Fusi F, Romano G, Speranza G, Agati G. Photon- and Singlet-Oxygen-Induced Cis-Trans Isomerization of the Water-Soluble Carotenoid Crocin.
Int J Mol Sci 2023;
24:10783. [PMID:
37445961 DOI:
10.3390/ijms241310783]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2023] [Revised: 06/20/2023] [Accepted: 06/25/2023] [Indexed: 07/15/2023] Open
Abstract
Studying the cis-trans isomerization process in crocin (CR), one of the few water-soluble carotenoids extracted from saffron, is important to better understand the physiological role of cis-carotenoids in vivo and their potential as antioxidants in therapeutic applications. For that, cis-trans isomerization of both methanol- and water-dissolved CR was induced by light or thermally generated singlet oxygen (1O2). The kinetics of molecular concentrations were monitored by both high-performance liquid chromatography (HPLC) and non-destructive spectrophotometric methods. These last made it possible to simultaneously follow the cis-trans isomerization, the possible bleaching of compounds and the amount of thermally generated 1O2. Our results were in accordance with a comprehensive model where the cis-trans isomerization occurs as relaxation from the triplet state of all-trans- or 13-cis-CR, whatever is the way to populate the CR triplet state, either by photon or 1O2 energy transfer. The process is much more (1.9 to 10-fold) efficient from cis to trans than vice versa. In H2O, a 1O2-induced bleaching effect on the starting CR was not negligible. However, the CR "flip-flop" isomerization reaction could still occur, suggesting that this process can represent an efficient mechanism for quenching of reactive oxygen species (ROS) in vivo, with a limited need of carotenoid regeneration.
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