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  • Title: Phosphated crosslinked guar for colon-specific drug delivery. II. In vitro and in vivo evaluation in the rat.
    Author: Gliko-Kabir I, Yagen B, Baluom M, Rubinstein A.
    Journal: J Control Release; 2000 Jan 03; 63(1-2):129-34. PubMed ID: 10640586.
    Abstract:
    Targeting of drugs to the colon, following oral administration, can be accomplished by the use of modified, biodegradable polysaccharides as vehicles. In a previous study, a crosslinked low swelling guar gum (GG) hydrogel was synthesized by reacting it with trisodium trimetaphosphate (STMP). In the present study the functioning of GG crosslinked products (GGP) as possible colon-specific drug carriers was analyzed by studying (a) the release kinetics of pre-loaded hydrocortisone from GGP hydrogels into buffer solutions with, or without GG degrading enzymes (alpha-galactosidase and beta-mannanase) and (b) direct measurements of the polymers' degradation in the cecum of conscious rats. The effect of GG diet on alpha-galactosidase and beta-mannanase activity in the cecum of the rat and GGP degradation was also measured. It was found that the product GGP-0.1 (loosely crosslinked with 0.1 equivalents of STMP) was able to prevent the release of 80% of its hydrocortisone load for at least 6 h in PBS, pH=6.4. When a mixture of alpha-galactosidase and beta-mannanase was added to the buffer solution, an enhanced hydrocortisone release was observed. In-vivo degradation studies in the rat cecum showed that despite the chemical modification of GG, it retained its enzyme-degrading properties in a crosslinker concentration-dependent manner. Eight days of GG diet prior to the study increased alpha-galactosidase activity in the cecum of the rat three-fold, compared to its activity without the diet. However, this increase in the enzyme activity was unable to improve the degradation of the different GGP products. The overall alpha-galactosidase activity in the rat cecum was found to be extracellular, while the activity of beta-mannanase was found to be bacterial cell-wall associated. It is concluded that because CG crosslinked with STMP can be biodegraded enzymatically and is able to retard the release of a low water-soluble drug, this polymer could potentially be used as a vehicle for colon-specific drug delivery.
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