Distribution profile of paraoxonase phenotypes among the Gujaratis

Genetic variation at Q192R and L55M polymorphisms in PON1

Earlier we have reported Q192R allele frequencies among four Indian populations as a part of an investigation of the distribution of Paraoxonase 1 polymorphisms. Here we present the results obtained after screening eleven populations representing different regions of India for Q192R and L55M. Population genetic analysis examining the effect of micro-evolutionary forces at these loci confirmed genetic differentiation at Q192R earlier suggested. The study groups showed high frequencies of L55 and differential distribution of Q192 and R192. Tests for deviation from neutrality indicated heterozygote excess at rs662 which has Q192R polymorphism. Higher levels of heterozygosity at Q192R than L55M might be because of its role in wide substrate specificity of the enzyme. A small but highly significant correlation between genetic and geographic distances was observed in a spatial autocorrelation analysis indicating non-random distribution of Q192 allele. Our findings are pertinent to toxicogenetic studies evaluating risk assessment towards organophosphate compounds among different continental groups.

The role of PON1 and CYP2D6 genes in susceptibility to organophosphorus chronic intoxication in Egyptian patients

BACKGROUND

Paraoxonase-1 (PON1) activity toward organophosphorus(OP) compounds shows inter-individual variations, rendering the identification of individuals' PON1 allozymes valuable in treating patients suffering from organophosphorus intoxication. One of the most important cytochrome P450 monooxygenases (CYPs) is CYP2D6. The CYP2D6 G1934A polymorphism leads to good, poor or no enzyme activity. Genetic testing helps identification of high risk individuals as well as management of chronic intoxicated patients.

OBJECTIVE

to investigate a possible association between genetic polymorphisms of PON1 Q192R, and CYP2D6 G1934A as well as PON1 and pseudo-cholinesterase (PChE) enzyme activity levels and chronic organophosphate exposed patients, and hence, susceptibility for organophosphorus chronic poisoning.

DESIGN AND METHODS

Thirty chronic organophosphate exposed farm workers were compared to 29 healthy controls as regards PON1 Q192R and CYP2D6 G1934A polymorphisms using PCR-RFLP technique. Also serum PON1 and PChE activities were determined spectrophotometrically.

RESULTS

Serum PChE was significantly reduced in chronic intoxicated patients compared to the control group (p=0.02), while PON1 activity was increased, but just failed to reach significance (p=0.06). PON1 192 RR genotype and R allele were significantly increased in chronic OP intoxicated patients (p=0.005 &p=0.002 respectively). CYP2D6 1934A allele was significantly increased in chronic OP patients (p=0.045). combining the two SNPs showed a significant statistical difference between the two groups with PON1QQ and CYP2D6 GG genotypes being more represented in the healthy controls (p=0.001). Fatigue and motor weakness were the most prevalent neurological symptoms seen in chronic cases (56.7%), followed by headache and lacrimation (30% each), depression (23%), tingling and sensory symptoms (20%), sleep disorders and limb pain (13%). The mean duration of environmental exposure to organophosphates was 7.7±5.2years and no association was found between chronic symptoms of intoxication and duration of exposure, provided that all workers were exposed for at least 3 years.

CONCLUSION

PON1 192RR genotype and CYP2D6 1934A allele were found to be related to the susceptibility to organophosphate chronic toxicity in Egyptians. Larger scale gene-environmental interaction studies are recommended to confirm results and Genotyping is recommended during selection of agricultural pesticide workers to exclude high risk group.

Allele frequencies of PON1 Q192R polymorphism in four populations of India

The allelic distribution at Paraoxonase 1 (PON1) Q192R polymorphism determines differential sensitivity towards certain organophosphate pesticides. The alleles Q (Glutamine) and R (Arginine) at amino acid position 192 are responsible for the lower and higher activity of the enzyme towards paraoxon respectively, making knowledge of this distribution in different populations vital. This study reports the genotype and allele frequencies of the Gln192Arg polymorphism of PON1 in four populations of India, comprising two caste and two tribal groups hitherto unexamined for this polymorphism. The R allele frequencies in Jat, Meo, Santhal and Zeliangrong populations were found to be 0.47, 0.45, 0.54 and 0.51 respectively. The gene diversity analyses show a high genetic differentiation at this locus indicative of the role of populations' history and other evolutionary forces. A comparison with allele frequencies among 106 populations from different continents showed a concordance with their geographic distribution which will have repercussions in policies targeting pesticide usage.

PON1 status evaluation in patients with chronic arterial occlusion of lower limbs due to atherosclerosis obliterans

INTRODUCTION

Human paraoxonase (PON1) is a calcium-dependent enzyme physically associated with HDL, and it is believed to contribute to the atheroprotective effect of HDL. The aim of the study was to evaluate PON1 status in patients with atherosclerosis obliterans as an effect of ischemia regarding its activity and phenotype distribution.

MATERIAL AND METHODS

The study group consisted of patients with chronic arterial occlusion of the lower limbs due to atherosclerosis obliterans (AO). The patients were divided into two groups according to the degree of ischemia: moderate (MI), and critical (CI). The ratio of the hydrolysis of salt-stimulated PON1 activity to the hydrolysis of phenylacetate was used to assign individuals to one of three possible phenotypes (low activity - A, medium activity - AB, high activity - B). It was observed that PON1 arylesterase activity was affected by ischemia of the lower limbs depending on its degree.

RESULTS

The odds ratio and the relative risk analysis showed that the patients with moderate ischemia are much more often characterized by phenotype A than by phenotype B. The low activity phenotype A occurs over twice as often in patients with chronic ischemia of the lower limbs as in individuals from the control group (OR = 2.125; 1.96 to 3.776, p = 0.0143).

CONCLUSIONS

This study presents the low activity phenotype A in relation to the risk of ischemia of the lower limbs due to atherosclerosis and shows the potentially important role of PON1 in conclusion of the process leading to intensification of ischemia degree.