Healthy bone marrow cells reduce progression of kidney failure better than CKD bone marrow cells in rats with established chronic kidney disease

Discrepancies between transcutaneous and estimated glomerular filtration rates in rats with chronic kidney disease

Accurate assessment of the glomerular filtration rate (GFR) is crucial for researching kidney disease in rats. Although validation of methods that assess GFR is crucial, large-scale comparisons between different methods are lacking. Both transcutaneous GFR (tGFR) and a newly developed estimated GFR (eGFR) equation by our group provide a low-invasive approach enabling repeated measurements. The tGFR is a single bolus method using FITC-labeled sinistrin to measure GFR based on half-life of the transcutaneous signal, whilst the eGFR is based on urinary sinistrin clearance. Here, we retrospectively compared tGFR, using both 1- and 3- compartment models (tGFR_1c and tGFR_3c, respectively) to the eGFR in a historic cohort of 43 healthy male rats and 84 male rats with various models of chronic kidney disease. The eGFR was on average considerably lower than tGFR-1c and tGFR-3c (mean differences 855 and 216 μL/min, respectively) and only 20 and 47% of measurements were within 30% of each other, respectively. The relative difference between eGFR and tGFR was highest in rats with the lowest GFR. Possible explanations for the divergence are problems inherent to tGFR, such as technical issues with signal measurement, description of the signal kinetics, and translation of half-life to tGFR, which depends on distribution volume. The unknown impact of isoflurane anesthesia used in determining mGFR remains a limiting factor. Thus, our study shows that there is a severe disagreement between GFR measured by tGFR and eGFR, stressing the need for more rigorous validation of the tGFR and possible adjustments to the underlying technique.

The effect of chronic kidney disease on tissue formation of in situ tissue-engineered vascular grafts

Vascular in situ tissue engineering encompasses a single-step approach with a wide adaptive potential and true off-the-shelf availability for vascular grafts. However, a synchronized balance between breakdown of the scaffold material and neo-tissue formation is essential. Chronic kidney disease (CKD) may influence this balance, lowering the usability of these grafts for vascular access in end-stage CKD patients on dialysis. We aimed to investigate the effects of CKD on in vivo scaffold breakdown and tissue formation in grafts made of electrospun, modular, supramolecular polycarbonate with ureido-pyrimidinone moieties (PC-UPy). We implanted PC-UPy aortic interposition grafts (n = 40) in a rat 5/6th nephrectomy model that mimics systemic conditions in human CKD patients. We studied patency, mechanical stability, extracellular matrix (ECM) components, total cellularity, vascular tissue formation, and vascular calcification in CKD and healthy rats at 2, 4, 8, and 12 weeks post-implantation. Our study shows successful in vivo application of a slow-degrading small-diameter vascular graft that supports adequate in situ vascular tissue formation. Despite systemic inflammation associated with CKD, no influence of CKD on patency (Sham: 95% vs CKD: 100%), mechanical stability, ECM formation (Sirius red⁺, Sham 16.5% vs CKD 25.0%-p:0.83), tissue composition, and immune cell infiltration was found. We did find a limited increase in vascular calcification at 12 weeks (Sham 0.08% vs CKD 0.80%-p:0.02) in grafts implanted in CKD animals. However, this was not associated with increased stiffness in the explants. Our findings suggest that disease-specific graft design may not be necessary for use in CKD patients on dialysis.

Potential therapeutic strategies for photoreceptor degeneration: the path to restore vision

Photoreceptors (PRs), as the most abundant and light-sensing cells of the neuroretina, are responsible for converting light into electrical signals that can be interpreted by the brain. PR degeneration, including morphological and functional impairment of these cells, causes significant diminution of the retina's ability to detect light, with consequent loss of vision. Recent findings in ocular regenerative medicine have opened promising avenues to apply neuroprotective therapy, gene therapy, cell replacement therapy, and visual prostheses to the challenge of restoring vision. However, successful visual restoration in the clinical setting requires application of these therapeutic approaches at the appropriate stage of the retinal degeneration. In this review, firstly, we discuss the mechanisms of PR degeneration by focusing on the molecular mechanisms underlying cell death. Subsequently, innovations, recent developments, and promising treatments based on the stage of disorder progression are further explored. Then, the challenges to be addressed before implementation of these therapies in clinical practice are considered. Finally, potential solutions to overcome the current limitations of this growing research area are suggested. Overall, the majority of current treatment modalities are still at an early stage of development and require extensive additional studies, both pre-clinical and clinical, before full restoration of visual function in PR degeneration diseases can be realized.

When Origin Matters: Properties of Mesenchymal Stromal Cells From Different Sources for Clinical Translation in Kidney Disease

Advanced therapy medicinal products (ATMPs) offer new prospects to improve the treatment of conditions with unmet medical needs. Kidney diseases are a current major health concern with an increasing global prevalence. Chronic renal failure appears after many years of impairment, which opens a temporary window to apply novel therapeutic approaches to delay or halt disease progression. The immunomodulatory, anti-inflammatory, and pro-regenerative properties of mesenchymal stromal cells (MSCs) have sparked interest for their use in cell-based regenerative therapies. Currently, several early-phase clinical trials have been completed and many are ongoing to explore MSC safety and efficacy in a wide range of nephropathies. However, one of the current roadblocks to the clinical translation of MSC therapies relates to the lack of standardization and harmonization of MSC manufacturing protocols, which currently hinders inter-study comparability. Studies have shown that cell culture processing variables can have significant effects on MSC phenotype and functionality, and these are highly variable across laboratories. In addition, heterogeneity within MSC populations is another obstacle. Furthermore, MSCs may be isolated from several sources which adds another variable to the comparative assessment of outcomes. There is now a growing body of literature highlighting unique and distinctive properties of MSCs according to the tissue origin, and that characteristics such as donor, age, sex and underlying medical conditions may alter the therapeutic effect of MSCs. These variables must be taken into consideration when developing a cell therapy product. Having an optimal scale-up strategy for MSC manufacturing is critical for ensuring product quality while minimizing costs and time of production, as well as avoiding potential risks. Ideally, optimal scale-up strategies must be carefully considered and identified during the early stages of development, as making changes later in the bioprocess workflow will require re-optimization and validation, which may have a significant long-term impact on the cost of the therapy. This article provides a summary of important cell culture processing variables to consider in the scale-up of MSC manufacturing as well as giving a comprehensive review of tissue of origin-specific biological characteristics of MSCs and their use in current clinical trials in a range of renal pathologies.

Expression Analysis of GDNF/RET Signaling Pathway in Human AD-MSCs Grown in HEK 293 Conditioned Medium (HEK293-CM)

Mesenchymal stem cells have been considered as the suitable source for the repair of kidney lesions. The study and identification of novel approaches could improve the efficiency of these cells in the recovery of kidney. In the present study, the effect of HEK 293 conditioned medium (HEK293-CM) was evaluated on the expression of GDNF/RET signaling pathway and their downstream genes in the human adipose-derived mesenchymal stem cells (AD-MSCs). For this purpose, the human AD-MSCs were cultured in the medium containing HEK293-CM. After the RNA extraction and cDNA synthesis, the expression level of GFRA1, GDNF, SPRY1, ETV4, ETV5, and CRLF1 genes were determined by SYBR Green Real time PCR. The obtained results indicated that the GDNF and GFRA1 expression enhanced in the AD-MSCs following treatment with 10% HEK293-CM-5%FBS as compared to the untreated AD-MSCs. These results were consistent with the decreased expression of SPRY1. The significant increased expression of ETV4, ETV5, and CRLF1 genes also showed that HEK293-CM activated the GDNF/RET signaling pathway in the AD-MSCs (P < 0.05). The obtained data suggested that the treatment with HEK293-CM activated the GDNF/RET signaling pathway in the human AD-MSCs.

Regulatory T Cells as a Novel Candidate for Cell-Based Therapy in Kidney Disease

Kidney disease is a significant health concern worldwide. Ineffective treatment can lead to disastrous consequences, such as organ failure and death. Research has turned to cell-based therapy, but has yet to produce an effective and reliable treatment for kidney disease. To address this problem, we examined four datasets of gene expression profiles from diseased and healthy kidney tissue in humans, mice, and rats. Differentially expressed genes (DEGs) were screened and subjected to enrichment analyses. Up-regulated genes in diseased kidney tissue were significantly enriched in pathways associated with regulatory T cells (Tregs). Analysis with the xCell tool showed that Tregs were generally increased in diseased kidney tissue in all species. To validate these results in vivo, kidneys were removed from mice with Adriamycin-induced nephropathy, and histology confirmed increase of Tregs. Furthermore, Tregs were adoptively transferred from healthy mice into mice with kidney injury, restoring normal structure to the damaged kidneys. Treg cells that were co-cultured with M2c macrophages exhibited up-regulation of chemokine receptors CCR2, CCR5, CCR7, CD62L, and CX3CR1. This may be the mechanism by which M2c cells enhance the migration of Tregs to the site of inflammation. We propose that Tregs may be an effective, novel candidate for cell-based therapy in pre-clinical kidney injury models.

Paracrine Proangiogenic Function of Human Bone Marrow-Derived Mesenchymal Stem Cells Is Not Affected by Chronic Kidney Disease

Background

Cell-based therapies are being developed to meet the need for curative therapy in chronic kidney disease (CKD). Bone marrow- (BM-) derived mesenchymal stromal cells (MSCs) enhance tissue repair and induce neoangiogenesis through paracrine action of secreted proteins and extracellular vesicles (EVs). Administration of allogeneic BM MSCs is less desirable in a patient population likely to require a kidney transplant, but potency of autologous MSCs should be confirmed, given previous indications that CKD-induced dysfunction is present. While the immunomodulatory capacity of CKD BM MSCs has been established, it is unknown whether CKD affects wound healing and angiogenic potential of MSC-derived CM and EVs.

Methods

MSCs were cultured from BM obtained from kidney transplant recipients (N = 15) or kidney donors (N = 17). Passage 3 BM MSCs and BM MSC-conditioned medium (CM) were used for experiments. EVs were isolated from CM by differential ultracentrifugation. BM MSC differentiation capacity, proliferation, and senescence-associated β-galactosidase activity was assessed. In vitro promigratory and proangiogenic capacity of BM MSC-derived CM and EVs was assessed using an in vitro scratch wound assay and Matrigel angiogenesis assay.

Results

Healthy and CKD BM MSCs exhibited similar differentiation capacity, proliferation, and senescence-associated β-galactosidase activity. Scratch wound migration was not significantly different between healthy and CKD MSCs (P = 0.18). Healthy and CKD BM MSC-derived CM induced similar tubule formation (P = 0.21). There was also no difference in paracrine regenerative function of EVs (scratch wound: P = 0.6; tubulogenesis: P = 0.46).

Conclusions

Our results indicate that MSCs have an intrinsic capacity to produce proangiogenic paracrine factors, including EVs, which is not affected by donor health status regarding CKD. This suggests that autologous MSC-based therapy is a viable option in CKD.

The gut microbiota and the brain-gut-kidney axis in hypertension and chronic kidney disease

Crosstalk between the gut microbiota and the host has attracted considerable attention owing to its involvement in diverse diseases. Chronic kidney disease (CKD) is commonly associated with hypertension and is characterized by immune dysregulation, metabolic disorder and sympathetic activation, which are all linked to gut dysbiosis and altered host-microbiota crosstalk. In this Review, we discuss the complex interplay between the brain, the gut, the microbiota and the kidney in CKD and hypertension and explain our brain-gut-kidney axis hypothesis for the pathogenesis of these diseases. Consideration of the role of the brain-gut-kidney axis in the maintenance of normal homeostasis and of dysregulation of this axis in CKD and hypertension could lead to the identification of novel therapeutic targets. In addition, the discovery of unique microbial communities and their associated metabolites and the elucidation of brain-gut-kidney signalling are likely to fill fundamental knowledge gaps leading to innovative research, clinical trials and treatments for CKD and hypertension.

Adipose tissue-derived mesenchymal stromal cells for treating chronic kidney disease: A pilot study assessing safety and clinical feasibility

Background

Chronic kidney disease (CKD) is a growing public health concern, and available treatments are insufficient in limiting disease progression. New strategies, including regenerative cell-based therapies, have emerged as therapeutic alternatives. Results from several groups, including our own, have reported evidence of a supportive role for mesenchymal stromal cells (MSCs) in functional recovery and prevention of tissue damage in murine models of CKD. Prompted by these data, an open pilot study was conducted to assess the safety and efficacy of a single injection of autologous adipose tissue-derived MSCs (AT-MSCs) for treatment of CKD.

Methods

AT-MSCs were infused intravenously into six CKD patients at a dose of 1 million cells/kg. Patients were stabilized and followed for one year prior to MSC infusion and one year following infusion.

Results

No patients presented with adverse effects. Statistically significant improvement in urinary protein excretion was observed in AT-MSCs transplanted patients, from a median of 0.75 g/day (range, 0.15-9.57) at baseline to 0.54 g/day (range, 0.01-2.66) at month 12 (P = 0.046). The glomerular filtration rate was not significantly decreased post-infusion of AT-MSCs.

Conclusion

Findings from this pilot study demonstrate that intravenous infusion of autologous expanded AT-MSCs into CKD patients was not associated with adverse effects and could benefit patients already undergoing standard medical treatment.

Apparent Correlations Between AMPK Expression and Brain Inflammatory Response and Neurological Function Factors in Rats with Chronic Renal Failure

To explore the correlations between AMP-activated protein kinase (AMPK) expression and brain inflammatory response and neurological function factors in rats with chronic renal failure. Chronic renal failure models in rats were established, and the healthy control group (normal group) was set. Chronic renal failure model rats were divided into model group (without any treatment), control group (intraperitoneal injection of normal saline), A-769662 group (intraperitoneal injection of AMPK specific activator), and compound C group (intraperitoneal injection of AMPK specific inhibitor). The results of HE staining showed renal tissue enlargement, and significant pathological changes. Compared with the normal group, AMPK level in peripheral blood and AMPK mRNA and protein expressions in brain tissue were significantly reduced, and AMPK pathway activation was significantly inhibited in other groups. Compared with the model group, rats in the A-769662 group had significantly decreased serum creatinine (Scr) and blood urea nitrogen (BUN) levels and γ-aminobutyric acid (γ-GABA) content, significantly increased brain-derived neurotrophic factor (BDNF) positive expressions and 5-hydroxytryptamine (5-HT) content, and decreased interleukin-1 (IL-1), tumor necrosis factor-α (TNF-α), and intercellular adhesion molecule 1 (ICAM-1) expressions (all P < 0.05), while it was just the opposite in compound C group (all P < 0.05). There is an apparent correlation between AMPK expression and brain inflammatory response in chronic renal failure rats. AMPK is expected to be an important pathway in the treatment of uremic encephalopathy.

Are cell-based therapies for kidney disease safe? A systematic review of preclinical evidence

The number of individuals affected by acute kidney injury (AKI) and chronic kidney disease (CKD) is constantly rising. In light of the limited availability of treatment options and their relative inefficacy, cell based therapeutic modalities have been studied. However, not many efforts are put into safety evaluation of such applications. The aim of this study was to review the existing published literature on adverse events reported in studies with genetically modified cells for treatment of kidney disease. A systematic review was conducted by searching PubMed and EMBASE for relevant articles published until June 2018. The search results were screened and relevant articles selected using pre-defined criteria, by two researchers independently. After initial screening of 6894 abstracts, a total number of 97 preclinical studies was finally included for full assessment. Of these, 61 (63%) presented an inappropriate study design for the evaluation of safety parameters. Only 4 studies (4%) had the optimal study design, while 32 (33%) showed sub-optimal study design with either direct or indirect evidence of adverse events. The high heterogeneity of studies included regarding cell type and number, genetic modification, administration route, and kidney disease model applied, combined with the consistent lack of appropriate control groups, makes a reliable safety evaluation of kidney cell-based therapies impossible. Only a limited number of relevant studies included looked into essential safety-related outcomes, such as inflammatory (48%), tumorigenic and teratogenic potential (12%), cell biodistribution (82%), microbiological safety with respect to microorganism contamination and latent viruses' reactivation (1%), as well as overall well-being and animal survival (19%). In conclusion, for benign cell-based therapies, well-designed pre-clinical studies, including all control groups required and good manufacturing processes securing safety, need to be done early in development. Preferably, this should be performed side by side with efficacy evaluation and according to the official guidelines of leading health organizations.

On the Choice of the Extracellular Vesicles for Therapeutic Purposes

Extracellular vesicles (EVs) are lipid membrane vesicles released by all human cells and are widely recognized to be involved in many cellular processes, both in physiological and pathological conditions. They are mediators of cell-cell communication, at both paracrine and systemic levels, and therefore they are active players in cell differentiation, tissue homeostasis, and organ remodeling. Due to their ability to serve as a cargo for proteins, lipids, and nucleic acids, which often reflects the cellular source, they should be considered the future of the natural nanodelivery of bio-compounds. To date, natural nanovesicles, such as exosomes, have been shown to represent a source of disease biomarkers and have high potential benefits in regenerative medicine. Indeed, they deliver both chemical and bio-molecules in a way that within exosomes drugs are more effective that in their exosome-free form. Thus, to date, we know that exosomes are shuttle disease biomarkers and probably the most effective way to deliver therapeutic molecules within target cells. However, we do not know exactly which exosomes may be used in therapy in avoiding side effects as well. In regenerative medicine, it will be ideal to use autologous exosomes, but it seems not ideal to use plasma-derived exosomes, as they may contain potentially dangerous molecules. Here, we want to present and discuss a contradictory relatively unmet issue that is the lack of a general agreement on the choice for the source of extracellular vesicles for therapeutic use.

Contribution of bone marrow-derived cells to in situ engineered tissue capsules in a rat model of chronic kidney disease

Tissue engineered blood vessels (TEBVs) hold great promise for clinical use in patients with end stage renal disease (ESRD) requiring vascular access for hemodialysis. A promising way to make TEBVs is to exploit foreign body response (FBR) of polymeric rods used as templates. However, since the FBR predominantly involves bone-marrow (BM) derived cells and ESRD coincides with impaired function of BM, it is important to assess the generation of TEBVs in conditions of renal failure. To this end, we implanted polymer rods in the subcutis of rats after BM-transplantation with GFP-labeled BM cells in a model of chronic kidney disease (CKD). At 3 weeks after implantation, rods were encapsulated by tissue capsule (TC) composed of collagen, myofibroblasts and macrophages. On average, 13% of CD68⁺ macrophages were GFP⁺, indicating BM origin. Macrophage-to-myofibroblasts differentiation appeared to play an important role in TC formation as 26% of SMA⁺/GFP⁺ myofibroblasts co-expressed the macrophage marker CD68. Three weeks after rod implantation, the cellular response changed towards tissue repair, characterized by 40% increase in CD68⁺/CD163⁺ repair associated macrophages and 95% increase in TGFβ and IL10 gene expression as compared to TCs harvested at 1 week. These results show that both BM derived and tissue resident cells, contribute to TC formation, whereas macrophages serve as precursors of myofibroblasts in mature TCs. Finally, the presence of CKD did not significantly alter the process of TC formation, which holds the potential to support our approach for future clinical use in ESRD patients.

Dissecting recipient from donor contribution in experimental kidney transplantation: focus on endothelial proliferation and inflammation

Kidney transplantation (Tx) is considered the only definite treatment for end-stage kidney disease (ESKD) patients. The increasing prevalence of ESKD has necessitated the introduction of transplantation with kidneys from suboptimal donors. There is, however, still a lack of fundamental and longitudinal research on suboptimal kidney transplants. Specifically, there is a demand for accurate pre-Tx predictors of donor kidney function and injury to predict post-Tx outcome. In the present study, we combine rat models of chronic kidney disease (CKD) and renal Tx to dissect the effects of healthy and CKD renal grafts on healthy and CKD recipients. We show that renal function at 6 weeks post-Tx is exclusively determined by donor graft quality. Using cell tracking within enhanced green fluorescent protein-positive (eGFP⁺) recipients, we furthermore show that most inflammatory cells within the donor kidney originate from the donor. Oxidative and vascular extra-renal damage were, in contrast, determined by the recipient. Post- versus pre-Tx evaluation of grafts showed an increase in glomerular and peritubular capillary rarefaction in healthy but not CKD grafts within a CKD environment. Proliferation of glomerular endothelium was similar in all groups, and influx of eGFP⁺ recipient-derived cells occurred irrespective of graft or recipient status. Glomerular and peritubular capillary rarefaction, severity of inflammation and macrophage subtype data post-Tx were, however, determined by more complicated effects, warranting further study. Our experimental model could help to further distinguish graft from recipient environment effects, leading to new strategies to improve graft survival of suboptimal Tx kidneys.

This article has an associated First Person interview with the first author of the paper.

Summary: Using experimental kidney transplantation, we dissected donor graft from recipient environment effects, focusing on the endothelium and inflammation. These results can direct strategies to improve graft survival after suboptimal transplantation.

Bone marrow-derived cells and their conditioned medium induce microvascular repair in uremic rats by stimulation of endogenous repair mechanisms

The reduced number of circulating stem/progenitor cells that is found in chronic kidney disease (CKD) patients may contribute to impaired angiogenic repair and decreased capillary density in the heart. Cell therapy with bone marrow-derived cells (BMDCs) has been shown to induce positive effects on the microvasculature and cardiac function, most likely due to secretion of growth factors and cytokines, all of which are present in the conditioned medium (CM); however, this is controversial. Here we showed that treatment with BMDC or CM restored vascular density and decreased the extent of fibrosis in a rat model of CKD, the 5/6 nephrectomy. Engraftment and differentiation of exogenous BMDCs could not be detected. Yet CM led to the mobilization and infiltration of endogenous circulating cells into the heart. Cell recruitment was facilitated by the local expression of pro-inflammatory factors such as the macrophage chemoattractant protein-1, interleukin-6, and endothelial adhesion molecules. Consistently, in vitro assays showed that CM increased endothelial adhesiveness to circulating cells by upregulating the expression of adhesion molecules, and stimulated angiogenesis/endothelial tube formation. Overall, our results suggest that both treatments exert vasculoprotective effects on the heart of uremic rats by stimulating endogenous repair mechanisms.

Low white blood cell count is independently associated with chronic kidney disease progression in the elderly: the CKD-ROUTE study

BACKGROUND

Elevated white blood cell (WBC) count is a well-known predictor of chronic kidney disease (CKD) progression. However, elderly patients commonly fail to develop a high WBC count in response to several diseased states and may instead present a low WBC count. Therefore, we hypothesized that low WBC count, in addition to high WBC count, is associated with CKD progression in the elderly.

METHODS

We conducted a prospective cohort study using 3-year follow-up data from the CKD Research of Outcomes in Treatment and Epidemiology study. In the present study, participants aged over 60 years with pre-dialysis CKD stages G2-G5 were eligible. Patients were stratified into three groups according to WBC count using tertiles (T). The primary outcome was a composite of end-stage renal disease and a 50% reduction in estimated glomerular filtration rate. Data were analyzed using Cox proportional hazard models with adjustments for covariates.

RESULTS

We enrolled 697 patients (males, 69%). The median WBC count was 6100 cells/µl (T1, <5400, n =  222; T2, 5400-6900, n =  235; T3, ≥6900, n = 240). During a median follow-up of 868 days, the primary outcome was observed in 170 patients, whereas 54 patients died. T1 and T3 had significantly higher hazard ratios (HR) than T2 (T1, HR 1.69, 95% confidence interval 1.14-2.51; T3, HR 1.63, 95% confidence interval 1.10-2.41). Moreover, T1 had a significantly higher adjusted HR (1.54, 95% confidence interval 1.00-2.37).

CONCLUSION

Low WBC count is independently associated with CKD progression in the elderly.

A perspective on chronic kidney disease progression

Chronic kidney disease (CKD) will progress to end stage without treatment, but the decline of renal function may not be linear. Compared with glomerular filtration rate and proteinuria, new surrogate markers, such as kidney injury molecule-1, neutrophil gelatinase-associated protein, apolipoprotein A-IV, and soluble urokinase receptor, may allow potential intervention and treatment in the earlier stages of CKD, which could be useful for clinical trials. New omic-based technologies reveal potential new genomic and epigenomic mechanisms that appear different from those causing the initial disease. Various clinical studies also suggest that acute kidney injury is a major risk for progressive CKD. To ameliorate the progression of CKD, the first step is optimizing renin-angiotensin-aldosterone system blockade. New drugs targeting endothelin, transforming growth factor-β, oxidative stress, and inflammatory- and cell-based regenerative therapy may have add-on benefit.

Strategies to Optimize Adult Stem Cell Therapy for Tissue Regeneration

Stem cell therapy aims to replace damaged or aged cells with healthy functioning cells in congenital defects, tissue injuries, autoimmune disorders, and neurogenic degenerative diseases. Among various types of stem cells, adult stem cells (i.e., tissue-specific stem cells) commit to becoming the functional cells from their tissue of origin. These cells are the most commonly used in cell-based therapy since they do not confer risk of teratomas, do not require fetal stem cell maneuvers and thus are free of ethical concerns, and they confer low immunogenicity (even if allogenous). The goal of this review is to summarize the current state of the art and advances in using stem cell therapy for tissue repair in solid organs. Here we address key factors in cell preparation, such as the source of adult stem cells, optimal cell types for implantation (universal mesenchymal stem cells vs. tissue-specific stem cells, or induced vs. non-induced stem cells), early or late passages of stem cells, stem cells with endogenous or exogenous growth factors, preconditioning of stem cells (hypoxia, growth factors, or conditioned medium), using various controlled release systems to deliver growth factors with hydrogels or microspheres to provide apposite interactions of stem cells and their niche. We also review several approaches of cell delivery that affect the outcomes of cell therapy, including the appropriate routes of cell administration (systemic, intravenous, or intraperitoneal vs. local administration), timing for cell therapy (immediate vs. a few days after injury), single injection of a large number of cells vs. multiple smaller injections, a single site for injection vs. multiple sites and use of rodents vs. larger animal models. Future directions of stem cell-based therapies are also discussed to guide potential clinical applications.

Challenges and opportunities for stem cell therapy in patients with chronic kidney disease

Chronic kidney disease (CKD) is a global health care burden affecting billions of individuals worldwide. The kidney has limited regenerative capacity from chronic insults, and for the most common causes of CKD, no effective treatment exists to prevent progression to end-stage kidney failure. Therefore, novel interventions, such as regenerative cell-based therapies, need to be developed for CKD. Given the risk of allosensitization, autologous transplantation of cells to boost regenerative potential is preferred. Therefore, verification of cell function and vitality in CKD patients is imperative. Two cell types have been most commonly applied in regenerative medicine. Endothelial progenitor cells contribute to neovasculogenesis primarily through paracrine angiogenic activity and partly by differentiation into mature endothelial cells in situ. Mesenchymal stem cells also exert paracrine effects, including proangiogenic, anti-inflammatory, and antifibrotic activity. However, in CKD, multiple factors may contribute to reduced cell function, including older age, coexisting cardiovascular disease, diabetes, chronic inflammatory states, and uremia, which may limit the effectiveness of an autologous cell-based therapy approach. This Review highlights current knowledge on stem and progenitor cell function and vitality, aspects of the uremic milieu that may serve as a barrier to therapy, and novel methods to improve stem cell function for potential transplantation.

Perinatal Inhibition of NF-KappaB Has Long-Term Antihypertensive and Renoprotective Effects in Fawn-Hooded Hypertensive Rats

BACKGROUND

Inhibition of transcription factor nuclear factor-kappa B (NFκB) is beneficial in various models of hypertension and renal disease. We hypothesized first that NFκB inhibition during renal development ameliorates hereditary hypertensive renal disease and next whether this was mediated via suppression of peroxisome proliferator-activated receptor (PPAR)γ coactivator 1α (PGC-1α).

METHODS AND RESULTS

Prior to the development of renal injury in fawn-hooded hypertensive (FHH) rats, a model of hypertension, glomerular hyperfiltration, and progressive renal injury, NFkB activity, measured by nuclear protein expression of NFkB subunit p65, was enhanced twofold in 2-day-old male and female FHH kidneys as compared to normotensive Wistar-Kyoto (WKY) rats (P < 0.05). Treating FHH dams with pyrrolidine di thio carbamate (PDTC), an NFκB inhibitor, from 2 weeks before birth to 4 weeks after birth diminished NFkB activity in 2-day-FHH offspring to 2-day-WKY levels (P < 0.01). Perinatal PDTC reduced systolic blood pressure from 20 weeks onwards by on average 25 mm Hg (P < 0.001) and ameliorated proteinuria (P < 0.05) and glomerulosclerosis (P < 0.05). In kidneys of 2-day-, 2-week-, and adult offspring of PDTC-treated FHH dams, PGC-1α was induced on average by 67% (quantitative polymerase chain reaction (qPCR)) suggesting that suppression of this factor by NFkB could be involved in renal damage. Follow-up experiments with perinatal pioglitazone (Pio), a PPARγ agonist, failed to confer persistent antihypertensive or renoprotective effects.

CONCLUSIONS

Perinatal inhibition of enhanced active renal NFκB in 2-day FHH had persistent antihypertensive and renoprotective effects. However, this was not the case for PPARγ stimulation. NFkB stimulation is therefore involved in renal damage in the FHH model of proteinuric renal disease by pathways other than via PPARγ.

Repeated treatment with bone marrow cell secretory products maintains long-term renoprotection in experimental chronic kidney disease: a placebo-controlled trial

Background

Bone marrow-derived early outgrowth cells (EOCs) secrete soluble factors that exert potent renoprotective effects, such that infusion of their conditioned medium recapitulates the affects of the cells themselves.

Objectives

The objective of this study is to test whether the protective effect of conditioned medium infusion wanes with time and whether tachyphylaxis occurs with repeated administration.

Design

This is a placebo-controlled animal study.

Setting

The study was conducted at St. Michael’s Hospital, Toronto, Ontario, Canada.

Subjects

Fischer 344 (F344) rats were used in this study.

Measurements

The following were measured: (1) urinary protein:creatinine ratio, (2) glomerular filtration rate, (3) systolic blood pressure, (4) body weight, (5) glomerular endothelial cell density, and (6) glomerular and tubulointerstitial type IV collagen deposition.

Methods

Subtotally nephrectomized F344 rats, a model of progressive chronic kidney disease, were randomized 4 weeks post-surgery to receive thrice-weekly intravenous injections of concentrated EOC-conditioned medium (EOC CM) or unconditioned medium (UCM) over 2 weeks. Three animal groups were studied, according to whether they were administered conditioned medium: once (Initial Therapy Only group), twice (Repeat Therapy group), or not at all (No Therapy group).

Results

Following initial therapy, EOC CM-treated animals excreted less urinary protein, a marker of renal injury, than their UCM-treated counterparts. At 10 weeks post-subtotal nephrectomy, however, mean urinary protein excretion in conditioned medium-treated animals was fourfold greater than at the completion of the initial treatment course. At this time point, conditioned medium-treated animals were randomized to receive a second course of either conditioned medium (Repeat Therapy group) or unconditioned medium (Initial Therapy Only group). At study end (14 weeks post-subtotal nephrectomy), Repeat Therapy animals demonstrated higher glomerular filtration rate, less proteinuria, preserved renal microvasculature, and diminished fibrosis when compared with the No Therapy group. Initial Therapy Only animals exhibited an intermediate effect.

Limitations

Testing the effect of EOC-conditioned medium in a single model of chronic kidney disease (CKD) has limitations.

Conclusions

These findings suggest that early outgrowth cell-derived factors, while renoprotective, have a limited duration of action. Repeated administration of these factors, however, is able to extend the duration of efficacy and attenuate the progression of experimental chronic kidney disease.

Ex vivo manipulation of bone marrow cells to rescue uremia-induced dysfunction for autologous therapy

Uremic toxins are known to affect the regenerative properties of tissue-resident and circulating stem cells and thus appear to be a limiting factor for autologous stem cell-based approaches for treating chronic kidney disease. The recent article by van Koppen and colleagues in Stem Cell Research & Therapy provides evidence that an ex vivo short-term pre-treatment with statins reverts the dysfunction of bone marrow stem cells isolated from rats with renal impairment. Indeed, statin pre-treated cells improved renal function in a model of established chronic kidney disease. Our commentary discusses the potential of this approach in the context of autologous cell therapy and the available knowledge on the mechanisms involved in uremia-induced stem cell dysfunction.

Ex vivo exposure of bone marrow from chronic kidney disease donor rats to pravastatin limits renal damage in recipient rats with chronic kidney disease

Introduction

Healthy bone marrow cell (BMC) infusion improves renal function and limits renal injury in a model of chronic kidney disease (CKD) in rats. However, BMCs derived from rats with CKD fail to retain beneficial effects, demonstrating limited therapeutic efficacy. Statins have been reported to improve cellular repair mechanisms.

Methods

We studied whether exposing CKD rat BMCs ex vivo to pravastatin improved their in vivo therapeutic efficacy in CKD and compared this to systemic in vivo treatment. Six weeks after CKD induction, healthy BMCs, healthy pravastatin-pretreated BMCs, CKD BMCs or CKD pravastatin-pretreated BMCs were injected into the renal artery of CKD rats.

Results

At 6 weeks after BMC injection renal injury was reduced in pravastatin-pretreated CKD BMC recipients vs. CKD BMC recipients. Effective renal plasma flow was lower and filtration fraction was higher in CKD BMC recipients compared to all groups whereas there was no difference between pravastatin-pretreated CKD BMC and healthy BMC recipients. Mean arterial pressure was higher in CKD BMC recipients compared to all other groups. In contrast, 6 weeks of systemic in vivo pravastatin treatment had no effect. In vitro results showed improved migration, decreased apoptosis and lower excretion of pro-inflammatory Chemokine (C-X-C Motif) Ligand 5 in pravastatin-pretreated CKD BMCs.

Conclusions

Short ex vivo exposure of CKD BMC to pravastatin improves CKD BMC function and their subsequent therapeutic efficacy in a CKD setting, whereas systemic statin treatment did not provide renal protection.

Assessment of intravenous adipose-derived allogeneic mesenchymal stem cells for the treatment of feline chronic kidney disease: a randomized, placebo-controlled clinical trial in eight cats

Objectives

Feline chronic kidney disease (CKD) is characterized by chronic tubulointerstitial nephritis, and inflammation contributes to the progression of renal fibrosis. Mesenchymal stem cells (MSCs) have demonstrated anti-inflammatory and antifibrotic effects in rodent CKD models. However, few randomized trials evaluating the effectiveness of MSC therapy for diseases in companion animals have been reported. The purpose of this study was to evaluate the effectiveness of allogeneic MSCs for the treatment of feline CKD using a randomized, placebo-controlled trial.

Methods

MSCs were isolated from the cryopreserved adipose tissues of specific pathogen-free research cats and culture expanded. CKD cats were enrolled in a randomized, placebo-controlled, blinded one-way crossover clinical study. Four CKD cats were randomized to receive 2 × 106 MSCs/kg intravenously at 2, 4 and 6 weeks. Four CKD cats were randomized to receive placebo, with two cats crossing over to the MSC treatment group and one cat failing to complete the trial. Complete blood counts, chemistry and urinalysis were performed at weeks 0, 2, 4, 6 and 8. Glomerular filtration rate (GFR) via nuclear scintigraphy and urine protein:creatinine ratio (UPC) were determined at weeks 0 and 8.

Results

Six cats received three doses of allogeneic MSC culture expanded from cryopreserved adipose without adverse effects. No significant change in serum creatinine, blood urea nitrogen, potassium, phosphorus, GFR by nuclear scintigraphy, UPC or packed cell volume was seen in cats treated with MSCs. Individual changes in GFR were 12%, 8%, 8%, 2%, –13% and –67% in treated cats compared with 16%, 36% and 0% in placebo-treated cats.

Conclusions and relevance

While administration of MSC culture expanded from cryopreserved adipose was not associated with adverse effects, significant improvement in renal function was not observed immediately after administration. Long-term follow-up is necessary to determine whether MSC administration affects disease progression in cats with CKD.

Cell-based therapies for experimental chronic kidney disease: a systematic review and meta-analysis

Cell-based therapy is a promising strategy for treating chronic kidney disease (CKD) and is currently the focus of preclinical studies. We performed a systematic review and meta-analysis to evaluate the efficacy of cell-based therapy in preclinical (animal) studies of CKD, and determined factors affecting cell-based therapy efficacy in order to guide future clinical trials. In total, 71 articles met the inclusion criteria. Standardised mean differences (SMD) and 95% confidence intervals (CI) were calculated for outcome parameters including plasma urea, plasma creatinine, urinary protein, blood pressure, glomerular filtration rate, glomerulosclerosis and interstitial fibrosis. Sub-analysis for each outcome measure was performed for model-related factors (species, gender, model and timing of therapy) and cell-related factors (cell type, condition and origin, administration route and regime of therapy). Overall, meta-analysis showed that cell-based therapy reduced the development and progression of CKD. This was most prominent for urinary protein (SMD, 1.34; 95% CI, 1.00–1.68) and urea (1.09; 0.66–1.51), both P<0.001. Changes in plasma urea were associated with changes in both glomerulosclerosis and interstitial fibrosis. Sub-analysis showed that cell type (bone-marrow-derived progenitors and mesenchymal stromal cells being most effective) and administration route (intravenous or renal artery injection) were significant predictors of therapeutic efficacy. The timing of therapy in relation to clinical manifestation of disease, and cell origin and dose, were not associated with efficacy. Our meta-analysis confirms that cell-based therapies improve impaired renal function and morphology in preclinical models of CKD. Our analyses can be used to optimise experimental interventions and thus support both improved preclinical research and development of cell-based therapeutic interventions in a clinical setting.

Extracellular vesicles: potential roles in regenerative medicine

Extracellular vesicles (EV) consist of exosomes, which are released upon fusion of the multivesicular body with the cell membrane, and microvesicles, which are released directly from the cell membrane. EV can mediate cell–cell communication and are involved in many processes, including immune signaling, angiogenesis, stress response, senescence, proliferation, and cell differentiation. The vast amount of processes that EV are involved in and the versatility of manner in which they can influence the behavior of recipient cells make EV an interesting source for both therapeutic and diagnostic applications. Successes in the fields of tumor biology and immunology sparked the exploration of the potential of EV in the field of regenerative medicine. Indeed, EV are involved in restoring tissue and organ damage, and may partially explain the paracrine effects observed in stem cell-based therapeutic approaches. The function and content of EV may also harbor information that can be used in tissue engineering, in which paracrine signaling is employed to modulate cell recruitment, differentiation, and proliferation. In this review, we discuss the function and role of EV in regenerative medicine and elaborate on potential applications in tissue engineering.

Bridging the gap: a Canadian perspective on translational kidney research

PURPOSE OF REVIEW

Chronic kidney disease affects approximately 3 million Canadians. Ongoing investment in high quality kidney research is needed to improve the care of patients with kidney disease. The barriers to translating such research are discussed in this review.

SOURCES OF INFORMATION

Personal knowledge, research funding body websites, and published reports.

FINDINGS

In this review, we discuss the meaning of the term translational research and present some of the programs aimed at ensuring efficient translation of scientific discoveries with a discussion of the barriers to translation. We highlight some successes and barriers to kidney research translation using recent examples of research in Canadian nephrology. We present the following examples of kidney research: (1) research aimed at identifying the causative genes for inherited kidney diseases; (2) recent discoveries in cell-based therapies for kidney disease; (3) an examination of the impact of acute kidney injury in renal transplant patients; and (4) the development of a kidney failure risk equation to improve prognosis accuracy.

LIMITATIONS

This review focuses on research conducted by the authors.

IMPLICATIONS

The process of research translation is prolonged and challenging and therefore requires resources, patience, and careful planning. With increased awareness and understanding of the barriers to research translation, researchers and funding bodies can work together to increase the rate at which important research findings reach clinical practice and improve the care of patients with kidney disease.

Mesenchymal stem cells from rats with chronic kidney disease exhibit premature senescence and loss of regenerative potential

Mesenchymal stem cell (MSC) transplantation has the potential for organ repair. Nevertheless, some factors might lessen the regenerative potential of MSCs, e.g. donor age or systemic disease. It is thus important to carefully assess the patient's suitability for autologous MSC transplantation. Here we investigated the effects of chronic kidney disease (CKD) on MSC function. We isolated bone marrow MSCs from remnant kidney rats (RK) with CKD (CKD-RK-MSC) and found signs of premature senescence: spontaneous adipogenesis, reduced proliferation capacity, active senescence-associated-β-galactosidase, accumulation of actin and a modulated secretion profile. The functionality of CKD-RK-MSCs in vivo was tested in rats with acute anti-Thy1.1-nephritis, where healthy MSCs have been shown to be beneficial. Rats received healthy MSCs, CKD-RK-MSC or medium by injection into the left renal artery. Kidneys receiving healthy MSCs exhibited accelerated healing of glomerular lesions, whereas CKD-RK-MSC or medium exerted no benefit. The negative influence of advanced CKD/uremia on MSCs was confirmed in a second model of CKD, adenine nephropathy (AD). MSCs from rats with adenine nephropathy (CKD-AD-MSC) also exhibited cellular modifications and functional deficits in vivo. We conclude that CKD leads to a sustained loss of in vitro and in vivo functionality in MSCs, possibly due to premature cellular senescence. Considering autologous MSC therapy in human renal disease, studies identifying uremia-associated mechanisms that account for altered MSC function are urgently needed.

Maintenance of hypertensive hemodynamics does not depend on ROS in established experimental chronic kidney disease

While the presence of oxidative stress in chronic kidney disease (CKD) is well established, its relation to hypertensive renal hemodynamics remains unclear. We hypothesized that once CKD is established blood pressure and renal vascular resistance (RVR) no longer depend on reactive oxygen species. CKD was induced by bilateral ablation of 2/3 of each kidney. Compared to age-matched, sham-operated controls all ablated rats showed proteinuria, decreased glomerular filtration rate (GFR), more renal damage, higher mean arterial pressure (MAP), RVR and excretion of oxidative stress markers and hydrogen peroxide, while excretion of stable nitric oxide (NO) metabolites tended to decrease. We compared MAP, RVR, GFR and fractional excretion of sodium under baseline and during acute Tempol, PEG-catalase or vehicle infusion in rats with established CKD vs. controls. Tempol caused marked reduction in MAP in controls (96±5 vs.79±4 mmHg, P<0.05) but not in CKD (130±5 vs. 127±6 mmHg). PEG-catalase reduced MAP in both groups (controls: 102±2 vs. 94±4 mmHg, P<0.05; CKD: 118±4 vs. 110±4 mmHg, P<0.05), but did not normalize MAP in CKD rats. Tempol and PEG-catalase slightly decreased RVR in both groups. Fractional excretion of sodium was increased by both Tempol and PEG-catalase in both groups. PEG-catalase decreased TBARS excretion in both groups. In sum, although oxidative stress markers were increased, MAP and RVR did not depend more on oxidative stress in CKD than in controls. Therefore reactive oxygen species appear not to be important direct determinants of hypertensive renal hemodynamics in this model of established CKD.

5/6th nephrectomy in combination with high salt diet and nitric oxide synthase inhibition to induce chronic kidney disease in the Lewis rat

Chronic kidney disease (CKD) is a global problem. Slowing CKD progression is a major health priority. Since CKD is characterized by complex derangements of homeostasis, integrative animal models are necessary to study development and progression of CKD. To study development of CKD and novel therapeutic interventions in CKD, we use the 5/6th nephrectomy ablation model, a well known experimental model of progressive renal disease, resembling several aspects of human CKD. The gross reduction in renal mass causes progressive glomerular and tubulo-interstitial injury, loss of remnant nephrons and development of systemic and glomerular hypertension. It is also associated with progressive intrarenal capillary loss, inflammation and glomerulosclerosis. Risk factors for CKD invariably impact on endothelial function. To mimic this, we combine removal of 5/6th of renal mass with nitric oxide (NO) depletion and a high salt diet. After arrival and acclimatization, animals receive a NO synthase inhibitor (NG-nitro-L-Arginine) (L-NNA) supplemented to drinking water (20 mg/L) for a period of 4 weeks, followed by right sided uninephrectomy. One week later, a subtotal nephrectomy (SNX) is performed on the left side. After SNX, animals are allowed to recover for two days followed by LNNA in drinking water (20 mg/L) for a further period of 4 weeks. A high salt diet (6%), supplemented in ground chow (see time line Figure 1), is continued throughout the experiment. Progression of renal failure is followed over time by measuring plasma urea, systolic blood pressure and proteinuria. By six weeks after SNX, renal failure has developed. Renal function is measured using 'gold standard' inulin and para-amino hippuric acid (PAH) clearance technology. This model of CKD is characterized by a reduction in glomerular filtration rate (GFR) and effective renal plasma flow (ERPF), hypertension (systolic blood pressure>150 mmHg), proteinuria (> 50 mg/24 hr) and mild uremia (>10 mM). Histological features include tubulo-interstitial damage reflected by inflammation, tubular atrophy and fibrosis and focal glomerulosclerosis leading to massive reduction of healthy glomeruli within the remnant population (<10%). Follow-up until 12 weeks after SNX shows further progression of CKD.

Human embryonic mesenchymal stem cell-derived conditioned medium rescues kidney function in rats with established chronic kidney disease

Chronic kidney disease (CKD) is a major health care problem, affecting more than 35% of the elderly population worldwide. New interventions to slow or prevent disease progression are urgently needed. Beneficial effects of mesenchymal stem cells (MSC) have been described, however it is unclear whether the MSCs themselves or their secretome is required. We hypothesized that MSC-derived conditioned medium (CM) reduces progression of CKD and studied functional and structural effects in a rat model of established CKD.

CKD was induced by 5/6 nephrectomy (SNX) combined with L-NNA and 6% NaCl diet in Lewis rats. Six weeks after SNX, CKD rats received either 50 µg CM or 50 µg non-CM (NCM) twice daily intravenously for four consecutive days. Six weeks after treatment CM administration was functionally effective: glomerular filtration rate (inulin clearance) and effective renal plasma flow (PAH clearance) were significantly higher in CM vs. NCM-treatment. Systolic blood pressure was lower in CM compared to NCM. Proteinuria tended to be lower after CM. Tubular and glomerular damage were reduced and more glomerular endothelial cells were found after CM. DNA damage repair was increased after CM. MSC-CM derived exosomes, tested in the same experimental setting, showed no protective effect on the kidney. In a rat model of established CKD, we demonstrated that administration of MSC-CM has a long-lasting therapeutic rescue function shown by decreased progression of CKD and reduced hypertension and glomerular injury.