Hepcidin-25 in diabetic chronic kidney disease is predictive for mortality and progression to end stage renal disease.

BACKGROUND: Anemia is common and is associated with impaired clinical outcomes in diabetic chronic kidney disease (CKD). It may be explained by reduced erythropoietin (EPO) synthesis, but recent data suggest that EPO-resistance and diminished iron availability due to inflammation contribute significantly. In this cohort study, we evaluated the impact of hepcidin-25--the key hormone of iron-metabolism--on clinical outcomes in diabetic patients with CKD along with endogenous EPO levels. METHODS: 249 diabetic patients with CKD of any stage, excluding end-stage renal disease (ESRD), were enrolled (2003-2005), if they were not on EPO-stimulating agent and iron therapy. Hepcidin-25 levels were measured by radioimmunoassay. The association of hepcidin-25 at baseline with clinical variables was investigated using linear regression models. All-cause mortality and a composite endpoint of CKD progression (ESRD or doubling of serum creatinine) were analyzed by Cox proportional hazards models. RESULTS: Patients (age 67 yrs, 53% male, GFR 51 ml/min, hemoglobin 131 g/L, EPO 13.5 U/L, hepcidin-25 62.0 ng/ml) were followed for a median time of 4.2 yrs. Forty-nine patients died (19.7%) and forty (16.1%) patients reached the composite endpoint. Elevated hepcidin levels were independently associated with higher ferritin-levels, lower EPO-levels and impaired kidney function (all p<0.05). Hepcidin was related to mortality, along with its interaction with EPO, older age, greater proteinuria and elevated CRP (all p<0.05). Hepcidin was also predictive for progression of CKD, aside from baseline GFR, proteinuria, low albumin- and hemoglobin-levels and a history of CVD (all p<0.05). CONCLUSIONS: We found hepcidin-25 to be associated with EPO and impaired kidney function in diabetic CKD. Elevated hepcidin-25 and EPO-levels were independent predictors of mortality, while hepcidin-25 was also predictive for progression of CKD. Both hepcidin-25 and EPO may represent important prognostic factors of clinical outcome and have the potential to further define "high risk" populations in CKD.

Endogenous erythropoietin and the association with inflammation and mortality in diabetic chronic kidney disease.

BACKGROUND AND OBJECTIVES: Anemia and inflammation are prevalent in diabetic patients with chronic kidney disease (CKD). The role of endogenous erythropoietin (EPO) in the pathophysiology of anemia in chronic diseases and its relationship to clinical outcomes remain uncertain. In this cohort study, we aimed to identify factors associated with endogenous EPO levels and investigate their relation to all-cause mortality. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: Between 2004 and 2005, 215 patients with type 2 diabetes were enrolled. Exclusion criteria included stage renal disease ESRD and any form of anemia therapy. The association of EPO levels with clinical and laboratory variables was investigated by linear regression modeling. Predictors of all-cause mortality were evaluated by Cox proportional hazards analyses. RESULTS: Patients (median age, 67 years; 52% men; median duration of diabetes, 10 years; median estimated GFR, 49 ml/min per 1.73 m²) were followed for up to 7.0 years. Forty-one patients died. Elevated EPO levels were independently associated with elevated C-reactive protein, low ferritin, and hypertension, in a multivariate model that also included age, cardiovascular disease, kidney function, albumin, cholesterol, and hemoglobin. Higher EPO levels were independently predictive for mortality, as were age, low levels of albumin, and cardiovascular disease. CONCLUSIONS: In diabetic patients with CKD, elevated endogenous EPO levels were predictive for mortality and were related mainly to markers of inflammation, independent of kidney function, and despite low hemoglobin levels. Understanding the phenomenon of EPO resistance and iron dysregulation caused by inflammation is crucial for effective and safe treatment of anemia in patients with CKD.

Ischemic acute renal failure in the rat: effects of L-arginine and superoxide dismutase on renal function.

BACKGROUND: Regulation of renal hemodynamics -- especially intraglomerular hemodynamics -- is closely related to the L-arginine (L-Arg)/nitric oxide (NO) pathway, both under basal conditions and in acute renal failure (ARF). Also, superoxide anions -- which may react with NO -- play a role in ischemic ARF. L-Arg not only has beneficial effects on glomerular filtration rate (GFR) but also reduces O2(-) production and prevents NO synthase isoform I up-regulation. Thus, it is of interest to elucidate whether the potential beneficial effects of L-Arg in reperfusion can be augmented by additional treatment with superoxide dismutase (SOD). METHODS: ARF was induced by renal artery clamping for 40 minutes. Animals were treated with either L-Arg, SOD, a combination of both, or saline. GFR, renal plasma flow (RPF), filtration fraction (FF) and blood pressure were recorded at baseline, after induction of ARF, during drug infusion and thereafter. RESULTS: Renal artery clamping induces a severe drop of GFR, RPF and FF, which all are improved by L-Arg and SOD. Increasing GFR is mainly due to better renal perfusion. FF fell after reperfusion and increased with L-Arg and SOD, indicating improvement of disturbed intrarenal hemodynamics. Combined administration of L-Arg and SOD showed similar effects in comparison with each substance alone, but did not induce additional effects on GFR and RPF. CONCLUSIONS: L-Arg and SOD exert beneficial effects in ischemic ARF. Probably, improvements in reducing NO availability and in enhancing O2(-) formation are both playing a mediating role. The underlying mechanisms regulating the interplay between NO availability and O2(-) formation need to be elucidated in further studies using -- aside from other means -- selective NOS inhibitors, intervention in different experimental phases and treatment for a longer period.

L-Arginine does not affect renal morphology and cell survival in ischemic acute renal failure in rats.

BACKGROUND: L-Arginine (L-Arg), a substrate of nitric oxide synthases, improves renal function in ischemic acute renal failure (iARF). We evaluated whether L-Arg improves renal morphology and cell survival in the course of iARF. METHODS AND RESULTS: iARF was induced in rats by bilateral clamping of renal arteries for 45 min. L-Arg was applied intraperitoneally during clamping, and orally during 14 days of follow-up. Morphology and cell survival of renal cortical and medullar tissue was analyzed on days 1, 3, 7, and 14 of follow-up, using toluidine blue staining and immunohistochemistry of perfusion-fixated tissue, and Western blot analysis of tissue homogenate. Renal tubular injury showed typical features of necrosis and was most severe on days 1 and 3 after clamping, predominantly in S3 segments, with almost complete recovery by day 14. Enhanced medullar monocyte infiltration, determined by ED-1 expression as well as by immunohistochemistry, and enhanced expression of proliferating cell nuclear antigen (PCNA), indicative of proliferation and regeneration, accompanied these morphological changes. Compared to controls, L-Arg had no impact on renal morphology, ED-1, and PCNA expression. Furthermore, expression of markers of apoptosis Bcl-2, Bax, and cleaved caspase-3 was only slightly increased in iARF rats, compared to sham-operated animals, and was also not influenced by L-Arg. CONCLUSION: Despite its repeatedly reported positive impact on renal function as also shown in our model, L-Arg does not alter cell death and proliferation in the course of iARF in our model. Thus, different mechanisms have to be considered, in particular improved intrarenal hemodynamics.

Advanced renal insufficiency in a 34-year-old man with Lowe syndrome.

Lowe syndrome, or oculocerebrorenal syndrome of Lowe (OCRL), is a rare X-chromosomal disorder characterized by renal dysfunction, congenital cataract, and, in the majority of cases, mental retardation. Although gradual loss of renal function has been seen in most patients, age of onset of deterioration in renal function and its severity and course over time in adult patients have not been documented in detail. We report a 34-year-old man with OCRL without histological changes in renal tissue at the ages of 5 and 8 years, whereas at the age of 29 years, focal and segmental glomerulosclerosis and tubular atrophy were found. During subsequent follow-up of 5 years, progressive loss of renal function occurred, and end-stage renal failure can be expected in a few years. Clinical diagnosis was strongly supported by detecting a nucleotide substitution (IVS19+1g-->a) in the evolutionarily strictly conserved splice consensus sequence of intron 19 of the OCRL1 gene, which may interfere with normal splicing. Clinical course, possible molecular consequences of this novel mutation, and correlation between genotype and phenotype are discussed.

L-Arginine counteracts nitric oxide deficiency and improves the recovery phase of ischemic acute renal failure in rats.

BACKGROUND: In ischemic acute renal failure (ARF), nitric oxide-dependent regulation of renal hemodynamics and glomerular function is disturbed. Previous studies indicate that the nitric oxide precursor l-arginine (l-Arg) has beneficial effects on renal function. Here we further analyzed the impact of l-Arg on functional and biochemical parameters of nitric oxide signaling during the course of ischemic ARF. METHODS: Ischemic ARF was induced in rats by bilateral clamping of renal arteries for 45 minutes. l-Arg was applied intraperitoneally during clamping, and orally during 14 days of follow-up. Glomerular filtration rate (GFR) and renal plasma flow (RPF) were measured, and biochemical parameters analyzed by protein immunoblots. RESULTS: Clamping resulted in 70% to 90% reduction of GFR and RPF, with a gradual recovery by day 14. Using an in situ assay with the oxidative fluorescent dye hydroethidine, increased tubular generation of O2- was detected in the early course of ischemic ARF, indicating enhanced oxidative stress. These findings were accompanied by up-regulation of the nitric oxide receptor, soluble guanylate cyclase, and by significant regulatory changes of inducible nitric oxide synthase (iNOS) and endothelial NOS expression. l-Arg had a beneficial effect on GFR and RPF, decreased O2- production, diminished up-regulation of soluble guanylate cyclase, and prevented up-regulation of iNOS. CONCLUSION: Ischemic ARF is accompanied by marked alterations in the expression of key enzymes of the nitric oxide pathway, indicative for deficiency of constitutive NOS activity. l-Arg supplementation reduces O2- generation and significantly improves the expression of nitric oxide signaling proteins as well as the recovery phase of ischemic ARF.

L-arginine deficiency and supplementation in experimental acute renal failure and in human kidney transplantation.

BACKGROUND: The "L-arginine paradox" refers to situations where L-arginine (L-Arg) supplementation stimulates nitric oxide (NO) synthesis, despite saturating intracellular concentrations. This paradox is frequently observed in acute renal failure (ARF). First, the effects of L-Arg on renal function of rats with ARF were studied. Based on the promising results from these initial studies, the second part of our study searched for a form of ARF in humans that could be studied easily under conditions with little variance and yet was linked with endothelial dysfunction. Thus, we investigated the effects of L-Arg supplementation immediately after kidney transplantation in 54 patients. METHODS: In uranyl nitrate-induced ARF in rats the effects of L-Arg and L-NNA (inhibitor of nitric oxide synthase; NOS) on glomerular filtration rate (GFR), renal plasma flow (RPF), blood pressure (BP) and NOx (NO2- +NO3-) excretion were examined. Tissue L-Arg levels, NOS activities, immunodetection of NOS and superoxide dismutase (SOD), activities of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and xanthine oxidase, and nitrotyrosine immunoreactive protein (NT-IR) were determined and compared to sham operated animals. Secondly, in a randomized, double-blind study, the effects of L-Arg on GFR and RPF were investigated in 54 kidney transplant recipients, receiving IV L-Arg for three days. GFR and RPF were measured on days 1, 3, 5 and 10 by scintigraphy. RESULTS: In experimental ARF, decreased RPF and GFR were associated with reduced tissue L-Arg levels, endothelial NOS-III expression, NO formation and NOx excretion. Reduction in GFR, RPF and NOx excretion were reversed upon administration of exogenous L-Arg. There also was a loss of Cu,Zn-SOD, a key enzyme against oxidative stress, and an elevation of NT-IR, an indicator of nitrosative stress and suggested marker for pathological actions of NO. However, NT-IR was not dependent on de novo NO synthesis and not related to the functional effects of l-Arg administration. In kidney transplant recipients receiving organs with a short cold ischemia time (CIT) and from young donors, that is, those with a higher likelihood of a functional endothelium, early administration of L-Arg improved renal function. CONCLUSION: Both experimental and clinical data show that \L-Arg deficiency and endothelial dysfunction are pathomechanistically relevant in ARF. The data suggest a therapeutic potential for the administration of L-Arg in ARF and kidney transplantation, at least in patients receiving kidneys with shorter CIT and from younger donors.