Abstract
Background: A large number of chemical compounds exert their antioxidant effects by activation of key transcriptional regulatory mechanisms, such as the transcription factor Nrf2. The aim of this study was to evaluate the activation of the Keap1-Nrf2 pathway by both the n-butanol extract obtained from the inner bark of Tabebuia rosea (Bertol) DC and specioside isolated from this extract. Methods: The antioxidant activity of the extract and specioside isolated from the inner bark of T. rosea were evaluated using the oxygen radical absorbance capacity (ORAC) and the 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity (DPPH) techniques, whereas their effects on the viability of HepG2 cells was determined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method. The effects of the compound and the extract on activating the Keap1-Nrf2 pathway were evaluated using a Nrf2 Transcription Factor Assay kit. Induction of the Nrf2-mediated antioxidant response genes HMOX-1 and NQO1 was evaluated by real-time PCR. The protective effects against H2O2-induced oxidative stress in HepG2 cells was determined as the percent protection using the MTT method. Results: Both the n-butanol extract and specioside exhibited activity at low concentrations without affecting cellular viability, since the cell viability was greater than 80% after 24 hours of exposure at each tested concentration. In addition, Nrf2 dissociated from Keap1 after treatment with the n-butanol extract at a concentration of 0.25 µg/mL after 4 hours of exposure. An increase in the Nrf2 level in the cytoplasm after 4 hours of exposure to 2 μM specioside was observed. Nrf2 levels stabilized in the nucleus 12 hours after stimulation with both specioside and the extract. After 6 hours of stimulation, both the extract and specioside induced the expression of HMOX-1 and NQO1. Conclusion: The n-butanol extract from the inner bark of T. rosea and specioside produced protective effects against H2O2-induced oxidative stress in HepG2 cells.
Highlights
Over the years, plants have been used to treat several diseases, are considered an important source of biologically active natural products, and many have been used for the synthesis of various drugs
Considering the potential health benefits and the possible pharmacological effects of extracts obtained from T. rosea, its abundance in Colombia and the few investigations regarding its antioxidant properties and the molecular mechanisms involved in its activity, the aim of this study was to evaluate the mechanism responsible for the in vitro antioxidant activity of the n-butanol extract obtained from the inner bark of T. rosea (Bertol) DC
Antioxidant activity and cell viability after treatment with the n-butanol extract and pure compounds The antioxidant activity of the n-butanol extract from the inner bark of T. rosea, the isolated compound specioside and the catalposide iridoid compound reported from the Bignoniaceae family were evaluated using the oxygen radical absorbance capacity (ORAC) and diphenyl-1picrylhydrazyl radical scavenging activity (DPPH) techniques[44]
Summary
Plants have been used to treat several diseases, are considered an important source of biologically active natural products, and many have been used for the synthesis of various drugs. The antioxidant capacity of extracts obtained from T. rosea has not been widely studied, this activity has been demonstrated in other species of the Tabebuia genus. The aim of this study was to evaluate the activation of the Keap1-Nrf[2] pathway by both the n-butanol extract obtained from the inner bark of Tabebuia rosea (Bertol) DC and specioside isolated from this extract. Methods: The antioxidant activity of the extract and specioside isolated from the inner bark of T. rosea were evaluated using the oxygen radical absorbance capacity (ORAC) and the 2,2-diphenyl-1picrylhydrazyl radical scavenging activity (DPPH) techniques, whereas their effects on the viability of HepG2 cells was determined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method. Nrf[2] levels stabilized in the nucleus 12 hours after stimulation with version 3 (revision)
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