Developed Defense Mechanisms Research Articles

Lysozyme--occurrence in nature, biological properties and possible applications

Lysozyme (LZ, muramidase, N-acetylmuramylhydrolase) is a protein occuring in animals, plants, bacteria and viruses. It can be found e.g. in granules of neutrophils, macrophages and in serum, saliva, milk, honey and hen egg white. The enzyme hydrolyzes the β-1,4 glycosidic bonds between N-acetylmuramic acid (NAM) and N-acetylglucosamine (NAG) of cell wall peptidoglycan (PG) in Gram-positive and Gram-negative bacteria. In the animal kingdom, three muramidase types have been identified: the c-type (chicken type), the g-type (goose-type) and the i-type (invertebrates). The c-type LZ from hen egg white is a model for the study of protein structure and function. Muramidase shows bactericidal activity mainly against Gram-positive bacteria. Cytolytic activity against cells of Gram-negative bacteria has not been proved. Bacterial cells have developed defense mechanisms that allow them to avoid the action of LZ. They are based e.g. on the production of enzyme inhibitors or modification of the PG. LZ is one of the most studied enzymes and yet not all aspects characterizing this protein are fully understood. One of the most important unresolved issues concerning the biological function of LZ is the role of muramidase in the bactericidal action of serum against Gram-negative bacteria. In order to clarify the function of LZ, the enzyme is e.g. removed from the serum by adsorption onto bentonite (montmorillonite, MMT). By using X-ray diffraction techniques it has been shown that MMT after contact with the serum is delaminated. The problems associated with folding of muramidase and LZ participation in the development of amyloidoses also await explanation.

Medicina darwiniana y psoriasis

Darwinian medicine, or evolutionary medicine, regards some pathological conditions as attempts by the organism to solve a problem or develop defense mechanisms. At certain stages of human evolution, some diseases may have conferred a selective advantage. Psoriasis is a high-penetrance multigenic disorder with prevalence among whites of up to 3%. Psoriatic lesions have been linked with enhanced wound-healing qualities and greater capacity to fight infection. Leprosy, tuberculosis, and infections caused by viruses similar to human immunodeficiency virus have been postulated as environmental stressors that may have selected for psoriasis-promoting genes in some human populations. The tendency of patients with severe psoriasis to develop metabolic syndrome may reflect the body's attempt to react to environmental stresses and warning signs by triggering insulin resistance and fat storage.

Uso de biomarcador histopatológico em brânquias de Centropomus undecimalis (Bloch, 1972) na avaliação da qualidade da água do Parque Ecológico Laguna da Jansen, São Luís - MA

Com o objetivo de analisar a intensidade das alterações histológicas em brânquias de Centropomus undecimalis para avaliar a qualidade da água do Parque Ecológico Laguna da Jansen, em São Luís, Estado do Maranhão, coletaram-se exemplares de peixes no período chuvoso de 2012 e amostras de água nos períodos seco de 2011 e chuvoso de 2012 para análises físico-química e bacteriológica. Os resultados mostraram que a maioria dos parâmetros físico-químicos e bacteriológicos estava de acordo com os valores estabelecidos pela Resolução do CONAMA nº 357 de 2005. As alterações histológicas observadas foram: elevação do epitélio lamelar; proliferação excessiva de células dos epitélios filamentar e lamelar causando fusão total ou parcial das lamelas; alteração da estrutura das lamelas; hiperplasia das células mucosas; ruptura do epitélio lamelar; espessamento descontrolado do tecido proliferativo filamentar e lamelar e aneurismas de vários tamanhos. Também foi observada a presença de parasito em alguns exemplares. O Índice de Alteração Histológica (IAH) por indivíduo variou de 2 a 114. O valor médio do IAH obtido foi de 40,3, demonstrando que as brânquias dos indivíduos amostrados da espécie C. undecimalis apresentaram alterações de moderadas para severas no tecido. As alterações histológicas encontradas indicam que esses indivíduos desenvolveram mecanismos de defesa contra a ação de estressores presentes na água da laguna e a um provável desequilíbrio parasito-hospedeiro-ambiente associado à baixa qualidade do ambiente.

MANIFESTAÇÕES PSICOSSOMÁTICAS ASSOCIADAS À SÍNDROME DE BURNOUT REFERIDAS POR TRABALHADORES DE SAÚDE

The work in the area of health has caused great physical and psychological workers who go on to develop defense mechanisms manifested by physical and psychological reactions, leading to the emergence of new diseases. We conducted a descriptive study with quantitative and workers who work in a hospital of medium complexity. The objective was to describe the physical symptoms reported by workers who had signs and symptoms of burnout syndrome. 160 professionals participated in the survey. It was observed that all who had signs and symptoms of burnout syndrome reported the presence of physical symptoms were the most common: headache, feeling of mental fatigue, changes in appetite, hypertension, and sleep difficulties. These symptoms may be severe and have a great impact on both the professional and personal lives of his victims. It is important to identify these symptoms early to ensure a more rapid and effective.

Comparative genomics analysis of Lactobacillus species associated with weight gain or weight protection

BACKGROUND:Some Lactobacillus species are associated with obesity and weight gain while others are associated with weight loss. Lactobacillus spp. and bifidobacteria represent a major bacterial population of the small intestine where lipids and simple carbohydrates are absorbed, particularly in the duodenum and jejunum. The objective of this study was to identify Lactobacillus spp. proteins involved in carbohydrate and lipid metabolism associated with weight modifications.METHODS:We examined a total of 13 complete genomes belonging to seven different Lactobacillus spp. previously associated with weight gain or weight protection. We combined the data obtained from the Rapid Annotation using Subsystem Technology, Batch CD-Search and Gene Ontology to classify gene function in each genome.RESULTS:We observed major differences between the two groups of genomes. Weight gain-associated Lactobacillus spp. appear to lack enzymes involved in the catabolism of fructose, defense against oxidative stress and the synthesis of dextrin, L-rhamnose and acetate. Weight protection-associated Lactobacillus spp. encoded a significant gene amount of glucose permease. Regarding lipid metabolism, thiolases were only encoded in the genome of weight gain-associated Lactobacillus spp. In addition, we identified 18 different types of bacteriocins in the studied genomes, and weight gain-associated Lactobacillus spp. encoded more bacteriocins than weight protection-associated Lactobacillus spp.CONCLUSIONS:The results of this study revealed that weight protection-associated Lactobacillus spp. have developed defense mechanisms for enhanced glycolysis and defense against oxidative stress. Weight gain-associated Lactobacillus spp. possess a limited ability to breakdown fructose or glucose and might reduce ileal brake effects.

NOCTUIDAE-INDUCED PLANT VOLATILES: CURRENT SITUATION AND PROSPECTS

Noctuids are phytophagous lepidopterans with some species causing significant damage to agriculture. The host plants, in turn, have developed defense mechanisms to cope with them, for instance chemical defenses. In this study we review the literature on plant volatiles induced by noctuids, and discuss the methodologies used to induce the production of volatiles that are usually employed in plant defense mechanisms. Future prospects involving this line of research in pest control are also discussed.

Cleavage of Phage DNA by the Streptococcus thermophilus CRISPR3-Cas System

Streptococcus thermophilus, similar to other Bacteria and Archaea, has developed defense mechanisms to protect cells against invasion by foreign nucleic acids, such as virus infections and plasmid transformations. One defense system recently described in these organisms is the CRISPR-Cas system (Clustered Regularly Interspaced Short Palindromic Repeats loci coupled to CRISPR-associated genes). Two S. thermophilus CRISPR-Cas systems, CRISPR1-Cas and CRISPR3-Cas, have been shown to actively block phage infection. The CRISPR1-Cas system interferes by cleaving foreign dsDNA entering the cell in a length-specific and orientation-dependant manner. Here, we show that the S. thermophilus CRISPR3-Cas system acts by cleaving phage dsDNA genomes at the same specific position inside the targeted protospacer as observed with the CRISPR1-Cas system. Only one cleavage site was observed in all tested strains. Moreover, we observed that the CRISPR1-Cas and CRISPR3-Cas systems are compatible and, when both systems are present within the same cell, provide increased resistance against phage infection by both cleaving the invading dsDNA. We also determined that overall phage resistance efficiency is correlated to the total number of newly acquired spacers in both CRISPR loci.

Regulation of Flvcr by Macrophages in Response to Lipopolysaccharide

Abstract 2111Pathogenic bacteria must acquire iron from their hosts to survive and have evolved multiple mechanisms to capture iron or iron-containing heme from the bloodstream or tissues. In response, mammals have developed defense mechanisms to keep iron from pathogens. For example, in response to inflammatory cytokines, hepcidin secreted by the liver binds to the iron exporter ferroportin (FPN1), leading to FPN1 internalization and degradation, decreasing gastrointestinal iron absorption and increasing macrophage iron storage. Much of the body's iron stores are complexed in heme. The Feline leukemia virus, subgroup C (FeLV-C) receptor, FLVCR, is a heme export protein. We showed previously that FLVCR is required for the normal development of the erythroid [Science (2008)319:825] and T cell lineages [Blood (ASH Annual Meeting Abstracts)114:913,2009].Although macrophages express high levels of FLVCR, the role of FLVCR in regulating heme-iron after infection remains unexplored. Other heme regulatory proteins, such as heme oxygenase-1 (HMOX1), a heme-degrading enzyme, are known to be transcriptionally regulated in macrophages in response to infection. We hypothesized that macrophages dynamically regulate Flvcr in response to bacterial infection. To test this hypothesis, we stimulated J774, a murine macrophage cell line, with lipopolysaccharide (LPS from E. coli O111:B4) at varying concentrations and durations. LPS, an outer membrane component from gram-negative bacteria, binds to Toll-like receptor 4 (TLR4) on macrophages and activates downstream signaling pathways. Using multiplex quantitative reverse transcription polymerase chain reaction (qRT-PCR), we measured mRNA levels of Flvcr, Hmox1, and Fpn1. We found that J774 cells down-regulated Flvcr transcript levels in response to LPS with a maximal decrease (69%) seen at 6–8 hours of stimulation. While the extent of Flvcr down-regulation was dose-responsive, a significant decrease (57%) occurred even with the lowest LPS dose (10 ng/ml). Macrophages decreased Fpn1 expression (71%) and increased Hmox1 expression (55%) in response to LPS stimulation as previously reported. Similar results were obtained with LPS from a different bacterial source (Salmonella minnesota Re595). We also performed these studies using primary macrophages cultured from murine bone marrow mononuclear cells and observed a similar decrease in Flvcr and Fpn1 (64 and 72%) and an increase in Hmox1 (40%) transcripts after stimulation with both O111:B4 and Re595 LPS.While Fpn1 transcriptional regulation by heme and oxidative stress has been studied, the mechanism by which LPS regulates Fpn1 transcription is less clear. The similar pattern and kinetics of LPS-induced Flvcr and Fpn1 expression changes raise the possibility that the same regulatory mechanism is responsible. Analysis of the human and mouse Flvcr promoter regions revealed several putative LPS downstream transcription factor binding sites including NF-κB, AP1, and C/EBPβ. In addition to transcriptional regulation, LPS downstream signaling could alter Flvcr and Fpn1 mRNA stability and translation, so we compared the 5’ untranslated regions (UTR) and 3’UTR of murine Flvcr and Fpn1. We found little similarity between the 5’UTR of Flvcr and the 5’UTR of Fpn1, known to contain an iron-responsive element (IRE) and be regulated by iron via iron regulatory proteins (IRP). However, alignment of the 3’UTR from Flvcr and Fpn1 showed similarity (pair wise score 65). Both the Flvcr and Fpn1 3’UTR are predicted to have a high degree of secondary structure based on their large negative fold energies (−421.25 and −300.74 kcal/mol), further suggesting that these 3’UTR may have a regulatory function. Studies are underway to determine the roles of the Flvcr promoter, 5’UTR, and 3’UTR in LPS-induced down-regulation.This work suggests that LPS-induced down-regulation of Flvcr and Fpn1 might act in concert to decrease heme and iron export from macrophages and sequester iron from bacterial pathogens. Heme export control through FLVCR could serve as a novel mechanism of iron regulation in response to infection. Disclosures:No relevant conflicts of interest to declare.

Identification of SNPs in candidate genes related to water stress in Eucalyptus

Background Forestry companies have occupied Northern and Northeastern of Brazil with plantations of Eucalyptus species; however, limitations on water supply are affecting the biomass production and reducing the yield significantly [1].Tolerant plants develop defense mechanisms like hormone production of abscisic acid (ABA) and osmoprotector glycine betain (GB) when submitted to drought conditions [2]. Identifying and studying genomic regions related to water stress tolerance are important for tree improvement programs. In this work, SNPs in candidate genes, 9-cis-epoxy-carotenoid dioxygenase (NCED) and choline monooxygenase (CMO), of ABA and GB biosynthetic pathways related to drought tolerance in a population of Eucalyptus were identified, as well as, a possible molecular marker associated to genomic regions related to plant response to water stress through AFLP technique [3] combined with bulk segregant analysis method [4].

Purification, crystallization and X-ray crystallographic analysis of Archaeoglobus fulgidus neelaredoxin.

Neelaredoxins are a type of superoxide reductase (SOR), which are blue 14 kDa metalloproteins with a catalytic nonhaem iron centre coordinated by four histidines and one cysteine in the ferrous form. Anaerobic organisms such as Archaeoglobus fulgidus, a hyperthermophilic sulfate-reducing archaeon, have developed defence mechanisms against toxic oxygen species in which superoxide reductases play a key role. SOR is responsible for scavenging toxic superoxide anion radicals (O(2)(*-)), catalysing the one-electron reduction of superoxide to hydrogen peroxide. Crystals of recombinant A. fulgidus neelaredoxin in the oxidized form (13.7 kDa, 125 residues) were obtained using polyethylene glycol and ammonium sulfate. These crystals diffracted to 1.9 A resolution and belonged to the tetragonal space group P4(1)2(1)2, with unit-cell parameters a = b = 75.72, c = 185.44 A. Cell-content analysis indicated the presence of a tetramer in the asymmetric unit, with a Matthews coefficient (V(M)) of 2.36 A(3) Da(-1) and an estimated solvent content of 48%. The three-dimensional structure was determined by the MAD method and is currently under refinement.

Shoot Development and Extension of Quercus serrata Saplings in Response to Insect Damage and Nutrient Conditions

Plants have the ability to compensate for damage caused by herbivores. This is important to plant growth, because a plant cannot always avoid damage, even if it has developed defence mechanisms against herbivores. In previous work, we elucidated the herbivory-induced compensatory response of Quercus (at both the individual shoot and whole sapling levels) in both low- and high-nutrient conditions throughout one growing season. In this study, we determine how the compensatory growth of Quercus serrata saplings is achieved at different nutrient levels. Quercus serrata saplings were grown under controlled conditions. Length, number of leaves and percentage of leaf area lost on all extension units (EUs) were measured. Both the probability of flushing and the length of subsequent EUs significantly increased with an increase in the length of the parent EU. The probability of flushing increased with an increase in leaf damage of the parent EU, but the length of subsequent EUs decreased. This indicates that EU growth is fundamentally regulated at the individual EU level. The probabilities of a second and third flush were significantly higher in plants in high-nutrient soil than those in low-nutrient soil. The subsequent EUs of damaged saplings were also significantly longer at high-nutrient conditions. An increase in the probability of flushes in response to herbivore damage is important for damaged saplings to produce new EUs; further, shortening the length of EUs helps to effectively reproduce foliage lost by herbivory. The probability of flushing also varied according to soil nutrient levels, suggesting that the compensatory growth of individual EUs in response to local damage levels is affected by the nutrients available to the whole sapling.

Mechanism by which bacterial flagellin stimulates host mucin production.

In their quest to colonize and infect host tissues, bacteria cause considerable damage to their hosts. Based on this, an evolutionary trend has occurred for host organisms to develop defense mechanisms against bacteria. One is mucin production. Mucin is a high molecular weight glycoprotein synthesized by non-keratinized epithelial cells at the boundary of the host with its environment. The size of a single mucin monomer can be as large as 1 million daltons, most of which is composed of carbohydrate residue. Mucin molecules polymerize by disulfide bonds and electrostatic interactions to form a viscoelastic gel that effectively augments the barrier between host and bacteria. In the respiratory tract, bacteria-laden mucus is conducted toward the throat by cilia and then either swallowed or expectorated. In the eye, bacteria-laden mucus is cleared by blinking.

Quinolones et fluoroquinolones dans l'univers bactérien

Due to their narrow range of activity which is limited to Gram-negative bacteria and to their specific pharmacokinetic properties which result in high urinary concentrations, the first-generation quinolones, the most important of which is nalidixic acid, have basically remained drugs for the treatment of urinary infections in the adult with enterobacterial infection. During the 1980s the fluoroquinolones were introduced for use as therapeutic drugs, in particular pefloxacin, ofloxacin, and ciprofloxacin, which are active against staphylococci and to a certain extent against Pseudomonas aeruginosa. The 1990s were marked by the appearance of new fluoroquinolones which had developed an activity at low concentrations against pneumococci, including both those that were sensitive and resistant to penicillin G, thereby permitting their range to be extended to the treatment of respiratory infections. In the past 40 years, the quinolone group has increased and gained ground over the bacterial environment. The latter has developed defense mechanisms, i.e., bacterial resistance. The role of the practitioner is to survey the use of these new antimicrobial agents so that their therapeutic effect is maintained or even reinforced. The essential condition for this is respect for good medical practice. As in all things, it is abuse rather than judicious use that creates problems.

Toward a Cultural Theory of Human Rights

Although the term `human rights' is traditionally taken to refer to fundamental rights enshrined in formal documents, certain basic `normative rights', such as turn-taking, are central to everyday social life. This paper moves toward a cultural theory of rights, proposing that certain fundamental relations, referred to as `primitive social relations', are inherent in human social life and relative to the local political orientation can appear as rights or duties. Second, normative rights/duties are maintained through evolutionary developed social skills that are integral to local cultures. Modernization has been associated with a nullification or `side-stepping' of evolutionary developed defense mechanisms protecting normative rights. Third, legislated rights/duties are a recent arrival in human cultural evolution, and they arose out of the new social relations inherent to large and complex Modern societies.

The stressful condition as a nutritionally dependent adaptive dichotomy.

The injured body manifests a cascade of cytokine-induced metabolic events aimed at developing defense mechanisms and tissue repair. Rising concentrations of counterregulatory hormones work in concert with cytokines to generate overall insulin and insulin-like growth factor 1 (IGF-1), postreceptor resistance and energy requirements grounded on lipid dependency. Salient features are self-sustained hypercortisolemia persisting as long as cytokines are oversecreted and down-regulation of the hypothalamo-pituitary-thyroid axis stabilized at low basal levels. Inhibition of thyroxine 5'-deiodinating activity (5'-DA) accounts for the depressed T3 values associated with the sparing of both N and energy-consuming processes. Both the liver and damaged territories adapt to stressful signals along up-regulated pathways disconnected from the central and peripheral control systems. Cytokines stimulate liver 5'-DA and suppress the synthesis of transthyretin (TTR), causing the drop of retinol-binding protein (RBP) and the leakage of increased amounts of T4 and retinol in free form. TTR and RBP thus work as prohormonal reservoirs of precursor molecules which need to be converted into bioactive derivatives (T3 and retinoic acids) to reach transcriptional efficiency. The converting steps (5'-DA and cellular retinol-binding protein-I) are activated by T4 and retinol, themselves operating as limiting factors of positive feedback loops. Healthy adults with normal macrophage functioning and liver parenchymal integrity, who submitted to a stress of medium severity, are characterized by TTR-RBP plasma levels reduced by half and an estimated ten-fold increase in free ligand disposal to target cells during the days ensuing injury. This transient hyperthyroid and hyperretinoid climate creates a second defense line strengthening and fine-tuning the effects primarily initiated by cytokines. The suicidal behavior of thyroxine-binding globulin (TBG), corticosteroid-binding globulin (CBG), and IGFBP-3 allows the occurrence of peak endocrine and mitogenic influences at the site of inflammation. The production rate of TTR by the liver is the main determinant of both the hepatic release and blood transport of holoRBP, which explains why poor nutritional status concomitantly impairs thyroid- and retinoid-dependent acute-phase responses, hindering the stressed body to appropriately face the survival crisis. The prognostic significance of low TT4 blood levels may be assigned to the exhaustion of extrathyroidal hormonal pools normally stored in liver and plasma but markedly shrunken in protein-depleted states. These data offer new insights into the mechanisms whereby preexisting malnutrition and stressful complications are interrelated, emphasizing the pivotal role played by TTR in that context.

Human toxicology of Mercury

This article describes the health effects of the two principal forms of mercury to which humans are exposed, namely mercury vapor and methylmercury compounds. Mercury vapor is the monatomic gas that vaporizes from liquid metallic mercury. It has a long history of human exposure dating back to ancient times. The earliest life forms on this planet may have received substantial exposure and developed defense mechanisms that we inherit to this day. Severe forms of poisoning from inhalation of mercury vapor are now rare. More commonly observed in occupational exposures are subtle neurobehavioral effects and preclinical changes in biochemical markers of kidney function. Methylmercury compounds may also date back to Archean times. The methylation of inorganic mercury by methanogenic bacteria is believed to be a protective mechanism for these cells that appeared early in evolution. Unfortunately, for life forms dependent on a central nervous system, what is protective for simple cells becomes a threat to the more complex life forms. Today, the main source of human exposure is from methylation of inorganic mercury in bodies of fresh and ocean water, the ensuing bioaccumulation in the aquatic food chain, and the consumption of fish or sea mammals by humans. Methylmercury selectively damages the brain. In adult humans, damage is focal, affecting specific cell types in certain anatomical areas such as the visual cortex and the cerebellum. Prenatal exposure disrupts the normal developmental processes of the fetal brain. Indeed, the prenatal period is widely believed to be the most susceptible stage of the life cycle. At present, two large epidemiological studies are underway to determine human health risks from methylmercury in fish. J. Trace Elem. Exp. Med. 11:303–317, 1998. © 1998 Wiley-Liss, Inc.

Human toxicology of Mercury

This article describes the health effects of the two principal forms of mercury to which humans are exposed, namely mercury vapor and methylmercury compounds. Mercury vapor is the monatomic gas that vaporizes from liquid metallic mercury. It has a long history of human exposure dating back to ancient times. The earliest life forms on this planet may have received substantial exposure and developed defense mechanisms that we inherit to this day. Severe forms of poisoning from inhalation of mercury vapor are now rare. More commonly observed in occupational exposures are subtle neurobehavioral effects and preclinical changes in biochemical markers of kidney function. Methylmercury compounds may also date back to Archean times. The methylation of inorganic mercury by methanogenic bacteria is believed to be a protective mechanism for these cells that appeared early in evolution. Unfortunately, for life forms dependent on a central nervous system, what is protective for simple cells becomes a threat to the more complex life forms. Today, the main source of human exposure is from methylation of inorganic mercury in bodies of fresh and ocean water, the ensuing bioaccumulation in the aquatic food chain, and the consumption of fish or sea mammals by humans. Methylmercury selectively damages the brain. In adult humans, damage is focal, affecting specific cell types in certain anatomical areas such as the visual cortex and the cerebellum. Prenatal exposure disrupts the normal developmental processes of the fetal brain. Indeed, the prenatal period is widely believed to be the most susceptible stage of the life cycle. At present, two large epidemiological studies are underway to determine human health risks from methylmercury in fish. J. Trace Elem. Exp. Med. 11:303–317, 1998. © 1998 Wiley-Liss, Inc.

Responses to a Model Predator of New Zealand’s Endangered Takahe and Its Closest Relative, the Pukeko

New Zealand's avifauna, characterized by several species of endemic flightless birds, has evolved in isolation from terrestrial mammalian predators. Consequently, there has been no selection pressure to develop defense mechanisms against terrestrial predators. When Polynesians (AD 1000-1200) and Europeans (AD 1850) arrived, much of New Zealand's naive avifauna became easy prey to predators introduced by these settlers (Diamond & Veitch 1981; Holdaway 1989). Vulnerability may have been exhibited by unusual tameness (lack of defensive behavior) or by nesting, roosting, and perching in areas exposed to introduced predators (Bell 1991). The Takahe (Porphyrio manteUO is a large, flightless gallinule endemic to New Zealand. It was thought extinct until its rediscovery in Fiordland in 1948 and is still among the most highly endangered bird species in the world. The Takahe population consists of approximately 120 adult birds in Fiordland's isolated alpine habitat and 30 others that have been established on four, small, predator-free islands (Crouchley 1994). Subfossil evidence indicates that Takahe were once found throughout New Zealand, apparently most abundant along forest margins and streams in lowland regions (Beauchamp & Worthy 1988). Bunin and Jamieson (1995) review the reasons behind the Takahe's decline, which began with the arrival of humans 800-1000 years ago. The main predatory threat to Takahe in their current environment is the stoat (Mustela erminea), first introduced with early European settlers toward the end of the nineteenth century (King 1990). There is a correlation between years of high stoat numbers in Fiordland

Response of human keratinocytes to extremely low concentrations of N-methyl- N′-nitro- N-nitrosoguanidine

Since alkylating agents are widely present in the environment and constitute a continuous challenge to genome integrity, cells and organisms have developed defense mechanisms to remove such lesions. We monitored the response of human keratinocytes to a very low concentration of a methylating agent, namely 2.5 nM N-methyl- N′-nitro- N-nitrosoguanidine (MNNG). The effect of a 60-min exposure of quiescent cells to 2.5 nM MNNG was studied in terms of DNA integrity, poly(ADP-ribose) metabolism, clonogenic survival and DNA synthesis. We observed two waves of DNA strand break formation and resealing. Interestingly, the amount of DNA strand breaks in exposed cells was lower than in unexposed control cells. This phenomenon was also observed when cells were exposed to MNNG in the presence of a protein synthesis inhibitor, or when they were maintained on ice during the treatment. A dose of 2.5 nM MNNG stimulated poly(ADP-ribose) turnover, reduced the intracellular NAD + content, stimulated DNA synthesis and caused a remarkable increase in clonogenic survival. Thus, the cellular responses to extremely low concentrations of MNNG differ sharply from those observed at higher doses of this carcinogen. We conclude that the very low dose response cannot be extrapolated from usual dose-response analyses.

Aerosolized Prostacyclin

Aerosolized Prostacyclin