In situ microscopic analysis of asbestos and synthetic vitreous fibers retained in hamster lungs following inhalation.

Abstract

Hamsters breathed, nose-only, for 13 weeks, 5 days/week, 6 hr/day, either man-made vitreous fiber (MMVF)10a, MMVF33, or long amosite asbestos at approximately 300 World Health Organization (WHO) fibers/cc or long amosite at 25 WHO fibers/cc. [World Health Organization fibers are longer than 5 microm and thicker than 3 microm, with aspect ratio >3.] After sacrifice, fiber burden was estimated (left lungs) by ashing and scanning electron microscopy (ashing/SEM) or (right middle lobes) by confocal laser scanning microscopy (CLSM) in situ. In situ CLSM also provided three-dimensional views of fibers retained, undisturbed, in lung tissue. Fibers of each type were lodged in alveoli and small airways, especially at airway bifurcations, and were seen fully or partly engulfed by alveolar macrophages. Amosite fibers penetrated into and through alveolar septa. Length densities of fibers in parenchyma (total length of fiber per unit volume of lung) were estimated stereologically from fiber transsections counted on two-dimensional optical sections and were 30.5, 25.3, 20.0, and 81.6 mm/mm3 for MMVF10a, MMVF33, and low- and high-dose amosite, respectively. Lengths of individual fibers were measured in three dimensions by tracking individual fibers through series of optical sections. Length distributions of amosite fibers aerosolized, but before inhalation versus after retention in the lung were similar, whether determined by ashing/SEM or in situ CLSM. In contrast, the fraction of short MMVF10a and MMVF33 fibers increased and the geometric mean fiber lengths of both MMVFs decreased by approximately 60% during retention. Most likely due to fiber deposition pattern and differences in sampling, fiber burdens [MMVF10a, MMVF33, and amosite (high dose; 269 WHO fibers/cc)] determined by ashing/SEM were 1.4, 1. 5, and 3.5 times greater, respectively, than those calculated from in situ CLSM data. In situ CLSM is able to provide detailed information about the anatomic sites of fiber retention and also fiber lengths and burdens in good agreement with ashing/SEM results.ImagesFigure 1Figure 2Figure 3Figure 4Figure 5Figure 6Figure 7Figure 8

Influence of airspace geometry and surfactant on the retention of man-made vitreous fibers (MMVF 10a).

“…Second, mechanical translocation (e.g., due to the formation of a pneumothorax) is another mechanism by which intact or broken fibers may have entered the blood circulation. Asbestos and glass fibers piercing the air-blood barrier have been demonstrated by others (Lee et al 1979;Rogers et al 1999). In the present study, this might have happened upon pneumothorax formation, but we did not see ruptured tissue near to the location where we found fibers.…”

“…The observation that fibers were preferentially deposited at bifurcations in airways and alveoli has also been reported for inhalation studies using other fiber types (Brody et al 1981;Brody and Roe 1983;Rogers et al 1999).…”

“…Long fibers may touch the inner surface with the tips of both ends and bridge the alveolar airspace. Such configurations have been observed (Rogers et al 1999). The fibers are immersed into the lining layer only at their ends.…”

The pathological response and fate in the lung and pleura of chrysotile in combination with fine particles compared to amosite asbestos following short-term inhalation exposure: interim results

“…The length distribution of the aerosol was consistent with that of the pre-Cyclotec processed chrysotile sample. Amosite used in this study was from the same batch as used in previous studies (Hesterberg et al, 1997(Hesterberg et al, , 1999aMcConnell et al, 1999;Rogers et al, 1999).…”

“…Image analysis procedures in some cases include: median filtering, selected pixel thresholding with reset to zero to remove background, and lookup table adjustment of slope, X-intercept and γ adjustment was performed to reduce background noise and highlight features of interest using ImageSpace software. 3D Projections, oriented in 3D space to show fiber profiles (when present) were rendered using VoxelView software (Rogers et al, 1999).…”