Post-translational aging of proteins in osteoarthritic cartilage and synovial fluid as measured by isomerized aspartate.

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INTRODUCTION: Aging proteins undergo non-enzymatic post-translational modification, including isomerization and racemization. We hypothesized that cartilage with many long-lived components could accumulate non-enzymatically modified amino acids in the form of isomerized aspartate and that its liberation due to osteoarthritis (OA)-related cartilage degradation could reflect OA severity. METHODS: Articular cartilage and synovial fluid were obtained from 14 randomly selected total knee arthroplasty cases (56 to 79 years old) and non-arthritis cartilage from 8 trauma cases (51 to 83 years old). Paired lesional cartilage and non-lesioned OA cartilage were graded histologically using a modified Mankin system. Paired cartilage and synovial fluids were assayed for isomerized aspartate, phosphate-buffered saline/EDTA (ethylenediaminetetraacetic acid) extractable glycosaminoglycans, and total protein. Macroscopically normal non-lesioned OA cartilage was separated into superficial and deep regions when cartilage thickness was at least 3 mm (n = 6). RESULTS: Normalized to cartilage wet weight, normal cartilage and deep non-lesioned OA cartilage contained significantly (P < 0.05) more isomerized aspartate than superficial non-lesioned OA cartilage and lesioned cartilage. Synovial fluid isomerized aspartate correlated positively (R2 = 0.53, P = 0.02) and glycosaminoglycans correlated negatively (R2 = 0.42, P = 0.04) with histological OA lesion severity. Neither synovial fluid isomerized aspartate nor glycosaminoglycans nor total protein correlated with histological scores of non-lesioned areas. CONCLUSIONS: We show for the first time that human cartilage and synovial fluid contain measurable quantities of an isomerized amino acid and that synovial fluid concentrations of isomerized aspartate reflected severity of histological OA. Further assessment is warranted to identify the cartilage proteins containing this modification and to assess the functional consequences and biomarker applications of this analyte in OA.





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Catterall, Jonathan B, Daniel Barr, Michael Bolognesi, Robert D Zura and Virginia B Kraus (2009). Post-translational aging of proteins in osteoarthritic cartilage and synovial fluid as measured by isomerized aspartate. Arthritis Res Ther, 11(2). p. R55. 10.1186/ar2675 Retrieved from

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Michael Paul Bolognesi

Virginia Flowers Baker Distinguished Professor of Orthopaedic Surgery

As chief of the adult reconstruction service, the majority of my research effort has been directed toward clinical outcomes, implant survivorship, functional recovery, the biology of hip and knee arthritis and cost effectiveness.


Virginia Byers Kraus

Mary Bernheim Distinguished Professor of Medicine

Virginia Byers Kraus, MD, PhD, is the Mary Bernheim Distinguished Professor of Medicine, Professor of Orthopaedic Surgery, Professor of Pathology and a faculty member of the Duke Molecular Physiology Institute in the Duke University School of Medicine. She is a practicing Rheumatologist with over 30 years’ experience in translational musculoskeletal research focusing on osteoarthritis, the most common of all arthritides. She trained at Brown University (ScB 1979), Duke University (MD 1982, PhD 1993) and the Duke University School of Medicine (Residency in Internal Medicine and Fellowship in Rheumatology). Her career has focused on elucidating osteoarthritis pathogenesis and translational research into the discovery and validation of biomarkers for early osteoarthritis detection, prediction of progression, monitoring of disease status, and facilitation of therapeutic developments. She is co-PI of the Foundation for NIH Biomarkers Consortium Osteoarthritis project. Trained as a molecular biologist and a Rheumatologist, she endeavors to study disease from bedside to bench.

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