Oligonucleotide transport in rat and human intestine ussing chamber models

Cellular and intestinal absorption of naked oligonucleotides (ONs) is limit ed and still remains a developmental challenge. A previous report in the li terature suggests that ON absorption occurs via a paracellular mechanism. T he aim of this study was to test this hypothesis using rat and human intest ine in a Ussing chamber and in Caco-2 cells. Transport of a S-35-labelled m ixed backbone ON (MBO) across human or rat intestinal tissue or across Caco -2 cells was measured after a 2-h incubation in the presence or absence of increasing MBO concentrations or with uptake inhibitors and enhancers. MBO intestinal absorption was compared with an internal standard, mannitol. S-3 5-MBO demonstrated very little absorption (<1%) across rat and human intest inal tissues. Transport appeared to be unsaturable up to 500 mu M, and rela tively insensitive to compounds that opened tight junctions or inhibited P- glycoprotein. However, preliminary studies with Caco-2 cells suggest a poss ible saturable mechanism at higher ON concentrations. Confocal fluorescence microscopy studies show that fluorescein isothiocyanate (FITC)-MBO was int ernalized into intestinal cells. Although some differences in ON transport were observed as a function of the transport model, MBO transport was mostl y consistent with a transcellular, rather than a paracellular, absorption m echanism. Copyright (C) 1999 John Wiley & Sons, Ltd.