[Intestinal fatty acid-binding protein (I-FABP) as a new biomarker for intestinal diseases]

Fatty acid binding protein (FABP) is one of the intracellular proteins, with a low molecular weight of approximately 15 kDa, that plays important roles in the transportation and metabolism of long-chain fatty acids. FABP family proteins could be used as tissue specific injury marker based on the following characteristics of FABP: (1) a soluble protein in the cytoplasm, (2) high tissue specificity, (3) abundance in the tissue, and (4) low molecular weight. Among the FABP family proteins, intestinal fatty acid-binding protein(I-FABP) is specifically and abundantly present in epithelial cells of the mucosal layer of the small intestinal tissue. I-FABP is also considered to be rapidly released into the circulation just after small intestinal mucosal tissue is injured. Based on this mechanism, many investigators have already reported the relationship between serum I-FABP concentration and small intestinal diseases from early 1990s. Recently, we have succeeded in establishing a sandwich ELISA system for measuring human I-FABP concentration by using the combination of antibodies highly specific to I-FABP. This ELISA system did not show any cross-reactivity with other types of FABP and indicated excellent quantitative characteristics such as reproducibility, dilution linearity, and recovery. Using this ELISA system, we determined that the reference value of serum I-FABP concentration is designated to 2.0 ng/mL or less in the circulation of normal healthy individuals. In considering the clinical potential of serum I-FABP concentration, this sandwich ELISA system may contribute as a tool to perform differential diagnosis of acute abdomen with mucosal damage of the small intestine.