Prooxidants carotenoids

PALOZZA p (1998) Prooxidant actions of carotenoids in biological systems , Nutr Rev, 56, 257. 

It has been established that carotenoid structure has a great influence in its antioxidant activity for example, canthaxanthin and astaxanthin show better antioxidant activities than 3-carotene or zeaxanthin. 3- 3 3-Carotene also showed prooxidant activity in oil-in-water emulsions evaluated by the formation of lipid hydroperoxides, hexanal, or 2-heptenal the activity was reverted with a- and y-tocopherol. Carotenoid antioxidant activity against radicals has been established. In order of decreasing activity, the results are lycopene > 3-cryptoxanthin > lutein = zeaxanthin > a-carotene > echineone > canthaxanthin = astaxanthin. ... 

Young, A.J. and Lowe, G.M., Antioxidant and prooxidant properties of carotenoids. Arch. Biochem. Biophys., 385, 20, 2001. 

Antioxidant and Prooxidant Actions and Stabilities of Carotenoids In Vitro and In Vivo and Carotenoid Oxidation Products... 

Many reviews have been written about the antioxidant activities of carotenoids. Some also describe prooxidant activities. - In consequence, only selected points about this very broad subject will be presented in the first part of this chapter. Linked to these properties and important for food nutritional value is the stability of caro-... 

A molecule that has a prooxidant effect can be dehned as a molecule that can react with reactive oxygen species (ROS) to form compounds more deleterious to biomolecules than the ROS alone. Possible prooxidant activity of carotenoids was for the first time mentioned by Burton and Ingold. Since then, many other examples of loss of antioxidant activity or prooxidant activity have been illustrated and reviewed in the literature. Increasing oxygen partial pressure (PO2) and/or carotenoid concentration can convert a carotenoid from antioxidant to prooxidant. Thus, depending on the environment, the same molecule can exert either antioxidant or prooxidant activity. ... 

Various types of cell-based in vitro studies have shown that carotenoids can exert prooxidant effects under certain conditions. Most of these studies show in fact decreases in antioxidant efficacy of carotenoids with increasing carotenoid concentration examples of true prooxidant effects are rarer. It is also important to pay attention to the experimental conditions and their biological relevance. Indeed, carotenoids have sometimes been proven to (I) exert prooxidant activity in an atmosphere of pure oxygen, (2) never occur in vivo, or (3) appear in concentrations that they would never reach in vivo. 

Two main mechanisms by which a carotenoid can become a prooxidant have been proposed and reviewed ... 

Carotenoid reactions with ROS or RNS (reactive nitrogen species) would generate prooxidative products. ... 

Interestingly, early examples of carotenoid autoxidation in the literature described the influence of lipids and other antioxidants on the autoxidation of carotenoids." " In a stndy by Budowski et al.," the influence of fat was fonnd to be prooxidant. The oxidation of carotenoids was probably not only cansed by molecnlar oxygen bnt also by lipid oxidation products. This now well-known phenomenon called co-oxidation has been stndied in lipid solntions, in aqueons solntions catalyzed by enzymes," and even in food systems in relation to carotenoid oxida-tion." The inflnence of a-tocopherol on the antoxidation of carotenoids was also stndied by Takahashi et al. ° who showed that carotene oxidation was snppressed as... 

As described in the preceding paragraphs, oxidation products of carotenoids can be formed in vitro as a result of their antioxidant or prooxidant actions or after their autoxidation by molecular oxygen. They can also be found in nature, possibly as metabolites of carotenoids. Frequently encountered products are the monoepoxide in 5,6- or 5, 6 -positions and the diepoxide in 5,6 5, 6 positions or rearrangement products creating furanoid cycles in the 5,8 or 5, 8 positions and 5,8 5, 8 positions, respectively. Products like apo-carotenals and apo-carotenones issued from oxidative cleavages are also common oxidation products of carotenoids also found in nature. When the fission occurs on a cyclic bond, the C-40 carbon skeleton is retained and the products are called seco-carotenoids. 

It has been found (Polyakov et al. 2001c) that when carotenoids are involved in a reaction cycle with the participation of iron as Fe2+, an increase of the total radical yield or a prooxidant effect will occur and will increase with decreasing carotenoid oxidation potential and its scavenging activity. The mechanism of the participating carotenoid is shown in Scheme 9.4 (Polyakov et al. 2001c). 

The interaction of carotenoids with cigarette smoke has become a subject of interest since the results of the Alpha-Tocopherol Beta-Carotene Cancer Prevention Study Group 1994 (ATBC) and CARET (Omenn et al. 1996) studies were released. P-Carotene has been hypothesized to promote lung carcinogenesis by acting as a prooxidant in the smoke-exposed lung. Thus, the autoxidation of P-carotene in the presence of cigarette smoke was studied in model systems (toluene) (Baker et al. 1999). The major product was identified as 4-nitro-P-carotene, but apocarotenals and P-carotene epoxides were also encountered. 

Baker, D. L. et al. (1999). Reactions of beta-carotene with cigarette smoke oxidants. Identification of carotenoid oxidation products and evaluation of the prooxidant antioxidant effect. Chem. Res. Toxicol. 12(6) 535-543. Bonnie, T. Y. P. and Y. M. Choo (1999). Oxidation and thermal degradation of carotenoids. J. Oil Palm Res. 11(1) 62-78. 

The development of either a harmful or beneficial cellular response by carotenoids will depend on their antioxidant or prooxidant characteristics, which are... 

Palozza, P. 1998. Prooxidant actions of carotenoids in biologic systems. Nutr. Rev. 56(9) 257-265. Parker, R.S. 1996. Absorption, metabolism and transport of carotenoids. FASEB J. 10 542-551. Peng, Y.M., Peng, Y.S., Childers, J.M., Hatch, K.D., Roe, D.J., Lin, Y. and Lin, P. 1998. Concentrations of carotenoids, tocopherols and retinol in paired plasma and cervical tissue of patients with cervical cancer, precancer and noncancerous diseases. Cancer Epidemiol. Biomark. Prev. 7 347-350. 

---