Radioprotectant and radiosensitizer effects on sterility of gamma-irradiated bone

Gamma radiation is widely used to sterilize bone allografts but may impair their strength. While radioprotectant use may reduce radiation damage they may compromise sterility by protecting pathogens. We assessed the radioprotective potential of various agents (L-cysteine, N-acetyl-L-cysteine, L-cysteine-ethyl-ester and L-cysteine-methyl-ester) to identify those which do not protect spores of Bacillus subtilis. We hypothesized charge of these agents will affect their ability to radioprotect spores. We also determined ability of these radioprotectants and a radiosensitizer (nitroimidazole-linked phenanthridinium) to selectively sensitize spores to radiation damage by intercalating into the nucleic acid of spores. Spores were treated either directly in solutions of these agents or treated after being embedded and sealed in bone to assess the ability of these agents to diffuse into bone. L-cysteine and L-cysteine-ethyl-ester did not provide radioprotection. Positively charged L-cysteine-methyl-ester protected the spores, whereas positively charged L-cysteine-ethyl-ester did not, indicating charge does not determine the extent of radioprotection. The spores were sensitized to radiation damage when irradiated in nitroimidazole-linked phenanthridinium solution and sensitization disappeared after rinsing, suggesting nitroimidazole-linked phenanthridinium was unable to intercalate into the nucleic acid of the spores. Some cysteine-derived radioprotectants do not shield bacterial spores against gamma radiation and may be suitable for curbing the radiation damage to bone grafts while achieving sterility.