Isolation and bioactivity screening of soy isoflavones from soybean glycolipids identifies daidzin as a promising anti-inflammatory agent.

Background: Soybean has long been utilized in the realm of traditional Chinese medicine. One of its extracts, soybean glycolipids, serves as a vital by-product of soybean oil refining, but its chemical composition and pharmacological potential have yet to be fully elucidated. Methods: In this study, the chemical components were isolated, and the inhibitory effects of these isolates were explored in different zebrafish inflammatory models by survival rate, Histological examination assay and quantitative Real-time PCR assay. The cytotoxicity of daidzin in RAW264.7 cells was evaluated by cell viability assay, and the effect of daidzin on the release of inflammatory cytokines in RAW264.7 cells was detected by enzyme linked immunosorbent assay (ELISA). Western blotting, immunofluorescence assay and alpha7 nicotinic acetylcholine receptors siRNA transfection assay were used to further explore the anti-inflammatory mechanism of daidzin. Results: Four compounds (verticilloside, soya-cerebroside I, soya-cerebroside II and daidzin) were firstly isolated from the soybean glycolipids, among which verticilloside and daidzin inhibited the lipopolysaccharide, CuSO4- and tail cut-stimulated zebrafish inflammation. Noticeably, daidzin exhibited anti-inflammatory activities by increasing the survival rate, alleviating the inflammatory cells infiltration, and down-regulating the expression of pro-inflammatory cytokines and nuclear factor kappa-B, NF-kappa-B inhibitor alpha, and signal transducer and activator of transcription3 in zebrafish. Moreover, daidzin decreased the secretion of IL-6 and TNF-α, inhibited the nuclear translocations of nuclear factor kappa-B p65 and p-signal transducer and activator of transcription3 as well as the NF-kappa-B inhibitor alpha phosphorylation at Ser32 in RAW 264.7 cells. More importantly, it elevated the expression level of alpha7 nicotinic acetylcholine receptors in both zebrafish and RAW 264.7 cells, and the inhibitory effect of daidzin was attenuated after the addition of alpha7 nicotinic acetylcholine receptors siRNA. Conclusion: Our study revealed that daidzin inhibited inflammation by activating the cholinergic anti-inflammatory pathway and further inhibiting the nuclear factor kappa-B and signal transducer and activator of transcription3 signaling. At the same time, it also promotes the recycling of crude soybean glycolipids and supports the potential use of daidzin as a functional food or natural dietary anti-inflammatory agent. [ABSTRACT FROM AUTHOR]