A six-year follow-up of the relationship between N-acetyl-beta-glucosaminidase and albuminuria in relation to retinopathy

Urinary biomarkers involved in type 2 diabetes: a review

Diabetes mellitus is one of the most challenging health concerns of the 21st century. With at least 30% of the diabetic population remaining undiagnosed, effective and early diagnosis is of critical concern. Development of a diagnostic test, more convenient and reliable than those currently used, would therefore be highly beneficial. Urine as a diagnostic medium allows for non-invasive detection of biomarkers, including some associated with type 2 diabetes and its complications. This review provides a synopsis of those urinary biomarkers that potentially may provide a basis for the development of improved diagnostic tests. Three main pathways for the sourcing of potential makers are identified: kidney damage, oxidative stress and low-grade inflammation including atherosclerosis/vascular damage. This review briefly presents each pathway and some of the most relevant urinary biomarkers that may be used to monitor the development or progression of diabetes and its complications. In particular, biomarkers of renal dysfunction such as transferrin, type IV collagen and N-acetyl-beta-D-glucosaminidase might prove to be more sensitive than urinary albumin, the current gold standard, in the detection of incipient nephropathy and risk assessment of cardiovascular disease. Inflammatory markers including orosomucoid, tumour necrosis factor-alpha, transforming growth factor-beta, vascular endothelial growth factor and monocyte chemoattractant protein-1, as well as oxidative stress markers such as 8-hydroxy-2'deoxyguanosine may also be useful biomarkers for diagnosis or monitoring of diabetic complications, particularly kidney disease. However, the sensitivity of these markers compared with albumin requires further investigation.

Serum N-acetyl-beta-D-glucosaminidase profiles in type 1 diabetes secondary complications: causes of changes and significance of determination

The connection between changes in the activity of serum N-acetyl-beta-D-glucosaminidase (NAG, E.C.3.2.1.30) and iso-enzymes and degree of secondary complications was analyzed in four groups of type 1 diabetic patients (n=69): without complications (n=22); with retinopathy (n=16); with retinopathy and polyneuropathy (n=13), and with retinopathy, neuropathy, and nephropathy (n=18). In all groups statistically significant higher (P<0.001) percent fraction of A form (83.84+/-6.09, 84.37+/-5.74, 81.76+/-6.02, 76.37+/-7.38%, resp.) and lower (P<0.001, P<0.01) fraction of B form (15.87+/-5.65, 15.66+/-5.74, 18.33+/-5.98, 23.63+/-7.38, resp.) in total NAG compared with the control (A=69.38+/-4.79%, B=30.61+/-4.78%) were found. The differences in A as well as B forms between diabetic groups were not statistically significant. Significant strong positive correlations between total NAG and glycemia (0.494-0.623), total NAG and A form (0.934-0.966), and A form and glycemia (0.512-0.638) were found in all groups. No correlation was found between the fractions of B and A forms, except in the fourth group. The A form of diabetic patients in the fourth group was more acidic compared with the control and other diabetic groups. It was concluded that the changes in serum NAG and iso-enzymic profiles in diabetes are the consequence of its increased exocytose, especially of the A form, in hyperglycemia and posttranslational modifications of iso-enzymes. The total activity of serum NAG and iso-enzymic profiles cannot be used for monitoring the development and distinction of type 1 diabetes secondary complications.

Early changes in glomerular size selectivity in young adults with type 1 diabetes and retinopathy. Results from the Diabetes Incidence Study in Sweden

OBJECTIVE

To investigate the relationship between early-onset retinopathy and urinary markers of renal dysfunction.

RESEARCH DESIGN AND METHODS

The Diabetes Incidence Study in Sweden (DISS) aims to register all new cases of diabetes in young adults (15-34 years). In 1987-1988, 806 patients were reported and later invited to participate in a follow-up study focusing on microvascular complications after approximately 10 years of diabetes. In the present study, 149 patients with type 1 diabetes, completed eye examination, and urine sampling were included.

RESULTS

The patients with retinopathy (n=58, 39%) had higher HbA(1c) (P<.001) and urinary IgG2/creatinine (P<.05) and IgG2/IgG4 ratios (P<.05). Patients with maculopathy had the highest levels. No significant differences in urinary albumin/creatinine, glycosaminoglycans (GAGs)/creatinine, Tamm-Horsfall protein (THP)/creatinine, and IgG4/creatinine ratios were found. Women had higher urinary albumin/creatinine (P<.01) and urinary IgG2/creatinine ratios (P<.01) than men.

CONCLUSIONS

Young adults with type 1 diabetes and early-onset retinopathy had higher IgG2/creatinine and IgG2/IgG4 ratios than patients without retinopathy indicating that retinopathy is associated with a change in glomerular size selectivity. This was found in association with normal urinary albumin and THP excretion and may be suspected to reflect early general vascular changes.

Effects of pentoxifylline administration on urinary N-acetyl-beta-glucosaminidase excretion in type 2 diabetic patients: a short-term, prospective, randomized study

BACKGROUND

Tubulointerstitial injury is a major feature of diabetic nephropathy and an important predictor of renal dysfunction. In 45 patients with type 2 diabetes mellitus (DM), we prospectively analyzed urinary excretion of N-acetyl-beta-glucosaminidase (NAG), a marker of tubular renal damage; the potential relationship with urinary protein excretion; and effects of pentoxifylline (PTF) administration.

METHODS

Forty-five patients with type 2 DM initially were compared with 15 healthy controls matched for age and sex. After randomization, PTF (1,200 mg/d) was administered for 4 months to 30 patients and results were compared with data from a control group (n = 15).

RESULTS

Proteinuria and urinary NAG excretion were significantly greater in patients with DM with respect to healthy controls. Before PTF administration, baseline parameters were similar in both groups of patients with DM. At the end of the study, urinary protein excretion and NAG-creatinine ratios decreased in the active group from 920 +/- 522 mg/d and 14.3 +/- 16.9 U/g to 803 +/- 523 mg/d (P < 0.001) and 10.5 +/- 9.3 U/g (P < 0.05), respectively. Conversely, proteinuria and urinary NAG excretion did not change in the control group. Regression analysis showed that urinary NAG excretion was significantly associated with duration of DM (r = 0.61; P < 0.001) and proteinuria (r = 0.51; P < 0.001).

CONCLUSION

Urinary NAG excretion is elevated in patients with type 2 DM compared with healthy individuals and increases as nephropathy progresses. PTF administration is effective in reducing proteinuria and urinary NAG excretion in these patients. These findings suggest that PTF may have beneficial effects on tubulointerstitial damage in diabetic kidney disease.

Pattern of renal dysfunction associated with myocardial revascularization surgery and cardiopulmonary bypass

BACKGROUND AND OBJECTIVE

A variable incidence rate of renal dysfunction (3-35%) after cardiac surgery with cardiopulmonary bypass has been reported. The aim was to define the typical pattern of renal dysfunction that follows coronary surgery with cardiopulmonary bypass using albumin, immunoglobulin (IgG), alpha1-microglobulin and beta-glucosaminidase (beta-NAG) excretion as indicators.

METHODS

Twenty patients with preoperative normal renal function, defined by plasma creatinine, creatinine clearance, fractional excretion of sodium and renal excretion of proteins, undergoing elective myocardial revascularization surgery with cardiopulmonary bypass, were prospectively studied. Variables recorded were demographic and haemodynamic variables, duration of cardiopulmonary bypass and aortic clamping, intra- and postoperative urine output, plasma creatinine concentration, creatinine clearance and excretion of sodium, albumin, IgG, beta-glucosaminidase (beta-NAG), and alpha1-microglobulin. Measurements were made preoperatively, immediately before and then during and immediately after cardiopulmonary bypass, and again at 1, 24, 72 h, 7 and 40 days following surgery.

RESULTS

Albumin and IgG excretion rose significantly during cardiopulmonary bypass (P < 0.05), remaining at these levels at 24 h postoperatively. An increase of alpha1-microglobulin and beta-NAG concentrations was observed during cardiopulmonary bypass (P < 0.05), which were maintained until the seventh postoperative day and remained elevated in some patients at the 40th postoperative day. This correlated with preoperative diabetes mellitus (P < 0.001), low cardiac output after cardiopulmonary bypass (P < 0.001) and the duration of stay in the intensive care unit (P < 0.001).

CONCLUSIONS

The pattern of renal dysfunction after cardiopulmonary bypass for myocardial revascularization is characterized by temporary renal dysfunction at both glomerular and tubular levels with an onset within 24 h of surgery and which lasts between 24 h and 40 days, respectively, following surgery.

Serum alpha-tocopherol and ascorbic acid concentrations in Type 1 and Type 2 diabetic patients with and without angiopathy

BACKGROUND

Alpha-tocopherol and ascorbic acid form a part of scavenger system influencing the level of oxidative stress in diabetes mellitus. The aim of this study was to evaluate serum concentrations of alpha-tocopherol and ascorbic acid in Type 1 and Type 2 diabetes mellitus and to compare them with the presence of vascular complications as well as with oxidative stress and endothelial dysfunction.

METHODS

A total of 38 Type 1 and 62 Type 2 diabetic patients were subdivided into those with and without angiopathy. Serum alpha-tocopherol and ascorbic acid concentrations were estimated in all patients and in 38 healthy persons. Their results were compared with diabetes control, with oxidative stress measured by plasma malondialdehyde and with endothelial dysfunction estimated by serum N-acetyl-beta-glucosaminidase activity. In addition, the differences in biochemical variables were compared between patients with and without angiopathy.

RESULTS

Serum alpha-tocopherol related to the sum of cholesterol and triglyceride concentrations (AT/CHT ratio) was significantly lower in diabetic patients with macroangiopathy than in those without vascular changes (p<0.05). Serum ascorbic acid levels were significantly lower only in Type 2 diabetic patients with macroangiopathy as compared with healthy controls as well as with patients without vascular disease (p<0.01). Positive relationship was observed between serum alpha-tocopherol and cholesterol or triglyceride concentrations in both Type 1 and Type 2 diabetic patients. The presence of oxidative stress together with endothelial dysfunction measured by N-acetyl-beta-glucosaminidase activity was accompanied by lower AT/CHT ratio (p<0.005) in Type 2 diabetic patients.

CONCLUSION

Diabetic patients with proven angiopathy or with advanced oxidative stress and endothelial dysfunction have significantly lower AT/CHT ratio and ascorbic acid concentration in serum. Their low concentrations may participate at the increased level of oxidative stress in these individuals.

Comparison of laser-Doppler flowmetry with biochemical indicators of endothelial dysfunction related to early microangiopathy in Type 1 diabetic patients

The aim of this study was to compare biochemical markers of endothelial activation with microcirculation measured by laser-Doppler flowmetry in Type 1 diabetic patients with or without microangiopathy. A total of 44 Type 1 diabetic patients were subdivided into those with (n=24) and without (n=20) microangiopathy according to ophthalmological findings and the presence or absence of microalbuminuria. The control group consisted of 25 healthy people of comparable age, sex, and body mass index. Postocclusive reactive hyperemia (PORH) and thermal hyperemia (TH, at 44 degrees C) were measured at the forearm. Serum N-acetyl-beta-glucosaminidase (NAG) activity, serum E-selectin, and ICAM-1 concentrations were used as biochemical markers of endothelial dysfunction. A significantly lower velocity of perfusion increase during postocclusive hyperemia (PORH(max) x t(1)(-1)) and during thermal hyperemia (TH(max) x t(2)(-1)) (P<.01) were accompanied by higher serum NAG activity (20.9+/-4.6 vs. 16.3+/-2.5 U l(-1), P<.01) in diabetic patients with microangiopathy as compared to healthy persons. An inverse relationship was found between PORH(max) x t(1)(-1) and NAG (r=-.33) results in diabetic patients. In addition, higher mean values of serum NAG activity, E-selectin, and ICAM-1 concentrations were associated with significantly lower values of microcirculation parameters (PORH(max) x t(2)(-1) and TH(max) x t(2)(-1)) in six patients without microangiopathy who had at least one of the above biochemical markers higher than mean+2 S.D. range. We suggest that serum NAG activity, E-selectin, and ICAM-1 concentrations may be used together with laser-Doppler flowmetry in Type 1 diabetic patients as early indicators of vascular changes in very early stage of diabetic microangiopathy.

Relationship of serum N-acetyl-beta-glucosaminidase activity to oxidative stress in diabetes mellitus

Serum N-acetyl-beta-glucosaminidase activity was evaluated in 40 Type 1 and 40 Type 2 diabetic patients and compared with parameters of diabetes control and oxidative stress. Significantly increased mean serum N-acetyl-beta-glucosaminidase activity was found in both groups of diabetic patients as compared with the corresponding group of healthy persons (p < 0.01). Oxidative stress measured by plasma malondialdehyde concentration was significantly higher in Type 2 than in Type 1 diabetic patients (p < 0.01) but in comparison with control subjects it was higher only in Type 2 diabetes. Plasma malondialdehyde concentration positively correlated with body mass index (r=0.77, p<0.001) and with serum N-acetyl-beta-glucosaminidase activities (r=0.57, p <0.001). Treatment of 10 Type 2 diabetic patients with antioxidant alpha-tocopherol caused a significant decrease in malondialdehyde concentration (p < 0.001) which was accompanied by a decrease of N-acetyl-beta-glucosaminidase activity (p < 0.01). We conclude that serum N-acetyl-beta-glucosaminidase activity may be influenced by oxidative stress which is more pronounced in Type 2 than in Type 1 diabetic patients.

Markers of diabetic nephropathy

It is well established that the detection of microalbuminuria in a patient with diabetes mellitus indicates the presence of glomerular involvement in early renal damage. Recent studies have demonstrated that there is also a tubular component to renal complications of diabetes, as shown by the detection of renal tubular proteins and enzymes in the urine. In fact, tubular involvement may precede glomerular involvement, as several of these tubular proteins and enzymes are detectable even before the appearance of microalbuminuria. This review looks at the studies reported so far on serum and urinary markers of diabetic nephropathy, both glomerular and tubular, and their roles in the early detection of renal damage. The advantages and disadvantages of some of these markers are also discussed. The markers reviewed include (1) glomerular--transferrin, fibronectin, and other components of glomerular extracellular matrix, and (2) tubular--low molecular weight proteins (beta 2 microglobulin, retinol binding protein, alpha 1 microglobulin, urine protein 1), other proteins such as Tamm-Horsfall protein, beta 2 glycoprotein-1, urinary enzymes (N-acetyl-beta-D-glucosaminidase, cholinesterase, gamma glutamyltranspeptidase, alanine aminopeptidase), and tubular brush-border antigen.

Glycosaminoglycan sulodexide decreases albuminuria in diabetic patients

Albuminuria is a dominant biochemical feature of developing diabetic nephropathy. A disturbed metabolism of heparan sulphate characterized by an increased loss of anionic charges in the basement membrane has been considered as one of the main factors causing an increased albumin output into urine. All therapeutic approaches inducing a reduction of the albumin excretion rate (AER) have a protective effect on renal function. The effect of glycosaminoglycan sulodexide on albuminuria was studied in a group of 53 diabetic patients (26 Type 1 and 27 Type 2) with micro and macroalbuminuria. Sulodexide (Vessel Due F) was administered intramuscularly in one daily dose (600 lipasemic units) for 3 weeks followed by a 6 week wash-out period. A significant decrease of AER was found in a total cohort of patients following just 1 week of sulodexide treatment (mean 162 micrograms/min, range 10-2708 micrograms/min vs mean 248 micrograms/min, range 20-3160 micrograms/min, P < 0.001). This effect lasted 3-6 weeks after drug withdrawal. Similar results were obtained if Type 1 and Type 2 diabetic patients were evaluated separately but a delay of the AER reduction was observed in the latter group. In all patients the mean AER was reduced to 60-65% of the initial values. A greater effect of sulodexide on albuminuria was observed in patients with AER above 200 micrograms/min than in those with microalbuminuria (a reduction to 47 vs 65% of the initial output). Sulodexide did not significantly reduce albuminuria in 28% of diabetic patients ('non-responders'). In conclusion, glycosaminoglycan sulodexide may reduce AER in patients with micro or macroalbuminuria and it could slow down development of diabetic nephropathy.

Screening for microalbuminuria in type 2 diabetic patients: the evaluation of a dipstick test in general practice

To evaluate the Micral test, a semiquantitative dipstick test, in a general practice setting, 317 Type 2 diabetic patients completed a screening for microalbuminuria by means of the Micral test as well as immuno-nephelometry with the Disc 120 immuno-nephelometer (Hyland, Nivelles, Belgium). Data were collected in 10 general practices performing the Nijmegen Monitoring Project. At a regular check-up each Type 2 diabetic patient was asked to collect first morning urine samples on three consecutive days. The sensitivity of the Micral test was 67%, the specificity 93%. Between the practices the sensitivity ranged from 58% to 81%, the specificity from 87% to 95%. Microalbuminuria, defined as a mean urine albumin concentration > or = 20 mg I-1 by nephelometry on three consecutive days, was found in 66 patients (21%). The first Micral test correctly picked out these patients with microalbuminuria in 70% of the cases and in 90% those patients without microalbuminuria. The diagnostic performance of the Micral test was further proved by a Receiver Operating Characteristic (ROC) curve. The Area Under the Curve (AUC) of the Micral test was 0.84 (95% CI 0.78-0.90). Micral test results of 0 and 10 should be regarded as negative.

Increased urinary N-acetyl-beta-glucosaminidase (NAG) excretion in young insulin-dependent diabetic patients

We evaluated urinary N-acetyl-beta-glucosaminidase (NAG) excretion in overnight and in second morning urine in 50 young diabetic patients, aged 7.4-25 years with a disease duration from 2-19.6 years. In all patients we evaluated urinary NAG and creatinine excretion, in both overnight and second morning urine, glycosuria, fasting blood glucose and HbA1c levels, insulin requirement, blood pressure, and the presence of microangiopathic complications. Urinary NAG excretion was also evaluated in 69 age- and sex-matched controls. NAG was determined using 3-cresolsulfonphtaleinyl-beta-N-acetylglucosaminide as substrate (Boehringer Mannheim, Germany). In the diabetic patients NAG/Cre ratios were significantly higher than in controls both in overnight and second morning urine (P < 0.0005, respectively). We observed significantly higher NAG/Cre ratio levels in the second morning than in overnight urine, both in controls and in diabetics (P < 0.0005, respectively). Elevated (above 2 S.D. of the mean) NAG/Cre ratios were found in 17/50 patients (34%) in overnight urine and in 29/50 (58%) in second morning urine. No correlation was observed between NAG/Cre ratio levels and age, duration of disease, pubertal stage, body mass index, fasting blood glucose, glycosuria, insulin requirement and blood pressure. The patients with one or more complications did show NAG/Cre ratio levels significantly higher than those without complications (P < 0.005) in second morning urine, but not in overnight urine. Our study has demonstrated an increased rate of urinary NAG excretion in young IDDM patients, in particular in those with microangiopathic complications.

Early changes of serum N-acetyl-beta-glucosaminidase, tissue plasminogen activator and erythrocyte superoxide dismutase in relation to retinopathy in type 1 diabetes mellitus

Biochemical markers of early changes that are characteristic for diabetic microangiopathy are not completely understood. We investigated activities of serum N-acetyl-beta-glucosaminidase (NAG), tissue plasminogen activator and erythrocyte superoxide dismutase in well defined groups of type 1 diabetic patients. Patients were selected on the basis of 4 year follow-up observation. Forty-two type 1 diabetic patients were subdivided into those without retinopathy (n = 13) throughout the study, those with newly developed or worsened retinopathy (n = 12) during 4 years and those with retinopathy already established at the beginning of the study and without evidence of its progression (n = 17). All diabetic patients had albustix-negative urine. A significant increase of the mean serum NAG activity during 4 years was found only in patients without retinopathy (P < 0.01) whereas no changes of the altered enzyme activities were present in patients with developing and established retinopathy. The mean activity of tissue plasminogen activator was elevated in all groups of diabetic patients compared with healthy subjects (P < 0.001). A significant positive correlation was found between plasminogen activator and serum NAG (r = 0.51, P < 0.01). Erythrocyte superoxide dismutase was higher in diabetic patients than in healthy persons (P < 0.01) but no differences were observed between the patients with or without retinopathy. Superoxide dismutase positively correlated with NAG (r = 0.57, P < 0.01). We conclude that early functional changes precede a morphological development of diabetic retinopathy as was evident from the altered enzyme activities.

Cost-effectiveness of screening for microalbuminuria using immunochemical dipstick tests or laboratory assays in diabetic patients

To analyse the cost-effectiveness ratio of screening for microalbuminuria in diabetic patients using either dipstick tests or laboratory assays, 506 diabetic patients were screened for microalbuminuria using both a traditional laboratory assay (strategy I) or a laboratory assay only in the case of a positive dipstick result (strategy II). Dipstick pre-screening was considered positive if at least one of the tests performed by the two different operators showed an albumin excretion rate > 20 micrograms min-1. It was performed using a new dipstick, Micral-Test, designed to distinguish low albumin concentrations. Biological assay was the reference method. Costs were related to laboratory assays (strategy I) or to dipstick tests and laboratory assays for positive results (strategy II). The loss of effectiveness was related to false negative results of strategy II. The double dipstick pre-screening showed a sensitivity of 90.8% and a specificity of 80.1%. Its predictive value was 97% for a negative result and 55.6% for a positive result. False positive results were associated with elevated urinary volumes. Compared with strategy I, strategy II showed a sensitivity of 90.8%, a specificity of 100%, and predictive values of 100% and 97.5%, respectively, for positive and negative results. In a fictitious cohort of 10,000 patients, strategy II yielded a gain of 16,750 pounds on the first year, which decreased to 5345 pounds after 30 years. The loss in effectiveness was estimated at 2.38 quality adjusted life years of a diabetic patient (QALYd) initially, and decreased to 0.91 QALYd after 30 years, the annual cost-effectiveness ratio being close to 6600 pounds QALYd-1.(ABSTRACT TRUNCATED AT 250 WORDS)