Structure-radical scavenging activity relationships of phenolic compounds from traditional Chinese medicinal plants

Traditional Chinese medicinal plants associated with anticancer contain a wide variety of natural phenolic compounds with various structural features and possessing widely differing antioxidant activity. The structure-radical scavenging activity relationships of a large number of representative phenolic compounds (e.g., flavanols, flavonols, chalcones, flavones, flavanones, isoflavones, tannins, stilbenes, curcuminoids, phenolic acids, coumarins, lignans, and quinones) identified in the traditional Chinese medicinal plants were evaluated using the improved ABTS*+ and DPPH methods. Different categories of tested phenolics showed significant mean differences in radical scavenging activity. Tannins demonstrated the strongest activity, while most quinones, isoflavones, and lignans tested showed the weakest activity. This study confirmed that the number and position of hydroxyl groups and the related glycosylation and other substitutions largely determined radical scavenging activity of the tested phenolic compounds. The differences in radical scavenging activity were attributed to structural differences in hydroxylation, glycosylation and methoxylation. The ortho-dihydroxy groups were the most important structural feature of high activity for all tested phenolic compounds. Other structural features played a modified role in enhancing or reducing the activity. Within each class of phenolic compounds, the structure-activity relationship was elucidated and discussed. This study reveals the structure-activity relationships of a large series of representative natural phenolic compounds more systematically and fully than previous work. Structure-radical scavenging activity relationships of some natural phenolics identified in the medicinal plants were evaluated for the first time.     

Contribution of Bioactive Compounds to the Antioxidant Capacity of the Edible Mushroom Neolentinus lepideus

Neolentinus lepideus is a fungus consumed by rural communities in Central America and Asia due to its rich flavor; however, little information on its chemical composition is available. With this in mind, the objective of this work was to determine the content of vitamin E and C, ergosterol, and phenolic compounds of this fungus, as well as its antioxidant capacity. The quantified bioactive compounds were two isoforms of vitamin E, highlighting α-tocopherol (3370.35 mg/100 g dry weight, DW) and ergosterol (11.70 mg/100 g DW). The total phenolic content was 164.80 mg gallic acid equivalents/100 g, and nine phenolic compounds were identified (protocatechuic, p-hydroxybenzoic, caffeic, vanillic, ferulic, salicylic, p-anisic, trans-cinnamic acids, and scopoletin). The highest antioxidant capacity was detected in the lipophilic extract with TEAC (27688 μmoles Trolox equivalents/100 g). These results suggest that lipophilic compounds are among the main bioactive compounds in N. lepideus, and they might exhibit the highest radical scavenging properties in non-polar extracts.     

Antioxidant activity of wheat extracts as affected by in vitro digestion

Phenolic compounds from soft wheat and its milling fractions were extracted and their in vitro antioxidant activity evaluated. Non-hydrolyzed extracts were prepared by extracting phenolics into distilled deionized water. To make hydrolyzed extracts samples were first subjected to pH adjustments in order to simulate gastrointestinal pH conditions. Total phenolic content (TPC) was determined using Folin-Ciocalteu's procedure. Total antioxidant activity (TAA) was determined using Trolox equivalents antioxidant capacity (TEAC) assay and expressed as Trolox equivalents (TE). Antioxidant activity of wheat extracts was determined using the procedures of inhibition of beta-carotene bleaching, scavenging of 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical and inhibition of oxidation of human low density lipoprotein (LDL) cholesterol. The TPC and TAA of wheat extracts tested were significantly increased following hydrolysis. Similarly, the antioxidant activity, as determined by different procedures, was considerably increased when the samples were subjected to simulated digestion conditions.     

Comparison of the total antioxidant content of 30 widely used medicinal plants of New Mexico

Teas made from medicinal plants are commonly used by a majority of the inhabitants of New Mexico and Mexico to treat various ailments including infections, arthritis, heart disorders, headaches, fever, asthma and menstrual pain. However, little is known about the identity or chemical nature of the bioactive substances and compounds responsible for the therapeutic effects of the teas made from the leaves, seeds, flowers stems, and roots of these medicinal plants. Some of the beneficial effects of these teas may be attributable to antioxidants contained in the medicinal plants from which they are brewed. In the present study we collected 30 medicinal plants that are widely used in the Rio Grande Valley and, using a two-stage Trolox based assay, analyzed the total antioxidant capacity of aqueous extracts prepared from these plants. The antioxidant content of the aqueous extracts was substantial, ranging from 27 to 972 micromol Trolox equivalent per gram dry weight. An extract of the leaves of the plant Ilex paraguensis (Mate leaf) contained the highest amount of antioxidant, followed by the flowers of the Rosa sp. (Rosa de Castillo, 804 micromol/g), the bark of Chinchona sp. (Copalquin, 692 micromol/g), Rumex hymenosepalus stems (Cana Agria, 672 micromol/g) and the leaves of Marrubium vulgare (Mastranzo, 560 micromol/g). The plants that had the lowest antioxidant capacity were the seeds of Linum lewissii (Linasa, 29 micromol/g) and Yucca sp. plant root (Amole, 27 micromol/g). It will be useful to further analyze those plants that contain the most antioxidant activity in order to identify the active principles.     

Enhancement of stilbene compounds and anti-inflammatory activity of methyl jasmonate and cyclodextrin elicited peanut hairy root culture

A highly stable and productive hairy root culture from peanut cultivar Tainan9 (T9-K599) was established using Agrobacterium rhizogenes strain K599 (NCPPB 2659)-mediated transformation. Valuable phenolic compounds with antioxidant activity and stilbene compounds were produced and secreted into the culture medium after elicitation with 100 µM methyl jasmonate (MeJA) and 6.87 mM cyclodextrin (CD). The antioxidant activity of the culture medium was increased to the highest Trolox equivalent antioxidant capacity (TEAC) value (28.30?±?2.70 mM Trolox/g DW) in the group treated with CD. The group co-treated with MeJA and CD exhibited the highest phenolic content, with a gallic acid equivalent (GAE) value of 10.80?±?1.00 µg gallic acid/g DW. The CuZn-SOD (CuZn superoxide dismutase) and APX (ascorbate peroxidase) antioxidant enzyme gene were up-regulated in the treatment with CD alone while the CuZn-SOD, GPX (glutathione peroxidase) and APX gene expression were down-regulated in the co-treatment with MeJA plus CD. The stilbene compounds resveratrol, trans-arachidin-1 and trans-arachidin-3 were detected by analysing the culture medium treated with CD alone and after co-treatment with MeJA and CD via HPLC. The LC-MS/MS results confirmed the presence of resveratrol, trans-arachidin-1, trans-arachidin-3, 4-Isopentadienyl-3,5,3′,4′-tetrahydroxystilbene (IPP), trans-3′-Isopentadienyl-3,5,4′-trihydroxystilbene (IPD) and arahypin-7. The results indicate that elicited peanut hairy roots can produce beneficial stilbene compounds that have antioxidant properties and anti-inflammatory activity. This peanut hairy root system could be applied as an experimental model to enhance the production of stilbene and other polyphenolic bioactive compounds.     

Characterization of the phenolic constituents in Mauritian endemic plants as determinants of their antioxidant activities in vitro

The phenolic constituents of Mauritian endemic plants from the Rubiaceae and Myrtaceae family were assessed and correlated with their potential antioxidant activities in vitro. The antioxidant activities of the plant extracts ranged from 0.27 to 1.49mmol Trolox equivalent/g FW and from 0.20 to 1.39mmol Fe(II) equivalent/g FW in the TEAC and FAP assays, respectively, with Syzygium commersonii showing the highest activity in these two systems. Eugenia orbiculata and all the Syzygium species were effective scavengers of hypochlorous acid while Monimiastrum acutisepalum was the most potent inhibitor of deoxyribose degradation. The plant extracts inhibited microsomal lipid peroxidation with low IC(50)s ranging from 0.02 to 1.75mgFW/mL when reaction was initiated with Fe(3+)/ascorbate and from 0.093 to 1.55mgFW/mL in the AAPH-dependent lipid peroxidation. The potential prooxidant nature of the plant extracts was compared with ascorbate (250microM) using copper-phenanthroline assay. The plant extracts at concentrations up to 5gFW/L were not prooxidant. However, Myonima nitens, Syzygium commersonii, Syzygium glomeratum and Syzygium mauritianum at concentrations of 10gFW/L had potency approaching 50% of the prooxidant activity of ascorbic acid in vitro, suggesting relative safeties. The total phenolics influenced the antioxidant activities in the TEAC, FRAP and HOCl scavenging assays whereas a negative correlation was observed with the deoxyribose assay. The high levels of polyphenolic compounds and the significant antioxidant activities of these Rubiaceae and Myrtaceae plant family make them suitable candidates as prophylactic agent.     

Characterization of plant phenolic compounds by cyclic voltammetry

Phenolic acids and flavonoids were characterized by cyclic voltammetry and total antioxidant activity in the reaction with the ABTS cation radical. Anode peak voltages (Eap) and their pH dependences were determined for the studied phenolic acids and flavonoids. The Eap and Trolox equivalent antioxidant capacity (TEAC) values were found to correlate for polyphenols, which react with the ABTS cation radical in two steps. Correlation between the half-wave potential (Ep/2) and TEAC was determined for electrochemically irreversible compounds. Mechanisms of the reaction of phenolics on the electrode involving one- and two-electron oxidation are proposed.     

Anticancer and Antimicrobial Activities of Some Antioxidant-Rich Cameroonian Medicinal Plants

Traditional remedies have a long-standing history in Cameroon and continue to provide useful and applicable tools for treating ailments. Here, the anticancer, antimicrobial and antioxidant activities of ten antioxidant-rich Cameroonian medicinal plants and of some of their isolated compounds are evaluated.The plant extracts were prepared by maceration in organic solvents. Fractionation of plant extract was performed by column chromatography and the structures of isolated compounds (emodin, 3-geranyloxyemodin, 2-geranylemodin) were confirmed spectroscopically. The antioxidant activity (AOA) was determined using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) bleaching method, the trolox equivalent antioxidant capacity (TEAC), and the hemoglobin ascorbate peroxidase activity inhibition (HAPX) assays. The anticancer activity was evaluated against A431 squamous epidermal carcinoma, WM35 melanoma, A2780 ovary carcinoma and cisplatin-resistant A2780cis cells, using a direct colorimetric assay. The total phenolic content in the extracts was determined spectrophotometrically by the Folin–Ciocalteu method. Rumex abyssinicus showed the best AOA among the three assays employed. The AOA of emodin was significantly higher than that of 3-geranyloxyemodin and 2-geranylemodin for both TEAC and HAPX methods. The lowest IC₅₀ values (i.e., highest cytotoxicity) were found for the extracts of Vismia laurentii, Psorospermum febrifugum, Pentadesma butyracea and Ficus asperifolia. The Ficus asperifolia and Psorospermum febrifugum extracts are selective against A2780cis ovary cells, a cell line which is resistant to the standard anticancer drug cisplatin. Emodin is more toxic compared to the whole extract, 3-geranyloxyemodin and 2-geranylemodin. Its selectivity against the platinum-resistant A2780cis cell line is highest. All of the extracts display antimicrobial activity, in some cases comparable to that of gentamycin.     

Chemical compositions by using LC–MS/MS and GC–MS and antioxidant activities of methanolic extracts from leaf and flower parts of Scabiosa columbaria subsp. columbaria var. columbaria L.

The members of the Scabiosa genus are one of the traditional medicinal plants used in the treatment of many diseases, in particular the treatment of scabies. In this study, it was aimed to determine antioxidant activities and chemical composition of methanolic extracts of leaves and flowers of Scabiosa columbaria subsp. columbaria var. columbaria. The phenolic contents of both parts of the plant were analyzed by LC–MS/MS. A total of 6 phenolic compounds were determined and chlorogenic acid was the major compound in both flower and leaf parts of the plants, with 5936.052 µg/g and 8021.666 µg/g, respectively. 6 different methods were used to determine the antioxidant activity of the plant parts. Both leaf and flower parts of the plant showed high antioxidant activity in all tested methods and the antioxidant activity values of the leaf part were measured higher than those of the flower part for four tests. The methanol extracts of the plant parts was analyzed with GC–MS and number of the essential oil compounds in the leaf and flower parts were determined as 17 and 13, respectively. Linalool compound was also found to be common in both parts of the plant. The major compounds of the essential oils were identified as 4-Octadecenal (30.01%) in the flower and carvone (35.44%) in the leaf. In addition, terpene derivatives was determined as 90.32% of the highest essential oil group in the leaf, while this value was determined as 1.42% in the flower. For the flower, aromatics were determined as the main component group with 21.31%.     

Variation in polyphenolic profile and in vitro antioxidant activity of eastern teaberry (Gaultheria procumbens L.) leaves following foliar development

Seasonal dynamics in the polyphenolic composition, antioxidant activity, and their relationships during plant development were evaluated for eastern teaberry (Gaultheria procumbens L.) leaves, a traditional herbal medicine of North American natives. With the complementary UHPLC-PDA-ESI-MS³, HPLC-PDA-fingerprint, Folin-Ciocalteau, and n-butanol/HCl assays of methanol-water (75:25, v/v) extracts, the dried leaf samples harvested monthly across the growing season under Polish climate conditions were found rich in structurally diverse polyphenols (149.2–210.7 mg/g DW) including the dominating salicylates (64.6–107.5 mg/g DW), proanthocyanidins (53.0–66.8 mg/g DW), and flavonoids (17.3–25.3 mg/g DW), and the accompanying chlorogenic acid isomers (2.4–4.4 mg/g DW) and simple phenolic acids (0.9–1.1 mg/g DW). Among 28 detected analytes, gaultherin (64.6–107.5 mg/g DW), miquelianin (14.6–21.1 mg/g DW), procyanidin A-type trimer (5.5–9.5 mg/g DW), and (–)-epicatechin (5.8–7.8 mg/g DW) were the most abundant. The phenolic levels and antioxidant activity parameters in the DPPH (EC₅₀, 15.0–18.2 μg DW/mL; 0.95–1.16 mmol Trolox equivalents/g DW) and FRAP (2.3–3.4 mmol Fe ²⁺/g DW; 0.86–1.26 mmol Trolox equivalents/g DW) assays showed parallel seasonal trends with maxima in September and October. As the subsequent correlation studies confirmed the determinative impact of polyphenols on the leaf antioxidant activity and its seasonal fluctuations, the Fall season could be recommended as optimal for harvesting the plant material for medicinal purposes and cost-effective production of natural health products.