Trans-4-hydroxy-2-hexenal is a neurotoxic product of docosahexaenoic (22:6; n-3) acid oxidation

Lipid peroxidation of docosahexaenoic (22:6; n-3) acid (DHA) is elevated in the CNS in patients with Alzheimer's disease and in animal models of seizure and ethanol withdrawal. One product of DHA oxidation is trans-4-hydroxy-2-hexenal (HHE), a six carbon analog of the n-6 fatty acid derived trans-4-hydroxy-2-nonenal (HNE). In this work, we studied the neurotoxic potential of HHE. HHE and HNE were toxic to primary cultures of cerebral cortical neurons with LD₅₀'s of 23 and 18 μmol/L, respectively. Toxicity was prevented by the addition of thiol scavengers. HHE and HNE depleted neuronal GSH content identically with depletion observed with 10 μmol/L of either compound. Using an antibody raised against HHE-protein adducts, we show that HHE modified specific proteins of 75, 50, and 45 kDa in concentration- and time-dependent manners. The time-dependent formation of HHE differed from that of F₄-neuroprostanes following in vitro DHA oxidation likely as a result of the different oxidation pathways involved. Using purified mitochondrial aldehyde dehydrogenase ALDH5A, we found that HHE was oxidized 6.5-fold less efficiently than HNE. Our data demonstrate that HHE and HNE have similarities but also differences in their neurotoxic mechanisms and metabolism.