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

Previously, we noted that carboxylated multi-walled carbon nanotubes (cMWNTs) coated with Pluronic(R) F-108 (PF108) bound to and were accumulated by macrophages, but that pristine multi-walled carbon nanotubes (pMWNTs) coated with PF108 were not (Wang et al., Nanotoxicology 2018, 12, 677). Subsequent studies with Chinese hamster ovary (CHO) cells that overexpressed scavenger receptor A1 (SR-A1) and with macrophages derived from mice knocked out for SR-A1 provided evidence that SR-A1 was a receptor of PF108-cMWNTs (Wang et al., Nanomaterials (Basel) 2020, 10, 2417). Herein, we replaced the PF108 coat with bovine serum albumin (BSA) to investigate how a BSA corona affected the interaction of multi-walled carbon nanotubes (MWNTs) with cells. Both BSA-coated cMWNTs and pMWNTs bound to and were accumulated by RAW 264.7 macrophages, although the cells bound two times more BSA-coated cMWNT than pMWNTs. RAW 264.7 cells that were deleted for SR-A1 using CRISPR-Cas9 technology had markedly reduced binding and accumulation of both BSA-coated cMWNTs and pMWNTs, suggesting that SR-A1 was responsible for the uptake of both MWNT types. Moreover, CHO cells that ectopically expressed SR-A1 accumulated both MWNT types, whereas wild-type CHO cells did not. One model to explain these results is that SR-A1 can interact with two structural features of BSA-coated cMWNTs, one inherent to the oxidized nanotubes (such as COOH and other oxidized groups) and the other provided by the BSA corona; whereas SR-A1 only interacts with the BSA corona of BSA-pMWNTs.

Automated summary

The study found that replacing the PF108 coating with bovine serum albumin (BSA) resulted in both cMWNTs and pMWNTs being able to bind to and accumulate in RAW 264.7 macrophages, with cMWNTs showing greater interaction than pMWNTs. Knocking out SR-A1 in RAW 264.7 cells using CRISPR-Cas9 technology significantly reduced the binding and accumulation of both BSA-coated cMWNTs and pMWNTs.