Renin angiotensin system-induced muscle wasting: putative mechanisms and implications for clinicians.

Renin angiotensin system (RAS) alters various mechanisms related to muscle wasting. The RAS system consists of classical and non-classical pathways, which mostly function differently. Classical RAS pathway, operates through angiotensin II (AngII) and angiotensin type 1 receptors, is associated with muscle wasting and sarcopenia. On the other hand, the non-classical RAS pathway, which operates through angiotensin 1-7 and Mas receptor, is protective against sarcopenia. The classical RAS pathway might induce muscle wasting by variety of mechanisms. AngII reduces body weight, via reduction in food intake, possibly by decreasing hypothalamic expression of orexin and neuropeptide Y, insulin like growth factor-1 (IGF-1) and mammalian target of rapamycin (mTOR), signaling, AngII increases skeletal muscle proteolysis by forkhead box transcription factors (FOXO), caspase activation and muscle RING-finger protein-1 transcription. Furthermore, AngII infusion in skeletal muscle reduces phospho-Bad (Ser136) expression and induces apoptosis through increased cytochrome c release and DNA fragmentation. Additionally, Renin angiotensin system activation through AT1R and AngII stimulates tumor necrosis factor-α, and interleukin-6 which induces muscle wasting, Last but not least classical RAS pathway, induce oxidative stress, disturb mitochondrial energy metabolism, and muscle satellite cells which all lead to muscle wasting and decrease muscle regeneration. On the contrary, the non-classical RAS pathway functions oppositely to mitigate these mechanisms and protects against muscle wasting. In this review, we summarize the mechanisms of RAS-induced muscle wasting and putative implications for clinical practice. We also emphasize the areas of uncertainties and suggest potential research areas.

A case of ifosfamide-induced acute kidney injury, Fanconi syndrome, and nephrogenic diabetes insipidus.

Ifosfamide, a cytotoxic antineoplastic drug, can induce rare complications of Fanconi syndrome and nephrogenic diabetes insipidus (DI). Ifosfamide-induced Fanconi syndrome tends to occur in patients with certain risk factors including young age, high cumulative ifosfamide dose, and coadministration of cisplatin. Nephrogenic DI causes polyuria from impaired urinary concentrating ability due to resistance to arginine vasopressin (AVP) at the collecting duct. These complications are serious and potentially fatal. Here, we describe a case of a middle-aged man without risk factors who was admitted for the management of acute kidney injury and electrolyte derangements after his fourth cycle of chemotherapy including ifosfamide for synovial sarcoma. He was found to have hypokalemia, hypophosphatemia, renal glycosuria, and aminoaciduria, likely from Fanconi syndrome, which were managed by electrolyte replacement therapy. In addition, polyuria and hypernatremia were considered due to nephrogenic DI, which partially responded to desmopressin treatment. This case highlights the importance of the routine electrolytes monitoring after ifosfamide treatment.

Arrhythmia in chronic hemodialysis as a function of predialysis electrolytes and interdialytic interval.

INTRODUCTION: People with end-stage renal disease on hemodialysis are at increased risk for death due to arrhythmia associated with the prolonged interdialytic interval that typically spans the weekend, with bradycardia being the arrhythmia most closely associated with sudden death. In this prospective observational study we assessed whether predialysis fluid and electrolytes values including hyperkalemia are risk factors for the arrhythmias associated with the prolonged interdialytic interval. METHODS: Sixty patients on hemodialysis with a history of hyperkalemia underwent cardiac monitoring for 1 week. Arrhythmia frequency, average QTc interval, and average root mean square of successive differences (rMSSD) per 4-h period were reported. Predialysis electrolytes and electrocardiograms were collected prior to pre- and post-weekend dialysis sessions. Clinical variables were assessed for correlation with arrhythmias. FINDINGS: Predialysis hyperkalemia occurred in 29 subjects and was more common at the post-weekend dialysis session. Bradycardia occurred in 11 subjects and increased before and during the post-weekend dialysis session, but was not correlated with any electrolyte or clinical parameter. Ventricular ectopy occurred in 50 subjects with diurnal variation unrelated to dialysis. Pre-dialysis prolonged QTc was common and not affected by interdialytic interval. Average QTc increased and rMSSD decreased during dialysis sessions and were not correlated with clinical parameters. DISCUSSION: The results confirm that arrhythmias are prevalent in dialysis subjects with bradycardia particularly associated with the longer interdialytic interval; EKG markers of arrhythmia risk are increased during dialysis independent of interdialytic interval. Larger sample size and/or longer recording may be necessary to identify the clinical parameters responsible.

CLIC4 localizes to mitochondrial-associated membranes and mediates cardioprotection.

Mitochondrial-associated membranes (MAMs) are known to modulate organellar and cellular functions and can subsequently affect pathophysiology including myocardial ischemia-reperfusion (IR) injury. Thus, identifying molecular targets in MAMs that regulate the outcome of IR injury will hold a key to efficient therapeutics. Here, we found chloride intracellular channel protein (CLIC4) presence in MAMs of cardiomyocytes and demonstrate its role in modulating ER and mitochondrial calcium homeostasis under physiological and pathological conditions. In a murine model, loss of CLIC4 increased myocardial infarction and substantially reduced cardiac function after IR injury. CLIC4 null cardiomyocytes showed increased apoptosis and mitochondrial dysfunction upon hypoxia-reoxygenation injury in comparison to wild-type cardiomyocytes. Overall, our results indicate that MAM-CLIC4 is a key mediator of cellular response to IR injury and therefore may have a potential implication on other pathophysiological processes.

A Zn2+-triggered two-step mechanism of CLIC1 membrane insertion and activation into chloride channels.

The chloride intracellular channel (CLIC) protein family displays the unique feature of altering its structure from a soluble form to a membrane-bound chloride channel. CLIC1, a member of this family, is found in the cytoplasm or in internal and plasma membranes, with membrane relocalisation linked to endothelial disfunction, tumour proliferation and metastasis. The molecular switch promoting CLIC1 activation remains under investigation. Here, cellular Cl- efflux assays and immunofluorescence microscopy studies have identified intracellular Zn2+ release as the trigger for CLIC1 activation and membrane insertion. Biophysical assays confirmed specific binding to Zn2+, inducing membrane association and enhancing Cl- efflux in a pH-dependent manner. Together, our results identify a two-step mechanism with Zn2+ binding as the molecular switch promoting CLIC1 membrane insertion, followed by pH-mediated activation of Cl- efflux.

Microbial Diversity and Interaction Specificity in Kombucha Tea Fermentations.

Despite the popularity of kombucha tea, the distribution of different microbes across kombucha ferments and how those microbes interact within communities are not well characterized. Using metagenomics, comparative genomics, synthetic community experiments, and metabolomics, we determined the taxonomic, ecological, and functional diversity of 23 distinct kombuchas from across the United States. Shotgun metagenomic sequencing demonstrated that the bacterium Komagataeibacter rhaeticus and the yeast Brettanomyces bruxellensis were the most common microbes in the sampled kombucha communities. To determine the specificity of bacterium-yeast interactions, we experimentally quantified microbial interactions within kombucha biofilms by measuring densities of interacting species and biofilm production. In pairwise combinations of bacteria and yeast, B. bruxellensis and individual strains of Komagataeibacter spp. were sufficient to form kombucha fermentations with robust biofilms, but Zygosaccharomyces bisporus, another yeast found in kombucha, did not stimulate bacteria to produce biofilms. Profiling the spent media of both yeast species using nuclear magnetic resonance spectroscopy suggested that the enhanced ability of B. bruxellensis to ferment and produce key metabolites in sucrose-sweetened tea may explain why it stimulates biofilm formation. Comparative genomics demonstrated that Komagataeibacter spp. with >99% genomic similarity can still have dramatic differences in biofilm production, with strong producers yielding five times more biofilm than the weakest producers. IMPORTANCE Through an integration of metagenomic and experimental approaches, our work reveals the diversity and nature of interactions among key taxa in kombucha microbiomes through the construction of synthetic microbial pairs. Manipulation of these microbes in kombucha has the potential to shape both the fermentation qualities of kombucha and the production of biofilms and is valuable for kombucha beverage producers, biofilm engineers, and synthetic ecologists.

Nephrotic range proteinuria associated with focal segmental glomerulosclerosis reversed with pioglitazone therapy in a patient with Dunnigan type lipodystrophy.

Familial partiallipodystrophy (FPLD)is a rare disorder associated withsevere insulin resistance, hypertriglyceridemia, lowserumHDLcholesterol and proteinuricrenaldisease. Although proteinuric renal disease is not common among in patients with partial lipodystrophy, we report a patient with Dunnigan type FPLD complicated by nephrotic syndrome which resolved following treatment with thePPARγagonist pioglitazone, CPAP, diet, and exercise.

Kidney-disease-associated variants of Apolipoprotein L1 show gain of function in cation channel activity.

Variants in Apolipoprotein L1 (ApoL1) are known to be responsible for increased risk of some progressive kidney diseases among people of African ancestry. ApoL1 is an amphitropic protein that can insert into phospholipid membranes and confer anion- or cation-selective permeability to phospholipid membranes depending on pH. Whether these activities differ among the variants or whether they contribute to disease pathogenesis is unknown. We used assays of voltage-driven ion flux from phospholipid vesicles and of stable membrane association to assess differences among ApoL1 isoforms. There is a significant (approximately twofold) increase in the cation-selective ion permease activity of the two kidney-disease-associated variants compared with the reference protein. In contrast, we find no difference in the anion-selective permease activity at low pH among the isoforms. Compared with the reference sequence, the two disease-associated variants show increased stable association with phospholipid vesicles under conditions that support the cation permease activity, suggesting that the increased activity may be due to more efficient membrane association and insertion. There is no difference in membrane association among isoforms under optimal conditions for the anion permease activity. These data support a model in which enhanced cation permeability may contribute to the progressive kidney diseases associated with high-risk ApoL1 alleles.

Immune reconstitution, glomerulonephritis, and successful treatment with rituximab.

BACKGROUND: Alemtuzumab can induce secondary autoimmunity affecting multiple organs. While kidney involvement is uncommon, it can be associated with devastating forms of glomerulonephritis (GN). CASE PRESENTATION: A 32-year-old African American woman presented with hypertension, proteinuria, and progressive renal failure. Her medical history was remarkable for secondary progressive multiple sclerosis (SPMS). She had received her first induction dose of alemtuzumab 1 year prior to presentation. Upon evaluation, she had scanning speech, multidirectional nystagmus, and mild edema. Her serum creatinine was 2 mg/dL. Urine studies revealed proteinuria and microscopic hematuria. Her serologic tests were positive for c-antineutrophil cytoplasmic antibodies (> 1 : 640). In addition, she was found to have new-onset severe thyroid dysfunction with antibodies against thyroglobulin and thyroid peroxidase. Kidney biopsy was diagnostic for pauci-immune crescentic GN. The patient was treated with methylprednisolone and rituximab with subsequent renal, thyroid, and neurological recovery. CONCLUSION: This is an atypical case of GN following therapy with alemtuzumab. We hypothesize that immune reconstitution may be a potential mechanism. Alemtuzumab is a new treatment for SPMS that can be associated with GN. Practice guidelines should address the management of its renal complications.

Distal renal tubular acidosis and severe hypokalemia: a case report and review of the literature.

BACKGROUND: Distal renal tubular acidosis is a relatively infrequent condition with complex pathophysiology that can present with life-threatening electrolyte abnormalities. CASE PRESENTATION: We describe a case of a 57-year-old Caucasian woman with previous episodes of hypokalemia, severe muscle weakness, and fatigue. Upon further questioning, symptoms of dry eye and dry mouth became evident. Initial evaluation revealed hyperchloremic metabolic acidosis, severe hypokalemia, persistent alkaline urine, and a positive urinary anion gap, suggestive of distal renal tubular acidosis. Additional laboratory workup and renal biopsy led to the diagnosis of primary Sjögren's syndrome with associated acute tubulointerstitial nephritis. After potassium and bicarbonate supplementation, immunomodulatory therapy with hydroxychloroquine, azathioprine, and prednisone was started. Nonetheless, her renal function failed to improve and remained steady with an estimated glomerular filtration rate of 42 ml/min/1.73 m2. The literature on this topic was reviewed. CONCLUSIONS: Cases of renal tubular acidosis should be carefully evaluated to prevent adverse complications, uncover a potentially treatable condition, and prevent the progression to chronic kidney disease. Repeated episodes of unexplained hypokalemia could be an important clue for diagnosis.

Apolipoprotein L1 confers pH-switchable ion permeability to phospholipid vesicles.

Apolipoprotein L1 (ApoL1) is a human serum protein conferring resistance to African trypanosomes, and certain ApoL1 variants increase susceptibility to some progressive kidney diseases. ApoL1 has been hypothesized to function like a pore-forming colicin and has been reported to have permeability effects on both intracellular and plasma membranes. Here, to gain insight into how ApoL1 may function in vivo, we used vesicle-based ion permeability, direct membrane association, and intrinsic fluorescence to study the activities of purified recombinant ApoL1. We found that ApoL1 confers chloride-selective permeability to preformed phospholipid vesicles and that this selectivity is strongly pH-sensitive, with maximal activity at pH 5 and little activity above pH 7. When ApoL1 and lipid were allowed to interact at low pH and were then brought to neutral pH, chloride permeability was suppressed, and potassium permeability was activated. Both chloride and potassium permeability linearly correlated with the mass of ApoL1 in the reaction mixture, and both exhibited lipid selectivity, requiring the presence of negatively charged lipids for activity. Potassium, but not chloride, permease activity required the presence of calcium ions in both the association and activation steps. Direct assessment of ApoL1-lipid associations confirmed that ApoL1 stably associates with phospholipid vesicles, requiring low pH and the presence of negatively charged phospholipids for maximal binding. Intrinsic fluorescence of ApoL1 supported the presence of a significant structural transition when ApoL1 is mixed with lipids at low pH. This pH-switchable ion-selective permeability may explain the different effects of ApoL1 reported in intracellular and plasma membrane environments.

Treatment of Gabapentin Toxicity With Peritoneal Dialysis: Assessment of Gabapentin Clearance.

Gabapentin is almost exclusively cleared by the kidney and thus presents challenges in patients with kidney failure. Gabapentin is known to be effectively cleared by hemodialysis, but the efficiency of clearance by peritoneal dialysis (PD) has not been previously described. We report a case of gabapentin toxicity in a patient on long-term PD who was treated with continuous automated cycling PD. We find that continuous PD provides significant clearance of gabapentin. With 2-L exchanges every 2 hours, we document an apparent elimination half-life of 41.33 hours, which is substantially shorter than the reported elimination half-life of 132 hours in the absence of kidney function. Further, our patient's symptoms of gabapentin toxicity gradually improved and had fully resolved after about 36 hours of dialysis. Gabapentin clearance by PD was estimated at 94% of urea clearance. We conclude that intensive PD provides gabapentin clearance that approximates that of urea and is an effective but slow method to treat gabapentin overdose and toxicity.

CLIC1 null mice demonstrate a role for CLIC1 in macrophage superoxide production and tissue injury.

We generated and studied CLIC1 null (C1KO) mice to investigate the physiological role of this protein. C1KO and matched wild-type (WT) mice were studied in two models of acute toxic tissue injury. CLIC1 expression is upregulated following acute injury of WT kidney and pancreas and is absent in C1KOs. Acute tissue injury is attenuated in the C1KOs and this correlates with an absence of the rise in tissue reactive oxygen species (ROS) that is seen in WT mice. Infiltration of injured tissue by inflammatory cells was comparable between WT and C1KOs. Absence of CLIC1 increased PMA-induced superoxide production by isolated peritoneal neutrophils but dramatically decreased PMA-induced superoxide production by peritoneal macrophages. CLIC1 is expressed in both neutrophils and macrophages in a peripheral pattern consistent with either plasma membrane or the cortical cytoskeleton in resting cells and redistributes away from the periphery following PMA stimulation in both cell types. Absence of CLIC1 had no effect on redistribution or dephosphorylation of Ezrin/ERM cytoskeleton in macrophages. Plasma membrane chloride conductance is altered in the absence of CLIC1, but not in a way that would be expected to block superoxide production. NADPH oxidase redistributes from an intracellular compartment to the plasma membrane when WT macrophages are stimulated to produce superoxide and this redistribution fails to occur in C1KO macrophages. We conclude that the role of CLIC1 in macrophage superoxide production is to support redistribution of NADPH oxidase to the plasma membrane, and not through major effects on ERM cytoskeleton or by acting as a plasma membrane chloride channel.

Both CLIC4 and CLIC5A activate ERM proteins in glomerular endothelium.

The chloride intracellular channel (CLIC) 5A is expressed at very high levels in renal glomeruli, in both endothelial cells (EC) and podocytes. CLIC5A stimulates Rac1- and phosphatidylinositol (4,5)-bisphosphate-dependent ERM (ezrin, radixin, moesin) activation. ERM proteins, in turn, function in lumen formation and in the development of actin-based cellular projections. In mice lacking CLIC5A, ERM phosphorylation is profoundly reduced in podocytes, but preserved in glomerular EC. Since glomerular EC also express CLIC4, we reasoned that, if CLIC4 activates ERM proteins like CLIC5A, then CLIC4 could compensate for the CLIC5A loss in glomerular EC. In glomeruli of CLIC5-deficient mice, CLIC4 expression was upregulated and colocalized with moesin and ezrin in glomerular EC, but not in podocytes. In cultured glomerular EC, CLIC4 silencing reduced ERM phosphorylation and cytoskeletal association, and expression of exogenous CLIC4 or CLIC5A rescued ERM de-phosphorylation due to CLIC4 silencing. In mice lacking either CLIC4 or CLIC5, ERM phosphorylation was retained in glomerular EC, but, in mice lacking both CLIC4 and CLIC5, glomerular EC ERM phosphorylation was profoundly reduced. Although glomerular EC fenestrae developed normally in dual CLIC4/CLIC5-deficient mice, the density of fenestrae declined substantially by 8 mo of age, along with the deposition of subendothelial electron-lucent material. The dual CLIC4/CLIC5-deficient mice developed spontaneous proteinuria, glomerular cell proliferation, and matrix deposition. Thus CLIC4 stimulates ERM activation and can compensate for CLIC5A in glomerular EC. The findings indicate that CLIC4/CLIC5A-mediated ERM activation is required for maintenance of the glomerular capillary architecture.

Data supporting characterization of CLIC1, CLIC4, CLIC5 and DmCLIC antibodies and localization of CLICs in endoplasmic reticulum of cardiomyocytes.

Chloride intracellular channel (CLICs) proteins show 60-70% sequence identity to each other, and exclusively localize to the intracellular organelle membranes and cytosol. In support of our recent publication, "Molecular identity of cardiac mitochondrial chloride intracellular channel proteins" (Ponnalagu et al., 2016) [1], it was important to characterize the specificity of different CLIC paralogs/ortholog (CLIC1, CLIC4, CLIC5 and DmCLIC) antibodies used to decipher their localization in cardiac cells. In addition, localization of CLICs in the other organelles such as endoplasmic reticulum (ER) of cardiomyocytes was established. This article also provides data on the different primers used to show the relative abundance of CLIC paralogs in cardiac tissue and the specificity of the various CLIC antibodies used. We demonstrate that the predominant CLICs in the heart, namely CLIC1, CLIC4 and CLIC5, show differential distribution in endoplasmic reticulum. CLIC1 and CLIC4 both show co-localization to the endoplasmic reticulum whereas CLIC5 does not.