Improved Tools for Accessing Pain Following Fracture and Enabling Standardized Pain Phenotyping

摘要

ABSTRACT Fractures are one of the most common injuries worldwide with The Lancet Global Burden of Diseases reporting 178 million new fractures and 445 million prevalent fractures in 2019.1 Delayed healing and non-union are qualitative clinical diagnoses based on the persistence of a fracture line in longitudinal radiographs and pain/ instability with weight bearing. While robust global estimates of delayed/non-union are not available, the best current data finds that 8-14% of fractures were readmitted for healing complications within 2 years post-injury.2 Delayed healing rates increase significantly if the fracture occurs in patients with high co-morbidity burdens such as increased age, diabetes, or obesity.3,4 Current standard-of-care for these fractures is surgery to alter hardware or implant bone grafts. There are currently no pharmacological agents approved to accelerate fracture healing. As such, there exists an unmet clinical need for biologics that could stimulate bone regeneration in a non-surgical delivery platform. The long-term goal of the Parent Grant is to develop and validate an injectable, biodegradable nanowire delivery platform for local and sustained release of a “painless” nerve growth factor (NGF) isoform to accelerate fracture healing in clinical scenarios of delayed healing. In support of the Parent Grant, we have published that NGF acts on chondrocytes to promote molecular programs associated with endochondral ossification5 and that NGF can be encapsulated into biomaterial platforms for controlled and localized delivery6. Opioids are the standard of care for addressing post-fracture pain.7-11 The goal of this Pain Supplement is to validate a novel technology with machine learning for measuring induced and spontaneous pain following fractures. An innovative and central premise of the Parent Grant is the therapeutic use of a “painless” isoform of NGF to promote fracture healing in murine models of delayed repair. Painless NGF results from a naturally occurring point mutation in the wild type NGFβ sequence (NGFR100W) that enables binding to the TrkA receptor, responsible for the trophic activity of NGF, but not to the p75 receptor responsible for pain.12 In our progress report for the Parent Grant, we shared new data demonstrating that NGFR100W does not induce pain sensitization at a dose 10-fold higher than NGFβ in the hindpaw of an unfractured limb. However, standard reflexive avoidance assays were not reliable for induced pain when translated to a fractured limb. In this grant, we present the first data using a novel technology, the BlackBox, coupled with DeepLabCutTM machine learning to monitor how quantifiable behavioral endpoints of pain shift after bone fracture. We then utilize this technology to understand perturbations to fracture pain by evaluating (Aim 1) induced pain in response to the injected NGF therapy, (Aim 2) changes in spontaneous pain in models of delayed fracture healing, and (Aim 3) the role of the NGF receptors in modulating pain response. We accomplish these three Aims by establishing a new collaboration outside of our current research base that has expertise in pain research (NOSI Goal B: Allan Basbaum Laboratory).