The recombinant human fibroblast growth factor-18 (sprifermin) improves tendon-to-bone healing by promoting chondrogenesis in a rat rotator cuff repair model

Anti-Leukotriene Receptor Blockers Improve Tendon-Bone Interface Healing in a Rat Model of Acute Rotator Cuff Tear

BACKGROUND

Excessive expression of proinflammatory cytokines after rotator cuff (RC) surgery impairs the quality of tendon-bone interface (TBI) healing. There is evidence that the asthma drug montelukast (MS) inhibits the expression of proinflammatory cytokines. This study was conducted to verify the effect of MS administration on TBI healing after RC repair.

MATERIALS AND METHODS

Thirteen rats in the MS group were intraperitoneally administered 10 mg/kg of the drug daily for 2 weeks after RC surgery, and 13 rats in the control group were administered only 0.9% saline. The healing effect of the TBI was assessed through histologic and biomechanical analysis 4 weeks after tendon repair.

RESULTS

In the MS group, the expression of interleukin-1 beta (IL-1β; P<.01) and interleukin 6 (IL-6; P<.01) was significantly reduced compared with the control group. In the evaluation of supraspinatus fatty infiltration, the MS group showed significant inhibition of fatty infiltration compared with the control group (P<.001). Histologic analysis showed that the MS group had significant improvements in collagen density (P=.035) and alignment (P=.011). Biomechanical analysis after systemic administration of MS showed an increase in the cross-sectional area (P<.001) and elongation (P<.01) of the TBI.

CONCLUSION

The use of MS improved tendon elasticity through suppressing fatty infiltration and improving TBI collagen density and arrangement. The mechanism is down-regulation of IL-1β and IL-6. These results strongly support the use of MS as an anti-inflammatory agent that does not impair tendon healing. [Orthopedics. 2025;48(2):e105-e112.].

Stable Gastric Pentadecapeptide BPC 157 as Therapy After Surgical Detachment of the Quadriceps Muscle from Its Attachments for Muscle-to-Bone Reattachment in Rats

BACKGROUND

This is a novel rat study using native peptide therapy, focused on reversing quadriceps muscle-to-bone detachment to reattachment and stable gastric pentadecapeptide BPC 157 per-oral therapy for shared muscle healing and function restoration.

METHODS

Pharmacotherapy recovering various muscle, tendon, ligament, and bone lesions, and severed junctions (i.e., myotendinous junction), per-oral in particular (BPC 157/kg/day 10 µg, 10 ng), provides muscle-to-bone reattachment after quadriceps muscle detachment, both complete (rectus muscle) and partial (vastus muscles).

RESULTS

Immediately post-injury, and at 1, 2, 3, 5, 7, 14, 21, 28, 60, and 90 days post-injury, quadriceps muscle-to-bone detachment showed definitive healing failure (impaired walking and permanent knee flexure). Contrarily, macro/microscopic, ultrasonic, magnetic resonance, biomechanical, and functional assessments revealed that BPC 157 therapy recovering effects for all time points were consistent. All parameters of the walking pattern fully improved, and soon after detachment and therapy application, muscle approached the bone, leaving a minimal gap (on ultrasonic assessment), and leg contracture was annihilated. The healing process occurs immediately after detachment from both sides: the muscle and the bone. The reattachment fibers from the ends of the muscle could be traced into the new bone formed at the surface (note, at day 3 post-detachment, increased mesenchymal cells occurred with periosteum reactivation). Consequently, at 3 months, the form was stable, and the balance between the muscle and bone was the following: well-organized bone, newly formed as more cortical bone providing a narrower bone marrow space, and the muscle and mature fibers were oriented parallel to the bone axis and were in close contact with bone.

CONCLUSIONS

Therefore, to achieve quadriceps muscle-to-bone reattachment, the BPC 157 therapy reversing course acts from the beginning, resolving an otherwise insurmountable deleterious course.

Injectable Fibrocartilage-Forming Cores Enhance Bone-Tendon Healing in a Rat Rotator Cuff Model

BACKGROUND

After surgical repair of rotator cuff (RC) tears, the torn tendon heals unsatisfactorily to the greater tuberosity owing to limited regeneration of the bone-tendon (BT) insertion. This situation motivates the need for new interventions to enhance BT healing in the RC repair site.

PURPOSE

To develop injectable fibrocartilage-forming cores by tethering fibroblast growth factor 18 (FGF18) on acellular fibrocartilage matrix microparticles (AFM-MPs) and evaluate their efficacy on BT healing.

STUDY DESIGN

Controlled laboratory study.

METHODS

We harvested normal fibrocartilage tissue from the porcine RC insertion, after which it was decellularized and then micronized for fabricating AFM-MPs. The collagen-binding domain was fused into the N-terminus of FGF18 to synthesize recombinant FGF18 (CBD-FGF18), which was tethered to the collagen fibers of AFM-MPs to prepare the injectable fibrocartilage-forming cores (CBD-FGF18@AFM-MPs). After examining the influence of the CBD-FGF18@AFM-MPs on the viability and chondrogenic differentiation of bone marrow mesenchymal stem cells in vitro, we determined the function of the CBD-FGF18@AFM-MPs on BT healing in a rat RC tear model. A total of 80 Sprague-Dawley rats with RC injuries were randomly assigned to 4 supplemental treatments during RC repair: saline injection (control group), AFM-MPs injection, natural FGF18@AFM-MPs injection, and CBD-FGF18@AFM-MPs injection. At 4 and 8 weeks postoperatively, the harvested RC specimens were evaluated via micro-computed tomography, histologic staining, and mechanical testing.

RESULTS

In vitro, the CBD-FGF18@AFM-MPs were highly biomimetic, suitable for cell growth and proliferation, and superior in stimulating chondrogenesis. In vivo micro-computed tomography results showed that the CBD-FGF18@AFM-MPs group had significantly more new bone formation and better bone remodeling than the other 3 groups. Histologically, at 4 and 8 weeks postoperatively, the CBD-FGF18@AFM-MPs group had the best continuity of the BT insertion with regular collagen alignment and extensive fibrocartilage regeneration. Importantly, at 8 weeks postoperatively, the RC specimens from the CBD-FGF18@AFM-MPs group presented the highest failure load and stiffness.

CONCLUSION

The injectable fibrocartilage-forming cores provide a new biological intervention to promote RC healing.

CLINICAL RELEVANCE

The injectable fibrocartilage-forming cores may be a new complementary treatment for surgical repair of RC tears.

Ezetimibe/Atorvastatin, a Treatment for Hyperlipidemia, Inhibits Supraspinatus Fatty Infiltration and Improves Bone-Tendon Interface Healing in a Rotator Cuff Tear Rat Model

BACKGROUND

Multiple factors, such as muscle fatty infiltration (FI), tendon collagen content, and collagen arrangement, determine bone-tendon interface (BTI) healing after rotator cuff (RC) repair.

PURPOSE

To evaluate the effects of systemic administration of ezetimibe-atorvastatin (EZE/ATZ) combination on muscle FI and tendon collagen density and arrangement in an RC repair rat model.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 26 male Sprague-Dawley rats were randomly divided equally into control and EZE/ATZ groups and subjected to RC tendon repair surgery. Postoperatively, the EZE/ATZ group rats received a combination of EZE (10 mg/kg/d) and ATZ (20 mg/kg/d) for 4 weeks, after which they were sacrificed. Oil Red O staining was used to assess FI in the supraspinatus muscle. The expression of biomarkers related to muscle atrophy and FI was measured using quantitative real-time polymerase chain reaction. For the qualitative and quantitative analysis of FI-related biomarkers, immunohistochemical staining was performed. Biomechanical and histological analyses were performed to evaluate the quality of BTI healing after RC repair.

RESULTS

The EZE/ATZ group showed significantly lower FI compared with the control group (P < .001) and significantly downregulated expression of gene markers related to muscle atrophy and FI. On histological analysis, the EZE/ATZ group exhibited increased collagen type I contents, consistent collagen arrangement (P = .005), and significantly higher collagen density (P = .003) compared with the control group. Biomechanical analysis of the BTI healing revealed that the EZE/ATZ group had significantly increased ultimate strength (P = .006) compared with the control group.

CONCLUSION

Systemic EZE/ATZ administration suppressed supraspinatus FI by downregulating muscle atrophy-related and FI-related genes after RC repair. Additionally, EZE/ATZ use improved collagen biosynthesis, density, and arrangement at the BTI and significantly increased tensile strength.

CLINICAL RELEVANCE

The results of the current study strongly advocate the use of EZE/ATZ to improve shoulder function and tendon healing after RC repair.

Computer-assisted stabilization of fibroblast growth factor FGF-18

The fibroblast growth factors (FGF) family holds significant potential for addressing chronic diseases. Specifically, recombinant FGF18 shows promise in treating osteoarthritis by stimulating cartilage formation. However, recent phase 2 clinical trial results of sprifermin (recombinant FGF18) indicate insufficient efficacy. Leveraging our expertise in rational protein engineering, we conducted a study to enhance the stability of FGF18. As a result, we obtained a stabilized variant called FGF18-E4, which exhibited improved stability with 16 °C higher melting temperature, resistance to trypsin and a 2.5-fold increase in production yields. Moreover, the FGF18-E4 maintained mitogenic activity after 1-week incubation at 37 °C and 1-day at 50 °C. Additionally, the inserted mutations did not affect its binding to the fibroblast growth factor receptors, making FGF18-E4 a promising candidate for advancing FGF-based osteoarthritis treatment.

Drug Delivery Approaches to Improve Tendon Healing

Tendon injuries disrupt the transmission of forces from muscle to bone, leading to chronic pain, disability, and a large socioeconomic burden. Tendon injuries are prevalent; there are over 300,000 tendon repair procedures a year in the United States to address acute trauma or chronic tendinopathy. Successful restoration of function after tendon injury remains challenging clinically. Despite improvements in surgical and physical therapy techniques, the high complication rate of tendon repair procedures motivates the use of therapeutic interventions to augment healing. While many biological and tissue engineering approaches have attempted to promote scarless tendon healing, there is currently no standard clinical treatment to improve tendon healing. Moreover, the limited efficacy of systemic delivery of several promising therapeutic candidates highlights the need for tendon-specific drug delivery approaches to facilitate translation. This review article will synthesize the current state-of-the-art methods that have been used for tendon-targeted delivery through both systemic and local treatments, highlight emerging technologies used for tissue-specific drug delivery in other tissue systems, and outline future challenges and opportunities to enhance tendon healing through targeted drug delivery.

Bioengineering Approaches for Delivering Growth Factors: A Focus on Bone and Cartilage Regeneration

Growth factors are bio-factors that target reparatory cells during bone regeneration. These growth factors are needed in complicated conditions of bone and joint damage to enhance tissue repair. The delivery of these growth factors is key to ensuring the effectiveness of regenerative therapy. This review discusses the roles of various growth factors in bone and cartilage regeneration. The methods of delivery of natural or recombinant growth factors are reviewed. Different types of scaffolds, encapsulation, Layer-by-layer assembly, and hydrogels are tools for growth factor delivery. Considering the advantages and limitations of these methods is essential to developing regenerative therapies. Further research can accordingly be planned to have new or combined technologies serving this purpose.