Urinary transforming growth factor-β1 is an indicator of histological chronicity in IgA nephropathy

SUMMARY: This study examined urinary excretion of transforming growth factor-β1 (TGF-β1) in adult IgA nephropathy and compared this with clinical and histological parameters. TGF-β1 was measured by enzyme-linked immunosorbent assay in 24-h urine specimens from 25 patients with IgA nephropathy (17 men, eight women). Urine from eight age-matched control subjects served as the control. Serum TGF-β1 was also measured in 16 out of the 25 patients and six age-matched control subjects. TGF-β1 was detected in the urine in 72% of IgA nephropathy patients(18/25), but was not detected in any of the control subjects. Patients with decreased renal function (creatinine clearance (Ccr) < 80 mL/min) had higher urine levels of TGF-β1 than those with normal renal function (Ccr ≥ 80 mL/min) (141.8 ± 60.0 ng/day vs 39.7 ± 33.2 ng/day, P < 0.01). The level of TGF-β1 gave a negative correlation with Ccr ( r = −0.62, P = 0.001), but not with proteinuria ( r = 0.11, P = 0.58). Twenty-two of the patients were evaluated histologically. The urinary TGF-β1 levels correlated with both global sclerosis and interstitial volume ( r = 0.52, P < 0.05, and r = 0.51, P < 0.05, respectively). However, there was no correlation between TGF-β1 levels and glomerular intracapillary inflammatory cell score, mesangial proliferation score or the matrix score. No correlation was found between TGF-β1 levels and the number of glomerular or interstitial CD68⁺ cells. No significant differences in serum TGF-β1 levels were observed between patients with normal Ccr and those with decreased Ccr. Also, its levels were found to be independent of the urine levels. In conclusion, 24-h urinary TGF-β1 excretion was found to correlate with Ccr, global sclerosis and interstitial volume, demonstrating that urinary TGF-β1 is an indicator of chronicity in adult IgA nephropathy.