An extract from Lactuca indica showed significant free radical scavenging activity, and protected phix174 supercoiled DNA against strand cleavage and reduced oxidative stress in human promyelocytic leukemia HL-60 cells. On account of protocatechulic acid, methyl p-hydroxybenzoate, caffeic acid, 3,5-dicaffeoylquinic acid, luteolin 7-O-p-glucopyranoside, and quercetin 3-O-p-glucopyranoside are the major antioxidative constituents (111).
Note that luteolin, a naturally occurring flavonoid, induces apoptosis in various cancer cell lines through death receptor (DR) 5 upregulation. Luteolin induced the expression of DR5, along with Bcl-2-interacting domain cleavage and the activation of caspase-8, -10, -9, and -3. In addition, suppression of DR5 expression with siRNA efficiently limited luteolin-induced caspase activation and apoptosis. Human recombinant DR5/Fc also abrogated luteolin-induced apoptosis (112).
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