Stimulation of different phospholipase A2 isoforms by TNF-alpha and IL-1beta in adult rat ventricular myocytes

Re-Evaluating Biologic Pharmacotherapies that Target the Host Response during Sepsis

Multiple organ dysfunction syndrome (MODS) caused by the systemic inflammatory response during sepsis is responsible for millions of deaths worldwide each year, and despite broad consensus concerning its pathophysiology, no specific or effective therapies exist. Recent efforts to treat and/or prevent MODS have included a variety of biologics, recombinant proteins targeting various components of the host response to the infection (e.g., inflammation, coagulation, etc.) Improvements in molecular biology and pharmaceutical engineering have enabled a wide range of utility for biologics to target various aspects of the systemic inflammatory response. The majority of clinical trials to date have failed to show clinical benefit, but some have demonstrated promising results in certain patient populations. In this review we summarize the underlying rationale and outcome of major clinical trials where biologics have been tested as a pharmacotherapy for MODS in sepsis. A brief description of the study design and overall outcome for each of the major trials are presented. Emphasis is placed on discussing targets and/or trials where promising results were observed. Post hoc analyses of trials where therapy demonstrated harm or additional risk to certain patient subgroups are highlighted, and details are provided about specific trials where more stringent inclusion/exclusion criteria are warranted.

Gender-Dependent Alteration of Ca2+ and TNFα Signaling in db/db Mice, an Obesity-Linked Type 2 Diabetic Model

Cardiovascular complications are the primary death cause in type 2 diabetes, where inflammation can play a role. We, and others, have previously shown that, in diabetic cardiomyopathy, cardiac dysfunction is associated with Ca²⁺ mishandling. It is possible that diabetic cardiomyopathy differently affects men and women, as the latter present higher risk to develop heart failure and a higher plasmatic level of the pro-inflammatory cytokine, tumor necrosis factor alpha (TNFα), than men. However, the gender-dependent regulation of Ca²⁺ signaling in diabetes and its relationship with TNFα signaling are still unclear. Here, we analyzed TNFα signaling pathway and its role in Ca²⁺ signaling dysfunction in male and female rodent models of type 2 diabetes linked to obesity (db/db mice) using confocal microscopy in freshly isolated cardiomyocytes. TNFα increased [Ca²⁺]_i transient amplitude and accelerated its decay without affecting SR Ca²⁺ load or Ca²⁺ spark frequency in cells from control mice. All TNFα effects on Ca²⁺ handling were prevented by the inhibition of the ceramidase and the phospholipase A2 (PLA2). While the plasmatic level of TNFα was similar in male and female db/db mice, only male db/db hearts over-expressed both TNFα converting enzyme (TACE) and the protective TNFα receptors 2 (TNF-R2). TNFα receptor 1 (TNF-R1) expression, involved in negative inotropic response of TNFα, was unchanged in both male and female db/db mice compared to controls. We found that male db/db mice cardiomyocytes presented a decrease in [Ca²⁺]_i transient amplitude associated to a drop of sarcoplasmic reticulum Ca²⁺ load, not seen in female db/db mice. Interestingly, sustained incubation with TNFα did not restored Ca²⁺ signaling alteration observed in male db/db mice but still induces an increase in Ca²⁺ spark frequency as seen in control littermates. In cardiomyocytes from female db/db mice, TNFα had no visible effects on Ca²⁺ handling. In conclusion, our study shows that the alteration of Ca²⁺ signaling and TNFα, seen in db/db mice, is gender specific presenting an increase in TNFα cardio-protective pathway in male mice.

Tumor Necrosis Factor-α in Heart Failure: an Updated Review

PURPOSE OF THE REVIEW

Proinflammatory cytokines are consistently elevated in congestive heart failure. In the current review, we provide an overview on the current understanding of how tumor necrosis factor-α (TNFα), a key proinflammatory cytokine, potentiates heart failure by overwhelming the anti-inflammatory responses disrupting the homeostasis.

RECENT FINDINGS

Studies have shown co-relationship between severity of heart failure and levels of the proinflammatory cytokine TNFα and one of its secondary mediators interleukin-6 (IL-6), suggesting their potential as biomarkers. Recent efforts have focused on understanding the mechanisms of how proinflammatory cytokines contribute towards cardiac dysfunction and failure. In addition, how unchecked proinflammatory cytokines and their cross-talk with sympathetic system overrides the anti-inflammatory response underlying failure. The review offers insights on how TNFα and IL-6 contribute to cardiac dysfunction and failure. Furthermore, this provides a forum to begin the discussion on the cross-talk between sympathetic drive and proinflammatory cytokines and its determinant role in deleterious outcomes.

Proinflammatory Cytokines Mediate GPCR Dysfunction

Proinflammatory reaction by the body occurs acutely in response to injury that is considered primarily beneficial. However, sustained proinflammatory cytokines observed with chronic pathologies such as metabolic syndrome, cancer, and arthritis are detrimental and in many cases is a major cardiovascular risk factor. Proinflammatory cytokines such as interleukin-1, interleukin-6, and tumor necrosis factor α (TNFα) have long been implicated in cardiovascular risk and considered to be a major underlying cause for heart failure (HF). The failure of the anti-TNFα therapy for HF indicates our elusive understanding on the dichotomous role of proinflammatory cytokines on acutely beneficial effects versus long-term deleterious effects. Despite these well-described observations, less is known about the mechanistic underpinnings of proinflammatory cytokines especially TNFα in pathogenesis of HF. Increasing evidence suggests the existence of an active cross-talk between the TNFα receptor signaling and G-protein-coupled receptors such as β-adrenergic receptor (βAR). Given that βARs are the key regulators of cardiac function, the review will discuss the current state of understanding on the role of proinflammatory cytokine TNFα in regulating βAR function.

Discriminant biomarkers of acute respiratory distress syndrome associated to H1N1 influenza identified by metabolomics HPLC-QTOF-MS/MS platform

Acute respiratory distress syndrome (ARDS) is a serious complication of influenza A (H1N1) virus infection. Its pathogenesis is unknown and biomarkers are lacking. Untargeted metabolomics allows the analysis of the whole metabolome in a biological compartment, identifying patterns associated with specific conditions. We hypothesized that LC-MS could help identify discriminant metabolites able to define the metabolic alterations occurring in patients with influenza A (H1N1) virus infection that developed ARDS. Serum samples from patients diagnosed with 2009 influenza A (H1N1) virus infection with (n = 25) or without (n = 32) ARDS were obtained on the day of hospital admission and analyzed by LC-MS/MS. Metabolite identification was determined by MS/MS analysis and analysis of standards. The specificity of the patterns identified was confirmed in patients without 2009 influenza A(H1N1) virus pneumonia (15 without and 17 with ARDS). Twenty-three candidate biomarkers were found to be significantly different between the two groups, including lysophospholipids and sphingolipids related to inflammation; bile acids, tryptophan metabolites, and thyroxine, related to the metabolism of the gut microflora. Confirmation results demonstrated the specificity of major alterations occurring in ARDS patients with influenza A (H1N1) virus infection.

Diabetic macular edema, retinopathy and age-related macular degeneration as inflammatory conditions

Diabetic macular edema (DME) and diabetic retinopathy (DR) are complications affecting about 25% of all patients with long-standing type 1 and type 2 diabetes mellitus and are a major cause of significant decrease in vision and quality of life. Age-related macular degeneration (AMD) is not uncommon, and diabetes mellitus affects the incidence and progression of AMD through altering hemodynamics, increasing oxidative stress, accumulating advanced glycation end products, etc. Recent studies suggest that DME, DR and AMD are inflammatory conditions characterized by a breakdown of the blood-retinal barrier, inflammatory processes and an increase in vascular permeability. Key factors that seem to have a dominant role in DME, DR and AMD are angiotensin II, prostaglandins and the vascular endothelial growth factor and a deficiency of anti-inflammatory bioactive lipids. The imbalance between pro- and anti-inflammatory eicosanoids and enhanced production of pro-angiogenic factors may initiate the onset and progression of DME, DR and AMD. This implies that bioactive lipids that possess anti-inflammatory actions and suppress the production of angiogenic factors could be employed in the prevention and management of DME, DR and AMD.

Mouse Strain Impacts Fatty Acid Uptake and Trafficking in Liver, Heart, and Brain: A Comparison of C57BL/6 and Swiss Webster Mice

C57BL/6 and Swiss Webster mice are used to study lipid metabolism, although differences in fatty acid uptake between these strains have not been reported. Using a steady state kinetic model, [1-(14)C]16:0, [1-(14)C]20:4n-6, or [1-(14)C]22:6n-3 was infused into awake, adult male mice and uptake into liver, heart, and brain determined. The integrated area of [1-(14)C]20:4n-6 in plasma was significantly increased in C57BL/6 mice, but [1-(14)C]16:0 and [1-(14)C]22:6n-3 were not different between groups. In heart, uptake of [1-(14)C]20:4n-6 was increased 1.7-fold in C57BL/6 mice. However, trafficking of [1-(14)C]22:6n-3 into the organic fraction of heart was significantly decreased 33 % in C57BL/6 mice. Although there were limited differences in fatty acid tracer trafficking in liver or brain, [1-(14)C]16:0 incorporation into liver neutral lipids was decreased 18 % in C57BL/6 mice. In heart, the amount of [1-(14)C]16:0 and [1-(14)C]22:6n-3 incorporated into total phospholipids were decreased 45 and 49 %, respectively, in C57BL/6 mice. This was accounted for by a 53 and 37 % decrease in [1-(14)C]16:0 and 44 and 52 % decrease in [1-(14)C]22:6n-3 entering ethanolamine glycerophospholipids and choline glycerophospholipids, respectively. In contrast, there was a significant increase in [1-(14)C]20:4n-6 esterification into all heart phospholipids of C57BL/6 mice. Although changes in uptake were limited to heart, several significant differences were found in fatty acid trafficking into heart, liver, and brain phospholipids. In summary, our data demonstrates differences in tissue fatty acid uptake and trafficking between mouse strains is an important consideration when carrying out fatty acid metabolic studies.

Putative binding sites for arachidonic acid on the human cardiac Kv 1.5 channel

BACKGROUND AND PURPOSE

In human heart, the Kv 1.5 channel contributes to repolarization of atrial action potentials. This study examined the electrophysiological and molecular mechanisms underlying arachidonic acid (AA)-induced inhibition of the human Kv 1.5 (hKv 1.5) channel.

EXPERIMENTAL APPROACH

Site-directed mutagenesis was conducted to mutate amino acids that reside within the pore domain of the hKv 1.5 channel. Whole-cell patch-clamp method was used to record membrane currents through wild type and mutant hKv 1.5 channels heterologously expressed in CHO cells. Computer docking simulation was conducted to predict the putative binding site(s) of AA in an open-state model of the Kv 1.5 channel.

KEY RESULTS

The hKv 1.5 current was minimally affected at the onset of depolarization but was progressively reduced during depolarization by the presence of AA, suggesting that AA acts as an open-channel blocker. AA itself affected the channel at extracellular sites independently of its metabolites and signalling pathways. The blocking effect of AA was attenuated at pH 8.0 but not at pH 6.4. The blocking action of AA developed rather rapidly by co-expression of Kv β1.3. The AA-induced block was significantly attenuated in H463C, T480A, R487V, I502A, I508A, V512A and V516A, but not in T462C, A501V and L510A mutants of the hKv 1.5 channel. Docking simulation predicted that H463, T480, R487, I508, V512 and V516 are potentially accessible for interaction with AA.

CONCLUSIONS AND IMPLICATIONS

AA itself interacts with multiple amino acids located in the pore domain of the hKv 1.5 channel. These findings may provide useful information for future development of selective blockers of hKv 1.5 channels.

Potential role of polyunsaturated fatty acids in diabetic retinopathy

Diabetic retinopathy (DR) is a serious complication of long-standing diabetes mellitus. It affects about 25% of all patients with diabetes mellitus and causes a significant decrease in the quality of life. Despite many years of research, the exact pathway that leads to the development and progression of DR is not clear. Recent studies suggest that polyunsaturated fatty acids (PUFAs) and their metabolites could play a significant role in DR. There is evidence to suggest that an imbalance between pro- and anti-inflammatory eicosanoids and enhanced production of pro-angiogenic factors may initiate the onset and progression of DR. This implies that PUFAs and their metabolites that possess anti-inflammatory actions and suppress the production of angiogenic factors could be employed in the prevention and management of DR.

The tumour suppressor Ras-association domain family protein 1A (RASSF1A) regulates TNF-α signalling in cardiomyocytes

Aims

Tumour necrosis factor-α (TNF-α) plays a key role in the regulation of cardiac contractility. Although cardiomyocytes are known to express the TNF-α receptors (TNFRs), the mechanism of TNF-α signal transmission is incompletely understood. The aim of this study was to investigate whether the tumour suppressor Ras-association domain family protein 1 isoform A (RASSF1A) modulates TNF-α signalling in cardiomyocytes.

Methods and results

We used RASSF1A knockout (RASSF1A^−/−) mice and wild-type (WT) littermates in this study. Acute stimulation with a low dose of TNF-α (10 µg/kg iv) increased cardiac contractility and intracellular calcium transients' amplitude in WT mice. In contrast, RASSF1A^−/− mice showed a blunted contractile response. Mechanistically, RASSF1A was essential in the formation of the TNFR complex (TNFRC), where it functions as an adaptor molecule to facilitate the recruitment of TNFR type 1-associated death domain protein and TNFR-associated factor 2 to form the TNF-α receptor complex. In the absence of RASSF1A, signal transmission from the TNF-α receptor complex to the downstream effectors, such as cytoplasmic phospholipase A2 and protein kinase A, was attenuated leading to the reduction in the activation of calcium handling molecules, such as L-type Ca²⁺ channel and ryanodine receptors.

Conclusion

Our data indicate an essential role of RASSF1A in regulating TNF-α signalling in cardiomyocytes, with RASSF1A being key in the formation of the TNFRC and in signal transmission to the downstream targets.

Smooth muscle-specific expression of calcium-independent phospholipase A2β (iPLA2β) participates in the initiation and early progression of vascular inflammation and neointima formation

Whether group VIA phospholipase A(2) (iPLA(2)β) is involved in vascular inflammation and neointima formation is largely unknown. Here, we report that iPLA(2)β expression increases in the vascular tunica media upon carotid artery ligation and that neointima formation is suppressed by genetic deletion of iPLA(2)β or by inhibiting its activity or expression via perivascular delivery of bromoenol lactone or of antisense oligonucleotides, respectively. To investigate whether smooth muscle-specific iPLA(2)β is involved in neointima formation, we generated transgenic mice in which iPLA(2)β is expressed specifically in smooth muscle cells and demonstrate that smooth muscle-specific expression of iPLA(2)β exacerbates ligation-induced neointima formation and enhanced both production of proinflammatory cytokines and vascular infiltration by macrophages. With cultured vascular smooth muscle cell, angiotensin II, arachidonic acid, and TNF-α markedly induce increased expression of IL-6 and TNF-α mRNAs, all of which were suppressed by inhibiting iPLA(2)β activity or expression with bromoenol lactone, antisense oligonucleotides, and genetic deletion, respectively. Similar suppression also results from genetic deletion of 12/15-lipoxygenase or inhibiting its activity with nordihydroguaiaretic acid or luteolin. Expression of iPLA(2)β protein in cultured vascular smooth muscle cells was found to depend on the phenotypic state and to rise upon incubation with TNF-α. Our studies thus illustrate that smooth muscle cell-specific iPLA(2)β participates in the initiation and early progression of vascular inflammation and neointima formation and suggest that iPLA(2)β may represent a novel therapeutic target for preventing cardiovascular diseases.

Curcumin and enalapril ameliorate renal failure by antagonizing inflammation in 5/6 nephrectomized rats: role of phospholipase and cyclooxygenase

Previously, we showed that curcumin prevents chronic kidney disease (CKD) development in ⅚ nephrectomized (Nx) rats when given within 1 wk after Nx (Ghosh SS, Massey HD, Krieg R, Fazelbhoy ZA, Ghosh S, Sica DA, Fakhry I, Gehr TW. Am J Physiol Renal Physiol 296: F1146-F1157, 2009). To better mimic the scenario for renal disease in humans, we began curcumin and enalapril therapy when proteinuria was already established. We hypothesized that curcumin, by blocking the inflammatory mediators TNF-α and IL-1β, could also reduce cyclooxygenase (COX) and phospholipase expression in the kidney. Nx animals were divided into untreated Nx, curcumin-treated, and enalapril-treated groups. Curcumin (75 mg/kg) and enalapril (10 mg/kg) were administered for 10 wk. Renal dysfunction in the Nx group, as evidenced by elevated blood urea nitrogen, plasma creatinine, proteinuria, segmental sclerosis, and tubular dilatation, was comparably reduced by curcumin and enalapril, with only enalapril significantly lowering blood pressure. Compared with controls, Nx animals had higher plasma/kidney TNF-α and IL-1β, which were reduced by curcumin and enalapril treatment. Nx animals had significantly elevated kidney levels of cytosolic PLA(2), calcium-independent intracellular PLA(2), COX 1, and COX 2, which were comparably reduced by curcumin and enalapril. Studies in mesangial cells and macrophages were carried out to establish that the in vivo increase in PLA(2) and COX were mediated by TNF-α and IL-1β and that curcumin, by antagonizing the cytokines, could significantly reduce both PLA(2) and COX. We conclude that curcumin ameliorates CKD by blocking inflammatory signals even if it is given at a later stage of the disease.

Mechanism of acute pancreatitis complicated with injury of intestinal mucosa barrier

Acute pancreatitis (AP) is a common acute abdomen in clinic with a rapid onset and dangerous pathogenetic condition. AP can cause an injury of intestinal mucosa barrier, leading to translocation of bacteria or endotoxin through multiple routes, bacterial translocation (BT), gut-origin endotoxaemia, and secondary infection of pancreatic tissue, and then cause systemic inflammatory response syndrome (SIRS) or multiple organ dysfunction syndrome (MODS), which are important factors influencing AP's severity and mortality. Meanwhile, the injury of intestinal mucosa barrier plays a key role in AP's process. Therefore, it is clinically important to study the relationship between the injury of intestinal mucosa barrier and AP. In addition, many factors such as microcirculation disturbance, ischemic reperfusion injury, excessive release of inflammatory mediators and apoptosis may also play important roles in the damage of intestinal mucosa barrier. In this review, we summarize studies on mechanisms of AP.

Inhibition of L-type Ca2+channel current and negative inotropy induced by arachidonic acid in adult rat ventricular myocytes

We have previously shown an increase in arachidonic acid (AA) release in response to proinflammatory cytokines in adult rat ventricular myocytes (ARVM). AA is known to alter channel activities; however, its effects on cardiac L-type Ca2+channel current ( ICa,L) and excitation-contraction coupling remain unclear. The present study examined effects of AA on ICa,L, using the whole cell patch-clamp technique, and on cell shortening (CS) and the Ca2+transient of ARVM. ICa,Lwas monitored in myocytes held at −70 mV and internally equilibrated and externally perfused with Na+- and K+-free solutions. Exposure to AA caused a voltage-dependent block of ICa,Lconcentration dependently (IC508.5 μM). The AA-induced inhibition of ICa,Lis consistent with its hyperpolarizing shift in the voltage-dependent properties and reduction in maximum slope conductance. In the presence of AA, BSA completely blocked the AA-induced suppression of ICa,Land CS. Intracellular load with AA had no effect on the current density but caused a small depolarizing shift in the ICa,Lactivation curve, suggesting a site-specific action of AA. Moreover, intracellular AA had no effect on the extracellular AA-induced decrease in ICa,L. Pretreatment with indomethacin, an inhibitor of cyclooxygenase, or addition of nordihydroguaiaretic acid, an inhibitor of lipoxygenase, had no effect on AA-induced changes in ICa,L. Furthermore, AA suppressed CS and Ca2+transients of intact ARVM with no significant effect on SR function and myofilament Ca2+sensitivity. Therefore, these results suggest that AA inhibits contractile function of ARVM, primarily due to its direct inhibition of ICa,Lat an extracellular site.

Legionella pneumophila-induced PKCα-, MAPK-, and NF-κB-dependent COX-2 expression in human lung epithelium

Legionella pneumophila causes community- and hospital-acquired pneumonia. Lung airway and alveolar epithelial cells comprise an important barrier against airborne pathogens. Cyclooxygenase (COX) and microsomal PGE2synthase-1 (mPGES-1)-derived prostaglandins like prostaglandin E2(PGE2) are considered as important regulators of lung function. Herein we tested the hypothesis that L. pneumophila induced COX-2 and mPGES-1-dependent PGE2production in pulmonary epithelial cells. Legionella induced the release of PGE2in primary human small airway epithelial cells and A549 cells. This was accompanied by an increased expression of COX-2 and mPGES-1 as well as an increased PLA2activity in infected cells. Deletion of the type IV secretion system Dot/Icm did not impair Legionella-related COX-2 expression or PGE2release in A549 cells. L. pneumophila induced the degradation of IκBα and activated NF-κB. Inhibition of IKK blocked L. pneumophila-induced PGE2release and COX-2 expression. We noted activation of p38 and p42/44 MAP kinase in Legionella-infected A549 cells. Moreover, membrane translocation and activation of PKCα was observed in infected cells. PKCα and p38 and p42/44 MAP kinase inhibitors reduced PGE2release and COX-2 expression. In summary, PKCα and p38 and p42/44 MAP kinase controlled COX-2 expression and subsequent PGE2release by Legionella-infected lung epithelial cells. These pathways may significantly contribute to the host response in Legionnaires' disease.

Activation of MAPKs in thrombin-stimulated ventricular myocytes is dependent on Ca2+-independent PLA2

Thrombin stimulation of isolated rabbit ventricular myocytes activates a membrane-associated, Ca2+-independent PLA2(iPLA2) that selectively hydrolyzes plasmalogen phospholipids and results in increased production of arachidonic acid and lysoplasmenylcholine. To determine whether MAPK regulates myocardial iPLA2activity, we isolated ventricular myocytes from rabbit heart by collagenase digestion and pretreated them with MAPK inhibitors before stimulating them with thrombin. Pretreatment with PD-98059 to inhibit p42/44 MAPK or SB-203580 to inhibit p38 MAPK had no significant effect on thrombin-stimulated, membrane-associated iPLA2activity. Thrombin stimulation resulted in significant increases in both p42/44 and p38 MAPK activity after 2 min. Pretreatment with the iPLA2-selective inhibitor bromoenol lactone completely inhibited thrombin-stimulated MAPK activity, suggesting that activation of MAPKs was dependent on iPLA2activation. Ventricular myocyte MAPK activity was increased by incubation of the myocytes with lysoplasmenylcholine, a metabolite produced by iPLA2-catalyzed membrane plasmalogen phospholipid hydrolysis. Altogether, these data suggest that activation of MAPKs occurs downstream of and is dependent on iPLA2activation in thrombin-stimulated rabbit ventricular myocytes.

Inhibition of sarcoplasmic reticular function by chronic interleukin-6 exposure via iNOS in adult ventricular myocytes

Interleukin (IL)-6 has been shown to decrease cardiac contractility via a nitric oxide synthase (NOS)-dependent pathway during acute exposure. We previously reported that IL-6 decreases contractility and increases inducible NOS (iNOS) in adult rat ventricular myocytes (ARVM) after 2 h exposure. The goal of this study was to investigate the cellular mechanism underlying this chronic IL-6-induced negative inotropy and the role of iNOS. Pretreatment for 2 h with 10 ng ml-1 IL-6 decreased the kinetics of cell shortening (CS) and contractile responsiveness to Ca2+o ([Ca2+]o from(0) to 2 mM) in ARVM. We first examined whether IL-6 reduced Ca2+ influx via L-type Ca2+ -channel current (ICa,L). Whole-cell ICa,L in ARVM was measured under conditions similar to those used for CS measurements, and it was found to be unaltered by IL-6. The sarcoplasmic reticular (SR) function was then assessed by examining postrest potentiation (PRP) and caffeine responsiveness of CS. Results showed that treatment with IL-6 for 2 h significantly decreased PRP, which was concomitant with a decrease in the phosphorylation of phospholamban. Following removal of IL-6, PRP and responsiveness to 10 mM caffeine were also reduced. Meanwhile, the IL-6-induced increase in nitric oxide (NO) production after 2 h (but not 1 h) was abolished by NG-monomethyl-l-arginine (l-NMMA) and 2-amino-5,6-dihydro-6-methyl-4H-1,3-thiazine (AMT; a selective inhibitor of iNOS). Furthermore, IL-6-elicited suppressions of PRP and responsiveness to caffeine and Ca2+o were abolished by L-NMMA and AMT. Thus, these results suggest that activation of iNOS mediates IL-6-induced inhibition of SR function in ARVM during chronic exposure.

Interference of arachidonic acid and its metabolites with TNF-α release by ochratoxin A from rat liver

We investigated the role of arachidonic acid and its metabolites on the ochratoxin A (OTA) provoked release of proinflammatory and apoptotic cytokine TNF-alpha from blood-free perfused rat liver. OTA induced TNF-alpha release dose- and time-dependently yielding 2600 pg TNF-alpha/ml at 2.5 micromol/l after 90 min without significant release of LDH and lactate. Aristolochic acid, 50 micromol/l, a phospholipase A2 inhibitor, and 10 micromol/l of exogenous arachidonic acid decreased TNF-alpha below normal level. Indomethacin, 10 micromol/l, a potent inhibitor of the cyclooxygenase (COX) pathway, almost doubled TNF-alpha concentrations in the perfusion solution to reach 5500 pg/ml at 90 min. On the other hand, inhibition of lipoxgenase (LPX) by 30 micromol/l nordihydroguaiaretic acid (NDGA) and the cytochrome P-450 (CYP) pathway by 100 micromol/l of metyrapone decreased TNF-alpha below normal levels as well. Concurrent administration of two blockers (COX inhibitor with LPX inhibitor, or COX inhibitor with CYP-450 inhibitor, or LPX inhibitor with CYP-450 inhibitor) blocked TNF-alpha release below normal levels. In addition, 10 micromol/l caffeic acid phenylethyl ester, a NF-(kappa)B inhibitor, blocked OTA mediated TNF-alpha release. In conclusion, arachidonic acid and its cyclooxygenase metabolites are suppressors of OTA mediated TNF-alpha release from liver, whereas LPX and CYP-450-metabolites have the opposite effect. OTA-induced TNF-alpha release is likely to occur via the NF-(kappa)B transcription factor pathway in perfused rat liver.

Arachidonic acid incorporation and turnover is decreased in sympathetically denervated rat heart

Heart sympathetic denervation can accompany Parkinson's disease, but the effect of this denervation on cardiac lipid-mediated signaling is unknown. To address this issue, rats were sympathetically denervated with 6-hydroxydopamine (6-OHDA, 50 mg/kg ip) and infused with 170 muCi/kg of either [1-(14)C]palmitic acid ([1-(14)C]16:0) or [1-(14)C]arachidonic acid ([1-(14)C]20:4 n-6), and kinetic parameters were assessed using a steady-state radiotracer model. Heart norepinephrine and epinephrine levels were decreased 82 and 85%, respectively, in denervated rats, and this correlated with a 34% reduction in weight gain in treated rats. Fatty acid tracer uptake was not significantly different between groups for either tracer, although the dilution coefficient lambda was increased in [1-(14)C]20:4 n-6-infused rats, which indicates that less 20:4 n-6 was recycled in denervated rats. In [1-(14)C]16:0-infused rats, incorporation rate and turnover values of 16:0 in stable lipid compartments were unchanged, which is indicative of preservation of beta-oxidation. In [1-(14)C]20:4 n-6-infused rats, there were dramatic reductions in incorporation rate (60-84%) and turnover value (56-85%) in denervated rats that were dependent upon the lipid compartment. In addition, phospholipase A(2) activity was reduced 40% in treated rats, which is consistent with the reduction observed in 20:4 n-6 turnover. These results demonstrate marked reductions in 20:4 n-6 incorporation rate and turnover in sympathetic denervated rats and thereby suggest an effect on lipid-mediated signal transduction mediated by a reduction in phospholipase A(2) activity.

Docosahexaenoic acid and arachidonic acid release in rat brain astrocytes is mediated by two separate isoforms of phospholipase A2 and is differently regulated by cyclic AMP and Ca2+

1. Docosahexaenoic acid (DHA) and arachidonic acid (AA), polyunsaturated fatty acids (PUFAs), are important for central nervous system function during development and in various pathological states. Astrocytes are involved in the biosynthesis of PUFAs in neuronal tissue. Here, we investigated the mechanism of DHA and AA release in cultured rat brain astrocytes. 2. Primary astrocytes were cultured under standard conditions and prelabeled with [(14)C]DHA or with [(3)H]AA. Adenosine 5'-triphosphate (ATP) (20 micro M applied for 15 min), the P2Y receptor agonist, stimulates release of both DHA (289% of control) and AA (266% of control) from astrocytes. DHA release stimulated by ATP is mediated by Ca(2+)-independent phospholipase A(2) (iPLA(2)), since it is blocked by the selective iPLA(2) inhibitor 4-bromoenol lactone (BEL, 5 micro M) and is not affected either by removal of Ca(2+) from extracellular medium or by suppression of intracellular Ca(2+) release through PLC inhibitor (U73122, 5 micro M). 3. AA release, on the other hand, which is stimulated by ATP, is attributed to Ca(2+)-dependent cytosolic PLA(2) (cPLA(2)). AA release is abolished by U73122 and, by removal of extracellular Ca(2+), is insensitive to BEL and can be selectively suppressed by methyl arachidonyl fluorophosphonate (3 micro M), a general inhibitor of intracellular PLA(2) s. 4. Western blot analysis confirms the presence in rat brain astrocytes of 85 kDa cPLA(2) and 40 kDa protein reactive to iPLA(2) antibodies. 5. The influence of cAMP on regulation of PUFA release was investigated. Release of DHA is strongly amplified by the adenylyl cyclase activator forskolin (10 micro M), and by the protein kinase A (PKA) activator dibutyryl-cAMP (1 mM). In contrast, release of AA is not affected by forskolin or dibutyryl-cAMP, but is almost completely blocked by 2,3-dideoxyadenosine (20 micro M) and inhibited by 34% by H89 (10 micro M), inhibitors of adenylyl cyclase and PKA, respectively. 6. Other neuromediators, such as bradykinin, glutamate and thrombin, stimulate release of DHA and AA, which is comparable to the release stimulated by ATP. 7. Different sensitivities of iPLA(2) and cPLA(2) to Ca(2+) and cAMP reveal new pathways for the regulation of fatty acid release and reflect the significance of astrocytes in control of DHA and AA metabolism under normal and pathological conditions in brain.

JAK2/STAT3, not ERK1/2, mediates interleukin-6-induced activation of inducible nitric-oxide synthase and decrease in contractility of adult ventricular myocytes

Interleukin (IL)-6 decreases cardiac contractility via a nitric oxide (NO)-dependent pathway. However, mechanisms underlying IL-6-induced NO production remain unclear. JAK2/STAT3 and ERK1/2 are two well known signaling pathways activated by IL-6 in non-cardiac cells. However, these IL-6-activated pathways have not been identified in adult cardiac myocytes. In this study, we identified activation of these two pathways during IL-6 stimulation and examined their roles in IL-6-induced NO production and decrease in contractility of adult ventricular myocytes. IL-6 increased phosphorylation of STAT3 (at Tyr(705)) and ERK1/2 (at Tyr(204)) within 5 min that peaked at 15-30 min and returned to basal levels at 2 h. Phosphorylation of STAT3 was blocked by genistein, a protein tyrosine kinase inhibitor, and AG490, a JAK2 inhibitor, but not PD98059, an ERK1/2 kinase inhibitor. The phosphorylation of ERK1/2 was blocked by PD98059 and genistein but not AG490. Furthermore, IL-6 enhanced de novo synthesis of iNOS protein, increased NO production, and decreased cardiac contractility after 2 h of incubation. These effects were blocked by genistein and AG490 but not PD98059. We conclude that IL-6 activated independently the JAK2/STAT3 and ERK1/2 pathways, but only JAK2/STAT3 signaling mediated the NO-associated decrease in contractility.

Regulation of membrane-associated iPLA2 activity by a novel PKC isoform in ventricular myocytes

Thrombin stimulation of rabbit ventricular myocytes increases membrane-associated, Ca2+-independent phospholipase A2 (iPLA2) activity, resulting in accelerated hydrolysis of membrane plasmalogen phospholipids and increased production of arachidonic acid and lysoplasmenylcholine. This study was designed to investigate the signal transduction pathways involved in activation of membrane-associated iPLA2. Incubation of isolated membrane fractions suspended in Ca2+-free buffer with thrombin or phorbol 12-myristate 13-acetate resulted in a two- to threefold increase in iPLA2 activity. Prior treatment with the PKC inhibitor GF-109203X blocked iPLA2 activation by thrombin. These data suggest that a novel PKC isoform present in the membrane fraction modulates iPLA2 activity. Immunoblot analysis revealed a significant portion of PKC-epsilon present in the membrane fraction, but no other membrane-associated novel PKC isoform was detected by this method. These data indicate that activation of membrane-associated iPLA2 is mediated by a membrane-associated novel PKC isoform in thrombin-stimulated rabbit ventricular myocytes.

Arachidonic acid mediates dual effect of TNF-alpha on Ca2+ transients and contraction of adult rat cardiomyocytes

Tumor necrosis factor (TNF)-alpha has a biphasic effect on heart contractility and stimulates phospholipase A2 (PLA2) in cardiomyocytes. Because arachidonic acid (AA) exerts a dual effect on intracellular Ca2+ concentration ([Ca2+]i) transients, we investigated the possible role of AA as a mediator of TNF-alpha on [Ca2+]i transients and contraction with electrically stimulated adult rat cardiac myocytes. At a low concentration (10 ng/ml) TNF-alpha produced a 40% increase in the amplitude of both [Ca2+]i transients and contraction within 40 min. At a high concentration (50 ng/ml) TNF-alpha evoked a biphasic effect comprising an initial positive effect peaking at 5 min, followed by a sustained negative effect leading to 50-40% decreases in [Ca2+]i transients and contraction after 30 min. Both the positive and negative effects of TNF-alpha were reproduced by AA and blocked by arachidonyltrifluoromethyl ketone (AACOCF3), an inhibitor of cytosolic PLA2. Lipoxygenase and cyclooxygenase inhibitors reproduced the high-dose effects of TNF-alpha and AA. The negative effects of TNF-alpha and AA were also reproduced by sphingosine and were abrogated by the ceramidase inhibitor n-oleoylethanolamine. These results point out the key role of the cytosolic PLA2/AA pathway in mediating the contractile effects of TNF-alpha.

Inhibition of mitochondrial calcium-independent phospholipase A2 (iPLA2) attenuates mitochondrial phospholipid loss and is cardioprotective

Calcium-independent phospholipase A(2) (iPLA(2)) is the predominant phospholipase A(2) present in myocardium, and its pathophysiological role in acute myocardial infarction has been suggested by the rapid increase in membrane-associated iPLA(2) activity during myocardial ischaemia and reperfusion (I/R). We therefore examined iPLA(2) in mitochondrial fractions prepared from Langendorff-perfused adult rabbit hearts. Our studies indicate that iPLA(2)beta is present in rabbit heart mitochondrial inner membranes with no apparent translocation during ischaemia, I/R or preconditioning. Mitochondrion-associated iPLA(2) was catalytically competent and exhibited 2-, 3- and 2.5-fold increases in measured iPLA(2) activity following ischaemia, I/R and preconditioning, respectively, when compared with the activity of iPLA(2) measured in mitochondria from control hearts. Mitochondrial phospholipids are essential for maintaining the ordered structure and function of the organelle. I/R resulted in a rapid overall decrease in phosphatidylcholine and phosphatidylethanolamine glycerophospholipid species, as determined by electrospray ionization MS, that was partially alleviated by pretreatment of hearts with the iPLA(2)-specific inhibitor, bromoenol lactone (BEL). Pretreatment of I/R hearts with 10 microM BEL significantly reduced the infarct size almost to that of continuously perfused hearts and was cardioprotective only when administered prior to ischaemia. Cardioprotection by BEL was reversed by the simultaneous perfusion of 100 microM 5-hydroxydecanoate, implicating the mitochondrial K(ATP) channel in BEL-mediated protection from I/R. Preconditioning also significantly reduced the infarct size in response to I/R but protection was lost by concurrent perfusion of 10 microM arachidonic acid. Taken together, these data strongly implicate mitochondria-associated iPLA(2) in the signal transduction of myocardial I/R injury.

Effects of schisandrin B pretreatment on tumor necrosis factor-alpha induced apoptosis and Hsp70 expression in mouse liver

Tumor necrosis factor-alpha (TNFalpha) could cause apoptosis in hepatic tissue of D-galactosamine sensitized mice, as evidenced by the increase in the extent of DNA fragmentation. The hepatic apoptosis induced by TNFalpha was associated with hepatocellular damage as assessed by plasma alanine aminotransferase activity. Schisandrin B (Sch B) pretreatment at daily doses ranging from 0.5 to 2 mmol/kg for 3 days caused a dose-dependent protection against TNFalpha-induced apoptosis in mice. The hepatoprotection was accompanied by a parallel reduction in the extent of hepatocellular damage. The same Sch B pretreatment regimens increased hepatic Hsp70 level in a dose-dependent manner. The relevance of Sch B-induced increase in Hsp70 expression to the prevention of TNFalpha-triggered hepatic apoptosis remains to be elucidated.

Redistribution and abnormal activity of phospholipase A(2) isoenzymes in postinfarct congestive heart failure

Cardiac sarcolemmal (SL) cis-unsaturated fatty acid sensitive phospholipase D (cis-UFA PLD) is modulated by SL Ca(2+)-independent phospholipase A(2) (iPLA(2)) activity via intramembrane release of cis-UFA. As PLD-derived phosphatidic acid influences intracellular Ca(2+) concentration and contractile performance of the cardiomyocyte, changes in iPLA(2) activity may contribute to abnormal function of the failing heart. We examined PLA(2) immunoprotein expression and activity in the SL and cytosol from noninfarcted left ventricular (LV) tissue of rats in an overt stage of congestive heart failure (CHF). Hemodynamic assessment of CHF animals showed an increase of the LV end-diastolic pressure with loss of contractile function. In normal hearts, immunoblot analysis revealed the presence of cytosolic PLA(2) (cPLA(2)) and secretory PLA(2) (sPLA(2)) in the cytosol, with cPLA(2) and iPLA(2) in the SL. Intracellular PLA(2) activity was predominantly Ca(2+) independent, with minimal sPLA(2) activity. CHF increased cPLA(2) immunoprotein and PLA(2) activity in the cytosol and decreased SL iPLA(2) and cPLA(2) immunoprotein and SL PLA(2) activity. sPLA(2) activity and abundance decreased in the cytosol and increased in SL in CHF. The results show that intrinsic to the pathophysiology of post-myocardial infarction CHF are abnormalities of SL PLA(2) isoenzymes, suggesting that PLA(2)-mediated bioprocesses are altered in CHF.