Development of a new assay system for evaluating the permeability of various substances through three-dimensional tissue.

A novel assay system with cell-dense three-dimensional (3D) tissue was developed for measuring the permeability of substances. In this paper, the permeabilities of various molecules containing nutrients, a cytokine, and a chemokine were examined and analyzed. A single-layered cell sheet was approximately 20 mum thick, and as the number of layers of these cell sheets increased, so did the total thickness of the tissue. The diffusion rates of glucose and pyruvic acid were reduced to approximately 30-40% by a single-layered cell sheet compared with the control without the cell sheet, and the diffusion of both substances were completely inhibited by a quadruple-layered cell sheet. The diffusion rate of creatinin was reduced to approximately 50% and 15-20% by a single-layered and by a quintuplet-layered cell sheet, respectively. On the other hand, the diffusion rate of stromal cell-derived factor 1alpha, vascular endothelial growth factor, beta2-microglobulin, and transferrin was reduced to approximately 10%, 5%, 20%, and 10%, by only a single-layered cell sheet, respectively. The diffusion of these substances were completely inhibited by a double-layered cell sheet. These results show that the permeability of substances through 3D tissue significantly decreased with the increase of the molecular weight. Therefore, the system could give a simulated living-tissue condition for measuring the permeability of substances. To our knowledge, this is the first report about measuring the permeability of substances through cell-dense 3D tissues without scaffolds. The assay system is believed to contribute to the progress of physiology, metabology, biochemistry, and pharmacokinetics. Further, the system may give some hints for developing a new dialysis membrane technology for an artificial kidney.