Enhanced insulin absorption from sublingual microemulsions: effect of permeation enhancers.

Abstract

Microemulsions of insulin (50IU/mL) comprising permeation enhancers were formulated for sublingual delivery. Circular dichroism (CD) spectra indicated conformational stability, while chemical stability was confirmed by high-performance liquid chromatography (HPLC). CD spectra of insulin in combination with permeation enhancers revealed attenuation of molar ellipticity at 274nm in the order TCTP > TC-AOT > TC > TC-NMT > Sol P > insulin solution. The molar ellipticity ratios at 208/222nm confirmed dissociation of insulin in the microemulsions with the same rank order. Matrix-assisted laser diffraction ionization mass spectra (MALDI) revealed a significant shift in intensity signals towards monomer and dimers with a substantially high ratio of monomers, especially in the presence of the TCTP and TC-AOT. Permeation through porcine sublingual mucosa correlated with the dissociation data. A high correlation between the ratio of molar ellipticity at 208/222nm and serum glucose levels (r (2) > 0.958) and serum insulin levels (r (2) > 0.952) strongly suggests the role of dissociation of insulin on enhanced absorption. While all microemulsions revealed a reduction in serum glucose levels and increase in serum insulin levels, significant differences were observed with the TCTP and TC-AOT microemulsions. High pharmacological availability >60% and bioavailability >55% compared to subcutaneous insulin at a low dose of 2IU/kg appears highly promising. The data clearly suggests the additional role of the permeation enhancers on dissociation of insulin on enhanced sublingual absorption from the microemulsions.