Background: Obstructive nephropathy is characterized at the histologic level by tubular atrophy and interstitial monocyte infiltration. The molecular mechanisms underlying these histologic changes are still poorly defined. Epidermal growth factor (EGF) produced by tubular cells seems to play a pivotal role in the modulation of tubular cell growth, while monocyte chemotactic peptide-1 (MCP-1) is a powerful and specific chemotactic and activating factor for monocytes.
Methods: Twenty-four patients with congenital ureteropelvic junction obstruction [UPJO; 10 with recurrent urinary tract infection (UTI) and 10 with no UTI] and 15 healthy children were studied. Diagnosis was made by renal ultrasound, intravenous pielography, and MAG3 scan. Urinary samples were collected before and after surgery. In 10 patients, urine was also collected directly from the affected pelvis at the time of surgery. Urinary EGF and MCP-1 levels were measured by enzyme-linked immunosorbent assay. MCP-1 and EGF gene expression were evaluated by in situ hybridization in 15 biopsies from congenital UPJO and in 10 normal kidneys.
Results: In normal kidneys, there was a high expression of EGF mRNA, whereas MCP-1 mRNA was undetectable. MCP-1 gene expression was strikingly increased at the tubulointerstitial level in UPJO biopsies compared with controls and was directly correlated with the extent of monocyte infiltration. In addition, UPJO kidney sections showed a marked reduction in EGF gene expression that was directly correlated with the degree of tubular damage. EGF urine concentration was significantly reduced in UPJO when compared with control and directly correlated with its renal gene expression. On the other hand, the MCP-1 urine concentration was strikingly increased in UPJO patients. It is noteworthy that a significant and inverse correlation was observed between the MCP-1 concentration in the urine collected from the obstructed pelvis and the MAG3 clearance of the obstructed kidney (r = -0.76). The presence of recurrent UTI was associated with a significantly higher MCP-1 excretion and a slight reduction in EGF urine concentration. The surgical correction of UPJO was followed by an improvement of renal function together with a significant reduction in MCP-1 excretion and a marked increase in EGF urine concentrations. Interestingly, EGF urine concentration measured before surgery was significantly correlated with the difference between the MAG3 clearance of the obstructed kidney before and after surgery.
Conclusions: MCP-1 and EGF seem to be involved in the pathogenesis of tubulointerstitial damage in congenital obstructive nephropathy, and their urine excretion may represent a powerful prognostic marker in this form of renal disease.