Algal Derived Bioactive Compounds as Radiation Protectant: An Emerging Strategy for Future Applications.

Algae have shown an effective defense system that enables their survival in environments exposed to radiation stress, especially from ultraviolet (UV) light and ionizing radiation. Their protective system comprises specific photoprotective chemicals along with a multilayered antioxidant strategy that encompasses both non-enzymatic and enzymatic approaches. In this defence system, scytonemin and mycosporin-like amino acids play a crucial role in photoprotection by functioning as natural sunscreen with high photostability and strong UV-absorbing capacity. These chemical compounds also possess antioxidant properties that help minimize indirect damage produced by reactive oxygen species formed after radiation exposure. Scytonemin becomes significant due to its capability to block 90% of UV-radiation, effectively absorbing all types of UV (A, B and C) wavelengths. In the process of quenching photosensitization products and scavenging free radicals, carotenoids act as a stress reliever by preventing oxidative damage and lipid peroxidation. The internally generated ROS gets neutralized by algae, which utilize an enzymatic antioxidant system. In the enzymatic defence system of algae, ascorbate peroxidase, catalase, superoxide dismutase and glutathione reductase play important roles in ROS elimination. Additionally, α-tocopherol and ascorbic acid which are non-enzymatic antioxidants, complement the enzymatic reaction described above. The biochemical properties of these photoprotective and antioxidant compounds have significant biotechnological implications, applications in pharmaceuticals, cosmetics, anticancer treatments, nutraceuticals and antimicrobials. Interestingly, exposure to low-dose radiation has been shown to enhance algae growth, stimulate the production of valuable metabolites for biofuels and biomaterials and strengthen the resilience of cultivated strains against stressors.