Artemin sensitizes nociceptors that innervate the osteoarthritic joint to produce pain

OBJECTIVE

There have been significant developments in understanding artemin/GFRα3 signaling in recent years, and there is now accumulating evidence that artemin has important roles to play in pain signaling, including that derived from joint and bone, and that associated with osteorthritis (OA).

METHODS

A total of 163 Sprague-Dawley rats were used in this study. We used an animal model of mono-iodoacetate (MIA)-induced OA, in combination with electrophysiology, behavioral testing, Western blot analysis, and retrograde tracing and immunohistochemistry, to identify roles for artemin/GFRα3 signaling in the pathogenesis of OA pain.

RESULTS

We have found that: 1) GFRα3 is expressed in a substantial proportion of knee joint afferent neurons; 2) exogenous artemin sensitizes knee joint afferent neurons in naïve rats; 3) artemin is expressed in articular tissues of the joint, but not surrounding bone, early in MIA-induced OA; 4) artemin expression increases in bone later in MIA-induced OA when pathology involves subchondral bone; and 5) sequestration of artemin reverses MIA-induced sensitization of both knee joint and bone afferent neurons late in disease when there is inflammation of knee joint tissues and damage to the subchondral bone.

CONCLUSIONS

Our findings show that artemin/GFRα3 signaling has a role to play in the pathogenesis of OA pain, through effects on both knee joint and bone afferent neurons, and suggest that targeted manipulation of artemin/GFRα3 signaling may provide therapeutic benefit for the management of OA pain.

DATA AVAILABILITY

Data are available on request of the corresponding author.

Changes to the activity and sensitivity of nerves innervating subchondral bone contribute to pain in late-stage osteoarthritis

ABSTRACT

Although it is clear that osteoarthritis (OA) pain involves activation and/or sensitization of nociceptors that innervate knee joint articular tissues, much less is known about the role of the innervation of surrounding bone. In this study, we used monoiodoacetate (MIA)-induced OA in male rats to test the idea that pain in OA is driven by differential contributions from nerves that innervate knee joint articular tissues vs the surrounding bone. The time-course of pain behavior was assayed using the advanced dynamic weight-bearing device, and histopathology was examined using haematoxylin and eosin histology. Extracellular electrophysiological recordings of knee joint and bone afferent neurons were made early (day 3) and late (day 28) in the pathogenesis of MIA-induced OA. We observed significant changes in the function of knee joint afferent neurons, but not bone afferent neurons, at day 3 when there was histological evidence of inflammation in the joint capsule, but no damage to the articular cartilage or subchondral bone. Changes in the function of bone afferent neurons were only observed at day 28, when there was histological evidence of damage to the articular cartilage and subchondral bone. Our findings suggest that pain early in MIA-induced OA involves activation and sensitization of nerves that innervate the joint capsule but not the underlying subchondral bone, and that pain in late MIA-induced OA involves the additional recruitment of nerves that innervate the subchondral bone. Thus, nerves that innervate bone should be considered important targets for development of mechanism-based therapies to treat pain in late OA.

Mini review: The role of sensory innervation to subchondral bone in osteoarthritis pain

Osteoarthritis pain is often thought of as a pain driven by nerves that innervate the soft tissues of the joint, but there is emerging evidence for a role for nerves that innervate the underlying bone. In this mini review we cite evidence that subchondral bone lesions are associated with pain in osteoarthritis. We explore recent studies that provide evidence that sensory neurons that innervate bone are nociceptors that signal pain and can be sensitized in osteoarthritis. Finally, we describe neuronal remodeling of sensory and sympathetic nerves in bone and discuss how these processes can contribute to osteoarthritis pain.

Thymulin treatment attenuates inflammatory pain by modulating spinal cellular and molecular signaling pathways

Thymulin is a peptide hormone which is mainly produced by thymic epithelial cells and it has immune-modulatory and anti-inflammatory effects. In this study, we investigated the effects of different doses and various timings of thymulin intraperitoneal administration on spinal microglial activity and intracellular pathways in an inflammatory rat model of Complete Freund's adjuvant (CFA). Thymulin treatment was implemented following CFA-induced inflammation for 21 days. After conducting behavioral tests (edema and hyperalgesia), the cellular and molecular aspects were examined to detect the thymulin effect on inflammatory factors and microglial activity. We demonstrated that thymulin treatment notably reduced thermal hyperalgesia and paw edema induced by CFA. Furthermore, molecular investigations showed that thymulin reduced CFA-induced activation of microglia cells, phosphorylation of p38 MAPK and the production of spinal pro-inflammatory cytokines (TNF-α, IL-6) during the study. Our results suggest that thymulin treatment attenuates CFA-induced inflammation. This effect may be mediated by inhibition of spinal microglia and production of central inflammatory mediators which seems to be associated with the ability of thymulin to reduce p38 MAPK phosphorylation. These data provide evidence of the anti-hyperalgesic effect of thymulin on inflammatory pain and characterize some of the underlying spinal mechanisms.

The Effect of Orally Administered Probiotics on the Behavioral, Cellular, and Molecular Aspects of Adjuvant-Induced Arthritis

Introduction:

Rheumatoid Arthritis (RA) is a chronic autoimmune disease, which is accompanied with pain, hyperalgesia, and edema. Overproduction of pro-inflammatory cytokines and activation of intracellular signaling pathways sustain the RA symptoms considerably. There is a strong correlation between the expression of cytokines and opioid receptors in the arthritis process. Studies have shown that probiotics via different pathways such as reducing the levels of pro-inflammatory cytokines can alleviate inflammatory symptoms. Therefore, based on the crucial role of cellular and humoral immunity in induction of RA symptoms and potency of probiotics in modulation of immune responses, the purpose of this study was to investigate the effect of orally administered probiotics on the behavioral, cellular and molecular aspects of adjuvant-induced arthritis in male Wistar rats.

Methods:

Complete Freund’s Adjuvant (CFA)-induced arthritis was caused by single subcutaneous injection of CFA into the rat’s hind paw on day 0. Different doses of probiotics (1/250, 1/500 and 1/1000 [10⁹ CFU/g]) were administered daily (gavage) after CFA injection. Hyperalgesia, edema, serum IL-1β levels, μ-Opioid Receptor (MOR) expression, and p38MAPK (Mitogen-Activated Protein Kinase) activities were assessed on days 0, 7, 14 and 21 of the study.

Results:

The results of this study indicated the efficacy of probiotics in reducing hyperalgesia, edema, serum levels of Interleukin-1β, and p38MAPK pathway activity during different phases of arthritis as well as increasing the expression of MORs during chronic phase of CFA-induced arthritis.

Conclusion:

It seems that probiotics can effectively reduce inflammatory symptoms by inhibiting the intracellular signaling pathway and cytokine production.

Long term treatment by mesenchymal stem cells conditioned medium modulates cellular, molecular and behavioral aspects of adjuvant-induced arthritis

Neuroinflammation plays a crucial role in expression of symptoms of numerous autoimmune and neurodegenerative diseases such as pain during rheumatoid arthritis. Overproduction of pro-inflammatory cytokines and activation of intracellular signaling pathways have been strongly implicated in the generation of pathological pain states, particularly at central nervous system sites and induction of spinal neuroinflammatory symptoms. The wide ranges of research to define new therapeutic approaches, including neuroimmune-modulators like stem cells are in progress. Mesenchymal stem cells conditioned medium (MSC-CM) has anti-inflammatory factors which can regulate the immune responses. The aim of this study was to investigate the effect of administration of MSC-CM on behavioral, cellular and molecular aspects of adjuvant-induced arthritis in male Wistar rats. Complete Freund's adjuvant (CFA)-induced arthritis (AA) was caused by single subcutaneous injection of CFA into the rat's hind paw on day 0. MSC-CM was administered daily (i.p.) and during the 21 days of the study after injection. Hyperalgesia, Edema, Serum TNF-α levels and p38MAPK and NF-κB activities were assessed on days 0,7,14 and 21 of the study. The results of this study indicated the role of MSC-CM in reducing inflammatory symptoms, serum TNF-α levels and activity of intracellular signaling pathway factors during different phases of inflammation caused by CFA. It seems that MSC-CM treatment due to its direct effects on inhibition of intracellular signaling pathways and pro-inflammatory cytokines can alleviate inflammatory symptoms and pain during CFA-induced arthritis.

Long-Term Treatment by Vitamin B1 and Reduction of Serum Proinflammatory Cytokines, Hyperalgesia, and Paw Edema in Adjuvant-Induced Arthritis

INTRODUCTION

Immune system is involved in the etiology and pathophysiology of inflammation and vitamins are important sources of substances inducing nonspecific immunomodulatory effects. Given the proinflammatory role of cytokines in the inflammation and pain induction, this study aimed to assess the effects of long-term administration of vitamin B₁ on the proinflammatory cytokines, edema, and hyperalgesia during the acute and chronic phases of adjuvant-induced arthritis.

METHODS

On the first day of study, inflammation was induced by intraplantar injection of complete Freund's adjuvant (CFA) in the hindpaws of rats. Vitamin B₁ at doses of 100, 150, and 200 mg/kg was administrated intraperitoneally during 21 days of the study. Antinociceptive and anti-inflammatory effects of vitamin B₁ were also compared to indomethacin (5 mg/kg). Inflammatory symptoms such as thermal hyperalgesia and paw edema were measured by radiant heat and plethysmometer, respectively. Serum TNF-α and IL-1β levels were checked by rat standard enzyme-linked immune sorbent assay (ELISA) specific kits.

RESULTS

The results indicated that vitamin B₁(150 and 200 mg/kg) attenuated the paw edema, thermal hyperalgesia, and serum levels of TNF-α and IL-1β during both phases of CFA-induced inflammation in a dose-dependent manner. Effective dose of vitamin B₁(150 mg/kg) reduced inflammatory symptoms and serum levels of TNF-α and IL-1β compare to indomethacin during the chronic phase of inflammation.

CONCLUSION

Anti-inflammatory and antihyperalgesic effects of vitamin B1 during CFA-induced arthritis, more specifically after chronic vitamin B₁ administration, suggest its therapeutic property for inflammation.