Characterization of a compartment syndrome-like injury model.

INTRODUCTION: Acute compartment syndrome (CS) is caused by an elevation of pressure within a muscular compartment that can be caused by numerous factors, including blunt trauma. In this study, we characterized a rodent model of CS-like injury. METHODS: Forty male athymic rats received a standardized injury of ischemia and compression to their hindlimbs, while the intracompartmental pressure (ICP) was measured using an implantable transmitter. Tetanic muscle function was evaluated, and histology was performed on the tibialis anterior (TA) muscle. RESULTS: ICPs were held at 260.70 ± 2.70 mm Hg during injury. Injured muscles recovered 59% of their total function 4 weeks after injury, and histology showed high levels of edema, inflammation (CD68(+) ), angiogenesis (CD31(+) ), and fibrosis within 72 hours after injury. CONCLUSIONS: We describe a novel CS-like injury model and a novel method to measure ICP, which could potentially be used to develop innovative therapies to manage CS injury in patients.

Customized platelet-rich plasma with transforming growth factor ß1 neutralization antibody to reduce fibrosis in skeletal muscle.

UNLABELLED: The formation of fibrous tissue during the healing of skeletal muscle injuries leads to incomplete recovery of the injured muscle. Platelet-rich-plasma (PRP) contains beneficial growth factors for skeletal muscle repair; however, it also contains deleterious cytokines and growth factors, such as TGF-ß1, that can cause fibrosis and inhibit optimal muscle healing. OBJECTIVE: To test if neutralizing TGF-ß1's action within PRP, through neutralization antibodies, could improve PRP's beneficial effect on skeletal muscle repair. METHODS: PRP was isolated from in-bred Fisher rats. TGF-ß1 neutralization antibody (Ab) was used to block the TGF-ß1 within the PRP prior to injection. The effects of customized PRP (TGF-ß1 neutralized PRP) on muscle healing was tested on a cardiotoxin (CTX) induced muscle injury model. RESULTS: A significant increase in the numbers of regenerative myofibers was observed in the PRP and customized PRP groups compared to the untreated control. A significant decrease in collagen deposition was observed in customized PRP groups when compared to the control and PRP groups. Significantly enhanced angiogenesis and more Pax-7 positive satellite cells were found in the PRP and customized PRP groups compared to the control group. Macrophage infiltration was increased in the customized PRP groups when compared with the PRP group. More M2 macrophages were recruited to the injury site in the customized PRP groups when compared with the PRP and control groups. CONCLUSION: Neutralizing TGF-ß1 within PRP significantly promotes muscle regeneration while significantly reducing fibrosis. Not only did the neutralization reduce fibrosis, it enhanced angiogenesis, prolonged satellite cell activation, and recruited a greater number of M2 macrophages to the injury site which also contributed to the efficacy that the customized PRP had on muscle healing.

Use of an antifibrotic agent improves the effect of platelet-rich plasma on muscle healing after injury.

BACKGROUND: Muscle contusions are a common type of muscle injury and are frequently encountered in athletes and military personnel. Although these injuries are capable of healing in most instances, incomplete functional recovery often occurs because of the development of fibrosis in the muscle. We hypothesized that a combination of platelet-rich plasma (PRP) injection and oral administration of losartan (an antifibrotic agent) could enhance muscle healing by stimulating muscle regeneration and angiogenesis and by preventing fibrosis in contusion-injured skeletal muscle. METHODS: Contusion injuries were created in the tibialis anterior muscles of mice. Two treatments were tested, alone and in combination: 20 µL of PRP injected into the contusion site one day after injury, and 10 mg/kg/day of losartan administered beginning three days after injury and continuing until the end point of the experiment. Muscle regeneration and fibrosis development were evaluated by histological analysis, and functional recovery was measured by physiological testing. RESULTS: Muscle regeneration and muscle function were significantly promoted in the combined PRP + losartan treatment group compared with the other groups. Combined PRP + losartan treatment significantly decreased the expression of phosphorylated Smad2/3 and the development of fibrosis compared with PRP treatment alone, and it increased vascular endothelial growth factor (VEGF) expression and the number of CD31-positive structures compared with losartan treatment alone. Follistatin, a positive regulator of muscle growth, was expressed at a higher level in the PRP + losartan group compared with the other groups. CONCLUSIONS: PRP + losartan combinatorial therapy improved overall skeletal muscle healing after muscle contusion injury by enhancing angiogenesis and follistatin expression and by reducing the expression of phosphorylated Smad2/3 and the development of fibrosis. These results suggest that blocking the expression of transforming growth factor (TGF)-ß1 with losartan improves the effect of PRP therapy on muscle healing after a contusion injury. CLINICAL RELEVANCE: These findings could contribute to the development of biological treatments that aid in the healing of skeletal muscle after injury.