IgA-dominant infection-associated glomerulonephritis in the pediatric population.

BACKGROUND: IgA-dominant infection-associated glomerulonephritis is well-documented in adults but has not been studied in depth in children. We assessed the incidence of pediatric IgA-dominant infection-associated glomerulonephritis and clinical and kidney biopsy findings. METHODS: Pediatric native kidney biopsies over a 10-year period with IgA dominance, strong C3, and findings indicative of infection-associated etiology were identified. RESULTS: We identified 9 cases of IgA-dominant infection-associated glomerulonephritis, 0.8% of pediatric native kidney biopsies. Seven patients presented with elevated creatinine. All had hematuria and proteinuria. Eight patients had clinical evidence of infection: one each with central port infection by methicillin-sensitive Staphylococcus aureus, recurrent streptococcal pharyngitis and recent otitis media, streptococcal pharyngitis demonstrated 8 months after biopsy, suspected streptococcal scalded skin syndrome, and viral gastroenteritis, and three with serologic evidence of Streptococcal infection but no identified site of infection. All but one patient experienced short-term normalization of creatinine and resolution of proteinuria, though two eventually progressed to kidney failure: one 3 years later due to progressive disease and one 11 years later due to focal segmental glomerulosclerosis without concurrent immune deposits. CONCLUSIONS: Pediatric IgA-dominant infection-associated glomerulonephritis is rare, and generally has a favorable prognosis, contrasting that seen in adults with severe comorbidities. A higher resolution version of the Graphical abstract is available as Supplementary.

Erythropoietin-stimulating agent-resistant vitamin B6 deficiency anemia in a pediatric patient on hemodialysis.

BACKGROUND: Vitamin B6 is a rate-limiting coenzyme that plays an important role in the biosynthesis of heme and the incorporation of iron into protoporphyrin. Its deficiency is often seen in chronic kidney disease (CKD), particularly those requiring dialysis and following administration of erythropoietin-stimulating agent (ESA). CASE- DIAGNOSIS/TREATMENT: A 16-year-old African-American male with stage 5 CKD on chronic hemodialysis experienced a decrease in hemoglobin over a 3-month period from 11 to 6.5 g/dl while receiving ESA, resulting in multiple blood transfusions. His transferrin saturation was 41%, ferritin level 706 [80-388] ng/mL, mean corpuscular volume (MCV) 87 [78-98] µm3, corrected reticulocytes count 2.3% [0.2-1.8%], and vitamin B6 1.2 [5.3-46.7] µg/L. Bone marrow biopsy was normocellular (65%) with erythroid hyperplasia and rare dyserythropoiesis. Prussian blue staining showed increased iron storage. Supplemental vitamin B6 (100 mg daily) was initiated at hemoglobin 7.3 g/dL with correction of anemia. Eighteen months later, his hemoglobin is 11.7 g/dL, transferrin saturation 45%, with no additional blood transfusions. CONCLUSIONS: Vitamin B6 deficiency anemia should be considered in any pediatric patient on hemodialysis who does not respond to standard ESA and iron therapy.

Inhibition of cytochrome P450 2E1 and activation of transcription factor Nrf2 are renoprotective in myoglobinuric acute kidney injury.

Rhabdomyolysis accounts for ∼10% of acute kidney injuries. In glycerol-induced myoglobinuric acute kidney injury, we found an increase in the nuclear factor erythroid 2-related factor 2 (Nrf2) nuclear protein, a key redox-sensitive transcription factor, and Nrf2-regulated genes and proteins including upregulation of heme oxygenase-1. In in vitro studies, pretreatment of LLC-PK1 cells with an activator of Nrf2 before myoglobin exposure significantly decreased oxidant generation and cytotoxicity, whereas Nrf2 inhibition and gene silencing exacerbated the injury. Chlormethiazole, a specific CYP2E1 transcription inhibitor, prevented an increase in catalytic iron in the kidneys, decreased oxidative stress, blocked nuclear translocation of the Nrf2 protein, decreased heme oxygenase-1 upregulation, and provided functional and histological protection against acute kidney injury. CYP2E1 inhibitors and gene silencing in renal tubular epithelial cells significantly decreased reactive oxygen species generation and provided marked protection against myoglobin-induced cytotoxicity. Thus, during CYP2E1-induced oxidative stress, the transcription factor Nrf2 has a pivotal role in the early adaptive response. Inhibition of CYP2E1 coupled with the prior induction of Nrf2 may be a valuable tool to reduce CYP2E1-mediated rhabdomyolysis-induced acute kidney injury.

Coronavirus Disease 2019 (COVID-19) Associated Hemolytic Uremic Syndrome in a Toddler.

Coronavirus disease 2019 (COVID-19) is a heterogenous, predominantly pulmonary disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that has resulted in catastrophic illness around the world. Thrombotic microangiopathy (TMA) is a triad of hemolytic anemia, thrombocytopenia, and end organ damage. This is present in severe cases of COVID-19 and in hemolytic uremic syndrome (HUS) commonly caused by Escherichia coli (E.coli) 0157:H7. We report a novel case of a toddler who presented with classic features suggestive of HUS characterized by bloody diarrhea followed by thrombocytopenia, hemolytic anemia, and acute kidney injury, in whom a polymerase chain reaction (PCR) test for SARS-CoV-2 was positive.

Primary aldosteronism caused by a pI157S somatic KCNJ5 mutation in a black adolescent female with aldosterone-producing adenoma.

Aldosterone-producing adenoma is a rare cause of hypertension in children. Only a limited number of cases of aldosterone-producing adenomas with somatic KCNJ5 gene mutations have been described in children. Blacks are particularly more susceptible to developing long-standing cardiovascular effects of aldosterone-induced severe hypertension. Somatic CACNA1D gene mutations are particularly more prevalent in black males whereas KCNJ5 gene mutations are most frequently present in black females. We present here a novel somatic KCNJ5 p.I157S mutation in an aldosterone-producing adenoma from a 16-year-old black female whose severe drug-resistant hypertension significantly improved following unilateral adrenalectomy. Prompt diagnosis of aldosterone-producing adenoma and early identification of gene mutation would enable appropriate therapy and significantly reduce cardiovascular sequelae.

Cytochrome P450 2B1 mediates complement-dependent sublytic injury in a model of membranous nephropathy.

Membranous nephropathy is a disease that affects the filtering units of the kidney, the glomeruli, and results in proteinuria accompanied by loss of kidney function. Passive Heymann nephritis is an experimental model that mimics membranous nephropathy in humans, wherein the glomerular epithelial cell (GEC) injury induced by complement C5b-9 leads to proteinuria. We examined the role of cytochrome P450 2B1 (CYP2B1) in this complement-mediated sublytic injury. Overexpression of CYP2B1 in GECs significantly increased the formation of reactive oxygen species, cytotoxicity, and collapse of the actin cytoskeleton following treatment with anti-tubular brush-border antiserum (anti-Fx1A). In contrast, silencing of CYP2B1 markedly attenuated anti-Fx1A-induced reactive oxygen species generation and cytotoxicity with preservation of the actin cytoskeleton. Gelsolin, which maintains an organized actin cytoskeleton, was significantly decreased by complement C5b-9-mediated injury but was preserved in CYP2B1-silenced cells. In rats injected with anti-Fx1A, the cytochrome P450 inhibitor cimetidine blocked an increase in catalytic iron and ROS generation, reduced the formation of malondialdehyde adducts, maintained a normal distribution of nephrin in the glomeruli, and provided significant protection at the onset of proteinuria. Thus, GEC CYP2B1 contributes to complement C5b-9-mediated injury and plays an important role in the pathogenesis of passive Heymann nephritis.

p66SHC-mediated mitochondrial dysfunction in renal proximal tubule cells during oxidative injury.

Mitochondrial dysfunction is involved in pathopysiology of ischemia-reperfusion-induced acute kidney injury (AKI). The p66shc adaptor protein is a newly recognized mediator of mitochondrial dysfunction, which might play a role in AKI-induced renal tubular injury. Oxidative stress-mediated Serine36 phosphorylation of p66shc facilitates its transportation to the mitochondria where it oxidizes cytochrome c and generates excessive amount of reactive oxygen species (ROS). The consequence is mitochondrial depolarization and injury. Earlier we determined that p66shc plays an essential role in injury of cultured mouse renal proximal tubule cells during oxidative stress. Here, we studied the role of p66shc in ROS generation and consequent mitochondrial dysfunction during oxidative injury in renal proximal tubule cells. We employed p66shc knockdown renal proximal tubule cells and cells that overexpress wild-type, Serine phosphorylation (S36A), or cytochrome c-binding (W134F) mutants of p66shc. Inhibition of the mitochondrial electron transport chain or the mitochondrial permeability transition revealed that hydrogen peroxide-induced injury is mitochondrial ROS and consequent mitochondrial depolarization dependent. We also found that through Ser36 phosphorylation and mitochondria/cytochrome c binding, p66shc mediates those effects. We propose a similar mechanism in vivo as we demonstrated mitochondrial binding of p66shc as well as its association with cytochrome c in the postischemic kidneys of mice. Thus, manipulating p66shc might offer a new therapeutic modality to ameliorate renal ischemic injury.

Cytochrome-P450 2B1 gene silencing attenuates puromycin aminonucleoside-induced cytotoxicity in glomerular epithelial cells.

Previously, we demonstrated that cytochrome P450 2B1 (CYP2B1) can generate reactive oxygen species in puromycin aminonucleoside (PAN)-induced nephrotic syndrome, an animal model of minimal-change disease in humans. In this study we found that overexpression of CYP2B1 in rat glomerular epithelial cells in vitro significantly increased PAN-induced reactive oxygen species generation, cytotoxicity, cell death, and collapse of the actin cytoskeleton. All of these pathological changes were markedly attenuated by siRNA-induced CYP2B1 silencing. The cellular CYP2B1 protein content was significantly decreased whereas its mRNA level was markedly increased, suggesting regulation by protein degradation rather than transcriptional inhibition in the PAN-treated glomerular epithelial cells. This degradation of CYP2B1 was accompanied by the induction of heme oxygenase-1, an important indicator of heme-induced oxidative stress. In PAN-treated CYP2B1-silenced glomerular epithelial cells the induction of heme oxygenase-1 and caspase-3 activity were significantly decreased. Further, cleavage of the stress-induced pro-apoptotic endoplasmic reticulum-specific pro-caspase-12 was prevented in the silenced cells. Our results support a pivotal role of CYP2B1 for reactive oxygen species production in the endoplasmic reticulum in PAN-induced cytotoxicity.

Epigenetic modifiers exacerbate oxidative stress in renal proximal tubule cells.

BACKGROUND: Increased production of reactive oxygen species (ROS) by anticancer drugs has been described in patients with various malignancies, which might attribute to their nephrotoxicity. MATERIALS AND METHODS: The effects of two epigenetic modifiers - trichostatin A (TSA) and 5-aza-deoxycytidine (5AZA) - on ROS production and cell injury alone or in combination with mild oxidative stress were studied in mouse renal proximal tubule cells. RESULTS: Both agents increased mitochondrial ROS production and consequent lactate dehydrogenase (LDH) release either alone or in combination with a low dose of H(2)O(2). The antioxidant N-acetyl-cysteine (NAC) abolished LDH release. It was also found that CREB-mediated transcription, vital for survival of proximal tubule cells, is attenuated by these anticancer agents. CONCLUSION: The ROS-inducing activity of TSAI and 5AZA might explain the in vivo nephrotoxicity of epigenetic modifiers. The mechanisms that are responsible for this injury could involve attenuation of pro-survival signaling and/or activation of death signaling pathway(s) associated with mitochondrial ROS release.

The plant-derived natural compound Flavin 7 attenuates oxidative stress in cultured renal proximal tubule cells.

BACKGROUND: Cancer therapies and cancer progression can increase oxidative stress that might account for renal toxicity in cancer patients. Flavin 7 (F7) is a natural polyphenol-containing dietary supplement with potential antioxidant activity. Therefore, it might help to attenuate renal toxicity of chemotherapeutics. MATERIALS AND METHODS: Cultured mouse renal proximal tubule cells were subjected to H(2)O(2)-mediated oxidative stress. Potential antioxidant effects of F7 were assessed by measuring the production of reactive oxygen species (ROS), mitochondrial depolarization and injury (lactate dehydrogenase release as well as trypan blue exclusion) in cells that were pretreated with F7 prior to treatment with H(2)O(2). RESULTS: F7 pretreatment significantly attenuated H(2)O(2)-induced ROS production, mitochondrial depolarization and consequent injury in renal proximal tubule cells. CONCLUSION: F7 supplementation might be beneficial for cancer patients in order to prevent renal toxicity of anticancer drug- or cancer progression-related oxidative stress.

Novel COL4A3 mutations in African American siblings with autosomal recessive Alport syndrome.

We describe a novel mutational study in 2 African American siblings with autosomal recessive Alport syndrome. Both siblings were compound heterozygotes for 2 abnormal DNA sequences in exon 49 of the COL4A3 gene, p.Arg1496X (CGA-->TGA) and p.Arg1516X (CGA-->TGA). These are nonsense mutations in the noncollagenous domain resulting in premature termination codons and have not been previously reported. In an African American population in which autosomal recessive Alport syndrome is rarely seen, complete sequencing of the COL4A3 and COL4A4 genes may be necessary to identify the underlying mutation and confirm the diagnosis.

Acute peritoneal eosinophilia in a child with prune-belly syndrome following peritoneal dialysis catheter placement.

Peritoneal eosinophilia, although uncommon, was reported after placement of catheters for peritoneal dialysis. We describe a 7-year-old African-American boy with prune-belly syndrome who developed acute onset of peritoneal eosinophilia after placement of a peritoneal dialysis catheter. Peripheral-blood eosinophilia also was noted with the peritoneal eosinophilia, but was not correlative. Intraperitoneal and systemic corticosteroid therapy led to successful resolution of peritoneal eosinophilia. Radioallergosorbent tests indicated sensitization to latex. Unrecognized latex sensitization should be considered in any child with multiple urological surgeries who develops sudden onset of peritoneal eosinophilia.

Effect of cytochrome P450 2E1 inhibitors on cisplatin-induced cytotoxicity to renal proximal tubular epithelial cells.

BACKGROUND: We have demonstrated an important role of cytochrome P450 (CYP) as a significant source of catalytic iron in reactive oxygen species (ROS)-mediated cisplatin (CP)-induced renal injury. MATERIALS AND METHODS: The current study was designed to explore the role of CYP2E1 as a site for ROS generation and a source of iron in CP-induced cytotoxicity to the LLC-PK1 cells. RESULTS: CYP2E1 was identified in the LLC-PK1 cells. Exposure of LLC-PK1 cells to CP resulted in marked generation of hydrogen peroxide (H2O2), reduction of CYP2E1 content, increase in catalytic iron and hydroxyl radical formation accompanied by significant cytotoxicity. CYP2E1 inhibitors markedly reduced H2O2 generation with the preservation of CYP2E1 content, markedly decreased in iron and hydroxyl radical formation associated with significant attenuation in cytotoxicity. CONCLUSION: CYP2E1 plays an important role in CP-induced cytotoxicity by severing as a site for the generation of ROS and a significant source of catalytic iron.

Role of cytochrome P450 2B1 in puromycin aminonucleoside-induced cytotoxicity to glomerular epithelial cells.

Puromycin aminonucleoside (PAN)-induced glomerular injury in rats mimics minimal-change nephrotic syndrome (NS) in humans. We have demonstrated an important role of cytochrome P450 (CYP) as a significant source of catalytic iron in this model of NS. The current study was designed to identify CYP isozyme(s) present in the rat glomerular epithelial cells (GEC) and to explore the role of the specific CYP isozyme in PAN-induced cytotoxicity. CYP2B1 was identified in GEC by immunocytochemistry and Western blot. Treatment of GEC with PAN resulted in a marked generation of hydrogen peroxide (H(2)O(2)) and reduction of CYP2B1 content associated with significant increase in catalytic iron and hydroxyl radical formation. Preincubating GEC with CYP2B1 inhibitors (piperine and cimetidine) and H(2)O(2) scavenger (pyruvate) significantly reduced H(2)O(2 )generation, preserved CYP2B1 content, prevented the increase in catalytic iron and hydroxyl radical formation including PAN-induced cytotoxicity. We also observed the induction of heme oxygenase (HO-1) in PAN-treated GEC, and this up-regulation was reduced by pretreatment of the CYP inhibitors and pyruvate. Our data thus indicate an important role of CYP2B1 in PAN-induced cytotoxicity by serving as a site of reactive oxygen metabolite generation and a significant source of catalytic iron.

Cisplatin induces apoptosis through the ERK-p66shc pathway in renal proximal tubule cells.

The extracellular signal-regulated kinase (ERK) has been shown to mediate cisplatin (CP)-induced toxicity to renal proximal tubule cells. Here, we demonstrate that ERK serves as the kinase that phosphorylates the pro-apoptotic p66shc protein at its Serine36 residue in CP-treated renal proximal tubule cells. Pharmacologic or dominant-negative inhibition of ERK mitigates cisplatin-induced Ser36 phosphorylation of p66shc. Overexpression of p66shc exacerbates while its knockdown or mutation of the Serine36 site to alanine ameliorates CP-induced nephrotoxicity in vitro. Since p66shc is Serine36 phosphorylated in the kidneys of mice after treatment with CP, a similar mechanism might exist in vivo.

Oxidants in chronic kidney disease.

Chronic kidney disease is a worldwide public health problem that affects approximately 10% of the US adult population and is associated with a high prevalence of cardiovascular disease and high economic cost. Chronic renal insufficiency, once established, tends to progress to end-stage kidney disease, suggesting some common mechanisms for ultimately causing scarring and further nephron loss. This review defines the term reactive oxygen metabolites (ROM), or oxidants, and presents the available experimental evidence in support of the role of oxidants in diabetic and nondiabetic glomerular disease and their role in tubulointerstitial damage that accompanies progression. It concludes by reviewing the limited human data that provide some proof of concept that the observations in experimental models may be relevant to human disease.

Endoplasmic reticulum stress-associated caspase 12 mediates cisplatin-induced LLC-PK1 cell apoptosis.

Reactive oxygen metabolites are important mediators in cisplatin-induced apoptosis in renal tubular epithelial cells (LLC-PK1). Mitochondria have been implicated to play a principal role in cisplatin-induced apoptosis. Caspase 12, an endoplasmic reticulum (ER)-specific caspase, participates in apoptosis under ER stress. Cytochrome P450 system is crucial to the generation of reactive oxygen metabolites and is present at high concentration in the ER. The direct role of caspase 12 in any model of renal injury has not previously been described. In this study, cleavage of procaspase 12 preceded that of caspases 3 and 9 after cisplatin treatment of LLC-PK1 cells. The active form of caspase 8 was not detected throughout the course of study. Preincubation of the LLC-PK1 cells with the caspase 9 inhibitor did not attenuate caspase 3 activation and provided no significant protection. Caspase 3 inhibitor provided only modest protection against cisplatin-induced apoptosis. LLC-PK1 cells that were transfected with anti-caspase 12 antibody significantly attenuated cisplatin-induced apoptosis. Taken together, these data indicate that caspase 12 plays a pivotal role in cisplatin-induced apoptosis. It is proposed that the oxidative stress that results from the interaction of cisplatin with the ER cytochrome P450 leads to activation of procaspase 12, resulting in apoptosis.