Commentary of the SKLM to the EFSA opinion on risk assessment of N-nitrosamines in food.

Dietary exposure to N-nitrosamines has recently been assessed by the European Food Safety Authority (EFSA) to result in margins of exposure that are conceived to indicate concern with respect to human health risk. However, evidence from more than half a century of international research shows that N-nitroso compounds (NOC) can also be formed endogenously. In this commentary of the Senate Commission on Food Safety (SKLM) of the German Research Foundation (DFG), the complex metabolic and physiological biokinetics network of nitrate, nitrite and reactive nitrogen species is discussed with emphasis on its influence on endogenous NOC formation. Pioneering approaches to monitor endogenous NOC have been based on steady-state levels of N-nitrosodimethylamine (NDMA) in human blood and on DNA adduct levels in blood cells. Further NOC have not been considered yet to a comparable extent, although their generation from endogenous or exogenous precursors is to be expected. The evidence available to date indicates that endogenous NDMA exposure could exceed dietary exposure by about 2-3 orders of magnitude. These findings require consolidation by refined toxicokinetics and DNA adduct monitoring data to achieve a credible and comprehensive human health risk assessment.

Nitrite exposure leads to glycolipid metabolic disorder via the heme-HO pathway in teleost.

Nitrite is the most common nitrogen-containing compound in nature. It is widely used in food processing like in pickled foods so it has caused widespread public concern about the safety of nitrites due to the formation of nitrosamine, a carcinogen, during the food process. Recent research has shown nitrite has therapeutic potential for cardiovascular disease due to its similar function to NO, yet the safety of oral nitrite and the physiological and biochemical responses induced after oral administration still require further validation. In addition, the relationship between nitrite and glycolipid metabolism still needs to be elucidated. As aquatic animals, fish are more susceptible to nitrite compared to mammals. Herein, we utilized tilapia (Oreochromis niloticus) as an animal model to explore the relationship between nitrite and glycolipid metabolism in organisms. In the present study, we found that nitrite elicited a hypoxic metabolic response in tilapia and deepened this metabolic response under the co-stress of the pathogenic bacterium S.ag (Streptococcus agalactiae). In addition, nitrite-induced elevation of MetHb (Methemoglobin) and its by-product heme was involved in the metabolic response to nitrite-induced hypoxia through the HO/CO pathway, which has not yet been mentioned in previous studies. Moreover, heme affected hepatic metabolic responses through the ROS-ER stress-VLDL pathway. These findings, for the first time, reveal that nitrite exposure leads to glycolipid metabolic disorder via the heme-HO pathway in teleost. It not only provides new insights into the results of nitrite on the body but also is beneficial for developing healthy strategies for fish farming.

Acute nitrite exposure causes gut microbiota dysbacteriosis and proliferation of pathogenic Photobacterium in shrimp.

Nitrite exposure has become a significant concern in the aquaculture industry, posing a severe threat to aquatic animals such as shrimp. While studies have reported the adverse effects of nitrite on shrimp growth, the part played by the gut microbiota in shrimp mortality resulting from nitrite exposure is poorly understood. Here, the effects of nitrite on shrimp gut bacterial community were investigated using 16S rRNA amplicon sequencing, bacterial isolation, genomic analysis, and infection experiments. Compared to the control_healthy group, changes in the bacterial composition of the nitrite_dead group were associated with reduced abundance of specific beneficial bacteria and increased abundance of certain pathogenic bacteria. Notably, members of the Photobacterium genus were found to be significantly enriched in the nitrite_dead group. Genomic analysis of a representative Photobacterium strain (LvS-8n3) revealed a variety of genes encoding bacterial toxins, including hemolysin, adhesin, and phospholipase. Furthermore, it was also found that LvS-8n3 exhibits strong pathogenicity, probably due to its high production of pathogenic factors and the ability to utilize nitrite for proliferation. Therefore, the proliferation of pathogenic Photobacterium species appears pivotal for driving shrimp mortality caused by nitrite exposure. These findings provide novel insights into the disease mechanism in shrimp under conditions of environmental change.

Integrated histological, physiological, and transcriptome analysis reveals the post-exposure recovery mechanism of nitrite in Litopenaeus vannamei.

Nitrite is one of the most common toxic pollutants in intensive aquaculture and is harmful to aquatic animals. Recovery mechanisms post exposure to nitrite in shrimp have rarely been investigated. This study focuses on the effect of nitrite exposure and post-exposure recovery on the histological and physiological aspects of Litopenaeus vannamei and utilizes transcriptome sequencing to analyze the molecular mechanisms of adaptation to nitrite exposure. The results showed that histopathological damage to the hepatopancreas and gills caused by short-term nitrite exposure resolved with recovery. The total antioxidant capacity (T-AOC), superoxide dismutase (SOD), and catalase (CAT) of shrimp were significantly reduced during nitrite exposure and returned to the control level after recovery, malondialdehyde (MDA) levels were opposite to them. Restoration of the antioxidant system after exposure mitigated oxidative damage. Nitrite exposure results in reduced activity of the immuno-enzymes acid phosphatase (ACP) and alkaline phosphatase (AKP), which can be recovered to the control level. L. vannamei can adapt to nitrite exposure by regulating Na+/K+-ATPase (NKA) activity. Transcriptome analysis revealed that activation of glutathione metabolism and peroxisomal pathways facilitated the mitigation of oxidative damage in L. vannamei during the recovery period. Excessive oxidative damage activates the apoptosis and p53 pathways. Additionally, Sestrin2 and STEAP4 may have a positive effect on recovery in shrimp. These results provide evidence for the damage caused by nitrite exposure and the recovery ability of L. vannamei. This study can complement the knowledge of the mechanisms of adaptation and recovery of shrimp under nitrite exposure.

N-Nitrosamines: a potential hazard in processed meat products.

Nitrite, nitrate, and their salts are added to processed meat products to improve color, flavor, and shelf life and to lower the microbial burden. N-Nitrosamine compounds are formed when nitrosing agents (such as secondary nitrosamines) in meat products interact with nitrites and nitrates that have been added to the meat. With the consumption of such meat products, nitrosation reactions occur in the human body and N-nitrosamine formation occurs in the gastrointestinal tract. Despite the benefits nitrites and nitrates have on food, their tendency to create nitrosamines and an increase in the body's nitrous amine load presents health risks. The inclusion of nitrosamine compounds in possible and probable carcinogen classes according to the International Agency for Research on Cancer requires a re-examination of the literature review on processed meat products. This article evaluates the connections between various cancer types and nitrosamines found in processed meat products. © 2023 Society of Chemical Industry.

mARC dependent NO synthesis activates CanA-Relish-AMPs signal pathway in Eriocheir sinensis during nitrite stress.

As a signal molecule, nitric oxide (NO) can induce the production of antimicrobial peptides (AMPs) in invertebrate innate immunity and is produced through NO synthase (NOS) oxidation or nitrite reduction. Although the role of NOS-derived NO has been extensively studied, studies on nitrite-dependent NO are relatively scarce. In this study, we identified a mitochondrial amidoxime reducing component (mARC), a kind of nitrite reductase, in Eriocheir sinensis. Under nitrite stress, the expression level of EsmARC in the intestine of E. sinensis increased, and the production of NO increased. Furthermore, EsmARC knockdown resulted in a remarkable decrease in NO concentration. These findings indicate that nitrite stress induces the expression of mARC, which promotes the production of NO in E. sinensis. In addition, the expression levels of AMPs in the intestine were upregulated under nitrite stress. Moreover, EsmARC knockdown resulted in the downregulated expression of AMPs. EsmARC plays a positive role in the synthesis of AMPs under nitrite stress. Calcineurin subunit A (CanA) is a serine/threonine protein phosphatase involved in the process by which NO regulates the expression of AMPs. EsCanA knockdown significantly inhibited the transcription of EsRelish and the expression of AMPs under nitrite stress, and EsRelish silencing resulted in the downregulated expression levels of AMPs under nitrite stress. These results indicate that nitrite stress activates the CanA-Relish-AMP pathway in E. sinensis. In summary, mARC-dependent NO synthesis activates the CanA-Relish-AMP signal pathway in E. sinensis during nitrite stress. This research provides novel insights into the relationship between nitrite stress and NO-dependent immune signal activation in crustaceans.

Impact of nitrite exposure on oxidative stress and antioxidative-related genes responses in the gills of Procambarus clarkii.

Nitrite is the major environmental pollutant in the freshwater aquaculture environment, which has a negative impact on aquatic species growth. Currently, we know that the main way nitrite enters crustaceans is through their gills. In this study, a total of 96 h acute nitrite stress (60 mg/L) experiments were conducted, and the impact of the serum biochemical parameters, gill oxidase activity and oxidative-related gene expression of red swamp crayfish were evaluated. After exposure to nitrite for 0, 6, 12, 24, 48, and 96 h, hemolymph and gills samples were taken at each time point. In the serum, acute nitrite stress significantly increased glutamic-oxaloacetic transaminase (GOT) and alanine aminotransferase (ALT) activities after 6 h of exposure, decreased total protein (TP) and albumin (ALB) levels after 24 h and 48 h of exposure, respectively. In the gills, the activities of catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) were enhanced to the maximum level at 12 h, 24 h and 24 h, respectively. The contents of malondialdehyde (MDA) and lipid peroxide (LPO) were increased significantly after 12 h and 24 h exposure, respectively. In addition, the expression levels of antioxidative-related genes, including hsp70, fer and mt, were significantly upregulated in the gills after 6 h of exposure. The results indicated that acute nitrite stress changed the serum physiological status, induced oxidative stress and caused damage to gill cells in P. clarkii.

Effect of sub-lethal ammonia and nitrite stress on autophagy and apoptosis in hepatopancreas of Pacific whiteleg shrimp Litopenaeusvannamei.

Oxidative stress caused by ammonia and nitrite, affect the health and growth of aquaculture animals, results in oxidative damages. However, the toxic mechanism and pathogenesis of ammonia and nitrite to aquatic invertebrates are not completely clear. The present study was conducted to investigate the effects of sub-lethal ammonia and nitrite on autophagy and apoptosis in hepatopancreas of Pacific whiteleg shrimp Litopenaeus vannamei. Shrimps were exposed to sub-lethal ammonia (20 mg/L) and nitrite (20 mg/L) for 72 h, respectively. Hepatopancreas was collected for investigating the autophagy and apoptosis under stress conditions. The results showed that ammonia stress could induce up-regulated of autophagy (ATG3, ATG4, ATG10 and ATG12) and apoptosis (Caspase3 and P53) genes transcription. Nitrite stress could also induce up-regulated of autophagy (ATG3, ATG4, ATG5 and ATG10) and apoptosis (Caspase3) genes transcription. The expression of the autophagy related genes increased at first and then decreased with increasing exposure time. The atrophy, lysis, vacuolation of cell and other tissue damages in hepatopancreas were observed after 72h exposure to ammonia and nitrite. The results indicated that ammonia and nitrite stress could induce autophagy and apoptosis, and results in oxidative damage.

Nitrate and nitrite contamination in drinking water and cancer risk: A systematic review with meta-analysis.

BACKGROUND: Pollution of water sources, largely from wide-scale agricultural fertilizer use has resulted in nitrate and nitrite contamination of drinking water. The effects on human health of raised nitrate and nitrite levels in drinking water are currently unclear. OBJECTIVES: We conducted a systematic review of peer-reviewed literature on the association of nitrate and nitrite in drinking water with human health with a specific focus on cancer. METHODS: We searched eight databases from 1 January 1990 until 28 February 2021. Meta-analyses were conducted when studies had the same exposure metric and outcome. RESULTS: Of 9835 studies identified in the literature search, we found 111 studies reporting health outcomes, 60 of which reported cancer outcomes (38 case-control studies; 12 cohort studies; 10 other study designs). Most studies were set in the USA (24), Europe (20) and Taiwan (14), with only 3 studies from low and middle-income countries. Nitrate exposure in water (59 studies) was more commonly investigated than nitrite exposure (4 studies). Colorectal (15 studies) and gastric (13 studies) cancers were the most reported. In meta-analyses (4 studies) we identified a positive association of nitrate exposure with gastric cancer, OR = 1.91 (95%CI = 1.09-3.33) per 10 mg/L increment in nitrate ion. We found no association of nitrate exposure with colorectal cancer (10 studies; OR = 1.02 [95%CI = 0.96-1.08]) or cancers at any other site. CONCLUSIONS: We identified an association of nitrate in drinking water with gastric cancer but with no other cancer site. There is currently a paucity of robust studies from settings with high levels nitrate pollution in drinking water. Research into this area will be valuable to ascertain the true health burden of nitrate contamination of water and the need for public policies to protect human health.

Gut microbiota mediated the toxicity of high concentration of dietary nitrite in C57BL/6 mice.

Growing evidence indicates that exposure to high levels of nitrite for a prolonged time has adverse health effects. Although gut microbiota is responsible for the transformation of nitrite in the gut, the evidence concerning whether gut microbiota mediates the toxicity of nitrite is still lacking. The present study addressed the long-term effects of dietary nitrite on male C57BL/6 mice and employed fecal microbiota transplantation (FMT) to reveal whether gut microbiota mediated the effects of nitrite. Furthermore, the effect of azoxymethane (AOM) on gut microbiota was detected for mice drinking normal or nitrite-containing water. High nitrite had toxic effects on C57BL/6 mice. Meanwhile, high nitrite induced skin lesions in mice, accompanied with increased serum ALT, colon IL-6, TNF-α, and MDA levels, together with decreased serum Cr, colon sIgA, and T-AOC levels. After fecal microbiota was transplanted into the normal mice, the nitrite-regulated gut microbiota could also induce skin lesions, coupled with reduced serum Cr, and increased colon MDA. The high dose of nitrite caused the upregulations of Alistipes, Prevotella, and Ruminococcus, which could be transplanted into normal mice through FMT. Inversely, gut microbiota from normal mice reduced the effects of nitrite on serum ALT and Cr, together with colon sIgA and MDA. Gut microbiota from normal mice could also upregulate metabolic genes and downregulate stress genes in the nitrite-treated mice. It might due to the upregulation of Akkermansia and Parabacteroides caused by FMT from normal water-treated mice to nitrite-treated mice. In addition, AOM exhibited to be more toxic to the colon in the nitrite-treated mice in comparison with normal water-treated mice, and it might be due to the expression of Hspa1a and Hspa1b in the colon. Interestingly, gut microbiota was more influenced by AOM in the normal water-treated mice than the nitrite-treated mice. Overall, these data demonstrated that gut microbiota mediated the toxicity of a high concentration of dietary nitrite.

Evaluation of Sublethal Toxicity of Nitrite to a Suite of Aquatic Organisms in Support of the Derivation of a Chronic Environmental Water Quality Benchmark.

Nitrite is a naturally-occurring inorganic compound that occurs in aquatic environments as an intermediary between nitrate and ammonia in the nitrogen cycle. It is a contaminant of potential concern resulting from anthropogenic activities in some cases. While the acute toxicity of nitrite has been characterized in previous studies, its sublethal toxicity is less understood. To determine the sublethal toxicity of nitrite on freshwater organisms, a suite of organisms was tested including: two salmonids (Oncorhynchus mykiss and O. kisutch), an alga (Pseudokirchneriella subcapitata), an aquatic macrophyte (Lemna minor), and three invertebrates (Ceriodaphnia dubia, Chironomus dilutus, and Neocloeon triangulifer). Test organisms were exposed to nitrite concentrations ranging between 0.02 and 1.28 mg/L nitrite (NO2-N). The toxicity tests were conducted according to procedures specified in standardized methods, allowing for the estimation of multiple endpoints for each test species. Species sensitivity distributions (SSDs) were generated using endpoints from the toxicity testing results, as well as data from previous studies, from which water chemistry approximated that used in the tests (i.e., < 5 mg/L chloride, an important toxicity-modifying factor for nitrite). The mayfly, N. triangulifer, was the most sensitive species, followed by the two salmonids (which represented the second and third most sensitive species), although they were not as sensitive to nitrite exposure as reported in previous studies. The fifth percentile hazard concentration (HC5) generated from the SSD could be used for derivation of regulatory benchmarks and threshold values for site-specific aquatic risk assessments.

Acute Nitrite Exposure Induces Dysfunction and Oxidative Damage in Grass Carp Isolated Hemocytes.

To evaluate the effects of nitrite on the oxidative damage of blood cells of Grass Carp Ctenopharyngodon idella, the isolated hemocytes were exposed to nitrite (0, 1, 10, or 100 mg/L) for up to 24 h. Hemoglobin (Hb) and methemoglobin (MetHb) concentrations, reactive oxygen species (ROS) and malondialdehyde (MDA) levels, mitochondrial membrane potential (∆Ψm), and antioxidant enzyme activity were assayed to assess hematological parameters and the antioxidant defense mechanism. Results showed a remarkable decrease in Hb concentration with increasing nitrite concentration after a 24-h exposure, while the MetHb concentration increased significantly in nitrite exposure groups. The levels of ROS, ∆Ψm, and MDA increased to varying degrees with increases in nitrite exposure concentration and time. The total antioxidant capacity, catalase (CAT) activity, glutathione peroxidase (GPx) activity, and glutathione content showed a trend of rising initially and then decreasing with prolonged exposure time. Superoxide dismutase (SOD) activity was higher in the 1-mg/L nitrite exposure group and lower in the 100-mg/L group than in the control. The relative messenger RNA expression ratios of cat, sod1, and gpx were up-regulated significantly in the 1- and 10-mg/L groups and then declined in the 100-mg/L group. Therefore, it can be concluded that nitrite exposure activates the antioxidant defense mechanism of Grass Carp hemocytes and that the balance of oxidant-antioxidant homeostasis will be undermined by higher nitrite doses or longer exposure periods.

Molecular characterization and expression dynamics of three key genes in the PI3K-AKT pathway reveal its involvement in the immunotoxicological responses of the giant river prawn Macrobrachium rosenbergii to acute ammonia and nitrite stress.

Ammonia nitrogen and nitrite are two common forms of environmental toxicants for aquatic organisms including crustaceans. The PI3K-AKT pathway is an important intracellular signaling pathway related to cellular stress response, but involvement of this pathway in the immunotoxicological response of decapod crustaceans to aquatic toxicants such as ammonia nitrogen and nitrite still remains enigmatic. In this study, based on transcriptome mining and molecular cloning techniques, three key genes (named as MrPI3K, MrAKT and MrFoxO) in the PI3K-AKT signaling pathway were identified from the giant river prawn Macrobrachium rosenbergii. Sequence homology and phylogenetic analysis revealed that all the three genes harbored signature sequences of corresponding protein families, and shared high levels of similarities with their respective homologs from other species. MrPI3K, MrAKT and MrFoxO all displayed ubiquitous tissue distribution profiles, but their expression levels varied to a great extend among different tissues and between sexes. Following exposure to nitrite (20 mg/L nitrite-N) or ammonia (25 mg/L total ammonia-N) stresses for 24 h and 48 h, the three genes all responded by altering their expression levels at different time points, but they didn't show uniform expression patterns following these stresses, indicating the diversified roles of these genes in different tissues and the complexity of this signaling pathway. Remarkably, MrPI3K and MrAKT were induced only in the hemocytes and intestine, respectively, indicating their specific roles in these organs. Our study demonstrated the potential utility of these genes as biomarkers of acute ammonia or nitrite toxicity in prawns, and also provided evidence that the PI3K-AKT pathway is involved in the immunotoxicological responses to nitrite and ammonia stress in M. rosenbergii.

Toxic effects of waterborne nitrite exposure on antioxidant responses, acetylcholinesterase inhibition, and immune responses in olive flounders, Paralichthys olivaceus, reared in bio-floc and seawater.

Paralichthys olivaceus (mean weight, 280.1 ± 10.5 g; mean length, 28.37 ± 2.3 cm) was reared in bio-floc and seawater for 6 months to determine the toxic effects of waterborne nitrite exposure (0, 25, 50, 100, and 200 mg/L) for 1 week, compared to those observed with bio-floc and seawater only. The effects on antioxidant activity, immune responses, and acetylcholinesterase activity were measured. Following nitrite exposure, superoxide dismutase activity in the liver and gills was significantly elevated and catalase activity was significantly increased, except for in the gills of P. olivaceus reared in bio-floc. Further, glutathione S-transferase activity was significantly elevated in the liver and gills, and glutathione was significantly lower. Meanwhile, acetylcholinesterase activity in the liver and gills was significantly inhibited and plasma lysozyme activity and immunoglobulin M were considerably elevated.

Inorganic nitrogen compounds reduce immunity and induce oxidative stress in red seabream.

In this study, the effect of ammonia derived from different stocking densities on immunological, hematological, and oxidative stress parameters was analyzed in the blood or liver of red seabream. Density- and time-dependent increases in inorganic nitrogen compounds were measured for 20 days by analyzing the three major inorganic nitrogen compounds, total ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen. Three immunity parameters, alternative complement activity, lysozyme activity, and total immunoglobulin content were significantly decreased in the blood at the highest stocking density (10 kg m-3). The concentrations of hemoglobin and white blood cells were significantly decreased at 10 kg m-3, while there was no significant change in red blood cells. The significant increases in cortisol level and the enzymatic activities of alanine aminotransferase, aspartate aminotransferase, and alkaline phosphatase at 10 kg m-3 clearly supported inorganic nitrogen compounds-triggered stress. A significant elevation of lipid peroxidation value and depletion of intracellular glutathione were observed at 5 and/or 10 kg m-3 in the liver tissue. The hepatic enzymatic activities of antioxidant defense enzymes, catalase and superoxide dismutase were also significantly increased. When a protein skimmer removes the inorganic nitrogen compounds at the highest density, most parameters showed no significant change. Taken together, these results suggest that accumulated inorganic nitrogen compounds at the highest stocking density inhibit innate immunity and induce oxidative stress in red seabream. This information will be helpful to maintain homeostasis of red seabream by controlling immunity and oxidative status through inorganic nitrogen compounds removal in intensive culture condition.

The effect of nitrite and sulfide on the antioxidant capacity and microbial composition of the intestines of red swamp crayfish, Procambarus clarkii.

Nitrite and sulfide are harmful pollutants in water ecosystems that negatively influence the survival and growth of crayfish. It is currently known that the intestine of crustaceans acts as a significant immune organ, serving as the front line of defense against diseases. In this study, we investigated how the oxidative damage parameters, antioxidant status and microbial composition of the intestine of Procambarus clarkii were influenced under acute nitrite (60 mg/L) and sulfide (18 mg/L) stress for 72 h. Compared with the control, after exposure to nitrite and sulfide stress, the production of reactive oxygen species, and the lipid peroxide and malondialdehyde contents increased in the intestines and were significantly higher after 72 h of exposure. The superoxide dismutase, catalase and glutathione peroxidase activities increased to maximum levels at 6, 24 and 12 h, respectively. These activities then decreased gradually and were significantly lower than those of the control after 48 or 72 h of exposure. In the crayfish exposed to stress, the expression of antioxidant genes including heat shock protein 70, ferritin and metallothionein increased to their maximum values at 12, 48 and 12 h, respectively. The expression levels then decreased gradually, and after 72 h, were lower than, or lacked significant differences with, the expression levels in the control. Additionally, nitrite and sulfide exposure restructured the intestinal microbial community of P. clarkii. This led to decreases in the abundance of some genera such as Citrobacter. However, the abundance of other genera, such as Shewanella and Acinetobacter, increased. Therefore, the health of P. clarkii was seriously impaired when exposed to nitrite and sulfide stress.

Effect of acute exposure to nitrite on physiological parameters, oxidative stress, and apoptosis in Takifugu rubripes.

In the present study, we evaluated the effects of nitrite exposure on hematological parameters, oxidative stress, and apoptosis in juvenile Takifugu rubripes. The fish were exposed to nitrite (0, 0.5, 1, 3, and 6 mM) for up to 96 h. In the high nitrite concentration groups (i.e., 3 and 6 mM), the concentrations of methemoglobin (MetHb), cortisol, glucose, heat shock protein (Hsp)-70, Hsp-90, and potassium (K+) were significantly elevated. Whereas, the concentrations of hemoglobin (Hb), triglyceride (TG), total cholesterol (TC), and sodium (Na+) and chloride (Cl-) ions were significantly decreased. Compared with those of the control groups, the concentrations of the antioxidant enzymes, namely, superoxide dismutase (SOD), catalase (CAT), glutathione (GSH), and glutathione peroxidase (GPx), in the gills were considerably elevated at 12 and 24 h after exposure to nitrite (1, 3, and 6 mM), but reduced at 48 and 96 h. The increase in the antioxidant enzymes may contribute to the elimination of reactive oxygen species (ROS) induced by nitrite during early nitrite exposure, when the antioxidant system is not sufficiently effective to eliminate or neutralize excessive ROS. In addition, we found that nitrite exposure could alter the expression patterns of some key apoptosis-related genes (Caspase-3, Caspase-8, Caspase-9, p53, Bax, and Bcl-2). This indicated that the caspase-dependent apoptotic pathway and p53-Bax-Bcl-2 pathway might be involved in apoptosis induced by nitrite exposure. Furthermore, our study provides insights into how acute nitrite exposure affects the physiological responses and potential molecular mechanism of apoptosis in marine fish. The results can help elucidate the mechanisms involved in nitrite-induced aquatic toxicology in marine fish.

Acute toxicity of inorganic nitrogen (ammonium, nitrate and nitrite) to tadpoles of five tropical amphibian species.

Despite the higher diversity of amphibians and the increasing use of agrochemicals in tropical countries, knowledge on the ecotoxicity of such compounds to tropical amphibians remains very limited. The aim of this study was, therefore, to assess the acute lethal toxicity of three nitrogen salts (ammonium sulphate, sodium nitrate and sodium nitrite) to tadpoles of five tropical frog species: Rhinella ornata, Boana faber, B. pardalis, Physalaemus cuvieri, and P. olfersii. The order of sensitivity to the nitrogen salts for all five species was sodium nitrite > ammonium sulphate > sodium nitrate. There was not a single most sensitive species to all three nitrogen salts. However, differences in generated 4-d LC50 values between the most and least sensitive test species were small (a factor 2 to 6). A comparison with published toxicity values does not suggest an intrinsic higher, or lower, sensitivity of the tropical species tested as compared to their temperate counterparts. Reported nitrogen concentrations in sugarcane fields do not indicate a lethal risk to the amphibian species tested. Chronic-exposure and field studies are recommended to evaluate amphibian sensitivity under environmental-realistic multiple-stressor conditions.

Copper in Cultured Shrimp Litopenaeus vannamei and Its Reduction in Hepatopancreas After Exposure to Sublethal Nitrite Levels.

This research was to evaluate the load and mobility of Cu in juvenile Litopenaeus vannamei after exposure (48 h) to sublethal concentration of nitrite (5.3 mg/L NO2--N) at a salinity of 3.0 g/L. The hypothesis is that such exposure causes a Cu mobility in the tissues of shrimp. The Cu concentration in exoskeleton, hepatopancreas, muscle and hemolymph in the control group were 38.9 ± 3.0, 2478 ± 256, 11.9 ± 0.2 µg/g (dw) and 95.4 ± 19.1 µg/mL, while in the nitrite exposure, were 46.0 ± 0.1, 1546 ± 173, 11.3 ± 0.3 µg/g (dw) and 118.2 ± 10.5 µg/mL, respectively. Only hepatopancreas exhibited a significant (p < 0.05) reduction (37.6%) between the control and the nitrite exposure. This is evidence that nitrite has a significant effect on Cu accumulation in hepatopancreas when shrimp are exposed to sublethal levels in a salinity of 3 g/L. Results confirm the hypothesis that Cu mobility was only significant in hepatopancreas.

Manganese Oxide Biomineralization Provides Protection against Nitrite Toxicity in a Cell-Density-Dependent Manner.

Manganese biomineralization is a widespread process among bacteria and fungi. To date, there is no conclusive experimental evidence for how and if this process impacts microbial fitness in the environment. Here, we show how a model organism for manganese oxidation is growth inhibited by nitrite, and that this inhibition is mitigated in the presence of manganese. We show that such manganese-mediated mitigation of nitrite inhibition is dependent on the culture inoculum size, and that manganese oxide (MnOX) forms granular precipitates in the culture, rather than sheaths around individual cells. We provide evidence that MnOX protection involves both its ability to catalyze nitrite oxidation into (nontoxic) nitrate under physiological conditions and its potential role in influencing processes involving reactive oxygen species (ROS). Taken together, these results demonstrate improved microbial fitness through MnOX deposition in an ecological setting, i.e., mitigation of nitrite toxicity, and point to a key role of MnOX in handling stresses arising from ROS.IMPORTANCE We present here a direct fitness benefit (i.e., growth advantage) for manganese oxide biomineralization activity in Roseobacter sp. strain AzwK-3b, a model organism used to study this process. We find that strain AzwK-3b in a laboratory culture experiment is growth inhibited by nitrite in manganese-free cultures, while the inhibition is considerably relieved by manganese supplementation and manganese oxide (MnOX) formation. We show that biogenic MnOX interacts directly with nitrite and possibly with reactive oxygen species and find that its beneficial effects are established through formation of dispersed MnOX granules in a manner dependent on the population size. These experiments raise the possibility that manganese biomineralization could confer protection against nitrite toxicity to a population of cells. They open up new avenues of interrogating this process in other species and provide possible routes to their biotechnological applications, including in metal recovery, biomaterials production, and synthetic community engineering.