Lupus Nephritis; Kidney Biopsy; Systemic Lupus Erythematosus
Glomerular disease is a complex and evolving topic. In evaluating a specific case it is not unusual for the clinician to ask: Am I missing something? Should I biopsy? When? Should I treat first, then biopsy? This work, which is both evidence based and experience based, is intended to address each of these concerns, and many other issues relevant to the differential diagnosis of glomerular disease.
The central approach is the use of diagnostic algorithms that are based on quantitative measures routinely obtained early in the course of the diagnostic evaluation. The algorithms are designed to be easy to navigate, systematic, and inclusive. Also provided is a detailed and prioritized list of recommended diagnostic testing, and the rationale for each test.
This work is intended to facilitate accurate diagnosis in the individual patient presenting with evidence of glomerular disease.
glomerular disease; proteinuria; glomerulonephritis
Immune complex accumulation in the kidney is the hallmark of lupus nephritis and triggers a series of events that result in kidney inflammation and injury. Cytotoxic agents and corticosteroids are standard of care for lupus nephritis treatment, but are associated with considerable morbidity and suboptimal outcomes. Recently, there has been interest in using novel biologic agents and small molecules to treat lupus nephritis. These therapies can be broadly categorized as anti-inflammatory (laquinamod, anti–tumor necrosis factor–like weak inducer of apotosis, anti-C5, and retinoids), antiautoimmunity (anti-CD20, anti–interferon α, and costimulatory blockers), or both (anti–interleukin 6 and proteasome inhibitors). Recent lupus nephritis clinical trials applied biologics or small molecules of any category to induction treatment, seeking short-term end points of complete renal response. These trials in general have not succeeded. When lupus nephritis comes to clinical attention during the inflammatory stage of the disease, the autoimmune stage leading to kidney inflammation will have been active for some time. The optimal approach for using novel therapies may be to initially target kidney inflammation to preserve renal parenchyma, followed by suppression of autoimmunity. In this review, we discuss novel lupus nephritis therapies and how they fit into a combinatorial treatment strategy based on the pathogenic stage.
Lupus nephritis; systemic lupus erythematosus (SLE); novel therapies; biologics; small molecules
Biomarkers that evaluate the response to erythropoietic-stimulating agents largely measure inflammation and iron availability. While these are important factors in modifying an individual’s response to these agents, they do not address all aspects of a poor response. To clarify this, we isolated peptides in the serum of good and poor responders to erythropoietin in order to identify biomarkers of stimulating agent response. Ninety-one candidate biomarker targets were identified and characterized using mass spectrometry, of which tandem mass spectroscopy provided partial amino-acid sequence information of 17 different peptides for 16 peptide masses whose abundance significantly differed between poor and good responders. The analysis concluded that three peptides associated with a poor response were derived from oncostatin M receptor β (OSMRβ). The 13 serum peptides associated with a good response were derived from fibrinogen α and β, coagulation factor XIII, complement C3, and cysteine/histidine rich 1(CYHR1). Poor response was most strongly associated with the OSMRβ fragment with the largest molecular weight, while a good response was most strongly associated with CYHR1. Immunoblots found the abundance of intact OSMRβ and CYHR1 significantly differed between good and poor responders. Thus, two measurable biomarkers of the response to erythropoietic-stimulating agents are present in the serum of treated patients.
anemia; biomarker; erythropoietic; hemodialysis; peptidomics
Systemic lupus erythematosus (SLE) is a prototypic, inflammatory autoimmune disease characterized by significant gender bias. Previous studies have established a role for hormones in SLE pathogenesis, including the sex hormone estrogen. Estrogen regulates gene expression by translocating estrogen receptors (ER) α and β into the nucleus where they induce transcription by binding to estrogen response elements (EREs) of target genes. The ZAS3 locus encodes a signaling and transcriptional molecule involved in regulating inflammatory responses. We show that ZAS3 is significantly up-regulated in SLE patients at both the protein and mRNA levels in peripheral blood mononuclear cells (PBMCs). Furthermore, estrogen stimulates the expression of ZAS3 in vitro in several leukocyte and breast cancer cell lines of both human and murine origin. In vivo estrogen treatment mediates induction of tissue specific ZAS3 expression in several lymphoid organs in mice. Estrogen stimulation also significantly up-regulates ZAS3 expression in primary PBMCs, while treatment with testosterone has no effect. Mechanistically, estrogen induces differential ERα binding to putative EREs within the ZAS3 gene and ERα knockdown with siRNA prevents estrogen induced ZAS3 up-regulation. In contrast, siRNA targeting IFNα has no effect. These data demonstrate that ZAS3 expression is directly regulated by estrogen and that ZAS3 is overexpressed in lupus. Since ZAS3 has been shown to regulate inflammatory pathways, its up-regulation by estrogen could play a critical role in female-biased autoimmune disorders.
Systemic lupus erythematosus; estrogen; ZAS3; autoimmunity
To study the level of high-sensitivity C-reactive protein (hsCRP) and its relationship with disease activity, damage and cardiovascular risk factors in patients with systemic lupus erythematosus (SLE).
Consecutive patients who fulfilled ≥4 ACR criteria for SLE but did not have concurrent infection were recruited. Blood was assayed for hsCRP and disease activity, organ damage of SLE and cardiovascular risk factors were assessed. Linear regression was performed for the relationship among hsCRP, SLE activity, damage and cardiovascular risk factors.
289 patients were studied (94% women; age 39.0±13.1 years; SLE duration 7.8±6.7 years). The mean SLEDAI score was 4.9±5.6 and clinically active SLE was present in 122(42%) patients. The mean hsCRP level was 4.87±12.7mg/L, and 28(23%) patients with active SLE had undetectable hsCRP (<0.3mg/L). Linear regression revealed a significant correlation between hsCRP and musculoskeletal (Beta=0.21), hematological (Beta=0.19), serosal (Beta=0.46) and clinical SLEDAI score (Beta=0.24), adjusting for age, sex, body mass index, creatinine and the use of various medications (p<0.005 in all). Levels of hsCRP correlated significantly with anti-dsDNA titer (Beta=0.33;p<0.001) but not with complement C3 (Beta=0.07;p=0.26). Significantly more patients with hsCRP >3.0mg/L were men and chronic smokers, and had diabetes mellitus, higher atherogenic index and history of arterial thrombosis. hsCRP levels correlated significantly with pulmonary and endocrine damage score.
hsCRP is detectable in 77% of SLE patients with clinically active disease and correlates with SLEDAI scores, particularly serositis and in the musculoskeletal and hematological systems. Elevated hsCRP in SLE is associated with certain cardiovascular risk factors and history of arterial thromboembolism.
C-reactive protein; acute phase; disease activity; cardiovascular; damage; outcome
This paper describes a simple, highly efficient and robust proteomic workflow for routine liquid-chromatography tandem mass spectrometry analysis of Laser Microdissection Pressure Catapulting (LMPC) isolates. Highly efficient protein recovery was achieved by optimization of a “one-pot” protein extraction and digestion allowing for reproducible proteomic analysis on as few as 500 LMPC isolated cells. The method was combined with label-free spectral count quantitation to characterize proteomic differences from 3,000–10,000 LMPC isolated cells. Significance analysis of spectral count data was accomplished using the edgeR tag-count R package combined with hierarchical cluster analysis. To illustrate the capability of this robust workflow, two examples are presented: 1) analysis of keratinocytes from human punch biopsies of normal skin and a chronic diabetic wound and 2) comparison of glomeruli from needle biopsies of patients with kidney disease. Differentially expressed proteins were validated by use of immunohistochemistry. These examples illustrate that tissue proteomics carried out on limited clinical material can obtain informative proteomic signatures for disease pathogenesis and demonstrate the suitability of this approach for biomarker discovery.
Laser Capture Microdissection; Proteomics; Label-free; Biopsy; Mass Spectrometry
To investigate the relationship of urinary biomarkers (UBM) and established measures of renal function (EMRF) to the histological findings with lupus nephritis (LN); and to test whether certain combinations of the above mentioned laboratory measures are diagnostic of specific histological features of LN.
Urine samples of 76 patients were collected within 2 months of a kidney biopsy and assayed for the UBM: lipocalin-like prostaglandin-D synthetase (LPGDS), α1-acid-glycoprotein (AAG), transferrin (TF), ceruloplasmin (CP), neutrophil-gelatinase associated lipocalin (NGAL), and monocyte chemotactic factor 1 (MCP1). Using non-parametric analyses, UBM and EMRF levels were compared to histological features seen with LN: mesangial expansion, capillary proliferation, crescent formation, necrosis, wire loops, fibrosis, tubular atrophy, and epimembranous deposits. The area under the receiver operating characteristic (AUC) curve was calculated to predict LN activity, chronicity or membranous LN.
There was a differential increase of the UBM that formed a pattern reflective of specific histological features seen with active LN. The combination of MCP1, AAG, CP plus protein:creatinine ratio were excellent in predicting LN activity (AUC=0.85). NGAL together with creatinine clearance plus MCP1 was an excellent (AUC=0.83) and MCP1, AAG, creatinine clearance plus C4 (AUC=0.75) a good diagnostic test of LN chronicity and membranous LN, respectively.
Select UBM are associated with specific tissue changes observed with LN activity and chronicity. Especially in combination with select EMRF, UBM are well-suited to non-invasively quantify LN activity, LN chronicity, and the presence of membranous LN.
SLE; lupus nephritis; kidney biopsy; biomarker
An acute increase in the international normalized ratio (INR; a comparison of prothrombin time to monitor the effects of warfarin) over 3 in patients with chronic kidney disease (CKD) is often associated with an unexplained acute increase in serum creatinine (SC) and an accelerated progression of CKD. Kidney biopsy in a subset of these patients showed obstruction of the renal tubule by red blood cell casts, and this appears to be the dominant mechanism of the acute kidney injury. We termed this warfarin-related nephropathy (WRN), and previously reported cases of WRN only in patients with CKD. We now assess whether this occurs in patients without CKD, its risk factors, and consequences. In 15,258 patients who initiated warfarin therapy during a 5-year period, 4006 had an INR over 3 and SC measured at the same time; however, the large data set precluded individual patient clinical assessment. A presumptive diagnosis of WRN was made if the SC increased by over 0.3 mg/dl within 1 week after the INR exceeded 3 with no record of hemorrhage. WRN occurred in 20.5% of the entire cohort, 33.0% of the CKD cohort, and 16.5% of the no-CKD cohort. Other risk factors included age, diabetes mellitus, hypertension, and cardiovascular disease. The 1-year mortality was 31.1% with compared with 18.9% without WRN, an increased risk of 65%. Thus, WRN may be a common complication of warfarin therapy in high-risk patients and CKD doubles this risk. The mechanisms of these risks are unclear.
acute kidney injury; mortality; warfarin
Bath salts are substance of abuse that are becoming more common and are difficult to recognize due to negative toxicology screening. Acute kidney injury due to bath salt use has not previously been described. We present the case of a previously healthy male who developed acute kidney injury and dialysis dependence after bath salt ingestion and insufflation. This was self-reported with negative toxicology screening. Clinical course was marked by severe hyperthermia, hyperkalemia, rhabdomyolysis, disseminated intravascular coagulation, oliguria, and sepsis. We discuss signs and symptoms, differential diagnoses, potential mechanisms of injury, management, and review of the literature related to bath salt toxicity.
Background: Relapse or worsening of nephrotic syndrome (NS) in idiopathic membranous nephropathy (IMN) is generally assumed to be due to recurrent disease. Here we document that often that may not be the case. Subjects and Methods: This is a prospective study of 7 consecutive IMN patients whose renal status improved, then worsened after completing a course of immunosuppressive therapy. Each underwent detailed testing and repeat kidney biopsy. Results: In 4 patients (group A), the biopsy showed recurrent IMN (fresh subepithelial deposits). Immunosuppressive therapy was begun. In the other 3 patients (group B), the biopsy showed that the deposits had been eradicated. However, the glomerular basement membrane (GBM) was thickened and vacuolated. Immunosuppressive therapy was withheld. Groups A and B were comparable except that group B had very high intakes of salt and protein, based on 24-hour urine testing. Reducing their high salt intake sharply lowered proteinuria to the subnephrotic range and serum creatinine stabilized. Conclusion: This work is the first to demonstrate that relapse/worsening of NS can occur in IMN even though the GBM deposits have been eradicated. High salt and protein intake in combination with thickened and vacuolated GBM appears to be the mechanism.
Relapse of membranous nephropathy; Salt intake; Eradication of GBM deposits
The published criteria for the proteinuria increase that constitutes a proteinuric flare in lupus glomerulonephritis (SLE GN) vary widely, likely because they are largely based on expert opinion. Ideally, the threshold for proteinuric flare should be set sufficiently high so that spontaneous variation in proteinuria does not likely explain the increase, but not so high that the patient is needlessly exposed to prolonged heavy proteinuria before a flare is declared and therapy is increased. Here we describe an evidence-based approach to setting the threshold for proteinuric flare based on quantifying the spontaneous variation in urine protein/creatinine (P/C) ratio of SLE GN patients who are not experiencing SLE flare.
SLE GN patients (N = 71) followed in the Ohio SLE Study (OSS) were tested at pre-specified bimonthly intervals within windows of ± 1 week, median follow-up > 44 mo, visit compliance > 90%. To assess spontaneous P/C ratio variation under no-flare conditions, we excluded P/C ratios measured within ± 4 month of renal flare.
For those with mean no-flare P/C ratios ≤ 0.5, the published flare thresholds are set well above the 99% confidence interval (CI) of the no-flare P/C ratios. The opposite is seen in those with patients whose mean no-flare P/C ratios ≥ 1.0.
Current thresholds for proteinuric flare appear to be set either too high or too low. A randomized trial would be needed to test whether re-setting the thresholds would result in faster remission, less therapy, and less chronic kidney disease.
Tumor lysis syndrome (TLS) has been described in over 40% of patients with chronic lymphocytic leukemia (CLL) treated with the cyclin dependent kinase inhibitor, flavopiridol. We conducted a retrospective analysis to determine predictive factors for TLS. In 116 patients, the incidence of TLS was 46% (95% CI: 36%-55%). In univariable analysis, female gender, greater number of prior therapies, Rai stages III-IV, adenopathy ≥ 10 cm, splenomegaly, del(11q), decreased albumin, and increased absolute lymphocyte count, white blood cell count (WBC), β2-microglobulin, and lactate dehydrogenase (LDH) were associated (p<0.05) with TLS. In multivariable analysis, female gender, adenopathy ≥ 10 cm, elevated WBC, increased β2-microglobulin, and decreased albumin were associated with TLS (p<0.05). With respect to patient outcomes, 49% and 44% of patients with and without TLS, respectively, responded to flavopiridol (p=0.71). In a multivariable analysis controlling for number of prior therapies, cytogenetics, Rai stage, age, and gender, progression-free survival (PFS) was inferior in patients with TLS (p=0.01). Female patients and patients with elevated β2-microglobulin, increased WBC, adenopathy ≥ 10 cm, and decreased albumin were at highest risk and should be monitored for TLS with flavopiridol. TLS does not appear to be predictive of response or improved PFS in patients receiving flavopiridol.
chronic lymphocytic leukemia; flavopiridol; tumor lysis syndrome
A previous urine proteomic analysis from our laboratory suggested that hepcidin may be a biomarker for lupus nephritis flare. Immunohistochemical staining of kidney biopsies from lupus patients showed that hepcidin was expressed by infiltrating renal leukocytes. Here we investigated whether inflammatory cytokines relevant to the pathogenesis of lupus nephritis and other glomerular diseases regulate hepcidin expression by human monocytes.
Human CD14+ monocytes were incubated with interferon alpha (IFNα), interferon gamma (IFNγ), interleukin-6 (IL6), interleukin-1 beta (IL1β), monocyte chemotactic factor-1 (MCP1), or tumor necrosis factor alpha (TNFα). Hepcidin expression was examined by real-time PCR and enzyme immunoassay.
Monocyte hepcidin mRNA increased during adherence to the tissue culture wells, reaching a level 150-fold higher than baseline within 12 hours of plating. After accounting for the effects of adhesion, monocytes showed time and dose-dependent up-regulation of hepcidin mRNA upon treatment with IFNα or IL6. One hour of incubation with IFNα or IL6 increased hepcidin mRNA 20 and 80-fold respectively; by 24 hours the mRNA remained 5 and 2.4-fold higher than baseline. IL1β, IFNγ, and MCP-1 did not affect monocyte hepcidin expression. TNFα inhibited hepcidin induction by IL6 in monocytes by 44%. After 24 hours of treatment with IFNα or IL6, immunoreactive hepcidin production by monocytes increased 3 and 2.6-fold respectively.
Human monocytes produce hepcidin in response to adhesion and the pro-inflammatory cytokines IFNα and IL6.
The appearance of hepcidin in the kidneys or urine during glomerular diseases may be from infiltrating monocytes induced to express hepcidin by adherence and exposure to pro-inflammatory cytokines found in the renal milieu.
Hepcidin; Interferon Alpha; Human Monocytes; Nephritis
Some day we will have powerful targeted therapies for autoimmune diseases. Remission will be induced efficiently. Side effects will be mere ripples. Unfortunately, that day is not imminent. Current therapies are powerful but with unintended targets and side effects that can be equivalent to a sea change. For SLE, the current competition to select the ‘gold standard’ immunosuppressant has come down to two regimens: intravenous cyclophosphamide (IVCY, standard NIH protocol or its variations) versus oral mycophenolate (MMF). Until recently, IVCY reigned as the gold standard, a title it achieved through a curious journey that did not involve rigorous head-to-head competition. Oral cyclophosphamide (POCY) has not been invited to the current competition to select the gold standard immunosuppressant despite the substantial evidence that POCY can perform at least as well as IVCY or mycophenolate, and compared to IVCY, is far less expensive, easier for the patient, and maybe more effective in African-Americans. Here, we state the case for POCY as therapy for severe autoimmune diseases. We suggest that if POCY is allowed to compete, it will not disappoint.
SLE nephritis; Oral cyclophosphamide; Intravenous cyclophosphamide
We had previously reported that acute kidney injury (AKI) in warfarin-treated chronic kidney disease (CKD) patients may occur shortly after an acute increase in the International Normalization Ratio (INR) >3.0 with formation of occlusive red blood casts. Recovery from this warfarin-associated AKI is poor. Here we investigated whether excessive warfarin therapy could accelerate the progression of CKD.
We analyzed serum creatinine (SC) and INR in 103 consecutive CKD patients on warfarin therapy in our Nephrology program from 2005 to the present.
Forty-nine patients experienced at least 1 episode of INR >3.0. Of these, 18 patients (37%, Group 1) developed an unexplained increase in SC ≥0.3 mg/dl coincident with INR >3.0 (mean SC increase 0.61 ± 0.44 mg/dl); 31 patients (63%, Group 2) showed stable SC (mean SC change 0.04 ± 0.19 mg/dl). Subsequent CKD progression was accelerated in Group 1, but not in Group 2. The 2 groups were not different with respect to demographics, comorbidities, blood pressure, or therapies. However, African Americans were overrepresented in Group 1 (p = 0.035).
Overanticoagulation is associated with faster progression of CKD in a high percentage of patients. Our results indicate the need for prospective trials. Nevertheless, we suggest that our findings are sufficiently compelling at this point to justi- fy extra caution in warfarin-treated CKD patients to avoid overanticoagulation.
Warfarin; Serum creatinine; Acute kidney injury; Chronic kidney disease
The 24-h urine protein-to-creatinine ratio is the gold standard in evaluating proteinuria in lupus nephritis; however, the urine collection is inconvenient to the patient. Random spot urine protein-to-creatinine ratios, although convenient, have poor agreement with the 24-h ratios in these patients. Here, we sought to define a timed collection interval providing accurate and precise data and patient convenience. Urine from 41 patients, in 2 medical centers, with biopsy-proven lupus nephritis was collected at 6-h intervals for 24 h. The protein-to-creatinine ratio of each short collection was then compared with that of a 24-h collection made by combining the 6-h samples. A first morning void and spot urine samples were collected before and after the 24-h collection, respectively. There was significant diurnal variation with peak proteinuria at 6–12 h and nadir at 18–24 h. Each 6-h collection showed excellent correlation and concordance with the 24-h protein-to-creatinine ratio, but the 12–24-h interval had the best agreement. In contrast to the random spot urines, the first morning void also had excellent correlation and concordance, but underestimated the 24-h protein-to-creatinine ratio. Our study shows that a 12-h overnight urine collection is the best surrogate, with excellent agreement with the 24-h protein-to-creatinine ratio, and it is convenient for patients. There was little variability between centers, an important feature for clinical trials.
glomerulonephritis; lupus nephritis; nephritis; proteinuria systemic lupus erythematosus
Recently the American Rheumatologic Association (ARA) recommended random spot urine protein/creatinine ratio (P/C) to monitor systemic lupus erythematosus (SLE) glomerulonephritis (GN). Shortly afterward, 2 works were published, designated Study 1 and Study 2, which are the only studies to test spot P/C in SLE GN. Here we evaluate Study 1 and Study 2, which came to different conclusions.
Study 1 compared spot P/C to the P/C of intended 24-hour collections >50% complete, which reliably estimates 24-hour proteinuria. Study 2 compared spot P/C to the protein content of intended 24-hour collections >80% complete. To compare studies, Study 2 data were converted to P/C ratios.
Study 1 and Study 2 were found to be in agreement. Both showed that spot P/C and 24-hour P/C were highly correlated, but only when compared over the entire P/C range (0–8.0) (r = 0.842). Over the P/C range 0.5–3.0 (the most common P/C range encountered in SLE GN), correlation was present, but concordance was poor, rendering random P/C ratio unreliable.
Random spot P/C ratio is unreliable for detecting moderate proteinuria change. For example, random spot P/C would not reliably diagnose British Isles Lupus Assessment Group (BILAG) Category A or B proteinuric flares.
SLE glomerulonephritis; Proteinuria; SLE flare
Adiponectin is reported to have both pro- and anti-inflammatory effects. Because adiponectin circulates in isoforms of various sizes, and some responses to adiponectin are isoform-dependent, it was postulated that the pro-inflammatory effects of adiponectin may isoform-specific. To test this, peripheral blood mononuclear cells (PBMC), microvascular endothelial cells (MVEC), and human glomerular mesangial cells (HMC) were treated with high or low molecular weight (HMW, LMW) recombinant human adiponectin, and chemokine production was measured. The PBMC were isolated from healthy volunteers by density gradient centrifugation of EDTA anticoagulated whole blood through endotoxin-free Ficoll. The MVEC were of dermal origin, and the HMC were isolated from kidneys not suitable for transplantation. Overnight (16 hours) incubation with HMW adiponectin (0.01–1μg/ml for PBMC; 5–20μg/ml for MVEC, HMC) induced a dose-dependent increase in production of monocyte chemoattractant protein-1 and interleukin-8 by PBMC and MVEC, but had no effect on HMC chemokine production (n=3–5). LMW adiponectin at the same concentrations did not induce chemokine production in any of the cell types tested, and did not block cytokine-induced chemokine production by PBMC or MVEC (n=3–5). These in vitro data suggested that the HMW adiponectin isoform is pro-inflammatory. To examine the possibility of a relationship between HMW adiponectin and inflammation in vivo, the urine of patients with systemic lupus erythematosus (SLE) and kidney involvement, previously shown to contain immunoreactive adiponectin, was examined for the presence of specific adiponectin isoforms by non-denaturing gel electrophoresis. HMW adiponectin was found in the urine of patients with active lupus nephritis. Therefore, HMW adiponectin may contribute to the renal inflammation of SLE.
Adiponectin; Inflammation; Monocyte Chemotactic Protein-1; Interleukin-8; lupus
Although the prognosis for Lupus Nephritis (LN) has dramatically improved with aggressive immunosuppressive therapies, these drugs carry significant side effects. To improve the effectiveness of these drugs, biomarkers of renal flare cycle could be used to detect the onset, severity, and responsiveness of kidney relapses, and to modify therapy accordingly. However, LN is a complex disease and individual biomarkers have so far not been sufficient to accurately describe disease activity. It has been postulated that biomarkers would be more informative if integrated into a pathogenic-based model of LN.
This work is a first attempt to integrate human LN biomarkers data into a model of kidney inflammation. Our approach is based on a system of differential equations that capture, in a simplified way, the complexity of interactions underlying disease activity. Using this model, we have been able to fit clinical urine biomarkers data from individual patients and estimate patient-specific parameters to reproduce disease dynamics, and to better understand disease mechanisms. Furthermore, our simulations suggest that the model can be used to evaluate therapeutic strategies for individual patients, or a group of patients that share similar data patterns.
We show that effective combination of clinical data and physiologically based mathematical modeling may provide a basis for more comprehensive modeling and improved clinical care for LN patients.
TNF-like weak inducer of apoptosis (TWEAK) has been implicated as a mediator of chronic inflammatory processes via prolonged activation of the NF-κB pathway in several tissues, including the kidney. Evidence for the importance of TWEAK in the pathogenesis of lupus nephritis (LN) has been recently introduced. Thus, TWEAK levels may serve as an indication of LN presence and activity.
Multicenter cohorts of systemic lupus erythematosus (SLE) patients and controls were recruited for cross-sectional and longitudinal analysis of urinary TWEAK (uTWEAK) and/or serum TWEAK (sTWEAK) levels as potential biomarkers of LN. The performance of TWEAK as a biomarker for nephritis was compared with routinely used laboratory tests in lupus patients, including anti-double stranded DNA antibodies and levels of C3 and C4.
uTWEAK levels were significantly higher in LN patients than in non-LN SLE patients and other disease control groups (P = 0.039). Furthermore, uTWEAK was better at distinguishing between LN and non-LN SLE patients than anti-DNA antibodies and complement levels, while high uTWEAK levels predicted LN in SLE patients with an odds ratio of 7.36 (95% confidence interval = 2.25 to 24.07; P = 0.001). uTWEAK levels peaked during LN flares, and were significantly higher during the flare than at 4 and 6 months prior to or following the flare event. A linear mixed-effects model showed a significant association between uTWEAK levels in SLE patients and their disease activity over time (P = 0.008). sTWEAK levels, however, were not found to correlate with the presence of LN or the degree of nephritis activity.
High uTWEAK levels are indicative of LN, as opposed to non-LN SLE and other healthy and disease control populations, and reflect renal disease activity in longitudinal follow-up. Thus, our study further supports a role for TWEAK in the pathogenesis of LN, and provides strong evidence for uTWEAK as a candidate clinical biomarker for LN.
Lupus nephritis is a frequent and serious complication of systemic lupus erythematosus (SLE). Treatment often requires the use of immunosuppression, and may be associated with severe side effects. The ability to predict relapse, relapse severity, and recovery could be used to more effectively implement therapy and reduce toxicity. We postulated that a proteomic analysis of the low-molecular weight urine proteome using serial urine samples obtained before, during, and after SLE nephritis flares would demonstrate potential biomarkers of SLE renal flare. This study was undertaken to test our hypothesis.
Urine from 25 flare cycles of 19 WHO Class III, IV, and V SLE nephritis patients was used. Urine samples included a baseline, and pre-flare, flare, and post-flare specimens. The urines were fractionated to remove proteins larger than 30 kDa, and spotted onto weak cation exchanger (CM10) protein chips for analysis by surface-enhanced laser desorption/ionization time-of-flight mass spectrometry (SELDI-TOF MS).
SELDI-TOF MS screening showed 176 protein ions between 2-20 kDa of which 27 were found to be differentially-expressed between specific flare intervals. On-chip peptide sequencing by integrated tandem mass spectrometry was used to positively identify selected differentially-expressed protein ions. The identified proteins included the 20 and 25 amino acid isoforms of hepcidin, a fragment of α1-antitrypsin, and an albumin fragment. Hepcidin 20 increased 4 months pre-flare and returned to baseline at renal flare, whereas hepcidin 25 decreased at renal flare and returned to baseline 4 months post-flare.
Using SELDI-TOF urine protein profiling in lupus nephritis, several candidate biomarkers of renal flare were found. To verify these candidates as true biomarkers, further identification and validation are needed in an independent SLE cohort.
lupus nephritis; biomarker; SELDI
The type one complement receptor (CR1) contains a variable number of binding domains for C3b and C4b, formed through a nearly identical set of repeating units known as short consensus repeats (SCRs). Each SCR contains 4 cysteines that, by forming two disulfide bonds, impart a conformation critical for function. In this study, we identified a CR1 single nucleotide polymorphism (1597C>T) that results in an additional cysteine (483R>C) in SCR 8 of the N-terminal C3b/C4b binding domain, and occurring sporadically in corresponding SCRs of other repeated C3b/C4b binding domains. The normal carrier frequency for 483-C was 6.3% in 175 African Americans, and 2.4% in 153 Caucasians. In expression constructs containing one C3b/C4b binding domain, the 483-C residue reduced binding to C3b, C3bi, and C4b by over 80% (each p < 0.0001), versus the wildtype construct. Full-length CR1 from 483-C carriers also exhibited reduced binding to C3b and C4b, although the effect was influenced by the total number of binding domains present. Race-matched comparisons between SLE patients (86 African Americans, 228 Caucasians) and the normal cohort showed that 483-C carrier status alone is not a risk factor for SLE or lupus nephritis. The physiological role of this polymorphism remains to be determined.
CR1; polymorphism; complement; SLE
In human parturition, uterotonic prostaglandins (PGs) arise predominantly via increased expression of cyclooxygenase-2 (COX-2 [also known as prostaglandin synthase 2]) within intra-uterine tissues. Interleukin-1 (IL-1) and epidermal growth factor (EGF), both inducers of COX-2 transcription, are among numerous factors that accumulate within amniotic fluid with advancing gestation. It was previously demonstrated that EGF could potentiate IL-1β-driven PGE2 production in amnion and amnion-derived (WISH) cells. To define the mechanism for this observation, we hypothesized that EGF and IL-1β might exhibit synergism in regulating COX-2 gene expression. In WISH cells, combined treatment with EGF and IL-1β resulted in a greater-than-additive increase in COX-2 mRNA relative to challenge with either agent independently. Augmentation of IL-1β-induced transactivation by EGF was not observed in cells harboring reporter plasmids bearing nuclear factor-kappa B (NFκB) regulatory elements alone, but was evident when a fragment (−891/+9) of the COX-2 gene 5′-promoter was present. Both agents transiently activated intermediates of multiple signaling pathways potentially involved in the regulation of COX-2 gene expression. The 26 S proteasome inhibitor, MG-132, selectively abrogated IL-1β-driven NFκB activation and COX-2 mRNA expression. Only pharmacologic blockade of the p38 mitogen-activated protein kinase eliminated COX-2 expression following EGF stimulation. We conclude that EGF and IL-1β appear to signal through different signaling cascades leading to COX-2 gene expression. IL-1β employs the NFκB pathway predominantly, while the spectrum of EGF signaling is broader and includes p38 kinase. The synergism observed between IL-1β and EGF does not rely on augmented NFκB function, but rather, occurs through differential use of independent response elements within the COX-2 promoter.
cytokines; growth factors; parturition; placenta; signal transduction