Design and evaluation of a chitosan-aprotinin conjugate for the peroral delivery of therapeutic peptides and proteins susceptible to enzymatic degradation.

One main barrier for the peroral administration of therapeutic peptides and proteins is the enzymatic barrier, that is mediated by luminally secreted and membrane bound proteolytic enzymes. It was the aim of the study to synthesise, characterise and evaluate a novel polymer-inhibitor conjugate in order to improve the bioavailability of orally-administered peptides and proteins. The trypsin/chymotrypsin inhibitor aprotinin was covalently bound to chitosan. The percentage of the inhibitor in the polymer-inhibitor conjugate (m/m) was determined to be between 1.11 +/- 0.36 and 1.92 +/- 0.05%. In vitro enzyme assays clearly demonstrated the potential of the novel conjugate to inhibit trypsin and chymotrypsin. Moreover, studies in rats were performed to evaluate the efficacy of the conjugate in vivo. Eight hours after oral administration of tablets containing insulin and the novel chitosan-aprotinin conjugate, the mean blood glucose level decreased to 84 +/- 6%. In contrast, the mean blood glucose level in the control group increased to 121 +/- 8% of the initial measured blood glucose level. In conclusion it was demonstrated that chitosan-aprotinin conjugate represents a novel and promising tool for the oral administration of therapeutic peptides and proteins susceptible to enzymatic degradation caused by trypsin and chymotrypsin.