Anti-complementary activity of flavonoids from Gnaphalium affine D. Don

Abstract

Gnaphalium affine D. Don, is used as a vegetable as well as a folk medicine in China for its anti-inflammatory, antitussive, and expectorant activities. Phytochemical investigation of the ethyl acetate (EtOAc) fraction of this plant led to isolation of three new acylated flavonol glycosides, apigenin 4′-O-β-d-(6″-E-caffeoyl)-glucopyranoside, luteolin 4′-O-β-d-(6″-E-caffeoyl)-glucopyranoside, and quercetin 4′-O-β-d-(6″-E-caffeoyl)-glucopyranoside, together with 24 known compounds. The structures of these compounds were determined by spectroscopic methods. All compounds were evaluated for their anti-complementary activity on the classical pathway of the complement system in vitro, and luteolin 4′-O-β-d-(6″-E-caffeoyl)-glucopyranoside exhibited highest anti-complementary activity with an IC₅₀ value of 0.045 ± 0.005 mg/ml. This is the first report of anti-complementary activity of G. affine D. Don, which displays the initial evidence that this plant is a potent complement inhibitor.

Introduction

The genus Gnaphalium belongs to the family Compositae and comprises approximately 200 species all over the world, among which 19 grow in China (Qian & Chen, 1959). Some species in this genus have been used in folk medicine in Mexico for the treatment of various respiratory diseases (Gabriela, Juan, Jaime, & Victor, 2001). In addition, plants from the genus Gnaphalium are traditionally used for the relief of stomach diseases, swellings, wounds, prostatism, lumbago, neuritis, and angina ache, for the lowering of blood pressure, or as diuretic, antipyretic, and antimalarial in some Latin American countries (Patricia et al., 2005). Phytochemical investigations of the genus revealed the presence of flavonoids and diterpenes as major constituents (Meragelmana et al., 2003, Torrenegra et al., 1992), although acetylenes and carotenoids have also been isolated (Bohlmann & Ziesche, 1980).

Gnaphalium affine D. Don, is an annual herbaceous plant and widely distributed in many regions of China and Japan. G. affine is traditionally used as a wild vegetable in Guangdong and Fujian provinces, China (Guan et al., 2000, Li and Liu, 1999), as well as a folk medicine for its anti-inflammatory, antitussive, and expectorant activities (Yu, Du, Zhang, & Yao, 2006). Meanwhile, the aqueous extract of G. affine possessed inhibitory effects on normal pathogenic bacteria (Pan, 2006). Ethyl acetate and n-butanol fractions obtained from the hydroalcoholic extract of G. affine exert inhibition on aldose reductase (Li, Chang, Li, & Tu, 2004). Moreover, G. affine is well known in Japan for its antifeedant property (Morimoto et al., 2000, Morimoto et al., 2003). Papers from as early as the 1960s reported the isolation of flavonoids from G. affine (Aritomi and Kawasaki, 1974, Aritomi et al., 1964).

The complement system is an essential component of innate immunity and also plays an important role in modulating adaptive immunity (Zhu, Di, Zhang, Zhang, & Chen, 2009). It comprises more than 30 plasma and membrane-bound proteins and can be activated through three pathways: the classical, the alternative and the lectin pathways. Its activation contributes to the pathogenesis of several autoimmune and inflammatory conditions (Valeriya et al., 2011, Ballanti et al., 2011). Following complement activation, proinflammatory peptides like the anaphylatoxins C3a and C5a are generated and the membrane attack complex, C5b–9, is formed. Complement activation products, especially the anaphylatoxins, elicit a number of biological effects such as chemotaxis of leukocytes, degranulation of phagocytic cells, mast cells and basophils, smooth muscle contraction and the increase of vascular permeability (Hugli, 1986). In addition, generation of toxic oxygen radicals and the induction of synthesis and release of arachidonic acid metabolites and cytokines lead to the amplification of the inflammatory response (Chen et al., 2010, Michael, 1997). Therefore, the ability to modulate complement activity would clearly be beneficial in the therapy of inflammatory diseases. Data published revealed that many kinds of flavonoids have shown strong anti-complementary activity (Keun Young et al., 1998, Si-Hyung et al., 1999). It has been reported that flavonoids from different sources have different anti-complementary activities in vitro, depending on their structural features. The aim of the present study was to evaluate the anti-complementary activity of flavonoids from EtOAc fractions of G. affine on the classical pathway.