Synthesis, characterization and chondroprotective properties of a hyaluronan thioethyl ether derivative

Hyaluronan (HA), a non-sulfated glycosaminoglycan, is widely used in the clinic for viscosurgery, viscosupplementation, and treatment of osteoarthritis. Four decades of chemical modifications of HA have generated derivatives in which the biophysical and biochemical properties, as well as the rates of enzymatic degradation in vivo have been manipulated and tailored for specific clinical needs. One earlier modification adds multiple thiol groups to HA through hydrazide linkages, leading to a readily crosslinkable material for adhesion prevention and wound healing. We now describe the synthesis and chemical characterization of a novel thioethyl ether derivative of HA, HA-sulfhydryl (HASH), with a minimal tether between the HA and the thiol group. Unlike earlier thiol-modified HA derivatives, HASH cannot be readily crosslinked to form a hydrogel using either oxidative or bivalent electrophilic conditions, thus offering a unique polymeric polythiol that remains soluble. Moreover, HASH showed no cytotoxicity towards primary human fibroblasts and reduced the apoptosis rates of primary chondrocytes exposed to hydrogen peroxide in vitro. These properties foreshadow the clinical potential of HASH to moderate inflammation and to act as a chondroprotective agent in vivo.