Stimulus-specific production of cyclooxygenase and lipoxygenase metabolites of arachidonic acid by bovine alveolar macrophages

In-vitro studies on mechanisms of immunosuppression associated with bovine respiratory syncytial virus

Bovine respiratory syncytial virus (BRSV) depressed the proliferative reactivity of normal ovine peripheral blood lymphocytes to phytohaemagglutinin (PHA). This BRSV-induced reduction in proliferative reactivity was not reversed or ameliorated by the addition of (1) indomethacin or flunixin meglumine, substances known to inhibit the production of prostaglandins, or (2) the cytokines, interleukin-1 (IL-1) and interleukin-2 (IL-2), or (3) rat growth factor. The results suggest that the suppression of ovine lymphocyte reactivity to PHA associated with BRSV was not caused by the release of cyclooxygenase products such as prostaglandins, or the production of inhibitors of IL-1 or IL-2.

Effect of induced pyometra on luteal lifespan and uterine fluid concentrations of prostaglandins and interferons in cows

The objective was to determine whether occurrence of persistent corpora lutea in cows with pyometra could be explained by accumulation of prostaglandins and interferons in the uterus. Pyometra was induced by treatment with hCG, followed by intrauterine infusions of iodine and Actinomyces pyogenes . Five of the seven treated cows developed pyometra as indicated by extended estrous cycles (30-37 + d) and presence of purulent uterine exudate at slaughter (Day 37 after estrus). Mean (+/- standard error) concentrations of prostaglandins E(2) and F(2alpha) for the cows with pyometra were 34.7 +/- 14.4 and 96.3 +/- 28 ng/ml, while the concentrations in uterine flushings in the remaining 2 cows averaged 1.85 +/- 0.7 and 0.9 +/- 0.2 ng/ml, respectively. Based on Western blotting, none of the cows had detectable concentrations of either interferon-alpha or interferon-tau in uterine secretions. In conclusion, pyometra results in increased uterine prostaglandin secretion. While increased secretion of cytokines associated with bacterial infection may be contribute to this effect, there was no evidence in this study to suggest that interferons are involved in the mechanism which causes persistence of the corpus luteum in bovine pyometra.

Diminished arachidonic acid metabolite release by bovine alveolar macrophages exposed to surface-modified silica

Modification of the silica surface has been shown to reduce its cytotoxicity in vitro and its fibrogenic activity in vivo. We have shown silica to be a potent stimulator of arachidonic acid (AA) metabolism in bovine alveolar macrophages (BAM). To determine the effect of surface-modified silica on AA metabolism in BAM, we exposed BAM in vitro to silica treated with aluminum lactate or polyvinylpyridine-N-oxide (PVPNO). BAM were prelabeled with [3H]AA and incubated with 3 and 5 mg of silica. Unmodified silica at these doses elicited maximal AA metabolite release from BAM. AA metabolites were analyzed by high performance liquid chromatography. Lactate dehydrogenase release was quantitated to determine the cytotoxicity of treated and untreated silica on BAM. Treating silica with aluminum lactate or PVPNO significantly (P less than or equal to 0.05) reduced 5-lipoxygenase metabolite release and significantly (P less than or equal to 0.05) increased cyclooxygenase metabolite release. These changes in AA metabolite release were accompanied by a significant (P less than or equal to 0.05) reduction in the cytotoxicities of the treated silicas compared with untreated silica. Our results suggest that the reduced inflammatory and fibrogenic activity of surface-modified silica may in part be due to reduced AA metabolite release from exposed macrophages.

Comparison of arachidonate metabolism by alveolar macrophages from bighorn and domestic sheep

We have defined the metabolites of arachidonic acid (AA) secreted by alveolar macrophages (AMs) of bighorn sheep and domestic sheep in response to three agents: calcium ionophore A23187, phorbol myristate acetate (PMA), and opsonized zymosan. Cells were labeled with [3H]AA prior to stimulation and 11 tritiated metabolites, including prostaglandins (PGs), thromboxanes (TXs), leukotrienes (LTs), and hydroxyeicosatetraenoic acids (HETEs), were detected and quantitated by high-performance liquid chromotography and radiometry. Zymosan stimulation resulted in the release of significantly elevated quantities (P less than 0.05), of LTB4, [5(S), 12(R)-dihydroxy-6,14-cis-8,10-trans-eicosatetraenoic acid], 5-HETE, [5(S)-hydroxyeicosatetraenoic acid], and the nonenzymatic isomers of LTB4, [LTB I, 5(S),12(R)-6-trans-LTB4] and LTB II, [5(S), 12(S)-6-trans-LTB4], from domestic sheep AM when compared to bighorn sheep AM. Phorbol myristate acetate (PMA) stimulation released significantly elevated quantities (P less than 0.04), of TXB2, (thromboxane B2), HHT, [12(S)-12-hydroxy-5,8,10-heptadecaenoic acid], LTB I, LTB II, and 15-HETE, [15(S)-hydroxyeicosatetraenoic acid] from domestic sheep AMs when compared to bighorn sheep AMs. However, after A23187 challenge, only 15-HETE was significantly elevated (P less than 0.04) in domestic sheep AMs when compared to bighorn sheep AMs. These clear differences in AA metabolism of AMs obtained from bighorn and domestic sheep in response to three different agonists suggest not only different control mechanisms for lung metabolism of AA in the two species, but also suggest that differences in the metabolites released may lead to quite different regulation of lung defense mechanisms in the two sheep species.

The effects of different silicas on arachidonic acid metabolism in alveolar macrophages

Bovine alveolar macrophages (BAM) prelabeled with 3H-arachidonic acid (AA) were exposed in vitro to different doses of DQ-12, Minusil-5, and Sigma silicas, or carbonyl iron beads. Arachidonic acid metabolites released into the culture medium by BAM were identified and quantitated using high performance liquid chromatography (HPLC). Cytotoxicity was assessed by the release of lactate dehydrogenase (LDH). At doses of 0.1 or 0.25 mg of DQ-12 silica and of 0.25 or 0.5 mg of Minusil-5 and Sigma silica, the release of cyclooxygenase metabolites (TXB2, PGE2, PGF2, and HHT) comprised greater than 95% of the total released AA metabolites. Silica doses above 0.5 mg led to 5-lipoxygenase metabolite release (LTB4, its two nonenzymatic isomers, and 5-HETE). This shift to 5-lipoxygenase metabolite release paralleled increased cellular cytotoxicity and was observed for each of the silicas. In contrast to silica stimulation, carbonyl iron beads elicited only small quantities of cyclooxygenase metabolites, no 5-lipoxygenase metabolites, and showed little cytotoxicity toward BAM. The relative potency of each particulate for stimulating the release of AA metabolites and LDH was calculated with DQ-12 greater than Minusil-5 greater than Sigma much greater than carbonyl iron beads. Our results indicate that the cytotoxic and presumed fibrogenic potential of a silica may be correlated with the potency to stimulate the release of 5-lipoxygenase metabolites from AM.

Production of arachidonic acid metabolites by caprine alveolar macrophages

The in vitro release of arachidonic acid (AA) metabolites from caprine alveolar macrophages (CAM) stimulated with the calcium ionophore A23187 or opsonized zymosan was examined. Leukotriene B4 [5(S),12(R)-6,14-cis-8,10-trans-dihydroxyeicosatetraenoic acid] was the major AA metabolite elicited with either agonist; smaller amounts of 12- and 5-mono-hydroxyeicosatetraenoic acid (HETE), and 12-hydroxyheptadecatrienoic acid (HHT) were also detected. Zymosan stimulation also caused the release of very small quantities of prostaglandins E2 and F2 alpha, and thromboxane B2. Our report is the first to describe arachidonic acid metabolism in CAM.

Pathways of arachidonic acid metabolism in human amnion cells at term

We have compared the metabolism of (3H) arachidonic acid by monolayers of human amnion, cells obtained prior to or following labor at term. Radiolabel was either added exogenously or previously incorporated into cellular phospholipid pools to compare metabolism of arachidonic acid from different substrate sources. Cells obtained both prior to and following labor synthesized metabolites co-chromatographing on HPLC with di- and mono-HETEs and also a metabolite with polarity corresponding to a epoxyeicosatrienoic acid. Both types of cells were able to synthesize PGE2 when (3H) arachidonic acid was added exogenously. However, only those cells obtained following labor synthesized PGE2 from (3H) arachidonic acid incorporated into intracellular pools. These findings suggest that the cyclooxygenase and PGE2 isomerase enzymes are present in amnion prior to delivery but that exogenous arachidonic acid would be required for PGE2 synthesis at that time as the enzymes do not appear to be linked to a source of endogenous arachidonic acid. At the time of parturition, there may be a switching on of an enzyme system to generate arachidonic acid from intracellular pools specifically for PGE2 synthesis or alternatively coupling of such a system to a cyclooxygenase-PGE2 isomerase system resulting in PGE2 synthesis. These findings raise intriguing new possibilities for the regulation of eicosanoid synthesis in amnion which may include membrane topography, substrate pool-enzyme linking and regulation of specific phospholipase enzymes.

Stimulation of arachidonic acid metabolism in silica-exposed alveolar macrophages

The molecular events involved in both the initiation and development of silicosis are at present poorly defined, although mediators released from macrophages exposed to silica particles are believed to play a role. We have investigated the in vitro production of arachidonic acid (AA) metabolites in adherent bovine alveolar macrophages (BAM) incubated with crystalline silica. BAM were prelabeled with 3H-AA and incubated with 0.5-5.0 mg silica. Lipid metabolites released into the culture medium were analyzed by high-performance liquid chromatography. Simultaneously, lactate dehydrogenase (LDH) was assayed to provide an indication of cell injury. No 5-lipoxygenase metabolites were detected at the lowest silica dose tested (0.5 mg/well), but 5-hydroxyeicosatetraenoic acid (5-HETE) was the major AA metabolite detected between 1.5 and 5.0 mg of silica. A fivefold increase in the production of leukotriene B4 (LTB4) and its two nonenzymatic diastereomers (Isomers I and II) was observed as the silica concentration was increased from 1.0 to 5.0 mg. In contrast, the release of cyclooxygenase products declined with increasing concentrations of silica. LDH release increased in a linear, dose-dependent fashion in the range of silica doses used. The kinetics of eicosanoid release was investigated over a 3-h interval and LDH release was assayed for each time point. Within 15 min following silica addition, a shift to the production of 5-lipoxygenase metabolites was observed, accompanied by a reduction in cyclooxygenase products. This rapid alteration in AA metabolism preceded cell injury as measured by LDH release. These results demonstrate that silica is a powerful stimulator of arachidonic acid metabolism in BAM. Moreover, silica selectively stimulates the 5-lipoxygenase pathway as the dose of silica increases. Our results suggest that dysfunction in arachidonate metabolism could contribute to the pathogenesis of silicosis.