the cross - sectional study was based on data from a cohort used to identify biomarkers of diabetic nephropathy by proteomic analyses ( 10 ) . the population consisted of caucasian patients with type 1 diabetes and different levels of albuminuria recruited from the outpatient clinic at steno diabetes center in 2004 . based on albumin excretion in 24-h urine samples that were collected as part of the routine care of the patients before the present study , patients were divided into three groups : 58 with normoalbuminuria ( uaer < 30 mg/24 h ) , 45 with persistent microalbuminuria ( uaer between 30 and 300 mg/24 h in at least two of three consecutive samples ) and 45 with persistent macroalbuminuria ( uaer > 300 mg/24 h in at least two of three consecutive samples ) . arterial blood pressure was measured three times with an appropriate - sized cuff after at least a 10-min rest . urinary albumin concentration was measured by an enzyme immunoassay from early morning spot urine samples and expressed as the urinary albumin - to - creatinine ratio ( uacr ) . estimated gfr ( egfr ) was calculated using the reexpressed four - variable modification of diet in renal disease study equation ( egfr = 175  plasma creatinine  age  1.212 [ if black ] or  0.742 [ if female ] ) as defined previously ( 11 ) where egfr is expressed as milliliters per minute per 1.73 m and plasma creatinine is expressed as milligrams per deciliter . u - lfabp was measured in a two - step sandwich enzyme - linked immunosorbent assay ( 12 ) and expressed as the u - lfabp - to - creatinine ratio . plasma samples were stored at 80c , and urine samples were stored at 20c until analysis . the second study was a randomized double - masked crossover trial performed in 2005 ( 13 ) . patients were treated in random order with 20 , 40 , and 60 mg lisinopril , with each period lasting 2 months . a total of 56 patients with type 1 diabetes , hypertension ( > 135/85 mmhg ) , and diabetic nephropathy were randomly assigned in the study . albuminuria was determined in three consecutive 24-h urine collections completed immediately before the end of each treatment period . among the secondary end points measured at the end of each treatment period were 24-h ambulatory blood pressure and egfr . u - lfabp was also measured in 24-h urine collections ( micrograms per 24 h ) . for safety reasons , blood pressure , plasma potassium , plasma sodium , and plasma creatinine were determined 3 weeks after the beginning of each treatment period . gfr ( baseline ) was measured at baseline after a single intravenous injection of 3.7 mbq cr - edta at 8:30 a.m. by determining the radioactivity in venous blood samples taken 180 , 200 , 220 , and 240 min after injection . blood pressure was measured by a 24-h ambulatory blood pressure device ( takeda tm2421 ; a & d medical , tokyo , japan ) . the study was initiated by a 2-month washout period during which all antihypertensive drugs were withdrawn , except for slow - release furosemide in individual doses to prevent fluid retention and hyperkalemia and control blood pressure . thereafter , patients were treated in random order with 20 , 40 , and 60 mg lisinopril , with each period lasting 2 months both studies were performed according to the principles of the declaration of helsinki and the intervention study was approved by the ethics committee of copenhagen county . written informed consent was obtained from all patients . normally distributed variables are expressed as means  sd ( baseline characteristics ) and means  sem . u - lfabp and uacr are given as medians ( interquartile range [ iqr ] ) . all comparisons between groups of normally or log - normally distributed parameters were performed with a one - way anova , and ordinal data were compared using a kruskall - wallis and a mann - whitney u test . changes in variables between visits during the intervention study are expressed as mean differences ( 95% ci ) . comparisons of log - u - lfabp between each treatment period were performed using linear mixed models . the adapted model was one with fixed effects of treatment level , visit , and carryover ( i.e. , treatment level in the previous period ) and a random effect of person included to account for the person independence in data . linear regression analysis was used to analyze for correlations between the change from baseline in u - lfabp based on differences in log - transformed values and changes in uaer , ambulatory blood pressure , and egfr , respectively . data were evaluated using spss ( version 14.0 ; spss , chicago , il ) . normally distributed variables are expressed as means  sd ( baseline characteristics ) and means  sem . u - lfabp and uacr are given as medians ( interquartile range [ iqr ] ) . all comparisons between groups of normally or log - normally distributed parameters were performed with a one - way anova , and ordinal data were compared using a kruskall - wallis and a mann - whitney u test . changes in variables between visits during the intervention study are expressed as mean differences ( 95% ci ) . comparisons of log - u - lfabp between each treatment period were performed using linear mixed models . the adapted model was one with fixed effects of treatment level , visit , and carryover ( i.e. , treatment level in the previous period ) and a random effect of person included to account for the person independence in data . linear regression analysis was used to analyze for correlations between the change from baseline in u - lfabp based on differences in log - transformed values and changes in uaer , ambulatory blood pressure , and egfr , respectively . data were evaluated using spss ( version 14.0 ; spss , chicago , il ) . patients with normoalbuminuria and microalbuminuria were slightly older than control subjects and patients with macroalbuminuria . clinical data of control group and type 1 diabetic patients differentiated according to the level of albuminuria in cross - sectional study data are means  sd , * median ( range ) , or median ( iqr ) . we found a significant difference in systolic blood pressure among the groups ( p = 0.009 ) because of a difference between control subjects and patients with microalbuminuria ( p = 0.017 ) and macroalbuminuria ( p = 0.001 ) . diastolic blood pressure was significantly higher in control subjects , whereas there was no difference among diabetic groups . the significant difference in serum creatinine was due to differences between the macroalbuminuric group and all other groups . u - lfabp ratios were significantly higher in the normoalbuminuric group versus the control group ( median 2.6 [ iqr 1.34.1 ] vs. 1.9 [ 0.83.0 ] g / g creatinine , p = 0.02 ) and increased with increasing levels of albuminuria ( microalbuminuric group 4.2 [ 1.88.3 ] g / g creatinine and macroalbuminuric group 71.2 [ 8.1123.4 ] g / g creatinine , p < 0.05 for all comparisons . u - lfabp in control group and three diabetic groups with different levels of albuminuria . u - lfabp correlated with uacr ( r = 0.54 , p < 0.001 ) in the combined group of all diabetic patients . in the normoalbuminuric group , there was also a significant but weak association between uacr and u - lfabp ( r = 0.07 , p = 0.04 ) . in patients with macroalbuminuria , u - lfabp levels correlated with uacr ( r = 0.50 , p < 0.001 ) and egfr ( r = 0.34 , p when adjusted for egfr , there was still a significant difference in u - lfabp for comparisons between patients with macroalbuminuria and the other groups ( p < 0.01 ) . there was a significant correlation between u - lfabp and systolic blood pressure ( r = 0.07 , p < 0.001 ) . however , this may be explained by the association between u - lfabp and renal function because it disappeared after adjustment for egfr and uacr . there were no significant associations between u - lfabp and sex , age , bmi , diastolic blood pressure , cholesterol , or a1c . a total of 56 patients were randomly assigned in the study , and 49 patients completed the study . one patient did not have u - lfabp measured at baseline ; results are given for the remaining 48 . age at baseline was ( mean  sd ) 50  10 years and the duration of diabetes was 33  10 years . baseline uaer was ( geometric mean ) 365 mg/24 h ( 95% ci 240554 ) . baseline gfr ( cr - edta ) was 73  28 ml / min per 1.73 m. all doses of lisinopril significantly reduced uaer , u - lfabp , and arterial blood pressure compared with baseline ( table 2 ) . at baseline , reductions from baseline in u - lfabp were 43% ( 95% ci 1562 ) , 46% ( 1964 ) , and 40% ( 1160 ) with increasing doses of lisinopril ( no significant difference between doses ) . the reduction in u - lfabp was associated with the changes in 24-h systolic ambulatory blood pressure ( r = 0.22 , p < 0.01 ) ( similar for diastolic ambulatory blood pressure ) and uaer ( r = 0.38 , p < 0.001 ) but not with changes in egfr . ( data are given for change from baseline to 40 mg of lisinopril , which gave the largest response , but the same results were found for the other doses of lisinopril . ) the decline in u - lfabp was still significant when adjusted for the decline in uaer and for 24-h systolic blood pressure ( p = 0.011 ) . laboratory data during treatment with 20 , 40 , and 60 mg lisinopril in random order compared with baseline in 48 type 1 diabetic patients with diabetic nephropathy data are means  sem or mean difference ( 95% ci ) . the friedman test for several related samples was used followed by a paired - samples t test if significant . * patients with normoalbuminuria and microalbuminuria were slightly older than control subjects and patients with macroalbuminuria . clinical data of control group and type 1 diabetic patients differentiated according to the level of albuminuria in cross - sectional study data are means  sd , * median ( range ) , or median ( iqr ) . we found a significant difference in systolic blood pressure among the groups ( p = 0.009 ) because of a difference between control subjects and patients with microalbuminuria ( p = 0.017 ) and macroalbuminuria ( p = 0.001 ) . diastolic blood pressure was significantly higher in control subjects , whereas there was no difference among diabetic groups . the significant difference in serum creatinine was due to differences between the macroalbuminuric group and all other groups . u - lfabp ratios were significantly higher in the normoalbuminuric group versus the control group ( median 2.6 [ iqr 1.34.1 ] vs. 1.9 [ 0.83.0 ] g / g creatinine , p = 0.02 ) and increased with increasing levels of albuminuria ( microalbuminuric group 4.2 [ 1.88.3 ] g / g creatinine and macroalbuminuric group 71.2 [ 8.1123.4 ] g / g creatinine , p < 0.05 for all comparisons . u - lfabp in control group and three diabetic groups with different levels of albuminuria . u - lfabp correlated with uacr ( r = 0.54 , p < 0.001 ) in the combined group of all diabetic patients . in the normoalbuminuric group , there was also a significant but weak association between uacr and u - lfabp ( r = 0.07 , p = 0.04 ) . in patients with macroalbuminuria , u - lfabp levels correlated with uacr ( r = 0.50 , p < 0.001 ) and egfr ( r = 0.34 , p < 0.001 ) . when adjusted for egfr , there was still a significant difference in u - lfabp for comparisons between patients with macroalbuminuria and the other groups ( p < 0.01 ) . there was a significant correlation between u - lfabp and systolic blood pressure ( r = 0.07 , p < 0.001 ) . however , this may be explained by the association between u - lfabp and renal function because it disappeared after adjustment for egfr and uacr . there were no significant associations between u - lfabp and sex , age , bmi , diastolic blood pressure , cholesterol , or a1c . a total of 56 patients were randomly assigned in the study , and 49 patients completed the study . one patient did not have u - lfabp measured at baseline ; results are given for the remaining 48 . age at baseline was ( mean  sd ) 50  10 years and the duration of diabetes was 33  10 years . baseline uaer was ( geometric mean ) 365 mg/24 h ( 95% ci 240554 ) . baseline gfr ( cr - edta ) was 73  28 ml / min per 1.73 m. all doses of lisinopril significantly reduced uaer , u - lfabp , and arterial blood pressure compared with baseline ( table 2 ) . at baseline , reductions from baseline in u - lfabp were 43% ( 95% ci 1562 ) , 46% ( 1964 ) , and 40% ( 1160 ) with increasing doses of lisinopril ( no significant difference between doses ) . the reduction in u - lfabp was associated with the changes in 24-h systolic ambulatory blood pressure ( r = 0.22 , p < 0.01 ) ( similar for diastolic ambulatory blood pressure ) and uaer ( r = 0.38 , p < 0.001 ) but not with changes in egfr . ( data are given for change from baseline to 40 mg of lisinopril , which gave the largest response , but the same results were found for the other doses of lisinopril . ) the decline in u - lfabp was still significant when adjusted for the decline in uaer and for 24-h systolic blood pressure ( p = 0.011 ) . laboratory data during treatment with 20 , 40 , and 60 mg lisinopril in random order compared with baseline in 48 type 1 diabetic patients with diabetic nephropathy data are means  sem or mean difference ( 95% ci ) . the friedman test for several related samples was used followed by a paired - samples t test if significant . * in our cross - sectional study , we have shown that the marker of tubulointerstitial damage , u - lfabp , is elevated in type 1 diabetic patients compared with nondiabetic healthy control subjects . in addition , we have shown that u - lfabp is further increased in type 1 diabetic patients with micro- and macroalbuminuria , reflecting increased tubular damage with increasing levels of albuminuria . there were no significant correlations between u - lfabp and sex , age , or a1c . in our randomized , double - masked crossover study , ace inhibition with lisinopril reduced u - lfabp . there was no significant difference in effect between doses of lisinopril from 20 to 60 mg daily . previous studies of u - lfabp in diabetes were cross - sectional studies on u - lfabp in type 2 diabetic patients . ( 14 ) performed a cross - sectional study in 356 adult type 2 diabetic patients . they divided the patients into four groups : normoalbuminuric , microalbuminuric , macroalbuminuric , and renal failure , but no control group was included . they reported a significant association between the stage of diabetic nephropathy and u - lfabp , although no significant difference between the normoalbuminuric and microalbuminuric groups was seen . the results from our cross - sectional study show that patients with normoalbuminuria and type 1 diabetes had higher u - lfabp than the healthy control subjects ( table 1 ) . the normoalbuminuric group had a significantly higher level of albuminuria than the healthy control subjects , but even with adjustment for this result , there was still a significant difference in u - lfabp between the two groups ( p = 0.014 ) . however , this possibility is not likely because u - lfabp is not correlated with a1c . another hypothesis is that some of the patients in the normoalbuminuric group had higher levels of u - lfabp as a predictor of future development of microalbuminuria and diabetic nephropathy . the significant association between uacr and u - lfabp in the normoalbuminuric group also indicated this . however , to test this hypothesis we need prospective follow - up studies in normoalbuminuric type 1 diabetic patients . we also saw that with increasing levels of albuminuria , from normoalbuminuria to microalbuminuria and macroalbuminuria , u - lfabp is increasing . part of this association can be explained by the transport with albumin of fatty acids to the proximal tubules . here the fatty acids are absorbed into the proximal tubular cells , where the role of lfabp is to transport the fatty acids to the mitochondria . therefore , when albuminuria increases , the lfabp gene is upregulated and more lfabp is excreted into the urine ( 15 ) . u - lfabp is also elevated independently of albuminuria because of increased tubular production due to tubular hypoxia and oxidative stress ( 16 ) , which is seen in diabetes ( 17 ) . our study is cross - sectional , and therefore we can not draw conclusions on the time perspective between elevation in u - lfabp and development of nephropathy . however , from earlier studies in nondiabetic chronic renal disease , the potential of u - lfabp as an early predictor of nephropathy is supported . ( 18 ) performed a multicenter observational trial in 48 patients with nondiabetic chronic kidney disease . retrospectively , they divided the patients into progressors and nonprogressors in their chronic kidney disease based on changes in creatinine clearance during 1 year of follow - up . they found that u - lfabp had a higher sensitivity ( 94% ) than urinary albumin ( 69% ) but a lower specificity ( 63% ) than urinary albumin ( 94% ) in predicting progression in chronic kidney disease . u - lfabp is different from other suggested biomarkers , e.g. , 1- and 2-microglobulins : u - lfabp is produced in the tubular cells , whereas 1- and 2-microglobulins are freely filtered through the glomerular basement membrane . during poor glycemic control , urinary excretion of 2-microglobulin is increased ( 19 ) ; this is a result of a lack of reabsorption in the damaged tubular cell ( 20,21 ) . 2-microglobulin is unstable at low ph , causing an underestimate of the tubular damage ( 22 ) . in our randomized , crossover study , we saw that 2 months of ace inhibition reduces u - lfabp by 40% . there was no significant difference in the decline in u - lfabp among doses of lisinopril , suggesting an optimal effect with 20 mg lisinopril daily , which was in contrast to the increased decline in uaer when doses of lisinopril were increased from 20 to 40 mg . we observed that the decrease in u - lfabp is associated with a decrease in albuminuria , but the relatively weak association ( r = 0.38 , p < 0.001 ) supports the fact that the decline in u - lfabp is not only explained by reduced albuminuria but also suggests , as mentioned earlier , that the reduction also reflects reduced tubular damage . the decrease in u - lfabp indicates that the tubular damage and upregulation of the u - lfabp gene are reversible . our finding is in accordance with earlier studies in type 2 diabetic patients ( 23 ) , which showed a significant decrease in u - lfabp when these patients were treated with an angiotensin ii receptor antagonist . experimental studies in diabetic rats have shown that renin - angiotensin - aldosterone system blockade reduces antiapoptotic factors ( 24 ) and that oxidative stress in tubular cells is reduced and chronic hypoxia is corrected independent of the blood pressure  lowering effect ( 25 ) and thereby preserves tubular function . in summary , an early and progressive rise in tubulointerstitial damage as reflected by increased u - lfabp levels occurs in type 1 diabetic patients and is associated with albuminuria . our studies indicate that u - lfabp is a new marker of tubular damage and a potential supplement to the glomerular damage marker albuminuria for prognosis , diagnosis , and treatment of kidney injury , although further longitudinal studies are needed .
objectivewe 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 methodswe studied caucasians with type 1 diabetes : 58 with normoalbuminuria ( urinary albumin 
 < 30 mg/24 h ) , 45 with persistent microalbuminuria ( 30300 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.resultsin 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 1.34.1 ] vs. 19 [ 0.83.0 ] g / g creatinine , p = 0.02 ) and increased with increasing levels of albuminuria ( microalbuminuric group 4.2 [ 1.88.3 ] g / g creatinine and nephropathy group 71.2 [ 8.1123.4 ] , p < 0.05 for all comparisons ) . 
 u - lfabp correlates with the urinary albumin - to - 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).conclusionsan 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 .