Background: Controversy exists regarding the role of oxidative DNA damage and DNA repair in primary open angle glaucoma (POAG). We performed a case control study to test the hypothesis that oxidative DNA damage and base excision repair (BER) genes PARP1 and OGG1 are involved in POAG pathogenesis.
Materials and methods: The study included 116 POAG patients and 116 cataract patients as controls. The 8-hydroxy-2'-deoxyguanosine (8-OHdG) levels were measured by ELISA. RNA was extracted from blood by Trizol and converted to cDNA. The relative quantification of PARP1 and OGG1 genes normalized to β-actin was calculated by the 2-ΔCt method. Comparisons between groups were done by student's t-test and correlation between parameters was seen by Pearson correlation coefficient. All p values less than 0.05 were considered significant.
Results: Mean levels of 8-OHdG were (patients v/s controls) 19.53 ± 1.40 vs. 15.0 ± 2.6 ng/ml in plasma and 8.55 ± 1.94 vs. 5.15 ± 1.09 ng/ml in aqueous humor (p < 0.0001). Expression levels of PARP1 (0.44 ± 0.05 vs. 0.88 ± 0.04) and OGG1 (0.46 ± 0.05 vs. 0.8 ± 0.01) were significantly (p < 0.0001) less in the patients than controls. There was a significant negative correlation between the expression levels of PARP1 and OGG1 with plasma and aqueous 8-OHdG. There was a strong positive correlation between plasma and aqueous 8-OHdG levels.
Conclusion: These results support our hypothesis that oxidative stress-induced DNA damage is associated with POAG. Increased oxidative DNA damage in POAG may be attributed to decreased expression of DNA repair enzymes of the BER pathway.
Keywords: 8-hydroxy-2′-deoxyguanosine (8-OHdG); 8-oxoguanine DNA glycosylase (OGG1); glaucoma; oxidative stress; poly (ADP-ribose) polymerase 1 (PARP1).