Upregulation of articular synovial membrane μ-opioid-like receptors in an acute equine synovitis model

Longitudinal evaluation of fentanyl concentrations in equine plasma and synovial fluid following application of transdermal fentanyl patches over one carpal joint

OBJECTIVE

To determine if transdermally delivered fentanyl can achieve greater concentrations of fentanyl in synovial fluid when applied over a synovial structure.

STUDY DESIGN

Randomized, experimental study.

ANIMALS

Six healthy adult horses.

METHODS

Each horse had two 100 μg/h fentanyl matrix patches applied on the dorsal aspect of one, randomly assigned, carpometacarpal joint (CMCJ) for 48 h. Whole blood and bilateral synovial samples from the intercarpal joint were obtained at 0, 2, 6, 12, 24, 36 and 48 h. Fentanyl concentrations were measured with liquid chromatography-mass spectrometry.

RESULTS

All subjects achieved detectable concentrations of fentanyl in both plasma and synovial fluid. Time to peak synovial and plasma concentration was 12 h. At 6 h, the synovial concentration in the untreated carpus (0.104 ng/mL ± 0.106) was lower than plasma fentanyl concentrations 0.31 ± 0.27 (p = .036). At 12 h, both treated (0.55 ng/mL ± 0.3) and untreated (0.53 ng/mL ± 0.28) synovial fluid fentanyl concentrations were lower than plasma (0.87 ng/mL ± 0.48) concentrations (p < .001 and p = .001, respectively). Synovial concentrations of fentanyl did not differ between treated and untreated joints (p > 0.608 for all time points).

CONCLUSION

Application of fentanyl matrix patches directly over the CMCJ did not result in increased fentanyl concentrations in the synovial fluid of the treated intercarpal joint in normal horses.

CLINICAL SIGNIFICANCE

There is likely no analgesic advantage to placing fentanyl patches directly over the affected joint, as it did not result in increased synovial concentrations at the tested site.

Pharmacokinetics of intra-articular buprenorphine in horses with lipopolysaccharide-induced synovitis

The objective of this study was to describe the pharmacokinetics of intra-articular (IA) administered buprenorphine in horses with lipopolysaccharide (LPS)-induced synovitis. Radiocarpal synovitis was induced in six healthy adult horses with the IA injection of LPS (0.5 ng/joint) on two occasions in a randomized cross-over design. Treatments (IA buprenorphine (IAB) at 5 μg/kg plus intravenous saline; and intravenous buprenorphine (IVB) at 5 μg/kg plus IA saline) were administered 4 h following LPS injection. Concentrations of buprenorphine were assessed in plasma and synovial fluid (SF) at 0.5, 2, 6, 12, and 24 h after administration. Pharmacokinetic parameters after IVB and IAB in plasma and synovial fluid were calculated using a nonlinear mixed effects model. IAB was detectable in SF of all horses at 24 h [median concentration of 6.2 (3.46-22.6) ng/mL]. IAB resulted in a median plasma concentration of 0.59 (0.42-1.68) ng/mL at 0.5 h and was detectable in all subjects for up to 6 h and in two horses for up to 12 h. IVB resulted in SF concentrations detected up to 6 h in all horses [median concentration of 0.12 (0.07-0.82) ng/mL]. Results suggest that IA buprenorphine remains present in the inflamed joint for at least 24 h and systemic absorption occurs.

Buprenorphine has a concentration-dependent cytotoxic effect on equine chondrocytes in vitro

OBJECTIVE

To investigate the cytotoxic effects of 2 different concentrations of buprenorphine and compare them with bupivacaine and morphine on healthy equine chondrocytes in vitro.

SAMPLE

Primary cultured equine articular chondrocytes from 3 healthy adult horses.

PROCEDURES

Chondrocytes were exposed for 0 and 2 hours to the following treatments: media (CON; negative control); bupivacaine at 2.2 mg/mL (BUPI; positive control); morphine at 2.85 mg/mL (MOR); buprenorphine at 0.12 mg/mL (HBUPRE); or buprenorphine at 0.05 mg/mL (LBUPRE). Chondrocyte viability was assessed using live/dead staining, water-soluble tetrazolium salt-8 (WST-8) cytotoxic assay, LDH assay, and flow cytometry. All continuous variables were evaluated with a mixed ANOVA with treatment, time, and their interactions as the fixed effects and each horse as the random effect.

RESULTS

Buprenorphine showed a concentration-dependent chondrotoxic effect. The viability of chondrocytes was significantly decreased with exposure to HBUPRE and BUPI compared to CON, MOR, and LBUPRE.

CLINICAL RELEVANCE

Negligible chondrotoxic effects were observed in healthy cultured equine chondrocytes exposed to 0.05 mg/mL of buprenorphine, whereas higher concentrations (0.12 mg/mL) showed a marked cytotoxic effect. Based on these results, low concentrations of buprenorphine appear to be safe for intra-articular administration. Further evaluation of this dose in vivo is needed before recommending its clinical use.

The lipopolysaccharide model for the experimental induction of transient lameness and synovitis in Standardbred horses

An established lipopolysaccharide (LPS) model previously described in Warmbloods, was inconsistent in Standardbred horses, where lameness was not detected despite the presence of synovitis. The present study aimed to determine the dose of LPS from E. coli O55:B5 required to induce mild to moderate lameness following middle carpal joint injection in Standardbred horses and to quantitate the induced lameness over time, with and without anti-inflammatory pre-treatment. In a baseline trial, eight healthy, clinically sound Standardbred horses were used in a rule-based dose-escalation design trial, starting at a dose of 10 endotoxin units (EU). Lameness at trot was evaluated visually and quantitatively (using an inertial-sensor system and pressure plate analysis). Synovial fluid aspirates were analysed for total nucleated cell counts, total protein and prostaglandin E₂ (PGE₂). Following 2 months wash-out, the effective LPS-dose determined in the baseline trial was used to evaluate the effect of anti-inflammatory treatment. A mixed model for repeated measures with horse as random effect was used for analysis. After injection of 10 EU LPS, the desired degree of lameness was observed in the baseline trial, with maximal lameness at post-injection hour (PIH) 4, followed by a rapid decline and return to baseline by PIH 48. No lameness was observed following pre-treatment with meloxicam. In synovial fluid, PGE₂ was significantly higher at PIH 8 and PIH 24 in the baseline trial compared with following meloxicam pre-treatment. In conclusion, injection of the middle carpal joint with 10 EU LPS consistently induces a transient lameness and synovitis in Standardbred horses.

Intra-articular use of analgesic/antinflammatory drugs in dogs and horses

Joint pain is a major cause of lameness in animals such as horses and dogs, and it may affect their athletic performance and quality of life. The intra-articular administration of analgesic/antinflammatory drugs is a common practice in veterinary medicine, for both lameness diagnosis and joint pain management. It is used either perioperatively, such as in animals undergoing arthroscopy/arthrotomy, and in osteoarthritic animals. However, evidence regarding efficacy and safety of each drug is limited, and controversies persist in these areas. In particular, it is often uncertain whether a defined treatment is effective by simply relieving the symptomatic pain associated with the joint disease, or whether it has a positive effect on the joint environment. Moreover, there is still much hesitation about treatments for joint diseases, related to the time of their application for the best outcome, and to any possible deleterious side effects. This article includes a review of the literature concerning the main analgesic/antinflammatory drugs used intra-articularly for managing acute and chronic joint pain/inflammation in dogs and horses. Three main issues for each class of drugs are considered, including clinical efficacy, pharmacokinetics, and local cytotoxic effects.

Treatment effects of intra-articular triamcinolone acetonide in an equine model of recurrent joint inflammation

BACKGROUND

Intra-articular triamcinolone acetonide is a widely used treatment for joint inflammation despite limited scientific evidence of its efficacy.

OBJECTIVES

To investigate if intra-articular triamcinolone acetonide has sustained anti-inflammatory effects using an equine model of repeated joint inflammation.

STUDY DESIGN

Randomised controlled experimental study.

METHOD

For three consecutive cycles 2 weeks apart, inflammation was induced in both middle carpal joints of eight horses by injecting 0.25 ng lipopolysaccharide (LPS). After the first LPS injection only, treatment with 12 mg triamcinolone acetonide (TA) followed in one randomly assigned joint, while the contralateral joint was treated with sterile saline (control). Clinical parameters (composite welfare scores, joint effusion, joint circumference) were recorded and synovial fluid samples were analysed for various biomarkers (total protein, WBCC; PGE₂ ; CCL2; TNFα; MMP; GAGs; C2C; CPII) at fixed timepoints (post injection hours 0, 8, 24, 72 and 168). The effects of time and treatment on clinical and synovial fluid parameters and the presence of time-treatment interactions were tested using a linear mixed model for repeated measures with horse as a random effect, and time and treatment as fixed effects.

RESULTS

The TA treated joints showed significantly higher peak synovial GAG concentrations (Difference in means 283.1875 µg/mL, 95% CI 179.8, 386.6, P < 0.000), and PGE₂ levels (Difference in means 77.8025 pg/mL, 95% CI 21.2, 134.4, P < 0.007) after the first inflammation induction. Significantly lower TP levels were seen with TA treatment after the second induction (Difference in means -7.5 g/L, 95% CI -14.8, -0.20, P < 0.04) . Significantly lower WBCC levels were noted with TA treatment after the first (Difference in means -23.7125 × 10⁹  cells/L, 95% CI -46.7, -0.7, P < 0.04) and second (Difference in means -35.95 × 10⁹  cells/L, 95% CI -59.0, -12.9, P < 0.002) inflammation inductions. Significantly lower general MMP activity was also seen with TA treatment after the second inflammation inductions (Difference in means -51.65 RFU/s, 95% CI -92.4, -10.9, P < 0.01).

MAIN LIMITATIONS

This experimental study cannot fully reflect natural joint disease.

CONCLUSIONS

In this model, intra-articular TA seems to have some anti-inflammatory activity (demonstrated by reductions in TP, WBCC and general MMP activity) up to 2 weeks post treatment but not at 4 weeks. This anti-inflammatory effect appeared to outlast a shorter-lived, potentially detrimental effect illustrated by increased synovial GAG and PGE₂ levels after the first induction.

Inflamed synovial fluid induces a homeostatic response in bone marrow mononuclear cells in vitro: Implications for joint therapy

Synovial inflammation is a central feature of osteoarthritis (OA), elicited when local regulatory macrophages (M2-like) become overwhelmed, activating an inflammatory response (M1-like). Bone marrow mononuclear cells (BMNC) are a source of naïve macrophages capable of reducing joint inflammation and producing molecules essential for cartilage metabolism. This study investigated the response of BMNC to normal (SF) and inflamed synovial fluid (ISF). Equine BMNC cultured in autologous SF or ISF (n = 8 horses) developed into macrophage-rich cultures with phenotypes similar to cells native to normal SF and became more confluent in ISF (~100%) than SF (~25%). BMNC cultured in SF or ISF were neither M1- nor M2-like, but exhibited aspects of both phenotypes and a regulatory immune response, characterized by increasing counts of IL-10⁺ macrophages, decreasing IL-1β concentrations and progressively increasing IL-10 and IGF-1 concentrations. Changes were more marked in ISF and suggest that homeostatic mechanisms were preserved over time and were potentially favored by progressive cell proliferation. Collectively, our data suggest that intra-articular BMNC could increase synovial macrophage counts, potentiating the macrophage- and IL-10-associated mechanisms of joint homeostasis lost during the progression of OA, preserving the production of cytokines involved in tissue repair (PGE₂ , IL-10) generally impaired by frequently used corticosteroids.

Serotonin-evoked cytosolic Ca2+ release and opioid receptor expression are upregulated in articular cartilage chondrocytes from osteoarthritic joints in horses

Osteoarthritis is a pain-associated progressive disease and pain mediators, such as opioid receptors, expressed in articular cartilage could represent novel therapeutic targets. Acute and chronic stages of OA indicate different metabolic abilities of the chondrocytes depending on inflammatory state. This study aimed to investigate the response of healthy and osteoarthritic chondrocytes and their expression and release of pain mediators in response to acute inflammation. Interleukin-1 beta (IL-1β) and lipopolysaccharide (LPS) were used to induce an acute inflammatory response in cultured equine chondrocytes harvested from healthy joints (HC) and osteoarthritic joints (OAC), the latter representing acute exacerbation of a chronic inflammatory state. Intracellular Ca2+ release was determined after exposure to serotonin (5-hydroxytryptamine (5-HT), glutamate or ATP. Protein expression levels of F- and G-actin, representing actin rearrangement, and opioid receptors were investigated. Glutamate concentrations in culture media were measured. Cartilage was immunohistochemically stained for µ (MOR), κ (KOR), and δ (DOR) opioid receptors. Upon exposure to acute inflammatory stimuli, OAC showed increased intracellular Ca2+ release after 5-HT stimulation and increased expression of MOR and KOR. When cells were stimulated by inflammatory mediators, glutamate release was increased in both HC and OAC. Immunostaining for MOR was strong in OA cartilage, whereas KOR was less strongly expressed. DOR was not expressed by cultured HC and OAC and immunostaining of OA cartilage equivocal. We show that chondrocytes in different inflammatory stages react differently to the neurotransmitter 5-HT with respect to intracellular Ca2+ release and expression of peripheral pain mediators. Our findings suggest that opioids and neurotransmitters are important in the progression of equine OA. The inflammatory stage of OA (acute versus chronic) should be taken into consideration when therapeutic strategies are being developed.

Autologous bone marrow mononuclear cells modulate joint homeostasis in an equine in vivo model of synovitis

Osteoarthritis (OA) is characterized by macrophage-driven synovitis. Macrophages promote synovial health but become inflammatory when their regulatory functions are overwhelmed. Bone marrow mononuclear cells (BMNCs) are a rich source of macrophage progenitors used for treating chronic inflammation and produce essential molecules for cartilage metabolism. This study investigated the response to autologous BMNC injection in normal and inflamed joints. Synovitis was induced in both radiocarpal joints of 6 horses. After 8 h, 1 inflamed radiocarpal and 1 normal tarsocrural joint received BMNC injection. Contralateral joints were injected with saline. Synovial fluid was collected at 24, 96, and 144 h for cytology, cytokine quantification, and flow cytometry. At 144 h, horses were euthanatized, joints were evaluated, and synovium was harvested for histology and immunohistochemistry. Four days after BMNC treatment, inflamed joints had 24% higher macrophage counts with 10% more IL-10⁺ cells than saline-treated controls. BMNC-treated joints showed gross and analytical improvements in synovial fluid and synovial membrane, with increasing regulatory macrophages and synovial fluid IL-10 concentrations compared with saline-treated controls. BMNC-treated joints were comparable to healthy joints histologically, which remained abnormal in saline-treated controls. Autologous BMNCs are readily available, regulate synovitis through macrophage-associated effects, and can benefit thousands of patients with OA.-Menarim, B. C., Gillis, K. H., Oliver, A., Mason, C., Ngo, Y., Werre, S. R., Barrett, S. H., Luo, X., Byron, C. R., Dahlgren, L. A. Autologous bone marrow mononuclear cells modulate joint homeostasis in an equine in vivo model of synovitis.

Synovial butorphanol concentrations and mechanical nociceptive thresholds after intravenous regional limb perfusion in standing sedated horses

OBJECTIVE

To determine synovial butorphanol concentrations and mechanical nociceptive threshold (MNT) changes after butorphanol intravenous regional limb perfusion (IVRLP).

STUDY DESIGN

Experimental ANIMALS: Six adult horses.

METHODS

Cephalic IVRLP was performed with 10 mg butorphanol in sedated horses with a wide rubber tourniquet and a total volume of 30 mL. Radiocarpal synovial fluid and serum concentrations along with MNT were evaluated prior to and 0.5, 1, 2, 4, and 6 hours after IVRLP. Butorphanol concentrations were determined with liquid chromatography coupled to tandem mass spectrometry positive electrospray ionization.

RESULTS

Butorphanol concentrations reached mean (SD) peak concentrations of 9.47 ng/mL (±12.00) in synovial fluid and 3.89 ng/mL (3.29) in serum 30 minutes after IVRLP. Concentrations remained above baseline for 4 hours in synovial fluid (P ≤ .017) and for 2 hours in serum (P ≤ .016). The only difference in MNT was detected 1 hour after IVRLP, when MNT were higher in controls than in treated horses (P = .047).

CONCLUSION

Butorphanol IVRLP seemed well tolerated and resulted in measurable levels of butorphanol in the radiocarpal synovial fluid of five of six horses.

CLINICAL SIGNIFICANCE

Intravenous regional limb perfusion appears to be a viable alternative to administer butorphanol, but additional investigation is required to evaluate the dose and local concentrations required for analgesia.

Morphine, but not methadone, inhibits microsomal prostaglandin E synthase-1 and prostaglandin-endoperoxide synthase 2 in lipopolysaccharide-stimulated horse synoviocytes

Osteoarthritis (OA) is one of the main locomotor disorders in horses. Although nonsteroidal anti-inflammatory drugs are the first-line treatment for OA, opioids could also be used. In previous studies, opioids showed promising anti-inflammatory and analgesic effects. In this study, we aimed to investigate the effects of two opioids (morphine and methadone) against inflammation in lipopolysaccharide (LPS)-stimulated synoviocytes by analyzing microsomal prostaglandin E synthase-1 (mPGES-1) and prostaglandin-endoperoxide synthase 2 (PTGS2) expression. Synoviocytes were obtained from the joints at the distal limbs of dead animals. The cytotoxic effects of LPS, morphine, and methadone were investigated by using a cell viability assay with crystal violet dye. Synoviocytes were treated with LPS, LPS plus morphine, or LPS plus methadone for 3, 6, and 12 h, and mPGES-1 and PTGS2 expression was measured using real-time polymerase chain reaction. LPS, and morphine did not affect the viability of synoviocytes, even at high concentrations. LPS treatment increased mPGES-1 and PTGS2 expression, whereas morphine inhibited the increase in mPGES-1 and PTGS2 expression in LPS-stimulated synoviocytes. Methadone did not inhibit mPGES-1 or PTGS2 expression. These results suggest that morphine may exhibit anti-inflammatory effect; therefore, it might be beneficial for the treatment of OA.

Synovial membrane receptors as therapeutic targets: A review of receptor localization, structure, and function

Joint pathology and degeneration is a significant cause of pain. The synovial membrane plays an important role in maintenance of the joint, contributes to the pathology of many arthropathies and may be adversely affected in joint disease. Improving knowledge of the receptors present within the synovium will aid in a better understanding of joint pathology and the development of new treatments for diseases such as osteoarthritis and rheumatoid arthritis. Knowledge of the location and function of synovial membrane receptors (both in healthy and diseased synovium) may provide important targets in the treatment of various arthropathies. Classic pain receptors such as opioid receptors in the synovium are a mainstay in local and systemic management of chronic pain in many species. In addition to these, many other receptors such as bradykinin, neurokinin, transient receptor potential vanilloid, and inflammatory receptors, such as prostanoid and interleukin receptors have been discovered within the synovial membrane. These receptors are important in pain, inflammation, and in maintenance of normal joint function and may serve as targets for pharmacologic intervention in pathologic states. The goal of this review is to outline synovial membrane receptor localization and local therapeutic modulation of these receptors, in order to stimulate further research into pharmacological management of arthropathies at the local level. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1589-1605, 2017.

Pain Management in Horses

There has been great progress in the understanding of basic neurobiologic mechanisms of pain, but this body of knowledge has not yet translated into new and improved analgesics. Progress has been made regarding pain assessment in horses, but more work is needed until sensitive and accurate pain assessment tools are available for use in clinical practice. This review summarizes and updates the knowledge concerning the cornerstones of pain medicine (understand, assess, prevent, and treat). It highlights the importance of understanding pain mechanisms and expressions to enable a rational approach to pain assessment, prevention, and management in the equine patient.

Systematic pain assessment in horses

Accurate recognition and quantification of pain in horses is imperative for adequate pain management. The past decade has seen a much needed surge in formal development of systematic pain assessment tools for the objective monitoring of pain in equine patients. This narrative review describes parameters that can be used to detect pain in horses, provides an overview of the various pain scales developed (visual analogue scales, simple descriptive scales, numerical rating scales, time budget analysis, composite pain scales and grimace scales), and highlights their strengths and weaknesses for potential clinical implementation. The available literature on the use of each pain assessment tool in specific equine pain states (laminitis, lameness, acute synovitis, post-castration, acute colic and post-abdominal surgery) is discussed, including any problems with sensitivity, reliability or scale validation as well as translation of results to other clinical pain states. The review considers future development and further refinement of currently available equine pain scoring systems.

In vivo effects of phenylbutazone on inflammation and cartilage-derived biomarkers in equine joints with acute synovitis

Although phenylbutazone (PBZ) is commonly used in equine orthopaedic practice, little is known about its in vivo effects on joint inflammation and cartilage turnover. This study investigates the effects of PBZ on inflammatory parameters, matrix metalloproteinase (MMP) activity and cartilage biomarkers in equine joints with acute synovitis. In a two-period cross-over study, transient synovitis was induced at T = 0 h in the middle carpal joint of seven ponies by lipopolysaccharide (LPS) injection. Ponies received PBZ (2 mg/kg PO twice daily) or placebo for 1 week, starting at T = 2 h. Arthroscopic assessment of the middle carpal joint was performed at T = -504, 48 and 672 h. Synovial fluid (SF) was sampled at T = -504, 0, 8, 24, 48, 168, 336 and 672 h and analysed for leukocytes and total protein, substance P, general MMP activity, glycosaminoglycans (GAG), collagen II cleavage marker C2C and synthesis marker CPII. Markers in PBZ- vs. placebo-treated joints were compared over time using a linear mixed model. LPS injection caused marked transient synovitis without visible cartilage changes. Substance P and general MMP activity were not significantly reduced by PBZ treatment, nor were SF GAG or C2C concentrations at any time point. Concentration of CPII was significantly lower at T = 24 and 168 h in PBZ treated joints compared to placebo. Although PBZ is clinically effective in treating acute synovitis, it does not limit inflammation-induced cartilage catabolism and may transiently reduce collagen anabolism as evidenced by SF markers.