Preservation of the glomerular capillary ultrafiltration coefficient during rat nephrotoxic serum nephritis by a specific leukotriene D4 receptor antagonist

Cysteinyl-leukotrienes and the liver

Leukotrienes are potent biological mediators implicated in an increasing number of disease processes. This review outlines the basic biology of leukotrienes and discusses recent developments in our understanding of the specific role of cysteinyl-leukotrienes (cLTs) in cholestasis, hepatic inflammation, portal hypertension, and the pathogenesis of the hepatorenal syndrome (HRS).

Mechanisms of glomerular immune injury: effects of antioxidant treatment

Significant glomerular vasoconstriction and production of reactive oxygen species has been known to occur with exposure to anti-glomerular basement membrane antibody (AGBM-Ab) in the rat model. Previously published studies have demonstrated that such effects can be reduced by therapy with phentolamine, an alpha-adrenergic antagonist. It was hypothesized that antioxidant pretreatment with water-soluble probucol would improve glomerular hemodynamics 60 to 90 min after the administration of AGBM-Ab. These relationships were examined with both in vivo renal micropuncture and in vitro studies in rats. Single-nephron GFR (SNGFR) decreased markedly in untreated rats after AGBM-Ab as a result of afferent and efferent arteriolar vasoconstriction with consequent reductions in nephron plasma flow (SNPF) and decreases in the glomerular ultrafiltration coefficient (LpA). Basal SNGFR was increased, and SNGFR was significantly higher after AGBM-Ab in probucol-treated versus untreated rats. This finding was due solely to higher values for SNPF and prevention of afferent arteriolar constriction. A reduction in LpA after AGBM-Ab was not prevented by probucol treatment. In vitro analyses of glomeruli revealed reduced myeloperoxidase activity in antioxidant-treated rats. Lipoxygenase activity and leukotriene products, however, were not changed by antioxidant therapy, yet vasoconstriction was prevented. H(2)O(2) generation before and after formyl-methionyl-leucyl-phenylalanine stimulation was significantly reduced before and after AGBM-Ab in glomeruli harvested from rats that were treated with the antioxidant. Antioxidant therapy in this model of AGBM-Ab injury did not prevent reductions in LpA, an index of glomerular membrane damage, but did prevent afferent arteriolar vasoconstriction. Reactive oxygen species generation was reduced by probucol. The specific mechanisms whereby antioxidant therapy ameliorates glomerular hemodynamic effects will be defined in additional studies and is likely to involve either enhanced vasodilator or diminished vasoconstrictor activity.

Lipoxin, leukotriene, and PDGF receptors cross-talk to regulate mesangial cell proliferation

The lipoxygenase-derived leukotrienes (LTs) are important proinflammatory lipid mediators. Lipoxins (LXs), more recently described lipoxygenase products, modulate many proinflammatory actions of LTs and have impressive proresolution properties. Mesangial cell (MC) proliferation is a central event in the pathogenesis of glomerulonephritis. LTD4-induced proliferation of mesangial cells is modulated by LXA4. Here, we demonstrate that LXA4 inhibits PDGF- and LTD4-stimulated proliferation through modulation of platelet-derived growth factor receptor beta (PDGFRbeta) activation. Specifically, we demonstrate that LTD4 transactivates the PDGFRbeta, a process associated with c-src recruitment and ras activation. We demonstrate expression of cysLT1 and cysLT2 receptors in MCs. LTD4-induced c-src activation was insensitive to pertussis toxin and the cysLT1 receptor antagonist Zafirlukast but was blocked by the nonselective antagonist Pobilukast. We show that LXA4 inhibits LTD4-stimulated activation of the PDGFRbeta and that LXA4 modulates PDGF-BB-stimulated tyrosine phosphorylation of the PDGFRb and subsequent mitogenic events. Furthermore, expression of recombinant LXA4 receptor (ALXR) in CHOK1 cells was associated with an attenuation of serum-stimulated proliferation. These data demonstrate that LXA4 receptor (ALXR) activation is accompanied by antimitogenic effects coupled with inactivation of growth factor receptors, highlighting the complex cross-talk between G protein-coupled receptors and receptor tyrosine kinases in an inflammatory milieu. These data elaborate on the profile of cell signaling events that underpin the anti-inflammatory and proresolution bioactions of LX.

Induction of nephrotoxic serum nephritis in inbred mice and suppressive effect of colchicine on the development of this nephritis

Accelerated nephrotoxic serum (NTS) nephritis is successfully produced in C57BL/6 mice, using anti-murine glomerular basement membrane (GBM) rabbit antiserum. Anti-murine GBM rabbits antiserum was obtained by immunization of New Zealand white rabbit with trypsinized GBM antigen from normal C57BL/6 mice. Preimmunization with normal rabbit IgG and injection with 150 microl of NTS induced typical NTS nephritis with cellular proliferation in glomeruli, occlusion of glomerular loops, crescents, tubulointerstitial changes and hyperazotemia within 14 days. Polymorphonuclear leucocytes (PMN) have an important role in induction and development of NTS nephritis. Furthermore, clinically used colchicine is thought to suppress functions of PMN. Therefore, the therapeutic effect of colchicine on NTS nephritis was examined. The histological score (HS) of the group treated with 60 microg kg (-1) of colchicine (2.8 +/- 0.5) was significantly lower than that of positive control group (4.03 +/- 0.3).The direct immunofluorescent microscopic study revealed that there is no quantitative difference in the deposition of rabbit IgG, mouse IgG and C3 in GBM between these two groups. Urinary protein excretion and hyperazotemia were significantly suppressed by treatment with 60 microg kg (-1) of colchicine. A NTS nephritis model was established, it was found that colchicine may have a suppressive effect on the development of glomerular nephritis.

Lipoxin A4 antagonizes the mitogenic effects of leukotriene D4 in human renal mesangial cells. Differential activation of MAP kinases through distinct receptors

The lipoxygenase-derived eicosanoids leukotrienes and lipoxins are well defined regulators of hemeodynamics and leukocyte recruitment in inflammatory conditions. Here, we describe a novel bioaction of lipoxin A(4) (LXA(4)), namely inhibition of leukotriene D(4) (LTD(4))-induced human renal mesangial cell proliferation, and investigate the signal transduction mechanisms involved. LXA(4) blocked LTD(4)-stimulated phosphatidylinositol 3-kinase (PI 3-kinase) activity in parallel to inhibition of LTD(4)-induced mesangial cell proliferation. Screening of a human mesangial cell cDNA library revealed expression of the recently described cys-leukotriene(1)/LTD(4) receptor. LTD(4)-induced mesangial cell proliferation required both extracellular-related signal regulated kinase (erk) and PI 3-kinase activation and may involve platelet-derived growth factor receptor transactivation. LTD(4)-stimulated the MAP kinases erk and p38 via a pertussis toxin (PTX)-sensitive pathway dependent on PI 3-kinase and protein kinase C activation. On screening a cDNA library, mesangial cells were found to express the previously described LXA(4) receptor. In contrast to LTD(4), LXA(4) showed differential activation of erk and p38. LXA(4) activation of erk was insensitive to PTX and PI 3-kinase inhibition, whereas LXA(4) activation of p38 was sensitive to PTX and could be blocked by the LTD(4) receptor antagonist SKF 104353. These data suggest that LXA(4) stimulation of the MAP kinase superfamily involves two distinct receptors: one shared with LTD(4) and coupled to a PTX-sensitive G protein (G(i)) and a second coupled via an alternative G protein, such as G(q) or G(12), to erk activation. These data expand on the spectrum of LXA(4) bioactions within an inflammatory milieu.

Transfection of rat kidney with human 15-lipoxygenase suppresses inflammation and preserves function in experimental glomerulonephritis

The human 15-lipoxygenase (15-LO) gene was transfected into rat kidneys in vivo via intra-renal arterial injection. Three days later, acute (passive) or accelerated forms of antiglomerular basement membrane antibody-mediated glomerulonephritis were induced in transfected and nontransfected or sham-transfected controls. Studies of glomerular functions (filtration and protein excretion) and ex vivo glomerular leukotriene B(4) biosynthesis at 3 hr, and up to 4 days, after induction of nephritis revealed preservation or normalization of these parameters in transfected kidneys that expressed human 15-LO mRNA and mature protein, but not in contralateral control kidneys or sham-transfected animals. The results provide in vivo-derived data supporting a direct anti-inflammatory role for 15-LO during immune-mediated tissue injury.

MK-591 acutely restores glomerular size selectivity and reduces proteinuria in human glomerulonephritis

BACKGROUND

Leukotrienes are 5-lipoxygenated (5-LO) metabolites of arachidonic acid that mediate some of the glomerular hemodynamic and structural changes in experimental and human glomerulonephritis.

METHODS

We conducted an open-label, pilot study of the short-term effects of leukotriene biosynthesis inhibition using an orally active 5-LO activating protein (FLAP) antagonist (MK-591) on glomerular function in patients with glomerulonephritis. Eleven adult patients (seven women, median age 38 years) with glomerulonephritis (5 lupus nephritis, 2 IgA nephropathy, 1 membranoproliferative, 1 membranous, 1 C1q-deficiency, and 1 idiopathic crescentic) and moderate renal insufficiency [glomerular filtration rate (GFR) 62 +/- 9 ml/min/1.73 m2] were given MK-591 at a dose of 100 mg orally twice a day for four days.

RESULTS

MK-591 reduced proteinuria (albumin and IgG excretion rates) from 3233 +/- 1074 to 1702 +/- 555 microg/min and from 196 +/- 78 to 148 +/- 55 microg/min for albumin and IgG, respectively (P < 0.05 for both). This was not accompanied by a reduction in systemic arterial pressure, GFR, or renal plasma flow. By analysis of the fractional clearance of polydisperse dextrans, baseline proteinuria resulted from a loss of size selectivity with enhanced passage of large (>52 A) dextrans as compared with healthy controls. Treatment with MK-591 caused a selective improvement in the enhanced passage of large (>58 A) dextrans without affecting the handling of smaller dextrans, indicating an improvement in glomerular size selectivity. MK-591 was well tolerated, and no adverse effects were observed.

CONCLUSIONS

Short-term therapy with MK-591 reduces proteinuria by restoring glomerular size selectivity and thus reduces transglomerular protein trafficking. These benefits may result from glomerular leukotriene biosynthesis inhibition, but other MK-591-specific actions cannot be excluded.

The leukotriene B4 receptor antagonist ONO-4057 inhibits nephrotoxic serum nephritis in WKY rats

To evaluate the role of leukotriene B4 (LTB4) in glomerulonephritis, this study was conducted to examine whether ONO-4057, an LTB4 receptor antagonist, moderated nephritis caused by the injection of nephrotoxic serum (NTS) into Wistar-Kyoto rats. Rats were given intraperitoneal injections of ONO-4057 or phosphate-buffered saline 24 h before the injection of NTS. These rats subsequently received equal doses of ONO-4057 or phosphate-buffered saline 3 h and 1, 2, 3, 4, 5, and 6 d later. Compared with the control groups, ONO-4057 treatment significantly reduced proteinuria and hematuria, suppressed the glomerular accumulation of monocytes/macrophages, and reduced the formation of crescentic glomeruli in a dose-dependent manner. These results suggest that LTB4 is responsible for the crescentic formations and renal dysfunction associated with NTS nephritis. The LTB4 receptor antagonist ONO-4057 may thus be beneficial in the treatment of crescentic glomerulonephritis.

Cytokines, growth factors, and other inflammatory mediators in glomerulonephritis

Over the past decade, research has been centered on the identification of factors that mediate glomerular immune injury and the assessment of their roles in this disease process. The spectrum of mediators identified to date encompasses a diverse array of bioactive molecules such as phospholipids, including cytokines and growth factors, and lipid-derived mediators such as eicosanoids. Given the extensive number of potentially important mediators in glomerulonephritis (GN), I focus only on some of them, for which strong in vitro and in vivo data suggest a major role in the pathogenesis of immune-mediated renal injury. So, in the first part, I discuss some cytokines and growth factors; and in the second, some other important mediators, the eicosanoids and especially the lipoxygenase-derived products, leukotrienes and lipoxins.

Inhibition of leukotriene biosynthesis improves renal function in experimental glomerulonephritis

The development of renal dysfunction in experimental glomerulonephritis (GN) is mediated in part by enhanced leukotriene (LT) formation. In our studies the pathophysiological role of LTs was investigated through pharmacological inhibition of LT biosynthesis in a rat model of nephrotoxic serum nephritis. MK-0591, an indirect inhibitor of 5-lipoxygenase activity, was co-administered to rats injected with nephrotoxic rabbit serum, followed by assessment of renal function, morphology and microsomal LTC4 synthase activity on day 7. A significant improvement in glomerular function was noted (p < 0.05), together with a 50% reduction in proteinuria (p < 0.01) in animals receiving MK-0591 (60 mg kg-1 day-1). In addition, the fall in renal LTC4 synthase activity which occurred in nephritic rats (to 74% of control values, p < 0.01) was prevented in drug-treated animals. Based on these results, it appears that inhibition of LT biosynthesis protects against both renal impairment and alterations in LTC4 synthase activity during the development of experimental GN, and may provide a useful therapeutic adjunct in the treatment of this disease.

Protective effect of peptide leukotriene antagonist on renal failure induced by a tourniquet in rabbits

We studied the effects of a selective antagonist of peptide leukotriene D4/E4 (LY-171883) and 5-lipoxygenase inhibitor diethylcarbamazine (DEC) in renal failure induced by a tourniquet, because peptide leukotrienes (LTs) were suggested to play a key role in our previous study. The hind limbs of anesthetized rabbits were fastened for 5 h and then released for 6 h. LY171883 (4 mg/kg/h) and DEC (40 mg/kg/h) were administered via the aural vein from 30 min before the tourniquet and during the experiment in each tourniquet group. The tourniquet induced renal injuries represented by increases in serum BUN and creatinine, and the injuries in the fastened muscles represented increases in serum CPK and edema index of the fastened site. LY171883 and DEC significantly attenuated the aggravation of the renal functions induced by a tourniquet when compared with the vehicle-treated group. LY171883 did not affect the injuries in the fastened muscles, but DEC attenuated it significantly when compared with the vehicle-treated group. The protection of peptide LT antagonist and 5-lipoxygenase inhibitor in the tourniquet-induced renal failure elucidate that peptide LTs trigger renal failure induced by a tourniquet.

Renal leukotriene C4 synthase: characterization, partial purification and alterations in experimental glomerulonephritis

Cysteinyl leukotrienes (LT) play an important role in the development of experimental glomerulonephritis (GN). We have partially purified and characterized LTC4 synthase, the enzyme responsible for cysteinyl LT formation, from rat renal microsomes and have investigated this enzyme activity in nephritic rats. LTC4 formation, measured in vitro, was linear for > 10 min at 25 degrees C in the presence of 50 mM serine borate (an inhibitor of gamma-glutamyl transpeptidase), with Km values for LTA4 and GSH of 56 microM and 8.5 mM, respectively. Detergent solubilization and anion-exchange chromatography of microsomal proteins resulted in a 7-fold increase in enzyme specific activity. Enzymatic and immunoblot analysis demonstrated that cytosolic and microsomal glutathione S-transferase (GST) activities were distinct from LTC4 synthase activity. Comparison of LTC4 synthase activity in nephritic rats over 21 days revealed an initial increase over the first 24 h following injection of nephrotoxic sera, followed by a subsequent decline until day 7 and a gradual recovery by day 21. Inhibition of LT biosynthesis with MK-0591 (10 mg kg-1 d-1) reduced GN-associated proteinuria by 72% (P < 0.05). These results suggest a potential mechanism for enhanced cysteinyl LT formation in the development of experimental GN and further support their causal role in the etiology of this disease.

Effect of the dialysis membrane in the treatment of patients with acute renal failure

BACKGROUND

The mortality rate among patients with acute renal failure remains high, and the role of the biocompatibility of the dialysis membrane in the resolution of this disorder is not known.

METHODS

We prospectively studied 72 patients with acute renal failure who required hemodialysis and assigned them to two treatment groups. One group underwent dialysis with the widely used cuprophane dialysis membrane, which activates the complement system and leukocytes, and the other group underwent dialysis with a synthetic polymethyl methacrylate membrane, which has a more limited effect on complement and leukocytes. Scores on the Acute Physiology, Age, and Chronic Health Evaluation (APACHE II) were calculated at the initiation of dialysis. Survival and the recovery of renal function were determined with the use of proportional-hazards and exact logistic-regression analyses.

RESULTS

When dialysis was initiated, the patients in the two groups were similar in terms of age, APACHE II scores, the prevalence of oliguria, and biochemical indexes of renal failure. Twenty-three of the 37 patients (62 percent) in the group undergoing dialysis with the polymethyl methacrylate membrane recovered renal function, as compared with 13 of the 35 patients (37 percent) in the group undergoing dialysis with the cuprophane membrane (P = 0.04 after adjustment for the APACHE II score). The median number of dialysis treatments required before the recovery of renal function was 5 in the former group and 17 in the latter group (P = 0.02). Twenty-one patients (57 percent) undergoing dialysis with the polymethyl methacrylate membrane survived, as compared with 13 patients (37 percent) undergoing dialysis with the cuprophane membrane (P = 0.11). Of the 20 patients in each group who initially had nonoliguric acute renal failure, the survival rates were 80 percent with the polymethyl methacrylate membrane and 40 percent with the cuprophane membrane (P = 0.01).

CONCLUSIONS

Among patients with acute renal failure requiring hemodialysis, the use of the polymethyl methacrylate membrane, as compared with the cuprophane membrane, resulted in improved recovery of renal function.

Lipoxygenase products in normal and diseased glomeruli

Figure 4 is a schematic summary of current evidence implicating products of the 15-lipoxygenase pathway of arachidonic acid metabolism, principally 15-S-HETE and LXA4, as endogenous antagonists for the proinflammatory actions of leukotrienes. Here, we have presented evidence for the pathophysiologic relevance of leukotrienes in glomerular immune injury and the emerging data on the multifaceted counterinflammatory actions of 15-lipoxygenase products as they relate specifically to the renal glomerulus. Clearly, these concepts are of a broader nature and would be expected to pertain to inflammatory reactions in general, be they in the glomerulus, the renal interstitium, or in extrarenal sites. The extent to which these early observations can be exploited to design strategies for the control of self-destructive inflammatory reactions in the kidney and elsewhere will be determined by future studies. Imaginative design of molecular tools for the manipulation of these enzyme systems in vivo, however, represents a potentially fruitful area of research towards the attainment of a highly worthwhile goal: the cure of glomerulonephritis.

Elevated cysteinyl leukotriene excretion in experimental glomerulonephritis

The involvement of cysteinyl leukotrienes (LT) in the etiology of glomerulonephritis (GN) was investigated in a rat model of nephrotoxic serum nephritis in which renal function, morphology, LTC4 synthase activity and urinary cysteinyl LT excretion were monitored over seven days. Significant alterations in renal function and morphology were evident on day 1 in nephritic rats, with a 12% decline in creatinine clearance, a greater than three-fold increase in urinary protein excretion and histologic evidence of basement membrane thickening. Urinary LTC4 excretion in the nephritic rats was elevated at this time to 140 +/- 38 pg/hr (P < 0.01) compared to undetectable levels in control animals. On days 3 and 7, while proteinuria intensified and glomerular filtration remained depressed, LTC4 excretion declined 14% (NS) and 79% (P < 0.05), respectively. The temporal changes in urinary LTC4 excretion were paralleled by concomitant alterations in LTC4 synthase activity in renal cortical microsomes, where an 84% (P < 0.01) drop in enzyme activity occurred from day 1 to day 7 in the nephritic group. This data provides the first measurement of urinary cysteinyl LT excretion and altered LTC4 synthase activity in a model of experimental GN and supports an early role for LT's in the development of subsequent functional changes.

Co-regulated expression of glomerular 12/15-lipoxygenase and interleukin-4 mRNAs in rat nephrotoxic nephritis

Arachidonate 12- and 15-lipoxygenase (LO) products are generated in experimental glomerulonephritis. 15-S-HETE (a 15-LO product) and lipoxins (interaction products between 5-LO and either 12-LO or 15-LO) counteract the proinflammatory actions of leukotrienes. IL-4 has been shown to up-regulate 15-LO gene expression in human leukocytes. Based on homology with human 15-LO, we cloned a 0.76 kbp fragment of a rat LO cDNA from leukocytes stimulated by interleukin-4 (IL-4). The deduced amino acid sequence shows 71.0% and 60.1% homology to human 15-LO and 12-LO, respectively, and 100% homology to a recently cloned "leukocyte type" rat 12-lipoxygenase enzyme, which possesses significant 15-lipoxygenase activity (heretofore referred to as "12/15-LO"). A deletion mutant was utilized to generate internal standard cRNA in quantitative PCR assays. Glomerular 12/15-LO mRNA increased significantly over controls 24 and 48 hours after NTS injection, then decreased at 72 hours. RNA from NTS glomeruli contained higher levels of 12/15-LO mRNA than that from unstimulated peripheral leukocytes, suggesting that 12/15-LO transcription is up-regulated locally in native and/or infiltrating glomerular cells. Glomerular IL-4 mRNA increased markedly 16 hours post-NTS, and was then reduced, suggesting a potential role for T cell-derived IL-4 in directing the expression of 12/15-LO during glomerulonephritis. This represents the first demonstration of tandem regulated in vivo gene expression for a lymphokine (IL-4) and a lipoxygenase, both of which promote counter-inflammatory influences in immune complex-mediated injury.

Hemodialysis membrane biocompatibility in acute renal failure

Hemodialysis is a lifesaving procedure for patients with acute renal failure. Nevertheless, the institution of hemodialysis may result in a continued or accelerated decline in renal function. Loss of osmotic drive and hypotension may be partially responsible for this observation. However, multiple lines of evidence suggest that the nature of the hemodialysis membrane also influences renal function following acute renal failure. The cellulosic hemodialysis membrane activates humoral pathways and the cellular elements of blood. The inflammatory responses entrained from the activation result in hypersensitivity reactions attributable to anaphylatoxin generation, hypoxemia, increased susceptibility to infection, and catabolic events. In addition, recent studies indicate that the use of bioincompatible membranes delays recovery from acute renal failure. Increased numbers of neutrophils are found in the glomeruli following exposure to cellulosic membranes, suggesting that inflammatory events induced by complement activation may mediate continuing renal injury and prolonged recovery from acute renal failure. Membrane choice for patients with acute renal failure is emerging as an important therapeutic consideration, just as it is for those patients on long-term dialysis.

Hemodynamic role of arachidonate 12- and 5-lipoxygenases in nephrotoxic serum nephritis

The role of arachidonate 12- and 5-lipoxygenation eicosanoids in mediating acute changes in renal hemodynamics was assessed in nephrotoxic serum nephritis (NSN) in the rat. Following a single intravenous injection of nephrotoxic serum (NTS), significant decrements in glomerular filtration rate (GFR) and renal blood flow (RBF) occurred at one hour, and were associated with increments in glomerular polymorphonuclear leukocyte (PMN) counts and in the synthesis of thromboxane (Tx) B2, leukotriene (LT) B4 and 12-hydroxyeicosatetraenoic acid (12-HETE). Pretreatment of rats with the arachidonate 12-lipoxygenase inhibitor, baicalein, partially but significantly ameliorated the decrements in GFR and RBF, and blocked the enhanced glomerular synthesis of 12-HETE following administration of NTS. Likewise, pretreatment of rats with the arachidonate 5-lipoxygenase inhibitor, U-66858, partially ameliorated the decrements in GFR and RBF induced by NTS. Combined pretreatment of rats with baicalein and U-66858 ameliorated the decrements in GFR and RBF to an extent no different to that of U-66858 alone. In rats pretreated with the LTB4 receptor antagonist, U-75302, GFR and RBF remained depressed to levels no different than in animals which received NTS alone. These observations indicate that in NSN, the acute decrements in GFR and RBF are partially mediated by 12-HETE and arachidonate 5-lipoxygenation products. Leukotrienes other than LTB4, such as LTD4 and LTC4, are the likely candidates.

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.

Mesangial cell immune injury. Hemodynamic role of leukocyte- and platelet-derived eicosanoids

The role of leukocytes and platelets and of leukocyte- and platelet-derived eicosanoids in mediating acute changes in renal and glomerular hemodynamics was assessed in a model of antibody-induced mesangial cell injury in the rat. After a single intravenous injection (6 mg/kg) of the monoclonal antibody (ER4) against the mesangial cell membrane antigen Thy 1, significant decrements in glomerular filtration rate (GFR) and renal blood flow (RBF) were observed at 1 h, and were associated with increments in glomerular LC (+) leukocyte counts and in the synthesis of thromboxane (Tx)B2, leukotriene (LT)B4, and 12-hydroxyeicosatetraenoic acid (HETE). In rats with immune leukopenia, the rise in glomerular LC (+) leukocytes and in eicosanoid synthesis were abolished and the fall in GFR and RBF after administration of ER4 were completely ameliorated. Likewise, pretreatment of rats with both a thromboxane synthase and a 5-lipoxygenase inhibitor also blocked the fall in GFR and RBF and the rise in glomerular synthesis of TxB2 and LTB4 produced by ER4 without changing glomerular LC (+) leukocyte counts. Selective inhibition of thromboxane or 5-lipoxygenase alone only partially ameliorated the decrements in GFR and RBF produced by ER4. In animals with immune thrombocytopenia, the elevated glomerular synthesis of 12-HETE and fall in RBF but not GFR was ameliorated after administration of ER4. The ER4 antibody-induced fall in GFR was mainly caused by a marked decrement in the ultrafiltration coefficient, Kf, which was dependent on TxA2 and 5-lipoxygenase products, since pretreatment of animals with a thromboxane receptor antagonist or with a 5-lipoxygenase inhibitor partially ameliorated this decrement. Structural changes such as infiltration of glomerular capillaries by leukocytes and endothelial cell damage may also have accounted for the fall in Kf. These observations indicate that in antibody-mediated mesangial cell injury, infiltrating leukocytes and platelets mediate the changes in renal hemodynamics via synthesis of thromboxane and arachidonate 5-lipoxygenation products.

Adhesion promotes transcellular leukotriene biosynthesis during neutrophil-glomerular endothelial cell interactions: inhibition by antibodies against CD18 and L-selectin

Eicosanoid formation by transcellular routes can amplify the levels and types of lipid mediators within a local milieu. To evaluate the role of adhesion in this process, we assessed the influence of mAb against adhesion molecules on LTC4 generation by PMN-endothelial cell interaction. Transcellular LTC4 generation was initiated by addition of fMLP to coincubations of GM-CSF-primed PMN and TNF-activated endothelial cells cultured from kidney glomeruli. Both PMN-endothelial cell adhesion and transcellular LTC4 generation were inhibited by mAb against leukocyte L-selectin and CD18. These results indicate that cytokine-treated PMN and endothelial cells generate LTC4 via transcellular routes by receptor-triggered mechanisms. They suggest that adhesion promotes transcellular eicosanoid biosynthesis and that adhesion molecules may also be targets for blockade of transcellular biosynthesis of lipid mediators.

Synthesis and metabolism of cysteinyl leukotrienes by the isolated pig kidney

The metabolism and synthesis of cysteinyl leukotrienes by the isolated perfused pig kidney has been investigated. Kidneys were maintained for up to six hours in a recirculating perfusion system by using an oxygenated Krebs-Henseleit buffer containing albumin and the perfluorinated oxygen carrier, FC-43. Perfusion pressure was maintained at 12-13.5 kPa, with perfusion flow rates of 150-250 ml/min resulting in a urine output of between 20-180 ml/hr. Infusion of 3H-LTC4 into the renal artery resulted in rapid and complete metabolism, with the major urinary metabolites comprising LTE4, omega-hydroxy-LTE4, omega-carboxy-LTE4 and N-acetyl-omega-hydroxy-LTE4. The capacity of the isolated kidney to synthesize cysteinyl leukotrienes was monitored by measuring urinary LTE4 excretion; there was a basal urinary excretion of LTE4 (median 43 pg/min, range 8-470 pg/min). Neither lipopolysaccharide or human recombinant tumor necrosis factor alpha had any effect on basal excretion. Treatment with the calcium ionophore A23187, however, resulted in a 38.1 +/- 9.6-fold increase in urinary LTE4 excretion. We conclude that the isolated pig kidney, in the absence of circulating cells, can synthesize cysteinyl leukotrienes in the absence of circulating cells, which can then undergo extensive oxidative metabolism.

Essential fatty acid deficiency normalizes function and histology in rat nephrotoxic nephritis

The central lipid abnormality in essential fatty acid deficiency (EFAD) is the lack of availability of arachidonic acid. To examine the role of total eicosanoid's biosyntheses in the pathology and pathophysiology of glomerulonephritis, EFAD was induced in weanling rats, which were then subjected to antiglomerular basement membrane antibody (NTS)-induced injury in adulthood. Glomerular dynamics (as assessed by micropuncture), quantitative histology, and eicosanoid generation rates were measured at two hours and two weeks post-NTS, and compared to those of standard diet-fed (STD) controls. Two hours post-NTS, and despite the occurrence of proteinuria in both EFAD and STD animals, glomerular dynamics were essentially normal in EFAD rats, whereas STD animals had reduced values for glomerular filtration rate (GFR) and renal plasma flow rate (RPF). At two weeks, severe histologic changes were observed in STD animals including mesangial and stalk hypercellularity, moderate sclerosis, and interstitial nephritis, coupled with heavy proteinuria and reduced GFR and RPF. In dramatic contrast, EFAD rats displayed totally normal glomerular structures and functions. In parallel, glomerular generation rates of prostaglandin E2 and thromboxane A2 were suppressed markedly in EFAD rats. Thus, EFAD confers complete protection against the histopathologic and functional sequelae of immune-initiated injury in the glomerulus. The data suggest that the initial wave of complement-induced neutrophil infiltration (with resultant proteinuria) is not sufficient to perpetuate injury into the more destructive chronic phases. The results provide strong impetus for the design of more specific interventional therapies targeting the various enzymes and products of arachidonic acid metabolism in the attempts to control glomerular inflammation.

Fifteen-S-hydroxyeicosatetraenoic acid (15-S-HETE) specifically antagonizes the chemotactic action and glomerular synthesis of leukotriene B4 in the rat

In models of experimental glomerulonephritis, there is temporal concordance between the shift in the glomerular cellular infiltrate from neutrophils (PMN) to macrophages/monocytes and the suppression of glomerular leukotriene B4 (LTB4) generation. Since macrophages are a rich source of 15-lipoxygenase (15-LO) products, we investigated whether the principal product of arachidonate 15-lipoxygenation, 15-S-hydroxyeicosatetraenoic acid (15-S-HETE), was capable of antagonizing the proinflammatory actions of LTB4 in the rat. PMN exhibited chemotaxis to LTB4 in a dose dependent manner with an LC50 of 10(-8) M. When rat neutrophils were pre-treated with 15-S-HETE, chemotaxis to LTB4 was inhibited in a dose dependent manner (maximal at 30 microM 15-S-HETE) but, the same concentration did not inhibit chemotaxis to n-formyl-1-methionyl-1-phenylalanine (FMP). 12-S-HETE (30 microM) did not inhibit chemotaxis to LTB4. Glomeruli from rats injected with nephrotoxic serum three hours earlier generated increased levels of LTB4; prior exposure of such glomeruli to 15-S-HETE totally normalized LTB4 production. The glomerular production of 15-S-HETE and LTB4 was also determined 3 hours, 72 hours and 2 weeks after administration of nephrotoxic serum. Whereas there was an early, short-lived, burst of LTB4 followed by a return to baseline levels, the production of 15-S-HETE increased steadily over the two week period and was present in amounts fivefold greater than LTB4. Thus, these studies assign a role for locally generated 15-LO derivatives in arresting LTB4-promoted PMN infiltration and suppressing LTB4 synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of the 5-lipooxygenase pathway in obstructive nephropathy

Leukotrienes are products of the 5-lipooxygenase pathway of arachidonic acid metabolism that possess potent inflammatory properties. We examined the potential role of this pathway in the decrease in glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) observed in rats after unilateral release of bilateral ureteral obstruction (BUO) of 24 hours duration. Isolated glomeruli from rats with BUO produced significantly greater amounts of leukotriene B4 (LTB4) than glomeruli from sham-operated rats (SOR; P less than 0.0001). Glomeruli from rats with BUO given MK886, an inhibitor of the 5-lipooxygenase enzyme, or from rats with BUO subjected to both total body irradiation to prevent the leukocyte infiltration of the kidney and also given MK886 prior to obstruction, produced amounts of LTB4 not significantly different from those in glomeruli of SOR. Glomeruli from rats with BUO that had only total body irradiation prior to obstruction produced significantly less LTB4 than glomeruli from untreated BUO rats, but LTB4 production was still significantly greater than in glomeruli from SOR. There were no significant differences in GFR among SOR, SOR given MK886, and SOR subjected to total body irradiation. However, SOR given MK886 had significantly higher ERPF and lower renal vascular resistance (RVR) than SOR not pretreated with the lipooxygenase inhibitor. Rats with BUO given MK886, or subjected to total body irradiation, or both, prior to obstruction had significantly greater GFR and ERPF values and lower RVR than untreated BUO rats. Glomeruli from rats with BUO which were not pretreated had three times the leukocytes of glomeruli from SOR. This leukocyte infiltrate was composed of macrophages (about 55%) and neutrophils (about 45%).(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of R-75,317 on antiglomerular basement membrane glomerulonephritis in rats

Platelet-activating factor (PAF) is a potent inflammatory mediator which is released by various inflammatory cells and produced by certain tissues, including the kidney. PAF has been shown to increase glomerular permeability to protein and to decrease glomerular filtration rate (GFR) by contracting mesangium. On the basis of these observations, it has been suspected that PAF may play a role as mediator of glomerular damage in glomerular nephritis. To examine this possibility, we studied the effects of a specific PAF antagonist, R-75,317, on the development of an experimental model of anti-glomerular basement membrane (anti-GBM) glomerulonephritis. Glomerulonephritis was initiated by injecting rabbit anti-rat GBM serum into rats. Proteinuria gradually developed after serum injection, plateaued at week 2, and remained at the high level of week 2 throughout the experimental period (6 wk). Chronic treatment with R-75,317 (10 mg/kg/day i.p.) tended to delay the onset of proteinuria and significantly accelerated the recovery phase. Creatinine clearance (Ccr) fell to 40% at week 3. R-75,317 treatment completely prevented this decline of Ccr. Histological changes in this model (glomerular hypertrophy, proliferation of mesangial matrix and interstitial fibrosis) were also ameliorated by the R-75,317 treatment. The results suggest that PAF may play a role in the development of glomerulonephritis and that PAF antagonists could be used in the treatment of human renal disease.

Complement activation retards resolution of acute ischemic renal failure in the rat

We investigated the role of complement activation on the resolution of acute ischemic renal failure in the rat. Acute renal failure was induced by clamping of the renal arteries of Sprague-Dawley rats for 45 minutes (Day 0). On subsequent days, groups of rats with acute renal failure were exposed to daily zymosan infusion (an activator of the complement system), or to blood incubated with cuprophane (CUP) or polyacrylonitrile (PAN) dialysis membranes. We serially measured the change in BUN daily, glomerular filtration rate and 24-hour proteinuria on Day 3 and Day 5 following ischemia. On Day 6, the animals were sacrificed and their kidneys examined histologically. Zymosan and cuprophane exposed rats had a significant delay in the recovery of renal failure, reduced glomerular filtration rate, and histologically had more neutrophil infiltration than control or PAN exposed animals. To investigate the potential pathophysiology of these observations, we assessed the response of zymosan-exposed rats to infusion of deferoxamine (DFO), a potent inhibitor of hydroxyl radical formation (OH.). Infusion of DFO prior to zymosan significantly improved recovery of renal function. We also measured urinary thromboxane B2 levels in these groups of rats. While the groups of rats exposed to zymosan had the highest levels of thromboxane B2, these levels were not different between the groups exposed to zymosan alone, or to zymosan and DFO. These observations suggest a role for hydroxyl radicals in the prolongation of renal failure in this model. Taken together, these findings may have implications for the dialytic intervention in patients with acute renal failure.

Metabolism of cysteinyl leukotrienes by the isolated perfused rat kidney

The metabolism of cysteinyl leukotrienes by the isolated perfused rat kidney was investigated. For this purpose LTC4, LTD4 or LTE4 were studied in separate experiments. The isolated perfused rat kidney metabolized all cysteinyl leukotrienes to the final metabolite N-acetyl-LTE4. In the presence of 5% albumin 50% of LTC4 was metabolized to LTD4 (22%), LTE4 (15%) and N-acetyl-LTE4 (13%) within 60 min. Excretion of radioactivity into urine was less than 1%. In contrast, in the absence of albumin, LTC4 was completely metabolized within 45 min to N-acetyl-LTE4, the sole and final metabolite of LTC4 found in the perfusion medium as well as in urine. After 60 min 19% and 42% of total radioactivity were found in the perfusion medium and in urine, respectively. Isolated glomeruli metabolized LTC4 to LTD4 and to LTE4 but not to N-acetyl-LTE4 at a rate comparable to the rate observed by the isolated perfused kidney in the absence of albumin. In contrast to isolated glomeruli isolated tubuli metabolized LTE4 to N-acetyl-LTE4 at a rate comparable to that observed by the isolated perfused kidney in the absence of albumin. The present study shows that the isolated perfused rat kidney metabolizes cysteinyl leukotrienes to the sole and final metabolite N-acetyl-LTE4. In the presence of albumin metabolism is slowed down and excretion of N-acetyl-LTE4 into urine is prevented.

Enhanced renal leukotriene production in murine lupus: role of lipoxygenase metabolites

To investigate the potential role of leukotrienes in murine lupus, we measured renal hemodynamics and renal leukotriene production in MRL-lpr/lpr mice at 12 and 20 weeks of age. Over this age range, these animals develop overt manifestations of autoimmune disease with nephritis similar to human SLE. In the current study, we demonstrated that glomerular filtration rate (GFR) and PAH clearance (CPAH) deteriorated with age in MRL-lpr/lpr mice, but not in MRL(-)+/+ controls. Impaired renal hemodynamic function in MRL-lpr/lpr mice was associated with enhanced ionophore-stimulated production of both leukotriene B4 (LTB4) and leukotriene C4 (LTC4) by preparations of renal cortex. There was a significant inverse correlation between GFR and in vitro production of both LTC4 and LTB4 in kidneys from MRL-lpr/lpr mice, but not in control animals. In addition, in vitro LTC4 production was correlated with the severity of renal histomorphologic abnormalities. Administration of the specific peptidoleukotriene receptor antagonist SKF104353 to 20 week old MRL-lpr/lpr mice significantly improved both GFR and CPAH, whereas this agent had no effect of renal hemodynamics in MRL(-)+/+ controls. These results suggest that renal production of LTC4 and LTB4 is increased in MRL-lpr/lpr mice with nephritis, and that enhanced production of peptidoleukotrienes causes reversible renal dysfunction. Increased leukotriene production within the kidney may therefore be important in the pathogenesis of lupus nephritis.

Neutrophil adhesion to glomerular mesangial cells: regulation by lipoxygenase-derived eicosanoids

Our results suggest that leukotrienes promote rapid PMN adhesion to glomerular mesangial cells via actions on PMN (LTB4) and mesangial cells (LTD4). Leukotriene-induced adhesion appeared to be mediated by a CD11/CD18-dependent (LTB4) and -independent (LTD4) mechanisms. The specific epitopes mediating LTD4-induced adhesion remain to be defined. Lipoxins did not influence basal adhesion. In contrast, lipoxins markedly inhibited LTD4-, but not LTB4-induced responses. Further elucidation of the components of these adhesion processes, of the pathways for leukotriene and lipoxin biosynthesis in the inflamed glomerulus, and of the counterregulatory actions of lipoxins and leukotrienes may reveal sites for therapeutic intervention in GN. (graph; see text) Data are mean +/- SE of 3 experiments, each conducted in quadruplicate. Leukotriene-induced adhesion was not inhibited by vehicle alone.

Increased production of cysteinyl leukotrienes in hepatorenal syndrome

The cysteinyl leukotrienes C4 and D4 are potent renal vasoconstrictors which may modulate glomerular function in vivo, and may therefore be important in the pathogenesis of hepatorenal syndrome. Urinary leukotriene E4, the major metabolite of leukotrienes C4 and D4, was elevated in patients with hepatorenal syndrome (17.8 ng/h) when compared with normal controls (5.1 ng/h) or subjects with renal failure alone (1.9 ng/h). Urinary leukotriene E4 was also elevated in subjects with decompensated liver disease (cirrhosis with ascites 28.6 ng/h, severe hepatocellular dysfunction 57.5 ng/h), but normal in compensated liver disease (6.7 ng/h). In the early stages of hepatorenal syndrome, leukotriene E4 excretion rate was up to 100-fold higher (560 ng/h) than in normals, and fell in parallel with creatinine clearance, indicative of the glomerular filtration rate-dependent renal excretion. Following correction for creatinine clearance, leukotriene E4, excretion was considerably higher in hepatorenal syndrome (54.1 pg/ml creatinine clearance) compared with normals (1.0 pg/ml creatinine clearance), chronic renal failure (3.2 pg/ml creatinine clearance), decompensated liver disease (ascites 7.7 pg/ml creatinine clearance, and severe hepatocellular dysfunction 11.0 pg/ml creatinine clearance), and compensated liver disease (1.9 pg/ml creatinine clearance). To interpret the significance of these findings, we determined renal clearance and endogenous metabolism of the cysteinyl leukotrienes by infusion of [3H]leukotriene C4 into a single subject with hepato-renal syndrome and two control subjects. Renal clearance of leukotriene E4, was reduced in hepatorenal syndrome (2.4 ml/min) compared with controls (greater than 17 ml/min) which together with the increased excretion rate of leukotriene E4 demonstrates that there is increased cysteinyl leukotriene production in hepatorenal syndrome. This may be one of the factors involved in its pathogenesis.

Predominant functional roles for thromboxane A2 and prostaglandin E2 during late nephrotoxic serum glomerulonephritis in the rat

While much is known regarding acute nephrotoxic serum (NTS)-induced glomerular injury, the glomerular dynamics and pathophysiologic mediators of the more relevant chronic autologous phase remain poorly defined. Studies were performed in rats 14 d after injection of rabbit serum (n = 6), NTS in the absence (n = 6), or presence, of a cyclooxygenase inhibitor, ibuprofen (n = 6) or a thromboxane A2 (TxA2) receptor antagonist, L-670,596 (n = 5). A mesangial macrophage/monocyte infiltrate was noted with equal intensity in all NTS-treated rats. Glomerular generation rates of prostaglandin (PG) E2, PGF2a, and TxA2 in nephritic kidneys were dramatically increased as compared to controls. 2 wk after NTS, there was an increase in glomerular plasma flow rate (SNPF), attainment of filtration pressure disequilibrium, and augmentation of net transcapillary hydraulic pressure difference (delta P). Glomerular filtration rate (GFR), however, was reduced, due to a marked fall in the glomerular capillary ultrafiltration coefficient (Kf). Cyclooxygenase inhibition resulted in normalization of glomerular eicosanoid generation rates, amelioration of proteinuria, afferent vasoconstriction, and normalization of SNPF, delta P, Kf, and GFR. Selective antagonism of TxA2 also led to preservation of Kf, but was without effect on SNPF, thereby leading to elevated values for GFR. Thus, in contrast to the pathophysiologic role of arachidonate-lipoxygenase products in the early heterologous phase, PG-mediated vasodilatation and TxA2-induced reductions in Kf and GFR underlie glomerular functional changes during autologous mesangioproliferative glomerulonephritis.

Lipoxin A4 antagonizes cellular and in vivo actions of leukotriene D4 in rat glomerular mesangial cells: evidence for competition at a common receptor

Lipoxin A4 (LXA4) was competitive with [3H]leukotriene D4 (LTD4) for specific binding to cultured rat glomerular mesangial cells. Half-maximal inhibition was obtained with 100 nM LXA4, compared with 10 nM for unlabeled LTD4. At 10 and 50 nM LXA4 induced low, but significant, increases in mesangial-cell inositol trisphosphate generation: 48% and 44% increases as compared to vehicle controls, respectively (compared with 146% and 106% increments obtained for equimolar LTD4), which were abolished in the presence of 100-fold concentrations of the LTD4 receptor antagonist, SKF 104353. In addition, exposure to 100 nM LXA4 prevented mesangial cell inositol trisphosphate generation induced by 10 nM LTD4. To test the in vivo relevance of these results, we established a dose-response curve for the reducing effects of intrarenal arterial LTD4 on glomerular filtration rate and renal plasma flow in anesthetized rats (LTD4 doses were 0.5, 7.0, 14.0, and 20.0 micrograms/kg per min) without or with LXA4 at 1 microgram/kg per min. Mean percent decreases in glomerular filtration rate/renal plasma flow during LTD4 administration were 27*/24, 25*/40*, 70*/65*, and 73*/70* at the above doses, respectively (*P less than 0.05 versus baseline). With LXA4, these values were as follows: 9/20*, 11/37*, 42*/51*, and 50*/68*, the latter value representing a shift in the LTD4/glomerular filtration rate dose-response curve. Thus, LXA4 competes for [3H]LTD4 binding to mesangial cells, its presence prevents LTD4-induced inositol trisphosphate generation, and its own stimulation of mesangial-cell inositol trisphosphate is blocked by an LTD4 receptor antagonist. In vivo, LXA4 antagonizes LTD4-induced falls in glomerular filtration rate but not renal plasma flow, implying prevention of LTD4-mediated reductions in the glomerular ultrafiltration coefficient, a consequence of mesangial-cell contraction. These results suggest that LTD4 and LXA4 interact at a common site on rat mesangial cells at which LXA4 provokes partial agonist responses and competitively antagonizes both the cellular and physiological actions of LTD4. Moreover, these results provide evidence for a potential counterregulatory interaction between leukotrienes and lipoxins that may be relevant during glomerular inflammation.

Production of tumor necrosis factor by rat mesangial cells in response to bacterial lipopolysaccharide

Tumor necrosis factor (TNF) is a cytokine which is produced by mononuclear phagocytes upon activation by bacterial lipopolysaccharide (LPS) and various other stimuli. In immune-mediated glomerulonephritis, infiltration of glomeruli by monocytes-macrophages is associated with production of TNF. The purpose of the present experiments was to determine whether mesangial cells could also contribute to glomerular TNF synthesis. TNF activity has been determined in the culture medium of rat mesangial cells using a L-929 fibroblast lytic assay. This activity was detectable only when the cells were exposed to LPS (0.1 to 10 micrograms/ml) and for periods longer than one hour. The cytotoxic factor was identified as TNF since: (1) the lytic activity was completely inhibited by an anti-mouse TNF polyclonal antibody and was associated with suppression of lipoprotein lipase activity in adipocytes; (2) its molecular weight (110,000 daltons) corresponded to that observed for murine TNF under non-denaturing conditions; and (3) mRNA encoding TNF was expressed by mesangial cells two hours after addition of LPS. To assess the mechanisms whereby TNF production was regulated, the role of prostaglandin E2 (PGE2) was determined. LPS caused a dose-dependent increase of PGE2 synthesis by mesangial cells. Treatment by indomethacin promoted a suppression of PGE2 production together with an increase of TNF synthesis, indicating that PGE2 acted in a negative feedback manner to regulate the production of TNF. Addition of PGE2 (0.1 to 300 nM) or 8-bromo cyclic AMP (0.1 to 100 microM) induced similar dose-dependent reductions of TNF synthesis. Thus the inhibitory effect of PGE2 probably required in part cyclic AMP accumulation.(ABSTRACT TRUNCATED AT 250 WORDS)