Urinary albumin, transferrin and iron excretion in diabetic patients

Iron deficiency and supplementation in heart failure

Non-anaemic iron deficiency (NAID) is a strategic target in cardiovascular medicine because of its association with a range of adverse effects in various conditions. Endeavours to tackle NAID in heart failure have yielded mixed results, exposing knowledge gaps in how best to define 'iron deficiency' and the handling of iron therapies by the body. To address these gaps, we harness the latest understanding of the mechanisms of iron homeostasis outside the erythron and integrate clinical and preclinical lines of evidence. The emerging picture is that current definitions of iron deficiency do not assimilate the multiple influences at play in patients with heart failure and, consequently, fail to identify those with a truly unmet need for iron. Additionally, current iron supplementation therapies benefit only certain patients with heart failure, reflecting differences in the nature of the unmet need for iron and the modifying effects of anaemia and inflammation on the handling of iron therapies by the body. Building on these insights, we identify untapped opportunities in the management of NAID, including the refinement of current approaches and the development of novel strategies. Lessons learned from NAID in cardiovascular disease could ultimately translate into benefits for patients with other chronic conditions such as chronic kidney disease, chronic obstructive pulmonary disease and cancer.

Advance in Iron Metabolism, Oxidative Stress and Cellular Dysfunction in Experimental and Human Kidney Diseases

Kidney diseases pose a significant global health issue, frequently resulting in the gradual decline of renal function and eventually leading to end-stage renal failure. Abnormal iron metabolism and oxidative stress-mediated cellular dysfunction facilitates the advancement of kidney diseases. Iron homeostasis is strictly regulated in the body, and disturbance in this regulatory system results in abnormal iron accumulation or deficiency, both of which are associated with the pathogenesis of kidney diseases. Iron overload promotes the production of reactive oxygen species (ROS) through the Fenton reaction, resulting in oxidative damage to cellular molecules and impaired cellular function. Increased oxidative stress can also influence iron metabolism through upregulation of iron regulatory proteins and altering the expression and activity of key iron transport and storage proteins. This creates a harmful cycle in which abnormal iron metabolism and oxidative stress perpetuate each other, ultimately contributing to the advancement of kidney diseases. The crosstalk of iron metabolism and oxidative stress involves multiple signaling pathways, such as hypoxia-inducible factor (HIF) and nuclear factor erythroid 2-related factor 2 (Nrf2) pathways. This review delves into the functions and mechanisms of iron metabolism and oxidative stress, along with the intricate relationship between these two factors in the context of kidney diseases. Understanding the underlying mechanisms should help to identify potential therapeutic targets and develop novel and effective therapeutic strategies to combat the burden of kidney diseases.

Identifying diagnostic indicators for type 2 diabetes mellitus from physical examination using interpretable machine learning approach

Background

Identification of patients at risk for type 2 diabetes mellitus (T2DM) can not only prevent complications and reduce suffering but also ease the health care burden. While routine physical examination can provide useful information for diagnosis, manual exploration of routine physical examination records is not feasible due to the high prevalence of T2DM.

Objectives

We aim to build interpretable machine learning models for T2DM diagnosis and uncover important diagnostic indicators from physical examination, including age- and sex-related indicators.

Methods

In this study, we present three weighted diversity density (WDD)-based algorithms for T2DM screening that use physical examination indicators, the algorithms are highly transparent and interpretable, two of which are missing value tolerant algorithms.

Patients

Regarding the dataset, we collected 43 physical examination indicator data from 11,071 cases of T2DM patients and 126,622 healthy controls at the Affiliated Hospital of Southwest Medical University. After data processing, we used a data matrix containing 16004 EHRs and 43 clinical indicators for modelling.

Results

The indicators were ranked according to their model weights, and the top 25% of indicators were found to be directly or indirectly related to T2DM. We further investigated the clinical characteristics of different age and sex groups, and found that the algorithms can detect relevant indicators specific to these groups. The algorithms performed well in T2DM screening, with the highest area under the receiver operating characteristic curve (AUC) reaching 0.9185.

Conclusion

This work utilized the interpretable WDD-based algorithms to construct T2DM diagnostic models based on physical examination indicators. By modeling data grouped by age and sex, we identified several predictive markers related to age and sex, uncovering characteristic differences among various groups of T2DM patients.

Lipid peroxidation mediates the association between iron overload and liver injury: cross-sectional and longitudinal analyses in general Chinese urban adults

Iron overload has been associated with acute/chronic organ failure, but whether iron overload induces liver injury remains unclear. The objectives of this study were to assess the relationship between urinary iron and serum alanine aminotransferase (ALT, a biomarker for liver injury), and investigate the potential mediating roles of lipid peroxidation and oxidative DNA damage in such association. Levels of urinary iron, serum ALT, and urinary biomarkers of lipid peroxidation (8-iso-prostaglandin-F_2α [8-iso-PGF_2α]) and oxidative DNA damage (8-hydroxy-deoxyguano-sine [8-OHdG]) were measured among 5386 observations of 4220 participants from the Wuhan-Zhuhai cohort. The relationships of urinary iron with serum ALT and risk of hyperALT were evaluated by linear mixed model and logistic regression model, respectively. The mediating roles of 8-iso-PGF_2α and 8-OHdG were assessed by mediation analyses. This cross-sectional analysis found that urinary iron was positively associated with ALT (β = 0.032; 95% CI: 0.020, 0.044) and hyperALT prevalence (OR = 1.127; 95% CI: 1.065, 1.192). After 3 years of follow-up, participants with persistent high iron levels had increased risk of developing hyperALT (RR = 3.800; 95% CI: 1.464, 9.972) when compared with those with persistent low iron levels. In addition, each 1% increase in urinary iron was associated with a 0.146% (95% CI: 0.128%, 0.164%) increase and a 0.192% (95% CI: 0.154%, 0.229%) increase in 8-iso-PGF_2α and 8-OHdG, respectively. Urinary 8-iso-PGF_2α (β = 0.056; 95% CI: 0.039, 0.074) was positively associated with ALT, while the association between 8-OHdG and ALT was insignificant. Furthermore, increased 8-iso-PGF_2α significantly mediated 22.48% of the urinary iron-associated ALT increment. Our study demonstrated that iron overload was significantly associated with liver injury, which was partly mediated by lipid peroxidation. Controlling iron intake and regulating lipid peroxidation may help in preventing liver injury.

Revisiting PINI Scoring in Light of Recent Biological Advances

The prognostic inflammatory and nutritional index (PINI) is a simple scoring formula allowing the follow-up of dietary protein restriction and infectious complications affecting critically ill patients hospitalized in medical and surgical wards. The World Health organization (WHO) has recently recommended using the binary CRP (C-reactive protein) and AGP (α1-acid glycoprotein) numerators of the PINI formula in underprivileged inhabitants of developing countries to evaluate their (sub)clinical infectious states making their chronic malnutrition worse. These studies, mainly located in Africa and Asia, demonstrate that children and women enduring the combined effects of infectious burden and (micro)nutrient deprivation (principally retinol and iron) usually manifest persistent refractoriness and slackened recovery throughout dietary rehabilitation. The additive measurement of ALB (albumin) and TTR (transthyretin) composing the denominator of the PINI formula is shown to be helpful in grading the downsizing of lean body mass (LBM), a cornerstone of bodybuilding. The confrontation of these four objective parameters thus allows the quantification of the respective importance of nutritional and inflammatory components of any disease process, taking into account that TTR is the sole plasma protein remaining highly correlated to the fluctuations of LBM. The below review highlights the prevailing roles played by protein nutritional states in the release of plasma retinol to target tissues and to the restoration of iron-deficient anemias.

The first study on urinary loss of iron and transferrin in association with proteinuria in dogs with chronic kidney disease

Background and Aim

Anemia is an important factor in surviving chronic kidney disease (CKD). Anemia in CKD is associated with various factors, such as inadequate production of erythropoietin and the availability of iron and its binding protein. Reduced total iron-binding capacity (TIBC) and iron concentrations may be related to their urinary loss along with proteinuria. This study aimed to determine the urinary loss of iron and transferrin (TF) in relation to the degree of proteinuria.

Materials and Methods

The study was performed on 37 dogs with CKD. Dogs were divided according to the severity of proteinuria into two groups based on the mean of urinary protein-creatinine (UPC) ratio into UPC ratio <4 and UPC ratio >4. The hematocrit (HCT), blood chemistries, plasma iron, plasma TF, UPC ratio, urinary iron per creatinine ratio (U-Iron/CR), and urinary TF per creatinine ratio (U-TF/CR) were evaluated.

Results

Anemia was associated with the severity of renal impairment as demonstrated by reduction of HCT when staging of CKD was higher. Dogs with UPC ratio >4 had higher urinary loss of both U-Iron/CR (p < 0.01) and U-TF/CR (p < 0.001) with lower plasma TIBC (p < 0.001). The UPC ratio was positively correlated with both U-Iron/CR (r = 0.710, p < 0.001) and U-TF/CR (r = 0.730, p < 0.001) but negatively with TIBC (r = -0.462, p < 0.01).

Conclusion

Proteinuria was associated with urinary loss of both iron and TF which may contribute to anemia in CKD.

Evaluating renal iron overload in diabetes mellitus by blood oxygen level-dependent magnetic resonance imaging: a longitudinal experimental study

BACKGROUND

Iron overload plays a critical role in the pathogenesis of diabetic nephropathy. Non-invasive evaluation of renal iron overload in diabetes in the management and intervention of diabetic nephropathy is of great significance. This study aimed to explore the feasibility of blood oxygen level-dependent (BOLD) magnetic resonance imaging (MRI) in evaluating renal iron overload in diabetes using a rabbit model.

METHODS

The rabbits were randomly divided into control, iron-overload (I), diabetes (D), and diabetes with iron-overload (DI) groups (each n = 19). The diabetes models were generated by injecting intravenous alloxan solution, and the iron-overload models were generated by injecting intramuscular iron-dextran. BOLD MRI was performed immediately (week 0) and at week 4, 8, and 12 following modeling. The differences in renal cortex (CR2*) and outer medulla R2* (MR2*) and the ratio of MR2*-CR2* (MCR) across the different time points were compared.

RESULTS

Iron was first deposited in glomeruli in the I group and in proximal tubular cells in renal cortex in the D group. In the DI group, there was iron deposition in both glomeruli and proximal tubular cells at week 4, and the accumulation increased subsequently. The degree of kidney injury and iron overload was more severe in the DI group than those in the I and D groups at week 12. At week 8 and 12, the CR2* and MR2* in the DI group were higher than those in the I and D groups (all P < 0.05). The MCR in the I, D, and DI groups decreased from week 0 to 4 (all P < 0.001), and that in the I group increased from week 8 to 12 (P = 0.034). CR2* and MR2* values displayed different trends from week 0-12. Dynamic MCR curves in the D and DI groups were different from that in the I group.

CONCLUSION

It presents interactions between diabetes and iron overload in kidney injury, and BOLD MRI can be used to evaluate renal iron overload in diabetes.

Kidney tubule iron loading in experimental focal segmental glomerulosclerosis

Kidney iron deposition may play a role in the progression of tubulointerstitial injury during chronic kidney disease. Here, we studied the molecular mechanisms of kidney iron loading in experimental focal segmental glomerulosclerosis (FSGS) and investigated the effect of iron-reducing interventions on disease progression. Thy-1.1 mice were injected with anti-Thy-1.1 monoclonal antibody (mAb) to induce proteinuria. Urine, blood and tissue were collected at day (D)1, D5, D8, D15 and D22 after mAb injection. Thy-1.1 mice were subjected to captopril (CA), iron-deficient (ID) diet or iron chelation (deferoxamine; DFO). MAb injection resulted in significant albuminuria at all time points (p < 0.01). Kidney iron loading, predominantly in distal tubules, increased in time, along with urinary kidney injury molecule-1 and 24p3 concentration, as well as kidney mRNA expression of Interleukin-6 (Il-6) and Heme oxygenase-1 (Ho-1). Treatment with CA, ID diet or DFO significantly reduced kidney iron deposition at D8 and D22 (p < 0.001) and fibrosis at D22 (p < 0.05), but not kidney Il-6. ID treatment increased kidney Ho-1 (p < 0.001). In conclusion, kidney iron accumulation coincides with progression of tubulointerstitial injury in this model of FSGS. Reduction of iron loading halts disease progression. However, targeted approaches to prevent excessive kidney iron loading are warranted to maintain the delicate systemic and cellular iron balance.

Proteinuric chronic kidney disease is associated with altered red blood cell lifespan, deformability and metabolism

Anemia is a common complication of chronic kidney disease, affecting the quality of life of patients. Among various factors, such as iron and erythropoietin deficiency, reduced red blood cell (RBC) lifespan has been implicated in the pathogenesis of anemia. However, mechanistic data on in vivo RBC dysfunction in kidney disease are lacking. Herein, we describe the development of chronic kidney disease-associated anemia in mice with proteinuric kidney disease resulting from either administration of doxorubicin or an inducible podocin deficiency. In both experimental models, anemia manifested at day 10 and progressed at day 30 despite increased circulating erythropoietin levels and erythropoiesis in the bone marrow and spleen. Circulating RBCs in both mouse models displayed altered morphology and diminished osmotic-sensitive deformability together with increased phosphatidylserine externalization on the outer plasma membrane, a hallmark of RBC death. Fluorescence-labelling of RBCs at day 20 of mice with doxorubicin-induced kidney disease revealed premature clearance from the circulation. Metabolomic analyses of RBCs from both mouse models demonstrated temporal changes in redox recycling pathways and Lands' cycle, a membrane lipid remodeling process. Anemic patients with proteinuric kidney disease had an increased proportion of circulating phosphatidylserine-positive RBCs. Thus, our observations suggest that reduced RBC lifespan, mediated by altered RBC metabolism, reduced RBC deformability, and enhanced cell death contribute to the development of anemia in proteinuric kidney disease.

Iron status and erythropoiesis response to darbepoetin alfa in dogs with chronic kidney disease

Iron metabolism, hepcidin and some blood profiles were investigated in 13 healthy and 31 chronic kidney disease (CKD) dogs. The study consisted of 2 experiments, experiment I included healthy dogs (CONT) and CKD dogs (stage 2, 3 and 4), while experiment II consisted of anemic CKD dogs subjected to 28-day darbepoetin alfa treatment. The response to darbepoetin alfa could divide anemic CKD dogs into responder (RP) and non-responder (NRP) subgroups. The results from experiment I showed that packed cell volume (PCV) and plasma albumin concentration were significantly lower in CKD dogs of all stages while the total iron binding capacity (TIBC) was lower in only CKD stage 3 and 4 compared with dogs in CONT group. The PCV was related to both TIBC and albumin when considering among all dogs or only in CKD dogs. The hepcidin concentration in CKD dogs with anemia was lower than those without anemia (P<0.05). In experiment II before darbepoetin alfa treatment, RP subgroup had significantly higher iron and TIBC compared with NRP subgroup (P<0.05), the iron concentration was decreased only in RP subgroup after darbepoetin alfa treatment (P<0.05). The percent increase in PCV was correlated with initial TIBC (P<0.01). Plasma hepcidin concentration was not different between CONT and CKD groups and between RP and NRP subgroups both before and after darbepoetin alfa treatment. It is concluded that TIBC and plasma iron concentration play role on anemia and erythropoietic response to darbepoetin alfa treatment in CKD dogs.

The multifaceted role of iron in renal health and disease

Iron is an essential element that is indispensable for life. The delicate physiological body iron balance is maintained by both systemic and cellular regulatory mechanisms. The iron-regulatory hormone hepcidin assures maintenance of adequate systemic iron levels and is regulated by circulating and stored iron levels, inflammation and erythropoiesis. The kidney has an important role in preventing iron loss from the body by means of reabsorption. Cellular iron levels are dependent on iron import, storage, utilization and export, which are mainly regulated by the iron response element-iron regulatory protein (IRE-IRP) system. In the kidney, iron transport mechanisms independent of the IRE-IRP system have been identified, suggesting additional mechanisms for iron handling in this organ. Yet, knowledge gaps on renal iron handling remain in terms of redundancy in transport mechanisms, the roles of the different tubular segments and related regulatory processes. Disturbances in cellular and systemic iron balance are recognized as causes and consequences of kidney injury. Consequently, iron metabolism has become a focus for novel therapeutic interventions for acute kidney injury and chronic kidney disease, which has fuelled interest in the molecular mechanisms of renal iron handling and renal injury, as well as the complex dynamics between systemic and local cellular iron regulation.

Synthetic molecular recognition nanosensor paint for microalbuminuria

Microalbuminuria is an important clinical marker of several cardiovascular, metabolic, and other diseases such as diabetes, hypertension, atherosclerosis, and cancer. The accurate detection of microalbuminuria relies on albumin quantification in the urine, usually via an immunoturbidity assay; however, like many antibody-based assessments, this method may not be robust enough to function in global health applications, point-of-care assays, or wearable devices. Here, we develop an antibody-free approach using synthetic molecular recognition by constructing a polymer to mimic fatty acid binding to the albumin, informed by the albumin crystal structure. A single-walled carbon nanotube, encapsulated by the polymer, as the transduction element produces a hypsochromic (blue) shift in photoluminescence upon the binding of albumin in clinical urine samples. This complex, incorporated into an acrylic material, results in a nanosensor paint that enables the detection of microalbuminuria in patient samples and comprises a rapid point-of-care sensor robust enough to be deployed in resource-limited settings.

Renal iron accelerates the progression of diabetic nephropathy in the HFE gene knockout mouse model of iron overload

Diabetic nephropathy (DN) is the most common cause of end-stage renal disease associated with high mortality worldwide. Increases in iron levels have been reported in diabetic rat kidneys as well as in human urine of patients with diabetes. In addition, a low-iron diet or iron chelators delay the progression of DN in patients with diabetes and in animal models of diabetes. Possible maladaptive mechanisms of organ damage by tissue iron accumulation have not been well studied. We recently reported that iron induced the retinal renin-angiotensin system (RAS) and accelerated the progression of diabetic retinopathy. However, whether iron regulates the systemic RAS is unknown. To explore if iron alters the expression of intrarenal RAS and its role in the progression of DN, we used the high Fe iron (HFE) knockout mouse, a genetic model of systemic iron overload. We found that diabetes upregulated the expression of iron regulatory proteins and augmented tissue iron accumulation in the kidneys of both type 1 and type 2 diabetic mouse models. Iron accumulation in the kidneys of HFE knockout mice was associated with increase in serum and intrarenal renin expression. Induction of diabetes in HFE knockout mice using streptozotocin caused a much higher accumulation of renal iron and accelerated the progression of nephropathy compared with diabetic wild-type mice. Treatment of diabetic mice with the iron chelator deferiprone reversed the renin upregulation and reduced kidney injury. Thus, our results establish a new link between renal iron and RAS activity. Exploring the mechanisms of iron-induced RAS activation further may have a significant therapeutic impact on hypertension and DN.

Pharmacokinetics of ferric bepectate-a new intravenous iron drug for treating iron deficiency

IV iron is indicated in clinical conditions, where rapid anaemia alleviation and repletion of iron stores are required. The acute toxicity of IV iron is ascribed to the presence of labile iron in plasma. Thus, shorter plasma residence time might improve the safety profile, even for compounds holding‐on the iron tightly. In this single‐centre, open‐label, single‐dose escalation study, we evaluated the elimination kinetics of ferric bepectate (FBP) compared to those of ferric carboxymaltose (FCM). Thirty‐three iron‐depleted anaemic patients who had undergone cardiac surgery were included and received 200, 500 or 1500 mg FBP or 500 mg FCM. Plasma drug curves were subjected to model‐free analysis. Because saturation kinetics was found, a compartmental model with limited elimination capacity was applied. Urinary iron excretion was also analysed. The initial non‐compartmental analysis revealed an increasing AUC/dose ratio for FBP. For both drugs, the central distribution compartment corresponded to plasma volume, and elimination followed Michaelis‐Menten saturation kinetics. Maximal elimination rates (V_max) were 224 mg/h and 81 mg/h for FBP 500 mg and FCM 500 mg, respectively; drug concentrations at half V_max (K_m), 99 mg/L and 212 mg/L, respectively; and terminal plasma half‐life (T½), 3.05 h and 8.96 h, respectively. Both drugs were equally effective in eliciting an early ferritin rise. Urinary iron excretion was measurable in all patients receiving FCM but not in those receiving FBP, which was well tolerated. Intravenous iron drugs are subject to capacity‐limited elimination with different saturation thresholds. Urinary iron excretion can be used as a surrogate for labile plasma iron.

Cardiac and Renal Delayed Effects of Acute Radiation Exposure: Organ Differences in Vasculopathy, Inflammation, Senescence and Oxidative Balance

We have previously shown significant pathology in the heart and kidney of murine hematopoietic-acute radiation syndrome (H-ARS) survivors of 8.7-9.0 Gy total-body irradiation (TBI). The goal of this study was to determine temporal relationships in the development of vasculopathy and the progression of renal and cardiovascular delayed effects of acute radiation exposure (DEARE) at TBI doses less than 9 Gy and to elucidate the potential roles of senescence, inflammation and oxidative stress. Our results show significant loss of endothelial cells in coronary arteries by 4 months post-TBI (8.53 or 8.72 Gy of gamma radiation). This loss precedes renal dysfunction and interstitial fibrosis and progresses to abnormalities in the arterial media and adventitia and loss of coronary arterioles. Major differences in radiation-induced pathobiology exist between the heart and kidney in terms of vasculopathy progression and also in indices of inflammation, senescence and oxidative imbalance. The results of this work suggest a need for different medical countermeasures for multiple targets in different organs and at various times after acute radiation injury to prevent the progression of DEARE.

Systemic and local hepcidin as emerging and important peptides in renal homeostasis and pathology

Recent data suggest that the importance of hepcidin goes beyond its classical role in controlling systemic iron metabolism. Local hepcidins are emerging as important peptides for organ homeostasis in the brain, heart, blood vessels, and in cancer as well. Similarly, accumulating data indicate that hepcidin does seem to be an important factor in renal homeostasis. This review encompasses present knowledge concerning the role of hepcidin in renoprotection and its use as a biomarker of kidney diseases. Understanding the role of hepcidin in kidneys is important due to its relevance for kidney physiology and its potential therapeutic application in kidney pathologies. © 2018 BioFactors, 45(2):118-134, 2019.

Iron handling by the human kidney: glomerular filtration and tubular reabsorption both contribute to urinary iron excretion

In physiological conditions, circulating iron can be filtered by the glomerulus and is almost completely reabsorbed by the tubular epithelium to prevent urinary iron wasting. Increased urinary iron concentrations have been associated with renal injury. However, it is not clear whether increased urinary iron concentrations in patients are the result of increased glomerular iron filtration and/or insufficient tubular iron reabsorption and if these processes contribute to renal injury. We measured plasma and urine iron parameters and urinary tubular injury markers in healthy human subjects ( n = 20), patients with systemic iron overload ( n = 20), and patients with renal tubular dysfunction ( n = 18). Urinary iron excretion parameters were increased in both patients with systemic iron overload and tubular dysfunction, whereas plasma iron parameters were only increased in patients with systemic iron overload. In patients with systemic iron overload, increased urinary iron levels were associated with elevated circulating iron, as indicated by transferrin saturation (TSAT), and increased body iron, as suggested by plasma ferritin concentrations. In patients with tubular dysfunction, enhanced urinary iron and transferrin excretion were associated with distal tubular injury as indicated by increased urinary glutathione S-transferase pi 1-1 (GSTP1-1) excretion. In systemic iron overload, elevated urinary iron and transferrin levels were associated with increased injury to proximal tubules, indicated by increased urinary kidney injury marker 1 (KIM-1) excretion. Our explorative study demonstrates that both glomerular filtration of elevated plasma iron levels and insufficient tubular iron reabsorption could increase urinary iron excretion and cause renal injury.

Effect of Canagliflozin on Urinary Albumin Excretion in Japanese Patients with Type 2 Diabetes Mellitus and Microalbuminuria: A Pilot Study

BACKGROUND

Albuminuria characterizes the progression of kidney injury. The effect of canagliflozin on the excretion of microalbumin was assessed for investigating its renoprotective potential in Japanese patients with type 2 diabetes mellitus (T2DM).

PATIENTS AND METHODS

Twenty Japanese patients with T2DM and microalbuminuria were enrolled and administered with 100 mg of canagliflozin once a day for 12 weeks. These subjects were admitted to the clinic at the start and end of the treatment period for 24-h urine collection. The primary endpoint was the percentage change in geometric mean 24-h urinary albumin excretion from baseline to week 12.

RESULTS

The urinary albumin level decreased by 42.0% (95% confidence interval: 21.9-57.0; P = 0.0011) after 12 weeks of canagliflozin treatment. A number of blood and urinary parameters also significantly decreased, including hemoglobin A1c, fasting plasma glucose, estimated glomerular filtration rate, and creatinine clearance, while hematocrit was elevated. Among the biomarkers associated with kidney injury and inflammation, the urinary level of the oxidative stress marker 8-hydroxy-2'-deoxyguanosine was also decreased. There were no meaningful correlations noted between changes in urinary albumin excretion and other parameters/biomarkers. No severe adverse events were reported over the 12-week treatment period.

CONCLUSIONS

The results of this study indicate that canagliflozin decreases microalbuminuria in Japanese patients with T2DM. Albuminuria could be reduced as a result of changes in various physiological pathways; therefore, it is imperative that future, large-scale, studies attempt to determine the detailed mechanisms involved. Canagliflozin may offer a novel therapeutic option for Japanese patients with T2DM and incipient nephropathy.

Anemia modifies the prognostic value of glycated hemoglobin in patients with diabetic chronic kidney disease

A common complication of chronic kidney disease (CKD), anemia can influence glycated hemoglobin (HbA1c) levels. In diabetic patients, anemia occurs earlier and with higher severity over the course of CKD stages. To elucidate the effect of hemoglobin (Hb) on the predictive value of HbA1c, we enrolled 1558 diabetic patients with stages 3-4 CKD, categorized according to baseline Hb and HbA1c quartiles. Linear regression revealed that higher HbA1c correlated significantly with higher Hb in the Hb < 10 g/dL group (β = 0.146, P = 0.004). A fully-adjusted Cox regression model revealed worse clinical outcomes in patients with higher HbA1c quartiles in the Hb ≥ 10 g/dL group. Hazard ratios for end-stage renal disease (ESRD), all-cause mortality, and composite endpoint (cardiovascular events and all-cause mortality) in patients with Hb ≥ 10 g/dL and the highest HbA1c quartile were 1.92 (95% confidence interval [CI], 1.17-3.15), 1.76 (95% CI, 1.02-3.03), and 1.54 (95% CI, 1.03-2.31), respectively. By contrast, HbA1c was not associated with clinical outcomes in the Hb < 10 g/dL group. In conclusion, in stages 3-4 diabetic CKD, higher HbA1c is associated with a higher risk of poor clinical outcomes in patients with Hb ≥ 10 g/dL.

Tubular iron deposition and iron handling proteins in human healthy kidney and chronic kidney disease

Iron is suggested to play a detrimental role in the progression of chronic kidney disease (CKD). The kidney recycles iron back into the circulation. However, the localization of proteins relevant for physiological tubular iron handling and their potential role in CKD remain unclear. We examined associations between iron deposition, expression of iron handling proteins and tubular injury in kidney biopsies from CKD patients and healthy controls using immunohistochemistry. Iron was deposited in proximal (PT) and distal tubules (DT) in 33% of CKD biopsies, predominantly in pathologies with glomerular dysfunction, but absent in controls. In healthy kidney, PT contained proteins required for iron recycling including putative iron importers ZIP8, ZIP14, DMT1, iron storage proteins L- and H-ferritin and iron exporter ferroportin, while DT only contained ZIP8, ZIP14, and DMT1. In CKD, iron deposition associated with increased intensity of iron importers (ZIP14, ZIP8), storage proteins (L-, H-ferritin), and/or decreased ferroportin abundance. This demonstrates that tubular iron accumulation may result from increased iron uptake and/or inadequate iron export. Iron deposition associated with oxidative injury as indicated by heme oxygenase-1 abundance. In conclusion, iron deposition is relatively common in CKD, and may result from altered molecular iron handling and may contribute to renal injury.

Urinary Iron Excretion is Associated with Urinary Full-Length Megalin and Renal Oxidative Stress in Chronic Kidney Disease

BACKGROUND/AIMS

Megalin mediates the uptake of glomerular-filtered iron in the proximal tubules. Urinary full length megalin (C-megalin) excretion has been found to be increased in association with megalin-mediated metabolic load to the endo-lysosomal system in proximal tubular epithelial cells (PTECs) of residual nephrons. In the present study, we investigated the association between urinary iron and C-megalin in chronic kidney disease (CKD) patients, and the possible harmful effect of iron in renal tubules.

METHODS

Urinary levels of iron and C-megalin were measured in 63 CKD patients using automatic absorption spectrometry and a recently-established sandwich ELISA, respectively.

RESULTS

Although both urinary C-megalin and urinary total protein levels were correlated with urinary iron (C-megalin: ρ = 0.574, p <0.001; total protein: ρ = 0.500, p <0.001, respectively), urinary C-megalin alone emerged as an independent factor positively associated with urinary iron (β = 0.520, p <0.001) (R2 = 0.75, p <0.001). Furthermore, urinary iron was significantly and positively associated with urinary 8-hydroxydeoxyguanosine, an oxidative stress marker, while no association with other markers of renal tubular injury, i.e., β2-microglobulin and N-acetyl-β-D-glucosaminidase, was noted.

CONCLUSIONS

Our findings suggest that renal iron handling may be associated with megalin-mediated endo-lysosomal metabolic load in PTECs of residual nephrons and oxidative stress in renal tubules.

High urinary ferritin reflects myoglobin iron evacuation in DMD patients

Duchenne muscular dystrophy (DMD) is an X-linked disease caused by mutations in the dystrophin gene leading to the absence of the normal dystrophin protein. The efforts of many laboratories brought new treatments of DMD to the reality, but ongoing and forthcoming clinical trials suffer from absence of valuable biomarkers permitting to follow the outcome of the treatment day by day and to adjust the treatment if needed. In the present study the levels of 128 urinary proteins including growth factors, cytokines and chemokines were compared in urine of DMD patients and age related control subjects by antibody array approach. Surprisingly, statistically significant difference was observed only for urinary ferritin whose level was 50 times higher in young DMD patients. To explain the observed high urinary ferritin content we analysed the levels of iron, iron containing proteins and proteins involved in regulation of iron metabolism in serum and urine of DMD patients and their age-matched healthy controls. Obtained data strongly suggest that elevated level of urinary ferritin is functionally linked to the renal management of myoglobin iron derived from leaky muscles of DMD patients. This first observation of the high level of ferritin in urine of DMD patients permits to consider this protein as a new urinary biomarker in muscular dystrophies and sheds light on the mechanisms of iron metabolism and kidney functioning in DMD.

The Promise of Systems Biology for Diabetic Kidney Disease

Diabetic kidney disease (DKD) has a complex and prolonged pathogenesis involving many cell types in the kidney as well as extrarenal factors. It is clinically silent for many years after the onset of diabetes and usually progresses over decades. Given this complexity, a comprehensive and unbiased molecular approach is best suited to help identify the most critical mechanisms responsible for progression of DKD and those most suited for targeted intervention. Systems biological investigations provide such an approach since they examine the entire network of molecular changes that occur in a disease process in a comprehensive way instead of focusing on a single abnormal molecule or pathway. Systems biological studies can also start with analysis of the disease in humans, not in animal or cell culture models that often poorly reproduce the changes in human DKD. Indeed, in the last decade, systems biological approaches have led to the identification of critical molecular abnormalities in DKD and have directly led to development of new biomarkers and potential treatments for DKD.

Iron Overload Accelerates the Progression of Diabetic Retinopathy in Association with Increased Retinal Renin Expression

Diabetic retinopathy (DR) is a leading cause of blindness among working-age adults. Increased iron accumulation is associated with several degenerative diseases. However, there are no reports on the status of retinal iron or its implications in the pathogenesis of DR. In the present study, we found that retinas of type-1 and type-2 mouse models of diabetes have increased iron accumulation compared to non-diabetic retinas. We found similar iron accumulation in postmortem retinal samples from human diabetic patients. Further, we induced diabetes in HFE knockout (KO) mice model of genetic iron overload to understand the role of iron in the pathogenesis of DR. We found increased neuronal cell death, vascular alterations and loss of retinal barrier integrity in diabetic HFE KO mice compared to diabetic wildtype mice. Diabetic HFE KO mouse retinas also exhibited increased expression of inflammation and oxidative stress markers. Severity in the pathogenesis of DR in HFE KO mice was accompanied by increase in retinal renin expression mediated by G-protein-coupled succinate receptor GPR91. In light of previous reports implicating retinal renin-angiotensin system in DR pathogenesis, our results reveal a novel relationship between diabetes, iron and renin-angiotensin system, thereby unraveling new therapeutic targets for the treatment of DR.

Anemia in nephrotic syndrome: approach to evaluation and treatment

Nephrotic syndrome is one of the most common glomerular diseases that affect in children. Complications may occur in nephrotic syndrome as a result of the disease itself as well as its treatment. Most of these complications result from excessive urinary protein losses, and control of proteinuria is the most effective treatment strategy. Anemia is one of the many complications seen in patients with persistent nephrotic syndrome and may occur as a result of excessive urinary losses of iron, transferrin, erythropoietin, transcobalamin and/or metals. This leads to a deficiency of substrates necessary for effective erythropoiesis, requiring supplementation in order to correct the anemia. Supplementation of iron and erythropoietin alone often does not lead to correction of the anemia, suggesting other possible mechanisms which need further investigation. A clear understanding of the pathophysiologic mechanisms of anemia in nephrotic syndrome is necessary to guide appropriate therapy, but only limited evidence is currently available on the precise etiologic mechanisms of anemia in nephrotic syndrome. In this review we focus on the current state of knowledge on the pathogenesis of anemia in nephrotic syndrome.

Siderophore vaccine conjugates protect against uropathogenic Escherichia coli urinary tract infection

Uropathogenic Escherichia coli (UPEC) is the primary cause of uncomplicated urinary tract infections (UTIs). Whereas most infections are isolated cases, 1 in 40 women experience recurrent UTIs. The rise in antibiotic resistance has complicated the management of chronic UTIs and necessitates new preventative strategies. Currently, no UTI vaccines are approved for use in the United States, and the development of a highly effective vaccine remains elusive. Here, we have pursued a strategy for eliciting protective immunity by vaccinating with small molecules required for pathogenesis, rather than proteins or peptides. Small iron-chelating molecules called siderophores were selected as antigens to vaccinate against UTI for this vaccine strategy. These pathogen-associated stealth siderophores evade host immune defenses and enhance bacterial virulence. Previous animal studies revealed that vaccination with siderophore receptor proteins protects against UTI. The poor solubility of these integral outer-membrane proteins in aqueous solutions limits their practical utility. Because their cognate siderophores are water soluble, we hypothesized that these bacterial-derived small molecules are prime vaccine candidates. To test this hypothesis, we immunized mice with siderophores conjugated to an immunogenic carrier protein. The siderophore-protein conjugates elicited an adaptive immune response that targeted bacterial stealth siderophores and protected against UTI. Our study has identified additional antigens suitable for a multicomponent UTI vaccine and highlights the potential use of bacterial-derived small molecules as antigens in vaccine therapies.

Renal iron overload in rats with diabetic nephropathy

Diabetic nephropathy (DN) remains incurable and is the main cause of end-stage renal disease. We approached the pathophysiology of DN with systems biology, and a comprehensive profile of renal transcripts was obtained with RNA-Seq in ZS (F1 hybrids of Zucker and spontaneously hypertensive heart failure) rats, a model of diabetic nephropathy. We included sham-operated lean control rats (LS), sham-operated diabetic (DS), and diabetic rats with induced renal ischemia (DI). Diabetic nephropathy in DI was accelerated by the single episode of renal ischemia. This progressive renal decline was associated with renal iron accumulation, although serum and urinary iron levels were far lower in DI than in LS. Furthermore, obese/diabetic ZS rats have severe dyslipidemia, a condition that has been linked to hepatic iron overload. Hence, we tested and found that the fatty acids oleic acid and palmitate stimulated iron accumulation in renal tubular cells in vitro. Renal mRNAs encoding several key proteins that promote iron accumulation were increased in DI. Moreover, renal mRNAs encoding the antioxidant proteins superoxide dismutase, catalase, and most of the glutathione synthetic system were suppressed, which would magnify the prooxidant effects of renal iron loads. Substantial renal iron loads occur in obese/diabetic rats. We propose that in diabetes, specific renal gene activation is partly responsible for iron accumulation. This state might be further aggravated by lipid-stimulated iron uptake. We suggest that progressive renal iron overload may further advance renal injury in obese/diabetic ZS rats.

Albuminuria as a Risk Factor for Anemia in Chronic Kidney Disease: Result from the KoreaN Cohort Study for Outcomes in Patients With Chronic Kidney Disease (KNOW-CKD)

BACKGROUND

Anemia is a common complication among patients with chronic kidney disease (CKD), and it is associated with unfavorable clinical outcomes in patients with CKD independent of the estimated glomerular filtration rate (eGFR). We assessed the association of the urinary albumin-to-creatinine ratio (ACR) and eGFR with anemia in CKD patients.

METHODS

We conducted a cross-sectional study using baseline data from the KoreaN Cohort Study for Outcome in Patients With Chronic Kidney Disease (KNOW-CKD). Multiple regression analysis was performed to identify the independent association of albuminuria with anemia. Furthermore, odds ratios for anemia were calculated by cross-categorization of ACR and eGFR.

RESULTS

Among 1,456 patients, the mean age was 53.5 ± 12.4 years, and the mean eGFR and ACR were 51.9 ± 30.5 mL/min per 1.73 m2 and 853.2 ± 1,330.3 mg/g, respectively. Anemia was present in 644 patients (40.5%). Multivariate analysis showed that the odds ratio of anemia increased according to ACR levels, after adjusting for age, sex, eGFR, body mass index, pulse pressure, cause of CKD, use of erythropoiesis stimulating agents, serum calcium and ferritin (ACR < 30 mg/g as a reference group; 30-299 mg/g, adjusted odds ratio (OR) = 1.43, 95% confidence interval (CI) = 0.88-2.33; ≥300 mg/g, adjusted OR = 1.86, 95% CI = 1.12-3.10). In addition, graded associations were observed in cross-categorized groups of a higher ACR and eGFR compared to the reference group with an ACR <30 mg/g and eGFR ≥60 mL/min per 1.73 m2.

CONCLUSION

The present study demonstrated that albuminuria was a significant risk factor for anemia in CKD patients independent of the eGFR.

Urinary albumin and transferrin as early diagnostic markers of chronic kidney disease

Feline renal diseases are increasingly noted in veterinary practice. It is important to diagnose and identify the pathological basis of renal dysfunction accurately at an early stage, but there are only a few reports on this area in clinical veterinary medicine. We investigated the efficacy of measurement of urinary albumin (u-Alb) and urinary transferrin (u-Tf) for early diagnosis using 5-µl urine samples collected noninvasively by catheterization from normal (IRIS stage I) cats and cats with stage I chronic kidney disease (CKD). The u-Alb levels in normal and stage I CKD cats were 6.0 ± 4.5 and 11.2 ± 8.4 mg/dl, respectively, and the u-Tf levels were 0.09 ± 0.42 and 0.52 ± 0.79 mg/dl, respectively. Based on ROC curve analysis, the sensitivity and specificity of u-Alb and u-Tf were higher than those of the currently used biomarker, the plasma creatinine level. The sensitivity of u-Alb was higher than that of u-Tf, whereas the specificity of u-Tf was higher than that of u-Alb. The validity of the threshold albumin level (20 mg/dl) was confirmed by measurements using SDS-PAGE. Since leakage of u-Tf in urine precedes leakage of u-Alb, inclusion of u-Tf in biochemistry tests may be appropriate for IRIS staging as a diagnostic marker of early diagnosis of renal disorder in cats.

Dietary iron restriction inhibits progression of diabetic nephropathy in db/db mice

Excess iron causes oxidative stress through hydroxyl-radical production via Fenton/Haber-Weiss reactions. Recently, body iron reduction has been found to ameliorate diabetes. In the present study, we examined the protective effect of dietary iron restriction against diabetic nephropathy in the db/db mouse model of diabetic nephropathy using db/m mice as controls. The db/db mice were divided into two groups and fed a normal diet (ND) or a low-iron diet (LID). Increasing urinary albumin excretion was observed in the ND db/db mice, but this was suppressed in db/db mice with LID. Histologically, the db/db mice in the ND group had increased glomerular volume and mesangial area compared with the LID group. Augmented deposition of extracellular matrixes was decreased in db/db mice with LID. In terms of oxidative stress, increased superoxide production observed in the kidneys of the ND db/db mice was diminished in the LID group. NADPH oxidase activity and renal expression of NADPH oxidase components p22phox and NADPH oxidase 4 (NOX4) were augmented in the ND group, and this was abolished by LID. There were no differences in expression of renal iron importers, transferrin receptor, or divalent metal transporter-1 between db/m mice and db/db mice. The level of ferroportin, an iron exporter, increased in the kidneys of the db/db mice. Urinary iron excretion was significantly higher in ND db/db mice and was reduced in the LID group. These findings suggest that dietary iron restriction exerts a preventive effect on the progression of diabetic nephropathy partly due to the reduction of oxidative stress.

Effect of deferiprone, an oral iron chelator, in diabetic and non-diabetic glomerular disease

Compelling experimental evidence exists for the role of oxidants and iron in glomerular disease. In preliminary studies, we confirmed increased urinary catalytic iron in patients with glomerulonephritis and diabetic nephropathy. We conducted two separate single-center, prospective, single-armed, open-labeled, proof-of-concept studies to evaluate the safety and efficacy of an oral iron chelator in patients with glomerulonephritis and diabetic nephropathy. Study 1 comprised 15 patients with biopsy-proven glomerulonephritis who had persistent proteinuria despite treatment with steroids and/or cyclophosphamides. Study 2 comprised 38 adult patients with diabetic nephropathy. Patients in Study 1 were treated with deferiprone (50 mg/kg/day) in three divided doses for 6 months and Study 2 patients were treated for 9 months. In Study 1, two patients had severe gastrointestinal intolerance and withdrew from the study after one dose and are not included in the results. There was a significant reduction (47 ± 9% mean) in 24-h urinary protein (4.01 ± 1.61 to 2.21 ± 1.62 [p = 0.009]), with no significant changes in serum creatinine. In Study 2, treatment with deferiprone resulted in a marked, persistent drop in the mean albumin/creatinine ratio (187 ± 47 at baseline to 25 ± 7 mg/g, [p = 0.01]) and stable renal function over a 9-month period. No clinically significant adverse events were observed in either study. Although these are small, open-labeled, and non-randomized studies, our results suggest that future randomized, double-blind trials examining the utility of deferiprone to treat glomerular diseases appear warranted.

Urinary markers of glomerular injury in diabetic nephropathy

Diabetic nephropathy, the leading cause of renal failure worldwide, affects approximately one-third of all people with diabetes. Microalbuminuria is considered the first sign and the best predictor of progression to renal failure and cardiovascular events. However, albuminuria has several limitations. Therefore, earlier, more sensitive and specific biomarkers with greater predictability are needed. The aim of this paper is to discuss the current literature on biomarkers of glomerular injury that have been implicated in diabetic kidney disease.

Effect of FeSO4 treatment on glucose metabolism in diabetic rats

Iron, the prosthetic group of haemoglobin, was found to lower serum glucose levels of diabetic rats. Its regulative mechanism and effects on enzymatic activities of glucose metabolism are still unknown. In this study, the correlation between iron supply and enzymatic activities of glucose metabolism and respiratory chain were evaluated in liver and kidney tissues of alloxan induced-diabetic rats. After FeSO4 and metformin administration, serum samples were collected for serum glucose and fructosamine level measurements. Kidney and liver tissues were excised at the end of the study for assaying enzymatic activities of isocitrate dehydrogenase, succinate dehydrogenase, malate dehydrogenase, NADH-dehydrogenase and cytochrome-c-oxidase. Results showed significantly decreased serum glucose and fructosamine levels in treatment groups and enhanced enzymatic activities of several proteins as compared with the diabetic control group. Therefore, these data suggested that FeSO4 administration could increase the supply of oxygen, enhance enzymatic activities of glucose metabolism and the respiratory chain, accelerate glucose metabolism and consequently decrease serum glucose levels.

Suppressive Effects of Iron on TGF-β1 Production by Renal Proximal Tubular Epithelial Cells

BACKGROUND

TGF-beta1, which is one of the profibrogenic cytokines, is considered essential for both the tubulointerstitial fibrosis found in chronic kidney diseases and the repair of tissue damage in acute renal injury. Iron plays an important part in inflammatory damage since it supplies cytotoxic hydroxyl radicals. The aim of the present study was to examine the direct effects of iron on TGF-beta1 production and the expression of 8-hydroxy-2'-deoxyguanosine (8-OHdG), a marker of oxidative stress, by human renal proximal tubular epithelial cells (RPTEC).

METHODS

Using human RPTEC, TGF-beta1 expression was studied by immunohistochemical staining, ELISA and RNase protection assays. 8-OHdG expression was evaluated by immunohistochemical staining.

RESULTS

Ferric iron suppressed both TGF-beta1 secretion and mRNA expression, and enhanced 8-OHdG expression in RPTEC in a dose-dependent manner. Desferrioxamine, an iron chelator, eliminated the suppressive effect of ferric citrate on TGF-beta1 production.

CONCLUSIONS

The results suggest that iron may delay the repair of kidney injury during the acute inflammatory phase via a reduction in TGF-beta1 production by RPTEC. Iron chelation may therefore be a useful strategy in the treatment of inflammatory kidney diseases.

Altered expression of iron transport proteins in streptozotocin-induced diabetic rat kidney

Diabetes mellitus is associated with altered iron homeostasis in both human and animal diabetic models. Iron is a metal oxidant capable of generating reactive oxygen species (ROS) and has been postulated to contribute to diabetic nephropathy. Two proteins involved in iron metabolism that are expressed in the kidney are the divalent metal transporter, DMT1 (Slc11a2), and the Transferrin Receptor (TfR). Thus, we investigated whether renal DMT1 or TfR expression is altered in diabetes, as this could potentially affect ROS generation and contribute to diabetic nephropathy. Rats were rendered diabetic with streptozotocin (STZ-diabetes) and renal DMT1 and TfR expression studied using semi-quantitative immunoblotting and immunofluorescence. In STZ-diabetic Sprague-Dawley rats, renal DMT1 expression was significantly reduced and TfR expression increased after 2 weeks. DMT1 downregulation was observed in both proximal tubules and collecting ducts. Renal DMT1 expression was also decreased in Wistar rats following 12 weeks of STZ-diabetes, an effect that was fully corrected by insulin-replacement but not by cotreatment with the aldose reductase inhibitor, sorbinil. Increased renal TfR expression was also observed in STZ-diabetic Wistar rats together with elevated cellular iron accumulation. Together these data demonstrate renal DMT1 downregulation and TfR upregulation in STZ-diabetes. Whilst the consequence of altered DMT1 expression on renal iron handling and oxidant damage remains to be determined, the attenuation of the putative lysosomal iron exit pathway in proximal tubules could potentially explain lysosomal iron accumulation reported in human diabetes and STZ-diabetic animals.

Oxidants and iron in chronic kidney disease

Oxidants derived either from leukocytes in proliferative glomerular nephritis or from resident glomerular cells in nonproliferative glomerulonephritis have been shown to have several biologic effects relevant to chronic kidney disease. These include: the ability of oxidants to damage glomerular basement membrane (GBM) and to directly induce proteinuria; effects that would lead to a fall in the glomerular filtration rate; and effects that would account for the morphologic changes observed in chronic kidney disease. In experimental models the role of oxidants has been demonstrated in both proliferative glomerulonephritis (e.g., anti-GBM antibody disease) as well as experimental models of minimal change disease and membranous nephropathy. Oxidants have also been shown to be an important mediator of the various pathways that have been implicated in diabetic nephropathy. Antioxidants and iron chelators have also been shown to retard functional and morphologic changes observed in progressive kidney disease. Taken together, these experimental studies suggest an important role of oxidants in chronic kidney disease.

Increased urinary excretion of monocyte chemoattractant protein-1 in proteinuric renal diseases

Monocyte chemoattractant protein-1 (MCP-1) is a chemokine that is produced mainly by tubular epithelial cells in kidney and contributes to renal interstitial inflammation and fibrosis. More recently, we have demonstrated that urinary MCP-1 excretion is increased in proportion to the degree of albuminuria (proteinuria) and positively correlated with urinary N-acetylglucosaminidase (NAG) levels in type 2 diabetic patients. Based on these findings, we have suggested that heavy proteinuria, itself, probably aggravates renal tubular damage and accelerates the disease progression in diabetic nephropathy by increasing the MCP-1 expression in renal tubuli. In the present study, to evaluate whether urinary MCP-1 excretion is increased in the proteinuric states not only in diabetic nephropathy but also in other renal diseases, we examined urinary MCP-1 levels in IgA nephropathy patients with macroalbuminuria (IgAN group; n = 6), and compared the results with the data obtained from type 2 diabetic patients with overt diabetic nephropathy (DN group; n = 23) and those without diabetic nephropathy (non-DN group; n = 27). Urinary MCP-1 excretion levels in non-DN, DN, IgAN groups were 157.2 (52.8-378.5), 346.1 (147.0-1276.7), and 274.4 (162.2-994.5) ng/g creatinine, median (range), respectively. Expectedly, urinary MCP-1 and NAG excretion levels in DN and IgAN groups were significantly elevated as compared with non-DN group. Therefore, we suggest that MCP-1 expression in renal tubuli is enhanced in proteinuric states,irrespective of the types of renal disease, and that increased MCP-1 expression probably contributes to renal tubular damage in proteinuric states.

Association of monocyte chemoattractant protein-1 with renal tubular damage in diabetic nephropathy

Monocyte chemoattractant protein-1 (MCP-1), is a chemokine that mediates renal interstitial inflammation, tubular atrophy, and interstitial fibrosis by recruiting monocytes/macrophages into renal tubulointerstitium. Recent studies have demonstrated that protein overload in renal tubular cells up-regulates MCP-1 gene and its protein expression. Therefore, we hypothesized that increased expression of MCP-1 in renal tubuli, probably triggered by an increase in the leakage of plasma protein from glomerular capillary to tubular fluid, may contribute to renal tubular damage and accelerate the progression of diabetic nephropathy. To test this hypothesis, we examined urinary excretion levels of MCP-1 and N-acetylglucosaminidase (NAG), a sensitive marker of renal tubular damage, in Japanese Type II diabetic patients with normoalbuminuria (n=29), microalbuminuria (n=25), and macroalbuminuria (n=18). The median urinary excretion level of MCP-1 in patients with macroalbuminuria (394.4 ng/g creatinine) was significantly elevated compared to the levels in patients with normoalbuminuria and microalbuminuria (159.6 and 193.9 ng/g creatinine, respectively). Furthermore, the urinary MCP-1 excretion level was positively correlated with urinary excretion levels of albumin (r=.816, P<.001) and NAG (r=.569, P<.001) in all subjects. These results suggest that MCP-1 is produced in renal tubular cells and released into urine in proportion to the degree of proteinuria (albuminuria), and that increased MCP-1 expression in renal tubuli contributes to renal tubular damage. Therefore, we conclude that heavy proteinuria itself may accelerate the progression of diabetic nephropathy by increasing the MCP-1 expression in renal tubuli.

Transferrinuria in type 2 diabetic patients with early nephropathy and tubulointerstitial injury

BACKGROUND: Transferrinuria is thought to be a marker for early stages of diabetic nephropathy. Transferrin has also been proposed as a mediator of tubular toxicity because the reabsorption of transferrin results in the release of reactive iron in proximal tubular cells, promoting the formation of hydroxyl radicals. We evaluated the role of urinary transferrin excretion in diabetic patients with early nephropathy by comparing tubulointerstitial injury in renal biopsy specimens. PATIENTS AND METHODS: 45 type 2 diabetic patients with normoalbuminuria (urinary albumin excretion <30 mg/24 h) or microalbuminuria (30-300 mg/24 h) were studied. All patients with microalbuminuria underwent renal biopsy, and the severity of the tubulo-interstitial lesions was determined by a semiquantitative estimate of interstitial fibrosis, tubular atrophy, and interstitial inflammatory infiltrates. Subjects were classified into group A (normoalbuminuria, n=25), group B (microalbuminuria without tubulointerstitial changes, n=11) or group C (microalbuminuria with tubulointerstitial changes, n=9). RESULTS: Urinary transferrin excretion (UTf), as well as UTf/creatinine clearance (Ccr), and transferrin clearance (CTf/Ccr), was significantly higher in groups B and C than in group A, and it was significantly higher in group C than in group B. There were no significant differences in urinary albumin excretion or mesangial expansion rate (MR% estimated by quantitative morphometric studies) between groups B and C. Although urinary beta2-microglobulin excretion was significantly higher in group C than in groups A and B, urinary N-acetyl-beta-D-glucosaminidase activity was significantly higher in groups B and C than in group A. CONCLUSIONS: Increased transferrinuria in the microalbuminuric stage may lead to the development of tubulointerstitial injuries in type 2 diabetic patients.

Quantitative analyses of osteopontin mRNA expression in human proximal tubules isolated from renal biopsy tissue sections of minimal change nephrotic syndrome and IgA glomerulonephropathy patients

Osteopontin (OPN), a secreted phosphoprotein and chemotactic to monocytes/macrophages, is upregulated in renal cortical tubules in a variety of rodent models of renal injury and is believed to possibly have a role in tubulointerstitial injury. We previously reported the establishment of a system for the quantification of messenger RNA (mRNA) expression in isolated rat glomeruli using laser-manipulated microdissection and real-time polymerase chain reaction. This system was applied to human renal biopsy specimens. We quantified OPN mRNA expression in proximal tubules of 5 patients with minimal change nephrotic syndrome (MCNS) and 11 patients with mild immunoglobulin A (IgA) glomerulonephritis. We also examined the correlation between OPN mRNA expression in proximal tubules and clinical data and pathological findings in glomeruli and tubulointerstitial regions. Patients with MCNS showed a positive correlation between OPN mRNA expression in proximal tubules and urinary protein excretion (r = 0.93; P < 0.05), whereas for patients with IgA glomerulonephritis, logarithmic values of OPN mRNA expression in proximal tubules positively correlated with low urinary protein levels (r = 0.72; P < 0.05). Pathological changes, ranging from nonexistent to minor, in glomeruli and tubulointerstitium of these patients with mild IgA glomerulonephritis did not significantly correlate with OPN mRNA expression in proximal tubules. In patients with mild IgA glomerulonephritis, OPN mRNA expression in proximal tubules increased exponentially in response to a small amount of urinary protein (<1.2 g/d).

Increased urinary excretion of N-acetylglucosaminidase in subjects with impaired glucose tolerance

N-acetylglucosaminidase (NAG) is a lysosomal enzyme produced by renal proximal tubular cells and has been widely used as a marker, which indicates a degree of renal tubular damage. An increase in urinary NAG excretion is though to result from the renal tubular damage. The aim of this study was to evaluate whether even mild hyperglycemia causes an increase in urinary excretion of NAG, which is a renal tubular protein. We examined urinary NAG excretion in overnight urine in 22 Japanese men with impaired glucose tolerance (IGT) for more than two years (IGT group) and 41 healthy control subjects matched in age, gender, BMI and blood pressure (control group). Urinary NAG excretion levels of IGT group and control group were 2.89 (1.23-7.97) and 2.22 (0.60-4.93) U/g creatinine, median (range), respectively. The IGT group showed significantly higher urinary excretion of NAG compared to the control group (p < 0.01). Several studies have indicated that plasma proteins filtered through the glomerular capillary may have intrinsic renal toxicity. Recently, we have reported that urinary excretion of plasma proteins (ceruloplasmin, IgG4 and IgG) with molecular radii of approximately 45-55 A is increased in subjects with IGT compared to healthy control subjects with normal glucose tolerance. Considering the present result together with our recent finding, we suggest that increased urinary excretion of NAG in the mildly hyperglycemic subjects may be due to the adverse effects of the plasma proteins highly filtered through the glomerular capillary on tubular cells.

Iron deposition in renal biopsy specimens from patients with kidney diseases

This study was performed to investigate the correlation between clinical parameters and grading of iron deposition in renal biopsy specimens from 102 patients with various kidney diseases. Iron deposition in renal tissues was detected by Berlin blue staining. The extent of iron staining was semiquantitatively graded as negative (Fe(-)), grade 0, or positive (Fe(+)), including faint, grade 1; moderate, grade 2; or severe, grade 3, by light microscopy. Thirty-four of 102 patients (33%) showed positive iron staining. Fe(+) patients had various renal diseases, mainly consisting of 12 patients with immunoglobulin A nephropathy and 5 patients with benign nephrosclerosis. Mean arterial pressure (MAP), serum creatinine (sCr) levels, incidence of hematuria, and urinary N-acetylbeta-D-glucosaminidase (u-NAG) levels in Fe(+) patients were significantly greater than those in Fe(-) patients, and u-NAG levels correlated positively with the extent of iron deposition. Study patients were tentatively divided into two groups according to the extent of iron deposition: group A, patients with grades 2 and 3 staining, and group B, patients with grades 0 and 1 staining. In group A, MAP, sCr level, urinary protein excretion, and the incidence of hematuria were significantly greater than in group B. Our results suggest that the amount of iron deposition in renal tissue may contribute to the progression of chronic renal disease and may be an early and sensitive indicator of renal damage in certain renal diseases.

Erythropoietin and transferrin metabolism in nephrotic syndrome

Nephrotic syndrome is characterized by marked urinary excretion of albumin and other intermediate-size plasma proteins. This results in a profound alteration of the metabolism of many plasma proteins and protein-bound substances, as well as certain cellular and tissue proteins. This review summarizes available data on the effect of nephrotic syndrome on the metabolism and regulation of erythropoietin (EPO) and transferrin, which are essential for erythropoiesis. Studies of humans and animals have documented significant urinary losses of both EPO and transferrin in nephrotic syndrome. Urinary losses of EPO have been shown to cause EPO-deficiency anemia and prevent the normal increase in plasma EPO level in response to anemia and hypoxia in nephrotic syndrome. Similarly, transferrinuria and increased transferrin catabolism have been shown to cause hypotransferrinemia and, in some cases, iron-deficiency anemia. In addition, dissociation of iron from filtered transferrin, occasioned by a reduction in tubular fluid pH, can promote tubulointerstitial injury through the iron-catalyzed generation of oxygen free radicals. This can account in part for the role of proteinuria as a risk factor for the progression of renal disease. Subcutaneous administration of recombinant EPO has been successfully used in the management of EPO-deficiency anemia in nephrotic syndrome. Similarly, iron supplementation and nutritional support are indicated in nephrotic patients with severe transferrinuria and iron-deficiency anemia. However, correction or amelioration of the underlying proteinuria, when possible, is the ideal approach to reversal of these complications.

Transferrin synthesis is increased in nephrotic patients insufficiently to replace urinary losses

The urinary loss of transferrin is sufficient to reduce plasma transferrin concentrations in the nephrotic syndrome. Hypotransferrinemia may lead to iron loss and microcytic anemia. The mechanism responsible for the hypotransferrinemia in the nephrotic syndrome is, however, unknown. In the present study, synthesis rate of transferrin was measured in vivo in nephrotic patients (n = 7) compared with control subjects (n = 6) using L-[1-(13)C]-valine. Plasma transferrin and iron concentration in the patients were significantly lower than in control subjects (transferrin, 1.39 +/- 0.08 versus 2.57 +/- 0.11 g/L, P < 0.0001; iron, 10.2 +/- 0.8 versus 21.1 +/- 4.5 micromol/L, P = 0.02). Furthermore, albuminuria correlated with transferrinuria (r(2) = 0.901, P = 0.001). The absolute synthesis rate of transferrin was increased in the patients (10.0 +/- 1.1 versus 7.4 +/- 0.7 mg/kg per d, P = 0.07), although this value failed to achieve significance. C-reactive protein, plasma iron, and proteinuria did not correlate with transferrin synthesis. In contrast, transferrin synthesis correlated with albumin synthesis (r(2) = 0.648, P = 0.03; n = 7). The present study indicates that increased transferrin synthesis occurs in nephrotic patients but is insufficient to compensate for urinary losses. Because, overall, no significant relationship was found between transferrin synthesis and either C-reactive protein or iron, it is unlikely that inflammation suppresses or that iron deficiency stimulates increased transferrin synthesis in these patients. The correlation between transferrin synthesis and albumin synthesis suggests that transferrin synthesis is a component of a general response in hepatic protein synthesis in the nephrotic syndrome. This suggests that a therapeutic approach to maximize plasma transferrin concentrations in nephrotic patients should be aimed primarily at reducing urinary protein excretion.

Transferrin but not albumin mediates stimulation of complement C3 biosynthesis in human proximal tubular epithelial cells

Complement is increasingly implicated in the pathogenesis of progressive renal disease resulting from persistent proteinuria. We have previously shown that apical serum proteins stimulate C3 in cultured human proximal tubular epithelial cells (PTECs), and that the stimulant is a nonalbumin compound of 30 to 100 kd. We postulated in this study that transferrin and apotransferrin, also important components of proteinuric urine in this molecular-weight range, might be the culprit. Human PTECs were obtained by differential sieving of renal cortical tissue from the normal pole of tumor nephrectomy specimens and characterized to be predominantly of proximal tubular origin. Complement C3 messenger RNA (mRNA) expression was analyzed in confluent growth-arrested PTEC monolayers in media containing different concentrations (2.5 to 20 mg/mL) of transferrin by reverse transcription and polymerase chain reaction. Pure human albumin was used as a control protein. C3 protein secretion was detected and quantified by a sandwich enzyme-linked immunosorbent assay on cell culture supernatants after distinct time points. Transferrin enhanced the rate of C3 secretion in a dose-dependent manner, reaching maximal stimulation at doses of 10 mg/mL. Selected experiments using the Transwell technique showed that C3 release was predominantly apical in the resting state. The addition of 10 mg/mL of transferrin apically but not basolaterally stimulated both apical and basolateral C3 secretion and increased the basolateral-apical ratio of C3 secretion from 0.45 +/- 0.16 to 0.93 +/- 0.24 (P: < 0.02). Constitutive C3 mRNA expression was upregulated by transferrin in a time- and dose-dependent fashion, reaching a peak after 24 hours. A similar degree of C3 upregulation was reproduced when iron-poor transferrin, apotransferrin, was used instead. These results indicate that C3 synthesis in PTECs is upregulated by transferrin, for which protein rather than iron moiety may account for the observed effects. These findings provide evidence linking proteinuria with overexpression of tubular complement.

Role of iron in progressive renal disease

The importance of iron in renal injury is derived from the ease with which iron is reversibly oxidized or reduced, enabling it to participate in the production of free radicals. Experimental evidence for the role of oxidants and iron in progressive renal disease falls into two broad categories. First, considerable data implicate oxidants in the proteinuria of glomerular disease. To the extent that proteinuria is an important determinant of progression, reduction of proteinuria would result in retardation of progression. Evidence also suggests a role of oxidants and iron in diabetic nephropathy, a major cause of end-stage kidney disease. Second, more direct studies have examined the role of oxidants and iron in models of progressive renal disease. These studies include the demonstration of increased iron in the kidney in models of progressive kidney disease; enhanced generation of oxidants, providing a mechanism by which iron can be mobilized; and more direct evidence of the beneficial effect of iron-deficient diets and iron chelators. Although the collective information on the role of oxidants and iron derived from in vitro studies and animal models of glomerular disease and progressive renal failure is impressive, control studies of patients are needed to show the efficacy of antioxidants and/or iron chelators in retarding the progression of renal failure and may offer an important therapeutic modality to patients with renal disease.