In vitro phage display as a strategy to enhance the skin penetration of heparins

Low molecular weight heparins (LMWHs) are potent anticoagulant and antithrombotic drugs obtained by chemical or enzymatic depolymerization of unfractionated heparin (UFH). Depending on the production method, each LMWH has its own structure and peculiar physical, chemical and biological properties. In the last decades, several attempts have been made to find non-invasive routes of administration, alternative to the subcutaneous injection. Transdermal delivery may represent an attractive expedient, but the diffusivity of LMWHs through the skin is limited by their large molecular weight, hydrophilicity and negative charge. Several studies were carried out to enhance the skin penetration of heparins, but a comparative analysis of the permeability properties of such molecules is still missing at the best of our knowledge. A novel approach gaining interest to enhance the skin penetration of macromolecules is the use of the so called “skin penetrating peptides” which penetrate, without damaging, the biological membranes at low concentration and with high efficiency. They can be screened by phage display technique which uses phages as expression vectors. At date, by using this strategy and animal skin as membrane, only two peptides were identified to improve the permeation of macromolecules. In contrast, this technique has been never exploited to screen peptide enhancers using human skin. This work aimed to select a new skin penetrating peptide suitable for the enhancement of skin penetration of heparins. Preliminary, the influence of the main structural features of UFH and six commercially available LMWHs on their ability to diffuse through human skin was studied. The performances of the skin penetrating peptide selected using a phage display library was tested in vitro using UFH as model compound.