Radioprotective Properties of Baicalein

Radiation is an important source of free radicals in living systems. Ionizing radiations such as γ-rays exert their biological effects through generation of reactive oxygen species and the resultant damage to DNA and cellular membranes. Several natural compounds, especially with antioxidant abilities are known to be radioprotective. Baicalein (5,6,7-trihydroxy-2-phenyl-4H-1-benzopyran-4-one), a naturally occurring flavone, present in some Indian and Chinese medicinal plants (such as Terminalia arjuna Scutellaria rivularis, Scutellariae radix and Scutelleria baicalensis) has antioxidant effects. We have examined the radioprotective effects of baicalein using plasmid pBR322 DNA, calf thymus DNA and rat liver mitochondria as model systems. The assays used are strand-break estimation and DNA binding for measuring DNA damage besides protein oxidation, protein hydroperoxide formation, glutathione peroxidase, glutathione reductase, superoxide dismutase, succinate dihydrogenase and lipid peroxidation for estimating membrane damage. For estimating lipid peroxidation different products were used. Significant membrane damage was observed with 450 Gy and strand break formation with 6 Gy. Our results indicate that baicalein is a potent radioprotector at micromolar (550) levels. The protective effect, at 5 μM, was 80% against formation of thiobarbituric acid reactive substances (TBARS) and 50% against lipid hydroperoxide. The protective ability against protein carbonyl formation was 50% and protein hydroperoxide formation 85% at the same concentration. Similar protective effects were also observed against damage to glutathione peroxidase and superoxide dismutase. A concentration dependent effect also was seen with most of the parameters examined. Single-strand break formation induced by radiation also was accentuated with baicalein. It also inhibited the DNA binding caused by radiation. In conclusion our studies reveal the potent radioprotective effect of the natural compound baicalein.