Nephrology Dialysis Transplantation, Vol 14, Issue 3 635-640, Copyright © 1999 by Oxford University Press
T Machiguchi, H Yoshida, S Yonemoto, T Minakata, K Nomura, E Muso, T Tamura and S Sasayama
Background. Recent reports describe that
erythropoietin (Epo) is produced by peritubular interstitial
fibroblast-like cells in response to a hypoxic stimulus. We studied serum
Epo levels as a possible marker of tubulointerstitial damage in the
progression of IgA nephropathy (IgAN), in comparison with urinary (u-)
levels of N-acetyl-{beta}-D-glucosaminidase
(NAG), which is mainly derived from proximal tubular cells and is used as a
marker of tubular damage. Methods. Thirty-eight
patients with IgA nephropathy (IgAN) with relatively preserved renal
function (serum creatinine: sCr, 0.5-2.2 mg/dl) were examined. The severity
of glomerulosclerosis and interstitial fibrosis of the renal biopsy tissue
was expressed by semiquantitative grading scores. Clinical parameters
including serum creatinine (sCr), blood pressures, and 24-h proteinuria
levels were obtained at the renal biopsy. Epo was measured by a
radioimmunoassay (RIA) of sera obtained in the morning and u-NAG was
measured by colorimetric method of 24-h urine samples. Results.
The mean Epo level of the patients (17.7±6.3 mU/ml)
was not different from the control level (19.3±3.7 mU/ml). There
were no significant correlations between Epo levels and red blood cell
(RBC) counts, haematocrit (Hct), or haemoglobin (Hb) levels. The mean u-NAG
level of the patients (6.7±6.2 U/gCr) was significantly higher
than the control level (1.9±0.5 I/gCr). There was an inverse
quantitative correlation between Epo and u-NAG levels in the patients
(P<0.02). The u-NAG levels showed quantitative
positive correlations with sCr (P<0.001),
u-proteins (P<0.001), systolic (SBP)
(P<0.001), and diastolic blood pressures (DBP)
(P<0.05). Conversely, Epo levels were inversely
correlated with sCr, SBP and DBP (each P<0.05).
The patients with higher u-proteins (>2.0 g/day) showed
significantly decreased Epo levels (P<0.05)
than those with lower u-proteins (<2.0 g/day). The both scores of
glomerulosclerosis and interstitial fibrosis were positively correlated
with the u-NAG levels (each P<0.001), but were
not correlated with the Epo levels. Conclusions. The
significant correlation between u-NAG and serum Epo levels suggests that
tubular damage and interstitial cell dysfunction are associated each other
in the progression of IgAN. Serum Epo levels bearing inverse correlations
with sCr, blood pressure levels and heavy proteinuria seem to reflect
clinical severity of IgAN, whereas u-NAG can be more useful progression
marker of IgAN bearing correlations with both clinical and histological
findings. Keywords: anaemia; erythropoietin;
glomerulosclerosis; IgA nephropathy;
N-acetyl-{beta}-D--glucosaminidase;
tubulointerstitial damage
ORIGINAL ARTICLES
Does circulating erythropoietin reflect progression of IgA nephropathy? Comparison with urinary N-acetyl-{beta}-D-glucosaminidase
Department of Internal Medicine, Himeji National Hospital, Himeji, Japan; Division of Nephrology, Medical Research Institute, Kitano Hospital, 13-3 Kamiyama-cho, Kita-ku, Osaka City 530-0026, Japan; Department of Cardiovascular Medicine, Kyoto University, Kyoto, Japan; Corresponding author
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