Influence of antimonite, selenite, and mercury on the toxicity of arsenite in primary rat hepatocytes.

The long-term toxicity of arsenic (As) as a result of exposure to contaminated drinking water might be modified by coinciding exposures to elements like selenium, antimony, or mercury. In this study the influence of tetravalent selenite, trivalent antimonite, and divalent mercury was investigated in vitro using cultured primary rat hepatocytes. The cell vitality was assessed in the 3-[4,5-dimethylthiazol-2-yl-2,5-diphenyltetrazolium bromide] (MTT), assay with concurrent exposures of the cells to up to 50 microM sodium arsenite(III) and a potential modifier [50 microM sodium(IV) selenite, 10 microM antimony(III) chloride, 25 microM mercuric(II) chloride], which indicated an additive increase in the combined cytotoxicity. Sodium arsenite was tested for genotoxicity in the micronucleus test in a concentration range of 0.25 up to 7.5 microM. In this range, the MTT conversion was at least 80%, indicating high cell viability. Adose-dependent induction of micronuclei was observed. The lowest concentration causing a significantly elevated frequency of micronuclei was 1 microM As (p < 0.05). A significant influence (i.e., reduction of the combined genotoxicity as a result of the presence of a potential modifier) was only observed for 10 and 25 microM antimony chloride (p < 0.05, Fisher's exact test). The metabolic methylation of arsenite was not affected by concurrent incubation with any of the potential modifiers.

Lithium inhibits growth in a murine neural precursor cell line.

The influence of lithium on cell growth and cell viability was studied in short-term cultures of a neural precursor cell line (NT) developed from a murine teratocarcinoma. At very low concentrations ranging from 0.1 mM to 1 mM Li2CO3 (equivalent to therapeutic blood concentrations) there was no difference between untreated and treated cultures. 10 mM lithium (Li+) was found to be toxic with 33% of cell death, while there was inhibition of growth without cell death at concentrations of 2.5 mM and 5 mM of Li+. In experiments where 2.5 mM Li+ was added at the time of seeding, there was growth arrest on day 1 followed by recovery on day 2. Flow cytometric analysis revealed that cells treated with Li+ were blocked in S phase. At 5 mM concentration of Li+, the recovery occurred on day 3 and the plating efficiency was significantly low. The ability to form colonies in soft agar was reduced at 2.5 mM and 5 mM concentrations of Li+ to an equal extent. Thus, Li+ has growth inhibitory as well as anchorage-independent growth reducing effects. The NT cell line therefore would be a good model system to study the mechanism of teratogenic effect of Li+.

A neural precursor cell line derived from murine teratocarcinoma.

A cell line NT with phenotypic features of neural precursor cells has been established from an embryo-derived teratocarcinoma in Swiss mouse where, on serial transplantation, the developmental potential becomes restricted to neural pathway. All the cells are positive for nestin (a marker of neuroepithelial stem cells). Many of them are also positive for NFP and/or GFAP. Moreover there is a gradual decrease from 75% to 50% in reactivity for alkaline phosphatase, a marker for EC cells with repeated passages. The bipotential nature, and the probable decline of EC cells suggest that NT is a neural precursor cell line. The cells have doubling time of 12 h with a plating efficiency of 50%. The cells form colonies in soft agar within 7 days and tumorigenicity in syngeneic mice is lost after 70th passage. However, after 70 passages cells do form tumors in nude mice within 5 days and these tumors exhibit better differentiated morphology than the tumors in syngeneic mice. All the other characteristics remain stable. The myc and ras family of oncogenes do not show any alterations in early or late passages. This cell line may therefore be considered as a differentiated cell line derived from teratocarcinoma.

Developmental expression of neurofilament and glial filament proteins in rat cerebellum.

Neurofilament protein (NFP) consists of three subunits: NF200, NF150 and NF68. Several studies on expression of NFP in developing brain have shown that NF200 appears later than NF150 and NF68. However, there are some reports on simultaneous appearance of these subunits in development. The present study is an attempt to resolve this controversy. Rat cerebellum was chosen as most of its development takes place during the first three weeks of postnatal period. Cytoskeletal and NFP preparations from newborn (P0), postnatal day 8 (P8), P15, P21, P30 and adult (3 months) rat cerebella were subjected to electrophoresis on 7.5% SDS-PAGE. All the NFP subunits were present from P0 onwards and there was an increase in NFP content and glial fibrillary acidic protein (GFAP) with age as revealed by the densitometric scanning. Immunoblots of NFP preparations confirmed the presence of NF200 in the early postnatal cerebellum. In vivo phosphorylation studies indicated the presence of phosphorylated NF subunits from P8 onwards, which was confirmed by staining in immunoblots by SMI31. Immunohistochemical studies on Bouin's fixed tissues revealed that in P0 cerebella, the deeper neurones (soma and processes) expressed all the NFP subunits while from P8 onwards they were negative for NF200. Similarly, Purkinje cells (soma) expressed transiently NF200 subunits on P8 and ceased to express them from P15 onwards. The white matter was immunopositive for NF200 and NF150 on P0 and the intensity of staining increased progressively. Astrocytes expressing GFAP were seen in cerebellar white matter from P8 onwards and the staining in radial glia could be detected from P15 onwards.(ABSTRACT TRUNCATED AT 250 WORDS)

Regional distribution study of brain perfusion and metabolic agents in normal and tumour bearing rat brains using autoradiographic technique.

Regional distribution of brain perfusion imaging agents, [131I]N,N,N'-trimethyl-N'-[2-hydroxy-3-methyl-5-iodobenzyl]1,3 propanediamine (HIPDM) and [131I]-N-isopropyl-p-iodoamphetamine (IMP), was compared with the distribution of patterns of [14C]L-methionine and [14C]D-glucose in normal and tumour bearing rat brains using autoradiographic technique. There was higher concentration of the radiopharmaceutical in grey than white matter in normal rat brain. Autoradiographs of brain tumour sections showed very low uptake of [131I]HIPDM and [131I]IMP as compared to normal brain tissue. There was moderate concentration of [14C]D-glucose and avid uptake of [14C]L-methionine in tumours. Autoradiographic study is useful for evaluating distribution patterns of radiopharmaceuticals.

Rat renal mesenchymal tumor as an experimental model for human congenital mesoblastic nephroma: I. Induction.

The effect of low-dose (2 Gy) radiation on ethylnitrosourea (ENU)-induced neoplasms was studied in Sprague-Dawley and Holtzman strains of rats. With a 60 mg/kg dose of ENU administered on day 1 in Sprague-Dawley rats, 18.4% of the neoplasms induced were found in the kidney. When the same dose of ENU was given on day 10, the incidence of kidney tumors fell to 2.8%. Prior (2 Gy) radiation on day 9 enhanced kidney tumor induction to 16.1%, a trend also observed in the case of ENU-induced neural tumors. In Holtzman rats, 40 mg/kg ENU induced more kidney tumors (12.5%) when given on day 4 than on day 0, and prior irradiation enhanced the ENU-induced kidney tumors even though the interval between irradiation and carcinogen administration was fairly long--4 days.

Rat renal mesenchymal tumor as an experimental model for human congenital mesoblastic nephroma: II. Comparative pathology.

The morphological features of kidney neoplasms induced by ethylnitrosourea (ENU) with or without prior irradiation were examined with a view to comparing them with human renal tumors of childhood. The rat renal tumors consisted of poorly differentiated, highly mitotic mesenchymal cells frequently attempting to differentiate along fibroblastic and myofibroblastic lineages. Though the host renal tubules were frequently entrapped in these tumors, immature tubules and islands of epithelial cells occasionally were seen to form an integral part of the neoplasms. Rarely, adenomatous areas surrounded by mesenchymal proliferation were observed. None of the tumors had the blastemal component that is the hallmark of nephroblastoma. The rat mesenchymal tumors resembled the human congenital mesoblastic nephroma.

Effect of irradiation on ethyl nitrosourea induced neural tumours in Wistar rat.

Wistar rats received 2 Gy whole body irradiation followed immediately by 10 mg/kg of ethyl nitrosourea (ENU) on the day of birth. Out of 33 rats which were given ENU alone 14 developed 22 tumours of the nervous system, out of which 15 (68.2%) were gliomas and 7 (31.8%) were Schwannomas. Out of 34 rats which were given both irradiation and ENU 12 were found to harbour 15 neural tumours out of which 14 (93.3%) were gliomas and 1 (7.1%) was a Schwannoma. The pretreatment with irradiation seems to have resulted in selective suppression of Schwannoma induction.

Optical and ultrastructural pathology of vitamin A pretreated hamster cheek pouch--exposed to lime (Ca(OH)2) and tobacco over total life span.

A close correlation is postulated between tobacco chewing and the high incidence of oral cancer and precancer in many South East Asian nations. However, attempts to induce malignancy in laboratory animals by exposure to ingredients of betel quid are unsuccessful. This is another attempt to induce malignancy in the hamster cheek pouch epithelium by exposure to the ingredients of betel quid - lime and tobacco, for the total life span of the animals - 100 to 110 weeks. Parallel conditioning by exposure to vitamin A is also included. The cheek pouch epithelium of animals exposed to the test substances for total life span shows only epithelial dysplasia of a marked degree, but no evidence of malignancy. It is concluded that it is not possible to simulate the time-dose relationship in human addiction to tobacco or to betel chew in experimental animals due to their comparatively small life span.