Disease-dependent mechanisms of albuminuria

Serum Uric Acid and Microalbuminuria: Predictors of Renal Dysfunction in Type 2 Diabetes Patients in South-Western Uganda

Background Type 2 diabetes (T2D) is a chronic metabolic disorder characterized by insulin resistance and high blood glucose levels, which has become a global pandemic in recent decades and is associated with several health complications, including renal dysfunction. Serum uric acid levels are associated with kidney damage and have been linked to various health conditions. Urine microalbumin is a sensitive marker of kidney damage and is commonly used to monitor renal dysfunction in diabetes. The study aimed to compare the predictive value of serum uric acid and urine microalbumin in detecting kidney damage among T2D patients. Method This secondary data analysis used a cross-sectional dataset of 140 diabetic patients from Mbarara Regional Referral Hospital (MRRH) in Mbarara, Uganda. The main outcome was renal dysfunction, defined as estimated glomerular filtration rate (eGFR) <60 mL/min/1.73m². Key variables included serum uric acid, urinary microalbumin, and various demographic and clinical factors. Data were analyzed using logistic regression and receiver operating characteristic (ROC) curve analysis to evaluate predictive performance. Ethics approval was obtained from the Mbarara University Research Ethics Committee. Results This study involved 140 participants with a median age of 53 years (interquartile range (IQR) 44-60.5), predominantly females (95, 67.9%), primarily educated (76, 54.3%), and mostly married (104, 74.3%). Participants with renal dysfunction were older (median age 61 years, IQR 52-69) compared to those without (median age 49, IQR 40-56), with significant differences in urinary microalbumin and serum uric acid levels (p <0.05). Renal dysfunction prevalence was 33.6% (95% CI: 26.2-41.9), higher in participants with diabetes duration ≥5 years, microalbuminuria, certain marital statuses, and higher diastolic blood pressure. Microalbuminuria (adjusted odds ratio (aOR) 4.71, 95% CI: 1.27-17.50, P = 0.021) and serum uric acid (aOR 1.01, 95% CI: 1.0002-1.0153, P = 0.045) were significantly associated with renal dysfunction. Other associated factors included age, female gender, and diastolic hypertension. Both biomarkers had significant predictive power for renal dysfunction (area under the curve (AUC) 0.62 and 0.65, respectively). Conclusion This study confirms the high prevalence of renal dysfunction among T2D patients, with a finding of 33.6%. The significant association between microalbuminuria and renal dysfunction, as well as the predictive capacity of serum uric acid and urinary microalbumin, highlight the importance of these biomarkers in identifying individuals at risk of kidney complications.

Urine Albumin Measurements in Clinical Diagnostics

BACKGROUND

Measurement of urine albumin is critical for diagnosis, risk classification, and monitoring of chronic kidney disease (CKD). Guidelines recommend clinical decision cutoffs for the urine albumin-to-creatinine ratio (ACR) of 30 and 300 mg/g (3 and 30 mg/mmol). However, differences among manufacturers' routine urine albumin measurement procedures have been found to exceed 40%, suggesting CKD diagnosis and risk classification may vary depending upon the specific measurement procedure implemented in the laboratory.

CONTENT

This review discusses urine albumin pathophysiology and clinical practice guideline recommendations for CKD. The review also provides recommendations for urine specimen collection and storage, and results reporting for the ACR. Recent advances in measurement techniques and development of reference systems intended to facilitate standardization of urine albumin measurements are reviewed.

SUMMARY

Urine albumin is an important measurement procedure used for diagnosis, risk classification, and management of CKD. Urine albumin results should be reported as the ACR using quantitative measurement procedures. Random urine collections used for albuminuria screening should be followed by confirmation with first morning void collections to reduce variation and increase diagnostic accuracy for urine albumin measurement. Most measurement procedures utilize immunoturbidimetric or immunonephelometric techniques. However, results vary significantly among measurement procedures, potentially resulting in differences in classification or risk assessment for CKD. The National Institute for Standards and Technology (NIST) and other laboratories are developing reference systems, including liquid chromatography-tandem mass spectrometry candidate reference measurement procedures and reference materials, to enable standardization of routine measurement procedures.

Noninvasive Advanced Cardiovascular Magnetic Resonance-Derived Fontan Hemodynamics Are Associated With Reduced Kidney Function But Not Albuminuria

BACKGROUND

Kidney disease is the most important predictor of death in patients with a Fontan circulation, yet its clinical and hemodynamic correlates have not been well established.

METHODS AND RESULTS

A total of 53 ambulatory patients with a Fontan circulation (median age, 16.2 years, 52.8% male patients) underwent advanced cardiovascular magnetic resonance assessment, including 4-dimensional flow imaging and computational fluid dynamics. Estimated glomerular filtration rate (eGFR) <90 mL/min per 1.73 m2 was observed in 20.8% and albumin-to-creatinine ratio >3 mg/mmol in 39.6%. The average eGFR decline rate was -1.83 mL/min per 1.73 m2 per year (95% CI, -2.67 to -0.99; P<0.001). Lower eGFR was associated with older age, larger body surface area at examination, longer time since Fontan procedure, and lower systemic ventricular ejection fraction. Higher albumin-to-creatinine ratio was associated with absence of fenestration at the Fontan operation, and older age and lower systemic ventricular ejection fraction at the assessment. Lower cross-sectional area of the Fontan conduit indexed to flow (r=0.32, P=0.038), higher inferior vena cava-conduit velocity mismatch factor (r=-0.35, P=0.022), higher kinetic energy indexed to flow in the total cavopulmonary connection (r=-0.59, P=0.005), and higher total cavopulmonary connection resistance (r=-0.42, P=0.005 at rest; r=-0.43, P=0.004 during exercise) were all associated with lower eGFR but not with albuminuria.

CONCLUSIONS

Kidney dysfunction and albuminuria are common among clinically well adolescents and young adults with a Fontan circulation. Advanced cardiovascular magnetic resonance-derived metrics indicative of declining Fontan hemodynamics are associated with eGFR and might serve as targets to improve kidney health. Albuminuria might be driven by other factors that need further investigation.

Protease-Activated Receptor 1-Mediated Damage of Podocytes in Diabetic Nephropathy

There is clinical evidence that increased urinary serine proteases are associated with the disease severity in the setting of diabetic nephropathy (DN). Elevation of serine proteases may mediate [Ca2+]i dynamics in podocytes through the protease-activated receptors (PARs) pathway, including associated activation of nonspecific cation channels. Cultured human podocytes and freshly isolated glomeruli were used for fluorescence and immunohistochemistry stainings, calcium imaging, Western blot analysis, scanning ion conductance microscopy, and patch clamp analysis. Goto-Kakizaki, Wistar, type 2 DN (T2DN), and a novel PAR1 knockout on T2DN rat background rats were used to test the importance of PAR1-mediated signaling in DN settings. We found that PAR1 activation increases [Ca2+]i via TRPC6 channels. Both human cultured podocytes exposed to high glucose and podocytes from freshly isolated glomeruli of T2DN rats had increased PAR1-mediated [Ca2+]i compared with controls. Imaging experiments revealed that PAR1 activation plays a role in podocyte morphological changes. T2DN rats exhibited a significantly higher response to thrombin and urokinase. Moreover, the plasma concentration of thrombin in T2DN rats was significantly elevated compared with Wistar rats. T2DNPar1-/- rats were embryonically lethal. T2DNPar1+/- rats had a significant decrease in glomerular damage associated with DN lesions. Overall, these data provide evidence that, during the development of DN, elevated levels of serine proteases promote an excessive [Ca2+]i influx in podocytes through PAR1-TRPC6 signaling, ultimately leading to podocyte apoptosis, the development of albuminuria, and glomeruli damage.

ARTICLE HIGHLIGHTS

Increased urinary serine proteases are associated with diabetic nephropathy. During the development of diabetic nephropathy in type 2 diabetes, the elevation of serine proteases could overstimulate protease-activated receptor 1 (PAR1). PAR1 signaling is involved in the development of DN via TRPC6-mediated intracellular calcium signaling. This study provides fundamental knowledge that can be used to develop efficient therapeutic approaches targeting serine proteases or corresponding PAR pathways to prevent or slow the progression of diabetes-associated kidney diseases.

Cardiorenal Syndrome: A Literature Review

Cardiorenal syndrome (CRS) is a condition characterized by the intricate two-way relationship between the heart and kidneys, which can lead to acute or chronic dysfunction in these organs. The interplay between cardiorenal connectors and both hemodynamic and non-hemodynamic factors is crucial to understanding this syndrome. The clinical importance of these interactions is evident in the changes observed in hemodynamic factors, neurohormonal markers, and inflammatory processes. Identifying and understanding biomarkers associated with CRS is valuable for early detection and enabling intervention before significant organ dysfunction occurs. This comprehensive review focuses on the clinical significance of biomarkers in the diagnosis, prognosis, and management of CRS. Finally, it highlights the necessity for further advancements in managing this condition.

Albuminuria and cardiovascular risk

Cardiovascular risk (CVR) estimation is a fundamental tool for guiding therapy. Albuminuria indicates target organ damage in an accessible, economic and non-invasive manner. Improves high-risk patient identification, especially in chronic kidney disease (CKD) and diabetes mellitus (DM). In addition, anti-albuminuric treatments may improve CVR. This would position albuminuria as a guide and therapeutic objective. Although the capacity of albuminuria as an epidemiological CVR marker in specific populations (hypertension, CKD, DM) is accepted, its profile as a risk marker in the general population and as a therapeutic target is controversial. There is ambiguous evidence regarding its predictive capacity, added to the fact that treatments such as SLGT2 blockers reduce CVR events regardless of albuminuria presence or magnitude. This review analyzes the available evidence on albuminuria as a CVR marker, a treatment goal and therapeutic guide.

The association between visceral adiposity index and decreased renal function: A population-based study

Aims

We aimed to investigate the association of visceral adiposity index (VAI) with decreased renal function in US adults.

Design and methods

Cross-sectional data were analyzed for 35,018 adults in the National Health and Nutrition Examination Survey (NHANES) 2005–2018. VAI was determined using waist circumference, body mass index (BMI), triglycerides (TGs) and high-density lipoprotein-cholesterol. Albuminuria was defined as urinary albumin-to-creatinine ratio (ACR) &gt;30 mg/g. A low estimated-glomerular filtration rate (eGFR) was defined as an eGFR lower than 60 ml/min/1.73 m2. Chronic kidney disease (CKD) was defined as either albuminuria or low-eGFR. A multivariable logistic regression analysis was utilized to explore the relationship of VAI with albuminuria, low-eGFR and CKD. Subgroup analysis and interaction tests were also conducted.

Results

A total of 35,018 participants were enrolled with albuminuria, low-eGFR, and CKD prevalence rates of 5.18, 6.42, and 10.62%, respectively, which increased with the higher VAI tertiles. After full adjustment, a positive association of VAI with albuminuria (OR = 1.03, 95% CI: 1.00, 1.06) and CKD (OR = 1.04, 95% CI: 1.02, 1.06) was observed. Participants in the highest VAI tertile had a significantly 30% increased risk for albuminuria (OR = 1.30, 95% CI: 1.07, 1.58) and a 27% increased risk for CKD (OR = 1.27, 95% CI: 1.08, 1.49) compared with those in the lowest VAI tertile. No statistically significant association between VAI and low-eGFR was detected. Subgroup analysis and the interaction term indicated that there was no significant difference among different stratifications.

Conclusion

Visceral adiposity accumulation evaluating by VAI was associated with increased likelihood of the decline in renal function.

Targeting inflammation to treat diabetic kidney disease: the road to 2030

Diabetic kidney disease (DKD) is one of the fastest growing causes of chronic kidney disease and associated morbidity and mortality. Preclinical research has demonstrated the involvement of inflammation in its pathogenesis and in the progression of kidney damage, supporting clinical trials designed to explore anti-inflammatory strategies. However, the recent success of sodium-glucose cotransporter-2 inhibitors and the nonsteroidal mineralocorticoid receptor antagonist finerenone has changed both guidelines and standard of care, rendering obsolete older studies directly targeting inflammatory mediators and the clinical development was discontinued for most anti-inflammatory drugs undergoing clinical trials for DKD in 2016. Given the contribution of inflammation to the pathogenesis of DKD, we review the impact on kidney inflammation of the current standard of care, therapies undergoing clinical trials, or repositioned drugs for DKD. Moreover, we review recent advances in the molecular regulation of inflammation in DKD and discuss potential novel therapeutic strategies with clinical relevance. Finally, we provide a road map for future research aimed at integrating the growing knowledge on inflammation and DKD into clinical practice to foster improvement of patient outcomes.

The Effect of Nerolidol Renal Dysfunction following Ischemia-Reperfusion Injury in the Rat

Efforts to decrease the deleterious effects of renal ischemia-reperfusion injury (IRI) are ongoing. Recently, there has been increasing interest in using natural phytochemical compounds as alternative remedies in several diseases. Nerolidol is a natural product extracted from plants with floral odors and has been proven to be effective for the treatment of some conditions. We investigated the effect of nerolidol in a rat model of renal IRI. Nerolidol was dissolved in a vehicle and administered orally as single daily dose of 200 mg/kg for 5 days prior to IRI and continued for 3 days post IRI. G-Sham (n = 10) underwent sham surgery, whereas G-IRI (n = 10) and G-IRI/NR (n = 10) underwent bilateral warm renal ischemia for 30 min and received the vehicle/nerolidol, respectively. Renal functions and histological changes were assessed before starting the medication, just prior to IRI and 3 days after IRI. Nerolidol significantly attenuated the alterations in serum creatinine and urea, creatinine clearance, urinary albumin and the urinary albumin-creatinine ratio. Nerolidol also significantly attenuated the alterations in markers of kidney injury; proinflammatory, profibrotic and apoptotic cytokines; oxidative stress markers; and histological changes. We conclude that nerolidol has a renoprotective effect on IRI-induced renal dysfunction. These findings might have clinical implications.

Right Heart Function in Cardiorenal Syndrome

PURPOSE OF REVIEW

Since CRS is critically dependent on right heart function and involved in interorgan crosstalk, assessment and monitoring of both right heart and kidney function are of utmost importance for clinical outcomes. This systematic review aims to comprehensively report on novel diagnostic and therapeutic paradigms that are gaining importance for the clinical management of the growing heart failure population suffering from CRS.

RECENT FINDINGS

Cardiorenal syndrome (CRS) in patients with heart failure is associated with poor outcome. Although systemic venous congestion and elevated central venous pressure have been recognized as main contributors to CRS, they are often neglected in clinical practice. The delicate hemodynamic balance in CRS is particularly determined by the respective status of the right heart. The consideration of hemodynamic and CRS profiles is advantageous in tailoring treatment for better preservation of renal function. Assessment and monitoring of right heart and renal function by known and emerging tools like renal Doppler ultrasonography or new biomarkers may have direct clinical implications.

New insights into proteinuria/albuminuria

The fractional clearance of proteins as measured in healthy human subjects increases 10,000–100,000- fold when studied in nephrotic patients. This remarkable increase cannot be accounted for by extracellular biophysical mechanisms centered at the glomerular filtration barrier. Rather, it is the nephron and its combination of filtration and cellular uptake that can provide a plausible explanation of these fractional clearance changes. The nephron has two regions that critically determine the level proteinuria/albuminuria. Glomerular filtration of plasma proteins is primarily a size selective event that is basically unchanged in acquired and genetic kidney disease. The glomerular concepts of ‘charge selectivity’ and of ‘large pores’, previously used to explain proteinuria, are now recognized to be flawed and non-existent. Filtered proteins then encounter downstream two protein receptors of the Park and Maack type associated with the proximal tubular cell. The high capacity receptor is thought to retrieve the majority of filtered proteins and return them to the blood supply. Inhibition/saturation of this pathway in kidney disease may create the nephrotic condition and hypoproteinemia/hypoalbuminemia. Inhibitors of this pathway (possibly podocyte derived) are still to be identified. A relatively small proportion of the filtered protein is directed towards a high affinity, low capacity receptor that guides the protein to undergo lysosomal degradation. Proteinuria in normoproteinemic states is derived by inhibition of this pathway, such as in diabetes. The combination of glomerular sieving, and the degradation and retrieval pathways can quantitatively account for the changes in fractional clearance of proteins in the nephrotic condition. Finally, the general retrieval of filtered protein by the proximal tubular cell focuses on the teleological importance of this cell as this retrieval represents the third pillar of retrieval that this cell participates in (it also retrieves water and salt).

Systemic Immune-Inflammation Index Is Associated With Increased Urinary Albumin Excretion: A Population-Based Study

Background

Systemic immune-inflammation index (SII) is a novel inflammatory marker, and inflammation has been reported to be related with renal damage. We aimed to investigate the possible relationship between SII and albuminuria.

Methods

The present cross-sectional study was conducted among adults with complete data about SII and urinary albumin-to-creatinine ratio (ACR) in 2005–2018 National Health and Nutrition Examination Survey (NHANES). SII was calculated as the platelet count × neutrophil count/lymphocyte count. Albuminuria was defined as ACR >30mg/g. Weighted multivariable regression analysis and subgroup analysis were conducted to explore the independent relationship between SII and albuminuria.

Results

A total of 36,463 individuals were included in our analysis; 9.56% participants were categorized as having albuminuria overall and increased with the higher SII tertiles (tertile 1, 7.83%; tertile 2, 8.49%; tertile 3, 12.13%; p for trend <0.0001). Multivariable logistic regression showed that a higher SII level was associated with increased likelihood of albuminuria independently (OR = 1.31; 95% CI, 1.17–1.48, p<0.0001) after full adjustment. Subgroup analysis and interaction test showed that there was no significant dependence of gender, age, body mass index, hypertension, diabetes, non‐alcoholic fatty liver disease, and estimated glomerular filtration rate (eGFR) on this positive association (all p for interaction >0.05).

Conclusions

SII was positively associated with increased urinary albumin excretion in US adults. Further large-scale prospective studies are still needed to analyze the role of SII in albuminuria.

Albumin Uptake and Processing by the Proximal Tubule: Physiologic, Pathologic and Therapeutic Implications

For nearly 50 years the proximal tubule (PT) has been known to reabsorb, process, and either catabolize or transcytose albumin from the glomerular filtrate. Innovative techniques and approaches have provided insights into these processes. Several genetic diseases, nonselective PT cell defects, chronic kidney disease (CKD), and acute PT injury lead to significant albuminuria, reaching nephrotic range. Albumin is also known to stimulate PT injury cascades. Thus, the mechanisms of albumin reabsorption, catabolism, and transcytosis are being reexamined with the use of techniques that allow for novel molecular and cellular discoveries. Megalin, a scavenger receptor, cubilin, amnionless, and Dab2 form a nonselective multireceptor complex that mediates albumin binding and uptake and directs proteins for lysosomal degradation after endocytosis. Albumin transcytosis is mediated by a pH-dependent binding affinity to the neonatal Fc receptor (FcRn) in the endosomal compartments. This reclamation pathway rescues albumin from urinary losses and cellular catabolism, extending its serum half-life. Albumin that has been altered by oxidation, glycation, or carbamylation or because of other bound ligands that do not bind to FcRn traffics to the lysosome. This molecular sorting mechanism reclaims physiological albumin and eliminates potentially toxic albumin. The clinical importance of PT albumin metabolism has also increased as albumin is now being used to bind therapeutic agents to extend their half-life and minimize filtration and kidney injury. The purpose of this review is to update and integrate evolving information regarding the reabsorption and processing of albumin by proximal tubule cells including discussion of genetic disorders and therapeutic considerations.

Single and joint impact of type 2 diabetes and of congestive heart failure on albuminuria

AIMS

Albuminuria is a characteristic feature of diabetic nephropathy, and urine albumin excretion is also increased in patients with congestive heart failure (CHF). However, no data are available on the single and joint associations of type 2 diabetes mellitus (T2DM) and CHF with albuminuria. This issue was addressed in the present study.

METHODS

We investigated 4 groups of patients: 180 patients with CHF, of whom 83 had T2DM (CHF+/T2DM+) and 97 did not have diabetes (CHF+/T2DM-) and 223 controls without CHF, of whom 39 had T2DM (CHF-/T2DM+) and 184 did not have diabetes (CHF-/T2DM-).

RESULTS

The albumin-creatinine ratio (ACR) was 9.2 [5.7-16.9] mg/g in CHF-/T2DM- patients. Compared to this group it was higher in CHF-/T2DM+ patients (16.1 [7.7-27.8] mg/g; p = 0.004), in CHF+/T2DM- patients (22.0 [9.0-76.8] mg/g; p < 0.001) and in CHF+/T2DM+ patients (66.2 [16.0-177.0] mg/g; p < 0.001), in whom in turn it was higher than in CHF-/T2DM+ (p < 0.001) or in CHF+/T2DM- (p = 0.001) patients. The ACR did not differ significantly between CHF-/T2DM+ and CHF+/T2DM- patients (p = 0.188). In multivariate analysis of covariance, CHF and T2DM proved to be independent predictors of ACR after multivariate adjustment (F = 5.68; p = 0.018 and F = 4.79; p = 0.029, respectively).

CONCLUSIONS

We conclude that T2DM and CHF are mutually independent determinants of albuminuria.

Biomarkers in Cardiorenal Syndrome

Cardiorenal syndrome is a clinical manifestation of the bidirectional interaction between the heart and kidney diseases. Over the last years, in patients with cardiovascular diseases, several biomarkers have been studied in order to better assess renal function as well as to identify patients prone to experiencing chronic or acute worsening of renal function. The aim of this review is to focus on the possible clinical usefulness of the most recent biomarkers in the setting of cardiorenal syndrome.

Comparing different markers of tubular dysfunction in transfusion-dependent thalassemia patients

BACKGROUND

Renal tubular dysfunction was reported in transfusion-dependent thalassemia (TDT) patients and ranges from mild to severe. The objectives of our study were identification of the best marker of early renal tubular dysfunction in TDT patients among the three most commonly used urinary biomarkers, named neutrophil gelatinase-associated lipocalin (NGAL), retinol-binding protein (RBP) and N-acetyl-D-glucosaminidase (NAG) and correlation of these biomarkers with different patient variables.

METHODOLOGY

Sixty-one TDT patients and another 62 healthy children were enrolled in a cross-sectional study. Morning urine samples were taken for measurement of calcium, phosphorus, creatinine, microalbumin and markers of tubular dysfunction (NGAL, NAG and RBP). Urine NGAL/creatinine (UrNGAL/Cr), urine NAG/creatinine (UrNAG/Cr) and urine RBP/creatinine (UrRBP/Cr) ratios were used for accuracy. Patients were classified into 2 groups: group A, with tubular dysfunction and group b, without tubular dysfunction.

RESULTS

Group A showed statistically significant higher UrNGAL/Cr (p < 0.001), UrRBP/Cr (p < 0.001) and UrNAG/Cr (p <0.001) than group B. In group A, microalbuminuria was detected only in 7 patients (28%) while it was detected in 12 patients (33.3%) in group B. By using ROC curve analysis, the diagnostic cutoff values for UrNGAL/Cr, UrRBP/Cr and UrNAG/Cr were 3713.38, 1614.85 and 56.56 ng/g, respectively. We found a statistically significant superiority of UrNGAL/Cr over UrRBP/Cr (p < 0.001) and UrRBP/Cr over UrNAG/Cr (p < 0.001).

CONCLUSION

Evaluation of UrNGAL/Cr, UrRBP/Cr and UrNAG/Cr could early discriminate tubular dysfunction TDT patients from those with normal tubular function. UrNGAL/Cr is more accurate in early detection of tubular dysfunction when compared with the other two biomarkers.

Renal Handling of Albumin-From Early Findings to Current Concepts

Albumin is the main protein of blood plasma, lymph, cerebrospinal and interstitial fluid. The protein participates in a variety of important biological functions, such as maintenance of proper colloidal osmotic pressure, transport of important metabolites and antioxidant action. Synthesis of albumin takes place mainly in the liver, and its catabolism occurs mostly in vascular endothelium of muscle, skin and liver, as well as in the kidney tubular epithelium. Long-lasting investigation in this area has delineated the principal route of its catabolism involving glomerular filtration, tubular endocytic uptake via the multiligand scavenger receptor tandem—megalin and cubilin-amnionless complex, as well as lysosomal degradation to amino acids. However, the research of the last few decades indicates that also additional mechanisms may operate in this process to some extent. Direct uptake of albumin in glomerular podocytes via receptor for crystallizable region of immunoglobulins (neonatal FC receptor) was demonstrated. Additionally, luminal recycling of short peptides into the bloodstream and/or back into tubular lumen or transcytosis of whole molecules was suggested. The article discusses the molecular aspects of these processes and presents the major findings and controversies arising in the light of the research concerning the last decade. Their better characterization is essential for further research into pathophysiology of proteinuric renal failure and development of effective therapeutic strategies.

Relationship between High Blood Pressure and Microalbuminuria in Children Aged 6-9 Years in a South African Population

Though the association between high blood pressure and microalbuminuria is well established in adults, there is a paucity of information on microalbuminuria in children. This study investigated the relationship between high blood pressure and microalbuminuria in 6-9-year-old children. A cross-sectional study, which included 306 primary school children of age 6-9 years old from urban areas (n = 154) and rural areas (n = 152) of the Eastern Cape Province of South Africa, was conducted. Participants' anthropometric data were determined and systolic blood pressure (SBP), diastolic blood pressure (DBP) and heart rate (HR) were measured and converted to BP percentiles for age, sex and height. Creatinine and albumin concentrations were assayed in early morning midstream urine and the albumin to creatinine ratio (ACR) was calculated. There was a 42.8% prevalence of elevated blood pressure/high blood pressure (E-BP/H-BP) and a 10.1% prevalence of microalbuminuria. Among the 131 children with E-BP/H-BP, 17 had elevated ACR with a prevalence of 13.95%. SBP and HR increased with increasing range of ACR and, furthermore, SBP was significantly (p < 0.05) higher in children with moderately and severely increased ACR. SBP was associated with ACR and increased SBP predicted microalbuminuria (R2 = 0.42, adj R2 = 0.039, B: 0.120, p = < 0.05). In conclusion, microalbuminuria was present in 6-9-year-old South African children of African Ancestry and a weak association was observed with SBP in children.

Despite initial recovery of GFR, long-term renal functions deteriorate following short periods of unilateral ureteral obstruction

Following the release of short periods of unilateral ureteral obstruction (UUO), glomerular filtration rate (GFR) recovers by time. However, research in experimental animal models has demonstrated the presence of an ongoing element of renal interstitial fibrosis a few weeks following UUO reversal. Interstitial fibrosis can cause deterioration in GFR, and it is not known whether it leads to an ongoing slow deterioration in other renal functions despite the apparent initial recovery postreversal. To investigate this, rats underwent a 72-h reversible UUO. Renal functions of nonobstructed and previously obstructed kidneys were measured 1, 4, and 18 mo postreversal. GFR in nonobstructed and previously obstructed kidneys was similar up to 18 mo postreversal. However, there was ongoing tubulointerstitial fibrosis, and the degree of tubular atrophy and dilatation deteriorated by time. This was associated with an increase in urinary albumin leakage and alterations in renal injury markers, proinflammatory and profibrotic cytokines, and p53 from 4 mo onward despite the recovery in GFR. In conclusion, several aspects of renal functions continue to deteriorate following reversal of relatively short periods of UUO despite the initial recovery in GFR. This might stimulate further research in this area and might have clinical implications in terms of determining the best time for intervention following acute ureteral obstruction and long-term monitoring of these individuals.

A cellular model of albumin endocytosis uncovers a link between membrane and nuclear proteins

Cubilin (CUBN) and amnionless (AMN), expressed in kidney and intestine, form a multiligand receptor complex called CUBAM that plays a crucial role in albumin absorption. To date, the mechanism of albumin endocytosis mediated by CUBAM remains to be elucidated. Here, we describe a quantitative assay to evaluate albumin uptake by CUBAM using cells expressing full-length CUBN and elucidate the crucial roles of the C-terminal part of CUBN and the endocytosis signal motifs of AMN in albumin endocytosis. We also demonstrate that nuclear valosin-containing protein-like 2 (NVL2), an interacting protein of AMN, is involved in this process. Although NVL2 was mainly localized in the nucleolus in cells without AMN expression, it was translocated to the extranuclear compartment when coexpressed with AMN. NVL2 knockdown significantly impaired internalization of the CUBN-albumin complex in cultured cells, demonstrating an involvement of NVL2 in endocytic regulation. These findings uncover a link between membrane and nucleolar proteins that is involved in endocytic processes.

Risk factors and urinary biomarkers of non-albuminuric and albuminuric chronic kidney disease in patients with type 2 diabetes

BACKGROUND

A number of recent studies indicate a transformation in the natural course of chronic kidney disease (CKD) in type 2 diabetes (T2D) patients: an increasing prevalence of declined renal function without proceeding to the accompanying elevation of albuminuria. It has been suggested that albuminuric and non-albuminuric CKD patterns could be different in their phenotypes and pathogenic mechanisms.

AIM

To identify the risk factors and biomarkers of albuminuric and non-albuminuric patterns of CKD in patients with T2D.

METHODS

Three hundred sixty patients with T2D duration ≥ 10 years were included in this observational cross-sectional study. The associations of a panel of demographic and clinical characteristics, complications, comorbidities, and metabolic and hematology parameters with albuminuric and non-albuminuric CKD patterns were analyzed. The urinary excretion of nephrin and podocin, two podocyte-specific markers, and WAP-four-disulfide core domain protein 2 (WFDC-2), a marker of tubulointerstitial fibrosis, was determined by ELISA in comparison with healthy controls.

RESULTS

Non-albuminuric CKD was associated with age ≥ 65 years (P = 0.0001), female sex (P = 0.04), diabetes duration ≥ 15 years (P = 0.0009), and the use of diuretics (P = 0.0005). Male sex (P = 0.01), smoking (P = 0.01), waist-to-hip ratio >1.0 (P = 0.01) and hemoglobin A1c (HbA1c) > 8.0% (P = 0.005) were risk factors for elevated albuminuria not accompanied by a decrease in estimated glomerular filtration rate (eGFR). Duration of diabetes ≥ 15 years and the use of calcium channel blockers were risk factors for albuminuria with decreased eGFR (both P = 0.01). In multivariate logistic regression analysis, age, HbA1c, female sex and diuretics were significant predictors for reduced eGFR, while waist-to-hip ratio, HbA1c and male sex were associated with elevated urinary albumin-to-creatinine ratio (UACR). Excretion of nephrin and podocin was increased in patients with albuminuria, regardless of decline in renal function (P < 0.001), correlating positively with UACR. The urinary excretion of WFDC-2 was markedly higher in men than in women (P < 0.000001). Men with T2D demonstrated increased WFDC-2 levels independently of the CKD pattern (all P < 0.05). In T2D women, WFDC-2 excretion was increased in those with reduced renal function (P ≤ 0.01), correlating negatively with eGFR.

CONCLUSION

The data provide further evidence that albuminuric and non-albuminuric CKD phenotypes correspond to different pathways of diabetic kidney disease progression.

Effect of bardoxolone methyl on the urine albumin-to-creatinine ratio in patients with type 2 diabetes and stage 4 chronic kidney disease

Bardoxolone methyl attenuates inflammation by inducing nuclear factor erythroid-derived 2-related factor 2 and suppressing nuclear factor κB. The Bardoxolone Methyl Evaluation in Patients With Chronic Kidney Disease and Type 2 Diabetes (BEACON) trial was a phase 3 placebo-controlled, randomized, double-blind, parallel-group, international, multicenter trial in 2185 patients with type 2 diabetes mellitus and stage 4 chronic kidney disease. BEACON was terminated because of safety concerns, largely related to a significant increase in early heart failure events in patients randomized to bardoxolone methyl. Bardoxolone methyl resulted in increased estimated glomerular filtration rate (eGFR) and urine albumin-to-creatinine ratio. Herein, we present post hoc analyses characterizing the relation between the urine albumin-to-creatinine ratio and eGFR. The urine albumin-to-creatinine ratio and eGFR were assessed every four weeks through Week 12, followed by assessments every eight weeks thereafter, and 4 weeks after the last dose of bardoxolone methyl was administered. The initial increases in urine albumin-to-creatinine ratio observed in patients randomized to bardoxolone methyl were attenuated after six months. Multivariable regression analysis identified baseline eGFR and eGFR over time as the dominant factors associated with change in the urine albumin-to-creatinine ratio. Relative to placebo, bardoxolone methyl resulted in a significant decrease in albuminuria when indexed to eGFR (least-squared means: -0.035 [95% confidence interval -0.031 to -0.039]). Thus, among patients with type 2 diabetes mellitus and stage 4 chronic kidney disease treated with bardoxolone methyl, changes in albuminuria are directly related to changes in eGFR, challenging the conventional construct that increases in albuminuria universally reflect kidney injury and denote harm.

Association of renin-angiotensin system inhibitors with long-term outcomes in patients with systolic heart failure and moderate-to-severe kidney function impairment

PURPOSE

Although guidelines recommend that patients with heart failure with reduced ejection fraction (HFrEF) should be treated with renin-angiotensin system (RAS) inhibitors, the long-term efficacy of RAS inhibitors in HFrEF patients with moderate-to-severe chronic kidney disease (CKD) remains unclear.

METHODS

The present study included consecutive patients hospitalized for acute heart failure across five Japanese teaching hospitals. The impact of RAS inhibitors on 2-year all-cause mortality was evaluated in patients with an ejection fraction ≤40% and CKD, defined as an estimated glomerular filtration rate (eGFR) <45 mL/min/1.73 m², at discharge. Its severity was subclassified from 3B to 5 according to eGFR.

RESULTS

Overall, 553 patients (age, 76 ± 11 years; 68% male) were included. RAS inhibitors were prescribed more frequently in 227 patients with stage 3B (71.2%) than in 107 patients with stage 4 or 5 CKD (45.7%). All-cause mortality was recorded in 119 patients (23.4%) (55 [18.5%] patients with stage 3B; 64 [30.3%] patients with stage 4 or 5 CKD), within the median follow-up period of 609 (220-983) days. After many-to-one propensity score matching (87 pairs in stage 3; 60 pairs in stage 4 or 5 CKD), those with RAS inhibitors had reduced mortality rate in stage 3B (hazard ratio [HR], 0.39; 95% confidence interval [CI], 0.19-0.83) but not in stage 4 or 5 CKD (HR, 1.08; 95% CI, 0.57-2.03).

CONCLUSIONS

In HFrEF patients with CKD, RAS inhibitors are associated with reduction in mortality in stage 3B CKD, but the association is less clear in stage 4 or 5 CKD.

Rapid decline of kidney function in diabetic kidney disease is associated with high soluble Klotho levels

BACKGROUND

Klotho is found in two forms: a transmembrane form and a soluble form (s-Klotho). In order to be excreted, s-Klotho, that is too large to be filtered, will probably reach the proximal convoluted tubule by a transcytosis process. The aim of our study was to show the relationship between the levels of s-Klotho and tubular injury in patients with diabetic kidney disease (DKD), using as tubular injury marker the kidney injury molecule-1 (KIM-1).

METHODS

Our study included 63 DKD patients (stages 1-5, mean eGFR 65.15±32.45ml/min) with a mean age 58.13±12 years. In all patients we determined serum levels of: KIM-1 and s-Klotho using ELISA, urinary albumin/creatinine ratio (UACR) and reduction in the estimated glomerular filtration rate (eGFR) per year.

RESULTS

We found a strong statistically significant correlation of s-Klotho with the rate of reduction of eGFR/year (r=0.714, p=0.0004) and with the tubular injury marker KIM-1 (r=0.758, p=0.005) and strong correlations of UACR with the rate of reduction of eGFR/year (r=0.53, p<0.01), KIM-1 (r=0.49, p<0.05) and s-Klotho (r=0.52, p<0.01).

CONCLUSION

Despite previous published data, that shows a decrease of s-Klotho in chronic kidney disease, in our study the rapid annual decline of kidney function but not the level of eGFR was associated with increased s-Klotho. A possible explanation could be a more severe proximal tubule injury that could lead to a reduction of tubular excretion of s-Klotho as suggested by the correlation of s-Klotho levels with the serum levels of KIM-1.

Tubular dysfunction in extremely low birth weight survivors

BACKGROUND

Extremely low birth weight (ELBW) survivors may develop glomerulosclerosis due to low nephron number, whereas their tubular function remains unknown except for hypercalciuria and phosphaturia.

METHODS

Fifty-three subjects (30 boys and 23 girls, aged 7 months-19 years, median 36 months) were studied retrospectively. The median gestational age and birth weight were 26 weeks (range 22-32) and 745 g (range 316-999), respectively. Urine calcium-to-creatinine ratio (Ca/Cr), N-acetyl-β-D-glucosaminidase-to-creatinine ratio (NAG/Cr), β2 microglobulin-to-creatinine ratio (β2m/Cr), uric acid-to-creatinine ratio (UA/Cr), glucose-to-creatinine ratio (glu/Cr), and microalbumin-to-creatinine ratio (malb/Cr) were examined. We also assessed the association between urine parameters and current age, gestational age, birth weight, and predictors of renal injury. Follow-up data were analyzed in 43 subjects 4-6 years later.

RESULTS

Ninety percent of subjects had at least one tubular dysfunction. Frequency of elevated values was NAG/Cr 77.5%, UA/Cr 54.1%, β2m/Cr 38.2%, malb/Cr 30.4%, Ca/Cr 21.5%, and glu/Cr 20.5%. There were significant negative correlations between the current age and Ca/Cr, NAG/Cr, glu/Cr, and UA/Cr, suggesting tubular function maturation. Urine β2M/Cr and glu/Cr were negatively correlated with the gestational age. There were significant associations between elevated glu/Cr and asphyxia or neonatal acute kidney injury, and elevated NAG/Cr and indomethacin use, although these were not confirmed by multivariate analysis. At follow-up, the frequency of elevated NAG/Cr, glu/Cr, UA/Cr, and malb/Cr was reduced but that of elevated Ca/Cr, IgG/Cr, and β2m/Cr remained similar or increased.

CONCLUSION

Tubular dysfunction is common in ELBW survivors. Some abnormalities resolved with age while some remained persistent or even increased.

Visceral adiposity index is associated with increased urinary albumin excretion: A population-based study

BACKGROUND

The effects of visceral fat accumulation on the renal damage have drawn much attention. We aimed to investigate the possible relationship between visceral adiposity and albuminuria.

METHODS

We included information from a population-based study in 9473 subjects aged 40 years or older. As a novel and valid indicator for visceral adipose function, visceral adiposity index (VAI) was determined by gender-specific equations and calculated using simple anthropometric and functional parameters. Increased urinary albumin excretion was defined as albumin-to-creatinine ratio (ACR) 30 mg/g or greater.

RESULTS

The prevalence rate of increased urinary albumin excretion was 6.6% in this population and gradually increased across VAI quartiles. Participants with higher VAI had elevated age, blood pressure, cholesterol, fasting insulin and decreased high density lipoprotein cholesterol and estimated glomerular filtration rate (eGFR) level. In multivariate logistic regression analysis, the adjusted odds ratios (ORs) of increased urinary albumin excretion for increasing VAI quartiles were 1.00 (reference), 1.29 (95% confidence intervals [CI] 0.94-1.76), 1.46 (95% CI 1.08-1.97) and 1.79 (95% CI 1.33-2.41). In subgroup analysis and after multiple adjustments, significant relation between VAI level and prevalent increased urinary albumin excretion was detected in women, younger subjects, non-obesity subjects, those without diabetes and those with eGFR ≥60 ml/min per 1.73 m².

CONCLUSION

Visceral fat accumulation evaluating by VAI is independently associated with increased urinary albumin excretion in middle-aged and elderly Chinese.

Renal tubular ACE-mediated tubular injury is the major contributor to microalbuminuria in early diabetic nephropathy

Diabetic nephropathy is a major cause of end-stage renal disease in developed countries. While angiotensin-converting enzyme (ACE) inhibitors are used to treat diabetic nephropathy, how intrarenal ACE contributes to diabetic renal injury is uncertain. Here, two mouse models with different patterns of renal ACE expression were studied to determine the specific contribution of tubular vs. glomerular ACE to early diabetic nephropathy: it-ACE mice, which make endothelial ACE but lack ACE expression by renal tubular epithelium, and ACE 3/9 mice, which lack endothelial ACE and only express renal ACE in tubular epithelial cells. The absence of endothelial ACE normalized the glomerular filtration rate and endothelial injury in diabetic ACE 3/9 mice. However, these mice developed tubular injury and albuminuria and displayed low renal levels of megalin that were similar to those observed in diabetic wild-type mice. In diabetic it-ACE mice, despite hyperfiltration, the absence of renal tubular ACE greatly reduced tubulointerstitial injury and albuminuria and increased renal megalin expression compared with diabetic wild-type and diabetic ACE 3/9 mice. These findings demonstrate that endothelial ACE is a central regulator of the glomerular filtration rate while tubular ACE is a key player in the development of tubular injury and albuminuria. These data suggest that tubular injury, rather than hyperfiltration, is the main cause of microalbuminuria in early diabetic nephropathy.

Proximal tubular epithelial cells preferentially endocytose covalently-modified albumin compared to native albumin

AIM

Albumin can be covalently modified at surface lysine residues and thus the circulation contains a mixture of native albumin (i.e. not modified) and albumin with varying degrees of modification. Uptake and lysosomal degradation of glomerular filtered albumin by proximal tubular cells via the megalin scavenger receptor is considered an important mechanism to limit albumin loss in the urine. However, whether this is a general mechanism of tubular uptake of albumin or if this is restricted to modified albumin is unknown. To address this question, we investigated the uptake of modified versus native albumin by proximal tubular cells.

METHODS

A well-characterized proximal tubular cell model of albumin uptake was used to compare the uptake of modified albumin (covalent labelling of lysine residues with fluorescent probes) to that of native recombinant human albumin (rHA) labelled with ¹⁴ C during protein synthesis (¹⁴ C-rHA).

RESULTS

Opossum kidney (OK) cells showed significant uptake of fluorescence-labelled albumin via an endocytosis mechanism. This uptake was inhibited by an equimolar ratio of different types of covalently modified albumin; however, purified bovine serum albumin and rHA failed to compete with the uptake of fluorescence-labelled albumin. In contrast, OK cells failed to endocytose native ¹⁴ C-rHA despite efficiently endocytosing covalently modified rHA.

CONCLUSION

Our studies show that OK cells preferentially endocytose covalently-modified albumin compared to native albumin. This apparent selectivity of the megalin scavenger receptor complex suggests a specific role for this pathway in the removal of modified albumin from the circulation.

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

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

Intravital imaging of the kidney in a rat model of salt-sensitive hypertension

Hypertension is one of the most prevalent diseases worldwide and a major risk factor for renal failure and cardiovascular disease. The role of albuminuria, a common feature of hypertension and robust predictor of cardiorenal disorders, remains incompletely understood. The goal of this study was to investigate the mechanisms leading to albuminuria in the kidney of a rat model of hypertension, the Dahl salt-sensitive (SS) rat. To determine the relative contributions of the glomerulus and proximal tubule (PT) to albuminuria, we applied intravital two-photon-based imaging to investigate the complex renal physiological changes that occur during salt-induced hypertension. Following a high-salt diet, SS rats exhibited elevated blood pressure, increased glomerular sieving of albumin (GSC_alb = 0.0686), relative permeability to albumin (+Δ16%), and impaired volume hemodynamics (-Δ14%). Serum albumin but not serum globulins or creatinine concentration was decreased (-0.54 g/dl), which was concomitant with increased filtration of albumin (3.7 vs. 0.8 g/day normal diet). Pathologically, hypertensive animals had significant tubular damage, as indicated by increased prevalence of granular casts, expansion and necrosis of PT epithelial cells (+Δ2.20 score/image), progressive augmentation of red blood cell velocity (+Δ269 µm/s) and micro vessel diameter (+Δ4.3 µm), and increased vascular injury (+Δ0.61 leakage/image). Therefore, development of salt-induced hypertension can be triggered by fast and progressive pathogenic remodeling of PT epithelia, which can be associated with changes in albumin handling. Collectively, these results indicate that both the glomerulus and the PT contribute to albuminuria, and dual treatment of glomerular filtration and albumin reabsorption may represent an effective treatment of salt-sensitive hypertension.

Heart Failure and Kidney Disease

Kidney disease is commonly found in heart failure (HF) patients. They share many risk factors and common pathophysiological pathways which often lead to mutual dysfunction. Both haemodynamic and non-haemodynamic mechanisms are involved in the development of renal impairment in heart failure patients. Moreover, the presence of a chronic kidney disease is a significant independent predictor of worse outcome in chronic as well as in acute decompensated HF. As a consequence, an accurate evaluation of renal function plays a key role in the management of HF patients. Serum creatinine levels and glomerular filtration rate (GFR) estimates are the corner stones of renal function evaluation in clinical practice. However, to overcome their limits, several emerging glomerular and tubular biomarkers have been proposed over the last years. Alongside the renal biomarkers, imaging techniques could complement the laboratory data exploring different pathophysiological pathways. In particular, Doppler evaluation of renal circulation is a highly feasible technique that can effectively identify HF patients prone to develop renal dysfunction and with a worse outcome. Finally, some classes of drugs currently used in heart failure treatment can affect renal function and their use can be influenced by the presence of chronic kidney disease.

The Impact of Blood Pressure and Visceral Adiposity on the Association of Serum Uric Acid With Albuminuria in Adults Without Full Metabolic Syndrome

BACKGROUND

The impact of metabolic phenotypes on the association of uricemia with urinary albumin/creatinine ratio (uACR) remains unresolved. We evaluated the association between serum uric acid and uACR in persons with 0, and 1-2 metabolic syndrome (MetS) components and determined the modification effects of visceral adiposity index (VAI), mean arterial pressure (MAP), and fasting glucose on this association.

METHODS

Using data from a cross-sectional survey of a representative Czech population aged 25-64 years (n = 3612), we analyzed 1,832 persons without decreased glomerular filtration rate <60ml/min/1.73 m2, diabetes, and MetS. MetS components were defined using the joint statement of the leading societies.

RESULTS

Of the 1,832 selected participants, 64.1% (n = 1174) presented with 1-2 MetS components (age 46.3±11.2; men 51.7%), whereas 35.9% (n = 658) were free of any component (age 39.4±10.0; men 34.2 %). In fully adjusted multiple linear regression models for uricemia, uACR was an independent factor for increase in uric acid levels only in persons with 1-2 MetS components (standardized beta (Sβ) 0.048; P = 0.024); however, not in those without any component (Sβ 0.030; P = 0.264). Uric acid levels increased by the interaction of uACR with VAI (Sβ 0.06; P = 0.012), and of uACR with MAP (Sβ 0.05; P = 0.009). Finally, the association of uACR with uricemia was confined to persons whose VAI together with MAP were ≥the median of 1.35 and 98mm Hg, respectively (Sβ 0.190; P < 0.001).

CONCLUSIONS

We demonstrated a strong modification effect of VAI and MAP on the association between uACR and uricemia, which suggests obesity-related hypertension as the underlying mechanism.

Are filtered plasma proteins processed in the same way by the kidney?

In order to understand the mechanism of albuminuria we have explored how other plasma proteins are processed by the kidney as compared to inert molecules like Ficolls. When fractional clearances are plotted versus protein radius there is a remarkable parallelism between protein (molecular weight range 30-150kDa) clearance in healthy controls, in Dent's disease, in nephrotic states and the clearance of Ficolls. Although there are significant differences in the levels of fractional clearances in these states. Dent's disease results in a 2-fold increase in the fractional clearance of proteins as compared to healthy controls whereas in nephrotic states there is a further 3-fold increase in fractional clearance. Previous thinking that albumin uptake was controlled primarily by the megalin/cubilin receptor does not explain the albumin urinary excretion data and is therefore an incorrect concept. Protein clearance in nephrotic states approach the fractional clearance of inert Ficolls for a given radius. It therefore appears that there are two pathways processing these proteins. A low capacity pathway associated with megalin/cubilin that degrades filtered protein (that is inhibited in Dent's disease) and a high capacity pathway that retrieves the filtered protein and returns it to the blood supply (without retrieval nephrotic protein excretion will occur and this will account for hypoproteinemia). On the other hand low molecular weight proteins (<20kDa) are processed entirely differently by the kidney. They are not retrieved but are comprehensively degraded in the kidney with the degradation products predominantly returned to the blood supply.

Urinary N-acetyl-β-D-glucosaminidase, an early marker of diabetic kidney disease, might reflect glucose excursion in patients with type 2 diabetes

Recently, several renal tubular damage markers have gained considerable attention because of their clinical implications as sensitive and specific biomarkers for early stage diabetic kidney disease. However, little is known about the demographic and glucometabolic factors affecting levels of urinary N-acetyl-β-D-glucosaminidase (NAG), a marker of proximal tubular damage, in type 2 diabetes mellitus (T2DM).The aim of this study was to investigate the clinical relevance of urinary NAG with regard to demographic and glucometabolic parameters, as well as nephropathic parameters, by comparing the glomerulopathic marker of albuminuria.In this retrospective cross-sectional study, we enrolled a total of 592 patients with either prediabetes (N = 29) or T2DM (N = 563). Glucometabolic parameters (glucose, hemoglobin A1c, glycated albumin [GA], insulin, C-peptide, homeostasis model assessment [HOMA] of insulin resistance, HOMA-β, postprandial C-peptide-to-glucose ratio [PCGR], and urinary glucose-to-creatinine ratio) and nephropathic parameters (urinary NAG, albumin-to-creatinine ratio [ACR], and estimated glomerular filtration rate) were measured.The levels of urinary NAG showed moderate positive correlation with the levels of urinary ACR in T2DM (r = 0.46). In correlation analysis, urinary NAG was more strongly correlated with body mass index (BMI) (r = -0.22; P < 0.001 vs. r = -0.02; P = 0.74), plasma stimulated glucose (r = 0.25; P < 0.001 vs. r = 0.08; P = 0.10), GA (r = 0.20; P < 0.001 vs. r = 0.13; P = 0.01), PCGR (r = -0.17; P = 0.001 vs. r = -0.09; P = 0.11), and HOMA-β (r = -0.10; P = 0.05 vs. r = -0.02; P = 0.79) than urinary ACR. In multiple regression analysis, age, lower BMI, stimulated glucose, GA, and urinary ACR predicted increased urinary NAG.In conclusion, increase in urinary NAG may be related to glycemic parameters reflecting glucose fluctuation and decreased insulin secretory capacity in patients with T2DM. Further longitudinal, prospective studies are needed to investigate a causal relationship between glucose fluctuations, renal tubular damage, and other vascular complications of diabetes.

Advances in the evaluation of canine renal disease

Many recent advances in the evaluation of dogs with kidney disease have improved our diagnostic algorithms and have impacted our therapeutic strategies. Non-invasive techniques, such as urinary and serologic biomarker evaluation, can help a clinician diagnose and treat a patient that cannot undergo a renal biopsy for clinical or financial reasons. Some biomarkers might help localize the affected structure (glomerulus vs. tubule) and indicate the type or severity of injury present. Although more research is needed, studies indicate that some biomarkers (e.g. urine protein to creatinine ratio and urinary immunoglobulins) can be useful in predicting adverse outcomes. Importantly, the sensitivity and specificity of biomarkers for renal injury should be established and clinicians need to understand the limitations of these assays. If a renal biopsy is performed, then it should be evaluated by a specialty diagnostic service with expertise in nephropathology. A panel of special stains, immunofluorescence for the detection of immunoglobulins and complement factors, and transmission electron microscopy can be routinely employed in cases of glomerular disease. These advanced diagnostics can be used to detect immune deposits in order to definitively diagnose immune complex mediated glomerular disease. Integrating the results of biomarker assays and comprehensive renal biopsy evaluation, the clinician can make informed therapeutic decisions, such as whether or not to immunosuppress a patient.

Elevation of Non-Classical (CD14+/lowCD16++) Monocytes Is Associated with Increased Albuminuria and Urine TGF-β1 in HIV-Infected Individuals on Stable Antiretroviral Therapy

OBJECTIVE

High rates of albuminuria are observed among HIV-infected individuals on stable antiretroviral therapy (ART). Though pro-inflammatory and pro-fibrotic responses are described as components of albuminuria in the general population, it is unclear how these responses are associated to albuminuria in ART-treated chronic HIV. We investigated the relationship of monocyte subsets and urine inflammatory and fibrotic biomarkers to albuminuria in ART-treated HIV-infected participants.

DESIGN AND METHODS

Cross-sectional analyses were performed on Hawaii Aging with HIV-cardiovascular disease study cohort participants who were required at entry to be ≥40 years old and on ART ≥3 months. Monocyte subpopulations were determined in banked peripheral blood mononuclear cells (PBMC) using multi-parametric flow-cytometry. Entry random urine samples were assessed for albumin-to-creatinine ratios (UACR). Urine samples were measured for inflammatory and fibrotic biomarkers using Luminex technology.

RESULTS

Among 96 HIV-infected subjects with measured UACR (87% male, 59% Caucasian, and 89% undetectable HIV RNA with median CD4 of 495.5 cells/μL), 18 patients (19%) had albuminuria. Non-classical (CD14low/+CD16++) monocytes were significantly elevated in subjects with albuminuria (p = 0.034) and were correlated to UACR (r = 0.238, p = 0.019). Elevated non-classical monocyte counts were significant predictors of worsening albuminuria, independent of traditional- and ART-associated risk factors (β = 0.539, p = 0.007). Urine TGF-β1 and collagen-IV were significantly higher in albuminuric compared to non-albuminuric participants (TGF-β1; p = 0.039 and collagen-IV; p = 0.042). Urine TGF-β1 was significantly correlated with non-classical monocyte counts (r = 0.464, p = 0.017).

CONCLUSION

Alterations in monocyte subpopulations and urine pro-fibrotic factors may play a role in kidney dysfunction during chronic HIV infection and warrants further study.

The risk of death associated with proteinuria in heart failure is restricted to patients with an elevated blood urea nitrogen to creatinine ratio

BACKGROUND

Renal dysfunction (RD) is associated with reduced survival in HF; however, not all RD is mechanistically or prognostically equivalent. Notably, RD associated with "pre-renal" physiology, as identified by an elevated blood urea nitrogen to creatinine ratio (BUN/Cr), identifies a particularly high risk RD phenotype. Proteinuria, another domain of renal dysfunction, has also been associated with adverse events. Given that several different mechanisms can cause proteinuria, we sought to investigate whether the mechanism underlying proteinuria also affects survival in HF.

METHODS AND RESULTS

Subjects in the Studies of Left Ventricular Dysfunction (SOLVD) trial with proteinuria assessed at baseline were studied (n=6439). All survival models were adjusted for baseline characteristics and estimated glomerular filtration rate (eGFR). Proteinuria (trace or 1+) was present in 26% and associated with increased mortality (HR=1.2; 95% CI, 1.1-1.3, p=0.006). Proteinuria >1+ was less common (2.5%) but demonstrated a stronger relationship with mortality (HR=1.9; 95% CI, 1.5-2.5, p<0.001). In patients with BUN/Cr in the top tertile (≥17.3), any proteinuria (HR=1.3; 95% CI, 1.1-1.5, p=0.008) and >1+ proteinuria (HR=2.3; 95% CI, 1.7-3.3, p<0.001) both remained associated with mortality. However, in patients with BUN/Cr in the bottom tertile (≤13.3), any proteinuria (HR=0.95; 95% CI, 0.77-1.2, p=0.63, p interaction=0.015) and >1+ proteinuria (HR=1.3; 95% CI, 0.79-2.2, p=0.29, p interaction=0.036) were not associated with worsened survival.

CONCLUSION

Analogous to a reduced eGFR, the mechanism underlying proteinuria in HF may be important in determining the associated survival disadvantage.

Transforming growth factor-β1 and diabetic nephropathy

Transforming growth factor-β1 (TGF-β1) is established to be involved in the pathogenesis of diabetic nephropathy. The diabetic milieu enhances oxidative stress and induces the expression of TGF-β1. TGF-β1 promotes cell hypertrophy and extracellular matrix accumulation in the mesangium, which decreases glomerular filtration rate and leads to chronic renal failure. Recently, TGF-β1 has been demonstrated to regulate urinary albumin excretion by both increasing glomerular permeability and decreasing reabsorption in the proximal tubules. TGF-β1 also increases urinary excretion of water, electrolytes and glucose by suppressing tubular reabsorption in both normal and diabetic conditions. Although TGF-β1 exerts hypertrophic and fibrogenic effects in diabetic nephropathy, whether suppression of the function of TGF-β1 can be an option to prevent or treat the complication is still controversial. This is partly because adrenal production of mineralocorticoids could be augmented by the suppression of TGF-β1. However, differentiating the molecular mechanisms for glomerulosclerosis from those for the suppression of the effects of mineralocorticoids by TGF-β1 may assist in developing novel therapeutic strategies for diabetic nephropathy. In this review, we discuss recent findings on the role of TGF-β1 in diabetic nephropathy.

Inhibition of the metabolic degradation of filtered albumin is a major determinant of albuminuria

Inhibition of the degradation of filtered albumin has been proposed as a widespread, benign form of albuminuria. There have however been recent reports that radiolabeled albumin fragments in urine are not exclusively generated by the kidney and that in albuminuric states albumin fragment excretion is not inhibited. In order to resolve this controversy we have examined the fate of various radiolabeled low molecular weight protein degradation products (LMWDPs) introduced into the circulation in rats. The influence of puromycin aminonucleoside nephrosis on the processing and excretion of LMWDPs is also examined. The status and destinies of radiolabeled LMWDPs in the circulation are complex. A major finding is that LMWDPs are rapidly eliminated from the circulation (>97% in 2 h) but only small quantities (<4%) are excreted in urine. Small (<4%) but significant amounts of LMWDPs may have prolonged elimination (>24 h) due to binding to high molecular weight components in the circulation. If LMWDPs of albumin seen in the urine are produced by extra renal degradation it would require the degradation to far exceed the known catabolic rate of albumin. Alternatively, if an estimate of the role of extra renal degradation is made from the limit of detection of LMWDPs in plasma, then extra renal degradation would only contribute <1% of the total excretion of LMWDPs of albumin. We confirm that the degradation process for albumin is specifically associated with filtered albumin and this is inhibited in albuminuric states. This inhibition is also the primary determinant of the massive change in intact albuminuria in nephrotic states.

Novel urinary biomarkers in pre-diabetic nephropathy

BACKGROUND

Renal involvement was thought to occur more than 10 years after onset of diabetes, but recent studies provide evidence that it starts even in the pre-diabetes stage. However, there is no sensitive marker to detect these changes at such early stages. Novel urinary biomarkers have showed promising results in detection of early nephropathy in pre-diabetics.

METHODS

A total of 91 subjects (diabetes 61 and pre-diabetes 30) were enrolled into the study. Urinary biomarkers such as urine Neutrophil Gelatinase-Associated Lipocalin (NGAL), urine Cystatin C and urine albumin-creatinine ratio (UACR) were estimated. Subjects were further divided in four groups on the basis of UACR: pre-diabetes with normoalbuminuria (21); pre-diabetes with microalbuminuria (9); diabetes with normoalbuminuria (37); and diabetes with microalbuminuria (24). The relationship of UACR, NGAL, and Cystatin C was estimated.

RESULTS

Urine levels of NGAL and Cystatin C were significantly higher in microalbuminuria group compared to normoalbuminuria. UACR was positively correlated to urine NGAL-creatinine ratio (UNCR) and urine Cystatin C-creatinine ratio (UCCR) in both diabetes and pre-diabetes. On logistic regression odds ratio of UNCR to predict microalbuminuria in diabetes and pre-diabetes was 1.070 (p = 0.000) and 1.138 (p = 0.010), respectively. Area under curve was determined by ROC analysis, and UNCR was found to be better than UCCR for estimating microalbuminuria.

CONCLUSION

Tubular damage may play major role in development of nephropathy in pre-diabetes. Newer markers like urine NGAL and Cystatin C are raised early in diabetes and pre-diabetes nephropathy.

Association between renal function and cardiovascular structure and function in heart failure with preserved ejection fraction

AIM

Renal dysfunction is a common comorbidity in patients with heart failure and preserved ejection fraction (HFpEF). We sought to determine whether renal dysfunction was associated with measures of cardiovascular structure/function in patients with HFpEF.

METHODS

We studied 217 participants from the PARAMOUNT study with HFpEF who had echocardiography and measures of kidney function. We evaluated the relationships between renal dysfunction [estimated glomerular filtration rate (eGFR) >30 and <60 mL/min/1.73 m(2) and/or albuminuria] and cardiovascular structure/function.

RESULTS

The mean age of the study population was 71 years, 55% were women, 94% hypertensive, and 40% diabetic. Impairment of at least one parameter of kidney function was present in 62% of patients (16% only albuminuria, 23% only low eGFR, 23% both). Renal dysfunction was associated with abnormal LV geometry (defined as concentric hypertrophy, or eccentric hypertrophy, or concentric remodelling) (adjusted P = 0.048), lower midwall fractional shortening (MWFS) (P = 0.009), and higher NT-proBNP (P = 0.006). Compared with patients without renal dysfunction, those with low eGFR and no albuminuria had a higher prevalence of abnormal LV geometry (P = 0.032) and lower MWFS (P < 0.01), as opposed to those with only albuminuria. Conversely, albuminuria alone was associated with greater LV dimensions (P < 0.05). Patients with combined renal impairment had mixed abnormalities (higher LV wall thicknesses, NT-proBNP; lower MWFS).

CONCLUSION

Renal dysfunction, as determined by both eGFR and albuminuria, is highly prevalent in HFpEF, and associated with cardiac remodelling and subtle systolic dysfunction. The observed differences in cardiac structure/function between each type of renal damage suggest that both parameters of kidney function might play a distinct role in HFpEF.

Sex-specific effect of antenatal betamethasone exposure on renal oxidative stress induced by angiotensins in adult sheep

Prenatal glucocorticoid administration in clinically relevant doses reduces nephron number and renal function in adulthood and is associated with hypertension. Nephron loss in early life may predispose the kidney to other insults later but whether sex influences increases in renal susceptibility is unclear. Therefore, we determined, in male and female adult sheep, whether antenatal glucocorticoid (betamethasone) exposure increased 8-isoprostane (marker of oxidative stress) and protein excretion after acute nephron reduction and intrarenal infusions of angiotensin peptides. We also examined whether renal proximal tubule cells (PTCs) could contribute to alterations in 8-isoprostane excretion in a sex-specific fashion. In vivo, ANG II significantly increased 8-isoprostane excretion by 49% and protein excretion by 44% in male betamethasone- but not in female betamethasone- or vehicle-treated sheep. ANG-(1-7) decreased 8-isoprostane excretion but did not affect protein excretion in either group. In vitro, ANG II stimulated 8-isoprostane release from PTCs of male but not female betamethasone-treated sheep. Male betamethasone-exposed sheep had increased p47 phox abundance in the renal cortex while superoxide dismutase (SOD) activity was increased only in females. We conclude that antenatal glucocorticoid exposure enhances the susceptibility of the kidney to oxidative stress induced by ANG II in a sex-specific fashion and the renal proximal tubule is one target of the sex-specific effects of antenatal steroids. ANG-(1-7) may mitigate the impact of prenatal glucocorticoids on the kidney. P47 phox activation may be responsible for the increased oxidative stress and proteinuria in males. The protection from renal oxidative stress in females is associated with increased SOD activity.

Evaluation of urinary N-acetyl-beta-D-glucosaminidase as a marker of early renal damage in patients with type 2 diabetes mellitus

OBJECTIVE

To evaluate the clinical usefulness of urinary N-acetyl-beta-D-glucosaminidase (NAG) excretion for the detection of early tubular damage in type 2 diabetes mellitus (T2DM).

SUBJECTS AND METHODS

Thirty six patients with T2DM were divided into two groups based on urinary albumin to creatinine ratio (ACR): normoalbuminuria (ACR <30 mg/g; n=19) and microalbuminuria (ACR =30-300 mg/g; n=17). The following parameters were determined in both groups: urinary NAG and albumin, serum and urine creatinine, fasting plasma glucose and glycated hemoglobin (HbA1c).

RESULTS

Urinary NAG levels [Units/g creatinine; median (range)] were significantly increased in microalbuminuria group [17.0 (5.9 - 23.3)] compared to normoalbuminuria group [4.4 (1.5 - 9.2)] (P<0.001). No differences between groups were observed in fasting glucose, HbA1c, serum creatinine levels and estimated glomerular filtration rates (eGFR). Urinary NAG positively correlated with ACR (r=0.628; p<0.0001), while no significant association was observed between NAG and glycemia, HbA1c, serum creatinine and eGFR.

CONCLUSIONS

The increase of urinary NAG at the microalbuminuria stage of diabetic nephropathy (DN) suggests that tubular dysfunction is already present in this period. The significant positive association between urinary NAG excretion and ACR indicates the possible clinical application of urinary NAG as a complementary marker for early detection of DN in T2DM.

Hypertension increases urinary excretion of immunoglobulin G, ceruloplasmin and transferrin in normoalbuminuric patients with type 2 diabetes mellitus

OBJECTIVE

Increased urinary excretion of certain plasma proteins, such as immunoglobulin G (IgG), ceruloplasmin and transferrin, with different molecular radii of 55 Å or less and different isoelectric points have been reported to precede development of microalbuminuria in patients who have diabetes mellitus with hypertension. We examined how hypertension affects these urinary proteins in a diabetic state.

METHODS

Excretion of IgG, ceruloplasmin, transferrin, albumin, α2-macroglobulin with a large molecular radius of 88 Å and N-acetylglucosaminidase in first-morning urine samples were measured in normoalbuminuric patients (urinary albumin-to-creatinine ratio < 15 mg/g) with hypertension and nondiabetes mellitus (group hypertension, n = 32), type 2 diabetes mellitus and normotension (group diabetes mellitus, n = 52) and type 2 diabetes mellitus and hypertension (group Both, n =45), and in age-matched controls (n = 72).

RESULTS

Urinary IgG, ceruloplasmin, transferrin, albumin and N-acetylglucosaminidase and estimated glomerular filtration rate (eGFR) were significantly elevated in groups diabetes mellitus and Both compared with controls. Furthermore, urinary IgG, ceruloplasmin and transferrin in group Both were significantly higher than those in group diabetes mellitus. These exhibited a positive and relatively strong association with eGFR compared with controls. No significant difference in urinary albumin or N-acetylglucosaminidase was found between the two diabetic groups. In contrast, group hypertension had elevated urinary transferrin without any changes in the other compounds. Urinary α2-macroglobulin did not differ among the four groups.

CONCLUSION

These findings suggest that normoalbuminuric diabetic patients without hypertension have both glomerular hemodynamic changes such as increased intraglomerular hydraulic pressure and altered proximal tubules, and that hypertension increases intraglomerular hydraulic pressure. Increased urinary IgG, ceruloplasmin and transferrin may reflect an increase in intraglomerular hydraulic pressure.