Transferrin synthesis is increased in nephrotic patients insufficiently to replace urinary losses.
The urinary loss of transferrin is sufficient to reduce plasma transferrin concentrations in the nephrotic syndrome. Hypotransferrinemia may lead to iron loss and microcytic anemia. The mechanism responsible for the hypotransferrinemia in the nephrotic syndrome is, however, unknown. In the present study, synthesis rate of transferrin was measured in vivo in nephrotic patients (n = 7) compared with control subjects (n = 6) using L-[1-(13)C]-valine. Plasma transferrin and iron concentration in the patients were significantly lower than in control subjects (transferrin, 1.39 +/- 0.08 versus 2.57 +/- 0.11 g/L, P < 0.0001; iron, 10.2 +/- 0.8 versus 21.1 +/- 4.5 micromol/L, P = 0.02). Furthermore, albuminuria correlated with transferrinuria (r(2) = 0.901, P = 0.001). The absolute synthesis rate of transferrin was increased in the patients (10.0 +/- 1.1 versus 7.4 +/- 0.7 mg/kg per d, P = 0.07), although this value failed to achieve significance. C-reactive protein, plasma iron, and proteinuria did not correlate with transferrin synthesis. In contrast, transferrin synthesis correlated with albumin synthesis (r(2) = 0.648, P = 0.03; n = 7). The present study indicates that increased transferrin synthesis occurs in nephrotic patients but is insufficient to compensate for urinary losses. Because, overall, no significant relationship was found between transferrin synthesis and either C-reactive protein or iron, it is unlikely that inflammation suppresses or that iron deficiency stimulates increased transferrin synthesis in these patients. The correlation between transferrin synthesis and albumin synthesis suggests that transferrin synthesis is a component of a general response in hepatic protein synthesis in the nephrotic syndrome. This suggests that a therapeutic approach to maximize plasma transferrin concentrations in nephrotic patients should be aimed primarily at reducing urinary protein excretion.
Prinsen
Berthil H C M T
BHCMT
Department of Vascular Medicine and Metabolism, University Medical Center Utrecht, Utrecht, The Netherlands.|Department of Clinical Chemistry, University Medical Center Utrecht, Utrecht, The Netherlands.|Department of Metabolic Diseases, University Medical Center Utrecht, Utrecht, The Netherlands.
Velden
Monique G M DE Sain-VAN DER
MGMS
Department of Metabolic Diseases, University Medical Center Utrecht, Utrecht, The Netherlands.
Kaysen
George A
GA
Department of Medicine, Division of Nephrology, University of California-Davis, Davis, and Department of Veterans Affairs Northern California System of Clinics, Mather, California.
Straver
Helma W H C
HWHC
Department of Metabolic Diseases, University Medical Center Utrecht, Utrecht, The Netherlands.
Rijn
Herman J M VAN
HJMV
Department of Clinical Chemistry, University Medical Center Utrecht, Utrecht, The Netherlands.
Stellaard
Frans
F
Department of Nutrition and Metabolism, University Hospital Groningen, Groningen, The Netherlands.
Berger
Ruud
R
Department of Metabolic Diseases, University Medical Center Utrecht, Utrecht, The Netherlands.
Rabelink
Ton J
TJ
Department of Vascular Medicine and Metabolism, University Medical Center Utrecht, Utrecht, The Netherlands.
D000328:Adult; D000418:Albumins / Q000096:biosynthesis; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D007501:Iron / Q000097:blood; D007700:Kinetics; D008297:Male; D008875:Middle Aged; D009404:Nephrotic Syndrome / Q000150:complications / Q000378:metabolism* / Q000652:urine; D011507:Proteinuria / Q000209:etiology / Q000378:metabolism; D014168:Transferrin / Q000096:biosynthesis* / Q000652:urine
D000418:Albumins; D014168:Transferrin; D007501:Iron