Assessment of Phenolic Contents and Antibacterial, Cytotoxic, and Antioxidant Activities of Five Brown Algae from the Persian Gulf

Marine sources have attracted worldwide attention due to their various biological activities. This study reports the cytotoxic, antioxidant, and antibacterial activities and phenolic contents of solvent extracts sequentially prepared by 80% methanol (MeOH), MeOH, and dichloromethane (DCM), of five brown algae from the Persian Gulf: Colpomenia sinuosa (C. sinuosa), Sargassum acinaciforme (S. acinaciforme), Iyengaria stellata (I. stellata), Sirophysalis trinodis (S. trinodis), and Padina gymnospora (P. gymnospora). The cytotoxicity of the extracts was determined against human acute lymphoblastic leukemia (MOLT-4) cells. We have determined the DCM extracts of C. sinuosa and S. acinaciforme and I. stellata as the most potent cytotoxic agents with IC50 values of 23.95 ± 1.9, 31.6 ± 8.5, and 36.0 ± 6.0 µg/mL, respectively. Additionally, the extracts were subjected to 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging and Folin-Ciocalteu total phenolic assays. The MeOH extract of P. gymnospora showed the highest antioxidant activity with the highest radical scavenging potential (IC50 = 746.76 ± 94.15 µg/ml DPPH), which was consistent with its highest phenolic content (70.24 ± 5.40 mg equivalent to gallic acid in 1 g algal extract: mg EG/g AE). Finally, the antibacterial activity of the extracts was assessed against three Gram-positive and four Gram-negative bacteria using the broth dilution method by determination of the minimum inhibitory concentrations (MICs). The MeOH and 80% MeOH extracts of P. gymnospora and C. sinuosa exhibited the strongest antibacterial activity against all tested microorganisms, with the MIC values ranging from 0.62 to 5.00 mg/mL. In conclusion, the DCM extracts of the algae are suggested as the best sources of cytotoxic metabolites, while the MeOH and 80% algal extracts were week antioxidants (IC50s 746.76–5000 µg/ml DPPH) and contained lower amounts of phenolics (1.61–70.24 mg EG/g AE), but they are better source (0.62 to 5.00 mg/mL) of antibacterial metabolites.