The relationship between the insulin content and inhibitory effects of bovine colostrum on protein breakdown in cultured cells.

Protein Degradation in ten mammalian cell lines is markedly inhibited by small amounts of bovine colostrum. This response is consistent with the growth-promoting activity of colostrum that has been reported previously. Fractionation of colostrum on DEAE cellulose showed that most of the inhibitory activity against protein breakdown on H35 cells coeluted with insulin. Insulin concentrations in different batches of bovine colostrum ranged from 0.67 nM to 5.7 nM, approximately 100-fold higher than in blood. The sensitivity of protein breakdown in H35 or MH1C1 hepatoma lines to these colostrum samples was proportional to their insulin concentrations and could largely be accounted for by the amount of insulin present. Removal of insulin from colostrum by means of a protein A-anti-insulin antibody affinity column was accompanied by a loss of the ability of colostrum to inhibit protein breakdown in H35 or MH1C1 cells. However, in IMR90 fibroblasts, a cell line with a similar sensitivity to colostrum as the two hepatomas but very insensitive to insulin, protein breakdown was still inhibited by the insulin-free colostrum. These results suggest that, whereas the effect of bovine colostrum in H35 or MH1C1 cells is actually a response to insulin, different growth factors in colostrum account for the inhibition of protein breakdown in other cell lines.