Evaluation of the enzyme inhibitory effect of carboxymethylated chitosan
Oberholzer, Ian Dewald
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Degradation of peroral administered drugs by various enzymes in the gastrointestinal tract has proven to be troublesome for the absorption' and bioavailability of protein and peptide drugs. Mucoadhesive polymers such as poly(acrylates) have proven to inhibit protease enzymes responsible for initiating digestion of peptide drugs. Enzyme inhibitors have unique chemical properties enabling it to interact with enzymes to form complexes with such enzymes prohibiting it from functioning properly. Anionic carboxymethylated chitosan derivatives such as N,N-dicarboxymethyl chitosan and N, O-carboxymethyl chitosan display unique structural similarities to enzyme inhibitors being anionic polymers that may interact with bi-valent cations. N,N-dicarboxymethyl chitosan and N,N-dicarboxymethyl chitosan oligomer were synthesised and were tested together with N, O-carboxymethyl chitosan for inhibition of a-chymotrypsin, a luminal protease enzyme. The synthesised polymers were characterise by IH-NMR, IR and DSC. Inhibition of a-chymotrypsin by Carbopol 934P®, a known enzyme inhibitor, was also investigated to establish whether the method used was adequate and to compare the inhibition capabilities of the anionic chitosan derivatives with that ofCarbopoI934P®. N-trimethyl chitosan chloride or TMC, was also tested to illustrate and compare the enzyme inhibition capability of a cationic chitosan derivative with that of the anionic polymers. Carbopol 934P® showed very good inhibition of a-chymotrypsin whereas the anionic chitosan polymers, though showing inhibition, had a far less inhibitory effect on the enzyme. The low molecular weight N,N-dicarboxymethyl chitosan oligomer and high molecular weight N, O-carboxymethyl chitosan showed better inhibition than the high molecular weight N,N-dicarboxymethyl chitosan. This might be because of stereochemistry allowing N,N-dicarboxymethyl chitosan oligomer and high molecular weight N,O-carboxymethyl chitosan to interact more completely with bivalent cations. TMC did not show any inhibition of a-chymotrypsin. It was concluded that anionic chitosan derivatives does inhibit proteolytic achymotrypsin to some extend but it cannot be concluded if the inhibition would be sufficient to promote the bioavailability of suitable drugs in formulated dosage forms.
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