Duration of Reduction in Enduring Stress-induced Hyperalgesia via FK506-Binding Protein 51 Inhibition Depends on Timing of Administration Relative to Traumatic Stress Exposure

Chronic pain development is a frequent outcome of severe stressor exposure, with or without tissue injury. Enduring stress-induced hyperalgesia (ESIH) is believed to play a central role, but the precise mechanisms mediating the development of chronic posttraumatic pain, and the time-dependency of these mechanisms, remain poorly understood. Clinical and pre-clinical data suggest that the inhibition of FK506-binding protein 51 (FKBP51), a key stress system regulator, might prevent ESIH. We evaluated whether peritraumatic inhibition of FKBP51 in an animal model of traumatic stress exposure, the single prolonged stress (SPS) model, reversed ESIH evaluated via daily mechanical von Frey testing. FKBP51 inhibition was achieved using SAFit2, a potent and specific small molecule inhibitor of FKBP51, administered to male and female Sprague-Dawley rats via intraperitoneal injection. To assess timing effects, FKBP51 was administered at different times relative to stress (SPS) exposure. SAFit2 administration immediately after SPS produced a complete reversal in ESIH lasting >7d. In contrast, SAFit2 administration 72h following SPS produced only temporary hyperalgesia reversal, and administration 120h following SPS had no effect. Similarly, animals undergoing SPS together with tissue injury (plantar incision) receiving SAFit2 immediately post-surgery developed acute hyperalgesia but recovered by 4d and did not develop ESIH. These data suggest that (1) FKBP51 plays an important, time-dependent role in ESIH pathogenesis, (2) time windows of opportunity may exist to prevent ESIH via FKBP51 inhibition after traumatic stress, with or without tissue injury, and (3) the use of inhibitors of specific pathways may provide new insights into chronic post-traumatic pain development. Grant support from Rita Allen Foundation Pain Scholar Award R01NS118563.