Systematic Studies on the Paracellular Permeation of Model Permeants and Oligonucleotides in the Rat Small Intestine with Chenodeoxycholate as Enhancer

ABSTRACTThe objective of this study was to mechanistically and quantitatively analyze chenodeoxycholate‐enhanced paracellular transport of polar permeants and oligonucleotides in the rat jejunum and ileum. Micellar chenodeoxycholate solutions were used to perturbate the tight junctions. Supporting studies included assessment of the aqueous boundary layer (ABL) with ABL‐controlled permeants, measurements of the permeability coefficients and fluxes of the bile acid in dilute and micellar concentrations, and determinations of pore sizes with paracellular probes (urea, mannitol, and raffinose). The paracellular permeability coefficients, Ppara, of two model oligonucleotides (ON3 and ON6; 12‐ and 24‐mers with 11 and 23 negative charges, respectively) were determined. The enhanced permeabilities paralleled the increased fluxes of micellar bile salt solutions into mesenteric blood and the opening of the tight junctions as compared to controls. As the pore radius increased from 0.7 nm to a maximum of 2.4 nm in the jejunum and ileum, the absorption of ON3 was enhanced up to sixfold in the jejunum and about 14‐fold in the ileum with Ppara values between 0.5 × 10−6 and 6 × 10−6 cm/s, whereas ON6 was enhanced up to twofold in the jejunum and fivefold in the ileum with permeabilities between 0.3 × 10−6 and 2 × 10−6 cm/s. © 2007 Wiley‐Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:350–367, 2008