Effects of methotrexate on astrocytes in primary culture: light and electron microscopic studies

Recent studies on the animal model suggest that astrocytes may be a primary target for methotrexate (MTX) toxicity. To establish whether the astroglial alterations are due to a direct toxic effect of the drug, we studied the morphologic alterations, mitotic index, viability and growth rate of astrocytes in primary culture after exposure to varying concentrations of MTX in the absence or presence of dibutyryl cyclic AMP (dBcAMP). Dense bodies and cellular debris were noted by light and electron microscopy, and became more prominent with increasing doses and greater frequency of treatment. Degenerating cells and areas of necrosis were seen at higher concentrations. These changes became less conspicuous when MTX was given concurrently with dBcAMP. Large reactive-like astrocytes were also seen after MTX administration both in the absence or presence of dBcAMP. Mitotic rate inhibition was noted at all concentrations but was not dose-related. Cell viability was reduced and remained low up to 48 h after withdrawal of MTX and correlated well with drug concentration, although growth rate did not vary significantly from the control. Our findings show that pure populations of astrocytes can be adversely affected by MTX especially in the absence of bBcAMP, while also causing reactive-like changes in some cells. This report provides further evidence that astrocytes may be a primary target for MTX toxicity and suggests that the gliosis seen in MTX encephalopathy may in part be related to MTX-induced astrocytic injury.