Oxidative and nitrative stress caused by subcutaneous implantation of a foreign body accelerates sarcoma development in Trp53^+/- mice

Chronic inflammation is a recognized risk factor for human cancer at various sites because of persistent oxidative and nitrative tissue damage. Trp53^+/- mice show the predisposition to tumor development, such as sarcomas and lymphomas, compared with Trp53^+/+ mice. We investigated the effects of chronic inflammation, especially oxidative and nitrative stress, induced by subcutaneous implantation of a plastic plate (10 × 5 × 1 mm) as a foreign body on tumorigenesis in Trp53^+/- and Trp53^+/+ mice. The plastic plates were implanted at the age of about 11 weeks. Thirty out of 38 Trp53^+/- mice (79%) developed sarcomas around the implant (mean time of tumor appearance was 45.8 ± 12.0 weeks of age), whereas only one of 10 Trp53^+/+ mice with an implant (10%) developed a tumor, at 56 weeks. No sarcomas developed at a sham-operation site. Two of 10 Trp53^+/- mice with no implant (20%) also developed three sarcomas spontaneously at 77, 81 and 84 weeks. Increased immunostaining for markers of oxidative and nitrative stress (8-oxo-7,8-dihydro-2′-deoxyguanosine, 8-nitroguanine and 3-nitrotyrosine) and expression of inducible nitric oxide synthase in tumor cells and inflammatory cells were detected in implant-induced sarcomas compared with spontaneous sarcomas in Trp53^+/- mice. Furthermore, p53 loss of heterozygosity was observed in 26 out of 29 implant-induced sarcomas (90%). These results indicate that implanted foreign bodies significantly enhanced sarcoma development in Trp53^+/- mice, and this may be associated with increased oxidative and nitrative stress. Loss of the remaining wild-type p53 allele and loss of p53 function appears to be, at least in part, underlying molecular mechanisms during the development of sarcomas at the implantation site in Trp53^+/- mice. Such implant-induced sarcoma development in Trp53^+/- mice could be useful for studying molecular mechanisms and developing new strategies for chemoprevention in human carcinogenesis induced by chronic inflammation and/or foreign bodies.