Polyhydroxyethylaspartamide-based micelles for ocular drug delivery.

In this paper three copolymers of polyhydroxyethylaspartamide (PHEA), bearing in the side chains polyethylene glycol (PEG) and/or hexadecylamine (C(16)) (PHEA-PEG, PHEA-PEG-C(16) and PHEA-C(16) respectively) have been studied as potential colloidal drug carriers for ocular drug delivery. The physical characterization of all three PHEA derivatives, using the Langmuir trough (LT) and micellar affinity capillary electrophoresis (MACE) techniques allowed to assume that whereas alone PHEA backbone is an inert polymer with respect to the interactions with lipid membranes and drug complexation, when PHEA chains are grafted with long alkyl chains like C(16) or in combination C(16) chains and hydrophilic chains like PEG, copolymers with lipid membrane interaction ability and drug complexation capability are obtained. In vitro permeability studies performed on primary cultured rabbit conjunctival and corneal epithelia cells, using PHEA-C(16) and PHEA-PEG-C(16) as micelle carriers for netilmicin sulphate, dexamethasone alcohol and dexamethasone phosphate, demonstrated that in all cases drug loaded PHEA-C(16) and PHEA-PEG-C(16) micelles provide a drug permeation across ocular epithelia greater than simple drug solutions or suspensions. In particular PHEA-PEG-C(16) acts as the best permeability enhancer in our experimental model. In vivo bioavailability studies conducted with PHEA-PEG-C(16) micelles loaded with dexamethasone alcohol, confirmed that this system also provides a drug bioavailability greater in comparison with that obtained with water suspension of the same drug after ocular administration to rabbits.

Cytokeratin expression in primary epithelial cell culture from bovine conjunctiva.

Aim of the present study is to extend our previous observations on a model of primary epithelial cell culture obtained from bovine conjunctiva, and analyse the maintenance of the conjunctival phenotype, relative to cytokeratin (CK) expression, through extended periods of cultivation under different conditions. Conjunctival epithelial cells were grown in transwell filters, and cultured either under liquid covered (LC), or air-interface (AI) conditions. The physiological state of the cells was monitored daily by measurement of the trans-epithelial electrical resistance (TEER). Analysis of cytokeratin expression was then carried out at different time points (up until 14 days), and compared to the original profile of the conjunctival tissue in order to assess deviations from the primitive phenotype. Immunodetection studies, carried out by both western immunoblot and immunofluorescence analyses, revealed constant expression of the pan-epithelial marker AE3 (recognizing basic type cytokeratins), confirming the epithelial nature of the culture. Other cytokeratins characteristic of non-keratinized stratified epithelia (CK4 and CK13) were absent in corneal tissue, while in conjunctival epithelial cells were more expressed under AI than under LC culture conditions. Expression of CK12, a specific marker of corneal tissue, revealed by the antibody AE5, was never observed in conjunctival epithelial cells. These results indicate that the conjunctival phenotype is conserved during extended periods of culturing, making this system a reliable substitute of conjunctival tissue for pharmaceutical analyses.

In vivo-in vitro correlation of salbutamol release from a controlled release osmotic pump delivery system.

The drug release of salbutamol from a controlled release (osmotic pump) tablet was determined in vitro by four different dissolution apparatuses. From published in vivo data, percent of drug absorbed and percent of drug released in vivo were estimated. The highest correlation was obtained between percentage released in vitro versus percentage released in vivo using polynomial regression.