Elimination of brush border membrane protein in urine caused by toxic alterations of the tubular cell

Detection of renal brush border membrane enzymes for evaluation of renal injury in neonatal scleredema

OBJECTIVE

To evaluate renal brush border membrane enzymes in urine as an indicator for renal injury in neonatal scleredema (NS).

METHODS

Sixty nine NS patients in our hospital were enrolled and divided into mild group and moderate/severe group. Patients were further randomly divided into therapy and control subgroups for 7 days ligustrazine administration. Urine samples were collected to detect renal brush border membrane enzymes (RBBME) by ELISA and β2-microglobulin (β2-MG) by radioimmunoassay (RIA). The results were compared with those of 30 normal neonates. Data were statistically analyzed using SPSS13.0 software.

RESULTS

Both RBBME and β2-MG were found to be higher in urine in NS patients than normal controls (P < 0.01). Level of RBBME increased with the severity of NS (P <0.05), while urinary β2-MG did not (P >0.05). After being treated with ligustrazine, a medicine for renal function recovery, both RBBME and β2-MG were similarly significantly decreased comparing to untreated groups (P < 0.05). 79.7% of NS patients showed abnormal RBBME while only 52.2% had an abnormal urinary β2-MG (χ (2)=11.65，P < 0.01).

CONCLUSION

RBBME was more sensitive than β2-MG in reflecting the renal injury in NS. Examination of RBBME effectively reflected the recovery of renal injury after treatment with ligustrazine.

Proteinuria: changes and mechanisms in toxic nephropathies

During the last few decades, considerable progress has been made in the understanding of the pathophysiological mechanisms of proteinuria. A great variety of hemodynamic or biochemical mechanisms acting at different sites of the nephron have been shown to alter the renal handling and the urinary excretion of proteins. The finding which perhaps has had most practical implications is that the pattern of protein excretion quantitatively and qualitatively varies with the site and severity of renal damage. This has led to the development of a large array of methods for the identification and quantitation of specific urinary proteins. These methods have been most extensively used by toxicologists in experimental, epidemiological, or clinical studies on potentially nephrotoxic chemicals (e.g., drugs, heavy metals, solvents, etc.). The present review summarizes the current state of knowledge on the mechanisms of proteinuria and the use of urinary proteins as indicators of nephrotoxicity.

Radiation injury in the human kidney: a prospective analysis using specific scintigraphic and biochemical endpoints

Renal function was prospectively analyzed in 26 evaluable patients, irradiated to various doses on their kidneys for neoplastic disease. Glomerular function was assessed by 99mTc-DTPA renography, creatinine clearance, and serum beta 2-microglobulin, whereas tubular function was monitored by 99mTc-DMSA scintigraphy, urine beta 2-microglobulin, urine N-acetyl glucosaminidase, and alanine aminopeptidase and a urine concentration test. In the patients given the highest irradiation dose to the entire left kidney, that is, 40 Gy in 5 1/2 weeks, glomerular and tubular functional impairment, as assessed scintigraphically, progressed at a rate of 2.0 +/- 1.0% (+/- 1 SD) and 2.0 +/- 0.5% per month, respectively, down to 30-40% after 3 to 5 years. The overall glomerular function, as assessed by creatinine clearance, decreased by only 20%. In the patients irradiated unilaterally on the upper pole to 40 Gy in 4 weeks, glomerular and tubular function in the left kidney deteriorated at 0.75 +/- 0.33% and 0.75 +/- 0.20% per month in the first 2 years, down to 75-80% at 5 years. This smaller reduction was due to shielding of a part of the left kidney. No changes were observed, thus far, after bilateral whole kidney irradiation to 17-18 Gy in 3 1/2 weeks. The concentration capacity of the kidney after total volume irradiation was not impaired. There was a trend for an increase in diastolic blood pressure in 3 out of 5 patients given the high dose irradiation to the entire left kidney and in 2 out of 7 patients irradiated on the upper pole of the left kidney. The progressive nature of the radiation nephropathy stresses the need for long term follow-up to determine more accurately the "tolerance dose" of the human kidney for irradiation.

Immunological and ultrastructural analysis of loss of tubular membrane-bound enzymes in patients with renal damage

The pathophysiological background of shedding of membrane-bound enzymes from the proximal tubule was assessed in urine specimens of patients with renal damage applying immunospecific affinity-chromatography, immunotitration, ultracentrifugation, electroimmunodiffusion, immunohistology, as well as negative staining technique. Compared to healthy controls, patients with kidney injury, e.g. after administration of potentially nephrotoxic drugs (cytostatics, contrast media) revealed an increased excretion rate of vacuolar membrane fragments (50-500 nm) into urine. The brush border (BB) of the proximal tubule was identified as a main source of urinary blebs as concluded from immunoelectrophoretic and immunohistochemical analysis. In addition, the marker enzyme profile of urinary vacuolar blebs was similar to that of the BB membrane from human kidney. The results further evidenced that, during the initial phase of tubular injury, 5-10 nm surface glycoproteins of the BB, among them Ala-Leu-aminopeptidase and portions of gamma-glu-transpeptidase, are released into urine; this might be followed by increased blebbing of macromolecular BB fragments, indicating more severe membrane disruption.

Urinary excretion of brush-border antigen revealed by monoclonal antibody: early indicator of toxic nephropathy

Mouse monoclonal antibodies against brush-border antigens of the proximal tubule of human kidney were produced by the hybridisation technique. The urinary excretion of a brush-border protein with an apparent molecular weight of 50 000 (BB-50) was measured by a sandwich enzyme-linked immunosorbent assay with a mouse IgG1 against BB-50 and a polyclonal rabbit antiserum against human kidney as coating and second antibodies. The urinary excretion of BB-50 was fifty times higher in patients treated with cisplatin than in a matched control group and twice as high in workers occupationally exposed to water-soluble chromium(VI) compounds as in their matched controls. These findings suggest that the urinary excretion of kidney antigens revealed by monoclonal antibodies is a very sensitive and specific test for the assessment of toxic nephropathies.

Assessment of the nephrotoxic potential of ceftazidime and a ceftazidime/tobramycin combination in volunteers

Ten informed healthy volunteers with normal renal function received 2 X 3.0 g ceftazidime intravenously for three consecutive days. Four weeks later, ceftazidime was combined with 1 X 3 mg/kg body weight tobramycin, administered intramuscularly, for three consecutive days. The effect of the two treatments on parameters used to assess renal function was examined prior to administration, during administration for three days and for a follow-up period. Alanine-aminopeptidase (AAP) levels in 24 h urine samples were measured in addition to kidney function parameters. The urine from the volunteer who had shown the highest AAP levels in each series was examined by ultracentrifugation for the presence of membrane particles with AAP activity. Ceftazidime showed no effect on the proximal tubular membrane. No increased elimination of AAP could be demonstrated. The kidney function parameters remained unchanged. The combination of ceftazidime with tobramycin led to a cumulative increase in AAP activity which was not significantly different from the increase observed when the same dose of tobramycin is administered alone. No additive effects could be demonstrated. Ultracentrifugation showed no indication of an impairment of the membrane integrity when ceftazidime was administered alone or in combination with tobramycin.