Evaluation of a preemptive intervention regimen with hesperidin methyl chalcone in delayed-onset muscle soreness in young adults: a randomized, double-blinded, and placebo-controlled trial study

PURPOSE

Delayed-onset muscle soreness (DOMS) describes an entity characterized by ultrastructural muscle damage. Hesperidin methyl chalcone (HMC) is a synthetic flavonoid presenting analgesic, anti-inflammatory, and antioxidant properties. We evaluated the effects of HMC upon DOMS.

METHOD

In a preventive paradigm, 31 sedentary young men were submitted to a randomized, double-blinded parallel trial and received HMC 500 mg or one placebo capsule × 3 days before an intense dynamic exercise protocol (concentric/eccentric actions) applied for lower limbs for inducing muscle damage. Assessments were conducted at baseline, and 24 and 48 h after, comprising physical performance, and post-muscle soreness and damage, inflammation, recovery of muscle strength, and postural balance associated with DOMS. HMC safety was also evaluated. Thirty participants completed the study.

RESULTS

HMC improved the performance of participants during exercise (40.3 vs 51.3 repetitions to failure, p = 0.0187) and inhibited CPK levels (90.5 vs 57.9 U/L, p = 0.0391) and muscle soreness during passive quadriceps palpation (2.6 vs 1.4 VAS cm, p = 0.0439), but not during active actions, nor did it inhibit IL-1β or IL-10 levels. HMC improved muscle strength recovery, and satisfactorily refined postural balance, without inducing injury to kidneys or liver.

CONCLUSIONS

Preemptive HMC supplementation may be beneficial for boosting physical performance and for the amelioration of clinical parameters related to DOMS, including pain on muscle palpation, increased blood CPK levels, and muscle strength and proprioceptive deficits, without causing adverse effects. These data advance the understanding of the benefits provided by HMC for DOMS treatment, which supports its usefulness for such purpose.

Brief research report: Repurposing pentoxifylline to treat intense acute swimming-Induced delayed-onset muscle soreness in mice: Targeting peripheral and spinal cord nociceptive mechanisms

In this study, we pursue determining the effect of pentoxifylline (Ptx) in delayed-onset muscle soreness (DOMS) triggered by exposing untrained mice to intense acute swimming exercise (120 min), which, to our knowledge, has not been investigated. Ptx treatment (1.5, 4.5, and 13.5 mg/kg; i.p., 30 min before and 12 h after the session) reduced intense acute swimming-induced mechanical hyperalgesia in a dose-dependent manner. The selected dose of Ptx (4.5 mg/kg) inhibited recruitment of neutrophils to the muscle tissue, oxidative stress, and both pro- and anti-inflammatory cytokine production in the soleus muscle and spinal cord. Furthermore, Ptx treatment also reduced spinal cord glial cell activation. In conclusion, Ptx reduces pain by targeting peripheral and spinal cord mechanisms of DOMS.

Intense Acute Swimming Induces Delayed-Onset Muscle Soreness Dependent on Spinal Cord Neuroinflammation

Unaccustomed exercise involving eccentric contractions, high intensity, or long duration are recognized to induce delayed-onset muscle soreness (DOMS). Myocyte damage and inflammation in affected peripheral tissues contribute to sensitize muscle nociceptors leading to muscle pain. However, despite the essential role of the spinal cord in the regulation of pain, spinal cord neuroinflammatory mechanisms in intense swimming-induced DOMS remain to be investigated. We hypothesized that spinal cord neuroinflammation contributes to DOMS. C57BL/6 mice swam for 2 h to induce DOMS, and nociceptive spinal cord mechanisms were evaluated. DOMS triggered the activation of astrocytes and microglia in the spinal cord 24 h after exercise compared to the sham group. DOMS and DOMS-induced spinal cord nuclear factor κB (NFκB) activation were reduced by intrathecal treatments with glial inhibitors (fluorocitrate, α-aminoadipate, and minocycline) and NFκB inhibitor [pyrrolidine dithiocarbamate (PDTC)]. Moreover, DOMS was also reduced by intrathecal treatments targeting C-X₃-C motif chemokine ligand 1 (CX₃CL1), tumor necrosis factor (TNF)-α, and interleukin (IL)-1β or with recombinant IL-10. In agreement, DOMS induced the mRNA and protein expressions of CX₃CR1, TNF-α, IL-1β, IL-10, c-Fos, and oxidative stress in the spinal cord. All these immune and cellular alterations triggered by DOMS were amenable by intrathecal treatments with glial and NFκB inhibitors. These results support a role for spinal cord glial cells, via NFκB, cytokines/chemokines, and oxidative stress, in DOMS. Thus, unveiling neuroinflammatory mechanisms by which unaccustomed exercise induces central sensitization and consequently DOMS.

Redox interactions of immune cells and muscle in the regulation of exercise-induced pain and analgesia: implications on the modulation of muscle nociceptor sensory neurons

The mechanistic interactions among redox status of leukocytes, muscle, and exercise in pain regulation are still poorly understood and limit targeted treatment. Exercise benefits are numerous, including the treatment of chronic pain. However, unaccustomed exercise may be reported as undesirable as it may contribute to pain. The aim of the present review is to evaluate the relationship between oxidative metabolism and acute exercise-induced pain, and as to whether improved antioxidant capacity underpins the analgesic effects of regular exercise. Preclinical and clinical studies addressing relevant topics on mechanisms by which exercise modulates the nociceptive activity and how redox status can outline pain and analgesia are discussed, in sense of translating into refined outcomes. Emerging evidence points to the role of oxidative stress-induced signaling in sensitizing nociceptor sensory neurons. In response to acute exercise, there is an increase in oxidative metabolism, and consequently, pain. Instead, regular exercise can modulate redox status in favor of antioxidant capacity and repair mechanisms, which have consequently increased resistance to oxidative stress, damage, and pain. Data indicate that acute sessions of unaccustomed prolonged and/or intense exercise increase oxidative metabolism and regulate exercise-induced pain in the post-exercise recovery period. Further, evidence demonstrates regular exercise improves antioxidant status, indicating its therapeutic utility for chronic pain disorders. An improved comprehension of the role of redox status in exercise can provide helpful insights into immune-muscle communication during pain modulatory effects of exercise and support new therapeutic efforts and rationale for the promotion of exercise.

P2X4 Receptors on Muscle Macrophages Are Required for Development of Hyperalgesia in an Animal Model of Activity-Induced Muscle Pain

Activity-induced pain is common in those with chronic musculoskeletal pain and limits participation in daily activities and exercise. Our laboratory developed a model of activity-induced pain and shows that depletion of muscle macrophages prevents development of hyperalgesia. Adenosine triphosphate (ATP) is released from fatiguing muscle and activates purinergic receptors (P2X), and P2X4 receptors are expressed on macrophages. We hypothesized that exercise releases ATP to activate P2X4 receptors on muscle macrophages, which subsequently release interleukin-1β (IL-1β) to produce hyperalgesia. In an animal model of activity-induced pain, using male and female C57BL6/J mice, we show increased expression of P2X4 on muscle macrophages, and blockade of P2X4 receptors in muscle prevented development of hyperalgesia. Using a lentivirus expressing an artificial micro-RNA to P2X4 under the control of a CD68 promoter, we decreased expression of P2X4 mRNA in cultured macrophages, decreased expression of P2X4 protein in muscle macrophages in vivo, and prevented development of activity-induced hyperalgesia. We further show that macrophages primed with LPS differentially released IL-1β when treated with ATP in neutral or acidic pH. Lastly, blockade of IL-1β in muscle prevented development of hyperalgesia in this model. Thus, our data suggest that P2X4 receptors could be a valid pharmacological target to control activity-induced muscle pain experienced by patients with chronic musculoskeletal pain.

Protective Effects of Foam Rolling against Inflammation and Notexin Induced Muscle Damage in Rats

It is known that high-intensity exercise can cause inflammation and damage in muscle tissue, and in recent years, physical therapists and fitness professionals have begun to use foam rolling as a recovery method to improve performance. Despite the lack of basic science studies to support or refute the efficacy of foam rolling, the technique is very widely used in the sports world. In this respect, we investigated whether foam rolling could attenuate muscle damage and inflammation. Female Wistar rats were assigned to control (C), foam rolling (FR), notexin without foam rolling (N) and notexin with foam rolling (NFR) groups. A 4.5 x 2 cm foam roller was used to massage their hind legs (two 60-second repetitions twice a day for 3 days). Motor function tests (Balance Beam Test and Grip strength) were used. We detected an increase in time and foot faults when crossing a beam in the N group compared to C and FR rats. In contrast, a significant decrease was detected in both tests in NFR compared to N rats. Muscle power was measured with a grip strength test and better performance was detected in NFR rats compared to N rats. Furthermore, an increase of pro-inflammatory proteins was noted in the N group, while there was a decrease in the NFR group. On the contrary, an increase in PPAR-γ (anti-inflammatory protein) in the NFR group compared to the N group demonstrates the anti-inflammatory properties of the foam rolling technique. In summary, applying foam rolling after damage has benefits such as an increase in anti-inflammatory proteins and a reduction of pro-inflammatory proteins, resulting in muscle recovery and better performance.

Interleukin 1β inhibition contributes to the antinociceptive effects of voluntary exercise on ischemia/reperfusion-induced hypersensitivity

Issues of peripheral circulation have been increasingly suggested as an underlying cause of musculoskeletal pain in many conditions, including sickle cell anemia and peripheral vascular disease. We have previously shown in our model of transient ischemia and reperfusion (I/R) injury of the forelimb that individual group III and IV muscle afferents display altered chemosensitivity and mechanical thresholds 1 day after injury. Functional alterations corresponded to increased evoked and spontaneous pain-related behaviors and decreased muscle strength and voluntary activity-all actions that echo clinical symptoms of ischemic myalgia. These behavioral and physiological changes appeared to originate in part from the action of increased interleukin 1β (IL1β) in the injured muscles at its upregulated IL1 receptor 1 within the dorsal root ganglion. Here, we describe that two days of voluntary wheel running prior to I/R blocks both injury-induced IL1β enhancement and the subsequent development of ischemic myalgia-like behaviors. Furthermore, the protective effects of 2 days prior exercise on the I/R-evoked increases in pain-related behaviors were also paralleled with systemic injection of the IL1 receptor antagonist during I/R. Interleukin 1 receptor antagonist treatment additionally prevented the I/R-induced changes in mechanical and chemical sensitivity of individual primary muscle afferents. Altogether, these data strengthen the evidence that transient I/R injury sensitizes group III and IV muscle afferents via increased IL1β in the muscles to stimulate ischemic myalgia development. Targeting IL1β may, therefore, be an effective treatment strategy for this insidious type of muscle pain.

Dysregulation of the Inflammatory Mediators in the Multifidus Muscle After Spontaneous Intervertebral Disc Degeneration SPARC-null Mice is Ameliorated by Physical Activity

STUDY DESIGN

A longitudinal case-control animal model.

OBJECTIVE

The aim of this study was to investigate the inflammatory pathways active in the multifidus muscle after spontaneous intervertebral disc degeneration (IDD), and whether these IDD-related muscle changes can be ameliorated by exercise.

SUMMARY OF BACKGROUND DATA

A pro-inflammatory response is present in the multifidus muscle after an intervertebral disc lesion and has been proposed to drive the structural alterations present during low back pain. However, it is not known whether spontaneous IDD produces an inflammatory response. Furthermore, exercise/physical activity produces a strong anti-inflammatory response, but its effectiveness in ameliorating inflammation in the multifidus is unknown. We assessed the inflammatory profile of the multifidus and the effectiveness of physical activity as a treatment using an animal model of spontaneous model of IDD.

METHODS

Wild-type and SPARC null mice that were sedentary or housed with a running wheel were used in this study. Multifidus muscle segments were harvested from L2-L6 from the mice at 9 months of age after they had undergone a magnetic resonance imaging (MRI) scan to determine levels with IDD. The inflammatory profile of the multifidus was examined using quantitative polymerase chain reaction (PCR) assays.

RESULTS

Spontaneous IDD in the SPARC-null mice caused a dysregulation of interleukin (IL)-1β, IL6, transforming growth factor-beta (TGFβ1), and adiponectin expression. More specifically, the proximity and degree of IDD was related to levels of IL-1β expression. Physical activity reduced the pro-inflammatory response to IDD in the multifidus. IL-1β, tumor necrosis factor (TNF), IL-10, adiponectin, and leptin levels were lower in the physically active group.

CONCLUSION

These results reveal that spontaneous IDD causes dysregulation of the inflammatory pathways active in the multifidus muscle. These alterations were related to the severity of IDD and were prevented by physical activity.

LEVEL OF EVIDENCE

N/A.

Role of Exercise Activity in Alleviating Neuropathic Pain in Diabetes via Inhibition of the Pro-Inflammatory Signal Pathway

Hyperalgesia and allodynia are commonly observed in patients with diabetic neuropathy. The treatment and management of painful peripheral neuropathy is important in these patients. The purpose of this study was to examine the role of exercise in modulating neuropathic pain induced by diabetes. Diabetes was induced in rats by an intraperitoneal injection of streptozotocin (STZ). Control rats received saline injections. Groups included control rats without exercise (NT-control, n = 12), control rats with exercise (EX-control, n = 16), STZ rats without exercise (NT-STZ, n = 18), and STZ rats with exercise (EX-STZ, n = 22). Rats in EX groups ran on a treadmill 4 days/week for 5 weeks beginning from the week of STZ administration. Mechanical hypersensitivity (mechanical paw withdrawal thresholds [PWTs]) and glucose levels were tested weekly. Then, enzyme-linked immunoassay and Western blot analysis were used to determine the levels of pro-inflammatory cytokines (PICs) and their receptors in sensory nerves. PWTs were significantly increased after 4–5 weeks of exercise in STZ rats ( p < .05 vs. NT-STZ rats). Inhibition of neuropathic pain by exercise in STZ rats was accompanied by decreases in interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α levels and downregulated expression of their receptors. Furthermore, blocking individual PIC receptors elevated PWTs to a greater degree in STZ rats ( p < .05 vs. control rats). Overall, our data suggest that exercise can play a role in improving neuropathic pain induced by STZ and that PIC signaling is a part of the mechanism involved in this effect.

Peripheral Mechanisms of Ischemic Myalgia

Musculoskeletal pain due to ischemia is present in a variety of clinical conditions including peripheral vascular disease (PVD), sickle cell disease (SCD), complex regional pain syndrome (CRPS), and even fibromyalgia (FM). The clinical features associated with deep tissue ischemia are unique because although the subjective description of pain is common to other forms of myalgia, patients with ischemic muscle pain often respond poorly to conventional analgesic therapies. Moreover, these patients also display increased cardiovascular responses to muscle contraction, which often leads to exercise intolerance or exacerbation of underlying cardiovascular conditions. This suggests that the mechanisms of myalgia development and the role of altered cardiovascular function under conditions of ischemia may be distinct compared to other injuries/diseases of the muscles. It is widely accepted that group III and IV muscle afferents play an important role in the development of pain due to ischemia. These same muscle afferents also form the sensory component of the exercise pressor reflex (EPR), which is the increase in heart rate and blood pressure (BP) experienced after muscle contraction. Studies suggest that afferent sensitization after ischemia depends on interactions between purinergic (P2X and P2Y) receptors, transient receptor potential (TRP) channels, and acid sensing ion channels (ASICs) in individual populations of peripheral sensory neurons. Specific alterations in primary afferent function through these receptor mechanisms correlate with increased pain related behaviors and altered EPRs. Recent evidence suggests that factors within the muscles during ischemic conditions including upregulation of growth factors and cytokines, and microvascular changes may be linked to the overexpression of these different receptor molecules in the dorsal root ganglia (DRG) that in turn modulate pain and sympathetic reflexes. In this review article, we will discuss the peripheral mechanisms involved in the development of ischemic myalgia and the role that primary sensory neurons play in EPR modulation.

Muscle pain induced by static contraction in rats is modulated by peripheral inflammatory mechanisms

Muscle pain is an important health issue and frequently related to static force exertion. The aim of this study is to evaluate whether peripheral inflammatory mechanisms are involved with static contraction-induced muscle pain in rats. To this end, we developed a model of muscle pain induced by static contraction performed by applying electrical pulses through electrodes inserted into muscle. We also evaluated the involvement of neutrophil migration, bradykinin, sympathetic amines and prostanoids. A single session of sustained static contraction of gastrocnemius muscle induced acute mechanical muscle hyperalgesia without affecting locomotor activity and with no evidence of structural damage in muscle tissue. Static contraction increased levels of creatine kinase but not lactate dehydrogenase, and induced neutrophil migration. Dexamethasone (glucocorticoid anti-inflammatory agent), DALBK (bradykinin B1 antagonist), Atenolol (β1 adrenoceptor antagonist), ICI 118,551 (β2 adrenoceptor antagonist), indomethacin (cyclooxygenase inhibitor), and fucoidan (non-specific selectin inhibitor) all reduced static contraction-induced muscle hyperalgesia; however, the bradykinin B2 antagonist, bradyzide, did not have an effect on static contraction-induced muscle hyperalgesia. Furthermore, an increased hyperalgesic response was observed when the selective bradykinin B1 agonist des-Arg⁹-bradykinin was injected into the previously stimulated muscle. Together, these findings demonstrate that static contraction induced mechanical muscle hyperalgesia in gastrocnemius muscle of rats is modulated through peripheral inflammatory mechanisms that are dependent on neutrophil migration, bradykinin, sympathetic amines and prostanoids. Considering the clinical relevance of muscle pain, we propose the present model of static contraction-induced mechanical muscle hyperalgesia as a useful tool for the study of mechanisms underlying static contraction-induced muscle pain.

The Effect of Anakinra on Paclitaxel-Induced Peripheral Neuropathic Pain in Rats

OBJECTIVE

Paclitaxel is used in the treatment of cancer, and it may cause interleukin-1 beta (IL-1β)-related peripheral neuropathic pain. While our primary aim was to investigate the analgesic efficacy of an IL-1β antagonist, a secondary outcome was to assess whether a correlation exists between analgesic effects and antioxidant activity.

METHODS

A total of 24 albino Wistar male rats were divided into the following groups: paclitaxel-control, paclitaxel+50 mg kg^-1 anakinra, paclitaxel+100 mg kg^-1 anakinra and healthy group (HG). After the normal paw pain threshold in all animal groups was measured using a Basile algesimeter, a single dose of 2 mg kg^-1 paclitaxel was intraperitoneally administered on the 1^st, 3^rd, 5^th and 7^th days. Anakinra was intraperitoneally administered following the final paclitaxel administration. The paw pain thresholds in the groups were measured before and seven days after paclitaxel administration and at the 1^st and 3^rd hours after anakinra administration. After the third hour of measurement, the rats were killed with high doses of ketamine, and the paw tissues were removed. Malondialdehyde, myeloperoxidase and total glutathione levels were measured in claw tissues, and IL-1β gene expression was determined. The biochemical results were compared with the results of the HG; in the meanwhile the claw pain threshold results were compared with the results obtained after the last paclitaxel and the results obtained from the 1^st and 3^rd hours after the anakinra application.

RESULTS

The claw paw pain threshold of the rats decreased one and three hours after anakinra administration. Further, 100 mg kg^-1 anakinra had greater analgesic activity than 50 mg kg^-1 anakinra. A correlation was found between the antioxidant and analgesic activities of 100 mg kg^-1 anakinra.

CONCLUSION

Anakinra may be useful to reduce paclitaxel-induced neuropathic pain; further, 100 mg kg^-1 anakinra may have greater analgesic and antioxidant activities.

Quercetin Inhibits Peripheral and Spinal Cord Nociceptive Mechanisms to Reduce Intense Acute Swimming-Induced Muscle Pain in Mice

The present study aimed to evaluate the effects of the flavonoid quercetin (3,3´,4´,5,7-pentahydroxyflavone) in a mice model of intense acute swimming-induced muscle pain, which resembles delayed onset muscle soreness. Quercetin intraperitoneal (i.p.) treatment dose-dependently reduced muscle mechanical hyperalgesia. Quercetin inhibited myeloperoxidase (MPO) and N-acetyl-β-D- glucosaminidase (NAG) activities, cytokine production, oxidative stress, cyclooxygenase-2 (COX-2) and gp91^phox mRNA expression and muscle injury (creatinine kinase [CK] blood levels and myoblast determination protein [MyoD] mRNA expression) as well as inhibited NFκB activation and induced Nrf2 and HO-1 mRNA expression in the soleus muscle. Beyond inhibiting those peripheral effects, quercetin also inhibited spinal cord cytokine production, oxidative stress and glial cells activation (glial fibrillary acidic protein [GFAP] and ionized calcium-binding adapter molecule 1 [Iba-1] mRNA expression). Concluding, the present data demonstrate that quercetin is a potential molecule for the treatment of muscle pain conditions related to unaccustomed exercise.

Jararhagin-induced mechanical hyperalgesia depends on TNF-α, IL-1β and NFκB in mice

Jararhagin is a hemorrhagic metalloprotease from Bothrops jararaca snake venom. The hyperalgesic mechanisms of jararhagin were investigated focusing on the role of proinflammatory cytokines (TNF-α and IL-1β) and the transcription factor NFκB. Intraplantar administration of jararhagin (1, 10, 100 and 1000 ng/paw) induced mechanical hyperalgesia, and increased TNF-α levels at 1, 3 and 5 h, and IL-1β levels at 0.5, 1 and 3 h after its injection in the paw tissue. Pre-treatment with morphine (2, 6, 12 μg/paw) inhibited jararhagin-induced mechanical hyperagesia. The systemic or local pre-treatment with etanercept (10 mg/kg and 100 μg/paw) and IL-1ra (30 mg/kg and 100 pg/paw) inhibited jararhagin-induced mechanical hyperalgesia. Co-administration of jararhagin (0.1 ng/paw) and TNF-α (0.1 pg/paw) or jararhagin (0.1 ng/paw) and IL-1β (1 pg/paw) enhanced the mechanical hyperalgesia. The systemic or local pre-treatment with PDTC (NFκB inhibitor; 100 mg/kg and 100 μg/paw) inhibited jararhagin-induced mechanical hyperalgesia as well as PDTC decreased the jararhagin-induced production of TNF-α and IL-1β. Thus, these data demonstrate the involvement of pro-inflammatory cytokines TNF-α and IL-1β and nuclear transcription factor NFκB in jararhagin-induced mechanical hyperalgesia indicating that targeting these mechanisms might contribute to reduce the pain induced by B. jararaca snake venom.

Vanillic Acid Inhibits Inflammatory Pain by Inhibiting Neutrophil Recruitment, Oxidative Stress, Cytokine Production, and NFκB Activation in Mice

Vanillic acid (1) is a flavoring agent found in edible plants and fruits. It is an oxidized form of vanillin. Phenolic compounds form a substantial part of plant foods used as antioxidants with beneficial biological activities. These compounds have received considerable attention because of their role in preventing human diseases. Especially, 1 presents antibacterial, antimicrobial, and chemopreventive effects. However, the mechanisms by which 1 exerts its anti-inflammatory effects in vivo are incompletely understood. Thus, the effect of 1 was evaluated in murine models of inflammatory pain. Treatment with 1 inhibited the overt pain-like behavior induced by acetic acid, phenyl-p-benzoquinone, the second phase of the formalin test, and complete Freund's adjuvant (CFA). Treatment with 1 also inhibited carrageenan- and CFA-induced mechanical hyperalgesia, paw edema, myeloperoxidase activity, and N-acetyl-β-D-glucosaminidase activity. The anti-inflammatory mechanisms of 1 involved the inhibition of oxidative stress, pro-inflammatory cytokine production, and NFκB activation in the carrageenan model. The present study demonstrated 1 presents analgesic and anti-inflammatory effects in a wide range of murine inflammation models, and its mechanisms of action involves antioxidant effects and NFκB-related inhibition of pro-inflammatory cytokine production.

An experimental study of muscular injury repair in a mouse model of notexin-induced lesion with EPI® technique

BACKGROUND

The mechanisms of muscle injury repair after EPI® technique, a treatment based on electrical stimulation, have not been described. This study determines whether EPI® therapy could improve muscle damage.

METHODS

Twenty-four rats were divided into a control group, Notexin group (7 and 14 days) and a Notexin + EPI group. To induce muscle injury, Notexin was injected in the quadriceps of the left extremity of rats. Pro-inflammatory interleukin 1-beta (IL-1beta) and tumoral necrosis factor-alpha (TNF-alpha) were determined by ELISA. The expression of receptor peroxisome gamma proliferator activator (PPAR-gamma), vascular endothelial growth factor (VEGF) and vascular endothelial growth factor receptor-1 (VEGF-R1) were determined by western-blot.

RESULTS

The plasma levels of TNF-alpha and IL-1beta in Notexin-injured rats showed a significant increase compared with the control group. EPI® produced a return of TNF-alpha and IL-1beta values to control levels. PPAR-gamma expression diminished injured quadriceps muscle in rats. EPI® increased PPAR-gamma, VEGF and VEGF-R1 expressions. EPI® decreased plasma levels of pro-inflammatory TNF-alpha and IL-1beta and increased anti-inflammatory PPAR-gamma and proangiogenic factors as well as VEGF and VEGF-R1 expressions.

CONCLUSION

The EPI® technique may affect inflammatory mediators in damaged muscle tissue and influences the new vascularization of the injured area. These results suggest that EPI® might represent a useful new therapy for the treatment of muscle injuries. Although our study in rats may represent a valid approach to evaluate EPI® treatment, studies designed to determine how the EPI® treatment may affect recovery of injury in humans are needed.

Interleukin-10 limits intense acute swimming-induced muscle mechanical hyperalgesia in mice

NEW FINDINGS

What is the central question of this study? This study investigated the role of the endogenous anti-inflammatory cytokine interleukin-10 in intense acute swimming-induced muscle mechanical hyperalgesia in mice. What is the main finding and its importance? Endogenous interleukin-10 has a key role in limiting exercise-induced muscle pain in a model presenting similarities to delayed-onset muscle soreness in mice. Interleukin-10 reduced muscle pain by diminishing leucocyte recruitment, hyperalgesic cytokine production, oxidative stress and myocyte damage. Interleukin-10 (IL-10) is an antihyperalgesic cytokine. In this study, IL-10-deficient (IL-10(-/-) ) mice were used to investigate the role of endogenous IL-10 in intense acute swimming-induced muscle mechanical hyperalgesia, which presents similarities with delayed-onset muscle soreness. An intense acute swimming session of 1 or 2 h induced significant muscle mechanical hyperalgesia in a time-dependent manner in wild-type mice compared with the sham group 24 h after the session, which was further increased in IL-10(-/-) mice (P ˂ 0.05). Intraperitoneal treatment of wild-type mice with IL-10 (1-10 ng) reduced muscle mechanical hyperalgesia in a dose-dependent manner and reversed the enhanced muscle hyperalgesia in IL-10(-/-) mice (P ˂ 0.05). The 2 h swimming session induced increases in tumour necrosis factor-α, interleukin-1β and IL-10 production in the soleus muscle. However, tumour necrosis factor-α and interleukin-1β production in the soleus muscle were even higher in IL-10(-/-) mice between 2 and 6 h after the stimulus (P ˂ 0.05). There was no statistical difference in the levels of the antihyperalgesic cytokines interleukin-4, interleukin-5, interleukin-13 and transforming growth factor-β between wild-type and IL-10(-/-) mice (P ˃ 0.05). Interleukin-10 deficiency also resulted in increased myeloperoxidase activity, greater depletion of reduced glutathione levels, increased superoxide anion production and the maintenance of high plasma concentrations of creatine kinase (until 24 h after the swimming session) in soleus muscle (P ˂ 0.05). These results demonstrate that endogenous IL-10 controls intense acute swimming-induced muscle mechanical hyperalgesia by limiting oxidative stress and cytokine production.

Granulocyte-colony stimulating factor (G-CSF)-induced mechanical hyperalgesia in mice: Role for peripheral TNFα, IL-1β and IL-10

Granulocyte-colony stimulating factor (G-CSF) is a therapeutic approach to increase peripheral neutrophil counts after anti-tumor therapies. Pain is the major side effect of G-CSF. Intraplantar administration of G-CSF in mice induces mechanical hyperalgesia. However, the peripheral mechanisms involved in this effect were not elucidated. Therefore, the participation of pronociceptive cytokines tumor necrosis factor (TNF) alpha (TNFα), interleukin (IL)-1 beta (IL-1β) and antinociceptive cytokine IL-10 in G-CSF-induced mechanical hyperalgesia in mice was investigated. G-CSF-induced mechanical hyperalgesia was inhibited by systemic and local treatment with etanercept and IL-1 receptor antagonist (IL-1ra) or TNF receptor 1 (TNFR1) deficiency and increased in IL-10 deficient mice. In agreement, G-CSF injection induced significant TNFα, IL-1β and IL-10 production in paw tissue. G-CSF-induced hyperalgesia was dose-dependently inhibited by thalidomide (5-45mg/kg) and pentoxifylline (0.5-13.5mg/kg), and treatment with these drugs inhibited G-CSF-induced TNFα, IL-1β and IL-10 production. The combined treatment with pentoxifylline or thalidomide with morphine, at doses that are ineffective as single treatment, diminished G-CSF-induced hyperalgesia through inhibiting cytokine production. Indomethacin also reduces G-CSF hyperalgesia alone or combined with pentoxifylline or thalidomide. Thus, G-CSF-induced hyperalgesia might be mediate by peripheral production of pronociceptive cytokines TNFα and IL-1β and down-regulated by IL-10. Systemic IL-1ra reduced G-CSF-induced increase of peripheral neutrophil counts. However, local treatment with morphine, IL-1ra or etanercept, and systemic treatment with indomethacin, etanercept, thalidomide and pentoxifylline did not alter G-CSF-induced mobilization of neutrophils. Therefore, this study advances in the understanding of G-CSF-induced hyperalgesia and suggests therapeutic approaches for its control.

Preliminary evidence of a blunted anti-inflammatory response to exhaustive exercise in fibromyalgia

Exercise intolerance, as evidenced by a worsening of pain, fatigue, and stiffness after novel exertion, is a key feature of fibromyalgia (FM). In this pilot study, we investigate whether; insufficient muscle repair processes and impaired anti-inflammatory mechanisms result in an exaggerated pro-inflammatory cytokine response to exhaustive exercise, and consequently a worsening of muscle pain, stiffness and fatigue in the days post-exercise. We measured changes in muscle pain and tenderness, fatigue, stiffness, and serum levels of neuroendocrine and inflammatory cytokine markers in 20 women with FM and 16 healthy controls (HCs) before and after exhaustive treadmill exercise. Compared to HCs, FM participants failed to mount the expected anti-inflammatory response to exercise and experienced a worsening of symptoms post-exercise. However, changes in post-exertional symptoms were not mediated by post-exertional changes in pro-inflammatory cytokine levels. Implications of these findings are discussed.