Effect of Brazilian propolis (AF-08) on genotoxicity, cytotoxicity and clonogenic death of Chinese hamster ovary (CHO-K1) cells irradiated with 60Co gamma-radiation

The present study was conducted in order to evaluate the effect of Brazilian propolis (AF-08; 5, 10, 15, 30, 50, 100, and 200 μg/mL) in protecting CHO-K1 cells against genotoxic and cytotoxic damage and clonogenic death induced by 60Co gamma-radiation (1.0, 2.0, 4.0, and 6.0 Gy). For this purpose, three interlinked endpoints were analyzed: induction of DNA damage by use of the micronucleus (MN) test (genotoxic damage), cell viability by means of the MTS assay, and differential staining (cytotoxic damage) and clonogenic death via the colony-formation test (cytotoxic damage). The MN test revealed that propolis alone (5-100 μg/mL) was not genotoxic up to 100 μg/mL and that 30 μg/mL of propolis reduced the radiation-induced DNA damage (∼56% reduction, p < 0.05), exhibiting a radio-protective effect on irradiated CHO-K1 cells. On the other hand, analysis of cytotoxicity showed that a concentration of 50 μg/mL presented a significant proliferative effect (p < 0.001) when associated with radiation, decreasing the percentage of necrotic cells (p < 0.01). No mediated cytotoxic effect was found, but the concentration of 200 μg/mL was toxic when analyzed at 24 and 48 h via the differential staining technique, but not at 72 h after irradiation, analyzed with the MTS assay. Differential staining also showed that necrosis was the main death modality in irradiated cells and that apoptosis was induced only at the toxic concentration of propolis (200 μg/mL). Concerning the clonogenic capacity, a concentration of 50 μg/mL also exhibited a significant stimulating effect on cell proliferation (p < 0.001), in agreement with the data from differential staining. Taken together, these data suggest that the use of propolis AF-08 for the prevention of the adverse effects of ionizing radiation is promising. Nevertheless, additional investigations are necessary for a better understanding of potential applications of propolis to improve human health.