Effect of cytokines and growth factors on the macrophage colony-stimulating factor secretion by human bone marrow stromal cells

Hypoxic Preconditioning Improves the Therapeutic Potential of Aging Bone Marrow Mesenchymal Stem Cells in Streptozotocin-Induced Type-1 Diabetic Mice

Insulin replacement is the current therapeutic option for type-1 diabetes. However, exogenous insulin cannot precisely represent the normal pattern of insulin secretion. Another therapeutic strategy is transplantation of pancreatic islets, but this is limited by immune rejection, intrinsic complications, and lack of donor availability. Stem cell therapy that results in the regeneration of insulin-producing cells represents an attractive choice. However, with advancing age, stem cells also undergo senescence, which leads to changes in the function of various cellular processes that result in a decrease in the regeneration potential of these aging stem cells. In this study, the effect of young and aging mesenchymal stem cells (MSCs) on the regeneration of pancreatic beta cells in streptozotocin (STZ)-induced type-1 diabetic mice was observed after hypoxic preconditioning. Hypoxia was chemically induced by 2, 4-dinitrophenol (DNP). Plasma insulin and glucose levels were measured at various time intervals, and pancreatic sections were analyzed histochemically. The effect of DNP was also analyzed on apoptosis of MSCs by flow cytometry and on gene expression of certain growth factors by quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR). We observed that hypoxic preconditioning caused changes in the gene expression levels of growth factors in both young and aging MSCs. Young MSCs showed significant regeneration potential compared with the aging cells in vivo. However, hypoxic preconditioning was able to improve the regeneration potential of aging MSCs. It is concluded from the present study that the regeneration potential of aging MSCs into pancreatic β-cells can be enhanced by hypoxic preconditioning, which causes changes in the gene expression of certain growth factors.

Application of stem cell/growth factor system, as a multimodal therapy approach in regenerative medicine to improve cell therapy yields

Stem cells hold a great promise for regenerative medicine, especially for replacing cells in infarcted organ that hardly have any intrinsic renewal capacity, including heart and brain. Signaling pathways that regulate pluripotency or lineage-specific gene and protein expression have been the major focus of stem cell research. Between them, there are some well known signaling pathways such as GF/GFR systems, SDF-1α/CXC4 ligand receptor interaction and PI3K/Akt signaling, and cytokines may regulate cell fate decisions, and can be utilized to positively influence cell therapy outcomes or accentuate synergistic compliance. For example, contributing factors in the progression of heart failure are both the loss of cardiomyocytes after myocardial infarction, and the absence of an adequate endogenous repair signaling. Combining cell engraftment with therapeutic signaling factor delivery is more exciting in terms of host progenitor/donor stem cell survival and proliferation. Thus stem cell-based therapy, besides triggering signaling pathways through GF/GFR systems can become a realistic option in regenerative processes for replacing lost cells and reconstituting the damaged organ, as before.

MSCs transplantation with application of G-CSF reduces apoptosis or increases VEGF in rabbit model of myocardial infarction

The purpose of this study was to test whether mesenchymal stem cells (MSCs) transplantation with application of granulocyte colony-stimulating factor (G-CSF) would have beneficial effects on damaged heart in a rabbit model of myocardial infarction (MI). MI was created by ligation of the left anterior descending coronary artery. After induction of MI, 40 New Zealand white rabbits were randomly divided into 8 groups: (1) MSCs injection at 3 days after MI; (2) G-CSF injection at 3 days after MI; (3) MSCs + G-CSF (20 u/kg/day) injection at 3 days after MI; (4) PBS injection at 3 days after MI; (5) MSCs injection at 7 days after MI; (6) G-CSF injection at 7 days after MI; (7) MSCs + G-CSF (20 u/kg/day) injection 7 days after MI; and (8) PBS injection 7 days after MI. TUNEL analysis showed that the apoptotic cells were distributed in the marginal area of MI. In both 3 and 7 days after MI groups, there were less apoptotic cells in the MSCs and MSCs + G-CSF groups as compared with the PBS group (P < 0.05). However, no decrease in apoptosis was observed in the G-CSF only group (P > 0.05). Immunohistochemistry analysis demonstrated that the expression level of vascular endothelial growth factor was higher in the MSCs, MSCs + G-CSF and G-CSF groups as compared with the PBS group. The present study demonstrated a beneficial effect of MSCs transplantation with application of G-CSF in the treatment of rabbit MI.

Infusion of Trx-1-overexpressing hucMSC prolongs the survival of acutely irradiated NOD/SCID mice by decreasing excessive inflammatory injury

A protective reagent for ARI should have the ability to repair injured tissue caused by radiation and prevent continuous damage from secondary risk factors. Trx-1 was explored as a candidate therapy for ARI, as it scavenges reactive oxygen species, regulates cell growth and differentiation, participates in immune reactions, and inhibits apoptosis by acting inside and/or outside cells. Trx-1 can also decrease excessive inflammation in ARI by regulating the creation of inflamed media, by inhibiting the activation of complement, and by reducing the chemotaxis, adhesion, and migration of inflammatory cells. As effectively and stably expressing exogenous genes in the long term and regulating immune inflammation and tissue repair, MSC are a good choice for Trx-1 gene therapy. In this study, Trx-1-overexpressing hucMSC-Trx-1 were obtained by adenoviral vector-mediated infection. We first measured the redox capacity of hucMSC-Trx-1 with an antioxidant capacity (T-AOC) assay, a hydrogen peroxide (H2O2) content determination assay in vivo, a H2O2-induced oxidation hemolysis assay, and a lipid peroxidation assay in vitro. Then, we measured survival time, the protection of the hematopoietic system, and the regulation of inflammation in important organs in three treatment groups of NOD/SCID mice (treated with hucMSC-Trx-1, with hucMSC, and with saline) that were exposed to 4.5 Gy (60)Co-γ-ray radiation. The hucMSC-Trx-1 group achieved superior antioxidation results, protecting bone marrow hematopoietic stem cells (Lin(-)CD117(+): hucMSC-Trx-1 vs. hucMSC, P<0.05; hucMSC-Trx-1 vs. NS, P<0.01), promoting the formation of red blood cells and hemoglobin (hucMSC-Trx-1 vs. hucMSC or NS, P<0.05), reducing inflammation and damage in important organs (Bone marrow and lung: hucMSC-Trx-1 vs. NS, P<0.01; hucMSC-Trx-1 vs. hucMSC, P<0.05. Liver and intestine: hucMSC-Trx-1 vs. NS, P<0.05; hucMSC-Trx-1 vs. hucMSC, P<0.05), and prolonging survival (hucMSC-Trx-1 vs. hucMSC or NS, P<0.01). Therefore, hucMSC-Trx-1 combines the merits of gene and cell therapy as a multifunctional radioprotector for ARI.

Stromal cell-derived factor-1 receptor CXCR4-overexpressing bone marrow mesenchymal stem cells accelerate wound healing by migrating into skin injury areas

Stromal cell-derived factor-1 (SDF-1) and its membrane receptor C-X-C chemokine receptor type 4 (CXCR4) are involved in the homing and migration of multiple stem cell types, neovascularization, and cell proliferation. This study investigated the hypothesis that bone marrow-derived mesenchymal stem cells (BMSCs) accelerate skin wound healing in the mouse model by overexpression of CXCR4 in BMSCs. We compared SDF-1 expression and skin wound healing times of BALB/c mice, severe combined immunodeficiency (SCID) mice, and immune system-deficient nude mice after (60)Co radiation-induced injury of their bone marrow. The occurrence of transplanted adenovirus-transfected CXCR4-overexpressing male BMSCs in the wound area was compared with the occurrence of untransfected male BALB/c BMSCs in (60)Co-irradiated female mice skin wound healing areas by Y chromosome marker analyses. The wound healing time of BALB/c mice was 14.00±1.41 days, whereas for the nude and SCID mice it was 17.16±1.17 days and 19.83±0.76 days, respectively. Male BMSCs could be detected in the surrounding areas of (60)Co-irradiated female BALB/c mice wounds, and CXCR4-overexpressing BMSCs accelerated the wound healing time. CXCR4-overexpressing BMSCs migrate in an enhanced manner to skin wounds in a SDF-1-expression-dependent manner, thereby reducing the skin wound healing time.

Bone marrow derived mesenchymal stem cells from aged mice have reduced wound healing, angiogenesis, proliferation and anti-apoptosis capabilities

Decline in the function of stem cells with age, such as other cells of the body, results in an imbalance between loss and renewal. Increasing age of the donor thus diminishes the effectiveness of MSCs (mesenchymal stem cells) transplantation in age-related diseases. The clinical use of stem cell therapies needs autologous stem cell transplantation; it is essential therefore to study the repair ability and survivability of cells before transplantation. Bone marrow derived MSCs possess multi-lineage differentiation potential, but aging adversely affects their therapeutic efficacy. MSCs from young (2-3 months) and aged (23-24 months) GFP (green fluorescent protein)-expressing C57BL/6 mice were isolated and their regenerative potential was assessed in vitro. Real-time RT-PCR (reverse transcriptase-PCR) showed significantly higher expression of Sirt1 in MSCs isolated from young than older animals. Down-regulation of VEGF (vascular endothelial growth factor), SDF-1 (stromal-cell-derived factor 1), AKT (also known as protein kinase B) and up-regulation of p53, p21, Bax and p16 occurred in aged cells. Tube formation, wound healing and proliferative abilities of the young MSCs were better than the aged MSCs. The results suggest that age-related increased expression of apoptotic and senescent genes, with concomitant decrease in Sirt1 gene expression, inhibits to some extent stem cell functioning.

Supernatant of bone marrow mesenchymal stromal cells induces peripheral blood mononuclear cells possessing mesenchymal features

Increasing evidence shows that some cells from peripheral blood fibroblast-like mononuclear cells have the capacity to differentiate into mesenchymal lineages. However, the insufficiency of these cells in the circulation challenges the cell isolation and subsequently limits the clinical application of these cells. In the present study, the peripheral blood mononuclear cells (pbMNCs) were isolated from wound animals and treated with the supernatant of bone marrow mesenchymal stromal cells (bmMSCs). Results showed these pbMNCs were fibroblast-like, had stromal morphology, were negative for CD34 and CD45, but positive for Vimentin and Collagen I, and had the multipotency to differentiate into adipocytes and osteoblasts. We named these induced peripheral blood-derived mesenchymal stromal cells (ipbMSCs). Skin grafts in combination with ipbMSCs and collagen I were applied for wound healing, and results revealed ipbMSC exhibited similar potency and effectiveness in the promotion of wound healing to the bmMSCs. Hereafter, we speculate that the mixture of growth factors and chemokines secreted by bmMSCs may play an important roles in the induction of the proliferation and mesenchymal differentiation of mononuclear cells. Our results are clinically relevant because it provide a new method for the acquisition of MSCs which can be used as a candidate for the wound repair.

Expression of cardiac function genes in adult stem cells is increased by treatment with nitric oxide agents

Mesenchymal stem cells (MSCs) have received special attention for cardiomyoplasty because several studies have shown that they differentiate into cardiomyocytes both in vitro and in vivo. Nitric oxide (NO) is a free radical signaling molecule that regulates several differentiation processes including cardiomyogenesis. Here, we report an investigation of the effects of two NO agents (SNAP and DEA/NO), able to activate both cGMP-dependent and -independent pathways, on the cardiomyogenic potential of bone marrow-derived mesenchymal stem cells (BM-MSCs) and adipose tissue-derived stem cells (ADSCs). The cells were isolated, cultured and treated with NO agents. Cardiac- and muscle-specific gene expression was analyzed by indirect immunofluorescence, flow cytometry, RT-PCR and real-time PCR. We found that untreated (control) ADSCs and BM-MSCs expressed some muscle markers and NO-derived intermediates induce an increased expression of some cardiac function genes in BM-MSCs and ADSCs. Moreover, NO agents considerably increased the pro-angiogenic potential mostly of BM-MSCs as determined by VEGF mRNA levels.

M-CSF signals through the MAPK/ERK pathway via Sp1 to induce VEGF production and induces angiogenesis in vivo

Background

M-CSF recruits mononuclear phagocytes which regulate processes such as angiogenesis and metastases in tumors. VEGF is a potent activator of angiogenesis as it promotes endothelial cell proliferation and new blood vessel formation. Previously, we reported that in vitro M-CSF induces the expression of biologically-active VEGF from human monocytes.

Methodology and Results

In this study, we demonstrate the molecular mechanism of M-CSF-induced VEGF production. Using a construct containing the VEGF promoter linked to a luciferase reporter, we found that a mutation reducing HIF binding to the VEGF promoter had no significant effect on luciferase production induced by M-CSF stimulation. Further analysis revealed that M-CSF induced VEGF through the MAPK/ERK signaling pathway via the transcription factor, Sp1. Thus, inhibition of either ERK or Sp1 suppressed M-CSF-induced VEGF at the mRNA and protein level. M-CSF also induced the nuclear localization of Sp1, which was blocked by ERK inhibition. Finally, mutating the Sp1 binding sites within the VEGF promoter or inhibiting ERK decreased VEGF promoter activity in M-CSF-treated human monocytes. To evaluate the biological significance of M-CSF induced VEGF production, we used an in vivo angiogenesis model to illustrate the ability of M-CSF to recruit mononuclear phagocytes, increase VEGF levels, and enhance angiogenesis. Importantly, the addition of a neutralizing VEGF antibody abolished M-CSF-induced blood vessel formation.

Conclusion

These data delineate an ERK- and Sp1-dependent mechanism of M-CSF induced VEGF production and demonstrate for the first time the ability of M-CSF to induce angiogenesis via VEGF in vivo.

Bone marrow-derived mesenchymal stem cells for treatment of heart failure: is it all paracrine actions and immunomodulation?

Despite significant advances in medical and surgical management of heart failure, mostly of ischaemic origin, the mortality and morbidity associated with it continue to be high. Pluripotent stem cells are being evaluated for treatment of heart failure. Bone marrow-derived mesenchymal stem cells (MSCs) have been extensively studied. Emerging evidence suggests that locally delivered MSCs can lead to an improvement in ventricular function, but the cellular and molecular mechanisms involved remain unclear. Myocardial regeneration, as proposed by many researchers as the underlying mechanism, has failed to convince the scientific community. Recently some authors have ascribed improvement in ventricular function to paracrine actions of MSCs.A lot has been written about the host immune response triggered by embryonic stem cells and the consequent need for immunosuppression. Not enough work has been done on immune interactions involving allogeneic bone marrow cells. Full potential of stem cell therapy can be realised only when we are able to use allogeneic cells. The potential use of MSCs in cellular therapy has recently prompted researchers to look into their interaction with the host immune response. MSCs have immunomodulatory properties. They cause suppression of proliferation of alloreactive T cells in a dose-dependent manner.Tissue injury causes inflammation and release of several chemokines, cytokines and growth factors. They can cause recruitment of bone marrow-derived MSCs to the injured area. We review the literature on paracrine actions and immune interactions of allogeneic MSCs.

The effects of G-CSF and naproxen sodium on the serum TGF-beta1 level and fracture healing in rat tibias

Local and systemic release of transforming growth factor beta 1 (TGF-beta1) is known to increase during the process of fracture healing and this cytokine stimulates bone healing. The majority of the non steroidal anti inflammatory drugs (NSAIDs) inhibit fracture healing. Granulocyte colony stimulating factor (G-CSF) is a hematopoietic growth factor that stimulates bone marrow. In this study, the effects of the NSAID naproxen sodium, G-CSF, and both of them in combination on the TGF-beta1 serum level in rats with tibia fractures were measured and fracture healing was evaluated by histopathologic and radiologic examination. The TGF-beta1 serum levels obtained on day one (24 h after fracture but before administration of naproxen or G-CSF) were found to be similar in all of the five groups (p > 0.05). At the end of the first week, TGF-beta1 levels were significantly lower in naproxen-treated rats than those of the other groups excluding control (p = 0.002). Similar changes in TGF-beta1 levels were found at the end of the second and fourth weeks. TGF-beta1 levels were significantly higher in G-CSF-treated rats at the end of the first, second and fourth weeks (p < 0.05). Fracture healing scores measured with histopathological and radiological methods were higher in G-CSF-treated rats than in naproxen-treated ones. When both naproxen and G-CSF were given, the scores resumed to normal. The results point to the negative effect of naproxen sodium on fracture healing is due to its decreasing effect on the level of TGF-beta1, which may be a new possible mechanism. Moreover, this negative effect can be inhibited by the use of G-CSF.

Human periodontal ligament cells secrete macrophage colony-stimulating factor in response to tumor necrosis factor-alpha in vitro

BACKGROUND

Human periodontal ligament (HPDL) cells may support osteoclastogenesis by expressing receptor activator of nuclear factor-kappa B ligand (RANKL) in response to periopathogenic factors and inflammatory cytokines. Because osteoclastogenesis requires the presence of macrophage colony-stimulating factor (M-CSF), we examined whether HPDL cells secrete M-CSF in response to tumor necrosis factor-alpha (TNF-alpha).

METHODS

Cultured HPDL cells were treated with TNF-alpha in serum-free condition. The expression of M-CSF and RANKL was determined by reverse transcription-polymerase chain reaction and enzyme-linked immunosorbent assay. Inhibitors and anti-TNF receptor (TNFR) neutralizing antibodies were used for the inhibitory experiments. A migration assay was performed.

RESULTS

TNF-alpha upregulated M-CSF and RANKL in HPDL cells. The effect on M-CSF expression could be partially blocked by pyrrolidine-dithiocarbamate ammonium salt and LY294002 but not by NS398. Neutralizing antibody to TNFR1 could diminish the effect of TNF-alpha. In addition, TNF-treated culture medium exhibited chemotactic effect for RAW264.7.

CONCLUSIONS

HPDL cells are capable of secreting M-CSF and expressing RANKL in response to TNF-alpha. The upregulation of M-CSF is possibly one of the mechanisms essential for periodontal tissue destruction in response to inflammatory cytokines. The upregulation is partly through nuclear factor-kappa B (NF-kappaB) and phosphatidylinositol 3'-kinase and possibly involves TNFR1.

Paracrine action enhances the effects of autologous mesenchymal stem cell transplantation on vascular regeneration in rat model of myocardial infarction

BACKGROUND

There are several reports that engrafted mesenchymal stem cells (MSCs) stimulate angiogenesis in the ischemic heart, but the mechanism remains controversial. We hypothesize that transplantation of MSCs enhances vascular regeneration through a paracrine action.

METHODS

A transmural myocardial infarction was created by ligation of the left anterior descending coronary artery in rats. Those with an ejection fraction less than 0.70 1 week after myocardial infarction were included. Autologous MSCs (1 x 10(7); 0.2 mL) or culture medium (0.2 mL) was injected intramyocardially into the periinfarct zone (50 microL/injection at four sites; n = 20/group). At 2 weeks after transplantation, Western blot analysis was used to assay the paracrine factors and proapoptotic proteins. Echocardiography to assess heart function was performed on additional groups at 8 weeks after implantation.

RESULTS

The angiogenic factors basic fibroblast growth factor, vascular endothelial growth factor, and stem cell homing factor (stromal cell-derived factor -1alpha) increased in the MSC-treated hearts compared with medium-treated hearts. This was accompanied by a downregulation of proapoptotic protein Bax in ischemic myocardium. Similarly, capillary density increased about 40% in MSC-treated hearts compared with medium-treated hearts (p = 0.001). Left ventricular contractility, indicated by fractional shortening, improved in MSC-treated hearts at 2 months after implantation (MSCs: 48.6% +/- 19.9%; medium: 18.7% +/- 6.4%; p = 0.004).

CONCLUSIONS

Autologous MSC transplantation attenuates left ventricular remodeling and improves cardiac performance. The major mechanism appears to be paracrine action of the engrafted cells, increasing angiogenesis and cytoprotection.

Angiotensin II stimulates arachidonic acid release from bone marrow stromal cells

INTRODUCTION

Angiotensin II (Ang II) is recognised as a regulator of haematopoiesis, but its actions within the bone marrow are not fully understood. Support of haematopoiesis by bone marrow stromal cells (MSC) is dependent on factors that include arachidonic acid and macrophage colony stimulating factor (MCSF), both of which are increased by Ang II stimulation in other tissues. To further elucidate the mechanisms of Ang II-regulated haematopoiesis, we determined whether Ang II-stimulation alters arachidonic acid release and MCSF secretion from MSC.

METHODS

Cynomolgus monkey MSC isolated from bone marrow aspirates and the human HS-5 stromal cell line were studied for Ang II-mediated arachidonic acid (AA) release, while secretion of MCSF in response to Ang II was studied in HS-5 cells. Cells were labelled overnight with 3H-AA and the release of 3H-AA was measured in culture medium following 20 minutes stimulation with Ang II, alone or in combination with the AT1- or AT2-receptor antagonists, losartan and PD 123319, respectively. MCSF secretion into culture medium was measured using an enzyme immunoassay following 24 hours of treatment with Ang II alone or in combination with losartan or PD 123319. Phorbol-myristate-acetate, known to stimulate release of AA and MCSF, was used as a positive control in both experiments.

RESULTS

In response to Ang II, release of 3H-AA from monkey and human MSC was increased (p<0.05) to 147+/-4% and 124+/-3% of control, respectively. The AT1- and AT2-receptor antagonists, losartan and PD 123319, individually reduced Ang II-stimulated 3H-AA release. In contrast, Ang II had no effect on secretion of MCSF from HS-5 cells.

CONCLUSIONS

These results provide mechanistic evidence for Ang II-mediated haematopoiesis through AA release that may, in part, explain Ang II-facilitated recovery of haematopoiesis in experimental myelosuppression and the anaemias associated with Ang II receptor blockade.

Autologous mesenchymal stem cell transplantation induce VEGF and neovascularization in ischemic myocardium

Neovascularization induced by vascular endothelial growth factor (VEGF) represents an appealing approach for treating ischemic heart disease. However, VEGF therapy has been associated with transient therapeutic effects and potential risk for hemangioma growth. Adult mesenchymal stem cells (MSCs) derived from bone marrow are a promising source for tissue regeneration and repair. In order to achieve a safe and persistent angiogenic effect, we have explored the potential of autologous MSCs transplantation to enhance angiogenesis and cardiac function of ischemic hearts. One week after myocardial infarction induced by occlusion of left anterior descending artery, autologous MSCs expanded in vitro was administrated intramyocardially into the infarct area of the same donor rats. By 2 months, MSCs implantation significantly elevated VEGF expression levels, accompanied by increased vascular density and regional blood flow in the infarct zone. The neovascularization resulted in a decreased apoptosis of hypertrophied myocytes and markedly improved the left ventricular contractility (ejection fraction: 79.9+/-7.6% vs. 37.2+/-6.9% in control animals). Therefore, mechanisms underlying MSCs improvement of cardiac functions may involve neovascularization induced by differentiation of MSCs to endothelial cells and para-secretion of growth factors, in addition to the apoptosis reduction and previously reported cardiomyocytes regeneration. Two months after cell transplantation, there are significant improvement of left ventricular function. Hence, autologous MSCs transplantation may represent a promising therapeutic strategy free of ethical concerns and immune rejection, for neovascularization in ischemic heart diseases.

Fluctuations in plasma macrophage colony-stimulating factor levels during autologous peripheral blood stem cell transplantation for haematologic diseases

Plasma macrophage colony-stimulating factor (M-CSF) levels were measured in 13 haematologic patients treated with autologous peripheral blood stem cell transplantation (PBSCT). Six of the patients showed an increase in M-CSF peak levels (>3000 pg/ml) during the conditioning and stem cell infusion period. The peak levels of M-CSF in this phase correlated with thrombomodulin levels, indicating the endothelial origin of plasma M-CSF. However, the M-CSF levels were not influenced by TNFalpha. More patients with high M-CSF levels (>5000 pg/ml) suffered from organ failure than those with lower M-CSF levels. These results suggest that high M-CSF levels may correlate with cellular or organ damage in patients treated with PBSCT.

Severe osteopenia in a young boy with Kostmann's congenital neutropenia treated with granulocyte colony-stimulating factor: suggested therapeutic approach

Kostmann's syndrome is a congenital disorder that causes an impairment of myeloid differentiation in the bone marrow characterized by severe neutropenia, which can be treated with recombinant human granulocyte colony-stimulating factor (G-CSF). We present the case of a 13-year-old boy with Kostmann's syndrome who was treated with recombinant human G-CSF from age 3.5 years. His growth and development was normal, although complicated by intermittent infections. Bone mineral density (BMD) measurement revealed severe osteopenia at the spine and hips (lumbar spine BMD 0.486 g/cm(2); Z score -3.6), and he was referred to the Endocrine Service. Relevant laboratory evaluation showed a pretreatment ionized calcium level at the upper limit of normal (1.28 mmol/L; range: 1.13-1.32 mmol/L), suppressed intact parathyroid hormone (iPTH) level (12 pg/mL; range: 10-65 pg/mL), and a low 1,25-dihydroxy vitamin D level (21 pg/mL; range: 24-65 pg/mL). He had evidence of increased bone turnover evidenced by elevated urinary deoxypyridinoline (DPD) cross-links (46.9 nmol/mmol creatinine; range: 2-34 nmol/mmol creatinine) and a simultaneous increase in markers of bone formation with elevated osteocalcin level (200 ng/mL; normal: 20-80 ng/mL) and alkaline phosphatase level (236 IU/mL; normal: 38-126 IU/mL). Because of clinical concern for his skeletal health, bisphosphonate therapy with intravenous pamidronate was initiated. One month after treatment, the iPTH and DPD cross-links were in the normal range (54 pg/mL and 17.7 nmol/mmol creatinine, respectively) and the 1,25-dihydroxy vitamin D level was elevated (111 pg/mL). Four months after treatment, there was a striking increase in BMD at the lumbar spine (+30.86%), femoral necks (left, +20.02%; right, +17.98%), and total hips (left, +18.40%; right, +15.94%). Seven months after bisphosphonate therapy, his biochemical parameters showed a return toward pretreatment levels with increasing urinary DPD cross-links (28.7 nmol/mmol creatinine) and decreasing iPTH (26 pg/mL). However, the BMD continued to increase (8 months posttreatment), but the magnitude of the increment was attenuated (lumbar-spine, +4.8%; left total hip, +1.2% and right total hip +2.4%), relative to BMD at 4 months. Eight months after the initial treatment, his iPTH was suppressed at 14 pg/mL and he again received pamidronate (at a lower dose); 3 months later, he had an additional increase in BMD (lumbar spine +7.4%, left total hip +3.9%, right total hip +2.7%), relative to the previous study. We hypothesize that prolonged administration of G-CSF as treatment for Kostmann's syndrome is associated with increased bone resorption, mediated by osteoclast activation and leading to bone loss. In children, the resulting osteopenia can be successfully managed with antisreorptive bisphosphonate therapy with significant improvement in bone density. Measurements of biochemical parameters of bone turnover can be used to monitor the magnitude and duration of the therapeutic response and the need for BMD reassessment and, perhaps, retreatment.