Proteomic identification of urinary biomarkers of diabetic nephropathy

Low molecular weight proteins in urines from healthy subjects as well as diabetic, nephropathic and diabetic-nephropathic patients: a MALDI study

Urine samples from healthy subjects as well as diabetic, nephropathic and diabetic-nephropathic patients were analyzed by matrix assisted laser desorption/ionization (MALDI) mass spectrometry in order to establish evidence of some possible differences in the peptide profile related to the pathological states. Multivariate analysis suggested the possibility of a distinction among the considered groups of patients. Some differences have been found, in particular, in the relative abundances of three ions at m/z 1912, 1219 and 2049. For these reasons, further investigation was carried out by MALDI/TOF/TOF to determine the sequence of these peptides and, consequently, to individuate their possible origin. By this approach, the peptide at m/z 1912 was found to originate from uromodulin, and its lower expression in the case of nephropathy can be well related to the pathological condition. Ions at m/z 2049 and 1219 originate from the collagen alpha-1(I) chain precursor and from the collagen alpha-5 (IV) chain precursor, respectively, and, also in this case, their different expressions can be related to the pathologies under investigation. The obtained data seem to indicate that urine is an interesting biological fluid to investigate on the peptide profile and to obtain, consequently, information on the dismetabolism activated by specific pathologies.

Proteomic identification of salivary biomarkers of type-2 diabetes

The identification of biomarkers to noninvasively detect prediabetes/diabetes will facilitate interventions designed to prevent or delay progression to frank diabetes and its attendant complications. The purpose of this study was to characterize the human salivary proteome in type-2 diabetes to identify potential biomarkers of diabetes. Whole saliva from control and type-2 diabetic individuals was characterized by multidimensional liquid chromatography/tandem mass spectrometry (2D-LC-MS/MS). Label-free quantification was used to identify differentially abundant protein biomarkers. Selected potential biomarkers were then independently validated in saliva from control, diabetic, and prediabetic subjects by Western immunoblotting and ELISA. Characterization of the salivary proteome identified a total of 487 unique proteins. Approximately 33% of these have not been previously reported in human saliva. Of these, 65 demonstrated a greater than 2-fold difference in abundance between control and type-2 diabetes samples. A majority of the differentially abundant proteins belong to pathways regulating metabolism and immune response. Independent validation of a subset of potential biomarkers utilizing immunodetection confirmed their differential expression in type-2 diabetes, and analysis of prediabetic samples demonstrated a trend of relative increase in their abundance with progression from the prediabetic to the diabetic state. This comprehensive proteomic analysis of the human salivary proteome in type-2 diabetes provides the first global view of potential mechanisms perturbed in diabetic saliva and their utility in detection and monitoring of diabetes. Further characterization of these markers in a larger cohort of subjects may provide the basis for new, noninvasive tests for diabetes screening, detection, and monitoring.

Increased urinary excretion of orosomucoid is a risk predictor of diabetic nephropathy

AIM

Identification of the risk predictor of diabetic nephropathy (DN) remains a major challenge currently. Thus, proteomic approaches to identify DN-related biomarker were performed.

METHODS

A comparative proteomic approach of 2-D gel electrophoresis (2-DE) and mass spectrometry to identify biomarkers in urine samples from 12 DN patients (six type 1 and six type 2 diabetic patients) and six healthy controls. Then, the urinary level of identified protein biomarker was detected by immunoturbidimetry assay in urine samples from 90 type 1 and type 2 diabetic patients with normo-, micro- and macroalbuminuria (n = 30 in each group), and 30 healthy controls.

RESULTS

A novel DN-related protein, orosomucoid (alpha1-acid glycoprotein), was identified by proteomic method. Its abundance was highly upregulated (>eightfold) in DN patients. The data of immunoturbidimetry assay showed urinary orosomucoid excretion rate (UOER) was gradually increased in the normo-, micro- and macroalbuminuria group versus control (0.71 +/- 0.41, 1.93 +/- 0.68, 2.88 +/- 0.94 vs 0.39 +/- 0.28 ug/min, P < 0.05). The result indicated that UOER increased in early stage of DN and gradually increased with the development of DN. Also, Pearson's correlation analysis indicated UOER was positively correlated with urinary albumin excretion rate, serum creatinine and C-reactive protein (r = 0.830, 0.787 and 0.360, respectively; P < 0.05). Multivariate logistic regression analysis also showed that increased UOER was an independent risk factor for DN (odds ratio = 3.10, P < 0.0001).

CONCLUSION

Urinary orosomucoid is a DN-related biomarker, which is associated with the development and progression of DN. Furthermore, increased UOER is an independent risk factor of DN.

Agents in development for the treatment of diabetic nephropathy

BACKGROUND

Nephropathy is a major cause of morbidity and mortality in diabetic patients. Current treatments include optimization of glycemic and blood pressure control, but more innovative strategies are needed for the prevention and treatment of diabetic nephropathy.

OBJECTIVES

To review emerging therapies for diabetic nephropathy.

METHODS

This paper discusses the molecular mechanisms of diabetic nephropathy and the potential therapeutic interventions.

RESULTS/CONCLUSION

New therapies, including those targeting the accumulation of advanced glycation end products (AGEs) and reactive oxygen species (ROS) generation, are likely to feature in future treatment regimens. Other approaches that at this stage do not appear to be progressing include the glycosaminoglycan sulodexide and the protein kinase C-beta (PKC-beta) inhibitor, ruboxistaurin.

Urine in clinical proteomics

Urine has become one of the most attractive biofluids in clinical proteomics as it can be obtained non-invasively in large quantities and is stable compared with other biofluids. The urinary proteome has been studied by almost any proteomics technology, but mass spectrometry-based urinary protein and peptide profiling has emerged as most suitable for clinical application. After a period of descriptive urinary proteomics the field is moving out of the discovery phase into an era of validation of urinary biomarkers in larger prospective studies. Although mainly due to the site of production of urine, the majority of these studies apply to the kidney and the urinary tract, but recent data show that analysis of the urinary proteome can also be highly informative on non-urogenital diseases and used in their classification. Despite this progress in urinary biomarker discovery, the contribution of urinary proteomics to the understanding of the pathophysiology of disease upon analysis of the urinary proteome is still modest mainly because of problems associated to sequence identification of the biomarkers. Until now, research has focused on the highly abundant urinary proteins and peptides, but analysis of the less abundant and naturally existing urinary proteins and peptides still remains a challenge. In conclusion, urine has evolved as one of the most attractive body fluids in clinical proteomics with potentially a rapid application in the clinic.

Proteomics and diabetic nephropathy

Proteomic methods have found broad applications in kidney disease research and more specifically in diabetic nephropathy (DN) research. Proteomic methods such as 2-dimensional gel electrophoresis have been used to gain insight into glomerular and tubular nephropathies including DN. At the protein level, differences in high-abundant proteins in DN have been shown to reflect primarily differentially posttranslationally modified plasma proteins. Higher-sensitivity proteomic methods (eg, liquid chromatography-mass spectrometry) have pushed the boundaries on the known urinary proteome to include more than 1,500 proteins. These same high-sensitivity methods have been applied toward profiling urinary peptides, which has resulted in methods to diagnostically screen urine to differentiate between type-2 diabetes mellitus and type-1 diabetes mellitus urine, normal versus microalbuminuria, or by angiotensin II receptor blocker treatment. Proteomic methods are being used to show response to insulin gene therapy in an animal model or alterations in the renal cortex mitochondrial proteome with the development of the diabetic phenotype. Proteomic methods continue to aid in the discovery of new mechanisms of diabetic pathology and understanding of the etiology of diabetic complications.

Microalbuminuria as a target to improve cardiovascular and renal outcomes in diabetic patients

Microalbuminuria has been shown to be a risk factor for adverse renal and cardiovascular outcomes in patients with diabetes mellitus. This risk appears to increase with higher levels of albuminuria. There is also evidence that reducing the level of albuminuria improves these outcomes. This review focuses on the most recent advances in this area and reviews literature over the past year on this topic.