Abstract
Zoledronic acid, a highly potent nitrogen-containing bisphosphonate used for the treatment of pathological bone loss, is excreted unmetabolized via the kidney if not bound to the bone. In cancer patients receiving high doses of the compound renal excretion may be associated with acute tubular necrosis. The question of how zoledronic acid is internalized by renal tubular cells has not been answered until now. In the current work, using a primary human tubular cell culture system, the pathway of cellular uptake of zoledronic acid (fluorescently/radiolabeled) and its cytotoxicity were investigated. Previous studies in our laboratory have shown that this primary cell culture model consistently mimics the physiological characteristics of molecular uptake/transport of the epithelium in vivo. Zoledronic acid was found to be taken up by tubular cells via fluid-phase-endocytosis (from apical and basolateral side) as evidenced by its co-localization with dextran. Cellular uptake and the resulting intracellular level was twice as high from the apical side compared to the basolateral side. Furthermore, the intracellular zoledronic acid level was found to be dependent on the administered concentration and not saturable. Cytotoxic effects however, were only seen at higher administration doses and/or after longer incubation times. Although zoledronic acid is taken up by tubular cells, no net tubular transport could be measured. It is concluded that fluid-phase-endocytosis of zoledronic acid and cellular accumulation at high doses may be responsible for the acute tubular necrosis observed in some cancer patients receiving high doses of the compound.
Highlights
Zoledronic acid or zoledronate (Zometa; Novartis Pharma AG, Basel, Switzerland) is a third generation, highly potent nitrogen (N)-containing bisphosphonate that has shown beneficialPLOS ONE | DOI:10.1371/journal.pone.0121861 March 10, 2015Renal Handling of Zoledronic Acid
When cells were incubated for 4h, 24h or 48h with the same concentrations of zoledronic acid, a significant, dose-dependent reduction in viability was seen after 48h (Fig. 1D)
No difference could be observed in the localization of the fluorescent signal when the fluorescently labeled zoledronic acid was administered at the basolateral instead of the apical side of the monolayers
Summary
In order to better understand the observed renal toxicity of zoledronic acid, the aim of the present study was to investigate possible uptake routes and pharmacological handling of zoledronic acid by tubular epithelial cells using the above described primary human cell culture model
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