Inorganic polyphosphate stimulates cartilage tissue formation.

Clinical utilization of tissue-engineered cartilage constructs has been limited by their inferior mechanical properties compared to native articular cartilage. A number of strategies have been investigated to increase the accumulation of major extracellular matrix components within in vitro-formed cartilage, including the administration of growth factors and mechanical stimulation. In this study, the anabolic effect of inorganic polyphosphates, a linear polymer of orthophosphate residues linked by phosphoanhydride bonds, was demonstrated in both chondrocyte cultures and native articular cartilage cultured ex vivo. Compared to untreated controls, polyphosphate treatment of three-dimensional primary chondrocyte cultures induced increased glycosaminoglycan and collagen accumulation in a concentration- and chain length-dependent manner. This effect was transient, because chondrocytes express exopolyphosphatases that hydrolyze polyphosphate. The anabolic effect of polyphosphates was accompanied by a lower rate of DNA increase within the chondrocyte cultures treated with inorganic polyphosphate. Inorganic polyphosphate enhances cartilage matrix accumulation and is a promising approach to improve the quality of tissue-engineered cartilage constructs.