Can non-asbestiform amphibole fibers trigger carcinogenesis mechanisms?

Minerals defined as asbestos include only the fibrous varieties (length > 5 µm, diameter < 3 µm and length/diameter ratio > 3:1) and asbestiform (high tensile strength or flexibility) of serpentine and amphibole.

However, there are also prismatic varieties of amphiboles, which despite the same chemical composition, are not classified as asbestos. Their geometric ratio would fall within the concept of fiber, but the minerals are not asbestiform.

Starting from a fairly contradictory context, the goal of this work was to analyze the variables inherent the morphological, but above all, the clastogenic effect determined by exposure of both asbestiform and non-asbestiform amphiboles.

The asbestiform fibers (F3), and the other three samples containing non-asbestiform amphiboles (P1, P2, P3) were tested in A549 cells line. Each sample of fiber was inoculated in A549 cells at a concentration of 100 µg/ml for 48h. Experiments were assayed in triplicate and repeated twice. To evaluate the micronuclei number for each sample the fixed cells were dropped onto clean microscope slides, stained and observed by optical microscopy at 100X.

Obtained results showed a statistically significant increase (P < 0.05) of micronuclei in F3 exposed cells when compared to negative controls. Similar results were reported when A549 cells were exposed with non-asbestiform amphiboles P2. No significant increase of micronucleated cells was observed after exposure of cells line at samples P1 and P3.

Moreover, to investigate the effect long-term triggered after 24h post fiber exposure of the medium inoculated cells were replaced with fresh culture medium and the cultures were grown for 72h. Albeit a prolonged contact of the F3 and P3 fibers resulted in a statistically significant increase (P < 0.01) of the micronuclei, no increase was reported for P2.

These results indicate that the contact of non-asbestiform amphiboles in vitro, can determine a genetic disorder, a necessary step in the cancer development. However, the kinematic of processes and the bearing of results are to be further clarified. For this purpose, the same starting materials are presently tested to determinate the transformation efficiency in no-tumoral cells and will be analyzed the different pathway involved in the etiopathogeneses of diseases trigger by inhalation of fiber.