Radical-Scavenging Activity, Cytotoxicity and Chemical Constituents of Euphorbia orthoclada from Madagascar

Jeanne      Eliane R. Lantovololona; Ferdinand      Mouafo Talontsi; Lygie      Randriambola; Hartmut      Laatsch

Abstract

Aim of the study: This work was targeted to investigate the cytotoxic and antioxidant constituents of Euphorbia orthoclada leaves, traditionally used for treating kidney stones, abscesses, osteomyelitis, dysentery, and asthma as well as bacillary and other infectious diseases.

Methods: E. orthoclada leaves were extracted with methanol and the methanol phase was partitioned between cyclohexane. The ethyl acetate soluble fraction of the methanol extract was successively separated on silica gel and Sephadex LH-20 and the fractions were analysed by HPLC-UV-ESIMS and screened for cytotoxicity and antioxidant properties. The isolated compounds were elucidated by diverse spectroscopic and spectrometric methods.The cytotoxicity of fractions and pure compounds was evaluated using brine shrimp larvae (Artemia salina), while the antioxidant activity was determined by the DPPH radical-scavenging method.

Results: Both cyclohexane and ethyl acetate fractions were toxic against brine shrimp larvae (Artemia salina) at a concentration of 10 μg/mL with mortality rates of 62% and 70%, respectively; however, the ethyl acetate extract proved to have the most effective antioxidant activity with an EC50 value of 3.45 ± 0.01 μg/mL. Five phenolic compounds 1-5 were isolated from the EtOAc extract by successive chromatographic procedures (silica gel, Sephadex LH-20). Among them, quercetin-3-O-α-D-arabinoside (2) (28.5 ± 0.11 μg/mL), kaempferol-3-O-β-D-glucoside (4) (37.2 ± 0.17 μg/mL), kaempferol-3-O-α-D-arabinoside (3) (38.4 ± 0.13 μg/mL) and gallic acid (1) (55.22 ± 0.15 μg/mL) displayed the highest antioxidant activity, while 3,3',4'-trimethylellagic acid 4-O-glucoside (5) (63.90 ± 0.09 μg/mL) was more toxic than the other constituents on brine shrimp larvae when tested at 10 μg/mL (mortality rate of 65 %).

Conclusion: The medicinal plant Euphorbia orthoclada - namely its chemical constituents - has been investigated for the first time in this project. The cytotoxic and antioxidant properties of the pure secondary metabolites explain the use of this plant in traditional medicine. Moreover, the isolation of compounds 2, 3 and 4 from E. orthoclada emphasizes that these metabolites may be considered as chemotaxonomic markers of the genus Euphorbia.

Keywords: Euphorbia orthoclada, phenolic constituents, cytotoxicity, antioxidants, medicinal plant