Whole blood platelet deposition on extracellular matrix under flow conditions in preterm neonatal sepsis

The Role of the von Willebrand Factor Collagen-Binding Assay (VWF:CB) in the Diagnosis and Treatment of von Willebrand Disease (VWD) and Way Beyond: A Comprehensive 36-Year History

The von Willebrand factor (VWF) collagen binding (VWF:CB) assay was first reported for use in von Willebrand diagnostics in 1986, by Brown and Bosak. Since then, the VWF:CB has continued to be used to help diagnose von Willebrand disease (VWD) (correctly) and also to help assign the correct subtype, as well as to assist in the monitoring of VWD therapy, especially desmopressin (DDAVP). However, it is important to recognize that the specific value of any VWF:CB is predicated on the use of an optimized VWF:CB, and that not all VWF:CB assays are so optimized. There are some good commercial assays available, but there are also some "not-so-good" commercial assays available, and these may continue to give the VWF:CB "a bad reputation." In addition to VWD diagnosis and management, the VWF:CB found purpose in a variety of other applications, from assessing ADAMTS13 activity, to investigation into acquired von Willebrand syndrome (especially as associated with use of mechanical circulatory support or cardiac assist devices), to assessment of VWF activity in disease states in where an excess of high-molecular-weight VWF may accumulate, and lead to increased (micro)thrombosis risk (e.g., coronavirus disease 2019, thrombotic thrombocytopenic purpura). The VWF:CB turns 37 in 2023. This review is a celebration of the utility of the VWF:CB over this nearly 40-year history.

Neonatal Sepsis and Hemostasis

Neonatal sepsis is considered critical for a significant increase in neonatal morbidity and mortality among hospitalized neonates. Neonatal sepsis, in most cases, coexists with coagulopathy, which can prove to be life-threatening. Complex molecular and cellular systems are involved in the cross-talk between inflammation and hemostasis during sepsis. Disturbances in the regulating systems of the vascular endothelium, and platelet–endothelial and platelet–neutrophil interactions play a pivotal role in both inflammation and coagulation. This complex process is poorly understood in neonates. In addition to the developmental maturation of hemostasis and the immune response in neonatal sepsis, a cellular model of hemostasis during sepsis should be taken into account. This review focused on the molecular and cellular mechanisms underlying inflammation and hemostasis during neonatal sepsis, taking the developmental immune response and developmental hemostasis into account in order to provide future diagnostic approaches to be applied in everyday clinical settings. Regarding the diagnostic modalities, we briefly provide the limitations of the currently used conventional coagulation assays, focusing on viscoelastic tests and platelet flow cytometry.

Neonatal platelet physiology and implications for transfusion

The neonatal hemostatic system is different from that of adults. The differences in levels of procoagulant and anticoagulant factors and the evolving equilibrium in secondary hemostasis during the transition from fetal/neonatal life to infancy, childhood, and adult life are known as "developmental hemostasis." In regard to primary hemostasis, while the number (150,000-450,000/µl) and structure of platelets in healthy neonates closely resemble those of adults, there are significant functional differences between neonatal and adult platelets. Specifically, platelets derived from both cord blood and neonatal peripheral blood are less reactive than adult platelets to agonists, such as adenosine diphosphate (ADP), epinephrine, collagen, thrombin, and thromboxane (TXA₂) analogs. This platelet hyporeactivity is due to differences in expression levels of key surface receptors and/or in signaling pathways, and is more pronounced in preterm neonates. Despite these differences in platelet function, bleeding times and PFA-100 closure times (an in vitro test of whole-blood primary hemostasis) are shorter in healthy full-term infants than in adults, reflecting enhanced primary hemostasis. This paradoxical finding is explained by the presence of factors in neonatal blood that increase the platelet-vessel wall interaction, such as high von Willebrand factor (vWF) levels, predominance of ultralong vWF multimers, high hematocrit, and high red cell mean corpuscular volume. Thus, the hyporeactivity of neonatal platelets should not be viewed as a developmental deficiency, but rather as an integral part of a developmentally unique, but well balanced, primary hemostatic system. In clinical practice, due to the high incidence of bleeding (especially intraventricular hemorrhage, IVH) among preterm infants, neonatologists frequently transfuse platelets to non-bleeding neonates when platelet counts fall below an arbitrary limit, typically higher than that used in older children and adults. However, recent studies have shown that prophylactic platelet transfusions not only fail to decrease bleeding in preterm neonates, but are associated with increased neonatal morbidity and mortality. In this review, we will describe the developmental differences in platelet function and primary hemostasis between neonates and adults, and will analyze the implications of these differences to platelet transfusion decisions.

Rapid Proteome Changes in Plasma and Cerebrospinal Fluid Following Bacterial Infection in Preterm Newborn Pigs

Background: Neonatal infection and sepsis are common for preterm infants due to their immature immune system. Early diagnosis is important for effective treatment, but few early markers of systemic and neuro-inflammatory responses in neonates are known. We hypothesised that systemic infection with Staphylococcus epidermidis (SE), a Gram-positive bacteria, induces acute changes to proteins in the plasma and cerebrospinal fluid (CSF), potentially affecting the immature brain of preterm neonates.

Methods: Using preterm pigs as a model for preterm infants, plasma and CSF samples were collected up to 24 h after SE infection and investigated by untargeted mass spectrometry (MS)-based proteomics. Multiple differentially expressed proteins were further studied in vitro.

Results: The clinical signs of sepsis and neuroinflammation in SE-infected piglets were associated with changes of multiple CSF and plasma proteins. Eight plasma proteins, including APOA4, haptoglobin, MBL1, vWF, LBP, and sCD14, were affected 6 h after infection. Acute phase reactants, including complement components, showed a time-dependent activation pattern after infection. Feeding bovine colostrum reduced the sepsis-related changes in clinical indices and plasma proteins. Neuroinflammation-related neuropeptide Y (NPY), IL-18, and MMP-14 showed distinct changes in the CSF and several brain regions (the prefrontal cortex, PVWM, and hippocampus) 24 h after infection. These changes were verified in TLR2 agonist-challenged primary microglia cells, where exogenous NPY suppressed the inflammatory response.

Conclusion: Systemic infection with SE induces inflammation with rapid proteome changes in the plasma and CSF in preterm newborn pigs. The observed early markers of sepsis and neuroinflammation in preterm pigs may serve as novel biomarkers for sepsis in preterm infants.

Platelets in neonates: central mediators in haemostasis, antimicrobial defence and inflammation

Platelets are not only centrally involved in haemostasis, but also in antimicrobial defence and inflammation. Since evaluation of platelet physiology in the particular patient group of preterm and term neonatal infants is highly restricted for ethical reasons, there are hardly any data available in healthy and much less in extremely immature or ill neonates. By summarising current knowledge and addressing both platelet researchers and neonatologists, we describe neonatal platelet count and morphology, report on previous analyses of neonatal platelet function in primary haemostasis and provide insights into recent advances in platelet immunology that considerably impacts our clinical view on the critically ill neonatal infant. We conclude that neonatal platelets, originating from liver megakaryocytes, substantially differ from adult platelets and may play a pivotal role in the pathophysiology of neonatal sepsis or intraventricular haemorrhage, both complications which seriously augment perinatal morbidity and mortality.

Primary hemostasis in neonates with thrombocytopenia

OBJECTIVE

To evaluate the relationship between platelet counts and the platelet function analyzer-100 closure times (CTs) in neonates with thrombocytopenia, and to determine what other factors significantly affect CTs.

STUDY DESIGN

In a single institution prospective cross-sectional study, blood samples from neonates with platelet counts <150 × 10(9)/L were tested on the platelet function analyzer-100 with CT-collagen/epinephrine (CT-Epi) and CT-collagen/adenosine diphosphate (CT-ADP) cartridges.

RESULTS

The mean platelet count was 95 ± 28 × 10(9)/L for 48 infants with a mean gestational age 30.9 ± 5.3 weeks and median postnatal age of 5 (3-18) days. No association was evident between CT-Epi and platelet count. However, the CT-ADP was prolonged in many (but not all) infants with platelet counts <90 × 10(9)/L. Among infants <32 weeks gestational age, we found a moderate negative correlation between CT-ADP and platelet count (r = -0.54, P = .0045). The negative correlation was strongest in infants <32 weeks and <10 days old (r = -0.8, P = .0017). Other variables examined (hematocrit, infection, Score of Neonatal Acute Physiology II) did not have a significant effect on CT-ADP in a linear regression model.

CONCLUSIONS

Platelet counts <90 × 10(9)/L are associated with prolonged CT-ADP times in some but not all infants. Gestational and postnatal age-related differences in platelet function account for some of this variability. The predictive value of CT-ADP on neonatal bleeding risk remains to be studied.

Platelets in the neonatal period: developmental differences in platelet production, function, and hemostasis and the potential impact of therapies

Thrombocytopenia is a common problem among sick neonates admitted to the neonatal intensive care unit. Frequently, platelet transfusions are given to thrombocytopenic infants in an attempt to decrease the incidence or severity of hemorrhage, which is often intracranial. Whereas there is very limited evidence to guide platelet transfusion practices in this population, preterm infants in the first week of life (the highest risk period for bleeding) are nearly universally transfused at higher platelet counts than older infants or children. To a large extent, this practice has been influenced by the observation that neonatal platelets are hyporeactive in response to multiple agonists in vitro, although full-term infants exhibit normal to increased primary hemostasis. This apparently paradoxical finding is due to factors in the neonatal blood that enhance the platelet-vessel wall interaction and counteract the platelet hyporeactivity. Relatively few studies have evaluated the platelet function and primary hemostasis of preterm infants, the subset of neonates at highest risk of bleeding and those most frequently transfused. Current understanding of platelet production and function in preterm and full-term neonates, how these factors affect their response to thrombocytopenia and their primary hemostasis, and the implications of these developmental differences to transfusion medicine are reviewed herein.

Thrombocytopenia in the first 24 hours after birth and incidence of patent ductus arteriosus

BACKGROUND

Experimental studies suggest that platelet-triggered ductal sealing is critically involved in definite ductus arteriosus closure. Whether thrombocytopenia contributes to persistently patent ductus arteriosus (PDA) in humans is controversial. This was a retrospective study of 1350 very low birth weight (VLBW; <1500 g) infants, including 592 extremely low birth weight (ELBW; <1000 g) infants.

METHODS

All infants who had a platelet count in the first 24 hours after birth and an echocardiogram performed on day of life 4 to 5 were included. The incidence of thrombocytopenia was analyzed in infants with and without PDA, and in those who did or did not undergo PDA intervention. The impact of thrombocytopenia, gestational age, birth weight, gender, and sepsis on PDA was determined by receiver operating characteristic curve, odds ratio, and regression analyses.

RESULTS

Platelet numbers within the first 24 hours after birth did not differ between VLBW/ELBW infants with and without spontaneous ductal closure. Platelet numbers were not associated with subsequent PDA treatment. Low platelet counts were not related to failure of pharma-cologic PDA treatment and the need for subsequent surgical ligation. Lower gestational age or birth weight, male gender, and sepsis were linked to the presence of PDA in VLBW infants on day of life 4 to 5.

CONCLUSIONS

Thrombocytopenia in the first 24 hours after birth was not associated with PDA in this largest VLBW/ELBW infant cohort studied to date. Impaired platelet function, due to immaturity and critical illness, rather than platelet number, might play a role in ductus arteriosus patency.

Pathophysiology and treatment of septic shock in neonates

Neonatal septic shock is a devastating condition associated with high morbidity and mortality. Definitions for the sepsis continuum and treatment algorithms specific for premature neonates are needed to improve studies of septic shock and assess benefit from clinical interventions. Unique features of the immature immune system and pathophysiologic responses to sepsis, particularly those of extremely preterm infants, necessitate that clinical trials consider them as a separate group. Keen clinical suspicion and knowledge of risk factors will help to identify those neonates at greatest risk for development of septic shock. Genomic and proteomic approaches, particularly those that use very small sample volumes, will increase our understanding of the pathophysiology and direct the development of novel agents for prevention and treatment of severe sepsis and shock in the neonate. Although at present antimicrobial therapy and supportive care remain the foundation of treatment, in the future immunomodulatory agents are likely to improve outcomes for this vulnerable population.

Effects of beta2-glycoprotein-I on platelet aggregation in cord versus adult whole blood

We present a peculiarity of the neonatal hemostatic system that might contribute to establish a procoagulant readiness in neonatal blood by sensitizing neonatal platelets for ADP stimulation. beta2-glycoprotein-I (beta2-GP-I) is a plasma constituent capable of suppressing ADP-induced platelet aggregation. We found significant lower levels of beta2-GP-I in cord vs. adult plasma (120 +/- 27 vs. 180 +/- 37 microg/mL, P<0.001). We demonstrate dose-dependent inhibition of ADP-induced platelet aggregation in cord whole blood (WB) in the presence of increasing amounts of beta2-GP-I, evaluated by means of WB aggregometry employing the impedance method. Particularly, raising the beta2-GP-I concentration in cord WB from neonatal level up to the respective adult value caused significant reduction of amplitude (from 9.5 +/- 2.7 to 2.8 +/- 0.9 Omega, P<0.001) and of slope (from 5.9 +/- 2.4 to 1.89 +/- 0.9 Omega/min, P<0.001), and a significant prolongation of the aggregation time (from 51.8 +/- 22.9 to 110.8 +/- 60.3 s, P<0.001). In conclusion, physiological low levels of beta2-GP-I in cord WB cause enhanced responsiveness of neonatal platelets to ADP stimulation. This mechanism might help to explain the clinically observed well-functioning hemostasis in neonates.

Platelet function of newborns as tested by cone and plate(let) analyzer correlates with gestational Age

The issue of platelet function in infants and neonates is of interest, and current data are debatable. A new method for assessing platelet function involves using the cone and plate(let) analyzer (CPA), applicable for small (0.2 ml) whole blood volumes. We used polystyrene surface-coated plates to evaluate cord blood neonatal platelet function under flow. One hundred and sixty full-term and 29 preterm infants born at the Sheba Medical Center between March 2003 and January 2004 were evaluated for platelet adhesion measured as surface coverage (SC; the percentage of total area covered by platelets) and platelet aggregation, defined as the average size (AS) of the aggregates. Platelets from preterm infants displayed less platelet adhesion than did those from full-term infants. Platelet SC correlated with gestational age in all infants (p < 0.05), and both groups exhibited similar aggregation (AS). AS values, however, were significantly lower than the normal adult range in our laboratory. Infants born to mothers with pregnancy-induced hypertension displayed significantly lower SC. No association was found between CPA and postnatal complications.

CONCLUSION

CPA provides a rapid, feasible option for testing platelet function in neonates. Its potential predictive value deserves further attention, and more extensive studies are warranted.

Platelet function in term and preterm neonates

Platelet dysfunction likely contributes to the pathophysiology of catastrophic hemorrhages in preterm neonates. In vitro studies have demonstrated that platelets of both term and preterm neonates are hyporesponsive to a variety of agonists. In contrast,template bleeding times of term neonates are shorter than those from adults. Very little is known about this and other tests of primary hemostasis in premature and sick neonates in the neonatal intensive care unit (NICU). This article covers the current knowledge of platelet function in preterm and term neonates and review show new agents (such as recombinant thrombopoietin and recombinant factor VIIa) may enhance neonatal platelet function.