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PubMed1989

[Cytospectrophotometric research on hemoglobin in human erythrocytes. I. The methemoglobin content in intact erythrocytes and its alteration under the influence of chromosmon, ascorbic acid, riboflavin and glutathione].

The blood of healthy men and patients with methemoglobinemia of different genesis was incubated with chromosmon, ascorbic acid, riboflavin and glutathione, the percentage of erythrocytes with thorn-shaped protuberances-echinocytes being subsequently determined in the blood smears. The absorbtion spectra at the range 400-650 nm were investigated both in the smooth erythrocytes and in echinocytes. A correlation was found between the percentage of echinocytes and the methemoglobin content in the blood. The methemoglobin amount in the echinocytes was determined to be higher than in the smooth erythrocytes. It is discovered that effects of chromosmon, glutathione and riboflavin on production of methemoglobin depend on the dose, individual peculiarities of erythrocytes and on the illness that caused methemoglobinemia. The calculation of echinocyte percentage may be used as an express-diagnostics of methemoglobinemia and for purposes of studying the effect of methemoglobin-producing substances and drugs.

Ascorbic Acid↗
PubMed1977

Methemoglobin in hypoxic rats.

Methemoglobin levels have been found to vary with altitude and to shift the hemoglobin-oxygen dissociation curve. In this study, hematocrits and methemoglobin levels were monitored in rats exposed to hypoxia (420 torr absolute) for various intervals. Hematocrits gradually increased throughout the period of hypoxia, while methemoglobin levels rose by 12 h, peaked at 24 h and returned to control level by day 6. These data, in the context of other work, suggest that increased methemoglobin is important in acclimation to hypoxia.

Adaptation, Physiological↗
PubMedDate not supplied

Methemoglobin levels in smokers and non-smokers.

The authors analyzed the blood of a group of 336 smokers and 336 non-smokers to determine if tobacco smoke, potentially the major source of nitrogen oxide pollution for 40% of the adult population, significantly reduces oxygen carrying capacity as a result of methemoglobin formation. Each blood sample was analyzed for carboxyhemoglobin, methemoglobin, and hemoglobin using an automated spectrophotometer. The mean value of methemoglobin in the smokers did not exceed that in the non-smokers; in fact, the level in the non-smokers was significantly greater. As expected, carboxyhemoglobin levels in smokers substantially exceeded those in non-smokers. The authors conclude that methemoglobin arising from cigarette smoke exposure does not interfere with the oxygen carrying capacity of the blood in smokers.

Carboxyhemoglobin↗
PubMed1985

The laboratory use of butylnitrite for the production of methemoglobin.

The use of volatile butylnitrite in place of sodium nitrite for the in vitro production of methemoglobin was explored in studies of G6PD-deficient red cells and for measurements of the red cell methemoglobin reductase activity. It was found that butylnitrite vapor caused a more rapid oxidation of intracellular hemoglobin than sodium nitrite and required fewer washes for removal. Hence a more rapid preparation of the cells was possible. Both cytochemical detection of G6PD-deficient cells in a female heterozygote for G6PD deficiency and the screening test for a methemoglobin reductase deficiency could be performed with butylnitrite as well as with sodium nitrite. This small modification of these standard procedures promises to save time and facilitate processing of many samples during genetic screening of relevant populations.

Erythrocytes↗
PubMed1990

Rapid reduction of methemoglobin in rat bone marrow erythroid cells.

Methemoglobin reduction was shown to proceed much more rapidly in erythroid cells from rat bone marrow than in rat erythrocytes. Methemoglobin reduction in suspensions of intact, nitrite-treated bone marrow cells does not depend on the presence of glucose in the incubation mixture, even after the cells have been stored in substrate-free medium. 2-Deoxyglucose and iodoacetate prevent the reduction from proceeding to completion. The results suggest that, relative to erythrocytes, immature erythroid cells more efficiently catalyze methemoglobin reduction and more effectively store metabolites which provide electrons for this reaction.

Animals↗
PubMed1996

Evaluation of methemoglobin as an autologous intravascular MRI contrast agent.

Methemoglobin (MetHb) was evaluated as an intravascular paramagnetic contrast agent. Methemoglobin formation was induced by 4-dimethylaminophenol (4-DMAP), causing a reduction in blood T2* in vitro. The 4-DMAP generated metHb with a time constant of 62 s. A 4-DMAP bolus did not decrease measurably the signal intensity in the in vivo rabbit kidney in the first pass. At steady state, a MetHb concentration of 24.8 +/- 2.3% resulted in a signal decrease of 9.2 +/- 2.6% in the kidney. Methemoglobin is an effective vascular T2* relaxation agent, but the formation of MetHb by 4-DMAP is too slow for first-pass imaging. A more effective conversion agent resulting in a bolus of at least 25% MetHb within 5 s would result in a detectable first-pass signal and a viable contrast technique.

4-Aminopyridine↗
PubMed1979

Reduction of ferricytochrome c, methemoglobin and metmyoglobin by hydroxyl and alcohol radicals.

We have studied the reaction of ferricytochrome c, methemoglobin and metmyoglobin with OH and alcohol radicals (methanol, ethanol, ethylene glycol and glycerol). These radicals can be divided into three groups: 1. The OH radicals which reduce the ferricytochrome c with a yield of (30 +/- 10)% and methemoglobin with a yield of (40 +/- 10)%. They do not reduce metmyoglobin. The reduction is not a normal bimolecular reaction but is most probably an intramolecular electron transfer of a protein radical. 2. Methanol and ethanol radicals which reduce all three hemoproteins with a yield of (100 +/- 5)%. This reduction is a normal bimolecular reaction. 3. Glycerol radicals which do not reduce the ferrihemoproteins under our experimental conditions. Ethylene glycol radicals do not reduce ferricytochrome c and metmyoglobin but they do reduce methemoglobin with a yield of (30 +/- 10)%.

Alcohols↗
PubMed1983

The production of activated oxygen species by an interaction of methemoglobin with ascorbate.

Ascorbate reacts with methemoglobin to produce reactive oxygen species, most probably hydroxyl radicals. The main features of this system are: a) disappearance of ascorbate; b) consumption of oxygen with an ascorbate/O2 stoichiometry of 2:1; c) requirement of unliganded heme iron; d) formation of H2O2. The proposed mechanism involves an ascorbate-mediated interconversion of methemoglobin and oxy-hemoglobin, resulting in the production of H2O2. This product is decomposed by hemoglobin to produce hydroxyl radicals according to a Fenton-like reaction in which ascorbate recycles methemoglobin to hemoglobin. Alternative pathways of formation and of decomposition of H2O2 in this system appear to play a minor role.

Ascorbic Acid↗
PubMed1992

Temperature-jump studies and polarized absorption spectroscopy of methemoglobin-thiocyanate single crystals.

Association equilibria and association kinetics of the thiocyanate binding reaction to methemoglobin in single crystals and solution are studied using temperature-jump technique and polarized absorption spectroscopy. Different kinetic constants are found for the reaction in solution and crystal phase for the alpha- and beta-subunits of the methemoglobin tetramer. The reduction of the reactivity of the alpha- and beta-subunits in crystalline phase is 6-fold and 2.4-fold, respectively, compared to the values found in solution. The intramolecular binding reaction of the N epsilon of the distal histidine E7 which is observed in methemoglobin in solution cannot be detected in single crystals. Our results suggest that crystallization of hemoglobin has little influence on small-scale structural fluctuations which are necessary for ligands to get to the binding sites and large-scale structural motions are suppressed.

Animals↗
PubMed1984

The effect of acetaminophen on methemoglobin and blood glutathione parameters in the cat.

Acetaminophen (APAP) was given orally to 6 mature cats (3 male and 3 female) in single progressive doses of 20 (low), 60 (medium), or 120 (high) mg APAP/kg body weight, each 3 weeks apart. Methemoglobin (MHB), reduced blood glutathione (GSH) and APAP blood concentrations, and blood NADH methemoglobin reductase and NADPH glutathione reductase activities were measured periodically for 8 days after dosing. A statistically significant increase in MHB formation (21.7% and 45.5%, respectively) occurred following the medium and high doses. NADH methemoglobin reductase activity at the high dose decreased significantly. Red blood cell GSH concentrations decreased significantly during the first 24 h after the high APAP dose and returned to normal by 192 h. NADPH glutathione reductase activity decreased significantly following the high dose, but not after the lower APAP doses.

Acetaminophen↗
PubMed1990

Reduction of extracellular methemoglobin by erythrocytes.

Erythrocytes, suspended in a glucose-containing buffer, catalyzed the partial reduction of extracellular methemoglobin. Physiological concentrations of ascorbic acid or dehydroascorbic acid greatly enhanced the rate of reaction and the ultimate extent of reduction. The relationship between erythrocyte concentration and initial reaction rate was nonlinear, which suggested that the rate limiting factor was not an erythrocyte membrane enzyme. Also, significant dehydroascorbate-stimulated reduction occurred even when the erythrocytes and methemoglobin were separated by a dialysis membrane. The above observations indicate that the transfer of reducing equivalents across the erythrocyte membrane and reduction of extracellular methemoglobin can be accomplished by release and recycling of ascorbic acid.

Ascorbic Acid↗
PubMedDate not supplied

Carboxyhemoglobin and methemoglobin levels in banked blood.

Carboxyhemoglobin and methemoglobin levels in 312 units of banked blood and their relationship to the duration of storage were determined. The carboxyhemoglobin level decreased as the storage time increased, and its mean was 1.4% +/- 2.0% (SD) with a range from 0% to 9.6%. Methemoglobin increased during storage, showing a mean level of 1.6% +/- 0.4% and a range from 0.5% to 4.2%. In a separate study, blood drawn from six volunteers who had smoked two cigarettes each was stored as banked blood for 21 days. The mean initial level of carboxyhemoglobin was 4.4% +/- 1.6%, and the mean half-life of carboxyhemoglobin was approximately 47 days. Methemoglobin increased from an initial 1.3% +/- 0.2% to 2.4% +/- 0.6% at the end of storage. The use of banked blood containing high levels of these abnormal hemoglobins could be a potential risk in critically ill patients.

Aged↗
PubMed1987

Nonautocatalytic methemoglobin formation by sodium nitrite under aerobic and anaerobic conditions.

Aerobic exposure of human hemoglobin in 1:1 molar ratio to sodium nitrite induced an immediate and progressive formation of methemoglobin. Neither lag nor autocatalytic phases were observed, contrary to what was seen when diluted hemoglobin in buffered solutions was used. Hemolyzed whole blood, washed red cells with their plasma replaced by saline, and whole blood were exposed to identical sodium nitrite concentrations. In the presence of oxygen, the speed of methemoglobin formation was three to four times faster in the hemolyzed and plasma-free samples than in whole blood. The maximum rate was reached within the first minute of the reaction. Restoring plasma to washed red cells reduced the rate to that of whole blood; restoring plasma to hemolyzed red cells had no effect on rate. We advance the hypothesis that sodium nitrite or its derivatives form a complex with some element of the blood plasma which slows the passage of nitrite through the red cell membrane without hindering the oxidative capacity of the nitrite. With no free oxygen present, whole blood, washed red cells in saline, and hemolyzed blood all showed a similar rate of methemoglobin formation when exposed to a 1:1 molar ratio of sodium nitrite. The presence of nitrosylhemoglobin formed in the anaerobic reaction seems to be a for the lack of changes seen in the reaction.

Carbon Dioxide↗
PubMedDate not supplied

The role of methemoglobin in acute butyl nitrite toxicity in mice.

When mice were exposed to butyl nitrites in an inhalation chamber, a significant level of methemoglobinemia is produced. The potency order for methemoglobin production of the four butyl nitrites (n-, iso-, sec-, tert-) is the same as that of their lethal concentrations (LC50 values) and parallels the ability of the agents to cause methemoglobin formation in mouse erythrocytes in vitro. Pretreatment with a single dose of methylene blue prevents the methemoglobin formation and protects against the lethality of the butyl nitrites.

Animals↗
PubMed1982

Interaction between cytochrome b5 and human methemoglobin.

Complex formation between purified human methemoglobin and the tryptic fragment of bovine liver cytochrome b5 has been demonstrated by the observation of a difference spectrum produced on mixing the two proteins. The intensity of this difference spectrum has been used to determine the stoichiometry of the complex formed and its stability under a variety of conditions. At pH 6.2 [25 degrees C (cacodylate buffer), mu = 2 mM], the complex has a stoichiometry of 1:1 (heme: heme) with a stability constant, KA, of (3 +/- 2) X 10(5) M(-1). This stability constant is dependent on ionic strength, decreasing to a value of (9 +/- 3) X 10(3) M(-1) at mu = 12 mM [pH 6.2 (cacodylate buffer), 25 degrees C]. Analysis of this dependence by fitting the data to a form of the Debye-Hückel equation produces a charge product of -64 +/- 14 which is in reasonable agreement with the value anticipated on the basis of the amino acid sequences of the two proteins. Determination of the pH dependence of KA revealed that the complex is most stable at slightly acidic pH (pH 6.0-6.2) or, in other words, at a pH that is approximately midway between the isoelectric pH values of cytochrome b5 and methemoglobin. The variation of KA with temperature is consistent with delta H degree = -10 +/- 3 kcal/mol and delta S degree = -12 +/- 10 eu [pH 6.2 (cacodylate buffer), mu = 5 mM]. Together, these results generate a model for cytochrome b5-methemoglobin interaction in which each hemoglobin subunit binds one cytochrome b5 by means of complementary charge interactions between oppositely charged groups on the two proteins. The probable sites of cytochrome b5 binding on hemoglobin are discussed.

Animals↗
PubMed1985

Quaternary structure has little influence on spin states in mixed-spin human methemoglobins.

A key feature of the Perutz stereochemical model for cooperativity in hemoglobin is a strong coupling between quaternary structure and the spin state of the heme iron [Perutz, M. F. (1979) Annu. Rev. Biochem. 48, 327-386]. While this coupling appears to be present for carp azide methemoglobin, it should also be present for all liganded forms of human methemoglobin that exhibit a thermal high-spin in equilibrium low-spin equilibrium. To test this hypothesis, we have measured the changes in spin equilibria upon conversion of six mixed-spin forms of human methemoglobin from the R (high-affinity) to the T (low-affinity) quaternary structure by addition of inositol hexaphosphate. These experiments were done with a sensitive superconducting magnetic susceptibility instrument on solutions at 20 degrees C in 20 mM maleate buffer, pH 6. The data show zero or small increases in high-spin content upon switching from R to T, changes that are equivalent to a relative stabilization of the high-spin form by only 0-300 cal mol-1 heme-1. These changes in energy are far less than the 1200 cal mol-1 heme-1 predicted from the Perutz stereochemical model [Cho, K. C., & Hopfield, J. J. (1979) Biochemistry 18, 5826-5833]. That is, these data do not support a view that the low affinity of the T state is due to restraints acting through the iron-proximal histidine linkage. The mechanistic implications of these results and the differences between species and ferric ligands are discussed.

Calorimetry↗
PubMed1978

Conversion of oxyhemoglobin to methemoglobin by organic and inorganic reductants.

Human oxyhemoglobin is converted to methemoglobin by a wide array of organic and inorganic reductants. Depending upon the concentration and nature of the reductant, varying amounts of deoxyhemoglobin are produced. The general overall sequence is: FeO2 leads to (1) FeIII leads to (2) FeII. The intermediacy of methemoglobin can be demonstrated by direct spectral observation and by cyanide trapping. For organic reductants, the second-order rate constants for (1) vary from greater than 300 (phenylhydroxylamine) to 1.4 X 10(-4) M-1 s-1 (malononitrile). Generally the rates parallel the ease of hydrogen abstraction by iron-bound oxygen from the substrate, and simply hydrocarbons are reactive. Rates for these processes have been ascertained with recrystallized protein, lysed cells, and intact human erythrocytes. At room temperature oxyhemoglobin quantitatively converts benzaldehyde to benzoic acid and hydroquinone to benzoquinone. Rates for inorganic species (process 1) range from greater than 7 X 10(3) (chromous ion) to 0.015 M-1 s-1 (ferrocyanide). Ferrous ion rapidly deoxygenates oxyhemoglobin by direct attack on the oxy complex but methemoglobin is not an intermediate with this reagent. Taken together the results support the theoretical prediction that reductants should oxidize oxyhemoglobin, and they demonstrate at least some degree of radical character to the oxy complex.

Anions↗