"Idiopathic" minimal change nephrotic syndrome: a podocyte mystery nears the end

The discovery of zinc fingers and homeoboxes (ZHX) transcriptional factors and the upregulation of hyposialylated angiopoietin-like 4 (ANGPTL4) in podocytes have been crucial in explaining the cardinal manifestations of human minimal change nephrotic syndrome (MCNS). Recently, uncovered genomic defects upstream of ZHX2 induce a ZHX2 hypomorph state that makes podocytes inherently susceptible to mild cytokine storms resulting from a common cold. In ZHX2 hypomorph podocytes, ZHX proteins are redistributed away from normal transmembrane partners like aminopeptidase A (APA) toward alternative binding partners like IL-4Rα. During disease relapse, high plasma soluble IL-4Rα (sIL-4Rα) associated with chronic atopy complements the cytokine milieu of a common cold to displace ZHX1 from podocyte transmembrane IL-4Rα toward the podocyte nucleus. Nuclear ZHX1 induces severe upregulation of ANGPTL4, resulting in incomplete sialylation of part of the ANGPTL4 protein, secretion of hyposialylated ANGPTL4, and hyposialylation-related injury in the glomerulus. This pattern of injury induces many of the classic manifestations of human minimal change disease (MCD), including massive and selective proteinuria, podocyte foot process effacement, and loss of glomerular basement membrane charge. Administration of glucocorticoids reduces ANGPTL4 upregulation, which reduces hyposialylation injury to improve the clinical phenotype. Improving sialylation of podocyte-secreted ANGPTL4 also reduces proteinuria and improves experimental MCD. Neutralizing circulating TNF-α, IL-6, or sIL-4Rα after the induction of the cytokine storm in Zhx2 hypomorph mice reduces albuminuria, suggesting potential new therapeutic targets for clinical trials to prevent MCD relapse. These studies collectively lay to rest prior suggestions of a role of single cytokines or soluble proteins in triggering MCD relapse.

Cytokine storm-based mechanisms for extrapulmonary manifestations of SARS-CoV-2 infection

Viral illnesses like SARS-CoV-2 have pathologic effects on nonrespiratory organs in the absence of direct viral infection. We injected mice with cocktails of rodent equivalents of human cytokine storms resulting from SARS-CoV-2/COVID-19 or rhinovirus common cold infection. At low doses, COVID-19 cocktails induced glomerular injury and albuminuria in zinc fingers and homeoboxes 2 (Zhx2) hypomorph and Zhx2+/+ mice to mimic COVID-19-related proteinuria. Common Cold cocktail induced albuminuria selectively in Zhx2 hypomorph mice to model relapse of minimal change disease, which improved after depletion of TNF-α, soluble IL-4Rα, or IL-6. The Zhx2 hypomorph state increased cell membrane to nuclear migration of podocyte ZHX proteins in vivo (both cocktails) and lowered phosphorylated STAT6 activation (COVID-19 cocktail) in vitro. At higher doses, COVID-19 cocktails induced acute heart injury, myocarditis, pericarditis, acute liver injury, acute kidney injury, and high mortality in Zhx2+/+ mice, whereas Zhx2 hypomorph mice were relatively protected, due in part to early, asynchronous activation of STAT5 and STAT6 pathways in these organs. Dual depletion of cytokine combinations of TNF-α with IL-2, IL-13, or IL-4 in Zhx2+/+ mice reduced multiorgan injury and eliminated mortality. Using genome sequencing and CRISPR/Cas9, an insertion upstream of ZHX2 was identified as a cause of the human ZHX2 hypomorph state.

Determinants of survival in sudden cardiac arrest manifesting with pulseless electrical activity

OBJECTIVE

The proportion of sudden cardiac arrests (SCA) manifesting with pulseless electrical activity (PEA) has increased significantly, and the survival rate remains lower than ventricular fibrillation (VF). However, a subgroup of PEA-SCA cases does survive and may yield key predictors of improved outcomes when compared to non-survivors. We aimed to identify key predictors of survival from PEA-SCA.

METHODS

Our study sample is drawn from two ongoing community-based, prospective studies of out-of-hospital SCA: Oregon SUDS from the Portland, OR metro area (Pop. approx. 1 million; 2002-2017) and Ventura PRESTO from Ventura County, CA (Pop. approx. 850,000, 2015-2021). For the present sub-study, we included SCA cases with PEA as the presenting rhythm where emergency medical services (EMS) personnel attempted resuscitation.

RESULTS

We identified 1,704 PEA-SCA cases, of which 173 (10.2%) were survivors and 1,531 (89.8%) non-survivors. Patients whose PEA-SCA occurred in a healthcare unit (16.9%) or public location (18.1%) had higher survival than those whose PEA-SCA occurred at home (9.3%) or in a care facility (5.7%). Young age, witness status, PEA-SCA location and pre-existing COPD/asthma were independent predictors of survival. Among witnessed cases the survival rate was 10% even if EMS response time was >10 minutes.

CONCLUSIONS

Key determinants for survival from PEA-SCA were young age, witnessed status, public location and pre-existing COPD/asthma. Survival outcomes in witnessed PEA cases were better than expected, even with delayed EMS response.

P0046ZHX2 DOWNREGULATION DUE INSERTIONS AND DELETIONS IN THE HAS2-ZHX2 INTERGENIC REGION PREDISPOSE TO PODOCYTE DISEASE RELAPSE

Background and Aims

ZHX2 transcriptional factor is normally found in podocyte membrane forming complexes with ZHX1 and APA or ZHX3 and Ephrin B1. Altered ZHX2 expression disrupts these interactions and is related with the worsening of different primary glomerular diseases such as focal segmental glomerulosclerosis (FSGS) and minimal change disease (MCD).

A small percentage of Hodgkin lymphoma (HL) patients develop nephrotic syndrome (NS). Studies of Reed-Sternberg cell line L-1236 reveals a chromosomal rearrangement that leads to ZHX2 downregulation suggesting a possible role of ZHX2 in the development of NS in these patients.

Human podocyte disease relapse is common after a common cold probably mediated by cytokines released by immune cells and the rhinovirus.

Our aim is to study how the presence of insertions and deletions (InDels) between HAS2 and ZHX2 in patients with MCD, FSGS and HL could alter ZHX2 expression and the implication in podocyte disease relapse after a common cold and in HL.

Method

Genomic DNA between HAS2 and ZHX2 (Chr8:122624000-124001000 from UCSC hg19 GRCh37) was sequenced from 28 NS patients and 27 controls using Agilent Custom capture and high throughput Illumina sequencing. The CLC Genomics software was used to identify InDels (3-20 bp) present exclusively in patients. One of the identified InDels was replicated in human podocytes using CRISPR Cas9 and homology directed repair technology to study changes in ZHX2.

A common cold cytokine cocktail containing IL-2, IL-4R, IL-6, IL-10, INF-γ, TNF-α and ICAM-1 was injected into control (BALB/c, n=5) and ZHX2 deficient mice (BALB/cJ, n=5) (Dose X); podocyte specific ZHX2 deficient (ZHX2 flox/flox cre+/+, n=3) and floxed control mice (ZHX2 flox/flox, n=3) (dose X/15). Buffalo Mna (B. Mna) rats were also injected with the cytokine cocktail (X/50) to study relapse in FSGS (n=7).

Cell supernatant from HL Reed Sternberg cells (L-1236) (200µg of total protein) was injected into BALB/c (n=5) and BALB/cJ mice (n=5) and kidney function was assessed.

Results

Multiple InDels were found exclusively in the patient population, two of them, shared by two or more patients.

The insertion at 122,533,694 was presented in patients with MCD, FSGS and HL with NS and also in L-1236 cells. This insertion was replicated in human podocytes using CRISPR/Cas9 (CRISPR B). Another insertion noted both in patients and controls was generated for comparison (CRISPR A). A reduced ZHX2 expression was detected in CRISPR B but not in CRISPR A single cell clones.

The shared insertion at 122,787,088 was presented within the ZHX2 gene intron 1. BALB/cJ mice has lower ZHX2 expression in liver and podocytes due to an insertion in intron 1.

To study whether this insertion could be related with relapse of MCD and FSGS following a common cold, a cytokine cocktail was injected into BALB/cJ and BALB/c mice. BALB/cJ mice developed acute albuminuria after cytokine treatment (65.3±24.3 μg per 18h), but not control BALB/c mice (10.8±1.5 μg per 18h), when compared with baseline values (BALB/cJ 5.1±1.1 μg per 18h; BALB/c 6.5±1.1 μg per 18h) (p<0.05). BALB/cJ mice had also higher nuclear expression of ZHX1.

The cytokine cocktail also induced albuminuria in ZHX2 flox/flox/cre+/+ mice but not in control ZHX2 flox/flox, suggesting that ZHX2 deficiency in podocytes is responsible of kidney injury after cytokine injection.

To study common cold related relapse in FSGS, B. Mna rats were injected with a rat cytokine cocktail, showing a significant increase in proteinuria (61.5±4.2 mg per 18h) compared with baseline (47±4.1 mg per 18h).

Cell culture supernatant from L-1236 was injected into BALB/cJ and BALB/c mice to study the effect of secreted soluble mediators in NS. L-1236 supernatant (200 µg) had a nephrogenic effect in ZHX2 deficient mice but not in controls.

Conclusion

InDels between HAS2 and ZHX2 genes presented in patients with MCD, FSGS and HL, alter ZHX2 expression and are related to relapse following a common cold and in HL.

Novel therapeutic approaches for chronic kidney disease due to glomerular disorders

Improved understanding of glomerular disease mechanisms over the past decade has led to the emergence of new and targeted therapeutic strategies for chronic kidney disease (CKD). Most promising among these are the administration of recombinant mutated human angiopoietin-like 4, sialic acid-related sugars that induce sialylation in vivo, compounds related to Bis-T-23, and immune depletion of the soluble urokinase receptor from the circulation. Taking these therapeutic strategies into clinical trials will be the first step away from repurposed and relatively toxic drugs currently used for treating kidney disease.

The proteinuria-hypertriglyceridemia connection as a basis for novel therapeutics for nephrotic syndrome

The development of new and specific treatment options for kidney disease in general and glomerular diseases in specific has lagged behind other fields like heart disease and cancer. As a result, nephrologists have had to test and adapt therapeutics developed for other indications to treat glomerular diseases. One of the major factors contributing to this inertia has been the poor understanding of disease mechanisms. One way to elucidate these disease mechanisms is to study the association between the cardinal manifestations of glomerular diseases. Because many of these patients develop nephrotic syndrome, understanding the relationship of proteinuria, the primary driver in this syndrome, with hypoalbuminemia, hypercholesterolemia, hypertriglyceridemia, edema, and lipiduria could provide valuable insight. The recent unraveling of the relationship between proteinuria and hypertriglyceridemia mediated by free fatty acids, albumin, and the secreted glycoprotein angiopoietin-like 4 (Angptl4) offers a unique opportunity to develop novel therapeutics for glomerular diseases. In this review, the therapeutic potential of mutant forms of Angptl4 in reducing proteinuria and, as a consequence, alleviating the other manifestations of nephrotic syndrome is discussed.

Nephrotic syndrome: components, connections, and angiopoietin-like 4-related therapeutics

Nephrotic syndrome is recognized by the presence of proteinuria in excess of 3.5 g/24 h along with hypoalbuminemia, edema, hyperlipidemia (hypertriglyceridemia and hypercholesterolemia), and lipiduria. Each component has been investigated individually over the past four decades with some success. Studies published recently have started unraveling the molecular basis of proteinuria and its relationship with other components. We now have improved understanding of the threshold for nephrotic-range proteinuria and the pathogenesis of hypertriglyceridemia. These studies reveal that modifying sialylation of the soluble glycoprotein angiopoietin-like 4 or changing key amino acids in its sequence can be used successfully to treat proteinuria. Treatment strategies on the basis of fundamental relationships among different components of nephrotic syndrome use naturally occurring pathways and have great potential for future development into clinically relevant therapeutic agents.

Nephrotic syndrome: components, connections, and angiopoietin-like 4-related therapeutics

Nephrotic syndrome is recognized by the presence of proteinuria in excess of 3.5 g/24 h along with hypoalbuminemia, edema, hyperlipidemia (hypertriglyceridemia and hypercholesterolemia), and lipiduria. Each component has been investigated individually over the past four decades with some success. Studies published recently have started unraveling the molecular basis of proteinuria and its relationship with other components. We now have improved understanding of the threshold for nephrotic-range proteinuria and the pathogenesis of hypertriglyceridemia. These studies reveal that modifying sialylation of the soluble glycoprotein angiopoietin-like 4 or changing key amino acids in its sequence can be used successfully to treat proteinuria. Treatment strategies on the basis of fundamental relationships among different components of nephrotic syndrome use naturally occurring pathways and have great potential for future development into clinically relevant therapeutic agents.

Glomerular disease: looking beyond pathology

The National Institute of Diabetes and Digestive and Kidney Diseases-supported Kidney Research National Dialogue asked the scientific community to formulate and prioritize research objectives aimed at improved understanding of kidney function and disease progression. Over the past 2 years, 1600 participants posted almost 300 ideas covering all areas of kidney disease. An overriding theme that evolved through these discussions is the need to move beyond pathology to take advantage of basic science and clinical research opportunities to improve diagnostic classification and therapeutic options for people with primary glomerular disease. High-priority research areas included focus on therapeutic targets in glomerular endothelium and podocytes, regenerating podocytes through developmental pathways, use of longitudinal phenotypically defined disease cohorts to improve classification schemes, identifying biomarkers, disease-specific therapeutics, autoantibody triggers, and changing the clinical research culture to promote participation in clinical trials. Together, these objectives provide a path forward for improving clinical outcomes of glomerular disease.

Angiopoietin-like 4 based therapeutics for proteinuria and kidney disease

Current drugs used to treat proteinuric disorders of the kidney have been borrowed from other branches of medicine, and are only partially effective. The discovery of a central, mechanistic role played by two different forms of the secreted glycoprotein angiopoietin-like 4 (Angptl4) in human and experimental glomerular disease has opened new treatment avenues. Localized upregulation of a hyposialylated form (lacks sialic acid residues) of Angptl4 secreted by podocytes induces the cardinal morphological and clinical manifestations of human minimal change disease, and is also being increasingly recognized as a significant contributor toward proteinuria in experimental diabetic nephropathy. Oral treatment with low doses of N-acetyl-D-mannosamine, a naturally occurring precursor of sialic acid, improves sialylation of Angptl4 in vivo, and reduces proteinuria by over 40%. By contrast, a sialylated circulating form of Angptl4, mostly secreted from skeletal muscle, heart and adipose tissue in all major primary glomerular diseases, reduces proteinuria while also causing hypertriglyceridemia. Intravenous administration of recombinant human Angptl4 mutated to avoid hypertriglyceridemia and cleavage has remarkable efficacy in reducing proteinuria by as much as 65% for 2 weeks after a single low dose. Both interventions are mechanistically relevant, utilize naturally occurring pathways, and represent new generation therapeutic agents for chronic kidney disease related to glomerular disorders.

Circulating angiopoietin-like 4 links proteinuria with hypertriglyceridemia in nephrotic syndrome

The molecular link between proteinuria and hyperlipidemia in nephrotic syndrome is not known. We show in the present study that plasma angiopoietin-like 4 (Angptl4) links proteinuria with hypertriglyceridemia through two negative feedback loops. In previous studies in a rat model that mimics human minimal change disease, we observed localized secretion by podocytes of hyposialylated Angptl4, a pro-proteinuric form of the protein. But in this study we noted high serum levels of Angptl4 (presumably normosialylated based on a neutral isoelectric point) in other glomerular diseases as well. Circulating Angptl4 was secreted by extrarenal organs in response to an elevated plasma ratio of free fatty acids (FFAs) to albumin when proteinuria reached nephrotic range. In a systemic feedback loop, these circulating pools of Angptl4 reduced proteinuria by interacting with glomerular endothelial αvβ5 integrin. Blocking the Angptl4-β5 integrin interaction or global knockout of Angptl4 or β5 integrin delayed recovery from peak proteinuria in animal models. But at the same time, in a local feedback loop, the elevated extrarenal pools of Angptl4 reduced tissue FFA uptake in skeletal muscle, heart and adipose tissue, subsequently resulting in hypertriglyceridemia, by inhibiting lipoprotein lipase (LPL)-mediated hydrolysis of plasma triglycerides to FFAs. Injecting recombinant human ANGPTL4 modified at a key LPL interacting site into nephrotic Buffalo Mna and Zucker Diabetic Fatty rats reduced proteinuria through the systemic loop but, by bypassing the local loop, without increasing plasma triglyceride levels. These data show that increases in circulating Angptl4 in response to nephrotic-range proteinuria reduces the degree of this pathology, but at the cost of inducing hypertriglyceridemia, while also suggesting a possible therapy to treat these linked pathologies.

Reduced kidney lipoprotein lipase and renal tubule triglyceride accumulation in cisplatin-mediated acute kidney injury

Peroxisome proliferator-activated receptor-α (PPARα) activation attenuates cisplatin (CP)-mediated acute kidney injury by increasing fatty acid oxidation, but mechanisms leading to reduced renal triglyceride (TG) accumulation could also contribute. Here, we investigated the effects of PPARα and CP on expression and enzyme activity of kidney lipoprotein lipase (LPL) as well as on expression of angiopoietin protein-like 4 (Angptl4), glycosylphosphatidylinositol-anchored-HDL-binding protein (GPIHBP1), and lipase maturation factor 1 (Lmf1), which are recognized as important proteins that modulate LPL activity. CP caused a 40% reduction in epididymal white adipose tissue (WAT) mass, with a reduction of LPL expression and activity. CP also reduced kidney LPL expression and activity. Angptl4 mRNA levels were increased by ninefold in liver and kidney tissue and by twofold in adipose tissue of CP-treated mice. Western blots of two-dimensional gel electrophoresis identified increased expression of a neutral pI Angptl4 protein in kidney tissue of CP-treated mice. Immunolocalization studies showed reduced staining of LPL and increased staining of Angptl4 primarily in proximal tubules of CP-treated mice. CP also increased TG accumulation in kidney tissue, which was ameliorated by PPARα ligand. In summary, a PPARα ligand ameliorates CP-mediated nephrotoxicity by increasing LPL activity via increased expression of GPHBP1 and Lmf1 and by reducing expression of Angptl4 protein in the proximal tubule.

New insights into human minimal change disease: lessons from animal models

The pathogenesis of minimal change disease (MCD), considered to be the simplest form of nephrotic syndrome, has been one of the major unsolved mysteries in kidney disease. In this review, recent landmark studies that have led to the unraveling of MCD are discussed. A recent study now explains the molecular basis of major clinical and morphologic changes in MCD. Overproduction of angiopoietin-like 4 (ANGPTL4) in podocytes in MCD causes binding of ANGPTL4 to the glomerular basement membrane, development of nephrotic-range selective proteinuria, diffuse effacement of foot processes, and loss of glomerular basement membrane charge, but is not associated with changes shown by light microscopy in the glomerular and tubulointerstitial compartments. At least some of this ability of ANGPTL4 to induce proteinuria is linked to a deficiency of sialic acid residues because oral supplementation with sialic acid precursor N-acetyl-d-mannosamine improves sialylation of podocyte-secreted ANGPTL4 and significantly decreases proteinuria. Animal models of MCD, recent advances in potential biomarkers, and studies of upstream factors that may initiate glomerular changes also are discussed. In summary, recent progress in understanding MCD is likely to influence the diagnosis and treatment of MCD in the near future.

A case of infection-associated antiproteinase-3-negative cytoplasmic antineutrophil cytoplasmic antibody pauci-immune focal necrotizing glomerulonephritis

We present the case of a man with Gram-negative sepsis and exposure to oral silica who developed pauci-immune focal necrotizing glomerulonephritis (PI-FNGN) in the setting of a subacute polymicrobial central venous line (CVL) infection. He developed a cytoplasmic antineutrophil cytoplasmic autoantibody (C-ANCA) that was antiproteinase-3 (PR-3) and antimyeloperoxidase (MPO) antibody negative. We believe this is the first reported case of Gram-negative sepsis-associated PI-FNGN. Chronic silica exposure is a leading environmental risk factor in the development of ANCA vasculitis. Oral silica is a common pharmaceutical additive and its bioavailability is being recognized. Oral silica, therefore, may also be a risk for development of autoreactivity. The PI-FNGN resolved with antibiotic therapy alone. The C-ANCA titer declined as the PI-FNGN resolved. The case supports experimental and observational research that environmental exposures act as adjuvants for an immune response and also provide epigenetic triggers for autoreactivity. The C-ANCA was negative for PR-3, its major antigen. C-ANCA antigen specificity may depend on the pathogenesis of the underlying disease, potentially elicited by a cross-reaction of an antibody to foreign and self target antigen sequence homology or alternatively elicited by antigenic epitope spread.

Rap1b GTPase ameliorates glucose-induced mitochondrial dysfunction

The role of tubular injury in diabetic nephropathy is relatively unknown, despite that apoptosis of tubular epithelial cells is commonly observed in human renal biopsies. The GTPase Ras-proximate-1 (Rap1b) is upregulated in the hyperglycemic state and is known to increase B-Raf, an antiapoptotic effector protein. In this study, the effects of high glucose on renal tubular apoptosis and the potential ability for Rap1b to ameliorate these effects were investigated. In the kidneys of diabetic mice, apoptotic tubular cells and dysmorphic mitochondria were observed, Bcl-2 expression was decreased, and Bax expression was increased. Total Rap1b expression was slightly increased, but its associated GTPase activity was significantly decreased. In vitro, high extracellular glucose led to decreased Bcl-2 expression, reduced Rap1b GTPase activity, and increased levels of both Bax and GTPase activating protein in a proximal tubular cell line (HK-2). These changes were accompanied by increased DNA fragmentation, decreased high molecular weight mitochondrial DNA, altered mitochondrial morphology and function, disrupted Bcl-2-Bax and Bcl-2-Rap1b interactions, and reduced cell survival. Overexpression of Rap1b partially prevents these abnormalities. Furthermore, the BH4 domain of Bcl-2 was found to be required for successful protein-protein interaction between Bcl-2 and Rap1b. In summary, these data suggest that Rap1b ameliorates glucose-induced mitochondrial dysfunction in renal tubular cells.

Transcriptional regulation of podocyte disease

The podocyte is a highly specialized visceral epithelial cell that forms the outermost layer of the glomerular capillary loop and plays a critical role in the maintenance of the glomerular filtration barrier. Several transcriptional factors regulate the podocyte function under normal and disease conditions. In this review, the role of Wilms tumor 1 (WT1), LIM homeobox transcription factor 1, beta (Lmx1b), pod1, pax-2, kreisler, nuclear factor-kappa B (NF-kappaB), smad7, and zinc fingers and homeoboxes (ZHX) proteins in the development of podocyte disease is outlined. The regulation of several important podocyte genes, including transcriptional factors, by ZHX proteins, their predominant non-nuclear localization in the normal in vivo podocyte, and changes in ZHX expression related to the development of minimal change disease and focal and segmental glomerulosclerosis are discussed. Finally, some future therapeutic strategies for glomerular disease are proposed.

Early changes in gene expression that influence the course of primary glomerular disease

Serial changes in glomerular capillary loop gene expression were used to uncover mechanisms contributing to primary glomerular disease in rat models of passive Heymann nephritis and puromycin nephrosis. Before the onset of proteinuria, podocyte protein-tyrosine phosphatase (GLEPP1) expression was transiently decreased in the nephrosis model, whereas the immune costimulatory molecule B7.1 was stimulated in both models. To relate these changes to the development of proteinuria, the time of onset and intensity of proteinuria were altered. When the models were induced simultaneously, proteinuria and anasarca occurred earlier with the collapse of glomerular capillary loops. Upregulation of B7.1 with the downregulation of GLEPP1, Wilms' tumor gene (WT1), megalin, and vascular endothelial growth factor started early and persisted through the course of disease. In the puromycin and the combined models, changes in GLEPP1 expression were corticosteroid-sensitive, whereas B7.1, WT1, vascular endothelial growth factor, and most slit diaphragm genes involved later in the combined model, except podocin, were corticosteroid-resistant. There was a very early increase in the nuclear expression of podocyte transcription factors ZHX2 and ZHX1 that may be linked to the changes in gene expression in the combined proteinuric model. Our studies suggest that an early and persistent change in mostly steroid-resistant glomerular gene expression is the hallmark of severe and progressive glomerular disease.

ZHX proteins regulate podocyte gene expression during the development of nephrotic syndrome

Transcriptional regulation of podocyte gene expression in primary glomerular disease is poorly understood. In this study, we demonstrate a prominent role of members of the ZHX (zinc fingers and homeoboxes) family of proteins in regulating podocyte gene expression during the development of nephrotic syndrome. While studying mechanisms of glomerular disease, rat ZHX3 was cloned from a down-regulated gene fragment; its cellular localization, DNA binding, and transcriptional repressor properties were characterized; and its ability to influence podocyte gene expression directly or via ZHX1 and ZHX2 was studied. In eukaryotic promoters, ZHX3 bound to the CdxA binding motif. ZHX proteins were mostly sequestered in the non-nuclear compartment in the normal in vivo podocyte by virtue of heterodimer formation, and loss of heterodimerization was associated with entry into the nucleus. In experimental minimal change disease, ZHX3 was transiently down-regulated prior to the onset of proteinuria, and recovery of expression was associated with migration of ZHX3 protein into the nucleus and the development of proteinuria. This expression pattern mirrored the increased nuclear ZHX3 expression noted in vivo in the podocytes in human minimal change disease biopsies. In vitro, migration of ZHX3 protein into the nucleus during recovery from transient ZHX3 knockdown reproduced the gene expression profile of in vivo minimal change disease. Severe sustained knockdown of ZHX3 caused down-regulation of genes involved in focal sclerosis, including WT1, mediated mostly by increased nuclear entry of ZHX2 and ZHX1. In summary, ZHX proteins are major transcriptional mediators of podocyte disease.

Renal-specific oxidoreductase biphasic expression under high glucose ambience during fetal versus neonatal development

BACKGROUND

Renal-specific oxidoreductase (RSOR) has been recently identified in mice kidneys of diabetic animals, and it is developmentally regulated. Its expression during fetal, neonatal, and postnatal periods was assessed under high glucose ambience.

METHODS

Whole-mount immunofluorescence and confocal microscopy were performed to assess the effect of high glucose on the morphogenesis of mice fetal kidneys. RSOR mRNA and protein expression was assessed by competitive polymerase chain reaction (PCR) and immunoprecipitation methods in embryonic kidneys (day E13 to E17) subjected to high glucose ambience and by Northern and Western blot analyses of kidneys of newborn and 1-week-old mice with hyperglycemia. The spatiotemporal changes in the RSOR expression were assessed by in situ hybridization analyses and immunofluorescence microscopy. In addition, the extent of apoptosis in the kidneys was determined by terminal deoxynucleotidyl transferase (TdT)-mediated deoxyuridine triphosphate (dUTP) nick-end labeling (TUNEL) assay.

RESULTS

Whole-mount microscopy of the embryonic metanephroi revealed a dose-dependent disruption in the ureteric bud iterations with reduced population of the nascent nephrons. Both gene and protein expressions were reduced in day E13 to E17 metanephroi, while increased in kidneys of newborn and 1-week-old mice. In day E13 and day E15 kidneys, the RSOR was expressed in the ureteric bud branches and some of the immature tubules, and its expression was reduced with high glucose treatment. In day E17 kidneys the RSOR was expressed in the tubules of the deeper cortex, and its expression was marginally decreased. In newborn kidneys, this enzyme was expressed in the subcortical tubules and it spread to the entire width of the renal cortex in hyperglycemic state. In 1-week-old mice kidneys, the RSOR was localized to the entire cortex, and in animals with blood glucose above 300 mg/dL, its intensity increased with extension of expression into the outer medullary tubules. A dose-dependent fulminant apoptosis was observed in day E13 to E17 kidneys subjected to high glucose ambience. In newborn and 1-week-old mice control kidneys, the apoptosis was minimal although slightly increased during hyperglycemia.

CONCLUSION

High glucose has a differential effect on the RSOR expression in kidneys during the embryonic versus neonatal/postnatal period. This may partly be related to the differential degree of apoptosis, a process reflective of oxidant stress that is seen in diabetic milieu, which as previously has been shown to adversely effect the modulators of fetal development and thereby the morphogenesis of the kidney and RSOR expression.

Modulation of renal-specific oxidoreductase/myo-inositol oxygenase by high-glucose ambience

Biological properties of renal-specific oxidoreductase (RSOR), characteristics of its promoter, and underlying mechanisms regulating its expression in diabetes were analyzed. RSOR expression, normally confined to the renal cortex, was markedly increased and extended into the outer medullary tubules in db/db mice, a model of type 2 diabetes. Exposure of LLCPK cells to d-glucose resulted in a dose-dependent increase in RSOR expression and its enzymatic activity. The latter was related to one of the glycolytic enzymes, myo-inositol oxygenase. The increase in activity was in proportion to serum glucose concentration. The RSOR expression also increased in cells treated with various organic osmolytes, e.g., sorbitol, myoinositol, and glycerolphosphoryl-choline and H(2)O(2). Basal promoter activity was confined to -1,252 bp upstream of ATG, and it increased with the treatment of high glucose and osmolytes. EMSAs indicated an increased binding activity with osmotic-, carbohydrate-, and oxidant-response elements in cells treated with high glucose and was abolished by competitors. Supershifts, detected by anti-nuclear factor of activated T cells, and carbohydrate-response-element-binding protein established the binding specificity. Nuclear factor of activated T cells tonicity-enhancer-binding protein and carbohydrate-response-element-binding protein had increased nuclear expression in cells treated with high glucose. The activity of osmotic-response element exhibited a unique alternate binding pattern, as yet unreported in osmoregulatory genes. Data indicate that RSOR activity is modulated by diverse mechanisms, and it is endowed with dual properties to channel glucose intermediaries, characteristic of hepatic aldehyde reductases, and to maintain osmoregulation, a function of renal medullary genes, e.g., aldose reductase, in diabetes.

Co-existent crescentic glomerulonephritis and renal amyloidosis: a case report and literature review

Co-existent crescentic glomerulonephritis and renal amyloidosis have only rarely been reported thus far. To our knowledge, only about eighteen convincing cases (with >50% crescents) have been described, mostly in the context of rheumatoid arthritis. In this report, we add a case from our institution and review the existing literature, including a proposed mechanism of crescent formation in this setting. Although the relationship between crescentic glomerulonephritis, renal amyloidosis, and rheumatoid arthritis needs further investigation, we suggest that one should consider the development of crescentic glomerulonephritis with amyloidosis in patients with long-standing rheumatoid arthritis and worsening renal function.

Hyperglycemia: its imminent effects on mammalian nephrogenesis

A sustained exposure of the mammalian embryo to very high glucose ambience is associated with a multitude of congenital birth defects, including those of the cardiovascular, CNS, skeletal and urogenital systems during the first 6-8 weeks of gestation in humans. These urogenital abnormalities may be associated with "caudal regression syndrome" or may occur alone in the form of partial or total renal agenesis. Similarly, an increase in the incidence of morphogenetic defects is observed in the offspring of streptozotocin-induced diabetic rats and mice, and also in non-obese diabetic mice. In certain cases, failure during the growth of the lower parts of embryos or newborn mice involving the genitourinary system has been observed in animals with severe diabetes. Investigators have utilized whole organ culture systems to delineate the mechanisms relevant to dysmorphogenesis of the embryonic metanephros. A marked dysmorphogenesis of the metanephros is observed upon treatment with a high concentration of D: -glucose. Associated with it are changes that include branching dysmorphogenesis of the ureteric bud iterations, reduced population of nascent nephrons, decreased expression of basement membrane proteoglycans, depletion of ATP stores, and fulminant apoptosis of the cells at the interface of mesenchyme and ureteric bud epithelium. The latter findings suggest that disruption of epithelial:mesenchymal interactions may be the major event responsible for the metanephric dysmorphogenesis induced by high glucose ambience.

Cell Biology of Diabetic Kidney Disease

In large part cellular dysfunctions induced by chronic hyperglycemia are similar in type-1 and -2 diabetes. In both instances chronic hyperglycemia induces injury to a multitude of organs by affecting various target cells. The cells affected may include those derived from of epithelial or mesenchymal progenitors; and at times hyperglycemia may induce phenotypic changes with epithelial-mesenchymal transformation. In the majority of target cells the high-glucose ambience activates various intracellular pathways that are similar except for minor exceptions that are related to the selective expression of various molecules in a given cell type. Keeping in perspective a common paradigm applicable to most of the cells, a brief discussion of different hyperglycemia-induced cellular events pertaining to various pathways is described in this review. They include fluxes of glucose intermediaries in various cellular metabolic pathways, generation of advanced glycation end products (AGEs) and their extra- and intracellular effects, the role of protein kinase C, transforming growth factor-beta, guanosine triphosphate-binding proteins and reactive oxygen species (ROS) in various cellular signaling events. The latter, i.e., ROS, may be central to several intracellular pathways and modulate various events in a reciprocal manner. The information compiled under various subtitles of this synopsis is derived from an enormous amount of literature data summarized in several recent excellent reviews, and thus further reading of them is suggested to gather detailed comprehensive information on each of the subjects.

Update of extracellular matrix, its receptors, and cell adhesion molecules in mammalian nephrogenesis

One of the hallmarks of mammalian nephrogenesis includes a mesenchymal-epithelial transition that is accomplished by intercalation of the ureteric bud, an epithelium-lined tubelike structure, into an undifferentiated mesenchyme, and the latter then undergoes an inductive transformation and differentiates into an epithelial phenotype. At the same time, the differentiating mesenchyme reciprocates by inducing branching morphogenesis of the ureteric bud, which forms a treelike structure with dichotomous iterations. These reciprocal inductive interactions lead to the development of a functioning nephron unit made up of a glomerulus and proximal and distal tubules. The inductive interactions and differentiation events are modulated by a number of transcription factors, protooncogenes, and growth factors and their receptors, which regulate the expression of target morphogenetic modulators including the ECM, integrin receptors, and cell adhesion molecules. These target macromolecules exhibit spatiotemporal and stage-specific developmental regulation in the metanephros. The ECM molecules expressed at the epithelial-mesenchymal interface are perhaps the most relevant and conducive to the paracrine-juxtacrine interactions in a scenario where the ligand is expressed in the mesenchyme while the receptor is located in the ureteric bud epithelium or vice versa. In addition, expression of the target ECM macromolecules is regulated by matrix metalloproteinases and their inhibitors to generate a concentration gradient at the interface to further propel epithelial-mesenchymal interactions so that nephrogenesis can proceed seamlessly. In this review, we discuss and update our current understanding of the role of the ECM and related macromolecules with respect to metanephric development.

Molecular structure-function relationship in the slit diaphragm

The past 5 years have witnessed an exponential increase in our understanding of the structure and function of the glomerular slit diaphragm. The identification of nephrin as the first transmembrane slit diaphragm protein was a watershed event in slit diaphragm biology. This article correlates some of the observations of the prenephrin era with more recent studies, and elaborates on the individual characteristics of each slit diaphragm protein. Recent studies on protein-protein interactions related to slit diaphragm permeability and cell signaling are elaborated, along with observations on their expression in human disease and experimental models of proteinuria. Developmental expression of components of the slit diaphragm in normal and knockout mice also is discussed. Finally, some areas of future investigation are proposed.

Renal development in high-glucose ambience and diabetic embryopathy

Maternal diabetes has an adverse influence on the intrauterine growth of the fetus, which is attributable to the exposure of the mammalian embryo to an abnormal metabolic environment. A sustained exposure of the fetus to such an environment (ie, elevated concentration of glucose), during the first 6 to 8 weeks of gestation in humans may result in diabetic embryopathy, which is characterized by a multitude of congenital birth defects, including those of the nervous, cardiovascular, skeletal, and urogenital systems. The urogenital abnormalities may be associated with caudal regression syndrome or may occur alone in the form of partial or total renal agenesis. Similarly, an increase in the incidence of morphogenetic defects is observed in offsprings of streptozotocin-induced diabetic rats and mice and also in nonobese diabetic mice. In certain instances, failure in the growth of lower part of embryos or newborn mice has been observed in animals with a severe diabetic state. For further delineation of the mechanisms involved in the pathogenesis of diabetic embryopathy, the investigators used whole-embryo culture systems, and found that glucose can induce defects mainly confined to the lower part of the body involving the genitourinary system. Similarly, dysmorphogenesis of the embryonic metanephros is observed when it is subjected to high concentrations of D-glucose and its epimer D-mannose. This article discusses certain aspects of diabetic embryopathy with an emphasis on changes that occur in the fetal metanephros in high-glucose ambience.

Neph1 and nephrin interaction in the slit diaphragm is an important determinant of glomerular permeability

Neph1-deficient mice develop nephrotic syndrome at birth, indicating the importance of this protein in the development of a normal glomerular filtration barrier. While the precise subcellular localization of Neph1 remains unknown, its relationship with other components of the glomerular filtration barrier is of great interest in this field. In this paper, we localize the expression of Neph1 to the glomerular slit diaphragm by immunogold electron microscopy in rodents and describe its direct interaction with two other components of the slit diaphragm, nephrin and ZO-1. Both native and recombinant Neph1 associate with each other as dimers and multimers and interact with nephrin via their extracellular segments. Disruption of the Neph1-nephrin interaction in vivo by injecting combinations of individual subnephritogenic doses of anti-Neph1 and anti-nephrin results in complement- and leukocyte-independent proteinuria with preserved foot processes. This disruption modestly reduces Neph1 and nephrin protein expression in podocytes and dramatically reduces ZO-1 protein expression via the interaction of ZO-1 PDZ domains with the cytoplasmic tail of Neph1, independent of changes in mRNA expression of all three genes. The interaction between nephrin and Neph1 is specific and not shared by either protein with P-cadherin, another integral slit diaphragm protein. The interaction between nephrin and Neph1 therefore appears to be an important determinant of glomerular permeability.

High glucose stimulates synthesis of fibronectin via a novel protein kinase C, Rap1b, and B-Raf signaling pathway

The molecular mechanism(s) by which high glucose induces fibronectin expression via G-protein activation in the kidney are largely unknown. This investigation describes the effect of high glucose (HG) on a small GTP-binding protein, Rap1b, expression and activation, and the relevance of protein kinase C (PKC) and Raf pathways in fibronectin synthesis in cultured renal glomerular mesangial cells (MCs). In vivo experiments revealed a dose-dependent increase in Rap1b expression in glomeruli of diabetic rat kidneys. Similarly, in vitro exposure of MCs to HG led to an up-regulation of Rap1b with concomitant increase in fibronectin (FN) mRNA and protein expression. The up-regulation of Rap1b mRNA was mitigated by the PKC inhibitors, calphostin C, and bisindolymaleimide, while also reducing HG- induced FN expression in non-transfected MCs. Overexpression of Rap1b by transfection with pcDNA 3.1/Rap1b in MCs resulted in the stimulation of FN synthesis; however, the PKC inhibitors had no significant effect in reducing FN expression in Rap1b-transfected MCs. Transfection of Rap1b mutants S17N (Ser --> Asn) or T61R (Thr --> Arg) in MCs inhibited the HG-induced increased FN synthesis. B-Raf and Raf-1 expression was investigated to assess whether Rap1b effects are mediated via the Raf pathway. B-Raf, and not Raf-1, expression was increased in MCs transfected with Rap1b. HG also caused activation of Rap1b, which was largely unaffected by anti-platelet-derived growth factor (PDGF) antibodies. HG-induced activation of Rap1b was specific, since Rap2b activation and expression of Rap2a and Rap2b were unaffected by HG. These findings indicate that hyperglycemia and HG cause an activation and up-regulation of Rap1b in renal glomeruli and in cultured MCs, which then stimulates FN synthesis. This effect appears to be PKC-dependent and PDGF-independent, but involves B-Raf, suggesting a novel PKC-Rap1b-B-Raf pathway responsible for HG-induced increased mesangial matrix synthesis, a hallmark of diabetic nephropathy.

Renal gene expression in embryonic and newborn diabetic mice

Several novel genes that are upregulated in diabetic kidneys have been identified. Recently, transforming growth factor beta driven secreted proteins, i.e., connective tissue growth factor and gremlin (bone morphogenetic protein 2), have been identified, and their expression has been correlated with the tissue changes seen in diabetic nephropathy in the adult population. However, there are very few studies reported in the literature that describe the gene expression in the diabetic state during embryonic and neonatal life. It is well known that exposure to glucose or its epimer, i.e., mannose, induces marked dysmorphogenesis of the embryonic metanephros in an organ culture system. These changes are associated with ATP depletion and marked apoptosis, suggesting an oxidant stress in the induction of dysmorphogenesis of the embryonic metanephros. In view of the glucose-induced changes in the fetal metanephros, a diabetic state was induced by the administration of streptozotocin during pregnancy, and newborn mouse kidneys were processed for suppression subtractive hybridization-PCR. In addition, a diabetic state was induced in newborn diabetic mice, and after 1 week their kidneys were harvested and subjected to representational difference analysis of cDNA. Four novel genes with upregulated mRNA expression were identified. They included: (1) a translocase inner mitochondrial membrane 44 that is involved in the ATP-dependent import of preproteins from the cytosol into the mitochondrial matrix; (2) a kidney-specific aldo-keto reductase that utilizes NADPH and NADH as cofactors in the reduction of aromatic aldehydes and aldohexoses; (3) Rap1b, a Ras-related small GTP-binding protein that behaves as a GTPase and cycles between GTP-bound (active) and GDP-bound (inactive) states associated with conformational change, and (4) a fusion protein of ubiquitin polypeptide and ribosomal protein L40 (UbA(52) or ubiquitin/60) that is intimately involved in the ubiquitin-dependent proteasome pathway related to the accelerated degradation of proteins under various stress conditions, such as those seen in patients with cancer and diabetes mellitus.

Isolation and functional analysis of mouse UbA52 gene and its relevance to diabetic nephropathy

In delineating the mechanism(s) of diabetic nephropathy various novel genes have been isolated, whereas others remain to be discovered. We identified several up-regulated genes in the kidneys of diabetic newborn mice. Among them was UbA52, a ubiquitin ribosomal fusion protein. Its mRNA expression in the kidney was proportional to blood glucose levels. By in situ hybridization and immunohistochemistry, UbA52 was exclusively localized to renal tubules, and its expression was markedly increased in diabetic mice. The up-regulated UbA52 mRNA and protein expression were also observed in Madin-Darby canine kidney cells, a tubular cell line, treated with 30 mm glucose in both cell lysates and ribosomal fractions. To explore the mechanism(s) of its increased expression, UbA52 genomic DNA was isolated. A transcription start site at -22 bp from the initiation codon was identified and confirmed by primer extension analysis. The UbA52 promoter region included glucose response-related E-box sequences and stress response elements (STRE). Unlike in humans, mouse UbA52 gene had no introns in the coding or 5'-ATG-flanking regions. To identify the DNA segment with maximal promoter activity, deletion constructs were prepared using a pSEAP vector system and transfected into COS7 kidney cells. Maximal activity was confined to -198 to +68 bp, which included E-boxes and STRE motifs. A dose-dependent increase in the promoter activity was observed in cells exposed to high glucose. Mutations in the first E-box (CAGCTG --> TGGCTG) or STRE (CCCCT --> CATCT) resulted in a decrease in the SEAP activity under high glucose ambience. Given the presence of glucose-responsive motifs in the promoter region and decrease in the SEAP activity in E-box mutants in the presence of glucose, these data suggest that UbA52, a ribosomal fusion protein, may be relevant in the pathogenesis of diabetic nephropathy.

Amplified effects of d,l-sotalol in canine dilated cardiomyopathy

Despite the presence of well-described cardiac repolarization abnormalities in heart failure, d,l-sotalol effects on cardiac repolarization have not been evaluated in animal models of CHF. The authors hypothesized that the d,l-sotalol effects on cardiac repolarization are altered in canine dilated cardiomyopathy when compared to controls. Effects of d,l-sotalol were compared in seven dogs with tachycardia induced cardiomyopathy (CHF) and six control animals. In an open-chest model, contact monophasic action potential recordings were obtained from RV and LV endocardium/epicardium during and after two doses of d,l-sotalol (1 mg/kg and 3 mg/kg, each over 20 minutes). Effects of d,l-sotalol on action potential duration at 90% repolarization (APD90) were examined at pacing cycle lengths of 300-1,000 ms. Plasma d,l-sotalol levels were measured at baseline, 10, and 40 minutes following each dose. Prolongation of APD90 by d,l-sotalol, was significantly exaggerated in CHF animals versus controls (P < 0.05, ANOVA). These differences were magnified at slow heart rates (P < 0.05, ANOVA). There were no significant differences in plasma d,l-sotalol levels between the two groups. Effects of d,l-sotalol on cardiac repolarization are exaggerated in CHF without significant alterations in plasma drug levels. While using d,l-sotalol in heart failure, independent additional effects due to ventricular electrical remodeling may be a consideration.

Intra-atrial conduction block along the mitral valve annulus during accessory pathway ablation: evidence for a left atrial "isthmus"

INTRODUCTION

We observed a change in the atrial activation sequence during radiofrequency (RF) energy application in patients undergoing left accessory pathway (AP) ablation. This occurred without damage to the AP and in the absence of a second AP or alternative arrhythmia mechanism. We hypothesized that block in a left atrial "isthmus" of tissue between the mitral annulus and a left inferior pulmonary vein was responsible for these findings.

METHODS AND RESULTS

Electrophysiologic studies of 159 patients who underwent RF ablation of a left free-wall AP from 1995 to 1999 were reviewed. All studies with intra-atrial conduction block resulting from RF energy delivery were identified. Fluoroscopic catheter positions were reviewed. Intra-atrial conduction block was observed following RF delivery in 11 cases (6.9%). This was evidenced by a sudden change in retrograde left atrial activation sequence despite persistent and unaffected pathway conduction. In six patients, reversal of eccentric atrial excitation during orthodromic reciprocating tachycardia falsely suggested the presence of a second (septal) AP. A multipolar coronary sinus catheter in two patients directly demonstrated conduction block along the mitral annulus during tachycardia.

CONCLUSION

An isthmus of conductive tissue is present in the low lateral left atrium of some individuals. Awareness of this structure may avoid misinterpretation of the electrogram during left AP ablation and may be useful in future therapies of atypical atrial flutter and fibrillation.

Epidemiology and natural history of atrial fibrillation: clinical implications

With a substantial impact on morbidity and mortality, the growing "epidemic" of atrial fibrillation (AF) intersects with a number of conditions, including aging, thromboembolism, hemorrhage, hypertension and left ventricular dysfunction. Currently, the epidemiology and natural history of AF govern all aspects of its clinical management. The ongoing global investigative efforts toward understanding AF are also driven by epidemiologic findings. New developments, by affecting the natural history of the disease, could eventually alter the nature of decision making in patients with AF. The crucial issue of rate versus rhythm control awaits completion of the AF Follow-up Investigation of Rhythm Management trial. The processes of electrical and structural remodeling that perpetuate AF appear to be reversible. In the era of functional genomics, the molecular basis of this ubiquitous arrhythmia is in the process of being defined. Unraveling the molecular genetics of AF might provide new insights into the structural and electrical phenotypes resulting from genetic mutations and, as such, new approaches to treatment of this arrhythmia at the ion channel and cellular levels. Thus, current adverse trends are superimposed on a background of a rapidly developing knowledge base and potentially exciting new therapeutic options. Consequently, an understanding of the epidemiology and natural history of AF is crucial to the future allocation of resources and the utilization of an expanding range of therapies aimed at reducing the impact of this disease on a changing patient population.

Altered response to ibutilide in a heart failure model

OBJECTIVE

Despite the frequent use of anti-arrhythmic drugs in the general population, the electrophysiologic effects of these agents have not been elucidated in congestive heart failure (CHF).

METHODS

To examine the impact of left ventricular dysfunction on actions of type III anti-arrhythmic drugs, we evaluated the actions of ibutilide in a canine model of pacing-induced dilated cardiomyopathy. Following ablation of the atrioventricular node, effects on action potential duration at 90% (APD(90)) were compared in vivo, between eight CHF animals and seven controls. Monophasic action potential recordings were obtained from right and left ventricular endocardium/epicardium during and after three doses of ibutilide (0. 01, 0.02 and 0.05 mg/kg), at pacing cycle lengths of 300-1000 ms.

RESULTS

APD(90) prolongation with ibutilide (0.01 mg/kg) was significantly greater in CHF vs. controls (P=0.0026, ANOVA). However, plasma ibutilide levels at this dose, were not significantly different between the two groups. In CHF, maximal effects were observed at the lowest dose, whereas effects were gradual and dose-dependent in controls. With ibutilide administration (0.01 mg/kg), an increased dispersion of left-right ventricular APD(90) was observed in CHF, but not in controls (P=0.03). A trend was observed, for increased incidence of non-sustained polymorphic ventricular tachycardia in CHF.

CONCLUSIONS

In the presence of CHF, the actions of ibutilide are altered significantly. These findings may reflect altered tissue effects, as a consequence of myocardial electrical remodeling in CHF.

Electrophysiologic characteristics of diverse accessory pathway locations of antidromic reciprocating tachycardia

This study assessed antidromic reciprocating tachycardia (ART) in patients with paraseptal accessory pathways (APs). Previous clinical experience suggests that paraseptal APs are unable to serve as the anterograde limb during ART. Based on the reentry wavelength concept, we hypothesized that anatomic location of a paraseptal AP may not preclude occurrence of ART. If wavelength criteria were met due to prolonged conduction time retrogradely in the atrioventricular node or anterogradely in the AP, ART may be sustained. All patients who had ART in the electrophysiologic laboratory at our institution (1991 to 1998) were studied. Based on fluoroscopically guided electrophysiologic mapping and radiofrequency ablation, AP location was classified as paraseptal, posterior, or lateral. Conduction time and refractoriness measurements were made for all components of the ART circuit. Of 24 patients with ART, 5 (21%) had ART utilizing a paraseptal AP. Anterograde conduction time through the AP and retrograde atrioventricular nodal conduction time were significantly longer in patients with paraseptal versus lateral pathways. Isoproterenol was required for ART induction in 38% of patients with a posterior AP, 36% with lateral AP location, but not in patients with a paraseptal AP. There were no significant differences in tachycardia cycle length or refractoriness of anterograde and/or retrograde components of the macroreentry circuit between the 3 pathway locations. Thus, ART can occur in patients with a paraseptal AP. Slower anterograde pathway conduction, or retrograde atrioventricular nodal conduction renders the wavelength critical for completion of the antidromic re-entrant circuit.

Endocardial activation during ventricular fibrillation in normal and failing canine hearts

Because congestive heart failure (CHF) promotes ventricular fibrillation (VF), we compared VF in seven dogs with CHF induced by combined myocardial infarction and rapid ventricular pacing to VF in six normal dogs. A noncontact, multielectrode array balloon catheter provided full-surface real-time left ventricular (LV) endocardial electrograms and a dynamic color-coded display of endocardial activation projected onto a three-dimensional model of the LV. Fast Fourier transform (FFT) analysis of virtual electrograms showed no difference in peak or centroid frequency in CHF dogs compared with normals. The average number of simultaneous noncontiguous wavefronts present during VF was higher in normals (2.4 +/- 1.0 at 10 s of VF) than in CHF dogs (1.3 +/- 1.0, P < 0.005) and decreased in both over time. The wavefront "turnover" rate, estimated using FFT of the noncontiguous wavefront data, did not differ between normals and CHF and did not change over 5 min of VF. Thus the fundamental frequency characteristics of VF are unaltered by CHF, but dilated abnormal ventricles sustain fewer active wavefronts than do normal ventricles.

Sudden cardiac death with apparently normal heart

BACKGROUND

Mechanisms of sudden cardiac death (SCD) in subjects with apparently normal hearts are poorly understood. In survivors, clinical investigations may not establish normal cardiac structure with certainty. Large autopsy series may provide a unique opportunity to confirm structural normalcy of the heart before reviewing a patient's clinical history.

METHODS AND RESULTS

We identified and reexamined structurally normal hearts from a 13-year series of archived hearts of patients who had sudden cardiac death. Subsequently, for each patient with a structurally normal heart, a detailed review of the circumstances of death as well as clinical history was performed. Of 270 archived SCD hearts identified, 190 were male and 80 female (mean age 42 years); 256 (95%) had evidence of structural abnormalities and 14 (5%) were structurally normal. In the group with structurally normal hearts (mean age 35 years), SCD was the first manifestation of disease in 7 (50%) of the 14 cases. In 6 cases, substances were identified in serum at postmortem examination without evidence of drug overdose; 2 of these chemicals have known associations with SCD. On analysis of ECGs, preexcitation was found in 2 cases. Comorbid conditions identified were seizure disorder and obesity (2 cases each). In 6 cases, there were no identifiable conditions associated with SCD.

CONCLUSIONS

In 50% of cases of SCD with structurally normal hearts, sudden death was the first manifestation of disease. An approach combining archived heart examinations with detailed review of the clinical history was effective in elucidating potential SCD mechanisms in 57% of cases.

First evidence of premature ventricular complex-induced cardiomyopathy: a potentially reversible cause of heart failure

Tachycardia-induced cardiomyopathy is a well-recognized and reversible condition, but left ventricular dysfunction due to frequent isolated premature ventricular complexes (PVCs) has not been reported. We observed resolution of dilated cardiomyopathy in a patient after a focal source of PVCs was eliminated by radiofrequency ablation. In a subset of patients with heart failure, PVC-induced cardiomyopathy may be a potentially reversible cause of left ventricular dysfunction.