Production of arachidonic acid metabolites by macrophages exposed in vitro to asbestos, carbonyl iron particles, or calcium ionophore

Our plain-English summary of Production of arachidonic acid metabolites by macrophages exposed in vitro to asbestos, carbonyl iron particles, or calcium ionophore, by S. Kouzan, A.R. Brody, P. Nettesheim, et al (The American Review of Respiratory Disease, 1985).

The study

• Authors: S. Kouzan, A.R. Brody, P. Nettesheim, T. Eling
• Journal: The American Review of Respiratory Disease
• Published: 1985;131(4):624-32
• Cited by: 80 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Consequent to asbestos deposition, alveolar macrophages (AM) accumulate at alveolar duct bifurcations where they phagocytize fibers. Because phagocytosis can stimulate the release of arachidonic acid (AA) metabolites, the possibility that secretion of these powerful mediators of inflammation might be induced by chrysotile asbestos was investigated in vitro. Rat AM were treated in vitro with chrysotile asbestos, and the cyclooxygenase products--prostaglandins, thromboxane B2 (TXB2), 12-hydroxy-5,8,10-heptadecatrienoic acid (HHT)--and lipoxygenase products--leukotrienes (LT), hydroxyeicosatetraenoic acids (HETE)--secreted in the medium were isolated by high-performance liquid chromatography. Composition of the AA metabolites released was compared with that from those stimulated by the calcium ionophore A 23187 (20 microM) and by another particulate phagocytic stimulus, i.e., carbonyl iron beads. Calcium ionophore stimulation induced a marked release of various AA metabolites in the medium from both the cyclooxygenase pathway (HHT, TXB2, and PGE2, in decreasing quantities, respectively) and the lipoxygenase pathway (LTB4, 5-HETE, 12-HETE, and LTC4). The major product was LTB4. Treatment of the macrophages with asbestos fibers induced the release of a similar array of AA metabolites, although there were smaller amounts of LTC4 and 12-HETE, but increased quantities of PGF2 alpha. A time course study showed a steady increase in metabolite production for 1 h, followed by a plateau. In addition, the amount of metabolites released was dependent on asbestos concentrations. Phagocytosis of iron beads induced the secretion of the same metabolites as asbestos stimulation, but in larger quantities, probably reflecting the lack of cytotoxicity of the particle.(ABSTRACT TRUNCATED AT 250 WORDS)

In plain English

This laboratory study used alveolar macrophages (lung scavenger cells) washed out of the lungs of male rats. The cells were labeled with radioactive arachidonic acid. They were then exposed in dishes, usually for 35 minutes, to one of three things: Canadian chrysotile asbestos fibers, carbonyl iron beads, or a chemical called calcium ionophore A23187. The researchers measured the arachidonic acid products the cells released, which are inflammation-related substances such as prostaglandins, thromboxane and leukotrienes. Asbestos-exposed cells released products from both the cyclooxygenase and lipoxygenase pathways. Total radioactivity released was 45% of that seen with the ionophore. The ratio of lipoxygenase to cyclooxygenase products was 0.93 with asbestos and 4.73 with the ionophore. Release rose and then levelled off after 1 hour for most products, and it depended on the amount of asbestos. Iron beads, which the authors describe as nonfibrogenic, caused release of the same main products. Leaving out serum while the cells attached and were labeled reduced release, especially of cyclooxygenase products. The authors concluded that this release appears to be a nonspecific response of rat macrophages to particle uptake. They also concluded it seems improbable that these substances, by themselves, explain the lung changes asbestos causes.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: laboratory (in vitro) experiment on rat lung cells
• Who was studied: Alveolar macrophages obtained by lung lavage from male CD white rats aged 10 to 15 weeks (Charles River Breeding Laboratories). The lavage fluid was 98% alveolar macrophages. The number of rats is not stated.
• Exposure: Canadian chrysotile asbestos from Johns Manville, prepared so that 95% of fibers were less than 0.2 micrometres in diameter and less than 6 micrometres long. It was used at 0.1 mg per ml, about 16 micrograms per square centimetre of dish. Comparison stimuli were carbonyl iron beads (0.6 mg per square centimetre) and calcium ionophore A23187 (20 micromolar). Incubations lasted 35 minutes unless otherwise specified.
• Main results:
  • Unstimulated (control) macrophages released only small amounts of arachidonic acid metabolites, and no leukotrienes were detected.
  • Calcium ionophore increased the total radioactivity released into the medium 9-fold compared with control cultures.
  • In asbestos-treated macrophages, the total radioactivity released was 45% of that seen after calcium ionophore stimulation. Asbestos produced a similar absolute amount of cyclooxygenase metabolites, plus PGF2-alpha, which was not found with the ionophore. It produced fewer lipoxygenase metabolites, with little or no LTC4.
  • The ratio of lipoxygenase to cyclooxygenase metabolites was 0.93 after asbestos exposure and 4.73 after calcium ionophore stimulation.
  • After asbestos exposure, arachidonic acid was released within 5 minutes, followed by its metabolites. After 1 hour, levels plateaued for all metabolites except 5-HETE and 12-HETE.
  • Release depended on asbestos concentration. Reducing asbestos from 16 to 4.8 micrograms per square centimetre markedly reduced several metabolites. A further reduction to 1.6 produced only a small further decrease.
  • Carbonyl iron beads produced the same major metabolites as asbestos, and the total radioactivity released was similar. However, iron gave a lower percentage of unmetabolized arachidonic acid and greater amounts of LTB4, TXB2, HHT and 5-HETE.
  • Leaving serum out of the medium during cell adhesion and labeling decreased metabolite release after asbestos, iron or ionophore stimulation, especially of cyclooxygenase metabolites.
  • By scanning electron microscopy, asbestos fibers bound to and were taken up by the cells, and cell death was unusual during the 35-minute exposure.
• The authors' conclusion: The authors concluded that release of arachidonic acid metabolites after phagocytosis appears to be a nonspecific response of rat pulmonary macrophages, because nonfibrogenic iron particles caused the same response. They concluded that it seems improbable these metabolites could, by themselves, explain asbestos-induced lung alterations.
• Limitations the authors state:
  • The authors do not know whether LTB4 is produced in living animals on alveolar surfaces.
  • The preparation method (sonication) could not produce asbestos concentrations higher than 16 micrograms per square centimetre.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile.

Medical terms in this study, explained in our Lexicon: Macrophage, Deposition, Alveolar Macrophage, Phagocytosis, Inflammation, Chrysotile, PGE2.

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