Pulmonary injury after combined exposures to low-dose low-LET radiation and fungal spores

Combined radiation burn injuries: A note

Combined radiation injury occurs when radiation is accompanied by any other form of trauma. The past experiences of Hiroshima, Nagasaki, and Chernobyl have revealed that a large number of victims of such nuclear accidents or attacks suffer from combined radiation injuries. The possibility of a nuclear attack seems very far-fetched, but the destruction that would occur in such an event would be massive, with a huge lossof lives. Therefore, preparedness for the same should be done beforehand. The severity of combined radiation depends upon various factors, such as radiation dose, type, tissues affected, and traumas. The article focuses on combined radiation burn injury (CRBI) which may arise due to the combination of ionising radiation with thermal burns. CRBI can have varied effects on different organs like the hematopoietic, digestive, lymphatic, cardiovascular, and respiratory systems. Some of the most profound lethal effects are hematopoietic dysfunction, gastrointestinal leakage, bacterial translocation to other organ sites, pulmonary fibrosis, and pneumonitis. In this article, we have attempted to accumulate the knowledge of ongoing research on the functioning of different organ systems, which are affected due to CRBI and possible countermeasures to minimize the effects, thus improving survival.

Increased susceptibility of irradiated mice to Aspergillus fumigatus infection via NLRP3/GSDMD pathway in pulmonary bronchial epithelia

Background

Aspergillus fumigatus infection is difficult to diagnose clinically and can develop into invasive pulmonary aspergillosis, which has a high fatality rate. The incidence of Aspergillus fumigatus infection has increased die to widespread application of radiotherapy technology. However, knowledge regarding A. fumigatus infection following radiation exposure is limited, and the underlying mechanism remains unclear. In this study, we established a mouse model to explore the effect of radiation on A. fumigatus infection and the associated mechanisms.

Methods

In this study, a mouse model of A. fumigatus infection after radiation was established by irradiating with 5 Gy on the chest and instilling 5 × 10⁷/ml Aspergillus fumigatus conidia into trachea after 24 h to explore the effect and study its function and mechanism. Mice were compared among the following groups: normal controls (CON), radiation only (RA), infection only (Af), and radiation + infection (RA + Af). Staining analyses were used to detect infection and damage in lung tissues. Changes in protein and mRNA levels of pyroptosis-related molecules were assessed by western blot analysis and quantitative reverse transcription polymerase chain reaction, respectively. Protein concentrations in the serum and alveolar lavage fluid were also measured. An immunofluorescence colocalization analysis was performed to confirm that NLRP3 inflammasomes activated pyroptosis.

Results

Radiation destroyed the pulmonary epithelial barrier and significantly increased the pulmonary fungal burden of A. fumigatus. The active end of caspase-1 and gasdermin D (GSDMD) were highly expressed even after infection. Release of interleukin-18 (IL-18) and interleukin-1β (IL-1β) provided further evidence of pyroptosis. NLRP3 knockout inhibited pyroptosis, which effectively attenuated damage to the pulmonary epithelial barrier and reduced the burden of A. fumigatus.

Conclusions

Our findings indicated that the activation of NLRP3 inflammasomes following radiation exposure increased susceptibility to A. fumigatus infection. Due to pyroptosis in lung epithelial cells, it resulted in the destruction of the lung epithelial barrier and further damage to lung tissue. Moreover, we found that NLRP3 knockout effectively inhibited the pyroptosis and reducing susceptibility to A. fumigatus infection and further lung damage. Overall, our results suggest that NLRP3/GSDMD pathway mediated-pyroptosis in the lungs may be a key event in this process and provide new insights into the underlying mechanism of infection.

Combined radiation and burn injury results in exaggerated early pulmonary inflammation

Events such as a nuclear meltdown accident or nuclear attack have potential for severe radiation injuries. Radiation injury frequently occurs in combination with other forms of trauma, most often burns. Thus far, combined injury studies have focused mainly on skin wound healing and damage to the gut. Since both radiation exposure and remote burn have pulmonary consequences, we examined the early effects of combined injury on the lung. C57BL/6 male mice were irradiated with 5 Gy of total body irradiation followed by a 15% total body surface area scald burn. Lungs from surviving animals were examined for evidence of inflammation and pneumonitis. At 48 h post-injury, pathology of the lungs from combined injury mice showed greater inflammation compared to all other treatment groups, with marked red blood cell and leukocyte congestion of the pulmonary vasculature. There was excessive leukocyte accumulation, primarily neutrophils, in the vasculature and interstitium, with occasional cells in the alveolar space. At 24 and 48 h post-injury, myeloperoxidase levels in lungs of combined injury mice were elevated compared to all other treatment groups (P < 0.01), confirming histological evidence of neutrophil accumulation. Pulmonary levels of the neutrophil chemoattractant KC (CXCL1) were 3 times above that of either injury alone (P < 0.05). Further, monocyte chemotactic protein-1 (MCP-1, CCL2) was increased two- and threefold compared to burn injury or radiation injury, respectively (P < 0.05). Together, these data suggest that combined radiation and burn injury augments early pulmonary congestion and inflammation. Currently, countermeasures for this unique type of injury are extremely limited. Further research is needed to elucidate the mechanisms behind the synergistic effects of combined injury in order to develop appropriate treatments.

Reactive oxygen species and x-ray disrupted spontaneous [Ca²⁺]I oscillation in alveolar macrophages

Radiation leads to a rapid burst of reactive oxygen species (ROS), which is considered to be one of the major causes of radiation-induced injury. ROS have previously been shown to induce changes in cytosolic Ca²⁺ ([Ca²⁺]i) including [Ca²⁺]i oscillation. However, the role of radiation in [Ca²⁺]i oscillation is poorly understood. The purpose of this study was to identify the effect of ROS and X ray on [Ca²⁺]i oscillation, as well as their role in radiation-induced lung injury. Alveolar macrophages were cultured in the absence and presence of different doses of hydrogen peroxide (H₂O₂) or exposed to X-ray irradiation with or without pretreatment of diphenyleneiodonium chloride (DPI, an inhibitor of NADPH oxidases) or tetrandrine (TET, a calcium entry blocker) and cytosolic Ca²⁺ concentration was detected by fluorescent Ca²⁺ indicator Fura-2. Rat radiation lung injury was induced in vivo by using 40 Gy X ray and DPI or TET was used to prevent radiation-induced lung injury. The results showed that there was spontaneous [Ca²⁺]i oscillation in alveolar macrophages under normal conditions, and treatment of H₂O₂ (100-500 μM) or 2 Gy X ray inhibited the spontaneous [Ca²⁺]i oscillation and induced [Ca²⁺]i rise. TET abolished H₂O₂ or X ray induced [Ca²⁺]i rise in alveolar macrophages, and attenuated X ray- induced rat alveolitis in vivo. DPI prevented X-ray-induced inhibition of [Ca²⁺]i oscillation in alveolar macrophages and prevented X-ray-induced rat alveolitis. Taken together, the data suggest that the disruption of [Ca²⁺]i oscillation and induction of [Ca²⁺]i rise through ROS is involved in the mechanism of radiation-induced lung injury.