Permeability Barriers for Nicotine and Mannitol in Porcine Buccal Mucosa Studied by High-Resolution MALDI Mass Spectrometry Imaging

Improved nicotine permeability across buccal mucosa may enable more effective oromucosal nicotine replacement therapy products. It is essential to know the location and composition of the main barrier for drug diffusion to enhance the drug permeability. Matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI MSI) is a rapidly evolving technique that can be used to image the spatial distribution of drugs and drug metabolites in tissue cryo-sections, without prior labeling of the drug. In this study, the distribution of nicotine and mannitol in porcine buccal mucosa was imaged with 10 μm spatial resolution after apical as well as submucosal application of the drugs in order to localize the main permeability barrier(s). This was supported by ex vivo permeability studies across separated porcine buccal epithelium and submucosa. Lastly, the metabolism of nicotine in porcine buccal mucosa was evaluated by imaging of the main metabolite, cotinine. The results showed that the main permeability barrier to both nicotine and mannitol was located in the outer fourth of the epithelium. Further, it was shown that cotinine was sparsely distributed in excised porcine buccal mucosa, indicating that nicotine metabolism in excised porcine buccal mucosa was negligible. MALDI MSI was shown to be a useful method for imaging spatial distribution of drugs in buccal mucosa.