Pathways of Microvascular Permeability in the Synovium of Normal and Diseased Human Knees

Drug retention after intradiscal administration

Intradiscal drug delivery is a promising strategy for treating intervertebral disk degeneration (IVDD). Local degenerative processes and intrinsically low fluid exchange are likely to influence drug retention. Understanding their connection will enable the optimization of IVDD therapeutics. Release and retention of an inactive hydrophilic fluorine-19 labeled peptide (19F-P) as model for regenerative peptides was studied in a whole IVD culture model by measuring the 19F-NMR (nuclear magnetic resonance) signal in culture media and IVD tissue extracts. In another set-up, noninvasive near-infrared imaging was used to visualize IR-780, as hydrophobic small molecular drug model, retention upon injection into healthy and degenerative caudal IVDs in a rat model of disk degeneration. Furthermore, IR-780-loaded degradable polyester amide microspheres (PEAM) were injected into healthy and needle pricked degenerative IVDs, subcutaneously, and in knee joints with and without surgically-induced osteoarthritis (OA). Most 19F-P was released from the IVD after 7 days. IR-780 signal intensity declined over a 14-week period after bolus injection, without a difference between healthy and degenerative disks. IR-780 signal declined faster in the skin and knee joints compared to the IVDs. IR-780 delivery by PEAMs enhanced disk retention beyond 16 weeks. Moreover, in degenerated IVDs the IR-780 signal was higher over time than in healthy IVDs while no difference between OA and healthy joints was noted. We conclude that the clearance of peptides and hydrophobic small molecules from the IVD is relatively fast. These results illustrate that development of controlled release formulations should take into account the target anatomical location and local (patho)biology.

Association between synovial tissue damage and pain in late-stage knee osteoarthritis: A cross-sectional study

OBJECTIVE

To identify the presence and distribution of histopathological features of synovial inflammation and tissue damage, and to test their associations with ultrasound (US) imaging measures of synovitis and patient-reported measures of pain in knee osteoarthritis (OA).

DESIGN

In the cross-sectional study of 122 patients undergoing surgery for painful late-stage (Kellgren-Lawrence Grade 3 or 4) knee OA, we compared US measures of synovitis (n = 118) and pain (Knee Injury and Osteoarthritis Outcome Score) to histopathological measures of inflammation vs. synovial tissue damage in synovial tissue biopsies. Associations of histopathological features with US measures of inflammation or pain were assessed using linear or logistic regression while controlling for covariates.

RESULTS

Histopathological features of inflammation were associated with higher odds of moderate/severe US synovitis (odds ratio [OR] = 1.34 [95%CI 1.04, 1.74), whereas features of synovial tissue damage were associated with lower odds of moderate/severe US synovitis (OR = 0.77 [95%CI 0.57, 1.03]). Worse histopathological scores for synovial tissue damage were associated with more pain (-1.47 [95%CI -2.88, -0.05]), even while adjusting for synovial inflammation (-1.61 [95%CI -3.12, -0.10]).

CONCLUSIONS

Synovial tissue damage is associated with pain in late-stage knee OA, independent from inflammation and radiographic damage. These novel findings suggest that preventing synovial tissue damage may be an important goal of disease-modifying OA therapy.

Arthritis or an Adjacent Fascial Response? A Case Report of Combined Pyomyositis and Aseptic Arthritis

Pyomyositis, accompanied by aseptic arthritis, has been previously documented in several publications. However, none of the authors in the mentioned case reports offered a pathophysiological explanation for this unusual phenomenon or proposed a treatment protocol. We present a case of a healthy, 70-year-old male who was presented to the emergency department 4 days after tripping over a pile of wooden planks and getting stabbed by a nail to his thigh. The right thigh was swollen. Unproportional pain was produced by a light touch to the thigh. A laboratory test and a CT scan were obtained. The working diagnosis was pyomyositis of the thigh and septic arthritis of the ipsilateral knee. The patient underwent urgent debridement and irrigation of his right thigh. An arthroscopic knee lavage was performed as well. Intraoperative cultures from the thigh revealed the growth of Streptococcus pyogenes and Staphylococcus aureus. Cultures from synovial fluid were sterile; thus, septic arthritis was very unlikely. The source of the knee effusion might have been an aseptic inflammatory response due to the proximity of the thigh infection. Anatomically, the quadriceps muscle inserts on the patella, and its tendon fuses with the knee capsule, creating a direct fascial track from the thigh to the knee. The inflammatory response surrounding the infection may have followed this track, creating a domino effect, affecting adjacent capillaries within the joint capsule, and causing plasma leakage into the synovial space, leading to joint effusion. Our suggested treatment is addressing the primary infection with antibiotics and considering adding anti-inflammatory therapy, given our suspicion that this process has an inflammatory component.

A polymer network architecture provides superior cushioning and lubrication of soft tissue compared to a linear architecture

We report the relationships between linear vs. network polymer architecture and biomechanical outcomes including lubrication and cushioning when the polymers are applied to the surface of articulating knee cartilage. Aqueous formulations of the bioinspired polymer poly(2-methacryloyloxylethyl phosphorylcholine) (pMPC) exhibit tuneable rheological properties, with network pMPC exhibiting increased elasticity and viscosity compared to linear pMPC. Application of a polymer network, compared to a linear one, to articulating tissue surfaces reduces friction, lessens tissue strain, minimizes wear, and protects tissue - thereby improving overall tissue performance. Administration of the network pMPC to the middle carpal joint of skeletally mature horses elicits a safe response similar to saline as monitored over a 70 day period.

Transarterial Embolization of Neovascularity for Refractory Nighttime Shoulder Pain: A Multicenter, Open-Label, Feasibility Trial

PURPOSE

To assess the feasibility of transarterial embolization (TAE) for recalcitrant nighttime shoulder pain in a multicentric study.

MATERIALS AND METHODS

This prospective, open-label, feasibility trial included 100 patients treated at 5 institutions. TAE was performed in 76 patients with adhesive capsulitis (AC) and 24 patients with symptomatic rotator cuff tears (sRCTs). The ipsilateral radial artery was punctured, and imipenem/cilastatin sodium was infused as an embolic agent. Adverse events, 10 point pain numerical rating scale (NRS), range of motion (ROM) of the shoulder joint, and quality of life (via the EuroQol-5D [EQ-5D]) were evaluated.

RESULTS

All patients exhibited neovascularity on baseline angiography, and all TAE procedures were performed successfully. No patient experienced a major adverse event. The mean nighttime pain NRS scores at baseline and 1, 3, and 6 months after TAE were 6.4 ± 2.2, 3.4 ± 2.6, 2.3 ± 2.5, and 1.6 ± 2.2, respectively (for all, P < .001). The mean ROM of anterior elevation at baseline and 1, 3, and 6 months after TAE were 97° ± 29°, 119° ± 28°, 135° ± 27°, and 151° ± 17°, respectively (for all, P < .001). The mean EQ-5D scores at baseline and 1, 3, and 6 months after TAE were 0.63 ± 0.17, 0.73 ± 0.16, 0.80 ± 0.17, and 0.84 ± 0.17, respectively (for all, P < .001). There was no significant difference in the clinical success rate between the AC and sRCT groups.

CONCLUSIONS

TAE for nighttime shoulder pain caused by AC and sRCTs was feasible with sufficient safety and efficacy.

An orally available small molecule that targets soluble TNF to deliver anti-TNF biologic-like efficacy in rheumatoid arthritis

Tumor necrosis factor (TNF) is a pleiotropic cytokine belonging to a family of trimeric proteins with both proinflammatory and immunoregulatory functions. TNF is a key mediator in autoimmune diseases and during the last couple of decades several biologic drugs have delivered new therapeutic options for patients suffering from chronic autoimmune diseases such as rheumatoid arthritis and chronic inflammatory bowel disease. Attempts to design small molecule therapies directed to this cytokine have not led to approved products yet. Here we report the discovery and development of a potent small molecule inhibitor of TNF that was recently moved into phase 1 clinical trials. The molecule, SAR441566, stabilizes an asymmetrical form of the soluble TNF trimer, compromises downstream signaling and inhibits the functions of TNF in vitro and in vivo. With SAR441566 being studied in healthy volunteers we hope to deliver a more convenient orally bioavailable and effective treatment option for patients suffering with chronic autoimmune diseases compared to established biologic drugs targeting TNF.

Assessment of joint pharmacokinetics and consequences for the intraarticular delivery of biologics

Intraarticular (IA) injections provide the opportunity to deliver biologics directly to their site of action for a local and efficient treatment of osteoarthritis. However, the synovial joint is a challenging site of administration since the drug is rapidly eliminated across the synovial membrane and has limited distribution into cartilage, resulting in unsatisfactory therapeutic efficacy. In order to rationally develop appropriate drug delivery systems, it is essential to thoroughly understand the unique biopharmaceutical environments and kinetics in the joint to adequately simulate them in relevant experimental models. This review presents a detailed view on articular kinetics and drug-tissue interplay of IA administered drugs and summarizes how these can be translated into reasonable formulation strategies by identification of key factors through which the joint residence time can be prolonged and specific structures can be targeted. In this way, pros and cons of the delivery approaches for biologics will be evaluated and the extent to which biorelevant models are applicable to gain mechanistic insights and ameliorate formulation design is discussed.

What Function Do Platelets Play in Inflammation and Bacterial and Viral Infections?

The article presents the function of platelets in inflammation as well as in bacterial and viral infections, which are the result of their reaction with the endovascular environment, including cells of damaged vascular endothelium and cells of the immune system. This role of platelets is conditioned by biologically active substances present in their granules and in their specific structures - EV (extracellular vesicles).

Multichromatic near-infrared imaging to assess interstitial lymphatic and venous uptake in vivo

SIGNIFICANCE

Changes in interstitial fluid clearance are implicated in many diseases. Using near-infrared (NIR) imaging with properly sized tracers could enhance our understanding of how venous and lymphatic drainage are involved in disease progression or enhance drug delivery strategies.

AIM

We investigated multichromatic NIR imaging with multiple tracers to assess in vivo microvascular clearance kinetics and pathways in different tissue spaces.

APPROACH

We used a chemically inert IR Dye 800CW (D800) to target venous capillaries and a purified conjugate of IR dye 680RD with 40 kDa PEG (P40D680) to target lymphatic capillaries in vivo. Optical imaging settings were validated and tuned in vitro using tissue phantoms. We investigated multichromatic NIR imaging's utility in two in vivo tissue beds: the mouse tail and rat knee joint. We then tested the ability of the approach to detect interstitial fluid perturbations due to exercise.

RESULTS

In an in vitro simulated tissue environment, free dye and PEG mixture allowed for simultaneous detection without interference. In the mouse tail, co-injected NIR tracers cleared from the interstitial space via distinct routes, suggestive of lymphatic and venous uptake mechanisms. In the rat knee, we determined that exercise after injection transiently increased lymphatic drainage as measured by lower normalized intensity immediately after exercise, whereas exercise pre-injection exhibited a transient delay in clearance from the joint.

CONCLUSIONS

NIR imaging enables simultaneous imaging of lymphatic and venous-mediated fluid clearance with great sensitivity and can be used to measure temporal changes in clearance rates and pathways.

A Proteinase 3 Contribution to Juvenile Idiopathic Arthritis-Associated Cartilage Damage

A full understanding of the molecular mechanisms implicated in the etiopathogenesis of juvenile idiopathic arthritis (JIA) is lacking. A critical role for leukocyte proteolytic activity (e.g., elastase and cathepsin G) has been proposed. While leukocyte elastase’s (HLE) role has been documented, the potential contribution of proteinase 3 (PR3), a serine protease present in abundance in neutrophils, has not been evaluated. In this study we investigated: (1) PR3 concentrations in the synovial fluid of JIA patients using ELISA and (2) the cartilage degradation potential of PR3 by measuring the hydrolysis of fluorescently labeled collagen II in vitro. In parallel, concentrations and collagen II hydrolysis by HLE were assessed. Additionally, the levels of the co-secreted primary granule protein myeloperoxidase (MPO) were assessed in synovial fluid of patients diagnosed with JIA. We report the following levels of analytes in JIA synovial fluid: PR3—114 ± 100 ng/mL (mean ± SD), HLE—1272 ± 1219 ng/mL, and MPO—1129 ± 1659 ng/mL, with a very strong correlation between the PR3 and HLE concentrations (r_s = 0.898, p < 1 × 10^–6). Importantly, PR3 hydrolyzed fluorescently labeled collagen II as efficiently as HLE. Taken together, these novel findings suggest that PR3 (in addition to HLE) contributes to JIA-associated joint damage.

An ex-vivo model for transsynovial drug permeation of intraarticular injectables in naive and arthritic synovium

Estimation of joint residence time of a drug is a key requirement for rational development of intraarticular therapeutics. There is a great need for a predictive model to reduce the high number of animal experiments in early stage development. Here, a Franz-cell based porcine ex-vivo permeation model is proposed, and transsynovial permeation of fluorescently-labeled dextrans in the range of potential drug candidates (10-150 kDa), as well as a small molecule (fluorescein sodium) and charged dextran derivates, have been determined. In addition, a lipopolysaccharide (LPS) -induced synovitis model was assessed for inflammatory biomarker levels and its effect on permeation of the solutes. Size-dependent permeability was observed for the analytes, which distinctly differed from findings with an artificial polycarbonate membrane, which is a widely used model. LPS was found to successfully stimulate an inflammatory response and led to a reduced size selectivity of the synovial membrane. 150 kDa dextran flux was accelerated approximately 2.5-fold in the inflamed state, whereas the permeation of smaller molecules was little affected. Moreover, by varying the LPS concentrations, the ex-vivo model was shown to produce varying degrees of synovitis-like inflammation. A simple and highly relevant ex-vivo tool for investigation of transsynovial permeation was developed, offering the further advantage of mimicking synovitis-induced permeability changes. Thus, this model provides a promising method for formulation screening, while reducing the need for animal experiments.

Endothelin-1 inhibits size dependent lymphatic clearance of PEG-based conjugates after intra-articular injection into the rat knee

Clearance of particles from the knee is an essential mechanism to maintain healthy joint homeostasis and critical to the delivery of drugs and therapeutics. One of the limitations in developing disease modifying drugs for joint diseases, such as osteoarthritis (OA), has been poor local retention of the drugs. Enhancing drug retention within the joint has been a target of biomaterial development, however, a fundamental understanding of joint clearance pathways has not been characterized. We applied near-infrared (NIR) imaging techniques to assess size-dependent in vivo clearance mechanisms of intra-articular injected, fluorescently-labelled polyethylene glycol (PEG-NIR) conjugates. The clearance of 2 kDa PEG-NIR (τ = 171 ± 11 min) was faster than 40 kDa PEG-NIR (τ = 243 ± 16 min). 40 kDa PEG-NIR signal was found in lumbar lymph node while 2 kDa PEG-NIR signal was not. Thus, these two conjugates may be cleared through different pathways, i.e. lymphatics for 40 kDa PEG-NIR and venous for 2 kDa PEG-NIR. Endothelin-1 (ET-1), a potent vasoconstrictor of vessels, is elevated in synovial fluid of OA patients but, its effects on joint clearance are unknown. Intra-articular injection of ET-1 dose-dependently inhibited the clearance of both 2 kDa and 40 kDa PEG-NIR. ET-1 caused a 1.63 ± 0.17-fold increase in peak fluorescence for 2 kDa PEG-NIR and a 1.85 ± 0.15-fold increase for 40 kDa PEG-NIR; and ET-1 doubled their clearance time constants. The effects of ET-1 were blocked by co-injection of ET receptor antagonists, bosentan or BQ-123. These findings provide fundamental insight into retention and clearance mechanisms that should be considered in the development and delivery of drugs and biomaterial carriers for joint diseases. STATEMENT OF SIGNIFICANCE: This study demonstrates that in vivo knee clearance can be measured using NIR technology and that key factors, such as size of materials and biologics, can be investigated to define joint clearance mechanisms. Therapies targeting regulation of joint clearance may be an approach to treat joint diseases like osteoarthritis. Additionally, in vivo functional assessment of clearance may be used as diagnostics to monitor progression of joint diseases.

A Synthetic Bottle-brush Polyelectrolyte Reduces Friction and Wear of Intact and Previously Worn Cartilage

A poly(7-oxanorbornene-2-carboxylate) polymer containing pendent triethyleneglycol (TEG) chains of 2.8 MDa ("2.8M TEG") was synthesized and evaluated for long-term lubrication and wear reduction of ex vivo bovine cartilage as well as for synovitis in rats and dogs after intra-articular administration. Bovine cartilage surfaces were tested under torsional friction for 10,080 rotations while immersed in either saline, bovine synovial fluid (BSF), or 2.8M TEG. For each solution, coefficient of friction (μ), changes in surface roughness, and lost cartilage glycosaminoglycan were compared. To directly compare 2.8M TEG and BSF, additional samples were tested sequentially in BSF, BSF, 2.8M TEG, and then BSF. Finally, another set of samples were tested twice in saline to induce surface roughness and then tested in BSF, Synvisc, or 2.8M TEG to determine each treatment's effect on worn cartilage. Next, male Lewis rats were injected in one knee with 2.8M TEG or saline and evaluated for effects on gait, and female beagles were injected with either 2.8M TEG or saline in one knee, and their synovial tissues analyzed for inflammation by H&E staining. Treatment with 2.8M TEG lowers μ, lessens surface roughness, and minimizes glycosaminoglycan loss compared to saline. The 2.8M TEG also reduces μ compared to BSF in pairwise testing and on worn cartilage surfaces. Injection of 2.8M TEG in rat or beagle knees gives comparable effects to treatment with saline, and does not cause significant synovitis.

Development of a Porcine Lymph Drainage Model to Study Particle Migration

Background: Intra-articular wear particulate migration from the knee joint has been studied in various animal models as well as postmortem in patients who received total knee joint replacement. However, there still exists a need for a simple, yet analogous animal model for tracking the migration of wear debris from the knee joint, especially through the draining lymph nodes. Methods and Results: To fill this need, a proof-of-concept porcine model was developed for particle migration from the knee joint into the surrounding lymphatic system. Vitreous carbon particles were deposited both intra-articularly and extracapsularly in a bilateral manner to the hind limbs in pigs (n = 6). The regional/draining lymph nodes were qualitatively assessed weekly by a veterinarian by manual palpation to detect any enlargement or change in consistency when compared to the initial assessment before the surgical procedure. At 6 weeks, the draining lymph nodes were harvested and processed for histology. Microscopic evaluation showed carbon particle migration from the knee into 100% of the iliac lymph nodes, 50% of the inguinal lymph nodes, and 0% of the popliteal lymph nodes. Discussion: Overall, this study established a needed animal model for evaluating carbon particle migration to the draining lymph nodes from the knee joint.

Combinatorial Prg4 and Il-1ra Gene Therapy Protects Against Hyperalgesia and Cartilage Degeneration in Post-Traumatic Osteoarthritis

Osteoarthritis (OA) is a degenerative disease of synovial joints characterized by progressive loss of articular cartilage, subchondral bone remodeling, and intra-articular inflammation with synovitis that results in chronic pain and motor impairment. Despite the economic and health impacts, current medical therapies are targeted at symptomatic relief of OA and fail to alter its progression. Given the complexity of OA pathogenesis, we hypothesized that a combinatorial gene therapy approach, designed to inhibit inflammation with interleukin-1 receptor antagonist (IL-1Ra) while promoting chondroprotection using lubricin (PRG4), would improve preservation of the joint compared to monotherapy alone. Employing two surgical techniques to model mild, moderate and severe posttraumatic OA, we found that combined delivery of helper-dependent adenoviruses (HDVs), expressing IL-1Ra and PRG4, preserved articular cartilage better than either monotherapy in both models as demonstrated by preservation of articular cartilage volume and surface area. This improved protection was associated with increased expression of proanabolic and cartilage matrix genes together with decreased expression of catabolic genes and inflammatory mediators. In addition to improvements in joint tissues, this combinatorial gene therapy prolonged protection against thermal hyperalgesia compared to either monotherapy. Taken together, our results show that a combinatorial strategy is superior to monotherapeutic approaches for treatment of posttraumatic OA.

Prophylactic and therapeutic activity of alkaline phosphatase in arthritic rats: single-agent effects of alkaline phosphatase and synergistic effects in combination with methotrexate

Alkaline phosphatase (AP) is a gate-keeper of innate immune system responses by detoxifying inflammation triggering moieties released from endogenous and external sources. We examined whether AP's broad mechanism of action constitutes a safe therapeutic, either as single agent or combined with methotrexate (MTX), for chronic inflammatory disorders, for example, rheumatoid arthritis (RA). A rat model for RA was used with repeated intra-articular methylated bovine serum albumin (mBSA) injections in 1 knee ("arthritic" knee), with the contralateral knee serving as internal control. AP (200 µg, subcut) was administered before mBSA injections (prophylactic setting) or after arthritis induction (therapeutic setting) or combined with MTX (0.3 mg/kg or 1 mg/kg; intraperitoneally). As end point of treatment outcome, macrophage infiltration in knees, liver, and spleen was assessed by immunohistochemistry (ED1 and ED2 expression), immunofluoresence (macrophage marker folate receptor-β [FRβ]), and [¹⁸F]fluoro-polyethylene glycol-folate positron emission tomography (PET) (macrophage imaging) and ex vivo tissue distribution. Single-agent AP treatment and combinations with MTX were well tolerated. Both prophylactic and therapeutic AP markedly reduced synovial macrophage infiltration in arthritic knees (ED1: 3.5- to 4-fold; ED2: 3.5- to 6-fold), comparable with MTX treatment. AP-MTX combinations slightly improved on single agent effects. PET monitoring and ex vivo tissue distribution studies corroborated the impact of AP, MTX, and AP-MTX on reducing synovial macrophage infiltration. Beyond localized articular effects, AP also revealed systemic anti-inflammatory effects by a 2-fold reduction of ED1, ED2, and FRβ⁺ macrophages in liver and spleen of arthritic rats. Collectively, single-agent AP and AP combined with MTX elicited local and systemic anti-arthritic activity in arthritic rats.

Vascular Permeability and Remodelling Coincide with Inflammatory and Reparative Processes after Joint Bleeding in Factor VIII-Deficient Mice

Vascular remodelling is a prominent feature of haemophilic arthropathy (HA) that may underlie re-bleeding, yet the nature of vascular changes and underlying mechanisms remain largely unknown. Here, we aimed to characterize synovial vascular remodelling and vessel integrity after haemarthrosis, as well as temporal changes in inflammatory and tissue-reparative pathways. Thirty acutely painful joints in patients with haemophilia (PWH) were imaged by musculoskeletal ultrasound with Power Doppler (MSKUS/PD) to detect vascular abnormalities and bloody effusions. Nineteen out of 30 painful joint episodes in PWH were associated with haemarthrosis, and abnormal vascular perfusion was unique to bleeding joints. A model of induced haemarthrosis in factor VIII (FVIII)-deficient mice was used for histological assessment of vascular remodelling (α-smooth muscle actin [αSMA] expression), and monitoring of in vivo vascular perfusion and permeability by MSKUS/PD and albumin extravasation, respectively. Inflammatory (M1) and reparative (M2) macrophage markers were quantified in murine synovium over a 10-week time course by real-time polymerase chain reaction. The abnormal vascular perfusion observed in PWH was recapitulated in FVIII-deficient mice after induced haemarthrosis. Neovascularization and increased vessel permeability were apparent 2 weeks post-bleed in FVIII-deficient mice, after a transient elevation of inflammatory macrophage M1 markers. These vascular changes subsided by week 4, while vascular remodelling, evidenced by architectural changes and pronounced αSMA expression, persisted alongside a reparative macrophage M2 response. In conclusion, haemarthrosis leads to transient inflammation coupled with neovascularization and associated vascular permeability, while subsequent tissue repair mechanisms coincide with vascular remodelling. Together, these vascular changes may promote re-bleeding and HA progression.

Protein oxidation, nitration and glycation biomarkers for early-stage diagnosis of osteoarthritis of the knee and typing and progression of arthritic disease

Background

There is currently no blood-based test for detection of early-stage osteoarthritis (OA) and the anti-cyclic citrullinated peptide (CCP) antibody test for rheumatoid arthritis (RA) has relatively low sensitivity for early-stage disease. Morbidity in arthritis could be markedly decreased if early-stage arthritis could be routinely detected and classified by clinical chemistry test. We hypothesised that damage to proteins of the joint by oxidation, nitration and glycation, and with signatures released in plasma as oxidized, nitrated and glycated amino acids may facilitate early-stage diagnosis and typing of arthritis.

Methods

Patients with knee joint early-stage and advanced OA and RA or other inflammatory joint disease (non-RA) and healthy subjects with good skeletal health were recruited for the study (n = 225). Plasma/serum and synovial fluid was analysed for oxidized, nitrated and glycated proteins and amino acids by quantitative liquid chromatography-tandem mass spectrometry. Data-driven machine learning methods were employed to explore diagnostic utility of the measurements for detection and classifying early-stage OA and RA, non-RA and good skeletal health with training set and independent test set cohorts.

Results

Glycated, oxidized and nitrated proteins and amino acids were detected in synovial fluid and plasma of arthritic patients with characteristic patterns found in early and advanced OA and RA, and non-RA, with respect to healthy controls. In early-stage disease, two algorithms for consecutive use in diagnosis were developed: (1) disease versus healthy control, and (2) classification as OA, RA and non-RA. The algorithms featured 10 damaged amino acids in plasma, hydroxyproline and anti-CCP antibody status. Sensitivities/specificities were: (1) good skeletal health, 0.92/0.91; (2) early-stage OA, 0.92/0.90; early-stage RA, 0.80/0.78; and non-RA, 0.70/0.65 (training set). These were confirmed in independent test set validation. Damaged amino acids increased further in severe and advanced OA and RA.

Conclusions

Oxidized, nitrated and glycated amino acids combined with hydroxyproline and anti-CCP antibody status provided a plasma-based biochemical test of relatively high sensitivity and specificity for early-stage diagnosis and typing of arthritic disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-016-1154-3) contains supplementary material, which is available to authorized users.

Type II collagen C2C epitope in human synovial fluid and serum after knee injury--associations with molecular and structural markers of injury

PURPOSE

Investigate in a cross-sectional study time-dependent changes of synovial fluid type II collagen epitope C2C concentrations after knee injury and correlate to other joint injury biomarkers.

METHODS

Synovial fluid samples were aspirated between 0 days and 7 years after injury (n = 235). Serum was collected from 71 of the knee injured patients. Synovial fluid from 8 knee-healthy subjects was used as reference. C2C was quantified by immunoassay and structural injury was determined from magnetic resonance images (MRI) of the injured knee acquired 1-38 days after injury (n = 98). Additional joint injury biomarker results were from earlier investigations of the same samples.

RESULTS

Synovial fluid C2C concentrations were higher in injured knees than in knees of reference subjects from 1 day up to 7 years after injury. C2C concentrations in synovial fluid and serum were correlated (r = 0.403, P < 0.001). In synovial fluid from subjects early after injury (0-33 days), C2C concentrations were correlated with cross-linked C-telopeptide of type II collagen (r = 0.444, P = 0.003), ARGS-aggrecan (r = 0.337, P < 0.001), osteocalcin (r = 0.345, P < 0.001), osteopontin (r = 0.371, P < 0.001) and IL-8 (r = -0.385, P < 0.001), but not with structural joint injury as visualized on MRI.

CONCLUSION

The increased levels of synovial fluid C2C after injury, together with the associations seen with several other injury-related biomarkers, suggest that an acute knee injury is associated with an immediate and sustained local degradation of type II collagen.

Human xylosyltransferases--mediators of arthrofibrosis? New pathomechanistic insights into arthrofibrotic remodeling after knee replacement therapy

Total knee replacement (TKR) is a common therapeutic option to restore joint functionality in chronic inflammatory joint diseases. Subsequent arthrofibrotic remodeling occurs in 10%, but the underlying pathomechanisms remain unclear. We evaluated the association of xylosyltransferases (XT), fibrotic mediators catalyzing glycosaminoglycan biosynthesis, leading to arthrofibrosis as well as the feasibility of using serum XT activity as a diagnostic marker. For this purpose, synovial fibroblasts (SF) were isolated from arthrofibrotic and control synovial biopsies. Basal α-smooth muscle actin expression revealed a high fibroblast-myofibroblast transition rate in arthrofibrotic fibroblasts. Fibrotic remodeling marked by enhanced XT activity, α-SMA protein expression as well as xylosyltransferase-I, collagen type III-alpha-1 and ACTA2 mRNA expression was stronger in arthrofibrotic than in control fibroblasts treated with transforming growth factor-β1 (TGF-β1). Otherwise, no differences between serum levels of XT-I activity or common fibrosis markers (galectin-3 and growth differentiation factor-15 levels (GDF-15)) were found between 95 patients with arthrofibrosis and 132 controls after TKR. In summary, XT-I was initially investigated as a key cellular mediator of arthrofibrosis and a target for therapeutic intervention. However, the blood-synovial-barrier makes arthrofibrotic molecular changes undetectable in serum. Future studies on monitoring or preventing arthrofibrotic remodeling should therefore rely on local instead of systemic parameters.

The human knee: A window on the microvasculature

In synovial joints, the lining cells do not have tight junctions with their neighboring cells and they have no underlying basement membrane. Therefore, the synovial fluid within the articular cavity is continuous with the interstitial fluid of the synovial intima. These features, combined with ready access to the space via arthrocentesis, permit quantitative studies of microvascular function in the knees of unanesthetized, volunteer, human subjects both with and without chronic arthritis. This brief article reviews the principal findings of such work over ∼40 years at the University of Washington. Examined variables include bidirectional fenestral diffusion of small solutes, effective blood flow, lymphatic drainage, and endothelial pore size and permeability. The latter work introduced a new method using gel filtration chromatography of paired synovial fluid (SF) and serum (S) to obtain essentially continuous SF/S ratios over a range of radii between 1 and 12 nanometers.

Platelets in inflammation and infection

Although platelets are traditionally recognized for their central role in hemostasis, many lines of research clearly demonstrate these rather ubiquitous blood components are potent immune modulators and effectors. Platelets have been shown to directly recognize, sequester and kill pathogens, to activated and recruit leukocytes to sites of infection and inflammation, and to modulate leukocyte behavior, enhancing their ability to phagocytose and kill pathogens and inducing unique effector functions, such as the production of Neutrophil Extracellular Traps (NETs). This multifaceted response to infection and inflammation is due, in part, to the huge array of soluble mediators and cell surface molecules expressed by platelets. From their earliest origins as primordial hemocytes in invertebrates to their current form as megakaryocyte-derived cytoplasts, platelets have evolved to be one of the key regulators of host intravascular immunity and inflammation. In this review, we present the diverse roles platelets play in immunity and inflammation associated with autoimmune diseases and infection. Additionally, we highlight recent advances in our understanding of platelet behavior made possible through the use of advanced imaging techniques that allow us to visualize platelets and their interactions, in real-time, within the intact blood vessels of a living host.

A prodrug approach involving in situ depot formation to achieve localized and sustained action of diclofenac after joint injection

Long-acting nonsteroidal anti-inflammatory drug formulations for intra-articular injection might be effective in the management of joint pain and inflammation associated sports injuries and osteoarthritis. In this study, a prodrug-based delivery system was evaluated. The synthesized diclofenac ester prodrug, a weak base (pKa 7.52), has relatively high solubility at low pH (6.5 mg mL(-1) at pH 4) and much lower solubility at physiological pH (4.5 μg mL(-1) at pH 7.4) at 37°C. In biological media including 80% (v/v) human synovial fluid (SF), the prodrug was cleaved to diclofenac mediated by esterases. In situ precipitation of the prodrug was observed upon addition of a concentrated slightly acidic prodrug solution to phosphate buffer or SF at pH 7.4. The degree of supersaturation accompanying the precipitation process was more pronounced in SF than in phosphate buffer. In the rotating dialysis cell model, a slightly acidic prodrug solution was added to the donor cell containing 80% SF resulting in a continuous appearance of diclofenac in the acceptor phase for more than 43 h after an initial lag period of 8 h. Detectable amounts of prodrug were found in the rat joint up to 8 days after knee injection of the acidic prodrug solution.

Progress in intra-articular therapy

Diarthrodial joints are well suited to intra-articular injection, and the local delivery of therapeutics in this fashion brings several potential advantages to the treatment of a wide range of arthropathies. Possible benefits over systemic delivery include increased bioavailability, reduced systemic exposure, fewer adverse events, and lower total drug costs. Nevertheless, intra-articular therapy is challenging because of the rapid egress of injected materials from the joint space; this elimination is true of both small molecules, which exit via synovial capillaries, and of macromolecules, which are cleared by the lymphatic system. In general, soluble materials have an intra-articular dwell time measured only in hours. Corticosteroids and hyaluronate preparations constitute the mainstay of FDA-approved intra-articular therapeutics. Recombinant proteins, autologous blood products and analgesics have also found clinical use via intra-articular delivery. Several alternative approaches, such as local delivery of cell and gene therapy, as well as the use of microparticles, liposomes, and modified drugs, are in various stages of preclinical development.

The association of adipokine levels in plasma and synovial fluid with the severity of knee osteoarthritis

OBJECTIVE

We sought to determine the association between plasma and SF levels of leptin and adiponectin in patients with knee OA.

METHODS

Plasma and SF levels of adipokines and soluble leptin receptor (sOB-R) were determined by ELISA in 96 patients with knee OA at different stages, according to Ahlback's classification.

RESULTS

Levels of adiponectin, leptin, sOB-R and free leptin in plasma and SF did not differ significantly across categories of OA severity. However, the ratio of SF to plasma leptin was significantly lower in the advanced OA stage compared with early stages of the disease (P = 0.02). After adjustment for sex and BMI, plasma leptin positively correlated with categories of OA severity (r = 0.23, P = 0.02), whereas SF/plasma leptin negatively correlated with OA stage (r = -0.27, P = 0.01). Cluster analysis showed that all men were included in one cluster and distributed in different stages of OA, whereas women formed three clusters with similar BMI, but those who were older and had the highest plasma leptin levels suffered from advanced OA.

CONCLUSION

Plasma leptin positively correlated with the severity of knee OA. The ratio of SF to plasma leptin might be a marker related to the severity of knee OA. Further studies should investigate whether similar associations exist in other joints affected by OA.

Platelets can enhance vascular permeability

Platelets survey blood vessels, searching for endothelial damage and preventing loss of vascular integrity. However, there are circumstances where vascular permeability increases, suggesting that platelets sometimes fail to fulfill their expected function. Human inflammatory arthritis is associated with tissue edema attributed to enhanced permeability of the synovial microvasculature. Murine studies have suggested that such vascular leak facilitates entry of autoantibodies and may thereby promote joint inflammation. Whereas platelets typically help to promote microvascular integrity, we examined the role of platelets in synovial vascular permeability in murine experimental arthritis. Using an in vivo model of autoimmune arthritis, we confirmed the presence of endothelial gaps in inflamed synovium. Surprisingly, permeability in the inflamed joints was abrogated if the platelets were absent. This effect was mediated by platelet serotonin accumulated via the serotonin transporter and could be antagonized using serotonin-specific reuptake inhibitor antidepressants. As opposed to the conventional role of platelets to microvascular leakage, this demonstration that platelets are capable of amplifying and maintaining permeability adds to the rapidly growing list of unexpected functions for platelets.