M. Ellender

Loss of heterozygosity in spontaneous and x-ray–induced intestinal tumors arising in F1 hybrid Min mice: Evidence for sequential loss of Apc+ and Dpc4 in tumor development†

Min (multiple intestinal neoplasia) mice carry a mutant allele of the murine Apc (adenomatous polyposis coli) locus and are predisposed to intestinal adenoma formation in the intestinal tract. Early studies have shown complete loss of function of Apc by whole chromosome loss on the tumor‐sensitive C57BL/6J genetic background and in AKR × B6 F1 hybrids. Gamma‐radiation–induced chromosomal losses focus the critical region on wt Apc, but because of the limited number of polymorphic markers used, no other critical regions of loss on chromosome 18 were identified. Using intestinal tumors arising spontaneously and induced by X‐rays in CBA/H × C57BL/6J F1 hybrid mice and high‐resolution microsatellite loss of heterozygosity (LOH) techniques, we provide mapping data for wt Apc loss, which confirms and extends earlier observations. In addition, high‐frequency loss events at the Dpc4 locus were found in both spontaneous and radiation‐induced tumors. These data identified LOH of Dpc4 as a critical secondary event following complete functional loss of Apc. LOH across the Trp53 genomic region of chromosome 11 was not observed. No LOH was recorded for the Mom1 candidate gene Pla2g2a or for 9 out of 10 polymorphic markers from the Mom1 genomic region on murine chromosome 4. One marker mapping distal to Pla2g2a showed LOH in a small minority of spontaneous tumors. These data support the contention that Mom1 does not act as a classical tumor suppressor. Overall, our data indicates a significant role for Dpc4 mutation in intestinal tumor progression in the mouse and provides further evidence for the importance of interstitial chromosome losses in radiation tumorigenesis. Genes, Chromosomes and Cancer 28:387–394, 2000.

Efficacy of Tiron for Enhancing the Excretion of Uranium from the Rat

Tiron (sodium 4, 5-dihydroxybenzene-1,3-disulphonate) has been suggested as a possible antidote for acute uranium poisoning. In this study, the compound has been administered intraperitoneally to rats in dosages of 30, 300 or 1000 μmol kg-1 at 20, 60 and 180 min after the intratracheal instillation of uranyl nitrate. The amounts of uranium deposited in the lungs of rats were equivalent to intakes by workers of about 12 times the permitted daily limit of 2.5 mg. The average body content of uranium at 5 d after exposure were, respectively, about 100%, 78% and 65% of those in untreated animals. It is concluded that the administration of Tiron is of limited practical value for treatment of uranium exposures not greatly in excess of the permitted intake.

Induction of osteosarcoma and acute myeloid leukaemia in CBA/H mice by the alpha-emitting nuclides, uranium-233, plutonium-239 and amercium-241

Purpose : To compare tumour induction in CBA/H mice, principally osteosarcoma and acute myeloid leukaemia, resulting from exposure to the alpha-emitting nuclides, uranium-233, plutonium-239 and americium-241, and to relate differences between the three nuclides to the pattern of dose delivery within tissues. Materials and methods : Each nuclide was administered intraperitoneally in citrate solution to three groups of adult male CBA/H mice at levels of activity which gave estimated life-time average skeletal doses of about 0.25-0.3 Gy, 0.5-1 Gy and 1-2 Gy. Animals were carefully monitored and sacrificed as soon as they showed signs of ill health; tumours were identified by standard histopathological techniques. Results : Statistical modelling by Cox regression showed that, considering all three nuclides together, there was a highly significant increase in risk of death from osteosarcoma or myeloid leukaemia with increasing dose rate. For osteosarcoma, the effect was significantly greater for 239 Pu than 241 Am, while separate analysis for 233 U showed no significant increase with increasing dose rate. For example, the increase in relative risk of death from osteosarcoma for an increase in life-time average dose rate to bone of 1 mGy d -1 was 4.2 (2.7-6.5) for 239 Pu, 2.3 (1.4-3.4) for 241 Am and 1.1 (0.4-3.1) for 233 U. For myeloid leukaemia, there was no significant difference between 239 Pu and 241 Am in the effect of dose rate. The increase in relative risk from myeloid leukaemia for an increase in average dose rate of 1 mGy d -1 was 1.8 (1.1-2.8) for 239 Pu, 2.0 (1.4-2.9) for 241 Am and 1.5 (0.8-2.7) for 233 U. Significant increases in renal and hepatic carcinomas were also recorded in animals exposed to 233 U and 241 Am, respectively. Studies of the distribution of the nuclides within the skeleton, published separately, have shown differences in their retention in individual bones and within bone. The proportions of decays occurring near to endosteal bone surfaces and throughout bone marrow were in the order: 239 Pu > 241 Am > 233 U. Conclusions : For osteosarcoma, the relative effectiveness of the nuclides in terms of average bone dose, in the order 239 Pu > 241 Am > 233 U, is consistent with the proportion of dose delivered near to endosteal surfaces. For myeloid leukaemia, the greater effectiveness of 239 Pu and 241 Am than 233 U is consistent with their accumulation in marrow.PURPOSE To compare tumour induction in CBA/H mice, principally osteosarcoma and acute myeloid leukaemia, resulting from exposure to the alpha-emitting nuclides, uranium-233, plutonium-239 and americium-241, and to relate differences between the three nuclides to the pattern of dose delivery within tissues. MATERIALS AND METHODS Each nuclide was administered intraperitoneally in citrate solution to three groups of adult male CBA/H mice at levels of activity which gave estimated life-time average skeletal doses of about 0.25-0.3 Gy, 0.5-1 Gy and 1-2 Gy. Animals were carefully monitored and sacrificed as soon as they showed signs of ill health; tumours were identified by standard histopathological techniques. RESULTS Statistical modelling by Cox regression showed that, considering all three nuclides together, there was a highly significant increase in risk of death from osteosarcoma or myeloid leukaemia with increasing dose rate. For osteosarcoma, the effect was significantly greater for 239Pu than 241Am, while separate analysis for 233U showed no significant increase with increasing dose rate. For example, the increase in relative risk of death from osteosarcoma for an increase in life-time average dose rate to bone of 1 mGyd(-1) was 4.2 (2.7-6.5) for 239Pu, 2.3 (1.4-3.4) for 241Am and 1.1 (0.4-3.1) for 233U. For myeloid leukaemia, there was no significant difference between 239Pu and 241Am in the effect of dose rate. The increase in relative risk from myeloid leukaemia for an increase in average dose rate of 1 mGyd(-1) was 1.8 (1.1-2.8) for 239Pu, 2.0 (1.4-2.9) for 241Am and 1.5 (0.8-2.7) for 233U. Significant increases in renal and hepatic carcinomas were also recorded in animals exposed to 233U and 241Am, respectively. Studies of the distribution of the nuclides within the skeleton, published separately, have shown differences in their retention in individual bones and within bone. The proportions of decays occurring near to endosteal bone surfaces and throughout bone marrow were in the order: 239Pu> 241Am>233U. CONCLUSIONS For osteosarcoma, the relative effectiveness of the nuclides in terms of average bone dose, in the order 239Pu>241Am>233U, is consistent with the proportion of dose delivered near to endosteal surfaces. For myeloid leukaemia, the greater effectiveness of 239Pu and 241Am than 233U is consistent with their accumulation in marrow.

The Clearance of Uranium after Deposition of the Nitrate and Bicarbonate in Different Regions of the Rat Lung

This study investigated the tissue distribution and excretion of uranium after its deposition as either the nitrate or bicarbonate in the three regions of the respiratory system of the rat. Results confirm the recommendations of ICRP that uranyl nitrate and bicarbonate should be treated as class D compounds; but imply that some of the parameters used in the ICRP lung model are not applicable to soluble uranium compounds.

The Efficacies of Pure LICAM(C) and DTPA on the Retention of Plutonium-238 and Americium-241 in Rats after Their Inhalation as Nitrate and Intravenous Injection as Citrate

The pure carboxylated catechoyl amide LICAM(C) and the calcium and zinc salts of diethylenetriaminepenta-acetic acid (DTPA), were tested for efficacy for removing 238Pu and 241Am from rats after inhalation of the nitrate or intravenous injection of the citrate. The results were compared with the efficacy of methylated LICAM(C) used in previous experiments. It was shown that: (1) after inhalation of 238Pu nitrate, DTPA was far superior to pure LICAM(C); (2) after intravenous injection of 238Pu citrate, the infusion of DTPA plus LICAM(C) was only marginally more effective than DTPA alone; and (3) after inhalation or intravenous injection of 238Pu plus 241Am, the efficacy of pure LICAM(C) was only marginally more effective than the methylated form and neither form was effective for the decorporation of 241Am. It was concluded that DTPA, at present, remains the chelating agent of choice for treating persons accidentally contaminated with transportable forms of Pu and Am.

Removal of Inhaled Plutonium and Americium from the Rat by Administration Of ZnDTPA in Drinking Water

This study has examined the efficacy of ZnDTPA administered in drinking water for removing 238Pu and 241Am from the rat after their simultaneous inhalation as nitrates; the dosage used was 95 μmol kg-1d-1. The continuous administration of ZnDTPA over a 14 d interval, commencing 1 h after exposure, reduced the lung and total body contents of 238 Pu to, respectively, 11 % and 18% of those in untreated rats; the corresponding values for 241Am were 11 % and 14%. After the continuous administration of 95 μmol kg-1 from 4 d to 28 d post exposure, the lung and total body contents of 238Pu were, respectively, 5% and 16% of those in controls; the corresponding values for 241Am were 7% and 19%. Further reductions in the actinide contents of body tissues were found when treatment was extended to 52 d or 76 d. These regimens were as effective as twice weekly injections of 30 μmol kg-1 ZnDTPA commencing at 4 d. After the continuous administration of 95 μmol kg -1 d-1 for 72 d, some pathological changes to the gastrointestinal tract were observed but these were considered to be reparable. It was concluded that further work is required to evaluate the toxicity of the ligand and to establish the optimal treatment regimen.

The distribution and retention of plutonium, americium and uranium in CBA/H mice

Groups of male and female CBA/H mice were given intraperitoneal injections of 40 kBq kg-1 of 239Pu, 241Am and 233U citrate solutions and the retention and distribution of the three radionuclides compared at times up to 448 days. Similar results were obtained for males and females and showed that: 1. Whole body retention at 448 days was very similar for 239Pu and 241Am, accounting for about 20% of injected activity for each nuclide; retention of 233U was much lower at about 3%. 2. The skeleton accounted for 85% or more of retained 239Pu, 241Am and 233U activity from 6 weeks after injection. 3. The greatest concentrations of each radionuclide were measured in the main body of the spine, limb girdles and ribs, with lowest concentrations in the paw bones, head bones and caudal vertebrae. The inhomogeneity of distribution was in the order Pu > U > Am; with a trend to more uniform activity with time. 4. Average bone doses to 448 days were calculated as about 1.6 and 1.7 Gy for 239Pu and 241Am, respectively, and 0.3 Gy for 233U, with ranges for individual bones of 0.7-3.0 Gy, 1.1-2.5 Gy and 0.1-0.6 Gy, respectively. Average liver doses to 448 days were calculated as about 0.9 Gy, 0.6 Gy and 0.007 Gy for 239Pu, 241Am and 233U respectively, whilst the dose to the kidney for 233U was about 0.1 Gy. 5. Autoradiographic studies of the distribution of the nuclides in the femur showed differences in their initial distribution and subsequent movement. Initially, concentrations of 239Pu were greater on endosteal than periosteal surfaces while 241Am distributed more evenly on bone surfaces. The initial deposition of 233U on all surfaces was uneven with concentrations probably on active surfaces. Burial of all three nuclides in areas of bone growth was observed. Transfer of activity to the marrow was greatest for 239Pu and least for 233U.

Efficacies of LICAM (C) and DTPA for the decorporation of inhaled transportable forms of plutonium and americium from the rat

Fhe efficacies of N 1, N 5 , N 10 , N 14-tetrakis (2,3-dihydroxy-4-carboxybenzoyl)-tetra-azatetradecane LICAM(C)] and diethylenetriaminepenta-acetic acid (DTPA) (30 μmol/kg body wt.) have been nvestigated for plutonium (Pu) decorporation after inhalation as the nitrate or tributyl phosphate TBP) complexes and the data compared with those obtained after its intravenous injection as the :itrate. The efficacy of removal of americium (Am) inhaled as the nitrate has also been examined. The results show that: . whereas LICAM(C) and DTPA were similarly effective for removing Pu from the blood, -ICAM(C) was considerably inferior to DTPA when transportable forms of Pu were inhaled; LICAM(C) is ineffective for the decorporation of Am; the optimum treatment regimen for both Pu and Am involved the prompt and repeated administration of DTPA.

Metabolism of uranium in the rat after inhalation of two industrial forms of ore concentrate: the implications for occupational exposure.

Aerosols produced from two commercially available ore concentrates in which the uranium was present essentially in the one as ammonium diuranate (ADU) and in the other as uranium octoxide (U3O8) were administered to rats. The results show that: 1 uranium in the ADU bearing material was cleared rapidly from the lungs, mainly to the blood, such that the retention kinetics were similar to those for a class D (highly transportable) compound as defined by ICRP; 2 uranium in the U 3O8 bearing material was removed from the lungs principally by mechanical processes, the retention kinetics in this case being similar to those defined for a class Y (poorly transportable) compound; 3 for both materials the distribution of uranium amongst body tissues and the fraction of the systemic content excreted in urine were similar to those obtained after the injection of soluble hexavalent compounds; 4 for workers potentially exposed to both these materials, urine monitoring and lung radioactivity counting measurements should be used in addition to air sampling procedures for assessing the intake of uranium. 5 intakes of the ADU bearing material should be restricted to those permitted for short-term exposures on the basis of chemical toxicity, whereas those for the U3O 8 bearing material should be governed by radiation dose.

Metabolism of an industrial uranium trioxide dust after deposition in the rat lung

Uranium trioxide, produced industrially, was administered to rats either by inhalation or direct injection of an aqueous suspension into the lungs. The results: 1 show that uranium was cleared rapidly from the lungs, mainly to the blood; 2 show that distribution of uranium among body tissues, and the fraction of the systemic content excreted in urine, was similar to that obtained for other transportable hexavalent uranium compounds; 3 suggest that urine monitoring data would be of more value than lung radioactivity counting measurements for assessing occupational human exposure; 4 indicate that for setting exposure limits by inhalation the uranium trioxide should be considered a highly transportable compound. Thus intakes by workers should be restricted to those recommended for short-term exposures and not those based on an annual limit.