Radiosensitizer effect of usnic acid on Biomphalaria glabrata embryos

Some phytochemicals have shown the potential of being radiomodifiers, especially phenolic compounds, such as lichenic secondary metabolites. To evaluate the phytochemical usnic acid as a radiomodifier, embryonic cells of molluscs have been used due to their ease of collection, high sensitivity to physical and chemical agents, well-known embryology and low cost for analysis.

This study aimed to assess the radiosensitizing action of usnic acid on Biomphalaria glabrata embryos. Samples were irradiated with 4 Gy of gamma rays from a ⁶⁰Co source (dose rate 2.906 Gy/h). An acute toxicity test was performed using B. glabrata embryos in the blastula stage, in order to determine the toxicity of usnic acid and to establish the lethal Concentration for 50% (LC₅₀). Subsequently, the radiomodifing capacity of usnic acid was estimated using assays with B. glabrata embryos.

Irradiation increased the number of non-viable embryos compared to unirradiated controls. Additionally, it was observed that embryos exposed to a non-toxic concentration of usnic acid (0.6 µg/mL) before irradiation showed a further enhancement in non-viable embryos when compared with exposure to ionizing radiation alone.

The results presented here indicate that usnic acid makes cells more sensitive to the damaging effects of radiation.