Inhibitory effect of daylily buds at various stages of maturity on nitric oxide production and the involved phenolic compounds

The objective of this study was to investigate the antioxidant activity and anti-inflammatory ability of daylily buds during their various developmental stages, from green (stage 1) to ripe maturity (stage 4). Thus, the nitric oxide (NO) scavenging effects of the bud extract in sodium nitroprusside (SNP) system and the inhibitory effects on NO production in RAW 264.7 macrophages were determined. The highest total antioxidant activity was observed at stage 1, along with the highest content of total phenolics and flavonoids. Nevertheless, the NO scavenging activity of bud extracts increased from stage 1 to its maximum at stage 4; the data indicated that rutin might be the vital compound that was responsible for this activity. In the macrophage model system, the inhibitory effect of bud extracts on NO production was concentration-dependent. The strongest NO-suppressing activity was observed at stage 1 and decreased with advancing maturity as buds were extracted at a concentration of 400 μg/mL. Flavan-3-ol EGCG and (-)-epicatechin might be the primary active constituents in the extracts that inhibited NO production in lipopolysaccharide (LPS)-activated cells. Daylily buds are an effective NO scavenger and suppressor that may be favorable for the alleviation of inflammatory conditions and beneficial for human health.