When Fe2+ ions are added to rat-liver microsomes, lipid peroxidation begins after a short lag period. Fe2+-dependent peroxidation in the first few minutes of the incubation can be increased by adding Fe3+, ascorbic acid or Pb2+ ions; these stimulations are not additive. By contrast, Pb2+ ions inhibit peroxidation of microsomes in the presence of Fe3+/ascorbate or Fe3+-ADP/NADPH. In liposomes made from ox-brain phospholipids, Fe2+-dependent peroxidation is stimulated slightly by Fe3+, but much more so by ascorbic acid, Al3+ or Pb2+; these stimulations are not additive. Liposomal peroxidation in the presence of Fe3+/ascorbate is inhibited by Pb2+ or Al3+. These results argue against the participation of an Fe2+-Fe3+-O2 complex, or a critical 1:1 ratio of Fe2+ to Fe3+, in the initiation of lipid peroxidation in liposomes and rat-liver microsomes.

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1. Albumin is often administered intravenously to critically ill patients as a volume expander, to combat hypoalbuminaemia, and to decrease hyperbilirubinaemia. There is, however, an ongoing debate concerning the therapeutic benefit of the former which is an expensive form of treatment.2. Albumin has several biological functions, in particular as a ligand binder. It also acts as an extracellular transition metal ion-binding and radical-scavenging antioxidant. These functions are influenced by the presence of an exposed thiol group (cys 34) on the surface of the albumin molecule. 3. The ability of infused albumin to influence the plasma thiol pool, and hence antioxidant potential, was investigated in patients with sepsis syndrome.4. Plasma thiol levels rose rapidly after albumin infusion and remained elevated even after plasma albumin levels had declined significantly, due to interstitial leakage. Data are suggestive of some form of thiol exchange in the plasma of these patients between albumin and molecules containing oxidized thiol groups.5. Administration of albumin to patients with sepsis syndrome leads to a sustained increase in plasma thiols. Thiols have several important antioxidant functions, and thiol repletion in these patients, who are known to suffer from oxidative stress, may have beneficial antioxidant effects. Antioxidant repletion may represent an important facet of clinically administered albumin.