Metabolism and detoxification of nitrite by trout hepatocytes

Nitrite (NO2-) is one of the most important toxicants to fish. Freshwater fish are especially sensitive, particularly salmonids. Nitrite uptake is thought to occur via the HCO3-, Cl- -exchanger at the gill epithelia with nitrite substituting for chloride. In this way freshwater fish accumulate nitrite in the blood up to 100-fold from the surrounding water. Another source, endogenous nitrite as a degradation product of nitric oxide, rarely leads to pharmacologically relevant concentrations. We developed a new method for the determination of nitrate (NO3-) in biological samples and used it to measure nitrite oxidation in isolated rainbow trout (Oncorhynchus mykiss) hepatocytes which were found to detoxify nitrite to the almost non-toxic nitrate. Detoxification is inhibited by 0.05 mM bumetanide and 0.1 mM furosemide but not by SITS and DITS, suggesting the involvement of the Na+, K+, 2Cl- -cotransporter with nitrite or nitrate substituting for chloride. Oxidation of nitrite is strongly accelerated by 0.05 mM uric acid. The efficacy of this antioxidant suggests that similar reactions are involved as known for haemoglobin [33]. However, in the case of trout liver also membrane bound detoxificating activity can be observed which is also enhanced by uric acid. ATP concentrations remained constant in the hepatocytes during all experiments demonstrating that hepatocyte energy status was not influenced by nitrite oxidation. Thus nitrite resistance in fish is governed by at least two mechanisms, nitrite uptake and the rate of detoxification. It is unknown whether fish actually differ in their ability to distinguish between chloride and nitrite during branchial uptake, but evidence presented in this paper suggests a significant contribution of detoxification pathways to a possible nitrite tolerance of fish.

Acute toxicity of fire control chemicals to Daphnia magna (Straus) and Selenastrum capricornutum (Printz)

Acute toxicity tests were conducted exposing Daphnia magna Straus (daphnid) in soft and hard reconstituted waters (hardness 42 and 162 mg/liter as CaCO3, respectively), and Selenastrum capricornutum Printz (algae) in ASTM algal assay medium (hardness 15 mg/liter as CaCO3) to fire retardants Fire-Trol GTS-R, Fire-Trol LCG-R, and Phos-Chek D75-F, and foam suppressants Phos-Check WD-881 and Silv-Ex. The chemicals were slightly toxic to practically harmless to daphnids and moderately toxic to algae. Water quality did not consistently alter the toxicity of the test chemicals to daphnids. The most toxic chemical to daphnids was Silv-Ex (48-hr EC50 7 mg/liter in soft and hard waters), whereas the least toxic chemical to daphnids was Fire-Trol LCG-R (48-hr EC50 848 mg/liter in soft water, 813 mg/liter in hard water). The most toxic chemical to algae was Fire-Trol LCG-R (96-hr IC50 10 mg/liter), and the least toxic chemical was Phos-Chek D75-F (96-hr IC50 79 mg/liter). Un-ionized ammonia concentrations near the EC50 or IC50 value in tests with the Fire-Trol compounds were frequently equal to or above reported LC50 un-ionized ammonia concentrations. Un-ionized ammonia concentrations in tests with Phos-Chek D75-F were low, thus other toxic components present in the compounds probably contributed to the toxicity. When compared to the daphnids tested in ASTM soft water, the Fire-Trol compounds were most toxic to algae, whereas Phos-Chek D75-F and the foam suppressants were most toxic to daphnids. The results of these tests are comparable to those obtained from research conducted in other laboratories with the same species and similar chemicals. Accidental entry of fire-fighting chemicals into aquatic environments could adversely affect algae and aquatic invertebrates, thus disrupting ecosystem function.

Health implications of nitrate and nitrite in drinking water: an update on methemoglobinemia occurrence and reproductive and developmental toxicity

In 1987, an evaluation of the nitrate drinking water standard was performed with a primary focus on the effects of nitrate on methemoglobinemia and reproductive/developmental effects (Fan et al. (1987). Regul. Toxicol. Pharmacol. 7, 135-148). The present review presents an updated overview and evaluation of the available information on the same health effects of nitrate and nitrite with an emphasis on data not included in the previous review, which should be used as a compendium to this report. Recent epidemiologic data have suggested an association between developmental effects in offspring and the maternal ingestion of nitrate from drinking water, but a definite conclusion on the cause and effect relationship cannot be drawn. Animal experimental data have shown reproductive toxicity associated with high exposure levels to nitrate or nitrite, which are not likely to be encountered in drinking water. No teratogenic effects were observed in rats, mice, rabbits, and hamsters tested. Several cases of methemoglobinemia have been reported in infants in the United States using water containing nitrate at levels higher than the current maximum contaminant level (MCL) of 45 ppm (mg/liter) nitrate (NO3) or 10 ppm nitrate-nitrogen (nitrate-N), but none at or lower than the MCL. The uncertainties in the data base are discussed, noting that no uncertainty factor was applied in deriving the MCL in order to account for the uncertainties that exist in the data base.

Mutagenicity of 1-methyl-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid treated with nitrite in the presence of alcohols

The mutagenicity of a product produced from 1-methyl-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid (MTCCA), which is a component in soy sauce, after treatment with 50 mM nitrite at pH 3, 37 degrees C, for 60 min in the presence of 7.5% ethanol was much higher than that in the absence of ethanol during the nitrite treatment. The enhancement of the mutagenicity of nitrite-treated MTCCA by ethanol required simultaneous treatment of MTCCA with nitrite and ethanol. The mutagenicity of MTCCA treated with nitrite in the presence and absence of ethanol was detected in the same fractions on HPLC and was highest for Salmonella typhimurium strain YG1029 possessing elevated O-acetyltransferase activity among the several Salmonella test strains, suggesting that the same mutagen belonging to aromatic compounds was produced both in the presence and absence of ethanol. Methanol, n-propanol and isopropanol as well as ethanol were also observed to have an augmenting effect. However, the sugars glucose and sucrose had no effect. When MTCCA was treated with nitrite in the presence of commercial alcoholic beverages equivalent to 1.25-10% ethanol, Japanese 'sake' and 'shochu' were demonstrated to have a highly augmenting effect and beer, wine, whisky and brandy to have a mildly augmenting effect.

[Effects of iron deficiency on toxic action of nitrites and endogenous synthesis of N-nitrosamines]

Separate or joint ingestions of water solutions of sodium nitrite and/or N-diethylamine by rats fed iron deficiency diet caused sharp increasing of N-nitrosodiethylamine level in stomach, a decreasing of Hb and increasing of MetHb concentrations in blood of animal. These effects were greater on iron deficient diet than on control diet. The nitrite ingestion caused a decline level of cytochrome P-450 and inhibition of lipid peroxidation in rat liver.

Dose- (and time-) dependent blockade of pregnancy in Sprague-Dawley rats administered ammonium dinitramide in drinking water

Ammonium dinitramide (ADN) is a class 1.1 explosive oxidizer that can be used in solid rocket propellant mixtures and explosives. A 90-day general toxicity/ reproductive screen performed on this compound at doses of 162, 103, 29, and 0.0 mg ADN/kg/day resulted in a treatment-related adverse effect on litter production. Incidences of animals producing litters (1/11, 3/12, 12/12, and 11/12, respectively) and mean numbers of pups per litter (7, 7, 16, and 15, respectively) both were statistically significantly less than controls. In a follow-up study, mated dams treated with ADN at the same doses and examined at gestation days (GDs) 10 and 20 showed an effect in fetus loss similar to that seen in the reproductive screen. A pre- versus postimplantation dosing regimen indicated that implantation is vulnerable to ADN effects during the preimplantation period (GDs 1-3). No implantation sites were found in the rats treated with 2000 mg ADN/L drinking water (target dose of 160 mg ADN/kg/day) during GDs 1-3. Numbers of implantation sites found in the rats treated during GDs 4-8 were similar to those found in the control group. The pituitary was not identified specifically in this study as the site of primary action, but serum progesterone was reduced by 27%, which may have resulted in reduced fertility.

Local versus systemic immunotoxicity of isobutyl nitrite following subchronic inhalation exposure of female B6C3F1 mice

Female B6C3F1 mice were exposed to isobutyl nitrite (IBN) by inhalation at 0, 37.5, 75, or 150 ppm for 6 hr per day, 5 days per week for 15 weeks. The potential of this compound to induce immunotoxicity was assessed during the 3rd, 13th, 14th, and 15th week of exposure and after 2 weeks of recovery following the 15 weeks of exposure. Both systemic and lung immune functions were examined, including body and lymphoid organs weights, pulmonary macrophage function and host defense, expression of splenic lymphocyte cell-surface markers, natural killer cell function, mixed lymphocyte reaction, and induction of specific antibody to a T-cell-dependent antigen. There was a dose-related suppression of T-cell-dependent antibody-forming cell responses in the spleen following IBN exposure; however, other measures of T-cell and nonspecific immunity were not significantly affected. A dose-related increase of H202 production by alveolar macrophages was present after 12 but not after 68 exposures to IBN. In contrast, pulmonary host defense mechanisms against Klebsiella pneumoniae were unaffected. These results suggest that in the absence of changes in host resistance, IBN may have selective and partially reversible effects on the immune system.

Effect of wilting and processing on the nitrate and nitrite contents of some Nigerian leaf vegetables

Nitrate and nitrite contents of seven varieties of commonly consumed leaf vegetables were determined. Effect of cooking and wilting on the contents of these factors were investigated. Nitrate ranged from 48.10 in ewuro to 270.0 ppm ogunmo (mean 116.43+/- 78.31) while nitrite ranged from 0.024 ppm in tete to 0.064 in ogunmo (mean 0.044+/-0.018). Cooking reduced the nitrate levels in all the samples but nitrite levels inexplicably increased in all sample. On wilting nitrate levels decrease while nitrite levels increased up to 83% in tete. The nitrate and nitrite levels were not considered hazardous but toxicological implications of high consumption of these factors is briefly highlighted.

Reproductive toxicity screen of ammonium dinitramide administered in the drinking water of Sprague-Dawley rats

The Department of Defense is currently considering replacing ammonium perchlorate with ammonium dinitramide (ADN), a class 1.1 explosive oxidizer to be used in solid rocket propellant mixtures and explosives. This study was intended to evaluate the potential of ADN to produce alterations in paternal fertility, maternal pregnancy and lactation, and growth and development of offspring. Male and female rats received drinking water containing 0.0, 0.2, 1.0, or 2.0 g ADN/liter throughout the study. Mating occurred following 14 days of treatment. All dams, one-half the males, and representative pups were maintained for a total of 90 days of treatment. No mortality occurred in parental animals during the study. Treatment with ADN resulted in no adverse effects on mating; 92-100% of the animals mated. No treatment-related effects were seen in parental animals clinically or histopathologically. Adverse treatment-related effects were noted in maternal and paternal fertility indices, gestational indices, and live birth indices in both the mid- and high-dose groups. Litter sizes in the mid- and high-dose groups were significantly smaller than those of the low-dose and control groups. Mean pup weights showed no statistically significant differences between ADN-treated pups and controls. Gross and histopathological examination of the animals failed to identify the cause for the decrease in litter production in the mid- and high-dose dams. This study indicates that ADN is a reproductive toxicant. The no-observable-effect level (NOEL) is 29 mg/kg/day, the median dose of the low level female rats.

Mutagenic activity of dopamine after nitrosation

Dopamine hydrochloride is reported to be a new mutagen precursor in this study. After treatment with nitrite under acidic conditions, dopamine hydrochloride showed direct-acting mutagenicity on Salmonella typhimurium TA100, TA98 and Escherichia coli WP2uvra. The addition of S9 mix did not affect the mutagenicity of nitrosated dopamine significantly in these three strains. Meanwhile, a comparison of the mutagenicity of nitrosated dopamine with nitrosated tyramine was carried out.

Potency ranking of methemoglobin-forming agents

This study represents the first systematic attempt to rank methemoglobin-forming agents. It is a quantitative potency ranking study utilizing linear regression analysis of dose-response data for comparative purposes. Six agents that are direct-acting and eight that require bioactivation were tested for their ability to induce methemoglobin formation in Dorset sheep erythrocytes under defined in vitro conditions. The agents were then ranked according to three complementary methods based on the slope of the linear regression, the calculated dose expected to induce a given amount of methemoglobin formation and the calculated percentage methemoglobin response induced by 1 mmol l-1 of the agent. The direct-acting agents, ranked from most to least potent inducers of methemoglobin formation, are: p-dinitrobenzene > o-dinitrobenzene > copper = nitrite > chlorite > chlorate. The ranking from most to least potent inducers of the bioactivated agents are: alpha-naphthol > p-nitroaniline > m-nitroaniline, o-nitroaniline > p-nitrotoluene = aniline > m-nitrotoluene = o-nitrotoluene. The ranking procedures are discussed and issues of interindividual variation and agent-specific sensitivities are addressed.

Inhalation exposure to isobutyl nitrite inhibits macrophage tumoricidal activity and modulates inducible nitric oxide

Abuse of nitrite inhalants is common among male homosexuals and a history of abuse has been correlated with seropositivity to HIV and with the incidence of Kaposi's sarcoma among AIDS patients. The present study shows that inhalation exposure of mice to 900 ppm isobutyl nitrite for 45 min/day for 14 days compromised macrophage tumoricidal activity by up to 40% and it remained compromised for at least 7 days after terminating exposures. The inhalation exposures did not affect tumor cell binding but did inhibit inducible nitric oxide (NO zero). The NO zero synthase inhibitor NG-methyl-L-arginine totally inhibited both NO zero production and cytotoxicity, suggesting that reductions in NO zero due to inhalant exposure may be responsible for the reduced cytotoxic activity. Exposure to the inhalant increased constitutive production of tumor necrosis factor-alpha (TNF-alpha). TNF-alpha has been reported to stimulate the replication of HIV and the proliferation of Kaposi's sarcoma cells in vitro.

[The nitric oxide cycle in mammals and nitrite reducing activity of heme-containing proteins]

A nitric oxide cycle is proposed, which explains numerous experimental data demonstrating that under hypoxic conditions synthesis of NO was elevated. Two pathways appear to be fundamental for activation of NO formation: 1) activation of L-arginine utilization as its content was decreased in blood; 2) transfer of heme-containing proteins hemoglobin, myoglobin, cytochrome oxidase and cytochrome P-450 into their deoxy-form, where these proteins are able to reduce NO2- into NO. This suggests that the nitric oxide cycle may be considered as a compensatory mechanism which allowed the various cells to acquire reduced dependence on overloading under conditions of oxygen and energy deficiency.

Strains of Mycobacterium tuberculosis differ in susceptibility to reactive nitrogen intermediates in vitro

The effects on the viability of Mycobacterium tuberculosis strains and one Mycobacterium bovis strain from exposure to sodium nitrite for 24 h, in both neutral and acidic media, were tested. The in vitro resistance of mycobacteria to reactive nitrogen intermediates, generated at an acidic pH, was found to have a significant (P < 0.05) positive correlation to the virulence of strains in guinea pigs.

T cell functions are impaired by inhaled isobutyl nitrite through a T-independent mechanism

Isobutyl nitrite is representative of a group of inhalants abused by male homosexuals and adolescents. Inhalation exposure of mice to isobutyl nitrite at 900 ppm for 45 min per day for 14 days caused serious deficits in T cell-mediated immune responses. Cytotoxic T lymphocyte (CTL) activity was reduced by 36% following the exposure. T cell proliferative responses to mitogenic and allogeneic stimulation were reduced by 37% and 51%, respectively. The exposure did not directly alter the ability of cells to synthesize or respond to IL-2. Accessory cell function in facilitating T cell activation was inhibited by about 50% following exposure to the inhalant.

Toxicology of selected nitric oxide-donating xenobiotics, with particular reference to azide

Nitric oxide (NO) has been discovered recently to be a ubiquitous, endogenous mediator, which is responsible for a variety of normal physiological functions. However, NO also has been implicated in several pathophysiological processes. For example, the pulmonary toxicity of various nitrogen oxides, including NO, found in photochemical smog has been studied for decades; endogenous NO also is associated with bleomycin-induced lung damage, as well as other adverse effects. Recently, a variety of xenobiotics have been shown to owe their biological activity in vivo to their biotransformation to NO. Thus, the therapeutic vasodilatation produced by drugs such as nitroglycerin and sodium nitroprusside is now believed to result from their release of NO, which then mimics the effects of endogenously synthesized NO. The toxic effects of NO prodrugs are, therefore, a matter of concern, especially the extent to which, if any, NO contributes to their toxicity. As reviewed here, NO does not appear to contribute importantly to the toxicity of the NO donors nitrite, hydroxylamine, or nitroprusside. However, it is by no means clear whether or not the NO generated in vivo from sodium azide contributes in a major way to its toxicity. Azide is almost as acutely toxic as cyanide, with which it shares a number of biological effects; yet, azide also has certain cardiovascular actions in common with nitrite. Unlike either cyanide or nitrite, some evidence suggests a tendency for azide to produce low-grade cumulative toxicity. In laboratory animals, azide frequently produces nonasphyxial convulsions, whereas most human deaths appear to be the result of cardiovascular collapse. Neither of these azide-induced syndromes appears to be due to the inhibition of cytochrome c oxidase. Azide is widely used as a preservative in aqueous laboratory reagents and as the propellant in automobile air bags and aircraft escape chutes. Both of these inflable systems are generally safe, and will prevent untold numbers of injuries and deaths. However, to protect workers who handle these devices and others who may come into contact with the sodium azide propellant in these systems, our rudimentary knowledge of azide toxicity needs to be expanded.

The effects of nitrate, nitrite and N-nitroso compounds on human health: a review

The effects of nitrate, nitrite, and N-nitroso compounds on human health are reviewed. Special emphasis has been placed on the role of these compounds on infant methemoglobinemia and gastric cancer. The discussion on methemoglobinemia includes the source of nitrate or nitrite, diagnosis, treatment, prevention and the contributions of age, gastric pH, gastrointestinal illness, and ingestion of vitamin C to this illness. The maternal transfer of these compounds and the potential effect on fetal death and malformation are also described. The etiology and development of gastric cancer is reviewed as well as the roles of nitrate, nitrite, and N-nitroso compounds in this disease. Endogenous nitrosation and the experimental and epidemiologic evidence linking these compounds to gastric cancer is examined. Other sections include adult methemoglobinemia and acute toxicity, hypo- and hypertension, Balkan nephropathy, slowing of motor reflexes in children, nitrate esters dependence. Sources of nitrate, nitrite, and N-nitroso compounds are detailed. Future areas of research are given.