Water-Soluble Carbon Dots in Cigarette Mainstream Smoke: Their Properties and the Behavioural, Neuroendocrinological, and Neurotransmitter Changes They Induce in Mice

Yan Zhao,1 Fang Lu,2 Yue Zhang,2 Meiling Zhang,1 Yusheng Zhao,3 Juan Luo,1 Hui Kong,1 Huihua Qu4 1School of Traditional Chinese Medicine, Beijing University of Chinese Medicine, Beijing, 100029, People’s Republic of China; 2School of Life Science, Beijing University of Chinese Medicine, Beijing, 100029, People’s Republic of China; 3School of Chinese Materia Medica, Beijing University of Chinese Medicine, Beijing, 100029, People’s Republic of China; 4Beijing Institute of Traditional Chinese Medicine, Beijing University of Chinese Medicine, Beijing, 100029, People’s Republic of ChinaCorrespondence: Hui Kong; Huihua QuBeijing University of Chinese Medicine, No. 11, Bei San Huan Dong Lu, Chaoyang District, Beijing, 100029, People’s Republic of ChinaTel +86 10-62486705Email doris7629@126.com; quhuihuadr@163.comBackground: It is well known that smoking is harmful to health; however, it can also ameliorate anxiety. To date, it is unclear whether any nanoparticles found in cigarette mainstream smoke (CS) contribute to this effect.Aim: The aim of this study was to assess the particle composition of CS to identify novel anti-anxiety components.Methods: Carbon dots (CDs) from CS (CS-CDs) were characterised using high-resolution transmission electron microscopy, Fourier-transform infrared, ultraviolet, fluorescence, X-ray photoelectron spectroscopy, X-ray diffraction and high-performance liquid chromatography. The anti-anxiety effects of CS-CDs in mouse models were evaluated and confirmed with the elevated plus maze and open-field tests.Results: The quantum yield of CS-CDs was 13.74%, with a composition of C, O, and N. In addition, the surface groups contained O-H, C-H, C=O, C-N, N-H, C-O-C, and COO− bonds. Acute toxicity testing revealed that CS-CDs had low in vitro and in vivo toxicity within a certain concentration range. The results of the elevated plus maze and open-field tests showed that CS-CDs had a significant anti-anxiety effect and a certain sedative effect in mice. The mechanism of these effects may be related to the decrease in glutamate levels and promotion of norepinephrine production in the mouse brain, and the decrease in dopamine in mouse serum due to CS-CDs.Conclusion: CS-CDs may have anti-anxiety and certain sedative effects. This study provides a new perspective for a more comprehensive understanding of the components, properties, and functions of CS. Furthermore, it offers a novel target for the development of smoking cessation treatments, such as nicotine replacement therapy.Keywords: carbon dots, cigarette mainstream smoke, anxiety, smoking cessation therapy