Anabelle Opazo Saez

Eculizumab for Atypical Hemolytic–Uremic Syndrome

To the Editor: Atypical hemolytic–uremic syndrome is a disease of uncontrolled complement activation associated with a high mortality rate, and most cases progress to end-stage renal disease.1 Abou...

The Invs Gene Encodes a Microtubule-Associated Protein

Microtubule networks are important for many vital processes such as mitosis, cell polarity, and differentiation. Ciliary architecture and function closely depend on the microtubule cytoskeleton, and recent studies suggest a role of apical cilia of renal epithelia in the pathogenesis of polycystic kidney disease. This study evaluates the localization, potential interacting partners, and functional aspects of the Invs gene product inversin. Only recently, INVS has been identified as the gene that is mutated in nephronophthisis type 2, an autosomal recessive polycystic kidney disease. Using immunoprecipitation and co-pelleting assays, we show that the Invs gene product inversin forms a stable complex with tubulin in cultured renal epithelial cells. Inversin localizes to several components of the cytoskeleton including ciliary, random, and polarized microtubule pools. During cell divison, inversin is recruited to mitotic spindle fibers. After microtubule depolymerization using colcemid inversin and tubulin staining is no longer characterized by a network pattern but by homogeneous, diffuse distribution. Inversin does not coprecipitate with tubulin after addition of colcemid. After removal of colcemid, inversin immunofluorescence reappears together with tubulin in centrioles. Treatment with the microtubule stabilizing agent paclitaxel leads to severe alteration of the microtubule cytoskeleton with bundling and formation of long spindles of tubulin and inversin. In conclusion, inversin is closely associated with the microtubule cytoskeleton, and its spatial distribution is dependent on tubulin polymerization. Hence, altered inversin-tubulin interaction may impair ciliary function and thereby contribute to cyst development in nephronophthisis.

Can arterial stiffness parameters be measured in the sitting position

Despite the introduction of arterial stiffness measurements in the European recommendation, pulse wave velocity (PWV) and augmentation index (AI) are still not used routinely in clinical practice. It would be of advantage if such measurements were done in the sitting position as is done for blood pressure. The aim of this study was to evaluate whether there is a difference in stiffness parameters in sitting vs. supine position. Arterial stiffness was measured in 24 healthy volunteers and 20 patients with cardiovascular disease using three different devices: SphygmoCor (Atcor Medical, Sydney, Australia), Arteriograph (TensioMed, Budapest, Hungary) and Vascular Explorer (Enverdis, Jena, Germany). Three measurements were performed in supine position followed by three measurements in sitting position. Methods were compared using correlation and Bland–Altman analysis. There was a significant correlation between PWV in supine and sitting position (Arteriograph: P<0.0001, r=0.93; Vascular Explorer; P<0.0001, r=0.87). There were significant correlations between AI sitting and AI supine using Arteriograph (P<0.0001, r=0.97), Vascular Explorer (P<0.0001, r=0.98) and SphygmoCor (P<0.0001, r=0.96). When analyzed by Bland–Altman, PWV and AI measurements in supine vs. sitting showed good agreement. There was no significant difference in PWV obtained with the three different devices (Arteriograph 7.5±1.6 m s−1, Vascular Explorer 7.3±0.9 m s−1, SphygmoCor 7.0±1.8 m s−1). AI was significantly higher using the Arteriograph (17.6±15.0%) than Vascular Explorer and SphygmoCor (10.2±15.1% and 10.3±18.1%, respectively). The close agreement between sitting and supine measurements suggests that both PWV and AI can be reliably measured in the sitting position.

Effect of new‐onset diabetes mellitus on arterial stiffness in renal transplantation

New onset diabetes (NODM) is a common and serious complication of kidney transplantation, and is associated with increased cardiovascular morbidity and mortality. Cardiovascular morbidity and mortality, in turn, are closely associated with arterial stiffening. We hypothesize that NODM may be associated with an increase in arterial stiffness in renal transplantation. We compared pulse wave velocity (PWV) and augmentation index in 318 renal transplant patients with (n = 57) and without NODM (n = 261). PWV was determined from pressure tracing over carotid and femoral arteries. Augmentation‐index was derived by pulse‐wave‐analysis using radial applanation tonometry. PWV was significantly higher in transplant recipients with NODM (10.5 m/s) compared with transplant patients without NODM (8.7 m/s, P = 0.0002). There was no difference in augmentation index between patients with (27.7%) and without NODM (28.1%, P = 0.87). When analyzed by multiple regression analysis, PWV was only significantly correlated to age (P < 0.0001), NODM (P = 0.0325), and systolic blood pressure (P = 0.0081). NODM in renal transplant patients may accelerate arterial stiffening, thereby contributing to cardiovascular morbidity and mortality.

The mTOR pathway is activated in human autosomal-recessive polycystic kidney disease.

Background: An inappropriate activation of the mTOR pathway was demonstrated in the autosomal dominant (AD) form of polycystic kidney disease (PKD). To date it is unclear whether the mTOR pathway is activated in autosomal-recessive (AR) PKD, a cystic disease which occurs in childhood. The purpose of the present study was to evaluate the mTOR pathway in AR PKD. Methods: We evaluated the expression of mTOR pathway molecules in paraffin-embedded liver and kidney samples from patients with AR PKD and control specimens from animals as well as humans. Monoclonal antibodies, the phosphorylated proteins pmTOR, pS6-ribosomal-protein (pS6K), p4E-BP1, peIF4G, and phospho-tuberin/TSC2 were used. Results: mTOR was strongly expressed in renal cyst-lining cells and bile ducts from AR PKD specimen. S6K immunostaining was strong in smaller tubules and weak both in larger renal cysts and in the bile duct epithelium. In controls, mTOR and S6K were expressed in distal tubule segments. 4E-BP1-immunostaining was restricted to noncystic tubules in AR PKD. eIFG4-immunostaining was observed in bile duct epithelium in AR PKD, but not in control tissue. Tuberin/TSC2 immunostaining was negative in all specimens. Conclusion: Our data suggest that the mTOR pathway may be activated in AR PKD, and mTOR molecules may represent a potential target to slow down cyst development in this disease.

Clonidine lowers blood pressure by reducing vascular resistance and cardiac output in young, healthy males

Purpose: Clonidine is a classical sympatholytic drug that is widely used for the treatment of hypertension. Experimental and clinical studies suggest that Clonidine may activate baroreflex. The aim of this study was to determine the hemodynamic response to Clonidine under physiological conditions and to test the hypothesis that Clonidine would reduce cardiac output and blood pressure resulting in an increase in total peripheral resistance.Methods: Clonidine’s hemodynamic effect was evaluated in 28 young, healthy subjects after a single i.v. dose of 1 μ g × kg− 1. Impedance cardiography, systolic time intervals and pulse wave analysis were used to characterize myocardial and vascular function.Results: Clonidine lowered blood pressure, heart rate, left ventricular ejection time, and pulse wave velocity and increased pre-ejection period. Stroke volume and cardiac output decreased gradually over the investigation time of 240 min. Central systolic blood pressure (SBP) was lowered to a larger extent than peripheral SBP. Total peripheral resistance was characterized by an immediate fall of short duration followed by a continuous rise above baseline after 120 min. Placebo did not have any significant effect on hemodynamic parameters.Conclusions: Clonidine’s blood pressure lowering effect is mediated by both an immediate decrease in vascular resistance and a prolonged decrease in cardiac output, and Clonidine lowers central SBP more than peripheral SBP.

Endothelin-B-receptor-selective antagonist inhibits endothelin-1 induced potentiation on the vasoconstriction to noradrenaline and angiotensin II.

Objective Endothelin-A-receptor-antagonists inhibit angiotensin II- and noradrenaline-induced vasoconstriction. Whether functional constrictive endothelin-B-receptors play a role in the endothelin-1-mediated potentiation of vasoconstriction to angiotensin II and noradrenaline is thus far unknown. Methods We studied the effects of noradrenaline and angiotensin II (10−14,−16,−18 mol/l) in the presence of exogenous endothelin-1 (10−18 mol/l) with and without selective endothelin-B-receptor-blockade by BQ-788 (10−8 mol/l) and dual receptor blockade with BQ-788 and the endothelin-A-selective antagonist BQ-123 (10−8 mol/l) in 14 healthy male volunteers (aged 20–28). Studies were performed in the human skin microcirculation under in vivo conditions using laser-Doppler flowmetry and double injection technique. The area under the time-response curve of all doses was calculated. Results Endothelin-1 potentiated the effects of angiotensin II and noradrenaline (−944 ± 139 perfusion units (PU), P < 0.01; −926 ± 117 PU, P < 0.05, respectively). In the presence of BQ-788, the potentiating effect of endothelin-1 was significantly blunted (−624 ± 132 PU, P < 0.01; −549 ± 136 PU, P < 0.01, respectively). In the presence of BQ-123 and BQ-788 the vasoconstriction was fully inhibited (431 ± 108 PU, P < 0.001 and 421 ± 86 PU, P < 0.001, respectively). Conclusions These data suggest that functional vasoconstrictive endothelin-B receptors on vascular smooth muscle cells may contribute to the potentiating effects of high local concentrations of endothelin-1 on the vasoconstriction to noradrenaline and angiotensin II in human microcirculation.

N-cadherin is depleted from proximal tubules in experimental and human acute kidney injury

Ischemia remains the most common cause of acute kidney injury (AKI). Decreased intercellular adhesion and alterations in adhesion molecules may contribute to the loss of renal function observed in AKI. In the present study, we evaluated the distribution of adhesion molecules in the human kidney and analyzed their expression in human and experimental AKI. Specimens of human kidneys obtained from patients with and without AKI were stained for the cell adhesion molecules E-cadherin, N-cadherin and β-catenin. Experimental AKI in rats was induced by renal artery clamping. Immunostaining and immunoblotting were carried out for E-cadherin, N-cadherin and β-catenin. Proximal tubule cells from opossum kidneys (OKs) were used to analyze the effect of chemical hypoxia (ATP depletion) in vitro. In the adult human kidney, N-cadherin was expressed in proximal tubules, while E-cadherin was expressed in other nephron segments. β-Catenin was expressed in both proximal and distal tubules. In human AKI and in ischemic rat kidneys, N-cadherin immunostaining was depleted from proximal tubules. There was no change in E-cadherin or β-catenin. In vitro, OK cells expressed N-cadherin only in the presence of collagen, and ATP depletion led to a depletion of N-cadherin. Collagen IV staining was reduced in ischemic rat kidneys compared to controls. The results of the study suggest that N-cadherin may play a significant role in human and experimental AKI.

Differential tissue distribution of the Invs gene product inversin

Nephronophthisis is a common genetic cause of end-stage renal disease in childhood. Recently, Invs was identified as the gene mutated in the infantile form of nephronophthisis. Humans with nephronophthisis develop a large number of extrarenal manifestations, including situs variations, anomalies of the hepatobiliary system, retinal degeneration and cerebellar ataxia. Mice homozygous for a mutation in the Invs gene (inv mouse) die during the first week after birth as a result of renal and liver failure. Although organ anomalies have been characterized in human nephronophthisis and the inv mouse, little is known about the tissue expression of the Invs gene product, inversin. We have used laser confocal microscopy of paraffin-embedded murine tissue sections to provide the first detailed characterization of the distribution of inversin in various organs. Our results show that inversin is localized to distal tubules in the kidney, hepatic bile ducts, acinar and ductal pancreatic cells, epithelial intestinal cells, splenic germinal centres, bronchiolar epithelial cells, dendrites of cerebellar Purkinje cells, retinal neural cells and spermatocytes and spermatids in the testis. The localization of inversin in distal tubules in the kidney and in extrarenal tissues suggests that the expression of this protein has an important function in a variety of organs. Further studies are required to understand the way in which mutations in the Invs gene lead to the multi-organ pathology of inv mouse and human nephronophthisis.

Arterial Stiffness:A Potential Therapeutic Target to Reduce Cardiovascular Mortality

Stiffening of the arterial wall is one major mechanism responsible for morbidity and mortality in cardiovascular disease including hypertension and coronary heart disease. Various physiological and pathophysiological parameters influence arterial stiffening including age, gender, blood pressure, nutrition, smoking, and diseases such as hypertension, diabetes, renal failure, and hypercholesterolemia. Thus, assessing arterial stiffness has become a widely used tool to investigate the function of large arteries in epidemiological and clinical studies. Traditionally, arterial stiffness has been assessed by pulse wave velocity, a non-invasive parameter which has been shown to predict cardiovascular mortality. In addition, pulse wave analysis has been increasingly used to determine augmentation index, a parameter that describes the effect of pulse wave reflection on the central aortic pressure configuration. For many years arterial stiffness had been thought to be relatively unaffected by drugs. However, recent studies suggest that arterial stiffness can be pharmacologically modulated. Hence, improving arterial stiffness may be a potential therapeutic target to reduce cardiovascular mortality. This review attempts to summarize the current tools used to assess arterial stiffness and the drugs that modify large artery stiffness in-vivo.