Proteinuria: an underappreciated risk factor in cardiovascular disease

Early Diagnosis and Treatment of Kidney Injury: A Focus on Urine Protein

The kidney, an essential excretory organ of the body, performs a series of crucial physiological functions such as waste removal, maintenance of electrolyte and acid-base balance, and endocrine regulation. Due to its rich blood flow and high metabolic activity, the kidney is susceptible to damage. Currently, kidney injury is classified into acute kidney injury (AKI) and chronic kidney disease (CKD), both of which are associated with high rates of morbidity and mortality on a global scale. The current clinical diagnosis of renal injury relies on the assessment of renal filtration function using creatinine and urea nitrogen as "gold-standard" markers. However, the delayed response time, limited specificity, and reduced accuracy of creatinine and urea nitrogen in evaluating kidney injury have significantly hindered advancements in diagnostic methods for kidney injury. Urinary protein is widely utilized as a biomarker for the early diagnosis of kidney injury due to the selectivity of the glomerular filtration system determining whether proteins can pass through the filtration barrier based on their size and charge. Therefore, as a complex biological sample with varying charges and particle sizes, urinary protein is considered an ideal indicator for monitoring the progression of kidney disease. Exploring the relationship between urinary protein and the advancement of kidney injury based on differences in particle size and charge offers a new perspective for assessing and treating such injuries. Hence, we conducted a comprehensive review of 74 relevant studies to gain a thorough understanding of the physiological mechanism and significance of proteinuria production. The aim was to explore the challenges and opportunities in clinical urine protein detection, as well as to discuss strategies targeting glomerular filtration barriers in order to effectively reduce urine protein levels and treat kidney injury, which could provide a new perspective for identifying the progression of kidney injury.

Cardiac functions in children with steroid-sensitive nephrotic syndrome

BACKGROUND

The aim of the present study was to evaluate the presence of cardiac systolic and diastolic dysfunction in pediatric patients with steroid-sensitive nephrotic syndrome (NS).

METHODS

The study population consisted of 19 patients with debut-relapse of NS aged 1-18 years and 30 sex and age-matched healthy controls. Blood and urine samples, two M-mode conventional echocardiograms and tissue Doppler velocity imaging were evaluated in both attack and remission periods.

RESULTS

With regard to conventional pulse wave Doppler (cPWD), steroid-sensitive NS patients (both in debut / relapse and in remission periods) had a higher peak of late diastolic flow velocities (A peak), and patients in debut / relapse had a lower E/A ratio than the control group, indicating diastolic dysfunction (overall P = 0.003 and P = 0.006, respectively). Based on tissue Doppler velocity imaging echocardiography results, patients in debut/relapse had a higher A' and a lower E'/A' ratio (overall P < 0.001 and P = 0.001, respectively). There was also a significant difference in the cPWD E/TDI E' ratio between the patients showing an increased cPWD E/TDI E' ratio in remission periods compared to in debut/relapse periods (P = 0.09). The albumin levels were positively correlated with E'/A' and E/ E' ratio (r = 0.609; P = 0.007, r = 0.472; P = 0.041 respectively).

CONCLUSIONS

Systolic cardiac functions are preserved but diastolic functions are affected in steroid-sensitive NS patients both in debut/relapse and in remission periods in a relatively short time. The persistence of left ventricular (LV) dysfunction during the remission period requires special attention during the follow up for early detection of cardiac abnormalities.

Serum endocan levels, carotid intima-media thickness and microalbuminuria in patients with newly diagnosed hypertension

Background: Endocan is a particular protein of endothelial cells. The purpose of this study was to determine the relationship of serum endocan levels with carotid intima-media thickness (cIMT), inflammation, and microalbuminuria in patients with newly-diagnosed hypertension.Materials-Methods: This prospective study included 61 patients with newly-diagnosed hypertension (HT) and 30 controls. Endocan, microalbuminuria and cIMT measurements were taken from all patients.Results: The serum endocan levels, the mean cIMT and microalbuminuria levels of patients with HT were significantly higher than those of the control group (p < .0001, p = .015 and p < .001, respectively).Conclusion: We found that endocan levels were increased in our study. This increase in endocan levels shows a relation with cIMT and microalbuminuria, which are associated with endothelial dysfunction.

Proteinuria and its relation to cardiovascular disease

Chronic kidney disease (CKD) and its associated morbidity pose a worldwide health problem. As well as risk of endstage renal disease requiring renal replacement therapy, cardiovascular disease is the leading cause of premature death among the CKD population. Proteinuria is a marker of renal injury that can often be detected earlier than any tangible decline in glomerular filtration rate. As well as being a risk marker for decline in renal function, proteinuria is now widely accepted as an independent risk factor for cardiovascular morbidity and mortality. This review will address the prognostic implications of proteinuria in the general population as well as other specific disease states including diabetes, hypertension and heart failure. A variety of pathophysiological mechanisms that may underlie the relationship between renal and cardiovascular disease have been proposed, including insulin resistance, inflammation, and endothelial dysfunction. As proteinuria has evolved into a therapeutic target for cardiovascular risk reduction in the clinical setting we will also review therapeutic strategies that should be considered for patients with persistent proteinuria.

Effects of weight loss on renal function in obese CKD patients: a systematic review

Obesity is an independent risk factor for the development and progression of chronic kidney disease (CKD). We conducted a systematic review to assess the benefits of intentional weight loss in obese subjects with altered glomerular filtration rate (GFR), proteinuria or albuminuria. MEDLINE, EMBASE and CENTRAL databases were searched for articles reporting longitudinal data on the effect of weight loss on renal parameters in obese patients with altered kidney function. Thirty-one (2013 subjects) were included. In the 13 studies where weight loss was achieved by bariatric surgery, body mass index (BMI) significantly decreased in all studies; GFR decreased in six studies on hyperfiltration patients and increased in one study on patients with CKD Stage 3-4. Albuminuria decreased in six studies and proteinuria decreased in five studies. In six studies, weight loss was achieved by antiobesity agents: BMI decreased in all studies; GFR decreased in four studies and albuminuria in three. Eleven studies analysed the effects of diet, alone or in combination with lifestyle modifications. A significant decrease in BMI was reported in all studies; GFR increased in two studies, remained stable in four studies and decreased in two studies on hyperfiltration patients. Albuminuria decreased in six studies and remained stable in one study. Proteinuria decreased in five studies. In obese patients with altered renal function, weight loss, particularly if achieved by surgical interventions, improves proteinuria, albuminuria and normalizes GFR. Larger, long-term studies are needed to analyse the durability of this improvement and the effects on renal outcomes, such as CKD progression and the development of ESKD.

Genetic analysis of albuminuria in collaborative cross and multiple mouse intercross populations

Albuminuria is an important marker of nephropathy that increases the risk of progressive renal and chronic cardiovascular diseases. The genetic basis of kidney disease is well-established in humans and rodent models, but the causal genes remain to be identified. We applied several genetic strategies to map and refine genetic loci affecting albuminuria in mice and translated the findings to human kidney disease. First, we measured albuminuria in mice from 33 inbred strains, used the data for haplotype association mapping (HAM), and detected 10 genomic regions associated with albuminuria. Second, we performed eight F(2) intercrosses between genetically diverse strains to identify six loci underlying albuminuria, each of which was concordant to kidney disease loci in humans. Third, we used the Oak Ridge National Laboratory incipient Collaborative Cross subpopulation to detect an additional novel quantitative trait loci (QTL) underlying albuminuria. We also performed a ninth intercross, between genetically similar strains, that substantially narrowed an albuminuria QTL on Chromosome 17 to a region containing four known genes. Finally, we measured renal gene expression in inbred mice to detect pathways highly correlated with albuminuria. Expression analysis also identified Glcci1, a gene known to affect podocyte structure and function in zebrafish, as a strong candidate gene for the albuminuria QTL on Chromosome 6. Overall, these findings greatly enhance our understanding of the genetic basis of albuminuria in mice and may guide future studies into the genetic basis of kidney disease in humans.

Evaluation of right ventricle function in children with primary nephrotic syndrome

BACKGROUND

We aimed to evaluate right ventricle (RV) function in children with primary nephrotic syndrome (PNS).

METHODS

RV hemodynamics were evaluated by Doppler echocardiography in 50 children with PNS (aged 2.5-12 years), either at PNS onset (n = 37) or relapse (n = 13), and in 50 normal controls. Heart rate, stroke volume, cardiac output, RV enddiastolic and end-systolic volume, RV ejection fraction, RV end-diastolic pressure, RV peak systolic and end-systolic pressure were determined from pressure-volume loops. The maximal rates of RV pressure upstroke and fall (dP/d t(max) and dP/d t(min), respectively) were calculated. Effective pulmonary arterial elastance was calculated as end-systolic pressure divided by stroke volume. Plasma tumor necrosis factor-alpha (TNF-alpha) and insulin-like growth factor 1 (IGF-1) were also measured.

RESULTS

RV end-diastolic pressure was increased by an average of 20% in 39 of the patients with PNS, whereas RV ejection fraction was reduced by an average of 15% compared with controls (p < 0.05 for both). Cardiac output and stroke volume were maintained, indicating compensation at the expense of increased RV end-diastolic and end-systolic volumes and increased RV filling pressure (p < 0.05). Plasma TNF-alpha was elevated in patients with PNS (326 +/- 117 kU/L vs. 75 +/- 23 kU/L, p < 0.05); IGF-1 was similar in PNS patients and controls.

CONCLUSION

Right ventricle function was impaired in children with PNS. The characteristics were unrelated to blood pressure and IGF-1, but may be correlated with TNF-alpha and disease duration. Further studies are needed to evaluate the etiology and clinical implications of this abnormality.

Cardiac dysfunction in HgCl2-induced nephrotic syndrome

The experimental model of HgCl2 injection is characterized by a systemic autoimmune disease which leads to the development of nephrotic syndrome (NS). NS seems to be accompanied by cardiovascular alterations, since patients with NS present an increased incidence in cardiac disease. The aim of our work was to study the effects of HgCl2-induced NS on myocardial function and morphometry. Normotensive Brown–Norway rats were injected with HgCl2 (1 mg/kg, HgCl2 group; n = 6, subcutaneous) or the vehicle (control group; n = 6, subcutaneous) on days 0, 2, 4, 7, 9 and 11. The animals were placed in metabolic cages for evaluation of urinary excretion of noradrenaline, sodium, total proteins, albumin and creatinine. Fourteen and 21 days after the first HgCl2 injection, left ventricle (LV) hemodynamics was evaluated through pressure micromanometers in basal and isovolumetric heartbeats. The heart and gastrocnemius muscle weights and tibial length were also examined. In an additional group of animals cardiac dimensions and ejection fraction were assessed by echocardiography and LV apoptosis and fibrosis were studied. HgCl2-injected rats presented proteinuria, albuminuria, hyperlipidemia, anemia, sodium retention and ascites at day 14. These alterations were accompanied by LV hemodynamic changes only in isovolumetric heartbeats. Similarly, on day 21, HgCl2-injected rats presented proteinuria, albuminuria, hyperlipidemia, anemia, but no sodium retention or ascites. These animals presented LV systolic and diastolic dysfunction in both basal and isovolumetric heartbeats, as well as cardiac atrophy, LV fibrosis and an increase in myocyte apoptosis. In conclusion, HgCl2-induced NS is accompanied by LV dysfunction and can be a promising model for studying the link between NS and cardiac disease.

Protein and albumin-to-creatinine ratios in random urines accurately predict 24 h protein and albumin loss in patients with kidney disease

BACKGROUND

Random urine protein-to-creatinine (PCR) and albumin-to-creatinine (ACR) ratios have been proposed as alternatives to 24 h urine measurements to simplify sample collection and overcome errors. The aim of this study was to examine the ability of PCR and ACR to predict urinary 24 h protein and albumin loss, respectively, in patients with kidney disease, and determine the most appropriate time of collection.

METHODS

Eighty-three patients were recruited from a renal outpatient clinic. In a 24 h period, each collected an early-morning urine (EMU), second and third voids, and the remaining urine passed that day. PCR and ACR were determined in random urines and compared with the 24 h loss of protein and albumin, respectively.

RESULTS

For all patients, median (range) 24 h urine protein and albumin losses were 220 (30-15600) and 60 (<8-10,557) mg, respectively. Ratios derived from each of three random urines correlated well with 24 h protein or albumin loss (Spearman's r(s) > 0.87, P < 0.0001). Receiver operator characteristic (ROC) curve analysis showed PCR accurately predicted both an abnormal 24 h urine protein > or =150 mg/24 h (areas under curves [AUC] 0.90-0.92) and significant proteinuria above 300 mg/24 h (AUC between 0.97 and 1.00). ACR accurately predicted both an abnormal 24 h urine albumin > or =30 mg/24 h (AUC 0.98 to 0.99) and frank albuminuria at > or =300 mg/24 h or > or =700 mg/24 h (AUC between 0.99 and 1.00). EMU and random urines performed equally well in predicting proteinuria and albuminuria from PCR and ACR, respectively.

CONCLUSIONS

By careful choice of cut-offs, both PCR and ACR can be used in patients with kidney disease to rule in or rule out abnormal 24 h losses of protein and albumin. EMU and, importantly, random samples can be used as surrogates for 24 h urine collections.

Genetic analysis of albuminuria in a cross between C57BL/6J and DBA/2J mice

Chronic kidney disease (CKD) is a growing medical problem and a significant risk factor for the development of end-stage renal disease, cardiovascular disease, and cardiovascular mortality. The genetic basis of CKD is recognized, but knowledge of the specific genes that contribute to the onset and progression of kidney disease is limited, mainly because of the difficulty and expense of identifying genes underlying CKD in humans. Results from genetic studies of CKD in rodents often correspond to findings in humans; therefore, we used quantitative trait locus (QTL) analysis to detect genomic regions affecting albuminuria in a cross between C57BL/6J and DBA/2J mice, strains resistant and susceptible to CKD, respectively. We identified several independent and interacting loci affecting albuminuria, including one QTL on mouse chromosome (Chr) 2 that is concordant with QTL influencing urinary albumin excretion on rat Chr 3 and diabetic nephropathy on human Chr 20p. Because this QTL was identified in multiple mouse crosses, as well as in rats and in humans, we used comparative genomics, haplotype analysis, and expression profiling to narrow the initial QTL interval from 386 genes to 10 genes with known coding sequence polymorphisms or expression differences between the strains. These results support the continued use of multiple cross-mapping and cross-species comparisons to further our understanding of the genetic basis of kidney disease.

Mechanisms of target organ damage caused by hypertension: therapeutic potential

Hypertension is a major risk factor for cardiovascular mortality and morbidity through its effects on target organs like the brain, heart, and kidney. Structural alterations in the microcirculation form a major link between hypertension and target organ damage. In this review, we describe damages related to hypertension in these target organs and the mechanisms involved in the pathogenesis of hypertension-induced cardiovascular diseases such as dementia, cardiac ischemia and remodeling, or nephropathy. We also focus on the therapeutical potential on the basis of such mechanisms. Several antihypertensive agents like diuretics, angiotensin converting enzyme (ACE) inhibitors, angiotensin II (Ang II) receptor antagonists, beta-blockers, or calcium channel blockers (CCBs) have been shown to reduce effectively hypertension associated cardiovascular events and to improve end organ damage. More recently, aldosterone antagonism has also shown beneficial effects. Part of the favorable effects of these agents is due to blood pressure lowering as such. Other mechanisms such as oxidative stress, inflammation, or endothelial dysfunction have appeared to play a key role in the pathogenesis of target organ damage and therefore represent another important pathway for therapy. In this review, we discuss the different therapeutic approaches aiming at reducing cardiovascular events and damages induced by hypertension.

Factors associated with frequent remission of microalbuminuria in patients with type 2 diabetes

To estimate the frequency of remission/regression of microalbuminuria and to identify factors affecting such outcomes in Japanese patients with type 2 diabetes, we observed 216 patients with type 2 diabetes and microalbuminuria enrolled during an initial 2-year evaluation period for the next 6 years. Remission was defined as shift to normoalbuminuria and regression as a 50% reduction in urinary albumin excretion rate (AER) from one 2-year period to the next. Reduction of urinary AER was frequent, with a 6-year cumulative incidence of 51% (95% CI 42-60) for remission and 54% (45-63) for regression, whereas the frequency of progression to overt proteinuria was 28% (19-37). Microalbuminuria of short duration, the use of renin-angiotensin system-blocking drugs, and lower tertiles for HbA(1c) (<6.95%) and systolic blood pressure (<129 mmHg) were independently associated with remission or regression in the pooled logistic regression analysis. The results indicate that reduction in urinary AER occurs frequently in Japanese patients with type 2 diabetes. Early detection of microalbuminuria and a multifactorial control may result in improved outcomes for diabetic nephropathy and cardiovascular events.

Renal disease in cardiovascular disorders: an underrecognized problem

Chronic renal disease is generally appreciated as a major and rapidly growing health problem. In the United States alone, as many as 19.5 million people may have markers of early renal disease, and more than 660,000 people are expected to require renal replacement therapy by the year 2010. By contrast, the presence and pathological role of renal disease in patients with cardiovascular disease are somewhat underrecognized. Evidence now shows that even minor impairments in renal function, as indicated by measures including glomerular filtration rate and microalbuminuria, are common in cardiovascular disease states and predictive of cardiovascular events. Indeed, microalbuminuria may be a marker of systemic vascular disease rather than kidney dysfunction alone. In patients with hypertension, diabetes, metabolic syndrome, acute coronary syndromes, and stroke, markers of renal disease have proved to be at least as predictive of morbidity and mortality as conventional risk factors. Yet, chart reviews in a variety of clinical settings reflect poor recognition and management of renal disease in at-risk patients. Models for renal protection are based on the control of risk factors, particularly blood pressure, that are associated with renal and cardiovascular outcomes. Screening protocols for markers of renal disease should recognize the potential inaccuracy of serum creatinine concentrations and the preferability of glomerular filtration rate estimates that take age and gender into account. Pilot programs for screening high-risk populations have shown efficacy in detecting renal disease.

Unraveling the genetics of chronic kidney disease using animal models

Identifying genes underlying common forms of kidney disease in humans has proven difficult, expensive, and time consuming. Quantitative trait loci (QTL) for several complex traits are concordant among mice, rats, and humans, suggesting that genetic findings from these animal models are relevant to human disease. Therefore, we reviewed the literature on genetic studies of kidney disease in rat and mouse and examined the concordance between kidney disease QTL across species. Fifteen genomic regions contribute to kidney disease in the rat, with 12 replicated either in a separate rat cross or in another species. Five loci found in humans were concordant to QTL found in the rat. Two of these were found by homology to a previously identified rat QTL on chromosome 1, demonstrating that kidney disease loci in animal models can predict the location of kidney disease loci in humans. In contrast to the rat, the mouse has been underutilized in the genetic analysis of polygenic kidney disease, although mutagenesis and QTL analysis in the mouse are likely to contribute new findings in the near future. Knowledge of kidney disease loci conserved between the mouse and rat will identify prime candidate loci to test for association with chronic kidney disease in humans.

Cardiac disease in children with primary glomerular disorders-role of focal segmental glomerulosclerosis

Anecdotal reports suggest a higher frequency of serious cardiac complications, particularly cardiomyopathy and congestive heart failure (CHF), in children with focal segmental glomerulosclerosis (FSGS). We report the occurrence of cardiac disease in children with FSGS compared with other glomerular causes of primary nephrotic syndrome (NS). A chart review was performed on all patients evaluated at the Schneider Children's Hospital between 1985 and 2003 with a diagnosis of membranoproliferative glomerulonephritis (MPGN), membranous nephropathy (MN), focal global glomerulosclerosis (FGGS), and FSGS. Clinical and demographic data were compiled, specifically whether or not the patient had clinically evident cardiac disease. The blood pressure (BP) and hematocrit in patients with FSGS and chronic renal failure (CRF) (glomerular filtration rate <30 ml/min per 1.73 m(2)) in the 3 months prior to the development of cardiac complications were compared with the values in FSGS patients with CRF but no cardiac complications, and in patients with the other causes of primary NS in whom CRF developed. There were 48 patients with FSGS, 22 with MPGN, 19 with MN, and 4 with FGGS. Cardiac disease occurred in 6 children (mean age 11 years), all with FSGS. Four of these patients were black and 5 were female. CHF occurred in all patients, cardiomyopathy in 4, and left ventricular hypertrophy in 5 patients. There was no significant difference in the BP and the hematocrit levels between the 6 patients with both FSGS and cardiac disease, 3 patients with FSGS and CRF but no cardiac disease, and the 5 patients with the other glomerulopathies in whom CRF occurred ( P>0.1). Our findings suggest that there is a clinical association between FSGS and cardiac disease in pediatric patients. We speculate that the immune mechanism responsible for the development of FSGS may also affect the heart.