Toxicity of holotransferrin but not albumin in proximal tubule cells in primary culture.
Proteinuria has been invoked as a cause of tubulointerstitial injury in chronic renal disease, and in vivo studies have suggested indirectly the particular nephrotoxicity of one urinary protein holotransferrin (Tf-Fe). However, to date there has been no direct evidence for the nephrotoxicity of Tf-Fe. To examine the potential cytotoxicity of Tf-Fe and the mechanism involved, and to compare this to another urinary protein albumin, rat proximal tubule cells were studied in primary culture. Tf-Fe at pH 6.0 caused functional and ultrastructural injury, but no cytotoxicity was seen with cells exposed to albumin, apotransferrin (transferrin), or Tf-Fe at pH 7.4. The influence of pH on Tf-Fe-induced cytotoxicity was not due to pH per se, but could be explained by an effect on Tf-Fe uptake. At pH 6.0, uptake of 125I-Tf-Fe (3.55 +/- 0.05 versus 1.25 +/- 0.10 fmol/dish, P < 0.01) and intracellular iron concentration (1.14 +/- 0.25 versus 0.46 +/- 0.23 nmol/dish, P < 0.01) were increased compared with values at pH 7.4. In contrast, pH 6.0 did not increase iron uptake from FeCl3. Lysine (100 mM) inhibited Tf-Fe uptake, decreased intracellular iron concentration, and attenuated Tf-Fe-induced cytotoxicity. The iron chelator des-ferrioxamine (200 microM) and hydroxyl radical scavenger dimethylpyrroline N-oxide (32 mM) abolished lactate dehydrogenase leakage induced by Tf-Fe at pH 6.0. Lipid peroxidation, as assessed by production of malondialdehyde, preceded lactate dehydrogenase leakage. In summary, holotransferrin, but not albumin, is toxic to rat proximal tubule cells, a pH-dependent effect involving its uptake into tubule cells, its iron moiety, and its lipid peroxidation.
Chen
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Department of Renal Medicine, University of Sydney, Westmead Hospital, NSW, Australia.
Boadle
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RA
Harris
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D000818:Animals; D002478:Cells, Cultured; D005110:Extracellular Space / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007425:Intracellular Membranes / Q000378:metabolism; D007501:Iron / Q000378:metabolism; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000187:drug effects*; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008239:Lysine / Q000494:pharmacology; D008297:Male; D008315:Malondialdehyde / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D012709:Serum Albumin / Q000494:pharmacology*; D014168:Transferrin / Q000493:pharmacokinetics / Q000506:poisoning*
D012709:Serum Albumin; D014168:Transferrin; C110714:holotransferrin; D008315:Malondialdehyde; D007501:Iron; D007770:L-Lactate Dehydrogenase; D008239:Lysine