Laminin 332 deposition is diminished in irradiated skin in an animal model of combined radiation and wound skin injury.

Skin exposure to ionizing radiation affects the normal wound healing process and greatly impacts the prognosis of affected individuals. We investigated the effect of ionizing radiation on wound healing in a rat model of combined radiation and wound skin injury. Using a soft X-ray beam, a single dose of ionizing radiation (10-40 Gy) was delivered to the skin without significant exposure to internal organs. At 1 h postirradiation, two skin wounds were made on the back of each rat. Control and experimental animals were euthanized at 3, 7, 14, 21 and 30 days postirradiation. The wound areas were measured, and tissue samples were evaluated for laminin 332 and matrix metalloproteinase (MMP) 2 expression. Our results clearly demonstrate that radiation exposure significantly delayed wound healing in a dose-related manner. Evaluation of irradiated and wounded skin showed decreased deposition of laminin 332 protein in the epidermal basement membrane together with an elevated expression of all three laminin 332 genes within 3 days postirradiation. The elevated laminin 332 gene expression was paralleled by an elevated gene and protein expression of MMP2, suggesting that the reduced amount of laminin 332 in irradiated skin is due to an imbalance between laminin 332 secretion and its accelerated processing by elevated tissue metalloproteinases. Western blot analysis of cultured rat keratinocytes showed decreased laminin 332 deposition by irradiated cells, and incubation of irradiated keratinocytes with MMP inhibitor significantly increased the amount of deposited laminin 332. Furthermore, irradiated keratinocytes exhibited a longer time to close an artificial wound, and this delay was partially corrected by seeding keratinocytes on laminin 332-coated plates. These data strongly suggest that laminin 332 deposition is inhibited by ionizing radiation and, in combination with slower keratinocyte migration, can contribute to the delayed wound healing of irradiated skin.

Mitigation of radiation injuries via suppression of the renin-angiotensin system: emphasis on radiation nephropathy.

Radiation nephropathy and other normal tissue radiation injuries can be successfully mitigated, and also treated, by antagonists of the renin-angiotensin system (RAS). This implies a mechanistic role for that system in radiation nephropathy, yet no evidence exists to date of activation of the RAS by irradiation. RAS antagonists, including angiotensin converting enzyme inhibitors and angiotensin receptor blockers, are the standard of care in the treatment of subjects with other chronic progressive kidney diseases, in which they exert benefit by reducing both glomerular and tubulo-interstitial injury. These drugs are likely to act in a similar way to mitigate radiation nephropathy.

Vascular injury after whole thoracic x-ray irradiation in the rat.

PURPOSE: To study vascular injury after whole thoracic irradiation with single sublethal doses of X-rays in the rat and to develop markers that might predict the severity of injury. METHODS AND MATERIALS: Rats that received 5- or 10-Gy thorax-only irradiation and age-matched controls were studied at 3 days, 2 weeks, and 1, 2, 5, and 12 months. Several pulmonary vascular parameters were evaluated, including hemodynamics, vessel density, total lung angiotensin-converting enzyme activity, and right ventricular hypertrophy. RESULTS: By 1 month, the rats in the 10-Gy group had pulmonary vascular dropout, right ventricular hypertrophy, increased pulmonary vascular resistance, increased dry lung weights, and decreases in total lung angiotensin-converting enzyme activity, as well as pulmonary artery distensibility. In contrast, irradiation with 5 Gy resulted in only a modest increase in right ventricular weight and a reduction in lung angiotensin-converting enzyme activity. CONCLUSION: In a previous investigation using the same model, we observed that recovery from radiation-induced attenuation of pulmonary vascular reactivity occurred. In the present study, we report that deterioration results in several vascular parameters for

Treatment of radiation nephropathy with ACE inhibitors and AII type-1 and type-2 receptor antagonists.

Radiation nephropathy has emerged as a significant complication of bone marrow transplantation and radionuclide radiotherapy, and is a potential sequela of radiological terrorism and radiation accidents. In the early 1990's, it was demonstrated that experimental radiation nephropathy could be treated with a thiol-containing ACE inhibitor, captopril. Further studies have shown that enalapril (a non-thiol ACE inhibitor) is also effective in the treatment of experimental radiation nephropathy, as are both AII type-1 (AT(1)) and type-2 (AT(2)) receptor antagonists. ACE inhibitors and AII receptor antagonists are also effective in the mitigation (prevention) of radiation nephropathy. Other types of antihypertensive drugs are ineffective in mitigation, but brief use of a high-salt diet in the immediate post-irradiation period significantly decreases renal injury. There are differences between mitigation and treatment of radiation nephropathy that imply that different mechanisms are operating. First, a high-salt diet is effective in the mitigation of radiation nephropathy, but deleterious on the treatment of established disease. Second, AT(1) blockade is more effective than ACE inhibition for mitigation of radiation nephropathy, but equally effective for treatment. Third, the efficacy of AT(1) blockade and ACE inhibition is highly dependent on drug dose in mitigation of radiation nephropathy, but not so in treatment. Finally, while AT(2) blockade augments the benefit of AT(1) blockade in mitigation of radiation nephropathy, it does not do so in treatment. We hypothesize that while mitigation of radiation nephropathy works by suppression of the renin-angiotensin system, treatment of established radiation nephropathy requires blood pressure control in addition to (or possibly instead of) suppression of the renin-angiotensin system.

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 1990's, 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.

Dietary sodium modification and experimental radiation nephropathy.

PURPOSE: To determine whether suppression of the renin-angiotensin system (RAS) with high dietary sodium (salt) has the same beneficial effect on radiation nephropathy as suppression of the RAS with angiotensin-converting-enzyme (ACE) inhibitors or angiotensin II (AII) receptor antagonists. MATERIALS AND METHODS: Normal and irradiated rats were placed on high- or low-salt diets and assessed for effects on blood pressure, on AII levels and on the development of radiation nephropathy. RESULTS: In unirradiated animals, a high-salt diet suppressed AII and caused hypertension, while a low-salt diet produced no detectable effects. Use of a high-salt diet 3-9 weeks after irradiation exacerbated radiation-induced hypertension but attenuated the development of radiation nephropathy. Continuous use of a high-salt diet slowed the progression of radiation nephropathy, but eventually exacerbated radiation-induced hypertension and accelerated renal failure. Use of a high-salt diet in animals with established radiation nephropathy was deleterious. A low-salt diet had no effect on the development of radiation nephropathy. CONCLUSIONS: These studies provide further support for the hypothesis that the beneficial effect of AII receptor antagonists, ACE inhibitors and high dietary sodium in the prophylaxis of radiation nephropathy is due to their suppression of the RAS, not to their anti-hypertensive effects.

Prevention of radiation-induced nephropathy and fibrosis in a model of bone marrow transplant by an angiotensin II receptor blocker.

Nephropathy, interstitial pneumopathy, and renal and lung fibrosis are major complications of bone marrow transplantation (BMT). This study evaluated the antifibrotic property of an angiotensin II (A2) type-1 receptor blocker (L-159,809) and compared it with those of Captopril and Enalapril, two angiotensin-converting enzyme (ACE) inhibitors, in a rat model of BMT. Male WAG/Rij/MCW rats received a preparative regimen of 60 mg/kg body wt of cytoxan (i.p., Days 9 and 8) and 18.5 Gy of total body irradiation (TBI) in six twice daily fractions (Days 2, 1, and 0) followed immediately (Day 0) by BMT. Modifiers were given in drinking water from Day 10 until autopsy, 8 weeks after BMT. Rats treated with TBI plus cytoxan alone developed severe nephropathy. Trichrome staining showed marked collagen deposition in glomeruli, renal interstitium, and renal arteries and arterioles (especially in their adventitia). Collagen deposition and renal damage were markedly reduced by the three modifiers. Of the three, L-158,809-treated rats had slightly thinner vessels and slightly less collagen than nonirradiated normal controls. The study shows the effectiveness of these drugs in the protection of the renal parenchyma from the development of radiation-induced fibrosis. It also indicates a role for angiotensin II in the modulation of collagen synthesis.

Induction of heme oxygenase 1 in radiation nephropathy: role of angiotensin II.

Datta, P. K., Moulder, J. E., Fish, B. L., Cohen, E. P. and Lianos, E. A. Induction of Heme Oxygenase 1 in Radiation Nephropathy: Role of Angiotensin II. Radiat. Res. 155, 734-739 (2001). In a rat model of radiation-induced nephropathy, we investigated changes in expression of heme oxygenase 1 (Hmox1, also known as HO-1), an enzyme that catalyzes conversion of heme into biliverdin, carbon monoxide and iron. The study explored whether radiation induces Hmox1 expression in the irradiated kidney and whether angiotensin II (AII) mediates Hmox1 expression in glomeruli isolated from irradiated kidneys. To assess the effects of radiation on Hmox1 expression, rats received 20 Gy bilateral renal irradiation and were randomized to groups receiving an AII type 1 (AT(1)) receptor antagonist (L-158,809) or no treatment. Drug treatment began 9 days prior to bilateral renal irradiation and continued for the duration of the study. Estimation of Hmox1 levels in glomerular protein lysates assessed by Western blot analysis revealed a significant increase in Hmox1 protein at 50 and 65 days postirradiation. In animals treated with the AT(1) receptor antagonist, there was no induction of Hmox1, suggesting that AII may be a mediator of Hmox1 induction. To confirm that AII stimulates Hmox1 expression, animals were infused with 200, 400 or 800 ng/kg min(-1) of AII for 18-19 days, and Hmox1 protein levels in glomeruli were assessed. There was a significant induction of Hmox1 in glomeruli of animals infused with 800 ng/kg min(-1) of AII. These studies demonstrate that glomerular Hmox1 expression is elevated in the middle phase of radiation nephropathy and that AII can increase glomerular Hmox1 levels.

Early detection of radiation-induced glomerular injury by albumin permeability assay.

Renal irradiation leads predictably to glomerular vascular injury, cell lysis, matrix accumulation, sclerosis and loss of renal function. The immediate effects of renal irradiation that may be associated with glomerular pathology and proteinuria are not clear in the human disease or its rat model. We hypothesized that radiation-induced injury causes immediate and subtle alterations in glomerular physiology independent of the neurohumoral and hemodynamic regulatory mechanisms. We employed a sensitive in vitro functional assay of glomerular albumin permeability (P(alb)) to demonstrate radiation-induced damage to the glomerular filtration barrier immediately after total-body irradiation of rats. In blinded experiments, control rats were sham-treated, and experimental rats received 9.5 Gy X rays. Rats were killed humanely at 1 h to 9 weeks after irradiation and glomeruli were isolated. In parallel experiments, glomeruli were isolated from normal rats and irradiated in vitro. The change in glomerular capillary permeability due to an experimental oncotic gradient was determined using videomicroscopy and P(alb) was calculated. Results show that in vivo or in vitro irradiation of glomeruli caused an increased P(alb) at 1 h. Increased P(alb) was observed up to 3 weeks after irradiation. Glomeruli from mice irradiated with 9.5 or 19.0 Gy X rays did not show increased P(alb) at 1 h postirradiation. We conclude that glomerular protein permeability of irradiated rats increases in a dose-dependent manner immediately after irradiation and that it appears to be independent of hemodynamic or systemic influences.

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 cm2 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.

MRI measurements correctly predict the relative effects of tumor oxygenating agents on hypoxic fraction in rodent BA1112 tumors.

PURPOSE: We evaluate whether magnetic resonance imaging (MRI) with blood oxygenation level-dependent (BOLD) contrast correctly predicts the relative effects of tumor-oxygenating agents on hypoxic fraction in BA1112 rhabdomyosarcomas in WAG/Rij rats. METHODS AND MATERIALS: The response of ten tumors to carbogen (95% O(2)/5% CO(2)), a perfluorocarbon emulsion (PFC), and the combination of PFC + carbogen was studied with high spectral and spatial resolution MR imaging of the water resonance at 4.7 Tesla. Decreases in MR signal linewidth indicate increases in tumor blood oxygen levels. RESULTS: Average MR signal linewidth was decreased 2.0% by carbogen, 2.5% by PFC + air, and 4.9% by PFC + carbogen. PFC + carbogen caused a larger linewidth decrease than either treatment alone (p < 0.04 by ANOVA). Maps of pixels responding to treatment indicate that combining PFC with carbogen significantly enlarges the area of the tumor in which oxygen levels are increased (p < 0.01 by ANOVA). CONCLUSION: MRI predicts that PFC + carbogen will increase radiosensitivity more than either treatment alone; this agrees with the known effects of these treatments on hypoxic fraction. Utilizing MRI to choose the treatment that maximizes the size and extent of increases in tumor oxygenation could reduce hypoxic fraction.

Stenotic glomerulotubular necks in radiation nephropathy.

Fibrosis of the renal interstitium is well correlated with kidney function and a greater extent of fibrosis predicts renal failure. Recent work has shown striking fibrotic constrictions at the glomerulotubular neck in porcine radiation nephropathy and in Wegener's granulomatosis in man. The present studies were designed to identify stenotic necks in a third species and to evaluate the effect of captopril treatment. Experimental radiation nephropathy was established with 17 Gy total body irradiation of barrier-maintained rats. Kidneys were obtained at 99 and 203 days for histology, using perfusion fixation. There was renal injury, with a rise in BUN, as expected, which was attenuated by captopril treatment. There was stenotic neck formation at 99 and 203 days. Captopril did not influence the absolute fraction of necks that were stenotic but it did prevent the evolution of glomeruli with necks to atubular glomeruli. It is concluded that stenosis of the glomerulotubular neck is a general phenomenon of any scarring kidney disease; that stenotic necks are probably an intermediate step in the evolution towards atubular glomeruli; and that timely use of captopril may prevent the progression of a stenotic neck towards an atubular glomerulus.

Angiotensin II infusion exacerbates radiation nephropathy.

We hypothesized that angiotensin II will exacerbate radiation nephropathy in a time-specific manner. Experimental radiation nephropathy is treatable with angiotensin-converting enzyme inhibition or angiotensin II (AII) receptor blockers. These interventions are particularly important between 3 and 10 weeks after irradiation. We therefore undertook studies in which AII infusions were given at particular intervals after irradiation. Rats received total body irradiation (TBI) plus syngeneic bone marrow transplantation followed (or not) by AII infusion at 200 or 400 ng/kg/min. Infusions were given from 0 to 4 or 4 to 8 weeks after irradiation. An additional group was unirradiated but infused at 800 ng/kg/min for 8 weeks. Kidney function was assessed over 26 weeks, and histology was evaluated after the animals were killed. AII infusion alone did not cause azotemia. There was transient hypertension during AII infusion at 800 ng/kg/min but only minor histologic injury. Irradiation caused azotemia and hypertension, which were not exacerbated by AII infusion at 200 ng/kg/min. Irradiation plus AII infusion at 400 ng/kg/min from 4 to 8 weeks after TBI caused significantly greater azotemia than irradiation alone or irradiation with AII infusion from 0 to 4 weeks. The blood pressure was higher in irradiated rats infused with AII from 4 to 8 weeks. Arteriolar fibrinoid necrosis was a prominent feature in kidneys of rats infused with AII from 4 to 8 weeks after TBI. The worsening of radiation nephropathy by AII infusion from 4 to 8 weeks after irradiation strongly supports the idea of specific and sequential events in the pathogenesis of kidney failure in this model. Hypertension may play a role in these events in addition to the effect of AII alone. The occurrence of arteriolar fibrinoid necrosis in the irradiated, 4-to-8-week-infused animals suggests that vascular injury during that interval determines later outcome.

TGF-beta 1 production in radiation nephropathy: role of angiotensin II.

PURPOSE: Angiotensin II receptor antagonists are effective in the prophylaxis of radiation nephropathy. Studies were designed to determine whether TGF-beta 1, a fibrogenic cytokine, plays a role in mediating the protective effect of AII antagonism. These studies explored the time-course of glomerular TGF-beta 1 production in the irradiated kidney, and whether AII mediates TGF-beta 1 production in glomeruli isolated from irradiated rats. MATERIALS AND METHODS: Rats received 20 Gy of bilateral renal irradiation in five fractions and were randomized to receive an AII type 1 receptor antagonist (L-158,809) at 20mg/l in their drinking water, or no treatment. Drug therapy began 9 days prior to irradiation and continued for the duration of the study. RESULTS: Analysis of renal function showed a significant increase in urinary proteinuria and blood urea nitrogen by 37 days and 63 days after irradiation, respectively. Estimation of glomerular TGF-beta1 levels by quantitative sandwich enzyme immunoassay technique revealed a significant increase in latent but not active TGF-beta 1 levels at 50 days and 63 days after irradiation. In animals treated with the AT1 receptor antagonist, there was a complete elimination in the rise of TGF-beta 1. CONCLUSIONS: These studies demonstrate that glomerular TGF-beta 1 production is elevated in the course of radiation nephropathy, and that AII mediates this induction of TGF-beta 1.

Brief pharmacological intervention in experimental radiation nephropathy.

Brief postirradiation treatment with an angiotensin-converting enzyme (ACE) inhibitor has been shown to be effective in reducing the severity of radiation nephropathy in rats. The efficacy of brief treatment with an ACE inhibitor was shown to be greatest when the animals were young when irradiated and when the treatment was given 4 to 10 weeks after bone marrow transplantation (BMT). In further studies with a BMT nephropathy model, we have shown that brief treatment with an angiotensin II type I receptor antagonist (AII blocker) is even more effective than brief treatment with an ACE inhibitor. We have also shown that an NO synthase inhibitor, which exacerbated radiation nephropathy when given continuously, has no effect when given during the postirradiation interval when ACE inhibitors and AII blockers were most effective. Studies also showed that the loss of efficacy of brief treatment with increased age at irradiation parallels the decrease in radiosensitivity that occurs with increasing age at irradiation, but that this decrease in radiosensitivity is not sufficient to explain the loss of efficacy of brief treatment. These data indicate that the renin-angiotensin system is important in the expression of renal radiation injury, particularly between 4 and 10 weeks after irradiation.

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.

Successful brief captopril treatment in experimental radiation nephropathy.

Experimental renal irradiation is followed by a well-defined sequence of events leading to kidney failure. Inhibitors of angiotensin-converting enzyme can prevent the structural and functional changes that occur after renal irradiation, which suggests that the renin-angiotensin system plays a key role in their evolution. We therefore evaluated captopril, used for short intervals, in a total body irradiation model of radiation nephropathy. Irradiated 7- to 8-week-old rats that were treated with captopril from 3.5 to 9.5 weeks after irradiation had better kidney function and survival than irradiated animals treated at earlier or later intervals. At 26 weeks after irradiation, kidney function of these animals was similar to that of irradiated animals treated continuously with captopril, but their subsequent survival was less. Animals irradiated at 7 to 8 weeks of age and treated with captopril from 6 to 9 weeks after irradiation had better function and survival than animals treated at earlier or later intervals. Irradiated 15-week-old animals had significant functional and survival benefit from continuous captopril treatment but no protection from a 6-week interval of therapy. We conclude that radiation nephropathy may be significantly attenuated by the use of captopril from 3.5 to 9.5 weeks after irradiation in young animals. Although older animals did not appear to benefit from a short course of captopril, these data suggest that the renin-angiotensin system is important in the sequential expression of renal radiation injury, particularly between 3.5 and 9.5 weeks after irradiation.

Noncontinuous use of angiotensin converting enzyme inhibitors in the treatment of experimental bone marrow transplant nephropathy.

Angiotensin-converting enzyme (ACE) inhibitors can be used to prevent the development of radiation nephropathy after BMT. In previous BMT nephropathy studies, ACE inhibitor therapy was started pre-BMT and continued indefinitely. In preparation for clinical trials, studies were designed to determine whether effective prophylaxis could be achieved if ACE inhibitor therapy was started after engraftment, and to determine whether ACE inhibitors needed to be given indefinitely. The present studies in our rat syngeneic BMT model showed that captopril therapy started 25 days post-BMT was as effective as therapy started prior to BMT. When ACE inhibitor therapy was discontinued 28 weeks after BMT, the protective effect was not lost if adequate control of azotemia had been maintained for 26 weeks. If adequate control of azotemia was not maintained for 26 weeks, BMT nephropathy progressed rapidly when ACE inhibitor therapy ended, and slowly when it was continued. Failure to control azotemia was a better predictor of renal failure than failure to control hypertension or proteinuria. Based on these preclinical studies, it would appear that ACE inhibitor therapy will be effective in the prophylaxis of BMT nephropathy even if begun after engraftment, and that ACE inhibitors may not need to be given indefinitely.

Vitamin A deficiency alters rat neutrophil function.

Previous studies showed a higher percentage of neutrophils from vitamin A deficient rats are hypersegmented and contain lower levels of cathepsin G than the neutrophils from control rats. In this study chemotaxis, phagocytosis and oxidant generation were studied using either isolated neutrophils or neutrophils in whole blood from four dietary groups of rats: 1) vitamin A deficient rats; 2) vitamin A deficient rats that received vitamin A for 16, 8, 4 or 2 d prior to killing; 3) weight-matched rats pair-fed a vitamin A-complete diet; and 4) rats fed nonrestricted, vitamin A complete diet. Chemotaxis towards P. aeruginosa conditioned medium and formylated methinyl leucinyl phenylalanine was significantly lower for neutrophils from vitamin A-deficient rats than for neutrophils from weight-matched pair-fed rats, nonrestricted vitamin A sufficient rats and vitamin A deficient rats that received vitamin A for 16 d prior to killing. No differences in chemotaxis towards activated rat serum were noted among the neutrophils from the four groups of rats. Adhesion of P. aeruginosa organisms, phagocytosis of these organisms and generation of active oxidative molecules were significantly lower in the neutrophils from the vitamin A-deficient rats relative to these functions in the neutrophils from the vitamin A deficient rats that received vitamin A for 16 d, weight-matched rats pair-fed a vitamin A complete diet; and rats fed nonrestricted, vitamin A-complete diet. Eight days after vitamin A administration to vitamin A deficient rats, the ability of the neutrophils to phagocytose P. aeruginosa organisms and to generate active oxidant molecules was restored to the levels observed for weight-matched, pair-fed rats and rats fed nonrestricted, vitamin A complete diet. The elucidated alterations in neutrophil function in vitamin A deficient rats probably contribute to the altered ability of vitamin A deficient rats to fight infections.