Activation of the Keap1-Nrf2 pathway by specioside and the n-butanol extract from the inner bark of Tabebuia rosea (Bertol) DC

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.

In Vitro Anti-Toxoplasma Activity of Extracts Obtained from Tabebuia rosea and Tabebuia chrysantha: The Role of β-Amyrin

“…Another compound that was evaluated was catalposide, which was obtained from the butanol extract of the inner bark of T. rosea [ 20 ]. In this case, concentrations of 10, 5, 2.5, and 1.25 µg/mL were evaluated.…”

“…Plants of the genus Tabebuia , found mainly in the intertropical zone of the Americas, have been considered an important source of bioactive molecules such as naphthoquinones, quinones, phenols, and other molecules with anti-inflammatory, antioxidant, anti-proliferative, and antimicrobial activity [ 15 , 18 , 20 , 25 , 26 , 27 ]. Additionally, the results of ethnopharmacological studies highlight the use of plants from this genus for the treatment of various diseases [ 28 ].…”

“…Fractionation of the T. rosea chloroform extract was carried out, and the anti- Toxoplasma activity of this fraction was evaluated, as well as the β-amyrin isolated from the fraction TrH- CHF4- A [ 20 , 25 ], a pentacyclic triterpenoid. β-amyrin showed anti- Toxoplasma activity, significantly decreasing the intracellular proliferation of the parasite and, therefore, the number of infected cells, as well as the number of free tachyzoites in the culture medium, with an IC50 of 4.75 μg/mL and a TI of 15 ( Table 5 ), a value much higher than that reported in the literature for antibiotics used as controls.…”

“…Additionally, it was observed that the sulfadiazine pyrimethamine mixture used as a positive control did not affect cell viability. Another compound that was evaluated was catalposide, which was obtained from the butanol extract of the inner bark of T. rosea [20]. In this case, concentrations of 10, 5, 2.5, and 1.25 µg/mL were evaluated.…”

“…The activity of the fraction obtained from the chloroform extract of T. rosea leaves was evaluated using the RH strain of T. gondii that expresses the green fluorescent protein Another compound that was evaluated was catalposide, which was obtained from the butanol extract of the inner bark of T. rosea [20]. In this case, concentrations of 10, 5, 2.5, and 1.25 µg/mL were evaluated.…”