Dual Stimulus-Dependent Effect of Oenothera paradoxa Extract on the Respiratory Burst in Human Leukocytes: Suppressing for Escherichia coli and Phorbol Myristate Acetate and Stimulating for Formyl-Methionyl-Leucyl-Phenylalanine

Although a growing body of evidence suggests that plant polyphenols can modulate human immune responses, their simultaneous action on monocyte and neutrophil oxidative burst is currently poorly understood. Based on the hypothesis that various polyphenols contained in plant extracts might affect the oxidative burst of phagocytes, we evaluated the effects of ethanolicO. paradoxaextract polyphenols on monocyte and neutrophil oxidative burstin vitroactivated by different stimuli, including opsonized bacteriaE. coli, phorbol 12-myristate 13-acetate (PMA), and formyl-methionyl-leucyl-phenylalanine (fMLP). Samples were analyzed by the dihydrorhodamine flow cytometry assay. Our results showed that the extract repressed significantly and dose-dependently reactive oxygen species production in both cell types stimulated withE. coliand PMA (P< 0.05) and its inhibitory efficiency was stimulus- and cell-type-dependent. Interestingly, there was significant stimulatory effect of the extract on bursting phagocytes induced by fMLP (P< 0.05). Additionally, several flavonoids and phenolic compounds as well as penta-galloyl-β-(D)-glucose (PGG), the representative of hydrolyzable tannins, were identified in the 60% extract by high-performance liquid chromatography (HPLC) coupled to electrospray ionization in negative ion mode. In summary, the ethanolicO. paradoxaextract, rich in flavonoids and phenolic compounds, exhibits dual stimulus-dependent effect on the respiratory burst in human leukocytes; hence, it might affect immune responses in humans.