Stuart M. Roche

Inhibition of 5-LOX, COX-1, and COX-2 Increases Tendon Healing and Reduces Muscle Fibrosis and Lipid Accumulation After Rotator Cuff Repair

Background: The repair and restoration of function after chronic rotator cuff tears are often complicated by muscle atrophy, fibrosis, and fatty degeneration of the diseased muscle. The inflammatory response has been implicated in the development of fatty degeneration after cuff injuries. Licofelone is a novel anti-inflammatory drug that inhibits 5-lipoxygenase (5-LOX), as well as cyclooxygenase (COX)–1 and COX-2 enzymes, which play important roles in inducing inflammation after injuries. While previous studies have demonstrated that nonsteroidal anti-inflammatory drugs and selective inhibitors of COX-2 (coxibs) may prevent the proper healing of muscles and tendons, studies about bone and cartilage have demonstrated that drugs that inhibit 5-LOX concurrently with COX-1 and COX-2 may enhance tissue regeneration. Hypothesis: After the repair of a chronic rotator cuff tear in rats, licofelone would increase the load to failure of repaired tendons and increase the force production of muscle fibers. Study Design: Controlled laboratory study. Methods: Rats underwent supraspinatus release followed by repair 28 days later. After repair, rats began a treatment regimen of either licofelone or a vehicle for 14 days, at which time animals were euthanized. Supraspinatus muscles and tendons were then subjected to contractile, mechanical, histological, and biochemical analyses. Results: Compared with controls, licofelone-treated rats had a grossly apparent decrease in inflammation and increased fibrocartilage formation at the enthesis, along with a 62% increase in the maximum load to failure and a 51% increase in peak stress to failure. Licofelone resulted in a marked reduction in fibrosis and lipid content in supraspinatus muscles as well as reduced expression of several genes involved in fatty infiltration. Despite the decline in fibrosis and fat accumulation, muscle fiber specific force production was reduced by 23%. Conclusion: The postoperative treatment of cuff repair with licofelone may reduce fatty degeneration and enhance the development of a stable bone-tendon interface, although decreases in muscle fiber specific force production were observed, and force production in fact declined. Clinical Relevance: This study demonstrates that the inhibition of 5-LOX, COX-1, and COX-2 modulates the healing process of repaired rotator cuff tendons. Although further studies are necessary, the treatment of patients with licofelone after cuff repair may improve the development of a stable enthesis and enhance postoperative outcomes.

Reduced muscle fiber force production and disrupted myofibril architecture in patients with chronic rotator cuff tears

BACKGROUND A persistent atrophy of muscle fibers and an accumulation of fat, collectively referred to as fatty degeneration, commonly occur in patients with chronic rotator cuff tears. The etiology of fatty degeneration and function of the residual rotator cuff musculature have not been well characterized in humans. We hypothesized that muscles from patients with chronic rotator cuff tears have reduced muscle fiber force production, disordered myofibrils, and an accumulation of fat vacuoles. METHODS The contractility of muscle fibers from biopsy specimens of supraspinatus muscles of 13 patients with chronic full-thickness posterosuperior rotator cuff tears was measured and compared with data from healthy vastus lateralis muscle fibers. Correlations between muscle fiber contractility, American Shoulder and Elbow Surgeons (ASES) scores, and tear size were analyzed. Histology and electron microscopy were also performed. RESULTS Torn supraspinatus muscles had a 30% reduction in maximum isometric force production and a 29% reduction in normalized force compared with controls. Normalized supraspinatus fiber force positively correlated with ASES score and negatively correlated with tear size. Disordered sarcomeres were noted, along with an accumulation of lipid-laden macrophages in the extracellular matrix surrounding supraspinatus muscle fibers. CONCLUSIONS Patients with chronic supraspinatus tears have significant reductions in muscle fiber force production. Force production also correlates with ASES scores and tear size. The structural and functional muscle dysfunction of the residual muscle fibers is independent of the additional area taken up by fibrotic tissue. This work may help establish future therapies to restore muscle function after the repair of chronically torn rotator cuff muscles.

Changes in skeletal muscle and tendon structure and function following genetic inactivation of myostatin in rats

Myostatin is an important regulator of muscle mass and a potential therapeutic target for the treatment of diseases and injuries that result in muscle atrophy. Targeted genetic mutations of myostatin have been generated in mice, and spontaneous loss‐of‐function mutations have been reported in several species. The impact of myostatin deficiency on the structure and function of muscles has been well described for mice, but not for other species. We report the creation of a genetic model of myostatin deficiency in rats using zinc finger nuclease technology. The main findings of the study are that genetic inactivation of myostatin in rats results in increases in muscle mass without a deleterious impact on the specific force production and tendon mechanical properties. The increases in mass occur through a combination of fibre hypertrophy, hyperplasia and activation of the insulin‐like growth factor‐1 pathway, with no substantial changes in atrophy‐related pathways. This large rodent model has enabled us to identify that the chronic loss of myostatin is void of the negative consequences to muscle fibres and extracellular matrix observed in mouse models. Furthermore, the greatest impact of myostatin in the regulation of muscle mass may not be to induce atrophy directly, but rather to block hypertrophy signalling.

T lymphocytes are not required for the development of fatty degeneration after rotator cuff tear

Objectives Rotator cuff tears are among the most common and debilitating upper extremity injuries. Chronic cuff tears result in atrophy and an infiltration of fat into the muscle, a condition commonly referred to as ‘fatty degeneration’. While stem cell therapies hold promise for the treatment of cuff tears, a suitable immunodeficient animal model that could be used to study human or other xenograft-based therapies for the treatment of rotator cuff injuries had not previously been identified. Methods A full-thickness, massive supraspinatus and infraspinatus tear was induced in adult T-cell deficient rats. We hypothesised that, compared with controls, 28 days after inducing a tear we would observe a decrease in muscle force production, an accumulation of type IIB fibres, and an upregulation in the expression of genes involved with muscle atrophy, fibrosis and inflammation. Results Chronic cuff tears in nude rats resulted in a 30% to 40% decrease in muscle mass, a 23% reduction in production of muscle force, and an induction of genes that regulate atrophy, fibrosis, lipid accumulation, inflammation and macrophage recruitment. Marked large lipid droplet accumulation was also present. Conclusions The extent of degenerative changes in nude rats was similar to what was observed in T-cell competent rats. T cells may not play an important role in regulating muscle degeneration following chronic muscle unloading. The general similarities between nude and T-cell competent rats suggest the nude rat is likely an appropriate preclinical model for the study of xenografts that have the potential to enhance the treatment of chronically torn rotator cuff muscles. Cite this article: Bone Joint Res 2014;3:262–72.

Measurement of Maximum Isometric Force Generated by Permeabilized Skeletal Muscle Fibers.

Analysis of the contractile properties of chemically skinned, or permeabilized, skeletal muscle fibers offers a powerful means by which to assess muscle function at the level of the single muscle cell. Single muscle fiber studies are useful in both basic science and clinical studies. For basic studies, single muscle fiber contractility measurements allow investigation of fundamental mechanisms of force production, and analysis of muscle function in the context of genetic manipulations. Clinically, single muscle fiber studies provide useful insight into the impact of injury and disease on muscle function, and may be used to guide the understanding of muscular pathologies. In this video article we outline the steps required to prepare and isolate an individual skeletal muscle fiber segment, attach it to force-measuring apparatus, activate it to produce maximum isometric force, and estimate its cross-sectional area for the purpose of normalizing the force produced.

Assessment of the Contractile Properties of Permeabilized Skeletal Muscle Fibers.

Permeabilized individual skeletal muscle fibers offer the opportunity to evaluate contractile behavior in a system that is greatly simplified, yet physiologically relevant. Here we describe the steps required to prepare, permeabilize and preserve small samples of skeletal muscle. We then detail the procedures used to isolate individual fiber segments and attach them to an experimental apparatus for the purpose of controlling activation and measuring force generation. We also describe our technique for estimating the cross-sectional area of fiber segments. The area measurement is necessary for normalizing the absolute force to obtain specific force, a measure of the intrinsic force-generating capability of the contractile system.