palovarotene and Wounds-and-Injuries

Heterotopic ossification (HO) is associated with inflammation. The goal of this review is to examine recent findings on the roles of inflammation and the immune system in HO. We examine how inflammation changes in fibrodysplasia ossificans progressiva, in traumatic HO, and in other clinical conditions of HO. We also discuss how inflammation may be a target for treating HO.. Both genetic and acquired forms of HO show similarities in their inflammatory cell types and signaling pathways. These include macrophages, mast cells, and adaptive immune cells, along with hypoxia signaling pathways, mesenchymal stem cell differentiation signaling pathways, vascular signaling pathways, and inflammatory cytokines. Because there are common inflammatory mediators across various types of HO, these mediators may serve as common targets for blocking HO. Future research may focus on identifying new inflammatory targets and testing combinatorial therapies based on these results.

Topics: Adaptive Immunity; Animals; Anti-Inflammatory Agents, Non-Steroidal; Arthroplasty, Replacement, Hip; Blast Injuries; Brain Injuries, Traumatic; Burns; Cell Differentiation; Cytokines; Humans; Hypoxia; Immunosuppressive Agents; Inflammation; Janus Kinase Inhibitors; Macrophages; Mast Cells; Mesenchymal Stem Cells; Myositis Ossificans; Ossification, Heterotopic; Postoperative Complications; Pyrazoles; Receptors, Retinoic Acid; Retinoic Acid Receptor gamma; Signal Transduction; Sirolimus; Spinal Cord Injuries; Stilbenes; Wounds and Injuries

Heterotopic ossification (HO) involves formation of endochondral bone at non-skeletal sites, is prevalent in severely wounded service members, and causes significant complications and delayed rehabilitation. As common prophylactic treatments such as anti-inflammatory drugs and irradiation cannot be used after multi-system combat trauma, there is an urgent need for new remedies. Previously, we showed that the retinoic acid receptor γ agonist Palovarotene inhibited subcutaneous and intramuscular HO in mice, but those models do not mimic complex combat injury. Thus, we tested Palovarotene in our validated rat trauma-induced HO model that involves blast-related limb injury, femoral fracture, quadriceps crush injury, amputation and infection with methicillin-resistant Staphylococcus aureus from combat wound infections. Palovarotene was given orally for 14days at 1mg/kg/day starting on post-operative day (POD) 1 or POD-5, and HO amount, wound dehiscence and related processes were monitored for up to 84days post injury. Compared to vehicle-control animals, Palovarotene significantly decreased HO by 50 to 60% regardless of when the treatment started and if infection was present. Histological analyses showed that Palovarotene reduced ectopic chondrogenesis, osteogenesis and angiogenesis forming at the injury site over time, while fibrotic tissue was often present in place of ectopic bone. Custom gene array data verified that while expression of key chondrogenic and osteogenic genes was decreased within soft tissues of residual limb in Palovarotene-treated rats, expression of cartilage catabolic genes was increased, including matrix metalloproteinase-9. Importantly, Palovarotene seemed to exert moderate inhibitory effects on wound healing, raising potential safety concerns related to dosing and timing. Our data show for the first time that Palovarotene significantly inhibits HO triggered by blast injury and associated complications, strongly indicating that it may prevent HO in patients at high risk such as those sustaining combat injuries and other forms of blast trauma.

Topics: Animals; Blast Injuries; Chondrogenesis; Disease Models, Animal; Gene Expression Regulation; Male; Ossification, Heterotopic; Osteogenesis; Pyrazoles; Rats, Sprague-Dawley; Receptors, Retinoic Acid; Retinoic Acid Receptor gamma; Stilbenes; Wound Healing; Wounds and Injuries