Clinical Characteristics and Outcome of Canadian Patients Diagnosed With Atypical Hemolytic Uremic Syndrome.

BACKGROUND: Atypical hemolytic uremic syndrome (aHUS) is an extremely rare, heterogeneous disease of uncontrolled activation of the alternative complement pathway that is difficult to diagnose. We have evaluated the Canadian patients enrolled in the Global aHUS Registry to provide a Canadian perspective regarding the diagnosis and management of aHUS and the specific challenges faced. OBJECTIVE: To evaluate Canadian patients enrolled in the Global aHUS Registry to provide a Canadian perspective regarding the diagnosis and management of aHUS and the specific challenges faced. METHODS: The Global aHUS Registry is an observational, noninterventional, multicenter study that has prospectively and retrospectively collected data from patients of all ages with an investigator-made clinical diagnosis of aHUS, irrespective of treatment. Patients of all ages with a clinical diagnosis of aHUS were eligible and invited for enrollment, and those with evidence of Shiga toxin-producing Escherichia coli infection, or with ADAMTS13 activity ≤10%, or a subsequent diagnosis of thrombotic thrombocytopenic purpura were excluded. Data were collected at enrollment and every 6 months thereafter and were analyzed descriptively for categorical and continuous variables. End-stage renal disease (ESRD)-free survival was evaluated using Kaplan-Meier estimates, and ESRD-associated risk factors of interest were assessed using Cox proportional hazards regression models. Patients were censored at start of eculizumab for any outcome measures. RESULTS: A total of 37 Canadian patients were enrolled (15 pediatric and 22 adult patients) between February 2014 and May 2017; the median age at initial aHUS presentation was 25.9 (interquartile range = 6.7-51.7) years; 62.2% were female and 94.6% had no family history of aHUS. Over three-quarters of patients (78.4%) had no conclusive genetic or anti-complement factor H (CFH) antibody information available, and most patients (94%) had no reported precipitating factors prior to aHUS diagnosis. Nine patients (8 adults and 1 child) experienced ESRD prior to the study. After initial presentation, there appears to be a trend that children are less likely to experience ESRD than adults, with 5-year ESRD-free survival of 93 and 56% (P = .05) in children and adults, respectively. Enrolling physicians reported renal manifestations in all patients at initial presentation, and 68.4% of patients during the chronic phase (study entry ≥6 months after initial presentation). Likewise, extrarenal manifestations also occurred in more patients during the initial presenting phase than the chronic phase, particularly for gastrointestinal (61.1% vs 15.8%) and central nervous system sites (38.9% vs 5.3%). Fewer children than adults experienced gastrointestinal manifestations (50.0% vs 70.0%), but more children than adults experienced pulmonary manifestations (37.5% vs 10.0%). CONCLUSIONS: This evaluation provides insight into the diagnosis and management of aHUS in Canadian patients and the challenges faced. More genetic or anti-CFH antibody testing is needed to improve the diagnosis of aHUS, and the management of children and adults needs to consider several factors such as the risk of progression to ESRD is based on age (more likely in adults), and that the location of extrarenal manifestations differs in children and adults.

CONTEXTE: Le syndrome hémolytique et urémique atypique (SHUa) se caractérise par l'activation incontrôlée de la voie alternative du complément. Il s'agit d'une maladie rare, hétérogène et très difficile à diagnostiquer. Nous avons évalué les patients Canadiens inscrits au registre international du SHUa afin d'offrir une perspective canadienne sur le diagnostic et la prise en charge du SHUa, de même que sur les défis posés par la maladie. OBJECTIF: Évaluer les patients Canadiens inscrits au registre international du SHUa afin d'offrir une perspective canadienne sur le diagnostic et la prise en charge du SHUa, de même que sur les défis posés par la maladie. MÉTHODOLOGIE: Le registre international du SHUa est une étude observationnelle, non interventionnelle et multicentrique ayant recueilli, de façon rétrospective et prospective, des données auprès de patients de tous âges ayant reçu un diagnostic clinique de SHUa, quel que soit le traitement. Tous ces patients étaient admissibles et ont été invités à participer à l'étude. Les patients présentant une infection diagnostiquée à Escherichia coli producteur de shigatoxine, une activité de l'ADAMTS13 inférieure ou égale à 10 % ou un diagnostic subséquent de purpura thrombocytopénique thrombotique ont été exclus. Les données colligées à l'inclusion et à tous les six mois par la suite ont fait l'objet d'une analyze descriptive des variables catégorielles et continues. Des estimations de Kaplan-Meier ont été employées pour évaluer la survie sans insuffisance rénale terminale (IRT) et des modèles de régression à risques proportionnels de Cox ont servi à évaluer les facteurs de risques associés à l'IRT. Les patients ont été censurés au début du traitement par l'eculizumab pour la mesure des résultats. RÉSULTATS: Au total, 37 patients canadiens ont été inscrits (15 enfants et 22 adultes) entre février 2014 et mai 2017. L'âge médian lors de l'épisode initial était de 25,9 ans (intervalle interquartile: 6,7­51,7); 62,2 % des sujets étaient de sexe féminin et 94,6 % n'avaient pas d'antécédents familiaux de SHUa. Plus des trois quarts des patients (78,4 %) ne disposaient d'aucune information génétique ou relative aux anticorps anti-complément du facteur H concluante, et aucun facteur précipitant n'avait été rapporté avant le diagnostic pour la majorité des patients (94 %). Neuf patients (8 adultes et 1 enfant) avaient souffert d'IRT avant l'étude. Une tendance semble indiquer qu'après l'épisode initial, les enfants seraient moins susceptibles que les adultes de progresser vers l'IRT (survie sans IRT après 5 ans: 93 % et 56 % respectivement; P = 0,05). Les médecins-recruteurs ont observé des manifestations rénales chez tous les patients lors de l'épisode initial de SHUa et chez 68,4 % des patients au cours de la phase chronique (inscription à l'étude au moins 6 mois après l'épisode initial). Parallèlement, les manifestations extra-rénales sont également survenues chez davantage de patients lors de l'épisode initial que lors de la phase chronique, particulièrement pour les manifestations gastro-intestinales (61,1 % contre 15,8 %) et du système nerveux central (38,9 % contre 5,3 %). Les enfants ont été moins nombreux que les adultes à subir des manifestations gastro-intestinales (50,0 % contre 70,0 %), mais ont subi davantage de manifestations pulmonaires (37,5 % contre 10,0 %). CONCLUSION: Cette étude offre un éclairage sur le diagnostic et la prise en charge du SHUa chez les patients canadiens, de même que sur les défis posés par la maladie. Davantage de dépistage génétique et de dépistage des anticorps anti-CFH sont requis pour améliorer le diagnostic du SHUa. La prise en charge de la maladie doit tenir compte de plusieurs facteurs, notamment du risque de progression vers l'IRT qui varie selon l'âge (plus probable chez l'adulte) et du fait que le site des manifestations extrarénales diffère chez l'enfant et l'adulte.

KChIP2 attenuates cardiac hypertrophy through regulation of Ito and intracellular calcium signaling.

Recent evidence shows that the auxiliary subunit KChIP2, which assembles with pore-forming Kv4-subunits, represents a new potential regulator of the cardiac calcium-independent transient outward potassium current (I(to)) density. In hypertrophy and heart failure, KChIP2 expression has been found to be significantly decreased. Our aim was to examine the role of KChIP2 in cardiac hypertrophy and the effect of restoring its expression on electrical remodeling and cardiac mechanical function using a combination of molecular, biochemical and gene targeting approaches. KChIP2 overexpression through gene transfer of Ad.KChIP2 in neonatal cardiomyocytes resulted in a significant increase in I(to)-channel forming Kv4.2 and Kv4.3 protein levels. In vivo gene transfer of KChIP2 in aortic banded adult rats showed that, compared to sham-operated or Ad.beta-gal-transduced hearts, KChIP2 significantly attenuated the developed left ventricular hypertrophy, robustly increased I(to) densities, shortened action potential duration, and significantly altered myocyte mechanics by shortening contraction amplitudes and maximal rates of contraction and relaxation velocities and decreasing Ca(2+) transients. Interestingly, blocking I(to) with 4-aminopyridine in KChIP2-overexpressing adult cardiomyocytes significantly increased the Ca(2+) transients to control levels. One-day-old rat pups intracardially transduced with KChIP2 for two months then subjected to aortic banding for 6-8 weeks (to induce hypertrophy) showed similar echocardiographic, electrical and mechanical remodeling parameters. In addition, in cultured adult cardiomyocytes, KChIP2 overexpression increased the expression of Ca(2+)-ATPase (SERCA2a) and sodium calcium exchanger but had no effect on ryanodine receptor 2 or phospholamban expression. In neonatal myocytes, KChIP2 notably reversed Ang II-induced hypertrophic changes in protein synthesis and MAP-kinase activation. It also significantly decreased calcineurin expression, NFATc1 expression and nuclear translocation and its downstream target, MCiP1.4. Altogether, these data show that KChIP2 can attenuate cardiac hypertrophy possibly through modulation of intracellular calcium concentration and calcineurin/NFAT pathway.

Modulation of action potential duration on myocyte hypertrophic pathways.

Prolongation of the action potential duration (APD) has consistently been observed in experimental models of cardiac hypertrophy and failure as well as in humans and is partially attributed to a reduction of a hyperpolarizing current provided by the calcium-independent transient outward K(+) channel (I(to)). In the present study, we examined the effects of manipulating ion channel currents (I(to) and sodium/calcium exchanger (NCX)) and the associated alterations in action potential duration on cardiomyocyte hypertrophy and signaling induced by angiotensin II (AngII). Our aim was to examined whether distinct patterns of intracellular calcium manipulation could generate distinct patterns of MAPkinase activation and cellular hypertrophy. Cultured neonatal rat ventricular myocytes (NRVMs) were infected with Ad. beta-gal/GFP, Ad.Kv4.3, Ad.Kv4.3 antisense or Ad.NCX adenoviruses and hypertrophy induced by incubation with AngII. Overexpression of Kv4.3 increased I(to) density, shortened APD, decreased Ca(2+) influx and inhibited AngII-induced (3)H-leucine incorporation and ANF and beta-MHC expression. These hypertrophic changes were also paralleled by blockade of ERK MAP kinases activation as well as calcineurin expression. These electrical and hypertrophic changes produced by overexpression of Kv4.3 were completely and significantly reversed by Kv4.3 antisense and NCX gene transfer. Our findings indicate that AngII-mediated hypertrophy response in NRVMs can be abrogated by an enhancement of I(to) function through overexpression of Kv4.3 and that modulation of action potential duration can be important in the development of cardiac hypertrophy.

In vivo cardiac gene transfer of Kv4.3 abrogates the hypertrophic response in rats after aortic stenosis.

BACKGROUND: Prolongation of the action potential duration (APD) and decreased transient outward K+ current (I(to)) have been consistently observed in cardiac hypertrophy. The relation between electrical remodeling and cardiac hypertrophy in vivo is unknown. METHODS AND RESULTS: We studied rat hearts subjected to pressure overload by surgical ascending aortic stenosis (AS) and simultaneously infected these hearts with an adenovirus carrying either the Kv4.3 gene (Ad.Kv4.3) or the beta-galactosidase gene (Ad.beta-gal). I(to) density was reduced and APD50 was prolonged (P<0.05) in AS rats compared with sham rats. Kv4.2 and Kv4.3 expressions were decreased by 58% and 51%, respectively (P<0.05). AS rats infected with Ad.beta-gal developed cardiac hypertrophy compared with sham rats, as assessed by cellular capacitance and heart weight-body weight ratio. Associated with the development of cardiac hypertrophy, the expression of calcineurin and its downstream transcription factor nuclear factor of activated T cells (NFAT) c1 was persistently increased by 47% and 36%, respectively (P<0.05) in AS myocytes infected with Ad.beta-gal compared with sham myocytes. In vivo gene transfer of Kv4.3 in AS rats was shown to increase Kv4.3 expression, increase I(to) density, and shorten APD50 by 1.6-fold, 5.3-fold, and 3.6-fold, respectively (P<0.05). Furthermore, AS rats infected with Ad.Kv4.3 showed significant reductions in calcineurin and NFAT expression. (P<0.05). CONCLUSIONS: Downregulation of I(to), APD prolongation, and cardiac hypertrophy occur early after AS, and in vivo gene transfer of Kv4.3 can restore these electrical parameters and abrogate the hypertrophic response via the calcineurin pathway.

Targeting Ca2+ cycling proteins and the action potential in heart failure by gene transfer.

Cardiomyocytes isolated from failing human hearts are characterized by contractile dysfunction including prolonged relaxation, reduced systolic force and elevated diastolic force. These contractile abnormalities are paralleled by abnormal Ca2+ homeostasis such as reduced sarcoplasmic reticulum (SR) Ca2+ release, elevated diastolic Ca2+ and reduced rate of Ca2+ removal. In addition, failing human myocardium is characterized by a frequency-dependent decrease in systolic force and Ca2+ as opposed to normal myocardium where an increase in pacing rate results in potentiation of contractility and an increase in SR Ca2+ release. In the failing heart, the decrease in SR Ca2+ load has been linked to a decrease in SR Ca2+ ATPase (SERCA2a) function. We have recently shown that overexpression of SERCA2a by adenoviral gene transfer restores contractile function in cardiac myocytes from failing human hearts. In addition, we have shown that overexpression of SERCA2a in a model of pressure-overload hypertrophy in transition to failure improves contractile function and reserve in these animals. We are currently exploring the effect of long-term expression of SERCA2a in failing animals along with the energy cost of SERCA2a expression using NMR methods. We are also using a different strategy to improve SR Ca2+ ATPase activity which involves decreasing the expression of phospholamban by antisense strategies to enhance SR Ca2+ ATPase activity. The Na/Ca exchanger is also being targeted to enhance calcium removal in failing hearts. Action potential prolongation is attributed to reductions in transient outward current (Ito) density in human heart failure. This prolongation can alter contractility but can also cause afterdepolarization. Using gene transfer of various K channels responsible for Ito, we are investigating the molecular and the ionic basis of action potential prolongation in cardiac hypertrophy and failure and we are examining how intracellular calcium handling changes in response to alterations in action potential duration. Gene transfer, which serves initially as an experimental tool, may provide a novel therapeutic approach.

Myocardial infarction in rat eliminates regional heterogeneity of AP profiles, I(to) K(+) currents, and [Ca(2+)](i) transients.

Transient outward K(+) current density (I(to)) has been shown to vary between different regions of the normal myocardium and to be reduced in heart disease. In this study, we measured regional changes in action potential duration (APD), I(to), and intracellular Ca(2+) concentration ([Ca(2+)](i)) transients of ventricular myocytes derived from the right ventricular free wall (RVW) and interventricular septum (SEP) 8 wk after myocardial infarction (MI). At +40 mV, I(to) density in sham-operated hearts was significantly higher (P < 0.01) in the RVW (15.0 +/- 0.8 pA/pF, n = 47) compared with the SEP (7.0 +/- 1.1 pA/pF, n = 18). After MI, I(to) density was not reduced in SEP myocytes but was reduced (P < 0.01) in RVW myocytes (8.7 +/- 1.0 pA/pF, n = 26) to levels indistinguishable from post-MI SEP myocytes. These changes in I(to) density correlated with Kv4.2 (but not Kv4.3) protein expression. By contrast, Kv1.4 expression was significantly higher in the RVW compared with the SEP and increased significantly after MI in RVW. APD measured at 50% or 90% repolarization was prolonged, whereas peak [Ca(2+)](i) transients amplitude was higher in the SEP compared with the RVW in sham myocytes. These regional differences in APD and [Ca(2+)](i) transients were eliminated by MI. Our results demonstrate that the significant regional differences in I(to) density, APD, and [Ca(2+)](i) between RVW and SEP are linked to a variation in Kv4.2 expression, which largely disappears after MI.