THE ORIGIN AND NATURE OF NORMAL SYNOVIAL FLUID

Walter Bauer, Marian Wilkins Ropes, and the Massachusetts General Hospital

Walter Bauer was instrumental in the development of rheumatology as a medical subspecialty, promoting careful clinical observation and description and bringing basic scientists and clinicians together to study the "anatomy, chemical composition, and metabolism of connective tissue" in the laboratory. Marian Wilkins Ropes was a pioneering woman in medicine: the first female medical resident at the Massachusetts General Hospital, the first woman appointed as an assistant professor of clinical medicine at Harvard Medical School, the first woman elected to membership in the American Society of Clinical Investigation, and the first woman elected president of the American Rheumatism Association.

Berberine disrupts staphylococcal proton motive force to cause potent anti-staphylococcal effects in vitro

The presence of antibiotic resistance has increased the urgency for more effective treatments of bacterial infections. Biofilm formation has complicated this issue as biofilm bacteria become tolerant to antibiotics due to environmental factors such as nutrient deprivation and adhesion. In septic arthritis, a disease with an 11% mortality rate, bacteria in synovial fluid organize into floating, protein-rich, bacterial aggregates (mm-cm) that display depressed metabolism and antibiotic tolerance. In this study, Staphylococcus aureus (S. aureus), which is the most common pathogen in septic arthritis, was tested against different inhibitors that modulate bacterial surface protein availability and that should decrease bacterial aggregation. One of these, berberine, a quaternary ammonium compound, was found to reduce bacterial counts by 3-7 logs in human synovial fluid (aggregating medium) with no effect in tryptic soy broth (TSB, non-aggregating). Unlike traditional antibiotics, the bactericidal activity of berberine appeared to be independent of bacterial metabolism. To elucidate the mechanism, we used synovial fluid fractionation, targeted MRSA transposon insertion mutants, dyes to assess changes in membrane potential (DiSC3(5)) and membrane permeability (propidium iodide (PI)), colony counting, and fluorescence spectroscopy. We showed that berberine's activity was dependent on an alkaline pH and berberine killed both methicillin-sensitive S. aureus and MRSA in alkaline media (pH 8.5-9.0; p < 0.0001 vs. same pH controls). Under these alkaline conditions, berberine localized to S. aureus where berberine was isolated in cytoplasmic (∼95%) and DNA (∼5%) fractions. Importantly, berberine increased bacterial cell membrane permeability, and disrupted the proton motive force, suggesting a mechanism whereby it may be able to synergize with other antibacterial compounds under less harsh conditions. We suggest that berberine, which is cheap and readily available, can be made into an effective treatment.

Nanoscale insight into the degradation mechanisms of the cartilage articulating surface preceding OA

Osteoarthritis (OA) is a degenerative disease and leading cause of disability globally. We report the a fundamental study of the mechanisms underlying deterioration of hydrated cartilage in the presence of elevated calcium content preceding OA.

[Synovial fluid cytodiagnosis]

Synovial fluid samples represent only a very small percentage of routine work in a cytology laboratory. However, its microscopic examination allows us to observe different types of cells, particles and structures that, due to their morphological characteristics, may provide relevant data for cytodiagnosis. We present certain aspects related to arthrocentesis, the relationship between the gross appearance of synovial fluid and certain pathological processes, as well as the different techniques for processing and staining the smears. Furthermore, we describe the main cytological findings in various pathological conditions of the synovial joints, such as infections (bacterial and fungal), non-infectious inflammatory type (osteoarthrosis, rheumatoid arthritis, connective tissue diseases) and tumoral, distinguishing between primary and metastatic, both solid and haematological neoplasms.

Synovial fluid uric acid level aids diagnosis of gout

Examination of urate crystal in synovial fluid (SF) remains the gold standard for diagnosis of gout, but is not universally available. SF uric acid (UA) level may be measured by the uricase method with an automated analyzer. The present study aimed to evaluate the utility of SF to serum UA ratio (SSR) for diagnosis of gout. A cross-sectional study was conducted at the National Center for Rheumatic Diseases, Nepal. Patients presenting with acute (<1 day) joint pain and/or swelling were included. Aspiration was performed in all patients and fluid was subjected to testing for urate level, pH and cell counts and microscopy. Serum samples were also assessed for urate levels, and the SSR was calculated for each patient. A receiver operating characteristic curve was plotted to determine the cutoff value for indicating diagnosis of gout. The difference in SSR between gout and non-gout effusion was evaluated by one-way analysis of variance. A total of 181 patients were included of which 77 had gout. The remaining cases included osteoarthritis, pseudogout, rheumatoid arthritis and ankylosing spondylitis. SSR was significantly higher in gout patients than in any other group (P<0.05). An SSR of ≥1.01 had the highest sensitivity and specificity at 89.6 and 66.3%, respectively, for identifying gout effusion. The present results indicated that SSR may be used as an aid for gout diagnosis when polarizing microscopy is not available.

Staphylococcal adaptation to diverse physiologic niches: an overview of transcriptomic and phenotypic changes in different biological environments

Host niches can differ strongly regarding, for example, oxygen tension, pH or nutrient availability. Staphylococcus aureus and other staphylococci are common colonizers of human epithelia as well as important human pathogens. The phenotypes that they show in different host environments, and the corresponding bacterial transcriptomes and proteomes, are currently under intense investigation. In this review, we examine the available literature describing staphylococcal phenotypes, such as expression of virulence factors, gross morphologic characteristics and growth patterns, in various physiological environments. Going forward, these studies will help researchers and clinicians to form an enhanced and more detailed picture of the interactions existing between the host and staphylococci as some of its most frequent colonizers and invaders.

Culture expansion in low-glucose conditions preserves chondrocyte differentiation and enhances their subsequent capacity to form cartilage tissue in three-dimensional culture

Culture conditions that preserve a stable chondrocyte phenotype are desirable in cell-based cartilage repair to maximize efficacy and clinical outcome. This study investigates whether low-glucose conditions will preserve the chondrocyte phenotype during culture expansion. Articular chondrocytes were culture-expanded in media supplemented with either low (1 mM) or high (10 mM) glucose. The metabolic phenotype, reactive oxygen species generation, and mRNA expression of markers of differentiation or catabolism were assessed by reverse-transcription quantitative polymerase chain reaction after four population doublings (PDs) and subsequent tissue formation capacity determined using pellet cultures. Continuous monolayer culture was used to determine the population doubling limit. After expansion in monolayer for four PDs, chondrocytes expanded in low-glucose conditions exhibited higher expression of the differentiation markers SOX9 and COL2A1 and reduced expression of the catabolic metalloproteinase matrix metallopeptidase 13. When chondrocytes expanded in low glucose were cultured in micropellets, they consistently generated more cartilaginous extracellular matrix than those expanded in high glucose, as evaluated by wet weight, sulfated glycosaminoglycan content, and hydroxyproline assay for collagen content. The same pattern was observed whether high or low glucose was used during the pellet culture. During expansion, chondrocytes in high-glucose generated 50% more reactive oxygen species than low-glucose conditions, despite a lower dependence on oxidative phosphorylation for energy. Furthermore low-glucose cells exhibited >30% increased population doubling limit. These data suggests that low-glucose expansion conditions better preserve the expression of differentiation markers by chondrocytes and enhance their subsequent capacity to form cartilage in vitro. Therefore, low glucose levels should be considered for the expansion of chondrocytes intended for tissue engineering applications.

THE PASSAGE OF PROTEINS FROM THE VASCULAR SYSTEM INTO JOINTS AND CERTAIN OTHER BODY CAVITIES

1. Experiments designed to study, in the rabbit, the passage of foreign proteins from the blood stream into synovial fluid and to compare such passage with that taking place into the aqueous humor, spinal fluid, and urine are described. 2. Crystalline egg albumin and horse serum proteins regularly appeared in the knee joints within short periods of time following their intravenous injection. 3. These proteins also appeared promptly in the aqueous humor but in lower concentrations. In the spinal fluid they appeared only rarely and in minimal amounts. 4. Crystalline egg albumin was readily eliminated from the body via the urine. It was also removed rapidly from the knee joint and anterior chamber of the eye. 5. Horse serum proteins appeared only occasionally in the urine. Their concentration in the blood serum remained relatively high for several days. Their increased concentration in the joint fluids in the longer experiments indicates that the rate of entrance exceeded the rate of removal. 6. Foreign proteins of the type employed were all found in the joint fluids in higher concentrations than they were in the other body fluids examined. 7. The possible significance of this study with respect to normal joint physiology and to certain abnormal joint conditions has been commented upon.

Measurement of synovial fluid volume using urea

OBJECTIVE

To examine the utility of using urea concentrations for determining Synovial Fluid (SF) joint volume in effused and non-effused joints.

METHODS

Knee joint SF was aspirated from 159 human study participants with symptomatic osteoarthritis of at least one knee either directly (165 knees) or by lavage (110 knees). Serum was obtained immediately prior to SF aspiration. Participants were asked to rate individual knee pain, aching or stiffness. SF and serum urea levels were determined using a specific enzymatic method run on an automated CMA600 analyzer. Cell counts were performed on direct SF aspirates when volume permitted. The formula for calculating SF joint volume was as follows: V(j)=C(D)(V(I))/(C-C(D)) with V(j)=volume of SF in entire joint, C(D)=concentration of urea in diluted (lavage) SF, V(I)=volume of saline injected into joint, and C=concentration of urea in undiluted (neat) SF derived below where C=0.897(C(S)) and C(s)=concentration of urea in serum.

RESULTS

There was an excellent correlation (r(2)=0.8588) between SF and serum urea in the direct aspirates with a ratio of 0.897 (SF/serum). Neither urea levels nor the SF/serum ratio showed any correlation with Kellgren Lawrence (KL) grade, or cell count. While urea levels increased with age there was no change in the ratio. Intraarticular SF volumes calculated for the lavaged knees ranged from 0.555 to 71.71ml with a median volume of 3.048ml. There was no correlation of SF volume to KL grade but there was a positive correlation (P=0.001) between SF volume and self-reported individual knee pain.

CONCLUSION

Our urea results for direct aspirates indicate an equilibrium state between serum and SF with regard to the water fraction. This equilibrium exists regardless of disease status (KL grade), inflammation (cell count), or age, making it possible to calculate intraarticular volume of lavaged joints based upon this urea method. Most of the joint volumes we calculated fell within the previously reported range for normal knees of 0.5-4.0ml. The positive correlation between SF volume and knee symptoms reinforces the clinical utility of this method for quantifying SF volume.

Reflecting on 80 years of excellence

A small group of members of the American Society for Clinical Investigation began chatting in 1916 about the possibility of launching a new biomedical research journal. By October 1924, they managed to make the idea a reality with the publication of the first issue of the Journal of Clinical Investigation. Our 80th birthday seems an appropriate time to reflect on the history of biomedical science as it has been played out on our pages.

Urea as a passive transport marker for arthritis biomarker studies

OBJECTIVE

To develop a method to correct for the unknown dilution of synovial fluid that occurs during lavage of a joint, we evaluated the utility of urea, a molecule that is neither synthesized nor metabolized by joint tissues, as a means of correcting for the dilutional effects of lavage procedures and effusions.

METHODS

Joint fluids were obtained from normal canine joints by direct aspiration (n = 41) and lavage (n = 10). Acute joint injury was induced in 4 joints by intraarticular injection of chymopapain. Serum and joint fluid levels of urea and joint fluid concentrations of glucose, lactate, cartilage oligomeric matrix protein (COMP), and keratan sulfate (KS) were measured in these 55 joints.

RESULTS

Urea concentrations in joint fluid were directly proportional to those in serum throughout a wide range of concentrations in normal joints. From this relationship, the dilution factor introduced by joint lavage was determined. This method was applied to quantify biomarker concentrations in synovial lavage fluid and was found to successfully correct for lavage-induced dilution of glucose, lactate, COMP, and KS to levels equivalent to those in samples aspirated directly. In the context of chymopapain-induced joint effusion, urea concentrations continued to be proportional to serum concentrations, but were much lower, enabling an estimation of the change in the volume of distribution (V(d)) of a marker due to a change in joint water content in the setting of inflammation characterized by effusion. Lactate and KS levels rose markedly in response to chymopapain. After adjustment for the V(d), the glucose concentration in the chymopapain-injected joints did not change.

CONCLUSION

Urea provides a robust method of quantifying and correcting for the dilution of synovial fluid due to joint lavage or inflammation. This method is potentially applicable to surrogate marker studies in human arthritis.

The changes in human synovial fluid osmolality associated with traumatic or mechanical abnormalities of the knee

Synovial fluid osmolality was determined in 22 knees at the time of arthroscopic evaluation. The arthroscopy was for traumatic or mechanical abnormality of the knee. The results indicate no significant difference in osmolality among the conditions studied, but there was a significant decrease in synovial fluid osmolality compared to the values for the normal knee. The information presented provides baseline data for various pathologic conditions and a basis for future work.

Synovial fluid nutrient delivery in the diathrial joint: an analysis of rabbit knee ligaments

The role of synovial fluid in providing nutrition to rabbit knee ligaments and menisci was evaluated by intraarticular injection of a labeled collagen precursor, tritiated proline. Incorporation of this substrate as tritiated hydroxyproline was measured in collateral and cruciate ligaments and menisci. The injectate volume (0.35 ml) did not appreciably change the overall joint pressure as measured by a wick catheter; therefore, no alteration of synovial membrane diffusion characteristics resulted. The concentration of the injected proline (0.52 mg%) was well below that normally present in serum (2.65 mg%). Therefore, incorporation of this substrate was not driven by a concentration gradient and represented normal uptake of synovial fluid and physiological incorporation of label as measured by the presence of tritiated hydroxyproline. Autoradiography was performed on all ligaments and menisci, and demonstrated concentration of the isotope and its metabolite (tritiated proline and tritiated hydroxyproline, respectively) in and around fibroblasts. This study indicates that rabbit knee ligaments and menisci can derive nutrition from a synovial fluid source.

Acidosis of synovial fluid correlates with synovial fluid leukocytosis

The antibacterial activity of aminoglycoside antibiotics is significantly reduced by lowering the pH of the incubation medium. Since gram-negative septic arthritis responds poorly to aminoglycoside antibiotic therapy, we sought to determine whether synovial fluid acidosis contributes to this poor outcome. Synovial fluid samples from 22 patients with various forms of acute and chronic arthritis were examined for white blood cell count and pH. A close correlation (r = -0.92, p is less than 0.001) between an increasing white blood cell count and a decreasing pH was demonstrated. Since septic arthritis is associated with high white blood cell counts, in synovial fluid, the resultant low pH may contribute to the poor response to gram-negative septic arthritis treated with aminoglycoside antibiotics.

Soluble proteins in fluid from non-keratinizing jaw cysts in man

Fluids from non-keratinizing cysts of the jaws contain the main proteins found in plasma. The low relative concentration of macromolecular non-immunoglobulin proteins shows that there is no free passage of plasma proteins into the cyst fluid. Sufficient evidence was found to conclude that the immunoglobulins in cyst fluid are partly produced locally and partly derived from plasma. Cyst fluid immunoglobulins have antibody activity to rabbit erythrocytes. Accumulation of cyst fluid is primarily due to inadequate lymphatic drainage of the cyst cavity. Differential diagnosis between various types of non-keratinizing cysts cannot be based on the plasma protein patterns of their fluids.

Somatomedin activity in synovial fluid

Abnormalities of synovial fluid, as a lubricant and nutrient, may have relevance to the causation of certain articular diseases. The somatomedin activity in normal synovial fluid obtained from the knee joint of the ox has been studied and compared with the activity in serum from the same animal. The porcine costal cartilage bioassay of Van den Brande and Du Caju (1974) has been used with the isotopes 35S-sulphate and 3H-thymidine. The mean potency ratio of ox synovial fluid in terms of ox serum for 35S-sulphate incorporation was 0-28 (range 0-19-0-47) and for 3H-thymidine incorporation 0-35 (range 0-21-0-63). A significant correlation was found between the somatomedin activity (as measured by 35S-sulphate incorporation) and the total protein and albumin concentrations in the ox synovial fluids and the ox sera, but there was no significant relationship between the somatomedin potency ratios and the globulin concentrations. The possible relevance of these findings to injury and disease in synovial joint is discussed.

Studies on the physiological chemistry of the tibio-tarsal synovial fluid of healthy bovines

The physical properties, chemical composition and cytological content of the synovial fluid of healthy native breed cattle, obtained by tibio-tarsal arthrocentesis, was studied. Normally the synovial fluid of bovines is a clear, colourless or straw coloured, viscous, non-coagulable liquid with a normal mucin precipitate quality. The fluid is alkaline in reaction and with a lower specific gravity than serum. Bovine tibio-tarsal fluid exhibits no erythrocytes and presents a low leucocytic count which is dominated by lymphocytes and monocytes. Compared to bovine serum, synovial fluid contains almost the same levels of sugar, urea, creatinine and phosphorous; slightly lower calcium concentration and rather higher chlorides. The fluid is devoid of any traces of bilirubin. Young calves showed a significantly lower total leucocyte number, chloride level and sugar content and a higher calcium and inorganic phosphorous than bulls.