High-density lipoproteins: an emerging target in the prevention of cardiovascular disease

High-Density Lipoprotein (HDL) Triglyceride and Oxidized HDL: New Lipid Biomarkers of Lipoprotein-Related Atherosclerotic Cardiovascular Disease

Lipid markers are well-established predictors of vascular disease. The most frequently measured lipid markers are total cholesterol, high-density lipoprotein (HDL)-cholesterol (HDL-C), LDL cholesterol (LDL-C), and triglyceride. HDL reduces atherosclerosis by multiple mechanisms, leading to a reduced risk of cardiovascular disease, and HDL-C, as a metric of HDL quantity, is inversely associated with cardiovascular disease, independent of LDL-C. However, the quality of the HDL appears to be more important than its quantity, because HDL loses its antiatherogenic functions due to changes in its composition and becomes “dysfunctional HDL”. Although there is evidence of the existence of “dysfunctional HDL”, biomarkers for monitoring dysfunctional HDL in clinical practice have not yet been established. In this review, we propose a new lipid panel for the assessment of dysfunctional HDL and lipoprotein-related atherosclerotic cardiovascular disease. The lipid panel includes the measurement of lipid peroxide and triglyceride contents within HDL particles.

High density lipoprotein promotes proliferation of adipose-derived stem cells via S1P1 receptor and Akt, ERK1/2 signal pathways

INTRODUCTION

Adipose-derived stem cells (ADSC) are non-hematopoietic mesenchymal stem cells that have shown great promise in their ability to differentiate into multiple cell lineages. Their ubiquitous nature and the ease of harvesting have attracted the attention of many researchers, and they pose as an ideal candidate for applications in regenerative medicine. Several reports have demonstrated that transplanting ADSC can promote repair of injured tissue and angiogenesis in animal models. Survival of these cells after transplant remains a key limiting factor for the success of ADSC transplantation. Circulating factors like High Density Lipoprotein (HDL) has been known to promote survival of other stems cells like bone marrow derived stem cells and endothelial progenitor cells, both by proliferation and by inhibiting cell apoptosis. The effect of HDL on transplanted adipose-derived stem cells in vivo is largely unknown.

METHODS

This study focused on exploring the effects of plasma HDL on ADSC and delineating the mechanisms involved in their proliferation after entering the bloodstream. Using the MTT and BrdU assays, we tested the effects of HDL on ADSC proliferation. We probed the downstream intracellular Akt and ERK1/2 signaling pathways and expression of cyclin proteins in ADSC using western blot.

RESULTS

Our study found that HDL promotes proliferation of ADSC, by binding to sphingosine-1- phosphate receptor-1(S1P1) on the cell membrane. This interaction led to activation of intracellular Akt and ERK1/2 signaling pathways, resulting in increased expression of cyclin D1 and cyclin E, and simultaneous reduction in expression of cyclin-dependent kinase inhibitors p21 and p27, therefore promoting cell cycle progression and cell proliferation.

CONCLUSIONS

These studies raise the possibility that HDL may be a physiologic regulator of stem cells and increasing HDL concentrations may be valuable strategy to promote ADSC transplantation.

High density lipoprotein cholesterol promotes the proliferation of bone-derived mesenchymal stem cells via binding scavenger receptor-B type I and activation of PI3K/Akt, MAPK/ERK1/2 pathways

High-density lipoprotein (HDL) possesses protective properties in cardiovascular diseases. However, the effect of HDL on the mesenchymal stem cells (MSCs), which could be mobilized to the damaged myocardial tissue, has not been well elucidated yet. In the current study, we investigated the effect of HDL on the proliferation of MSCs so as to reveal its molecular mechanisms. MSCs derived from rats were treated with HDL in different concentrations and for different periods. The proliferation of MSCs was measured with MTT and BrdU cell proliferation assay. The phosphorylation of Akt, ERK1/2 and the expression of p21 were evaluated by Western blotting. After the activity of respective pathways was down-regulated by the specific inhibitor and the gene of scavenger receptor-B type I (SR-BI) was knocked down by RNA interference, BrdU assay was performed to examine this effect of HDL on MSCs. We found that the proliferation of MSCs induced by HDL, in a time- and concentration-dependent manner, was the phosphorylation of Akt- and ERK1/2-dependent, which was significantly attenuated by the specific inhibitor to respective pathways. Moreover, MAPK/ERK1/2 pathway exerted a more dominating effect on this process. SR-BI contributed to HDL-induced proliferation of MSCs, which was effectively abolished by the silencing of SR-BI. The results suggested that HDL was capable of improving MSCs proliferation, in which MAPK/ERK1/2 and PI3K/Akt pathways involved and SR-BI played a critical role as well.

To Establish the Reference Intervals of Lipid Profile in Punjab

Overnight fasting samples of 1,031 apparently healthy people of Punjab visiting the hospital over a period of 3 years were tested for serum lipid profile. The mean ± SD of serum total cholesterol, triglycerides, high density lipoprotein cholesterol, low density lipoprotein cholesterol and very low density lipoprotein cholesterol in mg/dl were 182.2 ± 33.9, 122.4 ± 33.4, 44.1 ± 6.8, 113.9 ± 32.0, 24.6 ± 7.1 respectively. When these subjects were grouped according to age and sex, no appreciable difference was observed between most of the groups. Serum triglycerides were found to be low and HDL-C was high in females when compared with males of similar age and vice versa. With advancing age, total cholesterol and low density lipoprotein cholesterol levels were found to be higher in women. The present study suggests that the obtained lipid values should be taken into consideration during clinical evaluation.

Simultaneous transfer of cholesterol, triglycerides, and phospholipids to high-density lipoprotein in aging subjects with or without coronary artery disease

OBJECTIVE

To verify whether the capacity of high-density lipoprotein (HDL) to simultaneously receive nonesterified cholesterol, triglycerides, cholesteryl esters, and phospholipids changes with aging and the presence of coronary artery disease.

DESIGN

Cross-sectional study with biochemical analyses.

SUBJECTS

Eleven elderly patients with coronary artery disease (74 ± 5 years) were compared with the following groups of non-coronary artery disease subjects (referred to as "healthy"): 25 young (25 ± 5 years), 25 middle-aged (42 ± 6 years), and 25 elderly subjects (75 ± 8 years).

METHODS

Plasma samples were incubated with a nanoemulsion labeled with radioactive lipids; the transfer of the lipids from the nanoemulsion to the HDL was measured in chemically precipitated HDL. HDL size and paraoxonase-1 activity were also determined.

RESULTS

The transfer of cholesteryl esters and phospholipids to high-density lipoprotein was significantly greater (p<0.001) in healthy elderly subjects than in the middle-aged and younger subjects. Non-esterified cholesterol and triglyceride transfer was not different among these three groups. The HDL size was significantly greater (p<0.001) in healthy elderly subjects than in the middle-aged and younger subjects. The paraoxonase-1 activity was similar among the groups. Compared with healthy elderly subjects, coronary artery disease elderly subjects had significantly less (p<0.05) transfer of non-esterified cholesterol, triglycerides, and cholesteryl esters to the HDL and a significantly smaller (p<0.05) HDL size.

CONCLUSION

Because lipid transfer is enhanced in healthy elderly subjects but not in those with coronary artery disease, increasing lipid transfer to HDL may be a protective mechanism against the disease.

Reference intervals for serum total cholesterol, HDL-cholesterol, LDL-cholesterol, triglycerides, Lp (a), apolipoprotein A-I, A-II, B, C-II, C-III, and E in healthy South Indians from Andhra Pradesh

The incidence of cardiovascular and cerebrovascular disease is steadily increasing in South East Asian countries including Indian sub continent. Many lipids, apolipoproteins and Lp (a) except HDL-C and apo A-I, A-II are implicated as risk factors for coronary artery disease and cerebrovascular disease. There is great need to have national guidelines for each country like the ATP III guidelines recommended for U.S. population. For recommending appropriate medical decision limits, it is mandatory that each country establishes reference intervals pertaining to their population due to dietary, genetic and environmental diversity. In the present study, reference intervals for serum lipids, apolipoproteins and Lp (a) were established in a total of 1923 healthy Indian reference individuals comprising 1161 healthy men and 762 healthy women from Andhra Pradesh. For each analyte viz., serum total cholesterol, HDL-C, LDL-C, triglycerides, Lp (a), Apo A-I, Apo A-II, B, C-II, C-III and E, mean, two SD, median, confidence limits of mean, different percentile values are presented. The study also includes decade wise changes in each analyte and comparison of lipids, lipoproteins and Lp (a) among few populations covering U.S., India, Japan, Sweden, Finland and China. Reference Intervals for all lipid and lipoprotein parameters will immensely help in assessing associated risk for cardiovascular and cerebrovascular diseases in India. Additionally, the results will be beneficial in formulating our own guidelines pertaining to Indian population.

Achieving Vascular Risk Factor Targets: A Survey of a London General Practice

We assessed lipid goal achievement in patients at high risk for vascular events from a general practice (London, United Kingdom). Patients were identified as those with a prescription for hypolipidaemic medication, a significant (>20%) Framingham risk, and from the myocardial infarction register. Two hundred forty-five patients were currently taking a statin (average dose, 23.1 mg/day). Cholesterol, high-density lipoprotein—cholesterol, low-density lipoprotein—cholesterol, and triglycerides changed significantly following statin treatment. Of 285 patients who had taken statins at some time point, 11 (3.9%) were intolerant, 5 of which subsequently tolerated another statin. Approximately 10.1% of patients discontinued statin treatment for unclear reasons. Only 64 patients (29.1% of 220) reached the Joint British Societies' Guidelines on Prevention of Cardiovascular Disease target of a total cholesterol of <4.0 mmol/L; 50 patients (38.8% of 129) reached the low-density lipoprotein—cholesterol target of <2.0 mmol/L. This value of low-density lipoprotein—cholesterol is similar to that recommended by the American Heart Association/American College of Cardiology. With regard to the General Medical Services guidelines target for total cholesterol, 162 (73.6% of 220) patients reached ≤5.0 mmol/L. The group that best achieved target cholesterol (Joint British Societies' Guidelines and General Medical Services) were those with comorbidities. In conclusion, while reaching General Medical Services targets was satisfactory, the percentage of patients reaching Joint British Societies' Guidelines targets was not. This discrepancy may reflect the presence of multiple guidelines. The current stricter lipid targets are difficult to achieve; possible methods that may be used to improve lipids further could involve using combination therapy, statin dose titration, and better education.

1H NMR metabonomics approach to the disease continuum of diabetic complications and premature death

Subtle metabolic changes precede and accompany chronic vascular complications, which are the primary causes of premature death in diabetes. To obtain a multimetabolite characterization of these high-risk individuals, we measured proton nuclear magnetic resonance (1H NMR) data from the serum of 613 patients with type I diabetes and a diverse spread of complications. We developed a new metabonomics framework to visualize and interpret the data and to link the metabolic profiles to the underlying diagnostic and biochemical variables. Our results indicate complex interactions between diabetic kidney disease, insulin resistance and the metabolic syndrome. We illustrate how a single 1H NMR protocol is able to identify the polydiagnostic metabolite manifold of type I diabetes and how its alterations translate to clinical phenotypes, clustering of micro- and macrovascular complications, and mortality during several years of follow-up. This work demonstrates the diffuse nature of complex vascular diseases and the limitations of single diagnostic biomarkers. However, it also promises cost-effective solutions through high-throughput analytics and advanced computational methods, as applied here in a case that is representative of the real clinical situation.

HDLs activate ADAM17-dependent shedding

The tumor necrosis factor-alpha (TNF) converting enzyme (ADAM17) is a metalloprotease that cleaves several transmembrane proteins, including TNF and its receptors (TNFR1 and TNFR2). We recently showed that the shedding activity of ADAM17 is sequestered in lipid rafts and that cholesterol depletion increased the shedding of ADAM17 substrates. These data suggested that ADAM17 activity could be regulated by cholesterol movements in the cell membrane. We investigated if the membrane cholesterol efflux induced by high-density lipoproteins (HDLs) was able to modify the shedding of ADAM17 substrates. HDLs added to different cell types, increased the ectodomain shedding of TNFR2, TNFR1, and TNF, an effect reduced by inhibitors active on ADAM17. The HDLs-stimulated TNF release occurred also on cell-free isolated plasma membranes. Purified apoA1 increased the shedding of TNF in an ABCA1-dependent manner, suggesting a role for the cholesterol efflux in this phenomenon. HDLs reduced the cholesterol and proteins (including ADAM17) content of lipid rafts and triggered the ADAM17-dependent cleavage of TNF in the non-raft region of the membrane. In conclusion, these data demonstrate that HDLs alter the lipid raft structure, which in turn activates the ADAM17-dependent processing of transmembrane substrates.

HDL slowing down endothelial progenitor cells senescence: a novel anti-atherogenic property of HDL

Numerical and functional impairment of circulating endothelial progenitor cells (EPCs) is thought to contribute to endothelial dysfunction and the associated increase in cardiovascular risk. Increased EPCs number and activity are associated with the inhibition of EPCs senescence, which involved activation of telomerase. Telomerase activity can be regulated by phosphatidylinositol-3-kinase/Akt (PI3K/Akt) signaling pathway which also modulates the activity of endothelial nitric oxide synthase (eNOS). Increased oxidative stress induces telomerase inactivity whereas nitric oxide (NO) can reduce oxidative stress, thus activates telomerase. Plasma high-density lipoprotein (HDL) cholesterol levels have an inverse correlation with incidence of ischemic heart disease as well as other atherosclerosis-related ischemic conditions. However, the exact mechanism by which HDL prevents ischemic disease is not fully understood. HDL not only increases NO by activating eNOS through PI3K/Akt signaling pathway, but also directly stimulates EPCs differentiation via PI3K/Akt pathway. Moreover HDL can increase circulating EPCs number and enhances ischemia-induced angiogenesis. On the basis of recent findings, this manuscript proposed a new hypothesis that HDL could against atherosclerotic cardiovascular disease partially through slowing down EPCs senescence by increasing NO and promoting telomerase activity via PI3K/Akt signaling pathway.