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Abstract
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.

Affiliations

Bora Nam #  1 , Woonghee Lee #  1 , Swarbhanu Sarkar #  1 , Jae-Hong Kim  2 , Abhinav Bhise  1 , Hyun Park  3 , Jung Young Kim  3 , Phuong Tu Huynh  1 , Subramani Rajkumar  1 , Kiwoong Lee  1 , Yeong Su Ha  1 , Seong Hwan Cho  1 , Jeong Eun Lim  1 , Kyung Won Kim  1 , Kyo Chul Lee  3 , Kyoungho Suk  2 , Jeongsoo Yoo  4
1 Department of Molecular Medicine, Brain Korea 21 four KNU Convergence Educational Program of Biomedical Sciences for Creative Future Talents, School of Medicine, Kyungpook National University, Daegu, 41944, South Korea.
2 Department of Pharmacology, Brain Korea 21 four KNU Convergence Educational Program of Biomedical Sciences for Creative Future Talents, School of Medicine, Brain Science & Engineering Institute, Kyungpook National University, Daegu, 41944, South Korea.
3 Division of Applied RI, Korea Institute of Radiological and Medical Sciences, Seoul, 01812, South Korea.
4 Department of Molecular Medicine, Brain Korea 21 four KNU Convergence Educational Program of Biomedical Sciences for Creative Future Talents, School of Medicine, Kyungpook National University, Daegu, 41944, South Korea. yooj@knu.ac.kr.
# Contributed equally.