Linker-Free Hyaluronic Acid-Dexamethasone Conjugates: pH-Responsive Nanocarriers for Targeted Anti-Inflammatory Therapy.

The covalent conjugation of pharmaceutical compounds to polymeric carriers represents an effective strategy for enhancing drug properties, including improved bioavailability, targeted delivery, and sustained release, while reducing systemic toxicity and adverse effects. By exploiting the physicochemical characteristics of biopolymers-particularly molecular charge and weight-we engineered a polymeric platform for glucocorticoid delivery with precisely controlled parameters including particle size, surface charge, targeting capability, and release kinetics. This study reports a linker-free synthesis of hyaluronic acid-dexamethasone (HA-DEX) conjugates through Steglich esterification, catalyzed by 4-dimethylaminopyridine (DMAP), which facilitates the acylation of sterically hindered alcohols. The reaction specifically couples carboxyl groups of hyaluronic acid with the C21 hydroxyl group of dexamethasone. Incorporation of hydrophobic dexamethasone moieties induced self-assembly into nanoparticles featuring a hydrophobic core and negatively charged hydrophilic shell (-20 to -25 mV ζ-potential). In vitro characterization revealed pH-dependent release profiles, with 80-90% dexamethasone liberated in mildly acidic phosphate buffer (pH 5.2) versus 50-60% in phosphate-buffered saline (pH 7.4) over 35 days, demonstrating both sustained release and inflammation-responsive behavior. The conjugates exhibited potent anti-inflammatory activity in a human tumor necrosis factor-α (TNFα)-induced inflammation model. These findings position HA-DEX conjugates as promising candidates for targeted glucocorticoid delivery to specific anatomical sites including ocular, articular, and tympanic tissues, where their combination of CD44-targeting capability, enhanced permeability and retention effects, and stimulus-responsive release can optimize therapeutic outcomes while minimizing off-target effects.