Ameliorating effect of chloride on nitrite toxicity to freshwater invertebrates with different physiology: a comparative study between amphipods and planarians

High nitrite concentrations in freshwater ecosystems may cause toxicity to aquatic animals. These living organisms can take nitrite up from water through their chloride cells, subsequently suffering oxidation of their respiratory pigments (hemoglobin, hemocyanin). Because NO(2)(-) and Cl(-) ions compete for the same active transport site, elevated chloride concentrations in the aquatic environment have the potential of reducing nitrite toxicity. Although this ameliorating effect is well documented in fish, it has been largely ignored in wild freshwater invertebrates. The aim of this study was to compare the ameliorating effect of chloride on nitrite toxicity to two species of freshwater invertebrates differing in physiology: Eulimnogammarus toletanus (amphipods) and Polycelis felina (planarians). The former species presents gills (with chloride cells) and respiratory pigments, whereas in the latter species these are absent. Test animals were exposed in triplicate for 168 h to a single nitrite concentration (5 ppm NO(2)-N for E. toletanus and 100 ppm NO(2)-N for P. felina) at four different environmental chloride concentrations (27.8, 58.3, 85.3, and 108.0 ppm Cl(-)). The number of dead animals and the number of affected individuals (i.e., number of dead plus inactive invertebrates) were monitored every day. LT(50) (lethal time) and ET(50) (effective time) were estimated for each species and each chloride concentration. LT(50) and ET(50) values increased with increases in the environmental chloride concentration, mainly in amphipods. Results clearly show that the ameliorating effect of chloride on nitrite toxicity was more significant in amphipods than in planarians, likely because of the absence of gills (with chloride cells) and respiratory pigments in P. felina. Additionally, this comparative study indicates that the ecological risk assessment of nitrite in freshwater ecosystems should take into account not only the most sensitive and key species in the communities, but also chloride levels in the aquatic environment.

HNO induces DNA deletions in the yeast S. cerevisiae

HNO is genotoxic but its mechanism is not well understood. There are many possible mechanisms by which HNO can attack DNA. Since HNO is electrophilic, it may react with exocyclic amine groups on DNA bases and through a series of subsequent reactions form a deaminated product. Alternatively, HNO may induce radical chemistry through O(2)-dependent (or possibly O(2)-independent) chemistry. In cell free systems, experiments have shown that HNO does react with DNA, resulting in base oxidation and strand cleavage. In this study, we used a whole-cell system in the yeast Saccharomyces cerevisiae to study the mechanism of HNO induced DNA damage with Angeli's salt as HNO donor. The yeast DEL assay provided a measure of intrachromosomal recombination leading to DNA deletions. We also examined interchromosomal recombination leading to genomic rearrangements and used the canavanine (CAN) assay to study induction of forward point mutations. HNO was a potent inducer of DNA deletions and recombination but it was negative for induction of point mutations. This suggests that HNO causes DNA strand breaks rather than base damage. Genotoxicity was observed under aerobic and anaerobic conditions and NAC protected against HNO induced DNA deletions. Since HNO is genotoxic under anaerobic conditions, NAC probably protected against radicals generated by HNO independent of oxygen.

Prospective study of cured meats consumption and risk of chronic obstructive pulmonary disease in men

Cured meats are high in nitrites. Nitrites generate reactive nitrogen species that may cause damage to the lung. The objective is to assess the relation between frequent consumption of cured meats and the risk of newly diagnosed chronic obstructive pulmonary disease (COPD). Between 1986 and 1998, the authors identified 111 self-reported cases of newly diagnosed COPD among 42,915 men from the Health Professionals Follow-up Study. The cumulative average intake of cured meats consumption (processed meats, bacon, hot dogs) was calculated from food frequency questionnaires administrated in 1986, 1990, and 1994 and divided according to servings per week (never/almost never, <1 serving/week, 1-3 servings/week, 4-6 servings/week, at least once/day). After adjustment for age, smoking status, pack-years, pack-years squared, energy intake, race/ethnicity, US region, body mass index, and physical activity, the consumption of cured meats was positively associated with the risk of newly diagnosed COPD (for highest vs. lowest intake: relative risk = 2.64, 95% confidence interval: 1.39, 5.00; p(trend) = 0.002). In contrast to these findings, the consumption of cured meats was not associated with the risk of adult-onset asthma. These data suggest that cured meat may worsen the adverse effects of smoking on risk of COPD.

Paradoxical ozone associations could be due to methyl nitrite from combustion of methyl ethers or esters in engine fuels

We review studies of the effects of low ambient ozone concentrations on morbidity that found a negative coefficient for ozone concentration. We call this a Paradoxical Ozone Association (POA). All studies were in regions with methyl ether in gasoline. All but one study carefully controlled for the effects of other criterion pollutants, so the phenomenon cannot be attributed to them. One was in southern California in mid-summer when ozone levels are highest. Because ozone is created by sunlight, the most plausible explanation for a POA would be an ambient pollutant that is rapidly destroyed by sunlight, such as methyl nitrite (MN). A previously published model of engine exhaust chemistry suggested methyl ether in the fuel will create MN in the exhaust. MN is known to be highly toxic, and closely related alkyl nitrites are known to induce respiratory sensitivity in humans. Support for the interpretation comes from many studies, including three linking asthma symptoms to methyl tertiary butyl ether (MTBE) and the observation that a POA has not been seen in regions without ether in gasoline. We also note that studies in southern California show a historical trend from more significant to less significant ozone-health associations. The timing of those changes is consistent with the known timing of the introduction of gasoline oxygenated with MTBE in that region.

Inhalant abuse in the military: an unrecognized threat

Although inhalant abuse represents the third most commonly abused class of drugs in the military, it is a frequently overlooked form of substance abuse in the active duty population. Inhalants' lack of visibility is also evident in the civilian community. In both the civilian and military communities, the factors leading to underrecognition of inhalant abuse include high availability, low cost, lack of drug screening and drug treatment programs, and frequent misdiagnosis by clinicians. This review seeks to inform care providers about the prevalence, health risks, diagnosis, and treatment of inhalant abuse in the active duty population, and encourages clinicians to be more aggressive in the identification of this serious but underrecognized problem.

Impact of nitrite exposure on endocrine, osmoregulatory and cytoprotective functions in the marine teleost Sparus sarba

The effects of nitrite, at varying concentrations (0, 25 and 50mg/l), on silver sea bream (Sparus sarba), was assessed after 7 days exposure. Nitrite exposure resulted in an elevated renosomatic index in parallel with increased kidney water content. Measurements of serum thyroid hormones demonstrated that levels of thyroxine (T(4)) were decreased upon nitrite exposure whereas triiodothyronine (T(3)) concentrations remained unchanged. Nitrite did not affect serum K and Na levels but did cause an increase in gill sodium pump (Na(+)-K(+)-ATPase) activity. Using immunoassays, it was found that the abundance of the water channel protein, aquaporin 3 (AQP3) was unchanged in gills but decreased in kidneys of sea bream upon nitrite exposure. Immunoassay analysis also demonstrated that the amount of the heat shock protein 70 (HSP70) family were increased in gills, kidney and liver during nitrite exposure whereas amounts of the heat shock protein 90 (HSP90) family increased in kidneys and liver. Taken together, the findings from this study provide new insights into how nitrite affects osmoregulatory, endocrine processes and heat shock protein expression in a marine fish.

Effects of ammonia, nitrite and nitrate on hemoglobin content and oxygen consumption of freshwater fish, Cyprinus carpio (Linnaeus)

Lethal effects of nitrogenous compounds ammonia, nitrite and nitrate on freshwater fish Cyprinus carpio were studied and the static LC50 values obtained for these 3 toxicants for 24 hr were 0.80 ppb, 171.36 ppm; 1075.10 ppm and continuous flowthrough LC50 values for 24 hr were 0.72 ppb, 154.31 ppm; 967.63 ppm respectively. The fish were exposed to lethal concentrations to study the changes in hematological parameters and the rate of oxygen consumption. During the period of exposure general decline in the content of hemoglobin was observed. Methemoglobin content increased in case of nitrite exposure consequently the hemoglobin levels decreased drastically. It is also observed that rate of oxygen consumption decreased progressively with the increase of toxicant concentration and duration of the exposure.

Nitric oxide metabolites induced in Anopheles stephensi control malaria parasite infection

Malaria parasite infection in anopheline mosquitoes is limited by inflammatory levels of nitric oxide metabolites. To assess the mechanisms of parasite stasis or toxicity, we investigated the biochemistry of these metabolites within the blood-filled mosquito midgut. Our data indicate that nitrates, but not nitrites, are elevated in the Plasmodium-infected midgut. Although levels of S-nitrosothiols do not change with infection, blood proteins are S-nitrosylated after ingestion by the mosquito. In addition, photolyzable nitric oxide, which can be attributed to metal nitrosyls, is elevated after infection and, based on the abundance of hemoglobin, likely includes heme iron nitrosyl. The persistence of oxyhemoglobin throughout blood digestion and changes in hemoglobin conformation in response to infection suggest that hemoglobin catalyzes the synthesis of nitric oxide metabolites in a reducing environment. Provision of urate, a potent reductant and scavenger of oxidants and nitrating agents, as a dietary supplement to mosquitoes increased parasite infection levels relative to allantoin-fed controls, suggesting that nitrosative and/or oxidative stresses negatively impact developing parasites. Collectively, our results reveal a unique role for nitric oxide in an oxyhemoglobin-rich environment. In contrast to facilitating oxygen delivery by hemoglobin in the mammalian vasculature, nitric oxide synthesis in the blood-filled mosquito midgut drives the formation of toxic metabolites that limit parasite development.

[Environmental factors in the development of type 1 diabetes -- a new insight]

According to the traditional model of pathogenesis of type 1 diabetes - it develops in genetically susceptible individuals in whom environmental factors trigger an autoimmune process of beta-cell destruction. Although susceptibility may be inherited, there is a growing body of evidence showing the role of environmental factors that might not only trigger but also perpetuate the chronic autoimmune process. These factors may exert their action long before the disease manifests itself clinically, which significantly hampers their identification. Three groups of environmental factors that were most widely studied include of viral infections, feeding patterns in infancy and toxic compounds (especially nitrites). Other factors possibly playing a role in modifying the development of the disease are vaccinations, psychological stress and climatological factors. The authors summarize the data supporting the role of environmental factors in the development of the disease and show a more recent model of type 1 diabetes pathogenesis. It may partly explain why the disease incidence increased has so much in the last three decades despite markedly improved hygiene and health care standards.

Coordinated regulation of the Neisseria gonorrhoeae-truncated denitrification pathway by the nitric oxide-sensitive repressor, NsrR, and nitrite-insensitive NarQ-NarP

Neisseria gonorrhoeae survives anaerobically by reducing nitrite to nitrous oxide catalyzed by the nitrite and nitric oxide reductases, AniA and NorB. P(aniA) is activated by FNR (regulator of fumarate and nitrate reduction), the two-component regulatory system NarQ-NarP, and induced by nitrite; P(norB) is induced by NO independently of FNR by an uncharacterized mechanism. We report the results of microarray analysis, bioinformatic analysis, and chromatin immunoprecipitation, which revealed that only five genes with readily identified NarP-binding sites are differentially expressed in narP(+) and narP strains. These include three genes implicated in the truncated gonococcal denitrification pathway: aniA, norB, and narQ. We also report that (i) nitrite induces aniA transcription in a narP mutant; (ii) nitrite induction involves indirect inactivation by nitric oxide of a gonococcal repressor, NsrR, identified from a multigenome bioinformatic study; (iii) in an nsrR mutant, aniA, norB, and dnrN (encoding a putative reactive nitrogen species response protein) were expressed constitutively in the absence of nitrite, suggesting that NsrR is the only NO-sensing transcription factor in N. gonorrhoeae; and (iv) NO rather than nitrite is the ligand to which NsrR responds. When expressed in Escherichia coli, gonococcal NarQ and chimaeras of E. coli and gonococcal NarQ are ligand-insensitive and constitutively active: a "locked-on" phenotype. We conclude that genes involved in the truncated denitrification pathway of N. gonorrhoeae are key components of the small NarQP regulon, that NarP indirectly regulates P(norB) by stimulating NO production by AniA, and that NsrR plays a critical role in enabling gonococci to evade NO generated as a host defense mechanism.

Haematological responses of acute nitrite exposure in walleye (Sander vitreus)

Nitrite (NO2-) is a toxic intermediary of the bacterial oxidation of nitrogenous wastes (e.g. ammonia) in an aquatic environment. It becomes most lethal when oxygen becomes limited due to high fish densities or in the presence of high bacterial activity due to waste build-up-both situations commonly found in intensive aquaculture. To date however, little is known about how this toxin affects the physiology of walleye, an intended culture species, particularly in intensive re-circulating systems. This study aims to define threshold concentrations of nitrite that affect haemoglobin-oxygen affinity and carrying capacity in walleye. During in vivo tests, fish (N=20) were subjected to a medium effective concentration (EC50) of nitrite (0.9 mmol L(-1)) for 48 h while the effects of nitrite accumulation on blood properties were measured. The effects of oxygenation state on red blood cell (RBC) nitrite uptake and metHb formation was further investigated by in vitro tonometry. In vitro nitrite exposure to 3 mmol L(-1) resulted in a significantly higher methaemoglobin formation in 50% air saturated than 100% air saturated RBCs. Both cell water content and haematocrit decreased with time in 50% air saturated treatments, whereas total Hb remained constant, suggesting a reduction in RBC volume. Similar effects were observed during 48 h in vivo and in vitro nitrite exposure tests, indicating the reduction in RBC volume likely was not the result of a catecholamine response. Walleye were found to be tolerant to an accumulation of blood-NO2- levels similar to common carp, a highly Mean Cellular Volume (MCV) tolerant species, before succumbing to methaemoglobinemia. The elevated tolerance to nitrite of walleye is a beneficial characteristic for successful rearing in a culture setting, where reduced oxygen and elevated MCV levels are prevalent. The findings from this study may be used in developing guidelines for species-specific management of nitrogenous wastes in aquaculture.

Correlation between induction of DNA fragmentation in lung cells from rats and humans and carcinogenic activity

Six chemicals, known to induce lung tumors in rats, were examined for their ability to induce DNA fragmentation in primary cultures of rat and human lung cells, and in the lung of intact rats. Significant dose-dependent increases in the frequency of DNA single-strand breaks and alkali-labile sites, as measured by the single-cell gel electrophoresis (Comet) assay, were obtained in primary lung cells from male rats with the following, minimally toxic, concentrations of the six test compounds: N-nitrosodimethylamine (NDMA; 2.5-10 mM), hydrazine (HZ; 0.5-4 mM), cadmium sulfate (CD; 31.2 and 62.5 μM), 4,4'-methylene bis (2-chloroaniline) (MOCA; 31.2-125 μM), isobutyl nitrite (IBN; 7.8-31.2 μM) and tetranitromethane (TNM; 1.9-15.6 μM). Similar degrees of DNA fragmentation were obtained in primary human lung cells; however, due to inter-donor differences, the minimum effective concentrations were in some donors lower and in others higher than in rats, and IBN induced DNA damage only in one of three donors. The DNA-damaging potency of HZ was higher in rats than in humans, and the opposite was true for MOCA. In agreement with these findings, statistically significant increases in the average frequency of DNA breaks were obtained in the lung of rats given a single oral dose (1/2 LD50) of the six test compounds. These findings give evidence that genotoxic lung carcinogens may be identified by use of the DNA fragmentation/Comet assay on rat lung cells as targets cells, and show that the six compounds tested produce in primary cultures of lung cells from human donors DNA-damaging effects substantially similar to those observed in rats.

Effects of flavonoids extracted from Scutellaria baicalensis Georgi on hemin–nitrite–H2O2 induced liver injury

Hemin-nitrite-H2O2 system may play a role in liver oxidative injury in some pathological events. In this paper, the effects of the three active components of the root of Scutellaria baicalensis Georgi, i.e. baicalin, baicalein and wogonin, on hemin-nitrite-H2O2 induced liver injury were studied in liver homogenate, liver microsome and human hepatoblastoma cell line HepG2 cells. It was found that hemin-nitrite-H2O2 could induce liver homogenate protein nitration, lipid peroxidation and liver microsome protein oxidation; it also caused a decrease of HepG2 cells viability. Baicalein, baicalin and wogonin could inhibit protein nitration and lipid peroxidation in liver homogenate as well as in HepG2 cells in a dose-dependent manner, the inhibition order was baicalein>baicalin>>wogonin. These three flavonoids also inhibited the oxidation of protein in liver microsome, the decrease of cell viability and the content of GSH in HepG2 cells, among which baicalin represented the most inhibitory effect. Besides, hemin-H2O2 induced cell injury could be augmented with the existence of nitrite, indicating protein nitration involved in hemin-nitrite-H2O2 induced liver injury. These results demonstrated hemin-nitrite-H2O2 could induce liver injury through oxidizing or nitrating different biomolecules. Baicalein, baicalin and wogonin could inhibit hemin-nitrite-H2O2 induced liver injury in dose-dependent manners by inhibiting oxidation and nitration.

A mosquito 2-Cys peroxiredoxin protects against nitrosative and oxidative stresses associated with malaria parasite infection

Malaria parasite infection in anopheline mosquitoes induces nitrosative and oxidative stresses that limit parasite development, but also damage mosquito tissues in proximity to the response. Based on these observations, we proposed that cellular defenses in the mosquito may be induced to minimize self-damage. Specifically, we hypothesized that peroxiredoxins (Prxs), enzymes known to detoxify reactive oxygen species (ROS) and reactive nitrogen oxide species (RNOS), protect mosquito cells. We identified an Anopheles stephensi 2-Cys Prx ortholog of Drosophila melanogaster Prx-4783, which protects fly cells against oxidative stresses. To assess function, AsPrx-4783 was overexpressed in D. melanogaster S2 and in A. stephensi (MSQ43) cells and silenced in MSQ43 cells with RNA interference before treatment with various ROS and RNOS. Our data revealed that AsPrx-4783 and DmPrx-4783 differ in host cell protection and that AsPrx-4783 protects A. stephensi cells against stresses that are relevant to malaria parasite infection in vivo, namely nitric oxide (NO), hydrogen peroxide, nitroxyl, and peroxynitrite. Further, AsPrx-4783 expression is induced in the mosquito midgut by parasite infection at times associated with peak nitrosative and oxidative stresses. Hence, whereas the NO-mediated defense response is toxic to both host and parasite, AsPrx-4783 may shift the balance in favor of the mosquito.

Formation of Genotoxic Nitro-PAH Compounds in Fish Exposed to Ambient Nitrite and PAH

Mutagenic nitrated polycyclic aromatic hydrocarbons (nitro-PAHs) have been known to arise in the environment through direct emissions from combustion sources and nitration of PAHs, primarily in the atmosphere. Here, we report the formation of nitro-PAH compounds in fish contaminated with PAH and exposed to nitrite (NO2-) in the ambient water. Electrospray ionization mass spectrometric analysis of the bile of the euryhaline fish Oreochromis mossambicus exposed simultaneously to field-relevant, sublethal concentrations of phenanthrene (1 microg/g) and NO2- (1 microM) and collision-induced dissociation of selected ions revealed the presence of two strongly genotoxic nitro-PAH metabolites, namely phenanthrene-6-nitro-1,2-dihydrodiol-3,4-epoxide (mass/charge [m/z] 273) and dihydrodihydroxy acetylamino nitrophenanthrene (m/z 359). These two metabolite peaks present only in the bile of fish exposed simultaneously to phenanthrene and NO2- constituted, respectively, about 3.1 and 2.7% of the highest peak among the putative unconjugated phenanthrene metabolites in the mass spectrum. The presence of the oxidized phenanthrene metabolite dihydroxyphenanthrene (m/z 233) in fish exposed to phenanthrene alone as well as phenanthrene plus NO2- suggested that oxidation of phenanthrene precedes nitration in the sequence of reactions leading to the formation of the observed nitrophenanthrene metabolites. However, the route of PAH administration seems to determine the nature of metabolites formed. Nearly 92% of the hepatic cells of the fish exposed to phenanthrene in the presence of NO2- were found to have suffered extensive DNA fragmentation on comet assay.

Toxicity of nitrite to three species of freshwater invertebrates

Nitrite is a compound with a high toxicity to aquatic animals. Several anthropogenic pollution sources are increasing the concentrations of this component of the nitrogen cycle. Despite this toxicity, there is little available literature on its effects on freshwater invertebrates. Laboratory bioassays were performed to obtain data on the lethal effects of nitrite to three species of freshwater invertebrates: the planarian Polycelis felina and the amphipods Echinogammarus echinosetosus and Eulimnogammarus toletanus. The LC(50), LC(10), and LC(0.01) values (mg/L NO(2)--N) at 24, 48, 72, and 96 h were calculated for each species. E. toletanus and E. echinosetosus were the most sensitive species, with 96 h LC(50) values of 2.09 and 2.59 mg/L NO(2)--N, respectively. In contrast, the planarian P. felina showed a higher tolerance to nitrite, with a 96 h LC(50) value of 60.0 mg/L NO(2)--N. The obtained results were compared with the reported nitrite data for other freshwater invertebrates. This study may contribute to a more appropriate assessment of the ecological risk of this compound in freshwater ecosystems.

Neurotoxicity of nitroxyl: insights into HNO and NO biochemical imbalance

Nitroxyl anion (NO-), and/or its conjugate acid, HNO, may be formed in the cellular milieu by several routes under both physiological and pathophysiological conditions. Since experimental evidence suggests that certain reactive nitrogen oxide species can contribute significantly to cerebral ischemic injury, we investigated the neurotoxic potential of HNO/NO- using Angeli's salt (AS), a spontaneous HNO/NO(-)-generating compound. Exposure to AS resulted in a time- and concentration-dependent increase in neural cell death that progressed markedly following the initial exposure. Coadministration of the donor with Tempol (1 mM), a one-electron oxidant that converts NO- to NO, prevented its toxic effect, as did the concomitant addition of Fe(III)TPPS. Media containing various chelators, catalase, Cu/Zn superoxide dismutase, or carboxy-PTIO did not ameliorate AS-mediated neurotoxicity, ruling out the involvement of transition metal complexes, H2O2, O2-, and NO, respectively. A concentration-dependent increase in supernatant protein 3-nitrotyrosine immunoreactivity was observed when cultures were exposed to AS under aerobic conditions, an effect lost in the absence of oxygen. A bell-shaped curve for augmented AS-mediated nitration was observed with increasing Fe(III)TPPS concentration, which contrasted with its linear effect on abating cytotoxicity. Finally, addition of glutamate receptor antagonists, MK-801 (10 microM) and CNQX (30 microM) to the cultures abrogated toxicity when given during, but not following, AS exposure; as did pretreatment with the exocytosis inhibitor, tetanus toxin (300 ng/ml). Taken together, our data suggest that under aerobic conditions, AS toxicity is initiated via HNO/NO- but progresses via secondary excitotoxicity.

Ecological risk assessment for aquatic species exposed to contaminants in Keelung River, Taiwan

An ecological risk assessment was conducted for Keelung River in northern Taiwan. The objective of this study was to assess the risk to fish, aquatic insects, and benthic macroinvertebrates associated with chemical-of-potential-concern (COPC) in the river and to rank ecological risk for these chemicals. The protection of at least 95% of the species 90% of the time from acute and chronic COPC exposures was the defined assessment endpoint. Nine inorganic and organic contaminants were selected to evaluate the impact to aquatic community in the Keelung River. The quotient method served as screen level estimation of risk. The Aquatic Ecological Risk Assessment model was used to analyze exposure and ecological effects and to estimate community level risk. The logarithmic regression model between probability and lethal concentration was established. The combined risks of multiple chemicals were evaluated under assumption of additive risk. The results indicated that zinc and copper pose higher risk among metals. Ammonia, copper, and zinc posed virtually all of the risk, while organic COPCs posed a negligible risk. Potential ecological risk from ammonia exposure was greatest. The probability of more than 5% of the species being affected by acute or chronic toxicity of COPCs is about 100%. In average (50% of the time), 99% of the species would be affected by acute toxicity of COPCs, and about all the species would be affected by chronic toxicity of COPCs. Uncertainties in this assessment were associated with variability in ecosystem stressors, exposure data, ecological effect data, and risk characterization.

Gastric DNA damage through tobacco chewing: in vitro mechanistic studies of DNA nitrite attack

Smokeless chewing tobacco or snuff has been linked to carcinogenic effects in upper aerodigestive organs. The presence of nitrite within the tobacco product is suspected to foster carcinogenic DNA mechanisms at lower pH. We studied the impact of sodium nitrite on DNA damage at single-strand conformers or hairpin loops, known to be present at fragile sites that have been shown to cause methyltransferase stalling and that can lead to chromosomal breakage. At a pH of 4.2, two base-damage products could be demonstrated at significant levels (1-5% of total nucleotides), with greater sensitivity to hairpin loops compared to a control Watson-Crick duplex. Pyrimidine-rich strands (CCG, CTG) were more reactive than purine-rich strands (CAG, CGG). The data support a mechanism for allele-specific predisposition to DNA damage. This mechanism may be of significance in gastric cancer initiation due to chewing tobacco.

Increased reproductive toxicity of landfill leachate after degradation was caused by nitrite

Leachate from the landfill Lindbodarna was suspected to cause reproductive effects on fish in a Swedish lake, called Molnbyggen. The acute toxicity of this landfill leachate is caused by ammonia. In the present study the acute and chronic toxicity of the leachate from the landfill was tested with Ceriodaphnia dubia before and after treatment, either with (inoculated) or without addition of microorganisms from activated sludge, in both 2000 and 2001. On both occasions, the acute toxicity decreased after treatment, more rapidly with inoculum than without, and the cause of the decrease was mainly explained by decreasing concentrations of ammonia. However, the chronic toxicity decreased after treatment with inoculum but increased after treatment without inoculum. Therefore, we performed a series of acute and reproductive tests with ammonia, nitrite and nitrate on C. dubia, and the 24-h EC50s were 1.0, 2.7 and 59 mM, respectively, which are consistent with literature data. However, the chronic toxicity of these compounds gave quite a different picture with 8-day EC50s for reproduction of 3.0 mM for ammonia, 0.016 mM for nitrite and 1.5 mM for nitrate. Thus, the acute-chronic ratios for these compounds were 0.33 for ammonia, 170 for nitrite and 39 for nitrate. These findings show that reproduction is more sensitive than survival for both nitrite and nitrate, and that nitrite is the more hazardous of the two. This implies that the chronic and reproductive toxicity of nitrite and nitrate on zooplankton may in fact increase effects of eutrophication. In this study the toxicity of the fresh leachate was dominated by ammonia, but after treatment the contribution of nitrite increased, and especially the chronic toxicity of the treated landfill leachate was dominated by nitrite toxicity.

Ontogenic delays in effects of nitrite exposure on tiger salamanders (Ambystoma tigrinum tigrinum) and wood frogs (Rana sylvatica)

Under certain conditions, nitrite can be present in freshwater systems in quantities that are toxic to the fauna. I exposed wood frog (Rana sylvatica) and eastern tiger salamander (Ambystoma tigrinum tigrinum) embryos and young tadpoles and larvae to elevated concentrations of nitrite in chronic toxicity tests: 0, 0.3, 0.6, 1.2, 2.1, 4.6, and 6.1 mg/L NO2-N, exposing individuals as both embryos and larvae. Nitrite caused significant declines in wood frog hatching success (3.4 mg/L NO2-N, wood frog), and lower concentrations caused significant mortality during the early larval stages (4.6 mg/L NO2-N, salamander; 0.5 mg/L NO2-N, wood frog). Later tests exposing individuals to nitrite only after hatching showed that both wood frog and tiger salamander vulnerability to nitrite declined shortly after hatching. Hence, examining a single life-history stage, especially later in development, may miss critical toxic effects on organisms, causing the researcher potentially to underestimate seriously the ecological consequences of nitrite exposure.

Nitrite enhances neutrophil-induced DNA strand breakage in pulmonary epithelial cells by inhibition of myeloperoxidase

Chronic inhalation of environmental particles is associated with pulmonary carcinogenesis. Although the mechanism has not yet been fully elucidated, influx of inflammatory cells, including neutrophils, is suggested to play a major role in this process. Typically, in the particle-exposed lung, influx of neutrophils is accompanied by an accumulation of nitrite. Previous studies indicated that nitrite may affect the toxicity of neutrophils, involving an interaction with neutrophil-derived myeloperoxidase (MPO). To evaluate the possible consequences of this interaction for inflammation-mediated genotoxicity, we investigated the effect of nitrite on neutrophil-induced DNA damage in pulmonary target cells. Therefore, activated neutrophils were co-cultured with alveolar type II epithelial cells (RLE), and DNA strand breakage was evaluated using single-cell gel electrophoresis (comet assay). In this system, addition of nitrite caused an increase in neutrophil-induced DNA strand breakage in RLE cells, which was associated with an inhibition of MPO activity. Similar results were obtained by co-culturing RLE cells with neutrophils in the presence of the specific MPO inhibitor 4-aminobenzoic acid hydrazide (4-ABAH). To further investigate the mechanism underlying these observations, in vitro experiments were performed using mixtures of nitrite, MPO and its substrate H2O2. DNA strand breakage by reagent H2O2 was inhibited when it was allowed to react with MPO before addition to the RLE cells. However, when MPO and H2O2 were pre-mixed in the presence of nitrite or 4-ABAH, the inhibitory effect of MPO on resultant DNA damage was reversed. Further studies using catalase indicated that DNA strand breakage by the pre-mixtures of MPO, H2O2 and nitrite was H2O2-specific, suggesting that nitrite prevents consumption of H2O2 by MPO. Collectively, our results show that nitrite enhances neutrophil-induced DNA strand breakage in pulmonary epithelial cells. This effect is probably due to an inhibition of MPO activity, which increases the availability of its DNA strand breaking substrate H2O2.

Effect of sublethal levels of nitrite on some blood parameters of juvenile Labeo rohita (Hamilton-buchanan)

Juveniles of L. rohita were exposed to sublethal levels of nitrite (0.02, 0.1 and 0.4 mg/l) for 2, 24, 48 and 96 hr. The time of exposure at individual concentrations of nitrite did not show any significant difference in haemoglobin, cortisol, chloride and lactic acid. Haematocrit showed significant reduction with increasing concentration of nitrite irrespective of duration of exposure. Fishes exposed to 0.4 mg/l nitrite showed significantly high levels of glucose beyond 2 hr. The mean erythrocytic fragility of fishes exposed to the 3 concentrations of nitrite for 3 exposure periods showed significant higher sensitivity to osmotic stress. The results suggest decrease in haematocrit and cell wall strength of erythrocytes creating stress to fish.