Clinical Perspective on Pain and Pain Phenotypes in Osteoarthritis

Pharmacotherapy for osteoarthritis-related pain: current and emerging therapies

INTRODUCTION

Osteoarthritis (OA) related pain has affected millions of people worldwide. However, the current pharmacological options for managing OA-related pain have not achieved a satisfactory effect.

AREAS COVERED

This narrative review provides an overview of the current and emerging drugs for OA-related pain. It covers the drugs' mechanism of action, safety, efficacy, and limitations. The National Library of Medicine (PubMed) database was primarily searched from 2000 to 2024.

EXPERT OPINION

Current treatment options are limited and suboptimal for OA pain management. Topical nonsteroidal anti-inflammatory drugs (NSAIDs) are the recognized and first-line treatment in the management of OA-related pain, and other drugs are inconsistent recommendations by guidelines. Emerging treatment options are promising for OA-related pain, including nerve growth factor (NGF) inhibitors, ion channel inhibitors, and calcitonin gene-related peptide (CGRP) antagonists. Besides, drugs repurposing from antidepressants and antiepileptic analgesics are shedding light on the management of OA-related pain. The management of OA-related pain is challenging as pain is heterogeneous and subjective. A more comprehensive strategy combined with non-pharmacological therapy needs to be considered, and tailored management options to individualized patients.

Clinical Assessment of Osteoarthritis Pain: Contemporary Scenario, Challenges, and Future Perspectives

The multifaceted nature of osteoarthritis (OA) pain presents a challenge in understanding and managing the condition. The diverse pain experiences, progression rates, individual responses to treatments, and complex disease mechanisms contribute to heterogeneity in the clinical studies outcomes. The lack of a standardized methodology for assessing and classifying OA pain challenges healthcare practitioners. This complicates the establishment of universally applicable protocols or standardized guidelines for treatment. This article explores the heterogeneity observed in clinical studies evaluating OA pain treatments, highlighting the necessity for refined methodologies, personalized patient categorization, and consistent outcome measures. It discusses the role of the multidimensional nature of OA pain, underlying pain mechanisms, and other contributing factors to the heterogeneity in outcome measures. Addressing these variations is crucial to establishing a more consistent framework for evidence-based treatments and advancing care of the patient with OA pain.

Nociceptor spontaneous activity is responsible for fragmenting non-rapid eye movement sleep in mouse models of neuropathic pain

Spontaneous pain, a major complaint of patients with neuropathic pain, has eluded study because there is no reliable marker in either preclinical models or clinical studies. Here, we performed a comprehensive electroencephalogram/electromyogram analysis of sleep in several mouse models of chronic pain: neuropathic (spared nerve injury and chronic constriction injury), inflammatory (Freund's complete adjuvant and carrageenan, plantar incision) and chemical pain (capsaicin). We find that peripheral axonal injury drives fragmentation of sleep by increasing brief arousals from non-rapid eye movement sleep (NREMS) without changing total sleep amount. In contrast to neuropathic pain, inflammatory or chemical pain did not increase brief arousals. NREMS fragmentation was reduced by the analgesics gabapentin and carbamazepine, and it resolved when pain sensitivity returned to normal in a transient neuropathic pain model (sciatic nerve crush). Genetic silencing of peripheral sensory neurons or ablation of CGRP+ neurons in the parabrachial nucleus prevented sleep fragmentation, whereas pharmacological blockade of skin sensory fibers was ineffective, indicating that the neural activity driving the arousals originates ectopically in primary nociceptor neurons and is relayed through the lateral parabrachial nucleus. These findings identify NREMS fragmentation by brief arousals as an effective proxy to measure spontaneous neuropathic pain in mice.

Phenotypes of osteoarthritis-related knee pain and their transition over time: data from the osteoarthritis initiative

BACKGROUND

Identification of knee osteoarthritis (OA) pain phenotypes, their transition patterns, and risk factors for worse phenotypes, may guide prognosis and targeted treatment; however, few studies have described them. We aimed to investigate different pain phenotypes, their transition patterns, and potential risk factors for worse pain phenotypes.

METHODS

Utilizing data from the Osteoarthritis Initiative (OAI), pain severity was assessed using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain subscale. We identified the activity-related pain phenotypes and estimated the transition probabilities of pain phenotypes from baseline to the 24-month using latent transition analysis. We examined the risk factors at baseline with the 24-month pain phenotypes and the transition of pain phenotypes.

RESULTS

In 4796 participants, we identified four distinct knee pain phenotypes at both baseline and 24-month follow-up: no pain, mild pain during activity (Mild P-A), mild pain during both rest and activity (Mild P-R-A), and moderate pain during both rest and activity (Mod P-R-A). 82.9% knees with no pain at baseline stayed the same at 24-month follow-up, 17.1% progressed to worse pain phenotypes. Among "Mild P-A" at baseline, 32.0% converted to no-pain, 12.8% progressed to "Mild P-R-A", and 53.2% remained. Approximately 46.1% of "Mild P-R-A" and 54.5% of "Mod P-R-A" at baseline experienced remission by 24-month. Female, non-whites, participants with higher depression score, higher body mass index (BMI), higher Kellgren and Lawrence (KL) grade, and knee injury history were more likely to be in the worse pain phenotypes, while participants aged 65 years or older and with higher education were less likely to be in worse pain phenotypes at 24-month follow-up visit. Risk factors for greater transition probability to worse pain phenotypes at 24-month included being female, non-whites, participants with higher depression score, higher BMI, and higher KL grade.

CONCLUSIONS

We identified four distinct knee pain phenotypes. While the pain phenotypes remained stable in the majority of knees over 24 months period, substantial proportion of knees switched to different pain phenotypes. Several socio-demographics as well as radiographic lesions at baseline are associated with worse pain phenotypes at 24-month follow-up visit and transition of pain phenotypes.

Personal factors and baseline function in patients undergoing non-operative management for chronic hip-related groin pain: a cross-sectional study

Aim

Little is known about the relationship between personal factors and perception of hip-related function among patients with chronic hip-related groin pain (HRGP) seeking non-operative management. This analysis was performed to determine if depressive symptoms, central sensitisation, movement evoked pain (MEP), pressure hypersensitivity and activity level were associated with patients' perception of hip-related function, represented by the International Hip Outcome Tool (iHOT-33).

Methods

This cross-sectional study used baseline data from a pilot randomised clinical trial. Participants had anterior hip symptoms for at least 3 of the past 12 months reproduced on examination. Depressive symptoms, central sensitisation and activity level were quantified with self-report questionnaires. MEP was assessed during step down and squat. Pain pressure threshold (PPT) was used to assess pressure hypersensitivity. Statistical analysis was performed to assess bivariate association between variables and independent association of variables with iHOT-33.

Results

Data from 33 participants (aged 18-40 years) with HRGP were analysed. Greater depressive symptoms (rs=-0.48, p=0.005), higher MEP during step down (rs=-0.36, p=0.040) and squat (rs=-0.39, p=0.024), and greater central sensitisation (rs=-0.33, p=0.058) were associated with lower (worse) iHOT-33 scores. Greater depressive symptoms (β=-0.47, 95% CI -0.76 to -0.17; p=0.003) and higher MEP during squat (β=-0.38, 95% CI -0.68 to -0.08; p=0.014) accounted for 37% of variability in iHOT-33. After adjusting for depressive symptoms and MEP, PPT, central sensitisation symptoms and activity level were not associated iHOT-33.

Conclusions

In patients with HRGP seeking non-operative management, greater depressive symptoms and MEP are independently associated with worse self-perceived hip function.

Trial registration number

NCT03959319.

Prescription analgesic medication use among osteoarthritis patients

OBJECTIVE

Pharmacotherapy is the most common strategies to reduce pain for osteoarthritis (OA) patients. To analyze the trend and pattern of prescription analgesic medication use in American OA patients. Besides, our study also tried to figure out the demographic characteristics of opioid use among OA population which may helpful for managing the use of opioids.

METHODS

We included 2214 OA patients from 2007 to 2018. We extracted data from National Health and Nutrition Examination Survey (NHANES) database. We compared analgesics and anti-depression medications use by category between survey participants with OA and without.

RESULTS

For OA patients, NSAIDs, acetaminophen and gabapentinoid were the mostly highly used analgesics (10.2%, 9.0% and 8.9%, respectively). However, we also found that opioids use was very common in OA patients (7.7%) and the duration of opioids use was significantly long. In addition, the opioids use did not decrease from 2007 to 2018, while gabapentinoid increased rapidly from recent decade (From 5.0% to 12.1%). The common analgesic combination used by OA population was opioids with acetaminophen and gabapentinoid with selective serotonin reuptake inhibitors (SSRIs) (2.9% and 2.7%, respectively).

CONCLUSION

The use of gabapentinoid increased rapidly from recent decade, while opioids use did not decrease. The long-term excessive use of opioids was also a serious problem for OA pain control. More improvements such as focusing more on healthcare education and paying more attention on non-pharmacotherapy and the psychological situation of patients are needed.

Three dimensions of pain in osteoarthritis: development and validation of the Osteoarthritis Symptom Inventory Scale

ABSTRACT

We describe here the development and validation of the Osteoarthritis Symptom Inventory Scale (OASIS), a new self-administered questionnaire specifically designed to evaluate the various osteoarthritis (OA) pain symptoms with different dimensions related to OA pain mechanisms. The initial development phase and qualitative study generated a list of 17 descriptors reflecting OA pain and other associated symptoms, leading to the first version of the questionnaire (OASIS17). Each item was quantified on a 0 to 10 Numerical Scale. Validation was performed using 123 consecutive patients with OA pain recruited at 28 centers in France, mainly general practitioner offices. Validation involved (1) determining the questionnaire's factorial structure through exploratory and confirmatory analyses, (2) analyzing convergent and divergent validities (ie, construct validity), (3) assessing each item's test-retest reliability, and (4) evaluating OASIS ability to detect treatment effects (ie, sensitivity to change). The final OASIS version includes 9 items discriminating and quantifying 3 distinct, clinically relevant OA pain dimensions sensitive to treatment. OASIS9 psychometric properties suggest that it could improve the characterization of OA pain profiles for 3 clinically relevant domains: localized, neuropathic-like, and deep pain. The OASIS9 questionnaire could be used to phenotype OA pain patients and identify responders to various therapeutic interventions as a function of OA pain dimensions.

The impact of waiting time for orthopaedic consultation on pain levels in individuals with osteoarthritis: a systematic review and meta-analysis

OBJECTIVE

Time spent waiting for access to orthopaedic specialist health services has been suggested to result in increased pain in individuals with osteoarthritis (OA). We assessed whether time spent on an orthopaedic waiting list resulted in a detrimental effect on pain levels in patients with knee or hip OA.

METHODS

We searched Ovid MEDLINE, EMBASE and EBSCOhost databases from inception until September 2021. Eligible articles included individuals with OA on an orthopaedic waitlist and not receiving active treatment, and reported pain measures at two or more time points. Random-effects meta-analysis was used to estimate the pooled effect of waiting time on pain levels. Meta-regression was used to determine predictors of effect size.

RESULTS

Thirty-three articles were included (n = 2,490 participants, 67 ± 3 years and 62% female). The range of waiting time was 2 weeks to 2 years (20.8 ± 18.8 weeks). There was no significant change in pain over time (effect size = 0.082, 95% CI = -0.009, 0.172), nor was the length of time associated with longitudinal changes in pain over time (β = 0.004, 95% CI = -0.005, 0.012). Body mass index was a significant predictor of pain (β = -0.043, 95% CI = -0.079, 0.006), whereas age and sex were not.

CONCLUSIONS

Pain remained stable for up to 1 year in patients with OA on an orthopaedic waitlist. Future research is required to understand whether pain increases in patients waiting longer than 1 year.

Intra-articular MMP-1 in the spinal facet joint induces sustained pain and neuronal dysregulation in the DRG and spinal cord, and alters ligament kinematics under tensile loading

Chronic joint pain is a major healthcare challenge with a staggering socioeconomic burden. Pain from synovial joints is mediated by the innervated collagenous capsular ligament that surrounds the joint and encodes nociceptive signals. The interstitial collagenase MMP-1 is elevated in painful joint pathologies and has many roles in collagen regulation and signal transduction. Yet, the role of MMP-1 in mediating nociception in painful joints remains poorly understood. The goal of this study was to determine whether exogenous intra-articular MMP-1 induces pain in the spinal facet joint and to investigate effects of MMP-1 on mediating the capsular ligament’s collagen network, biomechanical response, and neuronal regulation. Intra-articular MMP-1 was administered into the cervical C6/C7 facet joints of rats. Mechanical hyperalgesia quantified behavioral sensitivity before, and for 28 days after, injection. On day 28, joint tissue structure was assessed using histology. Multiscale ligament kinematics were defined under tensile loading along with microstructural changes in the collagen network. The amount of degraded collagen in ligaments was quantified and substance P expression assayed in neural tissue since it is a regulatory of nociceptive signaling. Intra-articular MMP-1 induces behavioral sensitivity that is sustained for 28 days (p < 0.01), absent any significant effects on the structure of joint tissues. Yet, there are changes in the ligament’s biomechanical and microstructural behavior under load. Ligaments from joints injected with MMP-1 exhibit greater displacement at yield (p = 0.04) and a step-like increase in the number of anomalous reorganization events of the collagen fibers during loading (p ≤ 0.02). Collagen hybridizing peptide, a metric of damaged collagen, is positively correlated with the spread of collagen fibers in the unloaded state after MMP-1 (p = 0.01) and that correlation is maintained throughout the sub-failure regime (p ≤ 0.03). MMP-1 injection increases substance P expression in dorsal root ganglia (p < 0.01) and spinal cord (p < 0.01) neurons. These findings suggest that MMP-1 is a likely mediator of neuronal signaling in joint pain and that MMP-1 presence in the joint space may predispose the capsular ligament to altered responses to loading. MMP-1-mediated pathways may be relevant targets for treating degenerative joint pain in cases with subtle or no evidence of structural degeneration.

Pain descriptors and determinants of pain sensitivity in knee osteoarthritis: a community-based cross-sectional study

Objectives

To explore pain characteristics in individuals with knee osteoarthritis (KOA), to compare pain sensitivity across individuals with KOA, chronic back pain (CBP) and pain-free individuals (NP), and to examine the relationship between clinical and pain characteristics with pain sensitivity in KOA.

Methods

Cross-sectional, community-based online survey. Two datasets were combined comprising Dutch individuals of ≥ 40 years of age, experiencing chronic knee pain (KOA, N = 445), chronic back pain (CBP, N = 504), or no pain (NP, N = 256). Demographic and clinical characteristics, global health, physical activity/exercise, and pain characteristics including intensity, spreading, duration, quality (SF-MPQ), and sensitivity (PSQ) were assessed. Differences between (sub)groups were examined using analyses of variance or Chi-square tests. Regression analyses were performed to examine determinants of pain sensitivity in the KOA group.

Results

Quality of pain was most commonly described as aching, tender, and tiring-exhausting. Overall, the KOA group had higher levels of pain sensitivity compared to NP group, but lower levels than the CBP group. Univariately, pain intensity, its variability and spreading, global health, exercise, and having comorbidities were weakly related to pain sensitivity (standardized betas: 0.12-0.27). Symptom duration was not related to pain sensitivity. Older age, higher levels of continuous pain, lower levels of global health, and exercise uniquely contributed, albeit modest, to pain sensitivity (P&lt;0.05).

Conclusion

Continuous pain such as aching and tenderness in combination with decreased physical activity may be indicative for a subgroup of individuals at risk for pain sensitivity and, ultimately, poor treatment outcomes.

Joint synovial macrophages as a potential target for intra-articular treatment of osteoarthritis-related pain

Osteoarthritis is the most common form of joint disease and is one of the leading causes of chronic pain. Given the multi-factorial nature, numerous efforts have been made to clarify the multiple factors impacting the pain symptoms and joint pathology, including synovial macrophages in particular. Accumulating evidence from studies involving human participants and experimental animal models suggests that accumulating macrophages in synovial tissue are implicated in peripherally mediated pain sensitization of affected joints in osteoarthritis. Crosstalk between synovial macrophages and the innervating primary nociceptive neurons is thought to contribute to this facilitated pain processing by the peripheral nervous system. Due to high plasticity and complexity of synovial macrophages in the joint, safe therapies targeting single cells or molecules are currently lacking. Using advanced technologies (such as single-cell RNA sequencing and mass cytometry), studies have shown that diverse subpopulations of synovial macrophages exist in the distinct synovial microenvironments of specific osteoarthritis subtypes. Considerable progress has been made in delineating the molecular mechanisms of various subsets of synovial macrophages in the development of osteoarthritis. To develop a novel intra-articular treatment paradigm targeting synovial macrophages, we have summarized in this review the recent advances in identifying the functional consequences of synovial macrophage sub-populations and understanding of the molecular mechanisms driving macrophage-mediated remodeling.

Insomnia Severity and Degree of Dysfunction: What Is to Be Learned When These Domains are Discordant?

OBJECTIVE/BACKGROUND

Illness severity and resultant dysfunction are often linearly related and tightly coupled (concordant). Some percentage of individuals, however, exhibit discordant associations (high illness severity and low dysfunction [HL] or low illness severity and high dysfunction [LH]). In the present study, a sample of subjects with insomnia complaints were evaluated to determine what percentage of subjects exhibited discordant associations.

PARTICIPANTS

Archival data were drawn from a community-based sample (n = 4,680; 61.8% female; Ages 18-105).

METHODS

Median splits were calculated for illness severity and daytime dysfunction and each individual was typed as High (H) or Low (L) for the concordant (HH and LL) and discordant domains (HL and LH).

RESULTS

Given this typology, 61% were classified as concordant and 39% were classified as discordant. Of these, 38% were sub-typed as HH, 23% as LL, 26% as LH, and 13% as HL.

CONCLUSIONS

We propose that some of the discordance may be ascribable to a mismatch between sleep need and sleep ability. Those "who need a lot, may suffer a lot, in the face of only a little (LH)", whereas those "who need a little, may suffer only a little, in the face of a lot (HL)".

Health-related quality of life in osteoarthritis patients: a systematic review and meta-analysis

The aim of this meta-analysis was to compare health-related quality of life (HRQoL) of Osteoarthritis (OA) patients and controls. A systematic literature search was performed on PubMed, Web of Science and EMBASE from database inception to 7 January 2020. Random effect model was performed to summarize the scores of each domain and the forest plot was used to compare the scores of OA patients with healthy controls. Subgroup analyses were conducted to explore the source of heterogeneity. Statistical analyses were executed using Review Manager (version 5.1). In total, six studies were included in this study, including 7094 patients with OA and 12 100 healthy controls, which were all reliable to summarize the scores of the Medical Outcomes Study 36-item Short-Form Health Survey (SF-36). Meta-analyses found that pooled mean HRQoL score for the SF-36 each domain (physical function, physical role function, body pain, general health, vitality, social function, emotional role function, mental health) was lower in patients with OA than in healthy controls, especially the score in the dimension of physical role function. OA have a substantial impact HRQoL. HRQoL is a significant component of measuring overall health, which contributes to formulate successful self-disease management plan, patient-centered care, and develop effective interventions target confidence.

The CB2 cannabinoid receptor as a therapeutic target in the central nervous system

INTRODUCTION

Targeting CB2 cannabinoid receptor (CB2r) represents a promising approach for the treatment of central nervous system disorders. These receptors were identified in peripheral tissues, but also in neurons in the central nervous system. New findings have highlighted the interest to target these central receptors to obtain therapeutic effects devoid of the classical cannabinoid side-effects.

AREAS COVERED

In this review, we searched PubMed (January 1991-May 2021), ClinicalTrials.gov and Cochrane Library databases for articles, reviews and clinical trials. We first introduce the relevance of CB2r as a key component of the endocannabinoid system. We discuss CB2r interest as a possible novel target in the treatment of pain. This receptor has raised interest as a potential target for neurodegenerative disorders treatment, as we then discussed. Finally, we underline studies revealing a novel potential CB2r interest in mental disorders treatment.

EXPERT OPINION

In spite of the interest of targeting CB2r for pain, clinical trials evaluating CB2r agonist analgesic efficacy have currently failed. The preferential involvement of CB2r in preventing the development of chronic pain could influence the failure of clinical trials designed for the treatment of already established pain syndromes. Specific trials should be designed to target the prevention of chronic pain development.

CircRNA circ_SEC24A upregulates DNMT3A expression by sponging miR-26b-5p to aggravate osteoarthritis progression

BACKGROUND

Osteoarthritis (OA) is a chronic degenerative disease characterized by degeneration and injury of articular cartilage. Circular RNA_SEC24A (circ_SEC24A; circBase ID: hsa_circ_0005105) is upregulated and promotes multiple tumor processes. However, its role in OA progression remained mostly unknown.

METHODS

Quantitative real-time PCR (qRT-PCR) was used to detect the RNA expression of circ_SEC24A, miR-26b-5p and DNA methyltransferase 3 alpha (DNMT3A). Cell proliferation was verified by 3-(4, 5-dimethyl-2-thiazolyl)-2, 5-diphenyl-2-H-tetrazolium bromide (MTT) and 5-ethynyl-2'-deoxyuridine (EdU) assays. Flow cytometry was used to detect apoptosis. Western blot was used to detect protein expression of DNMT3A, proliferating cell nuclear antigen (PCNA), extracellular matrix (ECM) proteins (Collagen II and Aggrecan), and ECM degrading enzymes (matrix metalloproteinase-13 [MMP13] and metallopeptidase with thrombospondin type 1 motif 5 [ADAMTS5]). The target relationship between miR-26b-5p and circ_SEC24A or DNMT3A was predicted by Statbase3.0 or TargetScan and confirmed by dual-luciferase reporter assay, RNA pull-down assay and RNA immunoprecipitation.

RESULTS

Circ_SEC24A was upregulated in osteoarthritic cartilage tissues and IL-1β-induced chondrocytes, accompanying with miR-26b-5p downregulation and DNMT3A upregulation. Circ_SEC24A expression was resistant to RNase R digestion and mainly expressed in the cytoplasm. Interfering circ_SEC24A abolished IL-1β-induced effects on proliferation inhibition, apoptosis, and ECM degradation in chondrocytes, but overexpressing circ_SEC24A had the opposite effects. Inhibiting miR-26b-5p counteracted but upregulating miR-26a-5p mimicked the functions of circ_SEC24A silencing. Reinforcing DNMT3A reversed miR-26b-5p overexpression's role in IL-1β-induced chondrocytes. Mechanically, circ_SEC24A and DNMT3A were competitive endogenous RNAs (ceRNAs) for miR-26b-5p.

CONCLUSION

Circ_SEC24A was a promoting factor for IL-1β-induced OA progression via circ_SEC24A/miR-26b-5p/DNMT3A ceRNA axis.

Involvement of Macrophages and Spinal Microglia in Osteoarthritis Pain

PURPOSE OF REVIEW

Chronic pain in osteoarthritis (OA) is characterized by pain sensitization, which involves both peripheral and central mechanisms. Studies suggest synovial macrophage and spinal microglia are implicated in pain sensitization in OA. We, therefore, reviewed the evidence of whether synovial macrophage and spinal microglia facilitated pain sensitization at diverse levels and how this event occurred in OA.

RECENT FINDINGS

Peripherally, joint inflammation is now believed to be a source of OA-related pain. Synovial macrophages accumulate in OA inflamed synovium and display a pro-inflammatory phenotype. Abundant macrophage-derived pro-inflammatory cytokines and other pain-causing substance facilitate hyperexcitation of primary sensory neuron in OA-related pain. Thus, activated synovial macrophage was considered a predictor for phenotyping of OA pain clinically. In response to affected joint-derived strong nociception, aberrant neuronal excitability is often associated with the hyperactivity of microglia in the spinal dorsal horn, thereby leading to central sensitization. Hyperactivity of synovial macrophage and spinal microglia underlies the mechanisms of pain sensitization at the peripheral and central level in OA. This concept provides not only a clinically relevant strategy for identifying the phenotype of OA-related pain but also has the potential to develop individualized interventions for OA, particularly in those patients with hyperactivity of macrophage and microglia.

Geraniol-mediated osteoarthritis improvement by down-regulating PI3K/Akt/NF-κB and MAPK signals: In vivo and in vitro studies

Osteoarthritis (OA) is a degenerative disease that has received increasing attention among the elderly. Its clinical manifestation is primarily long-term joint pain. Evidence for the pharmacological effects of geraniol in various diseases is accumulating. However, whether geraniol has a therapeutic effect against OA remains to be determined. In this study, we discussed the anti-inflammatory effects of geraniol in IL-1β-induced chondrocytes and the anti-cartilage degradation effects in a mouse model of destabilization of the medial meniscus (DMM). In cell experiments, we found that the treatment of geraniol inhibited the expression of IL-1β-induced PGE2, NO, COX-2, iNOS, TNF-α and IL-6 by western blot, qRT-PCR and immunofluorescence staining. Besides, geraniol inhibited the expression of MMP-9 and ADAMTS-5, and reversed the degradation of aggrecan and type II collagen. Mechanistically, we revealed that geraniol suppressed IL-1β-stimulated PI3K/Akt/NF-κB and MAPK activation. Importantly, we have found in animal experiments that oral treatment of geraniol was beneficial in protecting articular cartilage from degradation. Overall, these data indicated that geraniol may have the potential to be developed as an effective treatment for OA.

Byakangelicin inhibits IL-1β-induced mouse chondrocyte inflammation in vitro and ameliorates murine osteoarthritis in vivo

Osteoarthritis (OA) is a chronic musculoskeletal degeneration disease, resulting in severe consequences such as chronic pain and functional disability. Owing to the complex pathology, there are currently available preventative clinical therapies for OA. Several studies have reported the potential anti-inflammatory effects of byakangelicin (BYA), a component of the Angelica dahurica root extract; however, the effects of BYA in OA remain unknown. In this study, we investigated the protective effects of BYA in interleukin (IL)-1β-induced mouse chondrocytes in vitro and on surgical destabilization in a medial meniscus (DMM) mouse OA model in vivo. In vitro, BYA treatment inhibited IL-1β-mediated inducible nitric oxide synthase, cyclooxygenase-2, tumor necrosis factor-alpha, and IL-6 expression. Moreover, BYA promoted the expression of type two collagen and aggrecan but inhibited the expression of thrombospondin motifs 5 and matrix metalloproteinases, leading to degradation of the extracellular matrix. In addition, BYA mechanistically suppressed nuclear factor-kappa B signaling in the IL-1β-induced chondrocytes. The protective effects of BYA in OA development were also observed in vivo using the DMM model. In conclusion, our results highlight BYA as a candidate for OA treatment and prevention.

Metabolic syndrome and trajectory of knee pain in older adults

OBJECTIVES

To examine the association of metabolic syndrome (MetS) and its components with knee pain severity trajectories.

METHODS

Data from a population-based cohort study were utilised. Baseline blood pressure, glucose, triglycerides and high-density lipoprotein (HDL) cholesterol were measured. MetS was defined according to the National Cholesterol Education Program-Adult Treatment Panel III criteria. Radiographic knee osteoarthritis (ROA) was assessed by X-ray. Pain severity was measured by the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain questionnaire at each time-point. Group-based trajectory modelling was used to identify pain trajectories and multi-nominal logistic regression was used for analysis. Mediation analysis was performed to assess whether body mass index (BMI)/central obesity mediated the association between MetS, its components and pain trajectories.

RESULTS

Among 985 participants (Mean ± SD age: 62.9 ± 7.4, 50% female), 32% had MetS and 60% had ROA. Three pain trajectories were identified: 'Minimal pain' (52%), 'Mild pain' (33%) and 'Moderate pain' (15%). After adjustment for potential confounders, central obesity increased risk of belonging to both 'Mild pain' and 'Moderate pain' trajectories as compared to the 'Minimal pain' trajectory group, but MetS [relative risk ratio (RRR): 2.26, 95%CI 1.50-3.39], hypertriglyceridemia (RRR: 1.75, 95%CI 1.16-2.62) and low HDL (RRR: 1.67, 95%CI 1.10-2.52) were only associated with 'Moderate pain' trajectory. BMI/central obesity explained 37-70% of these associations. Results were similar in those with ROA.

CONCLUSION

MetS and its components are predominantly associated with worse pain trajectories through central obesity, suggesting that the development and maintenance of worse pain trajectories may be caused by MetS.

Musculoskeletal pain: determination of clinical phenotypes and the rational treatment approach

Personalized treatment is one of the basic principles of modern medicine. When administering a treatment, one should consider individual patient characteristics, comorbidities and, what is most important, the prevailing symptoms, as well as the clinical phenotype of a disease. This is directly related to chronic musculoskeletal pain (MSP), which occurs with underlying most prevalent joint and vertebral disorders. At present, MSP is considered to be an independent clinical syndrome.Predominant mechanisms of MSP pathophysiology allow for determination of its special phenotypes: “inflammatory”, “mechanical”, related to enthesopathy and central sensitization. Treatment strategies for MSP phenotypes should obviously be differentiated and based on a tailored and pathophysiologically sound of medical agents and non-medical measures with different mechanisms of pharmacological effects. Effective treatment of the “inflammatory” phenotype requires the use of non-steroidal anti-inflammatory drugs, topical glucocorticoids, disease modifying anti-inflammatory agents. The “mechanical” phenotype necessitates the correction of biomechanical abnormalities, the use of hyaluronic acid containing agents, whereas the “enthesopathic” phenotype is treated with local therapy. Treatment of the phenotype with central sensitization is performed with agents effective for neuropathic pain (anticonvulsants, anti-depressants).

Intra-articular targeting of nanomaterials for the treatment of osteoarthritis

Osteoarthritis is a prevalent and debilitating disease that involves pathological contributions from numerous joint tissues and cells. The joint is a challenging arena for drug delivery, since the joint has poor bioavailability for systemically administered drugs and experiences rapid clearance of therapeutics after intra-articular injection. Moreover, each tissue within the joint presents unique barriers to drug localization. In this review, the various applications of nanotechnology to overcome these drug delivery limitations are investigated. Nanomaterials have reliably shown improvements to retention profiles of drugs within the joint space relative to injected free drugs. Additionally, nanomaterials have been modified through active and passive targeting strategies to facilitate interactions with and localization within specific joint tissues such as cartilage and synovium. Last, the limitations of drawing cross-study comparisons, the implications of synovial fluid, and the potential importance of multi-modal therapeutic strategies are discussed. As emerging, cell-specific disease modifying osteoarthritis drugs continue to be developed, the need for targeted nanomaterial delivery will likely become critical for effective clinical translation of therapeutics for osteoarthritis. STATEMENT OF SIGNIFICANCE: Improving drug delivery to the joint is a pressing clinical need. Over 27 million Americans live with osteoarthritis, and this figure is continuously expanding. Numerous drugs have been investigated but have failed in clinical trials, likely related to poor bioavailability to target cells. This article comprehensively reviews the advances in nano-scale delivery vehicles designed to overcome the delivery barriers in the joint. This is the first review to analyze active and passive targeting strategies systematically for different target sites while also delineating between tissue homing and whole joint retention. By bringing together the lessons learned across numerous nano-scale platforms, researchers may be able to hone future nanomaterial designs, allowing emerging therapeutics to perform with clinically relevant efficacy and disease modifying potential.

Ligustilide attenuates nitric oxide-induced apoptosis in rat chondrocytes and cartilage degradation via inhibiting JNK and p38 MAPK pathways

Ligustilide (LIG) is the main lipophilic component of the Umbelliferae family of pharmaceutical plants, including Radix angelicae sinensis and Ligusticum chuanxiong. LIG shows various pharmacological properties associated with anti‐inflammation and anti‐apoptosis in several kinds of cell lines. However, the therapeutic effects of LIG on chondrocyte apoptosis remain unknown. In this study, we investigated whether LIG had an anti‐apoptotic activity in sodium nitroprusside (SNP)‐stimulated chondrocyte apoptosis and could delay cartilage degeneration in a surgically induced rat OA model, and elucidated the potential mechanisms. In vitro studies revealed that LIG significantly suppressed chondrocyte apoptosis and cytoskeletal remodelling, which maintained the nuclear morphology and increased the mitochondrial membrane potential. In terms of SNP, LIG treatment considerably reduced the expression levels of cleaved caspase‐3, Bax and inducible nitric oxide synthase and increased the expression level of Bcl‐2 in a dose‐dependent manner. The LIG‐treated groups presented a significantly suppressed expression of activating transcription factor 2 and phosphorylation of Jun N‐terminal kinase (JNK) and p38 mitogen‐activated protein kinase (MAPK). The inhibitory effect of LIG was enhanced by the p38 MAPK inhibitor SB203580 or the JNK inhibitor SP600125 and offset by the agonist anisomycin. In vivo studies demonstrated that LIG attenuated osteoarthritic cartilage destruction by inhibiting the cartilage chondrocyte apoptosis and suppressing the phosphorylation levels of activating transcription factor 2, JNK and p38 MAPK. This result was confirmed by histological analyses, micro‐CT, TUNEL assay and immunohistochemical analyses. Collectively, our studies indicated that LIG protected chondrocytes against SNP‐induced apoptosis and delayed articular cartilage degeneration by suppressing JNK and p38 MAPK pathways.