Photogeneration and quenching of singlet molecular oxygen by bacterial C40 carotenoids with long chain of conjugated double bonds

Measurement of photosensitized luminescence of singlet oxygen has been applied to studies of singlet oxygen generation and quenching by C40 carotenoids (neurosporene, lycopene, rhodopin, and spirilloxanthin) with long chain of conjugated double bonds (CDB) using hexafluorobenzene as a solvent. It has been found that neurosporene, lycopene, and rhodopin are capable of the low efficient singlet oxygen generation in aerated solutions upon photoexcitation in the spectral region of their main absorption maxima. The quantum yield of this process was estimated to be (1.5-3.0) × 10-2. This value is near the singlet oxygen yields in solutions of ζ-carotene (7 CDB) and phytoene (3 CDB) and many-fold smaller than in solutions of phytofluene (5 CDB) (Ashikhmin et al. Biochemistry (Mosc) 85:773-780, https://doi.org/10.1134/S0006297920070056 , 2020, Biochemistry (Mosc) 87:1169-1178, 2022, https://doi.org/10.1134/S00062979221001082022 ). Photogeneration of singlet oxygen was not observed in spirilloxanthin solutions. A correlation was found between the singlet oxygen yields and the quantum yields and lifetimes of the fluorescence of the carotenoid molecules. All carotenoids were shown to be strong physical quenchers of singlet oxygen. The rate constants of 1O2 quenching by the carotenoids with long chain of CDB (9-13) were close to the rate constant of the diffusion-limited reactions ≈1010 M-1 s-1, being many-fold greater than the rate constants of 1O2 quenching by the carotenoids with the short chain of CDB (3-7) phytoene, phytofluene, and ζ-carotene studied in prior papers of our group (Ashikhmin et al. 2020, 2022). To our knowledge, the quenching rate constants of rhodopin and spirilloxanthin have been obtained in this paper for the first time. The mechanisms of 1O2 photogeneration by carotenoids in solution and in the LH2 complexes of photosynthetic cells, as well as the efficiencies of their protective action are discussed.

Beneficial effect of ζ-carotene-like compounds on acute UVB irradiation by alleviating inflammation and regulating intestinal flora

ζ-Carotene is a key intermediate in the carotenoid pathway, but owing to its low content and difficulties in isolation, its application is restricted. In this study, three genes (pnCrtE, pnCrtB, and pnCrtP) in the carotenoid pathway of Antarctic moss were identified, recombined, and expressed in Escherichia coli (E. coli) BL21(DE3). The expression product was identified as one of the ζ-carotenes by UV absorbance spectrum, thin layer chromatography (TLC), and super-high-performance liquid chromatography-mass spectrum (UPLC-MS), and was called a ζ-carotene-like compound (CLC). Excessive exposure to ultraviolet B (UVB) irradiation is one of the main risk factors for skin photodamage. The purpose of this study was to investigate the preventive and therapeutic effects of CLC on UVB-induced skin photodamage in mice. In this paper, through histological examinations (hematoxylin-eosin, HE; Masson and TdT-mediated dUTP Nick-End Labeling, Tunel), biochemical index detection (reactive oxygen species, ROS; inflammatory factors; cyclobutyl pyrimidine dimers, CPDs and hyaluronic acid, HA), quantitative real time polymerase chain reaction (qRT-PCR), immunohistochemistry and intestinal content flora, etc., it is concluded that CLC has the potential to enhance skin antioxidant capacity by activating the nuclear transcription factor/antioxidant reaction element (Nrf2/ARE) pathway and also reduce skin inflammation and aging by inhibiting the mitogen-activated protein kinase (MAPK) pathway. Moreover, the regulation of intestinal flora may potentially mitigate skin damage induced by UVB radiation. This research not only developed a green and sustainable platform for the efficient synthesis of CLC but also laid a foundation for its application in functional food and medicine for skin resistance against UVB damage.