Urinary excretion of total proteins, albumin, and beta 2-microglobulin during rest and exercise in diabetic adolescents with and without retinopathy

Personalized medicine in diabetic kidney disease: a novel approach to improve trial design and patient outcomes

PURPOSE OF REVIEW

In the last decade many attempts have been made to reduce the high residual risk of end-stage kidney disease and cardiovascular disease in patients with diabetic kidney disease by targeting a variety of risk markers. Subsequent analyses revealed that the variation in individual drug response to the tested interventions partly explains why these trials did not result in additional kidney or cardiovascular protection. This review summarizes recent insights regarding individual variation in drug response. Additionally, we explore novel approaches to incorporate this drug response variability in the design of new clinical trials.

RECENT FINDINGS

Recent studies suggest that a plausible explanation for individual therapy resistance emanates from intrinsic individual characteristics such as genetic make-up or volume status and is likely only partially explained by drug characteristics such as the dose or type of intervention. Biomarker-based enrichment strategies to identify high-risk individuals and/or those who are more likely to respond to interventions offer opportunities to tailor therapies to individual patients.

SUMMARY

Individual drug response variability is a recognized phenomenon in clinical practice. It is time to implement novel approaches that take into account this response variability in the design of new trials in diabetic kidney disease in order to define optimal therapies for individual patients.

Variability in response to albuminuria-lowering drugs: true or random?

AIMS

Albuminuria-lowering drugs have shown different effect size in different individuals. Since urine albumin levels are known to vary considerably from day-to-day, we questioned whether the between-individual variability in albuminuria response after therapy initiation reflects a random variability or a true response variation to treatment. In addition, we questioned whether the response variability is drug dependent.

METHODS

To determine whether the response to treatment is random or a true drug response, we correlated in six clinical trials the change in albuminuria during placebo or active treatment (on-treatment) with the change in albuminuria during wash-out (off-treatment). If these responses correlate during active treatment, it suggests that at least part of the response variability can be attributed to drug response variability. We tested this for enalapril, losartan, aliskiren, atrasentan and paricalcitol.

RESULTS

No correlation between the on- and off-treatment albuminuria change was observed in the placebo arm of all clinical trials (R²  < 0.01). However, we observed significant associations between the on- and off-treatment response (R² 0.14 to 0.57; all P < 0.015) for different albuminuria lowering drugs. Additionally, the albuminuria responses strongly correlated when the same individual was re-exposed to the same drug at the same dose: lisinopril 10 mg day^-1 (R²  = 53%; P < 0.01), losartan 50 mg day^-1 (R²  = 63%; P < 0.01).

CONCLUSION

The degree of albuminuria lowering with antialbuminuric drugs varies between patients. This variability in response appears drug-class independent. Identifying which factors determine this initial short-term variation in drug response appears important since the degree of albuminuria lowering is related to subsequent long-term renoprotection.

Is exercise-induced blood pressure rise predictive of nephropathy in insulin-dependent diabetes?

A follow-up study was performed in 48 male diabetics and 17 age-matched male controls, who in 1963 and 1971 participated in an exercise study to evaluate if the results could predict later development of diabetic nephropathy. The inclusion criteria were: Type I (insulin-dependent) diabetes with age below 40, onset of diabetes before age of 30, duration of diabetes more than 7 years and no proteinuria at the time for the first study. The diabetics demonstrated higher systolic blood pressure (BP) at work but as good physical condition as the controls. Thirteen developed nephropathy after 23 years (range 15-36) of diabetes duration. It was found that exercise-induced, abnormally raised systolic BP was not associated with later development of diabetic nephropathy.

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.

Dietary management for children and adolescents with diabetes mellitus: personal experience and recommendations

Diet has traditionally played an important role in diabetic therapy. Over the years, various diets have been proposed, often without scientific evidence. One of the main errors was (is) to speculate that there exists a direct linear correlation between the injection of x units of insulin and the utilization of y grams of glucose. If this were true, one should give more insulin to practice physical activity. In reality, it is the reverse. Dietary recommendations issued over the last few years are the same for diabetic and non-diabetic individuals in order to avoid degenerative diseases. In many countries, the intake of fat is too high, and that of complex carbohydrates too low. The so-called 'Mediterranean diet', in combination with appropriate insulin therapy, may be optimal. This consists mainly of fiber-rich complex carbohydrates (grain), vegetables, fruits, fish, and olive oil. Explanations of this diet should focus on quality rather than quantity of foodstuffs, and should be given by a multidisciplinary team. Prescription of a highly rigid diet has proved ineffective in producing adequate metabolic control, and increases the risk of deviations from the diet. In our experience, the proper use of the two-injection regimen, in countries where the meal schedule allows correct allocation of diet, may lead to 'intensive conventional therapy' and good metabolic control. It is inadequate to systematically assign the multiple-insulin injection regimen to intensified insulin therapy, and the 'conventional' two-injection regimen to a non-intensified insulin therapy. The proper use of the basal-bolus regimen, with increased flexibility in daily life and dietary freedom, cannot always be applied successfully before adolescence. The adjustment of insulin dosage is more complicated than in the twice-daily injection regimen because dose alteration cannot be made only according to sliding scales based on the glycemia measured immediately before the insulin injection. The simplistic use of these non-physiological sliding scales is the main error in the multiple daily insulin injection regimen. The use of fast-acting insulin analogs in the basal-prandial regimen improves post-prandial glycemia at the expense of an increase in pre-prandial glucose levels, if the period between two meals, and therefore two injections, exceeds 3-4 hours, because of the short duration of action. If there are 4-6 or 7 hours between two meals, it is better to use a rapid-acting insulin. Avoid dogmatism--only objective results (good glycosylated hemoglobin and lipid levels, as well as good quality of life) are important.

Post-exercise albuminuria does not predict microalbuminuria in type 1 diabetic patients

To investigate whether post-exercise urinary albumin excretion in Type 1 diabetic children and adolescents may prospectively predict the development of microalbuminuria, we have assessed post-exercise urinary albumin excretion before and after 6.2 +/- 1.7 years of follow-up in 66 diabetic children and adolescents. Post-exercise urinary albumin excretion rose significantly above the pre-exercise values in diabetic patients by 2.7 (-3.8 to 84.2) micrograms min-1 (p < 0.001) and in a group of 9 healthy individuals by 3.9 (-0.7 to 13.7) micrograms min-1 (p < 0.02) without significant differences between groups. Post-exercise albuminuria was greater in postpubertal than prepubertal 9.8 vs 4.3 micrograms min-1 (p < 0.03) and pubertal 9.8 vs 6.0 micrograms min-1 (p < 0.02) patients; post-exercise changes in urinary albumin excretion were also positively related to glycated haemoglobin (r = 0.293; p < 0.05). Eight out of 66 patients developed microalbuminuria at follow-up. Urinary albumin excretion at follow-up was comparable between patients with normal and abnormal post-exercise urinary albumin excretion; moreover post-exercise urinary albumin excretion was within the normal range in 5 out of 8 patients with microalbuminuria at follow-up. In conclusion post-exercise albuminuria does not seem to be a useful predictor of the onset of microalbuminuria in Type 1 diabetic children and adolescents.

Anaerobic threshold can provoke microalbuminuria in non-insulin-dependent diabetics

We examined two groups of non-insulin-dependent diabetic men (group A, 13 patients without microalbuminuria; group B, 9 patients with intermittent microalbuminuria) to ascertain whether the anaerobic threshold (AT) can provoke microalbuminuria, comparing them with 12 healthy subjects matched for age and sex (group C). All subjects exercised on a bicycle ergometer until the AT was reached. In intermittent microalbuminuria, the albumin:creatinine ratio (ACR) was over 0.25 mg/mmol.Cr 1-3-fold in 5 measurements. The ACR after exercise was increased to over 0.25 mg/mmol.Cr in 4/9 cases in group B (P < 0.05), in 2/13 cases in group A, but not at all in group C. We also studied the mechanism of exercise-induced microalbuminuria. In group B, ACR before exercise correlated positively with the baseline plasma glucose. Furthermore, positive correlation was found between ACR after exercise and HbA1c in group B. The AT did not affect the urinary beta 2-microglobulin in any groups. The plasma atrial natriuretic factor (ANF) after exercise was elevated most prominently in group B (P < 0.05). Positive correlation was found between increments of ACR and increments of plasma ANF after exercise in group B. We conclude that the AT can provoke microalbuminuria in some non-insulin-dependent diabetics. The plasma ANF and metabolic control may play an important role in the pathophysiology of exercise-induced microalbuminuria.

Correlation between mitochondrial enlargement in renal proximal tubules and microalbuminuria in rats with early streptozotocin-induced diabetes

To clarify the ultrastructural changes in renal proximal tubules causing microalbuminuria in the early stage of diabetic nephropathy, three different groups of rats were prepared: rats with streptozotocin (STZ)-induced diabetes given no treatment (DMut; n = 7), rats with STZ-induced diabetes treated with insulin (DMt; n = 7), and non-diabetic rats injected with citrate buffer (control; n = 7). In each group, the laboratory findings, ATP content of the renal cortex, and the size of proximal tubule cells and their nuclei and mitochondria (MT) were determined. In two weeks after the start of the study, MT in renal proximal tubules showed diffuse enlargement in the DMut group as compared with those in the control group. Renal cortical ATP content, fractional sodium excretion (FENa), urinary excretion of beta 2-microglobulin and albumin were also increased significantly in the DMut group relative to the controls. In the DMt group, most of the examined parameters returned almost to normal. There were positive correlations between each of the following parameters: hyperglycemia and MT enlargement, MT enlargement and increased cortical ATP content, increased cortical ATP content and increased FENa, increased FENa and increased urinary excretion of beta 2-microglobulin and albumin. On the basis of these results, we conclude that mitochondrial enlargement, resulting from disturbed metabolism of ATP, may reduce active transport in renal proximal tubules, which, in turn, may impair reabsorption in the tubules. This would cause urinary excretion of low-molecular-weight proteins and microalbumin in the early stage of diabetic nephropathy.

Changes in urinary retinol binding protein excretion and other indices of renal tubular damage in patients with non-insulin dependent diabetes

Changes in urine retinol binding protein (RBP, M(r) 21,000) excretion and other indices of renal tubular damage were investigated in the patients with non-insulin dependent diabetes mellitus (NIDDM). Changes in urine RBP excretion were well paralleled with those of urine NAG excretion. In RBP-negative patients, the subjects with hypertension (systolic blood pressure > or = 140 mmHg or diastolic blood pressure > or = 90 mmHg) showed higher beta 2-microglobulin (beta 2-MG) excretion and albumin (Alb)/Cr ratios than normotensive ones. In addition, both urine beta 2-MG excretions and Alb/Cr ratios were significantly increased in RBP-positive patients. The measurement of urine RBP excretion may have an additional role in the diagnosis of renal tubular dysfunction in diabetic patients.

Urinary excretion of retinol-binding protein in type 1 (insulin-dependent) diabetic patients with microalbuminuria and clinical diabetic nephropathy

The urinary excretion of retinol-binding protein (RBP) was studied in 101 insulin-dependent diabetic patients allocated to three groups according to 24-h urinary albumin excretion rate (UAE) (median of three urine collections): group 1 (n = 45), normal UAE less than 30 mg/24 h; group 2 (n = 27), microalbuminuria (UAE 30-300 mg/24 h); and group 3 (n = 29), clinical diabetic nephropathy (UAE greater than 300 mg/24 h). We used 23 healthy subjects as controls. Fractional clearance of RBP (FC-RBP) and its 24-h urinary excretion rate (URBP) were higher in each diabetic group than in healthy subjects, the highest values being found in group 3. Groups 1 and 2 did not differ in URBP and FC-RBP. There was a correlation between FC-RBP and haemoglobin A1c in both the total diabetic cohort (P less than 0.001) and in diabetic patients in groups 1 and 2 with a glomerular filtration rate of more than 90 ml/min (P less than 0.05). No correlation was found between FC-RBP and UAE and/or duration of diabetes in any of the diabetic groups. We conclude that the increased urinary excretion of RBP, indicating proximal tubular dysfunction, is already present in normoalbuminuric insulin-dependent diabetic patients and correlates with metabolic control. Further deterioration in proximal tubular function was not observed in microalbuminuric patients, but is a late event in clinical diabetic nephropathy.

Microheterogeneity of urinary albumin and tubular proteinuria in juvenile diabetes mellitus

We studied differential urinary albumin excretion by a double one-dimensional gel electrophoresis with decyl sodium sulphate-polyacrylamide gel electrophoresis in the first, and isoelectric focusing in the second dimension in 37 diabetic children and 20 healthy subjects. In addition, total proteins, albumin, beta 2-microglobulin and molecular size distribution of urinary proteins were measured, the latter using sodium dodecyl sulphate-polyacrylamide gel electrophoresis. Whilst albuminuria was not significantly different from controls we found an increased microheterogeneity of urinary albumin in 38% of patients. In addition, low molecular weight protein (P less than 0.05) and beta 2-microglobulin excretion (P less than 0.01) were elevated. It is suggested that the appearance of highly heterogenous albumin in the pI range of 5.3-5.9 is the result of a decreased tubular reabsorption.

An acceptable exercise test to study microalbuminuria in type 1 diabetes

A modified test for studying the response of urinary albumin excretion (UAV) to exercise in diabetic patients is described. It is designed to produce a standardized increase in pulse rate (by 90-110%) rather than a standardized workload. Thirty-three normotensive Type 1 diabetic patients with normal pre-exercise UAV (less than 10 micrograms min-1) on the day of the test were compared with 25 non-diabetic subjects matched for age and sex. The patients developed a significantly greater increase in the median UAV (p less than 0.05) and systolic blood pressure (p less than 0.01) during exercise, despite the use of lower workloads (p less than 0.05). During exercise, the albumin excretion in the patients was not related to their heart rate, blood pressure, workload or fall in blood glucose; nor was it related to duration of diabetes, glycosylated haemoglobin or insulin dose. An exercise UAV greater than 15 micrograms min-1 was found in 10 of the 33 patients; it was significantly correlated (p less than 0.01) with the frequency of previous overnight microalbuminuria (greater than 10 micrograms min-1), and was associated with a greater progression of microalbuminuria (p less than 0.05) over a mean period of 24 months. Retinol-binding protein excretion rate was also measured as an indicator of proximal tubular function and did not increase in either group.

[Urinary proteins as indicators of diabetic nephropathy]

During the last ten years, several studies proved the applicability of urinary albumin quantification in the early diagnosis of diabetic nephropathy. Owing to its high accuracy and its comparable low methodological effort, only the albumin determination was emphasised. Parallel studies of urinary protein patterns, however, using sodium dodecylsulfate-polyacrylamide gel-electrophoresis demonstrated the increased excretion of other high- and low-molecular mass proteins in different stages of diabetic nephropathy. Consequently an extension of the mere albumin assay including a macromolecular (e.g. transferrin) and a micromolecular (e.g. alpha-1-microglobulin) protein seems meaningful. According to this study, both methodological lines (combined quantitative and qualitative analysis, respectively) are useful tools in the early detection and the follow up of diabetic nephropathy.

Effect of the exercise test on albuminuria, blood pressure and blood glucose in type I (insulin-dependent) diabetic patients

Twenty-nine male type I diabetic patients (age range 16-46 years) and thirteen healthy men (age range 18-43 years) were exercised on a cycling ergometer at 75 W and 100 W after having achieved a steady state of water diuresis. Diabetic patients were subdivided into Group A (n = 19, resting urinary albumin excretion rate - UAER less than or equal to 16 micrograms/min) and Group B (n = 10, 16 less than resting UAER less than 126 micrograms/min). The groups were comparable in weight, serum creatinine, duration of diabetes and glycosylated hemoglobin. Group B showed the highest elevation of UAER at the work load of 100 W, with no correlation between increase in UAER and increase in systolic blood pressure (SBP) at both work loads. The only correlation between these parameters was found in Group A at the work load of 100 W (p less than 0.05). No correlation was found between exercise UAER and actual blood glucose in either group. The difference in UAER between healthy subjects and Group B patients (p less than 0.001) remained on the same level during exercise as at rest, but the difference between Group A and Group B (p less than 0.001) decreased with increasing work load (p less than 0.05). The highest exercise-induced systolic and diastolic blood pressure (DBP) was found in Group B, although there was no difference between the diabetic groups in pre-exercise blood pressure and in mean SBP and DBP from previous outpatient check-ups. Blood glucose did not change significantly during exercise in either diabetic group. Working capacity of diabetic patients was lower than that of healthy subjects. The test revealed some diabetic patients with strong elevation of UAER and with abnormally raised systolic and diastolic BP during exercise. The value of the findings reported is to be clarified in a further longitudinal study.

Retinol binding protein as a small molecular weight marker of renal tubular function in diabetes mellitus

A radioimmunoassay has been developed for the measurement in urine of retinol-binding protein (alpha 2-microglobulin) and used as an index of renal tubular function in adult Type 1 (insulin-dependent) diabetics and to define reference ranges in non-diabetic controls. There was a significantly greater excretion (P less than 0.001) of retinol-binding protein in the diabetic group compared to the controls in both overnight and daytime samples. There was a weak positive correlation with albumin excretion (r = 0.33; P less than 0.01) but no correlation with HbA1, duration of diabetes or arterial blood pressure. The results indicate that retinol-binding protein excretion may be increased in diabetic subjects without increased albumin excretion. The possibility therefore exists that renal tubular damage may occur early in diabetic nephropathy without apparent glomerular dysfunction.

Peroneal motor nerve conduction velocity in diabetic children and adolescents. Relationships to metabolic control, HLA-DR antigens, retinopathy, and EEG

To investigate incipient diabetic neuropathy, peroneal motor nerve conduction velocity (PMNCV) was measured in 61 diabetic children and adolescents whose type 1 diabetes became clinically apparent before the age of 14 years. PMNCV in diabetic patients (48.3 +/- 5.6 m/s) was significantly lower than in controls (56.5 +/- 5.5 m/s), 23 diabetics (36%) having a value more than 2 SD below the mean for normals. There was a highly significant negative correlation between PMNCV and HbA1 levels concomitant with PMNCV measurement or mean annual HbA1 concentrations preceding PMNCV. The relationship between PMNCV and the clinical score of diabetic control since the onset of the disease was also significant. Age, duration of diabetes and HLR-DR antigens were unrelated to PMNCV. EEG abnormalities and retinopathy, whose pathogenesis is different, were not necessarily associated with subclinical neuropathy. Being easy and sensitive, PMNCV determination provides the paediatric diabetologist and the patient himself with an important motivation to improve diabetic control.

Exercise as a provocative test in early renal disease in type 1 (insulin-dependent) diabetes: albuminuric, systemic and renal haemodynamic responses

The value of exercise as a provocative test for early renal disease in Type 1 (insulin-dependent) diabetes was re-evaluated. Three carefully characterized groups of males were studied: 10 non-diabetic controls, 16 diabetic patients (group 1) with normal urinary albumin excretion (less than 15 micrograms/min) and 14 Albustix-negative diabetics (group 2) with increased urinary albumin excretion (15-122 micrograms/min). Assignment to a study group was made on the basis of three 24-h urine collections, and the groups were well matched for age, weight, height, and serum creatinine concentration. The two diabetic groups were similar with regard to duration of disease (13 +/- 6 versus 16 +/- 3 years), metabolic control (HbA1c: 8.4 +/- 1.4 versus 8.7 +/- 1.3%) and degree of diabetic complications (beat-to-beat variation and retinopathy). An exercise protocol of 450 and 600 kpm/min workloads was employed. In the resting state group 2 patients had elevated systolic blood pressure compared with the normal subjects (132 +/- 13 versus 119 +/- 9 mmHg), and their glomerular filtration rate was significantly reduced compared with group 1 (123 +/- 19 versus 138 +/- 15 ml/min per 1.73 m2, p less than 0.05). During exercise the urinary albumin excretion rate increased significantly in all three groups (normal subjects: 6 +/- 0.7 to 8 +/- 1.3 (microgram/min); group 1: 6 +/- 0.6 to 9 +/- 1 microgram/min and group 2: 48 +/- 10 to 113 +/- 23 micrograms/min), the relative increase being higher in group 2 (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Exercise and renal function

Exercise induces profound changes in the renal haemodynamics and in electrolyte and protein excretion. Effective renal plasma flow is reduced during exercise. The reduction is related to the intensity of exercise and renal blood flow may fall to 25% of the resting value when strenuous work is performed. The combination of sympathetic nervous activity and the release of catecholamine substances is involved in this process. The reduction of renal blood flow during exercise produces a concomitant effect on the glomerular filtration rate, though the latter decreases relatively less than the former during exertion. However, the degree of hydration has an important influence on the glomerular filtration rate. An antidiuretic effect is observed during intense exercise. Changes in urine flow are dependent on the plasma antidiuretic hormone levels which are increased by intense exercise. Heavy exercise has an inhibitory effect on most electrolytes (Na, Cl, Ca, P). With potassium, however, most studies report that potassium excretion is not consistently affected by moderate to heavy exercise. Increased aldosterone production helps the body to maintain sodium by increasing its reabsorption from the filtered tubular fluid. Recent studies suggest that sympathetic stimulation may be involved during exercise. Strenuous work leads to an increased excretion of erythrocytes and leucocytes in urine. Cylindruria has been regularly found in postexercise urine in different sports. Postexercise proteinuria is a common phenomenon in humans. It seems to be directly related to the intensity of exercise, rather than to its duration. This excretion of proteins in urine is a transient state with a half-time of approximately 1 hour. Postexercise proteinuria has a pattern different from normal physiological proteinuria. Immunochemical techniques demonstrate that postexercise proteinuria is of the mixed glomerular-tubular type, the former being predominant. The increased clearance of plasma proteins suggests an increased glomerular permeability and a partial inhibition of tubular reabsorption of macromolecules. Haemoglobinuria and myoglobinuria may be observed under special exercise conditions. The degree of hydration appears to be important to reduce these abnormalities.