Incorporation of protein in PLG-microspheres with retention of bioactivity.

The enzyme urease was incorporated into poly(lactide-co-glycolide) microspheres using a double emulsion solvent removal technique. Ethyl acetate was used as organic solvent since it is less toxic than the more commonly used methylene chloride. The effect of the two solvents on urease was compared. Although this preparation technique is well established, it is often associated with reduced bioactivity and low entrapment efficiency of proteins. In order to retain a high degree of bioactivity, the well known protein stabilisers: sucrose, trehalose and poloxamer 407, were added to the urease in the preparation. The bioactivity of the entrapped urease was reduced more by methylene chloride than by ethyl acetate. The gelled form of poloxamer was shown to highly favour the retention of bioactivity, demonstrated by an increase of 41% compared to preparations without poloxamer. Moreover, the presence of poloxamer strongly increased the in vitro release rate of urease from the microspheres. The entrapment efficiency was increased by 44% using the sugars in the preparation. These results clearly show the great potential of small quantities of additive in the formulation to control the properties of the microspheres. The amount and type of additive could be adjusted according to the therapeutic application of the preparation.