Targeting the BH3-interacting domain death agonist to develop mechanistically unique antidepressants

The BH3-interacting domain death agonist (Bid) is a pro-apoptotic member of the B-cell lymphoma-2 (Bcl-2) protein family. Previous studies have shown that stress reduces levels of Bcl-2 in brain regions implicated in the pathophysiology of mood disorders, whereas antidepressants and mood stabilizers increase Bcl-2 levels. The Bcl-2 protein family has an essential role in cellular resilience as well as synaptic and neuronal plasticity and may influence mood and affective behaviors. This study inhibited Bid in mice using two pharmacological antagonists (BI-11A7 and BI-2A7); the selective serotonin reuptake inhibitor citalopram was used as a positive control. These agents were studied in several well-known rodent models of depression-the forced swim test (FST), the tail suspension test (TST), and the learned helplessness (LH) paradigm-as well as in the female urine sniffing test (FUST), a measure of sex-related reward-seeking behavior. Citalopram and BI-11A7 both significantly reduced immobility time in the FST and TST and attenuated escape latencies in mice that underwent the LH paradigm. In the FUST, both agents significantly improved duration of female urine sniffing in mice that had developed helplessness. LH induction increased the activation of apoptosis-inducing factor (AIF), a caspase-independent cell death constituent activated by Bid, and mitochondrial AIF expression was attenuated by chronic BI-11A7 infusion. Taken together, the results suggest that functional perturbation of apoptotic proteins such as Bid and, alternatively, enhancement of Bcl-2 function, is a putative strategy for developing novel therapeutics for mood disorders.