Blebbistatin-Loaded Poly(d,l-lactide-co-glycolide) Particles For Treating Arthrofibrosis

Force-Bioreactor for Assessing Pharmacological Therapies for Mechanobiological Targets

Tissue fibrosis is a major health issue that impacts millions of people and is costly to treat. However, few effective anti-fibrotic treatments are available. Due to their central role in fibrotic tissue deposition, fibroblasts and myofibroblasts are the target of many therapeutic strategies centered primarily on either inducing apoptosis or blocking mechanical or biochemical stimulation that leads to excessive collagen production. Part of the development of these drugs for clinical use involves in vitro prescreening. 2D screens, however, are not ideal for discovering mechanobiologically significant compounds that impact functions like force generation and other cell activities related to tissue remodeling that are highly dependent on the conditions of the microenvironment. Thus, higher fidelity models are needed to better simulate in vivo conditions and relate drug activity to quantifiable functional outcomes. To provide guidance on effective drug dosing strategies for mechanoresponsive drugs, we describe a custom force-bioreactor that uses a fibroblast-seeded fibrin gels as a relatively simple mimic of the provisional matrix of a healing wound. As cells generate traction forces, the volume of the gel reduces, and a calibrated and embedded Nitinol wire deflects in proportion to the generated forces over the course of 6 days while overhead images of the gel are acquired hourly. This system is a useful in vitro tool for quantifying myofibroblast dose-dependent responses to candidate biomolecules, such as blebbistatin. Administration of 50 μM blebbistatin reliably reduced fibroblast force generation approximately 40% and lasted at least 40 h, which in turn resulted in qualitatively less collagen production as determined via fluorescent labeling of collagen.

The Prognosis of Arthrofibroses: Prevalence, Clinical Shortcomings, and Future Prospects

Fibrosis is the dysregulated biosynthesis of connective tissue that results from persistent infection, high serum cholesterol, surgery, trauma, or prolonged joint immobilization. As a disease that impacts connective tissue, it is prevalent across the body and disrupts normal extracellular and tissue organization. Ultimately, fibrosis impairs the tissue structural, mechanical, or biochemical function. This review describes the clinical landscape of joint fibrosis, that is, arthrofibrosis, including the risk factors and causes, as well as current clinical treatments and their shortcomings. Because treating arthrofibrosis remains an unmet clinical challenge, we present several animal models used for exploration of the physiopathology of arthrofibrosis and summarize their use for testing novel treatments. We then discuss therapeutics for the prevention or treatment of arthrofibrosis that are in preclinical development and in ongoing clinical trials. We conclude with recent findings from molecular biological studies of arthrofibroses that shed insight on future areas of research for improved treatments.

Human Adipocyte Conditioned Medium Promotes In Vitro Fibroblast Conversion to Myofibroblasts

Adipocytes and adipose tissue derived cells have been investigated for their potential to contribute to the wound healing process. However, the details of how these cells interact with other essential cell types, such as myofibroblasts/fibroblasts, remain unclear. Using a novel in-vitro 3D human adipocyte/pre-adipocyte spheroid model, we investigated whether adipocytes and their precursors (pre-adipocytes) secrete factors that affect human dermal fibroblast behavior. We found that both adipocyte and pre-adipocyte conditioned medium induced the migration of fibroblasts, but only adipocyte conditioned medium induced fibroblast differentiation into a highly contractile, collagen producing myofibroblast phenotype. Furthermore, adipocyte mediated myofibroblast induction occurred through a TGF-β independent mechanism. Our findings contribute to a better understanding on the involvement of adipose tissue in wound healing, and may help to uncover and develop fat-related wound healing treatments.

Targeting Cell Contractile Forces: A Novel Minimally Invasive Treatment Strategy for Fibrosis

Fibrosis is a complication of tendon injury where excessive scar tissue accumulates in and around the injured tissue, leading to painful and restricted joint motion. Unfortunately, fibrosis tends to recur after surgery, creating a need for alternative approaches to disrupt scar tissue. We posited a strategy founded on mechanobiological principles that collagen under tension generated by fibroblasts is resistant to degradation by collagenases. In this study, we tested the hypothesis that blebbistatin, a drug that inhibits cellular contractile forces, would increase the susceptibility of scar tissue to collagenase degradation. Decellularized tendon scaffolds (DTS) were treated with bacterial collagenase with or without external or cell-mediated internal tension. External tension producing strains of 2-4% significantly reduced collagen degradation compared with non-tensioned controls. Internal tension exerted by human fibroblasts seeded on DTS significantly reduced the area of the scaffolds compared to acellular controls and inhibited collagen degradation compared to free-floating DTS. Treatment of cell-seeded DTS with 50 mM blebbistatin restored susceptibility to collagenase degradation, which was significantly greater than in untreated controls (p < 0.01). These findings suggest that therapies combining collagenases with drugs that reduce cell force generation should be considered in cases of tendon fibrosis that do not respond to physiotherapy.

Sulfasalazine Resolves Joint Stiffness in a Rabbit Model of Arthrofibrosis

Joint stiffness due to fibrosis/capsule contracture is a seriously disabling complication of articular injury that surgical interventions often fail to completely resolve. Fibrosis/contracture is associated with the abnormal persistence of myofibroblasts, which over-produce and contract collagen matrices. We hypothesized that intra-articular therapy with drugs targeting myofibroblast survival (sulfasalazine), or collagen production (β-aminopropionitrile and cis-hydroxyproline), would reduce joint stiffness in a rabbit model of fibrosis/contracture. Drugs were encapsulated in poly[lactic-co-glycolic] acid pellets and implanted in joints after fibrosis/contracture induction. Capsule α-smooth muscle actin (α-SMA) expression and intimal thickness were evaluated by immunohistochemistry and histomorphometry, respectively. Joint stiffness was quantified by flexion-extension testing. Drawer tests were employed to determine if the drugs induced cruciate ligament laxity. Joint capsule fibroblasts were tested in vitro for contractile activity and α-SMA expression. Stiffness in immobilized joints treated with blank pellets (control) was significantly higher than in non-immobilized, untreated joints (normal) (p = 0.0008), and higher than in immobilized joints treated with sulfasalazine (p = 0.0065). None of the drugs caused significant cruciate ligament laxity. Intimal thickness was significantly lower than control in the normal and sulfasalazine-treated groups (p = 0.010 and 0.025, respectively). Contractile activity in the cells from controls was significantly increased versus normal (p = 0.001). Sulfasalazine and β-aminopropionitrile significantly inhibited this effect (p = 0.005 and 0.0006, respectively). α-SMA expression was significantly higher in control versus normal (p = 0.0021) and versus sulfasalazine (p = 0.0007). These findings support the conclusion that sulfasalazine reduced stiffness by clearing myofibroblasts from fibrotic joints. Statement of clinical significance: The results provide proof-of-concept that established joint stiffness can be resolved non-surgically. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:629-638, 2020.

Sustained Release of Hydrogen Sulfide (H2S) from Poly(Lactic Acid) Functionalized 4-Hydroxythiobenzamide Microparticles to Protect Against Oxidative Damage

Hydrogen sulfide (H2S) has emerged as a gaseous mediator capable of exhibiting many beneficial properties including cytoprotection, anti-inflammation, and vasodilation. The study presented here provides characterization of a poly(lactic acid) polymer with a functionalized 4-hydroxythiobenzamide (PLA-4HTB) capable of extended H2S release. The polymer was used to fabricate microparticles that can be potentially loaded with a drug allowing for co-release of the drug and H2S. Microparticles with the average diameter of 500 ± 207 nm were fabricated and shown to release 77.0 ± 1.76 µM of H2S over 4 weeks (release of H2S from 1 mg of particles). To test for the antioxidant properties of the PLA-4HTB microparticles, human embryonic kidney 293 cells were first incubated with PLA-4HTB microparticles and then oxidative stress was induced using CoCl2. Particle suspensions of 1 mg/mL were shown to protect cells resulting in reactive oxygen species (ROS) levels of superoxide that were similar to that of the control group. The microparticles fabricated from the PLA-4HTB released H2S over a sustained period of weeks to months, while providing protection from ROS. The microparticles described in this article represent a new platform technology that could be used to prevent and treat diseases caused by oxidative damage.

Targeting Myosin by Blebbistatin Derivatives: Optimization and Pharmacological Potential

Blebbistatin is a widely used inhibitor of myosin 2 that enables the study of a broad range of cytoskeleton-related processes. However, blebbistatin has several limitations hindering its applicability: it is fluorescent, poorly water soluble, cytotoxic, and prone to (photo)degradation. Despite these adverse effects, being the only available myosin 2-specific inhibitor, blebbistatin is rather a choice of necessity. Blebbistatin has been modified to improve its properties and some of the new compounds have proven to be useful replacements of the original molecule. This review summarizes recent results on blebbistatin development. We also discuss the pharmacological perspectives of these efforts, as myosins are becoming promising drug target candidates for a variety of conditions ranging from neurodegeneration to muscle disease, wound healing, and cancer metastasis.

Medicinal Chemistry and Use of Myosin II Inhibitor ( S)-Blebbistatin and Its Derivatives

( S)-Blebbistatin, a chiral tetrahydropyrroloquinolinone, is a widely used and well-characterized ATPase inhibitor selective for myosin II. The central role of myosin II in many normal and pathological biological processes has been revealed with the aid of this small molecule. The first part of this manuscript provides a summary of myosin II and ( S)-blebbistatin literature from a medicinal chemist's perspective. The second part of this perspective deals with the physicochemical deficiencies that trouble the use of ( S)-blebbistatin in advanced biological settings: low potency and solubility, fluorescence interference, (photo)toxicity, and stability issues. A large toolbox of analogues has been developed in which particular shortcomings have been addressed. This perspective provides a necessary overview of these developments and presents guidelines for selecting the best available analogue for a given application. As the unmet need for high-potency analogues remains, we also propose starting points for medicinal chemists in search of nanomolar myosin II inhibitors.