Abstract 661: Phosphatidylinositol Acts Through Mitogen and Stress Activated Protein Kinase Pathways to Stimulate Secretion of ApoA-I
Phosphatidylinositol (PI) has been shown to increase plasma apoA-I levels in animal models and human subjects. Orally administered PI significantly increased HDL and apoA-I levels and reduced plasma triglycerides over a 2 week period in healthy human subjects. Oral PI also increased plasma apoA-I levels by 45% in fat-fed rats over a similar treatment period. Cell culture experiments show that PI increases the synthesis and secretion of apoA-I into the media of both HepG2 and Caco-2 cell lines. The concentration of apoA-I was determined using an apoA-I ELISA. PI vesicles added to the cell media (10 ug/ml) doubled apoA-I secretion at 24h, while other anionic and uncharged phospholipids had no effect on apoA-I secretion. PI had a dose dependent effect on apoA-I secretion. PI dependent stimulation of apoA-I secretion was unaffected by inhibitors of PI-3 kinase (wortmannin and LY-294002), but was sensitive to inhibitors of the MAP kinase pathway. While the MAPKp38 inhibitor SB203580 had no effect on apoA-I secretion, the MEK1/2 inhibitor U0126 blocked PI-mediated apoA-I secretion. Proteomic analysis of PI treated HepG2 cell extracts confirmed this view and showed increased expression of B-Raf and MEK2 and phosphorylation of MEK1. In addition, HepG2 cell extracts also showed increased expression of ASK1 and JNK and increased phosphorylation of c-jun. The data suggest that PI acts through mitogen and stress-activated protein kinase pathways to increase plasma apoA-I levels.