Abstract
The identification of an agent effective for the treatment of intestinal and bone marrow injury following radiation exposure remains a major issue in radiological medicine. In this study, we evaluated the therapeutic impact of single agent or combination treatments with 2-(3-aminopropylamino) ethylsulphanyl phosphonic acid (WR-2721) and peptidoglycan (PGN, a toll-like receptor 2 (TLR-2) agonist) on radiation-induced injury of the intestine and bone marrow in lethally irradiated male C57BL/6 mice. A dose of 3 mg of WR-2721 per mouse (167 mg/kg, intraperitoneally) was given 30 min before irradiation, and 30 μg of PGN per mouse (1.7 mg/kg) was injected intraperitoneally 24 h after 10 Gy irradiation. Bone marrow cluster of differentiation (CD)45(+) and CD34(+) markers of multiple haematopoietic lineages, number of granulocyte-erythroid-macrophage-megakaryocyte (GEMM) progenitor colonies, bone marrow histopathology, leucine-rich repeat-containing G-protein-coupled receptor 5 (Lgr5) expression in the intestines, xylose absorption and intestinal histopathology were all assessed at various time-points after irradiation. Furthermore, nuclear factor kappa B (NF-κB) p65 protein in the ileum was stained by immunofluorescent labelling. PGN-treated irradiated mice showed an increase in CD45(+)CD34(+) cells compared with untreated mice 1.25 days after 10 Gy ionizing radiation (IR) (P < 0.05). Furthermore, combined PGN and WR-2721 treatment had an obviously synergistic radio-protective effect in nucleated cells in the bone marrow, including GEMM progenitors and CD45(+)CD34(+) cells 4 days after 10 Gy IR. Single agent PGN or WR-2721 treatment after 10 Gy IR clearly increased Lgr5-positive pit cells (P < 0.05) and xylose absorption (P < 0.05). However only PGN and WR-2721 combination treatment markedly increased villus height (P < 0.05), number of crypts (P < 0.05) and whole-body weights after 10 Gy whole-body irradiation (WBI). The NF-κB p65 subunit was translocated to the nucleus, and phosphate-IκBα (Ser32/Ser36) was detected after stimulation with either PGN or WR-2721, which indicates that these two agents act synergistically through the activation of the NF-κB pathway. Administration of PGN in combination with WR-2721 was demonstrated to have a synergistic effect on the increase in haematopoietic cells and intestinal reconstitution, as well as improved survival in lethally irradiated mice, but resulted in some degree of an immune disorder.