title: Glutamine synthetase activity as a marker of toxicity in cultures of embryonic chick brain and retina cells.
abstract: With the goal of developing a fast and sensitive primary cell culture assay for the determination of neurotoxic potential of compounds, the effect of various toxins on the morphology, cell number (estimated as total cell protein), and glutamine synthetase activity of chick embryonic neural cells has been tested. Isolated retina or brain cells, grown as reaggregates in suspension cultures or as monolayers in 24-well plates, were treated with the substances from day 2 to day 6 after the start of culture. Concentrations causing 50% reduction in protein content in brain cell monolayers were as follows: MeHgCl (0.8 mum), CdCl(2) (1 mum), 3-acetyl pyridine (0.1 mm), penicillin (above 0.1 mm), diazepam (0.25 mm), acrylamide (0.3 mm), 2,4,5-T (0.8 mm), lindane (1 mm). In general, retina cells were more sensitive than brain cells. The reaggregate cultures were less sensitive to 1-methyl-4-phenylpyridinium ion (MPP(+)) and cadmium than monolayer cultures, which may be attributable to their metabolic stability or to diffusional limitations. Glutamine synthetase (GS) activity, measured as glutamate production from glutamine, was a more sensitive indicator of toxicity than total protein. Retinal cells grown as reaggregates or monolayer cultures, produced two to four times more glutamate than brain cells grown in a similar fashion. This indicates that retinal glial cell (Müller cell) differentiation proceeds in vitro faster than brain astrocyte differentiation, which is consistent with the in vivo developmental pattern. In some cases (methylmercury, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, MPP(+), 3-acetyl pyridine, and lindane) a significant increase (as much as 30% of the basal level) was seen in the GS units/mug cell protein at concentrations of toxins below that reducing total cell protein. Thus, generation of neurotoxic glutamate might play a role in the cell destruction caused by the chemicals. Other substances (e.g. diazepam and cadmium) decreased the GS activity considerably, relative to decreases in total protein. This suggests that these xenobiotics act in a more general fashion to reduce metabolic activity and viability.
authors.affiliation: Swiss Institute for Alternatives to Animal Testing (SIAT), Technopark, Pfingstweidstrasse 30, CH-8005 Zürich, Switzerland.
authors.forename: C A
authors.initials: CA
authors.lastname: Reinhardt
authors.forename: C H
authors.initials: CH
authors.lastname: Schein