The pharmacokinetic parameters of a therapeutic molecule are crucial. Absorption in the first instance gives the drug the opportunity to enter the body and reach the systemic circulation. Some treatments are poorly or not at all absorbed through the epithelia. They are therefore invasively administered. Facilitating and increasing the absorption of molecules would make it possible to reduce administered doses and also to change the route of administration of certain treatments for non-invasive administration, such as a nasal spray or eye drops. Tight junctions (TJs) are a set of proteins responsible for holding cells together and regulating the permeability of exogenous nutrients and compounds across the cell layer. Controlled modulation of TJs could increase the absorption of drugs across the mucosa. The enzyme protein kinase C zeta (PKC ζ) has been shown to be one of the modulators responsible for the expression of TJs proteins such as occludin and Zonula occludens (ZO). This enzyme is also involved in the activation of these proteins to close TJs. Thus, inhibition of PKC ζ activity would prevent closure of TJs and transiently increase the permeability of molecules across the epithelium. In the structure of PKC ζ, a part called pseudosubstrate (PS) has been identified as the autoinhibitory segment of the enzyme's activity. The creation of a synthetic peptide with the same sequence as this segment could inhibit PKC ζ activity using the enzyme's natural mechanism. Our L-R5 pentapeptide with a myristoylated tail was used, optimised and tested throughout this thesis. The objectives of this PhD thesis were (1) to attest to the efficacy and non-toxicity of L-R5 in opening TJs, (2) to determine the exact mechanism of inhibition of PKC ζ activity by L-R5, (3) to explore the possibilities of optimisation in the sequence and structure of L-R5 and (4) to produce a L-R5 coupled insulin formulation for nasal administration.