Altered urinary beta 2-microglobulin excretion as an index of nephrotoxicity.

The experimental and clinical evidence indicate that beta 2-microglobulin (beta 2m) is actively reabsorbed from the glomerular filtrate by receptors on the brush border located in the proximal third of the proximal tubule. Increased beta 2m excretion in the absence of increased filtered load of beta 2m is indicative of nephrotoxicity. The data presented show that urine beta 2m increases and creatinine concentrations decrease within four hours of administration of diatrizoate megalumine (DMG). In 9 of the 20 patients, the urinary excretion of beta 2m (U beta 2m) increased to clearly abnormal values. In 12 of the 20 patients, the beta 2m excretion expressed as mg per g creatinine (Cr), increased from normal (less than 0.30) to an abnormal beta 2m excretion rate. The increased beta 2m excretion per g Cr occurring immediately after DMG administration lead us to conclude that this effect occurs when the nephrotoxic agent is present in the kidney. Based on these data we believe that the onset of abnormal urinary beta 2m excretion coincides with the presence of the causative agent. This criterion therefore, should prove to be useful in determining the time to conduct studies designed to search for the causative agent(s) in Balkan endemic nephropathy.

Nonmetabolizable glucose analogues and ornithine decarboxylase expression in LLC-PK1 cells.

This report examines the effect of nonmetabolizable glucose analogues on ornithine decarboxylase (ODC) activity in LLC-PK1 cells. The addition of Na(+)-dependent cotransported glucose analogues, 1-O-methyl-alpha-D-glucopyranoside (alpha-MDG) and 1-O-methyl-beta-D-glucopyranoside, to Earle's balanced salt solution minus glucose (EBSS-G) increased ODC activity five- to sevenfold above basal levels. The passive carrier-mediated transported glucose analogue 3-O-methyl-D-glucopyranose had very little effect on enzyme activity. alpha-MDG increased ODC activity in quiescent but not growing cells. ODC activity increased as a function of both the incubation time in EBSS-G + alpha-MDG and the concentration of alpha-MDG in EBSS-G. Phlorizin significantly reduced the level of enzyme activity induced by alpha-MDG. ODC expression by alpha-MDG was reduced in cells incubated in hypertonic EBSS-G + alpha-MDG. Enzyme activity, in the absence of extracellular organic substrates, was markedly elevated in cells incubated in hypotonic media. It is suggested that an influx of Na+ and/or an increase in cell volume elevates one or more signal transducers that regulate ODC expression.

Urinary N-acetyl-beta-glucosaminidase and the selection of children for radiologic evaluation after urinary tract infection.

Urinary levels of N-acetyl-beta-glucosaminidase (NAG) were measured in 147 consecutively enrolled children younger than 13 years of age with urinary tract infection to determine whether elevated levels were a predictor of urologic abnormalities. The children were classified as having cystitis if results of 0 or 1 of the following tests were positive and as having pyelonephritis if results of greater than or equal to 2 tests were positive: (1) temperature greater than 38 degrees C, (2) serum C-reactive protein greater than 1 mg/dL, (3) erythrocyte sedimentation rate greater than 25 mm/h, and (4) 1-deamino-8-D-arginine vasopressin-renal concentrating protein less than 810 mOsm/kg. Urinary NAG to creatinine ratios did not distinguish cases of cystitis from those of pyelonephritis. Urinary NAG was useful in identifying children with cystitis who had vesicoureteral reflux of grades II through V. Of 6 children with cystitis and vesicoureteral reflux, 5 had levels of NAG more than 1 SD above the mean, whereas of 75 children without vesicoureteral reflux, only 15 had such an elevation (P = .003). Of those children with a normal NAG level, 60 (98.4%) had normal radiologic evaluation results, and only 1 child (1.6%) had vesicoureteral reflux. Levels of NAG did not identify children with pyelonephritis who had vesicoureteral reflux. It is concluded that (1) urinary NAG is of no value in localizing the site of urinary tract infection, and (2) an NAG level within 1 SD of the mean in a child with cystitis indicates a low risk of urologic abnormalities, and radiologic evaluation may be omitted unless infection recurs.

The proteinuria of industrial lead intoxication.

Studies of protein excretion were undertaken in seven males, aged 35-42 years, who had more than 5 years exposure to industrial lead and had clinically established Pb intoxication. Heavy metal intoxication with Cd and Hg causes proximal tubular abnormalities, i.e., aminoaciduria, glycosuria, phosphaturia. Similar abnormalities occur in Pb intoxication except that the nature of the proteinuria remains controversial. Studies of urinary proteins included 24-hr urine protein excretion, dextran gel separations, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and beta 2 microglobulin (B2M) measurements. Creatinine clearances, and serum B2M concentrations were normal. Urine total protein distribution by SDS-PAGE and the B2M excretion rate were also normal. These data imply that the nephrotoxicity of Cd and Hg are different than that of Pb. We speculate on what might account for this difference. This study suggests that when examining a population exposed to Pb, the finding of tubular proteinuria should alert investigators to search for the presence of other toxic agents.

The renal handling of beta 2-microglobulin in the dog.

The renal extraction of beta 2-microglobulin (beta 2M) was investigated under steady-state conditions achieved by constant infusion of human beta 2M. Fifteen animal experiments were conducted. Beta 2 microglobulin was infused at rates ranging from 51 o 269 micrograms/min. The renal arterial and venous blood levels remained constant throughout the study period. The data showed that renal extraction of beta 2M exceeded the rate of filtration at all levels of beta 2M delivered to the kidney. The tubular uptake of filtered beta 2M increased linearly as did the extraglomerular extraction throughout the range investigated. There was no evidence of beta 2M (FE beta 2M) increased linearly with the fractional excretion of filtered water (FE H2O). The results are interpreted to indicate that beta 2M is extracted from renal blood by glomerular filtration and, in addition, by a mechanism independent of glomerular filtration rate (GFR). Under the conditions existing in these experimental animals, the linear relationship between FE beta 2M and FE H2O is evidence to suggest that factors affecting proximal tubular water reabsorption also affect beta 2M reabsorption.

Renal metabolism of beta 2-microglobulin. Experimental animal studies.

beta 2-microglobulin (beta 2M) is a protein of 11,800 daltons which occurs in the plasma of normal individuals at concentrations of approximately 2 microgram/ml. It is presumed to be relatively freely filterable. More than 99% of the filtered beta 2M is taken up by an active reabsorptive mechanism and catabolized by the renal tubule. The data presented here demonstrate that renal extraction is only slightly diminished by complete ureteral obstruction. The renal extraction of beta 2M is greater than can be accounted for by filtration alone. These data indicate that some uptake of beta 2M occurs from the peritubular capillary circulation. The loading of animals with beta 2M is associated with a marked tubular proteinuria suggesting that this protein may play a part in inducing tubular injury.

Characterization of human beta2-microglobulin by isoelectric focusing.

b2-Microglobulin (B2M) isolated from the urine of normal subjects and patients with cadaveric renal transplantation, showed 2 homologues by isoelectric focusing, one with a pI 5.3, the other with a pI 5.7. These proteins show identical molecular weights by dextran gel filtration and sodium dodecyl sulfate acrylamide gel electrophoresis. The immunogenic reactivity demonstrates partial identity using antiserum to human B2M from 2 different sources.