Pravastatin improves renal ischemia-reperfusion injury by inhibiting the mevalonate pathway.

Statins are known to lessen the severity of renal ischemia-reperfusion injury. The present study was undertaken to define the mechanism of renoprotective actions of statins using a mouse kidney injury model. Treatment of mice with pravastatin, a widely used statin, improved renal function after renal ischemia-reperfusion without lowering the plasma cholesterol level. Administration of pravastatin with mevalonate, a product of HMG-CoA reductase, eliminated renal protection suggesting an effect of pravastatin on mevalonate or its metabolism. In hypercholestrolemic apolipoprotein E knockout mice with reduced HMG-CoA reductase activity; the degree of injury was less severe than in control mice, however, there was no protective action of pravastatin on renal injury in the knockout mice. Treatment with a farnesyltransferase inhibitor (L-744832) mimicked pravastatin's protective effect but co-administration with the statin provided no additional protection. Both pravastatin and L-744832 inhibited the injury-induced increase in plasma IL-6 concentration to a similar extent. Our results suggest the protective effect of pravastatin on renal ischemia-reperfusion injury is mediated by inhibition of the mevalonate-isoprenoid pathway independent of its lipid lowering action.

Transfer of lymphocytes from mice with renal ischemia can induce albuminuria in naive mice: a possible mechanism linking early injury and progressive renal disease?

Severe ischemia-reperfusion injury (IRI) predisposes to long-term impairment in kidney function both in patients and experimentally through unknown mechanisms. Given emerging evidence implicating lymphocytes in the pathogenesis of early injury to kidney, liver, and lung after IRI, we hypothesized that kidney IRI would potentially release or expose normally sequestered antigens that would lead to proliferation of antigen-recognizing lymphocytes. This, in turn, would directly participate in progressive kidney injury. To test this hypothesis, we purified splenic lymphocytes from C57BL/6 mice with severe renal IRI or sham operation 6 wk postischemia and transferred these cells to normal mice. Donor mice with IRI had significant fibrosis and cellular inflammation. The recipient mice were followed for 6 or 12 wk. Donor lymphocytes were found to traffic into recipient kidney. Twelve weeks after transfer, kidneys from mice which received IRI-primed lymphocytes exhibited significantly increased urinary albumin excretion compared with lymphocytes from sham mice. Splenic CD3(+), CD4(+), CD3(+)CD25(+), and CD4(+)CD44(+) counts were significantly increased in mice after lymphocyte transfer from IRI mice vs. mice with lymphocytes from sham mice. These data demonstrate that lymphocytes from IRI mice can traffic to recipient kidney and directly mediate albuminuria. These data identify a novel mechanism by which initial kidney injury predisposes to long-term dysfunction and identify lymphocytes as potential therapeutic targets for progressive renal diseases.

Decreased capacity of immune cells to cause tissue injury mediates kidney ischemic preconditioning.

Ischemic preconditioning (IP) is a well-established phenomenon, and the underlying mechanisms of IP are thought to involve adaptive changes within the injured tissue. Because one of the main functions of immune cells is to harbor memory, we hypothesized that circulating immune cells could mediate IP by responding to an initial ischemia reperfusion injury (IRI) and then mediate decreased injury after a second IRI event. C57BL/6 mice underwent 30 min of bilateral renal clamping or sham operation. At 5 days after ischemia, purified leukocytes from spleen were adoptively transferred into T cell-deficient (nu/nu) mice. After 1 wk, these mice underwent 30 min of renal IRI. The nu/nu mice receiving leukocytes from ischemic wild-type mice had significantly reduced renal injury compared with nu/nu mice receiving leukocytes from sham-operated, wild-type mice. Infiltration of neutrophil and macrophage in postischemic kidney did not correlate with the protection. No difference in kidney C3d or IgG deposition was detected between groups. Given that inducible NO synthase (iNOS) has been implicated in IP, leukocytes from ischemic or sham-operated, iNOS-deficient mice were transferred into nu/nu mice. Effects similar to those of wild-type transfer of ischemic leukocytes were demonstrated; thus, iNOS was not mediating the IP effect of leukocytes. This is the first evidence that immune cells are primed after renal IRI and thereby lose the capacity to cause kidney injury during a second episode of IRI. This finding may also be relevant for elucidating the mechanisms underlying cross-talk between injured kidney and distant organs.

Ischemic acute tubular necrosis models and drug discovery: a focus on cellular inflammation.

Acute renal failure (ARF) is a common cause of mortality and morbidity in hospitalized patients. Ischemia is an important cause of ARF, and ARF caused by ischemic injury is referred to as ischemic acute tubular necrosis (ATN). There is growing evidence from models that ischemic ATN is associated with intrarenal inflammation. Consequently, intrarenal inflammation is an attractive target for the development of novel drug therapies for ARF. This review outlines ischemic ATN models, the pathophysiological roles of inflammatory cells such as T and B cells in ischemic ATN models, and effective T and B cell therapeutic reagents.

Effects of combined T- and B-cell deficiency on murine ischemia reperfusion injury.

B and T cells have been implicated in the pathogenesis of renal ischemia reperfusion injury (IRI); however, it is unknown if B and T cells interact in early injury responses, as seen in adaptive immune responses. Recent evidence has shown that B-cell deficient and T-cell deficient mice are partially protected from renal IRI. Renal IRI was induced in recombinase activating gene (RAG)-1 deficient mice, which lack both B and T cells. RAG-1 deficient mice from two different background strains were not protected from renal IRI. Adoptive transfer of either B or T cells into RAG-1 deficient mice led to a significant protection of renal injury, which was independent of effects on neutrophil trafficking. Neutrophil depletion in RAG-1 deficient mice did not protect from IRI. While deficiency of either B or T cells reduced IRI, combined lack of both is not protective. These results demonstrate that complex interactions between B and T cells are likely occurring in kidney IRI.

Persistent renal and extrarenal immune changes after severe ischemic injury.

BACKGROUND: Renal ischemia/reperfusion (I/R) injury is associated with delayed graft function and decreased long-term allograft function. However, most experimental studies evaluating renal I/R injury have focused on acute events after ischemia. T cells are potential candidates to link preservation injury, alloimmunity, and fibrosis. We hypothesized that severe renal I/R injury would generate long-term kidney damage and immune changes. METHODS: C57BL/6 mice underwent 60 minutes of warm unilateral I/R injury or sham surgery and were studied for 6 weeks. Serum creatinine, renal histology, and albumin excretion were measured. Phagocyte infiltration, CD4+ infiltration, renal cytokine expression, and splenic lymphocyte intracellular cytokine production were also measured in mice at 6 weeks. RESULTS: Serum creatinine levels rose following 60 minutes of unilateral I/R injury compared to sham mice. Histologic analysis of ischemic kidneys at 6 weeks revealed a pronounced loss of tubular architecture and infiltration of inflammatory cells. Phagocyte and CD4+ T-cell infiltration were significantly increased in ischemic kidneys. This was accompanied by a significant increase in interleukin (IL)-1beta and regulated upon activation, normal T-cell expressed and secreted (RANTES) expression. Despite similar splenic CD4 and CD8 numbers, intracellular cytokine staining of T cells revealed a significant increase in interferon-gamma (IFN-gamma) in I/R injury mice compared to sham mice. CONCLUSION: Persistent renal and extrarenal immune responses occur after a single episode of severe I/R injury. These immune processes resulting from injury could in turn have long-term consequences on progression of renal disease in transplanted and native kidneys.

B cell deficiency confers protection from renal ischemia reperfusion injury.

Recent data have demonstrated a role for CD4(+) cells in the pathogenesis of renal ischemia reperfusion injury (IRI). Identifying engagement of adaptive immune cells in IRI suggests that the other major cell of the adaptive immune response, B cells, may also mediate renal IRI. An established model of renal IRI was used: 30 min of renal pedicle clamping was followed by reperfusion in B cell-deficient ( mu MT) and wild-type mice. Renal function was significantly improved in mu MT mice compared with wild-type mice at 24, 48, and 72 h postischemia. mu MT mice also had significantly reduced tubular injury. Both groups of mice had similar renal phagocyte infiltration postischemia assessed by myeloperoxidase levels and similar levels of CD4(+) T cell infiltration postischemia. Peritubular complement C3d staining was also similar in both groups. To identify the contribution of cellular vs soluble mechanism of action, serum transfer into mu MT mice partially restored ischemic phenotype, but B cell transfers did not. These data are the first demonstration of a pathogenic role for B cells in ischemic acute renal failure, with a serum factor as a potential underlying mechanism of action.

Acute renal failure after whole body ischemia is characterized by inflammation and T cell-mediated injury.

Acute renal failure (ARF) commonly occurs after whole body ischemia. Most experimental models of ARF have relied on the isolated renal artery clamping model; however, there is a pressing need to develop and understand the pathogenesis of new models with more "clinical relevance." We evaluated a new murine model of ARF after whole body ischemia reperfusion injury (WBIRI). WBIRI was induced by an infusion of potassium chloride and a cardiac arrest period of 10 min. Resuscitation was achieved by cardiac compressions, ventilation, epinephrine, and fluids. WBIRI leads to a significant increase in serum creatinine (SCr) and renal tubular injury by 24 h. Renal myeloperoxidase (MPO) levels increased at 24 h after WBIRI. Increased expression of the proinflammatory genes, ICAM-1 and IL-6, was also observed in the kidney following WBIRI. On the basis of recent data that T cells are important mediators of isolated renal IRI, WBIRI was evaluated in T cell-deficient nu/nu mice. T cell-deficient mice had a significantly reduced rise in SCr and decreased tubular injury compared with wild-type mice. T cell-deficient mice had a decrease in ICAM-1 expression after WBIRI, but no decrease in renal MPO. This study describes a new, clinically relevant, model of ARF after WBIRI in mice and identifies the T cell as an important mediator of renal injury following WBIRI. Reduced ICAM-1 expression may provide a mechanism for this involvement.

The role of adhesion molecules and T cells in ischemic renal injury.

PURPOSE OF REVIEW: The pathophysiology of ischemic acute renal failure is complex, incompletely understood and there are no specific therapies. Descriptive observations in human acute renal failure, as well as mechanistic studies in animals, have demonstrated an important pathophysiological role for leukocytes and leukocyte adhesion molecules. The purpose of this review is to summarize and interpret the recent advances on the role of T cells and leukocyte adhesion molecules in ischemic acute renal failure. RECENT FINDINGS: Emerging data suggest that the T cell is involved in modulating the outcome of ischemic acute renal failure, as well as ischemic injury to other organs. These new data build on the established role of inflammation in acute renal failure, and identify novel therapeutic targets. In addition, identification of the role of the T cell in the immediate injury response extends current immunological models of T cell function. Studies on leukocyte adhesion in acute renal failure have now identified the selectins and their ligands as important components of the inflammatory response to ischemic injury. SUMMARY: The identification of T cells and new adhesion molecule pathways as modulators of ischemic acute renal failure offers novel and feasible therapeutic opportunities for both native and transplant acute renal failure. Rigorous clinical trials are required to translate these basic findings to the bedside. In addition, mechanistic studies are needed to elucidate the molecular mechanisms by which these pathways modulate kidney injury. The identification of T cell engagement in ischemic renal injury can also help explain long-standing observations linking alloantigen-independent and alloantigen-dependent renal damage.