Cell therapy in peripheral arterial disease

Cell Therapy of Severe Ischemia in People with Diabetic Foot Ulcers-Do We Have Enough Evidence?

This current opinion article critically evaluates the efficacy of autologous cell therapy (ACT) for chronic limb-threatening ischemia (CLTI), especially in people with diabetes who are not candidates for standard revascularization. This treatment approach has been used in 'no-option' CLTI in the last two decades and more than 1700 patients have received ACT worldwide. Here we analyze the level of published evidence of ACT as well as our experience with this treatment method. Many studies have shown that ACT is safe and an effective method for patients with the most severe lower limb ischemia. However, some trials did not show any benefit of ACT, and there is some heterogeneity in the types of injected cells, route of administration and assessed endpoints. Nevertheless, we believe that ACT plays an important role in a comprehensive treatment of patients with diabetic foot and severe ischemia.

Difference in Serum Endostatin Levels in Diabetic Patients with Critical Limb Ischemia Treated by Autologous Cell Therapy or Percutaneous Transluminal Angioplasty

The aim of this study was to compare the serum levels of the anti-angiogenic factor endostatin (S-endostatin) as a potential marker of vasculogenesis after autologous cell therapy (ACT) versus percutaneous transluminal angioplasty (PTA) in diabetic patients with critical limb ischemia (CLI). A total of 25 diabetic patients with CLI treated in our foot clinic during the period 2008–2014 with ACT generating potential vasculogenesis were consecutively included in the study; 14 diabetic patients with CLI who underwent PTA during the same period were included in a control group in which no vasculogenesis had occurred. S-endostatin was measured before revascularization and at 1, 3, and 6 months after the procedure. The effect of ACT and PTA on tissue ischemia was confirmed by transcutaneous oxygen pressure (TcPO₂) measurement at the same intervals. While S-endostatin levels increased significantly at 1 and 3 months after ACT (both P < 0.001), no significant change of S-endostatin after PTA was observed. Elevation of S-endostatin levels significantly correlated with an increase in TcPO₂ at 1 month after ACT (r = 0.557; P < 0.001). Our study showed that endostatin might be a potential marker of vasculogenesis because of its significant increase after ACT in diabetic patients with CLI in contrast to those undergoing PTA. This increase may be a sign of a protective feedback mechanism of this anti-angiogenic factor.

Cell therapy of critical limb ischemia in diabetic patients - State of art

In this review we report on the state of cell therapy of critical limb ischemia (CLI) with respect to differences between diabetic and non-diabetic patients mainly from the clinical point of view. CLI is the most severe form of peripheral arterial disease and its diagnosis and treatment in diabetic patients is very difficult. The therapeutic effect of standard methods of CLI treatment is only partial - more than one third of diabetic patients are not eligible for standard revascularization; therefore, new therapeutic techniques such as cell therapy have been studied in clinical trials. Presence of CLI in patients with diabetic foot disease is associated with worse clinical outcomes such as lack of healing of foot ulcers, major amputations and premature mortality. A revascularization procedure cannot be successful as the only method in contrast to patients without diabetes, but it must always be part of a complex therapy focused not only on ischemia, but also on treatment of infection, off-loading, metabolic control of diabetes and nutrition, local therapy, etc. Therefore, the main criteria for cell therapy may vary in diabetic patients and non-diabetic persons and results of this treatment method should always be assessed in the context of ensuring comprehensive therapy. This review carries out an analysis of the source of precursor cells, route of administration and brings a brief report of published data with respect to diabetic and non-diabetic patients and our experience with autologous cell therapy of diabetic patients with CLI. Analysis of the studies in terms of diabetes is difficult, because in most of them sub-analysis for diabetic patients is not performed separately. The other problem is that it is not clear if diabetic patients received adequate complex treatment for their foot ulcers which can strongly affect the rate of major amputation as an outcome of CLI treatment.

Age and Human Regenerative Capacity Impact of Cardiovascular Risk Factors

RATIONALE

We investigated aging of human endogenous reparative capacity and aimed to clarify whether it is affected by presence of cardiovascular disease or its risk factors (RFs).

OBJECTIVE

Circulating progenitor cell (PC) levels reflect endogenous regenerative potential. The effect on PC of healthy aging compared with aging with RFs or cardiovascular disease (CVD) is unknown. We examined whether exposure to RF and CVD leads to an accelerated decline in circulating PC with increasing age.

METHODS AND RESULTS

In 2792 adult subjects, 498 were free of RFs (smoking, diabetes mellitus, hypertension, or hyperlipidemia), 1036 subjects had 1 to 2 RF, and 1253 had ≥3 RFs or CVD. PC were enumerated by flow cytometry as CD45(med+) mononuclear cells expressing CD34 and subsets coexpressing CD133, CXCR4, and vascular endothelial growth factor receptor-2 epitopes. Younger age, male sex, and larger body size correlated with higher PC counts (P<0.01). After multivariable adjustment, both age and RF categories were independently associated with PC counts (P<0.05), with lower PC counts in older subjects and those with higher RF burden or CVD. PC counts remained unchanged with increasing age in healthy individuals. There were significant interactions between age and RF categories (P≤0.005), such that for younger subjects (<40 years), RFs were associated with increased PC counts, whereas for older subjects (>60 years), RFs and CVD were associated with lower PC counts.

CONCLUSIONS

Circulating PC levels do not decline with healthy aging; RF exposure at a younger age stimulates PC mobilization, whereas continued exposure is associated with lower PC levels in later life. Over the lifespan, exposure to RFs and CVD is associated with an initial stimulation and subsequent decline in circulating PC levels, which reflect endogenous regenerative capacity.

Magnetic manipulation of bacterial magnetic nanoparticle-loaded neurospheres

Specific targeting of cells to sites of tissue damage and delivery of high numbers of transplanted cells to lesion tissue in vivo are critical parameters for the success of cell-based therapies. Here, we report a promising in vitro model system for studying the homing of transplanted cells, which may eventually be applicable for targeted regeneration of damaged neurons in spinal cord injury. In this model system, neurospheres derived from human neuroblastoma SH-SY5Y cells labeled with bacterial magnetic nanoparticles were guided by a magnetic field and successfully accumulated near the focus site of the magnetic field. Our results demonstrate the effectiveness of using an in vitro model for testing bacterial magnetic nanoparticles to develop successful stem cell targeting strategies during fluid flow, which may ultimately be translated into in vivo targeted delivery of cells through circulation in various tissue-repair models.

Role of Serum Levels of Angiogenic Cytokines in Assessment of Angiogenesis after Stem Cell Therapy of Diabetic Patients with Critical Limb Ischemia

The release of proangiogenic cytokines into the circulation after stem cell (SC) therapy and compensatory increase of angiogenesis inhibitors may reflect local vasculogenesis but also can increase the risk of side effects. The aim of our study was to evaluate serum levels of angiogenic cytokines with regard to the assessment of local and systemic vasculogenesis in diabetic patients with no-option critical limb ischemia (NO-CLI). Twenty-five diabetic patients with NO-CLI treated with SCs isolated from bone marrow or stimulated peripheral blood were included in the study. Serum levels of proangiogenic cytokines (VEGF, bFGF, Ang-1, PDGF-AA, and PDGF-BB) and an antiangiogenic cytokine (endostatin) were assessed 6 months after cell treatment, compared to baseline values, and correlated with the number of injected CD34+ cells. The clinical effect of SC therapy (assessed by changes in TcPO2) and potential systemic vasculogenesis (assessed by eye fundus examination) were evaluated after 6 months. Serum levels of angiogenic inhibitor endostatin increased significantly after 1 and 3 months ( p = 0.0003), but no significant increase in serum levels of proangiogenic cytokines was observed. A significant correlation between number of injected CD34+ cells and serum levels of endostatin was observed ( r = 0.41, p < 0.05); however, proangiogenic cytokines did not correlate with CD34+ cells. No correlation between increase in TcPO2 after treatment and serum levels of any of the angiogenic cytokines were seen, and no signs of systemic vasculogenesis in the retina were observed after 6 months. Despite the significant increase in the levels of the angiogenic inhibitor endostatin following SC treatment, there was no risk of systemic vasculogenesis after SC therapy as documented by serum levels of proangiogenic cytokines or changes in the retina.

Revisiting cardiovascular regeneration with bone marrow-derived angiogenic and vasculogenic cells

Cell-based therapy has emerged as a promising therapy for cardiovascular disease. Particularly, bone marrow (BM)-derived cells have been most extensively investigated and have shown encouraging results in preclinical studies. Clinical trials, however, have demonstrated split results in post-myocardial infarction cardiac repair. Mechanistically, transdifferentiation of BM-derived cells into cardiovascular tissue demonstrated by earlier studies is now known to play a minor role in functional recovery, and humoral and paracrine effects turned out to be main mechanisms responsible for tissue regeneration and functional recovery. With this advancement in the mechanistic insight of BM-derived cells, new efforts have been made to identify cell population, which can be readily isolated and obtained in sufficient quantity without mobilization and have higher therapeutic potential. Recently, haematopoietic CD31(+) cells, which are more prevalent in bone marrow and peripheral blood, have been revealed to have angiogenic and vasculogenic activities and strong potential for therapeutic neovascularization in ischaemic tissues. This article will cover the recent advances in BM-derived cell-based therapy and implication of CD31(+) cells.

Clinical application of stem cells for therapeutic angiogenesis in patients with peripheral arterial disease

Peripheral arterial disease (PAD) may ultimately cause to the loss of the affected limb due to gangrene or infection. Some patients with PAD may have severe coexisting diseases and diffuse involvement of their distal arteries, and so they are poor candidates for revascularization procedures. Angiogenesis has recently been suggested to be a new emerging treatment strategy for patients with PAD. Angiogenesis is defined as the sprouting of new capillaries from pre-existing vascular structures; this process plays a major role in the development of collateral vessels in an ischemic limb. Yet, the exact mechanism of angiogenesis is currently poorly understood. It has been established that angiogenesis is initiated by hypoxia and it requires various pro-angiogenic factors such as vascular endothelial growth factor. Therapeutic angiogenesis is aimed at enhancing natural angiogenesis by the administration of the cells or genes that can trigger angiogenesis and this can lead to pain relief and wound healing by the development of collateral vessels. Most of the recent clinical trials have reported that stem cell therapy for promoting angiogenesis in patients with PAD improves the ischemic symptoms and enhances wound healing. However, there are several limitations to approve a standard treatment for PAD such as small sample size in several prevous studies, their diverse inclusion criteria and the lack of standard assessment methods for the safety and outcome. Therefore, multicenter, large-scale and randomized controlled studies are needed to prove the safety and efficacy of the clinically applying stem cells for therapeutic angiogenesis in patients with PAD.

Circadian variation in vascular function and regenerative capacity in healthy humans

Background

Progenitor cells (PCs) are mobilized in response to vascular injury to effect regeneration and repair. Recruitment of PCs requires intact nitric oxide (NO) synthesis by endothelial cells, and their number and activity correlate with cardiovascular disease risk burden and future outcomes. Whereas cardiovascular vulnerability exhibits a robust circadian rhythm, the 24‐hour variation of PCs and their inter‐relation with vascular function remain unknown. We investigated the circadian variation of PCs and vascular function with the hypothesis that this will parallel the pattern observed for cardiovascular events (CVEs).

Methods and Results

In 15 healthy subjects (9 men, 37±16 years), circulating PCs and vascular function were measured at 8 am, noon, 4 pm, 8 pm, midnight, 4 am (only PCs counts), and 8 am the following day. Circulating PCs were enumerated as mononuclear cells (MNCs; CD45^med) that express CD34 as well as CD133, and their activity was assessed as the number of colonies formed by culturing MNCs. Vascular function was evaluated by measurement of endothelium‐dependent, flow‐mediated vasodilation (FMD) of the brachial artery and tonometry‐derived indices of arterial stiffness. Higher CD34⁺ and CD34⁺/CD133⁺ cell counts were observed at 8 pm than any other time of the day (P‐ANOVA=0.038 and <0.001; respectively) and were lowest at 8 am. PC colony formation was highest at midnight (P‐ANOVA=0.045) and lowest in the morning hours. FMD was highest at midnight and lowest at 8 am and 8 pm, and systemic arterial stiffness was greatest at 8 am and lowest at 4 pm and midnight (P‐ANOVA=0.03 and 0.01; respectively).

Conclusion

A robust circadian variation in PC counts and vascular function occurs in healthy humans and both exhibit an unfavorable profile in the morning hours that parallels the preponderance of CVEs at these times. Whether these changes are precipitated by awakening and time‐dependent physical activity or governed by the endogenous circadian clock needs to be further investigated.

Both autologous bone marrow mononuclear cell and peripheral blood progenitor cell therapies similarly improve ischaemia in patients with diabetic foot in comparison with control treatment

BACKGROUND

The aim of our study was to compare the effect of bone marrow mononuclear cell and peripheral blood progenitor cell therapies in patients with diabetic foot disease and critical limb ischaemia unresponsive to revascularization with conservative therapy.

METHODS

Twenty-eight patients with diabetic foot disease (17 treated by bone marrow cells and 11 by peripheral blood cell) were included into an active group and 22 patients into a control group without cell treatment. Transcutaneous oxygen pressure and rate of major amputation, as the main outcome measures, were compared between bone marrow cells, peripheral blood cell and control groups over 6 months; both cell therapy methods were also compared by the characteristics of cell suspensions. Possible adverse events were evaluated by changes of serum levels of angiogenic cytokines and retinal fundoscopic examination.

RESULTS

The transcutaneous oxygen pressure increased significantly (p < 0.05) compared with baseline in both active groups after 6 months, with no significant differences between bone marrow cells and peripheral blood cell groups; however, no change of transcutaneous oxygen pressure in the control group was observed. The rate of major amputation by 6 months was significantly lower in the active cell therapy group compared with that in the control group (11.1% vs. 50%, p = 0.0032), with no difference between bone marrow cells and peripheral blood cell. A number of injected CD34+ cells and serum levels of angiogenic cytokines after treatment did not significantly differ between bone marrow cells and peripheral blood cell.

CONCLUSIONS

Our study showed a superior benefit of bone marrow cells and peripheral blood cell treatments of critical limb ischaemia in patients with diabetic foot disease when compared with conservative therapy. There was no difference between both cell therapy groups, and no patient demonstrated signs of systemic vasculogenesis.

Advances in bone marrow-derived cell therapy: CD31-expressing cells as next generation cardiovascular cell therapy

In the past few years, bone marrow (BM)-derived cells have been used to regenerate damaged cardiovascular tissues post-myocardial infarction. Recent clinical trials have shown controversial results in recovering damaged cardiac tissue. New progress has shown that the underlying mechanisms of cell-based therapy relies more heavily on humoral and paracrine effects rather than on new tissue generation. However, studies have also reported the potential of new endothelial cell generation from BM cells. Thus, efforts have been made to identify cells having higher humoral or therapeutic effects as well as their surface markers. Specifically, BM-derived CD31+ cells were isolated by a surface marker and demonstrated high angio-vasculogenic effects. This article will describe recent advances in the therapeutic use of BM-derived cells and the usefulness of CD31+ cells.

Engineering blood vessels using stem cells: innovative approaches to treat vascular disorders

Vascular disease is the leading cause of mortality in the USA, providing the impetus for new treatments and technologies. Current therapies rely on the implantation of stents or grafts to treat injured blood vessels. However, these therapies may be immunogenic or may incompletely recover the functional integrity of the vasculature. In light of these shortcomings, cell-based therapies provide new treatment options to heal damaged areas with more suitable substitutes. Current clinical trials employing stem cell-based therapies involve the transfusion of harvested endothelial progenitor cells. While the results from these trials have been encouraging, utilizing tissue-engineered approaches could yield technologically advanced solutions. This article discusses engineered stem cell-based therapies from three angles: the differentiation of adult stem cells, such as mesenchymal stem cells and endothelial progenitor cells, into vascular lineages; investigation of human embryonic stem cells and induced pluripotent stem cells as inexhaustible sources of vascular cells; and tissue-engineering approaches, which incorporate these vascular progenitor cells into biomimetic scaffolds to guide regeneration. The optimal solution to vascular disease lies at the interface of these technologies--embedding differentiated cells into engineered scaffolds to impart precise control over vascular regeneration.

Recombinant human interleukin-11 treatment enhances collateral vessel growth after femoral artery ligation

OBJECTIVE

To investigate the role of recombinant human interleukin-11 (rhIL-11) on in vivo mobilization of CD34(+)/vascular endothelial growth factor receptor (VEGFR) 2(+) mononuclear cells and collateral vessel remodeling in a mouse model of hindlimb ischemia.

METHODS AND RESULTS

We observed that treatment of Sv129 mice with continuous infusion of 200-μg/kg rhIL-11 per day led to in vivo mobilization of CD34(+)/VEGFR2(+) cells that peaked at 72 hours. Sv129 mice pretreated with rhIL-11 for 72 hours before femoral artery ligation showed a 3-fold increase in plantar vessel perfusion, leading to faster blood flow recovery; and a 20-fold increase in circulating CD34(+)/VEGFR2(+) cells after 8 days of rhIL-11 treatment. Histologically, experimental mice had a 3-fold increase in collateral vessel luminal diameter after 21 days of rhIL-11 treatment and a 4.4-fold influx of perivascular CD34(+)/VEGFR2(+) cells after 8 days of therapy. Functionally, rhIL-11-treated mice showed better hindlimb appearance and use scores when compared with syngeneic mice treated with PBS under the same experimental conditions.

CONCLUSIONS

These novel findings show that rhIL-11 promotes in vivo mobilization of CD34(+)/VEGFR2(+) mononuclear cells, enhances collateral vessel growth, and increases recovery of perfusion after femoral artery ligation. Thus, rhIL-11 has a promising role for development as an adjunctive treatment of patients with peripheral vascular disease.

Cell culture platform with mechanical conditioning and nondamaging cellular detachment

Cells implanted after injury may remodel undesirably with improper mechanical stimulation from surrounding tissue. Proper conditioning of tissue engineered constructs before implantation can lead to suitable tissue architectures, along with an extracellular matrix (ECM) environment that more closely mimics native tissue. Additionally, cell implantation without bulky polymeric scaffolding is often desirable. Previous researchers have created devices capable of applying mechanical forces to cells (e.g., stretch) but cellular removal from these devices, such as by trypsin, often results in irreversible damage. Conversely, devices are available that can detach intact cells, but these are inelastic, nonstretchable substrates. We have created a cell culture platform that allows for mechanical conditioning and then subsequent nondamaging detachment of those cells. We have modified silicone culture surfaces, to incorporate thermally responsive polymers of N-isopropylacrylamide (NIPAAm) to create an elastic substrate that can also change surface properties with temperature change. A copolymer of NIPAAm and 10percent w/w acrylic acid (AAc) was conjugated to an amine-bonded silicone surface through carbodiimide chemistry. Cells were able to attach to the resulting surfaces at 37 degreeC and showed detachment by rounded morphology at 25degreeC. Following mechanical stretching, cells were still able to spontaneously detach from these modified silicone surfaces with temperature change.

Systemic levels of G-CSF and interleukin-6 determine the angiogenic potential of bone marrow resident monocytes

There is considerable interest in the potential of cell-based approaches to mediate therapeutic angiogenesis for acute and chronic vascular syndromes. Using a mouse model of HLI, we showed previously that adoptive transfer of a small number of donor monocytes enhanced revascularization significantly. Herein, we provide data suggesting that the BM resident monocytes sense systemic signals that influence their future functional capacity. Specifically, following induction of distant ischemia, the angiogenic capacity of BM resident monocytes is reduced markedly. We provide evidence that G-CSF and IL-6 represent such "conditioning" signals. Systemic levels of G-CSF and IL-6 are increased significantly following induction of HLI. Accordingly, BM resident monocytes from ischemic mice exhibited increased pSTAT3 and STAT3 target gene expression. Finally, G-CSFR(-/-) and IL-6(-/-) mice were resistant to the deleterious effects of ischemic conditioning on monocyte angiogenic potential. RNA expression profiling suggested that ischemia-conditioned monocytes in the BM up-regulate the well-described M2 polarization markers Chi3l4 and Lrg1. Consistent with this observation, M2-skewed monocytes from SHIP(-/-) mice also had impaired angiogenic capacity. Collectively, these data show that G-CSF and IL-6 provide signals that determine the angiogenic potential of BM resident monocytes.

Marvels, mysteries, and misconceptions of vascular compensation to peripheral artery occlusion

Peripheral arterial disease is a major health problem and there is a significant need to develop therapies to prevent its progression to claudication and critical limb ischemia. Promising results in rodent models of arterial occlusion have generally failed to predict clinical success and led to questions of their relevance. While sub-optimal models may have contributed to the lack of progress, we suggest that advancement has also been hindered by misconceptions of the human capacity for compensation and the specific vessels which are of primary importance. We present and summarize new and existing data from humans, Ossabaw miniature pigs, and rodents which provide compelling evidence that natural compensation to occlusion of a major artery (i) may completely restore perfusion, (ii) occurs in specific pre-existing small arteries, rather than the distal vasculature, via mechanisms involving flow-mediated dilation and remodeling (iii) is impaired by cardiovascular risk factors which suppress the flow-mediated mechanisms and (iv) can be restored by reversal of endothelial dysfunction. We propose that restoration of the capacity for flow-mediated dilation and remodeling in small arteries represents a largely unexplored potential therapeutic opportunity to enhance compensation for major arterial occlusion and prevent the progression to critical limb ischemia in the peripheral circulation.

Treatment strategies for peripheral artery disease

Peripheral arterial disease is an underecognized manifestation of systemic atherosclerosis associated with high rates of cardiovascular morbidity and mortality. The rationale of therapy is to reduce cardiovascular risk, improve symptoms of intermittent claudication, and prevent the development of critical limb ischemia and amputation. Exercise therapy and several pharmacologic agents have been shown to improve walking distance in patients with intermittent claudication. Patients with lifestyle-interfering symptoms despite exercise, or those who progress to critical limb ischemia, frequently undergo revascularization. Endovascular techniques are commonly used in these patients. Combined pharmacological and endovascular strategies will play an increasing role in management of these patients in the future.

Platelet MPs obscure some EPC definitions

The cell surface phenotype used to define an EPC, in one commonly used in vitro assay, may arise from an uptake of contaminating platelet MPs by cultured mononuclear cells, resulting in a gross misinterpretation of the assay results.