Human serum paraoxonase (PON1) is a high-density lipoprotein-associated esterase that protects against organophosphate neurotoxicity, and is proposed to play a role in lipid metabolism and the onset of cardiovascular disease. In the present study, paraoxonase activities and phenotype distribution in serum of 132 healthy Iranian individuals aged 17-68 years were assessed using dual substrate method. In the study population, a wide interindividual variability (up to 15-fold) of paraoxonase activity was found. The mean of basal, salt-stimulated paraoxonase and arylesterase activities were 81.8 ± 57 U/ml, 153.1 ± 117.5 U/ml and 80.7 ± 12.8 kU/l, respectively. The ratio of salt-stimulated paraoxonase activity to arylesterase activity was used for definition of phenotypes. Based on the observed ratios, three distinct phenotypes AA (low activity), AB (intermediate activity) and BB (high activity) were determined. The PON1 ratio varied from 0.5 to 6.8. The paraoxonase phenotype frequencies were approximately 48% (AA), 41% (AB) and 11% (BB). In this work, serum triglycerides had significant positive correlation ( r = 0.334, P < 0.05) with paraoxonase activity, whereas high-density lipoprotein did not. No significant decrease in paraoxonase activity by smoking was observed. Age and sex had no influences on PON1 activities. In conclusion, the distribution of paraoxonase phenotypes in this Iranian population was trimodal and comparable to that of Caucasians from North America; however, overall enzyme activity was lower than that reported for Caucasians.

Paraoxonase (PON1) is a serum enzyme that plays an important role in prevention of atherosclerosis and also protects against organophosphate-induced neurotoxicity. PON1 displays a high variability in human populations. In this study, PON1-192 and -55 polymorphisms and correlation to serum PON1 activity were investigated in 132 healthy Iranian individuals from Isfahan province. The genotype frequencies for PON1-192 were approximately 48% (QQ), 42.% (QR), and 10% (RR) and for PON1-55 17% (MM), 48% (ML), and 35% (LL). Thus, the frequencies of alleles R and L were 0.31 and 0.59, respectively. PON1 activity toward paraoxon was markedly affected in both polymorphic populations in the following order QQ < QR < RR genotype for PON1-192 and MM < ML < LL genotype for PON1-55. Neither polymorphism significantly affected PON1 activity toward phenylacetate. The RR/LL individuals had the highest PON1 activity and QQ/MM individuals the least. The QR/ML haplotype was the most frequent seen in Iranians, and the RR/MM and QR/MM haplotypes were absent in this population. In conclusion, the frequencies of PON1-192 and -55 polymorphisms in this Iranian population were different from those seen in other Asian populations from Japan and China but similar to those for European Caucasians.