Visualization of the penetration modifying mechanism of laurocapram by Mass Spectrometry Imaging in buccal drug delivery

The aim of the study was to visualize the penetration modifying effect of laurocapram on the delivery of diazepam and codeine across buccal mucosa by MALDI Mass Spectrometry Imaging (MALDI-MSI). A qualitative ex vivo study was carried out by mounting porcine buccal mucosa in Ussing chamber sliders and applying a pretreatment of phosphate buffered saline (PBS) or a 50% (v/v) laurocapram:ethanol solution apically before incubation for 1 or 3 h with a 0.1 M diazepam or 0.1 M codeine solution. MALDI-MSI analysis was performed on vertical cryo-sections of porcine buccal mucosa. The analysis provided detailed images of the localisation of the drugs, laurocapram and endogenous lipids in the epithelium and connective tissue. While diazepam in the absence of laurocapram was distributed with a steady concentration gradient through the connective tissue, indicating passive diffusion, pre-treatment with laurocapram fundamentally altered the penetration of diazepam through the buccal mucosa. In the presence of laurocapram, the distribution of diazepam was restricted to areas where laurocapram itself was present, in particular in the outer epithelial cell layers and in certain islands in the connective tissue. In contrast, the penetration of codeine was unaffected by the presence of laurocapram in similar experiments. The co-localization of laurocapram and diazepam indicates a reservoir effect, which has previously been found in diffusion experiments in Ussing chambers. The major difference in the penetration of codeine and diazepam through the buccal mucosa in presence of laurocapram was explained by the physicochemical properties of the drugs. Codeine is characterized by being more hydrophilic than diazepam and was partly charged under the given experimental conditions.