4-Hydroxynonenal (4HNE) is the most prevalent toxic lipid peroxidation product formed during oxidative stress. It exerts its cytotoxicity mainly by the modification of intracellular proteins. The detection of 4HNE-modified proteins in several degenerative disorders suggests a role for 4HNE in the onset of these diseases. Efficient protection mechanisms are required to prevent the intracellular accumulation of 4HNE. The toxicity of 4HNE was tested with the small cell lung cancer cell lines GLC(4) and the multidrug-resistance-protein (MRP1)-overexpressing counterpart GLC(4)/Adr. In the presence of the MRP1 inhibitor MK571 or the GSH-depleting agent buthionine sulphoximine, both cell lines became more sensitive and showed decreased survival. Transport experiments were performed with the (3)H-labelled glutathione S-conjugate of 4HNE ([(3)H]GS-4HNE) with membrane vesicles from GLC(4)-derived cell lines with different expression levels of MRP1. [(3)H]GS-4HNE was taken up in an ATP-dependent manner and the transport rate was dependent on the amount of MRP1. The MRP1 inhibitor MK571 decreased [(3)H]GS-4HNE uptake. MRP1-specific [(3)H]GS-4HNE transport was demonstrated with membrane vesicles from High Five insect cells overexpressing recombinant MRP1. Kinetic experiments showed an apparent K(m) of 1.6+/-0.21 microM (mean+/-S.D.) for MRP1-mediated [(3)H]GS-4HNE transport. In conclusion, MRP1 has a role in the protection against 4HNE toxicity and GS-4HNE is a novel MRP1 substrate. MRP1, together with GSH, is hypothesized to have a role in the defence against oxidative stress.