Inflammatory cells in ischemic acute renal failure

Impact of Steroids on the Inflammatory Response after Ischemic Acute Kidney Injury in Rats

Inflammation plays a crucial role in acute kidney injury (AKI). The current study was designed to analyze the influence of prednisolone treatment on the inflammatory reaction during the first 96 h after AKI induction in a rat model. AKI was induced by unilateral clipping of the renal vessels. The treatment group received prednisolone 5 mg/kg s.c. daily. Infiltration rates of macrophages, leukocytes, and T-cells (24, 96 h) as well as plasma concentrations of the inflammatory markers intercellular adhesion molecule, interleukin-1 beta (IL-1β), IL-18, IL-6, and tumor necrosis factor-alpha (0, 6, 24, 96 h) were determined by fluorescence-activated cell sorting (FACS) analysis only. Ninety-six hours after AKI induction, the prednisolone group demonstrated significantly lower creatinine concentrations compared to the control group (P < 0.05). Twenty-four hours after induction of AKI, a significantly higher rate of infiltrating leukocytes was detectable with FACS analysis in the control group (P < 0.01) with a corresponding significantly higher rate of macrophages after 96 h (P < 0.01). IL-6 and IL-1β demonstrated a peak after 6 h with a significantly higher release in the control group (IL-6: P < 0.01; IL-1β: P < 0.05). In contrast to the control group, the prednisolone group demonstrated no further incline of IL-18 after 24 h. The results demonstrate the importance of stretching the observation period in an ischemia-reperfusion-induced AKI setting beyond the first 24 h. Despite the demonstrated protective effects of a continuous prednisolone application, it seems that this single anti-inflammatory agent will not be able to completely suppress the inflammatory response after an ischemia-reperfusion-induced AKI.

Sodium Pentosan Polysulfate Reduced Renal Ischemia-Reperfusion-Induced Oxidative Stress and Inflammatory Responses in an Experimental Animal Model

Acute kidney injury (AKI) remains an independent risk factor for mortality and morbidity after vascular surgery (affecting the renal arteries) or aortic surgery (requiring suprarenal aortic clamping). These types of vascular surgery produce renal ischemia/reperfusion (I/R) injury, a common cause of AKI. The present studies aimed at monitoring the course of renal I/R injury at the cellular level and investigating the efficacy of long-term preoperative and single-shot intraoperative administration of sodium pentosan polysulfate (PPS) to protect renal tissue from acute I/R injury both in native and diabetic kidneys in rats. Western blot analyses of the proapoptotic (bax) and antiapoptotic (bcl-2) signaling pathways, as well as the extent of DNA damage (phospho-p53), were performed. Oxidative stress followed upon the termination of malondialdehyde, reduced glutathione, thiol group, and superoxide dismutase plasma levels. Inflammatory changes were measured by the determination of serum tumor necrosis factor-α and interleukin-1 levels. Morphological changes were detected by histological examinations. Our results showed that the long-term administration of PPS has an advantage in reducing I/R kidney injury in diabetic rats, while high-dose, single-shot parenteral administration of PPS prior to revascularization might be useful in nondiabetic rats.

The Role of Extracellular Adenosine Triphosphate in Ischemic Organ Injury

OBJECTIVES

Ischemic tissue injury contributes to significant morbidity and mortality and is implicated in a range of pathologic conditions, including but not limited to myocardial infarction, ischemic stroke, and acute kidney injury. The associated reperfusion phase is responsible for the activation of the innate and adaptive immune system, further accentuating inflammation. Adenosine triphosphate molecule has been implicated in various ischemic conditions, including stroke and myocardial infarction.

STUDY SELECTION

Adenosine triphosphate is a well-defined intracellular energy transfer and is commonly referred to as the body's "energy currency." However, Laboratory studies have demonstrated that extracellular adenosine triphosphate has the ability to initiate inflammation and is therefore referred to as a damage-associated molecular pattern. Purinergic receptors-dependent signaling, proinflammatory cytokine release, increased Ca influx into cells, and subsequent apoptosis have been shown to form a common underlying extracellular adenosine triphosphate molecular mechanism in ischemic organ injury.

CONCLUSIONS

In this review, we aim to discuss the molecular mechanisms behind adenosine triphosphate-mediated ischemic tissue injury and evaluate the role of extracellular adenosine triphosphate in ischemic injury in specific organs, in order to provide a greater understanding of the pathophysiology of this complex process. We also appraise potential future therapeutic strategies to limit damage in various organs, including the heart, brain, kidneys, and lungs.

The multifaceted role of the renal microvasculature during acute kidney injury

Pediatric acute kidney injury (AKI) represents a complex disease process for clinicians as it is multifactorial in cause and only limited treatment or preventatives are available. The renal microvasculature has recently been implicated in AKI as a strong therapeutic candidate involved in both injury and recovery. Significant progress has been made in the ability to study the renal microvasculature following ischemic AKI and its role in repair. Advances have also been made in elucidating cell-cell interactions and the molecular mechanisms involved in these interactions. The ability of the kidney to repair post AKI is closely linked to alterations in hypoxia, and these studies are elucidated in this review. Injury to the microvasculature following AKI plays an integral role in mediating the inflammatory response, thereby complicating potential therapeutics. However, recent work with experimental animal models suggests that the endothelium and its cellular and molecular interactions are attractive targets to prevent injury or hasten repair following AKI. Here, we review the cellular and molecular mechanisms of the renal endothelium in AKI, as well as repair and recovery, and potential therapeutics to prevent or ameliorate injury and hasten repair.

Peptidyl arginine deiminase-4-deficient mice are protected against kidney and liver injury after renal ischemia and reperfusion

We previously demonstrated that renal peptidyl arginine deiminase-4 (PAD4) is induced after renal ischemia and reperfusion (I/R) injury and exacerbates acute kidney injury (AKI) by increasing the renal tubular inflammatory response. Here, we tested whether genetic ablation of PAD4 attenuates renal injury and inflammation after I/R in mice. After renal I/R, PAD4 wild-type mice develop severe AKI with large increases in plasma creatinine, neutrophil infiltration, as well as significant renal tubular necrosis, apoptosis, and proinflammatory cytokine generation. In contrast, PAD4-deficient mice are protected against ischemic AKI with reduced real tubular neutrophil infiltration, renal tubular necrosis, and apoptosis. In addition, hepatic injury and inflammation observed in PAD4 wild-type mice after renal I/R are significantly attenuated in PAD4-deficient mice. We also show that increased renal tubular PAD4 expression after renal I/R is associated with translocation of PAD4 from the nucleus to the cytosol. Consistent with PAD4 cytosolic translocation, we show increased renal tubular cytosolic peptidyl-citrullination after ischemic AKI. Mechanistically, recombinant PAD4 treatment increased nuclear translocation of NF-κB in cultured human as well as murine proximal tubule cells that is inhibited by a PAD4 inhibitor (2-chloroamidine). Taken together, our studies further support the hypothesis that renal tubular PAD4 plays a critical role in renal I/R injury by increasing the renal tubular inflammatory response and neutrophil infiltration after renal I/R perhaps by interacting with the proinflammatory transcription factor NF-κB in the cytosol and promoting its nuclear translocation.

Macrophages in kidney injury, inflammation, and fibrosis

Macrophages are found in normal kidney and in increased numbers in diseased kidney, where they act as key players in renal injury, inflammation, and fibrosis. Macrophages are highly heterogeneous cells and exhibit distinct phenotypic and functional characteristics in response to various stimuli in the local microenvironment in different types of kidney disease. In kidney tissue necrosis and/or infection, damage- and/or pathogen-associated molecular patterns induce pro-inflammatory macrophages, which contribute to further tissue injury, inflammation, and subsequent fibrosis. Apoptotic cells and anti-inflammatory factors in post-inflammatory tissues induced anti-inflammatory macrophages, which can mediate kidney repair and regeneration. This review summarizes the role of macrophages with different phenotypes in kidney injury, inflammation, and fibrosis in various acute and chronic kidney diseases. Understanding alterations of kidney microenvironment and the factors that control the phenotype and functions of macrophages may offer an avenue for the development of new cellular and cytokine/growth factor-based therapies as alternative treatment options for patients with kidney disease.

ROS-Mediated NLRP3 Inflammasome Activation in Brain, Heart, Kidney, and Testis Ischemia/Reperfusion Injury

Ischemia and reperfusion (I/R) causes a reduction in arterial blood supply to tissues, followed by the restoration of perfusion and consequent reoxygenation. The reestablishment of blood flow triggers further damage to the ischemic tissue through reactive oxygen species (ROS) accumulation, interference with cellular ion homeostasis, and inflammatory responses to cell death. In normal conditions, ROS mediate important beneficial responses. When their production is prolonged or elevated, harmful events are observed with peculiar cellular changes. In particular, during I/R, ROS stimulate tissue inflammation and induce NLRP3 inflammasome activation. The mechanisms underlying the activation of NLRP3 are several and not completely elucidated. It was recently shown that NLRP3 might sense directly the presence of ROS produced by normal or malfunctioning mitochondria or indirectly by other activators of NLRP3. Aim of the present review is to describe the current knowledge on the role of NLRP3 in some organs (brain, heart, kidney, and testis) after I/R injury, with particular regard to the role played by ROS in its activation. Furthermore, as no specific therapy for the prevention or treatment of the high mortality and morbidity associated with I/R is available, the state of the art of the development of novel therapeutic approaches is illustrated.

Hind limb perconditioning renoprotection by modulation of inflammatory cytokines after renal ischemia/reperfusion

Purpose Renal ischemia/reperfusion (I/R) injury is a common clinical problem associated with significant mortality and morbidity. One newly described strategy to reduce this damage is remote perconditioning (RPEC), in which short-time ischemia of a limb during renal ischemia reduces the I/R-induced kidney injury. This study aimed to assess whether RPEC confer protection through changes in pro-inflammatory mediators. Methods Rats were subjected to right nephrectomy and randomized into: sham (no intervention), I/R (subjected to 45-min left renal ischemia) and RPEC group (subjected to four cycles of 5-min I/R of the femoral artery administered during renal ischemia). After 24-h, blood, urine, and kidney samples were collected. Biochemical indicators of renal dysfunction were measured in the cases of Neutrophil gelatinase-associated lipocalin (NGAL), and N-acetyl-B-diglucosaminidase (NAG) activity. Inflammatory cytokines [interleukin (IL)-6 and tumor necrosis factor-alpha, TNF-α] expression in the renal tissues as well as Periodic acid-Schiff stained histological sections were evaluated. Results I/R resulted in renal dysfunction, as evidenced by higher renal NGAL expression and urinary NAG activities. This was accompanied by increased TNF-α and IL-6 expressions as well as histological changes in this group. However, RPEC improved renal histology and function compared with the I/R group. Furthermore, the RPEC group showed decreases in TNF-α and IL-6 expression. Conclusions These results suggest that RPEC reduces the dysfunction and injury associated with I/R of the kidney. This technique reduced the pro-inflammatory cytokine in the kidney. RPEC could be a promising strategy against I/R-induced acute kidney injury partly by down-regulation of inflammatory mediators.

Heat shock protein 72 (Hsp72) specific induction and temporal stability in urine samples as a reliable biomarker of acute kidney injury (AKI)

We demonstrated that urinary heat shock protein of 72 KDa (Hsp72) is a sensitive biomarker for the early detection of acute kidney injury (AKI). However, whether Hsp72 induction during an AKI episode is kidney-specific is unknown, as well as, the degree of Hsp72 stability in urine samples. In rats that underwent bilateral renal ischemia and reperfusion (I/R), Hsp72 levels were evaluated in several tissues and in collected urines under different storage and temperature conditions, as well as in variable numbers of freeze-thaw cycles. The effect of room temperature and five freeze-thaw cycles on urinary Hsp72 levels was also evaluated in urine samples from AKI patients. We found that Hsp72 increased exclusively in the renal cortex of I/R group, emphasizing its performance as an AKI biomarker. Urinary-Hsp72 remained constant at room temperature (48 h), during 9 months of storage and was not affected by five freeze/thaw cycles.

Dioscin attenuates renal ischemia/reperfusion injury by inhibiting the TLR4/MyD88 signaling pathway via up-regulation of HSP70

We previously reported the effect of dioscin against hepatic ischemia/reperfusion injury (IRI) in rats. However, little is known concerning the role of dioscin in renal IRI. In the present study, rats were subjected to IRI and dioscin was intragastrically administered for seven consecutive days before surgery. In vitro models of hypoxia/reoxygenation were developed in NRK-52E and HK-2 cells, which were prophylactically treated with or without dioscin. The results showed that dioscin significantly decreased serum BUN and Cr levels, and markedly attenuated cell injury. Mechanistic studies showed that dioscin significantly increased HSP70 levels, decreased the levels of TLR4, MyD88, TRAF6, COX-2, JNK, ERK and p38 MAPK phosphorylation, suppressed the nuclear translocation of NF-κB and HMGB1, and subsequently decreased the mRNA levels of IL-1β, IL-6, TNF-α, ICAM-1 and IFN-γ. Moreover, HSP70 siRNA or TLR4 DNA reversed the nephroprotective effects of dioscin, while dioscin still significantly down-regulated the TLR4 signaling pathway. Furthermore, by inhibiting MyD88 with ST2825 (a MyD88 inhibitor), renal IRI was significantly attenuated, suggesting that the effect of dioscin against renal IRI depended on MyD88. Our results suggested that dioscin had a potent effect against renal IRI through suppressing the TLR4/MyD88 signaling pathway by up-regulating HSP70. These data provide new insights for investigating the natural product with the nephroprotective effect against IRI, which should be developed as a new therapeutic agent for the treatment of acute kidney injury in the future.

The ABO Histo-Blood Group and AKI in Critically Ill Patients with Trauma or Sepsis

BACKGROUND AND OBJECTIVE

ABO blood types are determined by antigen modifications on glycoproteins and glycolipids and associated with altered plasma levels of inflammatory and endothelial injury markers implicated in AKI pathogenesis. We sought to determine the association of ABO blood types with AKI risk in critically ill patients with trauma or sepsis.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We conducted two prospective cohort studies at an urban, academic, level I trauma center and tertiary referral center; 497 patients with trauma admitted to the surgical intensive care unit between 2005 and 2010 with an injury severity score >15 and 759 patients with severe sepsis admitted to the medical intensive care unit between 2008 and 2013 were followed for 6 days for the development of incident AKI. AKI was defined by Acute Kidney Injury Network creatinine and dialysis criteria.

RESULTS

Of 497 patients with trauma, 134 developed AKI (27%). In multivariable analysis, blood type A was associated with higher AKI risk relative to type O among patients of European descent (n=229; adjusted risk, 0.28 versus 0.14; risk difference, 0.14; 95% confidence interval, 0.03 to 0.24; P=0.02). Of 759 patients with sepsis, AKI developed in 326 (43%). Blood type A again conferred higher AKI risk relative to type O among patients of European descent (n=437; adjusted risk, 0.53 versus 0.40; risk difference, 0.14; 95% confidence interval, 0.04 to 0.23; P=0.01). Findings were similar when analysis was restricted to those patients who did not develop acute respiratory distress syndrome or were not transfused. We did not detect a significant association between blood type and AKI risk among individuals of African descent in either cohort.

CONCLUSIONS

Blood type A is independently associated with AKI risk in critically ill patients with trauma or severe sepsis of European descent, suggesting a role for ABO glycans in AKI susceptibility.

Endothelial autophagy and Endothelial-to-Mesenchymal Transition (EndoMT) in eEPC treatment of ischemic AKI

BACKGROUND

Autophagy enables cells to digest endogenous/exogenous waste products, thus potentially prolonging the cellular lifespan. Early endothelial progenitor cells (eEPCs) protect mice from ischemic acute kidney injury (AKI). The mid-term prognosis in AKI critically depends on vascular rarefication and interstitial fibrosis with the latter partly being induced by mesenchymal transdifferentiation of endothelial cells (EndoMT). This study aimed to determine the impact of eEPC preconditioning with different autophagy inducing agents [suberoylanilide hydroxamic acid (SAHA)/temsirolimus] in ischemic AKI.

METHODS

Male C57/Bl6 N mice were subjected to bilateral renal ischemia (40 min). Animals were injected with either untreated, or SAHA- or temsirolimus-pretreated syngeneic murine eEPCs at the time of reperfusion. Mice were analyzed 48 h and 4 weeks later. In addition, cultured eEPCs were treated with transforming growth factor (TGF)-β ± SAHA, autophagy (perinuclear LC3-II), and stress-induced premature senescence (SIPS-senescence-associated β-galactosidase, SA-β-Gal), and were evaluated 96 h later.

RESULTS

Cultured eEPCs showed reduced perinuclear density of LC3-II + vesicles and elevated levels of SA-β-Gal after treatment with TGF-β alone, indicating impaired autophagy and aggravated SIPS. These effects were completely abrogated by SAHA. Systemic administration of either SAHA or tems pretreated eEPCs resulted in elevated intrarenal endothelial p62 at 48 h and 4 weeks, indicating stimulated endothelial autophagy. This effect was most pronounced after injection of SAHA-treated eEPCs. At 4 weeks endothelial expression of mesenchymal alpha-smooth muscle actin (αSMA) was reduced in animals receiving untreated and SAHA-pretreated cells. In addition, SAHA-treated cells reduced fibrosis at week 4. Tems in contrast aggravated EndoMT. Postischemic renal function declined after renal ischemia and remained unaffected in all experimental cell treatment groups.

CONCLUSION

In ischemic AKI, intrarenal endothelial autophagy may be stabilized by systemic administration of pharmacologically preconditioned eEPCs. Early EPCs can reduce postischemic EndoMT and fibrosis in the mid-term. Autophagy induction in eEPCs either increases or decreases the mesenchymal properties of intrarenal endothelial cells, depending on the substance being used. Thus, endothelial autophagy induction in ischemic AKI, mediated by eEPCs is not a renoprotective event per se.

Transplanting Kidneys from Deceased Donors With Severe Acute Kidney Injury

Our aim was to determine outcomes with transplanting kidneys from deceased donors with acute kidney injury, defined as a donor with terminal serum creatinine ≥2.0 mg/dL, or a donor requiring acute renal replacement therapy. We included all patients who received deceased donor kidney transplant from June 2004 to October 2013. There were 162 AKI donor transplant recipients (21% of deceased donor transplants): 139 in the standard criteria donor (SCD) and 23 in the expanded criteria donor (ECD) cohort. 71% of the AKI donors had stage 3 (severe AKI), based on acute kidney injury network (AKIN) staging. Protocol biopsies were done at 1, 4, and 12 months posttransplant. One and four month formalin-fixed paraffin embedded (FFPE) biopsies from 48 patients (24 AKI donors, 24 non-AKI) underwent global gene expression profiling using DNA microarrays (96 arrays). DGF was more common in the AKI group but eGFR, graft survival at 1 year and proportion with IF/TA>2 at 1 year were similar for the two groups. At 1 month, there were 898 differentially expressed genes in the AKI group (p-value <0.005; FDR <10%), but by 4 months there were no differences. Transplanting selected kidneys from deceased donors with AKI is safe and has excellent outcomes.

Protective Effect of CXCR3⁺CD4⁺CD25⁺Foxp3⁺ Regulatory T Cells in Renal Ischemia-Reperfusion Injury

Regulatory T cells (Tregs) suppress excessive immune responses and are potential therapeutic targets in autoimmune disease and organ transplantation rejection. However, their role in renal ischemia-reperfusion injury (IRI) is unclear. Levels of Tregs and expression of CXCR3 in Tregs were analyzed to investigate their function in the early phase of renal IRI. Mice were randomly divided into Sham, IRI, and anti-CD25 (PC61) + IRI groups. The PC61 + IRI group was established by i.p. injection of PC61 monoclonal antibody (mAb) to deplete Tregs before renal ischemia. CD4⁺CD25⁺Foxp3⁺ Tregs and CXCR3 on Tregs were analyzed by flow cytometry. Blood urea nitrogen (BUN), serum creatinine (Scr) levels, and tubular necrosis scores, all measures of kidney injury, were greater in the IRI group than in the Sham group. Numbers of Tregs were increased at 72 h after reperfusion in kidney. PC61 mAb preconditioning decreased the numbers of Tregs and aggravated kidney injury. There was no expression of CXCR3 on Tregs in normal kidney, while it expanded at 72 h after reperfusion and inversely correlated with BUN, Scr, and kidney histology score. This indicated that recruitment of Tregs into the kidney was related to the recovery of renal function after IRI and CXCR3 might be involved in the migration of Tregs.

Elevation of miR-21, through targeting MKK3, may be involved in ischemia pretreatment protection from ischemia-reperfusion induced kidney injury

BACKGROUND

Ischemia-reperfusion (IR) causes acute kidney injury (AKI), and ischemia pretreatment may exert protection. Mitogen-activated protein kinase kinase 3 (MKK3), which is involved in the signal transduction pathway in IR-induced injury, is a potential target of miR-21. We aimed to verify the targeting regulation of miR-21 on MKK3 and to explore the effects of miR-21-mediated MKK3 expression changes in AKI.

METHODS

Vectors containing the MKK3 3'UTR and mutated MKK3-3U-M were constructed and co-transfected with nonsense miR, miR-21-5p mimics or inhibitor in HEK293 cells. Gene expressions were detected by dual luciferase reporter assay. The effects of miR-21 on mRNA and protein of MKK3 were investigated in HK-2 cells. Male C57BL/6J mice were treated with ischemic preconditioning (IPC) and IR. Kidney functions were assessed through monitoring serum creatinine (Scr) and blood urea nitrogen (BUN). Pathological changes were observed and scored with histological samples of kidney. Expression levels of miR-21, MKK3, interleukin (IL)-6, tumor necrosis factor (TNF)-α before and after IPC and IR were examined by real-time polymerase chain reaction and/or immunohistochemistry.

RESULTS

miR-21 regulated the expression of MKK3 via 3'UTR. Following IR, MKK3, IL-6 and TNF-α levels were increased. Scr, BUN and pathological injuries were aggravated, and miR-21 expression was increased. IPC increased miR-21 levels ahead of IR and inhibited the increases in MKK3, IL-6 and TNF-α levels and the aggravation of Scr, BUN and pathological injuries.

CONCLUSIONS

miR-21 targets MKK3 in vivo and in vitro, inhibiting the downstream factors IL-6 and TNF-α. Therefore, miR-21 might be involved in protection of IPC against IR of the kidney.

Picroside II decreases the development of fibrosis induced by ischemia/reperfusion injury in rats

In kidney transplantation, renal ischemia and reperfusion injury was one of the leading factors to the development of renal fibrosis, which was the main cause of graft loss. The fibrogenic changes were associated with the long term inflammation elicited by ischemia and reperfusion injury. In the present study, we investigated the role of the Picroside II, the main active constituents of the extract of picrorrhiza scrophulariiflora roots, in attenuating renal fibrosis in a renal ischemia and reperfusion injury model. We induced ischemia and reperfusion injury in kidneys treated with or without Picroside II. We observed that inflammation and tissue fibrosis were increased in ischemia and reperfusion injury group compared to Picroside II group, however, these changes were significantly decreased by the treatment with Picroside II. We concluded that Picroside II can protect the ischemic kidney against renal fibrosis and its mechanism may be through the inhibition of the long term inflammation.

MicroRNAs in Kidney Transplantation: Living up to Their Expectations?

Since the discovery of microRNAs, ample research has been conducted to elucidate their involvement in an array of (patho)physiological conditions. Ischemia reperfusion injury is a major problem in kidney transplantation and its mechanism is still not fully known, nor is there an effective therapy. Furthermore, no biomarker is available to specifically measure (ischemic) damage after kidney transplantation or predict transplantation outcome. In this review, we summarize studies conducted on microRNAs in renal ischemia reperfusion injury and kidney transplantation. Although the number of publications on miRNAs in different areas of nephrology is increasing every year, only a limited number of reports that address the role of miRNAs in relation to ischemia reperfusion injury or kidney transplantation are available. All reports up to June 2014 on microRNAs in renal IRI, kidney transplantation, and renal allograft status were included. Design of the studies was highly variable and there was limited overlap between microRNAs found in these reports. No single microRNA expression pattern could be found, although multiple microRNAs involved in the immune response seem to be altered after ischemia reperfusion injury and kidney transplantation. Although there is a growing interest in microRNA research in kidney transplantation aiming to identify biomarkers and therapeutical targets, to date, no specific microRNA has been demonstrated to be applicable as either one, mostly because of lack of specificity. More systematical research is needed to determine whether microRNAs can be applied as biomarker, therapeutic target, or therapeutic agent in kidney transplantation.

Eculizumab reduces complement activation, inflammation, endothelial damage, thrombosis, and renal injury markers in aHUS

Atypical hemolytic uremic syndrome (aHUS) is a genetic, life-threatening disease characterized by uncontrolled complement activation, systemic thrombotic microangiopathy (TMA), and vital organ damage. We evaluated the effect of terminal complement blockade with the anti-C5 monoclonal antibody eculizumab on biomarkers of cellular processes involved in TMA in patients with aHUS longitudinally, during up to 1 year of treatment, compared with in healthy volunteers. Biomarker levels were elevated at baseline in most patients, regardless of mutational status, plasma exchange/infusion use, platelet count, or lactate dehydrogenase or haptoglobin levels. Eculizumab reduced terminal complement activation (C5a and sC5b-9) and renal injury markers (clusterin, cystatin-C, β2-microglobulin, and liver fatty acid binding protein-1) to healthy volunteer levels and reduced inflammation (soluble tumor necrosis factor receptor-1), coagulation (prothrombin fragment F1+2 and d-dimer), and endothelial damage (thrombomodulin) markers to near-normal levels. Alternative pathway activation (Ba) and endothelial activation markers (soluble vascular cell adhesion molecule-1) decreased but remained elevated, reflecting ongoing complement activation in aHUS despite complete terminal complement blockade. These results highlight links between terminal complement activation and inflammation, endothelial damage, thrombosis, and renal injury and underscore ongoing risk for systemic TMA and progression to organ damage. Further research regarding underlying complement dysregulation is warranted. This trial was registered at www.clinicaltrials.gov as #NCT01194973.

Renal endothelial dysfunction in acute kidney ischemia reperfusion injury

Acute kidney injury is associated with alterations in vascular tone that contribute to an overall reduction in GFR. Studies in animal models indicate that ischemia triggers alterations in endothelial function that contribute significantly to the overall degree and severity of a kidney injury. Putative mediators of vasoconstriction that may contribute to the initial loss of renal blood flow and GFR are highlighted. In addition, there is discussion of how intrinsic damage to the endothelium impairs homeostatic responses in vascular tone as well as promotes leukocyte adhesion and exacerbating the reduction in renal blood flow. The timing of potential therapies in animal models as they relate to the evolution of AKI, as well as the limitations of such approaches in the clinical setting are discussed. Finally, we discuss how acute kidney injury induces permanent alterations in renal vascular structure. We posit that the cause of the sustained impairment in kidney capillary density results from impaired endothelial growth responses and suggest that this limitation is a primary contributing feature underlying progression of chronic kidney disease.

Hepcidin Mitigates Renal Ischemia-Reperfusion Injury by Modulating Systemic Iron Homeostasis

Iron-mediated oxidative stress is implicated in the pathogenesis of renal ischemia-reperfusion injury. Hepcidin is an endogenous acute phase hepatic hormone that prevents iron export from cells by inducing degradation of the only known iron export protein, ferroportin. In this study, we used a mouse model to investigate the effect of renal ischemia-reperfusion injury on systemic iron homeostasis and determine if dynamic modulation of iron homeostasis with hepcidin has therapeutic benefit in the treatment of AKI. Renal ischemia-reperfusion injury induced hepatosplenic iron export through increased ferroportin expression, which resulted in hepatosplenic iron depletion and an increase in serum and kidney nonheme iron levels. Exogenous hepcidin treatment prevented renal ischemia-reperfusion-induced changes in iron homeostasis. Hepcidin also decreased kidney ferroportin expression and increased the expression of cytoprotective H-ferritin. Hepcidin-induced restoration of iron homeostasis was accompanied by a significant reduction in ischemia-reperfusion-induced tubular injury, apoptosis, renal oxidative stress, and inflammatory cell infiltration. Hepcidin -: deficient mice demonstrated increased susceptibility to ischemia-reperfusion injury compared with wild-type mice. Reconstituting hepcidin-deficient mice with exogenous hepcidin induced hepatic iron sequestration, attenuated the reduction in renal H-ferritin and reduced renal oxidative stress, apoptosis, inflammation, and tubular injury. Hepcidin-mediated protection was associated with reduced serum IL-6 levels. In summary, renal ischemia-reperfusion injury results in profound alterations in systemic iron homeostasis. Hepcidin treatment restores iron homeostasis and reduces inflammation to mediate protection in renal ischemia-reperfusion injury, suggesting that hepcidin-ferroportin pathway holds promise as a novel therapeutic target in the treatment of AKI.

Protective effect of baicalein on renal ischemia/reperfusion injury in the rat

OBJECTIVE

To investigate the protective effect and the mechanism of baicalein (Bai) in rats with renal ischemia-reperfusion injury (RIRI).

METHODS

Twenty-four male Sprague-Dawley rats were divided into three groups: sham, IR, and IR+Bai. Bai was administered by tail vein injection (30 mg/kg) 30 min before reperfusion in the IR+Bai group. The IR group and sham group received saline vehicle via the intravenous route.

RESULTS

Rats that underwent RIRI exhibited renal functional impairment, histological changes, significantly increased advanced oxidation protein product (AOPP) and malondialdehyde (MDA) levels (p<0.01), and ICAM-1 and MCP-1 protein and mRNA expression were significantly upregulated (p<0.01). Administration of Bai reduced AOPP and MDA levels, significantly inhibited expression of inflammatory factors (p<0.05), and markedly improved renal function.

CONCLUSION

Bai promotes the recovery of renal function in established acute RIRI, and alleviates kidney injury in a rat model.

MicroRNA-10b downregulation mediates acute rejection of renal allografts by derepressing BCL2L11

Kidney transplantation is the major therapeutic option for end-stage kidney diseases. However, acute rejection could cause allograft loss in some of these patients. Emerging evidence supports that microRNA (miRNA) dysregulation is implicated in acute allograft rejection. In this study, we used next-generation sequencing to profile miRNA expression in normal and acutely rejected kidney allografts. Among 75 identified dysregulated miRNAs, miR-10b was the most significantly downregulated miRNAs in rejected allografts. Transfecting miR-10b inhibitor into human renal glomerular endothelial cells recapitulated key features of acute allograft rejection, including endothelial cell apoptosis, release of pro-inflammatory cytokines (interleukin-6, tumor necrosis factor α, interferon-γ, and chemokine (C-C motif) ligand 2) and chemotaxis of macrophages whereas transfection of miR-10b mimics had opposite effects. Downregulation of miR-10b directly derepressed the expression of BCL2L11 (an apoptosis inducer) as revealed by luciferase reporter assay. Taken together, miR-10b downregulation mediates many aspects of disease pathogenicity of acute kidney allograft rejection. Restoring miR-10b expression in glomerular endothelial cells could be a novel therapeutic approach to reduce acute renal allograft loss.

The restrained expression of NF-kB in renal tissue ameliorates folic acid induced acute kidney injury in mice

The Nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kB) represent family of structurally-related eukaryotic transcription factors which regulate diverse array of cellular processes including immunological responses, inflammation, apoptosis, growth & development. Increased expression of NF-kB has often been seen in many diverse diseases, suggesting the importance of genomic deregulation to disease pathophysiology. In the present study we focused on acute kidney injury (AKI), which remains one of the major risk factor showing a high rate of mortality and morbidity. The pathology associated with it, however, remains incompletely known though inflammation has been reported to be one of the major risk factor in the disease pathophysiology. The role of NF-kB thus seemed pertinent. In the present study we show that high dose of folic acid (FA) induced acute kidney injury (AKI) characterized by elevation in levels of blood urea nitrogen & serum creatinine together with extensive tubular necrosis, loss of brush border and marked reduction in mitochondria. One of the salient observations of this study was a coupled increase in the expression of renal, relA, NF-kB2, and p53 genes and proteins during folic acid induced AKI (FA AKI). Treatment of mice with NF-kB inhibitor, pyrrolidine dithio-carbamate ammonium (PDTC) lowered the expression of these transcription factors and ameliorated the aberrant renal function by decreasing serum creatinine levels. In conclusion, our results suggested that NF-kB plays a pivotal role in maintaining renal function that also involved regulating p53 levels during FA AKI.

Protective effect of peptide GV1001 against renal ischemia-reperfusion injury in mice

BACKGROUND

Ischemia reperfusion injury (IRI) is a common complication after kidney transplantation. Peptide GV1001 is a peptide vaccine representing a 16-amino acid human telomerase reverse transcriptase sequence, which has been reported to possess potential antineoplastic and anti-inflammatory activity. This study aimed to investigate the potential effects of peptide GV1001 on renal IRI.

METHODS

Peptide GV1001 was subcutaneously administered to C57BL6/J mice 30 minutes before and 12 hours after bilateral IRI. Sham operation and phosphate-buffered saline (PBS) injection were used as controls. Blood and renal tissues were harvested at 1 day after IRI.

RESULTS

Peptide GV1001 treatment significantly attenuated renal functional deterioration after IRI (peptide GV1001 group vs PBS group; blood urea nitrogen, P < .05; creatinine, P < .05). Peptide GV1001 treatment also attenuated renal tissue injury (tubular injury score; the peptide GV1001 group vs PBS group; P < .001). Renal apoptosis was also lower in the peptide GV1001 group. Immunohistochemical studies showed that IRI increased perirenal infiltration of both neutrophils and macrophages, and that peptide GV1001 significantly attenuated this process. Expression of interleukin-6 and monocyte chemotactic protein-1 was significantly reduced by peptide GV1001 treatment.

CONCLUSIONS

Peptide GV1001 ameliorates acute renal IRI by reducing inflammation and apoptosis; therefore, it is promising as a potential therapeutic agent for renal IRI. The mechanisms of protection should be explored in further studies.

Intra-renal arterial injection of autologous bone marrow mesenchymal stromal cells ameliorates cisplatin-induced acute kidney injury in a rhesus Macaque mulatta monkey model

BACKGROUND

Clinically, acute kidney injury (AKI) is a potentially devastating condition for which no specific therapy improves efficacy of the repair process. Bone marrow mesenchymal stromal cells (BM-MSCs) are proven to be beneficial for the renal repair process after AKI in different experimental rodent models, but their efficacy in large animals and humans remains unknown. This study aims to assess the effect of autologous rhesus Macaque mulatta monkey BM-MSC transplantation in cisplatin-induced AKI.

METHODS

We chose a model of AKI induced by intravenous administration of 5 mg/kg cisplatin. BM-MSCs were transplanted through intra-arterial injection. The animals were followed for survival, biochemistry analysis and pathology.

RESULTS

Transplantation of 5 × 10(6) cells/kg ameliorated renal function during the first week, as shown by significantly lower serum creatinine and urea values and higher urine creatinine and urea clearance without hyponatremia, hyperkalemia, proteinuria and polyuria up to 84 d compared with the vehicle and control groups. The superparamagnetic iron oxide nanoparticle-labeled cells were found in both the glomeruli and tubules. BM-MSCs markedly accelerated Foxp3+ T-regulatory cells in response to cisplatin-induced damage, as revealed by higher numbers of Foxp3+ cells within the tubuli of these monkeys compared with cisplatin-treated monkeys in the control and vehicle groups.

CONCLUSIONS

These data demonstrate that BM-MSCs in this unique large-animal model of cisplatin-induced AKI exhibited recovery and protective properties.

Local therapeutic efficacy with reduced systemic side effects by rapamycin-loaded subcapsular microspheres

Kidney injury triggers fibrosis, the final common pathway of chronic kidney disease (CKD). The increase of CKD prevalence worldwide urgently calls for new therapies. Available systemic treatment such as rapamycin are associated with serious side effects. To study the potential of local antifibrotic therapy, we administered rapamycin-loaded microspheres under the kidney capsule of ureter-obstructed rats and assessed the local antifibrotic effects and systemic side effects of rapamycin. After 7 days, microsphere depots were easily identifiable under the kidney capsule. Both systemic and local rapamycin treatment reduced intrarenal mTOR activity, myofibroblast accumulation, expression of fibrotic genes, and T-lymphocyte infiltration. Upon local treatment, inhibition of mTOR activity and reduction of myofibroblast accumulation were limited to the immediate vicinity of the subcapsular pocket, while reduction of T-cell infiltration was widespread. In contrast to systemically administered rapamycin, local treatment did not induce off target effects such as weight loss. Thus subcapsular delivery of rapamycin-loaded microspheres successfully inhibited local fibrotic response in UUO with less systemic effects. Therapeutic effect of released rapamycin was most prominent in close vicinity to the implanted microspheres.

G31P, CXCR1/2 inhibitor, with cisplatin inhibits the growth of mice hepatocellular carcinoma and mitigates high‑dose cisplatin-induced nephrotoxicity

Cisplatin (DDP), a cytotoxic antitumor drug, functions in a dose-dependent manner. However, the pursuit for high‑dose therapeutic effects leads to more serious side effects including kidney toxicity. Nephrotoxicity caused due to endothelial cell dysfunction and neutrophils infiltration in kidneys. Interleukin-8 (IL-8) is an ELR+ chemokine binds with CXCR1/2 receptors and its role is primarily in neutrophils recruitment and also involved in invasion, angiogenesis and metastasis of different solid tumors including liver cancer. G31P, a CXCR1/2 antagonist, binds with CXCR1/2 with high affinity, and acts as an anti-inflammatory and antitumor agent. In the present study, we examined the antitumor effects of G31P and DDP on mouse liver cancer cells, and the effects exerted by G31P on cisplatin-induced renal injury. In vitro, effects of the G31P and DDP regimen on H22 cell proliferation were investigated by MTT assay. In vivo BALB/c mice were inoculated subcutaneously with 1x106 H22 cells and treated after one week with a high single dose of DDP with and without G31P on alternative days until the experiment was terminated. On the 15th day the mice were sacrificed, dissected and kidney tissues were analyzed using H&E staining. Myeloperoxidase (MPO) activity was assessed and RT-PCR was performed to detect inflammatory cytokines. Solid tumors were weighed for tumor growth and performed pathological examination, immunohistochemistry and western blotting were performed to detect tissue-related protein expressions in tumor tissue. The tumor inhibitory rate of DDP, G31P and DDP+G31P groups was 38.40, 40.74 and 74.80%, respectively, and the general state of mice in the DDP+G31P group was significantly improved as compared to the DDP group. The results indicated that G31P with DDP significantly inhibited the proliferation while the growth of H22 cell carnimona in vitro and in vivo enhanced the efficacy of cisplatin in cancer treatment with reduced side effects on acute renal failure.

The role of complement in the pathogenesis of renal ischemia-reperfusion injury and fibrosis

The complement system is a major component of innate immunity and has been commonly identified as a central element in host defense, clearance of immune complexes, and tissue homeostasis. After ischemia-reperfusion injury (IRI), the complement system is activated by endogenous ligands that trigger proteolytic cleavage of complement components via the classical, lectin and/or alternative pathway. The result is the formation of terminal complement components C3a, C5a, and the membrane attack complex (C5b-9 or MAC), all of which play pivotal roles in the amplification of the inflammatory response, chemotaxis, neutrophil/monocyte recruitment and activation, and direct tubular cell injury. However, recent evidence suggests that complement activity transcends innate host defense and there is increasing data suggesting complement as a regulator in processes such as allo-immunity, stem cell differentiation, tissue repair, and progression to fibrosis. In this review, we discuss recent advances addressing the role of complement as a regulator of IRI and renal fibrosis after organ donation for transplantation. We will also briefly discuss currently approved therapies that target complement activity in kidney ischemia-reperfusion and transplantation.

The role of complement in the pathogenesis of renal ischemia-reperfusion injury and fibrosis

The complement system is a major component of innate immunity and has been commonly identified as a central element in host defense, clearance of immune complexes, and tissue homeostasis. After ischemia-reperfusion injury (IRI), the complement system is activated by endogenous ligands that trigger proteolytic cleavage of complement components via the classical, lectin and/or alternative pathway. The result is the formation of terminal complement components C3a, C5a, and the membrane attack complex (C5b-9 or MAC), all of which play pivotal roles in the amplification of the inflammatory response, chemotaxis, neutrophil/monocyte recruitment and activation, and direct tubular cell injury. However, recent evidence suggests that complement activity transcends innate host defense and there is increasing data suggesting complement as a regulator in processes such as allo-immunity, stem cell differentiation, tissue repair, and progression to fibrosis. In this review, we discuss recent advances addressing the role of complement as a regulator of IRI and renal fibrosis after organ donation for transplantation. We will also briefly discuss currently approved therapies that target complement activity in kidney ischemia-reperfusion and transplantation.

Immune cells in experimental acute kidney injury

Acute kidney injury (AKI) prolongs hospital stay and increases mortality in various clinical settings. Ischaemia-reperfusion injury (IRI), nephrotoxic agents and infection leading to sepsis are among the major causes of AKI. Inflammatory responses substantially contribute to the overall renal damage in AKI. Both innate and adaptive immune systems are involved in the inflammatory process occurring in post-ischaemic AKI. Proinflammatory damage-associated molecular patterns, hypoxia-inducible factors, adhesion molecules, dysfunction of the renal vascular endothelium, chemokines, cytokines and Toll-like receptors are involved in the activation and recruitment of immune cells into injured kidneys. Immune cells of both the innate and adaptive immune systems, such as neutrophils, dendritic cells, macrophages and lymphocytes contribute to the pathogenesis of renal injury after IRI, and some of their subpopulations also participate in the repair process. These immune cells are also involved in the pathogenesis of nephrotoxic AKI. Experimental studies of immune cells in AKI have resulted in improved understanding of the immune mechanisms underlying AKI and will be the foundation for development of novel diagnostic and therapeutic targets. This Review describes what is currently known about the function of the immune system in the pathogenesis and repair of ischaemic and nephrotoxic AKI.

Apoptotic cell administration is detrimental in murine renal ischaemia reperfusion injury

Background

Acute kidney injury induced by renal ischaemia reperfusion injury (IRI) is characterised by renal failure, acute tubular necrosis (ATN), inflammation and microvascular congestion. The administration of apoptotic cells (ACs) has been shown to reduce inflammation in various organs including the liver and kidney. This study explored whether AC administration prior to the induction of renal IRI was protective.

Findings

Renal IRI was induced in Balb/c mice by clamping the renal blood vessels for either 20, 24 or 25 minutes to induce mild, moderate or severe kidney dysfunction respectively. Renal function and injury was determined 24 hours following IRI by measurement of plasma creatinine and ATN scoring respectively. ACs were generated from Balb/c thymocytes and classified as either predominantly early or late apoptotic by Annexin-V and propidium iodide staining. Early AC administration prior to severe IRI had no influence on plasma creatinine or ATN severity. In contrast, administration of early or late ACs significantly worsened renal function in mice with mild or moderate renal IRI, respectively, compared to PBS treated controls, though ATN scores were comparable. Despite ACs exerting pro-coagulant effects, the worsening of renal function was not secondary to increased microvascular congestion, inferred by fibrin and platelet (CD41) deposition, or inflammation, assessed by neutrophil infiltration.

Conclusions

Despite the AC-derived protection demonstrated in other organs, ACs do not protect mice from renal IRI. ACs may in fact further impair renal function depending on injury severity. These data suggest that AC-derived protection is not translationally relevant for patients with acute kidney injury induced by ischaemic injury.

Electronic supplementary material

The online version of this article (doi:10.1186/s12950-014-0031-6) contains supplementary material, which is available to authorized users.

T lymphocytes and acute kidney injury: update

The immune system is among the key pathogenic factors in acute kidney injury (AKI). Various immune cells, including dendritic cells, natural killer T cells, T and B lymphocytes, neutrophils and macrophages are involved. Conventional CD4+ lymphocytes are well established to participate in early injury, and CD4+CD25+FoxP3 regulatory T cells are protective and can accelerate repair. A newly identified kidney T cell receptor + CD4-CD8- (double-negative) T cell has complex functions, including potentially anti-inflammatory roles in AKI. In this mini review, we summarize the data on the role of lymphocytes in AKI and set the stage for further mechanistic studies as well as interventions to improve outcomes.

Near-term anti-CD25 monoclonal antibody administration protects murine liver from ischemia-reperfusion injury due to reduced numbers of CD4+ T cells

BACKGROUND

CD4(+) T cell is acknowledged as a key factor in the initiation phase of liver ischemia reperfusion injury. The purpose of current study is to demonstrate the effect of antecedent near-term anti-CD25 monoclonal antibody treatment on IR-induced liver injury by modulation of CD4(+) T cells.

METHODS

70% liver warm IR was induced in male C57BL/6 mice after anti-CD25 mAb or non-specific IgG administration. Liver function, histological damage, in vitro Proliferation, FACS, cytokine production, and immunofluorescence were assessed to evaluate the impact of antecedent near-term PC61 treatment on IR-induced liver injury.

RESULTS

After 70% liver ischemia, mice preconditioned with PC61 displayed significantly preserved liver function as characterized by less histological damage and reduced serum enzymes level. Mechanistic studies revealed that the protection effect of anti-CD25 mAb was associated with ameliorated intrahepatic inflammatory milieu and reduced CD4(+) T lymphocytes as manifested by the decrease of proinflammatory cytokine production (less expression of TNF-α, IFN-γ, IL-2, and IL-6) and the lower CD4/CD8 proportion.

CONCLUSIONS

Our results provide first line of evidence indicating that near-term treatment with anti-CD25 monoclonal antibody might provide protection for livers against IR-induced injury by reducing CD4(+) T cells, but not influencing functional Treg population. Therefore, our results demonstrate a potential function of anti-CD25 monoclonal antibody which was neglected in the past, and may be helpful in various clinical conditions, particularly in liver and kidney transplantations.

Effect of preemptive treatment with human umbilical cord blood-derived mesenchymal stem cells on the development of renal ischemia-reperfusion injury in mice

Human umbilical cord blood-derived mesenchymal stem cells (HUCB-MSCs) have been studied in several models of immune-mediated disease because of their unique immunomodulatory properties. We hypothesized that HUCB-MSCs could suppress the inflammatory response in postischemic kidneys and attenuate early renal injury. In 8- to 10-wk-old male C57BL/6 mice, bilateral ischemia-reperfusion injury (IRI) surgery was performed, and 1 × 10(6) HUCB-MSCs were injected intraperitoneally 24 h before surgery and during reperfusion. Renal functional and histological changes, HUCB-MSC trafficking, leukocyte infiltration, and cytokine expression were analyzed. Renal functional decline and tubular injury after IRI were attenuated by HUCB-MSC treatment. PKH-26-labeled HUCB-MSCs trafficked into the postischemic kidney. Although numbers of CD45-positive leukocytes in the postischemic kidney were comparable between groups, the expression of interferon-γ in the postischemic kidney was suppressed by HUCB-MSC treatment. The rapid decrease in intrarenal VEGF after IRI was markedly mitigated by HUCB-MSC treatment. In inflammatory conditions simulated in a cell culture experiment, VEGF secretion from HUCB-MSCs was substantially enhanced. VEGF inhibitor abolished the renoprotective effect of HUCB-MSCs after IRI. Flow cytometry analysis revealed the decreased infiltration of natural killer T cells and increased number of regulatory T cells in postischemic kidneys. In addition, these effects of HUCB-MSCs on kidney infiltrating mononuclear cells after IRI were attenuated by VEGF inhibitor. HUCB-MSCs attenuated renal injury in mice in the early injury phase after IRI, mainly by humoral effects and secretion of VEGF. Our results suggest a promising role for HUCB-MSCs in the treatment of renal IRI.

Hydrogen sulfide treatment ameliorates long-term renal dysfunction resulting from prolonged warm renal ischemia-reperfusion injury

INTRODUCTION

The incidence of renal cell carcinoma (RCC) continues to rise concurrently with the increased prevalence of end-stage renal disease worldwide. Treatment for small renal masses continues to be partial nephrectomy mostly involving the clamping of renal blood vessels. Although necessary, this technique results in warm renal ischemia and reperfusion injury (IRI) to the afflicted kidney. We have recently demonstrated that hydrogen sulfide (H2S), a novel endogenous gaseous molecule, protects against prolonged cold and short-term warm renal IRI. In the current study, we examined whether exogenous H2S has long-term protective effects against warm renal IRI associated with renal surgical procedures.

METHODS

Uni-nephrectomized Lewis rats underwent 1 hour of warm ischemia induced by clamping of the renal pelvis. Animals underwent either intraperitoneal treatment with phosphate buffered saline (PBS; IRI group) or PBS supplemented with 150 μM NaHS (H2S group), and were compared against Sham-operated rats.

RESULTS

H2S treatment improved long-term renal function as serum creatinine at day 7 was significantly decreased in the H2S group compared to IRI animals (p < 0.05). H2S treatment decreased the expression of pro-inflammatory markers TLR-4, TNF-α, IFNγ, IL-2 and ICAM-1, increased the expression of pro-survival molecule Bcl-2 and decreased the expression of pro-apoptotic marker BID at postoperative day 1. H2S-treated kidneys also showed a significant decrease (p < 0.05) in infiltration of macrophages at day 7 post-IRI compared to no treatment.

CONCLUSION

H2S treatment improved long-term renal function and decreased long-term inflammation associated with warm IRI, and may offer a novel therapeutic approach to preventing warm IRI-induced renal injury associated with renal surgical procedures.

Renal ischaemia reperfusion injury: a mouse model of injury and regeneration

Renal ischaemia reperfusion injury (IRI) is a common cause of acute kidney injury (AKI) in patients and occlusion of renal blood flow is unavoidable during renal transplantation. Experimental models that accurately and reproducibly recapitulate renal IRI are crucial in dissecting the pathophysiology of AKI and the development of novel therapeutic agents. Presented here is a mouse model of renal IRI that results in reproducible AKI. This is achieved by a midline laparotomy approach for the surgery with one incision allowing both a right nephrectomy that provides control tissue and clamping of the left renal pedicle to induce ischaemia of the left kidney. By careful monitoring of the clamp position and body temperature during the period of ischaemia this model achieves reproducible functional and structural injury. Mice sacrificed 24 hr following surgery demonstrate loss of renal function with elevation of the serum or plasma creatinine level as well as structural kidney damage with acute tubular necrosis evident. Renal function improves and the acute tissue injury resolves during the course of 7 days following renal IRI such that this model may be used to study renal regeneration. This model of renal IRI has been utilized to study the molecular and cellular pathophysiology of AKI as well as analysis of the subsequent renal regeneration.

Guidance cue netrin-1 and the regulation of inflammation in acute and chronic kidney disease

Acute kidney injury (AKI) is a common problem in the hospital setting and intensive care unit. Despite improved understanding, there are no effective therapies available to treat AKI. A large body of evidence strongly suggests that ischemia reperfusion injury is an inflammatory disease mediated by both adaptive and innate immune systems. Cell migration also plays an important role in embryonic development and inflammation, and this process is highly regulated to ensure tissue homeostasis. One such paradigm exists in the developing nervous system, where neuronal migration is mediated by a balance between chemoattractive and chemorepulsive signals. The ability of the guidance molecule netrin-1 to repulse or abolish attraction of neuronal cells expressing the UNC5B receptor makes it an attractive candidate for the regulation of inflammatory cell migration. Recent identification of netrin-1 as regulators of immune cell migration has led to a large number of studies looking into how netrin-1 controls inflammation and inflammatory cell migration. This review will focus on recent advances in understanding netrin-1 mediated regulation of inflammation during acute and chronic kidney disease and whether netrin-1 and its receptor activation can be used to treat acute and chronic kidney disease.

Mice with an absent stress response are protected against ischemic renal injury

Inducible heat shock proteins (HSP), regulated by heat shock factor-1 (HSF-1), protect against renal cell injury in vitro. To determine whether HSPs ameliorate ischemic renal injury in vivo, HSF-1functional knock-out mice (HSF-KO) were compared with wild-type mice following bilateral ischemic renal injury. Following injury, the kidneys of wild-type mice had the expected induction of HSP70 and HSP25; a response absent in the kidneys of HSF-KO mice. Baseline serum creatinine was equivalent between strains. Serum creatinines at 24 hours reflow in HSF-KO mice were significantly lower than in the wild-type. Histology showed similar tubule injury in both strains after ischemic renal injury but increased medullary vascular congestion in wild-type compared with HSF-KO mice. Flow-cytometry of mononuclear cells isolated from kidneys showed no difference between strains in the number of CD4⁺ and CD8⁺ T cells in sham operated animals. At 1 hour of reflow, CD4⁺ and CD8⁺ cells were doubled in the kidneys of wild type but not HSF-KO mice. Foxp3⁺ T regulatory cells were significantly more abundant in the kidneys of sham-operated HSF-KO than wild-type mice. Suppression of CD25⁺Foxp3⁺ cells in HSF-KO kidneys with the anti-CD25 antibody PC61 reversed the protection against ischemic renal injury. Thus, HSF-KO mice are protected from ischemic renal injury by a mechanism that depends on an increase in the T regulatory cells in the kidney associated with altered T cell infiltration early in reflow. Hence, stress response activation may contribute to early injury by facilitating T cell infiltration into ischemic kidney.