Tacrolimus@ZIF-8/HTCC eye drop mediated transcorneal delivery of tacrolimus for preventing high-risk keratoplasty rejection

• The tacrolimus@ zeolitic imidazolate framework-8 nanoparticles (<100 nm) penetrate cornea efficiently. • 2-Hydroxypropyltrimethyl ammonium chloride chitosan enhances the corneal adhesion of the tacrolimus@zeolitic imidazolate framework-8 nanoparticles. • The tacrolimus@ zeolitic imidazolate framework-8 nanoparticles/2-hydroxypropyltrimethyl ammonium chloride chitosan sol significantly prolongs graft survival. Immune-mediated graft rejection (IMGR) remains a leading cause of corneal transplant (CT) failure in high-risk cases. While transcorneal delivery of tacrolimus (FK506) is a promising strategy, the cornea’s barrier properties severely limit FK506′s bioavailability and therapeutic function. Here, we developed a transcorneal delivery system by loading FK506 into zeolitic imidazolate framework-8 (ZIF-8) to form the FK506@ZIF-8 nanoparticles (<100 nm) with 4.5 % drug-loading capacity, followed by mixing with 2-hydroxypropyltrimethyl ammonium chloride chitosan (HTCC) solution to form a homogeneous sol. In vitro studies demonstrated sustained FK506 release over 24 h of the FK506@ZIF-8 in a simulated ocular microenvironment via ZIF-8 framework hydrolysis (Weibull model) and confirmed its biosafety in human corneal epithelial cells (HCECs) at concentrations ≤ 20 μg/mL. The Draize test validated minimal ocular irritation of the FK506@ZIF-8/HTCC eye drop in rabbits. The nano-size of the FK506@ZIF-8 combined with the HTCC-mediated corneal adhesion (>240 min retention) synergistically enhanced transcorneal delivery of FK506. In a rabbit IMGR model, the FK506@ZIF-8/HTCC eye drop significantly prolonged graft survival, reduced inflammatory infiltration, and outperformed conventional FK506 eye drops, highlighting its therapeutic potential for overcoming corneal drug delivery barriers. In summary, the FK506@ZIF-8/HTCC sol hold great promise for preventing high-risk keratoplasty rejection in clinic in the future.