Antibodies against type II phospholipase A2 prevent renal injury due to ischemia and reperfusion in rats

Protective effect of N-(p-amylcinnamoyl) anthranilic acid, phospholipase A2 enzyme inhibitor, and transient receptor potential melastatin-2 channel blocker against renal ischemia-reperfusion injury

The production of reactive oxygen species and inflammatory events are the underlying mechanisms of ischemia-reperfusion injury (IRI). It was determined that transient receptor potential melastatin-2 (TRPM2) channels and phospholipase A₂ (PLA ₂ ) enzymes were associated with inflammation and cell death. In this study, we investigated the effect of N-( p-amylcinnamoyl) anthranilic acid (ACA), a TRPM2 channel blocker, and PLA ₂ enzyme inhibitor on renal IRI. A total of 36 male Sprague-Dawley rats were divided into four groups: control, ischemia-reperfusion (I/R), I/R + ACA 5 mg, I/R + ACA 25 mg. In I/R applied groups, the ischemia for 45 minutes and reperfusion for 24 hours were applied bilaterally to the kidneys. In the I/R group, serum levels of the blood urea nitrogen (BUN), creatinine, cystatin C (CysC), kidney injury molecule-1 (KIM-1), neutrophil gelatinase-associated lipocalin (NGAL), and interleukin-18 increased. On histopathological examination of renal tissue in the I/R group, the formation of glomerular and tubular damage was seen, and it was detected that there was an increase in the levels of malondialdehyde (MDA), caspase-3, total oxidant status (TOS), and oxidative stress index (OSI); and there was a decrease in total antioxidant capacity (TAC) and catalase enzyme activity. ACA administration reduced serum levels of BUN, creatinine, CysC, KIM-1, NGAL, interleukin-18. In the renal tissue, ACA administration reduced histopathological damage, levels of caspase-3, MDA, TOS, and OSI; and it increased the level of TAC and catalase enzyme activity. It has been shown with the histological and biochemical results in this study that ACA is protective against renal IRI.

Protective effect of quinacrine against glycerol-induced acute kidney injury in rats

BACKGROUND

Acute kidney injury (AKI) is a serious clinical problem with high rate of mortality and morbidity. Currently used prophylactic and therapeutic strategies to address AKI are limited and warrant further studies. In the present study an attempt was made to investigate the effect of quinacrine, a phospholipase A2 inhibitor against glycerol induced AKI in rats.

METHODS

Adult female Wistar rats were divided in to five groups. After 24 h of water deprivation rats in groups 3, 4 and 5 received an intraperitoneal injection of quinacrine (3 mg/kg, 10 mg/kg and 30 mg/kg of body weight respectively). Thirty minutes after the first injection of quinacrine animals in groups 3, 4 and 5 received an intramuscular injection of 25% glycerol (10 ml/kg of body weight). The animals in group 2 received 25% glycerol (10 ml/kg of body weight) only whereas rats in group 1 served as control . The quinacrine administration was continued once daily for three days, on the fourth day animals were sacrificed, blood and kidney were collected for various biochemical and histopathological studies.

RESULTS

Glycerol treatment produced significant renal structural abnormalities and functional impairment (increased urea and creatinine). Increase in myeloperoxidase (MPO) and malondialdehyde (MDA) clearly suggested the involvement of oxidative stress and neutrophilic activity following glycerol administration. Quinacrine dose dependently attenuated glycerol induced structural and functional changes in kidney.

CONCLUSION

The reversal of glycerol induced AKI by quinacrine points towards a role of phospholipase A2 (PLA2) in the pathogenesis of renal injury. The result of this study suggests that quinacrine may offer an alternative mode of treatment for AKI.

Once initiated, how does toxic tissue injury expand?

Once initiated, how tissue injury expands after high toxicant doses, even after their complete elimination, is not understood. Free-radical generation was initially proposed to mediate progression of injury. However, mechanisms proposed thus far have remained unsubstantiated. Necrotic injury is characterized by loss of osmoregulation, cell swelling, blebbing, and cell rupture. This exposes cytosolic enzymes, including proteases, phospholipases, and lysosomal Ca(2+)-dependent enzymes, to high extracellular calcium (Ca(2+)). Activated hydrolytic enzymes, termed 'death proteins,' hydrolyze their substrates in the plasma membrane of neighboring cells, commencing self-perpetuated injury progression. Likewise, ischemia-reperfusion injury exposes the hydrolytic enzymes to high Ca(2+), fuelling the progression of tissue injury. This mechanism is independent of the offending toxicant that initiates the injury. I present here a case for therapeutic intervention with inhibitors directed against death proteins as a means to avert organ failure and death well after the poisoning event.

Toll-like receptors in ischemia-reperfusion injury

Ischemia-reperfusion (I/R) injuries are implicated in a large array of pathological conditions such as myocardial infarction, cerebral stroke, and hepatic, renal, and intestinal ischemia, as well as following cardiovascular and transplant surgeries. The hallmark of these pathologies is excessive inflammation. Toll-like receptors (TLRs) are recognized as one of the main contributors to pathogen-induced inflammation and, more recently, injury-induced inflammation. Endogenous ligands such as low-molecular hyaluronic acid, fibronectin, heat shock protein 70, and heparin sulfate were all found to be cleaved in the inflamed tissue and to activate TLR2 and TLR4, initiating an inflammatory response even in the absence of pathogens and infiltrating immune cells. In this review, we discuss the contribution of TLR activation in hepatic, renal, cerebral, intestinal, and myocardial I/R injuries. A greater understanding of the role of TLRs in I/R injuries may aid in the development of specific TLR-targeted therapeutics to treat these conditions.

Secretory phospholipase A(2) in newborn infants with sepsis

OBJECTIVE

To investigate secretory phospholipase A(2) (sPLA(2)) activity in neonatal sepsis.

STUDY DESIGN

Plasma sPLA(2) activity, C-reactive protein (CRP) concentration, leukocyte count and immature/total neutrophil (I/T) ratio were assessed in a group of 156 infants admitted for neonatal intensive care, who were classified as documented sepsis (n=24), suspected infection (n=77) and controls (n=55). Interleukin-6 (IL-6) concentrations were assessed in a subgroup (n=29).

RESULT

sPLA(2) activity, CRP concentration and I/T ratio were higher in sepsis than in suspected infection or control groups. sPLA(2) activity advanced with increasing CRP, I/T ratio and IL-6 was highest in infants with respiratory distress syndrome (RDS). Compared to CRP, sPLA(2) had equal sensitivity and lower specificity. Compared to I/T ratio, sensitivity and specificity of sPLA(2) were higher.

CONCLUSION

Plasma sPLA(2) activity is increased in neonatal sepsis and highest in infants with RDS. Further studies should assess the potential of sPLA(2) inhibition in neonatal sepsis.

Bradykinin enhances reactive oxygen species generation, mitochondrial injury, and cell death induced by ATP depletion--a role of the phospholipase C-Ca(2+) pathway

This study aimed to study the effect of bradykinin on reactive oxygen species (ROS) generation, mitochondrial injury, and cell death induced by ATP depletion in cell culture. Renal tubular cells were subjected to ATP depletion. Cell death was evaluated with LDH release, sub-G0/G1 fraction, Hoechst staining, and annexin V binding assay. ROS generation, mitochondrial membrane potential (DeltaPsi(m)), and intramitochondrial calcium were evaluated with flow cytometry. Translocation of cytochrome c and activation of apoptotic protein were analyzed with cell fractionating and Western blotting. Intracellular calcium was measured with a spectrofluorometer. Bradykinin enhanced cellular LDH release, apoptosis, generation of superoxide, and hydrogen peroxide induced by ATP depletion. Bradykinin also enhanced the loss of DeltaPsi(m), translocation of cytochrome c into cytosol, and activation of apoptotic protein. The intracellular/mitochondrial calcium was higher in bradykinin-treated cells. All these effects were reversed by coadministration with bradykinin B2 receptor (B2R) antagonist. Besides, blocking the phospholipase C (PLC) could reverse the synergistic effect of bradykinin with ATP depletion on ROS generation, mitochondrial damage, accumulation of intracellular/mitochondrial calcium, and apoptosis. Activation of B2R aggravates ROS generation, mitochondrial damage, and cell death induced by ATP depletion. These effects may act through the PLC-Ca(2+) signaling pathway.

Group X secretory phospholipase A2 can induce arachidonic acid release and eicosanoid production without activation of cytosolic phospholipase A2 alpha

Group X secretory phospholipase A2 (sPLA2-X) and cytosolic phospholipase A2 alpha (cPLA2alpha) are involved in the release of arachidonic acid (AA) from membrane phospholipids linked to the eicosanoid production in various pathological states. Recent studies have indicated the presence of various types of cross-talk between sPLA2s and cPLA2alpha resulting in effective AA release. Here we examined the dependence of sPLA2-X-induced potent AA release on the cPLA2alpha activation by using specific cPLA2alpha or sPLA2 inhibitors as well as cPLA2alpha-deficient mice. We found that Pyrrophenone, a cPLA2alpha-specific inhibitor, did not suppress the sPLA2-X-induced potent AA release and prostaglandin E2 formation in mouse spleen cells. Furthermore, the amount of AA released by sPLA2-X from spleen cells was not significantly altered by cPLA2alpha deficiency. These results suggest that sPLA2-X induces potent AA release without activation of cPLA2a, which might be relevant to eicosanoid production in some pathological states where cPLA2a is not activated.

The role of the complement system in ischemia-reperfusion injury

Ischemia-reperfusion (I/R) injury is a common clinical event with the potential to seriously affect, and sometimes kill, the patient. Interruption of blood supply causes ischemia, which rapidly damages metabolically active tissues. Paradoxically, restoration of blood flow to the ischemic tissues initiates a cascade of pathology that leads to additional cell or tissue injury. I/R is a potent inducer of complement activation that results in the production of a number of inflammatory mediators. The use of specific inhibitors to block complement activation has been shown to prevent local tissue injury after I/R. Clinical and experimental studies in gut, kidney, limb, and liver have shown that I/R results in local activation of the complement system and leads to the production of the complement factors C3a, C5a, and the membrane attack complex. The novel inhibitors of complement products may find wide clinical application because there are no effective drug therapies currently available to treat I/R injuries.

Ceramide-induced enhancement of secretory phospholipase A2 expression via generation of reactive oxygen species in tumor necrosis factor-α-stimulated mesangial cells

Since prostanoids such as prostaglandin E2 play a pivotal role in modulating renal function, we investigated the involvement of ceramide in expression of secretory phospholipase A2 (sPLA2) and cyclooxygenase-2 (COX-2) in tumor necrosis factor-alpha (TNF-alpha)-stimulated mesangial cells. TNF-alpha stimulation increased ceramide generation in parallel with a decrease in sphingomyelin. Pretreatment with exogenous sphingomyelinase (SMase) dose-dependently enhanced TNF-alpha-stimulated increases in COX-2 protein and sPLA) activity. SMase also augmented TNF-alpha-mediated nuclear factor kappaB (NF-kappaB) activation. N-acetylcysteine (NAC), an antioxidant, completely inhibited the SMase-induced increase in sPLA2 activity, whereas NAC inhibited partially the activity stimulated with TNF-alpha alone. Under the conditions, NAC completely inhibited reactive oxygen species (ROS) production induced by SMase followed by TNF-alpha. These results suggest that ceramide elicits up-regulation of NF-kappaB through ROS production, which, in turn, leads to stimulation of COX-2 and sPLA2 expression. Therefore, ceramide may be implicated in the pathogenesis of renal abnormalities.

Induction of distinct sets of secretory phospholipase A(2) in rodents during inflammation

Although the expression of the prototypic secretory phospholipase A(2) (sPLA(2)), group IIA (sPLA(2)-IIA), is known to be up-regulated during inflammation, it remains uncertain if other sPLA(2) enzymes display similar or distinct profiles of induction under pathological conditions. In this study, we investigated the expression of several sPLA(2)s in rodent inflammation models. In lipopolysaccharide (LPS)-treated mice, the expression of sPLA(2)-V, and to a lesser extent that of sPLA(2)-IID, -IIE, and -IIF, were increased, whereas that of sPLA(2)-X was rather constant, in distinct tissues. 12-O-Tetradecanoylphorbol-13-acetate (TPA)-induced mouse ear edema, in which the expression of sPLA(2)-IID, -IIF and -V was increased, was significantly reduced by YM-26734, a competitive sPLA(2)-IIA inhibitor that turned out to inhibit sPLA(2)-IID, -IIE, -V and -X as well. In contrast, sPLA(2)-IIA was dominant in carageenin-induced pleurisy in rats, where the accumulation of exudate fluids and leukocytes was significantly ameliorated by YM-26734. These results indicate that distinct sPLA(2)s can participate in inflammatory diseases according to tissues, animal species, and types of inflammation.

Secretory Phospholipase A2

Secretory phospholipase A2 (sPLA2) is a growing family of structurally related, disulfide-rich, low molecular weight, lipolytic enzymes with a His-Asp catalytic dyad. sPLA2s are distributed in a wide variety of vertebrate and invertebrate animals, plants, bacteria, and viruses, and there are 10 catalytically active sPLA2 isozymes in mammals. Although the structural bases for mammalian sPLA2s have been well documented, their physiological functions are still subject to debate. Individual mammalian sPLA2s have distinct enzymatic properties and display distinct tissue expression patterns, suggesting that each enzyme acts on distinct phospholipid membrane moieties in vivo. In this article, we briefly review our latest understanding of the possible physiological functions of sPLA2s, in keeping with their diverse actions on mammalian and nonmammalian cell membranes.

A small molecule C5a receptor antagonist protects kidneys from ischemia/reperfusion injury in rats

BACKGROUND

C5a has been implicated in numerous pathophysiological conditions, including ischemia/reperfusion (I/R) injury of the kidney. We examined whether a novel and specific C5a receptor antagonist, the cyclic compound AcF-[OPdChaWR] could moderate I/R-induced renal injury in rats.

METHODS

Female Wistar rats were subjected to renal ischemia (60 min) and reperfusion (5 h). Rats were treated with either 1 mg/kg IV in 5% ethanol/saline or 10 mg/kg PO in 25% ethanol/saline prior to ischemia. I/R injury was characterized by significant tissue hemorrhage with increased microvascular permeability, elevated renal tissue levels of tumor necrosis factor-alpha (TNF-alpha) and myeloperoxidase (MPO), increased serum levels of creatinine and aspartate aminotransferase (AST) and hematuria.

RESULTS

Pre-ischemic treatment with the C5a receptor (C5aR) antagonist (1 mg/kg IV or 10 mg/kg PO) substantially inhibited or prevented I/R-induced hematuria, vascular leakage, tissue levels of TNF-alpha and MPO, and serum levels of AST and creatinine. Histological examination of kidneys from antagonist pretreated I/R animals showed a marked reduction in tissue damage compared to drug-free I/R rats. This antagonist, however, did not inhibit complement-mediated lysis of red blood cells, suggesting unimpaired formation of the membrane attack complex (MAC).

CONCLUSIONS

The results demonstrate for the first time that a selective antagonist of both human and rat C5a receptors, given either intravenously or orally, significantly protects the kidney from I/R injury in the rat. We conclude that C5a is an important pathogenic agent in renal I/R injury, and that C5a receptor antagonists may be useful therapeutic agents for the pretreatment of anticipated renal reperfusion injury in humans.

Phospholipase A2 enzymes

Phospholipase A2 (PLA2) catalyzes the hydrolysis of the sn-2 position of membrane glycerophospholipids to liberate arachidonic acid (AA), a precursor of eicosanoids including prostaglandins and leukotrienes. The same reaction also produces lysophosholipids, which represent another class of lipid mediators. So far, at least 19 enzymes that possess PLA2 activity have been identified and cloned in mammals. The secretory PLA2 (sPLA2) family, in which 10 isozymes have been identified, consists of low-molecular weight, Ca2+-requiring secretory enzymes that have been implicated in a number of biological processes, such as modification of eicosanoid generation, inflammation, and host defense. The cytosolic PLA2 (cPLA2) family consists of three enzymes, among which cPLA2alpha has been paid much attention by researchers as an essential component of the initiation of AA metabolism. The activation of cPLA2alpha is tightly regulated by Ca2+ and phosphorylation. The Ca2+-independent PLA2 (iPLA2) family contains two enzymes and may play a major role in phospholipid remodeling. The platelet-activating factor (PAF) acetylhydrolase (PAF-AH) family contains four enzymes that exhibit unique substrate specificity toward PAF and/or oxidized phospholipids. Degradation of these bioactive phospholipids by PAF-AHs may lead to the termination of inflammatory reaction and atherosclerosis.

ATTENUATION OF ISCHEMIA AND REPERFUSION INJURY OF CANINE LIVERS BY INHIBITION OF TYPE II PHOSPHOLIPASE A2 WITH LY3297221

BACKGROUND

Membrane phospholipid breakdown, caused by ischemia and reperfusion (I/R) of the liver, releases free fatty acids including arachidonic acids and lysophospholipids, which serve as precursors of various inflammatory lipid derivatives. Phospholipase A2 (PLA2) is a key enzyme that initiates this reaction. In this study, we tested our hypothesis that a type II PLA2 inhibitor, LY329722, could attenuate hepatic I/R injury caused by a 2-hr total hepatic vascular exclusion (THVE) in dogs.

METHODS

Eighteen beagle dogs, subjected to a 2-hr THVE, were divided into three groups. Group 1 (n=6) was untreated and served as a control group. LY329722 was administered to animals in group 2 (n=6) intravenously (0.2 mg x kg(-1) x hr(-1)) for 60 min before ischemia, and to animals in group 3 (n=6) for 60 min starting 15 min before reperfusion (0.2 mg x kg(-1) x hr(-1)). Animal survival, systemic and splanchnic hemodynamics, hepatic tissue blood flow, liver functions, energy metabolism, hepatic venous thromboxane B2 and endothelin-1 levels, phospholipid levels and tumor necrosis factor-a mRNA expression in liver tissue, and histopathologic findings were evaluated.

RESULTS

Two-week animal survival was 33% (two of six) in group 1, and 100% (six of six) in groups 2 and 3. LY329722 improved systemic and splanchnic hemodynamics, hepatic tissue blood flow, and energy metabolism, reduced liver enzyme, thromboxane B2, and endothelin-1 release, prevented hepatic phospholipid degradation and tumor necrosis factor-alpha mRNA expression, and lessened histopathologic damage and the number of neutrophil infiltrating into the liver tissue.

CONCLUSION

The present study demonstrated that a type II PLA2 inhibitor, LY329722, attenuated hepatic I/R injury caused by a 2-hr THVE model in dogs.

Functional association of type IIA secretory phospholipase A(2) with the glycosylphosphatidylinositol-anchored heparan sulfate proteoglycan in the cyclooxygenase-2-mediated delayed prostanoid-biosynthetic pathway

An emerging body of evidence suggests that type IIA secretory phospholipase A(2) (sPLA(2)-IIA) participates in the amplification of the stimulus-induced cyclooxygenase (COX)-2-dependent delayed prostaglandin (PG)-biosynthetic response in several cell types. However, the biological importance of the ability of sPLA(2)-IIA to bind to heparan sulfate proteoglycan (HSPG) on cell surfaces has remained controversial. Here we show that glypican, a glycosylphosphatidylinositol (GPI)-anchored HSPG, acts as a physical and functional adaptor for sPLA(2)-IIA. sPLA(2)-IIA-dependent PGE(2) generation by interleukin-1-stimulated cells was markedly attenuated by treatment of the cells with heparin, heparinase or GPI-specific phospholipase C, which solubilized the cell surface-associated sPLA(2)-IIA. Overexpression of glypican-1 increased the association of sPLA(2)-IIA with the cell membrane, and glypican-1 was coimmunoprecipitated by the antibody against sPLA(2)-IIA. Glypican-1 overexpression led to marked augmentation of sPLA(2)-IIA-mediated arachidonic acid release, PGE(2) generation, and COX-2 induction in interleukin-1-stimulated cells, particularly when the sPLA(2)-IIA expression level was suboptimal. Immunofluorescent microscopic analyses of cytokine-stimulated cells revealed that sPLA(2)-IIA was present in the caveolae, a microdomain in which GPI-anchored proteins reside, and also appeared in the perinuclear area in proximity to COX-2. We therefore propose that a GPI-anchored HSPG glypican facilitates the trafficking of sPLA(2)-IIA into particular subcellular compartments, and arachidonic acid thus released from the compartments may link efficiently to the downstream COX-2-mediated PG biosynthesis.

Regulation of type V phospholipase A2 expression and function by proinflammatory stimuli

Types IIA and V secretory phospholipase A2 (sPLA2) are structurally related to each other and their genes are tightly linked to the same chromosome locus. An emerging body of evidence suggests that sPLA2-IIA plays an augmentative role in long-term prostaglandin (PG) generation in cells activated by proinflammatory stimuli; however, the mechanism underlying the functional regulation of sPLA2-V remains largely unknown. Here we show that sPLA2-V is more widely expressed than sPLA2-IIA in the mouse, in which its expression is elevated by proinflammatory stimuli such as lipopolysaccharide. In contrast, proinflammatory stimuli induced sPLA2-IIA in marked preference to sPLA2-V in the rat. Cotransfection of sPLA2-V with cyclooxygenase (COX)-2, but not with COX-1, into human embryonic kidney 293 cells dramatically increased the interleukin-1-dependent PGE2 generation occurring over a 24 h of culture period. Rat mastocytoma RBL-2H3 cells overexpressing sPLA2-V exhibited increased IgE-dependent PGD2 generation and accelerated beta-hexosaminidase exocytosis. These results suggest that sPLA2-V acts as a regulator of inflammation-associated cellular responses. This possible compensation of sPLA2-V for sPLA2-IIA in many, if not all, tissues may also explain why some mouse strains with natural disruption of the sPLA2-IIA gene exhibit few abnormalities during their life-spans.