Mg ATP and antioxidants augment the radioprotective effect of surfactant copolymers

Mediated by reactive oxygen species, the damaging effects of high-intensity ionizing irradiation on tissues are dose, frequency, oxygen concentration, and tissue property dependent. Intense ionizing irradiation exposure may cause rapid cellular necrosis by peroxidation of membrane lipids leading to membrane disruption. This leads to a loss of the transmembrane ionic gradients and a subsequent depletion of the cellular ATP store, followed by cellular generation of reactive oxygen species. When membrane disruption is extensive, acute cellular necrosis follows. Triblock copolymer surfactants, such as Poloxamer 188 (P188), are able to seal damaged rhabdomyocyte membranes, increasing post-irradiation viability. Separated rat rhabdomyocytes were exposed to 40 Gy (Co 1.5 Gy min) irradiation and treated at 20 min intervals with combination permutations of P188, N-acetylcysteine (NAC), and Mg-ATP. Cell viability at 18 and 48 h was determined using Calcein-AM and Ethidium Homodimer-1 staining. At 18 h after irradiation, the combined administration of P188, ATP, and NAC restored cell viability rates to near sham-exposed levels of 60%. At 48 h post-irradiation, cell viability dropped substantially to the 7-20% range, regardless of attempted intervention. Nevertheless, the combination of P188, ATP, and NAC more than doubled cell viability at the 48-h time point. Neither 8 kDa polyethylene glycol nor 10 kDa neutral dextran was as effective in enhancing cell viability. These results indicate that antioxidants and cellular energy substrates improve the efficacy of membrane-sealing copolymer surfactants in prolonging cellular viability following massive radiation exposure.