Silica nanoparticles trigger phosphatidylserine exposure in red blood cells and induce thrombosis risk

Silica nanoparticles (SiNPs) have attracted increasing attention for their health effects due to the increased risk of exposure to human bodies via diverse routes. Considering that SiNPs enter the circulatory system and inevitably encounter red blood cells (RBCs), it is necessary to investigate their risk of causing erythrocytotoxicity. In this study, three sizes of SiNPs (SiNP-60, SiNP-120, and SiNP-200) were tested for their effects on mouse RBCs. The results showed that SiNPs could induce hemolysis, morphological changes, and phosphatidylserine (PS) exposure in RBCs in a particulate size-related manner. Further investigations on the underlying mechanism indicated that SiNP-60 exposure increased intracellular reactive oxidative species (ROS) generation and subsequently caused the phosphorylation of p38 and ERK1/2 in RBCs. The addition of antioxidants or inhibitors of mitogen-activated protein kinase (MAPK) signaling significantly attenuated PS exposure in RBCs and ameliorated SiNP-induced erythrocytotoxicity. Moreover, ex vivo assays using platelet-rich plasma (PRP) showed that SiNP-60-induced PS exposure in RBCs could trigger thrombin-dependent platelet activation. The contrary evidence from the assays of PS blockage and thrombin inhibition further confirmed that SiNP-60-induced platelet activation was dependent on PS externalization in RBCs, concomitantly with thrombin formation. These findings revealed the procoagulant and prothrombotic effects of SiNPs through the regulation of PS externalization in RBCs, and may be of great help in bridging the knowledge gap on the potential cardiovascular hazards of particulate silica from both artificial and naturally occurring origins.

Myricetin-induced suicidal erythrocyte death

BACKGROUND

Myricetin, a type of flavonol commonly found in fruits and herbs, has demonstrated anticancer properties by triggering the process of apoptosis or programmed cell death in tumor cells. Despite the absence of mitochondria and nuclei, erythrocytes can undergo programmed cell death, also known as eryptosis.This process is characterized by cell shrinkage, externalization of phosphatidylserine (PS) on the cell membrane, and the formation of membrane blebs. The signaling of eryptosis involves Ca²⁺ influx, the formation of reactive oxygen species (ROS), and the accumulation of cell surface ceramide. The present study explored the effects of myricetin on eryptosis.

METHODS AND RESULTS

Human erythrocytes were exposed to various concentrations of myricetin (2-8 µM) for 24 h. Flow cytometry was used to assess the markers of eryptosis, including PS exposure, cellular volume, cytosolic Ca²⁺ concentration, and ceramide accumulation. In addition, the levels of intracellular ROS were measured using the 2',7'-dichlorofluorescin diacetate (DCFDA) assay. The myricetin-treated (8 µM) erythrocytes significantly increased Annexin-positive cells, Fluo-3 fluorescence intensity, DCF fluorescence intensity, and the accumulation of ceramide. The impact of myricetin on the binding of annexin-V was significantly reduced, but not completely eliminated, by the nominal removal of extracellular Ca²⁺.

CONCLUSION

Myricetin triggers eryptosis, which is accompanied and, at least in part, caused by Ca²⁺ influx, oxidative stress and increase of ceramide abundance.

The ratio of ATP11C/PLSCR1 mRNA transcripts has clinical significance in sickle cell anemia

One of the physiologic mechanisms responsible to maintain asymmetric phospholipid distribution (in particular phosphatidylserine, PS) in human erythrocyte membranes is orchestrated by the balance between enzymes responsible for active transport of PS from the outer to the inner leaflet (ATP11C) and those whose counteracts these activities (PLSCR1). Using quantitative real-time polymerase chain reaction and standard flow cytometry procedures, we hypothesized that the aberrant expression of either or both ATP11C and PLSCR1 transcripts may disrupt the PS internalization/externalization process and become clinically relevant for patients with sickle cell anemia (SCA). Overall, neither ATP11C/PLSCR1 ratio or ATP11C and PLSCR1 (if analyzed separately) had impact on risk to present acute or chronic organ damage in 178 patients with SCA. By collecting a new set of samples from SCA patients during a vaso-occlusive crisis (VOC, crisis state, 13 patients) and comparing with new samples of patients in steady state (15 patients), we noticed that patients in steady state exhibited mean values of ATP11C/PLSCR1 ratio significantly higher (mean value: 18.2, range, 0.3-53) than those who were in crisis (mean value: 3.7, range, 0.5-9) (P = 0.013). Most importantly, there was a strong inverse correlation between PS exposure and ATP11C/PLSCR1 ratio in sickle erythrocytes (Pearson correlation coefficient, r: - 0.78). Based on these findings, it is conceivable that the ATP11C/PLSCR1 ratio may switch from high to low during a VOC, although the underlying reasons require further investigations.

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.

Of membranes and malaria: phospholipid asymmetry in Plasmodium falciparum-infected red blood cells

Malaria is a vector-borne parasitic disease with a vast impact on human history, and according to the World Health Organisation, Plasmodium parasites still infect over 200 million people per year. Plasmodium falciparum, the deadliest parasite species, has a remarkable ability to undermine the host immune system and cause life-threatening disease during blood infection. The parasite's host cells, red blood cells (RBCs), generally maintain an asymmetric distribution of phospholipids in the two leaflets of the plasma membrane bilayer. Alterations to this asymmetry, particularly the exposure of phosphatidylserine (PS) in the outer leaflet, can be recognised by phagocytes. Because of the importance of innate immune defence numerous studies have investigated PS exposure in RBCs infected with P. falciparum, but have reached different conclusions. Here we review recent advancements in our understanding of the molecular mechanisms which regulate asymmetry in RBCs, and whether infection with the P. falciparum parasite results in changes to PS exposure. On the balance of evidence, it is likely that membrane asymmetry is disrupted in parasitised RBCs, though some methodological issues need addressing. We discuss the potential causes and consequences of altered asymmetry in parasitised RBCs, particularly for in vivo interactions with the immune system, and the role of host-parasite co-evolution. We also examine the potential asymmetric state of parasite membranes and summarise current knowledge on the parasite proteins, which could regulate asymmetry in these membranes. Finally, we highlight unresolved questions at this time and the need for interdisciplinary approaches to uncover the machinery which enables P. falciparum parasites to hide in mature erythrocytes.

Type 1 interferon aggravates lipopolysaccharide-induced sepsis through upregulating Caspase-11 and Gasdermin D

This study aimed to investigate the mechanism of type I interferon (IFN) in aggravating sepsis in bacterial infection, focusing on the roles of Caspase-11 (Casp11) and Gasdermin D (Gsdmd) in this process. Type I interferons, including IFNα and IFNβ, were used to treat peritoneal macrophage harvested from wild-type or IFNα/βR1 knockout (KO) mice, of which the levels of Casp11 and Gsdmd were monitored using real-time polymerase chain reaction (RT-PCR) and Western blot, the exposure to phosphatidylserine was monitored by flow cytometry, and tissue factor (TF) activation was assessed by RT-PCR and TF chromogenic assay. Endotoxemia in wild-type mice led to upregulation of Casp11 and Gsdmd in myeloid cells, which in contrast was attenuated in IFNα/βR1 KO mice. IFNα or IFNβ treatment led to dose-dependent upregulation of Casp11 and Gsdmd in peritoneal macrophages harvested from wild-type mice, but induced negligible changes in IFNα/βR1 KO mice. Type I IFN promoted phosphatidylserine exposure in peritoneal macrophage from wild-type mice but not IFNα/βR1 KO mice. Type I IFN induced insignificant changes of TF expression levels in both wild-type mice and IFNα/βR1 KO mice, but the TF activity was markedly increased in wild-type mice after type I IFN treatment. Our data suggested that the upregulation of Casp11 and Gsdmd in myeloid cells and macrophages induced by endotoxemia was reliant on the expression of IFNα/βR1. IFNα or IFNβ treatment efficiently upregulated Casp11 and Gsdmd, phosphatidylserine exposure, and TF activity of macrophages. Therefore, type I IFN could aggravate sepsis through upregulating Casp11 and Gsdmd.

Plasma membrane lipid scrambling causing phosphatidylserine exposure negatively regulates NK cell activation

One of the hallmarks of live cells is the asymmetric distribution of lipids across their plasma membrane. Changes in this asymmetry due to lipid "scrambling" result in phosphatidylserine exposure at the cell surface that is detected by annexin V staining. This alteration is observed during cell death processes such as apoptosis, and during physiological responses such as platelet degranulation and membrane repair. Previous studies have shown that activation of NK cells is accompanied by exposure of phosphatidylserine at the cell surface. While this response was thought to be indicative of ongoing NK cell death, it may also  reflect the regulation of NK cell activation in the absence of cell death. Herein, we found that NK cell activation was accompanied by rapid phosphatidylserine exposure to an extent proportional to the degree of NK cell activation. Through enforced expression of a lipid scramblase, we provided evidence that activation-induced lipid scrambling in NK cells is reversible and does not lead to cell death. In contrast, lipid scrambling attenuates NK cell activation. This response was accompanied by reduced cell surface expression of activating receptors such as 2B4, and by loss of binding of Src family protein tyrosine kinases Fyn and Lck to the inner leaflet of the plasma membrane. Hence, lipid scrambling during NK cell activation is, at least in part, a physiological response that reduces the NK cell activation level. This effect is due to the ability of lipid scrambling to alter the distribution of membrane-associated receptors and kinases required for NK cell activation.

Nanoscale adhesion profiling and membrane characterisation in sickle cell disease using hybrid atomic force microscopy-IR spectroscopy

Sickle cell disease (SCD) presents a significant global health problem. At present there is no effective treatment, with most being supportive for its associated complications such as the vaso-occlusive crises that result from increased cell adhesion. Hypoxic sickle cells have previously shown greater phosphatidylserine (PS) exposure and oxidative damage, as well as being notably "stickier" suggesting that increased cell cohesion and adhesion to the blood vessel endothelium is a possible mechanism for vaso-occlusion. The present work uses the hybrid technique of atomic force microscopy nano-infrared spectroscopy (AFM-IR) to probe changes to the coefficient of friction and C-O IR intensity in SCD on a nanoscale for dried red blood cells (RBCs) fixed under conditions of hypoxia and correlates these observations with adhesive interactions at the membrane. Using functionalised AFM tips, it has been possible to probe adhesive interactions between hydrophilic and hydrophobic moieties exposed at the surface of the dried RBCs fixed under different oxygenation states and for different cell genotypes. The results are consistent with greater PS-exposure and oxidative damage in hypoxic sickle cells, as previously proposed, and also show strong correlation between localised oxidative damage and increased adhesion. A mechanistic explanation involving significant lipid tail disruption as a result of oxidative action, in combination with differing concentrations of externalised PS lipids, is proposed to explain the observed adhesion behaviour of each type of cell.

Cargo-laden erythrocyte ghosts target liver mediated by macrophages

Liver-targeted cargo delivery possesses great potential for the treatment of liver disease. It is urgent to find an efficient and biocompatible liver targeted delivery system. This study focused on the liver targeting properties of erythrocyte ghosts and its possible mechanism. Herein, we optimized conditions to fabricate human and mouse erythrocyte ghosts with sufficient room capable of incorporating various model substances. Erythrocyte ghosts are biocompatible cargo carriers because it is derived from autologous red blood cells (RBCs), and the cell size, zeta potential, and biconcave-disk shape of the ghosts were consistent with those of RBCs. An in vivo imaging system and positron emission tomography/computed tomography imaging showed that the ghosts were captured mainly in the liver by intravenous injection of fluorescence or ¹⁸F-fluorodeoxyglucose (FDG)-labelled ghosts into mice. In contrast, the main concentration of naked octreotide was trapped in the lungs while naked ¹⁸F-FDG was trapped in the heart. However, the concentration of cargo-loaded ghosts decreased significantly in the liver in macrophage-depleted mice. Accordingly, in vitro experiments showed that higher phosphatidylserine exposure was observed in the ghosts (38.9 %) compared to normal erythrocytes (0.69 %), and the phagocytic activity of the macrophage RAW 264.7. on the ghosts was significantly higher than that of normal erythrocytes (p < 0.001). Together they indicate that erythrocyte ghosts show liver targeting properties, and possibly owing to macrophage phagocytosis. This promising and effective therapeutic delivery system may provide therapeutic benefits for liver disease.

In vitro bioactivity approach of unripe genipap (Genipa americana L., Rubiaceae) fruit extract and its solid lipid microparticle

Growing awareness in favor of innovative and healthier alternatives is creating a noticeable shift from synthetic colorants to natural additives. And, such a swing in the consumer market is growing slowly but noticeably. In this context, genipap (Genipa americana L.) fruit represents an emerging source of blue colorants in Latin America with extensive application possibilities. This is despite the fact that there are few studies concerning its toxicity predictive factors. In this early-stage study we propose to investigate safety issues around genipap extract (IBBP); we also attempt to identify fingerprint profiling of both IBBP extract and solid lipid microparticles containing IBBP extract (SLM-IBBP) using in vitro assays. The main compounds identified were genipin, and genipin 1-β-gentiobioside. Results indicated that IBBP extract, at 25 µg/mL, was able to promote DNA damage in CHO-K1 cells, suggesting a genotoxic effect. On the other hand, the SLM-IBBP inhibited almost all cancer cell lines with GI₅₀ ranging from 0.25 μg/mL to 43.5 μg/mL. Also, IBBP-SLM seems to exert a desirable apoptosis induction (at 25 µg/mL dosage). The next steps for our work, therefore, will focus on other nanoparticle formulation approaches, in particular with the use of natural Brazilian starch. An evaluation of the metabolism and distribution of microparticles, and their safety for food and pharmaceutical purposes, are also required.

The marine cytotoxin portimine is a potent and selective inducer of apoptosis

Portimine is a recently discovered member of a class of marine micro-algal toxins called cyclic imines. In dramatic contrast to related compounds in this toxin class, portimine has very low acute toxicity to mice but is highly cytotoxic to cultured cells. In this study we show that portimine kills human Jurkat T-lymphoma cells and mouse embryonic fibroblasts (MEFs), with LC₅₀ values of 6 and 2.5 nM respectively. Treated cells displayed rapid caspase activation and phosphatidylserine exposure, indicative of apoptotic cell death. Jurkat cells overexpressing the anti-apoptotic protein Bcl-2 or Bax/Bak knockout MEFs were completely protected from portimine. This protection was apparent even at high concentrations of portimine, with no evidence of necrotic cell death, indicating that portimine is a selective chemical inducer of apoptosis. Treatment of the Bcl-2-overexpressing cells with both portimine and the Bcl-2 inhibitor ABT-737 proved a powerful combination, causing >90 % death. We conclude that portimine is one of the most potent naturally derived inducers of apoptosis to be discovered, and it displays strong selectivity for the induction of apoptotic pathways.

Inhibitory effects of ethyl pyruvate on platelet aggregation and phosphatidylserine exposure

Ethyl pyruvate (EP) is a stable lipophilic pyruvate derivative. Studies demonstrated that EP shows potent anti-oxidation, anti-inflammatory and anti-coagulant effects. Inflammation and coagulation are closely interacted with platelet activation. However, it is unclear whether EP has anti-platelet effects. Therefore, we investigated the anti-platelet effect of EP in this study in vitro. We found that EP inhibited agonists induced platelets aggregation, ATP release and adhesion to collagen. Flow cytometric analysis revealed that EP inhibited agonist induced platelets PAC-1 binding, as well as P-selectin and CD40L expression. The underlying mechanism of action may involve the inhibition of platelet PI3K/Akt and Protein Kinase C (PKC) signaling pathways. Additionally, EP dose dependently inhibited platelet PS exposure induced by high concentration thrombin. Lactate dehydrogenase (LDH) activity assay and mice platelet count implied that EP may have no toxic effect on platelets. Therefore, we are the first to report that EP has potent anti-platelet activity and attenuates platelet PS exposure in vitro, suggesting that the inhibitory effects of EP on platelets may also play important roles in improvement of inflammation and coagulation disorder in related animal models.

Effect of Lead(IV) Acetate on Procoagulant Activity in Human Red Blood Cells

Lead (Pb) is a ubiquitously occurring environmental heavy metal which is widely used in industry and human life. Possibly due to a global industrial expansion, recent studies have revealed the prevalent human exposure to Pb and increased risk of Pb toxicity. Once ingested by human, 95% of absorbed Pb is accumulated into erythrocytes and erythrocytes are known to be a prime target for Pb toxicity. Most of the studies were however, focused on Pb²⁺ whereas the effects of Pb⁴⁺, another major form of Pb on erythrocytes are poorly understood yet. In this study, we investigated and compared the effects of Pb⁴⁺, Pb²⁺ and other heavy metals on procoagulant activation of erythrocytes, an important factor for the participation of erythrocytes in thrombotic events in an effort to address the cardiovascular toxicity of Pb⁴⁺. Freshly isolated erythrocytes from human were incubated with Pb⁴⁺, Pb²⁺, Cd²⁺ and Ag⁺ and the exposure of phosphatidylserine (PS), key marker for procoagulant activation was measured using flow cytometry. As a result, while Cd²⁺ and Ag⁺ did not affect PS exposure, Pb⁴⁺ and Pb²⁺ induced significantly PS exposure in a dose-dependent manner. Of a particular note, Pb⁴⁺ induced PS exposure with a similar potency with Pb²⁺. PS bearing microvesicle (MV), another important contributor to procoagulant activation was also generated by Pb⁴⁺. These PS exposure and MV generation by Pb⁴⁺ were well in line with the shape change of erythrocyte from normal discocytes to MV shedding echinocytes following Pb⁴⁺ treatment. Meanwhile, nonspecific hemolysis was not observed suggesting the specificity of Pb⁴⁺-induced PS exposure and MV generation. These results indicated that Pb⁴⁺ could induce procoagulant activation of erythrocytes through PS exposure and MV generation, suggesting that Pb⁴⁺ exposure might ultimately lead to increased thrombotic events.