Hypoxia-induced post-translational changes in red blood cell protein map of newborns

Metabolite and protein shifts in mature erythrocyte under hypoxia

As the only cell type responsible for oxygen delivery, erythrocytes play a crucial role in supplying oxygen to hypoxic tissues, ensuring their normal functions. Hypoxia commonly occurs under physiological or pathological conditions, and understanding how erythrocytes adapt to hypoxia is fundamental for exploring the mechanisms of hypoxic diseases. Additionally, investigating acute and chronic mountain sickness caused by plateaus, which are naturally hypoxic environments, will aid in the study of hypoxic diseases. In recent years, increasingly developed proteomics and metabolomics technologies have become powerful tools for studying mature enucleated erythrocytes, which has significantly contributed to clarifying how hypoxia affects erythrocytes. The aim of this article is to summarize the composition of the cytoskeleton and cytoplasmic proteins of hypoxia-altered erythrocytes and explore the impact of hypoxia on their essential functions. Furthermore, we discuss the role of microRNAs in the adaptation of erythrocytes to hypoxia, providing new perspectives on hypoxia-related diseases.

Atomic Force Microscopy and High-Resolution Spectrophotometry for Study of Anoxemia and Normoxemia in Model Experiment In Vitro

The oxygen content in the blood may decrease under the influence of various physicochemical factors and different diseases. The state of hypoxemia is especially dangerous for critically ill patients. In this paper, we describe and analyze the changes in the characteristics of red blood cells (RBCs) with decreasing levels of oxygen in the RBC suspension from normoxemia to hypoxemia/anoxemia in an in vitro model experiment. The RBCs were stored in hypoxemia/anoxemia and normoxemia conditions in closed and open tubes correspondingly. For the quantitative study of RBC parameter changes, we used atomic force microscopy, digital spectrophotometry, and nonlinear curve fitting of the optical spectra. In both closed and open tubes, at the end of the storage period by day 29, only 2% of discocytes remained, and mainly irreversible types, such as microspherocytes and ghosts, were observed. RBC hemolysis occurred at a level of 25-30%. Addition of the storage solution, depending on the concentration, changed the influence of hypoxemia on RBCs. The reversibility of the change in hemoglobin derivatives was checked. Based on the experimental data and model approach, we assume that there is an optimal level of hypoxemia at which the imbalance between the oxidative and antioxidant systems, the rate of formation of reactive oxygen species, and, accordingly, the disturbances in RBCs, will be minimal.

In vitro assay for single-cell characterization of impaired deformability in red blood cells under recurrent episodes of hypoxia

Red blood cells (RBCs) are subjected to recurrent changes in shear stress and oxygen tension during blood circulation. The cyclic shear stress has been identified as an important factor that alone can weaken cell mechanical deformability. The effects of cyclic hypoxia on cellular biomechanics have yet to be fully investigated. As the oxygen affinity of hemoglobin plays a key role in the biological function and mechanical performance of RBCs, the repeated transitions of hemoglobin between its R (high oxygen tension) and T (low oxygen tension) states may impact their mechanical behavior. The present study focuses on developing a novel microfluidic-based assay for characterization of the effects of cyclic hypoxia on cell biomechanics. The capability of this assay is demonstrated by a longitudinal study of individual RBCs in health and sickle cell disease subjected to cyclic hypoxia conditions of various durations and levels of low oxygen tension. The viscoelastic properties of cell membranes are extracted from tensile stretching and relaxation processes of RBCs induced by the electrodeformation technique. Results demonstrate that cyclic hypoxia alone can significantly reduce cell deformability, similar to the fatigue damage accumulated through cyclic mechanical loading. RBCs affected by sickle cell disease are less deformable (significantly higher membrane shear modulus and viscosity) than normal RBCs. The fatigue resistance of sickle RBCs to the cyclic hypoxia challenge is significantly inferior to that of normal RBCs, and this trend is more significant in mature erythrocytes of sickle cells. When the oxygen affinity of sickle hemoglobin is enhanced by anti-sickling drug treatment of 5-hydroxymethyl-2-furfural (5-HMF), sickle RBCs show ameliorated resistance to fatigue damage induced by cyclic hypoxia. These results indicate an important biophysical mechanism underlying RBC senescence in which the cyclic hypoxia challenge alone can lead to mechanical degradation of the RBC membrane. We envision that the application of this assay can be further extended to RBCs in other blood diseases and other cell types.

Biomarkers of oxidative stress in the fetus and in the newborn

The dynamic field of perinatology entails ever-increasing search for molecular mechanisms of neonatal diseases, especially in the domain of fetal growth and neurodevelopmental outcome. There is an urgent need for new molecular biomarkers, to early identify newborn at high risk for developing diseases and to provide new treatment targets. The interest in biomarkers of oxidative stress in perinatal period have begun to grow in the last century, when it was evidenced the importance of the free radicals generation underlying the various disease conditions. To date, interesting researches have been carried out, representing milestones for implementation of oxidative stress biomarkers in perinatal medicine. Use of a panel of "oxidative stress biomarkers", particularly non protein bound iron, advanced oxidative protein products and isoprostanes, may provide valuable information regarding functional pathways underlying free radical mediated diseases of newborns and their early identification and prevention. Here, we will review recent advances and the current knowledge on the application of biomarkers of oxidative stress in neonatal/perinatal medicine including novel biomarker discovery, defining yet unrecognized biologic therapeutic targets, and linking of oxidative stress biomarkers to relevant standard indices and long-term outcomes.

Oxidative Stress as a Physiological Pain Response in Full-Term Newborns

This research paper aims to investigate if oxidative stress biomarkers increase after a painful procedure in term newborns and if nonpharmacological approaches, or sex, influence pain degree, and the subsequent OS. 83 healthy term newborns were enrolled to receive 10% oral glucose or sensorial saturation (SS) for analgesia during heel prick (HP). The ABC scale was used to score the pain. Advanced oxidation protein products (AOPP) and total hydroperoxides (TH) as biomarkers of OS were measured at the beginning (early-sample) and at the end (late-sample) of HP. The early-sample/late-sample ratio for AOPP and TH was used to evaluate the increase in OS biomarkers after HP. Higher levels of both AOPP and TH ratio were observed in high degree pain (4–6) compared with low degree pain score (0–3) (AOPP: p = 0.049; TH: p = 0.001). Newborns receiving SS showed a significantly lower pain score (p = 0.000) and AOPP ratio levels (p = 0.021) than those without. Males showed higher TH levels at the end of HP (p = 0.005) compared to females. The current study demonstrates that a relationship between pain degree and OS exists in healthy full-term newborns. The amount of OS is gender related, being higher in males. SS reduces pain score together with pain-related OS in the newborns.

Plasma Biomarkers of Oxidative Stress in Neonatal Brain Injury

Perinatal encephalopathy is a leading cause of lifelong disability. Increasing evidence indicates that the pathogenesis of perinatal brain damage is much more complex than originally thought, with multiple pathways involved. An important role of oxidative stress (OS) in the pathogenesis of brain injury is recognized for preterm and term infants. This article examines potential reliable and specific OS biomarkers that can be used in premature and term infants for the early detection and follow-up of the most common neonatal brain injuries, such as hypoxic-ischemic encephalopathy, intraventricular hemorrhage, and periventricular leukomalacia. The next step will be to explore the correlation between brain-specific OS biomarkers and functional brain outcomes.

Nitrosothiol formation and protection against Fenton chemistry by nitric oxide-induced dinitrosyliron complex formation from anoxia-initiated cellular chelatable iron increase

Dinitrosyliron complexes (DNIC) have been found in a variety of pathological settings associated with (•)NO. However, the iron source of cellular DNIC is unknown. Previous studies on this question using prolonged (•)NO exposure could be misleading due to the movement of intracellular iron among different sources. We here report that brief (•)NO exposure results in only barely detectable DNIC, but levels increase dramatically after 1-2 h of anoxia. This increase is similar quantitatively and temporally with increases in the chelatable iron, and brief (•)NO treatment prevents detection of this anoxia-induced increased chelatable iron by deferoxamine. DNIC formation is so rapid that it is limited by the availability of (•)NO and chelatable iron. We utilize this ability to selectively manipulate cellular chelatable iron levels and provide evidence for two cellular functions of endogenous DNIC formation, protection against anoxia-induced reactive oxygen chemistry from the Fenton reaction and formation by transnitrosation of protein nitrosothiols (RSNO). The levels of RSNO under these high chelatable iron levels are comparable with DNIC levels and suggest that under these conditions, both DNIC and RSNO are the most abundant cellular adducts of (•)NO.

Antioxidant strategies and respiratory disease of the preterm newborn: an update

Preterm newborns are challenged by an excessive oxidative burden, as a result of several perinatal stimuli, as intrauterine infections, resuscitation, mechanical ventilation, and postnatal complications, in the presence of immature antioxidant capacities. "Oxygen radical disease of neonatology" comprises a wide range of conditions sharing a common pathway of pathogenesis and includes bronchopulmonary dysplasia (BPD) and other main complications of prematurity. Antioxidant strategies may be beneficial in the prevention and treatment of oxidative stress- (OS-) related lung disease of the preterm newborn. Endotracheal supplementation or lung-targeted overexpression of superoxide dismutase was proved to reduce lung damage in several models; however, the supplementation in preterm newborn failed to reduce the risk of BPD, although long-term respiratory outcomes were improved. Also melatonin administration to small cohorts of preterm newborns suggested beneficial effects on lung OS. The possibility to identify single nucleotide polymorphism affecting the risk of BPD may help to identify specific populations with particularly high risk of OS-related diseases and may pose the basis for individually targeted treatments. Finally, surfactant replacement may lead to local anti-inflammatory and antioxidant effects, thanks to specific enzymatic and nonenzymatic antioxidants naturally present in animal surfactants.

Irreversible inactivation of glutathione peroxidase 1 and reversible inactivation of peroxiredoxin II by H2O2 in red blood cells

Catalase, glutathione peroxidase1 (GPx1), and peroxiredoxin (Prx) II are the principal enzymes responsible for peroxide elimination in RBC. We have now evaluated the relative roles of these enzymes by studying inactivation of GPx1 and Prx II in human RBCs. Mass spectrometry revealed that treatment of GPx1 with H(2)O(2) converts the selenocysteine residue at its active site to dehydroalanine (DHA). We developed a blot method for detection of DHA-containing proteins, with which we observed that the amount of DHA-containing GPx1 increases with increasing RBC density, which is correlated with increasing RBC age. Given that the conversion of selenocysteine to DHA is irreversible, the content of DHA-GPx1 in each RBC likely reflects total oxidative stress experienced by the cell during its lifetime. Prx II is inactivated by occasional hyperoxidation of its catalytic cysteine to cysteine sulfinic acid during catalysis. We believe that the activity of sulfiredoxin in RBCs is sufficient to counteract the hyperoxidation of Prx II that occurs in the presence of the basal level of H(2)O(2) flux resulting from hemoglobin autoxidation. If the H(2)O(2) flux is increased above the basal level, however, the sulfinic Prx II begins to accumulate. In the presence of an increased H(2)O(2) flux, inhibition of catalase accelerated the accumulation of sulfinic Prx II, indicative of the protective role of catalase.

Peroxiredoxin 2 and peroxide metabolism in the erythrocyte

Peroxiredoxin 2 (Prx2) is an antioxidant enzyme that uses cysteine residues to decompose peroxides. Prx2 is the third most abundant protein in erythrocytes, and competes effectively with catalase and glutathione peroxidase to scavenge low levels of hydrogen peroxide, including that derived from hemoglobin autoxidation. Low thioredoxin reductase activity in the erythrocyte is able to keep up with this basal oxidation and maintain the Prx2 in its reduced form, but exposure to exogenous hydrogen peroxide causes accumulation of the disulfide-linked dimer. The high cellular concentration means that although turnover is slow, erythrocyte Prx2 can act as a noncatalytic scavenger of hydrogen peroxide and a sink for hydrogen peroxide before turnover becomes limiting. The consequences of Prx2 oxidation for the erythrocyte are not well characterized, but mice deficient in this protein develop severe hemolytic anemia associated with Heinz body formation. Prx2, also known as calpromotin, regulates ion transport by associating with the membrane and activating the Gárdos channel. How Prx2 redox transformations are linked to membrane association and channel activation is yet to be established. In this review, we discuss the functional properties of Prx2 and its role as a major component of the erythrocyte antioxidant system.