Osteoarthritis is an important and costly problem in dogs, horses, and humans. In dogs, it is suggested that 20% of middle-aged and 90% of older dogs have osteoarthritis in 1 or more joints.1 The cause of osteoarthritis is unknown, but it inevitably results in degradation of articular cartilage, leading to pain, inflammation, and loss of motion in the joint.1 Because osteoarthritis is a widespread problem, veterinarians need a precise way to diagnose the disease early and accurately. Osteoarthritis is commonly diagnosed in the late and irreversible stages, where treatment can only be expected to decrease pain and slow progression of disease in a palliative manner.2 By developing methods for earlier diagnosis of osteoarthritis, prevention or even curative treatment strategies to manage the disease become more realistic.
Biomarkers are being investigated intensively for early diagnosis, identification of patients at increased risk, and monitoring therapeutic strategies in osteoarthritis.3 As such, a scheme for standardized classification of biomarkers was put forth by the Osteoarthritis Biomarker Network to categorize biomarkers under development into one or more of the following areas: burden of disease, investigative, prognostic, efficacy of intervention, and diagnostic.3 In our laboratory, we are particularly interested in identification and validation of biomarkers that can detect early stages of osteoarthritis to provide accurate diagnostic and prognostic information prior to onset of clinical disease. The study reported here focuses on a potential marker for diagnosis and staging of osteoarthritis in synovial fluid. Synovial fluid was chosen for this research as it is known to have sensitive and rapid responses to joint insult and injury, and these changes are primarily joint specific, which may be especially important in veterinary medicine. Hyaluronan was examined in this way because it is a major functional constituent of synovial fluid and articular cartilage, and it undergoes quantitative and qualitative changes in joint disease.4,5
Hyaluronan is synthesized by chondrocytes and synovial fibroblasts in articular cartilage and synovial intima, respectively.2 In the cartilage matrix, hyaluronan forms the backbone of proteoglycan aggregates that are interwoven with collagen to create the unique structure of hyaline cartilage.6 Synovial fluid hyaluronan provides joint lubrication and helps limit inflammation, pain, and cartilage degradation7 as well as acts as a shock absorber and allows the joint to move in a smooth, nearly frictionless manner.2 Alterations in joint biomechanics and physiologic characteristics as a result of insult, injury, or aging have direct effects on the quantity and quality of hyaluronan.2,7,8 When hyaluronan in synovial fluid or cartilage is abnormal in either respect, joint functions are further compromised, exacerbating progression toward irreversible osteoarthritis.2,5 Osteoarthritic joints in dogs are reported to have decreases in synovial fluid hyaluronan molecular weight and concentration as a result of fragmentation of hyaluronan and insufficient production of hyaluronan.2 Theses findings have encouraged investigators to study the effects of hyaluronan on joint function and pursue hyaluronan supplementation for treatment of osteoarthritis. To our knowledge, however, little has been reported regarding the use of hyaluronan as an osteoarthritis biomarker. One study8 investigated serum and synovial fluid hyaluronan as a potential diagnostic tool in dogs but did not find it useful as studied because of metabolic effects on serum hyaluronan concentrations and substantial overlap among disease states for synovial fluid concentrations. Therefore, we decided to focus on synovial fluid hyaluronan quality so as to avoid systemic influences on protein concentration and composition and to ascertain the importance of molecular weight subcategories in assessment of joint health. The objective of the study reported here was to determine the quantity (concentration) and quality (molecular weight) of synovial fluid hyaluronan with respect to presence and severity of osteoarthritis in stifle joints of dogs. We hypothesized that synovial fluid hyaluronan quantity and quality would be significantly altered in stifle joints of dogs insulted by surgical induction of osteoarthritis and in stifle joints of dogs with osteoarthritis resulting from CrCL disease, compared with synovial fluid from unaffected control stifle joints.
Cranial cruciate ligament
Cranial cruciate ligament transection
Femoral condylar articular cartilage groove creation
Echelon Biosciences Inc, Salt Lake City, Utah.
NuPAGE Novex Bis-Tris gels, Invitrogen Life Technologies, Carlsbad, Calif.
NuPage LDS sample buffer, Invitrogen Life Technologies, Carlsbad, Calif.
Invitrogen power supply, Invitrogen Life Technologies, Carlsbad, Calif.
BioRad cassette, BioRad, Hercules, Calif.
LumiGlo reagent, Cell Signaling Technology, Beverly, Mass.
Kuroki K, Cook JL, Kreeger JM. Mechanisms of action and potential uses of hyaluronan in dogs with osteoarthritis. J Am Vet Med Assoc 2002;221:944–950.
Johnson KA, Hay CW, Chu Q, et al. Cartilage-derived biomarkers of osteoarthritis in synovial fluid of dogs with naturally acquired rupture of the cranial cruciate ligament. Am J Vet Res 2002;63:775–781.
Pitsillides AA, Skerry TM, Edwards JC. Joint immobilization reduces synovial fluid hyaluronan concentration and is accompanied by changes in the synovial intimal cell populations. Rheumatology (Oxford) 1999;38:1108–1112.
Greenberg DD, Stoker A, Kane S, et al. Biochemical effects of two different hyaluronic acid products in a co-culture model of osteoarthritis. Osteoarthritis Cartilage 2006;14:814–822.
Canapp S, Cross A, Brown M, et al. Examination of synovial fluid and serum following intravenous injections of hyaluronan for the treatment of osteoarthritis in dogs. Vet Comp Orthop Traumatol 2005;3:169–174.
Cook JL, Tomlinson JL, Kreeger JM, et al. Induction of meniscal regeneration in dogs using a novel biomaterial. Am J Sports Med 1999;27:658–665.
Roy R, Wallace L, Johnston G, et al. A retrospective evaluation of stifle osteoarthritis in dogs with bilateral medial patellar luxation and unilateral surgical repair. Vet Surg 1992;21:475–479.
Fettig AA, Rand WM, Sato AF, et al. Observer variability of tibial plateau slope measurement in 40 dogs with cranial cruciate ligament-deficient stifle joints. Vet Surg 2003;32:471–478.
Hunt N, Sanchez-Ballester J, Pandit R, et al. Chondral lesions of the knee: a new localization method and correlation with associated pathology. Arthroscopy 2001;17:481–490.
Choi-Miura NH, Takahashi K, Yoda M, et al. Proteolytic activation and inactivation of serine protease activity of plasma hyaluronan binding protein. Biol Pharm Bull 2001;24:448–452.
Dahl LB, Dahl IM, Engström-Laurent A, et al. Concentration and molecular weight of sodium hyaluronate in synovial fluid from patients with rheumatoid arthritis and other arthropathies. Ann Rheum Dis 1985;44:817–822.