Differential Effects of Oxidative Stress on Hepatic Endothelial and Kupffer Cell Eicosanoid Release in Response to Endothelin-1

Abstract

Objective: The vasoconstrictor endothelin-1 can induce vasomodulators release like nitric oxide in the liver. Here the authors explored whether endothelin-1 can stimulate endothelial and Kupffer cells release of other vasomodulators under normal and stress conditions.

Methods: Cells were cultured for 24 h and treated with H₂O₂ (25 μM) for 6 h and subsequently with endothelin-1 (10 nM) for 10 min. Eicosanoid release was assessed in the media by enzyme immunoassay.

Results: Endothelin-1 mediated cPLA₂ phosphorylation and increased prostaglandin (PG) I₂, PGE₂ and thromboxane A₂ (TXA₂) release in endothelial cells while it only increased TXA₂ in Kupffer cells. H₂O₂ significantly increased PGI₂, PGE₂ and TXA₂ in endothelial cells through an upregulation of cyclooxygenase-2, thromboxane synthase A₂, and phosphorylation of cPLA₂. Endothelin-1-induced PGI₂, PGE₂, and TXA₂ release in endothelial cells were inhibited by H₂O₂ correlating with the absence of further cPLA₂ phosphorylation. In Kupffer cells, H₂O₂ only increased TXA₂ synthesis and further endothelin-1 stimulation of TXA₂ was possible through a higher increase in cPLA₂.

Conclusion: These results indicate that under normal conditions endothelial cells play a pivotal role in liver microcirculation regulation. Oxidative stress not only disrupts the basal balance of vasomodulators in the liver but also affects endothelin-1-induced effects in both Kupffer cells and endothelial cells.

Key words:

• cPLA₂
• eicosanoid
• endothelin-1
• H₂O₂
• liver

This work was supported by NIH Grants DK38201 and DK 60606.