Threshold Rigidity Values for the Asbestos-like Pathogenicity of High-Aspect-Ratio Carbon Nanotubes in a Mouse Pleural Inflammation Model

Abstract

The qualitative and quantitative evaluation of the physicochemical parameters associated with the pathogenicity of high-aspect-ratio nanomaterials is important for comprehensive regulation efforts and safety-by-design approaches. Here, we report quantitative data on the correlations between the rigidity of these nanomaterials and toxicity endpoints in vitro and in vivo. As measured by new ISO standards published in 2017, rigidity shows a strong positive correlation with inflammogenic potential, as indicated by inflammatory cell counts and IL-1β (a biomarker for frustrated phagocytosis) levels in both the acute and chronic phases. In vitro experiments using differentiated THP-1 cells find that only highly rigid multiwalled carbon nanotubes (MWCNTs) and asbestos fibers lead to piercing and frustrated phagocytosis. Thus, this study suggests a bending ratio of 0.97 and a static bending persistence length of 1.08 as threshold rigidity values for asbestos-like pathogenicity. However, additional research using MWCNTs with rigidity values that lie between those of non-inflammogenic (D b = 0.66 and SBPL = 0.87) and inflammogenic fibers (D b = 0.97 and SBPL = 1.09) is required to identify more accurate threshold values, which would be useful for comprehensive regulation and safety-by-design approaches based on MWCNTs.

Grouping all carbon nanotubes into a single substance category is scientifically unjustified

“…More specifically, the propensity of CNTs to induce damage to lysosomes -key organelles within the cell -as a function of their biological stiffness has been proposed as a general predictor of the pathogenicity of such materials 10 . Indeed, the rigidity of CNTs is strongly correlated with both acute and chronic inflammation 11 . The take-home message is that not all CNTs are created equal and specific properties including length, diameter and rigidity, as well as the degree of chemical functionalization, determine the biological reactivity or pathogenicity of these materials.…”

Potential Role of Soluble Metal Impurities in the Acute Lung Inflammogenicity of Multi-Walled Carbon Nanotubes

“…MWCNTs can induce asbestos-like toxicities, owing to their physical properties, such as high biopersistence, length of >5 µm, an aspect ratio of >3:1, and high rigidity (D b > 0.97 and SBPL > 1.08) [7,8]. In contrast to their physical properties, the role of chemical properties to the toxicity of MWCNTs is poorly understood.…”

“…MWCNTs were dispersed as described previously [7]. Briefly, a stock solution of MWCNTs was dispersed at 1 mg/mL in 30% heat-inactivated rat serum and sonicated for 1 h in a bath sonicator.…”

“…Therefore, the read-across study to evaluate the physicochemical parameters related to the toxicity endpoints of MWCNTs represents a promising approach to help establish the regulatory requirements [3][4][5]. Recent studies have suggested the biopersistent, long, and rigid fibers are more pathogenic than dissolving, short, or tangled fibers, because these physical parameters are related to frustrated phagocytosis, which is the major pathogenicity paradigm for asbestos fibers [2,[6][7][8].…”

Carbon nanomaterial-derived lung burden analysis using UV-Vis spectrophotometry and proteinase K digestion

“…Chemicals Co., Ltd., Gunsan, Korea), MWCNT (#CM-100; Hanwha Nanotech Co., Seoul, Korea), CNF (# T-CNF; Carbon Nano-material Technology Co., Pohang, Korea), and graphene (# 06-0230; Stream Chemical Inc., Newburyport, MA, USA). The size and shape of the CNMs were evaluated by TEM (JEM-1200EXII, JEOL, Tokyo, Japan) as described in our previous study [31]. The size of the CNMs was calculated by counting at least 300 CNMs using a built-in analysis program (JEOL).…”