Poor cell survival limits the beneficial impact of mesenchymal stem cell transplantation on acute kidney injury.

BACKGROUND: Although renal tubular epithelium has a great capacity for repair it has been suggested that the administration of mesenchymal stem cells may accelerate the recovery following severe ischemic injury. METHODS: Here we analyzed the survival rate and organ distribution of transplanted mesenchymal stem cells as well as their contribution to kidney regeneration after ischemic renal injury using functional tests, histological examination as well as quantitative real-time PCR. RESULTS: Intravenously injected stem cells were mainly trapped in lungs and liver. One hour after injection, less than 1% of the injected stem cells could be detected in the injured kidneys. These cells disappeared within the first few days and did not replace renal epithelial cells precluding substantial transdifferentiation. To clarify whether reinforced stem cell delivery might promote sustained survival or conversion to tubular epithelia, stem cells were directly injected into the injured kidneys. Although these grafted cells also did not show sustained survival or contribute to structural renal repair, stem cell injection was associated with a significant but transient initial decrease in serum creatinine. CONCLUSION: These data suggest that mesenchymal stem cells do not significantly contribute to epithelial renewal after ischemic injury, promoting the idea that the major impact of cell-based therapy for acute kidney injury may result from paracrine or endocrine effects unrelated to stem cell transdifferentiation.

Influence of cell treatment with PDGF-BB and reperfusion on cardiac persistence of mononuclear and mesenchymal bone marrow cells after transplantation into acute myocardial infarction in rats.

Bone marrow cells are used for cell therapy after myocardial infarction (MI) with promising results. However, cardiac persistence of transplanted cells is rather low. Here, we investigated strategies to increase the survival and cardiac persistence of mononuclear (MNC) and mesenchymal (MSC) bone marrow cells transplanted into infarcted rat hearts. MNC and MSC (male Fischer 344 rats) were treated with different doses of PDGF-BB prior to intramyocardial injection into border zone of MI (syngeneic females, permanent LAD ligation) and hearts were harvested after 5 days and 3 weeks. In additional experiments, untreated MNC and MSC were injected immediately after permanent or temporary LAD ligation and hearts were harvested after 48 h, 5 days, 3 weeks, and 6 weeks. DNA of the hearts was isolated and the number of donor cells was determined by quantitative real-time PCR with Y chromosome-specific primers. There was a remarkable though not statistically significant (p = 0.08) cell loss of approximately 46% between 5 days and 3 weeks in the control group, which was completely inhibited by treatment with high dose of PDGF-BB. Forty-eight hours after reperfusion only 10% of injected MSC or 1% for MNC were found in the heart, decreasing to 1% for MSC and 0.5% for MNC after 6 weeks. These numbers were lower than after permanent LAD ligation for both MNC and MSC at all time points studied. Treatment with PDGF-BB seems to prevent loss of transplanted bone marrow cells at later times presumably by inhibition of apoptosis, while reperfusion of the occluded artery enhances cell loss at early times putatively due to enhanced early wash-out. Further investigations are needed to substantially improve the persistence and survival of grafted bone marrow cells in infarcted rat hearts, in order to fully explore the therapeutic potential of this novel treatment modality for myocardial repair.

Functional impact of targeted closed-chest transplantation of bone marrow cells in rats with acute myocardial ischemia/reperfusion injury.

Intramyocardial transplantation of bone marrow-derived stem cells is a potential therapeutic option after myocardial infarction (MI). Intramyocardial administration is invasive but allows efficient and targeted stem cell delivery. Aims of this study were validation of minimal-invasive, echo-guided closed-chest cell transplantation (CTx) of mononuclear (MNC) or mesenchymal stem cells (MSC) and quantification of systolic left ventricular function and assessment of contractile reserve with high-resolution reconstructive 3D-echocardiography (r3D-echo) 3 weeks after CTx. Female Fischer344 rats received syngeneic male MNC, MSC, or medium after myocardial ischemia and reperfusion via echo-guided percutaneous injection (open-chest for control). Left ventricular systolic function was measured and dysfunctional myocardium was quantified with r3D-echo. For investigation of contractile reserve and myocardial viability r3D-echo was additionally conducted during low-dose dobutamine 3 weeks after CTx. Cell persistence after echo-guided CTx was quantified via real-time PCR; scar size was measured histologically. Echo-guided percutaneous CTx was feasible in all animals (n = 30) without periprocedural complications. After 3 weeks, 1.4 +/- 1.1% of transplanted MNC and 1.9 +/- 1.2% of MSC were detected. These numbers were comparable to those after open-chest intramyocardial injection of MNC (0.8 +/- 1.1%; n = 8, p = 0.3). In r3D-echo no functional benefit was associated with CTx after MI and reperfusion. All groups (MNC, MSC, and controls) revealed a significant decrease of dysfunctional myocardium and similar contractile reserve during inotropic stimulation.In conclusion, percutaneous echo-guided closed-chest CTx promises to be an effective and safe approach for CTx in small-animal research. However, intramyocardial CTx of MNC or MSC had no influence on systolic function and contractile reserve after reperfused MI.

Effective engraftment but poor mid-term persistence of mononuclear and mesenchymal bone marrow cells in acute and chronic rat myocardial infarction.

Bone marrow cells are used with promising results for cell therapy after myocardial infarction (MI). We determined the survival and organ distribution of transplanted mononuclear (MNC) or mesenchymal (MSC) bone marrow cells, and the influence of cell type, cell number and application time. MNC and MSC (male Fischer 344 rats) were injected into the border zone of MI (syngeneic females) immediately or 7 days after LAD ligation (10(5) or 10(6) cells, 50 microl). After 0 h, 48 h, 5 days, 3 weeks and 6 weeks, DNA of heart, lung, liver, spleen, kidney, blood, bone marrow, brain and skeletal muscle was isolated and the number of donor cells determined by quantitative real-time PCR with Y-chromosome specific primers (each n>or=4). The percentage of donor-cells in the heart decreased rapidly from 34-80% of injected cells (0 h) to 0.3-3.5% (6 weeks) independent from cell type, number and application time. The absolute number increased after increasing injected cell number (10(6) vs. 10(5)). In the lung, MNC and MSC were found at 0 h (126+/-48 and 140+/-3 per million organ cells), but in liver and kidney, only few. At 48 h and 6 weeks, an increasing number of MNC, but not MSC, were detected in the spleen (6 weeks, 602+/-173 per million organ cells vs. 95+/-50 in the heart, P=0.02). In all other organs, only few or no grafted cells of either cell type were detected at these times. Organ distribution was independent from injection time. The low survival of grafted cells may limit their therapeutic impact, while their distribution to other organs must be considered in all cell therapy applications.