An injectable thermosensitive hydrogel encapsulating tetramethylpyrazine nanocrystals alleviates angiogenesis and apoptosis in a choroidal neovascularization mouse model

Abstract

Neovascular age-related macular degeneration (nAMD) is a leading global cause of blindness characterized by vascular endothelial growth factor (VEGF)-mediated choroidal neovascularization (CNV), in which aberrant pathological angiogenesis extends from the choriocapillaris into the subretinal region. However, the lifelong regime of intraocular anti-VEGF agents, as the front-line treatment for excessive angiogenesis, is not effective for all patients and can induce devastating ocular complications. Thus, it is crucial to develop an available, durable, and affordable drug system capable of overcoming ocular obstacles and enabling the sustained release of a drug to target CNV. Owing to its multitarget properties, tetramethylpyrazine (TMP) has been widely used in clinics for its anti-angiogenic, anti-inflammatory, antioxidant, and anti-fibrotic effects. Yet, its potential clinical use in ocular disorders has been hindered by its lipophilic properties and poor absorption. Herein, we developed and optimized an injectable thermosensitive polymeric hydrogel using the solvent evaporation drying method and the “cold” approach in turn for the controlled release and high drug-loading of TMP nanoparticles, facilitating the sustained release of TMP both in vitro and in vivo. The hydrogel-encapsulated TMP nanocrystals (NCs) were synthesized and characterized by zeta potential, dynamic light scattering, scanning and transmission electron microscopy, and rheometer. The payload of the hydrophobic drug TMP to the symmetrical poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) hydrogel (TMP-NCs-gel) had a porous structure (pore size, 10–200 mm), and the transparent in situ hydrogel system immediately transitioned from the liquid to gel phase when the phase transition temperature was reached. We also demonstrated that the TMP-NCs-gel ameliorated abnormal angiogenesis and repressed photoreceptor apoptosis in vivo without inducing toxicity. Furthermore, the TMP-NCs-gel were observed to accumulate in CNV lesions in vivo, confirming their targeting characterization. Overall, this advanced formulation, combining TMP and an in situ gel system, is promising for AMD treatment and may represent an effective therapeutic strategy for patients with CNV.