Therapeutic neovascularization using cord blood-derived endothelial progenitor cells for diabetic neuropathy

Stem Cell Therapy in Diabetic Polyneuropathy: Recent Advancements and Future Directions

Diabetic polyneuropathy (DPN) is the most frequent, although neglected, complication of long-term diabetes. Nearly 30% of hospitalized and 20% of community-dwelling patients with diabetes suffer from DPN; the incidence rate is approximately 2% annually. To date, there has been no curable therapy for DPN. Under these circumstances, cell therapy may be a vital candidate for the treatment of DPN. The epidemiology, classification, and treatment options for DPN are disclosed in the current review. Cell-based therapies using bone marrow-derived cells, embryonic stem cells, pluripotent stem cells, endothelial progenitor cells, mesenchymal stem cells, or dental pulp stem cells are our primary concern, which may be a useful treatment option to ease or to stop the progression of DPN. The importance of cryotherapies for treating DPN has been observed in several studies. These findings may help for the future researchers to establish more focused, accurate, effective, alternative, and safe therapy to reduce DPN. Cell-based therapy might be a permanent solution in the treatment and management of diabetes-induced neuropathy.

The Effect of Schwann Cells/Schwann Cell-Like Cells on Cell Therapy for Peripheral Neuropathy

Peripheral neuropathy is a common neurological issue that leads to sensory and motor disorders. Over time, the treatment for peripheral neuropathy has primarily focused on medications for specific symptoms and surgical techniques. Despite the different advantages of these treatments, functional recovery remains less than ideal. Schwann cells, as the primary glial cells in the peripheral nervous system, play crucial roles in physiological and pathological conditions by maintaining nerve structure and functions and secreting various signaling molecules and neurotrophic factors to support both axonal growth and myelination. In addition, stem cells, including mesenchymal stromal cells, skin precursor cells and neural stem cells, have the potential to differentiate into Schwann-like cells to perform similar functions as Schwann cells. Therefore, accumulating evidence indicates that Schwann cell transplantation plays a crucial role in the resolution of peripheral neuropathy. In this review, we summarize the literature regarding the use of Schwann cell/Schwann cell-like cell transplantation for different peripheral neuropathies and the potential role of promoting nerve repair and functional recovery. Finally, we discuss the limitations and challenges of Schwann cell/Schwann cell-like cell transplantation in future clinical applications. Together, these studies provide insights into the effect of Schwann cells/Schwann cell-like cells on cell therapy and uncover prospective therapeutic strategies for peripheral neuropathy.

Recent Advances in Biomarkers and Regenerative Medicine for Diabetic Neuropathy

Diabetic neuropathy is one of the most common complications of diabetes. This complication is peripheral neuropathy with predominant sensory impairment, and its symptoms begin with hyperesthesia and pain and gradually become hypoesthesia with the loss of nerve fibers. In some cases, lower limb amputation occurs when hypoalgesia makes it impossible to be aware of trauma or mechanical stimuli. On the other hand, up to 50% of these complications are asymptomatic and tend to delay early detection. Therefore, sensitive and reliable biomarkers for diabetic neuropathy are needed for an early diagnosis of this condition. This review focuses on systemic biomarkers that may be useful at this time. It also describes research on the relationship between target gene polymorphisms and pathological conditions. Finally, we also introduce current information on regenerative therapy, which is expected to be a therapeutic approach when the pathological condition has progressed and nerve degeneration has been completed.

Direct Comparison of Therapeutic Effects on Diabetic Polyneuropathy between Transplantation of Dental Pulp Stem Cells and Administration of Dental Pulp Stem Cell-Secreted Factors

Stem cell transplantation is a potential novel therapy for diabetic polyneuropathy. Dental pulp stem cells (DPSCs) are attractive stem cell sources because DPSCs can be isolated from extracted teeth and cryopreserved while retaining viability. In this study, we directly compared the efficacy of the transplantation of DPSCs and the administration of the secreted factors from DPSCs (DPSC-SFs) on diabetic polyneuropathy. Eight weeks after streptozotocin injection, DPSCs (1.0 × 10⁶ cells/rat) or DPSC-SFs (1.0 mL/rat) were administered into the unilateral hindlimb skeletal muscles of diabetic Sprague-Dawley rats. DPSC transplantation and DPSC-SF administration did not affect blood glucose levels and body weights in the diabetic rats. Both DPSC transplantation and DPSC-SF administration significantly ameliorated sciatic nerve conduction velocity and sciatic nerve blood flow, accompanied by increases in muscle bundle size, vascular density in the skeletal muscles and intraepidermal nerve fiber density in the diabetic rats, while there was no difference between the results for DPSCs and DPSC-SFs. These results suggest that the efficacy of both DPSC transplantation and DPSC-SF administration for diabetic polyneuropathy four weeks after transplantation/administration was mainly due to the multiple secretomes secreted from transplanted DPSCs or directly injected DPSC-SFs in the early phase of transplantation/administration.

Transplantation of human dental pulp stem cells ameliorates diabetic polyneuropathy in streptozotocin-induced diabetic nude mice: the role of angiogenic and neurotrophic factors

BACKGROUND

Dental pulp stem cells (DPSCs) have high proliferation and multi-differentiation capabilities that maintain their functionality after cryopreservation. In our previous study, we demonstrated that cryopreserved rat DPSCs improved diabetic polyneuropathy and that the efficacy of cryopreserved rat DPSCs was equivalent to that of freshly isolated rat DPSCs. The present study was conducted to evaluate whether transplantation of cryopreserved human DPSCs (hDPSCs) is also effective for the treatment of diabetic polyneuropathy.

METHODS

hDPSCs were isolated from human impacted third molars being extracted for orthodontic reasons. Eight weeks after the induction of diabetes in nude mice, hDPSCs (1 × 10⁵/limb) were unilaterally transplanted into the hindlimb skeletal muscle, and vehicle (saline) was injected into the opposite side as a control. The effects of hDPSCs were analyzed at 4 weeks after transplantation.

RESULTS

hDPSC transplantation significantly ameliorated reduced sensory perception thresholds, delayed nerve conduction velocity, and decreased the blood flow to the sciatic nerve in diabetic mice 4 weeks post-transplantation. Cultured hDPSCs secreted the vascular endothelial growth factor (VEGF) and nerve growth factor (NGF) proteins. A subset of the transplanted hDPSCs was localized around the muscle bundles and expressed the human VEGF and NGF genes at the transplanted site. The capillary/muscle bundle ratio was significantly increased on the hDPSC-transplanted side of the gastrocnemius muscles in diabetic mice. Neutralizing antibodies against VEGF and NGF negated the effects of hDPSC transplantation on the nerve conduction velocity in diabetic mice, suggesting that VEGF and NGF may play roles in the effects of hDPSC transplantation on diabetic polyneuropathy.

CONCLUSIONS

These results suggest that stem cell transplantation with hDPSCs may be efficacious in treating diabetic polyneuropathy via the angiogenic and neurotrophic mechanisms of hDPSC-secreted factors.

Endothelial progenitor cells and peripheral neuropathy in subjects with type 2 diabetes mellitus

AIMS

To examine for differences in circulating progenitor cells (CPCs) and endothelial progenitor cells (EPCs) in patients with and without diabetic peripheral neuropathy (DPN).

METHODS

A total of 105 participants were included: 50 patients with type 2 diabetes (T2DM) and DPN, 30 patients with T2DM without DPN and 25 healthy individuals. CPCs and 6 different EPCs phenotypes were assessed with flow cytometry. We also measured plasma levels of vascular endothelial growth factor (VEGF), stromal cell-derived factor 1 (SDF-1), vascular cell adhesion protein-1 (VCAM-1), intracellular adhesion molecule-1 (ICAM) and tumor necrosis factor a (TNFa).

RESULTS

No difference was observed in the number of CPCs among the 3 groups. Patients with DPN had higher numbers of all 6 EPCs phenotypes when compared with patients without DPN and higher number of 5 EPCs phenotypes when compared with healthy individuals. Plasma VEFG, VCAM-1, ICAM-1 and TNFa levels did not differ among the 3 groups. Patients with DPN had lower SDF-1 levels in comparison with healthy individuals.

CONCLUSION

Circulating EPCs are increased while SDF-1 levels are decreased in the presence of DPN. Our findings suggest that DPN may be associated with impaired trafficking of EPCs and impaired EPCs homing to the injured endothelium.

Secreted factors from cultured dental pulp stem cells promoted neurite outgrowth of dorsal root ganglion neurons and ameliorated neural functions in streptozotocin-induced diabetic mice

AIMS/INTRODUCTION

Transplantation of stem cells promotes axonal regeneration and angiogenesis in a paracrine manner. In the present study, we examined whether the secreted factors in conditioned medium of stem cells from human exfoliated deciduous teeth (SHED-CM) had beneficial effects on diabetic polyneuropathy in mice.

MATERIALS AND METHODS

Conditioned medium of stem cells from human exfoliated deciduous teeth was collected 48 h after culturing in serum-free Dulbecco's modified Eagle's medium (DMEM), and separated into four fractions according to molecular weight. Dorsal root ganglion neurons from C57BL/6J mice were cultured with SHED-CM or DMEM to evaluate the effect on neurite outgrowth. Streptozotocin-induced diabetic mice were injected with 100 μL of SHED-CM or DMEM into the unilateral hindlimb muscles twice a week over a period of 4 weeks. Peripheral nerve functions were evaluated by the plantar test, and motor and sensory nerve conduction velocities. Intraepidermal nerve fiber densities, capillary number-to-muscle fiber ratio, capillary blood flow and morphometry of sural nerves were also evaluated.

RESULTS

Conditioned medium of stem cells from human exfoliated deciduous teeth significantly promoted neurite outgrowth of dorsal root ganglion neurons compared with DMEM. Among four fractions of SHED-CM, the only fraction of <6 kDa promoted the neurite outgrowth of dorsal root ganglion neurons. In addition, SHED-CM significantly prevented decline in sensory nerve conduction velocities compared with DMEM in diabetic mice. Although SHED-CM did not improve intraepidermal nerve fiber densities or morphometry of sural nerves, SHED-CM ameliorated the capillary number-to-muscle fiber ratio and capillary blood flow.

CONCLUSIONS

These results suggested that SHED-CM might have a therapeutic effect on diabetic polyneuropathy through promoting neurite outgrowth, and the increase in capillaries might contribute to the improvement of neural function.

The pivotal role of nuclear factor erythroid 2-related factor 2 in diabetes-induced endothelial dysfunction

Endothelial dysfunction (ED) is a key event in the onset and progression of vascular complications associated with diabetes. Regulation of endothelial function and the underlying signaling mechanisms in the progression of diabetes-induced vascular complications have been well established. Recent studies indicate that increased oxidative stress is an important determinant of endothelial injury and patients with hypertension display ED mediated by impaired Nitric Oxide (NO) availability. Further, oxidative stress is known to be associated with inflammation and ED in vascular remodeling and diabetes-associated hypertension. Numerous strategies have been developed to improve the function of endothelial cells and increasing number of evidences highlight the indispensable role of antioxidants in modulation of endothelium-dependent vasodilation responses. Nuclear factor Erythroid 2-related factor 2 (Nrf2), is the principal transcriptional regulator, that is central in mediating oxidative stress signal response. Having unequivocally established the relationship between type 2 diabetes mellitus (T2DM) and oxidative stress, the pivotal role of Nrf2/Keap1/ARE network, has taken the center stage as target for developing therapies towards maintaining the cellular redox environment. Several activators of Nrf2 are known to combat diabetes-induced ED and few are currently in clinical trials. Focusing on their therapeutic value in diabetes-induced ED, this review highlights some natural and synthetic molecules that are involved in the modulation of the Nrf2/Keap1/ARE network and its underlying molecular mechanisms in the regulation of ED. Further emphasis is also laid on the therapeutic benefits of directly up-regulating Nrf2-mediated antioxidant defences in regulating endothelial redox homeostasis for countering diabetes-induced ED.

Conditioned media from dental pulp stem cells improved diabetic polyneuropathy through anti-inflammatory, neuroprotective and angiogenic actions: Cell-free regenerative medicine for diabetic polyneuropathy

AIMS/INTRODUCTION

Dental pulp stem cells (DPSCs) can be easily obtained from teeth for general orthodontic reasons. We have previously reported the therapeutic effects of DPSC transplantation for diabetic polyneuropathy. As abundant secretomes from DPSCs are considered to play a central role in the improvement of diabetic polyneuropathy, we investigated whether direct injection of DPSC-conditioned media (DPSC-CM) into hindlimb skeletal muscles ameliorates diabetic polyneuropathy in diabetic rats.

MATERIALS AND METHODS

DPSCs were isolated from the dental pulp of Sprague-Dawley rats. Eight weeks after the induction of diabetes, DPSC-CM was injected into the unilateral hindlimb skeletal muscles in both normal and diabetic rats. The effects of DPSC-CM on diabetic polyneuropathy were assessed 4 weeks after DPSC-CM injection. To confirm the angiogenic effect of DPSC-CM, the effect of DPSC-CM on cultured human umbilical vascular endothelial cell proliferation was investigated.

RESULTS

The administration of DPSC-CM into the hindlimb skeletal muscles significantly ameliorated sciatic motor/sensory nerve conduction velocity, sciatic nerve blood flow and intraepidermal nerve fiber density in the footpads of diabetic rats. We also showed that DPSC-CM injection significantly increased the capillary density of the skeletal muscles, and suppressed pro-inflammatory reactions in the sciatic nerves of diabetic rats. Furthermore, an in vitro study showed that DPSC-CM significantly increased the proliferation of umbilical vascular endothelial cells.

CONCLUSIONS

We showed that DPSC-CM injection into hindlimb skeletal muscles has a therapeutic effect on diabetic polyneuropathy through neuroprotective, angiogenic and anti-inflammatory actions. DPSC-CM could be a novel cell-free regenerative medicine treatment for diabetic polyneuropathy.

Effects of adipose derived stromal vascular fraction on diabetic neuropathy: an experimental study

The stromal vascular fraction (SVF) obtained from inguinal adipose tissue was injected into the sciatic nerve region in diabetic rats. The effects of the SVF on the sciatic nerve and functional, electrophysiological and histopathological changes were examined in this study. Rats were divided into five groups; a non-diabetic control group, and four diabetic groups. In the first diabetic rat group, the SVF was obtained from inguinal adipose tissue. The remaining diabetic groups included a sham control group, a phosphate-buffered saline (PBS) injection group and an SVF injection group. Injections were made into the sciatic nerve region. Electromyography and walking track analyses were conducted on all groups at the beginning of the experiment. Diabetes was induced via a single dose of streptozotocin. Walking track analysis and electromyography measurements were repeated in week 8. SVF or PBS was injected into the right sciatic nerve region on week 8 of experiment group rats. Walking track analysis and electromyography were repeated in week 12 and all sciatic nerves were examined histopathologically. In the diabetic SVF group, the sciatic functional index calculated from walking track analysis in week 12 was better than week 8. Additionally, the myelin sheaths of the right sciatic nerve were thicker and more uniform and the nerve fibers were thicker than those of the left, untreated sciatic nerve. No statistical differences were detected in electromyographic measurements. The adipose-derived SVF may be beneficial for nerve regeneration in diabetic neuropathy.

Bone Tissue Engineering Using Human Cells: A Comprehensive Review on Recent Trends, Current Prospects, and Recommendations

The use of proper cells for bone tissue engineering remains a major challenge worldwide. Cells play a pivotal role in the repair and regeneration of the bone tissue in vitro and in vivo. Currently, a large number of differentiated (somatic) and undifferentiated (stem) cells have been used for bone reconstruction alone or in combination with different biomaterials and constructs (e.g., scaffolds). Although the results of the cell transplantation without any supporting or adjuvant material have been very effective with regard to bone healing. Recent advances in bone scaffolding are now becoming new players affecting the osteogenic potential of cells. In the present study, we have critically reviewed all the currently used cell sources for bone reconstruction and discussed the new horizons that are opening up in the context of cell-based bone tissue engineering strategies.

Therapeutic effects of stem cells from human exfoliated deciduous teeth on diabetic peripheral neuropathy

OBJECTIVE

To evaluate the therapeutic potential of stem cells from human exfoliated deciduous teeth (SHED) for diabetic peripheral neuropathy.

METHODS

The biological characteristics of SHED were identified by flow cytometric study and evaluation of differentiation potential. Using high-fat feeding, diabetes was induced in GK rats, and SHED were transplanted into the caudal veins of these rats. Immunohistochemical analysis was used to compare the capillary to muscle fiber ratio and intra-epidermal nerve fiber density between SHED- and saline-treated diabetic rats. Further, the expressions of angiogenesis-related and neurotrophic factors were quantified by real-time PCR and western blot.

RESULTS

SHED had a capacity of multiple differentiation and shared typical characteristics of mesenchymal stem cells. SHED transplantation relieved diabetic neuropathic pain, enabled functional recovery of the peripheral nerves, and increased the capillary to muscle fiber ratio and intra-epidermal nerve fiber density compared to the saline group and normal controls. Real-time PCR results showed that the expressions of CD31, vWF, bFGF, NGF, and NT-3 in the skeletal muscles were higher in the SHED group than in the saline groups. Western blot results indicated that the levels of the CD31 and NGF proteins were higher in the SHED transplantation group than the saline group.

CONCLUSION

SHED transplantation ameliorated diabetic peripheral neuropathy in diabetic GK rats. Thus, systemic application of SHED could be a novel strategy for the treatment of diabetic peripheral neuropathy.

Schwann Cells as Crucial Players in Diabetic Neuropathy

Schwann cells maintain peripheral nerve structure and function by ensheathment of unmyelinated axons, myelination of myelinated axons, and secretion of neurotrophic factors, and these cells also play a crucial role in the pathogenic mechanisms of diabetic neuropathy. A decrease in unmyelinated and small myelinated axons appeared earlier than a decrease in large myelinated fibers in diabetic neuropathy. Electron microscopic studies of human diabetic neuropathy demonstrated edematous cell cytoplasm, aggregates of glycogen particles, and hyperplasia of the surrounding basal lamina in Schwann cells. Diabetic conditions also induces metabolic disorders, such as polyol pathway hyperactivity, activation of protein kinase C, and increased advanced glycosylation end products in Schwann cells, followed by the depletion of neurotrophic factor production.Cell transplantation using progenitor or stem cells is expected to cure diabetic neuropathy. Many studies demonstrated that the paracrine effect of abundant secreted factors from transplanted stem cells was crucial for the success of cell transplantation in diabetic neuropathy. Transplantation of progenitor or stem cells in diabetic animal models ameliorated impaired nerve conduction velocity, nerve blood flow, sensory disorders, and intraepidermal nerve fiber density, with an increase of myelin thickness. The supernatant from cultured dental pulp stem cells increased the proliferation and production of myelin-related protein in Schwann cells, suggesting that Schwann cells is the main target of cell transplantation for diabetic neuropathy.

Is Regenerative Medicine Ready for Prime Time in Diabetic Polyneuropathy?

PURPOSE OF REVIEW

After a prolonged warm-up period of basic research, several modalities of cell replacement therapies are under development for diseases with no available cure. Diabetic polyneuropathy (DPN) is one of the most prevalent chronic diabetes complications that causes sensorimotor dysfunction, subsequent high risks for lower limb amputations, and high mortality. Currently, no disease modifying therapy exists for DPN.

RECENT FINDINGS

Several types of well-documented stem/progenitor cells have been utilized for cell transplantation therapies in DPN model rodents: mesenchymal stromal cells (MSCs), endothelial progenitor cells (EPCs), and cells with similar characteristics of MSCs or EPCs derived from embryonic stem cells or induced pluripotent stem cells. Some recent experimental studies reported that these immature cells may have beneficial effects on DPN. Although the role of nerve regeneration in the pathology of DPN has not been sufficiently elucidated, many intervention studies attempting regenerative therapy of DPN have been reported. Further studies are needed to better evaluate the potential of regeneration in reversing the pathology of DPN.

Transplantation of dental pulp stem cells improves long-term diabetic polyneuropathy together with improvement of nerve morphometrical evaluation

Background

Although previous reports have revealed the therapeutic potential of stem cell transplantation in diabetic polyneuropathy, the effects of cell transplantation on long-term diabetic polyneuropathy have not been investigated. In this study, we investigated whether the transplantation of dental pulp stem cells (DPSCs) ameliorated long-term diabetic polyneuropathy in streptozotocin (STZ)-induced diabetic rats.

Methods

Forty-eight weeks after STZ injection, we transplanted DPSCs into the unilateral hindlimb skeletal muscles. Four weeks after DPSC transplantation (i.e., 52 weeks after STZ injection) the effects of DPSC transplantation on diabetic polyneuropathy were assessed.

Results

STZ-induced diabetic rats showed significant reductions in the sciatic motor/sensory nerve conduction velocity, increases in the current perception threshold, and decreases in capillary density in skeletal muscles and intra-epidermal nerve fiber density compared with normal rats, all of which were ameliorated by DPSC transplantation. Furthermore, sural nerve morphometrical analysis revealed that the transplantation of DPSCs significantly increased the myelin thickness and area. DPSC-conditioned media promoted the neurite outgrowth of dorsal root ganglion neurons and increased the viability and myelin-related protein expression of Schwann cells.

Conclusions

These results indicated that the transplantation of DPSCs contributed to the neurophysiological and neuropathological recovery from a long duration of diabetic polyneuropathy.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-017-0729-5) contains supplementary material, which is available to authorized users.

Functional recovery upon human dental pulp stem cell transplantation in a diabetic neuropathy rat model

Diabetic neuropathy (DN) is among the most debilitating complications of diabetes. Here, we investigated the effects of human dental pulp stem cell (DPSC) transplantation in Streptozotocin (STZ)-induced neuropathic rats. Six weeks after STZ injection, DPSCs were transplanted through two routes, intravenous (IV) or intramuscular (IM), in single or two repeat doses. Two weeks after transplantation, a significant improvement in hyperalgesia, grip-strength, motor coordination and nerve conduction velocity was observed in comparison with controls. A rapid improvement in neuropathic symptoms was observed for a single dose of DPSC IV; however, repeat dose of DPSC IV did not bring about added improvement. A single dose of DPSC IM showed steady improvement, and further recovery continued upon repeat IM administration. DPSC single dose IV showed greater improvement than DPSC single dose IM, but IM transplantation brought about better improvement in body weight. A marked reduction in tumor necrosis factor (TNF) α and C-reactive protein (CRP) levels was observed in the blood plasma for all treated groups, as compared with controls. With respect to inflammatory cytokines, repeat dose of DPSC IM showed further improvement, suggesting that a repeat dose is required to maintain the improved inflammatory state. Gene expression of inflammatory markers in liver confirmed amelioration in inflammation. Arachidonic acid level was unaffected by IV DPSC transplantation but showed noticeable increase through IM administration of a repeat dose. These results suggest that DPSC transplantation through both routes and dosage was beneficial for the retrieval of neuropathic parameters of DN; transplantation via the IM route with repeat dose was the most effective.

Endothelial and cardiac progenitor cells for cardiovascular repair: A controversial paradigm in cell therapy

Stem cells have the potential to differentiate into cardiovascular cell lineages and to stimulate tissue regeneration in a paracrine/autocrine manner; thus, they have been extensively studied as candidate cell sources for cardiovascular regeneration. Several preclinical and clinical studies addressing the therapeutic potential of endothelial progenitor cells (EPCs) and cardiac progenitor cells (CPCs) in cardiovascular diseases have been performed. For instance, autologous EPC transplantation and EPC mobilization through pharmacological agents contributed to vascular repair and neovascularization in different animal models of limb ischemia and myocardial infarction. Also, CPC administration and in situ stimulation of resident CPCs have been shown to improve myocardial survival and function in experimental models of ischemic heart disease. However, clinical studies using EPC- and CPC-based therapeutic approaches have produced mixed results. In this regard, intracoronary, intra-myocardial or intramuscular injection of either bone marrow-derived or peripheral blood progenitor cells has improved pathological features of tissue ischemia in humans, despite modest or no clinical benefit has been observed in most cases. Also, the intriguing scientific background surrounding the potential clinical applications of EPC capture stenting is still waiting for a confirmatory proof. Moreover, clinical findings on the efficacy of CPC-based cell therapy in heart diseases are still very preliminary and based on small-size studies. Despite promising evidence, widespread clinical application of both EPCs and CPCs remains delayed due to several unresolved issues. The present review provides a summary of the different applications of EPCs and CPCs for cardiovascular cell therapy and underlies their advantages and limitations.

Endothelial progenitor cells transplantation attenuated blood-brain barrier damage after ischemia in diabetic mice via HIF-1α

Background

Blood-brain barrier impairment is a major indicator of endothelial dysfunction in diabetes. Studies showed that endothelial progenitor cell (EPC) transplantation promoted angiogenesis and improved function recovery after hind limb ischemia in diabetic mice. The effect of EPC transplantation on blood-brain barrier integrity after cerebral ischemia in diabetic animals is unknown. The aim of this study is to explore the effect of EPC transplantation on the integrity of the blood-brain barrier after cerebral ischemia in diabetic mice.

Methods

EPCs were isolated by density gradient centrifugation and characterized by flow cytometry and immunostaining. Diabetes was induced in adult male C57BL/6 mice by a single injection of streptozotocin at 4 weeks before surgery. Diabetic mice underwent 90-minute transient middle cerebral artery occlusion surgery and received 1 × 10⁶ EPCs transplantation immediately after reperfusion. Brain infarct volume, blood-brain barrier permeability, tight junction protein expression, and hypoxia inducible factor-1α (HIF-1α) mRNA level were examined after treatment.

Results

We demonstrated that neurological deficits were attenuated and brain infarct volume was reduced in EPC-transplanted diabetic mice after transient cerebral ischemia compared to the controls (p < 0.05). Blood-brain barrier leakage and tight junction protein degradation were reduced in EPC-transplanted mice (p <0.05). EPCs upregulated HIF-1α expression while HIF-1α inhibitor PX-478 abolished the beneficial effect of EPCs.

Conclusions

We conclude that EPCs protected blood-brain barrier integrity after focal ischemia in diabetic mice through upregulation of HIF-1α signaling.

MSCs ameliorates DPN induced cellular pathology via [Ca2+ ]i homeostasis and scavenging the pro-inflammatory cytokines

The MSCs of various origins are known to ameliorate or modulate cell survival strategies. We investigated, whether UCB MSCs could improve the survival of the human neuronal cells and/or fibroblast assaulted with DPN sera. The results showed, the co-culture of UCB MSCs with human neuronal cells and/or fibroblasts could effectively scavenge the pro-inflammatory cytokines TNF-α, IL-1β, IFN-ɤ and IL - 12 and control the pro-apoptotic expression of p53/Bax. Further co-culture of UCB MSCs have shown to induce anti-inflammatory cytokines like IL-4, IL-10 and TGF-β and anti-apoptotic Bclxl/Bcl2 expression in the DPN sera stressed cells. Amelioration of elevated [Ca²⁺ ]_i and cROS, the portent behind the NFκB/Caspase-3 mediated inflammation in DPN rescued the cells from apoptosis. The results of systemic administration of BM MSCs improved DPN pathology in rat as extrapolated from human cell model. The BM MSCs ameliorated prolonged distal motor latency (control: 0.70 ± 0.06, DPN: 1.29 ± 0.13 m/s DPN + BM MSCs: 0.89 ± 0.02 m/s, p < 0.05) and lowered high amplitude of compound muscle action potentials (CMAPs) (control: 12.36 ± 0.41, DPN: 7.52 ± 0.61 mV, DPN + MSCs: 8.79 ± 0.53 mV, p < 0.05), while slowly restoring the plasma glucose levels. Together, all these results showed that administration of BM or UCB MSCs improved the DPN via ameliorating pro-inflammatory cytokine signaling and [Ca²⁺ ]_i homeostasis.

The Use of Endothelial Progenitor Cells for the Regeneration of Musculoskeletal and Neural Tissues

Endothelial progenitor cells (EPCs) derived from bone marrow and blood can differentiate into endothelial cells and promote neovascularization. In addition, EPCs are a promising cell source for the repair of various types of vascularized tissues and have been used in animal experiments and clinical trials for tissue repair. In this review, we focused on the kinetics of endogenous EPCs during tissue repair and the application of EPCs or stem cell populations containing EPCs for tissue regeneration in musculoskeletal and neural tissues including the bone, skeletal muscle, ligaments, spinal cord, and peripheral nerves. EPCs can be mobilized from bone marrow and recruited to injured tissue to contribute to neovascularization and tissue repair. In addition, EPCs or stem cell populations containing EPCs promote neovascularization and tissue repair through their differentiation to endothelial cells or tissue-specific cells, the upregulation of growth factors, and the induction and activation of endogenous stem cells. Human peripheral blood CD34(+) cells containing EPCs have been used in clinical trials of bone repair. Thus, EPCs are a promising cell source for the treatment of musculoskeletal and neural tissue injury.

Stem Cells for Diabetes Complications: A Future Potential Cure

Long-standing diabetes leads to structural and functional alterations in both the micro- and the macrovasculature. Designing therapies to repair these abnormalities present unique and sophisticated challenges. Vascular endothelial cells are the primary cells damaged by hyperglycemia-induced adverse effects. Vascular stem cells that give rise to endothelial progenitor cells and mesenchymal progenitor cells represent an attractive target for cell therapy for diabetic patients. In this review, we shed light on challenges and recent advances surrounding stem cell therapies for diabetes vascular complications and discuss limitations for their clinical adoption.

Endothelial progenitor cells from human fetal aorta cure diabetic foot in a rat model

OBJECTIVE

Recent evidence has suggested that circulating endothelial progenitor cells (EPCs) can repair the arterial endothelium during vascular injury. However, a reliable source of human EPCs is needed for therapeutic applications. In this study, we isolated human fetal aorta (HFA)-derived EPCs and analyzed the capacity of EPCs to differentiate into endothelial cells. In addition, because microvascular dysfunction is considered to be the major cause of diabetic foot (DF), we investigated whether transplantation of HFA-derived EPCs could treat DF in a rat model.

METHODS

EPCs were isolated from clinically aborted fetal aorta. RT-PCR, fluorescence-activated cell sorting, immunofluorescence, and an enzyme-linked immunosorbent assay were used to examine the expressions of CD133, CD34, CD31, Vascular Endothelial Growth Factor Receptor 2 (VEGFR2), von Willebrand Factor (vWF), and Endothelial Leukocyte Adhesion Molecule-1 (ELAM-1). Morphology and Dil-uptake were used to assess function of the EPCs. We then established a DF model by injecting microcarriers into the hind-limb arteries of Goto-Kakizaki rats and then transplanting the cultured EPCs into the ischemic hind limbs. Thermal infrared imaging, oxygen saturation apparatus, and laser Doppler perfusion imaging were used to monitor the progression of the disease. Immunohistochemistry was performed to examine the microvascular tissue formed by HFA-derived EPCs.

RESULTS

We found that CD133, CD34, and VEGFR2 were expressed by HFA-derived EPCs. After VEGF induction, CD133 expression was significantly decreased, but expression levels of vWF and ELAM-1 were markedly increased. Furthermore, tube formation and Dil-uptake were improved after VEGF induction. These observations suggest that EPCs could differentiate into endothelial cells. In the DF model, temperature, blood flow, and oxygen saturation were reduced but recovered to a nearly normal level following injection of the EPCs in the hind limb. Ischemic symptoms also improved. Injected EPCs were preferentially and durably engrafted into the blood vessels. In addition, anti-human CD31+-AMA+-vWF+ microvasculars were detected after transplantation of EPCs.

CONCLUSION

Early fetal aorta-derived EPCs possess strong self-renewal ability and can differentiate into endothelial cells. We demonstrated for the first time that transplanting HFA-derived EPCs could ameliorate DF prognosis in a rat model. These findings suggest that the transplantation of HFA-derived EPCs could serve as an innovative therapeutic strategy for managing DF.

Mesenchymal Stem Cells as a Prospective Therapy for the Diabetic Foot

The diabetic foot is a serious complication of diabetes. Mesenchymal stem cells are an abundant source of stem cells which occupy a special position in cell therapies, and recent studies have suggested that mesenchymal stem cells can play essential roles in treatments for the diabetic foot. Here, we discuss the advances that have been made in mesenchymal stem cell treatments for this condition. The roles and functional mechanisms of mesenchymal stem cells in the diabetic foot are also summarized, and insights into current and future studies are presented.

Is Stem Cell Transplantation Ready for Prime Time in Diabetic Polyneuropathy?

Diabetic polyneuropathy (DPN) is the most common complication that emerges early in patients who have diabetes. Curative treatment for overt or symptomatic DPN has not been established, requiring much effort to explore new modalities. Thus, the use of various kinds of stem cells as a potential therapeutic option for DPN is of particular interest. The beneficial effects were proposed to be attributed to either cytokine released from transplanted stem cells or the differentiation of stem cells to substitute the damaged peripheral nerve. Furthermore, based on the concept that humoral factors secreted from stem cells play a pivotal role in tissue regeneration, the utilization of conditioned medium derived from the stem cell culture serves as a novel tool for regenerative therapy. However, many questions have not been yet answered to determine whether stem cell therapy is essential in clinical application of DPN. In this report, we review the current status of preclinical studies on stem cell therapy for DPN and discuss future prospects.

Transplantation of Human Placenta-Derived Mesenchymal Stem Cells Alleviates Critical Limb Ischemia in Diabetic Nude Rats

Neovasculogenesis induced by stem cell therapy is an innovative approach to improve critical limb ischemia (CLI) in diabetes. Mesenchymal stem cells (MSCs) are ideal candidates due to their angiogenic and immunomodulatory features. The aim of this study is to determine the therapeutic effects of human placenta-derived MSCs (P-MSCs) on diabetic CLI, with or without exogenous insulin administration, and the underlying mechanism of any effect. A series of in vitro experiments were performed to assess the stemness and vasculogenic activity of P-MSCs. P-MSCs were intramuscularly injected at two different doses with and without the administration of insulin. The efficacy of P-MSC transplantation was evaluated by ischemia damage score, ambulatory score, laser Doppler perfusion image (LDPI), capillary, and vascular density. In vivo imaging was applied to track the implanted P-MSCs. In vivo differentiation and in situ secretion of angiogenic cytokines were determined. In vitro experimental outcomes showed the differentiation potential and potent paracrine effect of P-MSCs. P-MSCs survived in vivo for at least 3 weeks and led to the acceleration of ischemia recovery, due to newly formed capillaries, increased arterioles, and secretion of various proangiogenic factors. P-MSCs participate in angiogenesis and vascularization directly through differentiation and cytokine expression.

Pyruvate Dehydrogenase Kinase-mediated Glycolytic Metabolic Shift in the Dorsal Root Ganglion Drives Painful Diabetic Neuropathy

The dorsal root ganglion (DRG) is a highly vulnerable site in diabetic neuropathy. Under diabetic conditions, the DRG is subjected to tissue ischemia or lower ambient oxygen tension that leads to aberrant metabolic functions. Metabolic dysfunctions have been documented to play a crucial role in the pathogenesis of diverse pain hypersensitivities. However, the contribution of diabetes-induced metabolic dysfunctions in the DRG to the pathogenesis of painful diabetic neuropathy remains ill-explored. In this study, we report that pyruvate dehydrogenase kinases (PDK2 and PDK4), key regulatory enzymes in glucose metabolism, mediate glycolytic metabolic shift in the DRG leading to painful diabetic neuropathy. Streptozotocin-induced diabetes substantially enhanced the expression and activity of the PDKs in the DRG, and the genetic ablation of Pdk2 and Pdk4 attenuated the hyperglycemia-induced pain hypersensitivity. Mechanistically, Pdk2/4 deficiency inhibited the diabetes-induced lactate surge, expression of pain-related ion channels, activation of satellite glial cells, and infiltration of macrophages in the DRG, in addition to reducing central sensitization and neuroinflammation hallmarks in the spinal cord, which probably accounts for the attenuated pain hypersensitivity. Pdk2/4-deficient mice were partly resistant to the diabetes-induced loss of peripheral nerve structure and function. Furthermore, in the experiments using DRG neuron cultures, lactic acid treatment enhanced the expression of the ion channels and compromised cell viability. Finally, the pharmacological inhibition of DRG PDKs or lactic acid production substantially attenuated diabetes-induced pain hypersensitivity. Taken together, PDK2/4 induction and the subsequent lactate surge induce the metabolic shift in the diabetic DRG, thereby contributing to the pathogenesis of painful diabetic neuropathy.

Transplantation of dental pulp stem cells suppressed inflammation in sciatic nerves by promoting macrophage polarization towards anti-inflammation phenotypes and ameliorated diabetic polyneuropathy

Aims/Introduction

Dental pulp stem cells (DPSCs) are thought to be an attractive candidate for cell therapy. We recently reported that the transplantation of DPSCs increased nerve conduction velocity and nerve blood flow in diabetic rats. In the present study, we investigated the immunomodulatory effects of DPSC transplantation on diabetic peripheral nerves.

Materials and Methods

DPSCs were isolated from the dental pulp of Sprague–Dawley rats and expanded in culture. Eight weeks after the streptozotocin injection, DPSCs were transplanted into the unilateral hindlimb skeletal muscles. Four weeks after DPSC transplantation, neurophysiological measurements, inflammatory gene expressions and the number of CD68‐positive cells in sciatic nerves were assessed. To confirm the immunomodulatory effects of DPSCs, the effects of DPSC‐conditioned media on lipopolysaccharide‐stimulated murine macrophage RAW264.7 cells were investigated.

Results

Diabetic rats showed significant delays in sciatic nerve conduction velocities and decreased sciatic nerve blood flow, all of which were ameliorated by DPSC transplantation. The number of CD68‐positive monocytes/macrophages and the gene expressions of M1 macrophage‐expressed cytokines, tumor necrosis factor‐α and interleukin‐1β, were increased in the sciatic nerves of the diabetic rats. DPSC transplantation significantly decreased monocytes/macrophages and tumor necrosis factor‐α messenger ribonucleic acid expression, and increased the gene expression of the M2 macrophage marker, CD206, in the sciatic nerves of the diabetic rats. The in vitro study showed that DPSC‐conditioned media significantly increased the gene expressions of interleukin‐10 and CD206 in lipopolysaccharide‐stimulated RAW264.7 cells.

Conclusions

These results suggest that DPSC transplantation promoted macrophages polarization towards anti‐inflammatory M2 phenotypes, which might be one of the therapeutic mechanisms for diabetic polyneuropathy.

Endothelial colony-forming cells: Biological and functional abnormalities in patients with recurrent, unprovoked venous thromboembolic disease

INTRODUCTION

Endothelial cells (ECs) are an important component of the blood coagulation system because it maintains blood fluid. Because in patients with venous thromboembolic disease (VTD) a thrombophilic condition is not found sometimes, we investigated if endothelial colony-forming cells (ECFCs) from these patients have biological and functional abnormalities.

PATIENTS AND METHODS

Human mononuclear cells (MNCs) were obtained from peripheral blood from patients with VTD and controls to obtain ECFCs. These cells were assayed for their immunophenotype and electron microscopy characteristics and their ability to form capillary-like structures and to produce pro-inflammatory and pro-angiogenic cytokines and reactive oxygen species (ROS).

RESULTS

ECFCs appeared at 7 and 21 days of culture in VTD patients and controls, respectively. ECFCs increased 8-fold in patients and emerged 1 week earlier. No differences in the size of the colonies of ECFCs were found. Numbers and time of appearance of ECFCs was different between groups. ECFC-derived ECs (ECFC-ECs) of both groups expressed CD31, CD34, CD146, and CD-309 but none expressed CD45, CD14, or CD90. Interest CD34 was highly expressed in ECFC-ECs from patients. In both groups, ECFC-ECs showed similar capacity to form capillary-like structures but ECFC-ECs from patients had significant abnormalities in the mitochondrial membrane. We found a significant increase in ROS production in ECFC-ECs from patients. There were significant differences in cytokine profiles between VTD patients and controls.

CONCLUSIONS

We found a dysfunctional state in ECFC from VTD patients resembling some characteristics of dysfunctional ECs. These findings may help to understand some pathophysiological aspects of VTD.

Are Endothelial Progenitor Cells the Real Solution for Cardiovascular Diseases? Focus on Controversies and Perspectives

Advanced knowledge in the field of stem cell biology and their ability to provide a cue for counteracting several diseases are leading numerous researchers to focus their attention on “regenerative medicine” as possible solutions for cardiovascular diseases (CVDs). However, the lack of consistent evidence in this arena has hampered the clinical application. The same condition affects the research on endothelial progenitor cells (EPCs), creating more confusion than comprehension. In this review, this aspect is discussed with particular emphasis. In particular, we describe biology and physiology of EPCs, outline their clinical relevance as both new predictive, diagnostic, and prognostic CVD biomarkers and therapeutic agents, discuss advantages, disadvantages, and conflicting data about their use as possible solutions for vascular impairment and clinical applications, and finally underline a very crucial aspect of EPCs “characterization and definition,” which seems to be the real cause of large heterogeneity existing in literature data on this topic.

Enhanced Viability of Endothelial Colony Forming Cells in Fibrin Microbeads for Sensor Vascularization

Enhanced vascularization at sensor interfaces can improve long-term function. Fibrin, a natural polymer, has shown promise as a biomaterial for sensor coating due to its ability to sustain endothelial cell growth and promote local vascularization. However, the culture of cells, particularly endothelial cells (EC), within 3D scaffolds for more than a few days is challenging due to rapid loss of EC viability. In this manuscript, a robust method for developing fibrin microbead scaffolds for long-term culture of encapsulated ECs is described. Fibrin microbeads are formed using sodium alginate as a structural template. The size, swelling and structural properties of the microbeads were varied with needle gauge and composition and concentration of the pre-gel solution. Endothelial colony-forming cells (ECFCs) were suspended in the fibrin beads and cultured within a perfusion bioreactor system. The perfusion bioreactor enhanced ECFCs viability and genome stability in fibrin beads relative to static culture. Perfusion bioreactors enable 3D culture of ECs within fibrin beads for potential application as a sensor coating.

Transplantation of cultured dental pulp stem cells into the skeletal muscles ameliorated diabetic polyneuropathy: therapeutic plausibility of freshly isolated and cryopreserved dental pulp stem cells

Introduction

Dental pulp stem cells (DPSCs) are mesenchymal stem cells located in dental pulp and are thought to be a potential source for cell therapy since DPSCs can be easily obtained from teeth extracted for orthodontic reasons. Obtained DPSCs can be cryopreserved until necessary and thawed and expanded when needed. The aim of this study is to evaluate the therapeutic potential of DPSC transplantation for diabetic polyneuropathy.

Methods

DPSCs isolated from the dental pulp of extracted incisors of Sprague–Dawley rats were partly frozen in a −80 °C freezer for 6 months. Cultured DPSCs were transplanted into the unilateral hindlimb skeletal muscles 8 weeks after streptozotocine injection and the effects of DPSC transplantation were evaluated 4 weeks after the transplantation.

Results

Transplantation of DPSCs significantly improved the impaired sciatic nerve blood flow, sciatic motor/sensory nerve conduction velocity, capillary number to muscle fiber ratio and intra-epidermal nerve fiber density in the transplanted side of diabetic rats. Cryopreservation of DPSCs did not impair their proliferative or differential ability. The transplantation of cryopreserved DPSCs ameliorated sciatic nerve blood flow and sciatic nerve conduction velocity as well as freshly isolated DPSCs.

Conclusions

We demonstrated the effectiveness of DPSC transplantation for diabetic polyneuropathy even when using cryopreserved DPSCs, suggesting that the transplantation of DPSCs could be a promising tool for the treatment of diabetic neuropathy.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0156-4) contains supplementary material, which is available to authorized users.

Diabetes and stem cell function

Diabetes mellitus is one of the most common serious metabolic diseases that results in hyperglycemia due to defects of insulin secretion or insulin action or both. The present review focuses on the alterations to the diabetic neuronal tissues and skeletal muscle, including stem cells in both tissues, and the preventive effects of physical activity on diabetes. Diabetes is associated with various nervous disorders, such as cognitive deficits, depression, and Alzheimer's disease, and that may be caused by neural stem cell dysfunction. Additionally, diabetes induces skeletal muscle atrophy, the impairment of energy metabolism, and muscle weakness. Similar to neural stem cells, the proliferation and differentiation are attenuated in skeletal muscle stem cells, termed satellite cells. However, physical activity is very useful for preventing the diabetic alteration to the neuronal tissues and skeletal muscle. Physical activity improves neurogenic capacity of neural stem cells and the proliferative and differentiative abilities of satellite cells. The present review proposes physical activity as a useful measure for the patients in diabetes to improve the physiological functions and to maintain their quality of life. It further discusses the use of stem cell-based approaches in the context of diabetes treatment.

Human mesenchymal stem cells improve the neurodegeneration of femoral nerve in a diabetic foot ulceration rats

Neuropathy is observed in 50% of diabetic patients with diabetic foot. This study attempted to explore the potential role of human mesenchymal stem cells-umbilical cord blood (hMSCs-UC) in femoral nerve (FN) neuropathy. The model rats were established by one time administration of streptozotocin and empyrosis on the dorsal hind foot. At 3d, 7d, 14d after treatment with hMSCs-UC or saline through left femoral artery, the serum NGF was examined by ELISA; NF-200 expression in FN was evaluated by immunohistochemistry; the diameter and roundness of FN, the ratio of capillary and muscular fiber of gastrocnemius were calculated under light microscope; and neuronal degenerations, such as demyelization, axonal atrophy, and loose arrangement of nerve fibers, were observed by electronic microscope. The results showed that, in hMSCs-UC-treated model rats, serum NGF was increased with higher positive rate of NF-200. Although the difference in FN diameters was not established among groups, improvement of roundness of FN was confirmed with increase in the numbers of capillary in FN-innervated gastrocnemius; additionally, degenerative neuropathy was significantly improved. Importantly, the functional study of electroneurogram (ENG) showed that, slowed conduction of FN in model rats was significantly restored by hMSCs-CU treatment. These data suggested that hMSCs-UC-treatment partially reverse the neuronal degeneration and nerve function of FN, which might be contributed by the upregulation of NGF with dramatic angiogenesis in FN-innervated gastrocnemius, consequently reversing neuronal structure and function, preventing or curing foot ulceration.

Angioblast Derived from ES Cells Construct Blood Vessels and Ameliorate Diabetic Polyneuropathy in Mice

BACKGROUND

Although numerous reports addressing pathological involvements of diabetic polyneuropathy have been conducted, a universally effective treatment of diabetic polyneuropathy has not yet been established. Recently, regenerative medicine studies in diabetic polyneuropathy using somatic stem/progenitor cell have been reported. However, the effectiveness of these cell transplantations was restricted because of their functional and numerical impairment in diabetic objects. Here, we investigated the efficacy of treatment for diabetic polyneuropathy using angioblast-like cells derived from mouse embryonic stem cells.

METHODS AND RESULTS

Angioblast-like cells were obtained from mouse embryonic stem cells and transplantation of these cells improved several physiological impairments in diabetic polyneuropathy: hypoalgesia, delayed nerve conduction velocities, and reduced blood flow in sciatic nerve and plantar skin. Furthermore, pathologically, the capillary number to muscle fiber ratios were increased in skeletal muscles of transplanted hindlimbs, and intraepidermal nerve fiber densities were ameliorated in transplanted plantar skin. Transplanted cells maintained their viabilities and differentiated to endothelial cells and smooth muscle cells around the injection sites. Moreover, several transplanted cells constructed chimeric blood vessels with recipient cells.

CONCLUSIONS

These results suggest that transplantation of angioblast like cells induced from embryonic stem cells appears to be a novel therapeutic strategy for diabetic polyneuropathy.

Therapeutic efficacy of bone marrow-derived mononuclear cells in diabetic polyneuropathy is impaired with aging or diabetes

Aims/Introduction

Recent studies have shown that cell transplantation therapies, such as endothelial precursor cells, bone marrow-derived mononuclear cells (BM-MNCs) and mesenchymal stem cells, are effective on diabetic polyneuropathy through ameliorating impaired nerve blood flow in diabetic rats. Here, we investigated the effects of BM-MNCs transplantation in diabetic polyneuropathy using BM-MNCs derived from adult (16-week-old) diabetic (AD), adult non-diabetic (AN) or young (8-week-old) non-diabetic (YN) rats.

Materials and Methods

BM-MNCs of AD and AN were isolated after an 8-week diabetes duration. The BM-MNCs were characterized using flow cytometry analysis of cell surface markers and reverse transcription polymerase chain reaction of several cytokines. BM-MNCs or saline were injected into hind limb muscles. Four weeks later, the thermal plantar test, nerve conduction velocity, blood flow of the sciatic nerve and capillary-to-muscle fiber ratio were evaluated.

Results

The number of CD29⁺/CD90⁺ cells that host mesenchymal stem cells in BM-MNCs decreased in AD compared with AN or YN, and transcript expressions of basic fibroblast growth factor and nerve growth factor in BM-MNCs decreased in AD compared with AN or YN. Impaired thermal sensation, decreased blood flow of the sciatic nerve and delayed nerve conduction velocity in 8-week-diabetic rats were significantly ameliorated by BM-MNCs derived from YN, whereas BM-MNCs from AD or AN rats did not show any beneficial effect in these functional tests.

Conclusions

These results show that cytokine production abilities and the mesenchymal stem cell population of BM-MNCs would be modified by aging and metabolic changes in diabetes, and that these differences could explain the disparity of the therapeutic efficacy of BM-MNCs between young and adult or diabetic and non-diabetic patients in diabetic polyneuropathy.

Cell-based therapies for the preterm infant

The severely preterm infant receives a multitude of life-saving interventions, many of which carry risks of serious side effects. Cell therapy is an important and promising arm of regenerative medicine that may address a number of these problems. Most forms of cellular therapy use stem/progenitor cells or stem-like cells, which have the capacity to migrate, engraft and exert anti-inflammatory effects. Although some of these cell-based therapies have made their way to clinical trials in adults, little headway has been made in the neonatal patient group. This review discusses the efficacy of cell therapy in preclinical studies to date and their potential applications to diseases that afflict many prematurely born infants. Specifically, we identify the major hurdles that must be overcome before cell therapies can be safely used in the neonatal intensive care unit.

Non-hematopoietic stem cells in umbilical cord blood

Allogeneic umbilical cord blood (UCB) transplantation has been used to treat a variety of malignant and non-malignant diseases. Recent studies show convincing evidence that UCB contains not only hematopoietic progenitors, but also several types of stem and progenitor cells providing a high proliferative capacity and a variety of differentiation potentials. UCB-derived cells offer multiple advantages over adult stem cells from other sources like bone marrow (BM), because UCB can be collected without painful procedure, easily available in virtually unlimited supply, and has not been exposed to immunologic challenge. In addition, cord blood transplantation is now an established field with great potential and no serious ethical issue by establishment of public UCB banks throughout the world. Therefore UCB-derived non-hematopoietic stem cells may provide an attractive cell source for tissue repair and regeneration. It is generally accepted that UCB contains endothelial progenitor cells (EPC), mesenchymal stromal cells (MSC), unrestricted somatic stem cells (USSC), very small embryonic-like stem cells (VSEL), multilineage progenitor cells (MLPC), and neuronal progenitor cells. This review focuses on biological properties of these non-hematopoietic stem/progenitor cells derived from human UCB and their potential use in cell based therapies.

High glucose impairs the proliferation and increases the apoptosis of endothelial progenitor cells by suppression of Akt

Aims/Introduction:  Endothelial progenitor cells (EPC) play a critical role in adult vasculogenesis and vascular repair. Previous studies have described the dysfunction of EPC in diabetic patients, but the precise mechanism is still unclear. To elucidate the dysfunction of EPC in diabetic patients, we investigated the functions and intracellular signaling of EPC under normal or high glucose conditions. We also examined the number of EPC in the peripheral blood of Japanese type 2 diabetic patients.

MATERIALS AND METHODS

  EPC were cultured with normal or high glucose. Subsequently, the proliferation and the apoptosis of EPC were assessed in the presence or absence of vascular endothelial growth factor (VEGF). The phosphorylation of Akt was assessed by western blot analyses. We compared the number of CD34(+)CD45(low) progenitor cells, which is considered as a marker of EPC in non-diabetic and type 2 diabetic subjects, using flow cytometry.

RESULTS

  High glucose decreased the proliferation of EPC and increased the number of apoptotic cells. VEGF significantly increased the proliferation and suppressed the apoptosis of EPC, both of which were abolished by PI 3-kinase inhibitor, LY294002. High glucose significantly suppressed the basal and VEGF-stimulated phosphorylation of Akt in EPC. Furthermore, the number of circulating EPC was decreased in type 2 diabetic patients, although there were no significant differences in the serum levels of VEGF between control subjects and diabetic patients.

CONCLUSIONS

  These findings suggest that high glucose impairs the functions of EPC through the suppression of Akt phosphorylation stimulated by VEGF. (J Diabetes Invest, doi: 10.1111/j.2040-1124.2010.00093.x, 2011).

Erythropoietin attenuates oxidative stress and apoptosis in Schwann cells isolated from streptozotocin-induced diabetic rats

OBJECTIVES

High glucose-evoked oxidative stress and apoptosis within Schwann cells (SCs) are mechanisms facilitating the procession of diabetic peripheral neuropathy (DPN). Although erythropoietin (EPO) was demonstrated to have neuroprotective effects in neurodegenerative diseases, the effects of EPO on glucose-evoked oxidative stress and apoptosis of SCs remain unknown.

METHODS

Primary cultured SCs isolated from streptozotocin (STZ)-induced diabetic peripheral neuropathic rats and normal control rats were exposed to high or normal glucose condition with or without EPO incubation for 72 h. Cell viability, apoptotic rate, cellular reactive oxygen species (ROS) level, total glutathione (GSH) level, EPO mRNA and erythropoietin receptor (EPOR) mRNA levels were assayed.

KEY FINDINGS

SCs from diabetic rats showed a lower cell viability and a higher apoptotic rate. High glucose culture condition elevated ROS level and diminished total GSH level of SCs. EPO improved cell viability and decreased cell apoptotic rate of SCs. EPO also elevated total GSH level and decreased intracellular ROS level. SCs from diabetic rats exhibited higher EPO mRNA and EPOR mRNA levels than SCs from normal control rats.

CONCLUSIONS

The data of this study offered fresh viewpoints for interpreting the pathogenesis of DPN and novel pharmacological principles implicit in the therapeutic effect of EPO.

A reappraisal of the role of circulating (progenitor) cells in the pathobiology of diabetic complications

Traditionally, the development of diabetic complications has been attributed to the biochemical pathways driving hyperglycaemic cell damage, while reparatory mechanisms have been long overlooked. A more comprehensive view of the balance between damage and repair suggests that an impaired regenerative capacity of bone marrow (BM)-derived cells strongly contributes to defective re-endothelisation and neoangiogenesis in diabetes. Although recent technological advances have redefined the biology and function of endothelial progenitor cells (EPCs), interest in BM-derived vasculotropic cells in the setting of diabetes and its complications remains high. Several circulating cell types of haematopoietic and non-haematopoietic origin are affected by diabetes and are potentially involved in the pathobiology of chronic complications. In addition to classical EPCs, these include circulating (pro-)angiogenic cells, polarised monocytes/macrophages (M1 and M2), myeloid calcifying cells and smooth muscle progenitor cells, having disparate roles in vascular biology. In parallel with the study of elusive progenitor cell phenotypes, it has been recognised that diabetes induces a profound remodelling of the BM stem cell niche. The alteration of circulating (progenitor) cells in the BM is now believed to be the link among distant end-organ complications. The field is rapidly evolving and interest is shifting from specific cell populations to the complex network of interactions that orchestrate trafficking of circulating vasculotropic cells.

Exploring a new therapy for diabetic polyneuropathy - the application of stem cell transplantation

Diabetic polyneuropathy (DPN) is the most common complication that emerges early in diabetic patients. Intervention with strict blood glucose control or treatment with aldose reductase inhibitor is reported to be effective in early stages of DPN. Curative treatment for overt or symptomatic DPN, however, has not been established, thus requiring much effort to explore a new therapy. Recent preclinical studies on the use of gene or cell therapy have provided promising results in the treatment of DPN. Of particular interest, induced pluripotent stem cells are introduced. In these studies, restoration of DPN was proposed to be attributed to either neurotrophic factors released from transplanted stem cells or differentiation of stem cells to substitute the damaged peripheral nerve. There are still several problems, however, that remain to be overcome, such as perturbed function, fragility, or limited survival of transplanted cells in diabetes milieu and risk for malignant transformation of transplanted cells. Questions, which cell is the most appropriate as the source for cell therapy, or which site is the best for transplantation to obtain the most effective results, remain to be answered. In this communication, we overview the current status of preclinical studies on the cell therapy for DPN and discuss the future prospect.

Mesenchymal stem cell-like cells derived from mouse induced pluripotent stem cells ameliorate diabetic polyneuropathy in mice

Background. Although pathological involvements of diabetic polyneuropathy (DPN) have been reported, no dependable treatment of DPN has been achieved. Recent studies have shown that mesenchymal stem cells (MSCs) ameliorate DPN. Here we demonstrate a differentiation of induced pluripotent stem cells (iPSCs) into MSC-like cells and investigate the therapeutic potential of the MSC-like cell transplantation on DPN. Research Design and Methods. For induction into MSC-like cells, GFP-expressing iPSCs were cultured with retinoic acid, followed by adherent culture for 4 months. The MSC-like cells, characterized with flow cytometry and RT-PCR analyses, were transplanted into muscles of streptozotocin-diabetic mice. Three weeks after the transplantation, neurophysiological functions were evaluated. Results. The MSC-like cells expressed MSC markers and angiogenic/neurotrophic factors. The transplanted cells resided in hindlimb muscles and peripheral nerves, and some transplanted cells expressed S100β in the nerves. Impairments of current perception thresholds, nerve conduction velocities, and plantar skin blood flow in the diabetic mice were ameliorated in limbs with the transplanted cells. The capillary number-to-muscle fiber ratios were increased in transplanted hindlimbs of diabetic mice. Conclusions. These results suggest that MSC-like cell transplantation might have therapeutic effects on DPN through secreting angiogenic/neurotrophic factors and differentiation to Schwann cell-like cells.

Transplantation of Neural Crest-Like Cells Derived from Induced Pluripotent Stem Cells Improves Diabetic Polyneuropathy in Mice

Impaired vascularity and nerve degeneration are the most important pathophysiological abnormalities of diabetic polyneuropathy (DPN). Therefore, regeneration of both the vascular and nervous systems is required for the treatment of DPN. The neural crest (NC) is a transient embryonic structure in vertebrates that differentiates into a vast range of cells, including peripheral neurons, Schwann cells, and vascular smooth muscle cells. In this study, we investigated the ability of transplantation of NC-like (NCL) cells derived from aged mouse induced pluripotent stem (iPS) cells in the treatment of DPN. iPS cells were induced to differentiate into neural cells by stromal cell-derived inducing activity (SDIA) and subsequently supplemented with bone morphogenetic protein 4 to promote differentiation of NC lineage. After the induction, p75 neurotrophin receptor-positive NCL cells were purified using magnetic-activated cell sorting. Sorted NCL cells differentiated to peripheral neurons, glial cells, and smooth muscle cells by additional SDIA. NCL cells were transplanted into hind limb skeletal muscles of 16-week streptozotocin-diabetic mice. Nerve conduction velocity, current perception threshold, intraepidermal nerve fiber density, sensitivity to thermal stimuli, sciatic nerve blood flow, plantar skin blood flow, and capillary number-to-muscle fiber ratio were evaluated. Four weeks after transplantation, the engrafted cells produced growth factors: nerve growth factor, neurotrophin 3, vascular endothelial growth factor, and basic fibroblast growth factor. It was also confirmed that some engrafted cells differentiated into vascular smooth muscle cells or Schwann cell-like cells at each intrinsic site. The transplantation improved the impaired nerve and vascular functions. These results suggest that transplantation of NCL cells derived from iPS cells could have therapeutic effects on DPN through paracrine actions of growth factors and differentiation into Schwann cell-like cells and vascular smooth muscle cells.

Synergistic vasculogenic effects of AMD3100 and stromal-cell-derived factor-1α in vasa nervorum of the sciatic nerve of mice with diabetic peripheral neuropathy

Autologous endothelial progenitor cell (EPC) transplantation has been suggested as a potential therapeutic approach in diabetic neuropathy (DN). However, such treatment might be limited by safety concerns regarding possible unwanted proliferation or differentiation of the transplanted stem cells. An alternative approach is the stimulation of endogenous bone-marrow-derived EPC (BM-EPC) recruitment into ischemic lesions by the administration of stem cell mobilization agents or chemokines. We first tested the EPC mobilization effect of vascular endothelial growth factor (VEGF) and AMD3100 in a mouse model of diabetes and found that AMD3100 was effective as an EPC mobilization agent, whereas VEGF did not increase circulating EPCs in these animals. Because recent studies have suggested that deceased local expression of stromal-cell-derived factor (SDF)-1α in diabetes is the main cause of defective EPC migration, AMD3100 was administrated systemically to stimulate EPC mobilization and SDF-1α was injected locally to enhance its migration into the streptozotocin-induced DN mice model. This combined therapy increased local expression levels of vasculogenesis-associated factors and newly formed endothelial cells in the sciatic nerve, resulting in the restoration of the sciatic vasa nervorum. The treatment also improved the impaired conduction velocity of the sciatic nerve in DN mice. Thus, AMD3100 might be an effective EPC mobilization agent in diabetes, with local SDF-1α injection synergistically increasing vascularity in diabetic nerves. This represents a novel potential therapeutic option for DN patients.

Tissue-engineered blood vessel substitute by reconstruction of endothelium using mesenchymal stem cells induced by platelet growth factors

BACKGROUND

Cardiovascular diseases remain leaders as the major causes of mortality in Western society. Restoration of the circulation through construction of bypass surgical treatment is regarded as the gold standard treatment of peripheral vascular diseases, and grafts are necessary for this purpose. The great saphenous vein is often not available and synthetic grafts have their limitations. Therefore, new techniques to produce alternative grafts have been developed and, in this sense, tissue engineering is a promising alternative to provide biocompatible grafts. This study objective was to reconstruct the endothelium layer of decellularized vein scaffolds, using mesenchymal stem cells (MSCs) and growth factors obtained from platelets.

METHODS

Fifteen nonpregnant female adult rabbits were used for all experiments. Adipose tissue and vena cava were obtained and subjected to MSCs isolation and tissue decellularization, respectively. MSCs were subjected to differentiation using endothelial inductor growth factor (EIGF) obtained from human platelet lysates. Immunofluorescence, histological and immunohistochemical analyses were employed for the final characterization of the obtained blood vessel substitute.

RESULTS

The scaffolds were successfully decellularized with sodium dodecyl sulfate. MSCs actively adhered at the scaffolds, and through stimulation with EIGF were differentiated into functional endothelial cells, secreting significantly higher quantities of von Willebrand factor (0.85 μg/mL; P < .05) than cells cultivated under the same conditions, without EIGF (0.085 μg/mL). Cells with evident morphologic characteristics of endothelium were seen at the lumen of the scaffolds. These cells also stained positive for fascin protein, which is highly expressed by differentiated endothelial cells.

CONCLUSIONS

Taken together, the use of decellularized bioscaffold and subcutaneous MSCs seems to be a potential approach to obtain bioengineered blood vessels, in the presence of EIGF supplementation.