Platelets in sepsis: beyond hemostasis

Modes of action and diagnostic value of miRNAs in sepsis

Sepsis is a clinical syndrome defined as a dysregulated host response to infection resulting in life-threatening organ dysfunction. Sepsis is a major public health concern associated with one in five deaths worldwide. Sepsis is characterized by unbalanced inflammation and profound and sustained immunosuppression, increasing patient susceptibility to secondary infections and mortality. microRNAs (miRNAs) play a central role in the control of many biological processes, and deregulation of their expression has been linked to the development of oncological, cardiovascular, neurodegenerative and metabolic diseases. In this review, we discuss the role of miRNAs in sepsis pathophysiology. Overall, miRNAs are seen as promising biomarkers, and it has been proposed to develop miRNA-based therapies for sepsis. Yet, the picture is not so straightforward because of the versatile and dynamic features of miRNAs. Clearly, more research is needed to clarify the expression and role of miRNAs in sepsis, and to promote the use of miRNAs for sepsis management.

Platelet Functions During Extracorporeal Membrane Oxygenation. Platelet-Leukocyte Aggregates Analyzed by Flow Cytometry as a Promising Tool to Monitor Platelet Activation

Extracorporeal membrane oxygenation (ECMO) is an extracorporeal circulation used to manage patients with severe circulatory or respiratory failure. It is associated with both high bleeding and thrombosis risks, mainly as a result of biomaterial/blood interface phenomena, high shear stress, and complex inflammatory response involving the activation of coagulation and complement systems, endothelial cells, leukocytes, and platelets. Besides their critical role in hemostasis, platelets are important players in inflammatory reactions, especially due to their ability to bind and activate leukocytes. Hence, we reviewed studies on platelet function of ECMO patients. Moreover, we addressed the issue of platelet–leukocyte aggregates (PLAs), which is a key step in both platelet and leukocyte activation, and deserves to be investigated in these patients. A reduced expression of GPIb and GPVI was found under ECMO therapy, due to the shedding processes. However, defective platelet aggregation is inconsistently reported and is still not clearly defined. Due to the high susceptibility of PLAs to pre-analytical conditions, defining and strictly adhering to a rigorous laboratory methodology is essential for reliable and reproducible results, especially in the setting of complex inflammatory situations like ECMO. We provide results on sample preparation and flow cytometric whole blood evaluation of circulating PLAs.

The Use of High Dose Eltrombopag in the Management of Sepsis-Associated Thrombocytopenia in Critically Ill Patients

Introduction

Sepsis is a life-threatening condition, and sepsis-associated thrombocytopenia (SAT) is a common consequence of the disease where platelet count falls drastically within a very short time. Multiple key factors may cause platelet over-activation, destruction and reduction in platelet production during the sepsis. Eltrombopag is a thrombopoietin receptor agonist and is the second-line drug of choice in the treatment of chronic immune thrombocytopenia (ITP).

Aim of the study

The objective of this study was to observe the therapeutic outcome of high dose eltrombopag in SAT management in critically ill patients.

Material and Methods

This 6-month-long single group, observational study was conducted on seventeen ICU patients with SAT. Eltrombopag 100 mg/day in two divided doses was given to each patient. Platelet counts were monitored. A low platelet blood count returning to 150 K/μL or above, is taken as indicative of a successful reversal of a thrombocytopenia event.

Results

The mean Apache II score of patients (n= 17) was 18.71 (p-value: >0.05). No eltrombopag-induced adverse event was observed among the patients during the study period. Thrombocytopenia events were reversed successfully in 64.71% of patients (11; n= 17) within eight days of eltrombopag therapy.

Conclusions

The therapeutic potentiality of high dose eltrombopag regime in the management of sepsis-associated thrombocytopenia was found clinically significant in over two-thirds of critically ill adult patients enrolled in the study. These data may point to a new strategy in the management of acute type of thrombocytopenia in septic patients.

Early Host Interactions That Drive the Dysregulated Response in Sepsis

Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection. While many individual cells and systems in the body are involved in driving the excessive and sometimes sustained host response, pathogen engagement with endothelial cells and platelets early in sepsis progression, are believed to be key. Significant progress has been made in establishing key molecular interactions between platelets and pathogens and endothelial cells and pathogens. This review will explore the growing number of compensatory connections between bacteria and viruses with platelets and endothelial cells and how a better understanding of these interactions are informing the field of potential novel ways to treat the dysregulated host response during sepsis.

Platelets Drive Inflammation and Target Gray Matter and the Retina in Autoimmune-Mediated Encephalomyelitis

Despite growing evidence for platelets as active players in infection and immunity, it remains unresolved whether platelets contribute to, or are key elements in the development of neuroinflammation. Using the experimental autoimmune encephalomyelitis (EAE) model of multiple sclerosis, we identified platelet accumulation in the circulation by 7-day postinduction (dpi), ahead of clinical onset which occurs at 13-14 dpi. By inducing platelet depletion between 7 and 16 dpi, we demonstrate an association between platelet accumulation in the spinal cord and disease development. Additionally, we provide evidence for platelet infiltration in the white and gray matter parenchyma, but with different outcomes. Thus, while in white matter platelets are clearly associated with lesions, in gray matter large-scale platelet infiltration and expression of the platelet-specific molecule PF4 are detectable prior to T cell entry. In the retina, platelet accumulation also precedes clinical onset and is associated with significant increase in retinal thickness in experimental relative to control animals. Platelet accumulation increases over the disease course in this tissue, but without subsequent T cell infiltration. These findings provide definitive confirmation that platelet accumulation is key to EAE pathophysiology. Furthermore, they suggest an undescribed and, most importantly, therapeutically targetable mechanism of neuronal damage.

AST-to-Platelet Ratio Index as Potential Early-Warning Biomarker for Sepsis-Associated Liver Injury in Children: A Database Study

Background: Sepsis-associated liver injury (SALI) is a risk factor of poor outcome in patients with sepsis. The early warning biomarkers for identifying SALI remain poorly defined. Aims: To identify the potential predictors of occurrence of SALI in pediatric patients with sepsis. Methods: We retrospectively analyzed the sepsis database based on the medical records of patients admitted to the pediatric intensive care unit (PICU) in Shanghai Children's Hospital from July 2014 to June 2018. Patients' demographics, co-morbidities and laboratory variables were collected. Univariate and multivariate logistic analysis were used to explore risk factors of SALI, and receiver operating characteristic (ROC) curve analysis was used to evaluate their predictive significances for SALI occurrence. Results: Of 1,645 eligible patients, 1,147 patients were included, and 105 cases had SALI. The indexes including AST-to-platelet ratio index (APRI), γ-GT and lactate dehydrogenase (LDH) were independent risk factors for SALI. Moreover, APRI was powerful to predict SALI in children (AUC: 0.889, 95% CI: 0.851-0.927) with a sensitivity of 84.6 % and a specificity of 84.3 % at the cutoff point of 0.340. APRI was superior to LDH and not inferior to γ-GT for predicting SALI. Conclusion: APRI is an independent risk factor of SALI occurrence, and elevated APRI within 24 h after PICU admission (>0.340) is a potential predictor for SALI in children.

The Potential of Phage Therapy in Sepsis

Sepsis remains a difficult clinical challenge, since our understanding of its immunopathology is incomplete and no efficacious treatment currently exists. Its earlier stage results from an uncontrolled inflammatory response to bacteria while in the later stage disturbed immune response with immunodeficiency syndrome develops. More than a hundred of clinical trials have not provided an efficient therapy which could ascertain an improvement or cure. Recent advancements in immunobiology of bacterial viruses (phages) indicate that in addition to their well-known antibacterial action phages have potent immunomodulating properties. Those data along with preliminary observations in experimental animals and the clinic strongly suggest that clinical trials on the efficacy of phages in sepsis are urgently needed.

Increased Von Willebrand factor, decreased ADAMTS13 and thrombocytopenia in melioidosis

BACKGROUND

Melioidosis, caused by bioterror treat agent Burkholderia pseudomallei, is an important cause of community-acquired Gram-negative sepsis in Southeast Asia and Northern Australia. New insights into the pathogenesis of melioidosis may help improve treatment and decrease mortality rates from this dreadful disease. We hypothesized that changes in Von Willebrand factor (VWF) function should occur in melioidosis, based on the presence of endothelial stimulation by endotoxin, pro-inflammatory cytokines and thrombin in melioidosis, and investigated whether this impacted on outcome.

METHODS/PRINCIPAL FINDINGS

We recruited 52 controls and 34 culture-confirmed melioidosis patients at Sappasithiprasong Hospital in Ubon Ratchathani, Thailand. All subjects were diabetic. Platelet counts in melioidosis patients were lower compared to controls (p = 0.0001) and correlated with mortality (p = 0.02). VWF antigen levels were higher in patients (geometric mean, 478 U/dl) compared to controls (166 U/dL, p<0.0001). The high levels of VWF in melioidosis appeared to be due to increased endothelial stimulation (VWF propeptide levels were elevated, p<0.0001) and reduced clearance (ADAMTS13 reduction, p<0.0001). However, VWF antigen levels did not correlate with platelet counts implying that thrombocytopenia in acute melioidosis has an alternative cause.

CONCLUSIONS/SIGNIFICANCE

Thrombocytopenia is a key feature of melioidosis and is correlated with mortality. Additionally, excess VWF and ADAMTS13 deficiency are features of acute melioidosis, but are not the primary drivers of thrombocytopenia in melioidosis. Further studies on the role of thrombocytopenia in B. pseudomallei infection are needed.