Animal models of brain maldevelopment induced by cycad plant genotoxins

Cycads are long‐lived tropical and subtropical plants that contain azoxyglycosides (e.g., cycasin, macrozamin) and neurotoxic amino acids (notably β‐N‐methylamino‐l ‐alanine l ‐BMAA), toxins that have been implicated in the etiology of a disappearing neurodegenerative disease, amyotrophic lateral sclerosis and parkinsonism‐dementia complex that has been present in high incidence among three genetically distinct populations in the western Pacific. The neuropathology of amyotrophic lateral sclerosis/parkinsonism‐dementia complex includes features suggestive of brain maldevelopment, an experimentally proven property of cycasin attributable to the genotoxic action of its aglycone methylazoxymethanol (MAM). This property of MAM has been exploited by neurobiologists as a tool to study perturbations of brain development. Depending on the neurodevelopmental stage, MAM can induce features in laboratory animals that model certain characteristics of epilepsy, schizophrenia, or ataxia. Studies in DNA repair‐deficient mice show that MAM perturbs brain development through a DNA damage‐mediated mechanism. The brain DNA lesions produced by systemic MAM appear to modulate the expression of genes that regulate neurodevelopment and contribute to neurodegeneration. Epigenetic changes (histone lysine methylation) have also been detected in the underdeveloped brain after MAM administration. The DNA damage and epigenetic changes produced by MAM and, perhaps by chemically related substances (e.g., nitrosamines, nitrosoureas, hydrazines), might be an important mechanism by which early‐life exposure to genotoxicants can induce long‐term brain dysfunction. Birth Defects Research (Part C) 99:247–255, 2013. © 2013 Wiley Periodicals, Inc.     

Oxygen toxicity in the nervous tissue: Comparison of the antioxidant defense of rat brain and sciatic nerve

Nervous tissue, central and peripheral, is, as any other, subject to variations in oxygen tension, and to the attack of different xenobiotics; these situations may promote the generation of activated oxygen species of free radical character. Results are presented showing that the content of total glutathione (GSH) in brain is 10-fold that found in the sciatic nerve of the rat (2620 vs. 261 nmol/g wet weight, respectively). The existence of a relatively high superoxide dismutase activity in peripheral nervous tissue, when compared with brain or liver, in combination with the DT-diaphorase activity detected in the sciatic nerve might represent an effective defense mechanism against quinone toxicity, as is also discussed. Nervous tissue, both central and peripheral lack Se-independent GSH peroxidase activity. Finally, the activities of other glutathione-related enzymes studied in the sciatic nerve are very low, when compared with the central nervous tissue, thus suggesting a higher susceptibility of peripheral tissue to oxidative stress damage, since GSH concentration and/or any GSH-related enzymatic activities, e.g. GSH peroxidase or glutathione disulfide reductase, might become limiting.     

Herbivores and plant defences affect selection on plant reproductive traits more strongly than pollinators

Pollinators and herbivores can both affect the evolutionary diversification of plant reproductive traits. However, plant defences frequently alter antagonistic and mutualistic interactions, and therefore, variation in plant defences may alter patterns of herbivore‐ and pollinator‐mediated selection on plant traits. We tested this hypothesis by conducting a common garden field experiment using 50 clonal genotypes of white clover (Trifolium repens) that varied in a Mendelian‐inherited chemical antiherbivore defence—the production of hydrogen cyanide (HCN). To evaluate whether plant defences alter herbivore‐ and/or pollinator‐mediated selection, we factorially crossed chemical defence (25 cyanogenic and 25 acyanogenic genotypes), herbivore damage (herbivore suppression) and pollination (hand pollination). We found that herbivores weakened selection for increased inflorescence production, suggesting that large displays are costly in the presence of herbivores. In addition, herbivores weakened selection on flower size but only among acyanogenic plants, suggesting that plant defences reduce the strength of herbivore‐mediated selection. Pollinators did not independently affect selection on any trait, although pollinators weakened selection for later flowering among cyanogenic plants. Overall, cyanogenic plant defences consistently increased the strength of positive directional selection on reproductive traits. Herbivores and pollinators both strengthened and weakened the strength of selection on reproductive traits, although herbivores imposed ~2.7× stronger selection than pollinators across all traits. Contrary to the view that pollinators are the most important agents of selection on reproductive traits, our data show that selection on reproductive traits is driven primarily by variation in herbivory and plant defences in this system.     

Integrative control of the skeletal muscle microcirculation in the maintenance of arterial pressure during exercise.

Skeletal muscle blood flow and vascular conductance are influenced by numerous factors that can be divided into two general categories: central cardiovascular control mechanisms and local vascular control mechanisms. Central cardiovascular control mechanisms are thought to be designed primarily for the maintenance of arterial pressure and central cardiovascular homeostasis, whereas local vascular control mechanisms are thought to be designed primarily for the maintenance of muscle homeostasis. To support the high metabolic rates that can be generated during muscle contraction, skeletal muscle has a tremendous capacity to vasodilate and increase oxygen and nutrient delivery. During whole body dynamic exercise at maximal oxygen consumption (VO2 max), the skeletal muscle receives 85-90% of cardiac output. Yet despite receiving such a large fraction of cardiac output during high-intensity exercise, a vasodilator reserve remains with the potential to produce further elevations in skeletal muscle vascular conductance and blood flow. However, because maximal cardiac output is reached during exercise at VO2 max, further elevations in muscle vascular conductance would produce a fall in arterial pressure. Therefore, limits on muscle perfusion must be imposed during whole body exercise to prevent such drops in pressure. Effective arterial pressure control in response to a potentially hypotensive challenge during high-intensity exercise occurs primarily through reflex-mediated increases in sympathetic nerve activity, which are capable of modulating vasomotor tone of the skeletal muscle resistance vasculature. Thus skeletal muscle vascular conductance and perfusion are primarily mediated by local factors at rest and during exercise, but other centrally mediated control systems are superimposed on the dominant local control mechanisms to provide an integrated regulation of both arterial pressure and skeletal muscle vascular conductance and perfusion during whole body dynamic exercise.     

Induced defences in marine and freshwater phytoplankton: a review

Many organisms have developed defences to avoid predation by species at higher trophic levels. The capability of primary producers to defend themselves against herbivores affects their own survival, can modulate the strength of trophic cascades and changes rates of competitive exclusion in aquatic communities. Algal species are highly flexible in their morphology, growth form, biochemical composition and production of toxic and deterrent compounds. Several of these variable traits in phytoplankton have been interpreted as defence mechanisms against grazing. Zooplankton feed with differing success on various phytoplankton species, depending primarily on size, shape, cell wall structure and the production of toxins and deterrents. Chemical cues associated with (i) mechanical damage, (ii) herbivore presence and (iii) grazing are the main factors triggering induced defences in both marine and freshwater phytoplankton, but most studies have failed to disentangle the exact mechanism(s) governing defence induction in any particular species. Induced defences in phytoplankton include changes in morphology (e.g. the formation of spines, colonies and thicker cell walls), biochemistry (such as production of toxins, repellents) and in life history characteristics (formation of cysts, reduced recruitment rate). Our categorization of inducible defences in terms of the responsible induction mechanism provides guidance for future work, as hardly any of the available studies on marine or freshwater plankton have performed all the treatments that are required to pinpoint the actual cue(s) for induction. We discuss the ecology of inducible defences in marine and freshwater phytoplankton with a special focus on the mechanisms of induction, the types of defences, their costs and benefits, and their consequences at the community level.     

Mitochondria-targeted antioxidants and metabolic modulators as pharmacological interventions to slow ageing

Populations in many nations today are rapidly ageing. This unprecedented demographic change represents one of the main challenges of our time. A defining property of the ageing process is a marked increase in the risk of mortality and morbidity with age. The incidence of cancer, cardiovascular and neurodegenerative diseases increases non-linearly, sometimes exponentially with age. One of the most important tasks in biogerontology is to develop interventions leading to an increase in healthy lifespan (health span), and a better understanding of basic mechanisms underlying the ageing process itself may lead to interventions able to delay or prevent many or even all age-dependent conditions. One of the putative basic mechanisms of ageing is age-dependent mitochondrial deterioration, closely associated with damage mediated by reactive oxygen species (ROS). Given the central role that mitochondria and mitochondrial dysfunction play not only in ageing but also in apoptosis, cancer, neurodegeneration and other age-related diseases there is great interest in approaches to protect mitochondria from ROS-mediated damage. In this review, we explore strategies of targeting mitochondria to reduce mitochondrial oxidative damage with the aim of preventing or delaying age-dependent decline in mitochondrial function and some of the resulting pathologies. We discuss mitochondria-targeted and -localized antioxidants (e.g.: MitoQ, SkQ, ergothioneine), mitochondrial metabolic modulators (e.g. dichloroacetic acid), and uncouplers (e.g.: uncoupling proteins, dinitrophenol) as well as some alternative future approaches for targeting compounds to the mitochondria, including advances from nanotechnology.     

Phosphorylation of the BRCA1 C Terminus (BRCT) Repeat Inhibitor of hTERT (BRIT1) Protein Coordinates TopBP1 Protein Recruitment and Amplifies Ataxia Telangiectasia-mutated and Rad3-related (ATR) Signaling

The ataxia telangiectasia-mutated and Rad3-related (ATR) kinase functions as a central node in the DNA damage response signaling network. The mechanisms by which ATR activity is amplified and/or maintained are not understood. Here we demonstrate that BRIT1/microcephalin (MCPH1), a human disease-related protein, is dispensable for the initiation but essential for the amplification of ATR signaling. BRIT1 interacts with and recruits topoisomerase-binding protein 1 (TopBP1), a key activator of ATR signaling, to the sites of DNA damage. Notably, replication stress-induced ataxia telangiectasia-mutated or ATR-dependent BRIT1 phosphorylation at Ser-322 facilitates efficient TopBP1 recruitment. These results reveal a mechanism that ensures the continuation of ATR-initiated DNA damage signaling. Our study uncovers a previously unknown regulatory axis of ATR signaling in maintaining genomic integrity, which may provide mechanistic insights into the perturbation of ATR signaling in human diseases such as neurodevelopmental defects and cancer.     

In vivo antioxidative and neuroprotective effect of 4-Allyl-2-methoxyphenol against chlorpyrifos-induced neurotoxicity in rat brain

Chlorpyrifos exposure leads to various neurological disorders adverting disturbance in molecular pathways and normal brain functions. Major complications arise when these potent nerve agents access neuronal mechanisms causing adverse effect on acetylcholinesterase and brain lipids with generation of reactive oxygen species. Chlorpyrifos elicits chronic intoxication leading to redox disturbance with irreversible brain damage and oxidative stress. In the present study, neuroprotective and anti-apoptotic effects of eugenol (EO), a phenolic antioxidant, against chlorpyrifos-induced neurotoxicity was explored on rat brain cortex. Rats treated orally with chlorpyrifos [89.4 mg/kg body weight (BW)] for 15 consecutive days showed changes in brain lipid profile, increased levels of lipid peroxidation, inhibition of acetylcholinesterase activity, and changes in antioxidant enzymes. EO (250 mg/kg BW), administered 1 h after chlorpyrifos treatment, restored lipid, acetylcholinesterase, and antioxidant enzyme levels of brain cortex by suppressing chlorpyrifos-induced oxidative stress and neurotoxicity. Histological findings further demonstrated damage to brain morphology with increased protein levels of caspase-3 in CPF-treated animals. Alterations caused by neurotoxic effects of chlorpyrifos were attenuated by EO administration with decreased protein expressions of caspase-3. Thus, through its antioxidant and anti-apoptotic activities, EO showed protective effect against chlorpyrifos-induced neuronal damage.     

Impacts of urbanization on insect herbivory and plant defences in oak trees

Systematic comparisons of species interactions in urban versus rural environments can improve our understanding of shifts in ecological processes due to urbanization. However, such studies are relatively uncommon and the mechanisms driving urbanization effects on species interactions (e.g. between plants and insect herbivores) remain elusive. Here we investigated the effects of urbanization on leaf herbivory by insect chewers and miners associated with the English oak Quercus robur by sampling trees in rural and urban areas throughout most of the latitudinal distribution of this species. In performing these comparisons, we also controlled for the size of the urban areas (18 cities) and gathered data on CO₂ emissions. In addition, we assessed whether urbanization affected leaf chemical defences (phenolic compounds) and nutritional traits (phosphorus and nitrogen), and whether such changes correlated with herbivory levels. Urbanization significantly reduced leaf chewer damage but did not affect leaf miners. In addition, we found that leaves from urban locations had lower levels of chemical defences (condensed and hydrolysable tannins) and higher levels of nutrients (nitrogen and phosphorus) compared to leaves in rural locations. The magnitude of urbanization effects on herbivory and leaf defences was not contingent upon city size. Importantly, while the effects of urbanization on chemical defences were associated with CO₂ emissions, changes in leaf chewer damage were not associated with either leaf traits or CO₂ levels. These results suggest that effects of urbanization on herbivory occur through mechanisms other than changes in the plant traits measured here. Overall, our simultaneous assessment of insect herbivory, plant traits and abiotic correlates advances our understanding of the main drivers of urbanization effects on plant–herbivore interactions.     

The osmotic/calcium stress theory of brain damage: Are free radicals involved?

This overview presents data showing that glucose use increases and that excitatory amino acids (i.e., glutamate, aspartate), taurine and ascorbate increase in the extracellular fluid during seizures. During the cellular hyperactive state taurine appears to serve as an osmoregulator and ascorbate may serve as either an antioxidant or as a pro-oxidant. Finally, a unifying hypothesis is given for seizure-induced brain damage. This unifying hypothesis states that during seizures there is a release of excitatory amino acids which act on glutamatergic receptors, increasing neuronal activity and thereby increasing glucose use. This hyperactivity of cells causes an influx, of calcium (i.e. calcium stress) and water movements (i.e., osmotic stress) into the cells that culminate in brain damage mediated by reactive oxygen species.Special issue dedicated to Dr. Frederick E. Samson     

Commentary Oxidative Stress, Nutrition and Health. Experimental Strategies for Optimization of Nutritional Antioxidant Intake in Humans

Reactive oxygen species and reactive nitrogen species are formed in the human body. Endogenous antioxidant defences are inadequate to scavenge them completely, so that ongoing oxidative damage to DNA, lipids, proteins and other molecules can be demonstrated and may contribute to the development of cancer, cardiovascular disease and possibly neurodegenerative disease. Hence diet-derived antioxidants may be particularly important in protecting against these diseases. Some antioxidants (e.g. ascorbate, certain flavonoids) can exert pro-oxidant actions in vitro, often by interaction with transition metal ions. The physiological relevance of these effects is uncertain, as is the optimal intake of most diet-derived antioxidants. In principle, these questions could be addressed by examining the effects of dietary composition and/or antioxidant supplementation upon parameters of oxidative damage in vivo. The methods available for measuring steady-state damage (i.e. the balance between damage and repair or replacement of damaged molecules) and the actual rate of damage to DNA, proteins and lipids are reviewed, highlighting areas in which further methodological development is urgently required.     

You get what you pay for: reward-specific trade-offs among direct and ant-mediated defences in plants

Plant defences against herbivores include direct defences such as secondary metabolites or physical structures (e.g. trichomes) as well as indirect defences mediated via mutualistic interactions with other organisms including ants. Production of both direct defences and rewards for mutualistic ants may be costly for a plant, and it has been suggested that trade-offs may exist between direct and ant-mediated defences. We have conducted a meta-analysis of 25 studies testing the above hypothesis and found a significant negative correlation between plant allocation to direct and ant-mediated defences. The strength of correlation was similar for across- and within-species comparisons, and for chemical and physical direct defences. However, trade-offs with direct defences were significant only in plants which offered to ants more costly rewards such as food bodies and/or domatia, but not in plants which attracted ants with relatively cheap extrafloral nectaries. Our results therefore support the hypothesis that plant investment in ant-mediated defences may reduce the requirement for direct chemical and physical defences, but only in plants which offer more costly rewards to their bodyguards.     

Interaction between nanomaterials and the innate immune system across evolution

Interaction of engineered nanomaterials (ENMs) with the immune system mainly occurs with cells and molecules of innate immunity, which are present in interface tissues of living organisms. Immuno-nanotoxicological studies aim at understanding if and when such interaction is inconsequential or may cause irreparable damage. Since innate immunity is the first line of immune reactivity towards exogenous agents and is highly conserved throughout evolution, this review focuses on the major effector cells of innate immunity, the phagocytes, and their major sensing receptors, Toll-like receptors (TLRs), for assessing the modes of successful versus pathological interaction between ENMs and host defences. By comparing the phagocyte- and TLR-dependent responses to ENMs in plants, molluscs, annelids, crustaceans, echinoderms and mammals, we aim to highlight common recognition and elimination mechanisms and the general sufficiency of innate immunity for maintaining tissue integrity and homeostasis.     

Measurement and meaning of markers of reactive species of oxygen, nitrogen and sulfur in healthy human subjects and patients with inflammatory joint disease

Reactive species of oxygen, nitrogen and sulfur play cell signalling roles in human health, e.g. recent studies have shown that increased dietary nitrate, which is a source of RNS (reactive nitrogen species), lowers resting blood pressure and the oxygen cost of exercise. In such studies, plasma nitrite and nitrate are readily determined by chemiluminescence. At sites of inflammation, such as the joints of RA (rheumatoid arthritis) patients, the generation of ROS (reactive oxygen species) and RNS overwhelms antioxidant defences and one consequence is oxidative/nitrative damage to proteins. For example, in the inflamed joint, increased RNS-mediated protein damage has been detected in the form of a biomarker, 3-nitrotyrosine, by immunohistochemistry, Western blotting, ELISAs and MS. In addition to NO?, another cell-signalling gas produced in the inflamed joint is H2S (hydrogen sulfide), an RSS (reactive sulfur species). This gas is generated by inflammatory induction of H2S-synthesizing enzymes. Using zinc-trap spectrophotometry, we detected high (micromolar) concentrations of H2S in RA synovial fluid and levels correlated with clinical scores of inflammation and disease activity. What might be the consequences of the inflammatory generation of reactive species? Effects on inflammatory cell-signalling pathways certainly appear to be crucial, but in the current review we highlight the concept that ROS/RNS-mediated protein damage creates neoepitopes, resulting in autoantibody formation against proteins, e.g. type-II collagen and the complement component, C1q. These autoantibodies have been detected in inflammatory autoimmune diseases.     

Pharmacology of airway afferent nerve activity

Afferent nerves in the airways serve to regulate breathing pattern, cough, and airway autonomic neural tone. Pharmacologic agents that influence afferent nerve activity can be subclassified into compounds that modulate activity by indirect means (e.g. bronchial smooth muscle spasmogens) and those that act directly on the nerves. Directly acting agents affect afferent nerve activity by interacting with various ion channels and receptors within the membrane of the afferent terminals. Whether by direct or indirect means, most compounds that enter the airspace will modify afferent nerve activity, and through this action alter airway physiology.     

DNA damage induces Chk1-dependent centrosome amplification

Centrosomal abnormalities are frequently observed in cancers and in cells with defective DNA repair. Here, we used light and electron microscopy to show that DNA damage induces centrosome amplification, not fragmentation, in human cells. Caffeine abrogated this amplification in both ATM (ataxia telangiectasia, mutated)- and ATR (ATM and Rad3-related)-defective cells, indicating a complementary role for these DNA-damage-responsive kinases in promoting centrosome amplification. Inhibition of checkpoint kinase 1 (Chk1) by RNA-mediated interference or drug treatment suppressed DNA-damage-induced centrosome amplification. Radiation-induced centrosome amplification was abrogated in Chk1(-/-) DT40 cells, but occurred at normal levels in Chk1(-/-) cells transgenically expressing Chk1. Expression of kinase-dead Chk1, or Chk1S345A, through which the phosphatidylinositol-3-kinase cannot signal, failed to restore centrosome amplification, showing that signalling to Chk1 and Chk1 catalytic activity are necessary to promote centrosome overduplication after DNA damage.     

Serotonin Acts as a Radical Scavenger and Is Oxidized to a Dimer During the Respiratory Burst of Activated Microglia

Abstract: Serotonin (5-HT) is known to be readily oxidized and to act as a scavenger of reactive oxygen species produced, e.g., in the presence of peroxidase and H₂O₂ or during the respiratory burst of phagocytes. One major oxidation product formed under these conditions, the 5-HT dimer 5,5'-dihydroxy-4,4'-bitryptamine (DHBT), was suggested to have neurotoxic properties and to contribute to neuronal damage in neurodegenerative disorders. It is shown in the present study that the luminol-enhanced chemiluminescence signal measured after stimulation of the respiratory burst activity of cultivated rat microglial cells by the addition of phorbol 12-myristate 13-acetate is suppressed by 5-HT in a dose-dependent manner. During this process, 5-HT is oxidized to DHBT. Neither the intraventricular injection of DHBT nor the addition of DHBT to cultured astrocytes, neurons, or PC-12 cells was found to cause measurable cytotoxic effects. It is concluded that extracellular 5-HT locally released from platelets and 5-HT nerve endings at sites of brain damage or inflammation, through its suppressant effect on the release of reactive oxygen species during the respiratory burst of activated microglia, may contribute to attenuate secondary tissue damage in the CNS.     

Vascular effects of oxygen-derived free radicals

This review attempts to summarize the available data regarding the vascular actions of free oxygen radicals. Studies on blood vessels in situ and in vitro demonstrate that free oxygen radicals can evoke both vasodilation and vasoconstriction. Free oxygen radicals can modulate the tone of vascular smooth muscle by acting directly on the smooth muscle cells, and also via indirect mechanisms by changes in the production or biological activity of vasoactive mediators. The individual oxygen radicals may have different (sometimes opposite) vascular effects. Superoxide anion inactivates endothelium-derived relaxing factor and the adrenergic neurotransmitter norepinephrine. Hydrogen peroxide and the hydroxyl radical evoke vasodilation by acting directly on vascular smooth muscle and also by stimulating the synthesis/release of endothelium-derived relaxing factor. In acute arterial hypertension or experimental brain injury oxygen radicals are important mediators of vascular damage. Production of oxygen-derived free radicals by activated neutrophils may be responsible for vasodilation and increased permeability of capillary membrane during the acute inflammatory process. Free oxygen radicals also play an important role in reperfusion injury of various organs, and vascular actions of the free radicals may contribute to the damage of parenchymal tissues.