Occupational exposure and brain tumors

Epidemiological evidence of an occupational risk of brain cancer has been reported in four industries where chemical exposures are likely, most recently in a series of prospective studies in the petrochemical industry. However, only in the case of vinyl chloride exposure has an occupational central nervous system carcinogen been identified. This report reviews the convergence of epidemiological and laboratory evidence that established the occupational carcinogenicity of vinyl chloride, and discusses in detail the current evidence for an occupational risk of brain tumors in the petrochemical industry.

[Flow cytometric study of enhanced effect of anti-cancer drugs induced by nicardipine hydrochloride]

Flow cytometric analysis was used to study the effect of a calcium influx blocker, nicardipine hydrochloride, on the cytotoxicity of anti-cancer drugs in tumor cells. The parameters used for this study were DNA- and protein-cell distribution histograms. Cells and drugs used for this study were C6 cells from CD Fisher rat glioma and VCR, ADM and ACNU, respectively. The growth inhibitory effect estimated by concentration at ID50 on C6 cells was indicated as follows; VCR showed an 89-fold enhancement, while ACNU showed little enhancement following addition of nicardipine hydrochloride. DNA and protein histograms obtained by flow cytometry revealed almost the same effects as cells which were studied using high concentration of VCR without nicardipine hydrochloride. For the other drugs, ADM showed a small enhancement on histograms, while with ACNU, little enhancement was noted as well as the inhibitory effect of each drug described above. The results indicate that nicardipine hydrochloride greatly affects the cell cytotoxicity of VCR but not so much with ADM and ACNU. From these results, it appears that this drug enhances the action of anti-cancer drugs not only by merely blocking the efflux of drugs from cells but also by other mechanisms which remain to be clarified.

Carcinogenic and toxicologic effects of inhaled ethylene oxide and propylene oxide in F344 rats

The chronic inhalation toxicity and carcinogenicity of ethylene oxide (EO) and propylene oxide (PO) were evaluated in a 2-year inhalation bioassay. Five groups of male weanling Fischer 344 rats, 80 per group, were exposed at 0 ppm (shared control; filtered air), 50 ppm EO, 100 ppm EO, 100 ppm PO, or 300 ppm PO (7 hr/day, 5 days/week) for 104 weeks. Body weights from rats exposed to EO and PO at all exposure concentrations were significantly reduced compared to controls. A statistically significant increase in mortality was observed in all groups of exposed rats compared to controls. Skeletal muscle atrophy in the absence of any sciatic nerve neuropathology was found in rats exposed at 100 ppm EO and 300 ppm PO. Statistically significant associations between EO exposure and an increased incidence of the following rat neoplasms were observed: mononuclear cell leukemia, peritoneal mesothelioma, and mixed cell brain glioma. Among rats exposed to PO there was a dose-dependent increase in the incidence of complex epithelial hyperplasia in the nasal passages, and two adenomas were detected in the nasal passages of rats exposed at 300 ppm PO. The incidence of adrenal pheochromocytomas was elevated in both PO exposure groups, but not in a dose-related manner. All rat groups were affected by an outbreak of Mycoplasma pulmonis infection which occurred about 16 months into the study. This infection alone and in combination with the epoxide exposures affected the survival of rats in this study, and influenced the development of the proliferative lesions in the nasal mucosa of the PO-exposed rats. No treatment-related changes in any clinical chemistry or urinalysis indices were detected. PO exposure did not increase the incidence of the three neoplasms associated with EO exposure; however, adrenal pheochromocytomas and proliferative lesions of the nasal cavity were increased in rats exposed to PO.

[Ultrastructural organization of methylnitrosourea-induced brain tumors in the rat. Serial transplantation]

The specific ultrastructural features of two transplantable rat gliomas (221 and 223) are described. The tumors contained poorly differentiated anaplastic cells and differentiated cells with a great amount of gliofibrils. The resemblance of experimental gliomas to human gliomas is discussed. The capillary ultrastructure in the transplantable gliomas is described.

Reduction of N-nitroso-N-ethylurea-induced neurogenic tumors by X-radiation: a life-span study in rats

Whole-body X-irradiation after neonatal injection with N-nitroso-N-ethylurea (ENU) significantly reduced the incidence of induced neurogenic tumors in inbred HMT rats kept for their complete life-span. After administration of 10 mg ENU/kg and 1.25 Gy X-radiation, the incidence of schwannomas but not of gliomas was reduced as compared to the incidence in rats given 10 mg ENU/kg only. In contrast, after administration of 4 mg ENU/kg, 1.25 Gy reduced the incidence of gliomas but not of schwannomas. Administration of 1.25 Gy alone induced a remarkably high incidence of rats with neurogenic tumors (20%). Latency of tumor detection was not significantly affected by radiation. Among the most frequently occurring nonneurogenic tumors, squamous cell carcinomas were reduced in incidence by treatment with ENU, 1.25 Gy X-radiation, or both combined. No treatment affected the incidence of pituitary or mammary tumors. There was a preponderance of ovarian tumors in rats given 4 mg ENU/kg + 1.25 Gy. An incidental finding was the occurrence of granular cell tumors in 7 rats from different treatment groups.

Regional blood flow in ethylnitrosourea-induced brain tumors

Regional blood flow was measured in experimental brain tumors using iodoantipyrine labeled with carbon 14 and quantitative autoradiography. A total of fifteen oligodendrogliomas, sixteen mixed gliomas, one astrocytoma, one ependymoma, and three malignant schwannomas were studied in 9 rats. The mean tumor blood flows for all glioma classifications were similar, averaging 45 +/- 3 (standard error of the mean) ml . hg-1 . min-1. Flow was fairly uniform within individual oligodendrogliomas and there was no apparent correlation between blood flow and tumor size or location. The mixed gliomas were larger than the oligodendrogliomas and had a wider range of blood flow. Small focal areas of necrosis were observed in 7 mixed gliomas, and low flows were usually measured in these regions; these flows were not always the lowest regional values measured within the mixed gliomas or total group of tumors, however. Small tumor regions with increased vascularity, frequently with endothelial cell proliferation, were observed in oligodendrogliomas and to a greater extent in mixed gliomas; these regions were correlated with small elevations in blood flow (10 to 15 ml . hg-1 . min-1) in comparison with surrounding tumor tissue. Brain adjacent to tumor usually had higher blood flows than that in tumor periphery. Hemispheric differences in blood flow related to the site of primary tumor growth were not observed.

Early stage of development of transplacentally induced glioma with ethylnitrosourea in rats. Sequential historadioautographic and electron microscopic studies

Proliferative activity of possible preneoplastic cells (subependymal cells and glioblasts), early neoplastic cells and glioma cells induced by transplacental ethylnitrosourea (ENU) treatment in the rat was analysed by historadioautography and electron microscopy. Labeling index of 3H-thymidine in subependymal cells was the highest in the cerebrum of postnatal age, but no difference was observed between the normal and ENU treated groups. Thus, preneoplastic cells could not be distinguished from normal cells by morphology and proliferative activity. Focus of early neoplastic proliferation was composed of rather heterogenous and less differentiated cells, such as oligodendroblast-, glioblast- and subependymal cell-like cells, and preferentially located around the periventricular areas. Labeling index of early neoplastic proliferation was very low although the value gradually increased with age. Proliferative activity of glioma cells was higher than that of the early neoplastic cells and lower than subependymal cells, and further differed according to the degree of differentiation and morphological type. Finally, it is suggested that glioma might develop mainly through the differentiation from the focus of early neoplastic proliferation.

[Brain tumors in the rat induced by methylnitrosourea (induction, transplantation, monolayer cultivation)]

Tumors induced in rats by chronic methylnitrosourea administration are described. Two strains of transplantable brain gliomas obtained by serial intracerebral transplantation of primary neoplasms and their monolayer cultures are characterized. These tumors were similar to human malignant gliomas in morphological and biological properties. They possesses high oncogenicity and are easily cultured in a monolayer, which allows their application in oncological and biochemical studies.

Microvascular abnormalities in ethylnitrosourea (ENU)-induced rat brain tumors: structural basis for altered blood-brain barrier function

The fine structure, histometric characteristics, and permeability of microvessels were studied by electron microscopy in normal and in ethylnitrosourea (ENU)-induced glioma tissue from rats, using horseradish peroxidase (HRP) as a tracer. The tumor vessels were classified into (1) capillary buds (Type I); (2) round small to large capillaries (Type II); (3) sinusoidal or venule-like microvessels (Type III), and (4) abnormal arteriole-like microvessels (Type IV). All endothelial cells, basement membranes and periendothelial cells in the tumor tissue demonstrated changes in structure. The most striking alterations occurred in the endothelial cells; there were abnormal endothelial tight junctions, altered pinocytotic activity, and thickening. In the tracer study, the reaction product of HRP was present around some sinusoidal or venule-like microvessels (Type III) and extended to the widened extracellular spaces around the microvessels. The endothelial cells of Type III microvessels showed decreased nuclear and mitochondrial fractions, and increased euchromatin content and a rough endoplasmic reticulum fraction. The pinocytotic vesicles with the HRP reaction product in the endothelial cells were not increased in number. Fenestrations and gaps of the endothelial cells were observed. These alterations of the endothelial cells of sinusoidal or venule-like microvessels (Type III) are considered to be the main cause of breakdown of the blood-brain barrier in this tumor.

DNA repair kinetics in irradiated undifferentiated and terminally differentiated cells

The brains of male Fisher 344 rats bearing 80-150 mg intracerebral 9L/Ro tumors were irradiated with doses of 1,250-5,000 rads of x- or gamma-rays. At various times after irradiation, the cerebellum and tumor were excised, dissociated into single cells and the DNA from these cells sedimented through alkaline sucrose gradients in zonal rotors with slow gradient reorienting capability. Quantitation of the DNA repair kinetics demonstrated that the process in both tumor cells and neurons has a fast and slow phase. Although all other alternatives cannot be completely eliminated, we suggest that these two phases are most reasonably interpreted as representing repair of lesions in very accessible and less accessible regions of the genome rather than 1) repair of different types of lesions such as single- or double-strand breaks or 2) removal of immediate breaks and breaks induced during excision repair of latent base damage. The slow repair phase is saturable, but not inducible in both tumor cells and neurons. The data suggest that tumor cells restore their chromosomal DNA structure to the unirradiated state faster than neurons because 1) they contain more of the repair system per unit of DNA and 2) a larger proportion of their genetic material is comprised of very accessible regions. The data also suggest that the entire tumor cell genome may be accessible to the repair enzyme(s), while it is possible that a portion of the neuronal genome may be completely inaccessible.

Biochemical and histochemical evaluation of glycosaminoglycans in brain tumors induced in rats by nitrosourea derivatives

The occurrence, distribution and concentration of GAGs in ENU and MNU experimental brain tumors induced in the rat are reported. GAGs have been histochemically studied by Alcian Blue methods; they have been quantified and qualitatively evaluated by electrophoresis of brain extracts. The pattern of GAGs in normal rats is consistent with the data of the literature. No GAG accumulation precedes the tumor development. Early neoplastic proliferations, oligodendroglial and mixed glial microtumors are strongly alcian-positive; the alcianophilia spares clusters of cells developing a cytoplasm. In large tumors, GAGs are histochemically demonstrable in the honey-comb areas of oligodendrogliomas and in peripheral infiltration areas of polymorphic gliomas. The role of the normal nervous tissue and oligodendroglial cells in the accumulation of the GAGs is discussed. The accumulated GAGs seem to rise from the nervous tissue included in the tumors, rather than from the metabolism of tumor cells.

Distribution of bleomycin in ethylnitrosourea-induced gliomas in rats

We used a microbioassay to study the distribution of bleomycin in rat brain tumors induced in newborn Sprague-Dawley rats with 1-ethyl-1-nitrosourea (ENU, 50 mg/kg s.c.). Upon suspected successful tumor induction bleomycin (0.1 g/kg i.v.) was administered, and 2 hr later bleomycin concentrations in major organs and tumor tissues were bioassayed using Bacillus subtilis PCI 219 IMC. To determine their histology, the tumors were stained by the immunofluorescence- or immunoperoxidase method using antiserum to astroprotein in addition to the conventional staining methods. There were 11 gliomas each of the brain and spinal cord, 14 schwannomas of the trigeminal nerve and 4 adenomas of the pituitary gland; they developed within 8 (gliomas), 7.3 (schwannomas) and 15 (adenomas) months on average after ENU treatment. The bleomycin concentration and the tumor:plasma concentration ratio were 7.69 +/- 2.84 micrograms/g and 0.13 +/- 0.05 (brain gliomas), 7.10 +/- 3.15 micrograms/g and 0.27 +/- 0.12 (spinal cord gliomas), 5.40 +/- 1.41 micrograms/g and 0.23 +/- 0.05 (schwannomas), 4.83 +/- 1.05 micrograms/g and 0.21 +/- 0.08 (adenomas). Normal brain- and spinal cord tissues scarcely contained bleomycin.

[Local cerebral glucose utilization in the ethylnitrosourea-induced rat glioma]

Local cerebral glucose utilization (LCGU) of anesthetized rats bearing ethylnitrosourea (ENU)-induced gliomas was studied with 14C-deoxyglucose autoradiography. Single subcutaneous injection of ethylnitrosourea (50 mg/kg) was made to the newborn rats, and animals were used for experiment at 150 to 300 days after birth. Under ketamine anesthesia, 14C-deoxyglucose was injected through a venous catheter, and timed arterial sampling was made. Brains were removed at 45 min after injection, and prepared for macro-autoradiography. LCGU values were measured by the equation developed by Sokoloff et al. In the microtumors (less than 2 mm in diameter), mean LCGU value was 30 mumol/100 g/min, which was significantly (p less than 0.01) lower than mean value of normal cortex (63 mumol/100 g/min). In the macrotumors (greater than 2 mm in diameter). LCGU values in the tumor were separated to high part (mean; 49 mumol/100 g/min) and low part (mean; 38 mumol/100 g/min), which were still lower than mean cortical value and higher than mean white matter value (corpus callosum; 26 mumol/100 g/min). No LCGU changes were noted in the brain tissue adjacent to the microtumors. Whereas, macrotumor significantly reduced LCGU in the adjacent cortex. The present data may indicate that glucose metabolism of the ENU induced glioma and edematous peritumoral brain tissue is lower than that of normal cortex.

Serologic analysis of nitrosourea-induced rat gliomas

Inbred CDF rats (cesarean-delivered F344 rats) were immunized with either a nitrosourea-induced glioma EA-285 or its subline EA-285A and both with and without Corynebacterium parvum. A humoral immune response in syngeneic rats to the immunizing tumor was demonstrated with micromodifications of different rosette assays (immune adherence assay, protein-A assay, and anti-C3-mixed hemadsorption assay). Extensive absorption studies of two immune sera with the highest reactivity revealed two glioma-specific antigens (or two components of one antigen) on the cell surface of the cloned tumor subline. One antigen was present only on the cell surface of the subline of the glioma used for both immunization and absorption analyses. The other antigen appeared on the cell surface of both the cloned subline EA-285A and the parental cell line EA-285. These preliminary studies showed that CDF rats immunized against a syngeneic glioma mounted a humoral immune response that appeared to be individually tumor-specific.

Invasive pattern and phenotypic properties of malignant neurogenic rats cells in vivo and in vitro

Twelve malignant neurogenic rat cell lines induced by the carcinogen ethylnitrosourea (EtNU) have been investigated for invasiveness in an in vitro three-dimensional culture system. The histological pattern of invasiveness into embryonic chick heart fragments has been compared to the morphology in subcutaneous and intracerebral solid tumours as well as to other phenotypic properties of the cells. In all the cell lines invasiveness was seen both in vivo and in vitro. The site of in vivo transplantation seemed to influence the tumour-host tissue interface, since intracerebral tumours were more sharply delimited than subcutaneous tumours and primary EtNU-induced CNS tumours. The histological patterns in vivo (glioma versus neurinoma-like) were in most cases similar to invasive growth in vitro. The pattern of invasiveness did not correlate to other phenotypic properties of the cells (e.g. ploidy, doubling time, latency for tumour formation and surface microarchitecture). A rat fibroblastic cell line, RE-E was non-tumourigenic in rats and non-invasive in culture, but formed small subcutaneous tumours in nude mice.

In vitro sensitivity of nitrosourea-induced neurogenic tumors to ACNU

The effect of ACNU on the in vitro viability of a methylnitrosourea-induced gliosarcoma (T9) and two ethylnitrosourea-induced brain tumors, TR-481 (a malignant neurinoma) and EB-679 (a glioma) was studied. T9 was highly sensitive to ACNU, demonstrating loss of cells following a 3 hour exposure time to 5 microgram/ml; TR-481 was sensitive to 40 microgram/ml of ACNU and EB-679 was highly resistant to 40 microgram/ml of ACNU. The in vitro sensitivity of the tumor cell lines to ACNU is: T 9 greater than TR-481 greater than EB-679. This data indicates that variability of response to both concentration and exposure time of ACNU of malignant brain tumor cells must be taken into consideration in planning in vitro and/or in vivo treatment of experimental brain tumors.

Natural cytotoxicity against chemically induced neurogenic rat tumors

The 51Cr cytotoxicity assay was modified for ethylnitrosourea (ENU) and methylnitrosourea (MNU) induced rat neurogenic tumor cell lines. Investigations on "immune" lymphoid cytotoxicity showed little cytotoxicity above normal. Alteration in the level of lymphocytotoxicity was seen immediately after injection of a highly immunogenic tumor (EA-528). Natural cytotoxicity (NC) was present against all neurogenic tumor cell lines tested and xenogenic cell lines. The level of NC activity was dependent on age, specific tumor cell line and could be increased by isolating the nylon wool non-adherent "T" cell population. Allogenic WFu rat lymphocytes were tested for NC activity in vitro against CDF tumor cells. NC activity has potential use against these tumors in vivo.

Regional blood flow and capillary permeability in the ethylnitrosourea-induced rat glioma

Regional cerebral blood flow and capillary permeability of rat brains bearing ethylnitrosourea-induced gliomas of various size were investigated with 14C-antipyrine autoradiography and Evans blue staining. In the small tumors (less than 2 mm in diameter), blood flow was uniformly reduced when compared to the adjacent brain. Even in tiny tumors (0.3 to 0.4 mm in diameter), reduction in blood flow was evident. In the medium (2 to 4 mm in diameter) and large (greater than 4 mm in diameter) tumors, the blood flow increased or decreased depending on the part of the tumor examined. The necrotic center and peripheral edge had low blood flows, whereas the viable portion adjacent to the necrotic center had high blood flows. Blood flow in the brain tissue adjacent to medium and large tumors was lower than control brain tissue, probably due to local edema. Leakage of intravenous Evans blue in the tissue was only evident in the large tumors with central necrosis. The present findings suggest that neovascularization of the tumor may occur when the tumor reaches a certain size, and leaky new vessels may be the cause of brain edema associated with tumor.

[Changes of blood-brain barrier in the ethylnitrosourea induced rat glioma (author's transl)]

Capillary permeability of rat brains bearing ethylnitrosourea induced rat glioma was measured with quantitative autoradiography. In the small tumors (less than 2mm in diameter), no changes in capillary permeability was noted. When tumors became larger and neovascularization of the tumor occurred, increase in capillary permeability was evident. This change was more prominent in the center of the tumor than in the periphery. In the large tumors, the capillary permeability was markedly increases, and the value was similar to that in the choroid plexus. This indicates that blood-brain barrier(BBB) completely disappeared in the large tumors. This BBB change may be the main cause of tumor induced brain edema. The data also provide the information about pharmacokinetics of water soluble drugs in the brain tumors.

[Regional blood flow in the ethylnitrosourea induced rat glioma (author's transl)]

Regional cerebral blood flow of rat brains bearing ethylnitrosourea induced glioma of various size was investigated with 14C-antipyrine autoradiography. In the small tumors (less than 2 mm in diameter), blood flow was uniformly reduced when compared to the adjacent brain. Even in tiny tumors (0.3-0.4 mm in diameter), reduction in blood flow was evident. In the medium (2-4 mm in diameter) and large (greater than 4 mm in diameter) tumors, the blood flow increased in the viable center of the tumor and decreased in the necrosis and peripheral edge. High blood flow in the viable center may be attributable to the neovascularization of the tumor. Blood flow in the brain tissue adjacent to medium and large tumors was lower than control brain tissue probably due to local edema. This reduction in blood flow may be partly attributable to the appearances of the focal neurologic deficits. The result obtained may provide some information about growth regulation of glioma and also pharmacokinetic delivery of chemotherapeutic drugs to the malignant brain tumors.