Urinary liver type fatty acid binding protein in diabetic nephropathy

Deterioration of diabetic nephropathy (DN) is largely determined by the degree of tubulointerstitial changes rather than the extent of histological changes in the glomeruli. Therefore, a tubular marker that accurately reflects tubulointerstitial damage may be an excellent biomarker for early detection or prediction of DN. Liver-type fatty-acid binding protein (L-FABP) is a 14 kDa small molecule that is expressed in the cytoplasm of human proximal tubules. In vivo experimental studies revealed that renal L-FABP gene expression was up-regulated by various stresses that cause tubulointerstitial damage, such as massive proteinuria, hyperglycemia, hypertension, ischemia and toxins, and that urinary excretion of L-FABP was increased. Recent clinical studies of patients with type 1 or type 2 diabetes demonstrated that urinary excretion of L-FABP derived from proximal tubules is a suitable biomarker for predicting and monitoring deterioration of renal function in DN. Moreover, therapeutic interventions with renoprotective effects reduced urinary L-FABP concentrations. Therefore, urinary L-FABP measured using the Human L-FABP ELISA Kit developed by CMIC Co., Ltd. (Tokyo, Japan) was confirmed as a newly established tubular biomarker by the Ministry of Health, Labour and Welfare in Japan in 2010. This review article summarizes the clinical significance of urinary L-FABP in DN.