Development of coagulation regulatory proteins in the fetal and neonatal lamb

Contemporary tools for evaluation of hemostasis in neonates. Where are we and where are we headed?

The assessment of hemostatic disorders in neonates is crucial, but remains challenging for clinicians. Although the concept of developmental hemostasis is widely accepted among hemostasis specialists globally, it is probably under-recognized by clinicians and laboratory practitioners. In parallel with age-dependent hemostatic status maturation, comprehension of the differences between normal values is crucial for the accurate diagnosis of potential hemorrhagic and thrombotic disorders of the vulnerable neonatal population. This review outlines the basics of developmental hemostasis and the features of the available coagulation testing methods, with a focus on novel tools for evaluating the neonatal hemostatic profile. Common errors, issues, and pitfalls during the assessment of neonatal hemostasis are discussed, along with their impact on patient management. Current knowledge gaps and research areas are addressed. Further studying to improve our understanding of developmental hemostasis and its reflection on everyday clinical practice is warranted.

Hemostasis in the Pregnant Woman, the Placenta, the Fetus, and the Newborn Infant

The hemostasis system is composed of procoagulant, anticoagulant, and fibrinolytic proteins that interact with endothelial and blood cells and with each other in a complex system of checks and balances to maintain blood flow while preventing both hemorrhage and thrombosis. Pregnancy is a unique physiological state in which biological alterations predispose both mother and fetus to both bleeding and clotting. The placenta is a vascular interface for maternal and fetal blood exchange which predisposes the mother to hemorrhage. Maternal hemostasis presents a compensatory hypercoagulability including elevated factor VIII, von Willebrand factor, fibrinogen and thrombin generation, decreased thrombin regulation with resistance to activated protein C and decreased free protein S, and decreased fibrinolysis with increased plasminogen activator inhibitors. The placental vascular surface is of fetal trophoblastic origin that derives many characteristics of endothelium but differs in that tissue factor is constitutively expressed. Ontogeny of fetal hemostasis is characteristic. Platelets, von Willebrand factor, factor VIII, and fibrinogen are expressed and mature early in gestation, while vitamin K-dependent and contact factors exhibit delayed development. The fetal hemostatic system has a decreased capacity to generate or regulate thrombin, resulting in a fragile balance with little capacity to compensate under stress conditions, particularly in the infant born prematurely. Dysfunction of the maternal/placental/fetal unit gives rise to gestational disorders including preeclampsia, fetal growth restriction, placental abruption, and premature delivery. Knowledge of normal hemostasis levels and function are critical to evaluate bleeding or clotting syndromes in the pregnant woman and her fetus or newborn infant.

50 Years of Pediatric Hemostasis: Knowledge, Diagnosis, and Treatment

Studies from the past 50 years have contributed to the expanding knowledge regarding developmental hemostasis. This is a dynamic process that begins in the fetal phase and is characterized by physiological variations in platelet counts and function, and concentrations of most coagulation factors and the native coagulation inhibitors in early life, as compared with adulthood. The developmental hemostasis studies since the 1980 to 1990s established the laboratory reference values for coagulation factors. It was only a decade or two later, that thromboelastography (TEG) or (rotational thromboelastometry [ROTEM]) as well as thrombin generation studies, provided special pediatric reference values along with the ability to evaluate clot formation and lysis. In addition, global whole blood-based clotting assays provided point of care guidance for proper transfusion support to children hospitalized in intensive care units or undergoing surgery. Although uncommon, thrombosis in children and neonates is gaining increasing recognition, typically as a secondary complication in sick children. Bleeding in children, and particularly intracerebral hemorrhage in newborns, still represent a therapeutic challenge. Notably, our review will outline the advancements in understanding developmental hemostasis and its manifestations, with respect to the pathophysiology of thrombosis and bleeding complications in young children. The changes of transfusion policy and approach to thrombophilia testing during the last decade will be mentioned. Subsequently, a brief summary of the data on anticoagulant treatments in pediatric patients will be presented. Finally, we will point out the 10 most cited articles in the field of pediatric and neonatal hemostasis.

Thromboelastography in term neonates

BACKGROUND

Thromboelastography (TEG) is utilized as a point-of-care test of coagulation function to improve evidence-based blood product replacement in adults. In contrast to standard indices of coagulation, TEG reflects the dynamic interactions among the elements involved in hemostasis, including fibrinolysis. Although normal adult values and various abnormalities have been characterized, normative values for term neonates have not been described. Studies of neonatal TEG remain limited and have small sample sizes with inconsistent methodology. The aim of this study is to provide normative data on healthy term neonates, and to assess the impact of mode of delivery on TEG parameters at term.

METHODS

Venous umbilical blood was obtained from the placenta within 10 min of delivery. TEG analysis of citrated kaolin-activated samples was performed for 50 healthy term vaginal and 50 cesarean deliveries. Samples collected for cesarean sections were from scheduled cases or unscheduled ones due to failure of progression of labor.

RESULTS

Healthy neonates with uncomplicated vaginal term deliveries resulted in the following TEG parameters: R: 5.41 ± 1.34 (mean ± SD) min; K: 1.62 ± 0.75 min; α-angle: 65.39 ± 8.77°; MA: 65.86 ± 5.81 mm; and LY30: 1.40 ± 1.18%. Results for the cesarean delivery neonatal TEG assays showed: R: 5.51 ± 1.74 (mean ± SD) min; K: 1.52 ± 0.47 min; α-angle: 64.15 ± 4.61°; MA: 64.15 ± 4.61 mm; and LY30: 2.44 ± 3.51%. Of note, no statistical differences were observed (p < .01) between the groups.

CONCLUSION

TEG measurements from term neonates were no different when the neonates were delivered vaginally or by cesarean section. Labor had no effect on neonatal TEG levels. Neonatal TEG values may therefore serve as insight for fetal values at the appropriate postconceptional age.

Control of post-translational modifications in antithrombin during murine post-natal development by miR-200a

Background

Developmental haemostatic studies may help identifying new elements involved in the control of key haemostatic proteins like antithrombin, the most relevant endogenous anticoagulant.

Results

In this study, we showed a significant reduction of sialic acid content in neonatal antithrombin compared with adult antithrombin in mice. mRNA levels of St3gal3 and St3gal4, two sialyltransferases potentially involved in antithrombin sialylation, were 85% lower in neonates in comparison with adults. In silico analysis of miRNAs overexpressed in neonates revealed that mir-200a might target these sialyltransferases. Moreover, in vitro studies in murine primary hepatocytes sustain this potential control.

Conclusions

These data suggest that in addition to the direct protein regulation, microRNAs may also modulate qualitative traits of selected proteins by an indirect control of post-translational processes.

Measurement of platelet aggregation in ovine blood using a new impedance aggregometer

BACKGROUND

Whole blood platelet aggregometry (impedance) is an important method to investigate platelet function disorders. Examination of hemostatic function in sheep is important with respect to their role as an animal model of human disease.

OBJECTIVE

The aim of this study was to evaluate and optimize selected methodological aspects (anticoagulant, agonist concentration) of impedance aggregometry in ovine blood using the new Multiplate 5.0 analyzer.

METHODS

Blood samples were collected in hirudin anticoagulant from 40 clinically healthy sheep. Samples from selected sheep were collected in citrate, with or without the addition of calcium chloride. The agonists adenosine diphosphate (ADP), collagen, ristocetin, arachidonic acid, and thrombin receptor-activating peptide (TRAP) were added in several concentrations to induce aggregation.

RESULTS

Based on maximum aggregation values and internal precision, no significant difference was found between ADP concentrations of 3-10 micromol/L and collagen concentrations of 3-5 microg/mL (P>.05). The lowest interindividual variation of approximately 3-4-fold was seen with 4 and 5 micromol/L ADP and 4 and 5 microg/mL collagen. Ristocetin, arachidonic acid, and TRAP did not induce significant aggregation at any concentration. Aggregation results were significantly lower when measured in citrate- vs hirudin-anticoagulated blood, regardless of the presence of calcium chloride.

CONCLUSIONS

Our results indicate that the multiplate impedance aggregometer is suitable for the measurement of platelet aggregation in sheep using optimal agonist concentrations of 4-5 micromol/L ADP and 4-5 microg/mL collagen. Hirudin-anticoagulated blood is the preferred sample material.

Pharmacokinetics of protein C and antithrombin in the fetal lamb: a model to predict human neonatal replacement dosing

BACKGROUND

The preterm infant is at risk for consumptive coagulopathy and thrombosis due to late maturation of coagulation regulatory proteins. Replacement proteins are available, but neonatal pharmacokinetic data are lacking.

OBJECTIVE

The objective was to determine the pharmacokinetic properties of antithrombin (AT) and protein C (PC) in order to provide data for estimating doses in human infants.

METHODS

A catheterized ovine model was used to determine pharmacokinetic properties of AT and PC, including plasma recovery, volume of distribution (V(d)), clearance (Cl) and half-life (t((1/2))), in the fetal lamb relative to the ewe.

RESULTS

AT studies showed statistically significant differences between ewes and fetuses in recovery (p < 0.0001), V(d) (p = 0.0002) and Cl (p < 0.0001). The AT t((1/2)) was significantly shortened among fetuses (5.55 h, 95% CI: 4.01-7.08) compared to ewes (18.7 h, 95% CI: 11.6-25.8). PC recovery (p < 0.0001), V(d) (p < 0.0001) and Cl (p = 0.004) differed significantly between ewes and singleton fetuses as did the t((1/2)): 3.86 h (95% CI: 3.35-4.36) and 11.9 h (95% CI: 10.9-12.9) in the singletons and ewes, respectively. All PC parameters were significantly different for twins compared to ewes.

CONCLUSIONS

AT and PC show decreased recovery and t((1/2)) in the fetal lamb. These data can be used to estimate dosing for human neonates in comparison with human adult dosing recommendations.

Animal models of germinal matrix hemorrhage

Germinal matrix hemorrhage refers to bleeding that arises from the subependymal (or periventricular) germinal region of the immature brain. Clinical studies have shown that infants who experience germinal matrix hemorrhage can develop hydrocephalus or suffer from long-term neurologic dysfunction, including cerebral palsy, seizures, and learning disabilities. Understanding the causative factors and the pathogenesis of subsequent brain damage is important if germinal matrix hemorrhage is to be prevented or treated. Appropriate animal models are necessary to achieve this understanding. A number of animal species, including mice, rats, rabbits, sheep, pigs, dogs, cats, and primates, have been used to model germinal matrix hemorrhage. This literature review critically evaluates the animal models of germinal matrix hemorrhage. Each model has its own advantages and disadvantages; no single model is suitable for the study of all aspects of brain damage.