Relationship between induced sputum cytology and inflammatory status with lung structural and functional abnormalities in asbestosis

In vitro determinants of asbestos fiber toxicity: effect on the relative toxicity of Libby amphibole in primary human airway epithelial cells

Background

An abnormally high incidence of lung disease has been observed in the residents of Libby, Montana, which has been attributed to occupational and environmental exposure to fibrous amphiboles originating from a nearby contaminated vermiculite mine. The composition of Libby amphibole (LA) is complex and minimal toxicity data are available. In this study, we conduct a comparative particle toxicity analysis of LA compared with standard reference asbestiform amphibole samples.

Methods

Primary human airway epithelial cells (HAEC) were exposed to two different LA samples as well as standard amphibole reference samples. Analysis of the samples included a complete particle size distribution analysis, calculation of surface area by electron microscopy and by gas adsorption and quantification of surface-conjugated iron and hydroxyl radical production by the fibers. Interleukin-8 mRNA levels were quantified by qRT-PCR to measure relative pro-inflammatory response induced in HAEC in response to amphibole fiber exposure. The relative contribution of key physicochemical determinants on the observed pro-inflammatory response were also evaluated.

Results

The RTI amosite reference sample contained the longest fibers and demonstrated the greatest potency at increasing IL-8 transcript levels when evaluated on an equal mass basis. The two LA samples and the UICC amosite reference sample consisted of similar particle numbers per milligram as well as similar particle size distributions and induced comparable levels of IL-8 mRNA. A strong correlation was observed between the elongated particle (aspect ratio ≥3:1) dose metrics of length and external surface area. Expression of the IL-8 data with respect to either of these metrics eliminated the differential response between the RTI amosite sample and the other samples that was observed when HAEC were exposed on an equal mass basis.

Conclusions

On an equal mass basis, LA is as potent as the UICC amosite reference sample at inducing a pro-inflammatory response in HAEC but is less potent than the RTI amosite sample. The results of this study show that the particle length and particle surface area are highly correlated metrics that contribute significantly to the toxicological potential of these amphibole samples with respect to the inflammogenic response induced in airway epithelial cells.

Adipokine adipsin is associated with the degree of lung fibrosis in asbestos-exposed workers

OBJECTIVES

Asbestos-exposure causes an inflammatory response driven by alveolar macrophages that can lead to pulmonary fibrosis. In addition to classical inflammatory cytokines, macrophages produce adipokines which regulate the inflammatory response. We studied if adipokines are related to the degree of parenchymal fibrosis, impaired lung function and inflammation in asbestos-exposed subjects.

METHODS

Eighty-five males with moderate to heavy occupational exposure to asbestos and unexposed controls were studied. We measured plasma levels of adipokines adiponectin, adipsin, leptin and resistin, IL-6, IL-8, erythrocyte sedimentation rate (ERS), spirometry and D(L,CO). Degree of interstitial lung fibrosis (septal thickening, subpleural lines, parenchymal bands or honeycombing) was scored in classes 0-5 according to a validated scoring system. The subjects were divided into three groups: normal parenchymal finding (fibrosis class 0), borderline changes (classes 0.5-1.5) and fibrosis (i.e. asbestosis; classes 2-5).

RESULTS

Adipsin correlated positively with parenchymal fibrosis (rho=0.412, p<0.001) and there was a linear increasing trend of mean plasma adipsin levels among the three groups of asbestos-exposed subjects (from normal parenchymal finding to borderline changes and to fibrosis) (p<0.0001). Accordingly, plasma adipsin levels correlated positively with the extent of pleural plaques (r=0.245, p=0.043), and negatively with D(L,CO) (r=-0.246, p=0.023). Also, a positive correlation was found between adipsin and inflammatory markers ESR (r=0.315, p=0.008) and IL-6 (r=0.256, p=0.018).

CONCLUSIONS

Adipsin was associated with the degree of parenchymal fibrosis, impairment of pulmonary diffusing capacity and with inflammatory activity in asbestos-exposed subjects suggesting that adipsin may have a role in the pathogenesis or as a biomarker in asbestos-induced lung disease.

Effect of size fractionation on the toxicity of amosite and Libby amphibole asbestos

Abnormally high incidences of asbestos-related pulmonary disease have been reported in residents of Libby, Montana, because of occupational and environmental exposure to asbestos-contaminated vermiculite. The mechanism by which Libby amphibole (LA) causes pulmonary injury is not known. The purpose of this study is to compare the cellular stress responses induced in primary human airway epithelial cells (HAECs) exposed to a respirable size fraction (≤ 2.5 μm) of Libby amphibole (LA(2.5)) to a similar size fraction of a reference amphibole sample amosite (AM(2.5)). HAEC were exposed to 0, 2.64, 13.2, or 26.4 μg/cm(2) AM(2.5) or LA(2.5) or to equivalent doses of unfractionated amosite (AM) or LA for 2 or 24 h. Comparable messenger RNA transcript levels were observed for interleukin-8, cyclooxygenase-2, and heme oxygenase-1 in HAEC following a 24-h exposure to AM or LA. Conversely, exposure to AM(2.5) resulted in a 4- to 10-fold greater induction in these proinflammatory mediators compared with LA(2.5) after 24 h. Evaluation of the expression of 84 additional genes involved in cellular stress and toxicity responses confirmed a more robust response for AM(2.5) compared with LA(2.5) on an equal mass basis. Differences in total surface area (TSA) by gas adsorption, total particle number, or oxidant generation by the size-fractionated particles did not account for the observed difference in response. In summary, AM(2.5) and LA(2.5) are at least as potent in stimulating production of proinflammatory cytokines as unfractionated AM and LA. Interestingly, AM(2.5) was more potent at inducing a proinflammatory response than LA(2.5). This difference could not be explained by differences in mineral contamination between the two samples, TSA, or oxidant generation by the samples.

Induced sputum and occupational diseases other than asthma

PURPOSE OF REVIEW

Induced sputum noninvasively provides information on cellular and soluble material from airways. It has been successfully applied for assessing airway inflammation in asthma and chronic obstructive pulmonary disease, producing reliable results comparable to biopsy and bronchoalveolar lavage. Induced sputum research in the field of occupational medicine has mainly focused upon occupational asthma, and less to other types of occupational diseases.

RECENT FINDINGS

Particulate size distribution in induced sputum samples points to accumulation over time, leading to the consideration that this measurement may serve as a time-dependent marker for biological monitoring. Qualitative analysis of chemical composition of induced sputum particles is well correlated to the chemical elements spectrum in bronchoalveolar lavage lung cells and in biopsy thin sections. T cell subsets in induced sputum can be used as a marker of granulomatosis in chronic beryllium disease. Cytokines retrieved from induced sputum samples in exposed workers show a differential pattern compared to nonexposed workers.

SUMMARY

Induced sputum is a well tolerated, noninvasive technique that is opening a new window in the field of occupational diseases of the lung and can be integrated into the well established criteria for diagnosing and monitoring these diseases, especially when invasive techniques are clinically contraindicated or impractical.