Human macrophage cholesterol efflux potential is enhanced by HDL-associated 17beta-estradiol fatty acyl esters

Trehalose promotes atherosclerosis regression in female mice

Introduction

Atherosclerosis is a chronic inflammatory disease caused by the deposition of lipids within the artery wall. During atherogenesis, efficient autophagy is needed to facilitate efferocytosis and cholesterol efflux, limit inflammation and lipid droplet buildup, and eliminate defective mitochondria and protein aggregates. Central to the regulation of autophagy is the transcription factor EB (TFEB), which coordinates the expression of lysosomal biogenesis and autophagy genes. In recent years, trehalose has been shown to promote TFEB activation and protect against atherogenesis. Here, we sought to investigate the role of autophagy activation during atherosclerosis regression.

Methods and results

Atherosclerosis was established in C57BL/6N mice by injecting AAV-PCSK9 and 16 weeks of Western diet feeding, followed by switching to a chow diet to induce atherosclerosis regression. During the regression period, mice were either injected with trehalose concomitant with trehalose supplementation in their drinking water or injected with saline for 6 weeks. Female mice receiving trehalose had reduced atherosclerosis burden, as evidenced by reduced plaque lipid content, macrophage numbers and IL-1β content in parallel with increased plaque collagen deposition, which was not observed in their male counterparts. In addition, trehalose-treated female mice had lower levels of circulating leukocytes, including inflammatory monocytes and CD4+ T cells. Lastly, we found that autophagy flux in male mice was basally higher than in female mice during atherosclerosis progression.

Conclusions

Our data demonstrate a sex-specific effect of trehalose in atherosclerosis regression, whereby trehalose reduced lipid content, inflammation, and increased collagen content in female mice but not in male mice. Furthermore, we discovered inherent differences in the autophagy flux capacities between the sexes: female mice exhibited lower plaque autophagy than males, which rendered the female mice more responsive to atherosclerosis regression. Our work highlights the importance of understanding sex differences in atherosclerosis to personalize the development of future therapies to treat cardiovascular diseases.

Sex differences in vascular endothelial cells

Endothelial cells are important constituents of blood vessels and play a critical role in vascular homeostasis. They do not only control the exchanges between the blood and the surrounding tissues, but are also essential in regulating blood flow, modulating immune-cell trafficking and controlling vascular growth and repair. Endothelial dysfunction leads to cardiovascular diseases and is characterized by deficiency in secretion of vasodilator molecules, elevated reactive oxygen species (ROS), expression of adhesion molecules and excretion of proinflammatory cytokines. The sex hormones, estrogens, androgens and progestogens, regulate endothelial functions. Because cardiovascular disease risk increases after menopause, it is believed that female hormones, estrogens and progestogens promote endothelial cell health and function whereas androgens, the male hormones, might be detrimental. However, as illustrated in the present review, the picture might not be that simple. In addition, sex influences endothelial cell physiology independently of sex hormones but at genetic level.

Exploration of Metabolic Biomarkers Linking Red Meat Consumption to Ischemic Heart Disease Mortality in the UK Biobank

Growing evidence suggests that red meat consumption is a risk factor for cardiovascular health, with potential sex disparity. The metabolic mechanisms have not been fully understood. Using the UK Biobank, first we examined the associations of unprocessed red meat and processed meat with ischemic heart disease (IHD) mortality overall and by sex using logistic regression. Then, we examined the overall and sex-specific associations of red meat consumption with metabolites using multivariable regression, as well as the associations of selected metabolites with IHD mortality using logistic regression. We further selected metabolic biomarkers that are linked to both red meat consumption and IHD, with concordant directions. Unprocessed red meat and processed meat consumption was associated with higher IHD mortality overall and in men. Thirteen metabolites were associated with both unprocessed red meat and IHD mortality overall and showed a consistent direction, including triglycerides in different lipoproteins, phospholipids in very small very-low-density lipoprotein (VLDL), docosahexaenoic acid, tyrosine, creatinine, glucose, and glycoprotein acetyls. Ten metabolites related to triglycerides and VLDL were positively associated with both unprocessed red meat consumption and IHD mortality in men, but not in women. Processed meat consumption showed similar results with unprocessed red meat. Triglycerides in lipoproteins, fatty acids, and some nonlipid metabolites may play a role linking meat consumption to IHD. Triglycerides and VLDL-related lipid metabolism may contribute to the sex-specific associations. Sex differences should be considered in dietary recommendations.

Association of MARC1, ADCY5, and BCO1 Variants with the Lipid Profile, Suggests an Additive Effect for Hypertriglyceridemia in Mexican Adult Men

Epidemiological studies have reported that the Mexican population is highly susceptible to dyslipidemia. The MARC1, ADCY5, and BCO1 genes have recently been involved in lipidic abnormalities. This study aimed to analyze the association of single nucleotide polymorphisms (SNPs) rs2642438, rs56371916, and rs6564851 on MARC1, ADCY5, and BCO1 genes, respectively, with the lipid profile in a cohort of Mexican adults. We included 1900 Mexican adults from the Health Workers Cohort Study. Demographic and clinical data were collected through a structured questionnaire and standardized procedures. Genotyping was performed using a predesigned TaqMan assay. A genetic risk score (GRS) was created on the basis of the three genetic variants. Associations analysis was estimated using linear and logistic regression. Our results showed that rs2642438-A and rs6564851-A alleles had a risk association for hypertriglyceridemia (OR = 1.57, p = 0.013; and OR = 1.33, p = 0.031, respectively), and rs56371916-C allele a trend for low HDL-c (OR = 1.27, p = 0.060) only in men. The GRS revealed a significant association for hypertriglyceridemia (OR = 2.23, p = 0.022). These findings provide evidence of an aggregate effect of the MARC1, ADCY5, and BCO1 variants on the risk of hypertriglyceridemia in Mexican men. This knowledge could represent a tool for identifying at-risk males who might benefit from early interventions and avoid secondary metabolic traits.

Gender Differences in Atherosclerotic Vascular Disease: From Lipids to Clinical Outcomes

Cardiovascular diseases (CVDs) are one of the main reasons of death and morbidity in the world. Both women and men have high rates of cardiovascular morbidity and mortality, although gender-related differences in mortality and morbidity rates are observed in different age groups of the population. In the large cohort of cardiovascular disease, ischemic heart disease (IHD), heart failure (HF), systemic hypertension, and valvular heart disease are particularly common in the population. CVDs caused by atherosclerosis are in the first place in terms of frequency, that is why society is particularly interested in this problem. The development and course of atherosclerotic processes associated with lipid and other metabolic changes are characterized by a long latent period, the clinical manifestation is often an acute vascular catastrophe, which can lead to human disability and death. Differences associated with sex are observed in the clinical course and manifestations, which raises the suspicion that gender influences processes related to atherosclerosis. Atherosclerotic cardiovascular disease (ACD) includes two main most dangerous clinical manifestations: IHD and cerebrovascular disease (mainly ischemic stroke). Other less common clinical manifestations of atherosclerosis include aortic atherosclerosis and peripheral vascular disease. Gender-related differences were also identified concerning these diseases. The present review discusses the effects of gender and age on atherosclerotic processes, disease development, and clinical manifestations. The metabolic basis for the development of atherosclerosis appears to be related to sex hormones. Thus this issue is interesting and useful for doctors of different specialties.

Lipoprotein receptor signalling in atherosclerosis

The founding member of the lipoprotein receptor family, low-density lipoprotein receptor (LDLR) plays a major role in the atherogenesis through the receptor-mediated endocytosis of LDL particles and regulation of cholesterol homeostasis. Since the discovery of the LDLR, many other structurally and functionally related receptors have been identified, which include low-density lipoprotein receptor-related protein (LRP)1, LRP5, LRP6, very low-density lipoprotein receptor, and apolipoprotein E receptor 2. The scavenger receptor family members, on the other hand, constitute a family of pattern recognition proteins that are structurally diverse and recognize a wide array of ligands, including oxidized LDL. Among these are cluster of differentiation 36, scavenger receptor class B type I and lectin-like oxidized low-density lipoprotein receptor-1. In addition to the initially assigned role as a mediator of the uptake of macromolecules into the cell, a large number of studies in cultured cells and in in vivo animal models have revealed that these lipoprotein receptors participate in signal transduction to modulate cellular functions. This review highlights the signalling pathways by which these receptors influence the process of atherosclerosis development, focusing on their roles in the vascular cells, such as macrophages, endothelial cells, smooth muscle cells, and platelets. Human genetics of the receptors is also discussed to further provide the relevance to cardiovascular disease risks in humans. Further knowledge of the vascular biology of the lipoprotein receptors and their ligands will potentially enhance our ability to harness the mechanism to develop novel prophylactic and therapeutic strategies against cardiovascular diseases.

Molecular Insulin Actions Are Sexually Dimorphic in Lipid Metabolism

The increment in energy-dense food and low physical activity has contributed to the current obesity pandemic, which is more prevalent in women than in men. Insulin is an anabolic hormone that regulates the metabolism of lipids, carbohydrates, and proteins in adipose tissue, liver, and skeletal muscle. During obesity, nutrient storage capacity is dysregulated due to a reduced insulin action on its target organs, producing insulin resistance, an early marker of metabolic dysfunction. Insulin resistance in adipose tissue is central in metabolic diseases due to the critical role that this tissue plays in energy homeostasis. We focused on sexual dimorphism on the molecular mechanisms of insulin actions and their relationship with the physiology and pathophysiology of adipose tissue. Until recently, most of the physiological and pharmacological studies were done in males without considering sexual dimorphism, which is relevant. There is ample clinical and epidemiological evidence of its contribution to the establishment and progression of metabolic diseases. Sexual dimorphism is a critical and often overlooked factor that should be considered in design of sex-targeted therapeutic strategies and public health policies to address obesity and diabetes.

Dietary stearic acid and palmitic acid do not differently affect ABCA1-mediated cholesterol efflux capacity in healthy men and postmenopausal women: A randomized controlled trial

BACKGROUND

The saturated fatty acid stearic acid (C18:0) lowers HDL cholesterol compared with palmitic acid (C16:0). However, the ability of HDL particles to promote cholesterol efflux from macrophages (cholesterol efflux capacity; CEC) may better predict coronary heart disease (CHD) risk than HDL cholesterol concentrations.

OBJECTIVE

We examined effects of exchanging dietary palmitic acid for stearic acid on ATP-binding cassette transporter A1 (ABCA1)-mediated CEC, and other conventional and emerging cardiometabolic risk makers.

DESIGN

In a double-blind, randomized, crossover study with two 4-week isocaloric intervention periods, 34 healthy men and postmenopausal women (61.5 ± 5.7 years, BMI: 25.4 ± 2.5 kg/m²) followed diets rich in palmitic acids or stearic acids. Difference in intakes was 6% of daily energy. ABCA1-mediated CEC was measured from J774 macrophages to apolipoprotein (apo)B-depleted serum.

RESULTS

Compared with the palmitic-acid diet, the stearic-acid diet lowered serum LDL cholesterol (-0.14 mmol/L; p = 0.010), HDL cholesterol (-0.09 mmol/L; p=<0.001), and apoA1 (-0.05 g/L; p < 0.001). ABCA1-mediated CEC did not differ between diets (p = 0.280). Cholesteryl ester transfer protein (CETP) mass was higher on stearic acid (0.11 mg/L; p = 0.003), but CETP activity was comparable. ApoB100 did not differ, but triacylglycerol concentrations tended to be higher on stearic acid (p = 0.100). Glucose concentrations were comparable. Effects on insulin and C-peptide were sex-dependent. In women, the stearic-acid diet increased insulin concentrations (1.57 μU/mL; p = 0.002), while in men, C-peptide concentrations were lower (-0.15 ng/mL; p = 0.037). Interleukin 6 (0.15 pg/mL; p = 0.039) and tumor necrosis factor alpha (0.18 pg/mL; p = 0.005), but not high-sensitivity C-reactive protein, were higher on stearic acid. Soluble intracellular adhesion molecule (9 ng/mL; p = 0.033), but not soluble vascular cell adhesion molecule and endothelial-selectin concentrations decreased after stearic-acid consumption.

CONCLUSIONS

As expected, stearic-acid intake lowered LDL cholesterol, HDL cholesterol, and apoA1. Insulin sensitivity in women and low-grade inflammation might be unfavorably affected by stearic-acid intake. However, palmitic-acid and stearic-acid intakes did not differently affect ABCA1-mediated CEC.

CLINICAL TRIAL REGISTRY

This trial was registered at clinicaltrials.gov as NCT02835651.

Differential roles of Scavenger receptor class B type I: A protective molecule and a facilitator of atherosclerosis (Review)

The scavenger receptor class B type I (SR-BI) is a multi-ligand membrane protein receptor that binds to high-density lipoprotein (HDL) under physiological conditions, promoting the selective uptake of cholesterol esters from HDL into cells. SR-BI also promotes the reverse transport of excess cholesterol from peripheral tissues to the liver, contributing to the synthesis of bile acids for excretion and the removal of excess cholesterol from the body, thereby lowering the cholesterol load and exerting anti-atherosclerotic effects. Studies in mice and humans have demonstrated that a functional defect of SR-BI can cause atherosclerotic lesions and cardiovascular diseases, such as myocardial infarction and stroke. Additionally, SR-BI in vascular endothelial cells promoted the deposition of low-density lipoprotein under the endothelium. Although SR-BI is widely expressed in various tissues and cell types throughout the body, its expression level and function vary accordingly. The present review focuses on the biological functions and mechanisms of SR-BI in regulating atherosclerosis.

HDL (High-Density Lipoprotein) Cholesterol Efflux Capacity Is Associated With Incident Cardiovascular Disease in the General Population

Objective:

Focus is shifting from HDL-C (high-density lipoprotein cholesterol) as predictive biomarker for cardiovascular disease (CVD) towards antiatherogenic HDL functionalities. Still, limited data exist on the prospective association of HDL function metrics with CVD events. The current work aimed to determine, if baseline HDL-C efflux capacity (CEC) is associated with future CVD events in the general population.

Approach and Results:

We performed a prospective study among participants of the PREVEND (Prevention of Renal and Vascular End-stage Disease) cohort (follow-up, 12 years). From the overall n=8592 subjects 325 with previous CVD events were excluded; of the remaining 8267 eligible participants all subjects with new CVD events during follow-up were selected and individually matched to controls for age, sex, smoking status, and HDL-C levels. CEC at baseline was quantified using human THP-1-derived macrophage foam cells and apolipoprotein B-depleted plasma. Despite identical HDL-C and apoA (apolipoprotein)-I levels between cases (n=351) and controls (n=354) CEC was significantly lower in cases (0.93±0.29 versus 1.01±0.24 arbitrary units; P <0.001). In all subjects combined, CEC correlated positively with HDL-C and apoA-I and negatively with body mass index, hsCRP (high-sensitivity C-reactive protein), and urinary albumin excretion. CEC was inversely associated with incident CVD events, both expressed per quartile and per 1 SD change (odds ratio, 0.73; 95% CI, 0.62–0.86; P <0.001); this association remained significant after adjustments for HDL-C, hsCRP, kidney function, and several other clinical covariates.

Conclusions:

Combined these data demonstrate that in the general population baseline CEC is significantly associated with the future development of CVD events independent of HDL-C and apoA-I plasma levels.

Sex differences in lipid and lipoprotein metabolism

BACKGROUND

Endogenous sex hormones are important for metabolic health in men and women. Before menopause, women are protected from atherosclerotic cardiovascular disease (ASCVD) relative to men. Women have fewer cardiovascular complications of obesity compared to men with obesity. Endogenous estrogens have been proposed as a mechanism that lessens ASCVD risk, as risk of glucose and lipid abnormalities increases when endogenous estrogens decline with menopause. While baseline risk is higher in males than females, endogenously produced androgens are also protective against fatty liver, diabetes and ASCVD, as risk goes up with androgen deprivation and with the decline in androgens with age.

SCOPE OF REVIEW

In this review, we discuss evidence of how endogenous sex hormones and hormone treatment approaches impact fatty acid, triglyceride, and cholesterol metabolism to influence metabolic and cardiovascular risk. We also discuss potential reasons for why treatment strategies with estrogens and androgens in older individuals fail to fully recapitulate the effects of endogenous sex hormones.

MAJOR CONCLUSIONS

The pathways that confer ASCVD protection for women are of potential therapeutic relevance. Despite protection relative to men, ASCVD is still the major cause of mortality in women. Additionally, diabetic women have similar ASCVD risk as diabetic men, suggesting that the presence of diabetes may offset the protective cardiovascular effects of being female through unknown mechanisms.

A critical appraisal of the measurement of serum 'cholesterol efflux capacity' and its use as surrogate marker of risk of cardiovascular disease

The 'cholesterol efflux capacity (CEC)' assay is a simple in vitro measure of the capacities of individual sera to promote the first step of the reverse cholesterol transport pathway, the delivery of cellular cholesterol to plasma HDL. This review describes the cell biology of this model and critically assesses its application as a marker of cardiovascular risk. We describe the pathways for cell cholesterol export, current cell models used in the CEC assay with their limitations and consider the contribution that measurement of serum CEC provides to our understanding of HDL function in vivo.

Gender and cardiovascular disease: are sex-biased microRNA networks a driving force behind heart failure with preserved ejection fraction in women?

Cardiovascular disease (CVD) is the primary cause of death among men and women worldwide. Nevertheless, our comprehension of how CVD progresses in women and elicits clinical outcomes is lacking, leading CVD to be under-diagnosed and under-treated in women. A clear example of this differential presentation of CVD pathophysiologies in females is the strikingly higher prevalence of heart failure with preserved ejection fraction (HFpEF). Women with a history of pre-eclampsia or those who present with co-morbidities such as obesity, hypertension, and diabetes mellitus are at increased risk of developing HFpEF. Long understood to be a critical CVD risk factor, our understanding of how gender differentially affects the development of CVD has been greatly expanded by extensive genomic and transcriptomic studies. These studies uncovered a pivotal role for differential microRNA (miRNA) expression in response to systemic inflammation, where their co-ordinated expression forms a post-transcriptional regulatory network that instigates microcirculation defects. Importantly, the potential sex-biased expression of the given miRNAs may explain sex-specific cardiovascular pathophysiologies in women, such as HFpEF. Sex-biased miRNAs are regulated by oestrogen (E2) in their transcription and processing or are expressed from loci on the X-chromosome due to incomplete X-chromosome inactivation. Interestingly, while E2-induced miRNAs predominantly appear to serve protective functions, it could be argued that many X-linked miRNAs have been found to challenge microvascular and myocardial integrity. Therefore, menopausal E2 deficiency, resulting in protective miRNA loss, and the augmentation of X-linked miRNA expression, may well contribute to the molecular mechanisms that underlie the female-specific cardiovascular aetiology in HFpEF.

SR-B1: A Unique Multifunctional Receptor for Cholesterol Influx and Efflux

The scavenger receptor, class B type 1 (SR-B1), is a multiligand membrane receptor protein that functions as a physiologically relevant high-density lipoprotein (HDL) receptor whose primary role is to mediate selective uptake or influx of HDL-derived cholesteryl esters into cells and tissues. SR-B1 also facilitates the efflux of cholesterol from peripheral tissues, including macrophages, back to liver. As a regulator of plasma membrane cholesterol content, SR-B1 promotes the uptake of lipid soluble vitamins as well as viral entry into host cells. These collective functions of SR-B1 ultimately affect programmed cell death, female fertility, platelet function, vasculature inflammation, and diet-induced atherosclerosis and myocardial infarction. SR-B1 has also been identified as a potential marker for cancer diagnosis and prognosis. Finally, the SR-B1-linked selective HDL-cholesteryl ester uptake pathway is now being evaluated as a gateway for the delivery of therapeutic and diagnostic agents. In this review, we focus on the regulation and functional significance of SR-B1 in mediating cholesterol movement into and out of cells.

SR-BI: A Multifunctional Receptor in Cholesterol Homeostasis and Atherosclerosis

The HDL receptor scavenger receptor class B type I (SR-BI) plays crucial roles in cholesterol homeostasis, lipoprotein metabolism, and atherosclerosis. Hepatic SR-BI mediates reverse cholesterol transport (RCT) by the uptake of HDL cholesterol for routing to the bile. Through the selective uptake of HDL lipids, hepatic SR-BI modulates HDL composition and preserves HDL's atheroprotective functions of mediating cholesterol efflux and minimizing inflammation and oxidation. Macrophage and endothelial cell SR-BI inhibits the development of atherosclerosis by mediating cholesterol trafficking to minimize atherosclerotic lesion foam cell formation. SR-BI signaling also helps limit inflammation and cell death and mediates efferocytosis of apoptotic cells in atherosclerotic lesions thereby preventing vulnerable plaque formation. SR-BI is emerging as a multifunctional therapeutic target to reduce atherosclerosis development.

Sex Hormones and Sex Chromosomes Cause Sex Differences in the Development of Cardiovascular Diseases

This review summarizes recent evidence concerning hormonal and sex chromosome effects in obesity, atherosclerosis, aneurysms, ischemia/reperfusion injury, and hypertension. Cardiovascular diseases occur and progress differently in the 2 sexes, because biological factors differing between the sexes have sex-specific protective and harmful effects. By comparing the 2 sexes directly, and breaking down sex into its component parts, one can discover sex-biasing protective mechanisms that might be targeted in the clinic. Gonadal hormones, especially estrogens and androgens, have long been found to account for some sex differences in cardiovascular diseases, and molecular mechanisms mediating these effects have recently been elucidated. More recently, the inherent sexual inequalities in effects of sex chromosome genes have also been implicated as contributors in animal models of cardiovascular diseases, especially a deleterious effect of the second X chromosome found in females but not in males. Hormonal and sex chromosome mechanisms interact in the sex-specific control of certain diseases, sometimes by opposing the action of the other.

Role of Estrogens in the Regulation of Liver Lipid Metabolism

Before menopause, women are protected from atherosclerotic heart disease associated with obesity relative to men. Sex hormones have been proposed as a mechanism that differentiates this risk. In this review, we discuss the literature around how the endogenous sex hormones and hormone treatment approaches after menopause regulate fatty acid, triglyceride, and cholesterol metabolism to influence cardiovascular risk.The important regulatory functions of estrogen signaling pathways with regard to lipid metabolism have been in part obscured by clinical trials with hormone treatment of women after menopause, due to different formulations, routes of delivery, and pairings with progestins. Oral hormone treatment with several estrogen preparations increases VLDL triglyceride production. Progestins oppose this effect by stimulating VLDL clearance in both humans and animals. Transdermal estradiol preparations do not increase VLDL production or serum triglycerides.Many aspects of sex differences in atherosclerotic heart disease risk are influenced by the distributed actions of estrogens in the muscle, adipose, and liver. In humans, 17β-estradiol (E2) is the predominant circulating estrogen and signals through estrogen receptor alpha (ERα), estrogen receptor beta (ERβ), and G-protein-coupled estrogen receptor (GPER). Over 1000 human liver genes display a sex bias in their expression, and the top biological pathways are in lipid metabolism and genes related to cardiovascular disease. Many of these genes display variation depending on estrus cycling in the mouse. Future directions will likely rely on targeting estrogens to specific tissues or specific aspects of the signaling pathways in order to recapitulate the protective physiology of premenopause therapeutically after menopause.

Dichotomous roles for externalized cardiolipin in extracellular signaling: Promotion of phagocytosis and attenuation of innate immunity

Among the distinct molecular signatures present in the mitochondrion is the tetra-acylated anionic phospholipid cardiolipin, a lipid also present in primordial, single-cell bacterial ancestors of mitochondria and multiple bacterial species today. Cardiolipin is normally localized to the inner mitochondrial membrane; however, when cardiolipin becomes externalized to the surface of dysregulated mitochondria, it promotes inflammasome activation and stimulates the elimination of damaged or nonfunctional mitochondria by mitophagy. Given the immunogenicity of mitochondrial and bacterial membranes that are released during sterile and pathogen-induced trauma, we hypothesized that cardiolipins might function as "eat me" signals for professional phagocytes. In experiments with macrophage cell lines and primary macrophages, we found that membranes with mitochondrial or bacterial cardiolipins on their surface were engulfed through phagocytosis, which depended on the scavenger receptor CD36. Distinct from this process, the copresentation of cardiolipin with the Toll-like receptor 4 (TLR4) agonist lipopolysaccharide dampened TLR4-stimulated production of cytokines. These data suggest that externalized, extracellular cardiolipins play a dual role in host-host and host-pathogen interactions by promoting phagocytosis and attenuating inflammatory immune responses.

Atomistic MD simulation reveals the mechanism by which CETP penetrates into HDL enabling lipid transfer from HDL to CETP

Inhibition of cholesterol ester transfer protein (CETP), a protein mediating transfer of neutral lipids between lipoproteins, has been proposed as a means to elevate atheroprotective HDL subpopulations and thereby reduce atherosclerosis. However, off-target and adverse effects of the inhibition have raised doubts about the molecular mechanism of CETP-HDL interaction. Recent experimental findings have demonstrated the penetration of CETP into HDL. However, atomic level resolution of CETP penetration into HDL, a prerequisite for a better understanding of CETP functionality and HDL atheroprotection, is missing. We constructed an HDL particle that mimics the actual human HDL mass composition and investigated for the first time, by large-scale atomistic molecular dynamics, the interaction of an upright CETP with a human HDL-mimicking model. The results demonstrated how CETP can penetrate the HDL particle surface, with the formation of an opening in the N barrel domain end of CETP, put in evidence the major anchoring role of a tryptophan-rich region of this domain, and unveiled the presence of a phenylalanine barrier controlling further access of HDL-derived lipids to the tunnel of CETP. The findings reveal novel atomistic details of the CETP-HDL interaction mechanism and can provide new insight into therapeutic strategies.

Loss of sex difference in high-density lipoprotein cholesterol in diabetic women during acute stress

CONTEXT

The gender gap in high-density lipoprotein cholesterol (HDL-C) is well documented in health and also maintained in diverse chronic conditions, including menopause and diabetes. The mechanism for this difference in HDL-C and its regulation is not well understood. We evaluated whether this gender gap is maintained during acute stress.

SETTING AND DESIGN

Diabetic patients with metabolic decompensation (n=179) were studied in the fasting state within 24 hours of admission to hospital, and again at outpatient follow-up. Fasting lipids and measures of glycemic control were evaluated on both occasions. The population was predominately minority, 78% Hispanic or African American.

RESULTS

During admission, fasting lipid concentrations were not different in women (W) (n = 88) and men (M) (n = 91); serum total cholesterol (total-C), triglycerides (TG), low-density lipoprotein cholesterol (LDL-C), and HDL-C were similar. Glycemic control was also similar; hemoglobin A1c (A1C) and serum glucose at presentation to hospital were not different in men and women. Compared with a subset of patients with pre-admission data (W, 35; M, 24), a decline of HDL-C was observed, greater in women (P = .005). At outpatient follow-up after admission, median duration approximately 4 months in each group (P = .39), changes in TG, LDL-C, and total-C from baseline admission were not different in men and women. In contrast, whereas HDL-C increased in both groups, the increase (median [interquartile range]) was significantly greater in women, 11 (4, 23) vs 6 (-1, 15) mg/dL (P < .003). This larger increase restored the gender gap in fasting HDL-C, 48 (39, 61) and 41 (36, 49) mg/dL in women and men at follow-up (P < .002). A1C improved similarly in each group.

CONCLUSIONS

The sex difference in HDL-C levels is lost at time of admission to hospital in patients with diabetes, and returns when acute stress has resolved. These results raise the possibility that recurrent episodes of acute stress may lead to cumulative loss of the HDL-C advantage in women.

Regulation of endothelial nitric oxide synthase and high-density lipoprotein quality by estradiol in cardiovascular pathology

Estrogens have been recognized, in the last 3 decades, as important hormones in direct and indirect modulation of vascular health. In addition to their direct benefit on cardiovascular health, the presence of esterified estrogen in the lipid core of high-density lipoprotein (HDL) particles indirectly contributes to atheroprotection by significantly improving HDL quality and functionality. Estrogens modulate their physiological activity via genomic and nongenomic mechanisms. Genomic mechanisms are thought to be mediated directly by interaction of the hormone receptor complex with the hormone response elements that regulate gene expression. Nongenomic mechanisms are thought to occur via interaction of the estrogen with membrane-bound receptors, which rapidly activate intracellular signaling without binding of the hormone receptor complex to its hormone response elements. Estradiol in particular mediates early and late endothelial nitric oxide synthase (eNOS) activation via interaction with estrogen receptors through both nongenomic and genomic mechanisms. In the vascular system, the primary endogenous source of nitric oxide (NO) generation is eNOS. Nitric oxide primarily influences blood vessel relaxation, the heart rate, and myocyte contractility. The abnormalities in expression and/or functions of eNOS lead to the development of cardiovascular diseases, both in animals and in humans. Although considerable research efforts have been dedicated to understanding the mechanisms of action of estradiol in regulating cardiac eNOS, more research is needed to fully understand the details of such mechanisms. This review focuses on recent findings from animal and human studies on the regulation of eNOS and HDL quality by estradiol in cardiovascular pathology.

The impact of gender and serum estradiol levels on HDL-mediated reverse cholesterol transport

OBJECTIVE

Premenopausal women have a lower incidence of cardiovascular disease compared to men of the same age. Endogenous oestrogens, especially estradiol, presumably protect against atherosclerosis by a variety of mechanisms. Reverse cholesterol transport (RCT) mechanisms also provide protection against this disease. RCT is defined as the removal of cholesterol from peripheral macrophage foam cells, via high-density lipoproteins (HDL), and cholesterol transportation to the liver for excretion. We have previously shown in a preliminary study that HDL, isolated from premenopausal women, enhanced macrophage cholesterol efflux compared to HDL derived from age-matched male subjects.

MATERIALS AND METHODS

Here, we expanded this study by analysing a larger population of healthy volunteers and evaluated the capacity of HDL derived from women with high or low serum E2 concentrations, mainly representing premenopausal and postmenopausal women, respectively, or men (each group consisting of 30 subjects) to facilitate cholesterol removal from human THP-1 macrophages. HDL isolated from serum samples was incubated with [(3)H] cholesterol oleate-loaded macrophages for 16 h, after which cholesterol efflux to HDL was determined.

RESULTS

No significant differences in the efflux-promoting ability of HDL existed among the three groups. Relevant plasma factors involved in further steps of RCT, such as cholesterol ester transfer protein (CETP), phospholipid transfer protein (PLTP) and lecithin:cholesterol acyltransferase (LCAT) activities were also analysed, but no differences were observed among the study groups.

CONCLUSION

The results do not support a role for estradiol status or gender in modifying the initial step of RCT as a protective mechanism against cardiovascular disease.

Unraveling the complexities of the HDL lipidome

Plasma high density lipoproteins (HDL) are small, dense, protein-rich particles compared with other lipoprotein classes; roughly half of total HDL mass is accounted for by lipid components. Phospholipids predominate in the HDL lipidome, accounting for 40-60% of total lipid, with lesser proportions of cholesteryl esters (30-40%), triglycerides (5-12%), and free cholesterol (5-10%). Lipidomic approaches have provided initial insights into the HDL lipidome with identification of over 200 individual molecular lipids species in normolipidemic HDL. Plasma HDL particles, however, reveal high levels of structural, compositional, and functional heterogeneity. Establishing direct relationships between HDL structure, composition, and atheroprotective functions bears the potential to identify clinically relevant HDL subpopulations. Furthermore, development of HDL-based therapies designed to target beneficial subspecies within the circulating HDL pool can be facilitated using this approach. HDL lipidomics can equally contribute to the identification of biomarkers of both normal and deficient HDL functionality, which may prove useful as biomarkers of cardiovascular risk. However, numerous technical issues remain to be addressed in order to make such developments possible. With all technical questions resolved, quantitative analysis of the molecular components of the HDL lipidome will contribute to expand our knowledge of cardiovascular and metabolic diseases.

Autoimmune heart disease: role of sex hormones and autoantibodies in disease pathogenesis

Cardiovascular disease (CVD) and autoimmune diseases (ADs) are the first and third highest causes of death in the USA, respectively. Men have an increased incidence of the majority of CVDs, including atherosclerosis, myocarditis, dilated cardiomyopathy and heart failure. By contrast, nearly 80% of all ADs occur in women. However, in one category of ADs, rheumatic diseases, CVD is the main cause of death. Factors that link rheumatic ADs to CVD are inflammation and the presence of autoantibodies. In this review we will examine recent findings regarding sex differences in the immunopathogenesis of CVD and ADs, explore possible reasons for the increased occurrence of CVD within rheumatic ADs and discuss whether autoantibodies, including rheumatoid factor, could be involved in disease pathogenesis.

Estrogens and atherosclerosis: insights from animal models and cell systems

Estrogens not only play a pivotal role in sexual development but are also involved in several physiological processes in various tissues including vasculature. While several epidemiological studies documented an inverse relationship between plasma estrogen levels and the incidence of cardiovascular disease and related it to the inhibition of atherosclerosis, an interventional trial showed an increase in cardiovascular events among postmenopausal women on estrogen treatment. The development of atherosclerotic lesions involves complex interplay between various pro- or anti-atherogenic processes that can be effectively studied only in vivo in appropriate animal models. With the advent of genetic engineering, transgenic mouse models of atherosclerosis have supplemented classical dietary cholesterol-induced disease models such as the cholesterol-fed rabbit. In the last two decades, these models were widely applied along with in vitro cell systems to specifically investigate the influence of estrogens on the development of early and advanced atherosclerotic lesions. The present review summarizes the results of these studies and assesses their contribution toward better understanding of molecular mechanisms underlying anti- and/or pro-atherogenic effects of estrogens in humans.

Update on HDL receptors and cellular cholesterol transport

Efflux is central to maintenance of tissue and whole body cholesterol homeostasis. The discovery of cell surface receptors that bind high-density lipoprotein (HDL) with high specificity and affinity to promote cholesterol release has significantly advanced our understanding of cholesterol efflux. We now know that 1) cells have several mechanisms to promote cholesterol release, including a passive mechanism that depends on the physico-chemical properties of cholesterol molecules and their interactions with phospholipids; 2) a variety of HDL particles can interact with receptors to promote cholesterol transport from tissues to the liver for excretion; and 3) interactions between HDL and receptors show functional synergy. Therefore, efflux efficiency depends both on the arrays of receptors on tissue cells and HDL particles in serum.

The effect of 17β-estradiol on cholesterol content in human macrophages is influenced by the lipoprotein milieu

Estrogen and testosterone are thought to modulate coronary heart disease (CHD) risk. To examine how these hormones affect human macrophage cholesterol transport, a key factor in atherogenesis, we obtained monocytes from healthy male and postmenopausal female donors (age 50–70 years). Cells were allowed to differentiate in autologous serum. Human monocyte-derived macrophages (HMDMs) were exposed to estrogen, testosterone, or vehicle, during differentiation.Cells were cholesterol enriched with oxidized low-density lipoprotein (oxLDL) in the presence of treatment. Cell cholesterol mass, efflux, and the expression of proteins involved in HMDM cholesterol transport were examined.Estrogen significantly reduced cholesteryl ester (CE) content in both female and male HMDMs while having no measurable effect on cholesterol efflux. Testosterone did not affect cholesterol content or efflux. Both hormones significantly but modestly affected the gene expression of several proteins involved in HMDM transport, yet these effects did not translate into significant changes in protein expression. In THP-1 macrophages, the effect of estrogen on CE content was more potent in unloaded macrophages and was estrogen receptor dependent. A trend for a reduction in nonoxLDL uptake by estrogen was observed and was also found to be dependent upon estrogen receptor activation. Our data indicate that estrogen, but not testosterone, reduces CE accumulation in HMDMs obtained from a CHD age relevant population, independent of changes in the expression of proteins important to macrophage cholesterol transport. In THP-1 cells, this effect is reduced in the presence of oxLDL, indicating that a pro-atherogenic lipoprotein milieu is an important variable in sex hormone modulation of CHD.

Dehydroepiandrosterone fatty acyl esters in high density lipoprotein: interaction with human vascular endothelial cells and vascular responses ex vivo

Dehydroepiandrosterone (DHEA) fatty acyl esters once incorporated in high density lipoprotein (HDL) induce a stronger vasodilatory response in rat mesenteric arteries ex vivo compared to native HDL. We studied the role of HDL receptor, scavenger receptor class B, type 1 (SR-B1), as well as estrogen and androgen receptors in the vasodilatory response of HDL-associated DHEA fatty acyl esters. Using cultured human vascular endothelial cells (HUVEC), we investigated the possible internalization and cellular response of HDL-associated DHEA esters. We prepared DHEA ester-enriched HDL by incubating human plasma in the presence of DHEA. After isolation and purification, HDL was added in cumulative doses to arterial rings precontracted with noradrenaline. Inhibition of the function of SR-B1 almost completely abolished maximal vasorelaxation by DHEA-enriched HDL while estrogen or androgen receptor blockage had no significant effect. When HUVECs were incubated in the presence of [³H]DHEA ester-enriched HDL, the amount of intracellular [³H]-radioactivity increased steadily during 24 h. Blocking of SR-B1 reduced this uptake by a mean of 30%. The proportion of unesterified [³H]DHEA, as analyzed by thin-layer chromatography, increased intracellularly and in the cell culture media after several hours of incubation of the cells in the presence of [³H]DHEA ester-enriched HDL. This indicated slow hydrolysis of DHEA fatty acyl esters and subsequent excretion of unesterified DHEA by the cells. In conclusion, DHEA-enriched HDL induced vasorelaxation via the SR-B1-facilitated pathway. However, this vasodilation is not likely to be attributed to rapid hydrolysis of HDL-associated DHEA esters by the vascular endothelium.

Atherosclerosis and sex hormones: current concepts

CVD (cardiovascular disease) is the leading cause of death for women. Considerable progress has been made in both our understanding of the complexities governing menopausal hormone therapy and our understanding of the cellular and molecular mechanisms underlying hormone and hormone receptor function. Understanding the interplay of atherosclerosis and sex steroid hormones and their cognate receptors at the level of the vessel wall has important ramifications for clinical practice. In the present review, we discuss the epidemiology of CVD in men and women, the clinical impact of sex hormones on CVD, and summarize our current understanding of the pathogenesis of atherosclerosis with a focus on gender differences in CVD, its clinical presentation and course, and pathobiology. The critical animal and human data that pertain to the role of oestrogens, androgens and progestins on the vessel wall is also reviewed, with particular attention to the actions of sex hormones on each of the three key cell types involved in atherogenesis: the endothelium, smooth muscle cells and macrophages. Where relevant, the systemic (metabolic) effects of sex hormones that influence atherogenesis, such as those involving vascular reactivity, inflammation and lipoprotein metabolism, are discussed. In addition, four key current concepts in the field are explored: (i) total hormone exposure time and coronary heart disease risk; (ii) the importance of tissue specificity of sex steroid hormones, critical timing and the stage of atherosclerosis in hormone action; (iii) biomarkers for atherosclerosis with regard to hormone therapy; and (iv) the complex role of sex steroids in inflammation. Future studies in this field will contribute to guiding clinical treatment recommendations for women and help define research priorities.

Investigating the membrane orientation and transversal distribution of 17beta-estradiol in lipid membranes by solid-state NMR

17beta-Estradiol (E(2)) is a potent estrogen, which modulates many important cellular functions by binding to specific estrogen receptors located in the cell nucleus and also on the plasma membrane. We have studied the membrane interaction of E(2) using a combination of solid-state NMR methods. (2)H NMR results indicate that E(2) does not cause a condensation effect of the surrounding phospholipids, which is contrary to the effects of cholesterol, and only very modest E(2) induced alterations of the membrane structure were detected. (1)H magic-angle spinning NMR showed well resolved signals from E(2) as well as of POPC in the membrane-lipid layer. Two-dimensional NOESY spectra revealed intense cross-peaks between E(2) and the membrane lipids indicating that E(2) is stably inserted into the membrane. The determination of intermolecular cross-relaxation rates revealed that E(2) is broadly distributed in the membrane with a maximum of the E(2) distribution function in the upper chain region of the membrane. We conclude that E(2) is highly dynamic in lipid membranes and may undergo rotations as it exhibits two polar hydroxyl groups on either side of the molecule.

HDL lipids and insulin resistance

There is renewed interest in high-density lipoproteins (HDLs) due to recent findings linking atherosclerosis to the formation of dysfunctional HDL. This article focuses on the universe of HDL lipids and their potential protective or proinflammatory roles in vascular disease and insulin resistance. HDL carries a wide array of lipids including sterols, triglycerides, fat-soluble vitamins, and a large number of phospholipids, including phosphatidylcholine, sphingomyelin, and ceramide with many biological functions. Ceramide has been implicated in the pathogenesis of insulin resistance and has many proinflammatory properties. In contrast, sphingosine-1-phosphate, which is transported mainly in HDL, has anti-inflammatory properties that may be atheroprotective and may account for some of the beneficial effects of HDL. However, the complexity of the HDL lipidome is only beginning to reveal itself. The emergence of new analytical technologies should rapidly increase our understanding of the function of HDL lipids and their role in disease states.

Partial filling affinity capillary electrophoresis with cationic poly(vinylpyrrolidone)-based copolymer coatings for studies on human lipoprotein-steroid interactions

Human plasma lipoproteins have strong hydrophobic interactions with steroids and their fatty acyl derivatives such as estradiol fatty acyl esters. In this work, affinity capillary electrophoresis with the partial filling technique was applied to study the hydrophobic interactions between lipoproteins, which are nanometer-sized particles, and nonconjugated steroids. The capillaries were first rinsed with one of two novel poly(vinylpyrrolidone) (PVP)-based cationic copolymers that were strongly adsorbed onto the fused-silica surface via electrostatic interactions. This surface treatment greatly suppressed the adsorption of lipoproteins. Low-density lipoprotein (LDL) and high-density lipoprotein (HDL) particles were then employed in the coated capillaries as pseudostationary phase in the partial filling mode. The changes in corrected migration times of steroids increased linearly with the filling time of the lipoproteins. The affinity constants between the steroids and lipoproteins were calculated, and the most hydrophobic steroid studied, progesterone, had stronger affinity than testosterone or androstenedione toward both LDL and HDL. Affinity between steroids and LDL was stronger than that between steroids and HDL. Interactions between the steroids and lipoproteins were mainly nonspecific with particle lipid components, whereas some were site specific with the apolipoproteins. The developed technique has great potential for determination of the affinity of various compounds toward lipoproteins.