Repeated inhalation exposure of rats to aerosols of 144CeO2. II. Effects on survival and lung, liver, and skeletal neoplasms.

Groups of 94-day-old F344/Crl rats were exposed repeatedly to aerosols of 144CeO2 to reestablish desired lung burdens of 1.9, 9.2, 46, or 230 kBq of 144Ce every 60 days for 1 year (seven exposures). Other 94-day-old rats were exposed once to achieve similar desired initial lung burdens of 144Ce. Older rats were exposed once to achieve desired initial lung burdens of 46 or 230 kBq when 500 days of age, the same age at which rats had the last of the repeated exposures. Control rats were either unexposed, sham-exposed once or repeatedly, or exposed once or repeatedly to stable CeO2. Approximately equal numbers of male and female rats were used. The median survival time and cumulative percentage survival curves were significantly decreased only in male and female rats exposed repeatedly to reestablish a 230-kBq lung burden and among the 94-day-old male rats exposed once to achieve a 230-kBq lung burden of 144Ce. The crude incidences of primary lung cancers (well described by a single Weibull distribution function), time to death with lung tumors, and risk of lung cancer per unit of beta-radiation dose to the lungs were correlated with the cumulative beta-radiation dose rather than the rate at which the dose was accumulated. A linear function, 70 (+/- 7.3) + -0.15 (+/- 0.056) x dose (+/- SD), adequately described the excess numbers of rats with lung cancers over a beta-radiation dose range to the lungs of 6.8 to 250 Gy for two groups of rats with the highest doses to the lungs after a single exposure and for two groups with the highest doses after repeated exposure.     

Effects of protraction of the alpha dose to the lungs of mice by repeated inhalation exposure to aerosols of 239PuO2

To determine the long-term biological effects of protracted alpha irradiation of the lung, 84-day-old C57BL/6J mice were repeatedly exposed by inhalation to aerosols of 239PuO2 every other month for up to six exposures in 10 months to reestablish lung burdens of 20, 90, or 460 Bq. Other mice were exposed only once when either 84 or 460 days of age to achieve desired initial lung burdens of 20, 90, 460, or 2300 Bq. Suitable control groups were maintained. Groups of mice with similar cumulative alpha doses to the lung had 3.4 to 4.4 times greater incidence of pulmonary tumors (adenomas and adenocarcinomas) when the dose to the lung was protracted by the repeated inhalation exposures compared to mice that received a single inhalation exposure. Excess pulmonary tumors per unit dose to the lung were also greater in groups of repeatedly exposed mice compared to those exposed only once. Repeatedly exposed mice also died earlier with pulmonary tumors than did those exposed once. It appears that protraction of an alpha dose to lungs increases the carcinogenic risk of inhaled 239PuO2 in mice.     

Effects of the single or repeated inhalation exposure of Syrian hamsters to aerosols of 239PuO2

Male Syrian hamsters were scheduled to be exposed by inhalation approximately every 60 days for 1 year (7 exposures) to aerosols of 239PuO2 beginning at 84 days of age. Other hamsters were exposed once when 84 or 320 days of age. Plutonium-239 deposited in the lungs by the repeated inhalation exposures was cleared from the lungs at a rate similar to that following a single inhalation exposure. The incidence of radiation pneumonitis, bronchiolar epithelial hyperplasia, and alveolar squamous metaplasia were the only lesions that were related to radiation dose. Only two primary lung tumours were found among the hamsters exposed to 239PuO2. No primary lung tumours were found in the control hamsters. It was concluded that the incidence of lung tumours was not increased by the protraction of the alpha radiation dose to the lungs from repeated inhalation exposure.     

Lung lavage therapy to lessen the biological effects of inhaled 144Ce in dogs

To evaluate the therapeutic effects of removal of an internally deposited radionuclide on long-term biological effects, lung lavage was used to treat dogs that had inhaled 144Ce in a relatively insoluble form, in fused aluminosilicate particles. Either 10 lung lavages were performed between Days 2 and 56 after exposure or 20 lung lavages were performed between Days 2 and 84 after exposure. Approximately one-half of the 144Ce was removed by the lavages, resulting in a corresponding reduction in the total absorbed beta dose to lung. The mean survival time of the treated dogs was 1270 days compared to 370 days for untreated dogs whose initial pulmonary burdens of 144Ce were similar. Treated dogs died late from cancers of the lung or liver, whereas the untreated dogs died at much earlier times from radiation pneumonitis. Dogs treated with lung lavage but not exposed to 144Ce had a mean survival of 4770 days. We concluded that removal of 144Ce from the lung by lavage resulted in increased survival time and in a change in the biological effects from inhaled 144Ce from early-occurring inflammatory disease to late-occurring effects, principally cancer. In addition, the biological effects occurring in the treated dogs could be better predicted from the total absorbed beta dose in the lung and the dose rate after treatment rather than from the original dose rate to the lung. Therefore, we concluded that prompt treatment to remove radioactive materials could be of significant benefit to persons accidentally exposed to high levels of airborne, relatively insoluble, radioactive particles.     

Influence of radiation dose patterns on lung tumor incidence in dogs that inhaled beta emitters: a preliminary report

Different radiation dose patterns to the lung from inhaled beta-emitting radionuclides may influence the frequency and kind of biological effects. To determine the magnitude of this influence, groups of Beagle dogs were exposed to aerosols of 90Y, 91Y, 144Ce, or 90Sr in relatively insoluble particles and observed for their life spans. Different dose patterns were achieved by using these radionuclides having similar beta emissions and chemical form but having physical half-lives ranging from 2.6 days to 28 years. The range of initial lung burdens of radionuclides studied resulted in a range of biological effects from early deaths at the highest radiation doses to no discernible effects at the lowest doses. The effective half-lives of the four radionuclides in the lung ranged from 2.5 to 600 days. Within 1.5 years after exposure, some dogs died with radiation pneumonitis and pulmonary fibrosis. Between 1.5 and 10 years after exposure, 42 pulmonary carcinomas and 28 pulmonary sarcomas were observed in 163 dogs that died. Protracted irradiation of the lung from 90Sr or 144Ce resulted in a relatively high radiation dose and produced more total lung tumors but fewer lung tumors per rad than less protracted irradiation from 90Y or 91Y. At 10 years after inhalation exposure, the difference in risk per rad among the different dose patterns was a factor of 4 to 8, indicating that the different radiation dose patterns from inhaled beta emitters do influence lung tumor risk factors, at least at high (greater than 20,000 rad) doses to lung.     

Influence of dose rate on survival time for 239PuO2-induced radiation pneumonitis or pulmonary fibrosis in dogs.

Beagle dogs were exposed once or repeatedly to 0.75-microns-diameter monodisperse aerosols of 239PuO2 by pernasal inhalation. The dogs that were exposed once received alveolar depositions (+/- standard deviation) of 3.9 +/- 1.9 kBq/kg body mass and accumulated doses of 23 +/- 8 Gy to the lung before death at 5.4 +/- 1.7 years after exposure. Dogs exposed repeatedly received a total alveolar deposition of 5.3 +/- 0.9 kBq/kg body mass during 7 to 10 semiannual exposures and accumulated doses of 22 +/- 5 Gy to the lung before death at 4.9 +/- 0.7 years after first exposure. Clearance of the plutonium from the lung in the dogs exposed repeatedly was slower than in the dogs exposed once. All dogs in the repeated-exposure study and all but one dog in the single-exposure study died from radiation effects. Pulmonary fibrosis accounted for 72% of the radiation-related deaths in the single-exposure study and 87% in the repeated-exposure study. The remaining dogs died with pulmonary cancer. Based on total cumulative radiation dose, the times after exposure to death from radiation pneumonitis and pulmonary fibrosis were not significantly different for single and repeated exposures. Thus dose rate does not appear to be an important factor in predicting death from radiation pneumonitis or pulmonary fibrosis for dogs inhaling 239PuO2.     

Single inhalation exposure to 90SrCl2 in the beagle dog: hematological effects

The toxicity of 90Sr administered by the inhalation route was studied in young adult Beagle dogs exposed once to aerosols containing 90SrCl2. Due to its relatively soluble chemical form, 90Sr was rapidly translocated from lung to bone where a substantial portion was retained for a long period of time. This resulted in only a brief radiation exposure of the respiratory tract and a protracted exposure of the skeleton. The long-term retained burdens ranged from 0.037 to 4.4 MBq 90Sr/kg body wt. Dogs were subsequently observed throughout their life span. Six dogs with long-term retained burdens of 1.7 to 4.1 MBq 90Sr/kg died at less than 32 days after exposure from radiation-induced bone marrow hypoplasia. Review of hematological parameters of all dogs showed a similar, consistent, and dose-related pancytopenia in those animals having a long-term retained burden of greater than 0.37 MBq 90Sr/kg. Thrombocytopenia and neutropenia persisted in all exposed dogs through 1000 days after exposure. For reference purposes, a burden of 0.37 MBq 90Sr/kg is calculated to deliver an average radiation dose to the skeleton over 30, 100, and 1000 days after intake of 1.0, 2.8, and 17 Gy, respectively. The hematologic changes were similar to those seen in people exposed to high doses of whole-body external radiation.     

Cardiopulmonary function of dogs with plutonium-induced chronic lung injury

Beagle dogs had signs of restrictive lung disease 1 to 5 years after exposure by inhalation to 239PuO2 aerosols. The 239PuO2 aerosols were monodisperse with activity median aerodynamic diameters of 0.75, 1.5, or 3.0 microns. The plutonium particles produced protracted alpha irradiation of the lungs. Ten dogs had specific initial pulmonary burdens (IPB) of 330 to 4,100 kBq of 239PuO2/kg of body mass. The average onset time of clinical signs of lung injury was 3 years after exposure; the average time from the onset of signs until cardiorespiratory function evaluation was 5.5 years. A second group of 10 dogs had IPB of 110 to 2000 kBq of 239Pu/kg of body mass but no signs of lung injury. A third group of 10 dogs, not exposed to 239Pu, were matched for age and sex. Cardiopulmonary function tests were performed. Only the dogs in group I with signs of lung injury had a mild respiratory function disorder consisting of smaller lung volumes, reduced compliance, increased respiratory frequency and minute volume, and reduced carbon monoxide diffusing capacity. Cardiac function of all three groups was similar. These findings indicate that alpha irradiation of the lungs of man could produce restrictive lung disease at long times after initial exposure.     

Trickle infections with Nippostrongylus brasiliensis in rats: larval migration through the lungs

The effects of exposure of rats to repeated low-level (trickle) infections with Nippostrongylus brasiliensis were assessed by measuring intestinal and lung worm burdens. Worm recoveries from the intestine, made during a period of trickle infection in rats of different ages, showed a virtually complete rejection of intestinal worms in old rats and a partial rejection in young rats. Recoveries from lungs were made in young rats after challenge infection with 500 third-stage (L3) larvae, given after a 2- or 4-wk period of sensitization, during which rats were infected with 10 or 20 doses of 25 larvae. Such trickle infections elicited a strong host response to a challenge infection, manifested by low recoveries of larvae and an increased duration of larval retention in lungs. In another group of rats sensitized by a single dose of 250 L3 larvae, the recovery of larvae from challenge infection and their clearance from the lungs were similar to these observed in rats uninfected prior to challenge. The effect of trickle infections on preintestinal stages was most pronounced and consistent in rats exposed to larvae the greater numbers of times and over the longest period.     

Essential trace metals and specific organ weights in diet-restricted and ad lib-fed rats

Wistar male rats were exposed to nickel oxide (NiO) aerosols (mass median aerodynamic diameter, 1.2 μm). The average exposure concentration was controlled from low level (0.6 mg/m³) to high level (8.0 mg/m³) and total exposure time ranged from 140 to 216 h. Some rats were sacrificed just after the exposure, whereas others were exposed for 1 mo and kept for a 1-yr clearance period before sacrifice. There were no differences in body weight gain between NiO exposure groups and controls. Nickel concentrations in lungs of exposure groups were much higher than those of controls. No apparent deposition of nickel was observed in liver, kidney, spleen, heart, brain, and blood, but lung burdens of up to about 2.35 mg of NiO were found. The apparent deposition fractions were 19.8 and 14.5% after the exposure to average concentrations of 1.4 and 6.5–7.0 mg/m³, respectively. The clearance rate of NiO deposited in lungs may be small.     

Effect of short-term or intermittent hypobaric hypoxia on plasma lipids in young rats

Changes in the level of plasma lipids (cholesterol, fatty acids and lipoproteins) were followed in young rats exposed once or repeatedly to hypobaric hypoxia. A single exposure to hypoxia increased the level of LDL lipoproteins but did not influence the concentration of cholesterol and fatty acids in 18-day-old rats. Repeated exposure to hypobaric hypoxia caused a statistically significant increase in the concentration of cholesterol, fatty acids, chylomicra, low density beta-lipoproteins (LDL) and very-low-density beta-lipoproteins (VLDL) in 18-day-old rats, while the level of high-density alpha-lipoproteins (HDL) decreased. In animals that had been repeatedly exposed to hypoxia in their youth, a significant decrease of the LDL lipoprotein fraction was observed at the age of 108 days.     

Role of tumor necrosis factor in oxygen toxicity.

mRNA from lungs of mice exposed to high-dose oxygen (greater than 95%) for 3 days demonstrated increased expression of the genes for tumor necrosis factor (TNF), interleukin-1, and interleukin-6 compared with mRNA from lungs of mice exposed to room air. Daily treatment of mice exposed to high-dose oxygen with an antibody to TNF improved survival compared with mice receiving a similar dose of control immunoglobulin G. Pretreatment of mice with repetitive sublethal intraperitoneal doses of recombinant human TNF for 3 days or a single intravenous dose followed by exposure to high-dose oxygen afforded a significant survival advantage compared with high-dose oxygen-exposed mice pretreated with vehicle or interleukin-1. The repetitive intraperitoneal TNF pretreatment reduced the development of interstitial pneumonitis, pulmonary edema, and lung weight gain associated with oxygen toxicity and enhanced expression of the gene for the free radical protective enzyme manganous superoxide dismutase in lung tissue, a gene that is augmented as mice are exposed to high-dose oxygen. Furthermore a single intravenous dose of TNF 24 h after oxygen exposure was still protective. The results suggest that the toxicity of oxygen therapy can be partially ameliorated by either treatment with anti-TNF antibody or pretreatment and early treatment with TNF. These findings are consistent with the hypothesis that oxygen exposure induces TNF, which causes part of the toxicity of high-dose oxygen, and that pretreatment or early treatment with TNF induces the gene for an enzyme that recently has been shown to be very effective in protecting mice from the toxicity of oxygen.     

Inhalation carcinogenesis of high-fired 241AmO2 in rats

Wistar rats were given a single inhalation exposure to high-fired 241AmO2 particles and examined over their life span. A total of 310 rats were used: 259 exposed to 241Am for life-span study, 30 exposed to 241Am for early metabolism study, and 21 unexposed life-span controls. The activity median aerodynamic diameter of the aerosols was 0.75-1.39 microns. About 55% of alveolarly deposited 241Am was cleared from the lung with a half-life of 0.5 days, 37% with a half-life of 7 days, and 8% with a half-life of 580 days. Group mean lung doses ranged from less than 5.7 rad up to 1500 rad. Significant early mortality due to radiation pneumonitis was seen only in the highest exposure group. The percentage of rats with lung tumors was 0% for controls (21 rats), 1% at lifetime lung doses less than 10 rad (139 rats), 7% at 10-50 rad (86 rats), 0% at 50-100 rad (9 rats), 60% at 100-500 rad (10 rats), and 7% at 500 rad (15 rats). Only one liver and one bone tumor were found in all exposed rats, both at lifetime tissue doses less than 10 rad. The fate and carcinogenicity of inhaled 241AmO2 in the lung of rats were similar to what has previously been described for inhaled 244CmO2.     

Postnatal development of the denervated lung in normoxia, hypoxia, or hyperoxia.

We asked whether lung innervation was essential for the normal postnatal development of the lung in conditions of normoxia, hypoxia, or hyperoxia. Litters of newborn rats were assigned to a normoxic [inspired oxygen partial pressure (PIO2) = 150 Torr, eight litters], hypoxic (PIO2 = 100 Torr, nine litters), or hyperoxic (PIO2 = 360 Torr, nine litters) group. Each litter consisted of 12 pups. Two days after birth, one-third of the litter had the vagus and sympathetic trunk cut in the neck on the left side [left denervated (L)], one-third was denervated on the right side (R), and one-third was sham-operated (S). From day 3, all pups were exposed to the designed PIO2, until day 8 or days 21-22. Almost all rats, whether S, R, or L, survived in normoxia and hyperoxia, whereas in hypoxia survival at day 22 of R and L was approximately 60-65%. Body growth was the same in S, R, and L and less in hypoxia than in normoxia or hyperoxia. At days 8 and 22, hematocrit and hemoglobin concentration, heart and lung dry and wet weights, and lung DNA content did not differ among S, R, and L, whether the pups were raised in normoxia, hypoxia, or hyperoxia. At days 21-22, aerobic metabolism and breathing pattern, both measured during air breathing, as well as compliance of isolated lungs, were also similar among S, R, and L for each of the conditions in which the pups were raised.(ABSTRACT TRUNCATED AT 250 WORDS)     

Age-dependent lipid peroxidation in neonatal rat lung tissue.

A unique, age-specific pulmonary lipid peroxidation has been found to occur after incubation of neonatal rat lung homogenates in the absence of any added factors. As measured by the formation of malondialdehyde, lipid peroxidation was not detectable in rat lung homogenates prepared from animals immediately after birth but appeared by the second day and reached a maximum at 5 days of age. The effect gradually disappeared by 20 to 21 days after birth. The addition of NADPH did not enhance lipid peroxidation in the sensitive age group nor did it initiate lipid peroxidation when added to lung homogenates from either 1-day-old or adult rats. The activities and concentrations of various endogenous antioxidants were measured in neonatal lung tissue. When measured in lung tissue obtained from rats during the sensitive age period, no concomitant deficiencies of glutathione peroxidase, glutathione reductase, glucose 6-phosphate dehydrogenase, reduced glutathione, or a-tocopherol were observed. With the exception of α-tocopherol, none of these factors inhibited malondialdehyde formation when added to homogenized lung tissue prepared from 5-day-old rats. α-Tocopherol did inhibit malondialdehyde formation in 5-day-old rat lung homogenates but at a concentration much greater than the endogenous concentration found in adult rat lungs. The 21-day neonatal age period during which malondialdehyde is produced following incubation of lung tissue is similar to the 3-week period immediately after birth reported to be the time of maximum proliferation of rat lung fibroblasts, type 1 pneumocytes and type II pneumocytes.     

Distribution and biological effects of inhaled 239Pu(NO3)4 in cynomolgus monkeys.

Twenty male cynomolgus monkeys were exposed by inhalation either to an aerosol of 239Pu(NO3)4 to produce projected initial lung burdens of either 40, 10, or 4 kBq or to a carrier aerosol as a control. Animals died or were sacrificed at 0.01, 1, 3, 6, 12, 24, 40, and 99 months after inhalation, and the distribution and biological effects of the 239Pu were determined. The 239Pu cleared efficiently from the lungs so that less than 0.05 kBq remained at 99 months after exposure to 40 kBq. Total skeletal 239Pu activity was nearly constant after the first year, but the fraction of the body burden in skeleton at sacrifice increased with time up to 99 months because of clearance from other organs. Plutonium in the liver increased to a peak at 1 year and then decreased to about 10% of the peak value at 99 months. Plutonium in the testes was localized in the interstitial tissue with only 0.01 to 0.002% of the projected lung burden remaining in testes at 99 months after inhalation. Three animals exposed to 40 kBq of 239Pu died of radiation-related pulmonary pneumonitis and fibrosis. A primary papillary adenocarcinoma of the lung was identified in one animal exposed to 40 kBq initial lung burden and sacrificed 99 months after inhalation. The frequency of chromosome aberrations in blood lymphocytes was significantly elevated only in monkeys with projected deposits of 40 kBq of 239Pu. There was no change in aberration frequency in other exposure groups as a function of inhaled activity, time after exposure, or calculated total dose to the lungs. Only in monkeys that had marked radiation-induced pathological changes in the lung did the frequency of chromosome-type aberrations increase significantly, to a value about twice the control level. In cynomolgus monkeys, chromosome aberration frequency in blood lymphocytes is not a good indicator of radiation dose or damage from inhaled soluble plutonium.     

Lactate dehydrogenase isoenzyme pattern and total LDH activity in the lung and liver of rats chronically exposed to low and high oxygen concentrations.

Young adult rats were continuously exposed for 44 and 84 days to environments containing 9–11%, 20%, and 80% oxygen. Low and high oxygen atmospheres were achieved by using boxes laminated with silicone rubber membranes which have a differing permeability for oxygen on one side and for carbon dioxide and nitrogen on the other. Animals exposed to both extreme concentrations significantly slowed body growth, and the weight of the lungs was proportionally less. The pattern of LDH isoenzymes in the lung showed the presence of all five characteristically changing isoenzymes in relation to oxygen concentration. A marked increase of M subunits in the LDH in lungs of rats exposed to low oxygen indicated a higher tissue concentration of lactate. Thus, the percentage of M subunits was significantly higher in low oxygen and significantly lower in lungs of rats exposed to high oxygen as compared to controls. Under the same experimental conditions there were no changes in the liver LDH isoenzyme pattern. Total LDH activity in the lungs of rats exposed to either extreme oxygen atmosphere was significantly elevated as compared to controls kept at an ambient atmosphere. It is concluded that chronic exposure of rats to low as well as to high oxygen was injurious to the lung tissue, as evidenced by total LDH activity. Thus, LDH isoenzyme pattern in the lung reflected the actual gas exposure (pO₂), rather than local tissue metabolism.     

A comparison of asbestos burden in non-urban patients with and without lung cancer

Asbestos is a recognized carcinogen which is widely available for environmental exposure. Since all members of our society are exposed to asbestos containing environments and, indeed, have asbestos fibres in their lungs, the concern exists as to its significance in contributing to the incidence of lung cancer in such populations. The asbestos burden was compared in lung tissue from control and lung cancer patients who had resided in a non-urban environment. There were no significant differences between the asbestos burdens in both age matched groups; however, the proportions of amphiboles to chrysotile were different from those reported in previous urban based studies. This difference was suggested to be attributable to chrysotile exposure in urban air. All patients had appreciable non-asbestos fibres within their lungs. The results indicate that when comparing any dust burden in lungs, it is necessary to have data from regional control populations before attempting to explore causal-disease relationships.     

Respiratory mechanics in adult rats hypoxic in the neonatal period

Newborn rats were exposed to 10% O2 from 24 h to 6 days after birth, then returned to normoxia and examined at 50 days of age, i.e., after reaching sexual maturity. Despite the important impairment in somatic growth during hypoxia, at 50 days body weight and nose-tail length were as in control rats never exposed to hypoxia. Hypoxic rats had a bigger chest, with larger anteroposterior diameter, larger surface area of the muscle component of the diaphragm, and heavier and more expanded lungs. None of these structural changes were observed in a third group of rats, which were exposed for 6 days to hypoxia between 35 and 42 days of age, i.e., at a much more advanced stage of postnatal development. In addition, hypoxic rats had higher compliance of the respiratory system and of the lung and lower total pulmonary resistance than control rats. Frequency dependence of compliance was not different. We conclude that in the rat the structural changes induced by neonatal chronic hypoxia are not resolved by the return to normoxia but persist at least until postpuberty with modifications of the mechanical properties of the respiratory system.     

Effect of fly ash inhalation on biochemical and histomorphological changes in rat lungs

Effect of respirable fly ash particles inhalation on lungs of rats was investigated by exposing them to respirable aerosols of size classified power plant fly ash at average concentrations of up to 14.4 +/- 1.77 mg/m3 for 4 hr/day for 28 consecutive days. A remarkable increase was found in blood eosinophil counts of fly ash exposed animals. Biochemical indicators of pulmonary damage viz. lactate dehydrogenase (cytoplasmic enzyme used as a measure of cell injury), gamma-glutamyl transferase (Clara cell damage) and alkaline phosphatase (potential measure of Type 11 cell secretions) in broncho alveolar lavage fluid (BALF) of fly ash exposed group showed significant elevation. Clumping of fly ash particles in the lungs was observed as evidenced by fly ash ladened macrophage accumulation in the alveolar region. The results suggest a damage, local inflammation and remodelling of lung as indicated by hypertrophy and hyperplasia. These changes reflect the toxic effects of the fly ash inhalation.