Methemoglobin--it's not just blue: a concise review

OMX: A NOVEL OXYGEN DELIVERY BIOTHERAPEUTIC IMPROVES OUTCOMES IN AN OVINE MODEL OF CONTROLLED HEMORRHAGIC SHOCK

ABSTRACT

Hemorrhagic shock is a major source of morbidity and mortality worldwide. While whole blood or blood product transfusion is a first-line treatment, maintaining robust supplies presents significant logistical challenges, particularly in austere environments. OMX is a novel nonhemoglobin (Hb)-based oxygen carrier derived from the H-NOX (heme-nitric oxide/oxygen binding) protein family. Because of their engineered oxygen (O 2 ) affinities, OMX proteins only deliver O 2 to severely hypoxic tissues. Additionally, unlike Hb-based oxygen carriers, OMX proteins do not scavenge nitric oxide in the vasculature. To determine the safety and efficacy of OMX in supporting tissue oxygen delivery and cardiovascular function in a large animal model of controlled hemorrhage, 2-3-week-old lambs were anesthetized, intubated, and mechanically ventilated. Hypovolemic shock was induced by acute hemorrhage to obtain a 50% reduction over 30 min. Vehicle (n = 16) or 400 mg/kg OMX (n = 13) treatment was administered over 15 min. Hemodynamics, arterial blood gases, and laboratory values were monitored throughout the 6-h study. Comparisons between groups were made using t tests, Wilcoxon rank sum test, and Fisher's exact test. Survival was assessed using Kaplan-Meier curves and the log-rank test. We found that OMX was well-tolerated and significantly improved lactate and base deficit trends, and hemodynamic indices ( P < 0.05). Median survival time was greater in the OMX-treated group (4.7 vs. 6.0 h, P < 0.003), and overall survival was significantly increased in the OMX-treated group (25% vs. 85%, P = 0.004). We conclude that OMX is well-tolerated and improves metabolic, hemodynamic, and survival outcomes in an ovine model of controlled hemorrhagic shock.

Macroporous resin purification of phenolics from Irish apple pomace: Chemical characterization, and cellular antioxidant and anti-inflammatory activities

Apple pomace (AP) is a highly prevalent waste product worldwide in the fruit processing sector. This study compared the chemical profile, antioxidant, and anti-inflammatory activities of crude (CE) and an extract purified using XAD-7 resin (PE). The purification process increased the total phenolic content, flavonoids, and tannins by 3.35, 40.31, and 8.87-fold, respectively. The main phenolic compounds identified in PE were phlorizin (20.54 mg/g), chlorogenic acid (10.01 mg/g), and hyperoside (2.77 mg/g). No difference was found between CE and PE in protecting human plasma against oxidation. In human erythrocytes, both CE and PE decreased the reactive oxygen species (ROS) generation and decreased lipoperoxidation. However, PE had stronger anti-inflammatory effects than CE by promoting HO-1 gene expression, suppressing NO production, and inhibiting IL-1β, IL-6, and IL-10 mRNA expression in lipopolysaccharide-challenged RAW.264.7 macrophages. Therefore, purifying apple pomace crude extract is a promising approach to boosting valuable antioxidants and anti-inflammatory phenolics.

Erythrocyte metabolism

Our aim is to present an updated overview of the erythrocyte metabolism highlighting its richness and complexity. We have manually collected and connected the available biochemical pathways and integrated them into a functional metabolic map. The focus of this map is on the main biochemical pathways consisting of glycolysis, the pentose phosphate pathway, redox metabolism, oxygen metabolism, purine/nucleoside metabolism, and membrane transport. Other recently emerging pathways are also curated, like the methionine salvage pathway, the glyoxalase system, carnitine metabolism, and the lands cycle, as well as remnants of the carboxylic acid metabolism. An additional goal of this review is to present the dynamics of erythrocyte metabolism, providing key numbers used to perform basic quantitative analyses. By synthesizing experimental and computational data, we conclude that glycolysis, pentose phosphate pathway, and redox metabolism are the foundations of erythrocyte metabolism. Additionally, the erythrocyte can sense oxygen levels and oxidative stress adjusting its mechanics, metabolism, and function. In conclusion, fine-tuning of erythrocyte metabolism controls one of the most important biological processes, that is, oxygen loading, transport, and delivery.

Methemoglobin levels in malaria: a systematic review and meta-analysis of its association with Plasmodium falciparum and Plasmodium vivax infections and disease severity

Reports indicate that Plasmodium infections influence methemoglobin levels. However, findings have been inconclusive or have varied across different geographic and demographic contexts. This systematic review and meta-analysis aimed to consolidate existing data regarding the association between Plasmodium infections and alterations in methemoglobin levels related to the severity of the infection. A comprehensive literature search of several databases, including Ovid, ProQuest, Embase, Scopus, MEDLINE, and PubMed, was conducted to identify relevant studies that examined methemoglobin levels in patients with malaria. Qualitative synthesis and meta-analysis of the pooled standardized mean difference were conducted to synthesize the differences in methemoglobin levels between: (1) patients with malaria and those without malaria and (2) patients with severe malaria and those with uncomplicated malaria based on various themes including publication year, study design, study area, Plasmodium species, age group, symptomatic status, severity status, and method of malaria detection. Of the 1846 studies that were initially identified from the main databases and additional searches on Google Scholar, 10 studies met the eligibility criteria and were selected for this review. The systematic review distinctly highlighted an association between malaria and elevated methemoglobin levels, an observation consistent across diverse geographical regions and various Plasmodium species. Furthermore, the meta-analysis confirmed this by demonstrating increased methemoglobin levels in patients with malaria compared to those without malaria (P < 0.001, Hedges' g 2.32, 95% CI 1.36-3.29, I2 97.27, 8 studies). Moreover, the meta-analysis found elevated methemoglobin levels in patients with severe malaria compared to those with uncomplicated malaria (P < 0.001, Hedges' g 2.20, 95% CI 0.82-3.58, I2 96.20, 5 studies). This systematic review and meta-analysis revealed increased methemoglobin levels in patients with P. falciparum and P. vivax infections, with a notable association between elevated methemoglobin levels and severe malaria. Future research should focus on elucidating the specific mechanisms by which changes in methemoglobin levels are related to infections by P. falciparum and P. vivax, particularly in terms of severity, and how these alterations could potentially impact patient management and treatment outcomes.

In vivo monitoring of hemoglobin derivatives in a rat thermal injury model using spectral diffuse reflectance imaging

INTRODUCTION

To demonstrate the feasibility of our previously proposed Diffuse reflectance spectral imaging (DRSI) method for in vivo monitoring of oxygenated hemoglobin, deoxygenated hemoglobin, methemoglobin, tissue oxygen saturation, and methemoglobin saturation in a rat scald burn wound model and assess whether the method could be used for differentiating the burn depth groups in rats based on the hemoglobin parameters.

METHODOLOGY

Superficial dermal burns (SDBs), deep dermal burns (DDBs), and deep burns (DBs) were induced in rat dorsal skin using a Walker-Mason method. An approach based on multiple regression analysis for spectral diffuse reflectance images aided by Monte Carlo simulations for light transport was used to quantify the hemoglobin parameters. Canonical discriminant analysis (CDA) was performed to discriminate SDB, DDB, and DB.

RESULTS

CDA using the total hemoglobin concentration, tissue oxygen saturation, and methemoglobin saturation as the independent variables showed good performance for discriminating the SDB, DDB, and DB groups immediately after burn injury and the SDB group from the DDB and DB groups 24-72 h after burn injury.

CONCLUSIONS

The DRSI method with multiple regression analysis for quantification of oxygenated hemoglobin, deoxygenated hemoglobin, and methemoglobin proved to be reliable for monitoring these hemoglobin derivatives in the rat experimental burn injury model. The parameters of tissue oxygen saturation, methemoglobin saturation, and total hemoglobin concentration are promising for the differentiating the degree of burn injury using CDA.

Pharmaceutical stability of methemoglobin-albumin cluster as an antidote for hydrogen sulfide poisoning after one-year storage in freeze-dried form

Long-term stability during storage is an important requirement for pharmaceutical preparations. The methemoglobin (metHb)-albumin cluster, in which bovine metHb is covalently enveloped with an average of three human albumin molecules, is a promising antidote for hydrogen sulfide (H2S) poisoning. In this study, we investigated the pharmaceutical stability of metHb-albumin cluster after storage for one year in solution and as freeze-dried powder. The lyophilized powder of metHb-albumin cluster stored for one year was readily reconstituted in sterile water for injection, yielding a homogeneous brown solution. Physicochemical measurements revealed that the overall structure of the metHb-albumin cluster was still maintained after preservation. Results of the pharmacological study showed that 100 % of the H2S-poisoned mice survived after treatment with the reconstituted solution of metHb-albumin cluster powder. Furthermore, the solution did not cause any toxic reactions. The antidotal efficacy of metHb-albumin cluster for H2S poisoning was preserved in freeze-dried powder form for at least one year.

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.

Can We Estimate Late-Onset Sepsis by Serial Methemoglobin Levels? An Observational Study in Preterm Neonates

Objective: To assess serial methemoglobin (MetHb) levels in preterm infants as a possible diagnostic method for late-onset sepsis (LOS). Methods: Preterm infants were assigned into two groups: those with culture-proven LOS and controls. Serial MetHb levels were measured. Results: The MetHb values of the LOS group were found to be significantly increased (p < 0.001). The cutoff value for the detection of LOS was calculated as MetHb > 1.75%, optimized for a sensitivity of 81.9% and specificity of 90%. After antimicrobial therapy, MetHb values were found to decrease significantly (p < 0.001). MetHb had an AUC of 0.810 for mortality using the calculated cutoff of >2% (p < 0.005). Conclusions: MetHb levels increase at the onset of LOS and decrease following treatment. MetHb can be added to other sepsis biomarkers as a rapid infectious process indicator for preterm neonates. MetHb > 2% is associated with LOS mortality.

Oxidative Stress in Healthy and Pathological Red Blood Cells

Red cell diseases encompass a group of inherited or acquired erythrocyte disorders that affect the structure, function, or production of red blood cells (RBCs). These disorders can lead to various clinical manifestations, including anemia, hemolysis, inflammation, and impaired oxygen-carrying capacity. Oxidative stress, characterized by an imbalance between the production of reactive oxygen species (ROS) and the antioxidant defense mechanisms, plays a significant role in the pathophysiology of red cell diseases. In this review, we discuss the most relevant oxidant species involved in RBC damage, the enzymatic and low molecular weight antioxidant systems that protect RBCs against oxidative injury, and finally, the role of oxidative stress in different red cell diseases, including sickle cell disease, glucose 6-phosphate dehydrogenase deficiency, and pyruvate kinase deficiency, highlighting the underlying mechanisms leading to pathological RBC phenotypes.

The artificial oxygen carrier erythrocruorin-characteristics and potential significance in medicine

The diminishing supply and increasing costs of donated blood have motivated research into novel hemoglobin-based oxygen carriers (HBOCs) that can serve as red blood cell (RBC) substitutes. HBOCs are versatile agents that can be used in the treatment of hemorrhagic shock. However, many of the RBC substitutes that are based on mammalian hemoglobins have presented key limitations such as instability and toxicity. In contrast, erythrocruorins (Ecs) are other types of HBOCs that may not suffer these disadvantages. Ecs are giant metalloproteins found in annelids, crustaceans, and some other invertebrates. Thus far, the Ecs of Lumbricus terrestris (LtEc) and Arenicola marina (AmEc) are the most thoroughly studied. Based on data from preclinical transfusion studies, it was found that these compounds not only efficiently transport oxygen and have anti-inflammatory properties, but also can be modified to further increase their effectiveness. This literature review focuses on the structure, properties, and application of Ecs, as well as their advantages over other HBOCs. Development of methods for both the stabilization and purification of erythrocruorin could confer to enhanced access to artificial blood resources.

Revealing a Third Dissolved-Phase Xenon-129 Resonance in Blood Caused by Hemoglobin Glycation

Hyperpolarized (HP) xenon-129 (¹²⁹Xe), when dissolved in blood, has two NMR resonances: one in red blood cells (RBC) and one in plasma. The impact of numerous blood components on these resonances, however, has not yet been investigated. This study evaluates the effects of elevated glucose levels on the chemical shift (CS) and T2* relaxation times of HP ¹²⁹Xe dissolved in sterile citrated sheep blood for the first time. HP ¹²⁹Xe was mixed with sheep blood samples premixed with a stock glucose solution using a liquid-gas exchange module. Magnetic resonance spectroscopy was performed on a 3T clinical MRI scanner using a custom-built quadrature dual-tuned ¹²⁹Xe/¹H coil. We observed an additional resonance for the RBCs (¹²⁹Xe-RBC1) for the increased glucose levels. The CS of ¹²⁹Xe-RBC1 and ¹²⁹Xe-plasma peaks did not change with glucose levels, while the CS of ¹²⁹Xe-RBC2 (original RBC resonance) increased linearly at a rate of 0.015 ± 0.002 ppm/mM with glucose level. ¹²⁹Xe-RBC1 T2* values increased nonlinearly from 1.58 ± 0.24 ms to 2.67 ± 0.40 ms. As a result of the increased glucose levels in blood samples, the novel additional HP ¹²⁹Xe dissolved phase resonance was observed in blood and attributed to the ¹²⁹Xe bound to glycated hemoglobin (HbA_1c).

Emergency treatment with intravenous infusion of methylene blue followed by oral administration in a cat presented with severe recurrent methemoglobinemia

OBJECTIVE

To describe the use of IV infusion followed by oral administration of methylene blue (MB) to successfully treat recurrent methemoglobinemia (MetHb) in a young cat.

CASE SUMMARY

A 6-month-old male Ragdoll cat presented with recurrent episodes of severe MetHb and was successfully managed with IV infusion of MB followed by a course of oral MB. Although the definitive cause of the patient's MetHb remains unknown, the cat made a full recovery following treatment without developing any significant side effects secondary to therapy and at the time of writing not had any further recurrences. Follow-up at 6 months found the patient in good health and without any long-term consequences.

NEW INFORMATION PROVIDED

To the authors' knowledge, this is the first report of a cat presented with severe MetHb quantitatively assessed via co-oximetry and successfully treated with both IV and oral administration of MB.

Isolation and identification of chlorate-reducing Hafnia sp. from milk

Chlorate has become a concern in the food and beverage sector, related to chlorine sanitizers in industrial food production and water treatment. It is of particular concern to regulatory bodies due to the negative health effects of chlorate exposure. This study investigated the fate of chlorate in raw milk and isolated bacterial strains of interest responsible for chlorate breakdown. Unpasteurized milk was demonstrated to have a chlorate-reducing capacity, breaking down enriched chlorate to undetectable levels in 11 days. Further enrichment and isolation using conditions specific to chlorate-reducing bacteria successfully isolated three distinct strains of Hafnia paralvei. Chlorate-reducing bacteria were observed to grow in a chlorate-enriched medium with lactate as an electron donor. All isolated strains were demonstrated to reduce chlorate in liquid medium; however, the exact mechanism of chlorate degradation was not definitively identified in this study.

Pharmaceutical Integrity of Lyophilized Methemoglobin-Albumin Clusters after Reconstitution

Covalent attachment of a ferric hemoglobin (metHb) core to three human serum albumin molecules to form metHb-albumin clusters has previously been used to develop an antidote for hydrogen sulfide poisoning. Lyophilization is one of the most effective approaches to preserve protein pharmaceuticals with minimum contamination and decomposition. However, there is concern that lyophilized proteins may undergo pharmaceutical alteration on reconstitution. This study investigated the pharmaceutical integrity of metHb-albumin clusters on lyophilization and reconstitution with three clinically available reconstitution fluids, (i) sterile water for injection, (ii) 0.9% sodium chloride injection, and (iii) 5% dextrose injection. The metHb-albumin clusters retained their physicochemical properties and structural integrity on lyophilization and reconstitution with sterile water for injection or 0.9% sodium chloride injection, along with comparable hydrogen sulfide scavenging ability compared to non-lyophilized metHb-albumin clusters. The reconstituted protein completely rescued lethal hydrogen sulfide poisoning in mice. On the other hand, lyophilized metHb-albumin clusters reconstituted with 5% dextrose injection showed physicochemical changes and a higher mortality rate in mice subjected to lethal hydrogen sulfide poisoning. In conclusion, lyophilization represents a potent preservation method for metHb-albumin clusters if either sterile water for injection or 0.9% sodium chloride injection is used for reconstitution.

Suicidal sodium nitrite intoxication: a case report focusing on the postmortem findings and toxicological analyses-review of the literature

Sodium nitrite (NaNO₂) is an inorganic compound that is commonly used as a preservative (E250) in the fish and meat industry. When ingested, sodium nitrite will lead to methemoglobinemia, hypotension, and arrhythmias. An increasing trend in the use of sodium nitrite as a suicide agent has been reported. In Belgium however it remains a rare phenomenon. The ingestion of sodium nitrite is not always apparent from the death scene investigation, especially in cases of covert administration or accidental ingestion. Hence, the forensic pathologist must be aware of this trend and the postmortem changes related to the ingestion of sodium nitrite to effectively identify these cases and determine the cause and manner of death. We describe a case of fatal self-poisoning following the oral ingestion of sodium nitrite with suicidal intent. Postmortem investigations showed signs of methemoglobinemia, such as a gray-brown discoloration of lividity and a chocolate brown discoloration of the blood. Postmortem toxicological investigation revealed methemoglobinemia (35%) in cardiac blood, hypernatremia (159.6 mmol/L) in vitreous humor, and the presence of nitrite in gastric contents (1.15 g/L) and, for the first time in a forensic case, in serum (38 µg/mL). A review of the existing literature regarding cases of sodium nitrite intoxications was performed to correlate these findings.

Close relationship between high HbA1c levels and methemoglobin generation in human erythrocytes: The enhancement of oxidative stress in the process

OBJECTIVE

This study aimed to investigate the effect of diabetic plasma on human red blood cells (RBCs) in order to highlight the amplification mechanisms of oxidative stress (OS) in relation to methemoglobin (metHb) production, a potential bio-indicator that could be related to diabetes disease.

RESEARCH DESIGN AND METHODS

Normal RBCs were co-incubated with the diabetic plasma of 24 patients at different HbA_1c levels, for 0, 24, and 48 h in order to assess cell turbidity and hemoglobin (Hb) stability. Hb and metHb production were quantified inside and outside RBCs. Malonaldehyde (MDA) level and cell morphology were concomitantly evaluated.

RESULTS

The cell turbidity was significantly decreased in the group co-incubated with diabetic plasma at high HbA_1c levels (0.074 ± 0.010 AU) compared to the control group (0.446 ± 0.019 AU). A significant decrease in intracellular Hb (0.390 ± 0.075 AU) and its stability (0.600 ± 0.001 AU) were revealed. Also, we found an important increase of metHb levels inside RBCs (0.186 ± 0.017 AU) and in its supernatant (0.086 ± 0.020 AU) after 48 h. Consequently, MDA absorbance increased significantly (0.320 ± 0.040 AU) in RBCs exposed to diabetic plasma with high HbA_1c.

CONCLUSION

These findings suggest that poor glycemic control in diabetes leads to metHb generation which is the main factor of the OS amplification.

Whole-blood ribonucleic acid sequencing analysis in methemoglobinemia: a case report

INTRODUCTION

Methemoglobinemia is a condition in which methemoglobin is increased and the oxygen carrying capacity of tissues is decreased, causing a lack of oxygen to the whole body. RNA (ribonucleic acid) sequencing technologies have made it possible to systematically examine how the human transcriptome responds to invasive pathologies. To our knowledge, no previous studies have reported the results of RNA sequencing in a patient with methemoglobinemia. We describe the analysis of RNAs from the whole blood of a patient with methemoglobinemia.

CASE PRESENTATION

A 31-year-old Japanese man was brought to our hospital with symptoms of dyspnea due to inhalation of gas from an acetic acid phosphonitrate storage tank at a factory. The nitrogen oxide concentration measured around the storage tank was over 2500 ppm, and he witnessed orange-brown smoke at that time. After entering the area and taking a few breaths, he suddenly became unwell, with dyspnea and numbness in his extremities. He was evacuated from the area within a few minutes, at which time he was suffering from whole-body cyanosis and was still aware of the above symptoms. On arrival at the hospital, his respiration rate was 18 breaths/minute, and his SpO₂ ranged from 80% to 85% on 15 L/minute of oxygen by mask (2.5 hours postexposure). Arterial blood gas testing revealed a methemoglobin level of 23.1%. After the administration of methylene blue, the patient's methemoglobin level normalized and his symptoms improved. Chest X-ray and chest computed tomography showed no evidence of pulmonary edema or interstitial pneumonia, and no other abnormal findings were observed. RNA sequencing was performed on the blood samples obtained at the time of the visit, with the blood sample collected on day 5 used as a control. To our knowledge, the present study is the first to describe the analysis of RNAs from the whole blood of a patient with methemoglobinemia. The RNA sequencing analysis showed that an activated "hydrogen peroxide catabolic process" may be associated with the pathogenesis of methemoglobinemia.

CONCLUSION

The results reported in the present study may explain the pathogenesis of methemoglobinemia.

Carboxyhemoglobin (COHb): Unavoidable Bystander or Protective Player?

Carbon monoxide (CO) is a cytoprotective endogenous gas that is ubiquitously produced by the stress response enzyme heme-oxygenase. Being a gas, CO rapidly diffuses through tissues and binds to hemoglobin (Hb) increasing carboxyhemoglobin (COHb) levels. COHb can be formed in erythrocytes or in plasma from cell-free Hb. Herein, it is discussed as to whether endogenous COHb is an innocuous and inevitable metabolic waste product or not, and it is hypothesized that COHb has a biological role. In the present review, literature data are presented to support this hypothesis based on two main premises: (i) there is no direct correlation between COHb levels and CO toxicity, and (ii) COHb seems to have a direct cytoprotective and antioxidant role in erythrocytes and in hemorrhagic models in vivo. Moreover, CO is also an antioxidant by generating COHb, which protects against the pro-oxidant damaging effects of cell-free Hb. Up to now, COHb has been considered as a sink for both exogenous and endogenous CO generated during CO intoxication or heme metabolism, respectively. Hallmarking COHb as an important molecule with a biological (and eventually beneficial) role is a turning point in CO biology research, namely in CO intoxication and CO cytoprotection.

Rescue Therapies for AKI in Onconephrology: Rasburicase and Glucarpidase

Tumor lysis syndrome (TLS) and high-dose methotrexate (HD MTX) toxicity can present with potentially severe complications, including acute kidney injury, in patients with malignancy. Guidelines for using rasburicase and glucarpidase as rescue therapies for TLS and HD MTX toxicity, respectively, are widely used by clinicians intending to mitigate organ toxicity and decrease morbidity and mortality as a consequence of cancer therapy. This review discusses the pathogenesis of TLS and HD MTX-associated toxicity, to understand the mechanism of action of these therapeutic agents and to review the currently available evidence supporting their use.

Cyclic iron tetra N-heterocyclic carbenes: synthesis, properties, reactivity, and catalysis

Cyclic iron tetracarbenes are an emerging class of macrocyclic iron N-heterocyclic carbene (NHC) complexes. They can be considered as an organometallic compound class inspired by their heme analogs, however, their electronic properties differ, e.g. due to the very strong σ-donation of the four combined NHCs in equatorial coordination. The ligand framework of iron tetracarbenes can be readily modified, allowing fine-tuning of the structural and electronic properties of the complexes. The properties of iron tetracarbene complexes are discussed quantitatively and correlations are established. The electronic nature of the tetracarbene ligand allows the isolation of uncommon iron(III) and iron(IV) species and reveals a unique reactivity. Iron tetracarbenes are successfully applied in C-H activation, CO₂ reduction, aziridination and epoxidation catalysis and mechanisms as well as decomposition pathways are described. This review will help researchers evaluate the structural and electronic properties of their complexes and target their catalyst properties through ligand design.

Methemoglobin-albumin clusters for cyanide detoxification

Sodium nitrite (NaNO₂) is a universal antidote for patients with cyanide poisoning. However, its use has serious drawbacks in terms of efficacy and safety. Herein, we present a promising antidote: methemoglobin (metHb)-albumin clusters. The metHb-albumin cluster is made by a metHb core wrapped by covalently bound human serum albumin. Spectral analyses proved that the metHb-albumin clusters possessed cyanide-binding properties similar to those of naked metHb. In vitro cell experiments showed that metHb-albumin clusters prevented the cyanide-induced inhibition of cytochrome c oxidase activity, resulting in a strong cytoprotective effect. In mice subjected to cyanide poisoning, metHb-albumin clusters reduced mortality and alleviated metabolic acidosis, while maintaining the activity of cytochrome c oxidase in organs; their efficacy was better than that of NaNO₂. Furthermore, the oxygen carrying capacity was maintained in poisoned mice treated with metHb-albumin clusters and was low in those treated with NaNO₂. These results indicate that metHb-albumin clusters could be a more effective and safer antidote against cyanide poisoning than NaNO₂.

Inhibition of erythrocyte's catalase, glutathione peroxidase or peroxiredoxin 2 - Impact on cytosol and membrane

Catalase (CAT), glutathione peroxidase (GPx) and Prx2 (peroxiredoxin 2) are the main antioxidant enzymatic defenses of erythrocytes. They prevent and minimize oxidative injuries in red blood cell (RBC) components, which are continuously exposed to oxidative stress (OS). The crosstalk between CAT, GPx and Prx2 is still not fully disclosed, as well as why these typically cytoplasmic enzymes bind to the RBC membrane. Our aim was to understand the interplay between CAT, GPx and Prx2 in the erythrocyte's cytosol and membrane. Under specific (partial) inhibition of each enzyme and increasing H₂O₂-induced OS conditions, we evaluated the enzyme activities and amounts, the binding of CAT, GPx and Prx2 to RBC membrane, and biomarkers of OS, such as the reduced and oxidized glutathione levels, thiobarbituric acid reactive substances (TBARS) levels, membrane bound hemoglobin and total antioxidant status. Our results support the hypothesis that when high levels of H₂O₂ get within the erythrocyte, CAT is the main player in the antioxidant protection of the cell, while Prx2 and GPx have a less striking role. Moreover, we found that CAT, appears to have more importance in the antioxidant protection of cytoplasm than of the membrane components, since when the activity of CAT is disturbed, GPx and Prx2 are both activated in the cytosol and mobilized to the membrane. In more severe OS conditions, the antioxidant activity of GPx is more significant at the membrane, as we found that GPx moves from the cytosol to the membrane, probably to protect it from lipid peroxidation.

Oxidized hemoglobin triggers polyreactivity and autoreactivity of human IgG via transfer of heme

Intravascular hemolysis occurs in diverse pathological conditions. Extracellular hemoglobin and heme have strong pro-oxidative and pro-inflammatory potentials that can contribute to the pathology of hemolytic diseases. However, many of the effects of extracellular hemoglobin and heme in hemolytic diseases are still not well understood. Here we demonstrate that oxidized hemoglobin (methemoglobin) can modify the antigen-binding characteristics of human immunoglobulins. Thus, incubation of polyclonal or some monoclonal human IgG in the presence of methemoglobin results in an appearance of binding reactivities towards distinct unrelated self-proteins, including the protein constituent of hemoglobin i.e., globin. We demonstrate that a transfer of heme from methemoglobin to IgG is indispensable for this acquisition of antibody polyreactivity. Our data also show that only oxidized form of hemoglobin have the capacity to induce polyreactivity of antibodies. Site-directed mutagenesis of a heme-sensitive human monoclonal IgG1 reveals details about the mechanism of methemoglobin-induced antigen-binding polyreactivity. Further here we assess the kinetics and thermodynamics of interaction of a heme-induced polyreactive human antibody with hemoglobin and myoglobin. Taken together presented data contribute to a better understanding of the functions of extracellular hemoglobin in the context of hemolytic diseases.

New C8-substituted caffeine derivatives as promising antioxidants and cytoprotective agents in human erythrocytes

New structurally diverse groups of C8-substituted caffeine derivatives were synthesized and evaluated for their chemical and biological properties. Mass spectrometry, FT-IR, and NMR characterizations of these derivatives were performed. The cytotoxic activity of the derivatives was estimated in vitro using human red blood cells (RBC) and in silico pharmacokinetic studies. The antioxidant capacity of the compounds was analyzed using a ferrous ion chelating activity assay. The ability of the derivatives to protect RBC from oxidative damage, including the oxidation of hemoglobin to methemoglobin, was assessed using a water-soluble 2,2'-azobis(2-methyl-propionamidine) dihydrochloride (AAPH) as a standard inducer of peroxyl radicals. The level of intracellular oxidative stress was assessed using the fluorescent redox probe 2',7'-dichlorodihydrofluorescein diacetate (DCF-DA). The results indicate that all derivatives are biocompatible compounds with significant antioxidant and cytoprotective potential dependent on their chemical structure. In order to explain the antioxidant and cytoprotective activity of the derivatives, a mechanism of hydrogen atom transfer (HAT), radical adduct formation (RAF), or single electron transfer (SET), as well as the specific interactions of the derivatives with the lipid bilayer of RBC membrane, have been proposed. The results show that selected modifications of the caffeine molecule enhance its antioxidant properties, which expands our knowledge of the structure-activity relationship of caffeine-based cytoprotective compounds.

Interactions of reactive sulfur species with metalloproteins

Reactive sulfur species (RSS) entail a diverse family of sulfur derivatives that have emerged as important effector molecules in H₂S-mediated biological events. RSS (including H₂S) can exert their biological roles via widespread interactions with metalloproteins. Metalloproteins are essential components along the metabolic route of oxygen in the body, from the transport and storage of O₂, through cellular respiration, to the maintenance of redox homeostasis by elimination of reactive oxygen species (ROS). Moreover, heme peroxidases contribute to immune defense by killing pathogens using oxygen-derived H₂O₂ as a precursor for stronger oxidants. Coordination and redox reactions with metal centers are primary means of RSS to alter fundamental cellular functions. In addition to RSS-mediated metalloprotein functions, the reduction of high-valent metal centers by RSS results in radical formation and opens the way for subsequent per- and polysulfide formation, which may have implications in cellular protection against oxidative stress and in redox signaling. Furthermore, recent findings pointed out the potential role of RSS as substrates for mitochondrial energy production and their cytoprotective capacity, with the involvement of metalloproteins. The current review summarizes the interactions of RSS with protein metal centers and their biological implications with special emphasis on mechanistic aspects, sulfide-mediated signaling, and pathophysiological consequences. A deeper understanding of the biological actions of reactive sulfur species on a molecular level is primordial in H₂S-related drug development and the advancement of redox medicine.

Advancement and Applications of Platelet-inspired Nanoparticles: A Paradigm for Cancer Targeting

Platelet-inspired nanoparticles have ignited the possibility of new opportunities for producing similar biological particulates, such as structural cellular and vesicular components, as well as various viral forms, to improve biocompatible features that could improve the nature of biocompatible elements and enhance therapeutic efficacy. The simplicity and more effortless adaptability of such biomimetic techniques uplift the delivery of the carriers laden with cellular structures, which has created varied opportunities and scope of merits like; prolongation in circulation and alleviating immunogenicity improvement of the site-specific active targeting. Platelet-inspired nanoparticles or medicines are the most recent nanotechnology-based drug targeting systems used mainly to treat blood-related disorders, tumors, and cancer. The present review encompasses the current approach of platelet-inspired nanoparticles or medicines that have boosted the scientific community from versatile fields to advance biomedical sciences. Surprisingly, this knowledge has streamlined to development of newer diagnostic methods, imaging techniques, and novel nanocarriers, which might further help in the treatment protocol of the various diseased conditions. The review primarily focuses on the novel advancements and recent patents in nanoscience and nanomedicine that could be streamlined in the future for the management of progressive cancers and tumor targeting. Rigorous technological advancements like biomimetic stem cells, pH-sensitive drug delivery of nanoparticles, DNA origami devices, virosomes, nano cells like exosomes mimicking nanovesicles, DNA nanorobots, microbots, etc., can be implemented effectively for target-specific drug delivery.

Farang (Psidium guajava L.) Dried Leaf Extracts: Phytochemical Profiles, Antioxidant, Anti-Diabetic, and Anti-Hemolytic Properties for Ruminant Health and Production

Due to its advantageous antioxidant phytochemical components, Psidium guajava L. has become an indispensable plant in pharmaceutical formulations, playing a crucial role in safeguarding human health. On ruminant animals, however, there has been limited investigation. The purpose of this investigation was to assess the phytochemical profiles and biological potential of Farang (P. guajava L.) leaf extracts for ruminant health. Methanolic and hexanoic extracts from various agricultural areas were prepared over a five-month period. By means of HPLC-DAD, vitamin C (ascorbic acid), essential oil (eugenol), tannin (gallic acid), cinnamic acids (caffeic acid, syringic acid, p-coumaric acid, sinapic acid, and ferulic acid), and flavonoids (catechin, rutin, myricetin, quercetin, apigenin, and kaempferol) were detected and quantified. Solvent type, but not cultivation site or sampling time, explained the observed variation in phytochemical profile. Phytochemicals were found in lower concentrations in hexanoic extracts than in methanolic extracts. Catechin and sinapic acid were discovered to be the two most abundant phytochemicals in the methanolic extract of Farang leaf, followed by other phenolic compounds, essential oils, and water-soluble vitamins. Compared with the methanolic extract, the hexanoic extract of Farang leaves was less effective at scavenging oxidation in terms of 1,1-diphenyl-2-picrylhydrazyl (DPPH), nitric oxide, and superoxide, and α-glucosidase inhibitory activity. Hexanoic extract was found to be less protective against oxidative damage in ruminant erythrocytes than methanolic extract in terms of inhibiting hemoglobin oxidation, lipid peroxidation, and hemolysis. According to the findings of this study, the leaves of Farang (P. guajava L.) are a potential source of phytochemical compounds with wellness properties for ruminant production.

Exploring the Phytochemical Profiles and Antioxidant, Antidiabetic, and Antihemolytic Properties of Sauropus androgynus Dried Leaf Extracts for Ruminant Health and Production

Sauropus androgynus has become an essential plant in pharmaceutical formulations due to its beneficial antioxidant phytochemical components, participating in the antioxidant defense system and playing an important role in protecting human health. However, no research has been conducted on ruminant animals. This study aimed to evaluate the phytochemical profiles and biological potential of S. androgynus leaf extracts for ruminant health. Methanolic and hexanoic extracts from each commercially and noncommercially cultivated site were prepared over the course of five consecutive months. By means of HPLC-DAD, vitamins (ascorbic acid), essential oils (eugenol), tannins (gallic acid), cinnamic acids (caffeic acid, syringic acid, p-coumaric acid, sinapic acid and ferulic acid), and flavonoids (catechin, rutin, myricetin, quercetin, apigenin, and kaempferol) were detected. Variations in phytochemical composition were depending on solvent type but not on cultivation site or sample period. Methanolic extracts contained more phytochemicals than hexanoic extracts. Ascorbic acid and rutin were discovered to be the two most abundant phytochemicals in the methanolic extract of S. androgynus leaf, followed by essential oils, cinnamic acids, and tannins. In comparison to hexanoic extract, methanolic extract of S. androgynus demonstrated to be more efficient against oxidation scavenging: 1,1-diphenyl-2-picrylhydrazyl (IC₅₀ = 13.14 ± 0.055 (mg/mL)), nitric oxide (IC₅₀ = 55.02 ± 1.338 (mg/mL)) and superoxide (IC₅₀ = 25.31 ± 0.886 (mg/mL)), as well as α-glucosidase inhibitory activity (IC₅₀ = 9.83 ± 0.032 (mg/mL)). Similarly, methanolic was found to be more protective than hexanoic against oxidative damage in ruminant erythrocytes, with IC₅₀ values (mg/mL) for hemoglobin oxidation, lipid peroxidation, and hemolysis of 11.96 ± 0.011, 13.54 ± 0.012, and 5.940 ± 0.005, respectively. These findings suggested that the leaves of S. androgynus are a prospective source of phytochemical substances with health-promoting qualities for ruminant production.

Novel insights into heme binding to hemoglobin

Under hemolytic conditions, hemoglobin and subsequently heme are rapidly released, leading to the toxic effects characterizing diseases such as β-thalassemia and sickle cell disease. Herein, we provide evidence that human hemoglobin can bind heme in a transient fashion via surface-exposed sequence motifs. Following the synthesis of potential heme-binding motifs (HBMs) as peptides, their heme-binding capacity was investigated by UV-vis spectroscopy and ranked according to their binding affinity. Heme binding to human hemoglobin was subsequently studied by UV-vis and surface plasmon resonance (SPR) spectroscopy, revealing a heme-binding affinity in the sub- to micromolar range and a stoichiometry that clearly exceeds a 1:1 ratio. In silico molecular docking and simulation studies confirmed heme binding to the respective motifs in the β-chain of hemoglobin. Finally, the peroxidase-like activity of hemoglobin and the hemoglobin-heme complex was monitored, which indicated a much higher activity (>1800%) than other heme-peptide/protein complexes reported so far. The present study provides novel insights into the nature of intact hemoglobin concerning its transient interaction with heme, which suggests for the first time potential heme-scavenging properties of the protein at concomitant disassembly and, consequently, a potentiation of hemolysis and related processes.

Chemical, Thermal, and Radiation Resistance of an Iron Porphyrin: A Model Study of Biosignature Stability

Metal complexes of porphyrins and porphyrin-type compounds are ubiquitous in all three domains of life, with hemes and chlorophylls being the best-known examples. Their diagenetic transformation products are found as geoporphyrins, in which the characteristic porphyrin core structure is retained and which can be up to 1.1 billion years old. Because of this, and their relative ease of detection, metalloporphyrins appear attractive as chemical biosignatures in the search for extraterrestrial life. In this study, we investigated the stability of solid chlorido(2,3,7,8,12,13,17,18-octaethylporphyrinato)iron(III) [FeCl(oep)], which served as a model for heme-like molecules and iron geoporphyrins. [FeCl(oep)] was exposed to a variety of astrobiologically relevant extreme conditions, namely: aqueous acids and bases, oxidants, heat, and radiation. Key results are: (1) the [Fe(oep)]⁺ core is stable over the pH range 0.0-13.5 even at 80°C; (2) the oxidizing power follows the order ClO^- > H₂O₂ > ClO₃^- > HNO₃ > ClO₄^-; (3) in an inert atmosphere, the iron porphyrin is thermally stable to near 250°C; (4) at high temperatures, carbon dioxide gas is not inert but acts as an oxidant, forming carbon monoxide; (5) a decomposition layer is formed on ultraviolet irradiation and protects the [FeCl(oep)] underneath; (6) an NaCl/NaHCO₃ salt mixture has a protective effect against X-rays; and (7) no such effect is observed when [FeCl(oep)] is exposed to iron ion particle radiation. The relevance to potential iron porphyrin biosignatures on Mars, Europa, and Enceladus is discussed.

High Doses of Inhaled Nitric Oxide as an Innovative Antimicrobial Strategy for Lung Infections

Since the designation of nitric oxide as “Molecule of the Year” in 1992, the scientific and clinical discoveries concerning this biomolecule have been greatly expanding. Currently, therapies enhancing the release of endogenous nitric oxide or the direct delivery of the exogenous compound are recognized as valuable pharmacological treatments in several disorders. In particular, the administration of inhaled nitric oxide is routinely used to treat patients with pulmonary hypertension or refractory hypoxemia. More recently, inhaled nitric oxide has been studied as a promising antimicrobial treatment strategy against a range of pathogens, including resistant bacterial and fungal infections of the respiratory system. Pre-clinical and clinical findings have demonstrated that, at doses greater than 160 ppm, nitric oxide has antimicrobial properties and can be used to kill a broad range of infectious microorganisms. This review focused on the mechanism of action and current evidence from in vitro studies, animal models and human clinical trials of inhaled high-dose nitric oxide as an innovative antimicrobial therapy for lung infections.

Asymptomatic benzocaine spray-induced methaemoglobinaemia in preoperative sedation for oesophagogastroduodenoscopy

Methaemoglobinaemia is defined as elevated methaemoglobin in the blood which is characterised by conversion of some of the reduced ferrous iron elements [Fe2+] to the oxidised ferric [Fe3+] form which does not have capacity to bind and transport oxygen resulting in functional anaemia. Causes can be genetic mutations or acquired by medications such as dapsone, nitrates or benzocaine. Benzocaine is currently being used as a topical anaesthetic agent before certain procedures. We report a case of benzocaine spray-induced methaemoglobinaemia in a patient who underwent oesophagogastroduodenoscopy for evaluation of upper gastrointestinal bleeding.

Superoxide Radicals in the Execution of Cell Death

Superoxide is a primary oxygen radical that is produced when an oxygen molecule receives one electron. Superoxide dismutase (SOD) plays a primary role in the cellular defense against an oxidative insult by ROS. However, the resulting hydrogen peroxide is still reactive and, in the presence of free ferrous iron, may produce hydroxyl radicals and exacerbate diseases. Polyunsaturated fatty acids are the preferred target of hydroxyl radicals. Ferroptosis, a type of necrotic cell death induced by lipid peroxides in the presence of free iron, has attracted considerable interest because of its role in the pathogenesis of many diseases. Radical electrons, namely those released from mitochondrial electron transfer complexes, and those produced by enzymatic reactions, such as lipoxygenases, appear to cause lipid peroxidation. While GPX4 is the most potent anti-ferroptotic enzyme that is known to reduce lipid peroxides to alcohols, other antioxidative enzymes are also indirectly involved in protection against ferroptosis. Moreover, several low molecular weight compounds that include α-tocopherol, ascorbate, and nitric oxide also efficiently neutralize radical electrons, thereby suppressing ferroptosis. The removal of radical electrons in the early stages is of primary importance in protecting against ferroptosis and other diseases that are related to oxidative stress.

Signaling Integration of Hydrogen Sulfide and Iron on Cellular Functions

Significance: Hydrogen sulfide (H₂S) is an endogenous signaling molecule, regulating numerous physiological functions from vasorelaxation to neuromodulation. Iron is a well-known bioactive metal ion, being the central component of hemoglobin for oxygen transportation and participating in biomolecule degradation, redox balance, and enzymatic actions. The interplay between H₂S and iron metabolisms and functions impacts significantly on the fate and wellness of different types of cells. Recent Advances: Iron level in vivo affects the production of H₂S via nonenzymatic reactions. On the contrary, H₂S quenches excessive iron inside the cells and regulates the redox status of iron. Critical Issues: Abnormal metabolisms of both iron and H₂S are associated with various conditions and diseases such as iron overload, anemia, oxidative stress, and cardiovascular and neurodegenerative diseases. The molecular mechanisms for the interactions between H₂S and iron are unsettled yet. Here we review signaling links of the production, metabolism, and their respective and integrative functions of H₂S and iron in normalcy and diseases. Future Directions: Physiological and pathophysiological importance of H₂S and iron as well as their therapeutic applications should be evaluated jointly, not separately. Future investigation should expand from iron-rich cells and tissues to the others, in which H₂S and iron interaction has not received due attention. Antioxid. Redox Signal. 36, 275-293.

Methaemoglobinaemia and the radical curative efficacy of 8-aminoquinoline antimalarials

Methaemoglobin results from the oxidation of ferrous to ferric iron in the centre of the haem moeity of haemoglobin. The production of dose-dependent methaemoglobinaemia by 8-aminoquinoline antimalarial drugs appears to be associated with, but is not directly linked to, therapeutic efficacy against latent Plasmodium vivax and P. ovale malarias (radical cure). Iatrogenic methaemoglobinaemia may be a useful pharmacodynamic measure in 8-aminoquinoline drug and dose optimization.

Recommendations for diagnosis and treatment of methemoglobinemia

Methemoglobinemia is a rare disorder associated with oxidization of divalent ferro‐iron of hemoglobin (Hb) to ferri‐iron of methemoglobin (MetHb). Methemoglobinemia can result from either inherited or acquired processes. Acquired forms are the most common, mainly due to the exposure to substances that cause oxidation of the Hb both directly or indirectly. Inherited forms are due either to autosomal recessive variants in the CYB5R3 gene or to autosomal dominant variants in the globin genes, collectively known as HbM disease. Our recommendations are based on a systematic literature search. A series of questions regarding the key signs and symptoms, the methods for diagnosis, the clinical management in neonatal/childhood/adulthood period, and the therapeutic approach of methemoglobinemia were formulated and the relative recommendations were produced. An agreement was obtained using a Delphi‐like approach and the experts panel reached a final consensus >75% of agreement for all the questions.

Methylene Blue-Based Nano and Microparticles: Fabrication and Applications in Photodynamic Therapy

Methylene blue (MB) has been used in the textile industry since it was first extracted by the German chemist Heinrich Caro. Its pharmacological properties have also been applied toward the treatment of certain diseases such as methemoglobinemia, ifosfamide-induced encephalopathy, and thyroid conditions requiring surgery. Recently, the utilization of MB as a safe photosensitizer in photodynamic therapy (PDT) has received attention. Recent findings demonstrate that photoactivated MB exhibits not only anticancer activity but also antibacterial activity both in vitro and in vivo. However, due to the hydrophilic nature of MB, it is difficult to create MB-embedded nano- or microparticles capable of increasing the clinical efficacy of the PDT. This review aims to summarize fabrication techniques for MB-embedded nano and microparticles and to provide both in vitro and in vivo examples of MB-mediated PDT, thereby offering a future perspective on improving this promising clinical treatment modality. We also address examples of MB-mediated PDT in both cancer and infection treatments. Both in-vitro and in-vivo studies are summarized here to document recent trends in utilizing MB as an effective photosensitizer in PDT. Lastly, we discuss how developing efficient MB-carrying nano- and microparticle platforms would be able to increase the benefits of PDT.

Long-term pharmaceutical stability of liposome-encapsulated methemoglobin as an antidote for cyanide poisoning

Liposome-encapsulated methemoglobin (metHb@Lipo) has been developed as a novel antidote for cyanide poisoning. Antidotes for lethal acute poisoning should be capable of being easily stored as ready-to-use formulations without temperature restrictions. Here, we investigated the pharmaceutical stability of the metHb@Lipo suspension after one-year storage as a ready-to-use formulation at 4 °C, room temperature (23-28 °C) and 37 °C. The liposomal integrity of metHb@Lipo was observed after one year of storage at all storage temperatures with no physicochemical change or methemoglobin leakage outside the liposome. Furthermore, the encapsulated methemoglobin remained intact without aggregation, fragmentation, denaturation, or dissociation of heme. Fresh and stored metHb@Lipo were equivalent in their binding affinity against cyanide. Moreover, all one-year stored metHb@Lipo suspensions improved the mortality rates of lethal cyanide poisoning mice comparable to fresh metHb@Lipo suspension. Additionally, all stored metHb@Lipo suspensions preserved high biocompatibility, including blood compatibility and the lack of organ toxicity. In conclusion, the metHb@Lipo suspension was a pharmaceutically stable antidote for cyanide poisoning for at least one year without any temperature restrictions.

Toxicity Assessment of Long-Term Exposure to Non-Thermal Plasma Activated Water in Mice

Non-thermal plasma activated water (PAW) has recently emerged as a powerful antimicrobial agent. Despite numerous potential bio-medical applications, studies concerning toxicity in live animals, especially after long-term exposure, are scarce. Our study aimed to assess the effects of long-term watering with PAW on the health of CD1 mice. PAW was prepared from distilled water with a GlidArc reactor according to a previously published protocol. The pH was 2.78. The mice received PAW (experimental group) or tap water (control group) daily for 90 days as the sole water source. After 90 days, the following investigations were performed on the euthanatized animals: gross necropsy, teeth mineral composition, histopathology, immunohistochemistry, hematology, blood biochemistry, methemoglobin level and cytokine profile. Mice tolerated PAW very well and no adverse effects were observed during the entire period of the experiment. Histopathological examination of the organs and tissues did not reveal any structural changes. Moreover, the expression of proliferation markers PCNA and Ki67 has not been identified in the epithelium of the upper digestive tract, indicating the absence of any pre- or neoplastic transformations. The results of our study demonstrated that long-term exposure to PAW caused no toxic effects and could be used as oral antiseptic solution in dental medicine.

Severe methemoglobinemia following intravenous lidocaine administration during coronary artery bypass surgery: The use of methylene blue and extracorporeal membrane oxygenator

A 63-year-old male patient underwent coronary artery bypass surgery under cardiopulmonary bypass. Preoperative test results were all normal. During surgery, sudden methemoglobinemia developed after the intravenous administration of lidocaine which was used to prevent arrhythmias. In the intensive care unit, methylene blue was given to the patient and an extracorporeal membrane oxygenator was used to correct deep hypotension and worsening hemodynamic parameters. However, the patient died from multiorgan failure secondary to hypoxia. In conclusion, many factors may play a role in the etiology of methemoglobinemia. Treatment options are limited. Methylene blue is used as an effective method in the treatment. Lidocaine is one of the most common drugs used in the practice of cardiology and cardiovascular surgery. Therefore, the possibility of developing methemoglobinemia should be always kept in mind.

The Role of RBC Oxidative Stress in Sickle Cell Disease: From the Molecular Basis to Pathologic Implications

Sickle cell disease (SCD) is an inherited monogenic disorder and the most common severe hemoglobinopathy in the world. SCD is characterized by a point mutation in the β-globin gene, which results in hemoglobin (Hb) S production, leading to a variety of mechanistic and phenotypic changes within the sickle red blood cell (RBC). In SCD, the sickle RBCs are the root cause of the disease and they are a primary source of oxidative stress since sickle RBC redox state is compromised due to an imbalance between prooxidants and antioxidants. This imbalance in redox state is a result of a continuous production of reactive oxygen species (ROS) within the sickle RBC caused by the constant endogenous Hb autoxidation and NADPH oxidase activation, as well as by a deficiency in the antioxidant defense system. Accumulation of non-neutralized ROS within the sickle RBCs affects RBC membrane structure and function, leading to membrane integrity deficiency, low deformability, phosphatidylserine exposure, and release of micro-vesicles. These oxidative stress-associated RBC phenotypic modifications consequently evoke a myriad of physiological changes involved in multi-system manifestations. Thus, RBC oxidative stress in SCD can ultimately instigate major processes involved in organ damage. The critical role of the sickle RBC ROS production and its regulation in SCD pathophysiology are discussed here.

Determinants of primaquine and carboxyprimaquine exposures in children and adults with Plasmodium vivax malaria

Background Primaquine is the only widely available drug for radical cure of Plasmodium vivax malaria. There is uncertainty whether the pharmacokinetic properties of primaquine are altered significantly in childhood or not. Methods Glucose-6-phosphate dehydrogenase normal patients with uncomplicated P. vivax malaria were randomized to receive either chloroquine (25mg base/kg) or dihydroartemisinin-piperaquine (dihydroartemisinin 7mg/kg and piperaquine 55mg/kg) plus primaquine; given either as 0.5 mg base/kg/day for 14 days or 1 mg/kg/day for 7 days. Pre-dose day 7 venous plasma concentrations of chloroquine, desethylchloroquine, piperaquine, primaquine and carboxyprimaquine were measured. Methemoglobin levels were measured on day 7. Results Day 7 primaquine and carboxyprimaquine concentrations were available for 641 patients. After adjustment for the primaquine mg/kg daily dose, day of sampling, partner drug, and fever clearance, there was a significant non-linear relationship between age and trough primaquine and carboxyprimaquine concentrations, and day methemoglobin levels. Compared to adults 30 years of age, children 5 years of age had trough primaquine concentrations 0.53 (95% CI: 0.39- 0.73) fold lower, trough carboxyprimaquine concentrations 0.45 (95% CI: 0.35- 0.55) fold lower, and day 7 methemoglobin levels 0.87 (95% CI: 0.58-1.27) fold lower. Increasing concentrations of piperaquine and chloroquine and poor metabolizer CYP 2D6 alleles were associated with higher day 7 primaquine and carboxyprimaquine concentrations. Higher blood methemoglobin concentrations were associated with a lower risk of recurrence. Conclusion Young children have lower primaquine and carboxyprimaquine exposures, and lower levels of methemoglobinemia, than adults. Young children may need higher weight adjusted primaquine doses than adults.

Hydrogen Sulfide Metabolite, Sodium Thiosulfate: Clinical Applications and Underlying Molecular Mechanisms

Thiosulfate in the form of sodium thiosulfate (STS) is a major oxidation product of hydrogen sulfide (H2S), an endogenous signaling molecule and the third member of the gasotransmitter family. STS is currently used in the clinical treatment of acute cyanide poisoning, cisplatin toxicities in cancer therapy, and calciphylaxis in dialysis patients. Burgeoning evidence show that STS has antioxidant and anti-inflammatory properties, making it a potential therapeutic candidate molecule that can target multiple molecular pathways in various diseases and drug-induced toxicities. This review discusses the biochemical and molecular pathways in the generation of STS from H2S, its clinical usefulness, and potential clinical applications, as well as the molecular mechanisms underlying these clinical applications and a future perspective in kidney transplantation.

Broadband diffuse optical spectroscopy of absolute methemoglobin concentration can distinguish benign and malignant breast lesions

SIGNIFICANCE

Noninvasive diffuse optical spectroscopy (DOS) is a promising adjunct diagnostic imaging technique for distinguishing benign and malignant breast lesions. Most DOS approaches require normalizing lesion biomarkers to healthy tissue since major tissue constituents exhibit large interpatient variations. However, absolute optical biomarkers are desirable as it avoids reference measurements which may be difficult or impractical to acquire.

AIM

Our goal is to determine whether absolute measurements of minor absorbers such as collagen and methemoglobin (metHb) can successfully distinguish lesions. We hypothesize that metHb would exhibit less interpatient variability and be more suitable as an absolute metric for malignancy. However, we would expect collagen to exhibit more variability, because unlike metHb, collagen is also present in the healthy tissue.

APPROACH

In this retrospective clinical study, 30 lesions with breast imaging reporting and database system score   (  BIRADS  )    >    =  3 (12 benign and 18 malignant) measured with broadband quantitative DOS were analyzed for their oxyhemoglobin (HbO), deoxyhemoglobin (HHb), water, lipids, collagen, metHb concentrations, and optical scattering characteristics. Wilcoxon rank sum test was used to compare benign and malignant lesions for all variables in both normalized and absolute forms.

RESULTS

Among all absolute DOS parameters considered, only absolute metHb was observed to be significant for lesion discrimination (0.43  ±  0.18  μM for benign versus 0.87  ±  0.32  μM for malignant, p  =  0.0002). Absolute metHb concentration was also determined to be the best predictor of malignancy with an area under the curve of 0.89.

CONCLUSIONS

Our findings demonstrate that lesion metHb concentration measured by DOS can improve noninvasive optical diagnosis of breast malignancies. Since metHb concentration found in normal breast tissue is extremely low, metHb may be a more direct indicator of malignancy that does not depend on other biomarkers found in healthy tissue with significant variability. Furthermore, absolute parameters require reduced measurement time and can be utilized in cases where healthy reference tissue is not available.

Probing Heme Active Sites of Hemoglobin in Functional Red Blood Cells Using Resonance Raman Spectroscopy

The UV–vis absorption, Raman imaging, and resonance Raman (rR) spectroscopy methods were employed to study cyanohemoglobin (HbCN) adducts inside living functional red blood cells (RBCs). The cyanide ligands are especially optically sensitive probes of the active site environment of heme proteins. The rR studies of HbCN and its isotopic analogues (¹³CN^–, C¹⁵N^–, and ¹³C¹⁵N^–), as well as a careful deconvolution of spectral data, revealed that the ν(Fe–CN) stretching, δ(Fe–CN) bending, and ν(C≡N) stretching modes occur at 454, 382, and 2123 cm^–1, respectively. Interestingly, while the ν(Fe–CN) modes exhibit the same frequencies in both the isolated and RBC-enclosed hemoglobin molecules, small frequency differences are observed in the δ(Fe–CN) bending modes and the values of their isotopic shifts. These studies show that even though the overall tilted conformation of the Fe–C≡N fragment in the isolated HbCN is preserved in the HbCN enclosed within living cells, there is a small difference in the degree of distortion of the Fe–C≡N fragment. The slight changes in the ligand geometry can be reasonably attributed to the high ordering and tight packing of Hb molecules inside RBCs.

Fatal methemoglobinemia in three suicidal sodium nitrite poisonings

Nitrites are chemicals that are abundant in the environment, widely used as preservatives for meat, and in pharmaceuticals. Volatile products containing nitrites have been used recreationally for the euphoric effect associated with mild hypoxia. Dietary exposure to small amounts is considered harmless. Deaths by ingestion of nitrite salts are not common, but accidental exposure and as suicidal and homicidal agents have been noted. Death is a consequence of oxidation of hemoglobin ferrous (Fe⁺² ) iron (Hb) to the ferric (Fe⁺³ ) form (methemoglobin, MetHb), causing a reduction in the oxygen-carrying capacity of the blood. We report three cases of ingestion of sodium nitrite in two college students (one mildly decomposed) and one adult in early middle age. All of the decedents in these cases developed fatal methemoglobinemia. Sodium nitrite in chemical form was found near the bodies. MetHb was detected in the postmortem blood of each decedent. The MetHb concentrations in the two decedents with a short postmortem interval were less than MetHb concentrations reported in the current literature. The MetHb concentrations reported in the mildly decomposed person were greater than for the other two, but still less than the concentration previously considered lethal. The data from these cases indicate that levels of MetHb can vary widely in fatal cases, and should not be used as the sole criterion for determination of a death caused by sodium nitrite. Following a discussion of the cases, there is a review of the pathophysiology of MetHb production and a current literature review.

In Vivo Transcutaneous Monitoring of Hemoglobin Derivatives Using a Red-Green-Blue Camera-Based Spectral Imaging Technique

Cyanosis is a pathological condition that is characterized by a bluish discoloration of the skin or mucous membranes. It may result from a number of medical conditions, including disorders of the respiratory system and central nervous system, cardiovascular diseases, peripheral vascular diseases, deep vein thrombosis, and regional ischemia. Cyanosis can also be elicited from methemoglobin. Therefore, a simple, rapid, and simultaneous monitoring of changes in oxygenated hemoglobin and deoxygenated hemoglobin is useful for protective strategies against organ ischemic injury. We previously developed a red-green-blue camera-based spectral imaging method for the measurements of melanin concentration, oxygenated hemoglobin concentration (C_HbO), deoxygenated hemoglobin concentration (C_HbR), total hemoglobin concentration (C_HbT) and tissue oxygen saturation (StO₂) in skin tissues. We leveraged this approach in this study and extended it to the simultaneous quantifications of methemoglobin concentration (C_metHb), C_HbO, C_HbR, and StO₂. The aim of the study was to confirm the feasibility of the method to monitor C_metHb, C_HbO, C_HbR, C_HbT, and StO₂. We performed in vivo experiments using rat dorsal skin during methemoglobinemia induced by the administration of sodium nitrite (NaNO₂) and changing the fraction of inspired oxygen (FiO₂), including normoxia, hypoxia, and anoxia. Spectral diffuse reflectance images were estimated from an RGB image by the Wiener estimation method. Multiple regression analysis based on Monte Carlo simulations of light transport was used to estimate C_HbO, C_HbR, C_metHb, C_HbT, and StO₂. C_metHb rapidly increased with a half-maximum time of less than 30 min and reached maximal values nearly 60 min after the administration of NaNO₂, whereas StO₂ dramatically dropped after the administration of NaNO₂, indicating the temporary production of methemoglobin and severe hypoxemia during methemoglobinemia. Time courses of C_HbT and StO₂, while changing the FiO₂, coincided with well-known physiological responses to hyperoxia, normoxia, and hypoxia. The results indicated the potential of this method to evaluate changes in skin hemodynamics due to loss of tissue viability and vitality.