Opportunities in multidimensional trace metal imaging: taking copper-associated disease research to the next level

Abstract

Copper plays an important role in numerous biological processes across all living systems predominantly because of its versatile redox behavior. Cellular copper homeostasis is tightly regulated and disturbances lead to severe disorders such as Wilson disease (WD) and Menkes disease. Age related changes of copper metabolism have been implicated in other neurodegenerative disorders such as Alzheimer’s disease (AD). The role of copper in these diseases has been topic of mostly bioinorganic research efforts for more than a decade, metal-protein interactions have been characterized and cellular copper pathways have been described. Despite these efforts, crucial aspects of how copper is associated with AD, for example, is still only poorly understood. To take metal related disease research to the next level, emerging multi dimensional imaging techniques are now revealing the copper metallome as the basis to better understand disease mechanisms. This review will describe how recent advances in X-ray fluorescence microscopy and fluorescent copper probes have started to contribute to this field specifically WD and AD. It furthermore provides an overview of current developments and future applications in X-ray microscopic methodologies.

Synthetic fluorescent probes for studying copper in biological systems

“…Traditional bulk techniques such as atomic absorption spectroscopy and inductively coupled plasma mass spectrometry (ICP-MS), 47 along with use of radioactive isotopes (e.g., 64 Cu), 48,49 provide direct information on total metal content. As the metal content of a single cell (10 −15 g) 50 is too low for bulk measurements, however, several synchrotron-based 51 methods for elemental analysis of single cells with greater sensitivity and with spatial resolution have emerged in recent years. X-ray fluorescence microscopy (XFM) 52 visualizes the elemental distribution of a chemically or cryofixed sample by detection of the characteristic fluorescence emission signatures from the constituent atoms with sensitivity of 10 −18 g, and it has been recently applied to copper biology.…”

Investigating Cellular Nanoscale with X-rays

“…Analysis of the emitted spectrum gives knowledge of the chemical composition of the specimen. X-ray fluorescence (XRF) spectroscopy [89] (panel b of Fig. 1.2) can highlight maps of elements (typically 10 to 15 at the same time) directly inside cells: phosphorous inside the nucleus, or copper everywhere.…”

“…Z ≥14). Hence cellular membrane cannot be easily visualised with XRF, unless using specific metal contrast agents [89]. XRF has now been turned into a nanotomography technique, with the possibility to map more than 10 elements at a resolution of 100 nm [90].…”

“…b) X-ray fluorescence maps of fibroblasts, phosphorous (P), iron (Fe) and copper (Cu) from ref. [89]. c) Scanning nano-diffraction of keratin rich cells SK8K18 (shown in the inset) from ref.…”

Biochemical and Biophysical Methods for Studying Mitochondrial Iron Metabolism

“…Emerging multidimensional imaging techniques are now revealing that analysis of metal distribution promotes better understanding of metal-related disease mechanisms (Hare et al, 2012;McRae, Bagchi, Sumalekshmy, & Fahrni, 2009;Vogt & Ralle, 2013). In situ analysis has the advantage over bulk analysis in that it can provide important, spatially resolved information on a cellular level, and can enable the experimentalist to avoid the use of cell fractionation procedures that can lead to elemental translocation and chemical changes.…”