Selective Uptake of Carboxylated Multi-Walled Carbon Nanotubes by Class A Type 1 Scavenger Receptors and Impaired Phagocytosis in Alveolar Macrophages

Abstract

The production and applications of multi-walled carbon nanotubes (MWNTs) have increased despite evidence that MWNTs can be toxic. Recently, we reported that the binding of Pluronic® F-108 (PF108)-coated carboxylated MWNTs (C-MWNTs) to macrophages is inhibited by class A scavenger receptors (SR-As) antagonists (R. Wang et al., 2018. Nanotoxicology 12:677–690). The current study investigates the uptake of PF108-coated MWNTs by macrophages lacking SR-A1 and by CHO cells that ectopically express SR-A1. Macrophages without SR-A1 failed to take up C-MWNTs and CHO cells that expressed SR-A1 did take up C-MWNTs, but not pristine MWNTs (P-MWNTs) or amino-functionalized MWNTs (N-MWNTs). The dependence of C-MWNT uptake on SR-A1 is strong evidence that SR-A1 is a receptor for C-MWNTs. The consequences of SR-A1-dependent C-MWNT accumulation on cell viability and phagocytic activity in macrophages were also studied. C-MWNTs were more toxic than P-MWNTs and N-MWNTs in cell proliferation and colony formation tests. C-MWNTs reduced surface SR-A1 levels in RAW 264.7 cells and impaired phagocytic uptake of three known SR-A1 ligands, polystyrene beads, heat-killed E. coli, and oxLDL. Altogether, results of this study confirmed that SR-A1 receptors are important for the selective uptake of PF108-coated C-MWNTs and that accumulation of the C-MWNTs impairs phagocytic activity and cell viability in macrophages.

Scavenger Receptor A1 Mediates the Uptake of Carboxylated and Pristine Multi-Walled Carbon Nanotubes Coated with Bovine Serum Albumin

“…In addition, there is indirect evidence that SRs bind carbon nanotubes [ 20 ]. Work from our lab also provided evidence that PF108-cMWNTs, but not PF108-pMWNTs, interact with SR-A1 [ 12 , 21 ]. Thus, SR-A1 is a potential receptor for BSA-MWNTs.…”

“…There were two notable observations in comparing the binding of BSA-coated MWNTs to that we previously described for PF108-coated MWNTs. First, BSA-pMWNTs bound to cells, whereas previous studies showed that PF108-coated pMWNTs did not [ 12 , 21 ]. This indicates that the BSA corona confers the ability of pMWNTs to bind cells.…”

“…Recently, we reported that alveolar macrophages derived from SR-A1 knockout mice did not bind or accumulate PF108-cMWNTs whereas they were accumulated by CHO cells that ectopically expressed SR-A1 [ 21 ]—strong evidence that SR-A1 is a receptor for PF108-coated cMWNTs. An interesting feature of PF108-coated cMWNTs is that they bind strongly to cells in the absence of serum or any exogenous protein, suggesting that a protein corona is not required for cMWNT binding to SR-A1 [ 12 ].…”

Femtosecond pulsed laser microscopy: a new tool to assess the in vitro delivered dose of carbon nanotubes in cell culture experiments

“…MWCNTs can act in the cells [ 25 , 26 ] or on the cell surface, e.g. by interacting with surface receptors [ 10 , 27 , 28 ]. MWCNTs next to the cells, e.g.…”

“…The responses recorded in THP-1 macrophages, which express scavengers receptors that bind MWCNT and contribute to their cellular uptake [ 28 ], highlight the importance of integrating the in vitro delivered dose for the interpretation of the experimental results. In the absence of FPLM data, the conclusion would be that the cytotoxic activity of MWCNTs increases from NC-7000 to CP-NH2, and that CP-NH2 possesses an enhanced capacity to release IL-1β.…”