The characterization of biomolecular processes controlling dopamine transport across the nasal mucosa

Dopamine, a catecholamine neurotransmitter, is involved in the etiology of CNS related disorders such as Parkinson's disease and schizophrenia. Dopamine shows poor CNS disposition following oral and IV administration due to its extensive metabolism in the GI tract and ionization at physiologic pH. However, enhanced CNS uptake of dopamine was observed following intranasal administration. The purpose of this project was to investigate the role of uptake carriers and nasal mucosal metabolism underlying the enhanced dopamine transport across the nasal mucosa.; Dopamine transporter (DAT) and organic cation transporter-2 (OCT-2) both mediate dopamine transport in various tissues. Western blotting revealed the expression of these transporters in both bovine olfactory and respiratory mucosae. Immunohistochemistry localized DAT to the apical and basolateral surfaces of the olfactory epithelium but only to basolateral surface of the nasal respiratory epithelium. DAT was localized predominantly to the basolateral surface of a human nasal epithelial cell culture (EpiAirway(TM)). OCT-2 was primarily observed in the submucosal region of both the olfactory and respiratory mucosae; OCT-2 was also observed in the epithelium of the EpiAirway(TM) tissues.; Bidirectional transport studies across the nasal explants were carried out to characterize any saturable, carrier-mediated processes in nasal dopamine transport. Dopamine flux across bovine olfactory and respiratory explants was saturable in the mucosal-submucosal direction; dopamine flux across the EpiAirway(TM) tissues was saturable in the basolateral-apical direction. A DAT inhibitor, GBR 12909, decreased dopamine flux only at low dopamine concentrations while an OCT-2 inhibitor, amantadine, decreased the flux at higher dopamine concentrations. Dihydroxy-phenylacetic acid, a dopamine metabolite, was observed in the solutions exposed to the mucosal and submucosal surfaces. Monoamine oxidase, catechol-O-methyl transferase and aldehyde dehydrogenase catalyze dopamine metabolism. MAO was localized to the submucosal tissues using immunohistochemistry.; These studies demonstrate that both DAT and OCT-2 play an important role in dopamine uptake across the nasal mucosa. MAO is capable of metabolizing dopamine, but minimal quantities of DOPAC, it's metabolite, were produced. These studies provide evidence which suggests that enhanced CNS disposition of dopamine following nasal delivery is the result of carrier-mediated transport and is not significantly limited by nasal mucosal metabolism.