Use of Cultures of Neuroblastoma and Glioma as a Model System to Study the Heavy Metal-Induced Neurotoxicity

Abstract

We have been using monolayer cultures of neuroblastoma (NB) and glioma cells as an experimental model to study the cellular and molecular mechanisms of toxicity of heavy metals on nervous tissue. We have obtained the following information: (a) Glioma cells are more sensitive to methylmercuric chloride (CH3HgCl) than neuroblastoma for the criterion of growth inhibition (due to cell death and inhibition of cell division). Inorganic mercury (HgCl2), organic lead (tri-n-butyl lead acetate), and acrylamide do not produce such a differential effect. (b) Vitamin E and inhibitors of cyclic nucleotide phosphodiesterase (papaverine, R020-1724, and isobutylxanthine) protect glioma cells against CH3HgCl-induced toxicity; however, it does not protect neuroblastoma cells. (c) Vitamin C enhances the effect of CH3HgCl on NB cells, but not on glioma cells. (d) Glioma cells produce factor(s) into the medium which enhances the effect of CH3HgCl on both glioma and NB cells. (e) CH3HgCl markedly reduces cyclic AMP-induced morphological differentiation of NB cells, but not of glioma cells. (f) Acute treatment of NB cells (1 μM) and of glioma cells (0.3 μM) with CH3HgCl increases the intracellular level of cyclic AMP. (g) Chronic treatment of glioma cells with CH3HgCl reduces the response of prostaglandin E1-sensitive adrenylate cyclase, but chronic treatment of NB cells does not produce such an effect. (h) The response of dopamine- and norepinephrine- sensitive adenylate cyclases in NB cells does not change after acute or chronic treatment with CH3HgCl. (i) Chronic and acute treatment of glioma cells with low concentrations (0.05 to 0.1 μM) of CH3HgCl produces marked changes (increases and decreases) in the amounts and net cyclic AMP-dependent and -independent phosphorylation profiles of specific proteins. Chronic treatment of NB cells (0.1 and 0.2 μM) does not produce any significant alterations in the amounts of specific proteins, but it causes marked changes in the cyclic AMP-dependent and -independent phosphorylation levels of cellular proteins. The morphology and doubling time of chronically treated glioma and NB cells are similar to those of untreated cells. These data show that the cultures of NB and glioma cells could be used as sensitive biological assay for investigating the effects of those environmental pollutants which are known to cause or which have potential to cause neurological disorders.