Document 7RymjZ8B4J499Do8JQ80Lg0xo

i 8073 R30 P FARB UA8 INVEST 379 f,,i/"-**'- 00-<83T/S3/49M-0379W100/ ' Usoiutosy iNvirncATioH Copyn*(li t19*3 by th* Uniud Suup-Ctaadioa Dmami of tho Inunuuoool Acadtay of Pttholao Editorial VoL . No.. p. yrt. tu Prvurt m I S A How Do Mineral Dusts Cause Lung Injury? The chronic inhalation of silica or asbeatoa particle* can lead to disabling pulmonary fibrosia. In addition, asbestos exposure is associated with at least two types of malignant tumors. By contrast, chronic inhalation of native carbon particles, such as soft coal or the soot from the burning of fossil fuels, is accompanied neither by significant pulmonary fibrosis nor by increased risk of neoplasia. It is now generally accepted that this difference between the response to fibrogenic minerals, t.g., silica and asbestos, and relatively inert carbon particles is a consequence of the ability of the former to kill the cells that engulf them. Analysis of th* mechanisms of silica and asbestos cytotoxicity has, therefore, become central to an understanding of the pneumoconioses that result from exposure to these and other mineral dusts. Silica and asbestos present unique problems to th* experimental toxicologist Th* chemical basis for their biologic activity is not readily apparent In addition, unlike other toxins that are distributed homogeneously in biologic media, silica and asbestos are insoluble minerals, the physical properties of which affect their biologic activity. Cytotoxicity seems to result from contact between silica and asbestos particles and target cells. For many years, the killing of these cells has been related to the fate of th* particles after this contact. Alveolar macrophages are the major cells that phagocytose the mineral dusts upon their inhalation. Tbs release of lysosomal enxymes into th* cytosol follows rapidly (1,3,7,9). The breakdown ofcellular components as a result of the release of lyaoeomal components has been hypothesized to produce irreversible cell injury (5). Although intracellular lysosomal rupture has been documented in silica- and asbestos-treated macrophages, th* evidence that it causes cell death is only circumstantial. Two conditions must be met before a causal relationship between lysosomal rupture and cell death can be inferred Lysosomal release must occur before cell injury becomes irreversible, and the mechanisms whereby such release leads to irreversible injury must be identified In th* case of most hepatotoxins, rupture of lysoeomes occurs after irreversible injury has developed (10). In these situations, th* late release of lysosomal enxymes simply accompanies lysis or enzymatic removal of dead cells. By contrast, lysosomal rupture is temporarily related to ceil death in the toxicity of silica and asbestos to macrophages. However, in these cases th* biochemical and functional consequences of intracellular lysosomal rupture have not been identified Furthermore, Kan* et aL (8) were able to dissociate intracellular lysosomal rupture from the subsequent cell death after exposure of macrophages to silica particles. Without extracellular calcium ions, phagocytosis of silica particles occurred followed by intracellular lysosomal rupture. However, all of th* cells remained viable over the time course that cells exposed to silica particles, in th* presence of extracellular calcium ions, were killed In addition, lysosomal rupture was not associated with measurable degradation of total DNA, RNA, protein, or phospholipid even in th* presence of extracellular calcium ions. This finding suggests that intracellular lysosomal rupture is not related to the cell death caused by silica and, presumably, therefore, also by asbestos. With silica, cell death was dependent on extracellular calcium ions and seemed to be a consequence of an influx' ^ of these ions across th* permeability barner at th*^ plasma membrane, which waa directly damaged by"H exposure to these particles. Such a conclusion places the problem of cell injury0 induced by mineral particles in th* same context as the study of the mechanisms of action of other hazards. It is becoming increasingly clear that disturbances in plasma0 membrane function are responsible for the genesis off'SJ irreversible cell injury with moet toxins (4). The study0 of mineral particle-inducad cell injury should therefore, increasingly focus on th* effects such agents have on cellular membranes. In this issue of Laboratory Irwtttigation, Brody, Berwyn, and Hill (2) extend our understanding of th* mechanism of the interaction of asbestos fibers with the erythrocyte membrane. Red blood cells lyse after exposure to asbestos or silica, and th* release of hemoglobin can be readily quantitated as an index of membrane damage. Red cell hemolysis is, therefore, a convenient experimental model with which to study the effect of mineral particlea on cellular membrane*. Brody et oL (2) have studied the interactions of chrysotil* and crocidolit* asbestos with red blood cell membranes. Data are provided to support the hypothesis that th* membrane disruption by asbestos is secondary to an initial interaction between positive charges on the fiber surface and negatively charged sialic acid residues on th* membrane. Previously, it was shown that treatment of erythrocytes with neuraminidase, an enzyme that removes sialic acid born th* cell surface, reduces the hemolytic activity of chrysotil* asbestos (6). Chrysotile, but not th* less active crocidolit* asbestos, has now been shown to prevent the neuraminidase-mediated removal of sialic acid from red blood cells, implying that th* CUPVHICHT 63 IU.1AMS 6 elLXINS Pflkai f T iAflhJG DOW 07524 / 380 FARBER LaMMUTOBV iNVOTKAIION inunction bttwran tht chrysotile and th membranebound lialic acid group* pnvantcd tha anzyma tram removing them. Tha authors than used a second aaaay to obtain a similar result. Wheat germ agglutinin ia known to bind to Af-Kctyl neuraminic (sialic) acid and Af-ecetyl glucosamine. Wheat garm agglutinin bound to red blood call membranea can be visualized, if it ia first conjugated with colloidal gold paniclea. Tha number of gold spheres bound to a membrane can than ba determined with scanning electron microscopy. Brady at aL (2) show that the pretreatment of red blood calls with chryaotile, but not with crocidoliu, asbestos reduced tha number of Au-wheat germ agglutinin-labeled sites to leas than 30% of the control level. On the basis of the present and previous studies, it may be presumed that the interaction between asbestos fibers and negatively charged sialic acid residues on the ted cell surface is followed by an increase in the permeability to sodium and potassium ions. An influx of sodium and accompanying water molecules would then lead to hemolysis. How does the interaction with asbestos fibers change the permeability of the red cell membrane? Brody et aL (2) do not provide any data relative to this critical question but do suggest a possible mechanism, namely, redistribution of membrane glycoproteins. Aggregations of these proteins could create new ion channels. Other possible mechanisms include an increased ordering of the phospholipids adjacent to the bound asbestos fibers. Altered lipid-protein or lipid-lipid interactions could affect the permeability of the membrane. Additional studies are needed to diatirgnifh between these potential mechanisms. It also remains to be shown that the findings regarding the nature of the interaction of asbestos fibers with erythrocytes are relevant to the effects on macrophages. The finding* of Brody at aL (2) are significant in that they serve to focus future investigations sharply on critical questions. Answers to such questions should bring us closer to a definitive understanding of the mechanisms of cell injury with this important and interesting group of environmental containments. John L. Father Department of Pathology and Laboratory Medicine Hahnemann University School of Medicine Philadelphia, Pennsylvania REFERENCES 1. Allison AC. Hshaewn JS. Birbsek M: An examination of tha cytotoxic offset* of (ilka oo macrophage*. J Eap Mod 124:141.1966 2. Brody AR. Bttvyn G. Hill LH: Inunctions of chrysolite and crocidoliu asbestos with nd blood ctU membrane*. Lab Invest 49:468,1983 3. Davis* P, Allison AC. Ackerman J. ButurfWd A. Williams S: Asbestos induces ulactive telaaaa of lysosomal enzymes from mononuclear phagocytes. Nature 231:423.1974 4. Farber JL: Msmbrsas injury and calcium homeostasis in tha pathofsnesia of coaeulstive necrosis. Lab Invest 47:114.1982 3. Goldstein LM. Wsiasman G: Intracellular digestion: lysosomas and cellular injury. In Handbook of Physiology, edited by Las. DHK. Vol 9. p 603. Bathsada. Maryland. Amsrican Physiological Society, 1977 6. Harington JS, Millar K. Maenab G: Hemolysis by aabaato*. Envi ron Re* 4:93,1971 7. Jauraad MC. Magna L Boulmtr JL Bignon J: In vitro inactivity of alveolar macrophages and ted blood cells with asbestos fibers treated with ozalic and. sulfur dioxide and b*nao-3.4-pyrme. Tozicology 21:323.1981 8. Kaos AB. Stanton RP. Raymond EG. Dobson ME, Knafsic ME. Farber JL: Dissociation of intracellular lysosomal rupture from tbs cell death caused by silica. J Cell Biol 87443. 1980 9. Nidler S, Gotdfischer S: Tbs intracellular release of lysosome conunu in macrophages that have ingested silica. J Hiacochsm Cytochem 18488,1970 10. Slaur TF, Greenbaum AL; Changes ia lysosomal tnzymas in acuu experimental liver injury. Biocbsm J 96:484.1963 iZ 09fi001S DOW 07525