Liver-type fatty acid binding protein (L-FABP) is a 14kDa protein found in the 
cytoplasm of human renal proximal tubules. Fatty acids are bound with L-FABP and 
transported to the mitochondria or peroxisomes, where fatty acids are 
beta-oxidized, and this may play a role in fatty acid homeostasis. Moreover, 
L-FABP has high affinity and capacity to bind long-chain fatty acid oxidation 
products, and may be an effective endogenous antioxidant. Renal L-FABP is rarely 
expressed in the kidneys of rodents. In order to evaluate the pathological 
dynamics of renal L-FABP in kidney disease, human L-FABP chromosomal transgenic 
mice were generated. Various stress, such as massive proteinuria, hyperglycemia, 
hypertension, and toxins overloaded in the proximal tubules were revealed to 
up-regulate the gene expression of renal L-FABP and increase the excretion of 
L-FABP derived from the proximal tubules into urine. In clinical studies of 
chronic kidney disease (CKD), urinary L-FABP accurately reflected the degree of 
tubulointerstitial damage and correlated with the rate of CKD progression. 
Furthermore, a multicenter trial has shown that urinary L-FABP is more sensitive 
than urinary protein in predicting the progression of CKD. With respect to 
diabetic nephropathy and acute kidney disease (AKI), urinary L-FABP is an early 
diagnostic of kidney disease or a predictive marker for renal prognosis. After 
many clinical studies, urinary L-FABP was approved as a new tubular biomarker 
promulgated by the Ministry of Health, Labour and Welfare in Japan.