Human mesenchymal stem cells improve rat islet functionality under cytokine stress with combined upregulation of heme oxygenase-1 and ferritin

Long-term safety of photobiomodulation exposure to beta cell line and rat islets in vitro and in vivo

This study evaluates the safety and potential benefits of PBM on pancreatic beta cells and islets. PBM was applied to insulin-secreting cell lines (MIN6) and rat pancreatic islets using a 670 nm light source, continuous output, with a power density of 2.8 mW/cm², from 5 s to several 24 h. Measure of cell viability, insulin secretion, mitochondrial function, ATP content, and cellular respiration were assessed. Additionally, a diabetic rat model is used for islet transplantation (pre-conditioning with PBM or not) experiments. Short and long-term PBM exposure did not affect beta cell islets viability, insulin secretion nor ATP content. While short-term PBM (2 h) increases superoxide ion content, this was not observed for long exposure (24 h). Mitochondrial respirations were slightly decreased after PBM. In the islet transplantation model, both pre-illuminated and non-illuminated islets improved metabolic control in diabetic rats with a safety profile regarding the post-transplantation period. In summary, for the first time, long-term PBM exhibited safety in terms of cell viability, insulin secretion, energetic profiles in vitro, and post-transplantation period in vivo. Further investigation is warranted to explore PBM's protective effects under conditions of stress, aiding in the development of innovative approaches for cellular therapy.

From the Clinical to the Bench: Exploring the Insulin Modulation Effects of Tacrolimus and Belatacept

Calcineurin inhibitors (CNIs) are critical in preventing rejection posttransplantation but pose an increased risk of post-transplant diabetes (PTD). Recent studies show that late conversion from CNIs to belatacept, a costimulation blocker, improves HbA1c in kidney transplant recipients with PTD or de novo diabetes. This study investigates whether the observed effects on PTD stem solely from CNI withdrawal or if belatacept influences PTD independently. The study assessed the impact of tacrolimus and belatacept on insulin secretion in MIN6 cells (a beta cell line) and rat islets. Tacrolimus and belatacept were administered to the cells and islets, followed by assessments of cell viability and insulin secretion. Tacrolimus impaired insulin secretion without affecting cell viability, while belatacept showed no detrimental effects on either parameter. These findings support clinical observations of improved HbA1c upon switching from tacrolimus to belatacept. Belatacept holds promise in islet or pancreas transplantation, particularly in patients with unstable diabetes. Successful cases of islet transplantation treated with belatacept without severe hypoglycemia highlight its potential in managing PTD. Further research is needed to fully understand the metabolic changes accompanying the transition from CNIs to belatacept. Preserving insulin secretion emerges as a promising avenue for investigation in this context.

Strategy for Clinical Setting of Co-transplantation of Mesenchymal Stem Cells and Pancreatic Islets

Islet transplantation may be the most efficient therapeutic technique for patients with type 1 diabetes mellitus (T1DM). However, the clinical application of this method is faced with numerous limitations, including isolated islet apoptosis, recipient rejection, and graft vascular reconstruction. Mesenchymal stem cells (MSCs) possess anti-apoptotic, immunomodulatory, and angiogenic properties. Here, we review recent studies on co-culture and co-transplantation of islets with MSCs. We have summarized the methods of preparation of co-transplantation, especially the merits of co-culture, and the effects of co-transplantation. Accumulating experimental evidence shows that co-culture of islets with MSCs promotes islet survival, enhances islet secretory function, and prevascularizes islets through various pretransplant preparations. This review is expected to provide a reference for exploring the use of MSCs for clinical islet co-transplantation.

Development of a cell-free strategy to recover aged skeletal muscle after disuse

Extended periods of bed rest and limb immobilization are required for healing post-injury or disease, yet disuse can result in significant muscle atrophy and decreased quality of life in older adults. Physical rehabilitation is commonly prescribed to recover these deficits, yet accumulation of reactive oxygen species and sustained rates of protein degradation persist during the rehabilitation period that can significantly delay or prevent recovery. Pericytes, considered the primary mesenchymal and vascular stromal cell in skeletal muscle, secrete beneficial factors that maintain baseline muscle mass, yet minimal information exists regarding the pericyte response to disuse and recovery. In the current study, single-cell RNA sequencing and functional assays were performed to demonstrate that pericytes in mouse skeletal muscle lose the capacity to synthesize antioxidants during disuse and recovery. This information was used to guide the design of a strategy in which healthy donor pericytes were stimulated with hydrogen peroxide (H2 O2 ) to produce small extracellular vesicles (sEVs) that effectively restored myofibre size in adult and aged muscle after disuse. Proteomic assessment detected 11 differentially regulated proteins in primed sEVs that may account for recovery of muscle, including proteins associated with extracellular matrix composition and anti-inflammatory and antioxidant processes. This study demonstrates that healthy H2 O2 -primed pericyte-derived sEVs effectively improve skeletal muscle recovery after immobilization, presenting a novel acellular approach to rebuild muscle mass in older adults after a period of disuse. KEY POINTS: Previous studies suggest that prolonged oxidative stress is a barrier to skeletal muscle recovery after a period of immobilization. In this study we demonstrate that muscle-resident perivascular stromal cells (pericytes) become dysfunctional and lack the capacity to mount an antioxidant defence after disuse in mice. Hydrogen peroxide treatment of healthy pericytes in vitro simulates the release of small extracellular vesicles (sEVs) that effectively recover skeletal muscle fibre size and extracellular matrix remodelling in young adult and aged mice after disuse. Pericyte-derived sEVs present a novel acellular strategy to recover skeletal muscle after disuse.

A Supportive Role of Mesenchymal Stem Cells on Insulin-Producing Langerhans Islets with a Specific Emphasis on The Secretome

Type 1 Diabetes (T1D) is a chronic autoimmune disease characterized by a gradual destruction of insulin-producing β-cells in the endocrine pancreas due to innate and specific immune responses, leading to impaired glucose homeostasis. T1D patients usually require regular insulin injections after meals to maintain normal serum glucose levels. In severe cases, pancreas or Langerhans islet transplantation can assist in reaching a sufficient β-mass to normalize glucose homeostasis. The latter procedure is limited because of low donor availability, high islet loss, and immune rejection. There is still a need to develop new technologies to improve islet survival and implantation and to keep the islets functional. Mesenchymal stem cells (MSCs) are multipotent non-hematopoietic progenitor cells with high plasticity that can support human pancreatic islet function both in vitro and in vivo and islet co-transplantation with MSCs is more effective than islet transplantation alone in attenuating diabetes progression. The beneficial effect of MSCs on islet function is due to a combined effect on angiogenesis, suppression of immune responses, and secretion of growth factors essential for islet survival and function. In this review, various aspects of MSCs related to islet function and diabetes are described.

Female Reproductive Aging and Oxidative Stress: Mesenchymal Stem Cell Conditioned Medium as a Promising Antioxidant

The recent tendency to delay pregnancy has increased the incidence of age-related infertility, as female reproductive competence decreases with aging. Along with aging, a lowered capacity of antioxidant defense causes a loss of normal function in the ovaries and uterus due to oxidative damage. Therefore, advancements have been made in assisted reproduction to resolve infertility caused by reproductive aging and oxidative stress, following an emphasis on their use. The application of mesenchymal stem cells (MSCs) with intensive antioxidative properties has been extensively validated as a regenerative therapy, and proceeding from original cell therapy, the therapeutic effects of stem cell conditioned medium (CM) containing paracrine factors secreted during cell culture have been reported to be as effective as that of direct treatment of source cells. In this review, we summarized the current understanding of female reproductive aging and oxidative stress and present MSC-CM, which could be developed as a promising antioxidant intervention for assisted reproductive technology.

Indirect co-culture of islet cells in 3D biocompatible collagen/laminin scaffold with angiomiRs transfected mesenchymal stem cells

Diabetes is an autoimmune disease in which the pancreatic islets produce insufficient insulin. One of the treatment strategies is islet isolation, which may damage these cells as they lack vasculature. Biocompatible scaffolds are one of the efficient techniques for dealing with this issue. The current study is aimed to determine the effect of transfected BM-MSCS with angiomiR-126 and -210 on the survival and functionality of islets loaded into a 3D scaffold via laminin (LMN). AngiomiRs/Poly Ethylenimine polyplexes were transfected into bone marrow-mesenchymal stem cells (BM-MSCs), followed by 3-day indirect co-culturing with islets laden in collagen (Col)-based hydrogel scaffolds containing LMN. Islet proliferation and viability were significantly increased in LMN-containing scaffolds, particularly in the miRNA-126 treated group. Insulin gene expression was superior in Col scaffolds, especially, in the BM-MSCs/miRNA-126 treated group. VEGF was upregulated in the LMN-containing scaffolds in both miRNA-treated groups, specifically in the miRNA-210, leading to VEGF secretion. MiRNAs' target genes showed no downregulation in LMN-free scaffolds; while a drastic downregulation was seen in the LMN-containing scaffolds. The highest insulin secretion was recorded in the Oxidized dextran (Odex)/Col^LMN+ group with miRNA-126. LMN-containing biocompatible scaffolds, once combined with angiomiRs and their downstream effectors, promote islets survival and restore function, leading to enhanced angiogenesis and glycemic status.

Towards human organ generation using interspecies blastocyst complementation: Challenges and perspectives for therapy

Millions of people suffer from end-stage refractory diseases. The ideal treatment option for terminally ill patients is organ transplantation. However, donor organs are in absolute shortage, and sadly, most patients die while waiting for a donor organ. To date, no technology has achieved long-term sustainable patient-derived organ generation. In this regard, emerging technologies of chimeric human organ production via blastocyst complementation (BC) holds great promise. To take human organ generation via BC and transplantation to the next step, we reviewed current emerging organ generation technologies and the associated efficiency of chimera formation in human cells from the standpoint of developmental biology.

Stem Cell Therapy Improves Human Islet Graft Survival in Mice via Regulation of Macrophages

Islet/β-cell transplantation offers great hope for patients with type 1 diabetes. We assessed the mechanisms of how intrahepatic coinfusion of human α-1 antitrypsin (hAAT)-engineered mesenchymal stromal cells (hAAT-MSCs) improves survival of human islet grafts posttransplantation (PT). Longitudinal in vivo bioluminescence imaging studies identified significantly more islets in the livers bearing islets cotransplanted with hAAT-MSCs compared with islets transplanted alone. In vitro mechanistic studies revealed that hAAT-MSCs inhibit macrophage migration and suppress IFN-γ-induced M1-like macrophages while promoting IL-4-induced M2-like macrophages. In vivo this translated to significantly reduced CD11c+ and F4/80+ cells and increased CD206+ cells around islets cotransplanted with hAAT-MSCs as identified by multiplex immunofluorescence staining. Recipient-derived F4/80+and CD11b+ macrophages were mainly present in the periphery of an islet, while CD11c+ and CD206+ cells appeared inside an islet. hAAT-MSCs inhibited macrophage migration and skewed the M1-like phenotype toward an M2 phenotype both in vitro and in vivo, which may have favored islet survival. These data provide evidence that hAAT-MSCs cotransplanted with islets remain in the liver and shift macrophages to a protective state that favors islet survival. This novel strategy may be used to enhance β-cell survival during islet/β-cell transplantation for the treatment of type 1 diabetes or other diseases.

The response of three-dimensional pancreatic alpha and beta cell co-cultures to oxidative stress

The pancreatic islets of Langerhans have low endogenous antioxidant levels and are thus especially sensitive to oxidative stress, which is known to influence cell survival and behaviour. As bioengineered islets are gaining interest for therapeutic purposes, it is important to understand how their composition can be optimized to diminish oxidative stress. We investigated how the ratio of the two main islet cell types (alpha and beta cells) and their culture in three-dimensional aggregates could protect against oxidative stress. Monolayer and aggregate cultures were established by seeding the alphaTC1 (alpha) and INS1E (beta) cell lines in varying ratios, and hydrogen peroxide was applied to induce oxidative stress. Viability, oxidative stress, and the level of the antioxidant glutathione were measured. Both aggregation and an increasing prevalence of INS1E cells in the co-cultures conferred greater resistance to cell death induced by oxidative stress. Increasing the prevalence of INS1E cells also decreased the number of alphaTC1 cells experiencing oxidative stress in the monolayer culture. In 3D aggregates, culturing the alphaTC1 and INS1E cells in a ratio of 50:50 prevented oxidative stress in both cell types. Together, the results of this study lead to new insight into how modulating the composition and dimensionality of a co-culture can influence the oxidative stress levels experienced by the cells.

Lack of ZnT8 protects pancreatic islets from hypoxia- and cytokine-induced cell death

Pancreatic β-cells depend on the well-balanced regulation of cytosolic zinc concentrations, providing sufficient zinc ions for the processing and storage of insulin, but avoiding toxic effects. The zinc transporter ZnT8, encoded by SLC30A8,is a key player regarding islet cell zinc homeostasis, and polymorphisms in this gene are associated with altered type 2 diabetes susceptibility in man. The objective of this study was to investigate the role of ZnT8 and zinc in situations of cellular stress as hypoxia or inflammation. Isolated islets of WT and global ZnT8-/- mice were exposed to hypoxia or cytokines and cell death was measured. To explore the role of changing intracellular Zn2+ concentrations, WT islets were exposed to different zinc concentrations using zinc chloride or the zinc chelator N,N,N',N'-tetrakis(2-pyridinylmethyl)-1,2-ethanediamine (TPEN). Hypoxia or cytokine (TNF-α, IFN-γ, IL1-β) treatment induced islet cell death, but to a lesser extent in islets from ZnT8-/- mice, which were shown to have a reduced zinc content. Similarly, chelation of zinc with TPEN reduced cell death in WT islets treated with hypoxia or cytokines, whereas increased zinc concentrations aggravated the effects of these stressors. This study demonstrates a reduced rate of cell death in islets from ZnT8-/- mice as compared to WT islets when exposed to two distinct cellular stressors, hypoxia or cytotoxic cytokines. This protection from cell death is, in part, mediated by a reduced zinc content in islet cells of ZnT8-/- mice. These findings may be relevant for altered diabetes burden in carriers of risk SLC30A8 alleles in man.

Tissue Engineering Strategies for Improving Beta Cell Transplantation Outcome

Purpose of Review

Beta cell replacement therapy as a form of islet transplantation is a promising alternative therapy with the possibility to make selected patients with type 1 diabetes (T1D) insulin independent. However, this technique faces challenges such as extensive activation of the host immune system post-transplantation, lifelong need for immunosuppression, and the scarcity of islet donor pancreas. Advancement in tissue engineering strategies can improve these challenges and allow for a more widespread application of this therapy. This review will discuss the recent development and clinical translation of tissue engineering strategies in beta cell replacement therapy.

Recent Findings

Tissue engineering offers innovative solutions for producing unlimited glucose responsive cells and fabrication of appropriate devices/scaffolds for transplantation applications. Generation of pancreatic organoids with supporting cells in biocompatible biomaterials is a powerful technique to improve the function of insulin-producing cell clusters. Fabrication of physical barriers such as encapsulation strategies can protect the cells from the host immune system and allow for graft retrieval, although this strategy still faces major challenges to fully restore physiological glucose regulation.

Summary

The three main components of tissue engineering strategies including the generation of stem cell-derived insulin-producing cells and organoids and the possibilities for therapeutic delivery of cell-seeded devices to extra-hepatic sites need to come together in order to provide safe and functional insulin-producing devices for clinical beta cell replacement therapy.

MSCs and Inflammatory Cells Crosstalk in Regenerative Medicine: Concerted Actions for Optimized Resolution Driven by Energy Metabolism

Mesenchymal stromal cells (MSCs) are currently widely used in cell based therapy regarding to their remarkable efficacy in controlling the inflammatory status in patients. Despite recent progress and encouraging results, inconstant therapeutic benefits are reported suggesting that significant breakthroughs in the understanding of MSCs immunomodulatory mechanisms of action remains to be investigated and certainly apprehended from original point of view. This review will focus on the recent findings regarding MSCs close relationship with the innate immune compartment, i.e. granulocytes and myeloid cells. The review will also consider the intercellular mechanism of communication involved, such as factor secretion, cell-cell contact, extracellular vesicles, mitochondria transfer and efferocytosis. Immune-like-properties of MSCs supporting part of their therapeutic effect in the clinical setting will be discussed, as well as their potentials (immunomodulatory, anti-bacterial, anti-inflammatory, anti-oxidant defenses and metabolic adaptation…) and effects mediated, such as cell polarization, differentiation, death and survival on various immune and tissue cell targets determinant in triggering tissue regeneration. Their metabolic properties in term of sensing, reacting and producing metabolites influencing tissue inflammation will be highlighted. The review will finally open to discussion how ongoing scientific advances on MSCs could be efficiently translated to clinic in chronic and age-related inflammatory diseases and the current limits and gaps that remain to be overcome to achieving tissue regeneration and rejuvenation.

Human Hemangioblast-Derived Mesenchymal Stem Cells Promote Islet Engraftment in a Minimal Islet Mass Transplantation Model in Mice

Islet transplantation can restore glycemic control in patients with type 1 diabetes. Using this procedure, the early stages of engraftment are often crucial to long-term islet function, and outcomes are not always successful. Numerous studies have shown that mesenchymal stem cells (MSCs) facilitate islet graft function. However, experimental data can be inconsistent due to variables associated with MSC generation (including donor characteristics and tissue source), thus, demonstrating the need for a well-characterized and uniform cell product before translation to the clinic. Unlike bone marrow- or adipose tissue-derived MSCs, human embryonic stem cell-derived-MSCs (hESC-MSCs) offer an unlimited source of stable and highly-characterized cells that are easily scalable. Here, we studied the effects of human hemangioblast-derived mesenchymal cells (HMCs), (i.e., MSCs differentiated from hESCs using a hemangioblast intermediate), on islet cell transplantation using a minimal islet mass model. The co-transplantation of the HMCs allowed a mass of islets that was insufficient to correct diabetes on its own to restore glycemic control in all recipients. Our in vitro studies help to elucidate the mechanisms including reduction of cytokine stress by which the HMCs support islet graft protection in vivo. Derivation, stability, and scalability of the HMC source may offer unique advantages for clinical applications, including fewer islets needed for successful islet transplantation.

Mesenchymal Stromal Cells in Viral Infections: Implications for COVID-19

Mesenchymal stromal cells (MSCs) constitute a heterogeneous population of stromal cells with immunomodulatory and regenerative properties that support their therapeutic use. MSCs isolated from many tissue sources replicate vigorously in vitro and maintain their main biological properties allowing their widespread clinical application. To date, most MSC-based preclinical and clinical trials targeted immune-mediated and inflammatory diseases. Nevertheless, MSCs have antiviral properties and have been used in the treatment of various viral infections in the last years. Here, we revised in detail the biological properties of MSCs and their preclinical and clinical applications in viral diseases, including the disease caused by the severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) infection (COVID-19). Notably, rapidly increasing numbers of MSC-based therapies for COVID-19 have recently been reported. MSCs are theoretically capable of reducing inflammation and promote lung regeneration in severe COVID-19 patients. We critically discuss the rationale, advantages and disadvantages of MSC-based therapies for viral infections and also specifically for COVID-19 and point out some directions in this field. Finally, we argue that MSC-based therapy may be a promising therapeutic strategy for severe COVID-19 and other emergent respiratory tract viral infections, beyond the viral infection diseases in which MSCs have already been clinically applied.

Protecting islet functional viability using mesenchymal stromal cells

Islet transplantation is an emerging treatment for type 1 diabetes which offers the prospect of physiological control of blood glucose and reductions in acute hypoglycaemic episodes. However, current protocols are limited by a rapid decline in islet functional viability during the isolation process, culture period, and post-transplantation. Much of this can be attributed to the deleterious effects of hypoxic and cytokine stressors on β cells. One experimental strategy to improve the functional viability of islets is coculture or cotransplantation with mesenchymal stromal cells (MSCs). Numerous studies have shown that MSCs have the capacity to improve islet survival and insulin secretory function, and the mechanisms of these effects are becoming increasingly well understood. In this review, we will focus on recent studies demonstrating the capacity for MSCs to protect islets from hypoxia- and cytokine-induced stress. Islets exposed to acute hypoxia (1%-2% O₂ ) or to inflammatory cytokines (including IFN-γ, TNF-α, and IL-B) in vitro undergo apoptosis and a rapid decline in glucose-stimulated insulin secretion. Coculture of islets with MSCs, or with MSC-conditioned medium, protects from these deleterious effects, primarily with secreted factors. These protective effects are distinct from the immunomodulatory and structural support MSCs provide when cotransplanted with islets. Recent studies suggest that MSCs may support secretory function by the physical transfer of functional mitochondria, particularly to metabolically compromised β cells. Understanding how MSCs respond to stressed islets will facilitate the development of MSC secretome based, cell-free approaches to supporting islet graft function during transplantation by protecting or repairing β cells.

Immunopathology of Type 1 Diabetes and Immunomodulatory Effects of Stem Cells: A Narrative Review of the Literature

Type 1 Diabetes (T1D) is a complex autoimmune disorder which occurs as a result of an intricate series of pathologic interactions between pancreatic β-cells and a wide range of components of both the innate and the adaptive immune systems. Stem-cell therapy, a recently-emerged potentially therapeutic option for curative treatment of diabetes, is demonstrated to cause significant alternations to both different immune cells such as macrophages, natural killer (NK) cells, dendritic cells, T cells, and B cells and non-cellular elements including serum cytokines and different components of the complement system. Although there exists overwhelming evidence indicating that the documented therapeutic effects of stem cells on patients with T1D is primarily due to their potential for immune regulation rather than pancreatic tissue regeneration, to date, the precise underlying mechanisms remain obscure. On the other hand, immune-mediated rejection of stem cells remains one of the main obstacles to regenerative medicine. Moreover, the consequences of efferocytosis of stem-cells by the recipients' lung-resident macrophages have recently emerged as a responsible mechanism for some immune-mediated therapeutic effects of stem-cells. This review focuses on the nature of the interactions amongst different compartments of the immune systems which are involved in the pathogenesis of T1D and provides explanation as to how stem cell-based interventions can influence immune system and maintain the physiologic equilibrium.

Oxidative stress in pancreatic alpha and beta cells as a selection criterion for biocompatible biomaterials

The clinical success rate of islet transplantation, namely independence from insulin injections, is limited by factors that lead to graft failure, including inflammation, acute ischemia, acute phase response, and insufficient vascularization. The ischemia and insufficient vascularization both lead to high levels of oxidative stress, which are further aggravated by islet encapsulation, inflammation, and undesirable cell-biomaterial interactions. To identify biomaterials that would not further increase damaging oxidative stress levels and that are also suitable for manufacturing a beta cell encapsulation device, we studied five clinically approved polymers for their effect on oxidative stress and islet (alpha and beta cell) function. We found that 300 poly(ethylene oxide terephthalate) 55/poly(butylene terephthalate) 45 (PEOT/PBT300) was more resistant to breakage and more elastic than other biomaterials, which is important for its immunoprotective function. In addition, it did not induce oxidative stress or reduce viability in the MIN6 beta cell line, and even promoted protective endogenous antioxidant expression over 7 days. Importantly, PEOT/PBT300 is one of the biomaterials we studied that did not interfere with insulin secretion in human islets.

Role of heme oxygenase-1 in human placenta on iron supply to fetus

INTRODUCTION

To date, details on how iron is supplied from the mother to the fetus through the placenta have remained unclear. Recently, increasing evidence has shown that heme oxygenase (HO)-1, which is an inducible isoform of the rate-limiting enzyme in the heme degradation pathway, may be involved in the effective reutilization of iron. In this study, we examined the distribution and gene expression of HO-1 in the villous tissue of human placenta at various periods of pregnancy.

METHODS

Using the placenta of 38 samples for which consent was obtained, chronological changes in the localization of HO-1 protein were examined by histological examination. RT-PCR was also performed to examine the expression of HO-1, transferrin receptor-1, and ferroportin 1. Ferric iron in the tissues was analyzed by Prussian blue staining.

RESULTS

Immunohistochemical studies showed that HO-1 protein was exclusively expressed in trophoblastic cells throughout gestation. In the miscarriage placenta in the first trimester, ho-1 mRNA levels were significantly higher than normal. Placenta with fetal death (miscarriage) in the first and second trimester indicate significantly higher ratio of ho-1 gene for iron production to the fpn-1 gene for iron excretion than normal. These suggest that the role of HO-1 with various physiological functions is changing throughout pregnancy.

DISCUSSION

These findings suggest that HO-1 in placenta plays an important role in iron supplying system in the second trimester to support fetal development.

The emerging antioxidant paradigm of mesenchymal stem cell therapy

Mesenchymal stem cells (multipotent stromal cells; MSCs) have been under investigation for the treatment of diverse diseases, with many promising outcomes achieved in animal models and clinical trials. The biological activity of MSC therapies has not been fully resolved which is critical to rationalizing their use and developing strategies to enhance treatment efficacy. Different paradigms have been constructed to explain their mechanism of action, including tissue regeneration, trophic/anti-inflammatory secretion, and immunomodulation. MSCs rarely engraft and differentiate into other cell types after in vivo administration. Furthermore, it is equivocal whether MSCs function via the secretion of many peptide/protein ligands as their therapeutic properties are observed across xenogeneic barriers, which is suggestive of mechanisms involving mediators conserved between species. Oxidative stress is concomitant with cellular injury, inflammation, and dysregulated metabolism which are involved in many pathologies. Growing evidence supports that MSCs exert antioxidant properties in a variety of animal models of disease, which may explain their cytoprotective and anti-inflammatory properties. In this review, evidence of the antioxidant effects of MSCs in in vivo and in vitro models is explored and potential mechanisms of these effects are discussed. These include direct scavenging of free radicals, promoting endogenous antioxidant defenses, immunomodulation via reactive oxygen species suppression, altering mitochondrial bioenergetics, and donating functional mitochondria to damaged cells. Modulation of the redox environment and oxidative stress by MSCs can mediate their anti-inflammatory and cytoprotective properties and may offer an explanation to the diversity in disease models treatable by MSCs and how these mechanisms may be conserved between species.

Mechanisms supporting potential use of bone marrow-derived mesenchymal stem cells in psychocardiology

Despite great efforts made in recent years, globally cardiovascular disease (CVD) remains the most common and devastating disease. Pharmacological, interventional and surgical treatments have proved to be only partly satisfactory for the majority of patients. A major underlying cause of poor prognosis is a high comorbidity rate between CVD and mental illness, which calls for the approaches of psychocardiology. As psychiatric disorders and CVD can influence each other bidirectionally, it is necessary to develop novel therapies targeting both systems simultaneously. Therefore, innovative stem cell (SC) therapy has become the most promising treatment strategy in psychocardiology. Bone marrow-derived mesenchymal stem/stromal cells (BM-MSCs), among all different types of SCs, have drawn the most attention due to unique advantages in terms of ethical considerations, low immunogenicity and simplicity of preparation. In this review, we survey recent publications and clinical trials to summarize the knowledge and progress gained so far. Moreover, we discuss the feasibility of the clinical application of BM-MSCs in the area of psychocardiology.

Polymeric Approaches to Reduce Tissue Responses Against Devices Applied for Islet-Cell Encapsulation

Immunoisolation of pancreatic islets is a technology in which islets are encapsulated in semipermeable but immunoprotective polymeric membranes. The technology allows for successful transplantation of insulin-producing cells in the absence of immunosuppression. Different approaches of immunoisolation are currently under development. These approaches involve intravascular devices that are connected to the bloodstream and extravascular devices that can be distinguished in micro- and macrocapsules and are usually implanted in the peritoneal cavity or under the skin. The technology has been subject of intense fundamental research in the past decade. It has co-evolved with novel replenishable cell sources for cure of diseases such as Type 1 Diabetes Mellitus that need to be protected for the host immune system. Although the devices have shown significant success in animal models and even in human safety studies most technologies still suffer from undesired tissue responses in the host. Here we review the past and current approaches to modulate and reduce tissue responses against extravascular cell-containing micro- and macrocapsules with a focus on rational choices for polymer (combinations). Choices for polymers but also choices for crosslinking agents that induce more stable and biocompatible capsules are discussed. Combining beneficial properties of molecules in diblock polymers or application of these molecules or other anti-biofouling molecules have been reviewed. Emerging are also the principles of polymer brushes that prevent protein and cell-adhesion. Recently also immunomodulating biomaterials that bind to specific immune receptors have entered the field. Several natural and synthetic polymers and even combinations of these polymers have demonstrated significant improvement in outcomes of encapsulated grafts. Adequate polymeric surface properties have been shown to be essential but how the surface should be composed to avoid host responses remains to be identified. Current insight is that optimal biocompatible devices can be created which raises optimism that immunoisolating devices can be created that allows for long term survival of encapsulated replenishable insulin-producing cell sources for treatment of Type 1 Diabetes Mellitus.