Erythrocytes Induce Vascular Dysfunction in COVID-19

Red blood cells from patients with ST-elevation myocardial infarction and elevated C-reactive protein levels induce endothelial dysfunction

Endothelial dysfunction is an early consequence of vascular inflammation and a driver of coronary atherosclerotic disease leading to myocardial infarction. The red blood cells (RBCs) mediate endothelial dysfunction in patients at cardiovascular risk, but their role in patients with acute myocardial infarction is unknown. This study aimed to investigate if RBCs from patients with ST-elevation myocardial infarction (STEMI) induced endothelial dysfunction and the role of systemic inflammation in this effect. RBCs from patients with STEMI and aged-matched healthy controls were coincubated with rat aortic segments for 18 h followed by evaluation of endothelium-dependent (EDR) and endothelium-independent relaxation (EIDR). RBCs and aortic segments were also analyzed for arginase and oxidative stress. The patients were divided into groups depending on C-reactive protein (CRP) levels at admission. RBCs from patients with STEMI and CRP levels ≥2 mg/L induced impairment of EDR, but not EIDR, compared with RBCs from STEMI and CRP <2 mg/L and healthy controls. Aortic expression of arginase 1 was increased following incubation with RBCs from patients with STEMI and CRP ≥2, and arginase inhibition prevented the RBC-induced endothelial dysfunction. RBCs from patients with STEMI and CRP ≥2 had increased reactive oxygen species compared with RBCs from patients with CRP <2 and healthy controls. Vascular inhibition of NADPH oxidases and increased dismutation of superoxide improved EDR. RBCs from patients with STEMI and low-grade inflammation induce endothelial dysfunction through a mechanism involving arginase 1 as well as increased RBC and vascular superoxide by NADPH oxidases.NEW & NOTEWORTHY Red blood cells from patients with STEMI and systemic inflammation induce endothelial dysfunction ex vivo. The RBC-induced endothelial dysfunction is mediated through increased arginase 1 and a shift in the redox balance toward oxidative stress. Inhibition of arginase or free radicals attenuates the impairment of endothelial function. The study suggests that red blood cells deserve attention as a key player in systemic inflammation and STEMI.

Nitric Oxide Signaling and Regulation in the Cardiovascular System: Recent Advances

Nitric oxide (NO) from endothelial NO synthase importantly contributes to vascular homeostasis. Reduced NO production or increased scavenging during disease conditions with oxidative stress contribute to endothelial dysfunction and NO deficiency. In addition to the classical enzymatic NO synthases (NOS) system, NO can also be generated via the nitrate-nitrite-NO pathway. Dietary and pharmacological approaches aimed at increasing NO bioactivity, especially in the cardiovascular system, have been the focus of much research since the discovery of this small gaseous signaling molecule. Despite wide appreciation of the biological role of NOS/NO signaling, questions still remain about the chemical nature of NOS-derived bioactivity. Recent studies show that NO-like bioactivity can be efficiently transduced by mobile NO-ferroheme species, which can transfer between proteins, partition into a hydrophobic phase, and directly activate the soluble guanylyl cyclase-cGMP-protein kinase G pathway without intermediacy of free NO. Moreover, interaction between red blood cells and the endothelium in the regulation of vascular NO homeostasis have gained much attention, especially in conditions with cardiometabolic disease. In this review we discuss both classical and nonclassical pathways for NO generation in the cardiovascular system and how these can be modulated for therapeutic purposes. SIGNIFICANCE STATEMENT: After four decades of intensive research, questions persist about the transduction and control of nitric oxide (NO) synthase bioactivity. Here we discuss NO signaling in cardiovascular health and disease, highlighting new findings, such as the important role of red blood cells in cardiovascular NO homeostasis. Nonclassical signaling modes, like the nitrate-nitrite-NO pathway, and therapeutic opportunities related to the NO system are discussed. Existing and potential pharmacological treatments/strategies, as well as dietary components influencing NO generation and signaling are covered.

Post-Acute COVID-19 Syndrome: Prevalence of Peripheral Microvascular Endothelial Dysfunction and Associations with NT-ProBNP Dynamics

BACKGROUND

Post-acute COVID-19 syndrome (PACS) has been linked to microvascular endothelial dysfunction as a potential underlying pathomechanism and can manifest even following a mild course of the initial infection. Prevalence of microvascular endothelial dysfunction and circulating natriuretic peptides in such PACS patients remains unknown.

METHODS

This prospective, cross-sectional cohort study enrolled 92 patients (82% females, median age 48 years) with PACS. Reactive hyperemia index (RHI) was evaluated with peripheral arterial tonometry, where <1.67 was defined as microvascular endothelial dysfunction, 1.67-2.0 as impaired function, and >2 normal endothelial function, on average 31 months after the acute infection. N-terminal pro-B-type natriuretic peptide (NT-proBNP) levels were collected at 2 different time points within over a 1-year span.

RESULTS

In total, 41% of PACS subjects had microvascular endothelial dysfunction and 20% had impaired RHI. No major differences in clinical characteristics, routine chemistry laboratory testing, or symptom burden were observed across the groups. Only subjects with microvascular endothelial dysfunction and impaired endothelial function had a significant increase in NT-proBNP levels over time, and those with larger increase in NT-proBNP had significantly lower RHI. There was a significant correlation between relative or absolute increase in NT-proBNP and RHI, which remained significant in a multivariable adjusted linear regression.

CONCLUSIONS

Peripheral microvascular endothelial dysfunction was prevalent in a symptomatic PACS population long after recovery from a mild acute infection. Increases in NT-proBNP levels were associated with microvascular endothelial dysfunction, suggesting a link between, and providing a foundation for, future studies on post viral microvascular endothelial dysfunction in PACS.

Red blood cell in preeclampsia: attenuated nitric oxide generation and enhanced reactive oxygen species formation and eryptosis

Preeclampsia (PE) pathogenesis is strongly related to diminished nitric oxide (NO) bioavailability and enhanced oxidative stress. Emerging evidence suggests that red blood cells (RBCs) eNOS enzyme contributes to systemic NO bioavailability by its ability of both NO and ROS generation. We aimed to investigate RBC eNOS enzyme activity, NO and ROS generation capacity, eryptosis index and aggregation levels in preeclamptic and uncomplicated pregnant women. Fifty-eight PE patients and 36 healthy pregnant women were included to the investigation. RBC eNOS enzyme activity, intracellular NO, calcium and ROS concentrations and eryptosis levels were determined via flow cytometric methods. RBC deformability and aggregation were measured via LORRCA. Intracellular NO and phosphorylated RBC eNOS levels decreased in PE group compared to healthy pregnant group (p < 0.05, p < 0.001 respectively). Intracellular ROS and calcium levels, eryptosis values and aggregation indexes in the PE group were significantly higher than healthy pregnant group (p < 0.05, p < 0.01, p < 0.05, p < 0.05 respectively). Our results demonstrate for the first time that RBC produce lower NO and higher ROS under PE conditions. Further, RBC of PE patients were more prone to eryptosis and aggregation compared to control group. Our results suggest that, in addition to endothelial cells, RBC also contribute to decreased plasma NO bioavailability via producing less NO and high ROS in PE. Considering increased tendency to eryptosis and aggregation, RBC seem to play role in haemodynamic changes of PE pathogenesis.

Photobiomodulation Treatment with a Home-Use Device for COVID-19: A Randomized Controlled Trial for Efficacy and Safety

Background: Photobiomodulation therapy (PBMT) using devices to deliver red and/or near-infrared light to tissues has shown promising effects in clinical settings for respiratory diseases, including potential benefits in managing symptoms associated with COVID-19. Objective: To determine if at-home self-administered PBMT for patients with COVID-19 is safe and effective. Methods: This was a randomized controlled trial (RCT) carried out at home during the COVID-19 pandemic (September 2020 to August 2021). The treatment group self-administered the Vielight RX Plus PBMT device (635 nm intranasal and 810 nm chest LEDs) and were monitored remotely. Eligible patients scored 4-7 (out of 7) for severity on the Wisconsin Upper Respiratory Symptom Survey (WURSS-44). Patients were randomized equally to Control group receiving standard-of-care (SOC) only or Treatment group receiving SOC plus PBMT. The device was used for 20 min 2X/day for 5 days and, subsequently, once daily for 30 days. The primary end-point was time-to-recovery (days) based on WURSS-44 question 1, "How sick do you feel today?". Subgroup analysis was performed, and Kaplan-Meier and Cox Proportional Hazards analysis were employed. Results: One hundred and ninety-nine eligible patients (18-65 years old) were divided into two subgroups as follows: 136 patients with 0-7 days of symptoms at baseline and 63 patients with 8-12 days of symptoms. Those with 0-7 days of symptoms at baseline recovered significantly faster with PBMT. The median for Treatment group was 18 days [95% confidence interval (CI), 13-20] versus the Control group 21 days (95% CI, 15-28), p = 0.050. The treatment:control hazard ratio was 1.495 (95% CI, 0.996-2.243), p = 0.054. Patients with symptom duration ≥7 days did not show any significant improvement. No deaths or severe adverse events (SAEs) occurred in the Treatment group, whereas there was 1 death and 3 SAEs requiring hospitalization in the Control group. Conclusions: Patients with ≤7 days of COVID-19 symptoms recovered significantly faster with PBMT compared to SOC. Beyond 7 days, PBMT showed no superiority over SOC. Trial Registration: ClinicalTrials.gov NCT04418505.

Cardiovascular dysautonomia in postacute sequelae of SARS-CoV-2 infection

Coronavirus disease 2019 (COVID-19) has led to a worldwide pandemic that continues to transform but will not go away. Cardiovascular dysautonomia in postacute sequelae of severe acute respiratory syndrome coronavirus 2 infection has led to persistent symptoms in a large number of patients. Here, we define the condition and its associated symptoms as well as potential mechanisms responsible. We provide a careful and complete overview of the topic addressing novel studies and a generalized approach to the management of individuals with this complex and potentially debilitating problem. We also discuss future research directions and the important knowledge gaps to be addressed in ongoing and planned studies.

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.

Development of a risk assessment model for cardiac injury in patients newly diagnosed with acute myeloid leukemia based on a multicenter, real-world analysis in China

BACKGROUND

Studies have revealed that acute myeloid leukemia (AML) patients are prone to combined cardiac injury. We aimed to identify hematological risk factors associated with cardiac injury in newly diagnosed AML patients before chemotherapy and develop a personalized predictive model.

METHODS

The population baseline, blood test, electrocardiogram, echocardiograph, and genetic and cytogenetic data were collected from newly diagnosed AML patients. The data were subdivided into training and validation cohorts. The independent risk factors were explored by univariate and multivariate logistic regression analysis respectively, and data dimension reduction and variable selection were performed using the least absolute shrinkage and selection operator (LASSO) regression models. The nomogram was generated and the reliability and generalizability were verified by receiver operating characteristic (ROC) curves, the area under the curve (AUC) and calibration curves in an external validation cohort.

RESULTS

Finally, 499 AML patients were included. After univariate logistic regression, LASSO regression and multivariate logistic regression analysis, abnormal NT-proBNP, NPM1 mutation, WBC, and RBC were independent risk factors for cardiac injury in AML patients (all P < 0.05). The nomogram was constructed based on the above four variables with high accuracy. The area under the curve was 0.742, 0.750, and 0.706 in the training, internal validation, and external validation cohort, respectively. The calibration curve indicated that the model has good testing capability. The Kaplan-Meier curve showed that the higher the risk of combined cardiac injury in AML patients, the lower their probability of survival.

CONCLUSIONS

This prediction nomogram identifies hematological risk factors associated with cardiac injury in newly diagnosed AML patients and can help hematologists identify the risk and provide precise treatment options.

Dysregulations in hemostasis, metabolism, immune response, and angiogenesis in post-acute COVID-19 syndrome with and without postural orthostatic tachycardia syndrome: a multi-omic profiling study

Post-acute COVID-19 (PACS) are associated with cardiovascular dysfunction, especially postural orthostatic tachycardia syndrome (POTS). Patients with PACS, both in the absence or presence of POTS, exhibit a wide range of persisting symptoms long after the acute infection. Some of these symptoms may stem from alterations in cardiovascular homeostasis, but the exact mechanisms are poorly understood. The aim of this study was to provide a broad molecular characterization of patients with PACS with (PACS + POTS) and without (PACS-POTS) POTS compared to healthy subjects, including a broad proteomic characterization with a focus on plasma cardiometabolic proteins, quantification of cytokines/chemokines and determination of plasma sphingolipid levels. Twenty-one healthy subjects without a prior COVID-19 infection (mean age 43 years, 95% females), 20 non-hospitalized patients with PACS + POTS (mean age 39 years, 95% females) and 22 non-hospitalized patients with PACS-POTS (mean age 44 years, 100% females) were studied. PACS patients were non-hospitalized and recruited ≈18 months after the acute infection. Cardiometabolic proteomic analyses revealed a dysregulation of ≈200 out of 700 analyzed proteins in both PACS groups vs. healthy subjects with the majority (> 90%) being upregulated. There was a large overlap (> 90%) with no major differences between the PACS groups. Gene ontology enrichment analysis revealed alterations in hemostasis/coagulation, metabolism, immune responses, and angiogenesis in PACS vs. healthy controls. Furthermore, 11 out of 33 cytokines/chemokines were significantly upregulated both in PACS + POTS and PACS-POTS vs. healthy controls and none of the cytokines were downregulated. There were no differences in between the PACS groups in the cytokine levels. Lastly, 16 and 19 out of 88 sphingolipids were significantly dysregulated in PACS + POTS and PACS-POTS, respectively, compared to controls with no differences between the groups. Collectively, these observations suggest a clear and distinct dysregulation in the proteome, cytokines/chemokines, and sphingolipid levels in PACS patients compared to healthy subjects without any clear signature associated with POTS. This enhances our understanding and might pave the way for future experimental and clinical investigations to elucidate and/or target resolution of inflammation and micro-clots and restore the hemostasis and immunity in PACS.

The 4-Hydroxynonenal–Protein Adducts and Their Biological Relevance: Are Some Proteins Preferred Targets?

It is well known that oxidative stress and lipid peroxidation (LPO) play a role in physiology and pathology. The most studied LPO product with pleiotropic capabilities is 4-hydroxynonenal (4-HNE). It is considered as an important mediator of cellular signaling processes and a second messenger of reactive oxygen species. The effects of 4-HNE are mainly attributed to its adduction with proteins. Whereas the Michael adducts thus formed are preferred in an order of potency of cysteine > histidine > lysine over Schiff base formation, it is not known which proteins are the preferred targets for 4-HNE under what physiological or pathological conditions. In this review, we briefly discuss the methods used to identify 4-HNE–protein adducts, the progress of mass spectrometry in deciphering the specific protein targets, and their biological relevance, focusing on the role of 4-HNE protein adducts in the adaptive response through modulation of the NRF2/KEAP1 pathway and ferroptosis.

Erythrocytes Functionality in SARS-CoV-2 Infection: Potential Link with Alzheimer's Disease

Coronavirus disease 2019 (COVID-19) is a rapidly spreading acute respiratory infection caused by SARS-CoV-2. The pathogenesis of the disease remains unclear. Recently, several hypotheses have emerged to explain the mechanism of interaction between SARS-CoV-2 and erythrocytes, and its negative effect on the oxygen-transport function that depends on erythrocyte metabolism, which is responsible for hemoglobin-oxygen affinity (Hb-O2 affinity). In clinical settings, the modulators of the Hb-O2 affinity are not currently measured to assess tissue oxygenation, thereby providing inadequate evaluation of erythrocyte dysfunction in the integrated oxygen-transport system. To discover more about hypoxemia/hypoxia in COVID-19 patients, this review highlights the need for further investigation of the relationship between biochemical aberrations in erythrocytes and oxygen-transport efficiency. Furthermore, patients with severe COVID-19 experience symptoms similar to Alzheimer's, suggesting that their brains have been altered in ways that increase the likelihood of Alzheimer's. Mindful of the partly assessed role of structural, metabolic abnormalities that underlie erythrocyte dysfunction in the pathophysiology of Alzheimer's disease (AD), we further summarize the available data showing that COVID-19 neurocognitive impairments most probably share similar patterns with known mechanisms of brain dysfunctions in AD. Identification of parameters responsible for erythrocyte function that vary under SARS-CoV-2 may contribute to the search for additional components of progressive and irreversible failure in the integrated oxygen-transport system leading to tissue hypoperfusion. This is particularly relevant for the older generation who experience age-related disorders of erythrocyte metabolism and are prone to AD, and provide an opportunity for new personalized therapies to control this deadly infection.

The ultimate tradeoff: how red cell adaptations to malaria alter the host response during critical illness

The human immune system evolved in response to pathogens. Among these pathogens, malaria has proven to be one of the deadliest and has exerted the most potent selective pressures on its target cell, the red blood cell. Red blood cells have recently gained recognition for their immunomodulatory properties, yet how red cell adaptations contribute to the host response during critical illness remains understudied. This review will discuss how adaptations that may have been advantageous for host survival might influence immune responses in modern critical illness. We will highlight the current evidence for divergent host resilience arising from the adaptations to malaria and summarize how understanding evolutionary red cell adaptations to malaria may provide insight into the heterogeneity of the host response to critical illness, perhaps driving future precision medicine approaches to syndromes affecting the critically ill such as sepsis and acute respiratory distress syndrome (ARDS).

Sympathetic Neural Overdrive, Aortic Stiffening, Endothelial Dysfunction, and Impaired Exercise Capacity in Severe COVID-19 Survivors: A Mid-Term Study of Cardiovascular Sequelae

BACKGROUND

COVID-19 has become a dramatic health problem during this century. In addition to high mortality rate, COVID-19 survivors are at increased risk for cardiovascular diseases 1-year after infection. Explanations for these manifestations are still unclear but can involve a constellation of biological alterations. We hypothesized that COVID-19 survivors compared with controls exhibit sympathetic overdrive, vascular dysfunction, cardiac morpho-functional changes, impaired exercise capacity, and increased oxidative stress.

METHODS

Nineteen severe COVID-19 survivors and 19 well-matched controls completed the study. Muscle sympathetic nerve activity (microneurography), brachial artery flow-mediated dilation and blood flow (Doppler-Ultrasound), carotid-femoral pulse wave velocity (Complior), cardiac morpho-functional parameters (echocardiography), peak oxygen uptake (cardiopulmonary exercise testing), and oxidative stress were measured ~3 months after hospital discharge. Complementary experiments were conducted on human umbilical vein endothelial cells cultured with plasma samples from subjects.

RESULTS

Muscle sympathetic nerve activity and carotid-femoral pulse wave velocity were greater and brachial artery flow-mediated dilation, brachial artery blood flow, E/e' ratio, and peak oxygen uptake were lower in COVID-19 survivors than in controls. COVID-19 survivors had lower circulating antioxidant markers compared with controls, but there were no differences in plasma-treated human umbilical vein endothelial cells nitric oxide production and reactive oxygen species bioactivity. Diminished peak oxygen uptake was associated with sympathetic overdrive, vascular dysfunction, and reduced diastolic function in COVID-19 survivors.

CONCLUSIONS

Our study revealed that COVID-19 survivors have sympathetic overactivation, vascular dysfunction, cardiac morpho-functional changes, and reduced exercise capacity. These findings indicate the need for further investigation to determine whether these manifestations are persistent longer-term and their impact on the cardiovascular health of COVID-19 survivors.

The red blood cell as a mediator of endothelial dysfunction in patients with familial hypercholesterolemia and dyslipidemia

BACKGROUND

Patients with familial hypercholesterolemia (FH) display high levels of low-density lipoprotein cholesterol (LDL-c), endothelial dysfunction, and increased risk of premature atherosclerosis. We have previously shown that red blood cells (RBCs) from patients with type 2 diabetes induce endothelial dysfunction through increased arginase 1 and reactive oxygen species (ROS).

OBJECTIVE

To test the hypothesis that RBCs from patients with FH (FH-RBCs) and elevated LDL-c induce endothelial dysfunction.

METHODS AND RESULTS

FH-RBCs and LDL-c >5.0 mM induced endothelial dysfunction following 18-h incubation with isolated aortic rings from healthy rats compared to FH-RBCs and LDL-c <2.5 mM or RBCs from healthy subjects (H-RBCs). Inhibition of vascular but not RBC arginase attenuated the degree of endothelial dysfunction induced by FH-RBCs and LDL-c >5.0 mM. Furthermore, arginase 1 but not arginase 2 was elevated in the vasculature of aortic segments after incubation with FH-RBCs and LDL-c >5.0 mM. A superoxide scavenger, present throughout the 18-h incubation, attenuated the degree of endothelial dysfunction induced by FH-RBCs and LDL-c >5.0 mM. ROS production was elevated in these RBCs in comparison with H-RBCs. Scavenging of vascular ROS through various antioxidants also attenuated the degree of endothelial dysfunction induced by FH-RBCs and LDL-c >5.0 mM. This was corroborated by an increase in the lipid peroxidation product 4-hydroxynonenal. Lipidomic analysis of RBC lysates did not reveal any significant changes across the groups.

CONCLUSION

FH-RBCs induce endothelial dysfunction dependent on LDL-c levels via arginase 1 and ROS-dependent mechanisms.

Decreased oxidative stress and altered urinary oxylipidome by intravenous omega-3 fatty acid emulsion in a randomized controlled trial of older subjects hospitalized for COVID-19

Proinflammatory bioactive lipid mediators and oxidative stress are increased in coronavirus disease 2019 (COVID-19). The randomized controlled single-blind trial COVID-Omega-F showed that intravenous omega-3 polyunsaturated fatty acids (n-3 PUFA) shifted the plasma lipid signature of COVID-19 towards increased proresolving precursor levels and decreased leukotoxin diols, associated with a beneficial immunodulatory response. The present study aimed to determine the effects of n-3 PUFA on the urinary oxylipidome and oxidative stress in COVID-19. From the COVID-Omega-F trial, 20 patients hospitalized for COVID-19 had available serial urinary samples collected at baseline, after 24-48 h, and after completing 5 days treatment with one daily intravenous infusion (2 mL/kg) of either placebo (NaCl; n = 10) or a lipid emulsion containing 10 g of n-3 PUFA per 100 mL (n = 10). Urinary eicosanoids and isoprostanes were analyzed by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). Erythrocytes obtained at the different time-points from n = 10 patients (n = 5 placebo and n = 5 n-3 PUFA) were used for determination of reactive oxygen species. Intravenous n-3 PUFA emulsion administration altered eicosanoid metabolites towards decreased levels for mediators of inflammation and thrombosis, and increased levels of the endothelial function mediator prostacyclin. Furthermore, non-enzymatic metabolism was skewed towards n-3 PUFA-derived metabolites with potential anti-inflammatory and pro-resolving effects. The oxidative stress marker 15-F_2t-isoprostane was significantly lower in patients receiving n-3 PUFA treatment, who also exhibited significantly decreased erythrocyte oxidative stress compared with placebo-treated patients. These findings point to additional beneficial effects of intravenous n-3 PUFA emulsion treatment through a beneficial oxylipin profile and decreased oxidative stress in COVID-19.

Unidirectional fluxes of monovalent ions in human erythrocytes compared with lymphoid U937 cells: Transient processes after stopping the sodium pump and in response to osmotic challenge

Recently, we have developed software that allows, using a minimum of required experimental data, to find the characteristics of ion homeostasis and a list of all unidirectional fluxes of monovalent ions through the main pathways in the cell membrane both in a balanced state and during the transient processes. Our approach has been successfully validated in human proliferating lymphoid U937 cells during transient processes after stopping the Na/K pump by ouabain and for staurosporine-induced apoptosis. In present study, we used this approach to find the characteristics of ion homeostasis and the monovalent ion fluxes through the cell membrane of human erythrocytes in a resting state and during the transient processes after stopping the Na/K pump with ouabain and in response to osmotic challenge. Due to their physiological significance, erythrocytes remain the object of numerous studies, both experimental and computational methods. Calculations showed that, under physiological conditions, the K+ fluxes through electrodiffusion channels in the entire erythrocyte ion balance is small compared to the fluxes through the Na/K pump and cation-chloride cotransporters. The proposed computer program well predicts the dynamics of the erythrocyte ion balance disorders after stopping the Na/K pump with ouabain. In full accordance with predictions, transient processes in human erythrocytes are much slower than in proliferating cells such as lymphoid U937 cells. Comparison of real changes in the distribution of monovalent ions under osmotic challenge with the calculated ones indicates a change in the parameters of the ion transport pathways through the plasma membrane of erythrocytes in this case. The proposed approach may be useful in studying the mechanisms of various erythrocyte dysfunctions.

Red Blood Cell Malfunction in COVID-19: Molecular Mechanisms and Therapeutic Targets

The world has been facing a pandemic for the past 2 years. COVID-19 still leads to millions of deaths worldwide, while deteriorating the global economy. The need for therapeutic targets, thus, remains. Interestingly, red blood cells, apart from gas exchange, also serve as modulators of innate and adaptive immunity. This function is accommodated mainly by surface molecules (proteins, lipids, and carbohydrates) and increased antioxidant capacity. However, under the circumstances of a disease state, red blood cells can become proinflammatory cells. Recent evidence has shown that, in the context of COVID-19, erythrocytes present protein oxidation, decreased antioxidant capacity, increased glycolysis, altered membrane lipidome, increased binding of Cytosine-Guanine (CpG) DNA and complement proteins, and low CD47 levels. These changes lead to an erythrocyte-dependent inflammation, which possibly participates in the hyperinflammation status of COVID-19. The current knowledge for the dysfunction of red blood cells during COVID-19 implies that the BAND3 protein and toll-like receptor 9 are potential therapeutic targets for COVID-19.

Portal Vein and Mesenteric Artery Thrombosis Following the Administration of an Ad26.COV2-S Vaccine-First Case from Romania: A Case Report

COVID-19 has significantly affected public health, social life, and economies worldwide. The only effective way to combat the pandemic is through vaccines. Although the vaccines have been in use for some time, safety concerns have still been raised. The most typical adverse effects of receiving a COVID-19 vaccine are localized reactions near the injection site, followed by general physical symptoms such as headaches, fatigue, muscle pain, and fever. Additionally, some people may experience VITT (vaccine-induced immune thrombotic thrombocytopenia), a rare side effect after vaccination. We present the case of a 60-year-old female patient that developed VITT-like symptoms with spleno-portal thrombosis and intestinal ischemia two weeks after the administration of the Ad26.COV2-S vaccine. Surgical treatment consisted of extensive bowel resection with end jejunostomy and feeding ileostomy. Two weeks after the first operation, a duodenal-ileal anastomosis was performed. The patient was discharged five weeks after the onset of the symptoms. Although some rare adverse effects are associated with the SARS-CoV-2 vaccines, the risk of hospitalization from these harmful effects is lower than the risk of hospitalization from COVID-19. Therefore, recognizing VITT is significant for ensuring the early treatment of clots and proper follow-up.

Hyperbaric oxygen for treatment of long COVID-19 syndrome (HOT-LoCO): protocol for a randomised, placebo-controlled, double-blind, phase II clinical trial

INTRODUCTION

Long COVID-19, where symptoms persist 12 weeks after the initial SARS-CoV-2-infection, is a substantial problem for individuals and society in the surge of the pandemic. Common symptoms are fatigue, postexertional malaise and cognitive dysfunction. There is currently no effective treatment and the underlying mechanisms are unknown, although several hypotheses exist, with chronic inflammation as a common denominator. In prospective studies, hyperbaric oxygen therapy (HBOT) has been suggested to be effective for the treatment of similar syndromes such as chronic fatigue syndrome and fibromyalgia. A case series has suggested positive effects of HBOT in long COVID-19. This randomised, placebo-controlled clinical trial will explore HBOT as a potential treatment for long COVID-19. The primary objective is to evaluate if HBOT improves health-related quality of life (HRQoL) for patients with long COVID-19 compared with placebo/sham. The main secondary objective is to evaluate whether HBOT improves endothelial function, objective physical performance and short-term HRQoL.

METHODS AND ANALYSIS

A randomised, placebo-controlled, double-blind, phase II clinical trial in 80 previously healthy subjects debilitated due to long COVID-19, with low HRQoL. Clinical data, HRQoL questionnaires, blood samples, objective tests and activity metre data will be collected at baseline. Subjects will be randomised to a maximum of 10 treatments with hyperbaric oxygen or sham treatment over 6 weeks. Assessments for safety and efficacy will be performed at 6, 13, 26 and 52 weeks, with the primary endpoint (physical domains in RAND 36-Item Health Survey) and main secondary endpoints defined at 13 weeks after baseline. Data will be reviewed by an independent data safety monitoring board.

ETHICS AND DISSEMINATION

The trial is approved by the Swedish National Institutional Review Board (2021-02634) and the Swedish Medical Products Agency (5.1-2020-36673). Positive, negative and inconclusive results will be published in peer-reviewed scientific journals with open access.

TRIAL REGISTRATION NUMBER

NCT04842448.

Immunomodulatory roles of red blood cells

PURPOSE OF THE REVIEW

To discuss recent advances supporting the role of red blood cells (RBCs) in the host immune response.

RECENT FINDINGS

Over the last century, research has demonstrated that red blood cells exhibit functions beyond oxygen transport, including immune function. Recent work indicates that the nucleic acid sensing receptor, toll-like receptor 9 (TLR9), is expressed on the RBC surface and implicated in innate immune activation and red cell clearance during inflammatory states. In addition to this DNA-sensing role of RBCs, there is growing evidence that RBCs may influence immune function by inducing vascular dysfunction. RBC proteomics and metabolomics have provided additional insight into RBC immune function, with several studies indicating changes to RBC membrane structure and metabolism in response to severe acute respiratory syndrome coronavirus 2 infection. These structural RBC changes may even provide insight into the pathophysiology of the 'long-coronavirus disease 2019' phenomenon. Finally, evidence suggests that RBCs may influence host immune responses via complement regulation. Taken together, these recent findings indicate RBCs possess immune function. Further studies will be required to elucidate better how RBC immune function contributes to the heterogeneous host response during inflammatory states.

SUMMARY

The appreciation for nongas exchanging, red blood cell immune functions is rapidly growing. A better understanding of these RBC functions may provide insight into the heterogeneity observed in the host immune response to infection and inflammation.

On the origin of nitrosylated hemoglobin in COVID-19: Endothelial NO capture or redox conversion of nitrite?: Experimental results and a cautionary note on challenges in translational research

In blood, the majority of endothelial nitric oxide (NO) is scavenged by oxyhemoglobin, forming nitrate while a small part reacts with dissolved oxygen to nitrite; another fraction may bind to deoxyhemoglobin to generate nitrosylhemoglobin (HbNO) and/or react with a free cysteine to form a nitrosothiol. Circulating nitrite concentrations in healthy individuals are 200-700 nM, and can be even lower in patients with endothelial dysfunction. Those levels are similar to HbNO concentrations ([HbNO]) recently reported, whereby EPR-derived erythrocytic [HbNO] was lower in COVID-19 patients compared to uninfected subjects with similar cardiovascular risk load. We caution the values reported may not reflect true (patho)physiological concentrations but rather originate from complex chemical interactions of endogenous nitrite with hemoglobin and ascorbate/N-acetylcysteine. Using an orthogonal detection method, we find baseline [HbNO] to be in the single-digit nanomolar range; moreover, we find that these antioxidants, added to blood collection tubes to prevent degradation, artificially generate HbNO. Since circulating nitrite also varies with lifestyle, dietary habit and oral bacterial flora, [HbNO] may not reflect endothelial activity alone. Thus, its use as early marker of NO-dependent endothelial dysfunction to stratify COVID-19 patient risk may be premature. Moreover, oxidative stress not only impairs NO formation/bioavailability, but also shifts the chemical landscape into which NO is released, affecting its downstream metabolism. This compromises the endothelium's role as gatekeeper of tissue nutrient supply and modulator of blood cell function, challenging the body's ability to maintain redox balance. Further studies are warranted to clarify whether the nature of vascular dysfunction in COVID-19 is solely of endothelial nature or also includes altered erythrocyte function.

The Potential of Thyroid Hormone Therapy in Severe COVID-19: Rationale and Preliminary Evidence

Tissue hypoxia is one of the main pathophysiologic mechanisms in sepsis and particularly in COVID-19. Microvascular dysfunction, endothelialitis and alterations in red blood cell hemorheology are all implicated in severe COVID-19 hypoxia and multiorgan dysfunction. Tissue hypoxia results in tissue injury and remodeling with re-emergence of fetal programming via hypoxia-inducible factor-1α (HIF-1a)-dependent and -independent pathways. In this context, thyroid hormone (TH), a critical regulator of organ maturation, may be of relevance in preventing fetal-like hypoxia-induced remodeling in COVID-19 sepsis. Acute triiodothyronine (T3) treatment can prevent cardiac remodeling and improve recovery of function in clinical settings of hypoxic injury as acute myocardial infarction and by-pass cardiac surgery. Furthermore, T3 administration prevents tissue hypoxia in experimental sepsis. On the basis of this evidence, the use of T3 treatment was proposed for ICU (Intensive Care Unit) COVID-19 patients (Thy-Support, NCT04348513). The rationale for T3 therapy in severe COVID-19 and preliminary experimental and clinical evidence are discussed in this review.

Changes in the Blood Viscosity in Patients With SARS-CoV-2 Infection

Coronavirus disease 2019 (COVID-19) is caused by a novel virus known as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). SARS-CoV-2-induced hyperinflammation together with alteration of plasma proteins, erythrocyte deformability, and platelet activation, may affect blood viscosity. Thus, this review aimed to study the link between SARS-CoV-2 infection and alteration of blood viscosity in COVID-19 patients. In order to review findings related to hyperviscosity in COVID-19, we suggested a protocol for narrative review of related published COVID-19 articles. Hyperviscosity syndrome is developed in different hematological disorders including multiple myeloma, sickle cell anemia, Waldenstorm macroglobulinemia, polycythemia, and leukemia. In COVID-19, SARS-CoV-2 may affect erythrocyte morphology via binding of membrane cluster of differentiation 147 (CD147) receptors, and B and 3 proteins on the erythrocyte membrane. Variations in erythrocyte fragility and deformability with endothelial dysfunction and oxidative stress in SARS-CoV-2 infection may cause hyperviscosity syndrome in COVID-19. Of interest, hyperviscosity syndrome in COVID-19 may cause poor tissue perfusion, peripheral vascular resistance, and thrombosis. Most of the COVID-19 patients with a blood viscosity more than 3.5 cp may develop coagulation disorders. Of interest, hyperviscosity syndrome is more commonly developed in vaccine recipients who had formerly received the COVID-19 vaccine due to higher underlying immunoglobulin concentrations, and only infrequently in those who have not received the COVID-19 vaccine. Taken together, these observations are untimely too early to give a final connotation between COVID-19 vaccination and the risk for development of hyperviscosity syndrome, consequently prospective and retrospective studies are necessary in this regard.

The resolvin D2 - GPR18 axis is expressed in human coronary atherosclerosis and transduces atheroprotection in apolipoprotein E deficient mice

Chronic inflammation in atherosclerosis reflects a failure in the resolution of inflammation. Pro-resolving lipid mediators derived from omega-3 fatty acids reduce the development of atherosclerosis in murine models. The aim of the present study was to decipher the role of the specialized proresolving mediator (SPM) resolvin D2 (RvD2) in atherosclerosis and its signaling through the G-protein coupled receptor (GPR) 18. The ligand and receptor were detected in human coronary arteries in relation to the presence of atherosclerotic lesions and its cellular components. Importantly, RvD2 levels were significantly higher in atherosclerotic compared with healthy human coronary arteries. Furthermore, apolipoprotein E (ApoE) deficient hyperlipidemic mice were treated with either RvD2 or vehicle in the absence and presence of the GPR18 antagonist O-1918. RvD2 significantly reduced atherosclerosis, necrotic core, and pro-inflammatory macrophage marker expression. RvD2 in addition enhanced macrophage phagocytosis. The beneficial effects of RvD2 were not observed in the presence of O-1918. Taken together, these results provide evidence of atheroprotective pro-resolving signalling through the RvD2-GPR18 axis.