Paraoxonase 1 phenotype distribution in a cohort of healthy Sri Lankan population

Human serum paraoxonase 1 is an enzyme synthesised mainly by the liver. Paraoxonase 1 Q192R polymorphism involves amino acid substitution of glutamine (Q isoform) to arginine (R isoform) at position 192. Paraoxonase 1 activity and polymorphism is associated with many disease conditions. In Sri Lankan context, data is lacking on the distribution of Paraoxonase 1 phenotypes. The aim of this study was to assess the phenotypic distribution of Paraoxonase 1 in a cohort of healthy Sri Lankan individuals using dual substrate method. Serum samples of 77, apparently healthy individuals were used for the study. Paraoxonase activity was measured by a kinetic method using paraoxon as the substrate at 412 nm and 25 ^oC. Salt stimulated paraoxonase 1 activity was measured in the presence of 1M NaCl. Arylesterase activity was measured by a kinetic method using phenylacetate as the substrate at 270 nm and 25 ^oC. The ratio of salt stimulated paraoxonase activity to arylesterase activity was used to assign phenotypes. Basal and salt stimulated paraoxonase activities were bimodally distributed. Arylesterase activity was unimodally distributed. Salt stimulated paraoxonase activity/ arylesterase activity ratio was trimodally distributed. The three modes corresponded to QQ (lower activity), QR (intermediate activity) and RR (higher activity) phenotypes.   The percentage distribution of QQ, QR and RR phenotypes were 36 %, 51 % and 13 %, respectively. This study has set the baseline data on phenotypic distribution of paraoxonase1 in a cohort of healthy Sri Lankan individuals.