Mechanisms of hormone-mediated carcinogenesis of the ovary in mice.

Experimental ovarian carcinogenesis has been investigated in inbred and hybrid strains of mice and induced by a diversity of mechanisms including X-irradiation, oocytotoxic xenobiotic chemicals, ovarian grafting to ectopic or orthotopic sites, neonatal thymectomy, mutant genes reducing germ cell populations, and aging. The mechanisms are briefly reviewed whereby disruptions in the function of graafian follicles results in a spectrum of ovarian proliferative lesions including tumors. The findings in mutant mice support the concept of a secondary (hormonally-mediated) mechanism of ovarian carcinogenesis in mice associated with sterility. Multiple pathogenetic factors that either destroy or diminish the numbers of graafian follicles in the ovary result in decreased sex hormone secretion (especially estradiol-17 beta) leading to a compensatory over-production of pituitary gonadotrophins (particularly luteinizing hormone), which places the mouse ovary at an increased risk to develop tumors. The intense proliferation of ovarian surface epithelium and stromal (interstitial) cells with the development of unique tubular adenomas in response to sterility does not appear to have a counterpart in the ovaries of women.

Comparison of the up-and-down, conventional LD50, and fixed-dose acute toxicity procedures.

The up-and-down procedure (UDP), fixed-dose procedure (FDP) and conventional LD50 tests were compared to determine their consistency in chemical hazard classification for acute oral toxicity according to the European Economic Community (EEC) system. There was consistent classification for 23 out of 25 cases between the UDP and the conventional LD50 results, in 16 out of 20 cases between the FDP and the conventional LD50, and in seven out of 10 cases between the UDP and the FDP. The UDP needed only between six and 10 animals of one sex (fewer than either the LD50 or the FDP). Available literature indicates that the sexes are usually similar in their acute toxicity responses and that of females are often more sensitive than males when acute toxicity differences do exist, thus obviating the need for both sexes to be tested in most cases. Unlike the FDP, the UDP also estimates an LD50, thus providing data directly applicable to all current hazard classification systems based on acute oral toxicity.

Spontaneous corneal dystrophy and generalized basement membrane changes in Fischer-344 rats.

Groups of young, sexually mature Fischer-344 rats (n = 25/sex) obtained from commercial breeders were examined ophthalmologically and histopathologically to determine the prevalence and severity of corneal basement membrane lesions (corneal dystrophy) and basement membrane changes in select nonocular tissues. Results disclosed a high incidence of corneal basement membrane dystrophy in rats of both sexes from all breeders; however, severity levels were significantly increased in rats obtained from one breeder when compared to others. Furthermore, rats that displayed the most advanced corneal lesions also exhibited more severe basement membrane changes in other organs, especially renal tubules and vascular internal laminae. These findings suggest that both ocular and nonocular dystrophic changes may have been linked through common physiologic (or genetic) mechanisms. Animals that displayed basement membrane lesions were not considered to represent compromised biologic test systems.

Spontaneous basophilic foci of hepatocellular alteration in Fischer 344 female rats do not exclude iron.

Iron exclusion has been used to identify foci of hepatocellular alteration (FHA) in rats exposed to known carcinogens. This study investigates whether basophilic FHA occurring spontaneously in aged female Fischer 344 rats also exclude iron. Female rats 514-544 days of age were given supplemental iron by injection for 2 weeks prior to being killed. Serial sections of the liver stained with hematoxylin and eosin or Gomori's stain were examined. Seventy-five basophilic FHA were identified; none excluded iron. It may be possible to differentiate spontaneous basophilic FHA from carcinogen-induced, iron-excluding FHA by the use of this staining method.

Effects of nitrofurantoin on the primary and secondary reproductive organs of female B6C3F1 mice.

The National Toxicology Program (NTP) has reported female mice fed high doses of Nitrofurantoin (NFT) were found to have ovarian atrophy as diagnosed histologically and increased benign ovarian tumors after 24 months of exposure (30). This result contrasts with 4 other recent carcinogenicity assays in rodents with NFT, all with no evidence of an ovarian effect. An extensive database documents benign tubular adenomas develop secondary to ovarian atrophy in many mouse strains, including B6C3F1. The present study was initiated to confirm this mechanism could be responsible for the ovarian tumors in the NTP study and to investigate the time course of ovarian changes seen in female B6C3F1 mice. Mice were provided diet containing NFT at doses of 350 and 500 mg/kg body weight/day and examined after 4, 8, 13, 17, 43 and 64 weeks. A dose-related decrease in feed consumption, feed efficiency and body weight gain was seen and persisted throughout the study. Sexual maturity was delayed in a dose-related fashion, compatible with previously reported effects of reduced food consumption in rodents (12, 16). All groups of mice eventually did have normal estrous cycles, but cycle lengths were increased in a dose-related fashion. Both doses of NFT resulted in histological evidence of senile ovarian atrophy by week 43. Based on the reported association between sterility and ovarian tumors, we conclude the benign tubular adenomas seen at 2 yr in the NTP carcinogenicity study with NFT were secondary to the ovarian atrophy induced in this strain of mouse and not an indication NFT, itself, is a carcinogen.

Morphological and stereological characterization of hepatic foci of cellular alteration in control Fischer 344 rats.

Quantitative evaluation of altered hepatocellular foci (AHF), followed by stereological analysis was performed on standard hematoxylin and eosin-stained liver sections from control Fischer 344 (F344) rats of both sexes from seven 2-yr carcinogenicity studies conducted by the National Toxicology Program (NTP). Liver samples were collected at 6, 9, 12, 15, 18, and/or 24 months on study. Although AHF had a broad spectrum of morphological features, they could be classified into the following 5 types using previously published criteria: basophilic, eosinophilic, clear, vacuolated, mixed cell foci. Approximately 50% of the animals had foci at 6 months, and the incidence reached nearly 100% at 15 months in both sexes. The number, size and volume fraction of AHF increased with age in both sexes; these changes were most evident for basophilic and clear cell foci. The number of basophilic foci was significantly greater in females than in males while clear cell foci were more numerous in males. This sex difference was observed at each time point. Mean number of all types of AHF in males and females at 24 months was 547 and 460 per cubic centimeter of liver, respectively. Despite the high incidence of AHF in control rats, the incidence of hepatocellular neoplasms is low. The implication is that most foci do not progress to neoplasia in control F344 rats used in 2-yr studies.

Ethylenediaminetetra(methylenephosphonic acid): genotoxicity, biodistribution, and subchronic and chronic toxicity in rats.

Ethylenediaminetetra(methylenephosphonic acid), EDITEMPA, was tested for oral toxicity in rats in a 13-wk feeding study (at doses of 0, 5, 50 and 500 mg/kg/day) and in a chronic feeding study (at doses of 0, 4, 20 and 100 mg/kg/day). EDITEMPA was also tested for genotoxicity in the Ames, mouse lymphoma, unscheduled DNA synthesis, and in vivo cytogenetics assays. Additionally, absorption, distribution and excretion (ADE) studies were conducted following administration of [14C]EDITEMPA to rats by gavage and via the feed and drinking-water. The principal finding in the 13-wk study was mild anaemia in male and female rats given 500 mg/kg/day, which was resolved during a 9-wk recovery period. In the chronic study, there was no substantial evidence of any treatment-related toxicity or carcinogenicity. Differences in survival of control and treated females (noted late in the study) were interpreted to represent unusually good survival in controls; however, a compound-related increase in mortality could not be completely ruled out. Tests for genotoxicity were all negative. ADE studies revealed that [14C]EDITEMPA was poorly absorbed from the gastro-intestinal tract and that most of the absorbed dose was rapidly excreted by the kidneys or sequestered in bone. The gavage route of administration led to four- to six-fold increases in bone EDITEMPA levels as compared with administration in the feed and drinking-water, respectively. These results suggest that no significant toxicity or carcinogenicity concerns arise from EDITEMPA when it is administered in the feed at the concentrations tested. Reversible anaemia was seen only at very high doses and was interpreted as being secondary to EDITEMPA's ability to interfere with iron absorption and utilization. Localization of EDITEMPA in bone indicated a high degree of affinity for mineralizing tissues, consistent with its chelating properties. There was, however, no effect on bone resorption or mineralization. A comparison of human drinking-water levels of 3500 ppm EDITEMPA (based on a no-effect level of 100 mg/kg/day in rats) with the estimated worst-case exposure in humans of 0.01 ppm suggested a safety margin greater than 1 x 10(5).

Effect of continuous, whole-body gamma irradiation upon canine lymphohematopoietic (CFU-GM, CFU-L) progenitors and a possible hematopoietic regulatory population.

Clonogenic assays for granulocytes-macrophages (CFU-GM) in bone marrow and for T lymphocytes (CFU-L) in peripheral blood were performed on dogs continuously exposed to 60Co irradiation (0.02, 0.04, or 0.11 Gy/day). When decreased numbers of CFU-GM were observed they correlated well with the clinical status of the dogs but were not generally associated with increasing cumulative doses of absorbed irradiation. In clinically normal, irradiated animals, decreased CFU-GM values and myeloid-erythroid ratios were observed, suggesting that chronic irradiation may affect the granulocytic series well before decreased peripheral blood values are seen. In hypocellular dogs the number of CFU-GM were significantly decreased compared to values obtained from control or clinically normal irradiated dogs, while virtually no CFU-GM were observed in the leukemic dogs. Only the CFU-GM values of the hypocellular group showed an association, e.g., a suggestion of an abortive regenerative effort, with increasing absorbed dose. Proliferative capacity of T lymphocytes (CFU-L) was not affected by either increasing absorbed irradiation or the presence of leukemia. D0 values were determined on marrow fibroblastic cells to ascertain whether a radioresistant subpopulation of stromal elements would result from continuous in vivo irradiation. No correlation was found between absorbed dose and increased D0 values. However, seven of eight dogs which developed acute nonlymphocytic leukemia displayed marrow fibroblastic cells with elevated D0 values. These radioresistant marrow fibroblastic cells were assayed for their ability to support normal granulopoiesis and found to be not significantly different from control fibroblasts.

Fetal liver cell transplantation in dogs: results with DLA-compatible and incompatible grafts.

We evaluated the ability of fetal liver hematopoietic cells to reconstitute hematopoiesis and immunity in lethally irradiated dogs. Nineteen consecutive dogs received transplants of fetal liver cells from donors identical or mismatched for DLA antigens. Six animals received 16 Gy fractionated total body irradiation (TBI) followed by transplantation of DLA-identical fetal liver. Three other dogs received transplants of fetal liver that was homozygous for a DLA haplotype shared by the recipient. No post-transplant immunosuppressive treatment was administered. All nine dogs had rapid and sustained restoration of hematopoiesis and none developed graft-versus-host disease. T and B-lymphocyte function recovered slowly over several months in all animals with sustained engraftment and they remained free of infection in open kennel conditions. These data indicate that a single DLA-identical fetal liver can reconstitute hematopoiesis in lethally irradiated dogs. This conditioning regimen was inadequate for transplantation of DLA-mismatched fetal liver cells; 6 of 6 dogs failed to engraft. We evaluated whether more intensive conditioning with 18 Gy fractionated TBI or 16 Gy TBI followed by post transplant treatment with methotrexate was feasible in 4 dogs. These regimens produced severe mucositis and gastrointestinal toxicity; 2 recipients of DLA-matched fetal liver transplants survived but 2 dogs receiving DLA-haploidentical fetal liver had engraftment but died of toxicity. Further studies are required to develop an effective, yet tolerable conditioning regimen in this setting. Fetal liver transplantation may ultimately be useful as a source of hematopoietic cells for transplantation in human patients if an effective conditioning regimen can be developed to allow engraftment of histoincompatible transplants.

The influence of fibroblast-like cells derived from canine fetal hematopoietic tissues on the regulation of lymphohematopoiesis.

Media conditioned by fibroblast-like cells derived from organs active in fetal lymphohematopoiesis were studied for their effects on adult granulocyte/macrophage colony-forming units (CFU-GM). Fibroblasts from fetal liver produced a factor stimulatory for CFU-GM, whereas fibroblasts from fetal marrow produced a factor inhibitory for CFU-GM which was not completely relieved by adding indomethacin to the assay. Our studies indicated that neither fetal marrow nor fetal liver produced factors affecting lymphocyte colony-forming units (CFU-L). Cell-cell interactions between fibroblast-like cells derived from fetal liver or marrow and normal adult CFU-GM were also studied. We observed that fibroblasts derived from both fetal and adult marrow inhibited colony formation, whereas inhibition in the presence of fetal liver fibroblasts was minimal. Loss of inhibitory activity by a liver fibroblast cell line over repeated passages was seen. Differential analysis of colonies formed above an adherent layer of fetal marrow fibroblasts suggested that these fibroblasts suppress myeloid/macrophage differentiation to a far greater degree than did adult marrow fibroblasts. A role in the regulation of fetal lymphohematopoiesis may be played by stromal fibroblasts.

In vitro radiation response studies on bone marrow fibroblasts (CFU-F) obtained from normal and chronically irradiated dogs.

The radiation resistance of bone marrow fibroblasts as measured by their proliferative potential was evaluated in chronically irradiated dogs. Bone marrows were obtained from eight dogs that had been chronically irradiated beginning at 21 days of gestation or after birth and eight age-matched controls. Of these irradiated dogs, four were either preleukemic or exhibited frank acute nonlymphocytic leukemia. The other four were clinically normal but demonstrated abnormalities in their marrow that could be attributed to radiation effects and/or other pathologic changes. Fibroblasts from six of the irradiated dogs were significantly more radioresistant than those of their controls. Five of these six dogs subsequently succumbed to hematopathologic disease, while the two irradiated dogs with normal fibroblasts remained clinically normal, suggesting that this observed radioresistance may be linked to the disease process.

Characterization of canine fetal lymphohematopoiesis: studies of CFUGM, CFUL, and CFUF.

We assayed the colony forming units for granulocyte-macrophages (CFUGM), T-lymphocytes (CFUL) and fibroblasts (CFUF) in the blood, bone marrow, liver and spleen of the canine at 45 and 55 days of gestation and 4 and 30 days post partum. As the number of CFUGM per 5 x 10(5) cells increased in the fetal liver, the number of CFUGM increased in circulating blood, whereas when the number of CFUGM decreased in liver and blood, CFUGM increased in both bone marrow and spleen. This suggests that CFUGM are produced in the liver, are released into the circulation and then transported to the spleen and bone marrow. CFUF studies showed that canine fetal bone marrow and spleen are active sites of fibroblast proliferation, whereas the liver is not. Morphologic examination of colonies derived from concanavalin-A stimulated progenitors ("CFUL") demonstrated that these colonies from fetal tissues and adult bone marrow were not exclusively lymphoid but were also made up of significant numbers of precursors of the myeloid and monocytic series. Lymphocyte stimulation tests (LST) showed the presence of a large population of mitogen-independent dividing cells, suggesting that fetal lymphohematopoiesis may be at least partially under the influence of factors other than those of adult cells.

Myelomonocytic myeloproliferative diseases in a horse.

Myelomonocytic myeloproliferative disease in a horse was diagnosed on the basis of hematologic, enzymatic, and histopathologic findings. It was characterized clinically by depression, weight loss splenomegaly, lymphadenopathy, coagulopathy, and bacteremia. Hematologic findings included severe refractory anemia, thrombocytopenia, monocytosis, and pleomorphic leukocytes, with a left shift of the myeloid series. The serum lysozyme concentration was 14.5 microgram/ml (normal, less than 5 microgram/ml). The bone marrow contained many immature cells of the myeloid series and had a myeloid-to-erythroid ratio of 30.5 to 1. The horse died after brief hospitalization. Necropsy revealed generalized lymphadenopathy and hemorrhages throughout the body. Histopathologically, primitive cells were seen in several tissues. Cells that proliferated in the bone marrow were primarily myeloblastic, with some additional erythropoietic cells. Myeloblastic cells with evidence of normal erythropoiesis were seen in numerous lymph nodes and in the spleen, whereas primarily normal erythropoietic cells proliferated in the adrenal glands. Myeloid blast-type cells predominated in the lungs, myocardium, liver, and kidneys.