Effects of paraoxonase activity and gene polymorphism on coronary vasomotion

Investigating the genetic characteristics of CAD: Is there a role for myocardial perfusion imaging techniques?

Several environmental and genetic factors have been found to influence the development and progression of coronary artery disease (CAD). Although the effects of the environmental hazards on CAD pathophysiology are well documented, the genetic architecture of the disease remains quite unclear. A number of single-nucleotide polymorphisms have been identified based on the results of the genome-wide association studies. However, there is a lack of strong evidence regarding molecular causality. The minority of the reported predisposing variants can be related to the conventional risk factors of CAD, while most of the polymorphisms occur in non-protein-coding regions of the DNA. However, independently of the specific underlying mechanisms, genetic information could lead to the identification of a population at higher genetic risk for the long-term development of CAD. Myocardial single-photon emission computed tomography (SPECT) and positron emission tomography (PET) are functional imaging techniques that can evaluate directly myocardial perfusion, and detect vascular and/or endothelial dysfunction. Therefore, these techniques could have a role in the investigation of the underlying mechanisms associated with the identified predisposing variants, advancing our understanding regarding molecular causality. In the population at higher genetic risk, myocardial SPECT or PET could provide important evidence through the early depiction of sub-clinical dysfunctions, well before any atherosclerosis marker could be identified. Notably, SPECT and PET techniques have been already used for the investigation of the functional consequences of several CAD-related polymorphisms, as well as the response to certain treatments (statins). Furthermore, therefore, in the clinical setting, the combination of genetic evidence with the findings of myocardial SPECT, or PET, functional imaging techniques could lead to more efficient screening methods and may improve decision making with regard to the diagnostic investigation and patients' management.

Association of PON1 genotype and haplotype with susceptibility to coronary artery disease and clinical outcomes in dual antiplatelet-treated Han Chinese patients

PURPOSE

The aim of this study was to evaluate the association of PON1 genetic variants with the susceptibility to coronary artery disease (CAD) and with the clinical endpoints in aspirin and clopidogrel (dual antiplatelet therapy)-treated Han Chinese patients with CAD after percutaneous coronary intervention (PCI).

METHODS

A total of 538 Han Chinese patients undergoing PCI and receiving dual-antiplatelet therapy were sequentially recruited to the study and followed for up to 1 year. Healthy controls (n = 539) were enrolled during the same period. All study participants were genotyped for five genetic variants in PON1 and the cytochrome P450 2C19*2 mutation (CYP2C19*2). The effect of genetic variants on disease risk and clinical outcome of major adverse cardiac events (MACE) within 1 year or bleeding within 6 months was assessed.

RESULTS

CYP2C19*2 was associated with a higher risk of MACE (adjusted P = 0.0098), but a lower risk of bleeding events (adjusted P = 0.0016). The PON1 Q192R polymorphism was significantly associated with a lower risk of bleeding events [odds ratio (OR) 0.61, 95% confidence interval (CI) 0.43-0.87, adjusted P = 0.0066). The haplotype bearing the PON1 -126C allele was associated with a higher risk to CAD (OR 1.48, 95% CI 1.04-2.09, P = 0.029) and a higher risk of bleeding events (OR 1.68, 95% CI 1.10-2.56, P = 0.017) compared to the most frequent haplotype. The transcription activity of haplotype p-162A-126C-108C in the PON1 promoter was 2.6-fold higher than that of the most frequent haplotype (p-162G-126G-108T).

CONCLUSIONS

Based on these results, we suggest that the haplotype-bearing PON1 -126C allele contributes to the disease risk and the risk of bleeding events in dual antiplatelet-treated CAD patients after PCI.

Paraoxonase 1 and homocysteine metabolism

Paraoxonase 1 (PON1), a component of high-density lipoprotein (HDL), is a calcium-dependent multifunctional enzyme that connects metabolisms of lipoproteins and homocysteine (Hcy). Both PON1 and Hcy have been implicated in human diseases, including atherosclerosis and neurodegeneration. The involvement of Hcy in disease could be mediated through its interactions with PON1. Due to its ability to reduce oxidative stress, PON1 contributes to atheroprotective functions of HDL in mice and humans. Although PON1 has the ability to hydrolyze a variety of substrates, only one of them-Hcy-thiolactone-is known to occur naturally. In humans and mice, Hcy-thiolactonase activity of PON1 protects against N-homocysteinylation, which is detrimental to protein structure and function. PON1 also protects against neurotoxicity associated with hyperhomocysteinemia in mouse models. The links between PON1 and Hcy in relation to pathological states such as coronary artery disease, stroke, diabetic mellitus, kidney failure and Alzheimer's disease that emerge from recent studies are the topics of this review.