Quantitative Outcome Measures of Cartilage Repair in Patients Treated by Tissue Engineering

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Abstract
Reliable and reproducible outcome measures are essential to assess the efficacy of competing and novel tissue-engineering techniques. The aim of this study was to compare traditional histological analyses with newly developed quantitative biochemical outcome measures for the repair of articular cartilage. The production of a new anti-peptide antibody and the development and validation of a novel method for the extraction and immunoassay of type I collagen are described. The assay was used, in conjunction with existing assays for type II collagen and proteoglycans, to measure levels of the matrix components in repair tissue biopsies obtained from patients treated with the new tissue-engineering therapy Hyalograft® C. Frozen sections cut from the same biopsies were stained for proteoglycans, using safranin O, and immunohistochemical analysis was used to assess type I and II collagen staining. Although there was general agreement between the extent of staining and the amounts of the three matrix components, there was a large degree of overlap in biochemical content between biopsies classified histologically on the basis of low, moderate, or abundant staining. The results demonstrate that histological grading of matrix protein abundance to classify repair cartilage as hyaline or fibrocartilagenous is often misleading. In addition, we demonstrate for the first time the ability to measure collagen cross-links in repair tissue biopsies and show that it can be used as a surrogate marker for tissue maturity. Our new range of biochemical techniques provides a standardized method to assess the quality of both engineered cartilage produced in vitro and repair tissue biopsies obtained after in vivo implantation.