Novel Endoplasmic Reticulum-Targeted Luminescent Probe for Visualization of Carbon Monoxide in Drug-Induced Liver Injury

Drug-induced liver injury (DILI) is a major hepatic dysfunction commonly caused by hepatotoxic drug overdose, resulting in a considerable number of fatalities worldwide. Recent studies have highlighted the regulatory and hepatoprotective effects of carbon monoxide (CO) during the liver injury process. However, precisely tracking the dynamic changes in the composition of CO in DILI is still a great challenge. In this work, leveraging the innovative "quencher-insertion" strategy, a unique endoplasmic reticulum (ER)-targetable lanthanide complex-based luminescence probe, ER-ANBTTA-Eu³⁺/Tb³⁺, has been developed for the selective and accurate monitoring of CO fluxes in live cells and laboratory animals. The new probe is composed of three covalently linked functional moieties: the terpyridine polyacid-Eu³⁺/Tb³⁺-mixed chelates as the long-lived luminophore, a p-toluenesulfonamide moiety as the ER-anchoring motif, and an allyloxy-nitrobenzyl ether moiety as the CO-specific recognition unit. Upon reaction with CO in the presence of Pd²⁺ ions, the Tsuji-Trost reaction leads to the cleavage of the allyloxy-nitrobenzyl group from the Eu³⁺/Tb³⁺-mixed chelates, which results in the restoration of Tb³⁺ emission at 538 nm and the attenuation of Eu³⁺ emission at 688 nm, leading to a dramatic increase of the I₅₃₈/I₆₈₈ ratio. In addition to the exceptional response sensitivity and selectivity toward CO, ER-ANBTTA-Eu³⁺/Tb³⁺ also exhibits the outstanding ER-locating capability, which allows the probe to be used for imaging of CO in the ER of live cells. Using this probe, combined with the time-gated luminescence imaging mode, the exogenous and endogenous CO in ER of live cells were monitored without the interference of background autofluorescence. Moreover, the upregulation of hepatic CO in DILI mice was successfully visualized. The results suggested the potential of ER-ANBTTA-Eu³⁺/Tb³⁺ for deeply exploring the functions of CO in DILI pathogenesis.