Changes of platelet surface antigens in patients suffering from abdominal septic shock

Current knowledge of thrombocytopenia in sepsis and COVID-19

Thrombocytopenia, characterized by a decrease in platelet count, is commonly observed in sepsis and COVID-19. In sepsis, thrombocytopenia can result from various mechanisms, including impaired platelet production in the bone marrow, accelerated platelet destruction due to increased inflammation, sequestration of platelets in the spleen, immune-mediated platelet destruction, or dysregulated host responses. Similarly, thrombocytopenia has been reported in COVID-19 patients, but the immune-related mechanisms underlying this association remain unclear. Notably, interventions targeting thrombocytopenia have shown potential for improving outcomes in both sepsis and COVID-19 patients. Understanding these mechanisms is crucial for developing effective treatments.

An Insight into Recent Advances on Platelet Function in Health and Disease

Platelets play a variety of roles in vascular biology and are best recognized as primary hemostasis and thrombosis mediators. Platelets have a large number of receptors and secretory molecules that are required for platelet functionality. Upon activation, platelets release multiple substances that have the ability to influence both physiological and pathophysiological processes including inflammation, tissue regeneration and repair, cancer progression, and spreading. The involvement of platelets in the progression and seriousness of a variety of disorders other than thrombosis is still being discovered, especially in the areas of inflammation and the immunological response. This review represents an integrated summary of recent advances on the function of platelets in pathophysiology that connects hemostasis, inflammation, and immunological response in health and disease and suggests that antiplatelet treatment might be used for more than only thrombosis.

CD63 and C3AR1: The Potential Molecular Targets in the Progression of Septic Shock

Background

The molecular mechanism of septic shock is unknown. We studied the pathogenesis of septic shock and provide a novel strategy for treating and improving the prognosis of septic shock.

Methods

Gluten-Sensitive Enteropathy (GSE) 131761, GSE119217, GSE26378 datasets were downloaded from the Gene Expression Omnibus (GEO) database. The three datasets included 204 septic shock samples and 48 normal samples. The R packages “affy” and “limma” were employed to identify the differently expressed genes (DEGs) between septic shock and normal samples. Weighted gene co-expression network analysis (WGCNA) was performed to search for modules that play an important role in septic shock. Functional annotation of DEGs and construction and analysis of hub genes were used to explore the pathomechanism of septic shock. The receiver operating characteristic (ROC) curves were obtained using MedCalc software. The drug molecules that could regulate hub genes associated with septic shock were searched for in the CMap database. An animal model of septic shock was constructed to analyze the role of these hub genes.

Results

The merged series contained 321 up-regulated and 255 down-regulated genes. WGCNA showed the brown module had the highest correlation with the status of septic shock. GO and KEGG enrichment analysis results of the brown module genes showed they were mainly enriched in “leukocyte differentiation”, “Ras-proximate-1 (Rap1) signaling pathway”, and “cytokine–cytokine receptor interaction”. Through construction and analysis of a protein–protein interaction (PPI) network, cluster of differentiation 63 (CD63) and complement component 3a receptor 1 (C3AR1) were identified as hub genes of septic shock. The area under curve (AUC) of C3AR1 for the septic shock is 0.772 (P<0.001), and the AUC of CD63 for the septic shock is 0.871 (P<0.001). Small molecule drugs were filtered by the number of instances (n>3) and P-values <0.05, including “monensin”, “verteporfin”, “ikarugamycin”, “tetrahydroalstonine”, “cefamandole”, “etoposide”. In the animal model, the relative expression levels of interleukin-6 (IL-6), Tumor Necrosis Factor-α (TNF-α), and lactic acid were significantly higher in the septic shock group compared with the control group. Results of Real Time Quantitative PCR (RT-qPCR) and enzyme-linked immunosorbent assay (ELISA) analysis for CD63 and C3AR1 showed that their relative expression levels were significantly lower in the septic shock group compared with the control group (P<0.05).

Conclusion

CD63 and C3AR1 are significant hub genes of septic shock and may represent potential molecular targets for future studies of septic shock.

Exosomal CD63 in critically ill patients with sepsis

CD63 is one of the tetraspanin protein family members that is ubiquitously expressed on exosomes and is involved in the signal transduction of various types of immune cells. It may thus contribute to immunometabolic mechanisms of cellular and organ dysfunction in sepsis. Nonetheless, the association of exosomal CD63 with the severity and mortality of sepsis is not well known. Therefore, in the present study, the overall levels of exosomal CD63 were evaluated to ascertain whether they were associated with organ failure and mortality in patients with sepsis. Exosomal CD63 was measured from prospectively enrolled critically-ill patients with sepsis (n = 217) and healthy control (n = 20). To detect and quantify exosomes in plasma, a commercially available enzyme-linked immunosorbent assay kit was used according to the manufacturer's protocol. The total number of exosomal CD63 was determined by quantifying the immunoreactive CD63. The association between plasma levels of exosomal CD63 and sequential organ failure assessment (SOFA) score was assessed by a linear regression method. The best cut-off level of exosomal CD63 for 28-day mortality prediction was determined by Youden's index. Among 217 patients with sepsis, 143 (66%) patients were diagnosed with septic shock. Trends of increased exosomal CD63 levels were observed in control, sepsis, and septic-shock groups (6.6 µg/mL vs. 42 µg/mL vs. 90 µg/mL, p < 0.001). A positive correlation between exosomal CD63 and SOFA scores was observed in patients with sepsis (r value = 0.35). When patients were divided into two groups according to the best cut-off level, the group with higher exosomal CD63 levels (more than 126 µg/mL) was significantly associated with 28-day and in-hospital mortality. Moreover, the Kaplan-Meier survival method showed a significant difference in 90-day survival between patients with high- and low-exosomal CD63 levels (log-rank p = 0.005). Elevated levels of exosomal CD63 were associated with the severity of organ failure and predictive of mortality in critically ill patients with sepsis.

Research Advances in the Subtype of Sepsis-Associated Thrombocytopenia

The incidence and mortality of sepsis in the intensive care unit (ICU) are extremely high. Thrombocytopenia, one of the most common laboratory abnormalities, is correlated with prognosis in sepsis. The pathophysiology of sepsis-associated thrombocytopenia (SAT) remains unclear and may be associated with several factors such as platelet activation due to vascular injury and pathogen, suppression of bone marrow, platelet-targeted antibodies and desialylation. This review summarized all these possible mechanisms in the 3 subtypes of SAT: increased platelet consumption, reduced platelet production and increased platelet destruction. Based on the clinically available platelet parameters, the evidence for identifying SAT subtypes and the recent progress in treatments according to these subtypes are proposed to provide new prospects for the management of SAT.

Current understanding and future implications of sepsis-induced thrombocytopenia

Sepsis is a global health burden that needs intensive medical care. Thrombocytopenia in sepsis is well known to increase morbidity as well as mortality. Several studies have been performed both in animal models and in humans to understand the mechanism by which sepsis causes thrombocytopenia. Recent studies have shown that inhibiting thrombocytopenia improves outcomes in sepsis patients. Understanding these mechanisms to identify targets in use of newer treatment modalities besides using resuscitation measures, antibiotics and removal of thrombocytopenia inducing agent could potentially help us improve outcomes in sepsis.

Antiplatelet Agents in Sepsis-Putting it all together: A Call to Action

How to cite this article: Tiwari NR, Chaudhari KS, Sharma R, Haas KP, Sharma VR. Antiplatelet Agents in Sepsis-Putting it all together: A Call to Action. Indian J Crit Care Med 2020;24(6):483-484.

The effect of red blood cell transfusion on platelet function in critically ill patients

INTRODUCTION

Red blood cell (RBC) transfusion is associated with an increased risk of pro-thrombotic events, but the underlying mechanism is poorly understood. We hypothesized that RBC transfusion modulates platelet activity in critically ill patients with and without sepsis.

METHODS

In a prospective cohort study, 37 critically ill patients receiving a single RBC unit to correct for anemia were sampled prior to and 1 h after transfusion. Platelet exposure of P-selectin, CD63 and binding of PAC-1 as well as formation of platelet-leukocyte complexes were measured by flow cytometry. The ability of plasma from critically ill patients to induce ex vivo platelet aggregation was assessed by flow cytometry after incubation with platelets from a healthy donor.

RESULTS

RBC transfusion neither triggered the expression of platelet activation markers nor the formation of platelet-leukocyte complexes. Plasma from critically ill patients induced more spontaneous platelet aggregation prior to RBC transfusion compared to healthy controls, which was further augmented following RBC transfusion. Also collagen-induced platelet aggregation was already increased prior to RBC transfusion compared to healthy controls, and this response was unaffected by RBC transfusion. In contrast, ristocetin-induced platelet agglutination was decreased when compared to controls, suggesting impaired vWF-dependent platelet agglutination, even in the presence of high vWF levels. Following RBC transfusion, ristocetin-induced platelet agglutination further decreased. There were no differences between septic and non-septic recipients in all assays.

CONCLUSION

Ex vivo platelet aggregation is disturbed in the critically ill. Transfusion of a RBC unit may further increase the spontaneous platelet aggregatory response.

Platelets in Sepsis: An Update on Experimental Models and Clinical Data

Beyond their important role in hemostasis, platelets play a crucial role in inflammatory diseases. This becomes apparent during sepsis, where platelet count and activation correlate with disease outcome and survival. Sepsis is caused by a dysregulated host response to infection, leading to organ dysfunction, permanent disabilities, or death. During sepsis, tissue injury results from the concomitant uncontrolled activation of the complement, coagulation, and inflammatory systems as well as platelet dysfunction. The balance between the systemic inflammatory response syndrome (SIRS) and the compensatory anti-inflammatory response (CARS) regulates sepsis outcome. Persistent thrombocytopenia is considered as an independent risk factor of mortality in sepsis, although it is still unclear whether the drop in platelet count is the cause or the consequence of sepsis severity. The role of platelets in sepsis development and progression was addressed in different experimental in vivo models, particularly in mice, that represent various aspects of human sepsis. The immunomodulatory function of platelets depends on the experimental model, time, and type of infection. Understanding the molecular mechanism of platelet regulation in inflammation could bring us one step closer to understand this important aspect of primary hemostasis which drives thrombotic as well as bleeding complications in patients with sterile and infectious inflammation. In this review, we summarize the current understanding of the contribution of platelets to sepsis severity and outcome. We highlight the differences between platelet receptors in mice and humans and discuss the potential and limitations of animal models to study platelet-related functions in sepsis.

Can hypertonic saline influence platelet P selectin expression and platelet-leukocyte aggregation?

OBJECTIVES

Part of platelet function involves aggregation and activation. Activation leads to platelet P selectin expression and platelet-leukocyte aggregation. Hypertonic saline inhibits platelet aggregation, although the effects of hypertonic saline on platelet activation are not known. We evaluated the effects of hypertonic saline on platelet activation as measured by platelet P selectin expression and platelet-leukocyte aggregation.

METHODS

Blood samples from healthy volunteers (n = 6) were treated in vitro with various solutions including 23.5%, 7.5%, 3%, and 0.9% saline; Ringer's solution; 5% dextrose in water; and 10% hydroxyethyl starch. Blood was diluted with each type of solution to 2.5%, 5%, 10%, 20%, and 30% (vol/vol) dilution. All blood samples were activated with adenosine diphosphate (20 micromol/L), stained with fluorochrome-conjugated antibodies, and analyzed by flow cytometry to measure platelet P selectin expression and platelet-leukocyte aggregation.

RESULTS

The 23.5% saline solution reduced P selectin expression at 20% and 30% dilutions and platelet-leukocyte aggregation at 10%, 20%, and 30% dilutions. The 7.5% solution saline had no effect on P selectin expression and significantly inhibited platelet-leukocyte aggregation only at 30% dilution. Other solutions had no effect on platelet P selectin expression or platelet-leukocyte aggregation.

CONCLUSIONS

Our data suggest that hypertonic saline does not affect platelet P selectin expression or platelet-leukocyte aggregation at therapeutic plasma concentrations but that an inhibitory effect occurs at supratherapeutic doses. Dilutions of other solutions caused the least disturbance of platelet activation.

Lidocaine priming reduces ADP-induced P-selectin expression and platelet-leukocyte aggregation

BACKGROUND

Activation of platelets, which plays an important role in inflammation, has recently been reported to enhance platelet P-selectin expression and form platelet-leukocyte aggregation (PLA). Platelet P-selectin expression and PLA formation have been reported to be potential markers of inflammatory diseases such as sepsis, thrombosis, myocardial ischemic disorders and stroke. Lidocaine, one of the most commonly used anesthetics, is known to inhibit platelet function, but its effect on platelet P-selectin expression and PLA remains unclear.

METHODS

To determine the effect of lidocaine on platelet activation, and on platelet activation-related septic condition (lipopolysaccharide-induced), we treated platelets with lidocaine (0.03-3 mM) and then measured platelet P-selectin expression and PLA. Whole blood for in vitro study was obtained from healthy men aged 27 to 33 years who had not taken any medication for at least 15 days.

RESULTS

All samples were analyzed by flow cytometry. We found that lidocaine produced a concentration-dependent inhibition of P-selectin expression and PLA. Moreover, in lipopolysaccharide-challenged samples, lidocaine at concentrations of 1-3 mM inhibited PLA.

CONCLUSION

Our findings may help to elucidate the inhibitory role of lidocaine on platelet P-selectin expression and PLA and infer possible therapeutic targets in the treatment of inflammatory diseases. However, further investigations are needed to determine whether the observed attenuation of excessive inflammatory responses has clinical implications. These results suggest that lidocaine might have potential clinical application in the modulation of excessive platelet activation, inflammatory response and septic condition.

CD36: a multiligand molecule

CD36 is a multiligand receptor associated with a broad array of physiological processes and involved in markedly diverse disorders, including atherosclerosis, insulin resistance and diabetes, dyslipidemia, tumor angiogenesis, and host defense against Plasmodium falciparum. CD36 deficiency has proved to be common, particularly in ethnic groups such as African Americans and Asians. CD36 is commonly expressed on blasts in acute monocytic leukemia, megakaryoblastic leukemia, and erythroleukemia. The role of CD36 in sickle cell crises and cerebral malaria is debatable. As a receptor for thrombospondin 1, CD36 plays a role in the regulation of angiogenesis, which may be a therapeutic strategy for controlling the dissemination of malignant neoplasms. The future challenge will be to further understand the mechanisms by which CD36 affects these diverse functions and to design therapeutic strategies that can alter the course of the diseases.

Platelet function in sepsis

BACKGROUND

Coagulation abnormalities and thrombocytopenia are common in severe sepsis, but sepsis-related alterations in platelet function are ill-defined.

OBJECTIVES

The purpose of this study was to elucidate the effect of sepsis on platelet aggregation, adhesiveness, and growth factor release.

PATIENTS AND METHODS

Agonist-induced platelet aggregation was measured in platelet-rich plasma separated from blood samples collected from 47 critically ill patients with sepsis of recent onset. Expression of platelet adhesion molecules was measured by flow cytometry and the release of vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF) was measured by ELISA in the supernatant of platelet aggregation.

RESULTS

Septic patients had consistently decreased platelet aggregation compared with controls, regardless of the platelet count, thrombin generation, or overt disseminated intravascular coagulation (DIC) status. The severity of sepsis correlated to the platelet aggregation defect. Adhesion molecules, receptor expression (CD42a, CD42b, CD36, CD29, PAR-1), and alpha-granule secretion detected by P-selectin expression remained unchanged but the release of growth factors was differentially regulated with increased VEGF and unchanged PDGF after agonist activation even in uncomplicated sepsis.

CONCLUSIONS

Sepsis decreases circulating platelets' hemostatic function, maintains adhesion molecule expression and secretion capability, and modulates growth factor production. These results suggest that sepsis alters the hemostatic function of the platelets and increases VEGF release in a thrombin-independent manner.

Extensive Coagulation Monitoring in Patients After Implantation of the MicroMed Debakey Continuous Flow Axial Pump

Ventricular assist device (VAD) implantation is associated with impaired primary hemostasis and thromboembolic complications. Recently, a new generation of implantable continuous flow axial pumps was introduced into clinical application. To study the potential thrombogenic properties of this type of pump, we applied extensive platelet monitoring was applied. In our institution, 13 patients received the MicroMed DeBakey VAD as a bridge to transplantation. Routine coagulation tests (platelet count, activated partial thromboplastin time, prothrombin time, antithrombin III activity) and platelet function tests (whole blood aggregometry, thrombelastography, flow cytometry) were performed. No clinically relevant thromboembolic events were detected. No correlation was found between global function tests, platelet aggregation, and thrombelastography. No correlation was detected between platelet activation and hemolysis parameters. Platelet aggregation and coagulation index were significantly suppressed early after operation. A subsequent phase of hyper-aggregability, starting around day 6, suggested the initiation of antiaggregation therapy. Platelet activation markers were upregulated in the postoperative period but were returned to preoperative levels after initiation of aspirin. In contrast to routine coagulation monitoring, platelet function tests reflect in detail the coagulation status of blood pump recipients and the efficiency of antiaggregation therapy. Aspirin and dipyridamole therapy in addition to oral anticoagulation using phenprocoumon may contribute to platelet function and clot mechanics restoration and is, therefore, recommended for patients after VAD implantation.

The hematologic system as a marker of organ dysfunction in sepsis

Sepsis with acute organ dysfunction (severe sepsis) results from a systemic proinflammatory and procoagulant response to infection. Organ dysfunction in the patient with sepsis is associated with increased mortality. Although most organs have discrete anatomical boundaries and carry out unified functions, the hematologic system is poorly circumscribed and serves several unrelated functions. This review addresses the hematologic changes associated with sepsis and provides a framework for prompt diagnosis and rational drug therapy. Data sources used include published research and review articles in the English language related to hematologic alterations in animal models of sepsis and in critically ill patients. Hematologic changes are present in virtually every patient with severe sepsis. Leukocytosis, anemia, thrombocytopenia, and activation of the coagulation cascade are the most common abnormalities. Despite theoretical advantages of using granulocyte colony-stimulating factor to enhance leukocyte function and/or circulating numbers, large clinical trials with these growth factors are lacking. Recent studies support a reduction in the red blood cell transfusion threshold and the use of erythropoietin treatment to reduce transfusion requirements. Treatment of thrombocytopenia depends on the cause and clinical context but may include platelet transfusions and discontinuation of heparin or other inciting drugs. The use of activated protein C may provide a survival benefit in subsets of patients with severe sepsis. The hematologic system should not be overlooked when assessing a patient with severe sepsis. A thorough clinical evaluation and panel of laboratory tests that relate to this organ system should be as much a part of the work-up as taking the patient's blood pressure, monitoring renal function, or measuring liver enzymes.

The effects of sevoflurane and desflurane in vitro on platelet-leukocyte adhesion in whole blood

The interaction between platelets and leukocytes plays an important role in inflammatory and thrombotic processes. We investigated whether the volatile anaesthetics sevoflurane and desflurane alter the formation of platelet-leukocyte aggregates and the expression of P-selectin on platelets. Whole blood was incubated with 1 and 2 minimum alveolar concentration (MAC) sevoflurane or desflurane. Unstimulated and adenosine diphosphate, or thrombin receptor agonist peptide-6-stimulated samples were stained with fluorochrome-conjugated antibodies. The formation of platelet-leukocyte conjugates and the expression of P-selectin on platelets were measured using flow cytometry. Sevoflurane was found to enhance the binding of platelets to lymphocytes, neutrophils and monocytes, it also increased the expression of P-selectin on platelets especially in the stimulated samples. Desflurane decreased the percentage of lymphocyte-platelet, neutrophil-platelet and monocyte-platelet conjugates principally in unstimulated samples. The results show that these two volatile anaesthetics have differing effects on the formation of platelet-leukocyte conjugates in vitro. Sevoflurane also enhanced the expression of P-selectin on platelets.

Platelet and leukocyte activation correlate with the severity of septic organ dysfunction

This study was conducted to investigate the extent of platelet-leukocyte adhesion and platelet, monocyte, and neutrophil activation in septic patients and to analyze whether these variables correlate with the severity of sepsis. Forty-seven patients consecutively admitted to the operative ICU of a University Medical Centre and 12 control patients prior to elective surgery were included in this prospective cohort study. Patients were evaluated daily for sepsis criteria and sepsis-associated organ failure assessment (SOFA) score was used to describe the extent of sepsis-associated organ failure. Indicators for cell activation (CD62P on platelets and CD11b on neutrophils and monocytes) and binding of platelets to neutrophils and monocytes were analyzed by flow cytometry. CD62P was increased on platelets from patients with sepsis compared with patients who did not have sepsis. Patients with sepsis also had higher CD11b expression on neutrophils and monocytes. Statistical analyses revealed a positive correlation between platelet CD62P expression and severity of sepsis, as well as a positive correlation between the SOFA score and CD11b on monocytes. No correlation was found between the SOFA score and CD11b on neutrophils. Higher values for platelet-neutrophil adhesion were observed in patients with uncomplicated sepsis compared either with controls or to patients with septic shock. An inverse relation between severity of sepsis and extent of platelet-neutrophil adhesion was also obvious from correlation analysis. The results indicate that flow cytometry can be used to measure these parameters of cell activation in sepsis and that activation of platelets and monocytes as well as adhesion of platelets to neutrophils does play a role in the development of organ dysfunction.

Comparison of in vitro closure time (PFA-100) with whole blood electrical aggregometry and platelet surface antigen expression in healthy volunteers

It was the aim of this study to compare in vitro closure time (PFA-100), reflecting platelet-related primary hemostasis, to more platelet-specific tests like whole blood electrical aggregometry and platelet surface antigen expression in healthy volunteers. In vitro closure time was measured using a PFA-100. Platelet surface antigen expression (CD63, CD62-P, CD42b, CD36, CD31) was determined in accordance with the consensus protocol for flow-cytometric characterisation of platelet function. Platelet aggregometry was performed using a whole blood electrical aggregometer (ADP and arachidonic acid as agonists). Analysis of the obtained data revealed only a few significant correlations between the different platelet function tests used. This finding can be explained by the various aspects of platelet function being focused by these tests in different extents. Whenever platelet function is analysed, the investigator should be aware of the specific and limited evidence of the method used. For screening purposes, it may be useful to introduce a platelet function index, referring to basal platelet activity, platelet adhesion and platelet aggregation at low and high shear stress forces.