Liver-type fatty acid-binding protein (l-FABP) is expressed in renal proximal tubules and is reported to be a useful marker for progression of chronic glomerulonephritis. The aim of this study was to determine whether urinary l-FABP levels are altered at various stages of diabetic nephropathy and whether pitavastatin affects urinary l-FABP levels in early diabetic nephropathy. Fifty-eight patients with type 2 diabetes (34 men and 24 women, median age 52 years) and 20 healthy, age-matched subjects (group E) were recruited for the study. The diabetic patients included 12 patients without nephropathy (group A), 20 patients with microalbuminuria (group B), 14 patients with macroalbuminuria and normal renal function (group C), and 12 patients with chronic renal failure but not undergoing hemodialysis (blood creatinine >1.2 mg/dl; mean 2.5 mg/dl, group D). Twenty group B patients were randomly assigned to receive 1 mg/day pitavastatin (10 patients, group B1) or placebo (10 patients, group B2). Treatment was continued for 12 months. Urinary l-FABP levels were measured by enzyme-linked immunosorbent assay. Urinary 8-hydroxydeoxyguanosine and serum free fatty acids (FFAs) were also measured in group B. Urinary l-FABP levels in groups A-D were 6.2 +/- 4.6 microg/g creatinine, 19.6 +/- 13.5 microg/g creatinine, 26.8 +/- 20.4 microg/g creatinine, and 52.4 +/- 46.8 microg/g creatinine, respectively. Urinary l-FABP levels in groups B-D were significantly higher than those in healthy subjects (group E, 5.8 +/- 4.0 microg/g creatinine) (group B, P < 0.05; group C, P < 0.01; group D, P < 0.01). In group B1, urinary albumin excretion (UAE) and urinary l-FABP levels were decreased after pitavastatin treatment (UAE before, 110 +/- 74 microg/min; 6 months, 88 +/- 60 microg/min, P < 0.05; 12 months, 58 +/- 32 microg/min, P < 0.01; l-FABP before, 18.6 +/- 12.5 microg/g creatinine; 6 months, 12.2 +/- 8.8 microg/g creatinine, P < 0.05; 12 months, 8.8 +/- 6.4 microg/g creatinine, P < 0.01). In group B2, UAE and l-FABP levels showed little change during the experimental period. In group B1, urinary 8-hydroxydeoxyguanosine was decreased 12 months after pitavastatin treatment (before 32.5 +/- 19.5 ng/mg creatinine, after 18.8 +/- 14.5 ng/mg creatinine, P < 0.01), but in group B2, these showed little difference during the experimental period. In both groups B1 and B2, serum FFAs showed little difference during the experimental period. Urinary l-FABP levels appear to be associated with the progression of diabetic nephropathy, and pitavastatin may be effective in ameliorating tubulointerstitial damage in early diabetic nephropathy.