Radiation-Induced Lung Injury Is Mitigated by Blockade of Gastrin-Releasing Peptide

Abstract

Gastrin-releasing peptide (GRP), secreted by pulmonary neuroendocrine cells, mediates oxidant-induced lung injury in animal models. Considering that GRP blockade abrogates pulmonary inflammation and fibrosis in hyperoxic baboons, we hypothesized that ionizing radiation triggers GRP secretion, contributing to inflammatory and fibrotic phases of radiation-induced lung injury (RiLI). Using C57BL/6 mouse model of pulmonary fibrosis developing ≥20 weeks after high-dose thoracic radiation (15 Gy), we injected small molecule 77427 i.p. approximately 1 hour after radiation then twice weekly for up to 20 weeks. Sham controls were anesthetized and placed in the irradiator without radiation. Lung paraffin sections were immunostained and quantitative image analyses performed. Mice exposed to radiation plus PBS had increased interstitial CD68(+) macrophages 4 weeks after radiation and pulmonary neuroendocrine cells hyperplasia 6 weeks after radiation. Ten weeks later radiation plus PBS controls had significantly increased pSmad2/3(+) nuclei/cm(2). GRP blockade with 77427 treatment diminished CD68(+), GRP(+), and pSmad2/3(+) cells. Finally, interstitial fibrosis was evident 20 weeks after radiation by immunostaining for α-smooth muscle actin and collagen deposition. Treatment with 77427 abrogated interstitial α-smooth muscle actin and collagen. Sham mice given 77427 did not differ significantly from PBS controls. Our data are the first to show that GRP blockade decreases inflammatory and fibrotic responses to radiation in mice. GRP blockade is a novel radiation fibrosis mitigating agent that could be clinically useful in humans exposed to radiation therapeutically or unintentionally.

Gastrin-releasing peptide induces fibrotic response in MRC5s and proliferation in A549s

“…In another study, hyperplasia of PNECs, increased nuclear p-Smad2/3 immunoreactivity, induced α-SMA expression and interstitial collagen accumulation were observed in the 6th, 10th and 20th weeks following the administration of high-dose of thoracic radiation to murine lungs. The administrations of GRP antagonist to mice (1 h after radiation exposure on the 20th week) resulted in the regression of these alterations [16]. Although this last study showed that GRP might modulate the pathogenesis of pulmonary fibrosis, the target cells and signalling pathways of GRP-mediated generation of fibrotic response were not investigated.…”

“…These alterations in the pathway resulted in a fibrotic response in the lung, by increasing the expression of α-SMA and procollagen-1 genes. Although there is no direct evidence that GRP stimulates TGF-β signalling pathway, Zhou and colleagues showed that the radiation induced fibrosis by increasing the number of p-Smad2/3 immunoreactive cells in the lungs of mice and the administration of GRP inhibitor regressed the pulmonary fibrosis by decreasing the number of p-Smad2/3 in the lungs [16]. The present study reveals that GRP stimulates Smad3-dependent TGF-β1 signalling, by increasing the expressions of SMAD3 and SMAD4 mRNAs, total Smad2/3, p-Smad2/ 3 and Smad4 proteins and reducing the expression of SMAD7 mRNA in MRC5 cells.…”

“…Ashour and colleagues detected exogenous GRP-induced myofibroblast proliferation, and an increased thickness of the alveolar wall in new-born murine lungs [15]. Recently, an increased number of PNECs and macrophages containing GRP in the lung of mouse exposed to ionizing irradiation has been reported in addition to increased alpha-smooth muscle actin (α-SMA) and p-Smad2/3 immunoreactive cells associated with the fibrotic response [16]. These data clearly show the possible contribution of GRP released from PNECs to pulmonary fibrosis generation.…”

Constrictive bronchiolitis in diffuse idiopathic pulmonary neuroendocrine cell hyperplasia

“…[25] The most widely accepted pathophysiologic mechanism underlying the development of peribronchiolar fibrosis and constrictive bronchiolitis in DIPNECH is that bioactive substances (e.g., bombesin) secreted in larger-than-normal amount by the hyperplastic PNECs exert pro-fibrotic and pro-inflammatory effects on the adjacent airways. [8,26] , [27] This hypothesis triggered some physicians to propose two plausible therapeutic approaches to DIPNECH: 1) using SSAs to decrease the secretion of bioactive substances from the hyperplastic PNECs, [10,28] and 2) using steroids (inhaled and/or systemic) to control inflammation and prevent further parenchymal and airway damage. [13] Nassar et al summarized 25 cases of DIPNECH reported in the literature.…”

Oxygen, Gastrin-Releasing Peptide, and Pediatric Lung Disease: Life in the Balance

“…Using a well-characterized mouse model of PF developing ~20 weeks after high-dose thoracic RT (15 Gy) (104), we injected GRP blocking small molecule 77427 1 h after RT then twice weekly for up to 20 weeks (8). Mice given RT plus PBS had increased interstitial CD68 + macrophages 4 weeks later and increased GRP + /PGP9.5 + PNECs 6 weeks later.…”