Bioactive constituents from the edible seaweed <i>Halymenia hawaiiana</i> (Rhodophyta).

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Context: The marine macroalga, Halymenia hawaiiana, holds significant commercial potential due to its culinary uses among various ethnic groups in Hawai'i and its success in aquaculture.Objective: To investigate the chemical components and potential medicinal properties of H. hawaiiana.Materials and methods: Dried, ground H. hawaiiana was sequentially extracted with three solvents: ethyl acetate, methanol, and n-butanol. Chromatographic procedures were sequentially applied, leading to the isolation of several compounds. Structure determination of these compounds was performed using spectroscopic methods. The isolated compounds were then assessed through several in vitro assays.Results: A total of 11 compounds were isolated and identified: two nucleosides (1 and 2), a cytosine analog (3), five saturated long-chain fatty acids (4-8), cholesterol (9), and two of its derivatives (10-11) were isolated. Compounds 10 and 11 displayed promising antimicrobial activity against Staphylococcus aureus, both exhibiting MIC values of 8 μg/mL, and methicillin-susceptible S. aureus, with MIC values of 32 and 64 μg/mL, respectively. Furthermore, using a cell culture model, compounds 9, 10, and 11 exhibited significant anti-inflammatory effects as indicated by their inhibition of lipopolysaccharide (LPS)-induced nitric oxide (NO) production, with IC₅₀ values ranging from 50.2 to 60.8 µM. These compounds also effectively inhibited the generation of reactive oxygen species (ROS)/reactive nitrogen species (RNS) in RAW 264.7 mouse macrophage cells with IC₅₀ values of 55-73.7 µM without inducing cytotoxicity. Compounds 9-11 also exhibited mild cytotoxicity against the non-small cell lung cancer cell line A549, with compound 10 eliciting the strongest response (IC₅₀ 86.1 µM).Conclusions: This study uncovered a diverse array of constituents from H. hawaiiana. Notably, compounds 10 and 11, which feature peroxide side chains, show significant promise as lead compounds for the development of novel anti-inflammatory and antimicrobial agents.