Neutralization of excessive levels of active TGF-β1 reduces MSC recruitment and differentiation to mitigate peritendinous adhesion

Peritendinous adhesion: Therapeutic targets and progress of drug therapy

Peritendinous adhesion (PA) is one of the most common complications following hand surgery and characterized with abnormal hyperplasia of connective tissue and excessive deposition of extracellular matrix. Subsequently, various clinical symptoms such as chronic pain, limb dyskinesia and even joint stiffness occur and patients are always involved in the vicious cycle of "adhesion - release - re-adhesion", which seriously compromise the quality of life. Until present, the underlying mechanism remains controversial and lack of specific treatment, with symptomatic treatment being the only option to relieve symptoms, but not contributing no more to the fundamentally rehabilitation of basic structure and function. Recently, novel strategies have been proposed to inhibit the formation of adhesion tissues including implantation of anti-adhesion barriers, anti-inflammation, restraint of myofibroblast transformation and regulation of collagen overproduction. Furthermore, gene therapy has also been considered as a promising anti-adhesion treatment. In this review, we provide an overview of anti-adhesion targets and relevant drugs to summarize the potential pharmacological roles and present subsequent challenges and prospects of anti-adhesion drugs.

Human Tendon-on-a-Chip for Modeling the Myofibroblast Microenvironment in Peritendinous Fibrosis

Understanding the myofibroblast microenvironment is critical to developing therapies for fibrotic diseases. Here the development of a novel human tendon-on-a-chip (hToC) is reported to model this crosstalk in peritendinous adhesions, which currently lacks biological therapies. The hToC facilitates cellular and paracrine interactions between a vascular component, which contains endothelial cells and monocytes, and a tissue hydrogel component that houses tendon cells and macrophages. It is found that the hToC replicates some aspects of in vivo inflammatory and fibrotic phenotypes in preclinical and clinical samples, including activated mTOR signaling, vascular inflammation, tissue contraction induced by myofibroblast activation, inflammatory cytokines secretion, and transendothelial migration of monocytes to the tissue hydrogel. Transcriptional analysis demonstrates significant overlap in enriched pathways in the hToC with human tenolysis samples, including the activation of mTOR signaling. Rapamycin suppresses the vascular inflammation and fibrotic phenotype in the hToC, which provides proof-of-concept of its utility as an in vitro tool for investigating multicellular crosstalk in fibrosis and testing therapeutics to mitigate it.

Challenges in tendon-bone healing: emphasizing inflammatory modulation mechanisms and treatment

Tendons are fibrous connective tissues that transmit force from muscles to bones. Despite their ability to withstand various loads, tendons are susceptible to significant damage. The healing process of tendons and ligaments connected to bone surfaces after injury presents a clinical challenge due to the intricate structure, composition, cellular populations, and mechanics of the interface. Inflammation plays a pivotal role in tendon healing, creating an inflammatory microenvironment through cytokines and immune cells that aid in debris clearance, tendon cell proliferation, and collagen fiber formation. However, uncontrolled inflammation can lead to tissue damage, and adhesions, and impede proper tendon healing, culminating in scar tissue formation. Therefore, precise regulation of inflammation is crucial. This review offers insights into the impact of inflammation on tendon-bone healing and its underlying mechanisms. Understanding the inflammatory microenvironment, cellular interactions, and extracellular matrix dynamics is essential for promoting optimal healing of tendon-bone injuries. The roles of fibroblasts, inflammatory cytokines, chemokines, and growth factors in promoting healing, inhibiting scar formation, and facilitating tissue regeneration are discussed, highlighting the necessity of balancing the suppression of detrimental inflammatory responses with the promotion of beneficial aspects to enhance tendon healing outcomes. Additionally, the review explores the significant implications and translational potential of targeted inflammatory modulation therapies in refining strategies for tendon-bone healing treatments.

Ultrasound-guided Hydrogel Injection Provides Better Therapeutic Effects After Hand Tendon Surgery Than Intraoperative Injection: A Randomized Controlled Trial

BACKGROUND

Hydrogels are used to provide a barrier against peritendinous adhesion formation, but when implanted intraoperatively, they degrade rapidly and aggravate early inflammatory pain. It is uncertain whether clinical efficacy can be improved by avoiding the inflammatory phase when hydrogels are delivered during adhesion formation.

QUESTIONS/PURPOSES

(1) Compared with intraoperative hydrogel application, does ultrasound-guided postoperative application result in better total active motion (TAM) at 12 months after tendon injury? (2) Does ultrasound-guided postoperative application of hydrogels result in lower pain, better function, and better satisfaction?

METHODS

This open-label, prospective, single-center, randomized controlled trial was conducted by reparative and reconstructive surgeons at the National Orthopedics Clinical Medical Center, Shanghai, People's Republic of China. Between May 2021 and December 2022, 53% (168 of 317) of patients who met our inclusion criteria were recruited, and 47% (149 of 317) of patients were excluded because of the exclusion criteria. Finally, 84 patients were randomized to the postoperative group to receive ultrasound-guided carboxymethyl chitosan (CMC) hydrogel delayed injection, and 84 patients were randomized to the intraoperative group to receive CMC hydrogel intraoperative application. Another 8% (7 of 84) of patients in the postoperative group and 10% (8 of 84) of patients in the intraoperative group were lost before the minimum study follow-up time of 1 year or had incomplete datasets, leaving 91% (153 of 168) of patients with data for analysis. Data on outcome events were analyzed according to the intention-to-treat principle, which included all patients who underwent randomization. Follow-up visits were completed at 3 weeks, 6 weeks, 3 months, 6 months, and 12 months after tendon repair. The primary outcome was TAM (ie, the sum of the degrees of active metacarpophalangeal joint, proximal interphalangeal joint, and distal interphalangeal joint flexion less the degrees from full extension; minimum clinically important difference [MCID] 20°) at 12 months. Secondary outcomes included pain (measured with a VAS; range 0 to 10, a higher score indicating worse pain; MCID 0.6), Michigan Hand Outcomes Questionnaire activities of daily living (MHQ-ADL) score (range 0 to 100, a higher score indicating better outcomes; MCID 10.1), and MHQ satisfaction (MHQ-SAT) score (range 0 to 100, a higher score indicating better outcomes; MCID 33.0).

RESULTS

At 12 months, the ultrasound-guided postoperative injection group had improved TAM (intraoperative 189° [95% CI 179° to 199°] versus postoperative 209° [95% CI 199° to 219°], mean difference 20° [95% CI 6° to 35°]; p = 0.006; the mean difference in the primary outcome fulfilled the MCID value at all time points). At 6 weeks, we found no clinically important difference in VAS pain scores among groups (intraoperative mean ± SD 2.0 ± 1.0 versus postoperative 1.7 ± 1.0, mean difference 0.3 [95% CI 0.1 to 0.7]; p = 0.02); however, at 3 weeks, the VAS pain scores showed clinically important difference among groups (3.6 ± 1.4 versus 2.9 ± 1.2, mean difference 0.7 [95% CI 0.3 to 1.1]; p = 0.001). At 3 months, the ultrasound-guided postoperative injection group had higher MHQ-ADL scores (intraoperative 62 ± 10 versus postoperative 75 ± 10, mean difference 13 [95% CI 11 to 17]; p < 0.001), and the mean difference of MHQ-ADL scores reached the MCID value at all time points. At 3 months, there was no clinically important difference in MHQ-SAT scores between groups (intraoperative 62 ± 8 versus postoperative 70 ± 8, mean difference 8 [95% CI 6 to 11]; p < 0.001).

CONCLUSION

Compared with intraoperative CMC hydrogel injection, postoperative ultrasound-guided injection improved the TAM and function of the affected limb, showed a short-term pain control effect, and did not increase the risk of complications. Clinical trials are needed to confirm the safety and efficacy of ultrasound-guided postoperative injection of CMC hydrogels and to determine the most effective dose and the health and economic benefits of treatment.

LEVEL OF EVIDENCE

Level I, therapeutic study.

Myeloid Cells and Sensory Nerves Mediate Peritendinous Adhesion Formation via Prostaglandin E2

Peritendinous adhesion that forms after tendon injury substantially limits daily life. The pathology of adhesion involves inflammation and the associated proliferation. However, the current studies on this condition are lacking, previous studies reveal that cyclooxygenase-2 (COX2) gene inhibitors have anti-adhesion effects through reducing prostaglandin E2 (PGE2) and the proliferation of fibroblasts, are contrary to the failure in anti-adhesion through deletion of EP4 (prostaglandin E receptor 4) gene in fibroblasts in mice of another study. In this study, single-cell RNA sequencing analysis of human and mouse specimens are combined with eight types of conditional knockout mice and further reveal that deletion of COX2 in myeloid cells and deletion of EP4 gene in sensory nerves decrease adhesion and impair the biomechanical properties of repaired tendons. Furthermore, the COX2 inhibitor parecoxib reduces PGE2 but impairs the biomechanical properties of repaired tendons. Interestingly, PGE2 local treatment improves the biomechanical properties of the repaired tendons. These findings clarify the complex role of PGE2 in peritendinous adhesion formation (PAF) and tendon repair.

Nanofiber Hydrogel Drug Delivery System for Prevention of Postsurgical Intestinal Adhesion

Intestinal adhesion is one of the complications that occurs more frequently after abdominal surgery. Postsurgical intestinal adhesion (PIA) can lead to a series of health problems, including abdominal pain, intestinal obstruction, and female infertility. Currently, hydrogels and nanofibrous films as barriers are often used for preventing PIA formation; however, these kinds of materials have their intrinsic disadvantages. Herein, we developed a dual-structure drug delivery patch consisting of poly lactic-co-glycolic acid (PLGA) nanofibers and a chitosan hydrogel (NHP). PLGA nanofibers loaded with deferoxamine mesylate (DFO) were incorporated into the hydrogel; meanwhile, the hydrogel was loaded with anti-inflammatory drug dexamethasone (DXMS). The rapid degradation of the hydrogel facilitated the release of DXMS at the acute inflammatory stage of the early injury and provided effective anti-inflammatory effects for wound sites. Moreover, PLGA composite nanofibers could provide sustained and stable release of DFO for promoting the peritoneal repair by the angiogenesis effects of DFO. The in vivo results indicated that NHP can effectively prevent PIA formation by restraining inflammation and vascularization, promoting peritoneal repair. Therefore, we believe that our NHP has a great potential application in inhibition of PIA.

Multi-omics analysis of human tendon adhesion reveals that ACKR1-regulated macrophage migration is involved in regeneration

Tendon adhesion is a common complication after tendon injury with the development of accumulated fibrotic tissues without effective anti-fibrotic therapies, resulting in severe disability. Macrophages are widely recognized as a fibrotic trigger during peritendinous adhesion formation. However, different clusters of macrophages have various functions and receive multiple regulation, which are both still unknown. In our current study, multi-omics analysis including single-cell RNA sequencing and proteomics was performed on both human and mouse tendon adhesion tissue at different stages after tendon injury. The transcriptomes of over 74 000 human single cells were profiled. As results, we found that SPP1+ macrophages, RGCC+ endothelial cells, ACKR1+ endothelial cells and ADAM12+ fibroblasts participated in tendon adhesion formation. Interestingly, despite specific fibrotic clusters in tendon adhesion, FOLR2+ macrophages were identified as an antifibrotic cluster by in vitro experiments using human cells. Furthermore, ACKR1 was verified to regulate FOLR2+ macrophages migration at the injured peritendinous site by transplantation of bone marrow from Lysm-Cre;R26RtdTomato mice to lethally irradiated Ackr1-/- mice (Ackr1-/- chimeras; deficient in ACKR1) and control mice (WT chimeras). Compared with WT chimeras, the decline of FOLR2+ macrophages was also observed, indicating that ACKR1 was specifically involved in FOLR2+ macrophages migration. Taken together, our study not only characterized the fibrosis microenvironment landscape of tendon adhesion by multi-omics analysis, but also uncovered a novel antifibrotic cluster of macrophages and their origin. These results provide potential therapeutic targets against human tendon adhesion.

Diamond-Like Carbon Depositing on the Surface of Polylactide Membrane for Prevention of Adhesion Formation During Tendon Repair

Post-traumatic peritendinous adhesion presents a significant challenge in clinical medicine. This study proposes the use of diamond-like carbon (DLC) deposited on polylactic acid (PLA) membranes as a biophysical mechanism for anti-adhesion barrier to encase ruptured tendons in tendon-injured rats. The results indicate that PLA/DLC composite membrane exhibits more efficient anti-adhesion effect than PLA membrane, with histological score decreasing from 3.12 ± 0.27 to 2.20 ± 0.22 and anti-adhesion effectiveness increasing from 21.61% to 44.72%. Mechanistically, the abundant C=O bond functional groups on the surface of DLC can reduce reactive oxygen species level effectively; thus, the phosphorylation of NF-κB and M1 polarization of macrophages are inhibited. Consequently, excessive inflammatory response augmented by M1 macrophage-originated cytokines including interleukin-6 (IL-6), interleukin-1β (IL-1β), and tumor necrosis factor-α (TNF-α) is largely reduced. For biocompatibility evaluation, PLA/DLC membrane is slowly absorbed within tissue and displays prolonged barrier effects compared to traditional PLA membranes. Further studies show the DLC depositing decelerates the release of degradation product lactic acid and its induction of macrophage M2 polarization by interfering esterase and PLA ester bonds, which further delays the fibrosis process. It was found that the PLA/DLC membrane possess an efficient biophysical mechanism for treatment of peritendinous adhesion.

TGF-β signaling in health, disease, and therapeutics

Transforming growth factor (TGF)-β is a multifunctional cytokine expressed by almost every tissue and cell type. The signal transduction of TGF-β can stimulate diverse cellular responses and is particularly critical to embryonic development, wound healing, tissue homeostasis, and immune homeostasis in health. The dysfunction of TGF-β can play key roles in many diseases, and numerous targeted therapies have been developed to rectify its pathogenic activity. In the past decades, a large number of studies on TGF-β signaling have been carried out, covering a broad spectrum of topics in health, disease, and therapeutics. Thus, a comprehensive overview of TGF-β signaling is required for a general picture of the studies in this field. In this review, we retrace the research history of TGF-β and introduce the molecular mechanisms regarding its biosynthesis, activation, and signal transduction. We also provide deep insights into the functions of TGF-β signaling in physiological conditions as well as in pathological processes. TGF-β-targeting therapies which have brought fresh hope to the treatment of relevant diseases are highlighted. Through the summary of previous knowledge and recent updates, this review aims to provide a systematic understanding of TGF-β signaling and to attract more attention and interest to this research area.

The role of macrophage polarization in tendon healing and therapeutic strategies: Insights from animal models

Tendon injuries, a common musculoskeletal issue, usually result in adhesions to the surrounding tissue, that will impact functional recovery. Macrophages, particularly through their M1 and M2 polarizations, play a pivotal role in the inflammatory and healing phases of tendon repair. In this review, we explore the role of macrophage polarization in tendon healing, focusing on insights from animal models. The review delves into the complex interplay of macrophages in tendon pathology, detailing how various macrophage phenotypes contribute to both healing and adhesion formation. It also explores the potential of modulating macrophage activity to enhance tendon repair and minimize adhesions. With advancements in understanding macrophage behavior and the development of innovative biomaterials, this review highlights promising therapeutic strategies for tendon injuries.