Metabolism of 4-hydroxynonenal by rat Kupffer cells

Kupffer cells are known to participate in the early events of liver injury involving lipid peroxidation, 4-Hydroxy-2,3-(E)-nonenal (4-HNE), a major al dehydic product of lipid peroxidation, has been shown to modulate numerous cellular systems and is implicated in the pathogenesis of chemically induce d liver damage. The purpose of this study was to characterize the metabolic ability of Kupffer cells to detoxify 4-HNE through oxidative (aldehyde deh ydrogenase; ALDH), reductive (alcohol dehydrogenase; ADH), and conjugative (glutathione S-transferase; GST) pathways. Aldehyde dehydrogenase and GST a ctivity was observed, while ADH activity was not detectable in isolated Kup ffer cells. Additionally, immunoblots demonstrated that Kupffer cells conta in ALDH 1 and ALDH 2 isoforms as well as GST A4-4, P1-1, Ya, and Yb. The cy totoxicity of 4-HNE on Kupffer cells was assessed and the TD50 value of 32. 5 +/- 2.2 muM for 4-HNE was determined. HPLC measurement of 4-HNE metabolis m using suspensions of Kupffer cells incubated with 25 muM 4-HNE indicated a loss of 4-HNE over the 30-min time period. Subsequent production of 4-hyd roxy-2-nonenoic acid (HNA) suggested the involvement of the ALDH enzyme sys tem and formation of the 4-HNE-glutathione conjugate implicated GST-mediate d catalysis. The basal level of glutathione in Kupffer cells (1.33 +/- 0.3 nmol of glutathione per 10(6) cells) decreased significantly during incubat ion with 4-HNE concurrent with formation of the 4-HNE-glutathione conjugate . These data demonstrate that oxidative and conjugative pathways are primar ily responsible for the metabolism of 4-HNE in Kupffer cells. However, this cell type is characterized by a relatively low capacity to metabolize 4-HN E in comparison to other liver cell types. Collectively, these data suggest that Kupffer cells are potentially vulnerable to the increased concentrati ons of 4-HNE occurring during oxidative stress. (C) 2001 Academic Press.