Functional consequences for primary human alveolar macrophages following treatment with long, but not short, multiwalled carbon nanotubes

Abstract

Purpose: Multiwalled carbon nanotubes (MWCNTs) are a potential human health hazard, primarily via inhalation. In the lung, alveolar macrophages (AMs) provide the first line of immune cellular defense against inhaled materials. We hypothesized that, 1 and 5 days after treating AMs with short (0.6 μm in length; MWCNT-0.6 μm) and long (20 μm in length; MWCNT-20 μm) MWCNTs for 24 hours, AMs would exhibit increased markers of adverse bioreactivity (cytokine release and reactive oxygen species generation) while also having a modified functional ability (phagocytosis and migration). Methods: Primary human AMs were treated with short and long MWCNTs for 24 hours, 1 and 5 days after which toxicity end points, including cell death, reactive oxygen species generation, and inflammatory mediator release, were measured. AM functional end points involving phagocytic ability and migratory capacity were also measured. Results: AM viability was significantly decreased at 1 and 5 days after treatment with MWCNT-20 μm, while superoxide levels and inflammatory mediator release were significantly increased. At the same time, there was reduced phagocytosis and migratory capacity alongside increased expression of MARCO; this coincided with frustrated phagocytosis observed by scanning electron microscopy. In contrast, the adverse bioreactivity of the shorter MWCNT-0.6 μm with AMs (and any resulting reduction in AM functional ability) was substantially less marked or absent altogether. Conclusion:This study shows that after 24-hour treatment with long, but not short, MWCNTs, AM function is severely affected up to 5 days after the initial exposure. This has potentially significant pathophysiological consequences for individuals who may be intentionally (via therapeutic applications) or unintentionally exposed to these nanomaterials.

Different Cellular Response of Human Mesothelial Cell MeT-5A to Short-Term and Long-Term Multiwalled Carbon Nanotubes Exposure

“…Cell migration is a crucial step in many physiological or pathological processes such as wound-healing, cancer, and inflammation [ 22 ]. It is reported that long MWCNT (20 μ m) reduced the migratory capacity in primary human alveolar macrophages (AMs) along with increased expression of MARCO [ 23 ]. In contrast, MWCNT promoted cell migration in RAW263.7 macrophage cell lines and human microvascular endothelial cells (HMVEC) [ 24 , 25 ].…”

Cellular Toxicity and Immunological Effects of Carbon-based Nanomaterials

“…One in vitro study investigated the potential pathophysiological consequences of primary human alveolar macrophages exposed to long MWCNTs (20 μm in length) and short MWCNTs (0.6 μm in length). After a 24-hour treatment with long MWCNTs, alveolar macrophage viability decreased, superoxide levels increased, and inflammatory mediator release increased, and phagocytosis and migratory capacity of alveolar macrophages decreased [ 96 ]. In addition to causing cytotoxicity, pristine MWCNTs and functionalized MWCNTs with COOH and PEG reportedly induce significant production of inflammatory cytokines, including TNF-α, IL-1β and IL-6, at different concentrations from 25 to 200 μg/ml [ 97 ].…”

Mechanisms of lung fibrosis induced by carbon nanotubes: towards an Adverse Outcome Pathway (AOP)

“…Further studies should be conducted to investigate the direct relationship between CNT phagocytosis, oxidative stress and their impact on the release of IL-1β, for example by using endocytosis inhibitors. Moreover, frustrated phagocytosis also led to CNT biopersistence, as the clearance of inhaled material is hampered, and to the release of pro-inflammatory (IL-6 and IL-8) and pro-fibrotic mediators (TGF-β) [ 58 , 59 ]. These data suggest a relevant role of oxidative stress in CNT-induced IL-1β release and fibrosis development.…”

“…; length 20–50 μm and diameter 50 nm) stimulated the release of TGF-β in vivo, as measured by immunohistochemistry, contrary to short CNT (length 0.5-2 μm and diameter 50 nm). Long MWCNT (10 μg/ml; length 20 μm), but not short fibers (length 0.6 μm), were also shown to affect alveolar macrophage function, including cell death, ROS generation and pro-inflammatory (IL-6 and IL-8) mediator release [ 58 ]. A stronger ROS generation was also observed in A549 epithelial cells exposed to long CNT (length 5–30 μm; doses 5–20 μg/ml) compared to short fiber (length 0.5–2 μm) [ 76 ].…”