Asbestos fiber type in malignant Mesothelioma: An analytical scanning electron microscopic study of 94 cases

Although the association between asbestos exposure and malignant mesothelioma is indisputable, controversy continues regarding the relative contribution of the various types of asbestos fibers to the development of mesothelioma. We examined the types of asbestos fibers recovered from lung parenchyma in more than 90 cases of malignant mesothelioma from the United States, using an analytical scanning electron microscope. Almost half of the patients were former asbestos insulators or shipyard workers. The fibers were recovered from lung tissues obtained at autopsy or surgical resection by means of a sodium hypochlorite digestion procedure. Amosite absestos was identified in 81% of the cases and accounted for 58% of all fibers 5 μm or greater in length. Tremolite/actinolite/anthophyllite were identified in 55% of the cases and accounted for 10% of all fiber types. Chrysotile was identified in 21% of the cases and accounted for 3% of fibers exceeding 5 μm in length. Crocidolite was found in 16% of the cases and accounted for 3% of fibers exceeding 5 μm in length. Nonasbestos mineral fibers (commonly found in the lungs of the general population) were observed in 71% of the cases and accounted for 25% of all fibers 5 μm or greater in length. The findings in this study are at odds with the assertion that crocidolite asbestos is responsible for most mesotheliomas in the United States. © 1993 Wiley-Liss, Inc.     

Fiber size and number in workers exposed to processed chrysotile asbestos, chrysotile miners, and the general population

We analyzed chrysotile and chrysotile-associated amphibole (largely tremolite) asbestos fibers in 21 workers exposed to various types of processed (milled) chrysotile ore, 20 long-term chrysotile miners, and 20 members of the general population (controls). Significantly greater amounts of both chrysotile and tremolite were found in processed-ore workers and miners than in controls. On average, the mean fiber lengths and aspect ratios for the mining and processed-ore-exposed workers were similar and were significantly greater than the values seen in the controls; within the processed-ore group, there was a marked variation in these parameters, and some workers appeared to be exposed to fairly long, thin fibers. It was found empirically that the fiber size data, and to a lesser extent the concentration data, could be used to classify workers accurately into those with processed-ore exposure and controls. We conclude that fiber sizes in the lungs of processed-ore-exposed workers are similar to those of chrysotile miners and are considerably longer than those found in the general population; some processed-ore workers have longer fibers which might be responsible for higher disease incidences in certain working groups; tremolite accompanies chrysotile in a variable proportion of workers exposed to processed chrysotile products and might be important in the genesis of mesothelioma in such workers; and mineralogic analysis will usually detect exposure even when chrysotile has largely disappeared from lung tissue.     

Effects of Microbial Cocultivation on Inflammatory and Cytotoxic Potential of Spores

Abstract

Microbial growth on moisture-damaged building materials is commonly associated with adverse health effects in the occupants. In moisture damage situations, the environmental conditions as well as the dominant microbial species will vary, leading to a diversity of microbes and continual changes in the different microbial populations. Currently, very little is known about the effects of microbial cocultures on the potential harmfulness of the microbial population. In this study we have investigated the effects of cocultivation of certain indoor air microbes on the inflammatory and cytotoxic potential of their spores. We grew various microbial combinations made from strains of Streptomyces californicus, Stachybotrys chartarum, Aspergillus versicolor, and Penicillium spinulosum on wetted plasterboard. After 5 or 10 wk of growth, the spores were collected from the plasterboards, mouse RAW264.7 macrophages were exposed to the spores, and after 24 h the induced inflammatory and cytotoxic responses were analyzed. Among all the tested microbes and their combinations, the spores of Str. californicus proved to be the most potent inducer of cytotoxicity and inflammatory responses. These results indicate also that microbial coculture may support the growth of certain microbes with high immunotoxic potency such as Str. californicus. Furthermore, coculture containing S. chartarum and A. versicolor caused a synergistic increase in cytotoxicity compared to the sum response induced by the pure cultures, but no effect on inflammatory responses was detected. Generally, spore-induced cytotoxicity and production of inflammatory markers increased during the growth period from 5 to 10 wk, suggesting that the immunotoxic potency of spores increases with time.     

Analytical Transmission Electron Microscopy of Amphibole Fibers From the Lungs of Quebec Miners

The objective of this study is to describe the morphology, molecular structure, and chemistry of amphibole fibers from lung samples from workers in the chrysotile mines at Asbestos and Thetford Mines, Quebec. A fibrous tremolite-actinolite contaminant in an asbestos ore sample from the deposit at Asbestos was used for comparison. Lattice imaging was performed using high-resolution transmission electron microscopy (HRTEM). Silica-rich amorphous coatings (SIRA) that may be related to carcinogenesis are noted on all of the HRTEM photographs of fibers retained in lung, but not on fiber surfaces of the bulk comparison sample. Fibers found in lung samples and in a bulk comparison sample are produced primarily by splitting of thicker crystals and, as such, might not be considered asbestos fibers on the basis of certain mineralogical criteria. Implications of SIRA coatings with respect to carcinogenesis are worthy of further study.     

X-ray findings, lung function, and respiratory symptoms in black South African vermiculite workers

Health effects have been documented among American vermiculite workers who mined and processed vermiculite contaminated with amphibole asbestos, viz., tremolite-actinolite. Workers mining and processing South Africa vermiculite (N = 172), which contains very little asbestos, underwent x-ray examination and lung function testing and completed a respiratory symptom questionnaire. The vermiculite workers were compared with other workers involved in the mining or refining of copper. Only two of the vermiculite workers showed evidence of small opacities of 1/0 or more (according to the ILO 1980 classification); lung function was comparable with the other groups of workers, and there was no excess of respiratory symptoms among the vermiculite workers. It is concluded that workers exposed to vermiculite that is minimally contaminated with asbestos are probably not at risk for pneumoconiosis, lung function impairment, or respiratory symptoms. It is likely that the health effects observed in other studies of vermiculite workers are the result of concomitant asbestos exposure. A risk of mesothelioma caused by the fiber content of the vermiculite cannot be excluded by this study.     

中药阳起石、阴起石的X衍射谱鉴别研究

该研究应用粉末X衍射(X-ray diffraction,XRD) Fourier谱确定中药阳起石和阴起石的基原,指导二者的鉴别。实验对22批市售阳起石、阴起石样品进行性状鉴别及常规理化分析,并采集XRD Fourier谱,解析物相组成,对比各样品物相组成及性状特点,从而确定阴起石药材的基原为硅酸盐类滑石族矿物滑石片岩,阳起石药材的基原为硅酸盐类角闪石族矿物阳起石、透闪石。结果表明,XRD法分析矿物药阳起石、阴起石,结果快速、准确。阳起石、阴起石功效主治相差甚远,主要矿物组成亦不同,二者不可混用。     

中药阳起石壮阳作用实验研究

目的通过动物实验研究阳起石的壮阳功效。方法选用以透闪石为基源的阳起石商品药材,观察其对小鼠交尾作用和血清睾酮水平的影响,以及对幼年雄性小鼠的促雄激素样作用。结果高剂量阳起石能显著增加正常小鼠交尾次数（P〈0．05）,提高雄性小鼠血清睾酮含量。阳起石对幼年雄性小鼠无促雄激素样作用。结论以透闪石为基源的阳起石药材具有壮阳作用,作用机理可能与其富含微量元素有关。     

Carcinogenic implications of the lack of tremolite in UICC reference chrysotile

Using light and electron microscopy analysis, as well as electron diffraction, and energy-dispersive x-ray analysis, an aliquot of UICC chrysotile B was analyzed with special attention given to any tremolite contamination. Polarized light microscopy, with its limit of detection of approximately 1 μm when using dispersion staining, revealed chrysotile as the only fibrous asbestos component. Analytical electron microscopy at 333,000× of more than 20,000 consecutive fibers showed only the tubular morphology characteristic of chrysotile. These findings highlight that when this sample was used for exposure disease induced in animal models correlates with chrysotile-induced pathology, and does not support an explanation based on the “amphibole hypothesis.” Thus, chrysotile should be considered as having the biologic ability to produce cancers, including mesotheliomas, based on the extensive use of this material as a standard reference material. Am. J. Ind. Med. 34:314–317, 1998. © 1998 Wiley-Liss, Inc.     

Frequent homozygous deletion of Cdkn2a/2b in tremolite‐induced malignant mesothelioma in rats

The onset of malignant mesothelioma (MM) is linked to exposure to asbestos fibers. Asbestos fibers are classified as serpentine (chrysotile) or amphibole, which includes the crocidolite, amosite, anthophyllite, tremolite, and actinolite types. Although few studies have been undertaken, anthophyllite has been shown to be associated with mesothelioma, and tremolite, a contaminant in talc and chrysotile, is a risk factor for carcinogenicity. Here, after characterizing the length and width of these fibers by scanning electron microscopy, we explored the cytotoxicity induced by tremolite and anthophyllite in cells from an immortalized human mesothelial cell line (MeT5A), murine macrophages (RAW264.7), and in a rat model. Tremolite and short anthophyllite fibers were phagocytosed and localized to vacuoles, whereas the long anthophyllite fibers were caught on the pseudopod of the MeT5A and Raw 264.7 cells, according to transmission electron microscopy. The results from a 2‐day time‐lapse study revealed that tremolite was engulfed and damaged the MeT5A and RAW264.7 cells, but anthophyllite was not cytotoxic to these cells. Intraperitoneal injection of tremolite in rats induced diffuse serosal thickening, whereas anthophyllite formed focal fibrosis and granulomas on peritoneal serosal surfaces. Furthermore, the loss of Cdkn2a/2b, which are the most frequently lost foci in human MM, were observed in 8 cases of rat MM (homozygous deletion [5/8] and loss of heterozygosity [3/8]) by array‐based comparative genomic hybridization techniques. These results indicate that tremolite initiates mesothelial injury and persistently frustrates phagocytes, causing subsequent peritoneal fibrosis and MM. The possible mechanisms of carcinogenicity based on fiber diameter/length are discussed.