Comparative study of the effects of seven lanthanides onto two mammalian kidney cell lines

Exposure to lanthanides (Ln) poses a serious health risk to animals and humans. Since these elements are mainly excreted with urine, we investigated the effect of Ln in concentrations of 10⁻⁹ – 10⁻³ M on normal rat kidney cells (NRK-52E) and human embryonal kidney cells (HEK-293) after 24 and 48 h, respectively. Cell viability was measured using the XTT test and cell morphology was studied with light microscopy as well as fluorescence microscopy after immuno-chemical staining. Solubility of the Ln in the cell culture medium was determined with ICP-MS and Ln speciation was investigated using TRLFS as well as thermodynamic modelling.
The results from cell culture experiments demonstrate that the effect of Ln onto the cell viability are concentration- and time-dependent as well as cell line- and element-specific. Dose-response curves of all Ln reveal no cytotoxicity up to 10⁻⁴ M, whereas higher concentrations cause gradual loss of cell viability in both cell lines. Effective concentrations, for which cell viability was reduced to 50 % (EC50), were calculated. In general, first and last elements of the Ln family affect the cell viability more than Ln in the middle of the series. However, Ce exhibits the significantly strongest effect of all Ln. Besides the loss of cell viability, exposed cells undergo morphological changes like rounding and shrinking prior to cell death. Comparing both cell lines reveals NRK-52E being significantly more sensitive to Ln exposure than HEK-293.
ICP-MS measurements of Ln supplemented cell culture medium after filtration through 0.45 μm filters demonstrate that the Ln are 100 % soluble. Furthermore, TRLFS results reveal that Ln speciation in the cell culture medium is most probably dominated by a complex species formed with a protein from FBS. Due to a huge lack of complex formation and solubility constants of Ln with constituents from cell culture media as well as the unknown and variable composition of FBS, thermodynamic modelling failed to reproduce the experimental results and predicts a speciation dominated by several carbonate and phosphate species instead.
The results of this study underline the importance of combining biological, chemical, and spectroscopic methods in studying the effect of Ln on cells in-vitro and can contribute to the improvement of current risk assessment for Ln in the human body.