Pathophysiology of disease progression in proteinuric nephropathies

Urine protein-to-creatinine ratio in cattle with subclinical renal disease

BACKGROUND

Urinalysis is not routinely used in bovine medicine, and there is no evidence as to whether urine protein-to-creatinine ratio (UPC) could be used for the diagnosis of renal diseases in cattle.

OBJECTIVE

The goal of the study was to determine alterations in UPCs observed with different subclinical renal diseases in clinically healthy cattle and to investigate whether UPC can efficiently differentiate cattle with and without subclinical renal pathology.

METHODS

Kidney and urine samples from 57 clinically healthy adult dairy (44) and beef (13) cattle were collected after slaughter. Urinary protein and creatinine concentrations were measured in an automatic analyzer, and urinary-specific gravity (USG) was measured using a temperature compensated refractometer. Kidney samples underwent histopathologic examination, and the cattle were classified as NL (no renal lesion) and L (lesions detected even in one kidney). Based on USG, the cattle were divided into the Normal USG (≥1.020) and Low USG (<1.020) groups. The cattle with either histopathologic lesions or low specific gravities were considered to have renal disease.

RESULTS

Renal lesions were detected in 37 cattle. UPC values were significantly affected (P < .05) by USG values, and not by the type of lesion detected, breed, or age, and their interactions (P > .05). The analysis revealed that a UPC of ≥0.19 provided an optimal cut-off point for the differentiation between normal animals and those with renal disease with 66.0% sensitivity and 90% specificity.

CONCLUSIONS

The UPC calculation is a useful tool for the differentiation of normal cattle and those with renal disease. A UPC of less than 0.19 is associated with the absence of renal damage, whereas higher values raise suspicion for renal disease.

Effects of Niaoduqing Particles () on Delaying Progression of Renal Dysfunction: A Post-trial, Open-Label, Follow-up Study

OBJECTIVE

To follow up the participants of the randomized clinical trial "Efficacy and Safety of Niaoduqing Particles () for Delaying Moderate-to-Severe Renal Dysfunction", and assess the long-term effects of Niaoduqing Particles on delaying the progression of renal dysfunction.

METHODS

Participants, who had previously been randomly assigned to receive Niaoduqing Particles or placebo for 24 weeks (146 cases in each group), were invited to follow-up and all were administered Niaoduqing Particles 5 g thrice daily and 10 g before bedtime for 24 weeks. The primary endpoints were changes in baseline serum creatinine (Scr) and estimated glomerular filtration rate (eGFR) after completion of the open-label treatment period.

RESULTS

After the double-blind period, the median (interquartile range) changes in Scr were 1.1 (-13.0-24.1) and 11.7 (-2.6-42.9) μmol/L for the Niaoduqing Particle and placebo groups, respectively (P=0.008), and the median changes in eGFRs were-0.2 (-4.3-2.7) and-2.21 (-5.7-0.8) mL•min^-1•1.73 m^-2, respectively (P=0.016). There were significant differences in the double-blind period changes in renal function between groups. After the open-label period, the median changes in Scr were 9.0 (-10.0-41.9) and 17.5 (-6.0-50.0) μmol/L for the Niaoduqing Particle and placebo groups according to baseline grouping, respectively (P=0.214), and the median changes in eGFRs were-2.3 (-6.4-1.9) and-3.7 (-7.5-1.1) mL•min^-1•1.73 m^-2, respectively (P=0.134). There were no statistical differences in the open-label period changes in renal function between groups. The eGFR reduction of participants who accepted Niaoduqing Particle treatment for 48 weeks was projected to 2.5 mL•min^-1•1.73 m^-2 per year.

CONCLUSION

Niaoduqing Particles appear to have long-term efficacy for patients with moderate-to-severe renal dysfunction. Although there was no statistical difference, the early use of Niaoduqing Paticles seems to ameliorate the worsening of renal function. (Trial registration No. ChiCTR-TRC-12002448).

A comparison of biochemical and histopathologic staging in cats with chronic kidney disease

Chronic kidney disease (CKD) is prevalent in elderly cats. Frequently, a diagnosis is made in later stages of disease, by which time many renal lesions are irreversible. As such, little headway has been made in identifying an etiology and preventing this common disease. The aim of this study was to evaluate the presence and severity of both reversible and irreversible histopathologic changes in the kidneys of cats at each stage of CKD and, in addition, to determine if lesion prevalence and character were different between stages. A total of 46 cats with CKD were classified according to the International Renal Interest Society (IRIS) as stage I (3 cats), stage II (16 cats), stage III (14 cats), and stage IV (13 cats). Eleven young, nonazotemic and 10 geriatric, nonazotemic cats were included as controls. The severity of tubular degeneration, interstitial inflammation, fibrosis, and glomerulosclerosis was significantly greater in later stages of CKD compared with early stages of disease. Proteinuria was associated with increased severity of tubular degeneration, inflammation, fibrosis, tubular epithelial single-cell necrosis, and decreased normal parenchyma. Presence of hyperplastic arteriolosclerosis, fibrointimal hyperplasia, or other vascular lesions were not found to be significantly different between hypertensive and normotensive cats. The greater prevalence and severity of irreversible lesions in stage III and IV CKD implies that therapeutic interventions should be targeted at earlier stages of disease.

Urinary immunoglobulin G to albumin ratio and N-Acetyl-Beta-D-Glucosaminidase as early predictors of therapeutic response in ANCA-associated glomerulonephritis

Background

The aim of our study was to evaluate the prognostic value of glomerular and tubular proteinuria and tubular enzymuria as early indicators of therapeutic response to induction therapy with i.v. pulse cyclophosphamide (CyC) and methylprednisolone (MP) in patients with antineutrophil cytoplasmic antibody (ANCA) associated glomerulonephritis.

Methods and Findings

An observational single-center study was conducted in 30 patients with ANCA-associated glomerulonephritis. Patients were divided into subgroups with good or poor response to CyC therapy according to clinical and laboratory parameters. The diagnosis of ANCA-associated glomerulonephritis was based on the Chapel-Hill disease definitions. Good response to induction therapy was significantly associated with higher absolute values of urine N-acetyl-beta-D-glucosaminidase (NAG) to creatinine ratio (above 14.83 microcat/mol) and urine immunoglobulin G (IgG) to albumin ratio (above 0.09) at the time of diagnosis, while albuminuria or proteinuria did not have any early predictive value. The remission of renal disease was anticipated as early as 3 months after introduction of induction therapy in patients with reduction of urine NAG to creatinine ratio below the baseline value and in patients with at least 24% rise in eGFR.

Conclusions

Urine IgG to albumin and urine NAG to creatinine ratio are better early predictors of treatment response in patients with ANCA-associated glomerulonephritis than proteinuria or albuminuria.

Fenofibrate, a PPARα agonist, has renoprotective effects in mice by enhancing renal lipolysis

As renal lipotoxicity can lead to chronic kidney disease (CKD), we examined the role of peroxisome proliferator-activated receptor (PPAR)-α, a positive regulator of renal lipolysis. Feeding mice a high-fat diet induced glomerular injury, and treating them with fenofibrate, a PPARα agonist, increased the expression of lipolytic enzymes and reduced lipid accumulation and oxidative stress in glomeruli, while inhibiting the development of albuminuria and glomerular fibrosis. In mice given an overload of free fatty acid-bound albumin to induce tubulointerstitial injury, fenofibrate attenuated the development of oxidative stress, macrophage infiltration, and fibrosis, and enhanced lipolysis in the renal interstitium. Fenofibrate inhibited palmitate-induced expression of profibrotic plasminogen activator inhibitor-1 (PAI-1) in cultured mesangial cells, and the expression of both monocyte chemoattractant protein-1 and PAI-1 in proximal tubular cells along with the overexpression of lipolytic enzymes. Thus, fenofibrate can attenuate lipotoxicity-induced glomerular and tubulointerstitial injuries, with enhancement of renal lipolysis. Whether amelioration of renal lipotoxicity by PPARα agonists will turn out to be a useful strategy against CKD will require direct testing.

Comparison of three methods for isolation of urinary microvesicles to identify biomarkers of nephrotic syndrome

Urinary microvesicles, such as 40-100 nm exosomes and 100-1000 nm microparticles, contain many proteins that may serve as biomarkers of renal disease. Microvesicles have been isolated by ultracentrifugation or nanomembrane ultrafiltration from normal urine; however, little is known about the efficiency of these methods in isolating microvesicles from patients with nephrotic-range proteinuria. Here we compared three techniques to isolate microvesicles from nephrotic urine: nanomembrane ultrafiltration, ultracentrifugation, and ultracentrifugation followed by size-exclusion chromatography (UC-SEC). Highly abundant urinary proteins were still present in sufficient quantity after ultrafiltration or ultracentrifugation to blunt detection of less abundant microvesicular proteins by MALDI-TOF-TOF mass spectrometry. The microvesicular markers neprilysin, aquaporin-2, and podocalyxin were highly enriched following UC-SEC compared with preparations by ultrafiltration or ultracentrifugation alone. Electron microscopy of the UC-SEC fractions found microvesicles of varying size, compatible with the presence of both exosomes and microparticles. Thus, UC-SEC following ultracentrifugation to further enrich and purify microparticles facilitates the search for prognostic biomarkers that might be used to predict the clinical course of nephrotic syndrome.

Endothelin receptor selectivity in chronic kidney disease: rationale and review of recent evidence

Endothelin (ET) is a potent vasoconstrictory peptide with proinflammatory and profibrotic properties that exerts its biological effects through two pharmacologically distinct receptor subtypes, namely ET(A) and ET(B). In addition to its substantial contribution to normal renal function, a large body of evidence suggests that derangement of the renal ET system is involved in the initiation and progression of chronic kidney disease (CKD) in diabetes, hypertension and glomerulonephritis. Thus, the use of ET receptor antagonists (ERAs) may offer potential novel treatment strategies in CKD. Recent literature on the role of the renal ET system in the healthy kidney was reviewed. In addition, an unbiased PubMed search was performed for studies published during the last 5 years that addressed the effects of ERAs in CKD. A particular objective was to extract information regarding whether selective or nonselective ERAs may have therapeutic potential in humans. ET-1 acts primarily as an autocrine or paracrine factor in the kidney. In normal physiology, ET-1 promotes diuresis and natriuresis by local production and action through ET(B) receptors in the renal medulla. In pathology, ET-1 mediates vasoconstriction, mesangial-cell proliferation, extracellular matrix production and inflammation, effects that are primarily conveyed by ET(A) receptors. Results obtained in animal models and in humans with the use of ERAs in CKD are encouraging; nevertheless, it is still under debate which receptor subtype should be targeted. According to most studies, selective inhibition of ET(A) receptors appears superior compared with nonselective ERAs because this approach does not interfere with the natriuretic, antihypertensive and ET clearance effects of ET(B) receptors. Although preliminary data in humans are promising, the potential role of ERAs in patients with CKD and the question of which receptor subtype should be targeted can only be clarified in randomized clinical trials.

Protein load impairs factor H binding promoting complement-dependent dysfunction of proximal tubular cells

Intrarenal complement activation plays an important role in the progression of chronic kidney disease. A key target of the activated complement cascade is the proximal tubule, a site where abnormally filtered plasma proteins and complement factors combine to promote injury. This study determined whether protein overloading of human proximal tubular cells (HK-2) in culture enhances complement activation by impairing complement regulation. Addition of albumin or transferrin to the cells incubated with diluted human serum as a source of complement caused increased apical C3 deposition. Soluble complement receptor-1 (an inhibitor of all 3 activation pathways) blocked complement deposition while the classical and lectin pathway inhibitor, magnesium chloride-EGTA, was, ineffective. Media containing albumin as well as complement had additive proinflammatory effects as shown by increased fractalkine and transforming growth factor-beta mRNA expression. This paralleled active C3 and C5b-9 generations, effects not shared by transferrin. Factor H, one of the main natural inhibitors of the alternative pathway, binds to heparan sulfate proteoglycans. Both the density of heparan sulfate and factor H binding were reduced with protein loading, thereby enhancing the albumin- and serum-dependent complement activation potential. Thus, protein overload reduces the ability of the tubule cell to bind factor H and counteract complement activation, effects instrumental to renal disease progression.

Treatment with pyrrolidine dithiocarbamate improves proteinuria, oxidative stress, and glomerular hypertension in overload proteinuria

We evaluated whether the blockade of the proinflammatory transcription factor NF-kappaB would modify the oxidative stress, inflammation, and structural and hemodynamic alterations found in the kidney as a result of massive proteinuria. Twenty male Sprague-Dawley rats were injected with 2 g of BSA intraperitoneally daily for 2 wk. Ten of them received in addition the inhibitor of NF-kappaB activation pyrrolidine dithiocarbamate (PDTC; 200 mg.kg(-1).day(-1) sc) and the rest received vehicle. Seven rats that received intraperitoneal saline were used as controls. Glomerular hemodynamics were studied after 14 days. Markers of oxidative stress (NF-kappaB subunit p65+ cells, 3-nitrotyrosine, and 4-hydroxynonenal), inflammation (cortical CD68+ cells and NOS-II), and afferent arteriole damage were assessed by immunohistochemistry and morphometry. Activity of antioxidant enzymes superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase was evaluated in renal cortex and medulla. Albumin overload induced massive proteinuria, oxidative stress with reduced activity of antioxidant enzymes, NF-kappaB activation, inflammatory cell infiltration, a significant presence of proteinaceous casts, systemic and glomerular hypertension, as well as arteriolar remodeling. Treatment with PDTC prevented or improved all of these findings. In this model of nephrotic syndrome, we demonstrate a key role for oxidative stress and inflammation in causing systemic and glomerular hypertension and proteinuria. Oxidative stress and inflammation may have a key role in accelerating renal injury associated with intense proteinuria.

Complement-mediated dysfunction of glomerular filtration barrier accelerates progressive renal injury

Intrarenal complement activation leads to chronic tubulointerstitial injury in animal models of proteinuric nephropathies, making this process a potential target for therapy. This study investigated whether a C3-mediated pathway promotes renal injury in the protein overload model and whether the abnormal exposure of proximal tubular cells to filtered complement could trigger the resulting inflammatory response. Mice with C3 deficiency were protected to a significant degree against the protein overload-induced interstitial inflammatory response and tissue damage, and they had less severe podocyte injury and less proteinuria. When the same injury was induced in wild-type (WT) mice, antiproteinuric treatment with the angiotensin-converting enzyme inhibitor lisinopril reduced the amount of plasma protein filtered, decreased the accumulation of C3 by proximal tubular cells, and protected against interstitial inflammation and damage. For determination of the injurious role of plasma-derived C3, as opposed to tubular cell-derived C3, C3-deficient kidneys were transplanted into WT mice. Protein overload led to the development of glomerular injury, accumulation of C3 in podocytes and proximal tubules, and tubulointerstitial changes. Conversely, when WT kidneys were transplanted into C3-deficient mice, protein overload led to a more mild disease and abnormal C3 deposition was not observed. These data suggest that the presence of C3 increases the glomerular filtration barrier's susceptibility to injury, ultrafiltered C3 contributes more to tubulointerstitial damage induced by protein overload than locally synthesized C3, and local C3 synthesis is irrelevant to the development of proteinuria. It is speculated that therapies targeting complement combined with interventions to minimize proteinuria would more effectively prevent the progression of renal disease.

Mechanisms of progression of chronic kidney disease

Chronic kidney disease (CKD) occurs in all age groups, including children. Regardless of the underlying cause, CKD is characterized by progressive scarring that ultimately affects all structures of the kidney. The relentless progression of CKD is postulated to result from a self-perpetuating vicious cycle of fibrosis activated after initial injury. We will review possible mechanisms of progressive renal damage, including systemic and glomerular hypertension, various cytokines and growth factors, with special emphasis on the renin-angiotensin-aldosterone system (RAAS), podocyte loss, dyslipidemia and proteinuria. We will also discuss possible specific mechanisms of tubulointerstitial fibrosis that are not dependent on glomerulosclerosis, and possible underlying predispositions for CKD, such as genetic factors and low nephron number.

Mechanisms of disease: Fibroblasts--a new look at an old problem

Fibroblasts are one of the most important and episodically active cell types in the kidney. Under normal conditions, these cells provide a delicate collagenous matrix that partitions the interstitial spaces between nephrons, blood vessels and the renal capsule. Fibroblasts also remodel the interstitium as kidneys grow with age. This episodic activity of various fibroblast populations has a biological basis. Most fibroblasts are created locally through a process called epithelial-mesenchymal transition (EMT) and, once formed, they can proliferate in response to local mitogens. EMT is driven by an alteration in the balance of local cytokine concentrations that reverses the differentiation of selected epithelia along tubular nephrons. During persistent injury and inflammation, fibroblasts further increase their numbers and secrete excess interstitial collagens, and EMT is particularly aggressive in this setting. The mechanisms by which fibroblasts simultaneously destroy normal interstitial architecture and disable epithelial nephrons are more comprehensible today. Recent therapeutic clues for attenuating fibroblast formation during renal fibrogenesis also suggest an advantage in shifting local cytokine balance to favor mesenchymal-epithelial transition. This review examines these issues and identifies new targets for the treatment of one of the most difficult problems facing clinical nephrology.

Relationship Between Clinical Predictors and Tubulointerstitial Damage in Adult-onset Primary Nephrotic Syndrome

BACKGROUND

Tubulointerstitial damage (TID) is an important mediator in the progression of chronic proteinuric nephropathies. Our aim in this study was to evaluate the relationship between several clinical predictors and TID in adult-onset primary nephrotic syndrome in China.

METHODS

One hundred ninety-five adult inpatients who were diagnosed with primary nephrotic syndrome based on clinical presentation and biopsy results were enrolled in this study from March 2003 to September 2005. The degree of TID was graded by a semiquantitative method including <2 score and >or=2 score.

RESULTS

In all patients, the rate of glomerulosclerosis was correlated with the severity of TID. Serum creatinine and uric acid (r = 0.183, p = 0.012 and r = 0.377, p = 0.00001, respectively) but not serum lipid or total 24-h urinary protein were related with TID. In 64 patients, urinary excretion of IgG (r = 0.443, p = 0.00001) but not of albumin, transferrin, retinal-binding protein, or alpha1-microglobulin were significantly associated with the extent of TID. Proteinuria selectivity index based upon IgG also correlated significantly with the extent of TID (p = 0.0001) (score 0-1 vs. score >or=2).

CONCLUSIONS

These results showed that serum creatinine and uric acid, the excretion of urinary IgG and proteinuria selectivity index based upon IgG, were highly correlated with the severity of TID in adult-onset primary nephrotic syndrome. These clinical parameters might be useful for predicting the development and progression of proteinuric nephropathy as independent risk factors.

Development of new therapies, including regeneration of the kidney, for chronic kidney diseases

The increasing number of patients on chronic hemodialysis is a great problem in the field of nephrology in Japan and Western countries. Current therapies for chronic kidney diseases (CKDs) can retard the progression of renal failure, but cannot completely stop their progression to endstage renal failure (ESRD). Many researchers are now studying new therapeutic targets for CKDs, by various methods. Furthermore, because organ donation for kidney transplantation is very limited in Japan, research on kidney regeneration is an important issue for the therapy of ESRD. To regenerate the kidney, stem cells and growth factors for the kidney are being extensively studied, although the clinical application of the results of these studies has not yet taken place.