Ex vivo stimulation of renal tubular p -aminohippurate transport by dexamethasone and triiodothyronine in human renal cell carcinoma

Abstract

This paper is the third of a long-term planned series of papers dealing with ex vivo investigations of drug transport in human kidney. The aims of this study are (a) to investigate whether or not human renal cell carcinoma (RCC) can actively accumulate p-aminohippurate (PAH) and (b) to test the response of RCC on dexamethasone or triiodothyronine (T3) using tissue slices ex vivo. By this approach, the accumulation capacity of RCC should be stimulated as a prerequisite for an increased uptake of anti-tumour drugs. Tissue slices of RCC samples of 30 patients were incubated for 24 h in Williams medium E containing 0.01-50 microM dexamethasone or T3. Thereafter, slices were placed in PAH-containing Cross-Taggart medium, and PAH uptake into kidney tissue was measured for 2h under standardised conditions as described previously. In intact human renal cortical slices, PAH uptake capacity, expressed as slice to medium ratio (QS/M), was about 2.8 +/- 0.16 after 24 h of incubation and increased significantly in dexamethasone-containing medium in a concentration-dependent manner, up to approximately 150%, whereas T3 did not influence PAH accumulation. On the other hand, in RCC the PAH accumulation capacity was completely abolished (QsM approximately 1). However, after administration of dexamethasone, the accumulated amount of PAH increased significantly in RCC tissue in a concentration-dependent manner, up to approximately 190%. T3 was without effect in RCC, too. Surprisingly, the dexamethasone-mediated stimulation could be differentiated into responders and non-responders, with maximal effects at different concentrations for each patient. Nevertheless, the maximal transport rates remained low in RCC, even under hormone influence. In conclusion, a moderate stimulation of tubular transport capacity can be shown ex vivo in human RCC. This phenomenon is only of a relatively low degree compared with intact renal tissue. However, in principle, the response of RCC on dexamethasone could form a basis for further therapeutic strategies to overcome multi-drug resistance in RCC patients. For this purpose, additional experiments analysing the expression of transporters of the ABC cassette-type are in progress.

Characterization of the Uptake of Organic Anion Transporter (OAT) 1 and OAT3 Substrates by Human Kidney Slices

“…Kidney slices from experimental animals have been widely used to characterize the renal uptake of organic anions through the basolateral membrane. Fleck et al (2000) demonstrated that human kidney slices retain organic anion transport activity. The present study focused on the use of human kidney slices to characterize the uptake of hOAT1 and hOAT3 substrates.…”

“…In vitro studies of the uptake of drugs by mammalian kidney slices have proved useful for examining uptake mechanisms. Fleck et al (2000Fleck et al ( , 2002 prepared kidney slices from human kidney and demonstrated the active accumulation of PAH and methotrexate, suggesting that human kidney slices also retain the activities of organic anion transporters. However, transport studies using human kidney tissue have not been thoroughly investigated focusing on the contribution of different transporters.…”

Molecular and Cellular Physiology of Renal Organic Cation and Anion Transport

“…Tubular transport of PAH is influenced by glucocorticoids (30), 1,25-dihydroxycholecalciferol (31), and sex steroids (29, 48 -50). PAH accumulation in human renal slices is increased by exposure to dexamethasone (114). Treatment of rats (particularly 5-to 10-day-old rats with immature kidney function) with the glucocorticoids prednisolone or dexamethasone results in increased renal excretion of PAH and increased PAH accumulation in renal cortical slices (30).…”

Use ofin vitrotransporter assays to understand hepatic and renal disposition of new drug candidates

“…Human and rat kidney slices have been used as a tool to evaluate basolateral compound uptake into the kidney [172,173], drug-drug interactions [172,174] and nephrotoxicity [175]. Although these provide an effective tool, the uptake of compounds into kidney slices is lower than the in vivo renal intrinsic uptake clearance, which is partially due to diffusion from the surface of the kidney slice [18].…”