PEPTIDIC BIOMARKERS IN URINE FOR THE DIAGNOSIS AND PROGNOSIS OF RENAL DISEASE ASSOCIATED WHIT DIABETES MELLITUS

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In this context, we will address the main physiological changes that comprehend this pathology, where, glomerular hyperfiltration corresponds to a detonating factor in the early stages of ND. This is a complex multifactorial hemodynamic phenomenon which included numerous humoral factors such as nitric oxide, prostaglandins, renin angiotensin aldosterone system, natriuretic atrial peptide, reactive oxygen species and other humoral and growth factor. Those, basically act either by potentiating vasodilation of the afferent arteriole or by vasoconstriction of the efferent arteriole, considered as primary vascular factors (Barber Fox and Barber Gutiérrez 2003). In this process, glomerular hemodynamics is being compromised due to shear stress and mechanical stain; releasing paracrine and autocrine cytokines and growing factors that produce structural changes. Some of the possible pivotal phenomena involved aim to an increasement of glomerular filtration rate by intact macula-densa mechanism that promotes sodium chloride reabsorption in proximal tubules or henle loop (Vinod 2012).

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5. STRUCTURAL AND HISTOLOGICAL CHANGES DURING DN

The clinical manifestations of DN are strongly related to structural changes. Glomerular basement membrane thickness and mesangial expansion are the first noticeable changes related with glomerular lesion presence commonly, with nodular origin (Kimmelstiel-Wilson) leading to glomerular dysfunction (Tervaert, Mooyaart et al. 2010). Both mesangial expansion and glomerular basement membrane (GBM) and tubular basement membrane (TBM) thickening are a consequence of extracellular matrix (ECM) accumulation. due the increased deposition of the normal ECM local components of types IV and VI collagen, laminin and fibronectin due to their increased production, decreased degradation or both (Fioretto and Mauer 2007). Whereas the expression of heparin sulfate and the extent of sulfation decreases. In contrast to the mesangial matrix in which the α1 and α2 of type IV collagen are mainly expressed, the GBM contains α3, α4, and α5 chains. In DN, there is an up-regulation of α1 (IV) and α2 (IV) chains in mesangial cells, whereas α3 (IV) and α4 (IV) expression is increased in the GBM. Deposition of collagen type I and III in the mesangial area occurs late in glomerulosclerosis and is not an early event (Vinod 2012).

Based on major structural changes during DN progression, The Renal Pathology Society (RPS) has provides a histopathological classification (Ekinci et al., 2013). It divides DN into four hierarchical glomerular lesions. Although the evaluation of interstitial and vascular changes has been separated, in this classification, the damage inflicted by glomerular lesions is the lowest in group one but increases throughout the groups. Glomerular alterations as most important lesions were classified as follows: class I: glomerular basement membrane thickening; class IIa: mild mesangial expansion; class IIb: severe mesangial expansion; class III: nodular sclerosis and class IV: global glomerulosclerosis in >50% of glomeruli. In figure 2, major pathophysiological changes responsible of DN establishments are shown.

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[pic 2]

Figure 2. Major pathophysiological changes during diabetic nephropathy

6. URINARY PROTEOMIC STUDIES

Proteins such as neutrophil-associated gelatinase (NGAL) lipocalin, kidney damage molecule I (KIM-1), interleukin 18 (IL-18), liver fatty acid binding protein (L-FABP), Fibroblast growth factor 23 (FGF-23), chemotactic protein 1 (MCP-1), retinol binding protein (Urbp4) and insulin-like growth factor (IGFBP7) have emerged as potential biomarkers of DN (Simsek, et al., 2012, Aregger, et al., 2014). Although these molecules possess high specificity of binding to kidney, they are not specific for ND, which discards its application in the diagnosis of this pathology.

On the other hand, in a study by Malagrino, Venturini et al. (AADC), S-methylmethionine-homocysteine ​​S-methyltransferase (AADC), and the presence of a specific protein in the urine specimen BHMT2), cytosolic betaglucosidase (BGC) and dipeptidyl peptidase IV (DPPIV). The expression of the latter has been mostly observed in the proximal renal tubule and small intestine, although it also occurs in low proportions in the lungs, pancreas, liver, spleen, stomach and heart. However, a DPPIV study in urine suggests that its DPPIV excretion comes from tubular epithelial cells and may be related to early tubular deterioration (Malagrino, Venturini et al., 2016). Treatment with DPPIV inhibitors has shown an improvement in renal function. The detection of specific multi-markers is essential for reducing the lack of specificity in diagnostic methods.

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6. URINARY PEPTIDE STUDIES

Recently, a special interest in urinary peptides has been shown, their search has been enhanced since they represent at least a 10-fold molar excess compared to protein content of urine (Ling, Mellins et al. 2010). Some studies indicate an increase in protein degradation during glomerular filtration (Osicka and Comper 1997). Meanwhile, trials of both diabetic human and mice have shown extensive degradation (~ 95%) of albumin filtered to low molecular mass (~ 10 kD) peptides excreted in urine (Strong, Osicka et al. 2005)

In addition, the concentration of excreted urinary peptides increased as a function of albuminuria values, suggesting damage in the protein degradation process (Osicka, Houlihan et al. 2000). It should be highlighted that the protein degradation pathway in the kidneys has not been fully elucidated, but is suggested to occur in the tubular epithelial cells where albumin is subjected to endocytosis to be subsequently transported to the lysosomes, degraded and excreted through the urine. On the other hand, although the origin of the urinary peptides has not been established, the presence of peptides derived from such protein degradation has not been observed in blood samples (Eppel, Pratt et al. 2002). While, a urinary peptide increase in patients with renal damage has been clearly demonstrated (Wittke, Fliser et al. 2003).

Additionally, an international study related to the validation of a classifier system for the diagnosis of nephropathy in type 2 diabetes, from a panel of urinary peptides called CKD 273, which was performed