Novel histone deacetylase (HDAC) inhibitors with improved selectivity for HDAC2 and 3 protect against neural cell death

Neurodegenerative disorders, such as motor neurone disease, Alzheimer’s disease and responses to brain traumas such as stroke, involve the unwanted death of neural cells. Although the exact underlying mechanisms leading to neural cell death are not well defined, one contributory event in many situations is the over-excitation of cells caused by too much of the neurotransmitter glutamate. Drugs that inhibit enzymes called histone deacetylases (HDACs) can protect neural cells from glutamate excitotoxicity. However, current inhibitors lack specificity and although they function in vitro, they have a substantial potential for adverse side effects in vivo. HDAC2 and 3 have been implicated in neurotoxicity and here we investigated the neuroprotective potential of three novel HDAC inhibitors that show selectivity for these. The ability of these HDAC inhibitors to protect against glutamate excitotoxicity was tested using cultured organotypic cerebral slices from 7-day-old (P7) Wistar rats. Glutamate excitotoxicity was induced by 200 µM of the glutamate transporter blocker, DL-threo-β-benzyloxyaspartate (DL-TBOA). This was applied alone and alongside 1 µM of the novel HDAC2 and 3 selective inhibitors AH51, AH61 and AH62. Neural cell viability in slices was quantified from assays using the fluorescent stains, 4′,6-diamidino-2-phenylindole and ethidium homodimer-1. The induction of glutamate excitotoxicity by DL-TBOA resulted in 41.3 ± 6.1% (n = 7, P < 0.01) loss in cell viability as judged by ethidium homodimer-1 staining. All three novel HDAC inhibitors significantly prevented neural cell death in response to DL-TBOA (P < 0.01), with cell viabilities of 107.5 ± 6.01% (n = 4), 97.1 ± 16.5% (n = 3) and 106.7 ± 6.45% (n = 4) for AH51, AH61 and AH62, respectively. This study has shown that inhibitors selective for HDAC2 and 3 can protect neural cells from death and thus have potential as therapeutic agents against neurotoxicity.