Paraoxonase Genotype, LDL-oxidation and Carotid Atherosclerosis in Male Life-long Smokers

Modulation of the antioxidant enzyme paraoxonase-1 for protection against cardiovascular diseases

AIM

The enzyme paraoxonase 1 (PON1) bound to high-density lipoprotein has received special attention for its protective role against stress-mediated damage and use as a potential regulatory target in atherosclerosis and related vascular diseases.

DATA SYNTHESIS

We present an overview of the literature on PON1 activity and mRNA levels by investigating its modulation for clinical translations. Specifically, the expression of PON1 and its regulated activity can be modified in different ways with natural substances, drugs, and lifestyle factors thar affect the development of atherosclerosis.

CONCLUSIONS

The endothelial contribution of PON1 to overcome differences considering an individual's disease development risk is supported by polymorphism interaction data and the susceptibility to modify PON1 responses in chronic events composed by biological and environmental factors.

Role of Paraoxonase1 in the Regulation of High-Density Lipoprotein Functionality and in Cardiovascular Protection

Significance: Human paraoxonase (PON) is a member of the gene family that includes paraoxonase 1 (PON1), PON2, and PON3. PON is known for its capacity to hydrolyze a wide range of substrates, including organophosphorus compounds, nerve gases, and aromatic carboxylic acid esters. Recent Advances: Several studies have highlighted the involvement of PON, particularly PON1, in the modulation of the capacity of high-density lipoprotein (HDL) to protect against the atherosclerosis process and its clinical manifestations. PON1 exhibits antioxidant and anti-inflammatory activities and may be involved in the regulation of the principal antiatherogenic activity of HDL, that is, the regulation of the reverse cholesterol transport process. Critical Issues: Although epidemiological studies have shown that there is an inverse relationship between HDL levels and cardiovascular risk, several studies have emphasized the importance of HDL functionality in protecting against cardiovascular diseases (CVD). Given that PON1 is involved in several atheroprotective functions of HDL, the aim of this article is to review the existing literature on PON1 and to discuss the principal mechanisms by which PON1 may exert its different activities. Future Directions: The elucidation of the mechanisms by which PON1 modulates the functionality of HDL as well as the identification of the interventions that stimulate PON1 activity and/or increase its plasma concentration would make it possible to propose new strategies to prevent CVD. Antioxid. Redox Signal. 34, 191-200.

Extra-medial thickness of carotid artery in patients with Behçet's disease: evaluation of atherosclerotic vessel wall changes with a novel carotid artery ultrasound index

OBJECTIVES

Chronic inflammation and endothelial dysfunction are the characteristic features of Behçet's disease (BD). We researched carotid extra-medial thickness (cEMT), a novel ultrasound parameter for atherosclerotic vessel wall changes, and carotid intima media thickness (cIMT), a widely accepted marker of subclinical atherosclerosis, in patients with BD, and we evaluated the relationship between these two parameters.

MATERIALS AND METHODS

In total, 31 patients with BD were matched to 26 control subjects based on age, gender, and major cardiovascular risk factors. Laboratory parameters, including lipid profile, were measured for both patients and controls. B-mode ultrasonography was used to assess the cEMT and cIMT.

RESULTS

There was no significant difference in the cEMT values between the patients with BD and the control group (P = 0.90). cIMT in the BD group was significantly higher compared with the control group (P = 0.021). There was a significant positive correlation between cIMT and cEMT (r = 0.585, P = 0.001). Both cEMT and cIMT were positively correlated with age and the presence of arthritis. There was linear correlation with sedimentation, C-reactive protein, and cEMT.

CONCLUSIONS

To the best of our knowledge, this is the first study to evaluate both cEMT and cIMT in BD. This study presents morphological evidence of subclinical atherosclerosis in terms of cIMT. Although there was no significant increment in cEMT, it has the potential to assess endothelial dysfunction in BD. Further studies are required to confirm this finding.

Mass Spectrometry-Based Proteomic Study Makes High-Density Lipoprotein a Biomarker for Atherosclerotic Vascular Disease

High-density lipoprotein (HDL) is a lipid and protein complex that consists of apolipoproteins and lower level HDL-associated enzymes. HDL dysfunction is a factor in atherosclerosis and decreases patient survival. Mass spectrometry- (MS-) based proteomics provides a high throughput approach for analyzing the composition and modifications of complex HDL proteins in diseases. HDL can be separated according to size, surface charge, electronegativity, or apoprotein composition. MS-based proteomics on subfractionated HDL then allows investigation of lipoprotein roles in diseases. Herein, we review recent developments in MS-based quantitative proteomic techniques, HDL proteomics and lipoprotein modifications in diseases, and HDL subfractionation studies. We also discuss future directions and perspectives in MS-based proteomics on HDL.

Paraoxonase-1 gene Q192R polymorphism and reactive oxygen metabolites

OBJECTIVE

Paraoxonase-1 (PON1) is a high-density lipoprotein-associated antioxidant enzyme. The Q192R polymorphism of the PON1 gene can protect against oxidative conditions, but the relationship between Q192R polymorphism and oxidative stress-related markers remains controversial. In this study, the diacron reactive oxygen metabolites (d-ROMs) test was used to investigate the relationship between Q192R polymorphism and oxidative stress-related markers in Japanese subjects.

METHODS

Patients without a history of overt cardiovascular disease who were not receiving antioxidant medication were enrolled in a cross-sectional clinic-based study. An allele-specific polymerase chain reaction method was used to assess the PON1 Q192R polymorphism and compare the level of d-ROMs between genotypes.

RESULTS

A total of 103 subjects were analysed. The RR genotype was associated with a significantly lower level of d-ROMs than the RQ and QQ genotypes. After multivariate analysis the relationship between the genotypes and level of d-ROMs remained independently significant.

CONCLUSIONS

The RR genotype may be protective against oxidative stress in cardiovascular diseasefree Japanese subjects. In addition, the d-ROMs test can be useful for examining the role of the PON1 Q192R polymorphism under oxidative conditions.

Impact of low-and high-density lipoprotein cholesterol levels on carotid intima-media thickness differs by smoking status in middle-aged men

AIM

Cigarette smoking is a strong risk factor for atherosclerotic disease; however, it remains unclear whether the impact of other risk factors differs by smoking status. The aim of this study was to investigate this issue, especially with regard to low-density and high-density lipoprotein (LDL/HDL) levels.

METHODS

In total, 448 healthy, middle-aged men (aged 37 to 61) participated in this study. Smoking habits were recorded, carotid intima-media thickness (IMT) was measured by B-mode ultrasound, and serum lipids and other biochemical parameters were determined from fasted blood samples.

RESULTS

Among the overall subjects, multivariate regression analyses showed that IMT was significantly associated with age (p < 0.0001 for mean IMT, p= 0.002 for max IMT), body mass index (BMI, mean IMT, p= 0.028), LDL-C levels (mean/max IMT, p= 0.001), HDL-C levels (max IMT, p= 0.022) and current smoking habit (mean IMT, p=0.012). Subgroup analyses according to smoking status revealed that LDL-C levels were significantly associated with mean/max IMT in current smokers (p=0.001) but not in ex- or nonsmokers (never smoked subjects). After adjusting for age, BMI, systolic blood pressure, hemoglobin A1c and serum lipids, mean IMT respectively increased and decreased progressively across LDL-C and HDL-C quartiles (p= 0.004 and 0.045) in the overall subjects. These associations were observed in current smokers (p= 0.01) but not in ex- or nonsmokers for LDL-C, and were observed in ex- and nonsmokers (p= 0.025, 0.017, respectively) but not in current smokers for HDL-C.

CONCLUSION

The impact of LDL-C/HDL-C levels on carotid IMT differs by smoking status. These observations imply that distinct mechanisms are involved in the (anti) atherogenesis of LDL/HDL according to smoking status.

Genetic and environmental determinants of the PON-1 phenotype

BACKGROUND

Paraoxonase (PON-1) is a high-density lipoprotein (HDL)-associated enzyme that may protect against cardiovascular disease (CVD), because it hydrolyses oxidized phospholipids of low-density lipoprotein (LDL) and therefore prevents the detrimental effects on the arterial wall. The current report describes the determinants of PON-1 bioavailability and activity.

MATERIALS AND METHODS

This is the largest (n = 1527) cross-sectional evaluation performed on PON-1 genotypes (Q192R, T-107C and L55M) and environmental determinants to PON-1 catalytic activity and bioavailability in serum of postmenopausal women. PON-1 catalytic activity and PON-1 bioavailability were measured, in vitro, with a paraoxon hydrolysis assay and a phenylacetate hydrolysis assay, respectively.

RESULTS

The major determinant of paraoxon hydrolytic activity is the Q192R genotype, but there was also a relation with the C-107T and L55M genotype, HDL levels and alcohol consumption. Phenylacetate hydrolytic activity was most strongly affected by the C-107T genotype followed by the L55M genotype, HDL levels, alcohol consumption and smoking.

CONCLUSIONS

PON-1 Q192R, C-107T and L55M genotype, alcohol consumption, smoking and HDL levels are determinants of serum PON-1 phenotype. The contributions of the genetic markers to the PON-1 phenotype are stronger than the contributions of the lifestyle determinants.

Genetic determinants of carotid ultrasound traits

Atherosclerosis is a complex disease with various intermediate phenotypes that are themselves complex and influenced by many factors. Through the use of carotid ultrasound techniques, the intermediate stages of vascular disease can be imaged and studied for association with potential genetic determinants. In this article we review the most recent available data (reports published since 2004) on the genetic determinants of atherosclerosis, as measured by one-, two-, and three-dimensional ultrasonography of the carotid arteries. In general, associations are disparate and modest. For intima-media thickness, promising associations have been found for both TNFRSF1A R92Q and PPARG P12A, but associations also differed in the same individuals depending on the specific ultrasound trait studied (eg, linear intima-media thickness versus total plaque volume in carotid arteries). Some of the challenging issues for future studies include accounting for gene-environment interactions, sex-specific associations, and the distinctiveness of different carotid ultrasound measures.

Paraoxonase-1 and linoleic acid oxidation in familial hypercholesterolemia

Serum paraoxonase-1 (PON1) is a high-density lipoprotein-associated enzyme that can inhibit low-density lipoprotein (LDL) oxidation in vitro. The role of PON1 in vivo still remains to be clarified. We investigated the effect of PON1 genotype (-107C > T and 192Q > R), concentration, paraoxonase activity, and arylesterase activity on the early phase of lipid peroxidation in plasma samples of 110 patients with heterozygous familial hypercholesterolemia. The degree of lipid oxidation was assessed by quantitation of oxidized-linoleic acid (the most abundant fatty acid present in LDL) using high performance liquid chromatography. We found a significant inverse correlation between paraoxonase activity and the oxidized-linoleic acid concentration (r = -0.22, P = 0.03), independent of baseline linoleic acid levels. These findings support an anti-oxidative role for PON1 in patients with FH, and thus may give insight into the functioning of PON1 in vivo.

Paraoxonases and cardiovascular diseases: pharmacological and nutritional influences

PURPOSE OF REVIEW

To summarize the new articles published in the last year on paraoxonases, including their expression in cardiovascular diseases, and regulation by pharmacological and nutritional means.

RECENT FINDINGS

The elucidation of the crystal structure of the paraoxonase 1 (PON1) gene, obtained by directed evolution, shows that it consists of a six-bladed beta-propeller with a unique active site. PON1 is present in HDL but also in lipoprotein-deficient serum, in VLDL and in chylomicrons. PON1 protects lipids in lipoproteins, in macrophages and in erythrocytes from oxidation. Cellular PON2 and PON3 were also shown to reduce oxidative stress. Beyond its antioxidative properties, PON1 possesses additional antiatherogenic properties against macrophage foam cell formation: attenuation of cholesterol and oxidized lipids influx, inhibition of macrophage cholesterol biosynthesis and stimulation of macrophage cholesterol efflux. The PON1 gene is regulated by Sp1 and protein kinase C, whereas the PON2 gene in macrophages is regulated by nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. PON1 activity and mass are both reduced in cardiovascular diseases and the hypocholesterolemic drugs, statins, increase serum PON1 activity (by reducing oxidative stress, or by upregulating hepatic PON1 expression). Expression of cellular PON2, like PON1, was upregulated by statins. Nutritional antioxidants, such as polyphenols, increase PON1 mRNA expression and activity, by an aryl hydrocarbon receptor-dependent mechanism.

SUMMARY

The elucidation of PON1 structure and its active center has enabled a better understanding of its mechanism of action, including its physio-pathological substrate(s). Some drugs and nutrients including dietary antioxidants and polyphenols considerably increase the activities of paraoxonases which, in turn, can reduce oxidative stress and atherosclerosis development.