Expression of high affinity binding sites for erythropoietin on L8057 cells, a mouse megakaryoblastic cell line, associated with cell differentiation

Erythropoietin in spinal cord injury

Spinal cord injury (SCI) is a devastating condition for individual patients and costly for health care systems requiring significant long-term expenditures. Cytokine erythropoietin (EPO) is a glycoprotein mediating cytoprotection in a variety of tissues, including spinal cord, through activation of multiple signaling pathways. It has been reported that EPO exerts its beneficial effects by apoptosis blockage, reduction of inflammation, and restoration of vascular integrity. Neuronal regeneration has been also suggested. In the present review, the pathophysiology of SCI and the properties of endogenous or exogenously administered EPO are briefly described. Moreover, an attempt to present the current traumatic, ischemic and inflammatory animal models that mimic SCI is made. Currently, a clearly effective pharmacological treatment is lacking. It is highlighted that administration of EPO or other recently generated EPO analogues such as asialo-EPO and carbamylated-EPO demonstrate exceptional preclinical characteristics, rendering the evaluation of these tissue-protective agents imperative in human clinical trials.

Pegylated recombinant human megakaryocyte growth and development factor suppresses the development of megakaryoblastic leukemia in mice

We examined the effects of pegylated recombinant human megakaryocyte growth and development factor (PEG-rHuMGDF) on the development of L-8057, a murine megakaryoblastic leukemia that expresses the thrombopoietin receptor c-Mpl, in mice. PEG-rHuMGDF administration prolonged survival of L-8057 leukemic mice, in which L-8057 cell growth in the spleen was decreased. L-8057 cells harvested from PEG-rHuMGDF-treated leukemic mice had decreased ability to generate leukemic colonies in vitro as well as to induce leukemia in vivo. PEG-rHuMGDF administration also resulted in prolonged survival of mice transplanted with a c-Mpl-expressing erythroleukemia, but had no effect on survival of mice transplanted with a myeloblastic leukemia that does not possess c-Mpl. Thus, PEG-rHuMGDF suppresses the development of c-Mpl-expressing leukemia in vivo in mice.

The Effect of Recombinant Human Erythropoietin on Platelet Counts Is Strongly Modulated by the Adequacy of Iron Supply

The effect of recombinant human erythropoietin (rHuEpo) on megakaryopoiesis remains controversial. Treatment with rHuEpo in renal failure patients has been associated with a slight elevation of platelet counts. In animal studies, high doses of rHuEpo produced an increase of platelet counts followed by a gradual return to normal after 7 to 15 days or even a substantial degree of thrombocytopenia. However, because iron deficiency is also known to be associated with thrombocytosis, (functional) iron deficiency during rHuEpo could be contributing to these observations. We investigated the impact of iron supply on changes in platelet counts induced by rHuEpo. Rats were either fed normal food (normal rats) or received 1% carbonyl iron for 2 weeks or 3 months, as well as during the experiment, to achieve iron supplementation or overload, respectively. Rats of all three categories then received daily intravenous injections of rHuEpo (10, 50, or 150 U) or normal saline (0 U) for 20 days. With 0 to 10 U rHuEpo, platelets remained stable. In normal rats receiving 50 to 150 U rHuEpo, platelets increased to 120% to 140% of baseline at 4 to 12 days to level off at 120% at 16 to 20 days. This response was less sustained in splenectomized animals. Iron-supplemented rats receiving 50 to 150 U rHuEpo also increased platelets initially, but the peak was at day 4, followed by a gradual return to baseline and even a moderate thrombocytopenia later on. Iron-overloaded rats receiving 50 to 150 U rHuEpo also had increased platelets at day 4, but the duration of platelet increase was shorter, and they experienced a more pronounced degree of thrombocytopenia in proportion to the dose of rHuEpo. Because the early elevation of platelets was of larger magnitude than hematocrit changes, it is unlikely that it could be accounted for by shrinkage of plasma volume. Because it was observed in all three iron conditions, there appears to be some direct positive effect of rHuEpo on platelet production. However, after this transient effect, expanded erythropoiesis appears to exert a negative impact upon platelet production. Secondary thrombocytopenia was not related to splenic pooling, and its very slow correction after cessation of rHuEpo therapy is not compatible with changes in platelet survival. Rather, it is consistent with stem cell competition between erythroid and megakaryocytic development. However, this secondary thrombocytopenia is masked by (functional) iron deficiency in rats not receiving an adequate iron supply from food or stores.

Effects of recombinant human granulocyte colony-stimulating factor on the growth potential of two murine myeloid leukemias

We investigated the in vitro and in vivo effects of recombinant human granulocyte colony-stimulating factor (rhG-CSF) on the proliferation of two murine leukemic cell lines. The rhG-CSF stimulated leukemic colony formation of the promyelocytic leukemic cell line L-8801 in methylcellulose culture and increased the number of L-8801 cells in liquid culture. However, rhG-CSF treatment prolonged the median survival period of mice implanted with L-8801 cells and the emergence of the leukemic blast cells in peripheral blood. Meanwhile, rhG-CSF had no influence on that of the megakaryoblastic leukemic cells L-8057 and failed to prolong the median survival period of L-8057 leukemic mice. Receptor binding analysis revealed that L-8801 cells expressed a G-CSF receptor (Kd=125 pM, 479 binding sites/cell) and L-8057 cells had no G-CSF receptors. Then, we examined the growth potential of these cells. The median survival period was longer for mice implanted with L-8801 cells cultured with rhG-CSF for 72 h in vitro than for cells grown without rhG-CSF. Furthermore, the median survival period of mice implanted with spleen cells from L-8801 leukemic mice treated with rhG-CSF was prolonged compared with those from leukemic mice without rhG-CSF. In contrast, there was no effect of rhG-CSF on the growth potential of the spleen from L-8057 leukemic mice. The results of our present study demonstrate that rhG-CSF reduced the growth of L-8801 leukemic cells in vitro and in vivo mediated through G-CSF receptors, thereby suppressing the development of leukemia.

Effects of erythropoietin, IL-3, IL-6 and LIF on a murine megakaryoblastic cell line: growth enhancement and expression of receptor mRNAs

We examined the effects of recombinant human erythropoietin (rhEPO), recombinant murine interleukin 3 (rmIL-3), recombinant human interleukin 6 (rhIL-6), recombinant human interleukin 11 (rhIL-11), recombinant murine leukemia inhibitory factor (rmLIF) and recombinant murine granulocyte-macrophage colony-stimulating factor (rmGM-CSF) on the growth of murine megakaryocytic cell lines. In serum-free methylcellulose culture supplemented with bovine serum albumin (BSA), the addition of rhEPO (0.1-10 U/ml), rmIL-3 (10-500 U/ml), rhIL-6 (100-10,000 U/ml), rmLIF (100-10,000 U/ml), or rmGM-CSF (10-1000 U/ml) enhanced colony growth in L8057Y5 cells, which had been maintained in protein-free culture, mostly in a dose-dependent fashion; rhIL-11 did not have any stimulatory effect at the tested doses (10-1000 U/ml). In addition, colony growth of L8057 cells, which had been maintained in serum-containing culture, was enhanced, but to a lesser extent, by the addition of these cytokines except rhEPO (the cultures were supplemented with 1% fetal bovine serum. Among the cytokines that showed growth-enhancing effects on L8057 cells, the expression of mRNAs encoding receptors for EPO, IL-6 and IL-3 was examined by northern blot analysis or reverse transcription polymerase chain reaction (RT-PCR). In both cell lines, mRNAs for EPO-R, IL-6R, gp130, IL-3R alpha and beta chains were constitutively expressed. The results suggest that L8057 and L8057Y5 cell lines have characteristics of megakaryoblastic cells in their biological responses to cytokines, as well as in the expression of cytokine receptor mRNAs, and that the growth-enhancing effects of these cytokines on the cell lines may be achieved through specific receptors. Our findings show the value of these cell lines for investigating the mechanisms of growth signal transduction in megakaryopoiesis.

Effect of recombinant human erythropoietin on platelets in patients with anemia of renal failure: correlation of platelet count with erythropoietic activity and iron parameters

We examined the effect of treatment with rHuEpo on platelet counts in 61 hemodialysis patients and correlated them with changes in erythropoietic activity, iron status and inflammation. Platelets (10(9)/1) increased from 220 +/- 80 to 245 +/- 102 after 14 days and stabilized at that level up to day 90 (p < 0.0001). The increment was similar in complete or partial responders but was not observed in failures. Serum transferrin receptor (sTfR, a measure of total erythropoiesis) and Het rose much more progressively, but relative platelet increments correlated with relative increases in sTfR and Hct. Relative platelet increments correlated inversely with relative changes of SeFe or transferrin saturation, but not with their absolute values, nor with baseline ferritin or its progressive decrease. Although baseline platelet count was 12% higher in patients with inflammation and correlated with serum haptoglobin, relative increases were similar in patients with or without inflammation. In conclusion, rHuEpo produced a clinically minor but consistent elevation of platelet counts. These modifications were not related primarily to modifications in iron stores, functional iron deficiency, or inflammation, but paralleled the expansion of erythropoietic activity. The results suggest that rHuEpo has a small positive effect on platelet production, but it cannot be ruled out that this could be partially mediated through functional iron deficiency.