Renal tubular acidosis: a new look at an old problem

The Effect of Acetylcysteine on Renal Function in Experimental Models of Cyclophosphamide-and Ifosfamide-Induced Cystitis

Introduction

Urotoxicity is a characteristic attribute of cy-clophosphamide and ifosfamide. Acetylcysteine is perceived as a uroprotective and possible nephroprotective compound. The purpose of the study was to assess the effect of acetylcysteine treatment on the morphology of the kidneys and the urinary bladder, and renal function in rats with cystitis induced by cyclophosphamide or ifosfamide.

Methods

Cystitis was induced in rats belonging to groups 2 and 3, as well as 4 and 5, by five administrations of cyclophosphamide (75 mg/kg) or ifosfamide (80 mg/kg) respectively. Additionally, groups 3 and 5 received acetylcysteine (200 mg/kg). Group 1 was "sham treated" as a control. Upon conclusion of the experiment, the animals were euthanized and their kidneys and urinary bladders were collected for histopathological analysis. The assessment of renal function was based on classic nitrogen blood parameters (urea, creatinine, and uric acid), as well as proteinuria and cystatin C (CysC) and kidney injury molecule-1 (KIM-1) urinary concentrations, and their 24-hour elimination with urine.

Results

Reduction of blood urea nitrogen and uric acid, and urinary pH with a significant increase of CysC and KIM-1 urinary concentrations, and their 24-hour elimination with urine were observed in groups 2 and 4. The acetylcysteine treatment did not cause a significant change of blood parameters, but significantly decreased 24-hour elimination of CysC and KIM-1 with urine, and accounted for alleviation of the histopathological abnormalities of urinary bladders, with no significant effects on the structure of the kidneys.

Conclusions

Acetylcysteine used in the experimental model of cyclophosphamide- and ifosfamide-induced cystitis had a uroprotective effect and also reduced renal dysfunction, which suggests its potential use as a nephroprotective compound in cyclophosphamide/ifosfamide therapy.

Impaired growth outcomes in children with congenital colorectal diseases

BACKGROUND

Cloaca, Hirschsprung disease, and anorectal malformations (CHARM) are congenital anomalies of the hindgut. Small series have suggested that children suffering from one of these anomalies may be at risk for growth impairment. We sought to expand on these findings in a comprehensive cohort, hypothesizing that patients with Medicaid insurance or African-American (AA) race would be at higher risk for poor growth.

METHODS

Following Institutional Review Board (IRB) approval, single-institution retrospective review of children with CHARM anomalies was performed (2009-2016). Body mass index (BMI) value Z-scores were obtained using the 2006 World Health Organization (age 0-24 mo) and 2000 Centers for Disease Control (CDC) (age >2 y) growth charts and calculators (statistical analysis system). Patient factors and BMI Z-scores were analyzed with descriptive statistics and Fisher's exact test.

RESULTS

One hundred sixty-six patients (Cloaca n = 16, Hirschsprung disease [HD] n = 71, anorectal malformation [ARM] n = 79) were identified. The BMI Z-score distribution for the entire CHARM cohort was lower than controls (P < 0.0001). HD and ARM BMI Z-scores were also lower versus controls (P < 0.0007, P < 0.0037). Requiring more or less than the average number of surgeries did not impact BMI Z-score [P = non-significant (NS)]. Patients with Medicaid had lower Z-scores versus private or commercial insurance (P < 0.0001). AA race BMI Z-score distribution was lower than controls (P < 0.0002), but there was no statistical difference in BMI Z-scores when comparing AA versus non-AA CHARM patients (P = NS).

CONCLUSIONS

Patients born with CHARM anomalies are at risk for impaired growth. Furthermore study is warranted to identify modifiable risk factors contributing to this impairment. Longitudinal follow-up should include interventions to mitigate these risks.

Growth morbidity in patients with cloacal exstrophy: a 42-year experience

PURPOSE

Cloacal exstrophy is associated with multiple comorbidities that affect growth. This report describes long-term growth outcomes in a large cohort of patients with cloacal exstrophy and explores associated comorbidities.

METHODS

Records of 71 patients with cloacal exstrophy who were treated between 1974 and 2015 were reviewed, and 62 patients with growth data from 2 to 20years of age were included. Genetic sex, gender of rearing, and all heights, weights, and comorbidities were noted for each patient. Height-for-age, weight-for-age, and body mass index z-scores (HAZ, WAZ, and BMIZ) were determined using US Centers for Disease Control 2000 growth data, and average patient z-scores were calculated.

RESULTS

There were 904 height and 1301 weight measurements available for 62 patients. 31 were genetically 46,XY, 21 of whom underwent gonadectomy in infancy and were raised female. 46,XX patients, 46,XY male patients, and 46,XY female patients all had median HAZ and WAZ substantially lower than the general population, with median HAZ less than -2, while maintaining normal BMIZ. Short bowel syndrome and enterocystoplasty with intestine were associated with lower z-scores for all parameters.

CONCLUSIONS

Patients with cloacal exstrophy have significant multifactorial long-term growth failure. These benchmark data can be used to further optimize management.

LEVEL OF EVIDENCE

2b.

Fanconi-Bickel syndrome as an example of marked allelic heterogeneity

Renal tubular acidosis (RTA) encompasses many renal tubular disorders characterized by hyperchloremic metabolic acidosis with a normal anion gap. Untreated patients usually complain of growth failure, osteoporosis, rickets, nephrolithiasis and eventually renal insufficiency. Fanconi-Bickel syndrome (FBS) is an example of proximal RTA due to a single gene disorder; it is caused by defects in the facilitative glucose transporter 2 gene that codes for the glucose transporter protein 2 expressed in hepatocytes, pancreatic β-cells, enterocytes and renal tubular cells. It is a rare inherited disorder of carbohydrate metabolism manifested by huge hepatomegaly [hence it is classified as glycogen storage disease (GSD) type XI; GSD XI], severe hypophosphatemic rickets and failure to thrive due to proximal renal tubular dysfunction leading to glucosuria, phosphaturia, generalized aminoaciduria, bicarbonate wasting and hypophosphatemia. The disorder has been reported from all parts of Europe, Turkey, Israel, Arabian countries, Japan and North America. Many mutant alleles have been described, its exact frequency is unknown and there is no single mutation found more frequently than the others. The presence of consanguinity in affected families suggests an autosomal recessive pattern of inheritance. New cases of FBS have been recently reported in the Middle and Far East in collaboration with specialized centers. Two novel mutations have been discovered in two unrelated Egyptian families. The first was two bases deletion, guanine and adenine, (c.253_254delGA) causing a frameshift mutation (p. Glu85fs) and the second is mutation in exon6 in splicing acceptor site with intron5 (c.776-1G>C or IVS5-1G>A). Moreover, a new different mutation was described in a 3 year old Indian boy.

Molecular pathophysiology of renal tubular acidosis

Renal tubular acidosis (RTA) is characterized by metabolic acidosis due to renal impaired acid excretion. Hyperchloremic acidosis with normal anion gap and normal or minimally affected glomerular filtration rate defines this disorder. RTA can also present with hypokalemia, medullary nephrocalcinosis and nephrolitiasis, as well as growth retardation and rickets in children, or short stature and osteomalacia in adults. In the past decade, remarkable progress has been made in our understanding of the molecular pathogenesis of RTA and the fundamental molecular physiology of renal tubular transport processes. This review summarizes hereditary diseases caused by mutations in genes encoding transporter or channel proteins operating along the renal tubule. Review of the molecular basis of hereditary tubulopathies reveals various loss-of-function or gain-of-function mutations in genes encoding cotransporter, exchanger, or channel proteins, which are located in the luminal, basolateral, or endosomal membranes of the tubular cell or in paracellular tight junctions. These gene mutations result in a variety of functional defects in transporter/channel proteins, including decreased activity, impaired gating, defective trafficking, impaired endocytosis and degradation, or defective assembly of channel subunits. Further molecular studies of inherited tubular transport disorders may shed more light on the molecular pathophysiology of these diseases and may significantly improve our understanding of the mechanisms underlying renal salt homeostasis, urinary mineral excretion, and blood pressure regulation in health and disease. The identification of the molecular defects in inherited tubulopathies may provide a basis for future design of targeted therapeutic interventions and, possibly, strategies for gene therapy of these complex disorders.

Renal tubular acidosis

Renal tubular acidosis is a relatively uncommon clinical syndrome characterized by the inability of the kidney to adequately excrete hydrogen ions, retain adequate bicarbonate, or both. This syndrome can be categorized into 3 separate disorders, each with unique clinical characteristics. Although an uncommon finding, prompt and inexpensive tests can lead to early intervention and subsequently reduce complications from persistent renal dysfunction. The purpose of this article was to bring awareness of the clinical manifestations, diagnosis, and treatments of renal tubular acidosis to critical care nurses.

Sodium bicarbonate: basically useless therapy

Common clinical practices often are unsupported by experimental evidence. One example is the administration of sodium bicarbonate to neonates. Despite a long history of widespread use, objective evidence that administration of sodium bicarbonate improves outcomes for patients in cardiopulmonary arrest or with metabolic acidosis is lacking. Indeed, there is evidence that this therapy is detrimental. This review examines the history of sodium bicarbonate use in neonatology and the evidence that refutes the clinical practice of administering sodium bicarbonate during cardiopulmonary resuscitation or to treat metabolic acidosis in the NICU.

Inherited renal acidoses

Inherited acidosis may result from a primary renal defect in acid-base handling, emphasizing the central role of the kidney in control of body pH; as a secondary phenomenon resulting from abnormal renal electrolyte handling; or from excess production of acid elsewhere in the body. Here, we review our current understanding of the inherited renal acidoses at a genetic and molecular level.

Distal RTA with nerve deafness: clinical spectrum and mutational analysis in five children

Distal renal tubular acidosis (RTA) with nerve deafness is caused by mutations in the ATP6V1B1 gene causing defective function of the H+ -ATPase proton pump. We report five acidotic children (four males) from four unrelated families: blood pH 7.21-7.33, serum bicarbonate 10.8-14.7 mEq/l, minimum urinary pH 6.5-7.1 and fractional excretion of bicarbonate in the presence of normal bicarbonatemia 1.1-5.7%. Growth retardation and nephrocalcinosis, but not hypercalciuria, were common presenting manifestations. Hearing was normally preserved in one of the patients whose sister was severely deaf. One child was homozygous for a known mutation in exon 1: C>T (R31X). Three children were homozygous for a splicing mutation, intron 6 + 1G>A. The other patient was a compound heterozygote, having this mutation and a previously unreported mutation in exon 10: G>A (E330K). Our report shows that hearing loss is not always present in the syndrome of distal renal tubular acidosis with nerve deafness and the absence of hypercalciuria at diagnosis and describes a new mutation responsible for the disease in the ATP6V1B1 gene.

The Role of Nutrition in Chronic Renal Insufficiency of Childhood: How Much Do We Know?

Dietary protein restriction in the treatment of symptomatic renal failure has been utilized for many years, especially as a means for reduction of 'fixed acid" load. Studies in animal models of renal failure suggest that low protein intake may retard the progression of renal disease as well. However, large, well-organized investigations into this question in humans have fallen prey to difficulties that are almost impossible to overcome. Chief among these difficulties is the problem of chronically reducing protein intake in patients with a lifelong intake far above the recommended daily allowance (RDA). Another is the fact that all previous studies have been performed in patients with moderate to severe compromise of renal function. Thus, the potential efficacy of reduced protein intake in the retardation of the progression of renal disease remains an open question. In this article, we discuss the current state of knowledge and propose an approach to answering this question.

Sex differences in patients referred for evaluation of poor growth

OBJECTIVES

The objective of this study was to compare sex differences among referrals for evaluation of poor growth.

STUDY DESIGN

This study was based on chart reviews of all new-patient encounters at Children's Hospital of Philadelphia Diagnostic and Research Growth Center for short stature or poor growth evaluations during 2001. Outcome measures were patient growth characteristics, frequency of underlying pathology, and frequency of laboratory and radiologic investigations before referral.

RESULTS

One hundred eighty-two boys and 96 girls were referred ( P < .0001). Girls were shorter, relative to the general population (median height z score, -2.4 vs -1.9 for boys, P = .02) and mid-parental target heights (median deficit, 1.9 vs 1.3 SD, P < .01). Differences were more pronounced starting at age 9 years. Median time to referral from initial fall-off on the growth curve was 35 months in girls and 24 months in boys (not significant). The percentage of girls (41%) with organic disease significantly exceeded that of boys (15%). Conversely, more boys (72%) than girls (48%) were of normal height or short but healthy ( P < .0001). Sex was not associated with frequency of tests before referral; neither was severity of short stature.

CONCLUSIONS

Sex differences in short stature referrals may delay diagnosis of diseases in girls while promoting overzealous evaluations of healthy boys who do not appear to be tall enough.

Antimicrobial-associated renal tubular acidosis

OBJECTIVE

To review the literature documenting the association of various antimicrobial medications with the development of renal tubular acidosis (RTA).

DATA SOURCES

A search of the English literature via MEDLINE (1966-November 2003) and International Pharmaceutical Abstracts (1970-November 2003) was conducted to identify human reports of RTA associated with various drugs from all available classes of antimicrobial agents. Major search terms included renal tubular acidosis, acidosis, antibiotics, and antimicrobials. Bibliographies of selected articles were also searched to identify additional reports of RTA.

STUDY SELECTION AND DATA EXTRACTION

Case reports, observational studies, and experimental studies documenting the association of any antimicrobial agent with the development of RTA were included.

DATA SYNTHESIS

Antimicrobial-associated RTA is a relatively uncommon adverse effect, with most reports involving amphotericin B, trimethoprim/sulfamethoxazole, and outdated tetracycline. These agents may induce RTA either through direct tubular toxicity or as a function of their pharmacologic action. The time course for the development of RTA varies depending on the antimicrobial utilized. In most instances, RTA is reversible; however, some patients may experience prolonged recovery after the offending agent is removed.

CONCLUSIONS

Given that antimicrobial-associated RTA is a relatively uncommon adverse effect, review of the patient's drug regimen may reveal these agents as otherwise unrecognized causes of RTA. Likewise, underlying causes of RTA other than medications must be ruled out. Diagnosing antimicrobial-induced RTA may be difficult, given many of these agents may be used in combination and some are intrinsically nephrotoxic.