Arsenite-enhanced procoagulant activity through phosphatidylserine exposure in platelets

Environmental Exposures and Extracellular Vesicles: Indicators of Systemic Effects and Human Disease

PURPOSE OF REVIEW

Environmental pollutants contribute to the pathogenesis of numerous diseases including chronic cardiovascular, respiratory, and neurodegenerative diseases, among others. Emerging evidence suggests that extracellular vesicles (EVs) may mediate the association of environmental exposures with chronic diseases. The purpose of this review is to describe the impact of common environmental exposures on EVs and their role in linking environmental pollutants to the pathogenesis of chronic systemic diseases.

RECENT FINDINGS

Common environmental pollutants including particulate matter, tobacco smoke, and chemical pollutants trigger the release of EVs from multiple systems in the body. Existing research has focused primarily on air pollutants, which alter EV production and release in the lungs and systemic circulation. Air pollutants also impact the selective loading of EV cargo including microRNA and proteins, which modify the cellular function in recipient cells. As a result, pollutant-induced EVs often contribute to a pro-inflammatory and pro-thrombotic milieu, which increases the risk of pollutant-related diseases including obstructive lung diseases, cardiovascular disease, neurodegenerative diseases, and lung cancer. Common environmental exposures are associated with multifaceted changes in EVs that lead to functional alterations in recipient cells and contribute to the pathogenesis of chronic systemic diseases. EVs may represent emerging targets for the prevention and treatment of diseases that stem from environmental exposures. However, novel research is required to expand our knowledge of the biological action of EV cargo, elucidate determinants of EV release, and fully understand the impact of environmental pollutants on human health.

MARTX toxin of Vibrio vulnificus induces RBC phosphatidylserine exposure that can contribute to thrombosis

V. vulnificus-infected patients suffer from hemolytic anemia and circulatory lesions, often accompanied by venous thrombosis. However, the pathophysiological mechanism of venous thrombosis associated with V. vulnificus infection remains largely unknown. Herein, V. vulnificus infection at the sub-hemolytic level induced shape change of human red blood cells (RBCs) accompanied by phosphatidylserine exposure, and microvesicle generation, leading to the procoagulant activation of RBCs and ultimately, acquisition of prothrombotic activity. Of note, V. vulnificus exposed to RBCs substantially upregulated the rtxA gene encoding multifunctional autoprocessing repeats-in-toxin (MARTX) toxin. Mutant studies showed that V. vulnificus-induced RBC procoagulant activity was due to the pore forming region of the MARTX toxin causing intracellular Ca²⁺ influx in RBCs. In a rat venous thrombosis model triggered by tissue factor and stasis, the V. vulnificus wild type increased thrombosis while the ΔrtxA mutant failed to increase thrombosis, confirming that V. vulnificus induces thrombosis through the procoagulant activation of RBCs via the mediation of the MARTX toxin.

The pathophysiological mechanism of venous thrombosis associated with Vibrio vulnificus infection remains largely unknown. In this work, the authors investigate this association, focusing on effects of the pore-forming MARTX toxin of V. vulnificus on red blood cells, and the utilisation of a rat venous thrombosis model.

Arsenic induces platelet shape change through altering focal adhesion kinase-mediated actin dynamics, contributing to increased platelet reactivity

Arsenic, an environmental contaminant in drinking water worldwide is well-established to increase cardiovascular diseases (CVDs) in humans. Of these, thrombotic events represent a major adverse effect associated with arsenic exposure, for which an abundance of epidemiological evidence exists. Platelet aggregation constitutes a pivotal step in thrombosis but arsenic alone doesn't induce aggregation and the mechanism underlying arsenic-induced thrombosis still remains unclear. Here we demonstrated that arsenic induces morphological changes of platelets, i.e., contraction and pseudopod projection, the primal events of platelet activation, which can increase platelet reactivity. Arsenite induced prominent platelet shape changes in a dose-dependent manner in freshly isolated human platelets. Of note, arsenite suppressed focal adhesion kinase (FAK) activity, which in turn activated RhoA, leading to altered actin assembly through LIMK activation, and subsequent cofilin inactivation. Arsenic-induced platelet shape change appeared to increase the sensitivity to thrombin and ADP-induced aggregation. Supporting this, latrunculin A, an inhibitor of actin-dynamics abolished it. Taken together, we demonstrated that arsenic induces cytoskeletal changes and shape changes of platelets through FAK-mediated alteration of actin dynamics, which renders platelets reactive to activating stimuli, ultimately contributing to increased thrombosis.

Thrombin Generation and Cancer: Contributors and Consequences

The high occurrence of cancer-associated thrombosis is associated with elevated thrombin generation. Tumour cells increase the potential for thrombin generation both directly, through the expression and release of procoagulant factors, and indirectly, through signals that activate other cell types (including platelets, leukocytes and erythrocytes). Furthermore, cancer treatments can worsen these effects. Coagulation factors, including tissue factor, and inhibitors of coagulation are altered and extracellular vesicles (EVs), which can promote and support thrombin generation, are released by tumour and other cells. Some phosphatidylserine-expressing platelet subsets and platelet-derived EVs provide the surface required for the assembly of coagulation factors essential for thrombin generation in vivo. This review will explore the causes of increased thrombin production in cancer, and the availability and utility of tests and biomarkers. Increased thrombin production not only increases blood coagulation, but also promotes tumour growth and metastasis and as a consequence, thrombin and its contributors present opportunities for treatment of cancer-associated thrombosis and cancer itself.

Hyperglycemia enhances arsenic-induced platelet and megakaryocyte activation

Objective

Low to moderate inorganic arsenic (iAs) exposure is independently associated with cardiovascular disease (CVD), particularly for patients with diabetes mellitus (DM). The mechanism of increased CVD risk from iAs exposure in DM has not been adequately characterized. We evaluated whether increasing concentrations of glucose enhance the effects of iAs on platelet and megakaryocyte activity, key steps in atherothrombosis.

Methods

Healthy donor whole blood was prepared in a standard fashion and incubated with sodium arsenite in a range from 0 to 10 µM. iAs-induced platelet activation was assessed by platelet receptor CD62P (P-selectin) expression and monocyte-platelet and leukocyte-platelet aggregation (MPA and LPA, respectively) in the presence of increasing sodium arsenite and glucose concentrations. Megakaryocyte (Meg-01) cell adhesion and gene expression was assessed after incubation with or without iAs and increasing concentrations of d-glucose.

Results

Platelet activity markers increased significantly with 10 vs. 0 µM iAs (P < 0.05 for all) and with higher d-glucose concentrations. Platelet activity increased significantly following co incubation of 1 and 5 µM iAs concentrations with hyperglycemic d-glucose (P < 0.01 for both) but not after incubation with euglycemic d-glucose. Megakaryocyte adhesion was more pronounced after co incubation with iAs and hyperglycemic than euglycemic d-glucose, while gene expression increased significantly to iAs only after co incubation with hyperglycemic d-glucose.

Conclusion

We demonstrate that glucose concentrations common in DM potentiate the effect of inorganic arsenic exposure on markers of platelet and megakaryocyte activity. Our results support recent observational cohort data that DM enhances the vasculotoxic effects of arsenic exposure, and suggest that activation of the platelet-megakaryocyte hemostatic axis is a pathway through which inorganic arsenic confers atherothrombotic risk, particularly for patients with DM.

Endogenous signalling control of cell adhesion by using aptamer functionalized biocompatible hydrogel

Design of biological signal-responsive biomaterials is essential for controlling cell-cell and cell-matrix interactions. Herein, we developed a dynamic hydrogel to control cell adhesion with biological signals in a cellular microenvironment. The basic principle was based on using nucleic acid aptamer to recognize cell signalling and control the display of bioligands on the hydrogel. Not only exogenous signalling but also endogenous signalling secreted by surrounding cells could activate the dynamic scaffold and tune the cell adhesion state. Since diverse aptamers have been developed, our design can be extended to multiple biological inputs. The biochemical signal-responsive system will greatly enhance the understanding of complex biological processes as well as the ability to manipulate cellular behaviors.

Doxorubicin-induced platelet procoagulant activities: an important clue for chemotherapy-associated thrombosis

Thrombotic risk associated with chemotherapy including doxorubicin (DOX) has been frequently reported; yet, the exact mechanism is not fully understood. Here, we report that DOX can induce procoagulant activity in platelets, an important contributor to thrombus formation. In human platelets, DOX increased phosphatidylserine (PS) exposure and PS-bearing microparticle (MP) generation. Consistently, DOX-treated platelets and generated MPs induced thrombin generation, a representative marker for procoagulant activity. DOX-induced PS exposure appeared to be from intracellular Ca²⁺ increase and ATP depletion, which resulted in the activation of scramblase and inhibition of flippase. Along with this, apoptosis was induced by DOX as determined by the dissipation of mitochondrial membrane potential (Δψ), cytochrome c release, Bax translocation, and caspase-3 activation. A Ca²⁺ chelator ethylene glycol tetraacetic acid, caspase inhibitor Q-VD-OPh, and antioxidants (vitamin C and trolox) can attenuate DOX-induced PS exposure and procoagulant activity significantly, suggesting that Ca²⁺, apoptosis, and reactive oxygen species (ROS) were involved in DOX-enhanced procoagulant activity. Importantly, rat in vivo thrombosis model demonstrated that DOX could manifest prothrombotic effects through the mediation of platelet procoagulant activity, which was accompanied by increased PS exposure and Δψ dissipation in platelets.

Arsenic trioxide induces procoagulant activity through phosphatidylserine exposure and microparticle generation in endothelial cells

BACKGROUND

Coagulopathy is a major cause of early death when arsenic trioxide (As(2)O(3)) therapy fails. In addition to the procoagulant properties of blast cells, the cytotoxic therapy may contribute to the coagulation disorders. The aim of the present study was to evaluate the possible impact of As(2)O(3) on membrane alterations, including phosphatidylserine (PS) exposure and microparticle generation, and the consequent procoagulant properties of endothelial cells.

METHODS

Procoagulant activity (PCA) of human umbilical vein endothelial cells (HUVECs) was assessed by measuring clotting time and through purified coagulation complex assays. PS exposure on HUVEC membrane was observed by confocal microscopy and quantified with flow cytometry. In addition, counts and PCA of endothelial microparticles were determined by flow cytometry and plasma coagulation assay.

RESULTS

As(2)O(3) increased the ability of HUVECs to accelerate coagulation process and promote formation of coagulation complexes. Procoagulant activity corresponded to PS exposed on HUVECs. In coincidence with the PS externalization, As(2)O(3) increased the production of PS-bearing microparticles, which then accelerated fibrin strand formation significantly. By blocking PS, lactadherin was able to inhibit over 90% of the intrinsic tenase/prothrombinase activity of As(2)O(3)-treated HUVECs, and restored coagulation times of As(2)O(3)-treated cells and microparticles to control levels.

CONCLUSIONS

As(2)O(3) increases PCA of HUVECs through PS exposure and PS-bearing microparticle generation, which might cause thrombosis and act as a contributing factor in As(2)O(3) therapy-related coagulopathy.

A phase I clinical trial of darinaparsin in patients with refractory solid tumors

PURPOSE

Darinaparsin, an organic arsenic, targets essential cell survival pathways. We determined the dose-limiting toxicity (DLT) and maximum tolerated dose of darinaparsin in patients with advanced cancer.

EXPERIMENTAL DESIGN

Patients with solid malignancies refractory to conventional therapies were treated with i.v. darinaparsin daily for 5 days every 4 weeks. The starting dose (78 mg/m(2)) escalated to 109, 153, 214, 300, 420, and 588 mg/m(2). A conventional "3 + 3" design was used.

RESULTS

Forty patients (median age, 61.5 years; median number of prior therapies, 5) received therapy; 106 cycles were given (median, 2; range, 1-12). Twenty patients reported no drug-related toxicities. No DLTs were reported at a dose of <420 mg/m(2). At 588 mg/m(2), two of four patients developed DLTs, including grade 3 altered mental status and ataxia. Of four patients treated at the de-escalated dose of 500 mg/m(2), one developed similar toxicities. De-escalating the dose to 420 mg/m(2) (n = 8) resulted in two neurologic DLTs. Further de-escalation to 300 mg/m(2) (n = 3) resulted in no drug-related toxicities. Arsenic plasma levels peaked on treatment day 3, plateaued on day 5, and returned to baseline on day 7. Plasma levels varied within cohorts but increased with increasing doses. The median plasma arsenic half-life was 16.2 hours. Seven (17.5%) patients had stable disease for > or =4 months (median, 6; range, 4-11), including 4 of 17 with colorectal and 2 of 3 with renal cancer.

CONCLUSIONS

The recommended dose for phase II trials is 300 mg/m(2) i.v. given daily for 5 days every 4 weeks.

Verapamil but not calpain or creatine alters arsenate-induced cardiac cell death

The objective of this study was to examine the potential of arsenate to induce cardiomyocyte cell death and to explore the cellular mechanisms of arsenate toxicity. Isolated cardiomyocytes in culture from embryonic chick hearts were treated with a pentavalent arsenic species (H3AsO4) or arsenate. Arsenate produced a significant ( P < 0.01) concentration-dependent increase in cell death with an EC50 about 1 mM. Cardiomyocytes manifested a loss of actin structure, reduced size, and damaged nuclei. Creatine 0.1–100 uM did not significantly modify arsenate-induced cell death. In contrast, verapamil, 0.01–1 uM, produced a significant concentration-dependent accentuation of arsenate-induced cell death. The effect of verapamil was evident at low concentrations of arsenate, which produced only a small increase in cell death, and at high concentrations of arsenate, which induced a large amount of cell death. Verapamil alone did not alter cardiomyocyte cell death. By comparison, calpain inhibitor II did not modify arsenate-induced cardiomyocyte cell death. These data suggest that cardiomyocytes are vulnerable to the effects of verapamil to increase the cellular toxicity of arsenate. Two potential cellular mechanisms of arsenate toxicity, however, are likely not involved in arsenate toxicity namely calpain activation and reduction of creatine phosphate production.

Trivalent methylated arsenical-induced phosphatidylserine exposure and apoptosis in platelets may lead to increased thrombus formation

Trivalent methylated metabolites of arsenic, monomethylarsonous acid (MMA(III)) and dimethylarsinous acid (DMA(III)), have been found highly reactive and toxic in various cells and in vivo animal models, suggesting their roles in the arsenic-associated toxicity. However, their effects on cardiovascular system including blood cells, one of the most important targets for arsenic toxicity, remain poorly understood. Here we found that MMA(III) and DMA(III) could induce procoagulant activity and apoptosis in platelets, which play key roles in the development of various cardiovascular diseases (CVDs) through excessive thrombus formation. In freshly isolated human platelets, treatment of MMA(III) resulted in phosphatidylserine (PS) exposure, a hallmark of procoagulant activation, accompanied by distinctive apoptotic features including mitochondrial membrane potential disruption, cytochrome c release, and caspase-3 activation. These procoagulant activation and apoptotic features were found to be mediated by the depletion of protein thiol and intracellular ATP, and flippase inhibition by MMA(III), while the intracellular calcium increase or reactive oxygen species generation was not involved. Importantly, increased platelet procoagulant activity by MMA(III) resulted in enhanced blood coagulation and excessive thrombus formation in a rat in vivo venous thrombosis model. DMA(III) also induced PS-exposure with apoptotic features mediated by protein thiol depletion, which resulted in enhanced thrombin generation. In summary, we believe that this study provides an important evidence for the role of trivalent methylated arsenic metabolites in arsenic-associated CVDs, giving a novel insight into the role of platelet apoptosis in toxicant-induced cardiovascular toxicity.

Methylated Organic Metabolites of Arsenic and their Cardiovascular Toxicities

Recently, arsenic-toxicity has become the major focus of strenuous assessment and dynamic research from the academy and regulatory agency. To elucidate the cause and the mechanism underlying the serious adverse health effects from chronic ingestion of arsenic-contaminated drinking water, numerous studies have been directed on the investigation of arsenic-toxicity using various in vitro as well as in vivo systems. Neverthless, some questions for arsenic effects remain unexplained, reflecting the contribution of unknown factors to the manifestation of arsenic-toxicity. Interestingly, very recent studies on arsenic metabolites have discovered that trivalent methylated arsenicals show stronger cytotoxic and genotoxic potentials than inorganic arsenic or pentavalent metabolites, arguing that these metabolites could play a key role in arsenic-associated disorders. In this review, recent progress and literatures are summarized on the metabolism of trivalent methylated metabolites and their toxicity on body systems including cardiovascular system in an effort to provide an insight into the future research on arsenic-associated disorders.

Arsenic-induced suicidal erythrocyte death

Environmental exposure to arsenic has been associated with anemia, which could result from suicidal erythrocyte death or eryptosis, characterized by cell shrinkage and phosphatidylserine exposure at the erythrocyte surface. Eryptosis is triggered by increase in cytosolic Ca2+ concentration, ceramide and energy depletion. The present experiments explored, whether arsenic stimulates eryptosis. According to annexin V-binding, arsenic trioxide (7 microM) within 48 h significantly increased phosphatidylserine exposure of human erythrocytes without inducing hemolysis. According to forward scatter, arsenic trioxide (7 microM) significantly decreased cell volume. Moreover, Fluo3-fluorescence showed that arsenic (10 microM) significantly increased cytosolic Ca2+ concentration. According to binding of respective fluorescent antibodies, arsenic trioxide (10 microM) significantly increased ceramide formation. Arsenic (10 microM) further lowered the intracellular ATP concentration. Removal of extracellular Ca2+ or inhibition of the Ca2+-permeable cation channels with amiloride blunted the effects of arsenic on annexin V-binding and cell shrinkage. In conclusion, arsenic triggers suicidal erythrocyte death by increasing cytosolic Ca2+ concentration, by stimulating the formation of ceramide and by decreasing ATP availability.