Peripheral brain-derived neurotrophic factor contributes to chronic osteoarthritis joint pain

Brain-derived neurotrophic factor contributes to activity-induced muscle pain in male but not female mice

Activity-induced muscle pain increases interleukin-1β (IL-1β) release from muscle macrophages and the development of hyperalgesia is prevented by blockade of IL-1β in muscle. Brain derived neurotrophic factor (BDNF) is released from sensory neurons in response to IL-1β and mediates both inflammatory and neuropathic pain. Thus, we hypothesize that in activity-induced pain, fatigue metabolites combined with IL-1β activate sensory neurons to increase BDNF release, peripherally in muscle and centrally in the spinal dorsal horn, to produce hyperalgesia. We tested the effect of intrathecal or intramuscular injection of BDNF-Tropomyosin receptor kinase B (TrkB) inhibitors, ANA-12 or TrkB-Fc, on development of activity-induced pain. Both inhibitors prevented the hyperalgesia when given before or 24hr after induction of the model in male but not female mice. BDNF messenger ribonucleic acid (mRNA) and protein were significantly increased in dorsal root ganglion (DRG) 24hr after induction of the model in both male and female mice. Blockade of IL-1β in muscle had no effect on the increased BNDF mRNA observed in the activity-induced pain model, while IL-1β applied to cultured DRG significantly induced BDNF expression, suggesting IL-1β is sufficient but not necessary to induce BNDF. Thus, fatigue metabolites, combined with IL-1β, upregulate BDNF in primary DRG neurons in both male and female mice, but contribute to activity-induced pain only in males.

Characterization of pain-related behaviors in a rat model of acute-to-chronic low back pain: single vs. multi-level disc injury

Introduction

Low back pain is the most common type of chronic pain. We examined pain-related behaviors across 18 weeks in rats that received injury to one or two lumbar intervertebral discs (IVD) to determine if multi-level disc injuries enhance/prolong pain.

Methods

Twenty-three Sprague-Dawley adult female rats were used: 8 received disc puncture (DP) of one lumbar IVD (L5/6, DP-1); 8 received DP of two lumbar IVDs (L4/5 & L5/6, DP-2); 8 underwent sham surgery.

Results

DP-2 rats showed local (low back) sensitivity to pressure at 6- and 12-weeks post-injury, and remote sensitivity to pressure (upper thighs) at 12- and 18-weeks and touch (hind paws) at 6, 12 and 18-weeks. DP-1 rats showed local and remote pressure sensitivity at 12-weeks only (and no tactile sensitivity), relative to Sham DP rats. Both DP groups showed reduced distance traveled during gait testing over multiple weeks, compared to pre-injury; only DP-2 rats showed reduced distance relative to Sham DP rats at 12-weeks. DP-2 rats displayed reduced positive interactions with a novel adult female rat at 3-weeks and hesitation and freezing during gait assays from 6-weeks onwards. At study end (18-weeks), radiological and histological analyses revealed reduced disc height and degeneration of punctured IVDs. Serum BDNF and TNFα levels were higher at 18-weeks in DP-2 rats, relative to Sham DP rats, and levels correlated positively with remote sensitivity in hind paws (tactile) and thighs (pressure).

Discussion

Thus, multi-level disc injuries resulted in earlier, prolonged and greater discomfort locally and remotely, than single-level disc injury. BDNF and TNFα may have contributing roles.

The Role of the Brain-Derived Neurotrophic Factor in Chronic Pain: Links to Central Sensitization and Neuroinflammation

Chronic pain is sustained, in part, through the intricate process of central sensitization (CS), marked by maladaptive neuroplasticity and neuronal hyperexcitability within central pain pathways. Accumulating evidence suggests that CS is also driven by neuroinflammation in the peripheral and central nervous system. In any chronic disease, the search for perpetuating factors is crucial in identifying therapeutic targets and developing primary preventive strategies. The brain-derived neurotrophic factor (BDNF) emerges as a critical regulator of synaptic plasticity, serving as both a neurotransmitter and neuromodulator. Mounting evidence supports BDNF's pro-nociceptive role, spanning from its pain-sensitizing capacity across multiple levels of nociceptive pathways to its intricate involvement in CS and neuroinflammation. Moreover, consistently elevated BDNF levels are observed in various chronic pain disorders. To comprehensively understand the profound impact of BDNF in chronic pain, we delve into its key characteristics, focusing on its role in underlying molecular mechanisms contributing to chronic pain. Additionally, we also explore the potential utility of BDNF as an objective biomarker for chronic pain. This discussion encompasses emerging therapeutic approaches aimed at modulating BDNF expression, offering insights into addressing the intricate complexities of chronic pain.

The modulation effects of the mind-body and physical exercises on the basolateral amygdala-temporal pole pathway on individuals with knee osteoarthritis

Background/Objective

To investigate the modulatory effects of different physical exercise modalities on connectivity of amygdala subregions and its association with pain symptoms in patients with knee osteoarthritis (KOA).

Methods

140 patients with KOA were randomly allocated either to the Tai Chi, Baduanjin, Stationary cycling, or health education group and conducted a 12 week-long intervention in one of the four groups. The behavioral, magnetic resonance imaging (MRI), and blood data were collected at baseline and the end of the study.

Results

Compared to the control group, all physical exercise modalities lead to significant increases in Knee Injury and Osteoarthritis Outcome Score (KOOS) pain score (pain relief) and serum Programmed Death-1 (PD-1) levels. Additionally, all physical exercise modalities resulted in decreased resting state functional connectivity (rsFC) of the basolateral amygdala (BA)-temporal pole and BA-medial prefrontal cortex (mPFC). The overlapping BA-temporal pole rsFC observed in both Tai Chi and Baduanjin groups was significantly associated with pain relief, while the BA-mPFC rsFC was significantly associated with PD-1 levels. In addition, we found increased fractional anisotropy (FA) values, a measurement of water diffusion anisotropy of tissue that responded to changes in brain microstructure, within the mind-body exercise groups' BA-temporal pole pathway. The average FA value of this pathway was positively correlated with KOOS pain score at baseline across all subjects.

Conclusions

Our findings suggest that physical exercise has the potential to modulate both functional and anatomical connectivity of the amygdala subregions, indicating a possible shared pathway for various physical exercise modalities.

Brain-derived neurotrophic factor contributes to activity-induced muscle pain in male but not female mice

Activity-induced muscle pain increases release of interleukin-1β (IL-1β) in muscle macrophages and the development of pain is prevented by blockade of IL-1β. Brain derived neurotrophic factor (BDNF) is released from sensory neurons in response to IL-1β and mediates both inflammatory and neuropathic pain. Thus, we hypothesized that metabolites released during fatiguing muscle contractions activate macrophages to release IL-1β, which subsequently activate sensory neurons to secrete BDNF. To test this hypothesis, we used an animal model of activity-induced pain induced by repeated intramuscular acidic saline injections combined with fatiguing muscle contractions. Intrathecal or intramuscular injection of inhibitors of BDNF-Tropomyosin receptor kinase B (TrkB) signaling, ANA-12 or TrkB-Fc, reduced the decrease in muscle withdrawal thresholds in male, but not in female, mice when given before or 24hr after, but not 1 week after induction of the model. BDNF messenger ribonucleic acid (mRNA) was significantly increased in L4-L6 dorsal root ganglion (DRG), but not the spinal dorsal horn or gastrocnemius muscle, 24hr after induction of the model in either male or female mice. No changes in TrkB mRNA or p75 neurotrophin receptor mRNA were observed. BDNF protein expression via immunohistochemistry was significantly increased in L4-L6 spinal dorsal horn and retrogradely labelled muscle afferent DRG neurons, at 24hr after induction of the model in both sexes. In cultured DRG, fatigue metabolites combined with IL-1β significantly increased BDNF expression in both sexes. In summary, fatigue metabolites release, combined with IL-1β, BDNF from primary DRG neurons and contribute to activity-induced muscle pain only in males, while there were no sex differences in the changes in expression observed in BDNF.

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.

Circulating Inflammatory Biomarkers Predict Pain Change Following Exercise-Induced Shoulder Injury: Findings From the Biopsychosocial Influence on Shoulder Pain Preclinical Trial

Shoulder pain is a highly prevalent musculoskeletal condition that frequently leads to suboptimal clinical outcomes. This study tested the extent to which circulating inflammatory biomarkers are associated with reports of shoulder pain and upper-extremity disability for a high-risk genetic by psychological subgroup (catechol-O-methyltransferase [COMT] variation by pain catastrophizing [PCS]). Pain-free adults meeting high-risk COMT × PCS subgroup criteria completed an exercise-induced muscle injury protocol. Thirteen biomarkers were collected and analyzed from plasma 48 hours after muscle injury. Shoulder pain intensity and disability (Quick-DASH) were reported at 48 and 96 hours to calculate change scores. Using an extreme sampling technique, 88 participants were included in this analysis. After controlling for age, sex, and BMI, there were moderate positive associations between higher c-reactive protein (CRP; βˆ = .62; 95% confidence interval [CI] = -.03, 1.26), interleukin-6 (IL-6; βˆ = 3.13; CI = -.11, 6.38), and interleukin-10 (IL-10; βˆ = 2.51; CI = -.30, 5.32); and greater pain reduction from 48 to 96 hours post exercise muscle injury. Using an exploratory multivariable model to predict pain changes from 48 to 96 hours, we found participants with higher IL-10 were less likely to experience a high increase in pain (βˆ = -10.77; CI = -21.25, -2.69). Study findings suggest CRP, IL-6, and IL-10 are related to shoulder pain change for a preclinical high-risk COMT × PCS subgroup. Future studies will translate to clinical shoulder pain and decipher the complex and seemingly pleiotropic interplay between inflammatory biomarkers and shoulder pain change. PERSPECTIVE: In a preclinical high-risk COMT × PCS subgroup, 3 circulating inflammatory biomarkers (CRP, IL-6, and IL-10) were moderately associated with pain improvement following exercise-induced muscle injury.

Transcranial direct current stimulation attenuates chronic pain in knee osteoarthritis by modulating BDNF/TrkB signaling in the descending pain modulation system

Knee osteoarthritis (KOA) is the most common cause of chronic pain, but its pain mechanisms are complex and may be closely related to the descending pain modulation system. Transcranial direct current stimulation (tDCS) is used for relieving pain, but its analgesic mechanisms are still being explored. The purpose of this study was to investigate the role of BDNF/TrkB signaling in chronic pain in KOA and to investigate whether this signaling is related to the analgesic effect of tDCS. Rats were injected with monosodium iodoacetate (MIA) into the left knee joint to establish a chronic pain model and then received 20 min of tDCS for 8 days. Rats were respectively administered the TrkB inhibitor ANA-12 after MIA modeling and exogenous BDNF after tDCS treatment. Behaviors testing was assessed by hot plate and von Frey hairs using the up-down method. In addition, the expression levels of BDNF and TrkB on the periaqueductal gray (PAG)-the rostral ventromedial medulla (RVM)-the spinal dorsal horn (SDH) axis were detected by Western blot and Immunohistochemistry staining. Behavioral results show that tDCS treatment and ANA-12 injection reversed MIA-induced allodynia while reducing BDNF and TrkB expression levels. Furthermore, injection of exogenous BDNF reversed the therapeutic effect of tDCS on pain. These results indicate that upregulation of the BDNF/TrkB signaling in the descending pain modulation system may play an important role in KOA-induced chronic pain in rats, and tDCS may reduce KOA-induced chronic pain by inhibiting the BDNF/TrkB signaling in the descending pain modulation system.

Biomarkers and longitudinal changes in lumbar spine degeneration and low back pain: the Johnston County Osteoarthritis Project

OBJECTIVE

To determine if baseline biomarkers are associated with longitudinal changes in the worsening of disc space narrowing (DSN), vertebral osteophytes (OST), and low back pain (LBP).

DESIGN

Paired baseline (2003-2004) and follow-up (2006-2010) lumbar spine radiographs from the Johnston County Osteoarthritis Project were graded for severity of DSN and OST. LBP severity was self-reported. Concentrations of analytes (cytokines, proteoglycans, and neuropeptides) were quantified by immunoassay. Pressure-pain threshold (PPT), a marker of sensitivity to pressure pain, was measured with a standard dolorimeter. Binary logistic regression models were used to estimate odd ratios (OR) and 95% confidence intervals (CI) of biomarker levels with DSN, OST, or LBP. Interactions were tested between biomarker levels and the number of affected lumbar spine levels or LBP.

RESULTS

We included participants (n = 723) with biospecimens, PPT, and paired lumbar spine radiographic data. Baseline Lumican, a proteoglycan reflective of extracellular matrix changes, was associated with longitudinal changes in DSN worsening (OR = 3.19 [95% CI 1.22, 8.01]). Baseline brain-derived neuropathic factor, a neuropeptide, (OR = 1.80 [95% CI 1.03, 3.16]) was associated with longitudinal changes in OST worsening, which may reflect osteoclast genesis. Baseline hyaluronic acid (OR = 1.31 [95% CI 1.01, 1.71]), indicative of systemic inflammation, and PPT (OR = 1.56 [95% CI 1.02, 2.31]) were associated with longitudinal increases in LBP severity.

CONCLUSION

These findings suggest that baseline biomarkers are associated with longitudinal changes occurring in structures of the lumbar spine (DSN vs OST). Markers of inflammation and perceived pressure pain sensitivity were associated with longitudinal worsening of LBP.

Pain Intensity and Trajectory Following Intra-Articular Injection of Mono-Iodoacetate in Experimental Osteoarthritis: A Meta-Analysis of In Vivo Studies

OBJECTIVE

Although most frequently used in experimental osteoarthritis (OA) pain induction, intra-articular mono-iodoacetate (MIA) injection lacks concluded references for dose selection and timing of intervention. Herein, we aimed to compare the pain intensity of rats induced by different doses of MIA and explored the trajectory of pain.

DESIGN

PubMed, Embase, and Web of Science were searched up to June 2021 for literatures involving MIA experiments investigating OA pain. Pain intensity was measured based on weightbearing distribution (WBD) and paw withdrawal thresholds (PWT), and the pain trajectory was constructed by evaluating pain intensity at a series of time points after MIA injection. A conventional meta-analysis was conducted.

RESULTS

A total of 140 studies were included. Compared with saline, MIA injections caused significantly higher pain intensity for WBD and PWT. Dose-response relationships between different doses of MIA and pain intensity were observed (P-for-trend<0.05). A pronounced increase in pain occurred from day 0 to day 7, but the uptrend ceased between day 7 and day 14, after which the pain intensity continued to rise and reached the maximum by day 28.

CONCLUSIONS

Pain intensity after intra-articular MIA injection increased in a dose-dependent manner and the pain trajectory manifested a specific pattern consistent with the pathological mechanisms of MIA-induced pain, providing possible clues for proper dose selection and timing of specific OA pain interventions.

Interplay between cellular changes in the knee joint, circulating lipids and pain behaviours in a slowly progressing murine model of osteoarthritis

BACKGROUND

Synovial inflammation has known contributions to chronic osteoarthritis (OA) pain, but the potential role in transitions from early to late stages of OA pain is unclear.

METHODS

The slowly progressing surgical destabilization of the medial meniscus (DMM) murine OA model and sham control, was used in male C57BL/6J mice to investigate the interplay between knee inflammation, plasma pro- and anti-inflammatory oxylipins and pain responses during OA progression. Changes in joint histology, macrophage infiltration, chemokine receptor CX3CR1 expression, weight bearing asymmetry, and paw withdrawal thresholds were quantified 4, 8 and 16 weeks after surgery. Plasma levels of multiple bioactive lipid mediators were quantified using liquid chromatography with tandem mass-spectrometry (LC-MS/MS).

RESULTS

Structural joint damage was evident at 8 weeks post-DMM surgery onwards. At 16 weeks post-DMM surgery, synovial scores, numbers of CD68 and CD206 positive macrophages and pain responses were significantly increased. Plasma levels of oxylipins were negatively correlated with joint damage and synovitis scores at 4 and 8 weeks post-DMM surgery. Higher circulating levels of the pro-resolving oxylipin pre-cursor 17-HDHA were associated with lower weight bearing asymmetry at week 16.

CONCLUSIONS

The transition to chronic OA pathology and pain is likely influenced by both joint inflammation and plasma oxylipin mediators of inflammation and levels of pro-resolution molecules.

SIGNIFICANCE

Using a slow progressing surgical model of osteoarthritis we show how the changing balance between local and systemic inflammation may be of importance in the progression of pain behaviours during the transition to chronic osteoarthritis pain.

Biological Targets of Multimolecular Therapies in Middle-Age Osteoarthritis

Knee osteoarthritis (OA) is a common condition, prevalent in middle-agedness, associated with chronic pain and impaired quality of life. Two interrelated biological processes fuel early OA progression: inflammation and structural tissues catabolism. Procatabolic and proinflammatory mediators are interconnected and form part of a self-perpetuating loop. They leverage OA research complexity because of the impossibility to discern certain spatiotemporal tissues' changes from others. Both are shared targets of versatile regenerative multimolecular therapies. In particular, platelet-rich plasma can interfere with inflammation and inflammatory pain. The therapeutic approach is to alter the vicious inflammatory loop by modifying the molecular composition of the synovial fluid, thereby paracrine cellular cross talk. Intra-articular injections of platelet-rich plasma can provide key factors balancing proinflammatory and anti-inflammatory factors, targeting macrophage dysfunction and modulating immune mechanisms within the knee.

Experimental models to study osteoarthritis pain and develop therapeutics

Pain is the predominant symptom of osteoarthritis (OA) that drives patients to seek medical care. Currently, there are no pharmacological treatments that can reverse or halt the progression of OA. Safe and efficacious medications for long-term management of OA pain are also unavailable. Understanding the mechanisms behind OA pain generation at onset and over time is critical for developing effective treatments. In this narrative review, we first summarize our current knowledge on the innervation of the knee joint, and then discuss the molecular mechanism(s) currently thought to underlie OA pain. In particular, we focus on the contribution of each joint component to the generation of pain. Next, the current experimental models for studying OA pain are summarized, and the methods to assess pain in rodents are presented. The potential application of emerging microphysiological systems in OA pain research is especially highlighted. Lastly, we discuss the current challenge in standardizing models and the selection of appropriate systems to address specific questions.

Neurogenic inflammation as a novel treatment target for chronic pain syndromes

Chronic pain syndrome is a heterogeneous group of diseases characterized by several pathological mechanisms. One in five adults in Europe may experience chronic pain. In addition to the individual burden, chronic pain has a significant societal impact because of work and school absences, loss of work, early retirement, and high social and healthcare costs. Several anti-inflammatory treatments are available for patients with inflammatory or autoimmune diseases to control their symptoms, including pain. However, patients with degenerative chronic pain conditions, some with 10-fold or more elevated incidence relative to these manageable diseases, have few long-term pharmacological treatment options, limited mainly to non-steroidal anti-inflammatory drugs or opioids. For this review, we performed multiple PubMed searches using keywords such as "pain," "neurogenic inflammation," "NGF," "substance P," "nociception," "BDNF," "inflammation," "CGRP," "osteoarthritis," and "migraine." Many treatments, most with limited scientific evidence of efficacy, are available for the management of chronic pain through a trial-and-error approach. Although basic science and pre-clinical pain research have elucidated many biomolecular mechanisms of pain and identified promising novel targets, little of this work has translated into better clinical management of these conditions. This state-of-the-art review summarizes concepts of chronic pain syndromes and describes potential novel treatment strategies.

Cell-free fat extract attenuates osteoarthritis via chondrocytes regeneration and macrophages immunomodulation

Background

The prevalence of osteoarthritis (OA) is increasing, yet clinically effective and economical treatments are unavailable. We have previously proposed a cell-free fat extract (CEFFE) containing multiple cytokines, which possessed antiapoptotic, anti-oxidative, and proliferation promotion functions, as a “cell-free” strategy. In this study, we aimed to evaluate the therapeutic effect of CEFFE in vivo and in vitro.

Methods

In vivo study, sodium iodoacetate-induced OA rats were treated with CEFFE by intra-articular injections for 8 weeks. Behavioral experiments were performed every two weeks. Histological analyses, anti-type II collagen, and toluidine staining provided structural evaluation. Macrophage infiltration was assessed by anti-CD68 and anti-CD206 staining. In vitro study, the effect of CEFFE on macrophage polarization and secretory factors was evaluated by flow cytometry, immunofluorescence, and quantitative reverse-transcription polymerase chain reaction (qRT-PCR). The effect of CEFFE on cartilage regeneration was accessed by cell counting kit-8 assay and qRT-PCR. The generation of reactive oxygen species (ROS) and levels of ROS-related enzymes were investigated by qRT-PCR and western blotting.

Results

In rat models with sodium iodoacetate (MIA)-induced OA, CEFFE increased claw retraction pressure while decreasing bipedal pressure in a dose-dependent manner. Moreover, CEFFE promoted cartilage structure restoration and increased the proportion of CD206⁺ macrophages in the synovium. In vitro, CEFFE decreased the proportion of CD86⁺ cells and reduced the expression of pro-inflammatory factors in LPS + IFN-γ induced Raw 264.7. In addition, CEFFE decreased the expression of interleukin-6 and ADAMTs-5 and promoted the expression of SOX-9 in mouse primary chondrocytes. Besides, CEFFE reduced the intracellular levels of reactive oxygen species in both in vitro models through regulating ROS-related enzymes.

Conclusions

CEFFE inhibits the progression of OA by promoting cartilage regeneration and limiting low-grade joint inflammation.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02813-3.

BDNF and TrKB expression levels in patients with endometriosis and their associations with dysmenorrhoea

BACKGROUND

Brain-derived neurotrophic factor (BDNF) is a known regulator of the development and maintenance of chronic pain in various chronic disorders. Together with its high-affinity tyrosine kinase type B (TrKB) receptor, BDNF is extensively expressed in the mammalian female reproductive system. However, BDNF and TrKB expression in different stages of endometriosis and the relationship between the expression of each in ectopic lesions and endometriosis pain remain unclear.

METHODS

Sixty-two women who underwent laparoscopic surgery were enrolled in this study: forty-six diagnosed with ovarian endometrioma (study group) and sixteen diagnosed with ovarian benign tumours (control group). Samples from eutopic endometrium and ovarian endometriotic lesions were obtained at laparoscopic surgery. BDNF and TrKB messenger RNA (mRNA) and proteins levels in the eutopic and ectopic endometrium of both groups were measured by real-time PCR and immunohistochemical staining, respectively. Before the surgery the visual analogue scale (VAS) was used to measure dysmenorrhoea.

RESULTS

BDNF and TrKB expression levels were higher in ovarian endometriotic lesions than in eutopic endometrium and normal endometrium (P < 0.05), and there was no cyclical change. Furthermore, their expression levels were higher in eutopic endometrium than in normal endometrium (P < 0.05), and BDNF and TrKB levels were higher in stage IV ovarian endometriotic lesions than in stage II and III lesions (P < 0.05), with their expression being non-significantly higher in stage III than in stage II (P > 0.05). Additionally, correlation coefficients for the association analysis between the mRNA expression of BDNF or TrKB in eutopic endometrium and the dysmenorrhoea VAS score were r = 0.52 and r = 0.56 for BDNF and TrKB, respectively (P < 0.05). The correlation coefficients for the associations between BDNF and TrKB in both the eutopic and ectopic endometrium were r = 0.82 and r = 0.66, respectively (P < 0.05).

CONCLUSIONS

BDNF and TrKB are closely related to dysmenorrhoea caused by endometriosis and may be important in the pathobiology or pathophysiology of endometriosis.

Oral squamous cell carcinoma-released brain-derived neurotrophic factor contributes to oral cancer pain by peripheral tropomyosin receptor kinase B activation

ABSTRACT

Oral cancer pain is debilitating and understanding mechanisms for it is critical to develop novel treatment strategies treatment strategies. Brain-derived neurotrophic factor (BDNF) signaling is elevated in oral tumor biopsies and is involved with tumor progression. Whether BDNF signaling in oral tumors contributes to cancer-induced pain is not known. The current study evaluates a novel peripheral role of BDNF-tropomyosin receptor kinase B (TrkB) signaling in oral cancer pain. Using human oral squamous cell carcinoma (OSCC) cells and an orthotopic mouse tongue cancer pain model, we found that BDNF levels were upregulated in superfusates and lysates of tumor tongues and that BDNF was expressed by OSCC cells themselves. Moreover, neutralization of BDNF or inhibition of TrkB activity by ANA12, within the tumor-bearing tongue reversed tumor-induced pain-like behaviors in a sex-dependent manner. Oral squamous cell carcinoma conditioned media also produced pain-like behaviors in naïve male mice that was reversed by local injection of ANA12. On a physiological level, using single-fiber tongue-nerve electrophysiology, we found that acutely blocking TrkB receptors reversed tumor-induced mechanical sensitivity of A-slow high threshold mechanoreceptors. Furthermore, single-cell reverse transcription polymerase chain reaction data of retrogradely labeled lingual neurons demonstrated expression of full-form TrkB and truncated TrkB in distinct neuronal subtypes. Last but not the least, intra-TG siRNA for TrkB also reversed tumor-induced orofacial pain behaviors. Our data suggest that TrkB activities on lingual sensory afferents are partly controlled by local release of OSCC-derived BDNF, thereby contributing to oral cancer pain. This is a novel finding and the first demonstration of a peripheral role for BDNF signaling in oral cancer pain.

Potential value of serum brain-derived neurotrophic factor, vascular endothelial growth factor, and S100B for identifying major depressive disorder in knee osteoarthritis patients

BACKGROUND

The chronic pain and functional limitations in osteoarthritis (OA) patients can increase risk of psychiatric disorders, e.g., major depression disorder (MDD), which may further aggravate the clinical symptoms of OA. Early detection of MDD is essential in the clinical practice of OA.

MATERIALS AND METHODS

Two hundred and fifteen participants with knee OA were recruited, including 134 MDD patients (i.e., MDD group) and 81 ones without MDD (i.e., control group). Among them, 81 OA participants in the control group received a 3-year follow-up and were divided into trans-MDD group (who transforming into MDD; N = 39) and non-MDD group (who keeping non-MDD; N = 42) at the end of the follow-up. The 17-item Hamilton Depression Scale (HAMD-17), Self-Rating Depression Scale (SDS), and Visual Analogue Scale (VAS) were performed. Furthermore, serum levels of brain-derived neurotrophic factor (BDNF), vascular endothelial growth factor (VEGF), S100B, and IGF-1 were detected.

RESULTS

(1) Compared with OA participants without MDD, there were significant decrease in serum BDNF and significant increase in serum VEGF and S100B and VAS scores in OA participants with MDD. (2) A mediation of the association was found between the VAS scores and the HAMD-17 scores through the BDNF as mediator in OA participants with MDD. (3) Significantly lower baseline BDNF levels and higher baseline S100B levels were detected in OA participants who transforming to MDD after a 3-year follow-up when compared with those who keeping non-MDD. (4) In the trans-MDD group, significant associations of the change of serum BDNF levels with rate of change of HAMD-17 scores were found, and baseline serum S100B levels positively correlated with the HAMD-17 scores at the end of the follow-up. (5) In OA participants, the composite indicator of BDNF, VEGF, and S100B differentiated MDD patients from controls with the area under the curve (AUC) value of 0.806, and the combined indicator of baseline BDNF and S100B distinguished trans-MDD participants from non-MDD ones with an AUC value of 0.806.

CONCLUSION

Serum BDNF, VEGF, and S100B may be potential biomarkers to identify MDD in OA patients. Meanwhile, serum BDNF and S100B shows great potential to predict the risk of MDD for OA.

Nanostring technology on Fibrous Dysplasia bone biopsies. A pilot study suggesting different histology-related molecular profiles

Identifying the molecular networks that underlie Fibrous Dysplasia (FD) is key to understand the pathogenesis of the disease, to refine current diagnostic approaches and to develop efficacious therapies. In this study, we used the NanoString nCounter Analysis System to investigate the gene signature of a series of nine Formalin Fixed Decalcified and Paraffin-Embedded (FFDPE) bone biopsies from seven FD patients.

We analyzed the expression level of 770 genes. Unsupervised clustering analysis demonstrated partitioning into two clusters with distinct patterns of gene expression. Differentially expressed genes included growth factors, components of the Wnt signaling system, interleukins and some of their cognate receptors, ephrin ligands, matrix metalloproteinases, neurotrophins and genes encoding components of the cAMP-dependent protein kinase. Interestingly, two tissue samples obtained from the same skeletal site of one patient one year apart failed to segregate in the same cluster. Retrospective histological review of the samples revealed different microscopic aspects in the two groups.

The results of our pilot study suggest that the genetic signature of FD is heterogeneous and varies according to the histology and, likely, to the age of the lesion. In addition, they show that the Nanostring technology is a valuable tool for molecular translational studies on archival FFDPE material in FD and other rare bone diseases.

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We used the NanoString technology to analyze Formalin Fixed Decalcified Paraffin Embedded (FFDPE) Fibrous Dysplasia samples.

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We show that Fibrous Dysplasia lesions may have different molecular profiles consistent with its histological heterogeneity.

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NanoString technology is a valuable tool for molecular studies on rare bone diseases by using FFDPE archival material.

NEAT1/miR-146a-3p/TrkB/ShcB axis regulates the development and function of chondrocyte

The current study aimed to explored the regulatory effect of Tropomyosin-related kinases B (TrkB) in the development and function of chondrocyte. Correlation between clinicopathological characteristics and osteoarthritis (OA) were analyzed. The expressions of TrkA, brain-derived neurotrophic factor (BDNF), TrkB, Src homolog and collagen homolog B (ShcB), and ShcC in OA cartilage tissue and IL-1β-stimulated chondrocytes from normal cartilage were determined by Western blot/qRT-PCR. After manipulating the expressions of TrkA, shTrkB, ShcB, miR-146a-3p and nuclear paraspeckle assembly transcript 1 (NEAT1), the differentiation-related molecules, and apoptosis-related molecules were examined by Western blot/qRT-PCR, and migration, invasion, proliferation, tube formation, and apoptosis rate in IL-1β-stimulated chondrocyte were examined by scratch, Transwell, colony formation, and tube formation, and flow cytometry assays, respectively. Bioinformatics, dual-luciferase and Spearman were used to analyze the binding and correlation of target genes. The findings showed that OA was related to body mass Index (BMI). The expressions of TrkA, TrkB and ShcB and NEAT1 were up-regulated in OA and IL-1β-stimulated chondrocytes, while miR-146a-3p was donwnregulated and was negatively correlated with TrkB or NEAT1. NEAT1 competed with TrkB in chondrocytes for miR-146a-3p binding. ShTrkB reversed the decrease in expressions of differentiation-related molecules, migration, invasion and proliferation, and the increase in ShcB expression and tube formation, of IL-1β-stimulated chondrocytes. Overexpressed ShcB reversed effect of shTrkB on the functions of IL-1β-stimulated chondrocytes. MiR-146a-3p inhibitor reversed effects of shTrkB on the function and apoptosis-related molecules on IL-1β-stimulated chondrocytes, while NEAT1 reversed role of miR-146a-3p. This paper demonstrated that NEAT1/miR-146a-3p/TrkB/ShcB axis regulates the development and function of chondrocyte.

Efficacy of Methotrexate on Rat Knee Osteoarthritis Induced by Monosodium Iodoacetate

Objective

To explore whether methotrexate (MTX) prevents joint destruction and improves pain-related behaviors in the acute phase of knee osteoarthritis (OA) induced by monosodium iodoacetate (MIA) in a rat model.

Methods

Twenty of 25 male Wistar rats (10–14 weeks old) received 3 mg MIA via intra-articular injection into their right knee and were then administered a vehicle control (n=10) or 3 mg/kg MTX orally weekly (n=10). We assessed differences in pain-related behavior, spontaneous lifting behavior, micro-computed tomography (CT), histopathology, and expression of pain- and inflammatory-related genes using reverse transcription-quantitative polymerase chain reaction (RT-qPCR) between the two groups for 4 weeks. Five rats were used as untreated controls to assess pain- and inflammatory-related mRNA expression in the dorsal root ganglia (DRG) and knee joints using RT-qPCR.

Results

Joint destruction and mechanical hyperalgesia were observed in the vehicle group. Decreases in mechanical pain thresholds for the knee joint and calf muscles were improved after MTX administration; however, joint damage assessed by micro-CT and histopathology was not significantly inhibited by MTX administration, while upregulation levels of transient receptor potential cation channel, subfamily V, member 1 (TRPV-1) (P<0.01) and brain-derived neurotrophic factor (BDNF) (P=0.02) mRNA in the DRG and nerve growth factor NGF mRNA (P=0.03) in the affected knee joints were significantly suppressed in the MTX group compared with the vehicle group at week 4.

Conclusion

Our results imply that MTX administration improves pain-related behaviors and suppresses expression of pain-related mRNAs in the DRG and knee joint; however, MTX is not expected to prevent cartilage degeneration in MIA-induced OA in rat knee.

Peripheral pain mechanisms in osteoarthritis

There is a well-established historical observation that structural joint damage by plain X-ray correlates poorly with symptomatic disease in osteoarthritis (OA). This is often attributed to the inability to visualise soft-tissue pathology within the joint and the recognition of heterogeneous patient factors that drive central pain sensitisation. A major issue is the relative paucity of mechanistic studies in which molecular pathogenesis of pain is interrogated in relation to tissue pathology. Nonetheless, in recent years, three broad approaches have been deployed to attempt to address this: correlative clinical studies of peripheral and central pain outcomes using magnetic resonance imaging, where soft-tissue processes can be visualised; molecular studies on tissue from patients with OA; and careful molecular interrogation of preclinical models of OA across the disease time course. Studies have taken advantage of established clinical molecular targets such as nerve growth factor. Not only is the regulation of nerve growth factor within the joint being used to explore the relationship between tissue pathology and the origins of pain in OA, but it also provides a core model on which other molecules present within the joint can modulate the pain response. In this narrative review, how molecular and pathological tissue change relates to joint pain in OA will be discussed. Finally, a model for how tissue damage may lead to pain over the disease course will be proposed.

Update on pain in arthritis

PURPOSE OF REVIEW

Osteoarthritis is a degenerative joint disease that features pain as a hallmark symptom. This review summarises progress and obstacles in our understanding of pain mechanisms in arthritis.

RECENT FINDINGS

Pain phenotypes in osteoarthritis are poorly characterized in clinical studies and animal studies are largely carti-centric. Different animal models incur variable disease progression patterns and activation of distinct pain pathways, but studies reporting both structural and pain outcomes permit better translational insights. In patients, classification of osteoarthritis disease severity is only based on structural integrity of the joint, but pain outcomes do not consistently correlate with joint damage. The complexity of this relationship underlines the need for pain detection in criteria for osteoarthritis classification and patient-reported outcome measures.

SUMMARY

Variable inflammatory and neuropathic components and spatiotemporal evolution underlie the heterogeneity of osteoarthritis pain phenotypes, which must be considered to adequately stratify patients. Revised classification of osteoarthritis at different stages encompassing both structural and pain outcomes would significantly improve detection and diagnosis at both early and late stages of disease. These are necessary advancements in the field that would also improve trial design and provide better understanding of basic mechanisms of disease progression and pain in osteoarthritis.

Brain-Derived Neurotrophic Factor and Immune Cells in Osteoarthritis, Chronic Low Back Pain, and Chronic Widespread Pain Patients: Association with Anxiety and Depression

Background and Objectives: Musculoskeletal dysfunction can induce several types of chronic pain syndromes. It is of particular interest to elucidate the pathomechanism of different forms of chronic pain. It is possible that patients who have developed chronic widespread pain (CWP) may endure different pathomechanisms as compared to those who suffer from local pain (osteoarthritis, OA) and regional pain (chronic low back pain, cLBP), especially with regard to pain regulation and its related biomediators. The aim of this study was to determine the differences in pathomechanisms among these patients by measuring pain-related biomediators, particularly brain-derived neurotrophic factor (BDNF). Additionally, subpopulations of immune cells were determined in parallel. Materials and Methods: Patients and healthy subjects (HSs) were recruited (age and gender-matched). BDNF was measured from serum samples of patients and HSs and the data of body composition parameters were recorded. Additionally, both patients and HSs were asked to fill in questionnaires related to pain intensity, anxiety, and depression. Results: Our results highlight that the levels of both free and total BDNF are significantly lower in pain patients compared to HSs, with p values of 0.041 and 0.024, respectively. The number of CD3- CD56bright natural killer (NK) cells shows significant differences between the groups. Comparing all chronic pain patients with HSs reveals a significantly lower number of CD4+ CD8+ T cells (p = 0.031), CD3- CD56bright NK cells (p = 0.049) and CD20+ CD3- cells (p = 0.007). Conclusions: To conclude, it seems that a general conformity between the pathomechanisms of different chronic pain diseases exists, although there are unique findings only in specific chronic pain patients.

Serum brain-derived neurotrophic factor levels in patients with diabetic neuropathic pain

OBJECTIVE

Diabetic neuropathic pain (DNP) is one of the most common and severe complications in patients with diabetes. This study aimed to investigate serum brain-derived neurotrophic factor (BDNF) levels in patients with DNP and to evaluate the association between BDNF and disease severity.

METHODS

A total of 143 T2DM patients were included, according to clinical characteristics and douleur neuropathique 4 (DN4) questionnaire are divided into the DNP group (n = 78) and without the DNP group (n = 65). BDNF levels were measured by an enzyme-linked immunosorbent assay. Additionally, other biochemical characteristics were measured using routine laboratory methods.

RESULTS

Serum levels of BDNF was increased significantly in the DNP group compared to without DNP group. Meanwhile, a binary logistic regression model identified as revealed BDNF (OR = 1.178, 95 %CI = 1.064-1.305,p = 0.002) was a risk factor in T2DM patients. Furthermore, the serum BDNF levels positively correlated with VAS score in the DNP patients.

CONCLUSIONS

Serum BDNF was elevated in DNP patients and increased gradually with the VAS score. BDNF was identified as risk factors for pain in all T2DM patients.

Targeting neurotrophic factors: Novel approaches to musculoskeletal pain

Chronic pain represents a substantial unmet medical need globally. In recent years, the quest for a new generation of novel, safe, mechanism-based analgesic treatments has focused on neurotrophic factors, a large group of secreted proteins that control the growth and survival of different populations of neurons, but that postnatally are involved in the genesis and maintenance of pain, with biological activity in both the periphery and the central nervous system. In this narrative review, we discuss the two families of neurotrophic proteins that have been extensively studied for their role in pain: first, the neurotrophins, nerve growth factor (NGF) and brain-derived growth factor (BDNF), and secondly, the GDNF family of ligands (GFLs). We provide an overview of the pain pathway, and the pain-producing effects of these different proteins. We summarize accumulating preclinical and clinical findings with a focus on musculoskeletal pain, and on osteoarthritis in particular, because the musculoskeletal system is the most prevalent source of chronic pain and of disability, and clinical testing of these novel agents - often biologics- is most advanced in this area.