Grouping MWCNTs based on their similar potential to cause pulmonary hazard after inhalation: a case-study

Abstract

Background The EU-project GRACIOUS developed an Integrated Approach to Testing and Assessment (IATA) to support grouping high aspect ratio nanomaterials (HARNs) presenting a similar inhalation hazard. Application of grouping reduces the need to assess toxicity on a case-by-case basis and supports read-across of hazard data from substances that have the data required for risk assessment (source) to those that lack such data (target). The HARN IATA, based on the fibre paradigm for pathogenic fibres, facilitates structured data gathering to propose groups of similar HARN and to support read-across by prompting users to address relevant questions regarding HARN morphology, biopersistence and inflammatory potential. The IATA is structured in tiers, allowing grouping decisions to be made using simple in vitro or in silico methods in Tier1 progressing to in vivo approaches at the highest Tier3. Here we present a case-study testing the applicability of GRACIOUS IATA to form an evidence-based group of multiwalled carbon nanotubes (MWCNT) posing a similar predicted fibre-hazard, to support read-across and reduce the burden of toxicity testing. Results The case-study uses data on 15 different MWCNT, obtained from the published literature. By following the IATA, a group of 2 MWCNT was identified (NRCWE006 and NM-401) based on a high degree of similarity. A pairwise similarity assessment was subsequently conducted between the grouped MWCNT to evaluate the potential to conduct read-across and fill data gaps required for regulatory hazard assessment. The similarity assessment, based on expert judgement of Tier 1 assay results, predicts both MWCNT are likely to cause a similar acute in vivo hazard. This result supports the possibility for read-across of sub-chronic and chronic hazard endpoint data for lung fibrosis and carcinogenicity between the 2 grouped MWCNT. The implications of accepting the similarity assessment based on expert judgement of the MWCNT group are considered to stimulate future discussion on the level of similarity between group members considered sufficient to allow regulatory acceptance of a read-across argument. Conclusion This proof-of-concept case-study demonstrates how a grouping hypothesis and IATA may be used to support a nuanced and evidence-based grouping of ‘similar’ MWCNT and the subsequent interpolation of data between group members to streamline the hazard assessment process.

High aspect ratio nanomaterial-induced macrophage polarization is mediated by changes in miRNA levels

“…This may suggest that the more rigid NM-401 fibers induce cellular membrane damage which may contribute to the enhanced effects observed by these fibers. In agreement with our findings, a grouping effort of MWCNT for risk assessment (69) conclude that NM-400 occurs as tangled agglomerates which are not able to induce frustrated phagocytosis (65), while NM-401 cause lysosomal disruption, intracellular 'vesicle escape' (66) and frustrated phagocytosis in macrophages both in vitro and in vivo (65). As several studies have demonstrated that MWCNT-induced fibrosis is Th2-type response mediated (reviewed in 38), the involvement of M2 polarization events has been suggested (35)(36)(37).…”

“…For MWCNT, a progression from acute inflammation to chronic fibrotic changes suggests that a resolution of inflammation involving Th2 responses may underlie the fibrotic events (38). It is also evident that long and rigid MWCNT typically induce more prominent inflammation and fibrotic responses than shorter coiled MWCNT (61,64,69). In agreement, this study showed that the long and rigid NM-401 fibers gave more severe effects on macrophage markers, as illustrated by increased M2 markers Arg1, Ear11, and Mrc1, and cytokine secretion, compared to the shorter and more coiled NM-400 fibers.…”

Lung Persistence, Biodegradation, and Elimination of Graphene‐Based Materials are Predominantly Size‐Dependent and Mediated by Alveolar Phagocytes

“…[ 40 ] Moreover, presence of multinucleated macrophages in lungs has been previously associated with frustrated phagocytosis and clearance issue following the inhalation of high aspect ratio materials (HARN) such as long MWCNTs. [ 41,42 ] Herein, only the largest material namely LGO (≈8 µm), but not LFLG (≈1 µm), led to the formation of multinucleated macrophages, suggesting that only this material could not be cleared properly from the lungs, in agreement with the HARN frustrated phagocytosis paradigm and its associated 5 µm threshold. [ 18,41,42 ]…”

“…This is in sharp contrast to the response found for the positive control, namely long and rigid MWCNTs, which have been repeatedly reported to induce chronic inflammation, fibrosis, tissue remodeling, and even cancer. [41,42] However, the presence of multinucleated macrophages, granulomalike structures, and persistent material agglomerates in LGOtreated mouse lungs warrants further investigations, in particular to assess the long-term fate and possible consequences of these biopersistent materials in the lungs.…”

Grouping of orally ingested silica nanomaterials via use of an integrated approach to testing and assessment to streamline risk assessment

“…Another work includes the testing of the high aspect ratio nanomaterials (HARNs) IATA [ 5 ]. Murphy and co-authors tested 15 different multiwalled carbon nanotubes (MWCNT) demonstrating the successful application of the HARN IATA to group some MWCNT with a similar hazard potential after inhalation exposure, while discriminating from others without a similar inhalation hazard [ 56 ].…”