P-305 - Radiation-induced response of mitochondrial energy metabolism in tumor cells

Abstract

To evaluate mitochondrial responses in tumor cells exposed to X-rays, a novel ESR oximetry was developed by using lithium 5,9,14,18,23,27,32,36-octa-n-butoxy-2,3-naphthalocyanine (LiNc-BuO) in the absence and presence of a variety of reagent against mitochondria electron transport chain (ETC), i.e., oligomycin, CCCP and rotenone/antimycin A. This ESR oximetry demonstrated that basal respiration, ATP-linked respiration, proton-leak, maximal respiration and reserve capacity increased in HeLa cells at 24 h after 10 Gy X-irradiation (IR). By standardization of OCR by the mitochondria membrane content, the radiation-induced increase-responses in the respiratory parameters were disappeared, indicating that this increase response was due to increase of mitochondrial content but not activation of mitochondrial respiratory-related enzymes. In addition, ESR spectroscopy of frozen whole HeLa cells showed that mitochondrial semiquinone (SQ) radical was enhanced at 24 h after IR, suggesting increase of electron flow in ETC.