Transition From Pediatric to Adult Nephrology Care: Program Report of a Single-Center Experience

Purpose of program

Adolescents and young adults with chronic disease face many personal and systemic barriers that may impede their successful transition from pediatric to adult care, putting them at risk for treatment nonadherence, loss to follow-up, and poor health outcomes. Such barriers include impaired socioemotional functioning, overreliance on adult caregivers, lack of disease-specific knowledge, and poor coordination between pediatric and adult health care services. In 2007, we established a specialized youth to adult nephrology transition clinic at a tertiary care center to address these barriers and provide adolescents and young adults with renal disease followed at the affiliated children's hospital with a seamless transition to adult care.

Sources of information

The attending clinic nephrologist collected data prospectively for this quality improvement report.

Methods

The features of this specialized clinic included (1) single point of entry and single triage adult nephrologist, (2) ongoing follow-up with a single adult nephrologist who communicated with the pediatric nephrologists, and (3) a single specialized clinic nurse who provided disease-specific education and helped to ensure ongoing patient engagement and follow-up. Importantly, the transition patients were booked into regular appointment slots in the adult nephrologist's general clinic, which facilitated regular follow-up without additional resources. The salary of the transition clinic nurse was covered by an unrestricted grant. Patient visits were in-person, except between 2020 and 2021 when visits were by telephone due to the pandemic.

Key findings

A total of 213 patients were referred and assessed in the transition clinic from February 2007 until October 2022. Most referrals were from pediatric nephrologists. Among the patients, 29% had a hereditary kidney disease; in 71%, the disease was acquired. The most common disease was glomerulonephritis and ~30% of the patients suffered from a "rare" disease. Of the 213 patients, 123 (58%) continue to be followed up (mean follow-up: 4.8 years), 27 (13%) were transferred to other physicians, in part to accommodate treatment closer to patients' homes, and 29 (14%) without ongoing care needs were discharged. Only 33 (15%) were lost to follow-up. There were several advantages to the clinic, including the maintenance of accurate records, a process to minimize loss to follow-up, and a "critical mass" of patients with rare diseases, which facilitated development of special expertise in rare disease pathogenesis, diagnosis, treatment, and management of complications. Patients with glomerulonephritis demonstrated a stable serum creatinine over 3 to 15 years, and morbidity (as reflected by emergency room visits and hospitalizations) was low.

Limitations

Due to the relatively small numbers of patients in the disease categories, it was not possible to determine conclusively whether attendance of patients in the transition clinic reduced the rate of progression of kidney disease or morbidity.

Implications

A dedicated referral, triage, and follow-up process post-transition with only modest financial resources and personnel can result in accurate tracking of clinic data, as well as consistent and reliable follow-up and expert patient care.

Tubular Diseases and Stones Seen From Pediatric and Adult Nephrology Perspectives

The tubular system of the kidneys is a complex series of morphologic and functional units orchestrating the content of tubular fluid as it flows along the nephron and collecting ducts. Renal tubules maintain body water, regulate electrolytes and acid-base balance, reabsorb precious organic solutes, and eliminate specific metabolites, toxins, and drugs. In addition, decisive mechanisms to adjust blood pressure are governed by the renal tubules. Genetic as well as acquired disorders of these tubular functions may cause serious diseases that manifest both in childhood and adulthood. This article addresses a selection of tubulopathies and the underlying pathomechanisms, while highlighting the important differences in pediatric and adult nephrology care. These range from rare monogenic conditions such as nephrogenic diabetes insipidus, cystinosis, and Bartter syndrome that present in childhood, to the genetic and acquired tubular pathologies causing hypertension or nephrolithiasis that are more prevalent in adults. Both pediatric and adult nephrologists must be aware of these conditions and the age-dependent manifestations that warrant close interaction between the two subspecialties.

Unraveling the natural history of presymptomatic cystinuria

PURPOSE OF REVIEW

Servais et al. recently published clinical practice recommendations for the care of cystinuria patients. However, these guidelines were largely based on retrospective data from adults and children presenting with stones. Significant questions remain about the natural history of cystinuria in presymptomatic children.

RECENT FINDINGS

We review the natural history of cystinuria in presymptomatic children followed from birth. In total, 130 pediatric patients were assigned putative genotypes based on parental urinary phenotype: type A/A (N = 23), B/B (N = 6), and B/N (N = 101). Stones were identified in 12/130 (4% of A/A, 17% of B/B, and 1% of B/N patients). Type B/B patients had lower cystine excretion than type A/A patients. Although urine cystine/creatinine fell with age, urine cystine/l rose progressively in parallel with the risk of nephrolithiasis. Each new stone was preceded by 6-12 months of urine specific gravity of more than 1.020. However, average urine specific gravity and pH were not different in stone formers vs. nonstone formers, suggesting that intrinsic stone inhibitors or other unknown factors may be the strongest determinants of individual risk.

SUMMARY

The current study reviews the clinical evolution of cystinuria in a cohort of children identified by newborn screening, who were categorized by urinary phenotype and followed from birth.

A no-nonsense approach to hereditary kidney disease

The advent of a new class of aminoglycosides with increased translational readthrough of nonsense mutations and reduced toxicity offers a new therapeutic strategy for a subset of patients with hereditary kidney disease. The renal uptake and retention of aminoglycosides at a high intracellular concentration makes the kidney an ideal target for this approach. In this review, we explore the potential of aminoglycoside readthrough therapy in a number of hereditary kidney diseases and discuss the therapeutic window of opportunity for subclasses of each disease, when caused by nonsense mutations.

From podocyte biology to novel cures for glomerular disease

The podocyte is a key component of the glomerular filtration barrier. Podocyte dysfunction is central to the underlying pathophysiology of many common glomerular diseases, including diabetic nephropathy, glomerulonephritis and genetic forms of nephrotic syndrome. Collectively, these conditions affect millions of people worldwide, and account for the majority of kidney diseases requiring dialysis and transplantation. The 12th International Podocyte Conference was held in Montreal, Canada from May 30 to June 2, 2018. The primary aim of this conference was to bring together nephrologists, clinician scientists, basic scientists and their trainees from all over the world to present their research and to establish networks with the common goal of developing new therapies for glomerular diseases based on the latest advances in podocyte biology. This review briefly highlights recent advances made in understanding podocyte structure and metabolism, experimental systems in which to study podocytes and glomerular disease, disease mediators, genetic and immune origins of glomerulopathies, and the development of novel therapeutic agents to protect podocyte and glomerular injury.

Hypophosphatemic Rickets

Hypophosphatemic rickets, mostly of the X-linked dominant form caused by pathogenic variants of the PHEX gene, poses therapeutic challenges with consequences for growth and bone development and portends a high risk of fractions and poor bone healing, dental problems and nephrolithiasis/nephrocalcinosis. Conventional treatment consists of PO4 supplements and calcitriol requiring monitoring for treatment-emergent adverse effects. FGF23 measurement, where available, has implications for the differential diagnosis of hypophosphatemia syndromes and, potentially, treatment monitoring. Newer therapeutic modalities include calcium sensing receptor modulation (cinacalcet) and biological molecules targeting FGF23 or its receptors. Their long-term effects must be compared with those of conventional treatments.

Wilms Tumor Suppressor, WT1, Cooperates with MicroRNA-26a and MicroRNA-101 to Suppress Translation of the Polycomb Protein, EZH2, in Mesenchymal Stem Cells

Hereditary forms of Wilms arise from developmentally arrested clones of renal progenitor cells with biallelic mutations of WT1; recently, it has been found that Wilms tumors may also be associated with biallelic mutations in DICER1 or DROSHA, crucial for miRNA biogenesis. We have previously shown that a critical role for WT1 during normal nephrogenesis is to suppress transcription of the Polycomb group protein, EZH2, thereby de-repressing genes in the differentiation cascade. Here we show that WT1 also suppresses translation of EZH2. All major WT1 isoforms induce an array of miRNAs, which target the 3' UTR of EZH2 and other Polycomb-associated transcripts. We show that the WT1(+KTS) isoform binds to the 5' UTR of EZH2 and interacts directly with the miRNA-containing RISC to enhance post-transcriptional inhibition. These observations suggest a novel mechanism through which WT1 regulates the transition from resting stem cell to activated progenitor cell during nephrogenesis. Our findings also offer a plausible explanation for the fact that Wilms tumors can arise either from loss of WT1 or loss of miRNA processing enzymes.

Wilms tumor suppressor, WT1, suppresses epigenetic silencing of the β-catenin gene

The mammalian kidney is derived from progenitor cells in intermediate mesoderm. During embryogenesis, progenitor cells expressing the Wilms tumor suppressor gene, WT1, are induced to differentiate in response to WNT signals from the ureteric bud. In hereditary Wilms tumors, clonal loss of WT1 precludes the β-catenin pathway response and leads to precancerous nephrogenic rests. We hypothesized that WT1 normally primes progenitor cells for differentiation by suppressing the enhancer of zeste2 gene (EZH2), involved in epigenetic silencing of differentiation genes. In human amniotic fluid-derived mesenchymal stem cells, we show that exogenous WT1B represses EZH2 transcription. This leads to a dramatic decrease in the repressive lysine 27 trimethylation mark on histone H3 that silences β-catenin gene expression. As a result, amniotic fluid mesenchymal stem cells acquire responsiveness to WNT9b and increase expression of genes that mark the onset of nephron differentiation. Our observations suggest that biallelic loss of WT1 sustains the inhibitory histone methylation state that characterizes Wilms tumors.

Biallelic DICER1 mutations occur in Wilms tumours

DICER1 is an endoribonuclease central to the generation of microRNAs (miRNAs) and short interfering RNAs (siRNAs). Germline mutations in DICER1 have been associated with a pleiotropic tumour predisposition syndrome and Wilms tumour (WT) is a rare manifestation of this syndrome. Three WTs, each in a child with a deleterious germline DICER1 mutation, were screened for somatic DICER1 mutations and were found to bear specific mutations in either the RNase IIIa (n = 1) or the RNase IIIb domain (n = 2). In the two latter cases, we demonstrate that the germline and somatic DICER1 mutations were in trans, suggesting that the two-hit hypothesis of tumour formation applies for these examples of WT. Among 191 apparently sporadic WTs, we identified five different missense or deletion somatic DICER1 mutations (2.6%) in four individual WTs; one tumour had two very likely deleterious somatic mutations in trans in the RNase IIIb domain (c.5438A>G and c.5452G>A). In vitro studies of two somatic single-base substitutions (c.5429A>G and c.5438A>G) demonstrated exon 25 skipping from the transcript, a phenomenon not previously reported in DICER1. Further we show that DICER1 transcripts lacking exon 25 can be translated in vitro. This study has demonstrated that a subset of WTs exhibits two 'hits' in DICER1, suggesting that these mutations could be key events in the pathogenesis of these tumours.

T-cell factor/β-catenin activity is suppressed in two different models of autosomal dominant polycystic kidney disease

During murine kidney development, canonical WNT signaling is highly active in tubules until about embryonic days E16-E18. At this time, β-catenin transcriptional activity is progressively restricted to the nephrogenic zone. The cilial protein genes PKD1 and PKD2 are known to be mutated in autosomal dominant polycystic kidney disease (ADPKD), and previous studies proposed that these mutations could lead to a failure to suppress canonical WNT signaling activity. Several in vitro studies have found a link between cilial signaling and β-catenin regulation, suggesting that aberrant activity might contribute to the cystic phenotype. To study this, we crossed T-cell factor (TCF)/β-catenin-lacZ reporter mice with mice having Pkd1 or Pkd2 mutations and found that there was no β-galactosidase staining in cells lining the renal cysts. Thus, suppression of canonical WNT activity, defined by the TCF/β-catenin-lacZ reporter, is normal in these two different models of polycystic kidney disease. Hence, excessive β-catenin transcriptional activity may not contribute to cystogenesis in these models of ADPKD.

PAX3 is expressed in the stromal compartment of the developing kidney and in Wilms tumors with myogenic phenotype

Wilms tumor (WT) is the most frequent renal neoplasm of childhood; a myogenic component is observed in 5% to 10% of tumors. We demonstrate for the first time that myogenic WTs are associated with expression of PAX3, a transcription factor known to specify myoblast cell fate during muscle development. In a panel of 20 WTs, PAX3 was identified in 13 of 13 tumor samples with myogenic histopathology but was absent in 7 of 7 tumors lacking a myogenic component. Furthermore, we show that PAX3 is expressed in the metanephric mesenchyme and stromal compartment of developing mouse kidney. Modulation of endogenous PAX3 expression in human embryonic kidney (HEK293) cells influenced cell migration in in vitro assays. Mutations of WT1 were consistently associated with PAX3 expression in WTs, and modulation of WT1 expression in HEK293 cells was inversely correlated with the level of endogenous PAX3 protein. We demonstrate abundant PAX3 and absence of PAX2 expression in a novel cell line (WitP3) isolated from the stromal portion of a WT bearing a homozygous deletion of the WT1 gene. We hypothesize that PAX3 sets stromal cell fate in developing kidney but is normally suppressed by WT1 during the mesenchyme-to-epithelium transition leading to nephrogenesis. Loss of WT1 permits aberrant PAX3 expression in a subset of WTs with myogenic phenotype.

Canonical WNT signaling during kidney development

The canonical WNT signaling pathway plays a crucial role in patterning of the embryo during development, but little is known about the specific developmental events which are under WNT control. To understand more about how the WNT pathway orchestrates mammalian organogenesis, we studied the canonical beta-catenin-mediated WNT signaling pathway in kidneys of mice bearing a beta-catenin-responsive TCF/betaGal reporter transgene. In metanephric kidney, intense canonical WNT signaling was evident in epithelia of the branching ureteric bud and in nephrogenic mesenchyme during its transition into renal tubules. WNT signaling activity is rapidly downregulated in maturing nephrons and becomes undetectable in postnatal kidney. Sites of TCF/betaGal activity are in proximity to the known sites of renal WNT2b and WNT4 expression, and these WNTs stimulate TCF reporter activity in kidney cell lines derived from ureteric bud and metanephric mesenchyme lineages. When fetal kidney explants from HoxB7/GFP mice were exposed to the canonical WNT signaling pathway inhibitor, Dickkopf-1, arborization of the ureteric bud was significantly reduced. We conclude that restricted zones of intense canonical WNT signaling drive branching nephrogenesis in fetal kidney.

Pax2 gene dosage influences cystogenesis in autosomal dominant polycystic kidney disease

Mutations in PKD1 cause dominant polycystic kidney disease (PKD), characterized by large fluid-filled kidney cysts in adult life, but the molecular mechanism of cystogenesis remains obscure. Ostrom et al. [Dev. Biol., 219, 250-258 (2000)] showed that reduced dosage of Pax2 caused increased apoptosis, and ameliorated cystogenesis in Cpk mutant mice with recessive PKD. Pax2 is expressed in condensing metanephrogenic mesenchyme and arborizing ureteric bud, and plays an important role in kidney development. Transient Pax2 expression during fetal kidney mesenchyme-to-epithelial transition, as well as in nascent tubules, is followed by marked down-regulation of Pax2 expression. Here, we show that in humans with PKD, as well as in Pkd1(del34/del34) mutant mice, Pax2 was expressed in cyst epithelial cells, and facilitated cyst growth in Pkd1(del34/del34) mutant mice. In Pkd1(del34/del34) mutant kidneys, the expression of Pax2 persisted in nascent collecting ducts. In contrast, homozygous Pkd1(del34/del34) fetal mice carrying mutant Pax2 exhibited ameliorated cyst growth, although reduced cystogenesis was not associated with increased apoptosis. Pax2 expression was attenuated in nascent collecting ducts and absent from remnant cysts of Pkd1(del34/del34)/Pax2(1Neu/+) mutant mice. To investigate whether the Pkd1 gene product, Polycystin-1, regulates Pax2, MDCK cells were engineered constitutively expressing wild-type Pkd1; Pax2 protein levels and promoter activity were both repressed in MDCK cells over-expressing Pkd1, but not in cells without transgenic Pkd1. These data suggest that polycystin-1-deficient tubular epithelia persistently express Pax2 in ADPKD, and that Pax2 or its pathway may be an appropriate target for the development of novel therapies for ADPKD.

Rapid loss of renal parenchyma after acute obstruction

Urinary tract obstruction (UTO) is a frequent cause of renal failure in the pediatric population. We report a patient with type I/I cystinuria, followed prospectively from birth with yearly ultrasonography, who developed acute UTO due to a cystine stone at 10 years of age. In animal models of UTO, acute obstruction produces rapid loss of renal parenchyma secondary to apoptosis of tubular cells. Since we had prospectively obtained serial ultrasonographic measurements of renal growth, we were able to document sudden decrease in kidney size and function following UTO, suggesting that programmed cell death may similarly have caused the rapid irreversible loss of renal parenchyma in our patient. Despite surgical relief of the obstruction, kidney size decreased for at least 3-4 months. We speculate that anti-apoptotic drugs might be considered as a therapeutic strategy to protect ongoing renal parenchyma loss in UTO.

PAX2 suppresses apoptosis in renal collecting duct cells

PAX2 is a transcription factor belonging to the evolutionarily conserved paired box family and is required during development of the central nervous system and genitourinary axis. Mutations in the PAX2 gene cause a rare autosomal dominant renal-coloboma syndrome, characterized by optic nerve colobomas and renal hypoplasia. Recent analysis of a spontaneous PAX2 mutant mouse model (1Neu) revealed that the major cause of renal hypoplasia is reduced branching of the ureteric bud (UB) and fewer nephrons. We have observed that this abnormality is associated with a striking increase in the number of UB cells undergoing programmed cell death during nephrogenesis. To ascertain whether apoptosis is directly linked to the level of PAX2 expression, we have studied the role of PAX2 in cultured renal cells. We show that mIMCD-3 cells, a murine collecting duct cell line with high endogenous PAX2 expression, undergo apoptosis when transfected with anti-sense PAX2. In contrast, HEK293 cells expressing exogenous PAX2 are protected against apoptotic death induced by caspase-2. PAX2 has no effect on proliferation of embryonic kidney or in cultured kidney cells. Our observations imply a direct role for PAX2 in survival of ureteric bud cells.

Renal chloride channel, CLCN5, mutations in Dent's disease

Dent's disease is an X-linked renal tubular disorder characterized by low-molecular-weight proteinuria, hypercalciuria, nephrocalcinosis, nephrolithiasis, and renal failure. Patients with Dent's disease may also suffer from rickets and other features of the renal Fanconi Syndrome. Patients may have mutations in the X-linked renal chloride channel gene, CLCN5, which encodes a 746-amino-acid protein with 12-13 transmembrane domains. We have investigated the 11 coding exons of CLCN5 for mutations in eight unrelated patients with Dent's disease. Leukocyte DNA was used for the polymerase chain reaction amplification of CLCN5 and the products analyzed for single-stranded conformational polymorphisms (SSCPs). Abnormal SSCPs were sequenced and revealed eight mutations. These consisted of three nonsense mutations (Arg34Stop, Arg648Stop, Arg704Stop), four deletions involving codons 40, 86, 157, and 241, and one acceptor splice consensus sequence mutation tgcag --> tgaag. The mutations were confirmed either by restriction endonuclease or sequence-specific oligonucleotide hybridization analysis. In addition, an analysis of 110 alleles from 74 unrelated normal individuals demonstrated that the DNA sequence changes were not common polymorphisms. All of the mutations predict truncated chloride channels that are likely to result in a functional loss. Thus, our findings expand the spectrum of CLCN5 mutations associated with Dent's disease and the results will help to elucidate further the functional domains of this novel chloride channel.

Clinical features of X-linked nephrolithiasis in childhood

X-linked recessive nephrolithiasis (XRN) is a rare hereditary form of progressive renal failure characterized by (1) proximal tubular dysfunction and low molecular weight proteinuria; (2) hypercalciuria with nephrocalcinosis and nephrolithiasis. Because the clinical features are non-specific and variable, affected families in different parts of the world were initially thought to have several distinct syndromes. However, positional cloning of the relevant gene (CLCN5) demonstrated that these families have, in common, mutations affecting a chloride channel expressed throughout the renal tubule. To expand the description of early clinical and pathological manifestations of XRN, we describe three patients diagnosed in the 1st decade of life. Renal tubular dysfunction may be evident even in the neonatal period, hypophosphatemic rickets may develop in the first years of life, and nephrocalcinosis (but not nephrolithiasis) with glomerulosclerosis are consistent features in childhood. One of our patients is indistinguishable from the others on clinical grounds, yet no mutations of the coding regions of the CLCN5 gene were found, raising the possibility of genetic heterogeneity in the XRN syndrome.

CLCN5 chloride-channel mutations in six new North American families with X-linked nephrolithiasis

BACKGROUND

X-linked nephrolithiasis, or Dent's disease, encompasses several clinical syndromes of low molecular weight (LMW) proteinuria, hypercalciuria, nephrocalcinosis, nephrolithiasis, and renal failure, and is associated with mutations in the CLCN5 gene encoding a kidney-specific voltage-gated chloride channel. Some patients from Europe have rickets, and all symptomatic patients confirmed by mutation analysis have been male.

METHODS

We analyzed the CLCN5 DNA sequence in six new families with this disease.

RESULTS

In three probands, a single-base substitution yielded a nonsense triplet at codons 28, 34, and 343, respectively, and in two families, one of which was Hispanic, we found single-base deletions at codons 40 and 44, leading to premature termination of translation. In the sixth family, a single-base change from C to T predicted substitution of leucine for serine at codon 244, previously reported in two European families with prominent rickets, though this patient of Ashkenazi origin did not have rickets. Each of these mutations was confirmed by restriction endonuclease analysis, or repeat sequencing and CFLP. The R34X mutation occurred in a Canadian infant with severe rickets. The family with the R28X nonsense mutation included one woman with recurrent kidney stones and another woman with glomerular sclerosis. In another family, a woman heterozygous for the W343X mutation also had nephrolithiasis.

CONCLUSIONS

These studies expand the range of mutations identified in this disease, and broaden the phenotypic range to include clinically affected women and the first North American case with severe rickets.

Novel mutations in the thiazide-sensitive NaCl cotransporter gene in patients with Gitelman syndrome with predominant localization to the C-terminal domain

Gitelman syndrome (familial hypokalemia-hypomagnesemia syndrome) is an autosomal recessive inherited renal disorder characterized by defective tubular reabsorption of magnesium and potassium. In this study a group of 18 unrelated and 2 related Gitelman patients, collected from six different countries have been screened for mutations in the human thiazide-sensitive sodium-chloride cotransporter (SLC12A3) gene. Fourteen novel SLC12A3 mutations are presented along with six mutations described earlier, and three neutral polymorphisms. Among the tested patients are two who carry a total of three heterozygous SLC12A3 mutations. Two-thirds of the total number of mutant SLC12A3 alleles are amino acid substitutions. Most SLC12A3 gene mutations, 14 out of a total of 20, are localized at the intracellular carboxy-terminal domain of the NCCT protein. The pathogenicity of individual SLC12A3 mutations is based upon their predicted effect on SLC12A3 protein, and segregation in family members. Evolutionary conservation of substituted amino acid residues and their frequency in control chromosomes is presented. Identical mutations have been found in Gitelman families from different geographical origin, suggesting ancient mutations originating from a common ancestor. As yet, we have not found any evidence for a possible genotype-phenotype correlation.

Effects of PAX2 expression in a human fetal kidney (HEK293) cell line

PAX2, a member of the "paired-box" family of homeotic genes, is a nuclear transcription factor expressed in the early stages of nephrogenesis by induced blastemal cells as they progress from mesenchymal condensates to the "S-shaped" stage and also by the ureteric bud. Spontaneous mutations in one copy of PAX2 in humans causes a syndrome of proteinuric renal failure and coloboma of the eye (P. Sanyanusin et al., Nat. Genet. 9 (1995) 358-363); transgenic mice with disruption of the PAX2 gene are anephric (M. Torres et al., Development 121 (1995) 4057-4067. Although PAX2 is clearly critical for normal kidney development, its direct effects on kidney cell phenotype are unknown. To address this issue, we developed stable transfectants of the HEK293 human fetal kidney epithelial cell line expressing human PAX2 protein under tetracycline-regulatable promoter. In these cells, PAX2 had no effect on the proliferative rate, but increased the expression of the Wilms' tumor gene (2-fold) and E-cadherin (7-fold). PAX2 had a strong inhibitory effect on vimentin; vimentin/GAPDH mRNA ratio was suppressed to 8% of control whereas cytokeratin-18/GAPDH mRNA ratio was unchanged. During nephrogenesis, loss of vimentin and onset of low-level WT1 and E-cadherin expression occur in mesenchymal condensates. Our observations suggest that these events may be, in part, regulated by PAX2.

Molecular genetics of cystinuria in French Canadians: identification of four novel mutations in type I patients

Cystinuria, a hereditary disorder of cystine and dibasic amino acid reabsorption, has been classified into three subtypes on the basis of urinary excretion in obligate heterozygous parents. Thirteen cystinuric patients, identified primarily through the Quebec newborn urinary screening program, were investigated by phenotypic classification and by mutational analysis of the D2H (rBAT) gene. Mutations were identified on 7 of 25 alleles; all of these 7 mutant alleles were associated with Type I cystinuria. Four of the mutations (a large deletion, a 5'splice site mutation, a 2 bp deletion, and a nonsense mutation) have not been previously reported. These findings suggest that abnormalities in the D2H gene may account for only one subtype (Type I) of cystinuria, and that this subtype can be caused by a wide variety of population-specific mutations.

Rabbit pancreatic acini express CFTR as a cAMP-activated chloride efflux pathway

Cystic fibrosis transmembrane conductance regulator (CFTR) is responsible for adenosine 3',5'-cyclic monophosphate (cAMP)-activated chloride transport in epithelial cells. Isolated rabbit pancreatic acini possess a cAMP-activated chloride efflux mechanism distinct from zymogen granule secretion. To determine whether CFTR is expressed in acini, we used polymerase chain reaction (PCR) to amplify a 480-base pair (bp) sequence from reverse-transcribed rabbit acinar RNA. The PCR product was consistent with a 480-bp band amplified in T84 cells, and its sequence was > 90% homologous to human CFTR. CFTR antibody M3A7 recognized a 180- and a 160-kDa protein from acinar membranes consistent with bands seen in Chinese hamster ovary (CHO) cells transfected with CFTR. To determine if CFTR was responsible for the cAMP-activated chloride efflux previously demonstrated in pancreatic acini, we incubated acinar cells for 20 h with 1.75 microM CFTR antisense or sense oligodeoxynucleotide. Chloride efflux, in response to 8-bromoadenosine 3',5'-cyclic monophosphate and phorbol ester but not to calcium ionophore, was selectively inhibited by CFTR antisense oligodeoxynucleotide. Antisense oligodeoxynucleotide did not inhibit acinar amylase secretion. These findings indicate that isolated pancreatic acini can be used for future studies of CFTR expression and function.

Insulin-like growth factor-1 enhances epidermal growth factor receptor activation and renal tubular cell regeneration in postischemic acute renal failure

Growth factors such as insulin-like growth factor-1 (IGF-1), epidermal growth factor (EGF), and hepatocyte growth factor have been shown to accelerate the recovery from postischemic acute renal failure (ARF) with a concomitant increase in DNA synthesis. Interactions between growth factors have been demonstrated in a number of in vitro studies. This study examined the effect of exogenous IGF-1 on the DNA synthesis and EGF receptor (EGF-R) activation in postischemic rat kidneys. Thirty minutes after the relief of 30-minute total occlusion of the left renal artery in anesthetized 225 to 300 gm Sprague-Dawley rats, either IGF-1 (75 micrograms/kg) or normal saline solution (NS, 0.2 ml) was given by intravenous bolus, followed by twice daily subcutaneous injections of IGF-1 (50 micrograms/kg) or 0.2 ml NS for 4 days, respectively, in IGF-1-Tx) and NS treated (NS-Tx) groups (n = 8 each). On the day after the completion of treatment, inulin clearance (ml/kg/min) of the postischemic kidneys in the IGF-1-Tx group was significantly higher (p < 0.01) than inulin clearance of kidneys in the NS-Tx group. This was associated with improved kidney morphology. IGF-1 treatment also enhanced the labeling index of 5-bromo-2'-deoxyuridine (percent of stained tubule cells), a marker for active DNA synthesis, in the outer medulla of postischemic kidneys at 1 day and 2 days after the injury. EGF-R tyrosine phosphorylation (which reflects receptor activation) increased in postischemic kidneys in both NS-Tx (n = 5) and IGF-1-Tx (n = 3) groups 1 day after the injury as compared with nonischemic contralateral kidneys. In the IGF-1-Tx group there was also increased iodine 125-labeled EGF binding and EGF-R protein. Our results demonstrate a beneficial effect of IGF-1 on postischemic ARF. Furthermore, they suggest that EGF-R activation is involved in tubular regeneration and that IGF-1 may enhance EGF-R activation by increasing EGF-R expression.

Epidermal growth factor receptor activation in developing rat kidney

Epidermal growth factor (EGF) binding increases in late-gestational rat kidney and then falls toward basal adult levels postnatally during the 1st wk. We report that the increase in EGF binding is accompanied by an increase in EGF receptor (EGFR) protein and activation of EGFR tyrosine kinase. Multiple proteins were endogenously tyrosine phosphorylated in kidney membranes from fetal rats, and the phosphorylation pattern was similar in rats ranging from 16 to 21 days of gestation. Tyrosine phosphorylation was, however, almost undetectable in 12-wk adult rat kidneys (controls). Among the phosphoproteins in fetal kidney, a prominent 170-kDa protein was identified as EGFR. Endogenous tyrosine phosphorylation of EGFR (reflecting receptor activation) was 30-fold higher in fetal kidney membranes than in adult (3- to 7-fold higher when adjusted for differences in EGF binding or EGFR protein content). The EGFR substrate, phospholipase C-gamma 1, was tyrosine phosphorylated in fetal kidneys but not adult, and a greater proportion was membrane-associated in fetal kidneys, consistent with activation of phospholipase C-gamma 1. Thus EGFR tyrosine kinase activity is increased in late-gestational rat kidney. Induction and activation of EGFR may mediate perinatal renal cell growth and development.

Expression of the epidermal growth factor receptor in fetal kidney

Formation of the human kidney begins at the 6th week of fetal life when the first generations of nephrons are generated from foci of metanephric mesenchyme through contact with the branches of the ureteric bud. This process requires a proliferative burst which must be tightly regulated by local signals. In this report, we review the evidence that the epidermal growth factor receptor molecule is an important arbiter of these events.

Prospective analysis and classification of patients with cystinuria identified in a newborn screening program

Patients who inherit mutant cystinuria genes excrete high concentrations of cystine, ornithine, arginine, and lysine in the urine. At least three variants of cystinuria can be distinguished in heterozygotes. To determine whether certain combinations of mutant genes are more disadvantageous than others, we analyzed amino acid excretion in families of 17 probands with cystinuria identified by the Quebec neonatal screening program. Parents of the probands were classified into the three known phenotypes by calculating the sum of cystine, ornithine, arginine, and lysine excretion. Although parents of type I/I homozygotes excreted amounts of cystine in the normal range, their offspring excreted significantly greater amounts of urinary cystine than did children who have type I/III genetic compounds. This observation suggests that types I and III cystinuria mutations might involve two distinct genetic loci. Children with type I/I homozygous cystinuria often excrete cystine at levels greater than the theoretic solubility limit and may be at greatest risk for nephrolithiasis. We outline an approach to monitoring children with cystinuria who come to medical attention before formation of cystine stones.

Eicosanoids enhance epidermal growth factor receptor activation and proliferation in glomerular epithelial cells

Proliferation of glomerular epithelial cells (GEC) and release of prostaglandins (PG) and thromboxane (Tx) A2 may occur in glomerular injury. We studied the relationship of eicosanoids to epidermal growth factor (EGF)-induced proliferation of rat GEC in culture. After 48 h of serum-deprivation, EGF stimulated [3H]thymidine incorporation ninefold above serum-deprived cells. Inhibition of cyclooxygenase with indomethacin or of Txsynthase with OKY-046 decreased the proliferative effect of EGF by 50 and 38%, respectively. The effect of indomethacin was reversed by addition of PGE2. Synthesis of PGE2, PGF2 alpha, and TxA2 by serum-deprived GEC was not enhanced by EGF. Scatchard analysis of 125I-EGF binding to GEC demonstrated two populations of EGF receptors; the high-affinity site had a dissociation constant (Kd) of 444 pM and 24,864 receptors/cell. EGF receptor autophosphorylation (reflecting receptor activation) was studied by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting of GEC membrane proteins with anti-phosphotyrosine antibody. EGF increased phosphorylation of a protein of approximately 170 kDa, which comigrated with proteins immunoprecipitated from [35S]methionine-labeled GEC with antibodies to EGF receptor. Indomethacin and OKY-046 decreased the EGF-dependent phosphorylation of the 170-kDa protein, and this decrease was overcome by addition of PGE2. Indomethacin and OKY-046 did not, however, reduce 125I-EGF binding. Thus, in GEC, the basal synthesis of eicosanoids enhanced EGF-induced proliferation. This effect appears to be due to enhancement of EGF receptor activation.

Transforming growth factor-alpha and the ontogeny of epidermal growth factor receptors in rat kidney

Epidermal growth factor exerts potent receptor-mediated mitogenic effects on a variety of target cells in vitro, but its importance in normal organ development is not yet fully understood. We report that the specific high-affinity receptors for EGF/TGF-Alpha increase dramatically in late gestational rat kidney (from 2.3% at 16 days gestation to 6.4% at term) and then fall toward basal adult levels (< 1% binding) during the first week of post-natal life. This post-natal fall-off in EGF binding corresponds temporally to the period when replication of rat kidney DNA begins to slow (4-7 days of post-natal life). EGF mRNA is not detectable in rat kidney by Northern analysis until the second week of post-natal life, but high levels of transforming growth factor-alpha are demonstrable by specific radioimmunoassay in extracts of fetal kidney (52.2 +/- 8.2 pmoles/gram kidney) and amniotic fluid (4.49 +/- 0.75 pmoles/ml). We speculate that induction of EGF-receptors in fetal rat kidney may confer responsiveness to local transforming growth factor-alpha and dictate the rate of hyperplastic renal growth in the perinatal period.

Congenital deficiency of a 20-kDa subunit of mitochondrial complex I in fibroblasts

The first component of the mitochondrial electron-transport chain is especially complex, consisting of 19 nuclear and seven mitochondrion-encoded subunits. Accordingly, a wide range of clinical manifestations are produced by the various mutations occurring in human populations. In this study, we analyze the subunit structure of complex I in fibroblasts from two patients who have distinct clinical phenotypes associated with complex I deficiency. The first patient died in the second week of life from overwhelming lactic acidosis. Severe complex I deficiency was evident in her fibroblasts, since alanine oxidation was markedly reduced whereas succinate oxidation was normal. Absence of a 20-kDa subunit was demonstrable when newly synthesized proteins were immunoprecipitated from pulse-labeled fibroblasts by anti-complex I antibody. Disordered assembly or decreased stability of the complex was suggested by deficiency of multiple subunits on Western immunoblots. The second patient exhibited a milder clinical phenotype, characterized by moderate lactic acidosis and developmental delay in childhood and by onset of seizures at 8 years of age. Oxidation studies demonstrated expression of the complex I deficiency in fibroblasts, but no subunit abnormalities were detected by immunoprecipitation or Western immunoblotting. This report demonstrates the utility of cultured fibroblasts in studying mutations affecting synthesis and assembly of complex I.

Expression of growth-related genes in human fetal kidney

By the end of gestation, nephron formation in the human kidney is complete. Following local induction of metanephric mesenchyma, committed cells of each primitive renal vesicle must undergo a phase of rapid cell division. In order to identify genes which might regulate these events, we examined the expression profile of 22 proto-oncogenes in fetal versus adult human kidney. Among those expressed at especially high levels in the fetal tissue was the gene for epidermal growth factor receptor (EGFR). We were able to detect mRNA (by polymerase chain reaction [PCR] amplification) and peptide (by specific radioimmunoassay) for transforming growth factor-alpha (TGF-alpha) in fetal kidney, whereas epidermal growth factor (EGF) peptide was undetectable in midgestation kidney and amniotic fluid. TGF-alpha/EGFR interactions may direct renal cell proliferation in fetal life.

Expression of transforming growth factor-alpha and epidermal growth factor receptor in human fetal kidneys

Beginning at the fifth week of fetal life, successive generations of individual nephrons are induced by contact between metanephric mesenchyme and ureteric bud. Following phenotypic transformation, cells of each primitive renal vesicle undergo a phase of rapid cell division. In order to identify genes which might regulate nephron development in man, we screened adult and fetal kidney RNA for expression of a panel of growth-related genes. Among the genes which were expressed at higher levels in fetal kidney was the epidermal growth factor (EGF) receptor. There is controversy as to the most likely physiologic EGF receptor ligand in fetal kidney; we were able to identify a transcript for transforming growth factor-alpha (TGF-alpha) but not EGF on Northern blots of fetal kidney RNA. Since the abundance of TGF-alpha mRNA is low, we confirmed its presence by polymerase chain reaction amplification. Using specific radioimmunoassays, we also provide direct evidence for TGF-alpha but not EGF peptide in extracts of fetal kidney and mid-gestational amniotic fluid. We suggest that TGF-alpha/EGF receptor interactions may serve an important function in development of human fetal kidney.

Deficiency of complex III of the mitochondrial respiratory chain in a patient with facioscapulohumeral disease

Facioscapulohumeral disease (FSHD), an inherited neuromuscular disorder, is characterized by progressive wasting of specific muscle groups, particularly the proximal musculature of the upper limbs; the primary defect in this disorder is unknown. We studied a patient with FSHD to determine whether the mitochondrial respiratory chain was functionally abnormal. Muscle biopsy revealed fiber atrophy with patchy staining for oxidative enzymes. Electron microscopy of a liver section showed many enlarged mitochondria with paracrystalline inclusions. Decreased oxidation of the respiratory substrates-alanine and succinate-in skin fibroblasts suggested a deficiency of complex III of the electron-transport chain; cytochrome c oxidase activity (complex IV) was in the normal range. Biochemical analysis of liver supported the fibroblast data, since succinate oxidase activity (electron-transport activity through complexes II-IV) was reduced, whereas complex IV activity was normal. Furthermore, analysis of the cytochrome spectrum in liver revealed typical peaks for cytochromes cc1 and aa3, whereas cytochrome b (a component of complex III) was undetectable. Southern blot analysis of fibroblast mtDNA revealed no major deletions or rearrangements. Our study provides the first documentation of a specific enzyme-complex deficiency associated with FSHD.

Renal synthesis of epidermal growth factor is unchanged by vitamin D deficiency

In mammalian kidney, epidermal growth factor (EGF) is produced as a small internal domain of an abundant high molecular weight peptide associated with the luminal membrane of the thick ascending limb of Henle's loop and distal convoluted tubule. At present, there is no evidence to indicate a mitogenic function for the EGF-containing molecule in kidney; consideration of its molecular structure suggests the possibility of a membrane-associated physiologic role. In this study, we examine regulation of renal EGF synthesis during induction of vitamin D deficiency in mice. Despite evidence of marked hyperparathyroidism, urinary excretion of EGF was equivalent in control (2.54 +/- 0.72 micrograms/mg creatinine) and vitamin D deficient (2.13 +/- 0.97 micrograms/mg creatinine) animals. Similarly, EGF mRNA levels in kidney were comparable in the two groups. These data indicate that parathyroid hormone has no effect on renal EGF regulation, although it is known to stimulate calcium reabsorption in distal nephron segments.

Excretion of epidermal growth factor-like material in acute Henoch-Schönlein purpura nephritis

In Henoch-Schönlein purpura nephritis (HSPN), glomeruli may develop cellular "crescents" composed of infiltrating monocytes and proliferating renal epithelia. In this study, we demonstrate that peripheral human monocytes can release an epidermal growth factor (EGF)-like substance detectable by a radioreceptor assay, which recognizes both EGF and transforming growth factor-alpha (TGF-alpha), but not with a radioimmunoassay, which recognizes only EGF. Furthermore, we report that urine from pediatric patients during the acute phase of HSPN contains a similar EGF-like species in addition to the endogenous EGF which is normally present. The EGF-like material was not present in urine from nine healthy children or from six children with acute post-streptococcal glomerulonephritis. The extent of crescent formation in our patients is uncertain, since renal biopsy was performed in only one case. However, we speculate that the urinary material resembling TGF-alpha which appears during the acute phase of HSPN may derive from monocytes infiltrating the kidney.

Renal tubular cells are potential targets for epidermal growth factor

Epidermal growth factor (EGF) is a potent polypeptide mitogen with various receptor-mediated growth effects on cells from the skin, breast, and gastrointestinal tract. Recent studies indicate that EGF is produced in the kidney and is excreted in the urine, but the biological significance of renal EGF is uncertain. We demonstrate in vitro mitogenicity of EGF for LLC-PK1 cells, a tubular epithelial cell line derived from pig kidney cortex. Furthermore, when subconfluent monolayers of LLC-PK1 cells are exposed to EGF for 24 h, sodium-dependent phosphate transport is stimulated (209-410% of control). These cells possess EGF-specific high-affinity binding sites at their surface (Kd 300-700 pM) but cannot synthesize the growth factor. EGF binding sites are not a peculiarity of the LLC-PK1 cell line, since similar sites are present on MDCK cells (derived from dog kidney distal tubule or collecting duct), primary cultures of mouse proximal tubular cells, and freshly prepared membrane fractions from mouse kidney. Cortical basolateral membranes are highly enriched in EGF binding sites, whereas EGF binding by brush-border membrane fractions is minimal and is compatible with contamination.

Nephrocalcinosis and its relationship to treatment of hereditary rickets

Renal ultrasonography was performed on 23 patients with X-linked hypophosphatemic rickets (XLH) and 11 patients with autosomal recessive vitamin D-dependent rickets (ARVDD). A pattern of increased echogenicity of the renal pyramids (ERP) was identified in 11/23 patients with XLH and 3/11 patients with ARVDD; this ultrasonographic finding has previously been associated with medullary nephrocalcinosis. Patients with XLH and ERP had significantly higher mean serum calcium and phosphate concentrations, more frequent episodes of hypercalcemia, and higher doses of oral vitamin D and phosphate during the first 3 years of therapy. Episodes of hypercalcemia were more frequent when patients received higher doses of vitamin D2 (greater than 4000 IU/kg/day) or 1,25-dihydroxycholecalciferol (greater than 40 ng/kg/day). Episodes of hypercalciuria were significantly increased at doses of greater than 20 ng/kg/day 1,25-dihydroxycholecalciferol. In patients with ARVDD, ERP was also correlated with vitamin D dose and frequency of hypercalcemia episodes. ERP was not associated with an elevation of serum creatinine or loss of urinary concentrating ability in either patient group.

Amelioration of murine lupus nephritis by dimethylsulfoxide

Dimethylsulfoxide was given to NZB/W F1 female mice from age 10 weeks to see if proteinuria and glomerular injury could be reduced. Twenty mice were randomly assigned to saline or DMSO treatment groups and the following studies were done: urine protein determination, serum concentrations of creatinine, IgG, C3, and albumin; and ANA titers. Kidney tissue were studied by light, immunofluorescent and electron microscopy. DMSO-treated mice had significant reductions in protein excretion at 5 and 6.5 months of age; in urine protein/creatinine ratio at 6.5, 7, and; 7.5 months; in serum C3 at 7.5 months; and in serum creatinine concentration. There were no significant differences among serum IgG, nor among the ANA titers. Histopathologic studies revealed nearly normal kidneys in 5/6 DMSO-treated mice whereas 4/8 controls had severe mixed membranous and membranoproliferative glomerulonephritis. Ultrastructural studies revealed mesangial, subendothelial, and subepithelial deposits and membranous transformation of the glomerular capillary wall. DMSO therefore appears capable of ameliorating glomerular injury in NZB/W F1 mice.

Colchicine reduces proteinuria in passive Heymann nephritis

Colchicine was given to rats in the heterologous phase of passive Heymann nephritis to see whether this drug could reduce proteinuria. Treatment with 0.06 mg/day for 14 days caused significant reductions in proteinuria and albuminuria. Administration of dimethyl sulfoxide (DMSO) alone or in combination with colchicine also reduced protein and albumin excretion. In a long-term experiment, rats treated with colchicine had significantly less proteinuria. After stopping therapy, urine protein excretion was similar to controls. No differences in glomerular C3 and IgG deposition were found between treated and control rats 24 h, 3,7 and 14 days after immunization. Depressed serum C3 levels were measured at 24 h in colchicine-treated rats. No difference in serum-circulating immune complexes was detected between the two groups. Concurrent administration of indomethacin and colchicine to rats with passive Heymann nephritis (PHN) partially reversed the reduction in proteinuria and albuminuria seen in rats treated with colchicine alone. The G.F.R, however, was significantly reduced in colchicine-treated rats as well as in rats treated with colchicine and indomethacin. Serum cholesterol and triglyceride levels were significantly lower in colchicine-treated rats than in controls. Serum cholesterol concentrations in rats given both colchicine and indomethacin were similar to control values. These findings suggest that colchicine reduces urine protein and albumin excretion, and hyperlipidemia in PHN. The finding that indomethacin partially blocks the effects of colchicine suggests that renal prostaglandin stimulation by colchicine may have been involved in the reduction in proteinuria.

Analysis of the Heymann nephritogenic glycoprotein in rat, mouse, and human kidney

Passive Heymann nephritis is induced in rats by intravenous administration of antiserum raised against antigens of the renal proximal tubule. Evidence by Kerjaschki and Farquhar indicates that the critical nephritogenic is a high molecular weight glycoprotein (HMWgp) of rat renal brush border membrane. Their immunocytochemical studies also localize the nephritogenic antigen to the glomerular epithelial cell surface and may explain in situ formation of immune complexes at this locus in Heymann nephritis. We have confirmed the observations of Kerjaschki and Farquhar by demonstrating the HMWgp in extracts of rat brush border membrane and isolated glomeruli on sodium dodecyl sulfate-polyacrylamide (SDS-PA) (5%) gels. An antiserum raised to purified rat HMWgp identifies the antigen from rat or mouse kidney on Western blots. However, unlike rodent kidney, we were unable to detect a comparable HMWgp in extracts of human kidney on SDS-PA gels and found no cross-reactive material on Western blots of human brush border membrane proteins. Our observations suggest that human kidney lacks the nephritogenic antigen critical to initiation of Heymann nephritis in rodents.

Interactions of dimethyl sulfoxide and nonsteroidal anti-inflammatory agents in passive Heymann's nephritis

The effect of treatment with indomethacin on the ability of dimethyl sulfoxide (DMSO) to reduce proteinuria in rats with passive Heymann's nephritis (PHN) was studied. PHN rats treated with DMSO alone excreted significantly less protein by day 14 than PHN rats treated with buffer or with indomethacin alone. Rats treated with DMSO excreted 19 +/- 6.0 mg protein/24 hr, and those treated with DMSO and indomethacin excreted 161 +/- 27.4 mg protein/24 hr (P less than 0.001). Rats treated with DMSO alone had significantly higher serum albumin and significantly lower serum cholesterol and triglyceride concentrations than those given the two drugs together. Glomerular deposits of C3 were reduced in DMSO-treated rats, but serum C3 concentrations and rat antirabbit serum antibody titers were similar in the two groups. When a higher dose of indomethacin (5 mg/kg) plus DMSO was used, protein excretion was significantly reduced. Rats treated with DMSO and acetylsalicylic acid (ASA) (37 mg/kg/day) or DMSO and meclofenamate (5 mg/kg/day) did not have a significant reduction in protein excretion compared with untreated controls. High-dosage indomethacin alone did not reduce proteinuria. Low doses of nonsteroidal anti-inflammatory agents therefore appear to block the effect of DMSO on proteinuria. This was in marked contrast to the finding of reduction of proteinuria induced by larger doses of indomethacin (5 mg/kg) plus DMSO. DMSO did not reduce proteinuria in rats with nephrosis induced by puromycin of aminonucleoside.

A gamma-aminobutyric acid-specific transport mechanism in mammalian kidney

We describe high-affinity, sodium-dependent transport of gamma-aminobutyric acid in slices exposing basal lateral membranes and brush-border membrane vesicles prepared from rat renal cortex. In the presence of aminooxyacetic acid, to block gamma-aminobutyric acid oxidation, uptake into the intracellular space of slices was saturable (apparent Kt, 26 +/- 4 microM, mean and S.E.) and concentrative (steady-state distribution ratio at 50 microM gamma-aminobutyric acid, 47.7 +/- 2.4, mean and S.E.). Brush-border membrane vesicles accumulated gamma-aminobutyric acid in the presence of an inward-directed sodium chloride gradient, (apparent Kt, 30-36 microM) with the peak of 'overshoot' at 10 min. Uptake by vesicles responded to manipulation of the transmembrane potential gradient with valinomycin or impermeant anion. beta-Alanine inhibited gamma-aminobutyric acid transport by slices and brush-border membrane vesicles; inhibitors of neuronal-type gamma-aminobutyric acid transport (e.g., nipecotic and diaminobutyric acids) did not. An 'ABC test' indicated that gamma-aminobutyric acid and beta-alanine do not share a single carrier in either the brush-border or basal-lateral membrane of renal cortex. Influx of gamma-aminobutyric acid into brush-border membrane vesicles, at transequilibrium NaCl, was stimulated by trans-gamma-aminobutyric acid but not by trans-taurine. Ion gradient-driven gamma-aminobutyric acid co-transport was unaffected in freeze-thawed brush-border membrane vesicles; this treatment abolished beta-alanine and taurine co-transport. We conclude that rat kidney membranes (brush-border and basal-lateral) possess a gamma-aminobutyric acid-preferring, high-affinity transport mechanism.

Inherited lactic acidosis: correction of the defect in cultured fibroblasts

We report a case of familial lactic acidosis, lethal in the newborn period. Studies in intact fibroblasts identified a defect in the oxidative pathway of pyruvate metabolism. Although assay of pyruvate dehydrogenase on cell sonicates was not appreciably reduced, flux through the enzyme and other mitochondrial multienzyme dehydrogenases was severely impaired in intact cells. Deficient lactate conversion to carbon dioxide could be repaired by the addition to the incubation medium of electron acceptors such as methylene blue (25 micrograms/ml) or dichlorophenolindophenol (25 micrograms/ml).

Reduction of protein excretion by dimethyl sulfoxide in rats with passive Heymann nephritis

Passive Heymann nephritis, a model of immune complex nephritis, was produced in rats by injection of rabbit antibrush border membrane vesicle antibodies to examine the effect of treatment of epimembranous glomerulonephritis with dimethyl sulfoxide. Administration of DMSO twice a day, 5 days a week for 4 weeks significantly reduced protein excretion in the autologous phase of the model. This beneficial effect occurred in animals in which treatment was started a day after administration of the antibody and persisted for 4 weeks after treatment was discontinued. Serum triglyceride concentrations were significantly decreased, whereas, BUN, serum cholesterol, and globulin levels were significantly, but not reproducibly, reduced. That DMSO did not reduce proteinuria to normal values in rats treated after proteinuria was well established, but was able to reduce proteinuria significantly. Treatment of normal rats and those with nephrotoxic serum nephritis did not reduce protein excretion. Glomeruli of rats with passive Heymann nephritis treated with DMSO studied by immunofluorescent microscopy appeared to have less fluorescence for IgG than control rats, but these differences were not significant. However, C3 deposits were significantly decreased in treated rats, but only during the first week of the disease and in vitro C3 fixation was also significantly reduced in glomeruli of rats that had been treated with DMSO. There was very little effect on serum complement activity: CH50 was reduced only on day 1 of treatment, whereas the alternate pathway activity and serum C3 concentration were unaffected. DMSO may therefore reduce protein excretion, in part, by inhibiting C3-dependent proteinuria. These studies indicate that DMSO is capable of significantly reducing protein excretion in rats with passive Heymann nephritis and that its action may involve reduction of complement deposition within the glomeruli during the heterologous phase. Toxic effects included a 2.5% mortality and decreased weight gain while being treated with larger doses of DMSO. Treatment with a much smaller dose succeeded in reducing proteinuria significantly without affecting weight gain. There was no evidence of drug-induced liver or renal damage.

A perimortem protocol for suspected genetic disease

A considerable portion of pediatric deaths represent disease with risk of recurrence in subsequent family members. Procedures to obtain samples of body fluids and tissues suitable for diagnosis of mendelian and chromosomal disorders are described. These procedures, the "perimortem protocol," are used in studying children who died of suspected but undiagnosed genetic disease.

Properties of gamma-aminobutyric acid synthesis by rat renal cortex

Substantial synthesis of gamma-aminobutyric acid occurs in rat renal cortex. Renal glutamate decarboxylase activity (24.3 +/- 2.9 (S.E.) nmols/mg protein per h) is 15% of that in brain; renal gamma-aminobutyric acid content (39.5 +/- 5.3 (S.E.) nmols/g wet wt.) is 5% of the whole brain concentration. Properties of glutamate decarboxylase were studied in homogenates of rat renal cortex and rat brain under conditions for which gamma-aminobutyric acid formation from [2,3-3H]glutamate and CO2 release from [1(-14)C]glutamate were equal. Several properties of renal glutamate decarboxylase distinguish it from the corresponding brain enzyme: (1) renal glutamate decarboxylase is selectively inhibited by cysteine sulfinic acid (Ki = 5X10(-5) M); (2) renal glutamate decarboxylase is less sensitive (Ki = 3-5X10(-5) M) to inhibition by aminooxyacetic acid than is the brain enzyme (Ki = 1X10(-6) M); (3) brain but not renal glutamate decarboxylase activity can be substantially stimulated in vitro by the addition of exogenous pyridoxal 5'-phosphate; (4) renal glutamate decarboxylase is significantly decreased in renal cortex from rats on a low-salt diet. Proximal tubules are enriched in glutamate decarboxylase compared to the activity in whole renal cortex or glomeruli (42, 22 and 14 nmols/mg protein per h, respectively). We speculate that renal gamma-aminobutyric acid synthesis does not reflect the presence of GABAergic renal nerves, but may serve a function in proximal tubular cells.

Turner's syndrome, 46X, del (X) (p 11), persistent complement activation and membranoproliferative glomerulonephritis

An adolescent girl with short stature and learning disability was found to have an unusual variant of Turner's syndrome, 46X, del (X) (p 11) and an abnormal urinary sediment. Further studies demonstrated persistent depression of C3 and histologic evidence of membranoproliferative glomerulonephritis (MPGN). The occurrence of MPGN in this case may have been a manifestation of the known tendency for Turner patients to develop immunologic disease.

Antenatal betamethasone and renal ammoniagenesis in the newborn

As part of a double-blind clinical trial of antenatal betamethasone, we studied the effects of this drug on urinary ammonia excretion in 28 premature infants. Betamethasone was administered before 34 weeks of gestation according to dosage schedules which have been shown to alter the incidence of respiratory distress syndrome. Although glucocorticoids affect renal ammoniagenesis in adults, the antenatal betamethasone trial did not augment ammonia excretion measured during the first day of postnatal life. We speculate that precocious maturation of renal ammoniagenesis cannot be triggered by glucocorticoids during the gestational period studied.

The relationship of 4-aminobutyric acid metabolism to ammoniagenesis in renal cortex

Mitochondrial 4-aminobutyrate aminotransferase in rat kidney can utilize pyruvate as the acceptor for the amino group of 4-aminobutyrate. Renal 4-aminobutyrate aminotransferase activity at saturating equimolar concentration of 4-aminobutyrate and 5 mM pyruvate is 42.8 +/- 2.5 mumol/g protein per h (mean +/- S.E.M.) or 70% of 4-aminobutyrate aminotransferase activity with equimolar alpha-ketoglutarate. 4-Aminobutyrate aminotransferase in brain does not transaminate with pyruvate. Since pyruvate is an important mitochondrial metabolite in kidney, net disposal of glutamate via the 4-aminobutyrate pathway is possible. The renal 4-aminobutyrate pathway in the rat has other distinctive features when compared with the pathway in rat brain. Most inhibitors of rat neuronal glutamate decarboxylase were ineffective against the renal form of the enzyme, but 20 mM semicarbazide inhibited the latter form by 80% (P < 0.001) in vitro and reduced renal 4-aminobutyrate content by 75% (P < 0.001) in vivo. In the presence of 20 mM semicarbazide, ammoniagenesis by rat renal cortex slices incubated in 1 mM glutamine was inhibited 26% (P < 0.01). Semicarbazide was proportionately less effective (15% inhibition) when ammonia-genesis was stimulated (+243%) in slices prepared from chronically acidotic animals, and was no deterrant to ammoniagenesis when non-acidotic slices were incubated in supraphysiologic concentrations of 10 mM glutamine. We conclude that whereas integrity of the renal 4-aminobutyrate pathway may contribute to glutamate disposal and thus ammoniagenesis under physiologic conditions, the pathway is a passive participant in the overall process of ammoniagenesis.