A Novel Approach for Fluorescent Visualization of Glycyrrhetic Acid on a Cell with a Quantum Dot

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Jie Hou^1,2*, Qian Shi², Meirong Cao², Pengwei Pan², Guangbo Ge^3*, Xuran Fan³, Gang Bai², and Yi Xin¹

¹Department of Biochemistry and Molecular Biology, Dalian Medical University, Dalian 116044, China; fax: +86-411-8611-0350; E-mail: houjie@nankai.edu.cn

²College of Pharmacy, Nankai University, Tianjin 300071, China; fax: +86-2223-508-371; E-mail: houjie@nankai.edu.cn

³Laboratory of Pharmaceutical Resource Discovery, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China; fax: +86-411-8467-6961; E-mail: geguangbo@dicp.ac.cn

^* To whom correspondence should be addressed.

Received January 29, 2013; Revision received October 22, 2013

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Glycyrrhetic acid (GA), a pentacyclic triterpenoid derivative obtained from hydrolysis of glycyrrhizic acid, was found to have synergistic anti-asthmatic effects with the β₂-adrenergic receptor (β₂AR) agonist via the β₂AR-mediated pathway. This study visualized the location of GA on a human cell expressing β₂AR via chemical biological approaches. A CdTe/ZnS quantum dot modified with an alkynyl group (QD-AL) was first synthesized, and an azide-terminal GA (ATGA) was also prepared. The QD-AL was used for fluorescence visualization of the distribution of GA on human embryonic kidney 293 cells expressing fusion β₂AR (HEK293-β₂AR) through the “click reaction” between QD-AL and ATGA. The average size of the QD-AL nanoparticle was about 10 nm, and its fluorescent emission wavelength was 620 nm. The location of GA on the HEK293-β₂AR cell membrane can be visualized by the click reaction (between QD-AL and ATGA). The ability of QD-AL targeting to ATGA on the cell membrane of a HEK293-β₂AR cell was further investigated using both confocal laser-scanning microscopy and a cellular uptake-inhibition assay. The results reveal that QD-AL can recognize ATGA on the cell membrane through the click reaction, which provides a new approach for visualizing the location of GA on the cell in an indirect way, and it can be applied to explore the synergistic anti-asthmatic mechanism of GA with β₂AR agonist through the β₂AR mediated pathway.

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KEY WORDS: fluorescent visualization, glycyrrhetic acid, quantum dot, click reaction

DOI: 10.1134/S0006297914010040

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