Evaluation of antioxidant and anticancer activity of crude extract and different fractions of Chlorella vulgaris axenic culture grown under various concentrations of copper ions

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.

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.

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.