Evaluation of podocin in urine in horses using qualitative and quantitative methods

Abstract

No sensitive method for diagnosing early kidney dysfunction in horses has been identified so far. Many studies carried out in humans and small animals show that podocin can be useful to diagnose various kidney diseases, mainly affecting the glomeruli. The aim of this study was to perform a qualitative and quantitative analysis of podocin in urine samples obtained from healthy horses, horses with clinical kidney dysfunction and horses at risk of acute kidney injury. The study objectives aimed to assess: (1) whether the selected podocin tryptic peptide for LC-MS-MRM allows for podocin detection in horse; and (2) whether the species-specific ELISA test makes this detection possible as well;, (3) whether the chosen methods are sensitive enough to detect kidney dysfunction and glomerular injury, (4) whether the results of the tests applying both methods correspond with one another, (5) whether the results correlate with the hematological and biochemical data. The signals that may indicate the presence of trypsin fragments of podocin were found in three healthy horses, all the horses diagnosed with kidney dysfunction and half of the animals at risk for acute kidney injury. The concentration of podocin, diagnosed with the ELISA test was as follows: from 0.19 to 1.2 ng/ml in healthy animals, from 0.19 to 20.0 ng/ml in AKI horses, from 0.29 to 5.71 ng/ml in horses at risk for acute kidney injury. The results of both methods corresponded significantly. Podocin may be a potential biomarker of clinical kidney disease in horses and may be used in the detection of glomerular injury. However, its use is limited by the possibility of physiological podocyturia. LC-MS-MRM seems to be a more sensitive method to evaluate the presence of podocin than the ELISA test, whilst selected tryptic peptides of podocin appear to apply to horses. The ELISA test showed greater effectiveness in excluding the disease than in confirming it.

Measurement of Selected Renal Biochemical Parameters in Healthy Adult Donkeys Considering the Influence of Gender, Age and Blood Freezing

“…The mean value of SDMA in healthy donkeys corresponded to the results obtained in horses [12][13][14]. None of the donkeys in our study had SDMA levels above the upper reference limit established for horses and small animals [5].…”

“…In the available literature, there are no studies estimating the values of FENa and FEK in donkeys, while large discrepancies can be found in individual equine studies [11,12,25]. Nevertheless, the reference values for horses were set at <1% for FENa and 24-75% for FEK [5].…”

“…Apart from the classical parameters, biomarkers that enable the earlier detection of kidney dysfunction, such as symmetric dimethylarginine (SDMA), enzyme gammaglutamyl transferase (GGTP)-to-creatinine ratio and fractional electrolyte excretion (FE), are also assessed in horses [2,[7][8][9][10][11][12]. SDMA is a biomarker of kidney dysfunction routinely used in human and small animal medicine.…”

Detecting acute kidney injury in horses by measuring the concentration of symmetric dimethylarginine in serum

“…The results of the basic blood assays have been published previously [30]. Table 1 shows the selected serum and urine parameters in different groups of animals alongside the number of animals with abnormal findings.…”

“…Samples collected for as part of another study were used. A detailed description of study groups and additional results have been previously published [30].…”