Efficacy and Safety of Bleselumab in Preventing the Recurrence of Primary Focal Segmental Glomerulosclerosis in Kidney Transplant Recipients: A Phase 2a, Randomized, Multicenter Study

BACKGROUND

Focal segmental glomerulosclerosis (FSGS) is a common cause of end-stage kidney disease and frequently recurs after kidney transplantation. Recurrent FSGS (rFSGS) is associated with poor allograft and patient outcomes. Bleselumab, a fully human immunoglobulin G4 anti-CD40 antagonistic monoclonal antibody, disrupts CD40-related processes in FSGS, potentially preventing rFSGS.

METHODS

A phase 2a, randomized, multicenter, open-label study of adult recipients (aged ≥18 y) of a living or deceased donor kidney transplant with a history of biopsy-proven primary FSGS. The study assessed the efficacy of bleselumab combined with tacrolimus and corticosteroids as maintenance immunosuppression in the prevention of rFSGS >12 mo posttransplantation, versus standard of care (SOC) comprising tacrolimus, mycophenolate mofetil, and corticosteroids. All patients received basiliximab induction. The primary endpoint was rFSGS, defined as proteinuria (protein-creatinine ratio ≥3.0 g/g) with death, graft loss, or loss to follow-up imputed as rFSGS, through 3 mo posttransplant.

RESULTS

Sixty-three patients were followed for 12 mo posttransplantation. Relative decrease in rFSGS occurrence through 3 mo with bleselumab versus SOC was 40.7% (95% confidence interval, -89.8 to 26.8; P = 0.37; absolute decrease 12.7% [95% confidence interval, -34.5 to 9.0]). Central-blinded biopsy review found relative (absolute) decreases in rFSGS of 10.9% (3.9%), 17.0% (6.2%), and 20.5% (7.5%) at 3, 6, and 12 mo posttransplant, respectively; these differences were not statistically significant. Adverse events were similar for both treatments. No deaths occurred during the study.

CONCLUSIONS

In at-risk kidney transplant recipients, bleselumab numerically reduced proteinuria occurrence versus SOC, but no notable difference in occurrence of biopsy-proven rFSGS was observed.

Chronic Microangiopathy Due to DCR-MYC, a Myc-Targeted Short Interfering RNA

Thrombotic microangiopathy (TMA) is an emerging complication of oncologic therapy. Cancer-related causes of renal endothelial cell damage include cytotoxic chemotherapies, radiation given for myeloablation, and direct involvement of renal vasculature by tumor cells. Another class of therapeutic agents that has been implicated in TMA is the vascular endothelial growth factor (VEGF) pathway inhibitors, including the anti-VEGF monoclonal antibody bevacizumab and the VEGF receptor tyrosine kinase inhibitor sunitinib. These TMAs have been termed type II cancer drug-induced TMA and are distinguished from those associated with some cytotoxic chemotherapies (ie, type I) in that they are not dose dependent and patients are more likely to demonstrate some recovery of kidney function. Determination of the cause of TMA in oncologic patients often presents a significant challenge because patients frequently receive multiple chemotherapeutic agents simultaneously and clinicopathologic features often demonstrate substantial overlap, regardless of cause. We present a case of TMA with predominantly chronic features in a 70-year-old patient being treated for adenoid cystic carcinoma of the breast with a single agent, a short interfering RNA targeted against Myc (DCR-MYC).

The Epidemiologic Burden of Tacrolimus Variability among Kidney Transplant Recipients in the United States

BACKGROUND

Within-patient tacrolimus level variability >30% has been shown to be a risk factor for de novo donor-specific antibody formation and death-censored graft failure among kidney transplant recipients. The burden of tacrolimus variability and the correlation between variability and subtherapeutic tacrolimus levels were examined in a large national data set.

METHODS

All tacrolimus levels drawn at LabCorp® facilities in the United States with a diagnosis code for kidney transplant between November 2011 and September 2017 were examined, excluding values that could represent new allografts. Tacrolimus variability was calculated if at least 3 levels were available. The percentage of subtherapeutic (<4.0 ng/dL) tacrolimus levels (%subT) was also calculated. Interdependence between %subT and tacrolimus variability was assessed with correlation analysis and linear regression.

RESULTS

There were 410,257 tacrolimus levels among 27,375 patients, who had 11 (interquartile range [IQR] 6-20) tacrolimus levels over a median follow-up of 26.5 (IQR 12.8-46.1) months. Median tacrolimus variability was 30.6%, and 51.6% of patients exceeded 30% variability. Median %subT was 11.1% (IQR 0-30.8%), and 34.3% of patients had no subtherapeutic levels. The correlation coefficient between tacrolimus variability and %subT was 0.253 (p< 0.001). In linear regression, tacrolimus variability increased 1.86% for each 10% increase in %subT (p < 0.001), but R-squared for this model was only 0.06.

CONCLUSION

More than half of established kidney transplant patients from a large national sample exhibited levels of tacrolimus variability that have been associated with inferior transplant outcomes. Tacrolimus variability has a weak association with subtherapeutic levels, but represents a more complicated constellation of clinical factors.

Hypertensive APOL1 risk allele carriers demonstrate greater blood pressure reduction with angiotensin receptor blockade compared to low risk carriers

Background

Hypertension (HTN) disproportionately affects African Americans (AAs), who respond better to thiazide diuretics than other antihypertensives. Variants of the APOL1 gene found in AAs are associated with a higher rate of kidney disease and play a complex role in cardiovascular disease.

Methods

AA subjects from four HTN trials (n = 961) (GERA1, GERA2, PEAR1, and PEAR2) were evaluated for blood pressure (BP) response based on APOL1 genotype after 4–9 weeks of monotherapy with thiazides, beta blockers, or candesartan. APOL1 G1 and G2 variants were determined by direct sequencing or imputation.

Results

Baseline systolic BP (SBP) and diastolic BP (DBP) levels did not differ based on APOL1 genotype. Subjects with 1–2 APOL1 risk alleles had a greater SBP response to candesartan (-12.2 +/- 1.2 vs -7.5 +/- 1.8 mmHg, p = 0.03; GERA2), and a greater decline in albuminuria with candesartan (-8.3 +/- 3.1 vs +3.7 +/- 4.3 mg/day, p = 0.02). APOL1 genotype did not associate with BP response to thiazides or beta blockers. GWAS was performed to determine associations with BP response to candesartan depending on APOL1 genotype. While no SNPs reached genome wide significance, SNP rs10113352, intronic in CSMD1, predicted greater office SBP response to candesartan (p = 3.7 x 10⁻⁷) in those with 1–2 risk alleles, while SNP rs286856, intronic in DPP6, predicted greater office SBP response (p = 3.2 x 10⁻⁷) in those with 0 risk alleles.

Conclusions

Hypertensive AAs without overt kidney disease who carry 1 or more APOL1 risk variants have a greater BP and albuminuria reduction in response to candesartan therapy. BP response to thiazides or beta blockers did not differ by APOL1 genotype. Future studies confirming this initial finding in an independent cohort are required.

Bowman capsulitis predicts poor kidney allograft outcome in T cell-mediated rejection

Acute T cell-mediated rejection (TCMR) is an important cause of renal allograft loss. The Banff classification for tubulointerstitial (type I) rejection is based on the extent of both interstitial inflammation and tubulitis. Lymphocytes may also be present between parietal epithelial cells and Bowman capsules in this setting, which we have termed "capsulitis." We conducted this study to determine the clinical significance of capsulitis. We identified 42 patients from the pathology archives at The University of Chicago with isolated Banff type I TCMR from 2010 to 2015. Patient demographic data, Banff classification, and graft outcome measurements were compared between capsulitis and noncapsulitis groups using Mann-Whitney U test. Capsulitis was present in 26 (62%) and was more frequently seen in Banff IB than in IA TCMR (88% versus 44%, P = .01). Patients with capsulitis had a higher serum creatinine at biopsy (4.6 versus 2.9 mg/dL, P = .04) and were more likely to progress to dialysis (42% versus 13%, P = .06), with fewer recovering their baseline serum creatinine (12% versus 38%, P = .08). Patients with both Banff IA TCMR and capsulitis have clinical outcomes similar to or possibly worse than Banff IB TCMR compared with those with Banff IA and an absence of capsulitis. Capsulitis is an important pathologic parameter in the evaluation of kidney transplant biopsies with potential diagnostic, prognostic, and therapeutic implications in the setting of TCMR.

Patient-Reported Barriers to the Prekidney Transplant Evaluation in an At-Risk Population in the United States

Background:

Despite our knowledge of barriers to the early stages of the transplant process, we have limited insight into patient-reported barriers to the prekidney transplant medical evaluation in populations largely at-risk for evaluation failure.

Methods:

One-hundred consecutive adults were enrolled at an urban, Midwestern transplant center. Demographic, clinical, and quality of life data were collected prior to patients visit with a transplant surgeon/nephrologist (evaluation begins). Patient-reported barriers to evaluation completion were collected using the Subjective Barriers Questionnaire 90-days after the initial medical evaluation appointment (evaluation ends), our center targeted goal for transplant work-up completion.

Results:

At 90 days, 40% of participants had not completed the transplant evaluation. Five barrier categories were created from the 85 responses to the Subjective Barriers Questionnaire. Patient-reported barriers included poor communication, physical health, socioeconomics, psychosocial influences, and access to care. In addition, determinants for successful evaluation completion included being of white race, higher income, free of dialysis, a lower comorbid burden, and reporting higher scores on the Kidney Disease Quality of Life subscale role-emotional.

Conclusion:

Poor communication between patients and providers, and among providers, was the most prominent patient-reported barrier identified. Barriers were more prominent in marginalized groups such as ethnic minorities and people with low income. Understanding the prevalence of patient-reported barriers may aid in the development of patient-centered interventions to improve completion rates.

TNF causes changes in glomerular endothelial permeability and morphology through a Rho and myosin light chain kinase-dependent mechanism

A key function of the endothelium is to serve as a regulated barrier between tissue compartments. We have previously shown that tumor necrosis factor (TNF) plays a crucial role in lipopolysaccharide (LPS)‐induced acute kidney injury, in part by causing injury to the renal endothelium through its receptor TNFR1. Here, we report that TNF increased permeability to albumin in primary culture mouse renal endothelial cells, as well as human glomerular endothelial cells. This process occurred in association with changes in the actin cytoskeleton and was associated with gaps between previously confluent cells in culture and decreases in the tight junction protein occludin. This process was dependent on myosin light chain activation, as seen by its prevention with Rho‐associated kinase and myosin light chain kinase (MLCK) inhibitors. Surprisingly, permeability was not blocked by inhibition of apoptosis with caspase inhibitors. Additionally, we found that the renal glycocalyx, which plays an important role in barrier function, was also degraded by TNF in a Rho and MLCK dependent fashion. TNF treatment caused a decrease in the size of endothelial fenestrae, dependent on Rho and MLCK, although the relevance of this to changes in permeability is uncertain. In summary, TNF‐induced barrier dysfunction in renal endothelial cells is crucially dependent upon the Rho/MLCK signaling pathway.

Complement in Lupus Nephritis: New Perspectives

BACKGROUND

Systemic lupus erythematosus (SLE) is an autoimmune disorder caused by loss of tolerance to self-antigens, the production of autoantibodies and deposition of complement-fixing immune complexes (ICs) in injured tissues. SLE is characterized by a wide range of clinical manifestations and targeted organs, with lupus nephritis being one of the most serious complications. The complement system consists of three pathways and is tightly controlled by a set of regulatory proteins to prevent injudicious complement activation on host tissue. The involvement of the complement system in the pathogenesis of SLE is well accepted; yet, its exact role is still not clear.

SUMMARY

Complement plays dual roles in the pathogenesis of SLE. On the one hand, the complement system appears to have protective features in that hereditary homozygous deficiencies of classical pathway components, such as C1q and C4, are associated with an increased risk for SLE. On the other hand, IC-mediated activation of complement in affected tissues is clearly evident in both experimental and human SLE along with pathological features that are logical consequences of complement activation. Studies in genetically altered mice have shown that lack of complement inhibitors, such as complement factor H (CFH) or decay-accelerating factor (DAF) accelerates the development of experimental lupus nephritis, while treatment with recombinant protein inhibitors, such as Crry-Ig, CR2-Crry, CR2-DAF and CR2-CFH, ameliorates the disease development. Complement-targeted drugs, including soluble complement receptor 1 (TP10), C1 esterase inhibitor and a monoclonal anti-C5 antibody (eculizumab), have been shown to inhibit complement safely, and are now being investigated in a variety of clinical conditions.

KEY MESSAGES

SLE is an autoimmune disorder which targets multiple systems. Complement is centrally involved and plays dual roles in the pathogenesis of SLE. Studies from experimental lupus models and clinical trials support the use of complement-targeted therapy in the treatment of SLE.

Transcriptional profiling reveals that C5a alters microRNA in brain endothelial cells

Blood-brain barrier (BBB) disturbance is a crucial occurrence in many neurological diseases, including systemic lupus erythematosus (SLE). Our previous studies showed that experimental lupus serum altered the integrity of the mouse brain endothelial layer, an important constituent of the BBB. Complement activation occurs in lupus with increased circulating complement components. Using a genomics approach, we identified the microRNA (miRNA) altered in mouse brain endothelial cells (bEnd3) by lupus serum and the complement protein, C5a. Of the 318 miRNA evaluated, 23 miRNAs were altered by lupus serum and 32 were altered by C5a alone compared with controls. Seven miRNAs (P < 0 · 05) were differentially expressed by both treatments: mmu-miR-133a*, mmu-miR-193*, mmu-miR-26b, mmu-miR-28*, mmu-miR-320a, mmu-miR-423-3p and mmu-miR-509-5p. The microarray results were validated by quantitative RT-PCR. In line with the in vitro results, expression of miR-26b and miR-28* were also significantly up-regulated in lupus mouse brain which was reduced by C5a receptor inhibition. Target prediction analysis revealed miR gene targets encoding components involved in inflammation, matrix arrangement, and apoptosis, pathways known to play important roles in central nervous system lupus. Our findings suggest that the miRNAs reported in this study may represent novel therapeutic targets in central nervous system lupus and other similar neuroinflammatory settings.

Cell cycle arrest in a model of colistin nephrotoxicity

Colistin (polymixin E) is an antibiotic prescribed with resurging frequency for multidrug resistant gram negative bacterial infections. It is associated with nephrotoxicity in humans in up to 55% of cases. Little is known regarding genes involved in colistin nephrotoxicity. A murine model of colistin-mediated kidney injury was developed. C57/BL6 mice were administered saline or colistin at a dose of 16 mg/kg/day in 2 divided intraperitoneal doses and killed after either 3 or 15 days of colistin. After 15 days, mice exposed to colistin had elevated blood urea nitrogen (BUN), creatinine, and pathologic evidence of acute tubular necrosis and apoptosis. After 3 days, mice had neither BUN elevation nor substantial pathologic injury; however, urinary neutrophil gelatinase-associated lipocalin was elevated (P = 0.017). An Illumina gene expression array was performed on kidney RNA harvested 72 h after first colistin dose to identify differentially expressed genes early in drug treatment. Array data revealed 21 differentially expressed genes (false discovery rate < 0.1) between control and colistin-exposed mice, including LGALS3 and CCNB1. The gene signature was significantly enriched for genes involved in cell cycle proliferation. RT-PCR, immunoblot, and immunostaining validated the relevance of key genes and proteins. This murine model offers insights into the potential mechanism of colistin-mediated nephrotoxicity. Further studies will determine whether the identified genes play a causative or protective role in colistin-induced nephrotoxicity.

Genetic and epigenetic variants contributing to clofarabine cytotoxicity

2-chloro-2-fluoro-deoxy-9-D-arabinofuranosyladenine (Clofarabine), a purine nucleoside analog, is used in the treatment of hematologic malignancies and as induction therapy for stem cell transplantation. The discovery of pharmacogenomic markers associated with chemotherapeutic efficacy and toxicity would greatly benefit the utility of this drug. Our objective was to identify genetic and epigenetic variants associated with clofarabine toxicity using an unbiased, whole genome approach. To this end, we employed International HapMap lymphoblastoid cell lines (190 LCLs) of European (CEU) or African (YRI) ancestry with known genetic information to evaluate cellular sensitivity to clofarabine. We measured modified cytosine levels to ascertain the contribution of genetic and epigenetic factors influencing clofarabine-mediated cytotoxicity. Association studies revealed 182 single nucleotide polymorphisms (SNPs) and 143 modified cytosines associated with cytotoxicity in both populations at the threshold P ≤ 0.0001. Correlation between cytotoxicity and baseline gene expression revealed 234 genes at P ≤ 3.98 × 10(-6). Six genes were implicated as: (i) their expression was directly correlated to cytotoxicity, (ii) they had a targeting SNP associated with cytotoxicity, and (iii) they had local modified cytosines associated with gene expression and cytotoxicity. We identified a set of three SNPs and three CpG sites targeting these six genes explaining 43.1% of the observed variation in phenotype. siRNA knockdown of the top three genes (SETBP1, BAG3, KLHL6) in LCLs revealed altered susceptibility to clofarabine, confirming relevance. As clofarabine's toxicity profile includes acute kidney injury, we examined the effect of siRNA knockdown in HEK293 cells. siSETBP1 led to a significant change in HEK293 cell susceptibility to clofarabine.

Endotoxemia alters tight junction gene and protein expression in the kidney

Intact tight junctional (TJ) proteins are required for tubular ion transport and waste excretion. Disruption of TJs may contribute to a decreased glomerular filtration rate in acute kidney injury (AKI) via tubular backleak. The effect of LPS-mediated AKI on murine TJs has not been studied extensively. We hypothesized LPS endotoxin administration to mice would disrupt tubular TJ proteins including zonula occludens-1 (ZO-1), occludin, and claudins. ZO-1 and occludin immunofluorescence 24 h post-LPS revealed a marked change in localization from the usual circumferential fencework pattern to one with substantial fragmentation. Renal ZO-1 expression was significantly reduced 24 h after LPS (decrease of 56.1 ± 7.4%, P < 0.001), with subsequent recovery. ZO-1 mRNA expression was increased 24 h post-LPS (4.34 ± 0.87-fold, P = 0.0019), suggesting disruption of ZO-1 protein is not mediated by transcriptional regulation, but rather by degradation or changes in translation. Similarly, claudin-4 protein expression was decreased despite elevated mRNA. LPS administration resulted in dephosphorylation of occludin and fragmented tubular redistribution. Protein expression of claudin-1, and -3 was increased after LPS. ZO-1, occludin, and claudin-1, -3, and -4 gene expression were increased 48 h after LPS, suggesting a renal response to strengthen TJs following injury. Interestingly, reduced mRNA expression was found only for claudin-8. This study provides further support that LPS-induced AKI is associated with structural injury and is not merely due to hemodynamic changes.

TNF induces caspase-dependent inflammation in renal endothelial cells through a Rho- and myosin light chain kinase-dependent mechanism

The pathogenesis of LPS-induced acute kidney injury (AKI) requires signaling through tumor necrosis factor-alpha (TNF) receptor 1 (TNFR1), which within the kidney is primarily located in the endothelium. We showed previously that caspase inhibition protected mice against LPS-induced AKI and in parallel significantly inhibited LPS-induced renal inflammation. Therefore we hypothesized that caspase activation amplifies TNF-induced inflammation in renal endothelial cells (ECs). In cultured renal ECs, TNF induced apoptosis through a caspase-8-dependent pathway. TNF caused translocation of the p65 subunit of NF-kappaB to the nucleus, resulting in upregulation of inflammatory markers such as adhesion molecules ICAM-1 and VCAM-1. However, the broad-spectrum caspase inhibitor Boc-d-fmk reduced NF-kB activation as assessed by gel shift assay, reduced phosphorylation of subunit IkappaBalpha, and significantly inhibited TNF-induced expression of ICAM-1 and VCAM-1 as assessed by both real-time PCR and flow cytometry. Broad-spectrum caspase inhibition markedly inhibited neutrophil adherence to the TNF-activated endothelial monolayer, supporting the functional significance of this effect. Specific inhibitors of caspases-8 and -3, but not of caspase-1, reduced TNF-induced NF-kappaB activation. Caspase inhibition also reduced TNF-induced myosin light chain (MLC)-2 phosphorylation, and activation of upstream regulator RhoA. Consistent with this, MLC kinase (MLCK) inhibitor ML-7 reduced TNF-induced NF-kappaB activation. Thus caspase activation influences NF-kappaB signaling via its affect on cytoskeletal changes occurring through RhoA and MLCK pathways. These cell culture experiments support a role for caspase activation in TNF-induced inflammation in the renal endothelium, a key event in LPS-induced AKI.

The role of ICAM-1 in endotoxin-induced acute renal failure

The pathogenesis of acute renal failure (ARF) occurring during the course of sepsis is incompletely understood. Intercellular adhesion molecule-1 (ICAM-1) is a key cell adhesion molecule upregulated by LPS, which binds to the integrins CD11a/CD18 and CD11b/CD18 present on the surface of leukocytes. We hypothesized that ICAM-1 facilitates renal injury in LPS-induced ARF. To test this, three groups of mice (n = 8 per group) were injected intraperitoneally with 6 mg/kg LPS: 1) normal C57BL/6 mice, 2) mice with a targeted deficiency of ICAM-1 (ICAM-1(-/-)), and 3) mice expressing very low levels of CD18 (CD18-def). ICAM-1(-/-) mice were significantly resistant to LPS-mediated ARF, as opposed to CD18-def mice, which developed severe ARF, as did wild-type controls (48 h blood urea nitrogen 143 +/- 31.5, 70.8 +/- 24.4, and 185 +/- 16.6 mg/dl in wild-type, ICAM-1(-/-), and CD18-def mice, respectively, P < 0.05). At death, ICAM-1(-/-) mice had significantly less renal neutrophil infiltration than the other two groups, as well as less histological tubular injury. Depletion of neutrophils with mAb Gr-1 led to a profound exaggeration of tumor necrosis factor (TNF) release and high mortality, but neutrophil-depleted mice receiving 10-fold less LPS were protected against ARF despite TNF release similar to what is normally associated with LPS-induced ARF. LPS caused a significant increase in renal expression of chemokines; however, this increase was significantly exaggerated in CD18-def mice, which may account for their lack of protection. In conclusion, these data show that ICAM-1 plays a key role in LPS-induced ARF.

Contrasting roles of complement activation and its regulation in membranous nephropathy

The complement system is involved in defense against microorganisms, the processing of immune complexes and apoptotic debris, and the development of an appropriate immune response. Along with these physiologic effects, complement activation has the potential to result in tissue pathology. To limit this, various complement regulatory proteins (CRP) are present on host cells, including the glomerular podocyte. Experimental data from the Heymann nephritis (HN) rat model of human membranous nephropathy (MN) have shown that IgG antibodies in subepithelial immune deposits initiate complement activation and C5b-9-mediated damage of the overlying podocyte. Although IgG can activate the classical pathway, there also is evidence that alternative pathway activation occurs in MN, which could occur because of absent, dysfunctional, or inhibited podocyte CRP. Related to this are experimental data in HN showing the presence of antibodies that bind and inhibit podocyte CRP; although such antibodies have not been documented in human MN, a decrease in CR1 quantity on the podocyte has been observed. A s a result of a relative lack of CRP and the exposure of activating complement proteins to tubular cells, alternative complement pathway activation and C5b-9-mediated tubular injury can occur in MN and other proteinuric diseases. Overall, in a disease such as MN, the balance between complement regulation and activation is tipped toward its being activated. Therefore, a number of therapeutic approaches have been developed to counteract this, including recombinant forms of endogenous CRP and complement-inhibitory monoclonal antibodies. There is good reason to be optimistic that approaches to block complement activation will become viable therapy for human MN in the future.

Acute renal failure in endotoxemia is dependent on caspase activation

In previous work, it was demonstrated that apoptosis occurs in the kidney during LPS-induced acute renal failure (ARF). However, the relative importance of apoptosis in LPS-induced ARF remained unproven. Because the caspase enzyme cascade is responsible for carrying out apoptosis, it was hypothesized that treatment with a caspase inhibitor would protect mice from LPS-induced ARF. C57BL/6 mice received an injection of LPS and were treated with either the broad-spectrum caspase inhibitor z-VAD-fmk or vehicle and compared with unmanipulated mice. LPS induced a significant increase in caspase-3 activity in vehicle-treated mice, which was significantly inhibited by z-VAD. Mice that were treated with z-VAD were protected from ARF and demonstrated significantly less apoptosis as measured by both terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling staining and DNA laddering. Although apoptosis is classically described as a noninflammatory process, z-VAD treatment significantly attenuated multiple markers of inflammation, such as renal neutrophil infiltration and renal expression of the neutrophil chemotactic factor macrophage inflammatory protein-2. Thus, caspase inhibition may protect against LPS-induced ARF not only by preventing apoptotic cell death but also by inhibiting inflammation. These data raise the possibility that apoptotic kidney cells may actually be a source of this local inflammation, contributing to subsequent nonapoptotic renal injury.

Role of Toll-like receptor 4 in endotoxin-induced acute renal failure

Toll-like receptor 4 (TLR4) is present on monocytes and other cell types, and mediates inflammatory events such as the release of TNF after exposure to LPS. C3H/HeJ mice are resistant to LPS-induced mortality, due to a naturally occurring mutation in TLR4. We therefore hypothesized that LPS-induced acute renal failure (ARF) requires systemic TNF release triggered by LPS acting on extrarenal TLR4. We injected C3H/HeJ mice and C3H/HeOuJ controls with 0.25 mg of LPS, and sacrificed them 6 h later for analysis of blood urea nitrogen (BUN) and kidney tissue (n = 8 per group). In contrast to C3H/HeOuJ controls, C3H/HeJ mice were completely resistant to LPS-induced ARF (6-h BUN of 32.3 +/- 1.1 vs 61.7 +/- 5.6 mg/dl). C3H/HeJ mice released no TNF into the circulation at 2 h (0.00 vs 1.24 +/- 0.16 ng/ml), had less renal neutrophil infiltration (6.4 +/- 1.0 vs 11.4 +/- 1.3 neutrophils per high power field), and less renal apoptosis, as assessed by DNA laddering. Transplant studies showed that C3H/HeJ recipients of wild-type kidneys (n = 9) were protected from LPS-induced ARF, while wild-type recipients of C3H/HeJ kidneys (n = 11) developed severe LPS-induced ARF (24-h BUN 44.0 +/- 4.1 vs 112.1 +/- 20.0 mg/dl). These experiments support our hypothesis that LPS acts on extrarenal TLR4, thereby leading to systemic TNF release and subsequent ARF. Renal neutrophil infiltration and renal cell apoptosis are potential mechanisms by which endotoxemia leads to functional ARF.

Decay-accelerating factor expression in the rat kidney is restricted to the apical surface of podocytes

BACKGROUND

Decay-accelerating factor (DAF) has inhibitory activity toward complement C3 and C5 convertases. DAF is present in human glomeruli and on cultured human glomerular visceral epithelial cells (GEC). We studied the distribution and function of rat DAF.

METHODS

Function-neutralizing antibodies (Abs) were raised against DAF. The distribution of DAF in vivo was determined by immunoelectron microscopy. Functional studies were performed in cultured GEC and following IV injection of anti-DAF Abs into rats.

RESULTS

DAF was present exclusively on the apical surfaces of GEC, and was not present on the basal surfaces of GEC, nor other glomerular or kidney cells. DAF was functionally active on cultured GEC, and served to limit complement activation in concert with CD59, an inhibitor of C5b-9 formation. Upon injection into normal rats, anti-DAF F(ab')2 Abs bound to GEC in vivo, yet there was no evidence for complement activation and animals did not develop abnormal albuminuria. Anti-megalin complement-activating IgG Abs were "planted" on GEC, which activated complement as evidenced by the presence of C3d on GEC. Attempts to inhibit DAF function with anti-DAF Abs did not affect the quantity of complement activation by these anti-megalin Abs, nor did it lead to development of abnormal albuminuria. In contrast, in the puromycin aminonucleoside model of GEC injury and proteinuria, anti-DAF Abs slowed the recovery from renal failure that occurs in this model.

CONCLUSION

In cultured rat GEC, DAF is an effective complement regulator. In vivo, DAF is present on GEC apical surfaces. Yet, it appears that DAF is not essential to prevent complement activation from occurring under normal circumstances and in those cases in which complement-activating Abs are present on the basal surfaces of GEC in vivo. However, in proteinuric conditions, DAF appears to be protective to GEC.

Acute renal failure in endotoxemia is caused by TNF acting directly on TNF receptor-1 in kidney

Bacterial endotoxin (LPS) is responsible for much of the widespread inflammatory response seen in sepsis, a condition often accompanied by acute renal failure (ARF). In this work we report that mice deficient in TNFR1 (TNFR1(-/-)) were resistant to LPS-induced renal failure. Compared with TNFR1(+/+) controls, TNFR1(-/-) mice had less apoptosis in renal cells and fewer neutrophils infiltrating the kidney following LPS administration, supporting these as mediators of ARF. TNFR1(+/+) kidneys transplanted into TNFR1(-/-) mice sustained severe ARF after LPS injection, which was not the case with TNFR1(-/-) kidneys transplanted into TNFR1(+/+) mice. Therefore, TNF is a key mediator of LPS-induced ARF, acting through its receptor TNFR1 in the kidney.

A complement-dependent model of thrombotic thrombocytopenic purpura induced by antibodies reactive with endothelial cells

Thrombotic thrombocytopenic purpura (TTP) is an immunologically mediated disease characterized by thrombocytopenia, hemolytic anemia, and pathologic changes in various organs, including the kidney, which are secondary to widespread thromboses. Central to TTP is platelet activation, which may occur from a variety of mechanisms, including endothelial cell activation or injury. In this study, injection of K6/1, a monoclonal antibody with widespread reactivity toward endothelia, led to dose-dependent thrombocytopenia in rats. This was magnified if animals were preimmunized with mouse IgG, thereby resulting in an accelerated autologous phase of injury. In this setting, significant anemia also resulted. Rats injected with K6/1 developed renal injury, consisting of tubular damage and glomerular thrombi. Thrombocytopenia and renal morphological abnormalities were eliminated if animals were complement depleted with cobra venom factor prior to K6/1 injection and worsened when the activity of the ubiquitous complement regulator Crry was inhibited with function-neutralizing antibodies. Therefore, we have developed a complement-dependent model of TTP in rats by injecting monoclonal antibodies reactive with endothelial cells. Antibody-directed complement activation leads to stimulation of platelets, through direct interactions with complement fragments and/or indirectly through endothelial cell activation or injury, with the subsequent development of TTP.

Transgenic expression of a soluble complement inhibitor protects against renal disease and promotes survival in MRL/lpr mice

To investigate the role of complement in lupus nephritis, we used MRL/lpr mice and a transgene overexpressing a soluble complement regulator, soluble CR1-related gene/protein y (sCrry), both systemically and in kidney. Production of sCrry in sera led to significant complement inhibition in Crry-transgenic mice relative to littermate transgene negative controls. This complement inhibition with sCrry conferred a survival advantage to MRL/lpr mice. In a total of 154 animals, 42.5% transgene-negative animals had impaired renal function (blood urea nitrogen > 50 mg/dl) compared with 16.4% mice with the sCrry-producing transgene (p < 0.001). In those animals that died spontaneously, MRL/lpr mice with the sCrry-producing transgene did not die of renal failure, while those without the transgene did (blood urea nitrogen values of 46.6 +/- 9 and 122 +/- 29 mg/dl in transgene-positive and transgene-negative animals, respectively; p < 0.001). Albuminuria was reduced in those transgenic animals in which sCrry expression was maximally stimulated (urinary albumin/creatinine = 12.4 +/- 4.3 and 36.9 +/- 7.7 in transgene-positive and transgene-negative animals, respectively; p < 0.001). As expected in the setting of chronic complement inhibition, there was less C3 deposition in glomeruli of sCrry-producing transgenic mice compared with transgene-negative animals. In contrast, there was no effect on glomerular IgG deposition, levels of anti-dsDNA Ab and rheumatoid factor, or spleen weights between the two groups. Thus, long-term complement inhibition reduces renal disease in MRL/lpr mice, which translates into improved survival. MRL/lpr mice in which complement is inhibited still have spontaneous mortality, yet this is not from renal disease.

Injury in renal ischemia-reperfusion is independent from immunoglobulins and T lymphocytes

Ischemia-reperfusion injury (IRI) is a complex and incompletely understood process involving a cascade of events that culminates in apoptotic and/or necrotic cell death. Natural IgM antibodies and complement have been implicated in the pathogenesis of IRI in a variety of organ systems as have T lymphocytes in renal IRI. To investigate the role of Ig and T lymphocytes in renal IRI, recombination-activating gene (RAG)-1-deficient mice were studied. RAG-1(-/-) mice were not protected from acute renal failure induced by 27.5 min of bilateral renal ischemia and subsequent reperfusion [serum urea nitrogen levels 30 h after reperfusion, 155.2 +/- 5.6 and 152.8 +/- 11.4 mg/dl in RAG-1(-/-) and wild-type mice, respectively; n = 13 each]. Histological examination showed acute tubular necrosis and neutrophilic infiltration with no significant differences between groups. In contrast with other organ systems, Igs were not found in kidneys at time points ranging from 1 min to 30 h after ischemia. Thus Igs and mature T lymphocytes do not appear to play a significant role in the pathogenesis of IRI in the kidney.

Glomerular complement regulation is overwhelmed in passive Heymann nephritis

BACKGROUND

An injection of anti-Fx1A antibodies in rats leads to passive Heymann nephritis (PHN), a model of membranous nephropathy. Fx1A is a crude extract of renal cortex that contains megalin as a principal component. However, when rats are given anti-megalin antibodies, abnormal proteinuria does not occur. Because of the established complement dependence of PHN, we hypothesized that antibodies neutralizing complement regulatory proteins in the rat glomerulus also were required to induce PHN. Two likely targets are Crry and CD59, proteins abundant on the rat podocyte and contained within Fx1A that inhibit the C3 convertase and C5b-9 assembly, respectively.

METHODS

Rats were injected with anti-megalin monoclonal antibodies, followed by anti-Crry and/or anti-CD59 F(ab')(2) antibodies five days later. In a second group of experiments, rats were injected with anti-Fx1A or anti-Fx1A immunodepleted of reactivity against Crry and/or CD59.

RESULTS

In the setting of podocyte-associated anti-megalin monoclonal antibodies, simultaneous neutralization of Crry and CD59 function led to the development of significant proteinuria (11.0 +/- 2.1 mg/day, P < 0.001 vs. all other groups). In contrast, animals that had neither or only one of these complement regulators inhibited had normal urinary protein excretion (< or =6 mg/day). In animals given anti-Fx1A depleted of anti-Crry and/or anti-CD59, all groups developed typical PHN, characterized by heavy proteinuria and extensive glomerular deposition of C3 and C5b-9.

CONCLUSION

Crry and CD59 play an important role in restraining complement-mediated injury following subepithelial immune complex deposition; however, in PHN, their regulatory capacity is overwhelmed.

A protein with characteristics of factor H is present on rodent platelets and functions as the immune adherence receptor

Complement-coated particles interact with specific immune adherence receptors (IAR). In primates, this function is served by complement receptor 1 (CR1) on erythrocytes. In contrast, rodent platelets bear IAR distinct from CR1, the identity of which was studied here. A 150-kDa C3b-binding protein was isolated from rat platelets, which had immunochemical and biochemical identity to plasma factor H. Immunofluorescence microscopy and flow cytometry demonstrated that factor H was present on the surface of rat and mouse platelets, which could be removed by treatment with neuraminidase. Sheep erythrocytes bearing C3b underwent immune adherence with rat and mouse platelets, which was blocked with anti-factor H F(ab')(2) antibodies, but not with antibodies binding to the complement regulator, Crry, on the platelet surface. By reverse transcription-polymerase chain reaction using rat platelet RNA and primers designed from mouse factor H, a 472-base pair product was generated that was identical in sequence to that produced from rat liver RNA. The translated protein product was 85% similar to mouse liver factor H. The 3'-nucleotide sequence from platelets predicted a soluble factor H protein. By Northern analysis, liver and platelets had identically sized factor H mRNA. Thus, rat and mouse platelets have a membrane protein with characteristics of factor H that is linked via sialic acid residues and functions as the IAR. Whether platelet factor H is acquired by passive adsorption from sera and/or is produced by platelets remains to be determined.

Inhibiting the complement system does not reduce injury in renal ischemia reperfusion

The complex pathogenesis of ischemia reperfusion injury (IRI) includes endothelial expression of adhesion molecules, leukocyte recruitment and activation, reactive oxygen species production, and apoptotic and necrotic cell death. A role for complement in IRI of different organs, including kidney, has been proposed on the basis of results of experiments that used pharmacologic inhibitors as well as animals that were deficient in individual complement proteins. Here, renal IRI in mice was examined. Animals that were deficient in C3 had partial protection from IRI induced by 27.5 min of bilateral renal ischemia, followed by 20 h of reperfusion (blood urea nitrogen [BUN] values, 46.6 +/- 6.9 and 68.4 +/- 7.9 mg/dl in C3 -/- and C3 +/+ mice; n = 7 and 8, respectively; P = 0.033). Given the reduction in IRI in C3 -/- mice, it was investigated, by use of the rodent C3 convertase inhibitor CR1-related gene/protein y-Ig (Crry-Ig), whether exogenous administration of a complement inhibitor could lessen renal injury. Despite the use of Crry-Ig in high doses, there was no significant reduction of injury induced by 20 to 30 min of ischemia followed by up to 30 h of reperfusion. Histologic examination revealed acute tubular necrosis and neutrophilic infiltration, both of which correlated significantly with BUN values (P < 0.001). Of interest, C3 deposition around renal tubules was significantly less in animals with IRI, compared with that in unmanipulated controls (P < 0.001). In Crry-Ig-treated animals, C3 deposition was inversely proportional to BUN values (r = -0.63; P < 0.001), which presumably indicates that severe vascular IRI allowed access of the 160 kD Crry-Ig to the interstitium. Thus, renal IRI in mice may have a partial complement dependence, yet pharmacologic inhibition of the complement system does not seem to be effective, likely because of the presence of other mediator systems that operate in parallel.

Expression of a soluble complement inhibitor protects transgenic mice from antibody-induced acute renal failure

Crry is a potent complement regulator in rodents that inhibits C3 convertases. In rats, intrarenal arterial injection of anti-glomerular endothelial cell (GEN) antibodies leads to complement-dependent microvascular injury and acute renal failure. In this study, a mouse variant of this model and the effects of complement inhibition were examined. Transgenic mice that overexpressed soluble Crry systemically and in their kidneys were studied. Anti-GEN IgG was injected intravenously into eight Crry transgenic mice and seven transgene-negative littermates (which were used as control animals). Thirty h after injection, blood urea nitrogen (BUN) levels were 30.3 +/- 4.4 and 114.8 +/- 23.5 mg/dl for transgene-positive and -negative animals, respectively (P = 0.012). Four of five transgene-negative animals with BUN levels of > 100 mg/dl were anuric; the remaining animal exhibited minimal albuminuria and no detectable urinary C3. In animals with renal failure, glomerular capillary collapse and tubular necrosis were observed. There was significant tubular staining for C3 in transgene-negative animals, with cellular and basal distributions, both of which were statistically greater than those in transgene-positive animals. Tubular cell C3 staining was strongly correlated with BUN values (r = 0.83, P < 0.001), as was C9 staining (r = 0.56, P = 0.037), suggesting that complement activation to the C5b-9 membrane attack complex had a casual role in renal failure. Thus, systemic injection of anti-GEN antibodies into mice leads to acute renal failure, with glomerular and tubular injury. Animals that overexpress soluble Crry in renal tubules and elsewhere are protected from the acute renal failure that occurs in this model, which ultimately seems to develop because of complement activation focused on tubules.

Complement is activated in kidney by endotoxin but does not cause the ensuing acute renal failure

BACKGROUND

Acute renal failure (ARF) in sepsis occurs when the release of multiple inflammatory mediators is induced by bacterial endotoxins. C3 mRNA is markedly up-regulated in mouse kidney after exposure to lipopolysaccharide (LPS). We hypothesized that LPS could induce tubular synthesis and secretion of C3, leading to activation of the complement cascade and direct renal tubular injury.

METHODS

ARF was induced in mice by intravenous injection of LPS and was confirmed by an acute rise in blood urea nitrogen (BUN) and histologically by acute tubular necrosis. Three separate strategies were used to investigate the role of the complement system in this model of ARF: (1) Crry-Ig, a recombinant protein containing the potent murine complement C3 activation inhibitor Crry was injected at the same time as LPS (N = 8). (2) LPS was injected into transgenic mice overexpressing Crry in glomeruli and tubules (N = 8), and (3) LPS was injected into C3-deficient mice (N = 5).

RESULTS

Compared with unmanipulated mice, C3 staining by immunofluorescence (IF) microscopy in mice injected with LPS was greater in renal cortical tubular cells (IF score of 2. 1 +/- 0.1 vs. 1.4 +/- 0.2 in controls, P = 0.013), most prominently at the basolateral surface. LPS injection led to a 16- to 42-fold increase in urinary C3 excretion. Despite reduction or complete elimination of renal C3 with maneuvers suppressing complement activation, BUN values were not statistically different across all groups. In no experiment did BUN values correlate with the extent of C3 staining.

CONCLUSION

Although LPS up-regulates renal C3 synthesis, resulting in basolateral tubular C3 deposition, this is not responsible for LPS-induced ARF in mice.