Antioxidant and selective anticancer activities of two Euphorbia species in human acute myeloid leukemia

Abstract

In this study, two Euphorbia species (i.e. terracina and paralias) were investigated for their cytotoxic and antioxidant activities. Cytotoxicity of plant methanol and chloroform fractions was examined towards human acute myeloid leukemia (THP1) and human colon epithelial (Caco2) cancer cell lines, as well as CD 14 and IEC-6 normal cells by targeting various modulators of apoptosis or inflammation. Moreover, secondary metabolite pools (phenolic classes, alkaloids, terpenes, saponins) and antioxidant activities (DPPH, ABTS and O₂- scavenging, as well as FRAP tests) were assessed in plant extracts. Both Euphorbia species appeared to be rich in phenolic compounds and terpenoids, Moreover, E. terracina polar and apolar fractions and E. paralias polar fraction were highly active against THP1 cells, with IC₅₀ values of 2.08, 14.43 and 54.58μg/mL, respectively. However, no cytotoxicity was found against normal cells (CD14⁺ monocytes). The results indicate that the three fractions induce apoptosis in THP1 cell line after 6h of exposure. Furthermore, apoptosis caused by apolar fraction was related to a caspase-dependent process, whereas other death pathways seemed to be involved with the polar fractions. An enhanced production of reactive oxygen species was detected upon cell treatment with plant extracts. Interestingly, they have no effect on cytokine TNF-α secretion in THP1 and normal cells compared to untreated cells, indicating that the three fractions caused no inflammation. Euphorbia terracina and E. paralias polar fractions showed strong antioxidant activity with potent scavenging capacity against DPPH, ABTS and superoxide radicals. Moreover, these fractions displayed a very high ferric reducing power. These findings confirm the strong antioxidant capacity of Euphorbia plants and suggest a targeted anti-cancer effect with a potent anti-proliferative property of E. terracina and E. paralias extracts, which induce programmed cell death in leukemia cell lines but not in normal monocytes cells.

Keywords: Antioxidants; Apoptosis; E. paralias; E. terracina; In vitro cytotoxicity; Inflammatory; Leukemia.