TPEN, a Well-Known Zinc Chelator, Sequesters Attomolar-Buffered Cellular Cu(I) Through an Oxygen-Dependent Mechanism.

The metal ion chelator TPEN is widely used to study the role of mobile zinc in biology; however, its high affinity for other metal ions raises questions about the specificity when interpreting biological effects of TPEN. Using the Cu(I)-selective chelator PSP-2, we found that the chelation of copper, and not zinc, likely stimulates axon regeneration after optic nerve injury, thus challenging the previous viewpoint that dysregulation of mobile zinc contributes to regenerative failure upon optic nerve damage. Spectroscopic and electrochemical measurements revealed that TPEN sequesters subattomolar buffered Cu(I) through a novel redox-trapping mechanism, which was corroborated by fluorescence imaging studies with a Cu(I)-selective probe in live cells. These findings highlight the ambiguity of TPEN-induced biological effects and identify PSP-2 as a versatile tool for dissecting the role of copper in biological processes.