CONGENITAL METHEMOGLOBINEMIA. A CLINICAL AND BIOCHEMICAL STUDY OF A CASE

Mechanisms and physiological function of daily haemoglobin oxidation rhythms in red blood cells

Cellular circadian rhythms confer temporal organisation upon physiology that is fundamental to human health. Rhythms are present in red blood cells (RBCs), the most abundant cell type in the body, but their physiological function is poorly understood. Here, we present a novel biochemical assay for haemoglobin (Hb) oxidation status which relies on a redox-sensitive covalent haem-Hb linkage that forms during SDS-mediated cell lysis. Formation of this linkage is lowest when ferrous Hb is oxidised, in the form of ferric metHb. Daily haemoglobin oxidation rhythms are observed in mouse and human RBCs cultured in vitro, or taken from humans in vivo, and are unaffected by mutations that affect circadian rhythms in nucleated cells. These rhythms correlate with daily rhythms in core body temperature, with temperature lowest when metHb levels are highest. Raising metHb levels with dietary sodium nitrite can further decrease daytime core body temperature in mice via nitric oxide (NO) signalling. These results extend our molecular understanding of RBC circadian rhythms and suggest they contribute to the regulation of body temperature.

The Serious Impact of Comorbidities on Methemoglobinemia: A Case Report

Methemoglobinemia is a rare, life-threatening condition that occurs when the body is exposed to oxidative stress. We present the case of a 72-year-old female with a past medical history of hypertension, obesity, dyslipidemia, and heart failure who was admitted to the emergency department with altered mental status and respiratory failure. After admission, we also identified an atrioventricular block 2:1, anemia, and skin discoloration. We performed endotracheal intubation and started mechanical ventilation due to respiratory failure; however, the patient retained an oxygen "saturation gap" despite adequate ventilation. In the initial laboratory evaluation, methemoglobinemia was found to be 13%, reaching a maximum level of 16%. An electroencephalogram revealed status epilepticus after her admission to the intensive care unit. Despite all efforts and supportive care, methylene blue therapy was never attempted, and the patient died. Our case emphasizes the importance of a high index of suspicion for methemoglobinemia, especially in the presence of an oxygen "saturation gap," and that despite relatively low levels of methemoglobinemia, it can have a more severe clinical presentation in patients with comorbidities. In these patients, a reduced threshold for administering methylene blue should be taken into account.

A Case of Cyanosis With Saturation Gap: Dapsone-Induced Methemoglobinemia

Dapsone is an antibiotic used in the management of dermatologic infections and opportunistic infection prophylaxis in developed countries. Methemoglobinemia (MetHb) is a known complication of dapsone use that can result in cyanosis. MetHb is an aberrant form of hemoglobin produced physiologically by auto-oxidation. An impairment in the process of auto-oxidation due to genetic defects or the use of drugs/toxins causes its levels to rise. Management involves timely recognition and the use of methylene blue (MB) or ascorbic acid. We describe the diagnosis and management of a patient with acquired MetHb as a result of dapsone use.

A Case of Congenital Methemoglobinemia: Rare but Real

Methemoglobin (MetHb) is a form of hemoglobin in which iron in Hb is in an oxidized form (ferric) instead of ferrous, making it difficult to bind with oxygen. Usually, MetHb is present in small quantities (<1%) in humans, but once MetHb increases beyond 3%, the condition is known as methemoglobinemia. It can be further classified into hereditary and acquired. Hereditary forms are a rare cause of hypoxia and cyanosis. Only a few cases have been reported worldwide. Here, we present a case of a 33-year-old female with congenital methemoglobinemia who remains relatively healthy in spite of her underlying condition. This case report focuses on knowledge sharing and practical aspects of managing patients with congenital methemoglobinemia.

Once in a blue moon: Primaquine-induced methemoglobinemia - A case report

Methemoglobinemia is a rare blood disorder that should be suspected in patients with cyanosis and low oxygen saturation of around 85%, especially when both do not improve despite supplemental oxygen. We describe the case of a 67-year-old lung transplant patient who was treated with primaquine and clindamycin because of a positive Pneumocystis jirovecii polymerase chain reaction on bronchoalveolar lavage fluid. Soon thereafter the patient developed increasing shortness of breath, central cyanosis and hypoxia, with an oxygen saturation of 86% on pulse oximetry despite supplemental oxygen. Arterial blood gas analysis showed a peculiar dark brown color and a significantly increased methemoglobin percentage. A diagnosis of methemoglobinemia due to primaquine was made. As treatment option, we preferred ascorbic acid over methylene blue because of concerns of possibly eliciting a serotonin syndrome. Our patient recovered rapidly after initiation of appropriate treatment. A high index of suspicion is crucial since this condition is potentially fatal.

[Liposuction with consequences: what to consider when using prilocaine]

Aetiologically, prilocaine-induced methaemoglobinaemia is a rare form of acquired methaemoglobinaemia, which occurs rarely in the first place. The following report highlights a potentially dangerous complication arising after application of prilocaine during liposuction.A young female visited the Accident and Emergency Department following a pre-syncopal fall. As a consequence of her fall, she experienced debilitating wrist pain and exhibited a laceration on her chin. She had undergone liposuction of the lower extremity as an outpatient approximately 12 hours earlier and received regional anaesthesia in the process. A large volume of an anaesthetic solution containing prilocaine had been injected into the tissue.The patient was normotensive and slightly tachycardic and had oxygen saturations of 90 % on room air. She was cyanotic and her lips were pale. Initial arterial blood gas analysis showed a methaemoglobin fraction, which was increased significantly to 10.9 %. Conventional radiography confirmed the presence of a minimally dislocated distal radius fracture. Following subsequent oxygen therapy over a four-hour period, the patient's methaemoglobin level dropped to 6 %, her lip cyanosis abated and her vital parameters stabilised. The laceration of her chin was sutured and her wrist immobilised in a split plaster brace. After a 12-hour hospital stay, the patient was discharged. At her six-week follow-up appointment, the fracture had healed and both the functional and cosmetic aspects of her chin wound were adequate. We hope that this report draws the attention of emergency care personnel to the possible diagnosis of prilocaine-induced methaemoglobinaemia after liposuction and encourages more general discussions around the use of prilocaine.

A severe case of methaemoglobinaemia in a Brazilian hairdresser

Methaemoglobinaemia is an extremely rare condition with multiple causes, both genetic and acquired. We present a severe case of methaemoglobinaemia occurring in a Brazilian hairdresser working in the UK. She presented after several days of preparing popular 'Brazilian blowdry' treatments for customers at a hair salon. She had been exposed to multiple volatile chemicals, including formaldehyde, without any respiratory protection, and we postulate that this may have caused her illness. If so, this would be the first published case of methaemoglobinaemia caused by exposure to the volatile components of beauty products.

Red Blood Cell Function and Dysfunction: Redox Regulation, Nitric Oxide Metabolism, Anemia

SIGNIFICANCE

Recent clinical evidence identified anemia to be correlated with severe complications of cardiovascular disease (CVD) such as bleeding, thromboembolic events, stroke, hypertension, arrhythmias, and inflammation, particularly in elderly patients. The underlying mechanisms of these complications are largely unidentified. Recent Advances: Previously, red blood cells (RBCs) were considered exclusively as transporters of oxygen and nutrients to the tissues. More recent experimental evidence indicates that RBCs are important interorgan communication systems with additional functions, including participation in control of systemic nitric oxide metabolism, redox regulation, blood rheology, and viscosity. In this article, we aim to revise and discuss the potential impact of these noncanonical functions of RBCs and their dysfunction in the cardiovascular system and in anemia.

CRITICAL ISSUES

The mechanistic links between changes of RBC functional properties and cardiovascular complications related to anemia have not been untangled so far.

FUTURE DIRECTIONS

To allow a better understanding of the complications associated with anemia in CVD, basic and translational science studies should be focused on identifying the role of noncanonical functions of RBCs in the cardiovascular system and on defining intrinsic and/or systemic dysfunction of RBCs in anemia and its relationship to CVD both in animal models and clinical settings. Antioxid. Redox Signal. 26, 718-742.

Methemoglobin reduction mediated by D-amino acid dehydrogenase in Propsilocerus akamusi (Tokunaga) larvae

A methemoglobin (metHb) reduction system is required for aerobic respiration. In humans, Fe(III)-heme-bearing metHb (the oxidized form of hemoglobin), which cannot bind oxygen, is converted to Fe(II)-heme-bearing oxyhemoglobin (oxyHb, the reduced form), which can bind oxygen, in a system comprising NADH, NADH-cytochrome b5 reductase, and cytochrome b5. However, the mechanism of metHb reduction in organisms that inhabit oxygen-deficient environments is unknown. In the coelomic fluid of the larvae of Propsilocerus akamusi, which inhabit a microaerobic environment, we found that metHb was reduced by D-alanine. We purified an FAD-containing enzyme, D-amino acid dehydrogenase (DAD), and component V hemoglobin from the larvae. Using the purified components and spectrophotometric analyses, we showed a novel function of DAD: DAD-mediation of P. akamusi component V metHb reduction with using D-alanine as an electron donor. P. akamusi larvae possess this D-alanine-DAD metHb reduction system in addition to a previously discovered NADH-NADH-cytochrome b5 reductase system. This is the first report of the presence of DAD in a multicellular organism. The molecular mass of DAD was estimated to be 45 kDa. The optimal pH and temperature of the enzyme were 7.4 and 20 °C, respectively, and the optimal substrate was D-alanine. The enzyme activity was inhibited by benzoate and sulfhydryl-binding reagents.

Methemoglobin reduction by NADH-cytochrome b(5) reductase in Propsilocerus akamusi larvae

For oxygen respiration, a methemoglobin (metHb) reduction system is needed in the cell because metHb cannot bind oxygen. We examined the insect Propsilocerus akamusi larvae to elucidate the metHb reduction system in an organism that inhabits an oxygen-deficient environment. NADH-dependent reduction of metHb in coelomic fluid suggested the coexistence of cytochrome b5 reductase (b5R) and cytochrome b5 with hemoglobin in the fluid and that these proteins were involved in physiological metHb reduction in the larvae. The presence of b5R was revealed by purifying b5R to homogeneity from the midge larvae. Using purified components, we showed that larval metHb was reduced via the NADH-b5R (FAD)-cytochrome b5-metHb pathway, a finding consistent with that in aerobic vertebrates, specifically humans and rabbits, and b5R function between mammal and insect was conserved. b5R was identified as a monomeric FAD-containing enzyme; it had a molecular mass of 33.2 kDa in gel-filtration chromatography and approximately 37 kDa in SDS-PAGE analysis. The enzyme's optimal pH and temperature were 6.4 and 25 °C, respectively. The apparent Km and Vmax values were 345 μM and 160 μmol min(-1) mg(-1), respectively, for ferricyanide and 328 μM and 500 μmol min(-1) mg(-1), respectively, for 2,6-dichlorophenolindophenol. The enzyme reaction was inhibited by benzoate, p-hydroxymercuribenzoate, iodoacetamide, and iodoacetate, and was not inhibited by metal ions or EDTA.

Cytochromeb5is a major reductant in vivo of human indoleamine 2,3-dioxygenase expressed in yeast

The evolutionary relationship of indoleamine 2,3-dioxygenase (IDO) to some gastropod myoglobins suggests that IDO may undergo autoxidation in vivo such that one or more currently unidentified electron donors are required to maintain IDO heme iron in the active, ferrous state. To evaluate this hypothesis we have used yeast knockout mutants in combination with a recently developed yeast growth assay for IDO activity in vivo to demonstrate a role for cytochrome b(5) and cytochrome b(5) reductase in maintaining IDO activity in vivo.

Methemoglobinemia induced by topical vaginal sulfanilamide cream in a patient with cervical cancer: a case report

BACKGROUND

Methemoglobinemia is a rare disorder most commonly associated with the ingestion or topical application of an offending exogenous agent. The clinical consequences of acute methemoglobinemia can be devastating and include lethargy, headache, and dyspnea and, as methemoglobin concentrations rise, respiratory depression, confusion, seizures, and even death.

CASE

Here we present a case of acute methemoglobinemia induced by exposure to topical vaginal sulfanilamide cream in a 36-year-old woman with a FIGO stage IIIB squamous cell cervical carcinoma.

CONCLUSION

Although methemoglobinemia associated with topical anesthetics has been well documented, to our knowledge this is the first reported case of methemoglobinemia induced by exposure to topical sulfanilamide cream. Although patients undergoing intracavitary radiation treatment for cervical cancer are at risk for cyanosis due to the development of deep vein thromboses and pulmonary embolism, methemoglobinemia should be suspected in the setting of acute cyanosis with a normal arterial oxygen pressure.

Effect of UVB radiation on human erythrocytes in vitro

In order to evaluate the UVB radiation induced phototoxic effect, the human erythrocytes (RBCs) were used an alternate biological model and rate of photohaemolysis was assessed in vitro at various intensities of UVB radiation (0-2.0 mW/cm2) for an exposure period of 0-240 min. The alterations of biochemical activities in RBC membrane (ghosts), caused by its exposure under an average incident intensity of UVB radiation (0.5 mW/cm2) in sunlight at earth surface, were also determined to understand the possible mechanism of photohaemolysis. We observed UVB dose dependent lysis of erythrocytes by recording haemoglobin and methemoglobin (oxidized form of haemoglobin) in photohaemolysate. We also observed significant inhibition in ATPase, acetylcholinesterase, glucose-6-phosphate dehydrogenase activites and an increased amount of thiobarbituric acid-reactive substance (TBA-RS) in RBC ghosts exposed to UVB radiation (0.5 mW/cm2) for a period of 0-100 min (doses: 0, 0.33, 0.66, 1.0, 1.5 and 3.0 J). The changes were found UVB dose dependent. A decrease of glutathione content in RBC ghosts at low dose level of UVB exposure (0.33 J) was found to be recovered at higher dose levels (0.66-1.5 J). These observations suggested, UVB dose dependent toxicity to human erythrocytes in vitro. Thus the erythrocytes can be used for an assessment of UVB induced biological effects and to understand possible mechanism of the phototoxicity.

Severe methemoglobinemia after transesophageal echocardiography

Methemoglobinemia, an increased concentration of methemoglobin in the blood, is an altered state of hemoglobin whereby the ferrous form of iron is oxidized to the ferric state, rendering the heme moiety incapable of carrying oxygen. This can cause hypoxia, cyanosis, or even death. Severe methemoglobinemia resulting from oral benzocaine spray before endoscopic procedures has been reported as a rare complication. We report a case of severe acquired methemoglobinemia resulting from topical benzocaine use before transesophageal echocardiography. This case serves to highlight the severity of methemoglobinemia that can result from an otherwise innocuous agent even in small doses and the fact that prompt recognition and treatment of this disorder can be lifesaving.

Anesthetic management of a patient with methemoglobinemia

Methemoglobinemia results from the oxidation of the ferrous iron in hemoglobin to the ferric iron state. Methemoglobin is incapable of carrying O2, and high levels may impact on O2 delivery to the tissues. Methemoglobinemia may result from congenital deficiencies of enzymes that normally convert methemoglobin to hemoglobin, alterations in the hemoglobin molecule itself or, most commonly, from the ingestion of medications or toxins that oxidize the ferrous iron of hemoglobin. Several issues must be considered when anesthetizing patients with methemoglobinemia, including the potential for decreased O2 delivery, which may be exacerbated by intraoperative blood loss and anemia, interference with normal intraoperative monitoring devices, and the potential for medications to cause or exacerbate methemoglobinemia. We describe a patient with acquired methemoglobinemia from dapsone therapy who required anesthetic care for shoulder arthroscopy. The patient's drug-induced methemoglobinemia was diagnosed intraoperatively during previous anesthesia on the basis of discrepancy between the O2 saturation noted by pulse oximetry and that obtained from arterial blood gas analysis. Anesthetic care for patients with methemoglobinemia is discussed and a review of methemoglobinemia presented.

Electron transfer between cytochrome b(5) and some oxidised haemoglobins: the role of ionic strength

We have compared experimental measurements and Brownian dynamic calculations for the reduction of oxidised adult human haemoglobin by reduced bovine cytochrome b(5) over a range of ionic strengths. Our calculations suggest that the presence of molecular electrostatic fields have a significant role to play in the formation of the electron transfer complexes. These results predict that electron transfer occurs within an ensemble of similarly weakly docked complexes, the formation of which is strongly ionic strength dependent. Application of electron tunneling analysis to the complexes allows us to predict the rates of electron transfer within each ensemble of complexes as a function of ionic strength. The outcome of this theoretical study is compared with experimental rate measurements. A comparison of the results obtained from adult and embryonic haemoglobins, at a fixed ionic strength, indicates a significant difference in the characteristics of complex formation. These data emphasise the role played by electrostatic interactions in this important physiological reaction.

Severe methemoglobinemia on reexposure to benzocaine

We report a 65-year-old male who developed severe methemoglobinemia only on reexposure to benzocaine. The patient needed two awake fiberoptic intubations for emergency surgeries. On the second exposure, the patient was septic and malnourished, and he was taking acetaminophen. He developed a methemoglobin level of 55%. Possible reasons for the methoglobinemia on reexposure are discussed in this report.

Cytochrome b5, its functions, structure and membrane topology

The first part of the present communication reviews recent advances in our understanding of the known physiological functions of cytochrome b5. In addition, one section is devoted to a description of a recently discovered function of cytochrome b5, namely its involvement in the synthesis of the oncofetal antigen N-glycolylneuraminic acid. The second part of the article summarizes site-directed mutagenesis studies, primarily conducted in the author's laboratory, in both the catalytic heme-binding and membrane-binding domain of cytochrome b5. These studies have shown that: 1) the membrane binding domain of cytochrome b5 spans the bilayer; 2) cytochrome b5 lacking 19 COOH-terminal amino acids does not bind to membrane bilayers; and 3) specific amino acids in the membrane binding domain have been mutated and shown not to be essential for the function of cytochrome b5 with its redox partners.

Concise review: methemoglobinemia

The ferrous iron of hemoglobin is exposed continuously to high concentrations of oxygen and, thereby, is oxidized slowly to methemoglobin, a protein unable to carry oxygen. To restore hemoglobin function, methemoglobin (ferrihemoglobin) must be reduced to hemoglobin (ferrohemoglobin). Under physiological conditions, methemoglobin reduction is accomplished mainly by red cell NADH-cytochrome b5 reductase (NADH-methemoglobin reductase) so efficiently that there is insignificant amounts of methemoglobin in the circulating blood. However, should methemoglobin formation be increased--e.g., due to the presence of oxidant drugs, or an abnormal methemoglobin not amenable to reduction (hemoglobin M), or a deficiency in red cell cytochrome b5 reductase--methemoglobinemia will result. Most methemoglobinemias have no adverse clinical consequences and need not be treated. Under certain conditions, such as exposure to large amounts of oxidant or in young infants, rapid treatment is necessary. In hereditary cytochrome b5 deficiency, treatment is often directed at improving the poor cosmetic effect of persistent cyanosis with the minimum amount of drugs to give satisfactory clinical results.

Chemically induced methaemoglobinaemia in a neonate

A case of toxic methaemoglobinaemia is presented, which followed the use of a local anaesthetic containing prilocaine (Citanest, Astra Pharmaceuticals Ltd) which was used to provide analgesia prior to the suturing of a facial laceration. Although this complication is well documented, this case is unusual in that it involved a neonate and was not produced by an overdose of prilocaine (the recommendations of the British National Formulary and the product monograph were followed). Explanations for the increased susceptibility of neonates and young infants to methaemoglobinaemia are presented together with the salient clinicopathological features. The diagnostic dilemmas and investigative procedures related to the condition are considered together with the various treatments available.

Utilization of red-cell FAD by methaemoglobin reductases at the expense of glutathione reductase in heterozygous beta-thalassaemia

FAD-dependent methaemoglobin reductases (MHR) were studied in red cells in heterozygous beta-thalassaemia to investigate how they related to low FAD-dependent glutathione reductase (GR). In contrast to GR, MHR activities were usually normal or increased. In particular, whether expressed in relation to haemoglobin or number of red cells, NADPH-MHR activity was markedly increased in most subjects, probably being a response to increased oxidative stress. Oral riboflavin had no effect on MHR activities, indicating saturation with FAD even though GR was deficient. A strong correlation between percent stimulation of GR by FAD and NADPH-MHR activity indicates that FAD is utilized by MHR at the expense of GR. This could be an important influence on GR in heterozygous beta-thalassaemia. Thus, the low activity resulting from an inherited deficiency of FAD is decreased further.

Electron spin resonance of bloodstains and its application to the estimation of time after bleeding

The degradation of blood constituents in unheparinized dry blood was studied with electron spin resonance (ESR) at various temperatures. The intensity of ESR signals of methemoglobins, non-heme irons and organic radicals in dried human blood increases with time. Considering the kinetics of the signal growth, the formation mechanism of the paramagnetic species was discussed. The ESR signal (g = 4.3) of non-heme iron is usable in estimating the time after bleeding or injury using bloodstains.

Methemoglobinemia

Oxygen transport, the major function of hemoglobin, is dependent upon reduced heme iron. In the red cell, the heme iron is maintained in the reduced form by the methemoglobin reduction system. When the balance between oxidation and reduction of heme iron is perturbed due to the presence of excessive oxidants, decreased reducing capacity or the presence of abnormal hemoglobin, methemoglobinemia ensues. In most cases methemoglobinemia is transitory and of no major clinical consequence. Occasionally, however, it can be life threatening and must be rapidly diagnosed and treated. When methemoglobinemia is of hereditary nature, either due to deficiency of red cell NADH-methemoglobin reductase or due to the presence of M hemoglobin, it is a lifelong problem. Since most of these patients do not have major disabling symptoms, the treatment is aimed at correction of cyanosis.

The influence of beta-93 sulfhydryl groups, organic phosphate and heme concentration on methemoglobin reduction

Native and modified methemoglobin (beta-93-SH groups blocked) were reduced by NADH-dependent methemoglobin reductase in the absence and the presence of organic phosphate (inositol hexaphosphate). These experiments were performed with dilute as well as concentrated methemoglobin solutions (physiological heme concentration). It is shown that: (a) in dilute solutions the blockage of beta-93-SH groups lowers the rate of methemoglobin reduction in the absence of organic phosphate but the rates of native and modified methemoglobin reduction are similar in the presence of organic phosphate; (b) at physiological heme concentration the blockage of beta-93-SH groups does not affect the rate of reduction but the organic phosphate stimulates the reduction of both native and modified methemoglobins in a similar fashion, as it does in dilute solutions. It is concluded that, although in dilute solutions the blockage of beta-93-SH groups alters the reduction rate, at physiological heme concentration the presence of free beta-93-SH groups does not have any significant effect on methemoglobin reduction. On the contrary, the organic phosphates do accelerate the rate of reduction at all ranges of heme concentration.

Effects of hemolysate concentration, ionic strength and cytochrome b5 concentration on the rate of methemoglobin reduction in hemolysates of human erythrocytes

An assay for determining the rate of methemoglobin reduction in hemolysates of human erythrocytes has been developed. The rates obtained by this assay, when corrected for dilution, are comparable to those obtained with intact cells. Increased ionic strength inhibits the reaction, whereas EDTA increases the rate of reduction. The rate with NADPH as electron donor is 65-70% of the rate with NADH. Added cytochrome b5 stimulates the reaction. The assay has been used to examine erythrocytes from two methemoglobinemic sisters and their asymptomatic mother. Hemolysates of the two patients have both decreased dichlorophenolindophenol reductase activity and decreased ability to reduce methemoglobin. Hemolysates from the heterozygous mother have intermediate dichlorophenolindophenol reductase activity and intermediate methemoglobin reduction ability. The data presented in this paper indicate that the concentrations of cytochrome b5 and cytochrome b5 reductase determine the rate of methemoglobin reduction in hemolysates.

[On the mechanism of ascorbic acid induced methemoglobin reduction of human erythrocytes (author's transl)]

Ascorbic acid and dehydroascorbic acid penetrate the human erythrocyte membrane. In vitro methemoglobin is reduced nonenzymatically by both substances in concentrations of 10(-2) M to 10(-3) M. Dehydroascorbic acid is reduced nonenzymatically to ascorbic acid by GSH, even with low GSH-content of erythrocytes. Under physiological conditions ascorbic acid induced methemoglobin reduction is far less important than reduction by the NADH dependent methemoglobin reductase system. In methemoglobinemic conditions caused by toxic effects or by congenital methemoglobin reductase deficiency treatment with ascorbic acid is possible. However, critically increased methemoglobin content of the blood higher than 30% makes therapy with methylene blue necessary.