Inhibition of Caco-2 cell proliferation by (n-3) fatty acids: Possible mediation by increased secretion of insulin-like growth factor binding protein-6

The present study was performed to examine the effect of various polyunsatu rated fatty acids (PUFAs) on the proliferation of the human colon adenocarc inoma cell line, Caco-2 cells. The ability of individual PUFAs to stimulate cell proliferation was examined by culturing cells in serum-free medium. E icosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) inhibited cell pr oliferation, and therefore, cells cultured with 100 mu M EPA or DHA reached much lower final densities compared to cells cultured with 2 mu M linoleic acid (control) or 100 mu M linoleic acid (LA). Insulin-like growth factors (IGFs) are autocrine and paracrine growth promoters of a variety of cells, and a family of IGF binding proteins (IGFBPs) modulates the biological act ions of IGF-I and IGF-II. Since IGF-II has been shown to be an autocrine re gulator of Caco-2 cells, we investigated the effects of these PUFAs on IGF- II and IGFBP secretion in association with Caco-2 cell proliferation. Immun oblot analysis of serum-free conditioned medium using a monoclonal anti-IGF -II antibody showed that concentrations of both mature 7,500 M-r and higher M-r forms of pro IGF-II were lower in conditioned medium by cells treated with EPA or DHA compared with LA. Ligand blot analysis revealed that the se cretion of IGFBP-6 was significantly higher in cells treated with 100 mu M EPA or DHA compared to LA. Northern blot analysis demonstrated that the ste ady state levels of IGFBP-6 mRNA were higher in cells cultured with EPA or DHA compared to the controls. Exogenously added IGFBP-6 inhibited Caco-2 ce ll proliferation. We propose that low IGF-II/IGFBP-6 ratios may have result ed in less free IGF-II and, consequently, the slower proliferation of Caco- 2 cells treated with EPA or DHA. (C) 2000 Elsevier Science Inc.