A polymorphism in the human intestinal fatty acid binding protein alters fatty acid transport across Caco-2 cells

The human intestinal fatty acid binding protein (IFABP) binds long-chain fatty acids in vitro, but its intracellular function has remained speculative. A poly morphism in the gene that encodes IFABP results in an alanine (Ala(54)) to threonine (Thr(54)) substitution at codon 54 that alters the in vitro binding affinity of the protein for long-chain fatty acids. To identify potential functional variability between Ala(54) and Thr(54) IFABP, we established permanently transfected Caco-2 cell lines that express either Ala(54) or Thr(54) IFABP. We found that Caco-2 cells expressing Thr(54) IFABP transport long-chain fatty acids and secrete triglycerides to a greater degree than Caco-2 cells expressing Ala(54) IFABP. These results provide the first demonstration that IFABP participates in the intracellular transport of long-chain fatty acids. In addition, the observed increase in transport of fatty acids across cells expressing Thr(54) IFABP suggests a plausible physiologic mechanism for our prior observation that Pima Indians with a Thr(54) IFABP genotype have increased post-absorptive lipid oxidation rates and are more insulin-resistant than Pimas with a Ala(54) IFABP genotype.