Urinary cystatin C as a biomarker for diabetic nephropathy and its immunohistochemical localization in kidney in Zucker diabetic fatty (ZDF) rats

Diabetic Nephropathy: Pathogenesis, Mechanisms, and Therapeutic Strategies

Diabetic nephropathy represents a predominant etiology of end-stage renal disease (ESRD) on a global scale, significantly impacting the morbidity and mortality rates of individuals with diabetes. The primary objective of this analysis is to furnish a comprehensive examination of the etiology, fundamental mechanisms, and treatment modalities for DN. The development of DN stems from a multitude of factors, encompassing a intricate interplay involving metabolic irregularities induced by hyperglycemia, alterations in hemodynamics, inflammatory responses, oxidative stress, and genetic susceptibility. Principal mechanisms encompass the generation of advanced glycation end products (AGEs), activation of protein kinase C (PKC), and overexpression of the renin-angiotensin-aldosterone system (RAAS). These processes precipitate glomerular hyperfiltration, hypertrophy, and eventually, fibrosis and scarring of the renal parenchyma. Initially, hyperglycemia triggers mesangial proliferation and thickening of the glomerular basement membrane in the incipient stages of DN, subsequently leading to progressive glomerular sclerosis and tubulointerstitial fibrosis. Inflammatory cascades, notably involving cytokines like TGF-β and NF-κB, play pivotal roles in the advancement of DN by fostering the accumulation of extracellular matrix and renal fibrosis. Inflammation pathways, particularly those involving cytokines like TGF-β and NF-κB, play essential roles in diabetic nephropathy progression by stimulating extracellular matrix accumulation and renal fibrosis. The presence of oxidative stress, worsened by dysfunctional mitochondria, contributes further to renal injury via lipid peroxidation and DNA damage. Current therapeutic approaches for diabetic nephropathy concentrate on optimizing glycemic control, controlling hypertension, and suppressing the renin-angiotensin-aldosterone system. Among antihypertensive medications, ACE inhibitors and angiotensin II receptor blockers are crucial for decelerating disease advancement.

Urinary biomarkers in diabetic nephropathy

Diabetic nephropathy (DN), a significant consequence of diabetes, is associated with adverse cardiovascular and renal disease as well as mortality. Although microalbuminuria is considered the best non-invasive marker for DN, better predictive markers are needed of sufficient sensitivity and specificity to detect disease in general and in early disease specifically. Even prior to appearance of microalbuminuria, urinary biomarkers increase in diabetics and can serve as accurate nephropathy biomarkers even in normoalbuminuria. In this review, a number of novel urine biomarkers including those reflecting kidney damage caused by glomerular/podocyte damage, tubular damage, oxidative stress, inflammation, and intrarenal renin-angiotensin system activation are discussed. Our review also includes emerging biomarkers such as urinary microRNAs. These short noncoding miRNAs regulate gene expression and could be utilized to identify potential novel biomarkers in DN development and progression. .

A diet containing cod backbone proteins attenuated the development of mesangial sclerosis and tubular dysfunction in male obese BTBR ob/ob mice

PURPOSE

The obese black and tan, brachyuric (BTBR) ob/ob mouse spontaneously develops features comparable to human diabetic nephropathy. The primary aim of the present study was to investigate if a diet containing fish proteins would attenuate or delay the development of glomerular hypertrophy (glomerulomegaly), mesangial sclerosis and albuminuria in obese BTBR ob/ob mice.

METHODS

Obese BTBR.CgLepob/WiscJ male mice were fed diets containing 25% of protein from Atlantic cod backbones and 75% of protein from casein (Cod-BB group), or casein as the sole protein source (control group). Kidneys were analysed morphologically, and markers for renal dysfunction were analysed biochemically in urine and serum.

RESULTS

The Cod-BB diet attenuated the development of mesangial sclerosis (P 0.040) without affecting the development of glomerular hypertrophy and albuminuria. The urine concentration of cystatin C (relative to creatinine) was lower in mice fed the Cod-BB diet (P 0.0044).

CONCLUSION

A diet containing cod backbone protein powder attenuated the development of mesangial sclerosis and tubular dysfunction in obese BTBR ob/ob mice, but did not prevent the development of glomerular hypertrophy and albuminuria in these mice.

Modeling SILAC Data to Assess Protein Turnover in a Cellular Model of Diabetic Nephropathy

Protein turnover rate is finely regulated through intracellular mechanisms and signals that are still incompletely understood but that are essential for the correct function of cellular processes. Indeed, a dysfunctional proteostasis often impacts the cell's ability to remove unfolded, misfolded, degraded, non-functional, or damaged proteins. Thus, altered cellular mechanisms controlling protein turnover impinge on the pathophysiology of many diseases, making the study of protein synthesis and degradation rates an important step for a more comprehensive understanding of these pathologies. In this manuscript, we describe the application of a dynamic-SILAC approach to study the turnover rate and the abundance of proteins in a cellular model of diabetic nephropathy. We estimated protein half-lives and relative abundance for thousands of proteins, several of which are characterized by either an altered turnover rate or altered abundance between diabetic nephropathic subjects and diabetic controls. Many of these proteins were previously shown to be related to diabetic complications and represent therefore, possible biomarkers or therapeutic targets. Beside the aspects strictly related to the pathological condition, our data also represent a consistent compendium of protein half-lives in human fibroblasts and a rich source of important information related to basic cell biology.

Molecular Mechanisms of Diabetic Kidney Disease

The inflammatory component of diabetic kidney disease has become of great interest in recent years, with genetic and epigenetic variants playing a fundamental role in the initiation and progression of the disease. Cells of the innate immune system play a major role in the pathogenesis of diabetic kidney disease, with a lesser contribution from the adaptive immune cells. Other components such as the complement system also play a role, as well as specific cytokines and chemokines. The inflammatory component of diabetic kidney disease is of great interest and is an active research field, with the hope to find potential innovative therapeutic targets.

Cardiovascular Characteristics of Zucker Fatty Diabetes Mellitus Rats, an Animal Model for Obesity and Type 2 Diabetes

Zucker fatty diabetes mellitus (ZFDM) rats harboring the missense mutation (fa) in a leptin receptor gene have been recently established as a novel animal model of obesity and type 2 diabetes (T2D). Here, we explored changes in cardiovascular dynamics including blood pressure and heart rate (HR) associated with the progression of obesity and T2D, as well as pathological changes in adipose tissue and kidney. There was no significant difference in systolic blood pressure (SBP) in ZFDM-Lepr^fa/fa (Homo) compared with ZFDM-Lepr^fa/+ (Hetero) rats, while HR and plasma adrenaline in Homo were significantly lower than Hetero. The mRNA expression of monocyte chemotactic protein-1 in perirenal white adipose tissue (WAT) from Homo was significantly higher than Hetero. Interscapular brown adipose tissue (BAT) in Homo was degenerated and whitened. The plasma blood urea nitrogen in Homo was significantly higher than Hetero. In summary, we demonstrated for the first time that HR and plasma adrenaline concentration but not SBP in Homo decrease with obesity and T2D. In addition, inflammation occurs in WAT from Homo, while whitening occurs in BAT. Further, renal function is impaired in Homo. In the future, ZFDM rats will be useful for investigating metabolic changes associated with the progression of obesity and T2D.

Effects of intact and hydrolysed blue whiting proteins on blood pressure and markers of kidney function in obese Zucker fa/fa rats

PURPOSE

To investigate the effects of diets containing intact or hydrolysed proteins from blue whiting (Micromesistius poutassou) on the development of high blood pressure and markers of kidney function in obese Zucker fa/fa rats which are prone to develop hypertension and renal failure.

METHODS

Male rats were fed isocaloric diets containing either intact blue whiting whole meal (BW-WM), blue whiting protein hydrolysate prepared with Alcalase^® (BW-HA) or blue whiting protein hydrolysate prepared with Protamex^® (BW-HP) as 1/3 of total protein with the remaining 2/3 as casein, or casein as sole protein source (control group). Blood pressure was measured at Day 0 and Day 32. Rats were housed in metabolic cages for 24 h for collection of urine in week 4. After 5 weeks, rats were euthanized and blood was drawn from the heart. The renin and angiotensin-converting enzyme (ACE) inhibition capacities for casein and blue whiting proteins were measured in vitro.

RESULTS

The blood pressure increase was lower in rats fed diets containing blue whiting proteins when compared to the control group, whereas markers of kidney function were similar between all groups. The three blue whiting proteins inhibited renin activity in vitro, whereas casein had no effect. The in vitro ACE inhibition was similar for casein, BW-WM and BW-HP proteins, whereas BW-HA protein was less potent.

CONCLUSION

Blue whiting protein feeding attenuated the blood pressure increase in obese Zucker fa/fa rats, possibly mediated through the renin-angiotensin system and without affecting markers of kidney function.

Animal Models and Renal Biomarkers of Diabetic Nephropathy

Diabetes mellitus (DM) is the first cause of end stage chronic kidney disease (CKD). Animal models of the disease can shed light on the pathogenesis of the diabetic nephropathy (DN) and novel and earlier biomarkers of the condition may help to improve diagnosis and prognosis. This review summarizes the most important features of animal models used in the study of DN and updates the most recent progress in biomarker research.

Angiotensin blockade attenuates diabetic nephropathy in hypogonadal adult male rats

This study examined the effect of the aromatase inhibitor letrozole (0.5 mg/kg) alone or in combination with the angiotensin-receptor blocker valsartan (30 mg/kg) against streptozocin-induced diabetic nephropathy (DN) in hypogonadal (HG) rats for 12 weeks. First, we tested the HG effect on hormone levels, inflammatory cytokines, and oxidative stress in nondiabetic (ND) and diabetic (D) rats. HG was induced with the luteinizing hormone-releasing hormone antagonist cetrorelix (0.71 mg/kg). Diabetes enhanced hormonal hypogonadism and increased inflammation and oxidative stress. Next, experiments examined the effect of early letrozole and valsartan intervention on DN in HG rats. HG-ND and HG-D rats were treated with letrozole alone or in combination with valsartan. HG-D rats developed proteinuria and had increased blood urea nitrogen and creatinine, and histopathological evidence of renal injury, including glomerular hypertrophy and mesangial expansion. Valsartan alone or in combination with letrozole reduced proteinuria, improved renal functions, and reduced diabetes-induced renal angiotensin II. Both agents ameliorated nuclear factor kappa light chain enhancer of activated B cells, interleukin 1β, interleukin 6, and tumor necrosis factor alpha levels. The combination decreased superoxide dismutase, malondialdehyde, and glutathione peroxidase levels, and prevented glomerular hypertrophy. In HG-D rats, valsartan reduced renal collagen IV and transforming growth factor-beta 1, especially when the testosterone level was corrected by letrozole. Thus, normalizing testosterone and inhibiting renal angiotensin II have a renoprotective effect against DN in HG male rats.

Effects of Chronic Administration of Capsaicin on Biomarkers of Kidney Injury in Male Wistar Rats with Experimental Diabetes

Capsaicin is an agonist of the transient receptor potential vanilloid type 1 (TRPV1) channel, which has been related to the pathophysiology of kidney disease secondary to diabetes. This study aimed to evaluate the chronic effect of capsaicin administration on biomarkers of kidney injury in an experimental rat model of diabetes. Male Wistar rats were assigned to four groups: (1) healthy controls without diabetes (CON), (2) healthy controls plus capsaicin at 1 mg/kg/day (CON + CAPS), (3) experimental diabetes without capsaicin (DM), and (4) experimental diabetes plus capsaicin at 1 mg/kg/day (DM + CAPS). For each group, 24-h urine samples were collected to determine diuresis, albumin, cystatin C, β2 microglobulin, epidermal growth factor (EGF), alpha (1)-acid glycoprotein, and neutrophil gelatinase-associated lipocalin (NAG-L). Blood samples were drawn to measure fasting glucose. After 8 weeks, the CON + CAPS and DM + CAPS groups showed increased diuresis compared to the CON and DM groups, but the difference was significant only in the DM + CAPS group. The two-way ANOVA only showed a statistically significant effect of CAPS on the urinary EGF levels, as well as a tendency to have a significant effect in the urinary NAG-L levels. The EGF levels decreased in both CAPS-treated groups, but the change was only significant in the CON + CAPS group vs. CON group; and the NAG-L levels were lower in both CAPS-treated groups. These results show that capsaicin had a diuretic effect in healthy and diabetic rats; additionally, it increased the urinary EGF levels and tended to decrease the urinary NAG-L levels.

Dapagliflozin attenuates early markers of diabetic nephropathy in fructose-streptozotocin-induced diabetes in rats

Early detection and clinical interference are major challenges for the prevention of diabetic nephropathy (DN) progression. This study investigated the effects of dapagliflozin, a sodium glucose co-transporter 2 inhibitor, on some early markers for DN in fructose-streptozotocin (Fr-STZ)-induced diabetes in rats. Fr-STZ rats were treated with either dapagliflozin (1 mg/kg p.o. daily), metformin (350 mg/kg p.o. daily), or their combination for 6 weeks. Fr-STZ rats displayed marked early tubular renal damage and glomerular podocyte injury as evidenced by renal KIM-1, NGAL, cystatin C, and vanin-1 mRNA, as well as urinary NAG elevation and nephrin mRNA suppression, associated with the development of marked renal interstitial fibrosis and glomerulosclerosis despite the presence of normoalbuminuria. Propagation of oxidative, inflammatory, fibrotic, and apoptotic reactions was obvious in the setting of renal glucose overload. Dapagliflozin significantly attenuated the renal tubular injury makers namely KIM-1, NGAL, vanin-1 and urinary NAG. In addition, it restored glomerular nephrin expression and reversed renal histopathological changes. Oxidative, inflammatory, and fibrotic processes were also alleviated. This study suggests that dapagliflozin exerts a renoprotective effect against early features of DN in rats presumably by inhibition of diabetes-induced renal tubular and glomerular injury thereby modulating oxidative, inflammatory, and fibrotic as well as apoptotic mechanisms elicited during hyperglycemia.

Dietary intake of cod protein beneficially affects concentrations of urinary markers of kidney function and results in lower urinary loss of amino acids in obese Zucker fa/fa rats

Obesity increases the risk for developing kidney disease, and protection of kidneys through changes in diet should be investigated. Fish intake has been associated with reduced risk of developing kidney disease; therefore, we wanted to investigate whether cod protein intake could prevent or delay the development of kidney damage in an obese rat model that spontaneously develops proteinuria and focal segmental glomerulosclerosis. The aim of the study was to investigate any effects of cod protein intake on established markers of kidney function, amino acid composition, protein utilisation and growth in obese Zucker fa/fa rats in the early stage of decreased renal function. Male obese Zucker fa/fa rats (HsdOla:Zucker-Lepr) were fed cod muscle proteins in an amount corresponding to 25 % of dietary protein, with the remaining protein from a casein/whey mixture (COD diet). A control group was fed a diet with a casein/whey mixture as the only protein source (CAS diet). The intervention started when rats were 9–10 weeks old, and the rats were fed these diets for 4 weeks. At the end of the study, rats fed the COD diet had lower urine concentration of cystatin C, T-cell immunoglobulin mucin-1 (TIM-1), amino acids, carbamide, uric acid and ammonium and higher concentrations of creatine, trimethylamine N-oxide, 1-methylhistidine and 3-methylhistidine, lower kidney concentration of TIM-1 and showed better growth when compared with the CAS group. To conclude, cod protein may have the potential to delay the development of kidney damage in young obese Zucker rats and to improve protein utilisation and growth.

Urinary epidermal growth factor as a prognostic marker for the progression of Alport syndrome in children

BACKGROUND

Alport syndrome is a rare hereditary kidney disease manifested with progressive renal failure. Considerable variation exists in terms of disease progression among patients with Alport syndrome. Identification of patients at high risk of rapid progression remains an unmet need. Urinary epidermal growth factor (uEGF) has been shown to be independently associated with risk of progression to adverse kidney outcome in multiple independent adult chronic kidney disease (CKD) cohorts. In this study, we aim to assess if uEGF is associated with kidney impairment and its prognostic value for children with Alport syndrome.

METHODS

One hundred and seventeen pediatric patients with Alport syndrome and 146 healthy children (3-18 years old) were included in this study. uEGF was measured in duplicates in baseline urine samples using ELISA (R&D) and concentration was normalized by urine creatinine (uEGF/Cr). In patients with longitudinal follow-up data (n = 38), progression was defined as deteriorated kidney function (CKD stage increase) during follow-up period (follow-up length is about 31 months in average). The association of baseline uEGF/Cr level with estimated glomerular filtration rate (eGFR) slope and Alport syndrome patients' progression to a more advanced CKD stage during the follow-up period was used to evaluate the prognostic value of the marker.

RESULTS

We found that uEGF/creatinine (uEGF/Cr) decreases with age in pediatric patients with Alport syndrome with a significantly faster rate than in healthy children of the same age group. uEGF/Cr is significantly correlated with eGFR (r = 0.75, p < 0.001), after adjustment for age. In 38 patients with longitudinal follow-up, we observed a significant correlation between uEGF/Cr and eGFR slope (r = 0.58, p < 0.001). Patients with lower uEGF/Cr level were at increased risk of progression to a higher CKD stage. uEGF/Cr was able to distinguish progressors from non-progressors with an AUC of 0.88, versus 0.77 by eGFR and 0.81 by 24-h urinary protein (24-h UP).

CONCLUSIONS

Our study suggests that uEGF/Cr is a promising biomarker for accelerated kidney function decline in pediatric patients with Alport syndrome. It may help to identify patients at high risk of progression for targeted clinical care and improve the patients' stratification in interventional trials.

Megalin dependent urinary cystatin C excretion in ischemic kidney injury in rats

Background

Cystatin C, a marker of kidney injury, is freely filtered in the glomeruli and reabsorbed by the proximal tubules. Megalin and cubilin are endocytic receptors essential for reabsorption of most filtered proteins. This study examines the role of these receptors for the uptake and excretion of cystatin C and explores the effect of renal ischemia/reperfusion injury on renal cystatin C uptake and excretion in a rat model.

Methods

Binding of cystatin C to megalin and cubilin was analyzed by surface plasmon resonance analysis. ELISA and/or immunoblotting and immunohistochemistry were used to study the urinary excretion and tubular uptake of endogenous cystatin C in mice. Furthermore, renal uptake and urinary excretion of cystatin C was investigated in rats exposed to ischemia/reperfusion injury.

Results

A high affinity binding of cystatin C to megalin and cubilin was identified. Megalin deficient mice revealed an increased urinary excretion of cystatin C associated with defective uptake by endocytosis. In rats exposed to ischemia/reperfusion injury urinary cystatin C excretion was increased and associated with a focal decrease in proximal tubule endocytosis with no apparent change in megalin expression.

Conclusions

Megalin is essential for the normal tubular recovery of endogenous cystatin C. The increase in urinary cystatin C excretion after ischemia/reperfusion injury is associated with decreased tubular uptake but not with reduced megalin expression.

Longitudinal Changes in Measured Glomerular Filtration Rate, Renal Fibrosis and Biomarkers in a Rat Model of Type 2 Diabetic Nephropathy

BACKGROUND

Obese ZSF-1 rats display many features of human type II diabetes including nephropathy (DN). The study aimed to further understand the relevance of this model to DN, for which glomerular filtration rate (GFR), renal fibrosis and several urinary/tissue biomarkers was followed over 24 weeks in ZSF-1 rats.

METHODS

Intact/sham or uninephrectomized male and female ZSF-1 rats were studied. GFR was measured by transdermal clearance of fluorescein isothiocyanate-sinistrin. Urine was collected every 2-4 weeks for biomarker analysis. Renal tissue was examined histologically for fibrosis and for levels of inflammatory and fibrotic genes.

RESULTS

Male obese ZSF-1 rats demonstrated metabolic syndrome and proteinuria. Female counterparts were hyperlipidemic with delayed proteinuria, but were not hyperglycemic. Kidney hyperfiltration was observed in male obese rats in weeks 2-4 after surgery, and subsequently declined to levels significantly lower than controls. Tubulointerstitial/glomerular fibrosis in male obese rats was significantly elevated by week 12 post surgery and continued to expand in the ensuing weeks, particularly in uninephrectomized rats. Female rats had less severe fibrosis. Except for epidermal growth factor which decreased, the levels of several key inflammatory, injury and fibrotic factors were elevated in both tissue (mRNA) and urine (protein) of male obese rats.

CONCLUSION

Male obese ZSF-1 rats represent an important DN model, manifesting key pathophysiological features including metabolic syndrome, proteinuria, progressive tubular and glomerular fibrosis, and transient hyperfiltration followed by progressive decline in renal function. Uninephrectomy significantly accelerated disease progression. Females were less severe in disease manifestation. Several urinary and tissue biomarkers were identified in the male obese rats that tracked with disease progression.

Novel Tubular Biomarkers Predict Renal Progression in Type 2 Diabetes Mellitus: A Prospective Cohort Study

Background. Tubulointerstitial injury is both a key feature of diabetic nephropathy and an important predictor of renal dysfunction. Novel tubular biomarkers related to renal injury in diabetic nephropathy could improve risk stratification and prediction. Methods. A total of 303 type 2 diabetic patients were followed up. The baseline urine values of cystatin-C to creatinine ratio (UCCR), angiotensinogen to creatinine ratio (UANG), NGAL to creatinine ratio (UNGAL), and KIM-1 to creatinine ratio (UKIM-1) were measured. The primary outcome was a decline in estimated GFR of ≥25% yearly from baseline. Results. Urine tubular biomarkers of UCCR, UANG, UNGAL, and UKIM-1 were significantly higher according to the degree of albuminuria and all were significantly higher among patients with rapid decline in estimated GFR of ≥25% yearly from baseline. All biomarkers predicted primary outcomes with ROC for UCCR of 0.72; 95% CI 0.64-0.79, for UANG of 0.71; 95% CI 0.63-0.79, for UNGAL of 0.64; 95% CI 0.56-0.72, and for UKIM-1 of 0.71; 95% CI 0.63-0.79. Using multivariate Cox regression analysis, the number of patients with rapid renal progression was higher among those in the upper quartiles of all biomarkers than in those in the lower quartiles. Conclusions. Type 2 diabetic patients with high levels of urine tubular biomarkers had a more rapid decline in renal function.

Routine kidney variables, glomerular filtration rate and urinary cystatin C in cats with diabetes mellitus, cats with chronic kidney disease and healthy cats

OBJECTIVES

Diabetic kidney disease (DKD) is a frequent and serious complication in human diabetic patients, but data are limited in cats. This study was undertaken to assess whether diabetic cats are susceptible to DKD.

METHODS

Kidney function was compared between 36 cats with diabetes mellitus (DM), 10 cats with chronic kidney disease (CKD) and 10 age-matched healthy cats by measuring routine kidney variables (serum creatinine [sCreat], serum urea [sUrea], urine specific gravity [USG], urinary protein:creatinine ratio [UPC]), urinary cystatin C:creatinine ratio and glomerular filtration rate (GFR). Urinary cystatin C (uCysC) was measured with a human particle-enhanced nephelometric immunoassay, validated to measure feline cystatin C, in all but two diabetic cats. GFR was evaluated by exo-iohexol clearance in 17 diabetic cats, all cats with CKD and all healthy cats.

RESULTS

Diabetic cats had significantly (mean ± SD) lower sCreat (123 ± 38 vs 243 ± 80 µmol/l), sUrea (11 ± 3 vs 18 ± 7 mmol/l) and urinary cystatin C:creatinine ratio (6 ± 31 vs 173 ± 242 mg/mol), and a significantly higher USG (1.033 ± 0.012 vs 1.018 ± 0.006) and GFR (2.0 ± 0.7 vs 0.8 ± 0.3 ml/min/kg) compared with cats with CKD. Compared with healthy cats, diabetic cats only had significantly lower USG (1.033 ± 0.012 vs 1.046 ± 0.008). Proteinuria (UPC >0.4) was present in 39% of diabetic cats, in 30% of cats with CKD and in none of the healthy cats. However, the UPC did not differ statistically between the three groups.

CONCLUSIONS AND RELEVANCE

Based on evaluation of routine kidney variables, GFR and uCysC as a tubular marker at a single time point, a major impact of feline DM on kidney function could not be demonstrated.

High expression of neutrophil gelatinase-associated lipocalin (NGAL) in the kidney proximal tubules of diabetic rats

PURPOSE

Recent evidence suggests that neutrophil gelatinase-associated lipocalin (NGAL) plays important roles in many physiological and pathological processes including diabetic nephropathy (DN), in which a markedly increasing in NGAL levels in patient's serum and urine has been reported. This study investigated the expression of NGAL in the kidney of diabetic rats.

MATERIALS/METHODS

Sixty-four Sprague Dawley rats were randomly divided into 2 groups: non-diabetic control groups and diabetic groups. Diabetes was induced by intraperitoneal injection of streptozotocin. Relevant indicators were separately evaluated 2, 4, 8 and 12 weeks after induction of diabetes.

RESULTS

In the diabetic groups, urinary NGAL values were markedly increased even before the appearance of pathological albuminuria. Moreover, diabetic rats showed significant upregulation of NGAL mRNA expression starting at week 2 (1.0±0.03 vs. 3.09±0.40, NGAL/β-actin, P<0.05), while the increase of NGAL protein expression appeared subsequently (0.58±0.03 vs. 0.65±0.01, NGAL/β-actin, P<0.05). At the end of week 12, kidney NGAL mRNA and protein levels were increased to 5.95-fold and 1.24-fold of the control groups, respectively. Observable ultrastructural alterations of renal tubules were not detected until week 4, while pathological changes gradually became apparent in the course of the study. Strong positive immunohistochemical staining of NGAL was visualized in the proximal tubular cells of diabetic rats at week 12.

CONCLUSIONS

High expression of NGAL in the kidney is associated with diabetic kidney injury in STZ rats, suggesting NGAL may play a role in tubular injury of DN.

The use of urinary and kidney SILAM proteomics to monitor kidney response to high dose morpholino oligonucleotides in the mdx mouse

Phosphorodiamidate morpholino oligonucleotides (PMO) are used as a promising exon-skipping gene therapy for Duchenne Muscular Dystrophy (DMD). One potential complication of high dose PMO therapy is its transient accumulation in the kidneys. Therefore new urinary biomarkers are needed to monitor this treatment. Here, we carried out a pilot proteomic profiling study using stable isotope labeling in mammals (SILAM) strategy to identify new biomarkers to monitor the effect of PMO on the kidneys of the dystrophin deficient mouse model for DMD (mdx-23). We first assessed the baseline renal status of the mdx-23 mouse compared to the wild type (C57BL10) mouse, and then followed the renal outcome of mdx-23 mouse treated with a single high dose intravenous PMO injection (800 mg/kg). Surprisingly, untreated mdx-23 mice showed evidence of renal injury at baseline, which was manifested by albuminuria, increased urine output, and changes in established urinary biomarker of acute kidney injury (AKI). The PMO treatment induced further transient renal injury, which peaked at 7 days, and returned to almost the baseline status at 30 days post-treatment. In the kidney, the SILAM approach followed by western blot validation identified changes in Meprin A subunit alpha at day 2, then returned to normal levels at day 7 and 30 after PMO injection. In the urine, SILAM approach identified an increase in Clusterin and γ-glutamyl transpeptidase 1 as potential candidates to monitor the transient renal accumulation of PMO. These results, which were confirmed by Western blots or ELISA, demonstrate the value of the SILAM approach to identify new candidate biomarkers of renal injury in mdx-23 mice treated with high dose PMO. Chemical compounds studied in this article: Phosphorodiamidate morpholino (PubChem CID: 22140692); isoflurane (PubChem CID: 3763); formic acid (PubChem CID: 284); acetonitrile (PubChem CID: 6342); acetone (PubChem CID: 180); methanol (PubChem CID: 887).

Urinary exosomes: a novel means to non-invasively assess changes in renal gene and protein expression

Background

In clinical practice, there is a lack of markers for the non-invasive diagnosis and follow-up of kidney disease. Exosomes are membrane vesicles, which are secreted from their cells of origin into surrounding body fluids and contain proteins and mRNA which are protected from digestive enzymes by a cell membrane.

Methods

Toxic podocyte damage was induced by puromycin aminonucleoside in rats (PAN). Urinary exosomes were isolated by ultracentrifugation at different time points during the disease. Exosomal mRNA was isolated, amplified, and the mRNA species were globally assessed by gene array analysis. Tissue-specific gene and protein expression was assessed by RT-qPCR analysis and immunohistochemistry.

Results

Gene array analysis of mRNA isolated from urinary exosomes revealed cystatin C mRNA as one of the most highly regulated genes. Its gene expression increased 7.5-fold by day 5 and remained high with a 1.9-fold increase until day 10. This was paralleled by a 2-fold increase in cystatin C mRNA expression in the renal cortex. Protein expression in the kidneys also dramatically increased with de novo expression of cystatin C in glomerular podocytes in parts of the proximal tubule and the renal medulla. Urinary excretion of cystatin C increased approximately 2-fold.

Conclusion

In this proof-of-concept study, we could demonstrate that changes in urinary exosomal cystatin C mRNA expression are representative of changes in renal mRNA and protein expression. Because cells lining the urinary tract produce urinary exosomal cystatin C mRNA, it might be a more specific marker of renal damage than glomerular-filtered free cystatin C.

New urinary biomarkers for diabetic kidney disease

Diabetic kidney disease is the leading cause of end-stage renal disease in developed and developing countries. Microalbuminuria is the gold standard for detection and prediction of diabetic kidney disease and cardiovascular risk disease in clinical practice. However, microalbuminuria has several limitations, such as lower sensitive, larger variability. It is urgent to explore higher sensitivity and specificity for earlier detection of diabetic kidney disease and more accurate prediction of the progression to end stage renal disease. We reviewed some new and important urinary biomarkers, such as: transferrin, immunoglobulin G, immunoglobulin M, Cystanic C, podocytes, type IV collagen, 8-oxo-7, 8-dihydro-2'-deoxyguanosine, ceruloplasmin, monocyte chemoattractant protein-1 and so on. We need good quality, long-term, large longitudinal trials to validate published biomarkers and find new biomarkers, considering biomarkers reviewed here are from small cross-sectional studies.

Kidney Toxicity Induced by 13 Weeks Exposure to the Fruiting Body of Paecilomyces sinclairii in Rats

Paecilomyces sinclairiis (PS) is known as a functional food or human health supplement. However concerns have been raised about its kidney toxicity. This study was performed to investigate the kidney toxicity of PS by 13 week-oral administration to rats. Blood urea nitrogen (BUN), serum creatinine, and kidney damage biomarkers including beta-2-microglobulin (β2m), glutathione S-transferase alpha (GST-α), kidney injury molecule 1 (KIM-1), tissue inhibitor of matrix metalloproteinase 1 (TIMP-1), vascular endothelial growth factor (VEGF), calbindin, clusterin, cystatin C, neutrophil gelatinase-associated lipocalin (NGAL) and osteopontin were measured during or after the treatment of PS. BUN, creatinine and kidney damage biomarkers in serum were not changed by PS. However, kidney cell karyomegaly and tubular hypertrophy were observed dose-dependently with higher severity in males. KIM-1, TIMP-1 and osteopontin in kidney and urine were increased dose dependently in male or at the highest dose in female rats. Increased urinary osteopontin by PS was not recovered at 2 weeks of post-exposure in both genders. Cystatin C in kidney was decreased at all treatment groups but inversely increased in urine. The changes in kidney damage biomarkers were more remarkable in male than female rats. These data indicate that the PS may provoke renal cell damage and glomerular filtration dysfunction in rats with histopathological lesions and change of kidney damage biomarkers in kidney or urine. Kidney and urinary KIM-1 and cystatin C were the most marked indicators, while kidney weight, BUN and creatinine and kidney damage biomarkers in serum were not influenced.