Contents of endometriotic cysts, especially the high concentration of free iron, are a possible cause of carcinogenesis in the cysts through the iron-induced persistent oxidative stress

Abstract

Purpose: Endometriotic cysts are known to transform into ovarian cancers, such as clear cell and endometrioid carcinomas. We hypothesized that an iron-rich environment produced by the repetition of hemorrhage in the endometriotic cysts during the reproductive period may play a crucial role in carcinogenesis in the cysts through the iron-induced persistent oxidative stress.

Experimental design: Contents of human ovarian cysts, including 21 endometriotic cysts, 4 clear cell carcinomas, and 11 nonendometriotic cysts, were analyzed for the concentrations of free "catalytic" iron, lactose dehydrogenase, potential antioxidant, lipid peroxide, and 8-hydroxy-2'-deoxyguanosine (8-OHdG). Iron deposition and 8-OHdG levels were also analyzed histologically. Reactive oxygen species and the mutagenicity of the contents in endometriotic cyst were determined in vitro.

Results: The concentration of free iron in endometriotic cysts (100.9 mmol/L) was significantly higher than that in nonendometriotic cysts (0.075 mmol/L; P < 0.01). The average concentrations of lactose dehydrogenase, potential antioxidant, lipid peroxide, and 8-OHdG were also significantly higher in endometriotic cysts (P < 0.01). There was a correlation between the concentration of free iron and that of 8-OHdG (P < 0.01). Histologically, we could observe iron deposits more abundantly in endometriotic cysts than in nonendometriotic cysts (P < 0.01). The level of 8-OHdG in carcinoma associated with endometriosis was higher than that of carcinoma without endometriosis (P < 0.05). In vitro analyses showed that the contents of endometriotic cyst could produce more reactive oxygen species and could induce gene mutations more frequently than the contents in the other cysts.

Conclusions: Abundant free iron in the contents of endometriotic cysts was strongly associated with greater oxidative stress and frequent DNA mutations. A long-standing history of the RBCs accumulated in the ovarian endometriotic cysts during the reproductive period produces oxidative stress that is a possible cause for the malignant change of the endometriotic cyst.