Oxidative DNA damage in pterygium.

PURPOSE

Epidemiological evidence suggests that UV irradiation plays the most important role in pterygial formation. The noxious effects of UV irradiation are either directly by a UV phototoxic effect or indirectly by formation of radical oxygen species (ROS). ROS are very harmful to cells, because they injure cellular DNA, proteins, and lipids (called oxidative stress). Among numerous types of oxidative DNA damage, the formation of 8-hydroxydeoxyguanosine (8-OHdG) presents only a minor fraction of UV induced DNA damage, but it is a ubiquitous marker of oxidative stress. If pterygium is related to UV, we surmised oxidative stress exists in pterygium. To provide the molecular evidence of UV radiation, 8-OHdG was detected in pterygium. Moreover, human 8-oxoguanine glycosylase (hOGG1) is the key component responsible for the removal of 8-OHdG. To determine whether the hOGG1 was expressed in pterygium, this enzyme was also evaluated.

METHODS

Immunohistochemical staining using a monoclonal antibody to 8-OHdG and hOGG1 were performed on 52 pterygial specimens and 6 normal conjunctiva.

RESULTS

There were 12 (23.1%) pterygial specimens positive for 8-OHdG staining, limited to the nuclei of the epithelial layer. No substantial staining was visible in the subepithelial fibrovascular layers. In pterygium with 8-OHdG staining, there were 4 (4/11, 36.4%) specimens with hOGG1 expression. However, in pterygium without 8-OHdG staining, there were only 3 (3/41, 7.3%) specimens with hOGG1 expression. hOGG1 expression was significantly associated with 8-OHdG positive staining. All normal controls were negative for 8-OHdG and hOGG1 staining.

CONCLUSIONS

Our study demonstrated for the first time 8-OHdG in pterygium, which represented oxidative stress in pterygium. The increased level of 8-OHdG in pterygium is not due to decreased expression of hOGG1, while increased levels of 8-OHdG induced the expression of hOGG1.