The anti-inflammatory potential of protein-bound anthocyanin compounds from purple sweet potato in LPS-induced RAW264.7 macrophages

Interaction between proteins and anthocyanins spontaneously occurs in most of food systems, resulting the formation of protein-bound anthocyanin compounds, and the interactions between anthocyanins and proteins might impact activity of anthocyanins. In the present study, predominant anthocyanin compounds in free anthocyanin compounds from purple sweet potato (FAC-PSP) were identified and protein in protein-bound anthocyanin compounds from purple sweet potato (p-BAC-PSP) were assayed. Furthermore, the effects of pretreatment of cells with p-BAC-PSP and FAC-PSP on cell viability, inflammatory mediators, reactive oxygen species, cytokines and gene expression were determined in LPS-induced RAW264.7 macrophages. The results revealed 17 protein groups and pigmented polymers in p-BAC-PSP, and 3 different anthocyanins in FAC-PSP. There were no significant differences (p > 0.05) in the anti-inflammatory effect between p-BAC-PSP and FAC-PSP. p-BAC-PSP significantly (p < 0.05) reduced the expression of inducible nitric oxide synthases (iNOS) and tumor necrosis factor-alpha (TNF-alpha) in RAW264.7 cells stimulated by LPS, thereby suppressing the release of NO and TNF-alpha. Moreover, p-BAC-PSP markedly inhibited LPS-induced reactive oxygen species (ROS) accumulation via heme oxygenase-1 (HO-1) and factor erythroid 2-related factor 2 (Nrf2). Further analysis revealed that p-BAC-PSP suppressed both LPS-induced activation of c-Jun N-terminal kinase (JNK), and the nuclear translocation of activator protein-1 (AP-1). Our research suggested that naturally occurring p-BAC-PSP has the potential to be a dietary supplement with anti-inflammatory effect, which would meaningful from the actual utilization points of view for purple sweet potato production industry.