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Josef T Prchal

Publications and source records attributed to Josef T Prchal.

At least 19 recordsLinked to original sources
PubMed2007

Philadelphia chromosome-negative myeloproliferative disorders: biology and treatment.

The Philadelphia chromosome (Ph)-negative myeloproliferative disorders (MPDs) include essential thrombocythemia (ET), idiopathic myelofibrosis (IMF), and polycythemia vera (PV). All of these disorders are clonal hematologic malignancies originating at the level of the pluripotent hematopoietic stem cell. Recently, activating mutations of the intracellular cytokine-signaling molecule JAK2 have been identified in > 90% of patients with PV and in 50% of those with IMF and ET. In addition, a mutation of the thrombopoietin receptor, MPLW515L, has been documented in some patients with IMF. Both mutations activate JAK-STAT signaling pathways and likely play a role in disease progression. Both ET and PV are associated with prolonged clinical courses associated with frequent thrombotic and hemorrhagic events, and progression to myelofibrosis and acute leukemia. IMF has a much poorer prognosis and is associated with cytopenias, splenomegaly, extramedullary hematopoiesis, and bone marrow fibrosis. Stratification of risk for the development of complications from Ph-negative MPDs has guided the identification of appropriate therapies for this population. Intermediate/high-risk IMF or myelofibrosis after ET or PV is associated with a sufficiently poor prognosis to justify the use of allogeneic stem cell transplantation, which is capable of curing such patients. Reduced-intensity conditioning in preparation for allogeneic stem cell transplantation has permitted older patients with IMF to undergo transplantation with increasing success.

Hematopoietic Stem Cell Transplantation↗
PubMed2007

Polycythemia vera is not initiated by JAK2V617F mutation.

OBJECTIVE: The somatic JAK2(V617F) mutation is seen in most polycythemia vera (PV) patients; however, it is not clear if JAK2(V617F) is the PV-initiating mutation. METHODS: In order to examine this issue, we developed a novel real-time quantitative allele-specific PCR, in which allelic discrimination is enhanced by the synergistic effect of a mismatch in the -1 position, and a locked nucleic acid (LNA) nucleoside at the -2 position. RESULTS: Determination of allelic frequencies was reproducible (SD = 1.5%) and sensitive--0.1% mutant allele detected in 40 ng of DNA. The JAK2(V617F) frequency in clonal granulocytes from 3 PV females was less than 50% (27.5 +/- 11) and in 7 females greater than 50% (75 +/- 10.5). We also found that wild-type JAK2 BFU-E colonies from PV patients can grow without erythropoietin. The identification of the primary genetic lesion resulting in PV is essential for the development of novel therapeutic strategies. CONCLUSION: Our studies correlating the frequency of JAK2(V617F) mutant allele and clonality, as well as the presence of homozygous wild-type JAK2 erythropoietin-independent erythroid colonies, provide compelling evidence that the JAK2(V617F) is not the PV-initiating mutation. This supports a model wherein the JAK2(V617F) mutation arises as a secondary genetic event. Furthermore, our results indicate that an undefined molecular lesion, preceding JAK2(V617F), is responsible for clonal hematopoiesis in PV. We conclude that development of therapeutic strategies that target the JAK2(V617F) clonal cells may not be sufficient for eradication of PV.

Clone Cells↗
PubMed2006

Redefining endothelial progenitor cells via clonal analysis and hematopoietic stem/progenitor cell principals.

The limited vessel-forming capacity of infused endothelial progenitor cells (EPCs) into patients with cardiovascular dysfunction may be related to a misunderstanding of the biologic potential of the cells. EPCs are generally identified by cell surface antigen expression or counting in a commercially available kit that identifies "endothelial cell colony-forming units" (CFU-ECs). However, the origin, proliferative potential, and differentiation capacity of CFU-ECs is controversial. In contrast, other EPCs with blood vessel-forming ability, termed endothelial colony-forming cells (ECFCs), have been isolated from human peripheral blood. We compared the function of CFU-ECs and ECFCs and determined that CFU-ECs are derived from the hematopoietic system using progenitor assays, and analysis of donor cells from polycythemia vera patients harboring a Janus kinase 2 V617F mutation in hematopoietic stem cell clones. Further, CFU-ECs possess myeloid progenitor cell activity, differentiate into phagocytic macrophages, and fail to form perfused vessels in vivo. In contrast, ECFCs are clonally distinct from CFU-ECs, display robust proliferative potential, and form perfused vessels in vivo. Thus, these studies establish that CFU-ECs are not EPCs and the role of these cells in angiogenesis must be re-examined prior to further clinical trials, whereas ECFCs may serve as a potential therapy for vascular regeneration.

Adult↗
PubMed2006

Hypoxia-inducible factor-1 deficiency results in dysregulated erythropoiesis signaling and iron homeostasis in mouse development.

Hypoxia-inducible factor-1 (HIF-1) regulates the transcription of genes whose products play critical roles in energy metabolism, erythropoiesis, angiogenesis, and cell survival. Limited information is available concerning its function in mammalian hematopoiesis. Previous studies have demonstrated that homozygosity for a targeted null mutation in the Hif1alpha gene, which encodes the hypoxia-responsive alpha subunit of HIF-1, causes cardiac, vascular, and neural malformations resulting in lethality by embryonic day 10.5 (E10.5). This study revealed reduced myeloid multilineage and committed erythroid progenitors in HIF-1alpha-deficient embryos, as well as decreased hemoglobin content in erythroid colonies from HIF-1alpha-deficient yolk sacs at E9.5. Dysregulation of erythropoietin (Epo) signaling was evident from a significant decrease in mRNA levels of Epo receptor (EpoR) in Hif1alpha-/- yolk sac as well as Epo and EpoR mRNA in Hif1alpha-/- embryos. The erythropoietic defects in HIF-1alpha-deficient erythroid colonies could not be corrected by cytokines, such as vascular endothelial growth factor and Epo, but were ameliorated by Fe-SIH, a compound delivering iron into cells independently of iron transport proteins. Consistent with profound defects in iron homeostasis, Hif1alpha-/- yolk sac and/or embryos demonstrated aberrant mRNA levels of hepcidin, Fpn1, Irp1, and frascati. We conclude that dysregulated expression of genes encoding Epo, EpoR, and iron regulatory proteins contributes to defective erythropoiesis in Hif1alpha-/- yolk sacs. These results identify a novel role for HIF-1 in the regulation of iron homeostasis and reveal unexpected regulatory differences in Epo/EpoR signaling in yolk sac and embryonic erythropoiesis.

Animals↗
PubMed2006

High levels of circulating CD34 cells, dacrocytes, clonal hematopoiesis, and JAK2 mutation differentiate myelofibrosis with myeloid metaplasia from secondary myelofibrosis associated with pulmonary hypertension.

We studied 25 patients with myelofibrosis with myeloid metaplasia and 19 patients with secondary myelofibrosis associated with pulmonary hypertension (PH). In these 2 groups, we compared the peripheral-blood CD34 count, the clonality of granulocytes and platelets in peripheral blood, the mutational status of the JAK2 kinase gene, and the morphology of the peripheral blood and bone marrow. We found that the following were distinctive features of myelofibrosis with myeloid metaplasia but not of secondary myelofibrosis due to PH: high circulating CD34 cell count, the presence of clonal platelets and granulocytes and of peripheral-blood dacrocytes, and a JAK2 1849G>T (V617F) mutation. We conclude that these are intrinsic features of clonal progenitors present in patients with myelofibrosis due to myeloproliferative disorders and that these features are not due to the abnormal marrow architecture seen in secondary myelofibrosis.

Adult↗
PubMed2006

Polycythemia vera and its molecular basis: an update.

The molecular basis of polycythemia vera is discussed in the context of the JAK2 V617F mutation, in our view the most important advance in understanding the pathogenesis of polycythemia vera. This chapter discusses the nature of the JAK2 V617F mutation including the studies demonstrating its role in erythropoietin independence and hypersensitivity and endogenous erythroid colony formation. The evolving evidence that JAK2 V617F is not specific for polycythemia vera pathogenesis and the development of disease phenotype is presented as well as alternative candidates for pathogenic mutations such as the protein tyrosine phosphatases and SOCS-3. Finally, the clinical correlations and implications of the JAK2 V617F mutation are discussed.

Humans↗
PubMed2006

Idiopathic erythrocytosis and other non-clonal polycythemias.

Idiopathic erythrocytosis (IE) is characterized by an increase of red blood cell mass without an identified cause. Its diagnosis is based on the exclusion of polycythemia vera (PV), secondary acquired polycythemias and various congenital primary and secondary polycythemias. The frequency of IE has been estimated to be 1.1 per 1000 subjects, which is higher than that observed in PV. Heterogeneous mechanisms underlying IE have been suggested, including 'early' PV and unrecognized secondary or congenital polycythemia. However, the transition of a patient initially classified as IE into PV is a rare occurrence, when more sophisticated diagnostic techniques are employed. IE is a stable disease with a low thrombotic risk and a low, if any, tendency to spontaneous progression to acute leukemia or myelofibrosis. Phlebotomy in patients with IE is controversial. Myelosuppressive drugs should be avoided since their use is associated with evolution into acute leukemia in about 10% of patients.

Humans↗
PubMed2006

Vascular complications in Chuvash polycythemia.

Chuvash polycythemia is characterized by a homozygous 598C> T germline mutation in the von Hippel-Lindau gene ( VHL), upregulation of hypoxia-inducible factor-1alpha during normoxia, and resulting augmentation of erythropoietin and several other hypoxia-controlled genes. Although endemic to the Chuvash population of Russia, this mutation occurs worldwide and usually originates from a single ancient event. Matched-cohort and case-control analyses have shown that VHL 598C> T homozygosity is associated with lower peripheral blood pressures, varicose veins, vertebral hemangiomas, lower white blood cell and platelet counts, and elevated serum concentrations of vascular endothelial growth factor and plasminogen activator inhibitor-1. These studies have also shown associations with arterial and venous thrombosis, major bleeding episodes, cerebral vascular events, and premature mortality. Spinocerebellar hemangioblastomas, renal carcinomas, and pheochromocytomas typical of classical VHL tumor predisposition syndrome have not been found, and no increased risk of cancer has been demonstrated. Retrospective analyses among patients with Chuvash polycythemia have not shown benefit for therapy with phlebotomy or aspirin, but these and other modes of therapy should be studied prospectively. Further investigation of the vascular complications of Chuvash polycythemia may increase our fundamental knowledge of thrombophilia, bleeding diatheses, and protection from cancer.

Aspirin↗
PubMed2006

Endothelin-1, vascular endothelial growth factor and systolic pulmonary artery pressure in patients with Chuvash polycythemia.

BACKGROUND AND OBJECTIVES: Endothelin-1 has been associated with development of hypoxia-related pulmonary hypertension and vascular endothelial growth factor (VEGF) with protection from this complication. In Chuvash polycythemia, homozygous germline von Hippel-Lindau (VHL) 598C->T leads to up-regulation during normoxia of hypoxia inducible factor-1a and several hypoxia-controlled genes including erythropoietin and VEGF. We postulated that endothelin-1 and pulmonary artery pressure may be elevated in Chuvash polycythemia. DESIGN AND METHODS: Systolic pulmonary artery blood pressure was estimated by Doppler echocardiography and plasma concentrations of endothelin-1, VEGF and erythropoietin were determined in 14 patients with Chuvash polycythemia and 14 controls. Results. Plasma endothelin-1 (p=0.010), VEGF (p=0.022) and erythropoietin (p<0.0005) concentrations and Doppler-estimated systolic pulmonary artery pressures (p<0.0005) were higher in the patients while systolic systemic blood pressures were lower (p=0.001). Five (36%) patients and no controls had mild pulmonary hypertension defined as systolic pulmonary artery pressure (c) 35 mmHg. Among the patients with Chuvash polycythemia, the trends of association of estimated pulmonary artery pressure with plasma concentrations of endothelin-1 (R = +0.236), VEGF (R = -0.389) and erythropoietin (R = +0.220) were not statistically significant. INTERPRETATIONS AND CONCLUSIONS: Estimated systolic pulmonary artery pressure and plasma concentrations of endothelin-1 and VEGF are increased in patients with Chuvash polycythemia patients. The lack of significant associations of estimated systolic pulmonary artery pressure with plasma endothelin-1 and VEGF levels could conceivably be due to the small sample size. Further studies are indicated, especially in view of the reported efficacy of endothelin-1 receptor blockers in treating hypoxia-associated pulmonary hypertension.

Altitude↗
PubMed2006

Idiopathic myelofibrosis without dacryocytes.

Idiopathic myelofibrosis (IMF) typically presents with marrow fibrosis, splenomegaly, progressive anemia, and a leukoerythroblastic blood smear with dacryocytes. We present a patient with IMF who did not have dacryocytes.

Aged↗
PubMed2006

A novel mutation of the cytochrome-b5 reductase gene in an Indian patient: the molecular basis of type I methemoglobinemia.

We report here a novel mutation in the cytochrome b5 reductase gene resulting in type I methemoglobinemia. A single T->C transition in exon 8 at position 25985 was identified, changing codon 217 from Leu to Pro (L217P). The mutation is located in the NADH binding domain at the base of alpha-helix Nalpha3, a region of sequence highly conserved from yeast to man. A quantitative assessment of the thermodynamic cost of this mutation at 37 degrees C revealed a ten-fold drop in the free energy of stability. Alterations in hydrogen bonding and solvent accessibility surrounding residue 217 were predicted based on computer modeling.

Adult↗
PubMed2005

JAK2 mutation 1849G>T is rare in acute leukemias but can be found in CMML, Philadelphia chromosome-negative CML, and megakaryocytic leukemia.

An activating 1849G>T mutation of JAK2 (Janus kinase 2) tyrosine kinase was recently described in chronic myeloproliferative disorders (MPDs). Its role in other hematologic neoplasms is unclear. We developed a quantitative pyrosequencing assay and analyzed 374 samples of hematologic neoplasms. The mutation was frequent in polycythemia vera (PV) (86%) and myelofibrosis (95%) but less prevalent in acute myeloid leukemia (AML) with an antecedent PV or myelofibrosis (5 [36%] of 14 patients). JAK2 mutation was also detected in 3 (19%) of 16 patients with Philadelphia-chromosome (Ph)-negative chronic myelogenous leukemia (CML), 2 (18%) of 11 patients with megakaryocytic AML, 7 (13%) of 52 patients with chronic myelomonocytic leukemia, and 1 (1%) of 68 patients with myelodysplastic syndromes. No mutation was found in Ph(+)CML (99 patients), AML M0-M6 (28 patients), or acute lymphoblastic leukemia (20 patients). We conclude that the JAK2 1849G>T mutation is common in Ph(-) MPD but not critical for transformation to the acute phase of these diseases and that it is generally rare in aggressive leukemias.

Humans↗
PubMed2005

Constitutive mobilization of CD34+ cells into the peripheral blood in idiopathic myelofibrosis may be due to the action of a number of proteases.

Idiopathic myelofibrosis (IM) is characterized by increased numbers of CD34(+) cells in the peripheral blood (PB). We explored the possible mechanisms underlying this abnormal trafficking of CD34(+) cells. Plasma levels of neutrophil elastase (NE), total and active matrix metalloproteinase 9 (MMP-9), and soluble vascular cell adhesion molecule-1 (sVCAM-1) were dramatically increased in IM. The absolute number of CD34(+) cells in the PB was correlated with the levels of sVCAM-1. Marked elevations of the levels of NE but not total and active MMP-9 as well as MMP-2 were detected in media conditioned by IM mononuclear cells (MNCs) as compared with that of healthy volunteers. IM MNC-conditioned media, however, was shown by zymographic analysis to contain increased gelatinolytic activity corresponding to the molecular weight of MMP-9. IM MNC-conditioned media also exhibited a greater ability to cleave VCAM-1 and c-kit in vitro, consistent with the biologic actions of NE. In addition, the increased ability of IM PB CD34(+) cells to migrate through a reconstituted basement membrane was diminished by several inhibitors of MMP-9 activity, indicating that these cells express increased levels of this MMP. These data indicate that a proteolytic environment exists in IM which might result in the sustained mobilization of CD34(+) cells.

Antigens, CD34↗
PubMed2005

Allogeneic hematopoietic stem-cell transplantation with reduced-intensity conditioning in intermediate- or high-risk patients with myelofibrosis with myeloid metaplasia.

A total of 21 patients with myelofibrosis with myeloid metaplasia (MMM), with a median age of 54 years (range, 27-68 years), were prepared with a reduced-intensity conditioning (RIC) regimen. The patients received an allogeneic marrow (n = 3) or peripheral blood stem-cell (n = 18) transplant from HLA-matched related (n = 18) or unrelated (n = 2), or 1 Ag-mismatched related (n = 1), donors. RIC regimens included fludarabine/total body irradiation 200 cGy (n = 5) or 450 cGy (n = 1), fludarabine/melphalan (n = 7), thiotepa/cyclophosphamide (n = 7), and thiotepa/fludarabine (n = 1). At the time of transplantation, all of the patients were at intermediate (n = 13) or high (n = 8) risk, according to the Dupriez classification. Of the patients, 19 had grade III or IV marrow fibrosis. All of the patients achieved full engraftment but one. Posttransplantation chimerism analysis showed more than 95% donor cells in 18 patients, while 2 patients achieved complete donor chimerism after donor leukocyte infusion (DLI). Acute graft-versus-host disease (GVHD) grades II to IV was observed in 7 patients, grades III to IV in 2, and extensive chronic GVHD in 8 of 18 evaluable patients. There were 3 patients who died from acute GVHD, infection, and relapse. There are 18 patients alive 12 to 122 months (median, 31 months) after transplantation, and 17 are in remission (1 after a second transplantation). The use of RIC regimens in allogeneic stem cell transplantation results in prolonged survival in intermediate/high-risk MMM patients.

Adult↗
PubMed2005

Lessons from familial myeloproliferative disorders.

By definition, myeloproliferative disorders (MPDs) are caused by an acquired somatic mutation of a hematopoietic progenitor/stem cell and have sporadic occurrence. However, well-documented families exist with first-degree relatives acquiring one or several MPDs. It is reasonable to assume that the germ-line mutation(s) or genetic background must facilitate or predispose for one or several somatic mutation(s) that lead to the MPD that is indistinguishable from the sporadic form. This is best documented in familial polycythemia vera (PV), which appears to be inherited as an autosomal dominant disorder with incomplete penetrance. However, there are also families wherein members develop any combination of MPDs, including PV, essential thrombocythemia (ET), chronic myelocytic leukemia (CML), and idiopathic myelofibrosis (IMF). A separate group of familial diseases is the familial thrombocythemias, wherein germ-line mutations in the genes for thrombopoietin or its receptor, MPL, cause polyclonal hereditary thrombocythemia, which may be clinically indistinguishable from ET. Patients with the congenital polycythemic condition "primary familial and congenital polycythemia" (PFCP) have characteristically decreased erythropoietin (Epo) levels similar to PV, hypersensitive erythroid progenitors, and low Epo levels; as such, this condition is often confused with PV. Therefore, PFCP will also be discussed here, while other congenital polycythemic states such as the Chuvash polycythemia that have elevated or inappropriately normal Epo levels will be omitted from this review in view of their distinct phenotype and unique laboratory features.

Chromosomes, Human, X↗