Stephen Futterweit

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% bovineγ-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-β1 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.

Increased urinary nitrite excretion in children with minimal change nephrotic syndrome

OBJECTIVE We tested the hypothesis that nitric oxide synthesis by the kidney is increased in children with primary nephrotic syndrome. METHODS We examined the urinary excretion of nitrite, a stable metabolite of nitric oxide, using the Griess reaction, in children with nephrotic syndrome. RESULTS In comparison with healthy children, patients with minimal change nephrotic syndrome had increased urinary nitrite excretion regardless of whether the disease was in relapse or remission (p < 0.025). In contrast, urinary nitrite excretion was similar in control subjects and patients with focal segmental glomerulosclerosis or IgA nephropathy. CONCLUSION These findings indicate that measurement of urinary nitrite excretion may be a useful test to help discriminate between minimal change nephrotic syndrome and focal segmental glomerulosclerosis in children with idiopathic nephrotic syndrome.

Taurine and osmoregulation. IV. Cerebral taurine transport is increased in rats with hypernatremic dehydration.

ABSTRACT: Taurine is an organic osmolyte in brain cells. We studied whether cerebral taurine transport is enhanced as part of the cell volume regulatory adaptation to hypernatremia. Hypernatremic dehydration was induced for 48 h. Synaptosomes, metabolically active nerve terminal vesicles, were isolated by homogenization of brain and purification on a discontinuous Ficoll gradient. Taurine transport was evaluated in vitro using a rapid filtration assay. After 48 h of hypernatremia, there was a 22.4% increment in Na+-specific taurine transport from 2.99 ± 0.16 to 3.66 ± 0.13 μmol/mg protein/30 min (p < 0.001). Dehydration for 48 h without hypertonic saline loading had no effect on taurine uptake. Glycine transport was unaltered by hypernatremia. The adaptation in taurine uptake resulted from an enhanced Vmax of the high affinity-low capacity transport system [265 ±17, control versus 337 ±19 nmol/min/ mg protein, experimental (p < 0.03)] without a change in the Km (≈60 μM). Under both control and hypernatremic conditions, Na+ and Cl− were required for maximal total Na+-mediated taurine uptake. Oubain (1 mM) decreased taurine uptake by 25%, whereas addition of β-alanine or hypotaurine (500 μM) to the external media reduced taurine transport by 45–65% in both control and experimental conditions (p < 0.01). Synaptosomal taurine uptake in hypernatremic rats was inhibited by 15–20% (p < 0.01) after addition of 4-acetamido-4′-isothiocyanostilbene-2,2′-disulfonic acid (0.1 mM) or 4,4′-diisothiocyanostiIbene-2,2′-disulfonic acid (0.1 mM) to the external medium. We conclude that hypernatremic dehydration of moderate severity and duration results in stimulation of brain taurine uptake, mediated by increased activity of the β-amino acid carrier. An intact anionic binding site is required for maximal taurine uptake during hypernatremia.

Angiotensin converting enzyme inhibitor therapy in children with Alport syndrome: effect on urinary albumin, TGF-β, and nitrite excretion

BackgroundAngiotensin converting enzyme inhibitors are routinely prescribed to patients with chronic kidney disease because of their known renoprotective effects. We evaluated the effect of short-term therapy with the angiotensin converting enzyme inhibitor, enalapril, in early Alport syndrome, defined as disease duration less than 10 years and a normal glomerular filtration rate.Methods11 children with early Alport syndrome were investigated. Two consecutive early morning urine specimens were collected at the start of the study for measurement of urinary creatinine, total protein, albumin, TGF-β, and nitrite excretion. Patients were treated with enalapril, ≅ 0.2 mg/kg/day, once a day for 14 days. Two early morning urine specimens were collected on days 13 and 14 of enalapril treatment and two weeks later for measurement of urinary creatinine, total protein, albumin, TGF-β, and nitrite excretion.ResultsPrior to treatment, urinary excretion of transforming growth factor-β and nitrite, the major metabolite of nitric oxide, was within normal limits in all patients. Administration of enalapril for 2 weeks did not alter urinary albumin, transforming growth factor-β, or nitrite excretion.ConclusionThese findings suggest that early Alport syndrome represents a disease involving exclusively intrinsic glomerular barrier dysfunction. At this stage of the illness, there is no evidence of angiotensin II-mediated proteinuria or increased production of transforming growth factor-β and, therefore, routine treatment with an angiotensin converting enzyme inhibitor may not be warranted.

The Effect of Recombinant Human Insulin-Like Growth Factor-I on Chronic Puromycin Aminonucleoside Nephropathy in Rats

We recently demonstrated that recombinant hGH exacerbates renal functional and structural injury in chronic puromycin aminonucleoside (PAN) nephropathy, an experimental model of glomerular disease. Therefore, we examined whether recombinant human (rh) IGF-I is a safer alternative for the treatment of growth failure in rats with chronic PAN nephropathy. The glomerulopathy was induced by seven serial injections of PAN over 12 wk. Experimental animals(n = 6) received rhIGF-I, 400 μg/d, whereas control rats(n = 6) received the vehicle. rhIGF-I improved weight gain by 14%(p < 0.05), without altering hematocrit or blood pressure in rats with renal disease. Urinary protein excretion was unaltered by rhIGF-I treatment in rats with chronic PAN nephropathy. After 12 wk, the inulin clearance was higher in rhIGF-I-treated rats, 0.48 ± 0.08versus 0.24 ± 0.06 mL/min/100 g of body weight in untreated PAN nephropathy animals, p < 0.05. The improvement in GFR was not associated with enhanced glomerular hypertrophy or increased segmental glomerulosclerosis, tubulointerstitial injury, or renal cortical malondialdehyde content. In rats with PAN nephropathy, administration of rhIGF-I increased IGF-I and GH receptor gene expression, without altering the steady state level of IGF-I receptor mRNA. In normal rats with intact kidneys, rhIGF-I administration (n = 4) did not alter weight gain, blood pressure, proteinuria, GFR, glomerular planar area, renal cortical malondialdehyde content, or glomerular or tubulointerstitial damage, compared with untreated animals (n = 4). rhIGF-I treatment reduced the steady state renal IGF-I mRNA level but did not modify gene expression of the IGF-I or GH receptors. We conclude that: 1) administration of rhIGF-I improves growth and GFR in rats with chronic PAN nephropathy and 2) unlike rhGH, long-term use of rhIGF-I does not worsen renal functional and structural injury in this disease model.

Vascular Endothelial Growth Factor (VEGF) does not Regulate Nitric Oxide (NO) Production by Cultured Rat Mesangial Cells (RMC) 1845

Mesangial cells contain the enzyme inducible nitric oxide synthase (iNOS) and produce NO after exposure to cytokines. This short-lived messenger molecule is involved in the regulation of many aspects of kidney function. VEGF modulates NO production by endothelial and vascular smooth muscle cells. Moreover, VEGF may contribute to vascular injury in diabetes. Human mesangial cells express the VEGF receptors and the cytokine stimulates proliferation. Therefore, we examined whether VEGF regulates NO production by cultured mesangial cells.

FOCAL SEGMENTAL GLOMERULOSCLEROSIS (FSGS) FACTOR REDUCES EXPRESSION OF INDUCIBLE NITRIC OXIDE SYNTHASE (iNOS) AND PRODUCTION OF NITRIC OXIDE (NO) IN RAT MESANGIAL CELLS (RMC) |[dagger]| 1696

Nearly 25% of patients with FSGS develop recurrent disease following renal transplantation. A plasma factor has been isolated from these patients which increases glomerular permeability to protein in vitro. NO modulates renal hemodynamics and extracellular matrix production. Therefore, we studied whether the FSGS plasma factor alters NO synthesis by RMC.

EFFECT OF TRIIODOTHYRONINE (T3) ON NITRIC OXIDE (NO) PRODUCTION IN MESANGIAL CELLS (MC) AND RENAL TUBULAR EPITHELIAL (RTE) CELLS. |[dagger]| 2211

T3 regulates renal cell growth and tubular transport, NO is synthesized by MC and RTE using the enzyme inducible nitric oxide synthase (NOS) and may mediate the effects of T3. Therefore, we conducted experiments to ascertain the interaction between T3 and renal cell NO production.

Taurine and osmoregulation: An assessment using in vivo and in vitro experimental systems

Taurine, 2-aminoethane sulfonic acid, is present in nearly all body tissues and frequently is the most abundant free amino acid in the cytosol [1]. In invertebrate marine species, taurine serves an osmoregulatory role to maintain cell volume constant in the face of fluctuations in environmental osmolality [2]. In mammals, there is also circumstantial evidence in favor of a cerebral osmoprotective function of taurine. It is known that the brain content of taurine varies in direct relationship to the serum Na+ concentration in rats with chronic hyponatremia and hyper-natremia [3,4]. In order to gain a more complete picture of the role of taurine in osmoregulation, we conducted the following experiments with two goals in mind; 1) to directly evaluate the importance of taurine in cerebral osmoregulation by studying the impact of dietary manipulation of brain taurine content on animal tolerance of chronic hypo- and hypernatremia. Cats were utilized in these experiments since their limited capacity to synthesize taurine and obligatory use of this amino acid in bile conjugation make them critically dependent on taurine administration in the diet [5]; 2) to determine whether the contribution of taurine to cerebral osmoregulation during chronic hypo- and hypernatremia involves an adaptive increase in transmembrane taurine flux in brain synaptosomes. These are sealed, metabolically active, neuronal membrane fragments that can be used in in vitro assay systems to evaluate intrinsic changes in membrane function [6].