Indian Pediatrics 2003; 40:410-414 

Urinary N-acetyl-beta-D-glucosaminidase Activity in Type I Diabetes Mellitus

N. Mungan, B. Yuksel, M. Bakman, A.K. Topaloglu, G. Ozer

From the Division of Pediatric Endocrinology and Metabolism, Cukurova University, Faculty of Medicine, Adana, Turkey.

Correspondence to: Dr. N. Mungan, Cukurova University, Faculty of Medicine, Division of Pediatric Endocrinology and Metabolism, Balcali, Adana, Turkey 10330. E-mail: [email protected]

Manuscript received: May 25, 2002; Initial review completed: August 26, 2002; Revision accepted: December 23, 2002.

We measured urinary albumin excretion rate (AER) and N-acetyl-beta-D-glucosaminidase (NAG) activity in relation to disease duration, acetylated hemoglobin (HbA1c), hypertension and puberty in 44 children and adolescents with type 1 diabetes mellitus. AER and Urinary NAG activity were significantly higher in the patients compared to controls (AER 19.4 ± 35.8 vs 4.7 ± 4.4, NAG activity 5.6 ± 0.6U vs. 1.6 ± 0.2U). Microalbuminuria was present in seven patients (15.9%), all of whom were pubertal. There was no correlation between AER and urinary NAG activity. There was a significant direct correlation between AER and disease duration (P <0.05), HbA1c (P <0.05), diastolic blood pressure (P <0.05) and puberty (P <0.05). None of the microalbuminuria related variables was significantly correlated with urinary NAG activity. Puberty was an independent factor for elevated urinary NAG activity. This study shows that urinary NAG is elevated in children and adolescents with type 1 diabetes mellitus, but is not associated with AER related factors except for puberty. Urinary NAG activity does not appear to be a useful marker for early detection of diabetic nephropathy in children and adolescents with type 1 diabetes mellitus.

Key words: Microalbuminuria, Type 1 diabetes mellitus.

It is well established that micro-albuminuria precedes overt diabetic nephro-pathy. Microalbuminuria in insulin dependent diabetes mellitus (type 1 diabetes mellitus) is usually seen in pubertal or postpubertal patients and is precipitated by poor glycemic contol, prolonged disease duration, hyper-tension and smoking(1). N-acetyl-beta-D-glucosaminidase (NAG) is a lysosomal enzyme located in the proximal renal tubuli. Urinary NAG activity has been shown to be elevated in patients with type 1 diabetes mellitus(2-4). It has been claimed that elevated urinary NAG activity may be an indicator of early diabetic nephropathy and directly correlate with the degree of metabolic control(2,5,6). However, this veiw has been challenged by others(7-9). In this study, we investigated urinary NAG activity in relation to microalbuminuria and standard diabetic nephropathy related parameters i.e. disease duration, glycosylated (Alc) hemolgobin, hypertension and puberty.

Subjects and Methods

Study population consisted of 44 randomly selected patients with type 1 diabetes mellitus aged 6-20 years with disease duration of 2.0-11.0 years. Forty-four age and sex matched healthy controls were randomly selected from the Well Child Clinic. Urinary NAG activity in morning urine samples from 36 diabetic patients and 15 controls was determined by a colorimetric method using 3-cresolsulfonphataleiny1-beta-N-acetyl-glucosaminidase as the substrate (Boehringer Mannheim, Germany)(10) and factored by urinary creatinine (Cr) concentration. The result was expressed as NAG/Cr.

Albumin in 12 h overnight urine sample was measured by an immunoturbidimetric method. Microalbuminuria was defined as an albumin excretion rate above 20 µg/min but below 200 µg/min in two out of three overnight urine collections. Hemoglobin A1c value for each patient was obtained by averaging four hemoglobin Alc measure-ments with a turbidometric inhibition immunoassay (Boehringer Mannheim, Germany) within the preceding year. Blood pressures were measured using a standard sphygmomanometer with an appropiate cuff size in resting supine position. Pubertal staging was done according to the Tanner criteria(11).

Statistical significance was calculated using Student ‘t’ test and Chi square test. For those variables with non normal distribution, Mann-Whitney ‘U’ test was used. Pearson correla-tion coefficients were calculated to examine associations between the parameters. A multiple linear regression analysis was carried out to determine predictor(s) of increased urinary NAG activity. SPSS software package was used for all statistical analysis.

Results

There was no significant difference between the patient and the control groups in age, sex, pubertal status, body mass index, systolic and diastolic blood pressures (Table 1). However, albumin excretion rate and urinary NAG/Cr were both significantly higher in the patient group. When only cases with urinary NAG/Cr values were taken into comparison, there was a significant difference between the patient and the control groups only in albumin excretion rate and urinary NAG/Cr. Microalbuminuria was present in 7 patients (15.9%) all of whom were pubertal. There was significant direct correlation between albumin excretion rate and disease duration (r 0.34, P <0.05), HbA1c (r 0.31, P <0.05), diastolic blood pressure (r 0.26, P <0.05) and puberty (r 0.34, P <0.05). None of the variables were significantly correlated with urinary NAG/Cr. Also, there was no correlation between albumin excretion rate and urinary NAG/Cr. Pubertal patients, when compared to prepubertal ones, showed significantly higher values for disease duration, HbA1c, albumin excretion rate and urinary NAG/Cr (Table II). Disease duration, HbA1c, albumin excretion rate and urinary NAG/Cr in the pubertal patients remained significantly higher when only those cases with urinary NAG/Cr values were taken into comparison. There was no significant difference in urinary NAG/Cr between prepubertal and pubertal control gropus (1.0 ± 1.2 vs 2.0 ± 1.2; P >0.05). Pubertal patients had significantly higher urinary NAG/Cr when compared to the pubertal controls (6.5 ± 6.5 vs 2.0 ± 1.2; P <0.001). Likewise, prepubertal patients had significantly higher urinary NAG/Cr than prepubertal controls (3.9 ± 4.5 vs 1.0 ± 1.2; P <0.05). Presence of puberty was a significant independent factor for urinary NAG activity after adjustments for age, sex, disease duration and HbA1c in multiple regression analysis.

Table I 

Comparison of Patient and Control Groups.

	Patients (n = 44) Mean ± SD	Control (n = 44) Mean ± SD
Age (yr)	12.9 ± 3.3	12.1 ± 3.0
Sex	M:F::1:1	M: 24 (54.6%) F: 20(45.4%)
Prepubertal/ Pubertal	16/28	17/27
Body Mass Index	18.6 ± 3.1	18.8 ± 2.4
Systolic blood pressure (mmHg)	111.9 ± 12.7	109.8 ± 19.6
Diastolic blood pressure (mmHg)	74.1 ± 9.4	71.4 ± 7.7
Albumin excretion rate (µg/min)	19.4 ± 35.8	4.7 ± 4.4†
NAG/Cr (U/g)*	5.6 ± 0.6 (n = 36)	1.6 ± 0.19† (n = 15)

* N-acetyl-D-glucosaminidase creatinine.
† p <0.05 

Table II 

Comparison of Prepubertal and Pubertal Patients and Controls

	Prepubertal patients Mean±SD (n=16)	Pubertal Patients Mean±SD (n=28)	P	Prepubertal controls Mean±SD (n=17)	Pubertal controls Mean±SD (n=27)	P
Disease duration (yr)	3.9±1.5	5.7±2.9	-	-	-	-
Diastolic blood pressure (mmHg)	67.2±8.6	78.0±7.4	<0.001	65.9±6.2	74.8±6.4	<0.01
HbA1c (%)	7.4±0.0	9.7±2.9	<0.05	-	-	-
Albumin excretion rate (µg/min)	4.9±2.7	30.0±49.9	<0.05	3.5±2.2	5.3±4.0	NS
NAG/Cr (U/g)	3.9±4.5 (n = 12)	6.5±6.5 (n = 24)	<0.05	0.9±1.2 (n = 5)	2.0±1.2 (n = 10)	NS

Discussion

It is well established that micro-albuminuria precedes overt diabetic nephro-pathy. Poor metabolic control, puberty, hypertension, prolonged disease duration and smoking are known factors associated with the development of microalbuminuria(1). Our results confirm these previously known associations.

There has been a debate whether elevated urinary NAG activity could indicate incipient diabetic nephropathy. Any such potential candidate should have a consistent relationship with albumin excretion rate. Several studies have shown that urinary NAG activity is elevated in patients with type 1 diabetes mellitus and correlate with albumin excretion(2,5,6). They also demonstrated a direct correlation between urinary NAG and poor glycemic control, the major precipitating factor for microalbuminuria. In this study, we found that urinary NAG activity is elevated in-patients with type 1 diabetes mellitus. However, we detected no correlation between urinary NAG activity and albumin excretion. Moreover, urinary NAG activity was not associated with microalbuminuria related factors including levels of HbA1c, disease duration or hypertension. Several other studies, have also failed to show any associaltion between urinary NAG activity and micro-albuminuria(7-9). Hsiao, et al. found an association between urinary NAG and HbA1c but not with microalbuminuria and claimed that urinary NAG activity is an indicator of glycemic control in the early diabetic period before microalbuminuria appears(4). However, we did not find an association between urinary NAG and HbA1c.

We found a pubertal effect on urinary NAG activity. As for albumin excretion rate, urinary NAG activity was marked in pubertal patients. Absence of any significant difference in urinary NAG activity between prepubertal and pubertal controls in this study suggests that puberty may not have a significant role(1). Moreover, the fact that presence of puberty was a significant independent factor for urinary NAG activity after adjusting for age, sex, disease duration and HbA1c, suggests that puberty may elevate urinary NAG activity by diabetes.

In summary, this study shows that urinary NAG activity is elevated in children and adolescents with type 1 diabetes mellitus. However, this increase is not associated with albumin excretion rate or microalbuminuria related factors except for puberty. Therefore, urinary NAG activity does not appear to be a clinically useful marker for early detection of diabetic nephropathy in children and adolescents.

Contributors: BY, MB and GO collected the data, NM and AKT interpreted the results and wrote the manuscript.

Funding: None

Competing interests: None Stated.

 References