More than 100 substances have been identified as biomarkers of acute kidney injury. These markers can help to diagnose acute kidney injury (AKI) in its early phase, when the creatinine level is not increased. The two markers most frequently studied in plasma and serum are cystatin C and neutrophil gelatinase-associated lipocalin (NGAL). The former is a marker of kidney function and the latter is a marker of kidney damage. Some other promising serum markers, such as osteopontin and netrin-1, have also been proposed and studied. The list of promising urinary markers is much longer and includes cystatin C, NGAL, kidney injury molecule-1 (KIM-1), liver-type fatty-acid-binding protein (L-FABP), interleukin 18, insulin-like growth factor binding protein 7 (IGFBP-7), tissue inhibitor of metalloproteinases-2 (TIMP-2) and many others. Although these markers are increased in urine for no longer than a few hours after nephrotoxic agent action, they are not widely used in clinical practice. Only combined IGFBP-7/TIMP-2 measurement was approved in some countries as a marker of AKI. Several studies have shown that the levels of urinary AKI biomarkers are increased after physical exercise. This systematic review focuses on studies concerning changes in new AKI biomarkers in healthy adults after single exercise. Twenty-seven papers were identified and analyzed in this review. The interpretation of results from different studies was difficult because of the variety of study groups, designs and methodology. The most convincing data concern cystatin C. There is evidence that cystatin C is a better indicator of glomerular filtration rate (GFR) in athletes after exercise than creatinine and also at rest in athletes with a lean mass lower or higher than average. Serum and plasma NGAL are increased after prolonged exercise, but the level also depends on inflammation and hypoxia; therefore, it seems that in physical exercise, it is too sensitive for AKI diagnosis. It may, however, help to diagnose subclinical kidney injury, e.g., in rhabdomyolysis. Urinary biomarkers are increased after many types of exercise. Increases in NGAL, KIM-1, cystatin-C, L-FABP and interleukin 18 are common, but the levels of most urinary AKI biomarkers decrease rapidly after exercise. The importance of this short-term increase in AKI biomarkers after exercise is doubtful. It is not clear if it is a sign of mild kidney injury or physiological metabolic adaptation to exercise.

Uremic toxins play a critical role in the manifestation of the uremic syndrome. This is a consequence of retention of such substances in chronic renal failure patients and interactions between them. To date >100 uremic compounds have been discovered. The aim of this study was to elucidate potential relationships between N-methyl-2-pyridone-5-carboxamide (Me2PY) and N-methyl-4-pyridone-5-carboxamide (Me4PY), two uremic compounds, and different parameters of oxidative stress. Forty-three non-dialyzed patients at the Nephrological Outpatients Clinic of Gdansk were enrolled and divided into two groups: (i) 20 patients with a mean estimated glomerular filtration rate (eGFR) of 22.7 ml/min/1.73 m(2); and (ii) 23 patients with a mean eGFR of 12.4 ml/min/1.73 m(2). In both groups, the plasma concentrations of uremic toxins (Me2PY, Me4PY, creatinine), malonyldialdehyde (MDA) and carbonyl groups and the erythrocyte concentration of glutathione (GSH) were analyzed. Correlations between uremic toxins and oxidative stress markers were calculated using Pearson's correlation. We observed significant correlations between serum creatinine and Me2PY (r=0.68; p=0.00001), eGFR and Me2PY (r=-0.55; p=0.00001), Me4PY and serum creatinine (r=0.64, p=0.00001), Me4PY and eGFR (r=-0.59; p=0.00008), MDA and Me2PY (r=0.42; p=0.006), MDA and Me4PY (r=0.38; p=0.02), GSH and Me2PY (r=-0.37; p=0.02) and GSH and Me4PY (r=-0.46; p=0.005), and in particular in patients with severe renal impairment. We conclude that there is a relationship between the novel uremic toxins described and oxidative stress markers. However, elucidation of the exact pathogenetic links requires further detailed studies.

Deficiencies in iron and vitamin D are frequently observed in athletes. Therefore, we examined whether different baseline vitamin D₃ levels have any impact on post-exercise serum hepcidin, IL-6 and iron responses in ultra-marathon runners. In this randomized control trial, the subjects (20 male, amateur runners, mean age 40.75 ± 7.15 years) were divided into two groups: experimental (VD) and control (CON). The VD group received vitamin D₃ (10,000 UI/day) and the CON group received a placebo for two weeks before the run. Venous blood samples were collected on three occasions—before the run, after the 100 km ultra-marathon and 12 h after the run—to measure iron metabolism indicators, hepcidin, and IL-6 concentration. After two weeks of supplementation, the intervention group demonstrated a higher level of serum 25(OH)D than the CON group (27.82 ± 5.8 ng/mL vs. 20.41 ± 4.67 ng/mL; p < 0.05). There were no differences between the groups before and after the run in the circulating hepcidin and IL-6 levels. The decrease in iron concentration immediately after the 100-km ultra-marathon was smaller in the VD group than CON (p < 0.05). These data show that various vitamin D₃ status can affect the post-exercise metabolism of serum iron.

Chronic renal failure is a disease of the elderly. The elderly are the fastest growing population among dialysis patients and also on waiting lists for kidney transplantation. The objective for this study was to analyze the results of the renal transplantation in recipients elder than 60 years. To minimize the donor variability and bias, a paired kidney analysis was used. The older renal transplantation (ORT) group included 44 patients (30 men, 14 women) aged 60 to 72 (mean 64+/-3) years. Their pairs created a younger renal transplantation (YRT) group consisting of 44 patients (30 men, 14 women) aged 14 to 59 (mean 40+/-12) years. Graft function estimated 1 year after transplantation applying abbreviated Modification of Diet in Renal Disease formula was significantly better in ORT (46.8+/-10.2 ml/min) versus YRT (43.7+/-16.8 ml/min). Studied groups (ORT vs. YRT) did not differ significantly with respect to 1-year patient survival (93.2% vs. 95.5%), 1-year graft survival (88.6% vs. 86.3%), 1-year death-censored graft survival (93% vs. 90.1%), and the incidences of delayed graft function and acute rejection. The most common complications noticed after ORT were cardiovascular complications, surgical complications, and infections. Our single-center results confirm that renal transplantation is a good option of renal replacement therapy in patients older than 60 years. Thorough recipient selection and preparation as well as customized immunosuppressive protocols are particularly important in that group of renal transplant recipients.

Acute kidney injury (AKI) is described as a relatively common complication of exercise. In clinical practice the diagnosis of AKI is based on serum creatinine, the level of which is dependent not only on glomerular filtration rate but also on muscle mass and injury. Therefore, the diagnosis of AKI is overestimated after physical exercise. The aim of this study was to determine changes in uremic toxins: creatinine, urea, uric acid, asymmetric dimethylarginine (ADMA), symmetric dimethylarginine (SDMA), trimethylamine N-oxide (TMAO) and urinary makers of AKI: albumin, neutrophil gelatinase-associated lipocalin (uNGAL), kidney injury molecule-1 and cystatin-C (uCyst-C) after long runs. Sixteen runners, mean age 36.7 ± 8.2 years, (2 women, 14 men) participating in 10- and 100-km races were studied. Blood and urine were taken before and after the races to assess markers of AKI. A statistically significant increase in creatinine, urea, uric acid, SDMA and all studied urinary AKI markers was observed. TMAO and ADMA levels did not change. The changes in studied markers seem to be a physiological reaction, because they were observed almost in every runner. The diagnosis of kidney failure after exercise is challenging. The most valuable novel markers which can help in post-exercise AKI diagnosis are uCyst-C and uNGAL.