Discovery and development of the N-terminal procollagen type II (NPII) biomarker: a tool for measuring collagen type II synthesis

SummaryObjectiveProgression of joint damage in osteoarthritis (OA) is likely to result from an imbalance between cartilage degradation and synthesis processes. Markers reflecting these two components appear to be promising in predicting the rate of OA progression. Both N- and C-terminal propeptides of type II collagen reflect the rates of collagen type II synthesis. The ability to quantify the procollagen peptides in biological fluids would enable a better understanding of OA disease pathology and provide means for assessing the proof of mechanism of anabolic disease modifying OA drugs (DMOADs).MethodsA polyclonal antibody that recognizes the sequence GPKGQKGEPGDIKDI in the propeptide region of rat, dog, and human type II collagen was raised in chicken and peptide-affinity purified. The immunoaffinity liquid chromatography mass spectrometry (LC-MS/MS) was used to extensively characterize N-terminal procollagen type II (NPII) peptides found in biological fluids. The novel competition enzyme-linked immunosorbent assay (ELISA) assay was developed to quantitatively measure the NPII peptides.ResultsSeveral peptides ranging from 17 to 41 amino acids with various modifications including hydroxylations on proline and lysine residues, oxidation of lysines to allysines, and attachments of glucose and galactose moieties to hydroxylysines were identified in a simple system such as ex vivo cultures of human articular cartilage (HAC) explants as well as in more complex biological fluids such as human urine and plasma. A competitive ELISA assay has been developed and applied to urine, plasma, and synovial fluid matrices in human, rat and dog samples.ConclusionA novel NPII assay has been developed and applied to OA and normal human subjects to understand the changes in collagen type II synthesis related to the pathology of OA

MRI-derived T2 relaxation times and cartilage morphometry of the tibio-femoral joint in subjects with and without osteoarthritis during a 1-year follow-up

SummaryObjectiveTo assess differences in magnetic resonance imaging (MRI)-based compositional (T2) and morphometric (volume and thickness) parameters of the tibio-femoral joint cartilage in subjects with and without osteoarthritis (OA) and compare these with clinical assessment tools during a 1-year follow-up.MethodThree Tesla MRI of the knee joint was performed in eight female patients (body mass index [BMI]>30) with early OA and 10 age-matched female controls (BMI<30) at baseline (BL) and after 3, 6 and 12 months. Cartilage T2 maps, volume and average thickness were calculated in five compartments (medial/lateral femoral condyle, medial/lateral tibia and trochlea). These data were correlated with changes in clinical parameters and joint space width determined in standardized knee radiographs using a mixed random effects model.ResultsAt BL, T2 was significantly higher (P<0.05) across the cartilage in patients (45.68±5.17ms) compared to controls (41.75±4.33ms). Patients had significantly (P<0.05) less cartilage volume and less average cartilage thickness in the tibia than controls (2.10±0.53cm3 vs 2.91±0.49cm3 and 1.59±0.24mm vs 1.90±0.29mm, respectively). A significant change in clinical parameters of OA, cartilage T2 values or a decrease of volume and average thickness could not be demonstrated within both groups.ConclusionSignificant differences between the groups indicate that both T2 and morphometric parameters may be useful in quantifying early OA related changes. In a 12-month follow-up, however, no significant alterations of the studied parameters were found, which may be due to the length of the observation interval