Iron overload of human colon adenocarcinoma cells studied by synchrotron-based X-ray techniques
Fast- and slow-proliferating human adenocarcinoma colorectal cells, HT-29 and HCA-7, respectively, overloaded with transferrin (Tf), Fe(III) citrate, Fe(III) chloride and Fe(II) sulfate were studied by synchrotron radiation total-reflection X-ray spectrometry (TXRF), TXRF-X-ray absorption near edge structure (TXRF-XANES), and micro-X-ray fluorescence imaging to obtain information on the intracellular storage of overloaded iron (Fe). The determined TfR1 mRNA expression for the investigated cells correlated with their proliferation rate. In all cases, the Fe XANES of cells overloaded with inorganic Fe was found to be similar to that of deliquescent Fe(III) sulfate characterized by a distorted octahedral geometry. A fitting model using a linear combination of the XANES of Tf and deliquescent Fe(III) sulfate allowed to explain the near edge structure recorded for HT-29 cells indicating that cellular overload with inorganic Fe results in a non-ferritin-like fast Fe storage. Hierarchical cluster analysis of XANES spectra recorded for Fe overloaded HT-29 and HCA-7 cells was able to distinguish between Fe treatments performed with different Fe species with a 95 % hit rate, indicating clear differences in the Fe storage system. Micro-X-ray fluorescence imaging of Fe overloaded HT-29 cells revealed that Fe is primarily located in the cytosol of the cells. By characterizing the cellular Fe uptake, Fe/S content ratios were calculated based on the X-ray fluorescence signals of the analytes. These Fe/S ratios were dramatically lower for HCA-7 treated with organic Fe(III) treatments suggesting dissimilarities from the Tf-like Fe uptake.
KeywordsCancer cells Fe storage Micro-X-ray imaging Transferrin
The technical as well as financial supports from DESY and Diamond Light Source contract No I-20110800 EC and 10230, respectively, are hereby acknowledged. The authors express their gratitude to Ian Pape and Kawal J. S. Sawhney for their efforts made in preparing the X-ray imaging experiments. The research leading to these results has also received funding from the European Community’s Seventh Framework Programme (FP7/2007–2013) under Grant agreement No 226716.
- 21.Meirer F, Singh A, Pianetta P, Pepponi G, Meirer F, Streli C, Homma T (2010) TrAC 29:479–496Google Scholar