Investigation of the prophylactic effect of oral and topical squalene administration in A skin carcinogenesis model developed by ultraviolet-B radiation in mice

Skin cancer is the most common type of cancer that can cause morbidity and mortality all over the world, especially among white people. Skin cancer prophylaxis studies have become important because skin cancer is widespread all over the world and its incidence is increasing. The antioxidant, cytoprotective and anti-aging effect of squalene, the intermediate metabolite in cholesterol synthesis; protective effect against colon cancer and lung cancer has been shown. In our study, the protective effect of squalene on squamous cell carcinoma of skin was investigated and its mechanism of action was aimed to be detected. In skin cancer models in the literature, tumors called papilloma, which are actinic keratosis-like premalignant lesions, were formed in mice by chemical carcinogenesis or ultraviolet carcinogenesis methods. Invasive carcinoma has been shown to develop as carcinogen exposure to these tumors persists. The effect of chemoprophilactic agents on the tumors called premalign papilloma was investigated. Similarly, actinic keratosis-like papillomas which are accepted as the precursor lesion of squamous cell carcinoma in our study have been named as "tumor" like in the literature. In the study 28 female BALB/c mice of 25-30 gr weight were used. Four groups were determined as seven mice in each group and ultraviolet-B (UVB) rays were applied to the back region of each mouse to form a skin carcinogenesis model. The squalene solvent (acetone) was applied to the dorsal skin of Group-1 (control group) and the topical squalene dissolved with acetone was applied to the dorsal skin of Group-2. While the squalene solvent (acetone) was applied to the dorsal skin of mice and the peroral squalene was given at the same time in Group-3, topical squalene (dissolved with acetone) was applied to the back and peroral squalene was given in Group-4. All of these applications were performed regularly throughout the experiment. To produce skin tumors in the experimental animals, the dorsal skin was irradiated with 540 millijoule/cm2 UVB radiation for the first ten days. Following a four-day break, 540 milliJoules/cm2 UVB was administered daily for three days a week during 16 weeks. Squalene was applied topically in the relevant groups 30 minutes before UVB irradiation for 18 weeks on the purpose of protection. In addition oral squalene was given perorally by the gavage cannula to Group 2 and 4 on UVB irradiation days. The mice in the groups were followed regularly in terms of the number of tumors they developed and compared at the end of the experiment. The dorsal skin of sacrificed mice were excised and examined under light microscope after haematoxylin eosin stain protocol. Premalign masses consistent with actinic keratosis, including dysplasia and mitoses, were detected. All skin specimens were examined and the thickness of the epithelium in the region where epithelial hyperplasia and atypia were the most intensive was measured excluding the keratin layer. The inflammatory cells were counted by locating the areas where inflammation was most intense and groups compared. In addition, in order to determine the effect of squalene on p53 mutation in tumor pathogenesis, mutant p53 protein was examined by immunohistochemical methods in the samples taken from tumors and the groups were compared again. Significant decrease in tumor number and epithelial thickness and a significant increase in inflammatory cell ratio were observed in the 2nd and 4th groups using topical squalene compared to the other groups. Stained cell ratio of mutant p53 protein was not significantly different between all groups. With all these information, it can be said that the topical application of squalene significantly reduces premalignant actinic keratosis like papilloma lesions, retards the time of emergence, increases the number of immune system cells and thus has a protective effect against squamous cell carcinoma of skin.