Raimund Pichler

Proteinuria in diabetic kidney disease: A mechanistic viewpoint

Proteinuria is the hallmark of diabetic kidney disease (DKD) and is an independent risk factor for both renal disease progression, and cardiovascular disease. Although the characteristic pathological changes in DKD include thickening of the glomerular basement membrane and mesangial expansion, these changes per se do not readily explain how patients develop proteinuria. Recent advances in podocyte and glomerular endothelial cell biology have shifted our focus to also include these cells of the glomerular filtration barrier in the development of proteinuria in DKD. This review describes the pathophysiological mechanisms at a cellular level which explain why patients with DKD develop proteinuria.

Delayed Graft Function and Cast Nephropathy Associated with Tacrolimus Plus Rapamycin Use

Delayed graft function (DGF) occurs in 15 to 25% (range, 10 to 62%) of cadaveric kidney transplant recipients and up to 9% of living donor recipients. In addition to donor, recipient, and procedural factors, the choice of immunosuppression may influence the development of DGF. The impact of immunosuppression on DGF was studied. The frequency of DGF was evaluated in first cadaveric or living donor kidney allograft recipients (n = 144) transplanted at the University of Washington from November 1999 through September 1, 2001. Donor, recipient, and procedural factors, as well as biopsy results, were compared between patients who developed DGF and those who did not. DGF was more common in patients treated with rapamycin than without (25% versus 8.9%, P = 0.02) and positively correlated with rapamycin dose (P = 0.008). In those developing DGF, the duration of posttransplant dialysis increased with donor age (P = 0.003) but decreased with mycophenolate mofetil use (P = 0.01). All biopsies during episodes of DGF demonstrated changes of acute tubular injury. Of the patients with tubular injury, 12 treated with rapamycin and tacrolimus developed intratubular cast formation indistinguishable from myeloma cast nephropathy. Histologic, immunohistochemical, and ultrastructural studies indicated that these casts were composed at least in part of degenerating renal tubular epithelial cells. These findings suggest that rapamycin therapy exerts increased toxicity on tubular epithelial cells and/or retards healing, leading to an increased incidence of DGF. Additionally, rapamycin treatment combined with a calcineurin inhibitor may lead to extensive tubular cell injury and death and a unique form of cast nephropathy.

IL-1 Up-Regulates Osteopontin Expression in Experimental Crescentic Glomerulonephritis in the Rat

Osteopontin (OPN) is a macrophage chemotactic and adhesion molecule that acts to promote macrophage infiltration in rat anti-glomerular basement membrane (GBM) glomerulonephritis. The present study investigated the role of interleukin-1 (IL-1) in the up-regulation of renal OPN expression in this disease model. Accelerated anti-GBM glomerulonephritis was induced in groups of six rats. Animals were treated by a constant infusion of the IL-1 receptor antagonist or saline (control) over days -1 to 14 (induction phase) or days 7 to 21 (established disease). In normal rat kidney, OPN was expressed in a few tubules (<5%) and absent from glomeruli. During the development of rat anti-GBM disease (days 7 to 21), there was substantial up-regulation of OPN mRNA and protein expression in glomeruli (>5 cells per glomerular cross-section) and tubular epithelial cells (50-75% OPN-positive). Up-regulation of OPN expression was associated with macrophage accumulation within the kidney, severe proteinuria, loss of renal function, and severe histological damage including glomerular crescentic formation and tubulointerstitial fibrosis. In contrast, IL-1 receptor antagonist treatment of either the induction phase of disease or established disease significantly reduced OPN mRNA and protein expression in glomeruli (/75-85%, P < 0.001) and tubules (/45-60%, P < 0.001). The reduction in OPN expression was associated with significant inhibition of macrophage accumulation and progressive renal injury. In vitro, the addition of IL-1 to the normal rat tubular epithelial cell line NRK52E up-regulated OPN mRNA and protein levels, an effect that was dose-dependent and inhibited by the addition of IL-1 receptor antagonist, thus demonstrating that IL-1 can act directly to up-regulate renal OPN expression. In conclusion, this study provides in vivo and in vitro evidence that IL-1 up-regulates OPN expression in experimental kidney disease and support for the argument that inhibition of OPN expression is one mechanism by which IL-1 receptor antagonist treatment suppresses macrophage-mediated renal injury.

Higher Levels of Leflunomide Are Associated with Hemolysis and Are not Superior to Lower Levels for BK Virus Clearance in Renal Transplant Patients

BACKGROUND AND OBJECTIVES Leflunomide use in renal transplantation has been increasing. Outcome correlation and safety data are still to be refined. The goals of this study were to report one centers experience with leflunomide, specifically the correlation of leflunomide levels with the outcomes of BK nephropathy and the observed toxic effects during the treatment with leflunomide. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS Leflunomide was used in 21 patients with BK nephropathy. These patients were divided into two groups on the basis of the leflunomide levels achieved: Low-level group (<40 microg/ml) and high-level group (>40 microg/ml). RESULTS During 13 mo of follow-up, there was no difference in the rate of serum BK viral clearance between the groups. There were three graft losses in the low-level group and one in the high-level group; however, creatinine levels were higher at the time of starting leflunomide in the low-level group. Leflunomide was also used in six patients with chronic allograft injury. No graft loss was observed during the follow-up period of 16 mo. Treatment with leflunomide seemed to be associated with a new toxicity, hemolysis, seen in four of the 27 patients so treated. Patients with hemolysis had high leflunomide levels (81.4 +/- 14 microg/ml) and worsening allograft function. Two patients had histologic evidence of thrombotic microangiopathy, which led to graft loss in one patient. CONCLUSIONS The clinical correlation between leflunomide levels and outcomes needs to be further refined. This study described a possible association of leflunomide with thrombotic microangiopathy, especially at higher levels.

The Role of Cell Cycle Proteins in Glomerular Disease

Although initially identified and characterized as regulators of the cell cycle and hence proliferation, an extended role for cell cycle proteins has been appreciated more recently in a number of physiologic and pathologic processes, including development, differentiation, hypertrophy, and apoptosis. Their precise contribution to the cellular response to injury appears to be dependent on both the cell type and the nature of the initiating injury. The glomerulus offers a remarkable situation in which to study the cell cycle proteins, as each of the 3 major resident cell types (the mesangial cell, podocyte, and glomerular endothelial cell) has a specific pattern of cell cycle protein expression when quiescent and responds uniquely after injury. Defining their roles may lead to potential therapeutic strategies in glomerular disease.

Cell cycle control in glomerular disease.

Abstract. The sequential activation of the cyclin-dependent kinases by their partner cyclins underlies the progression of the cell cycle from quiescence through growth to cell division. More recently a role for these proteins and their inhibitors has been appreciated in several diverse renal and non-renal cell processes, including proliferation, development, differentiation, hypertrophy and apoptosis. The glomerulus represents a unique micro-environment in which to study the cellular outcome following injury, as each of the three resident cell types undergoes a specific and distinct response to a given stimulus. The mesangial cell is capable of marked proliferation, often accompanied by the deposition of extracellular matrix. In contrast, the podocyte has previously been considered a relatively inert cell, and the reparative proliferation of glomerular endothelial cells following injury has recently been described. There is currently increasing awareness of the need to prevent, control and ameliorate the progression of renal diseases. Knowledge of the cell cycle and an understanding of how this may be beneficially manipulated may be crucial to improving the outlook for patients with both diabetic and non-diabetic glomerular disease.

Immunity and inflammation in diabetic kidney disease: translating mechanisms to biomarkers and treatment targets

Increasing incidences of obesity and diabetes have made diabetic kidney disease (DKD) the leading cause of chronic kidney disease and end-stage renal disease worldwide. Despite current pharmacological treatments, including strategies for optimizing glycemic control and inhibitors of the renin-angiotensin system, DKD still makes up almost one-half of all cases of end-stage renal disease in the United States. Compelling and mounting evidence has clearly demonstrated that immunity and inflammation play a paramount role in the pathogenesis of DKD. This article reviews the involvement of the immune system in DKD and identifies important roles of key immune and inflammatory mediators. One of the most recently identified biomarkers is serum amyloid A, which appears to be relatively specific for DKD. Novel and evolving treatment approaches target protein kinases, transcription factors, chemokines, adhesion molecules, growth factors, advanced glycation end-products, and other inflammatory molecules. This is the beginning of a new era in the understanding and treatment of DKD, and we may have finally reached a tipping point in our fight against the growing burden of DKD.

Dual Renin-Angiotensin-Aldosterone System Blockade for Diabetic Kidney Disease

Blockade of the renin-angiotensin-aldosterone system (RAAS) prevents the development and progression of diabetic kidney disease (DKD). It is controversial whether the simultaneous use of two RAAS inhibitors (ie, dual RAAS blockade) further improves renal outcomes. This review examines the scientific rationale and current clinical evidence addressing the use of dual RAAS blockade to prevent and treat DKD. It is concluded that dual RAAS blockade should not be routinely applied to patients with low or moderate risk of progressive kidney disease (normoalbuminuria or microalbuminuria with preserved glomerular filtration rate). For patients with high risk of progressive kidney disease (substantial albuminuria or impaired glomerular filtration rate), clinicians should carefully weigh the potential risks and benefits of dual RAAS blockade on an individual basis until ongoing clinical trials provide further insight.

Donor-recipient size matching influences early but not late graft function after pediatric en-bloc kidney transplantation.

Background. Pediatric en-bloc kidney transplantation into adult recipients is an accepted technique to expand the donor pool. Concerns about adequate “nephron dosing” have traditionally favored placing these kidneys into smaller recipients. Methods. We reviewed 20 pediatric en-bloc transplants performed at our institution between 2002 and 2008. We examined the impact of donor age, donor weight, recipient sex, combined kidney length, recipient weight, recipient-to-donor weight ratio, and recipient weight gain on serum creatinine over time using regression analysis. Results. Patient survival was 100%. Two grafts were lost early from vascular thrombosis. Of the remaining 18 recipients, all had immediate and excellent long-term function with average creatinine of 0.91±0.38 mg/dL at a mean follow-up of 1257±656 days. For 17 patients with 1 year follow-up, recipient weight, recipient-to-donor weight ratio, and recipient male sex negatively influenced renal function at 1 month. However, this relationship was lost by 1 year with increasing function in the smallest donors and largest size mismatches. Between 1 month and 1 year posttransplant, estimated creatinine clearance improved from 59±13 mL/min at 1 month posttransplant to 88±41 mL/min (P<0.015). Weight gain after transplant was associated with improved creatinine clearance, suggesting continued adaptation over time. Conclusions. We conclude that donor or recipient size matching up to a recipient-to-donor weight ratio of 7.5 does not significantly impact later renal function after pediatric en-bloc kidney transplantation into adults.

Mechanisms of progressive glomerulosclerosis and tubulointerstitial fibrosis

In this paper we provide an overview of the cellular changes that accompany progressive glomerulosclerosis and tubulointerstitial fibrosis. Emphasis is placed on the role of platelet-derived growth factor (PDGF) in the proliferation of the mesangial cell and interstitial fibroblast. PDGF also stimulates the synthesis and expression of a protein called secreted protein acidic and rich in cysteine (SPARC) and of thrombospondin 1 (TSP1). TSP1 may have an important role in the conversion of transforming growth factor (TGF)-β from its latent to active form. In turn, TGF-β appears to have a major role in mediating the extracellular matrix deposition that occurs with progressive glomerular and interstitial scarring.