A method to attach lectins to the surface of spermine alginate microcapsules based on the avidin biotin interaction

To serve as model cell or tissue specific drug delivery systems spermine alginate capsules were surface modified by attachment of proteins with carbohydrate specific binding properties, i.e. lectins. In the first of a two step process avidin was covalently bound to the capsule surfaces using a hydroxy-succinimide catalysed carbodiimide reagent. Surface bound avidin was quantitated by lysing the capsules in hypertonic phosphate buffered saline (PBS) and measuring the change in absorbance at 500 nm in the interaction with 2-(4'hydroxyazobenzene) benzoic acid. A time course study of the avidin-binding reaction showed avidin surface concentrations averaged 5.4 nM/cm2 after 16h. In the second step avidin-coated capsules were incubated in aqueous solutions of biotinylated-lectin derivatives. To quantitate lectin uptake, avidin-coated capsules were lysed in PBS and titrated to the turbidance endpoint with ten different biotinylated lectins. Lectin surface concentrations ranged from 2.0 to 6.8 nm/cm2, well below the theoretical limit of 4 biotinylated ligands per molecule of avidin. Individual lectins bound to capsular surfaces retained their respective ligand specific binding properties as demonstrated by measurement of the selective saturable uptake of radiolabeled ligands when incubated with variously lectin coated capsules. The presence of porcine gastric mucin in concentrations up to 4% w/v did not inhibit binding of 14C-labelled mannose or galactose by concanavalin A-coated capsules.