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Effect of stereotactic radiosurgery on lipids and proteins of normal and hypoperfused rat brain homogenates: A Fourier transform infrared spectroscopy study

Purpose: The effect of stereotactic radiosurgery on lipids and proteins of normal and hypoperfused rat brain was investigated to see if hypoxic areas are really more resistant to radiation effects or not. Materials and methods: Rat brain samples from contol, stereotactically irradiated and chronically hypoperfused plus stereotactically irradiated groups were homogenized separately with saline phosphate buffer, and centrifuged at 125,000 g for 15 min. Membrane rich parts (pellet) of these homogenates were used for Fourier Transform Infrared (FTIR) spectroscopy studies. Mann-Whitney U tests were performed on the groups, two by two, to test the significance of the differences between the control group and stereotactically irradiated group as well as the control group and chronically hypoperfused plus stereotactically irradiated group. Results: After a single high dose of X-rays to healthy rat brain, the lipid concentration increased slightly, protein content decreased significantly (p < 0.05) and protein-to-lipid ratio decreased slightly. The secondary structure of the proteins was altered in the irradiated brain samples such that the content of α-helical structure decreased significantly (p < 0.01) and random coil increased dramatically (p < 0.05). The effect of radiation on the content of α-helical structure was not found to be significant in the hypoperfused group, but the decrease in the content of random coil was significant (p < 0.01). Conclusion: Stereotactic radiosurgery of the brain increased the lipid concentration, decreased the protein concentration and consequently resulted in a decrease in the protein to lipid ratio compared to unirratiated brain. Radiation also altered the secondary structure of protein. The variations in lipid and protein content and the resulting lipid to protein ratio imply that chronically hypoperfused brain is more vulnerable to radiation than non-hypoperfused brain and suggests chronic hypoperfusion does not prevent cerebral damage caused by irradiation. However, irradiation of hypoperfused brain resulted in less alteration in protein structure than in non-hypperfused brain, suggesting higher resistance to irradiation using this endpoint.