Molecular Structure of Paraoxonase-1 and Its Modifications in Relation to Enzyme Activity and Biological Functions-A Comprehensive Review

PON1 is a Ca2+-dependent enzyme that indicates a hydrolytic activity towards a broad spectrum of substrates. The mechanism of hydrolysis catalyzed by this enzyme is poorly understood. It was shown that the active site of PON1 is highly dynamic. The catalytic center of this enzyme consists of side chains of amino acids binding two calcium ions, from which the first one performs a structural function and the other one is responsible for the catalytic properties of PON1. This review summarizes available information on the structure of PONs, the role of amino acids located in the active site in specificity, and multiple substrate affinity of enzymes for understanding and explaining the basis of the physiological function of PONs. Moreover, in this paper, we described the changes in the structure of PONs induced by environmental and genetic factors and their association with diseases. The detoxification efficiency depends on the polymorphism of the PON1 gene, especially Q192R. However, data on the association between single-nucleotide polymorphisms (SNPs) in the PON1 gene and cardiovascular or neurodegenerative diseases are insufficient. The reviewed papers may confirm that PON1 is a very promising tool for diagnostics, but further studies are required.

Association of Paraoxonase-2 (C1053G) Gene Polymorphism with the Expression of Paraoxonase-2 Gene in Patients of Ischemic Stroke - A Pilot Study in Indian Population

Background and Objective

Oxidative stress plays an important role in atherosclerosis and ischemic stroke. Due to antioxidant properties of Paraoxonase-2, we studied the implication of Paraoxonase-2 gene polymorphism (C1053G) on expression of Paraoxonase-2 gene at mRNA level in ischemic stroke patients.

Material and Methods

40 patients of ischemic stroke and 40 age and sex-matched controls were included. Paraoxonase-2 genotypes were evaluated by Polymerase Chain Reaction and Restriction Fragment Length Polymorphism and expression of Paraoxonase-2 gene at mRNA level was determined by quantitative real time Polymerase Chain Reaction analysed as delta-CT (△CT).

Result and Discussion

The observed allele frequencies in patients for C and G allele were 0.61 and 0.39 respectively, and were 0.72 and 0.28 in control group. No significant association was found in C allele of C1053G polymorphism and ischemic stroke. The average △ CT value is significantly (p = 0.0001) higher in patients group (7.68 ± 2.0) as compared to controls (5.70 ± 1.8). We found a significant difference in the average delta-CT value (p = 0.0001), wherein down-regulated paraoxonase-2 gene expression (approximately 0.25 fold) was observed in case of patients as compared to controls. Down-regulated expression of paraoxonase-2 gene was observed in patients with GG genotype as compared to CG and CC genotypes in patients with ischemic stroke (p = 0.0001).

Conclusion

Down-regulated Paraoxonase-2 gene expression, as evidenced by low mRNA levels in GG genotype may be one of the contributory factors in the progression of ischemic stroke.

PON1 (Paraoxonase 1) Q192R gene polymorphism in ischemic stroke among North Indian population

Background:

PON1 is an High Density Lipoprotein (HDL)-associated esterase. Two common polymorphisms in the PON1 gene, Q192R and L55M substitutions, determine the inter-individual variation in PON1 activity. The association of these polymorphisms with the risk of ischemic stroke remains controversial. In the present study, the role of PON1 Q192R gene polymorphism in ischemic stroke was studied in the Indian population.

Design and Methods:

In the present case-control study, the PON1 Q192R gene polymorphism was screened in ischemic stroke patients (n: 63) and age, sex-matched controls (n: 63) using thePolymerase Chain Reaction-Restriction Segment Length Polymorphism (PCR-RFLP) method.

Results:

The mean age of stroke presentation was 58.11 ± 15.4 years. A total of 17.4% cases presented with young stroke (<45 years age) and 9.52% cases were seen to have a recurrent stroke. The distribution of -192Q/R PON1 gene polymorphism was not seen to differ between cases and controls. The traditional stroke risk factors did not have any effect on the PON1 genotype expression. A multivariate logistic regression analysis was done in order to assess an independent association of age, gender, traditional stroke risk factors, and PON1 polymorphism with acute ischemic stroke. However, neither the RR genotype nor the presence of the R allele was associated with an increase in the risk of acute ischemic stroke (OR [RR genotype]-4.76, P value: 0.24, 95% CI: 0.3497–64.8531; OR [R allele]-0.94, P value: 0.90, 95% CI: 0.3516–2.4989).

Conclusion:

PON1 Q192R gene polymorphism is not associated with an increased risk of acute ischemic stroke in the North Indian population. Further studies with a larger sample size are needed before PON1 Q192R gene polymorphism can be considered as a genetic risk factor for ischemic stroke.

Association of PON1 and PON2 polymorphisms with PON1 activity and significant coronary stenosis in a Tunisian population

PON1 and PON2 have attracted considerable attention as candidate genes for coronary heart disease because their enzymes function as key factors in lipoprotein catabolism pathways. We studied the distribution of PON1 and PON2 polymorphisms, including genotyping, lipid profile, and PON1 activity, and their association with PON1 activity and significant coronary stenosis (SCS) in a Tunisian population. PON1 activity was lower in patients with SCS than in controls. It increased with the R allele (QQ < QR < RR) in PON1-192 genotypes and with the L allele (MM < ML < LL) in PON1-55 genotypes. In the presence of metabolic syndrome and diabetes, PON1-192RR and PON2-311CC were associated with an increased risk of SCS and PON1-55MM seems to have lower risk. This association was evident among nonsmokers for PON1-55MM and among smokers for PON1-192RR and PON2-311CC. The GTGC haplotype seemed to increase the risk of SCS compared with the wild haplotype in a Tunisian population.

Four genetic polymorphisms of paraoxonase gene and risk of coronary heart disease: a meta-analysis based on 88 case-control studies

OBJECTIVE

The human paraoxonase (PON) is calcium dependent HDL associated ester hydrolase which has attracted considerable attention as a candidate gene for coronary heart disease based on its enzyme function as a key factor in lipoprotein catabolism pathways. Many studies have examined the association between polymorphisms in the PON gene and risk of coronary heart disease (CHD), but the results have been inconsistent.

METHODS

We conducted a meta-analysis of 88 studies on 4 PON polymorphisms [Q192R, L55M, and T(-107)C in the PON1 and the S311C in the PON2] published before August 2010, including a total of 24,702 CHD cases and 38,232 controls. We also systematically explored potential sources of heterogeneity.

RESULT

In a combined analysis, the summary per-allele odds ratio for CHD of the 192R was 1.11 (95% CI: 1.05-1.17). However, when the analyses were restricted to 10 larger studies (n>500 cases), the summary per-allele odds ratio was 0.96 (95% CI: 0.90-1.02). Our analyses detected a possibility of publication bias with an overestimate of the true association by smaller studies. A meta-analysis of studies on the 55M, (-107)T, and 311C variant showed no significant overall association with CHD, yielding a per-allele odds ratio of 0.94 (95% CI: 0.88-1.00), 1.02 (95% CI: 0.91-1.15) and 1.02 (95% CI: 0.90-1.16) respectively.

CONCLUSIONS

This meta-analysis suggested an overall weak association between the R192 polymorphism and CHD risk.

The Role of Polymorphisms Within Paraoxonases (192 Gln/Arg in PON1 and 311Ser/Cys in PON2) in the Modulation of Cardiovascular Risk: A Pilot Study

Paraoxonases (PONs) may exert anti-atherogenic action by reducing lipid peroxidation. We evaluated the influence of 2 polymorphisms within PON1 (192 Gln/ Arg) and PON2 (311 Ser/Cys) genes in 407 young Poles: 273 patients who experienced a first myocardial infarction (MI) under the age of 45 (study group) and 134 healthy volunteers (control group) with a HEART Score ≤2 (low risk). Paraoxonase 1 polymorphism 192Gln/Arg influenced the risk of premature MI (P = .0054). A positive family history of coronary artery disease (CAD) was associated with the 192Arg allele (P = .0107). The association between PON1 genotype (192 Gln/Arg) and low-density lipoprotein cholesterol (LDL-C) (P = .036) levels was also observed. However, we did not find any relationship between polymorphism 311Ser/Cys and CAD risk (P = .418). PON1 polymorphism 192Gln/Arg influenced the risk of premature MI. The association between PON1 genotype (192 Gln/Arg) and serum LDL-C levels may be explained by PON participation in reverse cholesterol transport.