László Wagner

Protection of Wistar Furth Rats from Chronic Renal Disease Is Associated with Maintained Renal Nitric Oxide Synthase

Wistar Furth (WF) rats do not develop renal injury after severe reduction of renal mass. Because clinical and animal studies suggested that nitric oxide (NO) deficiency occurs and may contribute to chronic renal disease (CRD), the status of the NO system in WF versus Sprague Dawley (SD) rats was examined with the 5/6 renal ablation/infarction (A/I) model of CRD. Eleven weeks after A/I, SD rats developed proteinuria, severe kidney damage, decreased renal function, and marked decreases in total and renal NO synthase (NOS), specifically neuronal NOS. In contrast, WF rats exhibited elevated baseline and maintained post-A/I total NO production, with no decrease in renal cortex NOS activity despite a decrease in remnant neuronal NOS abundance. When low-dose chronic Nomega-nitro-L-arginine methyl ester treatment was added for WF A/I-treated rats, rapid progression of CRD was observed. In conclusion, elevated NO production in WF rats was associated with protection from the progression of CRD after renal mass reduction. The protection might be attributable to greater total and renal NO-generating capacity and increased nephron number, compared with SD rats. NOS inhibition rendered WF rats susceptible to progression, suggesting a possible critical threshold for NO production, below which renal injury occurs.

Post‐transplant diabetes mellitus in children following renal transplantation

Abstract:  PTDM plays a role in chronic allograft nephropathy and decreases graft and patient survival. Considering the serious outcome of chronic hyperglycemia, the importance of early recognition and the few data in children, in this retrospective analysis we studied the characteristics and risk factors of PTDM in 45 pediatric renal transplant recipients receiving Tac or CyA‐based immunosuppression. Fasting blood sampling and OGTT were performed. PTDM has been developed in six patients (13%), while seven children (16%) had IGT, with the overall incidence of a glucose metabolic disorder of 29% in pediatric renal transplants. Patients in the PTDM + IGT group were younger and had higher systolic blood pressure and serum triglyceride level than children with normal glucose tolerance. Multivariate analysis identified Tac treatment, Tac trough level, steroid pulse therapy and family history of diabetes to be associated with the onset of PTDM. In pediatric renal transplants, OGTT and frequent assessment of blood glucose levels might be essential not only in the post‐transplant management, but also prior to transplantation, particularly with family history of diabetes. Careful monitoring and modified protocols help to minimize the side effects of Tac and corticosteroids.

Cigarette Smoke-Induced Alterations in Endothelial Nitric Oxide Synthase Phosphorylation: Role of Protein Kinase C

Endothelial nitric oxide synthase (eNOS) is regulated by phosphorylation of Ser(1177) and Thr(495), which affects NO bioavailability. Cigarette smoke disturbs the eNOS-cGMP-NO pathway and causes decreased NO production. Here the authors investigated the acute effects of cigarette smoke on eNOS phosphorylation, focusing on protein kinases (PKs). Endothelial cell culture was concentration- and time-dependently treated first with cigarette smoke buffer (CSB), then with reduced glutathione (GSH) or various PK inhibitors (H-89, LY-294002, Ro-318425, and ruboxistaurin). eNOS, phospho-Ser(1177)-eNOS, phospho-Thr(495)-eNOS, Akt(PKB), and phospho-Akt protein levels were determined by Western blot. CSB increased the phosphorylation of eNOS at Ser(1177) and more at Thr(495) in a concentration- and time-dependent manner (p < .01, p < .05 versus control, respectively) and resulted in the dissociation of the active dimeric form of eNOS (p < .05). GSH decreased the phosphorylation of eNOS at both sites (p < .05 versus CSB without GSH) and prevented the decrease of dimer eNOS level. CSB treatment also decreased the level of phospho-Ser(473)-Akt (p < .05 versus control). Inhibition of PKA by H-89 did not affect CSB-induced phosphorylation, whereas the PKB inhibitor LY-294002 enhanced it at Ser(1117). The PKC blockers Ro-318425 and ruboxistaurin augmented the CSB-induced phosphorylation at Ser(1177) but decreased phosphorylation at Thr(495) (p < .05 versus CSB). Cigarette smoke causes a disruption of the enzymatically active eNOS dimers and shifts the eNOS phosphorylation to an inhibitory state. Both effects might lead to reduced NO bioavailability. The shift of the eNOS phosphorylation pattern to an inhibitory state seems to be independent of the PKA and phosphoinositol 3-kinase (PI3-K)/Akt pathways, whereas PKC appears to play a key role.

Na+,K+‐ATPase is modulated by angiotensin II in diabetic rat kidney – another reason for diabetic nephropathy?

Angiotensin II (ANGII) plays a central role in the enhanced sodium reabsorption in early type 1 diabetes in man and in streptozotocin‐induced (STZ) diabetic rats. This study investigates the effect of untreated STZ‐diabetes leading to diabetic nephropathy in combination with ANGII treatment, on the abundance and localization of the renal Na+,K+‐ATPase (NKA), a major contributor of renal sodium handling. After 7 weeks of STZ‐diabetes (i.v. 65 mg kg−1) a subgroup of control (C) and diabetic (D7) Wistar rats were treated with ANGII (s.c. minipump 33 μg kg−1 h−1 for 24 h; CA and D7A). We measured renal function and mRNA expression, protein level, Serin23 phosphorylation, subcellular distribution, and enzyme activity of NKA α‐1 subunit in the kidney cortex. Diabetes increased serum creatinine and urea nitrogen levels (C versus D7), as did ANGII (C versus CA, D7 versus D7A). Both diabetes (C versus D7) and ANGII increased NKA α‐1 protein level and enzyme activity (C versus CA, D7 versus D7A). Furthermore, the combination led to an additive increase (D7 versus D7A, CA versus D7A). NKA α‐1 Ser23 phosphorylation was higher both in D7 and ANGII‐treated rats in the non‐cytoskeletal fraction, while no signal was detected in the cytoskeletal fraction. Control kidneys showed NKA α‐1 immunopositivity on the basolateral membrane of proximal tubular cells, while both D7 and ANGII broadened NKA immunopositivity towards the cytoplasm. Our study demonstrates that diabetes mellitus (DM) increases the mRNA expression, protein level, Ser23 phosphorylation and enzyme activity of renal NKA, which is further elevated by ANGII. Despite an increase in total NKA quantity in diabetic nephropathy, the redistribution to the cystosol suggests the Na+ pump is no longer functional. ANGII also caused translocation from the basolateral membrane, thus in diabetic states where ANGII level is acutely elevated, the loss of NKA will be exacerbated. This provides another mechanism by which ANGII blockade is likely to be protective.

Aldosterone antagonists in monotherapy are protective against streptozotocin-induced diabetic nephropathy in rats

Angiotensin converting enzyme inhibitors (ACEi) and angiotensin II receptor blockers (ARB) are the standard clinical therapy of diabetic nephropathy (DN), while aldosterone antagonists are only used as adjuncts. Previously in experimental DN we showed that Na/K ATPase (NKA) is mislocated and angiotensin II leads to superimposed renal progression. Here we investigated the monotherapeutic effect of aldosterone blockers on the progression of DN and renal NKA alteration in comparison to ACEi and ARBs. Streptozotocin-diabetic rats developing DN were treated with aldosterone antagonists; ACEi and ARB. Renal function, morphology, protein level and tubular localization of NKA were analyzed. To evaluate the effect of high glucose per se; HK-2 proximal tubular cells were cultured in normal or high concentration of glucose and treated with the same agents. Aldosterone antagonists were the most effective in ameliorating functional and structural kidney damage and they normalized diabetes induced bradycardia and weight loss. Aldosterone blockers also prevented hyperglycemia and diabetes induced increase in NKA protein level and enzyme mislocation. A monotherapy with aldosterone antagonists might be as, or more effective than ACEi or ARBs in the prevention of STZ-induced DN. Furthermore the alteration of the NKA could represent a novel pathophysiological feature of DN and might serve as an additional target of aldosterone blockers.

Genetic analysis and functional characterization of novel mutations in a series of patients with atypical hemolytic uremic syndrome.

Atypical hemolytic uremic syndrome (aHUS) is a rare disorder caused by dysregulation of the complement alternative pathway, and associated with mutations in genes of complement components and regulators. In the recent years several studies have been published describing these mutations, however, no data is available from the Central and Eastern European region. In this study we present a detailed genetic analysis of our 30 patients, hospitalized with the diagnosis of aHUS in the past 7 years. We analyzed the genetic variants of genes CFH, CFI, CD46, THBD, CFB and C3; furthermore the possible effect of mutations that may alter the function or level of factor H protein was also investigated. We identified 27 (12 novel and 15 previously described) potentially disease-causing mutations in the candidate genes in 23 patients. Genetic analysis of family members revealed that in most cases the disease develops in individuals with multiple genetic risk factors, which may explain the low penetrance of the mutations. Here we showed that two novel mutations (p.W198R, p.P1161T) and a previously reported one (p.R1215Q) in CFH caused impaired regulation as indicated by increased lysis in hemolytic test, while four CFH mutations (p.V609D, p.S722X, p.T1216del and p.C448Y) were associated with decreased factor H protein level in serum as determined by allele-specific immunoassay. These results further point to the necessity of complete genetic workup of patients with aHUS and to the importance of functional characterization of novel variations.

Role of iron in the interaction of red blood cells with methylglyoxal. Modification of L-arginine by methylglyoxal is catalyzed by iron redox cycling.

Diabetes mellitus is characterized by increased methylglyoxal (MG) production. The aim of the present study was to investigate the role of iron in the cellular and molecular effects of MG. A red blood cell (RBC) model and L-arginine were used to study the effects of MG in the absence and presence of iron. Intracellular free radical formation and calcium concentration were measured using dichlorofluorescein and Fura-2-AM, respectively. Effects of MG were compared to the effect of ferrous iron. Reaction of L-arginine with MG was investigated by electron spin resonance (ESR) spectroscopy and by a spectrophotometric method. MG caused an iron dependent oxidative stress in RBCs and an elevation of the intracellular calcium concentration due to formation of reactive oxygen species. Results of co-incubation of MG with ferrous iron in the RBC model suggested an interaction of MG and iron; one interaction was a reduction of ferric iron by MG. A role of iron in the MG-L-arginine reaction was also verified by ESR spectroscopy and by spectrophotometry. Ferric iron increased free radical formation as detected by ESR in the MG-L-arginine reaction; however, ferrous iron decreased it. The reaction of MG with L-arginine yielded a brown product as detected spectrophotometrically and this reaction was catalyzed at a lower rate with ferric iron but at a higher rate with ferrous iron. These data suggest that MG causes oxidative stress in cells, which is due at least in part to ferric iron reduction by MG and to the modification of amino acids e.g. L-arginine by MG, which is catalyzed by iron redox cycling.

Effects of angiotensin type 1 receptor blockade on arginine and ADMA synthesis and metabolic pathways in fawn-hooded hypertensive rats

BACKGROUND The fawn-hooded hypertensive (FHH) rat develops spontaneous glomerulosclerosis that is ameliorated by inhibition of the angiotensin II type 1 receptor (AT-1). Since kidney damage is associated with nitric oxide (NO) deficiency, we investigated how AT-1 antagonism influenced nitric oxide synthase (NOS), as well as NOS substrate [L-arginine (L-Arg)] and inhibitor [asymmetric dimethylarginine (ADMA)]. L-Arg is synthesized by renal argininosuccinate synthase/argininosuccinate lyase (ASS/ASL) and then either consumed within the kidney by arginase II or NOS or released into the circulation. L-Arg is then taken up from plasma into cells where it can be utilized by NOS and other pathways. The competitive inhibitor of NOS, ADMA, is degraded by dimethylarginine dimethylaminohydrolase (DDAH). METHODS AND RESULTS Male FHH rats were put on a 40% casein diet for 13 weeks, and some received AT-1 antagonist which reduced blood pressure and kidney weight and prevented glomerulosclerosis and hyperfiltration. The AT-1 antagonist reduced the expression of DDAH2, increased DDAH1 and increased total DDAH activity in the kidney cortex, although there was no change in plasma or kidney cortex ADMA levels. The AT-1 antagonist caused no change in the expression of renal ASS/ASL, but reduced renal and aortic arginase expression and renal arginase activity, which could explain the increased plasma L-Arg. In separate studies, 1 week of AT-1 blockade in young FHH rats had no effect on any of these parameters. CONCLUSION Thus, the net result of AT-1 antagonist was an improved L-Arg to ADMA ratio due to the prevention of renal and vascular arginase activation which favours increased NO production. Since 1 week of AT-1 blockade in the absence of kidney damage was without effect on arginases, this suggests that the reduction in arginase activity is secondary to the prevention of structural damage rather than a direct immediate effect of AT-1 antagonism.

Cigarette smoke and its formaldehyde component inhibit bradykinin-induced calcium increase in pig aortic endothelial cells

Bradykinin-induced increase in the intracellular concentration of free calcium evokes an activation of the endothelial nitric oxide synthase (eNOS) enzyme, producing nitric oxide (NO). Cigarette smoke inhibits the eNOS-NO-cGMP signaling pathway. The pathomechanism of this deleterious effect of smoke on NO production is unknown. The aim of this study was to investigate the effect of gas phase smoke trapped in a buffer (smoke buffer, SB) on the bradykinin-induced calcium increase in cultured endothelial cells. FURA-2-AM was used to detect bradykinin-induced calcium increase. A sensitive, fluorescent method using O-phthaldialdehyde was used for the determination of intracellular reduced glutathione (GSH) and protein-thiol levels. SB caused a time- and concentration-dependent inhibition of bradykinin-induced calcium increase. Formaldehyde, a component of SB, inhibited bradykinin-induced calcium increase in concentrations characteristic for SB. SB decreased both the intracellular GSH (0.22 +/- 0.06 vs. 2.23 +/- 0.32 mumol/g protein, SB vs. control, p < .001) and protein-thiol levels (4.98 +/- 0.54 vs. 7.31 +/- 0.97 microEqu GSH/g protein, SB vs. control, p < .05) in the endothelial cells. Intracellular GSH and protein-thiol levels were not changed by 80 microM formaldehyde. GSH (4 mM) prevented the effect of SB (p < .001) and formaldehyde (p < .05) on the bradykinin-induced calcium increase. Our data support the premise that SB inhibits bradykinin-induced calcium increase. This inhibition is partially due to protein-thiol oxidation but may also be caused by the formaldehyde content of SB, which inhibits calcium increase in a protein-thiol-independent manner.

σ1-Receptor Agonism Protects against Renal Ischemia-Reperfusion Injury

Mechanisms of renal ischemia-reperfusion injury remain unresolved, and effective therapies are lacking. We previously showed that dehydroepiandrosterone protects against renal ischemia-reperfusion injury in male rats. Here, we investigated the potential role of σ1-receptor activation in mediating this protection. In rats, pretreatment with either dehydroepiandrosterone or fluvoxamine, a high-affinity σ1-receptor agonist, improved survival, renal function and structure, and the inflammatory response after sublethal renal ischemia-reperfusion injury. In human proximal tubular epithelial cells, stimulation by fluvoxamine or oxidative stress caused the σ1-receptor to translocate from the endoplasmic reticulum to the cytosol and nucleus. Fluvoxamine stimulation in these cells also activated nitric oxide production that was blocked by σ1-receptor knockdown or Akt inhibition. Similarly, in the postischemic rat kidney, σ1-receptor activation by fluvoxamine triggered the Akt-nitric oxide synthase signaling pathway, resulting in time- and isoform-specific endothelial and neuronal nitric oxide synthase activation and nitric oxide production. Concurrently, intravital two-photon imaging revealed prompt peritubular vasodilation after fluvoxamine treatment, which was blocked by the σ1-receptor antagonist or various nitric oxide synthase blockers. In conclusion, in this rat model of ischemia-reperfusion injury, σ1-receptor agonists improved postischemic survival and renal function via activation of Akt-mediated nitric oxide signaling in the kidney. Thus, σ1-receptor activation might provide a therapeutic option for renoprotective therapy.