Dibutyryl cAMP attenuates asbestos-induced pulmonary epithelial cell cytotoxicity and decline in ATP levels

Our plain-English summary of Dibutyryl cAMP attenuates asbestos-induced pulmonary epithelial cell cytotoxicity and decline in ATP levels, by V.A. Israbian, S.A. Weitzman, D.W. Kamp (The American Journal of Physiology, 1994).

The study

• Authors: V.A. Israbian, S.A. Weitzman, D.W. Kamp
• Journal: The American Journal of Physiology
• Published: 1994;267(5 Pt 1):L518-25
• Cited by: 9 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Adenosine 3',5'-cyclic monophosphate (cAMP) analogues prevent lung injury in various models by mechanisms that remain unknown. We speculated that cAMP attenuates asbestos-induced pulmonary epithelial cell injury by limiting the effects of an oxidant stress. Agents that increase intracellular cAMP [dibutyryl cAMP (DBcAMP), terbutaline, or aminophylline] but not guanosine 3',5'-cyclic monophosphate (cGMP) attenuated WI-26 cell-specific 51Cr release caused by asbestos. The protective effects of DBcAMP were associated with negligible alterations in asbestos-induced .OH formation or decline in WI-26 cell glutathione levels. Cycloheximide, an inhibitor of protein synthesis, failed to diminish the effects of DBcAMP. ATP levels were measured to determine whether the effects of DBcAMP are due to preservation of cellular ATP. Asbestos caused dose-dependent reductions in cellular ATP and DB-cAMP attenuated these effects. To determine whether the protective effects of DBcAMP related to alterations in WI-26 cell growth, we assessed the effects of DBcAMP on WI-26 cell number over time. DBcAMP diminished WI-26 cell replication and increased the doubling time. These results demonstrate that DBcAMP diminishes asbestos-induced cytotoxicity to cultured WI-26 cells in part by maintaining intracellular ATP levels and inhibiting cellular replication. The reduction in asbestos-induced WI-26 cell injury occurs despite a persistent oxidant stress. The data suggest a novel strategy to limit pulmonary toxicity from asbestos that warrants further investigation.

In plain English

This was a laboratory study of cultured cells, not people. The authors exposed WI-26 cells, an epithelial-like human embryonal lung cell line, to amosite asbestos (500 micrograms per ml) for 18 hours. Asbestos raised cell injury, measured as specific release of radioactive chromium, to 35.6 ± 3.8%; control was 0% by definition. With dibutyryl cAMP (DBcAMP, 1.0 mM) added, release was 6.2 ± 1.1%. Terbutaline and aminophylline, which also raise cAMP, reduced injury too, but dibutyryl cGMP gave negligible protection. DBcAMP did not reduce asbestos-induced hydroxyl radical production or prevent the asbestos-induced fall in cell glutathione. It stayed protective when cycloheximide cut a measure of protein synthesis by about 75%. After 18 hours, asbestos lowered cell ATP levels, and DBcAMP lessened this fall. In serum-containing medium, DBcAMP slowed cell growth, lengthening doubling time from 7.6 ± 1.2 to 9.7 ± 1.5 hours; in serum-free salt solution like that used in the injury test, it arrested growth. The authors concluded that DBcAMP protects these cells partly by maintaining ATP and inhibiting replication. They said the relevance of these in vitro findings awaits further studies.

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: In vitro laboratory experiment on a cultured human cell line (51Cr release cytotoxicity assay plus biochemical assays)
• Who was studied: WI-26 (VA4) cells, a clonal cell line with epithelial-like morphology derived from human embryonal lung, purchased from the American Type Culture Collection; at least six experiments per group
• Exposure: Amosite asbestos (UICC reference standard), mainly 500 micrograms per ml (263 micrograms per square cm) for 18 hours; 50 micrograms per ml was also used in ATP tests. Exposure was with or without DBcAMP, dibutyryl cGMP, terbutaline, aminophylline or cycloheximide.
• Main results:
  • In asbestos-exposed cells, specific 51Cr release was 35.6 ± 3.8% without DBcAMP and 6.2 ± 1.1% with DBcAMP 1.0 mM (P < 0.05)
  • Protection by DBcAMP was dose-dependent. The smallest dose (0.02 mM) gave negligible protection. Maximal protection (about 80%) was seen at doses of 0.25 mM or more (printed as '20.25 mM' in the scan).
  • Dibutyryl cGMP (0.1 and 0.25 mM) gave negligible protection against asbestos-induced injury
  • Agents that raise intracellular cAMP (DBcAMP, aminophylline and terbutaline) reduced the toxic effects of asbestos on the cells. Combining terbutaline and aminophylline gave no additional protection over either alone.
  • Media from asbestos-exposed cells had increased hydroxyl radical levels compared with unexposed cells (9.4 ± 0.6 vs 0.5 ± 0.4). DBcAMP at 0.1 and 1.0 mM did not reduce this.
  • Asbestos (500 micrograms per ml) lowered cell glutathione after 18 hours (control 2.16 ± 0.45 vs asbestos 0.69 ± 0.31 per mg protein, P < 0.05). DBcAMP did not prevent this drop.
  • Cycloheximide reduced protein synthesis by 75 ± 9% but did not diminish the protective effect of DBcAMP
  • After 18 hours, DBcAMP significantly lessened the asbestos-induced fall in cell ATP. Paired values were 6.1 ± 0.9 vs 4.8 ± 0.8 at 50 micrograms per ml of asbestos and 5.5 ± 0.7 vs 3.4 ± 0.8 at 500 micrograms per ml (P < 0.05). The pairs are not explicitly labeled by group.
  • In serum-containing medium, DBcAMP (1.0 mM) increased cell doubling time compared with untreated control (9.7 ± 1.5 vs 7.6 ± 1.2 hours, P < 0.05)
  • In serum-containing medium, DBcAMP-treated cultures had 50% fewer cells than controls. In serum-free HBSS (conditions similar to the cytotoxicity assay), DBcAMP-treated cells remained growth arrested.
• The authors' conclusion: The authors concluded that the protective effect of DBcAMP against asbestos-induced injury to these cultured cells is due in part to maintaining cellular ATP and inhibiting cell growth. They suggested cAMP analogues may offer a novel strategy to limit asbestos-induced lung injury, pending further studies.
• Limitations the authors state:
  • The findings come from cultured cells, and the authors state that their relevance must await further studies
  • The mechanism by which DBcAMP preserves ATP after asbestos exposure is not known

Topics

Medical terms in this study, explained in our Lexicon: Glutathione (GSH).

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• Cigarette smoke augments asbestos-induced alveolar epithelial cell injury: role of free radicals — D.W. Kamp, M.J. Greenberger, et al. (1998)
• Asbestos-induced injury to cultured human pulmonary epithelial-like cells: role of neutrophil elastase — D.W. Kamp, M. Dunne, et al. (1993)
• Role of alphavbeta5 integrin receptor in endocytosis of crocidolite and its effect on intracellular glutathione levels in human lung epithelial (A549) cells — P. Pande, T.A. Mosleh, et al. (2006)
• Cytotoxicity, oxidative stress and genotoxicity induced by glass fibers on human alveolar epithelial cell line A549 — V. Rapisarda, C. Loreto, et al. (2015)
• Asbestos causes DNA strand breaks in cultured pulmonary epithelial cells: role of iron-catalyzed free radicals — D.W. Kamp, V.A. Israbian, et al. (1995)

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