Thrombopoietin in the fetus and neonate

Romiplostim for the management of pediatric immune thrombocytopenia: drug development and current practice

Since successful cloning of thrombopoietin (TPO) in 1994, significant advances have been made in the development of recombinant TPO receptor agonists. The US Food and Drug Administration (FDA) has approved 2 agents for use in patients with immune thrombocytopenia (ITP): eltrombopag and romiplostim. Romiplostim is a once-weekly subcutaneous injection that has been shown to increase the platelet count, lessen bleeding, and reduce concurrent medication use in adults with ITP. In December 2018, the US FDA approved romiplostim for use in pediatric patients ≥1 year of age with ITP of >6 months' duration and insufficient response to corticosteroids, immunoglobulins, or splenectomy, based on similarly favorable clinical trial data. In addition, romiplostim is well tolerated, making it an attractive option for the treatment of children. Expansion of off-label romiplostim use is being reported in children for ITP <6 months, neonatal thrombocytopenia, hereditary thrombocytopenias, and chemotherapy- and bone marrow transplant-associated thrombocytopenia. We review here the development of romiplostim with a focus on pediatric use.

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.

Platelet indices in late preterm newborns

BACKGROUND

The current study objective was to compare blood platelet indices in late preterm newborns (LPN) and full term newborns (FTN).

MATERIALS AND METHODS

We recruited 58 LPN and 71 FTN. Platelet indices were estimated in blood samples collected from the umbilical artery.

RESULTS

LPN demonstrated a decreased count of blood platelets (249 × 10³/μL) as compared to FTN (295 × 10³/μL), p < 0.001. Platelet hematocrit (PCT) also showed substantial differences in both groups (LPN = 0.2% vs. FTN = 0.23%; p < 0.001). Mean platelet volume (MPV) was found to be nearly the same (LPN = 7.98fl, FTN = 7.9fl). Platelet distribution width (PDW) was higher in LPN (52.8%) than in FTN (50.6%), p = 0.02. Large platelet count (LP) was lower in LPN (4.0%) in comparison with FTN (6.0%), (p = 0.01).

CONCLUSIONS

The obtained results may indicate immaturity of thrombopoiesis in newborns born late preterm. Decrease in platelet count, platelet hematocrit and large platelets can cause disturbances in the hemostatic system and lead to bleeding complications and can increase the risk of infections. Morphological parameters of blood platelets in infants born late preterm differ from those of term neonates as in other preterm infants. This reflects the immaturity of this newborn and shows the need to pay special diagnostic and therapeutic care to them.

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.

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.

Thrombopoietin following transfusion of platelets in preterm neonates

Thrombocytopenia is common in the neonatal intensive care unit. Transfusion of platelets is often required. The purpose of our study was to determine changes in thrombopoietin (Tpo) following transfusion of platelets in preterm neonates. Preterm neonates undergoing platelet transfusion were randomized to receive a transfusion volume of either 10 or 15 ml/kg. Blood was obtained for Tpo measurement pre-transfusion, one and 24 hours post-transfusion. Platelet Factor 4 (PF4) was also measured to quantify platelet activation. Statistical analysis was performed using repeated measures ANOVA, and Mann-Whitney U test as appropriate. Ten infants were enrolled in each group. Gestational age, birth weight, etiology of thrombocytopenia, and timing of transfusion did not differ between the 10 and 15 ml/kg groups. There were no differences between the groups in platelet count prior to and/or following transfusion. Both transfusion volumes were equally well tolerated. Tpo and PF4 did not differ between groups at any of the study time points. When both groups were analysed together, Tpo dropped 43% (95% confidence 37-49%, p = 0.01) 1-hour post compared to pre-transfusion. In conclusion the observed decrease in Tpo following platelet transfusion suggests that Tpo kinetics in neonates is similar to adults following transfusion. PF4 was not affected by transfusion. There was not an increase in platelet count following transfusion volume of 15 ml/kg compared to 10 ml/kg.

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.

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.

Thrombopoietin level is increased in the serum of asphyxiated neonates: a prospective controlled study

BACKGROUND

Thrombopoietin (TPO) is a growth factor that controls platelet production. Despite the known association of chronic hypoxia and acute asphyxia with hematologic changes, TPO had not been studied in neonatal asphyxia.

OBJECTIVE

To assess TPO concentrations in the serum of asphyxiated and nonasphyxiated neonates, and examine any correlation with the severity of asphyxia.

DESIGN/METHODS

This prospective study was carried out on 32 asphyxiated neonates and 30 control subjects admitted at Cairo University Medical Center. Asphyxia was defined if two of the following were found: (1) Apgar score </=3 at 1 minute or </=6 at 5 minutes, (2) umbilical cord arterial pH </=7.2 combined with base deficit >/=-10 and (3) clinical evidence of perinatal asphyxia. Encephalopathy was classified clinically according to Sarnat's stages during the first day of life. Platelet count and TPO level (pg/ml) were measured at 1st, 3rd and 7th day of life.

RESULTS

: TPO measured on the first day of life did not differ between cases and controls (900.2+/-526.4 vs 726.6+/-441.9 pg/ml, p=0.2). It increased on the 3rd day of life and was significantly higher in asphyxiated infants compared to controls (1291.4+/-627.9 vs 885.5+/-400.3 pg/ml, respectively; p=0.004). This difference remained significant in a logistic regression model controlling for birth weight, sex and mode of delivery (regression coefficient=476.9+/-146.8; p=0.002). In asphyxiated infants (n=32), encephalopathy was classified as mild (n=17), moderate (n=10) and severe (n=5). TPO correlated with the degree of clinical severity on the 7th day of life (r=0.59, p=0.003). TPO did not differ between survivors (n=24) and nonsurvivors (n=8) within the asphyxia group (1197.1+/-596.8 vs 1613.1+/-605.9 pg/ml; p=0.09). Platelet counts correlated negatively with TPO measured on day 1 (r=-0.415; p=0.02), day 3 (r=-0.64; p=0.001) and day 7 (r=-0.562; p=0.007).

CONCLUSIONS

TPO increased and correlated with severity of asphyxia at 3 and 7 days of life. It correlated negatively with the platelet count at all times.

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.

Epidemiologic and outcome studies of patients who received platelet transfusions in the neonatal intensive care unit

STUDY DESIGN

We conducted a historic cohort study of neonates who received platelet transfusions at the National Institute of Perinatology, Mexico City, from January 1997 to May 2000. We obtained descriptive and outcome data, and assessed demographic and laboratory means of predicting "good candidates" for a future recombinant thrombopoietin (rTpo) trial.

RESULTS

A minority of the transfused patients (11.4%) received only one transfusion; the majority (88.6%) received multiple transfusions. Neonates who received one or more platelet transfusions were more likely to die (24.5% mortality) than neonates who received no platelet transfusions (3.7% mortality). Regression analyses indicated that the presence of liver disease was the best predictor of a "good candidate" for rTpo administration.

CONCLUSION

The majority of neonates in our institution who receive platelet transfusions receive multiple, not single, transfusions. Receiving any platelet transfusion is a marker for high risk of death. Neonates with liver disease who receive platelet transfusions might be a reasonable group for a phase I rTpo trial.