Martha Rosales-Castro

Antioxidant activity of fractions from Quercus sideroxyla bark and identifi cation of proanthocyanidins by HPLC-DAD and HPLC-MS

Abstract The most active phenolics in Quercus sideroxyla Humb. & Bonpl. residual bark were identified and evaluated following a chromatographic fractionation. Bark powder was defatted with hexane and crude extract (CE) was obtained by extraction with aqueous acetone (70%). A liquid partition with ethyl acetate was performed to produce an organic extract (OE), which was subsequently purified by column chromatography (Toyopearl HW-40F, methanol), and resulted in six methanolic fractions (MF1 to MF6) and an oligomeric fraction (OLF) eluted with acetone 67%. Extraction yields, total phenolic and flavanol contents were determined. The antioxidant activity of bark extracts was measured by 2,2-diphenyl-1-picrylhydrazyl (DPPH), Trolox (6-hydroxy-2,5,7,8-tetramethyl-chroman-2-carboxylic-acid)-equivalent antioxidant capacity (TEAC), and ferric ion reducing antioxidant power (FRAP) assays. Their median effective concentration (EC50) data and rate constants for DPPH radical scavenging were also estimated. Identification of major phenolics was carried out by high performance liquid chromatography with diode array detection (HPLC-DAD) and high performance liquid chromatography with electrospray ionization coupled to mass spectrometry (HPLC-ESI-MS) instruments. Bioactive gallic acid, catechin, epicatechin, gallocatechin, catechin gallate, dimeric procyanidins, galloylated dimeric proanthocyanidins, trimeric procyanidins, and tetrameric proanthocyanidins were detected and identified in Q. sideroxyla bark extracts. MF2 was the most active fraction containing gallocatechin as its major compound; MF5 and OLF contain galloylated procyanidins, which may explain their higher antiradical activity. OLF besides galloylated procyanidins has gallocatechin, which presumably contributes to its higher antiradical activity. Consequently, Q. sideroxyla bark could be a good source of therapeutic health products or nutraceutical ingredients that may exert a potential prevention or treatment action against diseases in biological systems.

ANTIOXIDANT PHENOLIC COMPOUNDS OF ETHANOLIC AND AQUEOUS EXTRACTS FROM PINK CEDAR (ACROCARPUS FRAXINIFOLIUS WHIGHT & ARN.) BARK AT TWO TREE AGES

In Central Mexico, commercial plantations of pink cedar (Acrocarpus fraxinifolius Whight & Arn.) from 7 to 15 years old are ready for harvesting to obtain wood products without current bark use. Therefore, the aim of this work was to study ethanolic and hot water extracts from A. fraxinifolius bark of 7-year-old (young) and 13-year-old (mature) trees. Yields, total phenolic, flavonoid, and proanthocyanidin contents, as well radical scavenging activity by 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2-azinobis-(3-ethylbenzothiazoline-6-sulfonate) (ABTS) radicals, as well by ferric-reducing antioxidant power (FRAP) and low-density lipoprotein inhibition assays were estimated. Extracts of young tree barks showed higher phenolic content and better scavenging activity than extracts from mature tree barks; ethanolic extracts were superior to the aqueous ones. Positive correlations between polyphenol content and scavenging activity were observed. Results suggest that A. fraxinifolius bark loses phenolic content and antiradical activity as it ages. Bioactive phenolics such as gallic acid, catechin, epicatechin, and catechin gallate were identified by HPLC-DAD.

Efecto del solvente y de la relación masa/solvente, sobre la extracción de compuestos fenólicos y la capacidad antioxidante de extractos de corteza de Pinus durangensis y Quercus sideroxyla

En la busqueda de compuestos bioactivos de las plantas, la corteza de especies maderables es un subproducto promisorio, ya que contiene compuestos fenolicos de interes terapeutico. La extraccion de estos metabolitos depende del disolvente que se utilice y de variables aplicadas en el proceso. Para un fin terapeutico, la medicina tradicional utiliza unicamente mezclas de etanol y agua. Se realizaron extracciones de la corteza de Pinus durangensis y Quercus sideroxyla, bajo un diseno experimental 2x3x3 para estudiar el efecto de soluciones hidroetanolicas 20, 50 y 80%, y la relacion masa a extraer/volumen de disolvente 1/10, 1/20 y 1/30 sobre el rendimiento en solidos, donde 28,72 ±0,9% correspondio a Pinus durangensis (PdE50-1/20) y 24,95±1,2% para Quercus sideroxyla (QsE50-1/30), la maxima concentracion de fenoles totales se obtuvo con etanol 80%- 1/10 en ambas especies (PdE80- 1/10 con 712,36±13,4 mg equivalentes de acido galico (GAE)/g) y QsE80-1/10 de 592,97±10,6 (GAE/g), mientras que la capacidad antioxidante evaluada mediante las tecnicas de DPPH, ABTS y FRAP, mostro que PdE20-1/30 y QsE50-1/10, tuvieron la mayor actividad. Se encontraron diferencias estadisticas (p<0,05) entre los tratamientos aplicados. La concentracion de etanol tuvo mayor efecto que la relacion masa/volumen de extraccion. Pinus durangensis contiene mayor concentracion de fenoles y de flavonoides, respecto a Quercus sideroxyla, mientras que la cantidad de proantocianidinas es similar en ambas especies. Los flavonoides de Pinus durangensis son principalmente de tipo flavanona y flavonol, mientras que Quercus sideroxyla contiene acido galico y flavan-3-ol (catequinas).

Chemical Analysis of Polyphenols with Antioxidant Capacity from Pinus durangensis Bark

The most active phenolics in Pinus durangensis residual bark were identified and evaluated following a chromatographic fractionation. Bark powder was defatted with hexane, and a crude extract (CE) was obtained by extraction with aqueous acetone (67%). A liquid partition with ethyl acetate was performed to produce an organic extract (OE), which was subsequently purified by column chromatography (Toyopearl HW-40F, methanol), resulting in ten fractions (MF1 to MF10) and an oligomeric fraction eluted with acetone 67% (OLF). Subfraction MF6-1 was obtained by a second chromatographic purification of MF6. Extraction yields, total phenolics, flavonoids, and flavanols contents were determined in CE and OE. The antioxidant activity of bark extracts was measured by DPPH and ABTS assays at 100 µg/mL, expressed in percentage, median effective concentration (IC50), and TEAC (mM). Also the low density lipoprotein inhibition was evaluated. Identification of major phenolics was carried out by HPLCESI–MS and HPLC–DAD instruments. Bioactive taxifolin (dihydroquercetin), dihydromyricetin, myricetin, quercetin, pinomyricetin (myricetin-methoxy), pinoquercetin (quercetin-methoxy), trimeric, and tetrameric procyanidins were detected and identified in P. durangensis bark extracts. Polyphenols found are similar to those contained in Pycnogenol and other Pinus species.

Evaluation of Hypoglycemic and Genotoxic Effect of Polyphenolic Bark Extract from Quercus sideroxyla

Quercus sideroxyla is a wood species whose bark has phenolic compound and should be considered to be bioactive; the hypoglycemic and genotoxic properties of Q. sideroxyla bark were evaluated in this study. Total phenolic compound was determined in crude extract (CE) and organic extract (OE). The OE has the highest amount of phenols (724.1 ± 12.0 GAE/g). Besides, both CE and OE demonstrated effect over the inhibition of α-amylase in vitro. Hypoglycemic activity was assessed by glucose tolerance curve and the area under curve (UAC); OE showed the highest hypoglycemic activity. In addition, diabetes was induced by streptozotocin (65 mg/kg) and the extracts (50 mg/kg) were administered for 10 days; OE showed hypoglycemic effect compared with diabetic control and decreased hepatic lipid peroxidation. Acute toxicity and genotoxicity were evaluated in CE; results of acute toxicity did not show any mortality. Besides, the comet assay showed that CE at a dose of 100 mg/kg did not show any genotoxic effect when evaluated at 24 h, whereas it induced slight damage at 200 mg/kg, with the formation of type 1 comets.