Purpose: This study aimed to find an alternative route for erythropoietin (EPO) ocular administration because of its neuroprotective and neuroregenerative known properties. Ocular penetration of EPO after subconjunctival injection was assessed, and potential side-effects on the haematocrit for a 28-day period were also evaluated.
Methods: Wistar Hannover female albino rats (n = 42) divided into seven groups of six were used. One group (n = 6) served as control. Six groups (n = 36) received 1,000 UI of EPO through the subconjunctival route in one of the eyes. According to the group, animals were humanely killed at 12 h (n = 6), 24 h (n = 6), 36 h (n = 6), 48 h (n = 6), and 60 h (n = 6), after EPO administration, in a total of 30 animals. Enucleation of both eyes was performed, and EPO protein distribution in the rat's retina was analyzed by immunohistochemistry. Another group of animals (n = 6) was used to collect blood samples and perform haematocrit analysis at 0, 7, 14, 21, and 28 days after unilateral EPO subconjunctival administration.
Results: The evaluation of EPO expression in the animals' retinas after subconjunctival administration yielded a strong immunostaining signal. Among the retina's layers, EPO expression was more evident in the RGC layer 24 h after the administration, and was still present on that layer till the end of the study (60 h). When administered subconjunctivally EPO reached several neuronal cells, in all retinal layers. The subconjunctival EPO administration did not cause significant changes in the haematocrit values over a 28-day period.
Conclusion: In this study, it was demonstrated that EPO reached the retinal ganglion cell layers when administered subconjunctivally. EPO reached the retina 24 h after the subconjunctival administration, and was still present 60 h after the administration. Furthermore, it was also proved that EPO subconjunctival administration did not cause any haematopoietic significant side-effects. The subconjunctival route was shown to be a promising alternative for EPO ocular delivery.