Isoform 6-selective histone deacetylase inhibition reduces lesion size and brain swelling following traumatic brain injury and hemorrhagic shock

Background: Nonselective histone deacetylase (pan-HDAC) inhibitors, such as valproic acid (VPA), have demonstrated neuroprotective properties in trauma models. However, isoform-specific HDAC inhibitors may provide opportunity for more effective drug administration with fewer adverse effects. We investigated HDAC6 inhibition with ACY-1083 in an in vitro and an in vivo large animal model of injury.

Methods: Mouse hippocampal cells were subjected to oxygen-glucose deprivation (0% O2, glucose-free and serum-free medium, 18 hours) and reoxygenation (21% O2, normal culture media, 4 hours) with/without VPA (4 mmol/L) or ACY-1083 (30 nmol/L, 300 nmol/L). Cell viability was measured by methylthiazolyl tetrazolium assay. Expression of hypoxia-inducible factor-1α, heat shock protein 70, and effectors in the phosphoinositide-3 kinase/mammalian target of rapamycin pathway were measured by Western blot analysis. Additionally, swine were subjected to combined traumatic brain injury and hemorrhagic shock and randomized to three treatment groups (n = 5/group): (i) normal saline (NS; 3× hemorrhage volume); (ii) NS + VPA (NS; 3× hemorrhage volume, VPA; 150 mg/kg), and (iii) NS + ACY-1083 (NS; 3× hemorrhage volume, ACY-1083; 30 mg/kg). After 6 hours, brain tissue was harvested to assess lesion size and brain swelling.

Results: Significant improvement in cell viability was seen with both HDAC inhibitors in the in vitro study. ACY-1083 suppressed hypoxia-inducible factor-1α expression and up-regulated phosphorylated mammalian target of rapamycin and heat shock protein 70 in a dose-dependent manner. Lesion size and brain swelling in Animals treated with pharmacologic agents (VPA and ACY-1083) were both smaller than in the NS group. No differences were observed between the VPA and ACY-1083 treatment groups.

Conclusions: In conclusion, selective inhibition of HDAC6 is as neuroprotective as nonselective HDAC inhibition in large animal models of traumatic brain injury and hemorrhagic shock.