Kidney function during exercise in healthy and diseased humans. An update

Critical Velocity, Maximal Lactate Steady State, and Muscle MCT1 and MCT4 after Exhaustive Running in Mice

Although the critical velocity (CV) protocol has been used to determine the aerobic capacity in rodents, there is a lack of studies that compare CV with maximal lactate steady state intensity (iMLSS) in mice. As a consequence, their physiological and molecular responses after exercise until exhaustion at CV intensity remain unclear. Thus, we aimed to compare and correlate CV with iMLSS in running mice, following different mathematical models for CV estimation. We also evaluated their physiological responses and muscle MCT1 and MCT4 after running until exhaustion at CV. Thirty C57BL/6J mice were divided into two groups (exercised-E and control-C). Group E was submitted to a CV protocol (4 days), using linear (lin1 and lin2) and hyperbolic (hyp) mathematical models to determine the distance, velocity, and time to exhaustion (tlim) of each predictive CV trial, followed by an MLSS protocol. After a running effort until exhaustion at CV intensity, the mice were immediately euthanized, while group C was euthanized at rest. No differences were observed between iMLSS (21.1 ± 1.1 m.min-1) and CV estimated by lin1 (21.0 ± 0.9 m.min-1, p = 0.415), lin2 (21.3 ± 0.9 m.min-1, p = 0.209), and hyp (20.6 ± 0.9 m.min-1, p = 0.914). According to the results, CV was significantly correlated with iMLSS. After running until exhaustion at CV (tlim = 28.4 ± 8,29 min), group E showed lower concentrations of hepatic and gluteal glycogen than group C, but no difference in the content of MCT1 (p = 0.933) and MCT4 (p = 0.123) in soleus muscle. Significant correlations were not found between MCT1 and MCT4 and tlim at CV intensity. Our results reinforce that CV is a valid and non-invasive protocol to estimate the maximal aerobic capacity in mice and that the content of MCT1 and MCT4 was not decisive in determining the tlim at CV, at least when measured immediately after the running effort.

Calcium carbide-ripened plantain induced alterations in plasma electrolytes concentration and kidney function in rats

INTRODUCTION

Artificial fruit ripening agents such as ethanol, ethylene, ethephon, and calcium carbide (CaC2) is usually employed in stimulating the fruit ripening process. Currently, there is a paucity of information regarding the effects of various artificial fruits ripening methods on the health status of consumers. In this study, the physiological effects and possible health hazards associated with the consumption of plantain ripened by CaC2 and other non-chemical methods on the kidneys were investigated.

METHODS

Artificially ripened plantain was mixed with rat feed and fed to Wistar albino rats for four weeks, and the levels of plasma electrolytes (Na+, HCO3-, K+, and Cl-), urea, creatinine, as well as histological changes in the kidneys were determined.

RESULTS

Results indicated that rats fed with carbide-ripened plantain had a significantly high level of plasma bicarbonate (HCO3-) compared to control rats., but there was no difference in the level of plasma sodium (Na+). However, the levels of plasma potassium (K+) and chloride (Cl-) were significantly low in rats fed with CaC2-ripened plantain as compared to the control rats. Furthermore, the levels of urea and creatinine were significantly high in rats fed with CaC2-ripened plantain compared to the control animals. Histological analyses showed glomeruli atrophy and tubular necrosis in kidneys of rats fed with CaC2-ripened plantain, thereby further indicating toxicity to the kidneys.

CONCLUSIONS

Histological evidence and alterations in the level of the plasma electrolytes, urea, and creatinine suggest that consumption of fruits ripened with calcium carbide may be harmful to the kidneys.

Renal physiology and kidney injury during intense (CrossFit®) exercise

BACKGROUND

High-intensity training (HIT) programmes are popularly associated with improvements in exercise efficiency and body composition, although, at extremes, have been accompanied by concerns of secondary rhabdomyolysis and severe acute kidney injury (AKI). Beyond the anecdotal, robust literature on the physiological impact of HIT on renal function is currently limited.

AIMS

To investigate the acute impact of high-intensity (CrossFit®) training on renal function, and to evaluate the incidence of AKI by Risk, Injury, Failure, Loss, End-stage renal disease (RIFLE) criteria following CrossFit® training.

METHODS

Clinical and biochemical parameters were measured in 22 healthy adults before and after two CrossFit® workouts: 'Fran' (12 men, 10 women) and 'Macho Man' (9 men, 4 women).

RESULTS

Serum creatinine increased by 16 ± 10 μmol/L following Fran and 18 ± 12 μmol/L following Macho Man (P < 0.05). Cystatin C did not change significantly following Fran and increased by 0.06 ± 0.06 mg/L (P < 0.05) following Macho Man. AKI, as defined by RIFLE 'Risk' criteria, was observed in 5/22 (23%) participants following Fran and 5/13 (38%) participants following Macho Man. Urinary albumin/creatinine ratio rose by 18.7 ± 18.3 and 5.2 ± 6.0 mg/mmol following Fran and Macho Man respectively off non-albuminuric baselines (P < 0.05).

CONCLUSIONS

Intense (CrossFit®) exercise is associated with significant metabolic demands and alterations in parameters of renal physiology and function. The observed rise in both conventional and novel biomarkers of renal function following the workout Macho Man specifically might indicate a degree of transient subclinical functional impairment with CrossFit®-type training.

Is It Time for a Requiem for Creatine Supplementation-Induced Kidney Failure? A Narrative Review

Creatine has become one of the most popular dietary supplements among a wide range of healthy and clinical populations. However, its potential adverse effects on kidney health are still a matter of concern. This is a narrative review of the effects of creatine supplementation on kidney function. Despite a few case reports and animal studies suggesting that creatine may impair kidney function, clinical trials with controlled designs do not support this claim. Creatine supplementation may increase serum creatinine (Crn) concentration for some individuals, but it does not necessarily indicate kidney dysfunction, as creatine is spontaneously converted into Crn. Based on studies assessing kidney function using reliable methods, creatine supplements have been shown to be safe for human consumption. Further studies with people who have pre-existing kidney disease remain necessary.

Acute effects of moderate vs. vigorous endurance exercise on urinary metabolites in healthy, young, physically active men-A multi-platform metabolomics approach

Introduction: Endurance exercise alters whole-body as well as skeletal muscle metabolism and physiology, leading to improvements in performance and health. However, biological mechanisms underlying the body's adaptations to different endurance exercise protocols are not entirely understood. Methods: We applied a multi-platform metabolomics approach to identify urinary metabolites and associated metabolic pathways that distinguish the acute metabolic response to two endurance exercise interventions at distinct intensities. In our randomized crossover study, 16 healthy, young, and physically active men performed 30 min of continuous moderate exercise (CME) and continuous vigorous exercise (CVE). Urine was collected during three post-exercise sampling phases (U01/U02/U03: until 45/105/195 min post-exercise), providing detailed temporal information on the response of the urinary metabolome to CME and CVE. Also, fasting spot urine samples were collected pre-exercise (U00) and on the following day (U04). While untargeted two-dimensional gas chromatography-mass spectrometry (GC×GC-MS) led to the detection of 608 spectral features, 44 metabolites were identified and quantified by targeted nuclear magnetic resonance (NMR) spectroscopy or liquid chromatography-mass spectrometry (LC-MS). Results: 104 urinary metabolites showed at least one significant difference for selected comparisons of sampling time points within or between exercise trials as well as a relevant median fold change >1.5 or <0. 6 ¯ (NMR, LC-MS) or >2.0 or <0.5 (GC×GC-MS), being classified as either exercise-responsive or intensity-dependent. Our findings indicate that CVE induced more profound alterations in the urinary metabolome than CME, especially at U01, returning to baseline within 24 h after U00. Most differences between exercise trials are likely to reflect higher energy requirements during CVE, as demonstrated by greater shifts in metabolites related to glycolysis (e.g., lactate, pyruvate), tricarboxylic acid cycle (e.g., cis-aconitate, malate), purine nucleotide breakdown (e.g., hypoxanthine), and amino acid mobilization (e.g., alanine) or degradation (e.g., 4-hydroxyphenylacetate). Discussion: To conclude, this study provided first evidence of specific urinary metabolites as potential metabolic markers of endurance exercise intensity. Future studies are needed to validate our results and to examine whether acute metabolite changes in urine might also be partly reflective of mechanisms underlying the health- or performance-enhancing effects of endurance exercise, particularly if performed at high intensities.

Alterações induzidas por plátano maturado com carbureto de cálcio na concentração plasmática de eletrólitos e na função renal em ratos

Resumo Introdução: Agentes de maturação artificial como etanol, etileno, etefon e carbureto de cálcio (CaC2) são comumente empregados para estimular o amadurecimento de frutas. Atualmente, há uma escassez de informações a respeito dos efeitos de diversos métodos artificiais de maturação de frutas no estado de saúde dos consumidores. Neste estudo, investigaram-se os efeitos fisiológicos e possíveis riscos à saúde associados ao consumo de plátano maturado por CaC2 e outros métodos não químicos nos rins. Métodos: O plátano artificialmente amadurecido foi misturado com ração de rato e fornecido a ratos albinos Wistar por quatro semanas, e determinaram-se os níveis de eletrólitos plasmáticos (Na+, HCO3−, K+, e Cl−), ureia, creatinina, bem como alterações histológicas nos rins. Resultados: Ratos alimentados com plátano amadurecido com carbureto apresentaram um nível significativamente maior de bicarbonato plasmático (HCO3−) em comparação com ratos controle, mas não houve diferença no nível plasmático de sódio (Na+). Entretanto, os níveis plasmáticos de potássio (K+) e cloreto (Cl−) foram significativamente baixos em ratos alimentados com plátano maturado com CaC2 comparados com ratos controle. Além disso, os níveis de ureia e creatinina foram significativamente mais elevados em ratos alimentados com plátano amadurecido com CaC2, em comparação com os animais controle. Análises histológicas mostraram atrofia glomerular e necrose tubular em rins de ratos alimentados com plátano amadurecido com CaC2, indicando assim ainda mais toxicidade aos rins. Conclusões: Evidências histológicas e alterações nos eletrólitos plasmáticos, ureia e creatinina sugerem que o consumo de frutas amadurecidas com carbureto de cálcio pode ser prejudicial aos rins.

The effects of exercise on kidney injury: the role of SIRT1

In patients with kidney injury, muscle mass and strength decrease with altered muscle protein synthesis and degradation along with complications such as inflammation and low physical activity. A treatment strategy to maintain muscle metabolism in kidney injury is important. One of the proposed strategies in this regard is exercise, which in addition to inducing muscle hypertrophy, reducing plasma creatinine and urea and decreasing the severity of tubal injuries, can boost immune function and has anti-inflammatory effects. One of the molecules that have been considered as a target in the treatment of many diseases is silent information regulator 1 (SIRT1). Exercise increases the expression of SIRT1 and improves its activity. Therefore, studies that examined the effect of exercise on kidney injury considering the role of SIRT1 in this effect were reviewed to determine the direction of kidney injury research in future regarding to its prevalence, especially following diabetes, and lack of definitive treatment. In this review, we found that SIRT1 can be one of renoprotective target pathways of exercise. However, further studies are needed to determine the role of SIRT1 in different kidney injuries following exercise according to the type and severity of exercise, and the type of kidney injury.

Effect of Multiple-Nutrient Supplement on Muscle Damage, Liver, and Kidney Function After Exercising Under Heat: Based on a Pilot Study and a Randomised Controlled Trial

Objective: This study explored the effect of multiple-nutrient supplementation on muscle damage and liver and kidney function after vigorous exercise under heat.

Methods: After an initial pilot trial comprising 89 male participants, 85 participants were recruited and assigned into three groups: a multiple-nutrient (M) group, a glucose (G) group, and a water (W) group. Multiple-nutrient supplements contain glucose, fructose, maltose, sodium, potassium, vitamin B₁, vitamin B₂, vitamin C, vitamin K, and taurine. Participants were organised to take a 3-km running test (wet-bulb globe temperature 32°C) after a short-term (7 days) supplement. Blood samples were obtained to detect biochemical parameters [glucose (GLU), aspartate aminotransferase (AST), alanine aminotransferase (ALT), blood urea nitrogen (BUN), uric acid (UA), creatinine (Cr), creatine kinase (CK), lactate dehydrogenase (LDH), and lactic acid], inflammation factors [interleukin-6 (IL-6) and tumour necrosis factor-α (TNF-α)], and oxidative stress biomarkers [superoxide dismutase (SOD) and 8-iso-prostaglandin F (2alpha) (8-iso-PGF2α)].

Results: In the pilot trial, BUN decreased significantly in the M and G groups immediately after the running test. AST, Cr, and UA were significantly reduced 24 h after the running test with single-shot multiple-nutrient supplementation. In the short-term trial, multiple nutrients further prevented the elevation of CK (p = 0.045) and LDH (p = 0.033) levels 24 h after strenuous exercise. Moreover, we found that multiple nutrients significantly reduced IL-6 (p = 0.001) and TNF-α (p = 0.015) elevation immediately after exercise. Simultaneously, SOD elevation was significantly higher in the M group immediately after exercising than in the other two groups (p = 0.033). 8-iso-PGF2α was reduced in the M group 24 h after exercise (p = 0.036).

Conclusions: This study found that multiple-nutrient supplementation promoted the recovery of muscle damage and decreased liver and kidney function caused by strenuous exercise in a hot environment, probably through the inhibition of secondary damage induced by increased inflammatory reactions and oxidative stress. In this respect, the current study has important implications for the strategy of nutritional support to accelerate recovery and potentially prevent heat-related illness. This study was prospectively registered on clinicaltrials.gov on June 21, 2019 (ID: ChiCTR1900023988).

Proteinuria in a high-altitude 161-km (100-mile) ultramarathon

PURPOSE

Urine dipstick analysis (UDA) is a useful tool in clinical practices. Abnormalities in UDA parameters have been observed as a result of extreme exercise. The exact incidence of UDA abnormalities, particularly proteinuria, as the result of running ultramarathons is unknown. The purpose of this study was to estimate the incidence of proteinuria and to identify the characteristics of those with proteinuria.

METHODS

We conducted a prospective observational study using urine samples from volunteer athletes before and immediately after the Leadville Trail 100 Run in August 2014. There were 33 runners with both pre-race and post-race samples and a total of 70 provided post-race samples. Demographic information was collected as a part of a larger study.

RESULTS

At least one abnormality was demonstrated in 89% of post-race urine samples. Twenty-one (30%) runners had post-race proteinuria (≥1+). Serum creatine kinase concentration (CK) was the only variable that was significantly correlated with the incidence of proteinuria in a multiple logistic regression model.

CONCLUSION

A majority of runners developed abnormalities in their UDA. Proteinuria was common and found to be associated with serum CK concentration.

Changes in Urinary Biomarkers of Organ Damage, Inflammation, Oxidative Stress, and Bone Turnover Following a 3000-m Time Trial

Strenuous exercise induces organ damage, inflammation, and oxidative stress. Currently, to monitor or investigate physiological conditions, blood biomarkers are frequently used. However, blood sampling is perceived to be an invasive method and may induce stress. Therefore, it is necessary to establish a non-invasive assessment method that reflects physiological conditions. In the present study, we aimed to search for useful biomarkers of organ damage, inflammation, oxidative stress, and bone turnover in urine following exercise. Ten male runners participated in this study and performed a 3000-m time trial. We measured biomarkers in urine collected before and immediately after exercise. Renal damage markers such as urea protein, albumin, N-acetyl-β-D-glucosaminidase (NAG), and liver-fatty acid binding protein (L-FABP), and an intestinal damage marker, intestine-fatty acid binding protein (I-FABP), increased following exercise (p < 0.05). However, a muscle damage marker, titin N-terminal fragments, did not change (p > 0.05). Inflammation-related factors (IRFs), such as interleukin (IL)-1β, IL-1 receptor antagonist (IL-1ra), IL-6, complement (C) 5a, myeloperoxidase (MPO), calprotectin, monocyte chemoattractant protein (MCP)-1, and macrophage colony-stimulating factor (M-CSF), increased whereas IRFs such as IL-4 and IL-10 decreased following exercise (p < 0.05). IRFs such as tumor necrosis factor (TNF)-α, IL-2, IL-8, IL-12p40, and interferon (IFN)-γ did not change (p > 0.05). Oxidative stress markers, such as thiobarbituric acid reactive substances (TBARS) and nitrotyrosine, did not change following exercise (p > 0.05) whereas 8-hydroxy-2'-deoxyguanosine (8-OHdG) decreased (p < 0.05). Bone resorption markers, such as cross-linked N-telopeptide of type I collagen (NTX) and deoxypyridinoline (DPD), did not change following exercise (p > 0.05). These results suggest that organ damage markers and IRFs in urine have the potential to act as non-invasive indicators to evaluate the effects of exercise on organ functions.

Exercise as a therapeutic option for acute kidney injury: mechanisms and considerations for the design of future clinical studies

Acute kidney injury (AKI) is a known risk factor for chronic kidney disease (CKD) and end stage kidney disease (ESKD). The progression from AKI to CKD, despite being well recognised, is not completely understood, although sustained inflammation and fibrosis are implicated. A therapeutic intervention targeting the post AKI stage could reduce the progression to CKD, which has high levels of associated morbidity and mortality. Exercise has known anti-inflammatory effects with animal AKI models demonstrating its use as a therapeutic agent in abrogating renal injury. This suggests the use of an exercise rehabilitation programme in AKI patients following discharge could attenuate renal damage and improve long term patient outcomes. In this review article we outline considerations for future clinical studies of exercise in the AKI population.

Kidney physiology and pathophysiology during heat stress and the modification by exercise, dehydration, heat acclimation and aging

The kidneys' integrative responses to heat stress aid thermoregulation, cardiovascular control, and water and electrolyte regulation. Recent evidence suggests the kidneys are at increased risk of pathological events during heat stress, namely acute kidney injury (AKI), and that this risk is compounded by dehydration and exercise. This heat stress related AKI is believed to contribute to the epidemic of chronic kidney disease (CKD) occurring in occupational settings. It is estimated that AKI and CKD affect upwards of 45 million individuals in the global workforce. Water and electrolyte disturbances and AKI, both of which are representative of kidney-related pathology, are the two leading causes of hospitalizations during heat waves in older adults. Structural and physiological alterations in aging kidneys likely contribute to this increased risk. With this background, this comprehensive narrative review will provide the first aggregation of research into the integrative physiological response of the kidneys to heat stress. While the focus of this review is on the human kidneys, we will utilize both human and animal data to describe these responses to passive and exercise heat stress, and how they are altered with heat acclimation. Additionally, we will discuss recent studies that indicate an increased risk of AKI due to exercise in the heat. Lastly, we will introduce the emerging public health crisis of older adults during extreme heat events and how the aging kidneys may be more susceptible to injury during heat stress.

Effects of resistance training on kidney morphology of aged ovariectomized rats

With the advancing age, there is an increase of the incidence of chronic renal diseases. However, it is suggested that exercise, as resistance training, is a key factor in positively modulate the kidney structure and function. Thus, this study aimed to analyze the effects of estrogen deprivation and a moderate resistance protocol on the right kidney structure of rats. A total of 32 animals were randomly divided in four groups (n = 8/per group): control group (CG); resistance trained animals (RT); control ovariectomized animals (OvxC); and trained ovariectomized animals (OvxT). Sections of the right kidney were stained with hematoxylin and eosin for morphometry and blood was collected for biochemical analysis. Our results showed that the group submitted to both ovariectomy and resistance training had significant impact on renal corpuscle components (Bowman's space, renal corpuscle area, and visceral layer), and proximal and distal tubules. Additionally, resistance training, with or without estrogen deprivation, increases creatine phosphokinase and decreases ultrasensitive C-reactive protein. In summary, we suggested that moderate resistance training may be a key factor to maintain the kidney structure and function across age. However, future studies are need to corroborate with our findings.

A circulating exosomal microRNA panel as a novel biomarker for monitoring post-transplant renal graft function

Accurate and effective biomarkers for continuous monitoring of graft function are needed after kidney transplantation. The aim of this study was to establish a circulating exosomal miRNA panel as non‐invasive biomarker for kidney transplant recipients. Plasma exosomes of 58 kidney transplant recipients and 27 healthy controls were extracted by gel exclusion chromatography and characterized by transmission electron microscopy, nanoparticle tracking analysis and Western blotting. Post‐transplant renal graft function was evaluated by estimated glomerular filtration rate (eGFR). Quantitative real‐time polymerase chain reaction was used to determine the expression of exosomal microRNAs (miRNAs). Exosomal miR‐21, miR‐210 and miR‐4639 showed negative correlations with eGFR in the training set and were selected for further analysis. In the validation set, miR‐21, miR‐210 and miR‐4639 showed the capability to discriminate between subjects with chronic allograft dysfunction (eGFR < 60 mL/min/1.73 m²) and those with normal graft function (eGFR > 90 mL/min/1.73 m²). Three‐miRNA panel exhibited higher accuracy compared with individual miRNAs or double indicators. One‐year follow‐up revealed a stable recovery of allograft function in subjects with low calculated score from three‐miRNA panel (below the optimal cut‐off value). In conclusion, a unique circulating exosomal miRNA panel was identified as an effective biomarker for monitoring post‐transplant renal graft function in this study.

Both hyperthermia and dehydration during physical work in the heat contribute to the risk of acute kidney injury

Occupational heat stress increases the risk of acute kidney injury (AKI) and kidney disease. This study tested the hypothesis that attenuating the magnitude of hyperthermia (i.e., increase in core temperature) and/or dehydration during prolonged physical work in the heat attenuates increases in AKI biomarkers. Thirteen healthy adults (3 women, 23 ± 2 yr) exercised for 2 h in a 39.7 ± 0.6°C, 32 ± 3% relative-humidity environmental chamber. In four trials, subjects received water to remain euhydrated (Water), continuous upper-body cooling (Cooling), a combination of both (Water + Cooling), or no intervention (Control). The magnitude of hyperthermia (increased core temperature of 1.9 ± 0.3°C; P < 0.01) and dehydration (percent loss of body mass of -2.4 ± 0.5%; P < 0.01) were greatest in the Control group. There were greater increases in the urinary biomarkers of AKI in the Control trial: albumin (increase of 13 ± 11 μg/mL; P ≤ 0.05 compared with other trials), neutrophil gelatinase-associated lipocalin (NGAL) (increase of 16 ± 14 ng/dL, P ≤ 0.05 compared with Cooling and Water + Cooling groups), and insulin-like growth factor-binding protein 7 (IGFBP7) (increase of 227 ± 190 ng/mL; P ≤ 0.05 compared with other trials). Increases in IGFBP7 in the Control trial persisted after correcting for urine production/concentration. There were no differences in the AKI biomarker tissue inhibitor of metalloproteinase 2 (TIMP-2) between trials (P ≥ 0.11). Our findings indicate that the risk of AKI is highest with greater magnitudes of hyperthermia and dehydration during physical work in the heat. Additionally, the differential findings between IGFBP7 (preferentially secreted in proximal tubules) and TIMP-2 (distal tubules) suggest the proximal tubules as the location of potential renal injury.NEW & NOTEWORTHY We demonstrate that the risk for acute kidney injury (AKI) is higher in humans with greater magnitudes of hyperthermia and dehydration during physical work in the heat and that alleviating the hyperthermia and/or limiting dehydration equally reduce the risk of AKI. The biomarker panel employed in this study suggests the proximal tubules as the location of potential renal injury.

Identification of Urinary Biomarkers for Exercise-Induced Immunosuppression by iTRAQ Proteomics

Purpose

To identify noninvasive immune biomarkers of exercise-induced immunosuppression using the iTRAQ proteomics technique.

Methods

Fifteen healthy males were recruited and subjected to a four-week incremental treadmill running training program. After each week of training, WBC counts and CD4⁺ and CD8⁺ lymphocytes were measured to monitor the immune function status. iTRAQ proteomics technology was used to identify differential proteins and their characteristics in urine.

Results

Our data showed that the WBC counts, CD4⁺ lymphocytes, and CD4⁺/CD8⁺ ratio decreased by more than 10% after four weeks of training, suggesting exercise-induced immunosuppression. A total of 1854 proteins were identified in urine during the incremental running using the iTRAQ technology. Compared with the urine before training, there were 89, 52, 77, and 148 proteins significantly upregulated and 66, 27, 68, and 114 proteins significantly downregulated after each week, respectively. Among them, four upregulated proteins, SEMG-1, PIP, PDGFRL, and NDPK, increased their abundance with the increased exercise intensity. Bioinformatics analysis indicates that these proteins are involved in stress response and immune function.

Conclusion

Four weeks of incremental treadmill running induced immunosuppression in healthy males. By using iTRAQ proteomics, four proteins in the urine, SEMG-1, PIP, PDGFRL, and NDPK, were found to increase incrementally with the increased exercise intensity, which have the potential to be used as noninvasive immune biomarkers of exercise-induced immunosuppression.

Reliability and agreement of human renal and segmental artery hemodynamics measured using Doppler ultrasound

To optimize study design and data interpretation, there is a need to understand the reliability of Doppler ultrasound-derived measures of blood velocity (BV) measured in the renal and segmental arteries. Thus, this study tested the following two hypotheses: 1) renal and segmental artery BV measured over the current standard of three cardiac cycles have good agreement with measurements over nine cardiac cycles (study 1); and 2) renal and segmental artery BV measurements have relatively poor day-to-day reliability (study 2). In study 1, there was excellent agreement between measurements over three and nine cardiac cycles for BV in both the renal and segmental arteries, as evidenced by BV measurements that were not statistically different (P ≥ 0.68), were highly consistent (r ≥ 0.99, P < 0.01), had a coefficient of variation ≤2.5 ± 1.8%, and 97% (renal artery) and 92% (segmental artery) of the individual differences fell within the 95% limits of agreement. In study 2, there was relatively good day-to-day reliability in renal artery BV as evidenced by no differences between three separate days (P ≥ 0.30), an intraclass correlation coefficient (ICC) of 0.92 (0.78, 0.98), and 7.4 ± 5.5% coefficient of variation. The day-to-day reliability was relatively poor in the segmental artery with an ICC of 0.77 (0.41, 0.93) and 9.0 ± 5.6% coefficient of variation. These findings support measuring renal and segmental artery hemodynamics over three cardiac cycles and the utility in reporting renal BV across days. However, because of the variation across days, hemodynamic responses in the segmental arteries should be reported as changes from baseline when making comparisons across multiple days.NEW & NOTEWORTHY The present study indicates that Doppler ultrasound-derived measures of renal and segmental artery hemodynamics over three cardiac cycles have excellent agreement with those over nine cardiac cycles. These findings support the current practice of measuring renal and segmental artery blood velocity over three cardiac cycles. This study also demonstrates that there is excellent day-to-day reliability for measures of renal artery blood velocity, which supports reporting absolute values of renal artery blood velocity across days. However, it was also found that the day-to-day reliability of segmental artery measurements is relatively poor. Thus, to account for this variability, we suggest that segmental artery hemodynamics be compared as relative changes from baseline across separate days.

Mild dehydration following voluntary water intake reduction does not affect anaerobic power performance

BACKGROUND

Dehydration is common among athletes. The negative impact of dehydration on aerobic performance is well characterized. However, little is known about the effect of dehydration on anaerobic performance particularly when dehydration results from insufficient water intake, not water loss due to body temperature regulation. The purpose of this study was to examine the effect of dehydration on anaerobic performance following voluntary water intake reduction.

METHODS

Fifteen healthy adults completed two exercise sessions, euhydrated (EUD) and dehydrated (DEH). Sessions consisted of baseline anthropometric and blood lactate measurement followed by a 30-second Wingate test and three vertical jump trials to measure anaerobic performance. Additional blood lactate measurements were taken immediately and at 5, 10, and 15 minutes after taking the Wingate test.

RESULTS

The dehydration protocol resulted in a reduction in body mass (EUD 69.1±17.2 kg, DEH 68.1±16.6 kg, P=0.039). The 30-s Wingate peak power (EUD 971±302 W, DEH 960±316 W, P=0.578) was not different between conditions, nor was the vertical jump height (EUH 26.4±4.5 cm, DEH 26.6±3.6 cm, P=0.778). Blood lactate (P<0.001) was elevated immediately following the 30-s Wingate test which remained throughout the trial. There were no differences in blood lactate between conditions.

CONCLUSIONS

Acute anaerobic power and exercise performance is not negatively affected by voluntary dehydration.

Factors influencing post-exercise proteinuria after marathon and ultramarathon races

Post-exercise proteinuria is one of the most common findings observed after short and intensive physical activity, but is observed also after long runs with low intensity. The aim of this study was to analyze factors influencing proteinuria after marathon runs. Two groups of male amateur runners were studied. The results of 20 marathon finishers (42.195 m), with a mean age of 49.3 ± 6.85 years; and 17 finishers of a 100-km ultramarathon with a mean age of 40.18±4.57 years were studied. Urine albumin to creatinine ratio (ACR) was calculated before and after both races. The relationship between ACR and run pace, metabolites (lactate, beta hydroxybutyrate), markers of inflammation (CRP, IL-6) and insulin was studied. The significant increase in ACR was observed after both marathon races. ACR increased from 6.41 to 21.96 mg/g after the marathon and from 5.37 to 49.64 mg/g after the ultramarathon (p<0.05). The increase in ACR was higher after the ultramarathon that after the marathon. There was no correlation between run pace and proteinuria. There was no correlation between ACR and glucose, free fatty acids, lactate, beta-hydroxybutyrate and insulin levels. There was significant negative correlation between ACR and interleukin 6 (IL-6) (r =-0.59, p< 0.05) after ultramarathon. Proteinuria is a common finding after physical exercise. After very long exercises it is related to duration but not to intensity. There is no association between metabolic and hormonal changes and ACR after marathon runs. The role on inflammatory cytokines in albuminuria is unclear.

Antioxidant Effect of Virgin Coconut Oil on Urea and Creatinine Levels on Maximum Physical Activity

BACKGROUND:

Maximal physical activity can produce an imbalance between reactive oxygen species (ROS) and antioxidants which are possibly related to fatigue and tissue injury. One of the natural sources that contain antioxidants is virgin coconut oil (VCO).

AIM:

This study aimed to determine the protective effects antioxidant of virgin coconut oil (VCO) treatment on urea and creatine level on maximum physical activity

METHODS:

This study used 24 healthy male rats. The rats were divided into four groups, randomly consisted of six rats in each group. The control group (P0) was given 2 mL water, the treatment groups (VCO-1, VCO-2, and VCO-4) were given VCO 1 mL/200 gBW, 2 mL/200 gBW and 4 ml/200 gBW, respectively, per day using gavage spuit. After 28 days, the rats were forced to perform maximal activity by putting the rats in water with no exit. Blood samples were collected immediately after the maximum physical activity. The urea, creatinine, malondialdehyde and glutation peroxidase level was then measured.

RESULTS:

This study used 24 healthy male rats. The rats were divided into four groups randomly consisted of six rats in each group. The control group (P0) was given 2 mL water, the treatment groups (VCO-1, VCO-2, and VCO-4) were given VCO 1 mL/200 gBW, 2 mL/200 gBW and 4 ml/200 gBW, respectively, per day using gavage spuit. After 28 days, the rats were forced to perform the maximal activity by putting the rats in water with no exit. Blood samples were collected immediately after the maximum physical activity. The urea, creatinine, malondialdehyde and glutathione peroxidase level was then measured.

CONCLUSION:

The results of this study indicate that virgin coconut oil is effective in the prevention of oxidative stress following maximum physical activity.

Urinary Alpha-1-Acid Glycoprotein Is a Sensitive Marker of Glomerular Protein Leakage at Altitude

Talks, Ben J., Susie B. Bradwell, John Delamere, Will Rayner, Alex Clarke, Chris T. Lewis, Owen D. Thomas, and Arthur R. Bradwell. Urinary alpha-1-acid glycoprotein is a sensitive marker of glomerular protein leakage at altitude. High Alt Med Biol. 19:295-298, 2018.-Proteinuria is an established feature of ascent to altitude and may be caused by a loss of negative charges on glomerular capillary walls (GCWs). To test this hypothesis, we measured two similar sized but oppositely charged proteins in urine: negatively charged alpha-1-acid glycoprotein (α1-AGP, 41-43 kDa) and positively charged dimeric lambda free light chains (λ-FLCs, 50 kDa). Twenty-four-hour urinary leakage was compared with albumin, a 66 kDa negatively charged protein. We studied 23 individuals (ages 23-78 years, male = 17) at baseline (140 m) and daily during an expedition to 5035 m. The results showed a significant increase in median urinary leakage of α1-AGP (p < 0.0001; 6.85-fold) and albumin (p = 0.0006; 1.65-fold) with ascent to altitude, but no significant increase in leakage of λ-FLCs (p = 0.39; 1.14-fold). α1-AGP correlated with the daily ascent profile (p = 0.0026) and partial pressure of oxygen (p = 0.01), whereas albumin showed no correlation (p = 0.19). Urinary α1-AGP was a more sensitive marker of altitude proteinuria than urinary albumin and λ-FLCs, and supported the possibility of loss of GCW negative charges at altitude.

Impact of acute versus prolonged exercise and dehydration on kidney function and injury

Exercise and dehydration may be associated with a compromised kidney function and potential signs of kidney injury. However, the kidney responses to exercise of different durations and hypohydration levels are not yet known. Therefore, we aimed to compare the effects of acute versus prolonged exercise and dehydration on estimated glomerular filtration rate (eGFR) and kidney injury biomarkers in healthy male adults. A total of 35 subjects (23 ± 3 years) were included and invited for two study visits. Visit 1 consisted of a maximal cycling test. On Visit 2, subjects performed a submaximal exercise test at 80% of maximal heart rate until 3% hypohydration. Blood and urine samples were taken at baseline, after 30 min of exercise (acute effects; low level of hypohydration) and after 150 min of exercise or when 3% hypohydration was achieved (prolonged effects, high level of hypohydration). Urinary outcome parameters were corrected for urinary cystatin C, creatinine, and osmolality. Subjects dehydrated on average 0.6 ± 0.3% and 2.9 ± 0.7% after acute and prolonged exercise, respectively (P < 0.001). The eGFRcystatin C did not differ between baseline and acute exercise (118 ± 11 vs. 116 ± 12 mL/min/1.73 m2 , P = 0.12), whereas eGFRcystatin C was significantly lower after prolonged exercise (103 ± 16 mL/min/1.73 m2 , P < 0.001). We found no difference in osmolality corrected uKIM1 concentrations after acute and prolonged exercise (P > 0.05), and elevated osmolality corrected uNGAL concentrations after acute and prolonged exercise (all P-values < 0.05). In conclusion, acute exercise did barely impact on eGFRcystatin C and kidney injury biomarkers, whereas prolonged exercise is associated with a decline in eGFRcystatin C and increased biomarkers for kidney injury.

The Renin-Angiotensin System, Not the Kinin-Kallikrein System, Affects Post-Exercise Proteinuria

BACKGROUND/AIMS

Temporary proteinuria post-exercise is common and is caused predominantly by renal haemodynamic alterations. One reason is up-regulation of angiotensin II (Ang II) due to the reducing effect of angiotensin-converting enzyme (ACE) inhibitors. However, another, ignored, reason could be the kininase effect of ACE inhibition. This study investigated how ACE inhibition reduces post-exercise proteinuria: by either Ang II up-regulation inhibition or bradykinin elevation due to kininase activity inhibition.

METHODS

Our study included 10 volunteers, who completed 3 high-intensity exercise protocols involving cycling at 1-week intervals. The first protocol was a control arm, the second evaluated the effect of ACE inhibition and the third examined the effect of angiotensin type 1 receptor blockade. Upon application, both agents reduced systolic and diastolic blood pressure; however, there were no statistically significant -differences. In addition, total protein, microalbumin and -β2-microglobulin excretion levels in urine specimens were analysed before, 30 min after and 120 min after the exercise protocols.

RESULTS

Total protein levels in urine samples were elevated in all 3 protocols after 30 min of high-intensity exercise, compared to baseline levels. However, both ACE inhibition and angiotensin type 1 receptor blockade suppressed total protein in the 30th min. In each protocol, total protein levels returned to the baseline after 120 min. Urinary microalbumin and β2-microglobulin levels during the control protocol were significantly higher 30 min post-exercise; however, only angiotensin type 1 receptor blockade suppressed microalbumin levels.

CONCLUSION

The results indicated Ang II up-regulation, not bradykinin elevation, plays a role in post-exercise proteinuria.

Urine specific gravity as an indicator of dehydration in Olympic combat sport athletes; considerations for research and practice

Urine specific gravity (U_SG) is the most commonly reported biochemical marker used in research and applied settings to detect fluid deficits in athletes, including those participating in combat sports. Despite the popularity of its use, there has been a growing debate regarding the diagnostic accuracy and the applicability of U_SG in characterizing whole-body fluid status and fluctuations. Moreover, recent investigations report universally high prevalence of hypohydration (∼90%) via U_SG assessment in combat sport athletes, often in spite of stable body-mass. Given the widespread use in both research and practice, and its use in a regulatory sense as a 'hydration test' in combat sports as a means to detect dehydration at the time of weigh-in; understanding the limitations and applicability of U_SG assessment is of paramount importance. Inconsistencies in findings of U_SG readings, possibly as a consequence of diverse methodological research approaches and/or overlooked confounding factors, preclude a conclusive position stand within current combat sports research and practice. Thus the primary aim of this paper is to critically review the literature regarding U_SG assessment of hydration status in combat sports research and practice. When taken on balance, the existing literature suggests: the use of laboratory derived benchmarks in applied settings, inconsistent sampling methodologies, the incomplete picture of how various confounding factors affect end-point readings, and the still poorly understood potential of renal adaptation to dehydration in combat athletes; make the utility of hydration assessment via U_SG measurement quite problematic, particularly when diet and training is not controlled.

Reliability of Urinary Dehydration Markers in Elite Youth Boxers

PURPOSE

To determine the reliability and diagnostic accuracy of noninvasive urinary dehydration markers in field-based settings on a day-to-day basis in elite adolescent amateur boxers.

METHODS

Sixty-nine urine samples were collected daily from 23 athletes (17.3 ± 1.9 y) during their weight-stable phase and analyzed by field and laboratory measures of hydration status. Urine osmolality (U_OSM), urine specific gravity (U_SG), total protein content (T_PC), and body-mass stability were evaluated to determine fluid balance and hydration status. Overall macronutrient and water intake were determined using dietary records. According to their anthropometric characteristics, athletes were assigned into 2 groups: lightweight (L_WB) and heavyweight (H_WB) boxers.

RESULTS

Data presented on U_OSM demonstrated a uniform increment by 11.2% ± 12.8% (L_WB) and 19.9% ± 22.7% (H_WB) (P < .001) over the course of the study, even during the weight-stable phase (body mass, ICC = .99) and ad libitum fluid intake (42 ± 4 mL · kg^-1 · d^-1). The intraclass correlation coefficients (ICCs) ranged from .52 to .55 for U_SG and .38 to .52 for U_OSM, further indicating inconsistency of the urinary dehydration markers. Poor correlations were found between U_SG and T_PC metabolites (r = .27, P = .211).

CONCLUSIONS

Urinary dehydration markers (both U_SG and U_OSM) exhibit high variability and seem to be unreliable diagnostic tools to track actual body-weight loss in real-life settings. The ad libitum fluid intake was apparently inadequate to match acute fluid loss during and after intense preparation. The applicability of a single-time-point hydration-status assessment concept may preclude accurate assessment of actual body-weight deficits in youth boxers.

Firefighter Work Duration Influences the Extent of Acute Kidney Injury

PURPOSE

We tested the hypothesis that elevations in biomarkers of acute kidney injury are influenced by the magnitude of hyperthermia and dehydration elicited by two common firefighter work durations.

METHODS

Twenty-nine healthy adults (10 females) wearing firefighter protective clothing completed two randomized trials where they walked at 4.8 km·h, 5% grade in a 38°C, 50% RH environment. In the short trial, subjects completed two 20-min exercise bouts. In the long trial (LONG), subjects completed three 20-min exercise bouts. Each exercise bout was separated by 10 min of standing rest in an ~20°C environment. Venous blood samples were obtained before and immediately after exercise, and after 1 h recovery. Dependent variables included changes in core temperature, body weight, plasma volume, serum creatinine, and plasma neutrophil gelatinase-associated lipocalin, a marker of renal tubule injury.

RESULTS

Changes in core temperature (+2.0°C ± 0.7°C vs +1.1°C ± 0.4°C, P < 0.01), body weight (-0.9% ± 0.6% vs -0.5% ± 0.5%, P < 0.01), and plasma volume (-11% ± 5% vs -8% ± 6%, P < 0.01) during exercise were greater in LONG. Increases in creatinine were higher in LONG postexercise (0.18 ± 0.15 vs 0.08 ± 0.07 mg·dL, P < 0.01) and after recovery (0.21 ± 0.16 vs 0.14 ± 0.10 mg·dL, P < 0.01). Increases in neutrophil gelatinase-associated lipocalin were greater in LONG postexercise (27.0 ± 20.5 vs 12.7 ± 18.0 ng·mL, P = 0.01) and after recovery (16.9 ± 15.6 vs 1.5 ± 15.1 ng·mL, P = 0.02).

CONCLUSIONS

Biomarkers of acute kidney injury are influenced by the magnitude of hyperthermia and hypovolemia elicited by exercise in the heat.

Acute exercise does not impair renal function in nondialysis chronic kidney disease patients regardless of disease stage

Exercise has been overlooked as a potential therapy in chronic kidney disease (CKD), mainly because of a lack of understanding on its safety aspects. Notably, there are no data on renal function after exercise in CKD considering its stages. We investigated the acute effects of a 30-min moderate-intensity aerobic exercise bout on glomerular filtration rate (GFR) and albuminuria in 22 nondialysis CKD patients divided into: CKD stages 1 and 2 (CKD_1-2) and CKD stages 3 and 4 (CKD_3-4). Eleven body mass index-, age-, and sex-matched healthy individuals served as control (CON). Blood and urine samples were collected before, immediately after, and up to 90 min postexercise for creatinine and albumin assessments. GFR was determined by creatinine clearance (GFR_Cr-Cl). All CKD patients had significantly lower peak oxygen uptake than CON. CKD_1-2 and CKD_3-4 had increasingly higher serum creatinine than CON (9.6 ± 2.6, 25.6 ± 1.01, and 7.5 ± 1.4 mg/l, respectively); however, no within-group changes in serum or urinary creatinine were observed across time. GFR_Cr-Cl was decreased in CKD_1-2 and CKD_3-4 compared with CON (91 ± 17 ml·min^-1·1.73 m^-2; 34 ± 15 ml·min^-1·1.73 m^-2; 122 ± 20 ml·min^-1·1.73 m^-2, respectively). Most importantly, exercise did not affect GFR_Cr-Cl in none of the groups across time. Albuminuria was significantly higher in CKD_3-4 (297 ± 284 µg/min) than in CON (5.4 ± 1.4 µg/min), but no within-group changes were observed after exercise. In conclusion, a single 30-min moderate-intensity aerobic exercise bout does not impair renal function in nondialysis CKD patients, regardless of disease stage, supporting the notion that exercise training can be safe in this disease.

Acute kidney injury associated with endurance events-is it a cause for concern? A systematic review

INTRODUCTION

A growing body of evidence suggests even small rises in serum creatinine (SCr) are of considerable clinical relevance. Given that participants in endurance events are exposed to potential (repeated) renal insults, a systematic review was undertaken to collate current evidence for acute kidney injury (AKI), complicating such events.

METHODS

A systematic review of studies and case reports meeting inclusion criteria on Medline and EMBASE (inception to October 2015). Included: studies with markers of renal function before and after endurance or ultraendurance events; case reports of severe AKI. Two reviewers assessed risk of bias using the Newcastle-Ottawa scale.

RESULTS

Eleven case report publications (n=27 individuals) of severe AKI, were retrieved, with risk factors including systemic illness or nephrotoxic medications usually identified. From 30 studies of endurance and ultraendurance events, mean rise in SCr was 29 (±12.3) µmol/L after marathon or ultramarathon (17 studies, n=568 participants) events. Where follow-up tests were conducted, SCr returned to baseline within 48 hours. Rises in biomarkers suggest potential parenchymal insult, rather than simply muscle breakdown. However, evidence of long-term deleterious effects is lacking.

CONCLUSIONS

Raised levels of SCr are reported immediately after endurance events. It is not clear whether this is either clinically significant, or if repeated participation predisposes to long-term sequelae. The aetiology of severe exercise-associated AKI is usually multifactorial, with risk factors generally identified in the rare cases reported. On-site biochemistry, urine analysis and biomarkers of AKI may help identify collapsed runners who are at significant short-term risk and allow suitable follow-up.

Improved reliability of the urine lactate concentration under controlled hydration after maximal exercise

CONTEXT

Urine lactate may be a novel biomarker of lactate production capacity but its reliability has been unsatisfactory so far.

OBJECTIVE

To compare the reliability of urine lactate between controlled hydration and no hydration after maximal exercise.

MATERIAL AND METHODS

Athletes performed swimming exercise four times: two followed by consumption of 1 L of water and two followed by no water intake. Blood and urine lactate was measured.

RESULTS

The reliability of urine lactate was good and similar to that in blood only after controlled hydration. Blood and urine lactate were correlated under both hydration conditions.

DISCUSSION AND CONCLUSION

Controlled hydration after exercise provides satisfactory reliability of urine lactate.

Nitrate supplementation and human exercise performance: too much of a good thing?

PURPOSE OF REVIEW

Ergogenic supplements in sport events are widely used by popular and competitive athletes to enhance performance and reduce oxygen cost. Beetroot juice and nitrate salts have been increasingly used for the past 5-6 years. The present review discusses the scientific background, the efficiency and potential adverse effects of excessive nitrate supplementation.

RECENT FINDINGS

There is clear evidence that nitrate from different food ingredients (such as beetroot juice and other vegetables) is converted into nitrite and possibly into nitric oxide, which may promote vasodilation, angiogenesis and mitochondrial biogenesis. The high affinity of nitric oxide towards different enzyme pathways inhibits excessive mitochondrial respiration and, therefore, tissue oxygen consumption. In addition, L-arginine supplements are proposed to stimulate nitric oxide synthesis in the endothelium. On the basis of these biochemical properties, nitrate supplementation has been suggested to athletes to enhance exercise performance.

SUMMARY

The recent publications in human individuals based on L-arginine, beetroot juice or nitrate supplementation revealed either a minor positive effect or no systematic effect on exercise performance, especially in trained athletes. Of note, the sugar content of whole beetroot juice might induce a slightly more pronounced effect. Although reasonable intake of nitrate salts (up to 1 g/day) has no detrimental effect on kidney function, the risk and benefit of higher nitrate intake needs to be evaluated to define the optimal range of supplementation.

Knowledge among nephrologists about the importance of exercise in the intradialytic period

[Purpose] To assess knowledge among nephrologists at hemodialysis services about routine intradialytic therapeutic exercise, in the city of Recife. [Subjects and Methods] A cross-sectional study, consisting of 49 nephrologists working in public and/or private hemodialysis services, who responded to a semi-structured questionnaire about their academic background, medical residency, and knowledge about exercise during the intradialytic period. [Results] About 56.3% practiced for more than 10 years as nephrologists, 69.4% did not receive information about intradialytic physical exercise while in residency, 81.6% considered intradialytic exercise to be important, and 53.0% did not prescribe exercise during hemodialysis. About 61.2% consider the level of physical activity among their patients to be poor. Nephrologists graduating within 2 years were 10 times more likely to prescribe exercise, compared to those with more than 2 years since graduation. [Conclusion] Our study found that the nephrologists interviewed do not usually prescribe intradialytic therapeutic exercise, despite understanding its importance as part of the treatment process. It is necessary to update doctors about the importance of exercise for patients during the intradialytic period, as well as to incorporate this knowledge at the undergraduate level.

Effects of exercise on the urinary proteome

Exercise-induced proteinuria has been observed and studied for more than a century. It was found that different sport disciplines alter the urinary proteome in different ways. Moderate-intensity exercise results in increased glomerular filtration, meaning that medium-sized proteins are excreted in higher amounts, while high-intensity exercise of short duration also increases the excretion of low molecular weight proteins as a result of tubular dysfunction. Exhaustive exercise may lead to the excretion of hemoglobin or myoglobin, which changes the urinary proteome considerably. Studies comparing protein maps of different sport types compared to a control group showed that quality and quantity of urinary proteins are interindividually different. In addition, urine samples collected before and after exercise exhibit substantially different protein patterns even from the same person. Therefore, further studies investigating the urinary proteome are desirable. As the variation of protein content and composition in urine are generally much higher than in other matrices, respective studies need to be well controlled and homogenous groups of volunteers should be chosen. In addition to the sport-related physiological and biochemical interest, exercise-induced protein changes also need to be considered for biomarker measurements from urine samples for kidney or other diseases.

Physical activity - an important preanalytical variable

The concentration of several biochemical and hematological biomarkers is strongly influenced by a number of preanalytical variables. Several lines of evidence attest that short, middle, and long-term exercise, as well as the relative intensity of physical effort (from mild to strenuous), may influence a broad array of laboratory variables. The amount of extracellular release and clearance from blood of most of these biomarkers is markedly influenced by the biological characteristics of the molecule(s), level of training, type, intensity and duration of exercise, and time of recovery after training. It is hence noteworthy that test results that fall outside the conventional reference ranges in athletes not only may reflect the presence of a given disease, but may frequently mirror an adaptation to regular training or changes that have occurred during and/or following strenuous exercise, and which should be clearly acknowledged to prevent misinterpretation of laboratory data. The aim of this narrative review is to provide an update about the most significant changes of some biochemical and hematological biomarkers in response to physical exercise, for appropriate interpretation of these changes in the context of physically active subjects.

RBC deformability and amino acid concentrations after hypo-osmotic challenge may reflect chronic cell hydration status in healthy young men

Biomarkers of chronic cell hydration status are needed to determine whether chronic hyperosmotic stress increases chronic disease risk in population-representative samples. In vitro, cells adapt to chronic hyperosmotic stress by upregulating protein breakdown to counter the osmotic gradient with higher intracellular amino acid concentrations. If cells are subsequently exposed to hypo-osmotic conditions, the adaptation results in excess cell swelling and/or efflux of free amino acids. This study explored whether increased red blood cell (RBC) swelling and/or plasma or urine amino acid concentrations after hypo-osmotic challenge might be informative about relative chronic hyperosmotic stress in free-living men. Five healthy men (20-25 years) with baseline total water intake below 2 L/day participated in an 8-week clinical study: four 2-week periods in a U-shaped A-B-C-A design. Intake of drinking water was increased by +0.8 ± 0.3 L/day in period 2, and +1.5 ± 0.3 L/day in period 3, and returned to baseline intake (0.4 ± 0.2 L/day) in period 4. Each week, fasting blood and urine were collected after a 750 mL bolus of drinking water, following overnight water restriction. The periods of higher water intake were associated with significant decreases in RBC deformability (index of cell swelling), plasma histidine, urine arginine, and urine glutamic acid. After 4 weeks of higher water intake, four out of five participants had ½ maximal RBC deformability below 400 mmol/kg; plasma histidine below 100 μmol/L; and/or undetectable urine arginine and urine glutamic acid concentrations. Work is warranted to pursue RBC deformability and amino acid concentrations after hypo-osmotic challenge as possible biomarkers of chronic cell hydration.

Effects of voluntary wheel running on the kidney at baseline and after ischaemia-reperfusion-induced acute kidney injury: a strain difference comparison

Exercise-induced vascular endothelial adaptations in the kidney are not well understood. Therefore, we investigated the impact of voluntary wheel running (VWR) on the abundance of endothelial nitric oxide synthase (eNOS) and extracellular superoxide dismutase (EC SOD), in kidney and lung, and other SOD isoforms and total antioxidant capacity (TAC), in kidney. We also determined whether VWR influences susceptibility to acute kidney injury (AKI). Male Sprague-Dawley and Fisher 344 rats, VWR or sedentary for 12 weeks, were subjected to AKI (uninephrectomy (UNX) and 35 min of left kidney ischaemia-24 h reperfusion, IR). We measured glomerular filtration rate (GFR) and renal plasma flow (RPF), and analysed renal structural injury. Running was comparable between strains and VWR reduced body weight. In Sprague-Dawley rats, VWR reduced eNOS and EC SOD, but increased Mn SOD in kidney. Similar changes were seen after 6 weeks of VWR in Sprague-Dawley rats. In Fisher 344 rats, VWR increased eNOS, all SOD isoforms and TAC in kidney. Both strains increased eNOS and EC SOD in lung with VWR. Compared to UNX alone, UNX-IR injury markedly reduced renal function for both strains; however, in the Sprague-Dawley rats, VWR exacerbated falls in GFR and RPF due to UNX-IR, whereas in the Fisher 344 rats, GFR was unaffected by VWR. Some indices of renal structural injury due to UNX-IR tended to be worse in SD vs. F344. Our study demonstrates that genetic background influences the effect of exercise on kidney eNOS and EC SOD, which in turn influence the susceptibility to AKI.

A critical review of recommendations to increase dietary protein requirements in the habitually active

Some scientists and professional organisations have called for an increase in dietary protein for those who reach a threshold level of exercise, i.e. endurance athletes. But there are individual scientists who question this recommendation. Limitations in the procedures used to justify changing the recommended daily allowance (RDA) are at issue. N balance has been used to justify this increase; but it is limiting even when measured in a well-controlled clinical research centre. Experimental shortcomings are only exacerbated when performed in a sports or exercise field setting. Another laboratory method used to justify this increase, the isotope infusion procedure, has methodological problems as well. Stable isotope infusion data collected during and after exercise cannot account for fed-state gains that counterbalance those exercise losses over a 24 h dietary period. The present review concludes that an adaptive metabolic demand model may be needed to accurately study the protein health of the active individual.

Effect of exercise intensity on albuminuria in adolescents with Type 1 diabetes mellitus

AIMS

Exercise may be useful to detect patients with diabetes prone to develop persistent microalbuminuria. We studied the relationship between exercise intensity, measured as maximal oxygen consumption (VO(2)max), and microalbuminuria in patients with Type 1 diabetes mellitus patients.

METHODS

We studied 10 patients, age range 10-18 years, with Type 1 diabetes who were normotensive and normoalbuminuric, with less than 10 years since diagnosis. Patients had normal renal function, without infections or clinical evidence of complications. Metabolic control was intensively adjusted in all patients. They underwent three consecutive physical exercise tests, reaching 100, 80 and 60% of the maximal cardiac frequency response.

RESULTS

Eight patients had adequate to regular metabolic control. All patients had lower than predicted VO(2)max values. At 60%, only three patients showed microalbuminuria in excess of 20 μg/min, two of them had inadequate metabolic control. Post-exercise microalbuminuria exceeded normal values in nine, seven and three patients when submitted to 100, 80 and 60% of exercise intensity, respectively.

CONCLUSIONS

Microalbuminuria increased with exercise intensity. Sex, body composition and VO(2)max were the main factors associated with microalbuminuria. The prognostic significance of albuminuria induced by intense exercise in these subjects with Type 1 diabetes is not yet known.

Exercise-induced changes in renal URAT1 activity and expression in rats

During exercise, the plasma urate levels and urinary excretion increase due to the enhanced purine degradation in skeletal muscle. Although urate transporter-1 (URAT1) is the main transporter responsible for the reabsorption of filtered urate, potential changes in its activity and expression during exercise have not been studied yet. Therefore, the effect of heavy muscle activity on renal URAT1 activity and expression was investigated in this study. Wistar rats were used in the study and the experimental design consisted of three groups: a control group, an exercise group where animals were exhausted once a day for 5 days, and a hyperuricemia group, which was induced by an uricase inhibitor, oxonic acid. URAT1 activity measurements were performed in isolated proximal tubule segments and expression of URAT1 mRNA and protein levels were determined by the reverse transcription polymerase chain reaction and western blot analyses, respectively. Increased citrate synthase activity in soleus muscle of exercised animals proved the efficiency of our exercise protocol. Proteinuria, glucosuria, and hypoglycemia were observed only in exercised animals; however, plasma and urinary urate levels were found to be elevated in both exercising and hyperuricemia groups. Moreover, in both of the groups URAT1 transporter activity was found to be increased despite the significant decrease in URAT1 protein levels. Considering the similar changes of urate metabolism observed in both exercising and hyperuricemic rats, our results suggest that exercise-induced changes in URAT1 expression and activity depend on the increased urate concentration in plasma.

Physical exercise with weight reduction lowers blood pressure and improves abnormal left ventricular relaxation in pharmacologically treated hypertensive patients

In spite of appropriate pharmacologic therapy, many hypertensive patients develop an abnormal left ventricular relaxation with preserved systolic function. This cardiac dysfunction increases the risk of cardiovascular complications. The authors assessed the therapeutic effects of an intervention with exercise training and weight reduction in patients with pharmacologically well-treated hypertension who had abnormal left ventricular relaxation with normal systolic function. Eighty-eight (44%) of 202 medically treated hypertensive patients had abnormal ventricular relaxation with normal ejection fraction. These patients were randomized to either a 6-month intervention program (cycle ergometer training twice a day for 5 days a week and a hypocaloric diet) or a control program (unchanged pharmacologic therapy without exercise and diet. Body weight, blood pressure, New York Heart Association class, glomerular filtration rate, and exercise capacity and workload were measured. Cardiac function was assessed by measuring N-terminal pro-B-type natriuretic peptide values, the electrocardiographic QT dispersion interval, and echocardiography (left atrial size, Doppler-derived E/A ratio, and mitral deceleration time). Physical exercise with weight reduction reduced blood pressure, decreased cardiovascular risks, and improved abnormal left ventricular relaxation. Measuring left atrial size is the best method for assessing changes in left ventricular relaxation with preserved systolic function.

Regular moderate exercise reduces advanced glycation and ameliorates early diabetic nephropathy in obese Zucker rats

Advanced glycation end products (AGEs) play a key role in the pathogenesis of diabetes and its complications, including the diabetic nephropathy. The renoprotective effects of exercise are well known; however, the mechanisms remain elusive. Here we examined whether a regular moderate exercise in obese Zucker rats (OZR), a model of diabetes- and obesity-associated nephropathy, will affect the development of early renal injury in OZR possibly via alteration of AGEs formation. The OZR were left without exercise (sedentary) or subjected to 10 weeks intermittent treadmill running of moderate intensity. Compared with sedentary OZR, kidneys of running OZR had significantly less glomerular mesangial expansion and tubulointerstitial fibrosis. Running OZR had significantly lower plasma AGEs-associated fluorescence and N(epsilon)-carboxymethyllysine. Correspondingly, renal AGEs and N(epsilon)-carboxymethyllysine content were lower in running OZR. Systemically, exercise increased aerobic metabolism, as apparent from urinary metabolite profiling. No differences in plasma glucose, insulin, or lipid profile were found between the 2 groups. Apart from lower advanced oxidation protein products (a marker of myeloperoxidase activity), no other marker of inflammation was altered by exercise, either systemically or locally in kidneys. No indication of changed oxidative status was revealed between the groups. Exercise in OZR decreased advanced glycation. This might represent the early event of exercise-induced renoprotection in diabetic nephropathy in OZR. If confirmed in clinical studies, regular moderate exercise could represent an easy and effective nonpharmacologic approach to reduce advanced glycation.

Chronic kidney disease, exercise, and sports in children, adolescents, and adults

Individuals with chronic kidney disease have poor exercise tolerance and are easily fatigued compared with their healthy peers. The primary reasons for poor exercise tolerance include anemia, effects of chronic uremia and metabolic acidosis on the heart and skeletal muscles, and lower levels of physical activity. Studies suggest that regular and early implementation of both aerobic and resistance exercise programs in persons with chronic kidney disease have positive effects on muscle function, exercise tolerance, and quality of life. Before starting any exercise program, a medical assessment and exercise testing are generally recommended. No consensus exists regarding allowing young athletes with a solitary kidney who want to participate in contact or collision sports. Decisions to allow participation in different sports and leisure activities should be made on an individual basis, considering multiple factors. This article reviews factors that affect exercise tolerance in persons with chronic kidney disease, the effects of exercise, and exercise recommendations.

Potential sources of oxidative stress that induce postexercise proteinuria in rats

Exercise-induced proteinuria is a common consequence of physical activity and is caused predominantly by alterations in renal hemodynamics. Although it has been shown that exercise-induced oxidative stress can also contribute to the occurrence of postexercise proteinuria, the sources of reactive oxygen species that promote it are unknown. We investigated the enzymes nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and xanthine oxidase (XO) as possible sources of oxidative stress in postexercise proteinuria. First, we evaluated the effect of blocking the NADPH oxidase enzyme on postexercise proteinuria. We found a significant increase in urinary protein level, kidney thiobarbituric acid-reactive substances (TBARS), and protein carbonyl content after exhaustive exercise, and NADPH oxidase activity was induced by exercise. Rats that were treated with an NADPH oxidase inhibitor for 4 days before exhaustive exercise showed no increase in kidney TBARS or protein carbonyl derivative level and no proteinuria or NADPH oxidase activation. In the next set of experiments, we investigated the effect of XO blockage on postexercise proteinuria. Oxypurinol, an XO inhibitor was administered to rats for 3 days before exercise. Although XO inhibition significantly decreased kidney TBARS levels and protein carbonyl content in exercised rats, the inhibition did not prevent exercise-induced proteinuria. However, plasma and kidney XO activity was not induced by exercise, but rather it was suppressed under oxypurinol treatment. These results suggest that increased NADPH oxidase activity induced by exhaustive exercise is an important source of elevated oxidative, stress during exercise, which contributes to the occurrence of postexercise proteinuria.