Asbestos Bodies in Human Lung: Localization of Iron and Carbon in the Coating

Abstract

Asbestos is a term that includes six fibrous mineral phases related to different lung diseases, including asbestosis, lung cancer, and Malignant Pleural Mesothelioma (MPM). Since the last century, these minerals have been widely studied under their mineralogical/chemical and physical aspects with in vivo and in vitro studies to understand the mechanisms of their carcinogenicity. There are several techniques described in the literature, as optical and electron microscopies, for the identification of coated (asbestos bodies, ABs) and uncoated fibers, but only micro-Raman spectroscopy permits a sure characterization of these minerals—and of the related phases—directly in the histological sections of pulmonary parenchyma without any manipulation. In this case, the risk of the loss of associated inorganic phases from asbestos bodies (ABs) and fibers (e.g.: iron or carbonaceous micro-particles) is avoided. Asbestos bodies are produced by the activity of alveolar macrophages with degradation/inactivation of asbestos fibers. Inside the alveolar macrophages, organic and inorganic material settles on the foreign fibers forming an iron-rich proteic and carbonaceous coating. In this study, Variable Pressure Scanning Electron Microscopy with annexed Electron Dispersive Spectroscopy (VP-SEM/EDS) and micro-Raman spectroscopy were applied to the characterization of the phases in the ABs. Characterization of carbonaceous materials (CMs), observed in pristine asbestos phases in previous works, was therefore performed, addressing the micro-Raman laser beam on different points of the asbestos bodies, and Raman mappings on ABs were carried out for the first time. Coupling the data obtained by VP-SEM/EDS and micro-Raman spectroscopy, it was possible to collect information about the iron and carbonaceous phases adhered to the fibers, probably lost during the classical tissue digestion procedures. Information about both mineral and carbonaceous components might be useful to understand the whole structure of “asbestos bodies” and the inflammogenic and carcinogenic effects of the asbestos phases coupled to CMs, that might derive from cigarette smoke or from environmental pollution; this study might be useful to deepen also the possible detrimental role of ABs in the tissues.