Biomedical subjects

H Miyazaki

Publications and source records attributed to H Miyazaki.

At least 271 records · Page 15Linked to original sources

PubMed1997

[Short-term intensive treatment for acute myelogenous leukemia (excluding M3 subtype) in adults].

Thirty-two adults (median age 48 years) with acute myelogenous leukemia (excluding M3) have been treated with short-term intensive therapy (M90 therapy). After induction therapy with daunorubicin, cytosine arabinoside (araC), 6-mercaptopurine, prednisolone, mitoxantrone (MIT) and etoposide (VP16), three regimens of post-induction chemotherapy were conducted as short an intercycle time as possible. The first regimen was with MIT and VP16, the second with behenoyl-araC and aclarubicin and the third with VP16, araC, vincristine and vinblastine. No further therapy was given. Complete remission was achieved in 24 (75%) of 32 patients and 24% of all patients were projected to remain free of disease at 5 years. The median duration of the entire therapy was 120 days with a range of 95 to 157 days. Post-induction regimens resulted in severe myelosuppression and their toxicity included treatment-related death in one patient. The treatment results of this short-term therapy were comparable to a former treatment protocol, M84 therapy with a median duration of the entire treatment therapy of 515 days. To confirm the advantages of such short-term therapy, prospective randomized comparisons with conventional post-induction therapy may be required.

Aclarubicin↗

PubMed1997

[An autopsy case of corticobasal degeneration mimicking frontal Pick's disease].

A pathologically proven case of corticobasal degeneration (CBD) with marked psychiatric symptoms was reported. A 59-year-old female was admitted to our hospital in October 1989 because of her "forgetfulness". Her abnormal behavior began in August 1989, and she had no psychiatric signs before that time. On this admission she was diagnosed to have panhypopituitarism due to Sheehan syndrome. Cortisone and levothyroxine were administered, but her mental symptoms deteriorated. Strange behaviors such as buying same materials every day and wandering around all day long fully dressed with all of her jewels were observed. She could not perform her housework after March 1991. She was in a bed ridden state after 1992 and died in March 1993, at the age of 62. The total duration of her illness was 3 years and 7 months. Her clinical course resembled frontal Pick's disease. At autopsy advanced gastric cancer without metastasis and infarct of the pituitary gland were found. The weight of the brain was 987g and atrophy of the bilateral frontal lobes was evident on macroscopical examination. Neuronal loss, proliferation of the glia, and spongy state were observed in the superficial layer of the frontal cerebral cortex. Widespread appearance of ballooned neurones was also observed in the deep layers of the frontal cerebral cortex. Neuronal loss and gliosis were found in the striatum, pallidum, thalamus, and substantia nigra. There was neither senile plaques nor Pick bodies. Numerous argyrophilic threads were found by Gallyas-Braak method and all these pathological findings were compatible with the previously reported cases of CBD. Although CBD is considered as predominantly a motor disorder, there are a few reports of pathologically proven cases of CBD mimicking Pick's disease. These cases suggest clinical diversity of CBD and further investigations are essential to establish the disease entity of CBD and Pick's disease.

Basal Ganglia Diseases↗

PubMed1997

[A mesenchymal malignant mesothelioma that changed from mixed type to purely sarcomatous type].

A 65-year-old man was admitted to the hospital because of an abnormal shadow on a chest roentgenogram. A diagnosis of mixed-type malignant mesothelioma was made after transcutaneous needle biopsy and thoracoscopic biopsy. The tumor was considered to be inoperable because it had diffusely invaded surrounding tissue, and therefore the patient was treated with chemotherapy only. About one year later, he died of acute pneumonia. At autopsy, a mesenchymal malignant mesothelioma that did not have an epithelial component was found. We know of no previous report of a case in which a tumor with a biopsy-proven epithelial component apparently changed to a purely sarcomatous type. No satisfactory explanation for this phenomenon has been offered.

Aged↗

PubMed1997

[A patient with spontaneous intracranial hypotension--comparison between MRI findings and meningeal pathology].

We report a 44-year-old woman with spontaneous intracranial hypotension (SIH) who developed an acute, severe, nonthrobbing headache. The headache remained more severe in the occipital region and was markedly worse with upright posture. Cerebrospinal fluid (CSF) examination revealed an opening pressure of 55 mmH2O, and the CSF contained 38 cells/mm3 and 57 mg/dl of protein. The results of other laboratory examinations were unremarkable. T1-weighted MR images (MRI) of the head revealed an extensive diffuse pachymeningeal gadolinium enhancement and bilateral subdural fluid accumulation. On the 21st hospital day, a meningeal biopsy was performed through a right parietal craniotomy. On histologic examination, the dural border cell layer demonstrated nonspecific granulation tissue with mild inflammatory changes. The remaining layers of the dura mater and the arachnoid membrane showed no obvious pathological changes. We speculated that the inflammatory changes of the dural border cell layer correspond to the zone of pachymeningeal gadolinium enhancement of the MRI. The granulation tissue of the dural border cell layer and subdural fluid accumulation may represent secondary reactive phenomena, and were suspected to have been caused by downward displacement of the brain due to decreased intracranial pressure.

Adult↗

PubMed1997

Cellular localization of thrombopoietin mRNA in the liver by in situ hybridization.

The expression of thrombopoietin (TPO) mRNA is observed in several tissues, including liver, kidney, brain, skeletal muscle, intestine, spleen, and bone marrow. Among these organs, the highest expression of TPO mRNA is detected in the liver. We identified cells producing TPO by means of in situ hybridization of adult rat liver using digoxigenin-11-UTP-labeled cRNA probes. We found that the cells expressing TPO mRNA also expressed serum albumin mRNA. TPO mRNA was detected in parenchymal cells (hepatocytes) but not in non-parenchymal cells (including endothelial cells, epithelial cells, and so forth). To determine the location of TPO expression in embryogenesis, sections of fetal mice were further analyzed by in situ hybridization. TPO mRNA was detected only in hepatocytes of fetal liver, which was also the major site of hematopoiesis. The expression of TPO mRNA in fetal liver was observed from 12.5 days postcoitus. Northern blot analysis showed that mouse liver transcribed the same size of TPO mRNA in the fetus and in the adult. These results clearly demonstrate that hepatocytes are the primary site of TPO production in the liver from fetus to adult.

Animals↗

PubMed1997

[Effects of oral amezinium metilsulfate in patients with sick sinus syndrome].

The effects of amezinium metilsulfate (Risumic) were studied in patients with sick sinus syndrome. Four males and 11 females with clinical symptoms were treated with 0.5 mg/kg for 1 to 40 weeks. In all patients, the length of sinus pause observed during 24-hour Holter monitoring was longer than 2.0 sec, and/or the sinus node recovery time in the electrophysiologic study was longer than 2.0 sec. The effects were evaluated by Holter monitoring and standard electrocardiography. The total number of heart beats every 24 hours by Holter monitoring were significantly increased from 78,917 +/- 15,983 (mean +/- SD) to 85,753 +/- 17,849 beats after the treatment. The length of the sinus pause was significantly decreased from 3.89 +/- 1.24 to 2.36 +/- 1.45 sec. Patients with sinus node recovery time of less than 5.0 sec showed the effects especially clearly. The total number of premature ventricular contractions was decreased from 530 +/- 767 to 123 +/- 182 beats. The PQ, QRS and QTc intervals did not change. Only diastolic pressure was slightly increased. Clinical symptoms disappeared in almost all patients and the clinical courses were favorable. Amezinium metilsulfate, which stimulates the intrinsic sympathetic nervous system, increased total heart beat and shortened sinus pause in patients with sick sinus syndrome. Few side effects, such as arrhythmogenecity or increase of blood pressure were observed. These results show that amezinium metilsulfate is useful in the treatment of patients with sick sinus syndrome, if the disease is not so severe as to require implantation of a cardiac pacemaker.

Administration, Oral↗

PubMed1997

Recombinant human c-Mpl ligand (thrombopoietin) not only acts on megakaryocyte progenitors, but also on erythroid and multipotential progenitors in vitro.

To determine the hematopoietic actions of recombinant human c-Mpl ligand (thrombopoietin [TPO]), we studied its effects on the proliferation and differentiation of highly purified CD34+ blood progenitors in plasma-containing and serum-free culture. TPO alone promoted the growth of small megakaryocyte colonies (CFU-Meg) in numbers two to three times greater than those produced by interleukin (IL)-3. The combination of TPO and stem cell factor (SCF) exerted a significant synergistic effect on CFU-Meg formation. In the presence of TPO and IL-3 or granulocyte/macrophage-colony stimulating factor (GM-CSF), a significant number of mixed colonies (CFU-Mix) were observed. The combination of TPO and Epo did not increase the number of CFU-Meg, but did support erythroid-burst (BFU-E) and CFU-Mix colony formation. Interestingly, the combination of TPO with cytokines known to have burst-promoting activity (BPA), including IL-3, GM-CSF, IL-9, and SCF, increased the number of BFU-E and CFU-Mix in the presence of Epo. The BPA of TPO was further investigated by delayed addition of Epo on day 6 after incubation with TPO from day 0. None of the BFU-E or CFU-Mix survived, indicating that TPO acted as a costimulant exclusively for Epo. Moreover, a neutralizing anti-human Mpl receptor polyclonal antibody completely abrogated the BPA of TPO, demonstrating that this effect was mediated through the Mpl receptor. Finally, experiments in single-cell clone sorting and serum-free culture clearly demonstrated that a combination of TPO and Epo directly supported BFU-E and CFU-Mix. These results suggest that TPO acts not only in megakaryocytopoiesis but also in the early stage of hematopoiesis.

Antigens, CD34↗

PubMed1997

Studies on the first-pass metabolism of ebastine in rats.

The metabolic conversion of ebastine (CAS 90729-43-4, LAS-90), an antiallergic agent, to its active principle carebastine (CAS 90729-42-3) in the rat intestine and liver was investigated using intravenous-intraportal infusion techniques and jejunum loop preparations. The steady state blood concentrations of ebastine and carebastine were determined during continuous intravenous or intraportal infusion of ebastine to evaluate their respective activity to metabolize ebastine in the intestine and liver. Total body clearance of ebastine was calculated to be approximately 22-26 ml/ min. The intestinal and hepatic clearances were 6.7 ml/min and 15.4 ml/min, respectively, accounting for about 32% and 60% of the total clearance, respectively. The ratio of the concentrations of carebastine in portal blood to that in arterial blood was 1.41 during intravenous infusion, suggesting the single-pass metabolic conversion of ebastine to carebastine in the intestine. The ratio of the arterial blood concentration of carebastine during intraportal infusion to that during intravenous infusion was 1.88, suggesting the single-pass metabolic conversion in the liver. The contribution of the intestine to form carebastine from ebastine present in the systemic circulation was thus about 1/2 (0.41/0.88) of that of the liver under these conditions. When [14C]ebastine was administered in the jejunal loop, carebastine was detected in the mesenteric plasma circulated from the loop, as the major component accounting for approximately 56% of the plasma radioactivity, while the unchanged ebastine was only about 13%. Therefore, the jejunal tissue converted > 1/2 of the permeated fraction of ebastine to carebastine under these conditions. The results in the infusion studies suggested that metabolic potential to convert ebastine to carebastine was higher in the liver than in the intestine. However, since after oral administration all of the drug appeared in the systemic circulation firstly permeated the mucosa of small intestine and then passed through the liver, the contribution of the small intestine in the metabolic conversion of ebastine given orally would be greater than that of the liver, as suggested by the above in situ jejunum loop study.

Animals↗

PubMed1997

[Bitemporal hemianopsia after skull base fracture].

We report a case of bitemporal hemianopsia after skullbase fracture. An 18-year-old male presented with frontal head hit due to a traffic accident. Consciousness level on admission was JCS 10. Initial CT scan revealed traumatic SAH and pneumocephalus. We treated him conservatively. Ten hours after the accident, consciousness level went down, and CT imaging disclosed bilateral frontal hemorrhage. The three dimensional CT (3D-CT) imaging showed two fracture lines from the roof of the ethmoid sinus to the planum sphenoidale. Although his consciousness improved gradually, he complained of rhinorrhea, anosmia and double vision. On preoperative visual field examination, bitemporal hemianopsia was noticed. Repair operation for CSF rhinorrhea was performed. Operative findings revealed two fracture lines corresponding to the 3D-CT scan. The optic chiasm was compressed by the tuberculum sellae. We could not find obvious tearings or stretchings of the chiasm. Reports on operative findings of traumatic chiasmal syndrome are rare, and most of the reports presume that bitemporal hemianopsia results from tearing or stretching of the chiasm. We could confirm that, in some cases, bitemporal hemianopsia could result from direct pressure of the tuberculum sellae.

Adolescent↗

PubMed1996

Soluble thrombopoietin receptor (Mpl) and granulocyte colony-stimulating factor receptor directly stimulate proliferation of primitive hematopoietic progenitors of mice in synergy with steel factor or the ligand for Flt3/Flk2.

In an effort to establish the specificity of the thrombopoietin (TPO) effects on murine multipotential progenitors, we tested the effects of soluble TPO receptor (sTPOR; sMpl) on multilineage colony formation that was supported by a combination of TPO and steel factor (SF). Surprisingly, sTPOR did not suppress colony formation from primitive progenitors. This led to the discovery that sTPOR synergizes with SF or Flt3/Flk2 ligand (FL) to support the formation of various types of hematopoietic colonies including multilineage colonies. The colonies supported by the combination of sTPOR and SF were capable of expressing both myeloid and B-lymphoid potentials. Studies using micromanipulation and serum-free culture showed that the effects of sTPOR and SF on the primitive progenitors are direct, not mediated by contaminating stromal cells, and not dependent on factors present in the serum. TPOR belongs to the cytokine receptor group that includes granulocyte colony-stimulating factor receptor (G-CSFR) and erythropoietin receptor (EPOR). Therefore, we tested the effects of sG-CSFR and sEPOR on primitive progenitors. sG-CSFR, but not sEPOR, was able to synergize with SF or FL in supporting the proliferation of primitive progenitors. The direct effects of the soluble receptors appear to be mediated through interactions with their respective membrane-bound receptors expressed on the primitive hematopoietic progenitors.

Animals↗

PubMed1996

The angiotensin II type 2 receptor primarily inhibits cell growth via pertussis toxin-sensitive G proteins.

We examined the effects of angiotensin II (Ang II) and its analogue CGP42112 on cell growth through the Ang II type 2 receptor (AT2) and the involvement of pertussis toxin (PTX)-sensitive G proteins in the AT2-mediated pathway. Both Ang II and CGP42112 inhibited DNA synthesis in serum-stimulated NIH3T3 fibroblast cells stably expressing recombinant AT2 in a dose-dependent manner with almost the same potency. This effect was abolished by the AT2-selective antagonist PD123319, but not by the Ang II type 1 receptor-specific antagonist DuP753, suggesting that AT2 mediates the event. The anti-proliferative effect was also blocked by PTX treatment. Together, these data suggest that CGP42112 as well as Ang II primarily has an AT2-mediated inhibitory activity on serum-stimulated cell growth, and PTX-sensitive G proteins are essential in this AT2-induced event.

3T3 Cells↗

PubMed1996

Functional analysis of the cytoplasmic domain of the human Mpl receptor for tyrosine-phosphorylation of the signaling molecules, proliferation and differentiation.

To investigate the functional domains for signal transduction of human Mpl, we constructed a series of human c-mpl cDNAs with various deletions in the cytoplasmic domain, and then introduced each cDNA into murine IL-3-dependent myeloid leukemia FDC/P2 cells to establish stable transformants. We examined the growth and differentiation responses and tyrosine phosphorylation of the intracellular signaling proteins including Jak2, Tyk2, Stat3, Stat5, Vav, SHPTP2, Cbl, Shc and Shc-associated p145 when receptor stimulation occurred after thrombopoietin (TPO) binding. TPO stimulated cell proliferation and induced the expression of megakaryocyte lineage-specific AP-51 and CD61 cell surface antigens and tyrosine phosphorylation of the signaling proteins in transformants expressing full length human Mpl. These results suggested that Mpl not only induced proliferation but also transduced megakaryocyte-specific differentiation signals into FDC/P2 cells. Mutational analysis of human Mpl indicated that the N-terminal region of its cytoplasmic domain is necessary and sufficient to transduce proliferation and differentiation signals into cells, while the C-terminal region may also play important roles in transducing the differentiation signals.

Animals↗

PubMed1996

The biologic properties of recombinant human thrombopoietin in the proliferation and megakaryocytic differentiation of acute myeloblastic leukemia cells.

Thrombopoietin (TPO) is implicated as a primary regulator of megakaryopoiesis and thrombopoiesis. However, the biologic effects of TPO on human acute myeloblastic leukemia (AML) cells are largely unknown. To determine if recombinant human (rh) TPO has proliferation-supporting and differentiation-inducing activities in AML cells, 15 cases of AML cells that were exclusively composed of undifferentiated leukemia cells and showed growth response to rhTPO in a short-term culture (72 hours) were subjected to long-term suspension culture with or without rhTPO. Of 15 cases, rhTPO supported proliferation of AML cells for 2 to 4 weeks in 4 cases whose French-American-British subtypes were M0, M2, M4, and M7, respectively. In addition to the proliferation-supporting activity, rhTPO was found to induce AML cells to progress to some degree of megakaryocytic differentiation at both morphologic and surface-phenotypic level in 2 AML cases with M0 and M7 subtypes. The treatment of AML cells with rhTPO resulted in rapid tyrosine phosphorylation of the TPO-receptor, c-mpl, and STAT3 in all of cases tested. By contrast, the expression of erythroid/megakaryocyte-specific transcription factors (GATA-1, GATA-2, and NF-E2) was markedly induced or enhanced in only 2 AML cases that showed megakaryocytic differentiation in response to rhTPO. These results suggested that, at least in a fraction of AML cases, TPO could not only support the proliferation of AML cells irrespective of AML subtypes, but could also induce megakaryocytic differentiation, possibly through activation of GATA-1, GATA-2, and NF-E2.

Acute Disease↗

PubMed1996

p120c-cbl is present in human blood platelets and is differentially involved in signaling by thrombopoietin and thrombin.

To investigate the signaling processes induced by recombinant thrombopoietin, we used human platelets to recently show that thrombopoietin induces rapid tyrosine phosphorylation of Jak2, Tyk2, Shc, Stat3, Stat5, and other proteins in human platelets. Because the apparent molecular weight of a major tyrosine-phosphorylated protein in platelets stimulated by thrombopoietin is approximately 120 kD, we examined the possibility that this could be p120c-cbl, a protein known to be involved in signaling by many growth factors. Specific antisera against p120c-cbl recognized the same 120-kD protein in lysates of Jurkat cells, which are known to express p120c-cbl, and platelets, indicating that platelets have p120c-cbl. Thrombopoietin induced rapid tyrosine phosphorylation of p120c-cbl in platelets. Thrombopoietin also induced tyrosine phosphorylation of p120c-cbl in FDCP cells genetically engineered to express the thrombopoietin receptor, c-Mpl. Interestingly, FDCP cells, expressing a truncated c-Mpl devoid of the box-2 domain, proliferate in response to thrombopoietin. However, no increase in tyrosine phosphorylation of p120c-cbl was observed upon treatment of these cells with thrombopoietin, indicating that in this system tyrosine phosphorylation of p120c-cbl may not be essential for cell proliferation. This suggests that tyrosine phosphorylation of p120c-cbl may be required for nonmitogenic responses induced by thrombopoietin in postmitotic cells such as platelets. On the other hand, p120c-cbl was not significantly tyrosine-phosphorylated upon treatment of platelets with thrombin. However, it became incorporated into the Triton X-100-insoluble, 10,000g-sedimentable residue in an aggregation-dependent manner, suggesting that it may have a regulatory role in platelet cytoskeletal processes. p120c-cbl was constitutively associated with a 28-kD adapter protein, Grb2, that was also incorporated into the Triton X-100-insoluble, sedimentable residue dependent on aggregation. Further, we found that p120c-cbl is an endogenous substrate for calpain, a protease that may play a role in postaggregation signaling processes. Our data suggest that p120c-cbl may be involved in signal transduction following ligand binding to c-Mpl through its inducible tyrosine phosphorylation, and it may also be involved in signaling during platelet aggregation by its redistribution to the cytoskeleton.

Adaptor Proteins, Signal Transducing↗

PubMed1996

Incidence of intracranial meningiomas in Nagasaki atomic-bomb survivors.

Among the Nagasaki atomic-bomb survivors registered at the Scientific Data Center for Atomic-Bomb Disaster, Nagasaki University School of Medicine, 45 cases of surgically treated intracranial meningioma were collected from 6 hospitals with departments of neurosurgery in or near Nagasaki City during the period from 1973 to 1992. All 45 patients were over 40 years of age at the time of diagnosis. Subsequently, the 45 cases were statistically analyzed in relationship to the estimated distance from the hypocenter by age, gender, intracranial location, histology and latent period. The analysis showed a high correlation between incidence of meningiomas and distance from the hypocenter. The incidence among Nagasaki atomic-bomb survivors over 40 years of age, especially in those proximally exposed, appears to be increasing, in inverse proportion to the exposure distance, since 1981, 36 years after the explosion of the atomic bomb.

Adult↗

PubMed1996

Thrombopoietin supports proliferation of human primitive hematopoietic cells in synergy with steel factor and/or interleukin-3.

We have studied the effects of recombinant human thrombopoietin (TPO; mpl ligand) on the proliferation of human primitive hematopoietic progenitors in vitro. CD34+ cells were enriched for cell-cycle-dormant primitive progenitors by separation on the basis of expression of c-kit and CD38. In the presence of varying combinations of TPO, Steel factor (SF), and interleukin-3 (IL-3), CD34+/c-kit(low)/CD38neg/low cells produced fewer colonies than CD34+/c-kit(low)/CD38high cells. However, when cultured in suspension for 7 days and replated in methylcellulose culture for measurement of colony-forming cells, the former population generated more colony-forming cells than the latter. In suspension culture of CD34+/c-kit(low)/CD38neg/low cells, TPO acted synergistically with SF and/or IL-3 in support of the production of colony-forming cells for granulocyte/macrophage colonies, erythroid colonies, and mixed colonies. Culture studies of individual CD34+/c-kit(low)/CD38neg/low cells provided the evidence for the direct nature of the effects of TPO. When combined with SF, TPO showed stronger stimulation of production of progenitors in suspension culture than other early-acting factors, such as IL-6, IL-11, and granulocyte colony-stimulating factor (G-CSF). TPO may be an important cytokine for in vitro manipulation of human hematopoietic stem cells.

Adult↗

PubMed1996

Establishment and characterization of the thrombopoietin-dependent megakaryocytic cell line, UT-7/TPO.

UT-7 is a human megakaryoblastic leukemia cell line with absolute dependence on interleukin-3, granulocyte-macrophage colony-stimulating factor, or erythropoietin (EPO) for growth and survival. We investigated the effect of thrombopoietin (TPO), the ligand for the receptor encoded by c-mpl proto-oncogene, on the proliferation and differentiation of UT-7 and its sublines. We found that UT-7/GM, which is a subline of UT-7, but neither UT-7 nor UT-7/EPO, can proliferate in response to TPO. The subline, UT-7/TPO, was established from UT-7/GM by culture at lower concentrations of TPO. UT-7/TPO cells had morphologically mature megakaryocytic characteristics such as developed demarcation membrane in the cytoplasm and multinucleated appearance. This was also confirmed by the high expression of platelet factor-4 and glycoprotein IIb at the mRNA levels and by the high level of DNA content. UT-7/TPO can be maintained by TPO alone, with a doubling time of 24 hours in log growth phase. In the absence of TPO, the majority of the cells died within a few days. Thus, UT-7/TPO has an absolute dependence on TPO for growth and survival and has mature megakaryocytic features. The mRNA for c-mpl was detected in UT-7/TPO and, to a lesser degree, in UT-7/GM. The mRNA level of NF- E2 p45, reported to be an erythroid-specific transcription factor, was upregulated in UT-7/TPO, whereas it was down-regulated in the erythroid subline, UT-7/EPO. There were no significant differences in GATA-1 and GATA-2 mRNA levels among UT-7 and its sublines. Not only EPO but also TPO induced the tyrosine phosphorylation of JAK2 tyrosine kinase and STAT5-related protein. These findings indicate that UT-7/TPO would be a useful model with which to analyze the gene regulation of megakaryocytic maturation-associated proteins and to study the specific actions of TPO.

Cell Differentiation↗

PubMed1996

Thrombopoietin primes human platelet aggregation induced by shear stress and by multiple agonists.

Recombinant thrombopoietin has been reported to stimulate megakaryocytopoiesis and thrombopoiesis and it may be quite useful to treat patients with low platelet counts after chemotherapy. As little is known regarding the possible activation of platelets by thrombopoietin, we examined the effects of thrombopoietin on platelet aggregation induced by shear stress and various agonists in native plasma. Using hirudin as an anticoagulant, thrombopoietin (1 to 100 ng/mL) enhanced platelet aggregation induced by 2 micromol/L adenosine-diphosphate (ADP) in a dose dependent fashion. The enhancement was not affected by treatment of platelets with 1 mmol/L aspirin plus SQ-29548 (a thromboxane antagonist, 1 micromol/L) but was inhibited by a soluble form of the thrombopoietin receptor, suggesting that the enhancement was mediated by the specific receptors and does not require thromboxane production. Epinephrine (1 micromol/L), which does not induce platelet aggregation in hirudin platelet rich plasma (PRP), did so in the presence of thrombopoietin (10 ng/mL). Thrombopoietin (10 ng/mL) also enhanced or primed platelet aggregation induced by collagen (0.5 micron.mL),. thrombin, serotonin, and vasopressin. Thrombopoietin does not induce any rise in cytosolic ionized calcium concentration nor activation of protein kinase C, as estimated by phosphorylation of preckstrin, indicating that the priming effects of thrombopoietin does not require those processes. The ADP- or thrombin-induced rise in cytosolic ionized calcium concentration was not enhanced by thrombopoietin (100 ng/mL). Further, shear (ca. 90 dyn/cm2)-induced platelet aggregation was also potentiated by thrombopoietin. The priming effect on epinephrine-induced platelet aggregation in hirudin PRP was unique to thrombopoietin, with no effects seen using interleukin-6 (IL-6), IL-11, IL-3, erythropoietin, granulocyte-colony stimulating factor, granulocyte macrophage-colony stimulating factor, or c-kit ligand. These data indicate that monitoring of platelet functions may be necessary in the clinical trials of thrombopoietin.

Adenosine Diphosphate↗