Numerous disease development processes are caused or accompanied by oxidative stress, which refers to cellular damage that is caused by reactive oxygen intermediates (ROI)—especially in age-related disorders. Since oxidative stress is an important factor in the beginning of several pathologies, from cancer to cardiovascular and other neurodegenerative diseases,15-21 an effective approach is sought to improve antioxidant nutrition to protect the body against the harmful consequences of oxid-ative stress. In this respect, antioxidants from natural sources are believed to have higher bioavailability and greater protective efficacy than synthetic antioxidants.22 Restated, Spirulina is attracting more interest because of its potential pharmaceutical and neutraceutical value.
The antioxidant property of Spirulina or phycocyanin has been examined in vitro.13-14,23-26 Since then, Spirulina or its specific component, phycocyanin, has been studied with reference to the role of antioxidants in improving health and preventing diseases.27 Experimental investigations have established the importance of antioxidant activity of Spirulina in decreasing lead-induced lipid peroxidation and brain lead deposition.23 Moreover, they have the following properties: efficacy in anti-inflammation,28 inhibit zymosan-induced arthritis,29 protects against heavy metal caused hepatic toxicity,30 reverses age-induced increases in concentrations of proinflammatory cytokines, and declines in cerebellar i-adrenergic function.24 Spirulina also inhibits tumor development and reduces incidence,31,32 and helps to prevent chronic diffusion associated with liver disease.33
Our group14 has devoted considerable effort to determining the antioxidant activity of Spirulina and chlorella, and their antiproliferative effect on liver cancer cells (Hep G2) and hepatic stellate cells (HSCs). Accordingly, the free radical scavenging activity of Spirulina and chlorella water extracts was determined using the DPPH* method and the ABTS*+ method, respectively. Experimental results revealed that the patterns of antioxidant activity of Spirulina and chlorella determined by the ABTS*+ and the DPPH* methods were similar. The results of DPPH* assay, in which ascorbic acid was used as a standard reference compound, demonstrated that 50% effective concentration (EC50) was 19.39 ± 0.65 ^mol of ascorbic acid equivalent/g of Spirulina extract and 14.04 ± 1.06 ^mol of ascorbic acid equivalent/g of chlorella extract. The free radical scavenging ability of Spirulina was better than that of chlorella according to the ABTS*+ method using trolox as a standard reference compound (EC50: 72.44 ± 0.24 ^mol of trolox equivalent/g of Spirulina extract vs. 56.09 ± 1.99 ^mol of trolox equivalent/g of chlorella extract).
Romay's group25,26 applied a chemiluminescence (CL) assay to determine the scavenging capacity of phycocyanin to remove alkoxyl and hydroxyl radicals. They assayed the decrease in the CL intensity, by reacting ieri-butyl hydroperoxide reacted with ferrous ions in the presence of luminol, while a water-soluble analogue of vitamin E (6-hydroxy-2,5,7,8-tetramethylchroman-2-carhoxylic acid) was used as the standard reference. The IC50 of 0.1 ^M of trolox had approximately the same effect as 2 ^M of phycocyanin at 50% inhibition of the produced CL intensity. In addition, the hydroxyl radical scavenging capacity of phycocyanin could be determined from the protection against 2-deoxyribose damage; phycocyanin inhibited deoxyribose damage in a dose-dependent manner.11,25,26 The same method has been used to determine the IC50 values of phycocyanin as 19 ^M and 28 ^M, respectively.25,26 Since free radicals are important to the pathogenesis of inflammation, a powerful antioxidant may also be a potential anti-inflammation candidate. Parij et al. (1995)34 obtained a reaction rate constant of approximately 1.9 to 3.5 x 1011 M-1S-1 for the interaction of phycobiliprotein with hydroxyl radicals, and 1.8 x 1010 for the interaction between ibuprofen and indomethacin, which are nonsteroidal anti-inflammatory drugs (NSAIDs), suggesting that phycobiliprotein may be an alternative anti-inflammatory therapeutic agent.
Padyana et al. (2001)35 solved the crystal structure of phycocyanin, a phycobili-protein, by molecular replacement. Complexes of phycobiliprotein, constituting the main light-harvesting antenna in blue-green microalgae for oxygenic photosynthesis, form supermolecules known as phycobilisome assemblies. In phycobiliproteins, the chromophore, a linear tetrapyrrole (bilin), is covalently attached to the apoprotein
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