Comparative health effects in mice of Libby amphibole asbestos and a fibrous amphibole from Arizona

Exposure to silicates and systemic autoimmune-related outcomes in rodents: a systematic review

BACKGROUND

Autoimmunity can result from the interplay between genetic background and effects of environmental and/or occupational exposure to hazardous materials. Several compounds, including silica dust, have been linked with systemic autoimmunity and systemic autoimmune diseases, based on epidemiological evidence. For asbestos, a strong link with systemic autoimmune diseases does not yet exist, however, several studies have documented features of autoimmunity following asbestos exposure. Even so, human studies are limited in their ability to identify and examine isolated exposures, making it difficult to demonstrate causation or to assess pathogenic mechanisms. Therefore, this systematic review examines the existing animal evidence regarding autoimmunity and exposure to silicates (silica and asbestos).

METHODS

PubMed and EMBASE were systematically searched for peer-reviewed studies examining systemic autoimmune disease-related outcomes after silicate exposure in rodents. Literature databases were searched up to September 2021 for studies written in English and where the full text was available. Search strings were established based on a PECO (Population, Exposure, Comparator, Outcome) format. After title, abstract, and full-text screening, thirty-four studies were identified for further analysis. Quality assessment through ToxR tool and qualitative analysis of the results was performed.

RESULTS

Although there was significant heterogeneity in the included studies in terms of exposure protocol and genetic background of the rodent models used, it was noted that both genetic background and exposure to silicates [(crystalline) silica and asbestos] are highly relevant to the development of (sub-) clinical systemic autoimmune disease.

CONCLUSION

Parallels were observed between the findings from the animal (this review) and human (epidemiological) studies, arguing that experimental animal models are valuable tools for examining exacerbation or development of autoimmune disease after silicate exposure. However, genetic background and synergism between exposures should be considered in future studies.

Late Inflammation Induced by Asbestiform Fibers in Mice Is Ameliorated by a Small Molecule Synthetic Lignan

Exposure to Libby amphibole (LA) asbestos-like fibers is associated with increased risk of asbestosis, mesothelioma, pulmonary disease, and systemic autoimmune disease. LGM2605 is a small molecule antioxidant and free radical scavenger, with anti-inflammatory effects in various disease models. The current study aimed to determine whether the protective effects of LGM2605 persist during the late inflammatory phase post-LA exposure. Male and female C57BL/6 mice were administered daily LGM2605 (100 mg/kg) via gel cups for 3 days before and 14 days after a 200 µg LA given via intraperitoneal (i.p.) injection. Control mice were given unsupplemented gel cups and an equivalent dose of i.p. saline. On day 14 post-LA treatment, peritoneal lavage was assessed for immune cell influx, cytokine concentrations, oxidative stress biomarkers, and immunoglobulins. During the late inflammatory phase post-LA exposure, we noted an alteration in trafficking of both innate and adaptive immune cells, increased pro-inflammatory cytokine concentrations, induction of immunoglobulin isotype switching, and increased oxidized guanine species. LGM2605 countered these changes similarly among male and female mice, ameliorating late inflammation and altering immune responses in late post-LA exposure. These data support possible efficacy of LGM2605 in the prolonged treatment of LA-associated disease and other inflammatory conditions.

Differential responses of murine alveolar macrophages to elongate mineral particles of asbestiform and non-asbestiform varieties: Cytotoxicity, cytokine secretion and transcriptional changes

Human exposures to asbestiform elongate mineral particles (EMP) may lead to diffuse fibrosis, lung cancer, malignant mesothelioma and autoimmune diseases. Cleavage fragments (CF) are chemically identical to asbestiform varieties (or habits) of the parent mineral, but no consensus exists on whether to treat them as asbestos from toxicological and regulatory standpoints. Alveolar macrophages (AM) are the first responders to inhaled particulates, participating in clearance and activating other resident and recruited immunocompetent cells, impacting the long-term outcomes. In this study we address how EMP of asbestiform versus non-asbestiform habit affect AM responses. Max Planck Institute (MPI) cells, a non-transformed mouse line that has an AM phenotype and genotype, were treated with mass-, surface area- (s.a.), and particle number- (p.n.) equivalent concentrations of respirable asbestiform and non-asbestiform riebeckite/tremolite EMP for 24 h. Cytotoxicity, cytokines secretion and transcriptional changes were evaluated. At the equal mass, asbestiform EMP were more cytotoxic, however EMP of both habits induced similar LDH leakage and decrease in viability at s.a. and p.n. equivalent doses. DNA damage assessment and cell cycle analysis revealed differences in the modes of cell death between asbestos and respective CF. There was an increase in chemokines, but not pro-inflammatory cytokines after all EMP treatments. Principal component analysis of the cytokine secretion showed close clustering for the s.a. and p.n. equivalent treatments. There were mineral- and habit-specific patterns of gene expression dysregulation at s.a. equivalent doses. Our study reveals the critical nature of EMP morphometric parameters for exposure assessment and dosing approaches used in toxicity studies.

Autoimmune markers for progression of Libby amphibole lamellar pleural thickening

Exposure to Libby Asbestiform Amphibole (LAA) is associated with asbestos-related diseases, including mesothelioma, pulmonary carcinoma, pleural fibrosis, and systemic autoimmune diseases. The pleural fibrosis can manifest as a rapidly progressing lamellar pleural thickening (LPT), which causes thoracic pain, dyspnea, and worsening pulmonary function tests (PFT). It is refractory to treatment and frequently fatal.Objective: Because of the immune dysfunction that has been described in the LAA-exposed population and the association of pleural manifestations with the presence of autoantibodies, this study tested whether specific immunological factors were associated with progressive LPT and whether they could be used as markers of progressive disease.Methods: Subjects were placed into three study groups defined as (1) progressive LPT, (2) stable LPT, (3) no LPT. Serum samples were tested for antinuclear autoantibodies, mesothelial cell autoantibodies, anti-plasminogen antibodies, IL1 beta, and IL17; which have all been shown to be elevated in mice and/or humans exposed to LAA.Results: Group 1 had significantly higher mean values for all of the autoantibodies, but not IL1 or IL-17, compared to the control Group 3. All three autoantibody tests had high specificity but low sensitivity, but ROC area-under-the-curve values for all three antibodies were over 0.7, statistically higher than a test with no value. When all LPT subjects were combined (Progressive plus Stable), no marker had predictive value for disease.Conclusion: The data support the hypothesis that progressive LPT is associated with immunological findings that may serve as an initial screen for progressive LPT.

Synthetic secoisolariciresinol diglucoside (LGM2605) inhibits Libby amphibole fiber-induced acute inflammation in mice

BACKGROUND

Exposure to the Libby amphibole (LA) asbestos-like fibers found in Libby, Montana, is associated with inflammatory responses in mice and humans, and an increased risk of developing mesothelioma, asbestosis, pleural disease, and systemic autoimmune disease. Flaxseed-derived secoisolariciresinol diglucoside (SDG) has anti-inflammatory, anti-fibrotic, and antioxidant properties. We have previously identified potent protective properties of SDG against crocidolite asbestos exposure modeled in mice. The current studies aimed to extend those findings by evaluating the immunomodulatory effects of synthetic SDG (LGM2605) on LA-exposed mice.

METHODS

Male and female C57BL/6 mice were given LGM2605 via gavage initiated 3 days prior to and continued for 3 days after a single intraperitoneal dose of LA fibers (200 μg) and evaluated on day 3 for inflammatory cell influx in the peritoneal cavity using flow cytometry.

RESULTS

LA exposure induced a significant increase (p < 0.0001) in spleen weight and peritoneal influx of white blood cells, all of which were reduced with LGM2605 with similar trends among males and females. Levels of peritoneal PMN cells were significantly (p < 0.0001) elevated post LA exposure, and were significantly (p < 0.0001) blunted by LGM2605. Importantly, LGM2605 significantly ameliorated the LA-induced mobilization of peritoneal B1a B cells.

CONCLUSIONS

LGM2605 reduced LA-induced acute inflammation and WBC trafficking supporting its possible use in mitigating downstream LA fiber-associated diseases.

SUMMARY

Following acute exposure to Libby amphibole (LA) asbestos-like fibers, synthetic SDG (LGM2605), a small synthetic molecule, significantly reduced the LA-induced increase in spleen weight and peritoneal inflammation in C57BL/6 male and female mice. Our findings highlight that LGM2605 has immunomodulatory properties and may, thus, likely be a chemopreventive agent for LA-induced diseases.