Eicosapentaenoic acid suppresses PDGF-induced DNA synthesis in rat mesangial cells: Involvement of thromboxane A(2)

Background. The administration of eicosapentaenoic acid (EPA) derived from marine oils has been shown to suppress vascular myocyte, lymphocyte, kerati nocyte, and mesangial cell proliferation in vitro, although the effects are variable and most reports provide fragmented insight into the mechanism(s) responsible for altering cell growth, particularly the relationship of mem brane lipid remodeling to changes in cell proliferation. Thus. these studie s were designed to elucidate the effects of mesangial cell membrane fatty a cid remodeling (induced by EPA) on cell growth, and to define the relevance of changes in the synthesis of growth-modulating eicosanoids. Methods. Mesangial cells were grown in RPMI and 17% fetal calf serum, and w ere subcultured and grown for 48 hours in 17% delipidated serum or delipida ted serum supplemented with 0 to 50 mu g/mL of EPA. Quiescent EPA-loaded an d control mesangial cells were subjected to stimulation with 20 ng/mL of pl atelet-derived growth factor (PDGF) followed by measurement of H-3-thymidin e incorporation and cell number. Results. Mesangial cells remodeled with EPA exhibited a significant decreas e in PDGF-stimulated H-3-thymidine incorporation and cell number associated with a reduction in thromboxane A(2) (TXA(2)) in the media. Importantly, t he phospholipid fatty acid composition of mesangial cells grown in media en riched with EPA revealed an increase in EPA (0.5 +/- 0.02% to 17.02 +/- 0.5 2%) coupled with a reciprocal decrease in the precursor for TXA(2), arachid onic acid (18.19 +/- 3.17% to 3.55 +/- 0.30%). Blockade of TXA(2) synthesis in mesangial cells treated with indomethacin (0.1 to 100 mu mol/L) or the specific TXA(2) synthase inhibitor, U-63557A (0.1 to 100 mu mol/L), evoked a similar reduction in PDGF-stimulated proliferation and TXA(2) synthesis. Coincubation of PDGF with the TXA(2) mimetic, U-46619 (1 mu mol/L), reverse d the growth suppression induced by cell membrane remodeling. Conclusions. These studies suggest that changes in membrane fatty acid comp osition induced by EPA modulates PDGF-stimulated proliferation by engenderi ng a change in PDGF-stimulated TXA(2) synthesis. Furthermore, we conclude t hat TXA(2) functions as a comitogen for PD GF-stimulated mesangial cell gro wth.