Serum paraoxonase phenotype distribution in exudative age-related macular degeneration and its relationship to homocysteine and oxidized low-density lipoprotein.

PURPOSE: Disequilibrium between oxidative stress and antioxidant levels has been proposed as an important case of exudative age-related macular degeneration (AMD). The aim of the present study was to investigate homocysteine (Hcy) level and antioxidant paraoxonase 1 (PON1) activity within its phenotypes together with oxidized low-density lipoprotein (OX-LDL) levels in the patients with exudative AMD.
METHODS: Serum PON1 activity and plasma Hcy and OX-LDL levels were analyzed in 45 exudative AMD patients and compared with 45 healthy controls. Paraoxonase 1 activity was measured in serum using paraoxon and phenylacetate as substrates. The PON1 phenotype was determined using double-substrate method. Homocysteine and OX-LDL levels were determined by enzyme-linked immunosorbent assay method.
RESULTS: The distribution of PON1 phenotypes was significantly different between the patients with exudative AMD and control subjects (chi-square = 6.17, P = 0.01). AA phenotype with low activity was significantly more frequent in exudative AMD patients compared with healthy subjects (62.2% vs. 35.6%, respectively). Other phenotype frequencies in the patients compared with controls were as AB phenotype (intermediate activity) 28.9% versus 46.7% and BB phenotype (high activity) 8.9% versus 17.8%, respectively. Except in BB phenotype (P = 0.2), patients with AA and AB phenotypes had higher plasma Hcy levels in comparison to those of controls (P = 0.02 and P = 0.03, respectively). The mean OX-LDL levels, in all 3 phenotypes (P < 0.05), and OX-LDL/high-density lipoprotein ratio, in AA and AB phenotypes (P = 0.001, P = 0.1, respectively) but not in BB (P = 0.1), were significantly higher in the patients than controls. No significant differences in comparison of Hcy and OX-LDL levels between 3 PON1 phenotypes in both control (P = 0.6 for Hcy, P = 0.7 for OX-LDL) and patients (P = 0.8 for Hcy, P = 0.6 for OX-LDL) were found
CONCLUSION: Increased plasma OX-LDL levels and ratios of OX-LDL/high-density lipoprotein, as biomarkers of lipoprotein oxidative stress, higher levels of Hcy, as oxidant agent, and more common low or intermediate PON1 activity in patients with exudative AMD, compared with controls, indicate that PON1 activity is insufficient to explain the increased oxidative stress observed in exudative AMD.