Mistargeting of peroxisomal EHHADH and inherited renal Fanconi's syndrome.

BACKGROUND: In renal Fanconi's syndrome, dysfunction in proximal tubular cells leads to renal losses of water, electrolytes, and low-molecular-weight nutrients. For most types of isolated Fanconi's syndrome, the genetic cause and underlying defect remain unknown. METHODS: We clinically and genetically characterized members of a five-generation black family with isolated autosomal dominant Fanconi's syndrome. We performed genomewide linkage analysis, gene sequencing, biochemical and cell-biologic investigations of renal proximal tubular cells, studies in knockout mice, and functional evaluations of mitochondria. Urine was studied with the use of proton nuclear magnetic resonance ((1)H-NMR) spectroscopy. RESULTS: We linked the phenotype of this family's Fanconi's syndrome to a single locus on chromosome 3q27, where a heterozygous missense mutation in EHHADH segregated with the disease. The p.E3K mutation created a new mitochondrial targeting motif in the N-terminal portion of EHHADH, an enzyme that is involved in peroxisomal oxidation of fatty acids and is expressed in the proximal tubule. Immunocytofluorescence studies showed mistargeting of the mutant EHHADH to mitochondria. Studies of proximal tubular cells revealed impaired mitochondrial oxidative phosphorylation and defects in the transport of fluids and a glucose analogue across the epithelium. (1)H-NMR spectroscopy showed elevated levels of mitochondrial metabolites in urine from affected family members. Ehhadh knockout mice showed no abnormalities in renal tubular cells, a finding that indicates a dominant negative nature of the mutation rather than haploinsufficiency. CONCLUSIONS: Mistargeting of peroxisomal EHHADH disrupts mitochondrial metabolism and leads to renal Fanconi's syndrome; this indicates a central role of mitochondria in proximal tubular function. The dominant negative effect of the mistargeted protein adds to the spectrum of monogenic mechanisms of Fanconi's syndrome. (Funded by the European Commission Seventh Framework Programme and others.).

Elevated urinary sVCAM-1, IL6, sIL6R and TNFR1 concentrations indicate acute kidney transplant rejection in the first 2 weeks after transplantation.

We tested the hypothesis that increased urinary cytokine concentrations may indicate an acute kidney transplant rejection. Eight patients with an early rejection in their protocol biopsy about 14days after transplantation (group A), 9 patients with a biopsy proven rejection 2-3months after transplantation (group B) and 18 patients without acute rejection in their protocol biopsies both at 14days and 3months (group C, represents the control group) were chosen for this study. At the time of biopsy, the mean urinary concentration of interleukin 6 (IL6), soluble IL6 receptor (sIL6R), tumor necrosis factor receptor 1 (TNFR1), and soluble vascular cell adhesion molecule -1 (sVCAM-1) were significantly higher in patients with an early acute transplant rejection, i.e. in group A compared to patients in the control group (p<0.01). Additionally we found already 14days after transplantation significantly higher concentrations of urinary sIL6R and sVCAM-1 in group B patients who suffered of late acute rejection compared to patients with no acute rejection (group C, p<0.05). No significant correlation could be shown for interleukin 1 receptor antagonist (IL1ra), TNF, and TNFR2. In conclusion, elevated urinary concentrations of IL6, sIL6R, TNFR1 and sVCAM-1 clearly indicate an early acute transplant rejection. Especially sVCAM-1 may also serve as an early marker of an upcoming late rejection. However, further studies are warranted to verify the value of individual cytokine profiles to predict acute rejection episodes.

Toll-like receptor 4 in experimental kidney transplantation: early mediator of endogenous danger signals.

The role of toll-like receptors (TLRs) has been described in the pathogenesis of renal ischemia/reperfusion injury, but data on the expression and function of TLR4 during renal allograft damage are still scarce. We analyzed the expression of TLR4 in an experimental rat model 6 and 28 days after allogeneic kidney transplantation in comparison to control rats and rats after syngeneic transplantation. On day 6, a significant induction in TLR4 expression--restricted to the glomerular compartment--was found in acute rejecting allografts only. TLR4 expression strongly correlated with renal function, and TLR4 induction was accompanied by a significant increase in CC chemokine expression within the graft as well as in urinary CC chemokine excretion. TLR4 induction may be caused by an influx of macrophages as well as TLR4-expressing intrinsic renal cells. Fibrinogen deposition in renal allografts correlated with renal TLR4 expression and may act as a potent stimulator of chemokine release via TLR4 activation. This study provides, for the first time, data about the precise intrarenal localization and TLR4 induction after experimental kidney transplantation. It supports the hypothesis that local TLR4 activation by endogenous ligands may be one pathological link from unspecific primary allograft damage to subsequent chemokine release, infiltration and activation of immune cells leading to deterioration of renal function and induction of renal fibrosis.

Cyclosporine A impairs norepinephrine-induced vascular contractility.

Usage of cyclosporine A (CsA) after kidney transplantation may be associated with development of nephrotoxicity and vasculopathy, but the mechanisms by which CsA causes vascular dysfunction are still under scrutiny. We established a transplantation model and investigated the effect of CsA on vascular contractility with the aid of a pressurized myograph in comparison with control and unilaterally nephrectomized rats. Results were correlated with mRNA expression studies of α- and ß-adrenoreceptors, in mesenteric resistance arteries versus the thoracic aorta. Consequences of everolimus on functional properties as well as adrenoreceptor expression were also studied. CsA significantly downregulated expression of mesenteric adrenoreceptors, whereas no effect on aortic adrenoreceptors was seen. Administration of everolimus had no influence on mRNA adrenoreceptor expression in mesenteric resistance arteries. Furthermore, contractile responses of mesenteric resistance arteries to norepinephrine were markedly reduced after treatment with CsA, while there was no difference in contraction by endothelin. Everolimus did not alter the contractility response at all. In summary, norepinephrine-induced, but not endothelin-induced, contractile responses of mesenteric resistance arteries are blunted in CsA-treated rats. This finding was accompanied by a marked downregulation of adrenoreceptors in mesenteric resistance arteries and was limited to the usage of CsA.

Detection of autosomal dominant polycystic kidney disease by NMR spectroscopic fingerprinting of urine.

Autosomal dominant polycystic kidney disease (ADPKD) is a frequent cause of kidney failure; however, urinary biomarkers for the disease are lacking. In a step towards identifying such markers, we used multidimensional-multinuclear nuclear magnetic resonance (NMR) spectroscopy with support vector machine-based classification and analyzed urine specimens of 54 patients with ADPKD and slightly reduced estimated glomerular filtration rates. Within this cohort, 35 received medication for arterial hypertension and 19 did not. The results were compared with NMR profiles of 46 healthy volunteers, 10 ADPKD patients on hemodialysis with residual renal function, 16 kidney transplant patients, and 52 type 2 diabetic patients with chronic kidney disease. Based on the average of 51 out of 701 NMR features, we could reliably discriminate ADPKD patients with moderately advanced disease from ADPKD patients with end-stage renal disease, patients with chronic kidney disease of other etiologies, and healthy probands with an accuracy of >80%. Of the 35 patients with ADPKD receiving medication for hypertension, most showed increased excretion of proteins and also methanol. In contrast, elevated urinary methanol was not found in any of the control and other patient groups. Thus, we found that NMR fingerprinting of urine differentiates ADPKD from several other kidney diseases and individuals with normal kidney function. The diagnostic and prognostic potential of these profiles requires further evaluation.

Impact of Toll-like receptor 2 expression in renal allograft rejection.

BACKGROUND: An important role of TLR2 has been shown in various experimental models of renal ischaemia/reperfusion injury. To study the expression of TLR2 in renal allograft rejection systematically, we established an experimental rat transplantation model. METHODS: TLR2 expression was analysed in 99 human renal allograft biopsies, and in rat allografts at Day 6 and 28 after experimental renal transplantation. To discriminate whether regulation of TLR2 was following immunological processes after allogeneic transplantation or was a consequence from ischaemia/reperfusion injury, control animals subjected to syngeneic transplantation or to ischaemia/reperfusion damage were also investigated. RESULTS: TLR2 mRNA was significantly elevated in rat allografts with acute rejection on Day 6 and decreased spontaneously towards Day 28. TLR2 induction correlated with renal function and TLR2 excretion in the urine of transplanted rats. TLR2 staining was also significantly increased in human allografts with acute rejection. TLR2 protein could be localized in tubular epithelial cells and vascular endothelial cells, and in CD68- and CD4-positive infiltrating cells. CONCLUSIONS: TLR2 is markedly up-regulated in both experimental and human acute renal allograft rejection. Our data suggest a role for TLR2 during allogen-dependent graft damage after renal transplantation.

Traditional and nontraditional cardiovascular risk factors and estimated risk for coronary artery disease in renal transplant recipients: a single-center experience.

BACKGROUND/AIMS: The prevalence of cardiovascular disease in renal transplant recipients is markedly higher than in the general population due to the high prevalence of traditional cardiovascular risk factors, renal transplant function impairment and treatment with immunosuppressive drugs that affect blood pressure, cholesterol and blood glucose levels. METHODS: Cross-sectional analysis using our renal transplant clinic cohort investigating (1) the cardiovascular risk factors present in this cohort, and (2) estimating their impact on the risk of coronary artery disease (CAD) by using the Framingham algorithm. RESULTS: Control of modifiable cardiovascular risk factors in 231 renal transplant recipients is suboptimal, i.e. 47.2% of patients are hypertensive, 10.3% actively smoke, 39.4% have serum cholesterol concentrations >200 mg/dl, and 19.7% have diabetes mellitus. Blood pressure, age, hyperlipidemia, smoking and diabetes modulate the estimated CAD risk in males and females. Furthermore, a short time period (less than 1 year) since transplantation and increased serum creatinine levels negatively influenced the CAD risk in this patient population. CONCLUSION: According to current guidelines, the control of modifiable cardiovascular risk factors in renal transplant recipients is suboptimal. The decreasing CAD risk over time after transplantation may be due to the reduction of immunosuppressive drugs with time and survival bias.

High osmolality induces the kidney-specific chloride channel CLC-K1 by a serum and glucocorticoid-inducible kinase 1 MAPK pathway.

The kidney-specific chloride channels CLC-K1/2 and their functionally important subunit barttin, by mediating solute transport in medulla, contribute to the osmotic gradient. We sought to determine whether they themselves are regulated by variations of osmolality. The expression of CLC-K1 and barttin mRNA and protein was significantly increased in a distal convoluted tubule cell line after a shift to high osmolar medium. This upregulation paralleled that of serum and glucocorticoid-inducible kinase 1 (SGK1), a gene known to be upregulated by cell shrinkage. Specific knockdown of SGK1 or addition of the p38 MAPK pathway inhibitor SB203580 abolished the induction of SGK1, CLC-K1 and barttin by high osmolarity suggesting that a functional MAPK pathway is required to mediate osmotic-driven induction of all three genes. The physiological relevance of our in vitro data was confirmed by water deprivation of male C57BL6 mice, which caused a significant increase in serum osmolality along with induction of CLC-K1, barttin and SGK1. Our study shows that change in intracellular volume, because of high osmolality, result in SGK1 upregulation and the subsequent increase of CLC-K1/barttin expression in distal renal tubular cells in vivo and in vitro.

Lipoxygenase products in the urine correlate with renal function and body temperature but not with acute transplant rejection.

Acute transplant rejection is the leading cause of graft loss in the first months after kidney transplantation. Lipoxygenase products mediate pro- and anti-inflammatory actions and thus we aimed to correlate the histological reports of renal transplant biopsies with urinary lipoxygenase products concentrations to evaluate their role as a diagnostic marker. This study included a total of 34 kidney transplant recipients: 17 with an acute transplant rejection and 17 controls. LTE4, LTB4, 12-HETE and 15-HETE concentrations were measured by enzyme immunoassay. Urinary lipoxygenase product concentrations were not significantly changed during an acute allograft rejection. Nevertheless, LTB4 concentrations correlated significantly with the body temperature (P ≤ 0.05) 3 months after transplantation, and 12- and 15-HETE concentrations correlated significantly with renal function (P ≤ 0.05) 2 weeks after transplantation. In conclusion, our data show a correlation for LTB4 with the body temperature 3 months after transplantation and urinary 12- and 15-HETE concentrations correlate positively with elevated serum creatinine concentrations but do not predict acute allograft rejection.

Nephron-specific expression of components of the renin-angiotensin-aldosterone system in the mouse kidney.

INTRODUCTION: The renin-angiotensin-aldosterone system (RAAS) plays an integral role in the regulation of blood pressure, electrolyte and fluid homeostasis in mammals. The capability of the different nephron segments to form components of the RAAS is only partially known. This study therefore aimed to characterize the nephron-specific expression of RAAS components within the mouse kidney. MATERIALS AND METHODS: Defined nephron segments of adult C57B/16 mice were microdissected after collagenase digestion. The gene expression of renin, angiotensinogen (AGT), angiotensin-converting enzyme (ACE), angiotensin II receptors 1a (AT1a), 1b (AT1b), and 2 (AT2) was assessed by reverse transcriptase polymerase chain reaction (RT-PCR). RESULTS: Renin mRNA was present in glomeruli, in proximal tubules, in distal convoluted tubules (DCT) and cortical collecting ducts (CCD). AGT mRNA was found in proximal tubules, descending thin limb of Henle's loop (dTL) and in the medullary part of the thick ascending limb (mTAL). ACE mRNA was not detectable in microdissected mouse nephron segments. AT1a, AT1b and AT2 mRNA was detected in glomeruli and proximal convoluted tubules. CONCLUSIONS: Our data demonstrate a nephron-specific distribution of RAAS components. All components of the local RAAS - except ACE - are present in proximal convoluted tubules, emphasizing their involvement in sodium and water handling.

Renal function during rofecoxib therapy in patients with metastatic cancer: retrospective analysis of a prospective phase II trial.

BACKGROUND: Angiostatic/antiinflammatory therapy with COX-II inhibitors and pioglitazone seems to be a well tolerated and promising regimen in patients with metastatic cancer. COX-II inhibitors may have less gastrointestinal side effects than conventional non-steroidal antiinflammatory drugs, but their impact on renal function seems to be similar. METHODS: 87 patients with metastatic/advanced cancer were treated up to 12 months (mean 19.5 weeks) with rofecoxib, pioglitazone and either capecitabine (group A with gastrointestinal and urological cancer, n = 50) or trofosfamide (group B with non-gastrointestinal/non-urological cancer, n = 37) and followed for further 6 months. RESULTS: Baseline serum creatinine concentration was 0.81 ± 0.28 mg/dl, and increased by about 0.15 mg/dl during months 1-3. Accordingly estimated glomerular filtration rate (eGFR) decreased from 90.3 ml/min ± 3.6 ml/min at baseline by about 10 ml/min during months 1-3. Renal function decreased in 75 patients (86%) in the first month (p < 0.0001). This decrease went along with clinical signs of volume expansion. Renal function tended to recover after discontinuation of the study medication. CONCLUSIONS: Therapy with rofecoxib in an antiangiogenic/antiinflammatory setting results in a decrease of renal function in nearly every patient. TRIAL REGISTRATION NUMBER: German Clinical Trials Register DRKS: DRKS00000119.

Is inflammation prior to renal transplantation predictive for cardiovascular and renal outcomes?

OBJECTIVES: Markers of non-specific inflammation, such as C-reactive protein (CRP) or leukocyte count are increased in end-stage renal disease patients. Recent studies have shown positive associations between inflammatory markers and cardiovascular mortality in kidney transplant recipients, but these analyses had been limited by sample size. The aim of our study was to determine the association between pretransplant CRP levels and leukocyte counts with posttransplant outcome in a prospectively enrolled cohort of kidney transplant recipients. METHODS: 459 consecutive patients transplanted from July 1995 to December 2007 were analyzed. Both markers were obtained prior to transplantation and patients were grouped according to baseline CRP levels (<5mg/l or >or=5mg/l) or leukocyte counts (<10,000/microl or >or=10,000/microl). RESULTS: Major cardiac events were associated with elevated pretransplant CRP levels (p<0.00003) but not leukocyte counts. Furthermore, more acute rejection episodes within 4 weeks or 6 months, as well as a lower probability of survival at 6 months were found in patients with elevated pretransplant CRP levels or leukocyte counts. CONCLUSION: Elevated pretransplant serum CRP level is a risk predictor for major cardiac events in renal transplant patients. It is also predictive, besides leukocyte counts, for acute rejection episodes. Elevated CRP levels and initial high leukocyte counts may prove to be useful markers for posttransplant course and warrant the close follow-up of such patients.

Gene expression of 5-, 12-, and 15-lipoxygenases and leukotriene receptors along the rat nephron.

The arachidonate signaling pathways comprise prostanoids formed by cyclooxygenases, EETs, and HETEs formed by cytochrome P-450 (CYP) enzymes and HETEs and leukotrienes generated by lipoxygenases. Whereas the intrarenal localization of cyclooxygenases and of some CYP enzymes along the nephron has already been determined, the localization of lipoxygenases and leukotriene-forming enzymes together with leukotriene receptors in the kidney is less clear. This study therefore aimed to determine the expression of 5-, 12-, and 15-lipoxygenases as well as the leukotriene receptors along the rat nephron. The kidneys were dissected into cortex and outer and inner medulla, and the microdissected nephron segments were collected after a collagenase digestion. mRNA abundance was determined by RT-PCR and real-time PCR. 15-LOX mRNA showed a characteristic expression pattern along the distal nephron. 12-LOX mRNA was only found in the glomerulus. Similarly, 5-LOX mRNAs together with 5-LOX-activating protein mRNAs were expressed in the glomerulus and also in the vasa recta. The leukotriene A4 hydrolase was found in all nephron segments, whereas leukotriene C4 synthase mRNA could not be found in any nephron segment. The leukotriene receptor B4 and the cysteinyl leukotriene receptor type 1 were selectively expressed in the glomerulus, whereas cysteinyl receptor type 2 was not found in any nephron segment. Our data suggest that the glomerulus is a major source and target for 5- and 12-HETE and for leukotrienes. The collecting duct system, on the other hand, appears to be a major source of 15-HETE.