Peroxidase-Like Activity of Ferruginous Bodies Isolated by Exploiting their Magnetic Property

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.

Acknowledgments

The authors acknowledge grants from Friuli Venezia Giulia Region, Commissione Amianto, 2009.

Notes

VB carried out all the purification and characterization procedures of ferruginous bodies and was involved in acquisition, analysis, and interpretation of results, and drafted the article. ET carried out assays for the evaluation of peroxidase and cytotoxic activity of ferruginous bodies. FV carried out electron microscopy analysis of ferruginous bodies. CB and CR contributed to the technical aspects of treatment of human samples and were responsible for ferruginous body counting. MM provided, as an expert in diagnosis of asbestos-related diseases, the rational interpretation of the study. GZ directed the work, the rational interpretation of the study, and critically revised the article. All authors read and approved the final article.