Astrocytic biotransformation of trans-4-hydroxy-2-nonenal is dose-dependent.

Elevated levels of trans-4-hydroxy-2-nonenal (HNE) are observed in brain tissues in patients with neurodegenerative diseases. Although astrocytes are known to play a crucial role in regulating and supporting neuronal processes, their capacity to detoxify HNE is unknown. In this work, we examined the extent to which HNE undergoes phase I and phase II metabolism in astrocytes. Murine astrocytes were exposed to three different concentrations of HNE. The loss of HNE was approximately 90%, 80%, and 70% for 1, 5, and 15 microM HNE, respectively, following a 10 min incubation. The expected metabolites trans-4-hydroxy-2-nonenoic acid (HNEAcid), (4-hydroxynonanal-3-yl)glutathione (GSHNE), and (1,4-dihydroxynonane-3-yl)glutathione (GSDHN) accounted for 90% of HNE lost at 1 microM HNE. However, when astrocytes were exposed to 5 and 15 microM HNE, those metabolites accounted only for 50% and 17%, respectively. Binding to macromolecules accounted for only 5-10% of HNE loss. Furthermore, depletion of GSH content had only a small effect on HNE metabolism without elevating HNE oxidation and suggests that other unidentified metabolic pathways are functioning. We identified two novel metabolites of HNE, gamma-nonalactone and the potent pyrrole forming compound, 4-oxo-nonanal (ONA). Occurrence of 1,4-dihydroxynonene was observed as well. These data suggest that the biotransformation of HNE yields products with differing or enhanced toxicity, as well as nontoxic products.