PubMed · 6538167
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J Hopkins. 1984. Epidemiological studies on ingested asbestos.. https://doi.org/10.1016/0278-6915(84)90112-1
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In this report, we show that enhanced shedding of CD44 might contribute to the down-regulation of this receptor observed after phagocytosis of MnO2 particles by PMA-differentiated U-937. The apparent Mr of the soluble CD44 detected in culture supernatants was slightly lower than that of the membrane form suggesting that shedding resulted from proteolytic cleavage. Increased shedding of CD44 was also noted with other mineral particles (chrysotile and DQ12) but to a lower extent whereas some (TiO2 and amosite) had no effect on this process. These results indicate that shedding enhancement was particle-specific rather than a general consequence of phagocytosis. The ability of the particles to enhance CD44 shedding was not directly dependent on their cytotoxic potency. Different patterns of reactivity were noted with CD11b, suggesting that the underlying mechanisms are specific.
Production and export figures of South African asbestos were analyzed over 1959-1993. They show stable sales of chrysotile. Those of crocidolite and amosite reached their peaks in the mid-1970s, after which trade fell drastically, crocidolite to 5% of its earlier peak and amosite to nil. Factors responsible for these virtual collapses were health issues, stricter legislation in First World countries, and litigation. In 1992, 21 countries continued to import crocidolite, although in reduced quantities. In the early 1960s, Europe and North America were the major recipients of South African asbestos. By 1989-91, these regions were surpassed by the Far East, which took over 90% of chrysotile and 70% of amosite. For crocidolite at that time, the Middle East took nearly 40%, Europe 28%, and Africa 21%. This implies that the newly importing countries can confidently expect an increase in asbestos-related disease and death well into the twenty-first century, even if the trade ceased now.
Treatment of aqueous suspensions of different asbestos fibers (amosite, anthophyllite, chrysotile, and crocidolite) at 0-4 degrees C and pH 7.2 with H2O2 results in the consumption of H2O2 with concomitant release of iron and production of O2. During incubations, [H2O2] decreased in proportion to the mass of the suspended fiber, the duration of incubation, and the initial [H2O2]. The consumption of H2O2, production of O2 and release of iron all vary synergistically with the structure of the asbestos fiber. Release of silicon during the incubation was small relative to the decrement in [H2O2], reflecting a lack of dissolution of the fiber. The data are consistent with a redox process for the release of surface bound iron and it is significant that iron release occurs in the absence of a Fe(II) or Fe(III) chelator. The implications of iron release from the asbestos surface may be important in inflammatory disorders in which both silicate bound iron and H2O2 accumulate.