Preliminary screening of antioxidant and cytotoxic potential of green seaweed, Halimeda opuntia (Linnaeus) Lamouroux

Marine natural products have displayed numerous advantageous effects on biological activities, including antioxidants and cytotoxicity. The total lipids, carotenoids, chlorophyll a and b content, total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activity of methanolic crude extract of the green seaweed Halimeda opuntia were all measured in this study. The TPC of the extracts was determined according to the Folin-Ciocalteu method, yielding a result of 55.04 ± 0.98 mg GAE/g of extract. As determined by the aluminium chloride colorimetric method, the TFC of the extract was 40.02 ± 0.02 mg QE/g of extract. Antioxidant activity was determined by using a 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay with different concentrations that ranged between 200 and 1000 µg/mL, noted H. opuntia as the highest in DPPH reduction (63.61 %) at 1000 µg/mL concentration. Total antioxidant capacity (TAC) of the extract was 57.36 ± 0.004 mg AAE/g extract at concentration of 1.0 mg/mL. The cytotoxic activity of this seaweed was pre-screened against a panel of cell lines including estrogen receptor-positive human breast adenocarcinoma (MCF-7), estrogen negative human breast adenocarcinoma (MDA-MB-231), human colorectal adenocarcinoma (HT-29), human hepatocellular carcinoma (HepG2), and mouse embryonic fibroblast (3T3) using the MTT assay. The content of total lipids in H. opuntia was 1.60 ± 0.002 %. Total carotenoids were 115.57 ± 0.98 µg/g, while chlorophyll a and b were 148.73 ± 2.60 µg/g and 290.83 ± 9.46 µg/g, respectively. In terms of cytotoxicity activity, methanolic extract of H. opuntia was found to be highly cytotoxic to MCF-7 cells, with an IC₅₀ of 25.14 ± 1.02 g/mL, and slightly less so to 3T3 cells (IC₅₀ 65.23 ± 0.25 µg/mL). This study's findings suggest that natural pigments (carotenoids and chlorophyll), phytochemicals like phenolic and flavonoid compounds found in this species may play an important role and could be used as a natural cancer treatment.