Macrophage stimulating protein may promote tubular regeneration after acute injury.

Macrophage-stimulating protein (MSP) exerts proliferative and antiapoptotic effects, suggesting that it may play a role in tubular regeneration after acute kidney injury. In this study, elevated plasma levels of MSP were found both in critically ill patients with acute renal failure and in recipients of renal allografts during the first week after transplantation. In addition, MSP and its receptor, RON, were markedly upregulated in the regenerative phase after glycerol-induced tubular injury in mice. In vitro, MSP stimulated tubular epithelial cell proliferation and conferred resistance to cisplatin-induced apoptosis by inhibiting caspase activation and modulating Fas, mitochondrial proteins, Akt, and extracellular signal-regulated kinase. MSP also enhanced migration, scattering, branching morphogenesis, tubulogenesis, and mesenchymal de-differentiation of surviving tubular cells. In addition, MSP induced an embryonic phenotype characterized by Pax-2 expression. In conclusion, MSP is upregulated during the regeneration of injured tubular cells, and it exerts multiple biologic effects that may aid recovery from acute kidney injury.

Polymyxin-B hemoperfusion inactivates circulating proapoptotic factors.

OBJECTIVE: To test the hypothesis that extracorporeal therapy with polymyxin B (PMX-B) may prevent Gram-negative sepsis-induced acute renal failure (ARF) by reducing the activity of proapoptotic circulating factors. SETTING: Medical-Surgical Intensive Care Units. PATIENTS AND INTERVENTIONS: Sixteen patients with Gram-negative sepsis were randomized to receive standard care (Surviving Sepsis Campaign guidelines) or standard care plus extracorporeal therapy with PMX-B. MEASUREMENTS AND RESULTS: Cell viability, apoptosis, polarity, morphogenesis, and epithelial integrity were evaluated in cultured tubular cells and glomerular podocytes incubated with plasma from patients of both groups. Renal function was evaluated as SOFA and RIFLE scores, proteinuria, and tubular enzymes. A significant decrease of plasma-induced proapoptotic activity was observed after PMX-B treatment on cultured renal cells. SOFA and RIFLE scores, proteinuria, and urine tubular enzymes were all significantly reduced after PMX-B treatment. Loss of plasma-induced polarity and permeability of cell cultures was abrogated with the plasma of patients treated with PMX-B. These results were associated to a preserved expression of molecules crucial for tubular and glomerular functional integrity. CONCLUSIONS: Extracorporeal therapy with PMX-B reduces the proapoptotic activity of the plasma of septic patients on cultured renal cells. These data confirm the role of apoptosis in the development of sepsis-related ARF.

Circulating plasma factors induce tubular and glomerular alterations in septic burns patients.

BACKGROUND: Severe burn is a systemic illness often complicated by sepsis. Kidney is one of the organs invariably affected, and proteinuria is a constant clinical finding. We studied the relationships between proteinuria and patient outcome, severity of renal dysfunction and systemic inflammatory state in burns patients who developed sepsis-associated acute renal failure (ARF). We then tested the hypothesis that plasma in these patients induces apoptosis and functional alterations that could account for proteinuria and severity of renal dysfunction in tubular cells and podocytes. METHODS: We studied the correlation between proteinuria and indexes of systemic inflammation or renal function prospectively in 19 severe burns patients with septic shock and ARF, and we evaluated the effect of plasma on apoptosis, polarity and functional alterations in cultured human tubular cells and podocytes. As controls, we collected plasma from 10 burns patients with septic shock but without ARF, 10 burns patients with septic shock and ARF, 10 non-burns patients with septic shock without ARF, 10 chronic uremic patients and 10 healthy volunteers. RESULTS: Septic burns patients with ARF presented a severe proteinuria that correlated to outcome, glomerular (creatinine/urea clearance) and tubular (fractional excretion of sodium and potassium) functional impairment and systemic inflammation (white blood cell (WBC) and platelet counts). Plasma from these patients induced a pro-apoptotic effect in tubular cells and podocytes that correlated with the extent of proteinuria. Plasma-induced apoptosis was significantly higher in septic severe burns patients with ARF with respect to those without ARF or with septic shock without burns. Moreover, plasma from septic burns patients induced an alteration of polarity in tubular cells, as well as reduced expression of the tight junction protein ZO-1 and of the endocytic receptor megalin. In podocytes, plasma from septic burns patients increased permeability to albumin and decreased the expression of the slit diaphragm protein nephrin. CONCLUSION: Plasma from burns patients with sepsis-associated ARF contains factors that affect the function and survival of tubular cells and podocytes. These factors are likely to be involved in the pathogenesis of acute tubular injury and proteinuria, which is a negative prognostic factor and an index of renal involvement in the systemic inflammatory reaction.

Magnetic resonance imaging of gadolinium-labeled pancreatic islets for experimental transplantation.

New imaging techniques that couple anatomical resolution to sensitivity may greatly contribute to improving islet transplantation. In the present work, a report is given of the direct detection of islets by magnetic resonance imaging (MRI) after ex vivo cell labeling with the MRI T(1) contrast agent GdHPDO3A. Experiments on mouse and human islets demonstrated well-tolerated uptake of GdHPDO3A, based on morphology, viability, glucose-dependent insulin response and apoptosis/toxicity gene array profile. GdHPDO3A loading was sufficient for in vitro MRI cell detection. In vivo isotransplanted mouse islets into the kidney capsule and xenotransplanted human islets within the mouse liver were detected. Imaging specificity was supported by the absence of signal in unlabeled islet transplants, its persistence upon using fat-suppression MRI protocols and the colocalization with the transplanted islets. In conclusion, direct islet imaging with high spatial and contrast resolution after labeling with GdHPDO3A is demonstrated, allowing visualization of kidney subcapsular mouse islet grafts and intrahepatic human islet xenografts.

Platelet-activating factor synthesis and response on pancreatic islet endothelial cells: relevance for islet transplantation.

BACKGROUND: Recent data suggest that donor intraislet endothelial cells may survive islet transplantation and participate to the events that influence islet engraftment. However, the mechanisms that regulate islet endothelial behavior in this setting are poorly known. METHODS: We obtained immortalized human (hIECs) and mouse (mIECs) islet endothelial cells by transfection with SV40-T-large antigen and studied the synthesis and response to Platelet-activating factor (PAF), a multipotent phospholipid that acts as endothelial mediator of both inflammation and angiogenesis. RESULTS: HIECs showed typical endothelial markers such as expression of vWF, CD31, and CD105, uptake of acetylated-LDL and binding to ULE-A lectin. Moreover, they expressed nestin, the PAF-receptor and possess surface fenestrations and in vitro angiogenic ability of forming tubular structures on Matrigel. Likewise, mIECs showed expression of vWF, CD31, nestin, PAF-receptor and CD105, and uptake of acetylated-LDL. HIECs and mIECs rapidly produced PAF under stimulation with thrombin in a dose-dependent way. Exogenous PAF or thrombin-induced PAF synthesis increased leukocyte adhesion to hIECS and mIECs and cell motility of both endothelial cell lines. Moreover, PAF or thrombin-induced PAF synthesis accelerated in vitro formation of vessel-like tubular structures when hIECs are seeded on Matrigel. Notably, gene-microarray analysis detected up-regulation of beta3 integrin gene on hIECs stimulated with PAF, that was confirmed at the protein level. CONCLUSIONS: Based on the novel development of immortalized islet endothelium, these results suggest that PAF may have a dual role that links inflammation to angiogenesis in the early events of islet transplantation.

Mesenchymal stem cells contribute to the renal repair of acute tubular epithelial injury.

Acute renal failure (ARF) is a common disease with high morbidity and mortality. Recovery from ARF is dependent on the replacement of necrotic tubular cells with functional tubular epithelium. Recent advancement in developmental biology led to the discovery of immature mesenchymal stem cells (MSCs) in bone marrow and several established organs and to the definition of their potential in the recovery from tissue injury. We investigated the effect of MSCs infusion on the recovery from ARF induced by intramuscle injection of glycerol in C57/BL6 mice. In this model, ARF is associated with an extensive necrosis of tubular epithelial cells due to myoglobin- and hemoglobin-induced injury. MSCs were obtained from bone marrow of transgenic mice expressing green fluorescent protein (GFP). MSC GFP-positive cells (MSC-GFP(+)) injected intravenously homed to the kidney of mice with glycerol-induced ARF but not to the kidney of normal mice. MSC-GFP(+) localized in the context of the tubular epithelial lining and expressed cytokeratin, indicating that MSCs engrafted in the damaged kidney, differentiated into tubular epithelial cells and promoted the recovery of morphological and functional alterations. Moreover, MSCs enhanced tubular proliferation as detected by the increased number of proliferating cell nuclear antigen (PCNA) positive cells. A significant contribution of the engrafted MSCs in the regeneration of tubular epithelial cells was shown by the presence of a consistent number of GFP(+) tubular cells 21 days after the induction of injury. In conclusion, these results indicated a tropism of MSCs for the injured kidney and a potential contribution of these cells to tubular regeneration and to the recovery from ARF.