ABSTRACT
BACKGROUND: Poly-gamma glutamic acid (gamma-PGA) is a natural polymer that is synthesized by Bacillus subtilis. Because of the reported anti-tumor effect, gamma-PGA and its derivatives have attracted enormous interest in the past few years. OBJECTIVE: The anti-tumor effects of gamma-PGA against ultraviolet B (UVB) were evaluated by irradiating hairless mice with UVB. METHODS: The experimental animals were 12-week-old male Albino hairless Skh:HR-1 mice. Thirty-two mice were divided into 4 groups: a chronologic aging (control); irradiation with UVB without gamma-PGA administration (T1); irradiation with UVB and 2,000 kDa gamma-PGA orally (T2); and irradiation with UVB and 5,000 kDa gamma-PGA orally (T3). The irradiation period was 12 weeks. The anti-tumor effect of gamma-PGA was evaluated with photographs and skin biopsy. A 51Cr release assay was performed to determine nutural killer cell (NK cell) activity. RESULTS: After 20 weeks of UVB irradiation, seborrheic keratosis, actinic keratosis, Bowen's disease, squamous cell carcinoma, and basal cell carcinoma were observed on the backs of mice. The most common skin lesion was seborrheic keratosis. gamma-PGA showed inhibitory effects on the total number of skin tumors and the premalignant and malignant skin lesions induced by UVB. The NK cell activities showed a tendency to increase based on the molecular weight of gamma-PGA. CONCLUSION: We suggest that gamma-PGA shows anti-tumor effects that inhibit the tumor generation induced by UVB, and the antitumor effects are related to the molecular weight of gamma-PGA.