Systemic administration of mesenchymal stem cells combined with parathyroid hormone therapy synergistically regenerates multiple rib fractures

Dmitriy Sheyn,Dan Gazit,Eran Yalon,Zulma Gazit,Eric J Ley,Maxim Bez,Xiaoyu Da,Wafa Tawackoli,Alin Yaya,Gadi Pelled,Afeef Sirhan,May Amira,Shiran Ben-David,Sandra De Mel,Yeshai Schary,Doron Cohn Yakubovich

doi:10.1186/s13287-017-0502-9

Abstract

BackgroundA devastating condition that leads to trauma-related morbidity, multiple rib fractures, remain a serious unmet clinical need. Systemic administration of mesenchymal stem cells (MSCs) has been shown to regenerate various tissues. We hypothesized that parathyroid hormone (PTH) therapy would enhance MSC homing and differentiation, ultimately leading to bone formation that would bridge rib fractures.MethodsThe combination of human MSCs (hMSCs) and a clinically relevant PTH dose was studied using immunosuppressed rats. Segmental defects were created in animals’ fifth and sixth ribs. The rats were divided into four groups: a negative control group, in which animals received vehicle alone; the PTH-only group, in which animals received daily subcutaneous injections of 4 μg/kg teriparatide, a pharmaceutical derivative of PTH; the hMSC-only group, in which each animal received five injections of 2 × 106 hMSCs; and the hMSC + PTH group, in which animals received both treatments. Longitudinal in vivo monitoring of bone formation was performed biweekly using micro-computed tomography (μCT), followed by histological analysis.ResultsFluorescently-dyed hMSCs were counted using confocal microscopy imaging of histological samples harvested 8 weeks after surgery. PTH significantly augmented the number of hMSCs that homed to the fracture site. Immunofluorescence of osteogenic markers, osteocalcin and bone sialoprotein, showed that PTH induced cell differentiation in both exogenously administered cells and resident cells. μCT scans revealed a significant increase in bone volume only in the hMSC + PTH group, beginning by the 4th week after surgery. Eight weeks after surgery, 35% of ribs in the hMSC + PTH group had complete bone bridging, whereas there was complete bridging in only 6.25% of ribs (one rib) in the PTH-only group and in none of the ribs in the other groups. Based on the μCT scans, biomechanical analysis using the micro-finite element method demonstrated that the healed ribs were stiffer than intact ribs in torsion, compression, and bending simulations, as expected when examining bone callus composed of woven bone.ConclusionsAdministration of both hMSCs and PTH worked synergistically in rib fracture healing, suggesting this approach may pave the way to treat multiple rib fractures as well as additional fractures in various anatomical sites.

Highlights

A devastating condition that leads to trauma-related morbidity, multiple rib fractures, remain a serious unmet clinical need
More DiI-stained cells were counted in ribs of animals given both Human mesenchymal stem cell (hMSC) and parathyroid hormone (PTH) than in animals given hMSCs only (Fig. 2a): 15 DiI-positive cells per × 40 field compared to 5 DiIpositive cells, respectively
When we looked exclusively at DAPI-positive cells in all groups, we calculated the percentages of DiI-positive cells to be on average 12% in the hMSC + PTH group and only 2.5% in the hMSC group—no more than the percentages of DiI-positive cells among DAPI-positive cells found in the other groups, which had not been given any cells at all

Summary

Introduction

A devastating condition that leads to trauma-related morbidity, multiple rib fractures, remain a serious unmet clinical need. Affecting 350,000–400,000 patients each year in the United States, rib fractures occur in 10–15% of patients who sustain blunt trauma and are associated with morbidity and mortality rates in up to 25% of these patients [1]. Common complications are respiratory failure due to lung contusions and impaired mechanical properties as well as severe pain originating from the fractured rib. Patients rate their pain on average as 9.2 on a 1–10 scale and may not be able to return to work for at least 8.5 weeks [2]. Another study showed that 56% of patients older than 60 years who died of chest injury suffered no injury worse than a rib fracture [6]

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