A Ready-To-Use Purified Exosome Product for Volumetric Muscle Loss and Functional Recovery.

Large skeletal muscle defects due to trauma or following tumor extirpation can result in substantial functional impairment. Purified exosomes are now available clinically and have been used for wound healing. The objective of this study was to evaluate the regenerative capacity of commercially available exosomes on an animal model of volumetric muscle loss (VML) and potential translation to human muscle injury. An established VML rat model was used. In the in-vitro experiment, rat myoblasts were isolated and co-cultured with 5% purified exosome product (PEP) to validate uptake. Myoblast proliferation and migration was evaluated with increasing concentrations of PEP (2.5%, 5%, and 10%) in comparison to control media(F10) and myoblast growth media (MGM). In the in-vivo experiment, a lateral gastrocnemius-VML defect was made in the rat hindlimb. Animals were randomized into four experimental groups; defects were treated with either surgery alone, fibrin sealant, fibrin sealant and PEP, or platelet rich plasma (PRP). The groups were further randomized into four recovery timepoints (14, 28, 45, or 90 days). The isometric tetanic force (ITF), which was measured as a percentage of force compared to normal limb, was used for functional evaluation. Florescence microscopy confirmed that 5% PEP demonstrated cellular uptake around 8-12 hrs. Compared to control, myoblasts showed faster proliferation with PEP irrespective of concentration. PEP concentrations of 2.5 and 5% promoted myoblast migration faster compared to control (<0.05). At 90 days postop, both the PEP and fibrin sealant and PRP groups showed greater ITF compared to control and fibrin sealant alone (<0.05). At 45 days postop, PEP with fibrin sealant had greater cellularity compared to control (<0.05). At 90 days postop, both PEP with fibrin sealant and the PRP treated groups had greater cellularity compared to fibrin sealant and control (<0.05). PEP promoted myoblast proliferation and migration. When delivered to a wound with a fibrin sealant, PEP allowed for muscle regeneration producing greater functional recovery and more cellularity in vivo compared to untreated animals. PEP may promote muscle regeneration in cases of VML, further research is warranted to evaluate PEP for the treatment of clinical muscle defects.