Chlorinated Guaiane-Type Sesquiterpene Lactones as Cytotoxic Agents against Human Tumor Cells

This article belongs to the Section Bioactives and Nutraceuticals.Guaiane-type sesquiterpene lactones are naturally occurring compounds which have attracted attention due to their array of biological activities. In this study, chlorinated guaianolides 1–8, isolated from plants of the genus Centaurea, were evaluated against the human leukemia cell lines HL-60, U-937, a specific U-937 cell line that overexpresses the anti-apoptotic Bcl-2 protein and the human melanoma cell line SK-MEL-1. This established the relevant structure-growth inhibition relationships. Chlorohyssopifolins A (1), C (3) and D (4) and linichlorin A (6) were the most potent compounds in terms of inducing growth inhibition in the four cell lines. IC50 values were below 10 μM in all cases. Chlorohyssopifolins A (1) and D (4) and linichlorin A (6) were potent apoptotic inducers in human U-937 leukemia cells, as determined by fluorescent microscopy and flow cytometry, and their mechanism of action was associated with cytochrome c release, caspase activation and poly(ADP-ribose)polymerase cleavage. Overall this study shows that guaianolides induce cytotoxicity against human tumor cells and provides important insights into the cell death pathways that are involved.This research was funded by FEDER and AGENCIA CANARIA DE INVESTIGACIÓN, INNOVACIÓN Y SOCIEDAD DE LA INFORMACIÓN (PROID2017010095 FEDER/ACIISI) and in part by the Spanish Ministry of Science, Innovation and Universities and the European Regional Development Fund (PGC2018-094503-B-C21)

De Novo Sporophyte Transcriptome Assembly and Functional Annotation in the Endangered Fern Species Vandenboschia speciosa (Willd.) G. Kunkel

We sequenced the sporophyte transcriptome of Killarney fern (Vandenboschia speciosa (Willd.) G. Kunkel). In addition to being a rare endangered Macaronesian-European endemism, this species has a huge genome (10.52 Gb) as well as particular biological features and extreme ecological requirements. These characteristics, together with the systematic position of ferns among vascular plants, make it of high interest for evolutionary, conservation and functional genomics studies. The transcriptome was constructed de novo and contained 36,430 transcripts, of which 17,706 had valid BLAST hits. A total of 19,539 transcripts showed at least one of the 7362 GO terms assigned to the transcriptome, whereas 6547 transcripts showed at least one of the 1359 KEGG assigned terms. A prospective analysis of functional annotation results provided relevant insights on genes involved in important functions such as growth and development as well as physiological adaptations. In this context, a catalogue of genes involved in the genetic control of plant development, during the vegetative to reproductive transition, in stress response as well as genes coding for transcription factors is given. Altogether, this study provides a first step towards understanding the gene expression of a significant fern species and the in silico functional and comparative analyses reported here provide important data and insights for further comparative evolutionary studies in ferns and land plants in general.Spanish Ministerio de Economía y Competitividad and FEDER founds, grant: CGL2010-14856 (subprograma BOS)

Mechanism of Mercury Electrooxidation in the Presence of Hydrogen Peroxide and Antioxidants

The oxidation process occurring on mercury electrodes in the presence of hydrogen peroxide has been analized in basic solutions by polarography and voltammetry in their linear scan and differential pulse modes. The process involves Hg(I) ion – in addition to Hg(II) ion – and hydroperoxide radicals, these last formed at trace levels. To demonstrate this radical generation radical scavengers (antioxidants), characterized with the DPPH• radical scavenging assay, were employed. The interaction of the radicals with the antioxidant originate the decrease in signal, but the antioxidant itself does not react with the hydrogen peroxide in the absence of Hg. In the absence of antioxidant, the process is two-electron, being the rate-determining step the second electron transfer; at high concentrations of antioxidant, the oxidation corresponds to a reversible one-electron transfer followed by a chemical reaction between the hydroperoxide radicals and the antioxidant. A reaction scheme is proposed for intermediate antioxidant concentrations.Departamento de Ingeniería Química, Química Física y Ciencias de los Materiale

Electrochemical Oxidation Pathways of Hydroxycoumarins on Carbon Electrodes Examined by LSCV and LC–MS/MS

It is reported the voltammetric behavior and the identification of the oxidation products of four different hydroxycoumarins, namely, 3-, 4-, 6- and 7-hydroxycoumarin (3HC, 4HC, 6HC and 7HC), on carbon electrodes by performing bulk electrolyses in buffered solutions. LC–MS/MS in high resolution mode is used for the product identification. It was found that the voltammetric behaviours of the four compounds are quite different, as well as the corresponding oxidation products. For 3HC the end product was 2 hydroxymandelic acid [2-hydroxy-2-(2-hydroxyphenyl)acetic acid]: for 4HC, salicylic acid [2 hydroxybenzoic acid]; for 6HC, 2H-1-benzopyran-2,6(8aH)-dione and for 7HC no low-molecular weight products were identified. Based on these products and on the voltammetric results, the overall oxidation pathways are formulated as four-electron processes for 3HC and 4HC, and two-electron processes for 6HC. 7HC oxidation is proposed to be an electropolymerization reaction.Ministerio de Economía y Competitividad (research project CTQ-2015-68813R)Departamento de Ingeniería Química, Química Física y Ciencias de los Materiale

A Contribution on the Elucidation of the Electrooxidation Mechanism of Gentisaldehyde on a Glassy Carbon Electrode

The electrochemical behavior of gentisaldehyde (2,5-dihydroxibenzaldehyde) on a glassy carbon electrode is studied by linear-sweep cyclic voltammetry finding one to three oxidation peaks, depending on both the number of cycles recorded and the pH, and one reduction peak. The oxidation product was the formyl-p-benzoquinone, generated by the oxidation of the biphenolic ring, and not the 2,5-dihydroxybenzoic acid (gentisic acid) that could be formed by oxidation of the aldehyde group. The mechanism proposed at pH pK2 (10.93) the process becomes of the EE type (electrochemical-electrochemical steps), no H+ ions being involved. Radicals species found justify the antioxidant capacity of gentisaldehyde.Funding from Córdoba University through “Ayudas puente para el desarrollo de proyectos de I+D precompetitivos XX Programa Propio 2016” is gratefully acknowledged.Departamento de Ingeniería Química, Química Física y Ciencias de los Materiale

Identification and Characterization of TALE Homeobox Genes in the Endangered Fern Vandenboschia speciosa

We report and discuss the results of a quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis of the expression patterns of seven three amino acid loop extension (TALE) homeobox genes (four KNOTTED-like homeobox (KNOX) and three BEL1-like homeobox (BELL) genes) identified after next generation sequencing (NGS) and assembly of the sporophyte and gametophyte transcriptomes of the endangered fern species Vandenboschia speciosa. Among the four KNOX genes, two belonged to the KNOX1 class and the other two belonged to the KNOX2 class. Analysis of the deduced amino acid sequences supported the typical domain structure of both types of TALE proteins, and the homology to TALE proteins of mosses, lycophytes, and seed plant species. The expression analyses demonstrate that these homeodomain proteins appear to have a key role in the establishment and development of the gametophyte and sporophyte phases of V. speciosa lifecycle, as well as in the control of the transition between both phases. Vandenboschia speciosa VsKNAT3 (a KNOX2 class protein) as well as VsBELL4 and VsBELL10 proteins have higher expression levels during the sporophyte program. On the contrary, one V. speciosa KNOX1 protein (VsKNAT6) and one KNOX2 protein (VsKNAT4) seem important during the development of the gametophyte phase. TALE homeobox genes might be among the key regulators in the gametophyte-to-sporophyte developmental transition in regular populations that show alternation of generations, since some of the genes analyzed here (VsKNAT3, VsKNAT6, VsBELL4, and VsBELL6) are upregulated in a non-alternating population in which only independent gametophytes are found (they grow by vegetative reproduction outside of the range of sporophyte distribution). Thus, these four genes might trigger the vegetative propagation of the gametophyte and the repression of the sexual development in populations composed of independent gametophytes. This study represents a comprehensive identification and characterization of TALE homeobox genes in V. speciosa, and gives novel insights about the role of these genes in fern development.This research has been financed by the Spanish Ministerio de Economía y Competitividad and FEDER founds, grant: CGL2010-14856 (subprograma BOS).M. Bakkali wishes to thank the Spanish Ministerio de Economía y Competitividad for granting him with a Ramón y Cajal Fellowship, the BFU2010-16438 grant, and an FPI studentship to R. Martín-Blázquez

Elucidation of the Electrochemical Oxidation Mechanism of the Antioxidant Sesamol on a Glassy Carbon Electrode

The dissociation constant of Sesamol (5-hydroxy-1,3-benzodioxol) was determined from the dependence of the UV-visible spectra with the medium acidity. A pK value of 10.1 ± 0.1, corresponding to the hydroxyl group, was obtained. The oxidation of sesamol was investigated on carbon electrodes using controlled-potential electrolysis, linear-sweep cyclic voltammetry and measurements at the foot of the first oxidation peak. Up to three oxidation peaks and one reduction peak were found. The dioxol ring of the dissociated sesamol undergoes a cleavage to give 3-substituted 1,4-benzoquinone, being the rate-determining step the second electron transfer. The formation of radicals in the ring cleavage explains in part the ability of sesamol to interact with reactive oxygen species (ROS).Financial support from Junta de Andalucía (Research Groups FQM-0198, RNM-371 and FQM-0348) is gratefully acknowledged.Departamento de Ingeniería Química, Química Física y Ciencias de los Materiale

An Electrochemical Method for the Determination of Antioxidant Capacities Applied to Components of Spices and Condiments

The antioxidant activity of a set of 17 active principles present in foods is studied by using two sets of methods: i) spectrophotometric, DPPH radical scavenging method and CUPRAC assay; ii) electrochemical, using either a mercury electrode or a glassy carbon electrode covered with poly-neutral red and doped with Pt nanoparticles. The modified glassy carbon electrode assesses the scavenging activity of the antioxidants studied, improving the measurement time and easiness respect to the rest of the methods. Compared to Hg electrode, the measurements can be made in conditions close to the physiological conditions (pH 7 and aqueous medium). Using this sensor, antioxidants without activity in the DPPH radical scavenging assay can be studied. Finally, with respect to CUPRAC, the advantages of the modified electrode are the absence of organic solvent, with the consequent closeness to physiological conditions, and the lower measuring time involved. The sensitivity of this sensor is comparable with those shown by DPPH or CUPRAC.Funding from Córdoba University through “Ayudas puente para el desarrollo de proyectos de I+D precompetitivos XX Programa Propio 2016” is gratefully acknowledged.Departamento de Ingeniería Química, Química Física y Ciencias de los Materiale