The effects of various n-3 and n-6 polyunsaturated fatty acids on the secretion of insulin like growth factor-I (IGF-I) by MC3T3-E1 osteoblast-like cells

Abstract

Previous research has shown that some PUFAs have a positive effect on bone, although the cellular mechanism for this is unclear. One such hypothesis is that PUFAs may increase the secretion of IGF-I by osteoblasts. IGFs are autocrine and paracrine stimulators of osteoblasts resulting in increased gene transcription and proliferation. The purpose of this pilot study was to test this hypothesis by treating the cells with various representatives of the PUFA families and examining the effects thereof on secretion of IGF-I. MC3T3-E1 murine osteoblast-like cells were exposed to the n-6 PUFAs arachidonic acid (AA) and gamma-linolenic acid, the n-3 PUFAs eicosapentaenoic acid and docosahexaenoic acid at concentrations of 20ug/ml and a vehicle (ethanol, 0.1%). Prostaglandin E2 (1uM), a product of AA metabolism, as well as parathyroid hormone (0.01uM) were included in the study as positive controls. In some cases indomethacin (1uM) a cyclo-oxygenase blocker was added 45 minutes prior to addition of AA. After 24 hours the conditioned media were harvested and stored at -70 degrees celsius until IGF-I concentrations were determined by means of ELISA. Cell numbers were obtained by means of a standardised crystal violet staining method. Results from this experiment showed that parathyroid hormone increased IGF-I secretion as expected. The PUFAs all stimulated IGF-I secretion with the n-3 PUFAs having the largest effect. PGE2 did not increase IGF-I secretion as expected, this could be due to the fact that the concentration used might not have been optimal for this model. The results obtained support the claims that the n-3 PUFAs have a beneficial effect on osteoblastic IGF-I secretion, however, more experiments need to be conducted in order to verify these results. This work was supported by grants from the National Research Foundation (M.Coetzee) and the Research Development Fund (M.Coetzee).