Radioprotectant and Radiosensitizer Effects on Sterility of γ-irradiated Bone

Abstract

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-cysteinemethyl-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.

Gamma Radiation Sterilization Reduces the High-cycle Fatigue Life of Allograft Bone

“…Methods to reduce the effect of irradiation or recover allograft strength therefore remain important to pursue. Irradiated bone allograft can be subjected to free radical scavenger treatment or crosslinking agents to restore some of the strength of the collagen backbone after testing [3,39,58,61,62]. Our study provides an S-N relationship at standard radiation dose, which can be useful in future studies that seek to maintain allograft strength after sterilization.…”

γ-Irradiation sterilized bone strengthened and toughened by ribose pre-treatment

“…Ribose was chosen because: (a) it can diffuse into the bone (o300 Da) (Kattaya et al, 2008;Tami et al, 2003), (b) it crosslinks bone collagen (Vashishth et al, 2001;Willett et al, 2013), (c) crosslinking is oxidation dependent (Fu et al, 1992), d) ribose polymerizes when exposed to γ-irradiation (Bailey et al, 1961) and e) good cytocompatibility of ribose cross-linked collagen matrices has been reported (Brodsky et al, 1990;Girton et al, 1999;Roy et al, 2008).…”

Effects of high-dose gamma irradiation on tensile properties of human cortical bone: Comparison of different radioprotective treatment methods

“…It is recommended to use a molecule with molecular weight smaller than 300 Da in order to increase the diffusion in cortical bone matrix (Akkus et al, 2005;Shuster, 2005). An investigation of the radioprotectant and radiosensitizer effects on sterility of gamma irradiated bones showed that the LC did not have radioprotective effect on spores of Bacillus subtilis irradiated in the range of 0.64 Mrad (Kattaya et al, 2008). Furthermore, it has been reported that the negatively and neutral charged scavengers are repelled from the capsule by the repulsion of charges, and therefore those scavengers do not enter the intracellular space and do not protect the bacteria (Shuster, 2005).…”

“…In this regard, Shuster (2005) suggested that the proper scavenger should allow for the protection of the collagen structure of the allograft tissue but not the pathogens during irradiation. In another study, Kattaya et al (2008) investigated some cysteine-derived radioprotectants which can efficiently perfuse bone yet minimally protect pathogens. They showed that LC radioprotectant does not shield bacterial spores against gamma radiation and may be suitable for curbing the radiation damage to bone grafts while achieving sterility.…”

“…Before irradiation, all samples of different groups were kept refrigerated (4 1C) to minimize bacterial degradation. The control and irradiated treatment groups were kept in similar solutions for 24 h (Kattaya et al, 2008) (the LC was absent from the solution used for keeping the control group). The LC treatment was conducted at room temperature.…”