Phosphodiesterase 2 inhibitor Hcyb1 reverses corticosterone-induced neurotoxicity and depression-like behavior

Rationale: Currently available PDE2 inhibitors have poor brain penetration that limits their therapeutic utility in the treatment of depression. Hcyb1 is a novel selective PDE2 inhibitor that was introduced more lipophilic groups with polar functionality to the scaffold pyrazolopyrimidinone to improve the blood-brain barrier (BBB) penetration. Our previous study suggested that Hcyb1 increased the neuronal cell viability and exhibited antidepressant-like effects, which were parallel to the currently available PDE2 inhibitor Bay 60-7550. Objectives: The present study investigated whether Hcyb1 protected HT-22 cells against corticosterone-induced neurotoxicity and produced antidepressant-like effects in behavioral tests in stressed mice. Methods: The neuroprotective effects of Hcyb1 against corticosterone-induced cell lesion were examined by cell viability (MTS) assay. The enzyme-linked immunosorbent assay (ELISA) and immunoblot analysis were used to determine the levels of cAMP or cGMP and expression of pCREB or BDNF, respectively, in the corticosterone-treated HT-22 cells. The antidepressant-like effects of Hcyb1 were determined in the tail suspension and novelty suppressed feeding tests in stressed mice. Results: In the cell-based assay, Hcyb1 significantly increased cell viability of HT-22 cells against corticosterone-induced neurotoxicity in a time- and dose-dependent manner. Hcyb1 also rescued corticosterone-induced decreases in both cGMP and cAMP levels, pCREB/CREB and BDNF expression. These protective effects of Hcyb1 were prevented by pretreatment with either the PKA inhibitor H89 or the PKG inhibitor KT5823. Moreover, Hcyb1 reversed acute stress–induced increases in immobility time and the latency to feed in the tail suspension and novelty suppressed feeding tests, respectively, which were prevented by pretreatment with H89 or KT5823. Conclusion: These findings provide evidence that the neuroprotective effects of Hcyb1 are mediated by PDE2-dependent cAMP/cGMP signaling.