Peroxidase-like activity of ferruginous bodies isolated by exploiting their magnetic property

Our plain-English summary of Peroxidase-like activity of ferruginous bodies isolated by exploiting their magnetic property, by V. Borelli, E. Trevisan, F. Vita, et al (Journal of Toxicology and Environmental Health. Part a, 2012).

The study

• Authors: V. Borelli, E. Trevisan, F. Vita, C. Bottin, M. Melato, C. Rizzardi, G. Zabucchi
• Journal: Journal of Toxicology and Environmental Health. Part a
• Published: 2012;75(11):603-23
• Cited by: 6 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Ferruginous bodies (FB) are polymorphic structures whose formation is macrophage dependent, and are composed of a core, which may consist of an asbestos fiber coated with proteins, among which ferritin is the main component. Within ferritin, the ferric and ferrous ions are coordinated as ferrihydrite, which is the main iron (Fe) storage compound. However, when ferritin accumulates in some tissues following Fe overload it also contains magnetite along with ferrihydrite, which endows it with magnetic properties. Recently studies showed that magnetite exerts peroxidase-like activity, and since ferruginous bodies display magnetic properties, it was postulated that these particular structures may also contain magnetite within the ferritin coating, and thus may also exert peroxidase-like activity. Histochemical analysis for peroxidase of isolated FB smears demonstrated positive staining. Samples isolated from 4 different autopsy lung fragments were also able to oxidize 3,3',5,5'-tetramethyl-benzidine to a blue colored compound that absorbs at 655 nm. This activity was (1) azide and heat insensitive with optimal pH from 5 to 6, and (2) highly variable, changing more than 25-fold from one sample to another. These findings, together with evidence that the peroxidase-like activity of ferruginous bodies has a hydrogen peroxide and substrate requirement different from that of human myeloperoxidase, can exclude that this enzyme gives a significant contribution to the formation of FB. Standard Fe-rich asbestos fibers also express a peroxidase-like activity, but this appears negligible compared to that of ferruginous bodies. Strong acidification of standard Fe-containing asbestos fibers or magnetically isolated ferruginous bodies liberates a high amount of peroxidase-like activity, which is probably accounted for by the release of Fe ions. Further, FB also damage mesothelial cells in vitro. Data suggest that FB exert peroxidase-like activity and cytotoxic activity against mesothelial cells, and hence may be an important factor in pathogenesis of asbestos-related diseases.

In plain English

This laboratory study examined ferruginous bodies, iron-coated fiber structures that form in the lung. The authors isolated them magnetically from autopsy lung tissue of four people who died of mesothelioma after asbestos exposure in shipbuilding. Analysable cores were mostly amosite, with crocidolite in a few cases. All four samples showed peroxidase-like (enzyme-like) activity, varying more than 25-fold between samples. Unlike the white-blood-cell enzyme myeloperoxidase, it was only weakly blocked by azide. The authors wrote that boiling did not significantly inhibit it, but their table shows a large drop for one sample. Its best pH was 5 to 6. Standard crocidolite, amosite and anthophyllite fibers showed activity the authors judged negligible by comparison. Chrysotile and wollastonite showed none in the standard assay and weak activity after strong acidification. Strong acid released soluble activity, possibly free iron. In cultured human mesothelial cells, one sample plus hydrogen peroxide caused damage within 3 hours; neither alone did. The authors concluded the bodies may be an important factor in asbestos-related diseases. Magnetite, their suspected active compound, had not yet been shown to be present.

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) study of ferruginous bodies isolated magnetically from autopsy lung tissue, with standard asbestos fibers and a human mesothelial cell line
• Who was studied: lung tissue from four autopsies (samples 61, 104, 110 and 113) of patients who died of mesothelioma and had a history of asbestos exposure from employment in shipbuilding. Each sample had more than 120,000 ferruginous bodies per gram of dried lung tissue.
• Exposure: ferruginous bodies whose analysable cores were mostly amosite, with crocidolite in a few cases. Standard UICC crocidolite, amosite, anthophyllite and chrysotile were also tested, with wollastonite (a nonasbestos silicate) as a control.
• Main results:
  • Ferruginous bodies stained positive for peroxidase-like activity in the presence of hydrogen peroxide in samples 104, 110 and 113. In sample 61 the reaction was harder to detect.
  • All four samples oxidized the test substance TMB. Activity varied more than 25-fold between samples: 0.024 for sample 104 versus 0.534 for sample 113 (OD655 nm per 60 min per 10,000 bodies, with hydrogen peroxide).
  • The text states that boiling for 5 minutes did not significantly inhibit the activity of the ferruginous bodies, whereas human myeloperoxidase was completely inhibited by heat. However, Table 1 shows sample 113 falling from 0.534 to 0.073 after boiling, while the text says boiling increased that sample's activity by more than 35%.
  • Azide inhibited myeloperoxidase almost completely (98%). Inhibition of the ferruginous body samples and of standard crocidolite was significantly lower.
  • The optimal pH of the ferruginous body activity was in the range 5 to 6.
  • Standard crocidolite, amosite and anthophyllite fibers showed some activity, which the authors judged negligible as a contribution to ferruginous body activity.
  • Under the standard assay, activity was absent in chrysotile and wollastonite.
  • After strong acidification, anthophyllite, chrysotile and wollastonite showed weak activity, higher than at pH 4.8.
  • After strong acid treatment, the fiber-free liquid from crocidolite oxidized TMB, indicating that soluble activity was released. The authors suggested this may be free iron ions.
  • Sample 113 plus hydrogen peroxide damaged human mesothelial cells (MET-5A) within 3 hours, measured by LDH release. Ferruginous bodies alone or hydrogen peroxide alone had no effect.
• The authors' conclusion: The authors concluded that ferruginous bodies exert peroxidase-like activity that significantly injured mesothelial cells, and that the bodies may therefore be an important factor in the development of asbestos-related diseases.
• Limitations the authors state:
  • Some structures in every sample may have formed on a nonasbestos core, so the samples are described generally as ferruginous bodies.
  • Black amorphous iron-rich particles contaminated the samples (60%, 25%, 30% and 12% of particles in samples 61, 104, 110 and 113). Their effect could not be confirmed until they can be separated from the bodies.
  • The suggestion that magnetite is responsible for the activity has not been demonstrated.

Topics

Medical terms in this study, explained in our Lexicon: Ferruginous Bodies, Macrophage, Ferritin, Ferrihydrite, Autopsy, Mesothelial Cells.

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