Iron overload as a risk factor for poor graft function following allogeneic hematopoietic stem cell transplantation

Abstract

Hematological malignancies are increasingly treated with allogeneic hematopoietic stem cell transplantation (allo‐HSCT). Unfortunately, iron overload is a frequent adverse effect of allo‐HSCT and is associated with poor prognosis. In the present study, we investigated hematopoiesis in iron‐overloaded mice and elucidated the effects of iron overload on the bone marrow (BM) microenvironment. Iron‐overloaded BALB/C mice were generated by injecting 20 mg/mL saccharated iron oxide intraperitoneally. Hematoxylin‐eosin staining was performed to evaluate the effects of an iron overload in mice. BM cells obtained from C57BL/6 mice were transplanted into irradiated BALB/C mice (whole‐body irradiation of 4 Gy, twice with a 4‐hours interval) by tail vein injection. Two weeks after allo‐HSCT, the hematopoietic reconstitution capacity was evaluated in recipients by colony‐forming assays. Histopathological examinations showed brown‐stained granular deposits, irregularly arranged lymphocytes in the liver tissues, and blue‐stained blocks in the BM collected from mice received injections of high‐dose saccharated iron oxide (20 mg/mL). Iron‐overloaded mice showed more platelets, higher‐hemoglobin (HGB) concentration, fewer granulocyte‐macrophage colony‐forming units (CFU‐GM), erythrocyte colony‐forming units (CFU‐E), and mixed granulocyte/erythrocyte/monocyte/megakaryocyte colony‐forming units (CFU‐mix) than healthy mice. Iron‐overloaded recipients presented with reduced erythrocytes and HGB concentration in peripheral blood, along with decreased marrow stroma cells, CFU‐GM, CFU‐E, and CFU‐mix relative to healthy recipients. Taken together, our findings demonstrate that iron overload might alter the number of red blood cells after transplantation in mice by destroying the BM microenvironment, thereby affecting the recovery of BM hematopoietic function.

1. INTRODUCTION

Allogeneic hematopoietic stem cell transplantation (allo‐HSCT) is an effective treatment method for various malignant and nonmalignant hematological diseases. ¹ Poor graft function (PGF) remains a serious complication, which affects 5% to 27% of patients and contributes to a considerably high transplant‐related mortality, especially in the cases of unsatisfactory therapeutic outcomes for haploidentical donor HSCT. ² , ³ Despite significant improvements made in the prevention and treatment of complications postallo‐HSCT, PGF still occurs frequently due to many pre‐ and post‐transplantation factors, such as immunologically mediated graft rejection, ⁴ myelotoxic agents, ⁵ acute and chronic graft‐vs‐host disease, ⁶ T‐cell depletion, ⁷ viral infections, ⁸ conditioning regimen intensity, and stem cell sourcing. ⁹ , ¹⁰ In addition to these risk factors, impaired bone marrow (BM) microenvironment prior to allo‐HSCT may also delay the hematopoietic reconstitution of successfully engrafted donor hematopoietic stem cells (HSCs), resulting in the occurrence of PGF post‐allo‐HSCT.

HSCs residing in a carefully calibrated BM microenvironment are required for effective engraftment or hematopoiesis recovery. ¹¹ The BM microenvironment sustains homeostatic production of erythroid, myeloid or, lymphoid cells, as well as appropriate bone mass and health. Once disturbed, this microenvironment can increase the likelihood of hematological diseases occurrence. ¹² Therefore, more studies focusing on factors influencing the BM microenvironment are necessary in order to understand the development of allo‐HSCT. In particular, persistent impairment of BM microenvironment occurs in high‐dose chemotherapeutic and/or radiotherapeutic regimens used for treating hematologic malignancies. ¹³ In addition, requirements for high‐transfusion volumes in myelodysplastic syndromes (MDS) result in iron overload, which has been associated with poor survival in patients with MDS after allo‐HSCT. ¹⁴ Based on a recent murine study reporting BM microenvironment impairment in iron‐overloaded mice, ¹⁵ we set out to investigate this same process in the pathophysiology of PGF. In this study, we generated a model of iron‐overloaded mice transplanted with BM stromal cells and evaluated the effects of excessive iron on the hematopoietic reconstitution capacity.

2. MATERIALS AND METHODS

2.1. Ethics statement

The study was conducted in strict accordance with the Experimental Animal Ethics Committee of Fujian Provincial Key Laboratory of Hematologic Diseases in Fujian Medical University Union Hospital (Approval Number: 201803004). The animal experiment strictly adhered to the principle of using the least number of animals to complete the experiment and to minimize the pain of experimental animals.

2.2. Animals

In this study, 28 BALB/C male mice (16‐18 g; 4 weeks), 42 BALB/C male mice (18‐24 g; 8 weeks old), and 14 C57BL/6 pure male mice (age: 6 weeks) were all purchased from Shanghai SLAC Laboratory Animal Co., Ltd. (Shanghai, China), and raised in specific‐pathogen‐free conditions at the Animal Laboratory of Fujian Medical University Experimental Animal Center. All experimental mice were housed at seven mice per cage, and maintained under a constant temperature and humidity environment, with 12 hours light/dark cycle (08:00‐20:00) and with routine provision of food and water.

2.3. Establishment of iron overload mouse model

A total of 28 BALB/C pure mice aged 4 weeks old were randomly partitioned into a control group, a low‐dose group (5 mg/mL), a medium‐dose group (10 mg/mL), and a high‐dose group (20 mg/mL), with seven mice per group. Mice in the iron‐overloaded groups were intraperitoneally injected with 0.2 mL sucrose iron injection every other day for 12 times. Mice in the control group were intraperitoneally injected with an equivalent amount of normal saline at the same time. Meanwhile, the body weight, hair, activity, and behavior of mice were observed and recorded every week. The mice were euthanized after 4 weeks of injection.

2.4. Hematoxylin‐eosin staining

Mice were euthanized and hearts, livers, spleens, and lungs were harvested and weighed. Organ coefficient was expressed as the ratio of visceral organ weight to body weight. The liver and spleen tissues were fixed in 10% neutral formalin solution for 12 to 24 hours, dehydrated, paraffin‐embedded, sliced into 4‐mm sections, and heated at 65°C for 30 minutes to 1 hour. After being fixed in formalin, the femur was decalcified in decalcification solution for 12 to 24 hours. The sections were soaked two times in xylene (10 minutes each time) and dehydrated in a graded ethanol series (5 minutes each concentration). The tissue sections were then immersed in freshly prepared hematoxylin for 12 minutes, immersed in 1% HCl/ethanol mixtures for 2 seconds, and then immersed in ammonia for 5 seconds. After being stained with eosin for 30 seconds, the sections were soaked in 95% ethanol for 5 seconds and dried. The sections were placed into HCl/ethanol mixtures and soaked in 75% ethanol. The iron depositions in various viscera and BM, as well as the cell morphology of BM, were observed under a light microscope.

2.5. Enzyme‐linked immunosorbent assay

Before BM transplantation, blood was harvested from the mouse orbital inner canthus vein, allowed to stand at room temperature for 2 hours, and centrifuged to collect the supernatant. According to the instructions of mouse blood serum ferritin enzyme‐linked immunosorbent assay (ELISA) kits (Abcam, Cambridge, UK), serum was added to a 96‐well plates and incubated at room temperature for 60 minutes. Unbound proteins and impurities were then washed off with buffer solution. Afterward the serum was incubated with enzyme‐labeled antibody at room temperature for 10 minutes in the dark, followed by the addition of the color developing solution at room temperature for 10 minutes in the dark. Next, the reaction termination solution was added into the wells. The optical density at 450 nm was detected by a microplate reader, and a standard curve was plotted to calculate the sample concentration.

2.6. Prussian blue staining of BM

The BM sections were deparaffinized and washed with distilled water. Potassium ferrate and hydrochloric acid solution were mixed in equal volumes to prepare the staining solution. The sections were rinsed in the staining solution for 3 minutes, washed with distilled water, stained with nuclear fast red staining solution for 5 minutes, and washed five times with distilled water, followed by dehydration with 95% alcohol. The cellular morphological changes and iron deposition (in blue) were observed under a light microscope.

2.7. BM and HSC transplantation

BALB/C mice aged 8 weeks old were randomly grouped into healthy recipient mice and iron‐overloaded recipient mice. The mouse model of iron overload was established as above. Twenty‐one healthy recipient BALB/C mice were randomly allocated into the control group, irradiation group, and healthy transplantation group. Twenty‐one BALB/C recipient mice in the mouse model of iron overload were randomly assigned into the iron‐overloaded group, iron‐overloaded irradiation group, and iron‐overloaded transplantation group. The BALB/C mice were fed with sterile water containing gentamicin (3.2 × 10⁵ U/L) 3 days before transplantation and raised under sterile conditions. One day before transplantation, mice in the irradiation group, the healthy transplantation group, the iron‐overloaded irradiation group, and the iron‐overloaded transplantation group received two times of systemic X‐ray with 4 Gy each time at an interval of 4 hours. The bilateral femurs of C57BL/6 mice were aseptically separated. The BM cell suspension was prepared to collect the BM cells. The cells were counted under the microscope and adjusted to 25 × 10⁶ cells/mL. Mice in the healthy transplantation group and the iron‐overloaded transplantation group were injected with 10 × 10⁶ BM cells (in 0.4 mL volume) through the tail intravenous injection, respectively, while mice in the other groups were injected with the same dose of normal saline in the same approach.

2.8. Peripheral blood cell counting

Blood was collected from the orbital inner canthus vein of mice twice: 2 weeks prior to and then post‐BM‐transplantation. Blood collection was followed by heparin anticoagulation and the peripheral blood of surviving mice in each group was counted by an automatic blood cell analyzer.

2.9. Colony formation assays

The mice were euthanized 2 weeks after BM transplantation. The left femur of mice in each group was washed with phosphate‐buffered saline to obtain BM single‐cell suspension. A total of 200 μL of cells (2 × 10⁵ cells/mL) were incubated at 4°C with 2 mL M3434 solution, and then 500 μL cell suspension was added into a 24‐well plate. Six parallel wells were set in each group. The culture plate was cultured in a 5% CO₂ incubator at 37°C. The colony‐forming unit of granulocyte‐macrophage (CFU‐GM), colony‐forming unit of erythrocyte (CFU‐E), and colony‐forming unit of mixed line (CFU‐mix) were counted under an inverted microscope on the fifth, eighth, and 11th day of culture, respectively. The number of cells >30 was regarded as a positive colony. The colony formation was observed under a low‐power microscope. The classification and count were conducted under a high‐power microscope.

2.10. Statistical analysis

All data were processed by the SPSS 19.0 statistical software (IBM Corp. Armonk, New York). The experimental results are expressed by mean ± SD. The difference between the groups was tested by the chi‐square test. Data conforming to a normal distribution, the least significant difference was used for comparison between two groups. For the data not conforming to the normal distribution, the rank‐sum test was used. P < .05 was statistically significant.

3. RESULTS

3.1. Characteristics of iron overload in mice

Here, the effects of iron overload on hair, body weight, and biological behaviors of the mice were measured. As a baseline, mice in the control group had dense hair with fine gloss, no brown changes in the skin, and no blackening of the testicles. In contrast, by the second week of injection, the fur of mice in the low‐, medium‐ and high‐dose groups became sparse, rough, and dull, and their testicles became dark. These changes in appearance became more obvious in a time‐ and dose‐dependent manner (Figure 1A,B). In terms of biological behavior, mice in the control group showed normal activity, while the mice in the low‐, medium‐, and high‐dose iron groups exhibited decreased activity concurrent with an increase in administration time due to a higher and higher cumulative dose. The manic biological behaviors of mice were observed when they were grasped. In addition, the overall weight of mice in the control group was elevated, while the weight of the mice in the low‐, medium‐ and high‐dose groups increased slowly or reduced with the prolonging of administration time and cumulative dose.

FIGURE 1.

Iron overload affects hair, body weight, and biological behavior of mice. A, Hair and skin of mice in the control group on the 14th day. B, Hair and skin of mice in the iron overload group on the 14th day

3.2. Iron overload promotes iron deposition in the liver and increase of an organ coefficient

Next, we investigated the effects of an iron overload on iron deposition in viscera, and furthermore, organ coefficients were determined in order to assess potential toxic effects. No iron deposition was found in the abdominal cavity of healthy mice, and the liver color was yellow after cold saline irrigation. In contrast, a large amount of iron deposition was found in the abdominal cavity of the mice that received iron sucrose injections, and the liver color was dark red after cold saline irrigation (Figure 2). The heart, liver, spleen, and lung coefficients of mice in each group are shown in Table 1. Compared with mice in the control group, the organ coefficients for the liver and spleen of mice in the high‐dose group were increased (P < .05). No other significant differences were observed between all groups in the remaining organ coefficients (P > .05). Thus, we found that iron overload can advance iron deposition in the liver while also increasing the liver and spleen organ coefficients.

FIGURE 2.

Iron deposition and organ coefficients are increased in response to iron overload. The mice were euthanized after 4 weeks of injections. A, Iron deposition of mice in the control group. B, Iron deposition of mice in the iron overload group. C, Liver color of mice in the control group. D, Liver color of mice injected with iron sucrose injection

TABLE 1.

Organ coefficient of mice in each group

Group	Heart	Liver	Spleen	Lung
Control group (n = 7)	0.51 ± 0.12	5.06 ± 0.46	0.42 ± 0.09	0.75 ± 0.27
Low‐dose group (n = 7)	0.52 ± 0.06	6.05 ± 0.45	0.51 ± 0.09	0.73 ± 0.34
Medium‐dose group (n = 7)	0.49 ± 0.07	5.67 ± 0.10	0.50 ± 0.10	0.71 ± 0.36
High‐dose group (n = 7)	0.48 ± 0.29	6.17 ± 0.79 a	0.62 ± 0.12 b	0.69 ± 0.07

^a P < .05 compared with the control group.

^b P < .02 compared with the control group. The measurement data were expressed by mean ± SD, and the comparison among groups was analyzed by one‐way ANOVA. The experiment was repeated three times.

3.3. Iron overload increases serum ferritin level

In light of our results showing that iron overload increases iron deposition and organ coefficients, our next experiment focused on the effects of iron overload on ferritin levels in the serum. To test , we performed an anti‐ferritin ELISA on blood samples collected from iron overload and control mice (Figure 3). In the control group, the level of serum ferritin did not change over time and was (85 ± 2.40) μg/mL after 4 weeks. The level of serum ferritin in the high‐dose group gradually increased concomitant with the administration time and cumulative dose. After 4 weeks, the level of serum ferritin in mice injected with iron sucrose was (156 ± 5.10) μg/mL, which was significantly higher than the control group serum ferritin levels (P < .05). Overall, we found that iron overload can elevate serum ferritin levels.

FIGURE 3.

Serum ferritin level is elevated following iron overload. * P < .05 compared with the control group (n = 7). The measurement data were expressed by mean ± SD, and the comparison among groups was analyzed by one‐way ANOVA. The experiment was repeated three times

3.4. Histopathological examination of iron‐overloaded mice

HE staining and Prussian blue iron staining was conducted to measure the pathological changes in the liver, spleen, and BM tissues in order to confirm whether the mouse model of iron overload was successfully established. The results showed that no obvious pathological changes were observed in the livers of mice in the control and low‐dose groups; cells were uniformly aligned with normal morphology and no brown iron deposition was observed under the light microscope. The liver structure of mice in the medium‐dose group was normal with a small amount of iron depositions, while the livers of mice in the high‐dose group showed lumpy brown iron depositions around hepatocytes, with some cells appeared enlarged (Figure 4A). In the spleen, no obvious pathological changes in cell morphology were observed under the light microscope between the control and low‐dose groups, as tissues from both samples displayed normal splenic corpuscles and lacked brown iron depositions. In contrast, brown iron depositions were found in the spleens of mice injected with medium and high‐doses of iron sucrose, while the structure of spleen corpuscles was disordered (Figure 4B).

FIGURE 4.

The mouse model with iron overload is successfully established. A, HE staining of liver in each group (×200). B, HE staining of spleen in each group (×100). C, HE staining of bone marrow in each group (×400). D, Prussian blue iron staining of bone marrow in each group (×1000). HE,hematoxylin‐eosin staining

In BM tissues, the BM cells of the control group and the low‐dose group showed normal morphology, and no brown iron depositions were found. No morphological changes were monitored in the BM cells in the medium‐dose group and the high‐dose group, but a large number of iron depositions were seen (Figure 4C). At the same time, the results of Prussian blue iron staining of BM tissues showed normal cell morphology in the control and low‐dose groups and, no blue iron depositions were found. No morphological changes were found in the BM cells in the medium‐dose group and the high‐dose group, but a large number of blue iron depositions were revealed (Figure 4D). Given the above results, we concluded that our iron overload mouse model has been successfully established. High‐dose iron sucrose was superior to low and medium dose in inducing the pathological changes, thus high‐dose iron sucrose was used in subsequent experiments.

3.5. Allo‐HSCT in an iron‐overloaded mice negatively impacts survival rate and behaviors

After the establishment of the mouse model of allo‐HSCT, the behavior and subsequent survival rate, and behaviors of the mice were measured. The mice in the health irradiation group and the iron‐overload irradiation group all died within 1 week after irradiation. The two‐week survival rate of mice was 100% in the control, iron overload, and healthy transplantation groups without statistical difference (P > .05) and 85% in the iron‐overloaded transplantation group (Figure 5). In addition, the body weight was increased, and the posture, fur appearance, and general activity of the mice fell within normal limits in the control group as well as the healthy transplantation group. However, in the iron overload and the iron‐overloaded transplantation groups, no significant changes in weight were noted; however, the fur was sparse and mice exhibited decreased activity and hunched posture. Altogether, allo‐HSCT after iron overload could exert negative effects on survival rate and general behavior of mice.

FIGURE 5.

Iron overload has poor effect on survival rate of mice following allo‐HSCT. Allo‐HSCT, allogeneic hematopoietic stem cell transplantation

3.6. Iron overload reduces peripheral red blood cells and hemoglobin in mice after allo‐HSCT

After the survival rate and general behavior of mice in the allo‐HSCT experiment were determined, peripheral blood cells of mice in each group were counted at 2 weeks after transplantation. Unexpectedly, all the mice in the healthy irradiation and iron‐overloaded irradiation groups died within 1 week postirradiation. Nevertheless, the control group had significantly more platelets and a higher‐hemoglobin (HGB) concentration compared to the iron‐overload group (P < .001); however, white and red blood cell (RBC) counts did not differ (P > .05). Compared with the healthy transplantation group, the number of peripheral RBCs (P < .001) and HGB concentration (P < .02) in the iron‐overloaded transplantation group were decreased, while the white blood cells and platelet counts showed no significant difference (P > .05; Table 2). Taken together, our results show that allo‐HSCT after iron overload decreases the concentration of peripheral RBCs and HGB in the blood.

TABLE 2.

Differential count of peripheral blood cells of mice in each group 2 weeks after transplantation

Group	WBC (×109/L)	PLT (×109/L)	RBC (×1012/L)	HGB (g/L)
Healthy irradiation group (n = 7)	All dead
Iron overload irradiation group (n = 7)	All dead
Control group (n = 7)	5.26 ± 1.46	649.57 ± 280.44	8.80 ± 1.06	111.14 ± 16.06
Iron overload group (n = 7)	5.20 ± 1.54	949.14 ± 199.31 a	9.45 ± 1.18	135.85 ± 16.84 b
Healthy transplantation group (n = 7)	2.52 ± 0.78	650.14 ± 139.33	9.93 ± 2.67	116.00 ± 28.01
Iron overload transplantation group (n = 7)	2.39 ± 0.48	677.57 ± 174.62	6.42 ± 1.00 c	95.85 ± 14.55 d

Abbreviations: HGB, hemoglobin; PLT, platelet; RBC, red blood cell; WBC, white blood cell.

^a P < .001 compared with the control group.

^b P < .001 compared with the control group.

^c P < .001 compared with the healthy transplantation group was statistically significant.

^d P < .02 compared with the healthy transplantation group. The measurement data were expressed by mean ± SD, and the comparison among groups was analyzed by one‐way ANOVA. The experiment was repeated three times.

3.7. Iron overload may affect the BM microenvironment to mediate homeostatic production in mice following allo‐HSCT

Next, we found that only the iron‐overloaded transplantation group showed decreased BM stromal cells numbers when compared with the healthy transplantation group (Figure 6A‐D). Compared to the control group, the numbers of CFU‐GM and CFU‐E were decreased in the iron‐overload group (P < .05) while the number of CFU‐mix was diminished as well (P < .002). Compared to the healthy transplantation group, the numbers of CFU‐GM (P < .002), CFU‐E (P < .005), and CFU‐mix (P < .001) were reduced in the iron‐overload transplantation group (Figure 6E). These results show that allo‐HSCT iron overload may affect the BM microenvironment by inhibiting the function of BM hematopoietic stem cells or progenitor cells, thus suppressing the hematopoietic recovery of mice after transplantation.

FIGURE 6.

Allo‐HSCT after iron overload causes the destruction of bone marrow microenvironment and inhibition of the function of bone marrow hematopoietic stem cells/progenitor cells, thus influencing the hematopoietic recovery of mice. A, HE staining of bone marrow in the control group (×400). B, HE staining of bone marrow in the iron overload group (×400). C, HE staining in the healthy transplant group (×400). D, HE staining of bone marrow in the iron overload transplantation group (×400). E, The number of CFU‐GM, CFU‐E, and CFU‐mix of each group. * P < .05 compared with the control group; ** P < .002 compared with the control group; # P < .005 compared with the healthy transplantation group; ## P < .002 compared with the healthy transplantation group; ### P < .001 compared with the healthy transplantation group (n = 7). The measurement data were expressed by mean ± SD. The comparison among the groups was analyzed by one‐way ANOVA, and the experiment was repeated three times. Allo‐HSCT, allogeneic hematopoietic stem cell transplantation; HE,hematoxylin‐eosin staining

4. DISCUSSION

Iron overload is a common consequence in transfusion‐dependent MDS, and it has been established that it leads to negative effects on hematopoiesis. Abnormal function of the BM microenvironment is unfavorable for the survival, differentiation, and proliferation of hematopoietic cells. Recent evidence demonstrated that iron overload induces damage in the BM microenvironment. Based on these findings, we hypothesized that iron overload influences the hematopoietic function in mice after allo‐HSCT, partially due to impaired BM microenvironment. In this study, we generated iron‐overloaded mouse models and examined whether and how iron overload influences the hematopoietic function in mice after allo‐HSCT. We found that iron overload delays homeostatic production after allo‐HSCT, as evidenced by decreased peripheral RBCs and HGB concentration in the iron‐overloaded mice following allo‐HSCT relative to healthy mice with allo‐HSCT. In addition, our results showed that iron overload failed to significantly affect the BM microenvironment in healthy mice, but it decreased BM stromal cells in mice with allo‐HSCT, suggesting impaired BM microenvironment may be responsible for the delayed hematopoietic reconstitution capacity induced by iron overload.

In the present study, iron overload reduces peripheral RBCs and HGB in mice after allo‐HSCT. Iron overload has been suggested to have negative effects on BM stroma and hematopoietic stem cells, which can also impair hematopoietic function. ¹⁶ A previous study showed that iron overload could change the frequency and function of normal hematopoietic stem and progenitor cells, especially in erythroid cells. ¹⁷ Our findings are consistent with another study which found that iron overload may postpone hematopoietic recovery following BM transplantation, suggesting that iron overload may affect the hematopoietic microenvironment of BM. ¹⁸

Subsequently, observations revealed that colony formation, peripheral RBC counts and HGB concentration were reduced, while platelet counts were increased in response to iron overload after allo‐HSCT. In a previous study conducted by Chai et al, the colony‐forming cell assays demonstrated that iron overload resulted in the decline of hematopoietic colony‐forming count and damaged the colony formation and the hematopoietic reconstitution in HSCs. ¹⁹ Several RBC transfusions could bring iron overload since there are no available physiological pathways eliminating excess iron stored in the reticuloendothelial and endocrine systems as well as in the liver and heart. ²⁰ Another study demonstrated that decreased RBC counts were associated with reduced complications related to transfusion as secondary iron overload. ²¹ The essential effects of decreased HGB level on the assessment of iron overload patients were also previously reported. ²² The study found that the iron overload could promote the level of serum ferritin. Serum ferritin has been taken as an alternate marker for iron overload, while its feature as a protein in the acute phase reduces its specificity to examine iron overload under concurrent infection and/or inflammation. ²³ Moreover, it is often found that elevated levels of serum ferritin prior to transplantation closely correlated with increased mortality within 5 years of the recipients receiving allo‐HSCT. ²⁴ Enhanced iron content in BM might be a sign of poor survival in allo‐HSCT recipients and BM assessment before transplantation would be a promising diagnostic method of iron overload. ²⁵ Interestingly, Chansiw et al found that platelet numbers of the mice fed with 0.2% ferrocene and treated with different doses of a novel orally active bidentate iron chelator, showed upward trends in platelet numbers relative to those of the non‐chelated‐fed mice as well as those of the normal diet‐fed mice. ²⁶ However, the possible positive correlation of platelet counts with iron overload warrants further investigation. Therefore, the concentration of peripheral RBCs and HGB are reduced in response to iron overload, thus promoting the level of serum ferritin and iron content in mice after allo‐HSCT.

In summary, the major findings in the current study provides evidence that iron overload could influence the recovery of BM hematopoietic function by affecting the BM microenvironment in mice after allo‐HSCT. However, due to lack of other measures of clinically relevant iron overload, we could find few studies on the correlation of biochemical markers like serum ferritin with the effects of iron overload on BM hematopoietic function. Additionally, a recent murine study suggested that iron overloaded impaired the BM microenvironment and then destroyed the maturation of blood cells in mice. ¹⁵ Thus, there is an urgent need for further assessment of the detailed mechanism for how iron overload impacts hematopoietic function following allo‐HSCT.

CONFLICT OF INTEREST

All authors declare no potential conflict of interest.

Wu X‐Q, Lin K‐N, Chen M‐M, et al. Iron overload as a risk factor for poor graft function following allogeneic hematopoietic stem cell transplantation. Kaohsiung J Med Sci. 2020;36:825–833. 10.1002/kjm2.12238