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Complement system inhibitor constituents of the dichloromethane extract from leaves of Acalypha guatemalensis
Acalypha guatemalensis Pax & Hoffm. (Euphorbiaceae), a plant native from Guatemala and Honduras, is used in folk medicine to treat protozoal infections, gastrointestinal and venereal diseases, rheumatism, cancer and for several other purposes . In a previous work, the dichloromethane extract from dried leaves showed an inhibitory effect on classical pathway of the complement system by in vitro assays . The aim of the present investigation is the characterization of its active fractions and/or constituents. Powdered dried leaves were submitted to extraction with increasing polarity solvents: hexane and dichloromethane. The active extract was submitted to a bioassay-guided fractionation through silica gel CC eluted with a gradient of CH2Cl2:MeOH (99:1 to 60:40), affording twelve fractions. Their activity on classical complement pathway was determined in human serum by hemolytic assay, using quercetin as positive control [3,4]. The active fractions: AGD-II, AGD-V, AGD-VIII and AGD-XII (IC50=5.83, 2.39, 4.15 and 4.73µg/mL, respectively), were successively fractionated through silica gel and SephadexR LH-20 CC, giving mixtures of free sterols and their acetates. Their structures were elucidated by standard spectroscopic techniques and by comparison with literature data. Phytosterols, particularly sitosterol, stigmasterol and campesterol, have been previously described as potent inhibitors of the complement system [5–7], which plays an important role in host defence, inflammation or allergic reactions.
Acknowledgements: S. Sciotto to Fondazione Antonio Imbesi, Universitá degli Studi di Messina, Messina, Italy.
References: 1. Cáceres, A. (2009) Vademecum Nacional de Plantas Medicinales. Editorial Universitaria, Universidad de San Carlos de Guatemala. Guatemala.
2. Risco, E. et al. (2002) 50th Annual Congress of the Society for Medicinal Plant Research, Barcelona, Spain.
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