Indomethacin reduces proteinuria in passive Heymann nephritis in rats

Cyclooxygenase metabolites in the kidney

In the mammalian kidney, prostaglandins (PGs) are important mediators of physiologic processes, including modulation of vascular tone and salt and water. PGs arise from enzymatic metabolism of free arachidonic acid (AA), which is cleaved from membrane phospholipids by phospholipase A2 activity. The cyclooxygenase (COX) enzyme system is a major pathway for metabolism of AA in the kidney. COX are the enzymes responsible for the initial conversion of AA to PGG2 and subsequently to PGH2, which serves as the precursor for subsequent metabolism by PG and thromboxane synthases. In addition to high levels of expression of the "constitutive" rate-limiting enzyme responsible for prostanoid production, COX-1, the "inducible" isoform of cyclooxygenase, COX-2, is also constitutively expressed in the kidney and is highly regulated in response to alterations in intravascular volume. PGs and thromboxane A2 exert their biological functions predominantly through activation of specific 7-transmembrane G-protein-coupled receptors. COX metabolites have been shown to exert important physiologic functions in maintenance of renal blood flow, mediation of renin release and regulation of sodium excretion. In addition to physiologic regulation of prostanoid production in the kidney, increases in prostanoid production are also seen in a variety of inflammatory renal injuries, and COX metabolites may serve as mediators of inflammatory injury in renal disease.

Nonsteroidal Anti-Inflammatory Drugs and the Kidney

Non-steroidal anti-inflammatory drugs (NSAIDs) inhibit the isoenzymes COX-1 and COX-2 of cyclooxygenase (COX). Renal side effects (e.g., kidney function, fluid and urinary electrolyte excretion) vary with the extent of COX-2-COX-1 selectivity and the administered dose of these compounds. While young healthy subjects will rarely experience adverse renal effects with the use of NSAIDs, elderly patients and those with co-morbibity (e.g., congestive heart failure, liver cirrhosis or chronic kidney disease) and drug combinations (e.g., renin-angiotensin blockers, diuretics plus NSAIDs) may develop acute renal failure. This review summarizes our present knowledge how traditional NSAIDs and selective COX-2 inhibitors may affect the kidney under various experimental and clinical conditions, and how these drugs may influence renal inflammation, water transport, sodium and potassium balance and how renal dysfunction or hypertension may result.

Experimental Models of Membranous Nephropathy

Membranous nephropathy (MN) is one of the commonest glomerular diseases, typically presenting in older males with nephrotic syndrome. The development and characterization of animal models of MN, in particular, the passive Heymann nephritis model (PHN), has greatly advanced our understanding of this disease. In this review we discuss the different animal models of human MN that are available, with an emphasis on the PHN model, including technical issues, the typical disease course and its application to human disease.

Inducible rodent models of acquired podocyte diseases

Glomerular diseases remain the leading cause of chronic and end-stage kidney disease. Significant advances in our understanding of human glomerular diseases have been enabled by the development and better characterization of animal models. Diseases of the glomerular epithelial cells (podocytes) account for the majority of proteinuric diseases. Rodents have been extensively used experimentally to better define mechanisms of disease induction and progression, as well as to identify potential targets and therapies. The development of podocyte-specific genetically modified mice has energized the research field to better understand which animal models are appropriate to study acquired podocyte diseases. In this review we discuss inducible experimental models of acquired nondiabetic podocyte diseases in rodents, namely, passive Heymann nephritis, puromycin aminonucleoside nephrosis, adriamycin nephrosis, liopolysaccharide, crescentic glomerulonephritis, and protein overload nephropathy models. Details are given on the model backgrounds, how to induce each model, the interpretations of the data, and the benefits and shortcomings of each. Genetic rodent models of podocyte injury are excluded.

Suppression of cytokine responses by indomethacin in podocytes: a mechanism through induction of unfolded protein response

We found that, in murine podocytes, expression of monocyte chemoattractant protein 1 ( MCP- 1) in response to TNF-α was suppressed by indomethacin but not by ibuprofen. This anti-inflammatory potential was correlated with induction of 78-kDa glucose-regulated protein ( GRP78), a marker of unfolded protein response (UPR). Indomethacin, but not ibuprofen, also triggered expression of CHOP, another endogenous indicator of UPR, as well as repression of endoplasmic reticulum stress-responsive alkaline phosphatase, an exogenous indicator of UPR. Like ibuprofen, other nonsteroidal anti-inflammatory drugs including aspirin and sulindac also did not induce UPR, indicating that the induction of UPR by indomethacin was independent of cyclooxygenase inhibition. The induction of UPR by indomethacin was observed similarly in other cells including mesangial cells and tubular epithelial cells. In tumor necrosis factor (TNF)-α-treated cells, suppression of MCP-1 by indomethacin was inversely correlated with induction of UPR, and other inducers of UPR including tunicamycin, thapsigargin, and A23187 reproduced the suppressive effect. Reporter assays showed that indomethacin as well as thapsigargin attenuated activation of NF-κB by TNF-α, and it was associated with enhanced degradation of TNF receptor-associated factor 2 (TRAF2) and blunted degradation of IκBβ. Subsequent experiments revealed that acute ablation of GRP78 protein by AB5 subtilase cytotoxin caused reinforcement of MCP-1 induction and NF-κB activation by TNF-α and that transfection with GRP78 significantly suppressed the cytokine-induced activation of NF-κB. These results suggested that indomethacin suppressed the response of podocytes to TNF-α via UPR and that UPR-triggered induction of GRP78 and degradation of TRAF2 may be responsible, at least in part, for the suppressive effect of indomethacin.

Glomerular clusterin is associated with PKC-alpha/beta regulation and good outcome of membranous glomerulonephritis in humans

Mechanisms for human membranous glomerulonephritis (MGN) remain elusive. Most up-to-date concepts still rely on the rat model of Passive Heymann Nephritis that derives from an autoimmune response to glomerular megalin, with complement activation and membrane attack complex assembly. Clusterin has been reported as a megalin ligand in immunodeposits, although its role has not been clarified. We studied renal biopsies of 60 MGN patients by immunohistochemistry utilizing antibodies against clusterin, C5b-9, and phosphorylated-protien kinase C (PKC) isoforms (pPKC). In vitro experiments were performed to investigate the role of clusterin during podocyte damage by MGN serum and define clusterin binding to human podocytes, where megalin is known to be absent. Clusterin, C5b-9, and pPKC-alpha/beta showed highly variable glomerular staining, where high clusterin profiles were inversely correlated to C5b-9 and PKC-alpha/beta expression (P=0.029), and co-localized with the low-density lipoprotein receptor (LDL-R). Glomerular clusterin emerged as the single factor influencing proteinuria at multivariate analysis and was associated with a reduction of proteinuria after a follow-up of 1.5 years (-88.1%, P=0.027). Incubation of podocytes with MGN sera determined strong upregulation of pPKC-alpha/beta that was reverted by pre-incubation with clusterin, serum de-complementation, or protein-A treatment. Preliminary in vitro experiments showed podocyte binding of biotinilated clusterin, co-localization with LDL-R and specific binding inhibition with anti-LDL-R antibodies and with specific ligands. These data suggest a central role for glomerular clusterin in MGN as a modulator of inflammation that potentially influences the clinical outcome. Binding of clusterin to the LDL-R might offer an interpretative key for the pathogenesis of MGN in humans.

Prostaglandin E2 promotes cell survival of glomerular epithelial cells via the EP4 receptor

Visceral glomerular epithelial cells (GEC) are crucial for glomerular permselectivity and structural integrity in the kidney. The current study addressed the role of cyclooxygenase (COX)-2 and its product prostaglandin (PG) E2 in GEC survival. We generated a subclone of cultured rat GEC, which overexpress COX-2 in an inducible manner. When COX-2 was induced, GEC survived better in serum-deprived conditions. Induction of COX-2 was correlated with increased PGE2 generation, increased activation of extracellular signal-regulated kinase, decreased apoptosis, and increased cell proliferation. Rat GEC abundantly expressed the EP4 isoform of PGE2 receptor. Induction of COX-2 and addition of exogenous PGE2 both lead to decreased serum deprivation-induced apoptosis, which was accompanied by activation of the survival kinase Akt. Anti-apoptotic effect of COX-2 induction was reversed by the specific inhibitor of the EP4 receptor, L-161982. PGE2 also inhibited puromycin aminonucleoside-induced GEC apoptosis in vitro. Acute puromycin aminonucleoside nephrosis (PAN) is a rat model of GEC injury and proteinuria. In rats with PAN, glomerular apoptosis, quantified as caspase-3 activity, as well as urinary protein excretion were significantly increased, compared with control rats. Administration of L-161982 in rats with PAN further exacerbated caspase-3 activation and proteinuria. Thus COX-2 and its product PGE2 may have anti-apoptotic/protective effect on GEC via the EP4 receptor of PGE2.

Experimental membranous nephropathy redux

Membranous nephropathy (MN) is a common cause of nephrotic syndrome in adults. Active and passive Heymann nephritis (HN) in rats are valuable experimental models because their features so closely resemble human MN. In HN, subepithelial immune deposits form in situ as a result of circulating antibodies. Complement activation leads to assembly of C5b-9 on glomerular epithelial cell (GEC) plasma membranes and is essential for sublethal GEC injury and the onset of proteinuria. This review revisits HN and focuses on areas of substantial progress in recent years. The response of the GEC to sublethal C5b-9 attack is not simply due to disruption of the plasma membrane but is due to the activation of specific signaling pathways. These include activation of protein kinases, phospholipases, cyclooxygenases, transcription factors, growth factors, NADPH oxidase, stress proteins, proteinases, and others. Ultimately, these signals impact on cell metabolic pathways and the structure/function of lipids and key proteins in the cytoskeleton and slit-diaphragm. Some signals affect GEC adversely. Thus C5b-9 induces partial dissolution of the actin cytoskeleton. There is a decline in nephrin expression, reduction in F-actin-bound nephrin, and loss of slit-diaphragm integrity. Other signals, such as endoplasmic reticulum stress, may limit complement-induced injury, or promote recovery. The extent of complement activation and GEC injury is dependent, in part, on complement-regulatory proteins, which act at early or late steps within the complement cascade. Identification of key steps in complement activation, the cellular signaling pathways, and the targets will facilitate therapeutic intervention in reversing GEC injury in human MN.

Complement C5b-9 membrane attack complex increases expression of endoplasmic reticulum stress proteins in glomerular epithelial cells

In the passive Heymann nephritis (PHN) model of membranous nephropathy, complement C5b-9 induces glomerular epithelial cell (GEC) injury, proteinuria, and activation of cytosolic phospholipase A(2) (cPLA(2)). This study addresses the role of endoplasmic reticulum (ER) stress proteins (bip, grp94) in GEC injury. GEC that overexpress cPLA(2) (produced by transfection) and "neo" GEC (which expresses cPLA(2) at a lower level) were incubated with complement (40 min), and leakage of constitutively expressed bip and grp94 from ER into cytosol was measured to monitor ER injury. Greater leakage of bip and grp94 occurred in complement-treated GEC that overexpress cPLA(2), as compared with neo, implying that cPLA(2) activation perturbed ER membrane integrity. After chronic incubation (4-24 h), C5b-9 increased bip and grp94 mRNAs and proteins, and the increases were dependent on cPLA(2). Expression of bip-antisense mRNA reduced stimulated bip protein expression and enhanced complement-dependent GEC injury. Glomerular bip and grp94 proteins were up-regulated in proteinuric rats with PHN, as compared with normal control. Pretreatment of rats with tunicamycin or adriamycin, which increase ER stress protein expression, reduced proteinuria in PHN. Thus, C5b-9 injures the ER and enhances ER stress protein expression, in part, via activation of cPLA(2). ER stress protein induction is a novel mechanism of protection from complement attack.

Complement activates the c-Jun N-terminal kinase/stress-activated protein kinase in glomerular epithelial cells

In the rat passive Heymann nephritis model of membranous nephropathy, complement C5b-9 induces sublethal glomerular epithelial cell (GEC) injury and proteinuria. C5b-9 activates cytosolic phospholipase A(2) (cPLA(2)), and products of cPLA(2)-mediated phospholipid hydrolysis modulate GEC injury and proteinuria. In the present study, we demonstrate that C5b-9 activates c-Jun N-terminal kinase (JNK) in cultured rat GECs and that JNK activity is increased in glomeruli isolated from proteinuric rats with passive Heymann nephritis, as compared with control rats. Stable overexpression of cPLA(2) in GECs amplified complement-induced release of arachidonic acid (AA) and JNK activity, as compared with neo (control) GECs. Activation of JNK was not affected by indomethacin. Incubation of GECs with complement stimulated production of superoxide, and pretreatment with the antioxidants, N-acetylcysteine, glutathione, and alpha-tocopherol as well as with diphenylene iodonium, an inhibitor of the NADPH oxidase, inhibited complement-induced JNK activation. Conversely, H(2)O(2) activated JNK, whereas exogenously added AA stimulated both superoxide production and JNK activity. Overexpression of a dominant-inhibitory JNK mutant or treatment with diphenylene iodonium exacerbated complement-dependent GEC injury. Thus, activation of cPLA(2) and release of AA facilitate complement-induced JNK activation. AA may activate the NADPH oxidase, leading to production of reactive oxygen species, which in turn mediate the activation of JNK. The functional role of JNK activation is to limit or protect GECs from complement attack.

Effect of high dose ramipril with or without indomethacin on glomerular selectivity

BACKGROUND

Despite the accumulating evidence of their efficacy, angiotensin-converting enzyme inhibitors (ACEi) still provide imperfect renoprotection. Up-titration above conventional doses and combined therapy with other antiproteinuric agents may serve to achieve renoprotection in patients at risk of rapid disease progression.

METHODS

The effect of maximum tolerated ACEi doses (ramipril 15 mg/day, range 5 to 20) alone or combined with indomethacin (75 mg x 2/day) on urinary protein excretion (UPE) and glomerular barrier size-selective function was evaluated in 19 patients with chronic non-diabetic nephropathies and persistent proteinuria.

RESULTS

Maximum ramipril doses decreased UPE more effectively than non-ACEi therapy. Proteinuria reduction was associated with significant reduction (>50%) of the non-selective glomerular membrane shunt, but did not correlate with concomitant changes in arterial pressure and renal hemodynamics, nor was it influenced by treatment duration. The reduction in UPE and sieving coefficient of the largest neutral dextrans exceeded by twofold the reduction achieved by conventional ACEi doses in historical controls with similar renal dysfunction and proteinuria, previously studied under identical experimental conditions. Indomethacin did not influence renal effects of maximum ramipril doses and was prematurely withdrawn in six patients because of reversible side effects. Serum potassium significantly increased only in combination with indomethacin and never required treatment withdrawal.

CONCLUSIONS

Up-titration to maximally tolerated doses safely increases ACEi antiproteinuric effect and may serve to achieve maximum renoprotection in the long-term. Combination with indomethacin is poorly tolerated and ineffective. Innovative approaches are needed to use ACEi more effectively.

Intraperitoneal protein injection in the axolotl: the amphibian kidney as a novel model to study tubulointerstitial activation

BACKGROUND

A substantial body of experimental evidence suggests that protein loading causes activation of proximal tubular epithelial cells with consecutive interstitial fibrosis. These studies have mostly been performed using mammalian in vivo models of glomerular damage or tissue cultures of mammalian tubulointerstitial cells. The kidney of the axolotl contains not only closed nephrons, but also nephrons with ciliated peritoneal funnels called nephrostomes that have access to the peritoneal fluid. Injection of protein into the peritoneal cavity fails to expose closed nephrons to a protein load, but causes selective uptake and transient storage of proteins in tubular epithelial cells of nephrons with nephrostomes. The purpose of the present study was to determine whether (a) the axolotl kidney can be used as a model to assess protein uptake by tubular cells in vivo in the absence of glomerular damage, and (b) this is accompanied by any evidence of tubular epithelial cell activation and interstitial fibrosis.

METHODS

Male and female axolotl (80 to 120 g of weight) were given a daily intraperitoneal injection of 1.5 mL endotoxin-free calf serum or saline as control. Kidneys were harvested after 4 or 10 days using perfusion fixation for light microscopy (fibrous tissue stain) and saline perfusion for immunohistochemistry (fibronectin, TGF-beta and collagen I).

RESULTS

The findings document selective storage of protein and lipids, progressive with time, in proximal tubular epithelial cells of nephrons draining the coelomic cavity. In addition, progressive focal accumulation of fibrous tissue was noted around protein-storing tubules. Immunohistochemical staining demonstrated the presence of fibronectin and TGF-beta in the tubular epithelial cells and interstitial cells.

CONCLUSION

The axolotl kidney provides a novel in vivo model to study tubulointerstitial activation and induction of interstitial fibrosis by protein loading. The findings are independent of alterations of glomerular function that may have potential confounding effects on peritubular hemodynamics, pO2, cell traffic, etc.

Indomethacin protects permeability barrier from focal segmental glomerulosclerosis serum

BACKGROUND

Eicosanoids are believed to play a role in the pathophysiology of several models of glomerular disease. The cyclooxygenase inhibitor indomethacin reduces proteinuria in patients with focal segmental glomerulosclerosis (FSGS) or other glomerular diseases. We have shown that sera of some patients with FSGS significantly increase glomerular albumin permeability (Palb) in an in vitro assay.

METHODS

To determine the role of eicosanoids in the increased Palb caused by the FSGS factor, glomeruli were isolated from normal rats, preincubated with indomethacin, then incubated with FSGS serum or normal serum and Palb was calculated. To study the direct effect of individual eicosanoids on Palb, glomeruli were incubated with prostaglandin E2, prostaglandin F2alpha or a thromboxane A2 mimetic, and Palb was calculated. In the final set of experiments, normal glomeruli were preincubated with the thromboxane synthase inhibitor furegrelate, incubated with FSGS serum, and Palb was calculated.

RESULTS

Preincubation of isolated glomeruli with either the cyclooxygenase inhibitor indomethacin or the thromboxane synthase inhibitor furegrelate protected glomeruli from the increase in Palb caused by FSGS serum. Each of the three principal glomerular eicosanoids significantly increased Palb of isolated glomeruli.

CONCLUSIONS

These studies implicate a product of the cyclooxygenase pathway of arachidonic acid metabolism as mediating the increased Palb caused by FSGS serum in our in vitro assay and possibly the proteinuria seen in patients with FSGS.

Complement C5b-9 induces cyclooxygenase-2 gene transcription in glomerular epithelial cells

In rat membranous nephropathy, complement C5b-9 induces glomerular epithelial cell (GEC) injury and proteinuria, which is partially mediated by eicosanoids. Rat GEC in culture express cyclooxygenase (COX)-1 constitutively, whereas COX-2 expression is induced by C5b-9. Both isoforms contribute to complement-induced prostaglandin generation. The present study addresses mechanisms of complement-induced COX-2 expression in GEC. Downregulation of protein kinase C (PKC) blunted complement-induced upregulation of COX-2 mRNA. Complement and phorbol 12-myristate 13-acetate (PMA) both stimulated COX-2 promoter activity. C5b-9 activated c-Jun NH(2)-terminal kinase (JNK), and inhibition of JNK activity by transfection of a kinase-inactive JNK1 partially inhibited complement-induced (but not PMA-induced) COX-2 promoter activation. Conversely, a constitutively active mitogen-activated protein or extracellular signal-regulated kinase kinase kinase (MEKK)-1, a kinase upstream of JNK, increased COX-2 promoter activity. MEKK-induced COX-2 promoter activation was not affected by downregulation of PKC and was augmented by PMA. Thus, in GEC, PKC and JNK pathways contribute independently to complement-induced COX-2 expression. Nuclear factor-kappaB was also activated by complement in GEC but did not contribute to complement-induced COX-2 upregulation.

Complement C5b-9 induces cyclooxygenase-2 gene transcription in glomerular epithelial cells

First published July 12, 2001; 10.1152/ajprenal.0048.2001.—In rat membranous nephropathy, complement C5b-9 induces glomerular epithelial cell (GEC) injury and proteinuria, which is partially mediated by eicosanoids. Rat GEC in culture express cyclooxygenase (COX)-1 constitutively, whereas COX-2 expression is induced by C5b-9. Both isoforms contribute to complement-induced prostaglandin generation. The present study addresses mechanisms of complement-induced COX-2 expression in GEC. Downregulation of protein kinase C (PKC) blunted complement-induced upregulation of COX-2 mRNA. Complement and phorbol 12-myristate 13-acetate (PMA) both stimulated COX-2 promoter activity. C5b-9 activated c-Jun NH2-terminal kinase (JNK), and inhibition of JNK activity by transfection of a kinase-inactive JNK1 partially inhibited complement-induced (but not PMA-induced) COX-2 promoter activation. Conversely, a constitutively active mitogen-activated protein or extracellular signal-regulated kinase kinase kinase (MEKK)-1, a kinase upstream of JNK, increased COX-2 promoter activity. MEKK-induced COX-2 promoter activation was not affected by downregulation of PKC and was augmented by PMA. Thus, in GEC, PKC and JNK pathways contribute independently to complement-induced COX-2 expression. Nuclear factor-κB was also activated by complement in GEC but did not contribute to complement-induced COX-2 upregulation.

Complement C5b-9-mediated arachidonic acid metabolism in glomerular epithelial cells : role of cyclooxygenase-1 and -2

In the passive Heymann nephritis (PHN) model of membranous nephropathy, complement C5b-9 induces glomerular epithelial cell (GEC) injury and proteinuria, which is partially mediated by eicosanoids. This study addresses the role of cyclooxygenase (COX)-1 and -2 in C5b-9-mediated eicosanoid production in GEC. Unstimulated rat GEC in culture primarily express COX-1. When stimulated with sublytic C5b-9, COX-2 was significantly up-regulated, whereas COX-1 was not affected. Compared with control, complement-treated GEC produced 32% more prostaglandin (PG) E(2) in the presence of exogenous substrate, and the increase was abolished with the COX-2-selective inhibitor, NS-398. Release of arachidonic acid from GEC phospholipids via C5b-9-induced activation of cytosolic phospholipase A(2) was associated with a marked stimulation of PGE(2) production, which was inhibited by 60% with NS-398. The results in cultured GEC were extended to GEC injury in vivo by examining COX-1 and -2 expression in PHN. Glomeruli from rats with PHN expressed significantly more COX-1 and COX-2, as compared with normal rats. PGE(2) production in glomeruli of rats with PHN was about twofold greater than in control glomeruli, and the increase was partially inhibited with NS-398. Thus, in GEC in culture and in vivo, C5b-9-induced eicosanoid production is regulated by both isoforms of COX. The inducible COX-2 may be an important novel mediator of C5b-9-induced glomerular injury.

Complement-induced phospholipase A2 activation in experimental membranous nephropathy

BACKGROUND

In the passive Heymann nephritis (PHN) model of membranous nephropathy, C5b-9 induces glomerular epithelial cell (GEC) injury and proteinuria, which is partially mediated by eicosanoids. By analogy, in cultured rat GEC, sublytic C5b-9 injures plasma membranes and releases arachidonic acid (AA) and eicosanoids, due to activation of phospholipase A2 (PLA2). This study addresses the mechanisms of PLA2 activation.

METHODS

PLA2 expression was assessed with the polymerase chain reaction or immunoblotting, and activity was determined using an in vitro assay or by measurement of free AA.

RESULTS

Under basal conditions, GEC in culture expressed a relatively low level of cytosolic PLA2 (cPLA2) protein, while mRNAs of groups IB, IIA and V secretory PLA2s (sPLA2) were not detectable. Incubation of GEC with sublytic C5b-9 induced 1.5- to 2.0-fold increases in free [3H]AA at 40 minutes, and three and 24 hours. C5b-9 did not increase cPLA2 protein, and did not induce group IB, IIA or V sPLA2 mRNAs. Stable overexpression of cPLA2 in GEC amplified the C5b-9-induced increases in free [3H]AA, while analogous overexpression of group IIA sPLA2 had no effect. PLA2 activity was increased in glomeruli of rats with PHN, and this enhanced activity was characterized as cPLA2. There were no differences in cPLA2 protein expression between PHN and control glomeruli.

CONCLUSIONS

Release of AA by C5b-9 in GEC in culture and in vivo is mediated by cPLA2, and the mechanism is consistent with post-translational regulation of cPLA2 activity. C5b-9 does not induce expression or stimulate activity of sPLA2 isoforms in GEC.

Complement C5b-9 induces receptor tyrosine kinase transactivation in glomerular epithelial cells

In the passive Heymann nephritis (PHN) model of membranous nephropathy, C5b-9 induces glomerular epithelial cell (GEC) injury and proteinuria, which is partially mediated via production of eicosanoids. Using rat GEC in culture, we demonstrated that sublytic C5b-9 induced tyrosine phosphorylation of the epidermal growth factor receptor (EGF-R), Neu, fibroblast growth factor receptor-2, and hepatocyte growth factor receptor. In addition, C5b-9 stimulated increases in tyrosine(204) phosphorylation of extracellular signal-regulated kinase-2 (ERK2), as well as free [(3)H]arachidonic acid (AA) and prostaglandin E(2) (PGE(2)). Phosphorylated EGF-R bound the adaptor protein, Grb2, and the EGF-R-selective tyrphostin, AG1478, blocked the C5b-9-induced ERK2 phosphorylation, [(3)H]AA release, and PGE(2) production by 45 to 65%, supporting a functional role for EGF-R kinase in mediating the activation of these pathways. Glomeruli isolated from rats with PHN demonstrated increases in ERK2 tyrosine(204) phosphorylation and PGE(2) production, as compared with glomeruli from control rats, and these increases were partially inhibited with AG1478. Thus, C5b-9 induces transactivation of receptor tyrosine kinases, in association with ERK2 activation, AA release, and PGE(2) production in cultured GEC and glomerulonephritis in vivo. Transactivated tyrosine kinases may serve as scaffolds for assembly and/or activation of proteins, which then lead to activation of the ERK2 cascade and AA metabolism.

Complement activates phospholipases and protein kinases in glomerular epithelial cells

BACKGROUND

In rat membranous nephropathy, complement C5b-9 induces glomerular epithelial cell (GEC) injury and proteinuria, which in some models is partially mediated by eicosanoids. In cultured rat GEC, sublytic C5b-9 injures plasma membranes and releases arachidonic acid (AA) and eicosanoids, due to activation of cytosolic phospholipase A2 (cPLA2). In this study, we address the role of protein kinases in cPLA2 activation.

METHODS

GEC were stably transfected with cDNAs of wild-type (wt) cPLA2, and serine505-->alanine mutant (cPLA2-SA505), which lacks the mitogen-activated protein kinase (MAPK) phosphorylation site.

RESULTS

Complement stimulated protein kinase C (PKC) activity in GEC, and activated p42 (but not p38) MAPK. Overexpression of either cPLA2-wt or cPLA2-SA505 markedly amplified the release of [3H]AA by C5b-9. Depletion of PKC blocked the complement-dependent activation of cPLA2-wt or cPLA2-SA505, but inhibition of the p42 MAPK pathway had no effect. Epidermal growth factor was a strong activator of p42 MAPK, but stimulated PKC activity weakly. Unlike complement, activation of cPLA2-wt by epidermal growth factor was dependent on PKC, and was augmented significantly by p42 MAPK. Stable overexpression of phospholipase C-gamma 1 in GEC amplified C5b-9-induced production of [3H]inositol phosphates and [3H]diacylglycerol, an endogenous activator of PKC, and complement stimulated tyrosine phosphorylation of phospholipase C-gamma 1.

CONCLUSIONS

C5b-9 induces activation of cPLA2 that is dependent on the diacylglycerol-PKC pathway. The role of p42 MAPK in cPLA2 activation becomes redundant in the presence of relatively potent PKC activation.

Effect of lipo-prostaglandin E1 on crescentic-type anti-glomerular basement membrane nephritis in rats

The antinephritic effect of lipo-prostaglandin E1, prostaglandin E1 ((1R,2R,3R)-3-hydroxy-2-[(E)-(3S)-3-hydroxy-1-octenyl]-5-oxocyclopent ane heptanoic acid) incorporated in lipid microspheres was investigated using an experimental model of nephritis, crescentic-type anti-glomerular basement membrane nephritis. Lipo-prostaglandin E1 was given i.v. twice a day at 20, 40 and 80 microg/kg and azathioprine, an immunosuppressive agent, at 20 mg/kg was given p.o. once daily from the autologous phase, in which glomerulonephritis was fully developed (the 21 st day after injection of the anti-glomerular basement membrane serum), to the 50th day. Lipo-prostaglandin E1 (40 and 80 microg/kg x 2 per day) significantly inhibited the development of glomerular alterations as well as the elevation of proteinuria and plasma creatinine. Lipo-prostaglandin E1 (20 microg/kg x 2 per day) and azathioprine (20 mg/kg per day) significantly inhibited only the glomerular histopathological changes. Lipo-prostaglandin E1 at three doses significantly decreased the deposition of both rabbit immunoglobulin G and rat immunoglobulin G on the glomerular basement membrane in nephritic rats, but azathioprine apparently inhibited only the deposition of rat immunoglobulin G. A single administration of lipo-prostaglandin E1 inhibited the elevation of platelet aggregation and restored the decrease in renal tissue blood flow in nephritic rats. In addition, a single administration of lipo-prostaglandin E1 inhibited the elevation of glomerular thromboxane B2 and 6-keto prostaglandin F1alpha production in nephritic rats. These results suggest that lipo-prostaglandin E1 may be an effective agent for the treatment of glomerulonephritis. Its antinephritic effect may be due to the inhibition of platelet aggregation, an increase in renal tissue blood flow, a decrease in rabbit and rat immunoglobulin G deposition, and amelioration of the abnormal metabolism of arachidonic acid.

Thromboxane A2 interferes with a disposal process of aggregated protein in glomeruli

Immune complexes in glomeruli are involved in development of diverse glomerulonephritis. The disposal process of glomerular immune complexes has been unclarified. The present studies were undertaken to determine if thromboxane A2 (TXA2) is associated with the disposal of macromolecules in the glomeruli using mice injected with aggregated bovine serum albumin (a-BSA). A-BSA promptly accumulated in the glomeruli, the level reaching a plateau at 6 hr after the injection of a-BSA, and then decreased by 48 hr. The production of glomerular TXA2, prostaglandin E2 (PGE2) and prostaglandin I2 concomitantly increased with the decrease of a-BSA in the glomeruli. TXA2 synthase inhibitors and TXA2 receptor antagonists accelerated clearance of glomerular a-BSA without enhancing renal tissue blood flow. They did not affect a-BSA level in the plasma. In contrast, aminophylline, dopamine and mannitol significantly increased renal tissue blood flow, but did not decrease glomerular a-BSA. TXA2 synthase inhibitors decreased TXA2 production in the glomeruli. TXA2 synthase inhibitors and TXA2 receptor antagonists did not influence the generation of PGE2. The TXA2 analogue U-46619 significantly increased the accumulation of a-BSA in the glomeruli. We propose that TXA2 interferes with the disposal process of aggregated protein in the glomeruli. We also postulate that interception of glomerular activity of TXA2 may be an effective intervention for managing immune complex-mediated glomerulonephritis and glomerulosclerosis.

Effects of omega-3 fatty acids on complement-mediated glomerular epithelial cell injury

To define the mechanisms by which fish oil protects rats with passive Heymann nephritis (PHN) from proteinuria in vivo, we investigated whether omega-3 fatty acid substitution of glomerular epithelial cells (GEC) in culture alters their susceptibility or response to complement-mediated sublethal injury. The results show that GECs can be cultured under conditions that effectively incorporate omega-3 or omega-6 fatty acids into membrane phospholipids without causing toxicity. Under these conditions, sublethal injury with anti-Fx1A and C5b-9 stimulated a 6.6-fold increase in TxA2 production by GECs substituted with arachidonic acid (AA, omega-6) but no increase was detected in eicosapentaenoic acid (EPA, omega-3) substituted cells. Sublethal cell membrane injury was of equal severity in both groups as measured by the release of preloaded biscarboxyethyl carboxyfluorescein and by the transepithelial flux of albumin. In addition, omega-3 and omega-6 fatty acid substituted cells showed similar increases in diacylglycerol mass in response to sublethal injury by C5b-9, suggesting that omega-3 incorporation did not limit phospholipid (PL) hydrolysis by PLC. From this we can conclude that the protective effect of fish oil in PHN does not appear to result from the preservation of GEC integrity but is likely related to changes in the production of lipid mediators.

Effect of DP-1904, a thromboxane A2 synthase inhibitor, on passive Heymann nephritis in rats

The antinephritic effect of DP-1904 [6-(1-imidazolylmethyl)-5,6,7,8-tetrahydronaphthalene-2-carboxylic acid hydrochloride], a thromboxane A2 synthase inhibitor, was evaluated using an experimental model of membranous nephropathy, viz. accelerated passive Heymann nephritis in which the glomerular injury is mediated by immune complexes. DP-1904 markedly inhibited the develop-ent of glomerular alteration as well as the elevation of proteinuria and plasma creatinine. When the treatment was started from the 22nd day, at which time proteinuria is fully developed, DP-1904 showed beneficial effects on proteinuria and glomerular histopathological changes. DP-1904 apparently decreased the deposition of both rabbit immunoglobulin G and rat immunoglobulin G on glomerular basement membrane in nephritic rats. A single administration of DP-1904 restored the decreased renal tissue blood flow, inhibited glomerular thromboxane B2 production and increased glomerular prostaglandin E2 and 6-keto prostaglandin F1 alpha production in nephritic rats. These results suggest that DP-1904 may be an effective agent for the treatment of idiopathic membranous nephropathy and that the beneficial effect of this drug may be due to the elimination of glomerular immune deposits and to an increase in renal tissue blood flow related to amelioration of the abnormal metabolism of arachidonic acid.

Effect of DP-1904, a thromboxane A2 synthase inhibitor, administered from the autologous phase on crescentic-type anti-GBM nephritis in rats

The antinephritic effect of DP-1904 [6-(1-imidazolylmethyl)-5,6,7,8-tetrahydronaphthalene-2-carboxylic acid hydrochloride], a thromboxane (TX) A2 synthase inhibitor, was compared with that of OKY-046 and azathioprine, using an experimental model of nephritis, crescentic-type anti-glomerular basement membrane (GBM) nephritis. Test drugs were given p.o. once daily from an autologous phase in which proteinuria was already fully developed. DP-1904 (15 and 45 mg/kg per day) and OKY-046 (20 mg/kg per day), another TXA2 synthase inhibitor, significantly inhibited the development of glomerular alteration as well as the elevation of proteinuria. On the other hand, azathioprine (20 mg/kg per day), an immunosuppressive agent, failed to suppress the proteinuria. A single administration of DP-1904 or OKY-046 inhibited glomerular TXB2 production and increased glomerular prostaglandin (PG) E2 and 6-keto PGF1 alpha production in nephritic rats. Both drugs apparently decreased the depositions of both rabbit immunoglobulin (Ig) G and rat IgG on GBM in nephritic rats, but azathioprine inhibited only the deposition of rat IgG. These results suggest that DP-1904 may be an effective agent for the treatment of proliferative glomerulonephritis and its antinephritic effect may be due to the amelioration of abnormal metabolism of arachidonic acid.

Effects of endogenously produced arachidonic acid metabolites on rat mesangial cell proliferation

The role of endogenously produced arachidonic acid metabolites on glomerulonephritis was investigated using cultured rat mesangial cells. The cultured mesangial cells could produce prostaglandin (PG) E2 and F2 alpha and 12-hydroxyeicosatetraenoic acid (12-HETE). The treatment of the mesangial cells with indomethacin enhanced the cell growth stimulated by 10% fetal calf serum (FCS). This stimulatory effect was significantly attenuated by concomitant treatment with PGE2, but not with PGF2 alpha. To test whether the mechanism by which PGE2 inhibited the mesangial cell growth is related to in the increment of cyclic AMP (cAMP), we examined the effect of dibutyryl cAMP on mesangial cell growth. As expected, treatment with dibutyryl cAMP decreased the cell proliferation. Moreover treatment with KT-5720, a protein kinase A (PKA) inhibitor, stimulated the cell growth as well as indomethacin. These data strongly suggest that the inhibition of mesangial cell growth by PGE2 involves an activation of PKA. In contrast, treatment with baicalein, a specific inhibitor of 12-lipoxygenase, inhibited the mesangial cell growth. The up and down regulations by arachidonic acid metabolites were also observed in the growth induced by platelet-derived growth factor (PDGF). These results suggest that endogenously produced arachidonic acid metabolites are involved in the regulation of mesangial cell growth.

Effect of DP-1904, a thromboxane A2 synthetase inhibitor, on crescentic nephritis in rats

The antinephritic effect of DP-1904 [6-(1-imidazolylmethyl)-5,6,7,8-tetrahydronaphthalene-2-carboxylic acid hydrochloride], a thromboxane A2 synthetase inhibitor, was compared with that of OKY-046, using an experimental model of nephritis, crescentic-type anti-glomerular basement membrane nephritis. Test drugs were given p.o. once daily from the day after the the development of glomerular alteration as well as the elevation of proteinuria and plasma cholesterol. On the other hand, OKY-046 (20 mg/kg per day), a thromboxane A2 synthetase inhibitor, significantly inhibited only deterioration in the glomeruli. DP-1904 and OKY-046 inhibited glomerular thromboxane B2 production and increased glomerular prostaglandin E2 and 6-keto prostaglandin F1 alpha production in normal and nephritic rats. Both drugs inhibited the increase in platelet aggregability, restored decreased renal tissue blood flow to a near-normal level and decreased the deposition of rat immunoglobulin G on glomerular basement membrane in nephritic rats. These results suggest that DP-1904 may be an effective agent for the treatment of proliferative glomerulonephritis.

Leukotriene D4 is a mediator of proteinuria and glomerular hemodynamic abnormalities in passive Heymann nephritis

We assessed the role of leukotrienes (LTs) in Munich-Wistar rats with passive Heymann nephritis (PHN), an animal model of human membranous nephropathy. 10 d after injection of anti-Fx1A antibody, urinary protein excretion rate (Upr) in PHN was significantly higher than that of control. Micropuncture studies demonstrated reduced single nephron plasma flow and glomerular filtration rates, increased transcapillary hydraulic pressure difference, pre- and postglomerular resistances, and decreased ultrafiltration coefficient in PHN rats. Glomerular LTB4 generation from PHN rats was increased. Administration of the 5-LO activating protein inhibitor MK886 for 10 d markedly blunted proteinuria and normalized glomerular hemodynamic abnormalities in PHN rats. An LTD4 receptor antagonist SK&F 104353 led to an immediate reduction in Upr and to reversal of glomerular hemodynamic impairment. Ia(+) cells/glomerulus were increased in PHN rats. In x-irradiated PHN rats, which developed glomerular macrophage depletion, augmented glomerular LT synthesis was abolished. Thus, in the autologous phase of PHN, LTD4 mediates glomerular hemodynamic abnormalities and a hemodynamic component of the accompanying proteinuria. The synthesis of LTD4 likely occurs directly from macrophages or from macrophage-derived LTA4, through LTC4 synthase in glomerular cells.

Fish oil has protective and therapeutic effects on proteinuria in passive Heymann nephritis

Passive Heymann nephritis (PHN) is a rat model of membranous nephropathy induced by injecting anti-Fx1A. The onset of proteinuria in PHN is caused by complement-mediated injury to glomerular epithelial cells (GEC) accompanied by enhanced glomerular eicosanoid production. In addition, sublethal injury by complement of rat GECs in culture leads to phospholipase activation, phospholipid hydrolysis and release of arachidonic acid and dienoic prostanoids. Based on these findings, we undertook to determine if substituting arachidonic acid (omega-6) in GEC membrane phospholipids with omega-3 fatty acids derived from fish oil would alter the development and course of proteinuria in PHN. We found that rats fed a diet containing 10% fish oil for four weeks prior to antibody injection developed 50 to 60% less proteinuria between two and six weeks after anti-Fx1A than rats fed an equivalent diet containing 10% safflower oil, and had substantial enrichment of glomerular phospholipids with omega-3 fatty acids and displacement of arachidonic acid. This outcome was associated with a 50% reduction in release of glomerular thromboxane B2 (stable metabolite of thromboxane A2) in the fish oil group. More importantly, when PHN rats with well established proteinuria while on regular chow were randomized to three dietary groups, those fed fish oil had a 25 to 50% decline in proteinuria as compared to those fed lard or safflower oil. This difference was evident within two weeks of randomization and persisted until the end of the study after eight weeks. In neither study could the differences in urine protein excretion be accounted for by protein or calorie deprivation, or by differences in blood pressure, renal function, immune response to sheep IgG, or glomerular deposition of IgG or complement. Thus, our results indicate that dietary fish oil has protective and therapeutic effects with regard to proteinuria in PHN. These benefits may relate to alterations in membrane phospholipid composition in favor of omega-3 fatty acids and release of less reactive trienoic eicosanoids.

Refractory nephrotic syndrome in lupus nephritis: favorable response to indomethacin therapy

The effects of indomethacin on urinary protein excretion, levels of serum albumin and renal function were studied prospectively in six patients with systemic lupus erythematosus (SLE) and refractory nephrotic syndrome due to lupus nephritis. Two had membranoproliferative glomerulonephritis, two had diffuse proliferative glomerulonephritis, and one each had mesangioproliferative and membranous glomerulonephritis. All experienced a considerable reduction in urinary protein excretion and an increase in serum albumin. Indomethacin was discontinued in two patients because of side effects, and proteinuria recurred to pretreatment levels. The decrease of proteinuria continued during long-term treatment in three patients. Indomethacin did not cause a permanent decline in renal function. Our results suggest that therapy with indomethacin may be beneficial for the treatment of refractory nephrotic syndrome in selected SLE patients. However, because of potential side effects the administration of indomethacin should be monitored closely.

Prostaglandin inhibitors in the treatment of nephrotic syndrome

The management of nephrotic syndrome resistant to corticosteroid and cytotoxic therapy is unclear. In such patients, prostaglandin inhibitors can reduce proteinuria. Mechanisms may include a reduction in transcapillary hydraulic pressure and a decrease in capillary wall permeability. The antiproteinuric effect of these agents is enhanced by volume depletion induced by sodium restriction and thiazide diuretics. Complications may include aggravation of edema, hemodynamic renal failure, hyperkalemia, and drug nephrotoxicity. Although a reduction in protein excretion may improve the clinical status of nephrotic patients, it is unclear whether such methods will improve renal survival.

Effect of indomethacin on glomerular permselectivity and hemodynamics in nephrotoxic serum nephritis

The present study was undertaken to determine the effects of prostaglandin synthesis inhibition on glomerular hemodynamics in nephrotoxic serum nephritis and to elucidate the mechanisms by which prostaglandin synthesis inhibition reduces proteinuria in nephritic rats. Dextran sieving studies were performed before and after intravenous administration of indomethacin to control rats and to nephritic rats with heavy proteinuria. Indomethacin did not significantly alter mean arterial pressure, glomerular filtration rate or proteinuria in control rats nor were significant changes in dextran sieving observed. By contrast, in nephritic rats indomethacin significantly reduced glomerular filtration rate (2.58 +/- 0.50 vs. 1.39 +/- 0.27 ml/min, P less than 0.001), proteinuria (0.198 +/- 0.079 vs. 0.048 +/- 0.019 mg/min, P less than 0.05) and filtration rate-corrected proteinuria (0.059 +/- 0.033 vs. 0.031 +/- 0.013 mg/ml GFR, P less than 0.05). The fractional clearance of neutral dextrans with molecular radii exceeding 42 A were elevated above control values in nephritic rats (P less than 0.05). After administration of indomethacin, the fractional clearance of neutral dextrans uniformly declined toward control values and remained elevated only for molecular radii exceeding 54 A. Assessment of glomerular hemodynamics in nephritic rats before and after indomethacin showed significant declines in single nephron filtration rate (31.5 +/- 3.0 vs. 21.2 +/- 2.5 nl/min, P less than 0.02), glomerular plasma flow rate (99.5 +/- 6.7 vs. 68.5 +/- 7.8 nl/min, P less than 0.05) and glomerular ultrafiltration coefficient (0.0430 +/- 0.0033 vs. 0.0339 +/- 0.0032 nl.sec-1.mm Hg-1, p less than 0.05). Indomethacin did not significantly change these parameters in control rats.(ABSTRACT TRUNCATED AT 250 WORDS)