Wound-induced alterations in survival of 60Co irradiated mice: importance of wound timing

Cell Therapies for Acute Radiation Syndrome

The risks of severe ionizing radiation exposure are increasing due to the involvement of nuclear powers in combat operations, the increasing use of nuclear power, and the existence of terrorist threats. Exposure to a whole-body radiation dose above about 0.7 Gy results in H-ARS (hematopoietic acute radiation syndrome), which is characterized by damage to the hematopoietic system; higher doses result in further damage to the gastrointestinal and nervous systems. Only a few medical countermeasures for ARS are currently available and approved for use, although others are in development. Cell therapies (cells or products produced by cells) are complex therapeutics that show promise for the treatment of radiation injury and have been shown to reduce mortality and morbidity in animal models. Since clinical trials for ARS cannot be ethically conducted, animal testing is extremely important. Here, we describe cell therapies that have been tested in animal models. Both cells and cell products appear to promote survival and lessen tissue damage after whole-body irradiation, although the mechanisms are not clear. Because radiation exposure often occurs in conjunction with other traumatic injuries, animal models of combined injury involving radiation and future countermeasure testing for these complex medical problems are also discussed.

Combined injury: irradiation with skin or bone wounds in rodent models

A radiation combined injury is defined as an injury that occurs in the setting of irradiation, such as those expected after a nuclear accident, radiation dispersal device release (a 'dirty bomb'), or a nuclear weapon detonation. There is much research on irradiation-associated burns and their healing, but there is less known about other injuries sustained in the context of irradiation. Animal models are limited in their correlations to clinical situations but can support research on specific questions about injuries and their healing. Mouse models of irradiation with skin or bone wounds are validated as highly reproducible and quantitative. They show dose-dependent impairment of wound healing, with later recovery. Irradiation-induced delay of bone wound healing was mitigated to different extents by single doses of gramicidin S-nitroxide JP4-039, a plasmid expressing manganese superoxide dismutase, amifostine/WR2721, or the bifunctional sulfoxide MMS-350. These models should be useful for research on mechanisms of radiation dermal and osseous damage and for further development of new radioprotectors. They also provide information of potential relevance to the effects of clinical radiation therapies.

Wound Trauma Exacerbates Acute, but not Delayed, Effects of Radiation in Rats: Mitigation by Lisinopril

The goal of this study is to understand and mitigate the effects of wounds on acute radiation syndrome (ARS) and delayed effects of acute radiation exposure (DEARE), for preparedness against a radiological attack or accident. Combined injuries from concomitant trauma and radiation are likely in these scenarios. Either exacerbation or mitigation of radiation damage by wound trauma has been previously reported in preclinical studies. Female WAG/RijCmcr rats received 13 Gy X-rays, with partial-body shielding of one leg. Within 2 h, irradiated rats and non-irradiated controls were given full-thickness skin wounds with or without lisinopril, started orally 7 days after irradiation. Morbidity, skin wound area, breathing interval and blood urea nitrogen were measured up to 160 days post-irradiation to independently evaluate wound trauma and DEARE. Wounding exacerbated morbidity in irradiated rats between 5 and 14 days post-irradiation (during the ARS phase), and irradiation delayed wound healing. Wounding did not alter delayed morbidities from radiation pneumonitis or nephropathy after 30 days post-irradiation. Lisinopril did not mitigate wound healing, but markedly decreased morbidity during DEARE from 31 through 160 days. The results derived from this unique model of combined injuries suggest different molecular mechanisms of injury and healing of ARS and DEARE after radiation exposure.

Hemorrhage enhances cytokine, complement component 3, and caspase-3, and regulates microRNAs associated with intestinal damage after whole-body gamma-irradiation in combined injury

Hemorrhage following whole-body γ-irradiation in a combined injury (CI) model increases mortality compared to whole-body γ-irradiation alone (RI). The decreased survival in CI is accompanied by increased bone marrow injury, decreased hematocrit, and alterations of miRNA in the kidney. In this study, our aim was to examine cytokine homeostasis, susceptibility to systemic bacterial infection, and intestinal injury. More specifically, we evaluated the interleukin-6 (IL-6)-induced stress proteins including C-reactive protein (CRP), complement 3 (C3), Flt-3 ligand, and corticosterone. CD2F1 male mice received 8.75 Gy 60Co gamma photons (0.6 Gy/min, bilateral) which was followed by a hemorrhage of 20% of the blood volume. In serum, RI caused an increase of IL-1, IL-2, IL-3, IL-5, IL-6, IL-12, IL-13, IL-15, IL-17A, IL-18, G-CSF, CM-CSF, eotaxin, IFN-γ, MCP-1, MIP, RANTES, and TNF-α, which were all increased by hemorrhage alone, except IL-9, IL-17A, and MCP-1. Nevertheless, CI further elevated RI-induced increases of these cytokines except for G-CSF, IFN- γ and RANTES in serum. In the ileum, hemorrhage in the CI model significantly enhanced RI-induced IL-1β, IL-3, IL-6, IL-10, IL-12p70, IL-13, IL-18, and TNF-α concentrations. In addition, Proteus mirabilis Gram(-) was found in only 1 of 6 surviving RI mice on Day 15, whereas Streptococcus sanguinis Gram(+) and Sphingomonas paucimobilis Gram(-) were detected in 2 of 3 surviving CI mice (with 3 CI mice diseased due to inflammation and infection before day 15) at the same time point. Hemorrhage in the CI model enhanced the RI-induced increases in C3 and decreases in CRP concentrations. However, hemorrhage alone did not alter the basal levels, but hemorrhage in the CI model displayed similar increases in Flt-3 ligand levels as RI did. Hemorrhage alone altered the basal levels of corticosterone early after injury, which then returned to the baseline, but in RI mice and CI mice the increased corticosterone concentration remained elevated throughout the 15 day study. CI increased 8 miRNAs and decreased 10 miRNAs in serum, and increased 16 miRNA and decreased 6 miRNAs in ileum tissue. Among the altered miRNAs, CI increased miR-34 in the serum and ileum which targeted an increased phosphorylation of ERK, p38, and increased NF-κB, thereby leading to increased iNOS expression and activation of caspase-3 in the ileum. Further, let-7g/miR-98 targeted the increased phosphorylation of STAT3 in the ileum, which is known to bind to the iNOS gene. These changes may correlate with cell death in the ileum of CI mice. The histopathology displayed blunted villi and villus edema in RI and CI mice. Based on the in silico analysis, miR-15, miR-99, and miR-100 were predicted to regulate IL-6 and TNF. These results suggest that CI-induced alterations of cytokines/chemokines, CRP, and C3 cause a homeostatic imbalance and may contribute to the pathophysiology of the gastrointestinal injury. Inhibitory intervention in these responses may prove therapeutic for CI and improve recovery of the ileal morphologic damage.

Further Characterization of the Mitigation of Radiation Lethality by Protective Wounding

There continues to be a major effort in the United States to develop mitigators for the treatment of mass casualties that received high-intensity acute ionizing radiation exposures from the detonation of an improvised nuclear device during a radiological terrorist attack. The ideal countermeasure should be effective when administered after exposure, and over a wide range of absorbed doses. We have previously shown that the administration of a subcutaneous incision of a defined length, if administered within minutes after irradiation, protected young adult female C57BL/6 mice against radiation-induced lethality, and increased survival after total-body exposure to an LD_50/30 X-ray dose from 50% to over 90%. We refer to this approach as "protective wounding". In this article, we report on our efforts to further optimize, characterize and demonstrate the validity of the protective wounding response by comparing the response of female and male mice, varying the radiation dose, the size of the wound, and the timing of wounding with respect to administration of the radiation dose. Both male and female mice that received a subcutaneous incision after irradiation were significantly protected from radiation lethality. We observed that the extent of protection against lethality after an LD_50/30 X-ray dose was independent of the size of the subcutaneous cut, and that a 3 mm subcutaneous incision is effective at enhancing the survival of mice exposed to a broad range of radiation doses (LD₁₅-LD₁₀₀). Over the range of 6.2-6.7 Gy, the increase in survival observed in mice that received an incision was associated with an enhanced recovery of hematopoiesis. The enhanced rate of recovery of hematopoiesis was preceded by an increase in the production of a select group of cytokines. Thus, a thorough knowledge of the timing of the cytokine cascade after wounding could aid in the development of novel pharmacological radiation countermeasures that can be administered several days after the actual radiation exposure.

Enhanced survival from radiation pneumonitis by combined irradiation to the skin

PURPOSE

To develop mitigators for combined irradiation to the lung and skin.

METHODS

Rats were treated with X-rays as follows: (1) 12.5 or 13 Gy whole thorax irradiation (WTI); (2) 30 Gy soft X-rays to 10% area of the skin only; (3) 12.5 or 13 Gy WTI + 30 Gy skin irradiation after 3 hours; (4) 12.5 Gy WTI + skin irradiation and treated with captopril (160 mg/m(2)/day) started after 7 days. Our end points were survival (primary) based on IACUC euthanization criteria and secondary measurements of breathing intervals and skin injury. Lung collagen at 210 days was measured in rats surviving 13 Gy WTI.

RESULTS

After 12.5 Gy WTI with or without skin irradiation, one rat (12.5 Gy WTI) was euthanized. Survival was less than 10% in rats receiving 13 Gy WTI, but was enhanced when combined with skin irradiation (p < 0.0001). Collagen content was increased at 210 days after 13 Gy WTI vs. 13 Gy WTI + 30 Gy skin irradiation (p < 0.05). Captopril improved radiation-dermatitis after 12.5 Gy WTI + 30 Gy skin irradiation (p = 0.008).

CONCLUSIONS

Radiation to the skin given 3 h after WTI mitigated morbidity during pneumonitis in rats. Captopril enhanced the rate of healing of radiation-dermatitis after combined irradiations to the thorax and skin.

Subcutaneous wounding postirradiation reduces radiation lethality in mice

The detonation of an improvised nuclear device during a radiological terrorist attack could result in the exposure of thousands of civilians and first responders to lethal or potentially lethal doses of ionizing radiation (IR). There is a major effort in the United States to develop phamacological mitigators of radiation lethality that would be effective particularly if administered after irradiation. We show here that giving female C57BL/6 mice a subcutaneous surgical incision after whole body exposure to an LD50/30 X-ray dose protects against radiation lethality and increases survival from 50% to over 90% (P = 0.0001). The increase in survival, at least in part, appears to be due to enhanced recovery of hematopoiesis, notably red blood cells, neutrophils and platelets. While a definitive mechanism has yet to be elucidated, we propose that this approach may be used to identify potentially novel mechanisms and pathways that could aid in the development of novel pharmacological radiation countermeasures.

Skin injuries reduce survival and modulate corticosterone, C-reactive protein, complement component 3, IgM, and prostaglandin E 2 after whole-body reactor-produced mixed field (n + γ-photons) irradiation

Skin injuries such as wounds or burns following whole-body γ-irradiation (radiation combined injury (RCI)) increase mortality more than whole-body γ-irradiation alone. Wound-induced decreases in survival after irradiation are triggered by sustained activation of inducible nitric oxide synthase pathways, persistent alteration of cytokine homeostasis, and increased susceptibility to systemic bacterial infection. Among these factors, radiation-induced increases in interleukin-6 (IL-6) concentrations in serum were amplified by skin wound trauma. Herein, the IL-6-induced stress proteins including C-reactive protein (CRP), complement 3 (C3), immunoglobulin M (IgM), and prostaglandin E2 (PGE2) were evaluated after skin injuries given following a mixed radiation environment that might be found after a nuclear incident. In this report, mice received 3 Gy of reactor-produced mixed field (n + γ-photons) radiations at 0.38 Gy/min followed by nonlethal skin wounding or burning. Both wounds and burns reduced survival and increased CRP, C3, and PGE2 in serum after radiation. Decreased IgM production along with an early rise in corticosterone followed by a subsequent decrease was noted for each RCI situation. These results suggest that RCI-induced alterations of corticosterone, CRP, C3, IgM, and PGE2 cause homeostatic imbalance and may contribute to reduced survival. Agents inhibiting these responses may prove to be therapeutic for RCI and improve related survival.

The Effect of Whole-body γ-irradiation on Localized β-irradiation-induced Skin Reactions in Mice

The combined effects of whole-body radiation and localized radiation trauma have received scant experimental attention. However, in the recent accidents at Chernobyl and Goiania skin damage from beta-contamination was combined with total-body radiation and in many cases the skin lesions which covered large surfaces of the body were severe and recovery was prolonged. This paper models the immunosuppressive effects of whole-body gamma-radiation in the sublethal to lethal range (1-11 Gy) on the skin reactions produced by 50 Gy of superficial beta-radiation. For gamma ray doses < 4 Gy no synergistic effects were detectable. For gamma-ray doses of 4, 6 and 8 Gy there was a 4-5-day prolongation in time-course of the skin reaction but no significant exacerbation of its severity. The overall time for the resolution of the skin reaction (45 days) was also unaffected by the relatively high whole-body doses. These rather surprising findings of minimal synergy between whole-body exposure and a localized severe beta burn to the skin are perhaps explained by the mismatch between the maximal immunosuppression at 2-10 days postirradiation and the timing of the skin damage at 10-25 days.

Quantitative study of wound infection in irradiated mice

Bacterial infection of simple wounds was studied directly and quantitatively in adult mice given 6.5 Gy 60Co. Three days later, when neutropenia was evident, the skin and the medial gluteus muscle of anaesthetized mice were incised. A suspension of Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae or Streptococcus pyogenes was inoculated into the wound. Bacteria per mg muscle were enumerated 3, 4 or 7 days later. The geometric means of bacteria per mg were greater in irradiated than in non-irradiated mice. Phagocytic cells were present in the wounded tissue. Hence sublethal ionizing radiation enhanced the susceptibility of mice to infections of wounds by these four bacterial species.