Injury of primary afferent neurons may contribute to osteoarthritis induced pain: an experimental study using the collagenase model in rats

Mechanical hyperalgesia and neuropathic pain qualities impart risk for chronic postoperative pain after total knee replacement

Total knee replacement (TKR) is the gold-standard treatment for end-stage chronic osteoarthritis pain, yet many patients report chronic postoperative pain after TKR. The search for preoperative predictors for chronic postoperative pain following TKR has been studied with inconsistent findings. This study investigates the predictive value of quantitative sensory testing (QST) and PainDETECT for postoperative pain 3, 6, and 12 months post-TKR. We assessed baseline and postoperative (3- and 6-months) QST measures in 77 patients with knee OA (KOA) and 41 healthy controls, along with neuropathic pain scores in patients (PainDETECT). QST parameters included pressure pain pressure threshold (PPT), pain tolerance threshold (PTT), conditioned pain modulation (CPM), and temporal summation (TS) using cuff algometry, alongside mechanical hyperalgesia, and mechanical temporal summation to repeated pinprick stimulation. Compared to healthy controls, KOA patients at baseline demonstrated hyperalgesia to pinprick stimulation at the medial OA-affected knee and cuff pressure on the ipsilateral calf. Lower cuff algometry PTT and mechanical pinprick hyperalgesia were associated with baseline KOA pain intensity. Moreover, baseline pinprick pain hyperalgesia explained 25% of variance in pain intensity 12 months post-TKR and preoperative neuropathic pain scores also captured 30% and 20% of the variance in postoperative pain at 6- and 12-months, respectively. A decrease in mechanical pinprick hyperalgesia from before surgery to 3 months after TKR was associated with lower postoperative pain at the 12 months post-TKR follow-up, and vice-versa. Our findings suggest that preoperative pinprick hyperalgesia and PainDETECT neuropathic-like pain symptoms show predictive value for the development of chronic post-TKR pain.

Translational evaluation of gait behavior in rodent models of arthritic disorders with the CatWalk device - a narrative review

Arthritic disorders have become one of the main contributors to the global burden of disease. Today, they are one of the leading causes of chronic pain and disability worldwide. Current therapies are incapable of treating pain sufficiently and preventing disease progression. The lack of understanding basic mechanisms underlying the initiation, maintenance and progression of arthritic disorders and related symptoms represent the major obstacle in the search for adequate treatments. For a long time, histological evaluation of joint pathology was the predominant outcome parameter in preclinical arthritis models. Nevertheless, quantification of pain and functional limitations analogs to arthritis related symptoms in humans is essential to enable bench to bedside translation and to evaluate the effectiveness of new treatment strategies. As the experience of pain and functional deficits are often associated with altered gait behavior, in the last decades, automated gait analysis has become a well-established tool for the quantitative evaluation of the sequalae of arthritic disorders in animal models. The purpose of this review is to provide a detailed overview on the current literature on the use of the CatWalk gait analysis system in rodent models of arthritic disorders, e.g., Osteoarthritis, Monoarthritis and Rheumatoid Arthritis. Special focus is put on the assessment and monitoring of pain-related behavior during the course of the disease. The capability of evaluating the effect of distinct treatment strategies and the future potential for the application of the CatWalk in rodent models of arthritic disorders is also addressed in this review. Finally, we discuss important consideration and provide recommendations on the use of the CatWalk in preclinical models of arthritic diseases.

Early pain in females is linked to late pathological features in murine experimental osteoarthritis

Background

Osteoarthritis (OA) is a progressive joint disease and a major cause of chronic pain in adults. The prevalence of OA is higher in female patients, who tend to have worse OA outcomes, partially due to pain. The association between joint pain and OA pathology is often inconclusive. Preclinical research studies have largely overlooked sex as a potential determinant in joint pain during OA. This study aimed to investigate the role of sex in joint pain in the collagenase-induced OA (CiOA) model and its link with joint pathology.

Methods

Multiple aspects of pain were evaluated during identically executed experiments of CiOA in male and female C57BL/6J mice. Cartilage damage, osteophyte formation, synovial thickness, and cellularity were assessed by histology on day 56. The association between pain and pathology was investigated, disaggregated by sex.

Results

Differences in pain behavior between sexes were found in the majority of the evaluated pain methods. Females displayed lower weight bearing ability in the affected leg compared to males during the early phase of the disease, however, the pathology at the end stage was comparable between sexes. In the second cohort, males displayed increased mechanical sensitivity in the affected joint compared to females but also showed more cartilage damage at the end stage of the model. Within this cohort, gait analysis showed varied results. Males used the affected paw less often and displayed dynamic weight-bearing compensation in the early phase of the model. These differences were not observed in females. Other evaluated parameters displayed comparable gait behavior between males and females. A detailed analysis of individual mice revealed that seven out of 10 pain measurements highly correlated with OA histopathology in females (Pearson r range: 0.642-0.934), whereas in males this measurement was only two (Pearson r range: 0.645-0.748).

Conclusion

Our data show that sex is a determinant in the link between pain-related behavior with OA features. Therefore, to accurately interpret pain data it is crucial to segregate data analysis by sex to draw the correct mechanistic conclusion.

Comparison of chemical-induced temporomandibular osteoarthritis rat models (monosodium iodoacetate versus collagenase type II) for the study of prolonged drug delivery systems

OBJECTIVE

To compare two agents that can induce a rat model of temporomandibular joint osteoarthritis (TMJOA) by chemical induction: monosodium iodoacetate (MIA) and collagenase type 2 (Col-2). We wished to ascertain the best agent for assessing drug-delivery systems (DDSs).

METHOD

Male Wistar rats underwent intra-articular injection with MIA or Col-2. They were manipulated for 30 days. The head withdrawal threshold (HWT), immunohistological assessment, and positron emission tomography (PET) were used to evaluate the relevance of our models.

RESULTS

For both the MIA and Col-2 groups, pain persisted for 30 days after injection. Change in the HWT showed that Col-2 elicited a strong action initially that decreased progressively. MIA had a constant action upon pain behavior. Histology of TMJ tissue from both groups showed progressive degradation of TMJ components.

CONCLUSIONS

MIA and Col-2 induced orofacial pain by their local chemical action on TMJs. However, based on a prolonged and greater sustained effect on the pain threshold, persistent histological changes, and imaging results, MIA appeared to be more suitable for creation of a rat model of TMJOA for the study of DDSs.

Pilot comparison of outcome measures across chemical and surgical experimental models of chronic osteoarthritis in the rat (Rattus norvegicus)

Relatively little work has evaluated both the disease of osteoarthritis (OA) and clinically-relevant pain outcome measures across different OA models in rats. The objective of this study was to compare sensitivity, pain, and histological disease severity across chemical and surgical models of OA in the rat. Stifle OA was induced in Sprague-Dawley rats via intraarticular injection of monoiodoacetate (MIA) or surgical transection of anterior cruciate ligament and/or destabilization of medial meniscus (ACL+DMM or DMM alone). Reflexive (e.g., mechanical and thermal stimuli) measures of sensitivity and non-reflexive assays (e.g., lameness, static hindlimb weight-bearing asymmetry, dynamic gait analysis) of pain were measured over time. Joint degeneration was assessed histologically. Six-weeks post OA-induction, the ACL+DMM animals had significantly greater visually observed lameness than MIA animals; however, both ACL+DMM and MIA animals showed equal pain as measured by limb use during ambulation and standing. The MIA animals showed increased thermal, but not mechanical, sensitivity compared to ACL+DMM animals. Joint degeneration was significantly more severe in the MIA model at 6 weeks. Our pilot data suggest both the ACL+DMM and MIA models are equal in terms of clinically relevant pain behaviors, but the MIA model is associated with more severe histological changes over time potentially making it more suitable for screening disease modifying agents. Future work should further characterize each model in terms of complex pain behaviors and biochemical, molecular, and imaging analysis of the sensory system and joint tissues, which will allow for more informed decisions associated with model selection and investigative outcomes.

Antinociceptive and modulatory effect of pathoplastic changes in spinal glia of a TLR4/CD14 blocking molecule in two models of pain in rat

The role of spinal glia in the development and maintenance of chronic pain has become over the last years a subject of increasing interest. In this regard, toll-like receptor 4 (TLR4) signaling has been proposed as a major trigger mechanism. Hence, in this study we explored the implications of TLR4 inhibition in the periphery and primarily in the CNS, focusing on the impact this inhibition renders in pain development and glia activation in the dorsal horn in two models of pain. Making use of a synthetic cluster of differentiation 14 (CD14)/TLR4 antagonist, the effect of TLR4 blockade on tactile allodynia and heat hyperalgesia was evaluated in osteoarthritic and postoperative rat models. An in vitro parallel artificial membrane permeation assay was performed to determine the proneness of the drug to permeate the blood-brain barrier prior to systemic and central administration. Findings suggest a dominant role of peripheral TLR4 in the model of incisional pain, whilst both peripheral and central TLR4 seem to be responsible for osteoarthritic pain. That is, central and peripheral TLR4 may be differently involved in the etiopathology of diverse types of pain what potentially seems a promising approach in the management of pain.

Intra-articular delivery of flurbiprofen sustained release thermogel: improved therapeutic outcome of collagenase II-induced rat knee osteoarthritis

Knee osteoarthritis (OA) is a common degenerative disease. Intra-articular administration of flurbiprofen is frequently employed in clinic to treat OA, while repeated injections are required because of the limited effective duration. To improve therapeutic outcome and prolong the treatment interval, a poly(ε-caprolactone-co-lactide)-b-poly(ethylene glycol)-b-poly(ε-caprolactone-co-lactide) (PCLA-PEG-PCLA) triblock copolymer based flurbiprofen thermosensitive gel for the sustained intra-articular drug delivery was designed in this study. The anti-OA effects of this flurbiprofen thermogel were investigated on collagenase II-induced rat knee OA model by multiple approaches and compared with that of conventional sodium hyaluronate and flurbiprofen injecta. In vitro drug release studies indicated that flurbiprofen was sustained released from the thermosensitive gel for more than three weeks. This sustained drug release system exerted comparable short-term analgesic effects and distinctly improved long-term analgesic efficacy in terms of the increased percentage of the total ipsilateral paw print intensity and the reduced Knee-Bend scores of OA rats. The inflammatory response was attenuated in the samples of flurbiprofen gel treated group by showing decreased IL-1, IL-6, and IL-11 levels in the joint fluid and down-regulated IL-1, IL-6, IL-11, COX-2, TNF-α, and NF-κB/p65 expression in the articular cartilages. The results suggest the suitability of thermosensitive copolymer PCLA-PEG-PCLA for sustained intra-articular effects of flurbiprofen and provide in vivo experimental evidence for potential clinical application of this flurbiprofen delivery system to better management of OA cases.

Intra-articular collagenase in the spinal facet joint induces pain, DRG neuron dysregulation and increased MMP-1 absent evidence of joint destruction

Degeneration is a hallmark of painful joint disease and is mediated by many proteases that degrade joint tissues, including collagenases. We hypothesized that purified bacterial collagenase would initiate nociceptive cascades in the joint by degrading the capsular ligament's matrix and activating innervating pain fibers. Intra-articular collagenase in the rat facet joint was investigated for its effects on behavioral sensitivity, joint degeneration, and nociceptive pathways in the peripheral and central nervous systems. In parallel, a co-culture collagen gel model of the ligament was used to evaluate effects of collagenase on microscale changes to the collagen fibers and embedded neurons. Collagenase induced sensitivity within one day, lasting for 3 weeks (p < 0.001) but did not alter ligament structure, cartilage health, or chondrocyte homeostasis. Yet, nociceptive mediators were increased in the periphery (substance P, pERK, and MMP-1; p ≤ 0.039) and spinal cord (substance P and MMP-1; p ≤ 0.041). The collagen loss (p = 0.008) induced by exposing co-cultures to collagenase was accompanied by altered neuronal activity (p = 0.002) and elevated neuronal MMP-1 (p < 0.001), suggesting microscale collagen degradation mediates sensitivity in vivo. The induction of sustained sensitivity and nociception without joint damage may explain the clinical disconnect in which symptomatic joint pain patients present without radiographic evidence of joint destruction.

MicroRNA-375 exacerbates knee osteoarthritis through repressing chondrocyte autophagy by targeting ATG2B

Objective: This study aimed to explore the underlying mechanism of miR-375 in exacerbating osteoarthritis (OA).

Results: MiR-375 expression were upregulated in OA cartilage tissues, whereas ATG2B expression was decreased. MiR-375 targeted ATG2B 3’ UTR and inhibited its expression in the chondrocytes, and then suppressed autophagy and promoted endoplasmic reticulum stress (ERs). The apoptosis rate of chondrocytes was increased after being transfected with miR-375 mimics. In vivo results further verified that inhibition of miR-375 could relieve OA-related symptoms.

Conclusion: miR-375 can inhibit the expression of ATG2B in chondrocytes, suppress autophagy and promote the ERs. It suggests that miR-375 could be considered to be a key therapy target for OA.

Methods: Differential expression analyses for mRNA and miRNA microarray datasets from ArrayExpress were performed. MiR-375 and ATG2B expressions in cartilage tissues were detected by qRT-PCR. Dual luciferase assay was applied to verify the targeting relationship between ATG2B and miR-375. In vitro, the role of miR-375 on chondrocyte autophagy and ERs was investigated by western blot and immunofluorescence. The apoptotic rate was quantified by flow cytometry. In vivo, OA mice model was established, HE and Safranin O and Fast Green staining, as well as the OARSI and modified Mankin scores, were applied to measure the OA cartilage damage severity.

Comparison of early-stage changes of osteoarthritis in cartilage and subchondral bone between two different rat models

Osteoarthritis (OA) is a chronic degenerative joint disease and the major cause of joint pain and disability in the elderly. It is mainly characterized by articular cartilage degradation and subchondral bone remodeling. There are two main types of OA: natural occurring OA and secondary OA, mainly associated with aging and trauma, respectively. In this study, we established two OA models in rat knee joints to simulate the two types of OA, using the type II collagenase injection (CI) and anterior cruciate ligament transection (ACLT), respectively. After intervention for 2-6 weeks, cartilage and subchondral bone changes were detected in histological staining, immunochemistry, and micro-CT. Results showed that both models with typical pathology changes of OA were successfully induced, while the development and severity of OA process in the models were different. In ACLT rats, the cartilage damage was milder, lasted for a shorter time, and subchondral bone reconstruction occurred earlier, compared with the changes in CI rats. The cartilage damage was secondary to subchondral bone change in ACLT rats, while subchondral bone change was secondary to cartilage degeneration in CI rats. In conclusion, the interaction between cartilage and subchondral bone is different between the natural-occurring and secondary OA models. These two models not only suggest potential different mechanisms of the two types of OA, but also provide new directions for OA treatment and prevention.

Profiling of inflammatory mediators in the synovial fluid related to pain in knee osteoarthritis

Background

Inflammatory mediators in the synovial fluid (SF) play critical roles in the initiation and development of pain in knee osteoarthritis (KOA). However, data for inflammatory marker expression are conflicting, and the role of SF inflammatory mediators in neuropathic pain is not clear. Therefore, the aim of this study was to identify SF inflammatory mediators associated with nociceptive and neuropathic pain in KOA.

Methods

Levels of IL-1β, IL-6, TNF-α, macrophage colony-stimulating factor, MMP-3, MMP-13, metalloproteinase with thrombospondin motifs 5, calcitonin gene-related peptide, neuropeptide Y, substance P and bradykinin were measured using enzyme-linked immunosorbent assays in 86 patients. Nociceptive pain was assessed using the numeric rating scale (NRS), visual analog scale (VAS) and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain score. Neuropathic pain was determined using the PainDETECT questionnaire. Moreover, knee function was evaluated by the WOMAC score and range of motion (ROM) assessments. Radiological grade was defined using the Kellgren-Lawrence (K-L) grading scale.

Results

Pain scores measured using different methods correlated highly with each other. A worse K-L grade and knee function were associated with worse pain. Expression of IL-1β and IL-6 was increased in the early stage compared with the late stage. The NRS score correlated positively with age, K-L grade, and the WOMAC score and negatively with ROM and TNF-α expression. The VAS correlated positively with age, K-L grade, and the WOMAC score but negatively with ROM and levels of IL-1β, IL-6 and TNF-α. The WOMAC pain score did not correlate with any of the inflammatory mediators measured; it correlated only with ROM. The PainDETECT score correlated only with the WOMAC score. Expression of other inflammatory mediators did not correlate with any of the pain scores.

Conclusions

IL-1β, IL-6 and TNF-α play critical roles in pain in the early stage of KOA and correlate with pain. The catabolic enzymes and neuropeptides measured do not correlate with nociceptive and neuropathic pain. New biomarkers related to pain in the late stage need to be further investigated.

Subclinical lipopolysaccharide from Salmonella Enteritidis induces neuropeptide dysregulation in the spinal cord and the dorsal root ganglia

Background

Despite increasing evidence that lipopolysaccharide (LPS) affects the biological active substances of dorsal root ganglia (DRG) we have limited knowledge of the influence of a single low dose of LPS, which does not result in any clinical symptoms of disease (subclinical LPS) on neuropeptides connected with the sensory pathway. Accordingly, in this work, we investigated the influence of subclinical LPS from Salmonella Enteritidis on selected neuropeptides: substance P (SP), galanin (GAL), neuropeptide Y (NPY), vasoactive intestinal peptide (VIP) and somatostatin (SOM) in the cervical, thoracic, lumbar and sacral regions of the DRG and spinal cord.

Methods

This study was performed on immature female pigs of the Pietrain × Duroc breed. Seven days after the intravenous injection of saline solution for control animals (n = 5) and 5 μg/kg b.w. LPS from S. Enteritidis for the experimental group (n = 5), the DRG and the spinal cord were collected to extract the neuropeptides using solid-phase extraction technology.

Results

Our results demonstrated that subclinical LPS in DRG was able to change the levels of all studied neuropeptides except SOM, whereas in the spinal cord it down-regulated all studied neuropeptides in the sacral spinal cord, maintaining the concentration of all studied neuropeptides in other regions similar to that observed in the control animals. The significant differences in the intensity and character of observed changes between particular regions of the DRG suggest that the exact functions of the studied neuropeptides and mechanisms of responses to subclinical LPS action depend on specific characteristics and functions of each examination region of DRG.

Conclusions

The mechanisms of observed changes are not fully understood and require further study of the molecular interactions between subclinical LPS from S. Enteritidis and neuronal and non-neuronal cells of DRG and spinal cord. The peripheral and central pain pathways must be analysed with the aspect of unknown long-term consequences of the influence of subclinical LPS from S. Enteritidis on neuropeptides in the spinal cord and the dorsal root ganglia.

Gait Assessment of Pain and Analgesics: Comparison of the DigiGait™ and CatWalk™ Gait Imaging Systems

Investigation of pain requires measurements of nociceptive sensitivity and other pain-related behaviors. Recent studies have indicated the superiority of gait analysis over traditional evaluations (e.g., skin sensitivity and sciatic function index [SFI]) in detecting subtle improvements and deteriorations in animal models. Here, pain-related gait parameters, whose criteria include (1) alteration in pain models, (2) correlation with nociceptive threshold, and (3) normalization by analgesics, were identified in representative models of neuropathic pain (spared nerve injury: coordination data) and inflammatory pain (intraplantar complete Freund’s adjuvant: both coordination and intensity data) in the DigiGait™ and CatWalk™ systems. DigiGait™ had advantages in fixed speed (controlled by treadmill) and dynamic SFI, while CatWalk™ excelled in intrinsic velocity, intensity data, and high-quality 3D images. Insights into the applicability of each system may provide guidance for selecting the appropriate gait imaging system for different animal models and optimization for future pain research.

Peripheral Mechanisms Contributing to Osteoarthritis Pain

PURPOSE OF REVIEW

Osteoarthritis (OA) is the most common form of arthritis and a major source of pain and disability worldwide. OA-associated pain is usually refractory to classically used analgesics, and disease-modifying therapies are still lacking. Therefore, a better understanding of mechanisms and mediators contributing to the generation and maintenance of OA pain is critical for the development of efficient and safe pain-relieving therapies.

RECENT FINDINGS

Both peripheral and central mechanisms contribute to OA pain. Clinical evidence suggests that a strong peripheral nociceptive drive from the affected joint maintains pain and central sensitization associated with OA. Mediators present in the OA joint, including nerve growth factor, chemokines, cytokines, and inflammatory cells can contribute to sensitization. Furthermore, structural alterations in joint innervation and nerve damage occur in the course of OA. Several interrelated pathological processes, including joint damage, structural reorganization of joint afferents, low-grade inflammation, neuroplasticity, and nerve damage all contribute to the pain observed in OA. It can be anticipated that elucidating exactly how these mechanisms are operational in the course of progressive OA may lead to the identification of novel targets for intervention.

The Interface of Mechanics and Nociception in Joint Pathophysiology: Insights From the Facet and Temporomandibular Joints

Chronic joint pain is a widespread problem that frequently occurs with aging and trauma. Pain occurs most often in synovial joints, the body's load bearing joints. The mechanical and molecular mechanisms contributing to synovial joint pain are reviewed using two examples, the cervical spinal facet joints and the temporomandibular joint (TMJ). Although much work has focused on the macroscale mechanics of joints in health and disease, the combined influence of tissue mechanics, molecular processes, and nociception in joint pain has only recently become a focus. Trauma and repeated loading can induce structural and biochemical changes in joints, altering their microenvironment and modifying the biomechanics of their constitutive tissues, which themselves are innervated. Peripheral pain sensors can become activated in response to changes in the joint microenvironment and relay pain signals to the spinal cord and brain where pain is processed and perceived. In some cases, pain circuitry is permanently changed, which may be a potential mechanism for sustained joint pain. However, it is most likely that alterations in both the joint microenvironment and the central nervous system (CNS) contribute to chronic pain. As such, the challenge of treating joint pain and degeneration is temporally and spatially complicated. This review summarizes anatomy, physiology, and pathophysiology of these joints and the sensory pain relays. Pain pathways are postulated to be sensitized by many factors, including degeneration and biochemical priming, with effects on thresholds for mechanical injury and/or dysfunction. Initiators of joint pain are discussed in the context of clinical challenges including the diagnosis and treatment of pain.

Glial activation in the collagenase model of nociception associated with osteoarthritis

Background

Experimental osteoarthritis entails neuropathic-like changes in dorsal root ganglia (DRG) neurons. Since glial activation has emerged as a key player in nociception, being reported in numerous models of neuropathic pain, we aimed at evaluating if glial cell activation may also occur in the DRG and spinal cord of rats with osteoarthritis induced by intra-articular injection of collagenase.

Methods

Osteoarthritis was induced by two injections, separated by three days, of 500 U of type II collagenase into the knee joint of rats. Movement-induced nociception was evaluated by the Knee-Bend and CatWalk tests during the following six weeks. Glial fibrillary acidic protein (GFAP) expression in satellite glial cells of the DRG was assessed by immunofluorescence and Western Blot analysis; the pattern of GFAP and activating transcription factor-3 (ATF-3) expression was also compared through double immunofluorescence analysis. GFAP expression in astrocytes and IBA-1 expression in microglia of the L3–L5 spinal cord segments was assessed by immunohistochemistry and Western Blot analysis. The effect of the intrathecal administration of fluorocitrate, an inhibitor of glial activation, on movement-induced nociception was evaluated six weeks after the first collagenase injection.

Results

GFAP expression in satellite glial cells of collagenase-injected animals was significantly increased six weeks after osteoarthritis induction. Double immunofluorescence showed GFAP upregulation in satellite glial cells surrounding ATF-3-positive neurons. In the spinal cord of collagenase-injected animals, an ipsilateral upregulation of GFAP and IBA-1 was also observed. The inhibition of glial activation with fluorocitrate decreased movement- and loading-induced nociception.

Conclusion

Collagenase-induced knee osteoarthritis leads to the development of nociception associated with movement of the affected joint and to the activation of glial cells in both the DRG and the spinal cord. Inhibition of glial cell activation by fluorocitrate decreases these osteoarthritis-associated nociceptive behaviours. These results suggest that glial cell activation may play a role in the development of chronic pain in this experimental model of osteoarthritis.

Asymptomatic and symptomatic individuals with the same radiographic evidence of knee osteoarthritis walk with different knee moments and muscle activity

There is an established discordance between the structural joint damage and clinical symptoms of knee osteoarthritis; however, there has been little investigation into the differences in joint level biomechanics and muscle activation patterns during gait between symptomatic and asymptomatic individuals with the same radiographic evidence of osteoarthritis. The objective of this study was to examine three-dimensional knee joint biomechanics and muscle activation differences during gait between asymptomatic and symptomatic individuals with radiographic knee osteoarthritis. A total of 54 asymptomatic and 59 symptomatic individuals with a Kellgren-Lawrence osteoarthritis radiographic grade of 2 underwent a comprehensive gait analysis to examine differences in the magnitude and patterns of the knee flexion angle, three-dimensional net resultant moments, and electromyography of the quadriceps, hamstrings, and gastrocnemii during over ground walking between the two groups. The symptomatic group walked with significantly higher overall magnitudes and less mid-stance unloading of the net resultant knee adduction moment, lower peak flexion moments, and higher lateral hamstrings and quadriceps activity during stance than the Asymptomatic group (p < 0.05, sex-adjusted analysis), with a trend (p = 0.07) toward greater transverse plane range of moment over stance. The differences found suggest a "stiffer" frontal and sagittal plane pattern with symptomatic individuals, but with more muscle activity and a trend toward more torsional loading in the transverse plane, which may have implications for shear loading of the joint. This is the first evidence of differences in three-dimensional knee joint biomechanics and muscle activation between asymptomatic and symptomatic individuals with the same radiographic grade. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1661-1670, 2017.

Origins and Neurochemical Characteristics of Porcine Intervertebral Disc Sympathetic Innervation: a Preliminary Report

Intervertebral disc diseases (IVDDs) form a group of a vertebral column disorders affecting a large number of people worldwide. It is estimated that approximately 30% of individuals at the age of 35 and approximately 90% of individuals at the age of 60 and above will have some form of disc-affecting pathological changes leading to disc herniation, prolapse and degeneration as well as discogenic pain. Here, we aimed to establish the origins and neurochemical characteristics of porcine intervertebral disc sympathetic innervation involved in pain signalling in IVDD patients. Pigs were given an injection of the Ominipaque contrast agent and Fast Blue (FB) retrograde tracer into the L₄-L₅ intervertebral disc and euthanized at 2, 1, and 3 months post injection. Following euthanasia, bilateral sympathetic chain ganglia (SChG) Th₁₃ to C₁ were collected. The presence, distribution and neurochemical characteristics of retrogradely labelled SChG neurons were examined. The majority (88.8%) of all FB+ cells were found in the L₃-L₅ SChG. Most FB+ neurons stained for dopamine beta hydroxylase (DBH); one-third to one-quarter stained for somatostatin (SOM), neuropeptide Y (NPY) or leu-enkephalin (LENK); and only a few stained for galanin (GAL). Compared with the control, the greatest decline in neurochemical immunostaining was observed 2 weeks post injection, and the lowest decline was noticed 1 month post injection. Our study, for the first time, provides insight into the complex patterns of intervertebral disc sympathetic innervation and suggests that the best time for neurochemical balance restoration therapy would be 1 month post-injury, when the neuronal concentration of all studied substances is close to the initial physiological level, thus providing favourable conditions for successful recovery.

Role of autophagy in the progression of osteoarthritis: The autophagy inhibitor, 3-methyladenine, aggravates the severity of experimental osteoarthritis

Accumulating evidence suggests that autophagy is closely related to the pathogenesis of osteoarthritis (OA). The aim of this study was to determine the changes in autophagy during the progression of OA and to elucidate the specific role of autophagy in OA. For this purpose, a cellular model of OA was generated by stimulating SW1353 cells with interleukin (IL)-1β and a rabbit model of OA was also established by an intra-articular injection of collagenase, followed by treatment with the autophagy specific inhibitor, 3-methyladenine (3-MA). Cell viability was analyzed by MTS assay, and the mRNA expression levels of matrix metalloproteinases (MMP)-13 and tissue inhibitor of metalloproteinase (TIMP)-1 were determined by RT-qPCR. Cartilage degeneration was examined under a light microscope, and autophagosome and chondrocyte degeneration was observed by transmission electron microscopy. The protein expression of Beclin-1 and light chain 3 (LC3)B was evaluated by western blot analysis and immunofluorescence staining. We found that the autophagy was enhanced during the early stages and was weakened during the late stages of experimental OA. The inhibition of autophagy by 3-MA significantly aggravated the degeneration of chondrocytes and cartilage in experimental OA. Our results thus determine the changes in autophagy during different stages of OA, as well as the role of impaired autophagy in the development of OA. Our data suggest that the regulation of autophagy may be a potential therapeutic strategy with which to attenuate OA.

The paradox of painless periodontal disease

Periodontal diseases, primarily gingivitis and periodontitis, are characterised by progressive inflammation and tissue destruction. However, they are unusual in that they are not also accompanied by the pain commonly seen in other inflammatory conditions. This suggests that interactions between periodontal bacteria and host cells create a unique environment in which the pro-algesic effects of inflammatory mediators and factors released during tissue damage are directly or indirectly inhibited. In this review, we summarise the evidence that periodontal disease is characterised by an accumulation of classically pro-algesic factors from bacteria and host cells. We then discuss several mechanisms by which inflammatory sensitisation of nociceptive fibres could be prevented through inactivation or inhibition of these factors. Further studies are necessary to fully understand the molecular processes underlying the endogenous localised hypoalgesia in human periodontal disease. This knowledge might provide a rational basis to develop future therapeutic interventions, such as host modulation therapies, against a wide variety of other human pain conditions.

The protective role of autophagy in experimental osteoarthritis, and the therapeutic effects of Torin 1 on osteoarthritis by activating autophagy

Background

Recent studies have shown that autophagy was associated with the development of osteoarthritis (OA), the purpose of this research was to determine the exact role of autophagy in OA and investigate effective therapeutic drugs to inhibit the pathological progression of OA.

Methods

In this study, a cellular OA model was generated by stimulating SW1353 cells with IL-1β and a rabbit OA model was established by intra-articular injection of collagenase, followed by treatment with Torin 1 or 3-Methyladenine (3-MA). The mRNA expression levels of VEGF, MMP-13 and TIMP-1 were determined by quantitative real-time PCR. The caitilage degeneration was examined by histological evaluation, chondrocytes degeneration and autophagosomes were observed by transmission electron microscopy. Expression levels of Beclin-1 and LC3 were evaluated by western blotting and immunofluorescence.

Results

The degeneration of SW 1353 cells, cartilage and chondrocytes was related to the loss of autophagy in experimental OA. 3-MA increased the severity of degeneration of cells and cartilage by autophagy inhibition, while Torin 1 reduced that by autophagy activation.

Conclusions

The loss of autophagy is linked with the experimental OA and autophagy may play a protective role in the pathogenesis of OA. Treatment of Torin 1 can inhibit the degenerative changes of experimental OA by activating autophagy and it may be a useful therapeutic drug for OA.

Electronic supplementary material

The online version of this article (doi:10.1186/s12891-016-0995-x) contains supplementary material, which is available to authorized users.