Formation of diacylglycerol, inositol phosphates, arachidonic acid and its metabolites in macrophages

Potential Role of Fluoride in the Etiopathogenesis of Alzheimer's Disease

The etiopathogenesis of Alzheimer's disease has not been fully explained. Now, the disease is widely attributed both to genetic and environmental factors. It is believed that only a small percentage of new AD cases result solely from genetic mutations, with most cases attributed to environmental factors or to the interaction of environmental factors with preexistent genetic determinants. Fluoride is widespread in the environment and it easily crosses the blood⁻brain barrier. In the brain fluoride affects cellular energy metabolism, synthesis of inflammatory factors, neurotransmitter metabolism, microglial activation, and the expression of proteins involved in neuronal maturation. Finally, and of specific importance to its role in Alzheimer's disease, studies report fluoride-induced apoptosis and inflammation within the central nervous system. This review attempts to elucidate the potential relationship between the effects of fluoride exposure and the pathogenesis of Alzheimer's disease. We describe the impact of fluoride-induced oxidative stress and inflammation in the pathogenesis of AD and demonstrate a role for apoptosis in disease progression, as well as a mechanism for its initiation by fluoride. The influence of fluoride on processes of AD initiation and progression is complex and warrants further investigation, especially considering growing environmental fluoride pollution.

Fluoride as a factor initiating and potentiating inflammation in THP1 differentiated monocytes/macrophages

It is well known that exposure to fluorides lead to an increased ROS production and enhances the inflammatory reactions. Therefore we decided to examine whether cyclooxygenases (particular COX-2) activity and expression may be changed by fluoride in THP1 macrophages and in this way may change the prostanoids biosynthesis. In the present work we demonstrate that fluoride increased concentration of PGE2 and TXA2 in THP1 macrophages. Following exposure to 1-10 μM NaF, COX-2 protein and COX-2 transcript increased markedly. COX-2 protein up-regulation probably is mediated by ROS, produced during fluoride-induced inflammatory reactions. Additional fluoride activates the transcription factor, nuclear factor (NF)-kappaB, which is involved in the up-regulation of COX-2 gene expression. This study indicated that even in small concentrations fluoride changes the amounts and activity of COX-1 and COX-2 enzymes taking part in the initiating and development of inflammatory process.

Interleukin-1β inhibits synthesis of 5-lipooxygenase in lipopolysaccharide-stimulated equine whole blood

Interleukin-1β (IL-1β) is a pro-inflammatory cytokine. It induces the synthesis of prostaglandin E2 (PGE2) catalyzed by cyclooxygenase (COX) and microsomal prostaglandin E synthase (m-PGES). Besides its pro-inflammatory properties, PGE2 also exhibits anti-inflammatory properties by inhibiting synthesis of 5-lipooxygenase (5-LO) products which are in themselves, pro-inflammatory mediators. Thus, inhibition of 5-LO products is beneficial in regulating immune-responses and pro-inflammatory processes. To investigate the hypothesis that IL-1β is responsible for the increase in the synthesis of PGE2 and in the reduction of 5-LO products, equine whole blood (EWB) was treated with lipopolysaccharide (LPS). In vitro treatment of EWB with LPS resulted in increased expression of IL-1β while expression of 5-LO was suppressed. Quantification of eicosanoids using liquid-chromatography-mass spectrometry/multiple reaction monitoring (LC-MS/MRM) showed increased concentrations of prostaglandins and decreased 5-LO products in LPS-treated EWB. Pretreatment of EWB with IL-1β followed by calcium ionophore A23187 (CI) reduced synthesis of 5-LO products. However, pretreatment of EWB with COX-2 inhibitor (NS-398) or m-PGES-1 inhibitor (CAY 10526) and IL-1β followed with CI resulted in a significant (p<0.0001) increase in 5-LO products. Pretreatment of EWB with phospholipase C inhibitor (U73122) followed with LPS reduced PGE2 production but increased 5-LO products. The result of this study indicated that increased PGE2 production led to reduction in 5-LO products in LPS-treated EWB via IL-1β. However, other pathways, cytokines and mediators may be involved in inhibiting 5-LO products but the present study did not include those other potential pathways. Inhibition of 5-LO products by PGE2 in EWB may regulate the initiation and pathogenesis of inflammatory responses in the horse.

Activation of phospholipase A(2) by low levels of fluoride in THP1 macrophages via altered Ca(2+) and cAMP concentration

Phospholipases (PLA's) participate in the regulation of physiological and pathological processes in the cell, including the release of pro-inflammatory mediators and stimulation of inflammatory processes. It is also well known that fluoride can increase the inflammatory reactions. Therefore we decided to examine the effect of fluorides in concentrations determined in human serum on cPLA(2) and sPLA(2) activity. The incubation of macrophages in fluoride solutions significantly increased the amount of synthesized cellular cAMP, intracellular calcium and sPLA(2) activity in a dose-dependent pattern. The cPLA(2) activity, estimated by the amount of released arachidonic acid, increased significantly when 10 μM NaF was used. The results of our study suggest that fluoride may change the activity of phospholipases in macrophage cells. Probably, increased cAMP concentration activates protein kinase C (PKC) and thus stimulates PLA(2). cAMP also regulates the passage of Ca(2+) through ion channels, which additionally influence PLA(2) throughout Ca(2+)-calmodulin dependent protein kinase.

Changes in the inositol lipid signal system and effects on the secretion of TNF-α by macrophages in severely scalded mice

AIM

In order to study the mechanism of abnormal macrophage (Mϕ) function in pro-inflammatory cytokine changes after burn, the inositol lipid signal system and its role in tumour necrosis factor-alpha (TNF-α) secretion by peritoneal Mϕs was observed in severely scalded mice.

METHODS

Eighteen percent total body surface area (TBSA) full-thickness scalded mice were used as animal model in this experiment. Peritoneal Mϕs stimulated by lipopolysaccharide in vitro were collected at different time intervals (0, 2, 6, 12, 24 and 48 after burn hour (PBH)), The activities of phosphatidylinositol-phospholipase C (PI-PLC), inositol-1, 4,5, -triphosphate (IP(3)), protein kinase C (PKC), diacylglycerol (DAG) and TNF-α and the level of Ca(2+) concentration in peritoneal Mϕs were measured, and the effects of specific PKC inhibitor H-7 and calmodulin antagonist W-7 on the production of TNF-α were also observed.

RESULTS

After scald, increased activities of TNF-α and PLC of Mϕ were observed and peaked at 12 PBH. The activities of DAG and IP(3) and the concentration of Ca(2+) were markedly increased and reached their peaks at 24 PBH simultaneously. Membrane PKC activity was up-regulated after scald and showed a positive correlation with the change of DAG (r=0.83, P<0.05). There was also positive correlation between IP(3) and Ca(2+) activity (r=0.946, P<0.01). When 12 PBH was chosen as the time point for in vitro intervention with the pre-treatment by H-7, both membrane PKC and TNF-α activity decreased significantly. There was no obvious change of TNF-α activity with the application of W-7.

CONCLUSIONS

These results indicated that the abnormal activity of TNF-α of Mϕs might be regulated by the inositol lipid signal system following severe burn. The DAG-PKC signal pathway showed closer relationship than IP(3)-Ca(2+) in TNF-α production and could be the optimal target in the prevention and treatment of the systemic inflammatory response syndrome.

Differential effect of chondroitin-4-sulfate on the immediate and delayed prostaglandin E2 release from osteoblasts

The present study examines the effect of chondroitin-4-sulfate (C4S) on the immediate (non-inflammatory conditions) and the delayed (inflammatory conditions) prostaglandin E(2) (PGE(2)) release from rat calvarial osteoblasts. An immediate low release of PGE(2) was induced by PAF, phorbol ester and arachidonic acid but not by IL1beta, TNF-alpha and LPS whereas a delayed high release of PGE(2) was induced by the inflammatory agents IL1beta, TNF-alpha and LPS but not by PAF, phorbol ester and arachidonic acid. C4S had no effect on the immediate PGE(2) release but inhibited the delayed release of PGE(2). IL1beta, TNF-alpha and LPS enhanced the expression of COX-2 and mPGES1 whereas phorbol ester enhanced COX-2 expression only. PAF and arachidonic acid had no effect on the expression of COX-2 and mPGES1. C4S inhibited the enhanced expression of COX-2 and mPGES1 but had no effect on the IL1beta-induced decrease of I-kappaBalpha and nuclear translocation of NF-kappaB. These results indicate that the beneficial effects of C4S in bone inflammatory diseases might be due to a specific inhibition of the delayed high PGE(2) release from osteoblasts.

COX-1 and COX-2 contribute differentially to the LPS-induced release of PGE2 and TxA2 in liver macrophages

LPS induces an immediate release of thromboxane TxA2 and a delayed release of PGE2. Dexamethasone suppresses the LPS-induced release of TxA2 and PGE2. In the first 8 h after LPS addition, the specific COX-2 inhibitor SC236 inhibits the PGE2 and TxA2 release by about 80% and 20%, whereas the release of PGE2 and TxA2 between 8 and 24 h is inhibited by about 40% and 35%, respectively. Resident liver macrophages express substantial amounts of COX-1, TxAS, cPGES and mPGES-2, small amounts of COX-2 but almost no detectable amounts of mPGES-1. LPS induces an increase of COX-2 and mPGES-1, but does not change COX-1, cPGES, mPGES-2 and TxAS at protein level. Dexamethasone suppresses almost completely the LPS-induced effects on COX-2 and mPGES-1. It is concluded that (1) COX-1 and COX-2 are involved in the LPS-induced synthesis of TxA2 and PGE2; (2) TxA2 release is catalyzed at early time-points by the combined action of COX-1 and TxAs, whereas at later time points the newly expressed COX-2 couples to TxAS and contributes to the TxA2 release; (3) PGE2 release within the first 8 h is predominantly catalyzed by COX-2, whereas at later time-points COX-1 couples to the newly expressed mPGES-1 and contributes to the PGE2 release.

The hemodynamic effects of zymosan in the perfused rat liver

The actions of zymosan on hepatic microcirculation and on the cell membrane permeability were investigated using the multiple-indicator dilution technique. The experimental system was the perfused rat liver. [(3)H]Water, [(3)H]sucrose and [(14)C]urea or [(14)C]bicarbonate were simultaneously injected into the portal vein. Mean transit times, distribution spaces, variances, linear superpositions and transfer coefficients across the plasma membrane were calculated. Zymosan had no net effect on the great vessels space but increased the extracellular sucrose space and decreased the aqueous cell space. Zymosan impaired the flow-limited distribution and increased the normalized variances of all tracers. The increase in the portal pressure caused by zymosan results most probably from a constriction just after or at the exit of the sinusoids. Impairment of the flow-limited distribution of tracers in the sinusoidal bed indicates that zymosan induces the formation of permeability barriers, which could make the access of the solutes to transporters or enzymes located on the outer surface of the plasma membrane difficult.

Diverse functional coupling of cyclooxygenase 1 and 2 with final prostanoid synthases in liver macrophages

Lipopolysaccharide (LPS) treatment of resident liver macrophages resulted in a coordinated enhanced expression of cytosolic phospholipase A(2) (cPLA(2)), cyclooxygenase (COX)-2 and prostaglandin E(2)-synthase. LPS-pretreated liver macrophages showed a higher release of PGE(2) after zymosan, phorbol ester and A23187, of PGF(2alpha) after zymosan and A23187, whereas the release of thromboxane B(2) and PGD(2) was unchanged. Inhibition of COX-1 and -2 by specific inhibitors (SC560, SC236) inhibited the prostanoid release between 50-80% and 20-40%, respectively, indicating a predominant role for COX-1. In detail (1) the zymosan-induced release of all prostanoids was inhibited to a similar degree by the COX-1 inhibitor (about 70%) and the COX-2 inhibitor (20-30%), (2) PGE(2) release after all stimuli was inhibited to a greater extent by SC560 (70-90%) compared to SC236 (5-30%), (3) the phorbol ester- and A23187-induced release of PGF(2alpha) and PGD(2) was inhibited equally (40-50%) by both inhibitors, (3) TxB(2) release after phorbol ester and A23187 was inhibited by SC560 by 50 and 30%, and by SC236 by 50 and 70%, respectively. cPLA(2), COX-1 and -2, and the final prostanoid synthases were found in different subcellular fractions. These results indicate, that the functional coupling of COX-1 and -2 to final prostanoid synthases depends on the stimulation of the cells.

Zymosan-induced changes in glucose release and fatty acid oxidation in the perfused rat liver

The aim of the present study was to investigate the actions of zymosan on glucose release and fatty acid oxidation in perfused rat livers and to determine if Kupffer cells and Ca2+ ions are implicated in these actions. Zymosan caused stimulation of glycogenolysis in livers from fed rats. In livers from fasted rats zymosan caused gradual inhibition of glucose production and oxygen consumption from lactate plus pyruvate. Ketogenesis, oxygen consumption, and [14C-]-CO2 production were inhibited by zymosan when the [1-14C]-palmitate was supplied exogenously. However, ketogenesis and oxygen consumption from endogenous sources were not inhibited. An interference with substrate-uptake by the liver may be the cause of the changes in gluconeogenesis and oxidation of fatty acids from exogenous sources. The pretreatment of the rats with gadolinium chloride and the removal of Ca2+ ions did not suppress the effects of zymosan on glucose release, a finding that argues against the participation of Kupffer cells or Ca2+ ions in the liver responses. The hepatic metabolic changes caused by zymosan could play a role in the systemic metabolic alterations reported to occur after in vivo zymosan administration.

Functional coupling of cyclooxygenase 1 and 2 to discrete prostanoid synthases in liver macrophages

The profile of released prostanoids after addition of exogenous arachidonic acid to resident liver macrophages is different from the profile obtained in lipopolysaccharide-pretreated cells. In resident and lipopolysaccharide-pretreated cells, AA leads to a release of thromboxane B(2), prostaglandin F(2alpha), E(2), and D(2). A specifically enhanced formation of prostaglandin E(2) is obtained in lipopolysaccharide-pretreated cells. Resident liver macrophages express cyclooxygenase 1, and thromboxane A(2)-, prostaglandin F(2alpha)-, E(2)-, and D(2)-synthase. Treatment with lipopolysaccharide induces-in addition to cyclooxygenase 2-an enhanced expression of the prostaglandin E(2) synthase. In resident liver macrophages, the formation of prostanoids from exogenous arachidonic acid is completely inhibited by SC560 (a specific inhibitor of cyclooxygenase 1), but remains unchanged with SC236 (a specific inhibitor of cyclooxygenase 2). In lipopolysaccharide-pretreated liver macrophages, the formation of thromboxane B(2), prostaglandin F(2alpha) and D(2) is equally inhibited by SC560 and SC236 by about 50%. In contrast, the formation of prostaglandin E(2) is inhibited to a greater extent by SC560 (75%) compared to SC236 (26%). We conclude from these data, that in lipopolysaccharide-pretreated liver macrophages (i) cyclooxygenase 1 and 2 couple both to discrete prostanoid synthases, (ii) the functional coupling of cyclooxygenase 1 and 2 to the thromboxane A(2)-, prostaglandin F(2alpha)-, and D(2)-synthase is almost identical, and (iii) the enhanced prostaglandin E(2) synthesis is due to an enhanced expression of the prostaglandin E(2) synthase, which is coupled more efficiently to cyclooxygenase 1.

Prostaglandin E2 affects differently the release of inflammatory mediators from resident macrophages by LPS and muramyl tripeptides

LPS and MTP-PE (liposome-encapsulated N-acetyl-muramyl-L-alanyl-D-isoglutaminyl-L-alanine-2-:[1',2'dipalmitoyl -sni-glycero-3-(hydroxy-phosphoryl-oxyl)] etylamide) induce in liver macrophages a synthesis and release of TNF-alpha, nitric oxide and prostanoids. Both agents induce an expression of mRNA's encoding TNF-alpha, inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX)-2, and of corresponding proteins. LPS and MTP-PE induce a rapid activation of the extracellular regulated kinase (ERK) isoenzymes-1 and -2. Inhibition of map kinase isoenzymes leads to a decreased release of TNF-alpha, nitric oxide and prostaglandin (PG) E2 after both agents. The transcription factors NF-kappaB and AP-1 are strongly activated by LPS within 30 minutes. MTP-PE induces a weak activation of both transcription factors only after 5 hours. Inhibition of NF-kappaB inhibits the LPS- but not the MTP-PE-induced release of TNF-alpha, nitric oxide and PGE2. PGE2 release after LPS is higher than after MTP-PE. Exogenously added PGE2 inhibits the activation of map kinase and TNF-alpha release by LPS, but not by MTP-PE. Release of nitric oxide after LPS and MTP-PE is enhanced after prior addition of PGE2. PGD2 is without any effect. MTP-PE, but not LPS, induces a cytotoxicity of Kupffer cells against P815 tumor target cells. The MTP-PE-induced cytotoxicity is reduced by TNF-alpha neutralizing antibodies, indicating the involvement of TNF-alpha. Thus our results suggest that the different potencies of LPS and MTP-PE as immunomodulators probably result from different actions on Kupffer cells, resulting in differences in the amounts and kinetics of released TNF-alpha and PGE2, and that PGE2 plays an important regulatory role in the action of LPS, but not in the actions of MTP-PE.

Pharmacological comparison of UTP- and thapsigargin-induced arachidonic acid release in mouse RAW 264.7 macrophages

1. Although stimulation of mouse RAW 264.7 macrophages by UTP elicits a rapid increase in intracellular free Ca2+ ([Ca2+]i), phosphoinositide (PI) turnover, and arachidonic acid (AA) release, the causal relationship between these signalling pathways is still unclear. In the present study, we investigated the involvement of phosphoinositide-dependent phospholipase C (PI-PLC) activation, Ca2+ increase and protein kinase activation in UTP-induced AA release. The effects of stimulating RAW 264.7 cells with thapsigargin, which cannot activate the inositol phosphate (IP) cascade, but results in the release of sequestered Ca2+ and an influx of extracellular Ca2+, was compared with the effects of UTP stimulation to elucidate the multiple regulatory pathways for cPLA2 activation. 2. In RAW 264.7 cells UTP (100 microM) and thapsigargin (1 microM) caused 2 and 1.2 fold increases, respectively, in [3H]-AA release. The release of [3H]-AA following treatment with UTP and thapsigargin were non-additive, totally abolished in the Ca2+-free buffer, BAPTA (30 microM)-containing buffer or in the presence of the cPLA2 inhibitor MAFP (50 microM), and inhibited by pretreatment of cells with pertussis toxin (100 ng ml(-1)) or 4-bromophenacyl bromide (100 microM). By contrast, aristolochic acid (an inhibitor of sPLA2) had no effect on UTP and thapsigargin responses. 3. U73122 (10 microM) and neomycin (3 mM), inhibitors of PI-PLC, inhibited UTP-induced IP formation (88% and 83% inhibition, respectively) and AA release (76% and 58%, respectively), accompanied by a decrease in the [Ca2+]i rise. 4. Wortmannin attenuated the IP response of UTP in a concentration-dependent manner (over the range 10 nM-3 microM), and reduced the UTP-induced AA release in parallel. RHC 80267 (30 microM), a specific diacylglycerol lipase inhibitor, had no effect on UTP-induced AA release. 5. Short-term treatment with PMA (1 microM) inhibited the UTP-stimulated accumulation of IP and increase in [Ca2+]i, but had no effect on the release of AA. In contrast, the AA release caused by thapsigargin was increased by PMA. 6. The role of PKC in UTP- and thapsigargin-mediated AA release was shown by the blockade of these effects by staurosporine (1 microM), Ro 31-8220 (10 microM), Go 6976 (1 microM) and the down-regulation of PKC. 7. Following treatment of cells with SK&F 96365 (30 microM), thapsigargin-, but not UTP-, induced Ca2+ influx, and the accompanying AA release, were down-regulated. 8. Neither PD 98059 (100 microM), MEK a inhibitor, nor genistein (100 microM), a tyrosine kinase inhibitor, had any effect on the AA responses induced by UTP and thapsigargin. 9. We conclude that UTP-induced cPLA2 activity depends on the activation of PI-PLC and the sustained elevation of intracellular Ca2+, which is essential for the activation of cPLA2 by UTP and thapsigargin. The [Ca2+]i-dependent AA release that follows treatment with both stimuli was potentiated by the activity of protein kinase C (PKC). A pertussis toxin-sensitive pathway downstream of the increase in [Ca2+]i was also shown to be involved in AA release.

Lipoxygenase metabolites as mediators of UTP-induced intracellular acidification in mouse RAW 264.7 macrophages

In previous studies, we have shown that mouse RAW 264.7 macrophages possess pyrimidinoceptors, coupled to a phosphoinositide-specific phospholipase C, with a higher specificity for UTP than for ATP. In the current study, we explored the mechanism involved in the UTP-induced intracellular acidification seen in this cell line. UTP (30 microM) caused a reversible pHi decrease of 0.16 +/- 0.01 unit; this effect was not influenced by the removal of extracellular Cl- or Na+ ions or by pretreatment with 5-(N-ethyl-N-isopropyl)-amiloride (10 microM), 5-nitro-2-(3-phenylpropylamino)benzoic acid (100 microM), staurosporine (1 microM), or Ro 31-8220 (1 microM) but was completely abolished by the removal of extracellular Ca2+. UTP (30 microM), thapsigargin (1 microM), and ionomycin (1 microM) each induced a similar extent of external Ca2+-dependent acidification with a similar time-dependency, but the effects were nonadditive. To further investigate the Ca2+-dependent mechanism, we studied the involvement of arachidonic acid (AA) and eicosanoid metabolites. The addition of AA (10 microM) but not arachidic acid (100 microM) produced a reduction in pHi. UTP, thapsigargin, and ionomycin induced Ca2+-dependent AA release. Furthermore, 4-bromo-phenacyl bromide [30 microM, a phospholipase A2 (PLA2) inhibitor-, nordihydroguaiaretic acid (50 microM, a lipoxygenase inhibitor), and MK-886 (10 microM, a 5-lipoxygenase-activating protein inhibitor) abolished the UTP- or ionomycin-induced responses, whereas indomethacin (30 microM, a cyclooxygenase inhibitor) and baicalein (10 microM, a selective 12-lipoxygenase inhibitor) had no effect. MAFP (a cPLA2 inhibitor) and REV 5901 (a 5-lipoxygenase inhibitor as well as a competitive antagonist of peptide leukotrienes), but not RHC 80267 (a diacylglycerol lipase inhibitor), also inhibited the UTP-induced response. In contrast, the pHi response to AA was unaffected by the presence of 4-bromo-phenacyl bromide or the removal of extracellular Ca2+ ions but abolished by addition of NDGA. Exogenous 5-hydroperoxyeicosatetraenoic acid (2 microM) also produced marked acidification, and UTP and ionomycin both induced peptide leukotriene formation. In conclusion, this is the first report indicating that lipoxygenase metabolites act as mediators of the Ca2+-dependent acidification seen in macrophages in response to UTP or ionomycin via activation of cPLA2 and AA release.

Role of cytosolic phospholipase A2 in arachidonic acid release of rat-liver macrophages: regulation by Ca2+ and phosphorylation

In this study we have verified the existence of a cytosolic phospholipase A2 (cPLA2) in rat-liver macrophages. Stimulation of these cells with phorbol 12-myristate 13-acetate (PMA), zymosan and lipopolysaccharide (LPS), but not with the Ca(2+)-ionophore A23187, leads to phosphorylation of cPLA2 and activation of mitogen-activated protein (MAP) kinase, supporting the hypothesis that MAP kinase is involved in cPLA2 phosphorylation. We show furthermore, that the tyrosine kinase inhibitor genistein prevents the LPS- but not the PMA- or zymosan-induced phosphorylation of cPLA2 and activation of MAP kinase, indicating that tyrosine kinases participate in LPS- but not in PMA- and zymosan-induced cPLA2 phosphorylation and MAP kinase activation. Phosphorylation of cPLA2 does not strongly correlate with stimulation of the arachidonic acid (AA) cascade: (1) A23187, a potent stimulator of AA release, fails to induce cPLA2 phosphorylation; (2) withdrawal of extracellular Ca2+, which inhibits PMA-stimulated AA release (Dieter, Schulze-Specking and Decker (1988) Eur. J. Biochem. 177, 61-67), has no effect on PMA-induced phosphorylation of cPLA2; (3) LPS induces cPLA2 phosphorylation within minutes, whereas increased AA release upon treatment with LPS is detectable for the first time after 4 h; and (4) genistein, which prevents LPS-induced cPLA2 phosphorylation, does not inhibit AA release in response to LPS. From these data we suggest that a rise in intracellular Ca2+, but not phosphorylation of cPLA2, is essential for activation of the AA cascade in rat-liver macrophages.

Differential regulation of phospholipase D and phospholipase C by protein kinase C-beta and -delta in liver macrophages

We have studied activation of phospholipase (PL) C and PLD in liver macrophages labelled with [3H]arachidonic acid. Zymosan, phorbol 12-myristate 13-acetate (PMA), A23187 and fluoride but not arachidonic acid or lipopolysaccharide (LPS) induce an activation of PLD ([3H]phosphatidylethanol (PEt) accumulation). An activation of PLC ([3H]diacylglycerol (DAG) accumulation) is measured with zymosan, PMA and fluoride but not with A23187, LPS or arachidonic acid whereas inositol phosphates are formed with zymosan, only. Removal of extracellular calcium reduces the formation of [3H]PEt and [3H]DAG while pretreatment of the cells with dexamethasone reduces [3H]PEt formation, only. PMA- and zymosan-induced activation of PLD and PMA-induced activation of PLC both seem to be mediated by protein kinase (PK) C-beta whereas zymosan-induced activation of PLC is negatively controlled by PKC-delta. We could furthermore present evidence that the release of [3H]arachidonic acid in these cells occurs independent of an activation of PLD.

Differential activation of transcription factors NF-kappa B and AP-1 in rat liver macrophages

Liver macrophages (Kupffer cells) respond to many stimulations with the production of bioactive substances including cytokines, eicosanoids, and inorganic radicals. In this study the activation of transcription factors by substances inducing cytokine gene expression or superoxide formation in rat Kupffer cells was examined. Using primary cultures of rat Kupffer cells the role of NF-kappa B and activator protein 1 (AP-1) in the expression of the tumor necrosis factor-alpha (TNF-alpha) gene by lipopolysaccharide (LPS) was investigated. Both transcription factors were strongly activated but with different kinetics. Maximal DNA-binding activity was induced with 50 ng of LPS/mL of medium and persisted for at least 24 hours. At that time, NF-kappa B- as well as AP-1-DNA complexes decreased their mobilities in native gels. Among the cytokines tested only TNF-alpha and macrophage colony-stimulating factor (M-CSF) were able to activate NF-kappa B in Kupffer cells. Phorbol ester and zymosan activated AP-1 but not NF-kappa B; the treatment of zymosan yielding a modified form of AP-1. Of all substances found to interfere with TNF-alpha production by Kupffer cells (pyrrolidine dithiocarbamate, dexamethasone, prostaglandin E2, interleukin [IL]-4, IL-10, and transforming growth factor-beta [TGF-beta]) only pyrrolidine dithiocarbamate was able to completely inhibit the activation of NF-kappa B by LPS. Although not abrogating the LPS activation of NF-kappa B, dexamethasone inhibited that of AP-1. The results indicate a direct participation of NF-kappa B in the regulation of TNF-alpha synthesis and a differential effect of LPS on NF-kappa B and AP-1, respectively.

Signal transduction pathways leading to arachidonic acid release from neutrophilic HL-60 cells. The involvement of G protein, protein kinase C and phospholipase A2

Arachidonic acid release from undifferentiated and neutrophilic HL-60 cells was studied. In neutrophilic cells it was stimulated by N-formyl-Met-Leu-Phe and mastoparan by a mechanism involving Gi protein and phospholipase C and was largely dependent on diacyglycerol lipase. Maximum release from both cell types was achieved with fluoride and required cellular energy. Inhibitor studies suggest that arachidonic acid release by fluoride stimulation leads to phospholipase A2 activation with signal transduction involving phospholipase C and protein kinase C. Only neutrophilic cells responded to phorbol ester if Ca(2+)-ionophore was simultaneously present but this effect was abolished by extended treatment with phorbol ester. Thus, protein kinase C plays a major role in highly stimulated neutrophilic cells. These cells are differently equipped with protein kinase C isoenzymes compared with undifferentiated cells. In contrast, both cell types contain similar levels of type II and cytosolic phospholipases A2, the former being by far the more prevalent.