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.

Beta 2-microglobulinuria as a predictor of death in a population exposed to Balkan endemic nephropathy.

During the year 1974, urinary beta 2-microglobulin (beta 2mu) was measured at monthly intervals using the first-morning urine sample of randomly selected individuals from the BEN affected village of Petka (416 persons) and from the nearby situated control village of Stubica (216 persons). Initial compliance was complete; over 90% of villagers had at least 10 tests performed. beta 2mu, as assessed by radial immunodiffusion (RID), was repeatedly (at least twice) positive in 12% and 1.4% of the populations of the endemic and control villages, respectively. Over the 15 years of follow-up (1974 to 1988), none from the control village developed BEN, while many medical records of the cohort exposed to BEN contained data suggestive of BEN. Death from/with BEN was used as a measure of outcome. Incidence density of 12 was 3.3 per 1000 person/years of observation (19/5723). A single positive beta 2mu test was a sensitive predictor of BEN death (sensitivity = 89.5%). Selecting two or more positive tests as the cut-off point, the specificity and positive predictive value were considerably increased. Using the sulfosalicylic acid test for detection of significant proteinuria, a similar level of validity indices was reached only by four testings.

Beta 2-microglobulin studies in endemic Balkan nephropathy.

The diagnosis of BEN and its differentiation from other chronic interstitial nephropathies are difficult because of the insidious onset as well as nonspecific morphological changes in the kidney. Early diagnosis of this disease is by clinical and laboratory findings which have not been universally accepted. This study was designed to determine if the frequency of increased urinary beta 2-microglobulin (U beta 2m) in village populations at risk to develop BEN was significantly higher than that seen in a control population. Individuals in the two population samples were classified in one of three categories: healthy, suspect or diseased. There were 23 individuals who met the criteria for the clinical diagnosis of BEN. Twenty (87%) of these had one or more positive tests for increased U beta 2m. The prevalence of kidney disease in the endemic village population sample was 13.4 times that for the control village population sample. The data show that the healthy individuals living in a village where BEN is endemic have 6.4 times greater chance of having tubular proteinuria than those living in a control area. The coincidence of the finding of U beta 2m in the urine of 87% of those sick with BEN and in 37 of the 342 (10.8%) people judged to be free of kidney disease suggests that a positive U beta 2m test is an early indicator of exposure to a nephrotoxic agent.

A fifteen year cohort based evaluation of beta 2-microglobulin as an early sign of Balkan endemic nephropathy.

The occurrence of elevated urinary beta 2-microglobulin (U beta 2m) has been established to be more common in village populations living in areas where BEN is endemic when compared to appropriate control population. In addition, beta 2-microglobulinuria is associated with BEN. It has been demonstrated that there is an increase in the U beta 2m in apparently healthy populations located in high risk areas. It is 15 years since the first systematic investigations of U beta 2m in the villages of Brod Posavina were conducted. The purpose of this study was to determine the value of a positive test for tubular proteinuria as defined by increased U beta 2m, in identifying individuals at risk to develop BEN. In these studies we followed two cohorts for 15 years: one group consisted of individuals who were positive for tubular proteinuria by U beta 2m testing in 1974; the second group was an age and sex matched group from the same village who were never positive after 12 testings in 1974. The results show that a positive test for U beta 2m is associated with 9.9 times greater relative risk of developing BEN when compared to controls that had no positive U beta 2m tests.

Relationship of anemia to Balkan endemic nephropathy.

Anemia has been reported to be an early sign of Balkan endemic nephropathy (BEN) occurring before the serum creatinine is elevated. This study was designed to determine if anemia occurred more frequently in an otherwise 'healthy' population living in an area where BEN is endemic when compared to a control population. Also, we wished to determine if any relationship existed between anemia and beta 2-microglobulinuria (beta 2mu) in these populations. The prevalence of anemia in the control village population was 7%, compared to 21.4% of the at-risk village population. These data suggest that anemia is a part of the pathophysiologic picture of endemic nephropathy, and that anemia can be found in an early, non-azotemic phase of the kidney disease.

Urinary protein excretion in children from families with Balkan nephropathy.

We studied the urinary excretion of total protein and five other proteins in urine samples from a total of 831 children and adolescents. The characteristics of the children were: (1.) they resided in areas where Balkan nephropathy (BEN) is endemic and also had family members suffering from BEN; (2.) they resided in areas where BEN is endemic, but the families had no members suffering from the disease; (3.) they lived in nonendemic settlements; (4.) they lived in the city of Nis. Urinary excretion of total protein (TP), albumin (ALB), alpha 2-macroglobulin (alpha 2m), transferrin (TF), IgG, and beta 2-microglobulin (beta 2m) were measured. This study showed that urinary excretion of beta 2m and albumin in children from endemic settlements and from families affected with Balkan nephropathy were not different from the control rural settlements. However, children residing in the city of Nis had significantly increased urinary beta 2m and albumin excretion, over 1.5 to 2.6 times the excretion in the other three groups, although excretion of either protein remained within accepted normal ranges in all groups. The increased excretion of beta 2m and albumin in children from the city of Nis could probably be related to the different growth conditions and/or the effect of toxic environmental factors. These data could serve as a reference base for future comparative studies of urinary protein excretion in children as well as in BEN populations.

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.

Identification of children requiring radiologic evaluation for urinary infection.

Sixty-nine children younger than 13 years of age with urinary tract infection were evaluated to identify risk factors for treatable urologic problems; i.e. those requiring surgery or prolonged antibiotic prophylaxis. All children had a renal ultrasound, intravenous pyelogram and voiding cystogram performed 4 to 6 weeks after the infection. Eleven children with treatable problems were identified, 10 with vesicoureteral reflux and 1 with a ureterocele. For identification of treatable problems the predictive value of a positive test was: (1) fever, 10 of 24 (41.7%); (2) abnormal D-deaminoarginine vasopressin renal concentrating ability, 8 of 24 (33.3%); (3) serum C-reactive protein greater than or equal to 1.0, 8 of 25 (32.0%); (4) Elevated urine N-acetylglucosaminidase, 5 of 16 (31.2%); (5) erythrocyte sedimentation rate greater than or equal to 25, 6 of 21 (28.6%); and (6) age less than 5 years, 10 of 43 (23.3%). Absence of fever denotes a low risk (less than 3%) of finding a treatable problem. Afebrile girls older than 5 years of age can have radiologic evaluation deferred until infection recurs. The presence of fever indicates a high risk of treatable urologic problems (41.7%) and warrants complete radiologic evaluation with the first urinary infection.

Family history of cancer among cases of upper urothelial tumours in a Balkan nephropathy area.

The highest relative risk of developing tumours of the renal pelvis and ureters (TPU) in a general population is confined to areas where Balkan nephropathy (BN) is endemic. Whether there is a higher frequency of cancer of any site in families with TPU cases from this BN endemic part of the world was tested by a case-referent study. A group of 65 rural patients with histologically proven TPU was individually matched with the same number of their nearest neighbours, who served as controls. Comparison of age-standardized ratios revealed that over a period of 30 years family members of the cases experienced a significantly higher risk of (non-urinary) cancer deaths than family members of their pairmates.

Renal lipidosis associated with arteriohepatic dysplasia (Alagille's syndrome).

We report a 20-year-old patient with arteriohepatic dysplasia (Alagille's syndrome) who developed progressive renal failure associated with extensive renal lipidosis. A renal biopsy showed diffuse thickening of glomerular basement membrane mimicking idiopathic membranous glomerulonephritis on light microscopy. Electron microscopy, however, demonstrated numerous intramembranous and mesangial lipid deposits, quite similar to those described in familial lecithin cholesterol acyltransferase deficiency. We believe the renal lipidosis developed secondary to hyperlipidemia associated with longstanding intrahepatic cholestasis. This case illustrates that extensive lipid deposition in the glomerular basement membrane may occur in patients with arteriohepatic dysplasia, and it may lead to progressive renal failure.

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 handling of beta-2-microglobulin in renal disorders: with special reference to hepatorenal syndrome.

A study of serum beta 2-microglobulin and urinary beta 2-microglobulin in patients with liver and/or kidney disease was done to determine if such information is of diagnostic help. Serum concentrations and beta 2M/Cr clearance ratios are higher in patients with primary tubular disorders than in those with glomerular diseases, a finding unaltered by hepatic disease. These data suggest either an increased production or decreased tubular degradation of beta 2M, independent of the glomerular filtration rate (GFR), in primary tubular disorders. The marked increase in urinary beta 2-microglobulin that followed insertion of the peritoneal-jugular shunt is evidence that this procedure resulted in improvement of the GFR, in previously underperfused nephrons.

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.

Demonstration of beta 2-microglobulin in the kidney by direct immunofluorescent staining.

Direct immunofluorescent staining with fluorescein isothiocyanate conjugated goat anti-human beta 2-microglobulin (beta 2M) was used to determine the localization of beta 2M in kidney tissue, obtained by biopsies or nephrectomies for various renal diseases. beta 2M was found in the renal tubular epithelial cell cytoplasm and occasionally in the tubular basement membranes in 48 out of 79 pathologic specimens tested, but not in 3 normals. beta 2M was seen in the tubular cells in all cases of primary tubulointerstitial disease and in all cases with secondary tubular damage associated with glomerular disease or systemic disease. This supports the concept that beta 2M is metabolized in proximal tubular epithelial cells, and its deposition indicates impairment of tubular handling.

Fetal renal tubular function during late pregnancy and diabetes mellitus.

The effect, if any, of diabetes mellitus on the fetal renal tubule has not been previously studied. The concentration of beta2 microglobulin in amniotic fluid is a marker of fetal renal tubular function and normally decreases with advancing gestation, implying increasing tubular function. This relationship was found to be disrupted in 12 diabetic pregnancies, suggesting that the fetal renal tubular cell may represent an example of altered fetal functional maturation occurring during diabetic pregnancy.