Three fresh water microalgal isolates [Phormidium ambiguum (Cyanobacterium), Pseudochlorococcum typicum and Scenedesmus quadricauda var quadrispina (Chlorophyta)] were tested for tolerance and remo...

To investigate the antioxidant and anticancer activities of aqueous extracts of nine microalgal species. Variable percentages of major secondary metabolites (total phenolic content, terpenoids and alkaloids) as well as phycobiliprotein pigments (phycocyanin, allophycocyanin and phycoerythrin) in the aqueous algal extracts were recorded. Antioxidant activity of the algal extracts was performed using 2, 2 diphenyl-1-picrylhydrazyl (DPPH) test and 2,2'- azino-bis (ethylbenzthiazoline-6-sulfonic acid (ABTS.(+)) radical cation assay. Anticancer efficiency of the algal water extracts was investigated against Ehrlich Ascites Carcinoma cell (EACC) and Human hepatocellular cancer cell line (HepG2). Antioxidant activity of the algal extracts was performed using DPPH test and ABTS.(+) radical cation assays which revealed 30.1-72.4% and 32.0-75.9% respectively. Anticancer efficiency of the algal water extracts was investigated against Ehrlich Ascites Carcinoma Cell (EACC) and Human Hepatocellular cancer cell line (HepG2) with an activity ranged 87.25% and 89.4% respectively. Culturing the promising cyanobacteria species; Nostoc muscorum and Oscillatoria sp. under nitrogen stress conditions (increasing and decreasing nitrate content of the normal BG11 medium, 1.5 g/L), increased nitrate concentration (3, 6 and 9 g/L) led to a remarkable increase in phycobilin pigments followed by an increase in both antioxidant and anticancer activities in both cyanobacterial species. While the decreased nitrate concentration (0.75, 0.37 and 0.0 g/L) induced an obvious decrease in phycobilin pigments with complete absence of allophycocyanin in case of Oscillatoria sp. Nitrogen starvation (0.00 g/L nitrate) induced an increase and comparable antioxidant and anticancer activities to those cultured in the highest nitrate content.

Algae like other plants produce a variety of remarkable compounds collectivity refereed to as secondary metabolites they are synthesized by these organisms at the end of the growth phase and/or due to metabolic alterations induced by environmental stress conditions. Carotenoids, phenolic compounds, phycobiliprotein pigments, polysaccharides and unsaturated fatty acids are same of the algal natural products which were reported to have variable biological activities, including antioxidant activity, anticancer activity, antimicroabial activity against bacteria-virus-algae-fungi, organic fertilizer and bioremediation potentials.

The human body uses an antioxidant defense system to neutralize the excessive levels of reactive oxygen species. This system consists of enzymatic and non enzymatic antioxidants,catalase, peroxidase, superoxide dismutase and gluatathion s-transferease as major defense enzymes. However, ascorbic acid, tocopherol, and phenolic compounds are considered as examples for non-enzymatic antioxidants. Increasing research on natural antioxidants in foods and development of new assays has prompted critical reflection on the field. It has been common practice to identify health benefits from antioxidant activity on the cellular level with antioxidant capacity of food measured in vitro. The use of antioxidants and their positive effects on food quality has been demonstrated in a large variety of foods and beverages using various methods for detection of lipid and protein oxidation or various assays based on electron transfer or hydrogen-atom transfer. There is a need for screening studies in order to identify the mode of action of different antioxidant compounds (enzymatic and non-enzymatic in addition, comparing between synthetic and natural antioxidant compounds) by different assays, in addition to highlighting the advantage and disadvantage of it. Some of these assays depend on hydrogen atom transfer methods or electron transfer methods in addition, metal chelating compounds and free radical scavenging activity. Key words: Synthetic and natural antioxidant compounds, assays, mechanism.

Background: Chlorella vulgaris is a microalga potentially used for pharmaceutical, animal feed, food supplement, aquaculture and cosmetics. The current study aims to study the antioxidant and prooxidant effect of Chlorella vulgaris cultivated under various conc. of copper ions. Methods: The axenic green microalgal culture of Chlorella vulgaris was subjected to copper stress conditions (0.00, 0.079, 0.158, 0.316 and 0.632 mg/L). The growth rate was measured at OD₆₈₀ nm and by dry weight (DW). Moreover, the Antioxidant activity against DPPH and ABTS radical, pigments and phytochemical compounds of the crude extracts (methylene chloride: Methanol, 1:1) were evaluated. The promising Cu crude extract (0.316 mg/L) further fractionated into twenty-one fractions by silica gel column chromatography using hexane, chloroform and ethyl acetate as a mobile phase. Results: The obtained results reported that nine out of these fractions exhibited more than 50% antioxidant activity and anticancer activity against Hela cancer cell lines. Based on IC₅₀, fraction No. 7 was found to be the most effective fraction possessing a significant increase in both antioxidant and anticancer potency. Separation of active compound (s) in fraction No 7 was performed using precoated silica gel plates (TLC F₂₅₄) with ethyl acetate: hexane (9:1 v/v) as mobile phase. Confirmation of active compound separation was achieved by two-dimensional TLC and visualization of the separated compound by UV lamp. The complete identification of the separated active compound was performed by UV- Vis- spectrophotometric absorption, IR, MS, H¹-NMRT C¹³-NMR. The isolated compound ((2E,7R,11R)-3,7,11,15-Tetramethyl-2-hexadecenol) have high antioxidant activity with IC₅₀ (10.59 μg/ml) against DPPH radical assay and comparable to the capacities of the positive controls, Butylated hydroxy toluene [BHT] (IC₅₀ 11.2 μg/ml) and Vitamin C (IC₅₀ 12.9 μg/ml). Furthermore, pure isolated compound exhibited a potent anticancer activity against Hela cell line with IC₅₀ (4.38 μg/ml) compared to Doxorubicin (DOX) as synthetic drug (13.3 μg/ml). In addition, the interaction of the pure compound with Hela cancer cell line and gene expression were evaluated. Conclusions: The authors recommend cultivation of Chlorella vulgaris in large scale under various stress conditions for use the crude extracts and semi purified fractions for making a pharmaco-economic value in Egypt and other countries.