Brian L. Fish

Control of radiation-induced pneumopathy and lung fibrosis by angiotensin-converting enzyme inhibitors and an angiotensin II type 1 receptor blocker

Purpose : This report summarizes our experiences on the protective effect of angiotensin-converting enzyme (ACE) inhibitors, especially captopril and an angiotensin II type 1 receptor blocker on radiation-induced pulmonary injury. Method : In the first series of experiments, adult male Sprague Dawley rats were given a single dose of either 20 or 30 Gy of gamma rays to a 35 cm 2 right hemithorax port, whilst shielding the left, contralateral, lung. Perfusion scans and autopsies were performed at intervals up to 12 months post-radiation. Three different ACE inhibitors, penicillamine and pentoxifylline were given as radiation protectors and their activity compared. A model of irradiation for total bone marrow transplant (BMT) was used for the second group of experiments. Male WAC/Rij/MCW rats received total-body irradiation and a regimen of cyclophosphamide (CTX) in preparation for bone marrow transplant. The modifiers were two ACE inhibitors, captopril and enalapril, and L-158,809, an angiotensin II (A II) type 1 receptor blocker. All drugs were administered in the rats‚ drinking water and all were well-tolerated. Results : In the irradiated rats, pulmonary damage progressed from the presence of blebs and detachment from basement membranes of endothelial cells a few days after injury, to severe arteritis and interstitial collagen deposition at 3 months, and then on to severe pneumonitis and extensive pulmonary fibrosis at 6 months. Marked increase of hydroxyproline was also found in the lungs at 6 months. These morphological changes were associated with significant decrease of ACE and plasminogen activator activity (PLA) and a marked increase of prostaglandins (PG12) and thromboxane (Txa2), substances considered as indicators of endothelial pulmonary damage. ACE inhibitors captopril, CL 24817, enalapril and CGS 13945 prevented the markers of endothelial dysfunction. Captopril and CL 24817, which contain a sulphydryl (-SH) radical in their moiety and the AII type 1 receptor blocker, L-158,809, were the most efficient in protecting the lung parenchyma from the inflammatory response and subsequent fibrosis. Penicillamine, an SH-containing compound with weak ACE inhibitory activity was also a strong antifibrotic agent but showed only modest anti-inflammatory properties. Additionally, in the irradiated rats, captopril also reduced the incidence of squamous cell skin carcinomas and subcutaneous sarcomas consequent to the highest doses of radiation. Conclusion : ACE inhibitors and one AII type 1 receptor blocker were effective in protecting lungs from radiation-induced pneumonitis and the development of lung fibrosis in two models of rat radiation injury. In the first series of experiments (unilateral irradiation), those ACE inhibitors containing a sulphydryl radical were more effective than those without it. This observation led to the question of whether this protective effect is related to inhibition of AII synthesis or rather to some of the collateral pharmacologic properties of these drugs, such as anti-oxidation or protease inhibition. The AII receptor blocker, however, was shown to be equally effective, if not better, in its antifibrotic capacity than any ACE inhibitor with or without an SH radical, reaffirming the role of AII in modulation of collagen synthesis.

Late toxicity of total body irradiation with bone marrow transplantation in a rat model

In defined-flora, barrier-maintained rats, radiation nephritis is the principle late toxicity seen after high dose-rate total body irradiation (TBI), when hematologic toxicity is prevented by bone marrow transplantation (BMT). Pneumonitis develops only if rats are placed in a conventional microbiological environment during and after BMT. Low dose-rate TBI gives qualitatively similar late toxicity, but at radiation doses twice as large. Fractionation of the TBI has little effect on the bone marrow ablation doses, but results in increased gastrointestinal and renal tolerance. The addition of immunosuppressive or cytotoxic drugs (cyclosporine-A, methotrexate, cis-platinum) after TBI and BMT greatly decreases the dose of TBI that can be tolerated. The use of a cyclophosphamide plus cytosine arabinoside conditioning regimen prior to TBI and BMT increases the bone marrow ablation dose, but has no effect on acute gastrointestinal toxicity or on renal toxicity. These results indicate that substantial late toxicity may be associated with the TBI conditioning regimens used for BMT even in the absence of cytotoxic and antibiotic drugs, immunosuppressive agents, infection and graft-versus-host disease; and that radiation may be a contributing factor in the nephritis sometimes observed after TBI and BMT.

Renin-Angiotensin System Suppression Mitigates Experimental Radiation Pneumonitis

PURPOSE To find the mitigators of pneumonitis induced by moderate doses of thoracic radiation (10-15 Gy). METHODS AND MATERIALS Unanesthetized WAG/RijCmcr female rats received a single dose of X-irradiation (10, 12, or 15 Gy at 1.615 Gy/min) to the thorax. Captopril (an angiotensin-converting enzyme inhibitor) or losartan (an angiotensin receptor blocker) was administered in the drinking water after irradiation. Pulmonary structure and function were assessed after 8 weeks in randomly selected rats by evaluating the breathing rate, ex vivo vascular reactivity, and histopathologic findings. Survival analysis was undertaken on all animals, except those scheduled for death. RESULTS Survival after a dose of 10 Gy to the thorax was not different from that of unirradiated rats for <or=1 year. Survival decreased to <50% by 45 weeks after 12 Gy and by 8-9 weeks after 15 Gy. Captopril (17-56 mg/kg/d) improved survival and reduced radiation-induced increases in breathing rate, changes in vascular reactivity, and histopathologic evidence of injury. Radiation-induced increases in the breathing rate were prevented even if captopril was started 1 week after irradiation or if it was discontinued after 5 weeks. Losartan, although effective in reducing mortality, was not as efficacious as captopril in mitigating radiation-induced increases in the breathing rate or altered vasoreactivity. CONCLUSION In rats, a moderate thoracic radiation dose induced pneumonitis and morbidity. These injuries were mitigated by captopril even when it was begun 1 week after radiation or if discontinued 5 weeks after exposure. Losartan was less effective in protecting against radiation-induced changes in vascular reactivity or tachypnea.

Treatment of radiation nephropathy with ace inhibitors

PURPOSE A previous study showed that radiation nephritis could be treated with captopril, an angiotensin-converting-enzyme inhibitor. These studies were designed to determine whether other angiotensin-converting-enzyme inhibitors would be effective, whether captopril would inhibit the development of the histopathologic lesions typical of radiation nephritis, and whether captopril could be used to treat the nephropathy observed in bone marrow transplant recipients conditioned with total body irradiation. METHODS AND MATERIALS In radiation nephritis studies, rats were given 17-27 Gy bilateral renal irradiation in 5 fractions. Six months after irradiation animals were stratified by blood urea nitrogen and assigned to no treatment, or treatment with captopril (500 mg/l) or enalapril (50 mg/l) in the drinking water. A subset of animals was sacrificed for histopathology after 3 months; the remaining animals continued on drugs for 7 months. In the bone marrow transplant nephropathy study, rats received 14-17 Gy total body irradiation in 6 fractions over 3 days followed by syngeneic bone marrow transplant. Six months after irradiation, animals were stratified by blood urea nitrogen and assigned to no treatment, or treatment with captopril (500 mg/l). Animals remained on drugs for 6 months. In all studies animals were followed with periodic renal function tests. RESULTS In the radiation nephritis study, survival and renal function were significantly enhanced by both captopril and enalapril, but there were no significant differences between the drugs. The histopathologic severity of the lesions of radiation nephritis correlated with the degree of renal dysfunction; and in irradiated animals with equal initial azotemia, captopril-treated rats developed less severe renal lesions. Finally, captopril also prolonged survival and preserved renal function in this rat bone marrow transplant nephropathy model. CONCLUSION Angiotensin-converting-enzyme inhibitors are an effective treatment for both radiation nephritis and bone marrow transplant nephropathy.

10 GY TOTAL BODY IRRADIATION INCREASES RISK OF CORONARY SCLEROSIS, DEGENERATION OF HEART STRUCTURE AND FUNCTION IN A RAT MODEL

Purpose: To determine the impact of 10 Gy total body irradiation (TBI) or local thorax irradiation, a dose relevant to a radiological terrorist threat, on lipid and liver profile, coronary microvasculature and ventricular function. Materials and methods: WAG/RijCmcr rats received 10 Gy TBI followed by bone marrow transplantation, or 10 Gy local thorax irradiation. Age-matched, non-irradiated rats served as controls. The lipid profile and liver enzymes, coronary vessel morphology, nitric oxide synthase (NOS) isoforms, protease activated receptor (PAR)-1 expression and fibrinogen levels were compared. Two-dimensional strain echocardiography assessed global radial and circumferential strain on the heart. Results: TBI resulted in a sustained increase in total and low density lipoprotein (LDL) cholesterol (190 ± 8 vs. 58 ± 6; 82 ± 8 vs. 13 ± 3 mg/dl, respectively). The density of small coronary arterioles was decreased by 32%. Histology revealed complete blockage of some vessels while cardiomyocytes remained normal. TBI resulted in cellular peri-arterial fibrosis whereas control hearts had symmetrical penetrating vessels with less collagen and fibroblasts. TBI resulted in a 32 ± 4% and 28 ± 3% decrease in endothelial NOS and inducible NOS protein, respectively, and a 21 ± 4% and 35 ± 5% increase in fibrinogen and PAR-1 protein respectively, after 120 days. TBI reduced radial strain (19 ± 8 vs. 46 ± 7%) and circumferential strain (−8 ± 3 vs. −15 ± 3%) compared to controls. Thorax-only irradiation produced no changes over the same time frame. Conclusions: TBI with 10 Gy, a dose relevant to radiological terrorist threats, worsened lipid profile, injured coronary microvasculature, altered endothelial physiology and myocardial mechanics. These changes were not manifest with local thorax irradiation. Non-thoracic circulating factors may be promoting radiation-induced injury to the heart.

ACE Inhibitors and AII Receptor Antagonists in the Treatment and Prevention of Bone Marrow Transplant Nephropathy

Radiation nephropathy has emerged as a major complication of bone marrow transplantation (BMT) when total body irradiation (TBI) is used as part of the regimen. Classically, radiation nephropathy has been assumed to be inevitable, progressive, and untreatable. However, in the early 1990s, it was demonstrated that experimental radiation nephropathy could be treated with a thiol-containing ACE inhibitor, captopril. Further studies showed that enalapril (a non-thiol ACE inhibitor) was also effective in the treatment of experimental radiation nephropathy, as was an AII receptor antagonist. Studies also showed that ACE inhibitors and AII receptor antagonists were effective in the prophylaxis of radiation nephropathy. Interestingly, other types of antihypertensive drugs were ineffective in prophylaxis, but brief use of a high-salt diet in the immediate post-irradiation period decreased renal injury. A placebo-controlled trial of captopril to prevent BMT nephropathy in adults is now underway. Since excess activity of the renin-angiotensin system (RAS) causes hypertension, and hypertension is a major feature of radiation nephropathy; an explanation for the efficacy of RAS antagonism in the prophylaxis of radiation nephropathy would be that radiation leads to RAS activation. However, current studies favor an alternative explanation, namely that the normal activity of the RAS is deleterious in the presence of radiation injury. On-going studies suggest that efficacy of RAS antagonists may involve interactions with a radiation-induced decrease in renal nitric oxide activity or with radiation-induced tubular cell proliferation. We hypothesize that while prevention (prophylaxis) of radiation nephropathy with ACE inhibitors, AII receptor antagonists, or a high-salt diet work by suppression of the RAS, the efficacy of ACE inhibitors and AII receptor antagonists in treatment of established radiation nephropathy depends on blood pressure control.

Treatment of radiation nephropathy with captopril

Both experimental and clinical radiation nephropathy are typically progressive, evolving to kidney failure over weeks to months. Other late radiation injuries (spinal cord, lung) are also progressive and have no known specific antidote. Recent reports of the efficacy of captopril in modifying radiation injury of the lung prompted this trial of captopril in treating established radiation nephropathy. Six months after 15-27 Gy in 12 fractions bilateral renal irradiation, 72 rats with blood urea nitrogen > 4.1 mmol/liter were started on captopril (500 mg/liter) or no drug in the drinking water. Subsequent survival was significantly enhanced in rats receiving captopril as opposed to no drug (P = 0.0013), and the rate of rise of blood urea nitrogen was significantly diminished (P < 0.0001) in the animals on captopril. Urine protein excretion was also reduced from initially elevated levels in the rats on captopril compared to levels in rats given no drug. We conclude that captopril therapy preserves kidney function, reduces proteinuria, and enhances survival in experimental radiation nephropathy.

Radiation nephropathy is treatable with an angiotensin converting enzyme inhibitor or an angiotensin II type-1 (AT1) receptor antagonist.

BACKGROUND AND PURPOSE Previous studies showed that progression of established radiation nephropathy could be delayed by continuous treatment with high doses of captopril, an angiotensin-converting-enzyme (ACE) inhibitor. The current studies were designed to determine whether a lower dose or a shorter treatment with captopril would be effective and whether an angiotensin II type-1 (AT1) receptor antagonist (AII blocker) would be effective. MATERIALS AND METHODS In the captopril studies, rats were given renal irradiation at doses sufficient to produce radiation nephropathy. Six months after irradiation, animals were stratified by azotemia and assigned to no treatment, continuous high- or low-dose captopril, or 6 weeks of high-dose captopril. Captopril was given in drinking water at 62.5 mg/l (low dose) or 500 mg/l (high dose). The AII blocker study had a similar design, except that the nephropathy was the result of total body irradiation and bone marrow transplantation and the treatments were no treatment or continuous treatment with an AII blocker, L-158,809 (20 mg/l in drinking water). Animals were followed for 1 year with periodic studies of renal function. RESULTS Survival and renal function were significantly enhanced by all treatments. Continuous captopril treatment was more effective than the 6-week course of treatment, but there was no difference in effectiveness between the high and low doses of captopril. In continuous therapy, captopril and the AII blocker had roughly equivalent efficacy. CONCLUSIONS Both the ACE inhibitor and the AII blocker were effective treatments for established radiation nephropathy. The best results with the ACE inhibitor required continuous therapy, but could be achieved with a low dose of the drug.

Angiotensin II receptor antagonists in the treatment and prevention of radiation nephropathy

PURPOSE Angiotensin-converting enzyme (ACE) inhibitors are effective in the prophylaxis of radiation-induced renal and lung injury. Studies were designed to determine whether blocking the angiotensin II (AII) receptor, rather than blocking AII synthesis with ACE inhibitors, would also be effective. MATERIALS AND METHODS Rats received total body irradiation (TBI) followed by bone marrow transplantation (BMT), and were randomized to: an ACE inhibitor (captopril); an AII type 1 (AT1) receptor antagonist (L-158,809); or no treatment. Drug therapy began 9 days prior to BMT and continued for the duration of the study. RESULTS Analysis of renal function, histopathology and animal survival showed that the AII blocker was more effective than the ACE inhibitor in the prophylaxis of BMT nephropathy. Further studies have shown that the AII blocker is as effective as captopril in the treatment of established radiation nephropathy, and that the AII blocker is at least as effective as captopril in the prophylaxis of lung injury induced by chemo-radiation therapy. CONCLUSIONS These studies indicate that blockage of the AT1 receptor by itself is sufficient for the treatment of radiation-induced renal and lung injury, hence the renin-angiotensin system is fundamentally involved in the pathogenesis of these injuries. These studies provide further evidence that there is more to late radiation injuries than delayed mitotic cell death.

Angiotensin II receptor antagonists in the prevention of radiation nephropathy

Angiotensin-converting enzyme (ACE) inhibitors can be used to prevent the development of radiation nephropathy. Current studies were designed to determine whether blocking the angiotensin II (AII) receptor, rather than preventing the creation of AII, would be effective in the prophylaxis of radiation nephropathy. Rats received 17 Gy total-body irradiation (TBI) in six fractions followed by syngeneic bone marrow transplantation (BMT). Prior to TBI the rats were randomized to groups receiving an ACE inhibitor (captopril), an AII type 1 (AT1) receptor antagonist (L-158,809) or no treatment. Renal function was assessed over 40 weeks, and a subset of animals were sacrificed for histopathology at 33 weeks. Renal function deteriorated progressively in animals receiving TBI alone, leading to renal failure by 34 weeks. Renal function was significantly better in animals receiving either captopril or L-158,809, and none of these animals had progressed to renal failure by 43 weeks. Analysis of both renal function and histopathology shows that the AII receptor antagonist is more effective than the ACE inhibitor in the prophylaxis of BMT nephropathy. This indicates that a reduction of activation of the AT1 receptor by AII, by itself, is sufficient for the prophylaxis of radiation nephropathy.