Omega-3 long-chain polyunsaturated fatty acids attenuate bile acid-induced apoptosis via Fas-dependent pathways

Purpose: Clinical studies have demonstrated improvement of parenteral nutrition (PN)-associated liver disease (PNALD) with omega-3 long chain polyunsaturated fatty acid (ω3PUFA) containing eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). One possible mechanism is attenuation of apoptosis induced by high levels retained hydrophobic bile acids (chenodeoxycholic acid (CDCA )) thereby activating death receptors. The aim of this study was to define specific apoptotic pathways through which ω3PUFA attenuate CDCA induced apoptosis.

Methods: Cultured HepG2 cells were treated for 0.5hours with 200μM CDCA in the presence and absence of ω3PUFA (5μM EPA+ 5μM DHA). Eighty-four genes involved in apoptosis were evaluated using quantitative RT-PCR.

Results: There was a 286-fold increase in Fas ligand (FasL) mRNA levels when cells were incubated with CDCA alone, compared to a 9.8-fold increase in FasL mRNA levels when incubated with CDCA with the addition of ω3PUFA (p<0.01). There was a 1.4-fold increase in Fas with CDCA alone, and a 2.0-fold decrease when treated with CDCA+ ω3PUFA. There was a 38-fold increase in Fas-associated death domain (FADD) mRNA levels when cells were incubated with CDCA alone, as compared to a 3.8-fold increase in FADD mRNA levels when incubated with CDCA and ω3PUFA (p<0.01). There was a 142-fold increase in caspase 8 (CASP8) mRNA levels when cells were incubated with CDCA alone, as compared to 45-fold increase in CASP8 mRNA levels when incubated with both CDCA and ω3PUFA (p<0.01).

Conclusions: Treatment with CDCA increased expression of FasL, Fas, FADD, and CASP8 genes and the addition of ω3PUFA resulted in less fold-increase in each of these mediators. This suggests attenuation of bile acid-induced apoptosis occurs via reduction of Fas ligand, thereby reducing binding to Fas and the activation of FADD and CASP8 necessary for mitochondrial amplification to trigger apoptosome formation, indicating that this pathway may have relevance to the pathophysiology and treatment of PNALD.