Urinary N-Acetyl B Glucosaminidase as an Earlier Marker of Diabetic Nephropathy and Influence of Low-Dose Perindopril/Indapamide Combination

Sitagliptin on Carotid Intima-Media Thickness in Type 2 Diabetes Mellitus Patients and Anemia: A Subgroup Analysis of the PROLOGUE Study

Introduction

Randomized clinical trials have not shown an additional clinical benefit of sitagliptin treatment over conventional treatment alone. However, studies of sitagliptin treatment have not examined the relationship between anemia and treatment group outcomes.

Methods

The PROLOGUE study is a prospective clinical trial of 442 participants with type 2 diabetes mellitus (T2DM) randomized to sitagliptin treatment or conventional treatment which showed no treatment differences [Estimated mean (± standard error) common carotid intima-media thickness (CIMT) was 0.827 ± 0.007 mm and 0.837 ± 0.007 mm, respectively, with a mean difference of -0.009 mm (97.2% CI −0.028 to 0.011, p = 0.309) at 24 mo of follow-up]. This is a post hoc subanalysis using data obtained from the PROLOGUE study; the study population was divided into anemic groups (n = 94) and nonanemic group (n = 343) based on hemoglobin level. And we analyzed for the changes in each CIMT parameter from baseline to 24 months in subgroups.

Results

The treatment group difference in baseline-adjusted mean common carotid artery- (CCA-) IMT at 24 months was −0.003 mm (95% CI −0.022 to 0.015, p = 0.718) in the nonanemic subgroup and −0.007 mm (95% CI −0.043 to 0.030, p = 0.724) in the anemic subgroup. Although there were no significant differences in the other CIMT parameters between the treatment groups in the anemic subgroup, the changes in mean and max ICA-IMT at 24 months in the nonanemic subgroup were significantly lower in the sitagliptin group than the conventional group [−0.104 mm (95% CI −0.182 to −0.026), p = 0.009 and −0.142 mm (−0.252 to −0.033), p = 0.011, respectively].

Conclusion

These data suggest that nonanemia may indicate a potentially large subgroup of those with T2DM patients that sitagliptin therapy has a better antiatherosclerotic effect than conventional therapy. Further research is needed to confirm these preliminary observations.

Urinary N-acetyl-beta-d-glucosaminidase levels in diabetic adults

Diabetes mellitus (DM) is known to be one of the most common causes of end-stage renal disease. The disease is usually not detected on time, because of the large functioning reserve of the kidney. Currently used markers (serum creatinine, creatinine clearance, urea, and electrolytes) remain relatively normal even when more than 50% of the renal nephron is not functioning. The aim of this study was to determine the level of urinary N-acetyl-beta-d-glucosaminidase (NAG) in diabetic adults in comparison with some currently used markers. A total of 56 diabetic patients between the ages of 23 and 63 were used for this study and 30 nondiabetic between the ages of 18 and 62 were used as control. The diabetic patients were classified into three groups based on how long they have been diagnosed: <2 years (25), 2–5 years (30), and >5 years (25). Spot midstream urine samples were collected into sterile containers, and blood samples were collected into plain tubes. All the analyses were done spectrophotometrically. Creatinine clearance was calculated using the Cockcroft–Gault Equation. There was a significant increase (P < 0.01) in NAG values of 2–5 years and above 5 years and control. The urinary microalbumin concentration of controls was significantly different (P < 0.05) only with those who have had DM for <2 years. Urinary creatinine concentration of control was significantly higher (P < 0.05) than values of all the diabetic groups. There was a significant increase (P < 0.01) in creatinine clearance of control group and those who have had DM for <2 years. It is thus concluded that urinary NAG can be used as an early marker in the diagnosis of diabetic nephropathy since urinary NAG increases first before the other markers analyzed in this current study begins to increase.

Association of neutrophil-gelatinase-associated lipocalin with microvascular complications in patients with type 2 diabetes: a cross-sectional study

Diabetic nephropathy and diabetic retinopathy are serious microvascular complications of diabetes mellitus. Recent studies have demonstrated that neutrophil-gelatinase-associated lipocalin (NGAL) may be accompanied by these complications during and before the appearance of microalbuminuria. In this study, we set out to research the role of NGAL in patients with diabetic nephropathy and diabetic retinopathy.

Material and methods

Eighty-two patients with type 2 diabetes were enrolled in our study. Urinary microalbumine and NGAL levels were measured in urine samples over 24 hours. We also studied NGAL levels in serum. All patients went through an ophthalmologic examination. The results were evaluated based on the presence of microalbuminuria and retinopathy.

Results

There were no significant differences in serum and urine NGAL levels between normoalbuminuric (n = 66) and microalbuminuric (n = 16) patients. We also did not find any significant difference in patients with retinopathy (n = 16) or without retinopathy (n = 66).

Conclusion

There are controversial findings about the role of NGAL in diabetic patients in medical literature. Standard values of urine and serum NGAL levels have yet to be determined. Our study suggests that NGAL is not a useful marker to differentiate microalbuminuric patients from normoalbuminuric subjects. We also did not find a relationship between NGAL levels and the presence of retinopathy. Additional studies with larger sample sizes will be required to confirm or refute these findings.

Elevated urinary N-acetyl-β-D-glucosaminidase is associated with high glycoalbumin-to-hemoglobin A1c ratio in type 1 diabetes patients with early diabetic kidney disease

Urinary N-acetyl-β-D-glucosaminidase (uNAG) predicted the progression of diabetic kidney disease (DKD) prior to development of albuminuria in diabetes patients. We sought whether uNAG level is associated with glycoalbumin-to-hemoglobin A1c ratio (G/A ratio), a marker of postprandial hyperglycemia and glycemic excursion, independent of albuminuria and kidney function. The association between uNAG excretion and G/A ratio was assessed in 204 consecutive subjects with type 1 diabetes (T1D) (mean age 43.9 years; 49.0% men). uNAG excretion level increased along with older age, hyperglycemia, and degree of albuminuria, but was not correlated with body mass index or estimated glomerular filtration rate (eGFR). Elevated uNAG showed robust association with higher G/A ratio (adjusted β = 0.103, P = 0.020) after adjustment for age, sex, body mass index, duration of diabetes, uACR, angiotensin blockers use, fasting plasma glucose, and hemoglobin level. uNAG showed better discriminatory performance for individuals with high G/A ratio than albuminuria (AUC 0.613 vs. 0.518, P = 0.038). Measurement of uNAG improved AUC for high G/A ratio from 0.699 to 0.748 (P = 0.043) when added to conventional risk factors (cutoff 5.24 U/g creatinine; sensitivity 62.5% and specificity 58.0%). In conclusion, Elevated uNAG was found to be associated with high G/A ratio in patients with T1D with early stage DKD, independent of age and albuminuria.

Antioxidative and renoprotective effects of residue polysaccharides from Flammulina velutipes

Three extractable polysaccharides including Ac-RPS, Al-RPS and En-RPS were extracted from the residue of Flammulina velutipes and their antioxidative and renoprotective effects on STZ-induced mice were investigated. Biochemical and antioxidant analysis showed that the En-RPS had potential effects in decreasing the serum levels of CRE, BUN, ALB and GLU significantly, increasing the renal activities of SOD, CAT and GSH-Px remarkably, and reducing the renal contents of MDA prominently. Furthermore, the histopathological observations also displayed that En-RPS could alleviate kidney damage. These results demonstrated that En-RPS extracted from the residue of F. velutipes possessed potent antioxidant activities, and could be used as a promising therapeutic agent for inhibiting the progression of diabetic nephropathy. In addition, the monosaccharide compositions of these three RPS were also analyzed.

Assessment of Neutrophil Gelatinase-Associated Lipocalin (NGAL) and Retinol-Binding Protein 4 (RBP4) in Type 2 Diabetic Patients with Nephropathy

Diabetic nephropathy (DN) is one of the most serious microvascular complications of diabetes. The study aims to evaluate the diagnostic value of serum neutrophil gelatinase-associated lipocalin (NGAL) and retinol-binding protein 4 (RBP4) as biomarkers for early detection of nephropathy in type 2 diabetic patients. The current study was performed on 150 type 2 diabetic patients. These patients were classified into three equal groups according to their albumin/creatinine ratio (ACR), including patients with normoalbuminuria (ACR <30 mg/g creatinine), patients with microalbuminuria (ACR = 30-300 mg/g creatinine), and patients with macroalbuminuria (ACR >300 mg/g creatinine). Fifty apparently healthy subjects matching the same age and socioeconomic status with diabetic subjects were selected as a control group. The plasma glucose, insulin, glycosylated hemoglobin (HbA1c), homeostasis model assessment of insulin resistance (HOMA-IR), lipid profile, urea, creatinine, cystatin C, glomerular filtration rate (GFR), NGAL, and RBP4 were measured in the studied groups. Significantly elevated NGAL and RBP4 levels were observed in micro- and macroalbuminuric diabetic groups when compared to the control and normoalbuminuric diabetic groups. NGAL and RBP4 were found to correlate positively with duration of diabetes, systolic and diastolic blood pressure, glucose, HbA1c, HOMA-IR, triacylglycerol, and ACR, but correlate inversely with GFR in DN groups. Receiver operating characteristic curves revealed that for early detection of DN, the best cutoff values to discriminate DN and diabetic without nephropathy groups were 91.5 ng/mL for NGAL with 87% sensitivity, 74% specificity, and area under the curve (AUC) = 0.881; 24.5 ng/mL for RBP4 with 84% sensitivity, 90% specificity, and AUC = 0.912; and 37.5 mg/g creatinine for ACR with 89% sensitivity, 72% specificity, and AUC = 0.819. RBP4 is more specific (90% specificity) than NGAL (74% specificity) and ACR (72% specificity). Therefore, RBP4 marker may serve as a tool to follow-up clinical monitoring of the development and progression of DN.

Association between Hemoglobin Concentration and the Progression or Development of Albuminuria in Diabetic Kidney Disease

AIMS

Anemia, which might contribute to pathogenesis of kidney dysfunction, is a common finding in patients with type 2 diabetes. The aim of this study was to investigate if hemoglobin concentration is associated with the degree of change in urinary albumin-creatinine ratio or the development of albuminuria in patients with type 2 diabetes.

METHODS

We measured hemoglobin concentration in 470 (296 men and 174 women) consecutive type 2 diabetic patients without albuminuria. We performed a follow-up study to assess the progression or development of albuminuria, the interval of which was 3.0 years. Then we evaluated relationships between hemoglobin concentration and albuminuria, using multivariate linear regression analyses and logistic regression analyses.

RESULTS

Eighty four patients developed albuminuria during follow-up duration. In multivariate analyses, hemoglobin concentration was negatively associated with a change in urinary albumin-creatinine ratio in men (ß = -0.259, P = 0.0002) and women (ß = -0.194, P = 0.030). Moreover, multivariate adjusted odds ratio associated with 1 g/L in hemoglobin for the development of albuminuria was 0.93 (95% confidence interval; 0.89-0.96) in men and 0.94 (95% confidence interval; 0.88-0.99) in women, respectively. And, multivariate analyses revealed that adjusted odds ratios for the development of albuminuria were 4.78 (95% confidence interval; 1.65-13.91) in men and 4.62 (95% confidence interval; 1.34-16.68) in women with anemia (hemoglobin < 130 g/L for men and < 120 g/L for women), which were higher than those without anemia.

CONCLUSIONS

Low hemoglobin concentration could be a predictor for the progression and development of albuminuria in patients with type 2 diabetes.

Cystatin C, Beta2 Microglobulin, N-Acetyl-beta-D-glucosaminidase, Retinol-Binding Protein, and Endothelin 1 Levels in the Evaluation of Sickle Cell Disease Nephropathy

OBJECTIVES

Renal involvement is common in sickle cell disease (SCD). Early demonstration of renal injury and commencement of appropriate treatment will increase survival and quality of life in these patients. We investigated renal manifestations in our pediatric and adult SCD patients and evaluated the role of cystatin C, Beta2 microglobulin (B2M), retinol-binding protein (RBP), N-acetyl-beta-D-glucosaminidase (NAG), and endothelin-1 (ET-1) to indicate renal damage.

METHODS

The study involved 45 pediatric and 10 adult patients with SCD and 20 healthy children and 10 healthy adults as a control. All the patients were questioned for possible renal manifestations. 24-hour urine samples were collected and glomerular filtration rates (GFRs) were calculated by using creatinine (GFR(creatinine)), Schwartz formula (GFR(Schwartz)), and cystatin C (GFR(cystatin C)). Blood and urine samples were collected and serum cystatin C, urine B2M, RBP, NAG, and ET-1 levels were measured.

RESULTS

Nocturnal enuresis and proteinuria were the most common renal manifestations in SCD patients. When the groups were compared in terms of GFR, GFR(creatinine) and GFR(Schwartz) levels were higher in group 1 and 2 patients than in control 1 and 2 patients (P < .05). Cystatin C, B2M, RBP, NAG, and ET-1 values were normal in both the patient and the control groups. However, B2M/creatinine levels were higher than 160 μg/mg creatinine levels in 10 patients.

CONCLUSIONS

Serum cystatin C, urine NAG, RBP, and ET-1 levels were found to be insufficient for the evaluation of SCD nephropathy. Increased B2M/creatinie levels can be valuable in estimating possible glomerular and tubular damage in SCD.

Determination of early urinary renal injury markers in obese children

BACKGROUND

Obesity is an important health issue, the prevalence of which is increasing in childhood. The aim of this study was to examine urinary renal injury markers in order to determine the renal effect of obesity and its comorbidities in a pediatric population.

METHODS

Eighty-four obese children and 64 healthy control subjects were enrolled in the study. We checked their urine using N-acetyl-beta-D-glucosaminidase (NAG), neutrophil gelatinase-associated lipocalin (NGAL), kidney injury molecule-1 (KIM-1), and microalbumin as renal injury markers. Associations of renal damage markers with hypertension, an impaired glucose tolerance test, and insulin resistance were assessed.

RESULTS

Obese individuals had higher urinary NAG and KIM-1 values compared to those of healthy controls (p = 0.027, p = 0.026). There was no difference in urinary NGAL between obese and lean subjects (p = 0.885). Urinary renal injury markers were not statistically different in the obese group when checked for impaired glucose tolerance, insulin resistance, and hypertension (p > 0.05).

CONCLUSIONS

This study shows that urinary NAG and KIM-1 could be used as a screening method for detection of early renal damage in obese children.

Evaluation of urinary N-acetyl-beta-D-glucosaminidase as a marker of early renal damage in patients with type 2 diabetes mellitus

OBJECTIVE

To evaluate the clinical usefulness of urinary N-acetyl-beta-D-glucosaminidase (NAG) excretion for the detection of early tubular damage in type 2 diabetes mellitus (T2DM).

SUBJECTS AND METHODS

Thirty six patients with T2DM were divided into two groups based on urinary albumin to creatinine ratio (ACR): normoalbuminuria (ACR <30 mg/g; n=19) and microalbuminuria (ACR =30-300 mg/g; n=17). The following parameters were determined in both groups: urinary NAG and albumin, serum and urine creatinine, fasting plasma glucose and glycated hemoglobin (HbA1c).

RESULTS

Urinary NAG levels [Units/g creatinine; median (range)] were significantly increased in microalbuminuria group [17.0 (5.9 - 23.3)] compared to normoalbuminuria group [4.4 (1.5 - 9.2)] (P<0.001). No differences between groups were observed in fasting glucose, HbA1c, serum creatinine levels and estimated glomerular filtration rates (eGFR). Urinary NAG positively correlated with ACR (r=0.628; p<0.0001), while no significant association was observed between NAG and glycemia, HbA1c, serum creatinine and eGFR.

CONCLUSIONS

The increase of urinary NAG at the microalbuminuria stage of diabetic nephropathy (DN) suggests that tubular dysfunction is already present in this period. The significant positive association between urinary NAG excretion and ACR indicates the possible clinical application of urinary NAG as a complementary marker for early detection of DN in T2DM.

Renal function in transfusion-dependent pediatric beta-thalassemia major patients

PURPOSE

In this study, the relationship between glomerular and tubular function and creatinine, glomerular filtration rate (GFR) and urine NAG in thalassemia major patients aged 7-16 years was investigated.

DESIGN AND SETTING

This is a case-control study comprising 280 individuals [144 (51·4%), males; 136 (48·6%), females].

MATERIALS AND METHODS

Patients were divided in groups of 14 individuals and age groups of 7-16 years. Sodium excretion fraction, fraction excretion of potassium, calcium-to-creatinine and uric acid-to-creatinine ratios, and duration of specific blood transfusion were determined in all age groups receiving deferoxamine.

RESULTS

GFR decreased with increasing age, but the correlation was not statistically significant. There was no significant correlation between the ferritin levels and the GFR changes. The mean value of NAG activity between thalassemic patients and controls has no significant difference. The difference in mean age of the groups with high NAG activity and normal NAG activity was statistically significant. Thirty-seven patients (52·1%) in the group with normal NAG activity, and 45 patients (6·25%) in the group with NAG activity above normal were observed with uricosuric effects with no significant difference. Four patients (6·9%) in the group with normal NAG activity and six patients (7·3%) in the group with NAG activity above normal were shown to have hematuria with no significant difference. The results show that the increase in serum ferritin is significantly correlated with the increase in NAG activity (P<0·001, r = 0·2). Of patients with normal NAG activity 1 (1·7%) and with NAG activity higher than normal, 13 (15·9%) cases experienced hypercalciuria that significant difference was existing. The data also indicated that the NAG changes do not correlate with GFR changes.

CONCLUSION

The results showed that kidney dysfunction in thalassemia increases with increasing age, duration, and levels of blood transfusion and hypercalciuria. It is therefore recommended that the presence of severe renal dysfunction in thalassemic patients should be investigated using sensitive and specific tests, mainly NAG, to prevent progress towards the complications.

New tubular injury markers in children with a solitary functioning kidney

BACKGROUND

The present study aimed to assess whether the urinary profiles of the lysosomal exoglycosidases N‑acetyl‑β‑hexosaminidase (HEX) and its isoenzymes A (HEX A) and B (HEX B), α-fucosidase (FUC), β-galactosidase (GAL), α-mannosidase (MAN), and β- glucuronidase (GLU) are useful biomarkers of tubular dysfunction in children with a solitary functioning kidney (SFK).

METHODS

We measured the urinary activity of HEX, its isoenzymes HEX A, HEX B, and FUC, GAL, MAN, and GLU in 52 patients with SFK. Patients were subdivided into two groups: congenital SFK (cSFK)-unilateral renal agenesis and acquired SFK (aSFK)-unilateral nephrectomy. The reference group (RG) contained 60 healthy sex- and age-matched children.

RESULTS

Urinary activity of all exoglycosidases in SFK was significantly higher than in RG (p < 0.05). There were no differences in exoglycosidase activity between cSFK and aSFK (p > 0.05). HEX and its isoenzymes HEX A and HEX B correlated negatively with estimated glomerular filtration rate (eGFR), and all estimated parameters correlated positively with albumin/creatinine ratio (p < 0.001).

CONCLUSION

Urinary activity of HEX, its isoenzymes HEX A and HEX B, and FUC, GAL, MAN, and GLU is elevated in children with SFK. Long-term follow-up studies in larger groups of children with SFK may help us to better understand their clinical significance.

Serum cystatin C and tubular urinary enzymes as biomarkers of renal dysfunction in type 2 diabetes mellitus

Renal tubulointerstitium plays an important role in the development and progression of diabetic nephropathy. The aim of this study was to assess serum cystatin C and 2 renal tubular enzymes, neutrophil gelatinase associated lipocalin (NGAL) and N-acetyl-beta-D-glucosaminidase (NAG), as screening markers for early renal dysfunction in patients with type 2 diabetes mellitus (T2DM). ROC curve analysis showed that urinary NAG is the most sensitive marker of microalbuminuria and early renal damage with sensitivity of 83.3%, while serum cystatin C was the most sensitive and specific marker of macroalbuminuria and damage progress with sensitivity of 70.8% and specificity of 83.3% versus 70.6% and 83.3% for uNGAL; and 64.7% and 66.7% for NAG, respectively. Our data indicate that urinary NAG is the most sensitive marker for early renal damage in diabetic patients. However, for damage progress, serum cystatin C is the most sensitive and specific marker for follow-up and monitoring renal dysfunction.

Diabetic nephropathy: traditional to proteomic markers

Diabetic nephropathy (DN) is one of the major microvascular complications of diabetes and it is defined as a rise in the urinary albumin excretion (UAE) rate and abnormal renal function. Currently, changes in albuminuria are considered a hallmark of onset or progression of DN. However, some patients with diabetes have advanced renal pathological changes and progressive kidney function decline even if urinary albumin levels are in the normal range, indicating that albuminuria is not the perfect marker for the early detection of DN. The present article provides an overview of the literature reporting some relevant biomarkers that have been found to be associated with DN and that potentially may be used to predict the onset and/or monitor the progression of nephropathy. In particular, biomarkers of renal damage, inflammation, and oxidative stress may be useful tools for detection at an early stage or prediction of DN. Proteomic-based biomarker discovery represents a novel strategy to improve diagnosis, prognosis and treatment of DN; however, proteomics-based approaches are not yet available in most of the clinical chemistry laboratories. The use of a panel with a combination of biomarkers instead of urinary albumin alone seems to be an interesting approach for early detection of DN, including markers of glomerular damage (e.g., albumin), tubular damage (e.g., NAG and KIM-1), inflammation (e.g., TNF-α) and oxidative stress (e.g., 8-OHdG) because these mechanisms contribute to the development and outcomes of this disease.

Alterations in kidney tissue following zinc supplementation to STZ-induced diabetic rats

Diabetes mellitus is a chronic disease characterized by anomalies forming in carbohydrate, lipid, protein metabolisms and the incidence of this disease varies widely throughout the world. Zinc is an important element which is essential for life and is present in nature. In this study, the animals were divided into four groups. These groups were named as untreated; zinc sulfate; streptozotocin (STZ); STZ and zinc sulfate. STZ (65 mg/kg) was dissolved in a freshly prepared 0.01 M pH 4.5 citrate buffer and given with intraperitoneal injection in a single dose. Zinc sulfate (100mg/kg) was dissolved in distilled water and given to the animals by gavage at a daily dose for 60 days. The rats were sacrificed under ether anesthesia. This study was aimed to investigate histological and biochemical changes of zinc supplementation on the kidney tissue in STZ-induced diabetic rats. In the current study, histological and histochemical observations showed that the occurred degenerative changes decreased after giving zinc in the kidney tissue of diabetic group. Kidney glutathione (GSH) levels decreased and lipid peroxidation (LPO), nonenzymatic glycosylation (NEG), urea and creatinine levels increased in diabetic rats. GSH levels increased, while LPO, NEG, urea and creatinine levels decreased in the kidney with administration of zinc to diabetic rats. As a result, we observed curative effects of zinc given to diabetic rats. We can say that zinc may be an important antioxidant for the treatment of secondary complications of diabetes in kidney tissue.

Urinary N-acetyl-β-D-glucosaminidase levels are positively correlated with 2-hr plasma glucose levels during oral glucose tolerance testing in prediabetes

BACKGROUND

Urinary N-acetyl-β-D-glucosaminidase (NAG) excretion is increased in patients with impaired glucose tolerance (IGT). This study investigated when during the oral glucose tolerance test (OGTT) the plasma glucose, urine glucose, and insulin levels correlate most strongly with urinary N-acetyl-β-d-glucosaminidase (NAG) levels in prediabetic subjects.

METHODS

The OGTT was administered to 80 subjects who had not yet received a diagnosis of diabetes mellitus (DM) and in whom HbA1c levels were ≤6.8% and fasting plasma glucose levels were <7.0 mmol/l. Forty-two subjects had normal glucose tolerance (NGT), 31 had impaired glucose tolerance (IGT), and 7 had DM according to World Health Organization criteria. Serum levels of cystatin C, the estimated glomerular filtration rate, the urinary albumin-to-creatinine (Cr) ratio, urinary and serum β2-microglobulin, and urinary NAG were measured as markers of renal function.

RESULTS

NAG levels were significantly higher in subjects with DM and in subjects with IGT than in subjects with NGT. No significant associations were observed between glycemic status and other markers of renal function. Multiple linear regression analysis showed that the NAG level was positively correlated with plasma glucose levels at 120 min of the OGTT and was associated with the glycemic status of prediabetic patients.

CONCLUSION

These results suggest that postprandial hyperglycemia is an independent factor that causes renal tubular damage in prediabetes patients.

Association between Urinary N-Acetyl-Beta-D-Glucosaminidase and Microalbuminuria in Diabetic Black Africans

Diabetes mellitus is the commonest cause of ESRD worldwide and third most common cause in Nigeria. Recent reports from Nigeria indicate the prevalence of diabetic nephropathy as an aetiology of ESRD is increasing necessitating early diagnosis of diabetic nephropathy. We measured the urinary excretion of N-acetyl-beta-D-glucosaminidase (NAG), NAG/creatinine ratio, urinary protein-creatinine ratio and calculated eGFR in 30 recently diagnosed nonhypertensive diabetics and 67 controls. The age and sex distribution, systolic blood pressure, serum and urinary creatinine were similar for both groups. There was higher urinary excretion of NAG (304 versus 184 μmol/h/L, P < 0.001) and NAG/creatinine ratio (21.2 versus 15.7 μmol/h/L/mmolCr, P < 0.001) in the diabetics than controls. There was a strong correlation between NAG/creatinine ratio and albumin/creatinine ratio (r = 0.74, P < 0.001). A multivariate linear regression model showed a significant linear relationship between NAG/creatinine ratio and albumin/creatinine ratio after adjusting for the effect of blood pressure, age, sex, and serum creatinine. The strong association found between albumin/creatinine ratio and NAG/creatinine ratio perhaps indicates the need for further investigation of the clinical utility of NAG/creatinine ratio as a screening tool for early nephropathy in African diabetics.

Drug-Induced Changes in Risk/Biomarkers and Their Relationship with Renal and Cardiovascular Long-Term Outcome in Patients with Diabetes

BACKGROUND

Optimal renal and cardiovascular risk management in diabetic patients includes optimal maintenance of blood pressure and control of glucose and lipids. Although the optimal control of these risk factors or “risk/biomarkers” has proven to be effective, it often is difficult to achieve. Consequently, the risk for renal and cardiovascular complications remains devastatingly high. Many risk/biomarkers have been discovered that accurately predict long-term renal and cardiovascular outcome. However, the aim of measuring risk/biomarkers may not be only to determine an individual's risk, but also to use the risk/biomarker level to guide therapy and thereby improve long-term clinical outcome.

CONTENT

This review describes the effects of various drugs on novel risk/biomarkers and the relationship between (drug induced) short-term changes in risk/biomarkers and long-term renal and cardiovascular outcome in patients with diabetes.

SUMMARY

In post hoc analyses of large trials, the short-term reductions in albuminuria, transforming growth factor-β, and N-terminal pro-B–type natriuretic peptide (NT-proBNP) induced by inhibitors of the renin-angiotensin-aldosterone system were associated with a decreased likelihood of long-term adverse renal and cardiovascular outcomes. However, the few studies that systematically investigated the utility of prospectively targeting novel risk/biomarkers such as hemoglobin or NT-proBNP failed to demonstrate long-term cardiovascular protection. The latter examples suggest that although a risk/biomarker may have superior prognostic ability, therapeutically changing such a risk/biomarker does not necessarily improve long-term outcome. Thus, to establish the clinical utility of other novel risk/biomarkers, clinical trials must be performed to prospectively examine the effects of therapeutically-induced changes in single or multiple risk/biomarkers on long-term risk management of patients with diabetes.

Hemoglobin concentration in men with type 2 diabetes mellitus

Anemia is a common but often overlooked complication of diabetes. We investigated the relationship between hemoglobin concentration and various factors as well as markers of subclinical atherosclerosis in men with type 2 diabetes mellitus. Hemoglobin concentration was measured in 319 men with type 2 diabetes mellitus. We evaluated the relationship between hemoglobin concentration and various factors including age, body mass index, and glycemic control, as well as between hemoglobin concentration and pulse wave velocity or ankle-brachial index (n = 209) and between hemoglobin concentration and carotid intima-media thickness or plaque score (n = 125). Mean hemoglobin concentration was 14.2 +/- 0.80 g/dL. Body mass index (r = 0.340, P < .0001) and estimated glomerular filtration rate (r = 0.219, P = .0011) were positively associated with hemoglobin concentration, whereas age (r = -0.388, P < .0001), glycated albumin (r = -0.148, P = .0121), serum creatinine concentration (r = -0.206, P = .0019), and log (urinary albumin excretion) (r = -0.188, P = .0010) were negatively associated with hemoglobin concentration. Multiple regression analysis identified age (beta = -0.222, P = .0019), body mass index (beta = 0.145, P = .0432), systolic blood pressure (beta = 0.214, P = .0015), total cholesterol concentration (beta = 0.170, P = .0077), and serum creatinine concentration (beta = -0.181, P = .0045) as independent determinants of hemoglobin concentration. No significant association was observed between hemoglobin concentration and serum erythropoietin concentration (r = -0.079, P = .2980). Negative correlations were found between hemoglobin concentration and pulse wave velocity (r = -0.289, P < .0001) and between hemoglobin concentration and plaque score (r = -0.275, P = .0024). In conclusion, hemoglobin concentration was associated with various factors; and decreased hemoglobin concentration was associated with subclinical markers of atherosclerosis in men with type 2 diabetes mellitus.

Early urinary markers of diabetic kidney disease: a nested case-control study from the Diabetes Control and Complications Trial (DCCT)

BACKGROUND

Urinary markers were tested as predictors of macroalbuminuria or microalbuminuria in patients with type 1 diabetes.

STUDY DESIGN

Nested case-control of participants in the Diabetes Control and Complications Trial (DCCT).

SETTING & PARTICIPANTS

87 cases of microalbuminuria were matched to 174 controls in a 1:2 ratio, while 4 cases were matched to 4 controls in a 1:1 ratio, resulting in 91 cases and 178 controls for microalbuminuria. 55 cases of macroalbuminuria were matched to 110 controls in a 1:2 ratio. Controls were free of micro-/macroalbuminuria when their matching case first developed micro-/macroalbuminuria.

PREDICTORS

Urinary N-acetyl-beta-d-glucosaminidase (NAG), pentosidine, advanced glycation end product (AGE) fluorescence, and albumin excretion rate (AER).

OUTCOMES

Incident microalbuminuria (2 consecutive annual AERs > 40 but < or = 300 mg/d) or macroalbuminuria (AER > 300 mg/d).

MEASUREMENTS

Stored urine samples from DCCT entry and 1-9 years later when macro- or microalbuminuria occurred were measured for the lysosomal enzyme NAG and the AGE pentosidine and AGE fluorescence. AER and adjustor variables were obtained from the DCCT.

RESULTS

Submicroalbuminuric AER levels at baseline independently predicted microalbuminuria (adjusted OR, 1.83; P < 0.001) and macroalbuminuria (adjusted OR, 1.82; P < 0.001). Baseline NAG excretion independently predicted macroalbuminuria (adjusted OR, 2.26; P < 0.001) and microalbuminuria (adjusted OR, 1.86; P < 0.001). Baseline pentosidine excretion predicted macroalbuminuria (adjusted OR, 6.89; P = 0.002). Baseline AGE fluorescence predicted microalbuminuria (adjusted OR, 1.68; P = 0.02). However, adjusted for NAG excretion, pentosidine excretion and AGE fluorescence lost the predictive association with macroalbuminuria and microalbuminuria, respectively.

LIMITATIONS

Use of angiotensin-converting enzyme inhibitors was not directly ascertained, although their use was proscribed during the DCCT.

CONCLUSIONS

Early in type 1 diabetes, repeated measurements of AER and urinary NAG excretion may identify individuals susceptible to future diabetic nephropathy. Combining the 2 markers may yield a better predictive model than either one alone. Renal tubule stress may be more severe, reflecting abnormal renal tubule processing of AGE-modified proteins, in individuals susceptible to diabetic nephropathy.

Advanced glycation end products inhibit Na+ K+ ATPase in proximal tubule epithelial cells: role of cytosolic phospholipase A2alpha and phosphatidylinositol 4-phosphate 5-kinase gamma

Chronic hyperglycaemia during diabetes leads to non-enzymatic glycation of proteins to form advanced glycation end products (AGEs) that contribute to nephropathy. In diabetes, renal Na+ K+ ATPase (NKA) activity is downregulated and phosphoinositide metabolism is upregulated. We examined the effects of AGEs on NKA activity in porcine LLC-PK1 and human HK2 proximal tubule epithelial cells. AGE-BSA increased cellular phosphoinositol 4,5 bisphosphate (PIP2) production as determined by immunofluorescence microscopy and thin layer chromatography. AGE-BSA (40 microM) induced 3H-arachidonic acid release and reactive oxygen species (ROS) production via cytosolic phospholipase A2 (cPLA2) activation. Within minutes, AGE-BSA significantly inhibited NKA surface expression and activity in a dose- and time-dependent manner as determined by immunofluorescence staining and [86Rb+] uptake, respectively, suggesting AGEs inhibit NKA by stimulating its endocytosis. The AGE-BSA-induced decrease in cell surface NKA was reversed by a cPLA2alpha inhibitor, neomycin, a PIP2 inhibitor, and PP2, a Src inhibitor. AGE-BSA increased binding of NKA to the alpha-adaptin but not beta2- or mu2-adaptin subunits of the AP-2 clathrin pit adaptor complex. Transfection of HK2 cells with PIP5Kgamma siRNA prevented AGE-BSA inhibition of NKA activity. AGEs may stimulate PIP5Kgamma to increase PIP2 production, which may enhance AP-2 localisation to clathrin pits, increase clathrin pit formation, enhance NKA cargo recognition by AP-2 and/or stimulate cPLA2alpha activity. These results suggest AGEs modulate arachidonic acid and phosphoinositide metabolism to inhibit NKA via clathrin-mediated endocytosis. Elucidation of new intracellular AGE signaling pathways may lead to improved therapies for diabetic nephropathy.

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.

Radionuclide Staging of Renal Function in Type 1 Diabetes Mellitus

AIM

The aim of this study was to assess renal function in different stages of type 1 diabetes mellitus by radionuclide methods. Additionally, glomerular and tubular functions were correlated with urinary albumin (UAER) and N-acetyl-beta-D-glucosaminidase (NAGA) excretion rates.

PATIENTS AND METHODS

Fifty-three patients with diabetes mellitus were classified into four groups: normoalbuminuric (NA, 18 patients), microalbuminuric (MiA, 12 patients), macroalbuminuric (MaA, 13 patients), and chronic renal failure group (CRF, 10 patients). Glomerular filtration rate (GFR) was estimated by diethylenetriamine pentaacetic acid-technetium 99m ((99m)Tc-DTPA) clearance rate while tubular function was calculated as a percentage of net injected activity fixed in both kidneys, 4 h after intravenous injection of dimercaptosuccinate acid-technetium 99m ((99m)Tc-DMSA). Additionally, (99m)Tc-DTPA clearance was correlated with estimated GFR (eGFR) by using modified Modification of Diet in Renal Disease (MDRD) Study Group formula.

RESULTS

(99m)Tc-DTPA clearance and (99m)Tc-DMSA fixation were found significantly higher in normoalbuminuric group (p < 0.05 and p < 0.02, respectively), unchanged in microalbuminuric group (p > 0.05, p > 0.05), and decreased in both macroalbuminuric (p < 0.0001, p < 0.00001) and chronic renal failure group (p < 0.0001, p < 0.00001). Renal function was denoted as normal, increased (hyperfunction), or decreased (hypofunction). It was found normal in a high percentage of patients with normalbuminuria (filtration 44.4%, fixation 72.2% pts) and microalbuminuria (66.7% and 66.7%). Renal hyperfunction was not only found frequent in normalbuminuric group (55.6% and 27.8%), but was also recorded in microalbuminuric group (8.3% and 8.3%). Renal hypofunction was present in all macroalbuminuric patients and in one-quarter of those with microalbuminuria as well. Such distribution of renal function conditions indicated normalbuminuric and microalbuminiric groups functionally heterogeneous. Regression analysis showed a significant correlation between (99m)Tc-DTPA clearance and eGFR in MaA and CRF groups only. Although urinary NAGA excretion rate was shown as a less sensitive staging parameter, being significantly increased when compared to control group only in MaA and CRF groups (p < 0.05), it significantly correlated with (99m)Tc-DTPA clearance rate (r = -0.485, p = 0.0004) and (99m)Tc-DMSA tubular fixation (r = -0.526, p = 0.0002).

CONCLUSIONS

The results of this study favor the performance of radionuclide studies together with the determination of urinary albumin excretion rate in patients with type 1 diabetes mellitus in order to achieve more reliable staging of diabetic kidney disease. The demonstration of glomerular hyperfiltration and tubular hyperfunction by radiopharmaceuticals contributes to the early detection of diabetic kidney disease, while the quantification of renal function enables the follow-up of the progressive function loss in the later course of the disease.

Erythropoietic stress and anemia in diabetes mellitus

Anemia is one of the world's most common preventable conditions, yet it is often overlooked, especially in people with diabetes mellitus. Diabetes-related chronic hyperglycemia can lead to a hypoxic environment in the renal interstitium, which results in impaired production of erythropoietin by the peritubular fibroblasts and subsequent anemia. Anemia in patients with diabetes mellitus might contribute to the pathogenesis and progression of cardiovascular disease and aggravate diabetic nephropathy and retinopathy. Anemia occurs earlier in patients with diabetic renal disease than in nondiabetic individuals with chronic kidney disease. Although erythropoietin has been used to treat renal anemia for nearly two decades, debate persists over the optimal target hemoglobin level. Most guidelines recommend that hemoglobin levels be maintained between 105g/l and 125g/l. The suggested role of anemia correction--to prevent the progression of left ventricular hypertrophy in patients with diabetes mellitus--is yet to be established. However, an emphasis on regular screening for anemia, alongside that for other diabetes-related complications, might help to delay the progression of vascular complications in these patients.

Determination of urinary enzymes as a marker of early renal damage in diabetic patients

Diagnosis of diabetic nephropathy in the early stages is very important since there are no clinical signs or symptoms. Urinary N-acetyl-beta-D-glucosaminidase (NAG) excretion has been recommended as a tubular dysfunction marker that elevates before other markers, such as microalbuminuria and a decrease in creatinine clearance. In this study, we compared excretion of urinary enzymes with other markers that are used routinely in diabetic nephropathy assessment. Urinary NAG, lactate dehydrogenase (LDH), alkaline phosphatase (AP) activities, urea, creatinine, and albumin, with levels of serum glucose and creatinine and whole blood glycosylated hemoglobin (HbA1c) were measured in 32 diabetes mellitus patients and 25 healthy subjects (controls). Notably, urinary NAG, AP, LDH excretion, and microalbuminuria in the diabetic patients group were significantly increased compared to those in the control groups (P<0.001, P<0.05, P<0.01, and P<0.01, respectively). Meanwhile, our results showed that the urinary NAG excretion had the highest sensitivity and specificity (100% and 87.5%, respectively) compared to other markers. We showed that measuring urinary NAG excretion could be useful for the assessment of renal failure in diabetes mellitus patients and confirmed the use of NAG as a routine screening test.

The influence of urinary flow rate in children on excretion of markers used for assessment of renal damage: albumin, gamma-glutamyl transpeptidase, N-acetyl-beta-D -glucosaminidase, and alpha1-microglobulin

The aim of the present study was to examine the influence of urinary flow rate on markers of renal function in children. A sub-study of the New England Children's Amalgam Trial collected 82 pairs of urine samples from children aged 10-16 years: a timed overnight collection and a spot daytime sample collected the following day. These samples were analyzed for albumin, gamma-glutamyl transpeptidase (gamma-GT), N-acetyl-beta-D-glucosaminidase (NAG), alpha1-microglobulin (A1M), and creatinine concentration. Regression analysis was used to model the effect of urinary flow rate in the timed overnight samples. A paired t-test compared concentrations and creatinine-corrected renal markers between overnight and daytime samples. Albumin, gamma-GT, NAG, and A1M excretion rates increased significantly with urinary flow rate. Their corresponding creatinine-corrected markers did not vary significantly with urinary flow rate, but the creatinine-corrected excretions of albumin, gamma-GT, and NAG were significantly higher in daytime samples than in overnight samples, with the same (non-significant) trend for A1M. The influence of urinary flow rate on creatinine-corrected markers of renal function was markedly less than its influence on excretion rates. Therefore, the use of creatinine-corrected markers seems to be a good choice in practice, with the caveat that daytime and overnight samples are not comparable.

Mechanisms of disease: the hypoxic tubular hypothesis of diabetic nephropathy

Diabetic nephropathy is traditionally considered to be a primarily glomerular disease, although this contention has recently been challenged. Early tubular injury has been reported in patients with diabetes mellitus whose glomerular function is intact. Chronic hypoxia of the tubulointerstitium has been recognized as a mechanism of progression that is common to many renal diseases. The hypoxic milieu in early-stage diabetic nephropathy is aggravated by manifestations of chronic hyperglycemia-abnormalities of red blood cells, oxidative stress, sympathetic denervation of the kidney due to autonomic neuropathy, and diabetes-mellitus-induced tubular apoptosis; as such, tubulointerstitial hypoxia in diabetes mellitus might be an important early event. Chronic hypoxia could have a dominant pathogenic role in diabetic nephropathy, not only in promoting progression but also during initiation of the condition. Early loss of tubular and peritubular cells reduces production of 1,25-dihydroxyvitamin D3 and erythropoietin, which, together with dysfunction of their receptors caused by the diabetic state, diminishes the local trophic effects of the hormones. This diminution could further compromise the functional and structural integrity of the parenchyma and contribute to the gradual decline of renal function.

The effect of age, sex, and race on urinary markers of kidney damage in children

BACKGROUND

The aim of this study is to examine the effects of age, sex, and race on the excretion and concentrations of albumin, gamma-glutamyl transpeptidase (gamma-GT), N-acetyl-beta-d-glucosaminidase (NAG), alpha(1)-microglobulin (alpha1M), and creatinine in children.

STUDY DESIGN

Secondary analysis of a clinical trial, The New England Children's Amalgam Trial, which examined effects of amalgam dental fillings.

SETTING & PARTICIPANTS

534 children aged 6 to 10 years at baseline were recruited from Boston, MA, and rural Maine.

PREDICTORS

Age, sex, and race.

OUTCOMES & MEASUREMENTS

Urine samples were collected annually for 5 years and analyzed for creatinine, albumin, gamma-GT, NAG, and alpha1M concentrations. Repeated-measures analysis of covariance was used to model effects of age, sex, and race on these values, as well as calculated excretion rates.

RESULTS

All measures of creatinine and gamma-GT increased significantly with age. Albumin and gamma-GT concentration and excretion (milligrams per gram of creatinine or units per gram creatinine) were significantly greater for girls compared with boys. alpha1M concentration and creatinine excretion were greater for boys compared with girls. Creatinine concentration was significantly greater for blacks than for whites and Hispanics. Creatinine excretion and all gamma-GT levels were significantly greater for blacks and Hispanics compared with non-Hispanic whites.

LIMITATIONS

The study population, recruited for a clinical trial, was of lower socioeconomic status than the general population. The high limit of detection for alpha1M resulted in a majority of samples less than the detection limit.

CONCLUSIONS

We recommend considering age, sex, and race in the interpretation of urinary markers. It also is recommended that epidemiological studies and clinical trials account for age, sex, and race in statistical models comparing urinary markers of kidney damage.

Damage of tubule cells in diabetic nephropathy type 2: urinary N-acetyl-beta-D-glucosaminidasis and gamma-glutamil-transferasis

BACKGROUND/AIM

A damage of tubular epithelial cells is followed by the release of cell enzymes and production of proinflammatory compounds, which lead to the tubulointerstitial damage. The aim of this study was to examine the function of renal tubules in the patients with diabetes mellitus type 2 (DM type 2) and the various proteinuria degrees, to establish the damage of the proximal tubule cells caused by DM type 2 by determining urinary N-acetyl-beta-D-glucosaminidasis (beta-NAG) and gamma-glutamil-transferasis (gamma-GT) activity in urine, as well as to compare the obtained results in the examined groups of patients with the values in the healthy examinees.

METHODS

A complete examination of renal function and selective enzymuria was performed in 37 patients with DM type 2, and 14 healthy examinees as the controls. The patients were divided in three groups according to the degree of proteinuria. The first group consisted of the patients with diabetes without microalbuminuria; the second one consisted of the patients with proteinuria of < 300 mg/24 h, and microalbuminuria of > 20 mg/24 h, while the third one included the patients with proteinuria of > 300 mg/24 h.

RESULTS

In the patients with DM type 2 and the preserved global renal function, fractional excretion of sodium, potassium and phosphates, as well as renal threshold of phosphates concentration, were not sensitive parameters for discovering the damage of the renal tubule function. The determination of beta-NAG activity proved to be the most sensitive parameter for early discovering of tubule cells damages. The difference among the examined groups was statistically highly significant.

CONCLUSION

The increased presence of beta-NAG in the urine of DM type 2 patients, pointed out an early tubular disorder and damage of cells, while gamma-GT was a less sensitive indicator of this damage.