Impact of amino acid replacements on in vitro permeation enhancement and cytotoxicity of the intestinal absorption promoter, melittin

Melittin is an amphipathic α-helical peptide known to cause the non-cell selective perturbation of cell membranes, especially erythrocytes. The well characterised interaction of the peptide with phospholipid bilayers has led to its use as a model to study lipid-peptide interactions. In recent years, melittin has emerged as a potential intestinal absorption promoter that increases paracellular marker permeability across both in vitro and in situ intestinal drug delivery models. Like many other promoters, inherent toxicity limits the drug delivery potential of melittin. The purpose of this study was to examine the effect of amino acid modifications of melittin on viability and drug permeation in human intestinal epithelial cell monolayers (Caco-2), where each structural change made to the peptide is known to reduce the cytolytic action of the peptide on cell membranes composed of zwitterionic phospholipids. Each of the 4 peptide analogues (PA) demonstrated reduced cytotoxicity in the methylthiazolyldiphenyl-tetrazolium bromide (MTT) conversion assay and lactate dehydrogenase (LDH) membrane integrity assay, which was correlated with a reduction in amphipathicity and hydrophobicity, as measured by RP-HPLC. The selected amino acid changes however, also attenuated the epithelial permeation enhancement activity of melittin, as measured by transepithelial electrical resistance (TEER) and flux of FITC-dextran-4 kDa across Caco-2 monolayers. This data suggests that the cytolytic action of melittin is responsible in part for permeation enhancement and that these effects are related to transcellular perturbation in addition to effects on tight junctions.