Biodegradation of Single‐Walled Carbon Nanotubes by Eosinophil Peroxidase

Abstract

Eosinophil peroxidase (EPO) is one of the major oxidant-producing enzymes during inflammatory states in the human lung. The degradation of single-walled carbon nanotubes (SWCNTs) upon incubation with human EPO and H2O2 is reported. Biodegradation of SWCNTs is higher in the presence of NaBr, but neither EPO alone nor H2O2 alone caused the degradation of nanotubes. Molecular modeling reveals two binding sites for SWCNTs on EPO, one located at the proximal side (same side as the catalytic site) and the other on the distal side of EPO. The oxidized groups on SWCNTs in both cases are stabilized by electrostatic interactions with positively charged residues. Biodegradation of SWCNTs can also be executed in an ex vivo culture system using primary murine eosinophils stimulated to undergo degranulation. Biodegradation is proven by a range of methods including transmission electron microscopy, UV-visible-NIR spectroscopy, Raman spectroscopy, and confocal Raman imaging. Thus, human EPO (in vitro) and ex vivo activated eosinophils mediate biodegradation of SWCNTs: an observation that is relevant to pulmonary responses to these materials.

Keeping it small: towards a molecular definition of nanotoxicology

“…The authors ascertained that "it is the small size of the SWCNT that makes its insertion into the hydrophobic core of a protein feasible, which results in the complete disruption of the active sites" (23). However, it should be noted that carboxylated SWCNTs can be degraded by proteins (peroxidases) in immune-competent cells including neutrophils and eosinophils and that this is suggested to occur through the interaction of the nanotubes with the active site of the enzyme (24,25), implying that all CNTprotein interactions are not a priori deleterious (for the protein).…”

Three‐Dimensional Graphene: A Biocompatible and Biodegradable Scaffold with Enhanced Oxygenation

“…This enzymatic biodegradation is also expected to take place when using other types of peroxidase, [ 41 ] or when carrying out the studies in vivo. [ 19 ] In addition, the speed of biodegradation can be tuned by pretreatment with O 2 plasma, which also enhances the wettability of the scaffold, as stated in the preparation method for cell culture.…”

“…For the O 2 -plasma case, fl akes were fi rst decomposed into Raman spectroscopy of this similarity is described in Supporting Information, Figure S5). [ 19,41 ] Since this biodegradation experiment was carried out at 4°C, the biodegradation of the bulk foams was slowed down relative to that at physiological temperatures. To demonstrate more clearly the effects on 3D-C, a second biodegradation test was carried out at room temperature (which speeded up the process signifi cantly).…”

“…The use of the enzyme peroxidase is specifi cally chosen as it is well established as a model system for the biodegradation of carbon-based materials [ 26,40 ] and it can be easily linked to processes that happen naturally in vivo. [ 41 ] The following quantities are the required amount per milligram of 3D-C. Two types of samples were tested, as-grown 3D-C and O 2 -plasmatreated 3D-C. First, the foams were suspended in 2.25 mL of PBS (Sigma Adv. Healthcare Mater.…”

Photodynamic Action of Single-Walled Carbon Nanotubes

“…SWNTs and MWNTs are reported to be biodegradable [69][70][71][72][73] and excretable from mice. 59 69) More importantly, the biodegraded SWNTs did not elicit a proinflammatory response in mice after pharyngeal aspiration, which was observed in previous studies for SWNTs 75) and MWNTs.…”