Antioxidant and cytotoxic activity of bioactive phenolic metabolites isolated from the yeast-extract treated cell culture of apple

Abstract

Apples are well known for their high nutritional value and health-protective properties. In this study, cell suspension cultures of apple (Malus domestica ‘florina’) were established and maintained in liquid Linsmaier and Skoog (LS) medium supplemented with 2 µM 2,4-dichlorophenoxyacetic acid (2,4-D) and 1 µM naphthaleneacetic acid (NAA). Elicitation of plant cell culture is a promising strategy to enhance and extend production of bioactive metabolites. Apple cell suspension culture in the linear growth phase was treated with yeast-extract elicitor and its effect on the antioxidant properties and accumulation of bioactive phenolic metabolites were characterized. Upon elicitor treatment, the total phenolics and flavonoids were significantly enhanced, preceded by the enhancement of the activity of phenylalanine ammonia lyase (PAL) enzyme. Methanolic extract from the elicited cell culture were analyzed by high performance liquid chromatography (HPLC) for the detection and quantification free phenolic acid and flavonoid. Predominant phenolics detected in the soluble fraction were protocatecuic acid, catechin, chlorogenic acid, vanillic acid, 4-coumaric acid, ferulic acid, benzoic acid and rutin. Out of these phenolics, the content of chlorogenic acid (112 µg/g DW), 4-coumaric acid (122 µg/g DW) ferulic acid (212 µg/g DW), benzoic acid (244 µg/g DW) and rutin (348 µg/g DW) were significantly enhanced upon elicitation. In addition, 1, 1-diphenyl-2-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP) radical scavenging activity was significantly enhanced upon yeast extract treatment, and this was positively correlated with increased accumulation of phenolic metabolites. Finally, cytotoxic effect of elicited cell culture extract was evaluated against human cervical (HeLa cells) and breast (MCF-7 cells) cancer cell lines using MTT assay. Elicited extract exhibited significant apoptosis mediated cell death in both breast (IC50: 31 µg/ml) and cervical (IC50: 38 µg/ml) cancer cell lines. No growth inhibition was observed in normal human embryonic kidney cell line (HEK-293). Our results indicated that yeast-extract treated cell culture of apple provides an promising system for sustainable production of natural antioxidants and anticancer therapeutics.