To clarify the renal disposition characteristics of oligonucleotides at the organ level, the renal handling of model end-capped oligonucleotides, 3'- methoxyethylamine 5'-biotin-decathymidylic acid containing phosphoramidate modifications at 3'- and 5'-terminal internucleoside linkages (T10) and its phosphorothioate (Ts10), were studied in the perfused rat kidney. In a single-pass indicator dilution experiment, venous outflow and urinary excretion patterns and tissue accumulation of radiolabeled oligonucleotides were evaluated under filtering or nonfiltering conditions. No significant binding to bovine serum albumin (BSA) in the perfusate was observed for T10, whereas more than 90% of Ts10 bound to BSA. The steady-state distribution volume of T10 calculated from the venous outflow pattern was larger than that of inulin, which corresponds to the extracellular volume of the kidney, whereas the distribution volume of Ts10 was larger than that of BSA (the intravascular volume). These results suggested their interaction with the vascular wall. Rapid urinary excretion was observed for T10, similar to inulin used as a marker of golmerular filtration rate. On the other hand, urinary excretion of Ts10 was greatly restricted due to its high binding ability (&gt
90%) to BSA in the perfusate. A significant amount of T10 and Ts10 was accumulated in the kidney (T10,1.8% of injected dose
Ts10, 1.3%) compared with inulin (0.2%) and BSA (&lt
0.1%). The accumulation of these oligonucleotides was ascribed to both tubular reabsorption and uptake from the capillary side. In addition, the uptake of T10 from the capillary side was significantly inhibited by simultaneous injection of dextran sulfate, suggesting that the oligonucleotide was taken up as an anionic molecule. These findings will be useful information for the development of delivery systems for antisense oligonucleotides. © 1995, Mary Ann Liebert, Inc. All rights reserved.