Thrombopoietin (Tpo) in the fetus and neonate: Tpo concentrations in preterm and term neonates, and organ distribution of Tpo and its receptor (c-mpl) during human fetal development

The hematopoietic microenvironment of the fetal liver and transient abnormal myelopoiesis associated with Down syndrome: A review

Transient abnormal myelopoiesis (TAM) in neonates with Down syndrome is a distinct form of leukemia or preleukemia that mirrors the hematological features of acute megakaryoblastic leukemia. However, it typically resolves spontaneously in the early stages. TAM originates from fetal liver (FL) hematopoietic precursor cells and emerges due to somatic mutations in GATA1 in utero. In TAM, progenitor cells proliferate and differentiate into mature megakaryocytes and granulocytes. This process occurs both in vitro, aided by hematopoietic growth factors (HGFs) produced in the FL, and in vivo, particularly in specific anatomical sites like the FL and blood vessels. The FL's hematopoietic microenvironment plays a crucial role in TAM's pathogenesis and may contribute to its spontaneous regression. This review presents an overview of current knowledge regarding the unique features of TAM in relation to the FL hematopoietic microenvironment, focusing on the functions of HGFs and the pathological features of TAM.

Immature Platelet Fraction and Its Kinetics in Neonates

Thrombocytopenia is a common abnormality encountered in the neonatal period, and immature platelet fraction (IPF) may be an informative indicator of thrombopoiesis; however, data on IPF in neonates are scarce. To define reference intervals (RIs) and factors affecting IPF in neonates, we measured the IPF of 533 consecutive neonates. With a multiple regression analysis of 330 newborns with normal platelet counts at birth, premature delivery, neonatal asphyxia, intrauterine infection, chromosomal abnormalities, and respiratory disorders were identified as independent factors for IPF%. The RIs of IPF% and absolute IPF value in neonates were determined to be 1.3% to 5.7% and 3.2 to 14.5×10 9 /L, respectively. On day 14 after birth, IPF% increased to twice the value at birth and thereafter returned to the previous value on day 28. Reticulocyte counts, in contrast, were the lowest at day 14. IPF% was increased in 16 thrombocytopenic patients with various clinical conditions, especially those with immune-mediated thrombocytopenia. IPF in neonates may be evaluated essentially based on the same RIs as in adults, although some precautions must be taken when evaluating IPF in neonates in the first 2 weeks of life. IPF may be useful for evaluating thrombopoiesis and thrombocytopenia in neonates.

Age- and sex-specific reference intervals for complete blood count parameters in capillary blood for Chinese neonates and infants: A prospective study

BACKGROUND

The reference intervals (RIs) of laboratory tests are essential for disease diagnosis, therapy monitoring, and health assessment. They are also significant for clinicians to discriminate between subjects with disease and healthy subjects. However, RIs for complete blood count (CBC) parameters in capillary blood for children are deficient. This study aimed to establish capillary blood RIs for blood cell parameters in neonates and infants from birth to 2 years of age in Zhengzhou.

METHODS

We prospectively collected a total of 1840 capillary blood specimens from healthy subjects from birth to 2 years of age. Hematology RIs were established by analyzing capillary blood sample data, and RIs and 90 % confidence intervals (CIs) were calculated according to Clinical and Laboratory Standards Institute (CLSI) C28-A3 guidelines.

RESULTS

RIs were established for hematological parameters of capillary blood in neonates and infants from birth to 2 years of age. The levels of almost all hematological parameters, except for the lymphocyte (LYMPH), platelet (PLT), and thrombocytocrit (PCT) parameters, peaked in the first month after birth and then decreased to lower levels within 6 months. There were significant sex differences in most erythrocyte-related parameters, with higher levels in males than in females. Erythrocyte-related parameters showed an increasing tendency with increasing age after the second month. Neutrophil (NEUT) levels were high on the third day of life, declined to a nadir in the first month, and then slowly increased with age. LYMPH levels were low at birth and began to increase after birth, peaked at approximately-six months of age and then gradually declined with age. PLT and PCT levels showed an increasing trend during the first month, while the other parameters showed a decreasing trend. All platelet-related and leukocyte-related parameters showed no significant difference with sex.

CONCLUSION

We provide comprehensive age- and sex-specific RIs, including RIs for neonates in Henan. Our study provides more comprehensive reference ranges for Child Health Hospital and children's medical institutions, which may facilitate preliminary screening, diagnosis, and therapy.

Distinct characteristics of neonatal platelet reactivity

Platelets undergo a process of developmental maturation, and hence its regulation of vascular integrity and control of hemostasis at various stages of neonatal ages deserves better characterization. Functional assays for platelets require a larger volume of blood than what is feasible to collect in neonates, creating a technical hurdle that has been a challenge to investigate neonatal platelets. For this reason, the current knowledge of neonatal platelet function has been based on studies from cord blood-derived platelets as a surrogate for neonatal peripheral blood. Studies indicate that neonatal platelets are hypofunctional to various agonists, although neonates tend to maintain normal hemostasis. This apparently paradoxical finding may be due to several factors, such as elevated functionally potent von Willebrand factor multimers or hematocrit levels, in the neonatal blood that enhance the platelet and vessel wall interaction, and counteract platelet hyporeactivity. This review describes the functional characteristics of neonatal platelets, differences in platelet reactivity between neonates and adults, and potential biomarkers of platelet activation.

Developmental differences between newborn and adult mice in response to romiplostim

Thrombocytopenia is frequent among sick neonates. While most cases are transient, some neonates experience prolonged and severe thrombocytopenia. These infants often pose diagnostic and therapeutic challenges, and may receive large numbers of platelet transfusions. Romiplostim (ROM) is a thrombopoietin (TPO)-receptor-agonist approved for treatment of adults with chronic immune thrombocytopenia (ITP). The immature platelet fraction (IPF) is a novel measure of newly produced platelets, which could aid with the diagnostic evaluation of thrombocytopenic neonates. This study had the following two objectives: (1) compare the response of newborn and adult mice to escalating doses of ROM in vivo and (2) assess the correlation between IPF and megakaryocyte (MK) mass in newborn and adult treated and untreated mice. In the first set of studies, newborn (day 1) and adult mice received a single subcutaneous (SC) dose of ROM ranging from 0 to 300 ng/g, and platelet counts were followed every other day for 14 days. Both sets of mice responded with dose-dependent platelet and IPF increases, peaking on days 5-7 post-treatment, but neonates had a blunted response (2.1-fold compared to 4.2-fold maximal increase in platelet counts, respectively). On day 5 post-treatment with 300 ng/g ROM, MKs in the bone marrow (BM) and spleen of adult mice were significantly increased in numbers and size (p < 0.0001 for both) compared to controls. MKs in the spleen and BM (but not liver) of treated neonates also increased in number, but not in size. The immature platelet count (IPC, calculated as IPF x platelet count) was highly correlated with the MK number and size in neonatal and adult BM and spleen, but not neonatal liver. The lack of response of neonatal liver MKs was not due to a cell-intrinsic reduced responsiveness to TPO, since neonatal liver progenitors were more sensitive to murine TPO (mTPO) in vitro than adult BM progenitor. In vivo treatment of newborn mice with high mTPO doses or with higher doses of ROM (900 ng/g) resulted in peak platelet counts approaching 3-fold of controls. Taken together, our data indicate that newborn mice are less responsive to ROM than adult mice in vivo, due to a combination of likely pharmacokinetic differences and developmental differences in the response of MKs to thrombopoietic stimulation, evidenced by neonatal MKs increasing in numbers but not in size. PK/PD studies in human infants treated with ROM are warranted.

Platelet function testing in pediatric patients

INTRODUCTION

Platelets play a key role in primary hemostasis and are also intricately linked to secondary hemostasis. Investigation of platelet function in children, especially in neonates, is seriously challenged by the volumes required to perform the majority of platelet function tests and due to the lack of standardization of these tests for use in children. Areas covered: The present review summarizes developmental hemostasis with a focus on the differences in platelet adhesion, activation and aggregation, between preterm neonates, full-term neonates, during childhood and in adults. Some of the most widely used platelet function tests are presented, including novel tests requiring only a small blood volume. Expert commentary: Currently available platelet function tests are limited as regards to investigation of neonates due to difficulties in obtaining adequate blood volume, poor standardization, lack of reference intervals for neonates and children, and an incomplete understanding of the functional phenotype of neonatal platelets, especially preterm neonatal platelets.

Neonatal and adult megakaryopoiesis

PURPOSE OF REVIEW

It has become increasingly clear that there are substantial biological differences between fetal/neonatal and adult megakaryopoiesis. Over the last 18 months, studies challenged the paradigm that neonatal megakaryocytes are immature and revealed a developmentally unique uncoupling of proliferation, polyploidization, and cytoplasmic maturation. Several studies also described substantial molecular differences between fetal/neonatal and adult megakaryocytes involving transcription factors, signaling pathways, cytokine receptors, and microRNAs.

RECENT FINDINGS

This review will summarize our current knowledge on the developmental differences between fetal/neonatal and adult megakaryocytes, and recent advances in the underlying molecular mechanisms, including differences in transcription factors, in the response to thrombopoietin (Tpo), and newly described developmentally regulated signaling pathways. We will also discuss the implications of these findings on the way megakaryocytes interact with the environment, the response of neonates to thrombocytopenia, and the pathogenesis of Down syndrome-transient myeloproliferative disorder (TMD) and Down syndrome-acute megakaryoblastic leukemia (DS-AMKL).

SUMMARY

A better characterization of the molecular differences between fetal/neonatal and adult megakaryocytes is critical to elucidating the pathogenesis of a group of disorders that selectively affect fetal/neonatal megakaryocyte progenitors, including the thrombocytopenia-absent radius (TAR) syndrome, Down syndrome-TMD or Down syndrome-AMKL, and the delayed platelet engraftment following cord blood transplantation.

Neonatal thrombocytopenia and megakaryocytopoiesis

Thrombocytopenia is common among sick neonates, affecting 20% to 35% of all patients admitted to the neonatal intensive care unit (NICU). While most cases of neonatal thrombocytopenia are mild or moderate and resolve within 7 to 14 days with appropriate therapy, 2.5% to 5% of NICU patients develop severe thrombocytopenia, sometimes lasting for several weeks and requiring >20 platelet transfusions. The availability of thrombopoietic agents offers the possibility of decreasing the number of platelet transfusions and potentially improving the outcomes of these infants. However, adding thrombopoietin (TPO) mimetics to the therapeutic armamentarium of neonatologists will require careful attention to the substantial developmental differences between neonates and adults in the process of megakaryocytopoiesis and in their responses to TPO. Taken together, the available data suggest that TPO mimetics will stimulate platelet production in neonates, but might do so through different mechanisms and at different doses than those established for adults. In addition, the specific groups of thrombocytopenic neonates most likely to benefit from therapy with TPO mimetics need to be defined, and the potential nonhematological effects of these agents on the developing organism need to be considered. This review summarizes our current understanding of neonatal megakaryocytopoiesis, and examines in detail the developmental factors relevant to the potential use of TPO mimetics in neonates.

Serum thrombopoietin level and thrombocytopenia during the neonatal period in infants with Down's syndrome

BACKGROUND

The pathogenesis of thrombocytopenia during the neonatal period in Down's syndrome (DS) infants remains unclear.

OBJECTIVE

To elucidate kinetic changes of serum thrombopoietin (TPO) level and platelet count, and their correlation in DS neonates.

STUDY DESIGN

Twelve DS infants (male/female: 7/5, term/late preterm: 10/2) born between 1997 and 2007 were included. Blood samples were serially collected during the neonatal period and serum TPO levels were determined in 44 sera using an enzyme-linked immunosorbent assay.

RESULTS

Thrombocytopenia <150 x 10(9) per liter was observed in seven (58%) patients. In 12 DS patients, the median TPO value showed 2.86 fmol ml(-1) on day 0, rose to 4.64 fmol ml(-1) on day 2, and thereafter decreased to 4.30 fmol ml(-1) on day 5, 2.40 fmol ml(-1) on days 11-15, and 1.75 fmol ml(-1) on days 28-30. This kinetics parallels that in historical non-DS controls. In 35 pair sample analysis from 11 patients without transient myeloproliferative disease, TPO level inversely correlated with platelet count (r=-0.38, P=0.023). However, there was no significant difference in TPO concentrations between thrombocytopenic and non-thrombocytopenic DS individuals.

CONCLUSIONS

This is the first study to describe the relationship between TPO level and platelet count in neonates with DS. Median TPO levels and their kinetic changes in DS neonates are comparable to those in non-DS controls. In contrast to earlier findings in several studies showing higher TPO concentrations in thrombocytopenic non-DS newborns than those in non-thrombocytopenic counterparts, the response of the TPO system to thrombocytopenia in DS during the neonatal period seems suboptimal.

Does prematurity affect thrombocytopoiesis?

Data concerning thrombocytopoiesis in newborns are poorly recognized. Platelets have a crucial role in hemostatic physiology, which is deficient in newborns, especially in preterm newborns. A total of 51 preterm newborns (PTN), 25 girls and 26 boys, were recruited for the study. The control group consisted of 25 female and 30 male healthy term newborns (HTN). Plasma thrombopoietin (TPO) was measured using Quantikine human TPO system. Reticulated platelets (PLRET) was estimated by means of Retic-Count Kit. Platelet count (PLT) was determined using Advia(TU) 120 Hematology System. TPO was evidently higher in PTN (110.9 pg/ml) than in HTN (71.5 pg/ml), (p < 0.001). The percentage of reticulated platelets (PLRET) was also twice as high in PTN (3.49%) in comparison to HTN (1.7%), (p < 0.001). The PLT count was lower in PTN (246.7 x 10(3) microL) than in HTN (287.2 x 10(3) microL), (p < 0.01). Increased TPO levels and the percentage of PLRET indicate that thrombocytopoiesis is more active in prematurity. Our finding may be useful in therapeutic strategies.

New insights into the mechanisms of nonimmune thrombocytopenia in neonates

Thrombocytopenia affects up to 35% of all patients admitted to the neonatal intensive care unit. The causes of thrombocytopenia in neonates are very diverse and include immune and nonimmune disorders. Most cases of thrombocytopenia encountered in the neonatal intensive care unit are nonimmune, and these will constitute the focus of this review. Specifically, we first discuss the biological differences between neonatal and adult megakaryocytopoiesis, which contribute to explain the vulnerability of neonates to develop thrombocytopenia. Next, we review new diagnostic tools that have allowed for a better evaluation of platelet production in neonates, without having to obtain a bone marrow sample. Finally, we summarize our current understanding of the mechanisms underlying the thrombocytopenia in several common neonatal conditions, such as chronic intrauterine hypoxia, sepsis and necrotizing enterocolitis, and viral infections. A better understanding of the mechanisms underlying these varieties of thrombocytopenia is critical to develop disease-specific treatment protocols and to begin to entertain the possibility of using novel thrombopoietic growth factors to treat selected neonates with severe thrombocytopenia.

The CBC: reference ranges for neonates

"Normal values" for blood parameters of neonates are generally unavailable, because blood is not usually drawn on healthy, normal neonates to establish normal ranges. Instead, "reference ranges" are used, consisting of the 5th to the 95th percentile values compiled from tests performed on neonatal patients with minimal pathology, under the premise that such ranges approximate normal values. In recent years, we have been seeking to establish reference ranges for various elements of the complete blood count (CBC) of neonates, using the large databases of Intermountain Healthcare, a health care system in the western United States. Establishing these reference ranges has been facilitated by using modern hematology analyzers and electronic data repositories of clinical and laboratory information. The present review brings together several of our recent reports, displaying reference ranges for elements of the CBC among neonates at various gestational and postnatal ages.

Platelet reference ranges for neonates, defined using data from over 47,000 patients in a multihospital healthcare system

OBJECTIVE

Identifying a platelet count as abnormal (thrombocytopenia or thrombocytosis) can facilitate recognizing various disease states. However, the published reference ranges for platelet counts in neonates may be imprecise, as they were generated from relatively small sample sizes and compiled before modern platelet enumeration methods.

STUDY DESIGN

We derived new neonatal reference ranges for platelet counts and mean platelet volume (MPV) measurements using electronic data accumulated during a recent 6-year period from a multihospital healthcare system.

RESULT

Platelet counts were obtained between the first and the 90th day after birth, from 47,291 neonates delivered at 22 to 42 weeks gestation. The first platelet counts obtained in the first 3 days of life, increased over the range of 22 to 42 weeks gestation. In those born < or =32 weeks gestation, the lower reference range (5th percentile) was 104,200 microl(-1), but it was 123,100 microl(-1) in late-preterm and -term neonates. Advancing postnatal age had a significant effect on platelet counts; during the first 9 weeks, the counts fit a sinusoidal pattern with two peaks; one at 2 to 3 weeks and a second at 6 to 7 weeks. The upper limit of expected counts (95th percentile) during these peaks were as high as 750,000 microl(-1).

CONCLUSION

The figures herein describe reference ranges for platelet counts and MPV determinations of neonates at various gestational ages during their first 90 days. Expected values differ substantially from the 150,000 microl(-1) to 450,000 microl(-1) range previously used to define neonatal thrombocytopenia and thrombocytosis. The new definitions will render the diagnoses of neonatal thrombocytopenia and thrombocytosis less commonly than when the old definitions were used, because the new ranges are wider than 150,000 microl(-1) to 450,000 microl(-1).

High Thrombopoietin Concentrations in The Cerebrospinal Fluid of Neonates with Sepsis And Intraventricular Hemorrhage May Contribute to Brain Damage

Thrombopoietin (TPO) and its receptor (TPOR) are expressed in the central nervous system (CNS). Although TPO shares significant homology with various neurotrophins, recent data indicate a proapoptotic function of TPO in the CNS. In this study, TPO concentrations were analyzed in the cerebrospinal fluid (CSF) of neonates. Human neuroblastoma-derived SH-SY5Y cells were established to elucidate the effects of inflammation and hypoxia on neuronal Tpo expression. TPO was detectable in the CSF of 6 of 15 neonates with bacterial infection/sepsis (median 140, range 2-613 pg/mL), 5 of 9 neonates with posthemorrhagic hydrocephalus (median 31, range 1.4-469 pg/mL), 3 of 4 neonates with posthemorrhagic hydrocephalus plus bacterial infection/sepsis or meningitis (median 97, range 6-397 pg/mL), but not in controls ( n = 3). Neither the presence of detectable TPO nor its level in the CSF significantly correlated with any clinical or laboratory parameter. In SH-SY5Y cells, TPO and TPOR expression was detected by RT-PCR and Western blot analysis. In vitro, interleukin-6 (IL-6) did not significantly change Tpo gene expression. In contrast, Tpo mRNA expression significantly decreased under hypoxia, whereas erythropoietin (EPO) mRNA expression increased. In conclusion, our data provide evidence that in neuronal cells, TPO production is regulated by different mechanisms than in hepatocytes.

Thrombocytopoiesis in healthy term newborns

AIMS

Thrombocytopoiesis was investigated in term newborns determining thrombopoietin (TPO), reticulated platelets (PLRET) and blood platelets (PLT) in relation to gender.

PATIENTS AND METHODS

The study was undertaken on 72 healthy term newborns, 33 girls and 39 boys. They fitted all criteria for healthy term newborns. Blood was collected from the umbilical vein immediately after cutting the umbilical cord. The evaluation of thrombocytopoiesis was performed by the following methods: TPO-Quantikine human TPO kit, PLRET- Retic-Count kit, PLT- Advia 120 hematology System.

RESULTS

Concentrations of TPO and percentages of reticulated platelets were greater in the female group than in the male group. The changes were not statistically significant, perhaps as a result of the very wide range of parameters tested. The blood platelet count was higher in female newborns than in male newborns, P<0.001.

CONCLUSION

The data may indicate that thrombocytopoiesis is more active in female than in male newborns.

Thrombocytosis in preterm infants: a possible involvement of thrombopoietin receptor gene expression

Transient thrombocytosis is commonly observed in preterm infants after birth, but its physiological mechanism is still unknown. To understand the mechanism of the transient thrombocytosis in preterm infants we firstly evaluated a correlation between platelet counts and thrombopoietin (TPO) levels in preterm infants and next c-mpl mRNA levels on platelets in healthy preterm infants longitudinally during a half-year of life. The mean platelet counts in 45 very low birth weight infants (mean gestational age 27.4+/-1.8 weeks, mean birth weight 1047+/-249 g) was 230+/-71x10(9)/l just after birth and thereafter gradually increased to 579+/-178x10(9)/l by 5 weeks of age. The platelet counts continued this level for about next 8 weeks. Serum TPO levels soon after birth and at 1 month of age were significantly higher than those at the age of 2-6 months. There was a significant negative correlation between platelet counts and serum TPO values. The c-mpl expression levels on platelets at birth and at 1 month of age tended to be lower than those on platelets from adults, and the c-mpl levels gradually increased through 6 months of age, although they were still lower than those of adults. Our results suggest that low expression of TPO receptor on platelets until 1 month after birth cause a decreased TPO clearance and keep a high level of free TPO in blood, thereby promoting platelet production from megakaryocytes or their progenitors in bone marrow, resulting in the subsequent thrombocytosis in preterm infants.

Megakaryocyte growth and development factor is a potent growth factor for primitive hematopoietic progenitors in the human fetus

Megakaryocyte growth and development factor (MGDF), or thrombopoietin, has received considerable attention as a therapeutic agent for treating thrombocytopenia or for its use in the ex vivo culture of hematopoietic stem cells. MGDF is known to support the growth of a broad spectrum of hematopoietic precursors obtained from adult or neonatal tissues, but its effects on the growth of fetal progenitors and stem cells has not been studied. Human CD38(+)CD34(2+) progenitors and CD38(-)CD34(2+) cells, a population that contains stem cells, were isolated from midgestation liver and grown under defined conditions with MGDF and various cytokines known to support the growth of primitive hematopoietic precursors. In clonal assays of colony-forming cells (CFCs), MGDF supported the growth of 15-25% of candidate stem cells when combined with granulocyte colony-stimulating factor, granulocyte-macrophage colony-stimulating factor (GM-CSF), flk-2/flt3 ligand, or stem cell factor. MGDF was observed to strongly support the early stages of hematopoiesis and expansion of high proliferative potential CFCs. More mature progenitors were expanded nearly 78-fold in 1 wk of culture with MGDF+SCF+GM-CSF. MGDF alone was also found to support the short-term (2 d) survival of CD38(-)CD34(2+) high proliferative potential CFCs. The effects of MGDF were more modest on CD38(+)CD34(2+) progenitors with only additive increases in colony formation being observed. These findings suggest that MGDF administration in fetuses and neonates may strongly affect the growth and mobilization of primitive hematopoietic progenitors and that MGDF may find use in the ex vivo growth and expansion of fetal stem cells.

Evaluation and treatment of severe and prolonged thrombocytopenia in neonates

Thrombocytopenia is one of the most common hematologic problems in the neonatal intensive care unit (NICU). Despite its prevalence,several basic pathophysiologic questions remain unanswered. For instance, there is a lack of evidence-based guidelines for treatment,and the kinetic mechanisms (decreased platelet production,increased platelet consumption, or sequestration) responsible for most varieties of neonatal thrombocytopenia are not well defined.Moreover, a clear correlation between degree of thrombocytopenia and the resulting bleeding risk has not been demonstrated, and no transfusion-trigger studies have been conducted in neonates. As a consequence of these deficiencies in knowledge, there is great variability in platelet transfusion practices among NICUs. This article presents an overview of the evaluation of a neonate with severe thrombocytopenia and a review of current and projected therapeutic options.

Longitudinal thrombopoietin plasma concentrations in fetuses with alloimmune thrombocytopenia treated with intrauterine PLT transfusions

BACKGROUND

The purpose of this study was to describe longitudinal thrombopoietin (TPO) plasma concentrations in fetuses with fetomaternal alloimmune thrombocytopenia (FMAIT).

STUDY DESIGN AND METHODS

Group 1 was the control group, 8 fetuses with normal hematopoiesis. Group 2 consisted of 4 nonthrombocytopenic fetuses with fetomaternal human PLT antigen incompatibility. Group 3 consisted of 14 fetuses with prenatal-diagnosed severe FMAIT owing to human PLT antigen-1a incompatibility. Fetal PLT counts, MoAb-specific immobilization of PLT antigen score, and TPO plasma concentrations were measured in a total number of 94 serial samples taken by cordocentesis before intrauterine PLT transfusion.

RESULTS

Normal fetal TPO plasma concentrations ranged between 15 and 119 pg per mL (Group 1 median, 67 pg/mL). In fetuses with risk of FMAIT but normal PLT counts, TPO concentrations were normal (Group 2 median, 72 pg/mL; range, <15-158 pg/mL). In FMAIT with thrombocytopenia, the median TPO concentration was significantly higher than in Groups 1 and 2 (Group 3 median, 172 pg/mL; range, 15-623 pg/mL; p < 0.001). In the longitudinal analysis, TPO concentrations remained constant (n = 8), peaked only transiently (n = 3), or increased at the end of gestation (n = 3). Elevated TPO concentrations (592 and 623 pg/mL) were detected in one patient, who already had intracranial hemorrhage in utero.

CONCLUSION

TPO concentrations are normal or slightly elevated in FMAIT. Further clinical information can be provided by the longitudinal analysis of TPO concentrations in severe FMAIT.

Thrombopoietin gene expression in the developing human central nervous system

Thrombopoietin gene expression in the human adult central nervous system (CNS) appears to be locally restricted. The aim of this study was to identify areas of thrombopoietin expression in the developing human CNS, and to compare the thrombopoietin mRNA content in the CNS to that in liver and kidneys as major sites of thrombopoietin production. Thrombopoietin protein concentrations in the cerebrospinal fluid (CSF) were measured by ELISA. In 14 fetuses and neonates with perinatal death, thrombopoietin mRNA expression was measured by competitive RT-PCR. Thrombopoietin mRNA was expressed in 29 of 32 specimens taken from the CNS. The following ranking of the intensity of expression in the CNS was possible: Spinal cord=cerebellum=cortex>>pituitary gland>>>brain stem=corpora amygdala=hippocampus. Whereas in the latter three tissues only trace amounts of thrombopoietin transcripts were detectable, thrombopoietin mRNA levels in the spinal cord were comparable to levels in liver and kidney. Thrombopoietin protein concentrations in CSF ranged between 41 and 75 pg/ml. In the developing human CNS, the thrombopoietin gene is abundantly expressed. Considering that thrombopoietin contains a neurotrophic sequence, it may well play a role in neuronal cell biology.

The thrombopoietin level in the cord blood in premature infants born to mothers with pregnancy-induced hypertension

OBJECTIVE

To investigate the level of thrombopoietin in the cord blood of preterm infants, and its relationship with neonatal platelet count and pregnancy-induced hypertension.

STUDY METHOD

Thrombopoietin levels in the cord blood of preterm neonates, with or without maternal pregnancy-induced hypertension, were measured by enzmye-linked immunosorbent assay.

RESULTS

The platelet count was significantly lower in very low birth weight infants, infants with maternal pregnancy-induced hypertension, and infants with maternal thrombocytopenia. Neonatal thrombocytopenia was associated with maternal pregnancy-induced hypertension and very low birth weight. The neonatal platelet count was correlated significantly with the birth weight and the maternal platelet count. There was no difference in the cord blood level of thrombopoietin between infants born to mothers with pregnancy-induced hypertension and those without. No correlation was found between the thrombopoietin level and the neonatal platelet count. A positive correlation between the cord blood thrombopoietin and the maternal platelet count was identified.

CONCLUSIONS

Maternal pregnancy-induced hypertension and very low birth weight were significantly associated with thrombocytopenia in premature infants, which cannot be explained by decreased thrombopoietin level.

Mechanisms underlying thrombocytopenia in the neonatal intensive care unit

Thrombocytopenia is one of the most common hematological problems among neonates in the neonatal intensive care unit (NICU), but in the majority of cases the kinetic mechanism responsible is unclear. This review focuses on both traditional and innovative methods used to evaluate the mechanisms responsible for thrombocytopenia in neonates, and analyzes the data generated from those methods.

CONCLUSION

Results of studies using new methods for evaluating thrombocytopenia, coupled with recent descriptions of marrow megakaryocyte mass, suggest that decreased platelet production complicates most cases of thrombocytopenia among neonates in the NICU.

Fetal and neonatal thrombopoietin levels in alloimmune thrombocytopenia

Thrombopoietin (Tpo) is the main hematopoietic growth factor for platelet production. Plasma Tpo levels in autoimmune thrombocytopenic patients are normal or slightly elevated. Although thrombocytopenia exists, Tpo levels are not increased because the produced megakaryocytes and platelets can bind circulating Tpo, thereby normalizing Tpo levels. In this study, plasma samples from fetuses and neonates with neonatal alloimmune thrombocytopenia (NAIT), a different form of immune thrombocytopenia, were measured. Umbilical cord samples from 50 fetuses before treatment because of severe thrombocytopenia and 51 fetuses after treatment, and peripheral blood samples of 21 untreated newborns with NAIT were analyzed. As controls, plasma Tpo levels were determined in 21 umbilical cord samples of 14 nonthrombocytopenic fetuses with hemolytic disease resulting from red blood cell alloimmunization and in umbilical cord samples of 51 healthy newborns. The values were also compared with the plasma Tpo levels in 193 healthy adults. Mean Tpo levels from the groups of fetuses and neonates, including both NAIT and control plasma, were slightly but significantly elevated compared with levels in healthy adults. Tpo levels in NAIT samples were not significantly different from the levels in hemolytic disease samples or in samples from healthy newborns. Thus, as in autoimmune thrombocytopenic patients, normal Tpo levels are present in NAIT patients.

Thrombopoietin in preterm infants: gestational age-dependent response

PURPOSE

To investigate the factors affecting thrombopoietin (TPO) levels in preterm infants and to determine if TPO levels differ in infants born to mothers with preeclampsia and those infants with culture-proven sepsis.

METHODS

Serial serum samples (N = 95) were obtained from 27 infants less than 33 weeks' gestation. Samples were analyzed for TPO using enzyme-linked immunosorbent assay. All samples had an accompanying complete blood count. Analysis of variance with post hoc analysis by least significant difference test, Mann-Whitney test, or chi2 was used to compare groups, as appropriate. Forward, stepwise linear regression was used to account for potential confounding variables. Data are expressed as mean +/- SD.

RESULTS

TPO levels were not significantly correlated with the absolute platelet counts (R = -0.04, P = 0.69). TPO levels were significantly correlated with gestational age (R= 0.50, P < 0.001) when the platelet count was less than 150,000/mm3. TPO levels were significantly elevated in infants with platelets less than 150,000/mm3 born to mothers with preeclampsia compared with infants with sepsis (1184 +/- 98 vs. 579 +/- 363 pg/mL, P < 0.01). After adjusting for confounding variables using multivariate analysis (model: r2 = 0.43, P < 0.01), gestational age (r2 = 0.26) and preeclampsia (r2 = 0.03) remained significantly associated with TPO levels, whereas sepsis did not contribute to the variability of TPO.

CONCLUSIONS

TPO response of infants with platelets less than 150,000/mm3 is dependent on gestational age. Infants with thrombocytopenia associated with preeclampsia have increased circulating levels of TPO. Infants with thrombocytopenia secondary to sepsis do not show an increase in TPO, but this appears to be an effect of low gestational age.

Early elevation of serum thrombopoietin levels and subsequent thrombocytosis in healthy preterm infants

To verify pathophysiological mechanisms underlying thrombocytosis in low-birth-weight (LBW) preterm babies, we evaluated kinetic changes in platelet counts and thrombopoietic cytokines including thrombopoietin (TPO), interleukin 6 (IL-6) and IL-11 in 24 uncomplicated preterm infants. Platelet counts in cord blood (CB) (265 +/- 64 x 10(9)/l) were similar to adult levels, increased by d 14 (473 +/- 140 x 10(9)/l), and then remained fairly constant. Thrombocytosis (> 500 x 10(9)/l) was observed in 9/24 (38%) subjects. Mean TPO level in CB was 5.11 +/- 1.51 fmol/ml, peaked at d 2 (7.64 +/- 3.28 fmol/ml), decreased at d 5 (3.93 +/- 1.67 fmol/ml), and thereafter kept fairly constant during the remaining neonatal period. Compared with term infants, mean TPO levels of preterm infants in CB and at d 2 were significantly higher (P < 0.01). There was an inverse correlation between platelet counts and TPO levels (r = 0.45, P < 0.001, n = 88). Preterm neonates with thrombocytosis had significantly higher TPO values in CB than those without thrombocytosis (P < 0.05). There was no significant relationship between platelet counts and IL-6. IL-11 was not detectable. These results suggest that an early elevation of serum TPO levels is related to the subsequent thrombocytosis in LBW preterm infants.

Platelet transfusions in the neonatal intensive care unit:factors predicting which patients will require multiple transfusions

BACKGROUND

Previous studies suggest that recombinant thrombopoietin (rTPO) will increase platelet production in thrombocytopenic neonates. However, the target populations of neonates most likely to benefit should be defined. Studies suggest that rTPO will not elevate the platelet count until 5 days after the start of treatment. Therefore, the neonates who might benefit from rTPO are those who will require multiple platelet transfusions for more than 5 days. This study was designed to find means of prospectively identifying these patients.

STUDY DESIGN AND METHODS

A historic cohort study of all patients in the neonatal intensive care unit (NICU) at the University of Florida who received platelet transfusions from January 1, 1997, through December 31, 1998, was conducted.

RESULTS

Of the 1389 patients admitted to the NICU during the study period, 131 (9.4%) received platelet transfusions. Seventeen were treated with extracorporeal membrane oxygenation and were excluded from further analysis. Of the remaining 114 patients, 55 (48%) received one transfusion and 59 (52%) received more than one transfusion (21 had >4). None of the demographic factors examined predicted multiple platelet transfusions. However, two clinical conditions did; liver disease and renal insufficiency. Neonates who received one platelet transfusion had a relative risk of death 10.4 times that in neonates who received none (p = 0.0001). Neonates who received >4 platelet transfusions had a risk of death 29.9 times that in those who received no transfusions (p = 0.0001).

CONCLUSION

NICU patients with liver disease or renal insufficiency who receive one platelet transfusion are likely to receive additional transfusions. Therefore, these patients constitute a possible study population for a Phase I/II rTPO trial.

Venous and arterial hematologic profiles of very low birth weight infants. European Multicenter rhEPO Study Group

OBJECTIVE

In very low birth weight (VLBW) infants, diagnostic and therapeutic decisions depend on hematologic values. As few data are available, we studied the course during the first 6 weeks of life.

DESIGN

Four prospective longitudinal cohort studies were retrospectively combined assessing hematologic profiles of 562 VLBW infants. For characterization of red blood cells and iron, infants receiving erythropoietin were excluded. For characterization of white blood cells and platelets, infants receiving antibiotics were excluded.

RESULTS

The third (3rd)/median/97th percentiles on day 3 were as follows: hemoglobin: 11.0/15.6/19.8 g/dL; hematocrit: 35/47/60%; red blood cells: 3.2/4.2/5.3 x 10(12)/L; reticulocytes:. 6/7.1/27.8%; platelets: 58/203/430 x 10(9)/L; white blood cells: 3. 6/9.5/38.3 x 10(9)/L; neutrophils:.7/4.7/25.3 x 10(9)/L; ferritin: 27/140/504 ng/mL; iron:.8/7.5/26.7 micromol/L; transferrin saturation: 2.6/22.7/79.8%. Transferrin saturation was <24% in 51%, ferritin concentration <100 ng/mL in 32%, and platelets <150 x 10(9)/L in 29% of this population. The steady decrease of red cell parameters was mitigated by transfusions. Neutrophils decreased steadily, and were <1.75 x 10(9)/L in 35% at 6 weeks.

CONCLUSIONS

Iron indices and platelet counts on day 3 and neutrophil counts at 2 to 6 weeks of age are lower than previously assumed in VLBW infants and lower than in larger prematures.

Evaluation and treatment of thrombocytopenia in the neonatal intensive care unit

Thrombocytopenia is a very frequent problem among sick neonates, affecting up to 35% of all infants admitted to the NICU. Although multiple clinical conditions have been causally associated with neonatal thrombocytopenia, the cause of the thrombocytopenia is unclear in up to 60% of affected neonates. This article provides neonatologists with a practical approach to the thrombocytopenic neonate, with an emphasis on conditions that could be life-threatening or could have significant implications for further pregnancies. An overview of the current therapeutic modalities is also presented, including a discussion of the possible use of recombinant thrombopoietic cytokines to treat certain groups of thrombocytopenic neonates.

Necrotizing enterocolitis and hematopoietic cytokines

The names of the hematopoietic cytokines are misleading because in addition to their effects on bone marrow and bone marrow-derived cells, they have many diverse effects, including effects on the gastrointestinal tract. These effects may be directly mediated by interaction with specific receptors on gastrointestinal epithelial cells, or they may result from their effects on circulating or bowel wall leukocytes and the cytokines these cells produce. As might be expected of factors largely defined by their effects on inflammatory cells, the hematopoietic cytokines are intimately involved in the processes of bowel injury. Further investigations are needed to define the role of hematopoietic cytokines in the human neonate's balance between local gastrointestinal host defense and bowel wall injury. This could lead to effective strategies for the treatment and prevention of NEC.

Thrombopoietin in the fetus and neonate

C-mpl ligand or thrombopoietin (Tpo) is increasingly recognised as the major regulator of platelet homeostasis in humans. Relatively little is known about Tpo in the fetus and neonate but no evidence has yet been found to suggest any fundamental difference in Tpo structure, function and regulation in the fetus and neonate compared to older age groups. Tpo mRNA transcripts have been detected in the fetus as early as 6 weeks post conception and the liver appears to be the main site of Tpo production in both the fetus and neonate. The vast majority of healthy newborns have detectable levels of circulating Tpo and raised Tpo levels are commonly, but not consistently, found in thrombocytopenic neonates. In adults receptor binding and subsequent metabolism of Tpo is proposed as the main method of regulation of the circulating Tpo level. Preliminary studies in neonates showing increased Tpo levels most often during thrombocytopenia accompanied by reduced megakaryocytopoiesis supports this concept. In addition to this demonstrable fetal and neonatal endogenous Tpo production megakaryocyte progenitor and precursor cells from the fetus and from preterm and term newborns proliferate and differentiate extensively in-vitro in response to exogenous Tpo. Furthermore a recent study has shown a marked rise in platelet count in newborn rhesus monkeys administered one form of recombinant Tpo. Although these studies remain at an early stage together these findings strongly suggest that, as in adults, Tpo is the major regulator of platelet homeostasis in the fetus and neonate. Thrombocytopenia is common in sick neonates and progress in understanding this important clinical problem is likely to be greatly enhanced by the current and future research into Tpo production, function and regulation in the healthy and thrombocytopenic fetus and neonate.

Stressful delivery influences circulating thrombopoietin (TPO) levels in newborns: possible role for cortisol in TPO-mpl binding

The regulation mechanism of circulating thrombopoietin (TPO) level in human newborns remains unknown. In the present study, we examined whether the TPO concentrations in cord blood were influenced by the difference in the delivery method and the presence or absence of maternal/fetal complications. Cortisol levels were simultaneously measured to assess the adrenal response of fetuses. Both the TPO level and the cortisol level were substantially greater in the neonates delivered vaginally with and without the complications than in those delivered by cesarean section without the complications. The binding assay showed that the incubation of mpl(+)/BaF3 cells with cortisol gave rise to a significant decrease in the binding sites of TPO. These results suggest that the stress to the fetuses near the time of delivery affects the cord blood TPO levels, which may be mediated in part by the action of cortisol on the TPO-mpl binding system.

Thrombopoietin levels in cord blood plasma and amniotic fluid in fetuses with alloimmune thrombocytopenia and healthy controls

To extend our knowledge of the kinetics of fetal thrombopoietin (TPO), we studied TPO levels in cord blood plasma and amniotic fluid collected from 15 fetuses considered to be at risk of fetomaternal alloimmune thrombocytopenia and also from 10 healthy controls at caesarean delivery. In the plasma of all 25 fetuses and newborn infants studied, TPO was detected above the lower limit of detection (7 pg/ml) and correlated inversely with platelet counts (r = -0.53, P = 0.006). At term, TPO detected in amniotic fluid was at significantly lower levels (7 pg/ml; range 0-22 pg/ml) than simultaneously obtained cord plasma TPO (114 pg/ml; range 43-201 pg/ml; P < 0.001). There was no correlation between levels of TPO in amniotic fluid and cord plasma or platelet counts. In the serial samples collected from the five fetuses with HPA-1a alloimmunization before 37 weeks' gestation, the TPO levels in amniotic fluid were significantly higher than at term (P = 0.013): from 22 to 28 weeks' gestation, 42 pg/ml (30-78 pg/ml); from 32 weeks', 24 pg/ml (17-33 pg/ml); at term, 8 pg/ml (4-13 pg/ml), correlating inversely with gestational age (r = -0.81, P = 0.003). Thus, TPO is present in amniotic fluid at levels apparently inversely related to gestational age. Whether these high levels seen early in pregnancy are normal or are associated with the HPA-1 alloimmunization remains to be shown.

Pharmacokinetics, pharmacodynamics, and safety of administering pegylated recombinant megakaryocyte growth and development factor to newborn rhesus monkeys

Thrombocytopenia is common among sick neonates. Certain groups of thrombocytopenic adults respond favorably to the administration of recombinant thrombopoietin or to pegylated recombinant human megakaryocyte growth and development factor (PEG-rHuMGDF), a recombinant human polypeptide that contains the receptor-binding N-terminal domain of thrombopoietin. The effectiveness and safety of such treatment in neonates, however, have not been reported. The purpose of the present study was to determine the biologic activity and safety of PEG-rHuMGDF administration to newborn rhesus monkeys. Eight monkeys were divided into four groups and treated subcutaneously with 0.00, 0.25, 1.00, or 2.50 microg/kg once daily for 7 d. Complete blood counts, serum chemistries, clotting panels, and MGDF levels were followed serially, and hematopoietic progenitor cell assays were performed on bone marrow aspirates before the first dose and again on d 8. Pharmacokinetic evaluations were performed on the animals that received the highest dose of PEG-rHuMGDF. All monkeys had normal growth during the study period, and all chemistries, clotting studies, and blood pressure measurements were normal. The peak serum MGDF concentration occurred at 3 h, and the half-life was 8.4 to 13.0 h. As in adult rhesus monkeys, platelet counts in the treated neonates began to rise on d 6, peaked on d 11, and returned to baseline by d 23. The two highest doses generated an 8- to 12-fold increase in platelets, whereas those treated with 0.25 microg/kg had a 6-fold increase. Other hematologic parameters measured were unaffected. Thus, newborn monkeys responded to doses of PEG-rHuMGDF that were similar to or smaller than (per kilogram body weight) those that are effective in adult animals and did so without obvious short-term toxicity.