Myeloperoxidase-induced biodegradation of single-walled carbon nanotubes is mediated by hypochlorite

Broadening prospects of using single-walled carbon nanotubes (SWNTs) in medicine and biotechnology raise the concerns about both their toxicity and the mechanisms of biodegradation and elimination from the body. SWNTs biodegradation as a result of catalytic activity of myeloperoxidase (MPO) was shown in the isolated MPO system as well as in the suspension of neutrophils [Kagan V.E. et al., 2010]. In the present study we analyzed the ability of different MPO-produced oxidants to oxidize and to degrade SWNTs. The comparison of the ability of various peroxidases to degrade SWNTs in vitro revealed that myeloperoxidase, due to its ability to produce hypochlorite, and lactoperoxidase, due to its ability to produce hypobromite, are extremely efficient in the degrading of carbon nanotubes. The biodegradation of SWNTs in the model system can also be induced by free radicals generated as a result of heme degradation and, to a lesser extent, by active oxoferryl intermediates of peroxidases. Our experiments showed that in the presence of blood plasma, peroxidase intermediates or free radical products of heme degradation were unable to initiate biodegradation of carbon nanotubes, only the generation of hypochlorite by MPO can cause the biodegradation of carbon nanotubes in vivo. At high concentrations, hypochlorite caused decrease in optical absorbance of plasma-containing SWNTs suspension, which is indicative of the nanotube degradation. Our results unambiguously suggest that hypochlorite can serve as a main oxidizing agent to modify and degrade nanotubes at the sites of inflammation and in phagosomes.