Oleic acid distribution in small intestinal epithelial cells expressing intestinal-fatty acid binding protein

Intestinal-fatty acid binding protein (I-FABP) has been proposed to target long chain fatty acids (LCFA) to triglyceride synthesis pathways in the intestinal epithelium. In the present studies hBRIE 380i cells, which endogenously express I-FABP only when fully differentiated, were used to investigate the role of I-FABP in LCFA incorporation and targeting by examining the relative distribution of [3H]-oleic acid in cellular lipids in these cells. [3H]-oleic acid incorporation into triglyceride was significantly higher in hBRIE 380i cells expressing I-FABP than in cells not expressing I-FABP. After l5 min, 1 and 4 h of incubation, cells expressing I-FABP incorporated 24.0%, 34.0% and 43.9% of [3H]-oleic acid into triglyceride, while newly confluent cells (no I-FABP expression) incorporated 15.6%, 18.3% and 31.9%. An I-FABP negative cell line, hBRIE 380i-neg cells, was stably transfected to investigate the effect of adding I-FABP to small intestinal epithelial cell lines. No measurable differences in [3H]-oleic acid incorporation into triglyceride was detected in these transfectants. Additionally I-FABP expression had no effect on [3H]-oleic acid incorporation or distribution within phospholipid subclasses in hBRIE 380i or transfected hBRIE 380i-neg(fabpi) cells. Our data from hBRIE 380i cells suggest that I-FABP can target LCFA to triglyceride synthesis pathway. However, endogenous I-FABP expression was also correlated to cellular differentiation and therefore raises the possibility that other differentiation-dependent factors may have a role in LCFA targeting. Because no effects of I-FABP were detected in the transfected hBRIE 380i-neg(fabpi) cells, it is concluded that factors in addition to I-FABP play a major role in determining the metabolic fate of LCFA in small intestinal epithelial cells.