Inhibition of iron toxicity in human hepatocyte cultures by pyoverdins Pa A and Pf, the peptidic siderophores of Pseudomonas aeruginosa and fluorescens

The protective effect of pyoverdins Pa A and Pf, peptidic siderophores secreted respectively by Pseudomonas aeruginosa and fluorescens, was studied in primary cultures of human hepatocytes exposed to iron (50 or 100 μM of iron-citrate). AST, ALT and MDA releases were measured as indexes of cytotoxicity. In order to demonstrate that these chelators were able to decrease iron uptake or increase iron release from the hepatocytes, labelled cells were obtained by maintaining the cultures in the presence of 1 μM 55 Fe ferric chloride plus 50 μM iron citrate. One day after iron treatment, an increase in AST, ALT and MDA release was observed with 50 or 100 μM of iron citrate; it appeared that the concentrations 50 and 100 μM of iron were highly toxic for human hepatocytes. In the presence of 50 or 100 μM of iron, the addition of 50 or 100 μM of Pa A or Pf was effective to inhibit the increase observed in the enzyme leakage and the MDA production resulting from iron exposure. In human hepatocytes cultured for 1 day in the presence of 1 μM 55 Fe-50 μM iron citrate plus 50 or 100 μM Pa A or Pf, a net decrease of iron uptake by the cells was observed, as demonstrated by the low intracellular iron level. When the hepatocytes were cultured for 1 day in the presence of 1 μM 55 Fe-50 μM iron citrate and then for a further day in the presence of 50 or 100 μM Pa A or Pf without additional iron, the chelators increased the extracellular iron level, indicating their iron release from the loaded cells; however, the effects of Pa A and Pf on iron release did not differ significantly. In conclusion, iron loading achieved by adding iron citrate to the culture medium is highly toxic for human hepatocytes. Pyoverdins Pa A and Pf are effective in protecting human hepatocytes against the toxic effect of iron by both decreasing the uptake of the metal and increasing its release from the loaded cells.