Protection of human HepG2 cells against oxidative stress by a methanolic extract of Hypericum perforatum elicited with Agrobacterium tumefaciens

Hypericum perforatum L. (HP), commonly known as St. John wort, is widely used in traditional medicine to treat several medical conditions including anxiety, depression, cuts, and burns [1]. Recent research showed its antioxidant and neuroprotective effects [2]. The pharmacological properties attributed to this plant may be explained by its wide variety of biologically active metabolites, including xanthones [3]. Recently, we have shown that HP cell suspension cultures elicited by co-cultivation with Agrobacterium tumefaciens (AT) increased the biosynthesis of existing xanthones, but also resulted in de novo production of new xanthones [4]. In the present work, we evaluated the ability of a methanolic extract of HP cells (control HP) and of HP cells elicited with AT (elicited HP) to protect against oxidative stress induced in HepG2 cells. The elicited HP extract, contrary to control HP, significantly inhibited tert-butyl hydroperoxide-induced cell death, GSH depletion and DNA damage, in pre- and co-incubation regimes. The extracts alone were not cytotoxic or genotoxic. As well, incubation of HepG2 cells with the extract from elicited HP cells significantly induced GSH levels and several cytoprotective enzymes, including HO-1, PRDX4, GCL, and NQO1, whereas the extract of control HP did not. These effects were associated with an increase of Nrf2 levels in the nucleus, which may explain the cytoprotective action of the elicited HP extract in the pre-incubation regime. In conclusion, these results suggest that elicitation of HP cells with AT is an interesting biotechnological approach for the production of pharmacologically active compounds.

Acknowledgements:This work was supported by FCT through project grants: NaturAge (PTDC/QUI-BIQ/101392/2008), Hyperi-Food (PTDC/AGR-ALI/105169/2008), AgroHyp (PTDC/AGR-GPL/119211/2010) and PEst-OE/AGR/UI4033/2014. ACC is supported by a FCT doctoral grant (SFRH/BD/86953/2012).

Keywords: Hypericum perforatum, elicitation, HepG2 cells, antioxidant effects, Nrf2 activation, cytoprotective enzymes induction

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