Diuretics in States of Volume Overload: Core Curriculum 2022

Volume overload, defined as excess total body sodium and water with expansion of extracellular fluid volume, characterizes common disorders such as congestive heart failure, end-stage liver disease, chronic kidney disease, and nephrotic syndrome. Diuretics are the cornerstone of therapy for volume overload and comprise several classes whose mechanisms of action, pharmacokinetics, indications, and adverse effects are essential principles of nephrology. Loop diuretics are typically the first-line treatment in the management of hypervolemia, with additional drug classes indicated in cases of diuretic resistance and electrolyte or acid-base disorders. Separately, clinical trials highlight improved outcomes in some states of volume overload, such as loop diuretics and sodium/glucose cotransporter 2 inhibitors in patients with congestive heart failure. Resistance to diuretics is a frequent, multifactorial clinical challenge that requires creative and physiology-based solutions. In this installment of AJKD's Core Curriculum in Nephrology, we discuss the pharmacology and therapeutic use of diuretics in states of volume overload and strategies to overcome diuretic resistance.

Assessment of Interobserver Reliability of Nephrologist Examination of Urine Sediment

IMPORTANCE

Urine sediment microscopy is commonly performed during the evaluation of kidney disease. Interobserver reliability of nephrologists' urine sediment examination has not been well studied.

OBJECTIVE

Assess interobserver reliability of the urine sediment examination.

DESIGN, SETTING, AND PARTICIPANTS

In this diagnostic test study, urine samples were prospectively collected from a convenience sample of adult patients from an academic hospital in the United States undergoing kidney biopsy from July 11, 2018, to March 20, 2019. Digital images and videos of urine sediment findings were captured using a bright-field microscope. These images and videos along with urine dipstick results were incorporated in online surveys and sent to expert nephrologists at 15 US teaching hospitals. They were asked to identify individual sediment findings and the most likely underlying disease process.

EXPOSURES

Urine dipstick results and urine sediment images from patients undergoing native kidney biopsy.

MAIN OUTCOMES AND MEASURES

Interobserver reliability of urine sediment microscopy findings estimated by overall percent agreement and Fleiss κ coefficients. Secondary outcomes included concordance of diagnoses suspected by nephrologists with corresponding kidney biopsy results.

RESULTS

In total, 10 surveys from 10 patients containing 76 study questions on individual features were sent to 21 nephrologists, 14 (67%) of whom completed them all. Their combined 1064 responses were analyzed. Overall percent agreement for casts was an estimated 59% (95% CI, 50%-69%), κ = 0.52 (95% CI, 0.42-0.62). For other sediment findings, overall percent agreement was an estimated 69% (95% CI, 61%-77%), κ = 0.65 (95% CI, 0.56-0.73). The κ estimates ranged from 0.13 (95% CI, 0.10-0.17) for mixed cellular casts to 0.90 (95% CI, 0.87-0.94) for squamous epithelial cells.

CONCLUSIONS AND RELEVANCE

In this study, substantial variability occurred in the interpretation of urine sediment findings, even among expert nephrologists. Educational or technological innovations may help improve the urine sediment as a diagnostic tool.

Contrast Nephropathy Associated with Percutaneous Coronary Angiography and Intervention

Contrast nephropathy (CN) is acute kidney injury (AKI) that occurs within 24 to 72 hours of iodinated contrast medium (ICM) administration. Mechanisms of CN include hyperviscosity, free radical formation, and renal medullary oxygen supply/demand mismatch. Although risk factors for CN have been identified, it remains uncertain whether ICM causes or is simply associated with AKI. The cornerstones of CN prevention are using low-osmolal ICM, intravenous hydration, and statins, especially in patients with chronic kidney disease. With appropriate CN risk mitigation, coronary angiography and intervention should not be routinely withheld from patients with acute coronary syndromes.

Kidney Diseases Associated With Parvovirus B19, Hanta, Ebola, and Dengue Virus Infection: A Brief Review

Viral infection-associated kidney diseases are an emerging public health issue in both developing and developed countries. Many new viruses have emerged with new paradigms of kidney injury, either directly through their cytopathic effect or indirectly through immune-mediated glomerulopathy, tubulointerstitial disease, and acute kidney injury as part of multiorgan failure. Herein, we will discuss Parvovirus, which causes glomerulopathy, and Hanta, Ebola, and Dengue viruses, which cause viral hemorrhagic fever and acute kidney injury. Clinical manifestations also depend on extrarenal organ systems involved. Diagnosis of these viral infections is mainly based on a high index of suspicion, serologic testing, and isolation of viral DNA/RNA. Management is largely conservative, as specific antiviral agents are unavailable.

Diuretics in the Management of Cardiorenal Syndrome

The leading cause of death worldwide is cardiovascular disease. The heart and the kidneys are functionally interdependent, such that dysfunction in one organ may cause dysfunction in the other. By one estimate, more than 60% of patients with congestive heart failure develop chronic kidney disease. Volume overload and congestion are hallmarks of heart failure, and these findings are associated with severe symptoms and poor outcomes. Given the importance of congestion, diuretics remain a cornerstone of heart failure management. However, diuretic treatment remains largely empirical, with little evidence currently available to guide decisions. In this review, we discuss the pathophysiology of cardiorenal syndrome, the pharmacology of loop diuretics, mechanisms of diuretic resistance, and evidence-based treatment paradigms.

Erdheim-Chester Disease: A Rare Presentation of a Rare Disease

Erdheim-Chester disease (ECD) is a rare, xanthogranulomatous, non-Langerhans cell histiocytosis with frequent systemic involvement. Although the diagnosis is based on characteristic histological and radiological findings, its identification can be challenging because of its heterogeneous presentation. Osteosclerosis of long bones, often associated with bone pain, is the most common initial manifestation, followed by extraskeletal manifestations in approximately 50% of cases. There is no standard treatment for ECD, although recommendations have been made on the basis of small studies. A systematic approach to the diagnosis of ECD is important, because its manifestations may be life-threatening and may require specific management. We report an atypical presentation of ECD, with early cardiac, renal, and central nervous system involvement, and only late skeletal manifestations.

Oral Hypoxia-Inducible Factor Prolyl Hydroxylase Inhibitor Roxadustat (FG-4592) for the Treatment of Anemia in Patients with CKD

BACKGROUND AND OBJECTIVES

Roxadustat (FG-4592), an oral hypoxia-inducible factor prolyl hydroxylase inhibitor that stimulates erythropoiesis, regulates iron metabolism, and reduces hepcidin, was evaluated in this phase 2b study for safety, efficacy, optimal dose, and dose frequency in patients with nondialysis CKD.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The 145 patients with nondialysis CKD and hemoglobin ≤10.5 g/dl were randomized into one of six cohorts of approximately 24 patients each with varying roxadustat starting doses (tiered weight and fixed amounts) and frequencies (two and three times weekly) followed by hemoglobin maintenance with roxadustat one to three times weekly. Treatment duration was 16 or 24 weeks. Intravenous iron was prohibited. The primary end point was the proportion of patients achieving hemoglobin increase of ≥1.0 g/dl from baseline and hemoglobin of ≥11.0 g/dl by week 17 (16 weeks of treatment). Secondary analyses included mean hemoglobin change from baseline, iron utilization, and serum lipids. Safety was evaluated by frequency/severity of adverse events.

RESULTS

Of the 145 patients enrolled, 143 were evaluable for efficacy. Overall, 92% of patients achieved hemoglobin response. Higher compared with lower starting doses led to earlier achievement of hemoglobin response. Roxadustat-induced hemoglobin increases were independent of baseline C-reactive protein levels and iron repletion status. Overall, over the first 16 treatment weeks, hepcidin levels decreased by 16.9% (P=0.004), reticulocyte hemoglobin content was maintained, and hemoglobin increased by a mean (±SD) of 1.83 (±0.09) g/dl (P<0.001). Overall mean total cholesterol level was reduced by a mean (±SD) of 26 (±30) mg/dl (P<0.001) after 8 weeks of therapy, independent of the use of statins or other lipid-lowering agents. No drug-related serious adverse events were reported.

CONCLUSIONS

In patients with nondialysis CKD who were anemic, various starting dose regimens of roxadustat were well tolerated and achieved anemia correction with reduced serum hepcidin levels. After anemia correction, hemoglobin was maintained by roxadustat at various dose frequencies without intravenous iron supplementation.

Anuric Acute Kidney Injury Induced by Acute Mountain Sickness Prophylaxis With Acetazolamide

Acetazolamide (ACZ) is a sulfonamide derivative that inhibits carbonic anhydrase and is the mainstay for prevention and treatment of acute mountain sickness (AMS). Acute kidney injury (AKI) is not well recognized as a complication of ACZ ingestion, especially when low doses are used for short periods of time. We report a case of a healthy, middle-aged man who developed severe AKI after the ingestion of ACZ for AMS prophylaxis. The patient presented with bilateral flank pain and anuric AKI without radiographic signs of obstructive uropathy. All blood and urine testing to determine the cause of AKI were negative or normal. The patient required 2 sessions of hemodialysis due to worsening metabolic derangements, which included severe anion gap metabolic acidosis and hyperphosphatemia. Renal function returned to baseline after 96 hours of supportive care. The pathogenesis of AKI in our patient was attributed to ACZ-induced sulfonamide crystalluria causing intratubular obstruction and retrograde urine flow, but not intraureteric precipitation or obstructive uropathy. This classic presentation of anuric AKI and renal colic has been previously described with higher doses of ACZ for prolonged periods of time but never with low doses for AMS prophylaxis such as in our patient (total dose of 1250 mg within 48 hours). Our case highlights the risk of adverse renal outcomes following ACZ ingestion, even in previously healthy individuals, and suggests that increased fluid intake may be advisable for travelers taking ACZ prophylaxis.

Contrast-induced acute kidney injury following coronary angiography: a cohort study of hospitalized patients with or without chronic kidney disease

BACKGROUND

Contrast-induced acute kidney injury (CIAKI) has been linked to unfavorable consequences. In routine clinical practice, small increases in serum creatinine (SCr) following coronary angiography tend to be underestimated, especially in patients without chronic kidney disease (CKD).

METHODS

We conducted a retrospective observational cohort study to analyze in-hospital and long-term outcomes of CIAKI following coronary angiography in patients with or without CKD (eGFR ≥ 60 mL/min/1.73 m(2)) from January 2008 through December 2009. CIAKI was defined as SCr either ≥ 25% or ≥ 0.5 mg/dL from baseline within 72 h after contrast exposure. Multivariable logistic regression for in-hospital mortality and Cox proportional hazards calculations for long-term mortality and requirement for dialysis were performed.

RESULTS

A total of 1160 patients were included in the study. CIAKI occurred in 19% of CKD patients and in 18% of non-CKD patients. In CKD and non-CKD patients, CIAKI was more frequent in patients requiring mechanical ventilation or inotropes or in those given furosemide, and it was associated with adverse in-hospital (prolonged hospitalization, acute dialysis and mortality) and long-term (increased creatinine, initiation of dialysis and mortality) outcomes. In multivariable analysis, CKD patients had greater in-hospital mortality if they developed CIAKI (adjusted OR 8, 95% CI 1.9-34.5, P = 0.005), and non-CKD patients had greater long-term mortality if they developed CIAKI (adjusted HR 2.2, 95% CI 1.2-4.1, P = 0.016).

CONCLUSIONS

CIAKI following coronary angiography was associated with adverse in-hospital and long-term outcomes in both CKD and non-CKD patients.

Prevalence of kidney disease in HIV-infected and uninfected Rwandan women

Background

In the United States, HIV-related kidney disease disproportionately affects individuals of African descent; however, there are few estimates of kidney disease prevalence in Africa. We evaluated the prevalence of kidney disease among HIV-infected and uninfected Rwandan women.

Methods

The Rwandan Women's Interassociation Study and Assessment prospectively enrolled 936 women. Associations with estimated glomerular filtration rate (eGFR)<60 mL/min/1.73 m² and proteinuria were assessed in separate logistic regression models.

Results

Among 891 non-pregnant women with available data, 2.4% had an eGFR<60 mL/min/1.73 m² (calculated by the Modification of Diet in Renal Disease equation, MDRD eGFR) and 8.7% had proteinuria ≥1+. The prevalence of decreased eGFR varied markedly depending on the estimating method used, with the highest prevalence by Cockcroft-Gault. Regardless of the method used to estimate GFR, the proportion with decreased eGFR or proteinuria did not differ significantly between HIV-infected and -uninfected women in unadjusted analysis. After adjusting for age and blood pressure, HIV infection was associated with significantly higher odds of decreased MDRD eGFR but not proteinuria.

Conclusion

In a well-characterized cohort of Rwandan women, HIV infection was associated with decreased MDRD eGFR. The prevalence of decreased eGFR among HIV-infected women in our study was lower than that previously reported in African-Americans and in other Central and East African HIV populations, although there was substantial variability depending on the equation used to estimate GFR. Future studies are needed to optimize GFR estimates and to determine the impact of antiretroviral therapy on kidney disease in this population.

Management of HIV-infected patients with ESRD

Patients infected with human immunodeficiency virus (HIV) often progress to ESRD. In the era of highly active antiretroviral therapy, the care of these patients has become increasingly complex as survival has improved. Patients infected with HIV who also have ESRD are at risk for critical interactions between medication regimens to treat both of these conditions. Within this population, hemo- and peritoneal dialysis as well as kidney transplantation are life sustaining but present a host of obstacles related to HIV monitoring and risk of transmission, access thrombosis, infection, and rejection. Knowledge of antiretroviral regimens, drug interactions, and HIV resistance as well as the management of ESRD in the presence of HIV infection will improve the care of these unique patients.

Phosphate binders in chronic kidney disease and end-stage renal disease: a patient-centered approach

Disorders of calcium and phosphorus metabolism are associated with significant morbidity and mortality in patients with advanced chronic kidney disease. These patients typically require oral phosphate binders to maintain phosphorus homeostasis, but the choice of which among several agents to use has been actively investigated and debated. Recent debate has been polarized between those who favor calcium-based binders for their proven efficacy and relatively low cost and those who favor sevelamer for its putative beneficial effects on inflammatory biomarkers and vascular calcification. This review summarizes the current state of the art of prescribing phosphate binders, ranging from large-scale clinical trials to focused mechanistic studies, and proposes that the available evidence does not conclusively prove the relative superiority of any one binder.

Negative trials in nephrology: what can we learn?

Chronic kidney disease is assuming epidemic proportions, and an increasing number of clinical trials are testing treatments developed to improve morbidity and mortality. Surprisingly, however, a large proportion of these trials have had negative or neutral results. When trials unexpectedly demonstrate either no benefit or a detrimental impact of a treatment, especially when that treatment is already used in practice, critics commonly argue that the results were dictated by flawed trial design rather than the intrinsic properties of the treatment. In kidney disease therapeutics, trials commonly rely on observational data and test the hypothesis that these associations may be extrapolated to cause-and-effect. Other key issues in trial design that may affect outcomes include the impact of enrolling relatively healthier subjects, the complexity of recruiting participants with specific characteristics while maintaining generalizability, and the subtleties of event adjudication and quality of life assessments. In this article, general principles of trial design will be discussed and the potential lessons learned from recent trials in nephrology will be critically reviewed.

Familial hypocalciuric hypercalcemia in the donor and recipient of a living related donor kidney transplant

Familial hypocalciuric hypercalcemia (FHH) is caused by heterozygous inactivation of the calcium-sensing receptor, which is notably expressed in parathyroid and kidney. FHH is characterized by asymptomatic hypercalcemia and hypophosphatemia and confers minimal, if any, morbidity. Renal transplantation in patients with FHH has not been described previously. This report describes a patient with FHH who developed end-stage renal disease from another cause and subsequently received a living related donor kidney transplant from her FHH-affected daughter. The excellent posttransplant clinical course of both recipient and donor is emphasized.

Impact of vitamin E on plasma asymmetric dimethylarginine (ADMA) in chronic kidney disease (CKD): a pilot study

BACKGROUND

Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of endothelial nitric oxide synthase and a proposed cardiovascular risk factor, is elevated in chronic kidney disease (CKD). Pharmacological strategies that lower plasma concentration of ADMA may be expected to increase nitric oxide (NO.) bioavailability and potentially limit atherosclerosis. We hypothesized that the antioxidant alpha-tocopherol (vitamin E) reduces ADMA levels in CKD.

METHODS

An open-label pilot interventional study using 800 IU of vitamin E was undertaken in eight stable out-patients with non-diabetic CKD (creatinine clearance <30 ml/min/1.73 m(2)) and six healthy controls, with the objective of measuring plasma ADMA levels at baseline and after 8 weeks of treatment. Plasma ADMA, symmetric dimethylarginine (SDMA) and alpha-tocopherol concentrations were determined at study entry and exit using high-performance liquid chromatography, while plasma total F2-isoprostanes, an index of oxidative stress, were measured using a commercially available enzyme-linked immunosorbent assay kit.

RESULTS

ADMA and SDMA concentrations were significantly higher in the plasma of patients compared with that of controls (P </= 0.001). After treatment with vitamin E, ADMA decreased by 23% in six of eight patients (P <0.001). The remaining two patients showed either an increase or no change (overall, P = 0.16). There was no significant change in plasma F2-isoprostanes with vitamin E treatment for 8 weeks.

CONCLUSIONS

Antioxidant therapy with vitamin E has the potential to lower ADMA levels in CKD patients, implying increased NO. availability. This strategy merits further exploration in the setting of CKD prior to renal replacement.

Inositol and higher inositol phosphates in neural tissues: homeostasis, metabolism and functional significance

Inositol phospholipids and inositol phosphates mediate well-established functions in signal transduction and in Ca2+ homeostasis in the CNS and non-neural tissues. More recently, there has been renewed interest in other roles that both myo-inositol and its highly phosphorylated forms may play in neural function. We review evidence that myo-inositol serves as a clinically relevant osmolyte in the CNS, and that its hexakisphosphate and pyrophosphorylated derivatives may play roles in such diverse cellular functions as DNA repair, nuclear RNA export and synaptic membrane trafficking.

The budding yeast Msh4 protein functions in chromosome synapsis and the regulation of crossover distribution

The budding yeast MSH4 gene encodes a MutS homolog produced specifically in meiotic cells. Msh4 is not required for meiotic mismatch repair or gene conversion, but it is required for wild-type levels of crossing over. Here, we show that a msh4 null mutation substantially decreases crossover interference. With respect to the defect in interference and the level of crossing over, msh4 is similar to the zip1 mutant, which lacks a structural component of the synaptonemal complex (SC). Furthermore, epistasis tests indicate that msh4 and zip1 affect the same subset of meiotic crossovers. In the msh4 mutant, SC formation is delayed compared to wild type, and full synapsis is achieved in only about half of all nuclei. The simultaneous defects in synapsis and interference observed in msh4 (and also zip1 and ndj1/tam1) suggest a role for the SC in mediating interference. The Msh4 protein localizes to discrete foci on meiotic chromosomes and colocalizes with Zip2, a protein involved in the initiation of chromosome synapsis. Both Zip2 and Zip1 are required for the normal localization of Msh4 to chromosomes, raising the possibility that the zip1 and zip2 defects in crossing over are indirect, resulting from the failure to localize Msh4 properly.

Increased expression of Galpha(q/11) and of phospholipase-Cbeta1/4 in differentiated human NT2-N neurons: enhancement of phosphoinositide hydrolysis

The CNS is enriched in phosphoinositide-specific phospholipase C (PLC) and in the G proteins linked to its activation. Although the regional distributions of these signaling components within the brain have been determined, neither their cell type-specific localizations (i.e., neuronal versus glial) nor the functional significance of their high expression has been definitively established. In this study, we have examined the expression of phosphoinositide signaling proteins in human NT2-N cells, a well characterized model system for CNS neurons. Retinoic acid-mediated differentiation of NT2 precursor cells to the neuronal phenotype resulted in five- to 15-fold increases in the expression of PLC-beta1, PLC-beta4, and Galpha(q/11) (the prime G protein activator of these isozymes). In contrast, the expression of PLC-beta3 and PLC-gamma1 was markedly reduced following neuronal differentiation. Similar alterations in cell morphology and in the expression of PLC-beta1, PLC-beta3, and Galpha(q/11) expression were observed when NT2 cells were differentiated with berberine, a compound structurally unrelated to retinoic acid. NT2-N neurons exhibited a significantly higher rate of phosphoinositide hydrolysis than NT2 precursor cells in response to direct activation of either G proteins or PLC. These results indicate that neuronal differentiation of NT2 cells is associated with dramatic changes in the expression of proteins of the phosphoinositide signaling system and that, accordingly, differentiated NT2-N neurons possess an increased ability to hydrolyze inositol lipids.

Regulation of Myo-inositol homeostasis in differentiated human NT2-N neurons

We have investigated the possible role of second messengers on inositol homeostasis in NT2-N cells, human central nervous system neurons obtained by terminal differentiation of teratocarcinoma precursors. Uptake of inositol into NT2-N neurons was inhibited approximately 10% by protein kinase C (PKC) activation but was unaffected by either the presence of cyclic nucleotide analogs or changes in the intracellular concentration of Ca2+. Efflux of inositol from NT2-N neurons was enhanced in hypotonic buffer but virtually eliminated by inclusion of the Cl- channel blocker 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid, a result which indicates the involvement of a volume-sensitive organic osmolyte-anion channel. Volume-sensitive inositol efflux was stimulated approximately 30% following activation of PKC or elevation of the cytosolic Ca2+ concentration but was unaffected by protein kinase A activation. These results suggest that whereas inositol uptake into NT2-N neurons is relatively refractory to regulation, volume-sensitive inositol efflux may be significantly affected by intracellular signaling events.

Differentiated human NT2-N neurons possess a high intracellular content of myo-inositol

myo-Inositol plays a key role in signal transduction and osmotic regulation events in the CNS. Despite the known high concentrations of inositol in the human CNS, relatively little is known about its distribution within the different cell types. In this report, inositol homeostasis was studied in NT2-N cells, a unique cell culture model of human CNS neurons. Differentiation of precursor NT2 teratocarcinoma cells into NT2-N neurons by means of retinoic acid treatment resulted in an increase in inositol concentration from 24 to 195 nmol/mg of protein. After measurement of intracellular water spaces, inositol concentrations of 1.6 and 17.4 mM were calculated for NT2 and NT2-N cells, respectively. The high concentrations of inositol in NT2-N neurons could be explained by (1) an increased uptake of inositol (3.7 vs. 1.6 nmol/mg of protein/h, for NT2-N and NT2 cells, respectively) and (2) a decreased efflux of inositol (1.7%/h for NT2-N neurons vs. 9.0%/h for NT2 cells). Activity of inositol synthase, which mediates de novo synthesis of inositol, was not detected in either cell type. The observation that CNS neurons maintain a high intracellular concentration of inositol may be relevant to the regulation of both phosphoinositide signaling and osmotic stress events in the CNS.

Coupling between genome translation and replication in an RNA virus

The replication of poliovirus RNA genomes containing amber mutations was studied to test whether viral proteins provided in trans could rescue the replication of an RNA genome that could not be completely translated itself. Mutants containing amber codons at different positions in the genome displayed vastly different abilities to be rescued by wild-type proteins provided by a helper genome. Amber-suppressing cell lines were used to ensure that the defects in the amber mutants arose from their failure to be translated, not from defects in RNA sequence or structure. An internal region of the poliovirus genome was identified whose translation is required in cis; failure to translate this region was shown to inhibit RNA replication. This coupling between translation and RNA replication could provide a late proofreading mechanism that enables poliovirus, and possibly many other RNA viruses, to prevent the replication of defective genomes.

Improved method for detecting poliovirus negative strands used to demonstrate specificity of positive-strand encapsidation and the ratio of positive to negative strands in infected cells

We have developed a ribonuclease protection method suitable for sensitive detection of an RNA species in the presence of a large excess of its complementary strand, as for the detection of negative strands of positive-strand RNA viruses. By using this method to probe for poliovirus negative strands in virions, we found that positive strands are present in at least 40,000-fold excess over negative strands. Thus, we have confirmed that poliovirus encapsidation is highly specific for positive strands and have demonstrated that the genome-linked protein VPg, which is covalently attached to the 5' ends of both positive and negative strands, cannot be the sole determinant of RNA packaging. We tested the ratios of viral positive strands to negative strands in cells at different times during infection; this value ranged from approximately 40/1 to 70/1, being highest at 4 h and lower at 2 and 6 h postinfection.