Carotenoid, antioxidant role

In plants, and more specifically in leaves, the antioxidant role of carotenoids is well demonstrated because they quench singlet oxygen as noted earlier. However, the antioxidant role of carotenoids in humans is still under debate. 

Oxidative stress is now recognized as an important etiological factor in the causation of several chronic diseases including cancer, cardiovascular diseases, osteoporosis, and diabetes. Antioxidants play an important role in mitigating the damaging effects of oxidative stress on cells. Lycopene, a carotenoid antioxidant, has received considerable scientific interest in recent years. Epidemiological, tissue culture, and animal studies provide... 

Vitamin activity in foods and food products serves as an example where typical problems arise with traditional liquid solvent extraction and then where SFE has been used to address these concerns [30]. In addition to the routine assay of food products, there is a considerable amount of research being conducted on the role of carotenoids and xanthans as antioxidants in the human body. This antioxidant-role may address many health concerns such as aging and various diseases. The "friendly-extracting-environment" of SFE has some merit of consideration for such studies, particularly with regard to the lesser possibility of oxidation of the analytes during the sample preparation step. 

Our results support the hypothesis that IO2 may trigger astaxanthin biosynthesis, and that carotenoids serve an antioxidant role in the yeast by reacting with peroxyl radicals. Generation of IO2 may explain the increase in carotenoid formation mediated by O2 and blue light in P. rhodozyma (44,45). Short light pulses of 15 minutes resulted in transient increases in astaxanthin levels in P. rhodozyma, but the highest carotenoid yields were obtained by continuous illumination. 

As has already been stated, the carotenoids are lipophilic and are therefore absorbed and transported in association with the lipoprotein particles. In theory, this fortuitous juxtaposition of lipid and carotenoid should confer protection on the lipid through the antioxidant properties of the carotenoid. No doubt some antioxidant protection is afforded by the presence of the carotenoids derived from the diet. However, with one or two exceptions, human supplementation studies have not supported a role for higher dose carotenoid supplements in reducing the susceptibility of the low-density lipoproteins to oxidation, either ex vivo or in vivo (Wright et al, 2002 Hininger et al, 2001 Iwamoto et al, 2000). 

Convincing evidence indicates that ROS generated both endogenously and also in response to diet and lifestyle factors may play a significant role in the etiology of atherosclerosis and CHD. Indeed, free radicals are responsible for LDL oxidation, which is involved in the initiation and promotion of atherosclerosis. Thus, protection from LDL oxidation by antioxidants such as carotenoids may lead to protection against human CHD. 

In atherosclerosis and other heart diseases, the role of carotenoids as antioxidants is probable, but for these types of diseases and also for other degenerative diseases such as cancers, non-antioxidant activities constitute other possible prevention mechanisms. These activities are, for example, stimulation of gap junction communications between cells, and the induction of detoxifying enzymes. The... 

Liebler, D.C. et al.. Antioxidant actions of beta-carotene in liposomal and microsomal membranes role of carotenoid-membrane incorporation and alfa-tocopherol, Arch. Biochem. Biophys., 338, 244, 1997. 

Esterbauer et al. (1991) have demonstrated that /3-carotene becomes an effective antioxidant after the depletion of vitamin E. Our studies of LDL isolated from matched rheumatoid serum and synovial fluid demonstrate a depletion of /8-carotene (Section 2.2.2.2). Oncley et al. (1952) stated that the progressive changes in the absorption spectra of LDL were correlated with the autooxidation of constituent fatty acids, the auto-oxidation being the most likely cause of carotenoid degradation. The observation that /3-carotene levels in synovial fluid LDL are lower than those of matched plasma LDL (Section 2.2.2) is interesting in that /3-carotene functions as the most effective antioxidant under conditions of low fOi (Burton and Traber, 1990). As discussed above (Section 2.1.3), the rheumatoid joint is both hypoxic and acidotic. We have also found that the concentration of vitamin E is markedly diminished in synovial fluid from inflamed joints when compared to matched plasma samples (Fairburn etal., 1992). This difference could not be accounted for by the lower concentrations of lipids and lipoproteins within synovial fluid. The low levels of both vitamin E and /3-carotene in rheumatoid synovial fluid are consistent with the consumption of lipid-soluble antioxidants within the arthritic joint due to their role in terminating the process of lipid peroxidation (Fairburn et al., 1992). 

Potential Protective Role of Carotenoids in the Retina as Antioxidants.312... 

POTENTIAL PROTECTIVE ROLE OF CAROTENOIDS IN THE RETINA AS ANTIOXIDANTS... 

Mascio, P.D., Murphy, M.E., Sies, H., 1991. Antioxidant defense systems The role of carotenoids, tocopherols, and thiols. Am J Clin Nutr. 53, 194S-200S. 

At the moment, the role of p53 and its related genes in the regulation of cell growth signaling by carotenoids is not well understood and the results appear controversial. It is possible that several factors may influence the modulatory effects of P-carotene and other carotenoids on p53 levels, including the concomitant presence of smoke, the type and the concentration of the carotenoid, the association with other antioxidants as well as the biological cellular environment. 

Naturally occurring compounds such as phytochemicals, which possess anticar-cinogenic and other beneficial properties, are referred to as chemopreventers. One of the predominant mechanisms of their protective action is due to their antioxidant activity and the capacity to scavenge free radicals. Among the most investigated chemopreventers are some vitamins, plant polyphenols, and pigments such as carotenoids, chlorophylls, flavonoids, and betalains. Resolution of the potential protective roles of... 

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