Relation of tubular interstitial disease to renal function

In vitro concentrative transport of PAH-3H was evaluated in human renal biopsies by section freeze-dry autoradiography. Renal cortical tissue obtained by biopsy was incubated in vitro in medium containing PAH-3H, and section freeze-dry autoradiographs prepared. The autoradiographs demonstrated that the number of proximal tubules which accumulate PAH-3H in vitro varies inversely with the amount of tubular interstitial disease and directly with glomerular filtration rate. In order to further examine the mechanisms of tubular-interstitial disease, we have developed a technique for simultaneous fluorescent microscopy and autoradiography in single freeze-dried sections. This technique permits evaluation of the relationship between concentrative transport and immunoglobulin deposition in individual tubules and should increase our knowledge of the biologic significance of immunoglobulin deposits in proximal tubules.

Fifty years of Balkan endemic nephropathy: daunting questions, elusive answers

Balkan endemic nephropathy (BEN) has remained a geographically constant endemic for 50 years. Despite extensive research, its etiology remains unknown. In the current issue, in a study in one of the earliest sites where the endemic was first recognized, Dimitrov et al. confirm the persistance of the endemic into a new generation and also identify a maternal link in the pathogenesis of BEN. This intriguing finding needs to be confirmed in other endemic areas.

Acute tubulointerstitial nephritis after wasp stings

A 61-year-old Caucasian man presented with acute renal failure after multiple wasp stings. The patient required dialysis support temporarily. Work-up failed to show rhabdomyolysis or hemolysis and a kidney biopsy revealed acute allergic interstitial nephritis. The patient's renal function recovered completely after a short course of steroid therapy. Acute renal failure after wasp stings is typically caused by acute tubular necrosis in the setting of hemolysis or rhabdomyolysis. Compared with previously reported cases of acute renal failure associated with bee stings, our patient is unique in that his renal failure was caused by a hypersensitivity reaction apparently to the wasp venom.

Cytotoxicity of myeloma light chains in cultured human kidney proximal tubule cells

We evaluated the effect of eight species of light chains on cultured human kidney proximal tubule cell proliferation. Exposure to light chains for 48 hours caused dose-dependent inhibition in tritium ((3)H)-thymidine incorporation by simian virus 40 immortalized human proximal tubule cells, although the effect was variable among different species of light chains. We studied cytotoxic effects of selected toxic light chains in further detail. Two of these light chains caused significant DNA degradation. A lambda-light chain caused lactate dehydrogenase release from exposed cells at 48 hours, but not at 24 hours. Cytomorphological and electron microscopic examination of cells exposed to light chains for 24 hours showed condensed nuclei, cell detachment, paucity of mitotic activity, and apoptosis, and at 48 hours of exposure, changes consistent with necrosis. Apoptosis assay by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling method showed a sixfold increase in the number of apoptotic cells exposed to the same lambda-light chain for 24 hours. Rhodamine-phalloidin staining showed variable but significant disruptions in the actin cytoskeleton. These studies show that some myeloma light chains are toxic to cultured human proximal tubule cells and induce cytoskeletal injury and DNA damage consistent with apoptosis followed by secondary necrosis. Direct proximal tubule cell toxicity may be an important mechanism of renal involvement in multiple myeloma.

Inhibition of Na-K-ATPase activity and gene expression by a myeloma light chain in proximal tubule cells

BACKGROUND

Light chain nephrotoxicity is frequently associated with Fanconi syndrome characterized by amino-aciduria, glycosuria, phosphaturia, and bicarbonaturia. The mechanisms of these transport abnormalities are unknown. To determine the role of Na-K-ATPase, we examined the effects of a lambda-light chain on both the activity and gene expression of Na-K-ATPase in primary cultures of rat proximal tubule cells.

METHODS

The lambda-light chain used here was isolated from urine of a patient with multiple myeloma and previously shown to inhibit sodium-dependent phosphate and glucose transport in proximal tubule cells. Na-K-ATPase was determined spectrophotometrically and the gene expression by Northern analysis in cells exposed to light chain.

RESULTS

In cells exposed to 200 mumol/L light chain Na-K-ATPase activity was reduced significantly, up to 73%, at 2, 24, and 48 hours compared with control cells (N = 12, P < 0.001). Northern analysis showed that in cells exposed to light chain for 24 and 48 hours the message for the alpha-1 isoform of Na-K-ATPase was suppressed significantly compared with control cells. The messages for GAPDH, beta-actin, and 28 S RNA in light chain exposed cells were also depressed in comparison with control cells. This light chain also significantly inhibited thymidine incorporation by proximal tubule cells in a dose-dependent manner.

CONCLUSIONS

These data suggest a general toxicity to cells by this light chain and indicate that inhibitory effects on both the activity and gene expression of Na-K-ATPase may be an important mechanism of light chain cytotoxicity on proximal tubule cells.

Cyclosporine-associated thrombotic microangiopathy in renal allografts

BACKGROUND

The association between cyclosporine (CsA) and thrombotic microangiopathy (TMA) in renal allografts is well documented. However, predisposing factors and therapy guidelines are not adequately characterized.

METHODS

We reviewed 188 patients with kidney or kidney-pancreas transplants who were treated between January 1994 and December 1996 with prednisone, CsA, or tacrolimus, and azathioprine or mycophenolate. We analyzed 50 patients who had graft biopsies: 26 with TMA and 24 with no TMA, as well as 19 patients with well-functioning grafts who never required biopsy.

RESULTS

TMA was observed in 26 of 188 renal graft recipients (14%). TMA was confined to the allograft kidney without any systemic evidence in 24 of the 26 patients. At the time of the diagnosis of TMA, 24 of the patients were on CsA, with 19 on the microemulsion form. Conversely, 5 of 18 control patients with no graft dysfunction were on the microemulsion form of CsA (P = 0.0026). Graft loss was seen in 8 of 26 patients with TMA. Conversion from CsA to tacrolimus resulted in a one-year salvage of graft function in 13 of 16 (81%) patients.

CONCLUSIONS

TMA was the cause of renal graft dysfunction in 14% of renal graft recipients and was associated with the use of the microemulsion form of CsA. Systemic signs of TMA were rare, underscoring the importance of the graft biopsy in making the diagnosis. The most successful strategy was switching from CsA to tacrolimus, with good graft function in 81% of the recipients one year after the TMA episode.

Myeloma light chains are ligands for cubilin (gp280)

Although myeloma light chains are known to undergo receptor-mediated endocytosis in the kidney, the molecular identity of the receptor has not been characterized. We examined the interaction between cubilin (gp280) and four species of light chains isolated from the urine of patients with multiple myeloma. Four lines of evidence identify cubilin, a giant glycoprotein receptor, which is restricted in distribution to endocytic scavenger pathways and which has potent effects on endosomal trafficking, as a potentially physiologically relevant binding site for light chains: 1) light chains coeluted during immunoaffinity purification of cubilin; 2) polyclonal antisera to cubilin but not control sera, displaced human light chain binding from rat renal brush-border membranes; 3) cubilin bound to multiple species of light chains during surface plasmon resonance; 4) anti-cubilin antiserum interfered with light chain endocytosis by visceral yolk sac epithelial cells. However, both binding of light chains to brush-border membranes and endocytosis of light chains by yolk sac epithelial cells were only partially inhibited by anticubilin antibodies, suggesting presence of additional or alternate binding sites for light chains. Excess light chain had a potent inhibitory effect on endosomal fusion in vitro. Binding showed dose and time-dependent saturability with low-affinity, high-capacity equilibrium binding parameters. These data demonstrate that cubilin plays a role in the endocytosis and trafficking of light chains in renal proximal tubule cells.

Receptor-mediated endocytosis of immunoglobulin light chains by renal proximal tubule cells

We examined the binding, endocytosis, and degradation of immunoglobulin light chains by primary cultures from rat renal kidneys and immortalized human proximal tubule cells. Both the association and dissociation of light chain were rapid and plateaued within 30 min at 4 degrees C. Up to 10(-3) M bovine serum albumin did not inhibit light chain binding to cells. Internalization studies with 125I-labeled kappa- and lambda-light chains by cells using the acid wash technique showed that up to 80% of total cell-associated binding at equilibrium (30 min) is rapidly internalized at 22 degrees C. Comparison of binding and internalization of light chains with transferrin, a ligand known to undergo receptor-mediated endocytosis, showed that both ligands displayed saturable kinetics. In contrast, endocytosis of sucrose, a marker for fluid-phase endocytosis, was unsaturable and nearly 200-fold less efficient than light chain internalization. Scatchard analysis of binding experiments done at 4 degrees C with trace 125I-labeled lambda-light chain in presence of 0 to 3.0 x 10(-3) M cold light chain revealed a single class of binding sites with a dissociation constant of 5.0 +/- 0.8 x 10(-5) and a maximal binding capacity of 1.6 +/- 0.3 x 10(-9) mol/mg cell protein. Hypertonic medium, a maneuver which interferes with the formation of the clathrin lattice, reduced endocytosis of light chain significantly but did not affect endocytosis of sucrose. Chloroquine and bafilomycin A, agents that interfere with vesicular acidification, also significantly suppressed light chain endocytosis. Using acid precipitation method, we observed that endocytosis of 125I-labeled lambda-light chain results in degradation by the rat renal proximal tubule cells. Degradation was maximum at 37 degrees C, significantly reduced at 22 degrees C, and absent at 4 degrees C. Excess light chain inhibited degradation of radiolabel, whereas excess albumin had no effect. These studies document the presence of binding sites for light chains on proximal tubule cells that mediate endocytosis of light chains by proximal tubule cells. The present data suggest that receptor-mediated endocytosis of light chains leads to delivery of this ligand to degradative sites through acidified vesicles.

A 31-year-old woman with lupus erythematosus and fatal multisystem complications

A 31-year-old woman with systemic lupus erythematosus presented with respiratory and renal symptoms followed by abdominal pain and seizure. Clinical diagnoses of lupus pneumonitis, nephritis, vasculitis, and cerebritis were made. The patient had a progressively downhill course with pancytopenia and hemolysis treated with aggressive immunosuppressive therapy and extended plasmapheresis. Lupus pneumonitis leading to diffuse alveolar damage was the immediate cause of death. Diffuse proliferative lupus nephritis was seen in the biopsy, and the autopsy demonstrated thrombotic microangiopathy. Extra-renal complications of lupus and response to therapy are discussed in the format of a Tulane Clinicopathologic Conference.

Phosphate transport inhibition by KW-3902, an adenosine A1 receptor antagonist, is mediated by cyclic adenosine monophosphate

We have previously demonstrated that 1,3-dipropyl-8-(3-noradamantyl) xanthine (KW-3902) has an inhibitory effect on phosphate (Pi) transport with no effect on glucose transport in the rat renal proximal tubular cell, similar to that of parathyroid hormone (PTH). In the current studies we investigated the effect of KW-3902, rat PTH (1-34), and 1,3-dipropyl-8-cyclopentylxanthine (DPCPX), another selective adenosine A1 receptor antagonist, on Pi transport and the production of cyclic adenosine monophosphate (cAMP). We then compared these effects of KW-3902 with those of rat PTH in rat renal proximal tubule cells. The results showed that both KW-3902 (30 mumol/L) and rat PTH (1-34, 5 mumol/L) significantly inhibited Pi uptake in proximal cells from a control level of 61 +/- 3 to 19 +/- 3 (a reduction of 69%) and 46 +/- 4 picomoles phosphate/mg protein/min (a reduction of 25%), respectively (P < 0.01). The inhibitory effect of 30 mumol/L KW-3902 alone on Pi transport was more than twice that of 5 mumol/L rat PTH (1-34) alone (P < 0.01). KW-3902 stimulated the production of cAMP in a dose-dependent manner (r = 0.997, P < 0.01). Rat PTH (1-34; 5 mumol/L) also stimulated cAMP production, which was greater than that induced by 30 mumol/L KW-3902 alone. A significant increase in cAMP production by 30 mumol/L DPCPX was also observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Low-molecular-weight protein competition for binding sites on renal brush border membranes

Immunoglobulin light chains, beta 2-microglobulin, insulin, and lysozyme are low-molecular-weight proteins (LMWP) shown to bind to renal brush border membranes. Competition among these proteins and the role of electrical charge in binding to brush border membranes have not been resolved. To investigate these factors, we performed displacement experiments with [125I]-labeled beta 2-microglobulin (pI = 5.6) using six species of LMWP over a pI range of 4.4-11.0. The inhibition constants, Ki, of these six competing ligands, kappa- and lambda-light chains, lysozyme, insulin, cytochrome c, and myoglobin, determined from the log displacement curves, ranged from 4 x 10(-5) to 8 x 10(-4) M. These experiments show marked cross-competition among LMWP for binding to brush border membranes. There was no correlation between Ki and pI indicating that the molecular structure is a more important determinant of LMWP binding to brush border membranes than net electrical charge.

Effect of myeloma light chains on phosphate and glucose transport in renal proximal tubule cells

Primary cultures of cells derived from the rat proximal tubule were exposed to up to 200 microM lambda- or kappa-light chain obtained from myeloma patients. Light chains inhibited the uptake of both phosphate and glucose by the cells while albumin had no effect. The half-maximal inhibitory concentration (IC50) of both the lambda- and kappa-light chains on phosphate transport were similar, 34 and 35 microM respectively. The IC50 of the kappa-light chain on glucose transport was 360 microM. The inhibitory effect of light chains was dose-dependent (r = 0.90, p < 0.01 for the lambda-light chain and r = 0.93, p < 0.001 for the kappa-light chain, on phosphate transport; and r = 0.93, p < 0.001 for glucose transport). Dixon and Line-weaver-Burk plot analyses were characteristic for noncompetitive inhibition. The inhibition constant 89 microM for phosphate uptake derived from the Dixon plot was similar to the IC50 calculated from the dose-response curves. These findings indicate that light chains, at concentrations found in the tubule fluid of a typical myeloma patient, are potent inhibitors of phosphate and glucose transport in proximal tubular cells, and that direct cell toxicity is a major mechanism of light chain nephrotoxicity.

Effect of KW-3902, a novel adenosine A1 receptor antagonist, on sodium-dependent phosphate and glucose transport by the rat renal proximal tubular cell

KW-3902, 1,3-dipropyl-8-(3-noradamantanyl)xanthine, is a novel potent and selective adenosine A1-receptor antagonist. KW-3902 has been found to cause significant diuresis and natriuresis. To investigate the action of this adenosine A1-receptor antagonist on phosphate transport in renal proximal tubular cells, we studied its effect on the uptake of phosphate by the cultured rat renal proximal tubular cell. KW-3902 significantly inhibited sodium-dependent uptake of phosphate at 10 minutes. The inhibitory effect was dose-dependent with maximum effect achieved at a KW-3902 concentration of 3 x 10(-5) M in the uptake media. The half-maximal inhibitory concentration, IC50, of KW-3902 on phosphate uptake was 2 x 10(-6) M. Dixon plot analysis of the uptake data was consistent with pure non-competitive inhibition. The inhibition constant, Ki, of 6.2 x 10(-6) M for phosphate transport, derived from the Dixon plot, was in close agreement with the IC50 calculated from a semilog dose response curve. Sodium-dependent glucose transport was not affected by KW-3902. These findings reveal that KW-3902 has a direct and specific inhibitory effect on phosphate uptake in renal proximal tubules.

Lead nephropathy, gout, and hypertension

The EDTA (calcium disodium edetate) lead mobilization test revealed lead as the probable cause of renal disease in industrial lead workers and in patients with gout or essential hypertension. The data reviewed here demonstrate persistence of lead nephropathy in the contemporary scene despite the introduction of modern industrial and environmental exposure standards. Renal function and biopsy studies showed that lead nephropathy is a chronic tubulointerstitial renal disease with modest proteinuria which frequently presents with hyperuricemia, gout and hypertension. Only evaluation of body lead stores by either the EDTA lead mobilization test or by x-ray fluorescence is helpful in diagnosing lead nephropathy. While chelation therapy is safe and helpful in reversing early lead nephropathy, the best treatment is prevention. These studies further raise the possibility that chronic environmental lead poisoning and associated renal disease and hypertension may be a more widespread problem than suspected. Assessment of the true extent of chronic lead poisoning requires large scale epidemiological studies.

Possible pathogenetic role of low-molecular-weight proteins in Balkan nephropathy

Balkan endemic nephropathy (BEN) is a tubulointerstitial disease characterized by increased-low-molecular-weight protein (LMWP), most notably, beta 2-microglobulin (beta 2m) excretion in urine. We previously demonstrated that two species of LMWPs, immunoglobulin light chains (LC) and recombinant alpha interferon (rIF), are toxic at proximal tubule cell membrane level. Myeloma LCs and rIF inhibit Na-dependent uptake of 14C-L-alanine and 14C-D-glucose by rat renal brush border membrane (BBM) vesicles at half-maximal inhibitory concentrations, IC50, ranging from 68 to 140 microM for LCs, and 5.4 to 18 nM for rIF. We further demonstrated that LCs bind to high-capacity, low-affinity sites on BBM with dissociation constants (Kd) ranging from 16 to 118 microM, a range similar to IC50s observed with the same LCs. Binding site occupancy is inversely related to alanine (r = -0.95, P less than 0.01), and glucose uptake (r = -0.96, P less than 0.01), implying that LC nephrotoxicity is determined by its binding to BBM. beta 2m shares behavioral and structural similarities with both LC and rIF. Preliminary studies in our laboratory showed that unlabeled LCs compete for the same binding sites on BBM with beta 2m. These observations confirm that all LMWP, including beta 2m, are potentially nephrotoxic. Thus, the characteristic beta 2-microglobulinuria of BEN may be more than a consequence of tubular dysfunction, and may play a pathogenetic role.

Light-chain binding sites on renal brush-border membranes

Immunoglobulin light chains are low-molecular-weight proteins filtered at the renal glomerulus and catabolized within the proximal tubular epithelium. Excessive production and urinary excretion of light chains are associated with renal dysfunction. They also interfere with proximal renal tubule epithelial functions in vitro. We studied the binding of 125I-labeled kappa- and lambda-light chains, obtained from the urine of multiple myeloma patients, to rat and human renal proximal tubular brush-border membranes. Light-chain binding to brush borders was also demonstrated immunologically by flow cytometry. Computer analysis of binding data was consistent with presence of a single class of low-affinity, high-capacity, non-cooperative binding sites with relative selectivity for light chains on both rat and human kidney brush-border membranes. The dissociation constants of light chains ranged from 1.6 X 10(-5) to 1.2 X 10(-4) M, and maximum binding capacity ranged from 4.7 +/- 1.3 X 10(-8) to 8.0 +/- 0.9 X 10(-8) (SD) mol/mg protein at 25 degrees C. Kappa- and lambda-light chains competed with each other for binding with comparable affinity constants. Competition by albumin and beta-lactoglobulin, however, was much weaker, suggesting relative site selectivity for light chains. These binding sites probably function as endocytotic receptors for light chains and possibly other low-molecular-weight proteins.

Hyponatremia and hypouricemia: differentiation from SIADH

Hypouricemia in coexistence with hyponatremia often differentiates the syndrome of inappropriate secretion of antidiuretic hormone (SIADH) from most other causes of hyponatremia. We report clearance studies in 5 cases of hyponatremia and hypouricemia that were not due to SIADH. One had metastatic pancreatic carcinoma with ascites, edema, hypoalbuminemia and hypophosphatemia. Two had adenocarcinoma of the lung with metastasis to the brain in 1, 1 had disseminated cryptococcus and 1 had Hodgkin's disease. None received radiation or known nephrotoxins at least 4 months prior to study. None had serum creatinine greater than 106.1 mumol/l (1.2 mg/dl). Two had postural hypotension and hyponatremia that responded to saline therapy. Fluid restriction corrected the hyponatremia in all patients, but the hypouricemia, high fractional excretion (FE) of urate, and high urine sodium concentration persisted. In 2 patients studied, ADH was appropriately suppressed after volume repletion but there was a defect in free water clearance due to high renal solute excretion. In contrast to patients with SIADH who correct their defect in renal urate transport with correction of hyponatremia by water restriction, our patients appear to have a persistent renal urate transport defect and abnormality in sodium conservation. Elevated FE urate of greater than 10% after correction of hyponatremia can thus differentiate these patients from SIADH. The diametrically opposing goals of fluid therapy emphasize the importance of differentiating one group from the other.

Effect of alpha interferon on glucose and alanine transport by rat renal brush border membrane vesicles

To investigate the pathogenetic mechanisms of interferon nephrotoxicity, we studied the effect of recombinant interferon alfa-2b on the uptake of 14C-D-glucose and 14C-L-alanine by rat renal brush-border-membrane vesicles. Interferon significantly inhibited 20 sec. sodium-dependent and 5 and 10 min. equilibrium uptake of both glucose and alanine. The inhibitory effect was dose dependent with maximum effect achieved at interferon concentration of 5 X 10(-8)M in the uptake media. The half-maximal inhibitory concentrations, IC50, of interferon on glucose uptake was 1.8 X 10(-8)M, and 5.4 X 10(-9)M on alanine uptake. Dixon plot analysis of uptake data was consistent with pure non-competitive inhibition. The inhibition constants, Ki, 1.5 X 10(-8)M for glucose uptake, and 7.3 X 10(-9)M for alanine uptake, derived from Dixon plots were in close agreement with the IC50s calculated from the semilog dose response curves. These observations reveal that direct interactions at the proximal tubule cell membrane are involved in the pathogenesis of interferon nephrotoxicity, and that its mechanism of nephrotoxicity is similar to that of other low molecular weight proteins.

Lead increases red cell sodium-lithium countertransport

The effect of 1, 3, 5, and 20 mumol/L lead on normal red cell sodium-lithium countertransport was studied in vitro. Red cell suspensions incubated with lead had increased sodium-lithium countertransport at all concentration levels compared with paired, unleaded controls when all groups were evaluated by analysis of covariance (F = 19.2, P less than 0.001). The effect of lead was concentration dependent (r = 0.998, P less than 0.001). These observations suggest that abnormalities in sodium transport are involved in the pathogenesis of lead-induced hypertension. Because increased red cell sodium-lithium countertransport is characteristic of essential hypertension, these observations further suggest that lead-induced and essential hypertension may share common pathophysiological mechanisms.

Effects of chronic peritoneal dialysis on thyroid function tests

Peritoneal dialysis is associated with large losses of protein. In order to quantify thyroid hormone excretion in the dialysate and to examine the possibility that peritoneal dialysis may result in clinical hypothyroidism, nine endstage renal disease (ESRD) patients undergoing either continuous ambulatory peritoneal dialysis (CAPD) or chronic intermittent peritoneal dialysis (IPD) were studied. Total protein excretion in the peritoneal fluid was 21.5 +/- 2.1 g/24 h and did not vary with the mode of peritoneal dialysis. Thyroid binding globulin (TBG) excretion was 6.4 +/- 1.3 mg/24 h, higher than the values reported in the literature for urinary TBG excretion in patients with the nephrotic syndrome. Despite the higher TBG losses, serum TBG remained in the normal range. Mean peritoneal total T4 and T3 were 8.1 +/- 1.6 micrograms/24 h and 89.5 +/- 14.6 ng/24 h, and there was a significant correlation between peritoneal T4 and TBG (r = 0.69; P less than 0.01) and between peritoneal total proteins and T4 (r = 0.80; P less than 0.001). Despite the finding that large amounts of protein are lost in peritoneal fluid, T4 and T3 losses were relatively modest and remained below their daily production rates, and none of the patients were overtly hypothyroid. Serum thyroid stimulating hormone (TSH) was mildly elevated in three of nine patients and was consistent with early thyroid failure. The patients' serum iodine levels were higher than normal but did not predict the patients' thyroid status. We conclude that major protein losses could predispose patients undergoing CAPD to thyroid failure and that long-term follow-up of thyroid function is warranted in these patients.

Light chain effects on alanine and glucose uptake by renal brush border membranes

Effect of varying concentrations (0 to 800 microM) of three different light chains on sodium-dependent L-(14C)alanine and D-(14C)glucose uptake by rat renal brush border membrane vesicles were studied. One kappa and two lambda type light chains (lambda-1 and lambda-2) were isolated from urines of patients with multiple myeloma. At maximal inhibitory concentrations the kappa chain reduced alanine uptake from 206 +/- 18 to 77 +/- 18 pmole/mg protein (P less than 0.005) and glucose uptake from 357 +/- 22 to 146 +/- 8 pmole/mg protein (P less than 0.001). lambda-1 reduced alanine uptake from 136 +/- 17 to 60 +/- 8 pmole/mg protein (P less than 0.005) and glucose uptake from 354 +/- 17 to 77 +/- 14 pmole/mg protein (P less than 0.001). lambda-2 reduced alanine uptake from 105 +/- 9 to 28 +/- 5 pmole/mg protein (P less than 0.001) and glucose uptake from 194 +/- 7 to 66 +/- 7 pmole/mg protein (P less than 0.001). The half maximal inhibitory concentrations (I50) of kappa, lambda-1 and lambda-2 light chains were 68, 76 and 140 microM for alanine uptake and 120, 70 and 105 microM for glucose uptake. Control experiments using bovine serum albumin and beta-lactoglobulin showed no inhibitory effect on alanine and glucose uptake by either protein. These data reveal brush border membrane effects by myeloma light chains and confirm that direct Bence Jones protein nephrotoxicity may play an important role in the pathogenesis of kidney dysfunction associated with multiple myeloma.

Oxalate accumulation in rat renal cortical slices

Tubular transport of oxalate is thought to be an energy-mediated process which may contribute to the renal deposition of calcium oxalate in a variety of pathologic states. In order to examine this possibility, the renal handling of oxalate was investigated in rat renal cortical slices in vitro. Slices incubated in vitro with 1 microM [14C]oxalate in Krebs-Ringer bicarbonate buffer at 25 degrees C for 180 min achieved a mean slice to medium ratio of 2.8 +/- 0.08 (SEM) and a mean tissue concentration of 7.7 +/- 0.2 mumol/kg dry wt (N = 64). Section freeze-dry autoradiographs demonstrated maximum uptake within proximal tubule cells but no crystals were evident. Substituting N2 for O2, adding KCN, or removing Ca2+ increased uptake of 14C-oxalate. Dinitrophenol (DNP) and iodoacetamide (IoAc), however, significantly decreased, and O degrees C eliminated slice uptake. Slices incubated with 100 microM [14C]oxalate showed a further increase in tissue accumulation and the appearance of [14C]oxalate crystals. Crystals formed in vitro were deposited throughout the tissue. Oxalic acid did not appear to share the organic acid by renal cortical slices in vitro is largely independent of energy-mediated mechanisms.

Renal and electrolyte effects of total parenteral nutrition

Effects of short-term (4-14 days) total parenteral nutrition on renal handling of water and electrolytes were studied retrospectively in 24 patients and prospectively in eight patients. There was 33% incidence of hyponatremia and significant reductions in serum creatinine (from 1.03 +/- 0.06 to 0.88 +/- 0.06 mg/dl, p less than 0.001), phosphorus (from 3.2 +/- 0.14 to 2.5 +/- 0.17 mg/dl, p less than 0.005) and uric acid (from 6.09 +/- 0.38 to 3.66 +/- 0.24 mg/dl, p less than 0.001) were observed. Hypouricemia correlated with increased fractional excretion of urate (r = 0.81, p less than 0.05). Hypophosphatemia was associated with increased tubular reabsorption of phosphate. Clearance studies in eight patients showed high urine flow rate (1.7 +/- 0.2 ml/min), osmolar clearance (3.2 +/- 0.7 ml/min), urinary nonelectrolyte, nonurea solute excretion (0.23 +/- 0.14 mmol/min), and negative free water clearance (TcH2O = 1.5 +/- 0.6 ml/min). These data suggest presence of compartmental shifts, expanded extracellular fluid volume, and possible direct effects on renal tubular transport functions during total parenteral nutrition.

Contribution of lead to hypertension with renal impairment

Hypertension of unknown cause is generally termed "essential." Because hypertension has long been considered a possible complication of lead poisoning and the EDTA lead-mobilization test has proved to be a sensitive indicator of excessive body stores of lead, we used this test to evaluate cumulative past lead absorption in 48 men diagnosed as having essential hypertension. Patients who had hypertension with reduced renal function (i.e., serum creatinine level greater than 1.5 mg per deciliter [133 mumols per liter]) had significantly larger amounts of mobilizable lead than did patients who had hypertension without renal impairment. The increase in mobilizable lead was not due to the renal disease itself, since 22 control patients without a history of essential hypertension but with comparable renal impairment from known causes excreted significantly less lead chelate during the three-day test. These data suggest that lead may have an etiologic role in the renal disease of some patients usually designated as having "essential" hypertension.

Transport of gentamicin in rat proximal tubule

The intrarenal distribution of tritiated gentamicin (GM) was determined in rat by combined immunofluorescence and section freeze-dry autoradiography, techniques that permit subcellular localization before and after diffusional redistribution. Tissue from these kidneys was also examined by electron microscopy. After parenteral administration of 4 to 100 mg/kg, GM accumulates in S1 and S2 but not S3 segments of proximal tubules. Within 10 minutes, autoradiography demonstrates 3H-GM in the lumina of proximal and distal tubules; a subapical distribution consistent with pinocytotic uptake is prominent in many proximal cells. After 1 hour, 3H-GM is diffusely distributed within the cytoplasm in section freeze-dry autoradiographs with minimal evidence of intracellular sequestration. At this time, 3H-GM is presumably within endocytotic vacuoles, and electron microscopy reveals only rare vacuoles containing single myeloid bodies. Subsequently, section freeze-dry autoradiography shows sequestration of the aminoglycoside, but this intracellular localization is lost during tissue processing for fluorescent microscopy up to 6 hours after injection. At 6 hours large cytoplasmic vacuoles containing multiple well-organized myelin figures first appear in S1 and S2 segments. By 48 hours, 3H-GM is firmly bound in these vacuoles and is maintained in situ in both section freeze-dry autoradiographs and immunofluorescent preparations in association with increased numbers of vacuoles containing multiple myeloid bodies by electron microscopy. These studies thus demonstrate diffusible 3H-Gm within the cell which is available to initiate nephrotoxicity 1 to 6 hours after administration.

Elevated 1,25-dihydroxyvitamin D levels: occurrence with sarcoidosis with end-stage renal disease

It is generally agreed that the kidneys are the only site of 1-hydroxylation of vitamin D and that the abnormal calcium metabolism in sarcoidosis is caused by increased production of 1,25-dihydroxyvitamin D (1,25-[OH]2D). We describe a patient with sarcoidosis with hypercalcemic nephropathy and end-stage renal disease undergoing long-term maintenance hemodialysis who was initially seen with hypercalcemia and elevated serum levels of 1,25-(OH)2D. Prednisone administration resulted in decreased serum calcium and 1,25-(OH)2D levels. These results confirm the recent evidence for extrarenal production of 1,25-(OH)2D in sarcoidosis and illustrate the importance of altered vitamin D metabolism in the development of hypercalcemia in sarcoidosis.

Effect of antitubular basement membrane and brush border antibodies on p-aminohippurate transport in kidney

The effect of antiproximal tubule basement membrane (TBM) and brush border (BB) antibodies on p-aminohippurate (PAH) transport was evaluated in a rat model of immunologically mediated interstitial nephritis. Immunized rats developed anti-TBM antibody titers ranging from 1 to 3,072 with continuous linear IgG and interrupted C3 deposits in the TBM. Circulating anti-BB antibodies were detected in half of the immunized rats in titers ranging from 1 to 128. Heavy IgG deposition was present in the BB when circulating anti-BB antibody titers exceeded eight and proteinuria was present. When anti-TBM antibody titers were 1,024 or greater the slice-to-medium PAH concentration ratio (S/M) was significantly reduced (p less than 0.001). Combined immunofluorescent microscopy and section freeze-dry autoradiography revealed normal cellular distribution of PAH-3H in all proximal tubules except in rat microscopic foci of interstitial nephritis in which concentrative transport was absent. However, luminal secretion of PAH-3H was strikingly reduced in tubules with heavy IgG BB deposits. 3-hour PAH secretion in vivo fell significantly in rats with circulating and tissue anti-BB antibodies. Antibody inhibition of PAH transport appeared to be independent of morphologic damage.

SUMMARY

Anti-TBM antibodies were associated with decreased slice uptake of PAH-3H while anti-BB antibodies were associated with decreased luminal PAH secretion in vitro and in vivo.