Exercise-induced proteinuria in children and adolescents

Effect of Metabolic Adaptation by Voluntary Running Wheel Activity and Aldosterone Inhibition on Renal Function in Female Spontaneously Hypertensive Rats

Metabolic effects of physical activity may be reno-protective in the context of hypertension, although exercise stresses kidneys. Aldosterone participates in renal disease in hypertension, but exercise affects the plasma concentration of aldosterone. This study was designed to evaluate whether physical activity and pharmacological treatment by aldosterone have additive effects on renal protection in hypertensive rats. Female spontaneously hypertensive rats (SHR) or normotensive Wistar rats performed voluntary running wheel activity alone or in combination with aldosterone blockade (spironolactone). The following groups were studied: young and pre-hypertensive SHR (n = 5 sedentary; n = 10 running wheels, mean body weight 129 g), 10-month-old Wistar rats (n = 6 sedentary; n = 6 running wheels, mean body weight 263 g), 10-month-old SHRs (n = 18 sedentary, mean body weight 224 g; n = 6 running wheels, mean body weight 272 g; n = 6 aldosterone, mean body weight 219 g; n = 6 aldosterone and running wheels, mean body weight 265 g). Another group of SHRs had free access to running wheels for 6 months and kept sedentary for the last 3 months (n = 6, mean body weight 240 g). Aldosterone was given for the last 4 months. SHRs from the running groups had free access to running wheels beginning at the age of 6 weeks. Renal function was analyzed by microalbuminuria (Alb/Cre), urinary secretion of kidney injury molecule-1 (uKim-1), and plasma blood urea nitrogen (BUN) concentration. Molecular adaptation of the kidney to hypertension and its modification by spironolactone and/or exercise were analyzed by real-time PCR, immunoblots, and histology. After six months of hypertension, rats had increased Alb/Cre and BUN but normal uKim-1. Voluntary free running activity normalized BUN but not Alb/Cre, whereas spironolactone reduced Alb/Cre but not BUN. Exercise constitutively increased renal expression of proprotein convertase subtilisin/kexin type 9 (PCSK9; mRNA and protein) and arginase-2 (mRNA). Spironolactone reduced these effects. uKim-1 increased in rats performing voluntary running wheel activity exercise irrespectively of blood pressure and aldosterone blockade. We observed independent but no additive effects of aldosterone blockade and physical activity on renal function and on molecules potentially affecting renal lipid metabolism.

Exercise-induced albuminuria is associated with perivascular renal sinus fat in individuals at increased risk of type 2 diabetes

AIMS/HYPOTHESIS

Microalbuminuria represents an established surrogate marker of early diabetic nephropathy and glomerular microangiopathy. Increasing evidence is emerging of a role of perivascular adipose tissue (PVAT) as an important link between obesity, insulin resistance and both macro- and microangiopathy. It is not known whether perivascular renal sinus fat (RSF) has an impact on microalbuminuria in the prediabetic stage. We investigated whether RSF quantified by MRI is associated with microalbuminuria before or after exercise.

METHODS

Non-diabetic individuals at increased risk of type 2 diabetes were recruited into the Tübingen Lifestyle Intervention Program (TULIP); 146 participants took part in the analysis. RSF was measured in axial MRI sections at the level of the renal artery. Urine was collected before and after exercise stress testing.

RESULTS

Participants (age 47 ± 12 years; mean ± SD) reached a mean exercise load of 176 ± 49 W, with a mean arterial peak pressure (MAPP) of 112 ± 14 mmHg. After adjusting for sex, age, visceral adipose tissue (VAT) and MAPP during exercise, RSF was significantly associated with postexercise albumin/creatinine ratio (ACR; p = 0.006). No association between RSF and baseline BP could be observed after adjusting for confounders (p = 0.26), and there was no association between RSF and baseline ACR either (p = 0.2).

CONCLUSIONS

RSF is associated with exercise-induced albuminuria independently of sex, age, VAT and MAPP in a non-diabetic cohort at diabetic risk. We conclude that PVAT in the renal sinus may play a role in the pathogenesis of microalbuminuria.

Current issues in measurement and reporting of urinary albumin excretion

BACKGROUND

Urinary excretion of albumin indicates kidney damage and is recognized as a risk factor for progression of kidney disease and cardiovascular disease. The role of urinary albumin measurements has focused attention on the clinical need for accurate and clearly reported results. The National Kidney Disease Education Program and the IFCC convened a conference to assess the current state of preanalytical, analytical, and postanalytical issues affecting urine albumin measurements and to identify areas needing improvement.

CONTENT

The chemistry of albumin in urine is incompletely understood. Current guidelines recommend the use of the albumin/creatinine ratio (ACR) as a surrogate for the error-prone collection of timed urine samples. Although ACR results are affected by patient preparation and time of day of sample collection, neither is standardized. Considerable intermethod differences have been reported for both albumin and creatinine measurement, but trueness is unknown because there are no reference measurement procedures for albumin and no reference materials for either analyte in urine. The recommended reference intervals for the ACR do not take into account the large intergroup differences in creatinine excretion (e.g., related to differences in age, sex, and ethnicity) nor the continuous increase in risk related to albumin excretion.

DISCUSSION

Clinical needs have been identified for standardization of (a) urine collection methods, (b) urine albumin and creatinine measurements based on a complete reference system, (c) reporting of test results, and (d) reference intervals for the ACR.

Renal alterations during exercise

Proteinuria and hematuria are common during exercise. Proteinuria is usually due to glomerular or tubular changes or to an excessive production of protein as in myeloma. Certain clinical conditions can, however, result in a functional or temporary proteinuria, especially during pregnancy, fever, orthostasis, or following physical activity. Sport-related proteinuria following marching, exercise, and stress, was first observed in soldiers after long marching. Prevalence of proteinuria during exercise ranges from 18% up to 100% depending on type of exercise and its intensity. A higher incidence of proteinuria has been observed in some sports requiring great exercise intensity and it is certainly related to muscular work intensity and would decrease after prolonged training. Indeed, exercise-induced proteinuria is strictly related to exercise intensity rather than to exercise duration. Exercise aggravates the proteinuria of various nephropathies and that of renal transplant recipients. The prevalence of hematuria is higher in the athletic than the general population and the main difference is that sport-related hematuria resolves spontaneously after physical exercise while hematuria found in nonathletic population can be chronic. Sport-induced hematuria is influenced by exercise duration and intensity. Among the mechanisms underlying the exercise induced hematuria are increased body temperature, hemolysis, increased production of free radicals, and excessive release of catecholamines. Lactic acidosis, generated during anaerobic conditions, causes the passage of erythrocytes into the urine, through increased glomerular permeability.

Proteinuria in South Asian children: prevalence and determinants

Proteinuria in children is a marker of kidney disease and atherosclerosis, both which are known predictors of cardiovascular mortality. Recent evidence suggests that migrant South Asian populations living in the West may be at higher risk of kidney disease than native Caucasians. However, the determinants of proteinuria in South Asian children have not been explored. Previously, we reported ethnic variation in the prevalence of proteinuria in the adult population of Pakistan. However, it is not known whether ethnic predisposition to proteinuria appears during childhood or whether it is acquired later in life as a result of prolonged exposure to undiagnosed diabetes and hypertension. Analyses were based on a subset of data for 4977 children aged 5 to less than 15 years collected as part of the broad National Health Survey of Pakistan, conducted between 1990 and 1994. Proteinuria was defined as a dipstick positive for protein on a random urine sample. Ethnicity was reported as "mother-tongue", which is specific for each of the five major ethnic subgroups of Pakistan: Muhajir, Punjabi, Sindhi, Pashtun, and Baluchi. The overall prevalence (95% CI) of proteinuria in the children was 3.3% (2.7-3.9%). It was 6.2% in Sindhis, 3.6% in Muhajirs, 2.8% in Punjabis, 2.8% in Baluchis, and 1.0% in Pashtuns (p<0.001). In multivariable analyses, proteinuria was associated with greater height (p=0.007), urban dwelling (p=0.03), lower socioeconomic status (p=0.02), and certain ethnicities (p=0.005). The ethnic variation in proteinuria in South Asian children mirrors variation among ethnic groups in adults. This suggests variations in susceptibility or early exposure to causes of chronic kidney disease, rather than long-term exposure to undiagnosed diabetes or hypertension. Further studies are needed to determine factors in early life that may differentially predispose certain ethnic groups to proteinuria.

Protein excretion after prolonged exercise

Random urine samples were obtained from 16 healthy subjects (nine men and seven women) before and after a 100 Km hill walk for the estimation of total protein, albumin, N-acetyl-beta-glucosaminidase (NAG), retinol binding protein (RBP) and creatinine. The excretion of total protein, albumin and NAG (expressed in relation to creatinine excretion) increased significantly after the walk. The relative clearance of protein and albumin also increased. In four subjects serial measurements were made for 4 days and the excretion of albumin and NAG on the fourth day were similar to the pre-walk values. We conclude that proteinuria of prolonged exercise is at least partly due to reduced tubular reabsorption.

Increased urinary transferrin excretion in exercising normoalbuminuric insulin-dependent diabetic patients

The median rate of urinary transferrin excretion is greatly increased by exercise in subjects with uncomplicated type 1 (insulin-dependent) diabetes. This increase is proportionally far greater than that seen in urinary albumin excretion rate after the same exercise. Non-diabetic control subjects showed no rise in urinary transferrin excretion rate following exercise. N-acetyl-beta-D-glucosaminidase excretion rate was higher in diabetic than control groups but did not rise with exercise. Our results suggest that patients with apparently uncomplicated diabetes have abnormal renal function. In this group an elevated urinary transferrin excretion rate appears to be a more sensitive indicator of altered renal function than is elevated albumin excretion rate. The mechanism underlying exercise-induced urinary loss of transferrin remains to be elucidated.

Effects of exercise on glomerular passage of macromolecules in patients with diabetic nephropathy and in healthy subjects

The effects of exercise on glomerular permeability were investigated in 12 proteinuric insulin-dependent diabetic patients and in 12 healthy controls by measuring the fractional protein and dextran clearances at rest and after exercise. Exercise significantly reduced the glomerular filtration rate (GFR) and the renal plasma flow (RPF) and markedly increased the filtration fraction (FF) in both diabetics and controls. The fractional clearances of albumin and IgG increased significantly during exercise in diabetics. Exercise also significantly increased the fractional clearance of albumin in healthy controls. The changes in the fractional protein clearances correlated significantly with the changes in the FF. In diabetics the fractional dextran clearances of molecules with a radius greater than or equal to 4.8 nm were significantly elevated after exercise. This was not found in healthy controls. It is concluded that exercise increases glomerular permeability by influencing the renal haemodynamics. Probably partial depletion of negative charges on the glomerular capillary wall plays a role in exercise-induced proteinuria in both healthy and diabetic subjects. In addition, the altered glomerular permeability during exercise is associated with increased size of the filtering pores in diabetic nephropathy.

Assessment of urinary protein excretion in the adolescent: effect of body position and exercise

We examined the effects of body position and exercise on the random urinary protein/creatinine ratio (Up/Ucr) in healthy adolescents, to provide reference data to be used in a simplified evaluation of proteinuria. Random urine samples were obtained during recumbency and after both ambulation and exercise in 116 subjects. The Up/Ucr was significantly (P less than 0.0001) higher with increasing levels of activity, and was widely variable, especially during the upright and postexercise periods. No sex-related differences in Up/Ucr were noted, except during recumbency, when values were significantly (P less than 0.001) higher in females. The urinary dipstick was found to be less sensitive as a tool to define abnormal degrees of recumbent proteinuria. We conclude that body position and exercise have significant effects on protein excretion, and suggest that the Up/Ucr in recumbent and upright urine samples will be useful in the evaluation of proteinuria.