MetHb Levels Research Articles

Inhaled nitric oxide as a salvage therapy in patients with severe ARDS

IntroductionInhaled nitric oxide (iNO) has been shown to preferentially dilate pulmonary vasculature within well ventilated regions of lung without causing systemic hypotension. Patients with severe ARDS may develop marked ventilation perfusion mismatch, severe hypoxemia, pulmonary hypertension, and right heart failure. Use of iNO may help mitigate these pathologic changes. So we used iNO to assess it as a salvage therapy in patients with severe ARDS. MethodsWe describe 4 cases of pneumonia with severe ARDS with right heart failure in which iNO was used as salvage therapy to improve right heart failure and oxygenation when they did not respond to conventional measures. iNO was delivered in inspiratory limb of ventilator circuit by NOxBOX mobile system. Dose of iNO was titrated between 5 and10 ppm. In each of these patients, we monitored hemodynamic status (pulse rate, intra-arterial blood pressure, vasopressor requirements), central venous pressure (CVP), serum lactate, methemoglobin (MetHb) levels, arterial blood gases (ABG) and PaO2/FiO2 (p/f) ratios every 6 h till first 24 h and then every 12 h till 24 h of stopping iNO. 2D Echo was done by a trained cardiologist before initiation of iNO and then every 24 h till 24 h of stopping NO and pulmonary artery systolic pressure (PASP) recorded. ResultsiNO was used for duration ranging from 30 to 120 h. In all patients hemodynamics, oxygenation and PASP showed improvement that persisted even after 24 h of discontinuing iNO. None of the 4 patients had methemoglobinemia or other serious side effects. ConclusioniNO may be used as a salvage therapy for refractory hypoxemia and right heart failure in severe ARDS.

Methemoglobinemia Caused by an Inert Ingredient after Intentional Ingestion of Pesticide

We report two cases of toxic methemoglobinemia caused by an inert ingredient in pesticide product after intentional ingestion of pesticide. First, 51-year-old male visited to the emergency department (ED) after the ingestion of pesticide in a suicide attempt. Initial methemoglobin (MetHb) level was 25.6%. We did not know the cause of methemoglobinemia at that time. Second, 56-year-old female visited to the ED after the ingestion of the same pesticide in a suicide attempt. MetHb level after 30 minutes was 16.1%. The patients were treated with methylene blue. We contacted to the Korean Rural Development Administration and estimated that magnesium nitrate was more likely to cause methemoglobinemia. This report highlights the importance of considering the possibility of methemoglobinemia caused by inert ingredient in pesticide and early antidotal therapy.

Methemoglobin measure in adult patients with sickle-cell anemia: influence of hydroxyurea therapy

Introduction: Hemoglobin S (HbS) is unstable hemoglobin that easily oxidizes, causing methemoglobin (MetHb) increased production in patients with sickle-cell anemia (SCA). Objectives: To determine MetHb levels and the influence of hydroxyurea (HU) therapy on this marker in patients with SCA. Materials and methods: Blood samples from 53 patients with SCA at the steady-state, with and without HU therapy, and 30 healthy individuals were collected to evaluate MetHb levels. The MetHb measurement was performed by spectrophotometry. Complete blood count, HU measurements, and fetal hemoglobin (HbF) and HbS concentrations were taken from medical records. Results: MetHb levels were statically higher in patients with SCA when compared to control group (p < 0.001). There was no statistical difference in MetHb level between SCA patients, either using or not HU. We obtained a positive correlation between MetHb measurements and HbS concentration (r = 0.2557; p = 0.0323). Conclusion: HbS presence favored hemoglobin breaking down, and consequently increased MetHb production. Treatment with HU, however, did not influence the levels of this marker.

Effects of supplementation of inorganic sulfur on some biochemical parameters in Angora goat’s diet containing high nitrate levels

The purpose of this study was to determine the effect of supplementation of sulfur to a diet containing sodium nitrate at a level that would cause chronic nitrate poisoning on some rumen and biochemical parameters in Angora goats. A total of 18 male Angora goats were used. The animals in the control group were fed the basal diet, while the animals were fed experimental concentrate containing 1500 mg/kg sodium nitrate in the nitrate group (N) and experimental concentrate containing 1500 mg/kg sodium nitrate plus 1.8% sodium sulfate in the nitrate-sulfur group (NS) throughout the study, which lasted for 6 months. While there were no differences among groups in live weights, nitrate supplementation to the diet increased the rumen nitrate content and the blood methemoglobin (MetHb) levels and decreased plasma vitamin A and carotene in the N and NS group. The supplementation of sulfur to a diet containing high sodium nitrate alleviated the negative effects of nitrate on the blood MetHb and plasma carotene significantly (P < 0.05). The results of this study suggest that Angora goats can tolerate diets containing the high sodium nitrate levels used in the present study, except for the results in regard to blood MetHb and plasma vitamin A and carotene.

Use of nitrate and Propionibacterium acidipropionici to reduce methane emissions and increase wool growth of Merino sheep

The effects of dietary nitrate and of Propionibacterium acidipropionici (PA) on methane and nitrous oxide emissions, methaemoglobinaemia, volatile fatty acid (VFA) concentration and productivity of sheep were studied. It was hypothesised that PA supplementation would increase the rate of nitrite reduction to ammonia in the rumen and therefore reduce risks of methaemoglobinaemia. Fine-wool Merino wethers (n = 28; 31.8 ± 3.7 kg; 11 months of age) were acclimated to four isonitrogenous and isoenergetic diets based on oaten chaff (1.0 kg/day) supplemented with either urea (1.1% of DM; T1 and T2) or a nitrate source (2.0% of DM; T3 and T4) while T2 and T4 were also supplemented with PA (11.5 × 1010 CFU/day). Replacing urea with nitrate lowered methane production (g/day) by 19% and methane yield (g/kg DMI) by 15%, improved clean wool growth by 12% (P &lt; 0.001) and tended to increase skin temperature (P &lt; 0.1). Nitrate increased ruminal acetate to propionate ratio by 27%, increased plasma nitrite and nitrate concentrations and blood methaemoglobin (MetHb) level up to 45% of total haemoglobin. Nitrous oxide emission from sheep confined in respiration chambers was higher (P &lt; 0.001) when nitrate was fed, lowering the net benefit of methane mitigation on global warming potential (CO2 equivalents/kg DMI) by 18%. In contrast, PA had little effect, decreasing total VFA concentration (P &lt; 0.05), increasing rumen pH (P &lt; 0.05) and clean wool growth (P &lt; 0.05) of urea-fed sheep. This study confirmed the beneficial effects of nitrate on net greenhouse gas reduction and wool growth, but showed that methaemoglobinaemia risks may be higher when diets are fed at a restricted level and contain only low levels of readily fermented carbohydrate. PA supplementation was not effective in reducing methaemoglobinaemia, but did increase clean wool growth of urea-fed sheep.

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Introduction: It is recognized that Methemoglobin (MetHb) levels are elevated in sepsis due to increased nitric oxide production. The degree of MetHb elevation may have prognostic significance, and unrecognized elevation may reflect outcome in non-septic acute hospital admissions. The additive outcome effect of MetHb, ionized calcium (iCa), and lactate may be of prognostic value. Methods: In a retrospective observational study. co-oximeter data from 1000 admissions over 18 months to a general ICU was interrogated for arterial MetHb, lactate, and iCa levels. Patient demographics, admission and ultimate diagnoses allowed classification into categories of Septic / Non-Septic, Survivor (S) / Non-Survivor (NS). T-testing after logistic transformation or Mann Whiney U testing was used to compare MetHb (%), lactate (mmol/L), iCa (mmol/L) levels between septic (n= 273) and non-septic (n=650) cases, also S (n=809) and NS (n=115). A regression analysis was also performed to determine the contribution of the above factors to outcome. p<0.05 was accepted for statistical significance. Results are expressed as median (Md) and range (R) or mean (Me) and 95% CI. The fit of the model was assessed with ROC analysis and the Hosmer Lemeshow (HL) test. Results: There was no age difference between the septic and non-septic groups. Of 1000 admissions, 927 had MetHb data. 2 patients had MetHb >2 (Md 1.0, range 0.5–3.1). Those with a diagnosis of sepsis (n=273) had significantly higher MetHb levels than non-septic patients (Md 1.0, R 0.5 – 3.1 vs 1.0, 0.5 – 2.0). NS with sepsis (n=46) had significantly higher MetHb levels than NS without sepsis (n=69) (Md 1.0, R 0.5 – 1.7 vs 0.9, 0.5 – 1.6). iCa was lower in NS than S (Md 1.04, R 0.45 – 1.9 vs 1.09, 0.35 – 1.76), and also lower in septic than non-septic patients, but with no difference between S and NS with sepsis. Lactate was significantly higher in NS than S (Me 2.7, 95% CI 2.3 – 3.2 vs 1.37, 1.3 – 1.4). Lactate was also significantly higher in septic compared to non-septic patients (1.6, 1.5 – 1.8 vs 1.4, 1.36 – 1.5) Age, presence or absence of sepsis, and lactate were included in the logistic regression analysis for outcome, with AUC for the ROC of 0.77 and HL>0.3. Conclusions: Methemoglobin levels above 2% are rare. MetHb is significantly elevated in our patient population with sepsis however the degree of elevation at admission in our group was not predictive of outcome. iCa, while lower in NS, does not predict outcome in a population with sepsis. Lactate elevation at admission, in this group, correlates with outcome, and the combination of lactate, age and sepsis shows comparable predictive value to established formulae.

Symptomatic-Low Grade Methemoglobinemia Because of Dapsone

Methemoglobinemia occurs when hemoglobin is oxidized to form methemoglobin (MetHb) rendering it incapable of oxygen transport and leading to tissue hypoxia. Typically, protective mechanisms keep MetHb levels below 1%, but a variety of compounds are capable of inducing methemoglobinemia including dapsone. Normally, symptoms correlate with MetHb level and treatment with methylene blue is reserved for patients with significantly elevated MetHb levels. We present a case of symptomatic low-grade methemoglobinemia because of dapsone therapy. This case illustrates a multiple hit hypothesis where comorbid conditions prompt symptoms at a low MetHb level. Understanding the impact of comorbid conditions in exacerbating low-grade methemoglobinemia is important in diagnosing and managing this condition. Treatment with methylene blue should be guided by the whole clinical picture rather than by the MetHb level alone.

Methemoglobin levels in umbilical cord blood of women with intrauterine growth restriction and preeclampsia

Objective: To measure nitric oxide (NO) levels, as assessed by methemoglobin (MetHb), in the umbilical cord arterial blood of women with preeclampsia (PE), normotensive pregnancies with intrauterine growth restriction (IUGR, <10th percentile for birth weight) and normotensive pregnancies with appropriate for gestational age (AGA) infants.Design/Methods: Prospective analysis of MetHb levels in umbilical arterial blood of pregnancies with PE, normotensive IUGR and normotensive AGA infants using spectrophotometry. Exclusion criteria included cigarette smoke exposure, hemolytic disorders, chronic hypertension, any significant medical illness and medications affecting NO or MetHb levels.Results: There were 42 women in the PE, 42 in the AGA and 37 in the IUGR group. Maternal age, mode of delivery, gravidity, parity and infant gender were similar in the three groups. MetHb levels were significantly lower in the IUGR group compared to the AGA group (p < 0.01). MetHb levels, while higher in the PE group compared to the AGA group, did not reach statistical significance.Conclusion: Our data suggests that NO may play a key role in the pathogenesis of IUGR. We also, for the first time, provide information on umbilical arterial MetHb levels in PE, normotensive IUGR and normotensive AGA pregnancies.

Investigation of in vivo toxicity of hydroxylamine sulfate and the efficiency of intoxication treatment by α-tocopherol acetate and methylene blue

Investigation of hydroxylamine sulfate toxicity mechanism in vivo and estimation of α-tocopherol acetate and methylene blue efficiency in poisoning treatments. In vivo experiments were conducted on 102 Wistar Han rats. The experiments investigated the hematotoxic and oxidative stress effects of hydroxylamine sulfate in acute and subacute toxicity treatment of animals. Electron Spin Resonance was used for quantitative determination of blood and liver tissue parameters alterations after intoxication. The osmotic fragility of erythrocytes, lipid peroxidation intensity and level of SH-groups in liver of rats were determined by established biochemical assays. Hydroxylamine sulfate cause an acute hematotoxicity and oxidative stress in vivo as demonstrated by the appearance of free oxidized iron in blood, reduced glutathione content and increased lipid peroxidation in liver. The experimental studies showed the formation of Hb-NO, MetHb in erythrocytes and as well of stable complex of reduced iron (Fe(2+)) with hydroxylamine sulfate. Methylene blue treatment does not reduce the Hb-NO or MetHb levels in intoxicated animals while administration of α-tocopherol acetate reduces substantially lipid peroxidation. Oxidative stress is a key mechanism of acute hematotoxicity caused by hydroxylamine sulfate. Methylene blue is not suitable antidote in case of hydroxylamine intoxication.

A Cross-Sectional Survey of Acquired Subclinical Methemoglobinemia among Hospital Healthcare Professionals in Sandstorm Episode of Ambient Air Pollution: Tehran-Iran, Pulse Co-Oximetry

Background : Subclinical methemoglobinemia (MetHb) is an occult disease. Clinical diagnosis is difficult. Acquired MetHb is a most common presentation in practice, and its detection help to improve health status of involved individuals. Healthcare professionals enumerate as one of the at risk groups against adverse health effects. Method: All the participations were hospital healthcare professionals and to follow designed criteria to the study. Results: A total of 117 healthcare professionals fulfilled the criteria of study. Mean age was 39±9 SD years, ranged 20-60 years. Female sex included 52%. Frequency of MetHb was detected in 6% of population. Of them, 71% were male. All the subjects were diagnosed with MetHb located at the poor-ventilated workplaces. There were significant differences between MetHb and carboxyhemoglobin levels (P<0.001). Conclusion: Subclinical MetHb was meaningful in the target of population. It may be originated due to ambient air pollution. There was high-frequency levels of involvement in men had. Evaluation the causal factors are an impact that will require the future studies.

A case of severe methemoglobinemia caused by hair dye poisoning

Hair dyes are widely used and very popular xenobiotics. Most of these products contain paraphenylenediamine (PPD) that can cause methemoglobinemia. We here report a case of severe methemoglobinemia that we treated using large amounts of methylene blue. A 30-year-old man visited a regional hospital with cyanosis. He was congenitally blind and had autism. For several weeks, he had mistaken hair dye for toothpaste. When he arrived at a regional hospital, he was drowsy with cyanosis and his initial serum methemoglobin (MetHb) level was 59.5%. After being treated with 2 mg/kg methylene blue (1 mg/kg × 2 administrations), he was transferred to a tertiary university hospital. Upon presentation at the Emergency Department in the tertiary hospital, his MetHb level was found to be 49.4% and his oxygen saturation was 80%. He was then admitted to the intensive care unit. After treatment with 4 mg/kg methylene blue (1 mg/kg × 4 administrations), he successfully recovered. Because PPD can result in serious methemoglobinemia, clinicians should test it in cyanotic patients who have been exposed to hair dye for an extended period.

Biomarkers of prolonged exposure to microcystin-LR in mice

The effects of prolonged exposure to microcystins (MCs) on health are not yet sufficiently understood and this type of poisoning is often undiagnosed. Even though chronic exposure has been linked with liver cancer and alterations have been described in liver damage marker enzymes in exposed populations, there are not profile parameters that indicate prolonged exposure to microcystins.The aim of this work is to determine, based on an animal model of prolonged exposure to successive i.p. doses of 25 μg MC-LR/kg body weight, several plasma parameters which could be useful as exposure biomarkers.Hemoglobin (Hb) and methemoglobin (MetHb) levels were determined on blood samples. We also studied plasma levels of hydroperoxides (ROOHs), α-tocopherol, glutathione and lipid profile as well as superoxide dismutase (SOD) and catalase (CAT) erythrocyte activities. In addition, the determination of MC-LR levels in liver, kidney, plasma, urine and feces of treated mice was carried out. We found that alteration in MetHb, ROOHs, glutathione, α-tocopherol levels, SOD activity and plasma lipid profile, correlates with those expected if the alteration derived from hepatic damage. The alterated plasma paramenters together with MC-LR determination could be used as biomarkers, helpful tools in screening and epidemiological studies.

Antidote for acquired methemoglobinemia: methylene blue

Methylene blue (MB) is an effective antidote for methemoglobinemia. MB is a basic dye, yielding a blue solution. In the human body, hemoglobin is the oxygen-carrying protein including a ferrous atom. Hemoglobin is oxidized to methemoglobin (MetHb) with the ferric atom, which cannot bind to or carry oxygen. Equilibrium between hemoglobin and MetHb is approximately 99:1. Thus a healthy man can have about 1% of methemoglobinemia. The cytochrome b5 MetHb reductase pathway plays a major role in reducing MetHb to hemoglobin. The nicotin amide adenine dinucleotide phosphate (NADPH) MetHb reductase pathway is a minor reducing system of MetHb, and it needs NADPH as a cofactor. However, to the exceeding exogenous oxidative stress, the cytochrome b5 MetHb reductase pathway is soon exhausted, and the NADPH MetHb reductase pathway can be activated 4 to 5 times by the exogenous cofactor, MB. The decision to initiate MB therapy for methemoglobinemia depends on the MetHb level and the symptoms. The indication for MB therapy in a symptomatic patient is a MetHb level >20% and in an asymptomatic patient, a MetHb level >30%. Patients with comorbidities such as anemia, heart disease, pneumonia, chronic obstructive pulmonary disease, or liver cirrhosis can be candidates for MB therapy with an even lower MetHb level. The recommended initial dose of MB is 1 to 2 mg/kg. It can be repeated every 30 minutes to 1 hour. However, the dose should not exceed 7 mg/kg. A high dose of MB may induce methemoglobinemia paradoxically and also cause hemolytic anemia. Like other antidotes, MB has its own adverse effects.

Metabolic activation by human arylacetamide deacetylase, CYP2E1, and CYP1A2 causes phenacetin-induced methemoglobinemia

Phenacetin has been used as an analgesic antipyretic but has now been withdrawn from the market due to adverse effects such as methemoglobinemia and renal failure. It has been suggested that metabolic activation causes these adverse effects; yet, the precise mechanisms remain unknown. We previously demonstrated that human arylacetamide deacetylase (AADAC) was the principal enzyme catalyzing the hydrolysis of phenacetin. In this study, we assessed whether AADAC was involved in phenacetin-induced methemoglobinemia. A high methemoglobin (Met-Hb) level in the blood was detected 1h after administration of phenacetin (250mg/kg, p.o.) to male C57BL/6 mice. Pre-administration of tri-o-tolylphosphate, a general esterase inhibitor, was found to decrease the levels of Met-Hb and the plasma concentration of p-phenetidine, a hydrolyzed metabolite of phenacetin. An in vitro study using red blood cells revealed that incubation of phenacetin or p-phenetidine with human liver microsomes (HLM) increased the formation of Met-Hb. To identify the enzymes involved in the formation of Met-Hb, we used recombinant enzymes and HLM treated with inhibitors in the measurement of the formation of Met-Hb. High levels of Met-Hb were observed following incubation of human AADAC with either cytochrome P450 (CYP) 1A2 or CYP2E1. Furthermore, the increased Met-Hb formation by the incubation of HLM with phenacetin was significantly inhibited to 25.1±0.7% of control by eserine, a potent AADAC inhibitor. In conclusion, we found that the hydrolysis by AADAC and subsequent metabolism by CYP1A2 and CYP2E1 play predominant roles in phenacetin-induced methemoglobinemia.

Potential behavioral and pro-oxidant effects of Petiveria alliacea L. extract in adult rats

Ethnopharmacological relevancePetiveria alliacea (Phytolaccaceae) is a perennial shrub indigenous to the Amazon Rainforest and tropical areas of Central and South America, the Caribbean, and sub-Saharan Africa. In folk medicine, Petiveria alliacea has a broad range of therapeutic properties; however, it is also associated with toxic effects. Aim of the studyThe present study evaluated the putative effects of Petiveria alliacea on the central nervous system, including locomotor activity, anxiety, depression-like behavior, and memory, and oxidative stress. Materials and methodsTwo-month-old male and female Wistar rats (n=7–10 rats/group) were administered with 900mg/kg of hydroalcoholic extracts of Petiveria alliacea L. The behavioral assays included open-field, forced swimming, and elevated T-maze tests. The oxidative stress levels were measured in rat blood samples after behavioral assays and methemoglobin levels were measured in vitro. ResultsConsistent with previous reports, Petiveria alliacea increased locomotor activity. It also exerted previously unreported anxiolytic and antidepressant effects in behavioral tests. In the oxidative stress assays, the Petiveria alliacea extract decreased Trolox equivalent antioxidant capacity levels and increased methemoglobin levels, which was related to the toxic effects. ConclusionsThe Petiveria alliacea extract exerted motor stimulatory and anxiolytic effects in the OF test, antidepressant effects in the FS test, and elicited memory improvement in ETM. Furthermore, the Petiveria alliacea extract also exerted pro-oxidant effects in vitro and in vivo, inhibiting the antioxidant status and increasing MetHb levels in human plasma, respectively.

EXPERIMENTAL ASSESSMENT OF SULFUR DIOXIDE AFFECT ON HAEMOPOETIC SYSTEM

Objective: to study the effect of sulfur dioxide on haemopoetic system of Аf line white mice. Material and methods. The object of the study is Af white mice (2,5-3 months) with mass of 22-28 g. The inhalation of sulfur dioxide (SO 2 ) was conducted on the facility UIN-2M for 2 hours with the concentration of gas in the chamber S SO2 of 5 mg/m 3 . The morphometric parameters of erythron system were studied in the Af mice after the 2-hour SO 2 inhalation. The methods of the study included hematologic, biochemical, immunological, and statistical. Results. Sulfur dioxide does not significantly affect liver and lungs mass. Spleen mass after SO 2 inhalation did not differ from the control one on day 7, and on day 14 it significantly reduced by 18 %. MetHb level to days 7-14 after the SO 2 inhalation on the mice was not significantly different from the control one (it had a tendency to increase by ~ 10 %). After the SO 2 effect on day 4 there were no NMGO changes, but on day 7 the reaction was significantly accelerated by the parameter t 1/2 by 20 %. By day 14 this trend persisted, in addition to reducing the lag phase, the acceleration of the reaction occurred at the expense of SMet/T increase, but without any significant differences. Conclusion. The carried out research showed that sulfur dioxide at the given concentration caused slight changes in hematopoietic system. The magnitude of the changes depended on the concentration and exposure time of the pollutant.

Methemoglobin Formation by Triapine, Di-2-pyridylketone-4,4-dimethyl-3-thiosemicarbazone (Dp44mT), and Other Anticancer Thiosemicarbazones: Identification of Novel Thiosemicarbazones and Therapeutics That Prevent This Effect

Thiosemicarbazones are a group of compounds that have received comprehensive investigation as anticancer agents. The antitumor activity of the thiosemicarbazone, 3-amino-2-pyridinecarboxaldehyde thiosemicarbazone (3-AP; triapine), has been extensively assessed in more than 20 phase I and II clinical trials. These studies have demonstrated that 3-AP induces methemoglobin (metHb) formation and hypoxia in patients, limiting its usefulness. Considering this problem, we assessed the mechanism of metHb formation by 3-AP compared with that of more recently developed thiosemicarbazones, including di-2-pyridylketone-4,4-dimethyl-3-thiosemicarbazone (Dp44mT). This was investigated using intact red blood cells (RBCs), RBC lysates, purified oxyhemoglobin, and a mouse model. The chelation of cellular labile iron with the formation of a redox-active thiosemicarbazone-iron complex was found to be crucial for oxyhemoglobin oxidation. This observation was substantiated using a thiosemicarbazone that cannot ligate iron and also by using the chelator, desferrioxamine, that forms a redox-inactive iron complex. Of significance, cellular copper chelation was not important for metHb generation in contrast to its role in preventing tumor cell proliferation. Administration of Dp44mT to mice catalyzed metHb and cardiac metmyoglobin formation. However, ascorbic acid administered together with the drug in vivo significantly decreased metHb levels, providing a potential therapeutic intervention. Moreover, we demonstrated that the structure of the thiosemicarbazone is of importance in terms of metHb generation, because the DpT analog, di-2-pyridylketone-4-cyclohexyl-4-methyl-3-thiosemicarbazone (DpC), does not induce metHb generation in vivo. Hence, DpC represents a next-generation thiosemicarbazone that possesses markedly superior properties. This investigation is important for developing more effective thiosemicarbazone treatment regimens.

Ferric Iron and Cobalt (III) Compounds to Safely Decrease Hydrogen Sulfide in the Body?

To sort out the putative roles of endogenous hydrogen sulfide (H2S) in clinical conditions wherein systemic inflammation or hypoxia is present, it becomes crucial to develop approaches capable of affecting H2S concentration that can be safely applied in humans. We have investigated a paradigm, which could achieve such a goal, using vitamin B12 (vit.B12), at the dose recommended in cyanide poisoning, and very low levels of methemoglobin (MetHb). Hydroxocobalamin in the plasma, supernatant of kidney, and heart tissue homogenates of rats that had received vit.B12 (140 mg.kg(-1) intravenous) was found in the μM range. Exogenous H2S (100 μM) added to the plasma or supernatants of these rats decreased at a significantly higher rate than in control rats. In the latter however a spontaneous oxidation of exogenous H2S occurred. In vitro, hydroxocobalamin solution (100 μM) decreased, within <2 min, an equimolar concentration of H2S by 80%. Three to five percent MetHb prevented H2S induced hyperventilation in vivo and decreased exogenous H2S in vitro by 25-40 μM within 30 s. Our observations lead to the hypothesis that innocuous levels of MetHb and vit.B12 could be a used as an effective and safe way to test the role of endogenous H2S in vivo.

Non‐invasive measurements of carboxyhemoglobin and methemoglobin in children with sickle cell disease

Assessment of oxyhemoglobin saturation in patients with sickle cell disease (SCD) is vital for prompt recognition of hypoxemia. The accuracy of pulse oximeter measurements of blood oxygenation in SCD patients is variable, partially due to carboxyhemoglobin (COHb) and methemoglobin (MetHb), which decrease the oxygen content of blood. This study evaluated the accuracy and reliability of a non-invasive pulse co-oximeter in measuring COHb and MetHb percentages (SpCO and SpMet) in children with SCD. We hypothesized that measurements of COHb and MetHb by non-invasive pulse co-oximetry agree within acceptable clinical accuracy with those made by invasive whole blood co-oximetry. Fifty children with SCD-SS underwent pulse co-oximetry and blood co-oximetry while breathing room air. Non-invasive COHb and MetHb readings were compared to the corresponding blood measurements. The pulse co-oximeter bias was 0.1% for COHb and -0.22% for MetHb. The precision of the measured SpCO was ± 2.1% within a COHb range of 0.4-6.1%, and the precision of the measured SpMet was ± 0.33% within a MetHb range of 0.1-1.1%. Non-invasive pulse co-oximetry was useful in measuring COHb and MetHb levels in children with SCD. Although the non-invasive technique slightly overestimated the invasive COHb measurements and slightly underestimated the invasive MetHb measurements, there was close agreement between the two methods.

Plasma methemoglobin as a potential biomarker of anemic stress in humans

Transfusion of allogeneic red blood cells (RBCs) is one of the main treatments of acute anemia secondary to blood loss and fluid resuscitation within the operating room. Decisions to transfuse blood are based largely on intermediate biological markers (hemoglobin, arterial oxygen saturation, blood pressure, heart rate) which may not accurately reflect inadequacy of tissue oxygen delivery. Based on experimental studies, we hypothesized that anemia-induced tissue hypoxia activates adaptive mechanisms which promote local vascular nitric oxide (NO) production to improve tissue perfusion and survival during acute anemia. Hemoglobin (Hb) oxidation to methemoglobin (MetHb) may be a byproduct of such local NO production. Therefore, we tested the hypothesis that MetHb is a biomarker of hypoxic-anemic stress during acute hemodilution associated with cardiopulmonary bypass. With institutional ethics approval, routine laboratory arterial blood gas and co-oximetry values were obtained from 295 patients undergoing heart surgery during February 1 to September 30, 2010, and the values were assessed retrospectively. All samples with an arterial oxygen saturation value ≥ 90% were included (n = 1,421). The maximal change in Hb associated with hemodilution on cardiopulmonary bypass was determined within 48 hr of surgery (n = 180). A chart review was performed to determine the incidence of RBC transfusion and exogenous nitrate administration. All anonymous data were analyzed by linear regression to determine the relationship between Hb and MetHb. A Wilcoxon Signed Rank Test and Student's t test were used to determine changes in Hb, MetHb, and carboxyhemoglobin (CarboxHb) levels. All data are presented as mean and significance was assigned at P < 0.05. A significant decrease in Hb [118 (20) g x L(-1) vs 94 (18) g x L(-1)] was associated with an increase in MetHb [0.88 (0.22)% vs 0.95 (0.24)%] (P < 0.001 for both), but not CarboxHb [1.08 (0.47)% vs 1.08 (0.49)%]. Regression analysis revealed a significant relationship between the change in Hb and MetHb (F = 40.3; P < 0.001) but not between the change in Hb and CarboxyHb (F = 0.2; P = 0.694). This correlation was not influenced by RBC transfusion or exogenous nitrate use. A negative correlation was observed between the change in Hb and MetHb in patients undergoing cardiac surgery and cardiopulmonary bypass. These data support the previously unreported hypothesis that MetHb may be a marker of anemic stress associated with reduced tissue perfusion during acute hemodilution in humans. Further prospective studies are needed to determine if these changes in MetHb are linked to adverse outcomes in patients undergoing cardiac surgery.