia in PubMed and Google Scholar with no date limitations. References within each article were also reviewed for additional relevant articles.

FINDINGS

Sex-specific risk factors and underrecognized conditions more predominant in women elevate ASCVD risk, creating further clinical challenges, such as the need for accurate risk stratification, compared with in men. Dyslipidemia frequently manifests or worsens during the menopausal transition. Therefore, identification during midlife and implementing lipid-lowering strategies to reduce ASCVD risk is imperative. Women have historically been poorly represented in cardiovascular (CV) outcome trials. However, more recent studies and meta-analyses have indicated that lipid-lowering therapies are equally effective in women and produce similar reductions in CV events and total mortality. Major cholesterol guidelines address many of the challenges that clinicians face when assessing ASCVD risk in women. Key points specific to women include obtaining a detailed history of pregnancy-related conditions, identification of common autoimmune disorders associated with systemic inflammation, and use of 10-year ASCVD risk calculators and imaging modalities (coronary artery calcium) to optimize ASCVD assessment. In terms of treatment, similar to men, women with existing ASCVD or high-risk primary prevention patients should be treated aggressively to achieve ≥50% LDL-C reductions and/or LDL-C goals as low as <55 mg/dL. Appropriate lipid-lowering therapies include high-intensity statins with or without ezetimibe and proprotein convertase subtilisin kexin/type 9 inhibitors. Women with lower ASCVD risk may be considered for low- to moderate-intensity statin therapy (approximately 30%-50% LDL-C reduction). All women, regardless of ASCVD risk category, should implement therapeutic lifestyle changes, which improve many common age-related cardiometabolic conditions.

IMPLICATIONS

Although ASCVD and current risk factor trends in women are concerning, numerous evidence-based approaches are available to protect women with ASCVD risk from life-changing CV events.

Precision Nutrition and Cardiovascular Disease Risk Reduction: the Promise of High-Density Lipoproteins

PURPOSE OF REVIEW

Emerging evidence supports the promise of precision nutritional approaches for cardiovascular disease (CVD) prevention. Here, we discuss current findings from precision nutrition trials and studies reporting substantial inter-individual variability in responses to diets and dietary components relevant to CVD outcomes. We highlight examples where early precision nutrition research already points to actionable intervention targets tailored to an individual's biology and lifestyle. Finally, we make the case for high-density lipoproteins (HDL) as a compelling next generation target for precision nutrition aimed at CVD prevention. HDL possesses complex structural features including diverse protein components, lipids, size distribution, extensive glycosylation, and interacts with the gut microbiome, all of which influence HDL's anti-inflammatory, antioxidant, and cholesterol efflux properties. Elucidating the nuances of HDL structure and function at an individual level may unlock personalized dietary and lifestyle strategies to optimize HDL-mediated atheroprotection and reduce CVD risk.

RECENT FINDINGS

Recent human studies have demonstrated that HDL particles are key players in the reduction of CVD risk. Our review highlights the role of HDL and the importance of personalized therapeutic approaches to improve their potential for reducing CVD risk. Factors such as diet, genetics, glycosylation, and gut microbiome interactions can modulate HDL structure and function at the individual level. We emphasize that fractionating HDL into size-based subclasses and measuring particle concentration are necessary to understand HDL biology and for developing the next generation of diagnostics and biomarkers. These discoveries underscore the need to move beyond a one-size-fits-all approach to HDL management. Precision nutrition strategies that account for personalized metabolic, genetic, and lifestyle data hold promise for optimizing HDL therapies and function to mitigate CVD risk more potently. While human studies show HDL play a key role in reducing CVD risk, recent findings indicate that factors such as diet, genetics, glycosylation, and gut microbes modulate HDL function at the individual level, underscoring the need for precision nutrition strategies that account for personalized variability to optimize HDL's potential for mitigating CVD risk.

Cell-free, high-density lipoprotein-specific phospholipid efflux assay predicts incident cardiovascular disease

BACKGROUNDCellular cholesterol efflux capacity (CEC) is a better predictor of cardiovascular disease (CVD) events than HDL-cholesterol (HDL-C) but is not suitable as a routine clinical assay.METHODSWe developed an HDL-specific phospholipid efflux (HDL-SPE) assay to assess HDL functionality based on whole plasma HDL apolipoprotein-mediated solubilization of fluorescent phosphatidylethanolamine from artificial lipid donor particles. We first assessed the association of HDL-SPE with prevalent coronary artery disease (CAD): study I included NIH severe-CAD (n = 50) and non-CAD (n = 50) participants, who were frequency matched for sex, BMI, type 2 diabetes mellitus, and smoking; study II included Japanese CAD (n = 70) and non-CAD (n = 154) participants. We also examined the association of HDL-SPE with incident CVD events in the Prevention of Renal and Vascular End-stage Disease (PREVEND) study comparing 340 patients with 340 controls individually matched for age, sex, smoking, and HDL-C levels.RESULTSReceiver operating characteristic curves revealed stronger associations of HDL-SPE with prevalent CAD. The AUCs in study I were as follows: HDL-SPE, 0.68; apolipoprotein A-I (apoA-I), 0.62; HDL-C, 0.63; and CEC, 0.52. The AUCs in study II were as follows: HDL-SPE, 0.83; apoA-I, 0.64; and HDL-C, 0.53. Also longitudinally, HDL-SPE was significantly associated with incident CVD events independent of traditional risk factors with ORs below 0.2 per SD increment in the PREVEND study (P < 0.001).CONCLUSIONHDL-SPE could serve as a routine clinical assay for improving CVD risk assessment and drug discovery.TRIAL REGISTRATIONClinicalTrials.gov NCT01621594.FUNDINGNHLBI Intramural Research Program, NIH (HL006095-06).

Association of HDL Subfraction Profile with the Progression of Insulin Resistance

Type 2 diabetes mellitus (T2DM) is a major global public health problem, as it is associated with increased morbidity, mortality, and healthcare costs. Insulin resistance (IR) is a condition characterized by disturbances in carbohydrate and lipid metabolism that precedes T2DM. The aim of the present study was to investigate the association between HDL and its subfraction profile and the progression of IR, as assessed by the Homeostatic Model Assessment for IR (HOMA-IR) index, and to define cut-off values to identify an increased risk of IR. Individuals with a HOMA-IR greater than 3.63 were considered to have IR. The HDL subfractions were separated using the Lipoprint system, which identifies ten subfractions (HDL-1-10) in three subclasses as large (HDL-L), intermediate (HDL-I) and small (HDL-S). Analyses were performed on samples from 240 individuals without IR and 137 with IR from the Hungarian general and Roma populations. The HDL-1 to -6 subfractions and the HDL-L and -I classes showed a significant negative association with the progression and existence of IR. Among them, HDL-2 (B = -40.37, p = 2.08 × 10-11) and HDL-L (B = -14.85, p = 9.52 × 10-10) showed the strongest correlation. The optimal threshold was found to be 0.264 mmol/L for HDL-L and 0.102 mmol/L and above for HDL-2. Individuals with HDL-L levels below the reference value had a 5.1-fold higher risk of IR (p = 2.2 × 10-7), while those with HDL-2 levels had a 4.2-fold higher risk (p = 3.0 × 10-6). This study demonstrates that the HDL subfraction profile (especially the decrease in HDL-2 and -L) may be a useful marker for the early detection and intervention of atherogenic dyslipidemia in subjects with impaired glucose and insulin metabolism.

Machine learning identifying peripheral circulating metabolites associated with intraocular pressure alterations

AIMS

To identify blood metabolite markers associated with intraocular pressure (IOP) in a population-based cross-sectional study.

METHODS

This study was conducted in a multiethnic Asian population (Chinese, n=2805; Indians, n=3045; Malays, n=3041 aged 40-80 years) in Singapore. All subjects underwent standardised systemic and ocular examinations, and biosamples were collected. Selected metabolites (n=228) in either serum or plasma were analysed and quantified using nuclear magnetic resonance spectroscopy. Least absolute shrinkage and selection operator regression was used for metabolites selection. Multivariable linear regression was used to evaluate the relationship between metabolites and IOP in each of the three ethnic groups, followed by a meta-analysis combining the three cohorts.

RESULTS

Six metabolites, including albumin, glucose, lactate, glutamine, ratio of saturated fatty acids to total fatty acids (SFAFA) and cholesterol esters in very large high-density lipoprotein (HDL), were significantly associated with IOP in all three cohorts. Higher levels of albumin (per SD, beta=0.24, p=0.002), lactate (per SD, beta=0.27, p=0.008), glucose (per SD, beta=0.11, p=0.010) and cholesterol esters in very large HDL (per SD, beta=0.47, p=0.006), along with lower levels of glutamine (per SD, beta=0.17, p<0.001) and SFAFA (per SD, beta=0.21, p=0.008) were associated with higher IOP levels.

CONCLUSION

We identify several novel blood metabolites associated with IOP. These findings may provide insight into the physiological and pathological processes underlying IOP control.

ABCA1 Deficiency: A Rare Cause of Premature Coronary Artery Disease

ATP-binding cassette transporter A1 (ABCA1) deficiency results in very low high-density lipoprotein cholesterol levels. Complete ABCA1 deficiency, or Tangier disease, is characterized by premature atherosclerotic cardiovascular disease, yellow-orange tonsils, hepatosplenomegaly, peripheral neuropathy, and corneal opacification. Early recognition of this condition can lead to regular monitoring for atherosclerotic cardiovascular symptoms and treatment of major modifiable risk factors. (Level of Difficulty: Beginner.).

Association between atherogenic index of plasma and prehypertension or hypertension among normoglycemia subjects in a Japan population: a cross-sectional study

OBJECTIVE

The atherogenic index of plasma (AIP), consisting of triglycerides and high-density lipoprotein cholesterol, is applied to estimate the cardiovascular disease risk. The evidence regarding the association between AIP and prehypertension or hypertension remains inconclusive. This study was conducted to investigate the association of AIP and prehypertension or hypertension in normoglycemic subjects in Japan.

METHODS

In the present cross-sectional study, 15,453 normoglycemic participants aged 18 years or older in Gifu, Japan, were evaluated. The selected participants were separated into four groups in the light of AIP quartiles, ranging from the lowest quartile (Q1) to the highest quartile (Q4). And the association between AIP and prehypertension or hypertension was explored with multivariate logistic regression by gradually adjusting model.

RESULTS

Among the 15,453 participants, aged of 43.7 ± 8.9 years, and of whom 45.5% were females, the prevalence rates of prehypertension or hypertension were 27.68% (4,278) and 6.23% (962) respectively. In multivariate logistic regression analyses, participants in the highest AIP quartile had an increase risk in prehypertension and hypertension, compared with participants the lowest one, the odds ratios (OR) were 1.15 (95%CI: 1.00-1.13, P = 0.045) for prehypertension and 1.54 (95%CI:1.16-2.04, P = 0.003) for hypertension after adjusting confounders. In subgroup analyses, the high risk of hypertension was also observed for female participants in the highest AIP quartile (Q4) (OR = 2.19, 95%CI: 1.37-3.49, P = 0.001), especially between the ages of 40 and 60 years (OR = 2.20, 95%CI: 1.24-3.88, P = 0.007).

CONCLUSIONS

Higher AIP is significantly and positively associated with the risk of prehypertension or hypertension in normoglycemic subjects in Gifu, Japan, which was more pronounced in the female population, especially between the years of 40 and 60.

Low concentrations of medium-sized HDL particles predict incident CVD in chronic kidney disease patients

Patients with chronic kidney disease (CKD) are at high risk for CVD. However, traditional CVD risk factors cannot completely explain the increased risk. Altered HDL proteome is linked with incident CVD in CKD patients, but it is unclear whether other HDL metrics are associated with incident CVD in this population. In the current study, we analyzed samples from two independent prospective case-control cohorts of CKD patients, the Clinical Phenotyping and Resource Biobank Core (CPROBE) and the Chronic Renal Insufficiency Cohort (CRIC). We measured HDL particle sizes and concentrations (HDL-P) by calibrated ion mobility analysis and HDL cholesterol efflux capacity (CEC) by cAMP-stimulated J774 macrophages in 92 subjects from the CPROBE cohort (46 CVD and 46 controls) and in 91 subjects from the CRIC cohort (34 CVD and 57 controls). We tested associations of HDL metrics with incident CVD using logistic regression analysis. No significant associations were found for HDL-C or HDL-CEC in either cohort. Total HDL-P was only negatively associated with incident CVD in the CRIC cohort in unadjusted analysis. Among the six sized HDL subspecies, only medium-sized HDL-P was significantly and negatively associated with incident CVD in both cohorts after adjusting for clinical confounders and lipid risk factors with odds ratios (per 1-SD) of 0.45 (0.22-0.93, P = 0.032) and 0.42 (0.20-0.87, P = 0.019) for CPROBE and CRIC cohorts, respectively. Our observations indicate that medium-sized HDL-P-but not other-sized HDL-P or total HDL-P, HDL-C, or HDL-CEC-may be a prognostic cardiovascular risk marker in CKD.

The distinct metabolism between large and small HDL indicates unique origins of human apolipoprotein A4

Apolipoprotein A4's (APOA4's) functions on HDL in humans are not well understood. A unique feature of APOA4 is that it is an intestinal apolipoprotein secreted on HDL and chylomicrons. The goal of this study was to gain a better understanding of the origin and function of APOA4 on HDL by studying its metabolism across 6 HDL sizes. Twelve participants completed a metabolic tracer study. HDL was isolated by APOA1 immunopurification and separated by size. Tracer enrichments for APOA4 and APOA1 were determined by targeted mass spectrometry, and metabolic rates were derived by compartmental modeling. APOA4 metabolism on small HDL (alpha3, prebeta, and very small prebeta) was distinct from that of APOA4 on large HDL (alpha0, 1, 2). APOA4 on small HDL appeared in circulation by 30 minutes and was relatively rapidly catabolized. In contrast, APOA4 on large HDL appeared in circulation later (1-2 hours) and had a much slower catabolism. The unique metabolic profiles of APOA4 on small and large HDL likely indicate that each has a distinct origin and function in humans. This evidence supports the notion that APOA4 on small HDL originates directly from the small intestine while APOA4 on large HDL originates from chylomicron transfer.