Alginates are one of the most important compounds of brown seaweeds. These compounds are employed in the food area, because of their important rheological properties, such as viscosity, gelling, and stabilizing features and as dietary fiber source. In this study, five species of dominant brown seaweeds were collected in the Red Sea (Padina boergesenii, Turbinaria triquetra, Hormophysa cuneiformis, Dictyota ciliolata, and Sargassum aquifolium) so as to characterize the alginate yield and its properties. The analysis demonstrated differences in the alginate yield among the seaweeds. The highest yield of alginate was recorded in the species T. triquetra (22.2 ± 0.56% DW), while the lowest content was observed in H. cuneiformis (13.3 ± 0.52% DW). The viscosity from the alginates varied greatly between the species, whereas the pH varied slightly. The alginate exhibited a moisture content between 6.4 and 13.1%, the ash content ranged between 12.3 and 20% DW, the protein reached values from 0.57 to 1.47% DW, and the lipid concentration varied from 0.3 to 3.5% DW. Thus, the phytochemical analysis demonstrated that the extracted alginates can be safely applied in the food industry. Furthermore, the alginate yield reveals the potential application of these seaweeds as a nutraceutical raw source, which can be exploited by the food industry.

With respect to the potential natural resources in the marine environment, marine macroalgae or seaweeds are recognized to have health impacts. Two marine algae that are found in the Red Sea, Codium tomentosum (Green algae) and Actinotrichia fragilis (Red algae), were collected. Antibacterial and antioxidant activities of aqueous extracts of these algae were evaluated in vitro. Polyphenols from the extracts were determined using HPLC. Fillet fish was fortified with these algal extracts in an attempt to improve its nutritional value, and sensory evaluation was performed. The antibacterial effect of C. tomentosum extract was found to be superior to that of A. fragilis extract. Total phenolic contents of C. tomentosum and A. fragilis aqueous extract were 32.28 ± 1.63 mg/g and 19.96 ± 1.28 mg/g, respectively, while total flavonoid contents were 4.54 ± 1.48 mg/g and 3.86 ± 1.02 mg/g, respectively. Extract of C. tomentosum demonstrates the highest antioxidant activity, with an IC₅₀ value of 75.32 ± 0.07 μg/mL. The IC₅₀ of L-ascorbic acid as a positive control was 22.71 ± 0.03 μg/mL. The IC₅₀ values for inhibiting proliferation on normal PBMC cells were 33.7 ± 1.02 µg/mL and 51.0 ± 1.14 µg/mL for C. tomentosum and A. fragilis, respectively. The results indicated that both algal aqueous extracts were safe, with low toxicity to normal cells. Interestingly, fillet fish fortified with C. tomentosum extract demonstrated the greatest overall acceptance score. These findings highlight the potential of these seaweed species for cultivation as a sustainable and safe source of therapeutic compounds for treating human and fish diseases, as well as effective food supplements and preservatives instead of chemical ones after performing in vivo assays.

Chemical studies on Acanthaster planci have afforded two steroids, 5α-cholesta-24-en-3β,20β-diol-23-one (1) and 5α-cholesta-9(11)-en-3β, 20β-diol (2). Structures compounds 1 and 2 were determined with the help of spectroscopic studies. Compound 1 showed strong antibacterial activity (21.0 ± 0.06 mm) against P. aeruginosa. Compounds 1 and 2 were also active against human breast carcinoma cells (MCF-7) with LC₅₀ values of 49 ± 1.6 and 57.5 ± 1.5 μg/ml, respectively. This bioactivity was comparable to the currently used anticancer agent, cisplatin (LC₅₀ 46 ± 1.1 µg/ml). Compounds 1 and 2 exhibited anti-α-glucosidase activity with IC₅₀ values of 58 ± 0.8 and 55 ± 0.5 µg/ml, respectively, whereas IC₅₀ of Acarbose as a positive control was found to be 36 ± 0.4 µg/ml in our bioassay. Graphical Abstract

Bioactive compounds were extracted from a locally available brittle star; Ophiocoma dentata, collected from the Red Sea, Egypt. Two new sesquiterpenoids; 8, 11-epoxy-9(15)-himachaladiene-4-ol (O8-ophiocomane) and, 11-epoxy-9(15)-himachaladiene-4-ol (O7-ophiocomane) were isolated and characterized using appropriate techniques. Structure elucidation was estimated via 1D NMR, 2D NMR, FT-IR and mass spectroscopy analyses. The isolated compounds were tested for cytotoxic, antibacterial and antifungal activities. Pure compounds showed a dose dependent reduction in MCF-7 cells viability with LC50 of 103.5 and 59.5 μg/ml for compounds 1 and 2 respectively compared to the chemotherapeutic drug cisplatin (47.4 µg/ml). In vivo experiments showed that O. dentate extract significantly reduced tumor progression and improved hematological parameters and liver functions of tumor-bearing mice when administered either before or after tumor cells’ injection. The most remarkable antimicrobial effects of O. dentate crude extract were against Staphylococcus aureus, Vibrio damsela and Pseudomonasaeruginosa while the pure compounds showed activity against P. aeruginosa alone. Neither the crude extract nor the pure compounds have shown activity against Aeromonas hydrophila. These results indicates that O. dentata extract and newly isolated compounds have shown a promising cytotoxic, antiproliferative and antimicrobial activities that might be useful for pharmaceutical applications.

The medicinal potential of marine invertebrates' bioactive components that may act as anti-COVID-19 demonstrated promising results. Ophiocoma dentata, which is common in the Red Sea, is one such source. Therefore, this study aimed to isolate a new compound from the brittle star, Ophiocoma dentata, and evaluate its efficacy as anti-COVID-19 in-silico and in-vitro. Standard procedures were followed in order to assess the isolated compound’s preliminary toxicity and anti-inflammatory properties. Computer virtual screening technology through molecular docking and ADMET studies was conducted as well as a new steroid derivative was isolated for the first time, named 5α-cholesta-4(27), 24-dien-3β, 23 β-diol. Investigation of the Anti-Covid-19 activity of the isolated compound using a Plaque reduction assay revealed 95% inhibition at a concentration of 5 ng/µl (12.48 µM). Moreover, this compound showed an IC₅₀ of 11,350 ± 1500 ng/ml against the normal fibroblast cells, indicating its safety. Interestingly, this compound exhibited anti-inflammatory activity with an IC₅₀ of 51.92 ± 0.03 μg/ml compared to a reference drug’s IC₅₀ of 53.64 ± 0.01 μg/ml, indicating that this compound is a potent anti-inflammatory. In silico data have proved that the isolated compound is a promising viral inhibitor against SARS-CoV2 and is thus recommended as a future nature preventive and curative antiviral drug.

Macroalgae are currently being explored as novel and sustainable sources of bioactive compounds. Ulva prolifera is a major member of the green algae, as it includes various bioactive compounds, including carotenoids, fucoidans, and phlorotannins, with various biological activities in pharmaceutical, nutraceutical, cosmeceutical, and functional foods industries. In the current work, the rbcL gene products were utilized in identifying U. prolifera molecularly. The antibacterial and antioxidant activities of the hexane, ethyl acetate, and methanol extracts of U. prolifera were carried out In vitro. The total antioxidant capacity method was utilized in assessing the antioxidant activity. Estimation of nutritional value of U. prolifera showed 5.4±0.04%, 1.7±0.04% and 43±0.5% dry weight for total proteins, lipids, and carbohydrates, respectively. The total antioxidant capacity of algal hexane, ethyl acetate, and methanol extract was 0.97±0.09, 1.23±0.04 and 1.63±0.09 mg equivalent ascorbic acid/gdw, respectively. Investigation of the antibacterial activity of U. prolifera against Staphylococcus aureus and Aeromonas hydrophila showed that the recorded diameter of the inhibition zones for the methanolic extract was 1.1cm. The antibacterial effect of hexane extract against Edwardsiella tarda was high which had a diameter of 1.5cm. Of interest, the ethyl acetate extract of U. prolifera showed potent antibacterial activity against the three bacteria, including Vibrio anguillarum, Aeromonas hydrophila, and Edwardsiella tarda. These results indicate that macroalgae U. prolifera contain bioactive substances with potential antioxidant and antibacterial effects.