Effects of nitrate and nitrite, chemical intermediates of inhaled nitrogen dioxide, on membrane components of red blood cells of rats

Rat Model to Investigate the Treatment of Acute Nitrogen Dioxide Intoxication

1 The pulmonary toxic events induced by acute nitrogen dioxide (NO)2 exposure were studied in the rat to develop an inhalation model to investigate therapeutic measures.

2 A good correlation was observed between the lung weights and severity of the atypical pneumonitis. The pulmonary effects observed, became more pronounced with increasing NO 2 concentrations (0, 25, 75, 125, 175 or 200 ppm, 1 ppm NO2=1.88 mg m-3 NO2) and exposure times (5, 10, 20 or 30 min).

3 An adequate NO 2 concentration is 175 ppm, because it can induce a severe lung injury without mortality. This makes it possible to investigate suitable therapeutic interventions for several days.

4 Following acute inhalatory NO2 intoxication, transformation of NO2 to nitrate is presumably more notable than transformation to nitrite.

5 The transformation of NO2 to nitrate in lung tissue causes a slight increase in the serum nitrite concentration, which does not induce measurable formation of methaemoglobin. 6 Presumably, methaemoglobin does not contribute to the toxicity of NO2 intoxication.

Nitric oxide-derived nitrate anion contributes to endotoxic shock and multiple organ injury/dysfunction

OBJECTIVE

Because nitrate represents the major end-product of nitric oxide in vivo and can affect enzyme activity, cell electrophysiological functions, and cell membrane integrity, we hypothesized that overaccumulated nitric oxide-derived nitrate anion in tissues or organs in vivo may contribute to endotoxic shock and multiple organ injury/dysfunction during endotoxemia.

DESIGN

Prospective, experimental animal study.

SETTING

Laboratory at a university hospital.

SUBJECTS

Sprague-Dawley rats.

INTERVENTIONS

Rats were injected intraperitoneally with 5, 10, or 20 mg/kg lipopolysaccharide or saline and were studied in groups at 0, 6, 12, and 24 hrs.

MEASUREMENTS AND MAIN RESULTS

Significant differences were seen between nitrate concentrations in the heart, lung, kidney, liver, brain, aorta, diaphragm, spleen, thymus, testis or ovary, hind limb muscle, intestine, adipose tissue, bone, bladder, urine and plasma, which imply a nitrate gradient between intracellular and extracellular compartments. Lipopolysaccharide significantly increased nitrate concentration at 12 hrs in most tissues and organs, except in the brain, adipose tissue, and muscle. It increased more in plasma than in tissues. The lipopolysaccharide dose-dependent nitrate concentration was observed only in the aorta and lungs. The nitrate concentration change was paralleled by the systemic inflammatory response syndrome, as indicated by alterations of myeloperoxidase activity and by impaired histologic and cellular membrane integrity in tissues and organs. Mean arterial pressure was negatively correlated with nitrate concentration modifications in the aorta during 24 hrs of endotoxemia.

CONCLUSIONS

These results collectively indicate that overaccumulated nitric oxide-derived nitrate anion in tissues or organs in vivo contributes to endotoxic shock and multiple organ injury/dysfunction during endotoxemia.

Inhibition of purified (Na+,K+)-ATPase activity from porcine cerebral cortex by NO generating drugs

We tested the effects of several nitric oxide (NO) generating compounds on the activity of sodium-potassium adenosine 5'-triphosphatase [(Na+,K+)-ATPase] purified from porcine cerebral cortex. Sodium nitroprusside (SNP), S-nitroso-N-acetylpenicillamine (SNAP), 3-morpholinosydnonimine (SIN-1) and (d1)-(E)-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexeneamide (NOR 3) inhibited the (Na+,K+)-ATPase activity dose dependently. Superoxide dismutase, a NO scavenger, and sulfhydryl (SH) compounds, reduced-form glutathione (rGSH) and dithiothreitol (DTT), prevented the inhibitory action of SNAP, SIN-1 and NOR 3 but not of SNP, when applied simultaneously with NO generating compounds, and this enzyme inhibition could be reactivated by the incubation with these SH compounds but not with SOD. The inhibitory action by SNP was magnified by simultaneous application of DTT. These results suggest that NO generating compounds, SNAP, SIN-1 and NOR 3 but not SNP, may release NO or NO-derived products and may inhibit (Na+,K+)-ATPase activity by interacting with a SH group at the active site of the enzyme.

Effect of nitrogen dioxide on surface membrane fluidity and insulin receptor binding of pulmonary endothelial cells

Nitrogen dioxide (NO2), an environmental oxidant pollutant, is known to peroxidize membrane lipids of lung cells. We evaluated the ability of NO2 to alter the surface membrane fluidity, lipid composition, and insulin receptor binding of porcine pulmonary artery endothelial cells in culture. After 3- to 24-hr exposure to 5 ppm NO2, cells were labeled with either 1-(4-trimethylaminophenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH), a cationic fluorescent aromatic hydrocarbon that anchors at the lipid-water interface, or fluorescamine, a fluorescent molecular probe that covalently binds with amino groups of surface phospholipids and proteins. Membrane fluidity was measured by monitoring changes in the steady-state fluorescence anisotropies (rs) for TMA-DPH and fluorescamine. Insulin specific receptor binding was monitored by measuring time-dependent binding of 125I-insulin. Following NO2 exposure, rs values for TMA-DPH and fluorescamine were increased significantly in a time-dependent fashion, with maximum increases at 24 hr (P less than 0.001). Similar increases in rs values were observed in isolated plasma membranes as well as in lipid vesicles prepared from total lipid extracts of endothelial cells or their plasma membranes. Phosphatidylethanolamine plus phosphatidylserine content in lipid extracts from 24-hr but not 3- to 12-hr NO2-exposed cells was increased significantly (P less than 0.01) compared to control cells. Specific binding of 125I-insulin to cells exposed to NO2 for 12 and 24 hr (but not 3 and 6 hr) was reduced significantly (P less than 0.05) compared to binding in control cells. Scatchard analysis of the binding data indicated that NO2 exposure caused a 5-fold reduction in insulin receptor binding sites in endothelial cells. Recovery was achieved 24 hr after NO2 exposure with, but not without, changing culture medium. These results indicate that NO2 exposure causes reversible changes in the physical state of lipids in the superficial lipid domains of the pulmonary endothelial cell plasma membrane, and these alterations may interfere with plasma membrane-dependent functions such as receptor-ligand interaction.

Effect of NO2 exposure on antioxidant defense of endothelial cells

Nitrogen dioxide (NO2), an environmental oxidant pollutant, is toxic to lung cells. We evaluated the changes in antioxidant enzyme activities in porcine pulmonary artery (PA) and aortic (AO) endothelial cells in monolayer cultures. Confluent PA or AO endothelial cells were exposed to 3 or 5 ppm NO2 or air (control) for 3-24 h and assayed for GSH-reductase (GSH-red), GSH-peroxidase (GSH-per), and glucose-6-phosphate dehydrogenase (G6PDH) activities as well as for intracellular GSH content. After 3, 6, or 12 h exposure to 3 or 5 ppm, GSH-red and G6PDH activities were not different from those of controls in both PA and AO endothelial cells. Exposure to 3 or 5 ppm NO2 for 24 h resulted in significant increases in GSH-red (P less than 0.05) and G6PDH (P less than 0.001) activities in both cell types. GSH-per activity and GSH content in NO2-exposed PA and AO endothelial cells were not different from those of controls, irrespective of NO2 concentration and exposure time. These results indicate that enzyme activities of G6PDH and GSH-red are increased in PA and AO endothelial cells exposed to NO2, and this response is comparable, in part, to that in the lungs from animals exposed to NO2.

An apparent acceleration of age-related changes of rat red blood cells by cadmium

The effect of cadmium at nonhemolytic concentrations on rat red blood cells was examined in vitro and compared with that of mercury. When rat red blood cells were incubated at 37 degrees C with 0.5 to 2.0 mM CdCl2 for 60 min, age-related changes of red blood cells occurred. These changes developed in a dose-dependent manner and included increases in cell density and in the number of echinocytes and a decrease in filterability. The incubation of red blood cells with 0.5 and 1.0 mM CdCl2 resulted in their shortened in vivo survival. Neither metabolic blockade, such as a fall in the adenosine triphosphate and glutathione contents, nor potassium leakage occurred at nonhemolytic concentrations of Cd. The effect of HgCl2 on age-related changes of red blood cells occurred at 5- to 20-fold lower concentrations than those of CdCl2. These results show that age-related changes were apparently accelerated by nonhemolytic concentrations of Cd and may be, at least in part, due to the interaction of Cd with thiol residues of cell membranes.

In vivo effects of nitrogen dioxide on the blood nitrate level and the Na+,K+-ATPase activity of red blood cells of rats

Male Wistar rats were exposed to 0.4, 1.2 and 4.0 ppm NO2 for 13 weeks to examine the effects of NO2 on the blood nitrate concentration and the Na+,K+-ATPase activity of red blood cells. Exposures to 1.2 and 4.0 ppm NO2 caused an elevation of the blood nitrate level at the first, third and eighth week. The maximum concentration attained was 148% (P less than 0.001, at the third week) and 201% (P less than 0.001, at the eighth week) of the controls at 1.2 and 4.0 ppm NO2, respectively. On the other hand, the nitrate concentration was decreased to the control level at the second, fourth and thirteenth weeks. 0.4 ppm NO2 caused a progressive but slight increase in the blood nitrate concentration from the third week and reached the maximum (122% of the control, P less than 0.001) at the eighth week. The Na+,K+-ATPase activity decreased slightly from the first week upon exposure to 4.0 ppm NO2 and reached the minimum (72% of the control, P less than 0.05) at the third week. Subsequently, the activity was increased to 159% (P less than 0.001) of the control at the eighth week. Exposure to 0.4 and 1.2 ppm NO2 caused fundamentally similar but less significant alterations of the Na+,K+-ATPase activity.