Advances in chemical and biological characterization of triterpenoid saponins from Anagallis arvensis L. using UHPLC-MS/MS and cell-based assays

A fraction enriched in triterpenoid saponins (F4) from Anagallis arvensis L. was chemically characterized by UHPLC-ESI-QTOF-MS/MS and NMR analyses. The results proposed the presence of nine monodesmosidic saponins derived from oleanolic acid, including two reported for the first time for this species, 3: 3-O-{β-D-glucopyranosyl (1→4)-[β-D-xylopyranosyl (1→2)]-β-D-glucopyranosyl (1→4)-[β-D-glucopyranosyl (1→2)]-α-L-arabinopyranosyl}-13β, 28-epoxy- 22 acetyl- 28 methoxy-16α, 24-oleananediol and 4: 3-O-{β-D-glucopyranosyl (1→4)-β-D-glucopyranosyl (1→4)-[β-D-xylopyranosyl (1→2)]-β-D-glucopyranosyl (1→4)-[β-D-glucopyranosyl (1→2)]-α-L-arabinopyranosyl}-13β, 28-epoxy- 16α, 30-oleananediol. Furthermore, haemolytic activity was determined by dot-blot autography, and cytotoxicity on human lymphocyte cultures was analysed according to metabolic activity (MTT assay) and membrane integrity (Trypan blue exclusion test). F4 showed mild cytotoxicity (%V > 50% at 100 μg/mL) on human lymphocytes under conditions of activation or not by LPS; moreover, showed haemolytic activity between 50 and 500 μg. This work contributed to phytochemical knowledge of the triterpenoid saponins from A. arvensis, and its cytotoxic effects on normal human cells.

Antifungal activity of Euphorbia species against moulds responsible of cereal ear rots

AIMS

This work aimed to identify secondary metabolites from aerial parts of Euphorbia species functional for control of toxigenic Fusarium species responsible of cereal grain rots.

METHODS AND RESULTS

Aerial parts of Euphorbia serpens, Euphorbia schickendantzii and Euphorbia collina were sequentially extracted with hexane, ethyl acetate and methanol. The extracts were tested against strains of Fusarium verticillioides and Fusarium graminearum by microdilution tests. The hexane extract of E. collina provided the lowest IC₅₀ s on both fungal species. Further fractionation showed that cycloartenol (CA) and 24-methylenecycloartanol are associated to the moderate inhibitory effect of the hexane extract on fungal growth.Sublethal concentrations of CA and 24MCA blocked deoxynivalenol (DON) and fumonisins production.CA and 24MCA co-applied with potassium sorbate, a food preservative used for Fusarium control, synergized the growth inhibition of fungi. The mixtures reduced mycotoxins accumulation when applied at sublethal concentrations.

CONCLUSIONS

CA and 24MCA inhibited both fungal growth and mycotoxins production. This fact is an advantage respect to potassium sorbate which increased the mycotoxins accumulation at sublethal concentrations.

SIGNIFICANCE AND IMPACT OF THE STUDY

CA and 24MCA synergized potassium sorbate and their mixtures offer a lower mycotoxigenic risk than potassium sorbate for control of the Fusarium species.

Efficacy of Argentinean propolis extracts on control of potato soft rot caused by Erwinia carotovora subsp

BACKGROUND

Erwinia carotovora subsp. cause the potato soft rot, which is a major disease in agriculture. Antibacterial agents currently applied on potato soft rot often offer a restricted control and have several disadvantages. Propolis has shown a wide range of antimicrobial activity, although its effect has not been investigated on E. carotovora subsp. In this work, we tested extracts from propolis samples of Northwest Argentina against E. carotovora subsp.

RESULTS

Ethanolic propolis extracts (EPEs) from samples of Santiago del Estero province, particularly from sample 4 (EPE4), showed the highest antibacterial activity, which was associated with the highest content of flavonoids. 2',4'-Dihydroxychalcone, 2',4'-dihydroxy-3'-methoxychalcone, galangin, and pinocembrin were identified as antibacterial constituents of EPE4. 2',4'-Dihydroxychalcone showed an antibacterial activity (minimum inhibitory concentration, MIC = 0.3-1.2 μg gallic acid equivalents (GAE) mL^-1 ; minimum bactericidal concentration, MBC = 0.6-4.8 μg GAE mL^-1 ) lower than that of bacterimycin (MIC = 2.4-9.6 μg mL^-1 ; MBC = 19.2-38.4 μg GAE mL^-1 ) and streptocycline (MIC = 19.2-38.4 μg mL^-1 ; MBC = 38.4-76.8 μg mL^-1 ). Preventive assays on unwounded and wounded potatoes showed that their immersion in EPE4 containing 87.5 μg GAE mL^-1 or streptocycline containing 40 μg mL^-1 was equally effective in controlling potato soft rot, reducing the disease incidence by 64.6-67.0% (unwounded tubers) and 88.0-86.0% (wounded tubers) and the disease severity by 49.8-49.8% (unwounded tubers) and 54.5-68.5% (wounded tubers).

CONCLUSIONS

Flavonoid-rich propolis extracts from Northwest Argentina efficiently reduced in vivo the incidence and severity of potato soft rot caused by E. carotovora subsp.

Antifungal metabolites from Schinopsis balansae Engl (Anacardiaceae): isolation, identification and evidences of their mode of action on Fusarium graminearum Schwabe

An antifungal activity-directed fractionation of leaf constituents from Schinopsis balansae on Fusarium graminearum yielded a fraction mainly made of a mixture of four 3-n-heptadec(en)ylcatechols (PALK). The PALK fraction showed on macroconidia germination a MIC₁₀₀ value of 500 μg/mL which was twofold higher than that required for prothioconazole (MIC₁₀₀ = 250 μg/mL). Sublethal concentrations of PALK modify the morphogenesis in germinating macroconidia, and decreased fungal production of H₂O₂ and deoxynivalenol biosynthesis at early fungal growth. Mixes of PALK and prothioconazole showed a synergic interaction. Our findings suggest that PALK constituents might restrict the adherence of F. graminearum to the surface of its hosts and its virulence on susceptible cereals. They deserve further research as additives of azole fungicides against F. graminearum.

Toxigenic potential of Fusarium graminearum isolated from maize of northwest Argentina

Twenty six isolates of Fusarium graminearum from grains of maize hybrids harvested in ±west Argentina were grown on autoclaved rice grain to assess their ability to produce type B trichothecenes. Chemical analysis indicated that 38% of isolates were nivalenol (NIV) producers only, 31% were major NIV producers with high DON(deoxynivalenol)/NIV ratios, 8% were major DON producers with minor NIV production, and 23% were DON producers only. Isolates showed a high variability in their toxigenic potential which was not related to fungal biomass. The distribution of the different chemotypes as well as the high and the low trichothecene-producing Fusarium isolates could not be associated to a geographical origin. Our results confirmed for the first time that isolates of Fusarium graminearum from maize of northwest Argentina are able to produce DON and NIV. A substancial contamination with both NIV and DON is likely in maize from northwest Argentina. Their contents should be quantified in regional surveillances for mycotoxin contamination.

A molecular based strategy for rapid diagnosis of toxigenic Fusarium species associated to cereal grains from Argentina

Fusarium species are worldwide causal agents of ear rot in cereals. Their toxigenic potential is a health risk for both humans and animals. In Argentina, most identification of these fungi has been based on morphological and cross-fertility criteria which are time consuming and require considerable expertise in Fusarium taxonomy and physiology. DNA based approaches have been reported as rapid, sensitive and specific alternatives to identify the main fumonisin and trichothecene-producing Fusarium species. In this work, we used PCR assays and the partial sequence of TEF1-alpha gene (Translation Elongation Factor-1 alpha) to identify the fumonisin and trichothecene-producing species in Fusarium isolates from diverse regions of Argentina. The relative efficiency and reliability of those methods to improve mycotoxin risk prediction in this country were also assessed. Species-specific PCR assays were targeted toward multicopy IGS (Intergenic Spacer of rDNA units) and on the toxin biosynthetic genes FUM1 (fumonisins) and TRI13 and TRI7 genes (trichothecenes). PCR assays based on FUM1 gene and IGS sequences allowed detection and discrimination of the fumonisin producers Fusarium proliferatum and Fusarium verticillioides. Molecular identification of nonfumonisin producers from Gibberella fujikuroi species complex was possible after determination of TEF1-alplha gene sequences, which indicated the presence of Fusarium subglutinans, Fusarium andiyazi and Fusarium thapsinum. TEF-1 alpha gene sequences also allowed discrimination of the different species of the Fusarium graminearum complex (F. graminearum sensu lato) as F. graminearum sensu stricto, Fusarium meridionale and Fusarium boothii. The last two species belonged to NIV chemotype and were detected for the first time in the subtropical region of Argentina while F. graminearum sensu stricto was DON producer only, which was also confirmed by specific PCR assays based on TRI137/TRI7 genes. Our results indicated that the PCR assays evaluated in this work are reliable diagnostic tools to detect the main toxigenic Fusarium species associated to cereal grains in Argentina. An extensive epidemiological survey based on the approach presented in this work is currently in progress to know the mycotoxigenic hazard of Fusarium species in cereal grains from the subtropical region of Argentina.

Purification and identification of antibacterial phenolics from Tripodanthus acutifolius leaves

AIMS

To perform an activity-guided purification, identification and quantification of antibacterial compounds from Tripodanthus acutifolius infusion. To validate the antibacterial activity of purified substances.

METHODS AND RESULTS

Bioautographic methods were employed as screening assays for purifying bioactive substances. Purification procedures included sephadex LH-20 column chromatography and reverse phase HPLC. Identification was achieved by spectroscopic methods (UV-Vis, MS, NMR and polarimetry) and chromatographic assays (paper chromatography and HPLC). Antibacterial activity was studied by microdilution, colony count and photometric assays, Sytox green stain and transmission electron microscopy (TEM). Four glycoflavonoids (rutin, nicotiflorin, hyperoside and isoquercitrin) and an unusual phenylbutanoid glycoside (tripodantoside) were purified and identified. Tripodantoside was found at 6.59 +/- 0.82 g per 100 g of dry leaves. The flavonoids showed bactericidal effect at a concentration of 4 mg ml(-1) against Staphylococcus aureus and Pseudomonas aeruginosa strains from American Type Culture Collection, while tripodantoside was almost four times more active than those compounds, with a minimum bactericidal concentration = 1.024 mg ml(-1) against these strains. Tripodantoside aglycone showed bacteriolytic effects on the assayed strains, causing evident damages on cell wall and membrane, while tripodantoside did not exhibit those effects.

CONCLUSIONS

The antibacterial activity of T. acutifolius infusion would be partially attributed to the purified glycoflavonoids and mainly to tripodantoside.

SIGNIFICANCE AND IMPACT

The high extraction yield and the antibacterial activity exhibited by tripodantoside makes this chemical structure of interest to support further studies dealing with chemical modifications to increase the antibacterial activity or to seek another activities.

Antibacterial activity of plant extracts from northwestern Argentina

AIMS

To determine the antibacterial and cytotoxic activities of aqueous and ethanolic extracts of northwestern Argentinian plants used in folk medicine. To compare the mentioned activities with those of five commercial antibiotics. To identify the compounds responsible for the antibacterial activity.

METHODS AND RESULTS

Plant extracts were prepared according to traditional uses in northwestern Argentina. Antibacterial activity was assayed by agar dilution in Petri dishes and broth dilution in 96-well plates. Lethal dose 50 (LD(50)) was determined by the Artemia salina assay. Phytochemical analysis was performed by sample adsorption on silica gel, thin-layer chromatography (TLC), bioautography and UV-visible spectra. The results showed that Tripodanthus acutifolius aqueous extracts have lower minimal inhibitory concentrations (MIC) (502 and 506 microg of extracted material (EM) per ml for infusion and decoction, respectively) than cefotaxim MIC (640 microg ml(-1)) against Acinetobacterfreundii (303). These data were lower than their LD(50). Tripodanthus acutifolius tincture showed lower MIC (110 microg of EM per ml) and minimal bactericidal concentration (MBC) (220 microg of EM per ml) than cefotaxim (MIC and MBC of 320 microg ml(-1)) for Pseudomonasaeruginosa. This extract also showed a MIC/MBC of 110/220 microg of EM per ml, lower than oxacillin (MIC/MBC of 160/220 microg ml(-1)) for Staphylococcus aureus (ATCC 25923). The cytotoxicity of all extracts were compared with that of commercial antibiotics. Rutin (3,3',4',5,7-pentahydroxyflavone 3-beta-rhamnosilglucoside), iso-quercitrin (3,3',4',5,7-pentahydroxyflavone 3-beta-glucoside) and a terpene would be partially responsible for the antibacterial activity of T. acutifolius infusion.

CONCLUSIONS

Tripodanthus acutifolius extracts had the ability to inhibit bacterial growth. The antibacterial activity differs with the applied extractive method, and it could be partially attributed to glycoflavonoids. This paper contributes to the knowledge of antibacterial capacity of plants from northwestern Argentina.

SIGNIFICANCE AND IMPACT OF THE STUDY

These antibacterial activities support further studies to discover new chemical structures that can contribute to alleviate or cure some illnesses.

Propolis from the northwest of Argentina as a source of antifungal principles

AIMS

To determine the antimycotic and cytotoxic activities of partially purified propolis extract on yeasts, xylophagous and phytopathogenic fungi. To compare these activities with pinocembrin and galangin isolated from this propolis and with the synthetic drugs ketoconazole and clortrimazole.

METHODS AND RESULTS

Ethanolic propolis extract was partially purified by cooling at -20 degrees C. Two of its components were isolated by HPLC and identified as pinocembrin and galangin. The antifungal activity was assayed by bioautography, hyphal radial growth, hyphal extent and microdilution in liquid medium. Cytotoxicity was studied with the lethality assay of Artemia salina. The obtained results were compared with the actions of ketoconazole and clortrimazole. The results showed that the antifungal potency of ketoconazole and clortrimazole is higher than pinocembrin, galangin and the partially purified propolis extract in this order. Otherwise, the cytotoxicity of the synthetic drugs is also the highest.

CONCLUSIONS

Partially purified propolis extract inhibits fungal growth. The comparison of its relative biocide potency and cytotoxicity with synthetic drugs and two components of this propolis (pinocembrin and galangin) showed that the propolis from 'El Siambón', Tucumán, Argentina, is a suitable source of antifungal products.

SIGNIFICANCE AND IMPACT OF THE STUDY

The partially purified propolis extract and its isolated compounds, pinocembrin and galangin, have the capacity of being used as antifungals without detriment to the equilibrium of agroecosystems. The impact of this study is that the preparation of agrochemicals with reduced economic costs using a partially purified preparation as the active principle is possible.

Plant growth inhibitors isolated from sugarcane (Saccharum officinarum) straw

Several compounds related with plant defense and pharmacological activities have been isolated from sugarcane. Straw phytotoxins and their possible mechanisms of growth inhibition are largely unknown. A bioassay-guided fractionation of the phytotoxic constituents leachated from a sugarcane straw led to the isolation of trans-ferulic (trans-FA), cis-ferulic (cis-FA), vanillic (VA) and syringic (SA) acids. The straw leachates and their identified constituents significantly inhibited root growth of lettuce and four weeds. VA was more phytotoxic to root elongation than FA and SA. The identified phenolic compounds significantly increased leakage of root cell constituents, inhibited dehydrogenase activity and reduced chlorophyll content in lettuce. VA and FA inhibited mitotic index while SA increased cell division. Additive (VA-FA and FA-SA) and synergistic (VA-SA) interactions on root growth were observed at the response level of EC(25). Although the isolated compounds differed in their relative phytotoxic activities, the observed physiological responses suggest that they have a common mode of action. HPLC analysis indicated that sugarcane straw can potentially release 1.43 (ratio 2:1, trans:cis), 1.14 and 0.14mmolkg(-1) (straw dry weight) of FA, VA and SA, respectively. As phenolic acids are often found spatially concentrated in the top soil layers under plant straws, further studies are needed to establish the impact of these compounds in natural settings.