Voluntary exercise blocks ongoing pain and diminishes bone remodeling while sparing protective mechanical pain in a rat model of advanced osteoarthritis pain

Environmental enrichment for neuropathic pain via modulation of neuroinflammation

Neuropathic pain causes tremendous biological and psychological suffering to patients worldwide. Environmental enrichment (EE) is a promising non-pharmacological strategy with high cost-effectiveness to reduce neuropathic pain and support rehabilitation therapy. Three researchers reviewed previous studies to determine the efficacy of EE for neuropathic pain to research how EE improves neuropathic pain through neuroinflammation. For this review, Embase, PubMed, and Cochran were searched. Three authors did study selection and data extraction. Out of 74 papers, 7 studies met the inclusion criteria. In the chronic constriction injury rats with acute or chronic detrimental stimulation, the change of pain behavior was influenced by environmental settings like start time, and cage size. Besides, physical EE has a larger effect than socially EE in inflammatory pain. These articles suggest employing various EE to regulate the release of pain-causing substances and changes in ion channels in the peripheral and central nerves to improve neuropathic pain behavior and depression and anxiety conditions. The existing proof provides important knowledge for upcoming preclinical investigations and the practical use of EE in clinical pain treatment. This analysis aids in the advancement of improved approaches for managing chronic pain, with a focus on internal mechanisms for controlling pain.

Reversing Microglial Polarisation by High Intensity Interval Training: A Novel Approach to Mitigate Inflammatory Responses in Osteoarthritis via Jak2/Stat3 Pathway

Osteoarthritis (OA) is associated with inflammatory responses linked to microglial polarisation within the central nervous system. However, exploring therapeutic approaches and their underlying mechanisms remains a direction for future research. The present study investigates the potential of high-intensity interval training (HIIT) to alleviate inflammation and facilitate the shift from M1 to M2 microglial polarisation via the Jak2/Stat3 pathway in an OA rat model. Wistar rats were induced with OA via intra-articular injection of monosodium iodoacetate and subsequently underwent HIIT for six consecutive weeks after a 4-week establishment period. Pain thresholds were measured using the von Frey test. Immunofluorescence detected Tmem119, SP, Glu, c-Fos, and IL-6, while flow cytometry analysed CD68 and CD163 levels. Proteomics compared the protein differences between the OA and HIIT groups. The Jak2/Stat3 pathway was activated in OA rats with C-A1 injections, followed by HIIT and subsequent Western blot analysis of inflammatory cytokines. The results indicated a significant decrease in pain threshold from the third to the tenth week in OA rats, while HIIT was found to increase pain thresholds. HIIT was found to promote M1 to M2 microglial polarisation and downregulate the expression of Tmem119, SP, Glu, c-Fos, and IL-6. Additionally, HIIT was more effective in suppressing Jak2 and Stat3 expression levels compared to OA rats. Activation of the Jak2/Stat3 pathway significantly increased the expression of Glu, c-fos, SP, and IL-6, but HIIT reversed these OA-induced increases. Compared to the OA + C-A1 group, the expression levels of Glu, c-fos, SP, and IL-6 were significantly reduced in the OA + C-A1 + HIIT group. In conclusion, HIIT effectively mitigates OA-induced inflammatory responses by reversing microglial polarisation through the Jak2/Stat3 pathway.

Sustained therapeutic effects of self-assembled hyaluronic acid nanoparticles loaded with α-Ketoglutarate in various osteoarthritis stages

Osteoarthritis (OA) is a prevalent degenerative disease characterized by irreversible destruction of articular cartilage, for which no current drugs are known to modify its progression. While intra-articular (IA) injections of hyaluronic acid (HA) offer temporary relief, their effectiveness and long-term benefits are debated. Alpha-ketoglutarate (αKG) has potential chondroprotective properties, but its use is limited by a short half-life and poor cartilage-targeting efficiency. Here, we developed self-assembled HA-αKG nanoparticles (NPs) to combine the benefits of both HA and αKG, showing stability, bioavailability, and sustained pH-responsive release in the knee joint. In both early and advanced OA stages in mice, HA, αKG, and HA-αKG NPs could relieve pain, enhance mobility, and reduce cartilage damage, with HA-αKG NPs demonstrating the best efficacy. Mechanistically, αKG not only promotes cartilage matrix synthesis but also inhibits degradation by activating the PERK-ATF4 signaling pathway to reduce endoplasmic reticulum stress (ERS) in chondrocytes. This study highlights the therapeutic potential of HA-αKG NPs for treating various OA stages, with efficient and sustained effects, suggesting rapid clinical adoption and high acceptability among clinicians and patients.

Wheel Running Exacerbates Joint Damage after Meniscal Injury in Mice, but Does Not Alter Gait or Physical Activity Levels

PURPOSE

Exercise and physical activity are recommended to reduce pain and improve joint function in patients with knee osteoarthritis (OA). However, exercise has dose effects, with excessive exercise accelerating OA development and sedentary behaviors also promoting OA development. Prior work evaluating exercise in preclinical models has typically used prescribed exercise regimens; however, in-cage voluntary wheel running creates opportunities to evaluate how OA progression affects self-selected physical activity levels. This study aimed to evaluate how voluntary wheel running after a surgically induced meniscal injury affects gait characteristics and joint remodeling in C57Bl/6 mice. We hypothesize that injured mice will reduce physical activity levels as OA develops after meniscal injury and will engage in wheel running to a lesser extent than the uninjured animals.

METHODS

Seventy-two C57Bl/6 mice were divided into experimental groups based on sex, lifestyle (physically active vs sedentary), and surgery (meniscal injury or sham control). Voluntary wheel running data were continuously collected throughout the study, and gait data were collected at 3, 7, 11, and 15 wk after surgery. At end point, joints were processed for histology to assess cartilage damage.

RESULTS

After meniscal injury, physically active mice showed more severe joint damage relative to sedentary mice. Nevertheless, injured mice engaged in voluntary wheel running at the same rates and distances as mice with sham surgery. In addition, physically active mice and sedentary mice both developed a limp as meniscal injury progressed, yet exercise did not further exacerbate gait changes in the physically active mice, despite worsened joint damage.

CONCLUSIONS

Taken together, these data indicate a discordance between structural joint damage and joint function. Although wheel running after meniscal injury did worsen OA-related joint damage, physical activity did not necessarily inhibit or worsen OA-related joint dysfunction or pain in mice.

Therapeutic exercise interventions in rat models of arthritis

Arthritis is the leading cause of musculoskeletal pain and disability worldwide. Nearly 50% of individuals over the age of 65 have arthritis, which contributes to limited function, articular pain, physical inactivity, and diminished quality of life. Therapeutic exercise is often recommended in clinical settings for patients experiencing arthritic pain, however, there is little practical guidance regarding the use of therapeutic exercise to alleviate arthritic musculoskeletal pain. Rodent models of arthritis allow researchers to control experimental variables, which cannot be done with human participants, providing an opportunity to test therapeutic approaches in preclinical models. This literature review provides a summary of published findings in therapeutic exercise interventions in rat models of arthritis as well as gaps in the existing literature. We reveal that preclinical research in this field has yet to adequately investigate the impact of experimental variables in therapeutic exercise including their modality, intensity, duration, and frequency on joint pathophysiology and pain outcomes.

Modelling skeletal pain harnessing tissue engineering

Bone pain typically occurs immediately following skeletal damage with mechanical distortion or rupture of nociceptive fibres. The pain mechanism is also associated with chronic pain conditions where the healing process is impaired. Any load impacting on the area of the fractured bone will stimulate the nociceptive response, necessitating rapid clinical intervention to relieve pain associated with the bone damage and appropriate mitigation of any processes involved with the loss of bone mass, muscle, and mobility and to prevent death. The following review has examined the mechanisms of pain associated with trauma or cancer-related skeletal damage focusing on new approaches for the development of innovative therapeutic interventions. In particular, the review highlights tissue engineering approaches that offer considerable promise in the application of functional biomimetic fabrication of bone and nerve tissues. The strategic combination of bone and nerve tissue engineered models provides significant potential to develop a new class of in vitro platforms, capable of replacing in vivo models and testing the safety and efficacy of novel drug treatments aimed at the resolution of bone-associated pain. To date, the field of bone pain research has centred on animal models, with a paucity of data correlating to the human physiological response. This review explores the evident gap in pain drug development research and suggests a step change in approach to harness tissue engineering technologies to recapitulate the complex pathophysiological environment of the damaged bone tissue enabling evaluation of the associated pain-mimicking mechanism with significant therapeutic potential therein for improved patient quality of life.

Graphical abstract

Rationale underlying novel drug testing platform development. Pain detected by the central nervous system and following bone fracture cannot be treated or exclusively alleviated using standardised methods. The pain mechanism and specificity/efficacy of pain reduction drugs remain poorly understood. In vivo and ex vivo models are not yet able to recapitulate the various pain events associated with skeletal damage. In vitro models are currently limited by their inability to fully mimic the complex physiological mechanisms at play between nervous and skeletal tissue and any disruption in pathological states. Robust innovative tissue engineering models are needed to better understand pain events and to investigate therapeutic regimes.