RENAL UPTAKE OF AN 18-MER PHOSPHOROTHIOATE OLIGONUCLEOTIDE

Renal uptake of a S-35 labeled 18-mer phosphorothioate oligodeoxynucle otide (molecular wt similar to 6,000) was evaluated following intraven ous infusion into rats. The kidneys contained 21 +/- 3% of the infused dose at five hours after infusion and 3 +/- 1% of the infused dose at four days after infusion. The concentration of oligonucleotide was gr eater in the kidney than in the liver, spleen, or plasma at both inter vals. Urine excretion of oligonucleotide label averaged 17 +/- 1%, 35 +/- 5%, and 64 +/- 3% of the infused dose at five hours, one day, and four days after infusion. Electrophoresis (PAGE) showed that oligonucl eotide was retained in the kidney as the intact 18-mer at both five ho urs and four days after infusion, while full size oligonucleotide was not found in the urine at either interval. Light microscopic autoradio graphy showed that oligonucleotide uptake was most prominent in the ea rly proximal tubule. Electron microscopic autoradiography indicated th at oligonucleotide was not confined to the brush border or endocytic-l ysosomal pathway. Micropuncture studies showed that the tubule fluid t o plasma concentration ratios of oligonucleotide label averaged 7 +/- 3% in Bowman's space and 6 +/- 2% in the distal tubule. Despite restri ction of filtration by plasma protein binding, as indicated by the low Bowman's space to plasma concentration ratio, the calculated tubular reabsorption rate for oligonucleotide was sufficient to account for th e large amount of oligonucleotide found in the kidney after intravenou s infusion. These results indicate that the proximal tubule plays a pr ominent role in the disposition of intravenously infused oligonucleoti de, and raise the possibility that oligonucleotides could exert antise nse effects in this nephron segment.