LAUSR

There is an increasing interest in using the zebrafish (Danio rerio) larva as a vertebrate screening model to study drug disposition. Since the pronephric kidney of zebrafish larvae shares high similarity with the anatomy of nephrons in higher vertebrates including humans, we explored in the present study whether 3 to 4 days old zebrafish larvae have a fully functional pronephron. Intravenous injection of fluorescent polyethylene glycol and dextran derivatives of different molecular weight revealed a cut-off of 4.4 to 7.6 nm in hydrodynamic diameter for passive glomerular filtration, which is in agreement with corresponding values in rodents and humans. Distal tubular reabsorption of a FITC-folate conjugate, covalently modified with PEG2000, via the folate receptor 1 was shown. Transport experiments of fluorescent substrates were assessed in the presence and absence of specific inhibitors in the blood systems. Thereby, functional expression in the proximal tubule of oat/slc22, mrp1/abcc1, mrp2/abcc2, mrp4/abcc4 and the zebrafish larvaes' p-glycoprotein analog abcb4 was shown. In addition, non-renal clearance of fluorescent substrates and plasmaprotein binding characteristics were assessed in vivo. Results of transporter studies were confirmed by extrapolation to ex vivo experiments in killifish (Fundulus heteroclitus) proximal kidney tubules. We conclude that the zebrafish larva has a fully functional pronephron at 96 hours post fertilization and is therefore an attractive translational vertebrate screening model to bridge the gap between cell culture-based test systems and pharmacokinetic experiments in higher vertebrates.