**3. Biomarkers of proximal tubules**

PENIA method designed primary for CYC determination in serum (Herget-Rosenthal et al., 2004). PENIA method (particle enhanced nephelometric immunoassay)allows for a CYC

**Proteinuria** reflects increased filtration plasma proteins to tubular fluid and disturbed protein reabsorption by renal proximal tubular cells (Haraldsson & Sörensson, 2004; Halbesma et al., 2006; Giorgio et al., 2004). Proteinuria over 0.5g/24 hours is a marker the severity of the tubular damage, independent risk factor of progressive tubular-interstitial fibrosis and strong predictor of the end-stage renal insufficiency. Evident proteinuria is symptomatic for estab‐ lished renal damage significantly connected with decreased GFR (Abbate et al., 2006; Eddy, 2004; Tryggvason & Pettersson, 2003; Zoja et al., 2003; Ofstad & Iversen, 2005). Even minimal proteinuria lasting one year after renal transplantation is an indicator of a poor renal graft function and may be a risk factor for renal graft failure (Kang et al., 2009). Urinary protein is a non-invasive and easy to perform parameter. It was reported that proteinuria (<0.5 g/24 h) occurred in half of patients within 3 month after renal transplantation (Sancho Calabuig et al., 2009). Higher than standard doses of everolimus (EVL) resulted in an increase of proteinuria. Therefore the standard doses of EVL are recommended which seems to be suitable for protecting against an acute graft rejection with better prognosis of renal function in longer perspective (Loriga et al., 2010). As chronic allograft nephropathy (CAN) is the most frequent reason for late loss of graft, immunosuppression with mycophenolate mofetil significantly improves graft function and in such circumstances evaluation of proteinuria seems to have

**Albuminuria** as a marker of glomerular filtration is more sensitive than proteinuria. Urinary albumin border value of 200 μg/min differentiates patients with albuminuria and proteinuria. Increase in urinary albumin excretion above 200 μg/min (macroalbuminuria) indicates damage to glomerular filtration membrane, a start of evident proteinuria, progression of kidney disease and cardiovascular changes (Ruggenenti & Remuzzi,2006). After exceeding maximal reab‐ sorption capacity of proximal tubular cells, protein of primary urine appeared in final urine (Luke, 1999; Remuzzi et al., 2006; Zoja et al., 2003). Excessive accumulation, in proximal tubular cells, plasma proteins excreted to primary urine, induced increase in local expression of cytokines and chemokines, which presence in final urine is a specific indicator of development and extent of renal damage (Lisowska-Myjak, 2010; Alachkar et al., 2010). Renal tubular cells exposed to increased amounts of filtered plasma proteins resulting cell injury. Microalbumi‐ nuria predicts a loss of renal graft. Determination of urinary albumin and UACR-urine albumin-to-creatinine ratios (UACR) are particularly recommended indicators for detection of changes in transplanted kidney (Erman et al., 2011). Microalbuminuria is considered to be a better indicator of kidney transplant condition than proteinuria (Bandukwala et al., 2009). Albuminuria, the marker of renal glomeruli damage and chronic damage of transplanted kidney, which may also reflect interstitial inflammatory process, is considered a predictor of

long-term allograft outcomes in a kidney graft recipient (Nauta et al., 2011).

detection at a concentration of 0.05-10.47 mg/L.

64 Current Issues and Future Direction in Kidney Transplantation

prognostic value (Grebe et al., 2004).

**α1-microglobulin (α1M)**is **a** 27 kDa glycoprotein related to retinol binding protein synthesized by liver cells, engaged in immunoregulation (binds lymphocytes T and B) and heme catabo‐ lism. Determination of α1M (stable in acid urine) is a sensitive indicator of renal proximal tubules damage (Guder, 2008; Lisowska-Myjak, 2010; Câmara et al., 2009). (Teppo et al., 2004) reported that six month after transplantation, 32% of patients presented microalbumi‐ nuria. Evaluation of a damage to renal proximal tubules, on the basis of an increase in urinary α1M concentration may be a consequence to a deterioration of glomerular filtration. Increase in α1M /creatinine ratio is an early and sensitive indicator of a poor function of the transplanted kidney, and indicates a poor prognosis of long term survival of renal transplanted patients (Teppo et al., 2004).

**Retinol binding protein (RBP)**, protein of the lipocalin family, synthesized mainly in a liver, supplies retinol to peripheral tissues. RBP removed from plasma by glomerular filtration is subsequently absorbed and catabolized in renal proximal tubules. Increased urinary RBP is caused by a disorder in glomerular filtration and reabsorption in renal proximal tubules (Guder, 2008; Kuźniar et al., 2006; Uchida & Gotoh, 2002; Câmara et al., 2009). It seems that urinary RBP is a better biomarker of proximal tubules damage than β2M, as RBP has greater stability in acid urine than β2M and renal insufficiency is only a clinical situation where an increase in urinary RBP concentration is observed.

**Adenosine deaminase binding protein (ABP)** is a glycoprotein (120-kDa) present in lungs, liver, placenta and brush border of renal proximal tubules. Increased expression in the urinary ABP is considered an early indicator of acute renal injury (AKI). Increase in urinary ABP was reported in patients with ischemia - without sepsis, after kidney transplantation, after toxic renal tubules damage, and in newborn with sepsis. Recently published opinion suggested that ABP to be the best marker of acute renal damage, better than β2-M or α1-M (Bagshaw, 2007). As ABP excretion was higher among kidney transplants recipients than in people with normal renal function, ABP is considered as a good indicator for detection of renal graft failure (Iglesias & Richard, 1994).

**Kidney injury molecule-1 (KIM-1)** is a transmembrane glycoprotein receptor (104 kDa) appearing as KIM-1a and KIM 1b. KIM-1 is produced in large quantities in renal proximal tubules after a toxic or ischemic damage. It is assumed that direct cause of KIM-1 induction is an increase of the protein concentration in glomerular ultrafiltration and presence of urinary protein casts favoring tubular obstruction, mechanical stress and an increase in glomerular pressure. An increase in urinary KIM-1 excretion is specific to the ischemic renal damage and is practically independent of chronic renal insufficiency or renal tract infection (Nickolas et al., 2008; Melnikov & Molitoris, 2008). It was reported that KIM-1 extracellular domain (fragment 90 kDa) reaches urine after cleavage by metalloproteinase (Han et al., 2002; Waanders et al., 2010). Urinary KIM-1 is particularly important in the diagnosis of the acute transplanted kidney insufficiency(AKI) (Halawa, 2011). As in renal graft recipients, contrary to urinary NGAL or IL-18, KIM determination gives better possibility for predicting a rate of the trans‐ planted kidney deterioration (Szeto et al., 2010), KIM-1 was proposed as an independent

Utility of Urinary Biomarkers in Kidney Transplant Function Assessment

http://dx.doi.org/10.5772/54746

67

**Urokinase-type plasminogen activator (uPA)** and its specific receptor (uPAR) regulate renal allograft function. Allogenic renal graft uPAR deficiency, strongly attenuates ischemia reperfusion injury and acute kidney allograft rejection. Deficiency of uPAR in renal graft diminished generation of reactive oxygen species and renal cells apoptosis (Gueler et al., 2008). Therefore serum and urinary uPA may be treated as an early marker of the acute kidney

**Matrix metalloproteinases (MMPs)** are extracellular proteases which depend on bound Ca2+ and Zn2+ for activity. Urinary panel of metalloproteinases was proposed for the early diagnosis of renal allograft rejection (Metzger et al., 2011; Sánchez-Escuredo et al., 2010; Hu et al., 2010).

**Tissue inhibitors of metalloproteinases (TIMP)** are extracellular inhibitors protease-specific, which bind tightly to the activated protease, blocking its activity. Presently 2% to 4% of renal allografts are rejected one year after from transplantation, because of chronic allograft injury. Mazanowska et al. (Mazanowska et al., 2011) suggest that determination of TIMP in urine may

**6. Immunological mediators of inflammatory state and fibrosis of renal**

**Urinary chemokines CXCL9 and CXCL10** may be treated as noninvasive screening markers of renal graft rejection in patients with interstitial fibrosis and tubular atrophy (IF/TA), leading to shorter life span of renal graft (Jackson et al., 2011; Schaub et al., 2009). Urinary CXCL10 may be a useful noninvasive screening test for tubulitis in renal graft recipients, and urinary

predictor of the long term renal graft survival (Ting et al., 2012).

**5. Proteins degrading extracellular matrix (ECM)**

confirm the process of an active rejection of the transplanted kidney.

transplant rejection (Alachkar, 2012).

**tissue**

**β2-microglobulin (β2M)** is a membrane protein of major histocompatibility complex HLA. β2M excretion is used for evaluation of nephrotoxic renal damage (aminoglycoside antibiotics, heavy metal salts) (Guder, 2008). It should be noted that determination β2M for evaluation function of transplanted kidney may be ambiguous because of coexistence of many factors influencing its plasma and urinary concentration (e.g. toxic drugs action, ischemia reperfusion complications or renal graft rejection). Measurement of urinary β2M may be helpful in evaluation of the condition of transplanted kidney, however the interpretation of result should be careful because of the plurality of factors influencing β2M plasma concentration, renal filtration ability and tubular function (Kuźniar et al., 2006).
