Copper is an essential metal in biology, as its redox activities facilitate basic cellular processes ranging from antioxidant defense to respiration along with emerging regulatory roles in cell signaling. However, this redox activity can be detrimental when their homeostasis is disrupted, leading to oxidative stress and damage associated with diseases spanning neurodegeneration, metabolic disorders, and cancer. The context in which copper esides within a biological environment significantly influences its activity in function. While recent years have seen a rise in tools for monitoring metal ions and have illuminated the diversity in metal speciation in biology, the majority of these tools are focused on probing metals in the intracellular space. The state-of-the-art methods for assessing metal status in extracellular fluids such as blood plasma and cellular media focus either on absolute quantitation or evaluate a limited number of metal-containing species. While these methods have offered important insight into extreme cases of metal deficiency in overload, subtle imbalances are more challenging to diagnose and understand with the available methods. Here we present two new tools, both for imaging and analyzing extracellular copper pools with specificity for labile and reactive forms of the metal. The first relies on a bioluminescent approach that harnesses secreted enzymes for location-specific monitoring of reactive copper(II). We show that the chemoselective imaging agent finds utility for monitoring copper changes both in human serum as well as in cell culture media under normal and diseased conditions. The second facilitates the identification of copper-binding species in human serum in plasma by integration of immobilized metal affinity chromatography into a mass spectrometry-based proteomics workflow. Taken together, these techniques offer important insight on copper populations with diagnostic potential for metabolic diseases and cancer.

New tools for monitoring extracellular copper fluxes in mammalian systems

ACS Spring 2022

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