Starch microspheres enhance insulin absorption across epithelial cells by affecting the integrity of tight junctions

206 The function of the intestinal epithelium is to provide a barrier between the body fluids of the animal and its environment. The effectiveness of this barrier can be determined by the use of inert hydrophilic molecules of different molecular weights. Indeed, this has been done extensively during the past decade ( 1). However, the use of different probes and different animal models has caused confusion in the extrapolation of the results to humans. Thus, there is a need for a comparison of permeability profiles of different in vitro models for intestinal absorption with those of the human intestine. We have studied the permeability profiles of monodisperse polyethyleneglycols with molecular weights ranging from 194 to 502 (g/mole) in two models for intestinal absorption, excised intestinal segments (ileum and colon) of the rat (2) and the human intestinal epithelial cell line Caco-2 (3). The corresponding permeability profiles for human jejunum, ileum and colon were calculated from literature data (4). In general, human ileum and colon were more permeable than the corresponding rat segments and the Caco-2 cells. However, the permeability profiles were comparable. Thus, good correlations between the permeability profiles of human ileum and rat ileum and between those of human colon, rat colon and Caco-2 cells could be established. The results indicate that excised rat ileum in vitro is a good permeability model for human ileum. Similarly, rat colon and Caco-2 cells are good permeability models for human colon.

marker, mannitol, as well as insulin was studied in the absence and presence of dry or hydrated DSM. A time and concentration dependent increase in absorption of mannitol was obtained when this com~und was administe~d together with dry DSM. The effects were reversible at intermediate concentrations of DSM. Hydrated DSM did not enhance the absorption. The absorption of insulin was also increased by dry DSM. However, the absorbed fraction of insulin was lower than that of mannitol. Transmission electron micrographs showed that the spaces between the tight junctions were widened after exposure to the dry DSM. The widening of the tight junctions coincided with the increased absorption rate. No signs of dehydration or other morphological changes were observed. At 180 min after exposure the morphology of the tight junctions and the absorption rate were indistinguishable from that of untreated monolayers. The results indicate that DSM enhance drug and insulin absorption by inducing an increased pe~eability of the tight junctions of the intestinal epithelium.

References

Effect of apical and/or basolateral application of EDTA on the permeability of hydrophilic compounds in a human intestinal epitheliai cell-line (Caco-2). A.B.J. Noach, M.C.M. Roosemalen, Y. Kurosaki, A.G. de Boer and D.D. Breimer, Center for 3io-Phar~aceMt~~al Sciences, Division of Phar~acolo~, P. 0. Box 9503, 2300 RA Leiden, The Netherlands. In the gastro-intestinal tract the absorption of hydrophilic compounds like peptides is severely hampered by the fact that these compounds are almost completely incapable to cross biological membranes, which restrict their uptake to fluidphase or receptor mediated endocytosis, or paraceIlular transport. Since calcium plays an important role in maintaining the integrity of the tight-junctions ( 1,2), we studied the effect of EDTA on enhancing the transport of hydrophilic compounds via the paracellular route. In addition, it was investigated if the “disturbing effect” was completely reversible within a reasonable period of time. As a model for gastrointestinal epithelium we used confluent monolayers of a human colon carcinoma cell line (Caco-2 ) These cells are characterized as being a good model for GLepithelium (3-6). EDTA was administered in various concentrations to the apical, basolateral or apical and basolateral side of the cells. The drop in transepithelial resistance (TEER) was measured and the enhancement of the permeability was checked by measuring the clearance of hydrophilic model compounds ( Fluorescein-Na, and FITC-dextrans of various molecular weight and molecular radius). From the resistance experiments it was clear that higher

1 P. Krugliak, D. Hollander, T.Y. Ma, D. Tran, V.D. Dadufala, K.D. Katz and K. Le (1989), Gastroe~terolo# 97:1164-1170 2 A.-L. Ungell, A. Andreasson, K. Lundin and L. Utter ( 199 1 ), J. Pharm. Sci. (submitted) 3 P. Artursson (1990), J. Pharm. Sci. 79:476-482 4 VS. Chadwick, SF. Phillips and A.F. Hofmann ( 1977), Gas~roenteralo~ 73~247-251 Starch microspheres enhance insulin absorption across epithelial cells by affecting the integrity of tight junctions. E. Bjiirk”, U. Isaksson’, P. Edman” and P. Artursson’, *Dept. of Pharmaceutics, Uppsala University, P. 0. Box 580, S- 75 1 23 Uppsaia, Sweden “KaabiPharmacia Therapeutics AB, 9 751 82, ~~psala, Sweden. Degradable starch microspheres (DSM) have been used to enhance the absorption of insulin across the nasal epithelium ( 1). The mechanism of the DSM mediated absorption enhancement is unknown. Since only dry and not hydrated DSM enhance absorption of insulin, it has been suggested that DSM dehydrate the epithelial mucosa with a reversible “shrinkage” and a subsequent physical separation of the intercellular junctions as a result. This hypothesis was tested using monolayers of human intestinal epithelial (Caco-2 ) cells as a model (2 ). This cell culture model has previously been used to study absorption enhancement across the intestinal epithelium (3). The absorption of a hydrophilic low molecular weight

References 1 E. Bjiirk and P. Edman (1988), In?. J. Pharm. 47:233-238 2 P. Artursson (1990) J. Pharm. Sci. 79:476-482 3 E.K. Anderberg, C. Nystriim and P. Artursson f 1990), Proc. I7th Int. Svmp. Controlled Release of Bioactive Materiak, pp. 345-346