Morphological changes and oxidative damage in Rett Syndrome erythrocytes

Molecular Mechanisms of Rett Syndrome: Emphasizing the Roles of Monoamine, Immunity, and Mitochondrial Dysfunction

Rett syndrome (RTT), which predominantly affects females, arises in most cases from mutations in the Methyl-CpG-binding Protein-2 (MECP2) gene. When MeCP2 is impaired, it disrupts the regulation of numerous genes, causing the production of dysfunctional proteins associated with various multi-systemic issues in RTT. In this review, we explore the current insights into molecular signaling related to monoamines, immune response, and mitochondrial function, and their implications for the pathophysiology of RTT. Research has shown that monoamines-such as dopamine, norepinephrine, epinephrine, serotonin, and histamine-exhibit alterations in RTT, contributing to a range of neurological symptoms. Furthermore, the immune system in RTT individuals demonstrates dysfunction through the abnormal activity of microglia, macrophages, lymphocytes, and non-immune cells, leading to the atypical release of inflammatory mediators and disruptions in the NF-κB signaling pathway. Moreover, mitochondria, essential for energy production and calcium storage, also show dysfunction in this condition. The delicate balance of producing and scavenging reactive oxygen species-termed redox balance-is disrupted in RTT. Targeting these molecular pathways presents a promising avenue for developing effective therapies.

A novel mini-invasive finger-prick protocol for preparing blood micro-samples for morphological analysis of human erythrocytes by scanning electron microscopy

Here we describe the development and optimization of a new protocol for the preparation and surface imaging by scanning electron microscope of human erythrocytes from blood micro-samples obtained by finger prick. By testing several key pre-analytical conditions for blood sampling, erythrocyte preservation, storage and imaging, we designed a rapid new minimally-invasive reproducible method for obtaining uniform deposition of an adequate number of erythrocytes with well-preserved morphology on a substrate. The possibility of obtaining reliable reproducible high resolution morphometric data on peripheral erythrocytes makes this protocol valuable for diagnostic and basic research purposes.

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.

Breathing Abnormalities During Sleep and Wakefulness in Rett Syndrome: Clinical Relevance and Paradoxical Relationship With Circulating Pro-oxidant Markers

Background

Breathing abnormalities are common in Rett syndrome (RTT), a pervasive neurodevelopmental disorder almost exclusively affecting females. RTT is linked to mutations in the methyl-CpG-binding protein 2 (MeCP2) gene. Our aim was to assess the clinical relevance of apneas during sleep-wakefulness cycle in a population with RTT and the possible impact of apneas on circulating oxidative stress markers.

Methods

Female patients with a clinical diagnosis of typical RTT (n = 66), MECP2 gene mutation, and apneas were enrolled (mean age: 12.5 years). Baseline clinical severity, arterial blood gas analysis, and red blood cell count were assessed. Breathing was monitored during the wakefulness and sleep states (average recording time: 13 ± 0.5 h) with a portable polygraphic screening device. According to prevalence of breath holdings, the population was categorized into the wakefulness apnea (WA) and sleep apnea (SA) groups, and apnea-hypopnea index (AHI) was calculated. The impact of respiratory events on oxidative stress was assessed by plasma and intra-erythrocyte non-protein-bound iron (P-NPBI and IE-NPBI, respectively), and plasma F2-isoprostane (F2-IsoP) assays.

Results

Significant prevalence of obstructive apneas with values of AHI > 15 was present in 69.7% of the population with RTT. The group with SA showed significantly increased AHI values > 15 (p = 0.0032), total breath holding episodes (p = 0.007), and average SpO2 (p = 0.0001) as well as lower nadir SpO2 (p = 0.0004) compared with the patients with WAs. The subgroups of patients with WA and SA showed no significant differences in arterial blood gas analysis variables (p > 0.089). Decreased mean cell hemoglobin (MCH) (p = 0.038) was observed in the group with WAs. P-NPBI levels were significantly higher in the group with WA than in that with SAs (p = 0.0001). Stepwise multiple linear regression models showed WA being related to nadir SpO2, average SpO2, and P-NPBI (adjusted R2 = 0.613, multiple correlation coefficient = 0.795 p < 0.0001), and P-NPBI being related to average SpO2, blood PaCO2, red blood cell mean corpuscular volume (MCV), age, and topiramate treatment (adjusted R2 = 0.551, multiple correlation coefficient = 0.765, p < 0.0001).

Conclusion

Our findings indicate that the impact of apneas in RTT is uneven according to the sleep-wakefulness cycle, and that plasma redox active iron represents a potential novel therapeutic target.

Topological Relationships Cytoskeleton-Membrane Nanosurface-Morphology as a Basic Mechanism of Total Disorders of RBC Structures

The state of red blood cells (RBCs) and their functional possibilities depend on the structural organization of the membranes. Cell morphology and membrane nanostructure are compositionally and functionally related to the cytoskeleton network. In this work, the influence of agents (hemin, endogenous oxidation during storage of packed RBCs, ultraviolet (UV) radiation, temperature, and potential of hydrogen (pH) changes) on the relationships between cytoskeleton destruction, membrane nanostructure, and RBC morphology was observed by atomic force microscope. It was shown that the influence of factors of a physical and biochemical nature causes structural rearrangements in RBCs at all levels of organization, forming a unified mechanism of disturbances in relationships “cytoskeleton-membrane nanosurface-cell morphology”. Filament ruptures and, consequently, large cytoskeleton pores appeared. The pores caused membrane topological defects in the form of separate grain domains. Increasing loading doses led to an increase in the number of large cytoskeleton pores and defects and their fusion at the membrane nanosurfaces. This caused the changes in RBC morphology. Our results can be used in molecular cell biology, membrane biophysics, and in fundamental and practical medicine.

Morphometry and Stiffness of Red Blood Cells—Signatures of Neurodegenerative Diseases and Aging

Human red blood cells (RBCs) are unique cells with the remarkable ability to deform, which is crucial for their oxygen transport function, and which can be significantly altered under pathophysiological conditions. Here we performed ultrastructural analysis of RBCs as a peripheral cell model, looking for specific signatures of the neurodegenerative pathologies (NDDs)—Parkinson’s disease (PD), amyotrophic lateral sclerosis (ALS) and Alzheimer’s disease (AD), utilizing atomic force (AFM) and conventional optical (OM) microscopy. We found significant differences in the morphology and stiffness of RBCs isolated from patients with the selected NDDs and those from healthy individuals. Neurodegenerative pathologies’ RBCs are characterized by a reduced abundance of biconcave discoid shape, lower surface roughness and a higher Young’s modulus, compared to healthy cells. Although reduced, the biconcave is still the predominant shape in ALS and AD cells, while the morphology of PD is dominated by crenate cells. The features of RBCs underwent a marked aging-induced transformation, which followed different aging pathways for NDDs and normal healthy states. It was found that the diameter, height and volume of the different cell shape types have different values for NDDs and healthy cells. Common and specific morphological signatures of the NDDs were identified.

The Alteration of Chloride Homeostasis/GABAergic Signaling in Brain Disorders: Could Oxidative Stress Play a Role?

In neuronal precursors and immature neurons, the depolarizing (excitatory) effect of γ-Aminobutyric acid (GABA) signaling is associated with elevated [Cl⁻]_i; as brain cells mature, a developmental switch occurs, leading to the decrease of [Cl⁻]_i and to the hyperpolarizing (inhibitory) effect of GABAergic signaling. [Cl⁻]_i is controlled by two chloride co-transporters: NKCC1, which causes Cl⁻ to accumulate into the cells, and KCC2, which extrudes it. The ontogenetic upregulation of the latter determines the above-outlined switch; however, many other factors contribute to the correct [Cl⁻]_i in mature neurons. The dysregulation of chloride homeostasis is involved in seizure generation and has been associated with schizophrenia, Down’s Syndrome, Autism Spectrum Disorder, and other neurodevelopmental disorders. Recently, much effort has been put into developing new drugs intended to inhibit NKCC1 activity, while no attention has been paid to the origin of [Cl⁻]_i dysregulation. Our study examines the pathophysiology of Cl⁻ homeostasis and focuses on the impact of oxidative stress (OS) and inflammation on the activity of Cl⁻ co-transporters, highlighting the relevance of OS in numerous brain abnormalities and diseases. This hypothesis supports the importance of primary prevention during pregnancy. It also integrates the therapeutic framework addressed to restore normal GABAergic signaling by counteracting the alteration in chloride homeostasis in central nervous system (CNS) cells, aiming at limiting the use of drugs that potentially pose a health risk.

Metabolic Signatures Differentiate Rett Syndrome From Unaffected Siblings

Rett syndrome (RTT, OMIM 312750), a severe neurodevelopmental disorder characterized by regression with loss of spoken language and hand skills, development of characteristic hand stereotypies, and gait dysfunction, is primarily caused by de novo mutations in the X-linked gene Methyl-CpG-binding protein 2 (MECP2). Currently, treatment options are limited to symptomatic management, however, reversal of disease phenotype is possible in mouse models by restoration of normal MECP2 gene expression. A significant challenge is the lack of biomarkers of disease state, disease severity, or treatment response. Using a non-targeted metabolomic approach we evaluated metabolite profiles in plasma from thirty-four people with RTT compared to thirty-seven unaffected age- and gender-matched siblings. We identified sixty-six significantly altered metabolites that cluster broadly into amino acid, nitrogen handling, and exogenous substance pathways. RTT disease metabolite and metabolic pathways abnormalities point to evidence of oxidative stress, mitochondrial dysfunction, and alterations in gut microflora. These observed changes provide insight into underlying pathological mechanisms and the foundation for biomarker discovery of disease severity biomarkers.

Effects of oral administration of common antioxidant supplements on the energy metabolism of red blood cells. Attenuation of oxidative stress-induced changes in Rett syndrome erythrocytes by CoQ10

Nutritional supplements are traditionally employed for overall health and for managing some health conditions, although controversies are found concerning the role of antioxidants-mediated benefits in vivo. Consistently with its critical role in systemic redox buffering, red blood cell (RBC) is recognized as a biologically relevant target to investigate the effects of oxidative stress. In RBC, reduction of the ATP levels and adenylate energy charge brings to disturbance in intracellular redox status. In the present work, several popular antioxidant supplements were orally administrated to healthy adults and examined for their ability to induce changes on the energy metabolism and oxidative status in RBC. Fifteen volunteers (3 per group) were treated for 30 days per os with epigallocatechin gallate (EGCG) (1 g green tea extract containing 50% EGCG), resveratrol (325 mg), coenzyme Q10 (CoQ10) (300 mg), vitamin C (1 g), and vitamin E (400 U.I.). Changes in the cellular levels of high-energy compounds (i.e., ATP and its catabolites, NAD and GTP), GSH, GSSG, and malondialdehyde (MDA) were simultaneously analyzed by ion-pairing HPLC. Response to oxidative stress was further investigated through the oxygen radical absorptive capacity (ORAC) assay. According to our experimental approach, (i) CoQ10 appeared to be the most effective antioxidant inducing a high increase in ATP/ADP, ATP/AMP, GSH/GSSG ratio and ORAC value and, in turn, a reduction of NAD concentration, (ii) EGCG modestly modulated the intracellular energy charge potential, while (iii) Vitamin E, vitamin C, and resveratrol exhibited very weak effects. Given that, the antioxidant potential of CoQ10 was additionally assessed in a pilot study which considered individuals suffering from Rett syndrome (RTT), a severe X-linked neuro-developmental disorder in which RBC oxidative damages provide biological markers for redox imbalance and chronic hypoxemia. RTT patients (n = 11), with the typical clinical form, were supplemented for 12 months with CoQ10 (300 mg, once daily). Level of lipid peroxidation (MDA production) and energy state of RBCs were analyzed at 2 and 12 months. Our data suggest that CoQ10 may significantly attenuate the oxidative stress-induced damage in RTT erythrocytes.

13-HODE, 9-HODE and ALOX15 as potential players in Rett syndrome OxInflammation

Mutations in the MECP2 gene are the main cause of Rett syndrome (RTT), a pervasive neurodevelopmental disorder, that shows also multisystem disturbances associated with a metabolic component. The aim of this study was to investigate whether an increased production of oxidized linoleic acid metabolites, specifically 9- and 13-hydroxyoctadecadienoic acids (HODEs), can contribute to the altered the redox and immune homeostasis, suggested to be involved in RTT. Serum levels of 9- and 13-HODEs were elevated in RTT and associated with the expression of arachidonate 15-Lipoxygenase (ALOX15) in peripheral blood mononuclear cells (PBMCs). Omega-3 polyunsaturated fatty acids supplementation has shown to lower HODEs levels in RTT. Statistically significant correlation was demonstrated between the increased plasma HODEs levels and the lipoprotein-associated phospholipase A2 (Lp-PLA2) activity. Collectively, these findings reinforce the concept of the key role played by lipid peroxidation in RTT, and the possible ability of omega-3 polyunsaturated fatty acids supplementation in improving the oxinflammation status in RTT.

Antioxidant Effects of Baoyuan Decoction on Dysfunctional Erythrocytes in High-Fat Diet-Induced Hyperlipidemic ApoE-/- Mice

Baoyuan decoction (BYD), a traditional representative formula, has a long usage history in the treatment of cardiovascular diseases. Since the hyperlipidemia-induced dysfunction of erythrocyte is one of the most important causes of cardiovascular diseases, the improving effects of BYD against high-fat diet (HFD) induced the physiological and physical function of the erythrocytic injury and the potential mechanisms were deeply researched in this study. After 6 weeks of drug treatment, all doses of BYD had significantly decreased the lipid peroxidation in plasma of HFD-induced ApoE^−/− mice, even if it had not improved the lipid levels. Then, the erythrocyte-related experimental results showed that BYD had reduced erythrocyte osmotic fragility, stabilized erythrocyte membrane skeleton protein 4.2, and reformed the erythrocyte morphological changes by decreasing erythrocyte membrane lipid peroxidation levels. This study demonstrated that BYD may ameliorate the physiological and physical function of erythrocyte in hyperlipidemic mice through the antioxidant effect on erythrocyte membranes.

Mitochondrial Electron Transport Chain Complex Dysfunction in MeCP2 Knock-Down Astrocytes: Protective Effects of Quercetin Hydrate

Astrocytes play the central role in CNS metabolism to support neuronal functions. Mehyl-CpG-binding protein 2 (MeCP2) is the global transcription factor with differential expression in neuronal and non-neuronal cells. MeCP2 mutation and downstream detrimental effects have been reported in astrocytes also in MeCP2-associated neurodevelopmental disorder-Rett syndrome. Several studies have shown mitochondrial impairment linked to ROS production and reduced ATP synthesis in Rett patients and models, but consequences of MeCP2 deficiency on mitochondrial electron transport chain complexes in astrocytes and effect of known antioxidant quercetin aglycone has not yet been reported. The present study aimed to investigate effect of quercetin on mitochondrial functioning in MeCP2-deficient astrocytes. Our data show onefold upregulated Uqcrc1 and Ndufv2 gene expression, subtle change in protein expression, and significantly reduced mitochondrial respiratory chain complex-II and complex-III enzyme activities in MeCP2 knock-down astrocytes. Intracellular calcium robustly increased and mitochondrial membrane potential decreased, while no change in ROS was observed in MeCP2 knock-down astrocytes. Quercetin increased MeCP2 and normalized Uqcrc1 and Ndufv2 gene expression but did not modulate MeCP2 and Ndufv2 proteins expression. Interestingly, quercetin upregulated significantly the mitochondrial respiratory complex-II, complex-III, and complex-IV activities in dose-dependent manner. It also restored intracellular calcium level and mitochondrial membrane potential. In vitro observations suggest the beneficial effect of quercetin in mitochondrial functioning in MeCP2-deficient condition. There are no reports focusing on role of quercetin in mitochondrial function in MeCP2-deficient astrocytes, and these observations serve as preliminary data to evaluate quercetin's effects in vivo.

Oxidative Stress in Autistic Children Alters Erythrocyte Shape in the Absence of Quantitative Protein Alterations and of Loss of Membrane Phospholipid Asymmetry

Red blood cells (RBCs) from people affected by autism spectrum disorders (ASDs) are a target of oxidative stress. By scanning electron microscopy, we analyzed RBC morphology from 22 ASD children and show here that only 47.5 ± 3.33% of RBC displayed the typical biconcave shape, as opposed to 87.5 ± 1.3% (mean ± SD) of RBC from 21 sex- and age-matched healthy typically developing (TD) controls. Codocytes and star-shaped cells accounted for about 30% of all abnormally shaped ASD erythrocytes. RBC shape alterations were independent of the anticoagulant used (Na₂-EDTA or heparin) and of different handling procedures preceding glutaraldehyde fixation, thus suggesting that they were not artefactual. Incubation for 24 h in the presence of antioxidants restored normal morphology in most erythrocytes from ASD patients. By Coomassie staining, as well as Western blotting analysis of relevant proteins playing a key role in the membrane-cytoskeleton organization, we were unable to find differences in RBC ghost composition between ASD and normal subjects. Phosphatidylserine (PS) exposure towards the extracellular membrane domain was examined in both basal and erythroptosis-inducing conditions. No differences were found between ASD and TD samples except when the aminophospholipid translocase was blocked by N-ethylmaleimide, upon which an increased amount of PS was found to face the outer membrane in RBC from ASD. These complex data are discussed in the light of the current understanding of the mode by which oxidative stress might affect erythrocyte shape in ASD and in other pathological conditions.

4-hydroxynonenal protein adducts: Key mediator in Rett syndrome oxinflammation

In the last 15 years a strong correlation between oxidative stress (OxS) and Rett syndrome (RTT), a rare neurodevelopmental disorder known to be caused in 95% of the cases, by a mutation in the methyl-CpG-binding protein 2 (MECP2) gene, has been well documented. Here, we revised, summarized and discussed the current knowledge on the role of lipid peroxidation byproducts, with special emphasis on 4-hydroxynonenal (4HNE), in RTT pathophysiology. The posttranslational modifications of proteins via 4HNE, known as 4HNE protein adducts (4NHE-PAs), causing detrimental effects on protein functions, appear to contribute to the clinical severity of the syndrome, since their levels increase significantly during the subsequent 4 clinical stages, reaching the maximum degree at stage 4, represented by a late motor deterioration. In addition, 4HNE-PA are only partially removed due to the compromised functionality of the proteasome activity, contributing therefore to the cellular damage in RTT. All this will lead to a characteristic subclinical inflammation, defined "OxInflammation", derived by a positive feedback loop between OxS byproducts and inflammatory mediators that in a long run further aggravates the clinical features of RTT patients. Therefore, in a pathology completely orphan of any therapy, aiming 4HNE as a therapeutic target could represent a coadjuvant treatment with some beneficial impact in these patients.‬‬‬.

Morphology, membrane nanostructure and stiffness for quality assessment of packed red blood cells

Transfusion of packed red blood cells (PRBC) to patients in critical states is often accompanied by post-transfusion complications. This may be related with disturbance of properties of PRBC and their membranes during long-term storage in the hemopreservative solution. The purpose of our work is the study of transformation of morphology, membranes stiffness and nanostructure for assessment of PRBC quality, in vitro. By atomic force microscopy we studied the transformation of cell morphology, the appearance of topological nanodefects of membranes and by atomic force spectroscopy studied the change of membrane stiffness during 40 days of storage of PRBC. It was shown that there is a transition period (20–26 days), in which we observed an increase in the Young’s modulus of the membranes 1.6–2 times and transition of cells into irreversible forms. This process was preceded by the appearance of topological nanodefects of membranes. These parameters can be used for quality assessment of PRBC and for improvement of transfusion rules.

Autonomic breathing abnormalities in Rett syndrome: caregiver perspectives in an international database study

BACKGROUND

Rett syndrome is a severe neurodevelopmental disorder associated with mutations in the MECP2 gene. Irregular breathing patterns and abdominal bloating are prominent but poorly understood features. Our aims were to characterize the abnormal breathing patterns and abdominal bloating, investigate the distribution of these by age and mutation type and examine their impact and management from a caregiver perspective.

METHODS

We invited previously recruited families from the International Rett Syndrome Study to complete a web-based questionnaire concerning their family member with Rett syndrome aged between 2 and 57 years. We used logistic regression to investigate presence, frequency and impact of breath-holding, hyperventilation, or abdominal bloating by age group and mutation type. Age of onset for both breathing abnormalities was investigated using time-to-onset analysis, and the Kaplan-Meier method was used to estimate the failure function for the study sample. Descriptive statistics were used to characterize the management of irregular breathing.

RESULTS

Questionnaires were returned by 413/482 (85.7%) families. Breath-holding was reported for 68.8%, hyperventilation for 46.4% and abdominal bloating for 42.4%. Hyperventilation was more prevalent and frequent in those younger than 7 years of age and abdominal bloating in those aged over 20 years. Onset of breathing irregularities usually occurred during early childhood. Caregivers perceived that daily life was considerably impacted for almost half (44.1%) of those with abdominal bloating and in just over than a third of those with breath-holding (35.8%) or hyperventilation (35.1%). Although perceived impact was broadly comparable between age and mutation groups for breath-holding, hyperventilation and abdominal bloating, girls and women with a p.Arg294* mutation were considered to be more affected by all three conditions. Only 31 individuals had received medically prescribed treatments including 12 different medications, added oxygen, rebreathing apparatus or non-invasive ventilation.

CONCLUSIONS

Autonomic disturbances are prevalent and burdensome in Rett syndrome. This information may guide the design of inclusion criteria and outcome measures for clinical intervention trials targeting autonomic abnormalities. Further investigation of available treatments is necessary to delineate evidence-based management pathways.

Mitochondrial Dysfunction in the Pathogenesis of Rett Syndrome: Implications for Mitochondria-Targeted Therapies

First described over 50 years ago, Rett syndrome (RTT) is a neurodevelopmental disorder caused primarily by mutations of the X-linked MECP2 gene. RTT affects predominantly females, and has a prevalence of roughly 1 in every 10,000 female births. Prior to the discovery that mutations of MECP2 are the leading cause of RTT, there were suggestions that RTT could be a mitochondrial disease. In fact, several reports documented altered mitochondrial structure, and deficiencies in mitochondrial enzyme activity in different cells or tissues derived from RTT patients. With the identification of MECP2 as the causal gene, interest largely shifted toward defining the normal function of MeCP2 in the brain, and how its absence affects the neurodevelopment and neurophysiology. Recently, though, interest in studying mitochondrial function in RTT has been reignited, at least in part due to observations suggesting systemic oxidative stress does play a contributing role in RTT pathogenesis. Here we review data relating to mitochondrial alterations at the structural and functional levels in RTT patients and model systems, and present a hypothesis for how the absence of MeCP2 could lead to altered mitochondrial function and elevated levels of cellular oxidative stress. Finally, we discuss the prospects for treating RTT using interventions that target specific aspects of mitochondrial dysfunction and/or oxidative stress.

Oxygen exchange and energy metabolism in erythrocytes of Rett syndrome and their relationships with respiratory alterations

Rett syndrome (RTT) is a neurodevelopmental disorder, mainly affecting females, which is associated to a mutation on the methyl-CpG-binding protein 2 gene. In the pathogenesis and progression of classic RTT, red blood cell (RBC) morphology has been shown to be an important biosensor for redox imbalance and chronic hypoxemia. Here we have evaluated the impact of oxidation and redox imbalance on several functional properties of RTT erythrocytes. In particular, we report for the first time a stopped-flow measurement of the kinetics of oxygen release by RBCs and the analysis of the intrinsic affinity of the hemoglobin (Hb). According to our experimental approach, RBCs from RTT patients do not show any intrinsic difference with respect to those from healthy controls neither in Hb's oxygen-binding affinity nor in O₂ exchange processes at 37 °C. Therefore, these factors do not contribute to the observed alteration of the respiratory function in RTT patients. Moreover, the energy metabolism of RBCs, from both RTT patients and controls, was evaluated by ion-pairing HPLC method and related to the level of malondialdehyde and to the oxidative radical scavenging capacity of red cells. Results have clearly confirmed significant alterations in antioxidant defense capability, adding important informations concerning the high-energy compound levels in RBCs of RTT subjects, underlying possible correlations with inflammatory tissue alterations.

Oxidative stress in sepsis. Possible production of free radicals through an erythrocyte-mediated positive feedback mechanism

BACKGROUND

Sepsis is an illness with a high morbidity for which no effective treatment exists. Its treatment has a high cost because it usually requires an intensive care unit and expensive antibiotics. The present study focus in the production of reactive oxygen species in the early stages of sepsis. This study aimed at investigating the production of reactive oxygen specie during the inflammatory response in patients with sepsis.

METHODS

Reactive oxygen specie production and insoluble myeloperoxidase obtained from fresh whole blood were measured by photon counting chemiluminescence in the blood of 18 septic patients and 12 healthy individuals. Modified red blood cells were evaluated by staining of blood smears. The production of reactive oxygen species by macrophages and polymorphonuclear leukocytes put into contact with modified red blood cells were also assessed by photon counting chemiluminescence.

RESULTS

The appearance of oxidatively modified erythrocytes, which is an evidence of oxidative stress, was supported by the detection of reactive oxygen species and insoluble myeloperoxidase in the whole blood of all septic patients. Peroxynitrite was the main reactive oxygen species found in the whole blood. Oxidatively modified erythrocytes activated phagocytic cells in vitro, leading to the considerable production of free radicals.

CONCLUSION

It was found that sepsis led to a high oxidative stress and to extensive modification of erythrocytes. It is proposed that a positive feedback mechanism, involving the activation of circulating leukocytes by these modified erythrocytes would maintain the pro-oxidative state even after the disappearance of bacteria.

Inflammatory protein response in CDKL5-Rett syndrome: evidence of a subclinical smouldering inflammation

BACKGROUND

Mutations in the cyclin-dependent kinase-like 5 gene cause a clinical variant of Rett syndrome (CDKL5-RTT). A role for the acute-phase response (APR) is emerging in typical RTT caused by methyl-CpG-binding protein 2 gene mutations (MECP2-RTT). No information is, to date, available on the inflammatory protein response in CDKL5-RTT. We evaluated, for the first time, the APR protein response in CDKL5-RTT.

METHODS

Protein patterns in albumin- and IgG-depleted plasma proteome from CDKL5-RTT patients were evaluated by two-dimensional gel electrophoresis/mass spectrometry. The resulting data were related to circulating cytokines and compared to healthy controls or MECP2-RTT patients. The effects of omega-3 polyunsaturated fatty acids (ω-3 PUFAs) were evaluated.

RESULTS

CDKL5-RTT mutations resulted in a subclinical attenuated inflammation, specifically characterized by an overexpression of the complement component C3 and CD5 antigen-like, both strictly related to the inflammatory response. Cytokine dysregulation featuring a bulk increase of anti-inflammatory cytokines, predominantly IL-10, could explain the unchanged erythrocyte sedimentation rate and atypical features of inflammation in CDKL5-RTT. Omega-3 PUFAs were able to counterbalance the pro-inflammatory status.

CONCLUSION

For the first time, we revealed a subclinical smouldering inflammation pattern in CDKL5-RTT consisting in the coexistence of an atypical APR coupled with a dysregulated cytokine response.

Red blood cells in Rett syndrome: oxidative stress, morphological changes and altered membrane organization

In this review, we summarize the current evidence on the erythrocyte as a previously unrecognized target cell in Rett syndrome, a rare (1:10 000 females) and devastating neurodevelopmental disorder caused by loss-of-function mutations in a single gene (i.e. MeCP2, CDKL5, or rarely FOXG1). In particular, we focus on morphological changes, membrane oxidative damage, altered membrane fatty acid profile, and aberrant skeletal organization in erythrocytes from patients with typical Rett syndrome and MeCP2 gene mutations. The beneficial effects of ω-3 polyunsaturated fatty acids (PUFAs) are also summarized for this condition to be considered as a 'model' condition for autism spectrum disorders.

Blood oxidative stress and metallothionein expression in Rett syndrome: Probing for markers

OBJECTIVES

Oxidative stress seems to be involved in Rett syndrome (RTT). The aim of this study was to assess the antioxidant status in RTT children with MECP2 gene mutations with respect to healthy controls, and to explore novel blood antioxidant markers for RTT severity.

METHODS

In erythrocytes from RTT females aged 2-14 years (n = 27) and age-matched controls (n = 27), we measured the levels of malonaldehyde and the activity of two antioxidant enzymes, Cu/Zn-superoxide dismutase and catalase, by spectrophotometric assays. In leukocytes, the expression of metallothioneins, the main non-enzymatic antioxidants, was assessed by real-time RT-PCR. In nine selected RTT children, methylome analysis was also performed.

RESULTS

Blood of RTT patients showed increased lipid peroxidation and a dysregulated pattern of MT expression, while enzymatic activities did not change significantly with respect to controls. Moreover, we observed no epigenetic dysregulation in CpG-enriched promoter regions of the analysed genes but significant hypomethylation in the random loci.

CONCLUSIONS

As the haematic level of MT-1A directly correlates with the phenotype severity, this metallothionein can represent a marker for RTT severity. Moreover, the attempt to link the level of blood oxidative stress with MECP2 mutation and specific clinical features led us to draw some interesting conclusions.

Exploring the possible link between MeCP2 and oxidative stress in Rett syndrome

Rett syndrome (RTT, MIM 312750) is a rare and orphan progressive neurodevelopmental disorder affecting girls almost exclusively, with a frequency of 1/15,000 live births of girls. The disease is characterized by a period of 6 to 18 months of apparently normal neurodevelopment, followed by early neurological regression, with a progressive loss of acquired cognitive, social, and motor skills. RTT is known to be caused in 95% of the cases by sporadic de novo loss-of-function mutations in the X-linked methyl-CpG-binding protein 2 (MECP2) gene encoding methyl-CpG binding protein 2 (MeCP2), a nuclear protein able to regulate gene expression. Despite almost two decades of research into the functions and role of MeCP2, little is known about the mechanisms leading from MECP2 mutation to the disease. Oxidative stress (OS) is involved in the pathogenic mechanisms of several neurodevelopmental and neurodegenerative disorders, although in many cases it is not clear whether OS is a cause or a consequence of the pathology. Fairly recently, the presence of a systemic OS has been demonstrated in RTT patients with a strong correlation with the patients' clinical status. The link between MECP2 mutation and the redox imbalance found in RTT is not clear. Animal studies have suggested a possible direct correlation between Mecp2 mutation and increased OS levels. In addition, the restoration of Mecp2 function in astrocytes significantly improves the developmental outcome of Mecp2-null mice and reexpression of Mecp2 gene in the brain of null mice restored oxidative damage, suggesting that Mecp2 loss of function can be involved in oxidative brain damage. Starting from the evidence that oxidative damage in the brain of Mecp2-null mice precedes the onset of symptoms, we evaluated whether, based on the current literature, the dysfunctions described in RTT could be a consequence or, in contrast, could be caused by OS. We also analyzed whether therapies that at least partially treated some RTT symptoms can play a role in defense against OS. At this stage we can propose that OS could be one of the main causes of the dysfunctions observed in RTT. In addition, the major part of the therapies recommended to alleviate RTT symptoms have been shown to interfere with oxidative homeostasis, suggesting that MeCP2 could somehow be involved in the protection of the brain from OS.

Advanced Glycation-Modified Human Serum Albumin Evokes Alterations in Membrane and Eryptosis in Erythrocytes

Increased burden of advanced glycation end-products (AGEs) in case of hyperglycemic conditions leads to the development of retinopathy, nephropathy, and cardiovascular and neurological disorders such as Alzheimer's disease. AGEs are considered as pro-oxidants, and their accumulation increases the oxidative stress. The prolonged exposure to these AGEs is the fundamental cause of chronic oxidative stress. Abnormal morphology of red blood cells (RBCs) and excessive eryptosis has been observed in diabetes, glomerulonephritis, dyslipidemia, and obesity, but yet the contribution of extracellular AGEs remains undefined. In this study, we investigated the effect of AGEs on erythrocytes to determine their impact on the occurrence of different pathological forms of these blood cells. Specifically, carboxymethyllysine (CML), carboxyethyllysine (CEL), and Arg-pyrimidine (Arg-P) which have been reported to be the most pre-dominant AGEs formed under in vivo conditions were used in this study. Results suggested the eryptotic properties of CML, CEL, and Arg-P for RBCs, which were evident from the highly damaged cell membrane and occurrence of abnormal morphologies. Methylglyoxal-modified albumin showed more severe effects, which can be attributed to the high reactivity and pro-oxidant nature of glycation end products. These findings suggest the possible role of AGE-modified albumin towards the morphological changes in erythrocyte's membrane associated with diabetic conditions.

Cytokine Dysregulation in MECP2- and CDKL5-Related Rett Syndrome: Relationships with Aberrant Redox Homeostasis, Inflammation, and ω-3 PUFAs

An involvement of the immune system has been suggested in Rett syndrome (RTT), a devastating neurodevelopmental disorder related to oxidative stress, and caused by a mutation in the methyl-CpG binding protein 2 gene (MECP2) or, more rarely, cyclin-dependent kinase-like 5 (CDKL5). To date, it is unclear whether both mutations may have an impact on the circulating cytokine patterns. In the present study, cytokines involved in the Th1-, Th2-, and T regulatory (T-reg) response, as well as chemokines, were investigated in MECP2- (MECP2-RTT) (n = 16) and CDKL5-Rett syndrome (CDKL5-RTT) (n = 8), before and after ω-3 polyunsaturated fatty acids (PUFAs) supplementation. A major cytokine dysregulation was evidenced in untreated RTT patients. In MECP2-RTT, a Th2-shifted balance was evidenced, whereas in CDKL5-RTT both Th1- and Th2-related cytokines (except for IL-4) were upregulated. In MECP2-RTT, decreased levels of IL-22 were observed, whereas increased IL-22 and T-reg cytokine levels were evidenced in CDKL5-RTT. Chemokines were unchanged. The cytokine dysregulation was proportional to clinical severity, inflammatory status, and redox imbalance. Omega-3 PUFAs partially counterbalanced cytokine changes, as well as aberrant redox homeostasis and the inflammatory status. RTT is associated with a subclinical immune dysregulation as the likely consequence of a defective inflammation regulatory signaling system.

Altered erythrocyte membrane fatty acid profile in typical Rett syndrome: effects of omega-3 polyunsaturated fatty acid supplementation

This study mainly aims at examining the erythrocyte membrane fatty acid (FAs) profile in Rett syndrome (RTT), a genetically determined neurodevelopmental disease. Early reports suggest a beneficial effects of omega-3 polyunsaturated fatty acids (ω-3 PUFAs) on disease severity in RTT. A total of 24 RTT patients were assigned to ω-3 PUFAs-containing fish oil for 12 months in a randomized controlled study (average DHA and EPA doses of 72.9, and 117.1mg/kgb.w./day, respectively). A distinctly altered FAs profile was detectable in RTT, with deficient ω-6 PUFAs, increased saturated FAs and reduced trans 20:4 FAs. FAs changes were found to be related to redox imbalance, subclinical inflammation, and decreased bone density. Supplementation with ω-3 PUFAs led to improved ω-6/ω-3 ratio and serum plasma lipid profile, decreased PUFAs peroxidation end-products, normalization of biochemical markers of inflammation, and reduction of bone hypodensity as compared to the untreated RTT group. Our data indicate that a significant FAs abnormality is detectable in the RTT erythrocyte membranes and is partially rescued by ω-3 PUFAs.

Redox imbalance and morphological changes in skin fibroblasts in typical Rett syndrome

Evidence of oxidative stress has been reported in the blood of patients with Rett syndrome (RTT), a neurodevelopmental disorder mainly caused by mutations in the gene encoding the Methyl-CpG-binding protein 2. Little is known regarding the redox status in RTT cellular systems and its relationship with the morphological phenotype. In RTT patients (n = 16) we investigated four different oxidative stress markers, F2-Isoprostanes (F2-IsoPs), F4-Neuroprostanes (F4-NeuroPs), nonprotein bound iron (NPBI), and (4-HNE PAs), and glutathione in one of the most accessible cells, that is, skin fibroblasts, and searched for possible changes in cellular/intracellular structure and qualitative modifications of synthesized collagen. Significantly increased F4-NeuroPs (12-folds), F2-IsoPs (7.5-folds) NPBI (2.3-folds), 4-HNE PAs (1.48-folds), and GSSG (1.44-folds) were detected, with significantly decreased GSH (-43.6%) and GSH/GSSG ratio (-3.05 folds). A marked dilation of the rough endoplasmic reticulum cisternae, associated with several cytoplasmic multilamellar bodies, was detectable in RTT fibroblasts. Colocalization of collagen I and collagen III, as well as the percentage of type I collagen as derived by semiquantitative immunofluorescence staining analyses, appears to be significantly reduced in RTT cells. Our findings indicate the presence of a redox imbalance and previously unrecognized morphological skin fibroblast abnormalities in RTT patients.

Beta-actin deficiency with oxidative posttranslational modifications in Rett syndrome erythrocytes: insights into an altered cytoskeletal organization

Beta-actin, a critical player in cellular functions ranging from cell motility and the maintenance of cell shape to transcription regulation, was evaluated in the erythrocyte membranes from patients with typical Rett syndrome (RTT) and methyl CpG binding protein 2 (MECP2) gene mutations. RTT, affecting almost exclusively females with an average frequency of 1∶10,000 female live births, is considered the second commonest cause of severe cognitive impairment in the female gender. Evaluation of beta-actin was carried out in a comparative cohort study on red blood cells (RBCs), drawn from healthy control subjects and RTT patients using mass spectrometry-based quantitative analysis. We observed a decreased expression of the beta-actin isoforms (relative fold changes for spots 1, 2 and 3: −1.82±0.15, −2.15±0.06, and −2.59±0.48, respectively) in pathological RBCs. The results were validated by western blotting and immunofluorescence microscopy. In addition, beta-actin from RTT patients also showed a dramatic increase in oxidative posttranslational modifications (PTMs) as the result of its binding with the lipid peroxidation product 4-hydroxy-2-nonenal (4-HNE). Our findings demonstrate, for the first time, a beta-actin down-regulation and oxidative PTMs for RBCs of RTT patients, thus indicating an altered cytoskeletal organization.

Inflammatory lung disease in Rett syndrome

Rett syndrome (RTT) is a pervasive neurodevelopmental disorder mainly linked to mutations in the gene encoding the methyl-CpG-binding protein 2 (MeCP2). Respiratory dysfunction, historically credited to brainstem immaturity, represents a major challenge in RTT. Our aim was to characterize the relationships between pulmonary gas exchange abnormality (GEA), upper airway obstruction, and redox status in patients with typical RTT (n = 228) and to examine lung histology in a Mecp2-null mouse model of the disease. GEA was detectable in ~80% (184/228) of patients versus ~18% of healthy controls, with “high” (39.8%) and “low” (34.8%) patterns dominating over “mixed” (19.6%) and “simple mismatch” (5.9%) types. Increased plasma levels of non-protein-bound iron (NPBI), F₂-isoprostanes (F₂-IsoPs), intraerythrocyte NPBI (IE-NPBI), and reduced and oxidized glutathione (i.e., GSH and GSSG) were evidenced in RTT with consequently decreased GSH/GSSG ratios. Apnea frequency/severity was positively correlated with IE-NPBI, F₂-IsoPs, and GSSG and negatively with GSH/GSSG ratio. A diffuse inflammatory infiltrate of the terminal bronchioles and alveoli was evidenced in half of the examined Mecp2-mutant mice, well fitting with the radiological findings previously observed in RTT patients. Our findings indicate that GEA is a key feature of RTT and that terminal bronchioles are a likely major target of the disease.

Mitochondrial dysfunction in the skeletal muscle of a mouse model of Rett syndrome (RTT): implications for the disease phenotype

Rett syndrome (RTT) is a severe neurodevelopmental disorder, predominantly caused by mutations in the X-linked Methyl-CpG-binding protein 2 (MECP2) gene. Patients present with numerous functional deficits including intellectual disability and abnormalities of movement. Clinical and biochemical features may overlap with those seen in patients with primary mitochondrial respiratory chain disorders. In the late stages of the disorder, patients suffer from motor deterioration and usually require assisted mobility. Using a mouse model of RTT (Mecp2(tm1Tam)), we studied the mitochondrial function in the hind-limb skeletal muscle of these mice. We identified a reduction in cytochrome c oxidase subunit I (MTCO1) at both the transcript and protein level, in accordance with our previous findings in RTT patient brain studies. Mitochondrial respiratory chain (MRC) enzyme activity of complexes II+III (COII+III) and complex IV (COIV), and glutathione (GSH) levels were significantly reduced in symptomatic mice, but not in the pre-symptomatic mice. Our findings suggest that mitochondrial abnormalities in the skeletal muscle may contribute to the progressive deterioration in mobility in RTT through the accumulation of free radicals, as evidenced by the decrease in reduced glutathione (GSH). We hypothesise that a diminution in GSH leads to an accumulation of free radicals and an increase in oxidative stress. This may impact on respiratory chain function and contribute in part to the progressive neurological and motor deterioration seen in the Mecp2-mutant mouse. Treatment strategies aimed at restoring cellular GSH levels may prove to be a novel target area to consider in future approaches to RTT therapies.

A plasma proteomic approach in Rett syndrome: classical versus preserved speech variant

Rett syndrome (RTT) is a progressive neurodevelopmental disorder mainly caused by mutations in the gene encoding the methyl-CpG-binding protein 2 (MeCP2). Although over 200 mutations types have been identified so far, nine of which the most frequent ones. A wide phenotypical heterogeneity is a well-known feature of the disease, with different clinical presentations, including the classical form and the preserved speech variant (PSV). Aim of the study was to unveil possible relationships between plasma proteome and phenotypic expression in two cases of familial RTT represented by two pairs of sisters, harbor the same MECP2 gene mutation while being dramatically discrepant in phenotype, that is, classical RTT versus PSV. Plasma proteome was analysed by 2-DE/MALDI-TOF MS. A significant overexpression of six proteins in the classical sisters was detected as compared to the PSV siblings. A total of five out of six (i.e., 83.3%) of the overexpressed proteins were well-known acute phase response (APR) proteins, including alpha-1-microglobulin, haptoglobin, fibrinogen beta chain, alpha-1-antitrypsin, and complement C3. Therefore, the examined RTT siblings pairs proved to be an important benchmark model to test the molecular basis of phenotypical expression variability and to identify potential therapeutic targets of the disease.

Erythrocyte shape abnormalities, membrane oxidative damage, and β-actin alterations: an unrecognized triad in classical autism

Autism spectrum disorders (ASDs) are a complex group of neurodevelopment disorders steadily rising in frequency and treatment refractory, where the search for biological markers is of paramount importance. Although red blood cells (RBCs) membrane lipidomics and rheological variables have been reported to be altered, with some suggestions indicating an increased lipid peroxidation in the erythrocyte membrane, to date no information exists on how the oxidative membrane damage may affect cytoskeletal membrane proteins and, ultimately, RBCs shape in autism. Here, we investigated RBC morphology by scanning electron microscopy in patients with classical autism, that is, the predominant ASDs phenotype (age range: 6–26 years), nonautistic neurodevelopmental disorders (i.e., “positive controls”), and healthy controls (i.e., “negative controls”). A high percentage of altered RBCs shapes, predominantly elliptocytes, was observed in autistic patients, but not in both control groups. The RBCs altered morphology in autistic subjects was related to increased erythrocyte membrane F₂-isoprostanes and 4-hydroxynonenal protein adducts. In addition, an oxidative damage of the erythrocyte membrane β-actin protein was evidenced. Therefore, the combination of erythrocyte shape abnormalities, erythrocyte membrane oxidative damage, and β-actin alterations constitutes a previously unrecognized triad in classical autism and provides new biological markers in the diagnostic workup of ASDs.

Isoprostanes and 4-hydroxy-2-nonenal: markers or mediators of disease? Focus on Rett syndrome as a model of autism spectrum disorder

Lipid peroxidation, a process known to induce oxidative damage to key cellular components, has been implicated in several diseases. Following three decades of explorations mainly on in vitro models reproducible in the laboratories, lipid peroxidation has become increasingly relevant for the interpretation of a wide range of pathophysiological mechanisms in the clinical setting. This cumulative effort has led to the identification of several lipid peroxidation end-products meeting the needs of the in vivo evaluation. Among these different molecules, isoprostanes and 4-hydroxy-2-nonenal protein adducts appear to be particularly interesting. This review shows how specific oxidation products, deriving from polyunsaturated fatty acids precursors, are strictly related to the clinical manifestations and the natural history of Rett syndrome, a genetically determined neurodevelopmental pathology, currently classified among the autism spectrum disorders. In our experience, Rett syndrome offers a unique setting for physicians, biologists, and chemists to explore the borders of the lipid mediators concept.

The role of oxidative stress in Rett syndrome: an overview

The main cause of Rett syndrome (RTT), a pervasive development disorder almost exclusively affecting females, is a mutation in the methyl-CpG binding protein 2 (MeCP2) gene. To date, no cure for RTT exists, although disease reversibility has been demonstrated in animal models. Emerging evidence from our and other laboratories indicates a potential role of oxidative stress (OS) in RTT. This review examines the current state of the knowledge on the role of OS in explaining the natural history, genotype-phenotype correlation, and clinical heterogeneity of the human disease. Biochemical evidence of OS appears to be related to neurological symptom severity, mutation type, and clinical presentation. These findings pave the way for potential new genetic downstream therapeutic strategies aimed at improving patient quality of life. Further efforts in the near future are needed for investigating the yet unexplored "black box" between the MeCP2 gene mutation and subsequent OS derangement.