Adipose-derived mesenchymal stem cells therapy for acute kidney injury induced by ischemia-reperfusion in a rat model

Exosomes Highlight Future Directions in the Treatment of Acute Kidney Injury

Acute kidney injury (AKI) is a severe health problem associated with high morbidity and mortality rates. It currently lacks specific therapeutic strategies. This review focuses on the mechanisms underlying the actions of exosomes derived from different cell sources, including red blood cells, macrophages, monocytes, mesenchymal stem cells, and renal tubular cells, in AKI. We also investigate the effects of various exosome contents (such as miRNA, lncRNA, circRNA, mRNA, and proteins) in promoting renal tubular cell regeneration and angiogenesis, regulating autophagy, suppressing inflammatory responses and oxidative stress, and preventing fibrosis to facilitate AKI repair. Moreover, we highlight the interactions between macrophages and renal tubular cells through exosomes, which contribute to the progression of AKI. Additionally, exosomes and their contents show promise as potential biomarkers for diagnosing AKI. The engineering of exosomes has improved their clinical potential by enhancing isolation and enrichment, target delivery to injured renal tissues, and incorporating small molecular modifications for clinical use. However, further research is needed to better understand the specific mechanisms underlying exosome actions, their delivery pathways to renal tubular cells, and the application of multi-omics research in studying AKI.

Novel strategies in nephrology: what to expect from the future?

Chronic kidney disease (CKD) will become the fifth global case of death by 2040. Its largest impact is on premature mortality but the number of persons with kidney failure requiring renal replacement therapy (RRT) is also increasing dramatically. Current RRT is suboptimal due to the shortage of kidney donors and dismal outcomes associated with both hemodialysis and peritoneal dialysis. Kidney care needs a revolution. In this review, we provide an update on emerging knowledge and technologies that will allow an earlier diagnosis of CKD, addressing the current so-called blind spot (e.g. imaging and biomarkers), and improve renal replacement therapies (wearable artificial kidneys, xenotransplantation, stem cell-derived therapies, bioengineered and bio-artificial kidneys).

Gallic Acid Improves Therapeutic Effects of Mesenchymal Stem Cells Derived from Adipose Tissue in Acute Renal Injury Following Rhabdomyolysis Induced by Glycerol

Acute kidney injury (AKI) is identified by a progressive reduction in the glomerular filtration rate (GFR) and retention of nitrogenous waste products. Traumatic and nontraumatic rhabdomyolysis is recently considered the main cause of AKI. According to several studies, stem cell treatment is a promising therapeutic strategy for many types of disorders including AKI. The main limitation of mesenchymal stem cells (MSCs) therapy is reducing cell survival in response to oxidative stress products in injured organ areas. Gallic acid (GA) as a well-known antioxidant has been reported to confer potent-free radical scavenging and anti-inflammatory properties. Therefore, the aim of the current study was to assess the influence of MSCs and GA in acute renal injury following rhabdomyolysis induced by glycerol. A total of 70 healthy rats were divided into seven groups (10 in each group): control, AKI (glycerol, intramuscular), cell therapy (AKI + intravenous injection of mesenchymal stem cells derived from adipose tissue (AMCs), AKI + AMCs + GA (50, 100, and 200 mg/kg, intraperitoneally, 3 days a week for 3 consecutive weeks), and positive control group (the most effective dose of gallic acid). After the treatment, rats were sacrificed; blood, urine, and kidney tissues were collected; and qualitative and quantitative parameters (including blood urea nitrogen (BUN), creatine kinase (CK), lactate dehydrogenase (LDH), alkaline phosphatase (ALP), aspartate transaminase (SGOT), oxidative stress markers kidney function parameters) and histopathological indexes were assayed. Our results revealed that co-treatment of AMCs plus GA into AKI rats decreased BUN and creatinine and ameliorated kidney injury parameters after 3 weeks. Improved oxidative stress markers such as decreased MDA and increased SOD and CAT were significant in the GA + AMCs group compared to the AMCs alone in AKI rats. Also, the histopathological appearances of AKI rats including renal tubule cavity expansion and renal tubular epithelial cell edema, and interstitial inflammation, were alleviated using GA + AMCs treatment compared to the control. The obtained results of the current study documented that antioxidants could make mesenchymal stem cells more resistant to the condition in which they are supposed to be transplanted and probably improve the efficacy of stem cell therapy in AKI patients.

Adipose-Derived Stem/Stromal Cells in Kidney Transplantation: Status Quo and Future Perspectives

Kidney transplantation (KT) is the gold standard treatment of end-stage renal disease. Despite progressive advances in organ preservation, surgical technique, intensive care, and immunosuppression, long-term allograft survival has not significantly improved. Among the many peri-operative complications that can jeopardize transplant outcomes, ischemia-reperfusion injury (IRI) deserves special consideration as it is associated with delayed graft function, acute rejection, and premature transplant loss. Over the years, several strategies have been proposed to mitigate the impact of IRI and favor tolerance, with rather disappointing results. There is mounting evidence that adipose stem/stromal cells (ASCs) possess specific characteristics that could help prevent, reduce, or reverse IRI. Immunomodulating and tolerogenic properties have also been suggested, thus leading to the development of ASC-based prophylactic and therapeutic strategies in pre-clinical and clinical models of renal IRI and allograft rejection. ASCs are copious, easy to harvest, and readily expandable in culture. Furthermore, ASCs can secrete extracellular vesicles (EV) which may act as powerful mediators of tissue repair and tolerance. In the present review, we discuss the current knowledge on the mechanisms of action and therapeutic opportunities offered by ASCs and ASC-derived EVs in the KT setting. Most relevant pre-clinical and clinical studies as well as actual limitations and future perspective are highlighted.

Therapeutic Effects of Stem Cells From Different Source on Renal Ischemia- Reperfusion Injury: A Systematic Review and Network Meta-analysis of Animal Studies

Objective: Although stem cell therapy for renal ischemia-reperfusion injury (RIRI) has made immense progress in animal studies, conflicting results have been reported by the investigators. Therefore, we aimed to systematically evaluate the effects of different stem cells on renal function of animals with ischemia-reperfusion injury and to compare the efficacies of stem cells from various sources. Methods: PubMed, Web of Science, Embase, Cochrane, CNKI, VIP, CBM, and WanFang Data were searched for records until April 2021. Two researchers independently conducted literature screening, data extraction, and literature quality evaluation. Results and conclusion: Seventy-two animal studies were included for data analysis. Different stem cells significantly reduced serum creatinine and blood urea nitrogen levels in the early and middle stages (1 and 7 days) compared to the negative control group, however there was no significant difference in the late stage among all groups (14 days); In the early stage (1 day), the renal histopathological score in the stem cell group was significantly lower than that in the negative control group, and there was no significant difference among these stem cells. In addition, there was no significant difference between stem cell and negative control in proliferation of resident cells, however, significantly less apoptosis of resident cells than negative control. In conclusion, the results showed that stem cells from diverse sources could improve the renal function of RIRI animals. ADMSCs and MDMSCs were the most-researched stem cells, and they possibly hold the highest therapeutic potential. However, the quality of evidence included in this study is low, and there are many risks of bias. The exact efficacy of the stem cells and the requirement for further clinical studies remain unclear.

Genetically Modified Mesenchymal Stromal/Stem Cells: Application in Critical Illness

Critical illnesses including sepsis, acute respiratory distress syndromes, ischemic cardiovascular disorders and acute organ injuries are associated with high mortality, morbidity as well as significant health care system expenses. While these diverse conditions require different specific therapeutic approaches, mesenchymal stem/stromal cell (MSCs) are multipotent cells capable of self-renewal, tri-lineage differentiation with a broad range regenerative and immunomodulatory activities, making them attractive for the treatment of critical illness. The therapeutic effects of MSCs have been extensively investigated in several pre-clinical models of critical illness as well as in phase I and II clinical cell therapy trials with mixed results. Whilst these studies have demonstrated the therapeutic potential for MSC therapy in critical illness, optimization for clinical use is an ongoing challenge. MSCs can be readily genetically modified by application of different techniques and tools leading to overexpress or inhibit genes related to their immunomodulatory or regenerative functions. Here we will review recent approaches designed to enhance the therapeutic potential of MSCs with an emphasis on the technology used to generate genetically modified cells, target genes, target diseases and the implication of genetically modified MSCs in cell therapy for critical illness.

Ghahremani, Massoud Saidijam, Jafar Kiani, Naser Ahmadbeigi. Trends of Stem Cell-Based Clinical Trials in Gastrointestinal Tract Diseases

Stem cells have great potential to be applied as a treatment for various types of disorders. These cells exert therapeutic effects by modulating the immune system with the capability to secrete cytokines and chemokines. Previous studies have indicated that stem cells could be used as a therapeutic agent for different complaints, such as gastrointestinal diseases. For a long time now, researchers have moved toward stem cells' clinical application in this context. With the increasing number of trials in stem cell therapy of gastrointestinal disease, it is now time to evaluate these clinical trials' status. This paper reviews clinical trials that have used stem cells for the treatment of gastrointestinal tract diseases.

Human amniotic epithelial cells ameliorate kidney damage in ischemia-reperfusion mouse model of acute kidney injury

BACKGROUND

Acute kidney injury (AKI) is a common clinical disease with complex pathophysiology and limited therapeutic choices. This prompts the need for novel therapy targeting multiple aspects of this disease. Human amnion epithelial cell (hAEC) is an ideal stem cell source. Increasing evidence suggests that exosomes may act as critical cell-cell communicators. Accordingly, we assessed the therapeutic potential of hAECs and their derived exosomes (hAECs-EXO) in ischemia reperfusion mouse model of AKI and explored the underlying mechanisms.

METHODS

The hAECs were primary cultured, and hAECs-EXO were isolated and characterized. An ischemic-reperfusion injury-induced AKI (IRI-AKI) mouse model was established to mimic clinical ischemic kidney injury with different disease severity. Mouse blood creatinine level was used to assess renal function, and kidney specimens were processed to detect cell proliferation, apoptosis, and capillary density. Macrophage infiltration was analyzed by flow cytometry. hAEC-derived exosomes (hAECs-EXO) were used to treat hypoxia-reoxygenation (H/R) injured HK-2 cells and mouse bone marrow-derived macrophages to evaluate their protective effect in vitro. Furthermore, hAECs-EXO were subjected to liquid chromatography-tandem mass spectrometry for proteomic profiling.

RESULTS

We found that systematically administered hAECs could improve mortality and renal function in IRI-AKI mice, decrease the number of apoptotic cells, prevent peritubular capillary loss, and modulate kidney local immune response. However, hAECs showed very low kidney tissue integration. Exosomes isolated from hAECs recapitulated the renal protective effects of their source cells. In vitro, hAECs-EXO protected HK-2 cells from H/R injury-induced apoptosis and promoted bone marrow-derived macrophage polarization toward M2 phenotype. Proteomic analysis on hAECs-EXO revealed proteins involved in extracellular matrix organization, growth factor signaling pathways, cytokine production, and immunomodulation. These findings demonstrated that paracrine of exosomes might be the key mechanism of hAECs in alleviating renal ischemia reperfusion injury.

CONCLUSIONS

We reported hAECs could improve survival and ameliorate renal injury in mice with IRI-AKI. The anti-apoptotic, pro-angiogenetic, and immunomodulatory capabilities of hAECs are at least partially, through paracrine pathways. hAECs-EXO might be a promising clinical therapeutic tool, overcoming the weaknesses and risks associated with the use of native stem cells, for patients with AKI.

The Efficacy of Mesenchymal Stem Cells in Therapy of Acute Kidney Injury Induced by Ischemia-Reperfusion in Animal Models

Mesenchymal stem cells (MSCs), discovered and isolated from the bone marrow in the 1960s and with self-renewal capacity and multilineage differentiation potential, have valuable immunomodulatory abilities. Acute kidney injury (AKI) refers to rapid renal failure, which exhibits as quickly progressive decreasing excretion in few hours or days. This study was performed to assess the efficacy of MSCs in the treatment of AKI induced by ischemia-reperfusion using a meta-analysis method. A literature search using corresponding terms was performed in the following databases: Embase, Cochrane Library, PubMed, and ISI Web of Science databases up to Dec 31, 2019. Data for outcomes were identified, and the efficacy of MSCs for AKI was assessed using Cochrane Review Manager Version 5.3. Nineteen studies were eligible and recruited for this meta-analysis. MSC treatment can reduce the Scr levels at 1 day, 2 days, 3 days, 5 days, and >7 days (1 day: WMD = -0.56, 95% CI: -0.78, -0.34, P < 0.00001; 2 days: WMD = -0.58, 95% CI: -0.89, -0.28, P = 0.0002; 3 days: WMD = -0.65, 95% CI: -0.84, -0.45, P < 0.00001; 5 days: WMD = -0.35, 95% CI: -0.54, -0.16, P = 0.0003; and >7 days: WMD = -0.22, 95% CI: -0.36, -0.08, P = 0.002) and can reduce the levels of BUN at 1 day, 2 days, 3 days, and 5 days (1 day: WMD = -11.72, 95% CI: -18.80, -4.64, P = 0.001; 2 days: WMD = -33.60, 95% CI: -40.15, -27.05, P < 0.00001; 3 days: WMD = -21.14, 95% CI: -26.15, -16.14, P < 0.00001; and 5 days: WMD = -8.88, 95% CI: -11.06, -6.69, P < 0.00001), and it also can reduce the levels of proteinuria at 3 days and >7 days and alleviate the renal damage in animal models of AKI. In conclusion, MSCs might be a promising therapeutic agent for AKI induced by ischemia-reperfusion.

In Vitro Cultures of Adipose-Derived Stem Cells: An Overview of Methods, Molecular Analyses, and Clinical Applications

Adipose-derived stem cells (ASCs) exhibiting mesenchymal stem cell (MSC) characteristics, have been extensively studied in recent years. Because they have been shown to differentiate into lineages such as osteogenic, chondrogenic, neurogenic or myogenic, the focus of most of the current research concerns either their potential to replace bone marrow as a readily available and abundant source of MSCs, or to employ them in regenerative and reconstructive medicine. There is close to consensus regarding the methodology used for ASC isolation and culture, whereas a number of molecular analyses implicates them in potential therapies of a number of pathologies. When it comes to clinical application, there is a range of examples of animal trials and clinical studies employing ASCs, further emphasizing the advancement of studies leading to their more widespread use. Nevertheless, in vitro studies will most likely continue to play a significant role in ASC studies, both providing the molecular knowledge of their ex vivo properties and possibly serving as an important step in purification and application of those cells in a clinical setting. Therefore, it is important to consider current methods of ASC isolation, culture, and processing. Furthermore, molecular analyses and cell surface properties of ASCs are essential for animal studies, clinical studies, and therapeutic applications of the MSC properties.

Locoregional delivery of stem cell-based therapies

Interventional regenerative medicine (IRM) uses image-guided, minimally invasive procedures for the targeted delivery of stem cell-based therapies to regenerate, replace, or repair damaged organs. Although many cellular therapies have shown promise in the preclinical setting, clinical results have been suboptimal. Most intravenously delivered cells become trapped in the lungs and reticuloendothelial system, resulting in little therapy reaching target tissues. IRM aims to increase the efficacy of cell-based therapies by locoregional stem cell delivery via endovascular, endoluminal, or direct injection into tissues. This review highlights routes of delivery, disease states, and mechanisms of action involved in the targeted delivery of stem cells.

The effect of intravenous human adipose-derived stem cells (hADSC) on transforming growth factor β1 (TGF-β1), collagen type 1, and kidney histopathological features in the unilateral ureteropelvic junction obstruction model of wistar rats

OBJECTIVE

The fibrotic process of kidney resulting in glomerulosclerosis was found in patients with ureteropelvic junction obstruction (UPJO) who underwent renal biopsy during pyeloplasty. Transforming growth factor β1 (TGF-β1) plays a role in collagen accumulation, resulting in fibrosis. Adipose tissue-derived stem cells (ADSCs) have an anti-apoptotic effect on target cells and enhance the kidney function recovery. We will further investigate the use of ADSC in the prevention of kidney fibrosis in the unilateral UPJO model of Wistar rats.

MATERIAL AND METHODS

A total of twenty-two 12-week-old Wistar rats were divided into three groups. We made the UPJO models using nylon 6-0 inside the left ureter and tied the ureter with nylon 6-0, creating partial ureteral obstruction. The treatment group was then injected with 1.0 × 10⁶ cells of human ADSC via the tail vein of rats. All rats were euthanized after 2 and 4 weeks of treatment. The left kidney used hematoxylin-eosin for histopathological examination. Statistical analysis using one-way analysis of variance (ANOVA) was done with SPSS version 21.0.

RESULTS

TGF-β1 concentration in the treatment group was significantly lower in the 4^th week of observation (p4=0.0001), as well as collagen type 1, which was also significantly lower in the 4^th week (p4=0.0001). There was a significant difference in the glomerulus count between the control group and the human ADSC (hADSC) group therapy in week 2 and week 4 (p2=0.0001 and p4=0.026).

CONCLUSION

Administration of hADSC therapy reduces TGF-β1 and collagen type 1 levels and then improves the histopathological features in the process of renal fibrosis in the UPJO model.

Stem cell-based treatment of kidney diseases

IMPACT STATEMENT

Stem cells hold great promise in regenerative medicine. Pluripotent stem cells have been differentiated into kidney organoids to understand human kidney development and to dissect renal disease mechanisms. Meanwhile, recent studies have explored the treatment of kidney diseases using a variety of cells, including mesenchymal stem cells and renal derivatives. This mini-review discusses the diverse mechanisms underlying current renal disease treatment via stem cell therapy. We postulate that clinical applications of stem cell therapy for kidney diseases can be readily achieved in the near future.

Fat Therapeutics: The Clinical Capacity of Adipose-Derived Stem Cells and Exosomes for Human Disease and Tissue Regeneration

Fat grafting is a well-established surgical technique used in plastic surgery to restore deficient tissue, and more recently, for its putative regenerative properties. Despite more frequent use of fat grafting, however, a scientific understanding of the mechanisms underlying either survival or remedial benefits of grafted fat remain lacking. Clinical use of fat grafts for breast reconstruction in tissues damaged by radiotherapy first provided clues regarding the clinical potential of stem cells to drive tissue regeneration. Healthy fat introduced into irradiated tissues appeared to reverse radiation injury (fibrosis, scarring, contracture and pain) clinically; a phenomenon since validated in several animal studies. In the quest to explain and enhance these therapeutic effects, adipose-derived stem cells (ADSCs) were suggested as playing a key role and techniques to enrich ADSCs in fat, in turn, followed. Stem cells - the body's rapid response 'road repair crew' - are on standby to combat tissue insults. ADSCs may exert influences either by releasing paracrine-signalling factors alone or as cell-free extracellular vesicles (EVs, exosomes). Alternatively, ADSCs may augment vital immune/inflammatory processes; or themselves differentiate into mature adipose cells to provide the 'building-blocks' for engineered tissue. Regardless, adipose tissue constitutes an ideal source for mesenchymal stem cells for therapeutic application, due to ease of harvest and processing; and a relative abundance of adipose tissue in most patients. Here, we review the clinical applications of fat grafting, ADSC-enhanced fat graft, fat stem cell therapy; and the latest evolution of EVs and nanoparticles in healing, cancer and neurodegenerative and multiorgan disease.

GDNF enhances the anti-inflammatory effect of human adipose-derived mesenchymal stem cell-based therapy in renal interstitial fibrosis

Adipose-derived mesenchymal stem cells (AMSCs) are a type of adult stem cell from the mesoderm with the capacity to migrate and differentiate into other cell lineages. As a morphogenetic state of stem cells, glial-derived neurotrophic factor (GDNF) has been found to promote cell proliferation and differentiation of stem cells. The aims of our study were to investigate the biological activity of AMSCs and whether the GDNF gene can enhance the anti-inflammatory properties of stem cells. In this study, stable proliferative GDNF-overexpressing AMSC lines were successfully established and the AMSCs/GDNF-AMSCs were cocultured with macrophages (Mφ) derived from THP-1 cells in a transwell system. The mRNA expression levels of tumor necrosis factor-alpha (TNF-α), inducible nitric oxide synthase (iNOS), interleukin (IL)-10 and IL-4 were detected by quantitative reverse transcription polymerase chain reaction (qRT-PCR). In addition, the expressions of CD163 and CD206, two markers of M2 macrophages, were detected with flow cytometric analysis. In animal experiments, AMSCs/GDNF-AMSCs (5 × 10⁵) were administered to unilateral ureteral obstruction (UUO) nude mice for 3 or 7 days. The expression levels of cyclooxygenase-2 (COX-2), IL-6, transforming growth factor β1 (TGF-β1) and α-Smooth muscle actin (α-SMA) were determined by Western blotting. Renal pathological changes of all groups were observed by hematoxylin and eosin (HE) and Masson staining. In conclusion, in vitro cultured AMSCs induced a shift in macrophage phenotype from the inflammatory (M1) phenotype to the reparative (M2) phenotype. In the UUO model, AMSC treatment was conducive to the recovery of renal function and interstitial fibrosis. Therefore, we determined that AMSC therapy could promote the phenotypic transformation of macrophages and reduce the progression of renal fibrosis by suppressing inflammation. GDNF could enhance the anti-inflammatory effect of AMSCs.

The Anti-Inflammatory, Anti-Oxidative, and Anti-Apoptotic Benefits of Stem Cells in Acute Ischemic Kidney Injury

Ischemia-reperfusion injury (IRI) plays a significant role in the pathogenesis of acute kidney injury (AKI). The complicated interaction between injured tubular cells, activated endothelial cells, and the immune system leads to oxidative stress and systemic inflammation, thereby exacerbating the apoptosis of renal tubular cells and impeding the process of tissue repair. Stem cell therapy is an innovative approach to ameliorate IRI due to its antioxidative, immunomodulatory, and anti-apoptotic properties. Therefore, it is crucial to understand the biological effects and mechanisms of action of stem cell therapy in the context of acute ischemic AKI to improve its therapeutic benefits. The recent finding that treatment with conditioned medium (CM) derived from stem cells is likely an effective alternative to conventional stem cell transplantation increases the potential for future therapeutic uses of stem cell therapy. In this review, we discuss the recent findings regarding stem cell-mediated cytoprotection, with a focus on the anti-inflammatory effects via suppression of oxidative stress and uncompromised immune responses following AKI. Stem cell-derived CM represents a favorable approach to stem cell-based therapy and may serve as a potential therapeutic strategy against acute ischemic AKI.

Modulation of Renal Parenchyma in Response to Allogeneic Adipose-Derived Mesenchymal Stem Cells Transplantation in Acute Kidney Injury

BACKGROUND AND OBJECTIVES

In regenerative medicine, mesenchymal stem cells derived from adipose tissues (Ad-MSCs) are a very attractive target to treat many diseases. In relation to nephrology, the aim of the current study is to investigate the effects of Ad-MSCs for the amelioration of acute kidney injury and to explore the mechanism of renal parenchymal changes in response to allogeneic transplantation of Ad-MSCs.

METHODS AND RESULTS

The nephrotoxicity was induced by cisplatin (CP) in balb/c mice according to RIFLE Class and AKIN Stage 3. PCR, qRT-PCR and fluorescent labeled cells infusion, histopathology, immunohistochemistry, functional analyses were used for genes and proteins expressions data acquisition respectively. We demonstrated that single intravenous infusion of 2.5×107/kg mAd-MSCs in mice pre-injected with CP recruited to the kidney, restored the renal structure, and function, which resulted in progressive survival of mice. The renal tissue morphology was recovered in terms of diminished necrosis or epithelial cells damage, protein casts formation, infiltration of inflammatory cells, tubular dilatation, and restoration of brush border protein; Megalin and decreased Kim-1 expressions in mAd-MSCs transplanted mice. Significant reduction in serum creatinine with slashed urea and urinary protein levels were observed. Anti-BrdU staining displayed enhanced tubular cells proliferation. Predominantly, downgrade expressions of TNF-α and TGF-β1 were observed post seven days in mAd-MSCs transplanted mice.

CONCLUSIONS

Ad-MSCs exerts pro-proliferative, anti-inflammatory, and anti-fibrotic effects. Ad-MSCs transplantation without any chemical or genetic manipulation can provide the evidence of therapeutic strategy for the origin of regeneration and overall an improved survival of the system in functionally deprived failed kidneys.

Potential therapeutic roles of stem cells in ischemia-reperfusion injury

Ischemia-reperfusion injury (I/RI), produced by an initial interruption of organ blood flow and its subsequent restoration, contributes significantly to the pathophysiologies of stroke, myocardial infarction, renal I/RI, intestinal I/RI and liver I/RI, which are major causes of disability (including transplant failure) and even mortality. While the restoration of blood flow is required to restore oxygen and nutrient requirements, reperfusion often triggers local and systemic inflammatory responses and subsequently elevate the ischemic insult where the duration of ischemia determines the magnitude of I/RI damage. I/RI increases vascular leakage, changes transcriptional and cell death programs, drives leukocyte entrapment and inflammation and oxidative stress in tissues. Therapeutic approaches which reduce complications associated with I/RI are desperately needed to address the clinical and economic burden created by I/RI. Stem cells (SC) represent ubiquitous and uncommitted cell populations with the ability to self-renew and differentiate into one or more developmental 'fates'. Like immune cells, stem cells can home to and penetrate I/R-injured tissues, where they can differentiate into target tissues and induce trophic paracrine signaling which suppress injury and maintain tissue functions perturbed by ischemia-reperfusion. This review article summarizes the present use and possible protective mechanisms underlying stem cell protection in diverse forms of ischemia-reperfusion.

Enhancement of the efficacy of mesenchymal stem cells in the treatment of ischemic diseases

Ischemic diseases refer to a wide range of diseases caused by reduced blood flow and a subsequently deficient oxygen and nutrient supply. The pathogenesis of ischemia is multifaceted and primarily involves inflammation, oxidative stress and an apoptotic response. Over the last decade, mesenchymal stem cells (MSCs) have been widely studied as potential cell therapy agents for ischemic diseases due to their multiple favourable functions. However, the low homing and survival rates of transplanted cells have been concerns limiting for their clinical application. Recently, increasing studies have attempted to enhance the efficacy of MSCs by various strategies including genetic modification, pretreatment, combined application and biomaterial application. The purpose of this review is to summarize these creative strategies and the progress in basic and preclinical studies.

Stem/Stromal Cells for Treatment of Kidney Injuries With Focus on Preclinical Models

Within the last years, the use of stem cells (embryonic, induced pluripotent stem cells, or hematopoietic stem cells), Progenitor cells (e.g., endothelial progenitor cells), and most intensely mesenchymal stromal cells (MSC) has emerged as a promising cell-based therapy for several diseases including nephropathy. For patients with end-stage renal disease (ESRD), dialysis or finally organ transplantation are the only therapeutic modalities available. Since ESRD is associated with a high healthcare expenditure, MSC therapy represents an innovative approach. In a variety of preclinical and clinical studies, MSC have shown to exert renoprotective properties, mediated mainly by paracrine effects, immunomodulation, regulation of inflammation, secretion of several trophic factors, and possibly differentiation to renal precursors. However, studies are highly diverse; thus, knowledge is still limited regarding the exact mode of action, source of MSC in comparison to other stem cell types, administration route and dose, tracking of cells and documentation of therapeutic efficacy by new imaging techniques and tissue visualization. The aim of this review is to provide a summary of published studies of stem cell therapy in acute and chronic kidney injury, diabetic nephropathy, polycystic kidney disease, and kidney transplantation. Preclinical studies with allogeneic or xenogeneic cell therapy were first addressed, followed by a summary of clinical trials carried out with autologous or allogeneic hMSC. Studies were analyzed with respect to source of cell type, mechanism of action etc.