Anti-complementary Constituents Of Giant Knotweed Rhizome

The complement system is essential for host defence and involved in various pathological and physiological processes. An intact complement cascade is required for protection against infection and for maintaining the well-being of the body. However, excessive or improper complement activation has led to a number of serious diseases such as systemic lupus erythematosus (SLE), rheumatoid arthritis, ischemia-reperfusion (I/R), septic shock, various renal diseases and acute respiratory distress syndrome (ARDS) et al. Based on the research, severe acute respiratory syndrome (SARS) and bird flu are also related to the excessive activation of the complement system. Effective and specific inhibitors with low toxicity are in great need in clinical for there is no ideal drug for the remedy of these diseases. Previous studies indicated that numerous traditional Chinese medicine (TCM) especially the heat-clearing and detoxifying drugs commonly possessed anti-complement activity. It is vital to develop the natural occurring inhibitors with high efficacy and low toxicity for the cure of these diseases. In this study, through screening of several TCM, Polygonum cuspidatum was selected as the target for the research of ant-complement agents. Anthraquinones, naphthaquinones and stibenes were isolated guided by anti-complement activity and all isolates were evaluated for their in vitro anti-complementary activities both on classical pathway and alternative pathway. Preliminary inhibitory mechanisms of the important constituents were also examined. The results are as follows:1. Anti-complementary P. cuspidatum and the active fraction of this plantThrough the hemolysis tests, P. cuspidatum showed strong anti-complement activity with CH50values of10±4μg/ml. Then, P. cuspidatum was fractioned with petroleum ether, ethyl acetate and n-butanol. The anti-complement test of all extract showed that the ethyl acetate and n-butanol extract possessed strong activity with CH50level of10μg/ml. So these two extract was chosen as the target fraction.2. Anti-complement activity-directed isolation of the EtOAc extract and the structure elucidation of the isolatesThrough anti-complement activity-directed isolation,21compounds were isolated from the the EtOAc and the n-butanol extract of P. cuspidatum including10anthraquinones:physcion (7), chrysophanol (8), questin (9), emodin-8-O-β-D-glucoside (10), emodin (11), rhein (12), fallacinol (13), citreorosein (14), xanthorin (15), and isorhodoptilometrin (16);6naphthoquinones:6-acetyl-5,8-dihydroxy-2-methoxy-7-methylnaphthalene-1,4-dione (1),6-acetyl-2-ethoxy-5-hydroxy-7-methylnaphthalene-1,4-dione (2), cuspidatumin C (3),3-acetyl-5-hydroxy-7-methoxy-2-methynaphthalene-1,4-dione (4),6-acetyl-5-hydroxy-2-methoxy-7-methylnaphthalene-1,4-dione (5), and torachrysone-8-O-D-glucoside (6);2stilbenes:resverotrol (17) and peceid (18);3other small molecular compounds:2,5-dimethyl-7-hydroxychromone (19),7-hydroxy-4-methoxy-5-methylcoumarin (20), and5,7-dihydroxy-l-isobenzofuranone (21). Among which compounds1,2, and3were new compounds,15and16were isolated from P. cuspidatum for the first time, and15was the first alizarin-type anthraquinone obtained from this plant.3. Anti-complement test and the targets of main compoundsThrough in-vitro hemolysis test, the isolated anthraquinones, naphthoquinones, and stilbenes were evaluated for their anti-complementary activities on the classical pathway and alternative pathway. The results showed that seven anthraquinones, cuspidatumin C, and two stilbenes possessed anti-complementary activity in different degrees with CH50values of5～50Oμg/ml and AP50values of50～800μg/ml, respectively. Fallacinol exhibited the most potent activity against the classical and alternative pathway (CH50=6±2μg/mL, AP50=50±5μg/mL) and it is a potential natural occurrence complement inhibitor for the cure of diseases related with excessive complement activation.In order to reveal the mechanism of active compounds acting to the complement system, this study selected fallacinol, emodin-8-O-β-D-glucoside, cuspidatumin C, resverotrol, and peceid as the target compounds. The preliminary mechanism study revealed that fallacinol acted on Clq, C2, C4and C9; emodin-8-O-β-D-glucoside interacted with C1q, C2and C9in complement activation cascade; cuspidatumin C selectively acted on Clq, C2, C3, and C9components in the complement activation cascade; resverotrol interacted with C2and C3, peceid blocked Clq, C2, and C9components of the complement system.