Tubular and Glomerular Injury in Diabetes and the Impact of ACE Inhibition

STINE E. NIELSEN TAKESHI SUGAYA PHD LISE TARNOW DMSC MARIA LAJER CANDSCI KATRINE J. SCHJOEDT ANNE SOFIE ASTRUP TSUNEHARU BABA PHD HANS-HENRIK PARVING DMSC PETER ROSSING DMSC OBJECTIVE We studied tubular and glomerular damage in type 1 diabetic patients by measuring urinary-liver fatty acid binding protein (U-LFABP) and albuminuria. Subsequently, we evaluated the effect of ACE inhibition on U-LFABP in patients with diabetic nephropathy. RESEARCH DESIGN AND METHODS We studied Caucasians with type 1 diabetes: 58 with normoalbuminuria (urinary albumin 30 mg/24 h), 45 with persistent microalbuminuria (30 -300 mg/24 h), and 45 with persistent macroalbuminuria (300 mg/24 h). A control group consisted of 57 healthy individuals. The groups were matched by sex and duration of diabetes. In addition, U-LFABP was measured in 48 type 1 diabetic patients with diabetic nephropathy in a randomized crossover trial consisting of 2 months of treatment with 20, 40, and 60 mg lisinopril once daily in random order. RESULTS In the cross-sectional study, levels of U-LFABP were significantly higher in normoalbuminuric patients versus those in the control group (median 2.6 [interquartile range 1.3- 4.1] vs. 19 [0.8 -3.0] g/g creatinine, P 0.02) and increased with increasing levels of albuminuria (microalbuminuric group 4.2 [1.8 - 8.3] g/g creatinine and nephropathy group 71.2 [8.1-123.4], P 0.05 for all comparisons). U-LFABP correlates with the urinary albuminto-creatinine ratio (R2 0.54, P 0.001). In the intervention study, all doses of lisinopril significantly reduced urinary albumin excretion rate and U-LFABP from baseline. The reductions in U-LFABP were 43, 46, and 40% with increasing doses of lisinopril (NS). CONCLUSIONS An early and progressive increase in tubulointerstitial damage as reflected by increased U-LFABP levels occurs in type 1 diabetic patients and is associated with albuminuria. Furthermore, ACE inhibition reduces the tubular and glomerular damage and dysfunction. - D common complication in diabetic iabetic nephropathy is a serious and patients. Although studies from selected centers suggest a declining incidence of diabetic nephropathy (1), still 30 40% of all patients with diabetes develop this complication (2). Diabetic nephropathy is associated with a higher risk of other complications such as cardiovascular disease, retinopathy, and neuropathy. It is the most common cause of endstage renal failure in Western countries. Therefore, it is of great interest to predict and prevent the development of diabetic nephropathy. Persistent microalbuminuria is the established predictor of development of diabetic nephropathy and progressive renal insufficiency. However, use of the urinary albumin excretion rate (UAER), as an in dicator of renal damage, has some limi t a t i o n s . S e v e r a l p a t i e n t s w i t h microalbuminuria do not progress to macroalbuminuria but continue having microalbuminuria (30%) or even regress to normoalbuminuria (1530% after 7.5 years of follow-up) (3). As reviewed previously, glomerular damage and tubulointerstitial damage are important factors in the pathology of diabetic nephropathy (2,4). Liver fatty acid binding protein (LFABP) is an intracellular carrier protein that is expressed in the proximal tubules in the human kidney and the liver (5). By immunohistochemical staining of renal biopsy specimens, it has been shown that urinary LFABP (U-LFABP) excretion is highly associated with structural and functional tubular kidney damage. This was confirmed in patients with chronic kidney disease including minimal-change nephritic syndrome, nephrosclerosis, lupus nephritis, and diabetic nephropathy (6). A previous study in chronic kidney disease has shown that serum LFABP levels do not affect the U-LFABP level, which suggests that there is no transglomerular passage of LFABP in chronic kidney disease and that the LFABP measured in urine originates primarily from tubular cells (7). It has been hypothesized that LFABP is a protective protein; however, previous studies have, to our knowledge, not been able to confirm this hypothesis (8). In patients with diabetic nephropathy, a reduction in albuminuria is a predictor of renoprotection (9). It is suggested that the combination of the two parameters, albuminuria and U-LFABP, would be useful in monitoring chronic kidney disease more than either alone. The relationship between albuminuria and U-LFABP has, to our knowledge, not been studied in type 1 diabetic patients. Furthermore, whether U-LFABP could be used to monitor the renoprotective effect on the decline in glomerular filtration rate (GFR) or the effect on urinary albumin excretion in short-term studies in type 1 diabetic patients with diabetic nephropathy has not been studied. The aim of this study was to investigate the levels of U-LFABP in a crosssectional study of type 1 diabetic patients tively. Plasma samples were stored at with different levels of albuminuria com- 80C, and urine samples were stored at pared with those in a nondiabetic control 20C until analysis. group. In addition, we wanted to explore The second study was a randomized the short-term effect of increasing doses double-masked crossover trial performed of the ACE inhibitor lisinopril on U- in 2005 (13). Patients were treated in ranLFABP levels in patients with type 1 dia- dom order with 20, 40, and 60 mg lisinbetes and diabetic nephropathy from a opril, with each period lasting 2 months. randomized, double-blind crossover A total of 56 patients with type 1 diabetes, study. hypertension (135/85 mmHg), and diabetic nephropathy were randomly asRESEARCH DESIGN AND signed in the study. METHODS The cross-sectional The primary end point was changes study was based on data from a cohort in UAER (micrograms per 24 h). Albuused to identify biomarkers of diabetic minuria was determined in three consecnephropathy by proteomic analyses (10). utive 24-h urine collections completed The population consisted of Caucasian immediately before the end of each treatpatients with type 1 diabetes and different ment period. Among the secondary end levels of albuminuria recruited from the points measured at the end of each treatoutpatient clinic at Steno Diabetes Center ment period were 24-h ambulatory blood in 2004. Based on albumin excretion in pressure and eGFR. U-LFABP was also 24-h urine samples that were collected as measured in 24-h urine collections (mipart of the routine care of the patients be- crograms per 24 h). For safety reasons, fore the present study, patients were di- blood pressure, plasma potassium, vided into three groups: 58 with plasma sodium, and plasma creatinine normoalbuminuria (UAER 30 mg/24 were determined 3 weeks after the beginh), 45 with persistent microalbuminuria ning of each treatment period. GFR (base(UAER between 30 and 300 mg/24 h in at line) was measured at baseline after a least two of three consecutive sam (...truncated)