Objective: Nasal administration of opioids may be useful in break- through pain due to rapid onset of analgesia. Water-soluble drugs such as morphine require drug absorption enhancing additives in nasal formulations. Chitosan is a cationic polysaccharide with ability to bind to negatively charged surfaces such as cell and "open" tight junctions, and is shown to improve nasal bioavailability of morphine in man. Transport of drugs through biological membranes can be examined in vitro in specially designed wells using gut epithelial cell-lines such as Caco-2. The aim of this study was to find chitosan related factors that promote transepithelial transport of morphine.
Methods: Commercially available Transwell Permeable supports and Caco-2 cells were employed. Incubations had duration of 3 h. Chitosan (50 or 250 mg/ml) with varying degree of acetylation (0.01 0.61) were compared. Morphine was added to one side of the epithelium at an initial concentration of 10 µM. Concentrations of morphine sampled at 90, 120 and 180 min from the other side of the cell membrane were determined by liquid chromatography-tandem mass-spectrometry. Several procedures for viability/toxicity testing were employed.
Results: Chitosan with the lowest degree of acetylation (0.01-0.35) caused the highest degree of transepithelial morphine transport. The higher concentration of chitosan (250 mg/ml) generally gave higher transport. It was no clear relation between cell toxicity/viablility tests and morphine transport, except for transepithelial electrical resistance.
Conclusion: Degree of acetylation and chitosan concentration were factors that influence transepithelial transport of morphine. It may be of significant importance to screen chitosan in vitro as a part of a nasal morphine formulation process before animal studies are commenced.