Differential effects of prostaglandin E2 and cyclic AMP on release of arachidonic acid metabolites from resting and lipopolysaccharide-stimulated macrophages

Arachidonic acid induces macrophage cell cycle arrest through the JNK signaling pathway

Background

Arachidonic acid (AA) has potent pro-apoptotic effects on cancer cells at a low concentration and on macrophages at a very high concentration. However, the effects of AA on the macrophage cell cycle and related signaling pathways have not been fully investigated. Herein we aim to observe the effect of AA on macrophages cell cycle.

Results

AA exposure reduced the viability and number of macrophages in a dose- and time-dependent manner. The reduction in RAW264.7 cell viability was not caused by apoptosis, as indicated by caspase-3 and activated caspase-3 detection. Further research illustrated that AA exposure induced RAW264.7 cell cycle arrested at S phase, and some cell cycle-regulated proteins were altered accordingly. Moreover, JNK signaling was stimulated by AA, and the stimulation was partially reversed by a JNK signaling inhibitor in accordance with cell cycle-related factors. In addition, nuclear and total Foxo1/3a and phosphorylated Foxo1/3a were elevated by AA in a dose- and time-dependent manner, and this elevation was suppressed by the JNK signaling inhibitor.

Conclusion

Our study demonstrated that AA inhibits macrophage viability by inducing S phase cell cycle arrest. The JNK signaling pathway and the downstream FoxO transcription factors are involved in AA-induced RAW264.7 cell cycle arrest.

Electronic supplementary material

The online version of this article (10.1186/s12944-018-0673-0) contains supplementary material, which is available to authorized users.

Molecular pharmacology of the beta-adrenergic receptor on THP-1 cells

The beta-adrenergic receptor, its occupancy and subsequent modulation of intracellular cAMP, and mRNA expression were characterized for the promonocytic leukemia cell line THP-1. We report that THP-1 cells appear to express a beta-1 receptor with a Kd of 1.8 +/- 0.3 x 10(-11) microM and a B max of 108 +/- 0.07 fmole/mg protein using 125I-iodocyanopindolol (125I-ICYP). The potency of various beta-adrenergic agonists to compete for the 125I-ICYP binding site followed the order: isoproterenol (0.8 microM) > dobutamine (2.1 microM) > salbutamol (3 microM) > epinephrine (3.8 microM) > soterenol (4.6 microM) > terbutaline (11.1 microM) > norepinephrine (13.8 microM). Occupancy of the beta receptor on THP-1 cells results in activation of adenyl cyclase suggesting that these cells have a functional beta-adrenergic receptor. This receptor also has specific immunoregulatory properties, reducing message levels for tumor necrosis factor--but not interleukin 1, following treatment with isoproterenol (approximate EC-50 of 0.01 microM). We conclude, based on the above criteria, that THP-1 cells express a beta-1 receptor which, following ligand binding, results in increased cAMP leading to downregulation of TNF expression.

Endotoxemia in horses. A review of cellular and humoral mediators involved in its pathogenesis

Endotoxemia remains the leading cause of death in horses, being intimately involved in the pathogenesis of gastrointestinal disorders that cause colic and neonatal foal septicemia. Endotoxins, normally present within the bowel, gain access to the blood across damaged intestinal mucosa, or endotoxemia occurs when gram negative organisms proliferate in tissues. Endotoxins are removed from the circulation by the mononuclear phagocyte system, and the response of mononuclear phagocytes to these lipopolysaccharides (LPS) play an important role in determining the severity of clinical disease. Macrophages become highly activated for enhanced secretory, phagocytic and cidal functions by LPS. Macrophage-derived cytokines are responsible for many of the pathophysiologic consequences of endotoxemia. The arachidonic acid metabolites, prostacyclin and thromboxane A2 likely mediate early hemodynamic dysfunction and the leukotrienes may potentiate tissue ischemia during endotoxemia. Interleukin 1 (IL-1) induces fever and is responsible for the inflammatory cascade, which constitutes the acute phase response. Tumor necrosis factor (TNF), an important proximal mediator of the effects of LPS, acts to initiate events and formation of other molecules that affect shock and tissue injury. Systemic administration of TNF produces most of the physiologic derangements that are associated with endotoxemia and antibodies that are directed against TNF significantly reduce LPS-induced mortality in experimental animals. In response to endotoxins, mononuclear phagocytes express thromboplastin-like procoagulant activity (PCA), which initiates microvascular thrombosis. Both IL-1 and TNF induce PCA expression, creating a positive feedback loop for LPS-induced coagulopathy. A macrophage-derived platelet activating factor contributes to coagulation dysfunction and further stimulates arachidonic acid metabolism. The ultimate consequences of endotoxemia are multiple system organ failure and death. The numerous feedback loops and intertwining cascades of mediators during endotoxemia defy simplistic methods of treatment. The optimal therapy likely involves methods to alter the generation of inflammatory mediators by mononuclear phagocytes.

Phorbol myristate enhanced specific incorporation of arachidonic acid into phospholipids through lysophospholipid acyltransferase in cultured smooth muscle cells

The effect of stimulation of phospholipase with phorbol 12-myristate 13-acetate and lipopolysaccharide on 1-acyl-glycerophospholipid acyltransferase was studied in cultured rabbit aorta smooth muscle cells. The acyltransferase in smooth muscle cells without stimulation was active on a wide range of unsaturated fatty acids and was not arachidonic acid specific. Upon increase in phospholipase activity, acyltransferase activity only with arachidonic acid as substrate increased in a time-dependent fashion. Apparent acyltransferase activity was increased most upon increase in phospholipase activity when lysophosphatidylcholine was used as acceptor. These results suggest that arachidonic acid specific acyltransferase was induced in smooth muscle cells by increase in phospholipase activity. The role of this acyltransferase is postulated to be the specific incorporation of endogenously released arachidonic acid.

Interleukin-1 stimulation of phospholipase activity in rat synovial fibroblasts. Possible regulation by cyclooxygenase products

Tritiated arachidonic acid (3H-AA)-labeled rat synovial fibroblasts stimulated with human recombinant interleukin-1 beta (rIL-1 beta) released incorporated radiolabel in a time-dependent and dose-dependent manner, with labeled prostaglandins representing 29% of the released radiolabel. Treatment of the cells with dibutyryl cAMP or prostaglandin E2 enhanced both spontaneous and rIL-1 beta-induced 3H-AA release; treatment with indomethacin or naproxen inhibited the response. The effects of these cyclooxygenase inhibitors on 3H-AA release were not reversed by the addition of prostaglandin E2. The activities of phospholipase A, phospholipase C, and diglyceride lipase were detected in the homogenates of rat synovial fibroblasts. Pretreatment of synovial cells with rIL-1 beta resulted in a threefold stimulation of phospholipase A activity and a slight increase in phospholipase C activity in cell homogenates. These data show that rIL-1 beta stimulates phospholipase activities in rat synovial fibroblasts and that at least one of these activities may be regulated by either prostaglandins or cAMP.

Phospholipid and arachidonic acid metabolism in zymosan-stimulated human monocytes: modulation by cAMP

Receptor-ligand interaction in mononuclear phagocytes is intimately linked to alterations in membrane phospholipids and release of arachidonic acid (AA). In addition, synthesis of bioactive lipids from released AA can result in further modification of cell responses. Upon challenge with opsonized zymosan, [3H]-arachidonic acid ([3H]-AA)-labeled human monocytes released 25 +/- 2% of their incorporated radiolabel within 30 min. Pretreatment of the monocytes with 5 X 10(-4) M isobutylmethylxanthine (IBMX) or 1 X 10(-3) M dibutyryl cyclic AMP (d-cAMP) inhibited total [3H]-AA release in the presence of zymosan by 47% and 42%, respectively. Analysis of incorporated [3H]-AA in cellular phospholipid pools indicated that significant amounts of label were lost from both phosphatidylcholine (PC) and phosphatidylinositol (PI) during zymosan stimulation. Treatment with d-cAMP substantially inhibited the loss of label from PC, but had no affect on PI. HPLC analysis of cell supernatants from zymosan-treated cells indicated that 5-HETE was the predominant metabolite generated from [3H]-AA, and its production was depressed during treatment with d-cAMP. Phospholipase activity in human monocyte homogenates was not effected by d-cAMP or IBMX at the highest concentrations used, whether these were added directly to the homogenate or by pretreatment of whole cells, demonstrating that inhibition required an intact cell. These results suggest that human monocytes exposed to opsonized zymosan release AA via two mechanisms and that modulation by cAMP is indirectly effecting a phospholipase directed towards PC.

Cyclic adenosine 3'5' monophosphate stimulates prostaglandin E production by human adherent synovial cells

Production of prostaglandin E (PGE) by rheumatoid synovium appears important to regulation of the pathologic process in rheumatoid arthritis. Cells derived from human synovium by proteolytic digestion produce large amounts of PGE which in turn can elevate synovial cell cAMP levels and inhibit cell proliferation. Data presented here indicate that cAMP can further increase production of PGE from adherent synovial cells (ASC). PGE production occurs over 12-72 hr and is not due to the ability of cAMP to inhibit cell proliferation. Exposure of cells to cAMP results in increased release of 3H arachidonic acid from precursors but not in activation of the cyclooxygenase enzyme. This phenomenon suggests the presence in adherent synovial cells of a mechanism for amplifying PGE production.

Differential regulation of the cyclooxygenase pathway in starch elicited rat peritoneal macrophages by prostaglandin E2, U-44069, a stable endoperoxide analogue and dibutyryl-cyclic AMP

The basal and carrageenin-stimulated release of thromboxane (TX) B2, the stable product of TXA2, 6-ketoPGF1 alpha, the stable breakdown product of prostacyclin (PGI2) and prostaglandin (PG) E2 from 24 h starch elicited rat peritoneal macrophages was inhibited by dibutyryl-cyclic AMP (db-cAMP). PGE2 also inhibited the release of TXA2 and 6-keto-PGF1 alpha whereas the stable endoperoxide analogue, U-44069, stimulated PGE2 and 6-keto PGF1 alpha release but inhibited TXB2 release. The effects of all three mediators tested were related to an increase of Mø intracellular cAMP content.

Arachidonic acid, an in vivo inhibitor of carrageenin induced granulomas in the rat

Arachidonic acid (AA) injected locally into carrageenin/sponge granulomas, but not if given orally, inhibited granuloma growth. Granuloma macrophage (M0) infiltration was inhibited, and prostaglandin E2 (PGE2) synthesis (ng/100 mg granuloma dry weight) stimulated, by AA treatment. M0 adenosine 3',5'-cyclic monophosphate (cAMP) levels and granuloma exudate volume were not affected. Granuloma M0s incubated in vitro with arachidonic acid synthesised thromboxane B2 (Txb2), 6-ketoprostaglandin F1 alpha (6-ketoPGF1 alpha), and preferentially, PGE2. The AA inhibition of granuloma growth was possibly mediated via the synthesis of PGE2.