In vivo detection of hydrogen sulfide in the brain of live mouse: application in neuroinflammation models

Purpose: Hydrogen sulfide (H₂S) plays important roles in brain pathophysiology. However, nuclear imaging probes for the in vivo detection of brain H₂S in living animals have not been developed. Here, we report the first nuclear imaging probe that enables in vivo imaging of endogenous H₂S in the brain of live mice.

Methods: Utilizing a bis(thiosemicarbazone) backbone, a fluorescent ATSM-FITC conjugate was synthesized. Its copper complex, Cu(ATSM-FITC) was thoroughly tested as a biosensor for H₂S. The same ATSM-FITC ligand was quantitatively labeled with [⁶⁴Cu]CuCl₂ to obtain a radioactive [⁶⁴Cu][Cu(ATSM-FITC)] imaging probe. Biodistribution and positron emission tomography (PET) imaging studies were performed in healthy mice and neuroinflammation models.

Results: The Cu(ATSM-FITC) complex reacts instantly with H₂S to release CuS and becomes fluorescent. It showed excellent reactivity, sensitivity, and selectivity to H₂S. Endogenous H₂S levels in living cells were successfully detected by fluorescence microscopy. Exceptionally high brain uptake of [⁶⁴Cu][Cu(ATSM-FITC)] (> 9% ID/g) was observed in biodistribution and PET imaging studies. Subtle changes in brain H₂S concentrations in live mice were accurately detected by quantitative PET imaging. Due to its dual modality feature, increased H₂S levels in neuroinflammation models were characterized at the subcellular level by fluorescence imaging and at the whole-body scale by PET imaging.

Conclusion: Our biosensor can be readily utilized to study brain H₂S function in live animal models and shows great potential as a novel imaging agent for diagnosing brain diseases.