Stimulatory effects of neopterin on hematopoiesis in vitro are mediated by activation of stromal cell function

Medical significance of simultaneous application of red blood cell distribution width (RDW) and neopterin as diagnostic/prognostic biomarkers in clinical practice

In our individual and collaborative studies, we have played a part in pioneering investigations on the usefulness of biomarkers – red blood cell distribution width (RDW) and neopterin. This mini review includes historical data on the topic and is related to the first contributions in this field, as well as to the possibilities for further improvement and simultaneous application of RDW and neopterin measurements in the prevention, prognosis and treatment of a great number of socially important disease conditions (arterial, cardiovascular, brain vascular, peripheral artery diseases, inflammations, autoimmune states, cancers and leukemias, addictions, etc.). When comparing the results obtained with the immunobiochemical biomarker neopterin with RDW, they are reported to be very similar as independent predictors of the same pathological states in the human body although their biomedical origins are very different. Both the parameters were until now successfully, but only separately used in medical practice. The combined use of these two biomarkers can shed some more light on their interrelationships and provide some clues as to how the interaction between immune system activation and red blood cells biology are intertwined.

Tetrahydrobiopterin determines vascular remodeling through enhanced endothelial cell survival and regeneration

BACKGROUND

Endothelial cell (EC) survival and regeneration are important determinants of the response to vascular injury that leads to neointimal hyperplasia and accelerated atherosclerosis. Nitric oxide (NO) is a key regulator of EC and endothelial progenitor cell function, but the pathophysiological mechanisms that regulate endothelial NO synthase in endothelial regeneration remain unclear.

METHODS AND RESULTS

Endothelium-targeted overexpression of GTP cyclohydrolase (GCH) I increased levels of the endothelial NO synthase cofactor, tetrahydrobiopterin, in an EC-specific manner and reduced neointimal hyperplasia in experimental vein grafts in GCH/apolipoprotein E-knockout mice. These effects were mediated through enhanced donor-derived survival and recipient-derived repopulation of GCH transgenic ECs, revealed by tracking studies in Tie2-LacZ/GCH-Tg/apolipoprotein E-knockout recipient mice or donor grafts, respectively. Endothelial GCH overexpression increased endothelial NO synthase coupling and enhanced the proliferative capacity of ECs and circulating endothelial progenitor cell numbers after vascular injury.

CONCLUSIONS

These observations indicate that endothelial tetrahydrobiopterin availability modulates neointimal hyperplasia after vascular injury via accelerated EC repopulation and growth. Targeting tetrahydrobiopterin-dependent endothelial NO synthase regulation in the endothelium is a rational therapeutic target to enhance endothelial regeneration and reduce neointimal hyperplasia in vascular injury states.

Neopterin, inflammation-associated product, prolongs erythropoiesis suppression in aged SAMP1 mice due to senescent stromal-cell impairment

Anemia induced by inflammation is well known to be more serious in the elderly than in non-elderly adults; however, the reason why this is so remains unclear. Neopterin produced by monocytes during inflammation promotes myelopoiesis but suppresses B-lymphopoiesis and erythropoiesis, by activating stromal cells in mice. Here, age-related changes in the erythropoietic response to neopterin were determined using senescence accelerated mice (SAMP1) with senescence stromal-cell impairment. Intravenous injection of neopterin into young mice (8-12 weeks old) resulted in a decrease in erythroid progenitor cell number in the bone marrow (BM), concomitant with an increase in myeloid progenitor cell number over one week. Intravenous injection of neopterin into aged mice (30-36 weeks old) resulted in a prolonged decrease in erythroid progenitor cell number in the BM over three weeks and a limited increase in myeloid progenitor cell number over one day. Neopterin treatment induced a decrease in serum erythropoietin concentrations in young mice but not in aged mice. The gene expression of tumor necrosis factor α (TNF-α), a negative regulator of erythropoiesis, was up-regulated in the BM of both young and aged mice, and the degree of TNF-α up-regulation was the same in both groups. The gene expression of interleukin (IL)-11, a positive regulator of erythropoiesis, was also up-regulated over one day in both young and aged mice. However, IL-11 gene expression remained up-regulated thereafter in young mice, whereas it was rapidly down-regulated in aged mice. These data suggest that prolonged suppression of erythropoiesis in aged mice may be due to a decrease in the production of positive regulators rather than to an increase in the production of negative regulators. Our combined data suggest that age-related impairment of stromal cells induces serious anemia in the elderly during inflammation.

Inflammatory biomarker, neopterin, predominantly enhances myelopoiesis, which suppresses erythropoiesis via activated stromal cells

Neopterin is produced by monocytes and is a useful biomarker for inflammation. We found previously that neopterin enhanced myelopoiesis but suppressed B-lymphopoiesis triggered by the positive and negative regulations of cytokines produced by stromal cells in mice. The effects of neopterin on erythropoiesis during the enhancement of myelopoiesis were determined in the present study using C57BL/6J mice. The intravenous injection of neopterin into mice resulted in a prolonged decrease in the number of femoral erythroid progenitor cells (BFU-Es and CFU-Es), whereas the number of femoral myeloid progenitor cells (CFU-GMs) was increased. Interestingly, the oscillatory changes in the number of erythroid progenitor cells were reciprocal to those of myeloid progenitor cells. The expression of Cdc42, a regulator of the balance between erythropoiesis and myelopoiesis, was down-regulated, implying that the suppression of erythropoiesis is due to myelopoietic predominance. Furthermore, the expression of SDF-1 in stromal cells, a negative regulator of erythropoiesis, was up-regulated. These results suggest that neopterin facilitates myelopoiesis in the bone marrow by suppressing erythropoiesis, thereby contributing to the potential up-regulation of inflammatory process.

Inflammatory biomarker, neopterin, enlarges splenic mast-cell-progenitor pool: Prominent impairment of responses in age-related stromal cell-impairment mouse SCI/SAM

Neopterin is produced by monocytes and is a useful biomarker of inflammatory responses. We found that neopterin enhances granulopoiesis, but suppresses B-lymphopoiesis triggered by the positive and negative regulations of cytokines produced by stromal cells in mice. In this study, neopterin was found to regulate mast cell development, which was confirmed in the mouse model of senescent stromal-cell impairment (SCI). In non-SCI mice (=less senescent stage of SCI mice), neopterin decreased the number of colonies of IL-3-dependent mast-cell progenitor cells (CFU-mast) from unfractionated bone-marrow cells, but not that from the lineage-negative bone-marrow cell population without stromal cells in a semisolid in vitro system. Neopterin increased the gene expression and protein production of TGF-beta, a negative regulator of CFU-mast, in cultured stromal cells, indicating that neopterin suppressed CFU-mast colony formation by inducing TGF-beta in stromal cells. In contrast to this in vitro study, in vivo treatment with neopterin did not significantly up-regulate TGF-beta. The intravenous injection of neopterin into mice decreased the number of femoral CFU-mast and the expression level of the gene for stem cell factor (SCF), a positive regulator of CFU-mast, whereas the number of splenic CFU-mast and SCF gene expression level increased. In SCI mice, the in vivo and in vitro responses of mast cell development and cytokine gene expression level to neopterin treatment were less marked than those in non-SCI mice. These results suggest that, firstly, neopterin augments the splenic pool of CFU-mast by the production of SCF, and secondly, such neopterin function becomes impaired during senescence because of an impaired stromal-cell function, resulting in the down-modulation of host-defense mechanisms.

Use of neopterin as a bone marrow hematopoietic and stromal cell growth factor in tissue-engineered devices

The in vitro response of early haematopoietic progenitors or stem cells (CD34+)--common for myeloid (granulocyte, eosinophil, megakaryocyte) and marrow stromal cell lineages, to neopterin, exogenously added to the liquid mouse bone marrow cultures, at doses 12.5-25 microg/ml culture medium, has been studied. The results obtained show a significant stimulation of common--myeloid and stromal/ mesenchymal progenitor cell proliferation and differentiation, as early as 24h to the 96h after the in vitro treatment with neopterin. On day 4 of cultivation the granulocyte/macrophageal proliferation and differentiation has been attenuated giving place to the marrow stromal/mesenchymal cell growth and differentiation. A functional role of neopterin as hematopoietic growth factor--essential for the proliferation and differentiation of bone marrow common (hematopoietic and stromal) progenitors is not yet clear and remains to be elucidated. The in vitro and ex vivo applying of neopterin--alone or in specific combinations with other cytokines (e.g. FGF-2) for the induction of marrow stromal/mesenchymal cell proliferation and differentiation, merits further investigations with regards to its future use in regenerative medicine. The results provide a theoretical basis for the application of neopterin in tissue-engineered devices: incorporated into biodegradable polymer microparticles (with encapsulated early bone marrow progenitors and other special supplements), it could be experimentally applied for fast and easy induction of endothelial, osteoblastic/osteogenic, neuronal and other cell lineage differentiation as well as for improving tissue trophical processes and reparative microenvironment.

Effects of Neopterin on the Hematopoietic Microenvironment of Senescence-Accelerated Mice (SAM)

The pteridine neopterin (NP) is produced by monocytes and is known to be a useful marker of immunological activation, although, it remains elusive whether neopterin itself exhibits biological functions. Recently, we found that NP stimulates hematopoietic cell proliferation and differentiation by activating bone marrow stromal cell function. In order to elucidate the biological effect of NP on stromal cells, its effects on hematopoiesis was determined in the mouse model of age-related stromal impairment, senescence-accelerated mice (SAMs). An intraperitoneal administration of NP increased the number of peripheral leukocytes and CFU-GM in the bone marrow and spleen of young SAMs, however, no increase of CFU-GM in old SAMs (stromal impairment) was observed when compared with young SAMs. NP also increased the CFU-GM colony formation of bone marrow and spleen cells from young SAMs in a soft agar culture system, but it did not enhance CFU-GM colony formation of cells from old SAMs cultured in this system. Treatment with NP induced the production of hematopoietic stimulating factors, including IL-6 and GM-CSF, by bone marrow stromal cells from young SAMs but stromal cells from old SAMs did not respond to NP stimulation. Further studies will be required to clarify the mechanism by which NP stimulates the production of hematopoietic growth factors from stromal cells, the results of this study indicate that NP is a potent hematopoietic regulatory factor by activating stromal cell function(s).

Effects produced by Royal Jelly on haematopoiesis: relation with host resistance against Ehrlich ascites tumour challenge

Royal jelly (RJ) was shown to exhibit immunomodulatory properties, although its biological activity is still unclear. In order to elucidate the mechanism whereby RJ activates the immunological system, we examined the role of this substance on the haematopoietic response of Ehrlich ascites tumour (EAT)-bearing mice. Our results demonstrated that RJ prevented the myelosupression induced by the temporal evolution of the tumour and abrogated the splenic haematopoiesis observed in EAT-bearing mice. The stimulating effect of RJ was also observed in vitro on the multipotent bone marrow stem cells, evaluated by the long-term bone marrow cultures (LTBMCs). The study of survival clearly showed the antitumour activity of RJ. Treatment was given prophylactically for 20 days and therapeutically for 3, 8 and 13 days. Except for the treatment with the lower dose of 500 mg/kg, given for 23 days, all the other dose schedules were able to prolong survival. A more effective antitumoural response was observed with the more prolonged treatment regimen. In this regard, the administration of RJ for 33 days produced the highest protection reaching an extension of survival at about 38%, 71% and 85% for the doses of 500, 1000 and 1500 mg/kg, respectively, whereas with the 23 and 28 days treatment schedules, survival increased at a rate of 19% and 23%, respectively, and comparable results were found among the effective doses of RJ. Increased survival rate might be related to the decreased Prostaglandin E2 (PGE2) levels observed in EAT-bearing mice after RJ treatment. These results point to RJ as a promising modifier of biological response leading to myeloprotection and antitumour activity.

The effects and the mechanism of YSEC-CM on the growth of yolk sac hematopoietic stem/progenitor cells

To explore the distinct background of bone marrow and embryonic yolk sac hematopoiesis performance, serum free murine yolk sac endothelial cell and bone marrow endothelial cell conditioned medium were compared for their effects on the development profiles of yolk sac hematopoietic stem/progenitor cells. The mRNAs expression techniques were applied to understand the cytokine and receptor genes expression and the possible mechanisms. The results suggested that the differential gene expressions were existed between the hematopoietic cells of yolk sac and bone marrow and between the microenvironment of yolk sac and bone marrow.

Ehrlich Ascites Tumor as a Tool in the Development of Compounds with Immunomodulatory Properties

In previous works, we have demonstrated that the myeloprotective properties of several natural and synthetic compounds are partly responsible for their antitumor activity in the Ehrlich ascites tumor (EAT) model. In this work, we present information that may be useful to the study of pharmacological and toxicological properties of compounds that affect the hematological compartment. Clonogenic studies in EAT-inoculated mice demonstrated a rapid decrease in bone marrow CFU-GM, whereas a progressive increase in splenic CFU-GM and cellularity was observed, followed by splenomegaly. Bone marrow cellularity declined on the third day after tumor challenge, returning to normal values thereafter. Serum from EAT-bearing mice produced detectable colony-stimulating activity in vitro. Similar results were observed with the conditioned medium from Ehrlich tumor cell cultures, but not with the cell-free Ehrlich tumor ascitic fluid. Tumor inoculation also resulted in a more striking depletion in the number of non-adherent cells in long-term bone marrow cell cultures (LTBMCs) with no bone marrow stroma formation. We speculate that the physiological alterations induced by the EAT growth can be used to assess the ability of compounds to modulate the hematopoietic response.

Allergenic sensitization prevents upregulation of haemopoiesis by cyclo-oxygenase inhibitors in mice

1. We evaluated whether immunization affects bone-marrow responses to indomethacin, because allergenic sensitization and challenge upregulate responses to haemopoietic cytokines (including IL-5-driven eosinopoiesis) in murine bone-marrow, while indomethacin upregulates haemopoiesis and protects bone-marrow from radiation damage. 2. Progenitor (semi-solid) and/or precursor (liquid) cultures were established from bone-marrow of: (a) normal mice; (b) ovalbumin-sensitized mice, with or without intranasal challenge. Cultures were established with GM-CSF (2 ng ml(-1)) or IL-5 (1 ng ml(-1)), respectively, alone or associated with indomethacin (10(-7) - 10(-11) M) or aspirin (10(-7) - 10(-8) M). Total myeloid colony numbers and numbers of eosinophil-peroxidase-positive cells were determined at day 7. 3. In naïve BALB/c mice, indomethacin (10(-7) - 10(-9) M) increased GM-CSF-stimulated myeloid colony formation (P=0.003 and P=0.009, respectively). In contrast, it had no effect on bone-marrow of ovalbumin-sensitized and challenged mice. Indomethacin (10(-7) - 10(-9) M) also increased eosinophil precursor responses to IL-5 in bone-marrow of naïve (P<0.001 and P=0.002 respectively), but not sensitized-challenged mice. Aspirin (10(-7) M) had similar effects, equally abolished by sensitization. Enhancement of haemopoiesis by indomethacin required adherent cells from naïve bone-marrow. Nonadherent cells responded to IL-5 but not to indomethacin. Indomethacin was effective on bone-marrow from sham-sensitized, ovalbumin-challenged, but not from sensitized, saline-challenged mice. Plasma transfer from immune mice abolished eosinophil precursor responses to indomethacin in bone-marrow of naïve recipients. This was not prevented by previous removal of antibody from immune plasma. 4. COX inhibitors enhance haemopoiesis in naïve but not allergic mice. Responsiveness to indomethacin can be abolished either by active sensitization or by immune plasma transfer. Specific antibody is not involved.

Neopterin measurement in clinical diagnosis

Neopterin is a marker associated with cell-mediated immunity. It is produced in monocytes/macrophages primarily upon stimulation with interferon-gamma. Due to its chemical structure, neopterin belongs to the class of pteridines. It is excreted in an unchanged form via the kidneys. Serum levels above 10 nmol/L are regarded as elevated. The levels of neopterin in body fluids are elevated in infections, autoimmune diseases, malignancies, allograft rejection, cardiac and renal failure, coronary artery disease and myocardial infarction. Neopterin measurements not only provide an insight into the present state of cell-mediated immune response but also allow monitoring and prognosis of disease progression.