Hyperlipidaemia and cardiovascular disease: HDL, inflammation and surprising results of AIM-HIGH study

Understanding high-density lipoprotein function in disease: recent advances in proteomics unravel the complexity of its composition and biology

Although the epidemiology of high-density lipoprotein (HDL) cholesterol and cardiovascular risk has been consistent, pharmacologic interventions to increase HDL-cholesterol by delaying HDL catabolism did not translate into reduction in cardiovascular risk. HDL particles are small, protein-rich when compared to other plasma lipoprotein classes. Latest progresses in proteomics technology have dramatically increased our understanding of proteins carried by HDL. In addition to proteins with well-established functions in lipid transport, iron transport proteins, members of the complement pathway, and proteins involved in immune function and acute phase response were repeatedly identified on HDL particles. With the unraveling of the complexity of the HDL proteome, different laboratories have started to monitor its changes in various disease states. In addition, dynamic aspects of HDL subgroups are being discovered. These recent studies clearly illustrate the promise of HDL proteomics for deriving new biomarkers for disease diagnosis and to measure the effectiveness of current and future treatment regimens. This review summarizes recent advances in proteomics and lipidomics helping to understand HDL function in health and disease.

Cardiovascular protection by ApoE and ApoE-HDL linked to suppression of ECM gene expression and arterial stiffening

Arterial stiffening is a risk factor for cardiovascular disease, but how arteries stay supple is unknown. Here, we show that apolipoprotein E (apoE) and apoE-containing high-density lipoprotein (apoE-HDL) maintain arterial elasticity by suppressing the expression of extracellular matrix genes. ApoE interrupts a mechanically driven feed-forward loop that increases the expression of collagen-I, fibronectin, and lysyl oxidase in response to substratum stiffening. These effects are independent of the apoE lipid-binding domain and transduced by Cox2 and miR-145. Arterial stiffness is increased in apoE null mice. This stiffening can be reduced by administration of the lysyl oxidase inhibitor BAPN, and BAPN treatment attenuates atherosclerosis despite highly elevated cholesterol. Macrophage abundance in lesions is reduced by BAPN in vivo, and monocyte/macrophage adhesion is reduced by substratum softening in vitro. We conclude that apoE and apoE-containing HDL promote healthy arterial biomechanics and that this confers protection from cardiovascular disease independent of the established apoE-HDL effect on cholesterol.

Novel common and rare genetic determinants of paraoxonase activity: FTO, SERPINA12, and ITGAL

HDL-associated paraoxonase 1 (PON1) activity is associated with cardiovascular and other human diseases. As the role of genetic variants outside of the PON gene cluster on PON1 activity is unknown, we sought to identify common and rare variants in such loci. We typed 33,057 variants on the CVD chip in 1,362 subjects to test for their effects on adjusted-PON1 activity. Three novel genes (FTO, ITGAL, and SERPINA12) and the PON gene cluster had SNPs associated with PON1 arylesterase (AREase) activity. These loci were carried forward for rare-variant analysis using Exome chip genotypes in an overlapping subset of 1,051 subjects using sequence kernel association testing. PON1 (P = 2.24 × 10(-4)), PON3 (P = 0.022), FTO (P = 0.019), and SERPINA12 (P = 0.039) had both common and rare variants associated with PON1 AREase. ITGAL variants were associated with PON1 activity when using weighted sequence kernel association testing (SKAT) analysis (P = 2.63 × 10(-3)). When adjusting for the initial common variants, SERPINA12 became marginally significant (P = 0.09), whereas all other findings remained significant (P < 0.05), suggesting independent rare-variant effects. We present novel findings that common and rare variants in FTO, SERPINA12, and ITGAL predict PON1 activity. These results further link PON1 to diabetes and inflammation and may inform the role of HDL in human disease.

Diabetes induces gender gap on LCAT levels and activity

AIM

High density lipoprotein (HDL) decreases in diabetic women more rapidly than what is observed in diabetic men. Here we aimed to study serum LCAT levels and LCAT activity in men and women with type 2 diabetes (T2DM) as well as healthy controls.

MAIN METHODS

We measured serum LCAT activity and levels in 40 patients with T2DM plus 40 age-sex and body mass index (BMI)-matched controls. The correlation between LCAT levels and activity was measured in the studied groups, stratified according to gender.

KEY FINDINGS

Patients had a lower LCAT activity, diastolic blood pressure, fasting blood sugar, triglyceride, low density lipoprotein cholesterol and a higher LCAT levels than controls. The lower LCAT activity in patients with T2DM was significant after multiple adjustments for age, LCAT levels and BMI, using general linear model (67.9 ± 1.8 vs. 86.5 ± 1.8; P<0.001). Women with T2DM had a lower LCAT activity and a higher LCAT and HDL levels compared to men. The lower LCAT activity in women remained significant after multiple adjustments for age, BMI and LCAT levels; (61.9 ± 3.1 vs. 74.17 ± 3.61; P<0.05). Statin treatment did not have any significant value on the results. HDL was not correlated with LCAT levels or activity in any of the studied populations.

SIGNIFICANCE

We showed that while LCAT activity is decreased in patients with T2DM, LCAT levels is increased. Patients with T2DM exhibit opposing effects on LCAT activity and LCAT production which is more severe in women. Future prospective studies may elucidate the underlying pathways for these observations.