[Size distribution of amphibole fibres from lung and pleural tissues sampled from mesothelioma cases due to environmental exposure]

BACKGROUND

It has been suggested that malignant mesothelioma might be mainly or only connected with the action of short and ultrathin fibres. On the basis of this hypothesis fibres less than 5 microm long and 0.2-0.1 microm thick would enter the pulmonary-pleura barrier and reach the parietal pleura thus inducing mesothelioma. The hypothesis raised a stimulating scientific discussion.

OBJECTIVES

The aim of this communication is to report the initial results obtained comparing the size of amphibole fibres from healthy lung tissue with those from pleural tissue sampled from subjects whose death cause of death was mesothelioma.

METHODS

Four mesothelioma cases due to environmental exposure were studied; the fibres were categorized by scanning electron microscopy; for every fibre, length and diameter were measured and the mineral type was defined by its chemical composition determined by X-ray microanalysis.

RESULTS

The most important characteristics of the detected fibres were: the average length offibres from the lung and pleural tissues taken from the same subject did not difer, in all cases, by more than 10-12%; 95% offibres found in the lung tissues of all subjects had a length greater than 5 microm; 98% of fibres found in the pleural tissues had a length greater than 5 microm; the average diameter of the fibres found in the pleural tissues was 70% of the diameter of the fibres from the lung tissues.

CONCLUSIONS

The experimental data obtained in this study confirm the correlation between malignant mesothelioma and the presence in the lung and pleural tissues of fibres with a length greater, even much greater, than 4-5 microm; thus the hypothesis that the chief factors inducing mesothelioma are the "ultrashort" and "ultrathin" fibres appears rather weak.

Erionite and asbestos differently cause transformation of human mesothelial cells

Malignant mesothelioma (MM) is an aggressive tumor associated with environmental or occupational exposure to asbestos fibers. Erionite is a fibrous zeolite, morphologically similar to asbestos and it is assumed to be even more carcinogenic. Onset and progression of MM has been suggested as the result of the cooperation between asbestos and other cofactors, such as SV40 virus infection. Nevertheless, several cases of MM were associated with environmental exposure to erionite in Turkey, where SV40 was never isolated in MM specimens. We show here that erionite is poorly cytotoxic, induces proliferating signals and high growth rate in human mesothelial cells (HMC). Long term exposure to erionite, but not to asbestos fibers, transforms HMC in vitro, regardless of the presence of SV40 sequences, leading to foci formation in cultured monolayers. Cells derived from foci display constitutive activation of Akt, NF-kappaB and Erk1/2, show prolonged survival and a deregulated cell cycle, involving cyclin D1 and E overexpression. Our results reveal that erionite is able per se to turn HMC into transformed highly proliferating cells and disclose the carcinogenic properties of erionite, prompting for a careful evaluation of environmental exposure to these fibers. The genetic predisposition to the effect of erionite is a separate subject for investigation.

Nature and extent of the exposure to fibrous amphiboles in Biancavilla

An epidemiological and environmental study in the Biancavilla area (Sicily, Italy) was recently prompted by an impressively high incidence of malignant pleural mesothelioma. Epidemiology suggested an environmental contamination by amphibole fibres rather than risks related to a specific occupational activity. The aim of this study is to describe the diffusion of fibrous amphiboles in the area and identify their source. Fibrous amphiboles were found in the products from the local quarries, which had been used for years to build houses. After sampling all around Biancavilla, three sites were detected and they were characterized by an abundant presence of mineral fibres. Fibrous amphiboles were also recovered from building materials (mortar and plasters) and airborne particulates sampled in urban sites with high dust emissions due mainly to unpaved roads. Moreover, amphibole fibres were detected in the lung tissue of a woman who died of pleural mesothelioma. The results of this study suggest that the amphibole fibre diffusion in the Biancavilla environment lasted for many years and had been maximum during the sixties and the seventies with the uncontrolled development of the local building industry. Today, the environmental situation results to be changed following both the closing of the stone quarries and the urbanization works after 2001, above all the asphalting of dusty roads. Anyway sporadic mesothelioma cases have still to be expected in the next years.

Multinucleation and pro-inflammatory cytokine release promoted by fibrous fluoro-edenite in lung epithelial A549 cells

An unusual cluster of malignant mesothelioma was evidenced in Biancavilla, a Sicily village where no inhabitant had been significantly and professionally exposed to asbestos. Mineralogical and environmental studies led to the identification of a new prismatic amphibole, named fluoro-edenite. We previously reported, by using the human lung epithelial A549 cells, that prismatic fluoro-edenite was unable to induce changes that could be somehow related to cellular transformation, and this was in accordance with studies carried out in vivo. More recently, a fibrous amphibole with a composition very similar to that of prismatic fluoro-edenite, was identified in Biancavilla. This fibrous fluoro-edenite was shown to induce mesothelioma in rats. In keeping with this effect in vivo, in the present work we observed multinucleation and spreading, common features of transformed cells, as well as pro-inflammatory cytokine release in A549 cells. Such cell changes occurred without interfering with the passage of the resulting multinucleated cells through the cell cycle and without condemning cells to death. Hence, in lung epithelial cells, fibrous fluoro-edenite behaved similarly to the unrelated asbestos type crocidolite, whose connection with severe inflammation and cancer of the lung is renowned.

[Results of an interlaboratory fibre count comparison program concerning the SEM technique]

BACKGROUND

The necessity of quality control for laboratories carrying out airborne asbestos fibre monitoring is recognized in Italian law concerning the worker and the environmental protection against asbestos. The scanning electron microscopy technique is prescribed to control the airborne fibre concentration after asbestos removal from buildings.

OBJECTIVES

In 2002 the Italian laboratories carrying out SEM analysis on asbestos were requested by the Istituto Superiore di Sanità to take part in a fibre count comparison program. Thirty-nine agreed to participate.

METHODS

Fifteen samples were exchanged among the laboratories participating in the program. Seven samples consisted of polycarbonate membranes and eight of cellulose ester membranes. The sample loads did not exceed 50 fibres/mm2. The fibre counting results were evaluated with reference to the mean value of each sample calculated from the results provided by all the participants.

RESULTS

Only 19% of the fibre count results were considered "insufficient", and the results falling within the 95% confidence interval were the 65% of the total. University and public laboratories obtained on the whole the best results.