Pharmacological targeting of glucose-6-phosphate dehydrogenase in human erythrocytes by Bay 11-7082, parthenolide and dimethyl fumarate

Hemocompatibility studies in nanotoxicology: Hemolysis or eryptosis? (A review)

Hemocompatibility evaluation is an important step in nanotoxicological studies. It is generally accepted that nanomaterials promote lysis of erythrocytes, blood clotting, alter phagocytosis, and upregulate pro-inflammatory cytokines. However, there are no standardized guidelines for testing nanomaterials hemocompatibility despite the fact that nanomaterials enter the bloodstream and interact with blood cells. In this review, the current knowledge on the ability of nanomaterials to induce distinct cell death modalities of erythrocytes is highlighted primarily focusing on hemolysis and eryptosis. This review aims to summarize the molecular mechanisms underlying erythrotoxicity of nanomaterials and critically compare the sensitivity and efficiency of hemolysis or eryptosis assays for nanomaterials blood compatibility testing. The list of eryptosis-inducing nanomaterials is growing, but it is still difficult to generalize how physico-chemical properties of nanoparticles affect eryptosis degree and molecular mechanisms involved. Thus, another aim of this review is to raise the awareness of eryptosis as a nanotoxicological tool to encourage the corresponding studies. It is worthwhile to consider adding eryptosis to in vitro nanomaterials hemocompatibility testing protocols and guidelines.

Desipramine induces eryptosis in human erythrocytes, an effect blunted by nitric oxide donor sodium nitroprusside and N-acetyl-L-cysteine but enhanced by Calcium depletion

Background: Desipramine a representative of tricyclic antidepressants (TCAs) promotes recovery of depressed patients by inhibition of reuptake of neurotransmitters serotonin (SER) and norepinephrine (NE) in the presynaptic membrane by directly blocking their respective transporters SERT and NET.Aims: To study the effect of desipramine on programmed erythrocyte death (eryptosis) and explore the underlying mechanisms.Methods: Phosphatidylserine (PS) exposure on the cell surface as marker of cell death was estimated from annexin-V-binding, cell volume from forward scatter in flow cytometry. Hemolysis was determined photometrically, and intracellular glutathione [GSH]i from high performance liquid chromatography.Results: Desipramine dose-dependently significantly enhanced the percentage of annexin-V-binding cells and didn´t impact glutathione (GSH) synthesis. Desipramine-induced eryptosis was significantly reversed by pre-treatment of erythrocytes with either nitric oxide (NO) donor sodium nitroprusside (SNP) or N-acetyl-L-cysteine (NAC). The highest inhibitory effect was obtained by using both inhibitors together. Calcium (Ca2+) depletion aggravated desipramine-induced eryptosis. Changing the order of treatment, i.e. desipramine first followed by inhibitors, could not influence the inhibitory effect of SNP or NAC.Conclusion: Antidepressants-caused intoxication can be treated by SNP and NAC, respectively. B) Patients with chronic hypocalcemia should not be treated with tricyclic anti-depressants or their dose should be noticeably reduced.

Casein kinase 1α mediates eryptosis: a review

Eryptosis is a coordinated non-lytic cell death of erythrocytes characterized by cell shrinkage, cell membrane scrambling, Ca²⁺ influx, ceramide accumulation, oxidative stress, activation of calpain and caspases. Physiologically, it aims at removing damaged or aged erythrocytes from circulation. A plethora of diseases are associated with enhanced eryptosis, including metabolic diseases, cardiovascular pathology, renal and hepatic diseases, hematological disorders, systemic autoimmune pathology, and cancer. This makes eryptosis and eryptosis-regulating signaling pathways a target for therapeutic interventions. This review highlights the eryptotic signaling machinery containing several protein kinases and its small molecular inhibitors with a special emphasis on casein kinase 1α (CK1α), a serine/threonine protein kinase with a broad spectrum of activity. In this review article, we provide a critical analysis of the regulatory role of CK1α in eryptosis, highlight triggers of CK1α-mediated suicidal death of red blood cells, cover the knowledge gaps in understanding CK1α-driven eryptosis and discover the opportunity of CK1α-targeted pharmacological modulation of eryptosis. Moreover, we discuss the directions of future research focusing on uncovering crosstalks between CK1α and other eryptosis-regulating kinases and pathways.

Giardia lamblia G6PD::6PGL Fused Protein Inhibitors Decrease Trophozoite Viability: A New Alternative against Giardiasis

Treatments to combat giardiasis have been reported to have several drawbacks, partly due to the drug resistance and toxicity of current antiparasitic agents. These constraints have prompted many researchers to investigate new drugs that act against protozoan parasites. Enzyme inhibition is an important means of regulating pathogen metabolism and has recently been identified as a significant alternative target in the search for new treatments. Glucose-6-phosphate dehydrogenase and 6-phosphogluconolactonase (G6PD::6PGL) is a bifunctional enzyme involved in the pentose phosphate pathway (PPP) in Giardia lamblia (G. lamblia). The G. lamblia enzyme is unusual since, unlike the human enzyme, it is a fused enzyme. Here, we show, through inhibition assays, that an in-house chemical library of 120 compounds and four target compounds, named CNZ-7, CNZ-8, CMC-1, and FLP-2, are potent inhibitors of the G. lamblia G6PD::6PGL fused enzyme. With a constant (k2) of 2.3, 3.2, and 2.8 M−1 s−1, respectively, they provoke alterations in the secondary and tertiary protein structure and global stability. As a novel approach, target compounds show antigiardial activity, with IC50 values of 8.7, 15.2, 15.3, and 24.1 µM in trophozoites from G. lamblia. Moreover, these compounds show selectivity against G. lamblia, since, through counter-screening in Caco-2 and HT29 human cells, they were found to have low toxicity. This finding positions these compounds as a potential and attractive starting point for new antigiardial drugs.

Myostatin Knockout Limits Exercise-Induced Reduction in Bovine Erythrocyte Oxidative Stress by Enhancing the Efficiency of the Pentose Phosphate Pathway

Moderate exercise can strengthen the body, however, exhaustive exercise generates large amounts of reactive oxygen species (ROS). Although erythrocytes have antioxidant systems that quickly eliminate ROS, erythrocytes become overwhelmed by ROS when the body is under oxidative stress, such as during exhaustive exercise. Myostatin (MSTN) has important effects on muscle hair development. Individuals lacking myostatin (MSTN) exhibit increased muscle mass. The purpose of this study was to investigate the mechanism by which MSTN affects erythrocyte antioxidant changes after exhaustive exercise in cattle. Antioxidant and metabolite detection analysis, western blotting, immunofluorescence, and fatty acid methyl ester analysis were used to assess exercise-associated antioxidant changes in erythrocytes with or without MSTN. Knockdown of MSTN enhances Glucose-6-phosphate dehydrogenase (G6PD) activity after exhaustive exercise. MSTN and its receptors were present on the erythrocyte membrane, but their levels, especially that of TGF-β RI, were significantly reduced in the absence of MSTN and following exhaustive exercise. Our results suggest that knockout of MSTN accelerates the pentose phosphate pathway (PPP), thereby enhancing the antioxidant capacity of erythrocytes. These results provide important insights into the role of MSTN in erythrocyte antioxidant regulation after exhaustive exercise.

Eryptosis: Programmed Death of Nucleus-Free, Iron-Filled Blood Cells

Human erythrocytes are organelle-free cells packaged with iron-containing hemoglobin, specializing in the transport of oxygen. With a total number of approximately 25 trillion cells per individual, the erythrocyte is the most abundant cell type not only in blood but in the whole organism. Despite their low complexity and their inability to transcriptionally upregulate antioxidant defense mechanisms, they display a relatively long life time, of 120 days. This ensures the maintenance of tissue homeostasis where the clearance of old or damaged erythrocytes is kept in balance with erythropoiesis. Whereas the regulatory mechanisms of erythropoiesis have been elucidated over decades of intensive research, the understanding of the mechanisms of erythrocyte clearance still requires some refinement. Here, we present the main pathways leading to eryptosis, the programmed death of erythrocytes, with special emphasis on Ca²⁺ influx, the generation of ceramide, oxidative stress, kinase activation, and iron metabolism. We also compare stress-induced erythrocyte death with erythrocyte ageing and clearance, and discuss the similarities between eryptosis and ferroptosis, the iron-dependent regulated death of nucleated blood cells. Finally, we focus on the pathologic consequences of deranged eryptosis, and discuss eryptosis in the context of different infectious diseases, e.g., viral or parasitic infections, and hematologic disorders.

Hop-derived fraction rich in beta acids and prenylflavonoids regulates the inflammatory response in dendritic cells differently from quercetin: unveiling metabolic changes by mass spectrometry-based metabolomics

Dendritic cells (DCs) represent a heterogeneous family of immune cells that link innate and adaptive immunity and their activation is linked to metabolic changes that are essential to support their activity and function. Hence, targeting the metabolism of DCs represents an opportunity to modify the inflammatory and immune response. Among the natural matrices, Humulus lupulus (Hop) compounds have recently been shown to exhibit immunomodulatory and anti-inflammatory activity. This study aimed to evaluate the ability of specific Hop fractions to modulate DCs metabolism after stimulation with lipopolysaccharide (LPS) by an untargeted metabolomics approach and compare their effect with flavonol quercetin. Following liquid chromatography-based fractionation, three fractions (A, B, and C) were obtained and tested. Cytokine and gene expression were evaluated using ELISA and qPCR, respectively, while the untargeted metabolomics analysis was performed using a combined HILIC-HRMS and DI-FT-ICR approach. The HOP C fraction and quercetin could both reduce the production of several inflammatory cytokines such as IL-6, IL-1α, IL-1β, and TNF, but differently from quercetin, the HOP C mechanism is independent of extracellular iron-sequestration and showed significant upregulation of the Nrf2/Nqo1 pathway and Ap-1 compared to quercetin. The untargeted analysis revealed the modulation of several key pathways linked to pro-inflammatory and glycolytic phenotypes. In particular, HOP C treatment could modulate the oxidative step of the pentose phosphate pathway (PPP) and reduce the inflammatory mediator succinate, citrulline, and purine-pyrimidine metabolism, differently from quercetin. These results highlight the potential anti-inflammatory mechanism of specific Hop-derived compounds in restoring the dysregulated metabolism in DCs, which can be used in preventive or adjuvant therapies to suppress the undesirable inflammatory response.

Human erythrocytes, nuclear factor kappaB (NFκB) and hydrogen sulfide (H2S) - from non-genomic to genomic research

Enucleated mature human erythrocytes possess NFĸBs and their upstream kinases. There is a negative correlation between eryptosis (cell death of erythrocytes) and the amount of NFĸB subunits p50 and Rel A (p65). This finding is based on the fact that young erythrocytes have the highest levels of NFĸBs and the lowest eryptosis rate, while in old erythrocytes the opposite ratio prevails. Human erythrocytes (hRBCs) effectively control the homeostasis of the cell membrane permeable anti-inflammatory signal molecule hydrogen sulfide (H2S). They endogenously produce H2S via both non-enzymic (glutathione-dependent) and enzymic processes (mercaptopyruvate sulfur transferase-dependent). They uptake H2S from diverse tissues and very effectively degrade H2S via methemoglobin (Hb-Fe3+)-catalyzed oxidation. Interestingly, a reciprocal correlation exists between the intensity of inflammatory diseases and endogenous levels of H2S. H2S deficiency has been observed in patients with diabetes, psoriasis, obesity, and chronic kidney disease (CKD). Furthermore, endogenous H2S deficiency results in impaired renal erythropoietin (EPO) production and EPO-dependent erythropoiesis. In general we can say: dynamic reciprocal interaction between tumor suppressor and oncoproteins, orchestrated and sequential activation of pro-inflammatory NFĸB heterodimers (RelA-p50) and the anti-inflammatory NFĸB-p50 homodimers for optimal inflammation response, appropriate generation, subsequent degradation of H2S etc., are prerequisites for a functioning cell and organism. Diseases arise when the fragile balance between different signaling pathways that keep each other in check is permanently disturbed. This work deals with the intact anti-inflammatory hRBCs and their role as guarantors to maintain the redox status in the physiological range, a basis for general health and well-being.

The specific PKC-α inhibitor chelerythrine blunts costunolide-induced eryptosis

Costunolide, a natural sesquiterpene lactone, has multiple pharmacological activities such as neuroprotection or induction of apoptosis and eryptosis. However, the effects of costunolide on pro-survival factors and enzymes in human erythrocytes, e.g. glutathione and glucose-6-phosphate dehydrogenase (G6PDH) respectively, have not been studied yet. Our aim was to determine the mechanisms underlying costunolide-induced eryptosis and to reverse this process. Phosphatidylserine exposure was estimated from annexin-V-binding, cell volume from forward scatter in flow cytometry, and intracellular glutathione [GSH]_i from high performance liquid chromatography. The oxidized status of intracellular glutathione and enzyme activities were measured by spectrophotometry. Treatment of erythrocytes with costunolide dose-dependently enhanced the percentage of annexin-V-binding cells, decreased the cell volume, depleted [GSH]_i and completely inhibited G6PDH activity. The effects of costunolide on annexin-V-binding and cell volume were significantly reversed by pre-treatment of erythrocytes with the specific PKC-α inhibitor chelerythrine. The latter, however, had no effect on costunolide-induced GSH depletion. Costunolide induces eryptosis, depletes [GSH]_i and inactivates G6PDH activity. Furthermore, our study reveals an inhibitory effect of chelerythrine on costunolide-induced eryptosis, indicating a relationship between costunolide and PKC-α. In addition, chelerythrine acts independently of the GSH depletion. Understanding the mechanisms of G6PDH inhibition accompanied by GSH depletion should be useful for development of anti-malarial therapeutic strategies or for synthetic lethality-based approaches to escalate oxidative stress in cancer cells for their sensitization to chemotherapy and radiotherapy.

Metabolomics analysis of the effects of quercetin on hepatotoxicity induced by acrylamide exposure in rats

Acrylamide (AA) widely exists in human diet, which makes the public inevitably exposed to AA in daily life. Thisstudy aimed to investigatethe effects of quercetin on AA-induced hepatotoxicity utilizing metabolomics technology. Sixty male Wistar Rats were randomly divided into six groups: control, two dosages of quercetinintervention[10 and 50 mg/kgbody weight (bw)], AA-treated [5 mg/kgbw], and two dosages of quercetin combined with AA intervention. AA and quercetin were given to rats via drinking water and gavage respectively. After 16 weeksoftreatment, liver samples were collected for metabolomics analysis. 16metabolites were finally identified, the intensities of glutathione and NADP were decreased (p < 0.01), whereas the intensities of taurodeoxycholic acid, glycocholic acid, cholic acid, sphingosine, sphingosine1-phosphate, stearidonyl carnitine, N-undecanoylglycine, cholesterol, 13,14-Dihydro-15-keto-PGE2, LysoPE (20:5), LysoPE (18:3), LysoPC (20:4), and PC (22:5) were increased (p < 0.01) in the AA-treated groupthan those in the control group. After high-dose quercetin (50 mg/kgbw) plus AA treated concurrently to rats, the contents of the above 16 metabolites were significantly restored. This research showed that 50 mg/kg quercetin can alleviate AA-induced hepatotoxicity by reducing oxidative stress and inflammatory injury and regulating lipid metabolism.

Reduction-responsive dehydroepiandrosterone prodrug nanoparticles loaded with camptothecin for cancer therapy by enhancing oxidation therapy and cell replication inhibition

The pentose phosphate pathway (PPP) plays a critical role by providing ribulose-5-phosphate (Ru5P) and NADPH for nucleotide synthesis and reduction energy, respectively. Accordingly, blocking the PPP process may be an effective strategy for enhancing oxidation therapy and inhibiting cell replication. Here, we designed a novel reduction-responsive PEGylated prodrug and constructed nanoparticles PsD@CPT to simultaneously deliver a PPP blocker, dehydroepiandrosterone (DHEA), and chemotherapeutic camptothecin (CPT) to integrate amplification of oxidation therapy and enhance cell replication inhibition. Following cellular uptake, DHEA and CPT were released from PsD@CPT in the presence of high glutathione (GSH) levels. As expected, DHEA-mediated reduction level decreases and CPT-induced oxidation level increases synergistically, breaking the redox balance to aggravate cancer oxidative stress. In addition, suppressing nucleotide synthesis by DHEA through the reduction of Ru5P and blocking DNA replication by CPT further motivates a synergistic inhibition effect on tumor cell proliferation. The results showed that PsD@CPT featuring multimodal treatment has satisfactory antitumor activity both in vitro and in vivo. This study provides a new tumor treatment strategy, which combines the amplification of oxidative stress and enhancement of inhibition of cell proliferation based on inhibition of the PPP process.

Targeting immunometabolism as an anti-inflammatory strategy

The growing field of immunometabolism has taught us how metabolic cellular reactions and processes not only provide a means to generate ATP and biosynthetic precursors, but are also a way of controlling immunity and inflammation. Metabolic reprogramming of immune cells is essential for both inflammatory as well as anti-inflammatory responses. Four anti-inflammatory therapies, DMF, Metformin, Methotrexate and Rapamycin all work by affecting metabolism and/or regulating or mimicking endogenous metabolites with anti-inflammatory effects. Evidence is emerging for the targeting of specific metabolic events as a strategy to limit inflammation in different contexts. Here we discuss these recent developments and speculate on the prospect of targeting immunometabolism in the effort to develop novel anti-inflammatory therapeutics. As accumulating evidence for roles of an intricate and elaborate network of metabolic processes, including lipid, amino acid and nucleotide metabolism provides key focal points for developing new therapies, we here turn our attention to glycolysis and the TCA cycle to provide examples of how metabolic intermediates and enzymes can provide potential novel therapeutic targets.

Targeting of oxidative stress and inflammation through ROS/NF-kappaB pathway in phosphine-induced hepatotoxicity mitigation

AIMS

Poisoning with aluminium phosphide (AlP) commonly has a high rate of mortality and morbidities. Phosphine gas is the main cause of AlP poisoning that has deleterious effect on multi-organs especially heart, kidney, and liver. Furthermore, several studies reported that resveratrol has cytoprotective effects through its pleiotropic property. The purpose of this study was to estimate the dose-dependent role of resveratrol on phosphine induced acute hepatic toxicity in rat model.

MAIN METHODS

The rats have been exposed to LD₅₀ of AlP (12 mg/kg) by gavage, and resveratrol doses (20, 40, and 80 mg/kg) were injected 30 min after intoxication. After 24 h, the serum and liver tissue were collected for present study.

KEY FINDINGS

The results indicated that phosphine causes an alteration in oxidative stress markers including elevation of ROS, and GSH level, MPO activity, reduction in SOD, catalase and G6PD activity as well as reduction in SOD1 and catalase expression. Furthermore, phosphine significantly induced phosphorylation of IkappaB, NF-kappaB and up-regulation of TNF-α, IL-1β, IL-6, and ICAM-1 expression. Also, phosphine induces markedly reduced hepatocytes lives cell and elevated apoptosis and necrosis. Co-treatment of resveratrol in a dose-dependent manner reversed aforementioned alterations. All in all, histological analysis indicated a deleterious effect of phosphine on the liver, which is mitigated by resveratrol administration.

SIGNIFICANCE

The results of the present study suggest targeting ROS/NF-kappaB signalling pathway by resveratrol may have a significant effect on the improvement of hepatic injury induced by phosphine. It also may be a possible candidate for the treatment of phosphine-poisoning.

Proliferating tumor cells mimick glucose metabolism of mature human erythrocytes

Mature human erythrocytes are dependent on anerobic glycolysis, i.e. catabolism (oxidation) of one glucose molecule to produce two ATP and two lactate molecules. Proliferating tumor cells mimick mature human erythrocytes to glycolytically generate two ATP molecules. They deliberately avoid or switch off their respiration, i.e. tricarboxylic acid (TCA) cycle and oxidative phosphorylation (OXPHOS) machinery and consequently dispense with the production of additional 36 ATP molecules from one glucose molecule. This phenomenon is named aerobic glycolysis or Warburg effect. The present review deals with the fate of a glucose molecule after entering a mature human erythrocyte or a proliferating tumor cell and describes why it is useful for a proliferating tumor cell to imitate a mature erythrocyte. Blood consisting of plasma and cellular components (99% of the cells are erythrocytes) may be regarded as a mobile organ, constantly exercising a direct interaction with other organs. Therefore, the use of drugs, which influences the biological activity of erythrocytes, has an immediate effect on the entire organism.

Abbreviations: TCA: tricarboxylic acid cycle; OXPHOS: oxidative phosphorylation; GSH: reduced state of glutathione; NFκB: Nuclear factor of kappa B; PKB (Akt): protein kinase B; NOS: nitric oxide synthase; IgG: immune globulin G; H₂S: hydrogen sulfide; slanDCs: Human 6-sulfo LacNAc-expressing dendritic cells; IL-8: interleukin-8; LPS: lipopolysaccharide; ROS: reactive oxygen species; PPP: pentose phosphate pathway; NADPH: nicotinamide adenine dinucleotide phosphate hydrogen; R5P: ribose-5-phophate; NAD: nicotinamide adenine dinucleotide; FAD: flavin adenine dinucleotide; O₂^●−: superoxide anion; G6P: glucose 6-phosphate; HbO₂: Oxyhemoglobin; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GAP: glyceraldehyde-3-phosphate; 1,3-BPG: 1,3-bis-phosphoglycerate; 2,3-BPG: 2,3-bisphosphoglycerte; PGAM1: phosphoglycerate mutase 1; 3-PG: 3-phosphoglycerate; 2-PG: 2-phosphoglycerate; MIPP1: Multiple inositol polyphosphate phosphatase; mTORC1: mammalian target of rapamycin complex 1; Ru5P: ribulose 5-phosphate; ox-PPP: oxidative branch of pentose phosphate pathway; PGK: phosphoglycerate kinase; IFN-γ: interferon-γ; LDH: lactate dehydrogenase; STAT3: signal transducer and activator of transcription 3; Rheb: Ras homolog enriched in Brain; H₂O₂: hydrogen peroxide; ROOH: lipid peroxide; SOD: superoxide dismutase; MRC: mitochondrial respiratory chain; MbFe²⁺-O₂: methmyoglobin; RNR: ribonucleotide reductase; PRPP: phosphoribosylpyrophosphate; PP_i: pyrophosphate; GSSG: oxidized state of glutathione; non-ox-PPP: non-oxidative branch of pentose phosphate pathway; RPI: ribose-5-phosphate isomerase; RPE: ribulose 5-phosphate 3-epimerase; X5P: xylulose 5-phosphate; TK: transketolase; TA: transaldolase; F6P: fructose-6-phosphate; AR2: aldose reductase 2; SD: sorbitol dehydrogenase; HK: hexokinase; MG: mehtylglyoxal; DHAP: dihydroxyacetone phosphate; TILs: tumor-infiltrating lymphocytes; MCTs: monocarboxylate transporters; pHi: intracellular pH; Hif-1α: hypoxia-induced factor 1; NHE1: sodium/H⁺ (Na⁺/H⁺) antiporter 1; V-ATPase: vacuolar-type proton ATPase; CAIX: carbonic anhydrase; CO₂: carbon dioxide; HCO₃⁻: bicarbonate; NBC: sodium/bicarbonate (Na⁺/HCO₃⁻) symporter; pHe: extracellular pH; GLUT-1: glucose transporter 1; PGK-1: phosphoglycerate kinase 1

Manipulating Eryptosis of Human Red Blood Cells: A Novel Antimalarial Strategy?

Malaria is a major global health burden, affecting over 200 million people worldwide. Resistance against all currently available antimalarial drugs is a growing threat, and represents a major and long-standing obstacle to malaria eradication. Like many intracellular pathogens, Plasmodium parasites manipulate host cell signaling pathways, in particular programmed cell death pathways. Interference with apoptotic pathways by malaria parasites is documented in the mosquito and human liver stages of infection, but little is known about this phenomenon in the erythrocytic stages. Although mature erythrocytes have lost all organelles, they display a form of programmed cell death termed eryptosis. Numerous features of eryptosis resemble those of nucleated cell apoptosis, including surface exposure of phosphatidylserine, cell shrinkage and membrane ruffling. Upon invasion, Plasmodium parasites induce significant stress to the host erythrocyte, while delaying the onset of eryptosis. Many eryptotic inducers appear to have a beneficial effect on the course of malaria infection in murine models, but major gaps remain in our understanding of the underlying molecular mechanisms. All currently available antimalarial drugs have parasite-encoded targets, which facilitates the emergence of resistance through selection of mutations that prevent drug-target binding. Identifying host cell factors that play a key role in parasite survival will provide new perspectives for host-directed anti-malarial chemotherapy. This review focuses on the interrelationship between Plasmodium falciparum and the eryptosis of its host erythrocyte. We summarize the current knowledge in this area, highlight the different schools of thoughts and existing gaps in knowledge, and discuss future perspectives for host-directed therapies in the context of antimalarial drug discovery.

Para-tertiary butyl catechol induces eryptosis in vitro via oxidative stress and hemoglobin leakage in human erythrocytes

Exposure of human population to industrial chemicals is believed as a significant contributing factor to the outgrowth of occupational diseases especially in developing countries due to improper safety measures and sanitary conditions. Para-tertiary butylcatechol (PTBC) widely employed in petrochemical, thermofax and phototypesetting industries, induces melanocytotoxicity and contact dermatitis leading to occupational leukoderma/vitiligo. Few vitiligo patients were reported for oxidative stress-induced hemolytic anemia and thrombocytopenia, however its impact on blood components is still not clear. Erythrocytes are the major cell population in circulation and play a prominent role in various diseases. In this work, the effect of PTBC on human erythrocytes is evaluated in vitro. PTBC induces oxidative stress-mediated eryptosis (erythrocyte death) causing detrimental changes such as depleted antioxidant levels, altered surface morphology, hemoglobin denaturation and heinz body formation. These findings validate that PTBC could induce toxic effects on human erythrocytes. Exposure of humans to toxic chemicals constitutes an important issue in various industries; one such issue is the exposure of PTBC at work place resulting in a spectrum of dermal complications. Therefore, it is imperative to appraise the long-term toxicities in order to further delineate the mechanisms of resultant disorders associated with PTBC and to establish the therapeutic interventions.

Signaling Pathways Regulating Redox Balance in Cancer Metabolism

The interplay between rewiring tumor metabolism and oncogenic driver mutations is only beginning to be appreciated. Metabolic deregulation has been described for decades as a bystander effect of genomic aberrations. However, for the biology of malignant cells, metabolic reprogramming is essential to tackle a harsh environment, including nutrient deprivation, reactive oxygen species production, and oxygen withdrawal. Besides the well-investigated glycolytic metabolism, it is emerging that several other metabolic fluxes are relevant for tumorigenesis in supporting redox balance, most notably pentose phosphate pathway, folate, and mitochondrial metabolism. The relationship between metabolic rewiring and mutant genes is still unclear and, therefore, we will discuss how metabolic needs and oncogene mutations influence each other to satisfy cancer cells’ demands. Mutations in oncogenes, i.e., PI3K/AKT/mTOR, RAS pathway, and MYC, and tumor suppressors, i.e., p53 and liver kinase B1, result in metabolic flexibility and may influence response to therapy. Since metabolic rewiring is shaped by oncogenic driver mutations, understanding how specific alterations in signaling pathways affect different metabolic fluxes will be instrumental for the development of novel targeted therapies. In the era of personalized medicine, the combination of driver mutations, metabolite levels, and tissue of origins will pave the way to innovative therapeutic interventions.

Glucose 6-phosphate dehydrogenase and the kidney

PURPOSE OF REVIEW

Glucose 6-phosphate dehydrogenase (G6PD) is the rate-limiting enzyme of the pentose phosphate pathway. G6PD is the main source of the essential cellular reductant, NADPH. The purpose of this review is to describe the biochemistry of G6PD and NADPH, cellular factors that regulate G6PD, normal physiologic roles of G6PD, and the pathogenic role altered G6PD/NADPH plays in kidney disease.

RECENT FINDINGS

NADPH is required for many essential cellular processes such as the antioxidant system, nitric oxide synthase, cytochrome p450 enzymes, and NADPH oxidase. Decreased G6PD activity and, as a result, decreased NADPH level have been associated with diabetic kidney disease, altered nitric oxide production, aldosterone-mediated endothelial dysfunction, and dialysis-associated anemia. Increased G6PD activity is associated with all cancers including kidney cancer. Inherited G6PD deficiency is the most common mutation in the world that is thought to be a relatively mild disorder primarily associated with anemia. Yet, intriguing studies have shown an increased prevalence of diabetes mellitus in G6PD-deficient people. It is not known if G6PD-deficient people are at more risk for other diseases.

SUMMARY

Much more research needs to be done to determine the role of altered G6PD activity (inherited or acquired) in the pathogenesis of kidney disease.

Target identification reveals protein arginine methyltransferase 1 is a potential target of phenyl vinyl sulfone and its derivatives

Phenyl vinyl sulfone (PVS) and phenyl vinyl sulfonate (PVSN) inactivate protein tyrosine phosphatases (PTPs) by mimicking the phosphotyrosine structure and providing a Michael addition acceptor for the active-site cysteine residue of PTPs, thus forming covalent adducts between PVS (or PVSN) and PTPs. We developed a specific antiserum against PVS. This antiserum can be used in general antibody-based assays such as immunoblotting, immunofluorescence staining, and immunoprecipitation. Target identification through immunoprecipitation and mass spectrometry analysis reveals potential targets of PVS, mostly proteins with reactive cysteine residues or low-pK_a cysteine residues that are prone to reversible redox modifications. Target identification of PVSN has been conducted because the anti-PVS antiserum can also recognize PVSN. Among the targets, protein arginine methyltransferase 1 (PRMT1), inosine-5'-monophosphate dehydrogenase 1, vimentin, and glutathione reductase (GR) were further confirmed by immunoprecipitation followed by immunoblotting. In addition, PVSN and Bay11-7082 inhibited GR activity, and PVS, PVSN, and Bay 11-7082 inhibited PRMT1 activity in in vitro assays. In addition, treatment of PVSN, Bay11-7082, or Bay 11-7085 in cultured HeLa cells can cause the quick decline in the levels of protein asymmetric dimethylarginine. These results indicate that the similar moiety among PVS, PVSN, Bay 11-7082, and Bay 11-7085 can be the key structure of lead compounds of PRMT1. Therefore, we expect to use this approach in the identification of potential targets of other covalent drugs.

Eryptosis - the Neglected Cause of Anemia in End Stage Renal Disease

End stage renal disease (ESRD) invariably leads to anemia which has been mainly attributed to compromised release of erythropoietin from the defective kidneys with subsequent impairment of erythropoiesis. However, erythropoietin replacement only partially reverses anemia pointing to the involvement of additional mechanisms. As shown more recently, anemia of ESRD is indeed in large part a result of accelerated erythrocyte loss due to suicidal erythrocyte death or eryptosis, characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine translocation to the cell surface. Phosphatidylserine exposing erythrocytes are bound to and engulfed by macrophages and are thus rapidly cleared from circulating blood. If the loss of erythrocytes cannot be fully compensated by enhanced erythropoiesis, stimulation of eryptosis leads to anemia. Eryptotic erythrocytes may further adhere to the vascular wall and thus impair microcirculation. Stimulators of eryptosis include complement, hyperosmotic shock, energy depletion, oxidative stress, and a wide variety of xenobiotics. Signaling involved in the stimulation of eryptosis includes increase of cytosolic Ca2+ activity, ceramide, caspases, calpain, p38 kinase, protein kinase C, Janus-activated kinase 3, casein kinase 1α, and cyclin-dependent kinase 4. Eryptosis is inhibited by AMP-activated kinase, p21-activated kinase 2, cGMP-dependent protein kinase, mitogen- and stress-activated kinase MSK1/2, and some illdefined tyrosine kinases. In ESRD eryptosis is stimulated at least in part by a plasma component, as it is triggered by exposure of erythrocytes from healthy individuals to plasma from ESRD patients. Several eryptosis-stimulating uremic toxins have been identified, such as vanadate, acrolein, methylglyoxal, indoxyl sulfate, indole-3-acetic acid and phosphate. Attempts to fully reverse anemia in ESRD with excessive stimulation of erythropoiesis enhances the number of circulating suicidal erythrocytes and bears the risk of interference with micocirculation, At least in theory, anemia in ESRD could preferably be treated with replacement of erythropoietin and additional inhibition of eryptosis thus avoiding eryptosis-induced impairment of microcirculation. A variety of eryptosis inhibitors have been identified, their efficacy in ESRD remains, however, to be shown.

Eryptosis in health and disease: A paradigm shift towards understanding the (patho)physiological implications of programmed cell death of erythrocytes

During the course of their natural ageing and upon injury, anucleate erythrocytes can undergo an unconventional apoptosis-like cell death, termed eryptosis. Eryptotic erythrocytes display a plethora of morphological alterations including volume reduction, membrane blebbing and breakdown of the membrane phospholipid asymmetry resulting in phosphatidylserine externalization which, in turn, mediates their phagocytic recognition and clearance from the circulation. Overall, the eryptosis machinery is tightly orchestrated by a wide array of endogenous mediators, ion channels, membrane receptors, and a host of intracellular signaling proteins. Enhanced eryptosis shortens the lifespan of circulating erythrocytes and confers a procoagulant phenotype; this phenomenon has been tangibly implicated in the pathogenesis of anemia, deranged microcirculation, and increased prothrombotic risk associated with a multitude of clinical conditions. Herein, we reviewed the molecular mechanisms dictating eryptosis and erythrophagocytosis and critically analyzed the current evidence leading to the pathophysiological ramifications of eryptotic cell death in the context of human disease.

Stimulation of Erythrocyte Cell Membrane Scrambling by C-Reactive Protein

Background: Eryptosis, the suicidal erythrocyte death characterized by cell shrinkage and phosphatidylserine-translocation, is triggered by fever and inflammation. Signaling includes increased cytosolic Ca2+-activity ([Ca2+]i), caspase activation, and ceramide. Inflammation is associated with increased plasma concentration of C-reactive protein (CRP). The present study explored whether CRP triggers eryptosis. Methods: Phosphatidylserine abundance at the cell surface was estimated from annexin-V-binding, cell volume from forward scatter, [Ca2+]i from Fluo3-fluorescence, ceramide abundance and caspase-3-activity utilizing FITC-conjugated antibodies. Moreover, blood was drawn from patients with acute appendicitis (9♀,11♂) and healthy volunteers (10♀,10♂) for determination of CRP, blood count and phosphatidylserine. Results: A 48h CRP treatment significantly increased the percentage of annexin-V-binding cells (≥5µg/ml), [Ca2+]i (≥5µg/ml), ceramide (20µg/ml) and caspase-activity (20µg/ml). Annexin-V-binding was significantly blunted by caspase inhibitor zVAD (10µM). The percentage of phosphatidylserine-exposing erythrocytes in freshly drawn blood was significantly higher in appendicitis patients (1.83±0.21%) than healthy volunteers (0.81±0.09%), and significantly higher following a 24h incubation of erythrocytes from healthy volunteers to patient plasma than to plasma from healthy volunteers. The percentage of phosphatidylserine-exposing erythrocytes correlated with CRP plasma concentration. Conclusion: C-reactive protein triggers eryptosis, an effect at least partially due to increase of [Ca2+]i, increase of ceramide abundance and caspase activation.

Camalexin-Induced Cell Membrane Scrambling and Cell Shrinkage in Human Erythrocytes

Background/Aims: The thaliana phytoalexin Camalexin has been proposed for the treatment of malignancy. Camalexin counteracts tumor growth in part by stimulation of suicidal death or apoptosis of tumor cells. Similar to apoptosis of nucleated cells, erythrocytes may enter suicidal death or eryptosis, which is characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine translocation to the erythrocyte surface. Cellular mechanisms contributing to the complex machinery executing eryptosis include increase of cytosolic Ca2+ activity ([Ca2+]i), oxidative stress, ceramide, protein kinase C and caspases. The present study explored, whether Camalexin induces eryptosis and, if so, to shed light on mechanisms involved. Methods: Phosphatidylserine exposure at the cell surface was estimated from annexin-V-binding, cell volume from forward scatter, [Ca2+]i from Fluo-3 fluorescence, ROS formation from DCFDA dependent fluorescence, and ceramide abundance utilizing specific antibodies. Results: A 48 hours exposure of human erythrocytes to Camalexin significantly increased the percentage of annexin-V-binding cells (≥ 10 µg/ml), significantly decreased forward scatter (≥ 5 µg/ml) and significantly increased Fluo-3-fluorescence (≥ 10 µg/ml), but did not significantly modify DCFDA fluorescence or ceramide abundance. The effect of Camalexin on annexin-V-binding was significantly blunted by removal of extracellular Ca2+, by kinase inhibitors staurosporine (1 µM) and chelerythrine (10 µM), as well as by caspase inhibitors zVAD (10 µM) and zIETD-fmk (50 µM). Conclusions: Camalexin triggers cell shrinkage and phospholipid scrambling of the erythrocyte cell membrane, an effect at least in part depending on Ca2+ entry, as well as staurosporine and chelerythrine sensitive kinase(s) as well as zVAD and zIETD-fmk sensitive caspase(s).