Preparation of CM-chitin microspheres by complexation with iron(III) in w/o emulsion and their biodisposition characteristics in mice

6-O-Carboxymethylchitin (CM-chitin) was partially deacetylated by alkaline treatment, and the 30% deacetylated product was named CM-DA30 and used for the preparation of microspheres. An aqueous solution of CM-DA30 was added to hexane containing 1% (w/w) sorbitan sesquioleate and emulsified by stirring and sonication, and iron(III) chloride was added. The formed microspheres (CM-MS) were washed with methanol and lyophilized after addition of polyethylene glycol. The mean particle diameter was less than a few μm, and longer sonication time tended to decrease the mean particle size. Sixty min of sonication enabled the production of CM-MS consisting of only the particles with a diameter of less than several μm. Iron(III) content and recovery of CM-DA30 were not markedly affected by the sonication time. CM-MS was spherical as was observed by scanning electron microscopy. Fluorescein moieties-containing microspheres (CM-MS-FTC) were prepared in the same manner but using fluorescein-isothiocyanate-labeled CM-DA30 (FTC-CM-DA30) instead of CM-DA30. After i.v. injection of CM-MS-FTC, its body distribution and urinary excretion of FTC-CM-DA30 were examined. CM-MS-FTC was located to some extent in the lung for an initial short time ( 1 h), soon cleared from the lung, and was retained for long in the liver and spleen. CM-MS-FTC was quickly eliminated from the blood circulation, and 60% of the dose was excreted into urine at 3 h after injection. From 3 h after injection, the urinary excretion rate markedly decreased, and the total excreted amount was 66% of the dose at 12 h after injection, which was not significantly different from that at 3 h after injection. The present preparation technique permits producing small microspheres of CM-chitin as a drug carrier possibly useful for the liver targeting.