In vivo biocompatibility and degradability of a novel injectable-chitosan-based implant

Glutaraldehyde is commonly used to control physical and biological properties of collagen structure by means of intramolecular and/or intermolecular crosslinking of collagen molecules. Solubility, antigenicity, and biodegradation of naturally occurring or reconstituted collagenous matrices are effectively reduced by glutaraldehyde treatment. Adverse biological reactions to glutaraldehyde have been limited to infrequent contact dermatitis and to biocidal effects which are exploited in chemical sterilization media. In the present study of glutaraldehyde-tanned collagen sponge, the presence of glutaraldehyde was correlated with cytotoxic effects upon fibroblasts in tissue culture and foreign body giant cell reaction to bioimplants of the sponge. Fibroblast growth in tissue culture is 99% inhibited at media concentrations of 3.0 ppm glutaraldehyde. Extracts of glutaraldehyde collagen sponge in aqueous media at pH 7 and 4.5 yielded 6 micrograms and 65 micrograms glutaraldehyde per gram of collagen sponge, respectively. The yield increased tenfold at pH 4.5. Observations indicate that leaching of the glutaraldehyde from glutaraldehyde-tanned collagen sponge is sufficient to produce potentially adverse cellular effects both in vivo and in vitro.

Geniposide, a main iridoid glucoside of Gardenia fruit, is transformed to genipin, a genuine choleretic, in vivo in rats (Aburada et al., J. Pharmacobio-Dyn., 1, 81 (1978)). As geniposide was not hydrolyzed to any metabolite by rat liver homogenate, which has beta-D-glucosidase and esterase activities, beta-D-glucosidases in intestinal bacteria seem to be required for an exhibition of its choleretic action. The crude extract of Eubacterium sp. A-44, a human intestinal anaerobe, hydrolyzed geniposide, but that of Ruminococcus sp. PO1-3, another human anaerobe, did not, though both extracts had beta-D-glucosidase activities for p-nitrophenyl beta-D-glucopyranoside. Only one of three beta-D-glucosidases from E. sp. A-44 and none of two from R. sp. PO1-3 hydrolyzed geniposide to genipin. However, carboxylesterases from E. sp. A-44 and pig liver were unable to hydrolyze geniposide to geniposidic acid, but hydrolyzed genipin to an aglycone of geniposidic acid, indicating that geniposide is first hydrolyzed to genipin by beta-D-glucosidases and subsequently to the aglycone of geniposidic acid by esterases. Thus, when geniposide is orally administered, genipin seems to be effectively produced in the intestine and then absorbed to act as a genuine choleretic.