Placental extract protects bone marrow-derived stem/progenitor cells against radiation injury through anti-inflammatory activity

Subcutaneous Anti-inflammatory Therapies to Prevent Burn Progression in a Swine Model of Contact Burn Injury

INTRODUCTION

If left untreated, burn injuries can deepen or progress in depth within the first 72 hours after injury as a result of increased wound inflammation, subsequently worsening healing outcomes. This can be especially detrimental to warfighters who are constrained to resource-limited environments with delayed evacuation times to higher roles of care and more effective treatment. Preventing this burn progression at the point of injury has the potential to improve healing outcomes but requires a field-deployable therapy and delivery system. Subcutaneous therapies known to treat inflammation delivered local to the wound site may prove to be one such avenue for success.

MATERIALS AND METHODS

Seven Yorkshire-cross swine received partial-thickness burn injuries using a previously established contact burn model. Each animal received one of the seven therapies: (1) saline, (2) heparin, (3) ibuprofen, (4) erythropoietin, (5) resolvin, (6) rapamycin, and (7) placental extract, all of which are either currently employed or are experimental in field use and indicated to treat inflammation. Treatments were delivered subcutaneously on the day of injury and 24 hours post-injury to simulate a prolonged field care scenario, before potential evacuation. Animals and wound development were observed for 28 days before euthanasia. Throughout the course of the study, wounds were observed macroscopically via non-invasive imaging. Histological analyses provided the critical metric of burn progression. Treatment success criteria were designated as the ability to prevent burn progression past 80% of the dermal depth in two of the three treated wounds, a clinically relevant metric of burn progression.

RESULTS

It was determined that the applied model successfully created reproducible partial-thickness burn injuries in this porcine study. No significant differences with regard to lateral wound size or the rate of lateral wound closure were observed in any treatments. Several treatments including resolvin, rapamycin, ibuprofen, and erythropoietin successfully reduced burn progression to less than 80% of the dermal depth in two of the three wounds, 24 hours after injury.

CONCLUSIONS

This report employs an established model of porcine contact burn injury in order to test the ability of local subcutaneous delivery of therapeutics to prevent burn progression at the point of injury, via what is believed to be the inhibition of inflammation. Several treatments successfully prevented burn progression to a full-thickness injury, potentially improving wound healing outcomes in a simulated battlefield scenario. Subcutaneously administered therapies combating burn-induced inflammation at the point of injury may serve as a field-deployable treatment modality to improve warfighter recovery and return to duty.

The human neuroprotective placental protein composition suppressing tinnitus and restoring auditory brainstem response in a rodent model of sodium salicylate-induced ototoxicity

The effect of neuroprotective placental protein composition (NPPC) on the suppression of tinnitus and the restoration of the auditory brainstem response (ABR) characteristics was explored in tinnitus-induced rats. The animals were placed into two groups: (1) the study group, rats received sodium salicylate (SS) at the dose of 200 mg/kg twice a day for two weeks, and then 0.4 mg of the NPPC per day, between the 14th and 28th days, (2) the placebo group, rats received saline for two weeks, and then the NPPC alone between the 14th and 28th days. The gap pre-pulse inhibition of the acoustic startle (GPIAS), the pre-pulse inhibition (PPI), and the ABR assessments were performed on animals in both groups three times (baseline, day 14, and 28). The GPIAS value declined after 14 consecutive days of the SS injection, while NPPC treatment augmented the GPIAS score in the study group on the 28th day. The PPI outcomes revealed no significant changes, indicating hearing preservation after the SS and NPPC administrations. Moreover, some changes in ABR characteristics were observed following SS injection, including (1) higher ABR thresholds, (2) lowered waves I and II amplitudes at the frequencies of 6, 12, and 24 kHz and wave III at the 12 kHz, (3) elevated amplitude ratios, and (4) prolongation in brainstem transmission time (BTT). All the mentioned variables returned to their normal values after applying the NPPC. The NPPC use could exert positive therapeutic effects on the tinnitus-induced rats and improve their ABR parameters.

Plumping up a Cushion of Human Biowaste in Regenerative Medicine: Novel Insights into a State-of-the-Art Reserve Arsenal

Major breakthroughs and disruptive methods in disease treatment today owe their thanks to our inch by inch developing conception of the infinitive aspects of medicine since the very beginning, among which, the role of the regenerative medicine can on no account be denied, a branch of medicine dedicated to either repairing or replacing the injured or diseased cells, organs, and tissues. A novel means to accomplish such a quest is what is being called “medical biowaste”, a large assortment of biological samples produced during a surgery session or as a result of physiological conditions and biological activities. The current paper accentuating several of a number of promising sources of biowaste together with their plausible applications in routine clinical practices and the confronting challenges aims at inspiring research on the existing gap between clinical and basic science to further extend our knowledge and understanding concerning the potential applications of medical biowaste.

Effects of novel Fufang Biejia Ruangan Tablets with sheep placenta as substitute for hominis placenta on CCl4-induced liver fibrosis

Objective

Fufang Biejia Ruangan Tablet (FBRT) is widely used for the treatment of liver fibrosis. However, Hominis Placenta (HP), as an important adjuvant of FBRT, has been restricted for medicinal using due to the limited availability, ethical controversy and safety issues. The present study aimed to investigate the therapeutic effects of novel FBRT (N-FBRT) with sheep placenta (SP) as substitute for HP on liver fibrosis and explore its possible mechanisms. Different dosages of SP in N-FBRT were also evaluated.

Methods

Rats were subcutaneously injected with CCl₄ to induce liver fibrosis and then treated with N-FBRT and FBRT. The anti-hepatic fibrosis effect was determined based on biomarkers analysis of liver function and hepatic fibrosis, and the liver pathology was visualized by H&E staining and Masson staining. The oxidative stress and inflammatory cytokines were also detected. Immunohistochemical staining of α-SMA, real time PCR and Western blotting were performed to evaluate hepatic stellate cells (HSCs) activation and TGF-β1/Smad signaling pathway.

Results

N-FBRT and FBRT could ameliorate CCl₄-induced liver fibrosis and improve liver function, as evidenced by lowering serum biomarkers levels of liver function and hepatic fibrosis, and decreasing hepatic Hyp content and collagen deposition, and improving the hepatic morphology and architecture changes. Moreover, the anti-liver fibrosis effect was better when the dosage of SP used in N-FBRT was 1/2 of HP in FBRT. Administration of N-FBRT markedly alleviated oxidative stress and inflammatory cytokines, and inhibited α-SMA expression. Furthermore, the mRNA expression of Col I, Col III, α-SMA and TGF-β1, and proteins expression of α-SMA, TGF-β1, Smad2/3 and p-Smad2/3 were significantly down-regulated by N-FBRT treatment.

Conclusion

SP can be used as substitute for HP to prepare N-FBRT for the treatment of liver fibrosis and the anti-liver fibrosis effect of N-FBRT is achieved by eliminating oxidative stress and inflammation, and inhibiting HSCs activation and ECM production by blocking TGF-β1/Smad signaling pathway.

Extracellular Vesicles (Secretomes) from Human Trophoblasts Promote the Regeneration of Skin Fibroblasts

To date, placental trophoblasts have been of interest in the fields of obstetrics and gynecology, mainly due to their involvement in the formation of a connection between the mother and fetus that aids in placental development and fetal survival. However, the regenerative capacities of trophoblasts for application in regenerative medicine and tissue engineering are poorly understood. Here, we aim to determine the skin regeneration and anti-aging capacities of trophoblast-derived conditioned medium (TB-CM) and exosomes (TB-Exos) using human normal dermal fibroblasts (HNDFs). TB-CM and TB-Exos treatments significantly elevated the migration and proliferation potencies of HNDF cells in a dose- and time-dependent manner. When RNA sequencing (RNA-seq) was used to investigate the mechanism underlying TB-CM-induced cell migration on scratch-wounded HNDFs, the increased expression of genes associated with C-X-C motif ligand (CXCL) chemokines, toll-like receptors, and nuclear factor-kappa B (NF-κB) signaling was observed. Furthermore, treatment of intrinsically/extrinsically senescent HNDFs with TB-CM resulted in an enhanced rejuvenation of HNDFs via both protection and restoration processes. Gene expression of extracellular matrix components in the skin dermis significantly increased in TB-CM- and TB-Exos-treated HNDFs. These components are involved in the TB-CM and Exo-mediated regeneration and anti-aging of HNDFs. Thus, this study demonstrated the regenerative and anti-aging efficacies of trophoblast-derived secretomes, suggesting their potential for use in interventions for skin protection and treatment.

Allogenic Use of Human Placenta-Derived Stromal Cells as a Highly Active Subtype of Mesenchymal Stromal Cells for Cell-Based Therapies

The application of mesenchymal stromal cells (MSCs) from different sources, including bone marrow (BM, bmMSCs), adipose tissue (atMSCs), and human term placenta (hPSCs) has been proposed for various clinical purposes. Accumulated evidence suggests that the activity of the different MSCs is indirect and associated with paracrine release of pro-regenerative and anti-inflammatory factors. A major limitation of bmMSCs-based treatment for autologous application is the limited yield of cells harvested from BM and the invasiveness of the procedure. Similar effects of autologous and allogeneic MSCs isolated from various other tissues were reported. The easily available fresh human placenta seems to represent a preferred source for harvesting abundant numbers of human hPSCs for allogenic use. Cells derived from the neonate tissues of the placenta (f-hPSC) can undergo extended expansion with a low risk of senescence. The low expression of HLA class I and II on f-hPSCs reduces the risk of rejection in allogeneic or xenogeneic applications in normal immunocompetent hosts. The main advantage of hPSCs-based therapies seems to lie in the secretion of a wide range of pro-regenerative and anti-inflammatory factors. This renders hPSCs as a very competent cell for therapy in humans or animal models. This review summarizes the therapeutic potential of allogeneic applications of f-hPSCs, with reference to their indirect pro-regenerative and anti-inflammatory effects and discusses clinical feasibility studies.

Non-Cell-Autonomous Activity of the Hemidesmosomal Protein BP180/Collagen XVII in Granulopoiesis in Humanized NC16A Mice

BP180 (also termed type XVII collagen) is a hemidesmosomal protein and plays a critical role in cell-cell matrix adhesion in the skin; however, its other biological functions are largely unclear. In this study, we generated a BP180 functional-deficient mouse strain by deleting its extracellular domain of humanized NC16A (termed ΔNC16A mice). We found that BP180 is expressed by bone marrow mesenchymal stem cells (BM-MSC), and its functional deficiency leads to myeloid hyperplasia. Altered granulopoiesis in ΔNC16A mice is through bone marrow stromal cells evidenced by bone marrow transplantation. Furthermore, the level of G-CSF in bone marrow and circulation were significantly increased in ΔNC16A mice as compared with wild-type mice. The increased G-CSF was accompanied by an increased activation of the NF-κB signaling pathway in bone marrow and BM-MSC of ΔNC16A mice. Blockade of G-CSF restored normal granulopoiesis in ΔNC16A mice. Inhibition of NF-κB signaling pathway significantly reduces the release of G-CSF from ΔNC16A BM-MSC in vitro and the level of serum G-CSF in ΔNC16A mice. To our knowledge, these findings provide the first direct evidence that BP180 plays an important role in granulopoiesis through regulating NF-κB signaling pathway in BM-MSC.

Porcine placental extract facilitates memory and learning in aged mice

Aging induces a decline in both memory and learning ability without predisposing an individual to diseases of the central nervous system, such as dementia. This decline can have a variety of adverse effects on daily life, and it can also gradually affect the individual and the people they are surrounded by. Since recent evidence indicated that placental extract has effects on brain function such as memory, we hypothesized that placental extract could ameliorate the age-associated reduction in cognitive function in aging. Here, we investigated the effect of new modified porcine placental extract (SD-F) on memory ability in aged mice at both the behavioral and molecular levels. Our results revealed that SD-F significantly enhanced memory ability in the object recognition and object location tasks in a dose-dependent manner in aged mice relative to controls. The numbers of Nissl-positive cells in the hippocampal cornu ammonis 3 (CA3) and dentate gyrus (DG) regions were increased in SD-F-treated aged mice relative to controls. RNA-seq analysis of the hippocampus of aged mice identified 542 differentially expressed genes, of which 216 were up-regulated and 326 were down-regulated in SD-F-treated mice relative to controls. Of the 216 up-regulated genes, we identified four characteristic genes directly related to memory, including early growth response protein 1 (Egr1), growth arrest and DNA-damage-inducible, beta (Gadd45b), NGFI-A binding protein 2 (Nab2), and vascular endothelial growth factor a (Vegfa). These results suggest that the efficacy of SD-F involves upregulation of these genes.

Anti-inflammatory Effect of the Water-Soluble Portion of Porcine Placental Extract in Lipopolysaccharide-Stimulated RAW264.7 Murine Macrophage Cells

Porcine placental extract (PPE) is used as a nonprescription drug for analeptics and in health foods and cosmetics in Japan, Korea and China. It was reported that PPE has anti-oxidative and anti-inflammatory activities; however, the mechanisms and the responsible molecules involved in these activities are still unclear. Here, we investigated how enzymatically prepared PPE affects proinflammatory factors such as interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α in a cultured macrophage cell line, RAW264.7, when co-stimulated with lipopolysaccharide (LPS). Enhanced production of IL-1β, IL-6 and TNF-α by LPS was significantly reduced by the addition of PPE and these effects were dose dependent. Nitric oxide (NO) production induced in cultured macrophages by LPS was also inhibited by PPE. Real-time PCR after the reverse transcription of total RNAs isolated from cells treated with PPE revealed that the mRNA expressions of IL-1β, IL-6, TNFα, and NO synthase (NOS)-2 were reduced. The necessary concentration of PPE prepared by enzymatic digestion to mediate anti-inflammatory effects compared with the reported value of that extracted by phosphate buffered saline without digestion was proportional to the amount of extracted materials from the same amount of placenta (about 10-fold). This suggests that the molecules responsible for the anti-inflammatory activity exists in the placenta and can be extracted by phosphate buffered saline, and thus might survive enzymatic digestion.

Anti‑apoptotic effects of human placental hydrolysate against hepatocyte toxicity in vivo and in vitro

Apoptosis and oxidative stress are essential for the pathogenesis of acute liver failure and fulminant hepatic failure. Human placental hydrolysate (hPH) has been reported to possess antioxidant and anti-inflammatory properties. In the present study, the protective effects of hPH against D-galactosamine (D-GalN)- and lipopolysaccharide (LPS)-induced hepatocyte apoptosis were investigated in vivo. In addition, the molecular mechanisms underlying the anti-apoptotic activities of hPH against D-GalN-induced cell death in vitro were examined. Male Sprague-Dawley rats were injected with D-GaIN/LPS with or without the administration of hPH. Rats were sacrificed 24 h after D-GaIN/LPS intraperitoneal injection, and the blood and liver samples were collected for future inflammation and hepatotoxicity analyses. Changes in cell viability, apoptosis protein expression, mitochondrial mass, mitochondrial membrane potential, reactive oxygen species generation, and the levels of proteins and mRNA associated with a protective mechanism were determined in HepG2 cells pretreated with hPH for 2 h prior to D-GalN exposure. The findings suggested that hPH treatment effectively protected against D-GalN/LPS-induced hepatocyte apoptosis by reducing the levels of alanine aminotransferase, aspartate aminotransferase, lactate dehydrogenase, interleukin-6, and tumor necrosis factor-α, and increasing the level of proliferating cell nuclear antigen. It was also found that hPH inhibited the apoptotic cell death induced by D-GalN. hPH activated the expression of antioxidant enzymes, including superoxide dismutase, glutathione peroxidase, and catalase, which were further upregulated by the Kelch-like ECH2-associated protein 1-p62-nuclear factor-erythroid 2-related factor 2 pathway, a component of oxidative stress defense mechanisms. Furthermore, hPH markedly reduced cytosolic and mitochondrial reactive oxygen species and rescued mitochondrial loss and dysfunction through the reduction of damage-regulated autophagy modulator, p53, and C/EBP homologous protein. Collectively, hPH exhibited a protective role in hepatocyte apoptosis by inhibiting oxidative stress and maintaining cell homeostasis. The underlying mechanisms may be associated with the inhibition of endoplasmic reticulum stress and minimization of the autophagy progress.

PreImplantation factor (PIF) therapy provides comprehensive protection against radiation induced pathologies

Acute Radiation Syndrome (ARS) may lead to cancer and death and has few effective countermeasures. Efficacy of synthetic PIF treatment was demonstrated in preclinical autoimmune and transplantation models. PIF protected against inflammation and mortality following lethal irradiation in allogeneic bone marrow transplant (BMT) model. Herein, we demonstrate that PIF imparts comprehensive local and systemic protection against lethal and sub-lethal ARS in murine models. PIF treatment 2 h after lethal irradiation led to 100% survival and global hematopoietic recovery at 2 weeks after therapy. At 24 h after irradiation PIF restored hematopoiesis in a semi-allogeneic BMT model. PIF-preconditioning provided improved long-term engraftment. The direct effect of PIF on bone marrow cells was also demonstrated in vitro: PIF promoted pre-B cell differentiation and increased immunoregulatory properties of BM-derived mesenchymal stromal cells. PIF treatment also improved hematopoietic recovery and reduced systemic inflammatory cytokine production after sub-lethal radiation exposure. Here, PIF also prevented colonic crypt and basal membrane damage coupled with reduced nitric oxide synthetase (iNOS) and increased (B7h1) expression. Global upper GI gene pathway analysis revealed PIF's involvement in protein-RNA interactions, mitochondrial oxidative pathways, and responses to cellular stress. Some effects may be attributed to PIF's influence on macrophage differentiation and function. PIF demonstrated a regulatory effect on irradiated macrophages and on classically activated M1 macrophages, reducing inflammatory gene expression (iNOS, Cox2), promoting protective (Arg1) gene expression and inducing pro-tolerance cytokine secretion. Notably, synthetic PIF is stable for long-term field use. Overall, clinical investigation of PIF for comprehensive ARS protection is warranted.

Placenta and Placental Derivatives in Regenerative Therapies: Experimental Studies, History, and Prospects

Placental structures, capable to persist in a genetically foreign organism, are a natural model of allogeneic engraftment carrying a number of distinctive properties. In this review, the main features of the placenta and its derivatives such as structure, cellular composition, immunological and endocrine aspects, and the ability to invasion and deportation are discussed. These features are considered from a perspective that determines the placental material as a unique source for regenerative cell therapies and a lesson for immunological tolerance. A historical overview of clinical applications of placental extracts, cells, and tissue components is described. Empirically accumulated data are summarized and compared with modern research. Furthermore, we define scopes and outlooks of application of placental cells and tissues in the rapidly progressing field of regenerative medicine.

Effect of porcine placental extract on the mild menopausal symptoms of climacteric women

OBJECTIVES

This study assessed the effects of oral porcine placental extract (PPE) on the mild menopausal symptoms of climacteric women.

METHODS

In this 12-week, multicenter, randomized, double-blind, placebo-controlled, parallel-group study, 50 climacteric Japanese women were randomized 1 : 1 to oral PPE (300 mg/day) or placebo. Menopausal symptoms were evaluated by using the Simplified Menopausal Index (SMI), as were serum estradiol (E2) and follicle stimulating hormone (FSH) levels. Blood biochemical and cellular and urinary tests were done to evaluate safety aspects of repeated oral administration of PPE.

RESULTS

The total SMI score of the PPE group was significantly more improved after 12 weeks than that of the placebo group (p = 0.031). This score and three subscores (vasomotor, psychological, and somatic symptoms) were significantly improved at 8 and/or 12 weeks compared with the initial values in the PPE group (p < 0.05). E2 and FSH levels were not improved in either group. No adverse events were observed.

CONCLUSIONS

Oral PPE at 300 mg/day improved the mild menopausal symptoms of climacteric women. Since oral PPE did not improve serum E2 and FSH levels, PPE is thought not to ameliorate hormonal balance itself but to improve subjective feelings of climacteric women.

Ionizing radiation promotes CCL27 secretion from keratinocytes through the cross talk between TNF-α and ROS

The skin-associated chemokine CCL27 and its receptor CCR10 mediate the immune response of skin-homing T cells. The CCL27 secreted from keratinocytes was reportedly involved in inflammatory skin diseases such as atopic dermatitis, contact dermatitis, and psoriasis. However, whether ionizing radiation increases the levels of CCL27 secretion still remains unclear. In HaCaT cells, a human keratinocyte cell line, CCL27 secretion was markedly increased after X-ray irradiation. We further found that irradiation boosted the generation of reactive oxygen species (ROS), which was concomitant with the release of tumor necrosis factor-alpha (TNF-α). Moreover, alteration of ROS in irradiated HaCaT cells correlated with TNF-α secretion, indicating a positive loop of TNF-α secretion and ROS generation. This positive loop regulated the secretion of CCL27 from irradiated cells. We therefore concluded that the cross talk between TNF-α and ROS after keratinocytes was exposed to radiation, triggered CCL27 secretion for subsequent inflammation response.

Placenta Peptide Can Protect Mitochondrial Dysfunction through Inhibiting ROS and TNF-α Generation, by Maintaining Mitochondrial Dynamic Network and by Increasing IL-6 Level during Chronic Fatigue

Background: Level of fatigue is related to the metabolic energy available to tissues and cells, mainly through mitochondrial respiration, as well fatigue is the most common symptom of poorly functioning mitochondria. Hence, dysfunction of these organelles may be the cause of the fatigue seen in Chronic fatigue (CF). Placenta has been used for treatment of fatigue and various disease, moreover peptides has known protect mitochondrial viability, and alleviate fatigue. These properties of placenta and peptides may link with its effect on mitochondria; therefore, it is highly important to investigate the effectiveness of placenta peptide on fatigue and mitochondrial dysfunction. Methods: After administration of sheep placenta peptide (SPP) for 1 month, mice's were forced to swim till exhaustion for 90 min to induce chronic fatigue. Electron microscopic examination of skeletal muscle mitochondrial structure, tissue Malondialdehyde (MDA), mitochondrial SOD and serum inflammatory cytokines level were investigated in order to determine the potential effect of SPP on mitochondria during CF. Rat skeletal muscle (L6 cell) were also treated with different concentration of SPP to determine the effect of SPP on cell viability using Thiazoyl blue tetrazolium assay. Results: Our finding revealed that forced swimming induced fatigue model can cause mitochondrial damage through Reactive oxygen species (ROS) mediated lipid peroxidation and Tumor Necrosis factor alpha (TNF-α) elevation. Whereas SPP protected fatigue induced mitochondrial dysfunction through preventing ROS and TNF-α generation, by maintaining mitochondrial dynamic network and by increasing serum IL-6 level. Conclusion: SPP can protect damage in mitochondrial components which will allow proper functioning of mitochondria that will in turn inhibit progression of chronic fatigue. Therefore, SPP may represent a novel therapeutic advantage for preventing mitochondrial dysfunction in patients with chronic fatigue.

Treatment of radiation-induced acute intestinal injury with bone marrow-derived mesenchymal stem cells

The aim of the present study was to investigate the ability of bone marrow-derived mesenchymal stem cells (BMSCs) to repair radiation-induced acute intestinal injury, and to elucidate the underlying repair mechanism. Male Sprague-Dawley rats were subjected to whole abdominal irradiation using a single medical linear accelerator (12 Gy) and randomly assigned to two groups. Rats in the BMSC-treated group were injected with 1 ml BMSC suspension (2×10⁶ cells/ml) via the tail vein, while the control group rats were injected with normal saline. BMSCs were identified by detecting the expression of CD29, CD90, CD34 and CD45 using flow cytometry. The expression of the cytokines stromal cell-derived factor 1 (SDF-1), prostaglandin E2 (PGE2) and interleukin (IL)-2 was detected using immunohistochemical techniques. Plasma citrulline concentrations were evaluated using an ELISA kit. Rat general conditions, including body weight, and changes in cellular morphology were also recorded. The results suggested that BMSCs exerted a protective effect on radiation-induced acute intestinal injury in rats. The histological damage was rapidly repaired in the BMSC-treated group. In addition, the BMSC-treated group showed significantly reduced radiation injury scores (P<0.01), mildly reduced body weight and plasma citrulline levels, significantly more rapid recovery (P<0.01), significantly reduced expression of the cytokines PGE2 and IL-2 (P<0.05) and significantly increased SDF-1 expression (P<0.01) compared with the control group. In summary, the present results indicate that BMSCs are able to effectively reduce inflammation and promote repair of the structure and function of intestinal tissues damaged by radiation exposure, suggesting that they may provide a promising therapeutic agent.

Sensitivity and dose dependency of radiation-induced injury in hematopoietic stem/progenitor cells in mice

We evaluated the sensitivity and dose dependency of radiation-induced injury in hematopoietic stem/progenitor cells. Adult C57BL/6 mice were daily exposed to 0, 2, 10, 50, and 250 mGy γ-ray for 1 month in succession, respectively. The damage of hematopoietic stem/progenitor cells in bone marrow were investigated within 2 hours (acute phase) or at 3 months (chronic phase) after the last exposure. Daily exposure to over 10 mGy γ-ray significantly decreased the number and colony-forming capacity of hematopoietic stem/progenitor cells at acute phase, and did not completely recover at chronic phase with 250 mGy exposure. Interestingly, the daily exposure to 10 or 50 mGy γ-ray decreased the formation of mixed types of colonies at chronic phase, but the total number of colonies was comparable to control. Immunostaining analysis showed that the formation of 53BP1 foci in c-kit⁺ stem/progenitor cells was significantly increased with daily exposure to 50 and 250 mGy at acute phase, and 250 mGy at chronic phase. Many genes involved in toxicity responses were up- or down-regulated with the exposures to all doses. Our data have clearly shown the sensitivity and dose dependency of radiation-induced injury in hematopoietic stem/progenitor cells of mice with daily exposures to 2 ~ 250 mGy γ-ray.