Crystals, inflammation, and osteoarthritis

Gram and acridine orange staining for diagnosis of septic arthritis in different patient populations

PURPOSE

The sensitivity of Gram staining is known to be suboptimal for the diagnosis of native joint septic arthritis. We lack information about the accuracy of Gram compared to other microscopic staining techniques for predicting infection in different patient populations.

METHODS

This was a cohort study with cost evaluations at the Orthopaedic Service of Geneva University Hospitals (January 1996-October 2012).

RESULTS

Among 500 episodes of arthritis (196 with immunosuppression, 227 with underlying arthroplasties and 69 with gout or other crystals in synovial fluid), Gram staining revealed pathogens in 146 episodes (146/500, 29 %) or in 146 of the 400 culture-positive episodes (37 %). Correlation between the Gram and acridine staining of the same sample was good (Spearman 0.85). Overall, the sensitivity, specificity, positive predictive value and negative predictive value of Gram stain for rapid diagnosis of septic arthritis was 0.37, 0.99, 0.99 and 0.28, respectively, compared to microbiological cultures. Quite similar values were recorded across the different patient subpopulations, in particular for sensitivity values that were 0.33 for patients with prosthetic joint infections, 0.40 for immunosuppressed patients, 0.36 for patients under antibiotic administration and 0.52 for patients with concomitant crystalline disease.

CONCLUSIONS

The sensitivity of Gram or acridine orange staining for a rapid diagnosis of episodes of septic arthritis is suboptimal compared to microbiological culture, regardless of underlying conditions, immunosuppression or antibiotic therapy. The sensitivity in the presence of synovial fluid crystals is moderate. Acridine orange and Gram stains are equivalent.

Metabolic and endocrine diseases, cartilage calcification and arthritis

PURPOSE OF REVIEW

Osteoarthritis is the most common form of rheumatologic disease, with numerous factors increasing the risk of developing the condition; calcification of cartilage is common place in osteoarthritis. Regardless of these risk factors, certain disorders predispose individuals to developing arthritis. Pathologic mechanisms in cartilage calcification and advances in their understanding are reviewed alongside metabolic and endocrine arthritis.

RECENT FINDINGS

There is growing evidence suggesting that changes in chondrocytes and the extracellular environment both contribute to the calcification. Further evidence suggests that signaling cascades that are involved in physiological mineralisation are involved in the pathological process(es); data in mouse models continue to add weight to these hypotheses and correlate with human osteoarthritis data. Recent study of rare forms of arthritis is adding useful information that may help understand joint diseases in the general population and how therapies may be targeted.

SUMMARY

There is little doubt that calcium-containing crystals are involved in the osteoarthritis process contributing both biomechanically and biochemically. Understanding the processes involved provides important therapeutic opportunities. Furthermore, important information is often discovered in studying rare conditions in which these pathologies are inevitable.

Supplementation of exogenous adenosine 5'-triphosphate enhances mechanical properties of 3D cell-agarose constructs for cartilage tissue engineering

Formation of tissue-engineered cartilage is greatly enhanced by mechanical stimulation. However, direct mechanical stimulation is not always a suitable method, and the utilization of mechanisms underlying mechanotransduction might allow for a highly effective and less aggressive alternate means of stimulation. In particular, the purinergic, adenosine 5'-triphosphate (ATP)-mediated signaling pathway is strongly implicated in mechanotransduction within the articular cartilage. We investigated the effects of transient and continuous exogenous ATP supplementation on mechanical properties of cartilaginous constructs engineered using bovine chondrocytes and human mesenchymal stem cells (hMSCs) encapsulated in an agarose hydrogel. For both cell types, we have observed significant increases in equilibrium and dynamic compressive moduli after transient ATP treatment applied in the fourth week of cultivation. Continuous ATP treatment over 4 weeks of culture only slightly improved the mechanical properties of the constructs, without major changes in the total glycosaminoglycan (GAG) and collagen content. Structure-function analyses showed that transiently ATP-treated constructs, and in particular those based on hMSCs, had the highest level of correlation between compositional and mechanical properties. Transiently treated groups showed intense staining of the territorial matrix for GAGs and collagen type II. These results indicate that transient ATP treatment can improve functional mechanical properties of cartilaginous constructs based on chondrogenic cells and agarose hydrogels, possibly by improving the structural organization of the bulk phase and territorial extracellular matrix (ECM), that is, by increasing correlation slopes between the content of the ECM components (GAG, collagen) and mechanical properties of the construct.

Role of inflammation in the pathogenesis of osteoarthritis: latest findings and interpretations

Osteoarthritis (OA) has traditionally been classified as a noninflammatory arthritis; however, the dichotomy between inflammatory and degenerative arthritis is becoming less clear with the recognition of a plethora of ongoing immune processes within the OA joint and synovium. Synovitis is defined as inflammation of the synovial membrane and is characteristic of classical inflammatory arthritidies. Increasingly recognized is the presence of synovitis in a significant proportion of patients with primary OA, and based on this observation, further studies have gone on to implicate joint inflammation and synovitis in the pathogenesis of OA. However, clinical OA is not one disease but a final common pathway secondary to many predisposing factors, most notably age, joint trauma, altered biomechanics, and obesity. How such biochemical and mechanical processes contribute to the progressive joint failure characteristic of OA is tightly linked to the interplay of joint damage, the immune response to perceived damage, and the subsequent state of chronic inflammation resulting in propagation and progression toward the phenotype recognized as clinical OA. This review will discuss a wide range of evolving data leading to our current hypotheses regarding the role of immune activation and inflammation in OA onset and progression. Although OA can affect any joint, most commonly the knee, hip, spine, and hands, this review will focus primarily on OA of the knee as this is the joint most well characterized by epidemiologic, imaging, and translational studies investigating the association of inflammation with OA.

Arthritis gene therapy and its tortuous path into the clinic

Arthritis is a disease of joints. The biology of joints makes them very difficult targets for drug delivery in a manner that is specific and selective. This is especially true for proteinaceous drugs ("biologics"). Gene transfer is the only technology that can solve the delivery problem in a clinically reasonable fashion. There is an abundance of preclinical data confirming that genes can be efficiently transferred to tissues within joints by intra-articular injection using a variety of different vectors in conjunction with ex vivo and in vivo strategies. Using the appropriate gene transfer technologies, long-term, intra-articular expression of anti-arthritic transgenes at therapeutic concentrations can be achieved. Numerous studies confirm that gene therapy is effective in treating experimental models of rheumatoid arthritis (RA) and osteoarthritis (OA) in the laboratory. A limited number of clinical trials have been completed, which confirm safety and feasibility but only 3 protocols have reached phase II; as yet, there is no unambiguous evidence of efficacy in human disease. Only 2 clinical trials are presently underway, both phase II studies using allogeneic chondrocytes expressing transforming growth factor-β1 for the treatment of OA. Phase I studies using adeno-associated virus to deliver interleukin-1Ra in OA and interferon-β in RA are going through the regulatory process. It is to be hoped that the recent successes in treating rare, Mendelian diseases by gene therapy will lead to accelerated development of genetic treatments for common, non-Mendelian diseases, such as arthritis.

Osteoarthritis as an inflammatory disease (osteoarthritis is not osteoarthrosis!)

Osteoarthritis (OA) has long been considered a "wear and tear" disease leading to loss of cartilage. OA used to be considered the sole consequence of any process leading to increased pressure on one particular joint or fragility of cartilage matrix. Progress in molecular biology in the 1990s has profoundly modified this paradigm. The discovery that many soluble mediators such as cytokines or prostaglandins can increase the production of matrix metalloproteinases by chondrocytes led to the first steps of an "inflammatory" theory. However, it took a decade before synovitis was accepted as a critical feature of OA, and some studies are now opening the way to consider the condition a driver of the OA process. Recent experimental data have shown that subchondral bone may have a substantial role in the OA process, as a mechanical damper, as well as a source of inflammatory mediators implicated in the OA pain process and in the degradation of the deep layer of cartilage. Thus, initially considered cartilage driven, OA is a much more complex disease with inflammatory mediators released by cartilage, bone and synovium. Low-grade inflammation induced by the metabolic syndrome, innate immunity and inflammaging are some of the more recent arguments in favor of the inflammatory theory of OA and highlighted in this review.

Systems analysis of eleven rodent disease models reveals an inflammatome signature and key drivers

A common inflammatome signature, as well as disease-specific expression patterns, was identified from 11 different rodent inflammatory disease models. Causal regulatory networks and the drivers of the inflammatome signature were uncovered and validated.

Representative inflammatome gene signatures, as well as disease model-specific gene signatures, were identified from 12 gene expression profiling data sets derived from 9 different tissues isolated from 11 rodent inflammatory disease models.

The inflammatome signature is highly enriched for immune response-related genes, disease causal genes, and drug targets.

Regulatory relationships among the inflammatome signature genes were examined in over 70 causal networks derived from a number of large-scale genetic studies of multiple diseases, and the potential key drivers were uncovered and validated prospectively.

Over 70% of the inflammatome signature genes and over 50% of the key driver genes have not been reported in previous studies of common signatures in inflammatory conditions.

Common inflammatome gene signatures as well as disease-specific signatures were identified by analyzing 12 expression profiling data sets derived from 9 different tissues isolated from 11 rodent inflammatory disease models. The inflammatome signature significantly overlaps with known drug targets and co-expressed gene modules linked to metabolic disorders and cancer. A large proportion of genes in this signature are tightly connected in tissue-specific Bayesian networks (BNs) built from multiple independent mouse and human cohorts. Both the inflammatome signature and the corresponding consensus BNs are highly enriched for immune response-related genes supported as causal for adiposity, adipokine, diabetes, aortic lesion, bone, muscle, and cholesterol traits, suggesting the causal nature of the inflammatome for a variety of diseases. Integration of this inflammatome signature with the BNs uncovered 151 key drivers that appeared to be more biologically important than the non-drivers in terms of their impact on disease phenotypes. The identification of this inflammatome signature, its network architecture, and key drivers not only highlights the shared etiology but also pinpoints potential targets for intervention of various common diseases.

Magnetic resonance imaging of shoulder arthropathies

The role of magnetic resonance imaging in evaluating shoulder arthropathies is evolving. This article reviews 4 of the major arthropathies: septic arthritis, rheumatoid arthritis, calcium pyrophosphate dihydrate (CPPD) deposition disease, and hydroxyapatite disease (HAD), with special attention to their magnetic resonance imaging features. Comfort with identifying these entities allows appropriate and prompt treatment, which is critical for joint preservation in the case of infection, for maximal therapeutic efficacy of disease-modifying drugs in the case of rheumatoid arthritis, and for expediting symptomatic relief in the cases of CPPD deposition disease and HAD.