A founder mutation in COL4A3 causes autosomal recessive Alport syndrome in the Ashkenazi Jewish population

Alport syndrome is an inherited progressive nephropathy arising from mutations in the type IV collagen genes, COL4A3, COL4A4, and COL4A5. Symptoms also include sensorineural hearing loss and ocular lesions. We determined the molecular basis of Alport syndrome in a non-consanguineous Ashkenazi Jewish family with multiple affected females using linkage analysis and next generation sequencing. We identified a homozygous COL4A3 mutation, c.40_63del, in affected individuals with mutant alleles inherited from each parent on partially conserved haplotypes. Large-scale population screening of 2017 unrelated Ashkenazi Jewish samples revealed a carrier frequency of 1 in 183 indicating that COL4A3 c.40_63del is a founder mutation which may be a common cause of Alport syndrome in this population. Additionally, we determined that heterozygous mutation carriers in this family do not meet criteria for a diagnosis of Thin Basement Membrane Nephropathy and concluded that carriers of c.40_63del are not likely to develop benign familial hematuria.

mRNA expression for insulin-like growth factor 1, receptors of growth hormone and IGF-1 and transforming growth factor-beta in the kidney and liver of Zucker rats

Kidney dysfunction and mesangial enlargement are consequences of obesity found in Zucker rats. This study examines some of the early mechanisms by which the kidneys of Zucker rats undergo these changes. Our study shows that the glomerular planar area in the genetically obese Zucker rat undergo enlargement as early as 12 weeks of life, compared to the lean controls. This suggests mesangial proliferation is already occurring at this time, earlier than previously shown. The mRNA expression for IGF-I, and GHR in the kidney and liver of the obese Zucker rats were significantly reduced compared to the lean controls. However, the mRNA of the IGF-IR was significantly elevated in the kidney of the obese Zucker rats. The increase in kidney IGF-1R mRNA in the obese Zucker rat may suggest an increase in IGF-1 binding leading to the kidney hypertrophy observed in these rats.

Cytoprotective effect of curcumin in human proximal tubule epithelial cells exposed to shiga toxin

We conducted the following experiments to determine whether curcumin, an antioxidant compound extracted from the spice tumeric, inhibits cell death induced by Shiga toxin (Stx) 1 and 2 in HK-2 cells, a human proximal tubule cell line. Cells were incubated for 24-48 h with Stx1 or Stx2, 0-100 ng/ml. Test media contained either no further additives or 10-50 microM curcumin. Exposure to Stx1 and Stx2, 100 ng/ml, reduced cell viability to approximately 25% of control values after 24 h and 20 microM curcumin restored viability to nearly 75% of control. Cell staining confirmed that Stx1 and Stx2-induced damage in HK-2 cells involved a combination of apoptosis and necrosis. Thus, Stx1 caused apoptosis and necrosis in 12.2 +/- 2.2 and 12.7 +/- 0.9% of HK-2 cells, respectively. Similarly, Stx2 caused apoptosis and necrosis in 13.4 +/- 2.1 and 9.0 +/- 0.5% of HK-2 cells, respectively. Addition of 20 microM curcumin decreased the extent of apoptosis and necrosis to 2.9 +/- 2.0 and 3.8 +/- 0.2%, respectively in the presence of Stx1 and to 3.0 +/- 2.1 and 3.9 +/- 0.3%, respectively, for Stx2 (P < 0.01). Stx-induced apoptosis and its inhibition by curcumin were confirmed by DNA gel electrophoresis and by an assay for fragmentation. The protective effect of curcumin against Stx1 and Stx2-induced injury to HK-2 was not related to its antioxidant properties. Instead, curcumin enhanced expression of heat shock protein 70 (HSP70) in HK-2 cells under control conditions and after exposure to Stx1 or Stx2. No injury was detectable after incubation of LLC-PK(1) or OK cells, non-human proximal tubule cell lines, with Stx1 or Stx2. Thus, curcumin inhibits Stx-induced apoptosis and necrosis in HK-2 cells in vitro. The cytoprotective effect of curcumin against Stx-induced injury in cultured human proximal tubule epithelial cells may be a consequence of increased expression of HSP70.

Pediatric biopsy of a single native kidney

Technological improvements have reduced the frequency of complications in children receiving a percutaneous renal biopsy. No study has systematically compared the safety of open and percutaneous kidney biopsy. Yet many nephrologists consider a single native kidney an absolute contraindication to percutaneous biopsy. We have established an international registry of single native kidney biopsies in children and we now report our early results. Eight biopsies are included. Seven patients had percutaneous biopsies and one an open biopsy. None of the patients had major complications, and adequate tissue was obtained from all. Our limited experience indicates that the presence of a single native kidney is not an absolute indication for an open approach. We encourage our colleagues to report to the international registry in order to further document the safety of percutaneous biopsy of the single native kidney in children.

Anti-apoptotic effect of L-arginine in cultured rat mesangial cells

Nitric oxide has been shown to be an important factor in the regulation of apoptosis in mesangial cells. The following studies were conducted to determine whether L-arginine, the metabolic precursor of nitric oxide synthesis, directly modulates programmed cell death in response to a variety of stimuli. Cultured rat mesangial cells were exposed for 24-48 h to one of the following four experimental conditions known to induce apoptosis: i) a cytokine combination consisting of interferon-gamma (50 U/ml), interleukin-1 (5 ng/ml), and LPS (10 microg/ml); ii) 0.75 mM hydrogen peroxide; iii) etoposide, 150 microg/ml; and iv) cis-platinum, 100 microg/ml. Addition of L-arginine resulted in a dose-dependent decrease in apoptosis in cytokine-treated RMC. This effect was demonstrable by gel electrophoresis, diphenylamine assay of DNA fragmentation, and an ELISA to detect DNA oligonucleosomes. The effect was not related to increased osmolality of the test media and was not reproduced by the addition of equimolar D-arginine. L-Arginine also reduced apoptosis and necrosis in RMC that were incubated with etoposide and cis-platinum. In contrast, the amino acid had no beneficial effect on RMC survival following exposure to hydrogen peroxide. These findings indicate that several components of the nitric oxide biosynthetic pathway including the precursor and the enzymatic product independently exert direct effects on apoptosis in cultured rat mesangial cells.

Bartter syndrome and focal segmental glomerulosclerosis: a possible link between two diseases

We describe a patient with signs and symptoms of classic Bartter syndrome. The patient tested negative for all known genetic abnormalities associated with this tubular disorder. Proteinuria was found within 1 year after the diagnosis of Bartter syndrome. A renal biopsy performed 6 months later, when her kidney function was normal, revealed focal segmental glomerulosclerosis (FSGS). We propose a link between stimulation of the renin-angiotensin system and sclerotic changes in the glomerulus. This lesion may explain previous reports of kidney failure in patients with Bartter syndrome.

Yield of renal arteriography in the evaluation of pediatric hypertension

The prevalence of renovascular disease is estimated to be 3%-5% in pediatric patients with hypertension. The utility of non-invasive imaging tests has not been evaluated in children, and renal arteriography remains the diagnostic test of choice. However, there are no established guidelines for the application of this test and information is not available about the likelihood of detecting an abnormality if an arteriogram is performed in children with hypertension. Therefore, we reviewed the yield of renal arteriography in pediatric patients if the test was performed based on the following two criteria: (1) severe hypertension exceeding the 99th percentile for age and sex or (2) failure to control high blood pressure with one antihypertensive drug. During the period 1983-1998, 28 children (mean age 11.7 years) who satisfied one of the above criteria underwent renal arteriography to investigate hypertension. None of the patients were renal transplant recipients. The average duration of hypertension was 11 months and the peak blood pressure was 168/107 mmHg. The renal arteriogram was abnormal in 12 patients (43%). Unilateral renal artery stenosis was the most-common abnormality. When the patients were divided into two groups - those with an abnormal or normal test result - they did not differ in age, sex, or racial distribution. The peak systolic blood pressure was higher in children with an abnormal renal arteriogram (P<0.05). Among those undergoing the arteriogram on the basis of the first criterion, i.e., severe hypertension, 11 of 23 (48%) studies were abnormal. Five children had an arteriogram based on the second criterion--failure to control the blood pressure with one medication--and in 1 patient (20%) the test was abnormal. We conclude that the prevalence of renovascular disease in a population of hypertensive children subjected to renal arteriography is around 40%. Two clinical criteria--namely severe hypertension or failure to control hypertension effectively with one drug--are useful to guide the application of renal arteriography in children with hypertension.

The role of nitric oxide in obstructive nephropathy

PURPOSE

Ureteral obstruction leads to tubulointerstitial fibrosis and loss of renal function. Nitric oxide production ameliorates fibrosis due to obstructive uropathy. However, nitric oxide is produced by 3 isoforms of the enzyme, nitric oxide synthase. We evaluated the role of inducible nitric oxide synthase in obstructive uropathy using nitric oxide synthase knockout mice, and determined whether the administration of L-arginine to promote nitric oxide synthesis by alternative nitric oxide synthase isoforms modulates renal fibrosis in these animals.

MATERIALS AND METHODS

Complete unilateral ureteral obstruction was created in wild-type C57 and inducible nitric oxide synthase knockout mice. Control animals of each strain underwent sham surgery. Throughout the experiment mice had free access to untreated tap water or water supplemented with 10 gm./l. L-arginine. Animals were sacrificed 1 and 2 weeks, respectively, after creation of unilateral ureteral obstruction. We obtained serum as well as bladder and obstructed renal pelvic urine, and determined the nitrite level in each fluid. Renal cortical thickness was measured in the normal and obstructed kidneys. The degree of tubulointerstitial fibrosis was evaluated by trichrome staining and type I collagen deposition in kidney tissue specimens.

RESULTS

Nitrite was significantly decreased in the serum, bladder and renal pelvic urine of inducible nitric oxide synthase knockout mice with unilateral ureteral obstruction compared with that in wild-type C57 mice at 1 and 2 weeks (p<0.05). In knockout mice with unilateral ureteral obstruction 1 week in duration that drank tap or L-arginine supplemented water nitrite in serum and each urine sample was higher than in sham operated knockout controls. The level returned to baseline after 2 weeks of obstruction (p<0.05). After 2 weeks of obstruction there was significantly greater cortical thinning in knockout than in C57 mice (p<0.05). Moreover, knockout mice given L-arginine supplemented water for 2 weeks had even greater cortical thinning than after 1 week or than mice given tap water for 1 to 2 weeks (p<0.05). Decreased renal cortical thickness in knockout mice after 2 weeks of obstruction was associated with less intense trichrome staining and a virtual absence of type I collagen deposition compared with findings in the wild-type C57 strain.

CONCLUSIONS

Inducible nitric oxide synthase knockout mice with unilateral ureteral obstruction have significantly lower nitrite in serum and urine than wild-type C57 mice. Knockout mice also have more severe renal cortical thinning than C57 animals after creation of unilateral ureteral obstruction. Providing L-arginine supplemented water to inducible nitric oxide synthase knockout mice exacerbates the loss of cortical thickness. Alterations in cortical thinning that we observed in knockout mice were associated with decreased tubulointerstitial fibrosis and a decreased net renal extracellular matrix accumulation. These data indicate that endothelial or neuronal nitric oxide synthase may be more important than inducible nitric oxide synthase for modulating renal fibrosis in obstructive uropathy.

Vitamin E treatment of focal segmental glomerulosclerosis: results of an open-label study

Experimental data indicate that excessive production of reactive oxygen molecules contributes to progressive renal injury and that treatment with antioxidants attenuates this damage. Therefore, we investigated whether vitamin E supplementation could ameliorate renal disease and reduce proteinuria in children with a variety of kidney disorders. Vitamin E, 200 IU twice daily, was administered orally to 11 children with focal segmental glomerulosclerosis (FSGS) (group A) and 9 patients with miscellaneous kidney diseases (group B) [Henoch-Schönlein purpura nephritis (n=3), urinary tract anomalies (n=2), non-specific immune complex glomerulonephritis (n=2), IgA nephropathy (n=1), and reflux nephropathy (n=1)]. The duration of vitamin E treatment, when no other therapy was introduced, was 2.9+/-0.4 months. Proteinuria was determined by measuring the protein:creatinine ratio (mg/mg) in an early morning urine specimen. In children with FSGS, administration of vitamin E lowered the protein:creatinine ratio in 10 of 11 patients from 9. 7+/-5.1 to 4.1+/-1.1 (P<0.005). In contrast, among children with miscellaneous renal diseases, vitamin E had no beneficial impact on urinary protein excretion-protein:creatinine ratio 2.5+/-1.0 pre versus 2.4+/-1.2 post antioxidant. Vitamin E supplementation had no effect on glomerular filtration rate, serum albumin, or cholesterol concentration in either group of patients. These findings suggest that reactive oxygen molecules may play a more-prominent role in causing renal injury in patients with FSGS than in other kidney disorders. Antioxidant therapy may be a useful adjunct in the treatment of children with FSGS and proteinuria that is refractory to standard medical management.

Pathogenesis, treatment, and therapeutic trials in hemolytic uremic syndrome

Diarrhea-associated hemolytic uremic syndrome is one of the most common causes of acute renal failure in childhood. Nearly all cases are the result of an antecedent infection by Shiga toxin--producing strains of Escherichia coli, especially the O157:H7 serotype. Most cases occur after ingestion of contaminated meat; however, new food sources such as leaf lettuce, alfalfa sprouts, and goat's milk have been identified, and diarrhea-associated hemolytic uremic syndrome can occur after exposure to contaminated water in recreational swimming sites. Diarrhea-associated hemolytic uremic syndrome is a systemic disease with activation of a variety of inflammatory cytokines. Kidney injury may result from direct effects of the Shiga toxin on renal tubular epithelial cells as well as endothelial cells. Early diagnosis of diarrhea-associated hemolytic uremic syndrome may be expedited by the introduction of new techniques to rapidly detect toxin and microorganism in stool samples. Optimal therapy of diarrhea-associated hemolytic uremic syndrome includes intensive management of the renal failure and serious extrarenal complications that may occur during the course of disease. The role of antibiotics in prevention and amelioration of diarrhea-associated hemolytic uremic syndrome remains controversial. Experimental therapies that are undergoing evaluation in clinical trials include SYNSORB Pk (SYNSORB Biotech, Inc., Calgary, Alberta, Canada), a drug designed to bind Shiga toxin in the lumen of gastrointestinal tract. Immunization strategies are also being developed and tested. It is hoped that with continued progress in this field the incidence of diarrhea-associated hemolytic uremic syndrome in children will be substantially reduced in the coming years.

Growth of rat mesangial cells on oxidized extracellular matrix increases inducible nitric oxide synthase activity

Biochemical modification of extracellular matrix (ECM) proteins can alter the function in overlying cells. We tested the hypothesis that metal-catalyzed oxidation of native ECM and individual matrix proteins modulates the activity of inducible nitric oxide synthase (iNOS) in cultured rat mesangial cells (RMC). Oxidized modification of native ECM resulted in a 32% increase in iNOS activity (P<0.01) without influencing the response to supplemental L-arginine or to the addition of the iNOS inhibitor, L-NAME. Immunoblot analysis indicated that enhanced iNOS activity was not associated with a parallel rise in the cytosolic content of iNOS. Synthesis of type IV collagen was unaffected by growth of RMC on oxidized native ECM. Oxidation of three normal constituents of the mesangial matrix - type IV collagen, laminin, and fibronectin - also stimulated iNOS activity in overlying RMC by 18-32% (P<0.05). Growth of RMC on oxidized type I collagen or Vitrogel had no effect on NO production. We conclude that oxidized modification of the mesangial matrix promotes increased iNOS activity and NO production by mesangial cells. Further work is required to determine whether this response limits glomerular injury or promotes damage to the mesangium in oxygen free radical-mediated diseases such as chronic renal failure, atherosclerosis and diabetes.

Circulating factor in patients with recurrent focal segmental glomerulosclerosis postrenal transplantation inhibits expression of inducible nitric oxide synthase and nitric oxide production by cultured rat mesangial cells

BACKGROUND

Primary focal segmental glomerulosclerosis (FSGS) recurs in nearly 30% of patients who progress to end-stage renal disease and then receive a kidney transplant. A circulating plasma factor has been isolated from these patients that increases glomerular permeability to albumin in vitro. Because of the pivotal role of the mesangial cell in the accumulation of extracellular matrix (ECM) material within the glomerulus and the modulation of matrix protein synthesis by nitric oxide (NO), we examined the effect of the FSGS factor on inducible nitric oxide synthase (iNOS) expression and NO production by cultured rat mesangial cells (RMC).

METHODS

RMC were incubated with the supernatant following 70% ammonium sulfate precipitation of serum from patients with recurrent FSGS.

RESULTS

Addition of the FSGS factor to cultured RMC led to a significant inhibition of nitrite accumulation, an index of NO synthesis. There was a parallel decline in iNOS gene and protein expression. Sera obtained from control patients or those with minimal change nephrotic syndrome or diabetic nephropathy that was processed in the same manner as FSGS samples had no effect NO synthesis or iNOS activity. The inhibitory effect of the FSGS factor on NO production persisted despite addition of indomethacin (0.1-1 mumol/L) or cyclosporine (25 micrograms/mL) to test media.

CONCLUSIONS

These data indicate that the FSGS factor independently alters two aspects of glomerular function--permselectivity and matrix protein synthesis--by distinct mechanisms. FSGS factor-induced disturbances in iNOS gene and protein expression and NO production by mesangial cells may antagonize the antifibrotic effect of NO within the mesangium and contribute to progressive glomerulosclerosis in patients with primary FSGS.

Influence of alpha-tocopherol over the time course of experimental IgA nephropathy

The present study investigated the pathogenesis and the time course of kidney injury in experimental IgA nephropathy. In order to determine an appropriate period in the course of experimental IgA nephropathy to study renal injury and repair, we examined proteinuria and IgA deposition in the renal mesangium after 4, 8, and 16 weeks of mucosal challenge by bovine gamma globulins (BGG) provided in the drinking water. The hallmark of IgA deposition in the mesangium was present after 4 weeks and 8 weeks of BGG inoculation, but by 16 weeks, the mesangial IgA deposition had resolved. In addition, we confirmed our previous report on the beneficial effects of alpha-tocopherol in reducing proteinuria in IgA nephropathy at 8 weeks, and extended this observation to investigate the effects of dietary supplementation of alpha-tocopherol at both 4 weeks and 16 weeks. Proteinuria resolved spontaneously at 16 weeks. There is oxidative stress, as suggested by the elevation in plasma and renal malondialdehyde content, and increased fibrogenic cytokine message, as suggested by elevated transforming growth factor beta1 mRNA. These increases were clearly blunted by alpha-tocopherol at both 4 weeks and 8 weeks. Treatment with alpha-tocopherol was associated with a significant reduction in the severity of proteinuria. Thus, our data suggest that the period between 4 and 8 weeks of BGG vaccination could be relevant in designing an appropriate model to study the molecular biology of the pathogenesis of renal injury and the effects of treatment. The 16-week model may be useful in exploring gene expression involved with spontaneous resolution.

Pharmacological treatment of nephrotic syndrome

In the "minimal change" nephrotic syndrome (MCNS), steroids induce remissions in most cases (93% in children and 81% in adults). Response occurs in an average time of 11 days in children but may take up to 16 weeks in adults. The dose of prednisone is 60 mg/m(2)/day (maximum 80 mg/day) given usually for 4 weeks and then reduced to 40 mg/m(2) on alternate days for a few weeks. The medication may be discontinued abruptly at the end of the course of treatment. Children who do not respond to prednisone should be biopsied. Those whose biopsy shows minimal changes may have a remission with more prolonged alternate day treatment, or may need cyclophosphamide or cyclosporine. Relapses of nephrotic syndrome are common and usually respond to steroids given daily until remission, then on alternate days for 4 weeks. In adults prednisone on alternate days for 1 year after the presenting attack decreases the risk of relapse. Toxicity is a problem only in steroid-dependent patients who may require other drugs. Cyclophosphamide (2-3 mg/kg/day) and chlorambucil (0.15 mg/kg/day) for 8-12 weeks induce long-term remissions in 25-70% of children and are also beneficial in adults. The effectiveness of cyclophosphamide in steroid-resistant MCNS is limited to bringing about a faster remission. In children with MCNS who are initially steroid-responsive and later become resistant, cyclophosphamide usually induces a remission and restores steroid responsiveness. The toxicity of cyclophosphamide and chlorambucil in MCNS has generally been mild and reversible. It includes bone marrow depression, hemorrhagic cystitis, some hair loss, infertility and, extremely rarely, oncogenesis. The risk of gonadal toxicity is minimized with total doses below 200 mg/kg for cyclophosphamide and 7-10 mg/kg for chlorambucil. Seizures have been reported in 8% of children treated with chlorambucil. Cyclosporine (6 mg/kg/day initially) produces complete remissions in 85% of children and 79% of adults with steroid dependence and in 67% of children and 61% of adults with steroid resistance. Levamisole may be helpful in steroid-dependent cases, but data about its efficacy are conflicting. Cyclosporine and levamisole usually do not induce permanent remissions.

Magnetic resonance imaging in acute pyelonephritis

The diagnosis of acute pyelonephritis in children remains a clinical challenge. We assessed the feasibility of magnetic resonance imaging (MRI) detection of pyelonephritis in four pediatric patients and compared the results with renal cortical scintigraphy. MRI revealed areas of high signal intensity in the kidney that coincided with photon-deficient regions in the radionuclide scans in two children with acute pyelonephritis. These findings confirm work in experimental animals and indicate that MRI can accurately detect acute pyelonephritis in children.

Effects of fish oil and alpha-tocopherol in immunoglobulin A nephropathy in the rat

Alpha-tocopherol and fish oil have been reported to modulate the progression of IgA nephropathy in animals and humans. Because fish oil has been reported to exacerbate renal disease in subtotal nephrectomized rats, we investigated the effects of fish oil, with and without alpha-tocopherol, on the course of IgA nephropathy. Experimental IgA nephropathy was induced in male Sprague-Dawley rats, weighing 170-200 g, by oral and i.v. immunization with bovine gamma-globulin for 8 wk. IgA nephropathy was evidenced by hematuria, proteinuria, and IgA deposition in the mesangium. Standard rodent chow, containing 30 IU of alpha-tocopherol/kg of diet, was given to the control and IgA nephropathy rats. Fish oil (20% wt/wt), stripped of alpha-tocopherol preservative, was given to control and a second group of IgA nephropathy rats. Alternatively, corn oil or fish oil was supplemented with alpha-tocopherol at 100 IU/kg of diet and given to the third and fourth groups of IgA nephropathy rats. All animals were killed at 8 wk. Urinary protein excretion, plasma and kidney alpha-tocopherol concentrations, as well as glomerular planar area, and kidney transforming growth factor-beta1 mRNA were analyzed. As determined by reductions in proteinuria, glomerular planar area, and TGF-beta1 mRNA, fish oil with alpha-tocopherol ameliorated the renal injury induced by bovine gamma-globulin, whereas fish oil without alpha-tocopherol did not. Our findings support the importance of alpha-tocopherol, more so than fish oil, in mitigating the injury and promoting repair in experimental IgA nephropathy.

High glucose enhances growth factor-stimulated nitric oxide production by cultured rat mesangial cells

Nitric oxide (NO) contributes to the alterations in glomerular hemodynamics and extracellular matrix accumulation observed in diabetic nephropathy. High glucose concentrations directly inhibit NO production by rat mesangial cells (RMC). However, the role of peptide growth factors and chemokines in regulating NO synthesis by RMC under normal and high glucose conditions has not been studied. Therefore, we examined the effect of IGF-I, EGF, TGF-beta and RANTES on NO production by RMC maintained in normal (5.6 mM) or high glucose (33.3 mM) for 48 h. No synthesis was determined by measuring nitrite accumulation in conditioned media with the Greiss reaction. In normal glucose media, IGF-I, EGF, and RANTES had no effect on nitrite accumulation while TGF-beta inhibited NO synthesis. In high glucose conditions, IGF-I and EGF significantly enhanced NO production. The effects of RANTES and TGF-beta were unchanged by an elevated glucose concentration. EGF-induced stimulation of NO production in high glucose media was associated with parallel alterations in iNOS gene and protein expression. The modest enhancement in nitrite accumulation provoked by IGF-I in high glucose conditions was not accompanied by demonstrable increases in iNOS mRNA abundance or protein content. In conclusion, peptide growth factors modulate the direct inhibitory effect of high glucose on NO production by cultured mesangial cells. These actions in vivo may limit the adverse consequences of reduced NO production in promoting diabetic nephropathy.

Effect of vascular endothelial growth factor on nitric oxide production by cultured rat mesangial cells

Vascular endothelial growth factor (VEGF) stimulates nitric oxide (NO) production by endothelial cells in vitro and in vivo. However, the impact of VEGF on inducible nitric oxide synthase (iNOS) activity and NO synthesis in cultured mesangial cells is not known. Therefore, we measured nitrite accumulation in cytokine-stimulated, rat mesangial cells (RMC) in response to graded concentrations of VEGF. Addition of VEGF (10-50 ng/ml) did not alter RMC viability or NO production in either normal (5.6 mM) or high (33.3 mM) glucose conditions. Exposure of RMC to VEGF did not modify the effects of L-arginine (20 mM) or L-NAME (1 mM) on nitrite accumulation in normal or high glucose media. The steady state abundance of iNOS mRNA and the cytosolic content of iNOS protein were unaffected by addition of VEGF. Cultured RMC expressed the high-affinity tyrosine kinase VEGF receptors, flt and flk/KDR, and the levels were not modulated by incubation in normal or high glucose media. We conclude that VEGF does not regulate proliferation or NO production in cultured RMC. These findings suggest that disturbances in the normal interaction between VEGF and NO are not involved in the pathogenesis of abnormal mesangial cell structure or function in diabetic nephropathy.

Nitric oxide and inflammatory bowel disease: evidence for local intestinal production in children with active colonic disease

BACKGROUND

Active colitis in patients with inflammatory bowel disease is associated with mucosal vasodilation, increased intestinal permeability and abnormal colonic motility. Nitric oxide is a messenger molecule with many functions, including regulation of local blood flow, vasomotor tone, and inflammation. Increased nitric oxide production and inducible nitric oxide synthase activity have been demonstrated in experimental models of colitis. This study was designed to determine the relationship between nitric oxide production and colonic inflammation in children with active colitis and in control subjects and whether expression of inducible nitric oxide synthase protein is demonstrable in the intestinal epithelium of these patients.

METHODS

Nitrate + nitrite were measured in urine, stool, and plasma using the Griess assay. Expression of inducible nitric oxide synthase protein in intestinal tissue was determined by immunohistochemical localization.

RESULTS

Urinary nitrate + nitrite levels were not significantly different in patients and control subjects. In contrast, stool and plasma nitrate + nitrite concentrations were significantly higher in children with inflammatory bowel disease compared with levels in control children (stool: 162.4 +/- 31.0 mumol/l versus 77.2 +/- 22.1 mumol/l; plasma: 65.2 +/- 9.9 mumol/l versus 38.1 +/- 6.6 mumol/L; p < 0.05). Stool nitrate + nitrite levels significantly correlated with plasma values. Immunohistochemical staining of colonic tissue from children with inflammatory bowel disease demonstrated inducible nitric oxide synthase protein located exclusively in epithelial cells.

CONCLUSION

Increased nitric oxide production and enhanced intestinal epithelial cell expression of inducible nitric oxide synthase protein are associated with active colonic inflammation.

Mutations in the chloride channel gene, CLCNKB, cause Bartter's syndrome type III

Analysis of patients with inherited hypokalaemic alkalosis resulting from salt-wasting has proved fertile ground for identification of essential elements of renal salt homeostasis and blood-pressure regulation. We now demonstrate linkage of this phenotype to a segment of chromosome 1 containing the gene encoding a renal chloride channel, CLCNKB. Examination of this gene reveals loss-of-function mutations that impair renal chloride reabsorption in the thick ascending limb of Henle's loop. Mutations in seventeen kindreds have been identified, and they include large deletions and nonsense and missense mutations. Some of the deletions are shown to have arisen by unequal crossing over between CLCNKB and the nearby related gene, CLCNKA. Patients who harbour CLCNKB mutations are characterized by hypokalaemic alkalosis with salt-wasting, low blood pressure, normal magnesium and hyper- or normocalciuria; they define a distinct subset of patients with Bartter's syndrome in whom nephrocalcinosis is absent. These findings demonstrate the critical role of CLCNKB in renal salt reabsorption and blood-pressure homeostasis, and demonstrate the potential role of specific CLCNKB antagonists as diuretic antihypertensive agents.

High glucose inhibits nitric oxide production in cultured rat mesangial cells

Hyperglycemia directly contributes to the development of diabetic nephropathy. A high-serum glucose concentration alters intraglomerular hemodynamics and promotes deposition of extracellular matrix in the kidney. Nitric oxide (NO) is a short-lived messenger molecule that participates in the regulation of renal blood flow, GFR, and mesangial matrix accumulation. Therefore, in this study it was tested whether high glucose directly modulates NO synthesis by rat mesangial cells in vitro by measuring the accumulation of nitrite, the stable metabolite of NO, in the incubation media. Raising the external glucose concentration to 33.3 mM for 24 to 72 h reduced nitrite levels in cell supernatants in a time-dependent manner to a nadir of 14 +/- 3% of the amount in normal glucose media (5.6 mM) (P < 0.01). The decline in NO synthesis in high glucose media was paralleled by decreased cyclic guanosine monophosphate generation; however, there was no alteration in rat mesangial cell expression of inducible NO synthase protein. The suppressive effect of high glucose on NO production by mesangial cells was not modified by inhibition of protein kinase C (H-7), the addition of antioxidants (vitamin E or superoxide dismutase), or a pan-specific anti-transforming growth factor-beta antibody. An elevated ambient glucose caused a time-dependent reduction in mesangial cell L-arginine content. Addition of L-arginine (10 to 20 mM) to external media partially reversed the inhibitory effect of high glucose on mesangial cell NO production in a dose-dependent manner. The highest dose of L-arginine (20 mM) increased mesangial cell L-arginine content to comparable levels in normal and high glucose media. These results indicate that high glucose causes depletion of L-arginine in mesangial cells and compromises NO synthesis. Limitation in the metabolic precursor and other, as yet unidentified, factors act to reduce NO production by mesangial cells in the presence of an elevated ambient glucose level, a change that may play a role in the development of diabetic glomerulosclerosis.

The year 1995-1996 in review: genetically re-engineering clinical nephrology

The discipline of medical genetics is rapidly transforming the face of nephrology. A number of important advances have been made during the past year in the identification of the molecular basis of renal diseases. This article will summarize how these new findings have expanded our understanding of whether diseases are homogeneous or heterogeneous entities (Bartter's syndrome versus Gitelman's syndrome), the medical basis of certain diseases of unclear etiology (enuresis), and the nature of risk factors for disease occurrence or progression (IgA nephropathy, chronic renal failure, and hemolytic uremic syndrome). It is anticipated that these exciting discoveries will become routine in the near future as medical genetics is fully incorporated into the practice of clinical nephrology.

Diagnosis and treatment of chronic renal failure in children

This activity is designed for primary care and specialist physicians.

GOAL

To provide an overview of the unique features and treatment of chronic renal failure in children.

OBJECTIVES

1. Describe the diagnosis of chronic renal failure in children. 2. Discuss the medical treatment of chronic renal failure in children. 3. Understand the treatment of end-stage renal disease in children. 4. Discuss the financial impact of caring for a child with chronic renal failure.

Acute interstitial nephritis associated with IgA nephropathy in children

IgA nephropathy (IgAN) is a relatively common glomerulopathy in children and adolescents. The etiology of this disease is uncertain. We previously reported a child with IgAN who developed acute interstitial nephritis. We now describe three pediatric patients, including the index case, who had IgAN and who developed concomitant acute interstitial nephritis in association with renal functional impairment. We suggest that this histopathological lesion be considered in any child with IgAN and unexpectedly severe kidney dysfunction.

IgA nephropathy: to treat or not to treat?

IgA nephropathy (Berger's disease) is thought to be the most common primary glomerulonephritis in the world. Characteristically, it presents with intermittent macroscopic hematuria in association with upper respiratory infections. The diagnosis is established by demonstrating predominant IgA deposits in the glomerular mesangium. One third of the cases progress slowly over 25 years to glomerulosclerosis and end-stage renal disease. This rate of disease progression has not been altered by any known treatment, including the use of corticosteroids or cyclosporine. The pathogenesis of this disease is unknown; however, recent data implicated oxygen free radicals in the development of IgA nephropathy. The recent controlled, double-blind, 2-year study from the Mayo Clinic showed that fish oil slowed the progression of IgA nephropathy. This contrasts with the previous studies where the use of fish oil either accelerated the rate of deterioration of renal function in patients with IgA nephropathy or showed no change compared to untreated subjects. Furthermore, in experimental uremia, marked renal functional deterioration with fish oil administration has been reported. Experimental models of IgA nephropathy have been developed in the past few years. In addition, molecular biology offers an unique opportunity to study kidney tissue obtained from patients and animals with IgA nephropathy. These advances will enable the identification of the critical sequence of events that result in renal injury and provide new insight into the pathogenesis and progression of IgA nephropathy. This will help clarify the role of free oxygen radical release on disease progression, and an understanding on the mechanisms of antioxidants, such as vitamin E, in preventing such renal injury.

Chemically modified tetracyclines inhibit inducible nitric oxide synthase expression and nitric oxide production in cultured rat mesangial cells

Tetracyclines inhibit matrix metalloproteinases (MMP) and attenuate connective tissue degradation in a wide variety of human and animal disorders. Chemically modified tetracyclines (CMT) have been synthesized in which the antibacterial potency has been eliminated but in which the anti-MMP efficacy is retained. Nitric oxide (NO) modulates MMP synthesis and activity in mesangial cells in vitro. Therefore, we examined whether CMT inhibit iNOS gene and protein expression and NO production in cultured rat mesangial cells. Mesangial cells were maintained in media containing IFN-gamma and LPS for 24-72 h. Test media contained either no further additives or CMT-1, 3, 5, or 8 at concentrations of 1, 2.5, 5, and 10 micrograms/ml. iNOS gene and protein expression were assessed and NO production was determined by the Griess reaction. Incubation of mesangial cells with CMT-3 and CMT-8 resulted in time- and dose-dependent inhibition of NO production that was maximal at 48 h (< 20% of control) and at a drug concentration of 5 micrograms/ml (P < 0.05). Addition of CMT-1 had a modest (40%) inhibitory effect and CMT-5 did not alter NO production. The impact of CMT on NO production was directly related to their potency as collagenase inhibitors. Moreover, CMT-induced changes in NO synthesis were associated with parallel alterations in steady-state iNOS mRNA abundance and protein expression. These agents may be useful to ameliorate NO-dependent glomerular inflammation.

Renal tubular epithelial cell-E. coli interaction products stimulate nitric oxide production in cultured rat renal medullary interstitial and mesangial cells

Tubulointerstitial and periglomerular inflammation and fibrosis are important consequences of pyelonephritis. The pathogenesis of these abnormalities is not fully understood. Renal tubular epithelial cells (RTEC) elaborate biologically active materials following incubation with bacteria. Nitric oxide (NO) is an inflammatory mediator and it modulates the accumulation of extracellular matrix proteins. Therefore, we studied whether RTEC-E. coli interaction products regulate NO production by cultured rat renal medullary interstitial cells (RMIC) and mesangial cells (MC). RMIC and MC were maintained in media containing IFN-gamma and LPS for 24-72 h. Test media contained either no further additives or 20% supernatants from RTEC incubated with E. coli or bacterial cell products. RTEC-E. coli interaction products significantly increased NO production in RMIC and MC. This stimulation in NO production was not associated with changes in inducible nitric oxide synthase (iNOS) gene or protein expression. These findings indicate that RTEC-E. coli interaction products increase NO production in RMIC and MC by directly stimulating iNOS enzymatic activity. Altered NO production by renal cells may contribute to tubulointerstitial inflammation in acute and chronic pyelonephritis.

Nutritional intake in children with renal insufficiency: a report of the growth failure in children with renal diseases study

OBJECTIVE

This study was designed to assess sequentially the nutrient intake in children with chronic renal insufficiency and its relationship to body size, the level of renal failure, and growth velocity.

METHODS

The nutrient intake from 401 4-day food records obtained from 120 children with renal insufficiency over a 6-month observation period was analyzed. The height and weight were measured at the beginning and end of the observation period. The glomerular filtration rate was estimated from the height and serum creatinine.

RESULTS

The mean caloric intake in these children was 80 +/- 23% (mean +/- SD) of the Recommended Dietary Allowance (RDA) for age. Fifty-six percent of the food records obtained from these children revealed a caloric intake that was less than 80% of the RDA. Caloric intake expressed as the %RDA for age decreased with increasing age. However, the mean caloric intake when factored by body weight was in the normal range. There was no correlation between caloric intake and height velocity. The mean protein intake in these children was 153 +/- 53% of the RDA. Further, 45% of the food records indicated a protein intake greater than 150% of the RDA. There was no relationship between the degree of renal insufficiency and caloric or protein intake. Calcium, vitamin, and zinc intakes were also low.

CONCLUSIONS

Children with chronic renal failure consume less calories than their age matched peers, but the majority of these children appear to ingest adequate amounts for their body mass. This reduction in caloric intake occurs early in renal insufficiency. They also ingest inadequate amounts of calcium, zinc, vitamin B6, and folate.

Genetic heterogeneity of Bartter's syndrome revealed by mutations in the K+ channel, ROMK

Mutations in the Na-K-2Cl cotransporter (NKCC2), a mediator of renal salt reabsorption, cause Bartter's syndrome, featuring salt wasting, hypokalaemic alkalosis, hypercalciuria and low blood pressure. NKCC2 mutations can be excluded in some Bartter's kindreds, prompting examination of regulators of cotransporter activity. One regulator is believed to be ROMK, an ATP-sensitive K+ channel that 'recycles' reabsorbed K+ back to the tubule lumen. Examination of the ROMK gene reveals mutations that co-segregate with the disease and disrupt ROMK function in four Bartter's kindreds. Our findings establish the genetic heterogeneity of Bartter's syndrome, and demonstrate the physiologic role of ROMK in vivo.

Vitamin E ameliorates renal injury in an experimental model of immunoglobulin A nephropathy

IgA nephropathy is one of the most common forms of glomerular disease. Nearly 25% of affected patients progress to end-stage renal disease over a 20-25-y follow-up period. IgA-containing immune complexes stimulate oxygen-free radical production by mesangial cells in vitro. The excessive oxidant stress may mediate glomerular injury in this disorder. Therefore, we studied whether dietary supplementation with the antioxidant agent, vitamin E, attenuates renal disease in an experimental model of incipient IgA nephropathy with mild kidney inflammation. IgA nephropathy was induced in male Lewis rats by oral immunization with 0.1% bovine gamma-globulin (BGG)-containing drinking water for 8 wk. At the completion of this period, animals received BGG, 1 mg/dose i.v., on three successive days. Experimental rats (n = 10) received a specially formulated diet containing 100 IU of vitamin E/kg of chow, whereas control animals (n = 10) were fed chow containing 30 IU of vitamin/kg of chow. The BGG immunization regimen induced mesangial IgA deposition in all rats. Vitamin E supplementation resulted in a nearly 5-fold increase in the serum vitamin E concentration. Vitamin E-treated rats gained more weight and had a lower incidence of hematuria, 20% versus 80% (p < 0.03). Moreover, proteinuria was decreased by 50%, and reduced renal plasma flow was restored to normal, compared with untreated rats with IgA nephropathy. Glomerular hypertrophy occurred in animals with IgA nephropathy, but less so in those receiving vitamin E supplementation. Renal cortical malondialdehyde content was reduced from 1.55 +/- 0.10 to 1.22 +/- 0.09 nmol/mg of protein (p < 0.01) in rats fed the vitamin E-enriched diet. Finally, renal transforming growth factor-beta 1 gene expression was reduced by 34% in rats with IgA nephropathy receiving vitamin E treatment (p < 0.05). We conclude that experimental IgA nephropathy is associated with increased renal oxidant injury. Dietary treatment with the antioxidant agent, vitamin E, attenuated renal functional and structural changes in this experimental glomerulopathy. These studies support the importance of clinical trials for the evaluation of the efficacy of antioxidant therapy in patients with IgA nephropathy.

Esophageal dysmotility in children breast-fed by mothers with silicone breast implants. Long-term follow-up and response to treatment

Our aims were to determine the long-term clinical and manometric follow-up of 11 children with previously documented esophageal dysmotility, who had been breast-fed by mothers with silicone breast implants, their response to prokinetic agents, and to analyze changes in macrophage activation. Seven of 11 children had subjective clinical improvement. Weight/ height ratios remained the same or improved in 9/11. Biopsies at follow-up endoscopy were either normal or demonstrated mild esophagitis in 8/10. LES and UES pressures and percent propagation were not significantly different at follow-up, while wave amplitude significantly increased. Following intravenous metoclopramide, LES pressure, percent propagation, and wave amplitude significantly increased while UES pressure was unchanged. Urinary neopterin significantly decreased at follow-up, while urinary nitrates were unchanged. Esophageal dysmotility is chronic in this group of children, suggesting persistent autonomic nervous system dysfunction. Prokinetic agents may be useful in long-term management. The decreasing urinary neopterin levels suggest that, ultimately, there may be improvement in esophageal motility.

Growth in children with moderate renal insufficiency: measurement, evaluation, and treatment

Essential in the treatment of children with chronic renal insufficiency (CRI) is the elimination of growth deficits. With the prospect of recombinant human growth hormone (rhGH) and other adjunct treatment, the appropriate measurement and assessment of growth retardation and growth recovery will document continued progress toward eliminating this disabling condition. Phases and determinants of growth at different ages are best described by growth velocity patterns. Nutritional, hormonal, and metabolic determinants interact throughout each phase of growth. Potential for growth loss and recovery is greatest during infancy and early childhood, as shown by the growth velocity index (GVI) of change in height standard deviation score (SDS) (deltaHt - SDS) divided by the growth velocity - SDS (GV - SDS) (GVI = deltaHT - SDS/GV - SDS). An appropriate target height based on potential from mid-parental heights should be set before intervention to establish goals for duration of treatment. Ultimate adult height is the only true measurement of outcome, although predictive formulas based on parental heights and bone age versus chronologic age (BA/CA) are mathematic tools to gauge the efficacy of ongoing regimes. True catch-up growth is defined as the full recovery of lost percentiles and cannot be assumed with an increase in growth velocity or incremental gain in Ht-SDS.

Effect of triiodothyronine on nitric oxide production in mesangial cells and renal tubular epithelial cells

Nitric oxide (NO) is a signalling molecule that is produced by mesangial cells and renal tubular epithelial (RTE) cells. It plays a role in the regulation of glomerular and tubular function. In renal cells, NO is synthesized by the inducible isoform of the enzyme nitric oxide synthase (NOS). Thyroid hormone modulates the activity of neuronal NOS; therefore, we examined whether triiodothyronine (T3) stimulated the activity of inducible iNOS in mesangial cells, LLC-PK1 cells (analogue of the proximal tubule) and MDCK cells (analogue of the distal tubule). T3 (concentration range: 10(-10)-10(-7) M) had no effect on NO synthesis or iNOS protein expression by the three renal cell types. In addition, T3 did not modulate NO production in RAW 264.7 cells, a murine macrophage cell line, confirming that the hormone had no effect on iNOS activity. We conclude that, unlike its effect on neuronal NOS, T3 does not regulate iNOS activity in mesangial cells, RTE cells, or macrophages, and that the effects of T3 on renal cell growth and function are not mediated by inducible increases in NO synthesis.