Bernhard K. Krämer

The Value of N-Acetylcysteine in the Prevention of Radiocontrast Agent-Induced Nephropathy Seems Questionable

Prevention of contrast agent-induced nephropathy is of crucial importance for a number of diagnostic studies. N-Acetylcysteine (NAC) was recently reported to decrease serum creatinine levels in this setting, and its administration before radiocontrast medium administration has been widely recommended. The objective of this prospective study was to investigate whether there are effects of NAC on serum creatinine levels that are independent of alterations in GFR. Volunteers with normal renal function who did not receive radiocontrast medium were studied. Fifty healthy volunteers completed the study protocol. NAC was administered orally at a dose of 600 mg every 12 h, for a total of four doses. Surrogate markers of renal function, such as serum creatinine, urea, albumin, and cystatin C levels, were measured and estimated GFR (eGFR) was assessed immediately before the administration of NAC and 4 and 48 h after the last dose. There was a significant decrease in the mean serum creatinine concentration (P < 0.05) and a significant increase in the eGFR (P < 0.02) 4 h after the last dose of NAC. The cystatin C concentrations did not change significantly. In several studies, a protective effect of NAC on renal function after radiocontrast medium administration has been postulated. This is the first study to demonstrate an effect of NAC on creatinine levels and eGFR, surrogate markers of renal injury, without any effect on cystatin C levels. Before renoprotective effects of NAC against contrast agent-induced nephropathy are considered, the direct effects of NAC on creatinine levels, urea levels, and eGFR should be assessed.

CC chemokine receptor 5 and renal-transplant survival

BACKGROUND About 1% of white populations are homozygous carriers of an allele of the gene for the CC chemokine receptor 5 (CCR5) with a 32 bp deletion (CCR5Delta32), which leads to an inactive receptor. During acute and chronic transplant rejection, ligands for CCR5 are upregulated, and the graft is infiltrated by CCR5-positive mononuclear cells. We therefore investigated the influence of CCR5Delta32 on renal-transplant survival. METHODS Genomic DNA from peripheral-blood leucocytes of 1227 renal-transplant recipients was screened by PCR for the presence of CCR5Delta32. Demographic and clinical data were extracted from hospital records. Complete follow-up data were available for 576 recipients of first renal transplants. Graft survival was analysed by Fishers exact test and Kaplan-Meier plots compared with a log-rank test. FINDINGS PCR identified 21 patients homozygous for CCR5Delta32 (frequency 1.7%). One patient died with a functioning graft. Only one of the remaining patients lost transplant function during follow-up (median 7.2 years) compared with 78 of the 555 patients with a homozygous wild-type or heterozygous CCR5Delta32 genotype. Graft survival was significantly longer in the homozygous CCR5Delta32 group than in the control group (log-rank p=0.033; hazard ratio 0.367 [95% CI 0.157-0.859]). INTERPRETATION Patients homozygous for CCR5Delta32 show longer survival of renal transplants than those with other genotypes, suggesting a pathophysiological role for CCR5 in transplant loss. This receptor may be a useful target for the prevention of transplant loss.

Donor Toll-like receptor 4 contributes to ischemia and reperfusion injury following human kidney transplantation

While studies in animal models have linked Toll-like receptor (TLR) 4 signaling to kidney injury induced by ischemia and reperfusion, the relevance of TLR4 activation to allograft injury in human kidney transplants is unknown. Here we show that TLR4 is constitutively expressed within all donor kidneys but is significantly higher in deceased-, compared with living-donor organs. Tubules from deceased- but not living-donor kidneys also stained positively for high-mobility group box-1 (HMGB1), a known endogenous TLR4 ligand. In vitro stimulation of human tubular cells with HMGB1, in a TLR4-dependent system, confirmed that HMGB1 can stimulate proinflammatory responses through TLR4. To assess the functional significance of TLR4 in human kidney transplantation, we determined whether TLR4 mutations that confer diminished affinity for HMGB1 influence intragraft gene-expression profiles and immediate graft function. Compared with kidneys expressing WT alleles, kidneys with a TLR4 loss-of-function allele contained less TNFα, MCP-1, and more heme oxygenase 1 (HO-1), and exhibited a higher rate of immediate graft function. These results represent previously undetected evidence that donor TLR4 contributes to graft inflammation and sterile injury following cold preservation and transplantation in humans. Targeting TLR4 signaling may have value in preventing or treating postischemic acute kidney injury after transplantation.

Effects of Donor Pretreatment With Dopamine on Graft Function After Kidney Transplantation A Randomized Controlled Trial

CONTEXT Kidney graft function after transplantation can be improved through pharmacological donor pretreatment to limit organ injury from cold preservation. OBJECTIVE To determine whether pretreatment of brain-dead donors with low-dose dopamine improves early graft function in human renal transplant recipients. DESIGN, SETTING, AND PATIENTS Randomized, open-label, multicenter, parallel-group trial of 264 deceased heart-beating donors and 487 subsequent renal transplants performed at 60 European centers between March 2004 and August 2007 (final follow-up, December 31, 2008). Eligible donors were stable under low-dose norepinephrine with a normal serum creatinine concentration on admission. INTERVENTIONS Donors were randomized to receive low-dose dopamine (4 mug/kg/min). MAIN OUTCOME MEASURES Dialysis requirement during first week after transplantation. RESULTS Dopamine was infused for a median of 344 minutes (IQR, 215 minutes). Dialysis was significantly reduced in recipients of a dopamine-treated graft. Fewer recipients in the treatment group needed multiple dialyses (56/227; 24.7%; 95% CI, 19.0%-30.3%; vs 92/260; 35.4%; 95% CI, 29.5%-41.2%; P = .01). The need for multiple dialyses posttransplant was associated with allograft failure after 3 years (HR, 3.61; 95% CI, 2.39-5.45; P < .001), whereas a single dialysis was not (HR, 0.67; 95% CI, 0.21-2.18; P = .51). Besides donor dopamine (OR, 0.54; 95% CI, 0.35-0.83; P = .005), cold ischemic time (OR, 1.07; 95% CI, 1.02-1.11 per hour; P = .001), donor age (OR, 1.03; 95% CI, 1.01-1.05 per year; P < .001), and recipient body weight (OR, 1.02; 95% CI, 1.01-1.04 per kg; P = .009) were independent explanatory variables in a multiple logistic regression model. Dopamine resulted in significant but clinically meaningless increases in the donors systolic blood pressure (3.8 mm Hg; 95% CI, 0.7-6.9 mm Hg; P = .02) and urine production before surgical recovery of the kidneys (29 mL; 95% CI, 7-51 mL; P = .009) but had no influence on outcome. CONCLUSION Donor pretreatment with low-dose dopamine reduces the need for dialysis after kidney transplantation. TRIAL REGISTRATION clinicaltrials.gov Identifier: NCT00115115.

Diuretic treatment and diuretic resistance in heart failure

Diuretic therapy decreases capillary wedge pressure and improves New York Heart Association (NYHA) functional class both in acute and chronic heart failure. In advanced symptomatic heart failure, loop diuretics are generally necessary to improve symptoms of congestion. Diuretic resistance in the edematous patient has been defined as a clinical state in which diuretic response is diminished or lost before the therapeutic goal of relief from edema has been reached. The major causes of diuretic resistance are functional renal failure (prerenal azotemia), hyponatremia, altered diuretic pharmacokinetics, and sodium retention caused by counterregulatory mechanisms intended to reestablish the effective arterial blood volume. Therapeutic approaches to combat diuretic resistance include restriction of fluid and sodium intake, use of angiotensin-converting-enzyme (ACE) inhibitors, changes in route (oral, intravenous) and timing (single dose, multiple doses, continuous infusion) of diuretic therapy, and use of diuretic combinations.

TLR4 Links Podocytes with the Innate Immune System to Mediate Glomerular Injury

Toll-like receptors (TLR) classically recognize pathogen-associated danger signals but are also activated via endogenous ligands. For evaluation of their role in inflammatory kidney disease, the function of TLR was analyzed in two mouse models of cryoglobulinemic membranoproliferative glomerulonephritis (MPGN; mice transgenic for thymic stromal lymphopoietin [TSLP], with or without deletion of the Fcgamma receptor IIb). Expression of TLR1 through 9 and TLR11 mRNA was detectable in whole kidneys and in isolated glomeruli of wild-type mice, with TLR3 and TLR4 having the highest absolute levels of expression. TLR1, 2, and 4 were increased in TSLP transgenic mice and even higher in TSLP transgenic FcgammaRIIb-deficient mice. TLR5 through 9 and 11 were upregulated to similar degrees in TSLP transgenic and TSLP transgenic FcgammaRIIb-deficient mice. Immunohistochemical studies of nephritic glomeruli localized TLR4 protein to podocytes. Cultured podocytes also expressed TLR4, and stimulation with TLR4-specific ligands resulted in a marked induction of chemokines; this was reduced by specific knockdown of TLR4 with siRNA. Fibrinogen, a potential endogenous TLR4 ligand, was shown to induce a similar profile of chemokines. In conclusion, it was demonstrated that TLR4 is constitutively expressed by podocytes and is upregulated in MPGN, where it may mediate glomerular injury by modulating expression of chemokines; therefore, TLR4 may link podocytes with the innate immune system to mediate MPGN triggered by the deposition of immune complexes.

Association of eGFR-Related Loci Identified by GWAS with Incident CKD and ESRD

Family studies suggest a genetic component to the etiology of chronic kidney disease (CKD) and end stage renal disease (ESRD). Previously, we identified 16 loci for eGFR in genome-wide association studies, but the associations of these single nucleotide polymorphisms (SNPs) for incident CKD or ESRD are unknown. We thus investigated the association of these loci with incident CKD in 26,308 individuals of European ancestry free of CKD at baseline drawn from eight population-based cohorts followed for a median of 7.2 years (including 2,122 incident CKD cases defined as eGFR <60ml/min/1.73m2 at follow-up) and with ESRD in four case-control studies in subjects of European ancestry (3,775 cases, 4,577 controls). SNPs at 11 of the 16 loci (UMOD, PRKAG2, ANXA9, DAB2, SHROOM3, DACH1, STC1, SLC34A1, ALMS1/NAT8, UBE2Q2, and GCKR) were associated with incident CKD; p-values ranged from p = 4.1e-9 in UMOD to p = 0.03 in GCKR. After adjusting for baseline eGFR, six of these loci remained significantly associated with incident CKD (UMOD, PRKAG2, ANXA9, DAB2, DACH1, and STC1). SNPs in UMOD (OR = 0.92, p = 0.04) and GCKR (OR = 0.93, p = 0.03) were nominally associated with ESRD. In summary, the majority of eGFR-related loci are either associated or show a strong trend towards association with incident CKD, but have modest associations with ESRD in individuals of European descent. Additional work is required to characterize the association of genetic determinants of CKD and ESRD at different stages of disease progression.

A Monocyte Chemoattractant Protein-1 (MCP-1) Polymorphism And Outcome After Renal Transplantation

Among the factors modulating transplant rejection and cardiovascular disease, chemokines and their respective receptors deserve special attention. In this respect, increased expression of MCP-1 and the corresponding receptor CCR2 have been demonstrated in renal transplant rejection and coronary artery disease. The impact of the MCP-1-2518G and CCR2-64I genotypes on renal allograft function was investigated in 232 patients who underwent transplantation over an 11-yr period. Genomic DNA was genotyped using PCR with sequence-specific primers followed by restriction fragment length polymorphism analysis. Eighteen (7.8%) patients were homozygous for the MCP-1-2518G mutation. The G/G allele of MCP-1 -2518 behaved as a determinant for long-term allograft survival and resulted in reduction of the mean graft survival, as compared with the heterozygous (A/G) or wild-type (A/A) allele (67 +/- 14 versus 95 +/- 4 mo; Log rank P = 0.0052). The 64I mutation of CCR2 had no effect on kidney graft failure (93 +/- 6 and 91 +/- 5 mo, respectively; P = 0.81). None of the investigated polymorphisms showed a significant shift in gene frequency in acute rejection and rejection-free groups. In conjunction with these findings, peripheral blood mononuclear cells from kidney transplant recipients carrying the G-allele were characterized by a 2.5-fold higher MCP-1 secretion (P < 0.05). In conclusion, recipients of renal transplants homozygous for the -2518 G mutation of the MCP-1 gene are at risk for premature kidney graft failure. This variant of MCP-1 may be a future predictor for long-term kidney graft failure.

Two corticosteroid-free regimens-tacrolimus monotherapy after basiliximab administration and tacrolimus/mycophenolate mofetil-in comparison with a standard triple regimen in renal transplantation : results of the Atlas study.

Background. The side effects associated with corticosteroids have led to efforts to minimize their use in renal transplant patients. In this study we compared two corticosteroid-free tacrolimus-based regimens with a standard triple therapy. Methods. This was a 6-month, phase III, open-label, parallel-group, multicenter study. The total analysis set comprised 451 patients, randomized (1:1:1) to receive tacrolimus (Tac) monotherapy following basiliximab (Bas) administration (n=153), Tac/mycophenolate mofetil (MMF) (n=151), or, Tac/MMF/corticosteroids triple therapy as a control (n=147). Results. The study was completed by 91.2% (triple therapy), 94.7% (Tac/MMF), and 82.4% (Bas/Tac) of patients. Patient baseline characteristics were similar in all groups. The incidences of biopsy-proven acute rejection were 8.2% (triple therapy), 30.5% (Tac/MMF), and 26.1% (Bas/Tac), p<0.001 (multiple test for comparison with triple therapy); Bas/Tac vs. Tac/MMF, p=ns. The incidences of corticosteroid-resistant acute rejection were 2.0%, 4.0%, and 5.2%, p=ns. Graft survival (95.9%, 96.7%, and 94.7%, p=ns) and patient survival (100%, 99.3%, and 99.3%, p=ns) were similar in all groups. Median serum creatinine at month 6 was 123.0 &mgr;mol/L (triple therapy), 134.7 &mgr;mol/L (Tac/MMF) and 135.8 &mgr;mol/L (Bas/Tac). The overall safety profiles were similar; differences (p<0.05) were reported for anaemia (24.5% vs. 12.6% vs. 14.5%), diarrhoea (12.9% vs. 17.9% vs. 5.9%), and leukopenia (7.5% vs. 18.5% vs. 5.9%) for the triple therapy, Tac/MMF, and Bas/Tac group, respectively. The incidences of new-onset diabetes mellitus were 4.6%, 7.1%, and 1.4%, respectively. Conclusion. Corticosteroid-free immunosuppression was feasible with the Bas/Tac and the Tac/MMF regimens. Both corticosteroid-free regimens were equally effective in preventing acute rejection, with the Bas/Tac therapy offering some safety benefits.

Adrenomedullin stimulates renin release and renin mRNA in mouse juxtaglomerular granular cells.

The recently discovered peptide adrenomedullin (AM) alters blood pressure through effects on the resistance vessels. Moreover, AM modifies the secretion of corticotropin and aldosterone and could thereby indirectly influence blood pressure through the renin-angiotensin-aldosterone system. Although plasma AM and renin concentration have been found to directly correlate, a causal linkage between AM and renin has not been shown. The present study tested the influence of AM on renin secretion and renin gene expression by renal juxtaglomerular granular cells. Prominent expression and release of AM by vascular structures has been reported; therefore, we investigated the local expression of AM in juxtaglomerular structures. Renin release from isolated perfused rat kidneys was dose-dependently increased by AM (1 to 30 nmol/L), whereas renal perfusate flow rate increased up to 17% at a constant perfusion pressure of 100 mm Hg. In primary cultures of mouse granular cells, AM augmented renin release, renin mRNA accumulation, and cAMP production in a dose- and time-dependent manner (threshold values in the range 10 pmol/L to 1 nmol/L). By reverse transcription-polymerase chain reaction, significant expression of the AM gene was detected in microdissected rat glomeruli with afferent arterioles and in primary cultures of mesangial and granular cells. We conclude that AM is expressed in juxtaglomerular structures and that it has a direct stimulatory effect on renin secretion and renin mRNA abundance by receptors on juxtaglomerular cells, possibly through increases in cAMP. AM could act as an autocrine/paracrine stimulatory factor in the control of renin secretion and renin gene expression.