Diabetes impairs mobilization of stem cells for the treatment of cardiovascular disease

The Effect of Short-Term NAD3® Supplementation on Circulating Adult Stem Cells in Healthy Individuals Aged 40-70 Years

Objective This study aimed to assess the impact of acute and short-term supplementation with NAD3®, a theacrine-containing supplement, on circulating adult stem cell numbers in a healthy male and female population aged 40-70 years. Methods This was a double-blind, placebo-controlled crossover study with 12 participants randomized to receive either NAD3® or a placebo for seven days. Blood samples were collected after an overnight fast, before and after the seven-day supplementation period, and one and two hours after the final supplement dose. Using flow cytometry, circulating stem cells, including lymphocytoid CD34+ stem cells (CD45dimCD34+), stem cells associated with vascular maintenance and repair (CD45dimCD34+CD309+), CD34+ stem cells linked to a progenitor phenotype (CD45dimCD34+CD309neg), circulating endothelial stem cells (CD45negCD31+CD309+), and mesenchymal stem cells (CD45negCD90+) were quantified. Results Acute NAD3® supplementation did not result in the mobilization of stem cells from the bone marrow. However, seven days of daily NAD3® supplementation resulted in selective changes in circulating stem cell numbers. A significant time*treatment interaction was observed for CD45dimCD34+ cells (p=0.04) and CD45dimCD34+CD309neg cells (p=0.04), indicating a decrease in cell numbers with supplementation. There was also a trend toward an increase in circulating endothelial cells (p=0.08) with seven days of NAD3®supplementation. Conclusion Short-term NAD3® supplementation demonstrated an effect on the quantity of bone marrow-derived stem cells in circulation. The study suggests that this theacrine-containing supplement may play a role in modulating adult stem cell populations, emphasizing the potential impact of NAD3® on regenerative processes. Further research with extended supplementation periods and larger sample sizes is warranted to elucidate the functional consequences of these changes and explore the therapeutic implications for age-related declines in stem cell function.

The impact of diabetes mellitus on hematopoietic stem cell mobilization, a-single center cohort study

BACKGROUND

Factors such as age, underlying hematological disease, chemotherapy and radiotherapy used, and bone marrow infiltration may cause mobilization failure. Several preclinical observed that diabetes mellitus (DM) leads to profound remodeling of the hematopoietic stem cell (HSC) niche, resulting in the impaired release of HSCs. We aim to examine the effect of DM on HSC mobilization and to investigate whether there is a relationship between complications developing in the DM process and drugs used to treat DM and mobilization failure.

METHODS

In Erciyes University Bone Marrow Transplantation Unit, 218 patients who underwent apheresis for stem cell mobilization between 2011 and 2021 were evaluated retrospectively. One hundred and nine patients had a diagnosis of DM, and 109 did not.

RESULTS

Mobilization failure developed in 17 (15.6 %) of the patients in the DM group, while it developed in 7 (6.4 %) patients in the non-DM group (p = 0.03). CD34+ stem cell count was 8.05 (1.3-30.2) × 106/kg in the DM group, while it was 8.2 (1.7-37.3) × 106/kg in the other group (p = 0.55). There was no statistically significant relationship between glucose and hemoglobin A1c levels and the amount of CD34+ cells (p = 0.83 and p = 0.14, respectively). Using sulfonylurea was the only independent predictor of mobilization failure (OR 5.75, 95 % CI: 1.38-24.05, p = 0.02).

CONCLUSION

DM should be considered a risk factor for mobilization failure. Further research is needed fully to understand the mechanisms underlying the mobilization failure effects of sulfonylureas and to develop strategies to improve stem cell mobilization in diabetic patients.

Bone marrow vasculature advanced in vitro models for cancer and cardiovascular research

Cardiometabolic diseases and cancer are among the most common diseases worldwide and are a serious concern to the healthcare system. These conditions, apparently distant, share common molecular and cellular determinants, that can represent targets for preventive and therapeutic approaches. The bone marrow plays an important role in this context as it is the main source of cells involved in cardiovascular regeneration, and one of the main sites of liquid and solid tumor metastasis, both characterized by the cellular trafficking across the bone marrow vasculature. The bone marrow vasculature has been widely studied in animal models, however, it is clear the need for human-specific in vitro models, that resemble the bone vasculature lined by endothelial cells to study the molecular mechanisms governing cell trafficking. In this review, we summarized the current knowledge on in vitro models of bone marrow vasculature developed for cardiovascular and cancer research.

Stem and Somatic Cell Monotherapy for the Treatment of Diabetic Foot Ulcers: Review of Clinical Studies and Mechanisms of Action

Diabetic foot ulcer (DFU) is one of the most severe complications of diabetes mellitus, often resulting in a limb amputation. A cell-based therapy is a highly promising approach for an effective DFU treatment. However, there is no consensus regarding the most effective cell type for DFU treatment. Various cell types contribute to chronic wound healing via different mechanisms. For example, application of keratinocytes can stimulate migration of native keratinocytes from the wound edge, while mesenchymal stem cells can correct limb ischemia. To assess the effectiveness of a certain cell type, it should be administered as a monotherapy without other substances and procedures that have additional therapeutic effects. In the present review, we described therapeutic effects of various cells and provided an overview of clinical studies in which stem and somatic cell-based therapy was administered as a monotherapy. Topical application of somatic cells contributes to DFU healing only, while injection of mesenchymal stem cells and mononuclear cells can break a pathophysiological chain leading from insufficient blood supply to DFU development. At the same time, the systemic use of mesenchymal stem cells carries greater risks. Undoubtedly, cell therapy is a potent tool for the treatment of DFU. However, it is vital to conduct further high-quality clinical research to determine the most effective cell type, dosage and way of administration for DFU treatment. Ischemia, neuropathy and neuro-ischemia are underlying factors of diabetic foot ulcer. Stem and somatic cells monotherapy can improve chronic wound healing via different mechanisms.

Unraveling and Targeting Myocardial Regeneration Deficit in Diabetes

Cardiomyopathy is a common complication in diabetic patients. Ventricular dysfunction without coronary atherosclerosis and hypertension is driven by hyperglycemia, hyperinsulinemia and impaired insulin signaling. Cardiomyocyte death, hypertrophy, fibrosis, and cell signaling defects underlie cardiomyopathy. Notably, detrimental effects of the diabetic milieu are not limited to cardiomyocytes and vascular cells. The diabetic heart acquires a senescent phenotype and also suffers from altered cellular homeostasis and the insufficient replacement of dying cells. Chronic inflammation, oxidative stress, and metabolic dysregulation damage the population of endogenous cardiac stem cells, which contribute to myocardial cell turnover and repair after injury. Therefore, deficient myocardial repair and the progressive senescence and dysfunction of stem cells in the diabetic heart can represent potential therapeutic targets. While our knowledge of the effects of diabetes on stem cells is growing, several strategies to preserve, activate or restore cardiac stem cell compartments await to be tested in diabetic cardiomyopathy.

Type 1 diabetes patients increase CXCR4+ and CXCR7+ haematopoietic and endothelial progenitor cells with exercise, but the response is attenuated

Exercise mobilizes angiogenic cells, which stimulate vascular repair. However, limited research suggests exercise-induced increase of endothelial progenitor cell (EPCs) is completely lacking in type 1 diabetes (T1D). Clarification, along with investigating how T1D influences exercise-induced increases of other angiogenic cells (hematopoietic progenitor cells; HPCs) and cell surface expression of chemokine receptor 4 (CXCR4) and 7 (CXCR7), is needed. Thirty T1D patients and 30 matched non-diabetes controls completed 45 min of incline walking. Circulating HPCs (CD34⁺, CD34⁺CD45^dim) and EPCs (CD34⁺VEGFR2⁺, CD34⁺CD45^dimVEGFR2⁺), and subsequent expression of CXCR4 and CXCR7, were enumerated by flow cytometry at rest and post-exercise. Counts of HPCs, EPCs and expression of CXCR4 and CXCR7 were significantly lower at rest in the T1D group. In both groups, exercise increased circulating angiogenic cells. However, increases was largely attenuated in the T1D group, up to 55% lower, with CD34⁺ (331 ± 437 Δcells/mL vs. 734 ± 876 Δcells/mL p = 0.048), CD34⁺VEGFR2⁺ (171 ± 342 Δcells/mL vs. 303 ± 267 Δcells/mL, p = 0.006) and CD34⁺VEGFR2⁺CXCR4⁺ (126 ± 242 Δcells/mL vs. 218 ± 217 Δcells/mL, p = 0.040) significantly lower. Exercise-induced increases of angiogenic cells is possible in T1D patients, albeit attenuated compared to controls. Decreased mobilization likely results in reduced migration to, and repair of, vascular damage, potentially limiting the cardiovascular benefits of exercise.Trial registration: ISRCTN63739203.

Endothelial Progenitor Cells Dysfunctions and Cardiometabolic Disorders: From Mechanisms to Therapeutic Approaches

Metabolic syndrome (MetS) is a cluster of several disorders, such as hypertension, central obesity, dyslipidemia, hyperglycemia, insulin resistance and non-alcoholic fatty liver disease. Despite health policies based on the promotion of physical exercise, the reduction of calorie intake and the consumption of healthy food, there is still a global rise in the incidence and prevalence of MetS in the world. This phenomenon can partly be explained by the fact that adverse events in the perinatal period can increase the susceptibility to develop cardiometabolic diseases in adulthood. Individuals born after intrauterine growth restriction (IUGR) are particularly at risk of developing cardiovascular diseases (CVD) and metabolic disorders later in life. It has been shown that alterations in the structural and functional integrity of the endothelium can lead to the development of cardiometabolic diseases. The endothelial progenitor cells (EPCs) are circulating components of the endothelium playing a major role in vascular homeostasis. An association has been found between the maintenance of endothelial structure and function by EPCs and their ability to differentiate and repair damaged endothelial tissue. In this narrative review, we explore the alterations of EPCs observed in individuals with cardiometabolic disorders, describe some mechanisms related to such dysfunction and propose some therapeutical approaches to reverse the EPCs dysfunction.

ACE2 gene transfer ameliorates vasoreparative dysfunction in CD34+ cells derived from diabetic older adults

Diabetes increases the risk for ischemic vascular diseases, which is further elevated in older adults. Bone marrow-derived hematopoietic CD34+ stem/progenitor cells have the potential of revascularization; however, diabetes attenuates vasoreparative functions. Angiotensin-converting enzyme 2 (ACE2) is the vasoprotective enzyme of renin-angiotensin system in contrast with the canonical angiotensin-converting enzyme (ACE). The present study tested the hypothesis that diabetic dysfunction is associated with ACE2/ACE imbalance in hematopoietic stem/progenitor cells (HSPCs) and that increasing ACE2 expression would restore reparative functions. Blood samples from male and female diabetic (n=71) or nondiabetic (n=62) individuals were obtained and CD34+ cells were enumerated by flow cytometry. ACE and ACE2 enzyme activities were determined in cell lysates. Lentiviral (LV) approach was used to increase the expression of soluble ACE2 protein. Cells from diabetic older adults (DB) or nondiabetic individuals (Control) were evaluated for their ability to stimulate revascularization in a mouse model of hindlimb ischemia (HLI). DB cells attenuated the recovery of blood flow to ischemic areas in nondiabetic mice compared with that observed with Control cells. Administration of DB cells modified with LV-ACE2 resulted in complete restoration of blood flow. HLI in diabetic mice resulted in poor recovery with amputations, which was not reversed by either Control or DB cells. LV-ACE2 modification of Control or DB cells resulted in blood flow recovery in diabetic mice. In vitro treatment with Ang-(1-7) modified paracrine profile in diabetic CD34+ cells. The present study suggests that vasoreparative dysfunction in CD34+ cells from diabetic older adults is associated with ACE2/ACE imbalance and that increased ACE2 expression enhances the revascularization potential.

Autologous Bone Marrow Mononuclear Cell Transplantation Therapy Improved Symptoms in Patients with Refractory Diabetic Sensorimotor Polyneuropathy via the Mechanisms of Paracrine and Immunomodulation: A Controlled Study

We recently reported that transplantation of autologous bone marrow mononuclear cells (BM-MNCs) may be an effective and promising therapy to treat refractory diabetic sensorimotor polyneuropathy (DSPN) in patients with type 2 diabetes mellitus (T2DM). This study was designed to investigate the potential mechanisms of BM-MNCs therapy, which recruited 60 patients with DSPN, 30 T2DM patients without complications, and 30 healthy control participants. All clinical parameters, the levels of inflammatory markers, and growth factors in the three groups were compared. Patients in DSPN group had higher level of tumor necrosis factor-α (TNF-α) (DSPN vs control, 412.90 ± 64.58 vs 374.81 ± 63.18 pg/mL, P < 0.01) and lower level of vascular endothelial growth factor (VEGF) (DSPN vs control, 140.93 ± 24.78 vs 157.39 ± 25.11 pg/mL, P < 0.01) than those in control group. DSPN group had the highest level of soluble intercellular adhesion molecule-1 (sICAM-1) among three groups (DSPN and DM vs control, 1477.56 ± 228.00 and 1342.17 ± 237.54 vs 1308.00 ± 200.94 ng/mL, P < 0.05). The level of nerve growth factor in the DSPN group was slightly lower than that in the DM group (DSPN vs DM, 3509.11 ± 438.39 vs 3734.87 ± 647.50 pg/mL, P < 0.05). All patients with DSPN received one intramuscular injection of BM-MNCs and clinical follow-ups after the therapy for 2 days, 1, 4, 12, 24, and 48 weeks. Neuropathic symptoms of foot pain, numbness, and weakness were significantly improved within 4 weeks after BM-MNCs injection. Patients with DSPN were divided into the responder (n = 35) and nonresponder groups (n = 19) based on the improvement of nerve conduction velocity at 12 weeks post-transplantation. Compared with nonresponders, responders were younger (57.3 ± 5.2 vs 62.0 ± 4.8, P < 0.01), had a shorter history of diabetes (7.1 ± 2.7 vs 11.2 ± 5.4 years, P < 0.01), and had higher numbers of mobilized CD34⁺ cells (17.61 ± 2.64 vs 14.79 ± 1.62 ×10⁵/L, P < 0.01) and BM-MNCs (12.05 ± 2.16 vs 9.84 ± 1.53 ×10⁸/L, P < 0.01). The levels of TNF-α and sICAM-1 decreased just after BM-MNCs injection in both groups and slowly reverted to baseline levels. The duration of the downtrend of TNF-α and sICAM-1 in the responder group lasted longer than that in the nonresponder group. Serum level of VEGF in the responder group increased immediately after BM-MNC therapy and reached the highest point after the injection for 12 weeks. On the other hand, VEGF levels in the nonresponder group only increased slightly. Binary logistic regression was performed to evaluate the corresponding prognostic factors for BM-MNCs treatment. The number of applied CD34⁺ cells and the duration of diabetes were the independent predictors of responding to BM-MNCs therapy. No adverse event associated with the treatment was observed during follow-up observations. These results indicated that BM-MNCs transplantation is an effective and promising therapeutic strategy to treat refractory DSPN. The immune regulation and paracrine function of BM-MNCs may contribute to the improvement of DSPN.

Targeting Angiotensin-Converting Enzyme-2/Angiotensin-(1-7)/Mas Receptor Axis in the Vascular Progenitor Cells for Cardiovascular Diseases

Bone marrow-derived hematopoietic stem/progenitor cells are vasculogenic and play an important role in endothelial health and vascular homeostasis by participating in postnatal vasculogenesis. Progenitor cells are mobilized from bone marrow niches in response to remote ischemic injury and migrate to the areas of damage and stimulate revascularization largely by paracrine activation of angiogenic functions in the peri-ischemic vasculature. This innate vasoprotective mechanism is impaired in certain chronic clinical conditions, which leads to the development of cardiovascular complications. Members of the renin-angiotensin system-angiotensin-converting enzymes (ACEs) ACE and ACE2, angiotensin II (Ang II), Ang-(1-7), and receptors AT1 and Mas-are expressed in vasculogenic progenitor cells derived from humans and rodents. Ang-(1-7), generated by ACE2, is known to produce cardiovascular protective effects by acting on Mas receptor and is considered as a counter-regulatory mechanism to the detrimental effects of Ang II. Evidence has now been accumulating in support of the activation of the ACE2/Ang-(1-7)/Mas receptor pathway by pharmacologic or molecular maneuvers, which stimulates mobilization of progenitor cells from bone marrow, migration to areas of vascular damage, and revascularization of ischemic areas in pathologic conditions. This minireview summarizes recent studies that have enhanced our understanding of the physiology and pharmacology of vasoprotective axis in bone marrow-derived progenitor cells in health and disease. SIGNIFICANCE STATEMENT: Hematopoietic stem progenitor cells (HSPCs) stimulate revascularization of ischemic areas. However, the reparative potential is diminished in certain chronic clinical conditions, leading to the development of cardiovascular diseases. ACE2 and Mas receptor are key members of the alternative axis of the renin-angiotensin system and are expressed in HSPCs. Accumulating evidence points to activation of ACE2 or Mas receptor as a promising approach for restoring the reparative potential, thereby preventing the development of ischemic vascular diseases.

Therapies for Type 1 Diabetes: Current Scenario and Future Perspectives

Type 1 diabetes (T1D) is caused by autoimmune destruction of insulin-producing β cells located in the endocrine pancreas in areas known as islets of Langerhans. The current standard-of-care for T1D is exogenous insulin replacement therapy. Recent developments in this field include the hybrid closed-loop system for regulated insulin delivery and long-acting insulins. Clinical studies on prediction and prevention of diabetes-associated complications have demonstrated the importance of early treatment and glucose control for reducing the risk of developing diabetic complications. Transplantation of primary islets offers an effective approach for treating patients with T1D. However, this strategy is hampered by challenges such as the limited availability of islets, extensive death of islet cells, and poor vascular engraftment of islets post-transplantation. Accordingly, there are considerable efforts currently underway for enhancing islet transplantation efficiency by harnessing the beneficial actions of stem cells. This review will provide an overview of currently available therapeutic options for T1D, and discuss the growing evidence that supports the use of stem cell approaches to enhance therapeutic outcomes.

Neuropathy and inflammation in diabetic bone marrow

Diabetes impairs the bone marrow (BM) architecture and function as well as the mobilization of immature cells into the bloodstream and number of potential regenerative cells. Circadian regulation of bone immature cell migration is regulated by β-adrenergic receptors, which are expressed on haematopoietic stem cells, mesenchymal stem cells, and osteoblasts in the BM. Diabetes is associated with a substantially lower number of sympathetic nerve terminal endings in the BM; thus, diabetic neuropathy plays a critical role in BM dysfunction. Treatment with mesenchymal stem cells, BM mononuclear cells, haematopoietic stem cells, and stromal cells ameliorates the dysfunction of diabetic neuropathy, which occurs, in part, through secreted neurotrophic factors, growth factors, adipokines, and polarizing macrophage M2 cells and inhibiting inflammation. Inflammation may be a therapeutic target for BM stem cells to improve diabetic neuropathy. Given that angiogenic and neurotrophic effects are two major barriers to effective diabetic neuropathy therapy, targeting BM stem cells may provide a novel approach to develop these types of treatments.

The pleiotropic cardiovascular effects of dipeptidyl peptidase-4 inhibitors

Patients with Type 2 diabetes have an excess risk for cardiovascular disease. One of the several approaches, included in the guidelines for the management of Type 2 diabetes, is based on dipeptidyl peptidase 4 (DPP-4; also termed CD26) inhibitors, also called gliptins. Gliptins inhibit the degradation of glucagon-like peptide-1 (GLP-1): this effect is associated with increased circulating insulin-to-glucagon ratio, and a consequent reduction of HbA1c. In addition to incretin hormones, there are several proteins that may be affected by DPP-4 and its inhibition: among these some are relevant for the cardiovascular system homeostasis such as SDF-1α and its receptor CXCR4, brain natriuretic peptides, neuropeptide Y and peptide YY. In this review, we will discuss the pathophysiological relevance of gliptin pleiotropism and its translational potential.

Therapeutic Efficacy of Autologous Non-Mobilized Enriched Circulating Endothelial Progenitors in Patients With Critical Limb Ischemia - The SCELTA Trial

BACKGROUND

The therapeutic efficacy of bone marrow mononuclear cells (BM-MNC) autotransplantation in critical limb ischemia (CLI) has been reported. Variable proportions of circulating monocytes express low levels of CD34 (CD14⁺CD34^lowcells) and behave in vitro as endothelial progenitor cells (EPCs). The aim of the present randomized clinical trial was to compare the safety and therapeutic effects of enriched circulating EPCs (ECEPCs) with BM-MNC administration.Methods and Results:ECEPCs (obtained from non-mobilized peripheral blood by immunomagnetic selection of CD14⁺and CD34⁺cells) or BM-MNC were injected into the gastrocnemius of the affected limb in 23 and 17 patients, respectively. After a mean of 25.2±18.6-month follow-up, both groups showed significant and progressive improvement in muscle perfusion (primary endpoint), rest pain, consumption of analgesics, pain-free walking distance, wound healing, quality of life, ankle-brachial index, toe-brachial index, and transcutaneous PO₂. In ECEPC-treated patients, there was a positive correlation between injected CD14⁺CD34^lowcell counts and the increase in muscle perfusion. The safety profile was comparable between the ECEPC and BM-MNC treatment arms. In both groups, the number of deaths and major amputations was lower compared with eligible untreated patients and historical reference patients.

CONCLUSIONS

This study supports previous trials showing the efficacy of BM-MNC autotransplantation in CLI patients and demonstrates comparable therapeutic efficacy between BM-MNC and EPEPCs.

Diabetes mellitus as a poor mobilizer condition

Hematopoietic stem cell (HSC) transplantation in an effective and curative therapy for numerous hematological malignancies. Mobilization of HSCs from bone marrow (BM) to peripheral blood (PB) followed by apheresis is the gold standard for obtaining HSCs for both autologous and allogeneic stem cell transplantation. After administration of granulocyte-colony stimulating factor (G-CSF), up to 30% of patients fail to mobilize "optimal" numbers of HSCs required for engraftment. This review summarizes the current experimental and clinical evidence that diabetes mellitus is a risk factor for poor mobilization. Diabetes causes a profound remodeling of the HSC niche, resulting in impaired release of HSCs. Experimental studies indicate that hyperglycemia hampers regulation of CXCL12 and clinical studies suggest that diabetes impairs HSC mobilization especially in response to G-CSF, but less to plerixafor. Understanding further the biochemical alterations in the diabetic BM will provide insights into future therapeutic strategies to reverse the so-called "diabetic stem cell mobilopathy".

Bone Marrow-Derived Progenitor Cells Are Functionally Impaired in Ischemic Heart Disease

To determine whether the presence of ischemic heart disease (IHD) per se, or rather the co-presence of heart failure (HF), is the primum movens for less effective stem cell products in autologous stem cell therapy, we assessed numbers and function of bone marrow (BM)-derived progenitor cells in patients with coronary artery disease (n = 17), HF due to ischemic cardiomyopathy (n = 8), non-ischemic HF (n = 7), and control subjects (n = 11). Myeloid and erythroid differentiation capacity of BM-derived mononuclear cells was impaired in patients with underlying IHD but not with non-ischemic HF. Migration capacity decreased with increasing IHD severity. Hence, IHD, with or without associated cardiomyopathy, is an important determinant of progenitor cell function. No depletion of hematopoietic and endothelial progenitor cells (EPC) within the BM was observed, while circulating EPC numbers were increased in the presence of IHD, suggesting active recruitment. The observed myelosuppression was not driven by inflammation and thus other mechanisms are at play.

Angiogenesis and Inflammation Crosstalk in Diabetic Retinopathy

Diabetic retinopathy (DR) is one of the most prevalent microvascular complications of diabetes and one of the most frequent causes of blindness in active age. Etiopathogenesis behind this important complication is related to several biochemical, hemodynamic and endocrine mechanisms with a preponderant initial role assumed by polyol pathways, increment of growth factors, accumulation of advanced glycation end products (AGE), activation of protein kinase C (PKC), activation of the renin-angiotensin-aldosterone system (RAAS), and leukostasis. Chronic and sustained hyperglycemia works as a trigger to the early alterations that culminate in vascular dysfunction. Hypoxia also plays an essential role in disease progression with promotion of neovascularization and vascular dystrophies with vitreous hemorrhages induction. Thus, the accumulation of fluids and protein exudates in ocular cavities leads to an opacity augmentation of the cornea that associated to neurodegeneration results in vision loss, being this a devastating characteristic of the disease final stage. During disease progression, inflammatory molecules are produced and angiogenesis occur. Furthermore, VEGF is overexpressed by the maintained hyperglycemic environment and up-regulated by tissue hypoxia. Also pro-inflammatory mediators regulated by cytokines, such as tumor necrosis factor (TNF-α) and interleukin-1 beta (IL-1β), and growth factors leads to the progression of these processes, culminating in vasopermeability (diabetes macular edema) and/or pathological angiogenesis (proliferative diabetic retinopathy). It was found a mutual contribution between inflammation and angiogenesis along the process. J. Cell. Biochem. 117: 2443-2453, 2016. © 2016 Wiley Periodicals, Inc.

Concise Review: Perspectives and Clinical Implications of Bone Marrow and Circulating Stem Cell Defects in Diabetes

Diabetes mellitus is a complex systemic disease characterized by severe morbidity and excess mortality. The burden of its multiorgan complications relies on an imbalance between hyperglycemic cell damage and defective endogenous reparative mechanisms. Inflammation and abnormalities in several hematopoietic components are typically found in diabetes. The discovery that diabetes reduces circulating stem/progenitor cells and impairs their function has opened an entire new field of study where diabetology comes into contact with hematology and regenerative medicine. It is being progressively recognized that such rare circulating cell populations mirror finely regulated processes involved in hematopoiesis, immunosurveillance, and peripheral tissue homeostasis. From a clinical perspective, pauperization of circulating stem cells predicts adverse outcomes and death. Furthermore, studies in murine models and humans have identified the bone marrow (BM) as a previously neglected site of diabetic end-organ damage, characterized by microangiopathy, neuropathy, fat deposition, and inflammation. As a result, diabetes impairs the mobilization of BM stem/progenitor cells, a defect known as mobilopathy or myelokathexis, with negative consequences for physiologic hematopoiesis, immune regulation, and tissue regeneration. A better understanding of the molecular and cellular processes that govern the BM stem cell niche, cell mobilization, and kinetics in peripheral tissues may uncover new therapeutic strategies for patients with diabetes. This concise review summarizes the current knowledge on the interplay between the BM, circulating stem cells, and diabetes, and sets the stages for future developments in the field. Stem Cells 2017;35:106-116.

Depletion of NAD pool contributes to impairment of endothelial progenitor cell mobilization in diabetes

OBJECTIVE

The impaired mobilization of endothelial progenitor cells (EPCs) from bone marrow (BM) critically contributes to the diabetes-associated vascular complications. Here, we investigated the relationship between the nicotinamide phosphoribosyltransferase (NAMPT)-controlled nicotinamide adenine dinucleotide (NAD) metabolism and the impaired mobilization of BM-derived EPCs in diabetic condition.

METHODS

The NAMPT-NAD pool in BM and BM-derived EPCs in wild-type (WT) and diabetic db/db mice was determined. Nicotinamide, a natural substrate for NAD biosynthesis, was administrated for 2weeks in db/db mice to examine the influence of enhancing NAD pool on BM and blood EPCs number. The modulations of stromal cell-derived factor-1α (SDF-1α) and endothelial nitric oxide synthase (eNOS) protein in BM were measured using immunoblotting. The EPCs intracellular NAMPT level and NAD concentration, as well as the blood EPCs number, were compared between 9 healthy people and 16 patients with type 2 diabetes mellitus (T2DM). The T2DM patients were treated with nicotinamide for two weeks and then the blood EPCs number was determined. Moreover, the association between blood EPCs numbers and EPCs intracellular NAD(+)/NAMPT protein levels in 21 healthy individuals was determined.

RESULTS

We found that NAD concentration and NAMPT expression in BM and BM-derived EPCs of db/db mice were significantly lower than those in WT mice BM. Enhancing NAD pool not only increased the EPCs intracellular NAD concentration and blood EPCs number, but also improved post-ischemic wound healing and blood reperfusion in db/db mice with hind-limb ischemia model. Enhancing NAD pool rescued the impaired modulations of stromal cell-derived factor-1α (SDF-1α) and endothelial nitric oxide synthase (eNOS) protein levels in db/db mice BM upon hind-limb ischemia. In addition, enhancing NAD pool significantly inhibited PARP and caspase-3 activates in db/db mice BM. The intracellular NAMPT-NAD pool was positively associated with blood EPCs number in healthy individuals. At last, we found that the EPC intracellular NAMPT and NAD(+) levels were reduced in T2DM patients and enhancing NAD pool elevated the circulating blood EPCs number in T2DM patients.

CONCLUSION

Our results indicate that the depletion of NAD pool may contribute to the impairment of EPCs mobilization in diabetic condition, and imply the potential therapeutic value of nicotinamide in the prevention and treatment for cardiovascular complications of diabetes.

Plerixafor improves the endothelial health balance. The effect of diabetes analysed by polychromatic flow cytometry

BACKGROUND AND AIMS

Diabetes damages the endothelium and reduces the availability of bone marrow (BM)-derived endothelial progenitor cells (EPCs). The mobilization of hematopoietic stem cells (HSCs) and EPCs in response to G-CSF is impaired by diabetes, owing to CXCL12 dysregulation. We have previously shown that the CXCR4/CXCL12 disruptor plerixafor rescues HSC and EPC mobilization in diabetes. We herein explored the effects of plerixafor on HSCs, EPCs, and circulating endothelial cells (CECs) in patients with and without diabetes.

METHODS

We re-analysed data gathered in the NCT02056210 trial, wherein patients with (n = 10) and without diabetes (n = 10) received plerixafor to test stem/progenitor cell mobilization. We applied a novel and very specific polychromatic flow cytometry (PFC) approach to identify and quantify HSCs, EPCs, and CECs.

RESULTS

We found that 7-AAD(-)Syto16(+)CD34(+)CD45(dim) HSC levels determined by PFC strongly correlated to the traditional enumeration of CD34(+) cells, whereas 7-AAD(-)Syto16(+)CD34(+)CD45(neg)KDR(+) EPCs were unrelated to the traditional enumeration of CD34(+)KDR(+) cells. Using PFC, we confirmed that plerixafor induces rapid mobilization of HSCs and EPCs in both groups, with a marginally significant defect in patients with diabetes. Plerixafor reduced live (7-AAD(-)) and dead (7-AAD(+)) Syto16(+)CD34(bright)CD45(neg)CD146(+) CECs more in patients without than in those with diabetes. The EPC/CEC ratio, a measure of the vascular health balance, was increased by plerixafor, but less prominently in patients with that in those without diabetes.

CONCLUSIONS

In addition to rescuing defective mobilization associated with diabetes, plerixafor improves the balance between EPCs and CECs, but the latter effect is blunted in patients with diabetes.

Impaired Mobilization of Vascular Reparative Bone Marrow Cells in Streptozotocin-Induced Diabetes but not in Leptin Receptor-Deficient db/db Mice

Diabetes is associated with impaired mobilization of bone marrow stem/progenitor cells that accelerate vascularization of ischemic areas. This study characterized mobilization of vascular reparative bone marrow progenitor cells in mouse models of diabetes. Age-matched control or streptozotocin (STZ)-induced diabetic, and db/db mice with lean-controls were studied. Mobilization induced by G-CSF, AMD3100 or ischemia was evaluated by flow cytometric enumeration of circulating Lin(-)Sca-1(+)cKit(+) (LSK) cells, and by colony forming unit (CFU) assay. The circulating WBCs and LSKs, and CFUs were reduced in both models with a shorter duration (10-12 weeks) of diabetes compared to their respective controls. Longer duration of STZ-diabetes (≥20 weeks) induced impairment of G-CSF- or AMD3100-mobilization (P < 0.01, n = 8). In db/db mice, mobilization by G-CSF or AMD3100 was either increased or unaffected (P < 0.05, n = 6 to 8). Proliferation, migration, and ischemia-induced mobilization, of LSK cells were impaired in both models. Leptin receptor antagonist, PESLAN-1, increased G-CSF- or AMD3100-mobilization of WBCs and LSKs, compared to the untreated. Leptin increased basal WBCs, decreased basal and AMD3100-mobilized LSK cells, and had no effect on G-CSF. These results suggest that mobilopathy is apparent in STZ-diabetes but not in db/db mice. Leptin receptor antagonism would be a promising approach for reversing diabetic bone marrow mobilopathy.

Collection and immunoselection of CD34+ cells: the impact of age, sex, and diabetes in patients with chronic heart failure

BACKGROUND

Mobilized peripheral blood is the most common source of CD34+ cells intended for transplantations. The collection and enrichment of CD34+ cells could be affected by various factors and there are some controversies regarding the effects of patient-related factors. The aim of this study was to assess the impact of age, sex, and diabetes on the CD34+ cell grafts in patients with chronic heart failure.

STUDY DESIGN AND METHODS

Cell grafts from 100 adult patients scheduled for autologous CD34+ cell transplantation were investigated. The CD34+ cells were collected using leukapheresis after granulocyte-colony-stimulating factor mobilization and further enriched using the immunomagnetic CD34+ selection. The number of CD34+ cells and their viability were determined by flow cytometry.

RESULTS

Older patients had significantly lower CD34+ cell counts than younger patients. The differences between men and women were not found. There was a trend toward an inverse relationship between diabetes and the CD34+ cell count, however, without any significance. No differences in the CD34+ cell viability (97.6% before and 97.9% after selection) were found. The mean CD34+ cell recovery was 59.7% and was not statistically different between age groups, sex, and diabetic patients.

CONCLUSION

Before the CD34+ cells are collected the patient's age should be considered. The study did not demonstrate a significant impact of sex and diabetes on the CD34+ cell count. While age and sex did not affect the immunoselection process, diabetes slightly reduced cell recovery. Cell viabilities before and after the cell enrichment were comparable between the tested samples.

Bone Marrow-Derived Stem Cells: a Mixed Blessing in the Multifaceted World of Diabetic Complications

Diabetes is one of the main economic burdens in health care, which threatens to worsen dramatically if prevalence forecasts are correct. What makes diabetes harmful is the multi-organ distribution of its microvascular and macrovascular complications. Regenerative medicine with cellular therapy could be the dam against life-threatening or life-altering complications. Bone marrow-derived stem cells are putative candidates to achieve this goal. Unfortunately, the bone marrow itself is affected by diabetes, as it can develop a microangiopathy and neuropathy similar to other body tissues. Neuropathy leads to impaired stem cell mobilization from marrow, the so-called mobilopathy. Here, we review the role of bone marrow-derived stem cells in diabetes: how they are affected by compromised bone marrow integrity, how they contribute to other diabetic complications, and how they can be used as a treatment for these. Eventually, we suggest new tactics to optimize stem cell therapy.

Efficacy of CD34+ Stem Cell Therapy in Nonischemic Dilated Cardiomyopathy Is Absent in Patients With Diabetes but Preserved in Patients With Insulin Resistance

We evaluated the association of diabetes and insulin resistance with the response to cell therapy in patients with nonischemic dilated cardiomyopathy (DCM). A total of 45 outpatients with DCM received granulocyte colony-stimulating factor for 5 days. CD34(+) cells were then collected by apheresis and injected transendocardially. Twelve patients had diabetes mellitus (DM group), 17 had insulin resistance (IR group), and 16 displayed normal glucose metabolism (no-IR group). After stimulation, we found higher numbers of CD34(+) cells in the IR group (94 ± 73 × 10(6) cells per liter) than in the no-IR group (54 ± 35 × 10(6) cells per liter) or DM group (31 ± 20 × 10(6) cells per liter; p = .005). Similarly, apheresis yielded the highest numbers of CD34(+) cells in the IR group (IR group, 216 ± 110 × 10(6) cells; no-IR group, 127 ± 82 × 10(6) cells; DM group, 77 ± 83 × 10(6) cells; p = .002). Six months after cell therapy, we found an increase in left ventricular ejection fraction in the IR group (+5.6% ± 6.9%) and the no-IR group (+4.4% ± 7.2%) but not in the DM group (-0.9% ± 5.4%; p = .035). The N-terminal pro-brain natriuretic peptide levels decreased in the IR and no-IR groups, but not in the DM group (-606 ± 850 pg/ml; -698 ± 1,105 pg/ml; and +238 ± 963 pg/ml, respectively; p = .034). Transendocardial CD34(+) cell therapy appears to be ineffective in DCM patients with diabetes. IR was associated with improved CD34(+) stem cell mobilization and a preserved clinical response to cell therapy.

SIGNIFICANCE

The present study is the first clinical study directly evaluating the effects of altered glucose metabolism on the efficacy of CD34(+) stem cell therapy in patients with nonischemic dilated cardiomyopathy. The results offer critical insights into the physiology of stem cell mobilization in heart failure and possibly an explanation for the often conflicting results obtained with stem cell therapy for heart failure. These results demonstrate that patients with dilated cardiomyopathy and diabetes do not benefit from autologous CD34(+) cell therapy. This finding could serve as a useful tool when selecting heart failure patients for future clinical studies in the field of stem cell therapy.

miR-92a Corrects CD34+ Cell Dysfunction in Diabetes by Modulating Core Circadian Genes Involved in Progenitor Differentiation

Autologous CD34(+) cells are widely used for vascular repair; however, in individuals with diabetes and microvascular disease these cells are dysfunctional. In this study, we examine expression of the clock genes Clock, Bmal, Per1, Per2, Cry1, and Cry2 in CD34(+) cells of diabetic and nondiabetic origin and determine the small encoding RNA (miRNA) profile of these cells. The degree of diabetic retinopathy (DR) was assessed. As CD34(+) cells acquired mature endothelial markers, they exhibit robust oscillations of clock genes. siRNA treatment of CD34(+) cells revealed Per2 as the only clock gene necessary to maintain the undifferentiated state of CD34(+) cells. Twenty-five miRNAs targeting clock genes were identified. Three of the miRNAs (miR-18b, miR-16, and miR-34c) were found only in diabetic progenitors. The expression of the Per2-regulatory miRNA, miR-92a, was markedly reduced in CD34(+) cells from individuals with DR compared with control subjects and patients with diabetes with no DR. Restoration of miR-92a levels in CD34(+) cells from patients with diabetes with DR reduced the inflammatory phenotype of these cells and the diabetes-induced propensity toward myeloid differentiation. Our studies suggest that restoring levels of miR-92a could enhance the usefulness of CD34(+) cells in autologous cell therapy.

Stem cell therapies in the treatment of diabetic retinopathy and keratopathy

Nonproliferative diabetic retinopathy (DR) is characterized by multiple degenerative changes that could be potentially corrected by stem cell therapies. Most studies so far have attempted to alleviate typical abnormalities of early retinopathy, including vascular hyperpermeability, capillary closure and pericyte dropout. Success was reported with adult stem cells (vascular progenitors or adipose stem cells), as well as induced pluripotent stem cells from cord blood. The cells were able to associate with damaged vessels in both pericyte and endothelial lining positions in models of DR and ischemia-reperfusion. In some diabetic models, functional amelioration of vasculature and electroretinograms was noted. Another approach for endogenous progenitor cell therapy is to normalize dysfunctional diabetic bone marrow and residing endothelial progenitors using NO donors, PPAR-δ and -γ agonists, or inhibition of TGF-β. A potentially important strategy would be to reduce neuropathy by stem cell inoculations, either naïve (e.g., paracrine-acting adipose stem cells) or secreting specific neuroprotectants, such as ciliary neurotrophic factor or brain-derived neurotrophic factor that showed benefit in amyotrophic lateral sclerosis and Parkinson's disease. Recent advances in stem cell therapies for diabetic retinal microangiopathy may form the basis of first clinical trials in the near future. Additionally, stem cell therapies may prove beneficial for diabetic corneal disease (diabetic keratopathy) with pronounced epithelial stem cell dysfunction.

Diabetes Limits Stem Cell Mobilization Following G-CSF but Not Plerixafor

Previous studies suggest that diabetes impairs hematopoietic stem cell (HSC) mobilization in response to granulocyte colony-stimulating factor (G-CSF). In this study, we tested whether the CXCR4 antagonist plerixafor, differently from G-CSF, is effective in mobilizing HSCs in patients with diabetes. In a prospective study, individuals with and without diabetes (n = 10/group) were administered plerixafor to compare CD34(+) HSC mobilization; plerixafor was equally able to mobilize CD34(+) HSCs in the two groups, whereas in historical data, G-CSF was less effective in patients with diabetes. In a retrospective autologous transplantation study conducted on 706 patients, diabetes was associated with poorer mobilization in patients who received G-CSF with/without chemotherapy, whereas it was not in patients who received G-CSF plus plerixafor. Similarly in an allogeneic transplantation study (n = 335), diabetes was associated with poorer mobilization in patients who received G-CSF. Patients with diabetes who received G-CSF without plerixafor had a lower probability of reaching >50/μL CD34(+) HSCs, independent from confounding variables. In conclusion, diabetes negatively impacted HSC mobilization after G-CSF with or without chemotherapy but had no effect on mobilization induced by G-CSF with plerixafor. This finding has major implications for the care of patients with diabetes undergoing stem cell mobilization and transplantation and for the vascular regenerative potential of bone marrow stem cells.

Bone Marrow Macrophages Contribute to Diabetic Stem Cell Mobilopathy by Producing Oncostatin M

Diabetes affects bone marrow (BM) structure and impairs mobilization of stem cells (SCs) into peripheral blood (PB). This amplifies multiorgan complications because BMSCs promote vascular repair. Because diabetes skews macrophage phenotypes and BM macrophages (BMMΦ) prevent SC mobilization, we hypothesized that excess BMMΦ contribute to diabetic SC mobilopathy. We show that patients with diabetes have increased M1 macrophages, whereas diabetic mice have increased CD169(+) BMMΦ with SC-retaining activity. Depletion of BMMΦ restored SC mobilization in diabetic mice. We found that CD169 labels M1 macrophages and that conditioned medium (CM) from M1 macrophages, but not from M0 and M2 macrophages, induced chemokine (C-X-C motif) ligand 12 (CXCL12) expression by mesenchymal stem/stromal cells. In silico data mining and in vitro validation identified oncostatin M (OSM) as the soluble mediator contained in M1 CM that induces CXCL12 expression via a mitogen-activated protein kinase kinase-p38-signal transducer and activator of a transcription 3-dependent pathway. In diabetic mice, OSM neutralization prevented CXCL12 induction and improved granulocyte-colony stimulating factor and ischemia-induced mobilization, SC homing to ischemic muscles, and vascular recovery. In patients with diabetes, BM plasma OSM levels were higher and correlated with the BM-to-PB SC ratio. In conclusion, BMMΦ prevent SC mobilization by OSM secretion, and OSM antagonism is a strategy to restore BM function in diabetes, which can translate into protection mediated by BMSCs.

Adipose-derived stem cells from diabetic mice show impaired vascular stabilization in a murine model of diabetic retinopathy

Diabetic retinopathy is characterized by progressive vascular dropout with subsequent vision loss. We have recently shown that an intravitreal injection of adipose-derived stem cells (ASCs) can stabilize the retinal microvasculature, enabling repair and regeneration of damaged capillary beds in vivo. Because an understanding of ASC status from healthy versus diseased donors will be important as autologous cellular therapies are developed for unmet clinical needs, we took advantage of the hyperglycemic Akimba mouse as a preclinical in vivo model of diabetic retinopathy in an effort aimed at evaluating therapeutic efficacy of adipose-derived stem cells (mASCs) derived either from healthy, nondiabetic or from diabetic mice. To these ends, Akimba mice received intravitreal injections of media conditioned by mASCs or mASCs themselves, subsequent to development of substantial retinal capillary dropout. mASCs from healthy mice were more effective than diabetic mASCs in protecting the diabetic retina from further vascular dropout. Engrafted ASCs were found to preferentially associate with the retinal vasculature. Conditioned medium was unable to recapitulate the vasoprotection seen with injected ASCs. In vitro diabetic ASCs showed decreased proliferation and increased apoptosis compared with healthy mASCs. Diabetic ASCs also secreted less vasoprotective factors than healthy mASCs, as determined by high-throughput enzyme-linked immunosorbent assay. Our findings suggest that diabetic ASCs are functionally impaired compared with healthy ASCs and support the utility of an allogeneic injection of ASCs versus autologous or conditioned media approaches in the treatment of diabetic retinopathy.

Concise review: diabetes, the bone marrow niche, and impaired vascular regeneration

Diabetes mellitus is a global health problem that results in multiorgan complications leading to high morbidity and mortality. Until recently, the effects of diabetes and hyperglycemia on the bone marrow microenvironment-a site where multiple organ systems converge and communicate-have been underappreciated. However, several new studies in mice, rats, and humans reveal that diabetes leads to multiple bone marrow microenvironmental defects, such as small vessel disease (microangiopathy), nerve terminal pauperization (neuropathy), and impaired stem cell mobilization (mobilopathy). The discovery that diabetes involves bone marrow-derived progenitors implicated in maintaining cardiovascular homeostasis has been proposed as a bridging mechanism between micro- and macroangiopathy in distant organs. Herein, we review the physiological and molecular bone marrow abnormalities associated with diabetes and discuss how bone marrow dysfunction represents a potential root for the development of the multiorgan failure characteristic of advanced diabetes. The notion of diabetes as a bone marrow and stem cell disease opens new avenues for therapeutic interventions ultimately aimed at improving the outcome of diabetic patients.

Specific role of impaired glucose metabolism and diabetes mellitus in endothelial progenitor cell characteristics and function

The disease burden of diabetes mellitus (DM) and its associated cardiovascular complications represent a growing and major global health problem. Recent studies suggest that circulating exogenous endothelial progenitor cells (EPCs) play an important role in endothelial repair and neovascularization at sites of injury or ischemia. Both experimental and clinical studies have demonstrated that hyperglycemia related to DM can induce alterations to EPCs. The reduction and dysfunction of EPCs related to DM correlate with the occurrence and severity of microvascular and macrovascular complications, suggesting a close mechanistic link between EPC dysfunction and impaired vascular function/repair in DM. These alterations to EPCs, likely mediated by multiple pathophysiological mechanisms, including inflammation, oxidative stress, and alterations in Akt and the nitric oxide pathway, affect EPCs at multiple stages: differentiation and mobilization in the bone marrow, trafficking and survival in the circulation, and homing and neovascularization. Several different therapeutic approaches have consequently been proposed to reverse the reduction and dysfunction of EPCs in DM and may represent a novel therapeutic approach to prevent and treat DM-related cardiovascular complications.

Emerging roles of hematopoietic cells in the pathobiology of diabetic complications

Diabetic complications encompass macrovascular events, mainly the result of accelerated atherosclerosis, and microvascular events that strike the eye (retinopathy), kidney (nephropathy), and nervous system (neuropathy). The traditional view is that hyperglycemia-induced dysregulated biochemical pathways cause injury and death of cells intrinsic to the organs affected. There is emerging evidence that diabetes compromises the function of the bone marrow (BM), producing a stem cell niche-dependent defect in hematopoietic stem cell mobilization. Furthermore, dysfunctional BM-derived hematopoietic cells contribute to diabetic complications. Thus, BM cells are not only a victim but also an accomplice in diabetes and diabetic complications. Understanding the underlying molecular mechanisms may lead to the development of new therapies to prevent and/or treat diabetic complications by specifically targeting these perpetrators.

Diabetes causes bone marrow autonomic neuropathy and impairs stem cell mobilization via dysregulated p66Shc and Sirt1

Diabetes compromises the bone marrow (BM) microenvironment and reduces the number of circulating CD34(+) cells. Diabetic autonomic neuropathy (DAN) may impact the BM, because the sympathetic nervous system is prominently involved in BM stem cell trafficking. We hypothesize that neuropathy of the BM affects stem cell mobilization and vascular recovery after ischemia in patients with diabetes. We report that, in patients, cardiovascular DAN was associated with fewer circulating CD34(+) cells. Experimental diabetes (streptozotocin-induced and ob/ob mice) or chemical sympathectomy in mice resulted in BM autonomic neuropathy, impaired Lin(-)cKit(+)Sca1(+) (LKS) cell and endothelial progenitor cell (EPC; CD34(+)Flk1(+)) mobilization, and vascular recovery after ischemia. DAN increased the expression of the 66-kDa protein from the src homology and collagen homology domain (p66Shc) and reduced the expression of sirtuin 1 (Sirt1) in mice and humans. p66Shc knockout (KO) in diabetic mice prevented DAN in the BM, and rescued defective LKS cell and EPC mobilization. Hematopoietic Sirt1 KO mimicked the diabetic mobilization defect, whereas hematopoietic Sirt1 overexpression in diabetes rescued defective mobilization and vascular repair. Through p66Shc and Sirt1, diabetes and sympathectomy elevated the expression of various adhesion molecules, including CD62L. CD62L KO partially rescued the defective stem/progenitor cell mobilization. In conclusion, autonomic neuropathy in the BM impairs stem cell mobilization in diabetes with dysregulation of the life-span regulators p66Shc and Sirt1.

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.

Diabetes-associated macrovascular complications: cell-based therapy a new tool?

Diabetes mellitus and its ongoing macrovascular complications represent one of the major health problems around the world. Rise in obesity and population ages correlate with the increased incidence of diabetes. This highlights the need for novel approaches to prevent and treat this pandemic. The discovery of a reservoir of stem/progenitors in bone marrow and in mesenchymal tissue has attracted interest of both biologists and clinicians. A number of preclinical and clinical trials were developed to explore their potential clinical impact, as target or vehicle, in different clinical settings, including diabetes complications. Currently, bone marrow, peripheral blood, mesenchymal, and adipose tissues have been used as stem/progenitor cell sources. However, evidences have been provided that both bone marrow and circulating progenitor cells are dysfunctional in diabetes. These observations along with the growing advantages in genetic manipulation have spurred researchers to exploit ex vivo manipulated cells to overcome these hurdles. In this article, we provide an overview of data relevant to stem-progenitors potential clinical application in revascularization and/or vascular repair. Moreover, the hurdles at using progenitor cells in diabetic patients will be also discussed.

Restoring stem cell mobilization to promote vascular repair in diabetes

Diabetes triggers endothelial dysfunction, which is linked to increased risk of cardiovascular diseases. Stem and progenitor cells from the bone marrow are involved in the maintenance of vascular integrity. Diabetic patients show a dysfunction of these cells, which might represent a novel pathophysiological mechanism of vascular disease. Specifically, stem and progenitor cells fail to egress from the bone marrow (BM) due to BM pathological alterations and unresponsiveness to mobilizing stimuli. In this review, we describe impaired stem cell mobilization in diabetes as a mechanism of failed vascular repair and we provide evidence that pharmacological strategies can restore mobilization. We discuss recent advances in the knowledge of aberrant organization of the diabetic BM and its implications for impaired mobilization. Finally, we describe in detail the pharmacological exploitation of the G-CSF/DPP-4(CD26)/SDF-1α axis as a novel strategy to improve mobilization and attain vascular repair in diabetes.