Towards a biological characterization of focal segmental glomerulosclerosis.

The primary form of focal segmental glomerulosclerosis (FSGS) has become one of the most common causes of end-stage renal disease in children and adolescents. FSGS was initially considered to be the histological expression of a single disease entity. However, evidence accumulated during the past four decades indicates that FSGS is heterogeneous in nature. It therefore is not surprising that the many therapeutic combinations and permutations that have been tried have yielded variable results in different hands. This has generated substantial confusion and frustration among physicians and patients alike. Recent progress in genetics and molecular biology has opened promising new vistas of investigation. Identification of genes that control components of the glomerular capillary, proteins that form the structural basis of podocytes, and genetic mutations that affect the integrity of these structures has revolutionized our understanding of the glomerular filtration barrier. Substantial progress also has been made in understanding the mechanisms that lead to progression of renal disease and, ultimately, sclerosis. Studies of these factors are likely to yield a mechanistic-based classification of FSGS that will allow us to design therapeutic regimens suited to specific subtypes of this disease.

Effect of an oral Shiga toxin-binding agent on diarrhea-associated hemolytic uremic syndrome in children: a randomized controlled trial.

CONTEXT: Diarrhea-associated hemolytic uremic syndrome (HUS) is the most common cause of acute renal failure in children. Most cases are caused by an intestinal infection with Shiga toxin-producing strains of Escherichia coli. OBJECTIVE: To determine if administration of an oral agent that binds Shiga toxin could diminish the severity of diarrhea-associated HUS in pediatric patients. DESIGN, SETTING, AND PATIENTS: Multicenter, randomized, double-blind, placebo-controlled clinical trial of 145 children (96 experimental and 49 placebo) aged 6 months to 18 years with diarrhea-associated HUS conducted between July 27, 1997, and April 14, 2001, at 26 tertiary care pediatric nephrology centers in the United States and Canada. Trial included 2 phases, the hospital course for treatment of the acute illness and a 60-day outpatient follow-up period after discharge from the hospital. INTERVENTION: Patients were assigned to receive the binding agent, 500 mg/kg daily, or cornmeal placebo orally for 7 days in a 2:1 randomization scheme. MAIN OUTCOME MEASURES: Combined frequency of death or serious extrarenal events and need for dialysis in the experimental vs placebo group. RESULTS: A total of 62 patients (43%) were male and 123 (85%) were white. The median age of the patients was 4.2 years. Most patients (59%) were transferred from other hospitals to participating sites. The severity of disease at the time of randomization was comparable in the 2 groups. The prevalence of death or serious extrarenal events was 18% and 20% in the experimental and placebo groups, respectively (P =.82). Dialysis was required in 42% of experimental and 39% of placebo groups (P =.86). CONCLUSIONS: Oral therapy with a Shiga toxin-binding agent failed to diminish the severity of disease in pediatric patients with diarrhea-associated HUS.

Cell-matrix interactions modulate transepithelial phosphate transport in P(i)-deprived OK cells.

In opossum kidney (OK) cells as well as in kidney proximal tubules, P(i) depletion increases apical (A) and basolateral (B) Na(+)-dependent P(i) cell influxes. In OK cells' monolayers in contrast to proximal tubules, there is no increase in transepithelial P(i) transport. This limitation may be due to altered cell-matrix interactions. A and B cell (32)P(i) uptakes and transepithelial (32)P(i) and [(14)C]mannitol fluxes were measured in OK cells grown on uncoated or on Matrigel-coated filter inserts. Cells were exposed overnight to solution of either low (0.25 mM) or high (2.5 mM) P(i). When grown on Matrigel, immunofluorescence of apical NaPi4 (an isoform of the sodium-phosphate cotransporter) transporters increased and A and B (32)P(i) uptakes into P(i) depleted cells were five and threefold higher than in P(i) replete cells (P < 0.001). P(i) deprivation resulted in larger increase in A to B (4.6x, P < 0.001) than in B to A (3.5x, P < 0.001) P(i) flux and net P(i) transport from A to B increased 10-fold (P < 0.001). With P(i) depletion increases in B to A (3.4x) and A to B (3.3x) paracellular [(14)C]mannitol fluxes were similar, and its net flux was opposite to that of P(i). In cells grown on uncoated filters, transepithelial and paracellular unidirectional and net P(i) fluxes decreased or did not change with P(i) depletion, despite twofold increases in apical and basolateral P(i) cell influxes. In summary, Matrigel-OK cell interactions, particularly in P(i)-depleted cells, led to enhanced expression of apical NaPi4 transporters resulting in higher P(i) transport rates across cell boundaries; apical P(i) readily entered the transcellular transport pool and paracellular fluxes were smaller fractions of transepithelial P(i) fluxes. These Matrigel-induced changes led to an increase in net transepithelial apical to basolateral P(i) transport.

Parathormone sensitivity and responses to protein kinases in subclones of opossum kidney cells.

Parathyroid hormone (PTH) inhibits sodium-dependent phosphate (Na(+)-Pi) transport in the renal proximal tubule and opossum kidney (OK) cells by mechanisms involving protein kinases (PK) A and C, and 20-hydroxyeicosatetraneoic acid (20-HETE). The magnitude of the effect of PKA and PKC on Na(+)-Pi transport in OK cells varies in different studies, suggesting that OK cell subclones are functionally heterogeneous despite their morphological similarity. We studied the effect of PTH and PK effectors in two separate sets of OK cells at two different time periods. Each group of cells were derived from the same stock, at passages 75-85. In one group of OK cells 20-HETE (10(-7 )M) induced a 24% decrease in Na-(32)Pi transport. Addition of PTH (10(-7) M) inhibited Pi transport by 44%. Addition of TPA (10(-8) M) resulted in a 32% decrease in Na-(32)Pi transport. Exposure of cells to the PKC inhibitor staurosporine (10(-7) M) induced a significant increase in Na-(32)Pi transport. Simultaneous addition of 20-HETE and staurosporine restored baseline Pi transport. Finally, Br-cAMP (10(-7) M) inhibited Na-(32)Pi transport by 32%. In another group of OK cells we reexamined the affect of these substances on Na-(32)Pi transport. 20-HETE (10(-7) M) induced a significant increase (30%) in Na-(32)Pi transport. PTH (10(-7) M) had no effect on Na-(32)Pi transport (P = 0.05). TPA (10(-8) M) induced a 42% increase in Na-(32)Pi transport (P < 0.01). Staurosporine (10(-7) M) induced a slight decrease in Na-(32)Pi transport (P < 0.05). Simultaneous addition of 20-HETE and staurosporine restored Na-(32)Pi transport to baseline levels. Finally, Br-cAMP (10(-7) M) inhibited Na-(32)Pi transport by 23%. We conclude that different groups OK cells have markedly different responses to regulators of Na-Pi cotransport.

Twenty-one years of developmental nephrology: the kidney then and now.

Developmental renal physiology was guided for a long time by the notion that the "immature" kidney is characterized by glomerular-tubular imbalance, with glomerular preponderance. In accordance with this concept, the filtering capacity of the developing kidney exceeds the ability of the renal tubules to handle the filtrate, resulting in the urinary loss of substances such as amino acids and bicarbonate. Estimates of age-related changes in glomerular volume, based on measurements of glomerular diameter, and of proximal tubular volume, based on measurements of tubular length and tubular diameter, appeared to support this contention. The experimental approach that led to these conclusions was based on the assumptions that the increase in glomerular size is distributed evenly between the vascular and nonvascular elements and that tubular volume increases pari passu with the luminal surface area. Both assumptions were proved wrong. Moreover, micropuncture studies performed in guinea pigs and rats revealed that the proportionality between glomerular filtration and proximal reabsorption of fluid (i.e., glomerulo-tubular balance) is maintained throughout development. Subsequent studies showed that several transport mechanisms function quite adequately from the first days of extrauterine life. Sodium is avidly reabsorbed in distal nephron segments, under the stimulus of the high levels of aldosterone present during infancy. The increase in the secretion of potassium that would occur in the adult under these circumstances is mitigated by the low expression of potassium channels. In the case of phosphate, there is enhanced reabsorption, particularly at the level of the proximal tubule, due in part to a growth-specific NaPi type II transporter. These different adaptive mechanisms converge towards the maintenance of a positive external balance for substances that are essential to growth. The emergence of cellular and molecular biology has also encouraged research in the field of renal morphology. The genes that control mesenchymal-epithelial interactions and the signaling factors that mediate their effect have been described. Progress is being made in the identification of genes involved in certain forms of renal malformations. Novel methods of investigation, such as DNA arrays, are likely to lead to an even fuller, dynamic portrayal of gene expression during nephrogenesis. Characterizing the functional correlates of these genes will require investigators who are not only proficient in molecular biology, but who are also masters of physiological methods.