Hematopoietic progenitor cells (HPCs) mobilization following high-intensity interval exercise in cancer patients undergoing bone marrow transplantation: preliminary results from a randomized controlled trial

Abstract

Background and objective

Hematopoietic progenitor cells (HPCs) mobilization is essential for successful bone marrow transplantation but may be impaired in cancer patients due to prior treatments. High-intensity interval exercise (HIIE) has been shown to enhance progenitor cell release in healthy individuals; however, its effects in patients with cancer remain unclear. This study aimed to evaluate the acute effects of HIIE on HPC mobilization in patients with cancer undergoing bone marrow transplantation.

Methods

In this randomized controlled trial (RCT), 20 patients with cancer undergoing bone marrow transplantation were randomly assigned to either an exercise (n = 10) or a control (n = 10) group. To determine peak power, patients in the exercise group performed a graded exercise test. After receiving granulocyte-colony stimulating factor, they performed an HIIE protocol consisting of 12 × 1-min efforts at 100% peak power, followed by 1-min active recovery at 20% peak power. Blood samples were collected before and immediately after exercise and analyzed for catecholamines and CD34 + cells.

Results

Data analyses revealed a significant increase in epinephrine, norepinephrine, and CD34 + cells after exercise compared with the control group (p < 0.05). In addition, a positive correlation between epinephrine and CD34 + cells was observed after exercise in the HIIE group. However, CD34 + cells and mononuclear cells did not differ significantly between the two groups (p > 0.05).

Conclusions

HIIE can mobilize HPCs by increasing epinephrine. However, the increased catecholamine levels and CD34 + cells after HIIE did not affect the apheresis products, possibly because of differences in HPCs time courses and homing.

Clinical trial registration: Registration of this trial protocol under the scientific name of “The effect of highintensity interval exercise and training on the mobilization of hematopoietic stem cells in autologous bone marrow transplant patients” has been approved in the Iranian Registry of Clinical Trials on 2023-01-08. The registration reference is IRCT20230101057012N1.

Introduction

Peripheral hematopoietic progenitor cells (HPCs) are mobilized from the bone marrow into the peripheral blood and subsequently collected as a major source of cells for hematopoietic cell transplantation, a well-established and promising therapeutic strategy for hematological malignancies such as lymphoma and multiple myeloma [1, 2].

HPCs are identified by their expression of the CD34 membrane phosphoglycoprotein [3]. For successful bone marrow transplantation, at least 5 million CD34⁺ cells/Kg of recipient body weight are required [4] and receiving less than 1–2 × 10⁶ CD34⁺ cells/kg may lead to delayed, partial, or failed engraftment [2]. The number of CD34⁺ cells also determines the time of apheresis [5]. Some factors, such as sex, disease status before mobilization, and body surface area, affect the mobilization and apheresis yield [5]. The amount of HPCs in peripheral blood follows a circadian rhythm, consistent with the rhythm of norepinephrine release, where activation of adrenergic receptor-2 on the HPCs surface by catecholamine can increase HPCs mobilization [6].

In healthy individuals, exercise can induce HPCs mobilization and serve as an adjuvant [7]. Previous studies have confirmed that maximal exercise in the form of rowing, running, and cycling increases HPCs mobilization between 1.5 and 4 fold [8–10] in an intensity [9] and time-dependent [10] manner. The increased levels remain elevated shortly after exercise and return to baseline within 30–60 min of recovery, likely because HPCs are removed from circulation to repair exercise-induced tissue damage [8]. In athletes, a 2-fold increase in CD34 + cell count has been reported after 1000 m of rowing on an ergometer [11]. Exercise is a feasible and safe lifestyle intervention for patients undergoing bone marrow transplantation [12] and helps HPCs mobilization during the inpatient period [13]. However, few studies have examined the effects of high-intensity exercise, particularly high-intensity interval exercise (HIIE), in the context of HPCs [12]. It has been reported that HIIE, as a discontinuous mode of exercise [13], has produced a greater change in catecholamine levels than continuous exercise [14]. Since norepinephrine release is associated with HPCs in the peripheral circulation, and activation of the sympathetic nervous system is a key mechanism for exercise-induced mobilization of HPCs [7]. On the one hand, acute exercise may facilitate successful bone marrow transplantation by increasing CD34 + cell numbers; on the other hand, HIIE can mobilize more CD34 + cells by elevating catecholamine levels. We hypothesized that HIIE can mobilize more CD34 + cells by increasing catecholamine levels. Therefore, we evaluated whether patients undergoing bone marrow transplantation benefit from increased CD34⁺ following HIIE. Additionally, to understand the mechanism of exercise-induced mobilization, we assessed potential correlations between changes in CD34 + and catecholamine levels following HIIE.

Materials and methods

Study design, sitting, and registration

This study was a randomized, double-blind, parallel-group clinical trial conducted in 2023 at Shahid Beheshti University of Medical Sciences (SBUMS), Tehran, Iran. The trial protocol was registered in the Iranian Registry of Clinical Trials on January 8, 2023 (IRCT20230101057012N1).

Ethical approval

Informed consent was obtained from all participants prior to enrollment. Each participant received a clear explanation of the study design, including potential risks and discomforts, and provided written consent after confirming their understanding of the procedures. The study adhered to high ethical standards for human research. All procedures were conducted in accordance with the Declaration of Helsinki. This project, entitled “The Effect of High Intensity Interval Exercise and Training on Hematopoietic Stem Cell Mobilization in Autologous Bone Marrow Transplant Patients” was approved by Ethics Committee of Shahid Beheshti University of Medical Sciences on 10 October 2021 (Approval Code: IR.SBMU.REC.1400.017).

Participants and eligibility criteria

Participants were adult patients admitted for autologous bone marrow transplantation with diagnoses of lymphoma or multiple myeloma. A total of 20 eligible patients were recruited and assigned to either the exercise group (n = 10) or the control group (n = 10).

Inclusion criteria were: age range of 18–55 years old, BMI less than 30 (non-obese), non-smoker, no history of comorbidities such as cardiovascular or pulmonary disease, autonomic dysfunction, kidney disease, hepatitis, and diabetes. The exclusion criteria included: the inability to perform the exercise with determined intensity and duration, and the physician’s opinion on activity cessation due to symptoms such as chest pain, dizziness, nausea, dyspnea, and sagging ST segment.

Randomization and blinding

Participants were randomized in a 1:1 ratio to either the exercise or control group using computer-generated random sequences with permuted blocks of four. Allocation concealment was maintained using sealed, opaque envelopes prepared by an independent researcher not involved in assessments or interventions.

Outcome assessors, laboratory personnel, and data analysts were blinded to group allocation. Due to the nature of the intervention, participants could not be blinded to exercise; however, they were unaware of the study hypotheses, and the control group underwent passive sitting to mimic the time structure of the intervention.

Exercise protocol

On the first day of hospitalization, patients underwent a graded exercise test to determine peak power. After 5 min of warm-up and stretching, the test began with an initial power output of 20 W, increasing by 10 W per minute until exhaustion. During the exercise test, heart rate was continuously measured with a pulse oximeter, and patients were asked to rate their perceived exertion (RPE) at the end of each stage using Borg’s 6–20 scale [15]. The test was terminated when the patient reached a perceived exertion of 20 or when the maximum heart rate calculated as 220-age was reached. For each patient, the power for the final stage of the test was recorded as peak power. Systolic and diastolic blood pressure were recorded at rest by using a digital blood pressure monitor (Omron M3, Omron Healthcare Co., Ltd., Japan).

Patients in both groups received granulocyte colony-stimulating factor (G-CSF) for five days. Patients in the exercise group performed a HIIE protocol 6 h after the last G-CSF dose. HIIE included 5 5-minute warm-ups at 10–20% of their peak power, followed by 12 repetitions of 1 min of cycling at 100% peak power, interspersed with 1 min of active recovery at 20% of peak power. Patients in the control group performed no exercise and sat for the same period of time. For both groups, blood samples were taken before and immediately after the HIIE protocol.

Blood sampling and analysis

Blood samples were obtained through a catheter from the cervical vein with minimal stasis and collected in EDTA tubes for complete blood counts (CBC) using an automated cell counter (Sysmex KX21, Japan) and CD34 + cell counts using a flow cytometer (BD FACS Calibur; BD Biosciences, San Jose, CA). The serum specimens were obtained by centrifuging blood samples containing clot activator at 1500 g for 10 min, then immediately frozen and stored at -80 °C for subsequent catecholamine analysis. Theenzyme-linked immunosorbent assay (ELISA) was performed to quantify epinephrine and norepinephrine using the human epinephrine and norepinephrine kits (ELISA Kit, MBS285087, Mybiosource, Germany).

Statistical analysis

Data were analyzed by using SPSS Statistics for Windows, version 22.0. The Shapiro-Wilk test was used to examine the distribution of data. The pre- and post-exercise values for catecholamine and CD34⁺ in the two groups were compared using a repeated-measures ANOVA with between-subject factors. The independent t-test was used to compare patients’ characteristics and apheresis products, including white blood cells (WBCs), CD34 + cells, and mononuclear cells (MNCs), between the two groups. The Pearson correlation test was used to assess the correlation between post-exercise catecholamine levels and the number of mobilized CD34⁺ cells in the peripheral blood. P ≤ 0.05 is considered significant.

Results

Patients’ Characteristics

The study included 20 patients, randomized equally to the HIIE (high-intensity interval exercise) group (n = 10) and the control group (n = 10). Sex distribution was comparable between arms (HIIE: 4 female/6 male; control: 5 female/5 male). Mean age was similar between groups (HIIE 32.2 ± 11.6 years vs. control 33.1 ± 9.5 years), as were BMI values (27.3 ± 4.8 vs. 25.9 ± 9.2 kg/m²). Diagnoses included Hodgkin lymphoma (HIIE 5; control 8), non-Hodgkin lymphoma (HIIE 2; control 0), and multiple myeloma (HIIE 3; control 2). Baseline demographic and clinical characteristics of patients are provided in Table 1. The independent t-test indicated no significant differences in baseline characteristics between the two groups (p > 0.05).

Table 1.

Patients’ general and disease characteristics

Characteristics	HIIE group (n = 10)	Control group (n = 10)
	Number
Female	4	5
Male	6	5
Non-Hodgkin Lymphoma	2	0
Hodgkin Lymphoma	5	8
Multiple Myeloma	3	2
Plerixafor administration	2	3
	Mean ± SD
Age (years)	32.2 ± 11.6	33.1 ± 9.5
BMI (kg/m2)	27.3 ± 4.8	25.9 ± 9.2
HR rest (bpm)	92.5 ± 7.7	87.5 ± 7.6
Systolic BP (mmHg)	121 ± 10	113 ± 10
Diastolic BP (mmHg)	75.0 ± 10.8	71.0 ± 5.6
Time from HSCT to engraft (days)	11.4 ± 1.7	11.1 ± 1.6
Neutrophil count in Engraftment (×103/uL)	740 ± 142	733 ± 150
Duration of the neutropenia (days)	9.1 ± 2.0	9.4 ± 3.74
No. of G-CSF administration (days)	5.1 ± 1.1	5.6 ± 1.1
No. of G-CSF administration (dose)	11.9 ± 2.3	12.7 ± 3.7

HIIE high-intensity interval exercise, BMI body mass index, BP blood pressure, HR heart rate, HSCT hematopoietic stem cell transplantation, G-CSF granulocyte colony-stimulating factor

Epinephrine, norepinephrine, and CD34+

Data analysis showed a significant difference in responses to epinephrine, norepinephrine, and CD34 + between the two groups (Fig. 1). These variables were increased significantly following HIIE in the exercise group compared to the control group. Besides, Pearson’s test demonstrated a positive correlation between epinephrine levels after exercise and the number of mobilized CD34⁺ cells in the peripheral blood (r = 0.738, p = 0.009).

Fig. 1.

Epinephrine (A), norepinephrine (B), and CD34+ (C) levels (mean ± SD) pre- and post-exercise. HIIE High-intensity interval exercise. *Shows statistically significant difference with the control group (p < 0.05)

WBC and apheresis content

WBC count on the day before apheresis showed no significant difference between the two groups (p > 0.05). Similarly, apheresis products, including WBCs, CD34⁺ cells, and MNCs, showed no significant (p > 0.05) differences (Table 2).

Table 2.

The WBC, Hb, and PLT count on the day before apheresis and apheresis content (mean ± SD)

Groups	HIIE (n = 10)	Control (n = 10)	p-value
Before the apheresis:
WBC (×103/uL)	34.5 ± 13.8	32.9 ± 14.2	0.80
Hb (g/dL)	12.0 ± 1.5	11.5 ± 2.3	0.61
PLT (×103/uL)	186 ± 58	146 ± 71	0.41
Apheresis products:
WBC (×106cells/kg)	10.9 ± 4.0	12.9 ± 5.5	0.08
CD34+ (×106cells/kg)	4.42 ± 1.68	4.62 ± 2.61	0.60
MNC (×106cells/kg)	7.28 ± 1.95	7.64 ± 2.59	0.24
CD34+ / MNC	0.64 ± 0.31	0.53 ± 0.17	0.31

HIIE high-intensity interval exercise, WBC white blood cells, PLT platelets, Hb Hemoglobin, MNC mononuclear cells

Discussion

This study aimed to investigate the effect of HIIE on HPCs mobilization in patients undergoing bone marrow transplantation. In our study, we observed a 46% increase in CD34 + cell count after exercise in the HIIE group. This result confirms that HIIE is capable of mobilizing HPCs from bone marrow to peripheral blood, which supports findings of previous studies reporting the beneficial effects of exercise, as an adjunctive method, in HPCs mobilization in healthy individuals [7] and patients undergoing bone marrow transplantation [16, 17]. A 2.5-fold increase in CD34⁺ cells was observed after exercise at 70% peak work rate, which confirms that HPCs mobilization after aerobic exercise is intensity-related [9]. Our findings are also in line with those who demonstrated a significant rise in CD34⁺ cell count after 15 min of strenuous exercise compared to moderate exercise [18].

Despite a reasonable number of investigations into the effects of acute exercise on HPCs mobilization, there is no consensus on the mechanisms or extent of these effects [19]. Activation of the sympathetic nervous system is one of the primary mechanisms responsible for exercise-induced mobilization of HPCs [7]. Circadian release of norepinephrine is correlated with HPCs concentration in the peripheral circulation, and overnight norepinephrine variation is related to changes in HPCs function [7]. Increased epinephrine decreases the CXC motif chemokine 12 (CXCL12) expression in the bone marrow niche, which leads to an increase in HPCs mobilization [7]. Furthermore, the nervous system has an adverse effect on stromal cell-derived factor 1 (SDF-1) and may have a positive impact on CXC chemokine receptor type 4 (CXCR4) [20]. Increased expression of proteolytic enzymes in stromal cells, inhibition of mesenchymal stem cell differentiation into osteoblasts, and greater osteoclast differentiation from HPCs are additional mechanisms that may contribute to HPCs mobilization [20]. On the other hand, increases in HPCs might depend on chemotactic factors, with HPCs migrating directly into and out of the bone marrow [21]. CXCL12/SDF‑1 is a key chemoattractant that, via CXCR4 on CD34+, regulates retention in marrow niches and guides trans‑endothelial migration through sinusoidal endothelium into the bloodstream [21]. HPCs must cross sinusoidal walls to enter the blood, a process controlled by chemokine gradients, proteolytic enzymes (e.g., MMPs), and changes in vascular permeability. Reductions or cleavage of CXCL12, antagonism of CXCR4, or increased MMP activity promote mobilization, while high CXCL12/CXCR4 signaling favors retention [21]. Therefore, in the present study, the exercise-induced increase in catecholamines may have altered the vascular permeability, chemoattractant signaling, and MMP activity, facilitating HPCs migration and increasing circulating CD34 + cells.

Higher expression of neural receptors, including dopamine and beta-adrenergic receptors (β2-AR), has been detected in the primitive CD34 + CD38low population compared to the CD34 + CD38high population [20]. Exercise-induced mobilization of CD34⁺ HPCs is more dependent on β2-AR signaling than on circulating G-CSF [18]. Similar to previous studies [22]We also found that exercise-induced increases in catecholamine levels can enhance stem cell mobilization during and after exercise, and this rise is entirely independent of G-CSF. Since the same amount of G-CSF was administered to both groups in our study, the higher CD34 + levels in the HIIE groups could be attributed to exercise rather than to G-CSF.

Positive correlations between post-exercise epinephrine and HPCs mobilization are another important finding of the present study. These findings were consistent with those of Stelzer et al. (2014), who reported a 10-fold accumulation of norepinephrine after a graded exercise test, which was correlated with HPCs mobilization in healthy male athletes [23]. In line with this study [23] our results indicated that epinephrine and norepinephrine levels increased significantly after HIIE by 480% and 126%, respectively. Therefore, our findings support the hypothesis that exercise-induced HPCs mobilization is triggered by catecholamines.

In addition, other factors were not measured in the present study, but may explain mobilization induced by acute exercise [24]. The HIIE increased several pro-angiogenic factors and enhanced the availability of nitric oxide metabolites that might play a role in exercise-induced mobilization [24]. HIIE, as a discontinuous mode of exercise comprising repeated short bouts of high-intensity exercise interspersed with low-intensity exercise [13], has elicited greater hemodynamic responses than moderate continuous exercise [25]. Increased hemodynamic responses can increase blood flow and the bioavailability of shear-stress-induced nitric oxide metabolites [26].

On the other hand, exercise-induced inflammation increases the number of HPCs in peripheral blood, which are later mobilized to the spleen [7]. It has been shown that IL-6, a primary mediator of this inflammatory response,increased up to 100-fold following exercise [7]. Moreover, stabilization of hypoxia-inducible factor-1α (HIF-1α), a regulator of the cell response to hypoxia, can enhance mobilization by vasodilating sinusoids through increased VEGF levels, further increasing mobilization [27]. Therefore, HPCs mobilization in the present study might be explained by HIIE-induced increases in HIF-1α expression [28] and in inflammatory markers.

We found that an HIIE session before apheresis did not affect the CD34⁺ cell count in the apheresis product. Saba et al. (2013) determined a time course for HPCs mobilization after the cycle ergometer test, with an increase in circulating HPCs at 10 min of recovery and a return to baseline at 30, 60, and 120 min post-exercise [29]. On the other hand, it has been shown that HPCs levels increase from 0 to 5 min after exercise, with no changes from 6 to 20 min [19]. Similarly, another study reported no changes in circulating HPCs counts at 0.5, 1, and 3 h after exercise [19]. Therefore, it might be concluded that exercise-induced increases in HPCs are transient and return to baseline shortly after exercise. In the present study, although the CD34⁺ cell count was significantly higher in the HIIE group, no significant difference in apheresis content was observed, suggesting that the increase in CD34 + cell count may be transient and return to baseline during apheresis.

Lastly, consistent with our results, 20 min of regular exercise during mobilization did not significantly increase CD34 + levels in the apheresis product [17]. This is likely due to the effect of exercise on specific subsets of CD34⁺ cells [17]. Certain chemotherapeutic agents in the conditioning regimen and exercise-induced ischemia might have masked the positive impact of exercise on the number of mobilized stem cells [17]. Future research is needed to determine the optimal intensity, duration, and frequency for optimizing HPCs mobilization.

Because the present research was an RCT and, for the first time, the HIIE protocol was designed for patients undergoing bone marrow transplantation, our study had several limitations. First, we were unable to continue exercise during apheresis or to obtain blood samples afterward to determine how long the increases in CD34 + cells persist after exercise. Secondly, our sample size was small, comprising 10 participants, due to the limited number of volunteers willing to participate in the study. Future studies with larger patient cohorts are warranted. Lastly, we were unable to measure certain confounding variables, such as inflammatory markers (e.g., IL-6), which might help justify our findings.

Conclusions

Based on the present study’s findings, a single HIIE session induces HPCs mobilization in patients undergoing bone marrow transplantation, which may be attributed to increased epinephrine levels, as evidenced by a positive correlation between epinephrine and immediate post-exercise CD34 + cell counts.

Abbreviations

BMI

Body mass index

CBC

Complete blood counts

CXCL12

CXC motif chemokine 12

CXCR4

CXC chemokine receptor type 4

ELISA

Enzyme-linked immunosorbent assay

G-CSF

Granulocyte colony-stimulating factor

HIF-1α

Hypoxia inducible factor-1α

HPCs

Hematopoietic progenitorcells

HIIE

High-intensity interval exercise

MMPs

Matrix metalloproteinases

RPE

Rate of perceived exertion

SDF-1

Stromal cell-derived factor1

WBCs

White blood cells

Author contributions

T.Z., S.A., and A.H. were responsible for the conceptualization and study design. T.Z. conducted experiments, and S.A. contributed to data acquisition. T.Z. contributed to data acquisition and manuscript writing. All authors assisted with data analysis and interpretation of findings. T.Z. and M.K. drafted the manuscript. S.A. and E.R. provided critical revision of the manuscript for important intellectual content. M.K. reviewed and revised the manuscript. All authors critically reviewed the content and approved the final version for publication.

Funding

This work was partially supported by the Hematopoietic Stem Cell Research Center, Shahid Beheshti University of Medical Sciences (SBUMS), Tehran, Iran.

Data availability

The datasets generated and/or analyzed in the current study are available from the corresponding author upon reasonable request.

Declarations

Ethics approval and consent to participate

Informed consent was obtained from all individual participants included in the study. This study met the high ethical standards for human research and has been approved by the University’s Ethics Committee (Code: IR.SBMU.REC.1400.017 – date of approval: 10-10-2021). This study was conducted in accordance with the Declaration of Helsinki.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.