Impact of Paraoxonase Polymorphism (Q192R) on Endothelial Function in Intact Coronary Circulation

Assessment of the role of paraoxonase gene polymorphism (Q192R) and paraoxonase activity in the susceptibility to atherosclerosis among lead-exposed workers

BACKGROUND AND OBJECTIVE

Lead exposure is a well known cause of cardiovascular damage, including atherosclerosis. Paraoxonase 1 (PON1), a high-density lipoprotein-associated antioxidant enzyme, is capable of hydrolyzing oxidized lipids and thus it protects against atherosclerosis. The mechanism by which heavy metals inhibit serum PON1 activity is still not clear. Our aim was to detect the association between lead exposure and serum PON1 activity and lipid profile and also to study the polymorphism of the PON1 gene.

DESIGN AND SETTING

A case-control, cross-sectional study conducted from June 2008 until May 2009.

SUBJECTS AND METHODS

Male workers (n=100) in a lead battery manufactory were recruited for this study. They were compared with 100 male age-matched workers not exposed to lead (control group). Serum lipid profile, paraoxonase activity and lead were measured in blood samples. The DNA was extracted for detecting the Q192R polymorphism of the PON1 gene by polymerase chain reaction followed by restriction fragment length polymorphism.

RESULTS

There was significant difference in triglycerides, total cholesterol and high-density lipoprotein cholesterol (HDL-C) (P=.01, .05 and .04, respectively) between cases and controls. Multiple linear regression analysis showed that blood lead levels were significantly associated with decreased serum paraoxonase activity (P=.03) in lead workers. The paraoxonase genotype QR was the most prevalent in 34/53 subjects (64%) among the lead-exposed groups, while the genotype QQ was more prevalent in the control group, in 15/25 subjects (60%), with a significant difference between the control and other groups (P<.05).

CONCLUSION

Lead exposure is associated with increased triglycerides, total cholesterol and low-density lipoprotein cholesterol and decreased HDL-C. Because of the protective role of PON1 in the development of atherosclerosis, a decrease in serum PON1 activity due to lead exposure may render individuals more susceptible to atherosclerosis.

The influence of PON1 192 polymorphism on endothelial function in diabetic subjects with or without hypertension

Hypertension and type 2 diabetes mellitus (T2DM) cause endothelial dysfunction probably through increased oxidant stress. Paraoxonase (PON1) is an high-density lipoprotein (HDL)-linked anti-oxidant enzyme whose capacity is influenced by a genetic polymorphism at codon 192. In the present study we have investigated the role of PON1 polymorphism on endothelial function in subjects with T2DM with or without hypertension. Three groups of male subjects were enrolled: 65 healthy control subjects without T2DM or hypertension (CON), 51 with only T2DM (DM), and 67 with both hypertension and T2DM (HYP+DM). The PON1 Gln192Arg polymorphism was determined by polymerase chain reaction (PCR) amplification and restriction analysis. Endothelial function was evaluated as flow-mediated vasodilatation (FMD) of the brachial artery after forearm ischemia. Data were analyzed according to the presence or absence of the Arg allele. Subjects with T2DM had markedly impaired FMD, compared with those of the CON group. In the CON and HYP+DM groups no difference was observed in FMD between subjects homozygous for the Gln allele and those carrying the Arg allele. In the DM group FMD was lower among those carrying the Arg allele compared with Gln/Gln homozygotes (2.1+/-2.4% vs. 6.2+/-5.2%, p=0.002). In conclusion, the present findings demonstrated that FMD was less impaired in normotensive diabetic subjects homozygous for the Gln allele, consistent with the notion that this isoform has a more effective antioxidant action that serves to protect circulating low-density lipoprotein (LDL). Hypertension seems to abolish the protective effect of the Gln isoform. These findings, however, warrant further investigation to clarify their clinical import.

Association between the paraoxonase-1 192Q>R allelic variant and coronary endothelial dysfunction in patients with early coronary artery disease

OBJECTIVE

To test the hypothesis that allelic variants of the paraoxonase-1 gene are associated with endothelial dysfunction, an early stage of atherosclerosis.

PATIENTS AND METHODS

We assessed 192Q>R and 55L>M allelic variants of the paraoxonase gene and coronary endothelial function in response to intracoronary acetylcholine in 99 patients (52 with homozygous QQ, 47 with homozygous RR or heterozygous QR). The study was conducted from September 1, 2002, through November 30, 2004.

RESULTS

Of 52 homozygous QQ patients, 39 (75%) had endothelial dysfunction vs 20 (43%) of the 47 RR/QR patients (P=.001), and this association remained significant after adjustment in a multivariable linear regression model (P=.005). In homozygous QQ vs RR/QR patients, epicardial arterial diameter decreased more (% change in diameter, -22%+/-21% vs -9%+/-16%, respectively, P=.002), coronary blood flow increased less (+37%+/-77% vs +75%+/-75%, P=.02) in response to acetylcholine, and oxidized LDL levels were higher. The 55L>M allelic variant was not significantly associated with endothelial dysfunction and had no effect on the association between endothelial dysfunction and the 192Q>R allelic variant.

CONCLUSION

The 192Q>R allelic variant of the paraoxonase-1 gene is associated with coronary endothelial dysfunction. The current study provides further information regarding the potential mechanisms by which this allelic variant contributes to early atherosclerosis in humans.

Reduced paraoxonase1 activity is a risk for atherosclerosis in patients with systemic lupus erythematosus

Excessive lipid peroxidation is a major factor of accelerated atherosclerosis, observed in patients with systemic lupus erythematosus (SLE). We aimed at the present study to determine the paraoxonasel (PON1) and arylesterase activities, and lipid-profile in 37 SLE patients and 30 age-/sex-matched controls. Association was analyzed between PON1 activity and SLEDAI, CRP, anti-oxLDL, and antiphospholipid antibody (aPL) levels, steroid dose, and atherothrombotic events. The age of patients was 40.8 +/- 13.9 year, follow-up time 6.7 +/- 6.2 year, SLEDAI 2 (0-15). PON1 and arylesterase activities were measured spectrophotometrically using paraoxon and phenyl acetate as substrates, respectively. Phenotypic distribution of PON1 was determined by dual substrate method. We measured antioxLDL and aPL levels by ELISA, the CRP by automated immunoassay. PON1 activity (121.9 +/- 65.9 U/mL) was reduced significantly (P < 0.001) in SLE as compared to control (188.1 +/- 78.9 U/mL), but arylesterase activity was not different. A negative correlation was found between PON1 activity and age. PON1 activity did not correlate with other measured parameters. Reduced PON1 activity associated with clinical atherothrombotic complications (P < 0.01). High activity BB phenotype was not present in SLE. Lipid parameters (TC, LDL-C, HDL-C, ApoAI, and ApoB) were within normal range in both groups. Results indicated reduced PON1 activity in lupus patients despite long disease duration and low inflammatory activity, and it was evidenced as a risk for atherosclerotic complications. As the arylesterase activity was normal, further examinations are required to find other mechanisms, such as anti-PON1 antibodies, genetic polymorphisms, and difference in distribution of HDL-subfractions or enzyme abnormalities in HDL remodeling.