Rat renal cortical slices: Maintenance of viability and use in in vitro nephrotoxicity testing

Organ slices as an in vitro test system for drug metabolism in human liver, lung and kidney

Metabolism of xenobiotics occurs mainly in the liver, but in addition, the lungs and kidneys may contribute considerably. The choice of the animal species during drug development as a predictive model for the human condition is often inadequate due to large interspecies differences. Therefore, a universal method for the preparation and incubation of human and animal liver, lung and kidney tissue is being developed for drug metabolism and toxicity testing using precision-cut organ slices. Human tissue was obtained from surgical waste material. Slices were made from rat and human liver, kidney and agar-filled (1.5%, w/v) lung tissue using a Krumdieck tissue slicer and incubated in six-well plates. The morphology and the ATP content show that viability is maintained during 3 hours of incubation. These organ slices show a variety of phase I (hydroxylation, oxidation and O- and N-deethylation) and phase II (glucuronidation and sulfation) metabolic routes using lidocaine, testosterone, 7-ethoxycoumarin and 7-hydroxycoumarin as substrates. The metabolic patterns and rates were found to be different for the various organs and species studied. The use of human tissue slices will enable us to collect more human-specific data on drug metabolism and toxicity. This may lead to a more adequate choice of animal species used during drug development and will result in a considerable reduction in the use of experimental animals.

Immunocytochemical characterization of the incubated rat renal cortical slices

The use of renal cortical slices in vitro and the data obtained in these studies have been subjects of controversy, largely due to uncertain viability, e.g., structural and functional integrity of the proximal and other tubules. However, detailed studies of tubule integrity have not been reported. To correlate functional and structural viability of the hand-cut rat renal cortical slices, incubated in optimally conditioned media for up to 25 h, we studied the time course of p-aminohippurate (PAH) uptake, the immunocytochemical distribution of several proteins that reside in the proximal tubule basolateral [Na/K-ATPase, organic anion transporters (OAT)1 and OAT3], or brush border [megalin, sodium-proton exchanger (NHE)3] membrane, as well as the general integrity of the tubule epithelium and its cytoskeleton (actin filaments, microtubules). PAH uptake in slices was proportional to time within 1 h of incubation and gradually declined thereafter. The immunostaining experiments indicated a fast, time-dependent loss of basolateral transporters, at a rate of OAT1 > Na/K-ATPase > OAT3. In the brush border membrane, the loss of megalin was faster than that of NHE3, and a partial redistribution of NHE3 into the basolateral domain indicated the loss of cell polarity. The loss of intracellular actin and tubulin cytoskeleton in the proximal tubule was already visible after 15 min of incubation and gradually increased with time, whereas a partial redistribution of actin to the basolateral domain indicated a compromised polarity of the cells. The data also revealed very early (after 15 min) necrotic events in the proximal tubule epithelium, with sloughing of brush border and cell debris into the tubule lumen, detachment of cells from the basal membrane, and opening and widening of the tubule lumen. We conclude that the loss of cellular structure, cytoskeleton, and cell membrane transporters in the nephron epithelium is a very early event in the incubated rat renal cortical slices.

Biotransformation studies using rat proximal tubule cells

The proximal tubule is the main target for nephrotoxic substances due to its specific properties, including efficient drug transport and biotransformation potential. The availability of a pure population of proximal tubule cells (PT cells) as a model to study a range of biological, pharmacological, and toxicological parameters is, therefore, of great value. A two-step PT cell-isolation procedure, based on density-gradient centrifugation, is described; this procedure can easily be introduced into each laboratory setting. The procedure routinely yields a highly pure PT cell population, comprising 20-40 × 10(6) cells, which can be used for preparation of subcellular fractions or brought into primary culture.