enalapril and Radiation-Pneumonitis

Victims of a radiological attack or nuclear accident may receive high-dose, heterogeneous exposures from radiation to the chest that lead to lung damage. Our goal is to develop countermeasures to mitigate such injuries. We used WAG/RijCmcr rats receiving 13 Gy to the whole thorax to induce pulmonary fibrosis within 210 days. The angiotensin converting enzyme (ACE) inhibitor enalapril was evaluated as a mitigator of these injuries at two doses (18 and 36 mg/m(2)/day) and 8 schedules: starting at 7, 35, 70, 105 and 140 days and continuing to 210 days or starting at 7 days and stopping at 30, 60 or 90 days after whole-thorax irradiation. The earliest start date at 7 days after irradiation would provide an adequate window of time for triage and dosimetry. Survival after 35 days, as permitted by our Institutional Animal Care and Use Committee (IACUC) was also recorded as a primary end point of pneumonitis. Pulmonary fibrosis was evaluated using the Sircol biochemical assay to measure lung collagen. Our results indicated that a short course of either dose of enalapril from 7-90 days improved survival. However, pulmonary fibrosis was only mitigated by the higher dose of enalapril (36 mg/m(2)/day). The latest effective start date for the drug was 35 days after irradiation. These results indicate that ACE inhibitors can be started at least a month after irradiation for mitigation of pneumonitis and/or pulmonary fibrosis.

Topics: Angiotensin-Converting Enzyme Inhibitors; Animals; Enalapril; Humans; Lung; Male; Radiation Injuries, Experimental; Radiation Pneumonitis; Rats; Thorax; Whole-Body Irradiation

Our long-term goal is to use angiotensin converting enzyme (ACE) inhibitors to mitigate the increase in lung collagen synthesis that is induced by irradiation to the lung, which could result from accidental exposure or radiological terrorism. Rats (WAG/RijCmcr) were given a single dose of 13 Gy (dose rate of 1.43 Gy/min) of X-irradiation to the thorax. Three structurally-different ACE inhibitors, captopril, enalapril and fosinopril were provided in drinking water beginning 1 week after irradiation. Rats that survived acute pneumonitis (at 6-12 weeks) were evaluated monthly for synthesis of lung collagen. Other endpoints included breathing rate, wet to dry lung weight ratio, and analysis of lung structure. Treatment with captopril (145-207 mg/m(2)/day) or enalapril (19-28 mg/m(2)/day), but not fosinopril (19-28 mg/m(2)/day), decreased morbidity from acute pneumonitis. Lung collagen in the surviving irradiated rats was increased over that of controls by 7 months after irradiation. This increase in collagen synthesis was not observed in rats treated with any of the three ACE inhibitors. Analysis of the lung morphology at 7 months supports the efficacy of ACE inhibitors against radiation-induced fibrosis. The effectiveness of fosinopril against fibrosis, but not against acute pneumonitis, suggests that pulmonary fibrosis may not be a simple consequence of injury during acute pneumonitis. In summary, three structurally-different ACE inhibitors mitigate the increase in collagen synthesis 7 months following irradiation of the whole thorax and do so, even when therapy is started one week after irradiation.

Topics: Angiotensin-Converting Enzyme Inhibitors; Animals; Captopril; Collagen; Dose-Response Relationship, Radiation; Drug Evaluation, Preclinical; Enalapril; Female; Fibrosis; Fosinopril; Gene Expression Regulation; Lung; Pulmonary Fibrosis; Radiation Pneumonitis; Rats; Renin-Angiotensin System; Thorax