Modulation of tight junctions by peptides to increase drug penetration across biological barriers

Abstract

Epithelial and endothelial cells form the anatomical and functional basis of biological barriers. The penetration of drugs across these barriers is limited due to closed intercellular gaps by tight junction proteins, and metabolic enzymes expressed in cells. These important barrier properties which on one hand provide protection, on the other hand prevent the effective treatment of several diseases. The paracellular permeability is one of the most important determinants of drug delivery across biological barriers and enhancing the permeability of drugs, especially large biopharmaceuticals is a great challenge in pharmaceutical research. In the case of biopharmacon delivery beside tight junctions enzymes of the metabolic barrier represent the most limiting factor, particularly at the BBB. We demonstrated the transfer of opiorphin, a bioactive peptide across a well characterized and validated co-culture BBB model. Our data also support, that opiorphin may have a potential for further development as a centrally acting novel drug for the treatment of pain or depression. One of the strategies to increase the penetration of large hydrophilic compounds is opening the paracellular gate by targeting TJ proteins. We studied six tight junction modulator peptides, ADT-6, HAV-6, C-CPE, AT-1002, 7-mer PN-78, PN159, which act on different targets, and compared their effects on intestinal epithelial and brain endothelial barriers. All peptides induced reversible opening of tight junctions as confirmed by different methods, but selectivity and differences in efficacy were observed. The targets of C-CPE, ADT-6 and HAV-6 peptides are expressed on epithelial cells which resulted in selective effects on epithelial cells. AT-1002 and 7-mer peptides caused enhanced permeability on both models but they were less effective on the intestinal barrier model. The selectivity of these peptides offers a great potential for innovative targeted drug delivery. PN159 peptide was the most effective permeability enhancer on both models: a rapid and reversible effect was found in low, non-toxic concentrations without permanent morphological changes. Potential targets of PN159 peptide were identified as claudin-1, -4, -5 and -7 but not claudin-3 by affinity measurement and molecular modeling. The secondary structure and the high thermostability of PN159 were also revealed, which can be important for the development of new pharmaceutical formulations and drug delivery systems. The presented results indicate that these peptides can be effectively and selectively used as potential pharmaceutical excipients to improve drug delivery across biological barriers.