Anti-inflammatory effects of cowpea (Vigna sinensis K.) seed extracts and its bioactive compounds

Abstract

Anti-inflammatory effects of methanol extract and solvent fractions of cowpea (Vigna sinensis K.; VS) seeds and the isolated compounds were evaluated. Ethyl acetate and n-butanol fractions of VS seeds were found to strongly inhibit nitric oxide (NO) production, and inducible nitric oxide synthase (iNOS) mRNA and protein expressions in lipopolysaccharides (LPS)-stimulated RAW264.7 macrophage cells. Compounds inhibiting NO production in RAW264.7 cells were isolated and identified via successive partitioning and spectroscopic characterization. The active compounds included oleanolic acid, linolenic acid (LnA), linoleic acid (LA), 7-ketositosterol, stigmasterol-glucose (glc), and soyasaponin 1. Among the isolated compounds, LnA and LA were found to inhibit NO production significantly. Contents of LnA and LA in VS seeds were 2.034 and 1.162 mg/g on dry weight basis, respectively. Reverse transcriptase-polymerase chain reaction (RTPCR) and Western blot analysis show inhibitory effects of these compounds. LnA and LA repressed mRNA and protein levels of iNOS in LPS-stimulated cells. LA suppressed the production of pro-inflammatory cytokines such as interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α in LPS-induced macrophage cells. Thus, VS was found to exhibit strong antiinflammatory activity, which may be partly attributed to the polyunsaturated fatty acids such as LnA and LA.