International Journal of Biomedical And Advance Research ISSN: 2229-3809 (Online) Journal DOI:10.7439/ijbar CODEN:IJBABN IJBAR (2014) 05 (01) www.ssjournals.com Research Article Paraoxonase1 activity, its Q192R polymorphism and diabetic retinopathy in type 2 diabetes mellitus Mahesh Harishchandra Hampe *1 and Mukund Ramchandra Mogarekar 2 1 Senior Manager, Preventine Lifecare, Turbhe (Navi Mumbai), India 2 Professor and Head of the Department of Biochemistry, SRTRGMC, Ambajogai, Dist- Beed, India * Correspondence Info: Mahesh Harishchandra Hampe, Senior Manager, Preventine Lifecare, Turbhe (Navi Mumbai), India E-mail: mahesh.hampe27@gmail.com \ 1. Introduction Diabetes mellitus (DM) is a major health problem world-wide and DR is the most common and devastating chronic ocular microvascular complication eventually leading to blindness. 1-3 The prevalence of DR in diabetic individuals is around 17% in India amongst which around 8% ends in vision threatening blindness. 4,5] The risk of retinopathy is directly related to the age at onset of hyperglycemic state, degree of glycemic control and duration of diabetes. 6-8 Several hypotheses have been proposed to explain the pathophysiological mechanism which contribute to the development of retinopathy in DM. These include polyol accumulation, formation of advanced glycation end products, oxidative stress and activation of protein kinase C which modulates the disease process through various cellular metabolic signaling. 9-11 Oxidative stress induced lipid peroxidation thought to play major role in the pathogenesis of DR. 10-14 Poor diabetic control is strongly associated with an increase in lipid peroxides and consequent microangiopathies in DM. 3 High density lipoprotein (HDL) cholesterol has been shown to have antioxidant potential and its low levels are more prevalent with poor glycemic control. 15 PON1 is an aryldialkylphosphatase (E.C. 3.1.8.1) mainly found in the circulation anchored on HDL and is considered to be the major contributor of the protective effects displayed by HDL. 16 PON1 activity is found to be decreased in DM. 17 PON1 has the ability to hydrolyse specific oxidised phospholipids and hydroperoxides in oxidised low density lipoproteins (LDL) and destroying the proinflammatory molecules involved in the initiation and progression of microvascular complications in diabetes. 18 Serum PON1 activity, based on the ability of the enzyme to hydrolyse the substrate paraoxon, found to possess interindividual variability. 19 The molecular basis of these variations is the single nucleotide polymorphism in the PON1 gene (7q21-22). 20 An amino acid substitution at position 192 (Q192R polymorphism) give rise to two alleles PON Q and PON R and three phenotypes PON1 QQ, PON1 QR and PON1 RR . The amino acid arginine at position 192 of the protein specifies Q allele which is more abundant in the population and is responsible for protective effects of PON, while glutamine at that position denotes R allele which is proposed to be related with oxidative stress. 16 PON1 Q192R polymorphism thus offers differential protection towards oxidative stress induced microvascular damage in genetically susceptible individuals. This gave us the insight to investigate diabetic patients to determine the association of DR with PON1 phenotypes. The aim of this study was to investigate whether the PON1 status (activity and polymorphism) were associated with occurrence of retinopathy in type 2 diabetic patients besides other established risk factors. 2. Material and Methods The cross-sectional study was conducted on 55 normotensive type 2 DM patients diagnosed as per the diagnostic criteria of American Diabetes Association 2007, selected randomly from the patients admitted in our hospital. 21 Diabetic patients with retinopathy formed the study group while diabetic patients without retinopathy served as the control group. Study protocol was approved by the institutional ethics committee of our medical College. Written informed consent was obtained from all patients. Patients with associated ischemic heart disease, rheumatoid arthritis, concomitant liver or kidney disease, history of exogenous hormone administration and DM of less than 5 years duration were excluded Abstract Background: The goal of this study was to investigate the role of paraoxonase1 (PON1) status i.e. activity and Q192R polymorphism, in the development of diabetic retinopathy (DR) in patients of type 2 diabetes mellitus. Methods: This cross-sectional study included 55 normotensive type 2 diabetic patients (duration more than 5 years) admitted in the hospital divided into two groups (with and without DR) on the basis of fundus examination by direct ophthalmoscopy. Serum samples of all patients were subjected for PON1 activity with and without salt using paraoxon as substrate and arylesterase activity of PON1 using phenylacetate as substrate. PON1 phenotyping is carried out using ratio of salt stimulated PON1 activity to arylesterase activity. Results: Arylesterase activity of PON1 was found significantly lower in diabetics with DR than diabetic patients without DR ( P = 0.01). Multivariate testing also showed its independent protective association in the development of DR (OR 0.958, [95% CI (0.915-1.004)], P value = 0.023). Moreover, DR was associated significantly in diabetic patients with PON1 R allele carriers (71.05%) than diabetic patients with PON1 QQ homozygotes (29.41%). PON1 R carriers had higher Odds ratio (OR) for DR in univariate analysis (OR 5.891, [95% CI (1.676-20.705)], P value = 0.006) and in multivariate analysis (OR 14.12 [95% CI (0.926-215.2)], P = 0.057) after adjustment of conventional risk factors of diabetes. Also diabetics with homozygous PON1 RR were associated significantly with severe forms of DR. Conclusions: Arylesterase activity of PON1 may be more important in the risk of retinopathy in diabetic individual than the paraoxon hydrolytic activity. Moreover PON1 R allele is associated with susceptibility to DR showing a graded risk relationship to the number of R alleles. Thus the determination of PON1 status may be useful in the risk assessment and management of DR. Key words: paraoxonase1, polymorphism, diabetic retinopathy, diabetes mellitus.