Injectable Gel-PEG hydrogels as promising delivery system for intravitreal PACAP release: Novel therapeutics for unilateral common carotid artery occlusion induced retinal ischemia

Retinal ischemia is an ophthalmic emergency often caused by cardiovascular diseases, leading to irreversible vision loss and even blindness. Innovative retinal ischemia treatments are needed due to limited options. The pathological mechanisms involve retinal cell apoptosis and microglial activation. The pituitary adenylate cyclase-activating polypeptide (PACAP) is a well distributed neuropeptide found in both central nervous system and peripheral organs. Though it shows great anti-apoptosis and anti-microglia activation properties, it is rapidly cleared by intravitreal injection. Herein, we established a novel poly(ethylene glycol) (PEG) hydrogel system by cross-linking 4arm-PEG-NHS and 4arm-PEG-NH₂ to load PACAP (PACAP@Gel-PEG), which exhibited great fluidity, injectability, structural recovery ability, moderate swelling ratio and drug release ability that were appropriate for drug delivery. Then the safety and effectiveness of the PACAP@Gel-PEG were evaluated in vitro in three retinal cell lines (ARPE-19, 661 W and rRMC) and in vivo using the unilateral common carotid artery occlusion (UCCAO) mice model. The CCK-8 test and live/dead staining demonstrated that PACAP@Gel-PEG exhibited excellent biocompatibility in three retinal cell lines. Furthermore, after PACAP@Gel-PEG treatment, a great anti-apoptotic effect was observed in cells treated by CoCl₂. Application of PACAP@Gel-PEG greatly improved the therapeutic efficacy of PACAP in restoring retinal function, maintaining retinal integrity, and suppressing apoptosis and microglia activation in retinal tissues. Moreover, in mice, the biosafety of PACAP@Gel-PEG was confirmed by H&E staining of systemic organs. Taken together, our results demonstrated PACAP@Gel-PEG as a promising therapeutic option for retinal ischemia, providing new strategies for vision restoration.