Indonesia has high biodiversity of algae that are under-utilised due to limitations in the processing techniques. Here, we observed the effect of two different extraction methods (cold maceration and ultrasonic-assisted extraction (UAE)) on multiple variables of Indonesian brown algae ethanol extracts (Sargassum polycystum, Sargassum cristaefolium, Sargassum aquifolium and Turbinaria ornata). The variables observed included metabolites screening by untargeted metabolomics liquid chromatography-high-resolution mass spectrometry (LC-HRMS), observation of total phenolic content (TPC), total flavonoid content (TFC), anti-oxidant and B16-F10 melanoma cells cytotoxicity. UAE extracts had higher extraction yield and TPC, but no TFC difference was observed. UAE extract had more lipophilic compounds, such as fatty acids (Palmitic acid, Oleamide, Palmitoleic acid, Eicosapentaenoic acid, α-Linolenic acid, Arachidonic acid), lipid-derived mediators (11,12-Epoxyeicosatrienoic acid ((±)11(12)-EET)), steroid derivatives (Ergosterol peroxide), lipophilic metabolite (Fucoxanthin), and lipid-soluble vitamins (all-trans-retinol). Principle component analysis (PCA) revealed that TPC, not TFC, in the UAE extracts was correlated with the anti-oxidant activities and cytotoxicity of the extracts towards B16-F10 melanoma cells. This means other non-flavonoid phenolic and lipophilic compounds may have contributed to its bioactivity. These results suggest that out of the two methods investigated, UAE could be a chosen method to extract natural anti-melanogenic agents from brown algae.

In some cases, the immune system in COVID-19 patients leads to the release of excess cytokine production (cytokine storm), which will potentially develop into pneumonia. Interleukin 6 (IL-6) plays the role of pro-inflammatory cytokine, it is a receptor mediated signalling system. Macroalgae is well known as a source of valuable bioactive substances with potential biological activities. Among them is the sulphated polysaccharide lambda-carrageenan λ-CGN which has been reported as an anti-inflammatory agent. However, its mechanism of action against IL-6 production is currently unknown. This study aims to predict potential molecular mechanisms of λ-CGN chemical compound against IL-6 expression through in silico study. Chemical compound of λ-CGN and target protein in this study were obtained from the pubchem and protein data bank (PDB). The molecular docking prediction was conducted with PyRx software, the result is λ-CGN compound showing strong binding energy to bind target protein IL-6 receptor with the value of -5.9 kcal/mol. Based on the results of in silico study, the sulphated polysaccharide λ-CGN potentially inhibits IL-6R expression by binding ligand pocket with six conventional hydrogen bonds (amino acid residus: His256, His 257, Trp 219, Arg 231, and Asp 221) and two carbon hydrogen bonds (amino acid residus: THR 218 and GLN 220). Binding with these amino acid residues potentially contributes to IL-6 receptor structural change which could result in functional change. Hence, further studies related to in vitro and in vivo investigations would be interesting to further understand the inhibitory mechanism of λ-CGN against IL-6.