Radiation-induced changes in lung tissue and development of fibrosis determined by quantitative morphometric methods

Captopril reduces lung inflammation and accelerated senescence in response to thoracic radiation in mice

The lung is sensitive to radiation and exhibits several phases of injury, with an initial phase of radiation-induced pneumonitis followed by delayed and irreversible fibrosis. The angiotensin-converting enzyme inhibitor captopril has been demonstrated to mitigate radiation lung injury and to improve survival in animal models of thoracic irradiation, but the mechanism remains poorly understood. Here we investigated the effect of captopril on early inflammatory events in the lung in female CBA/J mice exposed to thoracic X-ray irradiation of 17-17.9 Gy (0.5-0.745 Gy min-1). For whole-body + thoracic irradiation, mice were exposed to 7.5 Gy (0.6 Gy min-1) total-body 60Co irradiation and 9.5 Gy thoracic irradiation. Captopril was administered orally (110 mg kg-1 day-1) in the drinking water, initiated 4 h through to150 days post-irradiation. Captopril treatment increased survival from thoracic irradiation to 75% at 150 days compared with 0% survival in vehicle-treated animals. Survival was characterized by a significant decrease in radiation-induced pneumonitis and fibrosis. Investigation of early inflammatory events showed that captopril significantly attenuated macrophage accumulation and decreased the synthesis of radiation-induced interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) pro-inflammatory cytokines in the lungs of irradiated mice. Suppression of IL-1β and TNF-α correlated with an increase of the anti-inflammatory cytokine IL-10 in the spleen with captopril treatment. We also found that captopril decreased markers for radiation-induced accelerated senescence in the lung tissue. Our data suggest that suppression of inflammation and senescence markers, combined with an increase of anti-inflammatory factors, are a part of the mechanism for captopril-induced survival in thoracic irradiated mice.

A simple quantitative method for assessing pulmonary damage after x irradiation

Pulmonary damage after radiotherapy is typically characterized by an initial alveolar inflammation (pneumonitis) followed by chronic fibrosis. In the present study, changes in lung architecture were measured in the pneumonitis phase after whole-body low-dose X irradiation of C57BL/6 mice. Radiation damage was evaluated at 24 h and 1-8 weeks postirradiation. Three distinct scoring systems were used: ( 1 ) manually evaluating alveolar distortion and infiltration of inflammatory cells into the alveolar space using a continuous numerical scale across an entire lung section, ( 2 ) physically measuring the average thickness of the alveolar septa from multiple representative microscope fields, and ( 3 ) a new rapid automated mathematical algorithm based on image segmentation of alveolar space across an entire section. Each scoring method detected significant changes in alveolar architecture at the earliest times compared with sham-treated controls and gave comparable evaluations of injury. The results from the automated mathematical algorithm correlated significantly with both the manual evaluation method (Spearman's correlation coefficient rho = 0.044) and the direct physical measurement of septa thickness (rho = 0.002). These data demonstrate that evaluating alveolar space by segmentation analysis provides a reliable method for scoring early pulmonary radiation damage that is consistent with more established methodologies but is more rapid and is independent of potential operator and selection bias.

INFLAMMATORY CELL RECRUITMENT FOLLOWING THORACIC IRRADIATION

Ionizing radiation leads to a progressive injury in which a monocyte/macrophage-rich pneumonitis is followed by a chronic progressive fibrosis. In the present study, the role of macrophage/monocyte recruitment in the genesis of radiation-induced pulmonary fibrosis was examined. The objectives were threefold: (i) characterize the inflammatory cells recruited into the lung during the development of radiation-induced fibrosis; (ii) investigate changes in lung response following depletion of resident alveolar macrophages in vivo prior to radiation treatment; (iii) assess if inhalation of low levels of endotoxin would potentiate the radiation-initiated injury. One group of fibrosis-sensitive C57BL/6 mice was irradiated with a single dose of 15 Gy to the thorax. In a second group, resident inflammatory cells were depleted using clodronate, encapsulated into liposomes, 48 hours prior to irradiation with a single dose of 15 Gy to the thorax. Control animals were sham irradiated. All groups of animals then were examined 8, 16, or 24 weeks post irradiation. No difference in total cell numbers or cell differentials was observed between irradiated mice or those that were both liposome treated and irradiated at any time point. At 16 weeks, mice that received radiation showed a 5- to 6-fold increase in lymphocytes regardless of treatment as compared to control animals. At 24 weeks post irradiation, select groups were exposed to lipopolysaccharide (LPS) and examined 24 hours post inhalation. Lavageable protein was increased several fold in mice that received both radiation and LPS exposure as compared to 15 Gy or LPS exposure alone. These results demonstrate: (i) macrophages and lymphocytes are the predominately recruited cell types through 24 weeks post irradiation; (ii) recovery of inflammatory cells, regardless of prior macrophage depletion, were similar, suggesting that early responses are primarily driven by parenchymal cell injury; (iii) thoracic irradiation-induced injury can cause sensitization to a secondary stimulus that may result in injuries/responses not predicted by evaluating exposures individually.

Quantitation of allograft fibrosis and chronic allograft nephropathy

Despite improvements in the prevention and treatment of acute renal allograft rejection, the long-term survival of renal transplants has not increased. Immunologic and non-immunologic factors contribute to the gradual deterioration of graft function and to the histologic lesion characterized by vascular and interstitial fibrosis ('chronic rejection'). Quantitation of this process has been attempted using various invasive and non-invasive methods. These methods, performed at different times post-transplant, are reviewed in this article. In particular, pathology scoring systems and the potential of using computerized image analysis of biopsy material are discussed.

Oxidative stress in radiation-induced interstitial pneumonitis in the rat

The involvement of free radical metabolism in the pathogenesis of interstitial pneumonitis was investigated in an animal model. Male Wistar rats were irradiated at the thoracic region by gamma-rays from a 60Co source. Histopathological examination confirmed that 50% of the rats developed pneumonitis between 2 and 8 weeks following a single dose of 14 Gy. Parallel biochemical studies in the lung of these rats showed that mitochondria and microsomes had higher levels of lipid peroxidation. In the cytoplasmic fraction of the lung the activities of superoxide dismutase and catalase were markedly reduced in the pneumonitic rat. In lung mitochondria, however, the levels of these two enzymes were not significantly altered. On the contrary, lipid peroxidation and superoxide dismutase, as well as catalase activities in lung tissue in the non-pneumonitic group of the irradiated rat were comparable with that of control animals. The results indicate that free radical-induced oxidative stress following thoracic irradiation may be one of the causative factors in the development of interstitial pneumonitis.