Glutathionyl hemoglobin is elevated in iron deficiency anemia

Glutathionyl Hemoglobin and Its Emerging Role as a Clinical Biomarker of Chronic Oxidative Stress

Hemoglobin is one of the proteins that are more susceptible to S-glutathionylation and the levels of its modified form, glutathionyl hemoglobin (HbSSG), increase in several human pathological conditions. The scope of the present review is to provide knowledge about how hemoglobin is subjected to S-glutathionylation and how this modification affects its functionality. The different diseases that showed increased levels of HbSSG and the methods used for its quantification in clinical investigations will be also outlined. Since there is a growing need for precise and reliable methods for markers of oxidative stress in human blood, this review highlights how HbSSG is emerging more and more as a good indicator of severe oxidative stress but also as a key pathogenic factor in several diseases.

Changing Perspectives from Oxidative Stress to Redox Signaling-Extracellular Redox Control in Translational Medicine

Extensive research has changed the understanding of oxidative stress that has been linked to every major disease. Today we distinguish oxidative eu- and distress, acknowledging that redox modifications are crucial for signal transduction in the form of specific thiol switches. Long underestimated, reactive species and redox proteins of the Thioredoxin (Trx) family are indeed essential for physiological processes. Moreover, extracellular redox proteins, low molecular weight thiols and thiol switches affect signal transduction and cell–cell communication. Here, we highlight the impact of extracellular redox regulation for health, intermediate pathophenotypes and disease. Of note, recent advances allow the analysis of redox changes in body fluids without using invasive and expensive techniques. With this new knowledge in redox biochemistry, translational strategies can lead to innovative new preventive and diagnostic tools and treatments in life sciences and medicine.

Serum or plasma ferritin concentration as an index of iron deficiency and overload

BACKGROUND

Reference standard indices of iron deficiency and iron overload are generally invasive, expensive, and can be unpleasant or occasionally risky. Ferritin is an iron storage protein and its concentration in the plasma or serum reflects iron stores; low ferritin indicates iron deficiency, while elevated ferritin reflects risk of iron overload. However, ferritin is also an acute-phase protein and its levels are elevated in inflammation and infection. The use of ferritin as a diagnostic test of iron deficiency and overload is a common clinical practice.

OBJECTIVES

To determine the diagnostic accuracy of ferritin concentrations (serum or plasma) for detecting iron deficiency and risk of iron overload in primary and secondary iron-loading syndromes.

SEARCH METHODS

We searched the following databases (10 June 2020): DARE (Cochrane Library) Issue 2 of 4 2015, HTA (Cochrane Library) Issue 4 of 4 2016, CENTRAL (Cochrane Library) Issue 6 of 12 2020, MEDLINE (OVID) 1946 to 9 June 2020, Embase (OVID) 1947 to week 23 2020, CINAHL (Ebsco) 1982 to June 2020, Web of Science (ISI) SCI, SSCI, CPCI-exp & CPCI-SSH to June 2020, POPLINE 16/8/18, Open Grey (10/6/20), TRoPHI (10/6/20), Bibliomap (10/6/20), IBECS (10/6/20), SCIELO (10/6/20), Global Index Medicus (10/6/20) AIM, IMSEAR, WPRIM, IMEMR, LILACS (10/6/20), PAHO (10/6/20), WHOLIS 10/6/20, IndMED (16/8/18) and Native Health Research Database (10/6/20). We also searched two trials registers and contacted relevant organisations for unpublished studies.

SELECTION CRITERIA

We included all study designs seeking to evaluate serum or plasma ferritin concentrations measured by any current or previously available quantitative assay as an index of iron status in individuals of any age, sex, clinical and physiological status from any country.

DATA COLLECTION AND ANALYSIS

We followed standard Cochrane methods. We designed the data extraction form to record results for ferritin concentration as the index test, and bone marrow iron content for iron deficiency and liver iron content for iron overload as the reference standards. Two other authors further extracted and validated the number of true positive, true negative, false positive, false negative cases, and extracted or derived the sensitivity, specificity, positive and negative predictive values for each threshold presented for iron deficiency and iron overload in included studies. We assessed risk of bias and applicability using the Quality Assessment of Diagnostic Accuracy Studies (QUADAS)-2 tool. We used GRADE assessment to enable the quality of evidence and hence strength of evidence for our conclusions.

MAIN RESULTS

Our search was conducted initially in 2014 and updated in 2017, 2018 and 2020 (10 June). We identified 21,217 records and screened 14,244 records after duplicates were removed. We assessed 316 records in full text. We excluded 190 studies (193 records) with reasons and included 108 studies (111 records) in the qualitative and quantitative analysis. There were 11 studies (12 records) that we screened from the last search update and appeared eligible for a future analysis. We decided to enter these as awaiting classification. We stratified the analysis first by participant clinical status: apparently healthy and non-healthy populations. We then stratified by age and pregnancy status as: infants and children, adolescents, pregnant women, and adults. Iron deficiency We included 72 studies (75 records) involving 6059 participants. Apparently healthy populations Five studies screened for iron deficiency in people without apparent illness. In the general adult population, three studies reported sensitivities of 63% to 100% at the optimum cutoff for ferritin, with corresponding specificities of 92% to 98%, but the ferritin cutoffs varied between studies. One study in healthy children reported a sensitivity of 74% and a specificity of 77%. One study in pregnant women reported a sensitivity of 88% and a specificity of 100%. Overall confidence in these estimates was very low because of potential bias, indirectness, and sparse and heterogenous evidence. No studies screened for iron overload in apparently healthy people. People presenting for medical care There were 63 studies among adults presenting for medical care (5042 participants). For a sample of 1000 subjects with a 35% prevalence of iron deficiency (of the included studies in this category) and supposing a 85% specificity, there would be 315 iron-deficient subjects correctly classified as having iron deficiency and 35 iron-deficient subjects incorrectly classified as not having iron deficiency, leading to a 90% sensitivity. Thresholds proposed by the authors of the included studies ranged between 12 to 200 µg/L. The estimated diagnostic odds ratio was 50. Among non-healthy adults using a fixed threshold of 30 μg/L (nine studies, 512 participants, low-certainty evidence), the pooled estimate for sensitivity was 79% with a 95% confidence interval of (58%, 91%) and specificity of 98%, with a 95% confidence interval of (91%, 100%). The estimated diagnostic odds ratio was 140, a relatively highly informative test. Iron overload We included 36 studies (36 records) involving 1927 participants. All studies concerned non-healthy populations. There were no studies targeting either infants, children, or pregnant women. Among all populations (one threshold for males and females; 36 studies, 1927 participants, very low-certainty evidence): for a sample of 1000 subjects with a 42% prevalence of iron overload (of the included studies in this category) and supposing a 65% specificity, there would be 332 iron-overloaded subjects correctly classified as having iron overload and 85 iron-overloaded subjects incorrectly classified as not having iron overload, leading to a 80% sensitivity. The estimated diagnostic odds ratio was 8.

AUTHORS' CONCLUSIONS

At a threshold of 30 micrograms/L, there is low-certainty evidence that blood ferritin concentration is reasonably sensitive and a very specific test for iron deficiency in people presenting for medical care. There is very low certainty that high concentrations of ferritin provide a sensitive test for iron overload in people where this condition is suspected. There is insufficient evidence to know whether ferritin concentration performs similarly when screening asymptomatic people for iron deficiency or overload.

The Redox Potential of the β-93-Cysteine Thiol Group in Human Hemoglobin Estimated from In Vitro Oxidant Challenge Experiments

Glutathionyl hemoglobin is a minor form of hemoglobin with intriguing properties. The measurement of the redox potential of its reactive β-⁹³-Cysteine is useful to improve understanding of the response of erythrocytes to transient and chronic conditions of oxidative stress, where the level of glutathionyl hemoglobin is increased. An independent literature experiment describes the recovery of human erythrocytes exposed to an oxidant burst by measuring glutathione, glutathione disulfide and glutathionyl hemoglobin in a two-hour period. This article calculates a value for the redox potential E₀ of the β-⁹³-Cysteine, considering the erythrocyte as a closed system at equilibrium described by the Nernst equation and using the measurements of the literature experiment. The obtained value of E₀ of −121 mV at pH 7.4 places hemoglobin as the most oxidizing thiol of the erythrocyte. By using as synthetic indicators of the concentrations the electrochemical potentials of the two main redox pairs in the erythrocytes, those of glutathione–glutathione disulfide and of glutathionyl–hemoglobin, the mechanism of the recovery phase can be hypothesized. Hemoglobin acts as the redox buffer that scavenges oxidized glutathione in the oxidative phase and releases it in the recovery phase, by acting as the substrate of the NAD(P)H-cofactored enzymes.

Elevated levels of glutathionyl haemoglobin as an oxidative stress marker in patients with major depressive disorder

Background & objectives:

Oxidative stress has been implicated in the pathophysiology of major depressive disorder (MDD), but biomarkers to assess oxidative stress in patients with MDD have yielded ambiguous results. Glutathionyl haemoglobin (GS-Hb) has been reported as a stable and potential biomarker for oxidative stress in various clinical conditions. The objective of the study was to evaluate GS-Hb as a potential biomarker of oxidative stress in patients with MDD through its quantification and to compare the levels of GS-Hb in age- and gender-matched healthy controls.

Methods:

The levels of GS-Hb were estimated using liquid chromatography coupled to electrospray ionization mass spectrometry in patients diagnosed with MDD and in a subset of patients after six weeks of treatment with selective serotonin reuptake inhibitors (SSRIs).

Results:

GS-Hb levels in drug-naïve patients with MDD (n=26) were significantly elevated compared to matched healthy controls (n=17). GS-Hb levels were not significantly different between MDD patients with and without co-morbid anxiety disorders. There were no significant differences in GS-Hb levels following six weeks of treatment with SSRIs compared to baseline.

Interpretation & conclusions:

Compared to controls, GS-Hb level in patients with MDD was significantly elevated, suggestive of increased oxidative stress associated with MDD. However, six weeks of antidepressant treatment was not sufficient to modify the alterations in antioxidant/oxidant system. Further studies need to be done with a large sample of MDD patients with a longer duration of antidepressant treatment.

Structural analysis of glutathionyl hemoglobin using native mass spectrometry

Glutathionylation is an example of reversible post-translation modification of proteins where free and accessible cysteine residues of proteins undergo thiol-disulfide exchange with oxidized glutathione (GSSG). In general, glutathionylation occurs under the condition of elevated oxidative stress in vivo. In human hemoglobin, Cys93 residue of β globin chain was found to undergo this oxidative modification. Glutathionyl hemoglobin (GSHb) was reported to act as a biomarker of oxidative stress under several clinical conditions such as chronic renal failure, iron deficiency anemia, hyperlipidemia, diabetes mellitus, Friedreich's ataxia, atherosclerosis. Previously we showed that the functional abnormality associated with six-fold tighter oxygen binding of GSHb supposedly attributed to the conformational transition of the deoxy state of GSHb towards oxy hemoglobin like conformation. In the present study, we investigated the structural integrity and overall architecture of the quaternary structure of GSHb using native mass spectrometry and ion mobility mass spectrometry platforms. The dissociation equilibrium constants of both tetramer/dimer (K_d1) and dimer/monomer equilibrium (K_d2) was observed to increase by 1.91 folds and 3.64 folds respectively. However, the collision cross-section area of the tetrameric hemoglobin molecule remained unchanged upon glutathionylation. The molecular dynamics simulation data of normal human hemoglobin and GSHb was employed to support our experimental findings.

Characterization of residue-specific glutathionylation of CSF proteins in multiple sclerosis - A MS-based approach

Reduction of a disulfide linkage between cysteine residues in proteins, a standard step in the preanalytical preparation of samples in conventional proteomics approach, presents a challenge to characterize S-glutathionylation of proteins. S-glutathionylation of proteins has been reported in medical conditions associated with high oxidative stress. In the present study, we attempted to characterize glutathionylation of CSF proteins in patients with multiple sclerosis which is associated with high oxidative stress. Using the nano-LC/ESI-MS platform, we adopted a modified proteomics approach and a targeted database search to investigate glutathionylation at the residue level of CSF proteins. Compared to patients with Intracranial hypertension, the following CSF proteins: Extracellular Superoxide dismutase (ECSOD) at Cys195, α1-antitrypsin (A1AT) at Cys232, Phospholipid transfer protein (PLTP) at Cys318, Alpha-2-HS-glycoprotein at Cys340, Ectonucleotide pyrophosphate (ENPP-2) at Cys773, Gelsolin at Cys304, Interleukin-18 (IL-18) at Cys38 and Ig heavy chain V III region POM at Cys22 were found to be glutathionylated in patients with multiple sclerosis during a relapse. ECSOD, A1AT, and PLTP were observed to be glutathionylated at the functionally important cysteine residues. In conclusion, in the present study using a modified proteomics approach we have identified and characterized glutathionylation of CSF proteins in patients with multiple sclerosis.

Assessment of Cysteine Reactivity of Human Hemoglobin at Its Residue Level: A Mass Spectrometry-Based Approach

In general, the reactivity of cysteine residues of proteins is measured by 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB) kinetics using spectrophotometry. Proteins with several cysteine residues may exhibit varying DTNB kinetics but residue level information can only be obtained with the prior knowledge of their three-dimensional structure. However, this method is limited in its application to the proteins containing chromophores having overlapping absorption profile with 2-nitro-5-thiobenzoic acid, such as hemoglobin (Hb). Additionally, this method is incapable of assigning cysteine reactivity at the residue levels of proteins with unknown crystal structures. However, a mass spectrometry (MS)-based platform might provide a solution to these problems. In the present study, alkylation kinetics of cysteine residues of adult human Hb (Hb A; α₂β₂) and sickle cell Hb (Hb S; HBB: c.20A>T) were investigated using matrix-assisted laser desorption/ionization (MALDI) MS. Differential site-specific reactivities of cysteine residues of Hb were investigated using alkylation kinetics with iodoacetamide (IAM). The observed reactivities corroborated well with the differential surface accessibilities of cysteine residues in the crystal structures of human Hb. The proposed method might be used to investigate cysteine reactivities of all the genetic and post-translational variants of Hb discovered to date. In addition, this method can be extended to explore cysteine reactivities of proteins, irrespective of the presence of chromophores and availability of crystal structures.