Urinary protein excretion in Type 2 diabetes with complications

A candidate panel of eight urinary proteins shows potential of early diagnosis and risk assessment for diabetic kidney disease in type 1 diabetes

Diabetic kidney disease (DKD) poses a significant health challenge for individuals with diabetes. At its initial stages, DKD often presents asymptomatically, and the standard for non-invasive diagnosis, the albumin-creatinine ratio (ACR), employs discrete categorizations (normal, microalbuminuria, macroalbuminuria) with limitations in sensitivity and specificity across diverse population cohorts. Single biomarker reliance further restricts the predictive value in clinical settings. Given the escalating prevalence of diabetes, our study uses proteomic technologies to identify novel urinary proteins as supplementary DKD biomarkers. A total of 158 T1D subjects provided urine samples, with 28 (15 DKD; 13 non-DKD) used in the discovery stage and 131 (45 DKD; 40 pDKD; 46 non-DKD) used in the confirmation. We identified eight proteins (A1BG, AMBP, AZGP1, BTD, RBP4, ORM2, GM2A, and PGCP), all of which demonstrated excellent area-under-the-curve (AUC) values (0.959 to 0.995) in distinguishing DKD from non-DKD. Furthermore, this multi-marker panel successfully segregated the most ambiguous group (microalbuminuria) into three distinct clusters, with 80% of subjects aligning either as DKD or non-DKD. The remaining 20% exhibited continued uncertainty. Overall, the use of these candidate urinary proteins allowed for the better classification of DKD and offered potential for significant improvements in the early identification of DKD in T1D populations.

Diagnostic value of α1-MG and URBP in early diabetic renal impairment

Aims/Introduction: Diabetic kidney disease (DKD) is defined as diabetes with impaired renal function, elevated urinary albumin excretion, or both. DKD is one of the most common microvascular complications of diabetes and plays an important role in the cause of end-stage renal disease (ESRD). About 5% of people with type 2 diabetes (T2DM) already have kidney damage at the time they are diagnosed, but other triggers of renal insufficiency, such as obesity, hyperlipidemia, glomerular atherosclerosis are often present, making it difficult to define "diabetic kidney disease" or "diabetic nephropathy" precisely in epidemiology or clinical practice. Therefore, the aim of this study is to identify diabetic patients with CKD at an early stage, and evaluate the value of tubular injury markers including α1-microglobulin (α1-MG), β2-microglobulin (β2-MG), N-acetyl-beta-D-glucosaminidase (NAG) and Urinary retinol binding protein (URBP) in the development of diabetes to DKD. Materials and methods: We recruited a total of 182 hospitalized patients with T2DM in the First Affiliated Hospital of Zhengzhou University from February 2018 to April 2023. We collected basic clinical characteristics and laboratory biochemical parameters of the patients. Based on their levels of urinary albumin creatinine ratio (UACR) and glomerular filtration rate (GFR), patients were divided into DM group (UACR≤30 mg/g and eGFR≥90 mL/min/1.73 m2, n = 63) and DKD group (UACR>30 mg/g or eGFR<90 mL/min/1.73 m2, n = 119) excluding other causes of chronic kidney disease. We further developed diagnostic models to improve the ability to predict the risk of developing DKD by screening potential risk factors using univariate and multivariate logistic regression analysis. Calibration plots and curve analysis were used to validate the model and clinical usefulness. Next, we screened patients with relatively normal estimated glomerular filtration rate (eGFR) (≥90 mL/min/1.73 m2) to investigate whether tubular injury markers could accurately predict the risk of DKD in patients with normal renal function. We defined the rate of GFR decline as a prognostic indicator of renal function in patients and collected the information of the re-hospitalized DKD patients to determine whether the relevant indicators had an impact on the renal prognosis. Results: The patients with DKD had higher levels of tubular injury markers than patients with DM. URBP, α1-MG, eGFR were statistically different in both univariate and multivariate logistic regression analyses and displayed great predictive power after modeling with an area under curve of 0.987. The calibration curve showed medium agreement. Decision curve showed it would add more net benefits for clinical decision. After adjusting eGFR and serum creatinine (Scr), URBP was demonstrated to be associated with early renal function impairment. Conclusion: Tubular injury markers play an important role in early diabetic renal function impairment.

Association Between Early Markers of Renal Injury and Type 2 Diabetic Peripheral Neuropathy

OBJECTIVE

Diabetic kidney disease (DKD) and diabetic peripheral neuropathy (DPN) are both common chronic complications of type 2 diabetes mellitus (T2DM). The aim of this study was to examine whether some markers of early renal injury were associated with DPN.

METHODS

Retrospective hospitalization data from 471 patients with T2DM were analyzed. Subjects were divided into DPN group and non-DPN group according to clinical history, symptoms, signs and nerve conduction study. Markers of glomerular injury [urinary albumin/creatinine ratio (UACR) and estimated glomerular filtration rate (eGFR)] and tubular injury [urinary N-acetyl-β-D-glucosaminidase/creatinine ratio (NAG/Cr) and urinary β2 microglobulin (β2-MG)] were innovatively combined to assess the association with DPN. Staging of chronic kidney disease (CKD) was classified as G1, G2, G3a, G3b, G4 based on eGFR categories of ≥90, 60-89, 45-59, 30-44, 15-29 mL/min/1.73m2.

RESULTS

DPN was detected in 71.1% of our population. Subjects in DPN group suffered from older age, longer duration of diabetes and worse blood glucose control compared with non-DPN group. The levels of UACR, NAG/Cr and β2-MG were significantly increased in DPN group than those in non-DPN group, while eGFR was decreased. The prevalence of DPN increased gradually in G1, G2 and G3-4 of CKD, which were 66.3%, 73.2% and 82.7% (P = 0.014). After adjusting for confounding factors, NAG/Cr >1.41 U/mmol (the highest tertile) was a consistently independent risk factor for DPN [odds ratio, OR (95% confidence interval, CI) = 1.86 (1.04-3.33)]. However, UACR, eGFR and β2-MG did not significantly affect the risk of DPN.

CONCLUSION

When T2DM patients suffer from CKD, DPN will be more likely to appear, accelerate or deteriorate. Some easily available urinary markers of glomerular and tubular damage can be used for early prediction of DPN, in which increased NAG/Cr is an independent risk factor for DPN.

Diabetic nephropathy: A twisted thread to unravel

Diabetic nephropathy (DN), a persistent microvascular problem of diabetes mellitus is described as an elevated level of albumin excretion in urine and impaired renal activity. The morbidity and mortality of type-1 diabetics and type-2 diabetics due to end stage renal disease is also a result of the increased prevalence of DN. DN typically occurs as a consequence of an association among metabolic and hemodynamic variables, activating specific pathways leading to renal injury. According to current interventions, intensive glucose regulation decreases the threat of DN incidence and growth, and also suppressing the renin-angiotensin system (RAS) is a significant goal for hemodynamic and metabolism-related deformities in DN. However, the pathogenesis of DN is multifactorial so novel approaches other than glucose and blood pressure control are required for treatment. This review briefly summarizes the reported pathogenesis of DN, current interventions for its treatment, and possible novel interventions to unweave the thread of DN.

Association Between Early Markers of Renal Injury and Type 2 Diabetic Peripheral Neuropathy

OBJECTIVE

Diabetic kidney disease (DKD) and diabetic peripheral neuropathy (DPN) are both common chronic complications of type 2 diabetes mellitus (T2DM). The aim of this study was to examine whether some markers of early renal injury were associated with DPN.

METHODS

Retrospective hospitalization data from 471 patients with T2DM were analyzed. Subjects were divided into DPN group and non-DPN group according to clinical history, symptoms, signs and nerve conduction study. Markers of glomerular injury [urinary albumin/creatinine ratio (UACR) and estimated glomerular filtration rate (eGFR)] and tubular injury [urinary N-acetyl-β-D-glucosaminidase/creatinine ratio (NAG/Cr) and urinary β2 microglobulin (β2-MG)] were innovatively combined to assess the association with DPN. Staging of chronic kidney disease (CKD) was classified as G1, G2, G3a, G3b, G4 based on eGFR categories of ≥90, 60-89, 45-59, 30-44, 15-29 mL/min/1.73m².

RESULTS

DPN was detected in 71.1% of our population. Subjects in DPN group suffered from older age, longer duration of diabetes and worse blood glucose control compared with non-DPN group. The levels of UACR, NAG/Cr and β2-MG were significantly increased in DPN group than those in non-DPN group, while eGFR was decreased. The prevalence of DPN increased gradually in G1, G2 and G3-4 of CKD, which were 66.3%, 73.2% and 82.7% (P = 0.014). After adjusting for confounding factors, NAG/Cr >1.41 U/mmol (the highest tertile) was a consistently independent risk factor for DPN [odds ratio, OR (95% confidence interval, CI) = 1.86 (1.04-3.33)]. However, UACR, eGFR and β2-MG did not significantly affect the risk of DPN.

CONCLUSION

When T2DM patients suffer from CKD, DPN will be more likely to appear, accelerate or deteriorate. Some easily available urinary markers of glomerular and tubular damage can be used for early prediction of DPN, in which increased NAG/Cr is an independent risk factor for DPN.

Association of urinary non-albumin protein with the different urinary marker for glomerular and tubular damage in patients with type 2 diabetes

BACKGROUND/AIM

In recent years, the diagnostic utility of urinary protein levels has been demonstrated for the early detection and progression of kidney disease. This study aimed to evaluate the associations of the non-albumin protein (NAP) with different urinary marker for tubular and glomerular damage in patients with type 2 diabetes (T2D).

METHODS

In this observational cross-sectional study, 424 patients with T2D duration > 10 years were classified into two groups according to estimated glomerular filtration rate (eGFR). The ratios of different urinary markers (albumin, NAP, total protein, transferrin, retinol-binding protein (RBP), and neutrophil gelatinase-associated lipocalin (NGAL) to creatinine were analyzed.

RESULTS

The levels of urinary biomarkers increased significantly with decrease in eGFR levels. In the group with moderately decreased eGFR, the albumin to-creatinine ratio (ACR), non-albumin protein-to-creatinine ratio (NAPCR), and total protein-to-creatinine ratio (PCR) were independently associated with all urinary markers after being adjusted for risk factors. The area under the receiver operating characteristics (ROC) curve for ACR and PCR had a better diagnostic value than other urinary biomarkers. Comparing ROC curve of NAPCR with other urinary biomarkers, it was significantly better than NGAL/Cr (p = 0.033).

CONCLUSIONS

The findings of the present study confirm that ACR and PCR are diagnostic biomarkers in T2D patients with decreased eGFR. NAPCR in these patients diagnostically only outperformed NGAL/Cr.

Hyperinsulinemia contributes to impaired-glucose-tolerance-induced renal injury via mir-7977/SIRT3 signaling

Background:

Increasing evidence indicates that impaired glucose tolerance (IGT) is independently associated with chronic kidney disease, but the characteristics and underlying mechanisms remain largely unknown.

Methods:

Here, the cross-sectional study was performed to study the characteristics of IGT-induced renal injury (IGT-RI). Furthermore, urine microRNA profile was evaluated and microRNAs involved in tubular injury were determined by in-vitro experiments.

Results:

It was found that 12.1% of IGT patients had microalbuminuria, which we termed “IGT-RI.” Overall, 100% of patients with IGT-RI exhibited reabsorption dysfunction and 58.3% had structural damage in the renal tubules. Two-hour postprandial insulin, retinol-binding protein, and N-acetyl-β-glucosaminidase were significantly associated with microalbuminuria and they were independent risk factors for IGT-RI. The expression of mir-7977 was altered in IGT-RI patients and may be involved in cellular response to oxidative stress. In proximal tubule epithelial cells in vitro, a high level of insulin increased the expression of mir-7977 and decreased that of sirtuin 3 (SIRT3), leading to oxidative stress. Overexpression of mir-7977 further decreased SIRT3 expression, whereas inhibition of mir-7977 had the opposite effect. Furthermore, mir-7977 can bind to the 3′-untranslated region of SIRT3 mRNA and inhibit its expression. Moreover, inhibition of SIRT3 reduced the expression of cubilin and the endocytosis of albumin.

Conclusions:

In conclusion, IGT-RI mainly manifests as tubular injury, especially reabsorption dysfunction. Compensatory hyperinsulinemia may be involved. A high level of insulin can activate mir-7977/SIRT3 signaling, resulting in tubular injury by inducing oxidative stress as well as reabsorption dysfunction by inhibiting the expression of cubilin, ultimately contributing to IGT-RI.

Neutrophil Gelatinase-Associated Lipocalin and Retinol-Binding Protein-4 as Biomarkers for Diabetic Kidney Disease

AIMS

This study was designed to evaluate the conflicting association between 2 tubular protein markers including neutrophil gelatinase-associated lipocalin (NGAL) and retinol-binding protein-4 (RBP-4) with albuminuria and glomerular filtration rate (GFR) and calculate the accuracy of the role of NGAL and RBP-4 in diagnosis of diabetic nephropathy (DN) in patients with type2 diabetes.

METHODS

This is a cross-sectional study that included 133 patients with type 2 diabetes. There were 3 diabetic study groups with normoalbuminuria, moderately increased albuminuria, severely increased albuminuria, and non-diabetic control group without any renal disease. We analyzed the difference of urinary NGAL (uNGAL) and RBP-4 between nondiabetics and diabetics, as well as within the diabetic group. We also assessed the association between albuminuria and NGAL and RBP-4.

RESULTS

The urinary levels of NGAL and RBP-4 were higher in patients with type 2 diabetes compared to nondiabetics as well as in albuminuric diabetics compared to nonalbuminuric patients with diabetes (p value <0.001). These 2 proteins were higher in patients with severely increased albuminuria compared to patients with moderately increased albuminuria, even after adjustment for other metabolic factors (all p < 0.01). Moreover, areas under the curve of NGAL and RBP-4 for the diagnosis of chronic kidney disease were 80.6 and 74.6%, respectively.

CONCLUSION

uNGAL and RBP-4 are potential markers of tubular damage that may increase before the onset of glomerular markers such as albuminuria and GFR in patients with type 2 diabetes. Therefore, these markers can be used as complementary measurements to albuminuria and GFR in the earlier diagnosis of DN.

Potential Role and Excretion Level of Urinary Transferrin, KIM-1, RBP, MCP-1 and NGAL Markers in Diabetic Nephropathy

BACKGROUND

Analyzing urinary biomarkers may provide better insight into pathophysiological mechanisms of diabetic kidney diseases. The study aimed to analyze the pattern of selected excreted urinary biomarkers and its correlation with albuminuria and estimated glomerular filtration rate (eGFR) in patients with type 2 diabetes.

METHODS

A total of 185 patients with type 2 diabetes were categorized according to KDIGO guideline based on albuminuria and eGFR. The urinary markers (transferrin, KIM-1, RBP, MCP-1 and NGAL) were measured by ELISA.

RESULTS

The urinary markers were associated with eGFR (total protein/Cr, p=0.001; RBP/Cr, p=0.007; MCP-1/Cr, p=0.023; NGAL/Cr, p=0.011) and albuminuria (total protein/Cr, p<0.001; transferrin, p<0.001; RBP/Cr, p<0.001; MCP-1/Cr, p<0.001; NGAL/Cr, p=0.002).

CONCLUSION

The urinary marker levels (total protein, RBP, MCP-1, and NGAL) are elevated with severity of kidney damage and expressed more in progressive renal impairment.

Evaluation of urinary biomarkers for prediction of diabetic kidney disease: a propensity score matching analysis

BACKGROUND

The aim of this study was to evaluate the diagnostic value of six urinary biomarkers for prediction of diabetic kidney disease (DKD).

METHODS

The cross-sectional study recruited 1053 hospitalized patients with type 2 diabetes mellitus (T2DM), who were categorized into the diabetes mellitus (DM) with normoalbuminuria (NA) group (n = 753) and DKD group (n = 300) according to 24-h urinary albumin excretion rate (24-h UAE). Data on the levels of six studied urinary biomarkers [transferrin (TF), immunoglobulin G (IgG), retinol-binding protein (RBP), β-galactosidase (GAL), N-acetyl-beta-glucosaminidase (NAG), and β2-microglobulin (β2MG)] were obtained. The propensity score matching (PSM) method was applied to eliminate the influences of confounding variables.

RESULTS

Patients with DKD had higher levels of all six urinary biomarkers. All indicators demonstrated significantly increased risk of DKD, except for GAL and β2MG. Single RBP yielded the greatest area under the curve (AUC) value of 0.920 compared with the other five markers, followed by TF (0.867) and IgG (0.867). However, GAL, NAG, and β2MG were shown to have a weak prognostic ability. The diagnostic values of the different combinations were not superior to the single RBP.

CONCLUSIONS

RBP, TF, and IgG could be used as reliable or good predictors of DKD. The combined use of these biomarkers did not improve DKD detection.

Non-invasive detection of the early phase of kidney injury by photoacoustic/computed tomography imaging

The early diagnosis of kidney diseases, which can remarkably impair the quality of life and are costly, has encountered great difficulties. Therefore, the development of methods for early diagnosis has great clinical significance. In this study, we used an emerging technique of photoacoustic (PA) imaging, which has relatively high spatial resolution and good imaging depth. Two kinds of PA gold nanoparticle (GNP)-based bioprobes were developed based on their superior photo detectability, size controllability and biocompatibility. The kidney injury mouse model was developed by unilateral ureteral obstruction for 96 h and the release of obstruction model). Giving 3.5 and 5.5 nm bioprobes by tail vein injection, we found that the 5.5 nm probe could be detected in the bladder in the model group, but not in the control group. These results were confirmed by computed tomography imaging. Furthermore, the model group did not show changes in the blood biochemical indices (BUN and Scr) and histologic examination. The 5.5 nm GNPs were found to be the critical point for early diagnosis of kidney injury. This new method was faster and more sensitive and accurate for the detection of renal injury, compared with conventional methods, and can be used for the development of a PA GNP-based bioprobe for diagnosing renal injury.

The Promise of Systems Biology for Diabetic Kidney Disease

Diabetic kidney disease (DKD) has a complex and prolonged pathogenesis involving many cell types in the kidney as well as extrarenal factors. It is clinically silent for many years after the onset of diabetes and usually progresses over decades. Given this complexity, a comprehensive and unbiased molecular approach is best suited to help identify the most critical mechanisms responsible for progression of DKD and those most suited for targeted intervention. Systems biological investigations provide such an approach since they examine the entire network of molecular changes that occur in a disease process in a comprehensive way instead of focusing on a single abnormal molecule or pathway. Systems biological studies can also start with analysis of the disease in humans, not in animal or cell culture models that often poorly reproduce the changes in human DKD. Indeed, in the last decade, systems biological approaches have led to the identification of critical molecular abnormalities in DKD and have directly led to development of new biomarkers and potential treatments for DKD.

Kidney involvement in psoriasis: a case-control study from China

PURPOSE

Kidney involvement secondary to psoriasis is still a controversial issue. In this study, we aimed to evaluate the prevalence of urinary abnormalities in psoriasis patients and to find out whether the abnormality is related to the severity of psoriasis.

METHODS

Ninety-seven psoriasis patients (62 females, 35 males, mean age 35.74 ± 13.45 years) and ninety-six age- and gender-matched control subjects (58 males, 38 females, mean age 35.82 ± 13.48 years) without hypertension or diabetes were enrolled in this study. Psoriasis area and severity index (PASI) was used to assess the severity of psoriasis. Twenty-four-hour proteinuria, albuminuria, RBP, and NAG were measured in all patients and controls. Pathologic proteinuria was defined as the total protein excretion of more than 0.4 g/24 h, as measured by the turbidimetric assay. Pathologic albuminuria was defined as albumin excretion of more than 17 mg/24 h. Pathologic NAG and RBP were defined as the excretion of more than 16.5 u/g cr and 0.5 mg/L, respectively.

RESULTS

Increased 24-h microalbuminuria (11.53 ± 7.29 vs. 9.79 ± 3.72, P = 0.039) and 24-h proteinuria (0.24 ± 0.21 vs. 0.18 ± 0.09, P = 0.002) were found in patients with psoriasis compared with controls. Patients with psoriasis had an increased prevalence of pathological albuminuria (15.46 vs. 5.21%, P = 0.019), NAG (10.31 vs. 3.13%, P = 0.046), and RBP (9.28 vs. 2.08%, P = 0.031) compared with controls. PASI scores in patients with psoriasis correlated positively with 24-h albuminuria (χ ² = 10.75, P = 0.005).

CONCLUSIONS

The prevalence of abnormal urinalysis was more common in patients with psoriasis than in controls. The positive correlation between the prevalence of pathological albuminuria and psoriasis severity may indicate a subclinical renal dysfunction in patients with psoriasis.

Assessment of the diagnostic value of different biomarkers in relation to various stages of diabetic nephropathy in type 2 diabetic patients

Albuminuria is widely used to indicate early phases of diabetic nephropathy although it is limited by the fact that structural damage might precede albumin excretion. This necessitates identifying better biomarkers that diagnose or predict diabetic nephropathy. This is a cross-sectional hospital based study recruiting type 2 diabetic patients cohort aged 35–75 years with diabetes duration of ≥10 years. Out of total eligible 467 patients, 200 patients were with normal albumin excretion, 184 patients with microalbuminuria and 83 patients with macroalbuminuria. All the patients were tested for the 22 selected biomarkers including serum, plasma and urinary markers. Sensitivity, specificity, and area under the curve (AUC) were calculated as measures of diagnostic accuracy. Out of the tested biomarkers, urinary transferrin, urinary Retinol binding protein (RBP) and serum osteopontin had the best diagnostic value for diabetic nephropathy presence based on the AUC value. The rest of the biomarkers had comparatively less or even no discriminative power. The urinary transferrin and RBP and serum osteopontin, had the best diagnostic value in type 2 diabetic patients at different stages of diabetic nephropathy. Further longitudinal prospective studies are needed to evaluate the predictive power of those markers for detecting diabetic nephropathy before any structural damage occurs.

Early detection of diabetic kidney disease: Present limitations and future perspectives

Diabetic kidney disease (DKD) is one of the most common diabetic complications, as well as the leading cause of chronic kidney disease and end-stage renal disease around the world. To prevent the dreadful consequence, development of new assays for diagnostic of DKD has always been the priority in the research field of diabetic complications. At present, urinary albumin-to-creatinine ratio and estimated glomerular filtration rate (eGFR) are the standard methods for assessing glomerular damage and renal function changes in clinical practice. However, due to diverse tissue involvement in different individuals, the so-called “non-albuminuric renal impairment” is not uncommon, especially in patients with type 2 diabetes. On the other hand, the precision of creatinine-based GFR estimates is limited in hyperfiltration status. These facts make albuminuria and eGFR less reliable indicators for early-stage DKD. In recent years, considerable progress has been made in the understanding of the pathogenesis of DKD, along with the elucidation of its genetic profiles and phenotypic expression of different molecules. With the help of ever-evolving technologies, it has gradually become plausible to apply the thriving information in clinical practice. The strength and weakness of several novel biomarkers, genomic, proteomic and metabolomic signatures in assisting the early diagnosis of DKD will be discussed in this article.

Urinary Markers of Tubular Injury in Early Diabetic Nephropathy

Diabetic nephropathy (DN) is a common and serious complication of diabetes associated with adverse outcomes of renal failure, cardiovascular disease, and premature mortality. Early and accurate identification of DN is therefore of critical importance to improve patient outcomes. Albuminuria, a marker of glomerular involvement in early renal damage, cannot always detect early DN. Thus, more sensitive and specific markers in addition to albuminuria are needed to predict the early onset and progression of DN. Tubular injury, as shown by the detection of tubular injury markers in the urine, is a critical component of the early course of DN. These urinary tubular markers may increase in diabetic patients, even before diagnosis of microalbuminuria representing early markers of normoalbuminuric DN. In this review we summarized some new and important urinary markers of tubular injury, such as neutrophil gelatinase associated lipocalin (NGAL), kidney injury molecule-1 (KIM-1), liver-type fatty acid binding protein (L-FABP), N-acetyl-beta-glucosaminidase (NAG), alpha-1 microglobulin (A1M), beta 2-microglobulin (B2-M), and retinol binding protein (RBP) associated with early DN.

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.

N-Acetyl-β-D-Glucosaminidase Does Not Enhance Prediction of Cardiovascular or All-Cause Mortality by Albuminuria in a Low-Risk Population

Albuminuria is a well known risk factor for cardiovascular disease and mortality, but focus on renal tubular dysfunction as a potential risk factor is growing also. The association between the urinary activity of N-acetyl-β-D-glucosaminidase (NAG) and cardiovascular risk has been assessed mostly in cross-sectional studies. We studied the cross-sectional associations between urinary NAG and cardiovascular risk factors and the longitudinal associations between NAG, cardiovascular disease, and all-cause mortality in a general population. Urinary NAG/creatinine ratio (NAG ratio) and albumin/creatinine ratio (ACR) were measured in 6834 participants of the Tromsø Study in 1994-1995. During the median 17.5 years of follow-up, 958 myocardial infarctions, 726 ischemic strokes, and 2358 deaths were registered. In multivariable analyses adjusted for albuminuria and cardiovascular risk factors, a baseline NAG ratio in the highest quartile was associated with an increased risk of myocardial infarction (hazard ratio [HR], 1.43; 95% confidence interval [95% CI], 1.16 to 1.76), ischemic stroke (HR, 1.41; 95% CI, 1.10 to 1.80), and all-cause mortality (HR, 1.60; 95% CI, 1.39 to 1.84). Combined, ACR and NAG ratio above median associated with a 48%-80% increased risk for the three end points. However, the NAG ratio did not add significantly to the baseline risk-prediction models when assessed by area under the receiver operating characteristics curve or net reclassification improvement. In conclusion, the nonsignificant improvement of risk prediction does not support the clinical use of NAG ratio in cardiovascular risk assessment in a low-risk group.

Biomarkers in diabetic nephropathy: Present and future

Diabetic nephropathy (DN) is the leading cause of end stage renal disease in the Western world. Microalbuminuria (MA) is the earliest and most commonly used clinical index of DN and is independently associated with cardiovascular risk in diabetic patients. Although MA remains an essential tool for risk stratification and monitoring disease progression in DN, a number of factors have called into question its predictive power. Originally thought to be predictive of future overt DN in 80% of patients, we now know that only around 30% of microalbuminuric patients progress to overt nephropathy after 10 years of follow up. In addition, advanced structural alterations in the glomerular basement membrane may already have occurred by the time MA is clinically detectable.Evidence in recent years suggests that a significant proportion of patients with MA can revert to normoalbuminuria and the concept of nonalbuminuric DN is well-documented, reflecting the fact that patients with diabetes can demonstrate a reduction in glomerular filtration rate without progressing from normo-to MA. There is an unmet clinical need to identify biomarkers with potential for earlier diagnosis and risk stratification in DN and recent developments in this field will be the focus of this review article.

Nonalbuminuric proteinuria as a biomarker for tubular damage in early development of nephropathy with type 2 diabetic patients

AIM

The aim of this study was to evaluate the association between urinary nonalbumin protein (NAP) and urinary tubular markers in early diabetic nephropathy.

METHODS

Urinary NAP was measured in 118 patients with type 2 diabetes with estimated glomerular filtration rates (eGFR) ≥60 mL/min/1.73 m². Urine levels of tubular markers [kidney injury molecule (KIM)-1, neutrophil gelatinase-assoicated lipocalin (NGAL) and liver-type fatty acid-binding protein (L-FABP)] were measured by using an Enzyme-linked immunosorbent assay (ELISA). Patients were divided into three groups according to urinary NAP values.

RESULTS

The urine levels of KIM-1, NGAL and L-FABP were significantly higher in the third tertile group than in the first tertile group (all p < 0.001). There was a significant positive correlation between NAP and each tubular marker (KIM-1, NGAL and L-FABP) in univariate analysis (all p < 0.001). Urinary NAP was positively correlated with all urinary tubular markers after adjustment for age, duration of diabetes, systolic blood pressure, eGFR, low-density lipoprotein cholesterol, HbA1c and albumin-to-creatinine ratio (KIM-1 r = 0.170, p < 0.001; NGAL r = 0.142, p < 0.015 and L-FABP r = 0.262, p < 0.001). In normoalbuminuric patients (n = 58), urinary NAP was also significantly correlated with NGAL and L-FABP in multivariate regression analyses (r = 0.302, p = 0.030 and r = 0.430, p = 0.001).

CONCLUSIONS

These findings suggest that urinary NAP reflects tubular damage in the early-stage type 2 diabetic nephropathy (eGFR ≥ 60 mL/min/1.73 m²). We suggest that urinary NAP could be used as a biomarker for tubular damage in clinical practice.

New insights into the use of biomarkers of diabetic nephropathy

Diabetic nephropathy (DN) is a major microvascular complication of diabetes characterized by increasing albuminuria and progressive loss of kidney function. Increased excretion of albumin into the urine is a key feature of DN, and its assessment is considered to be an early marker predicting the onset and progression of DN. However, albuminuria has certain limitations; therefore, the quest for more reliable renal biomarkers with higher sensitivity and specificity are needed for early prediction of the onset and monitoring of the progression of DN. Furthermore, such biomarkers may also provide a better insight into identifying the complex pathophysiological processes responsible for DN. This article aims to provide a comprehensive and critical review of the current literature on relevant biomarkers of kidney injury, including markers of renal fibrosis, inflammation, and oxidative stress, as well as addressing contemporary proteomic approaches.

Urinary TNF-α and NGAL are correlated with the progression of nephropathy in patients with type 2 diabetes

The aim of this study was to investigate the correlation of the proinflammatory marker tumor necrosis factor-α (TNF-α) and the tubular marker neutrophil gelatinase-associated lipocalin (NGAL) with the progression of the early stage of type 2 diabetic nephropathy (DN). Baseline levels of urinary TNF-α and NGAL were measured in 63 non-diabetic controls and 201 patients with type 2 diabetes and different albuminuria statuses. The patients with diabetes (n=125) with normo- or microalbuminuria were subsequently followed-up for 28 (25-32) months, with routine measurements of creatinine and urinary albumin excretion (UAE). It was observed that baseline levels of urinary TNF-α and NGAL were significantly elevated and correlated with the severity of albuminuria in patients with diabetes. During the follow-up, the urinary levels of TNF-α and NGAL were observed to be significantly correlated with a rapid decline in the estimated glomerular filtration rate (eGFR). Following adjustment for other progression promoters, including albuminuria, TNF-α remained a significant predictor of eGFR decline. These results suggest that inflammation is important in the pathogenesis of DN and indicate that TNF-α may be used as an independent predictor for the progression of DN at the early stage.

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.

Delineating the degree of association between biomarkers of arsenic exposure and type-2 diabetes mellitus

Non-carcinogenic effects in low-level (< 100 μgL(-1)) arsenic (As)-impacted populations, such as the development and progression of type-2 diabetes mellitus (T2DM), are often neglected given the primary emphasis of public health authorities on As carcinogenicity. We gathered studies reporting urinary biomarkers of As exposure (U-As) and biomarkers associated with T2DM and its complications (U-T2DM), such as renal damage, oxidation stress, low-grade inflammation, and endothelial damage. Studied U-T2DM biomarkers were: 8-hydroxy-2'deoxyguanosine, N-acetyl-β-d-glucosaminidase, β2-microglobulin, and albumin. Data was expressed as: either arithmetic means and standard deviations, or geometric means and geometric standard deviations, or correlation coefficients of U-As and U-T2DM. Urinary As concentrations were consistently associated with the aforementioned biomarkers of T2DM pathologic complications. Despite the limited selectivity of the selected T2DM biomarkers, a per unit change in As exposure level was reflected in the corresponding T2DM biomarker urinary concentrations. Our systematic review provides new evidence on the role of environmental As exposures influencing the T2DM disease process. Additional epidemiologic studies onto the association between As and T2DM should incorporate both urinary As and T2DM biomarkers, as suggested in this study, in order to evaluate subclinical effects of low-level As exposures.

Elevated serum retinol-binding protein 4 concentrations are associated with chronic kidney disease but not with the higher carotid intima-media thickness in type 2 diabetic subjects

To examine the association of serum retinol-binding protein 4 (RBP4) concentrations with carotid intima-media thickness (CIMT) in type 2 diabetic subjects with chronic kidney disease (CKD). A total of 239 type 2 diabetic patients (64 ± 13 years, 154 males) were divided into two groups: one with CKD, defined as estimated glomerular filtration rate (eGFR) below 60 mL/min/1.73m(2) (n = 86), and one without (n = 153). We recorded clinical and biochemical data as well as CIMT. The patients with CKD were older, had had diabetes mellitus longer, and had higher incidence of hypertension, dyslipidemia and microalbuminuria than those without. They also had higher serum concentrations of RBP4 (44.8 ± 6.4 vs 39.5 ± 4.9 µg/mL, p < 0.001), higher mean CIMT (0.75 ± 0.16 vs 0.69 ± 0.14 mm, p = 0.0070), and higher incidence of carotid plaques (27.9 vs 11.8 %, p = 0.002). The RBP4 were negatively correlated with eGFR (r = -0.514, p < 0.001). However, the RBP4 were not correlated with mean CIMT (r = 0.065, p = 0.318). Moreover, when dividing the patients into two groups by the mean CIMT, those with mean CIMT above 0.71 mm did not have different RBP4 concentrations compared with those below (41.5 ± 5.7 vs 41.3 ± 6.3 µg/mL, p = 0.856). In conclusion, we observed an elevation of serum RBP4 concentrations and CIMT levels in type 2 diabetic subjects with CKD. However, the elevated RBP4 were not associated with the higher CIMT among these patients.

Vitamin D homeostasis is compromised due to increased urinary excretion of the 25-hydroxycholecalciferol-vitamin D-binding protein complex in the Zucker diabetic fatty rat

Altered serum concentrations of the major circulating form of vitamin D [25-hydroxycholecalciferol (25D(3))] and its active hormone derivative [1,25-dihydroxycholecalciferol (1,25D(3))] have been linked to non-insulin-dependent diabetes mellitus (NIDDM). However, a mechanistic basis for this occurrence has not been fully elucidated. Normally, renal reabsorption of vitamin D-binding protein-bound 25D(3) absolutely requires receptor-mediated endocytosis via a receptor complex containing megalin, cubilin, and disabled-2 (Dab2), whereas an absence of megalin or its endocytic partners can lead to a marked urinary loss of 25D and severe vitamin D deficiency. Therefore, we hypothesized that reduced serum vitamin D status in NIDDM may be due to reduced expression of megalin and/or its endocytic partners and increased urinary excretion of protein-complexed 25D(3). In the present study, we utilized Zucker diabetic fatty Rats (ZDF) to demonstrate that renal reuptake of the 25D(3)-DBP complex was compromised in ZDF animals, which was reflected by a reduction in expression of megalin and Dab2. Moreover, serum levels of both 25D(3) and 1,25D(3) were reduced, and urinary 25D(3), 1,25D(3), and DBP excretion were elevated in the ZDF animals compared with their lean controls regardless of vitamin D levels in the diet. Taken together, these are the first reports to our knowledge that associate compromised renal reabsorption of the 25D(3)-DBP complex with expression of megalin and its endocytic partners in NIDDM, which in turn can lead to compromised vitamin D status.

Proteomic identification of human urinary biomarkers in diabetes mellitus type 2

BACKGROUND

During the proteomic era, one of the most rapidly growing areas in biomedical research is biomarker discovery, particularly using proteomic technologies. The urinary proteome is known to be a valuable field of study and has become one of the most attractive subdisciplines in clinical proteomics for human diseases. We have described the levels of protein biomarkers specific to diabetes mellitus type 2 in the Pakistani population using proteomic technology.

METHODS

One hundred type 2 diabetes patients with 50 age- and sex-matched normal healthy controls were recruited from Sheikh Zayed Hospital, Lahore, Pakistan. Urinary proteins were analyzed by two-dimensional liquid chromatography, using chromatofocusing in the first dimension and reverse-phase chromatography in the second, followed by mass spectrometric analysis. Levels of the proteins, which were found to vary in the diabetes type 2 patients compared to the controls, were then determined by enzyme-linked immunosorbent assay in all the samples.

RESULTS

Levels of transthyretin, α-1-microglobulin/bikunin precursor, and haptoglobin precursor decreased by 30.8%, 55.2%, and 81.45%, whereas levels of albumin, zinc α2 glycoprotein, retinol binding protein 4, and E-cadherin increased by 486.5%, 29.23%, 100%, and 693%, respectively, in the diabetes patients compared to the controls.

CONCLUSIONS

Variation in the levels of these identified protein biomarkers have been reported in other pathological states. Assessment of the levels of these biomarkers will be helpful not only in early diagnosis but also in prognosis of diabetes mellitus type 2.

Minimal health impact from exposure to diet-sourced cadmium on a population in central Jamaica

Elevated concentrations of naturally occurring Cd have been found mainly in the bauxitic soils of central Jamaica at levels up to 100-1,000 times higher than typical worldwide averages. Some food crops cultivated on these soils absorb significant amounts of Cd. Autopsy studies of kidney Cd concentrations confirm elevated human exposure, and some long-term residents in central Jamaica exceed the general population average by a factor of two. Diet studies have ascertained that a population in central Jamaica is at risk of being exposed to Cd levels in excess of the Provisional Tolerable Weekly Intake (PTWI) set by the WHO of 7 μgCd/kg bodyweight/week, and the EU TWI of 2.5 μgCd/kg bodyweight/week. Elevated levels of urine cadmium (U-Cd) and beta-2 microglobulin (β2-MG) concentrations were confirmed with a strong correlation between soil Cd and the U-Cd. Also, higher β2-MG concentrations (>200μg/g creatinine) were found in the population with U-Cd concentrations greater than 2.5μg/L. While this identification is often taken to indicate impairment in the reabsorption capacity of the renal tubules leading to renal disease, there is no evidence in the mortality records of enhanced deaths in central Jamaica compared with the general population resulting from renal disease or diabetes related complications. The highest median age of death in the island is found in Manchester, the parish with the highest average Cd concentration. While we have identified a possible Cd linked renal dysfunction, significant indications of morbidity are not present in the general population.

Effect of high dose thiamine on the levels of urinary protein biomarkers in diabetes mellitus type 2

The proteomics is known to be a valuable field of study and has become one of the most attractive sub-disciplines in clinical proteomics for human diseases. In the present research work, the levels of urinary protein biomarkers of diabetes mellitus type 2 using proteomic technology have been identified and characterized. Effect of high dose thiamine has also been observed on the levels of these marker proteins. Above 100 type 2 diabetic patients, and 50 same age and sex-matched normal healthy controls were recruited from the Sheikh Zayed Hospital, Lahore, Pakistan and 40 diabetic and 20 control have completed the trial. The urine samples from control and diabetic groups before or after thiamine therapy were further analyzed and identified by 2-D liquid chromatographic system (HPLC) and mass spectrometry MALDI-TOF/TOF and microTOF analysis. All the samples belonging to the control and diabetic groups were then analyzed by ELISA and estimated the levels of some proteins which were found to vary. In the urine samples, the levels of transthyretin, AMBP, haptoglobin precursor were found to decrease while albumin, zinc α 2 glycoprotein, RBP4 and E cadherin were found to increase in the diabetic patients as compared to the controls. The level of albumin in the urine samples of diabetic patients only decreased by 34% after thiamine therapy as compared to the controls and the placebo, while other urinary protein markers did not show a significant change after the therapy. Assessment of the levels of these biomarkers will be helpful in the diagnosis and treatment of diabetes mellitus type 2.

Urine proteome analysis may allow noninvasive differential diagnosis of diabetic nephropathy

OBJECTIVE

Chronic renal insufficiency and/or proteinuria in type 2 diabetes may stem from chronic renal diseases (CKD) other than classic diabetic nephropathy in more than one-third of patients. We interrogated urine proteomic profiles generated by surface-enhanced laser desorption/ionization-time of flight/mass spectrometry with the aim of isolating a set of biomarkers able to reliably identify biopsy-proven diabetic nephropathy and to establish a stringent correlation with the different patterns of renal injury.

RESEARCH DESIGN AND METHODS

Ten micrograms of urine proteins from 190 subjects (20 healthy subjects, 20 normoalbuminuric, and 18 microalbuminuric diabetic patients and 132 patients with biopsy-proven nephropathy: 65 diabetic nephropathy, 10 diabetic with nondiabetic CKD [nd-CKD], and 57 nondiabetic with CKD) were run using a CM10 ProteinChip array and analyzed by supervised learning methods (Classification and Regression Tree analysis).

RESULTS

The classification model correctly identified 75% of patients with normoalbuminuria, 87.5% of those with microalbuminuria, and 87.5% of those with diabetic nephropathy when applied to a blinded testing set. Most importantly, it was able to reliably differentiate diabetic nephropathy from nd-CKD in both diabetic and nondiabetic patients. Among the best predictors of the classification model, we identified and validated two proteins, ubiquitin and β2-microglobulin.

CONCLUSIONS

Our data suggest the presence of a specific urine proteomic signature able to reliably identify type 2 diabetic patients with diabetic glomerulosclerosis.

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.

Transcriptomic comparison of the retina in two mouse models of diabetes

Mouse models of type I diabetes offer the potential to combine genetic approaches with other pharmacological or physiological manipulations to investigate the pathophysiology and treatment of diabetic retinopathy. Type I diabetes is induced in mice through chemical toxins or can arise spontaneously from genetic mutations. Both models are associated with retinal vascular and neuronal changes. Retinal transcriptomic responses in C57BL/6J mice treated with streptozotocin and Ins2(Akita/+) were compared after 3 months of hyperglycemia. Specific gene expression changes suggest a neurovascular inflammatory response in diabetic retinopathy. Genes common to the two models may represent the response of the retina to hyperglycemia, while changes unique to each model may represent time-dependent disease progression differences in the various models. Further investigation of the commonalities and differences between mouse models of type I diabetes may define cause and effect events in early diabetic retinopathy disease progression. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s12177-009-9045-3) contains supplementary material, which is available to authorized users.

Decreased clearance of serum retinol-binding protein and elevated levels of transthyretin in insulin-resistant ob/ob mice

Serum retinol-binding protein (RBP4) is secreted by liver and adipocytes and is implicated in systemic insulin resistance in rodents and humans. RBP4 normally binds to the larger transthyretin (TTR) homotetramer, forming a protein complex that reduces renal clearance of RBP4. To determine whether alterations in RBP4-TTR binding contribute to elevated plasma RBP4 levels in insulin-resistant states, we investigated RBP4-TTR interactions in leptin-deficient ob/ob mice and high-fat-fed obese mice (HFD). Gel filtration chromatography of plasma showed that 88-94% of RBP4 is contained within the RBP4-TTR complex in ob/ob and lean mice. Coimmunoprecipitation with an RBP4 antibody brought down stoichiometrically equal amounts of TTR and RBP4, indicating that TTR was not more saturated with RBP4 in ob/ob mice than in controls. However, plasma TTR levels were elevated approximately fourfold in ob/ob mice vs. controls. RBP4 injected intravenously in lean mice cleared rapidly, whereas the t(1/2) for disappearance was approximately twofold longer in ob/ob plasma. Urinary fractional excretion of RBP4 was reduced in ob/ob mice, consistent with increased retention. In HFD mice, plasma TTR levels and clearance of injected RBP4 were similar to chow-fed controls. Hepatic TTR mRNA levels were elevated approximately twofold in ob/ob but not in HFD mice. Since elevated circulating RBP4 causes insulin resistance and glucose intolerance in mice, these findings suggest that increased TTR or alterations in RBP4-TTR binding may contribute to insulin resistance by stabilizing RBP4 at higher steady-state concentrations in circulation. Lowering TTR levels or interfering with RBP4-TTR binding may enhance insulin sensitivity in obesity and type 2 diabetes.

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.

Serum levels of adipokine retinol-binding protein-4 in relation to renal function

OBJECTIVE

Retinol-binding protein (RBP)-4 was recently identified as an adipokine that induces insulin resistance. In the current study, we investigated RBP-4 serum levels in diabetic and nondiabetic patients on chronic hemodialysis (CD) compared with control subjects with a glomerular filtration rate >50 ml/min. The majority of the diabetic subjects used oral hypoglycemic agents or insulin.

RESEARCH DESIGN AND METHODS

RBP-4 was determined by enzyme-linked immunosorbent assay in control subjects (n = 59) and CD patients (n = 58) and correlated with clinical and biochemical measures of renal function, glucose and lipid metabolism, and inflammation in both groups.

RESULTS

Mean serum RBP-4 levels were almost fourfold higher in CD patients (102 +/- 30 mg/l) compared with control subjects (28 +/- 8 mg/l). Furthermore, serum creatinine independently predicted RBP-4 concentrations in multiple regression analyses in both control subjects and CD patients. In addition, C-reactive protein and systolic blood pressure independently and negatively correlated with RBP-4 serum concentrations in CD patients but not control subjects. In contrast, markers of glucose and lipid metabolism were not independently related to serum RBP-4 in control subjects or CD patients.

CONCLUSIONS

We show that markers of renal function are independently related to serum RBP-4 levels.

Urinary PGDS levels are associated with vascular injury in type 2 diabetes patients

BACKGROUND

The presence of metabolic syndrome has been shown to be predictors of cardiovascular morbidity and mortality in patients with type 2 diabetes. In a cross-sectional clinical study, we investigated the association of metabolic syndrome with asymptomatic lacunar strokes and cardiovascular disease (CVD) and we compared its significance with urinary protein markers.

METHODS

We studied Japanese type 2 diabetes patients (n=233, men=124, women=109). The diagnosis of metabolic syndrome was made according to WHO and International Diabetes Federation (IDF) criteria. Cardiovascular events were recorded and asymptomatic lacunar lesions were evaluated with magnetic resonance imaging (MRI). We also measured urinary levels of albumin, type IV collagen, beta2-microglobulin (beta2MG), N-acetyl-beta-d-glucosaminidase (NAG) and lipocalin-type prostaglandin D synthase (PGDS).

RESULTS

The prevalence of metabolic syndrome is 31.3% (IDF) and 52% (WHO) in 233 patients and microalbuminuria was present in 62 subjects (26.6%). Metabolic syndrome (WHO) significantly associated with asymptomatic lacunar lesions (p=0.035, OR=2.854, CI 1.075-7.579), while metabolic syndrome (IDF) or urinary markers failed to associate with presence of asymptomatic lacunar lesions. The presence of metabolic syndrome or microalbuminuria did not show significant association with CVD; however, the elevation of beta2MG, NAG and PGDS showed significant association with CVD. By a logistic regression analysis using urinary proteins as independent variables, the presence of higher PGDS excretion independently associated with history of CVD (p=0.025, OR=3.847, CI 1.180-12.545).

CONCLUSIONS

In type 2 diabetes patients, the elevation of urinary PGDS secretion closely associated with cardiovascular events and may be a supplemental or additional marker to the criteria of metabolic syndrome.