Cathepsin B as a soluble marker to monitor the phenotypic stability of engineered cartilage

The clinical need for improved human autologous chondrocyte transplantation has motivated the use of different biomaterials, which are aimed at fixing the cells in the defect area and permit their proliferation and differentiation. The maintenance of the original phenotype by isolated chondrocytes grown in vitro is an important requisite for their use in repairing damaged articular cartilage. The methods to verify the expression of cartilage-specific molecules usually involve destructive procedures to recover the cells from the scaffolds for tests. The aim of our study was to find a soluble marker able to attest the occurrence of a differentiation process by chondrocytes grown onto a biomaterial used for cell transplantation. We turned our attention to cathepsin B which is known to be abnormally synthesized in de-differentiated chondrocytes and scarcely produced in the differentiated ones. The production of cathepsin B by human articular chondrocytes expanded in vitro and then grown onto a hyaluronan-based polymer derivative (Hyaff(Jf)-11) three-dimensional scaffold was evaluated with a specific enzyme-immunoassay at different experimental times together with the expression of mRNA by real-time PCR. We showed that cathepsin B, which is abundantly produced by chondrocytes grown in a monolayer culture, decreases significantly after the cells are seeded onto the scaffold, giving further evidence of a re-differentiation process. This result suggests cathepsin B a practical soluble marker to evaluate the "good" quality of transplantable constructs. (C) 2003 Elsevier Science Ltd. All rights reserved.