Altered lectin binding sites in keratoconus corneas

Lectin binding in normal, keratoconus and cross-linked human corneas

In this study the characterization of various types of sugar residues in normal, keratoconus and cross-linked human corneas was performed using immunohistochemical localization with lectins. Corneal samples were collected and divided into three groups: (1) normal corneas from cadavers; (2) keratoconic corneal buttons; (3) keratoconic corneal buttons treated with cross-linking. A series of lectins including: DBA, SBA, PNA, ConA, WGA, UEA I, GNA, DSA, MAA, SNA, were used in combination with chemical and enzymatic treatments. Compared with the normal corneas, N-acetyl-D-glucosamine increased in the keratoconus corneas. L-fucose increased and/or appeared in the keratoconus and the cross-linked corneas. N-acetyl-D-galactosamine was more abundant in the epithelium of keratoconus corneas, but was lacking in the keratoconus and cross-linked endothelium. D-galactose-(β1-4)-N-acetyl-D-glucosamine was absent in the whole stroma of the keratoconus corneas and in the deep layers of the cross-linked ones. Sialic acids increased in the keratoconus corneas and decreased in the cross-linked ones. These results showed altered glycosylation in the keratoconic corneas and partially similar glycosylation in the cross-linked corneas, compared to the normal ones. This suggests a role played by sugar residues in maintaining the corneal structure. The changes could be related to structural alterations in keratoconus. The present findings contribute to our understanding of the effect of cross-linking treatment of keratoconic corneas in therapeutic attempts to re-establish the normal corneal structure.

Corneal wound-associated glycoconjugates analyzed by lectin histochemistry

PURPOSE

To examine changes in corneal glycoconjugates during wound healing in a pig model of refractive surgery.

METHODS

Pig corneas were wounded using a mechanized microkeratome. Lamellar keratectomy, without replacement of a corneal cap, or automated lamellar keratoplasty, with replacement of a corneal cap, was performed. Corneas were prepared for microscopy 1, 7, or 28 days after surgery. Cryosections of corneas were probed with lectins recognizing a variety of carbohydrate moieties. Glycoconjugates were characterized by glycosidase digestion and chemical extraction.

RESULTS

Of the lectins used, only that from Dolichus biflorus (DBA), specific for terminal N-acetylgalactosamine, exhibited a dramatic change in staining pattern after wounding. In unwounded corneas, DBA labeled the superficial epithelium, Bowman's layer, and occasional keratocytes. After wounding, DBA intensely labeled exposed stromal surfaces and keratocytes near wound sites. RESULTS of glycosidase treatments indicated that the DBA-binding material contains alpha-linked N-acetylgalactosamine. After extraction with lipid solvents, stromal DBA labeling was unchanged, while that of keratocytes was greatly diminished.

CONCLUSIONS

Corneal wounding results in the accumulation of specific glycoconjugates at surfaces and in keratocytes. After keratectomy, the exposed stromal surface is infiltrated with ocular surface components, including DBA-binding glycoproteins. The presence of these components may influence the course of wound healing. In addition, changes in keratocyte glycoconjugates may accompany their mobilization to the wound-repair phenotype.

Lectins for drug delivery within the oral cavity--investigation of lectin binding to oral mucosa

The aim of this study was to identify receptors present on the buccal mucosa in order to select appropriate lectins that will allow the retention of a dosage form within the oral cavity. Studies using human buccal cells, the avidin-biotin-complex/diaminobenzidine method for identifying lectin binding and a microdensitometer to allow a semi-quantitative analysis of stain intensity, showed a wide diversity of lectin receptors. Kinetic studies of lectin binding to buccal cells revealed significant binding after 20 s, particularly for lectins from Pisum sativum and Arachis hypogaea. A significant reduction in lectin binding was observed after exposing buccal cells to a series of lectin solutions pre-treated with a large excess of secretor or non-secretor saliva. However when bound to the buccal cells, there was little displacement of lectins on exposure to either saliva types. Further studies on rat oral tissue suggested that the lectins appeared to bind to varying degrees on whole oral epithelial surfaces although differences in binding between this and the human buccal cell model were evident. It was concluded that a wide range of possible target receptors for lectins are present on rat oral epithelium and human buccal cells. Lectin binding to these receptors can be affected by the exposure time and the presence of saliva.