I. Webster

An insoluble fibrogenic factor in macrophages from guinea pigs exposed to silica

Abstract A fibrogenic factor has been demonstrated in alveolar macrophages of guinea pigs exposed to a quartz dust cloud or following the intratracheal injection of quartz. This factor produces granulomata when implanted subcutaneously into guinea pigs. It is also very stable to such acids as a mixture of acetic and trichloroacetic acids at pH 4. The factor is associated with the insoluble debris produced after sonic disintegration of the macrophages but the fibrogenicity cannot be attributed to the unreacted silica associated with this debris. Extraction of the lipids with chloroform:methanol (2:1) does not impair the fibrogenic properties of the macrophage residue.

The morphology of mucus in mammalian pulmonary airways

Abstract When comparing the morphology of mucus in the trachea of rats as seen through the light and scanning electron microscopes, it is clear that a correlation has been established between the two methods. Both methods indicate that there is a discontinuity of mucus and that mucus is transported in streams in the larger airways of the rat. Detailed examination of the individual mucus entities largely confirms the concept that mucus is present as droplets, flakes, and plaques. More precise dimensions of these particles have been established.

A comparison of the effects of exposure of baboons to crocidolite and fibrous-glass dusts

Epidemiological studies have not revealed any significant health hazards from exposure to fibrous glass and animal experiments have been inconclusive. Baboons exposed to a fibrous-glass dust cloud with size features similar to those of crocidolite asbestos developed focal peribronchiolar fibrosis with scant ferruginous body formation. The lesions were similar to those produced by crocidolite but were less extensive. No neoplasms occurred.

The metabolism of benzo(a)pyrene in rat liver microsomes: The effect of asbestos-associated metal ions and pH

Abstract Experimental evidence is presented to support the hypothesis that trace metals and other factors associated with asbestos mined in different areas play a more critical role in the development of “asbestos tumours” than the actual fibre itself. In vitro experiments were performed to investigate the effect of these associated factors on the metabolism of benzo(a)pyrene, a carcinogen introduced into the lung as a result of smoking and atmospheric pollution. The amount of benzo(a)pyrene metabolized by the enzyme in rat liver microsomes was measured in the presence of increasing amounts of trace metal ions. Copper, zinc, lead, nickel, chromium, ferrous, ferric, and magnesium ions were found to inhibit enzyme activity to an increasing extent as their concentration increased; manganese was an exception in that it activated the enzyme at lower concentrations and inhibited it at higher concentrations. Enzyme activity was also considerably affected by changes in pH, with a great loss of activity at the high pH values measured for aqueous suspensions of crocidolite and chrysotile. The effect of manganese ions differed at various pH values, the enzyme-activating effect of these ions being restricted to a much smaller concentration range at a high pH.

Acute pleurisy in asbestos exposed persons

Abstract It has been clinically observed that pleural effusion occurs, not infrequently, in asbestos exposed persons with or without evidence of asbestosis. Nine such cases are presented, in seven of these, pleural biopsy has been carried out by needle or by open thoracotomy. The histological features are described. The suspicion of mesothelioma of the pleura necessarily arises in such cases. This problem is discussed. It is well known that a chronic pleural reaction of both the visceral and parietal pleura is common in asbestosis and frequently the dominating clinical feature. Webster (1970) for instance has found a very high incidence of chronic pleurisy (that is, fibrous thickening of the visceral pleura—usually diffuse—sometimes localised) in asbestos exposed persons.

The effect of asbestos-associated metal lons on the binding of benzo(a)pyrene to macromolecules in vitro

Abstract In seeking an explanation for the high risk of malignancy in workers exposed to both asbestos and benzo ( a ) pyrene inhaled in cigarette smoke, experiments have been carried out to test the effect of asbestos-associated trace metals on the covalent binding of benzo( a )pyrene in vitro . Most of the metals tested—nickel, cadmium, chromium, zinc, manganese, and copper—caused an overall decrease in the binding of benzo( a )pyrene in microsomal incubations containing exogenous DNA. That this represented a reduction in the binding to DNA was confirmed in the cases of zinc, nickel, and chromium. Magnesium caused a very slight increase in binding, and ferrous and ferric ions, while reducing the binding to DNA, caused an increase in binding to some component of high molecular weight in the incubation mixtures, over a narrow concentration range. The significance of these findings is discussed in relation to the development of malignant disease associated with asbestos exposure.

Massive fibrosis in asbestosis.

Abstract The occasional South African asbestos miner exposed to high concentrations of asbestos dust for approximately more than 10 years may develop radiological evidence of a large opacity. The pathologist is able to identify this change, whether it be in the upper or lower lung regions. The common feature is the presence of hyaline fibrosis with areas of concentric collagenisation, and this lesion could be referred to as “silicoasbestotic fibrosis.” The part that infective processes and other factors play in the production of this lesion remains as yet unsolved.

The visceral pleura in asbestosis

The visceral or pulmonary pleura is a serous membrane that covers the surface of the lungs and lines the fissures between the lobes (Gray’s Anatomy, 1973). The fissures are seen as a white hairline shadow (Simon, 1971), and their average thickness is about 0.2 mm on routine chest radiographs (Felson, 1973). Deviations from the normal thickness of interlobar fissures is easily assessed in chest roentgenograms. Postero-anterior, lateral, and oblique chest projections will produce an accurate radiographic assessment of interlobar fissure abnormalities. This paper emphasises that lissural thickening accompanies asbestosis.

The effects of asbestos-cement dust inhalation on baboons

Abstract To study the effects of asbestos-cement dust under laboratory conditions, baboons were exposed to dust collected from the extraction system in the hard-sheet cutting section of an asbestos-cement factory. The animals developed fibrosis of the lungs morphologically similar to asbestosis and most likely due to the asbestos component of the dust, possibly modified by the cement. Two of the animals also showed atypical metaplasia of the bronchiolar epithelium and a bronchiolo-alveolar carcinoma could not be excluded.

The effect of vinyl chloride monomer, chloroethylene oxide and chloracetaldehyde on DNA synthesis in regenerating rat liver.

Vinyl chloride monomer used in the manufacture of polyvinyl chloride is a chemical of increasing industrial importance but has recently been incriminated as a carcinogen, producing a mutagenic effect after being metabolized to active metabolites. The initial effect of vinyl chloride monomer and two of its presumed metabolites, chloracetaldehyde and chloroethylene oxide, on DNA synthesis was investigated in vivo in regenerating rat liver. The established control curve for the DNA synthesis rate after partial hepatectomy demonstrated two waves of synthetic activity at 21 and 30 h. Vinyl chloride, injected intravenously immediately on completion of the operation, depressed the first wave of DNA synthesis by 49.6%. The second peak of DNA synthetic activity was similar to that of the control. Chloracetaldehyde and chloroethylene oxide both produced similar effects on the first wave of DNA synthesis after partial hepatectomy, inhibiting the DNA synthesis rate by approx. 50%. After a regenerating period of 27 h, however, they produced very different effects, chloroethylene oxide raising the control DNA synthesis rate at 30 h by 49% while chloracetaldehyde tended to desynchronize the well-defined second peak of the control. The test compounds have been compared to literature reports of the inhibitory effects of various carcinogens on DNA synthesis.