Urinary fructose-1,6-bisphosphatase activity as a marker of the damage to the renal proximal tubules in children with idiopathic nephrotic syndrome.
BACKGROUND
Disturbances in the function of renal proximal tubules increase the activity of several enzymes in urine. Among them is fructose-1,6-bisphosphatase (FBP-1), the key enzyme of gluconeogenesis normally present in the renal convoluted, and to smaller degree, proximal renal tubular cells cytosol. FBP-1 activity in urine and serum was used for evaluation of the degree of graft ischemia during human kidney transplantation. The aim of our present research was to determine FBP-1 activity in urine as an indicator of damage to renal proximal tubules in children with idiopathic nephrotic syndrome (INS).


METHODS
We evaluated the excretion of FBP-1 into urine of 21 children (10 girls and 11 boys) with INS, aged from 10 to 15 years and 30 healthy children (14 girls and 16 boys), aged from 2 to 15 years. FBP-1 activity was determined by the Latzko and Gibbs method. Creatinine (mg%) in urine and blood serum was measured by the Jaffe method in Larsen modification. Protein in blood serum was determined by the biuret method (g/L), and albumin (mg%) by the Young method. Proteinuria in the urine collected over 24 h was measured with the Exton turbidimetric method by Tomaszewski with modification and expressed in mg/kg body weight/24 h.


RESULTS
In the urine of 30 healthy children, FBP-1 activity was in the range from 0-1.74 micromol FPB/h/mmol of creatinine. In 43% of the healthy children, FBP-1 activity in urine was not detectable. In the period of intensive proteinuria during the INS in children, FBP-1 activity and protein concentrations in urine were significantly higher than in the control group (p<0.0008 and p<0.0001, respectively). In the urine of children with active INS, we observed a very weak negative linear correlation between protein concentration and FBP-1 activity (r=-0.5018, p=0.067). After treatment with Encorton (prednisone), FBP-1 activity and protein concentration in urine dropped to values of the control group.


CONCLUSIONS
"The overload" of proximal renal tubules by proteins in children with INS releases FBP-1 into urine. FBP-1 activity in urine may therefore be considered as a marker of damage to the proximal renal tubules in children with INS.
Kepka
Alina
A
Department of Laboratory Diagnostics of the Institute "Pomnik-Centrum Zdrowia Dziecka", Warsaw, Poland.
Dariusz Szajda
Sławomir
S
Stypułkowska
Anna
A
Waszkiewicz
Napoleon
N
Jankowska
Anna
A
Chojnowska
Sylwia
S
Zwierz
Krzysztof
K
D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D003404:Creatinine / Q000097:blood / Q000652:urine; D005260:Female; D006597:Fructose-Bisphosphatase / Q000652:urine*; D006801:Humans; D007668:Kidney; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D008297:Male; D009404:Nephrotic Syndrome / Q000378:metabolism / Q000652:urine*; D011507:Proteinuria / Q000378:metabolism*; D012016:Reference Values
D003404:Creatinine; D006597:Fructose-Bisphosphatase