Intermediate filaments and anaplastic change of ENU-induced gliomass: immunohistochemical study with vimentin and astroprotein (GFAP)

To study the expression of two different subclasses of intermediate filaments in ethylnitrosourea-induced rat cerebral gliomas, the number of cells immunopositive for each subunit protein, vimentin and astroprotein (GFAP), was quantitatively analyzed. Vimentin is a subunit protein of non-specific intermediate filaments which appear transiently in immature glial cells, while astroprotein (GFAP) is a subunit protein of glial filaments, normally expressed in mature astrocytes. Although most normal astrocytes were negative for vimentin, many tumor cells showed weak to strong immunoreaction for vimentin. The expression of vimentin was more frequent and intense in anaplastic forms of gliomas than in benign forms. Accordingly, the vimentin/GFAP ratio [the number of vimentin-positive cells divided by the number of astroprotein (GFAP)-positive cells] was increased from 0.23 to 1.86, and from 0.26 to 1.85, respectively, as oligodendrogliomas and mixed gliomas become anaplastic. The present study demonstrated that the immunohistochemical study for those two subclasses of intermediate filaments can provide important informations on the cell biological nature of glial tumors.

Risk of astrocytic brain tumors associated with occupational chemical exposures. A case-referent study

A case-referent study was conducted on the risk of brain tumors among workers exposed to organic chemicals in petroleum refining and chemical manufacturing. Brain tumor cases in northern New Jersey, Philadelphia, and the Gulf Coast of Louisiana were identified from death certificates of a recent three-year period. The cases (N = 300) were white men aged greater than or equal to 30 years with a confirmed diagnosis of glioblastoma multiforme, astrocytoma, or a mixed glioma with astrocytic cells. The referents (N = 386) were white men who died from causes other than brain tumor, epilepsy, cerebrovascular disease, suicide, or homicide and were frequency-matched with the cases on age at death, year of death, and study area. Next-of-kin were interviewed for complete occupational histories. No statistically significantly elevated odds ratios (OR) were associated with employment in the chemical industry. The risk of astrocytic tumors was elevated among the subjects with production or maintenance jobs in petroleum refining (OR 1.7, 95% confidence interval 0.7-4.2); however, it decreased with duration employed. There were nonsignificant excess risks of astrocytic tumors among the men exposed to cutting fluids (OR 1.6) or organic solvents (OR 1.3), and also among the subjects exposed to lubricating oils (OR 1.4), organic solvents (OR 1.5), or cutting fluids (OR 1.8) for greater than or equal to 20 years.

Promoting effect of 12-O-tetradecanoylphorbol-13-acetate on neurogenic microtumors initiated by transplacental exposure to N-ethyl-N-nitrosourea

The promoting effect of 12-O-tetradecanoylphorbol-13-acetate (TPA) on the occurrence of neurogenic microtumors in SD-JCL rats initiated transplacentally with N-ethyl-N-nitrosourea (ENU) was investigated. The treatment with TPA induced earlier occurrence of microtumors than as compared with the initiation alone. Thus, TPA has tumor-promoting activity on the formation of neurogenic microtumors in rats prenatally exposed to ENU.

Morphological maturation of tumor cells induced by ethylnitrosourea (ENU) in rat brains. II. On the tumors by administration of ENU in the mid-gestational stage

In order to clarify the relationship between cellular characteristics of rat brain tumors and the administration time of chemical carcinogens, the incidence and morphology of microtumors in the offspring of five pregnant Sprague-Dawley rats injected with ethylnitrosourea (ENU) intraperitoneally on the 11th day of gestation (Group I) were compared with those of six pregnant rats injected with ENU on the 18th day of gestation (Group II). Twenty-four microtumors and 6 macrotumors were obtained in Group I and 58 microtumors and 5 macrotumors in Group II. Histologically, the macrotumors of Group I showed a poorly differentiated pattern which corresponded to primitive spongioblastomas in comparison with those of Group II which resembled human mature oligodendrogliomas, astrocytomas or mixed gliomas. The constituent cells of the microtumors of both groups were immature and were morphologically similar to each other. Immunohistochemically, the cells of microtumors of both groups were negative for Leu 7 and glial fibrillary acidic protein. Microtumors in Group I showed more infiltrative proliferation than those in Group II and had indistinct borders. The 3H-thymidine labeling index of the constituent cells of Group I was significantly higher than that of Group II (p less than 0.001). This study revealed that the constituent cells of microtumors of Group I, in spite of being morphologically similar with those of Group II, possess a greater growth potency than the latter. This difference in growth potency is responsible for the difference in the histological maturity of the macrotumors in each group. The difference in morphological maturation of enlarged gliomas induced by ENU appears to depend on the imperceptible difference of the target cell maturation at the initiation of oncogenesis.

Morphological maturation of tumor cells induced by ethylnitrosourea (ENU) in rat brains. I. On the tumors by administration of ENU in the late gestational stage

Sequential changes in the development of ethylnitrosourea (ENU)-induced rat brain tumors were examined histologically, immunohistochemically, electron microscopically and autoradiographically. In 47 Sprague-Dawley rats transplacentally administered ENU, 95 brain tumors developed, including 76 microtumors less than 1mm in diameter. Microtumors were found mainly in the paraventricular area, but some were found in the peripheral brain tissue. They were composed of small tumor cells which had round dark nuclei and scanty cytoplasm immunohistochemically negative for Leu 7 and glial fibrillary acidic protein (GFAP). The 19 macrotumors were mature gliomas, 3 of which histologically corresponded to oligodendrogliomas and 16 to mixed gliomas. The tumor cells of the former had small round nuclei with distinct perinuclear halos and a small amount of cytoplasm positive for Leu 7. The latter were chiefly composed of polygonal cells having large round nuclei and rich cytoplasm positive for GFAP. An autoradiographic study using 3H-thymidine revealed that the labeling index of the tumor cells was high in mixed gliomas and microtumors, but low in oligodendrogliomas. It may be concluded that the constituent cells of microtumors correspond to glioblasts or migrating neuroglias, which gradually mature to form oligodendrogliomas or astrocytomas.

Immunohistochemical studies on cellular character of microtumors induced by ethylnitrosourea in the rat brain utilizing anti-Leu 7 and anti-glial fibrillary acidic protein antibodies

To clarify the chronologic changes in the cellular morphology of ENU-induced rat brain tumors, microtumors in the early stage were examined immunohistochemically in comparison with macrotumors in the advanced stage. The tumor cells composing microtumors were negative for glial fibrillary acidic protein (GFAP), a specific marker of astrocytic cells, and Leu 7, a marker of oligodendrocytes, while cells of macrotumors were positive for either GFAP or Leu 7, showing characteristics of mature glial cells. The results suggested that the small round cells in the early developmental stage, generally thought to resemble mature oligodendrocytes, are not differentiated oligodendrocytes or astrocytes.

An improved rat brain-tumor model

The widely used intracerebral tumor implantation method by freehand injection into parietal or hippocampal areas of the rat brain has proven inadequate for reliable experimental therapeutic studies. Problems include poor intracerebral growth yields and significant rates of spread to extracranial tissues, lungs, and spinal cord. Major variables have been examined experimentally on a model using nitrosourea-induced nervous system tumor cell lines in sygeneic rats. A rapid stereotaxic method greatly improved the consistency of tumor placement. The optimal site was found to be the caudate nucleus. The production of a spheroid intracerebral growth was further facilitated by the use of 1% agar in the cell suspension medium and by an injection volume of 10 mu1 containing at least 10(4) cells. Further improvements involved injection technique and flushing of the operative field. These modifications have resulted in a 99% to 100% yield of intracerebral growth, with a marked reduction in the number and size of extracranial extensions and with distant metastasis rates of 0% to 5%. These results have continually improved with further experience. The method is satisfactory for radiation and chemotherapeutic trials in which survival time as an index of tumor size may be used an an end point.

Carcinogenicity of nitrosotrialkylureas in Fischer 344 rats

Three nitrosotrialkylureas were administered to female F344 rats as approximately 1-mM solutions in drinking water. Nitrosotrimethylurea, given for 47 weeks, gave rise to astrocytomas of the brain and tumors of the forestomach; nitrosotriethylurea induced a high incidence of adenocarcinomas of the breast and uterus and tumors of the forestomach. Nitrosomethyldiethylurea induced almost exclusively a high incidence of both astrocytomas of the brain and tumors of the spinal cord.

LDH isozyme analyses of ethylnitrosourea-induced central nervous system tumors in rats

To provide the significance of LDH isozymes in rat CNS tumors, the changes in lactic dehydrogenase isozyme and calculated ratios of H- to M- subunit were studied by means of polyacrylamide gel enzymoelectrophoresis in tumor extracts from CNS tumors (7 astrocytomas, 4 oligodendrogliomas, 7 mixed gliomas, 6 anaplastic gliomas, 3 glioependymomas, 1 astroblastoma, 11 neurinomas, 8 anaplastic neurinomas and 1 meningioma in Wistar rats which were induced by ethylnitrosourea). The isozyme patterns were compared to those obtained from normal rat CNS tissues. Among the glioma group, oligodendroglioma showed the highest H/M ratio followed by mixed glioma, glioependymoma, astrocytoma, astroblastoma and anaplastic glioma in order of decreasing of H/M ratios. On the other hand, the H/M ratio of neurinoma was significantly higher than that of anaplastic neurinoma. These observation suggested that determination of LDH isozyme patterns could supplement the histological evaluation of brain tumors.

N-ethyl-N-nitrosourea-induced spinal tumors in an inbred strain of W albino rats

Exposure to N-ethyl-N-nitrosourea (ENU) either transplacentally via the maternal bloodstream or postnatally by direct injection into the cerebellum or the cisterna magna resulted in a high incidence of spinal tumors in an inbred strain of W albino rats. After prenatal exposure to 60 mg ENU/kg maternal body weight, as many as 92% of the offspring developed 1 or more tumors in the spinal cord, whereas after postnatal exposure to 0.2 mg ENU/animal, 50% of the animals eventually developed spinal tumors. These tumors included relatively pure oligodendrogllomas, astrocytomas, and the usual mixed gllomas. Obvious clinical symptoms of paralysis of the limbs and weight loss accompanying the high incidence of tumors in the spinal cord make this system pertinent to the study of carcinogenesis in the central nervous system as well as to the study of related problems to the incidence of these tumors are discussed.

Tumor specific fluorescent and complement-dependent cytotoxic antibodies in the serum of rats with chemically induced brain gliomas

Brain tumors were induced in Sprague-Dawley and Long-Evans rats by administration of N-methyl-N-nitrosourea in the drinking water. Of these tumors, a grade 2 mixed glioma, a grade 2 to 3 astrocytoma and a grade 1 to 2 oligodendroglioma were established in vitro, maintained in culture and designated 75SD-G-376, 75SD-G-420 and 77LE-G-180, respectively. Of these mass cultures, two were successfully cloned and are currently available as 75SD-G-376C and 75SD-G-420C cell lines. Clonal lines produce S-100 protein and grow as tumors when isografted in young rats. Using the cultured cells as target cells , specific antibodies were searched for in the sera of the rats with the primary tumors by means of an indirect fluorescent antibody staining method and a complement-dependent antibody-mediated microcytotoxicity assay. Fluorescent and cytotoxic antibodies were demonstrated in the sera of the mixed glioma- and astrocytoma-bearing animals. However, a variable proportion of cells of the 75SD-G-376 and 75SD-G-420 lines showed no reaction with the corresponding sera. Furthermore, cytotoxic antibodies had a lytic effect on the autologous glioma cells only in the presence of rabbit complement.

[Cytophotometric determination of DNA concentration in the cells of experimental brain tumors. II. Primary tumors of rat cerebellum induced by 9, 10-dimethyl-1, 2-benzanthracene]

The Feulgen-DNA cytophotometry was applied for studies of 31 rat cerebellum tumors induced by 9, 10-dimetyl-1,2-bensantracene. Most of these gliomas (22) were astrocytomas of different grades of malignancy. The histological diagnosis of other tumors was: glioblastoma -- 4, oligoastrocytoma -- 2, oligodendroglioma -- 1, gliosarcoma 1. The majority cells of 26 tumors had diploid or paradiploid DNA quantity, 4 tumors (1 astrocytoma, 3 dedifferentiated astroyctomas) had triploid modal classes. The tetraploid modal class and a large number of polyploid cells were found only once for glioblastoma multiforme. A supposition was made that drastic changes of ploidy could arise for the second time during the process of tumor evolution. The authors failed to show any exact differences in the ploidy of gliomas in rats with athyreosis or hyperthyreosis, and in the ploidy of somatic cells in control animals.

Inhibitory effect of sodium ascorbate on ethylurea and sodium nitrite carcinogensis and negative findings in progeny after intestinal inoculation of precursors into pregnant hamsters

To assess their carcinogenic effects, the ethylnitrosourea (ENU) precursors, ethylurea and sodium nitrite, [were administered to pregnant hamsters as a single intragastic] dose on day 15 of gestation, or introduced into the cecum on day 14. Since sodium ascorbate (NaASC) inhibits the biosynthesis of nitrosamides, identical doses of the precursors were given concomitantly with NaASC. Progeny of mothers treater intragastrically developed significant incidences of neurogenic tumors of the peripheral nervous system, with a predominance in females. The concurrent administration of NaASC with ENU precursors prevented carcinogenic effects in the progency, whereas the simultaneous inoculation of the precursors into the cecum produced no carcinogenic effects in the offspring.

[Deoxyribonucleases in spontaneous and experimental tumors of the nervous system]

DNA- and RNA-concentrations, as well as in vitro activities of DNase I (EC 3.1.4.5), DNase II (EC 3.1.4.6), and DNase I inhibitor, have been determined in 63 spontaneous (man) and 22 experimentally induced (rat) nervous system blastomas of various types and of different degrees of malignancy. Generally, a distinct elevation of DNA concentrations and of the ratio (Q) of DNase II- to DNase I-activities has been observed when compared with control values. A statistically significant relationship could be demonstrated between increase of DNA concentrations and Q in experimentally induced neurinomas of rats as well as in human astrocytomas and glioblastomas. Whereas the increase of Q may be a biochemical expression of elevated DNA synthesis of tumour cells, no conclusions can be drawn as to the role of DNases in the process of malignant transformation.

Transplacental induction of neurogenic tumors in BD IX rats by intragastric administration of ethylnitrosourea precursors

The concurrent daily intragastric administration of ethylurea at two dose levels (50 mg/kg and 100 mg/kg bodyweight) together with one dose level of sodium nitrite (50 mg/kg bodyweight) by a stomach tube to pregnant BD IX rats from day 15 to day 22 of gestation resulted in the induction of neurogenic tumors in all offspring. Since both ENU-precursors alone do not produce neurogenic tumors, these results are evidence of ENU formation from its precursors under the influence of gastric juice. Differences in the survival time and the incidence of tumors at both dose levels were not significant. The amount of ethylnitrosourea synthesized in the animals was very close at both dose levels, and was dependent on the amount of sodium nitrite applied. The experimental results are consistent with the conclusion, that the rat fetuses had been exposed to a total amount of about 60 mg/kg ethylnitrosourea. Neurogenic tumors dominated with 98% incidence over the non-neurogenic. The incidence of neurogenic tumors per rat was high (6.0 for Group I and 6.7 for Group II). Neurogenic tumors were equally distributed among the central and peripheral nervous systems. The neurogenic tumors induced with the precursors of ethylnitrosourea were morphologically similar in all aspects to those induced with the carcinogen itself and could be classified as oligodendroglioma, astrocytoma, mixed glioma, anaplastic glioma, glioependymoma, ependymoma, and neurinoma. Three unusual tumors were found: one early anaplastic "septum ependymoma" in the dorsal column of the spinal cord, and two special mixed tumors of the cranial nerves, i.e. a neurinoma with portions of an oligodendroglioma and a neurinoma with parts of an invasive ependymoma.

Histopathological studies of the nervous system tumors in rats induced by N-nitroso-methyl-urea

Histopathological examinations were made on tumors of the nervous system induced in rats of Donryu strain by weekly intravenous injections with N-nitroso-methyl-urea (NMU) or by a single administration of NMU through the mothers. A total of 176 neural and nonneural neoplasms were produced in this study. It was suggested that the fetal nervous system of Donryu rats was also highly susceptible to the oncogenic effects of NMU. Of these tumors produced, those of the peripheral nervous system amounted to 121, comprising 68.7% of the total number of the neoplasm. Microscopically, most of the nerve tumors showed the histology corresponding to that of human neurinomas. Many tumors, however, disclosed more or less anaplastic cytological appearance. Fifteen gliomas were produced in the brain and spinal cord. Microscopically, they were classified into mixed glioma, oligondendroglioma and anaplastic astrocytoma. The commonest brain tumors produced in rats from intravenously treated group were periventricular mixed gliomas, while gliomas in rats from transplacentably treated group showed an isomorphic histology with a close resemblance to that of oligodendroglioma.