The Use of Platelet-Rich and Platelet-Poor Plasma to Enhance Differentiation of Skeletal Myoblasts: Implications for the Use of Autologous Blood Products for Muscle Regeneration

Platelet-Poor versus Platelet-Rich Plasma for the Treatment of Muscle Injuries

ABSTRACT

Muscle injury in sport results in significant lost time and potential for reinjury for athletes. Autologous blood product, namely, platelet-rich plasma (PRP), has been investigated for possible augmentation of the treatment timeline with prevention of reinjury; however, conflicting results have been identified. A growing body of basic science and clinical literature is forming that supports the use of platelet-poor plasma (PPP) for muscle injury. The purpose of this study was to provide a background of the basic science of PRP versus PPP for muscle injury and to identify and review the clinical evidence for both autologous blood products, including the author's clinical experience utilizing the blood products. At the tissue level, PRP causes myoblast proliferation while PPP has led to myoblast induction, potentially identifying improved native muscle healing. Conflicting studies have been identified for the use of PRP for muscle injury. A growing body of positive results for PPP was identified, but high-quality comparative studies are needed.

Platelet-Rich Plasma in Young and Elderly Humans Exhibits a Different Proteomic Profile

As people age, their ability to resist injury and repair damage decreases significantly. Platelet-rich plasma (PRP) has demonstrated diverse therapeutic effects on tissue repair. However, the inconsistency of patient outcomes poses a challenge to the practical application of PRP in clinical practice. Furthermore, a comprehensive understanding of the specific impact of aging on PRP requires a systematic investigation. We derived PRP from 6 young volunteers and 6 elderly volunteers, respectively. Subsequently, 95% of high-abundance proteins were removed, followed by mass spectrometry analysis. Data are available via ProteomeXchange with the identifier PXD050061. We detected a total of 739 proteins and selected 311 proteins that showed significant differences, including 76 upregulated proteins in the young group and 235 upregulated proteins in the elderly group. Functional annotation and enrichment analysis unveiled upregulation of proteins associated with cell apoptosis, angiogenesis, and complement and coagulation cascades in the elderly. Conversely, IGF1 was found to be upregulated in the young group, potentially serving as the central source of enhanced cell proliferation ability. Our investigation not only provides insights into standardizing PRP preparation but also offers novel strategies for augmenting the functionality of aging cells or tissues.

Traumatic Mid-substance Isolated Vastus Medialis Rupture in a Young Athlete: A Case Report

CASE

This is the first documented case of an isolated traumatic vastus medialis rupture that occurred in a 14-year-old athlete after direct impact during play. Imaging confirmed a rare mid-substance rupture. The patient underwent conservative management with physical therapy augmented by blood flow restriction therapy (BFRT) and platelet-poor plasma (PPP) injection to regain full function.

CONCLUSION

Isolated quadriceps mid-substance tears are rare. Determining an appropriate treatment technique for mid-substance tears is complex. This case documents the use of nonoperative management with BFRT and PPP to achieve full recovery and early return to play in a young athlete.

Nematic Fibrin Fibers Enabling Vascularized Thrombus Implants Facilitate Scarless Cutaneous Wound Healing

Autologous implantable scaffolds that induce vasculogenesis have shown great potential in tissue regeneration; however, previous attempts mainly relied on cell-laden hydrogel patches using fat tissues or platelet-rich plasma, which are insufficient for generating a uniform vasculature in a scalable manner. Here, implantable vascularized engineered thrombi (IVETs) are presented using autologous whole blood, which potentiate effective skin wound healing by constructing robust microcapillary vessel networks at the wound site. Microfluidic shear stresses enable the alignment of bundled fibrin fibers along the direction of the blood flow streamlines and the activation of platelets, both of which offer moderate stiffness of the microenvironment optimal for facilitating endothelial cell maturation and vascularization. Rodent dorsal skin wounds patched with IVET present superior wound closure rates (96.08 ± 1.58%), epidermis thickness, collagen deposition, hair follicle numbers, and neutrophil infiltration, which are permitted by enhanced microvascular circulation. Moreover, IVET treatment accelerates wound healing by recruiting M2 phenotype macrophages.

Action of Platelet-Rich Plasma on In Vitro Cellular Bioactivity: More than Platelets

Platelet-rich plasma (PRP) is a biological therapy in which one of the mechanisms of action is the stimulation of biological processes such as cell proliferation. The size of PRP’s effect depends on multiple factors, one of the most important being the composition of PRP. The aim of this study was to analyze the relationship between cell proliferation and the levels of certain growth factors (IGF-1, HGF, PDGF, TGF-β and VEG) in PRP. First, the composition and effect on cell proliferation of PRP versus platelet-poor plasma (PPP) were compared. Subsequently, the correlation between each growth factor of PRP and cell proliferation was evaluated. Cell proliferation was higher in cells incubated with lysates derived from PRP compared to those cultured with lysates derived from PPP. In terms of composition, the levels of PDGF, TGF-β, and VEGF were significantly higher in PRP. When analyzing the PRP growth factors, IGF-1 was the only factor that correlated significantly with cell proliferation. Of those analyzed, the level of IGF-1 was the only one that did not correlate with platelet levels. The magnitude of PRP’s effect depends not only on platelet count but also on other platelet-independent molecules.

Biologically Augmented Suture for Ligament Bracing Procedures Positively Affects Human Ligamentocytes and Osteoblasts In Vitro

PURPOSE

The purpose was to evaluate the response of human ligamentocytes and osteoblasts after biological augmentation with thrombin, concentrated bone marrow aspirate (cBMA), or platelet-rich plasma (PRP) on two different types of nonresorbable flat braided suture used for ligament bracing.

METHODS

Uncoated (U) and collagen-coated (C) flat braided suture material was augmented with either thrombin (T), cBMA (B), PRP (P), or a combination of these three (A), while platelet-poor plasma was used as a source for fibrin (F) in each assay. Previously cultured ligamentocytes and osteoblasts were added with a defined density and assayed after the required time period for adhesion, proliferation, and alkaline phosphatase activity.

RESULTS

Biological augmentation of uncoated [(UFT, UFBT, UFA; P < .001), (UFPT; P = .017)] and collagen-coated suture (CFT, CFPT, CFBT, CFA; P < .001) led to a significantly higher ligamentocyte adhesion. Significantly higher adhesion was also observed for osteoblasts (UFT, UFPT, UFBT, UFA; P < .001; CFT, CFPT, CFBT, CFA; P < .001). Similarly, ligamentocyte proliferation was significantly higher [(UFT, UFPT, UFA; P = .009), (UFBT; P = .001), (CFT; P = .009), (CFBT; P = .001), and (CFA; P = .01)]. Osteoblasts showed significantly higher proliferation as well [(UFT, UFPT, UFA; P = .002), (UFBT; P = .001); (CFT: P = .003), and (CFPT, CFBT, CFA; P = .001)]. Augmentation with thrombin, PRP, and BMA for uncoated (UFT; P = .006, UFPT; P = .035, UFBT; P = .001) and BMA for coated suture (CFBT; P = .027) led to significantly higher alkaline phosphatase activity.

CONCLUSION

Biological enhancement of suture used for ligament bracing significantly increased ligamentocyte and osteoblast adhesion and proliferation, as well as alkaline phosphatase activity of osteoblasts in an in vitro model. After biological augmentation, cellular adhesion, proliferation, and alkaline phosphatase activity changed up to 1,077%, 190%, and 78%, respectively. Furthermore, no overall superiority between uncoated or collagen-coated suture material was observed for cellular adhesion, proliferation, or alkaline phosphatase activity.

CLINICAL RELEVANCE

This study provides in vitro data on a new treatment concept of biologic augmentation for acute ligamentous lesions treated with ligament bracing that has not been widely described. This concept may improve the healing of injured ligaments, in addition to providing immediate biomechanical stabilization.

Minimally Invasive Successful Reconstruction of a Severely Traumatized Upper Extremity Using Platelet-Rich Plasma and Tissue Scaffold: A Case Report

Minimally invasive reconstruction combines principles of tissue engineering and regenerative medicine for healing complex wounds. This approach was successfully demonstrated on a 64-year-old diabetic and hypertensive male patient, who was brought unconscious to our emergency after surviving an automobile collision with severe brain and right-dominant upper extremity injuries. Uncontrolled hyperglycemia, severe anemia, diffuse axonal brain injury, wrist drop, and loss of thumb extension and abduction were noted. Extensive degloving, skin necrosis, extensor and flexor forearm muscle crush injuries, and ruptured extensor tendons were observed. Serial wound debridement combined with platelet-poor plasma injection into the muscles, platelet-rich plasma injections into the tendons and subcutis, and low-negative pressure wound therapy were performed sequentially to salvage the injured soft-tissues. Improvements were noticed during the second exploration after 5 days. Surviving muscles showed adequate vascularization and revival of innervation during the third exploration after another 5 days. Thereafter, absorbable synthetic tissue scaffold was applied over a sizeable 270 cm ² wound as a flap-alternative. Tissues regenerated well within the scaffold during the next 2 months, halving the wound area to 132 cm ² . A thick split-skin graft was applied over the remaining granulating neodermis, which “took” completely. Six months postoperatively, the patient regained most hand functions and performed all activities satisfactorily, while the grafted area appeared almost identical to surroundings. Minimally invasive reconstruction thus produced satisfying results with fewer shorter simpler surgeries, minimal anesthesia, short-duration hospitalization, lower health care costs, lesser risks, and excellent patient-reported outcomes.

Delivery of affordable and scalable encapsulated allogenic/autologous mesenchymal stem cells in coagulated platelet poor plasma for dental pulp regeneration

The main goal of regenerative endodontics procedures (REPs) is to revitalize teeth by the regeneration of healthy dental pulp. In this study, we evaluated the potential of combining a natural and accessible biomaterial based on Platelet Poor Plasma (PPP) as a support for dental pulp stem cells (DPSC) and umbilical cord mesenchymal stem cells (UC-MSC). A comparison study between the two cell sources revealed compatibility with the PPP based scaffold with differences noted in the proliferation and angiogenic properties in vitro. Additionally, the release of growth factors including VEGF, HGF and DMP-1, was detected in the media of cultured PPP and was enhanced by the presence of the encapsulated MSCs. Dentin-Discs from human molars were filled with PPP alone or with MSCs and implanted subcutaneously for 4 weeks in mice. Histological analysis of the MSC-PPP implants revealed a newly formed dentin-like structure evidenced by the expression of Dentin sialophosphoprotein (DSPP). Finally, DPSC induced more vessel formation around the dental discs. This study provides evidence of a cost-effective, xenofree scaffold that is compatible with either autologous or allogenic strategy for dental pulp regeneration. This attempt if successfully implemented, could make REPs treatment widely accessible, contributing in improving global health conditions.

Effectiveness of Hematoma Aspiration and Platelet-rich Plasma Muscle Injections for the Treatment of Hamstring Strains in Athletes

INTRODUCTION

The effect of platelet-rich plasma (PRP) treatment on recovery in acute hamstring injuries is controversial. Previous study results are inconsistent, and a standardized therapeutic approach has not been established yet.

PURPOSE

To assess the treatment effect using a combination of hematoma aspiration and muscle strain PRP injection in partial hamstring muscle tears (grade 2 strains) in athletes.

METHODS

Magnetic resonance imaging of athletes with grade 2 hamstring strains were reviewed from 2013 to 2018. From 2013 to 2015, athletes were treated conservatively, and from 2016 to 2018, with a combination of ultrasound-guided hematoma aspiration and PRP muscle strain injection. The outcome, including return-to-play (in days) and recurrence rate, was compared retrospectively between both groups (conservative vs aspiration/PRP) using ANOVA and Fisher's exact test. There was no significant difference in age, type of sport, and muscle involvement (including injury grade/location, hamstring muscle type, and length/cross-sectional area of the strain).

RESULTS

Fifty-five athletes (28 treated conservatively, 27 with hematoma aspiration/PRP injection) were included. Average return-to-play time (mean) was 32.4 d in the conservative group and 23.5 d in the aspiration/PRP group (P < 0.001). Recurrence rate of the hamstring strain was 28.6% (8/28) in the conservative treatment group and less than 4% (1/27) in the aspiration/PRP group (P = 0.025).

CONCLUSIONS

Athletes with grade 2 hamstring strains treated with a combination of hematoma aspiration and PRP injection had a significantly shorter return-to-play and a lower recurrence rate compared with athletes receiving conservative treatment.

The 2020 NBA Orthobiologics Consensus Statement

This 2020 NBA Orthobiologics Consensus Statement provides a concise summary of available literature and practical clinical guidelines for team physicians and players. We recognize that orthobiologic injections are a generally safe treatment modality with a significant potential to reduce pain and expedite early return to play in specific musculoskeletal injuries. The use of orthobiologics in sports medicine to safely reduce time loss and reinjury is of considerable interest, especially as it relates to the potential effect on a professional athlete. While these novel substances have potential to enhance healing and regeneration of injured tissues, there is a lack of robust data to support their regular use at this time. There are no absolutes when considering the implementation of orthobiologics, and unbiased clinical judgment with an emphasis on player safety should always prevail. Current best evidence supports the following: Key Points There is support for the use of leukocyte-poor platelet-rich plasma in the treatment of knee osteoarthritis. There is support for consideration of using leukocyte-rich platelet-rich plasma for patellar tendinopathy. The efficacy of using mesenchymal stromal cell injections in the management of joint and soft tissue injuries remains unproven at this time. There are very few data to suggest that current cell therapy treatments lead to any true functional tissue regeneration. Meticulous and sterile preparation guidelines must be followed to minimize the risk for infection and adverse events if these treatments are pursued.Given the high variability in orthobiologic formulations, team physicians must stay up-to-date with the most recent peer-reviewed literature and orthobiologic preparation protocols for specific injuries.Evidence-based treatment algorithms are necessary to identify the optimal orthobiologic formulations for specific tissues and injuries in athletes.Changes in the regulatory environment and improved standardization are required given the exponential increase in utilization as novel techniques and substances are introduced into clinical practice.

Proteomic analysis of platelet-rich and platelet-poor plasma

Background

Autologous blood products, such as platelet-rich plasma (PRP) are commercial products broadly used to accelerate healing of tissues after injuries. However, their content is not standardized and significantly varies in composition, which may lead to differences in clinical efficacy. Also, the underlying molecular mechanisms for therapeutic effects are not well understood.

Purpose

A proteomic study was performed to compare the composition of low leukocyte PRP, platelet poor plasma (PPP), and blood plasma. Pathway analysis of the proteomic data was performed to evaluate differences between plasma formulations at the molecular level. Low abundance regulatory proteins in plasma were identified and quantified as well as cellular pathways regulated by those proteins.

Methods

Quantitative proteomic analysis, using multiplexed isotopically labeled tags (TMT labeling) and label-free tandem mass spectrometry, was performed on plasma, low leukocyte PRP, and PPP. Plasma formulations were derived from two blood donors (one donor per experiment). Pathway analysis of the proteomic data identified the major differences between formulations.

Results

Nearly 600 proteins were detected in three types of blood plasma formulations in two experiments. Identified proteins showed more than 50% overlap between plasma formulations. Detected proteins represented more than 100 canonical pathways, as was identified by pathway analysis. The major pathways and regulatory molecules were linked to inflammation.

Conclusion

Three types of plasma formulations were compared in two proteomic experiments. The most represented pathways, such as Acute Phase Response, Coagulation, or System of the Complement, had many proteins in common in both experiments. In both experiments plasma sample sets had the same direction of biochemical pathway changes: up- or down-regulation. The most represented biochemical pathways are linked to inflammation.

Platelet-Rich Plasma Shortens Return to Play in National Football League Players With Acute Hamstring Injuries

Background:

Hamstring injuries are prevalent in professional athletes and can lead to significant time loss, with recurrent injury being common. The efficacy of platelet-rich plasma (PRP) for augmentation of nonoperative treatment of partial musculotendinous hamstring injuries is not well established.

Hypothesis:

The addition of PRP injections to nonoperative treatment for acute partial musculotendinous hamstring injuries will lead to a shortened return to play in National Football League (NFL) players.

Study Design:

Cohort study; Level of evidence, 3.

Methods:

NFL players from a single team who sustained acute grade 2 hamstring injuries, as diagnosed on magnetic resonance imaging (MRI) by a musculoskeletal radiologist from 2009 to 2018, were retrospectively reviewed. Average days, practices, and games missed were recorded. Players who did and did not receive PRP (leukocyte-poor) injections were compared. Those who received PRP did so within 24 to 48 hours after injury.

Results:

A total of 108 NFL players had MRI evidence of a hamstring injury, and of those, 69 athletes sustained grade 2 injuries. Thirty players received augmented treatment with PRP injections and 39 players underwent nonoperative treatment alone. Average time missed in those treated with PRP injections was 22.5 days, 18.2 practices, and 1.3 games. In those who did not receive PRP injections, time missed was 25.7 days (P = .81), 22.8 practices (P = .68), and 2.9 games (P < .05).

Conclusion:

Augmentation with PRP injections for acute grade 2 hamstring injuries in NFL players showed no significant difference in days missed or time to return to practice but did allow for faster return to play, with a 1 game overall difference. Owing to the possible large financial impact of returning to play 1 game sooner, PRP injections for treatment of grade 2 hamstring injuries may be advantageous in professional athletes.

Platelet Concentrates in Musculoskeletal Medicine

Platelet concentrates (PCs), mostly represented by platelet-rich plasma (PRP) and platelet-rich fibrin (PRF) are autologous biological blood-derived products that may combine plasma/platelet-derived bioactive components, together with fibrin-forming protein able to create a natural three-dimensional scaffold. These types of products are safely used in clinical applications due to the autologous-derived source and the minimally invasive application procedure. In this narrative review, we focus on three main topics concerning the use of platelet concentrate for treating musculoskeletal conditions: (a) the different procedures to prepare PCs, (b) the composition of PCs that is related to the type of methodological procedure adopted and (c) the clinical application in musculoskeletal medicine, efficacy and main limits of the different studies.

Classification systems for platelet-rich plasma

There is good scientific rationale to support the use of growth factors to promote musculoskeletal tissue regeneration. However, the clinical effectiveness of platelet-rich plasma (PRP) and other blood-derived products has yet to be proven. Characterization and reporting of PRP preparation protocols utilized in clinical trials for the treatment of musculoskeletal disease is highly inconsistent, and the majority of studies do not provide sufficient information to allow the protocols to be reproduced. Furthermore, the reporting of blood-derived products in orthopaedics is limited by the multiple PRP classification systems available, which makes comparison of results between studies challenging. Several attempts have been made to characterize and classify PRP; however, no consensus has been reached, and there is lack of a comprehensive and validated classification. In this annotation, we outline existing systems used to classify preparations of PRP, highlighting their advantages and limitations. There remains a need for standardized universal nomenclature to describe biological therapies, as well as a comprehensive and reproducible classification system for autologous blood-derived products.

Cite this article: Bone Joint J 2019;101-B:891–896.

Platelet-rich plasma for muscle injuries: A systematic review of the basic science literature

BACKGROUND

Platelet-rich plasma (PRP) is an increasingly used biologic adjunct for muscle injuries, as it is thought to expedite healing. Despite its widespread use, little is known regarding the mechanisms by which PRP produces its efficacious effects in some patients.

AIM

To clarify the effects of PRP on muscular pathologies at the cellular and tissue levels by evaluating the basic science literature.

METHODS

A systematic review of PubMed/MEDLINE and EMBASE databases was performed using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and checklist. Level III in vivo and in vitro studies examining PRP effects on muscles, myocytes and/or myoblasts were eligible for inclusion. Extracted data included PRP preparation methods and study results.

RESULTS

Twenty-three studies were included (15 in vivo, 6 in vitro, 2 in vitro/in vivo). Only one reported a complete PRP cytology (platelets, and red and white blood cell counts). Five in vitro studies reported increased cellular proliferation, four reported increased gene expression, and three reported increased cellular differentiation. Five in vivo studies reported increased gene expression, three reported superior muscle regeneration, and seven reported improved histological quality of muscular tissue.

CONCLUSION

The basic science literature on the use of PRP in muscle pathology demonstrates that PRP treatment confers several potentially beneficial effects on healing in comparison to controls. Future research is needed to determine optimal cytology, dosing, timing, and delivery methods of PRP for muscle pathologies.

Chondrogenic Progenitor Cells Exhibit Superiority Over Mesenchymal Stem Cells and Chondrocytes in Platelet-Rich Plasma Scaffold-Based Cartilage Regeneration

BACKGROUND

Platelet-rich plasma (PRP) has been considered a promising tool for cartilage regeneration. However, increasing evidence has demonstrated the controversial effects of PRP on tissue regeneration, partially due to the unsatisfactory cell source. Chondrogenic progenitor cells (CPCs) have gained increasing attention as a potential cell source due to their self-renewal and multipotency, especially toward the chondrogenic lineage, and, thus, may be an appropriate alternative for cartilage engineering.

PURPOSE

To compare the effects of PRP on CPC, mesenchymal stem cell (MSC), and chondrocyte proliferation, chondrogenesis, and cartilage regeneration.

STUDY DESIGN

Controlled laboratory study.

METHODS

Whole blood samples were obtained from 5 human donors to create PRPs (0, 1000 × 10⁹, and 2000 × 10⁹ platelets per liter). The proliferation and chondrogenesis of CPCs, bone marrow-derived MSCs (BMSCs), and chondrocytes were evaluated via growth kinetic and CCK-8 assays. Immunofluorescence, cytochemical staining, and gene expression analyses were performed to assess chondrogenic differentiation and cartilaginous matrix formation. The in vivo effects of CPCs, BMSCs, and chondrocytes on cartilage regeneration after PRP treatment were measured by use of histopathological, biochemical, and biomechanical techniques in a cartilage defect model involving mature male New Zealand White rabbits (critical size, 5 mm).

RESULTS

The CPCs possessed migration abilities and proliferative capacities superior to those of the chondrocytes, while exhibiting a chondrogenic predisposition stronger than that of the BMSCs. The growth kinetic, CCK-8, cytochemical staining, and biochemical analyses revealed that the CPCs simultaneously displayed a higher cell density than the chondrocytes and stronger chondrogenesis than the BMSCs after PRP stimulation. In addition, the in vivo study demonstrated that the PRP+CPC construct yielded better histological (International Cartilage Repair Society [ICRS] score, mean ± SEM, 1197.2 ± 163.2) and biomechanical (tensile modulus, 1.523 ± 0.194) results than the PRP+BMSC (701.1 ± 104.9, P < .05; 0.791 ± 0.151, P < .05) and PRP+chondrocyte (541.6 ± 98.3, P < .01; 0.587 ± 0.142, P < .01) constructs at 12 weeks after implantation.

CONCLUSION

CPCs exhibit superiority over MSCs and chondrocytes in PRP scaffold-based cartilage regeneration, and PRP+CPC treatment may be a favorable strategy for cartilage repair.

CLINICAL RELEVANCE

These findings provide evidence highlighting the preferable role of CPCs as a cell source in PRP-mediated cartilage regeneration and may help researchers address the problem of unsatisfactory cell sources in cartilage engineering.

Similar effect of ultrasound-guided platelet-rich plasma versus platelet-poor plasma injections for chronic plantar fasciitis

BACKGROUND

There are conflicting reports regarding the therapeutic effect of platelet-rich plasma (PRP) versus autologous whole-blood (platelet poor plasma, PPP) injections for plantar fasciitis. Therefore, this study was conducted to compare the effectiveness of a single ultrasound (US)-guided PRP versus PPP injection in patients with chronic plantar fasciitis.

MATERIALS AND METHODS

36 patients were recruited with clinical and sonographic evidence of chronic (>6 months) plantar fasciitis, refractory to analgesics and physical therapy in a double-blinded, randomized, prospective study. The patients were randomly allocated into two groups with a sealed envelope method. Group A included 18 patients who underwent a single US-guided PRP injection and group B included another 18 patients who underwent PPP injection with the same technique. Follow-up was set at 3 and 6 months; no patient was lost to follow-up. Pain, function and satisfaction were assessed using visual analogue scales, and occurrence of complications.

RESULTS

All scores statistically significantly improved for both groups from baseline at the 3- and 6-month follow-up evaluation, without, however, any statistically significant differences between the two groups with respect to pain, function and satisfaction scores. Complications were not observed.

CONCLUSIONS

A single US-guided PRP injection yields similar results with PPP injection in patients with chronic plantar fasciitis. Both treatments provide significant improvement at 3 and 6-month follow-up after the injection.

Platelet releasate promotes skeletal myogenesis by increasing muscle stem cell commitment to differentiation and accelerates muscle regeneration following acute injury

AIM

The use of platelets as biomaterials has gained intense research interest. However, the mechanisms regarding platelet-mediated skeletal myogenesis remain to be established. The aim of this study was to determine the role of platelet releasate in skeletal myogenesis and muscle stem cell fate in vitro and ex vivo respectively.

METHODS

We analysed the effect of platelet releasate on proliferation and differentiation of C2C12 myoblasts by means of cell proliferation assays, immunohistochemistry, gene expression and cell bioenergetics. We expanded in vitro findings on single muscle fibres by determining the effect of platelet releasate on murine skeletal muscle stem cells using protein expression profiles for key myogenic regulatory factors.

RESULTS

TRAP6 and collagen used for releasate preparation had a more pronounced effect on myoblast proliferation vs thrombin and sonicated platelets (P < 0.05). In addition, platelet concentration positively correlated with myoblast proliferation. Platelet releasate increased myoblast and muscle stem cell proliferation in a dose-dependent manner, which was mitigated by VEGFR and PDGFR inhibition. Inhibition of VEGFR and PDGFR ablated MyoD expression on proliferating muscle stem cells, compromising their commitment to differentiation in muscle fibres (P < 0.001). Platelet releasate was detrimental to myoblast fusion and affected differentiation of myoblasts in a temporal manner. Most importantly, we show that platelet releasate promotes skeletal myogenesis through the PDGF/VEGF-Cyclin D1-MyoD-Scrib-Myogenin axis and accelerates skeletal muscle regeneration after acute injury.

CONCLUSION

This study provides novel mechanistic insights on the role of platelet releasate in skeletal myogenesis and set the physiological basis for exploiting platelets as biomaterials in regenerative medicine.

Influence of Platelet-Rich and Platelet-Poor Plasma on Endogenous Mechanisms of Skeletal Muscle Repair/Regeneration

The morpho-functional recovery of injured skeletal muscle still represents an unmet need. None of the therapeutic options so far adopted have proved to be resolutive. A current scientific challenge remains the identification of effective strategies improving the endogenous skeletal muscle regenerative program. Indeed, skeletal muscle tissue possesses an intrinsic remarkable regenerative capacity in response to injury, mainly thanks to the activity of a population of resident muscle progenitors called satellite cells, largely influenced by the dynamic interplay established with different molecular and cellular components of the surrounding niche/microenvironment. Other myogenic non-satellite cells, residing within muscle or recruited via circulation may contribute to post-natal muscle regeneration. Unfortunately, in the case of extended damage the tissue repair may become aberrant, giving rise to a maladaptive fibrotic scar or adipose tissue infiltration, mainly due to dysregulated activity of different muscle interstitial cells. In this context, plasma preparations, including Platelet-Rich Plasma (PRP) and more recently Platelet-Poor Plasma (PPP), have shown advantages and promising therapeutic perspectives. This review focuses on the contribution of these blood-derived products on repair/regeneration of damaged skeletal muscle, paying particular attention to the potential cellular targets and molecular mechanisms through which these products may exert their beneficial effects.

The Influence of Naproxen on Biological Factors in Leukocyte-Rich Platelet-Rich Plasma: A Prospective Comparative Study

PURPOSE

To quantify and compare normative catabolic and anabolic factor concentrations in leukocyte-rich platelet-rich plasma (LR-PRP) at various time points, including baseline, 1 week after initiating naproxen use, and after a 1-week washout period.

METHODS

Asymptomatic healthy donors aged between 18 and 70 years were recruited (average age, 36.6 years; range, 25-64 years). Subjects were excluded from the study if they were actively taking any prescribed medications or nonsteroidal anti-inflammatory drugs (NSAIDs) or if they had any of the following at present or previously: blood or immunosuppression disorders, cancer, osteonecrosis, rheumatoid arthritis, avascular necrosis, NSAID intolerance, gastrointestinal or peptic ulcer disease, or kidney dysfunction. The anabolic factors vascular endothelial growth factor, fibroblast growth factor 2, platelet-derived growth factor AB (PDGF-AB), and platelet-derived growth factor AA (PDGF-AA) and the catabolic factors interleukin (IL) 1β, IL-6, IL-8, and tumor necrosis factor α in LR-PRP were measured. Peripheral blood was drawn at 3 time points: baseline, after 1 week of naproxen use, and after a 1-week washout period.

RESULTS

The angiogenic factors PDGF-AA (44% decrease in median) and PDGF-AB (47% decrease) significantly declined from baseline (P < .05) after 1 week of naproxen use. There was a significant recovery (P < .05) of PDGF-AA (94% increase) and PDGF-AB (153% increase) levels after the 1-week washout period, with a return to baseline levels. The catabolic factor IL-6 also had a significant decline from baseline (77% decrease in median, P < .05) after 1 week of naproxen use. After a 1-week washout period, the IL-6 level was similar to the baseline level (130% increase, P < .05).

CONCLUSIONS

Naproxen use diminished several biological factors in LR-PRP; however, a 1-week washout period was sufficient for the recovery of PDGF-AA, PDGF-AB, and IL-6 to return to baseline levels. Tumor necrosis factor α, IL-1β, IL-8, vascular endothelial growth factor, and fibroblast growth factor 2 did not show differences between the 3 time points of data collection. Discontinuing NSAIDs for a minimum of 1 week before LR-PRP treatment may improve certain biological factor levels.

LEVEL OF EVIDENCE

Level II, prospective comparative study.

Platelet-Rich Plasma

Platelet-rich plasma (PRP) is a promising treatment for musculoskeletal maladies and clinical data to date have shown that PRP is safe. However, evidence of its efficacy has been mixed and highly variable depending on the specific indication. Additional future high-quality large clinical trials will be critical in shaping our perspective of this treatment option. The heterogeneity of PRP preparations, both presently and historically, leads sweeping recommendations about its utility impossible to make. This heterogeneity has also made interpreting existing literature more complicated.

Platelet biology in regenerative medicine of skeletal muscle

Platelet-based applications such as platelet-rich plasma (PRP) and platelet releasate have gained unprecedented attention in regenerative medicine across a variety of tissues as of late. The rationale behind utilizing PRP originates in the delivery of key cytokines and growth factors from α-granules to the targeted area, which in turn act as cell cycle regulators and promote the healing process across a variety of tissues. The aim of the present review is to assimilate current experimental evidence on the role of platelets as biomaterials in tissue regeneration, particularly in skeletal muscle, by integrating findings from human, animal and cell studies. This review is composed of 3 parts: firstly, we review key aspects of platelet biology that precede the preparation and use of platelet-related applications for tissue regeneration. Secondly, we critically discuss relevant evidence on platelet-mediated regeneration in skeletal muscle focusing on findings from (i) clinical trials, (ii) experimental animal studies and (iii) cell culture studies; and thirdly, we discuss the application of platelets in the regeneration of several other tissues including tendon, bone, liver, vessels and nerve. Finally, we review key technical variations in platelet preparation that may account for the large discrepancy in outcomes from different studies. This review provides an up-to-date reference tool for biomedical and clinical scientists involved in platelet-mediated tissue regenerative applications.

Nonoperative treatment of muscle injuries - recommendations from the GOTS expert meeting

BACKGROUND

Muscle injuries are some of the most common injuries in sports; they have a high recurrence rate and can result in the loss of ability to participate in training or competition. In clinical practice, a wide variety of treatment strategies are commonly applied. However, a limited amount of evidence-based data exists, and most therapeutic approaches are solely based on "best practice". Thus, there is a need for consensus to provide strategies and recommendations for the treatment of muscle injuries.

METHODS

The 2016 GOTS Expert Meeting, initiated by the German-Austrian-Swiss Society for Orthopaedic Traumatologic Sports Medicine (GOTS), focused on the topic of muscle and tendon injuries and was held in Spreewald/Berlin, Germany. The committee was composed of twenty-two medical specialists. Nine of them were delegated to a subcommittee focusing on the nonoperative treatment of muscle injuries. The recommendations and statements that were developed were reviewed by the entire consensus committee and voted on by the members.

RESULTS

The committee reached a consensus on the utility and effectiveness of the management of muscle injuries.

MAIN RESULTS

the "PRICE" principle to target the first inflammatory response is one of the most relevant steps in the treatment of muscle injuries. Haematoma aspiration may be considered in the early stages after injury. There is presently no clear evidence that intramuscular injections are of use in the treatment of muscle injuries. The ingestion of non-steroidal anti-inflammatory drugs (NSAIDs) should be regarded critically because there is currently no hard evidence to support their use, although they are appropriate in exceptional cases.

CONCLUSIONS

The present work provides a structured overview of the various nonoperative treatment strategies of muscle injuries and evaluates their effectiveness with respect to the existing scientific evidence and clinical expertise in the context of basic science on the healing process of muscle injuries. The committee agreed that there is a compelling need for further studies, including high-quality randomized investigations to completely evaluate the effectiveness of the existing therapeutic approaches. The given recommendations may be updated and adjusted as further evidence will be generated.

Editorial Commentary: Hype, Hope and Everything in Between. What Produces the Real Effect for Blood-derived Products Including Platelet-Rich Plasma?

Biological approaches have a promising future in the orthopaedic field because of their potential benefits that include their minimal invasiveness, potential for accelerated healing, and promise for rapid recovery. However, as the initial hype for these therapies starts to fade, it should be replaced by solid basic and clinical science research to tailor each compound to a determined patient/pathology. Blood contains several products that can be both beneficial and detrimental for every specific tissue, and therefore a one-fits-all approach should be avoided. Although beneficial effects have been consistently reported for certain pathologies such as lateral elbow tendinopathy, as an adjunct for rotator cuff repairs and the symptomatic treatment of osteoarthritis, other conditions' outcomes with biologic treatment remain nebulous such as for Achilles tendinopathy. To determine the real effect of these therapies, it is important to maintain strict inclusion criteria in an attempt to isolate the effect of one biologic product that already has many inherent intrinsic variables per se.

Human serum and platelet lysate are appropriate xeno-free alternatives for clinical-grade production of human MuStem cell batches

BACKGROUND

Canine MuStem cells have demonstrated regenerative efficacy in a dog model of muscular dystrophy, and the recent characterization of human counterparts (hMuStem) has highlighted the therapeutic potential of this muscle-derived stem cell population. To date, these cells have only been generated in research-grade conditions. However, evaluation of the clinical efficacy of any such therapy will require the production of hMuStem cells in compliance with good manufacturing practices (GMPs). Because the current use of fetal bovine serum (FBS) to isolate and expand hMuStem cells raises several ethical, safety, and supply concerns, we assessed the use of two alternative xeno-free blood derivatives: human serum (HS) and a human platelet lysate (hPL).

METHODS

hMuStem cells were isolated and expanded in vitro in either HS-supplemented or hPL-supplemented media and the proliferation rate, clonogenicity, myogenic commitment potential, and oligopotency compared with that observed in FBS-supplemented medium. Flow cytometry and high-throughput 3'-digital gene expression RNA sequencing were used to characterize the phenotype and global gene expression pattern of hMuStem cells cultured with HS or hPL.

RESULTS

HS-supplemented and hPL-supplemented media both supported the isolation and long-term proliferation of hMuStem cells. Compared with FBS-based medium, both supplements enhanced clonogenicity and allowed for a reduction in growth factor supplementation. Neither supplement altered the cell lineage pattern of hMuStem cells. In vitro differentiation assays revealed a decrease in myogenic commitment and in the fusion ability of hMuStem cells when cultured with hPL. In return, this reduction of myogenic potential in hPL-supplemented cultures was rapidly reversed by substitution of hPL with HS or fibrinogen-depleted hPL. Moreover, culture of hMuStem cells in hPL hydrogel and fibrinogen-depleted hPL demonstrated that myogenic differentiation potential is maintained in heparin-free hPL derivatives.

CONCLUSIONS

Our findings indicate that HS and hPL are efficient and viable alternatives to FBS for the preparation of hMuStem cell batches in compliance with GMPs.