Valproic acid in normal therapeutic concentration has no neuroprotective or differentiation influencing effects on long term expanded murine neural stem cells

The antiepileptic drug valproic acid (VPA) has shown neuroprotective effects in different cell types including mesencephalic neural primary cultures. Furthermore, an influence on neural differentiation and neurite outgrowth has been described. Nevertheless, results in this regard are contradictory and data on long term expanded neural stem cells are missing. This is why we investigated possible neuroprotective effects of VPA on fetal mesencephalic neural stem cells (fmNSCs) in vitro, using the neurotoxic agent 1-methyl-4-phenyl-pyridin (MPP+). We also examined potential VPA effects on cell expansion and differentiation and the underlying signaling pathways. In our study, we could exclude any relevant toxic effects of 100 μg/ml and 200 μg/ml VPA on fmNSCs during expansion and differentiation for up to 96 h. MPP+ treatment in concentrations of 30 and 60 μM MPP+ significantly decreased the survival rate of fmNSCs during expansion and differentiation. In all used concentrations, VPA did neither reverse these MPP+ effects when applied simultaneously with MPP+ nor after pre-treatment with VPA for 24 h. In contrast, MPP+ effects were emphasized by VPA pretreatment for 24h when applied during cell expansion. Concerning the self-renewing capacity of fmNSCs, measured by BrdU and Ki67 staining, we did not find any significant influence of VPA. Additionally there was no significant influence of therapeutic VPA dosages on astroglial (GFAP), oligodendroglial (GalC) and neuronal (MAP2) differentiation, measured by immunostaining after 10 days of differentiation. Summing up, we did not find any neuroprotective effects of VPA on fmNSCs in vitro, neither during expansion nor during cell differentiation. Also the self-renewing and differentiation potential of the used fmNSCs was not altered. These findings have implications for the large community of patients having to take VPA on a chronic base, especially in the light of knowledge that a regular cell replacement out of hippocampal adult stem cells is mandatory for the maintenance of normal cognition through adulthood.