Enhancement by cyclo-oxygenase inhibitors of platelet-activating factor production in thapsigargin-stimulated macrophages

Possible participation of intracellular platelet-activating factor in NF-kappaB activation in rat peritoneal macrophages

As we had found previously that thapsigargin, an endomembrane Ca2+-ATPase inhibitor, induces production of intracellular platelet-activating factor (PAF) [Br. J. Pharmacol. 116 (1995) 2141], we decided to investigate the possible roles of intracellular PAF in nuclear factor (NF)-kappaB activation of thapsigargin-stimulated rat peritoneal macrophages. When rat peritoneal macrophages were stimulated with thapsigargin, the level of inhibitory protein of NF-kappaB-alpha (IkappaB-alpha) was decreased and the nuclear translocation of NF-kappaB was increased. The thapsigargin-induced activation of NF-kappaB was inhibited by the PAF synthesis inhibitor SK&F 98625 and the PAF antagonist E6123. Structurally unrelated PAF antagonists such as E5880 and L-652,731 also inhibited the thapsigargin-induced activation of NF-kappaB. Lipopolysaccharide (LPS)-induced activation of NF-kappaB was also suppressed by these drugs. In a culture of rat peritoneal macrophages, exogenously added PAF did not induce degradation of IkappaB-alpha. These findings suggest that the intracellular PAF produced by the stimulation with thapsigargin or LPS is involved in activation of the NF-kappaB pathway.

Participation of prostaglandin E2 and platelet-activating factor in thapsigargin-induced production of interleukin-6

Incubation of rat peritoneal macrophages in the presence of thapsigargin increased production of prostaglandin E2, intracellular platelet-activating factor (PAF) and interleukin-6. However, no PAF was detected in the conditioned medium. In the presence of SK&F 98625 (diethyl 7-(3,4,5-triphenyl-2-oxo-2,3-dihydroimidazol-1-yl)heptane phosphonate), a CoA-independent transacylase inhibitor, the thapsigargin-induced increases in the interleukin-6 mRNA level and interleukin-6 production were suppressed in a concentration-dependent manner. This inhibitor also suppressed the production of prostaglandin E2 and intracellular PAF. The PAF receptor antagonists such as E6123 ((S)-(+)-6-(2-chlorophenyl)-3-cyclopropanecarbonyl-8,11-dimethyl-2,3,4,5-tetrahydro-8H-pyrido[4',3':4,5]thieno[3,2-f][1,2,4]triazolo [4,3-a][1,4]diazepine) and L-652,731 (2,5-bis(3,4,5-trimethylphenyl)tetrahydrofuran) partially inhibited the thapsigargin-induced increase in the levels of interleukin-6 mRNA and interleukin-6 protein. The SK&F 98625-induced suppression of interleukin-6 mRNA accumulation and interleukin-6 production was partially restored by addition of exogenous prostaglandin E2. However, exogenous PAF failed to reverse the suppression suggesting that the intracellular PAF does not act in an autocrine mechanism. These findings suggested that the concurrently produced prostaglandin E2 and intracellular PAF participate in the thapsigargin-induced increase in the interleukin-6 mRNA level and interleukin-6 production by rat peritoneal macrophages.

Inhibition of prostalglandin E2 production by 2'-hydoxychalcone derivatives and the mechanism of action

The effects of 14 synthetic 2'-hydroxychalcone derivatives on prostaglandin E2 (PGE2) production in rat peritoneal macrophages stimulated by the protein kinase C activator, 12-O-tetradecanoylphorbol 13-acetate (TPA), were examined to clarify the structure-activity relationship. 2',4-Dihydroxy-4'-methoxychalcone (compound 3), 2',4-dihydroxy-6'-methoxychalcone (compound 8) and 2'-hydroxy-4'-methoxychalcone (compound 9) suppressed PGE2 production more potently than the other compounds. The IC50 (50% Inhibitory concentration) value for compounds 3, 8 and 9 was calculated to be 3 microM. The activity of cyclooxygenase (COX)-1 was inhibited slightly by compound 9, but that of COX-2 was not inhibited. At concentrations that inhibited the production of PGE2, compound 9 had no effect on the release of radioactivity from [3H]arachidonic acid-labelled macrophages stimulated by TPA. Western-blot analysis revealed that the induction of COX-2 protein by TPA was inhibited by compound 9 in parallel with the inhibition of PGE2 production. Compounds 3 and 8 had similar effects. These findings suggest that 4'-methoxyl and 6'-methoxyl groups are required for the expression of more potent inhibitory activity against PGE2 production, and that the inhibition of PGE2 production by these 2'-hydroxychalcone derivatives is due to the inhibition of TPA-induced COX-2 protein expression.

Participation of mitogen-activated protein kinase in thapsigargin- and TPA-induced histamine production in murine macrophage RAW 264.7 cells

1. Stimulation of the murine macrophage cell line RAW 264.7 with thapsigargin, an endomembrane Ca(2+)-ATPase inhibitor, induced histamine production in a time- and concentration-dependent manner. 2. The protein kinase C activator, 12-O-tetradecanoylphorbol 13-acetate (TPA), also enhanced histamine production. 3. alpha-Fluoromethylhistidine, a suicide substrate of L-histidine decarboxylase (HDC), suppressed the thapsigargin (30 nM)- and TPA (30 nM)-induced histamine production. 4. Both thapsigargin (30 nM) and TPA (30 nM) induced phosphorylation of p44/p42 MAP kinase and p38 MAP kinase. 5. PD98059, a specific inhibitor of MEK-1 which phosphorylates p44/p42 MAP kinase, strongly suppressed both the thapsigargin (30 nM)- and TPA (30 nM)-induced histamine production, whereas SB203580, a specific inhibitor of p38 MAP kinase, inhibited them only partially. 6. The other MEK-1 inhibitor, U-0126, also inhibited both the thapsigargin- and TPA-induced histamine production in a concentration-dependent manner. 7. Thapsigargin (30 nM) and TPA (30 nM) increased the levels of HDC mRNA at 4 h, but PD98059 suppressed both the thapsigargin- and TPA-induced increases in the HDC mRNA level. 8. These findings indicate that thapsigargin and TPA induce histamine production in RAW 264.7 cells by increasing the level of HDC mRNA, and that both the thapsigargin- and TPA-induced histamine production are regulated largely by p44/p42 MAP kinase and partially by p38 MAP kinase.

Possible participation of intracellular platelet-activating factor in tumor necrosis factor-alpha production by rat peritoneal macrophages

Stimulation of rat peritoneal macrophages by thapsigargin (46.1 nM) increased levels of tumor necrosis factor-alpha and prostaglandin E2 in the conditioned medium. Platelet-activating factor (PAF) was not detected in the conditioned medium, but the level of cell-associated PAF was increased transiently by thapsigargin. The PAF receptor antagonists such as E6123 ((S)-(+)-6-(2-chlorophenyl)-3-cyclopro-panecarbonyl-8,11-dim ethyl-2,3,4,5-tetrahydro-8 H-pyrido[4',3':4,5]thieno [3,2-f][1,2,4]triazolo[4,3-a][1,4]diazepine), L-652,73 1 (2,5-bis(3,4,5-trimethoxyphenyl) tetrahydrofuran) and CV-6209 (2-[N-acetyl-N-(2-methoxy-3-octadecyl-carbamoyloxy propoxycarbonyl)aminomethyl]-1-ethylpyridinium chloride) inhibited thapsigargin-induced production of tumor necrosis factor-alpha. The cyclooxygenase inhibitor indomethacin inhibited prostaglandin E2 production, and further enhanced thapsigargin-induced tumor necrosis factor-alpha production in parallel with further increase in cell-associated PAF production. The enhancement of tumor necrosis factor-alpha production induced by thapsigargin plus indomethacin was also inhibited by E6123, L-652,731 and CV-6209. However, exogenously added PAF up to 100 nM did not stimulate production of tumor necrosis factor-alpha. The level of tumor necrosis factor-alpha mRNA was increased by thapsigargin, but was lowered by the PAF receptor antagonist E6123, suggesting that the inhibition of tumor necrosis factor-alpha production by the PAF receptor antagonist is induced at the level of mRNA for tumor necrosis factor-alpha. These findings suggested that concurrently produced cell-associated PAF in thapsigargin-stimulated macrophages up-regulates production of tumor necrosis factor-alpha by acting as an intracellular signaling molecule and the PAF receptor antagonists might penetrate into the cells and antagonize the action of intracellular PAF.

Inhibition by tectorigenin and tectoridin of prostaglandin E2 production and cyclooxygenase-2 induction in rat peritoneal macrophages

Tectorigenin and tectoridin, isolated from the rhizomes of Korean Belamcanda chinensis (Iridaceae) which are used as Chinese traditional medicine for the treatment of inflammation, suppressed prostaglandin E2 production by rat peritoneal macrophages stimulated by the protein kinase C activator, 12-O-tetradecanoylphorbol 13-acetate (TPA), or the endomembrane Ca2+-ATPase inhibitor, thapsigargin. Tectorigenin inhibited prostaglandin E2 production more potently than tectoridin. Neither compound inhibited the release of radioactivity from [3H]arachidonic acid-labeled macrophages stimulated by TPA or thapsigargin. In addition, activities of isolated cyclooxygenase (COX)-1 and COX-2 were not inhibited by the two compounds. Western blot analysis revealed that the induction of COX-2 by TPA or thapsigargin was inhibited by the two compounds in parallel with the inhibition of prostaglandin E2 production. These findings suggest that one of the mechanisms of the anti-inflammatory activities of the rhizomes of Belamcanda chinensis is the inhibition of prostaglandin E2 production by tectorigenin and tectoridin due to the inhibition of the induction of COX-2 in the inflammatory cells.

Characterization of chromosomes and genome organization of Thapsia garganica L. by localizations of rRNA genes using fluorescent in situ hybridization

The karyotype (2n = 22) of Thapsia garganica L. (Apiaceae, Apioideae, Laserpitieae) was constructed using molecular cytogenetics. The size of the 22 chromosomes ranged between 5 and 10 microns. Two chromosomes had satellites on the short arms. The 18S-5.8S-26S rDNA genes were located to the two satellites by fluorescent in situ hybridization (FISH). The 5S rDNA repeat unit was amplified and located by FISH to one pair of the non-satellited chromosomes. Sequencing 5S rDNA of T. garganica revealed two classes of genes based on distinct intergenic spacer regions of 191/193-bp and 181-bp. respectively. The ITS1 and ITS2 of the 18S-5.8S-26S repeats were also amplified and phylogenetic analysis placed T. garganica in a distinct clade from the Daucus clade containing Laserpitium sp. The organization of T. garganica L. genome is tentatively divided in group A of 14 chromosomes with median centromere and of which one pair (q/p 1.22) contains single 5S rDNA locus on the long arm. Group B consists of six chromosomes with subterminal centromeres (q/p between 4.23 and 7.92) and finally group C with the satellited chromosome pair containing the 18S-5.8S-26S rDNA locus at the secondary constriction.

Inhibition by auranofin of the production of prostaglandin E2 and nitric oxide in rat peritoneal macrophages

In rat peritoneal macrophages, 12-O-tetradecanoylphorbol 13-acetate (TPA) (16.2 nM) stimulated production of both prostaglandin E2 and nitric oxide. TPA also increased the levels of mRNA for cyclooxygenase-2 and inducible nitric oxide synthase, suggesting that the increase in the production of prostaglandin E2 and nitric oxide is due to the increase in the levels of mRNA for cyclooxygenase-2 and inducible nitric oxide synthase, respectively. The TPA-induced increase in prostaglandin E2 production was partially inhibited by the inhibitor of nitric oxide synthase L-N(G)-monomethyl-L-arginine acetate (L-NMMA), and the TPA-induced increase in nitric oxide production was partially inhibited by the cyclooxygenase inhibitor indomethacin, suggesting that both the production of prostaglandin E2 and nitric oxide in TPA-stimulated macrophages is influenced by each other. The orally active chrysotherapeutic agent auranofin, at 3 and 10 microM, inhibited the TPA-stimulated production of prostaglandin E2 and nitric oxide, and suppressed the TPA-induced increase in the levels of mRNA for cyclooxygenase-2 and inducible nitric oxide synthase. These findings indicate that the inhibition by auranofin of the TPA-stimulated production of prostaglandin E2 and nitric oxide is due to the decrease in the levels of mRNA for cyclooxygenase-2 and inducible nitric oxide synthase, respectively, and the interaction of the production between prostaglandin E2 and nitric oxide may partly be involved in the mechanism for the inhibition by auranofin of the production of both prostaglandin E2 and nitric oxide.

Activation of the Epidermal Platelet-Activating Factor Receptor Results in Cytokine and Cyclooxygenase-2 Biosynthesis

Recent studies suggest that the lipid mediator platelet-activating factor (PAF) is involved in keratinocyte function and skin inflammation. Indeed, PAF is found in association with inflammatory skin diseases, intradermal injections of PAF induce inflammation, and keratinocytes express functional PAF receptors (PAF-R). One mechanism by which the keratinocyte PAF-R could contribute to epidermal functions and inflammatory states would be through the synthesis of inflammatory regulators, such as PAF, PGs, and cytokines. The ability of the epidermal PAF-R to induce the synthesis of these immunomodulators was tested using a model system created by transduction of the PAF-R-negative human epidermal cell line KB with the PAF-R. Activation of this epidermal PAF-R resulted in arachidonic acid release, and the biosynthesis of PAF and PGE2. In addition, the KB PAF-R triggered increased levels of mRNA and protein for the inducible isozyme of cyclooxygenase (COX-2) as well as IL-6 and IL-8, both of which have been implicated in skin inflammatory processes. Studies with the human keratinocyte-derived epidermal cell line HaCaT revealed that activation of the endogenous PAF-R led to the increased accumulation of COX-2, IL-6, and IL-8 mRNA similar to that seen with the KB PAF-R model system. Finally, treatment of HaCaT keratinocytes with IL-8 resulted in PAF biosynthesis, indicating the existence of a positive feedback loop between IL-8 and PAF in epidermal cells. These studies suggest involvement of PAF and the PAF-R in the epidermal cytokine network.

Inhibition of tumor necrosis factor-alpha production by SK&F 98625, a CoA-independent transacylase inhibitor, in cultured rat peritoneal macrophages

When rat peritoneal macrophages were incubated in medium containing thapsigargin, tumor necrosis factor-alpha (TNF-alpha) production was increased time-dependently. In the presence of SK&F 98625, a CoA-independent transacylase inhibitor, the thapsigargin-induced TNF-alpha production was inhibited dose-dependently. Platelet-activating factor (PAF) and prostaglandin E2 (PGE2) production were also inhibited by SK&F 98625. The SK&F 98625-induced inhibition of TNF-alpha production was not prevented by addition of PGE2. PAF antagonists such as E6123, L-652,731 and CV-6209 partially inhibited the thapsigargin-induced TNF-alpha production, suggesting that concurrently produced PAF in thapsigargin-stimulated macrophages up-regulates TNF-alpha production. The inhibition by SK&F 98625 of thapsigargin-induced TNF-alpha production might be partly due to the inhibition of PAF production.

Dual effects of auranofin on prostaglandin E2 production by rat peritoneal macrophages

Incubation of rat peritoneal macrophages in medium containing various concentrations of auranofin (1, 3 and 10 microM) increased prostaglandin E2 production at 4 h in a concentration-dependent manner, in accordance with the increase in the release of [3H]arachidonic acid from membrane phospholipids. However, at 20 h, no stimulation of prostaglandin E2 production by auranofin was observed. When the peritoneal macrophages were incubated in the presence of 12-O-tetradecanoylphorbol 13-acetate (TPA), thapsigargin or A23187, prostaglandin E2 production at 4 and 20 h was enhanced. The stimulator-induced prostaglandin E2 production at 20 h was suppressed by 10 microM of auranofin. Western blot analysis demonstrated that auranofin inhibited the induction of cyclooxygenase 2 by TPA, thapsigargin or A23187 at 4 and 20 h. The level of cyclooxygenase 1 did not change by treatment with these stimulators in the presence or absence of auranofin. These findings suggest that auranofin has dual effects on prostaglandin E2 production: without stimulation, auranofin increases prostaglandin E2 production at 4 h due to the increased release of arachidonic acid which is converted to prostaglandin E2 mainly by cyclooxygenase 1, but inhibits the stimulator-induced late-phase prostaglandin E2 production by inhibiting the induction of cyclooxygenase 2.

The mechanisms of action of NSAIDs in analgesia

Traditionally, the analgesic action of nonsteroidal anti-inflammatory drugs (NSAIDs) has been explained on the basis of their inhibition of the enzymes that synthesise prostaglandins. However, it is clear that NSAIDs exert their analgesic effect not only through peripheral inhibition of prostaglandin synthesis but also through a variety of other peripheral and central mechanisms. It is now known that there are 2 structurally distinct forms of the cyclo-oxygenase enzyme (COX-1 and COX-2). COX-1 is a constitutive member of normal cells and COX-2 is induced in inflammatory cells. Inhibition of COX-2 activity represent the most likely mechanism of action for NSAID-mediated analgesia, while the ratio of inhibition of COX-1 to COX-2 by NSAIDs should determine the likelihood of adverse effects. In addition, some NSAIDs inhibit the lipoxygenase pathway, which may itself result in the production of algogenic metabolites. Interference with G-protein-mediated signal transduction by NSAIDs may form the basis of an analgesic mechanism unrelated to inhibition of prostaglandin synthesis. These is increasing evidence that NSAIDs have a central mechanism of action that augments the peripheral mechanism. This effect may be the result of interference with the formation of prostaglandins within the CNS. Alternatively, the central action may be mediated by endogenous opioid peptides or blockade of the release of serotonin (5-hydroxytryptamine; 5-HT). A mechanism involving inhibition of excitatory amino acids of N-methyl-D-aspartate receptor activation has also been proposed.