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.
Englen
M D
MD
Department of Veterinary Microbiology and Pathology, College of Veterinary Medicine, Washington State University, Pullman 99164-7040.
Taylor
S M
SM
Laegreid
W W
WW
Liggitt
H D
HD
Silflow
R M
RM
Breeze
R G
RG
Leid
R W
RW
D000818:Animals; D001094:Arachidonate 5-Lipoxygenase / Q000378:metabolism; D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000378:metabolism*; D002417:Cattle; D004537:Eicosanoic Acids / Q000378:metabolism*; D066298:In Vitro Techniques; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism*; D011451:Prostaglandin-Endoperoxide Synthases / Q000378:metabolism; D011650:Pulmonary Alveoli / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D012822:Silicon Dioxide / Q000633:toxicity*; D012829:Silicosis / Q000209:etiology / Q000378:metabolism
D001095:Arachidonic Acids; D004537:Eicosanoic Acids; D016718:Arachidonic Acid; D012822:Silicon Dioxide; D001094:Arachidonate 5-Lipoxygenase; D011451:Prostaglandin-Endoperoxide Synthases