Biomedical subjects

W F Ward

Publications and source records attributed to W F Ward.

At least 19 recordsLinked to original sources

PubMed1997

Effect of age on the activity of phosphoenolpyruvate carboxykinase in the kidney following fasting and refeeding.

The activity of renal phosphoenolpyruvate carboxykinase (PEPCK) was measured in 3-18 month old male Fischer 344 rats after alternate periods of fasting and refeeding. To compare the induction of renal PEPCK activity in response to fasting in young and old rats, 3, 6, 12 and 18 month old animals were fasted for 30 h followed by a 24 h ad libitum refeeding period to reduce PEPCK activity toward basal levels. The refeeding period was followed by a second 24 h fasting period during which the time course of PEPCK induction was monitored in the young and old animals. The first fast resulted in over a 20% increase in renal PEPCK activity in the 3 month old and slightly over a 70% increase in the 6 month old animals. In contrast, the activity did not increase significantly in the 12 or 18 month old animals during this fasting period. Therefore the induction of PEPCK in the kidney in response to fasting appears to be altered in the older animals. Refeeding for 24 h resulted in a decrease in PEPCK activity in all four age groups; therefore there was no indication of an age-related impairment in the response of renal PEPCK to refeeding. After the refeeding period, the food was removed again and the activity was measured at short intervals over the next 24 h to determine the time course of the induction in PEPCK activity. Interestingly, during the second fast, the activity of renal PEPCK was not significantly induced in either the young or the older animals. However, the activity measured in the older 18 month rats was consistently lower during the first 12 h of the second fast as compared to the activity in the 6 month old rats. In summary, the induction of PEPCK activity in the kidney is altered with age during an initial fast; in addition, PEPCK activity is not induced in either young or old rats during a second fasting period.

Age Factors↗

PubMed1997

Annexin I concentration and prostacyclin production in rat lung and alveolar macrophages following irradiation.

The purpose of this study was to gather additional evidence in irradiated rat lung on the relationship between annexin I and prostaglandin synthesis. The right hemithorax of the animal was exposed to a single dose of 0 or 30 Gy of X-rays, and the animals were killed 3 months postirradiation. Levels of annexin I and synthesis of prostacyclin (PGI2) were determined in lungs, in cell-free bronchoalveolar lavage (BAL) fluid, and in macrophages lavaged from those lungs. In addition, protein concentration, lactate dehydrogenase (LDH) activity and macrophage count in BAL fluid obtained from irradiated lung were compared with that from sham-irradiated (0 Gy) lung. Levels of annexin I, the putative inhibitor of phospholipase A2, in lung and cell-free BAL fluid were decreased in samples from irradiated animals. By contrast, the level of annexin I in macrophages lavaged from irradiated lung was higher than that in macrophages from sham-irradiated lung. The irradiated lung produced nearly 3.5 times more prostacyclin than did the control lung. However, prostacyclin synthesis by macrophages lavaged from irradiated lung was no different than that of macrophages from sham-irradiated lung. Protein, LDH and macrophage number in BAL fluid from irradiated lungs were significantly higher than in corresponding specimens from sham-irradiated lungs. These data demonstrate that reduced levels of annexin I, as well as increased protein concentration, LDH activity and macrophage numbers in irradiated rat lung are reflected in BAL fluid. Therefore, information obtained from BAL fluid, but not from BAL macrophages, reflects lung status, and may serve as a minimally invasive index of radiation pneumonitis in this model. In irradiated lung, increased PGI2 synthesis coupled with a decreased annexin I level are consistent with the hypothesis of an inhibitory role of annexin I in prostaglandin metabolism. However, this hypothesis is not supported by findings in BAL macrophages, where increased annexin I concentration is not accompanied by a decrease in PGI2 production. In view of the latter findings, and a previous study from our laboratory demonstrating that phospholipase activity in irradiated rat lung is in fact decreased, despite the reduction in annexin I concentration and the hyperproduction of prostanoids, it would seem unlikely that annexin I negatively modulates prostaglandin synthesis via inhibition of phospholipase in this model.

6-Ketoprostaglandin F1 alpha↗

PubMed1997

KGF facilitates repair of radiation-induced DNA damage in alveolar epithelial cells.

Administration of exogenous keratinocyte growth factor (KGF) prevents or attenuates several forms of oxidant-mediated lung injury. Because DNA damage in epithelial cells is a component of radiation pneumotoxicity, we determined whether KGF ameliorated DNA strand breaks in irradiated A549 cells. Cells were exposed to 137Cs gamma rays, and DNA damage was measured by alkaline unwinding and ethidium bromide fluorescence after a 30-min recovery period. Radiation induced a dose-dependent increase in DNA strand breaks. The percentage of double-stranded DNA after exposure to 30 Gy increased from 44.6 +/- 3.5% in untreated control cells to 61.6 +/- 5.0% in cells cultured with 100 ng/ml KGF for 24 h (P < 0.05). No reduction in DNA damage occurred when the cells were cultured with KGF but maintained at 0 degree C during and after irradiation. The sparing effect of KGF on radiation-induced DNA damage was blocked by aphidicolin, an inhibitor of DNA polymerases-alpha, -delta, and -epsilon and by butylphenyl dGTP, which blocks DNA polymerase-alpha strongly and polymerases-delta and -epsilon less effectively. However, dideoxythymidine triphosphate, a specific inhibitor of DNA polymerase-beta, did not abrogate the KGF effect. Thus KGF increases DNA repair capacity in irradiated pulmonary epithelial cells, an effect mediated at least in part by DNA polymerases-alpha, -delta, and -epsilon. Enhancement of DNA repair capability after cell damage may be one mechanism by which KGF is able to ameliorate oxidant-mediated alveolar epithelial injury.

Aphidicolin↗

PubMed1996

Captopril inhibits angiogenesis and slows the growth of experimental tumors in rats.

Captopril, an inhibitor of angiotensin converting enzyme, is widely used clinically to manage hypertension and congestive heart failure. Here captopril is shown to be an inhibitor of angiogenesis able to block neovascularization induced in the rat cornea. Captopril acted directly and specifically on capillary endothelial cells, inhibiting their chemotaxis with a biphasic dose-response curve showing an initial decrease at clinically achievable doses under 10 microM and a further slow decline in the millimolar range. Captopril inhibition of endothelial cell migration was not mediated by angiotensin converting enzyme inhibition, but was suppressed by zinc. Direct inhibition by captopril of zinc-dependent endothelial cell-derived 72-and 92-kD metalloproteinases known to be essential for angiogenesis was also seen. When used systemically on rats captopril inhibited corneal neovascularization and showed the antitumor activity expected of an inhibitor of angiogenesis, decreasing the number of mitoses present in carcinogen-induced foci of preneoplastic liver cells and slowing the growth rate of an experimental fibrosarcoma whose cells were resistant to captopril in vitro. These data define this widely used drug as a new inhibitor of neovascularization and raise the possibility that patients on long term captopril therapy may derive unexpected benefits from its antiangiogenic activities.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed1996

Effect of age and food restriction on alkaline protease activity in rat liver.

The effect of age and food restriction on the hepatic alkaline protease activity of 100,000 x g supernatant has been investigated using 7-, 16-, and 26-month-old Fischer 344 rats. The proteasome, a major component of alkaline protease activity, is activated by sodium dodecyl sulfate (SDS) and this property was exploited to gain insight into the effects of age and food restriction on proteasome activity. Three alkaline protease activities, chymotrypsin-like (ChT-L), trypsin-like (T-L), and peptidylglutamyl peptide hydrolyzing (PGPH) activities were measured. These activities are also commonly used as measurement of proteasomal activities. Basal ChT-L and PGPH activities were not markedly altered by either age or food restriction. The level of T-L activity did not change with age, but was decreased by food restriction. SDS-activated ChT-L activity increased 15% between 7 and 26 months of age and this increase was blocked by food restriction. SDS-activated PGPH activity decreased 40% and the decrease was ameliorated by food restriction. In conclusion, we have shown that the alteration of alkaline protease activities by age and food restriction is not uniform and that the changes observed are likely due to alterations of proteasomal activity. The lack of uniformity in these alterations indicates that any assessment of alkaline protease activity requires the measurement of more than one of the enzymatic activities. Lastly, the first evidence suggesting that age and food restriction can modulate proteasomal activity is presented.

Aging↗

PubMed1996

Alteration of rat liver 20S proteasome activities by age and food restriction.

The effects of age and food restriction on proteasome function in rat liver supernatant (100,000 x g) were investigated. The cellular level of the proteasome has been quantitated by using Western blot analysis. The level of the proteasome was not affected by either age or food restriction. The three best-characterized proteasomal peptidase activities, chymotrypsin-like (ChT-L), trypsin-like (T-L), and peptidylglutamyl peptide hydrolyzing (PGPH) activities, were measured in the presence and absence of the proteasomal activator, sodium dodecyl sulfate (SDS). Basal ChT-L, T-L, and PGPH activities were not markedly affected by either age or food restriction. SDS-stimulated ChT-L and T-L activities increased approximately 15% and approximately 30%, respectively, between 7 and 26 months of age, and the increase of both activities was prevented by food restriction. In marked contrast, the SDS-stimulated PGPH activity decreased approximately 40% with age. Food restriction, while not preventing the age-related decline, maintained higher levels of SDS-stimulated PGPH activity at all ages. The proteolytic activity of the proteasome toward casein was not altered by either age or food restriction. In conclusion, the cellular level of the proteasome as well as the caseinolytic activity of the proteasome appear to be unaffected by either age or food restriction. It appears unlikely that the proteasome activity changes are related to the reported age-associated decline of protein degradation. Simultaneously, proteasomal peptidase activities appear to be differentially regulated by both age and food restriction. It suggests more subtle age-related changes in proteasome function, which could include an effect on proteasomal subunit composition.

Aging↗

PubMed1996

Evidence for two patterns of inheritance of sensitivity to induction of lung fibrosis in mice by radiation, one of which involves two genes.

We showed previously that autosomal recessive determinants control the development of pulmonary fibrosis in mice during the early and late phases after irradiation. The extent of fibrosis was inversely correlated with the intrinsic lung activity of both plasminogen activator (PLA) and angiotensin-converting enzyme (ACE). To test these observations further, two groups of mice were given a dose of 15 Gy to the thorax: offspring of a backcross between C57L/J ("fibrosing mice") and the F1 of CBA/J ("non-fibrosing in the early phase") x C57L/J, and additional F1 individuals of CBA/J x C57L/J. Mice were euthanized upon developing a substantial respiratory deficiency (50% reduction in carbon monoxide uptake) during the early phase (14-25 weeks postirradiation). Seventeen mice from the backcross were heavily fibrosed, 38 were classed as intermediate, and 15 contained no fibrosis. No evidence of sex linkage was seen. These data strongly support our earlier conclusions and suggest that two autosomal genes which function additively determine the extent of the principal type of fibrosis in these strains. As no indication of a bimodal distribution of lung PLA or ACE activity was obtained, it is unlikely that one of the genes controls the level of either enzyme. The F1 mice unexpectedly showed small amounts of an unusual type of fibrosis which was not associated with hyaline material or fibrin deposits, in contrast to all previous reports of fibrosis during the early phase in mice. Similar, fibrin-free fibrosis was found during the early phase in mast cell-deficient WBB6F1/J mice (and their normal siblings). In the F1 mice this unusual fibrosis appears to be regulated independently by two additional genes, one of which is sex-linked.

Animals↗

PubMed1996

Dose-response effects of radiation on the permeability of endothelial cells in culture.

Increased permeability is an early and universal response of the vasculature to radiation injury, yet the biological basis of this reaction is poorly understood. The present study determined the time course and the dose-response relationship of radiation-induced hyperpermeability in cultured bovine pulmonary artery endothelial (BPAE) cells. BPAE cells were grown to a confluent monolayer on microcarrier beads, and column chromatography methods were used to evaluate permeability to two low molecular weight compounds: sodium fluorescein (NaFlsc, mol. wt. = 342) and cyanocobalamin (B12, mol. wt. = 1355). This is a novel in vitro model to study mechanisms and modifiers of radiation-induced permeability of endothelial cells under flow conditions using nonradioactive tracers. Cell-covered beads were exposed to a single dose of 10 Gy Of 137Cs gamma rays and placed in the column, and permeability was measured every 30 min for 3 h. There was a time-dependent increase in permeability to both tracers, reaching significance by 2 h. Increased permeability was accompanied by perturbations in F-actin distribution in the BPAE cells as determined by rhodamine-phalloidin fluorescence microscopy. Neither catalase nor captopril ameliorated this hyperpermeability, but dibutyryl cAMP partially prevented it. At 3 h after 0, 1, 2, 5 and 10 Gy irradiation, permeability values of 11.8 +/- 2.1, 13.9 +/- 2.2, 20.9 +/- 3.6, 24.8 +/- 2.8 and 27.2 +/- 3.3 (10(-5) cm/s, +/- SEM), respectively, were observed using NaFlsc. The increase was significant (P < 0.05) at 2 Gy or higher. Permeability to B12 was significantly elevated after 5 or 10 Gy. These results suggest that permeability of endothelial cells to low molecular weight solutes increases within 3 h after therapeutic doses of radiation, and that cAMP ameliorates this response.

Actins↗

PubMed1996

Captopril preserves function and ultrastructure in experimental radiation nephropathy.

Captopril protects rat lung from radiation-induced pneumonitis and fibrosis and preserves function and survival in experimental radiation nephropathy. This study determined the structural benefit of captopril used preventively in radiation nephropathy. Twenty-eight Wag/RijMCW rats, divided in six groups, received 0 to 17 Gray total body irradiation followed by syngeneic bone marrow transplant. Captopril 0, 62.5, 125, 250, or 500 mg/l was given in the drinking water from the time of irradiation, and the rats were killed at 20 weeks. Using light and electron microscopy, kidneys of irradiated no-drug rats showed glomerular tuft capsular adhesions and hyalinization, focal tubular necrosis, severe interstitial fibrosis, and marked thickening and hyaline degeneration of the wall of interlobular arteries and arterioles, with intimal proliferation and periadventitial edema and inflammation. Lumens of the smaller arteries were often occluded. Significant collagen deposition was present in glomeruli, interstitium, and adventitia of interlobular arteries. Marked reduction of glomerular, tubular, vascular, and interstitial damage was seen in irradiated, captopril-treated animals, with only mild focal tubular interstitial injury and fibrosis seen. alpha smooth muscle actin-positive cells, probably myofibroblasts, were enhanced in the irradiated kidneys, and this expression was reduced in a dose-related fashion by captopril. There was also reduction in the arteriolar wall thickening, luminal occlusion, and collagen deposition in captopril-treated animals. The presence of elastin was not affected by radiation or drug treatment. Blood pressure and azotemia were lower and survival was higher in irradiated drug-treated rats compared with irradiated no-drug rats. We conclude that captopril exerts significant functional and structural protection against renal radiation injury. There was notable reduction in radiation-induced fibrosis in captopril-treated animals in this model, as in experimental lung radiation injury.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed1995

Sodium dodecyl sulfate (SDS) activation of the 20S proteasome in rat liver.

The peptidase activity of the 20S proteasome (multicatalytic protease complex) was examined in the 100,000g supernatant fraction prepared from rat liver tissue. Fluorogenic substrates for three proteasome peptidase activities were selected on the basis of (i) observation of an accelerated degradation in the presence of sodium dodecyl sulfate (SDS) and (ii) preferential degradation by the proteasome. Peptidase activities were assayed using an immunoprecipitation technique utilizing polyclonal antibodies raised against the purified rat proteasome. The ability to demonstrate SDS activation of the proteasome is shown to be dependent upon the choice of substrate. In addition, among the cytosolic peptidases, the property of SDS activation appears to be unique to the proteasome. SDS activation profiles were determined for each peptidase activity. Chymotrypsin-like and peptidylglutamyl peptide-hydrolyzing activities exhibit a broad plateau of activation between 0.04 and 0.05% SDS. Trypsin-like activity exhibits a sharp peak of activation at an SDS concentration of 0.04%. The SDS activation profile can be altered by changing the protein (proteasome) concentration, i.e., increasing protein (proteasome) concentration of the reaction mixture produces a marked rightward shift of the activation profile. On the other hand, changing the substrate concentration does not alter the profile. In conclusion, a technique for measuring proteasome peptidase activity in the 100,000g supernatant has been described. This approach increases the ease of measurement of peptidase activity and provides data which may more closely reflect the in vivo activity of the proteasome.

Amino Acid Sequence↗

PubMed1995

Effect of pentoxifylline on radiation-induced lung and skin toxicity in rats.

PURPOSE: There is currently substantial clinical interest in pentoxifylline as an inhibitor of radiation-related normal tissue injury. To further assess this drug's potential toxicity-sparing effects, pentoxifylline was studied in rats using a radiation-induced lung injury model. METHODS AND MATERIALS: Adult male rats were exposed to either sham irradiation or a single fraction of 21 Gy delivered to the left hemithorax. Four study groups were defined: those that received neither radiation nor pentoxifylline, those that received pentoxifylline (500 mg/L in drinking water) but no irradiation, those that underwent irradiation without pentoxifylline, and those that received both pentoxifylline and radiation. Lung injury was measured by changes in relative left:right lung perfusion ratios derived from quantitative gamma camera imaging of 99mTechnetium-macroaggregated albumin uptake in the pulmonary circulation. Serial scans were done over a 40-week period following radiation. Skin toxicity was also assessed. After 40 weeks, the animals were killed, and lung tissue was assayed for angiotensin converting enzyme activity as a marker for endothelial cell damage. RESULTS: Both groups of radiated (with or without pentoxifylline) rats showed equivalent acute sharp decreases in left:right lung perfusion ratios compared to the nonirradiated groups, reaching a mean nadir value of 0.29 at week 4. Irradiated lung perfusion in subsequent weeks in the radiation-only group showed minimal recovery, with a plateau mean ratio of 0.37 (0.36-0.39). However, there was apparent later recovery of lung perfusion in the radiation with pentoxifylline group from weeks 14 through 40, to a mean ratio of 0.47 (0.43-0.52) (p < 0.01 compared to the radiation-only group). Angiotensin converting enzyme activity correlated closely with lung perfusion data. No effect of pentoxifylline on acute or late skin toxicity was detected. CONCLUSIONS: This study suggests that pentoxifylline does not have any measurable effect on acute lung injury following hemithoracic irradiation in rats, but does result in sparing of later lung toxicity.

Animals↗

PubMed1995

Circulating hyaluronan levels in the rodent: effects of age and diet.

Circulating hyaluronan (HA) levels were investigated as a function of age and diet in Fischer 344 male rats. A biphasic pattern of age-related changes was observed in rats fed ad libitum a diet in which the protein source was soya/fish meal. HA levels in 3- to 6- and 22- to 29-mo-old rats were not statistically different. However, HA levels in 12- to 20-mo-old rats were 10-29% of the levels in younger or aged adults. HA levels were also measured in rats fed ad libitum a semisynthetic diet in which the protein source was hydrolyzed casein. Whereas the two colonies exhibited similar biphasic age-related changes, HA levels differed 4- to 20-fold at every age examined. Caloric restriction affected HA levels in 19-mo-old casein-fed rats; HA levels were 2.3 times higher than age-matched controls and were not statistically different from young or aged animals. Serum and plasma HA levels were identical in the same individuals at all ages tested. These data suggest that HA turnover and metabolism in the rat are affected by age, dietary composition, and caloric intake.

Aging↗

PubMed1995

Annexin I concentration, phospholipase activity and thromboxane synthesis in irradiated rat lung.

Annexin I, a member of a family of Ca(2+)-dependent phospholipid-binding proteins (PLBP), has been suggested as a regulator of prostaglandin metabolism as a result of its inhibitory effect on phospholipase A2. Synthesis of prostaglandin is increased in irradiated tissue, but the mechanism underlying this increase has not been delineated. It is conceivable that a decrease in the level of annexin I resulting in increased phospholipase activity may be responsible for the enhanced synthesis of prostaglandin. Accordingly, we measured the level of a lung 36 kDa PLBP, which possesses characteristics of annexin I, as well as the activity of phospholipase and the synthesis of thromboxane A2 (TXA2) in irradiated rat lung. The right lung of rats was irradiated with 0, 15 or 30 Gy of X rays and the animals were sacrificed after 3 months. Phospholipid binding protein was assayed by its ability to transfer unilamellar liposomes to multilamellar liposomes and by immunoblotting against anti-36 kDa rabbit PLBP antisera. Production of TXA2 by minced lung tissue was determined by radioimmunoassay of its stable metabolite TXB2. Phospholipase activity was assayed by hydrolysis of [14C]dioleoylphosphatidylcholine. Our results showed that PLBP activity in the lungs irradiated with 30 Gy was lower than that in the lungs irradiated with 0 and 15 Gy (8.82 +/- 0.47 compared to 9.73 +/- 0.49 and 9.95 +/- 0.78 nmol phospholipid transferred/mg protein, respectively). Western blotting demonstrated a near total depletion of annexin I in the lungs irradiated with 30 Gy. Phospholipase activity was also lower in the lungs irradiated with 30 Gy compared to that in the lungs irradiated with 0 Gy (0.23 +/- 0.01 vs 0.32 +/- 0.01 nmol phosphatidylcholine liberated/mg protein/min, P < 0.001). Reduced phospholipase activity was observed not only in the cytosolic or soluble fraction of lung homogenate, but also in precipitates obtained after 21,000g and 100,000g centrifugation. Despite this decline in phospholipase activity, there was a 2.8-fold increase in the synthesis of thromboxane (367 +/- 65 compared to 1076 +/- 143 pg TXB2/mg tissue/10 min for lungs irradiated with 0 and 30 Gy, respectively). These results are not consistent with the hypothesis that increased synthesis of thromboxane A2 in irradiated rat lung is a direct result of elevated phospholipase activity. In fact, phospholipase activity is decreased in the irradiated lung, despite a decline in the concentration of annexin I, its putative inhibitor.

Animals↗

PubMed1994

Effect of age on induction of hepatic phosphoenolpyruvate carboxykinase by fasting.

This study examines the effect of age on the induction of the rate-limiting enzyme in gluconeogenesis, phosphoenolpyruvate carboxykinase (PEPCK), in response to fasting and refeeding in male Fischer 344 rats aged 3-18 mo. The rats were fasted for 30 h to increase the activity of PEPCK and subsequently were refed for 24 h to lower activity toward basal levels. PEPCK activity increased 2.2-fold in the 3-mo-old rats and 2.3-fold in the 18-mo-old rats during the 30-h fast. Therefore PEPCK induction during the 30-h fast was not altered with age. Similarly, refeeding resulted in a significant decrease in PEPCK activity at all ages. After the 24-h refeeding period, the rats were fasted a second time, and the time course of induction from the basal refed level was measured. In the young rats (6 mo), the activity of PEPCK increased rapidly from 18.12 +/- 1.61 to 42.66 +/- 5.94 U/g protein (P < 0.01) within 8 h of fasting. However, in the 18-mo-old rats, the initiation of the induction of PEPCK activity was delayed, and, after 12 h, PEPCK activity had increased from 17.34 +/- 1.34 to only 32.50 +/- 3.21 U/g protein (P < 0.01). Furthermore, the rate of induction appears to be decreased in the older animals. The activity after 24 h of fasting was equivalent in all four age groups (ranging from 44.72 +/- 5.38 at 3 mo to 40.18 +/- 5.42 U/g protein at 18 mo).(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗

PubMed1994

Captopril inhibits proliferation of human lung fibroblasts in culture: a potential antifibrotic mechanism.

The angiotensin converting enzyme (ACE) inhibitor captopril, a free-thiol compound used widely as an antihypertensive agent, also inhibits radiation-induced pulmonary fibrosis in rats (Ward et al., Int J Radiat Oncol Biol Phys 19:1405, 1990). In an attempt to clarify the antifibrotic mechanism of captopril in vivo, the present study examined the effect of the drug on proliferation of human lung fibroblasts in culture. Captopril produced a drug dose-dependent reduction in fibroblast proliferation and 3H-thymidine incorporation during a 24-72-hr incubation. This cytostatic action of captopril was not the result of cytotoxicity as assessed by trypan blue exclusion, or by 51Cr or lactate dehydrogenase (LDH) release. Fibroblasts stimulated to proliferate by basic FGF were more sensitive to the antimitotic effect of captopril than were unstimulated cells. The ability of captopril to inhibit 3H-thymidine incorporation was not reversed by exogenous angiotensin 2, and was not mimicked by the nonthiol ACE inhibitor lisinopril. These data indicate that the cytostatic effect of captopril was not attributable to ACE inhibition. Penicillamine, a thiol compound with virtually no ACE inhibitory activity, also reduced fibroblast 3H-thymidine incorporation, indicating that the antimitotic action of captopril may represent a nonspecific sulfhydryl effect. This study suggests that the antifibrotic activity of captopril in irradiated lung may result in part from a direct inhibition of fibroblast proliferation, particularly in fibroblasts responding to mitogenic stimuli.

Angiotensin II↗

PubMed1993

Radiation pneumonitis in rats and its modification by the angiotensin-converting enzyme inhibitor captopril evaluated by high-resolution computed tomography.

Adult male Sprague-Dawley rats were irradiated to the right hemithorax with a range of total doses delivered in 10 equal daily fractions of 4 MeV X rays. Half of each dose group consumed control feed, and half consumed feed containing the angiotensin-converting enzyme inhibitor captopril (50 mg/kg/day) continuously after the last irradiation. High-resolution computed tomography (CT) of the entire thorax was performed at 4 and 8 weeks after the last irradiation, and the findings with CT were correlated with hemodynamic data, heart weight, and pulmonary histopathology. Rats exposed to 20 or 40 Gy in 10 fractions exhibited no acute changes in right lung density. After 60 Gy in 10 fractions, however, right lung density in rats on the control diet increased significantly at 4 weeks, and then returned to normal at 8 weeks. Captopril-treated rats exposed to 60 Gy/10 fractions did not exhibit this transient increase in right lung density. After 80 Gy/10 fractions, right lung density increased to 0.60-0.65 g/cm3 at 4 weeks regardless of diet. At 8 weeks after 80 Gy/10 fractions, right lung density increased further in rats given the control diet, but decreased to near normal levels in captopril-treated animals. The density of the shielded left lung based on the CT was independent of both contralateral radiation dose and diet. Histological examination of the irradiated lungs indicated that these acute changes detected by CT were associated with the exudative and edematous phases of radiation pneumonitis, and that captopril reduced the severity of these changes. Irradiated (40-80 Gy/10 fractions) animals fed the control diet exhibited a significant increase in central venous and pulmonary artery pressure, and cardiac right ventricular hypertrophy. Captopril prevented or attenuated these hypertensive reactions. These data demonstrate that high-resolution CT can detect radiation reactions in rat lung within 4 weeks after 60 Gy/10 fractions, and that captopril spares these acute changes detected by CT. The mechanism of captopril action is not clear, but may be due in part to a reduction in pulmonary arterial pressure, resulting in less severe edema in the irradiated lung.

Animals↗

PubMed1992

Radiation pneumotoxicity in rats: modification by inhibitors of angiotensin converting enzyme.

The present study determined whether inhibitors of angiotensin converting enzyme (ACE) can ameliorate radiation-induced pulmonary endothelial dysfunction and pulmonary fibrosis in rats sacrificed 2 months after a range of single doses of 60Co gamma rays to the right hemithorax. Four indices of pulmonary endothelial function were monitored: right lung ACE and plasminogen activator (PLA) activity, and prostacyclin (PGI2) and thromboxane (TXA2) production. Hydroxyproline (HP) content served as an index of pulmonary fibrosis. Rats consumed either control powdered chow or feed containing one of five modifying agents continuously after irradiation. The modifiers included three ACE inhibitors: Captopril, CL242817, and CGS13945, respectively, a thiol, a thioacetate, and a nonthiol compound. All of the ACE inhibitors are analogues of proline. Two additional modifiers were tested: penicillamine, a thiol with no ACE inhibitory activity; and pentoxifylline, a vasodilator that is neither a thiol nor an ACE inhibitor. Radiation produced a dose-dependent decrease in lung ACE and PLA activity, and an increase in PGI2 and TXA2 production and in HP content. All ACE inhibitors attenuated the radiation-induced suppression in lung ACE and PLA activity. All thiol or thioacetate compounds ameliorated the radiation-induced increase in PGI2, TXA2, and HP. The two agents that were both thiols and ACE inhibitors (Captopril and CL242817) spared all of the radiation reactions, while the compound that was neither a thiol nor an ACE inhibitor (pentoxifylline) spared none of the reactions. These data suggest a novel application for ACE inhibitors in general, and for Captopril in particular, as modifiers of radiation pneumotoxicity.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed1992

Pentoxifylline does not spare acute radiation reactions in rat lung and skin.

Male rats were exposed to single doses (0-30 Gy) of 60Co gamma rays to the right hemithorax. Half of each dose group consumed only control powdered chow after irradiation, and half consumed feed containing 0.10% (w/w) pentoxifylline (50 mg/kg/day). The severity of epilation and desquamation in the field of the radiation port was scored weekly. Two months after irradiation the animals were killed, and pulmonary endothelial function was monitored by the activity of lung angiotensin converting enzyme (ACE) and plasminogen activator (PLA), and by production of prostacyclin (PGI2) and thromboxane (TXA2). The amount of hydroxyproline (HP) in the lung served as an index of pulmonary fibrosis. Radiation produced a dose-dependent decrease in ACE and PLA activity in the right lung and an increase in the production of PGI2 and TXA2. This endothelial dysfunction was accompanied by an increase in wet weight and in protein and HP content in the irradiated lung. Pentoxifylline spared only the increase in lung wet weight and protein content, and actually elevated the radiation-induced hyperproduction of PGI2 and TXA2. The severity of the epilation and desquamation reactions increased with increasing radiation dose and time but was independent of diet. These data indicate that pentoxifylline, despite some promising pharmacological actions, has no beneficial effect on acute radiation reactions in rat lung and skin.

Administration, Oral↗