Fariheen Aisha Ansari

Sodium nitrite-induced oxidative stress causes membrane damage, protein oxidation, lipid peroxidation and alters major metabolic pathways in human erythrocytes.

Nitrite salts are present as contaminants in drinking water and in the food and feed chain. In this work, the effect of sodium nitrite (NaNO2) on human erythrocytes was studied under in vitro conditions. Incubation of erythrocytes with 0.1-10.0 mM NaNO2 at 37 °C for 30 min resulted in dose dependent decrease in the levels of reduced glutathione, total sulfhydryl and amino groups. It was accompanied by increase in hemoglobin oxidation and aggregation, lipid peroxidation, protein oxidation and hydrogen peroxide levels suggesting the induction of oxidative stress. Activities of all major erythrocyte antioxidant defense enzymes were decreased in NaNO2-treated erythrocytes. The activities of enzymes of glycolytic and pentose phosphate pathways were also compromised. However, there was a significant increase in acid phosphatase and also AMP deaminase, a marker of erythrocyte oxidative stress. Thus, the major metabolic pathways of cell were altered. Erythrocyte membrane damage was suggested by lowered activities of membrane bound enzymes and confirmed by electron microscopic images. These results show that NaNO2-induced oxidative stress causes hemoglobin denaturation and aggregation, weakens the cellular antioxidant defense mechanism, damages the cell membrane and also perturbs normal energy metabolism in erythrocytes. This nitrite-induced damage can reduce erythrocyte life span in the blood.

Sodium nitrite enhances generation of reactive oxygen species that decrease antioxidant power and inhibit plasma membrane redox system of human erythrocytes.

Nitrite/nitrate salts are used in fertilizers and as food preservatives. Human exposure to high levels of nitrite results in its uptake and subsequent entry into blood where it can interact with erythrocytes. We show that treatment of human erythrocytes with sodium nitrite (NaNO2) results in a dose‐dependent increase in the production of reactive oxygen species. This was accompanied by a decrease in the antioxidant power which lowered the free radical quenching and metal‐reducing ability. NaNO2 treatment also inhibited plasma membrane redox system (PMRS) of erythrocytes. These changes increase the susceptibility of erythrocytes to oxidative damage, decrease the antioxidant power of whole blood, and can be a major cause of nitrite‐induced cellular toxicity.

Acute oral dose of sodium nitrite induces redox imbalance, DNA damage, metabolic and histological changes in rat intestine

Industrialization and unchecked use of nitrate/nitrite salts for various purposes has increased human exposure to high levels of sodium nitrite (NaNO2) which can act as a pro-oxidant and pro-carcinogen. Oral exposure makes the gastrointestinal tract particularly susceptible to nitrite toxicity. In this work, the effect of administration of a single acute oral dose of NaNO2 on rat intestine was studied. Animals were randomly divided into four groups and given single doses of 20, 40, 60 and 75 mg NaNO2/kg body weight. Untreated animals served as the control group. An NaNO2 dose-dependent decline in the activities of brush border membrane enzymes, increase in lipid peroxidation, protein oxidation, hydrogen peroxide levels and decreased thiol content was observed in all treated groups. The activities of various metabolic and antioxidant defense enzymes were also altered. NaNO2 induced a dose-dependent increase in DNA damage and DNA-protein crosslinking. Histopathological studies showed marked morphological damage in intestinal cells. The intestinal damage might be due to nitrite-induced oxidative stress, direct action of nitrite anion or chemical modification by reaction intermediates.

Crocin protects human erythrocytes from nitrite-induced methemoglobin formation and oxidative damage.

Sodium nitrite (NaNO2) is a common contaminant of drinking water and food and feed chain. Nitrite induces oxidative damage in humans and animals. In this work, we studied the protective effect of crocin, the active constituent of Crocus sativus (saffron), on NaNO2‐induced oxidative damage in human erythrocytes. Changes in oxidative stress parameters following NaNO2 incubation of erythrocytes in presence and absence of crocin were determined. It was found that crocin pre‐treatment significantly attenuated NaNO2‐induced oxidative damage of proteins, lipids, and plasma membrane. Crocin reduced the level of methemoglobin, the primary acute effect of nitrite intoxication. It also improved the antioxidant capacity of cells and NaNO2‐induced morphological changes in erythrocytes. Crocin is thus a potent protective agent against nitrite‐induced cytotoxicity.

Sodium Nitrate Induces Reactive Oxygen Species That Lower the Antioxidant Power, Damage the Membrane, and Alter Pathways of Glucose Metabolism in Human Erythrocytes

Nitrate salts are widely used as food additives and nitrogenous fertilizers and are present as contaminants in drinking water supplies. The effect of different concentrations (1-15 mM) of sodium nitrate (NaNO3) on human erythrocytes was studied under in vitro conditions. Treatment of erythrocytes with NaNO3 resulted in increases in methemoglobin levels, lipid peroxidation, and protein oxidation and a decrease in glutathione content. There were changes in the activities of all major antioxidant defense enzymes, and the pathways of glucose metabolism were also affected. Increased generation of reactive oxygen species (ROS) took place while the antioxidant power was impaired. The osmotic fragility of cells was increased, and membrane-bound enzymes were greatly inhibited. All changes were statistically significant at a probability level of P < 0.05 at all concentrations of NaNO3 except the lowest (1 mM). Thus, NaNO3 generates ROS that cause significant damage to human erythrocytes and interfere in normal cellular pathways.

Acute oral dose of sodium nitrite causes redox imbalance and DNA damage in rat kidney

Sodium nitrite (NaNO2) is widely used as a food additive and preservative in fish and meat products. We have evaluated the effect of a single acute oral dose of NaNO2 on oxidative stress parameters, antioxidant capacity, and DNA in rat kidney. Male Wistar rats were divided into four groups and given single oral dose of NaNO2 at 20, 40, 60, and 75 mg/kg body weight; untreated rats served as the control group. All animals in NaNO2‐treated groups showed marked alterations in various parameters of oxidative stress as compared to the control group. This included increase in lipid peroxidation, protein oxidation, hydrogen peroxide levels, and decrease in reduced glutathione content and antioxidant capacity. Administration of NaNO2 also increased DNA damage as evident from release of free nucleotides and confirmed by comet assay. It also led to greater cross‐linking of DNA to proteins. Histological analysis showed marked morphological changes in the kidney of NaNO2‐treated animals. These alterations could be due to increased free radical generation or direct chemical modification by reaction intermediates. Our results suggest that nitrite‐induced nephrotoxicity is mediated through redox imbalance and results in DNA damage.

Ameliorative effect of carnosine and N-acetylcysteine against sodium nitrite induced nephrotoxicity in rats: ANSARI et al.

The widespread use of sodium nitrite (NaNO2) for various industrial purposes has increased human exposure to alarmingly high levels of nitrate/nitrite. Because NaNO 2 is a strong oxidizing agent, induction of oxidative stress is one of the mechanisms by which it can exert toxicity in humans and animals. We have investigated the possible protection offered by carnosine (CAR) and N‐acetylcysteine (NAC) against NaNO 2‐induced nephrotoxicity in rats. Animals orally received CAR at 100 mg/kg body weight/d for seven days or NAC at 100 mg/kg body weight/d for five days followed by a single oral dose of NaNO 2 at 60 mg/kg body weight. The rats were killed after 24 hours, and the kidneys were removed and processed for various analyses. NaNO 2 induced oxidative stress in kidneys, as shown by the decreased activities of antioxidant defense, brush border membrane, and metabolic enzymes. DNA‐protein crosslinking and DNA fragmentation were also observed. CAR/NAC pretreatment significantly protected the kidney against these biochemical alterations. Histological studies supported these findings, showing kidney damage in NaNO 2‐treated animals and reduced tissue impairment in the combination groups. The protection offered by CAR and NAC against NaNO 2‐induced damage, and their nontoxic nature, makes them potential therapeutic agents against nitrite‐induced nephrotoxicity.

Carnosine and N-acetyl cysteine protect against sodium nitrite-induced oxidative stress in rat blood

Sodium nitrite (NaNO2) is widely used in the food industry as a preservative and colorant in meat and fish products. Industrialization and improper agricultural practices have greatly increased human exposure to high nitrite levels, mainly through contaminated drinking water, causing various health disorders. We have investigated the protective effect of carnosine (CAR) and N‐acetyl cysteine (NAC) on NaNO2‐induced toxicity in rat blood. CAR is a bioactive dipeptide found in mammalian muscle while NAC is a synthetic sulfhydryl amino acid and an important precursor of glutathione. Animals were given a single acute oral dose of NaNO2 at 60 mg/kg body weight with or without prior administration of either CAR or NAC. Rats were sacrificed after 24 h, blood was withdrawn and plasma and erythrocytes were isolated. Administration of NaNO2 alone increased methemoglobin levels and methemoglobin reductase activity, decreased the activities of antioxidant defense and metabolic enzymes and significantly weakened the total antioxidant capacity of rat erythrocytes. Similar effects were seen in plasma of NaNO2‐treated rats. In contrast, administration of CAR or NAC, prior to NaNO2 treatment, markedly attenuated the NaNO2‐elicited deleterious effects. Thus, CAR and NAC can mitigate nitrite‐induced metabolic alterations and oxidative damage probably due to their intrinsic biochemical antioxidant properties. This study suggests that CAR and NAC can be potentially used as therapeutic/protective agents against NaNO2 toxicity.

Taurine mitigates nitrite-induced methemoglobin formation and oxidative damage in human erythrocytes

Nitrite is present as a noxious contaminant in drinking water and causes oxidative damage in various tissues of humans and animals. It is a well-known methemoglobin-forming agent that has been shown to damage blood cells. The protective effect of taurine, a semi-essential sulfur-containing amino acid, was studied on sodium nitrite (NaNO2)-induced oxidative damage in human erythrocytes. Erythrocytes were incubated with NaNO2, in the presence and absence of taurine, and changes in oxidative stress parameters determined. Pretreatment with taurine significantly ameliorated NaNO2-induced oxidative damage to lipids, proteins, and plasma membrane. It also reduced the NaNO2-induced increase in methemoglobin levels and ROS production. Taurine improved the antioxidant capacity of cells, restored the alterations in the activities of various metabolic enzymes, and prevented morphological changes in erythrocytes. Thus, taurine can be potentially used as a protective agent against the damaging effects of nitrite.