Valorization of the underutilized freshwater green alga Spirogyra sp.: ethyl gallate as a bioactive anti-inflammatory compound

Ethyl gallate (EG), a phenolic ester derivative of gallic acid previously identified from the freshwater green alga Spirogyra sp., was investigated in this study as a bioactive constituent contributing to the anti-inflammatory potential of this underutilized algal resource. The anti-inflammatory activity of EG was systematically evaluated using both in vitro and in vivo models. In lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophages, EG significantly suppressed nitric oxide (NO) production without inducing cytotoxicity at concentrations ranging from 6.25 to 25 μM. In addition, EG markedly reduced the secretion of major pro-inflammatory mediators, including prostaglandin E2 (PGE2), tumor necrosis factor-α (TNF-α), interleukin (IL)-6, and IL-1β. Mechanistic investigations revealed that EG downregulated the expression of inducible nitric oxide synthase and cyclooxygenase-2, accompanied by inhibition of IκBα phosphorylation and nuclear translocation of nuclear factor-κB (NF-κB) p65 and p50 subunits, indicating suppression of NF-κB signaling. In the zebrafish larvae model, the in vivo results supported protective effects of EG against LPSassociated oxidative and inflammatory phenotypes, where EG significantly improved survival rates and attenuated inflammation-associated markers, including NO accumulation and cellular damage. Collectively, these findings suggest the potential of Spirogyra sp. as a source of anti-inflammatory constituents, while the quantitative contribution of EG to the overall bioactivity of the crude extract requires further validation.