Presence of a non-neuronal cholinergic system and occurrence of up- and down-regulation in expression of M2 muscarinic acetylcholine receptors: new aspects of importance regarding Achilles tendon tendinosis (tendinopathy)

Substance P, A Promising Therapeutic Target in Musculoskeletal Disorders

A large number of studies have focused on the role of substance P (SP) and the neurokinin-1 receptor (NK1R) in the pathogenesis of a variety of medical conditions. This review provides an overview of the role of the SP-NK1R pathway in the pathogenesis of musculoskeletal disorders and the evidence for its role as a therapeutic target for these disorders, which are major public health problems in most countries. To summarize, the brief involvement of SP may affect tendon healing in an acute injury setting. SP combined with an adequate conjugate can be a regenerative therapeutic option in osteoarthritis. The NK1R antagonist is a promising agent for tendinopathy, rheumatoid arthritis, and osteoarthritis. Research on the SP-NK1R pathway will be helpful for developing novel drugs for osteoporosis.

Effects of Cross-Education After 6 Weeks of Eccentric Single-Leg Decline Squats Performed With Different Execution Times: A Randomized Controlled Trial

BACKGROUND

Cross-education of strength refers to the strength gain that is transferred to the contralateral limb after a unilateral training program.

HYPOTHESIS

Unilateral eccentric training using different muscle contraction times would improve the structural and functional properties of the untrained contralateral limb.

STUDY DESIGN

Randomized controlled trial.

LEVEL OF EVIDENCE

Level 2.

METHODS

Thirty-six participants were randomized into a control group, experimental group 1 (EG6s; eccentric contraction runtime = 6 seconds) and experimental group 2 (EG3s; eccentric contraction runtime = 3 seconds). The thickness and elastographic index of the patellar tendon (PT), lean mass and fat percentage of the thigh, contractile properties of the vastus lateralis (VL), as well as isometric, concentric, and eccentric knee extensor peak torques, and eccentric single-leg decline squat (SLDS_e) 1 repetition maximum (1-RM) were measured after 6 weeks of SLDS_e training (3 times per week, 80% of 1-RM) and after 6 weeks of detraining in the untrained contralateral limb.

RESULTS

After training, there was an increase in lean thigh mass of the untrained limb in both groups: EG6s (0.17 ± 0.29 kg;P = 0.03; effect size [ES] = 0.15) and EG3s (0.15 ± 0.23 kg; P = 0.04; ES = 0.19). Likewise, both EG6s (62.30 ± 19.09 kg; P < 0.001; ES = 4.23) and EG3s (68.09 ± 27.49 kg; P < 0.001; ES = 3.40) increased their 1-RM, isometric (EG6s: 48.64 ± 44.82 N·m, P < 0.001, ES = 0.63; EG3s: 34.81 ± 47.30 N·m, P = 0.004, ES = 0.38), concentric at 60 deg/s and 180 deg/s and eccentric at 60 deg/s and 180 deg/s knee extensor peak torques (P < 0.05) in the untrained limb. However, no differences were found in the contractile properties of the VL or in the thickness of the PT after eccentric training in either of the 2 experimental groups.

CONCLUSION

Regardless of the runtime of the contraction, 6 weeks of SLSD_e was effective for inducing structural and strength adaptations in the contralateral untrained limb. However, most of these adaptations were lost after 6 weeks of detraining.

CLINICAL RELEVANCE

Our study suggests that cross-education training can be of great importance for clinical application and musculoskeletal and neuromuscular rehabilitative processes after unilateral injury.

The Enhancement Effect of Acetylcholine and Pyridostigmine on Bone-Tendon Interface Healing in a Murine Rotator Cuff Model

BACKGROUND

How to improve rotator cuff healing remains a challenge. Little is known about the effect of the parasympathetic transmitter acetylcholine (ACh) and the acetylcholinesterase inhibitor pyridostigmine (PYR), both of which have anti-inflammatory properties, in the healing process of rotator cuff injury.

HYPOTHESIS

ACh and PYR could enhance bone-tendon interface healing in a murine model of rotator cuff repair.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 160 C57BL/6 mice underwent unilateral rotator cuff repair surgery. Fibrin gel (FG) was used as a drug carrier. The mice were randomly assigned to 4 groups with 40 mice per group: FG group (received FG alone), 10^-5 M ACh group (received FG containing 10^-5 M ACh), 10^-6 M ACh group (received FG containing 10^-6 M ACh), and PYR group (received FG containing 25 µg of PYR). Ten mice in each group were euthanized at 2, 4, 8, and 12 weeks postoperatively. Histologic, immunohistochemical, and biomechanical evaluations were performed for analysis.

RESULTS

Histologically, fibrocartilage-like tissue was shown at the repaired site. The proteoglycan content of the 10^-5 M ACh group was significantly increased compared with the FG group at 4 weeks. M2 macrophages were identified at the repaired site for all groups at 2 and 4 weeks. At 8 weeks, M2 macrophages withdrew back to the tendon in the FG group, but a number of M2 macrophages were retained at the repaired sites in the ACh and PYR groups. Biomechanically, failure load and stiffness of the ACh and PYR groups were significantly higher than those of the FG group at 4 weeks. The stiffness of the ACh and PYR groups was significantly increased compared with the FG group at 8 weeks (P < .001 for all). At 12 weeks, most of the healing properties of the ACh and PYR groups were not significantly different compared with the FG group.

CONCLUSION

ACh and PYR enhanced the early stage of bone-tendon insertion healing after rotator cuff repair.

CLINICAL RELEVANCE

These findings imply that ACh and PYR could serve as potential therapeutic strategies for rotator cuff healing.

The Cholinergic System Contributes to the Immunopathological Progression of Experimental Pulmonary Tuberculosis

The cholinergic system is present in both bacteria and mammals and regulates inflammation during bacterial respiratory infections through neuronal and non-neuronal production of acetylcholine (ACh) and its receptors. However, the presence of this system during the immunopathogenesis of pulmonary tuberculosis (TB) in vivo and in its causative agent Mycobacterium tuberculosis (Mtb) has not been studied. Therefore, we used an experimental model of progressive pulmonary TB in BALB/c mice to quantify pulmonary ACh using high-performance liquid chromatography during the course of the disease. In addition, we performed immunohistochemistry in lung tissue to determine the cellular expression of cholinergic system components, and then administered nicotinic receptor (nAChR) antagonists to validate their effect on lung bacterial burden, inflammation, and pro-inflammatory cytokines. Finally, we subjected Mtb cultures to colorimetric analysis to reveal the production of ACh and the effect of ACh and nAChR antagonists on Mtb growth. Our results show high concentrations of ACh and expression of its synthesizing enzyme choline acetyltransferase (ChAT) during early infection in lung epithelial cells and macrophages. During late progressive TB, lung ACh upregulation was even higher and coincided with ChAT and α7 nAChR subunit expression in immune cells. Moreover, the administration of nAChR antagonists increased pro-inflammatory cytokines, reduced bacillary loads and synergized with antibiotic therapy in multidrug resistant TB. Finally, in vitro studies revealed that the bacteria is capable of producing nanomolar concentrations of ACh in liquid culture. In addition, the administration of ACh and nicotinic antagonists to Mtb cultures induced or inhibited bacterial proliferation, respectively. These results suggest that Mtb possesses a cholinergic system and upregulates the lung non-neuronal cholinergic system, particularly during late progressive TB. The upregulation of the cholinergic system during infection could aid both bacterial growth and immunomodulation within the lung to favor disease progression. Furthermore, the therapeutic efficacy of modulating this system suggests that it could be a target for treating the disease.

Downregulation of type I collagen expression in the Achilles tendon by dexamethasone: a controlled laboratory study

Background

Spontaneous Achilles tendon rupture associated with long-term dexamethasone (Dex) use has been reported. However, few studies have investigated the potential mechanism. The aim of this study was to evaluate the effects of oral Dex on type I collagen in humans and rats and its association with tendon rupture.

Methods

First, six Achilles tendons from patients who received long-term Dex treatment, and another six normal tendons were harvested for histological evaluation. Secondly, 8-week-old rats (n = 72) were randomly assigned to a Dex group or a control group. Type I collagen was studied at the mechanical, histological, and molecular levels after 3 and 5 weeks. Tenocytes isolated from normal human and rat tendon were used to investigate the effect of Dex on cellular scale.

Results

Histological analysis of human and rat tendon tissue revealed an irregular, disordered arrangement of type I collagen in the Dex group compared with the control group. In addition, In the Dex+ group, type I collagen expression decreased in comparison with the Dex− group in both human and rat tenocytes. The mechanical strength of tendons was significantly reduced in the Dex group (68.87 ± 11.07 N) in comparison with the control group (81.46 ± 7.62 N, P = 0.013) after 5 weeks. Tendons in the Dex group were shorter with smaller cross-sectional areas (10.71 ± 0.34 mm², 1.44 ± 0.22 mm², respectively) after 5 weeks than those in the control group (11.13 ± 0.50 mm², P = 0.050, 2.74 ± 0.34 mm², P < 0.001, respectively).

Conclusions

This finding suggests long-term use of Dex that decreases the expression of type I collagen at molecular and tissue levels both in human and rat Achilles tendons. Furthermore, Dex decreases the mechanical strength of the tendon, thereby increasing the risk of Achilles tendon rupture.

A Combination of Oxo-M and 4-PPBP as a potential regenerative therapeutics for tendon injury

Tendons injuries frequently result in scar-like tissue with poor biochemical structure and mechanical properties. We have recently reported that CD146+ perivascular originated tendon stem/progenitor cells (TSCs), playing critical roles in tendon healing. Here, we identified highly efficient small molecules that selectively activate endogenous TSCs for tendon regeneration. Methods: From a pool of ERK1/2 and FAK agonists, Oxo-M and 4-PPBP were identified, and their roles in tenogenic differentiation of TSCs and in vivo tendon healing were investigated. Controlled delivery of Oxo-M and 4-PPBP was applied via PLGA µS. Signaling studies were conducted to determine the mechanism for specificity of Oxo-M and 4-PPBP to CD146+ TSCs. Results: A combination of Oxo-M and 4-PPBP synergistically increased the expressions of tendon-related gene markers in TSCs. In vivo, delivery of Oxo-M and 4-PPBP significantly enhanced healing of fully transected rat patellar tendons (PT), with functional restoration and reorganization of collagen fibrous structure. Our signaling study suggested that Oxo-M and 4-PPBP specifically targets CD146+ TSCs via non-neuronal muscarinic acetylcholine receptors (AChR) and σ1 receptor (σ1) signaling. Principal conclusions: Our findings demonstrate a significant potential of Oxo-M and 4-PPBP as a regenerative therapeutics for tendon injuries.

Prevalence of Coexistent Plantaris Tendon Pathology in Patients with Mid-Portion Achilles Pathology: A Retrospective MRI Study

Co-existence of Plantaris tendinopathy (PT) in patients with mid-Achilles tendinopathy (Mid-AT) is of clinical significance. This study aims to describe the MRI-based pathological characteristics of co-existing PT and Mid-AT. One-hundred MRI studies of patients diagnosed with Mid-AT were retrospectively analysed by an experienced musculoskeletal radiologist. Presence or absence of a Plantaris tendon, co-existing PT with Mid-AT, insertional characteristics of Plantaris tendon, and maximum anteroposterior thickness of the tendon in Mid-AT (axial images) were evaluated. When PT co-existed with Mid-AT, the location of the tendon pathologies in relation to calcaneal insertion was assessed (sagittal images) and their association was analysed using the coefficient of variation (CV) and Pearson’s correlation coefficient. Plantaris was present in 84 cases (84%), and Mid-AT and PT co-existed in 10 cases (10%). A greater variability in the location of Plantaris pathology (CV = 42%) than Achilles tendinopathy (CV = 42%) was observed. The correlation coefficient also revealed a low and non-significant association between the location of two pathologies when they exist together (r = +0.06; p = 0.88). Clinical evaluation of Achilles tendon pain needs careful consideration into the possible co-existence of Plantaris pathology. The considerable difference observed in the location of PT and Mid-AT suggest possible isolated pathologies and differentials for Achilles tendon pain.

Current trends in tendinopathy: consensus of the ESSKA basic science committee. Part II: treatment options

The treatment of painful chronic tendinopathy is challenging. Multiple non-invasive and tendon-invasive methods are used. When traditional non-invasive treatments fail, the injections of platelet-rich plasma autologous blood or cortisone have become increasingly favored. However, there is little scientific evidence from human studies supporting injection treatment. As the last resort, intra- or peritendinous open or endoscopic surgery are employed even though these also show varying results. This ESSKA basic science committee current concepts review follows the first part on the biology, biomechanics and anatomy of tendinopathies, to provide a comprehensive overview of the latest treatment options for tendinopathy as reported in the literature.

Tendinopathy: injury, repair, and current exploration

Both acute and chronic tendinopathy result in high morbidity, requiring management that is often lengthy and expensive. However, limited and conflicting scientific evidence surrounding current management options has presented a challenge when trying to identify the best treatment for tendinopathy. As a result of shortcomings of current treatments, response to available therapies is often poor, resulting in frustration in both patients and physicians. Due to a lack of understanding of basic tendon-cell biology, further scientific investigation is needed in the field for the development of biological solutions. Optimization of new delivery systems and therapies that spatially and temporally mimic normal tendon physiology hold promise for clinical application. This review focuses on the clinical importance of tendinopathy, the structure of healthy tendons, tendon injury, and healing, and a discussion of current approaches for treatment that highlight the need for the development of new nonsurgical interventions.

Noninsertional Achilles Tendinopathy Pathologic Background and Clinical Examination

The term tendinopathy includes a series of pathologies, all of which have a combination of pain, swelling, and impaired performance. The terms tendinosis, tendinitis and peritendinitis are all within the main heading of tendinopathy; this terminology provides a more accurate understanding of the condition and highlights the uniformity of clinical findings while distinguishing the individual histopathological findings of each condition. Understanding the clinical features and the underlying histopathology leads to a more accurate clinical diagnosis and subsequent treatment selection. Misuse of the term tendinitis can lead to the underestimation of chronic degenerative nature of many tendinopathies, affecting the treatment selection.

The effects of substance P and acetylcholine on human tenocyte proliferation converge mechanistically via TGF-β1

Previous in vitro studies on human tendon cells (tenocytes) have demonstrated that the exogenous administration of substance P (SP) and acetylcholine (ACh) independently result in tenocyte proliferation, which is a prominent feature of tendinosis. Interestingly, the possible link between SP and ACh has not yet been explored in human tenocytes. Recent studies in other cell types demonstrate that both SP and ACh independently upregulate TGF-β1 expression via their respective receptors, the neurokinin 1 receptor (NK-1R) and muscarinic ACh receptors (mAChRs). Furthermore, TGF-β1 has been shown to downregulate NK-1R expression in human keratocytes. The aim of this study was to examine if TGF-β1 is the intermediary player involved in mediating the proliferative pathway shared by SP and ACh in human tenocytes. The results showed that exogenous administration of SP and ACh both caused significant upregulation of TGF-β1 at the mRNA and protein levels. Exposing cells to TGF-β1 resulted in increased cell viability of tenocytes, which was blocked in the presence of the TGFβRI/II kinase inhibitor. In addition, the proliferative effects of SP and ACh on tenocytes were reduced by the TGFβRI/II kinase inhibitor; this supports the hypothesis that the proliferative effects of these signal substances are mediated via the TGF-β axis. Furthermore, exogenous TGF-β1 downregulated NK-1R and mAChRs expression at both the mRNA and protein levels, and these effects were negated by simultaneous exposure to the TGFβRI/II kinase inhibitor, suggesting a negative feedback loop. In conclusion, the results indicate that TGF-β1 is the intermediary player through which the proliferative actions of both SP and ACh converge mechanistically.

The sympathetic nervous system and tendinopathy: a systematic review

BACKGROUND

Tendinopathy is a clinical diagnosis of localised tendon pain often confirmed by imaging findings. The pathophysiological cause of the pain is unknown and the sympathetic nervous system (SNS) may be implicated.

OBJECTIVE

To review what is known regarding the role of the SNS in human tendinopathy.

STUDY SELECTION

Published data describing sympathetic innervation or an index of sympathetic activity in human tendons were eligible for inclusion.

DATA SOURCES

Bibliographical databases (AMED, Biological Abstracts, CINAHL Plus, EMBASE, MEDLINE, Scopus, SPORTDiscus and Web of Science) were searched for relevant articles. Reference lists from included articles were screened for additional articles.

STUDY APPRAISAL

Studies were scored with a quality assessment tool to identify potential sources of bias. Each question had an explicit decision rule to guide assessment.

RESULTS

Nine case-control and four cross-sectional studies examined sympathetic innervation of tendons. There was evidence suggesting a lack of difference in sympathetic innervation of tendon proper between tendinopathy biopsies and healthy controls. In contrast, the paratendinous tissue showed evidence of increased sympathetic innervation in painful tendons. The most notable increase in SNS markers was seen in abnormal tenocytes from painful tendons. Data from two studies were suitable for meta-analysis. These heterogeneous studies revealed no difference in sympathetic innervation between painful and pain-free tendons. No studies recorded SNS activity in vivo.

CONCLUSION

Sympathetic innervation in painful tendons depends on tissue type. Abnormal tenocytes may have increased capacity for self-production of sympathetic neurotransmitters. Future insight may be gained by measuring global in vivo sympathetic drive in tendinopathy.

Further proof of the existence of a non-neuronal cholinergic system in the human Achilles tendon: Presence of the AChRα7 receptor in tendon cells and cells in the peritendinous tissue

Human tendon cells have the capacity for acetylcholine (ACh) production. It is not known if the tendon cells also have the potential for ACh breakdown, nor if they show expression of the nicotinic acetylcholine receptor AChRα7 (α7nAChR). Therefore, tendon tissue specimens from patients with midportion Achilles tendinopathy/tendinosis and from normal midportion Achilles tendons were examined. Reaction for the degradative enzyme acetylcholinesterase (AChE) was found in some tenocytes in only a few tendinopathy tendons, and was never found in those of control tendons. Tenocytes displayed more regularly α7nAChR immunoreactivity. However, there was a marked heterogeneity in the degree of this reaction within and between the specimens. α7nAChR immunoreactivity was especially pronounced for tenocytes showing an oval/widened appearance. There was a tendency that the magnitude of α7nAChR immunoreactivity was higher in tendinopathy tendons as compared to control tendons. A stronger α7nAChR immunoreactivity than seen for tenocytes was observed for the cells in the peritendinous tissue. It is likely that the α7nAChR may be an important part of an auto-and paracrine loop of non-neuronal ACh that is released from the tendon cells. The effects may be related to proliferative and blood vessel regulatory functions as well as features related to collagen deposition. ACh can furthermore be of importance in leading to anti-inflammatory effects in the peritendinous tissue, a tissue nowadays considered to be of great relevance for the tendinopathy process. Overall, the findings show that tendon tissue, a tissue known to be devoid of cholinergic innervation, is a tissue in which there is a marked non-neuronal cholinergic system.

The pathogenesis of Achilles tendinopathy: a systematic review

Achilles tendinopathy is a degenerative, not an inflammatory, condition. It is prevalent in athletes involved in running sports. A systematic literature review on Achilles tendon tendinopathy has been performed according to the intrinsic (age, sex, body weight, tendon temperature, systemic diseases, muscle strength, flexibility, previous injuries and anatomical variants, genetic predisposition and blood supply) and extrinsic risk factors (drugs and overuse), which can cause tendon suffering and degeneration. Different theories have been found: Neurogenic, Angiogenic, Impingement and "Iceberg" Hypotheses. Multiple databases were utilized for articles published between 1964 and 2013. The different hypothesis were analyzed, differently considering those concerning the pathogenesis of tendinopathy and those concerning the etiology of complaints in patients. This review of the literature demonstrates the heterogeneity of Achilles tendinopathy pathogenesis. Various risk factors have been identified and have shown an interaction between them such as genes, age, circulating and local cytokine production, sex, biomechanics and body composition.

The peripheral neuronal phenotype is important in the pathogenesis of painful human tendinopathy: a systematic review

BACKGROUND

The pathogenesis of tendinopathy is complex and incompletely understood. Although significant advances have been made in terms of understanding the pathological changes in both the extracellular matrix and the cells involved, relatively little is known about the role of neuronal regulation in tendinopathy. The frequent mismatch between tendon pathology and pain may be explained, in part, by differences in the peripheral neuronal phenotype of patients.

QUESTIONS/PURPOSES

The primary purpose of this review was to determine whether evidence exists of changes in the peripheral neuronal phenotype in painful human tendinopathy and, if so, to identify the associated histological and molecular changes. The secondary purpose was to determine if any changes in the peripheral neuronal phenotype reported correlate with pain symptoms.

METHODS

We conducted a systematic review of the scientific literature using the PRISMA and Cochrane guidelines. The Medline and Embase databases were searched using specific search criteria. Only studies analyzing the peripheral tissue of patients with the clinical diagnosis of tendinopathy were included. Inclusion was agreed on by two independent researchers on review of abstracts or full text.

RESULTS

Overall in the 27 included studies, there was clear evidence of changes in the peripheral neuronal phenotype in painful human tendinopathy. The excitatory glutaminergic system was significantly upregulated in seven studies, there was a significant increase in sensory neuropeptide expression in four studies, and there were significant changes in the molecular morphology of tenocytes, blood vessels, and nerves. In rotator cuff tendinopathy, substance P has been shown to correlate with pain and the neural density in the subacromial bursa has been shown to correlate with rest pain.

CONCLUSIONS

The peripheral neuronal phenotype is an important factor in the pathogenesis of painful human tendinopathy. Further research in this area specifically correlating tissue changes to clinical scores has great potential in further developing our understanding of the disease process.

Neuronal regulation of tendon homoeostasis

The regulation of tendon homoeostasis, including adaptation to loading, is still not fully understood. Accumulating data, however, demonstrates that in addition to afferent (sensory) functions, the nervous system, via efferent pathways which are associated with through specific neuronal mediators plays an active role in regulating pain, inflammation and tendon homeostasis. This neuronal regulation of intact-, healing- and tendinopathic tendons has been shown to be mediated by three major groups of molecules including opioid, autonomic and excitatory glutamatergic neuroregulators. In intact healthy tendons the neuromediators are found in the surrounding structures: paratenon, endotenon and epitenon, whereas the proper tendon itself is practically devoid of neurovascular supply. This neuroanatomy reflects that normal tendon homoeostasis is regulated from the tendon surroundings. After injury and during tendon repair, however, there is extensive nerve ingrowth into the tendon proper, followed by a time-dependent emergence of sensory, autonomic and glutamatergic mediators, which amplify and fine-tune inflammation and regulate tendon regeneration. In tendinopathic condition, excessive and protracted presence of sensory and glutamatergic neuromediators has been identified, suggesting involvement in inflammatory, nociceptive and hypertrophic (degenerative) tissue responses. Under experimental and clinical conditions of impaired (e.g. diabetes) as well as excessive (e.g. tendinopathy) neuromediator release, dysfunctional tendon homoeostasis develops resulting in chronic pain and gradual degeneration. Thus there is a prospect that in the future pharmacotherapy and tissue engineering approaches targeting neuronal mediators and their receptors may prove to be effective therapies for painful, degenerative and traumatic tendon disorders.

Non-neuronal functions of the m2 muscarinic acetylcholine receptor

Acetylcholine is an important neurotransmitter whose effects are mediated by two classes of receptors. The nicotinic acetylcholine receptors are ion channels, whereas the muscarinic receptors belong to the large family of G protein coupled seven transmembrane helix receptors. Beyond its function in neuronal systems, it has become evident that acetylcholine also plays an important role in non-neuronal cells such as epithelial and immune cells. Furthermore, many cell types in the periphery are capable of synthesizing acetylcholine and express at least some of the receptors. In this review, we summarize the non-neuronal functions of the muscarinic acetylcholine receptors, especially those of the M₂ muscarinic receptor in epithelial cells. We will review the mechanisms of signaling by the M₂ receptor but also the cellular trafficking and ARF6 mediated endocytosis of this receptor, which play an important role in the regulation of signaling events. In addition, we provide an overview of the M₂ receptor in human pathological conditions such as autoimmune diseases and cancer.

Substance P enhances collagen remodeling and MMP-3 expression by human tenocytes

The loss of collagen organization is considered a hallmark histopathologic feature of tendinosis. At the cellular level, tenocytes have been shown to produce signal substances that were once thought to be restricted to neurons. One of the main neuropeptides implicated in tendinosis, substance P (SP), is known to influence collagen organization, particularly after injury. The aim of this study was to examine the influence of SP on collagen remodeling by primary human tendon cells cultured in vitro in three-dimensional collagen lattices. We found that SP stimulation led to an increased rate of collagen remodeling mediated via the neurokinin-1 receptor (NK-1 R), the preferred cell receptor for SP. Gene expression analysis showed that SP stimulation resulted in significant increases in MMP3, COL3A1 and ACTA2 mRNA levels in the collagen lattices. Furthermore, cyclic tensile loading of tendon cell cultures along with the administration of exogenous SP had an additive effect on MMP3 expression. Immunoblotting confirmed that SP increased MMP3 protein levels via the NK-1 R. This study indicates that SP, mediated via NK-1 R, increases collagen remodeling and leads to increased MMP3 mRNA and protein expression that is further enhanced by cyclic mechanical loading.

Human tenocytes are stimulated to proliferate by acetylcholine through an EGFR signalling pathway

Studies of human patellar and Achilles tendons have shown that primary tendon fibroblasts (tenocytes) not only have the capacity to produce acetylcholine (ACh) but also express muscarinic ACh receptors (mAChRs) through which ACh can exert its effects. In patients with tendinopathy (chronic tendon pain) with tendinosis, the tendon tissue is characterised by hypercellularity and angiogenesis, both of which might be influenced by ACh. In this study, we have tested the hypothesis that ACh increases the proliferation rate of tenocytes through mAChR stimulation and have examined whether this mechanism operates via the extracellular activation of the epidermal growth factor receptor (EGFR), as shown in other fibroblastic cells. By use of primary human tendon cell cultures, we identified cells expressing vimentin, tenomodulin and scleraxis and found that these cells also contained enzymes related to ACh synthesis and release (choline acetyltransferase and vesicular acetylcholine transporter). The cells furthermore expressed mAChRs of several subtypes. Exogenously administered ACh stimulated proliferation and increased the viability of tenocytes in vitro. When the cells were exposed to atropine (an mAChR antagonist) or the EGFR inhibitor AG1478, the proliferative effect of ACh decreased. Western blot revealed increased phosphorylation, after ACh stimulation, for both EGFR and the extracellular-signal-regulated kinases 1 and 2. Given that tenocytes have been shown to produce ACh and express mAChRs, this study provides evidence of a possible autocrine loop that might contribute to the hypercellularity seen in tendinosis tendon tissue.

Unilateral surgical treatment for patients with midportion Achilles tendinopathy may result in bilateral recovery

BACKGROUND

Bilateral midportion Achilles tendinopathy/tendinosis is not unusual, and treatment of both sides is often carried out. Experiments in animals suggest of the potential involvement of central neuronal mechanisms in Achilles tendinosis.

OBJECTIVES

To evaluate the outcome of surgery for Achilles tendinopathy.

METHODS

This observational study included 13 patients (7 men and 6 women, mean age 53 years) with a long duration (6-120 months) of chronic painful bilateral midportion Achilles tendinopathy. The most painful side at the time for investigation was selected to be operated on first. Treatment was ultrasound-guided and Doppler-guided scraping procedure outside the ventral part of the tendon under local anaesthetic. The patients started walking on the first day after surgery. Follow-ups were conducted and the primary outcome was pain by visual analogue scale. In an additional part of the study, specimens from Achilles and plantaris tendons in three patients with bilateral Achilles tendinosis were examined.

RESULTS

Short-term follow-ups showed postoperative improvement on the non-operated side as well as the operated side in 11 of 13 patients. Final follow-up after 37 (mean) months showed significant pain relief and patient satisfaction on both sides for these 11 patients. In 2 of 13 patients operation on the other, initially non-operated side, was instituted due to persisting pain. Morphologically, it was found that there were similar morphological effects, and immunohistochemical patterns of enzyme involved in signal substance production, bilaterally.

CONCLUSION

Unilateral treatment with a scraping operation can have benefits contralaterally; the clinical implication is that unilateral surgery may be a logical first treatment in cases of bilateral Achilles tendinopathy.

Novel information on the non-neuronal cholinergic system in orthopedics provides new possible treatment strategies for inflammatory and degenerative diseases

Anti-cholinergic agents are used in the treatment of several pathological conditions. Therapy regimens aimed at up-regulating cholinergic functions, such as treatment with acetylcholinesterase inhibitors, are also currently prescribed. It is now known that not only is there a neuronal cholinergic system but also a non-neuronal cholinergic system in various parts of the body. Therefore, interference with the effects of acetylcholine (ACh) brought about by the local production and release of ACh should also be considered. Locally produced ACh may have proliferative, angiogenic, wound-healing, and immunomodulatory functions. Interestingly, cholinergic stimulation may lead to anti-inflammatory effects. Within this review, new findings for the locomotor system of a more widespread non-neuronal cholinergic system than previously expected will be discussed in relation to possible new treatment strategies. The conditions discussed are painful and degenerative tendon disease (tendinopathy/tendinosis), rheumatoid arthritis, and osteoarthritis.

A randomized controlled trial of exercise versus wait-list in chronic tennis elbow (lateral epicondylosis)

BACKGROUND

Chronic tennis elbow (lateral epicondylosis) is a common disorder. Like other chronic soft-tissue pain conditions it is often difficult to treat successfully. The effects of exercise have been discussed, but no convincing evidence has been put forward so far, and a simple protocol for exercise is lacking.

AIMS OF THE STUDY

This study is a randomized, controlled, clinical trial of the effect of exercise versus expectation (wait-list) on pain, muscle strength, function, and quality of life in patients with long-standing lateral epicondylosis.

METHODS

Eighty-one subjects with tennis elbow lasting for more than 3 months were randomly allocated to an exercise group (n = 40) or a reference group (n = 41). The exercise group performed daily exercise, with weekly load increase, for 3 months. The reference group was wait-listed, but otherwise followed in the same way. Outcome measures were pain during maximum voluntary muscle contraction (Cozen's test) and pain during maximum muscle elongation with a load (modified Empty-can-test); muscle strength was measured with a Chatillon MSE 100 hand-held dynamometer, and the Disability of the Arm, Shoulder and Hand (DASH) and the Gothenburg Quality of Life questionnaires.

RESULTS

The exercise group had greater and faster regression of pain, both during muscle contraction and muscle elongation, than the reference group (p = 0.0005 and p = 0.0016, respectively). There was a non-significant muscle strength difference between the groups, but no differences regarding DASH scores or quality of life measures.

CONCLUSIONS

Exercise appears to be superior to expectation in reducing pain in chronic lateral epicondylosis.

Substance P is a mechanoresponsive, autocrine regulator of human tenocyte proliferation

It has been hypothesised that substance P (SP) may be produced by primary fibroblastic tendon cells (tenocytes), and that this production, together with the widespread distribution of the neurokinin-1 receptor (NK-1 R) in tendon tissue, could play an important role in the development of tendinopathy, a condition of chronic tendon pain and thickening. The aim of this study was to examine the possibility of endogenous SP production and the expression of NK-1 R by human tenocytes. Because tendinopathy is related to overload, and because the predominant tissue pathology (tendinosis) underlying early tendinopathy is characterized by tenocyte hypercellularity, the production of SP in response to loading/strain and the effects of exogenously administered SP on tenocyte proliferation were also studied. A cell culture model of primary human tendon cells was used. The vast majority of tendon cells were immunopositive for the tenocyte/fibroblast markers tenomodulin and vimentin, and immunocytochemical counterstaining revealed that positive immunoreactions for SP and NK-1 R were seen in a majority of these cells. Gene expression analyses showed that mechanical loading (strain) of tendon cell cultures using the FlexCell© technique significantly increased the mRNA levels of SP, whereas the expression of NK-1 R mRNA decreased in loaded as compared to unloaded tendon cells. Reduced NK-1 R protein was also observed, using Western blot, after exogenously administered SP at a concentration of 10⁻⁷ M. SP exposure furthermore resulted in increased cell metabolism, increased cell viability, and increased cell proliferation, all of which were found to be specifically mediated via the NK-1 R; this in turn involving a common mitogenic cell signalling pathway, namely phosphorylation of ERK1/2. This study indicates that SP, produced by tenocytes in response to mechanical loading, may regulate proliferation through an autocrine loop involving the NK-1 R.

Increased expression of cannabinoid CB₁ receptors in Achilles tendinosis

Background

The endogenous cannabinoid system is involved in the control of pain. However, little is known as to the integrity of the cannabinoid system in human pain syndromes. Here we investigate the expression of the cannabinoid receptor 1 (CB₁) in human Achilles tendons from healthy volunteers and from patients with Achilles tendinosis.

Methodology

Cannabinoid CB₁ receptor immunoreactivity (CB₁IR) was evaluated in formalin-fixed biopsies from individuals suffering from painful Achilles tendinosis in comparison with healthy human Achilles tendons.

Principal Findings

CB₁IR was seen as a granular pattern in the tenocytes. CB₁IR was also observed in the blood vessel wall and in the perineurium of the nerve. Quantification of the immunoreactivity in tenocytes showed an increase of CB₁ receptor expression in tendinosis tissue compared to control tissue.

Conclusion

Expression of cannabinoid receptor 1 is increased in human Achilles tendinosis suggesting that the cannabinoid system may be dysregulated in this disorder.

New insight into the non-neuronal cholinergic system via studies on chronically painful tendons and inflammatory situations

For certain parts of the body, it is nowadays accepted that there is a cholinergic system that is not related to cholinergic innervation, i.e. a non-neuronal cholinergic system. It might be argued that this system is of minor importance. New information obtained shows, however, that the non-neuronal cholinergic system is more widely distributed in the body than what is previously recognised. In recent studies, the existence of such a system has thus been shown for human tendons, especially in chronically painful situations (tendinopathy/tendinosis), in the synovial tissue of patients with rheumatoid arthritis and osteoarthritis, and in the mucosa of ulcerative colitis patients. There is evidence of both acetylcholine (ACh) production and a marked existence of muscarinic (M2) ACh receptors in these situations. The non-neuronal cholinergic system may be involved in the establishment of a 'cholinergic anti-inflammatory pathway' and in proliferative and tissue reorganisation processes via autocrine/paracrine effects. The new information obtained suggests that this system plays an important functional role in chronically painful tendons and in inflammatory conditions. The findings of such a system in various parts of the body, when taken together, show that not only should the classical neuronal cholinergic system be considered in discussion of the cholinergic influences in the body. Additionally, the production of ACh in local cells in the tissues represents an important extra supply of the transmitter. ACh effects can be obtained whether or not there is a cholinergic innervation in the tissue.

Presence of substance P and the neurokinin-1 receptor in tenocytes of the human Achilles tendon

Nerve signal substances, such as the tachykinin substance P (SP), may be involved in the changes that occur in response to tendinopathy (tendinosis). It is previously known that the level of SP innervation within tendon tissue is limited, but results of experimental studies have suggested that SP may have stimulatory, angiogenetic and healing effects in injured tendons. Therefore, it would be of interest to know if there is a local SP-supply in tendon tissue. In the present study, the patterns of expression of SP and its preferred receptor, the neurokinin-1 receptor (NK-1 R), in normal and tendinosis human Achilles tendons were analyzed by use of both immunohistochemistry and in situ hybridization. We found that there was expression of SP mRNA in tenocytes, and that tenocytes showed expression of NK-1 R at protein as well as mRNA levels. The observations concerning both SP and NK-1 R were most evident for tenocytes in tendinosis tendons. Our findings suggest that SP is produced in tendinosis tendons, and furthermore that SP has marked effects on the tenocytes via the NK-1 R. It cannot be excluded that the SP effects are of importance concerning the processes of reorganization and healing that occur for tendon tissue in tendinosis. In conclusion, it appears as if SPergic autocrine/paracrine effects occur in tendon tissue during the processes of tendinosis, hitherto unknown effects for human tendons.