Evaluation of inhibitors of histone deacetylases as potential neurotrophic agents

Neurodegenerative diseases including Parkinson's (PD), Alzheimer's (AD), Huntington's (HD) and Amyotrophic Lateral Sclerosis (ALS) occur as a result of progressive loss of structure or function of neurons, including death of neurons. Neurotrophic actions and neuroprotection leading to neuroplasticity and neurite outgrowth are important markers for neuroregeneration. Neuritogenesis or neuritic outgrowth is a fundamental process in the differentiation of neurons and plays an important role in neuronal development and formation of synapses. These processes are regulated by extrinsic and intrinsic determinants that affect gene expression profiles and signal transduction pathways. Within the past decade, there have been many studies showing neuroprotective effects of inhibitors of histone deacetylases (HDAC). The aim of this study is to evaluate pan and selective HDAC inhibitors for inducing neuritogenesis/neuronal differentiation in PC12 cells. NeuroScreen-1, a clone of PC12 (rat adrenal pheochromocytoma) cell line optimized for Nerve Growth Factor (NGF)-stimulated neuritic outgrowth, was used for this study. The cell cultures were treated with suberoylanilide hydroxamic acid (SAHA) (pan HDAC inhibitor), PCI-34051 (selective HDAC8 inhibitor), tubastatin (selective HDAC 6 inhibitor) belinostat (a Novel HDAC inhibitor) and tenovin (Sirtunin 1 and2 inhibitor) for 72 hrs. Cytotoxicity was measured and cell cultures were analyzed for neuritic outgrowth by digital microscope imaging and NIS element software for measurement of neurite/cell, mean neurite length, neurite length/cells. Vorinostat independently stimulated significant neurite outgrowth. While other HDAC inhibitors did not produce significant effect on neuritic outgrowth independently. However, belinostat and tenovin caused significant attenuation of NGF-stimulated outgrowth. Differential effects of the HDAC inhibitors on neurotropic signal transduction pathways may be responsible for disparities in actions of different HDAC inhibitors.