Hepatoprotectant Ursodeoxycholyllysophosphatidylethanolamide Evokes ERK/MAPK and PI3K/Akt Survival Signalling

Abstract

We had synthesized the bile acid-phospholipid conjugate ursodeoxycholyl lysophosphatidylethanolamide (UDCA-LPE) which was designed to target hepatocytes via bile-acid transport systems. By using a fluorescent labelled analog UDCA-NBDPE, we showed that the conjugate was taken up by HepG2 cells and also targeted the liver in vivo. We also showed that UDCA-LPE was cytoprotective in HepG2 cells during starvation and TNF-α-induced apoptosis. Here we demonstrated that PI3K inhibitor LY294002 reversed cytoprotective effects of UDCA-LPE in both experimental models indicating that PI3K/Akt pathway may be involved in cytoprotection. Western analyses revealed that UDCA-LPE activated phosphorylation of ERK1/2(Thr202/Tyr204) as well as Akt(Ser473). The activation of both pathways was inhibited by an inhibitor of EGFR activation PD168383; thus, UDCA-LPE may interact with and activated EGFR kinase in plasma membrane to trigger survival signals. Downstream of ERK1/2 activation, we found that UDCA-LPE consistently induced phosphorylation of p90RSK, and pBad(Ser112) in a dose- and time-dependent manner. Downstream of PI3K/Akt activation, UDCA-LPE (but not its metabolite LPE or UDCA) evoked phosphorylation of GSK-3α/β. UDCA-LPE also upregulated cFLIP expression and this was concomitant with an inhibition of cleaved caspase 8 during TNF-α-induced apoptosis. Collectively, UDCA-LPE is a potent hepatoprotectant by activating the two major survival ERK1/2 MAP kinase and PI3K/Akt pathways. UDCA-LPE may be of potential therapeutic importance for treatment of liver diseases.