High susceptibility to paraquat-driven lipid peroxidation of cultured hepatocytes loaded with linolenic acid.

Rat hepatocytes cultured without (normal cells) and with 1 mM alpha-linolenic acid-bovine serum albumin complex (alpha-linolenic acid [LNA]-loaded cells) for 12 hr were challenged with paraquat at concentrations ranging from 0.01 to 5 mM. The addition of paraquat to normal hepatocytes induced a relatively low level of lipid peroxidation as measured by the accumulation of malondialdehyde in the medium, even at a high paraquat concentration that caused severe cell injury. LNA-loaded hepatocytes markedly underwent lipid peroxidation on addition of paraquat, with a rise in the malondialdehyde accumulation beginning at the lowest concentration used (0.01 mM). The enhanced lipid peroxidation induced in LNA-loaded hepatocytes by the addition of paraquat was accompanied by the occurrence of cell injury at noncytotoxic paraquat concentrations for normal cells. Of further importance was that in LNA-loaded cells, lipid peroxidation promptly occurred after the addition of paraquat and was followed by the loss of cell viability. Addition of antioxidants such as N,N'-diphenyl-p-phenylenediamine and alpha-tocopherol with paraquat prevented lipid peroxidation in both normal and LNA-loaded hepatocytes but protected only the latter cells from cell injury. Neither lipid peroxidation nor cell injury in either group of hepatocytes was prevented by the presence of .OH scavengers such as mannitol and dimethyl sulfoxide. In addition, paraquat-driven lipid peroxidation in LNA-loaded hepatocytes was promoted by the addition of ascorbate but was rather suppressed by the addition of H2O2. In conclusion, it is likely that the addition of paraquat induced Fe(++)-lipid hydroperoxide-dependent lipid peroxidation that led to lethal cell injury in LNA-loaded hepatocytes.