Antioxidants improve early survival of cardiomyoblasts after transplantation to the myocardium

Identification of a Sesquiterpene Lactone from Arctium lappa Leaves with Antioxidant Activity in Primary Human Muscle Cells

Many pathologies affecting muscles (muscular dystrophies, sarcopenia, cachexia, renal insufficiency, obesity, diabetes type 2, etc.) are now clearly linked to mechanisms involving oxidative stress. In this context, there is a growing interest in exploring plants to find new natural antioxidants to prevent the appearance and the development of these muscle disorders. In this study, we investigated the antioxidant properties of Arctium lappa leaves in a model of primary human muscle cells exposed to H₂O₂ oxidative stress. We identified using bioassay-guided purification, onopordopicrin, a sesquiterpene lactone as the main molecule responsible for the antioxidant activity of A. lappa leaf extract. According to our findings, onopordopicrin inhibited the H₂O₂-mediated loss of muscle cell viability, by limiting the production of free radicals and abolishing DNA cellular damages. Moreover, we showed that onopordopicrin promoted the expression of the nuclear factor-erythroid-2-related factor 2 (Nrf2) downstream target protein heme oxygenase-1 (HO-1) in muscle cells. By using siRNA, we demonstrated that the inhibition of the expression of Nrf2 reduced the protective effect of onopordopicrin, indicating that the activation of the Nrf2/HO-1 signaling pathway mediates the antioxidant effect of onopordopicrin in primary human muscle cells. Therefore, our results suggest that onopordopicrin may be a potential therapeutic molecule to fight against oxidative stress in pathological specific muscle disorders.

Pathway-specific reporter genes to study stem cell biology

Little is known on the phenotypic characteristics of stem cells (SCs) after they are transplanted to the myocardium, in part due to lack of noninvasive platforms to study SCs directly in the living subject. Reporter gene imaging has played a valuable role in the noninvasive assessment of cell fate in vivo. In this study, we validated a pathway-specific reporter gene that can be used to noninvasively image the phenotype of SCs transplanted to the myocardium. Rat mesenchymal SCs (MSCs) were studied for phenotypic evidence of myogenic characteristics under in vitro conditions. After markers of myogenic characteristics were identified, we constructed a reporter gene sensor, comprising the firefly luciferase (Fluc) reporter gene driven by the troponin T (TnT) promoter (cardio MSCs had threefold expression in polymerase chain reaction compared to control MSCs) using a two-step signal amplification strategy. MSCs transfected with TnT-Fluc were studied and validated under in vitro conditions, showing a strong signal after MSCs acquired myogenic characteristics. Lastly, we observed that cardio MSCs had higher expression of the reporter sensor compared to control cells (0.005 ± 0.0005 vs 0.0025 ± 0.0008 Tnt-Fluc/ubiquitin-Fluc, P < .05), and that this novel sensor can detect the change in the phenotype of MSCs directly in the living subject. Pathway-specific reporter gene imaging allows assessment of changes in the phenotype of MSCs after delivery to the ischemic myocardium, providing important information on the phenotype of these cells. Imaging sensors like the one described here are critical to better understanding of the changes that SCs undergo after transplantation.

Ginkgo Biloba L. Extract Reduces H2O2-Induced Bone Marrow Mesenchymal Stem Cells Cytotoxicity by Regulating Mitogen-Activated Protein Kinase (MAPK) Signaling Pathways and Oxidative Stress

Background

The oxidative stress environment of pathological tissue has an adverse effect on the survival of bone marrow mesenchymal stem cells (BMSCs) transplantation. Ginkgo biloba L. extract (EGB) has a potent antioxidant effect. In this research, we assessed the protective effects of EGB and EGB-Containing Serum (EGB CS) on BMSCs against injury induced by hydrogen peroxide (H₂O₂).

Material/Methods

BMSCs were pretreated with EGB or EGB CS and treated with H₂O₂. The cell counting kit-8 (CCK-8) method was utilized to detect cell viability. The DCFH-DA Fluorescent Kit method was used to detect intracellular ROS level. Malondialdehyde (MDA), superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and (CAT) were determined. The Hoechst staining assay and qRT-PCR assay were utilized to evaluate the effect of EGB on cell apoptosis. Mitogen-activated protein kinases (MAPKs) signaling pathway were detected by western blot analysis.

Results

Compared to the H₂O₂ group, the number of apoptotic cells in the EGB and EGB CS pretreated groups significantly decreased. The mRNA expression ratio of Bax/Bcl-2 was also decreased. EGB and EGB CS can reduce the production of ROS in BMSCs exposed to H₂O₂. SOD, GSH-Px and CAT activities were significantly higher compared with those with H₂O₂ group. Furthermore, EGB or EGB CS pretreatment decreased the protein levels of p-p38MAPK and p-JNK in BMSCs compared to the H₂O₂ group.

Conclusions

Our findings suggested that EGB and EGB CS have protective effect on BMSCs against oxidative stress injury and increase the survival rate of BMSCs transplantation by regulating p38MAPK and JNK signaling.

New strategy to rescue the inhibition of osteogenesis of human bone marrow-derived mesenchymal stem cells under oxidative stress: combination of vitamin C and graphene foams

To rescue the oxidative stress induced inhibition of osteogenesis, vitamin C (VC) was chemically modified onto three-dimensional graphene foams (3D GFs), then their regulation on osteogenesis of human bone marrow-derived mesenchymal stem cells (BM-MSCs) was studied. Combined action of VC + GF significantly decreased H2O2-induced oxidative stress, and rescued H2O2-inhibited cell viability, differentiation and osteogenesis of BM-MSCs in vitro. Further studies revealed that Wnt pathway may be involved in this protection of osteogenesis. Furthermore, an in vivo mouse model of BM-MSCs transplantation showed that VC + GF remarkably rescued oxidative stress inhibited calcium content and bone formation. The combination of VC and GF exhibited more pronounced protective effects against oxidative stress induced inhibition of osteogenesis, compared to monotherapy of VC or GF. Our study proposed a new strategy in stem cell-based therapies for treating bone diseases.

Image-guided stem cells with functionalized self-assembling peptide nanofibers for treatment of acute myocardial infarction in a mouse model

AIM

To investigate the survival of bone marrow mesenchymal stem cells (BMSCs) and the therapeutic effect for acute myocardial infarction (AMI) after co-transplantation with the functionalized self-assembling peptide nanofiber RAD/PRG or RAD/KLT.

METHODS

AMI of balb/c mice was induced. Mice were randomly divided into four groups, and received treatment of phosphate buffered saline (PBS) (Group A), GFP/Fluc-BMSCs (Group B), GFP/Fluc-BMSCs + RAD/PRG (Group C), and GFP/Fluc-BMSCs + RAD/KLT (Group D), respectively. Bioluminescence imaging (BLI) was performed on day 1 (d-1), d-4, d-7, d-10, and d-13 after transplantation. Magnetic resonance imaging (MRI) was performed at baseline (d-4 before transplantation) and d-29 after treatment. Mice were euthanized on d-29 following treatment. Paraffin sections were obtained from the top, mid and bottom part of the infarcted region along the long-axis of the heart. Hematoxylin and eosin (HE) staining and immunohistochemical staining were performed. The infarct ratio micro-vascular density (MVD) was quantified.

RESULTS

There was a significant higher of BLI signal intensity of BMSCs in Group C than that in Group B (d-4, 9713±320 vs. 8164±378, P=0.0008; d-7, 6489±241 vs. 5417±361, P=0.0026; d-10, 3768±255 vs. 0, P < 0.0001). The left ventricular ejection fraction (LVEF) via MRI examination was significantly improved in both Group C and Group D. Infarct ratio and MVD were significantly improved in both Group C and Group D.

CONCLUSION

Our data highlights BMSCs combining functionalized self-assembling peptide nanofibers RAD/PRG or RAD/KLT as promising therapy for AMI.

Effects of Antioxidant Supplements on the Survival and Differentiation of Stem Cells

Although physiological levels of reactive oxygen species (ROS) are required to maintain the self-renewal capacity of stem cells, elevated ROS levels can induce chromosomal aberrations, mitochondrial DNA damage, and defective stem cell differentiation. Over the past decade, several studies have shown that antioxidants can not only mitigate oxidative stress and improve stem cell survival but also affect the potency and differentiation of these cells. Further beneficial effects of antioxidants include increasing genomic stability, improving the adhesion of stem cells to culture media, and enabling researchers to manipulate stem cell proliferation by using different doses of antioxidants. These findings can have several clinical implications, such as improving neurogenesis in patients with stroke and neurodegenerative diseases, as well as improving the regeneration of infarcted myocardial tissue and the banking of spermatogonial stem cells. This article reviews the cellular and molecular effects of antioxidant supplementation to cultured or transplanted stem cells and draws up recommendations for further research in this area.

Sitagliptin ameliorates oxidative stress in experimental diabetic nephropathy by diminishing the miR-200a/Keap-1/Nrf2 antioxidant pathway

BACKGROUND

Sitagliptin, a dipeptidyl peptidase-4 (DPP-4) inhibitor used in type 2 diabetes therapy, has demonstrated protective effects in diabetic chronic kidney disease, in part due to its pleiotropic actions. However, its potential direct effects on the kidney are still not completely defined. Here, by means of proteomics and miRNA profiling, we have further unveiled the role of sitagliptin in oxidative stress, as well as the underlying mechanisms.

METHODS

Renal cortex samples from 9-month-old wild-type (Wistar), type II diabetic Goto-Kakizaki (GK) and sitagliptin-treated GK rats (GK+Sita) (10 mg kg^-1 per day) were subjected to quantitative miRNA transcriptomic array, immunohistochemistry and Western blot studies. Renal GK and GK+Sita samples were also analyzed by differential in-gel electrophoresis. Bioinformatic tools were used to find out the relationships between altered proteins and related miRNA expression. Studies were also carried out in cultured tubular cells to confirm in vivo data.

RESULTS

Diabetic GK rats exhibited proteinuria, renal interstitial inflammatory infiltrates and fibrosis, which improved by 20 weeks of sitagliptin treatment. Proteomic analysis of diabetic GK and Wistar rats showed a differential expression of 39 proteins mostly related to oxidative stress and catabolism. In addition, 15 miRNAs were also significantly altered in GK rats.

CONCLUSION

Treatment with sitagliptin was associated with modulation of antioxidant response in the diabetic kidney, involving a downregulation of miR-200a, a novel Keap-1 inhibitor and miR-21, coincidentally with the clinical and the morphological improvement. These data further support the concept that DPP-4 inhibitors could exert a direct reno-protective effect in patients with diabetic nephropathy.

Preconditioning of mesenchymal stem cells with 2,4-dinitrophenol improves cardiac function in infarcted rats

AIMS

The aim of this study is to determine if preconditioning of bone marrow derived mesenchymal stem cells (MSCs) with 2,4-dinitrophenol (DNP) improves survival of transplanted stem cells in a rat model of myocardial infarction (MI), and to asses if this strategy has measurable impact on cardiac function.

MAIN METHODS

MSCs were preconditioned with DNP. In vitro cell adhesion assay and qRT-PCR were performed to analyze the expression of genes involved in cardiomyogenesis, cell adhesion and angiogenesis. MI was produced by occlusion of left anterior descending coronary artery. One million cells were transplanted by intramyocardial injection into the infarcted myocardium. Echocardiography was performed after two and four weeks of cellular transplantation. Hearts were harvested after four weeks and processed for histological analysis.

KEY FINDINGS

DNP treated MSCs adhered to the surface more (p<0.001) as compared to the normal MSCs. Gene expression levels were significantly upregulated in case of DNP treatment. The number of viable MSCs was more (p<0.001) in animals that received DNP treated MSCs, leading to significant improvement in cardiac function. Histological analysis revealed significant reduction in scar formation (p<0.001), maintenance of left ventricular wall thickness (p<0.001), and increased angiogenesis (p<0.01).

SIGNIFICANCE

The study evidenced for the first time that MSCs preconditioned with DNP improved cardiac function after transplantation. This can be attributed to improved survival, homing, adhesion, and cardiomyogenic and angiogenic differentiation of DNP treated MSCs in vivo.

Molecular imaging of stem cells for the treatment of acute myocardial infarction

Stem cell therapy has a unique potential and promises hope for the treatment of acute myocardial infarction. Preclinical studies have identified barriers to clinical translation, one of which involves the monitoring of transplanted cells and the elucidation of their fates in vivo. Molecular imaging may help the solutions for these challenges. In this review, we illustrate the mechanisms by which molecular imaging enables insights into and the development of stem cell therapy.

Ginkgo biloba extract promotes osteogenic differentiation of human bone marrow mesenchymal stem cells in a pathway involving Wnt/β-catenin signaling

Human bone marrow derived mesenchymal stem cells (BM-MSCs) are a novel cell source used in stem cell therapy to treat bone diseases owing to their high potential to differentiate into osteoblasts. Effective induction of osteogenic differentiation from human BM-MSCs is critical to fulfill their therapeutic potential. In this study, Ginkgo biloba extract (GBE), a traditional herbal medicine, was used to stimulate the proliferation and osteogenic differentiation of human BM-MSCs. The present study revealed that GBE improved the proliferation and osteogenesis of human BM-MSCs in a dose-dependent manner in the range 25-75 mg/l, as indicated by alkaline phosphatase (ALP) activity and calcium content. However, such effect was decreased or inhibited at 100mg/l or higher. The dose-dependent improvement in osteogenesis of human BM-MSCs by GBE was further confirmed by the dose-dependent upregulation of marker genes, osteopontin (OPN) and Collagen I. The increased osteoprotegerin (OPG) expression and minimal expression of receptor activator of nuclear factor-κB ligand (RANKL) suggested that GBE also inhibited osteoclastogenesis of human BM-MSCs. Further mechanistic study demonstrated that the transcriptional levels of bone morphogenetic protein 4 (BMP4) and runt-related transcription factor 2 (RUNX2) in the BMP signaling, β-catenin and Cyclin D1 in the Wnt/β-catenin signaling, increased significantly during GBE-promoted osteogenesis. Meanwhile, loss-of-function assay with the signaling inhibitor(s) confirmed that the BMP and Wnt/β-catenin signaling pathways were indispensable during the GBE-promoted osteogenesis, suggesting that GBE improved osteogenesis via upregulation of the BMP and Wnt/β-catenin signaling. The present study proposed GBE to be used to upregulate the osteogenic differentiation of human BM-MSCs for new bone formation in BM-MSC-based cell therapy, which could provide an attractive and promising treatment for bone disorders.

Mesenchymal Stromal Cells Improve Renovascular Function in Polycystic Kidney Disease

Polycystic kidney disease (PKD) is a common cause of end-stage renal failure, for which there is no accepted treatment. Progenitor and stem cells have been shown to restore renal function in a model of renovascular disease, a disease that shares many features with PKD. The objective of this study was to examine the potential of adult stem cells to restore renal structure and function in PKD. Bone marrow-derived mesenchymal stromal cells (MSCs, 2.5 × 10(5)) were intrarenally infused in 6-week-old PCK rats. At 10 weeks of age, PCK rats had an increase in systolic blood pressure (SBP) versus controls (126.22 ± 2.74 vs. 116.45 ± 3.53 mmHg, p < 0.05) and decreased creatinine clearance (3.76 ± 0.31 vs. 6.10 ± 0.48 µl/min/g, p < 0.01), which were improved in PKD animals that received MSCs (SBP: 114.67 ± 1.34 mmHg, and creatinine clearance: 4.82 ± 0.24 µl/min/g, p = 0.001 and p = 0.003 vs. PKD, respectively). MSCs preserved vascular density and glomeruli diameter, measured using microcomputed tomography. PCK animals had increased urine osmolality (843.9 ± 54.95 vs. 605.6 ± 45.34 mOsm, p < 0.01 vs. control), which was improved after MSC infusion and not different from control (723.75 ± 56.6 mOsm, p = 0.13 vs. control). Furthermore, MSCs reduced fibrosis and preserved the expression of proangiogenic molecules, while cyst size and number were unaltered by MSCs. Delivery of exogenous MSCs improved vascular density and renal function in PCK animals, and the benefit was observed up to 4 weeks after a single infusion. Cell-based therapy constitutes a novel approach in PKD.

Bioluminescent imaging of genetically selected induced pluripotent stem cell-derived cardiomyocytes after transplantation into infarcted heart of syngeneic recipients

Cell loss after transplantation is a major limitation for cell replacement approaches in regenerative medicine. To assess the survival kinetics of induced pluripotent stem cell (iPSC)-derived cardiomyocytes (CM) we generated transgenic murine iPSC lines which, in addition to CM-specific expression of puromycin N-acetyl-transferase and enhanced green fluorescent protein (EGFP), also constitutively express firefly luciferase (FLuc) for bioluminescence (BL) in vivo imaging. While undifferentiated iPSC lines generated by random integration of the transgene into the genome retained stable FLuc activity over many passages, the BL signal intensity was strongly decreased in purified iPS-CM compared to undifferentiated iPSC. Targeted integration of FLuc-expression cassette into the ROSA26 genomic locus using zinc finger nuclease (ZFN) technology strongly reduced transgene silencing in iPS-CM, leading to a several-fold higher BL compared to iPS-CM expressing FLuc from random genomic loci. To investigate the survival kinetics of iPS-CM in vivo, purified CM obtained from iPSC lines expressing FLuc from a random or the ROSA26 locus were transplanted into cryoinfarcted hearts of syngeneic mice. Engraftment of viable cells was monitored by BL imaging over 4 weeks. Transplanted iPS-CM were poorly retained in the myocardium independently of the cell line used. However, up to 8% of cells survived for 28 days at the site of injection, which was confirmed by immunohistological detection of EGFP-positive iPS-CM in the host tissue. Transplantation of iPS-CM did not affect the scar formation or capillary density in the periinfarct region of host myocardium. This report is the first to determine the survival kinetics of drug-selected iPS-CM in the infarcted heart using BL imaging and demonstrates that transgene silencing in the course of iPSC differentiation can be greatly reduced by employing genome editing technology. FLuc-expressing iPS-CM generated in this study will enable further studies to reduce their loss, increase long-term survival and functional integration upon transplantation.

Renin inhibition improves the survival of mesenchymal stromal cells in a mouse model of myocardial infarction

The aim of this study was to determine if renin inhibition is able to improve the survival of transplanted stem cells in a mouse model of myocardial infarction. Myocardial infarction was induced in FVB/NJ inbred mice (n = 23). Bone marrow-derived mouse mesenchymal stromal cells (mMSCs, 3 × 10(5)) expressing the reporter gene firefly luciferase were delivered intramyocardially (n = 12) and monitored non-invasively by bioluminescence imaging. A group of these mice (n = 6) received aliskiren (15 mg/kg/day) via an osmotic pump implanted subcutaneously. The survival of mMSCs was significantly increased in those animals that received aliskiren leading to a significant improvement in systolic function after myocardial infarction. Histological analysis revealed a significant reduction in inflammation and collagen deposition in those mice that received aliskiren compared to controls. Renin inhibition of the ischemic myocardium is able to modulate the microenvironment improving the survival and efficacy of transplanted mMSCs in a mouse model of myocardial infarction.

The cardiac regenerative potential of myoblasts remains limited despite improving their survival via antioxidant treatment

INTRODUCTION

Since myoblasts have been limited by poor cell survival after cellular myoplasty, the major goal of the current study was to determine whether improving myoblast survival with an antioxidant could improve cardiac function after the transplantation of the myoblasts into an acute myocardial infarction.

BACKGROUND

We previously demonstrated that early myogenic progenitors such as muscle-derived stem cells (MDSCs) exhibited superior cell survival and improved cardiac repair after transplantation into infarcted hearts compared to myoblasts, which we partially attributed to MDSC's higher antioxidant levels.

AIM

To determine if antioxidant treatment could increase myoblast survival, subsequently improving cardiac function after myoblast transplantation into infarcted hearts.

MATERIALS AND METHODS

Myoblasts were pre-treated with the antioxidant N-acetylcysteine (NAC) or the glutathione depleter, diethyl maleate (DEM), and injected into infarcted murine hearts. Regenerative potential was monitored by cell survival and cardiac function.

RESULTS

At early time points, hearts injected with NAC-treated myoblasts exhibited increased donor cell survival, greater cell proliferation, and decreased cellular apoptosis, compared to untreated myoblasts. NAC-treated myoblasts significantly improved cardiac contractility, reduced fibrosis, and increased vascular density compared to DEM-treated myoblasts, but compared to untreated myoblasts, no difference was noted.

DISCUSSION

While early survival of myoblasts transplanted into infarcted hearts was augmented by NAC pre-treatment, cardiac function remained unchanged compared to non-treated myoblasts.

CONCLUSION

Despite improving cell survival with NAC treated myoblast transplantation in a MI heart, cardiac function remained similar to untreated myoblasts. These results suggest that the reduced cardiac regenerative potential of myoblasts, when compared to MDSCs, is not only attributable to cell survival but is probably also related to the secretion of paracrine factors by the MDSCs.

Polycystic kidneys have decreased vascular density: a micro-CT study

OBJECTIVE

Polycystic kidney disease (PKD) is a common cause of end-stage renal failure and many of these patients suffer vascular dysfunction and hypertension. It remains unclear whether PKD is associated with abnormal microvascular structure. Thus, this study examined the renovascular structure in PKD.

METHODS

PKD rats (PCK model) and controls were studied at 10 weeks of age, and mean arterial pressure (MAP), renal blood flow, and creatinine clearance were measured. Microvascular architecture and cyst number and volume were assessed using micro-computed tomography, and angiogenic pathways evaluated.

RESULTS

Compared with controls, PKD animals had an increase in MAP (126.4 ± 4.0 vs. 126.2 ± 2.7 mmHg) and decreased clearance of creatinine (0.39 ± 0.09 vs. 0.30 ± 0.05 mL/min), associated with a decrease in microvascular density, both in the cortex (256 ± 22 vs. 136 ± 20 vessels per cm2) and medullar (114 ± 14 vs. 50 ± 9 vessels/cm2) and an increase in the average diameter of glomeruli (104.14 ± 2.94 vs. 125.76 ± 9.06 mm). PKD animals had increased fibrosis (2.2 ± 0.2 fold vs. control) and a decrease in the cortical expression in hypoxia inducible factor 1-α and vascular endothelial growth factor.

CONCLUSIONS

PKD animals have impaired renal vascular architecture, which can have significant functional consequences. The PKD microvasculature could represent a therapeutic target to decrease the impact of this disease.

Noninvasive monitoring of oxidative stress in transplanted mesenchymal stromal cells

OBJECTIVES

The goal of this study was to validate a pathway-specific reporter gene that could be used to noninvasively image the oxidative status of progenitor cells.

BACKGROUND

In cell therapy studies, reporter gene imaging plays a valuable role in the assessment of cell fate in living subjects. After myocardial injury, noxious stimuli in the host tissue confer oxidative stress to transplanted cells that may influence their survival and reparative function.

METHODS

Rat mesenchymal stromal cells (MSCs) were studied for phenotypic evidence of increased oxidative stress under in vitro stress. On the basis of their up-regulation of the pro-oxidant enzyme p67(phox) subunit of nicotinamide adenine dinucleotide phosphate (NAD[P]H oxidase p67(phox)), an oxidative stress sensor was constructed, comprising the firefly luciferase (Fluc) reporter gene driven by the NAD(P)H p67(phox) promoter. MSCs cotransfected with NAD(P)H p67(phox)-Fluc and a cell viability reporter gene (cytomegalovirus-Renilla luciferase) were studied under in vitro and in vivo pro-oxidant conditions.

RESULTS

After in vitro validation of the sensor during low-serum culture, transfected MSCs were transplanted into a rat model of myocardial ischemia/reperfusion (IR) and monitored by using bioluminescence imaging. Compared with sham controls (no IR), cardiac Fluc intensity was significantly higher in IR rats (3.5-fold at 6 h, 2.6-fold at 24 h, 5.4-fold at 48 h; p < 0.01), indicating increased cellular oxidative stress. This finding was corroborated by ex vivo luminometry after correcting for Renilla luciferase activity as a measure of viable MSC number (Fluc:Renilla luciferase ratio 0.011 ± 0.003 for sham vs. 0.026 ± 0.004 for IR at 48 h; p < 0.05). Furthermore, in IR animals that received MSCs preconditioned with an antioxidant agent (tempol), Fluc signal was strongly attenuated, substantiating the specificity of the oxidative stress sensor.

CONCLUSIONS

Pathway-specific reporter gene imaging allows assessment of changes in the oxidative status of MSCs after delivery to ischemic myocardium, providing a template to monitor key biological interactions between transplanted cells and their host environment in living subjects.

Molecular imaging: the key to advancing cardiac stem cell therapy

Cardiac stem cell therapy continues to hold promise for the treatment of ischemic heart disease despite the fact that early promising pre-clinical findings have yet to be translated into consistent clinical success. The latest human studies have collectively identified a pressing need to better understand stem cell behavior in humans and called for more incorporation of noninvasive imaging techniques into the design and evaluation of human stem cell therapy trials. This review discusses the various molecular imaging techniques validated to date for studying stem cells in living subjects, with a particular emphasis on their utilities in assessing the acute retention and the long-term survival of transplanted stem cells. These imaging techniques will be essential for advancing cardiac stem cell therapy by providing the means to both guide ongoing optimization and predict treatment response in humans.

Ginkgo biloba L. extract enhances the effectiveness of syngeneic bone marrow mesenchymal stem cells in lowering blood glucose levels and reversing oxidative stress

Bone marrow mesenchymal stem cells (BMSCs) are potential therapy for diabetes. Owing to the oxidative stress caused by hyperglycemia, these transplanted BMSCs are with high rate of apoptotic death after transplantation. Ginkgo biloba L. extract (EGB) is a potent antioxidant which can remove free radicals. The study was to investigate whether EGB can protect BMSCs from oxidative stress in vitro and enhance the efficacy of BMSCs in lowering blood glucose levels after transplantation. BMSCs were cultured with H2O2, EGB, or H2O2 and EGB. Cell viability, malondialdehyde (MDA), superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and cell death rates were determined. Diabetes was induced by single injection of streptozotocin (STZ) in male Wistar rats. Diabetic rats received EGB, BMSCs, or EGB/BMSCs. The serum levels of glucose, insulin, interleukin 6 (IL-6), tumor necrosis factor α (TNF-α), MDA, SOD, and GSH-Px were determined. PKCα expression and NF-κB activation in kidney were determined. The MDA levels and cell death rates in BMSCs cultured with H2O2 and EGB were significantly lower; cell viability, SOD, and GSH-Px activities were significantly higher compared with those with H2O2 alone. Compared with diabetic rats receiving BMSCs, diabetic rats receiving EGB before BMSCs transplantation showed (1) significantly lower levels of blood glucose, serum MDA, IL-6, and TNF-α, and higher levels of insulin, SOD, and GSH-Px activities; (2) significantly lower PKCα expression and NF-κB activation in the kidney. EGB administration before BMSC transplantation can enhance the effectiveness of BMSCs in lowering blood glucose levels and reversing oxidative stress in diabetic rats.

Glutathione peroxidase 3, a new retinoid target gene, is crucial for human skeletal muscle precursor cell survival

Protection of satellite cells from cytotoxic damages is crucial to ensure efficient adult skeletal muscle regeneration and to improve therapeutic efficacy of cell transplantation in degenerative skeletal muscle diseases. It is therefore important to identify and characterize molecules and their target genes that control the viability of muscle stem cells. Recently, we demonstrated that high aldehyde dehydrogenase activity is associated with increased viability of human myoblasts. In addition to its detoxifying activity, aldehyde dehydrogenase can also catalyze the irreversible oxidation of vitamin A to retinoic acid; therefore, we examined whether retinoic acid is important for myoblast viability. We showed that when exposed to oxidative stress induced by hydrogen peroxide, adherent human myoblasts entered apoptosis and lost their capacity for adhesion. Pre-treatment with retinoic acid reduced the cytotoxic damage ex vivo and enhanced myoblast survival in transplantation assays. The effects of retinoic acid were maintained in dystrophic myoblasts derived from facioscapulohumeral patients. RT-qPCR analysis of antioxidant gene expression revealed glutathione peroxidase 3 (Gpx3), a gene encoding an antioxidant enzyme, as a potential retinoic acid target gene in human myoblasts. Knockdown of Gpx3 using short interfering RNA induced elevation in reactive oxygen species and cell death. The anti-cytotoxic effects of retinoic acid were impaired in GPx3-inactivated myoblasts, which indicates that GPx3 regulates the antioxidative effects of retinoic acid. Therefore, retinoid status and GPx3 levels may have important implications for the viability of human muscle stem cells.

Characterization of superoxide dismutases in cardiac progenitor cells demonstrates a critical role for manganese superoxide dismutase

Transplantation of cardiac progenitor cells (CPCs) is currently in early clinical testing as a potential therapeutic strategy. Superoxide is increased in the ischemic myocardium and poor survival of cells is one of the major limitations of cell transplantation therapy. Superoxide dismutase (SOD) levels were analyzed in c-kit-positive CPCs isolated from rat myocardium to identify their roles in protection against oxidative stress-induced apoptosis in vitro. CPCs were subjected to oxidative stress using xanthine/xanthine oxidase (XXO) and little apoptosis was detected. CPCs contained significantly higher levels of SOD1 and SOD2 as compared with adult cardiac cell types, both at the protein and activity levels. Both SOD1 and SOD2 were increased by XXO at the mRNA and protein level, suggesting compensatory adaptation. Only knockdown of SOD2 and not SOD1 with siRNA sensitized the cells to XXO-apoptosis, despite only accounting for 10% of total SOD levels. Finally, we found XXO activated Akt within 10 min, and this regulated both SOD2 gene expression and protection against apoptosis. Rat CPCs are resistant to superoxide-induced cell death, primarily through higher levels of SOD2 compared to adult cardiac-derived cells. Exposure to superoxide increases expression of SOD2 in an Akt-dependent manner and regulates CPC survival during oxidative stress.

MicroRNA-1 transfected embryonic stem cells enhance cardiac myocyte differentiation and inhibit apoptosis by modulating the PTEN/Akt pathway in the infarcted heart

microRNAs (miRs) have emerged as critical modulators of various physiological processes including stem cell differentiation. Indeed, miR-1 has been reported to play an integral role in the regulation of cardiac muscle progenitor cell differentiation. However, whether overexpression of miR-1 in embryonic stem (ES) cells (miR-1-ES cells) will enhance cardiac myocyte differentiation following transplantation into the infarcted myocardium is unknown. In the present study, myocardial infarction (MI) was produced in C57BL/6 mice by left anterior descending artery ligation. miR-1-ES cells, ES cells, or culture medium (control) was transplanted into the border zone of the infarcted heart, and 2 wk post-MI, cardiac myocyte differentiation, adverse ventricular remodeling, and cardiac function were assessed. We provide evidence demonstrating enhanced cardiac myocyte commitment of transplanted miR-1-ES cells in the mouse infarcted heart as compared with ES cells. Assessment of apoptosis revealed that overexpression of miR-1 in transplanted ES cells protected host myocardium from MI-induced apoptosis through activation of p-AKT and inhibition of caspase-3, phosphatase and tensin homolog, and superoxide production. A significant reduction in interstitial and vascular fibrosis was quantified in miR-1-ES cell and ES cell transplanted groups compared with control MI. However, no statistical significance between miR-1-ES cell and ES cell groups was observed. Finally, mice receiving miR-1-ES cell transplantation post-MI had significantly improved heart function compared with respective controls (P < 0.05). Our data suggest miR-1 drives cardiac myocyte differentiation from transplanted ES cells and inhibits apoptosis post-MI, ultimately giving rise to enhanced cardiac repair, regeneration, and function.

Role of oxidative stress in hypoxia preconditioning of cells transplanted to the myocardium: a molecular imaging study

AIM

Cell-based therapies are a potential therapeutic alternative for the treatment of coronary artery disease (CAD). However, transplanted cells undergo significant death in the living subject. Hypoxic preconditioning (HPC) is a potential intervention to increase transplanted cell survival. However, the biological mechanisms of this benefit remain unclear. We hypothesize that the beneficial effect of HPC on stem cell survival is in part due to preservation of oxidant status, an effect that will be monitored using state-of-the-art molecular imaging.

METHODS

H9c2 rat cardiomyoblasts expressing the construct CMV-firefly luciferase (h9c2-fluc), with and without HPC, were exposed to hypoxia, and oxidative stress and cell survival were measured. Subsequently, H9c2-fluc cells, with and without HPC, were injected into the myocardium of rats and cell survival was monitored daily with Bioluminescence (BLI) using a CCD camera.

RESULTS

Compared to controls, cells exposed to hypoxia had increased amount of reactive oxygen species (ROS, control: 14.1±0.9 vs. hypoxia: 19.5 ± 2.0 RFU/µg protein, P=0.02) and decreased cell survival (control: 0.29 ± 0.005 vs. hypoxia: 0.24 ± 0.005 OD, P<0.001). HPC treatment decreased the amount of hypoxia-induced ROS (HPC: 11.5 ± 0.7RFU/µg protein, P=0.002 vs. hypoxia and P=0.11 vs. control), associated with improved survival (HPC: 0.27 ± 0.004OD/µg protein, P=0.002 vs. hypoxia and P=0.005 vs. control). Most importantly, compared to un-conditioned cells, HPC-cells had increased cell survival after transplantation to the myocardium (C: 34.7 ± 6.7% vs. HPC: 83.4 ± 17.5% at day 5 compared to day 1, P=0.01).

CONCLUSION

The beneficial effect of HPC is in part due to preservation of oxidant status. Molecular imaging can assess changes in cell survival in the living subject and has the potential to be applied clinically.