The interaction of monosodium urate with connective tissue components.

Monosodium urate deposits almost exclusively in the connective tissues of patients with gout. Acetone dried homogenates of bovine nasal cartilage, but not of other tissues, markedly enhances the solubility of urate in buffers having molarities and hydrogen ion concentrations similar to that of most body fluids. The components of cartilage responsible for this effect are the proteinpolysaccharides, compounds of protein and chondroitin sulfate, called PPL. A progressive increase in PPL concentration results in a corresponding increase in urate solubility. If, on the other hand, unbound chondroitin sulfate or PPL digested by trypsin is used, then no significant augmentation of urate solubility occurs indicating that the integrity of the molecule is essential. One subfraction of PPL, PPL(5), causes an even more exaggerated response while another, PPL(3), causes a lesser one. These proteinpolysaccharide macro-molecules also inhibit the crystallization of urate from a supersaturated medium. The mechanism of the solubilizing phenomenon is not known. It is suggested that some type of physical or chemical binding is responsible. When, as a result of normal or accelerated connective tissue turnover, PPL is enzymatically destroyed, urate crystals then precipitate from the saturated tissue fluids.