Reduced glomerular size- and charge-selectivity in clinically healthy individuals with microalbuminuria

Increased urinary angiotensin converting enzyme 2 and neprilysin in patients with type 2 diabetes

Angiotensin converting enzyme 2 (ACE2) and neprilysin (NEP) are metalloproteases that are highly expressed in the renal proximal tubules. ACE2 and NEP generate renoprotective angiotensin (1-7) from angiotensin II and angiotensin I, respectively, and therefore could have a major role in chronic kidney disease (CKD). Recent data demonstrated increased urinary ACE2 in patients with diabetes with CKD and kidney transplants. We tested the hypothesis that urinary ACE2, NEP, and a disintegrin and metalloproteinase 17 (ADAM17) are increased and could be risk predictors of CKD in patients with diabetes. ACE2, NEP, and ADAM17 were investigated in 20 nondiabetics (ND) and 40 patients with diabetes with normoalbuminuria (Dnormo), microalbuminuria (Dmicro), and macroalbuminuria (Dmacro) using ELISA, Western blot, and fluorogenic and mass spectrometric-based enzyme assays. Logistic regression model was applied to predict the risk prediction. Receiver operating characteristic curves were drawn, and prediction accuracies were calculated to explore the effectiveness of ACE2 and NEP in predicting diabetes and CKD. Results demonstrated that there is no evidence of urinary ACE2 and ADAM17 in ND subjects, but both enzymes were increased in patients with diabetes, including Dnormo. Although there was no detectable plasma ACE2 activity, there was evidence of urinary and plasma NEP in all the subjects, and urinary NEP was significantly increased in Dmicro patients. NEP and ACE2 showed significant correlations with metabolic and renal characteristics. In summary, urinary ACE2, NEP, and ADAM17 are increased in patients with diabetes and could be used as early biomarkers to predict the incidence or progression of CKD at early stages among individuals with type 2 diabetes.

Microalbuminuria: causes and implications

Management strategies are increasingly focused on tackling the increasing burden of cardiovascular disease worldwide. Microalbuminuria is a powerful predictor of cardiovascular disease and mortality in adults. This holds true in the general adult population but is particularly recognized in those with diabetes, where it identifies those likely to develop progressive atherosclerotic vascular disease and renal impairment. The atherosclerotic process begins in childhood with likely consequences in later life. In-depth understanding of the mechanisms through which microalbuminuria occurs holds promise for designing therapies to arrest its development in the future. Microalbuminuria arises from increased leakage of albumin through the complex glomerular sieve known as the glomerular filtration barrier. This requires changes in the physio-chemical properties of components of this barrier. However, the increased glomerular permeability confirmed in disease does not necessarily correlate with recognized histological changes in the glomerulus, suggesting that perhaps more subtle ultrastructural changes may be relevant. The epidemiology of microalbuminuria reveals a close association between systemic endothelial dysfunction and vascular disease, also implicating glomerular endothelial dysfunction in microalbuminuria. This review discusses the mechanisms of microalbuminuria in disease, particularly the emerging role of the glomerular endothelium and its glycocalyx, and examines its implications for cardiovascular disease in the pediatric population.

Microalbuminuria in Cerebrovascular Disease: A Modifiable Risk Factor?

Stroke is potentially preventable through risk factor modification. Over the past decade, there has been considerable interest on microalbuminuria as a risk factor for chronic diseases. The concept of microalbuminuria was originally introduced, about 25 years ago, to clinical practice as a useful marker of nephropathy. Since then various studies reported an association of microalbuminuria with the increased risk of cardiovascular events and all cause of mortality in subjects with or without diabetes. The presence of microalbuminuria was related to left ventricular dysfunction, stroke, and myocardial infarction. Microalbuminuria may be a predictor of stroke but further studies are required. However data on prognostic significance and therapeutic consequence, particularly in haemorrhagic stroke are lacking. This review focuses on the importance of microalbuminuria for cerebrovascular disease, stressing the clinical and therapeutic implications using antihypertensive therapy to control the urinary albumin excretion.

What is the mechanism of microalbuminuria in diabetes: a role for the glomerular endothelium?

Microalbuminuria is an important risk factor for cardiovascular disease and progressive renal impairment. This holds true in the general population and particularly in those with diabetes, in whom it is common and marks out those likely to develop macrovascular disease and progressive renal impairment. Understanding the pathophysiological mechanisms through which microalbuminuria occurs holds the key to designing therapies to arrest its development and prevent these later manifestations. Microalbuminuria arises from the increased passage of albumin through the glomerular filtration barrier. This requires ultrastructural changes rather than alterations in glomerular pressure or filtration rate alone. Compromise of selective glomerular permeability can be confirmed in early diabetic nephropathy but does not correlate well with reported glomerular structural changes. The loss of systemic endothelial glycocalyx--a protein-rich surface layer on the endothelium--in diabetes suggests that damage to this layer represents this missing link. The epidemiology of microalbuminuria reveals a close association with systemic endothelial dysfunction and with vascular disease, also implicating glomerular endothelial dysfunction in microalbuminuria. Our understanding of the metabolic and hormonal sequelae of hyperglycaemia is increasing, and we consider these in the context of damage to the glomerular filtration barrier. Reactive oxygen species, inflammatory cytokines and growth factors are key players in this respect. Taken together with the above observations and the presence of generalised endothelial dysfunction, these considerations lead to the conclusion that glomerular endothelial dysfunction, and in particular damage to its glycocalyx, represents the most likely initiating step in diabetic microalbuminuria.

Relationship between antinuclear antibody and microalbuminuria in the general population: the Takahata study

BACKGROUND

Microalbuminuria, a marker of vascular damage, is associated with increased risk of progressive renal deterioration, cardiovascular disease and mortality. However, the relationship between antinuclear antibody (ANA) and microalbuminuria in the general population is unknown. Thus, we conducted a cross-sectional study to examine the relationship between ANA and microalbuminuria.

METHODS

The subjects of this community-based study were individuals over 40 years old in Takahata, Japan. The urine albumin-creatinine ratio (UACR) was calculated from a single-spot urine specimen collected in the morning. ANA was examined by enzyme immunoassay (EIA).

RESULTS

Among the 2,875 subjects (mean age 63 years; men 1,276; women 1,599), positive ANA (ANA index >or=20.0) was detected in 16.9% of the total population (men 12.9%, women 20.3%) and the prevalence of positive ANA increased with age. The prevalence of microalbuminuria (UACR 30-300 mg/g), but not macroalbuminuria (UACR > 300 mg/g), was significantly higher in the positive ANA group than the negative ANA group (24.1% vs. 16.0%, respectively, P < 0.001). Along with the increase of the ANA index, the prevalence of microalbuminuria and UACR levels were increased. Multivariate logistic regression analyses showed that ANA was significantly associated with microalbuminuria (odds ratio [OR] 1.63 and 95% confidence interval [95%CI] 1.27-2.10). These associations were significant in women, but not men, when examined separately.

CONCLUSIONS

These results indicate that the presence of ANA is associated with microalbuminuria in the general population, especially women.

ACE gene insertion/deletion polymorphism modulates capillary permeability in hypertension

A D/D (deletion/deletion) polymorphism within the ACE (angiotensin 1-converting enzyme) gene increases the risk of microalbuminuria, a predictor of atherosclerotic vascular disease, in essential hypertension. It is unknown, however, whether this genetic profile is accompanied by disturbed macromolecular permeability of systemic capillary endothelium, possibly in the context of generalized endothelial dysfunction. In the present study, the ACE gene polymorphism was determined by PCR in 79 never-treated uncomplicated hypertensive men and 16 normotensive men as controls. Evaluation variables were TERalb (transcapillary escape rate of albumin; the 1-h decline rate of intravenous (125)I-albumin, a measure of integrity of systemic capillary endothelium), albuminuria and forearm vasodilation to intra-arterial acetylcholine, an index of NO (nitric oxide)-mediated vasomotion, in addition to a series of sensitive parameters of albumin permeation (blood pressure, metabolic status and smoking habits). Analyses were done by comparing D/D homozygotes with grouped I/D (insertion/deletion) and I/I (insertion/insertion) subjects. TERalb was higher in D/D hypertensives, who had higher albuminuria, more frequent microalbuminuria and comparable forearm responsiveness to intra-arterial acetylcholine. Fasting glucose and insulin, insulin sensitivity, 24-h blood pressure, smoking habits and metabolic parameters did not differ between the two groups. TERalb and urine albumin values were positively associated in the hypertensive subjects. In conclusion, ACE D/D homozygosis, independently of several confounding factors, associates with higher TERalb in men with essential hypertension. This may reflect noxious genetic influences on systemic vascular permeability, a critical control mechanism for atherogenesis in the absence of grossly impaired NO-mediated arteriolar responsiveness. The parallel behaviour of TERalb and albuminuria suggests some shared genetically mediated determinant of renal and systemic microvascular abnormalities in hypertension.

Microalbuminuria is determined by systolic and pulse pressure over a 12-year period and related to peripheral artery disease in normotensive and hypertensive subjects: the Three Areas Study in Greece (TAS-GR)

Microalbuminuria and peripheral artery disease represent 2 different forms of target organ damage due to raised blood pressure. The aim of this study was to investigate the association between blood pressure with microalbuminuria and the appearance of peripheral artery disease after more than a decade, and moreover, to address whether any relationship exists between microalbuminuria and peripheral disease in a Greek Caucasian population. In 1990, 635 normal subjects were examined and their blood pressure was recorded. Nine and 12 years later, subjects were reexamined and 361 of them (57%) were available at last visit for the determination of microalbuminuria and ankle-arm index. Microalbuminuria was detected in 35/361 (9.7%) and peripheral artery disease in 89/361 (24.7%). Both conditions were statistically correlated with pulse and systolic blood pressure at all time points during the 12-year follow-up period, while the relationship with diastolic and mean arterial pressure existed only for baseline values and was then abolished. Microalbuminuria was statistically correlated to peripheral artery disease (r = -0.460, p = 0.0001). Blood pressure levels seemed to predict the appearance of microalbuminuria and peripheral disease after 12 years. Microvasculature and macrovasculature abnormalities (microalbuminuria and peripheral disease, respectively) showed a significant relationship, suggesting a common pathogenetic mechanism.

Reductions in albuminuria and in electrocardiographic left ventricular hypertrophy independently improve prognosis in hypertension: the LIFE study

BACKGROUND

In the Losartan Intervention For Endpoint reduction in hypertension (LIFE) study, reduced urine albumin/creatinine ratio (UACR) as well as regression of left ventricular hypertrophy have been associated with lower incidence of cardiovascular events. We wanted to investigate whether these prognostic improvements were independent.

METHODS

In 6679 hypertensive patients included in the LIFE study, we measured UACR, left ventricular hypertrophy by electrocardiography, serum cholesterol, plasma glucose and blood pressure after 2 weeks of placebo treatment and again after 1 year of anti-hypertensive treatment with either an atenolol- or a losartan-based regimen. During this first year of treatment, 77 patients encountered a non-fatal stroke or myocardial infarction and were excluded to avoid bias. During the next 3-4 years, 610 composite endpoints [cardiovascular death (n = 228), fatal or non-fatal myocardial infarction or stroke] were recorded.

RESULTS

In Cox regression analyses, the composite endpoint was after adjustment for treatment allocation predicted by baseline logUACR [hazard ratio (HR) = 1.16 per 10-fold increase, P < 0.05], 1-year logUACR (HR = 1.29 per 10-fold increase), baseline Sokolow-Lyon voltage (HR = 1.01 per mm, both P < 0.001) and 1-year Cornell product (HR = 1.01 per 100 mm x ms, P < 0.01). Cardiovascular death was predicted by 1-year logUACR (HR = 1.59, P < 0.001), baseline Sokolow-Lyon voltage (HR = 1.01, P = 0.06) and 1-year Cornell product (HR = 1.02, P < 0.001). Both were predicted independent of age, Framingham risk score, current smoking, history of cardiovascular disease and diabetes. Gender, serum cholesterol, plasma glucose and blood pressure did not enter the models.

CONCLUSIONS

Baseline UACR and Sokolow-Lyon voltage, as well as in-treatment UACR and Cornell product, added to the risk prediction independent of traditional risk factors, indicating that albuminuria and left ventricular hypertrophy reflect different aspects of cardiovascular damage and are modifiable cardiovascular risk factors.

Microalbuminuria is associated with impaired glomerular permselectivity in lymphoma patients

Slightly increased urinary albumin excretion is frequently found in patients with lymphoma and other malignancies but the pathophysiological mechanisms have yet to be clarified. In this study, parameters of renal function in lymphoma patients with microalbuminuria were evaluated. Sixty-seven patients with histologically proven diffuse large B-cell lymphoma were included in the study at diagnosis. Urinary albumin excretion was measured by immunoturbidimetry and microalbuminuria was defined as an excretion rate between 20 and 200 microg/min. Glomerular function was further estimated by renal clearance of creatinine and IgG, and the IgG/IgG4 charge selectivity index. Tubular function was evaluated by renal clearance of beta(2)-microglobulin. The median value of IgG clearance was increased in the microalbuminuric patients (0.22 versus 0.18 microl/min; p = 0.03). The median selectivity index was significantly lower in patients with microalbuminuria (1.0 versus 2.2; p<0.0001). Urinary albumin excretion was correlated with both the renal clearance of IgG (p<0.0001) and the selectivity index (p<0.0001). These data suggest that a slightly elevated level of urinary albumin excretion in a population of patients with aggressive lymphoma reflects altered glomerular permselectivity probably due to a defect in charge selectivity. The glomerular sieving dysfunction may be associated with an inflammatory response to the malignancy. Further studies are needed to validate the clinical impact of the renal parameters in lymphoma patients.

Low-grade inflammation and microalbuminuria in hypertension

Background- Albuminuria and C-reactive protein (CRP), a marker of systemic low-grade inflammation, are frequently elevated in essential hypertension and predict cardiovascular prognosis independent of conventional risk factors. However, in spite of their potentially important links, the interrelationships between the 2 parameters have not been explored in depth in hypertensive patients.

METHODS AND RESULTS

Albuminuria (the mean of 3 overnight urine collections), high-sensitive CRP (hs-CRP), 24-hour blood pressure (BP), weight, lipids, poststimulative (75 g PO) plasma glucose, insulin, and insulin sensitivity by the homeostasis model assessment model were evaluated in 220 never treated, nondiabetic, uncomplicated essential hypertensive men. Albuminuria > or =15 microg/min was defined as microalbuminuria and hs-CRP values above and below median (2.3 mg/L) as high and low, respectively. Concentric left ventricular hypertrophy was diagnosed by echocardiography, and a full-blown metabolic syndrome was identified in presence of hypertension and at least 3 of following: obesity, subclinical hyperglycemia, low high-density lipoprotein (HDL) and high triglycerides. Microalbuminuria was present in 54 patients, 29 with high hs-CRP characterized by higher 24-hour systolic BP, postload glucose, body mass index, lower HDL cholesterol, more frequent metabolic syndrome, concentric LVH, and active smoking than those with either isolated microalbuminuria (n=27) or normoalbuminuria.

CONCLUSIONS

Microalbuminuria accompanied by evidence of subclinical inflammation is a strong correlate of metabolic abnormalities in essential hypertension and identifies a patient subset at very high cardiovascular risk. In contrast, isolated microalbuminuria may represent a distinct pathophysiological condition characterized by a more benign profile and possibly a better prognosis.

Albuminuria predicts cardiovascular events independently of left ventricular mass in hypertension: a LIFE substudy

We wanted to investigate whether urine albumin/creatinine ratio (UACR) and left ventricular (LV) mass, both being associated with diabetes and increased blood pressure, predicted cardiovascular events in patients with hypertension independently. After 2 weeks of placebo treatment, clinical, laboratory and echocardiographic variables were assessed in 960 hypertensive patients from the LIFE Echo substudy with electrocardiographic LV hypertrophy. Morning urine albumin and creatinine were measured to calculate UACR. The patients were followed for 60+/-4 months and the composite end point (CEP) of cardiovascular (CV) death, nonfatal stroke or nonfatal myocardial infarction was recorded. The incidence of CEP increased with increasing LV mass (below the lower quartile of 194 g to above the upper quartile of 263 g) in patients with UACR below (6.7, 5.0, 9.1%) and above the median value of 1.406 mg/mmol (9.7, 17.0, 19.0%(***)). Also the incidence of CV death increased with LV mass in patients with UACR below (0, 1.4, 1.3%) and above 1.406 mg/mmol (2.2, 6.4, 8.0%(**)). The incidence of CEP was predicted by logUACR (hazard ratio (HR)=1.44(**) for every 10-fold increase in UACR) after adjustment for Framingham risk score (HR=1.05(***)), history of peripheral vascular disease (HR=2.3(*)) and cerebrovascular disease (HR=2.1(*)). LV mass did not enter the model. LogUACR predicted CV death (HR=2.4(**)) independently of LV mass (HR=1.01(*) per gram) after adjustment for Framingham risk score (HR=1.05(*)), history of diabetes mellitus (HR=2.4(*)) and cerebrovascular disease (HR=3.2(*)). (*)P<0.05, (**)P<0.01, (***)P<0.001. In conclusion, UACR predicted CEP and CV death independently of LV mass. CV death was predicted by UACR and LV mass in an additive manner after adjustment for Framingham risk score and history of CV disease.

Elevated urinary albumin excretion is associated with impaired arterial dilatory capacity in clinically healthy subjects

BACKGROUND

Elevated urinary albumin excretion (UAE) predicts atherosclerotic cardiovascular disease. It is hypothesized that elevated UAE is associated with a generalized vascular dysfunction. This study tested this hypothesis for conduit arteries.

METHODS AND RESULTS

Clinically healthy subjects were selected: 19 with UAE >90th percentile in the background population (6.6 microgram/min<UAE<150 microgram/min) and 41 with normoalbuminuria (UAE <6.6 microgram/min). External ultrasound was used to measure the dilatory response of the brachial artery to postischemic increased blood flow (endothelium-dependent, flow-associated dilation) and to nitroglycerin (endothelium-independent, nitroglycerin-induced dilation). Plasma concentrations of the endothelial markers nitrate/nitrite, thrombomodulin, and von Willebrand factor antigen were also measured. Both flow-associated and nitroglycerin-induced dilations were significantly impaired in subjects with elevated UAE as compared with normoalbuminuric control subjects: 102.0+/-1.0% (mean+/-SEM) versus 104.3+/-0.6% (P<0.05) and 120.1+/-1.5% versus 123.8+/-1.0% (P<0.05). No differences in the plasma concentrations of endothelial markers were found. Conclusions-Slightly elevated UAE is associated with impaired conduit arterial dilatory capacity in clinically healthy subjects, and this impairment may be explained by a reduced dilatory response to nitric oxide of both endogenous and exogenous origin. Impaired arterial dilatory capacity may contribute to the increased cardiovascular risk in subjects with elevated UAE.

Elevated urinary albumin excretion is not linked to the angiotensin I-converting enzyme gene polymorphism in clinically healthy subjects

An elevated urinary albumin excretion (UAE) in non-diabetic subjects without renal or cardiovascular disease has been shown to be predictive of ischaemic heart disease. An insertion (I)/deletion (D) polymorphism in the angiotensin I-converting enzyme (ACE) gene has been identified and the D allele may be associated with cardiovascular disease. The aim of this study was to find a potential linkage between this polymorphism and elevated UAE. For studies of UAE and cardiovascular pathophysiology, a highly selected population sample has been identified comprising all clinically healthy subjects aged 40-65 years with elevated UAE in a dipstick negative urinary sample (n = 27) from The Copenhagen City Heart Study. Neither the ACE genotype distribution (p = 0.12) nor the D and I allele frequencies (p = 0.69) differed significantly between subjects with elevated UAE and a matched normoalbuminuric control group (n = 46). Elevated UAE in clinically healthy subjects is not linked to the ACE gene polymorphism.

Characteristics of protein excretion in patients with acute urinary retention

OBJECTIVE

To evaluate changes in protein leakage in the glomerular filtration barrier, and in the ability of the tubule to reabsorb proteins during and after acute urinary retention (AUR).

PATIENTS AND METHODS

Glomerular and tubular function was investigated in 24 men during AUR (mean age 68 years, mean retention time 31 h and mean retention volume 1140 mL) who were then followed for 6 months by measuring the urinary excretion of glomerular and tubular proteins, and the glomerular filtration rate (GFR). Retention was relieved by inserting a suprapubic catheter and the cause of retention treated one month later. No patient had a previous renal disease or diabetes.

RESULTS

During AUR, and after 1 and 6 months, albuminuria was detected in 100%, 92% and 54% of patients, and increased excretion of alpha1-microglobulin in 52%, 36% and 58%, of IgG in 79%, 58% and 40%, and of IgG4 in 67%, 42% and 20%, respectively. The mean GFR was normal during retention and during the follow-up.

CONCLUSION

AUR causes disturbances in both the glomerular filtration and tubular reabsorption of proteins. Albuminuria and increased excretion of IgG, IgG4 and alpha1-microglobulin occurred in most patients during AUR. After relieving retention, the albuminuria and elevated alpha1-microglobulin excretion persisted, indicating slight glomerular dysfunction and a permanent defect in the proximal tubule to reabsorb proteins. This could be caused partly by previous chronic obstruction. AUR should be relieved immediately and the basic cause treated effectively to prevent further deterioration of renal function.

Risk variables of insulin resistance syndrome in African-American and Caucasian young adults with microalbuminuria: the Bogalusa Heart Study

Microalbuminuria is a strong predictor of cardiovascular disease. Previous studies are inconsistent regarding the relationship between microalbuminuria and insulin resistance syndrome. Therefore, we examined this relationship in 1031 young adults (61% Caucasian, 39% African-American) aged 19 to 32 years. Individuals with either urinary albumin to creatinine ratio at or above the 90th percentile (age, race, and gender specific) or urinary albumin level at or above 30 mg/L were considered as having slightly elevated albumin excretion (microalbuminuria). The multiple risk variables of insulin resistant syndrome measured include body mass index, waist circumference, blood pressure (BP), triglycerides, high-density lipoprotein (HDL) cholesterol, glucose, insulin, insulin resistance index (calculated from a homeostasis model assessment equation), and uric acid. After controlling for age and gender, African-Americans with microalbuminuria by either measure had higher mean systolic (P < .001) and diastolic (P < .05) BP, prevalence of hypertension (P < .05), and, contrary to expectations, HDL cholesterol (P < .05) than those without this condition. On the other hand, Caucasians showed no such associations. In African-Americans, the above differences in BP levels persisted when hypertensive subjects were excluded. None of the other risk variables displayed any relation to microalbuminuria in both races. These results suggest that microalbuminuria is not necessarily an intrinsic component of the insulin resistance syndrome, at least in the young adult age. Furthermore, the observed association between hypertension and microalbuminuria among young African-Americans may reflect early evidence of renal dysfunction due to the burden of elevated BP in this group.

Glomerular permselectivity in early stages of overt diabetic nephropathy

BACKGROUND

Impairment of glomerular size selectivity has been demonstrated by the dextran-sieving technique in nephropathic diabetics with heavy, but not mild proteinuria. The purpose of the present study was to determine whether such a barrier defect could be demonstrated with mild proteinuria by substituting Ficoll 70, a polysucrose, for dextran as a probe of the filtration barrier.

METHODS

Differential solute clearances were performed in 12 individuals with early diabetic nephropathy on two occasions: after 60 days of treatment with losartan 50 mg daily or a placebo. An uncharged preparation of nonreabsorbable Ficoll 70 was infused along with inulin. Fractional clearance (theta) of Ficoll of discrete size was determined after separating molecules in urine and plasma in narrow 2 A fractions over a 20 to 60 A radius interval by size exclusion high-performance liquid chromatography (HPLC). A hydrodynamic theory of hindered ficoll transport through water-filled pores was used to characterize the pore size distribution of the glomerular barrier.

RESULTS

The theta for Ficoll molecules with radii> 50 A was selectively enhanced in placebo-treated diabetic nephropathy versus corresponding theta in healthy control subjects (N = 12). Computations revealed a lower distribution of glomerular pores that was unaltered in nephropathic diabetics. However, an upper distribution of large, shunt-like pores was more prominent, exceeding healthy controls by one order of magnitude in diabetic nephropathy (P = 0.01). A trend to lower theta for Ficoll in the 56 to 60 A radius range during losartan therapy is computed to have lowered the fraction of shunted filtrate by 26 to 44%, depending on whether glomerular pressure declined. The corresponding reduction in theta for endogenous albumin, IgG, and IgG4 was by 19 to 23% (P < 0.05).

CONCLUSION

Our findings suggest that shunt-like defects, partially reversible by angiotensin II blockade, are present early in the course of diabetic nephropathy. We estimate that such defects can account for immunoglobulinuria in this disorder. Additional impairment of either charge- or shape-selectivity must be invoked to explain the observed level of albuminuria, however.

Arterial hypertension, microalbuminuria, and risk of ischemic heart disease

Albumin excretion in urine is positively correlated with the presence of ischemic heart disease and atherosclerotic risk factors. We studied prospectively whether a slight increase of urinary albumin excretion, ie, microalbuminuria, adds to the increased risk of ischemic heart disease among hypertensive subjects. In 1983 and 1984, blood pressure, urinary albumin/creatinine concentration ratio, plasma total and HDL cholesterol levels, body mass index, and smoking status were obtained in a population-based sample of 2085 subjects, aged 30 to 60 years, who were free from ischemic heart disease, diabetes mellitus, and renal or urinary tract disease. Untreated arterial hypertension or borderline hypertension was present in 204 subjects, who were followed until 1993 by the National Hospital and Death Certificate Registers with respect to development of ischemic heart disease. During 1978 person-years, 18 (9%) of the hypertensive subjects developed ischemic heart disease. Microalbuminuria, defined as a urinary albumin/creatinine ratio above the upper decile (1.07 mg/mmol), was the strongest predictor of ischemic heart disease, with an unadjusted relative risk of 4.2 (95% CI 1.5 to 11.9, P=0.006) and a relative risk of 3.5 (95% CI 1.0 to 12.1, P=0.05) when adjusted for all other atherosclerotic risk factors, including age and gender. In conclusion, microalbuminuria confers a 4-fold increased risk of ischemic heart disease among hypertensive or borderline hypertensive subjects. Urinary albumin excretion should be measured regularly in a hypertension clinic, and a rigorous control of blood pressure and of other atherosclerotic risk factors is recommended in hypertensive patients with microalbuminuria.

Microalbuminuria in essential hypertension: significance, pathophysiology, and therapeutic implications

Some patients with essential hypertension manifest greater than normal urinary albumin excretion (UAE). The significance of this association, which is the object of this review, is not well established. Hypertensive patients with microalbuminuria manifest greater levels of blood pressure, particularly at night, and higher serum levels of cholesterol, triglycerides, and uric acid than patients with normal UAE. Levels of high-density lipoprotein cholesterol, on the other hand, were lower in patients with microalbuminuria than in those with normal UAE. Patients with microalbuminuria manifested greater incidence of insulin resistance and thicker carotid arteries than patients with normal UAE. After a follow-up of 7 years, we observed that 12 cardiovascular events occurred among 54 (21.3%) patients with microalbuminuria and only two such events among 87 patients with normal UAE (P < 0.0002). Stepwise logistic regression analysis showed that UAE, cholesterol level, and diastolic blood pressure were independent predictors of the cardiovascular outcome. Rate of creatinine clearance from patients with microalbuminuria decreased more than that from those with normal UAE. In conclusion, these studies suggest that hypertensive individuals with microalbuminuria manifest a variety of biochemical and hormonal derangements with pathogenic potential, which results in hypertensive patients having a greater incidence of cardiovascular events and a greater decline in renal function than patients with normal UAE.

Microalbuminuria in essential hypertension

Microalbuminuria is frequently seen in patients with established essential hypertension, and is a predictor of a higher risk for cardiovascular and probably renal dysfunction. The presence of microalbuminuria has been shown to correlate with the other cardiovascular risk factors commonly seen in hypertensive patients. This fact indicates that the detection of an increased urinary albumin excretion could probably be the best index of an increased global cardiovascular risk in a given patient. Blood pressure control is accompanied by a fall in the content of albumin in urine. Agents with the capacity to block the renin-angiotensin system have shown a capacity to decrease urinary albumin excretion, which is independent of their ability to lower blood pressure. Whether or not a decrease in urinary albumin excretion is accompanied by an improved renal and cardiovascular prognosis in hypertensive patients remains to be elucidated.

Ambulatory blood pressure and urinary albumin excretion in clinically healthy subjects

A slightly elevated urinary albumin excretion rate (UAER) is a predictor of atherosclerotic cardiovascular disease. The mechanism is unknown, but moderate office blood pressure elevation has been demonstrated as part of a clustering of known atherosclerotic risk factors in subjects with elevated UAER. Because 24-hour ambulatory blood pressure is a superior predictor of hypertensive target organ involvement, we aimed to investigate blood pressure profile in clinically healthy subjects with elevated UAER. Ambulatory blood pressure monitoring was performed with a portable recorder in 27 subjects with an elevated UAER (>6.6 microg/min, overnight urine collection) and 46 normoalbuminuric control subjects. Mean+/-SD systolic and diastolic ambulatory blood pressures (24-hour) were significantly higher in subjects with elevated UAER than in normoalbuminuric controls (134+/-12 versus 128+/-11 mm Hg and 78+/-7 versus 75+/-6 mm Hg, P<0.05), as were systolic and diastolic blood pressure loads [median (range): 42% (6 to 94%) versus 23% (1 to 89%) and 20% (0 to 68%) versus 6% (0 to 62%), P<0.05]. The circadian variation of blood pressure was normal in subjects with elevated UAER. However, the increased urinary loss of albumin could not be solely related to the higher blood pressure. In conclusion, apparently healthy subjects with elevated UAER had slightly but significantly higher 24-hour systolic and diastolic blood pressure levels in addition to increased blood pressure loads but normal circadian variation. The demonstrated differences in blood pressure may offer a partial explanation for the association between elevated urinary albumin excretion and atherosclerotic cardiovascular risk.