Confocal microscopic analysis of transport mechanisms of insulin across the cell monolayer

Abstract

Development of oral insulin formulations would significantly improve the quality of life of patients suffering from diabetes. Complexation hydrogels developed in our laboratory, are one of the most promising classes of materials for use in targeted oral delivery of proteins. Results from confocal microscopy analysis of insulin transport in Caco-2 cells indicated that the primary route of transport was the paracellular pathway and that the transcellular component of the transport was insignificant. In addition, studies with sodium caprate, a model permeation enhancer, showed that using a permeation enhancer with complexation hydrogels may cause permanent damage to the cell monolayer.

Uptake and Transport of Novel Amphiphilic Polyelectrolyte-Insulin Nanocomplexes by Caco-2 Cells—Towards Oral Insulin

“…6). Free insulin cannot passively diffuse across epithelial cells, as it is a large (5800 D) molecule with a low lipophilicity (16). Free insulin did not reduce TEER, indicating that insulin itself is able to cross cells possibly via insulin receptors, as shown in our cellular uptake study.…”

“…Free insulin did not reduce TEER, indicating that insulin itself is able to cross cells possibly via insulin receptors, as shown in our cellular uptake study. It is likely that insulin receptors in the GIT wall and in Caco-2 cells initiate receptor-mediated endocytosis (active transcellular transport) (16), where insulin can then be carried from apical to basal membranes via the Golgi-apparatus (16,38). It might have been expected that any insulin entering cells would have been degraded by intracellular proteases (16,39).…”

“…It is likely that insulin receptors in the GIT wall and in Caco-2 cells initiate receptor-mediated endocytosis (active transcellular transport) (16), where insulin can then be carried from apical to basal membranes via the Golgi-apparatus (16,38). It might have been expected that any insulin entering cells would have been degraded by intracellular proteases (16,39). However, the relatively large concentration of insulin used (3 μgmL −1 ) could have resulted in enzyme saturation, resulting in a small amount of insulin passing through the cells undegraded.…”

“…Several different technologies have been used to facilitate oral protein absorption and prevent degradation. These include the co-administration of enzyme inhibitors and/or penetration enhancers, pro-drug forms of proteins and colloids such as polyelectrolyte carrier systems (2,(6)(7)(8)12,(14)(15)(16)(17).…”

Oral insulin-delivery System for Diabetes Mellitus

“…Permeation enhancers increase the absorption of oral drugs in the GIT either by disruption of the cell membrane or by tight junction modulation with tight junction agonists [34]. The concern with permeation enhancers is that they act by local inflammation and thus can cause GIT infections [35].…”