Human insulin diffusion profile through a layer of Caco-2 cells

The Caco-2 human colon adenocarcinoma cell line undergoes a spontaneous differentiation in culture to enterocytic cells. The diffusion of human insulin through a layer of the enterocytic differentiated Caco-2 cell line was studied using a polycarbonate membrane as a mechanical support. Human insulin (100 U) was dissolved in Dulbecco's Modified Eagle's Medium (DME) and placed on the apical side of the cells grown in culture, and allowed to diffuse under sink conditions for a period of 24 hr (37 degrees C, pH = 7.4). Samples were collected from the receiver side at 0.5, 1, 2, 3, 4, 5, 6, 7, 8, and 24 hr. The samples were then analyzed for insulin content using an HPLC method. The calculated apparent permeability coefficient (P-app) for human insulin through the cells was (6.5 +/- 1.2) x 10(-7) cm/sec, mean +/- SE, n = 8. We conclude that using a Caco-2 cell line to study the diffusion of insulin through the intestinal barrier may be an alternative to other in vivo or in situ methods.