Binding of some Diocleinae lectins to the mucosal surfaces of the eye and mouth

Controlled delivery of diagnostic or therapeutically active agents to the e ye and oral cavity is limited by the efficient removal mechanisms that exis t in these areas. In this work, recently isolated, purified and characteris ed Brazilian bean lectins were examined for their ability to bind to the bu ccal and sublingual mucosa, cornea and conjunctiva of rat, with regard to t heir potential therapeutic use. These lectins were labelled using biotin (l ong arm) N-hydroxysuccinimide ester and a technique developed at the Univer sity of Portsmouth. Evaluation of binding after 15 min contact with intact (unfixed) rat eye and oral cavity epithelia was completed using a standard histological procedure involving the avidin-biotin reaction and formation o f a brown precipitate with a 3,3'-diaminobenzidine solution. When examined by affinity chromatography, all lectins studied were found to show high per centage biotinylation (i.e. less than 4% by weight of total lectin was elut ed from the column). The lectin : biotin ratio was estimated using sodium d odecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), and ranged b etween 1:2 (Cratylia floribunda) and 1:10.4 (Canavalia brasilensis). As wit h previous studies, all lectins bound to the mucosal surfaces to some exten t - the Cratylia floribunda lectin appearing to be the most promising, wher eas the Dioclea violacea lectin showed comparatively weak binding. In all c ases, the presence of glucose (the hapten sugar) reduced or eliminated bind ing. It was concluded that glucose-mannose binding sites are present on the se surfaces, and the lectins from C. floribunda showed a particular affinit y for these.