Impact of DTPA and 3,4,3-LI(1,2-HOPO) on Eu^III interactions with renal cells in vitro

This study represents a first comprehensive investigation on how the decorporation agents CaNa₃-DTPA (DTPA) and 3,4,3-LI(1,2-HOPO) (LIHOPO) affect Eu^III interactions with human and rat kidney cells in vitro. Cell biological investigations were complemented with physicochemical measurements to correlate cytotoxic impairments with intracellular metal uptake and Eu^III speciation. Upon exposure to sole DTPA or LIHOPO, cell viability and morphology are affected in a time- and concentration-dependent manner. For both decorporation agents, detailed EC₅₀ values for renal cells in vitro are reported. Simultaneous application of Eu^III + DTPA in the medium leads to formation of the soluble and largely cell impermeable EuDTPA^2- complex. At ligand excess, this significantly reduces intracellular Eu^III uptake. However, EuDTPA^2- was spectroscopically detected also inside cells indicating that small fractions of this complex are able to pass the plasma membrane. When Eu^III + LIHOPO is applied to the medium, the soluble EuLIHOPO^- complex is formed. In contrast to DTPA, this drastically enhances intracellular Eu^III uptake even at ligand deficit demonstrating that EuLIHOPO^- is highly cell permeable. Concomitantly, this complex was spectroscopically detected inside cells confirming its plasma membrane passage and intracellular stability. Nevertheless, due to stable Eu^III binding, the cell viability is not influenced by the increased intracellular Eu^III content. In fact, the applied ligand concentration is much more critical in this regard, emphasizing the need for cytotoxic investigations. Our results improve the knowledge of the cellular interactions of lanthanides ± decorporation agents and demonstrate the combination of in vitro cell culture and spectroscopy being a sophisticated toolbox for this.