Biofragmentation of Acetylated Starch by the α-Amylase of Aspergillus oryzae

Drug release from starch-acetate microparticles and films with and without incorporated α-amylase

Acetylation of starch considerably decreases its swelling and enzymatic degradation. Thus, starch-acetate (SA) based delivery systems may be suitable for controlled drug delivery. The aim of the present study was to evaluate drug release from the SA microparticles (SA mps) and SA films. The average degree of acetyl substitution (DS) per glucose residue in the starch was either 1.9 (SA DS 1.9) or 2.6 (SA DS 2.6). Timolol (mw 332), calcein (mw 623) and bovine serum albumin (BSA, mw 68,000) were used as model drugs. A continuous timolol release from the both SA mps was observed in phosphate buffer solution (PBS) pH 7.4 (50-days incubation). The release of timolol was faster from the SA DS 1.9 mps than from the SA DS 2.6 mps. Calcein release from both SA mps was continuous in PBS pH 7.4 (5-days incubation). But, calcein release profile from the SA DS 2.6 film in PBS pH 7.4 showed discontinuities. However, the release of calcein from both SA films was continuous in human serum in vitro during the 7-day incubation, i.e. enzymes enhanced calcein release. Thus, alpha-amylase was incorporated into the SA films in order to enhance drug release from the films. However, the effects of incorporation of alpha-amylase on the model macromolecule (BSA) release from the SA films were modest. In conclusion, this study demonstrates the achievement of slow release of different molecular weight model drugs from the SA mps and films as compared to fast release from the native starch preparations. DS of SA, physicochemical properties of a drug and the presence of enzymes can all affect drug release profiles from SA based preparations.

Drug release from starch-acetate films

The aim of the present work was to compare the drug release rates from the native and acetylated starches. The average degree of acetyl substitution per glucose residue of potato starch was either 1.9 (SA DS 1.9) or 2.6 (SA DS 2.6). Bovine serum albumin (BSA) (mol. wt. 68,000), FITC-dextran (mol. wt. 4400), timolol (mol. wt. 332, log P=1.91) and sotalol-HCl (mol. wt. 308, log P=-0.62) were used as model drugs. All of the model drugs were released rapidly from the potato starch film in PBS pH 7.4 with and without alpha-amylase in the dissolution medium (t50% varied from 0.17 to 3.37 h). When compared to the potato starch film, all of the studied drugs were released at a substantially slower rate from the SA films in the corresponding mediums. The release of the smaller drugs (sotalol, timolol) from the SA films was faster than that of the macromolecules (FITC-dextran, BSA). Furthermore, sotalol was released faster than the more lipohilic timolol from the SA films. Release of macromolecules from the SA films was biphasic with and without alpha-amylase in the dissolution medium: an initial fast release phase was followed by a slower release phase (SA DS 1.9) or no release occurred after the initial phase (SA DS 2.6). All of the drugs were released faster from the SA DS 1.9 film than the weight loss of the film itself. When compared to the SA DS 1.9 film, the model drugs (except sotalol) were released slower from the SA DS 2.6 film. The macromolecule release from the SA DS 2.6 film was erosion-controlled. The weight loss of the SA DS 2.6 film was slow with and without alpha-amylase in the incubation medium. The present results show that acetylation of potato starch can substantially retard drug release. The drug release profiles may be controlled by the degree of substitution, since drug release from the SA DS 1.9 film was faster than the corresponding release from the SA DS 2.6 film.