Cold-induced release of reactive oxygen species as a decisive mediator of hypothermia injury to cultured liver cells.

The mechanisms of hypothermia-induced cell injury are still unclear. The present study provides experimental evidence for the involvement of reactive oxygen species in hypothermia injury: cultured rat hepatocytes incubated in cold (4 degrees C) Krebs-Henseleit buffer or cell culture medium were injured under normoxic conditions and even more so under hyperoxic conditions, whereas the hepatocytes were protected under hypoxic conditions. During warm (37 degrees C) incubation in cell culture medium, on the other hand, cell injury was minimal under normoxic conditions, only slightly increased under hyperoxic conditions, but substantially increased under hypoxic conditions. The injury occurring during cold normoxic incubation was also largely decreased by the addition of the spin-trap 5,5-dimethyl-1-pyrroline N-oxide, the hydroxyl radical scavenger dimethyl sulfoxide, the flavonoid silibinin, or the transition metal chelator 2,2'-dipyridyl to the medium, or by preincubating the cells with the iron chelator deferoxamine or the lipophilic antioxidant alpha-tocopherol before the hypothermic incubation. In addition, marked lipid peroxidation was observed during cold incubations without inhibitors, but not during warm incubations. Similar results were obtained with cultured rat liver endothelial cells. These results suggest that in hepatocytes and in liver endothelial cells, cold-induced release of reactive oxygen species, most likely of hydroxyl radicals, is the main injurious factor under hypothermic conditions.