title: Is there a role of cyclosporine A on total homocysteine export from human renal proximal tubular epithelial cells?
abstract: BACKGROUND
  Immunosuppressive therapy may influence homocysteine metabolism in allograft recipients. We examined whether cyclosporine A influences the in vitro formation of homocysteine as determined by the measurement of total homocysteine (tHcy) concentrations in supernatants of human renal proximal tubule epithelial cells (hRPTEC), an important site of homocysteine metabolism.
  
  
  METHODS
  Cells were incubated with and without vitamins in the presence of low or high methionine concentrations at different cyclosporine A concentrations for 24, 48 and 72 hours (N = 7 for each experiment). The concentration of tHcy in culture supernatants was measured by a fluorescence polarization immunoassay. Data were analyzed by four-way ANOVA, three-way ANOVA and t tests.
  
  
  RESULTS
  The Hcy export from hRPTEC (tHcy in the culture supernatant) was 2.69 micromol/L during standard cell culture conditions at time point 24 hours and increased by 28.3% at 48 hours and by 44.6% at 72 hours. Comparisons of tHcy levels in culture supernatants over time by four way ANOVA showed that cyclosporine A at 200 or 800 ng/mL had no influence on tHcy export from hRPTEC (P = 0.67991). In contrast, the presence of vitamins in the medium (P = 0.000001), in vitro methionine loading (P < 0.000001), and prolonged incubation time (P < 0.000001) were associated with an increase of tHcy export from hRPTEC. Significant interactions in this analysis were "vitamins x methionine" (P = 0.001804), "vitamins x time" (P = 0.001478), "methionine x time" (P < 0.000001), and "vitamins x methionine x time" (P = 0.018128), pointing to a combined effect of vitamins in the presence of high methionine concentrations at the later time points.
  
  
  CONCLUSIONS
  Our study shows that hRPTEC export Hcy into the cell culture medium, an effect that is enhanced by in vitro methionine loading and modulated by the presence of vitamins. Cyclosporine A had no major influence on Hcy export from tubule cells. Therefore, our findings do not support the assumption that cyclosporine A elevates total homocysteine plasma levels in organ transplant patients.
authors.affiliation: Division of Nephrology and Dialysis, Department of Medicine III, University of Vienna, Vienna, Austria.
authors.forename: M C
authors.initials: MC
authors.lastname: Ignatescu
authors.forename: M
authors.initials: M
authors.lastname: Födiger
authors.forename: J
authors.initials: J
authors.lastname: Kletzmayr
authors.forename: C
authors.initials: C
authors.lastname: Bieglmayer
authors.forename: W H
authors.initials: WH
authors.lastname: Hörl
authors.forename: G
authors.initials: G
authors.lastname: Sunder-Plassmann
mesh_terms: D001693:Biological Transport, Active / Q000187:drug effects; D002478:Cells, Cultured; D016572:Cyclosporine / Q000494:pharmacology*; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism; D005492:Folic Acid / Q000494:pharmacology; D006710:Homocysteine / Q000378:metabolism*; D006801:Humans; D020138:Hyperhomocysteinemia / Q000209:etiology; D007166:Immunosuppressive Agents / Q000494:pharmacology*; D016030:Kidney Transplantation / Q000009:adverse effects; D007687:Kidney Tubules, Proximal / Q000187:drug effects* / Q000378:metabolism*; D008715:Methionine / Q000494:pharmacology; D011736:Pyridoxine / Q000494:pharmacology; D014805:Vitamin B 12 / Q000494:pharmacology
chemical_list: D007166:Immunosuppressive Agents; D006710:Homocysteine; D016572:Cyclosporine; D005492:Folic Acid; D008715:Methionine; D011736:Pyridoxine; D014805:Vitamin B 12