Peritoneal Inflammation in PD-Related Peritonitis Induces Systemic Eryptosis: In Vitro and In Vivo Assessments

Erythrocytes (RBCs) have a highly specialized and organized membrane structure and undergo programmed cell death, known as eryptosis. Our preliminary data show a significant increase in the eryptosis during peritoneal dialysis (PD)-associated peritonitis. The objectives of the present study were assessment of the incrementation of eryptosis in PD patients with peritonitis, evaluation of the relationship between systemic eryptosis in peritonitis and specific peritonitis biomarkers in PD effluent (PDE), and confirmation of the induction of eryptosis by peritonitis in a vitro setting. We enrolled 22 PD patients with peritonitis and 17 healthy subjects (control group, CTR). For the in vivo study, eryptosis was measured in freshly isolated RBCs. For the in vitro study, healthy RBCs were exposed to the plasma of 22 PD patients with peritonitis and the plasma of the CTR group for 2, 4, and 24 h. Eryptosis was evaluated by flow cytometric analyses in vivo and in vitro. PDE samples were collected for biomarkers analysis.The percentage of eryptotic RBCs was significantly higher in PD patients with peritonitis than in CTR (PD patients with peritonitis: 7.7; IQR 4.3-14.2, versus CTR: 0.8; IQR 0.7-1.3; p < 0.001). We confirmed these in vivo results by in vitro experiments: healthy RBCs incubated with plasma from PD patients with peritonitis demonstrated a significant increase in eryptosis compared to healthy RBCs exposed to plasma from the control group at all times. Furthermore, significant positive correlations were observed between eryptosis level and all analyzed peritoneal biomarkers of peritonitis. We investigated a potential connection between systemic eryptosis and peritoneal biomarkers of peritonitis. Up-regulation of inflammatory markers could explain the increased rate of systemic eryptosis during PD-related peritonitis.

Apoptosis and eryptosis: similarities and differences

Eryptosis is a regulated cell death (RCD) of mature erythrocytes initially described as a counterpart of apoptosis for enucleated cells. However, over the recent years, a growing number of studies have emphasized certain differences between both cell death modalities. In this review paper, we underline the hallmarks of eryptosis and apoptosis and highlight resemblances and dissimilarities between both RCDs. We summarize and critically discuss differences in the impact of caspase-3, Ca2+ signaling, ROS signaling pathways, opposing roles of casein kinase 1α, protein kinase C, Janus kinase 3, cyclin-dependent kinase 4, and AMP-activated protein kinase to highlight a certain degree of divergence between apoptosis and eryptosis. This review emphasizes the crucial importance of further studies that focus on deepening our knowledge of cell death machinery and identifying novel differences between cell death of nucleated and enucleated cells. This might provide evidence that erythrocytes can be defined as viable entities capable of programmed cell destruction. Additionally, the revealed cell type-specific patterns in cell death can facilitate the development of cell death-modulating therapeutic agents.

Eryptosis in Peritoneal Dialysis-Related Peritonitis: The Potential Role of Inflammation in Mediating the Increase in Eryptosis in PD

Background: Peritonitis and exit site infections are the main complications of patients treated with peritoneal dialysis (PD). Erythrocytes (red blood cells—RBCs) are very sensitive cells, and they are characterized by eryptosis (programmed cell death). The purpose of this research was to assess eryptosis in PD patients with PD-related peritonitis and its connection to inflammatory markers in vivo and in vitro. Material and Methods: In this study, we included 65 PD patients: 34 PD patients without systemic inflammation nor PD-related peritonitis in the previous 3 months, and 31 PD patients with an acute episode of PD-related peritonitis. We measured C-reactive protein (CRP) and cytokine (IL-1β, IL-6, and IL-18) levels as systemic inflammatory markers. Eryptosis was evaluated by flow cytometric analyses in freshly isolated RBCs. The induction of eryptosis due to in vitro exposure to IL-1β, IL-6, and IL-18 was verified. Results: Eryptosis was significantly higher in PD patients with peritonitis (9.6%; IQR 4.2−16.7), compared to the those in the other group (2.7%; IQR 1.6−3.9) (p < 0.0001). Significant positive correlations were noticed between eryptosis and CRP, IL-1β, and IL-6. RBCs, incubated with greater concentrations of all cytokines in vitro, resulted in significantly higher occurrences of eryptosis in comparison with those incubated with lower concentration and with untreated cell (p < 0.05), and for those with extensive exposure (p < 0.05). Conclusion: In conclusion, we investigated a potential relationship between systemic eryptosis and the in vivo and in vitro inflammatory damage of the peritoneal membrane during peritonitis. Thus, the presented results revealed that upregulated inflammatory markers and immune system dysregulation could be the cause of high levels of systemic eryptosis during PD-related peritonitis.

Impact of acute inflammation on Band 3 protein anion exchange capability in human erythrocytes

Objective: The impact of acute inflammation, revealed by C-reactive protein (CRP) plasma levels, has been studied on the erythrocytes anion exchanger Band 3 protein.Methods: Anion exchange capability through Band 3 protein, lipid peroxidation, -SH membrane groups and intracellular GSH levels have been measured on erythrocytes from patients with CRP >8 mg/L.Results: Under acute inflammation, a significant increase in anion exchange capability, increased lipid peroxidation, decreased-SH groups and GSH content were observed. Serum CRP levels recovery (after one week) was associated to -SH groups and GSH recovery, but not to anion exchange capability restoration. After 2 months, a total recovery of all parameters was observed.Conclusion: Band 3 protein anion exchange capability is affected by acute inflammation; the accelerated rate of anion exchange may be mainly due to lipid peroxidation, rather than to -SH groups oxidation; erythrocytes renewal could be needed to have a total recover of their function.

In Vitro Induction of Eryptosis by Uremic Toxins and Inflammation Mediators in Healthy Red Blood Cells

Eryptosis is the stress-induced RBC (red blood cell) death mechanism. It is known that eryptosis is largely influenced by plasma and blood composition, and that it is accelerated in patients affected by chronic kidney disease (CKD). The aim of this study is to evaluate the eryptosis rate in healthy RBCs treated with different concentration of IL-6, IL-1β, urea and p-cresol, comparable to plasmatic level of CKD patients, at different time points. We exposed healthy RBCs to increasing concentrations of IL-6, IL-1β, urea and p-cresol. Morphological markers of eryptosis (cell membrane scrambling, cell shrinkage and PS exposure at RBC surface) were evaluated by flow cytometric analyses. The cytotoxic effect of cytokines and uremic toxins were analyzed in vitro on healthy RBCs at 4, 8 and 24 h. Morphology of treated RBCs was dramatically deranged, and the average cell volume was significantly higher in RBCs exposed to higher concentration of all molecules (all, p < 0.001). Furthermore, healthy RBCs incubated with each molecules demonstrated a significant increase in eryptosis. Cytofluorimetric analysis of eryptosis highlighted significantly higher cell death rate in RBCs incubated with a higher concentration of both cytokines compared with RBCs incubated with a lower concentration (all, p < 0.05). In conclusion, our data show that cytokines and uremic toxins have a harmful effect on RBCs viability and trigger eryptosis. Further studies are necessary to validate these results in vivo and to associate abnormal eryptosis with cytokine levels in CKD patients. The eryptosis pathway could, moreover, become a new promising target for anemia management in CKD patients.

Band 3 protein function and oxidative stress in erythrocytes

Band 3 protein (B3p), anion transporter, allows the HCO₃ ^- /Cl^- exchange across plasma membrane and plays an important role for erythrocytes homeostasis. In addition, B3p is linked to proteins cytoskeleton, thus contributing to cell shape and deformability, essential to erythrocytes adjustment within narrowest capillaries. Taking into account that erythrocytes are a suitable cell model to investigate the response of the oxidative stress effects, B3p functions, and specifically anion exchange capability, determining the rate constant for SO₄ ^2- uptake, has been considered. As, in the latter years, rising attention has been addressed to membrane transport system, and particularly to this protein, the present mini-review has been conceived to report the most recent knowledge about B3p, with specific regard to its functions in oxidative stress conditions, including oxidative stress-related diseases.

The emerging roles of eryptosis in liver diseases

Erythrocytes undergo programmed cell death, similar to apoptosis, known as eryptosis. This process is a result of several factors including hyperosmolarity, oxidative stress, and exposure to xenobiotics, and is characterized by the breakdown of membrane phospholipid asymmetry, the clustering of band 3, and the generation of red blood cell-derived microparticles. Under pathological conditions, the liver is the primary site of erythrocyte clearance and plays an important role in iron recycling. Phosphatidylserine exposure and band-3 clustering on eryptotic erythrocytes represent mainly pro-phagocytic signals. Further, the percentage of eryptotic erythrocytes is enhanced in the circulating blood of patients with hepatic failure, hyperbilirubinemia, and nonalcoholic steatohepatitis. In this review, we concentrate on recent progress regarding the pathophysiological roles of eryptosis in liver diseases.

Inflammatory Pathways to Anemia in the Frail Elderly

Anemia is a common, yet often overlooked, geriatric syndrome characterized by reduced hemoglobin levels and associated with adverse health outcomes and early mortality. Evidence suggests that anemia is an independent risk factor for frailty in older adults. In this article, the authors review the evidence for the role of chronic inflammation in the pathogenesis of anemia in the frail elderly. Understanding the relationships between anemia, frailty, and chronic inflammation will pave the way for the development of novel interventional strategies for the treatment and prevention of anemia and, likely, also frailty in older adults.

Increased eryptosis in smokers is associated with the antioxidant status and C-reactive protein levels

Cigarette smoking has been linked with oxidative stress and inflammation. In turn, eryptosis, the suicidal erythrocyte death similar to apoptosis that can be triggered by oxidative stress, has been associated with chronic inflammatory diseases including atherosclerosis. However, the link between smoking and eryptosis has not been explored so far. The aim of the present study was to determine the level of eryptotic erythrocytes in healthy male smokers (n = 21) compared to non-smokers (n = 21) and assess its relationship with systemic inflammation (CRP) as well as with antioxidant defense (GSH) and their resistance to ex-vivo induced hemolysis. Smoking caused an increase in phosphatidylserine translocation outside the erythrocyte membrane (hallmark of eryptosis), significantly correlated to the plasma level of CRP (r = 0.546) and GSH concentration in erythrocytes (r=-0.475). With respect to non-smokers, smokers show a marginal increase of total leucocytes and erythrocyte volume, no modifications of the RBC resistance to oxidative stress-induced hemolysis and hematological and lipid parameters unvaried. We conclude that the inflammatory status (high CRP levels) and RBC oxidative stress (low GSH levels) caused by cigarette smoking are associated with an increase of eryptotic erythrocytes, a yet unknown relationship potentially involved with atherosclerosis and cardiovascular disease in smokers.