Inhaled isobutyl nitrite compromises T-dependent, but not T-independent, antibody induction

Habitual abuse of nitrite inhalants has been linked in epidemiological studies with seropositivity to human immunodeficiency virus and, separately, with Kaposi's sarcoma among AIDS patients. Mice exposed to isobutyl nitrite in an inhalation chamber for 45 min/day for 14 days had depressed IgM and IgG antibody responses. The inhibition was dose-dependent at 750-900 ppm, but antibody responses were increased at an intermediate (600 ppm) dose. Gender differences in immunotoxicity were not observed. Antibody responses to a T-independent antigen (DNP-ficoll) were not affected by the immunotoxic exposure, suggesting that B-cells were refractory to the toxic exposure. Toxic exposure to isobutyl nitrite did not selectively deplete a particular spleen cell population, but caused equivalent reductions of T-cells and B-cells. Finally, exposed mice remained immunocompromised for 3-5 days after terminating exposures. Normal immune responses returned by 5-7 days, suggesting that inhibition of cellular function was reversible.

S-nitrosyl glutathione-mediated hepatocyte cytotoxicity

1. The addition of n-butyl nitrite (BN) to isolated rat hepatocytes caused rapid S-nitrosyl glutathione (GSNO) formation, then a concomitant decrease in protein thiols, followed by a marked ATP depletion. Cytotoxic concentrations of BN also caused lipid peroxidation after a long lag period but before cytotoxicity ensued. 2. Prior glutathione (GSH) depletion protected hepatocytes against the BN-induced decrease in protein thiols, ATP depletion, lipid peroxidation and cytotoxicity. Thus cytotoxic effects were thought to be mediated via GSNO formed by reaction of BN with GSH, a reaction catalysed by the cytosolic fraction. 3. Cytotoxicity and lipid peroxidation, but not depletion of GSH, protein thiols or ATP, could be averted by the subsequent addition of antioxidants or the iron chelator, desferoxamine. 4. Addition of the thiol reductant, dithiothreitol to BN-treated hepatocytes restored GSH and protein thiols and also prevented cytotoxicity.

The effects of nitrate, nitrite, and N-nitroso compounds on animal health

The clinical signs of acute nitrate toxicity vary according to species. In general, ruminant animals develop methemoglobinemia while monogastric animals exhibit severe gastritis. Nitrate ingestion has also been linked to impairment of thyroid function, decreased feed consumption, and interference with vitamin A and E metabolism. Hematologic changes seen with chronic high nitrate exposure include both compensatory increases in red blood cells and anemia, along with increased neutrophils and eosinophils. Unlike nitrate, nitrite is capable of inducing methemoglobinemia in a wide range of species, ie cattle, sheep, swine, dogs, guinea pigs, rats, chickens and turkeys. In rats, chronic nitrite exposure causes pathologic changes in a variety of tissues, alterations in motor activity and brain electrical activity, and alters gastric mucosal absorption. Nitrite affects the metabolism of sulfonamide drugs in animals such as the pig, guinea pig, and rat. The N-nitroso compound dimethylnitrosamine causes toxic hepatosis in cattle, sheep, mink, and fox. Nitrosamines have been reported in cows milk and been found to pass into the milk of goats under experimental conditions.

Further studies on the effect of nitrogen dioxide on mast cells: the effect of the metabolite, nitrite

To evaluate the relationship between atmospheric nitrogen dioxide exposure and the development of allergic diseases, the effects of nitrite as a chemical product of inhaled nitrogen dioxide on mast cell functions were investigated. We have studied nitrite-induced histamine release from two functionally distinct mast cell populations, namely peritoneal mast cells (PMC) and intestinal mucosal mast cells (IMMC) of Nippostrongylus brasiliensis-infected rats. High concentrations of nitrite alone (10, 20, and 50 mM) induced histamine release from IMMC, but not from PMC. Moreover, histamine release from PMC and IMMC stimulated with sensitizing antigen was significantly enhanced by pretreatment with 50 mM nitrite or nitrate. No differences in histamine release from nitrite-treated and control PMC were seen below 1 mM. To investigate the effect of nitrite on tumor cell cytotoxic activity, PMC were incubated with various concentrations of nitrite. Pretreatment with 5 and 50 mM nitrite markedly depressed tumor necrosis factor (TNF)-alpha-dependent natural cytotoxicity of PMC for the tumor target WEHI-164. Thus, high concentrations of nitrite enhanced mast cell histamine release, but depressed TNF-alpha-dependent cytotoxicity. However, low concentrations of nitrite (< 1 mM) that would normally be produced by short-term atmospheric exposure to nitrogen dioxide may have no significant effects on mast cell functions.

Mutagenicity of iso-butyl nitrite vapor in the Ames test and some relevant chemical properties, including the reaction of iso-butyl nitrite with phosphate

We examined the mutagenicity of iso-butyl nitrite (IBN) vapor and aqueous IBN solution in the Ames test to help evaluate the hazard of sniffing this vapor, a habit which might play a role in the induction of Kaposi's sarcoma associated with acquired immune deficiency syndrome. Chemical analysis showed that the saturated vapor contained 190 micrograms IBN/ml at 25 degrees C, and saturated aqueous solution, 2.6 mg IBN/ml at 21-23 degrees C. When agar plates containing Salmonella typhimurium TA-1535 and rat liver S-9 were exposed to IBN vapor, the number of mutants reached a maximum after 40 min. A mean of 307 mutants/plate (22 x background) was observed when the plates were exposed to IBN vapor for 30 min. Addition of 0.2 ml saturated IBN solution in water to similar plates gave a mean of 179 mutants/plate (7.9 x background) in the absence of S-9, confirming published results. The S-9 did not affect the results. Based on the IBN level in medium exposed to IBN vapor, the vapor was apparently 11 times more mutagenic than IBN solution. This was attributed to continuous replenishment of unstable IBN in the medium by the vapor. The half-life of IBN at 21-23 degrees C was > 1 hr for solutions in water and < 3 min for solutions in the assay medium. This instability was traced to a reaction with phosphate, presumably hydrolysis to nitrite and iso-butanol. IBN in solution was 2.8 times more mutagenic than sodium nitrite, suggesting that IBN was not mutagenic because of its conversion to nitrite. Iso-butanol was not mutagenic. The results demonstrate the potential hazard of sniffing IBN vapor.

[Toxicological characterization of new nitrification inhibitors]

Study of the two new nitrification inhibitors HMDI and TMDI showed a low toxicity. The lower toxicity with single intragastric administration was 485 mg/kg for HMDI, and 460 mg/kg for TMDI.

The interactive effect of chlorine, copper and nitrite on methaemoglobin formation in red blood cells of Dorset sheep

Simultaneous exposure to chemicals which can oxidize the haemoglobin of the red blood cell to methaemoglobin is common. Although the effects of some of these agents have been documented individually, little research considers the interactive effects. In-vitro experiments on the treated blood of female Dorset sheep assessed the interactive capacity of chlorite, copper and nitrite to affect methaemoglobin formation. All combinations of doses which produced 2.5, 5, 10% methaemoglobin were tested in all possible combinations (a total of 80), as were the controls. This included data on each chemical alone, each two-way combination and the three-way combination. The response is largely additive (the sum of the individual effects) except for one of the two-way interactions, chlorite/nitrite (P less than .01), which showed antagonism. Chlorite may oxidize nitrite which could explain the less-than-additive response. Overall, the result of combining these agents on methaemoglobin was additive.

Hepatotoxicity and hepatocarcinogenicity in rats fed squid with or without exogenous nitrite

The popular seafood squid contains high levels of naturally occurring amines such as dimethylamine (DMA) trimethylamine and trimethylamine-N-oxide (TMAO). The hepatotoxicity and hepatocarcinogenicity of squid with or without exogenous nitrite were investigated in rats. Acute necrosis including polymorphogenic neutrophil infiltration, haemorrhage and cholangiofibrosis were observed in the livers of most rats fed squid. Hepatocellular carcinoma (HCC) was induced in two out of 12 rats (16%) by feeding 10% squid in Purina rat chow for 10 months. The incidence of HCC was increased to four out of 10 rats (33%) when 0.3% NaNO2 was added to the above diet. At the end of the experiment a marked elevation of serum gamma-glutamate transferase was observed in treated groups, but no significant changes in the activities of serum glutamic-oxaloacetic transaminase and glutamic-pyruvic transaminase were detected. Vitamin C (0.3%) gave partial protection against hepatic damage. The concentration of DMA in squid is estimated to be 0.19%; this concentration did not induce HCC under the experimental conditions used. Therefore it is suggested that another major naturally occurring amine in squid, TMAO, could be one of the important factors involved in the induction of hepatotoxicity and hepatocarcinogenicity in rats.

Killing of virulent Mycobacterium tuberculosis by reactive nitrogen intermediates produced by activated murine macrophages

Tuberculosis remains one of the major infectious causes of morbidity and mortality in the world, yet the mechanisms by which macrophages defend against Mycobacterium tuberculosis have remained obscure. Results from this study show that murine macrophages, activated by interferon gamma, and lipopolysaccharide or tumor necrosis factor alpha, both growth inhibit and kill M. tuberculosis. This antimycobacterial effect, demonstrable both in murine macrophage cell lines and in peritoneal macrophages of BALB/c mice, is independent of the macrophage capacity to generate reactive oxygen intermediates (ROI). Both the ROI-deficient murine macrophage cell line D9, and its ROI-generating, parental line J774.16, expressed comparable antimycobacterial activity upon activation. In addition, the oxygen radical scavengers superoxide dismutase (SOD), catalase, mannitol, and diazabicyclooctane had no effect on the antimycobacterial activity of macrophages. These findings, together with the results showing the relative resistance of M. tuberculosis to enzymatically generated H2O2, suggest that ROI are unlikely to be significantly involved in killing M. tuberculosis. In contrast, the antimycobacterial activity of these macrophages strongly correlates with the induction of the L-arginine-dependent generation of reactive nitrogen intermediates (RNI). The effector molecule(s) that could participate in mediating this antimycobacterial function are toxic RNI, including NO, NO2, and HNO2, as demonstrated by the mycobacteriocidal effect of acidified NO2. The oxygen radical scavenger SOD adventitiously perturbs RNI production, and cannot be used to discriminate between cytocidal mechanisms involving ROI and RNI. Overall, our results provide support for the view that the L-arginine-dependent production of RNI is the principal effector mechanism in activated murine macrophages responsible for killing and growth inhibiting virulent M. tuberculosis.

Exposure to inhaled isobutyl nitrite reduces T cell blastogenesis and antibody responsiveness

Isobutyl nitrite is a drug of abuse popular among male homosexuals and among adolescents. In order to approximate the nitrite exposures of inhalant abusers, mice were treated with 900 ppm isobutyl nitrite in an inhalation chamber for 45 min per day for 14 days. After 14 consecutive days of exposure to isobutyl nitrite, mice weighed an average of 4% less than mice exposed to air. The spleens of nitrite-exposed mice weighed 15% less and had 24% fewer cells per spleen than those of controls. Adjusted for equal cell numbers, T cell mitogenic and allogeneic proliferative responses were significantly reduced by 33 and 47%, respectively. The frequency of T-dependent plaque-forming cells (PFC) was inhibited by 63% and the total number of PFC per spleen was reduced by 72% in nitrite-exposed mice. In contrast, B cell proliferative responses to LPS were unaltered, suggesting that the toxicity of isobutyl nitrite did not affect all lymphoid cells equally. The data suggest that habitual inhalation of isobutyl nitrite could impair immune competence and that toxicity appeared to be directed toward T cell functions.

Pharmacotoxicological aspects of nitrate and nitrite in domestic fowls

1. The effects of nitrates and nitrites on growth, erythrocytic count, liver and kidney functions, humoral and cell mediated immune responses in cockerels were investigated. 2. Sodium nitrate (4.2 g/kg diet) and sodium nitrite (1.7 g/kg) retarded growth, caused methaemoglobinaemia and changes in erythrocytic count, serum concentrations of glutamic-pyruvic transaminase, creatinine and urea. 3. Cockerels given nitrate or nitrite in the food had reduced haemagglutination responses after injection of sheep erythrocytes and a reduced delayed hypersensitivity reaction to purified protein derivative tuberculin following sensitisation to Bacille Calmette Guerin. 4. Nitrates and nitrites are environmental pollutants present in food and water and they may contribute to the aetiology of liver and kidney diseases and problems related to failure of immunity in domestic fowls.

Nitrates, nitrites and N-nitrosocompounds: a review of the occurrence in food and diet and the toxicological implications

Data on occurrence of nitrate, nitrite and N-nitrosocompounds in food and drinking water, and on total dietary intakes are reviewed. Metabolic, toxicological and epidemiological studies are surveyed and the implications with respect to safety evaluation are addressed. It is concluded that, on the basis of recent long-term animal studies and of clinical experience in man, the current Acceptable Daily Intake (ADI) allocated to nitrate by the Joint FAO/WHO Expert Committee on Food Additives of 0-5 mg/kg body weight/day (expressed as sodium nitrate) might be increased to 0-25 mg/kg body weight/day. Based on similar criteria, the ADI for nitrite would be 0-0.1 mg/kg body weight/day (expressed as sodium nitrite). In view of the known carcinogenicity of N-nitrosocompounds, exposure to these compounds in food should be minimized by appropriate technological means, such as lowering the nitrite concentration in preserved foods to the minimum required to ensure microbiological safety and use of inhibitors of nitrosation like alpha-tocopherol or ascorbic acid. Further work is needed to define the minimal levels of nitrite in foods needed to inhibit outgrowth of Clostridium botulinum and toxin production.

Structural basis of the genotoxicity of nitrosatable phenols and derivatives present in smoked food products

The CASE methodology for studying structure-activity relationships has been applied to investigating the basis of the genotoxicity of phenols and derivatives following exposure to nitrous acid. The structural features identified include availability of positions para or ortho to the hydroxyl groups, that one meta position must remain unoccupied and one ortho or para position must be unsubstituted as well. The analyses revealed that genotoxicity is dependent upon the ease of formation of the active phenyldiazonium intermediate and is influenced only secondarily by the nature of the genotoxicant or its ease of entry into the cell. With this data base, CASE predicts the genotoxicity, following nitrosation, of a number of agents, including serotonin, acetaminophen, and of some naturally-occurring pesticides present in edible plants.

Protective effect of the calcium antagonist nimodipine on discrimination learning deficits and impaired retention behavior caused by prenatal nitrite exposure in rats

Discrimination learning behavior and retention of a passive avoidance response were studied in male adult offspring of gestating rats exposed to drinking water containing 2 g/l sodium nitrite, throughout the second half of pregnancy. Both in an auditory and visual discrimination learning paradigm NaNO2-exposed rats were inferior to controls. The long-term retention of a passive avoidance response was also impaired. The acquisition of simple learning tasks was not significantly disturbed. The concomitant prenatal daily treatment with the calcium antagonist nimodipine in a dose of 10 mg/kg p.o. interfered with the nitrite neurotoxicity and prevented the development of adult behavioral deficits. The results support the hypothesis that Ca2+ homeostasis of neurons is an important factor for normal development of brain and behavior.

Malignant transformation of mouse BALB/c3T3 cells induced by NaNO2

The addition of sodium nitrite (NaNO2; 5-20 mM) for 72 h to mouse BALB/c3T3 cells resulted in the induction of transformed foci (type III foci) in a dose-dependent manner. The cells isolated from the NaNO2-induced transformed foci produced progressively growing tumors when inoculated into nude mice subcutaneously at an inoculum size of 1 X 10(6) cells per site. In contrast, the original untreated cells did not take even at an inoculum size of 1 X 10(7) cells per site. The possibility that NaNO2 might react with cellular or medium components to make carcinogenic N-nitrosamines and that these might induce cell transformation was examined and almost excluded. Thus, nitrite itself seems to have a cell transforming activity. Recent evidence suggests that NO2- is produced by the activated macrophages of mammals. We also detected NO2- production in culture media in the mouse macrophage-like cell line J774-A1 after lipopolysaccharide (LPS) treatment, and also in the human promyeloleukemia cell line HL60 after differentiation into macrophage-like cells by 12-O-tetradecanoyl phorbol-13-acetate and further activation by LPS.

[Hygienic significance of soil concerning the health status of the population]

On the basis of epidemiological studies and literature data analysis it is possible to state that excessive contamination of soil by exogenous chemicals administered purposefully (pesticides and mineral fertilizers) and as a result, technologic pollution (lead, mercury, arsenic, molybdenum, etc.) causes high content of those contacting with soil: ambient air, water of water sources, cultivated plants. Human intake of significant amounts of exogenous chemicals, contaminating soil, may lead to changes in health status of the population, appearance of acute and chronic poisoning by exogenous chemicals.

Brain plasticity after damage

This is a brief summary of our research on the prevention or reduction of the effects of brain damage. I believe that the results contain a number of exciting promises. At this time, the greatest hope for effective remedial interventions comes from the choline and metyrapone studies. However, I am also reminded of the components a psychiatrist who worked with children in the heart of Philadelphia made some 20 years ago at a conference on mental retardation. He said that the most significant contribution to the elimination of mental retardation in his city would be the elimination of lead-based paints from the walls of ghetto apartments, an intervention second only in effectiveness to the elimination of the ghettos themselves. The importance of early interventions with individuals suffering brain damage, either general or specific, is clearly recognized. In research now well underway, Yong Shen, William Smotherman, and I have found encouraging results indicating that both short- and long-term effects of hypoxia induced by clamping the rat's umbilical cord can be attenuated by the prior administration of a calcium L channel antagonist. If those results are upheld in further studies, the principles of prevention of damage described in this article for the adult may prove to be even more potent in the young.