Cultured HeLa cells were irradiated with a single acute dose of either gamma rays (40 Gy) or low-energy proton beams (20 Gy). (1)H magnetic resonance spectra of intact cells harvested at different times after irradiation and of the correspondent perchloric acid (PCA) extracts prepared at different times after irradiation were run. Selected signals from glutathione and lactate were examined with the aim of investigating effects of irradiation on antioxidative stores and on mitochondrial activity. An increase of signal intensity of glutathione (GSH) takes place at 15 and 24 hr after irradiation, while a decrease of its signal intensity, accompanied by an increase of that of free glutamate, starts appearing 48 hr after irradiation. Lactate signal increases 48 hr after irradiation. Signals from lipid catabolites were also examined to explore their sensitivity in predicting the response to radiotherapy. Intensity ratios of signals of glycerophosphorylcholine and choline to that of phosphorylcholine increase with time after irradiation. Irradiating cells with gamma rays or proton beams at half a dose produces effects comparable to the metabolic variations presented here. The present experiments allow more insight into the complex pattern of the changes of GSH by irradiation and indicate that magnetic resonance spectroscopy signals from GSH, glutamate, lactate, and lipid catabolites are affected by irradiation. Finally, these data represent a first indication that the relative biological efficiency for some metabolic damage of low-energy proton beams with respect to gamma rays can reach a value of 2.
Copyright 2002 Wiley-Liss, Inc.