N-3 and n-6 fatty acid metabolism in undifferentiated and differentiated human intestine cell line (Caco-2). 
Metabolism of n-6 and n-3 fatty acids in the undifferentiated and differentiated human adenocarcinoma colon cell line (Caco-2) was studied.  In cells incubated with either 18:2n-6 or 18:3n-3, no significant amounts of long chain n-6 and n-3 metabolites were found.  Incubation with either 18:3n-6 or 18:4n-3 raised significantly the levels of 20:3n-6 and 20:4n-3, respectively.  In the undifferentiated cells, significant proportions of 20:3n-6 and 20:4n-3 were further delta 5-desaturated to form 20:4n-6 and 20:5n-3, respectively.  Incubation with either 20:4n-6 or 20:5n-3 raised the levels of their direct elongation products, 22:4n-6 and 22:5n-3, respectively.  Incubation with 22:4n-6 or 22:5n-3 increased the levels of 20:4n-6 and 20:5n-6.  These results suggest that delta 6-desaturation in the Caco-2 cells is less active in comparison with elongation, delta 5-desaturation and retro-conversion.  These enzymes were modulated by the state of differentiation, and appeared to be non-specific to n-3 and n-6 fatty acids.  When cells were incubated with 18:3n-6 and 18:4n-3 concomitantly, the levels of incorporation of total n-6 fatty acids into cellular lipids were greater than those of the n-3 fatty acids, whereas the ratios of 20+22 carbon metabolites to 18-carbon precursor favored n-3 over n-6 fatty acids.  These results suggest that n-3 and n-6 fatty acids were not metabolized identically in Caco-2 cells.