Role of glutathione S-transferases in the mode of action of herbicides that inhibit amino acid synthesis in Amaranthus palmeri

Acetolactate synthase inhibitors (ALS inhibitors) and glyphosate are two classes of herbicides that act by inhibiting an enzyme in the biosynthetic pathway of branched-chain or aromatic amino acids, respectively. Besides amino acid synthesis inhibition, both herbicides trigger similar physiological effects in plants. The main aim of this study was to evaluate the role of glutathione metabolism, with special emphasis on glutathione S-transferases (GSTs), in the mode of action of glyphosate and ALS inhibitors in Amaranthus palmeri. For that purpose, plants belonging to a glyphosate-sensitive (GLS) and a glyphosate-resistant (GLR) population were treated with different doses of glyphosate, and plants belonging to an ALS-inhibitor sensitive (AIS) and an ALS-inhibitor resistant (AIR) population were treated with different doses of the ALS inhibitor nicosulfuron. Glutathione-related contents, GST activity, and related gene expressions (glutamate-cysteine ligase, glutathione reductase, Phi GST and Tau GST) were analysed in leaves. According to the results of the analytical determinations, there were virtually no basal differences between GLS and GLR plants or between AIS and AIR plants. Glutathione synthesis and turnover did not follow a clear pattern in response to herbicides, but GST activity and gene expression (especially Phi GSTs) increased with both herbicides in treated sensitive plants, possibly related to the rocketing H2O2 accumulation. As GSTs offered the clearest results, these were further investigated with a multiple resistant (MR) population, compressing target-site resistance to both glyphosate and the ALS inhibitor pyrithiobac. As in single-resistant plants, measured parameters in the MR population were unaffected by herbicides, meaning that the increase in GST activity and expression occurs due to herbicide interactions with the target enzymes.

Activation of Liver X Receptors and Peroxisome Proliferator-Activated Receptors by Lipid Extracts of Brown Seaweeds: A Potential Application in Alzheimer's Disease?

The nuclear liver X receptors (LXRα/β) and peroxisome proliferator-activated receptors (PPARα/γ) are involved in the regulation of multiple biological processes, including lipid metabolism and inflammation. The activation of these receptors has been found to have neuroprotective effects, making them interesting therapeutic targets for neurodegenerative disorders such as Alzheimer's Disease (AD). The Asian brown seaweed Sargassum fusiforme contains both LXR-activating (oxy)phytosterols and PPAR-activating fatty acids. We have previously shown that dietary supplementation with lipid extracts of Sargassum fusiforme prevents disease progression in a mouse model of AD, without inducing adverse effects associated with synthetic pan-LXR agonists. We now determined the LXRα/β- and PPARα/γ-activating capacity of lipid extracts of six European brown seaweed species (Alaria esculenta, Ascophyllum nodosum, Fucus vesiculosus, Himanthalia elongata, Saccharina latissima, and Sargassum muticum) and the Asian seaweed Sargassum fusiforme using a dual luciferase reporter assay. We analyzed the sterol and fatty acid profiles of the extracts by GC-MS and UPLC MS/MS, respectively, and determined their effects on the expression of LXR and PPAR target genes in several cell lines using quantitative PCR. All extracts were found to activate LXRs, with the Himanthalia elongata extract showing the most pronounced efficacy, comparable to Sargassum fusiforme, for LXR activation and transcriptional regulation of LXR-target genes. Extracts of Alaria esculenta, Fucus vesiculosus, and Saccharina latissima showed the highest capacity to activate PPARα, while extracts of Alaria esculenta, Ascophyllum nodosum, Fucus vesiculosus, and Sargassum muticum showed the highest capacity to activate PPARγ, comparable to Sargassum fusiforme extract. In CCF-STTG1 astrocytoma cells, all extracts induced expression of cholesterol efflux genes (ABCG1, ABCA1, and APOE) and suppressed expression of cholesterol and fatty acid synthesis genes (DHCR7, DHCR24, HMGCR and SREBF2, and SREBF1, ACACA, SCD1 and FASN, respectively). Our data show that lipophilic fractions of European brown seaweeds activate LXRs and PPARs and thereby modulate lipid metabolism. These results support the potential of brown seaweeds in the prevention and/or treatment of neurodegenerative diseases and possibly cardiometabolic and inflammatory diseases via concurrent activation of LXRs and PPARs.

Cadmium-induced oxidative stress responses and acclimation in plants require fine-tuning of redox biology at subcellular level

Cadmium (Cd) is one of the most toxic compounds released into our environment and is harmful to human health, urging the need to remediate Cd-polluted soils. To this end, it is important to increase our insight into the molecular mechanisms underlying Cd stress responses in plants, ultimately leading to acclimation, and to develop novel strategies for economic validation of these soils. Albeit its non-redox-active nature, Cd causes a cellular oxidative challenge, which is a crucial determinant in the onset of diverse signalling cascades required for long-term acclimation and survival of Cd-exposed plants. Although it is well known that Cd affects reactive oxygen species (ROS) production and scavenging, the contribution of individual organelles to Cd-induced oxidative stress responses is less well studied. Here, we provide an overview of the current information on Cd-induced organellar responses with special attention to redox biology. We propose that an integration of organellar ROS signals with other signalling pathways is essential to finetune plant acclimation to Cd stress.

Role of oxidative stress in the physiology of sensitive and resistant Amaranthus palmeri populations treated with herbicides inhibiting acetolactate synthase

The aim of the present study was to elucidate the role of oxidative stress in the mode of action of acetolactate synthase (ALS) inhibiting herbicides. Two populations of Amaranthus palmeri S. Watson from Spain (sensitive and resistant to nicosulfuron, due to mutated ALS) were grown hydroponically and treated with different rates of the ALS inhibitor nicosulfuron (one time and three times the field recommended rate). Seven days later, various oxidative stress markers were measured in the leaves: H₂O₂, MDA, ascorbate and glutathione contents, antioxidant enzyme activities and gene expression levels. Under control conditions, most of the analysed parameters were very similar between sensitive and resistant plants, meaning that resistance is not accompanied by a different basal oxidative metabolism. Nicosulfuron-treated sensitive plants died after a few weeks, while the resistant ones survived, independently of the rate. Seven days after herbicide application, the sensitive plants that had received the highest nicosulfuron rate showed an increase in H₂O₂ content, lipid peroxidation and antioxidant enzymatic activities, while resistant plants did not show these responses, meaning that oxidative stress is linked to ALS inhibition. A supralethal nicosulfuron rate was needed to induce a significant oxidative stress response in the sensitive population, providing evidence that the lethality elicited by ALS inhibitors is not entirely dependent on oxidative stress.

Short-term effects of cadmium on leaf growth and nutrient transport in rice plants

Consumption of rice grains contaminated with high concentrations of cadmium (Cd) can cause serious long-term health problems. Moreover, even low Cd concentrations present in the soil can result in the abatement of plant performance, leading to lower grain yield. Studies examining the molecular basis of plant defense against Cd-induced oxidative stress could pave the way in creating superior rice varieties that display an optimal antioxidative defense system to cope with Cd toxicity. In this study, we showed that after one day of Cd exposure, hydroponically grown rice plants exhibited adverse shoot biomass and leaf growth effects. Cadmium accumulates especially in the roots and the leaf meristematic region, leading to a disturbance of manganese homeostasis in both the roots and leaves. The leaf growth zone showed an increased amount of lipid peroxidation indicating that Cd exposure disturbed the oxidative balance. We propose that an increased expression of genes related to the glutathione metabolism such as glutathione synthetase 2, glutathione reductase and phytochelatin synthase 2, rather than genes encoding for antioxidant enzymes, is important in combating early Cd toxicity within the leaves of rice plants. Furthermore, the upregulation of two RESPIRATORY BURST OXIDASE HOMOLOG genes together with a Cd concentration-dependent increase of abscisic acid might cause stomatal closure or cell wall modification, potentially leading to the observed leaf growth reduction. Whereas abscisic acid was also elevated at long term exposure, a decrease of the growth hormone auxin might further contribute to growth inhibition and concomitantly, an increase in salicylic acid might stimulate the activity of antioxidative enzymes after a longer period of Cd exposure. In conclusion, a clear interplay between phytohormones and the oxidative challenge affect plant growth and acclimation during exposure to Cd stress.

Cadmium inhibits cell cycle progression and specifically accumulates in the maize leaf meristem

It is well known that cadmium (Cd) pollution inhibits plant growth, but how this metal impacts leaf growth processes at the cellular and molecular level is still largely unknown. In the current study, we show that Cd specifically accumulates in the meristematic tissue of the growing maize leaf, while Cd concentration in the elongation zone rapidly declines as the deposition rates diminish and cell volumes increase due to cell expansion. A kinematic analysis shows that, at the cellular level, a lower number of meristematic cells together with a significantly longer cell cycle duration explain the inhibition of leaf growth by Cd. Flow cytometry analysis suggests an inhibition of the G1/S transition, resulting in a lower proportion of cells in the S phase and reduced endoreduplication in expanding cells under Cd stress. Lower cell cycle activity is also reflected by lower expression levels of key cell cycle genes (putative wee1, cyclin-B2-4, and minichromosome maintenance4). Cell elongation rates are also inhibited by Cd, which is possibly linked to the inhibited endoreduplication. Taken together, our results complement studies on Cd-induced growth inhibition in roots and link inhibited cell cycle progression to Cd deposition in the leaf meristem.

Give CRISPR a Chance: the GeneSprout Initiative

Did you know that a group of early-career researchers launched an initiative enabling open dialog on new plant breeding techniques, such as genome editing? We developed a wide-ranging initiative that aims to facilitate public engagement and provide a platform for young plant scientists to encourage participation in science communication.

Suppressor of Gamma Response 1 Modulates the DNA Damage Response and Oxidative Stress Response in Leaves of Cadmium-Exposed Arabidopsis thaliana

Cadmium (Cd) exposure causes an oxidative challenge and inhibits cell cycle progression, ultimately impacting plant growth. Stress-induced effects on the cell cycle are often a consequence of activation of the DNA damage response (DDR). The main aim of this study was to investigate the role of the transcription factor SUPPRESSOR OF GAMMA RESPONSE 1 (SOG1) and three downstream cyclin-dependent kinase inhibitors of the SIAMESE-RELATED (SMR) family in the Cd-induced DDR and oxidative challenge in leaves of Arabidopsis thaliana. Effects of Cd on plant growth, cell cycle regulation and the expression of DDR genes were highly similar between the wildtype and smr4/5/7 mutant. In contrast, sog1-7 mutant leaves displayed a much lower Cd sensitivity within the experimental time-frame and significantly less pronounced upregulations of DDR-related genes, indicating the involvement of SOG1 in the Cd-induced DDR. Cadmium-induced responses related to the oxidative challenge were disturbed in the sog1-7 mutant, as indicated by delayed Cd-induced increases of hydrogen peroxide and glutathione concentrations and lower upregulations of oxidative stress-related genes. In conclusion, our results attribute a novel role to SOG1 in regulating the oxidative stress response and connect oxidative stress to the DDR in Cd-exposed plants.

The Effect of Ambient Temperature on Brachypodium distachyon Development

Due to climate change, the effect of temperature on crops has become a global concern. It has been reported that minor changes in temperature can cause large decreases in crop yield. While not a crop, the model Brachypodium distachyon can help to efficiently investigate ambient temperature responses of temperate grasses, which include wheat and barley. Here, we use different accessions to explore the effect of ambient temperature on Brachypodium phenology. We recorded leaf initiation, heading time, leaf and branch number at heading, seed set time, seed weight, seed size, seed dormancy, and seed germination at different temperatures. We found that warmer temperatures promote leaf initiation so that leaf number at heading is positively correlated to temperature. Heading time is not correlated to temperature but accessions show an optimal temperature at which heading is earliest. Cool temperatures prolong seed maturation which increases seed weight. The progeny seeds of plants grown at these cool ambient temperatures show stronger dormancy, while imbibition of seeds at low temperature improves germination. Among all developmental stages, it is the duration of seed maturation that is most sensitive to temperature. The results we found reveal that temperature responses in Brachypodium are highly conserved with temperate cereals, which makes Brachypodium a good model to explore temperature responsive pathways in temperate grasses.

Cadmium and Plant Development: An Agony from Seed to Seed

Anthropogenic pollution of agricultural soils with cadmium (Cd) should receive adequate attention as Cd accumulation in crops endangers human health. When Cd is present in the soil, plants are exposed to it throughout their entire life cycle. As it is a non-essential element, no specific Cd uptake mechanisms are present. Therefore, Cd enters the plant through transporters for essential elements and consequently disturbs plant growth and development. In this review, we will focus on the effects of Cd on the most important events of a plant's life cycle covering seed germination, the vegetative phase and the reproduction phase. Within the vegetative phase, the disturbance of the cell cycle by Cd is highlighted with special emphasis on endoreduplication, DNA damage and its relation to cell death. Furthermore, we will discuss the cell wall as an important structure in retaining Cd and the ability of plants to actively modify the cell wall to increase Cd tolerance. As Cd is known to affect concentrations of reactive oxygen species (ROS) and phytohormones, special emphasis is put on the involvement of these compounds in plant developmental processes. Lastly, possible future research areas are put forward and a general conclusion is drawn, revealing that Cd is agonizing for all stages of plant development.

Corrigendum: Reciprocal Interactions between Cadmium-Induced Cell Wall Responses and Oxidative Stress in Plants

[This corrects the article on p. 1867 in vol. 8, PMID: 29163592.].

Reciprocal Interactions between Cadmium-Induced Cell Wall Responses and Oxidative Stress in Plants

Cadmium (Cd) pollution renders many soils across the world unsuited or unsafe for food- or feed-orientated agriculture. The main mechanism of Cd phytotoxicity is the induction of oxidative stress, amongst others through the depletion of glutathione. Oxidative stress can damage lipids, proteins, and nucleic acids, leading to growth inhibition or even cell death. The plant cell has a variety of tools to defend itself against Cd stress. First and foremost, cell walls might prevent Cd from entering and damaging the protoplast. Both the primary and secondary cell wall have an array of defensive mechanisms that can be adapted to cope with Cd. Pectin, which contains most of the negative charges within the primary cell wall, can sequester Cd very effectively. In the secondary cell wall, lignification can serve to immobilize Cd and create a tougher barrier for entry. Changes in cell wall composition are, however, dependent on nutrients and conversely might affect their uptake. Additionally, the role of ascorbate (AsA) as most important apoplastic antioxidant is of considerable interest, due to the fact that oxidative stress is a major mechanism underlying Cd toxicity, and that AsA biosynthesis shares several links with cell wall construction. In this review, modifications of the plant cell wall in response to Cd exposure are discussed. Focus lies on pectin in the primary cell wall, lignification in the secondary cell wall and the importance of AsA in the apoplast. Regarding lignification, we attempt to answer the question whether increased lignification is merely a consequence of Cd toxicity, or rather an elicited defense response. We propose a model for lignification as defense response, with a central role for hydrogen peroxide as substrate and signaling molecule.

Observational survey of NSAID-related upper gastro-intestinal adverse events in Belgium

OBJECTIVES

To evaluate the impact of NSAID use on current routine upper GI endoscopy (UGIE) and to compare the lesions found in NSAID users and non-users.

METHODS

Participating gastroenterologists consecutively documented outpatients with and without suspicion of bleeding, referred for upper gastrointestinal endoscopy. Patient characteristics, presence of risk factors, NSAID use and endoscopic findings were reported on standard data collection forms.

MAIN RESULTS

A total of 2685 non-bleeding and 159 bleeding patients were enrolled within a time period of 2 months. NSAID therapy was present in 20% of the non-bleeding patients and at least 9% of referrals for endoscopy were directly related to suspected NSAID adverse events. Nearly half of acute bleeding patients (42%) were NSAID users, including aspirin for cardioprevention. Warning digestive symptoms prior to acute bleeding were frequently absent (56%). Oesophagitis was the main endoscopic diagnosis (51% of patients). Gastroduodenal (GD) ulcer was significantly more frequent in NSAID users, whereas oesophagitis and bleeding oesophageal varices were more frequent among non-users. Analysis of odds ratio's demonstrated NSAID use to significantly increase the risk for gastric ulcer in the whole patient group (OR = 2.73; 95% confidence interval (CI): 1.98-3.77; p < 0.001) and, in addition, for duodenal ulcer in the elderly (> 65 y) subgroup (OR = 2.91; 95% CI: 1.52-5.59; p < 0.05).

CONCLUSIONS

This survey confirms the high incidence of GD ulcers in NSAID users and the risk for serious gastrointestinal complications, often occurring without warning symptoms. It underlines the impact of NSAID use on the routine endoscopy load, the necessity of careful selection of patients for NSAID prescriptions and the need for gastropreventive measures, particularly in elderly patients and patients associating multiple risk factors.

Pricing and reimbursement of pharmaceuticals in Belgium

The Belgian healthcare system has a tradition of access and equity at affordable prices. As in other countries, the system becomes pressured by increasing healthcare costs. This paper describes the actual situation in Belgium with special focus on pharmaceutical products and the potential role of pharmacoeconomics in decision making on price and reimbursement. Nearly all people in Belgium are covered by compulsory health insurance. The system is paid for by social security, the patients and the federal and regional authorities. The part of the consumption of pharmaceuticals that is charged to insurance was about 62.1 billion Belgian francs (BeF), i.e. about 50% of the pharmaceutical market in 1994. Price setting in Belgium has been rather low due to the positive reimbursement list, where the price of a new drug is compared to existing drugs in a comparable therapeutic class (so-called reimbursement criteria). The expenditure on pharmaceuticals is increasing faster than global funding for public health. In order to control drug budgets, different cost-containment measures have been or are being taken, i.e. a mix of price, reimbursement and volume controls. These cost-containment measures are not necessarily in accordance with a health economic approach. This paper suggests the scope for better implementation of pharmacoeconomic evaluation, which can lead to more flexible reimbursement systems in specific indications. Therefore, a formal recognition of the role of objective economic evaluations is needed for both hospital and ambulatory care. This process should be proceeded by improving the understanding and robustness of pharmacoeconomic evaluations.

Inhibition of steroid-protein interactions by dicyclohexane derivatives

Sixteen dicyclohexane derivatives including the parent compound d,1-3,4-bis (4-oxocyclohexyl)-hexane (PRDX) have been synthesized and studied for putative interference with androgen binding to transport proteins, metabolizing enzymes, and receptors from rat tissues. Several of these analogues inhibited competitively the binding of dihydrotestosterone to ABP, the epididymal androgen transport protein. One compound had an affinity for ABP as high as Kd = 70 nM. Some dicyclohexanes also inhibited the aromatase enzyme which catalyses conversion of androgens into estrogens, as well as the NADPH-dependent, particulate form of 3 alpha(beta)-hydroxysteroid dehydrogenase, the enzyme that converts dihydrotestosterone into 5 alpha-androstanediol. For both enzymes the inhibition potency Ki of PRDX was about equal to the Km of the substrate. All of these interactions were specific in that they were modulated by single substitutions on the dicyclohexane molecule and they did not occur with other steroid binding proteins such as 5 alpha-reductase and the intracellular androgen receptor. A conformational study showed that dicyclohexanes can assume a 'steroidoid' conformation that differs from the crystal structure and which could account for the specific interactions with the steroid binding sites described here.

Hematuria as presenting sign in Wissler-Fanconi syndrome

We describe a case of persistent microscopic hematuria as initial finding in incomplete Still's disease or Wissler-Fanconi syndrome. Renal biopsy findings were compatible with intravascular coagulation. Wissler-Fanconi syndrome and the associated renal abnormalities are briefly reviewed.

In vivo stimulation and inhibition of granulopoiesis: the effect of an inflammatory reaction on murine diffusion chamber granulopoiesis

Humoral factors influencing granulopoiesis have been evaluated using diffusion chambers (DC) implanted in the peritoneal cavity of mice challenged by an aseptic abscess produced by the subcutaneous implantation of copper rods. This resulted in an increase in peripheral blood neutrophils and an increase in tibial granulocytic elements. When DC loaded with bone-marrow cells were implanted into mice stimulated the day before by an aseptic abscess significantly more CFU-s, CFU-c, proliferative and non-proliferative granulocytes were produced, as compared to DC implanted into control hosts. When DC were implanted 4-6 d after the induction of inflammation in mice a significant depression of DC granulopoiesis was observed. Levels of serum and DC fluid CSF and serum inhibitors of in vitro colony growth showed no correlation with DC myelopoiesis. The data show that mice undergoing an inflammatory reaction elaborate first humoral substance(s) enhancing CFU-s and granulocytic growth in DC and next inhibitory factor(s) of DC granulopoiesis.

Comparative toxicity of detorubicin and doxorubicin, free and DNA-bound, for hemopoietic stem cells

We compared the toxicity of detorubicin (DET) and of doxorubicin (DOX) on the hematopoietic stem cells in C57BL6J mice by means of the CFUS and CFUC assays. On an equimolar basis DET appears to be less toxic than DOX for both the pluripotent stem cells and the granulocytic progenitor cells. Moreover, the administration of these anthracyclines as DNA complexes leads to a decreased toxicity to the pluripotent stem cells, while no such attenuated toxic effect is observed in committed stem cells.

Effects of daunorubicin and doxorubicin, free and associated with DNA, on hemopoietic stem cells

We have compared daunorubicin (DNR)-DNA with free DNR and doxorubicin (DOX)-DNA with free DOX for their effects in vivo in mice on pluripotent stem cells and granulocytic committed stem cells. Dose-survival, time-survival, and recovery curves were obtained after one i.v. injection of either drug. The dose-survival curves of colony-forming units-spleen (CFU-S) and colony-forming units-committed stem cells (CFU-C) were exponential in shape with both agents. DNR-DNA appeared more toxic to the hemopoietic precursor cells than did free DNR. In contrast, DOX-DNA was less toxic toward CFU-S and as toxic as DOX toward CFU-C. Time-survival curves indicated a minimum level of CFU-S and CFU-C at about 33 hr. After that, the recovery of CFU-S was rapid for DNR-treated mice but remained below 50% of the controls on Day 12 for the DNR-DNA-treated group. In mice previously given injections of DOX or DOX-DNA, the recovery of the CFU-S was more protracted in time with a better recovery in mice treated with DOX-DNA. Both DNR and DNR-DNA induced an initial CFU-C decrease followed by a rapid but transient rise with a maximum on Day 4 after chemotherapy. On Day 12, the CFU-C recovery was still incomplete in both DNR- and DNR-DNA-treated mice. In the groups treated with DOX, the CFU-C recovery was more important after DOX-DNA complex than after free DOX. The results are discussed in view of the "lysosomotropic chemotherapy" hypothesis.

The diffusion chamber technique as an in vivo assay in mice for the effectiveness of antitumor agents

The diffusion chamber (DC) technique has been applied to the culture of L1210 cells in view of determining their sensitivity to chemotherapic agents. The surviving fraction of L1210 cells cultivated in DC's 4 d after i.v. injection of the host mice with 10 mg/kg of daunorubicin or daunorubicin-DNA was 40% and 9% respectively. The results suggest that the DC technique could be a useful in vivo predictive test for cancer chemotherapy.

Comparative study in mice of the toxicity, pharmacology, and therapeutic activity of daunorubicin-DNA and doxorubicin-DNA complexes

We have compared the toxicologic, pharmacologic, and therapeutic properties of the DNA complexes of daunorubicin and doxorubicin, after intravenous (IV) administration into mice. The overall toxicity of doxorubicin is significantly reduced after IV injection as a DNA complex while daunorubicin-DNA is as toxic as free daunorubicin. On hemopoietic stem cells, daunorubicin-DNA was found to be more cytotoxic than daunorubicin, while the opposite was observed with doxorubicin and doxorubicin-DNA. Both complexes are more effective than the corresponding free drugs on the L1210 murine leukemia, when given IV at equitoxic doses. The tissue uptake in mice, after IV administration, is generally lower when the drugs are given bound to DNA. The stability of the two DNA complexes is very different in the bloodstream: daunorubicin-DNA behaves more like a prodrug of daunorubicin, while doxorubicin-DNA, remaining stable in the bloodstream, meets much more the requirements of an ideal drug-macromoleculare carrier entity.