Macrophages in acute glomerular inflammation

Metalloporphyrins as Tools for Deciphering the Role of Heme Oxygenase in Renal Immune Injury

Renal immune injury is a frequent cause of end-stage renal disease, and, despite the progress made in understanding underlying pathogenetic mechanisms, current treatments to preserve renal function continue to be based mainly on systemic immunosuppression. Small molecules, naturally occurring biologic agents, show considerable promise in acting as disease modifiers and may provide novel therapeutic leads. Certain naturally occurring or synthetic Metalloporphyrins (Mps) can act as disease modifiers by increasing heme oxygenase (HO) enzymatic activity and/or synthesis of the inducible HO isoform (HO-1). Depending on the metal moiety of the Mp employed, these effects may occur in tandem or can be discordant (increased HO-1 synthesis but inhibition of enzyme activity). This review discusses effects of Mps, with varying redox-active transitional metals and cyclic porphyrin cores, on mechanisms underlying pathogenesis and outcomes of renal immune injury.

Mechanisms of vascular damage in ANCA vasculitis

The discovery of anti-neutrophil cytoplasmic antibodies (ANCA) and their antigenic targets, myeloperoxidase (MPO) and proteinase 3 (PR3), has led to further understanding as to the pathophysiologic processes that underlie vascular and tissue damage in ANCA vasculitis. ANCA trigger neutrophil activation leading to vascular damage in ANCA vasculitis. However, decades of study have determined that neutrophil activation alone is not sufficient to cause disease. Inflammatory stimuli are drivers of ANCA autoantigen expression and ANCA production. Certain infections or bacterial peptides may be crucial players in the initial steps of ANCA immunopathogenesis. Genetic and epigenetic alterations of gene encoding for MPO and PR3 provide additional disturbances to the immune homeostasis which provide a substrate for pathogenic ANCA formation from an adaptive immune system predisposed to autoreactivity. Promoted by inflammatory cytokines, ANCA binding leads to neutrophil activation, a process characterized by conformational changes, production and release of cytotoxic substances, and alternative complement pathway activation, thus creating an intense inflammatory milieu. This cascade of events perpetuates a vicious cycle of further inflammatory cell recruitment and activation, culminating in tissue necrosis. Our understanding of the pathogenic process in ANCA vasculitis paves the way for the development of therapies targeting crucial steps in this process. The greater appreciation of the role for complement, monocytes, and the adaptive immune system has already led to novel complement blockers and is poised to lead to further innovations which will allow for tailored antigen- or cell-specific immunotherapy targeting the autoimmune process without exposure to undue risks or toxicities.

Light-Emitting Agents for Noninvasive Assessment of Kidney Function

The noninvasive assessment of kidney function and diagnosis of kidney disease have long been challenges. Traditional methods are not routinely available, because the existing protocols are cumbersome, time consuming, and invasive. In the past few years, significant progress in the area of diagnosing kidney function and disease on the basis of light-emitting agents has been made. Herein, we briefly review light-emitting agents, including organic fluorescent agents and inorganic renal clearable luminescent nanoparticles for the noninvasive and real-time monitoring of kidney function and disease. Moreover, some significant requirements and strategies regarding the design of ideal glomerular filtration rate agents and renal clearable nanoparticles are discussed. Finally, we discuss future challenges in expediting clinical translation of these developed light-emitting agents, along with considerations of the efforts that need to be made to develop new agents and diagnosing kidney disease.

Urinary soluble CD163 level reflects glomerular inflammation in human lupus nephritis

BACKGROUND

In addition to classically activated macrophages that have effector roles in tissue injury, alternatively activated M2 macrophages are involved in the resolution of inflammation in animal models of kidney disease. To clarify the clinical relevance of macrophage phenotypes in human glomerular diseases, we evaluated the renal accumulation of macrophages and plasma and urine levels of CD163, an M2 marker, in lupus nephritis (LN) patients.

METHODS

Kidney biopsies and plasma and urine samples were obtained from LN patients who underwent renal biopsy between 2008 and 2012. CD163⁺, CD68⁺ and CD204⁺ cells were counted in paraffin-embedded and frozen sections. LN histological activity was evaluated semiquantitatively using the biopsy activity index. Plasma and urinary soluble CD163 (sCD163) concentrations were also measured and evaluated for their significance as potential LN biomarkers.

RESULTS

Immunohistological analysis of glomeruli from LN patients revealed that >60% of CD68⁺ macrophages had merged with CD163⁺ cells. The increased number of glomerular CD163⁺ macrophages was correlated with LN severity, as determined by the biopsy active index (r = 0.635). Urinary (u-) sCD163 level was strongly correlated with glomerular CD163⁺ cell counts and histological disease score as well as urinary monocyte chemoattractant protein 1 levels (r = 0.638 and 0.592, respectively). Furthermore, the u-sCD163 level was higher in patients with active LN than in those with other diseases.

CONCLUSIONS

Glomerular CD163⁺ macrophages are the predominant phenotype in the kidneys of lupus patients. These findings indicate that the u-sCD163 level can serve as a biomarker for macrophage-dependent glomerular inflammation in human LN.

Expression of Ser729 phosphorylated PKCepsilon in experimental crescentic glomerulonephritis: an immunohistochemical study

PKCε, a DAG-dependent, Ca2+- independent kinase attenuates extent of fibrosis following tissue injury, suppresses apoptosis and promotes cell quiescence. In crescentic glomerulonephritis (CGN), glomerular epithelial cells (GEC) contribute to fibro-cellular crescent formation while they also transdifferentiate to a mesenchymal phenotype. The aim of this study was to assess PKCε expression in CGN. Using an antibody against PKC-ε phosphorylated at Ser729, we assessed its localization in rat model of immune-mediated rapidly progressive CGN. In glomeruli of control animals, pPKCε was undetectable. In animals with CGN, pPKCε was expressed exclusively in glomerular epithelial cells (GEC) and in GEC comprising fibrocellular crescents that had acquired a myofibroblast-type phenotype. In non-immune GEC injury induced by puromycin aminonucleoside and resulting in proteinuria of similar magnitude as in CGN, pPKCε expression was absent. There was constitutive pPKCε expression in distal convoluted tubules, collecting ducts and thick segments of Henley's loops in both control and experimental animals. We propose that pPKCε expression occurring in GEC and in fibrocellular crescentic lesions in CGN may facilitate PKCε dependent pathologic processes.

Applications of nanoparticles in the detection and treatment of kidney diseases

Nanoparticles have emerged in the medical field as a technology well suited for the diagnosis and treatment of various disease states. They have been heralded as efficacious in terms of improved therapeutic efficacy and reduction of treatment side effects in some cases. Various nanomaterials have been developed that can be tagged with targeting moieties as well as with drug delivery and imaging capability or a combination of both as a theranostic agent. These nanomaterials have been investigated for treatment and detection of various pathological conditions. The emphasis of this review is to demonstrate current research and clinical applications for nanoparticles in the diagnosis and treatment of kidney diseases.

Experimental crescentic glomerulonephritis: a new bicongenic rat model

Crescentic glomerulonephritis (CRGN) is a major cause of human kidney failure, but the underlying mechanisms are not fully understood. Wistar Kyoto (WKY) rats are uniquely susceptible to CRGN following injection of nephrotoxic serum, whereas Lewis (LEW) rats are resistant. Our previous genetic studies of nephrotoxic nephritis (NTN), a form of CRGN induced by nephrotoxic serum, identified Fcgr3 and Jund as WKY genes underlying the two strongest quantitative trait loci for NTN phenotypes: Crgn1 and Crgn2, respectively. We also showed that introgression of WKY Crgn1 or Crgn2 individually into a LEW background did not lead to the formation of glomerular crescents. We have now generated a bicongenic strain, LEW.WCrgn1,2, in which WKY Crgn1 and Crgn2 are both introgressed into the LEW genetic background. These rats show development of NTN phenotypes, including glomerular crescents. Furthermore, we characterised macrophage function and glomerular cytokine profiles in this new strain. Additionally, we show that LEW.WCrgn1,2 rats are resistant to the development of glomerular crescents that is usually induced following immunisation with recombinant rat α3(IV)NC1, the specific Goodpasture autoantigen located in the glomerular basement membrane against which the immune response is directed in experimental autoimmune glomerulonephritis. Our results show that the new bicongenic strain responds differently to two distinct experimental triggers of CRGN. This is the first time that CRGN has been induced on a normally resistant rat genetic background and identifies the LEW.WCrgn1,2 strain as a new, potentially valuable model of macrophage-dependent glomerulonephritis.

Keishibukuryogan reduces renal injury in the early stage of renal failure in the remnant kidney model

The effects of keishibukuryogan on the early stage of progressive renal failure were examined in rats subjected to 5/6 nephrectomy. Keishibukuryogan, one of the traditional herbal formulations, was given orally at a dose of 1% (w/w) and 3% (w/w) in chow. Administration of keishibukuryogan was started at 1 week after 5/6 nephrectomy and was continued for 4 weeks. At the end of the experiment, Azan staining did not reveal any severe histological changes in the kidneys of the nephrectomized rats. On the other hand, significant increases in mRNA expressions of transforming growth factor-β₁ and fibronectin related to tissue fibrosis, as examined by Reverse Transcriptase-Polymerase Chain Reaction, were observed in nephrectomized rats, and they were significantly suppressed by 3% keishibukuryogan treatment. Against gene expressions related to macrophage infiltration, 3% keishibukuryogan treatment significantly suppressed osteopontin mRNA levels, and monocyte chemoattractant protein-1 and vascular cell adhesion molecule-1 mRNA levels showed a tendency to decrease, but without statistical significance. It was also observed that 3% keishibukuryogan attenuated serum urea nitrogen and urinary protein excretion levels. From these results, it was suggested that keishibukuryogan exerts beneficial effects that result in slowing the progression of chronic renal failure.

Allogenic fetal membrane-derived mesenchymal stem cells contribute to renal repair in experimental glomerulonephritis

Mesenchymal stem cells (MSC) have been reported to be an attractive therapeutic cell source for the treatment of renal diseases. Recently, we reported that transplantation of allogenic fetal membrane-derived MSC (FM-MSC), which are available noninvasively in large amounts, had a therapeutic effect on a hindlimb ischemia model (Ishikane S, Ohnishi S, Yamahara K, Sada M, Harada K, Mishima K, Iwasaki K, Fujiwara M, Kitamura S, Nagaya N, Ikeda T. Stem Cells 26: 2625-2633, 2008). Here, we investigated whether allogenic FM-MSC administration could ameliorate renal injury in experimental glomerulonephritis. Lewis rats with anti-Thy1 nephritis intravenously received FM-MSC obtained from major histocompatibility complex-mismatched ACI rats (FM-MSC group) or a PBS (PBS group). Nephritic rats exhibited an increased urinary protein excretion in the PBS group, whereas the FM-MSC group rats had a significantly lower level of increase (P < 0.05 vs. PBS group). FM-MSC transplantation significantly reduced activated mesangial cell (MC) proliferation, glomerular monocyte/macrophage infiltration, mesangial matrix accumulation, as well as the glomerular expression of inflammatory or extracellular matrix-related genes including TNF-α, monocyte chemoattractant protein 1 (MCP-1), type I collagen, TGF-β, type 1 plasminogen activator inhibitor (PAI-1) (P < 0.05 vs. PBS group). In vitro, FM-MSC-derived conditioned medium significantly attenuated the expression of TNF-α and MCP-1 in rat MC through a prostaglandin E(2)-dependent mechanism. These data suggest that transplanted FM-MSC contributed to the healing process in injured kidney tissue by producing paracrine factors. Our results indicate that allogenic FM-MSC transplantation is a potent therapeutic strategy for the treatment of acute glomerulonephritis.

Aggravated renal inflammatory responses in TRPV1 gene knockout mice subjected to DOCA-salt hypertension

To test the hypothesis that deletion of the transient receptor potential vanilloid type 1 (TRPV1) channel exaggerates hypertension-induced renal inflammatory response, wild-type (WT) or TRPV1-null mutant (TRPV1(-/-)) mice were subjected to uninephrectomy and deoxycorticosterone acetate (DOCA)-salt treatment for 4 wk. Mean arterial pressure (MAP) determined by radiotelemetry increased in DOCA-salt-treated WT or TRPV1(-/-) mice, whereas there was no difference in MAP between two strains at the baseline or after DOCA-salt treatment. DOCA-salt treatment increased urinary excretion of albumin and 8-isoprostane in both WT and TRPV1(-/-) mice, and the increases were greater in magnitude in the latter strain. Periodic acid-Schiff and Mason's trichrome staining showed that kidneys of DOCA-salt-treated TRPV1(-/-) mice exhibited more severe glomerulosclerosis and tubulointerstitial injury compared with DOCA-salt-treated WT mice. NF-kappaB assay showed that DOCA-salt treatment increased renal activated NF-kappaB concentrations in TRPV1(-/-) mice compared with WT mice. Immunostaining and ELISA assay revealed that DOCA-salt-treated TRPV1(-/-) mice had enhanced renal infiltration of monocyte/macrophage and lymphocyte, as well as increased renal levels of proinflammatory cytokine (TNF-alpha, IL-6) and chemokine (MCP-1) compared with DOCA-salt-treated WT mice. Renal ICAM-1 but not VCAM-1 expression was also greater in DOCA-salt-treated TRPV1(-/-) than WT mice. Dexamethasone (DEXA), an immunosuppressive drug, conveyed a renoprotective effect that was greater in DOCA-salt-treated TRPV1(-/-) compared with WT mice. These data show that renal inflammation is exacerbated in DOCA-salt hypertension when TRPV1 gene is deleted and that the deterioration is ameliorated by DEXA treatment, indicating that TRPV1 may act as a potential regulator of the inflammatory process to lessen renal injury in DOCA-salt hypertension.

Genetic mapping found major QTLs for antibody-induced glomerulonephritis in WKY rats

Genetic bases of glomerulonephritis, a major cause of kidney dysfunction in humans and one of the most characteristic complications of autoimmune disorders such as Goodpasture syndrome, are complex. The Wistar-Kyoto (WKY) rat strain is well characterized for its susceptibility to autoantibodies against glomerular basement membrane (GBM), however the molecular mechanisms underlining the phenotype are largely unknown. Here we performed a whole genome scan using a backcross (BC) F(1) (WKY x DA) x WKY population, for which the DA rat is a nonsusceptible control strain. We found two significant QTLs on chromosomes 1 and 12, which were involved in elevated levels of proteinuria and kidney weight index, respectively. The relevance of these QTLs with the genetic factors involved in autoimmunity and renal disease is discussed.

Galectin-1 stimulates monocyte chemotaxis via the p44/42 MAP kinase pathway and a pertussis toxin-sensitive pathway

Galectin-1, the prototype of a family of beta-galactoside-binding proteins, has been implicated in a wide variety of biological processes. Data presented herein show that galectin-1 stimulates monocyte migration in a dose-dependent manner but is not chemotactic for macrophages. Galectin-1-induced monocyte chemotaxis is blocked by lactose and inhibited by an anti-galectin-1 antibody but not by nonspecific antibodies. Furthermore, galectin-1-mediated monocyte migration was significantly inhibited by MEK inhibitors in a rapid, time-dependent manner suggesting that MAP kinase pathways are involved in galectin-1. Migration was also almost completely blocked by pertussis toxin implying G-protein involvement in the galectin-1-induced chemotaxis. These results demonstrate a role for galectin-1 in monocyte chemotaxis which differs from galectin-3 in that macrophages are nonresponsive. Furthermore, our observations suggest that galectin-1 may be involved in chemoattraction at sites of inflammation in vivo and may contribute to disease processes such as atherosclerosis.

Losartan chemistry and its effects via AT1 mechanisms in the kidney

Besides the importance of the renin-angiotensin system (RAS) in the circulation and other organs, the local RAS in the kidney has attracted a great attention in research in last decades. The renal RAS plays an important role in the body fluid homeostasis and long-term cardiovascular regulation. All major components and key enzymes for the establishment of a local RAS as well as two important angiotensin II (Ang II) receptor subtypes, AT1 and AT2 receptors, have been confirmed in the kidney. In additional to renal contribution to the systemic RAS, the intrarenal RAS plays a critical role in the regulation of renal function as well as in the development of kidney disease. Notably, kidney AT1 receptors locating at different cells and compartments inside the kidney are important for normal renal physiological functions and abnormal pathophysiological processes. This mini-review focuses on: 1) the local renal RAS and its receptors, particularly the AT1 receptor and its mechanisms in physiological and pathophysiological processes; and 2) the chemistry of the selective AT1 receptor blocker, losartan, and the potential mechanisms for its actions in the renal RAS-mediated disease.

Molecular magnetic resonance imaging of the genitourinary tract: recent results and future directions

This article focuses on preclinical and early clinical applications of renal cell MR imaging, on new developments in MR control of intrarenal gene therapy, and on several potential applications of molecular imaging techniques, mainly targeting cell receptors and enzyme activity, which could find exciting applications within the genitourinary tract.

Analysis and classification of B-cell infiltrates in lupus and ANCA-associated nephritis

Intrarenal B cell infiltrates resembling secondary lymphoid tissue have been found in several forms of inflammatory kidney disease. Their role in renal inflammation is not well defined, perhaps because B cell clusters have been regarded as a single entity while being quite heterogeneous. Therefore we characterized intrarenal lymphoid clusters of 32 patients diagnosed with lupus nephritis and 16 with ANCA associated nephritis. We identified four increasingly organized levels of intrarenal aggregates from scattered B cells to highly compartmentalized B cell clusters with central follicular dendritic cell networks. Most B cells displayed a mature non-antibody producing phenotype with antigen presenting ability. In regions of B cell infiltration, expression of the lymphoid chemokine BCA-1 was found in cells of a dendritic-like morphology and most B cells expressed the corresponding receptor CXCR5. Biopsies containing B cells had significantly higher levels of BCA-1 mRNA expression compared to those without, suggesting a role of BCA-1 and CXCR5 for B cell infiltration into the kidney. Our study proposes a new classification of B cell clusters in lupus and ANCA associated nephritis which might help to study the function of intrarenal B cell clusters in a more differentiated manner.

Jund is a determinant of macrophage activation and is associated with glomerulonephritis susceptibility

Crescentic glomerulonephritis is an important cause of human kidney failure for which the underlying molecular basis is largely unknown. In previous studies, we mapped several susceptibility loci, Crgn1-Crgn7, for crescentic glomerulonephritis in the Wistar Kyoto (WKY) rat. Here we show by combined congenic, linkage and microarray studies that the activator protein-1 (AP-1) transcription factor JunD is a major determinant of macrophage activity and is associated with glomerulonephritis susceptibility. Introgression of Crgn2 from the nonsusceptible Lewis strain onto the WKY background leads to significant reductions in crescent formation, macrophage infiltration, Fc receptor-mediated macrophage activation and cytokine production. Haplotype analysis restricted the Crgn2 linkage interval to a 430-kb interval containing Jund, which is markedly overexpressed in WKY macrophages and glomeruli. Jund knockdown in rat and human primary macrophages led to significantly reduced macrophage activity and cytokine secretion, indicating conservation of JunD function in macrophage activation in rats and humans and suggesting in vivo inhibition of Jund as a possible new therapeutic strategy for diseases characterized by inflammation and macrophage activation.

Human T and natural killer cells possess a functional renin-angiotensin system: further mechanisms of angiotensin II-induced inflammation

The renin-angiotensin system (RAS) plays an important role in the regulation of inflammation and in the progression of chronic kidney disease. Accumulation of inflammatory cells into the renal parenchyma has been a hallmark of chronic kidney disease; however, little is known concerning the presence and the function of RAS elements in T and natural killer (NK) cells. Here is reported a co-stimulatory effect of angiotensin II (AngII) by showing an augmentation of mitogen and anti-CD3-stimulated T and NK cell proliferation with AngII treatment. Angiotensinogen and AngI also generated the same effect, suggesting that NK and T cells have functional renin and angiotensin-converting enzyme activity. Indeed, they express renin, the renin receptor, angiotensinogen, and angiotensin-converting enzyme by mRNA analysis. Flow cytometric analysis and Western blot revealed angiotensin receptor 2 (AT(2)) expression in T and NK cells, whereas AT(1) expression was found in T and NK cells and monocytes by Western blot. These receptors were shown to be functional in calcium signaling, chemotaxis, and proliferation. However, AT(1) and AT(2) antagonists alone or in combination were unable to abrogate completely the effects of AngII, suggesting that another AngII receptor may also be functional in leukocytes. This is the first study to show that T and NK cells are fully equipped with RAS elements and are potentially capable of producing and delivering AngII to sites of inflammation. Because their chemotaxis is enhanced by AngII, this creates a potential inflammatory amplification system.

Inhibition of p38 mitogen-activated protein kinase is effective in the treatment of experimental crescentic glomerulonephritis and suppresses monocyte chemoattractant protein-1 but not IL-1beta or IL-6

Activation of p38 mitogen-activated protein kinase (MAPK) is known to be important in cytokine production and cell survival in inflammation. This study examined the effect of inhibiting p38 MAPK after onset of renal injury in an experimental model of crescentic glomerulonephritis. Furthermore, this study investigated whether p38 MAPK inhibition would cause widespread suppression of the cytokine network in vivo or uncontrolled apoptosis. In the in vivo studies, daily treatment with a p38 MAPKalpha/beta inhibitor was started 1 h (early treatment study) or 4 d (late treatment study) after induction of nephrotoxic nephritis in Wistar Kyoto rats. The treated rats remained healthy with normal weight gain during the study. Both early and late treatment with p38 MAPK inhibitor reduced renal monocyte chemoattractant protein-1 (MCP-1) levels, the number of glomerular macrophages, the severity of tissue injury, and proteinuria compared with the vehicle group. Unexpected, treatment with p38 MAPK inhibitor did not suppress renal levels of IL-1beta or IL-6. In the in vitro study, the p38 MAPKalpha/beta inhibitor reduced production of MCP-1 and IL-6 by TNF-alpha-or IL-1beta-stimulated mesangial cells without any effect on cell viability or apoptosis. In conclusion, p38 MAPK inhibition is effective in reducing the severity of crescentic glomerulonephritis even when treatment is started after onset of disease. The therapeutic effect is associated with selective suppression of MCP-1, without widespread suppression of cytokine production or increased apoptosis. Therefore, p38 MAPK therapeutic blockade is a promising strategy in the treatment of antibody-mediated glomerulonephritis.

Contrast agents for functional and cellular MRI of the kidney

Low-molecular-weight gadolinium (Gd) chelates are glomerular tracers but their role in evaluation of renal function with magnetic resonance (MR) imaging is still marginal. Because of their small size, they diffuse freely into the interstitium and the relationship between measured signal intensity and concentration is complex. New categories of contrast agents, such as large Gd-chelates or iron oxide particules, with different pharmacokinetic and magnetic properties have been developed. These large molecules could be useful for both functional (quantification of perfusion, quantification of glomerular filtration rate, estimation of tubular function) and cellular imaging (intrarenal phagocytosis in inflammatory renal diseases). Continuous development of new contrast agents remains worthwhile to get the best adequacy between the physiological phenomenon of interest and the pharmacokinetic of the agent.

Effect of nitric oxide synthase inhibition on proteinuria in glomerular immune injury

In glomerular immune injury, the inducible isoform of nitric oxide synthase (iNOS) becomes a major catalyst of NO production. Although iNOS-catalyzed NO production is sustained and can be cytotoxic, iNOS inhibition exacerbates the magnitude of proteinuria that accompanies immune injury. To investigate putative mechanisms of this effect, we assessed changes in glomerular permeability to albumin by using the following two approaches: (i) an in vivo rat model of glomerular immune injury induced by antibody against the glomerular basement membrane (GBM), in which urine albumin excretion was measured under conditions of iNOS inhibition, and (ii) an ex vivo model of isolated rat glomeruli, in which changes in glomerular capillary permeability to albumin were assessed under conditions of NOS inhibition. In rats with anti-GBM antibody-induced glomerular injury, there was an increase in urine albumin excretion. Treatment with two structurally dissimilar iNOS inhibitors at doses sufficient to decrease urine nitrate and/or nitrite exacerbated proteinuria. In these animals, urine excretion of the isoprostane 8-iso-PGF2alpha (marker of oxidative stress) was increased. In isolated glomeruli incubated with the NOS inhibitor L-NMMA, the permeability to albumin increased. This effect was reversed by the NO donor DETA NONOate and by the superoxide dismutase mimetic Tempol. We conclude that NOS-catalyzed NO production is an important mechanism in regulating glomerular permeability to protein. This mechanism involves control of the bioavailability of superoxide.

MR imaging of nephropathies

Acute and chronic nephropathies are responsible for morphologic and functional renal changes. However, radiologic techniques currently play a minor role in imaging of parenchymal nephropathies in native or transplanted kidneys. From a morphologic point of view, three-dimensional magnetic resonance (MR) volumetric biomarkers of kidney function, such as renal and cortical volumes or cystic volume, in polycystic kidney diseases play a growing role in nephrologic practice. From a functional point of view, if scintigraphic techniques remain the major sources of renal performance assessment, new MR imaging systems and specific MR contrast agents may soon provide significant developments in the evaluation of renal performance (glomerular filtration rate measurement), in the search for prognostic factors (hypoxia, inflammation, cell viability, degree of tubular function, and interstitial fibrosis), and for monitoring new cell therapies. New developments that have provided higher signal-to-noise ratio and higher spatial and/or temporal resolutions have the potential to direct new opportunities for obtaining morphologic and functional information on tissue characteristics that are relevant for various renal diseases with respect to diagnosis, prognosis, and treatment follow-up.

Superoxide dismutase mimetic preserves the glomerular capillary permeability barrier to protein

Overproduction of superoxide (O2*) occurs in glomerular disease and may overwhelm the capacity of superoxide dismutase (SOD), thereby intensifying oxidant injury by O2* and related radical species that disrupt the glomerular capillary permeability barrier to protein. We examined the efficacy of the SOD mimetic tempol in preserving glomerular permeability to protein using 1) a rat model of glomerular immune injury induced by an antiglomerular basement membrane antibody (anti-GBM), and 2) isolated rat glomeruli in which injury was induced by the cytokine tumor necrosis factor-alpha (TNFalpha). To induce glomerular immune injury, rats received anti-GBM using a protocol that results in prominent infiltration of glomeruli by macrophages and in which macrophage-derived TNFalpha has been shown to mediate albuminuria. To increase glomerular capillary permeability to albumin (P(alb)) ex vivo, isolated glomeruli were incubated with TNFalpha at concentrations (0.5-4.0 microg/ml) known to stimulate O2* production. Increments in P(alb) were detected by measuring changes in glomerular volume in response to an applied oncotic gradient. Significant increases in the urine excretion of albumin and F(2alpha)-isoprostane were observed in rats with glomerular immune injury without a significant change in systolic blood pressure. Tempol treatment significantly reduced urine isoprostane and albumin excretion. In isolated glomeruli, TNFalpha increased P(alb) and tempol abrogated this effect, both in a dose-dependent manner. These observations indicate that SOD mimetics can preserve the glomerular permeability barrier to protein under conditions of oxidative stress from O2* production.

Interleukin-11 reduces renal injury and glomerular NF-kappa B activity in murine experimental glomerulonephritis

BACKGROUND/AIMS

There is now considerable evidence implicating T cells and macrophages in glomerular injury in crescentic glomerulonephritis. Recently, it has been shown that interleukin-11 (IL-11) has an immune modulatory function through its effect on both macrophages and T cells. We, therefore, examined the therapeutic effect of IL-11 in a murine model of experimental glomerulonephritis.

METHOD

Accelerated nephrotoxic nephritis was induced in C57BL/6 mice. IL-11 at a dose of 0.5 mg/kg/day (n = 10) in vehicle was given daily subcutaneously from the day of sensitization until day 14 after initiation of glomerulonephritis. Control mice (n = 10) received injection of vehicle alone with the same schedule.

RESULTS

IL-11 treatment markedly decreased albuminuria (6.2 +/- 1.9 vs. 18.2 +/- 4.5 mg/day, p < 0.05), the number of glomerular macrophages (1.1 +/- 0.2 vs. 1.7 +/- 0.3 cells/glomerular cross-section, p < 0.05) and glomerular fibrin deposition (fibrin score 0.9 +/- 0.3 vs. 2 +/- 0.3, p < 0.05). There was no difference in the glomerular T cell numbers between the IL-11-treated and the vehicle group. Glomerular NF-kappaB activity was markedly suppressed by 75% in the treated group (p = 0.0015).

CONCLUSION

In this study, we provide the first in vivo evidence that IL-11 treatment decreases glomerular NF-kappaB activity and reduces renal injury in experimental glomerulonephritis.

Infusion of angiotensin II reduces loss of glomerular capillary area in the early phase of anti-Thy-1.1 nephritis possibly via regulating angiogenesis-associated factors

Hyperphosphatemia in patients with chronic kidney disease leads to secondary hyperparathyroidism and renal osteodystrophy, and it is independently associated with mortality risk. The exact mechanism by which hyperphosphatemia increases mortality risk is unknown, but it may relate to enhanced cardiovascular calcification. The National Kidney Foundation Kidney Disease Outcomes Quality Initiative (K/DOQI) Clinical Practice Guidelines for Bone Metabolism and Disease in Chronic Kidney Disease recommends maintenance of serum phosphorus below 5.5 mg/dL, calcium-phosphorus (Ca x P) product less than 55 mg(2)/dL(2), intact parathyroid hormone (iPTH) 150 pg/mL to 300 pg/mL, and bicarbonate (HCO(3)) greater than 22 mEq/L. Although calcium-based phosphate binders (CBPB) are cost effective, there are long-term safety concerns pertaining to their postulated role in the progression of cardiovascular calcification. Sevelamer hydrochloride has been recommended as an alternative noncalcium phosphate binder. Results from the Calcium Acetate Renagel Evaluation (CARE) study indicate that calcium acetate is more effective than sevelamer hydrochloride in controlling serum phosphorous, Ca x P product, and HCO(3) in hemodialysis patients. In the Treat-to-Goal study, dialysis patients treated with sevelamer hydrochloride had slower progression of coronary and aortic calcification than patients treated with CBPB. The mechanism underlying the beneficial effect of sevelamer hydrochloride is unknown but may relate to decreased calcium loading, or to dramatic reductions in low-density lipoprotein (LDL) cholesterol in sevelamer hydrochloride-treated patients. At present, evidence incriminating CBPB in the progression of cardiovascular calcification in end-stage renal disease (ESRD) remains largely circumstantial. As calcium acetate is more efficacious and cost effective than sevelamer hydrochloride, it remains an accepted first-line phosphate binder. This review examines these issues and provides rational guidelines for the use of CBPB in patients on maintenance hemodialysis.

The chemokine receptor 5 Delta32 mutation is associated with increased renal survival in patients with IgA nephropathy

BACKGROUND

Chemokine receptor 5 (CCR5) plays an important role in the recruitment of monocytes and T cells in inflammation and experimental studies suggest that CCR5 might be involved in the pathogenesis of IgA nephropathy. A mutation in the CCR5 gene (CCR5 Delta32), leading to a nonfunctional receptor, was recently described. We therefore evaluated the potential role of this mutation on renal survival in patients with IgA nephropathy.

METHODS

The distribution of the CCR5 Delta32 genotype was determined by polymerase chain reaction (PCR) analysis in 228 patients with biopsy-proven IgA nephropathy. In 190 patients with available demographic and clinical follow-up data, the effect of the mutation on the clinical outcome was analyzed using the Log-rank test and the Cox proportional hazard model. In vitro, the influence of the CCR5 Delta32 genotype on the chemotactic response of monocytes was assessed.

RESULTS

Of the 190 patients, 158 (83.2%) had a CCR5 wild-type genotype, 29 (15.3%) were heterozygous, and three patients had a homozygous CCR5 Delta32 genotype (1.6%). Renal survival was significantly longer in patients with the CCR5 Delta32 genotype than in the wild-type group (Log-rank P < 0.001). Using the multivariate Cox proportional hazard model, the CCR5 Delta32 genotype was identified as an independent factor associated with a lower risk to develop end-stage renal disease (ESRD) [hazard ratio (HR) 0.23, 95% CI 0.09 to 0.57, P= 0.002]. In vitro analysis of monocytes from CCR5 Delta32 carriers showed a reduced chemotactic response to CCR5 ligands in vitro.

CONCLUSION

Our study demonstrates an independent role of the CCR5 Delta32 genotype for the clinical outcome in IgA nephropathy. In vitro experiments revealed a reduced chemotactic response of monocytes from CCR5 Delta32 carriers, thus pointing out a possible pathophysiologic explanation for the beneficial effect of the CCR5 Delta32 genotype.

Effect of antisense oligodeoxynucleotides for ICAM-1 on renal ischaemia-reperfusion injury in the anaesthetised rat

An antisense oligodeoxynucleotide (As-ODN) to the 3' untranslated region of the mRNA sequence expressing the intracellular adhesion molecule-1 (ICAM-1) was employed to determine ICAM-1's role in renal ischaemia-reperfusion injury in the rat. Wistar-Kyoto rats receiving i.v. either lipofectin-As-ODN (As-ODN group), lipofectin-reverse ODN (Rv-ODN group) or lipofectin (ischaemia control group) 8 h prior to study were anaesthetized and subjected to 30 min of renal artery occlusion. Renal haemodynamic and excretory parameters were monitored before and after renal ischaemia. On termination of the study renal tissue was subjected to histological and Western blot analysis. Renal blood flow decreased in the 3 h post-ischaemia period in the ischaemia control and Rv-ODN groups, but was maintained in the As-ODN group. Glomerular filtration rate was depressed initially but gradually increased to 10% above basal levels in the ischaemia control and Rv-ODN groups, but was below basal levels (20%) in the As-ODN group. There was a three- to fourfold increase in sodium and water excretion following ischaemia in the ischaemia control and reverse-ODN groups but not in the As-ODN treated group. The As-ODN ameliorated the histological evidence of ischaemic damage and reduced ICAM-1 protein levels to a greater extent in the medulla than cortex. These observations suggested that in the post-ischaemic period afferent and efferent arteriolar tone was increased with a loss of reabsorptive capacity which was in part due to ICAM-1. The possibility arises that the action of ICAM-1 at vascular and tubular sites in the deeper regions of the kidney contributes to the ischaemia-reperfusion injury.

Expression of MRP8 and MRP14 by macrophages is a marker for severe forms of glomerulonephritis

Expression of two S100 proteins, myeloid related protein (MRP)8 and MRP14, as well as their complex formation indicate proinflammatory properties of macrophages. We analyzed if the different forms of glomerulonephritis (GN) are associated with the appearance of certain phenotypes of infiltrating macrophages characterized by expression of MRP8 and MRP14 as well as their complex formation. Immunohistochemical analysis of 89 renal biopsies with different forms of nephritis revealed that expression and complex formation of MRP8 and MRP14 by infiltrating macrophages in the glomeruli correlated with the severity of the inflammatory process. As such, MRP8/MRP14-expressing monocytes prevailed in highly proliferating forms of GN, i.e., systemic lupus erythematosus GN and extracapillary GN. In contrast, a high percentage of macrophages in the renal interstitium expressed MRP8 and MRP14 without concomitant formation of their complex, and they indicated a chronic type of inflammatory reaction in GN. Immunosuppressive drugs had no direct effects on the expression of MRP8 and MRP14 in macrophages in vitro. The correlation of MRP8 and MRP14 expression with disease activity indicates that these calcium-binding proteins are of pathophysiological relevance in GN. In addition, our findings reflect differences in the inflammatory mechanisms underlying the various forms of GN, as they revealed that distinct macrophage subpopulations prevail in the different forms of GN.

Increased production of chemotactic cytokines and elevated proliferation and expression of intercellular adhesion molecule-1 in rat mesangial cells treated with erythrogenic toxin type B and its precursor isolated from nephritogenic streptococci

BACKGROUND

Previous reports have demonstrated the presence of streptococcal erythrogenic toxin type B (ETB) as well as proliferation and expression of adhesion molecules along with leukocyte infiltrations in biopsies from patients with acute post-streptococcal glomerulonephritis (APSGN). The purpose of the present study was to correlate infiltrative and proliferative events with interactions between ETB or its precursor (ETBP) and intrinsic mesangial cells.

METHODS

Rat mesangial cells were cultured with ETB or ETBP (50 micro g/ml) while measuring production of monocyte chemoattractant protein-1 (MCP-1) and macrophage inflammatory protein-2 (MIP-2) and while examining proliferation and expression of intercellular adhesion molecule-1 (ICAM-1). After 24, 48 and 96 h of incubation, MCP-1 and MIP-2 in culture supernatants were assessed by enzyme-linked immunosorbent assay (ELISA). Cells were assessed for proliferation by incorporation of radioactive thymidine and expression of ICAM-1 was measured by indirect immunofluorescence and by cellular ELISA.

RESULTS

Compared with controls, treatment with either ETBP or ETB significantly increased MCP-1 and MIP-2 levels in mesangial cell cultures. Mesangial cells also showed elevated proliferation at 96 h of culture when treated with streptococcal proteins. Although production of MCP-1 and MIP-2 was not correlated with proliferation, treatment with ETBP resulted in a significant correlation between MCP-1 production and proliferation. Immunofluorescence studies revealed an increased expression of ICAM-1 in ETBP/ETB-treated mesangial cells. In addition, cellular ELISA studies showed increased absorbance in cultures treated with ETBP/ETB. Finally, low serum concentrations in the culture medium potentiated the stimulatory effect of ETB on MCP-1 production.

CONCLUSIONS

Our findings, by demonstrating a role for cationic streptococcal ETB or ETBP in the induction of chemotactic molecules as well as the proliferation and expression of adhesion molecules, delineate an additional possible pathway for the pathogenesis of APSGN.

Selective regulation of ICAM-1 and RANTES gene expression after ICAM-1 ligation on human renal fibroblasts

Leukocyte infiltration of the cortico-interstitium is characteristic of many forms of progressive renal disease. The principal adhesion molecule expressed on resident interstitial cells and recognized by leukocytes is intercellular adhesion molecule-1 (ICAM-1). ICAM-1 is an inducible transmembrane receptor, which forms the counter-receptor for the leukocyte beta 2 integrins. ICAM-1-dependent binding induces the synthesis of the chemokine RANTES and of ICAM-1 itself. This study examines some of the signaling pathways involved in this induction. After ICAM-1 cross-linking on fibroblasts, the mRNA and protein for both RANTES and ICAM-1 were induced. This induction was calcium-dependent and inhibited by BAPTA-AM. The p38, ERK1, and ERK2 MAP kinases were activated in a [Ca2+]i-dependent manner, with a maximum phosphorylation at approximately 3 min after cross-linking. Through the use of selective inhibitors of p38 MAP kinase (SB203580) or MEKK (PD98059), p38 but not ERK activation was shown to be essential for the induction of ICAM-1. Neither was involved in RANTES activation, however. These mechanisms differed from those initiated by TNF-alpha, which were not [Ca2+]i-dependent. Electrophoretic mobility shift analysis demonstrated a time-dependent induction of both AP-1 and NF-kappaB binding activity in nuclear extracts, maximal at approximately 15 min after ICAM-1 cross-linking. Only AP-1 activation, however, was calcium-dependent, suggesting the central involvement of this transcription factor in ICAM-1 and RANTES induction after the ligation of ICAM-1. This study suggests an independent mechanism of inflammatory amplification, which may be characteristic of a persistent leukocytic involvement in areas of chronic inflammation rather than in cytokine-induced acute inflammation.

The polymorphism of monocyte chemoattractant protein-1 is associated with the renal disease of SLE

BACKGROUND

Renal involvement in patients with systemic lupus erythematosus (SLE) varies from none to full-blown disease. Monocyte chemoattractant protein (MCP-1) is implicated in the activation of inflammatory cells and has been suggested to affect the progression of lupus nephritis (LN).

METHODS

In the 5' flanking region of the MCP-1 gene, a guanine (G)/adenine (A) transition identified at position -2518 upstream from the transcription site was reported to be associated with circulating levels. We investigated whether the G/A polymorphism was associated with clinical manifestations of SLE in terms of renal involvement and the biological significance of this polymorphism.

RESULTS

Frequencies of MCP-1/-2518 polymorphisms were similar in patients and controls. Serum MCP-1 levels in patients with SLE were significantly greater than those of healthy controls, but amount of proteinuria did not correlate with serum MCP-1 level in patients. In AA homozygotes, patients with LN showed greater serum MCP-1 levels than patients without LN. In addition, urinary excretion of MCP-1 was greater in AA homozygotes compared with other genotypes in patients with LN. A positive correlation between urinary excretion of MCP-1 and proteinuria was observed in patients with SLE. Genetic constructs containing G at this site showed that G construct had lower activity (39%) than that shown by a construct containing A, and this response, which depended on MCP-1 genotype, was maintained after stimulation with tumor necrosis factor-alpha.

CONCLUSION

These results suggest that a genetic polymorphism in the 5' flanking region of the MCP-1 gene would be associated with nephritis in lupus through modulating MCP-1 expression.

Circulating monocyte chemoattractant protein-1 and early development of nephropathy in type 1 diabetes

OBJECTIVES

To investigate the possible role of hyperglycemia-dependent monocyte chemoattractant protein (MCP)-1 biosynthesis in the pathophysiology of early nephropathy in type 1 diabetes.

RESEARCH DESIGN AND METHODS

We studied 30 patients with type 1 diabetes (15 with and 15 without microalbuminuria) compared with matched healthy control subjects. Plasma MCP-1 and plasma oxidant status (vitamin E, fluorescent products of lipid peroxidation [FPLPs], malondialdehyde [MDA]), HbA(1c), and albumin excretion rate [AER]) were evaluated at baseline. Furthermore, MCP-1, vitamin E, AER, and HbA(1c) were also analyzed in the microalbuminuric diabetic patients and in the healthy volunteers after 8 weeks of high-dose (600 mg b.i.d.) vitamin E treatment.

RESULTS

FPLPs, MDA, and MCP-1 were significantly higher, whereas vitamin E was significantly lower in patients with microalbuminuria and poorer glycemic control as compared with normoalbuminuric patients and healthy control subjects. Plasma MCP-1 was positively correlated with HbA(1c), FPLPs, MDA, and AER, whereas plasma MCP-1 showed an inverse correlation with vitamin E. Interestingly, both MCP-1 and AER decreased significantly after vitamin E treatment, despite no changes in HbA(1c) values.

CONCLUSIONS

This study suggests that prolonged hyperglycemia may lead to early renal complications in type 1 diabetes by inducing MCP-1 biosynthesis via enhanced oxidative stress. Long-term treatment of high-dose vitamin E significantly decreased MCP-1, thus providing a rationale basis for evaluating vitamin E supplementation as therapy adjuvant to conventional insulin treatment in type 1 diabetic patients in whom an acceptable glycemic control is difficult to achieve despite appropriate insulin treatment.

Expression of monocyte chemoattractant protein-1 in proximal tubular epithelial cells in a rat model of progressive kidney failure

Impairment of kidney function in various types of glomerular disease is associated with tubulointerstitial changes. Monocyte chemoattractant protein-1 (MCP-1) is up-regulated in the tubulointerstitium and in the glomeruli in many human and experimental kidney disorders. We investigated the localization of MCP-1 expression in a rat model of progressive kidney failure. Male Wistar rats were subjected to subtotal nephrectomy (n = 30) or sham surgery (n = 30). Immunohistochemistry with immunoelectron microscopy and in situ hybridization were used to examine the expression of MCP-1 protein and messenger ribonucleic acid (mRNA) in the kidney, respectively. MCP-1 protein and mRNA were hardly detected in both glomeruli and tubulointerstitium of control rats. However, in the rats subjected to nephrectomy, MCP-1 expression was increased in the tubular cells of the remnant kidney, accompanied by significant macrophage infiltration. MCP-1 was observed mainly in the proximal tubular cells and only weakly in distal tubular cells. No significant expression of MCP-1 protein or mRNA was noted in the glomeruli. Immunoelectron microscopy showed the presence of MCP-1 in the rough endoplasmic reticulum of proximal tubular cells, confirming that MCP-1 is produced in proximal tubular cells. MCP-1 was also observed in endocytic vesicles adjacent to the brush border of proximal tubular cells, suggesting incorporation of MCP-1 from the tubular lumen. Our findings indicate localized expression of MCP-1 in proximal tubular cells in the remnant kidney and suggest that MCP-1 in proximal tubular cells is involved in tubulointerstitial damage in chronic kidney failure associated with glomerular hypertension.

Fractalkine expression and the recruitment of CX3CR1+ cells in the prolonged mesangial proliferative glomerulonephritis

BACKGROUND

We established the reversible and the prolonged models of mesangial proliferative glomerulonephritis (GN) with anti-Thy 1 antibody 1-22-3. However, the essential factors leading to the prolonged glomerular alterations have not been identified.

METHODS

The expressions of several chemokines and cytokines were compared in the reversible and the prolonged models. Expression of fractalkine and the number of the fractalkine receptor CX3CR1-positive cells in the glomeruli in the prolonged model were significantly higher than those in the reversible model. Then, the localization of fractalkine and the characteristics of CX3CR1+ cells were analyzed in glomeruli. To elucidate the significance of the fractalkine expression, we analyzed the expression in the model treated with angiotensin II receptor antagonist, candesartan.

RESULTS

Immunostaining of fractalkine was detected on endothelial cells on the fifth day, and fractalkine staining also was detected in the mesangial area on day 14. Major parts of the CX3CR1+ cells in the glomeruli were macrophages, especially ED3+ cells. Candesartan treatment ameliorated the glomerular morphological findings at six weeks after disease induction. Although the treatment did not ameliorate the morphological finding at two weeks, decreased expression of fractalkine and CX3CR1+ were already detected at two weeks in rats treated with candesartan.

CONCLUSIONS

Fractalkine expression and the recruitment of CX3CR1+ cells in glomeruli might play an important role in the development of the prolonged disease. These expressions could be predictors of the prolonged disease of the mesangial proliferative glomerulonephritis.

Angiotensin II infusion ameliorates the early phase of a mesangioproliferative glomerulonephritis

BACKGROUND

Inhibition of the renin-angiotensin system slows the progression of chronic renal disease.

METHODS

To test whether angiotensin II (Ang II) infusion aggravates or ameliorates an acute glomerulonephritis, the peptide was infused (200 ng/min by osmotic minipump) in rats with an anti-thymocyte antibody-induced glomerulonephritis (ATS).

RESULTS

Ang II significantly increased blood pressure. Following injection of the antibody, similar glomerular binding of rabbit IgG and rat complement C3 was detected in ATS and Ang II+ATS rats, indicating no differences in delivery and binding of the antibody. Ang II infusion, however, induced a significant reduction in glomerular monocyte infiltration, cell proliferation and matrix expansion in nephritic rats compared to rats with nephritis without Ang II. The antiproliferative effect of Ang II was inhibited by the Ang II type 1 (AT1) receptor blocker irbesartan, but not by the AT2 receptor blocker PD 123319, indicating that this effect was likely transduced by AT1 receptors. Norepinephrine infusion (600 ng/min) produced a similar degree of hypertension, but did not affect glomerular proliferation in nephritic rats. Ang II induced the glomerular expression of the cell cycle inhibitor p27KIP1 and of transforming growth factor-beta (TGF-beta) and inhibited expression of monocyte chemotactic protein 1 (MCP-1).

CONCLUSION

Ang II surprisingly ameliorates glomerular monocyte infiltration, proliferation and matrix expansion in ATS nephritis. Ang II-mediated induction of cyclin kinase inhibitors and TGF-beta may contribute to the protection of the glomerulus from inflammatory injury by inducing cell cycle arrest and attenuating activation of local and recruited cells. Alternatively, Ang II might protect the kidney at least in part by less inflow of disease activators due to reduction of renal blood flow. Therefore, activation of the renin-angiotensin system may have protective effects in certain pathophysiological situations.

Lacidipine inhibits adhesion molecule and oxidase expression independent of blood pressure reduction in angiotensin-induced vascular injury

Dihydropyridines can inhibit gene expression in-vitro and may have a protective vascular effect independent of blood pressure reduction. We tested the hypothesis that lacidipine prevents induction of inducible NO synthase (iNOS), influences leukocyte adhesion and infiltration, inhibits nuclear factor (NF)-kappaB transcription factor activity, and ameliorates end-organ damage in a transgenic rat model of angiotensin (Ang) II--dependent organ sclerosis. We treated rats transgenic for human renin and angiotensinogen (dTGR) from week 4 to 7 with lacidipine (0.3 or 3 mg/kg by gavage). Blood pressure was measured by tail cuff. Organ damage was assessed by histology and immunohistochemistry. Adhesion molecules and cytokines were analyzed by immunohistochemistry. Transcription factors were analyzed by mobility shift assays. Untreated dTGR developed moderate hypertension, cardiac hypertrophy, and severe renal damage with albuminuria. Lacidipine decreased blood pressure slightly at the low dose and substantially at the higher dose. However, both treatments reduced albuminuria and plasma creatinine to the same degree (P<0.05). Intercellular adhesion molecule-1 (ICAM-1) was markedly reduced by lacidipine as well as renal neutrophil and monocyte infiltration. Lacidipine reduced mitogen-activated protein (MAP) kinase phosphorylation and iNOS expression in both cortex and medulla. NF-kappaB and AP-1 were activated in dTGR but reduced by lacidipine. Lacidipine ameliorates Ang II-induced end-organ damage independent of blood pressure lowering, perhaps by inhibiting the MAP kinase pathway and NF-kappaB activation.

Transmembrane signalling in human monocyte/mesangial cell co-cultures: role of cytosolic Ca(2+)

BACKGROUND

Adhesion of monocytes triggers apoptosis, cytotoxicity, cytokine release, and later proliferation of cultured human mesangial cells (HMC). In the search for transmembrane signals transducing the interaction of HMC adhesion molecules with leukocyte counterreceptors, we measured variations of cytosolic Ca(2+) ([Ca(2+)](i)) in HMC and monocytes of the U937 cell line during 6-h co-cultures.

METHODS

Monolayer cultures of HMC and suspensions of U937 cells were loaded with the fluoroprobe fura 2-AM and subsequently co-cultured for 6 h while separately monitoring by microfluorometry the Ca(2+)-dependent 500 nm fluorescent emission of each cell line at fixed intervals upon excitation at 340/380 nm.

RESULTS

U937 and peripheral blood monocyte adhesion was followed in HMC by a slow, progressive rise of [Ca(2+)](i) from basal levels of 96+/-9 nM to 339+/-54 at 60 min and 439+/-44 nM at 3 h. The [Ca(2+)](i) elevation reached a steady state thereafter, while parallel monolayers incubated with control media maintained resting levels throughout the co-culture with stable fluoroprobe retention. Receptor sensitivity to vasoconstrictor agents, including compounds not released by monocytes, such as angiotensin II, was rapidly downregulated in HMC co-cultured with U937 cells. No [Ca(2+)](i) changes could be elicited by the octapeptide or by the TxA(2) analogue, U-46619, as early as 30 min after exposure to U937 cells. No [Ca(2+)](i) changes were observed in U937 cells throughout the co-culture. Conditioned media from monocytes and from co-cultured HMC+U937 cells had no effect on [Ca(2+)](i) of HMC. Ca(2+) entry leading to fura 2 saturation was still inducible by Ca(2+) ionophores, such as ionomycin and 4-Br-A23187, which also inhibited the responses to vasoconstrictors. Ca(2+)-free solutions prevented the [Ca(2+)](i) rise as well as subsequent receptor inactivation, implicating Ca(2+) influx through store-operated Ca(2+) channels (SOC), a major pathway for Ca(2+) entry in these cultured cells. Ca(2+) influx was confirmed by Mn(2+)-quenching of fura 2.

CONCLUSIONS

In HMC, early changes in [Ca(2+)](i) signal for monocyte adhesion in a co-culture model of glomerular inflammation. This signalling mechanism may mediate the functional responses elicited in glomerular cells by leukocytes, including downregulation of receptors for vasoactive agents.

Reactive oxygen species alter gene expression in podocytes: induction of granulocyte macrophage-colony-stimulating factor

It has been suggested that reactive oxygen radicals (ROS) play a crucial role in the pathogenesis of proteinuria and podocyte injury. It was investigated whether changes in gene expression might account for ROS-induced podocyte dysfunction. Differentiated podocytes were incubated with control media or with exogenous ROS from the xanthine/xanthine-oxidase reaction for 4 h. A PCR-based suppressive subtractive hybridization assay was applied to isolate and clone mRNAs that were differentially expressed by exogenous ROS. One differentially expressed clone was identified as the proinflammatory cytokine granulocyte macrophage-colony-stimulating factor (GM-CSF). Regulation of GM-CSF in podocytes was further studied by Northern analysis and enzyme-linked immunosorbent assay. Exogenous ROS caused a concentration-dependent, >10-fold induction of GM-CSF mRNA after 4 h. A >50-fold increase in GM-CSF protein release in podocytes that had been stimulated with ROS could be detected. Induction of GM-CSF protein was inhibited by actinomycin D, which indicated that increased mRNA transcription was involved. The ROS scavengers dimethyl-thio-urea and pyrrolidone-dithio-carbamate strongly inhibited increased GM-CSF production induced by ROS. GM-CSF release was also induced when internal ROS production was triggered with NADH, whereas H2O2 had only a small effect. GM-CSF release by podocytes was also stimulated by lipopolysaccharide (LPS), interleukin-1 (IL-1), and phorbolester (PMA). Dimethyl-thio-urea significantly inhibited the LPS-, IL-1-, and PMA-induced GM-CSF production. Activation of the transcription factor nuclear factor-kappaB (NF-kappaB) but not activator protein-1 was involved in the upregulation of ROS-induced GM-CSF production. The data indicate that GM-CSF is differentially expressed by ROS in podocytes. ROS also partially mediate the effects of PMA and IL-1 on podocyte GM-CSF production. Because GM-CSF can enhance glomerular inflammation and induces mesangial proliferation, these data might provide further insight into the mechanisms of ROS-induced glomerular injury.

Interleukin-11 attenuates nephrotoxic nephritis in Wistar Kyoto rats

Interleukin-11 (IL-11) is a multifuctional cytokine with anti-inflammatory activity. The effect of IL-11 was studied in an experimental model of necrotizing glomerulonephritis induced in Wistar Kyoto rats by an injection of anti-glomerular basement membrane antibody (nephrotoxic serum). Intraperitoneal injection was chosen as the route of IL-11 administration in all experiments. In experiment 1, recombinant human IL-11 (1360 microg) was given 2 h before nephrotoxic serum, then once daily until day 6. In experiment 2, a lower dose of IL-11 (800 microg/d) was used. Rats were treated either with IL-11 400 microg twice daily intraperitoneally or with 800 microg once daily intraperitoneally for 6 d. In experiment 3, the lower dose of IL-11 was given 2 h before nephrotoxic serum, then twice daily until day 2. In experiment 1, IL-11 significantly reduced proteinuria (13.2 +/- 3.3 versus 63.2 +/- 4.3 mg/24 h), fibrinoid necrosis (0.58 +/- 0.08 versus 1.52 +/- 0.06 quadrants/glomerular cross section [gcs]), macrophage infiltration (ED1-positive cells, 24.4 +/- 1.8 versus 39.3 +/- 1.9 cells/gcs), apoptosis (1.11 +/- 0.1 versus 2.39 +/- 0.2 apoptotic bodies/gcs), and proliferating cell nuclear antigen-positive cells (24.4 +/- 2.0 versus 37.3 +/- 2.3 cells/gcs). Inducible nitric oxide synthase-positive cells were significantly increased (3.1 +/- 0.3 versus 2.0 +/- 0.2 cells/gcs). In experiment 2, a lower dose of IL-11 significantly reduced proteinuria and fibrinoid necrosis. Macrophage infiltration was similar in treated and control groups, although the number of sialoadhesin-positive macrophages (ED3+) was significantly reduced in the IL-11-treated rats. In experiment 3, quantitative competitive reverse transcriptase-polymerase chain reaction showed that the mRNA ratio of IL-1 beta/beta-actin in the treated rats was reduced compared with controls. By the use of probes designed from mouse IL-11 receptor alpha-chain sequence, it was also shown that rat mesangial cells and macrophages expressed IL-11 receptor alpha-chain, demonstrating that they were capable of responding to IL-11. In this model of necrotizing glomerulonephritis, high-dose IL-11 treatment markedly reduced both proteinuria and fibrinoid necrosis. At the lower dose, there was a reduction in glomerular injury and macrophage sialoadhesin expression, but without an alteration of macrophage numbers, suggesting that IL-11 may be acting in part to reduce macrophage activation.

Angiotensin II and renal fibrosis

Angiotensin (Ang) II, the main peptide of the renin angiotensin system (RAS), is a renal growth factor, inducing hyperplasia/hypertrophy depending on the cell type. This vasoactive peptide activates mesangial and tubular cells and interstitial fibroblasts, increasing the expression and synthesis of extracellular matrix proteins. Some of these effects seem to be mediated by the release of other growth factors, such as TGF-beta. In experimental models of kidney damage, renal RAS activation, cell proliferation, and upregulation of growth factors and matrix production were described. In some of these models, blockade of Ang II actions by ACE inhibitors and angiotensin type 1 (AT(1)) antagonists prevents proteinuria, gene expression upregulation, and fibrosis, as well as inflammatory cell infiltration. Interestingly, Ang II could also be involved in the fibrotic process because of its behavior as a proinflammatory cytokine, participating in various steps of the inflammatory response: Ang II (1) activates mononuclear cells and (2) increases proinflammatory mediators (cytokines, chemokines, adhesion molecules, nuclear factor kappaB). Finally, Ang II also regulates matrix degradation. These data show that drugs controlling this complex vasoactive peptide are probably one of the best ways of avoiding fibrosis in progressive renal diseases.

Cell surface heparan sulfate proteoglycans control the response of renal interstitial fibroblasts to fibroblast growth factor-2

BACKGROUND

While the progression of renal disease to end stage is strongly correlated with tubulointerstitial changes, the control of the fibrotic process within the interstitium is poorly understood. Basic fibroblast growth factor (FGF-2) has been implicated as a major growth factor involved in fibroblast activation and extracellular matrix synthesis. Furthermore, in many cells, the activity of FGF-2 is controlled by a low-affinity but high-capacity interaction with heparan sulfate (HS) proteoglycans (PGs), such as members of the syndecan family. These molecules are likely to be central to the control of interstitial fibrosis, but as yet, there has been no characterization of their synthesis by interstitial cells.

METHODS

The expression of HSPG on the surface of NRK 49F fibroblasts was demonstrated by immunohistochemistry and by metabolic labeling with [(35)S]-sulfate. HSs were characterized by specific enzymatic digestion, size exclusion chromatography, and anion exchange chromatography. The mRNA for syndecan 1 through syndecan 4 in the fibroblasts was detected by semiquantitative reverse transcription-polymerase chain reaction. Fibroblast proliferation was measured by the MTT assay.

RESULTS

Immunohistochemistry and [(35)S]-sulfate-labeling demonstrated that renal fibroblasts expressed HSPGs on their surface. Furthermore, enzymatic removal of these HS (but not chondroitin sulfate) glycosaminoglycan (GAG) chains, or inhibition of GAG sulfation, abolished the proliferative response of both NRK cells and primary human cortical fibroblasts to FGF-2 but not to platelet-derived growth factor. The addition of conditioned medium, containing HS-GAG fragments, restored the proliferative response to FGF-2, confirming the specificity of the interaction. Finally, the mRNA for all four syndecans was detected in the fibroblasts, and that for syndecan 1 in particular was up-regulated by FGF-2.

CONCLUSIONS

The present study demonstrates that the expression of cell surface HSPG was essential for the proliferation of renal fibroblasts in response to FGF-2, and therefore may play a major role in the development and persistence of a proliferating phenotype during interstitial nephritis.

Macrophages in renal inflammation

This review describes recent advances in macrophage biology in the context of renal inflammation. It highlights the importance of the activated macrophage for the progression and resolution of renal disease, and discusses recent and potential future approaches to modify macrophage function selectively within the kidney to activate them specifically to promote the healing of kidney disease.

Nephrotoxic nephritis and obstructive nephropathy: evaluation with MR imaging enhanced with ultrasmall superparamagnetic iron oxide-preliminary findings in a rat model

PURPOSE

To evaluate the role of magnetic resonance (MR) imaging enhanced with ultrasmall superparamagnetic iron oxide (USPIO) in the evaluation and differentiation of different types of nephropathies.

MATERIALS AND METHODS

Two experimental rat models of nephropathies were studied: a model of nephrotoxic nephritis induced by means of intravenous injection of sheep anti-rat glomerular basement membrane serum (n = 43) and a model of obstructive nephropathy (n = 6). Imaging sessions were performed with a spectrometer operating at 4.7 T with fast low-angle shot, or FLASH, sequences. Signal intensity was measured in each kidney compartment before and 24 hours after intravenous injection of USPIO (90 micromol of iron per kilogram of body weight). MR findings were compared with histologic data and urine protein levels.

RESULTS

In the nephrotoxic nephritis model 24 hours after injection of USPIO, a significant signal intensity decrease (P: <.05) was present only in the cortex where the glomerular lesions were located. In the obstructive nephropathy model, the signal intensity decrease (P: <.05) was located in all kidney compartments in response to diffuse interstitial lesions. The decrease in signal intensity was due to iron uptake by either macrophages or mesangial cells gaining endocytic activity and was correlated, in the nephrotoxic nephritis model, to the degree of proteinuria.

CONCLUSION

Twenty-four-hour delayed USPIO-enhanced MR imaging may help identify and differentiate various types of nephropathies.

Glomerular monocyte-macrophage features in ANCA-positive renal vasculitis and cryoglobulinemic nephritis

Although it is widely known that many macrophages are present in glomeruli of antineutrophil cytoplasmic antibody (ANCA)-positive renal vasculitis (ANCA + RV) and are believed to contribute to necrotizing extracapillary damage, their precise role is not yet completely understood, especially in humans. The goal of this study was to provide evidence of glomerular macrophage properties in human vasculitis. Twenty-five renal biopsies of ANCA + RV and 18 cases of cryoglobulinemic glomerulonephritis (cryoGN), a disease characterized by massive glomerular macrophage infiltration but absence of necrotizing extracapillary lesions, were selected, and macrophage number, adhesion, acute activation, proliferation, and apoptosis were analyzed by immunohistochemistry and in situ hybridization. Accumulation of macrophages in ANCA + RV was found in areas of glomerular active lesions, whereas in cryoGN, they homogeneously occupied the entire glomerular tuft. Considering the areas of accumulation, comparable macrophage numbers were detected in both diseases. Glomerular vascular cell adhesion molecule-1 was found only in ANCA + RV and only in areas of active lesions. Acute macrophage activation (HLA class II, 27E10) and proinflammatory cytokine production (tumor necrosis factor-alpha, interleukin-1alpha) were prominent in ANCA + RV, whereas in cryoGN, 30% of glomerular macrophages seemed activated and cytokine expression was limited to a few glomerular cells (P: = 0.01). Moreover, only in ANCA + RV proliferative markers were shown on glomerular macrophages and apoptotic macrophages were found. From the data, it seems that ANCA + RV and cryoGN differ profoundly in macrophage properties, namely adhesion, proliferation, and apoptotic clearance. Moreover, acute activation and cytokine production seem to be present in a greater number of macrophages in ANCA + RV, giving this disease a stronger severity that could be taken into account for therapeutic strategies.

Cerivastatin prevents angiotensin II-induced renal injury independent of blood pressure- and cholesterol-lowering effects

BACKGROUND

Statins are effective in prevention of end-organ damage; however, the benefits cannot be fully explained on the basis of cholesterol reduction. We used an angiotensin II (Ang II)-dependent model to test the hypothesis that cerivastatin prevents leukocyte adhesion and infiltration, induction of inducible nitric oxide synthase (iNOS), and ameliorates end-organ damage.

METHODS

We analyzed intracellular targets, such as mitogen-activated protein kinase and transcription factor (nuclear factor-kappaB and activator protein-1) activation. We used immunohistochemistry, immunocytochemistry, electrophoretic mobility shift assays, and enzyme-linked immunosorbent assay techniques. We treated rats transgenic for human renin and angiotensinogen (dTGR) chronically from week 4 to 7 with cerivastatin (0.5 mg/kg by gavage).

RESULTS

Untreated dTGR developed hypertension, cardiac hypertrophy, and renal damage, with a 100-fold increased albuminuria and focal cortical necrosis. dTGR mortality at the age of seven weeks was 45%. Immunohistochemistry showed increased iNOS expression in the endothelium and media of small vessels, infiltrating cells, afferent arterioles, and glomeruli of dTGR, which was greater in cortex than medulla. Phosphorylated extracellular signal regulated kinase (p-ERK) was increased in dTGR; nuclear factor-kappaB and activator protein-1 were both activated. Cerivastatin decreased systolic blood pressure compared with untreated dTGR (147 +/- 14 vs. 201 +/- 6 mm Hg, P < 0.001). Albuminuria was reduced by 60% (P = 0.001), and creatinine was lowered (0.45 +/- 0.01 vs. 0.68 +/- 0.05 mg/dL, P = 0. 003); however, cholesterol was not reduced. Intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 expression was diminished, while neutrophil and monocyte infiltration in the kidney was markedly reduced. ERK phosphorylation and transcription factor activation were reduced. In addition, in vitro incubation of vascular smooth muscle cells with cerivastatin (0.5 micromol/L) almost completely prevented the Ang II-induced ERK phosphorylation.

CONCLUSION

Cerivastatin reduced inflammation, cell proliferation, and iNOS induction, which led to a reduction in cellular damage. Our findings suggest that 3-hydroxy-3-methylglutaryl coenzyme (HMG-CoA) reductase inhibition ameliorates Ang II-induced end-organ damage. We suggest that these effects were independent of cholesterol.

Proinflammatory gene expression and macrophage recruitment in the rat remnant kidney

BACKGROUND

Macrophage (Mphi) infiltration may contribute to chronic renal injury. We therefore sought to examine the expression of genes associated with Mphi recruitment in the rat remnant kidney model.

METHODS

Male Munich Wistar rats underwent 5/6 nephrectomy or sham operation (SHM, N = 18) and received no treatment (VEH, N = 18), enalapril 100 mg/L (ENA, N = 18), or candesartan 70 mg/L (CSN, N = 24) in drinking water. Competitive, quantitative reverse transcription-polymerase chain reaction was used to determine renal cortex mRNA levels for cell adhesion molecules vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1), the Mphi chemoattractant monocyte chemoattractant protein-1 (MCP-1), Mphi products interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha), and the profibrotic cytokine transforming growth factor-beta1 (TGF-beta1), at intervals post-nephrectomy.

RESULTS

Glomerular and interstitial Mphi infiltration in VEH rats was associated with an early (4 week) and sustained rise in MCP-1 and TGF-beta1 mRNA levels. Progressive increases in ICAM-1, VCAM-1, IL-1beta, and TNF-alpha expression followed at 8 and 12 weeks. Immunostaining in VEH rats localized TGF-beta1 to glomeruli, tubules, and interstitium; MCP-1 to tubules and interstitial cells; ICAM-1 to glomeruli; and IL-1beta and TNF-alpha to tubules and interstitial cells. At 12 weeks, both treatments normalized systolic blood pressure (ENA, 105 +/- 6; CSN, 97 +/- 3 mm Hg) and the urinary protein excretion rate (ENA, 8.4 +/- 0.9; CSN, 5.7 +/- 0.8 mg/day), prevented renal injury (focal and segmental glomerulosclerosis: ENA, 3.3 +/- 0.9; CSN, 1.3 +/- 0.4%), and suppressed Mphi infiltration and cytokine expression (with the exception of TNF-alpha) to near SHM levels.

CONCLUSIONS

These findings support the hypothesis that the coordinated up-regulation of several molecules regulating Mphi recruitment and activation is a fundamental response to renal mass ablation and is dependent on an intact renin-angiotensin system. We speculate that these responses may play a role in the pathogenesis of the ensuing glomerulosclerosis and tubulointerstitial fibrosis.

Renovascular hypertension does not influence repair of glomerular lesions induced by anti-thymocyte glomerulonephritis

BACKGROUND

Systemic hypertension is a risk factor for progression of renal disease. However, it is not clear whether hypertension has an effect on healing or regression of immune-mediated glomerular damage. To evaluate this effect, we applied a model of glomerulonephritis in rats with two-kidney, one-clip hypertension and studied the effect of hypertension on the healing process of this nephritis.

METHODS

The anti-thymocyte serum (ATS) glomerulonephritis was induced in rats six weeks after initiation of two-kidney, one-clip hypertension, when blood pressure was already increased. Renal structure and function were examined six weeks later. Glomerular expression of alpha smooth muscle actin, the cell cycle inhibitor p27Kip1, and transforming growth factor-beta (TGF-beta) was evaluated by Western blotting. Glomerular proliferation, monocyte infiltration, and fibronectin were examined by immunohistochemistry.

RESULTS

Decreased survival, an increase of proteinuria, as well as increased glomerular and tubulointerstitial damage, were found in hypertensive rats compared with normotensive rats. Expression of fibronectin, alpha-smooth muscle actin, TGF-beta, and p27Kip1 was increased in the nonclipped kidney. Complete healing of the glomerular changes associated with the nephritis occurred in normotensive nephritic rats. Surprisingly, complete healing of the nephritis was also found in the clipped as well as nonclipped kidneys of renovascular hypertensive rats. No significant differences could be found for survival, proteinuria, glomerular size, proliferation, monocyte/macrophage infiltration, sclerosis, tubulointerstitial damage, as well as expression of alpha-smooth muscle actin, TGF-beta, fibronectin, and p27Kip1 between hypertensive rats with and without nephritis.

CONCLUSION

These data demonstrate that renovascular hypertension does not influence healing of the glomerular lesions in the anti-thymocyte serum nephritis. This is a rather surprising observation and leaves the question open of which role, in fact, blood pressure may have on the reparative phase of an acute glomerulonephritis, or whether its role depends on the type of glomerulonephritis.