Pectolinarigenin from the leaves of Clerodendrum volubile shows potent immunomodulatory activity by inhibiting T − cell proliferation and modulating respiratory oxidative burst in phagocytes

There have been increasing interest in the use of plant-derived substance as immunomodulators for the treatment and management of inflammatory ailments. Clerodendrum volubile, a leafy vegetable is known for its folkloric applications in the treatments of several inflammatory related ailments, but with little scientific evidence. This study reports the isolation, structure elucidation and in vitro immunomodulatory potentials of pectolinarigenin from C. volubile leaves. The immunomodulatory potentials of the crude methanolic extract and fractions [n-hexane (Hex), dichloromethane (DCM), ethyl acetate (EtOAc) and n − butanol (BuOH)] were investigated on whole blood, neutrophil and macrophage phagocytic respiratory burst using luminol-amplified chemiluminescence technique. DCM fraction showed higher inhibitory activity on respiratory burst, indicating high suppressive immunomodulatory potency. The DCM fraction was further fractionated using a gravity column chromatography loaded with silica gel. The column was eluted with mixtures of Hex and DCM (92.5:7.5) in increasing order of polarity up to Hex: DCM (88:12) to afford 5,7-Dihydroxy-6,4′-dimethoxyflavone (pectolinarigenin). The structure of the compound was established using data obtained from ¹H- and ¹³C NMR spectroscopies and mass spectrometry. The isolated flavone was investigated for its inhibitory activity of neutrophil phagocytes respiratory burst as well as T − Cell proliferation. The compound exhibited significant activities (at p < 0.05) indicating high suppressive immunomodulatory potency. The potent suppressive effect of pectolinarigenin on polymorphonuclear neutrophils (PMNs) respiratory oxidative burst and T − cell proliferation suggests an immunomodulatory potential and pathway of the flavonoid.