Lycopene oxygen

There are basically two types of carotenoids those that contain one or more oxygen atoms are known as xanthophylls those that contain hydrocarbons are known as carotenes. Common oxygen substituents are the hydroxy (as in p-cryptoxanthin), keto (as in canthaxanthin), epoxy (as in violaxanthin), and aldehyde (as in p-citraurin) groups. Both types of carotenoids may be acyclic (no ring, e.g., lycopene), monocyclic (one ring, e.g., y-carotene), or dicyclic (two rings, e.g., a- and p-carotene). In nature, carotenoids exist primarily in the more stable all-trans (or all-E) forms, but small amounts of cis (or Z) isomers do occur. - ... 

The speed of autoxidation was compared for different carotenoids in an aqueous model system in which the carotenoids were adsorbed onto a C-18 solid phase and exposed to a continnons flow of water saturated with oxygen at 30°C. Major products of P-carotene were identified as (Z)-isomers, 13-(Z), 9-(Z), and a di-(Z) isomer cleavage prodncts were P-apo-13-carotenone and p-apo-14 -carotenal, and also P-carotene 5,8-epoxide and P-carotene 5,8-endoperoxide. The degradation of all the carotenoids followed zero-order reaction kinetics with the following relative rates lycopene > P-cryptoxanthin > (E)-P-carotene > 9-(Z)-p-carotene. 

In the second oxidation method, a metalloporphyrin was used to catalyze the carotenoid oxidation by molecular oxygen. Our focus was on the experimental modeling of the eccentric cleavage of carotenoids. We used ruthenium porphyrins as models of cytochrome P450 enzymes for the oxidation studies on lycopene and P-carotene. Ruthenium tetraphenylporphyrin catalyzed lycopene oxidation by molecular oxygen, producing (Z)-isomers, epoxides, apo-lycopenals, and apo-lycopenones. 

A similar system, but with a more hindered porphyrin (tetramesitylporphyrin = tetraphenylporphyrin bearing three methyl substituents in ortho and para positions on each phenyl group), was tested for P-carotene oxidation by molecular oxygen. This system was chosen to slow the oxidation process and thus make it possible to identify possible intermediates by HPLC-DAD-MS analysis. The system yielded the same product families as with lycopene, i.e., (Z)-isomers, epoxides, and P-apo-carotenals, together with new products tentatively attributed to diapocarotene-dials and 5,6- and/or 5,8-epoxides of P-apo-carotenals. The oxidation mechanism appeared more complex in this set-up. 

Di Mascio, R, Kaiser, S., and Sies, H., Lycopene as the most efficient biological carotenoid singlet oxygen quencher. Arch. Biochem. Biophys., 274, 532, 1989. Cantrell, A. et ah. Singlet oxygen quenching by dietary carotenoids in a model membrane environment. Arch. Biochem. Biophys., 412, 47, 2003. 

Studies on the autoxidation of carotenoids in liposomal suspensions have also been performed since liposomes can mimic the environment of carotenoids in vivo. Kim et al. have studied the autoxidation of lycopene (Kim et al. 2001), -carotene (Kim 2004), and phytofluene (Kim et al. 2005) in liposomal suspensions and identified oxygenated cleavage compounds. The stability to oxidation at room temperature of various carotenoids has also been studied when incorporated in pig liver microsomes (Socaciu et al. 2000), and taking into account membrane dynamics. After 3 h of reaction, P-carotene and lycopene had completely degraded, whereas the xanthophylls tested were shown to be more stable. 

The ozonolysis of carotenoids was employed in order to obtain oxygenated cleavage products for biological tests, for example, for lycopene. In this case, among a series of products, one product formed by a double oxidative cleavage was purified and characterized as ( , ,/ )- 4 - methyl - 8 -oxo-2,4,6-nonatrienal, and it was shown to be active in the induction of apoptosis in HL-60 cells (Zhang et al. 2003). 

FIGURE 11.4 Hypothesis of the sequence of events when lycopene is oxidized by molecular oxygen in the presence of ruthenium tetraphenylporphyrin. 

It should be noted that partial or total organic synthesis was used to produce carotenoid oxygenated cleavage products such as, for example, apo-8 -lycopenal (Surmatis et al. 1966). 

Di Mascio, P., S. Kaiser, and H. Sies. 1989. Lycopene as the most efficient biological carotenoid singlet oxygen quencher. Arch Biochem Biophys 274(2) 532-538. 

Bohm, F, R Edge, M Burke, and TG Truscott. 2001. Dietary uptake of lycopene protects human cells from singlet oxygen and ntirogen dioxide—ROS components from cigarette smoke. J Photochem Photobiol B 64 176-178. 

The differentiation effect of lycopene was associated with elevated expression of several differentiation-related proteins, such as cell surface antigen (CD14), oxygen burst oxidase and chemotactic peptide receptors (Amir et al., 1999). Recently, it has also been reported that lycopene was also able to stimulate the differentiation marker alkaline phosphatase activity in... 

Di Mascio P., Sandquist A., Devasagayam T., and Sies H. (1992). Assay of lycopene and other carotenoids as singlet oxygen quenchers. Methods Enzymol 213 429 438. 

The antioxidant activity of carotenoids depends on the number of conjugated double bonds and possibly the presence of oxygenated functions in the molecule (Schmidt 2004). The high antioxidant activity of lycopene has been identified against singlet... 

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