Thrombopoietin level in young patients is related to megakaryocyte frequency and platelet count

Thrombocytopenia in Patients With Chronic Hepatitis C: A Possible Role of HCV on Platelet Progenitor Cell Maturation

A total of 30 patients with chronic hepatitis C (HCV) thrombocytopenia (TP) and 20 healthy controls were studied. Both groups were subjected to complete medical history, clinical examination in addition to assessment of hepatitis markers: level of thrombopoietin (Tpo), Geimsa-stained bone marrow smears, and in vitro short-term megakaryocytic progenitors culture (CFU-MK). Serum Tpo level was significantly elevated in patients with TP HCV. Short-term CFU-MK showed an evident depression in the colony-forming unit—megakaryocyte (CFU-meg). There is a positive correlation between the number of CFU-meg and the platelet count and between serum Tpo level and prothrombin time, transaminase, albumin, and the Child Pugh score of liver disease; a negative correlation between serum Tpo level and the number of CFU-meg and between serum Tpo level and the platelet count. Thus, the level of Tpo could be an indicator of intact functional response of the hepatocytes.

Two candidate genes for low platelet count identified in an Asian Indian kindred by genome-wide linkage analysis: glycoprotein IX and thrombopoietin

A genome-wide linkage analysis of platelet count was carried out in a large Asian Indian kindred. Linkage analysis showed one marker (D3S1309) on chromosome 3q with a lod score of 3.26 and another (D3S1282) approximately 30 cM centromeric, with a lod score of 2.52. Multipoint analysis of chromosome 3q identified two peaks with maximum multipoint lod scores of 3.52 and 4.11 under markers D3S1309 and D3S1282, respectively. Two strong candidate genes for platelet variation were identified in the linked region; thrombopoietin (THPO) and glycoprotein IX (GPIX). Resequencing of four individuals revealed five single-nucleotide polymorphisms (SNPs) in THPO and one mutation in the transmembrane region of GPIX. Analysis of variance showed that the GPIX mutation and one THPO SNP accounted for 6 and 4% of the variation in platelet count, respectively. The THPO SNP lies in the 3' untranslated region of the gene and has not been previously reported. The G to A transition at nucleotide 653 resulted in an Ala 156 (GCC) to Thr (ACC) replacement in the GPIX protein. The GPIX mutation was recently identified in a Chinese patient with Bernard-Soulier syndrome (BSS), a rare recessive bleeding disorder characterized by thrombocytopenia and giant platelets. One copy of the GPIX mutation was found in 300 European individuals with platelet counts within the normal range. The results suggest that two QTLs on chromosome 3q influence platelet count variation in the Asian Indian kindred, with the GPIX transmembrane mutation and the 3' UTR SNP in THPO being strong candidates.

Association of single nucleotide polymorphisms in the thrombopoietin-receptor gene, but not the thrombopoietin gene, with differences in platelet count

Little is known about the mechanisms explaining the wide variation in platelet counts (PLT) and other hematologic parameters in humans. We previously showed that the sex-based difference in hematocrit was associated with nucleotide variation in the erythropoietin receptor gene (EPOR). We sought to identify new polymorphisms of the human thrombopoietin (TPO) and thrombopoietin receptor (TPOR) genes to determine any associations with blood PLT counts. We screened TPO and TPOR for polymorphisms using single-strand conformation polymorphism (SSCP) and DNA sequencing. Association of polymorphisms was studied in 304 normal subjects with low or high PLT counts. Distribution of allelic frequency was analyzed by the Chi-square statistic. Single nucleotide polymorphisms (SNPs) with two alleles were found in TPO and TPOR. The TPO SNP was a G to A transition at nucleotide 5753, and the TPOR SNP was a C to A transversion at position 550 in the 5'-promoter area. The allelic frequencies were 0.54 for G and 0.46 for A of TPO, and 0.62 for C and 0.38 for A of TPOR in a Caucasian population. The frequency of the TPOR allele "C" was significantly higher in subjects with high PLT count (>258 k/mm3) versus low PLT count (<224 k/mm3) and in males with high PLT count (>258 k/mm3) versus males with low PLT count (<212 k/mm3). In contrast, the frequency of the TPO alleles was not related to blood PLT counts. An association of TPO and TPOR allele distribution to red and white blood cell parameters was seen. These new SNPs found for the human TPO and TPOR genes help explain variations in blood PLT counts and may be useful in patient studies related to the roles of TPO and/or TPOR in disease.

Prospective screening of 205 patients with ITP, including diagnosis, serological markers, and the relationship between platelet counts, endogenous thrombopoietin, and circulating antithrombopoietin antibodies

Immune thrombocytopenia purpura (ITP) is characterized by destruction of circulating platelets and the presence of antiplatelet antibodies. Many of the current immunomodulatory therapies act by reducing platelet destruction and usually do not have a lasting effect. This prospective, exploratory study characterized patients with ITP by identifying their demographic and comorbid clinical factors, use of treatments, serologic markers of autoimmunity, and possible relationships between platelet counts, concentrations of endogenous thrombopoietin (eTPO), and the presence of circulating anti-TPO antibodies. Data including medical history and laboratory evaluations were collected at a single patient visit on 205 patients (19 children, 186 adults). Reported histories revealed a 5% rate of thrombotic/ischemic events. Autoimmune markers including direct antiglobulin test and antinuclear antibodies were found more frequently than in the normal population; antiplatelet antibody testing was not done. eTPO concentrations were comparable to concentrations found in healthy volunteers. Our study confirmed that no significant inverse correlation occurred between circulating concentrations of eTPO and platelet counts in patients with ITP (Spearman r = -0.15). Two of the 205 patients tested (1%) had neutralizing activity of recombinant human TPO in a biological assay; however, this activity was confirmed to be anti-TPO antibody in only 1 patient.

Is the Thrombopoietin Assay Useful for Differential Diagnosis of Thrombocytopenia? Analysis of a Cohort of 160 Patients with Thrombocytopenia and Defined Platelet Life Span

Background: Thrombopoietin (TPO), the major hormone controlling platelet production, has been measured in thrombocytopenias with discordant results. The aim of our work was to assess the value of the TPO assay for differential diagnosis of thrombocytopenias in a large cohort of patients classified according to the results of their platelet isotopic study.

Methods: We measured TPO (R&D Systems) in serum of 160 thrombocytopenic patients referred to our department for platelet life span isotopic studies. We classified patients as follows: (a) idiopathic or autoimmune thrombocytopenia group (ITP; patients with increased platelet destruction and shortened platelet life span; n = 67); (b) pure genetic thrombocytopenia group (patients with decreased platelet production, normal platelet life span, and without bone marrow aplasia; n = 55); (c) bone marrow aplasia group (BM; patients with decreased platelet production, normal platelet life span, and bone marrow aplasia; n = 13).

Results: In patients with pure genetic thrombocytopenia, TPO (median, 55 ng/L) was not different from TPO in patients with ITP (median, 58 ng/L) or controls (n = 54; median, 51 ng/L). Only in patients with bone marrow aplasia was TPO significantly higher (median, 155 ng/L) and negatively correlated to the platelet count (r2 = 0.5014).

Conclusions: Although the median serum TPO is increased in thrombocytopenia with decreased platelet production from bone marrow aplasia, it does not differentiate patients with pure genetic thrombocytopenia from those with ITP.

Colony-forming unit-megakaryocyte (CFR-meg) numbers and serum thrombopoietin concentrations in thrombocytopenic disorders: an inverse correlation in myelodysplastic syndromes

We studied both serum-free colony-forming unit-megakaryocyte (CFU-meg) numbers and serum thrombopoietin (TPO) levels in 14 patients with aplastic anemia (AA), 37 patients with myelodysplastic syndromes (MDS) and 23 patients with idiopathic thrombocytopenic purpura (ITP) to assess thrombopoiesis in these thrombocytopenic disorders. The mean CFU-meg numbers were lower in AA and MDS patients (10.7 +/- 11.4 and 42.3 +/- 58.5/10(5) BMLD cells) than in healthy controls (103.1 +/- 57.3/10(5) BMLD cells) (P < 0.0001 and P= 0.0053, respectively), although they were distributed variably in MDS. ITP patients showed higher CFU-meg numbers (223.2 +/- 143.5/10(5) BMLD cells) (P= 0.017). The mean TPO concentrations were higher in both AA (986.8 +/- 500.8 pg/ml) and MDS patients (838.2 +/- 639.1 pg/ml) than in healthy controls (80.7 +/- 38.8 pg/ml) (P < 0.0001), although they were distributed from high to low in MDS. ITP patients showed a slight elevation of TPO (123.1 +/- 55.3 pg/ml) P = 0.0106). The TPO levels was inversely correlated to both platelet counts and CFU-meg numbers (correlative coefficient (CC): -0.719 and -0.682, P < 0.0001) in AA, but not in ITP. In MDS, the inverse correlation to TPO was stronger in CFU-meg (CC: -0.678, P < 0.0001) than in platelet counts (CC: -0.538, P = 0.0014), suggesting that CFU-meg plays an important role in regulating TPO production in this heterogenous disorder. CFU-meg and TPO may provide useful information for understanding thrombopoiesis of MDS, especially for application of TPO.

Relationship between hematopoietic growth factors levels and hematological parameters in Argentine hemorrhagic fever

Argentine hemorrhagic fever (AHF) is a viral disease caused by Junin virus and characterized by hematologic and neurological involvement. The main hematologic features are leukopenia, thrombocytopenia, and bone marrow hypoplasia. Hematopoietic growth factors serum levels were measured by ELISA technique in forty-eight patients with confirmed diagnosis of AHF. Patients were classified according to the clinical picture in 15 severe (SCF), 17 moderate (MoCF), and 16 mild (MiCF) cases. Erythropoietin levels were decreased in 28 of 45 patients and raised in 4 SCF patients. Twenty-four of 38 patients had high G-CSF levels at admittance in accordance with clinical picture severity, while IL-3, GM-CSF, and TGF-beta were normal in most cases. A direct correlation was found between G-CSF and TNF-alpha levels. Thrombopoietin levels were found to be raised in 19 of 21 patients. In conclusion, the low levels of Epo may contribute to the severe bone marrow erythroblastopenia described in AHF patients, while G-CSF seems to be a marker of illness severity.

Measurement of thrombopoietic levels: clinical and biological relationships

Platelet production is primarily regulated by the thrombopoietic cytokine thrombopoietin (TPO). In most cases thrombopoietin serum levels are determined by the rate of c-mpl receptor-mediated degradation after TPO uptake into platelets and megakaryocytes. The contribution of increased TPO protein synthesis by a translational mechanism was recently appreciated as the cause for hereditary thrombocythemia and will have to be elucidated in other conditions of thrombocytosis in association with increased TPO levels.

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.

Thrombopoietin has a primary role in the regulation of platelet production in preterm babies

Thrombocytopenia in the first days of life, in association with evidence of reduced megakaryocytopoiesis and platelet production at birth, is common in sick preterm babies. Thrombopoietin (Tpo) is the major regulator of platelet production in adults. However, these babies have low Tpo levels at birth, suggesting that the Tpo response to thrombocytopenia may be impaired. To test this hypothesis we 1) measured Tpo levels, 2) measured circulating megakaryocyte progenitors serially over the first 12 d of life in 13 preterm babies with early onset thrombocytopenia and in 14 control babies with evidence of normal megakaryocytopoiesis, and 3) measured Tpo levels in thrombocytopenic children (n = 13). In control babies, platelet counts and progenitor numbers remained normal and Tpo levels were consistently low-d 1:160+/-23 pg/mL (mean+/-SEM), d 4/5: 154+/-18 pg/mL and d 12: 150+/-58 pg/mL. In thrombocytopenic babies, platelet counts and megakaryocyte progenitor numbers were significantly lower than controls at d 1: platelets 130+/-14 x 10(9)/L versus 255+/-20 x 10(9)/L (p < 0.001) and megakaryocyte progenitors 552 versus 3907 colonies/mL (mean, p < 0.001), and fell further to nadir on d 4/5: platelets 76+/-6 X 10(9)/L versus 259+/-21 x 10(9)/L (p < 0.001) and MK progenitors 479 versus 2742 colonies/mL (p < 0.05). Tpo levels were only slightly raised on d 1:247+/-52 pg/mL (p = 0.24), but then rose sharply by d 4/5: 425+/-75 pg/mL (p < 0.001). By d 12, platelet count, megakaryocyte progenitors and Tpo level (145+/-29 pg/mL) had returned to control levels. Tpo levels at platelet nadir in thrombocytopenic babies were significantly lower than in thrombocytopenic children: mean 425 versus 1383 pg/mL (p < 0.001). These data show that Tpo is important in platelet homeostasis in preterm babies, with a close reciprocal relationship with platelet count and progenitor numbers during thrombocytopenia. However, the increase in Tpo levels seen in these babies was modest, despite significantly impaired megakaryocytopoiesis, and when compared with that seen in children with thrombocytopenia. This offers further evidence that preterm babies have an impaired Tpo response to thrombocytopenia and suggests that recombinant human Tpo may have a role in the prevention/treatment of preterm thrombocytopenia.