Carotenoids: Importance in Daily Life—Insight Gained from EPR and ENDOR

Abstract

Carotenoids are indispensable molecules for life. They are present everywhere in plants, algae, bacteria whom they protect against free radicals and oxidative stress. Through the consumption of fruits and vegetables and some carotenoid-containing fish, they are introduced into the human body and, similarly, protect it. There are numerous health benefits associated with the consumption of carotenoids. Carotenoids are antioxidants but at the same time they are prone to oxidation themselves. Electron loss from the carotenoid forms a radical cation. Furthermore, proton loss from a radical cation forms a neutral radical. In this mini-review, we discuss carotenoid radicals studied in our groups by various physicochemical methods, namely the radical cations formed by electron transfer and neutral radicals formed by proton loss from the radical cations. They contain many similar hyperfine couplings due to interactions between the electron spin and numerous protons in the carotenoid. Different EPR and ENDOR methods in combination with DFT calculations have been used to distinguish the two independent carotenoid radical species. DFT predicted larger coupling constants for the neutral radical compared to the radical cation. Previously, INDO calculations miss assigned the large couplings to the radical cation. EPR and ENDOR have aided in elucidating the physisorb, electron and proton transfer processes that occur when carotenoids are adsorbed on solid artificial matrices, and predicted similar reactions in aqueous solution or in plants. After years of study of the physicochemical properties of carotenoid radicals, the different published results start to merge together for a better understanding of carotenoid radical species and their implication in biological systems. Up until 2008, the radical chemistry in artificial systems was elucidated but the correlation between quenching ability and neutral radical formation was an inspiration to look for these radical species in vivo. In addition, the EPR spin-trapping technique has been applied to study inclusion complexes of carotenoids with different delivery systems.

Dietary Carotenoids in Head and Neck Cancer—Molecular and Clinical Implications

“…In precancerous and carcinogenic intracellular disturbances, these phytochemicals may contribute to inhibiting tumour cell divisions, cell cycle regulation, and pro-apoptotic effects and to decreasing angiogenesis; thus, their administration may inhibit the development, progression, and metastasis of tumour cells because of their potential antioxidant, anti-inflammatory, and immunoprotective action, cellular membrane stabilisation, and inhibition of oncogenic signalling pathways and apoptosis activators [ 22 , 23 ]. In particular, the scavenging ability of carotenoids in reducing ROS, singlet oxygen 1 O 2 , and free oxygen radical levels supports DNA repair, while inhibiting oncogene transcription and stimulating of the numerous important genes coding antioxidant enzymes known to inhibit human carcinogenesis [ 33 , 34 ].…”

“…Phytochemicals such as dietary carotenoids have been extensively explored as antioxidants, anti-inflammatories, immunoprotectors, immune regulators, cellular membrane stabilizers, and oncogenic signalling and apoptosis regulators, as well as cell-cycle and angiogenesis valid controllers [ 22 , 23 ]. In particular, the scavenging ability of carotenoids reduces reactive oxygen species (ROS), promotes DNA repair, negatively regulates oncogenic transcription, and stimulates the transcription of a number of key genes encoding antioxidant enzymes [ 33 , 34 ]. Interestingly, except in the presence of unbalanced cellular redox reactions and at high oxidation pressures, an elevated level of carotenoids may induce prooxidant reactions [ 34 , 35 ].…”

“…In particular, the scavenging ability of carotenoids reduces reactive oxygen species (ROS), promotes DNA repair, negatively regulates oncogenic transcription, and stimulates the transcription of a number of key genes encoding antioxidant enzymes [ 33 , 34 ]. Interestingly, except in the presence of unbalanced cellular redox reactions and at high oxidation pressures, an elevated level of carotenoids may induce prooxidant reactions [ 34 , 35 ]. Moreover, inflammation has been associated with higher probability of recurrence and death due to head and neck cancer.…”

Carotenoids modulate stress tolerance and immune responses in aquatic animals

“…(Equations 1 and 2) [157][158][159][160] ; (ii) reacting rapidly with free radicals of different origins and convert them into more stable compounds or non-radical products (Equations 3-6) [161][162][163][164] ; (iii) preventing the formation of free radicals through the interruption of free radical-induced chain reactions and terminating free radical oxidations [165][166][167] ; and (iv) acting as metal chelators by facilitating the conversion of iron and copper derivatives into stable chelate complexes (harmless molecules). [168][169][170] Mechanisms of carotenoid action as physical quenchers of singlet molecular oxygen and free radical scavengers are represented by the followings:…”

Astaksantinin Sinir Sistemi Üzerindeki Etkileri

“…Fig. 1 Chemical structure of astaxanthin (Osterlie et al, 1999) The super-antioxidant astaxanthin is known for its ability to reverse cellular damage caused by free radicals (Focsan et al, 2021). Astaxanthin's conjugated double bonds terminate free radical chain reactions by providing electrons and interacting with free radicals within the cell, giving this molecule powerful antioxidant qualities (Yuan et al, 2011;Zuluaga et al, 2018).…”