Abstract
5877
Hydration with saline and administration of mannitol are used clinically to reduce the nephrotoxicity of cisplatin. To identify the mechanism of this protective effect we used a renal proximal tubule cell line. Increasing the salt concentration in the media, thereby raising the osmolarity from 230 mOsm/l to 310 mOsm/l, reduced the toxicity of cisplatin. We have shown previously that this protective effect, which is within the physiologic range of serum osmolarity, is not due to altered uptake of cisplatin. In this study we found that altering the extracellular salt concentration induced a transient stress response in the cell that protected against cisplatin toxicity. We pretreated sets of cell with medium containing varying levels of sodium chloride, then changed the medium on all cells to the same medium, exposed the cells to cisplatin for 3hr and measured viability at 72hr. The pretreatment caused the cells to equilibrate in various osmotic environments. Pre-equilibrating the cells in a low salt medium then increasing the salt concentration induced the protective stress response against cisplatin toxicity. The degree of protection increased with the time of pretreatment from 10 min to a maximum effect with 2h of pretreatment. We also analyzed the duration of the stress response after increasing the osmolarity of the extracellular medium. The response was maintained for at least 4h, but was gone at 24h. Changing the osmolarity of the external medium induced measurable changes in cell volume. Reducing the osmolarity from 350 mOsm/l to 230 mOsm/l resulted in cells swelling to their largest volume within 1min, the cells then underwent a regulatory volume decrease returning to their normal volume within 20min. The change in sensitivity to cisplatin was not a direct consequence of a change in cell volume as the effect on the cell was maintained beyond the time at which the cells re-equilibrated to their normal volume. Cisplatin kills the cells through a caspase-3 dependent apoptotic pathway. Caspase 3 activity is significantly lower in cells protected from cisplatin toxicity by the elevated salt. These data demonstrate that the change in osmolarity signals a transient stress response. These data indicate that in patients serum osmolarity prior to cisplatin administration can significantly affect nephrotoxicity of the drug. Studies to identify the molecular pathways involved in this response are on going.
[Proc Amer Assoc Cancer Res, Volume 46, 2005]