Antioxidant, antitumor, and anti-inflammatory activity of natural products obtained from the brown alga Cystoseira usneoides

Abstract

Macroalgae are an inexhaustible source of natural products that display a variety of pharmacological and biological activities. Among marine algae, the genus Cystoseira has proven to produce a wide variety of secondary metabolites that could benefit human health. However, studies on the natural products of the species Cystoseira usneoides and their respective biological properties are scarce. Hence, in this thesis, the extract of the brown alga Cystoseira usneoides and the natural products isolated therefrom were tested for antioxidant, anticancer, and antiinflammatory activities. The extract of C. usneoides exhibited potent radical-scavenging and inhibited the proliferation of HT-29 cancer cells by inducing apoptotis and G2/M arrest of the cell cycle. The extract was also found to inhibit the production of TNF-α in LPS-stimulated THP-1 human macrophages. The chemical study of the extract yielded six known algal meroterpenoids (AMTs): usneoidone Z (1), 11-hydroxy-1´-O-methylamentadione (2), cystomexicone B (3), cystomexicone A (4), 6-cis-amentadione-1′-methyl ether (5), and amentadione-1′-methyl ether (6), together with six new compounds: cystodiones A-F (7-12). AMTs 1-10 showed radical-scavenging activity in the ABTS assay. The most active were compounds 5, 6, 7, and 8, which exhibited antioxidant capacity equal or superior to that of the Trolox standard. AMTs 1-8 displayed significant cytotoxic activity against HT-29 human colon cancer cells, whereas lower cytotoxicity was observed against non-tumor cells CCD 841 CoN. Flow cytometry analysis revealed that AMTs 2, 3, and 5 caused apoptosis in HT-29 cells and compounds 1, 2, 3, 4, 5, and 7 induced cell cycle arrest in G2/M phase. Furthermore, AMTs 1-8 also inhibited the migration and invasion of colon cancer cells. Interestingly, exposure of HT-29 cells to different concentrations of AMTs 1-8 correlated with the down-regulation of p-ERK, p-JNK, and p-AKT pathways. Regarding to the anticancer effect of AMTs 1-8 against A549 human lung cancer cells, the cytotoxicity of all compounds was selective for A549 cells when compared to the non-tumor MRC-5 cells. Moreover, treatment of A549 cancer cells with AMTs 1-8 also led to cell cycle arrest in S and G2/M phases. In the in vitro anti-inflammatory assays, AMTs 1-8 showed significant activity as inhibitors of the production of the pro-inflammatory mediators TNF-α, IL-1β, IL-6, COX-2 and iNOS in LPSstimulated THP-1 human macrophages. The in vivo study clearly demonstrated that the compound 11-hydroxy-1´-O-methylamentadione (AMT-E, 2) significantly ameliorated DSS colitis (seven days), including the reduction of weight loss, disease activity, macroscopic and microscopic colonic injury. The levels of TNF-α, IL-1β, IL-10, COX-2 and iNOS expression were also significantly decreased in AMT-E treated DSS colitis. Taken together, these findings strengthen the potential of the natural products isolated from C. usneoides as leads for novel antioxidant, anticancer, and anti-inflammatory agents.