Abstract
Purpose: :
Mammalian esterases are broad spectrum enzymes that participate in the metabolism of a wide variety of clinical drugs. This study compares the relative expression and localization of carboxylesterase 1 (CE1) and 2 (CE2), butyrylcholinesterase (BChE), and acetylcholinesterase (AChE) in normal human, primate and rabbit ocular tissues.
Methods: :
Paraffin-embedded sections from 6 individual normal human donor eyes, 6 non-human primate and 6 rabbit eyes (Dutch Belted) were processed for immunohistochemistry with antibodies specific to CE1, CE2, BChE and AChE, and subsequently incubated with goat anti-rabbit or goat anti- mouse Alexa Fluor 568 secondary antibodies for detection. Fluorescence was visualized and acquired using the Hamamatsu Nanozoomer, the Caliper Life Sciences Vectra multispectral imaging system and/or the LSM710 Zeiss confocal microscope, and fluorescence intensities per unit of area were calculated and compared for various ocular structures with Metamorph Pro.
Results: :
In the anterior segment of the eye, CE1 expression was localized mainly in the corneal stroma in human, primate and rabbit ocular tissues, and in the corneal epithelium in rabbit only. Corneal CE1 expression was most prominent in human, followed by rabbit and primate. CE2 expression was localized to the corneal epithelium in human, rabbit and primate (in descending order), and in the corneal stroma in human only. BChE was localized in the corneal endothelium and the episcleral vasculature in all species, with similar expression levels. AChE was localized to fibers throughout the corneal stroma and epithelium, and the vasculature of the iris and limbus. In the posterior segment of the eye, CE1 expression was prominent in sclera and choroid and absent from retinal tissues, while CE2 was strongly expressed in choroid, in the retinal vasculature and the neural retina. BChE was present in choroid in all species and absent from the retina. AChE was strongly expressed in the neural retina, in cells in the ganglion cell layer and the inner nuclear layer, and fibers in the inner plexiform layer. In general, the expression levels for the four enzymes were similar for all species in the posterior segment.
Conclusions: :
This study suggests that the drug delivery method, whether topical, systemic or intraocular, will expose the drug to a differing group of esterases. Overall, the largely similar distribution of these enzymes in ocular tissues, indicates that primate and rabbit make appropriate animal models for studying the roles of esterases in drug metabolism and drug delivery aimed at human disease.
Keywords: enzymes/enzyme inhibitors • immunohistochemistry • microscopy: light/fluorescence/immunohistochemistry