Inflammatory cytokines induce DNA damage and inhibit DNA repair in cholangiocarcinoma cells by a nitric oxide-dependent mechanism.

TLDR

Chronic infection and inflammation are established risk factors for cholangiocarcinoma, yet the mechanistic link between inflammation and tumorigenesis remains unclear. The study tested whether inflammatory cytokines stimulate iNOS‑derived nitric oxide that impairs DNA repair, thereby promoting cholangiocarcinoma. In vitro, a cytokine mix (IL‑1β, IFN‑γ, TNF‑α) induced iNOS and NO in three cholangiocarcinoma cell lines, and comet assays and repair activity assays quantified NO‑dependent DNA damage and repair inhibition. iNOS and nitrotyrosine were detected in all 18 tumor samples, and cytokine‑induced NO caused DNA damage and a 70 % reduction in global DNA repair, supporting a link between inflammation‑driven NO and cholangiocarcinoma progression.

Abstract

Chronic infection and inflammation are risk factors for the development of cholangiocarcinoma, a highly malignant, generally fatal adenocarcinoma originating from biliary epithelia. However, the link between inflammation and carcinogenesis in these disorders is obscure. Because nitric oxide (NO) is generated in inflamed tissues by inducible nitric oxide synthase (iNOS) and because DNA repair proteins are potentially susceptible to NO-mediated nitrosylation, we formulated the hypothesis that inflammatory cytokines induce iNOS and sufficient NO to inhibit DNA repair enzymes leading to the development and progression of cholangiocarcinoma. iNOS and nitrotyrosine were demonstrated in 18/18 cholangiocarcinoma specimens. Furthermore, iNOS and NO generation could be induced in vitro by inflammatory cytokines (mixture of interleukin-1beta, IFN-gamma, and tumor necrosis factor alpha) in three human cholangiocarcinoma cell lines. NO-dependent DNA damage as assessed by the comet assay was demonstrated during exposure of the three cholangiocarcinoma cell lines to cytokines. Moreover, global DNA repair activity was inhibited by 70% by a NO-dependent process after exposure of cells to cytokines. Our data indicate that activation of iNOS and excess production of NO in response to inflammatory cytokines cause DNA damage and inhibit DNA repair proteins. NO inactivation of DNA repair enzymes may provide a link between inflammation and the initiation, promotion, and/or progression of cholangiocarcinoma.