Photodynamic apoptosis and antioxidant activities of Brassica napus extracts in U937 and SK-HEP-1 cells

Brassica napus is the most common feedstock for biodiesel production, and its cultivation area has been rapidly increased. Thus, B. napus residues left in the field after harvest are valuable resources. However, there have been few studies on biologically active substances from B. napus plant. The objective of this study is to evaluate cytotoxicity/photodynamic activity and antioxidant activity of B. napus plant extracts. B. napus plants were sequentially extracted with organic solvents (hexane, chloroform, ethanol, and water) and then screened for antioxidant activity and cytotoxicity against leukemia U937 and human liver cancer SK-HEP-1 cells. Among the solvent extracts, the cytotoxicity was the highest when cells treated with chloroform extract and irradiated. Degree of apoptosis substantially increased in both cell types in concentration-dependent manner, and non-irradiated cells showed similar results as the control cells. For the highest concentrations (100 μg/ml), toxicity effect in U937 and SK-HEP-1 cells was 94.62 ± 0.15% and 74.16 ± 1.54%, respectively. We observed the number of cells significantly decreased, and vesicles were floating in B. napus chloroform extract (BNCE) and light condition. BNCE induced DNA laddering pattern (between 300 and 1000 bp) and caspase-3/7 activation in both U937 and SK-HEP-1 cells. Total apoptotic U937 and SK-HEP-1 cells following BNCE 100 μg/ml and light treatment were significantly increased (92.62 ± 2.07% and 59.71 ± 4.38%, respectively) compared with control. Our results showed that U937 cells were more sensitive than SK-HEP-1 cells. For the antioxidant activity, B. napus ethanol extract was the highest (IC50 = 0.52 mg/ml).