scholarly journals A Single Intravenous Dose of Murine Megakaryocyte Growth and Development Factor Potently Stimulates Platelet Production, Challenging the Necessity for Daily Administration

Blood ◽  
1998 ◽  
Vol 91 (2) ◽  
pp. 466-474 ◽  
Author(s):  
Najat C. Daw ◽  
Julie T. Arnold ◽  
Basel A. Abushullaih ◽  
Paula E. Stenberg ◽  
Melanie M. White ◽  
...  
Keyword(s):  
Growth And Development ◽  
Intravenous Dose ◽  
Daily Administration ◽  
Moderate Increase ◽  
Single Intravenous Dose ◽  
Platelet Response ◽  
Platelet Production ◽  
Development Factor ◽  
Platelet Number ◽  
Single Versus

The thrombopoietic efficacy of recombinant forms of c-mplligand is being actively investigated in preclinical studies using daily dosing schedules. However, a comprehensive kinetic study of the thrombopoietic response to a single injection of recombinant c-mpl ligand has not been performed. Here, we present the results of a detailed kinetic analysis of the platelet response to a single intravenous administration of pegylated recombinant murine megakaryocyte growth and development factor (PEG-rmMGDF) in mice. In addition, we compare the efficacy of single versus daily dosing in stimulating platelet production. A single intravenous injection of PEG-rmMGDF produced a marked and dose-dependent elevation in platelet number and a moderate increase in mean platelet volume (MPV). After administration of 25 or 250 μg/kg of PEG-rmMGDF, platelet number was first increased on day 3 and peaked at 2.7-fold (25 μg/kg) and 5.7-fold of normal (250 μg/kg) on day 5. Thereafter, platelet number declined and returned to baseline by days 9 and 14, with the 25 and 250 μg/kg doses, respectively. MPV began to increase on day 2 after PEG-rmMGDF, reaching maximum values of 1.2-fold (25 μg/kg) and 1.5-fold of normal (250 μg/kg) on day 4. Subsequently, MPV declined and was downregulated on days 6 to 7 (25 μg/kg) and day 8 (250 μg/kg). Based on these results, we evaluated the platelet response to PEG-rmMGDF administered intravenously as a single dose versus daily for 5 days. A single administration of 100 μg/kg produced a higher platelet number on day 5 than daily administration of 100 or 20 μg/kg for 5 days. However, the thrombocytosis was less sustained after single versus daily dosing. The smaller platelet number increase on day 5 after daily dosing reflected the production of larger platelets, rather than suppression of thrombopoiesis. Our results indicate that PEG-rmMGDF administered as a single intravenous dose potently stimulates platelet production in mice, challenging the need for its daily administration. Adoption of an intermittent administration schedule of this cytokine could be more efficacious and is merited in future clinical trials.

scholarly journals A Single Intravenous Dose of Murine Megakaryocyte Growth and Development Factor Potently Stimulates Platelet Production, Challenging the Necessity for Daily Administration

Blood ◽  
1998 ◽  
Vol 91 (2) ◽  
pp. 466-474 ◽  
Author(s):  
Najat C. Daw ◽  
Julie T. Arnold ◽  
Basel A. Abushullaih ◽  
Paula E. Stenberg ◽  
Melanie M. White ◽  
...  
Keyword(s):  
Growth And Development ◽  
Intravenous Dose ◽  
Daily Administration ◽  
Moderate Increase ◽  
Single Intravenous Dose ◽  
Platelet Response ◽  
Platelet Production ◽  
Development Factor ◽  
Platelet Number ◽  
Single Versus

Abstract The thrombopoietic efficacy of recombinant forms of c-mplligand is being actively investigated in preclinical studies using daily dosing schedules. However, a comprehensive kinetic study of the thrombopoietic response to a single injection of recombinant c-mpl ligand has not been performed. Here, we present the results of a detailed kinetic analysis of the platelet response to a single intravenous administration of pegylated recombinant murine megakaryocyte growth and development factor (PEG-rmMGDF) in mice. In addition, we compare the efficacy of single versus daily dosing in stimulating platelet production. A single intravenous injection of PEG-rmMGDF produced a marked and dose-dependent elevation in platelet number and a moderate increase in mean platelet volume (MPV). After administration of 25 or 250 μg/kg of PEG-rmMGDF, platelet number was first increased on day 3 and peaked at 2.7-fold (25 μg/kg) and 5.7-fold of normal (250 μg/kg) on day 5. Thereafter, platelet number declined and returned to baseline by days 9 and 14, with the 25 and 250 μg/kg doses, respectively. MPV began to increase on day 2 after PEG-rmMGDF, reaching maximum values of 1.2-fold (25 μg/kg) and 1.5-fold of normal (250 μg/kg) on day 4. Subsequently, MPV declined and was downregulated on days 6 to 7 (25 μg/kg) and day 8 (250 μg/kg). Based on these results, we evaluated the platelet response to PEG-rmMGDF administered intravenously as a single dose versus daily for 5 days. A single administration of 100 μg/kg produced a higher platelet number on day 5 than daily administration of 100 or 20 μg/kg for 5 days. However, the thrombocytosis was less sustained after single versus daily dosing. The smaller platelet number increase on day 5 after daily dosing reflected the production of larger platelets, rather than suppression of thrombopoiesis. Our results indicate that PEG-rmMGDF administered as a single intravenous dose potently stimulates platelet production in mice, challenging the need for its daily administration. Adoption of an intermittent administration schedule of this cytokine could be more efficacious and is merited in future clinical trials.

Effects of megakaryocyte growth and development factor on platelet production, platelet life span, and platelet function in healthy human volunteers

Blood ◽  
2000 ◽  
Vol 95 (8) ◽  
pp. 2514-2522 ◽  
Author(s):  
Laurence A. Harker ◽  
Lorin K. Roskos ◽  
Ulla M. Marzec ◽  
Richard A. Carter ◽  
Judith K. Cherry ◽  
...  
Keyword(s):  
Life Span ◽  
Binding Sites ◽  
Growth And Development ◽  
Annexin V ◽  
Normal Function ◽  
Healthy Human ◽  
Platelet Production ◽  
Platelet Counts ◽  
Development Factor ◽  
Human Volunteers

The effects of thrombopoietic stimulation on megakaryocytopoiesis, platelet production, and platelet viability and function were examined in normal volunteers randomized to receive single bolus subcutaneous injections of 3 μg/kg pegylated recombinant megakaryocyte growth and development factor (PEG-rHuMGDF) or placebo in a 3:1 ratio. PEG-rHuMGDF transiently doubled circulating platelet counts, from 237 ± 41 × 103/μL to 522 ± 90 × 103/μL (P< .0001), peaking on day 12. Baseline and day-12 samples showed no differences in responsiveness of platelets to adenosine diphosphate or thrombin receptor agonist peptide (P > .4 in all cases); expression of platelet ligand-induced binding sites or annexin V binding sites (P > .6 in both cases); or density of platelet TPO-receptors (P > .5). Platelet counts normalized by day 28. The life span of autologous 111In-labeled platelets increased from 205 ± 18 hours (baseline) to 226 ± 22 hours (P < .01) on day 8. Platelet life span decreased from 226 ± 22 hours (day 8) to 178 ± 53 hours (P < .05) on day 18. The theoretical basis for senescent changes in mean platelet life span was illustrated by biomathematical modeling. Platelet turnover increased from 43.9 ± 11.9 × 103 platelets/μL/d (baseline) to 101 ± 27.6 × 103 platelets/μL/d (P = .0009), and marrow megakaryocyte mass expanded from 37.4 ± 18.5 fL/kg to 62 ± 17 × 1010 fL/kg (P = .015). Although PEG-rHuMGDF initially increased megakaryocyte volume and ploidy, subsequently ploidy showed a transient reciprocal decrease when the platelet counts exceeded placebo values. In healthy human volunteers PEG-rHuMGDF transiently increases megakaryocytopoiesis 2-fold. Additionally, peripheral platelets expand correspondingly and exhibit normal function and viability during the ensuing 10 days. The induced perturbation in steady state thrombopoiesis resolves by 4 weeks.

Platelet and Fibrinogen Production: Effect of Lipid a and Liposomes

1979 ◽  
Author(s):  
R.B. Ramsey ◽  
B.L. Evatt ◽  
B.M. Alving ◽  
C.R. Alving ◽  
M.B. Hamner
Keyword(s):  
Lipid A ◽  
Intravenous Dose ◽  
The Other ◽  
Response Relationship ◽  
Single Intravenous Dose ◽  
Dose Response Relationship ◽  
Platelet Production ◽  
E Coli ◽  
Lipid Moiety ◽  
New Zealand Rabbits

Previous studies have demonstrated that endotoxin administered in a single intravenous dose produced increased platelet and fibrinogen production. To determine if the lipid moiety of the endotoxin was implicated, we studied the effect of intact endotoxin (E. coli 026:B6), lipid A, lipid A incorporated into liposomes, and lipid A solubilized in triethylamine (TEA) on platelet and fibrinogen production in male New Zealand rabbits. Animals received these preparations by single intravenous 1 h infusions of 1.0, 5.0, 10.0, 25.0, or 50.0 μg/kg body weight. Selenomethionine-75Se was injected 18 h after infusion, and the percentages of incorporation into platelet and fibrinogen were used to measure thrombopoiesis and fibrinogen synthesis. All 4 types of infusions increased both platelet production and fibrinogen synthesis and a dose-response relationship was observed; however, the threshold dose for stimulation varied with the type of material infused. More lipid A (by weight) was required to stimulate either platelets or fibrinogen than any of the other materials infused. When incorporated into liposomes or solubilized with TEA, lipid A produced a response similar to that produced by intact endotoxin. These data suggest that the lipid A moiety itself can stimulate platelet and fibrinogen production.

Treatment of Thrombocytopenia in Chimpanzees Infected With Human Immunodeficiency Virus by Pegylated Recombinant Human Megakaryocyte Growth and Development Factor

Blood ◽  
1998 ◽  
Vol 91 (12) ◽  
pp. 4427-4433 ◽  
Author(s):  
Laurence A. Harker ◽  
Ulla M. Marzec ◽  
Francis Novembre ◽  
I. Birgitta Sundell ◽  
Edmund K. Waller ◽  
...  
Keyword(s):  
Human Immunodeficiency Virus ◽  
Growth And Development ◽  
Serum Levels ◽  
Platelet Production ◽  
Platelet Counts ◽  
Viral Loads ◽  
Development Factor ◽  
Immunodeficiency Virus ◽  
Baseline Values ◽  
Normal Controls

Three chimpanzees experimentally infected with human immunodeficiency virus (HIV) developed significant chronic thrombocytopenia after 5, 4, and 2 years, with peripheral platelet counts averaging 64 ± 19 × 103/μL (P = .004 compared with 228 ± 92 × 103/μL in 44 normal control animals), mean platelet volumes of 11.2 ± 1.8 fL (P > .5 compared with 10.9 ± 0.7 fL in normal controls), endogenous thrombopoietin (TPO) levels of 926 ± 364 pg/mL (P < .001 compared with 324 ± 256 pg/mL in normal controls), uniformly elevated platelet anti-glycoprotein (GP) IIIa49-66 antibodies, and corresponding viral loads of 534, 260, and 15 × 103 RNA viral copies/mL. Pegylated recombinant human megakaryocyte growth and development factor (PEG-rHuMGDF) was administered subcutaneously (25 μg/kg twice weekly for 3 doses) to determine the effects of stimulating platelet production on peripheral platelet concentrations in this cohort of thrombocytopenic HIV-infected chimpanzees. PEG-rHuMGDF therapy increased (1) peripheral platelet counts 10-fold (from 64 ± 19 to 599 ± 260 × 103 platelets/μL;P = .02); (2) marrow megakaryocyte numbers 30-fold (from 11.7 ± 6.5 × 106/kg to 353 ± 255 × 106/kg;P = .04); (3) marrow megakaryocyte progenitor cells fourfold (from a mean of 3.6 ± 0.6 to 14.1 × 103 CFU-Meg/1,000 CD34+ marrow cells); and (4) serum levels of Mpl ligand from 926 ± 364 pg/mL (endogenous TPO) to predosing trough levels of 1,840 ± 353 pg/mL PEG-rHuMGDF (P = .02). The peripheral neutrophil counts were also transiently increased from 5.2 ± 2.6 × 103/μL to 9.9 ± 5.0 × 103/μL (P= .01), but neither the erythrocyte counts nor the reticulocyte counts were altered significantly (P > .1). The serum levels of antiplatelet GPIIIa49-66 antibodies exhibited reciprocal reductions during periods of thrombocytosis (P < .07). PEG-rHuMGDF therapy did not increase viral loads significantly (395, 189, and 53 × 103 RNA viral copies/mL; P > .5 compared with baseline values). The striking increase in peripheral platelet counts produced by PEG-rHuMGDF therapy implies that thrombocytopenia in HIV-infected chimpanzees is attributable to insufficient compensatory expansion in platelet production resulting from HIV-impaired delivery of platelets despite stimulated megakaryocytopoiesis. These data suggest that PEG-rHuMGDF therapy may similarly correct peripheral platelet counts in thrombocytopenic HIV-infected patients.

scholarly journals Dose-response effects of pegylated human megakaryocyte growth and development factor on platelet production and function in nonhuman primates

Blood ◽  
1996 ◽  
Vol 88 (2) ◽  
pp. 511-521 ◽  
Author(s):  
LA Harker ◽  
UM Marzec ◽  
P Hunt ◽  
AB Kelly ◽  
A Tomer ◽  
...  
Keyword(s):  
Platelet Aggregation ◽  
Dose Response ◽  
Growth And Development ◽  
Nonhuman Primates ◽  
Ex Vivo ◽  
Dependent Manner ◽  
Platelet Production ◽  
Development Factor ◽  
And Function

Thrombopoietin (TPO) is the physiologic Mpl-ligand regulating platelet production. Pegylated human recombinant megakaryocyte growth and development factor (PEG-rHuMGDF), a truncated polypeptide Mpl-ligand derivitized with poly-(ethylene glycol), induces megakaryocyte endoreduplication and proliferation in vitro and in vivo. In the present study, the dose-response effects of PEG-rHuMGDF on pharmacokinetics, megakaryocytopoiesis, platelet production, and platelet function were characterized for dosing 0.05, 0.10, 0.50, or 2.5 micrograms/kg/d in 22 baboons for 28 days. Daily subcutaneous injections of PEG-rHuMGDF produced linear log-dose responses in (1) steady-state trough plasma levels of PEG-HuMGDF (P < 10(-3)); (2) marrow megakaryocyte volume (P < 10(-3)), ploidy (P <10(-4)), and number (P < .01); and (3) peripheral platelet concentrations (P < 10(- 4)) and platelet mass turnover (P < 10(-3)). Platelet morphology, life span, and recovery were normal, and peripheral leukocyte, neutrophil, and erythrocyte counts were not significantly affected by PEG-rHuMGDF (P > .1 in all cases). PEG-rHuMGDF at 0.5 micrograms/kg/d produced similar blood concentrations of Mpl-ligand and platelets as 10 times the dose of rHu-MGDF (5.0 micrograms/kg/d), reflecting the extended plasma half-life achieved through pegylation. Whereas PEG-rHuMGDF did not induce platelet aggregation in vitro, platelet aggregatory responsiveness induced by thrombin receptor agonist peptide (TRAP1–6) and collagen was transiently enhanced ex vivo during the initial few days of PEG-rHuMGDF administration. However, adenosine diphosphate (ADP)-induced platelet aggregation was not enhanced ex vivo by PEG- rHuMGDF therapy. 111In-platelet deposition on segments of homologous endarterectomized aorta (EA) and vascular graft (VG) interposed in arteriovenous femoral shunts increased in direct proportion to the circulating platelet concentration (P < 10(-4) for both EA and VG); 125l-fibrin accumulation was not affected by PEG-rHuMGDF-induced increases in peripheral platelet counts. Changes in platelet production and function produced by PEG-rHuMGDF returned to baseline within 2 weeks after discontinuing treatment. Thus, in nonhuman primates, PEG- rHuMGDF increases platelet production in a linear log-dose-dependent manner by stimulating megakaryocyte endoreduplication and new megakaryocyte formation from marrow hematopoietic progenitors. These findings suggest that appropriate dosing of PEG-rHuMGDF therapy during periods of chemotherapy-induced marrow suppression may maintain hemostatic concentrations of peripheral platelets without increasing the risk of thrombosis.

scholarly journals Platelet number and function in response to a single intravenous dose of vincristine

2021 ◽  
Author(s):  
Erin C. Allen ◽  
Jaime L. Tarigo ◽  
Dana N. LeVine ◽  
Jamie P. Barber ◽  
Benjamin M. Brainard
Keyword(s):  
Intravenous Dose ◽  
Single Intravenous Dose ◽  
Platelet Number ◽  
And Function

scholarly journals Regulation of platelet production and function by megakaryocyte growth and development factor in nonhuman primates

Blood ◽  
1996 ◽  
Vol 87 (5) ◽  
pp. 1833-1844 ◽  
Author(s):  
LA Harker ◽  
P Hunt ◽  
UM Marzec ◽  
AB Kelly ◽  
A Tomer ◽  
...  
Keyword(s):  
Binding Sites ◽  
Growth And Development ◽  
Vascular Graft ◽  
Nonhuman Primates ◽  
Ex Vivo ◽  
Platelet Production ◽  
Development Factor ◽  
Platelet Deposition ◽  
And Function

The primary physiologic regulator of platelet production, Mpl ligand, has recently been cloned and characterized. To define the regulatory role of Mpl ligand on platelet production and function we measured the effects of a recombinant truncated human Mpl ligand, megakaryocyte growth and development factor (rHu-MGDF) on megakaryocytopoiesis, platelet function, and thrombogenesis in nonhuman primates. rHu-MGDF was administered to 10 baboons for 28 days while performing pharmacokinetics and repeated measurements of the following: (1) platelet count, volume, turnover, and function ex vivo and in vitro; (2) marrow megakaryocyte number, volume, and ploidy; and (3) platelet deposition and fibrin accumulation on segments of vascular graft and endarterectomized aorta in vivo. Daily subcutaneous injections of rHu- MGDF (5 microgram/kg/d) attained plasma concentrations averaging 1,300 +/- 300 pg/mL 2 hours after injection with trough levels of 300 +/- 65 pg/mL before the next dose. These levels of rHu-MGDF incrementally increased the peripheral platelet concentration threefold by day 7 and fivefold by day 28 (P < 10(-4)) associated with a reciprocal decrease of 25% in mean platelet volumes (P < 10(-3)). Platelet mass turnover, a steady-state measure of platelet production, increased fivefold (P < 10(-4)). Platelet morphology, life span, and recovery were normal. No significant change occurred in peripheral leukocyte, neutrophil, or erythrocyte counts (P > .1 in all cases). The platelet count gradually returned to baseline within 2 weeks after discontinuing rHu-MGDF infections. Marrow megakaryocyte volume doubled (P < 10(-3)) three days after initiating rHu-MGDF therapy and the modal ploidy shifted from 16N to 64N (P < 10(-4)). Marrow megakaryocyte number increased twofold by day 7, and nearly fourfold by day 28 (P < 10(-4)), resulting in a 6.5- fold increase in marrow megakaryocyte mass (P < 10(-3)). The effects of rHu-MGDF on thrombosis were determined by comparing baseline, day 5, and day 28 rHu-MGDF-treatment measurements of 111In-platelet deposition and 125I-fibrin accumulation on segments of homologous endarterectomized aorta (EA) and vascular graft (VG) interposed in arteriovenous femoral shunts. rHu-MGDF increased 111In-platelet deposition in direct proportion to the circulating concentration of platelets for both EA and VG (r=.98 in both cases), without significant changes in fibrin accumulation (P > .5 in both cases). During the first week of rHu-MGDF treatment ex vivo platelet aggregatory responsiveness was enhanced to physiologic agonists (adenosine diphosphate, collagen, and thrombin receptor agonist peptide, TRAP1–6) (P < .05 in all cases). Although in vitro platelet aggregation was not induced by any concentration of rHu-MGDF tested (P > .5), rHu-MGDF enhanced aggregatory responses to low doses of physiologic agonists, effects that were maximal at 10 ng/mL for baboon platelets and 100 ng/mL for human platelets, and were blocked by excess soluble c-Mpl receptor. Flow cytometric expression of platelet activation epitopes was not increased on resting platelets (ligand-induced binding sites, P- selectin, or Annexin V binding sites; P > .1 in all cases). Megakaryocyte growth and development factor regulates platelet production and function by stimulating endoreduplication and megakaryocyte formation from marrow progenitor cells, and transiently enhancing platelet functional responses ex vivo. rHu-MGDF has the potential for achieving platelet hemostatic protection with minimal thrombo-occlusive risk.

Treatment of Thrombocytopenia in Chimpanzees Infected With Human Immunodeficiency Virus by Pegylated Recombinant Human Megakaryocyte Growth and Development Factor

Blood ◽  
1998 ◽  
Vol 91 (12) ◽  
pp. 4427-4433 ◽  
Author(s):  
Laurence A. Harker ◽  
Ulla M. Marzec ◽  
Francis Novembre ◽  
I. Birgitta Sundell ◽  
Edmund K. Waller ◽  
...  
Keyword(s):  
Human Immunodeficiency Virus ◽  
Growth And Development ◽  
Serum Levels ◽  
Platelet Production ◽  
Platelet Counts ◽  
Viral Loads ◽  
Development Factor ◽  
Immunodeficiency Virus ◽  
Baseline Values ◽  
Normal Controls

Abstract Three chimpanzees experimentally infected with human immunodeficiency virus (HIV) developed significant chronic thrombocytopenia after 5, 4, and 2 years, with peripheral platelet counts averaging 64 ± 19 × 103/μL (P = .004 compared with 228 ± 92 × 103/μL in 44 normal control animals), mean platelet volumes of 11.2 ± 1.8 fL (P &gt; .5 compared with 10.9 ± 0.7 fL in normal controls), endogenous thrombopoietin (TPO) levels of 926 ± 364 pg/mL (P &lt; .001 compared with 324 ± 256 pg/mL in normal controls), uniformly elevated platelet anti-glycoprotein (GP) IIIa49-66 antibodies, and corresponding viral loads of 534, 260, and 15 × 103 RNA viral copies/mL. Pegylated recombinant human megakaryocyte growth and development factor (PEG-rHuMGDF) was administered subcutaneously (25 μg/kg twice weekly for 3 doses) to determine the effects of stimulating platelet production on peripheral platelet concentrations in this cohort of thrombocytopenic HIV-infected chimpanzees. PEG-rHuMGDF therapy increased (1) peripheral platelet counts 10-fold (from 64 ± 19 to 599 ± 260 × 103 platelets/μL;P = .02); (2) marrow megakaryocyte numbers 30-fold (from 11.7 ± 6.5 × 106/kg to 353 ± 255 × 106/kg;P = .04); (3) marrow megakaryocyte progenitor cells fourfold (from a mean of 3.6 ± 0.6 to 14.1 × 103 CFU-Meg/1,000 CD34+ marrow cells); and (4) serum levels of Mpl ligand from 926 ± 364 pg/mL (endogenous TPO) to predosing trough levels of 1,840 ± 353 pg/mL PEG-rHuMGDF (P = .02). The peripheral neutrophil counts were also transiently increased from 5.2 ± 2.6 × 103/μL to 9.9 ± 5.0 × 103/μL (P= .01), but neither the erythrocyte counts nor the reticulocyte counts were altered significantly (P &gt; .1). The serum levels of antiplatelet GPIIIa49-66 antibodies exhibited reciprocal reductions during periods of thrombocytosis (P &lt; .07). PEG-rHuMGDF therapy did not increase viral loads significantly (395, 189, and 53 × 103 RNA viral copies/mL; P &gt; .5 compared with baseline values). The striking increase in peripheral platelet counts produced by PEG-rHuMGDF therapy implies that thrombocytopenia in HIV-infected chimpanzees is attributable to insufficient compensatory expansion in platelet production resulting from HIV-impaired delivery of platelets despite stimulated megakaryocytopoiesis. These data suggest that PEG-rHuMGDF therapy may similarly correct peripheral platelet counts in thrombocytopenic HIV-infected patients.

Effects of megakaryocyte growth and development factor on platelet production, platelet life span, and platelet function in healthy human volunteers

Blood ◽  
2000 ◽  
Vol 95 (8) ◽  
pp. 2514-2522 ◽  
Author(s):  
Laurence A. Harker ◽  
Lorin K. Roskos ◽  
Ulla M. Marzec ◽  
Richard A. Carter ◽  
Judith K. Cherry ◽  
...  
Keyword(s):  
Life Span ◽  
Binding Sites ◽  
Growth And Development ◽  
Annexin V ◽  
Normal Function ◽  
Healthy Human ◽  
Platelet Production ◽  
Platelet Counts ◽  
Development Factor ◽  
Human Volunteers

Abstract The effects of thrombopoietic stimulation on megakaryocytopoiesis, platelet production, and platelet viability and function were examined in normal volunteers randomized to receive single bolus subcutaneous injections of 3 μg/kg pegylated recombinant megakaryocyte growth and development factor (PEG-rHuMGDF) or placebo in a 3:1 ratio. PEG-rHuMGDF transiently doubled circulating platelet counts, from 237 ± 41 × 103/μL to 522 ± 90 × 103/μL (P&lt; .0001), peaking on day 12. Baseline and day-12 samples showed no differences in responsiveness of platelets to adenosine diphosphate or thrombin receptor agonist peptide (P &gt; .4 in all cases); expression of platelet ligand-induced binding sites or annexin V binding sites (P &gt; .6 in both cases); or density of platelet TPO-receptors (P &gt; .5). Platelet counts normalized by day 28. The life span of autologous 111In-labeled platelets increased from 205 ± 18 hours (baseline) to 226 ± 22 hours (P &lt; .01) on day 8. Platelet life span decreased from 226 ± 22 hours (day 8) to 178 ± 53 hours (P &lt; .05) on day 18. The theoretical basis for senescent changes in mean platelet life span was illustrated by biomathematical modeling. Platelet turnover increased from 43.9 ± 11.9 × 103 platelets/μL/d (baseline) to 101 ± 27.6 × 103 platelets/μL/d (P = .0009), and marrow megakaryocyte mass expanded from 37.4 ± 18.5 fL/kg to 62 ± 17 × 1010 fL/kg (P = .015). Although PEG-rHuMGDF initially increased megakaryocyte volume and ploidy, subsequently ploidy showed a transient reciprocal decrease when the platelet counts exceeded placebo values. In healthy human volunteers PEG-rHuMGDF transiently increases megakaryocytopoiesis 2-fold. Additionally, peripheral platelets expand correspondingly and exhibit normal function and viability during the ensuing 10 days. The induced perturbation in steady state thrombopoiesis resolves by 4 weeks.

scholarly journals Regulation of platelet production and function by megakaryocyte growth and development factor in nonhuman primates

Blood ◽  
1996 ◽  
Vol 87 (5) ◽  
pp. 1833-1844 ◽  
Author(s):  
LA Harker ◽  
P Hunt ◽  
UM Marzec ◽  
AB Kelly ◽  
A Tomer ◽  
...  
Keyword(s):  
Binding Sites ◽  
Growth And Development ◽  
Vascular Graft ◽  
Nonhuman Primates ◽  
Ex Vivo ◽  
Platelet Production ◽  
Development Factor ◽  
Platelet Deposition ◽  
And Function

Abstract The primary physiologic regulator of platelet production, Mpl ligand, has recently been cloned and characterized. To define the regulatory role of Mpl ligand on platelet production and function we measured the effects of a recombinant truncated human Mpl ligand, megakaryocyte growth and development factor (rHu-MGDF) on megakaryocytopoiesis, platelet function, and thrombogenesis in nonhuman primates. rHu-MGDF was administered to 10 baboons for 28 days while performing pharmacokinetics and repeated measurements of the following: (1) platelet count, volume, turnover, and function ex vivo and in vitro; (2) marrow megakaryocyte number, volume, and ploidy; and (3) platelet deposition and fibrin accumulation on segments of vascular graft and endarterectomized aorta in vivo. Daily subcutaneous injections of rHu- MGDF (5 microgram/kg/d) attained plasma concentrations averaging 1,300 +/- 300 pg/mL 2 hours after injection with trough levels of 300 +/- 65 pg/mL before the next dose. These levels of rHu-MGDF incrementally increased the peripheral platelet concentration threefold by day 7 and fivefold by day 28 (P < 10(-4)) associated with a reciprocal decrease of 25% in mean platelet volumes (P < 10(-3)). Platelet mass turnover, a steady-state measure of platelet production, increased fivefold (P < 10(-4)). Platelet morphology, life span, and recovery were normal. No significant change occurred in peripheral leukocyte, neutrophil, or erythrocyte counts (P > .1 in all cases). The platelet count gradually returned to baseline within 2 weeks after discontinuing rHu-MGDF infections. Marrow megakaryocyte volume doubled (P < 10(-3)) three days after initiating rHu-MGDF therapy and the modal ploidy shifted from 16N to 64N (P < 10(-4)). Marrow megakaryocyte number increased twofold by day 7, and nearly fourfold by day 28 (P < 10(-4)), resulting in a 6.5- fold increase in marrow megakaryocyte mass (P < 10(-3)). The effects of rHu-MGDF on thrombosis were determined by comparing baseline, day 5, and day 28 rHu-MGDF-treatment measurements of 111In-platelet deposition and 125I-fibrin accumulation on segments of homologous endarterectomized aorta (EA) and vascular graft (VG) interposed in arteriovenous femoral shunts. rHu-MGDF increased 111In-platelet deposition in direct proportion to the circulating concentration of platelets for both EA and VG (r=.98 in both cases), without significant changes in fibrin accumulation (P > .5 in both cases). During the first week of rHu-MGDF treatment ex vivo platelet aggregatory responsiveness was enhanced to physiologic agonists (adenosine diphosphate, collagen, and thrombin receptor agonist peptide, TRAP1–6) (P < .05 in all cases). Although in vitro platelet aggregation was not induced by any concentration of rHu-MGDF tested (P > .5), rHu-MGDF enhanced aggregatory responses to low doses of physiologic agonists, effects that were maximal at 10 ng/mL for baboon platelets and 100 ng/mL for human platelets, and were blocked by excess soluble c-Mpl receptor. Flow cytometric expression of platelet activation epitopes was not increased on resting platelets (ligand-induced binding sites, P- selectin, or Annexin V binding sites; P > .1 in all cases). Megakaryocyte growth and development factor regulates platelet production and function by stimulating endoreduplication and megakaryocyte formation from marrow progenitor cells, and transiently enhancing platelet functional responses ex vivo. rHu-MGDF has the potential for achieving platelet hemostatic protection with minimal thrombo-occlusive risk.

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