Elicitation of Hypericum perforatum cells with Agrobacterium tumefaciens induces production of bioactive phytochemicals that afford protection against oxidative stress induced in human HepG2 cells

Hypericum perforatum (HP) commonly known as St. John’s wort is an important medicinal plant traditionally used in several ailments including mild to moderate depression. In a recent study, elicitation of HP cells (culture of cells in suspension) with Agrobacterium tumefaciens (AT) increased significantly the production of compounds with antioxidant and antimicrobial properties [1]. The ability of methanolic extracts of elicited and control HP cells to protect human hepatocytes (HepG2 cell line) against oxidative stress were here investigated. When HepG2 cells were co-incubated with HP extracts (80μg/ml) and 800μM tert-butyl hydroperoxide (tert-BOOH), only the HP extract from elicited cells significantly protected against cell death and DNA damage, as measured by the MTT and comet assay, respectively. The same was observed when the extracts were pre-incubated for 5h with HP extracts, followed by a period of 16 h of recovery with fresh medium, prior to incubation with tert-BOOH. This suggested the ability of HP extract from elicited cells to induce intracellular antioxidant defenses in HepG2 cells. That was confirmed by the induction of about 40% in the content of glutathione in HepG2 cells, whereas control extract increased only 10%. As well, only the extract from elicited HP cells were able to induce the levels of cytoprotective enzymes such as HO-1 and NQO1. In conclusion, we observed that elicitation of HP cells with AT produced bioactive compounds present in the methanolic extract able to protect HepG2 cells against oxidative stress, and also to induce intracellular antioxidant defenses of this human cell line