Neonatal thrombocytopenia and megakaryocytopoiesis

Platelet Activation by Antisense Oligonucleotides (ASOs) in the Göttingen Minipig, including an Evaluation of Glycoprotein VI (GPVI) and Platelet Factor 4 (PF4) Ontogeny

Antisense oligonucleotide (ASO) is a therapeutic modality that enables selective modulation of undruggable protein targets. However, dose- and sequence-dependent platelet count reductions have been reported in nonclinical studies and clinical trials. The adult Göttingen minipig is an acknowledged nonclinical model for ASO safety testing, and the juvenile Göttingen minipig has been recently proposed for the safety testing of pediatric medicines. This study assessed the effects of various ASO sequences and modifications on Göttingen minipig platelets using in vitro platelet activation and aggregometry assays. The underlying mechanism was investigated further to characterize this animal model for ASO safety testing. In addition, the protein abundance of glycoprotein VI (GPVI) and platelet factor 4 (PF4) was investigated in the adult and juvenile minipigs. Our data on direct platelet activation and aggregation by ASOs in adult minipigs are remarkably comparable to human data. Additionally, PS ASOs bind to platelet collagen receptor GPVI and directly activate minipig platelets in vitro, mirroring the findings in human blood samples. This further corroborates the use of the Göttingen minipig for ASO safety testing. Moreover, the differential abundance of GPVI and PF4 in minipigs provides insight into the influence of ontogeny in potential ASO-induced thrombocytopenia in pediatric patients.

Developmental cues license megakaryocyte priming in murine hematopoietic stem cells

The fetal-to-adult switch in hematopoietic stem cell (HSC) behavior is characterized by alterations in lineage output and entry into deep quiescence. Here we identify the emergence of megakaryocyte (Mk)-biased HSCs as an event coinciding with this developmental switch. Single-cell chromatin accessibility analysis reveals a ubiquitous acquisition of Mk lineage priming signatures in HSCs during the fetal-to-adult transition. These molecular changes functionally coincide with increased amplitude of early Mk differentiation events after acute inflammatory insult. Importantly, we identify LIN28B, known for its role in promoting fetal-like self-renewal, as an insulator against the establishment of an Mk-biased HSC pool. LIN28B protein is developmentally silenced in the third week of life, and its prolonged expression delays emergency platelet output in young adult mice. We propose that developmental regulation of Mk priming may represent a switch for HSCs to toggle between prioritizing self-renewal in the fetus and increased host protection in postnatal life.

Iron status influences the response of cord blood megakaryocyte progenitors to eltrombopag in vitro

Eltrombopag (ELT) is a thrombopoietic agent approved for immune thrombocytopenia and also a potent iron chelator. Here we found that ELT exhibited dose-dependent opposing effects on in vitro megakaryopoiesis: low concentrations (≤6 µM, ELT6) stimulated megakaryopoiesis, but high concentrations (30 µM, ELT30) suppressed megakaryocyte (MK) differentiation and proliferation. The suppressive effects of ELT30 were reproduced by other iron chelators, supporting iron chelation as a likely mechanism. During MK differentiation, committed MK progenitors (CD34+/CD41+ and CD34-/CD41+ cells) were significantly more sensitive than undifferentiated progenitors (CD34+/CD41- cells) to the suppressive effects of ELT30, which resulted from both decreased proliferation and increased apoptosis. The antiproliferative effects of ELT30 were reversed by increased iron in the culture, as were the proapoptotic effects when exposure to ELT30 was short. Because committed MK progenitors exhibited the highest proliferative rate and the highest sensitivity to iron chelation, we tested whether their iron status influenced their response to ELT during rapid cell expansion. In these studies, iron deficiency reduced the proliferation of CD41+ cells in response to all ELT concentrations. Severe iron deficiency also reduced the number of MKs generated in response to high thrombopoietin concentrations by ∼50%, compared with iron-replete cultures. Our findings support the hypothesis that although iron deficiency can stimulate certain cells and steps in megakaryopoiesis, it can also limit the proliferation of committed MK progenitors, with severity of iron deficiency and degree of thrombopoietic stimulation influencing the ultimate output. Further studies are needed to clarify how megakaryopoiesis, iron deficiency, and ELT stimulation are clinically interrelated.

Incidence and Risk Factors of Thrombocytopenia in Neonates Admitted with Surgical Disorders to Neonatal Intensive Care Unit of Tikur Anbessa Specialized Hospital: A One-Year Observational Prospective Cohort Study from a Low-Income Country

BACKGROUND

Thrombocytopenia is one of the most common hematologic disorders affecting neonates admitted to the neonatal intensive care unit. The aim of this study was to determine the incidence and associated risk factors of neonatal thrombocytopenia in neonates admitted with surgical disorders.

METHODS

An observational prospective cohort study was conducted and all neonates admitted to neonatal intensive care unit of Tikur Anbessa Specialized Hospital with surgical disorders were included. Data were collected using a checklist and analyzed by SPSS version 23. Chi square test and independent sample t- test were used to assess the association among different variables.

RESULTS

A total of 210 neonates were included in the study, out of which 56.2% were males. The incidence of thrombocytopenia was 55.8%. Among neonates with thrombocytopenia, 90.9% had late onset thrombocytopenia and half were in the severe range (<50,000/µL). The presence of sepsis (P = 0.000) and atresia (P = 0.000) were found to be significantly associated with the development of thrombocytopenia. The mean non feeding hours were found to be significantly longer for patients with thrombocytopenia (t [199], 5.81, P = 0.000).

CONCLUSION

The incidence of thrombocytopenia is high in our institution. Prevention methods towards neonatal sepsis should be given due emphasis.

Medicinal Uses of Hematopoietic Growth Factors in Neonatal Medicine

This review focuses on certain hematopoietic growth factors that are used as medications in clinical neonatology. It is important to note at the chapter onset that although all of the pharmacological agents mentioned in this review have been approved by the US Food and Drug administration for use in humans, none have been granted a specific FDA indication for neonates. Thus, in a sense, all of the agents mentioned in this chapter could be considered experimental, when used in neonates. However, a great many of the pharmacological agents utilized routinely in neonatology practice do not have a specific FDA indication for this population of patients. Consequently, many of the agents reviewed in this chapter are considered by some practitioners to be nonexperimental and are used when they judge such use to be "best practice" for the disorders under treatment.The medicinal uses of the agents in this chapter vary considerably, between geographic locations, and sometimes even within an institutions. "Consistent approaches" aimed at using these agents in uniform ways in the practice of neonatology are encouraged. Indeed some healthcare systems, and some individual NICUs, have developed written guidelines for using these agents within the practice group. Some such guidelines are provided in this review. It should be noted that these guidelines, or "consistent approaches," must be viewed as dynamic and changing, requiring adjustment and refinement as additional evidence accrues.

Comprehensive comparison of neonate and adult human platelet transcriptomes

Understanding the underlying mechanisms of the well-substantiated platelet hyporeactivity in neonates is of interest given their implications for the clinical management of newborns, a population at higher bleeding risk than adults (especially sick and preterm infants), as well as for gaining insight into the regulatory mechanisms of platelet biology. Transcriptome analysis is useful in identifying mRNA signatures affecting platelet function. However, human fetal/neonatal platelet transcriptome analysis has never before been reported. We have used mRNA expression array for the first time to compare platelet transcriptome changes during development. Microarray analysis was performed in pure platelet RNA obtained from adult and cord blood, using the same platform in two independent laboratories. A high correlation was obtained between array results for both adult and neonate platelet samples. There was also good agreement between results in our adult samples and outcomes previously reported in three different studies. Gene enrichment analysis showed that immunity- and platelet function-related genes are highly expressed at both developmental stages. Remarkably, 201 genes were found to be differentially expressed throughout development. In particular, neonatal platelets contain higher levels of mRNA that are associated with protein synthesis and processing, while carrying significantly lower levels of genes involved in calcium transport/metabolism and cell signaling (including GNAZ). Overall, our results point to variations in platelet transcriptome as possibly underlining the hypo-functional phenotype of neonatal platelets and provide further support for the role of platelets in cellular immune response. Better characterization of the platelet transcriptome throughout development can contribute to elucidate how transcriptome changes impact different pathological conditions.

Thrombocytopenia and platelet transfusion in the neonate

Neonatal thrombocytopenia is widespread in preterm and term neonates admitted to neonatal intensive care units, with up to one-third of infants demonstrating platelet counts <150 × 10(9)/L. Thrombocytopenia may arise from maternal, placental or fetal/neonatal origins featuring decreased platelet production, increased consumption, or both mechanisms. Over the past years, innovations in managing neonatal thrombocytopenia were achieved from prospectively obtained clinical data on thrombocytopenia and bleeding events, animal studies on platelet life span and production rate and clinical use of fully automated measurement of reticulated platelets (immature platelet fraction). This review summarizes the pathophysiology of neonatal thrombocytopenia, current management including platelet transfusion thresholds and recent developments in megakaryopoietic agents. Furthermore, we propose a novel index score for bleeding risk in thrombocytopenic neonates to facilitate clinician's decision-making when to transfuse platelets.

Thrombocytopenia and Cornelia de Lange syndrome: Still an enigma?

Cornelia de Lange Syndrome (CdLS) is a rare genetic disorder caused by mutations in the cohesion complex and its regulators. The syndrome is characterized by multiple organ system abnormalities, pre- and post-natal growth retardation and typical facial features. Thrombocytopenia is a reduction in platelet count to <150 × 10(9)  L. It can be caused by congenital or acquired decreased production, increased destruction, or sequestration of platelets. In recent years, several papers reported thrombocytopenia and immune thrombocytopenia in patients affected by CdLS. In 2011, Lambert et al. estimated the risk of idiopathic thrombocytopenia purpura in CdLS patients to be 31-633 times greater than in the general population. We describe the incidence of thrombocytopenia in 127 Italian CdLS patients, identifying patients with transient or persistent thrombocytopenia, but a lower incidence of true idiopathic thrombocytopenic purpura (ITP).

Platelet mass index: is it a hope for reduction of platelet transfusion in NICU?

OBJECTIVE

Thrombocytopenia is a very common problem in neonatal intensive care unit whose only specific treatment is platelet (PLT) transfusion which has well-known risks. Our aim is to test whether using PLT mass-based transfusion guideline would result in fewer transfusions or not.

METHODS

One hundred neonates with PLT count <100,000/μl were randomized into two groups: Group 1 (n = 50) was transfused according to PLT count-based guideline, whereas Group 2 (n = 50) was transfused according to PLT mass-based guideline. Subjects receiving one or more PLT transfusions and total number of PLT transfusions, hemorrhages, morbidity and mortality in both groups were recorded.

RESULTS

Demographic characteristics, PLT counts of the infants and clinical conditions associated with thrombocytopenia in both groups were not different. There was no reduction in the number of subjects receiving PLT transfusions (54% in Group 1, 50% in Group 2; p = 0.69) and in the number of PLT transfusions per infant (0.82 ± 1.13 versus 0.8 ± 1.23; p = 0.95). There was also no difference with respect to bleeding, morbidity and mortality between the groups.

CONCLUSION

Transfusion according to PLT mass or PLT count-based guideline does not seem to influence number of transfusions or the number of infants who were transfused.

Mathematical model of platelet turnover in thrombocytopenic and nonthrombocytopenic preterm neonates

Neonatal thrombocytopenia affects 22-35% of all neonates admitted to neonatal intensive care units. The purpose of this study was to develop a mathematical model for characterizing platelet (PLT) kinetics in thrombocytopenic preterm neonates. Immature PLT fraction (IPF) and PLT counts were measured for up to 35 days after birth in 27 very low birth weight preterm neonates. PLT transfusions were administered to 8 of the 27 (24%) subjects. The final model included a series of four transit compartments to mimic the production and survival of IPF and PLT. Model parameters were estimated using nonlinear mixed effects modeling with the maximum likelihood expectation maximization algorithm. The model adequately captured the diverse phenotypes expressed by individual subject profiles. Typical population survival values for IPF and PLT life spans in nonthrombocytopenic patients were estimated at 0.912 and 10.7 days, respectively. These values were significantly shorter in thrombocytopenic subjects, 0.429 and 2.56 days, respectively. The model was also used to evaluate the influence of growth and laboratory phlebotomy loss on the time course of IPF and PLT counts. Whereas incorporating body weight was essential to correct for expanding blood volume due to growth, phlebotomy loss, a possible covariate, did not significantly influence PLT kinetics. This study provides a platform for identifying potential covariates that influence the interindividual variability in model parameters regulating IPF and PLT kinetics and for evaluating future pharmacological therapies for treating thrombocytopenic neonates.

Thrombocytopenia and Associated Factors in Neonates Admitted to NICU during Years 2010_2011

BACKGROUND

Thrombocytopenia is the most common hematological abnormality which is encountered in the neonatal intensive care unit (NICU). The incidence in neonates varies greatly, depending upon the population studies. According to the frequency of thrombocytopenia and its complications and because of lack of such research in Iran, this study was performed on neonates admitted to Shahid Sadughi NICU during years 2011-2012.

MATERIALS AND METHODS

In a retrospective study, 350 neonates who were admitted to NICU were enrolled in the study. They were categorized to three groups regarding platelet count: mild, moderate and severe thrombocytopenia. Incidence of thrombocytopenia was determined and contribution of variables such as sex, gestational age, intrauterine growth retardation, asphyxia, sepsis, necrotizing enterocolitis, blood group, placental insufficiency in Gestational Diabetes Mellitus (GDM) and hypertension (HTN) were analyzed.

RESULTS

Neonatal thrombocytopenia was found in 100(28.5%) of 350 subjects, consisted of 75.3% early onset and 24.7% late onset, which most of them (96.5%) had mild and moderate thrombocytopenia, and just 3.5% had developed severe thrombocytopenia. Thrombocytopenia was associated with sepsis, intrauterine growth retardation sepsis, asphyxia, GDM, maternal hypertension and prematurity. There was no relation between occurrence of thrombocytopenia and gender.

CONCLUSION

 The incidence of neonatal thrombocytopenia was 28.5 %. Significant maternal risk factors that lead to thrombocytopenia were HTN and preeclampsia, while risk factors of neonates were asphyxia, sepsis and Intera Uterus Growth Retardation.

A de novo T73I mutation in PTPN11 in a neonate with severe and prolonged congenital thrombocytopenia and Noonan syndrome

We observed a neonate with severe congenital thrombocytopenia and features of Noonan syndrome where evaluations were negative for immune-mediated thrombocytopenia, congenital infections, and Fanconi anemia. The marrow findings and a significantly elevated plasma thrombopoietin (Tpo) level were consistent with congenital amegakaryocytic thrombocytopenia; we sought a genetic mutation that could explain this phenotype. No mutations were identified in c-MPL (the Tpo receptor gene). Microarray analysis of peripheral blood did not reveal an abnormality. DNA sequencing of the PTPN11 gene showed a heterozygous C>T nucleotide substitution in exon 3 (c.218C>T) predicted to result in a threonine-to-isoleucine change at residue 73 (T73I). A 6-week trial of eltrombopag (an agonist of the Tpo receptor) failed to increase the platelet count. We propose this specific PTPN11 mutation results in abnormalities of the protein product SHP-2, which, because of its role in signal transduction, results in severe congenital thrombocytopenia refractory to c-MPL agonists.

Diagnosis and management of neonatal thrombocytopenia

Thrombocytopenia is the most common haematological abnormality in newborns admitted to neonatal care units and serves as an important indicator of underlying pathological processes of mother or child. In most cases thrombocytopenia is mild to moderate and resolves within the first weeks of life without any intervention. However, in some neonates thrombocytopenia is severe or may reflect an inborn platelet disorder. As clinical course and outcome of thrombocytopenia depend on the aetiology of thrombocytopenia, an appropriate work-up is essential to guide therapy in neonates with thrombocytopenia and to avoid severe bleeding.

Platelet indices in SGA newborns

PURPOSE

The current study objective was to compare blood platelet indices in full-term small-for-gestational-age newborns (SGA) and full-term appropriate-for-gestational-age newborns (AGA).

MATERIALS/METHODS

We introduced to our study 61 SGA newborns (31 females and 30 males) and 70 eutrophic infants (32 females and 38 males). The SGA newborns were divided into two groups: those weighing less than the 5th centile: 35 infants (16 females and 19 males) and those between the 5th and 10th centiles: 26 infants (15 females and 11 males). Platelet indices were estimated in blood samples collected from the umbilical artery.

RESULTS

SGA demonstrated a decreased count of blood platelets (238×103/μ) as compared with AGA (286×103/μL), p=0.0001. Platelet hematocrit (PTC) also showed differences in both groups (SGA=0.19% vs. AGA=0.22%; p=0.0005). Mean platelet volume (MPV) was higher in SGA (8.25fl) as compared with AGA (7.84fl); p=0.008. Large platelet count (LPLT) was higher in AGA 6.26% vs. SGA=4.75%; p=0.01. Platelet distribution width (PDW) was found to be nearly the same (SGA=47%, AGA=46%). PDW was higher in SGA newborns < 5th centile (43%) as compared with SGA infants between the 5th and 10th centiles (52%); p=0.008.

CONCLUSIONS

A decreased blood platelet count, platelet hematocrit and large metabolically active platelet count, which in addition to reduced synthesis and excessive consumption of coagulation factors in states of hiperclotting is characteristic of IUGR, enhances the possibility of bleeding complications and increases the risk of infections. From a clinical point of view, it is important to take into consideration the degree of intrauterine hypotrophy during the evaluation of hemostatic disorders.

Two patterns of thrombopoietin signaling suggest no coupling between platelet production and thrombopoietin reactivity in thrombocytopenia-absent radii syndrome

BACKGROUND

Thrombocytopenia with absent radii syndrome is defined by bilateral radius aplasia and thrombocytopenia. Due to impaired thrombopoietin signaling there are only few bone marrow megakaryocytes and these are immature; the resulting platelet production defect improves somewhat over time. A microdeletion on chromosome 1q21 is present in all patients but is not sufficient to form thrombocytopenia with absent radii syndrome. We aimed to refine the signaling defect in this syndrome.

DESIGN AND METHODS

We report an extended study of 23 pediatric and adult patients suffering from thrombocytopenia with absent radii syndrome in order to scrutinize thrombopoietin signal transduction by immunoblotting and gel electrophoretic shift assays. In addition, platelet immunotyping and reactivity were analyzed by flow cytometry. Results were correlated with clinical data including age and platelet counts.

RESULTS

Two distinct signaling patterns were identified. Juvenile patients showed abrogated thrombopoietin signaling (pattern #1), which is restored in adults (pattern #2). Phosphorylated Jak2 was indicative of activation of STAT1, 3 and 5, Tyk2, ERK, and Akt, showing its pivotal role in distinct thrombopoietin-dependent pathways. Jak2 cDNA was not mutated and the thrombopoietin receptor was present on platelets. All platelets of patients expressed normal levels of CD41/61, CD49b, and CD49f receptors, while CD42a/b and CD29 were slightly reduced and the fibronectin receptor CD49e markedly reduced. Lysosomal granule release in response to thrombin receptor activating peptide was diminished.

CONCLUSIONS

We show a combined defect of platelet production and function in thrombocytopenia with absent radii syndrome. The rise in platelets that most patients have during the first years of life preceded the restored thrombopoietin signaling detected at a much later age, implying that these events are uncoupled and that an unknown factor mediates the improvement of platelet production.

Platelet transfusion in the neonatal intensive care unit: benefits, risks, alternatives

Platelet transfusions were introduced into clinical medicine about 60 years ago when they were shown to reduce the mortality rate of patients with leukemia who were bleeding secondary to hyporegenerative thrombocytopenia. In modern neonatology units, platelet transfusions are integral and indeed lifesaving for some neonates. However, the great majority of platelet transfusions currently administered in neonatal intensive care units (NICUs) are not given in the original paradigm to treat thrombocytopenic hemorrhage, but instead are administered prophylactically with the hope that they will reduce the risk of spontaneous bleeding. Weighing the risks and benefits of platelet transfusion, although imprecise, should be attempted each time a platelet transfusion is ordered. Adopting guidelines specific for platelet transfusion will improve consistency of care and will also generally reduce transfusion usage, thereby reducing costs and conserving valuable blood bank resources. Initiating specific programs to improve compliance with transfusion guidelines can further improve NICU transfusion practice.