Biochemical, molecular and epigenetic mechanisms of valproic acid neuroprotection.

Valproic acid (VPA, 2-propylpentanoic acid) has been widely used as an antiepileptic drug and for the therapy of bipolar disorders for several years. Its mechanism of action was initially found to be primarily related to neurotransmission and modulation of intracellular pathways. More recently, it emerged as an anti-neoplastic agent as well, by acting on cell growth, differentiation and apoptosis. Here, it mainly exerts its effect by regulating gene expression at the molecular level, through epigenetic mechanisms. In particular, it has been demonstrated the effect of VPA in chromatin remodeling, as VPA directly inhibits histone deacetylases (HDACs) activity. Interestingly, it has been observed that these biochemical and molecular pathways are involved not only in beneficial effect of VPA against epilepsy and malignancies, but they are also responsible for more general neuroprotective mechanisms. In particular, it has been demonstrated that VPA is neuroprotective in several models of neurodegenerative diseases. Moreover, due to the involvement of the VPA-affected mechanisms in complex behaviors, VPA is increasingly used as a psychotherapeutic agent. This review summarizes the more recent data on VPA neuroprotective mechanisms at the biochemical, molecular and epigenetic levels, focusing on both in vitro and in vivo models of neurodegenerative diseases. In particular, attention is paid to mechanisms by which VPA affects neuronal survival/apoptosis and proliferation/differentiation balance, as well as synaptic plasticity, by acting both directly on neurons and indirectly through glial cells. Perspective applications of the VPA neuroprotective potential in human neurodegenerative diseases are discussed, when relevant.