Soluble receptor for advanced glycation end products (sRAGE) in plasma and synovial fluid is inversely associated with disease severity of knee osteoarthritis

Osteoclasts and osteoarthritis: Novel intervention targets and therapeutic potentials during aging

Osteoarthritis (OA), a chronic degenerative joint disease, is highly prevalent among the aging population, and often leads to joint pain, disability, and a diminished quality of life. Although considerable research has been conducted, the precise molecular mechanisms propelling OA pathogenesis continue to be elusive, thereby impeding the development of effective therapeutics. Notably, recent studies have revealed subchondral bone lesions precede cartilage degeneration in the early stage of OA. This development is marked by escalated osteoclast-mediated bone resorption, subsequent imbalances in bone metabolism, accelerated bone turnover, and a decrease in bone volume, thereby contributing significantly to the pathological changes. While the role of aging hallmarks in OA has been extensively elucidated from the perspective of chondrocytes, their connection with osteoclasts is not yet fully understood. There is compelling evidence to suggest that age-related abnormalities such as epigenetic alterations, proteostasis network disruption, cellular senescence, and mitochondrial dysfunction, can stimulate osteoclast activity. This review intends to systematically discuss how aging hallmarks contribute to OA pathogenesis, placing particular emphasis on the age-induced shifts in osteoclast activity. It also aims to stimulate future studies probing into the pathological mechanisms and therapeutic approaches targeting osteoclasts in OA during aging.

Inflammaging and Osteoarthritis

Osteoarthritis is a highly prevalent disease particularly in subjects over 65 years of age worldwide. While in the past it was considered a mere consequence of cartilage degradation leading to anatomical and functional joint impairment, in recent decades, there has been a more dynamic view with the synovium, the cartilage, and the subchondral bone producing inflammatory mediators which ultimately lead to cartilage damage. Inflammaging is defined as a chronic, sterile, low-grade inflammation state driven by endogenous signals in the absence of infections, occurring with aging. This chronic status is linked to the production of reactive oxygen species and molecules involved in the development of age-related disease such as cancer, diabetes, and cardiovascular and neurodegenerative diseases. Inflammaging contributes to osteoarthritis development where both the innate and the adaptive immune response are involved. Elevated systemic and local inflammatory cytokines and senescent molecules promote cartilage degradation, and antigens derived from damaged joints further trigger inflammation through inflammasome activation. B and T lymphocyte populations also change with inflammaging and OA, with reduced regulatory functions, thus implicating self-reactivity as an additional mechanism of joint damage. The discovery of the underlying pathogenic pathways may help to identify potential therapeutic targets for the management or the prevention of osteoarthritis. We will provide a comprehensive evaluation of the current literature on the role of inflammaging in osteoarthritis and discuss the emerging therapeutic strategies.

Association between Common Variants in VEGFA Gene and the Susceptibility of Primary Knee Osteoarthritis

OBJECTIVES

This study aimed to analyze the relationship between vascular endothelial growth factor A (VEGFA) gene polymorphisms, plasma VEGFA, and the susceptibility of knee osteoarthritis (OA).

DESIGN

A total of 404 subjects, 202 knee OA subjects and 202 healthy volunteers, were enrolled into the study. Four distinct polymorphisms of the VEGFA gene were evaluated using polymerase chain reaction-restriction fragment length polymorphism: -2578C/A (rs699947), -1154G/A (rs1570360), -634C/G (rs2010963), and +936C/T (rs3025039). Plasma VEGFA levels were analyzed using enzyme-linked immunosorbent assay.

RESULTS

The most common nucleotides in both knee OA subjects and healthy controls were CC for -2578C/A, GG for -1154G/A, CG for -634C/G, and CC for +936C/T in the VEGFA gene. Genotype distribution and allele frequencies of VEGFA -2578C/A, -1154G/A, -634C/G, and +936C/T single nucleotide polymorphisms did not differ between OA patients and the controls. Plasma VEGFA levels showed no difference between OA patients and the controls. In contrast, plasma VEGFA levels of -634C/C genotype were significantly higher in OA patients than in the controls (P = 0.035). According to the -2578A/A genotype, patients with early stage OA had a higher odds ratio than those with advanced stage OA (P = 0.023).

CONCLUSIONS

VEGFA -2578C/A (rs699947), -1154G/A (rs1570360), -634C/G (rs2010963), and +936C/T (rs3025039) polymorphisms may not be responsible for OA susceptibility in the Thai population. However, the OA patients with A/A genotype at the -2578C/A seemed to have a lower potential risk of developing severe OA than those with the C/A and C/C genotypes. These findings would help elucidate and facilitate a better understanding of the genetic fundamentals of OA.

Fatty Acid-Binding Protein 4 (FABP4) Is Associated with Cartilage Thickness in End-Stage Knee Osteoarthritis

BACKGROUND

There is no single blood biomarker for the staging of knee osteoarthritis (KOA). The purpose of this study was to assess the relationship of obesity, serum biomarkers, the hip-knee-ankle angle (HKAA) with sonographic cartilage thickness.

METHODS

We conducted a cross-sectional study of n = 33 patients undergoing knee arthroplasty. Body mass index (BMI) was recorded, and patients were grouped based on BMI. Serum blood samples were collected, and the following biomarkers were measured using the ELISA technique (subgroup of n = 23): oxidized low-density lipoprotein (oxLDL), soluble receptor for advanced glycation end-products (sRAGE), fatty acid-binding protein 4 (FABP4), membrane-bound phospholipase A2 (PLA2G2A). The HKAA was analyzed on full-length limb standing x-ray images. Cartilage thickness was assessed on ultrasound images. Multivariable regression analysis was performed to account for confounding.

RESULTS

After adjusting for age, gender, and HKAA, obese patients had thicker medial femoral cartilage (β = 0.165, P = 0.041). Furthermore, lateral cartilage thickness was negatively correlated with FABP4 level after adjusting for of age, gender, BMI, and HKAA (β = -0.006, P = 0.001). Confirming previous studies, after adjustment, FABP4 level was associated with a higher BMI group (β = 42.99, P < 0.001). None of the other markers (oxLDL, PLA2G2A, and sRAGE) was associated with BMI or cartilage thickness.

DISCUSSION

Our results indicate that BMI has a weak, positive association with cartilage thickness in end-stage KOA patients. FABP4 levels were negatively associated with cartilage thickness. While our study is limited by a small sample size, these results further highlight the role of FABP4 as promising biomarkers of burden of disease in KOA.

Synovial Fluid Biomarkers in Knee Osteoarthritis: A Systematic Review and Quantitative Evaluation Using BIPEDs Criteria

OBJECTIVE

The aim of this systematic review was to analyze the evidence about the efficacy of the several synovial fluid (SF) biomarkers proposed for knee osteoarthritis (OA), categorizing them by both molecular characteristics and clinical use according to the BIPEDs criteria, to provide a comprehensive and structured overview of the current literature.

DESIGN

A systematic review was performed in May 2020 on PubMed, Cochrane Library, and Embase databases about SF biomarkers in patients with knee OA. The search was limited to articles in the last 20 years on human studies, involving patients with knee OA, reporting SF biomarkers. The evidence for each selected SF biomarker was quantified according to the 6 categories of BIPEDs classification.

RESULTS

A total of 159 articles were included in the qualitative data synthesis and 201 different SF biomarkers were identified. Among these, several were investigated multiple times in different articles, for a total of 373 analyses. The studies included 13,557 patients with knee OA. The most promising SF biomarkers were C4S, IL-6, IL-8, Leptin, MMP-1/3, TIMP-1, TNF-α, and VEGF. The "burden of disease" and "diagnostic" categories were the most represented with 132 and 106 different biomarkers, respectively.

CONCLUSIONS

The systematic review identified numerous SF biomarkers. However, despite the high number of studies on the plethora of identified molecules, the evidence about the efficacy of each biomarker is supported by limited and often conflicting findings. Further research efforts are needed to improve the understanding of SF biomarkers for a better management of patients with knee OA.

Towards Secretome Standardization: Identifying Key Ingredients of MSC-Derived Therapeutic Cocktail

The therapeutic potential of the conditioned medium (CM) derived from MSCs (mesenchymal stem/stromal cells) in disparate medical fields, from immunology to orthopedics, has been widely suggested by in vitro and in vivo evidences. Prior to MSC-CM use in clinical applications, appropriate quality controls are needed in order to assess its reproducibility. Here, we evaluated different CM characteristics, including general features and precise protein and lipid concentrations, in 3 representative samples from adipose-derived MSCs (ASCs). In details, we first investigated the size and distribution of the contained extracellular vesicles (EVs), lipid bilayer-delimited particles whose pivotal role in intercellular communication has been extensively demonstrated. Then, we acquired Raman signatures, providing an overlook of ASC-CM composition in terms of proteins, lipids, and nucleic acids. At last, we analyzed a panel of 200 molecules including chemokines, cytokines, receptors, and inflammatory and growth factors and searched for 32 lipids involved in cell signalling and inflammation. All ASC-CM contained a homogeneous and relevant number of EVs (1.0 × 10⁹ ± 1.1 × 10⁸ particles per million donor ASCs) with a mean size of 190 ± 5.2 nm, suggesting the appropriateness of the method for EV retaining and concentration. Furthermore, also Raman spectra confirmed a high homogeneity among samples, allowing the visualization of specific peaks for nucleic acids, proteins, and lipids. An in depth investigation that focused on 200 proteins involved in relevant biological pathways revealed the presence in all specimens of 104 factors. Of these, 26 analytes presented a high degree of uniformity, suggesting that the samples were particularly homogenous for a quarter of the quantified molecules. At last, lipidomic analysis allowed the quantification of 7 lipids and indicated prostaglandin-E2 and N-stearoylethanolamide as the most homogenous factors. In this study, we assessed that ASC-CM samples obtained with a standardized protocol present stable features spanning from Raman fingerprint to specific marker concentrations. In conclusion, we identified key ingredients that may be involved in ASC-CM therapeutic action and whose consistent levels may represent a promising quality control in the pipeline of its preparation for clinical applications.

The role of soluble receptor for advanced glycation end-products (sRAGE) in the general population and patients with diabetes mellitus with a focus on renal function and overall outcome

Isoforms of the receptor for advanced glycation end-product (RAGE) protein, which lack the transmembrane and the signaling (soluble RAGE or sRAGE) domains are hypothesized to counteract the detrimental action of the full-length receptor by acting as a decoy, and they provide a potential tool to treat RAGE-associated diseases. Multiple studies have explored the relationship between sRAGE and endogenous secretory RAGE and its polymorphism and obesity, metabolic syndrome, atherosclerosis, kidney function, and increased mortality in the general population. In addition, sRAGE may be a key player in the pathogenesis of diabetes mellitus and its microvascular (e.g. kidney disease) as well as macrovascular (e.g. cardiovascular disease) complications. In this review, we focus on the role of sRAGE as a biomarker in these specific areas. As there is a lack of an underlying unifying hypothesis about how sRAGE changes according to the disease condition or risk factor, there is a call to incorporate all three players of the AGE-RAGE axis into a new universal biomarker/risk marker: (AGE + RAGE)/sRAGE. However, the measurement of RAGE in humans is not practical as it is a cell-bound receptor for which tissue is required for analysis. A high AGE/sRAGE ratio may be a valuable alternative and practical universal biomarker/risk marker for diseases associated with the AGE-RAGE axis, irrespective of low or high serum sRAGE concentrations.

Effects of dietary calcium fructoborate supplementation on joint comfort and flexibility and serum inflammatory markers in dogs with osteoarthritis

Our objective was to evaluate the short-term effects of calcium fructoborate (CFB) on gait, joint range of motion, serum inflammatory markers, and owner perception of pain in client-owned dogs. We used 59 osteoarthritic dogs with impairment, with dogs being randomly assigned to 4 treatments: placebo (60 mg fructose; = 15), low dose (69 mg CFB; = 14), high dose (127 mg CFB; = 14), or combination (69 mg CFB, 500 mg glucosamine hydrochloride and 200 mg chondroitin sulfate; = 16). Dogs up to 22.9 kg received 1 capsule/d, while dogs weighing 23 to 50 kg received 2 capsules/d. A physical examination, radiographs, goniometry measurements, gait analysis, blood sample collection, and a canine brief pain inventory questionnaire were performed on d 0 and 28. Change from baseline values were statistically analyzed among groups. After 28 d, dogs fed the low and high doses had an improved ( < 0.05) ability to rise from a lying position compared to placebo. Dogs fed the high dose also had a greater ( = 0.05) increase in soluble receptor for advanced glycation end products concentration than dogs fed the placebo. Sub-analysis of only large dogs (> 23 kg) showed that dogs fed the low dose had decreased ( < 0.05) pain severity score and pain at its worst compared to dogs fed the placebo. Large dogs fed the low dose also were shown to improve ( < 0.05) in their ability to rise from a lying position compared to dogs fed the placebo. Overall, CFB supplementation was well-tolerated and may aid in mitigating joint discomfort in dogs.

Increased expression of damage-associated molecular patterns (DAMPs) in osteoarthritis of human knee joint compared to hip joint

Osteoarthritis (OA) is a degenerative disease characterized by the destruction of cartilage. The greatest risk factors for the development of OA include age and obesity. Recent studies suggest the role of inflammation in the pathogenesis of OA. The two most common locations for OA to occur are in the knee and hip joints. The knee joint experiences more mechanical stress, cartilage degeneration, and inflammation than the hip joint. This could contribute to the increased incidence of OA in the knee joint. Damage-associated molecular patterns (DAMPs), including high-mobility group box-1, receptor for advanced glycation end products, and alarmins (S100A8 and S100A9), are released in the joint in response to stress-mediated chondrocyte and cartilage damage. This facilitates increased cartilage degradation and inflammation in the joint. Studies have documented the role of DAMPs in the pathogenesis of OA; however, the comparison of DAMPs and its influence on OA has not been discussed. In this study, we compared the DAMPs between OA knee and hip joints and found a significant difference in the levels of DAMPs expressed in the knee joint compared to the hip joint. The increased levels of DAMPs suggest a difference in the underlying pathogenesis of OA in the knee and the hip and highlights DAMPs as potential therapeutic targets for OA in the future.

Damage-associated molecular patterns in the pathogenesis of osteoarthritis: potentially novel therapeutic targets

Osteoarthritis (OA) is a chronic disease that degrades the joints and is often associated with increasing age and obesity. The two most common sites of OA in adults are the knee and hip joints. Increased mechanical stress on the joint from obesity can cause the articular cartilage to degrade and release damage-associated molecular patterns (DAMPs). These DAMPs are involved in various molecular pathways that interact with nuclear factor-kappa B and result in the transcription of inflammatory cytokines and activation of matrix metalloproteinases that progressively destroy cartilage. This review focuses on the interactions and contribution to the pathogenesis and progression of OA through the DAMPs: high-mobility group box 1 (HMGB-1), the receptor for advanced glycation end-products (RAGE), the alarmin proteins S100A8 and S100A9, and heparan sulfate. HMGB-1 is released from damaged or necrotic cells and interacts with toll-like receptors (TLRs) and RAGE to induce inflammatory signals, as well as behave as an inflammatory cytokine to activate innate immune cells. RAGE interacts with HMGB-1, advanced glycation end-products, and innate immune cells to increase local inflammation. The alarmin proteins are released following cell damage and interact through TLRs to increase local inflammation and cartilage degradation. Heparan sulfate has been shown to facilitate the binding of HMGB-1 to RAGE and could play a role in the progression of OA. Targeting these DAMPs may be the potential therapeutic strategies for the treatment of OA.

Possible role of methylglyoxal and glyoxalase in arthritis

OA (osteoarthritis) and RA (rheumatoid arthritis) lead to deterioration of the joints. Early OA is associated with loss of bone due to increased bone remodelling. A role for inflammation is thought to be integral to the pathology. RA is a chronic inflammatory disease of the synovium, a membrane lining the non-weight-bearing surfaces of the joint. The mainstay of RA diagnostic testing is for autoantibodies. Rheumatoid factor has been a primary diagnostic test; however, sensitivity is approximately 75%, but specificity is limited. Recently, detection of antibodies against cyclic citrullinated peptide, identified as a screening marker and marker of disease progression, has been proposed. Studies of glycation in arthritis have focused mostly on levels of AGEs (advanced glycation end-products), Nε-carboxymethyl-lysine and pentosidine. There was a weak correlation of skin and urinary pentosidine with joint damage in early-stage OA. RAGE (receptor for AGEs) is a cell-surface receptor in the synovial tissue of patients with OA and RA. The RAGE agonist S100A12 is increased in RA and OA. Activation of RAGE may decrease expression of Glo1 (glyoxalase I). Conflict between RAGE-activated inflammatory signalling and Nrf2 (nuclear factor-erythroid 2-related factor 2) regulation of basal and inducible expression of Glo1 may be involved. Thereby glyoxal- and methylglyoxal-derived AGEs may be increased in OA and RA. Further studies are now required to investigate the role of glyoxalase and dicarbonyl glycation in OA and RA for early-stage diagnosis and potential novel preventive therapy.

Republished: Value of biomarkers in osteoarthritis: current status and perspectives

Osteoarthritis affects the whole joint structure with progressive changes in cartilage, menisci, ligaments and subchondral bone, and synovial inflammation. Biomarkers are being developed to quantify joint remodelling and disease progression. This article was prepared following a working meeting of the European Society for Clinical and Economic Aspects of Osteoporosis and Osteoarthritis convened to discuss the value of biochemical markers of matrix metabolism in drug development in osteoarthritis. The best candidates are generally molecules or molecular fragments present in cartilage, bone or synovium and may be specific to one type of joint tissue or common to them all. Many currently investigated biomarkers are associated with collagen metabolism in cartilage or bone, or aggrecan metabolism in cartilage. Other biomarkers are related to non-collagenous proteins, inflammation and/or fibrosis. Biomarkers in osteoarthritis can be categorised using the burden of disease, investigative, prognostic, efficacy of intervention, diagnostic and safety classification. There are a number of promising candidates, notably urinary C-terminal telopeptide of collagen type II and serum cartilage oligomeric protein, although none is sufficiently discriminating to differentiate between individual patients and controls (diagnostic) or between patients with different disease severities (burden of disease), predict prognosis in individuals with or without osteoarthritis (prognostic) or perform so consistently that it could function as a surrogate outcome in clinical trials (efficacy of intervention). Future avenues for research include exploration of underlying mechanisms of disease and development of new biomarkers; technological development; the ‘omics’ (genomics, metabolomics, proteomics and lipidomics); design of aggregate scores combining a panel of biomarkers and/or imaging markers into single diagnostic algorithms; and investigation into the relationship between biomarkers and prognosis.

Expression of receptors of advanced glycation end product (RAGE) and types I, III and IV collagen in the vastus lateralis muscle of men in early stages of knee osteoarthritis

Alterations in the contractile and non-contractile proteins of the skeletal muscle may reduce muscle function in knee osteoarthritis (OA), and the formation and accumulation of advanced glycation end products, particularly in collagen, can influence the quality of these muscle proteins. The objective of this study was to evaluate the reactivity of types I, III and IV collagen and the expression and localization of receptor for advanced glycation end products (RAGE) in the vastus lateralis (VL) muscle in early stages of knee OA. The hypothesis was that these patients present a higher expression of RAGE and increased immunoreactivity in the collagen. Thirty-five men were divided into two groups: the control group (CG; n = 17) and the osteoarthritis group (OAG; n = 18). All participants were submitted to a biopsy of the VL. The muscle samples were analyzed by immunohistochemistry for collagen and for RAGE and laminin. The expression of RAGE was counted (intracellular, extracellular and total). Student's t-test for independent samples and Mann-Whitney U test were used for the RAGE's intergroup analysis (α ≤ 0.05). A semiquantitative analysis was performed to assess the collagen reactivity. No significant differences were observed in the intracellular, extracellular or total localization of RAGE (p > 0.05). Higher immunoreactivity was observed in the OAG for all types of collagen, with more reactivity for collagen III and IV. We concluded that in the initial stages of knee OA, no differences were observed for RAGE levels between the groups. However, the OAG's higher collagen expression may represent adaptations for reducing muscle stiffness and avoiding injury.

Value of biomarkers in osteoarthritis: current status and perspectives

Osteoarthritis affects the whole joint structure with progressive changes in cartilage, menisci, ligaments and subchondral bone, and synovial inflammation. Biomarkers are being developed to quantify joint remodelling and disease progression. This article was prepared following a working meeting of the European Society for Clinical and Economic Aspects of Osteoporosis and Osteoarthritis convened to discuss the value of biochemical markers of matrix metabolism in drug development in osteoarthritis. The best candidates are generally molecules or molecular fragments present in cartilage, bone or synovium and may be specific to one type of joint tissue or common to them all. Many currently investigated biomarkers are associated with collagen metabolism in cartilage or bone, or aggrecan metabolism in cartilage. Other biomarkers are related to non-collagenous proteins, inflammation and/or fibrosis. Biomarkers in osteoarthritis can be categorised using the burden of disease, investigative, prognostic, efficacy of intervention, diagnostic and safety classification. There are a number of promising candidates, notably urinary C-terminal telopeptide of collagen type II and serum cartilage oligomeric protein, although none is sufficiently discriminating to differentiate between individual patients and controls (diagnostic) or between patients with different disease severities (burden of disease), predict prognosis in individuals with or without osteoarthritis (prognostic) or perform so consistently that it could function as a surrogate outcome in clinical trials (efficacy of intervention). Future avenues for research include exploration of underlying mechanisms of disease and development of new biomarkers; technological development; the ‘omics’ (genomics, metabolomics, proteomics and lipidomics); design of aggregate scores combining a panel of biomarkers and/or imaging markers into single diagnostic algorithms; and investigation into the relationship between biomarkers and prognosis.

S100A12 levels in synovial fluid may reflect clinical severity in patients with primary knee osteoarthritis

This study aims to detect S100A12 in serum and synovial fluid (SF) of knee osteoarthritis (OA) patients and to investigate their correlation with clinical severity of the disease. This study enrolled 198 OA patients and 84 healthy controls. The radiological/symptomatic severity of the disease was assessed by the Kellgren-Lawrence (KL) grading system/Western Ontario McMaster University Osteoarthritis (WOMAC) scores. We demonstrated that S100A12 levels in SF but not serum were independently associated with KL grades and WOMAC scores. These results suggested that the S100A12 in SF might be a potential biomarker for predicting the development and progression of knee OA.

Serum fetuin-A levels are inversely associated with clinical severity in patients with primary knee osteoarthritis

The present study aimed to detect serum fetuin-A levels in knee osteoarthritis (OA) patients and to investigate their correlation with clinical severity. We enrolled 215 knee OA patients and 76 healthy controls. We measured serum fetuin-A levels by enzyme-linked immunosorbent assay and assessed the correlation between serum fetuin-A levels and Kellgren-Lawrence grades as well as Western Ontario and McMaster Universities Arthritis Index scores in OA patients. Our results demonstrated that serum fetuin-A levels were independently and negatively correlated with greater clinical severity in OA patients.

The interaction between obesity and RAGE polymorphisms on the risk of knee osteoarthritis in Chinese population

BACKGROUND

The receptor for advanced glycation end products (RAGE) has been reported to relate to osteoarthritis (OA), however, the role of RAGE genetic variants in OA remains unknown.

METHOD

A total of 233 patients with primary knee OA and 255 healthy volunteer were recruited. Three RAGE gene polymorphisms, namely, Gly82Ser (rs2070600). -374T/A (rs1800624) and 429T/C (rs1800625) were genotyped.

RESULTS

Of all three RAGE gene polymorphisms, only the genotype distributions and alleles frequencies of 82G/S polymorphisms significantly differed between knee OA and control subjects. The presence of SS genotype and S allele of 82G/S we significantly higher in knee OA subjects than in controls (34.76% vs. 19.61%, P for trend =0.004; 57.64% vs. 48.59%, P for trend <0.001, respectively). Multivariate logistic regression analysis showed a significantly increased risk for knee OA for the SS genotype compared with the AA genotype (OR= 1.984, 95% CI: 1.238-3.181; P =0.004). The adjusted OR for S allele carriage was significantly higher than G allele carriage (OR=1.440, 95% CI: 1.137-1.8231, P=0.002). Moreover, a significant multiplicative interaction was observed between 82G/S polymorphisms with obesity (Pinteraction=0.028). Taking the non-obese 82GG genotype as references, the OR for OA in non-obese SS carriers was 2.537 (95% CI 1.241-5.189, P=0.001). Notably, the OR in obese GS carriers was 2.304 (95% CI: 1.218-4.357, P=0.009) and in obese SS was 3.392 (95% CI: 1.672-6.885, P=0.001). The -374T/A and -429T/C did not show positive interaction with obesity and smoking status.

CONCLUSION

The AGE 82G/S polymorphisms, in interaction with obesity, may determine the susceptibility of OA in Chinese population.

Biological markers in osteoarthritis

Osteoarthritis (OA) is considered as a chronic disease with a long "silent" period. The diagnosis is generally based on clinical symptoms and radiographic changes. However X-ray has a poor sensitivity and a relatively large precision error that does not allow an early detection of OA or the monitoring of joint damage progression. The limitations of the tools that are currently available for OA assessment have been the impetus to identify specific biological markers that reflect quantitative and dynamic variations in joint remodeling. Research has focused on the structural components of cartilage matrix, especially type II collagen degradation markers. In spite of a significant increase of some markers in individuals with early stage of OA, the large overlap with control subjects indicates that the current biomarkers used alone have limited diagnostic potential. However, the combination of specific markers seems to improve the prediction of disease progression at the individual level. Several types of treatment have been investigated but the lack of medications with definitively demonstrated chondroprotective activity has limited the assessment of the potential role of biomarkers for monitoring patients' responses to the treatment of OA. In this review, we will use the BIPED classification that appeared in 2006 for OA markers to describe the potential usage of a given marker [5]. This article is part of a Special Issue entitled "Osteoarthritis".

Recent advances in biomarkers in osteoarthritis

PURPOSE OF REVIEW

Osteoarthritis is a joint disease characterized by a nonsymptomatic, preradiographical phase that if distinguished would allow earlier osteoarthritis diagnosis. Biochemical biomarkers offer a potential nonradiographical alternative to detect early, nonsymptomatic osteoarthritis.

RECENT FINDINGS

Biomarker development for osteoarthritis diagnosis is still in the forefront of the research repertoire in osteoarthritis. A number of previously identified biomarkers derived from cartilage breakdown or enzymes that cause cartilage degeneration still have prominence and are now better characterized with increasing use in identifying disease severity, progression, and testing treatment options. Combinations of cartilage-derived and bone-derived biomarkers have been used to subgroup osteoarthritis patients that could impact treatment and address the importance of bone turnover in cartilage integrity. Increasingly, inflammation markers have been used to profile osteoarthritis progression attesting to the inflammatory nature of osteoarthritis. The application of proteomic technologies has generated several new, nonconventional biomarkers that could allow better profiling of osteoarthritis.

SUMMARY

Biomarker combinations have the ability to subgroup the heterogenous osteoarthritis population to allow a better scrutiny of diagnosis and treatment options. The application of different technological platforms to osteoarthritis would allow a better understanding of its pathology and could provide for appropriate candidates for earlier detection of osteoarthritis.

Association of plasma and synovial fluid interferon-γ inducible protein-10 with radiographic severity in knee osteoarthritis

OBJECTIVES

The objective of this study was to investigate interferon-γ inducible protein-10 (IP-10) concentrations in plasma and synovial fluid of patients with knee osteoarthritis (OA) and to analyze their relationship with disease severity.

DESIGN AND METHODS

Forty OA patients and 15 healthy controls were enrolled in this study. OA grading was performed according to the Kellgren-Lawrence criteria. IP-10 levels in plasma and synovial fluid were assessed using enzyme-linked immunosorbent assay.

RESULTS

Plasma IP-10 levels in the knee OA patients were significantly lower than those of controls (P=0.006). IP-10 levels in plasma were markedly higher with regard to paired synovial fluid (P<0.001). Furthermore, IP-10 concentrations in plasma and synovial fluid displayed significant inverse correlation with radiographic severity (r=-0.713, P<0.001 and r=-0.561, P<0.001, respectively). Subsequent analysis revealed that plasma IP-10 levels were positively correlated with synovial fluid IP-10 levels (r=0.424, P=0.006).

CONCLUSIONS

IP-10 levels in both plasma and synovial fluid were inversely associated with the severity of knee OA. Accordingly, IP-10 could serve as a biomarker for determining disease severity and might play a possible role in the pathophysiology of osteoarthritis.

Soluble receptor for advanced glycation endproducts is decreased in patients with juvenile idiopathic arthritis (ERA category) and inversely correlates with disease activity and S100A12 levels

OBJECTIVE

Membrane-bound receptor for advanced glycation endproducts (mRAGE) is overexpressed in response to increasing concentrations of its ligand (e.g., S100A12) and triggers an inflammatory immune response. In contrast, soluble RAGE (sRAGE) acts as a decoy receptor and downmodulates inflammation. Decreased sRAGE levels are associated with autoimmune diseases; however, limited data are available in juvenile idiopathic arthritis (JIA). We studied sRAGE levels in patients with JIA [enthesitis-related arthritis (ERA) category].

METHODS

sRAGE levels were estimated in the serum of patients with ERA JIA (n = 101), systemic-onset JIA and polyarticular JIA (n = 10 each), and healthy controls (n = 45). Synovial fluid (SF) sRAGE was measured in patients with ERA, rheumatoid arthritis, reactive arthritis, and osteoarthritis (n = 10). Levels of S100A12 were also measured. Twenty-four patients with ERA were followed for 4 months. Disease activity was assessed by swollen joint count (SJC), tender joint count (TJC), and erythrocyte sedimentation rate (ESR). All levels are expressed as median (range).

RESULTS

The serum sRAGE (pg/ml) level was significantly lower in patients compared to healthy controls [515 (64-1887) vs 1542 (627-3159); p < 0.0001]. In paired samples, SF had lower levels compared to corresponding plasma level [102 (51-799) vs 481 (134-1006); p < 0.0001]. The level of S100A12 (ng/ml) was higher in SF (1042; 573-1415) than serum (638; 208-779). Serum sRAGE correlated negatively with S100A12 levels (r = -0.474; p < 0.01.), ESR (r = -0.306; p < 0.01), and SJC (r = -0.237; p < 0.05), but not with TJC (r = -0.134; p = NS). The levels of sRAGE remained stable over time in patients with stable disease.

CONCLUSION

Levels of sRAGE are reduced in patients with ERA and correlate negatively with disease activity and S100A12 levels. sRAGE may be a modulator of inflammation in these patients.

Osteoarthritis year 2010 in review: biochemical markers

At the 2010 Osteoarthritis Research Society International (OARSI) congress in Brussels I was asked to present on "Biochemical Markers" in the "Year in Review" session. This provided an opportunity to summarize ongoing work and consensus building in the osteoarthritis research community related to osteoarthritis biomarkers, and second, and an opportunity to briefly overview a subset of studies from the previous 12 months related to soluble biomarkers that provided novel insights in the field. This review therefore briefly summarizes the progress in 2010 of the OARSI OA Biomarkers Global Initiative and the OARSI FDA Biomarkers Working Group, and provides a summary of selected osteoarthritis biomarker studies reported over the previous 12 months based on a review of articles from seven musculoskeletal journals and a PubMed search using the terms biomarkers and osteoarthritis.