Glaucoma is a multifactorial optic neuropathy, and its most important risk factor is the elevated intraocular pressure (IOP). In this sense, melatonin (MEL), is a neurohormone synthesized in ocular tissues, which regulates IOP. Incorporation of MEL into the last generation of lipid nanoparticles (NLC) constitute a suitable strategy to enhance its efficacy in the retinal tissues.

Therefore, the purpose of this work is the encapsulation of MEL into NLC to decrease IOP. MEL-NLC production was carried out by hot high-pressure homogenization and their optimization was performed using the design of experiments approach by examining independent parameters and their influence on MEL-NLC properties (size, polydispersity index, zeta potential and encapsulation efficiency). In vitro ocular tolerance was studied using embryonated eggs by means of a quantitative-modified HET-CAM test using trypan blue staining (HET-CAM-TBS) to measure membrane damage.

The optimized formulation had a mean average size below 150 nm, a polydispersity index lower than 0.3, a zeta potential around 20 mV and an encapsulation efficiency above 50%. The in vitro ocular tolerance of MEL and MEL-NLC was studied by HET-CAM-TBS test. The results revealed an optimal ocular tolerance for both MEL-NLC and MEL solution, which can be classified, according to the trypan blue adsorption, as a non-irritant.

In conclusion, a novel formulation of MEL-NLC has been developed and optimized with suitable physicochemical parameters for glaucoma treatment showing an optimal ocular tolerance.