Plant species from Tabebuia genus are commonly found in Brazil and are used in folk medicine to treat several diseases. Previous studies have demonstrated antioxidant, anti-inflammatory and antitumor effects of Tabebuia spp 1,2. In this study it was evaluated the antioxidant activity of T. roseoalba barks ethanolic extract (TBEE). Free radicals are high reactive molecules and can cause cellular damage, being responsible for diseases. Antioxidant activity (AA) from TBEE was evaluated by three different assays (DPPH, ABTS and β-carotene/linoleic acid system) and calculated by the equation: % AA = [1 - (Test abs. - Control abs. / Blank abs)] x 100. Half-maximal effective concentration (EC50) was also calculated. Quercetin and Trolox were used as positive controls. For DPPH radical assay, TBBE was solubilized in distilled water/methanol. DPPH methanol solution was prepared (100 μg/mL). DPPH and extract solutions were added to the cuvette, incubated for 30 minutes at 25-30ºC and absorbance read using spectrophotometer (517 nm). Antioxidant activity was evaluated by the extract capacity of capturing DPPH. Reaction allows color to turn from violet to yellow, detected by spectrophotometer. TBEE (100 μg/ml) presented an AA of 54 % inhibition and EC50 of 88,07 μg/ml. Trolox (15 μg/ml) and Quercetin (10 μg/ml) presented an AA of 47 and 77,0 %, respectively. For ABTS•+ radical assay, TBBE was solubilized in distilled water/methanol. ABTS•+ radical was formed by reacting ABTS (7mM) with potassium persulfate (140 mM), incubated at 25ºC in dark room for 16 hours. ABTS•+ radical formed was diluted in ethanol until absorbance value reached 0,700 ± 0,05 at 734 nm. ABTS•+ and extract solutions were added to the cuvette, absorbance was read after 6 minutes using spectrophotometer (714 nm). AA, EC50, and TEAC (Trolox equivalent antioxidant capacity) were calculated (μg/ml). ABTS•+ radical formed has a green/blue color and antioxidant reaction discolor it, allowing its measurement by spectrophotometer and comparison with the positive controls. TBEE (40 μg/ml) presented an AA of 85 % inhibition, EC50 of 14,71 μg/ml and TEAC of 0,32 μg/ml. Trolox (8,0 μg/ml) and Quercetin (3,0 μg/ml) presented an AA of 56 and 93 %, respectively. Quercetin presented a TEAC value of 0,10 μg/ml. For β-carotene/linoleic acid system assay, TBBE was solubilized in distilled water/methanol. β-carotene/linoleic acid solution was prepared and mixed with extract solution, incubated at 40ºC. Emulsion oxidation was monitored using a spectrophotometer (470 nm) every 30 minutes for 120 minutes. Results were expressed as inhibition percentage (AA) and EC50 was calculated. This method allows to evaluating of the antioxidant inhibition power by radicals formed during linoleic acid peroxidation. TBEE (40 μg/ml) presented an AA of 80 % and EC50 of 2,33 μg/ml. Trolox (3,7 μg/ml)and Quercetin (4,0 μg/ml) presented 92 and 82 %, respectively. T. roseoalba barks ethanolic extract presented significant antioxidant activity in the three assays. TBEE showed the best AA by ABTS radical scavenger and β-carotene/linoleic acid system methods, which may indicate that there is more concentration of lipophilic antioxidants in this extract than polar components.
References:
1 OLMSTEAD, R.G. et al. American Journal of Botany, v. 96, n. 9, p. 1731-1743, 2009.
2 GROSE, S.O. and OLMSTEAD, R.G. Systematic Botany, v. 32, p. 650-659, 2007a.
3 SINGH, R. P. et al. Journal of Agricultural And Food Chemistry, 50, 81-86, 2002.
4 RUFINO, M.S.M. et al. Comunicado técnico, EMBRAPA, Fortaleza, n. 128, 4 p., 2007.
5 RUFINO, M.S.M. et al. Comunicado técnico, EMBRAPA, Fortaleza, n. 126, 2006.
This work was supported by FAPEMIG, Rede TOXIFAR/FAPEMIG, CNPq, CAPES and UFOP.