Polymer-enzyme inhibitor conjugates: influence of the molecular mass on the inhibition of membrane-bound aminopeptidase N activity

Abstract

Conjugates of mucoadhesive polymers and protease inhibitors have been developed to protect incorporated (poly)peptides from enzymatic attack by luminally secreted or membrane-bound proteases. Within the present study, the influence of the molecular mass of such polymer conjugates on the inhibition of membrane-bound enzyme activity was evaluated. The aminopeptidase N inhibitor bacitracin (Bac) was covalently immobilised on the mucoadhesive polymer model poly(acrylic acid) with a molecular mass of 2 kDa (PAA 2 ) and 3000 kDa (polycarbophil, PCP). The resulting conjugates PAA 2 -Bac and PCP-Bac exhibited comparable amounts of bacitracin (24.4 and 25.3% (m/m), respectively) and were used to perform inhibition studies on isolated and membrane-bound aminopeptidase N. The conjugates showed no differences in the inhibition of isolated aminopeptidase N, whereas PAA 2 -Bac exhibited a significantly higher inhibitory activity versus membrane-bound aminopeptidase than PCP-Bac. Due to its lower molecular mass, PAA 2 -Bac could more easily diffuse into the mucus layer to get in contact with the enzyme. Obtained results should provide helpful basic knowledge for the development of multifunctional polymers as auxiliary agents for the oral administration of peptide drugs.